Proceedings e report 90 - Firenze University Press [PDF]

Proceedings e report 90

ECOS 2012 The 25th International Conference on Efficiency, Cost, Optimization and Simulation of Energy Conversion Systems and Processes (Perugia, June 26th-June 29th, 2012)

edited by Umberto Desideri, Giampaolo Manfrida, Enrico Sciubba

firenze university press

2012

ECOS 2012 : the 25th International Conference on Efficiency, Cost, Optimization and Simulation of Energy Conversion Systems and Processes (Perugia, June 26th-June 29th, 2012) / edited by Umberto Desideri, Giampaolo Manfrida, Enrico Sciubba. – Firenze : Firenze University Press, 2012. (Proceedings e report ; 90) http://digital.casalini.it/9788866553229 ISBN 978-88-6655-322-9 (online) Progetto grafico di copertina Alberto Pizarro, Pagina Maestra snc Immagine di copertina: © Kts | Dreamstime.com

Peer Review Process All publications are submitted to an external refereeing process under the responsibility of the FUP Editorial Board and the Scientific Committees of the individual series. The works published in the FUP catalogue are evaluated and approved by the Editorial Board of the publishing house. For a more detailed description of the refereeing process we refer to the official documents published on the website and in the online catalogue of the FUP (http://www.fupress.com). Firenze University Press Editorial Board G. Nigro (Co-ordinator), M.T. Bartoli, M. Boddi, F. Cambi, R. Casalbuoni, C. Ciappei, R. Del Punta, A. Dolfi, V. Fargion, S. Ferrone, M. Garzaniti, P. Guarnieri, G. Mari, M. Marini, M. Verga, A. Zorzi. © 2012 Firenze University Press Università degli Studi di Firenze Firenze University Press Borgo Albizi, 28, 50122 Firenze, Italy http://www.fupress.com/ Printed in Italy

ECOS 2012 The 25th International Conference on Efficiency, Cost, Optimization and Simulation of Energy Conversion Systems and Processes

Perugia, June 26th-June 29th, 2012 Book of Proceedings - Volume VII Edited by: Umberto Desideri, Università degli Studi di Perugia Giampaolo Manfrida, Università degli Studi di Firenze Enrico Sciubba, Università degli Studi di Roma “Sapienza”

ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY EDITED BY UMBERTO DESIDERI, GIAMPAOLO MANFRIDA, ENRICO SCIUBBA FIRENZE UNIVERSITY PRESS, 2012, ISBN ONLINE : 978-88-6655-322-9

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Advisory Committee (Track Organizers) Building, Urban and Complex Energy Systems V. Ismet Ugursal Dalhousie University, Nova Scotia, Canada Combustion, Chemical Reactors, Carbon Capture and Sequestration Giuseppe Girardi ENEA-Casaccia, Italy Energy Systems: Environmental and Sustainability Issues Christos A. Frangopoulos National Technical University of Athens, Greece Exergy Analysis and Second Law Analysis Silvio de Oliveira Junior Polytechnical University of Sao Paulo, Sao Paulo, Brazil Fluid Dynamics and Power Plant Components Sotirios Karellas National Technical University of Athens, Athens, Greece Fuel Cells Umberto Desideri University of Perugia, Perugia, Italy Heat and Mass Transfer Francesco Asdrubali, Cinzia Buratti University of Perugia, Perugia, Italy Industrial Ecology Stefan Goessling-Reisemann University of Bremen, Germany Poster Session Enrico Sciubba University Roma 1 “Sapienza”, Italy Process Integration and Heat Exchanger Networks Francois Marechal EPFL, Lausanne, Switzerland Renewable Energy Conversion Systems David Chiaramonti University of Firenze, Firenze, Italy Simulation of Energy Conversion Systems Marcin Liszka Polytechnica Slaska, Gliwice, Poland System Operation, Control, Diagnosis and Prognosis Vittorio Verda Politecnico di Torino, Italy Thermodynamics A. Özer Arnas United States Military Academy at West Point, U.S.A. Thermo-Economic Analysis and Optimisation Andrea Lazzaretto University of Padova, Padova, Italy Water Desalination and Use of Water Resources Corrado Sommariva ILF Consulting M.E., U.K iii

Scientific Committee Riccardo Basosi, University of Siena, Italy Gino Bella, University of Roma Tor Vergata, Italy Asfaw Beyene, San Diego State University, United States Ryszard Bialecki, Silesian Institute of Tecnology, Poland Gianni Bidini, University of Perugia, Italy Ana M. Blanco-Marigorta, University of Las Palmas de Gran Canaria, Spain Olav Bolland, University of Science and Technology (NTNU), Norway Renè Cornelissen, Cornelissen Consulting, The Netherlands Franco Cotana, University of Perugia, Italy Alexandru Dobrovicescu, Polytechnical University of Bucharest, Romania Gheorghe Dumitrascu, Technical University of Iasi, Romania Brian Elmegaard, Technical University of Denmark , Denmark Daniel Favrat, EPFL, Switzerland Michel Feidt, ENSEM - LEMTA University Henri Poincaré, France Daniele Fiaschi, University of Florence, Italy Marco Frey, Scuola Superiore S. Anna, Italy Richard A Gaggioli, Marquette University, USA Carlo N. Grimaldi, University of Perugia, Italy Simon Harvey, Chalmers University of Technology, Sweden Hasan Heperkan, Yildiz Technical University, Turkey Abel Abel Hernandez-Guerrero, University of Guanajuato, Mexico Jiri Jaromir Klemeš, University of Pannonia, Hungary Zornitza V. Kirova-Yordanova, University "Prof. Assen Zlatarov", Bulgaria Noam Lior, University of Pennsylvania, United States Francesco Martelli, University of Florence, Italy Aristide Massardo, University of Genova, Italy Jim McGovern, Dublin Institute of Technology, Ireland Alberto Mirandola, University of Padova, Italy Michael J. Moran, The Ohio State University, United States Tatiana Morosuk, Technical University of Berlin, Germany Pericles Pilidis, University of Cranfield, United Kingdom Constantine D. Rakopoulos, National Technical University of Athens, Greece Predrag Raskovic, University of Nis, Serbia and Montenegro Mauro Reini, University of Trieste, Italy Gianfranco Rizzo, University of Salerno, Italy Marc A. Rosen, University of Ontario, Canada Luis M. Serra, University of Zaragoza, Spain Gordana Stefanovic, University of Nis, Serbia and Montenegro Andrea Toffolo, Luleå University of Technology, Sweden Wojciech Stanek, Silesian University of Technology, Poland George Tsatsaronis, Technical University Berlin, Germany Antonio Valero, University of Zaragoza, Spain Michael R. von Spakovsky, Virginia Tech, USA Stefano Ubertini, Parthenope University of Naples, Italy Sergio Ulgiati, Parthenope University of Naples, Italy Sergio Usón, Universidad de Zaragoza, Spain Roman Weber, Clausthal University of Technology, Germany Ryohei Yokoyama, Osaka Prefecture University, Japan Na Zhang, Institute of Engineering Thermophysics, Chinese Academy of Sciences, China iv

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The 25th ECOS Conference 1987-2012: leaving a mark The introduction to the ECOS series of Conferences states that “ECOS is a series of international conferences that focus on all aspects of Thermal Sciences, with particular emphasis on Thermodynamics and its applications in energy conversion systems and processes”. Well, ECOS is much more than that, and its history proves it! The idea of starting a series of such conferences was put forth at an informal meeting of the Advanced Energy Systems Division of the American Society of Mechanical Engineers (ASME) at the November 1985 Winter Annual Meeting (WAM), in Miami Beach, Florida, then chaired by Richard Gaggioli. The resolution was to organize an annual Symposium on the Analysis and Design of Thermal Systems at each ASME WAM, and to try to involve a larger number of scientists and engineers worldwide by organizing conferences outside of the United States. Besides Rich other participants were Ozer Arnas, Adrian Bejan, Yehia ElSayed, Robert Evans, Francis Huang, Mike Moran, Gordon Reistad, Enrico Sciubba and George Tsatsaronis. Ever since 1985, a Symposium of 8-16 sessions has been organized by the Systems Analysis Technical Committee every year, at the ASME Winter Annual Meeting (now ASME-IMECE). The first overseas conference took place in Rome, twenty-five years ago (in July 1987), with the support of the U.S. National Science Foundation and of the Italian National Research Council. In that occasion, Christos Frangopoulos, Yalcin Gogus, Elias Gyftopoulos, Dominick Sama, Sergio Stecco, Antonio Valero, and many others, already active at the ASME meetings, joined the core-group. The name ECOS was used for the first time in Zaragoza, in 1992: it is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), keywords that best describe the contents of the presentations and discussions taking place in these conferences. Some years ago, Christos Frangopoulos inserted in the official website the note that “ècos” (’ ) means “home” in Greek and it ought to be attributed the very same meaning as the prefix “Eco-“ in environmental sciences. The last 25 years have witnessed an almost incredible growth of the ECOS community: more and more Colleagues are actively participating in our meetings, several international Journals routinely publish selected papers from our Proceedings, fruitful interdisciplinary and international cooperation projects have blossomed from our meetings. Meetings that have spanned three continents (Africa and Australia ought to be our next targets, perhaps!) and influenced in a way or another much of modern Engineering Thermodynamics. After 25 years, if we do not want to become embalmed in our own success and lose momentum, it is mandatory to aim our efforts in two directions: first, encourage the participation of younger academicians to our meetings, and second, stimulate creative and useful discussions in our sessions. Looking at this years’ registration roster (250 papers of which 50 authored or co-authored by junior Authors), the first objective seems to have been attained, and thus we have just to continue in that direction; the second one involves allowing space to “voices that sing out of the choir”, fostering new methods and approaches, and establishing or reinforcing connections to other scientific communities. It is important that our technical sessions represent a place of active confrontation, rather than academic “lecturing”. In this spirit, we welcome you in Perugia, and wish you a scientifically stimulating, touristically interesting, and culinarily rewarding experience. In line with our 25 years old scientific excellency and friendship! Umberto Desideri, Giampaolo Manfrida, Enrico Sciubba vi

CONTENT MANAGEMENT The index lists all the papers contained all the eight volumes of the Proceedings of the ECOS 2012 International Conference. Page numbers are listed only for papers within the Volume you are looking at. The ID code allows to trace back the identification number assigned to the paper within the Conference submission, review and track organization processes.

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CONTENT VOLUME VII VII. 1 BUILDING, URBAN AND COMPLEX ENERGY SYSTEMS » A linear programming model for the optimal assessment of …….... sustainable energy action plans (ID 398) Gianfranco Rizzo, Giancarlo Savino

Pag. 1

» A natural gas fuelled 10 kW electric power unit based on a Diesel …….... automotive internal combustion engine and suitable for cogeneration (ID 477) Pietro Capaldi

Pag. 14

» Adjustment of envelopes characteristics to climatic conditions for …….... saving heating and cooling energy in buildings (ID 430) Christos Tzivanidis, Kimon Antonopoulos, Foteini Gioti

Pag. 24

» An exergy based method for the optimal integration of a building and …….... its heating plant. Part 1: comparison of domestic heating systems based on renewable sources (ID 81) Marta Cianfrini, Enrico Sciubba, Claudia Toro

Pag. 40

» Analysis of different typologies of natural insulation materials with …….... economic and performances evaluation of the same buildings (ID 28) Umberto Desideri, Daniela Leonardi, Livia Arcioni

Pag. 54

» Complex networks approach to the Italian photovoltaic energy …….... distribution system (ID 470) Luca Valori, Giovanni Luca Giannuzzi, Tiziano Squartini, Diego Garlaschelli, Riccardo Basosi

Pag. 72

» Design of a multi-purpose building "to zero energy consumption" …….... according to European Directive 2010/31/CE: Architectural and plant solutions (ID 29) Umberto Desideri, Livia Arcioni, Daniela Leonardi, Luca Cesaretti ,Perla Perugini, Elena Agabitini, Nicola Evangelisti

Pag. 90

» Effect of initial systems on the renewal planning of energy supply …….... systems for a hospital (ID 107) Shu Yoshida, Koichi Ito, Yoshiharu Amano, Shintaro Ishikawa, Takahiro Sushi, Takumi Hashizume

Pag. 107

» Effects of insulation and phase change materials (PCM) combinations …….... on the energy consumption for buildings indoor thermal comfort (ID 387) Christos Tzivanidis, Kimon Antonopoulos, Eleutherios Kravvaritis

Pag. 119

» Energetic evaluation of a smart controlled greenhouse for tomato …….... cultivation (ID 150) Nickey Van den Bulck, Mathias Coomans, Lieve Wittemans, Kris Goen, Jochen Hanssens, Kathy Steppe, Herman Marien, Johan Desmedt

Pag. 134

» Energy networks in sustainable cities: temperature and energy …….... consumption monitoring in urban area (ID 190) Luca Giaccone, Alessandra Guerrisi, Paolo Lazzeroni and Michele Tartaglia

Pag. 146

» Extended exergy analysis of the e conomy of Nova Scotia, Canada …….... (ID 215) David C Bligh, V.Ismet Ugursal

Pag. 160

-------------------------------------------------------------------------------------------------ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY EDITED BY UMBERTO DESIDERI, GIAMPAOLO MANFRIDA, ENRICO SCIUBBA FIRENZE UNIVERSITY PRESS, 2012, ISBN ONLINE : 978-88-6655-322-9

» Feasibility study and design of a low-energy residential unit in …….... Sagarmatha Park (Nepal) for envirnomental impact reduction of high altitude buildings (ID 223) Umberto Desideri, Stefania Proietti, Paolo Sdringola, Elisa Vuillermoz

Pag. 173

» Fire and smoke spread in low-income housing in Mexico (ID 379) …….... Raul R. Flores-Rodriguez, Abel Hernandez-Guerrero, Cuauhtemoc RubioArana, Consuelo A. Caldera-Briseño

Pag. 186

» Optimal lighting control strategies in supermarkets for energy …….... efficiency applications via digital dimmable technology (ID 136) Salvador Acha, Nilay Shah, Jon Ashford, David Penfold

Pag. 196

» Optimising the arrangement of finance towards large scale …….... refurbishment of housing stock using mathematical programming and optimisationg (ID 127) Mark Gerard Jennings, Nilay Shah, David Fisk

Pag. 213

» Optimization of thermal insulation to save energy in buildings (ID 174) …….... Milorad Boji , Marko Mileti , Vesna Marjanovi , Danijela Nikoli , Jasmina Skerli

Pag. 229

» Residential solar-based seasonal thermal storage system in cold …….... climate: building envelope and thermal storage (ID 342) Alexandre Hugo and Radu Zmeureanu

Pag. 239

» Simultaneous production of domestic hot water and space cooling …….... with a heat pump in a Swedish Passive House (ID 55) Johannes Persson, Mats Westermark

Pag. 251

» SOFC micro-CHP integration in residential buildings (ID 201) …….... Umberto Desideri, Giovanni Cinti, Gabriele Discepoli, Elena Sisani, Daniele Penchini

Pag. 261

» The effect of shading of building integrated photovoltaics on roof …….... surface temperature and heat transfer in buildings (ID 83) Eftychios Vardoulakis, Dimitrios Karamanis

Pag. 273

» The influence of glazing systems on energy performance and thermal …….... comfort in non-residential buildings (ID 206) Cinzia Buratti, Elisa Moretti, Elisa Belloni

Pag. 281

» Thermal analysis of a greenhouse heated by solar energy and …….... seasonal thermal energy storage in soil (ID 405) Yong Li, Jin Xu, Ru-Zhu Wang

Pag. 295

» Thermodynamic analysis of a combined cooling, heating and power …….... system under part load condition (ID 476) Qiang Chen, Jianjiao Zheng, Wei Han, Jun Sui, Hong-guang Jin

Pag. 304

VII. 2 COMBUSTION, CHEMICAL REACTORS » Baffle as a cost-effective design improvement for volatile combustion …….... rate increase in biomass boilers of simple construction (ID 233) Borivoj Stepanov, Ivan Pešenjanski, Biljana Miljkovi

Pag. 321

» Characterization of CH4-H2-air mixtures in the high-pressure DHARMA …….... reactor (ID 287) Vincenzo Moccia, Jacopo D'Alessio

Pag. 331

» Development of a concept for efficiency improvement and decreased …….... NOx production for natural gas-fired glass melting furnaces by switching to a propane exhaust gas fired process (ID 146) Jörn Benthin, Anne Giese

Pag. 343

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» Experimental analysis of inhibition phenomenon management for Solid Anaerobic Digestion Batch process (ID 348) …….... Francesco Di Maria, Giovanni Gigliotti, Alessio Sordi, Caterina Micale, Claudia Zadra, Luisa Massaccesi

Pag. 349

» Experimental investigations of the combustion process of n- …….... butanol/diesel blend in an optical high swirl CI engine (ID 85) Simona Silvia Merola, G. Valentino, C. Tornatore, L. Marchitto , F. E. Corcione

Pag. 358

» Flameless oxidation as a means to reduce NOx emissions in glass …….... melting furnaces (ID 141) Jörg Leicher, Anne Giese

Pag. 372

» Mechanism of damage by high temperature of the tubes, exposed to …….... the atmosphere characteristic of a furnace of pyrolysis of ethane for ethylene production in the petrochemical industry (ID 65) Jaqueline Saavedra Rueda, Francisco Javier Perez Trujillo, Lourdes Isabel Meriño Stand, Harbey Alexi Escobar, Luis Eduardo Navas, Juan Carlos Amezquita

Pag. 381

» Steam reforming of methane over Pt/Rh based wire mesh catalyst in …….... single channel reformer for small scale syngas production (ID 317) Haftor Orn Sigurdsson, Søren Knudsen Kær

Pag. 388

----------------------------------------------------------------------CONTENTS OF ALL THE VOLUMES -----------------------------------------------------------------------

VOLUME I I . 1 - SIMULATION OF ENERGY CONVERSION SYSTEMS » A novel hybrid-fuel compressed air energy storage system for China’s situation (ID 531) Wenyi Liu, Yongping Yang, Weide Zhang, Gang Xu,and Ying Wu » A review of Stirling engine technologies applied to micro-cogeneration systems (ID 338) Ana C Ferreira, Manuel L Nunes, Luís B Martins, Senhorinha F Teixeira » An organic Rankine cycle off-design model for the search of the optimal control strategy (ID 295) Andrea Toffolo, Andrea Lazzaretto, Giovanni Manente, Marco Paci » Automated superstructure generation and optimization of distributed energy supply systems (ID 518) Philip Voll, Carsten Klaffke, Maike Hennen, André Bardow » Characterisation and classification of solid recovered fuels (SRF) and model development of a novel thermal utilization concept through air- gasification (ID 506) Panagiotis Vounatsos, Konstantinos Atsonios, Mihalis Agraniotis, Kyriakos D. Panopoulos, George Koufodimos,Panagiotis Grammelis, Emmanuel Kakaras » Design and modelling of a novel compact power cycle for low temperature heat sources (ID 177) Jorrit Wronski, Morten Juel Skovrup, Brian Elmegaard, Harald Nes Rislå, Fredrik Haglind » Dynamic simulation of combined cycles operating in transient conditions: an innovative approach to determine the steam drums life consumption (ID 439) Stefano Bracco

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» Effect of auxiliary electrical power consumptions on organic Rankine cycle system with low-temperature waste heat source (ID 235) Samer Maalouf, Elias Boulawz Ksayer, Denis Clodic » Energetic and exergetic analysis of waste heat recovery systems in the cement industry (ID 228) Sotirios Karellas, Aris Dimitrios Leontaritis, Georgios Panousis, Evangelos Bellos, Emmanuel Kakaras » Energy and exergy analysis of repowering options for Greek lignite-fired power plants (ID 230) Sotirios Karellas, Aggelos Doukelis, Grammatiki Zanni, Emmanuel Kakaras » Energy saving by a simple solar collector with reflective panels and boiler (ID 366) Anna Stoppato, Renzo Tosato » Exergetic analysis of biomass fired double-stage Organic Rankine Cycle (ORC) (ID 37) Markus Preißinger, Florian Heberle, Dieter Brüggemann » Experimental tests and modelization of a domestic-scale organic Rankine cycle (ID 156) Roberto Bracco, Stefano Clemente, Diego Micheli, Mauro Reini » Model of a small steam engine for renewable domestic CHP system (ID 31 ) Giampaolo Manfrida, Giovanni Ferrara, Alessandro Pescioni » Model of vacuum glass heat pipe solar collectors (ID 312) Daniele Fiaschi, Giampaolo Manfrida » Modelling and exergy analysis of a plasma furnace for aluminum melting process (ID 254) Luis Enrique Acevedo, Sergio Usón, Javier Uche, Patxi Rodríguez » Modelling and experimental validation of a solar cooling installation (ID 296) Guillaume Anies, Pascal Stouffs, Jean Castaing-Lasvignottes » The influence of operating parameters and occupancy rate of thermoelectric modules on the electricity generation (ID 314) Camille Favarel, Jean-Pierre Bédécarrats, Tarik Kousksou, Daniel Champier » Thermodynamic and heat transfer analysis of rice straw co-firing in a Brazilian pulverised coal boiler (ID 236) Raphael Miyake, Alvaro Restrepo, Fábio Kleveston Edson Bazzo, Marcelo Bzuneck » Thermophotovoltaic generation: A state of the art review (ID 88) Matteo Bosi, Claudio Ferrari, Francesco Melino, Michele Pinelli, Pier Ruggero Spina, Mauro Venturini I . 2 – HEAT AND MASS TRANSFER » A DNS method for particle motion to establish boundary conditions in coal gasifiers (ID 49) Efstathios E Michaelides, Zhigang Feng » Effective thermal conductivity with convection and radiation in packed bed (ID 60) Yusuke Asakuma » Experimental and CFD study of a single phase cone-shaped helical coiled heat exchanger: an empirical correlation (ID 375) Daniel Flórez-Orrego, Walter Arias, Diego López, Héctor Velásquez » Thermofluiddynamic model for control analysis of latent heat thermal storage system (ID 207) Adriano Sciacovelli, Vittorio Verda, Flavio Gagliardi » Towards the development of an efficient immersed particle heat exchanger: particle transfer from low to high pressure (ID 202) Luciano A. Catalano, Riccardo Amirante, Stefano Copertino, Paolo Tamburrano, Fabio De Bellis xi

I . 3 – INDUSTRIAL ECOLOGY » Anthropogenic heat and exergy balance of the atmosphere (ID 122) Asfaw Beyene, David MacPhee, Ron Zevenhoven » Determination of environmental remediation cost of municipal waste in terms of extended exergy (ID 63) Candeniz Seckin, Ahmet R. Bayulken » Development of product category rules for the application of life cycle assessment to carbon capture and storage (537) Carlo Strazza, Adriana Del Borghi, Michela Gallo » Electricity production from renewable and non-renewable energy sources: a comparison of environmental, economic and social sustainability indicators with exergy losses throughout the supply chain (ID 247) Lydia Stougie, Hedzer van der Kooi, Rob Stikkelman » Exergy analysis of the industrial symbiosis model in Kalundborg (ID 218) Alicia Valero Delgado, Sergio Usón, Jorge Costa » Global gold mining: is technological learning overcoming the declining in ore grades? (ID 277) Adriana Domínguez, Alicia Valero » Personal transportation energy consumption (ID305) Matteo Muratori, Emmanuele Serra, Vincenzo Marano, Michael Moran » Resource use evaluation of Turkish transportation sector via the extended exergy accounting method (ID 43) Candeniz Seckin, Enrico Sciubba, Ahmet R. Bayulken » The impact of higher energy prices on socio-economic inequalities of German social groups (ID 80) Holger Schlör, Wolfgang Fischer, Jürgen-Friedrich Hake

VOLUME II II . 1 – EXERGY ANALYSIS AND 2ND LAW ANALYSIS » A comparative analysis of cryogenic recuperative heat exchangers based on exergy destruction (ID 129) Adina Teodora Gheorghian, Alexandru Dobrovicescu, Lavinia Grosu, Bogdan Popescu, Claudia Ionita » A critical exploration of the usefulness of rational efficiency as a performance parameter for heat exchangers (ID 307) Jim McGovern, Georgiana Tirca-Dragomirescu, Michel Feidt, Alexandru Dobrovicescu » A new procedure for the design of LNG processes by combining exergy and pinch analyses (ID 238) Danahe Marmolejo-Correa, Truls Gundersen » Advances in the distribution of environmental cost of water bodies through the exergy concept in the Ebro river (ID 258) Javier Uche Marcuello, Amaya Martínez Gracia, Beatriz Carrasquer Álvarez, Antonio Valero Capilla » Application of the entropy generation minimization method to a solar heat exchanger: a pseudo-optimization design process based on the analysis of the local entropy generation maps (ID 357) Giorgio Giangaspero, Enrico Sciubba

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» Comparative analysis of ammonia and carbon dioxide two-stage cycles for simultaneous cooling and heating (ID 84) Alexandru Dobrovicescu, Ciprian Filipoiu, Emilia Cerna Mladin, Valentin Apostol, Liviu Drughean » Comparison between traditional methodologies and advanced exergy analyses for evaluating efficiency and externalities of energy systems (ID 515) Gabriele Cassetti, Emanuela Colombo » Comparison of entropy generation figures using entropy maps and entropy transport equation for an air cooled gas turbine blade (ID 468) Omer Emre Orhan, Oguz Uzol » Conventional and advanced exergetic evaluation of a supercritical coal-fired power plant (ID 377) Ligang Wang, Yongping Yang, Tatiana Morosuk, George Tsatsaronis » Energy and exergy analyses of the charging process in encapsulted ice thermal energy storage (ID 164) David MacPhee, Ibrahim Dincer, Asfaw Beyene » Energy integration and cogeneration in nitrogen fertilizers industry: thermodynamic estimation of the efficiency, potentials, limitations and environmental impact. Part 1: energy integration in ammonia production plants (ID 303) Zornitza Vassileva Kirova-Yordanova » Evaluation of the oil and gas processing at a real production day on a North Sea oil platform using exergy analysis (ID 260) Mari Voldsund, Wei He, Audun Røsjorde, Ivar Ståle Ertesvåg, Signe Kjelstrup » Exergetic and economic analysis of Kalina cycle for low temperature geothermal sources in Brazil (ID 345) Carlos Eymel Campos Rodriguez, José Carlos Escobar Palacios, Cesar Adolfo Rodríguez Sotomonte, Marcio Leme, Osvaldo José Venturini, Electo Eduardo Silva Lora, Vladimir Melián Cobasa, Daniel Marques dos Santos, Fábio R. Lofrano Dotto, Vernei Gialluca » Exergy analysis and comparison of CO2 heat pumps (ID 242) Argyro Papadaki, Athina Stegou - Sagia » Exergy analysis of a CO2 Recovery plant for a brewery (ID 72) Daniel Rønne Nielsen, Brian Elmegaard, C. Bang-Møller » Exergy analysis of the silicon production process (ID 118) Marit Takla, Leiv Kolbeinsen, Halvard Tveit, Signe Kjelstrup » Exergy based indicators for cardiopulmonary exercise test evaluation (ID 159) Carlos Eduardo Keutenedjian Mady, Cyro Albuquerque Neto, Tiago Lazzaretti Fernandes, Arnaldo Jose Hernandez, Paulo Hilário Nascimento Saldiva, Jurandir Itizo Yanagihara, Silvio de Oliveira Junior » Exergy disaggregation as an alternative for system disaggregation in thermoeconomics (ID 483) José Joaquim Conceição Soares Santos, Atilio Lourenço, Julio Mendes da Silva, João Donatelli, José Escobar Palacio » Exergy intensity of petroleum derived fuels (ID 117) Julio Augusto Mendes da Silva, Maurício Sugiyama, Claudio Rucker, Silvio de Oliveira Junior » Exergy-based sustainability evaluation of a wind power generation system (ID 542) Jin Yang, B. Chen, Enrico Sciubba » Human body exergy metabolism (ID 160) Carlos Eduardo Keutenedjian Mady, Silvio de Oliveira Junior » Integrating an ORC into a natural gas expansion plant supplied with a co-generation unit (ID 273) Sergio Usón, Wojciech Juliusz Kostowski xiii

» One-dimensional model of an optimal ejector and parametric study of ejector efficiency (ID 323) Ronan Killian McGovern, Kartik Bulusu, Mohammed Antar, John H. Lienhard » Optimization and design of pin-fin heat sinks based on minimum entropy generation (ID 6) Jose-Luis Zuniga-Cerroblanco, Abel Hernandez-Guerrero, Carlos A. Rubio-Jimenez, Cuauhtemoc Rubio-Arana, Sosimo E. Diaz-Mendez » Performance analysis of a district heating system (ID 271) Andrej Ljubenko, Alojz Poredoš, Tatiana Morosuk, George Tsatsaronis » System analysis of exergy losses in an integrated oxy-fuel combustion power plant (ID 64) Andrzej Zi bik, Pawe G adysz » What is the cost of losing irreversibly the mineral capital on Earth? (ID 220) Alicia Valero Delgado, Antonio Valero II . 2 – THERMODYNAMICS » A new polygeneration system for methanol and power based on coke oven gas and coal gas (ID 252) Hu Lin, Hongguang Jin, Lin Gao, Rumou Li » Argon-Water closed gas cycle (ID 67) Federico Fionelli, Giovanni Molinari » Binary alkane mixtures as fluids in Rankine cycles (ID 246) M. Aslam Siddiqi, Burak Atakan » Excess enthalpies of second generation biofuels (ID 308) Alejandro Moreau, José Juan Segovia, M. Carmen Martín, Miguel Ángel Villamañán, César R. Chamorro, Rosa M. Villamañán » Local stability analysis of a Curzon-Ahlborn engine considering the Van der Waals equation state in the maximum ecological regime (ID 281) Ricardo Richard Páez-Hernández, Pedro Portillo-Díaz, Delfino Ladino-Luna, Marco Antonio Barranco-Jiménez » Some remarks on the Carnot's theorem (ID 325) Julian Gonzalez Ayala, Fernando Angulo-Brown » The Dead State (ID 340) Richard A. Gaggioli » The magnetocaloric energy conversion (ID 97) Andrej Kitanovski, Jaka Tusek, Alojz Poredos

VOLUME III THERMO-ECONOMIC ANALYSIS AND OPTIMIZATION » A comparison of optimal operation of residential energy systems using clustered demand patterns based on Kullback-Leibler divergence (ID 142) Akira Yoshida, Yoshiharu Amano, Noboru Murata, Koichi Ito, Takumi Hashizume » A Model for Simulation and Optimal Design of a Solar Heating System with Seasonal Storage (ID 51) Gianfranco Rizzo » A thermodynamic and economic comparative analysis of combined gas-steam and gas turbine air bottoming cycle (ID 232) Tadeusz Chmielniak, Daniel Czaja, Sebastian Lepszy » Application of an alternative thermoeconomic approach to a two-stage vapor compression refrigeration cycle with intercooling (ID 135) Atilio Barbosa Lourenço, José Joaquim Conceição Soares Santos, João Luiz Marcon Donatelli xiv

» Comparative performance of advanced power cycles for low temperature heat sources (ID 109) Guillaume Becquin, Sebastian Freund » Comparison of nuclear steam power plant and conventional steam power plant through energy level and thermoeconomic analysis (ID 251) S. Khamis Abadi, Mohammad Hasan Khoshgoftar Manesh, M. Baghestani, H. Ghalami, Majid Amidpour » Economic and exergoeconomic analysis of micro GT and ORC cogeneration systems (ID 87) Audrius Bagdanavicius, Robert Sansom, Nick Jenkins, Goran Strbac » Exergoeconomic comparison of wet and dry cooling technologies for the Rankine cycle of a solar thermal power plant (ID 300) Philipp Habl, Ana M. Blanco-Marigorta, Berit Erlach » Influence of renewable generators on the thermo-economic multi-level optimization of a poly-generation smart grid (101) Massimo Rivarolo, Andrea Greco, Francesca Travi, Aristide F. Massardo » Local stability analysis of a thermoeconomic model of an irreversible heat engine working at different criteria of performance (ID 289) Marco A. Barranco-Jiménez, Norma Sánchez-Salas, Israel Reyes-Ramírez, Lev Guzmán-Vargas » Multicriteria optimization of a distributed trigeneration system in an industrial area (ID 154) Dario Buoro, Melchiorre Casisi, Alberto de Nardi, Piero Pinamonti, Mauro Reini » On the effect of eco-indicator selection on the conclusions obtained from an exergoenvironmental analysis (ID 275) Tatiana Morosuk, George Tsatsaronis, Christopher Koroneos » Optimisation of supply temperature and mass flow rate for a district heating network (ID 104) Marouf Pirouti, Audrius Bagdanavicius, Jianzhong Wu, Janaka Ekanayake » Optimization of energy supply systems in consideration of hierarchical relationship between design and operation (ID 389) Ryohei Yokoyama, Shuhei Ose » The fuel impact formula revisited (ID 279) Cesar Torres, Antonio Valero » The introduction of exergy analysis to the thermo-economic modelling and optimisation of a marine combined cycle system (ID 61) George G. Dimopoulos, Chariklia A. Georgopoulou, Nikolaos M.P. Kakalis » The relationship between costs and environmental impacts in power plants: an exergybased study (ID 272) Fontina Petrakopoulou, Yolanda Lara, Tatiana Morosuk, Alicia Boyano, George Tsatsaronis » Thermo-ecological evaluation of biomass integrated gasification gas turbine based cogeneration technology (ID 441) Wojciech Stanek, Lucyna Czarnowska, Jacek Kalina » Thermo-ecological optimization of a heat exchanger through empirical modeling (ID 501) Ireneusz Szczygie , Wojciech Stanek, Lucyna Czarnowska, Marek Rojczyk » Thermoeconomic analysis and optimization in a combined cycle power plant including a heat transformer for energy saving (ID 399) Elizabeth Cortés Rodríguez, José Luis Castilla Carrillo, Claudia A. Ruiz Mercado, Wilfrido Rivera Gómez-Franco » Thermoeconomic analysis and optimization of a hybrid solar-electric heating in a fluidized bed dryer (ID 400) Elizabeth Cortés Rodríguez, Felipe de Jesús Ojeda Cámara, Isaac Pilatowsky Figueroa xv

» Thermoeconomic approach for the analysis of low temperature district heating systems (ID 208) Vittorio Verda, Albana Kona » Thermo-economic assessment of a micro CHP systems fuelled by geothermal and solar energy (ID 166) Duccio Tempesti, Daniele Fiaschi, Filippo Gabuzzini » Thermo-economic evaluation and optimization of the thermo-chemical conversion of biomass into methanol (ID 194) Emanuela Peduzzi, Laurence Tock, Guillaume Boissonnet, François Marechal » Thermoeconomic fuel impact approach for assessing resources savings in industrial symbiosis: application to Kalundborg Eco-industrial Park (ID 256) Sergio Usón, Antonio Valero, Alicia Valero, Jorge Costa » Thermoeconomics of a ground-based CAES plant for peak-load energy production system (ID 32) Simon Kemble, Giampaolo Manfrida, Adriano Milazzo, Francesco Buffa

VOLUME IV IV . 1 - FLUID DYNAMICS AND POWER PLANT COMPONENTS » A control oriented simulation model of a multistage axial compressor (ID 444) Lorenzo Damiani, Giampaolo Crosa, Angela Trucco » A flexible and simple device for in-cylinder flow measurements: experimental and numerical validation (ID 181) Andrea Dai Zotti, Massimo Masi, Marco Antonello » CFD Simulation of Entropy Generation in Pipeline for Steam Transport in Real Industrial Plant (ID 543) Goran Vu kovi , Gradimir Ili , Mi a Vuki , Milan Bani , Gordana Stefanovi » Feasibility Study of Turbo expander Installation in City Gate Station (ID 168) Navid Zehtabiyan Rezaie, Majid Saffar-Avval » GTL and RME combustion analysis in a transparent CI engine by means of IR digital imaging (ID 460) Ezio Mancaruso, Luigi Sequino, Bianca Maria Vaglieco » Some aspects concerning fluid flow and turbulence modeling in 4-valve engines (ID 116) Zoran Stevan Jovanovic, Zoran Masonicic, Miroljub Tomic IV . 2 - SYSTEM OPERATION CONTROL DIAGNOSIS AND PROGNOSIS » Adapting the operation regimes of trigeneration systems to renewable energy systems integration (ID 188) Liviu Ruieneanu, Mihai Paul Mircea » Advanced electromagnetic sensors for sustainable monitoring of industrial processes (ID 145) Uroš Puc, Andreja Abina, Anton Jegli , Pavel Cevc, Aleksander Zidanšek » Assessment of stresses and residual life of plant components in view of life-time extension of power plants (ID 453) Anna Stoppato, Alberto Benato and Alberto Mirandola » Control strategy for minimizing the electric power consumption of hybrid ground source heat pump system (ID 244) Zoi Sagia, Constantinos Rakopoulos xv i

» Exergetic evaluation of heat pump booster configurations in a low temperature district heating network (ID 148) Torben Ommen, Brian Elmegaard » Exergoeconomic diagnosis: a thermo-characterization method by using irreversibility analysis (ID 523) Abraham Olivares-Arriaga, Alejandro Zaleta-Aguilar, Rangel-Hernández V. H, Juan Manuel Belman-Flores » Optimal structural design of residential cogeneration systems considering their operational restrictions (ID 224) Tetsuya Wakui, Ryohei Yokoyama » Performance estimation and optimal operation of a CO2 heat pump water heating system (ID 344) Ryohei Yokoyama, Ryosuke Kato, Tetsuya Wakui, Kazuhisa Takemura » Performances of a common-rail Diesel engine fuelled with rapeseed and waste cooking oils (ID 213) Alessandro Corsini, Valerio Giovannoni, Stefano Nardecchia, Franco Rispoli, Fabrizio Sciulli, Paolo Venturini » Reduced energy cost through the furnace pressure control in power plants (ID 367) Vojislav Filipovi , Novak Nedi , Saša Prodanovi » Short-term scheduling model for a wind-hydro-thermal electricity system (ID 464) Sérgio Pereira, Paula Ferreira, A. Ismael Freitas Vaz

VOLUME V V . 1 - RENEWABLE ENERGY CONVERSION SYSTEMS » A co-powered concentrated solar power Rankine cycle concept for small size combined heat and power (ID 276) Alessandro Corsini, Domenico Borello, Franco Rispoli, Eileen Tortora » A novel non-tracking solar collector for high temperature application (ID 466) Wattana Ratismith, Anusorn Inthongkhum » Absorption heat transformers (AHT) as a way to enhance low enthalpy geothermal resources (ID 311) Daniele Fiaschi, Duccio Tempesti, Giampaolo Manfrida, Daniele Di Rosa » Alternative feedstock for the biodiesel and energy production: the OVEST project (ID 98) Matteo Prussi, David Chiaramonti, Lucia Recchia, Francesco Martelli, Fabio Guidotti » Assessing repowering and update scenarios for wind energy converters (ID 158) Till Zimmermann » Biogas from mechanical pulping industry – potential improvement for increased biomass vehicle fuels (ID 54) Mimmi Magnusson, Per Alvfors » Biogas or electricity as vehicle fuels derived from food waste - the case of Stockholm (ID 27) Martina Wikström, Per Alvfors » Compressibility factor as evaluation parameter of expansion processes in organic Rankine cycles (ID 292) Giovanni Manente, Andrea Lazzaretto » Design of solar heating system for methane generation (ID 445) Lucía Mónica Gutiérrez, P. Quinto Diez, L. R. Tovar Gálvez xv ii

» Economic feasibility of PV systems in hotels in Mexico (ID 346) Augusto Sanchez, Sergio Quezada » Effect of a back surface roughness on annual performance of an air-cooled PV module (ID 193) Riccardo Secchi, Duccio Tempesti, Jacek Smolka » Energy and exergy analysis of the first hybrid solar-gas power plant in Algeria (ID 176) Fouad Khaldi » Energy recovery from MSW treatment by gasification and melting technology (ID 393) Fabrizio Strobino, Alessandro Pini Prato, Diego Ventura, Marco Damonte » Ethanol production by enzymatic hydrolysis process from sugarcane biomass - the integration with the conventional process (ID 189) Reynaldo Palacios-Bereche, Adriano Ensinas, Marcelo Modesto, Silvia Azucena Nebra » Evaluation of gas in an industrial anaerobic digester by means of biochemical methane potential of organic municipal solid waste components (ID 57) Isabella Pecorini, Tommaso Olivieri, Donata Bacchi, Alessandro Paradisi, Lidia Lombardi, Andrea Corti, Ennio Carnevale » Exergy analysis and genetic algorithms for the optimization of flat-plate solar collectors (ID 423) Soteris A. Kalogirou » Experimental study of tar and particles content of the produced gas in a double stage downdraft gasifier (ID 487) Ana Lisbeth Galindo Noguera, Sandra Yamile Giraldo, Rene Lesme-Jaén, Vladimir Melian Cobas, Rubenildo Viera Andrade, Electo Silva Lora » Feasibility study to realize an anaerobic digester fed with vegetables matrices in central Italy (ID 425) Umberto Desideri, Francesco Zepparelli, Livia Arcioni, Ornella Calderini, Francesco Panara, Matteo Todini » Investigations on the use of biogas for small scale decentralized CHP applications with a focus on stability and emissions (ID 140) Steven MacLean, Eren Tali, Anne Giese, Jörg Leicher » Kinetic energy recovery system for sailing yachts (ID 427) Giuseppe Leo Guizzi, Michele Manno » Mirrors in the sky: status and some supporting materials experiments (ID 184) Noam Lior » Numerical parametric study for different cold storage designs and strategies of a solar driven thermoacoustic cooler system (ID 284) Maxime Perier-Muzet, Pascal Stouffs, Jean-Pierre Bedecarrats, Jean Castaing-Lasvignottes » Parabolic trough photovoltaic/thermal collectors. Part I: design and simulation model (ID 102) Francesco Calise, Laura Vanoli » Parabolic trough photovoltaic/thermal collectors. Part II: dynamic simulation of a solar trigeneration system (ID 488) Francesco Calise, Laura Vanoli » Performance analysis of downdraft gasifier - reciprocating engine biomass fired smallscale cogeneration system (ID 368) Jacek Kalina » Proposing offshore photovoltaic (PV) technology to the energy mix of the Maltese islands (ID 262) Kim Trapani, Dean Lee Millar

xv iii

» Research of integrated biomass gasification system with a piston engine (ID 414) Janusz Kotowicz, Aleksander Sobolewski, Tomasz Iluk » Start up of a pre-industrial scale solid state anaerobic digestion cell for the co-treatment of animal and agricultural residues (ID 34) Francesco Di Maria, Giovanni Gigliotti, Alessio Sordi, Caterina Micale, Luisa Massaccesi » The role of biomass in the renewable energy system (ID 390) Ruben Laleman, Ludovico Balduccio, Johan Albrecht » Vegetable oils of soybean, sunflower and tung as alternative fuels for compression ignition engines (ID 500) Ricardo Morel Hartmann, Nury Nieto Garzón, Eduardo Morel Hartmann, Amir Antonio Martins Oliveira Jr, Edson Bazzo, Bruno Okuda, Joselia Piluski » Wind energy conversion performance and atmosphere stability (ID 283) Francesco Castellani, Emanuele Piccioni, Lorenzo Biondi, Marcello Marconi V. 2 - FUEL CELLS » Comparison study on different SOFC hybrid systems with zero-CO2 emission (ID 196) Liqiang Duan, Kexin Huang, Xiaoyuan Zhang and Yongping Yang » Exergy analysis and optimisation of a steam methane pre-reforming system (ID 62) George G. Dimopoulos, Iason C. Stefanatos, Nikolaos M.P. Kakalis » Modelling of a CHP SOFC power system fed with biogas from anaerobic digestion of municipal wastes integrated with a solar collector and storage units (ID 491) Domenico Borello, Sara Evangelisti, Eileen Tortora

VOLUME VI VI . 1 - CARBON CAPTURE AND SEQUESTRATION » A novel coal-based polygeneration system cogenerating power, natural gas and liquid fuel with CO2 capture (ID 96) Sheng Li, Hongguang Jin, Lin Gao » Analysis and optimization of CO2 capture in a China’s existing coal-fired power plant (ID 532) Gang Xu, Yongping Yang, Shoucheng Li, Wenyi Liu and Ying Wu » Analysys of four-end high temperature membrane air separator in a supercritical power plant with oxy-type pulverized fuel boiler (ID 442) Janusz Kotowicz, Sebastian Stanis aw Michalski » Analysis of potential improvements to the lignite-fired oxy-fuel power unit (ID 413) Marcin Liszka, Jakub Tuka, Grzegorz Nowak, Grzegorz Szapajko » Biogas Upgrading: Global Warming Potential of Conventional and Innovative Technologies (ID 240) Katherine Starr, Xavier Gabarrell Durany, Gara Villalba Mendez, Laura Talens Peiro, Lidia Lombardi » Capture of carbon dioxide using gas hydrate technology (ID 103) Beatrice Castellani, Mirko Filipponi, Sara Rinaldi, Federico Rossi » Carbon dioxide mineralisation and integration with flue gas desulphurisation applied to a modern coal-fired power plant (ID 179) Ron Zevenhoven, Johan Fagerlund, Thomas Björklöf, Magdalena Mäkelä, Olav Eklund » Carbon dioxide storage by mineralisation applied to a lime kiln (ID 226) Inês Sofia Soares Romão, Matias Eriksson, Experience Nduagu, Johan Fagerlund, Licínio Manuel Gando-Ferreira, Ron Zevenhoven xix

» Comparison of IGCC and CFB cogeneration plants equipped with CO2 removal (ID 380) Marcin Liszka, Tomasz Malik, Micha Budnik, Andrzej Zi bik » Concept of a “capture ready” combined heat and power plant (ID 231) Piotr Henryk Lukowicz, Lukasz Bartela » Cryogenic method for H2 and CH4 recovery from a rich CO2 stream in pre-combustion CCS schemes (ID 508) Konstantinos Atsonios, Kyriakos D. Panopoulos, Angelos Doukelis, Antonis Koumanakos, Emmanuel Kakaras » Design and optimization of ITM oxy-combustion power plant (ID 495) Surekha Gunasekaran, Nicholas David Mancini, Alexander Mitsos » Implementation of a CCS technology: the ZECOMIX experimental platform (ID 222) Antonio Calabrò, Stefano Cassani, Leandro Pagliari, Stefano Stendardo » Influence of regeneration condition on cyclic CO2 capture using pre-treated dispersed CaO as high temperature sorbent (ID 221) Stefano Stendardo, Antonio Calabrò » Investigation of an innovative process for biogas up-grading – pilot plant preliminary results (ID 56) Lidia Lombardi, Renato Baciocchi, Ennio Antonio Carnevale, Andrea Corti, Giulia Costa, Tommaso Olivieri, Alessandro Paradisi, Daniela Zingaretti » Method of increasing the efficiency of a supercritical lignite-fired oxy-type fluidized bed boiler and high-temperature three - end membrane for air separation (ID 438) Janusz Kotowicz, Adrian Balicki » Monitoring of carbon dioxide uptake in accelerated carbonation processes applied to air pollution control residues (ID 539) Felice Alfieri, Peter J Gunning, Michela Gallo, Adriana Del Borghi, Colin D Hills » Process efficiency and optimization of precipitated calcium carbonate (PCC) production from steel converter slag (ID 114) Hannu-Petteri Mattila, Inga Grigali nait , Arshe Said, Sami Filppula, Carl-Johan Fogelholm, Ron Zevenhoven » Production of Mg(OH)2 for CO2 Emissions Removal Applications: Parametric and Process Evaluation (ID 245) Experience Ikechukwu Nduagu, Inês Romão, Ron Zevenhoven » Thermodynamic analysis of a supercritical power plant with oxy type pulverized fuel boiler, carbon dioxide capture system (CC) and four-end high temperature membrane air seprator (ID 411) Janusz Kotowicz, Sebastian Stanis aw Michalski VI . 2 - PROCESS INTEGRATION AND HEAT EXCHANGER NETWORKS » A multi-objective optimization technique for co- processing in the cement production (ID 42) Maria Luiza Grillo Renó, Rogério José da Silva, Mirian de Lourdes Noronha Motta Melo, José Joaquim Conceição Soares Santos » Comparison of options for debottlenecking the recovery boiler at kraft pulp mills – Economic performance and CO2 emissions (ID 449) Johanna Jönsson, Karin Pettersson, Simon Harvey, Thore Berntsson » Demonstrating an integral approach for industrial energy saving (ID 541) René Cornelissen, Geert van Rens, Jos Sentjens, Henk Akse, Ton Backx, Arjan van der Weiden, Jo Vandenbroucke » Maximising the use of renewables with variable availability (ID 494) Andreja Nemet, Jiri Jaromír Klemeš, Petar Sabev Varbanov, Zdravko Kravanja xx

» Methodology for the improvement of large district heating networks (ID 46) Anna Volkova, Vladislav Mashatin, Aleksander Hlebnikov, Andres Siirde » Optimal mine site energy supply (ID 306) Monica Carvalho, Dean Lee Millar » Simulation of synthesis gas production from steam oxygen gasification of Colombian bituminous coal using Aspen Plus® (ID 395) John Jairo Ortiz, Juan Camilo González, Jorge Enrique Preciado, Rocío Sierra, Gerardo Gordillo

VOLUME VIII VIII . 1 - ENERGY SYSTEMS : ENVIRONMENTAL AND SUSTAINABILITY ISSUES » A multi-criteria decision analysis tool to support electricity planning (ID 467) Fernando Ribeiro, Paula Ferreira, Madalena Araújo » Comparison of sophisticated life cycle impact assessment methods for assessing environmental impacts in a LCA study of electricity production (ID 259) Jens Buchgeister » Defossilisation assessment of biodiesel life cycle production using the ExROI indicator (ID 304) Emilio Font de Mora, César Torres, Antonio Valero, David Zambrana » Design strategy of geothermal plants for water dominant medium-low temperature reservoirs based on sustainability issues (ID 99) Alessandro Franco, Maurizio Vaccaro » Energetic and environmental benefits from waste management: experimental analysis of the sustainable landfill (ID 33) Francesco Di Maria, Alessandro Canovai, Federico Valentini, Alessio Sordi, Caterina Micale » Environmental assessment of energy recovery technologies for the treatment and disposal of municipal solid waste using life cycle assessment (LCA): a case study of Brazil (ID 512) Marcio Montagnana Vicente Leme, Mateus Henrique Rocha, Electo Eduardo Silva Lora,Osvaldo José Venturini, Bruno Marciano Lopes, Claudio Homero Ferreira » How will renewable power generation be affected by climate change? – The case of a metropolitan region in Northwest Germany (ID 503) Jakob Wachsmuth, Andrew Blohm, Stefan Gößling-Reisemann, Tobias Eickemeier, Rebecca Gasper, Matthias Ruth, Sönke Stührmann » Impact of nuclear power plant on Thailand power development plan (ID 474) Raksanai Nidhiritdhikrai, Bundhit Eua-arporn » Improving sustainability of maritime transport through utilization of liquefied natural gas (LNG) for propulsion (ID 496) Fabio Burel, Rodolfo Taccani, Nicola Zuliani » Life cycle assessment of thin film non conventional photovoltaics: the case of dye sensitized solar cells (ID 471) Maria Laura Parisi, Adalgisa Sinicropi, Riccardo Basosi » Low CO2 emission hybrid solar CC power system (ID 175) Yuanyuan Li, Na Zhang, Ruixian Cai » Low exergy solutions as a contribution to climate adapted and resilient power supply (ID 489) Stefan Goessling-Reisemann, Thomas Bloethe » On the use of MPT to derive optimal RES electricity generation mixes (ID 459) Paula Ferreira, Jorge Cunha xxi

» Stability and limit cycles in an exergy-based model of population dynamics (ID 128) Enrico Sciubba, Federico Zullo » The influence of primary measures for reducing NOx emissions on energy steam boiler efficiency (ID 125) Goran Stupar, Dragan Tucakovi , Titoslav Živanovi , Miloš Banjac, Sr an Beloševi ,Vladimir Beljanski, Ivan Tomanovi , Nenad Crnomarkovi , Miroslav Sijer » The Lethe city car of the University of Roma 1: final proposed configuration (ID 45) Roberto Capata, Enrico Sciubba VIII . 2 - POSTER SESSION » A variational optimization of a finite-time thermal cycle with a Stefan-Boltzmann heat transfer law (ID 333) Juan C.Chimal-Eguia, Norma Sanchez-Salas » Modeling and simulation of a boiler unit for steam power plants (ID 545) Luca Moliterno, Claudia Toro » Numerical Modelling of straw combustion in a moving bed combustor (ID 412) Biljana Miljkoviü, Ivan Pešenjanski, Borivoj Stepanov, Vladimir Milosavljeviü, Vladimir Rajs » Physicochemical evaluation of the properties of the coke formed at radiation area of light hydrocarbons pyrolysis furnace in petrochemical industry (ID 10) Jaqueline Saavedra Rueda , Angélica María Carreño Parra, María del Rosario Pérez Trejos, Dionisio Laverde Cataño, Diego Bonilla Duarte, Jorge Leonardo Rodríguez Jiménez, Laura María Díaz Burgos » Rotor TG cooled (ID 121) Chiara Durastante, Paolo Petroni, Michela Spagnoli, Vincenzo Rizzica, Jörg Helge Wirfs » Study of the phase change in binary alloy (ID 534) Aroussia Jaouahdou, Mohamed J. Safi, Herve Muhr » Technip initiatives in renewable energies and sustainable technologies (ID 527) Pierfrancesco Palazzo, Corrado Pigna

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ECOS 2012

VOLUME VII

PROCEEDINGS OF ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY

A Linear Programming model for the optimal assessment of Sustainable Energy Action Plans. Gianfranco Rizzoa , Giancarlo Savinob a

Department of Industrial Engineering, University of Salerno,Fisciano (SA), Italy, [email protected] b Energy Manager, City of Salerno, Italy, [email protected]

Abstract: A relevant effort is being spent to reac h the EU climate and energy goals by involving European cities and towns in sustainable energy planning. Many Italian and European cities are now involved in the development of S ustainable E nergy Action Plans (SEAP), pres enting in detailed way the actions finalized to the reduction of CO2 emissions. In most cases, a large number of actions are proposed, ranging from renewable energy production to energy saving and to information and communication actions. It therefore emerges the need of methodologies for guiding the administrators to the s election of the m ost effective actions for the achievement of the desired emission reduction, compatibly with budget and resource availability. A Linear Programming model for the optimal selection of the actions and of their priorities is presented. The model allows to allocate in optimal way the economic resources among different actions to achieve a given level of CO2 emissions reduction, considering resourc e constraints. The model has a user-friendly interface, and a complexity compatible with applications to municipal level. An example of application of the model t o a school is present ed and discussed.

Keywords: Model, Linear Programming, Energy Plan.

1. Introduction In last decades there are growing concerns about fossil fuel reserve depletion, greenhouse effect and related climate changes. After ratification of the Kyoto protocol [1], a relevant effort is being spent by Europe to enhance renewable energy production and to promote energy efficiency. In December 2008, the EU adopted an integrated energy and climate change policy (20/20/20), with ambitious targets for 2020: cutting greenhouse gases by 20%; reducing energy consumption by 20% through increased energy efficiency; meeting 20% of energy needs from renewable sources [2]. In order to reach these goals, an active participation of European cities and towns in sustainable energy planning has been stimulated by the European institutions. Many European cities are now involved in the development of Sustainable Energy Action Plans (SEAP), presenting in a detailed way the actions finalized to the reduction of CO2 emissions [3]. In Italy, 1225 municipalities have joined the Covenant of Major, while only 16% of them have already produced the SEAP (January 2012) [5]. Most of them are located in the North of Italy (Fig. 1). A study on a set of SEAP produced in eight representative Italian cities (Alessandria, Bergamo, Cesena, Modena, Padova, Piacenza, Torino, Udine) is being carried out by the authors, within the studies to develop the SEAP for the city of Salerno [26] [28]. In most cases, a large number of actions are proposed, ranging from renewable energy production to energy saving, to information and communication actions and to stakeholders involvement. The analysis has demonstrated a certain lack of quantitative data in part of the proposed actions. Moreover, when quantitative evaluations of costs and benefits in terms of CO 2 reduction and/or energy savings of each proposed action are provided (Table 1), any indication of priorities or selection criteria among them is missing. Actually, most of the planned actions have quite different cost effectiveness in terms of CO2 reductions and energy savings, as evidenced by the graphs 1

reported in Fig. 2, representing: i) the avoided CO 2 versus energy savings (upper part) and ii) their unit costs (lower part) for a set of actions and cities (listed in the legend). The analysis of the data shows that there is more than one order of magnitude between the unit costs related to different actions. Moreover, a significant spread between the unit costs of same actions for different cities also occurs [26].

Fig. 1. Number of Italian cities that have completed the SEAP Table 1. Analysis of a group of Italian SEAPs. Actions and Cities. Alessandria Berga mo Cesena Bi omass PV plants LED for tra ffi c lights Street li ghting optimi za tion Pri va te Building Opti miza tion Public Building Opti miza tion RSU Thermal Sola r Plants Dis tri ct Hea ting Public Transporta tion Total

1 0 0 0 0 0 0 1 1 1 4

0 1 1 1 1 1 0 0 1 0 6

1 1 0 0 1 0 0 1 0 0 4

Modena

Padova

Pia cenza

Torino

Udine

Total

0 1 1 1 1 0 0 0 0 0 4

0 1 1 1 0 0 0 0 0 1 4

0 0 1 1 0 0 0 0 1 0 3

0 0 1 1 1 1 1 1 0 1 7

1 1 1 1 0 1 0 1 1 0 7

3 5 6 6 4 3 1 4 4 3 39

Therefore, it is apparent that a selection criteria between different actions could be needed, at least in case of partial availability of financial resources. Moreover, some of these actions could be mutually exclusive or subject to some common constraints: for instance, space heating requirements could be satisfied by use of solar thermal panels or cogeneration plants, but also reduced by proper building insulation; similarly, the installation of solar thermal panels or photovoltaic panels on building roofs cannot exceed the available surface. It is evident that, in many cases, the decisions about possible alternative actions are somewhat interrelated and not independent of each other. The above considerations evidence the need of methodologies for guiding the administrators to the selection of the most effective actions for the achievement of the desired emission reduction, compatibly with budget and resource availability. A review on the models available in literature for energy and environmental planning is summarized in next chapter, while a model based on Linear Programming, particularly suitable for 2

small scale and municipal level, is presented in the following chapters, and some results are discussed. 3.5

x 10

5

3

Avoided CO2 [ t*year]

2.5

2

1.5

1

0.5

0 0

2. 5

x 10

1

2

3 4 5 Energy S aving [MWh*year]

6

7 x 10

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Avoided CO2 Cost [€/(t *year)]

2

1. 5

1

0. 5

0 0

500

1000 1500 2000 2500 3000 3500 Energy Saving Cost [€/(MWh*year)]

4000

Modena/PV Bergamo/PV Cesena/PV Udine/PV Padova/PV Torino/Public Transportation Padova/Public Transportation Alessandria/Public Transportation Bergamo/Building optimization (private) Cesena/Building optimization (private) Torino/Building optimization (private) Modena/Building optimization (private) Bergamo/Building optimization (public) Torino/Building optimization (public) Udine/Building optimization (public) Torino/Waste Disposal Bergamo/District Heating Piacenza/District Heating Udine/District Heating Alessandria/District Heating Udine/Thermal solar Alessandria/Thermal solar Cesena/Thermal solar Torino/Thermal solar Cesena/Biomass Udine/Biomass Alessandria/Biomass Torino/LED for traffic lights Modena/LED for traffic lights Piacenza/LED for traffic lights Padova/LED for traffic lights Bergamo/LED for traffic lights Udine/LED for traffic lights Torino/Street lighting optimization Modena/Street lighting optimization Piacenza/Street lighting optimization Padova/Street lighting optimization Bergamo/Street lighting optimization Udine/Street lighting optimization Natural Gas Electrical Energy

4500

Fig. 2. Analysis of a group of Italian SEAPs. Avoided CO2 vs Energy savings (up) - Avoided CO2 Unit Cost vs Energy savings unit cost (down)

3

2. Models for Energy Systems Several models have been developed to study and plan the evolution of complex systems involving interaction of economic, energetic and environmental aspects. A large review of models used for energy studies, at different levels and approaches, is available in [20]. In the early ‘70s, the model WORLD3 was used to model the interactions between population, industrial growth, food production and limits in the ecosystems of the Earth [6]. Some years later, the MARKAL models generator was developed by a consortium of 14 countries under the aegis of an IEA committee (Energy Technology Systems Analysis Development Programme, ETSAP), with a specific focus on energy system analysis [7]. Starting from the original formulation, further implementations have been carried out to account for different situation and purposes. A short overview of MARKAL models is presented in Table 2. The mathematical approach is mainly based on Linear Programming (LP), while Non-Linear Programming (NLP), Multiple Integer Programming (MIP) and Stochastic Programming (SP) are also used. Further details, with reference to selected bibliography, is available in [8]. The MARKAL models are now widely used in many countries to support energy-environmental planning at national and local scale [9][10][11]. Specific tools have also been developed at the Environmental Protection Agency (EPA) in U.S.. The “Integrated Planning Model” (IPM) allows to analyze the impact of air emissions policies on the U.S. electric power sector. EPA has used multiple iterations of the IPM model in various analyses of regulations and legislative proposals [13]. Table 2. Overview of the MARKAL family of models (from[8] ). Membe r /Version

Type of Model

MARKAL MARKAL-MACRO

LP NLP

MARKAL-MICRO

NLP

MARKAL-ED (MED)

LP

MARKAL

NLP

MARKAL

LP

MARKAL

SP

MARKAL – ETL

MIP

Short Description Standard model. Exogenous energy demand Coupling to macro-econo mic model energy demand endogenous. Coupling to micro-economic model, energy demand endogenous, responsive to price changes. As MARKAL-M ICRO but with step-wise linear representation of demand function. Linkage of mult iple countries specific MA RKA L-M ED With mu ltip le reg ions and MARKA L-MA CRO, including trade of emission Permits. Besides energy flows (electricity, heat) material flo ws with material flows and recycling of materials can be modeled in the RES. Stochastic Programming. Only with standard model. With Uncertainties Endogenous technology learning based on learning-by-doing curve. Specific cost decreases as function of cumu lative experience.

Some models address specifically the energy plans at municipal level [21]-[25]. Both general models [21] [22] [25] and specific models, i.e. for Solid Waste Management [23], have been developed. However, in some cases the term ‘municipal’ may be misleading, being referred to very large communities as Beijing [21]. The MARKAL and IPM models, in their numerous versions, can cover most, if not all, of the possible cases occurring in the study of an energy and environmental system, and could certainly be adapted to study actions at municipality level, as considered by SEAP. However, their modelling structure is quite complex, and their use is probably more suitable in academic and government agencies context rather than at municipal level, in particular for a small or medium size town or city. On the other hand, at a local level interactions with macro-economic aspects, material flows 4

and prices changes, representing the distinctive features of the MARKAL or IPM models, are of course less relevant than at regional or national level. In next chapter a simpler LP model will be presented, specifically tailored to the exigencies of small scale systems, as for a SEAP at municipal level.

3. The proposed LP model The proposed methodology is based on the solution of an optimal resource allocation problem by means of a Linear Programming (LP) approach. The classical LP problem consists of the determination of the decision variable vector x minimizing a linear objective function F(x): (1)

subject to linear equality constraints: (2)

and to linear inequality constraints: (3)

Starting from its basic formulation from Dantzig [15], several different versions of LP methods have been proposed, for the solution of different problems. In the present case, the solution is obtained by means of the Simplex method, as implemented in the Matlab function ‘linprog’ [16]. The decisions variables x i represent a measure of the investment in each action. Their units vary according to the specific action considered, as specified in Table 3. Regarding their nature, x i are real and non-negative numbers. In case of LED, x 3 should be indeed an integer number, representing the optimal number of lamps. However, it is treated as a real number, being its value quite large (particularly in applications at municipal level). The result of the optimization problem is therefore approximated to the nearest integer number. The objective function F(x) (1) is expressed as a linear combination of the product of decision variables x i and terms f i: (4)

where ii is the yearly unit investment and ri is the yearly unit revenue associated to the i-th action, while T is the time horizon, in years. The objective function therefore represents the global investment needed by the decision maker (the municipality) to achieve a given level of CO 2 emissions, minus the possible revenues associated to the actions, achieved in the given time horizon. Both short and long terms strategies can be examined by varying T. In particular, if T is set to zero, no revenues are considered. Therefore, the solutions corresponding to the minimum investment needed to achieve the given level of CO 2 reduction are sought. This solution would then represent the minimum cost strategy to achieve the given emissions reduction, regardless of future revenues. The variable Beq in the equality constraint (2) represents the global reduction of CO 2 emission, while the diagonal terms of the matrix Aeq contain the unit impact factors of the actions x i on CO2 emissions. The inequality constraints (3) express the availability of resources to be allocated to the actions x, where variable B is the maximum available resource for each group of actions, and the matrix A indicates the correspondence between each action and a group of resources. An additional inequality constraint (5) expresses the conditions that the total required investment I must be not greater than the available economic resource Imax:

5

(5)

The solution of the problem is achieved for two scenario’s with different time horizon, i.e. Short Term (T=0) and Long Term (T=20). In the former case, the solutions corresponding to the minimum investment compatible with the given emission reduction are obtained, regardless the long term result. In the second case, the maximum long term results are obtained, of course with a greater initial investment. The results corresponding to intermediate investment values between these two limit cases are also investigated, by imposing suitable values to the maximum allowed investment in (5). For each scenario, the whole range of emissions reduction Beq is examined. Therefore, a complete picture of the required actions, of their priorities and of the needed investment is provided, both in tabular and in graphical form. Some general comments on the linear assumption of the model seem necessary. As shown in Table 2 and in literature review presented in the previous chapter, Linear Programming is one of the most used techniques for energy planning problems. Although most physical systems involved in such problems are inherently non-linear in nature, the relationship between the decision variables and the output variables can often be approximated by linear relationships. With reference to the actions considered in this paper and in the on-going applications to municipal level, there are certainly some scale effects related to the size of the plant, affecting unit costs, and possibly efficiencies and CO2 emissions. In case that these effects are relevant, they could be treated by non- linear relationships, so leading to a non- linear optimization problem, characterized by a significant increase in complexity and computational burden with respect to a LP problem. Another way to tackle the problem is to consider separately the actions referring to small, medium or large plants, where each class of plants can be characterized by (approximate) linear relationships between decision variables and output variables. This approach, that seems more suitable at small or medium scale energy systems, could allow to maintain the advantages of Linear Programming with only a moderate increase in problem dimensionality.

4. An example of application In order to check the operation of the model on a small scale example, the case of a school has been considered. The energy required is for space heating (in the period from November 15 to April 30) and electricity and hot water (all the year, except August), while no air conditioning is required. Different solutions have been considered: A. Solar thermal collectors for hot water and space heating, with seasonal storage. B. Photovoltaic (PV) panels (the surplus electricity is sold to the grid). C. Reduction of electricity demand by adopting LED. D. Cogeneration plant (CHP), fueled with natural gas (the surplus electricity is sold to the grid). E. Reduction of thermal energy demand by building insulation. Investment costs, yearly savings and avoided CO 2 per unit are reported in Table 3, for each action. They represent respectively the terms i and r in equations (4) and (5), and the terms Aeq in equation (2). For instance, in case of PV panels (second row) the decision variable x 2 is represented by panel surface in m2 , the term f 2 (4) is equal to 300-50·T, while 70 is the estimated yearly avoided CO 2 per unit (square meter), representing the term Aeq2,2 in the equality constraint (2).

6

Table 3. Actions, unit cost, savings and avoided CO2 . Unit Actions Thermal Solar + Seasonal Storage PV panels LED CHP with methane Building insulation

m2 m2 No. of lamps kWe €

Unit cost € 750 300 100 2000 1

Savings €/year/unit 50 40 20 680 0,24

Avoided CO2 kg/year*unit 300 70 50 1600 0,45

The links between actions and resources are summarized in Table 4. In the second row the maximum available resource for each action is reported, representing the terms B in equation (3). They express the maximum allowed surface for solar panels (the sum of thermal and photovoltaic), the maximum number of LED lamps, the maximum electric power for co-generator and the actual thermal load of the building. The correspondence between each action and the resources, representing matrix A in (3), is also presented in the lower part of the table. In this case, the matrix expresses a link between solar thermal panels and PV panels (second column), whose surface cannot exceed the total available surface of 200 m2 . A further constraint (last column) connects thermal panels, CHP plant and building insulation, since their effect cannot exceed the given yearly thermal load, estimated in 91500 kWh. In other words, their effects are additive, and should not exceed the required thermal load to avoid energy waste. The use of LED lamps, instead, is not linked to the other actions related to electrical energy production (PV panels and CHP), since it is assumed that the excess electrical energy can be sold to the grid. Table 4. Actions and available resources. Resource Availability Actions Thermal Solar + Seasonal Storage PV panels LED CHP with methane Building insulation

Panel Surface [m2 ] 200

N lamps [/] 80

CHP [kWe] 100

Thermal load [kWht/year] 91500

1 1 0 0 0

0 0 1 0 0

0 0 0 1 0

450 0 0 17520 2,25

The data in the tables have been estimated starting from average producibility of solar plant, cost of natural gas and of electricity in Italy, studies on thermal solar plants with seasonal storage and literature data on building insulation costs and performance. It has to be remarked, however, that the main purpose of this calculation is to check and illustrate the features of the proposed method, rather than to design in detailed way the best energy system for a school. Of course, more precise and complex methods exist for thermal design and optimization of buildings, also including nonlinear and transient effects, that are not considered in this analysis [17], [18], [19].

4.1. Results A global picture of the results, in terms of investment, costs and CO 2 reduction, is provided in Fig. 3. The optimal size of investment and the related profit for each action is shown in Fig. 4, for the two scenarios (short term and long term). It is timely to remark that, both in short and long term scenarios, profits are evaluated after the same time horizon (i.e.20 years). However, while in long term scenario profit coincides with the objective function (1), in the short term case (T=0) the long term profit corresponding to the minimum investment is computed. 7

Cost-Benefit - Short Term vs Long Term Strategies 0.35 Investment (st) Profit (st) Investment (lt) Profit (lt)

0.3

0.25

M€

0.2

0.15

0.1

0.05

0 10

20

30

40

50 60 70 CO2 Reduction [%]

80

90

100

Fig. 3. Optimal results - Investment Costs and Profit vs CO2 reduction In Fig. 3, the short term scenario is indicated by continuous lines, while dotted lines represent the long term scenario. To achieve a given CO 2 reduction, different solutions are available, with investment costs ranging from a minimum value (continuous blue line) to a maximum value (dotted blue line). In correspondence, profit also ranges from a minimum value (red continuous line) to a maximum value (red dotted line). Intermediate results are indicated by blue and red stars. It can be observed that the investment costs (blue lines) are always increasing with CO 2 reduction. The dotted line stops at 0.1 M€, representing the maximum allowed investment Imax. The slope of profit (red lines), instead, tends to decrease, and to become negative. This tendency is much more evident for the dotted line (long term). In this case (upper part of Fig. 4), the actions corresponding to higher profit per avoided emission unit are first selected (building insulation, in this case), then the other actions (PV panels, LED and thermal panels). It can be observed that, when the emission reduction increases, a gradual substitution between PV and thermal panels occurs, due to the constraint on maximum available surface. Similarly, the investment in building insulation decreases when thermal solar panels are adopted. For the actions not conflicting with others (i.e. LED lamps), the investment gradually increases until the saturation level is reached. For the short term scenario (lower part of Fig. 4) the most convenient solutions in terms of initial investment versus CO 2 reduction are first selected. In this case, the suggested actions are CHP, LED and thermal solar panels. It can be also observed that, when investment for thermal solar panel increases, the size of CHP plant is reduced, to satisfy the constraint on the thermal load. It can be observed that there is a large difference between the minimum and the maximum profit, corresponding to short and long term scenarios. The difference is small at lower investment values, growths to their maximum at about 87% of CO 2 reduction, when the maximum allowed investment (blue dotted line) reaches the limit value of 0.1 M€ (Fig. 3). After this value, the differences between short and long terms scenarios tend to decrease again. It emerges, therefore, that, for a large range of CO2 emissions, even small differences in investment costs (blue) may produce large differences in profit, at the same level of CO 2 emissions. An analysis limited only to investment costs and related CO 2 emissions could therefore strongly penalize the long term results, while much better profits could be obtained with only a slight increase in initial investment. 8

Time Horizon=20[year]

Time Horizon=20[year]

0.06

0.2 0.15

0.04

Profit [M€]

Investment [M€]

0.05

0.03 0.02

0.1

0.05 0.01 0

0

50 CO2 Reduction [%]

0

100

0

Time Horizon=0[year] 0.08

0.08

0.06 Profit [M€]

Investment [M€]

100

Time Horizon=0[year]

0.1

0.06 0.04

0.04

0.02

0.02 0 0

50 CO2 Reduction [%]

50 CO2 Reduction [%]

0 0

100

50 CO2 Reduction [%]

100

Thermal Solar + Seasonal Storage PV with incentives LED CHP with methane Building insulation

Fig. 4. Optimal results - Investment and profit for each action vs CO2 reduction It is worth noting that the CO 2 reduction can even exceed 100% of the original CO 2 emissions. In fact, the production of electrical energy via CHP and PV panels is not necessarily limited to the electrical load of the school, since it can be sold to the grid. A graph with the ratio between profit and investment is presented in Fig. 5. This ratio ranges between 1 and 5,5, approximately. Similar graphs are obtained to describe the optimal size of the proposed actions, versus CO 2 reduction and investment. Two graphs refer to optimal surface of PV plant, reaching their maximum value at a CO 2 reduction of about 75% (Fig. 6), and to optimal number of LED lamps, that tend to be selected only for CO 2 reduction greater than 30% (Fig. 7). Similar graphs, not reported in the paper due to space constraints, are obtained for the other planned actions. The set of results presented above has been obtained by solving the LP problem (1)-(5) 45 times, for different values of constraints on CO 2 level and maximum allowed investment. About 100 graphs and several tables in Excel were automatically generated. Computational time is about 50 seconds on a Desktop PC (CPU Intel® Core™ i3, 4 GB RAM, 3.07 GHz). These results demonstrate that, even considering a relatively simple energy system as a school, a rather complex picture emerges and articulate strategies are needed to achieve the best results in 9

terms of CO2 reduction, with limited economic resources and in presence of constraints between the different actions. The best mix of solutions depends on the target emission reduction, and therefore on the available financial resources. Moreover, even if provided by a linear model, the solutions are not linear with respect to the output (CO2 emissions reduction): in other words, the best solution to achieve 100% reduction of CO2 is not simply obtainable (i.e. doubling each action) from the solution corresponding to 50% reduction, as clearly shown in Fig. 4. In fact, passing from 50% to 100% reduction, the best solution is obtained not only incrementing some actions, but also reducing some others. This implies that a clear picture of objectives and of available resources is required at the start of the project, since the best strategy to enhance system performance (i.e. increase CO 2 reduction) could not be simply obtained by additional investments on an existing plant, even if starting from an optimal solution. Profit/Investment

Investment [M€]

0.1

5.5

0.09

5

0.08

4.5

0.07

4

0.06

3.5

0.05

3

0.04

2.5

0.03

2

0.02

1.5

0.01

1 20

30

40

50 60 70 CO2 Reducti on [%]

80

90

100

Fig. 5. Optimal results – Ratio between profit and investment vs. CO2 reduction. PV with incenti ves 0.1

160

0.09

140

0.08 120 Investment [M€]

0.07 100 0.06 80

0.05 0.04

60

0.03

40

0.02

20

0.01 20

30

40

50 60 70 CO2 Reducti on [%]

80

90

100

Fig. 6. Optimal results – Optimal surface of PV panels (m 2 ) vs. CO2 reduction.

10

LED 0.1

80

0.09

70

0.08 60 Investment [M€]

0.07 50 0.06 40

0.05 0.04

30

0.03

20

0.02

10

0.01 20

30

40

50 60 70 CO2 Reducti on [%]

80

90

100

Fig. 7. Optimal results – Number of LED lamps vs. CO2 reduction.

5. Conclusions A methodology to assess the optimal combination of actions to achieve given CO 2 emission reduction, considering their effectiveness and costs, has been presented. The proposed procedure is particularly suitable at a municipality level, to assist the development of Sustainable Energy Action Plans. The methodology, based on a Linear Programming approach, provides the optimal selection of the actions and of their priorities in order to achieve the best environmental benefits in presence of limited economic resources and of constraints between the different actions. The results, obtained by application of the model to a school, have evidenced that not straightforward strategies can be required to achieve the best mix of the planned actions in order to maximize the environmental benefits, for different availability of economic resources. It has also been shown that the analysis cannot be limited to the minimization of investment costs for given emission reduction, since long term effects could be significantly penalized by this approach. This result is of practical relevance for the assessment of the Sustainable Energy Action Plans, since in most of the analyzed cases only investment costs and impact on CO 2 emissions were provided in the documents, regardless of their long term economic impact. This approach could lead into significant inefficiencies in terms of allocation of financial resources. The procedure is actually in course of application to the development of Sustainable Energy Action Plan for the city of Salerno, in South Italy. In this case, the actions are being treated at aggregate levels (i.e. buildings are not described individually, but as clusters of homogeneous cases; the same happens for infrastructures and transport systems). A study on SEAP of different Italian cities [5] [26] [28] has shown that the number of different actions considered is of the order of ten (Table 1). It is therefore expected that the total number of actions will be not very large, and that it will compatible with the proposed method, in terms of computational burden and of robustness.

References [1] The Kyoto Protocol, available at [2] European Commission, Climate Action Documents and Publications, available at [3] P.Bertoldi, D.Bornás Cayuela, S.Monni, R.Piers de Raveschoot, Existing Methodologies and Tools for the Development and Implementation of Sustainable Energy Action Plans (SEAP), 11

Publications Office of the European Union, 2010, JRC56513, ISBN: 978-92-79-14852-1, ISSN: 1018-5593. [4] Convenant of Majors, available at [5] Italian Cities belonging to Convenant of Majors, available at [6] D.H. Meadows, D.L. Meadows, J.Randers, and W.W. Behrens III. (1972), The Limits to Growth. New York: Universe Books. ISBN 0-87663-165-0. [7] Fishbone LG, Abilock H., MARKAL - A linear-programming model for energy syste m analysis: technical description of the BNL version. Int J Energy Res 1981;5:353–75. [8] Mohammad Reza Faraji Zonooz, Z.M. Nopiah, Ahmad Mohd Yusof, Kamaruzzaman Sopian, “A Review of MARKAL Energy Modeling”, European Journal of Scientific Research, ISSN 1450-216X Vol.26 No.3 (2009), pp.352-361 [9] E. Endoa, M. Ichinoheb, Analysis on market deployment of photovoltaics in Japan by using energy system model MARKAL, Solar Energy Materials & Solar Cells 90 (2006) 3061–3067 [10] M. Salvia, C. Cosmi, M. Macchiato, L. Mangiamele, Waste management system optimisation for Southern Italy with MARKAL model, Resources, Conservation and Recycling, 34 (2002) 91–106. [11] Johnsson J, Bjorkqvist O, Wene C-O. Integrated energy-emissions control planning in the community of Uppsala. Int J Energy Res 1992;16:173–95. [12] ETSAP, Energy Technology Systems Analysis Program, available at [13] EPA Integrated Planning Model, available at [14] City Energy Plan, Salerno (in Italian), available at [15] G.B Dantzig, Maximization of a linear function of variables subject to linear inequalities, 1947. Published pp. 339–347 in T.C. Koopmans (ed.):Activity Analysis of Production and Allocation, New York-London 1951 (Wiley & Chapman-Hall). [16] Linear Programming on Matlab, available at [17] D.B. Crawley, L.K. Lawrie, F.C. Winkelmann, W.F. Buhl, Y.J. Huang, C.O. Pedersen, R.K. Strand, R.J. Liesen, D.E. Fisher, M.J. Witte, J. Glazer, EnergyPlus: creating a new- generatio n building energy simulation program, Energy and Buildings, pp. 319-331, vol. 33, 2001 [18] J. A. Clarke, J. Cockroft, S. Conner, J. W. Hand, N. J. Kelly, R. Moore, T. O'Brien, P. Strachan, Simulation-assisted control in building energy management systems, Energy and Buildings, pp. 933-940, vol. 34, 2002. [19] Building Energy Software Tools Directory, US Dept. Of Energy, available on http://apps1.eere.energy.gov/buildings/tools_directory/subjects_sub.cfm [20] S. Jebaraja, S. Iniyanb, A review of energy models, Renewable and Sustainable Energy Reviews, 10 (2006) 281–311 [21] Q.G. Lin, G.H. Huang, Planning of energy system management and GHG emission control in the Municipality of Beijing - An inexact-dynamic stochastic programming model, Energy Policy 37(2009) 4463–4473. [22] Clas-Otto Wene, Bo Rydén, A comprehensive energy model in the municipal energy planning process, European Journal of Operational Research, Volume 33, Issue 2, January 1988, Pages 212–222

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[23] Guohe Huang, Brian W. Baetz and Gilles G. Patry, A Grey Linear Programming Approach for Municipal Solid Waste Management Planning under Uncertainty, Civil Engineering Systems, Volume 9, Issue 4, 1992 [24] Jenny Ivner, Municipal Energy Planning – Scope and Method Development, PhD Thesis, Linköping Studies in Science and Technology, Dissertation no. 1234 [25] Dag Henning, MODEST—An energy-system optimisation model applicable to local utilities and countries, Energy, Volume 22, Issue 12, December 1997, Pages 1135–1150 [26] Daniele Galdi, Piani d’Azione per l’Energia Sostenibile: analisi quantitativa delle azioni proposte, Bachelor Thesis in Mechanical Engineering, University of Salerno, February 2012, in Italian. [27] Gabriele Orlando, Modelli per la pianificazione energetica ed ambientale, Bachelor Thesis in Mechanical Engineering, University of Salerno, February 2012, in Italian. [28] Vito Di Guida, Analisi comparata dei Piani d’Azione per l’Energia Sostenibile, Bachelor Thesis in Mechanical Engineering, University of Salerno, February 2012, in Italian.

Acknowledgments The contributions given to the present analysis by Vito Di Guida, Daniele Galdi and Gabriele Orlando during their Master Thesis in Mechanical Engineering at the University of Salerno are gratefully acknowledged.

13

PROCEEDINGS OF ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY

A natural gas fuelled 10 kw electric power unit suitable for distributed energy conversion based on an automotive internal combustion engine Pietro Capaldi CNR-Istituto Motori, Naples, Italy, [email protected]

Abstract The paper discusses the concept and the overall performance of an auxiliary power unit, suitable for distributed energy conversion, based on a wide-spread automotive supercharged Diesel internal combustion engine. The latter has been converted into a spark ignition met hane/nat ural gas unit by Istituto Motori CNR of Italy and it has been specifically chos en among many other engines as a reliable, high efficiency, cost effective unit, suitable for energy conversion systems (such as microcogeneration for residential or commercial applications). The paper starts by defining the ratio which leaded to the adoption of an automotive four cylinders, Diesel internal combustion engine, in order to produce the above mentioned electric power. This is followed by a ex planation of the main modifications adopted to convert the former Diesel engine in a spark ignited stoichiometric unit, with a discussion over the most significant element and technical solution that c ould give the system a high efficiency, low gaseous emissions and long enduranc e. The unit has been coupled with a liquid cooled induction generator and then tested as an electricity and heat production system, ready for grid connection and to become a base for a future microcogeneration system, thanks to a new designed management/control system. During field test a complete report of its running behavior has been reported.

Keywords: Distributed generation, Microcogeneration, Micro-grids, Natural gas.

Introduction Micro-cogeneration plants seem to be a interesting solution to become a smart way of energy supplying for single houses, buildings and commercial activities; moreover it’s considered a simple and immediate form to enhance the full utilization of fuel energy and, consequently, a reduction for CO2 emissions, especially when natural gas is used as fuel. Actually there are some plants available on the European market, able to produce an electric power of about 15 kW (such as. Tandem [1], EnergyWerkestatt [2], EC-Power [3], Energ-Co [4]), offering interesting overall performances in terms of electric efficiency (between 25% and 31%) and Primary Energy Ratio (i.e. the energy utilization rate of fuel, comprised between 85% and 90%). However these units still have some disadvantages if compared to a conventional electricity and heat supply (i.e. by grid distribution and conventional gas heater), such as high cost, bulk and electric efficiency; for these reasons micro-cogeneration could be still far from high volume production, waiting for new solutions capable of reducing the effect of the above mentioned disadvantages, while still taking benefits deriving from full utilization of energy.

A first definition for a new 10 kw electric power unit In its simplest form, a 10 kW electric power unit could be conceived as a multicylinder internal combustion engine coupled to an electric generator and a number of heat exchangers, in order to recover as much heat as possible from cooling fluid and exhaust gas. The rated speed for these units is 14

normally set between 1500 rpm and 1800 rpm, depending on the specific electric generator (normally 4-poles synchronous or asynchronous generators) and/or grid frequency (50 or 60 Hz); this choice is made in order to keep both mean piston speed and noise as low as possible and get a longer expected life. It’s to be underlined that the last aspect is a basilar theme as regards microcogeneration units, as most of them are expected for a 40.000 hours running period. Based on these same elements, the Author focused his attention over a number of engines which could led to the required electric power, among some small industrial multipurpose units and several automotive engines, taking into account that the unit must produce a mechanical power comprised between 11 and 12 kW, considering the efficiency of a generic electric generator. Of course, just gas fuelled units have been considered, as Diesel or gasoline engine were both too far from European limits regarding low emissions and fuel economy. As regards industrial units, small scale gas engines are not very typical (as most of them are Diesel engine) as just higher power systems (> 50 kW) are today available on the market. So, another class of engines has been analyzed, i.e. the automotive engines. In this case, these units are close to the required power at the rated speed of 1500 rpm, showing quite interesting performances in terms of global efficiency, low noise and vibration. But at the same time they cannot be compared to the industrial units in terms of durability and reliability, as they have not been designed for heavy-duty service, but simply as mass-production spark- ignited automotive units. For this reason the Author concluded that, in order to reach a longer endurance even for small cogenerative engine, another kind of units should be considered. From this point of view, a modern automotive Diesel engine converted into a spark ignited unit results more similarly designed to large industrial engine, because it results more robustly constructed, as it has to undergo to much higher pressures. But another important aspect of this philosophy is that such kind of engine can run at higher loads (in terms of higher b.m.e.p. brake mean effective pressure) without reliability problems, while most of other spark ignited micro-cogenerators normally work under lower loads, in order to keep long term durability; so, in the first case, a higher mechanical efficiency can be expected, giving to this solution a higher potential in terms of global efficiency. In order to achieve a first definition of displacement for this unit, it can be observed that most of modern spark ignited internal combustion engine can express a specific torque of 80 Nm/liter around their highest volumetric efficiency. In order to reach a mechanical power of 12,5 kW at the rated speed of 1500 rpm (taking into account an electric efficiency of 0,80 to get the required electric power of 10 kW), a torque of about 80 Nm is needed: so, having fixed a (conservative) value of 65 Nm/liter for the engine at 1500 rpm, a 1200 cc displacement would be necessary.

The electric generating system The final aim of a microcogeneration unit suitable for domestic and commercial applications in Europe is the production of a single phase 230 VAC (Voltage in Alternating Current), characterized by a gridequivalent power quality; this could be obtained by a three-phase 400 VAC asynchronous machine (as most of the models cited in the introduction), together with some active power factor control systems and line filters, each different phase serving three different utility groups. The choice of the electric generator was made among some different units available on the European market, each of them capable of producing the required power at the rated tension, torque and speed. After some analysis it was clear that the required performances could only be assured by a water cooled unit, because of its high specific power and efficiency, but especially because of its intrinsic low noise, (due to the absence of cooling fan and fins) and the possibility to be placed, together with the internal combustion engine, into a completely closed containing case. Moreover, compactness was taken into account because a 15

significant volume and weight reduction could be obtained with this solution. So it was decided to design and make a water cooled generator (in collaboration with an Italian electric machine producer), with the aim of arrange not only a prototype, but a pre-industrial component.

Figure 1 – Water cooled asynchronous generator on the test bench This unit has been examined on a test bench as first and it has been characterized by varying the external torque; water temperature was fixed at 50°C, i.e. the same set as the incoming water-flow temperature into the future micro-cogenerator; a set of experimental data was produced and then reported in the following Table. 1; Load (%) 100 75 50 25

Power Current Power Efficiency Speed Voltage Mech. (kW) (A) factor (%) (rpm) (V) power 11,04 19 0,82 87,33 1565 388 12,6 8,28 16 0,75 88,5 1545 388 9,4 5,52 13 0,62 88,1 1532 388 6,3 2,67 10 0,38 83 1516 388 3,3 Table 1 – Asynchronous generator experimental data characteristic

Losses 1,606 1,076 0,746 0,565

The recorded data show an interesting behavior expressed by the prototype generator, with an efficiency of about 88% in most of its functioning curve, and higher than planned in the previous calculations where an electric efficiency of 80% was fixed. However the Author consider that some diminution in the generating efficiency of asynchronous machine will occur when the unit would be coupled with an internal combustion engine, because of its intrinsic torque and speed fluctuation [7].

The internal combustion engine After having known the behavior of the electric generator, as regard global performances, it can be better defined the engine displacement and the needed torque to move the electric machine. Several automotive Diesel has been considered during this analysis; at the end the chosen unit was a Fiat 1250 cm3 of displacement, turbocharged Diesel engine, even known as 1,3 MultiJet. This engine represents one of the most advanced unit today available on the market, owing to its double overhead cams with hydraulic lifters and integrated rocker-arms, four cross-valve with high turbulence intake design. This 16

unit has been transformed in a stoichiometric spark ignited engine, atmospheric pressure charged and natural gas fuelled, representing the very first 1,3 MultiJet Diesel unit to be transformed into a methane prototype. The high turbulence deriving from intake ducts (very typical for a Diesel unit) was considered to be an important issue by the Author, this aspect in order to sustain the flame propagation and avoiding knocking at the low speed of 1500 rpm even with an high compression ratio (12:1). As regards combustion chamber, the previous Saurer type has been replaced with a large central bowl with a very limited squish area, (similar to a Heron type) in order to give the combustion chamber an high volume/surface ratio (to improve thermal efficiency), to reduce HC formation and to avoid the swirl enhancing. This aspect must be controlled, in order to reduce heat transfer to chamber walls and it will be no doubt part of further developments of the engine in the future (together with compression ratio optimization), by means of CFD and combustion simulation programs; the internal piston shape can be easily seen in the following Fig 2.

Fig.2 Modified pistons with enlarged bowl In Fig.3 it can be seen the flat head with the four valves and the central spark plug; the glow plug hole of the original Diesel engine has been used to install a pressure sensor.

Fig. 3 Four valve head with spark plug As underlined before, another important issue for this prototype was reliability and endurance, being the same engine an important work-bench to test technical solutions in the future, especially regarding surface hardening and special lubricants. The most critical parts, as regards wear and friction, are some 17

mechanical couples, i.e. liners and pistons, valve and seat and finally rocker-arms and camshaft. So, as first step, the valve springs have been reduced in their pre-load and stiffness (if compared to the original engine version) in order to reduce friction [6], thanks to the lower rotational speed performed by this new unit. Moreover, special exhaust valve with Stellite coating have been adopted, together with hardened valve seat. Further developments will consider hardened liners (by PVD coatings) associated with new formulated fullurene added lubricants. As regards lubrication system, an auxiliary apparatus has been installed, made up of a large capacity oil- tank (21 liters) and of a constant oil- level device, which permits to fix the optimal lubricant amount in the sump. The oil circulation is forced by an external electric pump without any particular modification of the original lubricating system. The auxiliary tank has been dimensioned on the average oil consumption showed by this engine, this permitting to make oil change intervals longer than the standard engine (so reducing global costs). As regards the control and management system, the engine is provided with an especially designed integrated electronic platform, which has been conceived as a global control system (both of electric and thermal power) especially suitable for cogeneration plants. This equipment has been designed to perform different load strategies, such as electric load driven or heat load driven. As regards the first strategy, it makes the energy produced by the generating group just follow the energy requirement from a generic utility, through the control of an automotive electric driven throttle; in this way no energy flow can be delivered to the grid. At the same time, the system can control a straight stoichiometric operation, managing natural gas flow by means of a step motor valve put on the feeding line and thanks to two different oxygen sensors (before and after the three-way catalytic converter), in order to control both steady and transient load conditions. Other features of this system are an active cooling apparatus control (through an electric pump) and the active control of oil consumption and circulation. The system architecture has been conceived as very flexible, in order to permit future upgrades of the same through the installation of other sub-modules, in order to control more engine/system functions, such as ignition system, EGR control, power factor and other thermal regulating apparatuses. In the following Fig.4 and the prototype control system is shown, while in Fig.5 the engine with the catalytic converter and double oxygen sensor can be seen.

Fig. 4 Prototype cogenerator control/management system

18

Fig.5 The prototype with catalyst and double oxygen sensor In order to reduce NOx emissions an exhaust gas recirculation (EGR) has been set up. An important difference between the EGR system of the original Diesel engine and the one introduced in this prototype stands in the different achievable cooling of exhaust gas. In this prototype they are spilled at the end of the last stage of the heat recovery system, where a maximum temperature of 80°C can be reached at full load; this condition is very important in a spark ignited engine, in order to avoid knocking and obtain a higher global efficiency. The EGR mass flow is still not controlled by any adjustable valve, having been optimized just for full load conditions; as reported before, further development of global management system will consider a special module for active EGR control. As regards the ignition system, the global management platform was not fitted with an ignition module; so an automotive based component was adopted and modified in order to improve life cycle of the whole ignition apparatus. With this aim, an electronic ignition system (with high voltage distributor), coupled with a single special high voltage coil was employed. The latter was used to meet the heavy load conditions of high compression, natural gas fuelled engines, where sparks need a higher voltage to take place. The distributor, provided with an internal electronic pick-up, was put on the camshaft (in place of the Diesel high pressure pump), with the aim of getting a one-spark per cycle strategy, instead of a one-spark per round; in this way a significant excess load on the whole system was avoided, for a better durability and maintenance cost reduction, because of the lesser plug electrodes erosion.

The system as an electric and heat generator The two systems, separately analyzed before, have been finally coupled and tested, in order to get the global performance as electric and heat generator. The unit was tested with four different throttle openings, just connected to the electric grid and without any passive electric load to simulate a generic utility during the experiment. All tests have been performed with natural gas from the Italian distribution network, with a declared average LHV (Lower Heating Value) of 34.400 kJ/Sm3 . As regards laboratory setup, the apparatus which has been used to characterize the behavior of the electric generator was an API-COM motor/brake system, equipped with a low- inertia asynchronous machine. As regards the air and fuel flow metering, a hot wire flow meter (by VSE) has been adopted, together with a Coriolis fuel flow meter (by Emerson MicroMotion). As regards emissions, raw 19

exhaust gas has been analyzed with an API-COM measurement system (Mod. S-5000), consisting of the following analyzers: NDIR (Non-Dispersive Infrared Detector), CLD (Chemiluminescence Detector) and FID (Flame Ionization Detector) all by Emerson. The engine performances regarding electric and thermal output are showed below in Table 2, while global emissions (before and after catalyst) are reported in following Table 3. Load (%) 100 75 50 25 Load [%] 100 75 50 25

Electric Power (kW) 11,45 8,20 5,35 2,55

Speed Current Power Primary Electric Thermal Thermal Primary factor Energy efficiency power Efficiency Energy (rpm) (A) (kW) (%) (kW) (%) Ratio 1570 21,1 0,84 41,55 27,5 24,7 59,5 0,87 1548 17,3 0,74 32,6 25,1 20,8 63,9 0,89 1534 13,5 0,60 25,4 21,0 17,8 68,0 0,89 1518 10,8 0,35 18,6 14,2 13,1 75,8 0,90 Table 2: Global electric and thermal performance

THC NOx CO Exhaust THC NOx (bef. Kat) (bef. Kat) (bef. Kat) Temp. (aft. Kat) (aft. Kat) [p.p.m.] [p.p.m.] [%] [°C] [p.p.m.] [p.p.m.] 910 1270 0,18 525 110 130 1020 940 0,20 466 140 80 1190 510 0,21 398 150 65 1200 290 0,23 313 150 55 Table 3: Global emissions before and after catalyst

CO (aft. Kat) [%] 0,02 0,02 0,02 0,02

Exhaust Temp. [°C] 520 460 395 307

The obtained results are quite interesting if referred to an experimental unit; as regards the overall efficiency, the system showed an interesting 27,5%, with a net power generation of 11,5 kW and a thermal power generation of 19,7 kW, corresponding to a global Primary Energy Ratio (i.e. the sum of heat and electric power vs. potential fuel power) of 87% at full load. The electric power is higher than required, but capable of compensating the performance drop when very low pollution emissions are mandatory (especially regarding NOx), or in case of high wear and aging of the unit. Regarding thermal efficiency, global performances are very interesting if compared to other units, also because the system was not yet provided with a containing case; so that a significant amount of convective and irradiative heat was lost, with higher value for the higher loads because of the surface temperature rise. However, the system showed these results also because the external cooling fluid was kept at 50°C (because of the required maximum temperature for the electric generator), this causing water condensation in the exhaust gas and giving the system an extra heat amount. As regards the electric generating efficiency, it can be observed that generator behavior doesn’t seem to be much affected by torque variability of the internal combustion engine [7], this also because of a special elastic coupling between the generator and the I.C.E., the latter provided with a high inertia flywheel (as can be seen in the following Fig.9), which limited the rotational speed fluctuation of the whole system.

20

Fig.9 Elastic coupling with high inertia flywheel As regards emissions, the overall behavior reflects quite low global levels, owing to the stoichiometric setting and to the a methane optimized three-way catalyst. The NOx production before catalyst could be limited even more with a higher rate of exhaust gas recirculation (EGR), in order to meet the most stringent European limitation [5] and reduce, at the same time, both catalyst dimension and cost. In this case, a powered EGR valve is needed (controlled by the managing/control device), because of performance instability showed by I.C.E. at partial load conditions. The internal combustion engine coupled with the electric generator can be seen in the following. Fig.10.

Fig.10: The 10 kW power unit during endurance test

Conclusions The 10 kW power unit developed by Istituto Motori - CNR showed interesting global performances, similar to other commercial competitors and capable of being improved in many aspects in the future. The final goal of 10 kW electric power has been overlapped and it can even increase in the future 21

owing to further developments of the internal combustion engine, such as higher compression ratio (obtained with a new design combustion chamber and piston) and optimized intake ducts, being all these aspect capable of increasing global efficiency too. As regards thermal efficiency, a better result could be reached by mean of a containing case for the whole system and another cooling stage inside of the same volume, in order to control the internal temperature and perform a higher heat recovery [7]. The CNR system also showed to be an interesting prototype for the testing and the evaluation of technical solutions applied to microcogeneration in general, especially for further developments in the field of durability (materials and lubrication), noise and vibration reduction (silencers, suspension devices, noise absorbing panels), electric efficiency (different generators, flywheels an inverters) and other solutions to obtain higher Primary Energy Ratio (unconventional heat-exchangers). Finally, this unit, constructed with low cost industrial elements, showed that the introduction on the market of a reliable and cost-effective system could be no-doubt carried out by industry in a next future, being most of its components absolutely widespread in the automotive and domestic heater production.

Nomenclature E.E

Electric efficiency of microcogenerator;

T .E

Thermal efficiency of microcogenerator;

O.E

Overall efficiency of the internal combustion engine;

gen

Electric efficiency of generator;

Nm

Newton-meter (Torque unit);

cc

cubic centimeters (displacement unit);

LHV I.C.E.

Lower Heating Value; Internal combustion engine

b.m.e.p. Brake mean effective pressure

References [1] [2] [3] [4] [5]

http://www.energianova.it http://www.energiewerkstatt.de http://www.ecpower.co.uk http://www.energ.co.uk Bernd Thomas “Benchmark testing of Micro-CHP units” Applied thermal engineering, Volume 28, Issue 16, November 2008, pages 2049-2054 22

[6] Shigeto Suzuki, Tooru Maeda; “Development of a car-based, low NOx, highly reliable GHP engine” Small Engine Technology Conference (SETC), Vol 2, Pisa December1993; [7] P.Capaldi, A. DelPizzo, L. Piegari, R.Rizzo, “Prototype Of A Small Cogeneration Unit Suitable For Low Power Industrial Applications” EETI 2004, Rio de Janeiro

23

PROCEEDINGS OF ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY

Adjustment of envelopes characteristics to climatic conditions for saving heating and cooling energy in buildings C. Tzivanidisa ,K.A. Antonopoulosb ,F. Gioti c a

Lecturer, National Technical University of Athens (N.T.U.A.), School of Mechanical Engineering, Thermal Engineering Department, Refrigeration and Air-Conditioning Laboratory, Solar Energy Laboratory 9, Heroon Polytechniou, Zografou 157 73, Athens, Greece [email protected], CA b Professor, N.T.U.A., [email protected] c Ph. D. Candidate, N.T.U.A., [email protected]

Abstract Among buildings envelope elements, fenestration and insulation exert the most int ense influence on heating and cooling energy consumption. Fenestration permits entrance into the indoor space of large amounts of solar radiation, which are desired only during the heating period. The values combinations of fenestration and insulation characteristics for obtaining a “quasi-adiabatic” envelope, on a daily basis, have been predicted. It was found that such values combinations (a) depend strongly on the climatic conditions and they exist for the months from November to March and only for buildings with energetic heating systems, and (b) they are different for each one of these months. Therefore, for buildings operating during a specified period, the corresponding “quasi-adiabatic” envelope values may be used for minimizing heating energy consumption while for all year operating buildings, the yearly energy consumption, which is predicted in terms of the main envelope parameters, may be used for energy s aving. A critical value of the fenestration heat trans fer coefficient has been detected, for each level of insulation effectiveness, for which the yearly energy consumption becomes independent of fenestration percent age, thus providing the means to reduce the often undesired limitations concerning the size of fenestration area. The pres ent analysis is based on a developed implicit finit e-difference solution of a set of differential equations, which describe the transient thermal behavior of buildings. Although the findings and c onclusions of the analysis refer to the Greek Typical Reference Building (GTRB) under t he Athens typical weather conditions, they have a considerable degree of generality and may, therefore, be used not only for the thermal analysis of similar buildings under similar climates, but also for c ases with different conditions and requirements. Apart from its theoretical relevance, the information provided may be used by the consulting engineer for making preliminary energy consumption estimations for t he values combinations of the main envelope parameters, for selecting those which satisfy energy saving, low initial cost and aesthetic requirements.

Keywords: buildings envelope parameters, thermal comfort energy saving

fenestration,

building insulation,

quasi-adiabatic buildings envelope,

1. Introduction The effects of envelopes characteristics on the energy consumed for obtaining indoor thermal comfort of buildings have been studied in a large number of publications, for example refs [1-9]. In most of these, attention is focused on the envelopes elements with the lowest and highest thermal resistance, i.e. the fenestration and the insulation. Recent examples from the former class of studies may be found in refs [1-4]: In ref. [1] a fenestration heat a transfer model is developed on the basis of experimental and theoretical analysis of fenestration thermal behavior. In ref. [2] a simulation procedure is developed and used for the evaluation of the contribution of windows in buildings energy balance in Amman. Applications of advanced glazing and overhangs are proposed and the resulting shading effects on their overall 24

behavior are analysed in ref. [3]. Improvements of fenestration solar heat gain measurement systems are presented in ref. [4]. Recent examples from the latter class of studies, i.e. those related to the effects of insulation on heating energy consumption may be found in refs. [5-9], in most of which the insulation thickness is optimized using various criteria, i.e. the kind of energy source [5], the electricity tariff [6], or the life cycle cost [7]. A correlation between insulation thickness and thermal conductivity, for obtaining the optimum result, is developed in ref. [8]. In ref. [9] a case study on the influence of insulation in regions for extreme weather conditions is presented. The above studies represent only a small part from the large number of studies on the effects of envelope characteristics on energy consumption for buildings heating and cooling. However, little work has been done on the effects of envelope parameters combinations [10,11] and in particular on the combined effects of fenestration and insulation, which are the envelope elements with the strongest influence on building heating and cooling energy consumption. An effort towards this direction has been done in our recent studies [12-14], where the effect of fenestration and insulation parameters combinations on the heating energy consumption was predicted. In the first of the above publications [12] the concept of “quasi-adiabatic” or “pseudo-adiabatic” wall was introduced, while in the second [13] the analysis was extended to the “quasi-adiabatic” or “pseudo-adiabatic” envelope. In these studies the required fenestration and insulation parameters combinations for obtaining quasi-adiabatic walls and envelopes were predicted for specified weather conditions. The analysis refers only to buildings with energetic heating systems. In the present study, both energetic and passive systems are considered and the parameters of weather conditions are introduced. The required fenestration and insulation parameters combinations for quasi-adiabatic envelopes are predicted for various weather conditions, thus enabling consulting engineers to select the appropriate values combinations of fenestration and insulation parameters for obtaining minimization of the consumed energy for indoor thermal comfort at any specified climatic conditions or any month of the year. The corresponding values of the yearly energy consumed are also predicted for use in the case of buildings operating throughout the year. The analysis is based on a developed implicit finite-difference solution of a set of differential equations, which describe the transient thermal behavior of buildings.

2. Thermal behavior simulation of a Greek Typical Reference Building (GTRB) Existing computer codes, which are suitable for the simulation of buildings transient thermal behavior, as for example refs. [15,16], require extensive modifications for the purposes of the present study. Therefore, a new simulation procedure was developed, based on an implicit finitedifference solution of a set of differential equations, which describe the transient thermal behavior of a Greek Typical Reference Building (GTRB). GTRB characteristics have been defined by examining the Athens and other Greek cities buildings in conjunction with the related Hellenic Directive published in the official Government Gazette Issue 407/9-4-2010, which is based on the European Union Directive 91/2000 on the energy performance of buildings. The typical year weather data used have been obtained by statistical processing of 20 years hourly measurements of ambient temperature [17] and solar radiation [18,19] in the Athens area. Although GTRB characteristics may be found in our previous articles on related subjects [12,13], they are repeated below very briefly for the sake of completeness: 100 m2 detached one-storey house of square shape with exterior walls composed of 2 cm exterior finishing layer, 9 cm brickwork, 4 cm insulation with specific thermal conductivity ki=0.038 W/mK, 9 cm brickwork and 2 cm interior finishing layer; roof composed of 2 cm interior finishing layer, 14 cm reinforced concrete slab, 4 cm insulation and 10 cm of usual exterior waterproof and concrete mixtures layers; floor constructed from 10 cm upper floor tiles with cement mixture sub-layers, 4 cm insulation layer 25

and 10 cm reinforced concrete slab directly in contact with the ground; indoor walls of 30 m length made of single bricks with finishing layers on both sides; the four sides of the house are oriented towards the four main orientations and each one is composed of 25% fenestration with overall heat transfer coefficient 3.2 W/m2 K; outdoor and indoor convection coefficients 16 W/m2 o C and 8 W/m2 o C, respectively; light-coloured exterior envelope surface with absorption coefficient for solar radiation 0.44; constant ventilation of 1 indoor air changes per hour. The developed procedure for the simulation of the GTRB described above is based on previous procedures [20-26], presented and tested against experimental data and other numerical predictions in previous studies [27-29]. Therefore, only a very brief description will be given below, containing mainly the new points introduced. The thermal behaviour of the multilayer GTRB envelope elements e (i.e. exterior walls, fenestration, ceiling and floor) is expressed by the transient one-dimensional heat conduction differential equation: 2 Tej(t,x) / x2 , xj x xj + Bej , j = 1, 2, …,J (1) ejCej Tej(t,x) / t = kej as only the direction x normal to the walls and other extended surfaces present significant temperature variations. In the above equation Tej (t,x) is the temperature of any layer j of multilayer envelope element e at time t and depth x, measured from its outdoor surface; J is the number of layers each envelope element is composed of; ej, Cej, kej and Bej are the density, thermal capacity, thermal conductivity and thickness of each layer j of multilayer element e, respectively; and xj, xj+Bej are the coordinates of the jth layer surfaces of element e. The boundary conditions for the exterior walls may be written as qo,e(t) = ho [ To (t) – Te1 (t,x) ] , x = 0 (2) qi,e(t) = hi[TeJ(t,x) – Ti (t)] + v ge,v[ TeJ (t,x) –Tv (t)] + Re(t) , x = xJ+BeJ (3) where qi,e(t) and hi are the heat flow and the convection coefficient at the indoor surface, respectively, while qo,e(t) and ho denote the corresponding quantities for the outdoor wall surface; Ti(t) and To (t) are the indoor and the equivalent outdoor air temperature, which includes the effect of the incident solar radiation, according to the related ASHRAE [30] model; v denotes summation over indoor surfaces v; ge,v is the radiation heat-transfer factor between indoor surface of element e and any other indoor surface v of temperature Tv (t); and Re (t) expresses the part of solar radiation transmitted through any opposite fenestration, and the parts of the radiative loads from lighting, equipment and people, which are absorbed by the indoor surface of exterior walls. The same equations (2) and (3) express the boundary conditions for the outdoor and indoor fenestration surfaces, respectively, where To (t) now expresses the real ambient temperature Tamb(t) and the term Re(t) is omitted. The percentage of solar radiation absorbed by fenestration is taken as a source term in the corresponding transient heat conduction equation (1). Table 1. Greek Typical Reference Building (GTRB) parameters Area 100 m2 (square shape). External Wall 2cm finishing layer, 9cm brickwork, 4cm insulation, 9cm brickwork, 2cm finishing layer. Roof 2cm interior finishing layer, 14cm reinforced concrete slab, 4cm insulation, 10cm exterior waterproof and concrete mixtures layers. Floor 10cm upper floor tiles with cement mixture sub- layers, 4cm insulation layer, 10cm reinforced concrete slab. Indoor Wall 2cm finishing layer, 9cm brickwork, 2cm finishing layer. Fenestration 25% of each external’s wall orientation, U=3.2 W/m2 K Outdoor convection coefficient 8 W/m2o C Indoor convection coefficient 16 W/m2o C 26

Roof surfaces are treated in the same way as exterior walls, surfaces, i.e. eqs (2) and (3), are used as boundary conditions for the upper and lower roof surfaces, respectively. Adiabatic boundary conditions are imposed to the lower surface of floors directly in contact with the ground, or over an underground non- ventilated basement [30]. Equation (2) is imposed as boundary condition if the floors lower surface is in contact with the ambient. Boundary condition expressed by eq. (3) is imposed on the upper floors surface. The transient one-dimensional heat conduction equation (1) with subscript e replaced by p is used for the calculation of the temperature distribution Tpj(t,x) within any indoor multilayer partition p (indoor wall, ceiling or floor), composed of j=1,2,…,J layers, each one of thickness Bpj. Boundary conditions at the two sides of any partition p may be expressed as qp1 (t) = hi[Tp1 (t,0) – Ti (t)] + v gp,v [ Tp1 (t,0) –Tv (t)] + Rp1 (t) qpJ(t) = hi[TpJ(t, xJ+BpJ) – Ti (t)] + v gp,v [ TpJ(t, xJ+BpJ) –Tv (t)] + RpJ(t)

(4) (5)

where Tp1 (t,0) and TpJ(t, xJ+BpJ) denote the temperatures at the two sides (first and last layers j=1 and j=J) of partition p at time t, respectively; qp1 (t) and qpJ(t) stand for the heat flows at the corresponding sides of the partition; Ti (t) and hi are the indoor air temperature and the convection heat-transfer coefficient at partition surfaces, respectively; gp,v is the radiation heat-transfer factor between surfaces of partition p and any other indoor surface v of temperature Tv (t). The parts of solar radiation, transmitted through any opposite fenestration, and the parts of the radiative loads from lighting, equipment and people, which are absorbed by the two partitions sides 1 and J are expressed by terms Rp1 (t) and RpJ(t), respectively. Same equations as those for the indoor partitions, with subscript p replaced by f, are used to calculate the temperature distribution Tfj(t,x) within furniture, which is simulated by equivalent multilayer slabs composed of the usual furnishings materials, i.e. wood, plastics, glass, textile mater, metal, etc. The sum of heat flows from envelope indoor surface, partitions and equivalent furnishing slabs may be expressed as Q1 (t) =

eqi,e(t)Ae

+

p

[qp1 (t) + qpJ(t) ]Ap +

f[

qf1 (t) + qfJ(t) ]Af

(6)

where summation e refers to the e (=1,2,…) elements of building envelope, with corresponding indoor heat-transfer surfaces Ae and heat flows qi,e(t); summations p and f refer to the p(=1,2,..) indoor partitions and to the f (=1,2,..) equivalent furnishings slabs, respectively, with corresponding heat-transfer surfaces Ap and Af and heat flows at either sides (qp1 , qpJ) and (qf1 , qfJ). The parts of radiation from lighting, equipment, people and transmitted solar radiation through fenestration, which are directly or after reflection absorbed by the indoor air, as well as ventilation and infiltration, provide the indoor environment with a load Q 2 (t). An additional load Qo (t) 0 or Qo (t) [accessed 30.1.2012.]. [12] Eltrop L., Raab K., Schneider S., Schroeder G., Kaltschmitt M., Leitfaden Bioenergie Planung, Betrieb und Wirtschaftlichkeit von Bioenergieanlagen. Fachagentur Nachwachsende Rohstoffe – Available at [accessed 30.1.2012.]. [13] Nasserzadeh V, Swithenbank, J . Design optimization of a large municipal solid waste incinerator, Waste Menagement, 1991; 11: 249-261. [14] Scott A. J., Real- life emissions from residential wood burning appliances in New Zealand Available at [accessed 30.1.2012.]. [15] Todd J. J., Research relating to regulatory measures for improving the operation of solid fuel heaters. Eco-energy options, Prepared for the New South Wales Department of Environment and Conservation– Available at 329

[acc essed 30.1.2012.]. [16] Van Loo S., Koppejan J. (eds.), Handbook of biomass combustion and co-firing. Twente, the Netherlands: Twente university press; 2002. [17] Beer J. M., Lee K. B., The Effect of the Residence Time Distribution on the Performance and Efficiency of Combustors. Symposium (International) on Combustion 1965; 10 (1): 1187-1202. [18] Swithenbank J., Poll I., et al.,Combustion design fundamentals. Symposium (International) on Combustion 1973; 14(1): 627-638 [19] Star CCM+ manual, CD-Adapco. Melville, NY, USA. [20] Han J-H, Jeong K, Choi J H, Choi S. A hot-flow model analysis of the msw incinerator. International journal of energy research, 1997; 21: 899-910. [21] Fehr M, Vaclavinek, J. A cold model analysis of solid waste incineration. International journal of energy research, 1992; 16: 277-283. [22] Choi S, Lee J S, Kim S K, Shin D H. Cold flow simulation of municipal waste incinerators. In Proceedings of 25th Int. Symp. On Combustion; 1994. The Combustion Insitute, Irvine, California, U.S.A. [23] Ravichandran M, Gouldin F C. Numerical Simulation of Incinerator Overfire Mixing. Combustion Science & technology, 1992; 85: 165-185. [24] Nasserzadeh V, Swithenbank, J . Design optimization of a large municipal solid waste incinerator, Waste Menagement, 1991; 11: 249-261. [25] Nasserzadeh V, Swithenbank J, Schofield G, Scott D W, Loader, A. Effects of high speed jets and internal baflees on the gas residence times in large municipal incinerators, Environmental Progress, 1994;13 (2): 124-133. [26] Personal communication with PhD mentor professor Pešenjanski [27] Seeker W R, Lanier W S, Heap M P. Municipal waste combustion study: Combustion control of MSW combustors to minimize emission of trace organics. New York, US; EPA, 1987 May. Technical report: EPA/530-SW-87-021x. [28] Brki Lj., Živanovi T., Termi ki prora un parnih kotlova. Beograd, Srbija. Mašinski fakultet; 1984.

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PROCEEDINGS OF ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY

Characterization of CH4-H2-air mixtures in the high-pressure DHARMA reactor Vincenzo Mocciaa , Jacopo D’Alessiob a

Istituto Motori – C.N.R., Napoli, Italy, [email protected] CA b Istituto Motori – C.N.R., Napoli, Italy, [email protected]

Abstract: Experimental characterization of the burning behavior of gaseous mixtures has been carried out, analyzing spherical expanding flames. Tests were performed in the DHARMA (Device for Hydrogen-Air Reaction Mode Analysis) laboratory of Istituto Motori - CNR. Based on a high-pressure, constant-volume bomb, the activity is aimed at populating a systematic database on the burning properties of CH4, H2 and other species of interest, in conditions typical of i.c. engines and gas turbines. High-speed shadowgraph is used to rec ord the flame growth, allowing t o infer the laminar burning parameters and the flame stability properties. Mixtures of CH4, H2 and air have been analyzed at initial temperature 293÷305 K, initial pressure 3÷18 bar and equivalence ratio =1.0. The amount of H2 in the mixture was 0%, 20% and 30%. The effect of the initial pressure and of the Hydrogen content on the laminar burning velocity and the Markstein length has been evaluated: the relative weight and mutual interaction has been assessed of the two controlling parameters. Analysis has been carried out of the flame instability, expressed in terms of the critical radius for the onset of cellularity, as a function of the operating conditions.

Keywords: Combustion, Laminar burning velocity, Hydrogen, Met hane, Shadowgraph.

1. Introduction No matter the claim and the quest for new answers to the needs of an energy-thirstier society, thermal conversion systems will play a key role in the energy supply chain. This awareness, along with the urgent need of CO2 reduction (currently the main driver of technology advance), has some direct implications: introduction in the energy cycle of CO2-neutral fuels (biomass-derived) and design/development of more efficient conversion systems. The latter point can be anticipated to have a larger practical impact than the former, given the majority of energy sources will be represented by fossil fuels for many years to come. Sometimes placed in the category of “alternative” fuels, methane (CH4) is indeed a hydrocarbon, sporting the peculiarity of the lowest C/H ratio, if compared to other fuels: by trivial reasoning, the less the carbon, the less the CO2. This feature has boosted a renewed attention to CH4, which represents the main constituent of natural gas. CH4 has been used with heat engines for a long time, even if with the status of a “niche” solution: as a fuel for i.c. engines, it offers some advantages over gasoline, having wider flammable limits and better anti-knock characteristics, at the cost of a lower flame speed. A feasible opportunity to overcome the limits of CH4 is offered by H2: adding H2 to CH4 (or natural gas) can improve the flame speed/stability and lower the lean operating limit. The overall effect is to extend the stable operation map to extreme conditions (e.g. high EGR). Crucial for the development and design of i.c. engines and gas turbine combustors is the knowledge of laminar combustion properties: they offer the basis for modelling and simulation of flameturbulence interaction. Data on the combustion properties of gaseous fuels are widely available in the literature [1-8], but hardly in a systematic form: filling this gap is the scope of the DHARMA (Device for Hydrogen-Air Reaction Mode Analysis) project, aiming at generating a comprehensive and coherent grid of data on the combustion properties of CH4 and H2, obtained in conditions as close as possible to those of actual engines. 331

The project relies on an optically accessible constant-volume bomb (static P 20 MPa), where test are carried out on spherical expanding flames; the operating conditions (P0, T0), the equivalence ratio, the relative composition of the mixture, the ignition energy can be varied in a meaningful range. A shadowgraph setup, based on a c.w. laser source and a CMOS camera, is used to follow the flame growth with high time and space resolution. A high- frequency dynamic pressure sensor allows to record the combustion pressure. Operation of the reactor and the various subsystems is fully automated, for the sake of safety and repeatability. Experimental results are presented for the combustion in air of CH4-H2 mixtures: the H2 percentage varied from 0% to 30% (vol.); the initial pressure varied between 3 and 18 bar. The tests were performed at room temperature (293÷305 K), with stoichiometric mixtures. Data analysis yielded the (unstretched) laminar burning velocity and the Markstein length; the evaluation was carried out of the critical radius for the onset of cellularity, offering further details on flame properties.

2. Experimental setup and procedures

Fig. 1. Layout of the experimental apparatus.

The general arrangement of the experimental layout is shown in Fig. 1: a detailed description is given in [9]. The heart of the DHARMA laboratory is a constant-volume test reactor, made of stainless steel (AISI 316): the cylindrical chamber (i.d. = 0.070 m, h = 0.090 m) is rated for a maximum pressure of 20 MPa (static). A total of 6 optical accesses are available: the larger viewports (d = 0.065 m) are located normal to the chamber axis, providing nearly full access to chamber bore; smaller diameter ports are positioned on the chamber side, along two orthogonal axes. Hi- grade quartz windows (0.085 m diameter, 0.030 m thick) are installed in the main ports, the smaller side ports can be fitted either with quartz windows (0.049 m diameter, 0.020 m thick) or with a variety of stainless steel adapters (i.e. transducers, electrodes, sampling ports, etc.). 332

Four additional service ports are available, e.g. for the intake of the combusting mixture and the vent of the exhaust gases. The mixture is ignited with an automotive inductive ignition system (energy 60 mJ): the energy of discharge can be varied adjusting the time of charge (dwell time) of the coil. The spark discharge takes place in the center of the chamber between two pointed-tip tungsten electrodes (0.001 m diameter), with a 0.001 m gap. Pressure signal during the combustion events is detected by a high- frequency dynamic pressure transducer (resonant frequency 500 kHz, rise time 1 µs, sensitivity 14.5 mV/mbar). The sensor is pre-amplified and coupled to a matching signal conditioner (1MHz, 1:1 gain). Output voltage signal is acquired with a 200 MHz digital oscilloscope, interfaced to the main computer. A metal-shielded, type K thermocouple is used to monitor the temperature of the gases, save for the combustion phase. The gas handling system was designed to prepare combustible mixtures of variable composition with high accuracy, spanning a range of initial pressures which included values of relevance in spark-ignition engine operation. High purity gases (CH4 : 99.9995%, H2 : 99.999%, dry air: 99.999%, N 2 : 99.9995%) are used to prepare the mixtures, relying on the partial pressures method [2]: the amount of each gas is metered by a solenoid valve, controlled by a high-resolution (100 MHz) counter/timer board installed in the main computer. The pressure is monitored by a high-accuracy pressure transmitter (0-30 bar, accuracy ±0.08% FS). The gas supply system allows to prepare combustible mixtures up to 30 bar. After each test, the system is vented, N 2 purged and pumped down to 10-2 mbar. All the systems operate with a high degree of automation, to maximize safety and repeatability of the tests. The entire lab conforms to current safety standards on the use of combustible gases, and is fully provided with interconnected gas leak sensors, cylinder cut-off devices and forced venting systems. A parallel-beam direct shadowgraph layout [10] was set up for the analysis of spherical expanding flames. A Diode-Pumped Solid-State c.w. laser (2W @532nm) is used as the light source. Highresolution, time-resolved image acquisition is accomplished by means of a CMOS camera (Photron SA-5, 1024x1024 pixel, 1000000 fps, shutter time 368 ns), interfaced to an independent workstation.

3. Theoretical Background The shadowgraph images of the spherical expanding flame allow to evaluate the laminar burning parameters, according to a well-known approach [2-3, 5-8, 11-13]. The time evolution of ru (the flame radius on the unburned gas side) is obtained through frame-by- frame processing, assuming the luminous front in the shadowgraph corresponds to the radius on the unburned gas side [12, 13]. The stretched flame speed Vs can then be evaluated as

Vs

dru dt

(1)

The obtained speed includes the stretch effects associated to the propagation of a flame surface, which experiences curvature and flow dynamic strain [14-18]. The flame stretch is defined as the relative rate of change of the flame area: for a spherically expanding laminar flame it can be expressed as: 1 dA 2 dru V 2 s (2) A dt ru dt ru As originally suggested by Markstein, the relationship between flame speed and stretch is linear; it can be expressed after Clavin [17] as: Vs Vs 0 Lb (3) 333

where Vs0 is the unstretched flame speed and Lb is the burned gas Markstein length, which indicates how and to what extent the flame is influenced by the stretch. Positive Lb are associated to flames with speed decreasing with stretch (which are stable), while in the case of negative Lb the flame speed tends to increase with stretch, becoming unstable; moreover, the magnitude of Lb indicates to what extent the flame propagation is influenced by the stretch. According to (3), by plotting Vs against , the unstretched flame speed Vs0 can be estimated as the value assumed by Vs at = 0, and Lb as the gradient of the best straight line fit. The unstretched flame speed Vs0 refers to the limiting case of a plane flame front, with infinite radius and negligible curvature: in such a case, Vs0 can be related to the unstretched laminar burning velocity ul0 through the following relation: ul 0

Vs 0

b

(4)

u

where b is the density of burned gases and u the density of unburned gases. As far as the flame analysis is concerned, this relation only holds in the constant-pressure phase of flame propagation.

4. Results and discussion In the following, results are illustrated of the combustion behaviour of CH4 and of CH4 -H2 mixtures, characterized by a H2 content of 20% and 30% in volume: these are the limits currently agreed upon by the automotive industry for the potential evolution of CH4 -fueled engines, optimizing the trade-off between the extra technical complexity and the performance benefits [19, 20]. The initial temperature T0 varied in the range 293÷305 K, while the initial pressure P0 was set at 3, 6, 12 and 18 bar (abs.). Being targeted to the development of automotive internal combustion engines, operating with closed- loop three-way catalyst, the study was limited to stoichiometric airfuel mixtures (equivalence ratio = 1.0).

Fig. 2. Evolution of flame in the isobaric phase for stoichiometric CH4 and H2 -enriched mixtures (20% and 30% vol.) at 3 bar and room temperature. Window dia. 65mm. 334

4.1. Laminar burning properties Time-resolved shadowgraph images of spherical expanding flames were used to infer the laminar flame parameters. As stated earlier, laminar analysis can be meaningfully carried out in the constant-pressure phase only, before the chamber pressure shows a sensible increment. Moreover, as stated by Bradley et al. [4], the early stages of the flame kernel growth are affected by the spark energy release, and cannot be taken into account in the evaluation of laminar flame properties. The resulting measurement time-window starts after the ignition disturbances are over, and ends when the pressure shows an appreciable rise: the spanning of this phase depends on the experimental conditions. In the present case, spark energy was 20 mJ: being delivered by an inductive ignition coil, only a small fraction of this energy is released in the breakdown phase, which governs the early kernel growth [21, 22]: the extent of the ignition disturbances can be expected to be accordingly limited. The resulting range for data analysis was comprised between 2.5mm and 9.5mm (corresponding to 27% of the chamber radius). 2.5

2.0

1.5

1.0

0.5 6 bar

3 bar 0.0 H2 /(H2 +CH4 ) 0% 20% 30%

2.0

1.5

1.0

0.5 12 bar

18 bar

0.0 0

500 Stretch rate,

1000

0

(s-1 )

500 Stretch rate,

1000 (s-1 )

Fig. 3. Flame speed as a function of the stretch rate, obtained at different starting pressure, for stoichiometric CH4 and H2 -enriched mixtures (20% and 30% vol.) at room temperature. 335

Figure 2 shows three sets of frames, describing the flame development in the laminar, isobaric phase, at P0 = 3 bar. The combustion behaviour is compared for CH4 and H2 -CH4 mixtures with a H2 content of 20% and 30% vol. Recording speed was 7000 fps (143 µs between consecutive frames) with a shutter speed of 1 µs; optical magnification ratio was 3.27:1, resulting in a spatial resolution of 15.3 pixel/mm. Flames are smooth and virtually free of wrinkles, the crack shown for the 30% mixture is the self-similar development of initial ignition disturbances. The effect of H2 addition can be appreciated in the increased size of the flame ball at a given time. An image processing routine has been implemented to infer the flame radius ru from the shadowgraph data: for each frame, the flame contour is traced and the area of the projected flame ball is evaluated; the radius is estimated as that of a circle of equal area to the flame. The evolution of the flame radius ru can then be plotted as a function of time, offering the basis for the evaluation of the stretched flame speed Vs : the latter is obtained from derivation of a polynomial fit of the above-defined data subset, following (1) [7]. Being known Vs and ru , the stretch rate can be evaluated after (2): the plot of the stretched flame speed against is shown in Fig. 3 for CH4 and CH4 -H2 , at different starting pressure: each set of data corresponds to a single, time-resolved combustion event, which has been selected as representative of the test conditions (P0 , T0 , % H2 , ). According to (3), linear- fit extrapolation of the flame speed to = 0 gives the unstretched flame speed Vs0 , while the slope of the fit allows to estimate the burned gas Markstein length Lb . Figure 3 shows the distinct effect of the starting pressure and of the Hydrogen percentage on the flame characteristics: increasing the pressure has a detrimental effect on the flame speed, which, on the other hand, always benefits from the addition of H2 , even in limited amounts. 35 H2 / (CH4 +H2) 30

stable flame regim e

0% 20% 30%

25

0.4

0.2

20 0 15 -0.2

10 5 unstable flame regime

-0.4

0 0

3

6

9 12 Pressure, P0 (bar)

15

18

0

3

6

9 12 Pressure, P0 (bar)

15

18

Fig. 4. Unstretched laminar burning velocity (left) and burned-gas Markstein length (right) as a function of the starting pressure, for stoichiometric CH4 and H2 -enriched mixtures (20% and 30% vol.) at room temperature. The corresponding values of the unstretched laminar burning velocity ul0 were obtained through (4), where the expansion factor u b was evaluated from the properties of the reactant species and of equilibrated adiabatic products. The ul0 and Lb values are summarized in Fig. 4 as a function of initial pressure, for pure and H2 -enriched CH4 . As the starting pressure is increased from 3 to 18 bars, a decrease of the laminar burning velocity can be observed: the value at 18 bar being about 40% of 3 bar. The addition of Hydrogen to 336

Methane allows a net gain of burning velocity in all the cases. This gain has the effect of shifting to higher values the curve of ul0 vs. P0 . Aside from the effect on the magnitude of ul0 , as the starting pressure increases, the flame gets more and more unstable, as evidenced by the decreasing Markstein length: in the case of pure CH4 , Lb assumes values close to zero at 12 bar, falling in the unstable regime for larger values. Adding H2 to CH4 has the anticipated effect [4] of increasing flame instability: due to the combined synergy of initial pressure and Hydrogen content, high-pressure H2 -CH4 flames fall systematically in the unstable regime.

4.2. Flame stability and cellular structures The propensity of a flame to get unstable, as expressed by the burned-gas Markstein length Lb , can be inferred from the analysis of the expanding flame in the laminar (isobaric) regime, when, almost by definition, there is little or no sign of flame distortion (see e.g. Fig. 2). Experimental evidence of instability appears later, when the flame travelling the chamber volume may go through various stages of morphological alterations, characterized by the appearance of large cracks and, eventually, fine cellular structures [23-27].

Fig. 5. Evolution of flame instability for stoichiometric CH4 and H2 -enriched mixtures (20% and 30% vol.) at 6 bar and room temperature. Window dia. 65mm. Figure 5 shows three sets of frames obtained in the case of pure and H2 -enriched CH4 mixtures at 6 bar, at selected times after the spark: they were recorded at 7000 fps (143 µs between consecutive frames) and 1024x1024 pixel, with a shutter speed of 1 µs; optical magnification ratio was 3.27:1, resulting in a spatial resolution of 15.3 pixel/mm. At moderate values of the initial pressure (P0 = 6 bar), the CH4 flame keeps its laminar shape until it reaches the chamber walls. The addition of H2 to the mixture, even in limited amount (20%), is associated to the appearance of large cracks on the flame surface. The latter effect gets more striking as long as the flame travels the chamber, with the cracks being suddenly integrated by cellular structures [24, 27]. When the initial pressure gets larger, according to the findings shown in Fig. 4, the flame gets more unstable, even with pure CH4. This behaviour is shown in Fig. 6, which reports three sets of frames 337

obtained for the same mixtures at P0 = 12 bar: no matter the mixture composition, in all the cases the flame exhibits deviations from the laminar morphology, which take place earlier in the process (that is at smaller radii). The typical sequence of large cracks followed by smaller, uniformly distributed “cells” is always present; the main difference is in the characteristic times, which get shorter as the amount of H2 increases, leading to an earlier appearance of cellular structures.

Fig. 6. Evolution of flame instability for stoichiometric CH4 and H2 -enriched mixtures (20% and 30% vol.) at 12 bar and room temperature. Window dia. 65mm. As suggested by Law et al.[27], two characteristic instants can be identified: the first is related to the branching of large cracks across the flame surface, the second to the sudden appearance of cells, almost uniformly over the same surface, with a characteristic size much smaller than the large cracks. Following the convention of Law et al. [27], we chose to adopt the second instant as representative of the flame loosing stability: this allows to define the critical radius rcr for the onset of instability. Figure 7 reports the values of rcr evaluated in the current range of operating conditions as a function of the H2 content, at different starting pressures. Whatever the amount of H2 in the mixture, flames at P0 = 3 bar always show a laminar behaviour, hence the lack of data points for this case. At P 0 = 6 bar, a cellular structure appears with pure CH4 , when the flame reaches the chamber wall: these points were omitted, since they are likely influenced by additional phenomena, like flame-wall interaction. The data confirm the trends of the Markstein length obtained by flame stretch analysis (shown in Fig. 4): they allow to assess the effect of increasing pressure on flame instability, which shows up as a progressive reduction of the critical radius: the resulting picture is of a flame which departs earlier from the laminar regime, and mostly develops under a wrinkled regime, even in quiescent atmosphere. As anticipated, adding H2 to CH4 further reduces rcr, i.e. increases instability, even if the effect gets less marked as the pressure is increased: adding 30% of H2 to CH4 reduces rcr by 24% at 12 bar and by 21.5% at 18 bar. As far as the observed instabilities are concerned, it’s well established that flame cellularity can be hydrodynamic and thermo-diffusive in nature (if one neglects the body- force effects). The thermodiffusive instability originates from the diffusive disparity of heat conduction from the flame and reactant diffusion towards the flame [17]. A fitting parameter representing the effect of non338

equidiffusion is the flame Lewis number (Le) defined as the ratio of the heat diffusivity of the mixture to the mass diffusivity of the limiting reactant [16-18]. Values of Le equal or larger than a critical value Le* (typically slightly less than unity) correspond to flames which are diffusionally stable, while for Le < Le* the flames are unstable and diffusional cellularity is evidenced in the very early stages of flame development. The hydrodynamic instability is associated to the thermal expansion of the gas: it is enhanced when the thermal expansion ratio is increased and the flame thickness is decreased [26]. The current set of measurements, obtained in stoichiometric conditions ( = 1.0), were characterized by Le always above unity ( 1.25). The expansion ratio u b was almost constant ( 7.6). Flame thickness for CH4 decreased by an order of magnitude, increasing the pressure from 3 to 18 bar; moreover, in all cases, the addition of 30% (vol.) of H2 caused a reduction of 20% of flame thickness. The experimental results show flames remaining smooth after ignition (Le > 1), and later developing cells on the surface: in the light of the above considerations, this behaviour suggests that the observed cellularity should be essentially attributed to hydrodynamic instabilities [8, 23-29].

Fig. 7. Critical radius for the onset of flame instability as a function of H2 content in CH4 -H2 mixtures, at different starting pressure.

Summary The effect has been analyzed of the initial pressure and H2 content on the combustion of stoichiometric CH4 -H2 mixtures. Laminar burning parameters (unstretched burning velocity and Markstein length) and flame instability characteristics were evaluated for mixtures with different H2 percentage (0%, 20% and 30%), equivalence ratio = 1, initial temperature T0 = 293÷305 K and initial pressure P0 = 3÷18 bar. The main findings can be summarized as follows: Increasing the pressure, the laminar burning velocity decreases and the Markstein length becomes negative: in the case of CH4 , when P0 is raised from 3 to 18 bar, ul0 is reduced of 40%; in the same conditions Lb shifts from about 0.38 to -0.074, meaning the flame develops in the unstable regime. The addition of H2 to CH4 has a positive effect on the burning velocity: at 3 bar, ul0 increases by 20% if the amount of H2 in the mixture is 30%: the effect is proportionally stronger at higher pressure (+40% at 18 bar). The Markstein length of H2 -enhanced mixtures is shifted to smaller values, if compared to pure CH4 , and gets negative at P0 > 6 bar. 339

The critical radius for the onset of cellularity was found to decrease when either the pressure or the H2 content in the mixture were increased. No matter the amount of H2 , no sign of instability was observed at P0 = 3 bar: conversely, for P0 > 6 bar the flame get increasingly unstable.

Acknowledgments The research was partially supported by the Italian Ministry of Economic Development within the framework of the Program Agreement MiSE-CNR “Ricerca di Sistema Elettrico”.

Nomenclature A flame area, mm2 Le Lewis number Lb burned gas Markstein length, mm P pressure, bar rcr critical flame radius, mm ru cold flame front radius, mm T temperature, K ul0 unstretched laminar burning velocity, cm/s Vs stretched flame speed, m/s Vs0 unstretched flame speed, m/s Greek symbols flame stretch rate, 1/s equivalence ratio gas density, kg/m3 Subscripts and superscripts 0 initial b burned gas u unburned gas

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[6] Gu X.J., Haq M.Z., Lawes M., Woolley R., Laminar Burning Velocity and Markstein Lengths of Methane–Air Mixtures. Combust. Flame 2000;121(1-2):41-58. [7] Halter F., Chauveau C., Djebaili-Chaumeix N., Gokalp I., Characterization of the effects o f pressure and hydrogen concentration on laminar burning velocities of methane- hydrogen-air mixtures. Proceedings of the Combustion Institute 2005;30(1):201-208. [8] Verhelst S., Woolley R., Lawes M., Sierens R., Laminar and unstable burning velocities and Markstein lengths of hydrogen-air mixtures at engine-like conditions. Proceedings of the Combustion Institute 2005;30(1):209-216. [9] Moccia V., D’Alessio J., Evaluating the Burning Velocity of Gaseous Fuels for Engine Applications: the DHARMA Project. SAE Paper 2011-24-0056. [10] Settles G.S., Schlieren and Shadowgraph Techniques. Berlin, DE: Springer; 2001. [11] Huang Z., Zhang Y., Zeng K., Liu B., Wang Q., Jiang D., Measurements of laminar burning velocities for natural gas-hydrogen-air mixtures. Combust. Flame 2006;146(1-2):302-311. [12] Parsinejad F., Keck J., Metghalchi H., On the location of flame edge in Shadowgraph pictures of spherical flames: a theoretical and experimental study. Exp. Fluids 2007;43(6):887894. [13] Tahtouh T., Halter F., Mounaïm- Rousselle C., Measurement of laminar burning speeds and Markstein lengths using a novel methodology. Combust. Flame 2009;156(9):1735-1743. [14] Karlovitz B., Denniston Jr. D.W., Knapschaefer D.H., Wells F.E., Studies on Turbulent Flames : A. Flame Propagation Across Velocity Gradients, B. Turbulence Measurement in Flames. Symp. (Int.l) on Combustion 1953;4(1):613-620. [15] Strehlow R.A., Savage L.D., The Concept of Flame Stretch. Combust. Flame 1978;31:209– 211. [16] Matalon M., On Flame Stretch, Combust. Sci. Technol. 31(3):169–181, 1983. [17] Clavin P., Dynamic behavior of premixed flame fronts in laminar and turbulent flows. Prog. Energy Combust. Sci. 1985;11(1):1–59. [18] Law C.K., Sung C.J., Structure, aerodynamics, and geometry of premixed flamelets. Prog. Energy Combust. Sci. 2000;26(4-6):459-505. [19] Akansu S.O., Kahraman N., Çeper N., Experimental study on a spark ignition engine fuelled by methane-hydrogen mixtures. Int. J. Hydrogen Energy 2007;32(17):4279-4284. [20] Kahraman N., Çeper B., Akansu S.O., Aydin K., Investigation of combustion characteristics and emissions in a spark- ignition engine fuelled with natural gas-hydrogen blends. Int. J. Hydrogen Energy 2009;34(2):1026-1034. [21] Maly R., Vogel M., Initiation and propagation of flame fronts in lean CH4-air mixtures by the three modes of the ignition spark, Symp. (Int.l) on Combustion 1979;17(1):821-831. [22] Borghese A., Diana M., Moccia V., Tamai R., Early Growth of Flames, Ignited by Fast Sparks. Combust. Sci. Technol. 1991;76(4-6):219-231. [23] Groff E.G., The cellular nature of confined spherical propane-air flames. Combust. Flame 1982;48:51-62. [24] Bradley D., Harper C.M., The development of instabilities in laminar explosion flames. Combust. Flame 1994;99(3-4):562-572. [25] Tse S.D., Zhu D.L., Law C.K., Morphology and burning rates of expanding spherical flames in H2/O2/inert mixtures up to 60 atmospheres. Proceedings of the Combustion Institute 2000;28(2):1793-1800. [26] Kwon O.C., Rozenchan G., Law C.K., Cellular instabilities and self-acceleration of outwardly propagating spherical flames. Proceedings of the Combustion Institute 2002;29(2):1775-1783. 341

[27] Law C.K., Jomaas G., Bechtold, J.K., Cellular instabilities of expanding hydrogen/propane spherical flames at elevated pressures: theory and experiment. Proceedings of the Combustio n Institute 2005;30(1):159-167. [28] Hu E.J., Huang Z.H., He J.J., Zheng J.J., Miao H.J., Measurements of laminar burning velocities and onset of cellular instabilities of methane–hydrogen–air flames at elevated pressures and temperatures. Int. J. Hydrogen Energy 2009;34(13):5574-5584. [29] Vu T.M., Park J., Kwon O.B., Kim J.S., Effects of hydrocarbon addition on cellular instabilities in expanding syngas-air spherical premixed flames. Int. J. Hydrogen Energy 2009;34(16):6961-6969.

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PROCEEDINGS OF ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY

Development of a concept for efficiency improvement and decreased NOX production for natural gas-fired glass melting furnaces by switching to a propane exhaust gas fired process Jörn Benthina , Anne Giesea a

Gaswärme-Institut e.V, Essen, Germany, [email protected]

Abstract: The melting of glass is a very energy-intensive process. Very high standards for the security of gas-supply and tec hnical quality of glass melting tanks are set. Air preheating is a common method to achieve the required high melting t emperatures with minimum energy consumption. Regenerative and recuperative systems can be used. Regenerative glass melting furnaces are widespread and lead to a high firing efficiency and reduced energy consumption. The resulting high local flame temperature increases NOX emissions. Conventional methods for NOx reduction in regenerative glass furnaces are pus hed to their limits. On the one hand the designers, builders and operators of glass melting tank equipment like t o react flexibly on the present and future situation of the gas market and ensure security of supply. On the other hand they like to improve bot h the efficiency of the process and the glass quality and like to reduce the pollutant emissions as well. As part of a cooperation project with its project partners IWG engineering company Wagenbauer Zwiesel, Heinz Glas GmbH Kleintettau and the Gaswärme-Institut e. V. Essen, with regard to these needs, a concept for the c onversion of natural gas-fired glass melting furnaces to propane gas-fired and the associated NOX optimization was developed. The ability of the NOX reduction by exhaust gas recirculation in regeneratively fired glass furnaces has been dem onstrated with great success in previous studies [1]. Within the project, several meas urement campaigns were conducted at operational industrial glass melting t anks, a test tank and the experimental facilities of the GW I where temperature and species distributions were measured. The data obtained are used to validate the CFD simulation models created with the help of the gained dat a of propane gas-fired burners and their impact on technology, heat transfer and pollutant emissions, etc. are investigated and applied to real glass melting tanks. Initial findings have already been implemented on a small experimental tank. The design of the conversion t o propane gas-firing, including the control and regulation devices represents the completion of the project.

Keywords: Glass Melting Furnace, Energy Efficiency, Sustainability, NOX Emissions

1. Introduction The melting of glass is a very energy- intensive process. Very high standards for the security of gas supply and technical quality of glass melting tanks are set. With the liberalization of the European gas market and the diversification of gas supply sources, fluctuations in the gas composition in the public grids may increase in the future. The changes in combustion properties due to changes in the composition of natural gas have implications for both the process control and emissions, particularly in sensitive thermal processes such as glass production, where the flame is used as a tool and small changes in the species concentrations and temperatures can have significant influence on the process. Another crucial problem regarding the security of gas supply was shown in recent years. A disruption of gas supply can cause serious economic damage for industrial facilities that require continuous operation. Considering the liberalization of gas market, ensuring the gas supply is of growing importance. The high value of the gas supply became clear not at least in connection with

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the Russian-Ukrainian gas dispute in early 2009. In the gas sector - unlike in the electricity sector alternative energy sources exist which can replace natural gas in its fields of application. This is especially true in the main area of use, the heating market. However, conversion processes are costly and not always possible on short notice in most cases. In this respect, the avoidance of gaps in the gas sector has a high priority. By replacing the fuel natural gas with a defined fuel such as propane, the effect of future expected gas quality variations in gas composition due to the liberalization of gas markets and the diversification of gas supply sources should be avoided. The question of backup solutions to ensure the production operation is therefore becoming increasingly urgent. For existing facilities, particularly with regenerative U- fired furnaces and cross burner tanks which are mature in their burner combustion chamber configuration in terms of optimal heat transfer, the implementation of new burner systems may involve a high risk for operators. Since the glass melting furnaces tend to be operated at very near-stoichiometric conditions for efficiency reasons, it can at worst lead to redox reaction in the glass melt, thus endangering the entire production line. The aim of this research project was to develop a concept and an implementation plan for the steps necessary for the conversion of conventional natural gas- fired glass melting furnaces to an alternative firing with propane gas.

2. Procedure In early 2010 the research project began with the first basic research on the impact of fuel switching in glass tanks. Part one was the investigation of the burner systems used by the project partner Heinz glass in the experimental facilities of GWI. The aim was to investigate whether existing burner technology can be used. The necessary amounts of exhaust gas, air and generator gas respectively which has to be added to the propane were calculated in order to reach the same Wobbe index as natural gas. Comparative measurements were carried out with natural gas H and propane-nitrogen-carbon dioxide or propane-air mixtures. In addition to the analysis of the spectral radiative properties and UV flame visualization, the two-dimensional distributions of temperature and species concentrations were recorded. The two-dimensional distributions were measured with a 2 m long water cooled measuring probe. A steady state was assumed and a two-dimensional matrix with 215 measuring points in the burner cross section was recorded. For each point in the matrix the following values were recorded the concentration of CO2 , O2 , CO, NOx and the temperature. The program Origin was used to interpolate between the 215 points and generate a two-dimensional plot as seen in Fig. 1. The exhaust gas emissions of the various test runs are compared in Table 1. Table 1: Experimental results at the GWI test furnace

These measurements were used as reference for a series of CFD simulations. Experimental and simulation results were compared with each other (Fig. 2) to validate the simulations and verify their applicability to real systems. 344

Figure 1: measured temperature distribution of different fuel mixtures

Figure 2: Comparison of NOx emissions between measurement and calculation. The simulations with different model combinations were compared for their applicability and quality of results. Attention was focused on the mechanisms of turbulence, reaction, radiation, and pollutant formation. Based on both the findings of experiments and the simulations at GWI the first field tests on a small experimental glass furnace were conducted. The test facility was designed and built by the project partners (Figure 3).

345

Figure 3: Experimental glass melting tank

The aim of this measurement campaign was to determine the effects of the altered firing approach on glass quality, pollutant emissions, flame parameters and ignition behaviour in a real glass melting tank. In addition, the load and switching behaviour as well as varying the composition of the fuel gas were tested.

Figure 4: Time course of temperature in the experimental glass melting tank The internal addition of exhaust turned out to be difficult during the investigations. Depending on the sampling location in the regenerator flue gas line from the tank to the chimney of the plant, the O2 content in exhaust gas rose steadily. After cooling and filtration systems, the oxygen content went over 18 vol.%. This amount of inleaked air would not have been productive for the planned investigations. The withdrawal right behind the regenerators has led to considerable problems regarding the water content and the resulting condensation. A water separation had to be designed 346

and built for this extra amount of water. Another problem was the admixture of the exhaust gas to the fuel, which had a very low pressure in comparison with the fuel propane. An additional compressor was insufficient, and the admixture had to be realized through injector nozzles. After the modifications were done, the measurements could be performed. During the readjustment of the premix burner in the feeder area to propane gas it was necessary to ensure that the default setting for the mixing ratio of air and fuel had to be changed because otherwise a considerable excess of air would have been the result. In Figure 4 is an example of the temperature dependence of the glass melting furnace (floor, feeder and furnace element) shown for various fuels and loads while Figure 5 presents the O 2 and NOx concentrations over the feeder. The abbreviation n. c. stands for no cullets used and w. c. for glass melting with cullets.

Figure 5: Time course of O2 and NOx in the feeder in the experimental glass melting tank

The results of the tests at the GWI test rig are confirmed by investigations at the experimental glass melting tank. The temperature in the reaction zone drops when switching from natural gas to propane if the same load of the burners is maintained. This also means a drop in temperature in the glass melt, see bottom temperature in Figure 4 A balance can be created when the power output of the propane firing is considerably increased, in the case of the experimental glass furnace to approximately 160% of gas output. It is assumed that one reasons for this drop in temperature is the different radiation characteristics of a propane flame. The higher heat capacity of CO 2 compared to nitrogen might also be a cause of this behaviour. The CO 2 content in the exhaust gas increases from about 8.6 vol.-% for natural gas to 10.8 vol.-% in the wet flue gas for the propane-gas mixture.

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3. Conclusion The national and international demand for backup systems to ensure and secure the fuel offer is constantly growing due to the politically uncertain situation in some gas supplying countries. By replacing the natural gas with a defined fuel such as propane, the effect of future expected gas quality variations in gas composition due to the liberalization of gas markets and the diversification of gas supply sources should be avoided. Within the project the basic application of a propane-gas mixture has been shown to be capable for backup system. The used burners can be used. Difficulties arise from the temperature drop in the reaction zone and thus in the glass melt. This must be addressed by increasing the thermal load of the burners and thus increased fuel consumption has to be taken into account. Furthermore, the establishment of such a system has to note the following points: 1. The O2 content of the exhaust gas which should be admixed depends on the location of removal. 2. A water trap or additional cooling must be provided to handle the increased condensation. 3. The addition of the exhaust gas to the almost non-pressurized propane needs to be carried out by means of additional measures (compressors, injector nozzles, etc.).

4. References [1] A.Giese: Energieeinsparung und NO x-Minderung an regenerativ befeuerte n Glasschmelzwannen durch verdünnte Verbrennung - Verdünnte Verbrennung Final Report AiF-Nr.: 14755 N, 2008 [2] B. Fleischmann; A. Giese: Verbesserung des direkten Wärmeeintrages in die Glasschmelze durch Optimierung der Verbrennungsparameter bei unterschiedlichen Befeuerungsarten. Fina l Report AiF-Nr.: 15015 N, 2008

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PROCEEDINGS OF ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY

Experimental analysis of inhibition phenomena management for Solid Anaerobic Digestion Batch process Francesco Di Mariaa , Giovanni Gigliotti b , Alessio Sordi a , Caterina Micalea , Claudia Zadrab , Luisa Massaccesib a

b

Dipartimento di Ingegneria Industriale, Perugia, Italy, [email protected] Dipartimento di Scienze Agrarie ed Ambientali, Perugia, Italy, [email protected]

Abstract: Solid Batch A naerobic Digestion (SADB) is an int eresting process that c an lead to the production of quite high bio-methane from several biodegradable substrates. In particular the limited production of waste liquids discharged by the reactors, along with light pre-treatment requirement, makes this process suitable for a high spreading potential in many E uropean regions. Unfortunately, some inhibition phenomena occur when the anaerobic digestion is performed with high Tot al Solids conc entration, as in t he SA DB. These phenomena can affect negatively both the stability and t he viability of the process. Among the different solution exploitable for managing these phenomena, t he one based on percolate recirculation seems to be very interesting. The experimental runs conducted exploiting the Organic Fraction of Municipal Solid Waste, shows that the recirculation leads to a significant reduction of the Volatile Fatty Acids concentration along with an higher biogas production rate and stability. The biogas produced in the test with percolate recirculation is double and the VFA concentration results to be significantly lower.

Keywords: Biogas, Solid Anaerobic Digestion Batch, Volatile Fatty Acids

1. Introduction Anaerobic digestion is one of the technologies that seem to have a very high potential for contributing to the whole renewable energy production [1], [2]. The biogas produced by the bacterial activity in absence of oxygen, under given conditions, can have a high methane content [3], [4], [5], [6] and can be exploited as fuel in ICE, leading to high energetic efficiency even thou in low size facilities. Many questions still remain open about the AD to energy plants, concerning viability, costs and process stability [5], [7], [8], [9]. The most diffused technologies for AD process are represented by the wet or dry processes [10]. Wet process usually works with TS content inside the anaerobic reactor not higher than 10-15% w/w. Semi-dry process reactors are able to work with TS% up to 20% w/w. The large fraction of the AD plants works at mesophilic conditions, with a temperature inside the reactor of about 308K, even if the number of plants working at thermophilic conditions (i.e. 328K) is growing [10]. High humidity levels are necessary for achieving both higher process efficiency, in terms of biomethane production per kg of VS, but also for allowing a continuos feeding of the digester. From the other hand, this advantages leads to the production of a large amount of liquids discharged by the process. The management of this huge liquid fractions, depending on the feedstock origin and on the area in which the plants operates [10], [11] (i.e. spreading on field), can represent a relevant problem, both from the environment and from the O&M point of view. Increasing the TS content reduces the amount of liquids from the AD process. Passing from TS of 10 to 20% w/w leads to a significant but not decisive reduction of the problem. Furthermore, when working with biomasses with high impurities and low humidity contents, very important pre-treatments are required for achieving the features require by the wet or dry reactors. 349

Depending on biomass quality [12], shredding, grinding, screaning, diluition and pulping can be necessary for achieving the adequate fluidity and impurities concentration reduction necessary for pumping and mixing operations. All these operations represent further increase in plant complexity, investment and management costs. A possible solution to these problems can be represented by the adoption of Solid Anaerobic Digestion Batch process. In this case the biomass need very poor pretreatments, usually not more than mixing with shredded wood, and can be processed with TS content higher than 25% up to 50%. In this condition the digestate produced by the process, due to its low humidity, has a quite high consistency, being able to maintain its shape when arranged in open heap. Also the liquid discharged by the process [5] is narrowed, generally lower than 10%w/w. The management of the solid digestate, for several applications, is more environmentally and economically sound than the liquid one. The increase in the number of SADB reactors together with a lower automation level in biomass handling, seems to be an acceptable disadvantage for all that application that lack agricultural field or treats biodegradable substrates classified as waste. Another important aspect that has to be carefully analysed for AD working with high TS content, is represented by some biochemical inhibition phenomena that can affects both biomethane yield and process stability [13], [14]. Some solutions are possible for reducing the relevance of this phenomenon [13], [14], as increasing the amount of inoculums exploited for starting the AD process in each SADB reactor. This is a possible solution but in some cases can lead to an unacceptable increase of the reactor volume. A second possible approach can be represented by the percolation system. This paper is focused on the analysis of the inhibition phenomena comparison between a SADB process with and without percolation. Two parallel experimental tests have been started exploiting the same MSWOF mixture and I, and all the main process parameters have been controlled and measured.

2. System description and Methods 2.1. The SADB The Solid Anaerobic Digestion Batch [5], known also as Solid State AD [14] or High Solids AD [13], is an AD process performed with biodegradable materials with a TS content higher than 25% up to 50% w/w. In this condition the material is able to maintain its shape when arranged in open heap due to its low humidity content. TS higher than 50% implies a to much low humidity content that inhibits the bacterial activity.

Fig. 1. SADB biocell schematic. The most diffused reactors for SADB are represented by concrete, gastight biocells (Fig. 1), with a door through which the material can be charged and discharged. 350

The process is performed in static condition excepting a timed percolate spreading on the top of the material under treatment. The percolate exploited for spreading operation arises also from the one produced by previous AD processes. Inside the biocell all the main parameters can be controlled and measured, as T, P, Humidity, CH4 , O2 , H2 S, CO2 . Usually, the AD is performed at mesophilic conditions (308K), and the heat required by the process is recovered from the CHP fuelled by the produced biogas. Full scale SADB have from 6 to 12 biocells with a gross volume ranging from 600 to 1200 m3 , depending on the amount of mass treated.

2.2. Biomass characterization The biomass exploited in the runs is represented by the MSWOF arising from source segregated collection. This material has been mixed with 30% w/w of bark, for giving to the material the required level of porosity, and mixed with an equal weight of inoculums arising from previous SADB laboratory tests. The MSWOF has also been characterized by means of the main rapid biodegradable, the Fines (20mm) and inert components. The TS have been evaluated measuring the weight loss, on wet basis, before and after heating at 378.14 K for 24 h three different samples of the mixture. VS content has been evaluated, as weight loss, by heating at 823.14 K for 24 h the TS samples obtained from the previous analysis. The mixture TOC content was determined by the Springer and Klee wet dichromate oxidation method, while Total Nitrogen (TN) was obtained by Kjeldahl method. Phosphorus assimilated was extracted with 0.5 M NaHCO 3 solution at pH 8.5 then was analysed with a spectrophotometer. To perform the analysis of heavy metals content, samples were digested according to the US EPA 3050B method [15]. Heavy metals concentrations were determined by flame atomic absorption spectrophotometry using a Shimadzu AA-6800 apparatus.

2.3. Experimental tests Two parallel tests have been contemporary started, exploiting the mixture showed in Table 1. One test has been performed inside a large laboratory AD apparatus, designed for reproducing, in the most suitable way, the same SADB conditions of full scale facility (Fig. 2). This apparatus consist of a 100 litre cylindrical, gas tight AD reactor, with a removable top. The material under treatment is supported by a steel grate for separating the solid phase from the percolate that is collected and stored at the bottom of the reactor. A timed circulation pump provides to spread on the top of the material the percolate. A tap allows to samples the stored liquid. Test has been started by introducing in the reactor bottom, 10 litres of only pure demineralised water. Biogas produced is firstly piped in a moisture separator and then to a thermal gas flow meter (0.01% FS). The biogas methane content has been evaluated by an infrared sensor (±2%). Mesophilic conditions (308±2K) have been kept by the aid of a thermal band, embracing the reactor, controlled by a TDR. All data are measured and stored in a dedicate PC. Second test was started by utilizing 10 gastight bottles of 1 litres volume each one. The bottles where maintained at mesophilic condition by a thermal bath. Two bottles were also equipped by a gasometer apparatus for evaluating the biogas produced during the test. Table 1. MSWOF and AD mixture composition Parameter Value MSWOF components Rapid biodegradable 93 Inert 7 AD mixture MSWOF/I 1 Bark/MSWOF 30 351

Unit %w/w %w/w kg/kg (wb) %w/w (wb)

The main parameters evaluated during the runs are represented by the biogas production and by the evolution of the VFA concentration. At given number of days of treatment, about 500ml of percolate have been withdrawn from the experimental apparatus, and contemporary the content of a bottle was examined. The bottles with gasometer apparatus where examined last. VFA extraction of the bottle content was performed by extraction with demineralised water. Then the samples where firstly centrifuged at 5000 rpm, then filtered at 0.45 nm and finally analyzed with gaschromatograph. VFA up to 7 Carbon atoms where investigated.

Fig. 2. SADB experimental apparatus.

3. Main results and discussion The characterization of the I and of the MSWOF (Table 2) shows that the TS content of the I is of about 38% w/w whereas the TS content of the MSWOF is of about 27%. The ratio of the kg VS of MSWOF and I exploited in the tests is of 0.71, with mass ratio, on wet basis, of 1:1. The pH of the I is quite alkaline whereas the pH of the MSWOF results definitely acid. Table 2. I and MSWOF characterization Parameter I Humidity 62.28 VS 95.04 pH 8.90 N 1.03 C/N 40.78

MSWOF 72.67 93.27 4.97 2.67 10.90

Unit % w/w % db % db -

The BY of the SADB experimental apparatus results to be higher than the one produced by the same mixture in the bottles laboratory test (Fig. 3). During the first 7-10 days, the biogas rate per kg of VS results very similar for the two runs. After this initial period, the SADB apparatus biogas rate becomes decisively higher than the one produced by the bottles. This trend is also confirmed by the daily biogas production curves (Fig. 4). Infact, during the first 7-10 days the daily biogas rates curves overlaps with a high precision. After this period, the two curves become decisively divergent until 22nd day of the process. Infact, after 20 days, the SADB daily production curve achieve a maximum whereas the bottles one a minimum value. In the successive days the SADB curve show 352

a constant decrease (Fig. 4) whereas the bottles curve shows a growing trend, even if with a significant fluctuation around the mean value. Furthermore, this fluctuation seems to have a growing trend around the last days of the AD process. This behaviour is the consequence of the strong VFA concentration during the process. The TVFA concentration in the both tests is very similar, around 20,000 mg/l, until the 5th day (Fig. 5). Then, the TVFA concentration in the percolate of the SADB decrease significantly, achieving a concentration lower than 5,000 mg/l after the 25th day. The TVFA concentration in the bottles runs, without percolation, continues to rise constantly until the 30th day reaching a maximum value higher than 42,000 mg/l. After this maximum value the TVFA concentration show a decreasing trend, even if with significant oscillation. This phenomenon justifies the strong instability in the daily biogas production for the Bottles runs. 400

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significantly higher concentration during the whole bottle test compared to the one measured in the SADB apparatus. The significant variation of the different VFA, causes the strong instability of the daily biogas production instead of the one achieved in the SADB apparatus. 45000 40000 35000

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Fig. 6. Acetic and Butyric acids concentration evolution in the SADB experimental apparatus and Bottles runs. The experimental results show the higher biogas production and process stability of the process performed in the SADB apparatus. The main difference occurring among the two tests is represented by the presence of the percolate recirculation in the SADB apparatus. Infact, a fraction of the VFA produced are solubilised in the periodically recirculated percolate, reducing its concentration and inhibition effect in the solid phase of the SADB reactor. Furthermore, in the percolate stored at the bottom of the reactor, a second wet AD process take places. The high humidity at which this second process takes places, allows a rapid metabolism of the acids leading to a higher total biogas rate. This phenomenon contributes also to the higher stability shown by the process performed in the SADB apparatus. In the bottles runs, the AD process occurs with percolate in static conditions. This means that the solid and the liquid phase are not physically separated. During the fermentation phase, the alcohols 354

and VFA produced are continuosly solubilised in the liquid phase, leading to a very high concentration. This causes a process inhibition both in the liquid phase and at the solid particle surface. These preliminary results show that the percolate recirculation is able to reduces SADB inhibition phenomenon, increasing both process stability and biogas yield. This is an aspect of fundamental importance in the management of full scale SADB reactors, able to ensure a quite efficient and viable SADB process. Further positive effects of percolate recirculation can also lead to a significant reduction of I needs, with a consequent reduction in full scale investment costs. 8000

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4. CONCLUSION The effect of percolate recirculation results to be very positive for Solid Batch Anaerobic Digestion, mainly as a consequence of a strong reduction of the inhibition phenomenon induced by high Volatile Fatty Acids Concentration. In the first days of the process, the absence of recirculation can lead to a TVFA concentration higher than 40,000 mg/l with a quite null biogas production. This strong inhibiton conditions lasts for more than 40 days. Percolate recirculation leads to a TVFA peck of about 20,000 mg/l that is then rapidly reduced till quite null concentration in about 45 days. Further biogas production achieves about 400 Nl/kgVS instead of about 150 achieved by the test without recirculation. This results shows how the percolate recirculation can represent an interesting and sustainable solution to SADB inhibition phenomena reduction, instead of other solution as the increase of the amount of inoculums exploited per each cycle.

Nomenclature AD BY CHP I ICE COD MSWOF N

Anaerobic Digestion Biogas Yield (Nl/kgVS) Combined Heat and Power Inoculum Internal Combustion Engine Chemical Oxygen Demand (mg/l) Municipal Solid Waste Organic Fraction Nitrogen 355

O&M P SADB TDR T TN TOC TP TS TVFA VFA VS

Operating and Maintenance Phosphorous Solid Anaerobic Digestion Batch Temperature Detection Resistance Temperature (K) Total Nitrogen (%TS) Total Organic Carbon (%TS) Total Phosphorous (%TS) Total Solids (%w/w) Total Volatile Fatty Acids (mg/l) Volatile Fatty Acids (mg/l) Volatile Solids (%TS)

References [1] Directive 2001/77/CE of the European Parliament and of the Council of 27 September 2001 on the promotion of the electricity produced from renewable energy sources in the internal electricity market. Official Journal of the European Communities 27.10.2001. [2] Beurskens L.W.M., Hekkenberg M., Vethman P., ECN – Renewable Energy Projection as Published in the National Renewable Energy Action Plans of the European Members States – Available at: < http://www.ecn.nl/docs/library/report/2010/e10069.pdf>.[accessed 24.12.2011]. [3] Amon T., Amon B., Kryvoruchko V., Machmuller A., Hopfner-Sixt K., Bodiroza V., Hrbek R., Firedel J., Potsch E., Wagentristl H., Schreiner M., Zollotsch W., Methane production through anaerobic digestion of various energy crops grow in sustainable crop rotations. Bioresource Technology 2007; 98: 3204-3212. [4] Lastella G., Testa C., Cornacchia G., Notornicola M., Voltasio F., Anaerobic digestion of semisolid organica waste: biogas production and its purification. Energy Conversion and Management 2002; 43: 63-75. [5] Di Maria F., Sordi A., Micale C., Energy production from mechanical biological treatment and composting plants exploiting solid anaerobic digestion batch: an Italian case study. Energy Conversion and Management 2012; 56: 112-120. [6] Desideri U., Di Maria F., Leonardi D., Proietti S., Sanitary landfill energetci potential analysis: a real case study. Energy Conversion and Management 2003; 27 (5): 1969-1981. [7] Walla C., Schneeberger W., The optimal size for biogas plants. Biomass and Bioenergy 2008; 32: 551-557. [8] Vervaeren H., Hostyn K., Ghekiere G., Willems B., Biological ensilage additives as pretreatment for maize to increase the biogas production. Renewable Energy 2010; 35: 20892093. [9] Gebrezgabher S.A., Meuwissen M.P.M., Prins B.A.M., Lansink A.G.J.M.O., Economic analysis of anaerobic digestion – A case of Green power biogas plant in The Netherlands. NJAS Wageningen Journal of Life Sciences 2010; 57: 109-115. [10] De Baere L, Mattheeuws B, Anaerobic digestion in Europe: State of the art 2010. ORBIT 2010: Proceeding of the 7th International Conference on Organic Resource in the Carbon Economy; 2010 June 29 july 3; Heraklion, Crete.

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[11] Di Maria F., Pavesi G., Leombruni S., Improvement of an existign anaerobic digestion plant: technical and economic analysis. ORBIT 2008: Proceeding of the 6th International Conference on Moving Organic Waste Recycling towards Resource Management and for the Bio-based Economy; 2008 October 13-15; Wageningen, The Netherlands. [12] Vinot M, Perez CA, Turm P, Maillo A. Improvements in anaerobic digestion units and in pre-treatments performances beforehand. Venice 2010: Proceedings of the Third International Symposium on Energy From Biomass and Waste; 2010 November 8-11;Venice, Italy. [13] Schievano A., D’Imporzato G., Malagutti L., Fragali E., Ruboni G., Adani F., Evaluating inhibition conditions in high-solids anaerobic digestion of organic fraction of municipal solid waste. Bioresource Technology 2010; 101: 5728-5732. [14] Di Maria F., Sordi A., Micale C., Optimization of Solid State Anaerobic Digestion by Inoculum Recirculation: the Case of an Existing Mechanical Biological Treatment Plant. doi: 10.1016/j.apenergy.2011.12.093 [15] US EPA 3050 B (1996), Environmental Protection Agency.

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PROCEEDINGS OF ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY

Experimental investigations of the combustion process of n-butanol/diesel blend in an optical high swirl CI engine S. S. Merola a , G. Valentino b, C. Tornatore c, L. Marchitto d, F. E. Corcione e a

Istituto Motori -CNR, Napoli, Italy [email protected]; b [email protected]; c [email protected] d [email protected]; e [email protected]

Abstract: In diesel engines, fuel is injected into the engine cylinder close to the end of the compression stroke. During a phase known as ignition delay, the fuel spray atomizes into small droplets, vaporizes, and mixes with air. As the piston continues moving towards TDC, the mixture temperature reaches the fuel ignition point, causing instantaneous ignition of some pre-mixed amount of fuel and air. The balance of fuel that does not burn in premixed combustion is consumed in the rate-controlled combustion phase, also known as diffusion combustion. Fuel composition, charge dilution, injection pressure as well as injection timing are the main factors that influence combustion and emission formation in the compression ignition engine. In order to evaluate the effects of these factors on in-cylinder spray combustion and soot formation, UVvisible digital imaging and natural emission spectroscopy were applied in a single cylinder high swirl compression ignition engine. The engine was optically accessible and equipped with a common rail multi-jets injection system. Combustion tests were carried out using commercial diesel and a blend of 80% diesel with 20% n-butanol (BU20). Two injection pressures (70 and 140 MPa), two injection timings (11 CAD BTDC and 3 CAD BTDC) and a low and high EGR rate were tested. UV-visible emission spectroscopy was used for the detection of the chemical markers of combustion process. Chemiluminescence signals, due to OH, HCO and CO2 emission bands were detected. OH emission was correlated to NO measured at the exhaust. The soot spectral feature in the visible wavelength range was correlated to soot engine out emissions.

Keywords: Optical diagnostics; UV-visible spectroscopy; Combustion process; Common Rail CI engine; Diesel/butanol blend

1. Introduction The use of alternative fuels (as biodiesel, ethanol, methanol) for light and heavy duty engines to approach the target of ultra low NOx and PM emissions without fuel economy penalty was widely investigated [1 - 2, 3, 4, 5]. Although a dominant role in diesel substitutes is played by biodiesel produced from animal fats, algae or non-food crop plants, alcohols have become the most popular replacement to fossil fuels due to a variety of locally available feedstock. It is recent the growing interest in the butanol as a viable alternative either single or blended with conventional based fuels to help decrease the demand for non-renewable petroleum [6]. Like ethanol, butanol can be produced both by petrochemical and fermentative processes [7]. The production of bio-butanol by fermentation offers certain advantages in comparison with bio-ethanol: higher energy content, lower water adsorption and corrosive properties, better blending abilities and the ability to be used in conventional internal combustion engines without the need for modification. Although bio-butanol could not compete on a commercial scale with butanol produced synthetically and almost all production ceased as the petrochemical industry evolved, the increasing interest in use of biobutanol as a transport fuel has induced a number of companies to explore novel alternatives to traditional ABE fermentation, which would enable bio-butanol to be produced on an industrial 358

scale. Regarding the automotive use of butanol, scientific literature reports several experimental investigations to evaluate the effects of using blends of n-butanol with conventional diesel fuel on the performance, exhaust emissions, and combustion behaviour also in transient conditions [8 - 9, 10, 11, 12]. The almost totality of these studies consisted in the evaluation of performance, fuel consumption and exhaust emissions for different engine operating conditions. The aim of this paper is the better comprehension of phenomena correlated with butanol–diesel combustion in CI engine. In previous works [13, 14] cycle resolved visualization, UV-visible imaging were applied in an optically accessible high swirl multi-jets compression ignition engine fuelled with a commercial diesel and a blend of 80% diesel with 20% n-butanol (BU20). Combustion process was studied from the injection until the late combustion phase fixing the injection pressure at 70MPa and changing the injection timing and EGR rate in order to investigate low temperature combustion in partially premixed regime and in mixing controlled one. In this paper the effect of BU20 in the same c.i. engine was studied by UV-visible imaging and natural emission spectroscopy fixing two injection pressures (70 and 140 MPa) for two injection timings and high EGR rate. The spectroscopic methodology was applied to follow in the combustion chamber the formation and the evolution until the exhaust of the principal compounds and radical species to characterize the combustion process. OH and soot emission were correlated with the engine parameters and with the NOx and particulate engine out emissions, measured by conventional methods.

2. Experimental set-up The experiments were carried out in an external high swirl optically accessed combustion bowl connected to a single cylinder 2-stroke high pressure common rail compression ignition engine. The main engine specifications are reported in Table 1. The external combustion bowl (50 mm in diameter and 30 mm in depth) is suitable to stabilize, at the end of compression stroke, swirl conditions to reproduce the fluid dynamic environment similar to a real direct injection diesel engine. The implication of “cylindrical bowl” is related to the peculiar design of the prototype engine that has a large displacement as an air compressor. The main cylinder, connected to the external “swirled bowl” through a tangential duct, allows to supply compressed air flow to the bowl as the piston approaches TDC. The air flow, coming from the cylinder, is forced within the combustion chamber by means of the tangential duct. In this way, a counter clockwise swirl flow, with the rotation axis about coincident to the symmetry axis of the chamber, is generated. The injector was mounted within this swirled chamber with its axis coincident to the chamber axis; in this way the fuel, injected by the nozzle, is mixed up through a typical interaction with the swirling air flow. The combustion process starts and mainly proceeds in the Table 1 - Specifications of the engine chamber. As soon as the piston moves downward, the 2-stroke single cylinder ci engine flow reverses its motion and the hot gases flow through Cylindrical Bowl (mmxmm) 50x30 Bore (mm) 150 the tangential duct to the cylinder and finally to the Stroke (mm) 170 exhaust ports. The combustion chamber provides both Connecting Rod (mm) 360 a circular optical access (50 mm diameter), on one side Compression ratio 10.1:1 of it, used to collect images and a rectangular one (size Air supply Roots blower of 10 x 50 mm) at 90°, outlined on the cylindrical Abs. intake air pressure (MPa) 0.217 surface of the chamber, used for the laser illumination Bosch Injector nozzle 7/0.141/148° input. The injection equipment includes a common rail injection system with a solenoid controlled injector located on the opposite side of the circular optical access. The nozzle is a micro-sac 7 hole, 0.141 mm diameter, 148° spray angle nozzle. An external roots blower provided an intake air pressure of 0.217 MPa with a peak pressure within the combustion chamber of 4.9 MPa under motored conditions. 359

In the preliminary phase of the work, combustion process visualization was obtained using an intensified CCD camera equipped with a quartz lens (UV-Nikon 78-mm), collecting the light emission that passes through the optical access of the combustion chamber. The electronically gated ICCD camera had an array size of 512 x 512 pixels with a pixel size of 19x19 m and 16-bit dynamic range digitization at 100 kHz. The match between the ICCD and the lens allowed 185 m spatial resolution. The camera spectral range spread from UV (180 nm) until visible (700 nm). The line-of-sight light emission measurements were performed in the whole ICCD spectral range. The ICCD is not a cycle resolved detector, hence each acquisition was carried out at a fixed crank angle for different engine cycles setting the exposure time at 5 s. The temporal difference between two images was 50 s. The intensifier gain was adjusted so that the brightest region of images was on the threshold of the detector saturation and it was the same for all the engine tests. Pictures of the experimental apparatus for the optical investigations are reported in Figure 1. Common Rail injection system

Common rail injection system

S pectrograph

ICCD

Optically accessible combustion chamber

Optically accessible combustion bowl

Figure 1 - Experimental apparatus for the optical investigations and drawing of injector position in the optically accessible combustion chamber. For spectroscopic investigations, the radiative emissions from the combustion chamber were focused by a 78 mm focal length, f/3.8 UV Nikon objective onto the micrometer controlled entrance slit of a spectrometer with 150 mm focal length and 600 groove/mm grating. From the grating the radiations were detected by an intensified ICCD camera (array size of 1024 x 1024 pixels with a pixel size of 13x13 m and 16-bit dynamic range digitization at 100 kHz). The exposure time was fixed at 41.6 s and the dwell time between two consecutive acquisitions was set at 166 s. The central wavelength of the grating was fixed at 300 nm and 400 nm, respectively, in order to cover the spectral range from UV to visible. Spectroscopic investigations were carried out in the central region of the combustion chamber. For a better post-detection analysis the binning of 8 spectra was performed in correspondence to 8 chamber locations. The spectra were corrected for the optical setup efficiency using a deuterium lamp with a highly uniform full spectrum. The wavelength calibration was performed using a mercury lamp. The time evolution of combustion products was evaluated from spectroscopy investigations using a post-processing procedure. For each chemical species with well-resolvable narrow emission bands, the height of the band expressed in counts was evaluated after the subtraction of emission background and other species contribution. Thus OH emission was evaluated as height of the 310 nm band system after the subtraction of the emission background, evaluated as the mean value between the emissions measured at 300 nm and 320 nm, respectively. For broadband emission the mean intensity, at specific wavelength range, was considered. Thus, soot emission was evaluated as mean intensity at 530-532 nm. A routine, developed in Labview environment, allowed to simultaneously evaluate the emissions of the selected compounds and species for each spectrum and each time. Moreover, OH and soot emissions were calculated as average on all the spectra. A crank angle encoder signal synchronized the cameras and the engine, through a delay unit. The AVL Indimodul recorded the TTL signal from camera acquisitions together with the signal acquired by the pressure transducer. In this way, it was possible to determine the crank angles where optical 360

data were detected. Results of the in-cylinder pressure were computed averaging 300 consecutive engine cycles. Exhaust gaseous emissions were acquired by the AVL DiGas 4000 analyzer for NOx (1 ppm resolution), the Smoke Meter AVL 415S was used for FSN and soot concentration (0.01 mg/m³ resolution) measurements. All combustion tests were carried out running the engine at the fixed speed of 500 rpm, injecting a constant fuel amount of 30mg 1% at the pressure of 70 MPa and 140 MPa. Tests were carried out setting the electronic start of injection (SOI) of 11 CAD BTDC and 3 CAD BTDC. EGR rate was changed from 0% to 50% corresponding to 21 and 17% of O2 at intake, respectively. Combustion tests were carried out using two fuels. The baseline fuel was the European low sulphur (10 ppm) commercial diesel with a cetane number of 52. The blend was composed by 80% of baseline diesel and 20% of n-butanol by volume and denoted as BU20 (cetane number 44) [15].

3. Results and discussion Diesel combustion process is very complex due to the several physical and chemical phenomena that occur [16]. The efficiency of diesel combustion and its associated pollutant emissions are mainly affected by the fuel injection process, as well as by the fuel properties. The combustion process is usually described as consisting of three distinct phases: ignition delay, premixed combustion and mixing controlled combustion. Ignition delay is the time taken after the start of injection for the pre-ignition processes to produce the ignition nuclei and detectable combustion. The duration of the ignition delay is one of the most important criteria because it has a great effect on the combustion process, mechanical stresses, engine noise and exhaust emissions. Premixed combustion refers to the combustion of a portion of the fuel injected during the ignition delay period. Mixing controlled combustion is the phase in which the fuel, that has not burnt during the premixed combustion is consumed during the concluding engine cycle. During the mixing controlled combustion phase, the fuel controls the burning rate that is influenced by the rate it mixes with air and attains the condition to burn. This phase is characterized by a lower heat release peak than that reached in the premixed phase. The rate-controlled combustion phase is often referred to as diffusion combustion. Figure 2(a-b) shows the Ignition Delay (ID) and the maximum pressure (Pmax) measured for both fuels and for all the operating conditions. 1.40 1.30

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(a) (b) Figure 2. (a) Ignition Delay (ID) and (b) pressure peak signal (Pmax) measured for both fuels and for all the operating conditions.

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It can be observed that the combined effects of lower cetane number of Diesel_70MPa Diesel_140MPa BU20, which gives a longer ignition 85 BU20_70MPa delay compared to diesel fuel, and its BU20_140MPa higher volatility contribute to increase 80 the mixing time joined to a better 75 mixed charge that induced a highest peak pressure. Advancing the start of 70 injection with respect to TDC, a longer ignition delay may be 65 observed. This trend is confirmed both at EGR=0 and 50% even if the 60 increasing EGR rate reduced the 3BTDC_0% 3BTDC_50% 11BTDC_0% 11BTDC_50% effect of increasing injection pressure. Figure 3. Pressure signal area measured for both the fuels and for In particular at SOI=11 CAD BTDC all the operating conditions. and Pinj=140MPa the premixed phase can be considered equivalent for both fuels and the ignition delay represents the only feature parameter. In order to evaluate the engine efficiency of each selected operating condition, considering the used prototype engine, the areas under the combustion pressure signals were compared. The results, reported in Figure 3, were evaluated from the 300 cycles averaged pressures. As expected, at fixed SOI, the higher injection pressure induced a little increase in the engine working area. Same trend was observed advancing the start of injection at fixed injection pressure. No penalty was detected as effect of the EGR rate. For all the conditions, the engine efficiency for BU20 was higher than diesel fuel. This was due to higher BU20 volatility that improved the fuel charge mixing and reduced the amount of not completely burned fuel. Regarding the exhaust emissions, NOx and smoke were measured for all the selected engine test conditions. The results are reported in Figures 4a and 4b for the test at 70 MPa and 140 MPa, respectively. Firstly, a strong decrease of NOx at increasing EGR rate and delayed SOI was measured for both fuels. The effect was stronger at higher injection pressure. A trade-off trend was observed for soot. The results were due to the injection of most of fuel (>50%) before the start of ignition for all the operating conditions. This produced fast burning rates once combustion started, with high rates of pressure rise and high pressure peaks. The effect was enhanced by the increase of injection pressure and by advancing of SOI that caused the NOx increase. After the premixed burning phase, part of the mixture remained rich; the higher percentage of unburned mixture induced a higher soot tendency. Area under pressure signal [a.u.]

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(a) (b) Figure 4. Engine exhaust NOx and soot emission measured for both fuels and for the operating conditions with injection pressure equal to (a) 70MPa and (b) 140MPa. 362

A lower carbon content fuel with a lower cetane number and higher ignition delay allowed to reduce the unburned mixture amount. Thus soot was lower for BU20 fuel than diesel for all conditions. The 3.35°ASOI 3.50°ASOI 3.65°ASOI 3.80°ASOI effect of the fuel properties on the BU20 exhaust pollutant emissions is more evident for the operating conditions with lower injection pressure and SOI=3 CAD BTDC. For both the EGR rates, the soot concentration for BU20 was about a 4.10°ASOI 4.25°ASOI 4.40°ASOI 4.55°ASOI quarter of the neat diesel. The advanced 70MPa _ SOI_11°BTDC_0%EGR injection timing (11 CAD BTDC) diesel allowed the ignition of a leaner mixture inducing a more complete burning. Thus, low soot concentrations were measured for both fuels without effect of injection 2.90°ASOI 3.05°ASOI 3.20°ASOI 3.35°ASOI pressure and EGR rate. On the other BU20 hand, only at the lower injection pressure the NOx emissions were acceptable. In this condition, the higher EGR rate allowed to confine the NOx emission 3.65°ASOI 3.80°ASOI 3.95°ASOI 4.10°ASOI gap between the BU20 and Diesel within 50 ppm. Thus it may be concluded that 140MPa _ SOI_11°BTDC_0%EGR the blend BU20 with injection pressure diesel 70MPa, injection timing of 11 CAD ATDC and at 50% of EGR allowed the best compromise between soot and NOx engine out emissions. 2.75\ASOI 2.90\ASOI 3.05\ASOI 3.20\ASOI Figure 5 shows a selection of images BU20 detected in the first phase of ignition; UV-visible emissions were due to the first exothermic luminescence reactions. In some images, it is possible to observe 2.90\ASOI 3.05\ASOI 3.20\ ASOI 3.35\ASOI fuel jets due to the self-illumination 140MPa _ SOI_3°BTDC_0%EGR effect of the combustion process. As Figure 5. Selection of images detected in the first expected, the flame distributions in the phase of ignition. first images demonstrated that the autoignition occurred near the tip of the fuel jets. Then the flame went up the direction of the spray axis, following the stoichiometric air-fuel ratio path [17]. Due to the swirl motion, the flame spreads in the combustion chamber in anticlockwise way. In agreement with the results obtained by pressure related data, the ignition delay of the BU20 was longer than the diesel fuel, at fixed operating conditions. diesel

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To better understand the outcome fuel injection mode on the combustion process, natural emission spectroscopy measurements were performed. Figure 6 shows the UV emission spectra detected at 2.90 CAD ASOI for Diesel and at 3.65 CAD ASOI for BU20 corresponding to the early stage of combustion in two locations of the combustion chamber central region. For both fuels, the injection was set at 140MPa, SOI=11 CAD BTDC with 0% EGR. 2500

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Figure 6. UV emission spectra detected in the early stage of combustion in two locations of the combustion chamber central region. For both fuels, the injection occurred at 140MPa and SOI=11 CAD BTDC with 0%EGR For both signals, the spectral features of OH, the Diesel highest heads at 306-309 nm of OH band system 16000 4°ASOI (250-320 nm) were well resolved [18 - 20]. Excited OH radical was formed in the primary soot 12000 combustion zone by the chemiluminescent Loc.3 reaction: CH + O2 CO + OH. Loc.5 OH was observed far from the liquid jets, in 8000 regions characterized by a large amount of fuel in the vapor phase well mixed with the air entrained 4000 Loc.4 in the spray, primarily around the jet. Then, it OH proceeded toward the injector location [17, 21, 22]. The phenomenon is fast, because the swirl 0 280 300 320 340 360 moves the flame involving the whole chamber wavelength [nm] volume. It took less than 2 CAD to observe a 140MPa-SOI_11°BTDC_0%EGR strong soot emission in the center of the Figure 7. UV range of emission spectra combustion chamber. Soot was characterized by a broadband feature that increased with the detected at 4°ASOI. wavelength like a blackbody curve [23, 24]. Results reported in Figure 7 for Diesel showed the same trend of BU20 differing only in the intensity that was higher for Diesel. This confirmed the higher soot tendency of Diesel than BU20 [25]. For all the conditions the spectral behavior remained unchanged until the start of oxidation phase when the soot emission decreased and OH band system came out demonstrating OH radical as one of the principal marker of the soot oxidation [26]. As plotted in Figure 8, about 3 ms after the advanced injection timing and for the emission intensity [counts]

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condition at higher injection pressure, the soot was drastically reduced for BU20, while the Diesel fuel yet showed high soot emission. Similar trends were also observed for all the operating conditions. 25000

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140MPa-SOI_11°BTDC_0%EGR Figure 8. UV range of emission spectra detected at 9.5°ASOI After the soot reduction, a broadband emission form the UV to OH DIESEL visible got highlight. The band 8000 system was related to the CO2 5 6 chemiluminescence [27]. Even if in 7 CO2+Soot 6000 8 the flames there is not sufficient BU20 energy to excite stable atoms or BU20 1 4000 2 molecules to high electronic states, 3 CO2 electronic states of CO2 can be 4 5 2000 excited during the combustion by 6 7 consecutive transitions from the Location 4 8 ground state level to intermediate 0 300 360 420 480 540 vibrationally activated levels [28, wavelength [nm] 1 29]. The emission of CO2* appears 40MPa-SOI_11°BTDC_0%EGR as a continuum, which extends from Figure 9. UV – visible emission spectra detected at 300 nm to 600 nm with a broad maximum around 375 nm. As 10°ASOI shown in Figure 9, at 10 CAD after the advanced injection timing the CO2 chemiluminescence signal was well detectable together with OH emission band for BU20, while for Diesel fuel it was convoluted with soot signal. Same results were observed for the lower injection pressure and for both EGR rates. The spectroscopic data were processed, as previously described, in order to evaluate the integral evolution of OH and soot for both fuels and for all the operating conditions; the results are plotted in Figure 10-13. 10000

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Figure 10. Integral evolution of OH and soot for both fuels at 140MPa-SOI_11°BTDC 7000

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Figure 11. Integral evolution of OH and soot for both fuels at 140MPa-SOI_3°BTDC 5600

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Figure 13. Integral evolution of OH and soot for both fuels at 70MPa-SOI_3°BTDC The fuel injection timing strongly influenced OH emissions. Even if the highest OH was detected about 8 CAD after the start of injection, for all conditions, at the more advanced SOI (11 CAD BTDC) the early stages of combustion occurred during the engine compression phase. It facilitated the formation of higher OH concentration if compared to SOI=3 CAD BTDC. Regarding the injection pressure, this demonstrated a strong effect on the soot evolution. Thanks to the good fuel spray atomization and air mixture, the soot evolution was very fast for all the conditions at the injection pressure of 140MPa. Soot formation and oxidation occurred in less than 15 CAD. Due to the different carbon and oxygen contents, fuel quality and EGR rate mainly influenced the balance between the formation and the reduction of OH and soot. For all the conditions and both fuels, the optical investigations results were correlated with engine out emissions. As shown in Figure 14, the integral value of OH emission and NOx measured at the engine exhaust, presented similar trend, as expected by the extended Zeldovich mechanism [30]. Moreover, the integral value of soot, in the last combustion phase 20-30 CAD ASOI, was in agreement with exhaust soot concentration, as plotted in Figure 15.

Figure 14. In cylinder OH emission and NOx exhaust emission.

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Figure 15. In cylinder soot emission and soot exhaust emission.

4. Conclusions The combustion process of mineral diesel fuel and its blend with 20% n-butanol and their effects on diesel engine performance and emissions have been investigated. UV-visible digital imaging and natural emission spectroscopy were applied in a single cylinder optically accessible high swirl multi-jets compression ignition engine. Combustion tests were carried out using commercial diesel and a blend of 80% diesel with 20% nbutanol (BU20). Two injection pressures (70 and 140 MPa), two injection timings (11 CAD BTDC and 3 CAD BTDC) and a two different levels of EGR rate were tested. UV-visible emission spectroscopy was used for the detection of the chemical markers of combustion process. Chemiluminescence signals, due to OH, HCO and CO2 emission bands were detected. OH emission was correlated to NO measured at the exhaust. The soot spectral feature in the visible wavelength range was correlated to soot engine out emissions. The following main conclusions can be summarized: For all the conditions, the engine efficiency for BU20 was higher than for diesel fuel. This was due to higher BU20 volatility that improved the fuel charge mixing and reduced the amount of not completely burned fuel. Soot was lower for BU20 fuel than diesel for all conditions because of a lower carbon content fuel with a lower cetane number and higher ignition delay that allows to reduce the unburned mixture amount. The blend BU20 with injection pressure 70MPa, injection timing of 11 CAD ATDC and at 50% of EGR allowed the best compromise between soot and NOx engine out emissions. UV emission spectra detected at the early stage of combustion highlight OH formation far from the liquid jets, in regions characterized by a large amount of fuel in the vapor phase well mixed with the air entrained in the spray, primarily around the jet. UV-visible emission spectroscopy points out the same trend of soot formation both for Diesel and BU20 differing only in the intensity that was higher for Diesel. This confirmed the higher soot tendency of Diesel than BU20. For all the conditions the spectral behaviour remained unchanged until the start of oxidation phase when the soot emission decreased and OH band system came out demonstrating OH radical as one of the principal marker of the soot oxidation. The optical investigations results were correlated with engine out emissions. The integral value of OH emission and NOx measured at the exhaust, presented similar trend, as expected by the extended Zeldovich mechanism. 368

The integral value of soot, in the last combustion phase (20-30 CAD ASOI), was in agreement with exhaust soot concentration.

Acronyms ASOI After Start of Injection ATDC After Top Dead Centre BTDC Before Top Dead Centre BTDC Before Top Dead Centre BU20 20% n-butanol and 80% gasoline blend CAD Crank Angle Degree CAD Crank angle degrees CCD Charge Coupled Device CI Compression Ignition EGR Exhaust Gas Recirculation ICCD Intensified Charge Coupled Device ID Ignition Delay SOI Start of Injection TDC Top Dead Centre TTL Transistor-Transistor Logic UV Ultra Violet

Acknowledgements The authors would like to express their sincere appreciation to Mr. A. Mazzei for the technical support in preparing the equipment and during the experiments.

References [1] The Alternative Fuels and Advanced Vehicles Data Center (AFDC) _ [accessed 31.01.2012]. [2] Balat M., Balat H., (2009) Recent trends in global production and utilization of bio-ethanol fuel, Applied Energy, Volume 86, Issue 11, November 2009, Pages 2273-2282 [3] Kleinová A., Vailing I., Lábaj J., Mikulec J., Cvengroš J., (2011) Vegetable oils and animal fats as alternative fuels for diesel engines with dual fuel operation, Fuel Processing Technology, Volume 92, Issue 10, October 2011, Pages 1980-1986 [4] Lapuerta M., Armas O., Rodriguez-Fernandez J. Effect of biodiesel fuels on diesel engine emissions. Progress in Energy and Combustion Science 34(2), April 2008, pp. 198-223. [5] Pourkhesalian A.M., Shamekhi A.H., Salimi F. Alternative fuel and gasoline in an SI engine: A comparative study of performance and emissions characteristics. Fuel 9(5), May 2010, pp.10561063. [6] Do an O. The influence of n-butanol/diesel fuel blends utilization on a small diesel engine performance and emissions. Fuel 90(7), July 2011, pp. 2467-2472. [7] Chao J., Mingfa Y., Haifeng L., Chia-fon F.L., Jing J. Progress in the production and application of n-butanol as a biofuel. Renewable and Sustainable Energy Reviews 1(8), Oct2011, pp.4080-4106 [8] Rakopoulos D.C., Rakopoulos C.D., Giakoumis E.G., Dimaratos A.M. and Kyristis D.C., 2010. Effect of butanol-diesel fuel blends on the performance and emissions of a high-speed DI diesel engine. Energy Conversion and Management 51, pp.1989–1997. 369

[9] Rakopoulos C.D., Dimaratos A.M., Giakoumis E.G., Rakopoulos D.C (2011) Study of turbocharged diesel engine operation, pollutant emissions and combustion noise radiation during starting with bio-diesel or n-butanol diesel fuel blends. Applied Energy, vol.88(11), November 2011, pp. 3905-3916. [10] Rakopoulos D.C., Rakopoulos C.D., Papagiannakis R.G., Kyritsis D.C. (2011) Combustion heat release analysis of ethanol or n-butanol diesel fuel blends in heavy-duty DI diesel engine, Fuel 90, pp. 1855–1867. [11] Rakopoulos C.D., Dimaratos A.M., Giakoumis E.G., Rakopoulos D.C. (2010) Investigating the emissions during acceleration of a turbocharged diesel engine operating with bio-diesel or n-butanol diesel fuel blends. Energy 35(12), December 2010, pp. 5173-5184. [12] Valentino G., Corcione F.E., Iannuzzi S.E., Serra S. (2012) Experimental study on performance and emissions of a high speed diesel engine fuelled with n-butanol diesel blends under premixed low temperature combustion. Fuel 92(1), February 2012, pp.295-307. [13] Corcione F., Valentino G., Tornatore C., Merola S. et al., "Optical Investigation of Premixed Low-Temperature Combustion of Lighter Fuel Blends in Compression Ignition Engines," SAE Technical Paper 2011-24-0045, 2011. [14] Tornatore C., Marchitto L., Mazzei A., Valentino G., Esposito Corcione F., Merola S.S. Effect of butanol blend on in-cylinder combustion process. Part 2: compression ignition engine Journal of KONES Powertrain and Transport 2011, vol.18(3) pp. 473 – 483. [15] Murphy M.J., Taylor J.D., McCormick R.L. (2004) Compendium of experimental cetane number data, NREL Report, NREL/SR-540-36805. [16] Heywood J.B. Internal Combustion Engine Fundamentals, New York: McGraw-Hill, 1988. [17] Dec J.E. and Espey C. Chemiluminescence imaging of autoignition in a DI diesel engine. SAE Paper 982685, 1998. [18] Gaydon A.G., The Spectroscopy of Flames, Chapman and Hall ltd., 1957. [19] Alkemade C. Th. J., Herrmann, R., Fundamentals of Analytical Flame Spectroscopy, Hilger, Bristol, UK, 1979. [20] Dieke G.H., Crosswhite H.M. (1962). The ultraviolet bands of OH. J. Quant. Spectrosc. Radiat. Transfer, 2 pp.97-199. [21] Dec J.E. and Coy E.B. OH radical imaging in a DI diesel engine and the sructure of the early diffusion flame. SAE Paper 960831, 1996. [22] Singh S., Musculus M.P.B., Reitz R.D. (2009) Mixing and flame structures inferred from OHPLIF for conventional and low-temperature diesel engine combustion, Combustion and Flame, 156(10), pp.1898-1908. [23] Zhao H., Ladommatos N. (1998) Optical diagnostics for soot and temperature measurement in diesel engines. Progress in Energy and Combustion Science 24(3) pp.221-255. [24] Senda J., Choi D., Iwamuro M., Fujimoto H. et al., "Experimental Analysis on Soot Formation Process In DI Diesel Combustion Chamber by Use of Optical Diagnostics," SAE Technical Paper 2002-01-0893, 2002. [25] Pepiot-Desjardins P., Pitsch H., Malhotra R., Kirby S.R., Boehman A.L. (2008) Structural group analysis for soot reduction tendency of oxygenated fuels Original Combustion and Flame 154(1–2) pp.191-205. [26] Nagle J., Strickland-Constable R.F. (1961). Oxidation of Carbon Between 1000°-2000°C. Proc. 5th Conf. on Carbon – Pergamon. 370

[27] Samaniego J.M., Egolfopoulos F.N. and Bowman C.T. (1995) CO2* Chemiluminescence in Premixed Flames. Combust. Sci. and Tech. vol. 109, pp. 183-203. [28] Gaydon A.G. (1940) The flame spectrum of carbon monoxide. Proceedings of the Royal Society of London. Series A vol. 176 n. 967 pp. 505-521. [29] Dixon R.N. (1963) The carbon monoxide flame bands Proceedings of the Royal Society of London. Series A vol. 275 n. 1362 pp. 431-446. [30] Westbrook C. and Dryer F. Chemical Kinetic Modelling of Hydrocarbon Combustion. Prog. Energy Comb. Sci., page 1, 1984.

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Flameless Oxidation as a Means to Reduce NOx Emissions in Glass Melting Furnaces Jörg Leichera, Anne Giesea a

Gaswärme-Institut e.V, Essen, Germany, [email protected]

Abstract: Melting glass is a very energy intensive process, with process temperatures of more than 1600°C required to melt the raw materials in the furnace. Such high temperatures are usually achieved by intensive air preheating and near stoichiometric conditions. This leads to a significant production of nitrous oxides (NOX). As the emissions of nitrous oxides are regulated be increasingly stringent environmental legislation, the glass industry is very interested in combustion techniques which reduce NOX emissions without resorting to expensive flue gas treatment while maintaining the glass quality. In the steel industry, the so-called flameless oxidation (FLOX) combustion concept is firmly established as a state-of-the-art primary technique to reduce NOX formation in furnaces. This technology uses high momentum jets of fuel and oxidizer to generate an intense recirculation of hot, but chemically inert flue gas into the reaction zone. By mixing flue gas into the reaction zone, its shape changes from a quasi-twodimensional flame front into a three-dimensional reaction volume. A much more homogeneous temperature distribution is obtained while the formation of hot spots can be avoided, thus significantly reducing thermal NOX emissions. The name “Flameless Oxidation” derives from the fact that no visible flame can be observed with the naked eye since the local OH concentrations are very low due to the large amounts of recirculated flue gas. Experience from the steel industry shows great promise for the introduction of this technology into other industrial sectors as a means to reduce nitrous oxide emissions. In the course of a German research project, the Gaswärme-Institut e.V. Essen (GWI) in cooperation with several industrial partners investigated how to best introduce the flameless oxidation technique to glass melting furnaces equipped with recuperative burners, so-called unit melters. A furnace of a project partner, producing glass for compact fluorescent lamps, was chosen for conversion to FLOX burners. Initially, there was some skepticism with regards to the applicability of a combustion process without a visible flame in a glass furnace, as normally, a slow, highly luminous flame is considered desirable in such furnaces. Also, the high gas velocities in the fuel and oxidizer jets carry the risk of blowing dust from the batch into the central recuperator. Thus, a careful design of both the new burner system as well as their positions in the furnace was necessary to avoid high gas velocities immediately above the glass bath. In a first step, a FLOX burner system for recuperative glass melting furnaces was developed and optimized at GWI, using CFD simulations. This prototype was then tested at GWI’s semi-industrial test rig in order to verify that the new design was able to comply with the required NOX emissions limit. Compared to the burner originally mounted in the glass furnace, a reduction of almost 60 per cent was achieved. In order to reduce the downtime of the furnace to a minimum, the exchange of the burners was planned using CFD simulations. Different configurations were simulated in order determine potential problems and an optimum burner set up was found, which was subsequently implemented on the site. The retrofitted plant has been in operation for five years now still maintaining to produce the same glass quality as before the retrofit. The NOX emissions, on the other hand, were reduced by about 50 per cent. In addition the energy consumption of the process was reduced because an optimized burner positioning and more stable combustion allows for lower air ratios in the furnace, thus reducing fuel consumption.

Keywords: Glass Melting Furnace, Flameless Oxidation, NO X Emissions

1. Introduction The melting of glass on an industrial scale is a very energy-intensive process which, depending on the glass quality being manufactured, can easily require process temperatures of more than 1600 °C. These very high temperatures are usually achieved in glass melting furnaces by means of intensive 372

pre-heating of the combustion air, either recuperatively (maximum air pre-heat temperatures around 800 °C) or regeneratively (maximum air pre-heat temperature 1400 °C). These high temperatures, combined with a near-stoichiometric operation of the burners and long residence times due to the size of the furnaces and generally low flow velocities, often lead to a significant formation of nitrous oxides (NOX). As the emission of these pollutants is strictly regulated by emission laws, the glass industry is very interested in techniques to reduce NOX emissions without resorting to costly secondary flue gas treatment. Instead, techniques are preferred which reduce NOX formation in the furnace itself, of course without reducing the glass quality. One such potential primary technique to reduce NOX emissions is the so-called flameless oxidation (FLOX) technology, which is already well-established in the steel industry. Other common names for this technology are mild or colorless combustion. This technology, first developed in the 1980s [1], uses high momentum jets of fuel and air to entrain large amounts of hot, but chemically inert flue gas and mix it with fuel and combustion air. In this manner, the shape of the reaction zone is changed: instead of an almost two-dimensional reaction front, a three-dimensional reaction volume is created in which the reactants are diluted by the hot exhaust gas. The consequence of this change in the form of the reaction zone is that a much more homogeneous temperature distribution is obtained, without the temperature peaks usually found in conventional diffusion flames. As thermal NOX formation is highly dependent on local temperature, this much more homogeneous temperature distribution drastically reduces NOX emissions. Figure 1 shows a comparison between the standard and the FLOX modes of combustion while figure 2 shows flame images both in the visible and UV spectrum (using an OH chemoluminiscence method) of standard diffusion flames and FLOX combustion.

Figure 1: Principles of standard combustion (top) and flameless oxidation (bottom). On the right hand side, the temperature evolution is shown [2]. The name Flameless Oxidation derives from the fact that due to the dilution of the reaction zone, there is no visible flame while operating in FLOX mode, as can be seen on the lower left hand side of figure 2. Nevertheless, complete consumption of the fuel gas is achieved, which can be shown by 373

CO measurements in the exhaust gas. The different shapes of the reaction zones are visualized by the OH* chemoluminiscence images shown on the right hand side of figure 2. While the standard combustion shows a zone of intense combustion near the burner outlet, the reaction zone in the flameless mode is lifted off the burner throat and shows a more even OH distribution.

Figure 2 : Comparison of Standard (top) and FLOX (bottom) combustion modes in the visible and the UV spectrum

Figure 3: FLOX mode as a function of the partial pressure of O2 [3]

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As the intense mixing of the reactants with hot but chemically inert exhaust gas lifts local temperatures above the self-ignition limits, the local oxygen concentrations are reduced (cf. Fig. 3), leading to a unique form of combustion which is characterized by very homogeneous temperature and heat flux distributions, stable combustion behaviour and very low NOX emissions. Also, noise emissions are low compared to conventional burners. While the FLOX combustion mode has successfully established itself as a method to reduce of NOX in many high temperature applications, the glass industry was hesitant to adopt this burner technology as flames in glass furnaces are traditionally highly luminous while the reaction zones in FLOX combustion are almost entirely invisible. However, results from a previous research project called EURONITE [4] were promising enough that a glass manufacturer (OSRAM GmbH) and a burner manufacturer (Hotwork International) could be convinced to participate in a research project called GlasFLOX which investigated the applicability of FLOX technology for glass melting furnaces.

2. The GlasFLOX Project and Test Rig Experiments One of the defining characteristics of flameless oxidation burners is the very high momentum of the fuel jets and combustion air. It is therefore obvious that FLOX burners can only be applied to glass furnaces with recuperative air preheating because only in this configuration the required high velocities jets for the combustion air can be achieved. A schematic of such a recuperative glass melting furnace is shown in Figure 4.

Figure 4: Schematic of a recuperative glass melting furnace The primary objectives of the GlasFLOX project were to design a FLOX burner for operation in glass melting furnaces which would produce less than 500 mg/Nm 3 NOX and at the same time show good behavior at partial loads. Of course, maintaining the quality of the glass was of utmost importance. In a first step, a 500 kW FLOX burner for application in glass furnaces was designed. CFD simulations were carried out to find the optimum geometry for the burner which was then manufactured and extensively tested at one of GWI’s semi-industrial test rigs in order to validate that the targeted NOX emission levels were achieved. Figure 5 shows a comparison between the 375

original (HWI) and the newly designed GlasFLOX burner systems. In the lower half of the figure, the CFD-calculated velocity distributions can be seen. As intended, the reduced section area leads to much higher air velocities which impart a very high momentum to the gas/air jet. The higher velocities cause higher pressure drops in the burner but these were found to be within acceptable limits.

Figure 5: Comparison of the standard nozzle brick and the newly designed GlasFLOX nozzle brick with simulated velocity distributions Numerical simulations of the original and the GlasFLOX burners showed that lower maximum temperatures were achieved in the case of the flameless oxidation burner while the temperatures of the flue gas remained almost the same. These findings were validated by measurements. The experimental investigations of both the original and new burner system in GWI’s test rig prove that the GlasFLOX system was able to comply with the target emission values for NOX (cf. Figure 6), which was already significantly below the legal emission limits of 800 mg/Nm3. Due to these very promising results, the retrofit of an existing glass melting furnace with the new GlasFLOX burners was planned

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Figure 6: Measured NOX emissions of the original (HWI) burner and the new GlasFLOX burner

3. Conversion of a Glass Melting Furnace The glass melting furnace which was to be retrofitted with GlasFLOX burners is a side-fired furnace with ten burner positions, which are connected to a central recuperator to recover waste heat from the exhaust gas in order to preheat the combustion air. A sketch of the plant is shown in Figure7. The process operators did not want prolonged downtimes of the plant and hence loss of production, which is why the retrofit campaign was planned in advance aided by CFD simulations of the furnace. Several configurations were simulated and evaluated. In a first step, only four of the ten existing burners were substituted with GlasFLOX burners, those close to the batch inlet. However, simulations showed that this configuration led to increased gas velocities near the batch and the flue gas ducts. High velocities in this area are not desirable as this may lead to carry over from the dust-laden batch material into the recuperator which may cause increased wear and tear or even damage of the recuperator. Therefore, a second configuration was investigated in which all but the two burners closest to the batch inlet were swapped with GlasFLOX burners. In this way, low velocities close to batch inlet and flue gas ducts can be maintained, minimizing the risk of dust carry over into the recuperator. Figure 8 shows the various steps of the retrofit, while Figure 9 shows the calculated velocity distributions immediately above the glass melt for the various configurations [5, 6]. Also, several different alignments and configurations of the burners were simulated numerically in order to avoid collisions of the jets which might cause increased turbulence and hence disturbance of the glass bath and potential dust-ups. This was not a problem before as the burner exit velocities of the original burners were relatively low, but became important when using the flameless 377

oxidation burners with their much higher jet momentum. It was found that a burner alignment of 5 degrees off the burner axis was well-suited to avoid these issues.

Figure 7: Schematic of a glass melting furnace

Figure 8: Burner configurations for the various retrofit phases In the next phase, the conversion of the furnace was carried out based on the findings of the CFD simulations. Eight standard burners were replaced with GlasFLOX burners with the two burners closest to the batch inlet remaining untouched in order to maintain low gas velocities near the batch. After the retrofit, pollution emission measurements were performed in order to evaluate the impact of the new burner system on NOX emissions. Comparisons with NOX emission measurements taken prior the retrofit show a reduction of about 45% while maintaining constant fuel consumption and, most importantly, glass quality. Also, condensation in the flue gas ducts was found to be reduced by 378

about 30%. Due to the increased combustion stability inherent in the FLOX technology, it was even possible to reduce the excess air ratio.

Figure 9: Simulated velocity distributions near the glass bath for the various retrofit phases After nearly five years in operation, the plant operators are very pleased with the new burner system. NOX emissions remain low, and there was hardly any corrosion to be found at neither the burner tips nor the nozzle bricks. The burners themselves require less maintenance than the original equipment. While there were some reservations in the beginning to the use of high momentum burners in a glass furnace due to the fear of increased dust-ups, this was found not to be the case. In fact, the amount of dust in the flue gas decreased slightly.

4. Conclusion In the course of a research project carried out by the Gaswärme-Institut in cooperation with several industrial partners, namely OSRAM GmbH and Hotwork International AG, introduced the flameless oxidation technique into the glass industry. In the beginning, this combustion concept which has already been successfully implemented in various high temperature manufacturing processes, was regarded with some scepticism due to the lack of a visible flame and the requirement for high velocity gas flows in a glass melting furnace. However, using both experimental and numerical techniques on a lab-scale, it could be shown that this combustion concept can be successfully adapted for use in glass melting furnaces. The subsequent conversion of the furnace to flameless oxidation operation was prepared beforehand by extensive use of CFD simulations in order to minimize the downtime of the plant. The retrofitted furnace has been operating for about five years now, with an excellent operational track record. NOX emissions are about 45% lower than before the conversion, while maintaining the same glass quality as before. While fuel consumption has not decreased, it is possible to reduce the excess air ratio in the furnace since FLOX combustion is much more stable than conventional combustion systems.

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Figure 10: View into the GlasFLOX glass melting furnace

5. References [1] Wünning, J.G.: Flammlose Oxidation von Brennstoff, PhD Thesis, RWTH Aachen, Germany, 1996 [2] Wünning, J.G: FLOX-Flameless Combustion, Thermprocess Symposium Düsseldorf, Germany, 2003 [3] Milani, A.: “Mild Combustion” techniques applied to regenerative firing in industrial furnaces, 2nd International Seminar on High Temperature Combustion, Stockholm, Sweden, 2000 [4] Flamme, M.; Kösters, M.; Scherello, A.; Kremer, H. and Boß, M.: Experimental Study of Heat Transfer Intensification in Glass Melting Furnaces. Final report of task 2.2 of the EURONITE project (JOE3CT970083). Gaswärme-Institut e.V. Essen, Germany, 2000 [5] Giese, A., Konold, U., al-Halbouni, A. Görner, K., Schwarz, G., Köster, B.; Application of Flameless Oxidation in Glass Melting Furnaces, 7th International Symposium on High Temperature Air Combustion and Gasification, Phuket, Thailand, 2008 [6] Scherello, A.; Konold, U. and Görner, K.: Anwendung der flammenlosen Oxidation für Glasschmelzwannen mit rekuperativer Luftvorwärmung – GlasFLOX®, 23. Deutscher Flammentag, 12.-13. September 2007, Berlin, VDI-Bericht 1988

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Mechanism of damage by high temperature of the tubes, exposed to the atmosphere characteristic of a furnace of pyrolysis of ethane for ethylene production in the petrochemical industry Jaqueline Saavedra a , Javier Trujillo Pérez franciscob , Lourdes Meriño Standc, Harbey Alexi Escobard , Luis Eduardo Navas e, Juan Carlos Amézquitaf

a

Colombian Institute of petroleum, Ecopetrol, Santander, Colombia, [email protected] b Universidad Complutense of Madrid Faculty of chemical sciences, Madrid Spain, [email protected] c Department of chemical engineering, Industrial University of Santander, Bucaramanga, Colombia, [email protected] d Management Barrancabermeja refinery, Harbey Escobar, Colombia, [email protected] e Management Barrancabermeja refinery, Colombia, Luis Eduardo Navas, Luis. Navas. Ecopetrol.com.co f Department of chemical engineering, Industrial University of Santander, Bucaramanga, [email protected] .

Abstract: In this work he took as a case study a furnace of pyrolysis of et hane for production of ethylene, which analysed different injury mechanisms, in order to determine the most critical in this process. Making a background and historical review of the proc ess, it was determined that the carburización is the mechanism of most critical damage, which occurs primarily in the area of radiation from this type of ovens. The carburización is favoured by the undesired formation of Coke during t he process. Background and historical review became an analysis of t he influence of variables and factors such as temperature, time of residence, load flow, type of cargo, flow of heat and the severity of the process, the formation of Coke.

Keywords: Carburization, HP40, overheating, cooking, pyrolysis and coke.

1 Introduction The processes of thermal pyrolysis of hydrocarbons occur at high temperatures, causing the hydrocarbons of the burden to become unstable and are decomposed into hydrogen, methane, olefins (ethylene product), aromatic and coke. The pipe from the furnace of pyrolysis of ethane to ethylene production, suffers severe corrosion at high temperature, contact gaseous vapor and hydrocarbon mixtures. The most common damage include embossing, erosion, cracking and carburización. There are two kinds of reactions in pyrolysis process: the main reactions, which are that lead to the desired product and secondary that break down molecules of product into by-products as aromatic complex, higher olefins and Coke[1]. The environment of the process is characterized by a high activity of carbon to the inside of the pipe, where they occur reactions that involve the formation of carbon in the gas phase [2,3], which can induce the formation of layers of coke on the inner surface of the pipe, through different mechanisms [1, 2].Coke formed affects process, to generate the appearance of hotspots, increasing the pressure within the pipe drop, decreasing the efficiency and integrity of the oven, and heat 381

transfer, which implies increased consumption of fuel to keep constant temperature process and damage by carburización. The carburización is one of the most critical damage mechanisms in processes of hydrocarbons at high temperature [4], which affects properties such as the coefficient of thermal expansion, magnetization, thermal conductivity, hardness and ductility, among others [5]. The carburización occurs in the tubes of the furnace of pyrolysis of ethane to produce ethylene [6], which are exposed to environments with carbon at high temperatures and where the carbon is transferred from the atmosphere of the process towards the interior of the pipe metal matrix. In the carburización mechanism, carbon atoms diffuse through the metal matrix material [7], [8]. Widespread carbon can remain without react or react with constituents of the alloy to form carbides M23C6 and M7C3 (M: METAL), intergranulares and intragranulares, mostly with chromium, affecting the structural homogeneity of the material.

2. Experimental procedure Review of history and historical a furnace type cabin with two areas of heating, of convection and radiation, was made to analyse the different mechanisms of damage and the area in which they occur, in order to determine the most critical in the process of pyrolysis of ethane to ethylene production. They also analyze the influence of variables and factors such as temperature, residence time, load flow, type of load, heat flux and the severity of the process, the formation of Coke. This was complemented information with thermography taken in field of pyrolysis oven, in order to define the real conditions of operation and this way, establish the diagnosis of damage. Also made the analysis of a steel tube HP40, withdrawn from service in the furnace of pyrolysis case study, 72 000 hours of operation, which was obstructed by a thick layer of Coke, (fig. 1)

Fig 1. Length of pipe removed from service for to coking furnace pyrolysis of ethane to produce ethylene. To assess the State of damage of steel were used techniques of non destructive analysis such as sizing, visual inspection, magnetization and destructive analysis as chemical composition and hardness.

3 Teams The equipment used for the different analyses performed were: Analysis of chemical composition of the material: made by spectrometry of optical emission (EEO) technique according to standard ASTM E - 415-08 [9]. Analysis of hardness: hardness testing were conducted in scale Brinell - HB according to standard ASTM E 10-08 [10], with an uncertainty of measurement: ± 1.31 HB, a durometer Brinell Gnehm Horgen, applying 187, 5Kgf. Analysis metallography: made with 6V attack 10% oxalic acid electrolyte for 10 seconds [11], according to standard ASTM E-45

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Analysis of electronic microscopy of scanning SEM: this analysis was performed with an electron microscope, Leo1450VP, equipped with system of x-ray energy dispersed OXFORD INCA [12].

4. Results and analysis of results 4.1. Analysis of history and historical 4.1.1 Mechanisms of damage The information obtained in the revision of history and historical analyses of the process over a period of 8 years, related the frequency of failure with the affected area of the oven, as shown in the histogram of Figure 2 and it was determined that the causes for which pulled out sections of pipe from the furnace were: Presence of thick layers of Coke that can not be removed in the process of decoquizado with steam. Carburización. Cracking of tubes and diametrical deformation and warpage and buckling. Creep (creep). Metal dusting (accelerated Carburización). Excessive magnetism. The histogram shows that had been submitted 10 failures in the pipeline in the area of radiation. Followed in frequency of failure, damage to the housing, the refractory and burners in the oven. The analysis of the frequency of fails them, reveals that the radiation zone is indeed which presents more frequent damage. The Ues (frequency: 2) and the "Y" (frequency: 3) are part of the pipe of the coil of radiation, which has a 37.5% of failure in the radiation zone.

A) Pipelines - radiation zone ( B) "U" - the area of radiation (C) "and-radiation zone" (D) Refractory-zone radiation (E) Housing - re radiation area

(F) Coil- zone convection (G) Refractory-zone convection (H) Insulation- zone convection (I) Burners (J) of burners Hoyas

Fig 2. Histogram of failure of the furnace case study. 383

4.1.2 Influence of variables of the process on formation of coke Variables greater influence in the formation of coke in pyrolysis processes are: the severity of the process, the type of load, temperature, time of residence, heat flow, the partial pressure of hydrocarbons, whose interaction occurs on the figure 3.

Fig 3. Operation of process variables involved in pyrolysis. When there is this Coke, this acts as a resistance which decreases the thermal conductivity from the outside of the tube until the flow of the process (fig. 4), necessitating a greater flow of heat to maintain the required temperature of the process, which leads to sobrecalentatiento, contributing to the formation of more Coke.

Fig. 4. Heat flow pattern through To is the external temperature, Ti Tp is the temperature in the process gas.

the steel HP40 and coke is the internal temperature

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layer, where, of the tube,

4.2 Analysis situ of the oven We performed a visual internal inspection into the oven, in which there were irregularities in the area of radiation as tubes: warpage and buckling in some of them. Through thermography identified the actual temperatures of operation, which notes are to reach points of up to 1057.6 ° C (1935.7 ° F), which exceed the maximum temperature design of 1010 ° C (1850 ° F according to standard API 530), Figure 5, this overheating leads to envelope pyrolysis of loading, formation of Coke, mechanisms of damage as the carburización. Coke increases the activity of carbon in the environment of the process which joined the high temperatures facilitate the diffusion of carbon into the interior of the material, cause damage by carburización. Figure 3 shows the cyclical relationship between the high temperatures of the process and the presence of coke on the inside of the pipe, which results in effects such as: generation of an environment conducive to the emergence of damage in the alloy (such as carburización); reduction in the thermal efficiency of the oven.

Figure 5. Thermography for the Serpentine south eastern side of the furnace of study.

4.3 Analysis of damage mechanism High resistance materials as the HP40 tend to form a protective oxide layer which prevents the [13,14] carburización, the presence of coke in conditions of operation impaired such layer, as the elements that make up react with the carbon in the environment. In the absence of a uniform protective layer carbon diffuses towards the interior of the alloy. The HP40 material of the pipe withdrawn from service not presented a definite profile of carburización, however there is precipitation of carbides in matrix (grain boundaries, edges of dendrites), as shown in Figure 6.

Fig 6. Metallography of the study material (steel HP40) with presence of carburization.

385

Carbon who has entered the matrix material, produces changes in it because it forms carbides with M23C6 and M7C3 type alloy metals (M metal), mostly with chromium [15]. These carbides introduce efforts which deform the material structure, favouring the embrittlement, magnetization, plastic deformation and change in hardness among others, eventually reducing the material life[16]. The evaluated material presented a slight magnetic response, which is higher in the inner surface which in the external, indicating a change in the microstructure of the material, the alloy has originally a ParaMagnetic behavior [17, 18], this change is due to the formation of carbides implies a redistribution of chromium [19] (mainly) in the matrix of the material. Buckling and warpage problems found in the pipe are due to the loss of ductility of material and the elongation capacity, since carbides in matrix contribute to change the hardness of the material [20, 21]. Hardness average found for material removed from service is 188HB, while for new material is 170HB. This change in the material reduces the ability of elongation and ductility, which leads to sagging and warpage of the tubes during the thermal cycles[22]. The warpage and buckling of the pipe is also caused by the presence of Coke which hinders the heat dissipation during cooling, also acts as a thermal barrier that forces to increase the external temperature of the tubes to maintain the temperature of the process, which causes overheating, speeding up the formation of more coke and the carburización. With background, analysis of metallic samples analysis, evidence of presence of coke and temperature exceeding those of design determined to carburización, is the mechanism of most critical damage, which occurs primarily in the area of radiation from this type of ovens.

4 Conclusions The cooking of the pipe of pyrolysis ovens creating an environment that leads to the carburización of the pipe due to the abundant carbon available for dissemination and an increase in temperature, which must be submitted the tubes when there is a layer of Coke inside. In the different mechanisms of failure occur in the pipe from the furnace of pyrolysis, there is one common factor involved accelerating mechanism to a greater or lesser extent, such factor is the carburización of the material. Although it does not appear as the cause of the withdrawal of the piece, it affects the deterioration of the strength of steel with mechanisms such as the creep or magnetization. The carburización and overheating are factors contributing to damage such as plastic deformations, embrittlement, magnetization and change in hardness, the HP40 alloy tubing for the production of ethylene pyrolysis furnace. Through the analysis of history, analysis of metallic samples, the evidence of the presence of Coke, was determined that the carburización is the mechanism of most critical damage, which occurs primarily in the area of radiation from this type of ovens. When do not hold correct values of temperature, time of residence and severity induces a sobrepirólisis of load, speeding up the deposition of coke on the walls of the coil. Which, in turn, to reduce the transfer of heat to the process, requires to increase fuel consumption and decreases the performance of ethylene due to the fall of pressure generated by the decrease in the effective diameter of the pipe

References [1] Albright L.F.,C. F. McConnell, k. Welther. In Thermal HydrocarbonChemistry; Eddinger, r. T. Eds.; Advances in Chemistry Series 183; American Chemical Society: Washington, D.C., 1979; pp 175-191. [2] Albright L.F and j. C. Marekt. Mechanistic Model for Formation of Coke in Pyrolysis Units Producing Ethylene. School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907. 386

[3] G.C. Reyniers, G.F. Froment, F.D. Kopinke. Coke Formation in the Thermal Cracking o f Hydrocarbons: Modeling of Coke Formation in Naphtha Cracking. Ind. Eng. Chem. Res. 33, 2584-2590. (1994). [4] T. Maeda, f. X Terwijn (2005). Carburization resistance of high-CR high-Ni Weld overlayed tubes for ethylene pyrolysis furnace. In: Ethylene Producers Conference, Vol 14. 47 Session. [5] H. M. Tawancy (2009). Degradation of mechanical strength of pyrolysis furnace tubesby hightemperature carburization in a petrochemical plant. In: Engineering Failure Analysis, Vol. 16, Issue 7 pp. 2171-2178. [6] C. D. B. Meadowcroft and j. e. Oakey (1995). Guidelines for Plant Measurement of High Temperature Corrosion. In: European Federation of corrosion Publications, Vol. 14, pp. 1-9. [7] Damage Mechanisms Affecting Fixed Equipment in the Refining Industry, APIRP - 571, Recommended practice 571, December 2003. In: American Petroleum Institute, First edition, pp. 3-270. [8] ASTM G79–83 (Reapproved 1996). Standard Practice for Evaluation of Metals Exposed to Carburization Environments1 [9] ASTM E - 415-08 Standard Test Method for Atomic Emission Vacuum Spectrometric Analysis of Carbon and Low-Alloy Steel1. [10] ASTM E 10-08 "Standard Test Method for Brinell Hardness of Metallic Materials". [11] ASM American Society for Materials (1985). In: Metal Handbook, Properties and selection: Stainless steel. Vol 3. [12] ECOPETROL, (2010). Colombian Institute of the oil Institute, laboratory of electron microscopy, Colombian Petroleum Institute. Report 10000048 ID0146 T67 10 103-ECP, Piedecuesta. [13] Alvarez J. , Melo. D. Protective coatings against metal dusting. Surface & Coatings Technology, 203 (2008) 422-426. [14] H. M. Tawancy, (2009), Degradation of mechanical strength of pyrolysis furnace tubesby high-temperature carburization in a petrochemical plant. In: Engineering Failure Analysis, vol. 16, Issue 7 pp. 2171-2178. [15] Hall, D. et to the. Factors effecting carburization behavior of cast austenitic steels. Materials Performance, January, 1985, p. 25-26. [16] B . Terry, j. Wright, D. Hall, (1989). A model for prediction of carburization in steels for ethylene production furnaces. Institution of corrosion science & technology, 48. Vol 29, pp. 118. [17] I.C. Silva to Rebello J.M.A. BC Bruno, (b) P.J. Jacques, c B. Nystend and j. Dillee, (2008), Structural and magnetic characterization of to cast austenitic steel carburized. EM: Science Direct, Scripta Materialia, 1010-1013, pp. 1-4 [18] Saavedra J., Amezquita J.C., Díaz L.M. Evaluation of damage by carburization of a tube removed from a pyrolysis furnace. Ciencia e ingeniería Neogradadina,Vol. 20-2, pp. 1920,Bogota, Diembre 2010. [19] Haro SR, DL Lopez, Velasco AT RB Viramonetes.Microesturctural factors that determine the weldability of high Cr- high if HK40 alloy. Mater Chem Phys 2000; 66: 90-6 [20] Balikci Ercan, Mirschams RA. Raman a. Fracture Behavior of superalloy IN738LC with varius precipitate microstuctures. Mater Sci Eng A 1999: 265: 50 - 62 [21] Analysis of ethylene cracking tubes-Kaishu Guan failed **, Hong Xu, Zhiwen Wangmagazine Engineering Failure Analysis 12 (2005) 420-431.

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PROCEEDINGS OF ECOS 2012 - THE 25TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 26-29, 2012, PERUGIA, ITALY

Steam reforming of methane over Pt/Rh based wire mesh catalyst in single channel reformer for small scale syngas production Haftor Orn Sigurdssona , Søren Knudsen Kærb a

Aalborg University, Aalborg, Denmark, [email protected], CA b Aalborg University, Aalborg, Denmark, [email protected]

Abstract: The purpose of this study is to investigate a small scale steam methane reformer for syngas production for a micro combined heat and power (mCPH) unit under different operational conditions. The study presents an experimental analysis of the performance of a specially built single channel of a catalytic parallel plate type heat exchanger (CPHE) reformer stack, where coated Pt/Rh based wire mesh is us ed as a c atalyst. Heat is supplied to the endot hermic reaction with infrared electric heaters. All the experiments were performed under atmospheric pressure and at stable operating conditions. The following paramet ers are considered in the experiment: catalyst temperature, gas hourly space velocity (GHSV) and steam to carbon ratio (S/C). The catalyst was tested at temperatures between 600 and 900°C, S/C ratios between 2 and 5 and GHSV between 319 and 2201 h-1. The experimental results are used to evaluate the effect of flow maldistribution in a CPHE reformer stack on the CH4 conversion and H2 yield.

Keywords: Methane, steam reforming, syngas production, wire mes h catalyst, CPHE reformer.

1. Introduction Existing production and distribution infrastructure of natural gas makes it an important potential feedstock for small scale fuel cell based combined heat and power (mCHP) applications. Several methods exist to produce hydrogen from hydrocarbons such as natural gas, including steam reforming, partial oxidation, auto thermal reforming and dry reforming. Steam reforming has high process efficiency compared to the other processes and is therefore usually the preferred option [1]. Steam reforming of methane rich natural gas is the most widely used process to produce hydrogen, amounting to about 48 % of the world hydrogen production [2]. New methods of extracting natural gas from shale have added significantly to natural gas resources, it is estimated that supply can meet rising demand at reasonable prices. In Europe natural gas accounts for 25 % of the primary energy need, natural gas could bridge the transition period required while shifting from coal and oil to renewable energy sources [3]. Methane rich biogas is regarded as an renewable and widely available alternative to fossil fuels in the future [4,5]. In a fuel cell based mCHP unit, where natural gas is used as fuel, hydrogen is produced on site in a small scale steam reformer before it is converted simultaneously into electricity and heat in the fuel cell. Catalytic parallel plate type heat exchanger (CPHE) reformer is an attractive device for small scale hydrogen production due to low production cost, low unit volume, high heat transfer capability and potential for high degree of integration with other components of the CPHE system. Scaling of a CPHE reformer is more straightforward than in a conventional tubular reformer since the number of plates in the CPHE reformer can be increased to meet the hydrogen demand of the CPHE system. However care must be taken when increasing the amount of plates since longer manifold path can lead to flow maldistribution in the CPHE reformer. Flow maldistribution in a CPHE reformer can lead to heat maldistribution, hydrocarbon slip, increased overall pressure drop and carbon formation on the catalyst surface [6,7]. Flow maldistribution can occur in both the 388

reactor channels and the heating channels, flow maldistribution in the heating channels will lead to heat maldistribution in the reformer. This may lower the temperature on the catalyst in some of the catalyst channels, which will reduce the performance of the CPHE unit. The geometry of the CPHE reformer must be carefully designed to minimize flow maldistribution [8]. The CPHE reformer currently studied has 60 parallel channel with integrated coated woven wire mesh catalyst, and 61 parallel channels to provide heat to the steam reforming reactions from an external catalytic burner. Intake and exhaust manifolds are built into the CPHE reformer on the steam reforming side. The CPHE reformer has a Z-type flow arrangement, is single pass and counter current flow. An illustration of the CPHE reformer can be seen in Fig 1.

Fig 1. Layout of the CPHE reformer stack. The present study focuses on investigating the performance of a single reactor channel at different temperatures, space velocities (SV) and steam to carbon ratios (S/C) to evaluate the effect of flow and heat maldistribution on the CPHE performance. For this purpose a specially built single channel reactor has been realized. Temperature, SV and S/C are the most important parameters in the steam reforming process. Steam reforming on a large scale is usually carried out at temperatures between 800 and 900°C and S/C between 3 and 5. In this paper we investigate the performance of the single reactor channel at temperatures between 600 and 900°C, S/C between 2 and 5 and at SV between 319 and 2201 h-1.

2. Experimental 2.1. Experimental setup and procedure A schematic diagram of the experimental setup can be seen in Fig 2. Methane flows from the storage tank to the CH4 mass flow controller (MFC) from where it flows to the evaporator. Demineralized H2 O is continuously pumped to the evaporator where it evaporates and mixes with 389

the CH4 . The evaporator is filled with 6 mm glass spheres to ensure uniform gas distribution. The feed gas is superheated to 175°C in the evaporator before it enters the reformer through the inlet tube. In the reformer the feed gas is heated up to the reactor temperature in the heat exchanger part of the reformer. The feed gas then enters the reactor part of the reformer where the reactions take place. The reactor is heated to meet the energy demand of the endothermic reactions with eight 700 W infrared heaters. The product gas from the reformer passes through a condenser before the dry gas is analyzed. Demineralized water was supplied to the evaporator with a calibrated Grundfos dose pump. The feed flow rate of the CH4 was controlled with Bürkert MFC with a full scale range of 0-2 nl/m. Inert nitrogen was mixed with the product gas to meet the demand of the gas analyzer, the measurements from the gas analyzer were normalized. The evaporator is made of aluminum and is heated electrically with four 100 W tubular heaters. The reformer parts are made up of stainless steel. Temperatures of the catalyst wire mesh was measured with five N-type thermocouples. In addition three N-type thermocouples were used to measure the temperature of the feed gas in the heat exchanger. The thermocouples in the wire mesh catalyst were distributed evenly with 20 mm in between them in the centerline of the wire mesh, the first thermocouple was placed 10 mm from the catalyst opening. The tip of the thermocouples was pressed against the catalyst wire mesh to ensure good contact between the wire mesh thread and the thermocouple, and subsequently good temperature measurement. Major reactor dimensions and information can be found in Table 1.

Fig 2. Schematic diagram of the experimental setup The concentration of hydrogen in the product gas was measured using a Siemens CALOMAT 6 thermal conductivity gas analyzer, CH4 , CO and CO2 was measured using a Siemens ULTRAMAT 6 infrared analyzer. Mass flow and temperatures in the experimental reformer were controlled and recorded with LabVIEW data acquisition and control system. The product gas concentrations were continuously measured and recorded with LabVIEW, data was written to a file every two seconds. The reformer was heated from room temperature to the working temperature at a linearly programmed rate of 4°C/min. The catalyst was purged with N 2 during heating until desired operating temperature was reached. At the desired operating temperature H2 O was fed to the nitrogen stream for approximately 5 minutes. Afterwards CH4 was introduced gradually. Subsequently N2 flow was reduced gradually to zero. The reformer was operated for approximately one hour at standard conditions (T = 750°C, S/C = 3.5 and GHSV = 319h-1 ) after startup before the experiments were performed to ensure stable operating conditions. When the reformer was stable, logging of the data was started. Every experiment lasted for approximately 10 minutes. 390

Table 1 Major dimensions of the experimental steam reformer Name Reformer channel width Reformer channel height Reformer channel length Catalyst wire mesh width Catalyst wire mesh height Catalyst wire mesh width Plate thickness Catalyst wire mesh wire diameter Wire mesh void fraction Catalyst producer Catalyst composition

Value 90 mm 1.1 mm 198 mm 88 mm 1.05 mm 88 mm 0.5 mm 0.45 mm 0.38 Catator Pt/Rh/Al2 O3

The steam to carbon ratio (S/C) is the total number of H2 O molecules divided by the total number of carbon atoms in the feed gas. S/C is calculated with the following equation

S /C

NH2 O

mol mol

NCH4

(1)

where N H 2 O and N CH4 are the feed gas molar flow rates of H2 O and CH4 respectively. To reduce coke formation on the catalyst surface the S/C ratio is normally above 3. Gas hourly space velocity (GHSV) is defined as the ratio between the void of the catalyst and the total volumetric CH4 flow rate at the inlet. GHSV is calculated according to the following equation GHSV

VC H 4 Vcatalyst

h

1

(2)

where VCH 4 is the volume flow rate of CH4 at the inlet of the reformer and Vcatalyst is the void volume inside the catalyst. To compare the results of the experiments the conversion of CH4 and the H2 yield is calculated. Conversion of CH4 is calculated as X CH4

NCH4 ,FG

NCH4 ,SG

N CH4 ,FG

(3)

where FG refers to feed gas and SG refers to synthesis gas. The H2 yield is calculated as YH2

0.25

N H2 ,SG N CH4 ,FG

(4)

where N H2 is the molar flow rate of hydrogen in the synthesis gas.

2.1. Evaluation of flow distribution in the CPHE reformer stack Flow distribution in the CPHE reformer stack was evaluated experimentally by measuring the static pressure along the intake and exhaust manifolds with a mobile static pressure probe. Flow rates for the isothermal experiments were based on comparing Reynolds number under normal operating conditions for the CPHE reformer. The Reynolds number was based on the hydraulic diameter of the intake manifold. The dimensionless Reynolds number is defined as Dh V Re (5)

391

where Dh is the hydraulic diameter of the intake manifold, V is the velocity of the fluid entering the CPHE reformer, is the density of the fluid and is the dynamic viscosity of the fluid. The velocity of the fluid is calculated as

m Am

V

(6)

where m is the mass flow rate and Am is the cross sectional area of the intake manifold. Static pressure was measured at 20 evenly distribution positions inside the intake and exhaust manifolds. Inclined liquid nanometer filled with methanol was used to measure pressure difference between the manifolds. A Bürkert 8702 MFC supplied the reformer stack with constant flow of air. The exhaust of the reformer stack was open to the atmosphere. Fig 3 shows the static pressure probe and the CPHE reformer stack.

Fig 3: The static pressure probe (left) and the CPHE reformer stack (right). Pressure drop had been measured in a single cassette at different flow rates in an earlier study [9], the results were used to evaluate the mass flow maldistribution in the reformer stack. The normalized mass flow distribution can be seen in Fig 4. Channel 1 is defined as the first channel in the flow direction in the intake manifold. It can be seen from the figure that there is a large maldistribution in the CPHE reformer. Mass flow in the last 10 channels is almost 5 times the average flow, while in the first 10 channels it is on average 0.4 times the average flow in the reverse direction. The reverse flow near the intake is caused by rapid expansion from the intake tube of the reactor to the manifold. At perfect conditions the flow in each channel would result in a GHSP of 319 h-1 , to evaluate the effect of flow maldistribution on the reforming process the single channel reforming experiments are performed at GHSP of up to 7 times the average channel flow rate.

Fig 4. Flow distribution in the CPHE reformer stack under isothermal conditions.

3. Results and discussion 392

3.1 Catalyst stability The performance stability of the catalyst was investigated before all other experiments were carried out. Conditions for the stability test were as follows; temperature of 750°C, steam to carbon ratio 2.0 and GHSV of 627 h-1 . The conditions were kept constant during the period of the experiment and the composition of the syngas was measured. It was observed that the gas composition remained steady at up to 22 h; catalyst deactivation was not observed. The results are presented in Fig 5. On dry basis the average volumetric concentration of H2 , CO, CO2 and CH4 in the reformate gas was 76 %, 16 %, 6.3 % and 1.4 % respectively. No significant changes could be observed in the product gas composition during the stability experiment.

Fig 5. Composition of product gas as functions of time in hours. Conditions were as follows: catalyst average temperature 750°C, S/C ratio 3.5 and GHSV of 627 h-1 .

3.3. Effect of catalyst temperature In this set of experiments the GHSV and S/C ratio is kept constant at 319 h-1 and 3.5 respectively while the temperature of the reformer is varied from 600 to 900°C in steps of 50°C. The syngas composition was measured with the gas analyzer and the conversion of CH4 and H2 yield was calculated from the results.

(a)

(b)

Fig 6. CH4 conversion and H2 yield (a) and syngas composition (b) as a function of catalyst temperature at GHSV and S/C ratio of 319 h-1 and 3.5 respectively. Fig 6 (a) shows the conversion of CH4 and H2 yield as a function of catalyst temperature. It can be observed that as the temperature increases the conversion of CH4 increases, until about 750°C is 393

reached. After that the increase in CH4 conversion is very low. The H2 yield has a maximum around 700°C catalyst temperature, after that it decreases. The syngas composition as a function of temperature is given in Fig 6 (b). The composition of the syngas is affected by the water gas shift (WGS) equilibrium. At lower temperatures the water gas shift (WGS) reaction occurs and the CO level in the syngas is reduced. As the temperature increases the CO conversion is lower due to equilibrium limitation. At higher temperatures the increase of H2 production from the steam reforming reaction is lower than the decrease of H2 production from the WGS reaction. Considering conversion of CH4 and H2 yield the catalyst should be kept at about 750°C, at this temperature the conversion of methane and H2 production is high and the CO level is fairly low.

3.4. Effect of S/C ratio In this series of experiments the S/C ratio is varied at a constant reactor temperature of 750°C and at constant space velocity of 319 h-1 . Conversion of CH4 and H2 yield can be seen in Fig 7 (a). It can be observed that the conversion of CH4 increases slightly until S/C ratio is about 3.5, after that it stays the same until the S/C ratio reaches 5. Higher S/C ratio in the feed gas increases the selectivity toward hydrogen, the higher S/C ratio favour the production of H2 in both the steam reforming and WGS reactions. Fig 7 (b) shows the composition of product gas as a function of S/C. The concentration of H2 is constant at about 76 % for the different S/C ratios. On the other hand, the higher the S/C ratio is the more energy is required for the water evaporation process. The S/C ratio directly affects the efficiency of the process. Since little is gained in conversion of CH4 and H2 yield above S/C ratio of 3.5, that S/C ratio is used in the following experiments.

(a)

(b)

Fig 7. CH4 conversion and H2 yield (a) and product gas composition (b) as a function of S/C at GHSV and catalyst temperature of 319 h-1 and 750°C respectively.

3.5. Effect of space velocity and temperature In this set of experiments the effect of different space velocity on the CH4 conversion and H2 yield and composition of the syngas at different reformate gas temperatures was studied. Experiments were performed at reformate gas temperatures of 650, 750 and 850°C and at space velocities of 319, 627, 941, 1250, 1563, 1896 and 2201 h-1 . The CH4 conversion, H2 yield and product gas composition, as a function of GHSV, can be observed in Fig 8, Fig 9 and Fig 10 for reformer temperatures of 650, 750 and 850°C respectively. It can be observed from the figures that increasing the GHSV (reducing the gas contact time with the catalyst) has a high impact on the CH4 conversion and the H2 yield.

394

(a)

(b)

Fig 8. CH4 conversion and H2 yield (a) and product gas composition (b) as a function of space velocity at reformate gas temperatures of 650°C and S/C ratio of 3.5.

(a)

(b)

Fig 9. CH4 conversion and H2 yield (a) and product gas composition (b) as a function of space velocity at reformate gas temperatures of 750°C and S/C ratio of 3.5.

(b)

(a)

Fig 10. CH4 conversion and H2 yield (a) and product gas composition (b) as a function of space velocity at reformate gas temperatures of 850°C and S/C ratio of 3.5. The impact of higher GHSV on CH4 conversion and H2 yield is considerable higher at lower reformate gas temperatures. The CH4 conversion and H2 yield drops very rapidly as the GHSV is 395

increased at reformate gas temperature of 650°C. However at reformate gas temperatures of 750 and 850°C the drop in CH4 conversion and H2 yield is not as dramatic.

Fig 11. Average catalyst temperatures as a function of space velocity for reformate gas temperatures of 650, 750 and 850°C. The average catalyst wire mesh temperatures as a function of GHSV are shown in Fig 11 for reformate gas temperatures of 650, 750 and 850°C. It can be observed that due to the increased catalyst load, and insufficient heat transfer from the wall to the wire- mesh, the temperature of the catalyst wire mesh drops as the GHSV is increased.

4. Conclusion Steam reforming of methane over a Pt/Rh based wire mesh catalyst in a single channel plate reformer is investigated in the present paper, the results are summarized below. Experiments were performed at temperatures between 600 and 900°C, S/C ratio between 2 and 5 and at GHSP between 319 and 2201 h-1 . The catalyst temperature has a high impact on the CH4 conversion, H2 yield and purity of H2 . However the H2 yield reaches a maximum between 650 and 700°C at S/C ratio of 3.5. CH4 conversion and H2 yield drops significantly at reformer temperature of 650°C when GHSV is increased above the normal operating conditions of 319 h-1 . Increasing the S/C ratio increases the CH4 conversion and H2 yield, however the energy demand rises rapidly since evaporating and superheating water is energy demanding. The results show the importance of maintaining healthy flow distribution in a plate reformer since the heat input to the reforming channels would need to be increased significantly to meet the demand of the channel receiving the highest feed gas flow rates. Catalyst deactivation was not observed in the catalyst stability test, composition of the product gas was constant throughout the experiments. It is therefore concluded that deactivation does not affect the experimental results during these experiments.

Acknowledgments The authors would like to gratefully acknowledge the financial support from The European Regional Development Fund and the Department of Energy Technology at Aalborg University.

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