Grate Furnace Combustion: A Model for the Solid Fuel Layer PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr.ir. C.J. van Duijn, voor een commissie aangewezen door het College voor Promoties in het openbaar te verdedigen op dinsdag 24 juni 2008 om 16.00 uur door Hans Adriaan Johannes Arnoldus van Kuijk geboren te Raamsdonk Dit proefschrift is goedgekeurd door de promotor: prof.dr. L.P.H. de Goey Copromotoren: dr.ir. R.J.M. Bastiaans en dr.ir. J.A. van Oijen Copyright c 2008 by H.A.J.A. van Kuijk All rights reserved. No part of this publication may be reproduced, stored in a re- trieval system, or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of the author. Cover design: Alex Silberstein A catalogue record is available from the Eindhoven University of Technology Library ISBN: 978-90-386-1285-0 Preface Biomass is a renewable source of energy which will probably play an important role in the transition towards a more sustainable energy supply. This thesis contains a study aimed at developing models to study the formation of NOx-emissions of bio- mass grate furnace combustion, an attractive conversion technique for medium and small scale energy supply for power generation and district heating. In this preface, the social, scientific and organizational context in which the study was performed will be described. The study presented in this thesis offered me the opportunity to address the in- terests of different stakeholders that are involved in the global effort to make com- bustion processes cleaner, more efficient and more sustainable. For scientists, the results presented in this thesis lead to an improved understanding of solid fuel con- version and emission formation. For engineering companies, tools and results are described that can be used to meet the emissions regulations by optimizing the de- sign and operating conditions of a plant. For operators of grate furnaces, such opti- mized furnaces lead to reduced costs of acquirement and operation, less emissions and increased fuel flexibility, to name a few examples. For society, wider applica- tion of biomass grate furnace conversion will lead to a better environment due to reduced emission of greenhouse gasses and pollutants and a more secure energy supply due to decreased demand for fossil fuels. The present study offered me also the opportunity to work on an interesting scientific topic that involves different scientific disciplines. Different scientific disci- plines are involved because a large number of phenomena take place in a biomass conversion process. Examples of these phenomena are the thermal decomposition of solid fuel particles, gas phase kinetics and heat and mass transport. The present study therefore involves elements from chemistry (heterogenous and homogenous reactions), physics (fluid dynamics) and mechanical engineering (reactor design). The main scientific field in which the current study is performed is the discipline of combustion science, which offered valuable research tools and concepts (1-D mod- els, asymptotic methods, kinetic mechanisms, reactive flow solvers). In addition, the field of process technology is important for this study, because it considers grate furnace conversion as a process in which the output parameters (energy and emis- sions) can be optimized by adapting operating conditions, furnace design and fuel properties. The organizational framework in which this study has been performed is the project ”Optimization and Design of Biomass Combustion Systems”. This project was part of the Fifth Framework Programme of the European Union (Project num- ber: NNE52001-00693). Partners were the Netherlands Organization for Applied iv Research (The Netherlands; dynamic furnace modeling), Technical University Graz & Bios Bioenergy Systeme (Austria; CFD-based furnace design), Vyncke (Belgium; furnace construction) the National Swedish Testing Institute (Sweden; advisory role), the Instituto Superior T´ecnico (Portugal; dissemination), Eindhoven University of Technology (development of CFD modules for the fuel layer and gas phase). This in- ternational project group proved to be an interesting working environment in which different viewpoints on grate furnace combustion could meet. The results described in this thesis have been published and presented at na- tional and international congresses. Initial studies into a simple model with analyti- cal solutions to describe the conversion of a solid fuel layer was presented at various annual national symposia (Burgers Dag, NPS-symposium, Combura, FOM-Dagen, Physics@Veldhoven in the period 2003-2008) and at an international conference in Salzburg, 2005. This work has now been accepted for publication [1] and can be found in Chapter 4 of this thesis. The extension of the numerical model with a more detailed representation of the chemistry was presented at the International Biomass Conference in Berlin, Germany, 2007 and at the International Conference of Compu- tational Science in Beijing, China, 2007. Subsequently, this analysis was published in Refs. [2,3]. The work in chapter 6 is partly based on these publications. Finally, an experimental and numerical study of the role of heat losses in reverse combustion experiments was performed that is described in chapter 5. We have the intention to publish this study in the near future. There are also results of the project that are not presented in this thesis. During my Ph.D.-project, we presented the results of an experimental and theoretical study of biomass conversion in a grid reactor at the International Biomass Conference in Rome, Italy, 2004. This study that was performed during my graduation project at Faculty of Applied Physics under the supervision of professor Rini van Dongen. At the 4th European Combustion Meeting in Louvain La Neuve, Belgium, 2005, we presented results aimed at the validation of gas phase combustion models to describe NOx formation in a grate furnace. Both the work with the grid reactor and the gas phase combustion models was continued by co-workers in the Combustion Technology group. During the project, I was supported by a large number of people. Here, I would like to thank some of them. First, I would like to thank my promotor, professor Philip de Goey who gave me the opportunity to work on biomass conversion and to develop my professional skills. I would like to thank my first co-promotor Rob Bastiaans for his critical, but constructive comments that contributed to the quality of my work. I would like to thank my second co-promotor Jeroen van Oijen for shared with me his knowledge about the laminar flame code CHEM1D in which I implemented the solid fuel conversion model. Professor Bert Brouwers, professor Theo van de Meer and professor Gerrit Brem have carefully read the manuscript of this thesis, which resulted in significant improvements in the text. The Combustion Technology group and the division Thermofluids Engineering offered a pleasant working atmosphere. I would like to thank all my colleagues (Ph.D. students, postdocs, scientific staff and supporting staff) for this. The representatives of the OPTICOMB project partners offered a challenging and stimulating environment due to the opportunity to learn more about the viewpoints v of other research institutes and engineering firms. I would like to thank Robbert van Kessel, Arij van Berkel, Richard Arendsen, Maarten Jansen (TNO), Robert Scharler, Emil Widmann, Selma Zahirovic (TU Graz), Claes Tullin (SP), Hans Fastenaekels (Vynke) and Zdena Zsigraiova (IST) for this. Various Bachelor and Master Students contributed to the results that can be found in this thesis. Michiel Geurds, Martijn van Graafeiland, Mbelwa Katunzi, Lalit Agarwalla, Martijn Goorts, Gerben Jans and Pascal Bovij are acknowledged for this. My work for the board of the Young Energy Specialists and Development Coop- eration, a Dutch, national organization of young professionals active in the energy section, enabled me to place my work in a broader social and economic perspective. I would like to thank all my fellow board members (Haike van de Vegte, Gerard Stienstra, Jolien Snellen, Joost van Stralen, Diana Ros Riu, Maarten Mangnus) for this. Finally, I would like thank some people for more personal support. The group of friends that I made during my studies, which is informally known as ’Het Op- portunistisch Borrelgenootschap’ (Mark Bax, Martijn Toll, Menno van den Donker and Gerrit Kroesen) has preserved the pleasant and inspiring atmosphere that I ex- perienced during my studies. Gemmeke Groot, Happy Bongers, Armand Smits and Michiel Peters are also acknowledged for their personal. Finally, I would like to thank my family. My parents Jan and Ludy and my brother Frank have always sup- ported me in pursuing my goals. Eindhoven, April 2008, Hans van Kuijk Contents 1 Introduction 1 1.1 Introduction ................................. 1 1.2 Background ................................. 1 1.3 Gratefurnacecombustion . .. .. .. .. .. .. .. .. .. 3 1.3.1 Generalconversionprocess . 3 1.3.2 Gratefurnacemodeling . 5 1.3.3 Conversionofthesolidfuellayer. 6 1.4 Aimandoutline............................... 9 2 Literature overview reverse combustion 13 2.1 Introduction ................................. 13 2.2 Models .................................... 13 2.2.1 Modelclasses ............................ 13 2.2.2 Propertiesofdetailed1Dnumericalmodels. .. 16