TRITA-MET-062 ISSN 1403-493X ISRN KTH-MET/R-99/062-SE ISBN 91-7170-500-7 Design of Advanced Industrial Furnaces Using Numerical Modeling Method Wei Dong Doctoral Thesis Heat and Furnace Technology STOCKHOLM Department of Materials Science and Engineering Royal Institute of Technology March 2000 S-10044 Stockholm Sweden TRITA-MET-062 ISSN 1403-493X ISRN KTH-MET/R-99/062-SE ISBN 91-7170-500-7 Design of Advanced Industrial Furnaces Using Numerical Modeling Method Wei Dong Doctoral Thesis Heat and Furnace Technology Department of Materials Science and Engineering Royal Institute of Technology 10044 Stockholm Sweden 31 March 2000 Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm, framlägges för offentlig granskning för avläggande av teknisk doktorsexamen, onsdagen den 10 May 2000, kl. 10.00 i Kollegiesallen, Valhallavägen 79, Kungliga Tekniska Högskolan, Stockholm Doctoral Thesis Design of Advanced Industrial Furnaces Using Numerical Modeling Method Wei Dong Heat and Furnace Technology, Department of Materials Science and Engineering Royal Institute of Technology (KTH), S-10044 Stockholm, Sweden Abstract This doctoral thesis describes the fundamentals of mathematical modeling for the industrial furnaces and boilers and presents the results from the numerical simulations of some typical applications in advanced industrial furnaces and boilers. The main objective of this thesis work is to employ computational fluid dynamics (CFD) technology as an effective computer simulation tool to study and develop the new combustion concepts, phenomena and processes in advanced industrial furnaces and boilers. The applications concern on from retrofitted conventional grate boilers to the most advanced highly preheated and diluted air combustion (HPDAC) furnaces. In this work, several topics are specially concerned when applying CFD technology to combustion cases. These topics are including grate bed model, NOx modeling, mixing problem, air staging system, and highly preheated and diluted air combustion technology. In this work, a black-box grate bed model is developed and used in modeling of grate fired furnaces and boilers. It is based on the thermodynamic calculations and a set of conservation equations of mass, energy of fuel and air on the grate bed. One of benefits of this bed model is simple and feasible to be put into use in industry. For NOx modeling, besides the thermal NO and prompt NO, the HCN route fuel NO has been employed to predict the fuel NO emissions in coal/biomass fired furnaces. In addition, based on NH3 route of fuel NO formation, a SNCR scheme for NOx abatement has been proposed also. For mixing problem, the concepts of global degree of mixing and individual degree of mixing have been proposed and used successfully in practical applications. The new definition of degree of mixing overcomes some shortages of existed mixing parameters, such as the mixing factor and the degree of non-mixing, which are non-normalized and may lose physical meaning in some regions of the system. A new air staging system has been studied. It is used to improve the secondary or over-fire air configuration, thus to reduce the pollutant emissions and to enhance the combustion facilities’ efficiencies. In this work, the air staging system has been employed in coal and biomass combustion for grate fired furnaces/boilers. The performance of the new air staging system has been evaluated and optimized by using numerical modeling method together with physical modeling method. Results show that the new air staging system has a good potential of improving the combustion quality and reducing the pollutant emissions in industrial furnaces and boilers. Recently, the highly preheated and diluted air combustion technology has been regarded as the new generation energy technology for advanced industrial furnaces and boilers. In this work, the highly preheated and diluted air combustion phenomena have been studied by using different numerical models. A hybrid procedure of both the large eddy simulation using subgrid-scale stress Smagorinsky model, and the Reynolds stress model with eddy dissipation model has been also investigated to study the dynamic combustion process under the conditions of highly preheated and diluted air combustion. Results show that HPDAC technology possesses advantages of saving energy and low NOx emission, thus it has high potential to be used for the next generation of industrial furnaces and boilers. The large eddy simulation using subgrid-scale stress Smagorinsky model combined with Reynolds stress model /eddy dissipation model are possible to study the HPDAC dynamic process. Finally, this work shows that numerical modeling method is a very promising tool to deal with the complicated combustion processes even for practical applications in industry. Keywords: air staging, bed model, boiler, burner, computational fluid dynamics (CFD), Ecotube, fuel staging, furnace, grate combustion, highly preheated and diluted air combustion (HPDAC), large eddy simulation (LES), mathematical modeling, nitrogen oxides (NOx), numerical simulation Preface In the April 1996, I joined the combustion research for advanced industrial furnace development in the Division of Heat and Furnace Technology, Royal Institute of Technology (KTH), Stockholm, Sweden. My first research topic was the mathematical modeling of grate combustion and NOx emission with a new supply Ecotube system. After two years, I received the KTH licentiate degree under the supervision of Associate Professor Wlodzimierz Blasiak, the head of the Division. I am greatly indebted him for giving me this opportunity to work on this exciting research field, and for his continuous encouragement and support during the thesis work. Since then, I continued working on the field of advanced industrial combustion/furnace technology under his guidance. It results in this doctoral thesis, in which the numerical simulations are extended to the topics of different advanced combustion technologies with the numerical modeling and design for advanced industrial furnaces. This doctoral thesis is mainly based on the following six papers: Paper 1 Dong W. and Blasiak W. CFD Modeling of Ecotube System in Coal and Waste Grate Combustion. RAN98 special issue, Journal of Energy Conversion and Management, 1999 (accepted) Paper 2 Dong W. and Blasiak W. CFD Modeling and Optimizing of a New Ecotube Air System for Clean Combustion of Coal in a Grate Fired Boiler. Journal of the Institute of Energy, 1999 (submitted) Paper 3 Dong W., Vaclavinek J. and Blasiak W. Modeling of Fluid Flow and Mixing Patterns in an Etrained Boiler. Applied Thermal Engineering, 2000 (submitted) Paper 4 Dong W. and Blasiak W. Study on Mathematical Modeling of Highly Preheated Air Combustion. In 2nd High Temperature Air Combustion Symposium, Taiwan, 1999 Paper 5 Dong W. and Blasiak W. Numerical Modeling of Highly Preheated Air Combustion in a 580KW Testing Furnace at IFRF. International Journal of Energy, 2000 (submitted) Paper 6 Dong W. and Blasiak W. Large Eddy Simulation (LES) of a Single Jet Flow in Highly Preheated and Diluted Air Combustion. Archivum combustionis, 2000 (submitted) There are also author’s other papers and reports which may be referred in the thesis: [1] Dong W. Mathematical modeling of combustion and NOx emission in a grate fired boiler at Backhammrs Sweden. Final report. Internal Report A042, Royal Institute of Technology, Sweden, 2000 [2] Dong W. Three-dimensional computer simulation for combustion and NOx emission in a grate fired boiler at Backhammrs Sweden, Technical report, Royal Institute of Technology, Sweden, 1998 [3] Dong W. and Blasiak W. Evaluation of a new air supply system for grate fired boilers. IFRF, 12th Members Conference, 50th Anniversary of the IFRF, Netherlands, 1998 [4] Dong W. and Blasiak W. Modeling of a coal grate-fired boiler equipped with a new advanced over fire air technique. Expose över förbränningen i Sverige, Oct.21-22, Göteborg, Sweden, 1998 [5] Dong W. and Blasiak W. 3D numerical simulation for biomass combustion and NOx emission in a grate fired boiler, In 1st Energy from Waste'97, Ustron, Poland, 1997 [6] Dong W. Study on fixed-bed models for grate combustion, Unpublished work, Royal Institute of Technology, Sweden, 1997 [7] Dong W. Study on NOx modeling, Unpublished work, Royal Institute of Technology, Sweden, 1997 i [8] Dong W. and Blasiak W. Mathematical modeling for NOx emission in a bark boiler, Stage One: Flow patterns, Technical report, Royal Institute of Technology, Sweden, 1997 [9] Dong W., Jiri V. and Blasiak W. Analysis of combustion process in a grate fired boiler at Braviken Paper Mill, Technical report, Royal Institute of Technology, Sweden, 1997 [10] Dong W. and Blasiak W. Numerical simulation for Uppsala co-firing boiler, Study of flow pattern with using of FLUENT, Technical report, Royal Institute of Technology, Sweden, 1996 [11] Blasiak W., Dong W., Lille S., and Linda B. The research of highly preheated air combustion in Sweden. The 2nd International Seminar on High Temperature Combustion. Jan.17-18, Stockholm, Sweden, 2000 [12] Dong W. and Blasiak W. Numerical Modeling of Highly Preheated Air Combustion in a 580KW Testing Furnace at IFRF. The 3rd International Symposium on High Temperature Air Combustion and Gasification. CREST, March 7-9, Yokohama, Japan, 2000 I would like to thank my colleagues in our furnace research group: Associate Professor Jiri Vaclavinek, Christer Helen, Jan Bång, Rasmus Friberg, Simon Lille, Reza Fakhrai and Hilmer