This paper introduces a model for the description of the homogeneous combustion of various fuels in fluidized bed combustors (FBC) at temperatures lower than the classical value for solid fuels, i.e., . The model construction is based on a key bubbling fluidized bed feature: A fuel-rich (endogenous) bubble is generated at the fuel injection point, travels inside the bed at constant pressure, and undergoes chemical conversion in the presence of mass transfer with the emulsion phase and of coalescence with air (exogenous) bubbles formed at the distributor and, possibly, with other endogenous bubbles. The model couples a fluid-dynamic submodel based on two-phase fluidization theory with a submodel of gas phase oxidation. To this end, the model development takes full advantage of a detailed chemical kinetic scheme, which includes both the low and high temperature mechanisms of hydrocarbon oxidation, and accounts for about 200 molecular and radical species involved in more than 5000 reactions. Simple hypotheses are made to set up and close mass balances for the various species as well as enthalpy balances in the bed. First, the conversion and oxidation of gaseous fuels (e.g., methane) were calculated as a test case for the model; then, -dodecane was taken into consideration to give a simple representation of diesel fuel using a pure hydrocarbon. The model predictions qualitatively agree with some of the evidence from the experimental data reported in the literature. The fate of hydrocarbon species is extremely sensitive to temperature change and oxygen availability in the rising bubble. A preliminary model validation was attempted with results of experiments carried out on a prepilot, bubbling combustor fired by underbed injection of a diesel fuel. Specifically, the model results confirm that heat release both in the bed and in the freeboard is a function of bed temperature. At lower emulsion phase temperatures many combustible species leave the bed unburned, while post-combustion occurs after the bed and freeboard temperature considerably increases. This is a well-recognized undesirable feature from the viewpoint of practical application and emission control.
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March 2007
Research Papers
Modeling Homogeneous Combustion in Bubbling Beds Burning Liquid Fuels
Tiziano Faravelli
Tiziano Faravelli is a full Professor in the Chemical Engineering Department at Politecnico di Milano where he teaches Statistics and Data Analysis and Combustion. His research interests are in the areas of Chemical Processes Modeling and Simulation, Pyrolysis, Combustion, and Chemical Reaction Engineering. Current research involves detailed kinetic mechanisms of combustion of hydrocarbons, coal, and biomasses and thermal degradation of polymers.
Tiziano Faravelli
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Alessio Frassoldati
Alessio Frassoldati is a Post-Doc Research Associate in the Chemical Engineering Department at Politecnico di Milano where he obtained his Ph.D. in 2004. He teaches Unit Operations of Chemical Plants and System Analysis and conducts research in the areas of computational fluid dynamics (CFD), turbulent flames modeling, and detailed kinetic modeling of pollutants formation (NOx).
Alessio Frassoldati
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Eliseo Ranzi
e-mail: tiziano.faravelli@polimi.it
Eliseo Ranzi is a full Professor in the Chemical Engineering Department at Politecnico di Milano and teaches Chemical Reaction Engineering and Combustion. He has been conducting research in the areas of Chemical Processes Modeling and Simulation, Pyrolysis, Combustion, and Chemical Reaction Engineering. His current areas of academic interest include detailed kinetic mechanisms of pyrolysis and oxidation of hydrocarbons, coal and biomasses, and the formation of pollutants.
Eliseo Ranzi
Dipartimento di Chimica Industriale ed Ingegneria
, Chimica “Giulio Natta,” Politecnico di Milano, Piazza Leonardo da Vinci, 32 20133 Milano MI, Italy
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Miccio Francesco
e-mail: miccio@irc.na.cnr.it
Francesco Miccio was born on August 1, 1962. He graduated in 1987 in Chemical Engineering at University of Naples. Since his appointment in 1989 as researcher at Istituto Ricerche sulla Combustione CNR, he has been acquiring a large expertise in fluidized bed combustion and gasification as well as modeling of heterogeneous fuel conversion. He was visiting scientist at IVD—University of Stuttgart by a grant of the Alexander von Humboldt Foundation. He is currently detached at European Commission - JRC Institute for Energy (Petten NL) in the frame of a project concerning biomass and waste gasification for hydrogen production. F. Miccio is the author of more than 80 papers at international and national levels.
Miccio Francesco
Istituto di Ricerche sulla Combustione–CNR
, Via Metastasio, 17, 80125 Napoli NA, Italy
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Miccio Michele
Michele Miccio (Ph.D., Chem.Eng.) is Associate Professor at the Engineering Faculty of Salerno University. His main teaching subject is “Dynamics and Control of Chemical Processes.” Since 1985, he has been a research expert on bubbling Fluidized Bed Combustion (FBC) of coal, water-containing fuels and wastes and, more recently, conventional petroleum fuels at low temperature. Another research area concerns food drying mechanism and processes (e.g., salami ripening, fluidized bed batch freeze-drying). He acted as a reviewer for scientific journals, coordinator of Topical Areas in international conferences, and co-chair at the “Fluidization XI” conference. He is the author of more than 130 scientific papers.
Miccio Michele
Dipartimento di Ingegneria Chimica ed Alimentare,
e-mail: mmiccio@unisa.it
Università di Salerno
, Via Ponte don Melillo, 84084 Fisciano SA, Italy
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Tiziano Faravelli
Tiziano Faravelli is a full Professor in the Chemical Engineering Department at Politecnico di Milano where he teaches Statistics and Data Analysis and Combustion. His research interests are in the areas of Chemical Processes Modeling and Simulation, Pyrolysis, Combustion, and Chemical Reaction Engineering. Current research involves detailed kinetic mechanisms of combustion of hydrocarbons, coal, and biomasses and thermal degradation of polymers.
Alessio Frassoldati
Alessio Frassoldati is a Post-Doc Research Associate in the Chemical Engineering Department at Politecnico di Milano where he obtained his Ph.D. in 2004. He teaches Unit Operations of Chemical Plants and System Analysis and conducts research in the areas of computational fluid dynamics (CFD), turbulent flames modeling, and detailed kinetic modeling of pollutants formation (NOx).
Eliseo Ranzi
Eliseo Ranzi is a full Professor in the Chemical Engineering Department at Politecnico di Milano and teaches Chemical Reaction Engineering and Combustion. He has been conducting research in the areas of Chemical Processes Modeling and Simulation, Pyrolysis, Combustion, and Chemical Reaction Engineering. His current areas of academic interest include detailed kinetic mechanisms of pyrolysis and oxidation of hydrocarbons, coal and biomasses, and the formation of pollutants.
Miccio Francesco
Francesco Miccio was born on August 1, 1962. He graduated in 1987 in Chemical Engineering at University of Naples. Since his appointment in 1989 as researcher at Istituto Ricerche sulla Combustione CNR, he has been acquiring a large expertise in fluidized bed combustion and gasification as well as modeling of heterogeneous fuel conversion. He was visiting scientist at IVD—University of Stuttgart by a grant of the Alexander von Humboldt Foundation. He is currently detached at European Commission - JRC Institute for Energy (Petten NL) in the frame of a project concerning biomass and waste gasification for hydrogen production. F. Miccio is the author of more than 80 papers at international and national levels.
Miccio Michele
Michele Miccio (Ph.D., Chem.Eng.) is Associate Professor at the Engineering Faculty of Salerno University. His main teaching subject is “Dynamics and Control of Chemical Processes.” Since 1985, he has been a research expert on bubbling Fluidized Bed Combustion (FBC) of coal, water-containing fuels and wastes and, more recently, conventional petroleum fuels at low temperature. Another research area concerns food drying mechanism and processes (e.g., salami ripening, fluidized bed batch freeze-drying). He acted as a reviewer for scientific journals, coordinator of Topical Areas in international conferences, and co-chair at the “Fluidization XI” conference. He is the author of more than 130 scientific papers.
J. Energy Resour. Technol. Mar 2007, 129(1): 33-41 (9 pages)
Published Online: February 21, 2006
Article history
Received:
August 16, 2004
Revised:
February 21, 2006
