NDLI: Modeling of Solids and Gas Mixing Effects in Large-Scale CFB Combustors

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Luecke, Karsten Hartge, Ernst-Ulrich Werther, Joachim
Copyright Year	2003
Abstract	In a CFB combustor the reacting solids are locally fed into the combustion chamber. These reactants have to be dispersed across the reactor’s cross-sectional area. Since the rate of mixing is limited this leads to a mal-distribution of the reactants and to locally varying reaction conditions. In order to describe the influence of mixing a three-dimensional model of the combustion chamber is suggested here. The model is divided into three sub-topics. First, the flow structure in terms of local gas and solids velocities and solids volume concentrations is described. Second, mixing of the solids and the gas phase has to be quantified by defining dispersion coefficients, and finally the combustion process itself, i.e. the reaction kinetics, has to be modeled. Employing the information of the three sub-models mass balances for the reactants at each finite control volume inside the CFB combustion chamber can be formulated. The model was validated against data from measurements in the large-scale combustor of Chalmers University of Technology in Go¨teborg/Sweden. Concentration gradients concerning the char phase are only moderate. However, the spatial distribution of the oxygen shows strong non-uniformities, especially under conditions of staged combustion. In further predictive calculations, the influence of the fuel supply arrangement on the emissions of industrial sized CFB boilers was studied. Furthermore, the influence of the fuel composition on the feeding technique has been examined. High volatile fuels tend to form plumes of unburned hydrocarbons near the fuel feed point, and might therefore need more feed points per square meter cross-section area. Since the average gas residence time in the primary cyclone of a CFB plant is about 30–40% of the total gas residence time, a considerable burn-off of not completely oxidized gas species may occur here. An effectively used cyclone may remedy to a certain extent the negative impacts of incomplete mixing in the combustion chamber.
Sponsorship	Advanced Energy Systems
Starting Page	245
Ending Page	256
Page Count	12
File Format	PDF
ISBN	0791836800
DOI	10.1115/FBC2003-028
e-ISBN	0791836754
Conference Proceedings	17th International Conference on Fluidized Bed Combustion
Language	English
Publisher Date	2003-05-18
Publisher Place	Jacksonville, Florida, USA
Access Restriction	Subscribed
Subject Keyword	Oxygen Plumes (fluid dynamics) Three-dimensional models Chemical kinetics Solids Boilers Combustion Combustion chambers Fuels Modeling Flow (dynamics) Emissions
Content Type	Text
Resource Type	Article

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