Abstract
The furnace of a pulverised coal-fired utility boiler with an electrical output of 550 MW, the dimensions of 19m x 15m x 48m and 32 swirl burners located on four elevations is considered. Coal combustion is described by a four-step reaction scheme. The model covers two heterogeneous reactions for pyrolysis and char combustion and three gas-phase reactions for the oxidation of volatile matter. A standard k; ε-model is used for the description of turbulence. The interaction between turbulence and chemistry is modelled using the Eddy Dissipation Concept (EDC). Radiation is computed by means of the Discrete Ordinates method. The discretisation is based on a non-staggered finite-volume approach. The coupling of velocities and pressure is achieved by the SIMPLEC-method, and the UPWIND or MLU discretisation schemes are used for the computation of the convective fluxes. All gas phase transport equations are formulated in the Eulerian way in general curvilinear co-ordinates allowing an accurate treatment of boundaries and a very good distribution of the grid lines. The coal particle phase is either treated with a Eulerian description assuming no slip between the gas and particle phase, or with a Lagrangian description. The Lagrangian approach to the particle phase is fully coupled with the gas phase using the Particle-Source-in-Cell method and taking the turbulence effects of the gas phase on particle dispersion into account. The differences in the predictions using the Eulerian and Eulerian/Lagrangian approaches are elaborated by comparing the computational results with in-furnace measurements of carbon monoxide, carbon dioxide and oxygen concentrations.
Published Version
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