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Show tran fer, devolatilization, heterogeneous reaction , and particle motion. A three-dill1ensional model, PCGC-3 (Pulverized Coal Gasification/Con1bustion-3 Dimen ions) was u ed to simulate the utility furnace in this study. PCGC-3 is a generalized code for simulating steady-state, reacting and non-reacting gaseous or particle-laden systems, with an emphasis on turbulent, pulverized-coal combustion systems. The model uses conventional numerical methods and a differencing scheme for a completely arbitrary mesh, and can solve the large computational meshes required for simulating practical furnaces. The various components used in PCGC-3 are summarized in Table I, which lists the process or submodel, a brief description, and several key references. The model has been evaluated by comparisons of code predictions with experimental profile data from several coal combustion facilities. A more detailed discussion of the PCGC-3 and its evaluation is given by Hill and Smoot (1994).24 Nitrogen Pollutants Model After the nitrogen species have been released from the coal/char particles, the NOx pollutant model describes the homogeneous and heterogeneous reactions of the nitrogen-containing species. This submodel has the capability of predicting both fuel and thermal NOx formation. The NOx submodel is decoupled from the comprehensive combustion model and the pollutant calculations are performed after the flow characteristics and combustion process have been predicted. The basis for this assumption is that the formation of trace pollutant species does not affect the flow process or major species reactions. Fuel NO formation is assumed to proceed through HCN and NH3 which are oxidized to NO or competitively reduced to N2 as illustrated in Figure 1. Global reaction rates based on those reported by de Soete25 are used for the fuel NO mechanism shown in Figure 1. The kinetic parameters reported by Bose et al. 26 are available for an alternative global fuel-NO mechanism. Fuel nitrogen is assumed to evolve from coal as HCN or NH3. Experimental evidence indicates 3 |