Modeling of Limestone Injection for SO2 Capture in a Coal Fired Utility Boiler

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4.0 Full Scale Simulation - Results and Discussion Simulations of the full-scale boiler were performed upon the completion of the stages of the sorbent, momentum and heat transfer model and computational grid development, implementation and verification, as described above. All inlet flow rates and gas compositions were based on the furnace outlet data from C A N M E T using coal properties and boiler operating parameters as summarized in Table 2. In all simulations the sorbent was assumed to enter the boiler gas stream perfectly distributed at the superheater inlet plane (see Figure 1). The sulphur dioxide concentration at the inlet plane was specified assuming 100% conversion of coal sulphur to SO2. The gas composition profile, as in the C A N M E T simulations was also used. The inlet SO2 concentration profile was then specified using the CO2 distribution factored by the carbon to sulphur ratio in the feed coal, Table 2. The average inlet SO2 concentration for the boiler simulations, based on Highvale coal, was about 460 p p m by weight. Table 2 - Boiler Coal and Air Flows and Coal Analysis Coal Feed Rate Levels A to E Primary Air Levels A to E Fuel Air - Level A,B,D Level C Level E Secondary Air - Level A Level E-E All other Levels Overfire Air Air/Fuel Ratio % Excess Air Highvale Coal Analysis Proximate Moismre Ash Volatiles Fixed Carbon Ultimate C H S N 0 7.67 kg/s/corner (Level C off) 12.8 kg/s/corner (Level C off) 12.756 kg/s/comer 0.425 kg/s/comer 4.252 kg/s/comer 5.858 kg/s/comer 0.976 kg/s/comer 6.684 kg/s/comer 9.98 kg/s/corner 7 15.6 Weight % % - as rec'd 18.8 15.3 27.1 38.8 % - daf 73.58 4.57 0.25 0.86 20.74 The effects of gas inlet SO2 concentration and calcium to sulphur ratio on sulphur capture efficiency were investigated (see Table 3). Inspection of the simulation results in Table 3