EFFECT OF COAL RANK AND CIRCULATING FLUIDIZED-BED OPERATING PARAMETERS ON NITROUS-OXIDE EMISSIONS

The effects of operational parameters and coal type on N2O emissions i n a pilot-scale circulating fluidized-bed combustor (CFBC) were examin ed. Operational parameters included combustor temperature, excess comb ustion air, limestone feed rate, and primary:secondary combustion air split. Seven coals ranging in rank from lignite to high-volatile A bit uminous were used to study coal-related effects. At typical operating conditions (20 % excess air, 1120 K), N2O emissions ranged from 30 to 170 ppmv at 3 % excess O2 or 16 to 100 mg N2O/MJ heat input due to var iations in coal type. The relative impact of operational parameters on N2O emissions is given for Salt Creek coal by the relation: temperatu re > excess air, primary/secondary air split > sorbent feed. Increasin g combustion temperature was shown to decrease N2O emissions, while in creasing excess air was shown to increase N2O emissions. The effect of limestone addition was shown to be coal-dependent, with both increasi ng and decreasing trends in N2O emissions observed. The primary air-to -total-air ratio has a minimal impact on N2O emissions but tends to de crease emissions at higher temperatures, while the opposite trend occu rs at lower temperatures.