Process Simulation of Using Coal Pyrolysis Gas to Control NO and N2O Emissions during Coal Decoupling Combustion in a Circulating Fluidized Bed Combustor Based on Aspen Plus

Abstract

A process simulation model of CFB coal decoupling combustion process has been developed based on Aspen Plus and verified by comparing with the reported NO and N2O emissions from experiments. The detailed information on formation and decomposition of NO and N2O along the height of CFB riser column can be quantitatively simulated by the developed process simulation model. The simulated results show that about 99.9% of the emitted NO in flue gas is controlled by fuel-N combustion; however, the introduced NH3 in coal pyrolysis gaseous products as an NO precursor can play an important role on NO formation from about 39.7% to 97.6% in the dense phase region at the lower CFB riser column. About 98.9%-99.8% of NO decomposition along the height of CFB riser column is dominated by char particles reduction. About 91.8%-95.8% of the emitted N2O in flue gas is controlled by fuel-N combustion; however, the introduced HCN in coal pyrolysis gaseous products as an N2O precursor has an obvious effect on N2O formation from 74.2% to 94.6% in the dense phase region at the lower CFB riser column. The contribution of char particles reduction on N2O decomposition can be found as 1.8%-3.6% along the height of CFB riser column. A competitive relationship between O-2 oxidization and CO reduction on N2O decomposition along the height of CFB riser column during the CFB coal decoupling combustion process has been revealed.