Process Simulation of Emission and Control for NO and N2O during Coal Combustion in a Circulating Fluidized Bed Combustor Based on Aspen Plus

The profiles of temperature and gas component concentrations along the circulating fluidized-bed (CFB) riser height have been successfully simulated by the developed process simulation model of coal combustion in a 30 kW CFB combustor based on Aspen Plus. The average bed temperature increases from about 1025 to 1160 K along the CFB riser height of 6.63 m. The simulated effects of excess air percentage, the first stage stoichiometry, and the introducing position of secondary air on concentrations of gas components, especially NO and N2O, have good agreement with the experimentally measured results that increasing excess air percentage as well as the first stage stoichiometry can improve emissions of NO and N2O in flue gas, but coal rank also affects the pollutant emissions. The simulated results show that increasing the introducing position of secondary air reasonably can effectively decrease emissions of NO and N2O. The contribution ratios of all possibly existed reactions to the formation and decomposition of NO and N2O have been quantitatively predicted by the developed process simulation model to clarify the formation and emission mechanism of NO and N2O during CFB coal combustion.