Process simulation of formation and emission of NO and N _2O during coal decoupling combustion in a circulating fluidized bed combustor using Aspen Plus

摘要

A process simulation model of coal decoupling combustion in a 30kW circulating fluidized bed (CFB) combustor has been developed for predicting NO and N _2O emissions based on the built-in modules/blocks provided by Aspen Plus software as well as the external subroutines from FORTRAN compiler. The gas-solid hydrodynamics in the decoupling CFB combustor and macro-chemical reaction kinetics of coal combustion have been included in the process simulation model of CFB coal decoupling combustion. The profiles of average bed temperature and concentrations of gas components along the CFB riser height can be successfully predicted by the developed process simulation model. The effects of excess air percentage, first stage stoichiometry, and the introduction position of secondary air on concentrations of the emitted gaseous components, especially concentrations of NO and N _2O can be simulated by the developed process simulation model. The contribution ratios of all relevant combustion reactions to emissions of NO and N _2O can be quantitatively predicted. A good agreement between the simulated and measured results can be obtained during CFB coal decoupling combustion process under a large variation range of the CFB operation conditions.