Simulations of Coal Combustion in a Pressurized Supercritical CO_2 Circulating Fluidized Bed

摘要

The supercritical CO2 (S-CO2) power cycle circulating fluidized bed (CFB) integrated with pressurized combustion is a promising power generation technology with high efficiency and low exhaust heat discharge. In multiphase particle-in-cell (MP-PIC) simulations, a 3-D Eulerian-Lagrangian model with a coal combustion process was developed to investigate the combustion characteristics in CFB with S-CO2 wall boundaries under the pressurized conditions of 0.3-0.9 MPa compared with the atmospheric pressure condition (0.1 MPa), with the distribution of pressure, temperature, heat flux, pollution emissions, as well as boiler efficiency being comprehensively illustrated. Furthermore, effects of the excess air ratio corresponding to various pressures on combustion characteristics were deeply analyzed. Results showed that the pressurized combustion compared with the atmospheric pressure condition offered an enhanced combustion and heat transfer, lower pollution emissions, and increased combustion efficiency. Increasing the operating pressure obviously increased the furnace temperature and heating surfaces heat flux, indicating the enhancement of combustion and heat transfer, and meanwhile, emissions of CO, NO, and N2O decreased. Additionally, increasing the operating pressure contributed to the significant improvement of highly efficient coal combustion and the reduction of heat loss, and increasing the excess air ratio could also increase the combustion efficiency by up to 2.65% with more pronounced elevation at lower pressure.