Dynamic characteristics of pollutant emissions from CFB boilers during periodic fire banking and start-up

Abstract

It is difficult to control pollutant emissions during fire banking and start-up in CFB boilers, which poses threats to power plant operation, safety and environmental protection. A 350 MW supercritical CFB boiler was taken as the research object. Using the CPFD method and Barracuda software, a full-loop combustion and pollutant emission model was constructed to simulate periodic fire banking and start-up, and the gassolid flow characteristics and pollutant emission characteristics were analysed. The results showed that the bed material at the bottom of the furnace exhibits obvious stratification after being stationary, and this stratification has an impact on the generation, distribution and emission of NOx and SO2 in the furnace. Eighty-five percent of the bottom bed material is lower layer, and the NOx and SO2 concentrations are negatively correlated with the volume fraction of particles. The average NOx and SO2 concentrations in the lower layer are 120.05 mg/m3 and 1155.50 mg/m3, respectively. During the hot start-up process, the NOx concentration decreases with increasing bed height. The residence time of the desulfurization reaction is prolonged, the desulfurization efficiency is improved, and the SO2 concentration is reduced. These results provide a theoretical basis and a certain reference value for the periodic fire banking and start-up of supercritical CFB boilers.