Effect of Operating Conditions on the Combustion Characteristics of Coal, Rice Husk, and Co-firing of Coal and Rice Husk in a Circulating Fluidized Bed Combustor

Abstract

This study was performed to investigate the combustion characteristics of coal and rice husk and their co-combustion in a 100 kW circulating fluidized bed combustor (diam.: 150 mm, height: 6000 mm). Gaining insights into the effects that the primary and secondary excess air ratios (λPA and λSA), biomass fraction, and secondary air (SA) position have on CO and NOx emissions was also an aim of this study. In contrast to coal combustion, and co-combustion of coal and rice husk, the combustion of rice husk could not be sustained without the aid of an external heat source, and the released volatiles were found to be fired chiefly above the bottom bed. Air-staging substantially decreased NOx (40–75% reduction), but with a high CO penalty, compared to no air-staging. However, the effect of the SA position which was profoundly engaged with the char inventory in the bed was pronounced for coal combustion but not for rice husk combustion. Increase in λPA and λSA tended to reduce CO levels but enhanced NOx formation...