The effect of limestone on SO2 and NOX emissions of pulverized coal combustion preheated by circulating fluidized bed

A series of pulverized coal combustion experiments were carried out in order to investigate effects of limestone addition on SO2 and NOX emissions. The process takes place in two stages: first, the coal is preheated in a circulating fluidized bed with limestone addition; second, combustion of the resulting fuel gas and preheated char particles takes place in a down-fired combustor under air staging conditions. Four types of coal were used in the experiments including lignite, bituminous, anthracite, and semi-coke. Results showed that SO2 emission decreases after the addition of limestone to the circulation fluidized bed for all types of coal due to the reaction between H2S and CaO. The addition of limestone to the circulating fluidized bed was observed to have little effect on NOX emissions for low-volatile-content samples (anthracite and semi-coke), where as high-volatile-content coals (lignite and bituminous) displayed significant decreases in NOX emissions after the addition of limestone in this technique. (C) 2013 Elsevier Ltd. All rights reserved.