Experimental study on the combustion and NOx emission characteristics of a bituminous coal blended with semi-coke

Abstract

Combustion and NOx emission characteristics of a bituminous coal (BC) blended with semi-coke (SC) are investigated using a Thermogravimetric Analyzer (TGA) and Drop Tube Furnace (DTF) at a different SC blending ratio Xsc. TGA results show that BC and SC have similar mass loss patterns but BC-SC blends have a second trough on their DTG curves. The addition of semi-coke increases ignition and burnout temperatures of the blends, but barely affects the burnout rate. Within 95% mass loss, the overall combustion index first decreases and then increases with Xsc. DTF results reveal that the burnout rate and NOx emission of BC-SC blends are influenced by excess air ratio, furnace temperature, blending ratio and residence time. With sufficient air and residence time, the burnout rates of BC-SC blends and SC can be greater than 97% and SC blending slightly decreases the total NOx formation. Under O2-deficit conditions, the burnout rate decreases with increasing Xsc; SC blending and longer residence time will reduce NOx emission. The trends are significantly more obvious at smaller excess air ratios. The NOx formation of BC-SC blends cannot simply be predicted by linear superposition of the two fuels. Based on the burnout and NOx emission data, less than 40% SC blending and proper air staging are recommended for BC-SC co-combustion.