Experimental study of the combustion and NO emission behaviors during cofiring coal and biomass in O-2/N-2 and O-2/H2O

摘要

Oxy-H2O is considered to be a new generation of carbon capture and storage technology. The combustion and NO emission behaviors during co-combustion in O-2/N-2 and O-2/H2O were studied simultaneously in an isothermal thermogravimetric system, including the influence of blending ratio, coal type, biomass type, and oxygen concentration. The results show that replacing N-2 by H2O accelerates the burning rate of a blend significantly and reduces the NO emission obviously. In O-2/N-2 and O-2/H2O, blending biomass improves the burning rate and reduces the NO emission. The improvement of H2O on burning rate becomes weak with increasing blending ratio. There is an interactive effect on NO emission during co-combustion in both atmospheres. For cofiring bituminous coal and poplar wood, the NO yield decreases with increasing blending ratio, whereas the NO conversion ratio increases in both atmospheres. As different coal ranks blend with a certain biomass, the blend with a higher coal rank results in a more obvious improvement of burning rate and a higher NO conversion ratio in both atmospheres. As a coal blends with different biofuels, a higher volatile biofuel leads to a higher burning rate in O-2/N-2, whereas this behavior is not obvious in O-2/H2O. Blending coal with a higher nitrogen biofuel results in a lower NO conversion ratio in both atmospheres. In both atmospheres, the burning rate and NO conversion ratio of a blend both increase, as the oxygen concentration increases from 21% to 30%. The results provide direct guidance for the application of co-combustion in O-2/H2O.