NO formation characteristics and fuel-nitrogen transformation mechanism during co-firing of low-volatile carbon-based solid fuels with bituminous coal

Abstract

Co-firing of low-volatile carbon-based solid fuels with bituminous coal is an encouraging approach to realize the large-scale clean utilization of pyrolyzed and gasified semi-cokes. However, the interactions on co-combustion characteristics between bituminous coal and semi-cokes have yet to be fully understood, while less work has aimed at fuel-nitrogen migration mechanisms without the influence of thermal-NO generation. Here, an experimental investigation of bituminous coal blended with pyrolyzed semi-coke and/or gasified semi-coke in O2/Ar atmosphere was performed focusing on NO yield, burnout performance and fuel-nitrogen migration mechanisms. The characterization and reactivity of bituminous coal and semi-cokes were revealed by thermalgravimetric analyzer, etc. The results indicate that the promotion effects of bituminous coal on combustion of semi-coke are enhanced with the enlarged difference between volatile contents of various samples. The char-nitrogen of semi-cokes are mainly converted to NO firstly, and then might be converted to HCN and N2 by pyrolysis products HCN, NH3 and CHi. The method of staged feeding could lessen the interactions between semi-cokes and bituminous coal, which could significantly inhibit the conversion of fuel-nitrogen to NO compared with the strategy of out-furnace blending. The present research can offer guidance for co-firing of low-volatile semi-cokes with bituminous coal in power stations.