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 CH_i. 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.