Influence of stoichiometry air ratio on char characteristics and nitrogen conversion in circulating fluidized bed with post-combustion

Abstract

The post-combustion technology was one of the most promising de-NOx technologies, while the impact of stoichiometry air ratio in the furnace (λCFB) on char characteristics and nitrogen conversion under reduction atmosphere was not fully understood yet. Three different λCFB (0.75, 0.85 and 0.95) and two kinds of fuels, namely Fugu bituminous (FB) and its semi-coke (FS), were selected for this experiment when the combustion temperature maintained 960 °C. The results of Raman spectra indicated that the char reactivity had different degrees of improvement comparing with raw fuels. The char had the best reactivity when the λCFB was 0.85. Besides, the BET specific surface area and the BJH pore volume of FB char also reached maximum values of 4.99 m2/g and 13.43 mm3/g when the λCFB was 0.85. FS char also had the best reactivity and the most developed pore structure with the λCFB of 0.85. As λCFB decreasing, more fuel nitrogen (fuel-N) would remain in char rather than releasing into the gas phase. Simultaneously, even if fuel-N was released into the gas phase, it would exist in the form of NH3 and HCN instead of N2. Moreover, the yields of NH3 were always higher than HCN. Since the optimum char characteristics and appropriate fuel-N migration when the λCFB was 0.85, the NOx conversion ratios of FB and FS were the lowest, which were 2.81% and 3.81%, respectively. This study offered some useful information for the industrial application of post-combustion technology.