Effects of minerals and sodium addition on nitrogen release during coal combustion

Experiments have been carried out to investigate the effects of indigenous minerals and sodium additives on the releases of coal nitrogen during combustion on a TGA using Yibin coal of China. The experimental results show that much HCN and little NH₃ can be evolved during temperature-programmed combustion, as well as NO. During the combustion process, part of coal nitrogen can be firstly retained in the char and then released as NO at the later stage of coal combustion. The fractions of nitrogen released as NO and NH₃ are higher for parent coal than that for demineralized coal, but the fraction as HCN is lower. This is attributed to the low activity of parent coal and the diffusion resistance caused by the minerals in parent coal, which retards the HCN release and induces more NO and NH₃ conversion. Sodium compounds remarkably reduce NO and HCN release during temperature-programmed combustion. The effect of sodium chloride on NO reduction is greater than that of sodium carbonate. The catalysis of sodium containing compounds on the reactions between HCN precursor and NO may lead to the drastic reduction of both species.