NOx and H2S formation in the reductive zone of air-staged combustion of pulverized blended coals
Low NO combustion of blended coals is widely used in coal-fired boilers in China to control NO emission; thus, it is necessary to understand the formation mechanism of NO and H S during the combustion of blended coals. This paper focused on the investigation of reductive gases in the formation of NO and H S in the reductive zone of blended coals during combustion. Experiments with Zhundong (ZD) and Commercial (GE) coal and their blends with different mixing ratios were conducted in a drop tube furnace at 1200°C–1400°C with an excessive air ratio of 0.6–1.2. The coal conversion and formation characteristics of CO, H S, and NO in the fuel-rich zone were carefully studied under different experimental conditions for different blend ratios. Blending ZD into GE was found to increase not only the coal conversion but also the concentrations of CO and H S as NO reduction accelerated. Both the CO and H S concentrations inblended coal combustion increase with an increase in the combustion temperature and a decrease in the excessive air ratio. Based on accumulated experimental data, one interesting finding was that NO and H S from blended coal combustion were almost directly dependent on the CO concentration, and the CO concentration of the blended coal combustion depended on the single char gasification conversion.Thus, CO, NO , and H S formation characteristics from blended coal combustion can be well predicted by single char gasification kinetics.