Effect of high-temperature and microwave expanding modification on reactivity of coal char for char-NO interaction

Abstract

Coal-fired industrial boiler has become a large source of atmospheric pollutants in China, urging to achieve low NOx emissions. This paper adjusts the coal char structure with high-temperature/microwave expanding modification to investigate the char-NO interaction. The results show that after high-temperature or microwave expansion, the pore structure of char is further expanded with more new pore structure of 2–12 nm. The proper expansion temperature/power/treatment-time increases the ablation collapse of char pores and the order of carbon structure. With microwave, COC and CO bands break, forming a large amount of aromatic CC unsaturated carbon atoms, incrseasing the surface active sites of char-NO interaction. The optimum modifications of char-NO reactivity are 800 °C-90 s and 960 W-90 s. The reduction rate of NO by microwave modified char decreases with increase of inlet NO (<1200 ppm), and increases with increase of inlet CO (<8000 ppm). Burnout time of microwave modified char is shortened, with more rapid release of NO and larger conversion rate of char-N to NO. With microwave field, the conversion rate of char-N to NO at 900 °C is more significant than that at 600 °C. The too large microwave power cannot further shorten the char burnout time and the release time of NO.