Temperature-rising characteristics and product analysis of low-rank coal microwave pyrolysis under CH4 atmosphere

The effects of microwave power, irradiation time, particle size of coal samples, and gas flow rate on temperature-rising characteristics and yields of products in the low-rank coal microwave pyrolysis reaction under CH4 atmosphere were analyzed. The solid and liquid products under N-2 and CH4 atmospheres were detected by proximate and ultimate analysis, Fourier transform infrared spectrometry, and gas chromatography-mass spectrometry. Results showed that the evident effects of the tested parameters were observed, and maximum yield of the liquid product was obtained under 800 W of microwave power, 40 min of irradiation time, 5-10 mm of particle size, and 0.4 L/min of CH4 gas flow rate. These conditions resulted that the yields of bluecoke, coal tar, and water were 60.16%, 13.74%, and 6.25%, respectively. Compared with the products under N-2 atmosphere, the final temperature under CH4 atmosphere was obviously higher, resulting in increasement of the molecular unsaturation of bluecoke and the content of light-weight oil in tar, especially the content of lightweight oil with difference of 11.34%. Meanwhile, the good mass balance showed excellent experimental operation and error control in low-rank coal microwave pyrolysis reaction.