Characteristics of coal gasification with CO2 after microwave irradiation based on TGA, FTIR and DFT theory

Underground coal gasification (UCG) is a non-traditional mining technology while the gasification reactivity of coal seam is low. Microwave drying is considered as an effective method to enhance the performance of UCG. In this work, the bituminous coal samples are treated under different microwave irradiation time (t). Effect of microwave on coal gasification is studied with synchronous thermal analyzer, Fourier transform infrared spectrometer and quantum chemistry calculation. As t from 0 to 4 min, the gasification reaction rate increases first and then decreases when the temperature is higher. As t increases from 0 to 1 min, the content of Ar-OH increases from 27.95% to 31.19%, while the content of –CO- reduces from 40.80% to 39.26%. As t increases from 1 min to 4 min, Ar-OH decreases from 31.19% to 19.92% while –CO- increases from 39.26% to 56.67%. The decrease in the –CO- and increase in the Ar-OH can promote the gasification reactivity, compared with that of untreated coal sample. On the contrary, the increase in the –CO- and decrease in the Ar-OH are unfavorable for the gasification reactivity. This explains the non-monotonic effect of microwave time on the coal gasification reactivity.