Experimental Study on the Characteristics of Ignition during Microwave Drying of Lignite

Abstract The spontaneous combustion of lignite during microwave drying was evaluated with the focus on the effects of, for example, microwave power and output mode, the final temperature of the samples, and the oxygen content of the drying atmosphere on the moisture contents corresponding to the ignition (IMCs). This empirical study was performed using a laboratory‐scale microwave oven. The lowest IMCs and the optimal drying effect of lignite were achieved using a power level of 60 W g−1, final surface temperature of 85–90 °C, and a lower oxygen content; pulsed microwave radiation could significantly lower the risk of ignition by reducing the overall surface temperature. In addition, the ignition temperatures at different moisture contents were measured comparatively by using conventional and microwave heating methods. Fourier transform infrared analyses of the samples revealed that microwave drying can upgrade the coal rank without affecting the coal quality.