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.

Effect of Temperature and Microwave Power Levels on Microwave Drying Kinetics of Zhaotong Lignite

“…When the applied microwave power level is 800 W, an obviously constant rate period appears, which is similar to the former researchers' experimental results. Song et al [48] found that the constant rate period were discovered under 700 W, while it disappeared at 800 W. This can be explained by a great deal of heat energy generation and higher pressure difference at microwave power levels beyond 700 W, leading to the increasing drying rate and the final temperature of lignite reaching 181 °C, as can be observed in Figure 3a.…”