Revelation of non-thermal effects on microwave drying of lignite: Reactor design and drying characteristics

Abstract

Microwave non-thermal effects are controversial and its effects on lignite microwave drying remain blank. The lignite drying characteristics in shielded microwave drying (SMD) and unshielded microwave drying (USMD) using a self-designed SiC composite shielded sleeve were compared. The results showed that the positive influences of the non-thermal effects in lignite microwave drying were obtained. The non-thermal effects could significantly increase the microwave drying rate of lignite, enhance its ability to remove moisture, improve the average diffusion coefficient, and effectively reduce the drying activation energy. The lignite in USMD achieved a maximum drying rate of 0.86 g/g min after just 2 min of drying at 700 W. The average diffusion coefficient of lignite reached a maximum of 3.57 × 10-6 m2/s, and the activation energy reached a minimum of 113.15 W/g. This paper provides some new evidences for the existence of non-thermal effects, and firstly reveals its influences effects on lignite microwave drying.