Drying and Moisture Readsorption Characteristics of Lignite

Abstract

ABSTRACT The physical and chemical changes of three different types of lignite during drying at temperatures from 80 to 180°C were investigated using a moisture meter and an infrared spectroscopy system. The results showed that the drying of lignite could be classified into two stages, namely, a fast upgrading stage where surface moisture was lost, and a slower moderating stage where internal moisture diffused to the surface and evaporated. Some unstable oxygen-containing polar groups in the lignite decomposed during the drying process, resulting in an increased contact angle and reduced wettability. With increasing temperature, the size of the micropores decreased and the number of mesopores increased. The decrease in the specific surface area and the increase in the pore size and pore volume were observed. In addition, the moisture readsorption characteristics of lignite were closely related to the previous drying process. The reabsorption capacity of the treated lignite increased with increasing pre-drying temperature, while an extremely high drying temperature degraded the pore structure of partial lignite, such as Shengli lignite, reducing its ability to reabsorb moisture.