Thermal fragmentation and pulverization properties of lignite in drying process and its mechanism

Abstract

ABSTRACTThe fragmentation and pulverization properties of lignite in the different drying processes were investigated in this study. Lignite particles were dried at different temperatures (100, 140, and 180°C), particle sizes (6–25 mm) and drying time (0–60 min), and the parameters of fragmentation index (Sf) and pulverization ratio (β) were used to describe the fragmentation and pulverization properties of lignite. The results indicated the fragmentation index increased from 3.10 to 30.41 with the increase in temperature and particle size. Pulverization ratio increased slightly from 0.39 to 0.63% with temperature, and it decreased from 0.58 to 0.36% with particle size. Fragmentation index and pulverization ratio increased rapidly from 1.20 to 5.50 and 0.05 to 0.47%, respectively, and then tended to grow slowly with drying time. Fragmentation index was linearly related to the loss of moisture content. Different kinds of fragmentation and pulverization occurred at the same time: fine particles exfoliated from the surface, and there were also fragmentation at the outer zone or the core of the particles to produce the smaller particles. The evolutions of macropores might be the main reason of thermal fragmentation.