Hot-air drying behavior and fragmentation characteristic of single lignite particle

• Published in: Fuel (Guildford) 2019-07, Vol.247, p.209-216
• Main Authors: Gao, Mingqiang, Wan, Keji, Miao, Zhenyong, He, Qiongqiong, Ji, Pengchao, Pei, Zhen
• Format: Article
• Language: English
• Subjects: Air drying; Compressive strength; Computed tomography; Crack development; Cracks; Crushing strength; Drying; Fragmentation; High temperature; Image processing; Lignite; Moisture content; Surface cracks; Temperature; Temperature dependence; Temperature effects; Water content; Water treatment
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2019.03.055

The drying of lignite is a very significant topic due to its high economic value. However, fragmentation and pulverization of lignite during drying are also important factors because they affect the operation of the dryer. The aim of this study was to analyze the drying behavior of single lignite particle, as well as the development of both surface and internal cracks by image processing and micro-CT scanning. The results showed that the drying curve of single lignite particle can be divided into three stages, namely, a rapid drying stage (I), a transitional drying stage (II) and a drying equilibrium stage (III). The surface cracking rate increases with increasing drying temperature, and the number of surface cracks increases at the same time. Crack rate (CR) increases continuously in rapid drying stage (I) and transitional drying stage (II) when the drying temperature is 80 °C. For higher drying temperature (110, 140, and 170 °C), CR increases continuously in the rapid drying stage (I) and reaches the maximum near the end of the rapid drying stage (I). CR changes more smoothly in the transitional drying stage (II), and decreases slightly at the end of this stage. A small number of cracks appear near the surface at the beginning of drying. As the drying proceeds, the number of internal cracks increases and cracks develop towards the core. The crushing strength (CS) of single lignite particle, based on the definition in this paper, shows no clear dependence on drying temperature. The drying temperature might affect the moisture content in the sample, thus affecting the CS. Fragmentation is more likely to occur at high temperatures due to the rapid rate of water removal.