Pore structure evolution and fractal characteristics of Zhaotong lignite during drying

Abstract

While the drying of lignite is critical prior to its usage, the fragmentation and pulverization of lignite during drying inhibit the safe operation of this process. In this study, the changes in the physical structure of Zhaotong lignite during the drying process were examined by study its microstructure. Microstructure aspects like pore size distribution, pore volume distribution, and fractal dimension were used to determine the variation in pore structure, and the relationship between fractal dimension and water content was established. The results showed that open pores and pore connectivity decreased as the degree of drying increased. During the drying process, the number of pores larger than 100 nm decreased first, followed by a decrease in the number of pores smaller than 100 nm. The total pore volume and the pore volume of four types of pores showed a general trend of downward at different drying temperatures. The change in the fractal dimensions of Zhaotong lignite during drying can be divided into three stages. The change in the fractal dimension of the second stage (water content decreasing from 1.19 to 0.62 g/g) was found to be the most significant, since it entailed the destruction of the Zhaotong lignite pore structure.