Effects of pore structure on drying kinetics of lignite

The pore structure variation of Shengli and Zhaotong lignite were investigated in the low temperature drying process(60-140 ℃ ). Meanwhile,the effective moisture diffusivities(Deff ) of the two types of lignite were calculated, from which the relationship between pore structure and effective moisture diffusivities was discussed. The results indi- cate that pore structure of Shengli lignite is dominated by open cylindrical pores and cracks pores,whilst,it is mainly dead end pores closed at one end for Zhaotong lignite. Furthermore,by increasing the drying time,the specific surface area of two lignite decreases and the variation trend of pore volume is opposite to that of average pore diameter. While the specific surface area,pore volume and average pore size increase with the improvement of drying temperature and the variation trend of average pore size is the same as that of pore volume. The correlation dynamics parameters demon- strate that the pore volume fraction and specific surface area of coal samples have good correlation with Deff . The pore volume fraction of lignite is positively related to the specific surface area,and the Deff is linear with the specific surface area. With the increase of the temperature,the pore volume fraction of the Shengli lignite is increased when the pore diameter is less than 7 nm and decreased at 7-10 nm,but difference is that the pore volume fraction of Zhaotong lig- nite is increased when the pore diameter is less than 10 nm,and decreased at 10-20 nm. Deff is controlled by micro- pores and mesoporous pores. Meanwhile,the data manifest that Shengli lignite (16. 95 kJ / mol) possesses lower activa- tion energy than Zhaotong lignite (21. 84 kJ / mol) in the low temperature drying process,implying that the actual en- ergy required for the drying of Shengli lignite is relatively low.