Analysis of the effect of different pretreatment conditions on pore structure heterogeneity of low-rank coal based on multifractal theory

In order to select the pretreatment conditions of low-temperature nitrogen adsorption experiment more scientifically, low-temperature gas adsorption experiments of five particle-size subsamples pretreated at seven degassing temperatures were conducted. The results showed that the higher the degassing temperature, the faster the volatile and water separated, and some of pores collapsed. After mechanical crushing, some pores are filled and blocked by mineral particles. Multifractal analysis shows that the pore connectivity hardly improves with increasing degassing temperature, while the heterogeneity of pore distribution is enhanced. With the decrease of particle size, the heterogeneity of pore size distribution decreases, while the connectivity of pores increases. With the increase of degassing temperature or the decrease of particle size, nitrogen adsorption capacity, sample mass, pore volume and pore area all showed a three-stage decline. Ultimately, 120 degrees C and 40-60 mesh are recommended as the best degassing temperature and sample size for low-temperature gas adsorption method.