Study on Pore Structure Change Characteristics of Water-Immersed and Air-Dried Coal Based on SEM-BET

Abstract

ABSTRACT The pore structure of coal affects spontaneous combustion to a certain extent. The pore structure of the coal body will be altered after prolonged waterlogging and is highly susceptible to spontaneous combustion in the presence of elevated ground temperatures. To study the pore structure changes in the coal body after immersion and drying. The coal samples from the Jinjitan coal mine in Yulin, Shaanxi Province, the Tangkou coal mine in Jining, Shandong Province, and the Gaojiapu coal mine in Shaanxi Province were scanned by electron microscopy and low-temperature nitrogen adsorption experiments. This study indicates that after water immersion, the fracture pores of the coal body are developed, the morphology changes, and the percentage of pore fracture area increases significantly. With the increase in immersion time, the pore types of Coal samples A and C did not change, being delicate necked bottle-shaped pores and open, permeable pores, respectively. Coal sample B pore type developed from impermeable pores to open pores. The cumulative pore volume of coals from all three areas increased for the same pore size. The contribution of micropores to the BET specific surface area and total BJH pore volume was more significant than the original coal samples. The specific surface area of A90, B30, and C60 was larger than that of the other coal samples for the soaking time, so it can be assumed that A90, B30, and C60 have a higher propensity for spontaneous combustion. Underwater immersion, the pore type of coal samples from coal mines in Northwest China did not change, but the pore types of coal samples from coal mines in East China changed. Therefore, the pore structure of gas coal was easily changed underwater dissolution.