The dynamic change of pore structure for low-rank coal under refined upgrading pretreatment temperatures

Pore structure characteristics are significant factor in the evaluation of the physical characteristics of low-rank coal. In this study, three low-rank coal samples were collected from the Xishanyao Formation, Santanghu Basin, and low-temperature liquid-nitrogen adsorption (LP-N(2)A) measurements were taken under various pretreatment temperatures. Owing to the continuous loss of water and volatile matter in low-rank coal, the total pore volume assumes a three-step profile with knee temperatures of 150 degrees C and 240 degrees C. However, the ash in the coal can protect the coal skeleton. Pore collapse mainly occurs for mesopores with aperture smaller than 20 nm. Mesopores with apertures smaller than 5 nm exhibit a continuous decrease in pore volume, whereas the pore volume of mesopores with apertures ranging from 5 to 10 nm increases at lower pretreatment temperatures (<150 degrees C) followed by a faint decrease. As for mesopores with apertures larger than 10 nm, the pore volume increases significantly when the pretreatment temperature reaches 300 degrees C. The pore structure of low-rank coal features a significant heating effect, the pretreatment temperature should not exceed 150 degrees C when the LP-N(2)A is used to evaluate the pore structure of low-rank coal to effectively evaluate the reservoir characteristics of low-rank coal.

Automated summary

The pore structure characteristics of low-rank coal show variations under different pretreatment temperatures, with total pore volume changing accordingly. Ash content in the coal plays a role in protecting the coal skeleton, while pore collapse mainly occurs in mesopores with smaller apertures.