Study on the critical adsorption depth of middle-rank coal -taking Nanyu coal as an example

Abstract: This paper presents the theoretical significance of the temperature-pressure-adsorption equation (TPAE) over the limitations of the Langmuir isothermal adsorption equation. The series isothermal adsorption data of low-rank coal from Nanyu coal mine in Shanxi Province, China were used to verify the practicality of the TPAE, and four parameters were obtained. According to the TPAE sought, the adsorption value of any tests between 30°C -100°C and pressure between 0-30 MPa can be arbitrarily calculated, with an average relative error of less than 11.98 %, and expressed by a three-dimensional adsorption surface. According to the total differential of the multivariate function is the sum of the differentials of each independent variable, assuming that the ground temperature gradient of Nanyu coal mine is 3°C /100 m and the ground pressure gradient is 1.0 MPa/100 m, it can be precisely calculated that both partial deviations of temperature and pressure. It can be approximately calculated that the critical adsorption depth of the low-rank coal is about 700~800 m underground, the critical adsorption pressure is about 7.4 MPa, the critical adsorption temperature is about 36.4°C, and the critical adsorption capacity is 12.44 cm3/g.

Keywords: temperature-pressure-adsorption equation; Langmuir isothermal adsorption equation; partial deviations of temperature; partial deviations of pressure; the critical burial depth.