Adaption of Theoretical Adsorption Model on Coal: Physical Structure

Wu Guodai,Zhang Ruigang,Zhang Ye,Pan Linhua,Luan Jinhua,Sun Zheng,Huang Bingxiang

doi:10.3389/feart.2021.691311

Abstract

With the motivation to investigate the role of coal physical structure on the adsorption performance of coal reservoir, 18 different types of coal samples with different coal structures were collected from six coal profiles of four production mines located at China. The adsorption characteristics of CH4 on coal samples with different coal structures were examined, and then experimental results were fitted and analyzed by the Langmuir model and the adsorption potential model (D-R and D-A). The prominent factors in terms of adsorption capacity of coal with different coal structures and its adaptability to the model were discussed. Results indicate the following: a) under the condition of a similar coal rank, the adsorption performance of coal is governed by coal rock composition and adsorption heat, the effect of structural deformation on the adsorption performance of coal is not obvious; b) the Langmuir model has a certain adaptability to coal samples with different coal structures, while the D-R model is evidently not suitable to describe coal samples with scaly coal, part of broken coal with small vitrinite content; c) the D-A model has a high adaptability to coal samples with various coal structure types, and the stronger the coal deformation is, the higher the accuracy is.

Highlights

Adsorption is a kind of surface interaction between coal solid surface and gas or liquid, and coalbed methane mainly exists in the adsorption state in coal reservoirs
It can be seen that for the three models, the Langmuir model has a certain adaptability to different deformation types of tectonic coal, but the change is larger with the coal sample, while the D-R model is obviously not suitable for describing the scale coal and the D-A model has high adaptability to all kinds of coal structure types, the stronger coal deformation will contribute to higher accuracy
The results show that the isothermal adsorption capacity of coal increases with the increase of pressure and increases with the increase of structural deformation under the same pressure

Summary

INTRODUCTION

Adsorption is a kind of surface interaction between coal solid surface and gas or liquid, and coalbed methane mainly exists in the adsorption state in coal reservoirs. Because the premise of the application of the BET model is to determine four or five points in the range of P/Po (the ratio of equilibrium gas pressure and saturated vapor pressure) 0.05–0.35, and the monolayer adsorption volume (Vm) can be calculated, while the P/Po of the seven equilibrium points in isothermal adsorption test is mostly greater than 0.35, the calculation of BET model parameters from the data of seven equilibrium points will be seriously distorted or even have no FIGURE 2 | Adsorption Characteristics of coals with different structures on the same coal rock section. The saturated vapor pressure of CH4 is 11.68 MPa. Notably, SPSS17.0 software was used to fit the adsorption capacity of seven equilibrium points, and the seven parameters of the Langmuir, D-R, and D-A models, the standard deviation of each parameter, and the correlation degree of curve fitting (Table 2) were obtained. It can be seen that for the three models, the Langmuir model has a certain adaptability to different deformation types of tectonic coal, but the change is larger with the coal sample, while the D-R model is obviously not suitable for describing the scale coal and the D-A model has high adaptability to all kinds of coal structure types, the stronger coal deformation will contribute to higher accuracy

CONCLUSION

DATA AVAILABILITY STATEMENT