Sorption Kinetics of CH₄ and CO₂ Diffusion in Coal: Theoretical and Experimental Study

Abstract

Experimental and theoretical analyses with empirical correlations were framed for diffusion of gas species CH4 and CO2 in coal samples from Jharia coal fields, India, considering the intrinsic pore parameters. Coefficient of diffusion (D) and diffusivity (D eff) for a single and binary component coal–gas system were estimated by adopting unipore gas kinetic models for gas flow on the integration of Fick’s law and Langmuir relation. The rigorous study was carried out in estimating crossover pressure, which is dominant in distinguishing the flow regime for two primary types of diffusion: Knudsen and molecular as well as the transition between two regimes. Investigation reveals that experimental values of coefficients of diffusion of CH4 and CO2 in random homogeneous isotropic sphere packing of coal samples are in good agreement with the results of theoretical calculations. For the pressure range investigated, variation of coefficient of diffusion was found to follow a dual nature with a stable trend at pressures above 3500 kPa and an increasing trend for lower pressures. The practical implication of the investigation for the pressures that are characteristically encountered in the Jharia coalfields is a positive finding for the concomitant recovery of coalbed methane with CO2 sequestration. Additionally, the dynamic relation between sorption–diffusion reveals that the coefficient of diffusion significantly depends on the pore structure and pore size distribution, exhibiting a negative relationship with pressure variation.

Molecular simulation of CO2/CH4/H2O competitive adsorption and diffusion in brown coal

“…In another word, high pressure is disadvantageous to the diffusion of gas in brown coal, which is consistent of previous experimental research. 50 The trend of self-diffusion coefficient for CO 2 /CH 4 binary mixture with pressure in dry coal is displayed in Fig. 9.…”

Response characteristics of the resistivity and water content during the imbibition process in remolded coal without gas

“…55,56 The micropores and macropores are represented by the subscripts m and M, respectively. The average water saturation in remolded coal can be calculated using Equations (1) and (2). 57,58 (1)…”

“…Adsorbed state methane and free-state methane exist in coal bodies, and the adsorbed state usually accounts for more than 80% of these forms. [1][2][3] Coal-bed methane has been increasingly recognized as a type of clean, unconventional natural gas resource. [4][5][6] Therefore, it is very important to promote the conversion of adsorbed gas into free gas.…”

Investigation of effects of surface roughness on coal seam gas transport using a fractal-based lattice Boltzmann method

“…The production of CSG is largely affected by topological structures of coal which consist micropores within the matrix and macro fractures, so-called cleats (Laubach et al, 1998). The mechanism of microscale gas transport through so-called coal cleats which form a network of microchannels/fractures for gas transfer is an attractive spot for many scientists from many fields such as microstructural characterization (Mostaghimi et al, 2017), diffusion (Naveen et al, 2017), adsorption (Mayo et al, 2018) and adsorptioninduced deformation (Chen, 2012) studies. The gas flow is mainly supported by the cleat network for which the surface roughness is very significant throughout gas transport.…”