The Use of a Unipore Diffusion Model to Describe the Kinetics of Methane Release from Coal Spoil in the Longwall Environment

Abstract

Abstract:The unipore methane diffusion model based on the solution of the second Fick's law describes effectively the kinetics of methane release from coal grains. The knowledge of the model describing the kinetics of methane release from coal, the coalbed methane content, the sorption isotherm, the effective diffusion coefficient and the coal particle size distribution, enables the calculation of the volume of methane which is released from the coal spoil as a function of time. These assumptions became the basis for building the software that enables the analysis of methane emissions from coal during the longwall mining. Simulations were performed to determine the temporal and spatial methane inflow to the longwall. The share of methane emission from coal grains (taking into account both the emission kinetics and mass participation) of various classes has been analyzed. The results of the analysis showed that the methane from the small grains, in particular less than 0.1 mm in size, prevails. The mass fraction of these grains in the total weight does not exceed 5%. For the typical parameters determining the mining, geological and technological conditions of methane emissions at different moments of time and position of the longwall were determined.

Effect of micro-fractures on gas flow behavior in coal for enhanced coal bed methane recovery and CO2 storage

“…In this model, the main assumption is that coal consists of a network of interconnected micropores, and gas flow occurs primarily through these micropores. Also, the model assumes that gas diffusion through the micropores is the main mechanism for gas transport and that the diffusion rate and the concentration gradient of the gas are proportional to each other [ 80 ]. The diffusion coefficient is a function of the gas pressure and temperature and can be estimated using empirical relationships or measured directly in laboratory experiments.…”

Analysis of the Influence of Coal Petrography on the Proper Application of the Unipore and Bidisperse Models of Methane Diffusion

“…The most common and widely used physical model to describe sorption kinetics and methane diffusion phenomenon in hard coal is the unipore model [17,25,[34][35][36][37]. It assumes that the carbon matrix is homogeneous and is composed of a single type of pores in which the diffusion and sorption processes occur at equal rates [32,[38][39][40].…”

Methane Emission during Gas and Rock Outburst on the Basis of the Unipore Model

“…At the face of the fractured zone, the processes of gas transport in the direction of the excavation are initiated, which results in the decrease of the pore pressure. In spite of its lower mechanical strength, the fractured zone at the face of the excavation is a buffer against rock and gas outbursts [18]. The highest gas stresses occur in the unfractured coal zone subjected to the strongest mechanical tensions [19].…”