Abstract
In order to research on the law of methane released through the pore in coal particles, the methane desorption experiments were conducted, respectively, on four types of particle size of coal samples under three different initial adsorption pressures. The cumulative methane desorption quantity (CMDQ) with time increasing was obtained to show that the reciprocal of CMDQ was in linear relation with the reciprocal of the square root of time, and the correlation coefficients were all above 0.99, on basis of which an empirical formula of CMDQ was established. Then, according to Fick diffusion law and Darcy percolation law, the mathematical models of methane emission from the spherical coal particles were created, respectively, and the corresponding calculating software was programmed by the finite difference method to obtain the simulated CMDQ of each sample under different conditions. The methane emission rate functions (MERF) of the simulation and the experiment were also calculated, respectively. Comparative analysis between the numerically simulated outcomes and the assay results reveals that the simulation outcomes as per Darcy’s law match the experimental data better, while the simulated results by Fick’s law deviate greatly, which indicates that the methane flowing through coal particles is more in accordance with Darcy’s law.
Highlights
In China, there are large reserves of coalbed methane (CBM) [1,2,3]
Formula (9) to (11) forms a complete equation set of the methane flow in coal particles as per Fick’s law, in which the methane contents from 0 to N node are the unknown quantities at the jth moment
While no matter how we change the size of the methane diffusion coefficient D, the curves of cumulative methane desorption quantity (CMDQ) in Fick diffusion can never well accord with the experimental curve
Summary
In China, there are large reserves of coalbed methane (CBM) [1,2,3]. CBM can be taken as a kind of resource for comprehensive use [4, 5], but it is a hazardous factor underground, which directly threatens the normal production on the frontline and could cause gas explosion [6,7,8]. Many scholars [27, 28] considered that the law of gas flow is diverse in pores with different diameters, i.e., the gas flow obeys molecular diffusion in the small pores but laminar flow in the larger pores and cracks The majority of pores are micropores or transition pores, so most researchers believe that the gas flowing in micropores and transition pores obeys the Fick diffusion law, but in the larger pores, such as mesoporous, macropores, and cracks, it conforms to Darcy’s law [34, 35] Based on this precondition, some important researches were done. Particle diameter (μm) 4000–4750 1000–1180 425–550 250–270 the simulated results will be compared with the experimental results, so as to obtain a more reasonable methane flow pattern in coal particles
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