Abstract
A series of methane adsorption-desorption isotherm experiments on anthracite of No. 3 Sihe coal mine were conducted at 20°C, 25°C, 30°C, 35°C and 40°C respectively. Based on Clausius-Clapeyron equation, isosteric heat of adsorption and maximum heat of adsorption has been calculated. These calculations indicate that the maximum heat of adsorption in process of elevated pressure (adsorption) and lowered stress (desorption) is 23.31 KJ/mol and 24.02 KJ/mol, so it belongs to physical adsorption. However, the latter is higher than the former. From the point of view of thermodynamics, in the adsorption-desorption equilibrium system, dropping pressure alone does not lead to desorption, but it improves adsorption of water vapor molecules on the surface of the coal pores. The adsorption heat of water vapor molecules is greater than 40 KJ/mol, so the methane on the surface of coal pores will be easily replaced by water vapor, and the desorption of methane occurs eventually. Thus, the gas production in coalbed methane well by pressure reduction is consistent with the negative pressure for gas extraction.
Highlights
Coal methane mostly exists in the coal seams in the form of adsorption
The experiments were accomplished by employing AST-2000 simulation experimental apparatus for bulk sample coalbed methane adsorption and desorption
Called differential heat of adsorption [8], is the heat released as the infinitesimal methane molecules are adsorbed, with the adsorption capacity being constant
Summary
Coal methane mostly exists in the coal seams in the form of adsorption. The approach of coal methane desorption by drainage and lowering pressure for its ground production is widely adopted both at home and abroad. (2014) Thermodynamic Characteristics of Adsorption-Desorption of Methane in 3# Coal Seam of Sihe. The new approach has shed light on the theory of methane production, and demands careful exploration of the nature of drainage and lowering pressure production. Through the experiments on methane adsorption-desorption isotherm [1]-[3], by the calculations of isosteric heat of adsorption and maximum heat of adsorption with Clausius-Clapeyron equation, and by the contrast of the adsorption heat between methane and water vapor, the paper probes into the function and mechanism of water vapor in the process of water drainage and gas production
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