Experimental Study Of Temperature-pressure Coupling Effects On Transport Of Adsorbed Gas In Raw Coal From Deep Coal Mine

The present paper focuses on the transport process of adsorbed gas within the raw coal, to understand the complex physical mechanism over the gas emission with the gradual development of coal damage. A uniaxial test apparatus for stressed coal was especially developed to simultaneously measure deformation and gas pressure as well as gas flux during test, taking the characteristics of gas transport into consideration under stress-temperature conditions. Gas composition and its concentration were detected at different time intervals by chromatography technique. Results show that original gas adsorbed in raw coal tends to be desorbed considerably over 30?with the heating rate of 0.5?/min. Based on unipore diffusion model and Arrhenius equation, apparent diffusivity and apparent desorbed energy for different adsorbent were calculated respectively with elevated temperature. The uniaxial compressive tests for the coal samples were conducted to investigate the desorption process of adsorbed and free gas under different isothermal conditions. At the failure stage, the pressure of desorption gas released from the stressed coal underwent a rapid transition from negative to positive, which can be described as a "breathing effect". As a consequence, the clustered cracks enhanced the gas reservoir and also influenced the gas pressure within the coal samples. Increasing temperature not only results in the thermal expansion of coal matrix and further widens the aperture of existing pore and clear, but trigger the desorption of original gas within coal, which also lead to the shrinkage of coal matrix. It can be able to improve the porosity of coal and reduce the effective area of specimen, which lead to the decline of uniaxial compressive strength and elastic module.