Study On Replacement Effect Of Added Water On Coal Gas Under Isobaric Environment

In order to improve the effect of gas drainage in low permeability coal seam,currently the main measure to promote gas drainage is to artificially enhance the permeability and relieve the pressure of coal seam,changing the gas permeability of coal seam and the gradient of gas pressure,reducing gas pressure and gas content.Thereinto hydraulic measures have become the main technical method of reducing pressure,increasing permeability and enhancing gas drainage.However,the effects of water on coal containing gas in the process of hydraulic measures are multiple such as anti-reflection,displacement,replacement,inhibition,which causes difficulties in the study of mechanism.If we can have a quantitative study of a single function peeling off other effects,it will be helpful to reveal the outburst prevention mechanism of hydraulic measures.In recent years,some scholars have studied the replacement effect of added water on coal gas,but for the experimental system was a closed system,the replacement gas increased the pressure of the closed system,resulting in a part of the replacement gas readsorption,bringing that the results of the test could not really reflect the replacement effect.Based on these,the author of this paper carried out the study on replacement effect of added water on coal gas under isobaric environment.According to the characteristics of raw coal,granular coal,shape coal,combining with experimental purpose,this paper chosed shape coal as experimental coal sample,the size of shape coal Φ50mm×80mm,the size of center hole Φ22mm×80mm.This paper set up a high pressure adsorption~ sample coal isobaric water absorption~isobaric environment experimental platform.Using the experimental platform,the replacement effect of external water on coal gas was tested.Test results show that:with the extension of time,replacement quantity gradually increases until reaching a certain value,but the rate decreases;the maximum replacement quantity is positively correlated with water content and adsorption equilibrium pressure;under the same adsorption equilibrium pressure,the replacement rate increases with the rise of water content;under the same water content,the replacement rate has a gradually decreasing trend with the adsorption equilibrium pressure;the speed of replacement is divided into three stages,including rapid increase,slow persistence,and decay to zero.In the stage of rapid increase,water content and adsorption equilibrium pressure show promotion to the velocity of replacement as a whole,but in the other two stages,the influence of the two factors on the replacement velocity are not obvious.According to the results of isobaric environment,the maximum replacement quantity and replacement rate of non isobaric are smaller than of isobaric,and those difference can not be ignored.Based on the material foundation,driving force and process of replacement,this paper analyzed the mechanism of replacement.According to the test results and mechanism of replacement,the application of replacement in engineering was discussed.