Study On Gas Desorption Characteristics Of Gas Containing Coal During Low Temperature Coring

Based on the severe friction between coal seam and core pipe in the sampling process of conventional coring tube,which can increase the amount of gas loss,the core technology of low temperature coring is putting forward.The coal core is sealed in the low temperature environment through the modifying the core tube,adding refrigerant.The coal core which is collected by cryogenic coring technology is affected by the friction heat transfer of core process and the absorption of refrigerant in core process,which results in the change of coal core temperature,it will inevitably affect the gas desorption of coal core.In this paper,a low temperature core simulation platform is built,based on the measuring device of tube wall temperature in the sampling process of core-pulling pipe,the temperature change of the pipe wall under different sampling depths is collected,and the external heat input program for simulating cryogenic coring process is set up,and the refrigerant is dry ice.The temperature experiment and gas desorption experiment of different adsorption equilibrium pressure and different sampling depth are carried out to study the variation temperature and gas desorption characteristics of the coal core.The results of this paper are as follows:(1)The temperature change of the pipe wall in the process of core drilling is divided into three stages: the slow rising stage,the fast rising stage and the descenting stage,respectively corresponding to the drilling,collecting coal sample and the drilling process.When the core depth is certain,the time required in the drilling is longer than the back drilling,and the heating rate in the drilling is higher than the cooling rate in the back drilling.Tampling time of different core depth is equal.(2)The core temperature of coal varies in three stages: rapid decline,low temperature maintenance and temperature recovery;Under the conditions of a certain amount of refrigerants,when the initial adsorption equilibrium pressure is kept constant,the cooling time and the low temperature duration of the coal core decrease with the increase of the sampling depth,the heating time has no obvious change trend.Keeping the sampling depth unchanged,with the increase of initial adsorption equilibrium pressure,the coal core cooling time decreases,the heating time increases,the duration of low temperature has no obvious change trend.(3)The amount of gas desorption changes divided into three stages: prophase rapid increase stage,mid-term stable stage,anaphase slow increasing stage.With the increase of sampling depth,the gas adsorption equilibrium pressure desorption in the prophase rapid increase stage without significant changes;When the sampling depth is certain,with the increase of adsorption equilibrium pressure,the desorption of prophase rapid increase stage increases,the longer the time required to “stop” desorption.(4)The change of gas desorption velocity can be divided into four stages: rapid attenuation stage,mid-term stable stage,slow increase stage and slow attenuation stage.With the increase of sampling depth,the velocity of gas desorption under the different adsorption equilibrium pressure has no obvious change in the prophase increasing stage.When the sampling depth is certain,with the increase of adsorption equilibrium pressure,at the same time the rapid decay phase of gas desorption velocity increasing,the longer the time of the desorption rate reduced to mL/(g?min)is;in the slowly increasing stage,adsorption equilibrium pressure increases,the desorption rate can be increased to the stage the maximum value is greater;(5)There is a phenomenon of suck-back in the process of low temperature coring.With the increase of sampling depth,the suck-back rate increases,the suck-back duration shorten under a certain adsorption equilibrium pressure,but no obvious change trend of suck-back amount;When the sampling depth is certain,with the increase of adsorption equilibrium pressure,the suck-back amount less,the suck-back duration shorten and the suck-back rate showed a accelerate trend.