Study On Thermodynamic Properties The Reshaped Coal Body Under Freezing Condition

Coal and gas outburst not only seriously affect the normal mining replacement,but also cause major life safety accidents and huge material wealth damage.Among all kinds of coal and gas outburst,the accident of exposing coal in rock cross-cut coal uncovering is the most dangerous.A large number of engineering practices have been carried out for outburst prevention measures at rock cross-cut coal uncovering and abroad.This series of measures played an important role in rock cross-cut coal uncovering.But there are still two problems: One is that the process of uncovering coal is long,and another is that the inadequate prevention and control measures lead to insufficient security.Aiming at the characteristics of three dominant factors(physical and mechanical properties of coal and rock,the gas expansion energy and coal rock stress state)of coal and gas outburst in rock cross-cut coal uncovering,the idea of preventing outburst from coal uncovering in rock cross-cut coal uncovering by freezing method was put forward.Based on theoretical analysis,experiment test and numerical simulation,the two methods are used,the experimental study of gas adsorption and desorption under frozen condition(briquette)is carried out to reveal the dynamic response characteristics of coal and gas under freezing condition;in order to reveal the change law of mechanical parameters of the reshaped coal,the mechanical properties of the coal are tested under freezing conditions;the experimental test and numerical simulation of the heat transfer performance of the reshaped coal were carried out to reveal the time-varying characteristics of the rapid cooling of the coal body in the freezing process.The main conclusions are as follows:(1)Under the controlled temperature,the gas pressure in the closed space decreases with the decrease of the temperature of the coal core.The coal body is frozen and cooled,and the free gas is adsorbed in large quantities by the coal body;(2)The influence of temperature and moisture content on the compressive strength of reshaped coal samples is significant.With the decrease of the freezing temperature,the compressive strength and tensile strength of the specimen are obviously enhanced under the freezing temperature.The tensile strength of in the same freezing temperature and the same water content is 1/13-1/30 of the compressive strength;(3)The thermal conductivity of coal increases with the decrease of temperature.The fitting curves of different moisture content were obtained by using the binary method to compare the numerical simulation results with the experimental data;(4)As the freezing time increases,the radius of the effective freezing region increases gradually.The area of effective freezing increases obviously,and the effective freezing radius increases exponentially with the increase of the freezing time.The reasonable arrangement method can be arranged with the porous three-flower eye,and the spacing between the frozen holes can be set as two meters.