| When coal and gas outburst occur,the generated coal-gas two-phase flow will cause disturbance of the original airflow in the tunnel,and it will be extremely destructive to the ventilation system and tunnel facilities,which will eventually lead to casualties and property damage.The reverse damper is an important safety outburst prevention facility in the mine,which can effectively block the shock wave.However,after the occurrence of outburst,some energy still passes through the reverse damper through the hole,causing gas backflow and expanding the disaster area,resulting in the occurrence of prominent secondary disasters.Therefore,it is of great significance to study the propagation law of the coal and gas two-phase flow through the reverse damper hole for to prevent and control coal and gas outburst secondary disasters.Theoretically analyze the source of outburst energy and its consumption way,establish a coal and gas outburst simulation test platform to test the outburst coal and gas two-phase flow through the reverse damper hole under different outburst pressures,and establish a numerical simulation model corresponding to the physical test.The model is used to further improve the propagation law of the outburst coal and gas two-phase flow in the tunnel and its disaster-causing mechanism,so as to provide theoretical support for controlling the impact of prominent disasters and improving mine safety production.The main research contents and conclusions are as follows:(1)Theoretical analysis of the coal and gas outburst energy elements,sources and their consumption methods is carried out,and the formation process of the outburst coal and gas twophase flow and the propagation law in the roadway are briefly described.The calculation formula of overpressure after the outburst shock wave passes through reverse damper hole is deduced.Based on the one-dimensional steady flow model of coal and gas two-phase flow,the governing equations of outburst coal and gas two-phase flow are established.(2)Based on the similarity theory,a simulated physical test platform for coal and gas outburst was designed and built,and the outburst coal and gas two-phase flow through the reverse damper hole was carried out under the initial outburst pressure of 1 MPa,0.74 MPa and 0.5 MPa(with the20 mm damper bottom sill as the example)test.The test results show that: 1)The larger the initial outburst pressure,the larger the amount of pulverized coal outburst and the larger the overpressure of the outburst shock wave,and the outburst strength is positively correlated with the initial outburst pressure.The pulverized coal and outburst shock waves mainly propagate along the main roadway,and very little diverts to the branch roadway.2)The outburst pulverized coal shows obvious sorting phenomenon in the roadway: the quality of each particle size coal powder is evenly distributed;as the proportion of pulverized coal with particle size increases,and the pulverized coal with small particle size is more likely to continue to move forward through the air door holes.3)The overpressure curve has multiple sudden jumps,and the prominence is paroxysmal and occurs extremely fast.The shock wave propagating along the straight roadway will generate a reflected shock wave after colliding with the reverse damper.After superimposing with the incident shock wave,it will rise to the overpressure peak near the air door,so that the overpressure in the straight roadway in front of the air door is closer to the air door and the farther the protruding cavity is;the larger the overpressure is.4)Most of the pulverized coal and shock wave are blocked outside the damper.The loss rate of pulverized coal passing through the first damper is greater than 70%.The quality of the coal powder passing through the two damper is lower than 7% of the total outburst coal amount.The overpressure of the duct damper is less than 1.5 k Pa.The two reverse damper have a remarkable blocking effect on outburst coal dust and shock waves.5)The shock wave diverted to the branch roadway will propagate to the main roadway again,which may cause gas backflow.Therefore,an anti-backflow device should be installed in the branch roadway.6)The coal body through the first damper crushing work is 7% of the total crushing work of the test coal body.The mobile work of the coal body transported to the two damper under 0.5 MPa,0.74 MPa and 1 MPa accounted for 7.1%,9.0% and 9.6% of the total mobile power of the test coal body.(3)After simplifying the roadway,a three-dimensional numerical model of the outburst coal and gas two-phase flow was constructed,and the propagation law of the coal and gas two-phase flow in the roadway and through the reverse air door holes was simulated by ANSYS-FLUENT software.The simulation results are as follows: 1)The flow velocity of the shock wave is ahead of the velocity of the pulverized coal,and the velocity of the pulverized coal and the overpressure of the shock wave are positively correlated with the initial pressure,the larger the initial pressure the shorter the time required for the pulverized coal speed to reach the peak,and the further the coal and gas two-phase flow is transported.2)The speed of pulverized coal can be obtained in a short time and then reaches the maximum value,and the maximum value can exceed 100 m/s.Coal powder is fast in the central area of the roadway,and the speed of the edge is relatively slow,showing a velocity gradient phenomenon.The more obvious the powder velocity gradient.With the increase of propagation distance,the speed of pulverized coal tends to decrease,but it still passes through the holes of the reverse air door at a relatively large speed.After passing through the air door,the speed decreases due to energy consumption and other reasons.3)The superposition of the reflected shock wave generated by the collision of the protruding shock wave and the two dampers leads to an increase in the overpressure behind the damper.When setting the anti-protrusion device,the spacing of the dampers should be considered to avoid the occurrence of protruding secondary disasters.4)The numerical simulation of the overpressure change in the tunnel is consistent with the variation of overpressure in the physical test,indicating that the established three-dimensional solidgas coupling model is reasonable and reliable on studying the propagation law of outburst coal and gas two-phase flow through the reverse damper hole. |
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