Dynamic Evolution Law Of Solid-Gas Two-Phase Flow In Coal And Gas Outbursts

Coal and gas outburst is a very complex mine dynamic disaster.When the outburst occurs,a large number of broken coal and gas are thrown quickly into the excavation space.The thrown coal can directly impact the workers at the site of burying.The outburst shock wave will cause harm to people.The high concentration gas in the roadways after the outburst may also cause secondary disasters such as gas explosion.Because of the complexity of outburst mechanism,people can not completely prevent and control coal and gas outburst.Based on the existing research results,this thesis focuses on the dynamic evolution law of coal gas solid gas two-phase flow after outburst,and expounds the damage effect in a short period of time after the outburst,so as to further improve the evolution law of coal and gas outburst,and provide the basic theoretical basis for disaster prevention,resistance and relief of outburst mines.In this thesis,the formation process and propagation rule of the shock wave of coal and gas outburst as well as the movement rule of the two-phase flow of coal gas solid gas outburst are theoretically analyzed,and then a simulation test system of the two-phase flow of coal gas solid gas outburst is designed and manufactured.The propagation and evolution rule of the two-phase flow of coal gas outburst under different conditions are experimentally studied.Finally,the outburst is realized through the coupling of EDEMFLUENT.The results of theoretical analysis,experimental study and numerical simulation are mutually verified.The main research results of this thesis are as follows:(1)The theoretical model of coal and gas outburst shock wave is established,and the expression of outburst shock wave intensity is deduced according to shock wave theory,which can directly calculate and analyze the dynamic parameters such as shock wave intensity,shock wave development speed,shock airflow speed,etc.The velocity of the shock wave front is supersonic,and the higher the shock wave intensity is,the higher the propagation velocity is.According to the initial gas pressure and the intensity of outburst shock wave,the equivalent sonic velocity of coal gas solid gas two-phase flow can be calculated.The theoretical analysis also shows that the layout of underground roadway system has a great influence on the result of outburst shock wave.(2)The analysis of the flow pattern of coal gas two-phase flow in different flow stages shows that the solid phase in the whole process of outburst has both extremely dense and sparse stages,and stratified flow is the main form of coal gas two-phase flow.The force analysis of the outburst pulverized coal in different stages shows that the force on the pulverized coal with different particle size is different.When the particle size of the pulverized coal is small(such as 0.1mm),the drag force mainly affects the movement of the pulverized coal,and when the particle size is large(such as 10 mm),the gravity is also an important force.Due to the obvious difference between the formation principle of pressure in the solid particles and the gas phase,the solid phase can not be fully fluidized.It is necessary to abide by the three conservation laws of gas and the conservation laws of components in the two-phase flow of outburst coal and gas.(3)Based on the similarity theory,a simulation test system of coal gas solid gas twophase flow is designed and manufactured.The movement of outburst coal gas two-phase flow can be divided into two processes,one is the process of outburst coal gas suddenly thrown out from the outburst chamber,the other is the process of high-speed movement of outburst two-phase flow in the roadways.For process I,the elastic energy of highpressure gas is the power source and Mach criterion is selected;for process II,the viscous force of gas is the main influencing factor and Reynolds criterion is selected.Aiming at the problem that the traditional schlieren instrument can not observe the flow field in the circular pipe,the optical path system of the schlieren instrument is improved to realize the observation of the shock wave propagation process in the circular test roadways.The developed system can be used to study the dynamic evolution law of the outburst twophase flow of high gas pressure and dense phase pulverized coal.(4)The experimental pulverized coal was prepared and its basic parameters were measured and analyzed.Industrial analysis shows that with the decrease of the particle size of coal powder,the ash content increases gradually,which shows that some specific components of coal powder are easier to become fine particles in the process of pulverization,and the proportion of inorganic substances in these components is larger.SEM analysis shows that there are a large number of smaller particles and depressions on the surface of pulverized coal particles,which naturally act as a small support structure to prevent further contact of particles.The measurement of adsorption constant shows that with the increase of coal particle size,the Langmuir volume constant has little change,which shows that the change of particle size has no significant effect on the gas adsorption capacity under the test scale in this thesis.However,the Langmuir pressure constant increases significantly with the increase of particle size,which indicates that the path of methane molecules moving from the coal surface to the inside of particles increases with the increase of resistance.(5)The self-developed test system is used to simulate the two-phase flow of coal and gas outburst.The experimental results show that there is an acceleration stage at first,and when the shock wave overpressure is maximum,the wave front reaches the maximum speed,then attenuates,and the attenuation trend is slow first and then fast.The movement law of pulverized coal is similar to that of wave front,and there is acceleration stage.The propagation velocity of outburst shock wave is much faster than that of pulverized coal,but the impact pressure of pulverized coal is much higher than that of shock wave.(6)The simulation tests under different initial gas pressure,different pulverized coal particle size,different outburst orifice and different pulverized coal loading ratio were carried out.The test results show that the larger the initial gas pressure is,the greater the velocity,pressure and impact force of outburst shock wave front and coal powder are,and the increase proportion is roughly proportional to the increase of gas pressure.The smaller the particle size of pulverized coal is,the larger the dynamic parameters of shock wave front and pulverized coal are.The larger the outburst orifice is,the greater the shock wave pressure is,but the total amount of outburst pulverized coal is the largest when the outburst diameter is 60 mm.In the test,when the loading ratio of pulverized coal in the outburst chamber is 0.5,the dynamic phenomenon of outburst is obviously stronger than that when the pulverized coal is fully loaded.(7)It is found in the simulation test that it is very difficult for the separation of the coal dust in the roadway to appear in the laboratory simulation,or even the opposite phenomenon may appear.In this thesis,the theoretical modeling analysis is carried out.In the outburst site,the amount of coal and gas outburst is very large and lasts for a long time.The coal powder will experience three whole processes: acceleration,uniform speed and deceleration.In laboratory outburst simulation,pulverized coal may only accelerate and decelerate.By setting reasonable parameters into the theoretical formula,the contradiction between laboratory simulation and field practice is well explained.(8)The coupled model of EDEM-FLUENT is constructed and the numerical simulation of the two-phase flow of coal and gas outburst is completed.The simulation results show that the pulverized coal accelerates rapidly in a short time(tens of milliseconds)and approaches to the maximum speed,which can reach 60m/s.There is a good inverse proportion relationship between the speed of pulverized coal and the particle size.Compared with the theoretical calculation,the acceleration of particles in the numerical simulation is slower at the initial stage,and then the acceleration increases faster,but the overall movement trend of the two is the same.The accumulation angle of pulverized coal in the outburst chamber is about 21 °,which is far less than the natural accumulation angle of pulverized coal.It is consistent with the general phenomenon of coal and gas outburst,and the distribution of the outburst pulverized coal is not separable,which is consistent with the results of physical simulation test.There is no significant difference between the overpressure data of numerical simulation and physical simulation test,and the gap is within 10%.The simulation of the pressure change in the roads is completed in an instant.In the spatial relationship,the closest position to the outburst is not the maximum pressure,and the maximum pressure appears at a certain position from the outburst.