| Coalbed methane(gas)is a kind of clean energy with high quality and efficiency.Its efficient extraction can not only improve the utilization rate of energy in China,but also reduce the safety accidents in coal mines.Using high pressure abrasive gas jet technology to break coal and rock for pressure relief and permeability enhancement can improve gas extraction efficiency.The stress wave effect produced during coal breaking by high pressure abrasive gas jet will lead to the actual damage range of coal body larger than the impact area of abrasive particle beam,which can enhance the effect of abrasive jet on coal and rock breaking.However,there is no systematic research on it at present.Therefore,the stress wave effect of high pressure abrasive gas jet breaking coal is studied in this paper.In order to study the stress wave propagation law and effective coal breaking range during coal breaking by high pressure abrasive gas jet,the governing equation of stress wave for coal breaking by high pressure abrasive gas jet and the energy criterion for judging coal failure are established.The boundary and initial conditions for solving stress wave propagation model and energy criterion are proposed.The parameters of boundary,initial condition and energy criterion under different jet conditions were measured by experiment and numerical simulation.Based on the measured parameters,the stress wave propagation equation and the energy criterion of coal failure are solved numerically.At the same time,the DIC test is used to verify the distribution law of coal strain field and the breaking range of stress wave.The results of this study are as follows:(1)Based on the theory of porous media,the spherical stress wave equation of coal breaking by high pressure abrasive gas jet is established.The equation also considers the impact characteristics of gas/abrasive particles on the propagation law of stress wave.It can be used to study the stress wave effect in the process of coal breaking by pure gas jet or abrasive gas jet Based on fracture mechanics,the critical energy criterion of coal breaking by high pressure abrasive gas jet is established.The criterion takes into account the impact of jet impact parameters on the critical energy density of coal failure,and can be used to study the failure process of coal under different jet conditions.According to the characteristics of high pressure abrasive gas jet impacting coal,the boundary and initial conditions for solving stress wave propagation model and energy criterion are proposed.(2)The parameters of boundary and initial conditions under different jet pressures and target distances were measured by experiment and numerical simulation.The parameters include gas/abrasive particle impact frequency,impact radius,jet incident energy,energy consumption density of coal and diameter of fragments after coal breakage.I-scan and vibration sensor are used to measure the impact frequency of gas jet and abrasive particles respectively.It is concluded that the impact frequency of gas/abrasive depends only on the jet pressure.The impact radius and incident energy of abrasive jet are calculated by FLUENT.It is found that the impact radius of abrasive jet has a linear relationship with jet target distance,and the single incident energy of abrasive jet has a quadratic function with jet target distance and a primary function with jet pressure.SHPB is used to study coal parameters,and it is concluded that the energy consumption density of coal failure increases with the increase of strain rate.The relationship between the average diameter of fragments and the strain rate of coal samples is a first-order function.(3)Based on the test parameters,the propagation law of stress wave at two shock frequencies of gas and abrasive particles is numerically calculated.It is concluded that the stress wave generated by abrasive particles impacting coal body has high carrying energy,large attenuation coefficient and short propagation distance,which plays a major role in stress wave coal breaking.With the increase of propagation distance,the dispersion of stress wave is serious.Discreteness of coal sample will cause different morphology of coal sample after destruction. |
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