Study On Combustion Process Of Coalbed Gas-coal Dust Two-phase System

China's main energy source is coal,and it is the country that stores the most coal in the world,while China's coalbed gas resources account for 11.7% of the world's coalbed gas resources.The mining of coalbed gas can reduce the emission of gas,reduce the greenhouse effect to protect the environment and also reduce the gas content in the wells to provid a safe environment for underground workers.However,when mining coalbed gas,coalbed gas and coal powder will form a mixed state.It will explode under certain conditions.Therefore,in this paper,we used a modified Hartmann tube to study combustion process of coalbed gas-coal dust two-phase system and used a high-speed camera system to shoot combustion process.The flame propagation speed and flame propagation height were calculated.At the same time,the explosion pressure and explosion index in coalbed gas-coal dust combustion process were measured and analyzed.The effect of inert gases(CO₂,N₂)on the mixed combustion of coalbed gas-coal dust was also studied in this paper,which provided safety assurance for coalbed gas exploitation.The specific conclusions are as follows:The effects of coal dust particle size,coal dust concentration,ignition delay time,methane concentration and combustion tube length on the flame of mixed explosion of coalbed gas-coal dust two-phase system were investigated separately.The results showed that the smaller the particle size of coal dust,the greater the flame propagation speed and height of the mixed system;the most intense the mixed system burned when the coal dust concentration was 500 g/m3 and the ignition delay time was 100 ms;when the methane concentration was below 5%,the greater the methane concentration,the faster the mixed system burns;the longer the length of the combustion tube,the stronger the flame intensity.The effects of inert gases(CO₂,N₂)on coalbed gas-coal dust combustion were studied experimentally.The results showed that with the increase of the concentration of inert gas(CO₂ and N₂),the flame propagation speed and height of the mixed system decreased continuously,and by fitting its velocity,it was concluded that CO₂ had a significant effect on the flame propagation speed of the mixed system.In this paper,the effects of ignition energy and coal powder concentration on the explosion pressure and explosion index of coalbed gas-coal dust mixture system were studied,and the fitting analysis of the experimental results showed that when the concentration of coal powder was 500 g/m3,with the increase of ignition energy,the explosion pressure and explosion index of coalbed gas-coal dust two-phase mixture explosion also increased.When the ignition energy was 2 J,the maximum explosion pressure was 0.72 MPa,the maximum explosion index was 9.22 MPa·m/s,and the explosion danger grade was I.