Study On Dynamic Characteristics Of Coal And Gas Outburst Ejecta In Roadway

The occurrence of coal and gas outburst is accompanied by strong dynamic effect,the outburst shock wave and coal-gas two-phase flow burying will cause certain casualties.The outburst gas may reverse the wind flow into the air inlet system,then expand the scope of the accident,causing more suffocation casualties.In case of ignition sourees,it may also cause gas and coal dust explosion,causing more casualties.To study the dynamic behavior characteristics of coal and gas outburst can provide theoretical guidance for formulating scientific disaster prevention and relief measures and preventing the expansion of outburst disaster.In this paper,take the dynamic characteristics of coal and gas outburst ejecta in roadway as the research subject.Based on the field case analysis and utlizing the theoretical knowledge of aerodynamics,the outburst gas and coal-gas two-phase flow ejection characteristics are analyzed,and the dynamic model of coal and gas outburst is established.According to the similarity theory,a set of simulation experiment system for dynamic effect of coal and gas outburst was developed,and six outburst dynamic effect simulation experiments were carried out using fresh full size coal samples from K₁ coal seam of Huaying Longtan coal mine,and the dynamic response characteristics in the roadway during the outburst process were studied.The formation and propagation law of outburst shock wave in roadway are studied by using Fluent software.The main achievements are as follows:(1)A set of physical simulation experimental system which can simulate the dynamic characteristics of outburst is developed.The experimental system mainly includes four core modules:outburst hole power system,outburst excitation device,roadway simulation system and data acquisition and control center.The outburst hole power system can simulate different volumes(simulate different outburst strength)of outburst hole containing gas-bearing crushed coal,coal-gas two-phase flow,gas emission from hole wall,etc.The experimental system can simulate the formation and propagation of outburst shock wave with maximum overpressure of 233.33 k Pa.(2)The dynamic model of coal and gas outburst was established,and the mathematical expression of gas,coal-gas two-phase flow was deduced based on the aerodynamic theory.The simulation experiments of outburst dynamic effect with different gas pressure and outburst intensity were carried out,and the variation of outburst coal-gas two-phase flow intensity with the cavity gas pressure and time was analyzed.(3)The evolution model of coal and gas outburst disaster in the roadway is established.The results show that the shock wave is formed in the pipeline when outburst excitation,followed by the impact flow,outburst gas flow and coal gas two-phase flow.The speed relationship between them obeys:the outburst shock wave velocity>the impact gas velocity>the gas outburst velocity>the outburst coal gas two-phase flow front velocity.The experimental results show that the theoretical model of coal and gas outburst disaster evolution in the roadway is verified,and the dynamic effect in the outburst process is reappeared.(4)Through theoretical analysis and physical simulation experiment,the prediction model of outburst shock wave overpressure is established;based on experimental research,the law of peak overpressure attenuation of outburst shock wave with propagation distance in roadway is obtained,that is,the peak overpressure of shock wave is inversely proportional to the square of propagation distance(x²).(5)The initial migration velocity of outburst coal-gas two-phase flow front is positively correlated with outburst hole gas pressure,and the migration velocity has a certain fluctuation.The main reasons for the fluctuation are the uneven distribution of coal particle size and the state change of outburst gas flow.In the process of outburst,most of the energy is used for coal crushing,only a small part of the energy is used for coal throwing,and the crushing work is about an order of magnitude larger than the throwing work.Only a small part of adsorbed gas does work in outburst,but the expansion energy of adsorbed gas is the main energy source for outburst developing.(6)Based on the constitutive equation of compressible flow process,the dynamic model of high-pressure gas emission and migration is established.Combined with the physical simulation experiment model,the formation and propagation process of shock wave and outburst high-pressure gas are analyzed by means of Fluent numerical simulation software.Based on the simulation results,the overpressure prediction model of outburst shock wave established in Chater 2 is verified.