Study On Gas Emission Rules, Mechanism And Dynamic Model From Coal Particle

The research on gas emission rule, mechanism and model from coal particle is one ofthe key scientific problems to coal seam gas content determination, outburst hazardprediction parameter determination, gas emission of coal drop and CBM development etc.According to a large number of domestic and foreign research contributions, combiningwith the application problems of coal grain gas radiation law, the research objectives andthe main content are determined. The coal grain gas radiation law and its influence factors,gas radiation mechanism and physics&mathematics model are studied by physicalsimulation experiment, experimental determination of pore structure, mathematicalmodeling, theory analysis and numerical solver methods etc, which research resultssupport and promote the consummate of coal grain gas radiation law and mechanism.A novel high-efficiency gas absorption-desorption experimental system on largemass coal sample with temperature controlling function is designed and, by which theinfluence law and mechanism of adsorption balance pressure, metamorphic degree, theextent of damage, grain size, water and environmental temperature to coal grain gasradiation dynamics are studied; pore-crack structure parameters of different metamorphicdegree and different failure types tectonic coal using the mercury injection, lowtemperature liquid nitrogen adsorption isotherm and scanning electron microscopy （SEM）are measured. Combining previous research results of coal molecular and pore-crackstructure, the control characteristics of metamorphic degree and the extent of damage tocoal pore-crack structure are studied, and the dynamic metamorphism problem arediscussed, so that it further perfects the influence law and mechanism of metamorphicdegree and the extent of damage to coal pore-crack structure; According to the gasdiffusion theory in porous media complemented coal grain gas radiation mechanismbased on the experiment study, combined with the changing diffusion coefficient ruleestablished physics-mathematics diffusion model of coal grain gas having three storey’spore-crack structure, found the general solution of the model which got theoreticalanalysis and verification.The results of the study show that gas radiation speed under different adsorptionbalance pressure changes with time, which agree with the relationship: V=B·P^kp·t^-kt adsorption balance pressure gas have little influence on diffusioncoefficient which can be ignored. Metamorphic degree have the same influence on themax ultimate gas radiation and adsorption ability, diffusion coefficient increase with thedegree of metamorphic generally, metamorphic degree have little influence on the maxultimate gas radiation. gas radiation quantity, radiation coefficient and gas radiationspeed of soft coal significantly greater than the hard coal during the same time, basically,the changes between2to10times which decay with time significantly. Difference ofinitial velocity of the gas emission between soft coal and hard coal reduce with thedecrease of the coal sample size, put forward the original particle size concept, differenceof coal grain size is one of the defining features between soft and hard coal, gas radiationparameter KB increase with coal grain size decreases while gas radiation parameterdecreases with coal grain size decreases; Found out the influence mechanism lead to thatgaseous water not only decreases the amount of max ultimate gas radiation, bur alsoreducing initial velocity of the gas emission and diffusion coefficient; Set upexponentially correction change formula of gas radiation quantity and environmentaltemperature, diffusion coefficient increased with temperature rise, found out theinfluence mechanism of the temperature on the diffusion coefficient.The results of pore structure determination show that the degree of damage increasescoal of the total pore volume, mesopores, transition pores, the pore volume of macroporesand the specific surface area, of which mesopores increase most significantly, theconnectivity of pores also significantly improve, and micropores changeunconspicuously; With the improvement of metamorphic degree, overall, coal of totalpore volume have an index decreased, in the same time, macropores, mesopores and thetransition pores also appeared downward trend, micropores gradually increase, and thespecific surface area changes with U-shaped. With the molecular structure of coalresearch, dynamic metamorphism is not obvious.Theoretical analysis shows that it is a gas adsorption-desorption process of coalgrain, which describe by the available gas diffusion in porous media theory, the diffusionmodel includes pore diffusion, surface diffusion and crystal proliferation, in which coalparticles and pore diffusion determines the dynamics of gas the actual parameters of coalparticles by the pore diameter of the diffusion, pore size distribution, tortuosity and connectivity controlled pore structure, which has features with time attenuation.According to the research progress on cognition and gas in porous medium model,this paper established physics-mathematics diffusion model of coal grain gas having threelayers pore-crack structure, derived infinite series general solution of diffusion rate onbleeding time, and gained the exponential relationship between diffusion rate and time,which consistent with the law of coal gas diffusion experiment.