Research On Gas Desorption Characteristics Of Pulverized Coal And Its Quantitative Effect On Outburst Dynamics

With the continuous exploitation and utilization of coal resources,the mining depth of coal mine is increasing,which greatly improves the risk of coal and gas outburst.Disasters can not be avoided with the existing outburst theory and outburst prevention technology yet.The research on outburst propagation and disaster causing characteristics is very necessary.Coal and gas outbursts are accompanied by strong coal pulverization effect,and the gas desorbed by pulverized coal will in turn promote the development and spread of outbursts.Quantitative research on the energy contribution of desorption gas in outbursts and the effect of desorption gas on two-phase flow dynamics can enrich and improve the disaster-causing mechanism of coal-gas outburst and guide the work of outburst prevention and disaster reduction.Using the theoretical knowledge of rock mechanics,aerodynamics and two-phase fluid dynamics,this thesis quantitatively studies the energy contribution of pulverized coal rapid desorption gas to outburst process by means of theoretical analysis,numerical simulation,laboratory experiment and similar simulation,and works out the quantitative results of the effect of pulverized coal desorption gas on outburst two-phase flow dynamics.In the similar simulation experiment,the desorption/non-desorption gas control experiments are used to verify the important role of gas absorption in the development of outburst.The main conclusions are drawn as follows:（1）The particle size distribution of the outburst coal shows the characteristics of polarization,and the strongly pulverized coal below 3mm and large coal blocks account for a large proportion.The pulverization process will open the closed pores and fissures in the coal body,making more internal space in contact with external gas.In terms of desorption performance,the desorption amount of 0.075-0.15mm coal sample in the first 5s is 46.7-92.9%larger than that of 1-2.36mm coal sample,and the cumulative desorption amount within 1800s is 48.04-88.53%larger.Aiming at the short duration of outburst,an initial gas desorption model of pulverized coal is established,and the internal mechanism of rapid gas desorption in the early stage of highly pulverized coal is explained theoretically.（2）The formation of outburst two-phase flow is divided into two aspects:coal pulverization and gas emission.The failure pulverization of outburst coal has experienced three stages:stress concentration failure stage in front of the working face,outburst spalling and stripping stage,and collision pulverization stage in the propagation.The outburst gas mainly comes from the coal thrown out and the coal around the outburst hole.Based on the spalling and throwing process of coal during outburst,the prediction model of gas emission rate during and after outburst is constructed.Taking the real outburst case as the background,the reliability of the model is verified from three aspects:the total amount of outburst gas,the release law and the attenuation law of shock overpressure.（3）Based on the outburst gas emission rate model and Zhongliangshan outburst experiment,it is found that the desorption gas emission rate is low in the initial stage of outburst.With the increase of outburst coal,the desorption gas emission rate increases sharply,exceeding the free gas emission rate at 16.77s.The desorption gas accounts for 54.89%of the total gas emission amount in the duration of outburst.Combined with gas desorption data of pulverized coal in laboratory,it is found that the greater the adsorption equilibrium pressure（coal seam gas pressure）,the higher the pulverization degree of outburst coal（low coal strength）,and the higher the contribution rate of desorption gas.Among JG82 coal samples,the contribution rate of gas desorption of coal samples with particle size of 0.075-0.15mm is 5.03-5.93 times that of coal samples with particle size of 1-2.36mm.By comparing the variation range of desorption gas contribution rate of tectonic/non-tectonic coal（13.77～92.06%）,it can be concluded that desorption gas plays a decisive role in the development of outburst.（4）Through the quantitative research on the aerodynamic characteristics of outburst shock airflow,it is found that the main energy source of outburst dynamic effect is the expansion energy of high-pressure gas,and its state quantity gas pressure potential energy can be calculated by the formula.The greater the initial gas pressure,the stronger the outburst power generated.The initial gas pressure has a significant effect on the initial PPERR（Pressure potential energy release rate）value,and the relationship between them is basically linear,with a coefficient of 0.263.The solid particles in the two-phase flow hinder the release of pressure potential energy in the high-pressure cavity.When the caliber increases to 80%of the outburst chamber,the energy release rate from the chamber is the largest,which explains the outbursts in mines are so violent due to the spatial structure with small caliber and large internal space to some extent.（5）The maximum energy release intensity when considering the desorption gas in Zhongliangshan outburst is 4.82 times that without the desorption gas.Under the same conditions,the maximum energy release intensity when the desorption gas rate of tectonic coal is involved in the outburst is 3.92 times that with non-tectonic coal.Combined with the gas desorption conditions of pulverized coal,when the coal seam gas pressure is 3MPa,the maximum energy release rate of JG82 coal sample of0.075-0.15mm is 5.72 times that of 1-2.36mm coal sample.Gas pressure in coal seam and pulverization degree of outburst coal are the key factors affecting the intensity of outburst power,and they are also the important considerations in the evaluation of the outburst disaster grade for the coal seam.（6）Through the outburst similarity simulation control experiments,it is found that with the same outburst pressure,the relative outburst intensity of CO₂ as outburst gas is 8.08-12.48%higher than that of N₂,and the difference in the farthest outburst distance can reach 2.89m.When the outburst pressure is 0.5MPa,in the experiment of1-2.36mm coal sample with N₂,the overpressure attenuation from 1#sensor to 4#sensor is 83.01%,while it is only 63.16%using<0.25mm coal sample with CO₂.The results show that the desorption gas of pulverized coal participates in the outburst development process and plays an important role.The higher the degree of coal pulverization,the greater the contribution of desorption gas to outburst.（7）Through the results of the energy contribution of desorption gas in outburst experiments,it is found that the total outburst energy increases almost linearly with the increase of outburst pressure,and the total outburst energy of coal samples with particle size<0.25mm is 1.50～1.68 times that of coal samples with particle size of1-2.36mm.The energy contribution rate of desorption gas also increases with the increase of outburst pressure.For coal samples with larger particle size of 1-2.36mm,the energy contribution rate of desorption gas increased from 31.97%to 40.06%,while the contribution rate of desorption gas energy exceeded that of free gas for coal samples with particle size of<0.25mm,and the contribution rate reached 50.29～52.76%.The key role of desorption gas of pulverized coal in the outburst development was verified from the perspective of similar experiments.