Determination Of Danger Zone For Spontaneous Combustion Of Regenerated Roof Coal And Study On Particle Stabilizing Foam Control

Coal resource is one of the important energy resources in China.Every year,a large number of resource waste and economic losses are caused by coal spontaneous combustion.During the secondary mining of the top and bottom coal of medium thick coal seam and thin coal seam,the roof falling from the original goaf is mixed,compacted and cemented with the residual coal,gangue and water in the goaf through the action of stratum stress to form a regenerated roof.In the process of secondary mining,the stress field of coal and rock changes,and the regenerated roof is affected by the disturbance of coal mining.The primary cracks in the roof increase and expand,and the secondary cracks increase,forming a plurality of air leakage channels.Under the ventilation condition of the working face,the residual coal in the roof is in a good oxidation environment and has the possibility of natural ignition.The spontaneous combustion of residual coal in the roof will directly affect the roadway temperature and increase the concentration of toxic and harmful gases in the roadway,which poses a serious threat to the safe production and mining underground.In view of the problems that it is difficult to find the residual coal in the early stage of renewable roof,the law of air leakage is not clear,and the prevention and control work is difficult to carry out,this paper takes Zhoujing coal mine in Guangxi Zhuang Autonomous Region as an example,analyzes the spontaneous combustion characteristics of coal sample in coal seam 3 of Zhoujing coal mine through temperature programmed experiment,determines80 ℃ as the critical temperature of coal self combustion,and obtains the relationship between oxygen concentration and oxygen consumption rate of coal sample.Based on the field situation of 5304 working face in Zhoujing coal mine,the physical model of return air roadway and broken roof is established,and the air leakage law and oxygen concentration change law in the model are analyzed by using COMSOL multiphysics simulation software.The simulation results show that with the increase of wind speed,the risk area of coal spontaneous combustion increases gradually.When the wind speed is 1.5m/s,the dangerous area of coal spontaneous combustion still reaches 12.7% of the model volume,indicating that the hidden danger of coal spontaneous combustion still exists at low wind speed.On this basis,the temperature rise law in the dangerous area is further analyzed.The results show that the temperature field distribution under different wind speeds is relatively similar.The high-temperature area is mainly concentrated in the front half of the roof,and the high-temperature points are distributed about 28 m-38 m away from the air inlet.The time when the temperature in the roof reaches the critical temperature is different under different wind speeds.Increasing the ventilation volume of the roadway within a certain range will shorten the natural ignition time of coal.In view of the difficulties of prevention and control of regenerated roof,through characterization experiment,particle suspension experiment and stability experiment,it is determined that the best proportion of particle stabilized foam material is 0.4 wt% sodium alginate and 25 wt% fly ash,and the best mixing ratio is 5 times.The suspension mechanism and stability mechanism of the material are analyzed,and then the excellent inhibition characteristics of coal spontaneous combustion are determined by temperature programmed experiment and coal pile fire extinguishing experiment.Based on the high temperature monitoring results of 5304 coal mine,the on-site numerical control scheme of coal spontaneous combustion had been developed and implemented in time.Through the field control results,it verifies the veracity of the decision model of the spontaneous combustion danger area of the regenerated roof coal and the effectiveness of the particle stabilized foam material,and provides a reference scheme for the prevention and control of the spontaneous combustion of the same type of recycled roof coal.