| The tendency of coal spontaneous combustion in Ningdong coalfield is easy to spontaneous combustion and its shortest coal spontaneous combustion period only 18 days,resulting in frequent spontaneous combustion disasters in goaf.In the mining process of full-mechanized caving face,during the period of stoping and removing the frame,and the working face with large mining height,there are many accidents of coal spontaneous combustion closed working face,among them,the reburning occurred in a short time after the traditional fire-fighting measures were taken in the II020210 working face of Yangchangwan.Ningdong coal chemical industry base produces a large amount of carbon dioxide waste gas every year.If carbon dioxide is liquefied and used for cooling,inerting and other functions to normalize coal seam spontaneous combustion fire control and prevention,a win-win situation of waste utilization will be formed.This study based on liquid carbon dioxide inert and low temperature properties,selecting typical ningdong coal sample as the research object.Through the experimental analysis of liquid carbon dioxide in the loose coal adsorption,cooling and the diffusion rule,using numerical simulation software simulation migration regularity under different working conditions with the corresponding heat transfer and mass transfer process in goaf,the key technology of efficient fire prevention and control for large flow liquid carbon dioxide pipeline was studied.The results show that:(1)Liquid carbon dioxide is more easily adsorbed by coal than nitrogen,which is conducive to.the suppression of spontaneous combustion of coal;The larger the coal particle size,the better the cooling effect;Diffusion and movement of loose carbon in the form of free diffusion of gaseous carbon dioxide and impact of liquid carbon dioxide shock wave migration change cooling zone,convection cooling zone,conduction cooling zone and diffusion cooling zone;At the same time,the effect of cooling and preventing reignition is obviously better than that of liquid nitrogen.(2)The cooling area is mainly around the release port after the carbon dioxide is released from the goaf.In the longitudinal direction,heavy gas diffuses and gathers near the bottom of goaf.Transverse diffusion mainly depends on pressure and concentration gradient,and the concentration area is relatively concentrated.When the distance between the pressure injection port and the working face is 40-60m and the pressure injection flow rate is about 5kg/s,the inerting works better of carbon dioxide is the highest.The best way to diffuse carbon dioxide when the wind flow in the wind tunnel is 0.5m/s.(3)The calculation method of the minimum safe transport distance between horizontal and vertical sections in the process of liquid carbon dioxide pressure-retaining transport is VT×L?T0-Tc.The minimum safe conveying distance between horizontal and vertical conveying processes is determined,and the carbon dioxide can be transported safely in the pipeline in liquid and gas phases within the control range.At the scene,a liquid carbon dioxide transmission fire prevention technology with a flow rate of up to 60T/h,a horizontal conveying of 4000m,and a vertical conveying distance of 1000m was adopted.A typical coal spontaneous combustion hazard working face in Ningdong mining area was selected to carry out the application of efficient fire prevention technology for liquid carbon dioxide pipeline transportation.After controlling the closed fire area on Qingshuiying 110205 working face,all the indicators met the unsealing conditions and were successfully unsealed after 18 days.It has realized effective control and prevention of recurrence of II020210 working face in yangchangwan coal mine.In the meanwhile,it has been successfully applied in the prevention of spontaneous combustion in goaf during withdrawal period in 120215 open working face and temporary stoping period in II020205 fully-mechanized caving face of Yangchangwan coal mine. |
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