Study Of The Oxygen Depletion Characteristics Of Working Faces In Shallow Buried Close Coal Seam Groups

With the increasing depletion of mineral resources in the central and eastern regions of China,the strategic focus of coal mining has gradually shifted to the northwest region,which will serve as an important base for the supply of coal resources.In recent years,a number of large mines such as Shendong mine,Wuda mine,Jinggong mine and Datong mine have been built in the northwest region.Most of them have shallow buried close coal seams,and most of them have become depleted of oxygen in the corner of the working surface during mining,which threatens the mine production and personnel safety and needs to be solved urgently.This paper takes Daheng coal mine as the research object,through numerical simulation,field verification,experimental research and theoretical analysis,etc.,to carry out research on surface fissures and air leakage patterns of shallow buried close coal seam group mining,research on coal oxidation characteristics under anoxic conditions,and research on the causes of anoxia at the working face and prevention and control techniques.(1)The overburden destruction and fissure evolution law during the mining of the three-bedded coal was simulated by CDEM numerical simulation software,and the wind leakage channel penetration mechanism of the working face of the surface-overburden mining area-underburden coal seam was obtained.The results show that with the mining of the three seam coal,the overlying rock structure is destabilised and fissures are gradually developed to form wind leakage channels,and significant subsidence occurs at the surface.At the same time,SF6 tracer gas was used to verify the existence of air leakage channels,and the average oxygen concentration in the upper corner on a single day was recorded as 17.48%,which was lower than the prescribed standard oxygen concentration,making it clear that the formation of air leakage channels in the shallow buried near coal seam group mining led to the phenomenon of oxygen depletion at the working face.(2)Through the C600 microcalorimeter test system and the oxygen and nitrogen gas distribution system,the changes of heat flow,heat release and oxidation kinetic parameters in the coal oxidation reaction under oxygen-poor conditions were obtained.The results show that with the decreasing oxygen concentration,the heat generated by the oxidation reaction of the coal body still occurs under the depleted oxygen conditions,and the heat generated also decreases with the decreasing oxygen concentration,the heat flow curve shows a general trend of decreasing and then increasing,while the activation energy shows an increasing trend,and the heat generated by the coal oxygen reaction then accelerates the oxidation reaction and aggravates the depleted oxygen environment.(3)Through numerical simulation,field validation,experimental research and theoretical analysis,we obtained that the cause of oxygen depletion in the corner of the working face of the shallowly buried close coal seam group is the coupling effect of various factors,such as air leakage channels,oxygen depleted bodies,negative ventilation pressure and ventilation methods,and adopted a comprehensive prevention and control technology with the aim of sealing the air leakage,preventing the oxidation of coal relics in the mining area and local ventilation in the upper corner.The paper presents guidance for the production of mines with shallow buried close coal seams.The paper has 46 figures,15 tables and 96 references.