Research On The Space-time Evolution Law And Controlling Technology Of Coal Spontaneous Spontaneous Combustion For In Contiguous Coal Seam’s Composite Long-wall Gobs

The problem of coal spontaneous combustion in composite goaf in coal seam group at close range in China is extremely serious.So the research on the characteristics of coal spontaneous combustion in composite goaf and its technology of prevention and control has always been the focus and difficulty in the field of safety of coal mine in Shuangyashan Mining Area.Based on the actual field conditions and the characteristics of coal left in composite goaf in coal seam at close range,such as repeated oxidation,immersion and air dry and so on,the paper focuses on the characteristics of coal spontaneous combustion,mechanism of spontaneous combustion and gas change in composite goaf in coal seam at close range.By constructing the model of coal spontaneous combustion in the process of dynamic advance in the composite goaf,the temporal and spatial evolution of the temperature field in the goaf in the process of mining of the upper and lower coal seams in the composite goaf is mastered,which can predict and judge the high temperature region in advance.Finally,a comprehensive method with plugging,wind control and rapid inerting and cooling for prevention and control of coal spontaneous combustion in composite goaf in coal seam at close range is built.The main research results obtained are as follows:(1)The mechanism and process of coal spontaneous combustion are very complex due to the repeated oxidation of coal in goaf.The characteristics of spontaneous combustion of raw coal and preoxidized coal are compared and analyzed.The results show that the gas index of preoxidized coal,such as CO、C2H4、oxygen consumed et al.,substantial change time in the process of spontaneous combustion is about advance 50%earlier than that of raw coal.In addition,compared with raw coal,the apparent activation energy of preoxidized coal is reduced by 40%,and the times of adiabatic spontaneous combustion period is shortened by nearly 1/2.(2)The influence of preoxidation degree on coal spontaneous combustion process is analyzed.It is show that the TG curve of coal samples with different preoxidation degree is basically the same.As the degree of preoxidation increases,compared with the raw coal,the spontaneous combustion characteristic temperature of the secondary oxidized coal decreases first and then increases.The oxidation reaction rate and heating rate of the pre-oxidized coal at low temperature are both faster.The main gas products in pyrolysis process of different preoxidation degree are CO,CO2 and H2O.The amount of gas emission increases first and then decreases with the increase of temperature.Before the coal reached the ignition temperature(410-420 ℃),with the deepening of the degree of preoxidation,the gas product increased first and then decreased,but remained basically unchanged after the ignition temperature.(3)After water leaching and air drying,the specific surface area of coal increased significantly,the pore and fissure structure developed more,resulting in the increase of coal and oxygen contact opportunities,oxygen absorption increased,coal oxidation at low temperature increased heat release.At the same time,the number of oxygen-containing functional groups and aliphatic hydrocarbon groups on the surface of coal samples after soaking and drying were higher than that of raw coal samples.These changes lead to the increase of spontaneous combustion tendency of coal.(4)The large experiments of spontaneous combustion of coal show that the soaked coal in self-heating process can be divided into three stages:low temperature oxidation stage,water evaporation stage and accelerated oxidation stage.However,the coal of reburning process consists of slow oxidation process and accelerated oxidation process.In either stage,the self-heating rate of the reburning process is higher than that of the initial spontaneous combustion process,and the spontaneous combustion period of the coal sample after soaking and drying is lower than that of the initial spontaneous combustion 1/3.At low temperature,the production rate of CO,C2H4 and other gases of soaked coal in air-soaked coal samples is lower than that of raw coal samples.(5)On the theory of moving coordinates,the temperature field model in the goaf in the process of steady-state advance of the working face is established,and the dynamic simulation of the high-temperature area of coal spontaneous combustion in the composite goaf is conducted.According to the distribution characteristics of the temperature field and the field data,it is determined that the danger zone of spontaneous combustion in the composite goaf has obvious distribution along the air leakage channel and is close to the inlet side of the coal seam;the acceleration of mining speed will cause the significant reduce of the high temperature area in the upper goaf.Combined with the characteristics of the shortest spontaneous combustion period and the range of high temperature,the minimum advance of the composite coal seam in the No.2 mining area of Dongrong No.2 Mine is 3 m/d.(6)Finally,the comprehensive fire-fighting technology with plugging-inerting-lowering in composite goaf is proposed,namely plugging and reinforcement by sealing,pressure equalization,drilling and injecting composite colloidal material,injection of liquid carbon dioxide,etc.The spontaneous combustion of in coal seam group at close range of Dongrong No.2 Mine was effectively controlled,and the key technical system for prevention and control of coal spontaneous combustion in composite goaf was constructed.The research results have a great helpful for mastering the characteristics of spontaneous combustion,identification and location of fire positions in contiguous coal seam’s composite long-wall gobs.Finally,it is always important to application and prevention for underground coal fires.