| There are two types of fires:coal spontaneous combustion and gas combustion in the goaf of high gas coal mine.When the combustion range of gas is not large and there is no apparent thermal dynamic phenomenon,the macroscopic phenomena of gas combustion are similar to coal spontaneous combustion.It is easy to mistake the fire cause for coal spontaneous combustion,resulting in the failure to effectively control the fire in the goaf.At the same time,the coal mine site usually takes sealed measures to deal with the fire zone.The fire zone of the high gas coal mine has the hazard of gas explosion after sealed,which can cause heavy casualties and property losses.Based on this,This paper conducted the study on the fire causes in the goaf of high gas coal mines and the hazard of explosions after sealed.The major achievements and conclusions are as follows:The law of gas combustion in the goaf was explained and the four determination criteria for gas combustion in the goaf were proposed.The type of gas combustion in the goaf includes diffusion combustion and premixed combustion.Diffusion combustion is easy to occur at the boundary between the goaf and the working surface,especially in the upper corner,and the premixed combustion tends to occur in the middle of goaf where gas and oxygen are enough.Revealed that rock friction and coal spontaneous combustion are the main potential ignition sources for gas combustion in the goaf by the statistic and analysis of a large number of major gas explosion accidents.The four determination criteria for gas combustion:Firstly,there is no sign of coal spontaneous combustion before happening the fire in the goaf;secondly,the appearance of CO,C2H4,C2H2,etc.is sudden and no process;thirdly,the rockfall of the roof in the goaf has the ability to ignite gas;fourthly,The goaf has a gas combustion environment which can form explosive gas-air mixture.The characteristics of the gas ignite by rock friction in the goaf were studied.The types of rock friction in the fall of the goaf roof includes sliding friction and impact friction.Sliding friction between rocks can ignite gas,and its ignition capacity is related to lithology,friction speed and contact pressure.The higher the quartz content of the rock is,the stronger the friction ignition capacity is.When the lithology is the same,the higher the friction speed is andthe greater the contact pressure is,the stronger the ignition capacity is.Ignition capacity shows a trend of rapid increase after slow increase with the increase of the friction speed and the contact pressure.When the lithology and contact pressure are the same,rock sliding friction has the minimum friction speed and minimum friction distance for igniting gas.Impact friction between rocks can’t ignite gas,and its heating value is related to impact height,rock weight,and impact angle.The greater the impact height and the greater the weight of the rock,the greater the heating value of the impact friction.The heating value first increases and then decreases as the impact angle increases.A prediction model for the variation of gas and oxygen concentration in sealed fire zones was established.The model analysis shows that:When k is large,the gas concentration in the sealed fire zone rises rapidly to the range of explosion limit and the oxygen concentration drops rapidly,but it is hard to drop below the detonation oxygen concentration in a short period of time.It is said that there is the danger of a gas explosion in the fire zone with high gas emission and small volume after sealed in a short period of time;when k is small,the gas concentration in the sealed fire zone slowly increases and the oxygen concentration slowly declines in a short time.It is said that the concentration of gas can’t reach the explosion limit and does not have the hazard of gas explosion in the fire zone with a small ratio of gas emission and volumed uring a short period of time after sealed. |
