| Recently in the actual mining process of various coal scams in the mines in the north of Shaanxi province the problems of exceeding the limit of disaster gas such as CO in the upper comer of the working face have often appeared in different degrees,which has become a major dangerous source for restricting the safe production of mines.In this paper,the upper comer in the fully mechanized mining face of 1406 in Fengjiata Coal Mine is taken as the main research object.Through the combination of field survey,theoretical analysis and numerical simulation,the characteristics of the gas accumulation at the corner of the working face are studied,and the essence of energy dissipation in the process of gas accumulation in the lag zone is also studied to seek effective treaatment methodsThrough on-site inspection and investigation of the source of CO in the corner of Fengjiata 1406,it is concluded that the isolated coal pillar near the working face and the coal in the goaf are the main sources of CO overshoot in the upper corner.According to the CO source of the isolated coal pillar and the goaf,the the five main influencing factor such as the temperature in the goaf,the daily propulsion speed,the air volume in the return air,the air leakage and the cycle arc selected as the observaion factor.Applying the grey relational theory of embedded entropy weight,the entropy weight grey correlation model of CO overrun and its influencing factors is established.The correlation degree of each influencing factor to the CO concentration of the upper corner is obtained as follows:air leakage>return air Lane air volume>cycle to pressure step>daily propulsion>goaf temperatureBy implementing the observation method of the gas conccentration and air pressure on the working surface,the CO concentration in the upper corner generally shows a fan-shaped change trend from the upper corner to the zone of main wind.Based on the equivalence and uniformity of information entropy and thermodynamic entropy,the entropy analysis and entropy flow discrimination of the upper corner ventilation system are carried out.The results show that the trend of CO concentration and information entropy of CO concentration is basically consistent,showing the information entropy can well characterize the gas accumulation characteristics of the disaster gas in the upper corner,and the turbulence of the positive entropy property caused by the irreversible process such as eddy current loss and the energy flow are the essence of the local accumulation of dangerous gases in the upper corner.The pressure and kinetic energy in the upper corner region of the air flow flowing along the working surface are the energy flow of the negative entropy property of the system increasing the order degree and reducing the total entropy,which can realize the reduction process of the entropy flow of the change of the system from disorder to order.Based on the analysis of the law of overburden strata on the working face,the "lane-like"model for numerical simulation of the airflow field in the goaf of the working face is established,and combined with the characteristics of the local ventilation system of the 1406 working face,air flow field in the goaf in the working face is simulated.It can be concluded that the oxygen concentration generally showed a trend of increasing oxygen concentration from the bottom plate to the top plate.The CO concentration generally showed a high concentration near the top plate and a "U" type changing trend at the middle bottom.The airflow field in the local part of the Upper-corner is analyzed,and the influence of the spatial shape of the stope on the gas flow and accumulation law is studied.It is concluded that the irreversible process such as eddy current loss caused by the spatial shape of the lag zone in the upper corner is an important cause of gas accumulation.The eddy current phenomenon in the lag zone can be significantly eliminated by means of gas drainage of the gas-filled air bag. |
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