Study On Gas Drainage And Fire Prevention In Goaf Under CFD Model

Cyclonic static micro-bubble flotation is a new column separation method and device with China self-owned intellectual property.The successful application of this equipment in coal preparation along with its special cyclonic field structure has laid a solid base for the further application of column flotation in mineral processing.As a typical mining representative of high gas complex coal seams,Huai nan mining area has achieved great success in simultaneous extraction of coal and gas.This article takes the Dingji Coal Mine where gas production has high success rate as research field,the gas distribution law of pressure relief in mined out area under protective layer mining(the pressure relief gas distribution law in the gob under protective seam mining,gas migration law in gob under gas extraction,changes of three zone distribution under gas extraction and the optimum layout of ground well have been studied systematically in this paper.Based on the amount of gas emission,the prevention and control measures such as nitrogen injection have been proposed aimed at spontaneous combustion coal containing methane.The reasonable position of the ground well was determined according to the theory of high ring fracture zone in the gob.The relationship between the drilling gas production and mining active process of the protective layer face was investigated and analyzed.The flow pattern character of pressure relief gas,the ground drilling failure prevention measures and the rules of gas flow were summarized.We established the user-defined function to set up the gob permeability distribution,the gas emission quantity and parameters like this,using the computational fluid dynamics simulation software FLUENT as a research tool.The distribution law of gas migration and the effect of drainage on the distribution of three zone in the gob are obtained by the simulation:(1)The ground drilling extraction will form a low pressure area,which increases the invasion of the oxygen from the surrounding fracture to the gob.The distribution of the gas flow field in the gob is related to the location of the well.Well drainage near the face can effectively decrease the return airway gas concentration and the high concentration gas can form inert zone in the deep gob.The gas released by the protective layer can be drained effectively by well near the starting cut,but it is much easier to transfer the oxygen to the deep part of the gob,the gob oxygen content increases sharply when using the large flow drainage model.(2)Stereo drainage is easy to make the air leakage channel connectionto each other,the nitrogen injection can have good effect to inert the area in the intake airway side and the deep of the gob.Nitrogen injection in deep point can achieve better inert effect than in shallow point at the same injection flow.In the return side of the gob,nitrogen losing seriously duel to air leakage,which contribute to the existence of high temperature region.(3)Combined well drainage may form a relatively uniform low pressure area in the gob,which can distribute the pumping capacity of the well reasonably.At the same time,the oxygen enrichment zone in the gob will not increase rapidly,the maximum extraction of the gas in the gob can be achieved under combined drainage model.(4)while the mine gas emission quantity is less than 40m3/min,it is effective to control the gas transfinite problem by using the underground gas drainage.When the amount of gas emission is more than 40m3/min,it is necessary to take comprehensive measures to control the gas overrun problem.The engineering practice of pressure relief gas drainage at protective seam In Dingji coal mine shows that the gas flow rate changes with the advance of working face,the anti destruction ability of ground drilling has great influence on the efficiency drainage of gas.The high efficient drainage time of the well can last more than 6 months if the drilling work properly,when the face stop moving,the well can still drainage gas accumulated in the gob,the effective pumping period is more than 3years.During the investigation of Dingji mine,the monthly average pure flow rate of surface borehole is 6.32 ~ 14.27m3/min,the accumulate amount is 16635631m3,which accounted for 27.52% of the total extraction.The average monthly pure flow rate of high pumping lane and roof drilling is 2.87 ~ 20.63m3/min,the accumulate capacity is 30326880m3,which accounted for 50.16% of the total extraction.The drainage methods of surface well,high level suction roadway and strike drilling in the underground can get high concentration gas and have long pumping cycle,which will not affect the coal production and may control the gas disaster in the high gas coal seam effectively.The research of this article help to gas control and prevent the coal spontaneous combustion fire under the condition of gas-extraction in some degree.