Theoretical study on secondary crushing induced by coal particle impact during coal and gas outburst process
Coal and gas outburst is a typical dynamic disaster that threatens the safety produc-tion in coal mine.In this paper,the theoretical process of secondary crushing caused by the im-pact between coal particles or with roadways(obstacles)during the outburst process was ana-lyzed.Then,a mathematical model of secondary crushing was established,and the theoretical limit crushing rate for single and multiple impact of coal particles were calculated.Based on the experimental analysis of secondary crushing of coal particles,the influence of structural differ-ences in coal on secondary crushing and its impact on outburst were discussed.The results indi-cate that when the compressive strength is less than 2 MPa,the limit crushing rate for single impact of coal particles increases sharply with the decrease of compressive strength.When the compressive strength is greater than 2 MPa,the crushing rate increases slowly with the de-crease of compressive strength,and the crushing rate is less than 0.0415％.It is extremely dif-ficult to crush the particle size of coal to below 0.074 mm in two experiments,while the mass ratio of powdered coal below 0.074 mm is both less than 0.41％.The secondary crushing of outburst coal is a necessary process,and the small particles or pulverization coal formed by this secondary crushing play an important role in supplying gas energy during the outburst process.However,the mechanical strength and apparent structure of coal determine its ability to un-dergo secondary crushing.Compared to intact and high-strength coal with intact apparent structure,low strength structural coal is more prone to secondary crushing or pulverization due to particle impact,which also verifies that structural coal is prone to meeting the conditions for outburst.The research results have explained the causes of high fragmentation or pulverization for outburst coal,which help to further reveal the process and mechanism of outburst disasters.
coal and gas outbursttransportation processcoal particle impactsecondary crushingcrushing rate
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