Research on the rapid determination technology of the consistent coefficient f of coal based on the crushing method

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ABSTRACT The consistent coefficient f of coal is a comprehensive index of the ability to resist the damage of external forces determined by various properties of coal. In the Chinese coal industry, it is listed as one important basic index of the four single indexes to judge the risk of coal and gas outburst. At present, the consistent coefficient f can only be determined by the dropping hammer method in the laboratory after the coal sample is collected on the working surface, and cannot be directly determined under coal mines. But the dropping hammer method is relatively cumbersome to operate, and the determination process is easily affected by the operation of the experimenters, so it cannot achieve the purpose of rapid prediction of coal and gas outburst danger. Therefore, a new method for rapidly determining the consistent coefficient f of coal based on the pulverization method is proposed, the principle of this method and the specific determination steps are given. And the optimal combination scheme of the key parameters of coal sample pulverization is established by the orthogonal test, which are given as follows: the initial particle size of the coal sample is 6 ~ 7 mm, the pulverization speed is 8000 rpm, the coal sample mass is 150 g, and the pulverization time is 10 s. Based on the analysis of pulverization data of the original coal samples collected from more than sixty coal mines in eleven major coal-producing areas with different geographical distribution in China, the experimental results show that the logarithmic fitting relationship is shown between the ƒ value and the mass ratios of the coal particles under different particle size after coal samples pulverized. With the coal particle size increasing, the fitting correlation degree gradually decreases. Among them, the fitting correlation degree between the mass ratio of coal particles below 0.5 mm particle size and the f value is the highest, and the correlation coefficient R2 is 91.7%. Based on the findings, the model for rapidly determining the consistent coefficient f of coal based on the pulverization method is established. And the consistent coefficient ƒ determined by this new method is very close to the ƒ value determined by the dropping hammer method. The absolute value of the error is within the range of 0 ~ 0.06, and the absolute value of the relative error is controlled within 10%, about 7.9%. This new method realizes rapid determination of f value of coal, overcomes the factors affecting the accuracy of determination by the dropping hammer method widely used at present, has the characteristics of simple and convenient operation, fast and accurate determination, and can meet the actual determination requirements under various conditions. The research results lay a strong research foundation for directly and rapidly determining the consistent coefficient ƒ of coal under coal mines.