Experimental Study On Crushing Characteristics Of Granular Coal Containing Gas By Dropping Hammer

Coal and gas outburst is a dynamic phenomenon of coal and rock under the comprehensive action of many factors.According to the statistics of the outburst position,the outburst mainly occurs in the front working face of underground operation,and the excitation of outburst is generally affected by the impact condition of mining work.In this paper,according to the impact crushing characteristics of gas containing granular coal,we independently designed and built a drop hammer impact crushing experimental system for gas containing coal.Taking 7#coal seam of Xiaoqing coal mine and 3₂#coal seam of Zouzhuang coal mine as samples,we compared the differences of basic parameters of the two coal samples,and carried out drop hammer crushing experiments under different gas pressure conditions,and analyzed the particle size distribution of broken coal under each pressure.The main conclusions are as follows:(1)The basic physical parameters,gas adsorption capacity and pore structure characteristics of XQ and ZZ coal samples were compared and analyzed in detail through experiments.The two coal samples are medium rank coal with similar coal quality and adsorption capacity.The hardness of XQ coal sample is higher than that of ZZ coal sample.The pores of the two coal samples are mainly micro pores below100nm,but the development degree of micro pores of XQ coal sample is higher than that of ZZ coal sample,and the proportion of pores above 1000nm of ZZ coal sample is larger.The pore types of the two coal samples are similar,and there are a lot of ink bottle and conical pores.(2)Based on the drop hammer impact loading method,a set of experimental system which can be used for impact crushing of gassy coal is designed and built.Through the analysis of falling hammer time,the falling hammer speed and impact energy of different gas pressure in the instrument are explored.The greater the gas pressure,the greater the impact of gas resistance on the heavy hammer in the process of falling.The drop time,final drop velocity and average drop acceleration decrease with the increase of gas pressure.XQ coal sample and ZZ coal sample in different gas pressure after the same energy drop hammer impact,ZZ coal sample after crushing coal quality is greater.And with the increase of gas pressure,the quality of broken coal increases gradually,showing a certain exponential relationship with gas pressure.(3)The four commonly used particle size distribution models can describe the particle size distribution in a certain range after crushing.The results show that the mass percentage on the sieve of XQ coal sample after crushing obeys Gauss distribution,and the fitting degree decreases with the increase of gas pressure;the mass percentage on the screen of ZZ coal sample after crushing obeys Lognormal distribution,and the distribution result is little affected by gas pressure.The results show that the cumulative content distribution of coal particles under the sieve of XQ coal sample and ZZ coal sample after crushing obeys the Logistic distribution,and the fitting parameter d_k shows a decreasing trend with the increase of pressure.After the coal sample is broken,the volume average diameter,area average diameter,D10,median diameter D50 and D90 converted diameter of coal particles decrease with the increase of gas pressure,showing a exponential function.The influence of gas on impact fracture of two coal samples is different.For XQ coal sample,gas mainly affects its particle size distribution;For ZZ coal samples,gas mainly affects the amount of crushing.(4)According to the data of particle size distribution,the crushing specific work of coal sample is calculated.The influence of gas on coal and gas outburst index parameters such as crushing specific work and firmness coefficient is discussed.In the experimental pressure range,with the increase of gas pressure,the new surface area of two coal samples increases and the specific work of crushing decreases.The impact crushing of XQ coal sample is more affected by gas pressure than that of ZZ coal sample.The results show that the total crushing work,unit mass crushing work and specific crushing work have exponential relationship with the pressure.That is to say,under the same crushing energy,the greater the gas pressure,the less energy consumed by the impact crushing of coal sample,and the more prone to crushing or pulverization.When the gas pressure increases from 0 MPa to 0.75 MPa,the calculated value of firmness coefficient f of XQ coal sample decreases more than that of ZZ coal sample.The results show that the firmness coefficient of the harder XQ coal sample is greatly affected by gas pressure,while the softer ZZ coal sample is less affected by gas pressure.There is a negative exponential relationship between the firmness coefficient of coal sample and gas pressure.The thesis contains 44 figures,18 tables and 107 references.