| During mining of high gas deep coal seams that are prone to spontaneous combustion,the gas and coal spontaneous combustion?G-CSC?concurrent disasters has become the main factor restricting safe and efficient production in coal mines.Extremely complex formation process and various manifestations of G-CSC concurrent disasters make it rather difficult to research on the disaster and lead to the lack of systematic research.The structure and quantity of coal pores determine the physical adsorption capacity of CH4,O2,N2 and other mixed gases,which is an important link between gas disasters and spontaneous combustion disasters.Therefore,this paper investigates the pore evolution law and its influencing factors during coal spontaneous combustion and the influence of pore evolution on the adsorption characteristics of multiple gases such as CH4,O2 and N2.Through research methods such as theoretical analysis,physical experiments,and on-site investigations,the study of the pore evolution law during spontaneous combustion of coal has been carried out,revealing the hazard mechanism of the combined disaster of gas and coal spontaneous combustion under certain conditions,and providing scientific and practical measures to prevent and control composite disasters Theoretical basis.The main conclusions are as follows:The basic law of pore evolution at different scales during the spontaneous combustion of coal is as follows:in the early and middle stage?30110??,the oxidation temperature is low,and the coal-oxygen complex reaction is mainly concentrated on the surface of coal with a low rate,which leads to the slow growth of pore number at different scales,mainly composed of micropores and mesopores.Middle and later stage?110230??,the development of micro hole and the hole in the middle for the coal oxygen compound and migration has increased the amount of O2,making the coal oxygen compound reaction rate began to sharply increase and gradually shift to coal,which resulting in many different pores with higher rate of growth.The development of pores at different scales leads to the increase of total porosity,fragmentation and air leakage intensity of the coal,while the development of pores with different functions leads to the change of the coal's ability of gas adsorption and migration,subsequently reacting on the process of coal-oxygen composite reaction.Through the combination of coal and rock industrial component test system and coal spontaneous combustion simulation test system,the dynamic evolution rules of water content,volatilization,fixed carbon and ash in the coal with the increase of oxidation temperature were researched,and the internal mechanism of coal pore fissure development and its influence on the structural strength evolution in the spontaneous combustion process were revealed.The results showed that:1)In the early stage of spontaneous combustion,the development of coal pores mainly depended on the evaporation of internal water and hydrate dehydration;in the middle and late stage,it mainly depended on the oxidation decomposition of internal macromolecules of organic compounds and the high-temperature pyrolysis of minerals.2)In the spontaneous combustion process of different types of coal,the internal mechanism of pore fracture development is basically the same,which has nothing to do with the degree of metamorphism.However,due to the high content of water and volatile matter in coal with low metamorphism,the pore development rate and degree are higher.3)The increase of porosity in this process destroys the structural integrity of coal,resulting in the continuous decrease of structural strength,which is easy to be broken into coal with smaller particle size under the external forces.Based on the vacuum saturated water measurement system of coal porosity,the dynamic evolution law of porosity with the increase of oxidation temperature,O2concentration and CH4 concentration were studied,and the influence mechanism of different parameters on the evolution of porosity in the spontaneous combustion process of coal was revealed.The results showed that:1)in this process,with the increase of oxidation temperature,the porosity increased slowly at first and then rapidly.The increase in metamorphism does not change this trend,but decreases the increase in porosity at the same oxidation temperature.2)Porosity was positively correlated with O2 concentration.Since pore development in the early stage of spontaneous combustion mainly depends on water reduction,O2 has a more significant incentive effect on the increase of porosity in the middle and late stage of spontaneous combustion.3)Porosity is negatively correlated with CH4 concentration as a whole.When CH4 concentration and oxidation temperature were low,the inhibition CH4 on stomatal growth was not obvious and the extent was low.However,with the increase of CH4 concentration or oxidation temperature,the inhibition effect started to become significant and the amplitude increased.Based on building coal free radicals in situ electron spin resonance test system,studied the Ng g factor value,the concentration of free radicals and the line width?H with oxidation temperature,O2 concentration and the concentration of CH4 and evolution law of coal particle size change,reveals different oxidation parameter through the role in formation of free radicals and annihilation to influence the internal mechanism of pore development process.These showed that:1)In total,with the gradual increase of oxidation temperature,the free radical g factor value and line width?H showed a trend of slow decrease,while the concentration Ng showed a trend of gradual increase;2)The decrease of O2 concentration in the oxidizing atmosphere or the increase of CH4 concentration leaded to the decrease of Ng in the coal,which is basically consistent with the effect on the evolution of porosity.3)The evolution rule of Ng in the spontaneous combustion process of coal with different particle sizes is basically the same,but there is a difference in the Ng values of different particle sizes at the same oxidation temperature,and the difference gradually increases with the increase of the oxidation temperature;4)The pore development leaded to the gradual decrease of coal particle size in this process,thus accelerating the spontaneous combustion process and increasing the risk of spontaneous combustion in the early stage of the second oxidation.Multiple competitive adsorption gas measuring system based on building itself,respectively of the after study of coal low temperature oxidation of CH4 adsorption and initial oxidation temperature and high temperature coal CH4,O2,N2 adsorption capacity at room temperature with the increase of oxidation temperature evolution method,reveals the porosity evolution of CH4 in the process of coal spontaneous combustion,O2 and N2 gas absorption characteristics of the competition.The results showed that:1)The adsorption and initial oxidation temperature of CH4 in the process of low-temperature coal oxidation and the adsorption capacity of CH4,O2 and N2 at room temperature under high temperature were studied.2)Due to the dynamic evolution of the pore number and structure,Qmax-DA and Qmax-MG in the normal temperature state of coal after the initial oxidation showed an overall trend of first increasing and then it goes down as the initial oxidation temperature goes up;3)With the increase of primary oxidation temperature,the evolution trend of QO2-DA and QO2-MG is basically the same.As the adsorption capacity of coal to CH4 is obviously stronger than that of N2 and O2,QO2-MG is smaller than QO2-DA at the same primary oxidation temperature.There are 116 figures,29 tables and 205 references in this thesis. |
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