| Spontaneous combustion of coal is one of the main reasons for fires in mines.Spontaneous combustion of coal in goafs mainly occurs in leftover coal and cracked coal pillars.This part of coal is under pressure from the overlying rock and its oxidation environment changes.In addition,the cracks caused by mining make surface water and groundwater seep into the goaf,causing water to accumulate in the goaf.Moisture affects the surface structure of coal,heat absorption and heat release,free radicals,etc.,which will change the oxidation science of coal.The progress of the reaction.This paper takes coal with different moisture content as the research object,and uses a method of combining theoretical analysis and experiment to compare and analyze the physical structure and spontaneous combustion characteristics of coal with different moisture content under stress.At the same time,it analyzes the coal with different moisture content under stress.The microscopic characteristics of spontaneous combustion after oxidation reveal the reasons for the differences in the oxidation and spontaneous combustion characteristics of coal samples with different moisture content under different stress conditions.The experimental results have important practical significance for the prediction and prevention of coal spontaneous combustion under stress conditions in the goaf.The main research is conclusion as below:(1)Through particle size test,liquid nitrogen adsorption experiment and void ratio calculation,the changes in the physical structure of water-bearing coal under stress are studied,and the effect of stress on the particle size distribution,void ratio and specific surface area of water-bearing coal is analyzed.The results show that : The average particle size of the coal sample after the stress is reduced,and the particle size range is expanded.The particle size of the water-bearing coal sample is slightly smaller than that of the dry coal sample;at the same time,the porosity of the coal sample decreases with the increase of the stress,and the water-bearing coal sample.The overall porosity is smaller than that of dry coal samples.The damage of stress to coal structure makes the specific surface area of water-bearing coal increase with the increase of stress.(2)Using the self-designed test device for the spontaneous combustion characteristics of the loaded coal,the coal temperature program experiment under stress was carried out,and the heating characteristics,oxygen consumption rate,and release rate of water-bearing coal samples and dry coal samples under different stresses were analyzed.Spontaneous combustion characteristic parameters such as thermal intensity and activation energy,as well as the concentration of hydrocarbons and carbon-oxygen gases generated during the heating process.The results show that the spontaneous combustion characteristics of the dried coal sample and the water-containing coal sample are significantly different under the action of stress.The effect of stress on the oxidation characteristics of the dried coal sample is first suppressed and then promoted.The oxygen consumption rate and heat release of the coal at the same temperature under lower pressure.The strength and the concentration of generated gas are less than in the unstressed state;these parameters gradually increase at higher pressures and exceed those in the unstressed state.Compared with dry coal samples,stress mainly promotes the oxidation of water-bearing coal samples.The water-bearing coal sample has a stagnation period due to the evaporation and heat absorption of water.After the water vaporization is complete,the temperature increase rate is faster,the oxygen consumption rate increases,and the apparent activation energy decreases,showing a stronger Spontaneous combustion tendency.(3)Fourier transform infrared spectroscopy is used to analyze the microstructure changes of oxidized coal samples under different stresses and coal samples with different moisture content under different stresses.The results show that the functional groups of oxidized coal samples under different stresses are The quantity changes have a certain regularity.The hydroxyl groups,aliphatic hydrocarbons,aromatic rings,oxygen-containing functional groups,etc.in coal molecules show a trend of first decreasing and then increasing with the increase of stress.The functional group content of coal samples with different moisture content increases as the moisture content increases after oxidation.Shows a decreasing trend.The number of functional groups reflects the oxidation process of coal to a certain extent.This thesis has 36 figures,12 tables and 106 references. |
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