| Throughout the process of coal mining,the surrounding rock of the goaf is subjected to mining-induced stress,which forms mining-induced fractures.Groundwater enters the goaf through these fractures and wets the residual coal,forming water-containing coal.The coal-oxygen reaction process is affected by the moisture content,which causes certain differences.This includes the effect of moisture content on the coal’s physical adsorption of multi-component mixed gases and also on the self-ignition oxidation characteristics of coal.Considering that the vast majority of mines in China have entered deep mining,with many underground aquifers and large water inflows,it is necessary to conduct research on the effects of moisture on coal-oxygen adsorption and its low-temperature oxidation characteristics.This research can explore the impact of moisture on the coal-oxygen complex reaction and its role in self-ignition of coal,thus providing experimental and theoretical guidance for the prevention and control of mine self-ignition disasters.In this thesis,coal with varying levels of moisture content were chosen,and the adsorption characteristics of coal on CH4、O2、N2 and mixed gases were studied using a high-temperature and high-pressure adsorption instrument and a constant-pressure adsorption device.The impact of moisture content on gas production characteristics,apparent activation energy,and free radical parameters during the low-temperature oxidation process of coal was studied using a programmed temperature furnace,gas chromatograph,and electron spin resonance spectrometer.The following main conclusions were obtained through the above experiments:（1）Water has a significant inhibitory effect on the adsorption of single-component gases by coal.The adsorption amount and rate of coal on single-component gases gradually decrease as the moisture content in the coal increases.A multi-component gas adsorption prediction model was established by combining the linear fitting equation of single-component gas adsorption and the highest adsorption capacity of coal under atmospheric pressure.（2）As the moisture content in coal increases,the total adsorption amount of coal on multi-component mixed gases gradually decreases,but the volume fraction of each component gas in the total adsorption amount of mixed gases does not show a significant change.As the concentration of CH4 in the gas environment increases,the total adsorption amount of hydrated coal on mixed gases gradually increases,and the adsorption amount of methane in the total adsorption amount of mixed gases exceeds the volume fraction in the gas distribution scheme.The qualitative analysis of the model prediction results can explain the competitive adsorption phenomenon in the multi-component gas adsorption process.The moisture content in coal inhibits the adsorption of multi-component gases more significantly,but it does not change the competitive adsorption among the various component gases in the multi-component gas adsorption process.（3）During the initial stage of low-temperature oxidation of coal,the oxygen consumption,oxygen consumption rate,and CO production and generation rate decreases as the moisture content in the coal increases.As the reaction enters the rapid oxidation stage,the oxygen consumption,oxygen consumption rate,CO and CO2production and generation rate shows an initial increase followed by a decrease as the moisture content in the coal increases,and the apparent activation energy first decreases and then increases with The coal with a moisture content of 9.05%has the highest tendency for spontaneous combustion.For water-containing coal in different oxidation atmospheres,the oxygen consumption,oxygen consumption rate,CO and CO2production and generation rate decrease to a certain extent as it increase of CH4concentration in the oxidation atmosphere.（4）As the temperature increases,the g factor and Ng in the low-temperature oxidation process of coals with different moisture contents gradually increase,showing a dependence on temperature;the line width shows a continuous decreasing trend.As the moisture content in coal increases,the g factor and Ng first decrease and then increase at the same oxidation temperature,and the line width first increases and then decreases.Compared with dry air conditions,in a methane atmosphere,the g factor and Ng of the moist coal decrease,and the line width increases to a certain extent.（5）The influence of water on the low-temperature oxidation reaction and free radical chain reaction is the result of multiple factors.On one hand,when water contacts coal,hydrogen bonding occurs between water molecules and oxygen functional groups on the coal surface,making water molecules more easily adsorbed by coal.This results in a layer of water film on the coal surface,while excess water will flow into the pore channels and block some of the pores.Meanwhile,the evaporation of water will create a strong steam pressure effect in the coal pores,which will all have some inhibitory effect on the progress of coal-oxygen reaction.On the other hand,the swelling and pore expansion effects of water can promote the development of coal pores,and after water evaporation,more pore space and active groups will be exposed.These active groups are more likely to participate in the coal-oxygen reaction,which will result in more new free radicals produced from covalent bond cleavage and an increase in free radical concentration.When the water content in coal is low,water exists mostly in the form of adsorbed water,which can promote the dehydrogenation process of coal aliphatic structures and peroxide free radicals,producing more aliphatic hydrocarbon free radicals,and accelerating the formation of hydrogen peroxide,which in turn promotes the generation of hydroxyl free radicals.Hydroxyl free radicals have a strong promoting effect on coal-oxygen reaction.The increase of water content in coal leads to the increase of water-oxygen complexes in the initial stage of oxidation.At the same time,the contact between water and coal produces wetting heat,which provides initial energy for coal-oxygen reaction and accelerates the reaction rate and the coal-oxygen complex reaction process.These factors together make the effect of moisture on coal-oxygen reaction a dynamic changing process.As the dominant influencing factors of water on coal-oxygen composite reaction change,the effect of moisture on coal-oxygen reaction will correspondingly change.This Thesis includes 27 figures,21 tables and 99 references. |
