Study On Pore Structure And Oxidation Activity Of Active Groups Of Water-immersed Coal At High Ground Temperature

With the extension of mine mining to the depth,the temperature of the original rock keeps rising,and the erosion of the coal seam by groundwater,under the joint action of the two,the spontaneous combustion of coal has a great influence.On the one hand,the thermal decomposition of coal is easy to occur in high ground temperature environment and the heat generated is not easy to diffuse to the environment,which provides a good heat storage condition for coal spontaneous combustion.On the other hand,under the condition of long-term immersion,the pore structure of coal will change,which will affect the oxygen absorption capacity of coal.After mining exposure,this change will greatly affect the process of coal-oxygen recombination reaction.In summary,considering the practical background that high geothermal immersion affects coal spontaneous combustion characteristics,this thesis adopts the method of combining theoretical analysis and experimental testing to carry out systematic research on the pore structure development characteristics of coal under high geothermal immersion,the evolution of surface oxygen adsorption capacity,the characteristics of free radicals and the change law of functional group structure,etc.It provides the basis for the study of coal spontaneous combustion disaster control under the action of high ground temperature immersion.The main research results are as follows:The pore structure development and surface oxygen absorption capacity of water-immersed coal at high ground temperature were studied by using low temperature liquid nitrogen adsorption technology and high temperature and high pressure gas adsorption technology.The results show that,compared with raw coal,the specific surface area,cumulative pore volume and average pore diameter of water-immersed coal at high ground temperature increase,and the parameters of water-immersed coal for 3 months change obviously.Under the same immersion duration,pore structure parameters increase with the increase of immersion temperature.The cumulative pore volume showed a fluctuating trend,and the proportion of micropores increased with the increase of immersion temperature.The maximum oxygen adsorption capacity of coal is positively correlated with immersion temperature and immersion time.This indicates that the high ground temperature water immersion promotes the effect of"microporous"and"pore size expansion"in coal,resulting in the development of pore structure,enhanced connectivity,and improved oxygen absorption capacity on coal surface.The variation of free radical properties of water-immersed coal at high ground temperature and its spontaneous combustion process was studied by electron spin resonance spectroscopy.The results show that:compared with raw coal,the linear widthΔH,g factor and free radical concentration Ng of coal soaked in water at high ground temperature are increased,and the higher the immersion temperature is,the higher the g factor value and free radical concentration Ng will be.In the process of coal oxidation at low temperature,both the g factor value and the free radical concentration Ng increase with the increase of oxidation temperature,and the change trend is first slow increase and then fast increase.At the same time,with the increase of immersion temperature,g factor value and free radical concentration Ng increase.These results indicate that high ground temperature immersion enhances the free radical activity of coal,and with the increase of ground temperature,the enhancement effect is more significant,thus accelerating the coal oxygen recombination reaction rate.The changes of molecular active structure on the surface of water-immersed coal at high ground temperature and during its spontaneous combustion were studied by Fourier infrared spectroscopy.The results showed that the contents of-OH,-CH₃ and-CH₂-all increased with the increase of soaking time,while the aliphatic hydrocarbon chain length decreased,and the contents of-OH,-CH₃ and-CH₂-increased with the increase of soaking temperature at the same soaking time.With the increase of immersion time and temperature,the contents of-C=O and-C-O increased gently,while the content of aromatic hydrocarbon group decreased slightly.In the process of coal oxidation at low temperature,the contents of-OH,-CH₃ and-CH₂-decrease with the increase of oxidation temperature,while the contents of-C=O and-C-O-have little change,and the aromatic hydrocarbon group content has little change as a whole.Under the same soaking time,the higher the soaking temperature,the greater the content difference of-CH₃,-CH₂-,-OH,-C=O before and after oxidation reaction.This indicates that high ground temperature immersion promotes the fracture of aliphatic hydrocarbon side chain of coal,accelerates the reaction rate of main functional groups,and increases the unstable components in coal molecules,thus improving the low temperature oxidation activity of coal.The development characteristics of pore structure,surface oxygen adsorption capacity,free radical properties and functional group structure of raw coal and coal soaked in water at high ground temperature are compared and analyzed.Comprehensive analysis shows that high ground temperature soaking can promote the development of pore structure of coal,improve the surface oxygen absorption capacity of coal,enhance the reactive activity of active groups,so as to promote the occurrence of coal-oxygen complex reaction and increase the risk of coal spontaneous combustion.There are 33 figures,7 tables and 104 references in this thesis.