| The fires caused by spontaneously burning coal are one of the main accidents in coal mining.Because of the different geological conditions,many coal mines in China have problems with leaching materials.Long-term immersion changes the pore structure of the residual coal,and as the ground dries out quickly with rising ground temperatures,large areas of spontaneous combustion will soon develop in the mining area,and the burning of the residual coal will become more violent and more difficult to control with conventional fire-fighting measures.The pore structure and oxidation properties of the coal from the eastern and western mines also differ after long-term immersion in water.Therefore,it is important for the coal industry to investigate the pore structure and oxidation characteristics of long-term water-soaked and air-dried coal deposits in the eastern and western mining areas of China.In terms of the waterlogging potential and ground temperature,three coal samples with different waterlogging potential and ground temperature were selected from the Jinjitan coal mine in Yulin,Shaanxi,the Gaojiapu coal mine in Shaanxi and the Tangkou coal mine in Jining,Shandong,and immersion and air-drying experiments were carried out.Scanning electron microscopy（SEM）,low-temperature liquid nitrogen adsorption and thermogravimetric analysers were used.The influence of changes in pore structure,porosity,specimens characteristic temperature and activation energy on the spontaneous burning of coal was investigated for coal samples before and after submersion in water.The main conclusions are:（1）The surface of the raw coal in the mines with water damage problems was rougher,the coal softer,with more pores and cracks.Coal mines where water damage was not pronounced showed a smoother rough coal surface with fewer cracks,but with wider cracks.All three coal samples showed well-developed crack pairs when immersed in water.The nature of the presence of pores and cracks on the surface of the coal sample changed and the percentage of pores and cracks increased significantly.The types of pores in the Jinjitan and Gaojiapu coal samples are thin-walled bottle-shaped pores and open permeable pores,respectively.The pore type of Tangkou coal sample changed from impermeable pores to open pores.（2）The trends of BET SA and BJH PV of Jinjitan,Tangkou and Gaojiapu coal samples change with increasing annealing time.The BET and BJH pore volume of Jinjitan,Tangkou and Gaojiapu coal samples decreased and then increased,while the BET and BJH pore volume of Tangkou and Gaojiapu coal samples increased and then decreased.After softening and curing,the total pore volumes of all three coal samples increased to the same pore dimensions,and the proportion of micropores on the BET and the BJH was higher than that of the original coal samples.After the immersion drying period,the specific surface area of the coal samples was higher than that of the other coal samples taken during the immersion,probably due to the higher propensity for spontaneous combustion at that time.The pore types of the coal samples from the two coal shafts in the west mine remained unchanged after immersion,while the pore types of the coal samples from the coal shafts in the east mine changed.Due to the geological differences,the western mine coal samples have a higher specific surface area than the eastern mine samples,and the western mine coal samples are more susceptible to spontaneous combustion at higher ground temperatures.（3）As the soaking time increased,the characteristic temperature of coal samples from different areas and from different soaking periods differed.The characteristic temperature of Jinjitan coal samples decreased with increasing soaking time except T5 and T6.T5 decreased and then increased with increasing soaking time,but was lower than that of the original coal samples.T6 increased and then decreased with increasing soaking time.Tangkou coal samples T1,T2 and T5 decreased with increasing soaking time.T3 and T6 increased,then decreased and then increased,but the temperature of T3 after soaking was higher than that of the original coal,and T4 increased with increasing soaking time.T3 and T4 temperature was lower than that of the original coal at 30 and 60 days.T3 and T4 temperature was lower than that of the original coal at 30 and 60 days,but higher than that of the original coal at 90 days and higher than that of the original coal at 30 and 90 days.At 60 days,it was lower than that of the original coal,and T6 showed a significant temperature reduction compared to the original coal after softening.The best mechanism functions for the three coal samples were different at different stages after drying for several days of soaking.In the combustion weight loss phase,the activation energy of the impregnated coal samples was lower than that of the original coal samples.As the soaking time increases,the activation energy becomes lower and the coal has a greater tendency to spontaneously combust.（4）The activation energies of the three coal samples were as follows:Jinjitan coal sample>Tangkou coal sample>Gaojiapu coal sample.In other words,the Gaojiapu coal sample was the most susceptible to spontaneous combustion and the jinjitan coal sample was the least susceptible to spontaneous combustion.This is consistent with the findings of the scanning electron microscope experiments in Chapter 2 and the low temperature liquid nitrogen adsorption experiments in Chapter 3.Since Gaojiapu coal mine is rich in mine water and is a high-temperature soil coal mine.Tangkou mine is also a high soil temperature mine and has the potential of waterlogging.Therefore,from a comparison of these three coal samples,it can be concluded that coal exposed to moisture and high temperature for a long time is more susceptible to spontaneous combustion after drying.And the longer the soaking time,the more porous the coal is.The greater the porosity,the greater the contact area of the coal with oxygen and the more susceptible the coal becomes to spontaneous combustion. |
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