A Study On The Inhibition Of Spontaneous Combustion Characteristics Of Coal Using Modified Halogenated Flame Retardants

Coal,as the main basic energy source in China’s current stage,is easily affected by coal spontaneous combustion during the mining process,posing a serious threat to the safety of frontline mine workers.The conventional halide inhibitor is a common means of inhibiting coal spontaneous combustion,but it has the drawbacks of weak water absorption and short action time.Surface active agents can effectively improve the wettability of materials.And SDS as a typical anionic surface active agent,has the advantages of small amount,stable properties at low and high temperatures.Therefore,SDS was selected to modify the halide inhibitor（NaCl and MgCl₂）in the experiment,and the water-absorbing and water-releasing characteristics of the original coal samples,the inhibited coal samples,and the modified inhibited coal samples were compared and analyzed.A thermogravimetric-differential scanning calorimetry experiment was used to compare and analyze the oxidation characteristics and kinetic parameters,and the inhibitory effect of the modified inhibitor on coal spontaneous combustion was analyzed from a macroscopic level.In addition,combining the surface tension test of the inhibitor and modified inhibitor and the contact angle test of different coal samples,the mechanism of coal oxidation inhibition by modified inhibitors was revealed at the microscopic level.By conducting water-absorbing and water-releasing tests,the water-absorbing and water-retaining effects of different coal samples in the low-temperature oxidation stage were studied.It was found that with the increase of ambient temperature,the water-absorbing and water-retaining effects of the modified inhibited coal samples were significantly improved.After SDS modification,compared with before modification,th e water absorption of the inhibited coal samples increased by an average of 18.5%,and the water retention rate increased by an average of 8.3%.A liquid film was formed on the surface of the coal sample,and no water droplets insoluble in the coal sample were produced.After water release,a layer of salt shell was precipitated on the surface of the coal sample and attached to the coal body.Based on the water-absorbing and water-releasing characteristic test data and economic benefits,0.2 5%SDS+20%NaCl and 0.25%SDS+20%MgCl₂ were selected as the optimal modified concentrations.Based on the TG-DSC experiment,the characteristic temperatures,heat release,combustion index,and other oxidation characteristic parameters of the original coal,optimal inhibited coal,and modified inhibited coal samples were compared and analyzed.The oxidation kinetics of the coal samples before and after modification were calculated using the Coats-Redfern integral method.The results showed that the modified inhibitor had a significant inhibitory effect on the coal spontaneous combustion process.The six characteristic temperatures of the oxidation process of the modified inhibited coal sample were all higher than those of the original coal,and the quality loss of the oxidation process decreased,and the oxidation rate slowed down.The heat absorption of the coal body increased in the low-temperature oxidation process,and the heat release in the high-temperature stage decreased;the combustible index and the comprehensive co mbustion index both significantly decreased.The apparent activation energy of the modified inhibi ted coal sample increased in four oxidation process.Surface tension and contact angle tests of the inhibitors before and after modification and inhibited and modified inhibited coal samples were carried out,and the results showed that as the SDS concentration increased,the surface tension of the inhibitors gradually decreased until the SDS concentration reached the critical micelle concentration.The contact angle of the modified inhibited coal sample decreased by an average of 64°and 40°compared to raw coal and inhibited coal samples,respectively,and the surface exhibited hydrophilic properties.The halide inhibitors combined with surfactants can enhance the wetting properties of the surface and improve the inhibitory effect on coal spontaneous combustion.