Characteristic Study On Inhibition Of Coal Spontaneous Combustion By Intumescent Thermosensitive Hydrogel Co-acting Melatonin

Coal spontaneous combustion(CSC)occurs frequently in China,resulting in serious waste of resources and environmental pollution.Therefore,it’s of importance to study efficient and economical coal self-ignition inhibitors.Aiming at the problems of single inhibition effect of physical or chemical inhibitors and complex preparation of composite inhibitors.This paper prepared a physical inhibitor(Intumescent Thermosensitive Hydrogel,HPMC-CS-EM),preferred chemical inhibitor(Melatonin,MT),the preparation of composite inhibitor(intumesent thermosensitive hydrogel co-acting melatonin,HPMC-CS-EM/MT)was completed.By means of experimental test and mathematical calculation,the characteristics of compound inhibitors on coal oxidation were studied,and the action process of HPMC-CS-EM/MT on CSC was revealed.First,HPMC-CS-EM were prepared by using chitosan(CS),hydroxypropyl methylcellulose(HPMC)and expanded microspheres(EM).The effects of EM content and HPMC viscosity on HPMC-CS-EM were systematically studied.The HPMC-CS-EM that EM content of 0.5%and the HPMC viscosity of 50 mPa·s have good fluidity,no delamination during heating,and the highest expansion ability(1.33 times).Therefore,A50 and B50 were finally selected as the physical inhibition part of the composite inhibitor.A50,B50 and MT were mixed in different proportions to complete the preparation of HPMC-CS-EM/MT inhibited coal.The paramagnetic resonance spectroscopy experiment and thermogravimetric experiment were carried out on the raw coal,single inhibited coal and composite inhibited coal.The method of combining universal integration and differential was used to calculate the initial weight loss and slow oxidation of coal samples under multiple heating rates.The apparent activation energies of the phases were determined,and the most probable mechanism function was determined by the Bagchi method.The combination of A50 and MT was not strong compared with single inhibited coal.The growth trend of free radical concentration and species in the composite inhibiting coal compounded with B50 and MT is obviously slowed down,and the synergistic effect is obvious when the content of B50 is high.The maximum water loss rate temperature(T1),the ignition temperature point(T3)and the average apparent activation energy(Ea)of the compound inhibited coal were all increased.Based on the parameters of free radical concentration,line width,characteristic temperature and average apparent activation energy,the inhibition effect of B50:MT(1:1,3:1,5:1)composite inhibitory coal was evaluated,and the final choice was B50:MT(5:1)is the optimal ratio of compound inhibitor.Under this ratio,the T1,the dry cracking temperature and T3 of coal samples increased from 88.6℃ to 100.1℃,205.7℃ to 229.8℃,and 346.0℃ to 358.2℃,respectively.The Ea in two stages increased 49 and 115 kJ/mol,respectively.The change trend of aliphatic hydrocarbons and oxygen-containing functional groups in the oxidation process of raw coal and optimally inhibited coal was studied by in-situ diffuse reflectance infrared spectroscopy experiments.HPMC-CS-EM/MT can reduce the-CH2,-CH3,-OH,etc.,increase the content of-C-O-.The process of HPMC-CS-EM/MT in inhibiting coal oxidation is proposed.MT internally captures free radicals,reduces the content of aliphatic hydrocarbons and hydroxyl groups,and inerts the coal reactive center;HPMC-CS-EM gradually separates out moisture in the process of phase change and expansion,lowers the temperature of the coal body,and condenses and covers the surface of the coal body to block oxygen,prolonging the action time of MT and delaying the process of coal oxidation.The research results have important scientific value and practical guiding significance for efficient and green prevention and control of coal spontaneous combustion.