Synergistic inhibition effect of inorganic salt inhibitor and free radical scavenger on coal spontaneous combustion

From the aspects of isolating oxygen,lowering temperature and terminating free radical chain reaction,a compound inhibitor with continuous effective inhibition of coal spontaneous combustion was obtained from the combination of the inorganic salt inhibitors MgCl2 and CaCl2 with the radical scavengers N,N-dibenzylhydroxylamine (DBHA) and Butylated hydroxyl toluene (BHT).With the easy self-igniting long flame coal as the research object,the inhibitory performances of coal samples treated with different inhibitors were studied by using the inhibition performance test,the characterization of reactive functional group and thermal analysis experiments.Based on the correlations among CO emission,evolution of functional groups,and mass change trend during coal spontaneous combustion,the inhibition mechanism of composite inhibitors was discussed combining with the thermodynamic characteristics of oxidation reaction.The experimental results show that the compound inhibitor has a coordinate inhibitory effect during the whole process of coal spontaneous combustion,with physical and chemical double inhibition effect.Compared with the raw coal,the amount of CO released from coal sample treated by the compound inhibitor was reduced by 88.7% at128 ℃,and the inhibition rate reached 82.5% at 100 ℃.The inhibition ratio is higher than 80% during the initial weight loss stage and the oxygen absorption and weight increase stage.The compound inhibitor plays an inhibitory role by reducing the contents of hydroxyl,methyl,methylene groups and active components containing carbonyl groups in the coal,wherein,the relative content of a carbonyl compounds decreased obviously.The coal-oxygen chemisorption time for coal sample with the addition of composite inhibitor becomes short accompanied by the least adsorption quantity,and the weight gain rate decreased by 0.29%.The activation energy is increased with the development of coal spontaneous com-bustion,especially for the oxygen absorption and weight gain stages,with the activation energy increased by 53.2%.In the initial weight loss stage,the compound inhibitor exhibits physical inhibiting effects by the water retention due to inorganic salt.In weight gain stage,the compound inhibitor exhibits chemical inhibiting effects through the recombination of covalent bonds between free radical scavenger and the oxygen-containing active free radicals in the coal.DBHA releases free H+ and provides N and O atoms that do not share electrons.N,N-dibenzylhydroxylamine (DBHA) molecular structure contains multiple absorption sites,which can simulta-neously capture multiple free radicals in coal.Butylated hydroxyl toluene (BHT) reacts with free oxygen-containing functional groups to form stable compounds.Meanwhile,the formation paths for ketones and aldehydes are interrupted.Therefore,the compound inhibitor can control the process of coal spontaneous coal combustion via a chemical reaction pathway.