| Preventing coal spontaneous combustion fires and elucidating the intrinsic mechanism of coal spontaneous combustion can not only avoid the loss of people and property,but also reduce the waste of coal resources,which can play a role in saving resources.Coal is a complex mixture of organic and inorganic materials,and the proportion of inorganic minerals is about 10%～30%,which is the main carrier of metallic elements in coal.However,the widely accepted mechanism of coal spontaneous combustion-the coal-oxygen complex theory-only considers the oxidation reaction of organic matter,and does not consider the metal compounds inherent in coal.The transition metal copper was one of the first metallic catalysts recognized and used by man,and it is widely present in coal.Copper ions have unfilled d-electron orbitals,which are easily adsorbed to reactants and induce free radical chain reactions with high catalytic activity.Therefore,it is important to study the influence of copper metal compounds in coal on the process of oxidative spontaneous combustion of coal and the mechanism for preventing spontaneous combustion fires in coal.The elemental copper content in four coals with different degrees of metamorphism was measured by inductively coupled plasma mass spectrometry,and the contents of copper were obtained as 36.10,23.55,29.33,and 19.36μg/g,respectively;according to the fugitive state of copper in coal,eight copper-containing compounds were added to the raw coal,and the effects of copper-containing compounds on the spontaneous combustion process of coal were analyzed by simultaneous thermal analysis experiments The results showed that Cu SO4,Cu Cl2,Cu（NO3）2,Cu2O,Cu（OH）2,Cu CO3 and Cu Cl would shift the TG/DTG/DSC curves of the two lignites to the low temperature direction,decrease the ignition point by8.24%～23.14%,decrease the activation energy of ignition by 10.58%～51.92%,increase the total exothermic heat by 8.92%～37.47%,the peak level of oxidation exothermic peak is advanced by 3.2～25.4℃.Cu（NO3）2,Cu Cl2,Cu2O,Cu Cl will shift the TG/DTG/DSC curve of two bituminous coals to the low temperature direction,the ignition point is decreased by4.81%～29.27%,the activation energy of ignition is decreased by 8.01%～35.26%,the peak value of combustion peak is increased by 5.25%～54.95%,and the total heat release increased by 6.35%～36.59%.The catalytic ability was ranked as Cu SO4>Cu Cl2>Cu（NO3）2,Cu Cl>Cu CO3>Cu（OH）2>Cu2O.The copper-containing compounds had catalytic effect on coal spontaneous combustion,and the catalytic effect was mainly reflected in the accelerated oxidation stage.Using a programmed warming and gas chromatography coupling device to investigate the change pattern of gases generated during the warming and oxidation of coal,the results showed that the maximum concentrations of CO,CO2,CH4 and C2H4 generated during the warming and oxidation of four coals with the addition of copper-containing compounds increased 1.07～2.64 times,1.05～2.17 times,1.03～1.51 times and 1.12～2.07 times compared with the original coal times,the initial generation temperature of C2H4 was advanced by12～50℃,the oxygen consumption was increased by 2.6%～46.07%,and the oxygen consumption rate was increased by 9.54%～141.8%.The copper-containing compounds obviously promoted the generation of CO,CO2,CH4,C2H4 indicator gases and the consumption of O2,and promoted the oxidation process of coal.The group changes of coal during low-temperature oxidation before and after the addition of copper-containing compounds were investigated by in situ diffuse reflectance infrared spectroscopy experiments,and the results showed that the copper-containing compounds affected the organic chemical structure changes during coal oxidation and promoted the coal along the oxidation exothermic direction.The consumption rates of aliphatic hydrocarbons,C-H,-OH,-COOH,and C=O in the oxidation process of four coals after the addition of copper-containing compounds increased to 1.3～3 times,1.5～1.8 times,1.4～1.6 times,1.5～4 times,and 1.3～3.5 times of the original coal,and the temperature of the inflection point from rising to falling was advanced by 10～80℃for the-COOH content,by20～65℃for the C=O content,and by 10～80℃for the C=O content.20～65℃,and the temperature point at which the C=C bond content decreases drastically is significantly advanced.The copper-containing compounds accelerated the oxidation of aliphatic hydrocarbons,-OH,aromatic C-H and oxygen-containing functional groups in coal,and accelerated the breakage of the C=C double bond of the aromatic skeleton,which showed a strong promoting effect on the whole oxidative spontaneous combustion process of coal.Overall,the copper-containing compounds in coal enhance the spontaneous combustion properties of coal and play a catalytic role in the oxidative spontaneous combustion of coal. |
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