Study On Catalytic Mechanism To Spontaneous Combustion Of Coal And Inerting Of Metal Compounds In Coal

Preventing coal spontaneous combustion is an urgent problem to be solved in coal mine safety production.It is of great significance to the safety production of coal mine,saving coal resources,and protecting the ecological environment.Coal is a highly complex and heterogeneous mixture composed of organic and inorganic substances.Among them,inorganic minerals account for about 1% to 30% of the coal composition and are the main carrier of metal elements.The influence of metal compounds in coal on coal spontaneous combustion is of great significance for mine fire prevention.The combination of theoretical analysis and experimental research was used to study the effect of metal compounds on coal spontaneous combustion.The mechanism of calcium,iron and manganese compounds catalyzing coal spontaneous combustion is analyzed,and the corresponding inerting method is proposed,which provides new ideas and methods for preventing coal spontaneous combustion.The main research results are as follows:Hydrochloric acid was used to demineralize coal samples with different degrees of metamorphism.The changes in metal composition,structure and spontaneous combustion characteristics of coal samples were analyzed.The results showed that hydrochloric acid could effectively remove the metal components in coal.The content of exchangeable metal compounds in coal with low metamorphism is relatively high,while bituminous coal with medium and high metamorphism is relatively low.As the degree of coalification deepens,the content of oxygen-containing functional groups in the coal gradually decreases,and the metal ions connected to it gradually fall off and transfer to discrete minerals.After demineralization with hydrochloric acid,the spontaneous combustion tendency of low metamorphic coal decreases,while that of medium and high metamorphic bituminous coal increases,indicating that there are metal elements in low metamorphic coal that can catalyze the spontaneous combustion of coal.The analysis of the metal elements in the low metamorphic raw coal and its demineralised coal shows that the content of calcium,iron and manganese is higher in the raw coal and the demineralization rate is higher.According to the occurrence state of calcium,iron,and manganese in coal,the corresponding compounds are selected to be added to the raw coal,and the effects of these metal compounds on the spontaneous combustion of coal are determined by the temperature program experiment and adiabatic oxidation experiment.The results show that calcium oxide can increase the oxidation activity of coal and promote the spontaneous combustion of coal.Calcium carbonate and calcium acetate have a weak promotion effect on coal spontaneous combustion,calcium sulfate has a weak inhibitory effect on coal spontaneous combustion,and calcium chloride has a stronger effect on coal spontaneous combustion.Iron oxide and ferrous carbonate act as inert minerals,which can slightly inhibit the spontaneous combustion of raw coal.Manganese dioxide and manganese carbonate have a significant inhibitory effect on the spontaneous combustion of raw coal.In-situ diffuse reflectance infrared spectroscopy was used to analyze the effect of catalytic metal compounds on the functional groups in coal spontaneous combustion.Combining the basic chemical reaction principle,the mechanism of metal compound catalytic coal spontaneous combustion was proposed.The catalytic mechanism of calcium-containing compounds on coal spontaneous combustion is that calcium enters the coal structure by ion exchange,and catalyzes in the form of calcium oxide,which causes the alkyl side chain on the condensed aromatic hydrocarbon to crack,generating fatty hydrocarbons and small molecular hydrocarbon.The catalytic effect of calcium-containing compounds depends on the moisture and carboxyl content of coal.Iron compounds and manganese compounds play a catalytic role in the form of free metal ions.Iron ions and manganese ions catalyze the oxidation reaction of hydrocarbons and oxygen-containing functional groups through gain and loss of electrons,thereby promoting the chemical oxygen absorption reaction of coal and accelerating coal spontaneous combustion.In order to suppress the catalytic effect of metal compounds on coal spontaneous combustion and achieve the purpose of inerting of easily spontaneous combustion coal,three different types of metal chelating agents oxalic acid,Ethylene Diamine Tetraacetic Acid(EDTA)and phytic acid were added to the coal to conduct temperature programming experiments to study the effect of chelating agent on spontaneous combustion characteristics of coal.The results show that the oxalic acid can promote coal spontaneous combustion because the chelate formed by oxalic acid and metal ions is unstable and prone to decomposition.EDTA can form stable complexes with metal ions,and the inhibitory effect on coal oxidation reaction is weak in the low temperature section and more obvious in the high temperature section.Phytic acid has the most obvious effect of inhibiting coal spontaneous combustion,because the coal samples added with phytic acid can generate ethers,esters and hydrogen-bonded cross-linking structure to improve the stability of coal.In the process of oxidation,phytic acid can chelate with metal ions,reduce the free radical content of the system,inhibit the chemical adsorption of coal to oxygen,and inhibit coal spontaneous combustion.