Study On Coal Spontaneous Combustion Mechanisms And The Spontaneous Combustion Danger Index

For a long time, many people have done a lot of researches to the coal spontaneous combustion mechanization and coal oxidation and spontaneous combustion is easy or not, but because coal spontaneous combustion is a complex process, so the problem has not been fundamentally resolved. The molecule structure model of coal was established in this thesis by theory and experiment methods. And studied the coal spontaneous combustion mechanism by quantum chemical theory in a microscopic level. And on the basis of that, the dangerous index method of coal spontaneous combustion to judge spontaneous combust easy or not was established. The main contents and achievements in this thesis include several aspects as follow: Chemical structure study on basal structure cell of coal molecule Chemical structure of 80 species of coal samples from Datong, Shendong, Tiefa, Fuxin, Shuangyashan and Hegang coal mine areas were investigated by infrared spectrum analysis. And build the structure model of coal molecule by analyzing the infrared spectrum figures about coal molecule structure. Analyzing from the infrared spectrum figures about coal samples spontaneous combustion production, we can learn that the oxidation reaction of coal with O2 generates H₂O, CO₂, CO, CH₄ and C₂H₄. The formation of the five matters confirmed that there are benzene side chain groups in coal molecule structure model. The vibration frequency and the parameters of molecule structure such as bond length, bond angle and dihedral angle can be gained while optimizing the basal chemical structure cell of coal molecule at B3LYP/6-31G level by quantum chemical DFT method. The frequency gained by theory calculating was consistent with that gained by experiment. It means that the coal molecule structure built is correct. According to the molecule orbital theory, the oxidation spontaneous combustion reaction of coal takes place at the atoms which charge density is thick. Therefore the atoms at the groups, such as N92, C61, C99, C95, C74 and N122 in coal molecule, react with oxygen easily. Quantum chemical study on coal spontaneous combustion mechanism and laboratorial validation Based on the active constituent of the chemical reaction process about coal spontaneous combustion, which generates H2O, CO, CO2, CH4 and C2H4, was deduced by chemical reaction mechanism theory. The geometry of reactants, results, intermediates and transition state molecules were optimized at B3LYP/6-31G level by quantum chemical DFT method. And the vibration frequencies of the stagnation point in reaction process were calculated, every transition state was confirmed by vibration analysis, the zero point energy(ZPE) was gained, the intrinsic reaction coordinate(IRC) was calculated at the same level, the difference of the structure and the potential energy of the molecules which effect each other was compared while the reaction was alone the minimum energy path. Thus we can get the right relationship between the reactants, results, intermediates and transition state. Comparing the reactive barrier among the five reaction paths, the activity of the reaction between coal and oxygen is according to the change of the functional group under different temperature while coal spontaneous combust. The activity of the functional group in coal molecule which is predigested: -C(19)H2-N(22)H2 > -C(33)H2-C(36)H2-C(39)H2OH > -C(46)H2-C(49)H2-C(54)H3 >-C(25)H2C(28)H=C(29)H2. Use coal sample to make the warming oxidation spontaneous combustion experiments in laboratory, the coal sample and KBr pressed flake, use infrared spectral analysis testing technology to study the variational disciplinarian of the coal molecular structure every other 20℃, chemical bond and functional group in different temperature. Contrast the experimental results with the coal spontaneous combustion mechanization conclusion, the theoretical calculationsis consistent with experimental results, which proved the validity of theoretical research. Study on the dangerous index of coalspontaneous combustion According to investigation for coal surface structure by using scanning electron microscope (SEM), coal is porous media with abundant pore and specific surface area. The coal chemical activity determine the quantity of chemisorption, otherwise the coal specific surface area determine the ability of physisorption. It is different between the oxygen adsorbed by coal and the oxygen took part in chemical reaction, and there is no clear rules between oxygen absorbed and spontaneous combustion. With a different coal the adsorption quantity of a same inert gases is different, so the quantity of oxygen adsorption used to determine the coal spontaneous combustion is not comprehensive. The thermal gravimetric experiment indicated that there are three phases during coal spontaneous combustion process: evaporated-alleviative, oxidation-weight-increment and combustion-alleviative. Ignition activation energy means the energy from start to ending of weight increment on TG curve. Basing on the study on coal spontaneous combustion mechanism, we can learn that the ignition activation energy is the highest barrier of the chemical reaction between oxygen and coal molecule. So the ignition activation energy is just the activation energy we say in coal oxidation and combustion mechanisms. Use ignition activation energy which can reflect an integrated characteristics of coal oxidation and combustion as a new method to judge the coal combustion easy or hard is scientific. The dangerous index of coal spontaneous combustion is a number to judge the coal combusting easy or no. It can express by the ignition activation energy. The lower the dangerous index is the more easily combustion happen. Vice versa. The dangerous index of the coal samples from Datong, Shendong, Tiefa,Fuxin, Shuangyashan and Hegang coal mine areas were gained by calculating with the new appraisal method for coal spontaneous combustion. And comparing that to the results gained by oxygen absorbed method, the results gained by the dangerous index accord with fact more than the other.