Study On Oxidation Characteristics And Kinetics Of Non-stick Coal During Spontaneous Combustion

The main reason of coal self-ignition and fire is the heat released in the process of low temperature oxidation and combustion.In this paper,Thermogravimetry and differential scanning calorimetry(TG-DSC)experiment and Fourier Transform Infrared Spectrometer(FTIR)experiment are used to study the oxidation characteristics of coal from macro and micro perspectives.By analyzing the TG / DTG curve of non-stick coal,seven temperature values are determined,and the influence of particle size and heating rate on its characteristic temperature is discussed.The results show that the characteristic temperature of pulverized coal decreases with the decrease of particle size,and it is positively correlated with the heating rate.According to the characteristic temperature,the whole oxidation reaction of pulverized coal can be divided into four stages.By analyzing DSC curve and studying its exothermic performance,the oxidation combustion process of pulverized coal can be divided into two stages: endothermic stage and exothermic stage.The total exothermic energy obtained by integrating DSC curve by stages is far greater than the endothermic energy,so the oxidation reaction process of pulverized coal belongs to exothermic reaction in general.The two characteristic temperatures of DSC curve,the coal heat balance temperature and the maximum exothermic peak temperature,decrease with the decrease of particle size,and lag phenomenon appears with the increase of heating rate.Flynn-Wall-Ozawa and Vyazovkin and Weight models were used to calculate the activation energy in the range of 66.2-92.9 kJ / mol.Based on the Coats-Redfern model,nine kinds of gas-solid reaction mechanism functions are calculated.The results show that the pulverized coal belongs to two-dimensional diffusion reaction,three-dimensional diffusion two-stage reaction,random nucleation three-stage reaction and three-dimensional diffusion two-stage reaction in the loss of water,oxygen absorption and weight increase,pyrolysis and combustion stages,respectively.According to the characteristic temperature of TG curve,the in-situ FTIR experiment shows that there are four peaks in the process of coal oxidation.With the increase of oxidation temperature,the free hydroxyl group and intermolecular hydrogen bond break,leading to the disappearance of hydrocarbon groups.The main spectrum of aliphatic hydrocarbon is antisymmetric stretching vibration of methyl and methylene.The oxygen-containing functional groups have high reactivity and are easy to react with oxygen.They have disappeared at 245.42 ?,and the reaction will release a lot of heat,which is of great significance for coal oxidation.The peak intensity of aromatic hydrocarbon is the largest and the most obvious,indicating that the proportion of aromatic hydrocarbon in the molecular structure of coal is the largest.With the increase of oxidation temperature,the peak intensity decreases.In order to better study the chemical structure and obtain the detailed absorption peak parameters,the infrared spectrum is processed by the peak division fitting.The change of the number of key active functional groups in the oxidation process is studied quantitatively.With the increase of coal oxidation temperature,the content of coal molecular functional groups is gradually reduced.The difference of these functional groups in coal molecules results in the difference of coal molecular chemical structure,which determines the difficulty degree of spontaneous combustion tendency from the intrinsic property of coal.