Low Temperature Oxidation Characteristics Of Coking Coal And Its Kinetic Analysis

During open storage,low-temperature oxidation of coking coal will inevitably occur.Low-temperature oxidation not only increases the possibility of coal spontaneous combustion,but also deteriorates coking coal's physicochemical properties and technology properties,affecting its quality.Therefore,it is necessary to conduct a comprehensive study on the low-temperature oxidation behavior of coal.The main contents of this article are as follows:With the help of the oil bath low-temperature oxidation experiment system,the change rules of various index gases in the process of heating and isothermal oxidation were investigated.The results showed that the occurrence order and content change of different gases could reflect the degree of coal oxidation.CO concentration had a strong correspondence with the oxidation stage,so CO gas was suitable for use as the main indicator gas.During the isothermal process,the concentrations of CO and CO2 first increased,then decreased with time,and gradually stabilized.It indicated that the carbon-oxygen complexes produced by coal-oxygen reaction had a "saturation value",which was gradually consumed as time passed.The blank experiment in nitrogen atmosphere showed that CO mainly came from the oxidation reaction,while the main sources of CO2 were gas desorption of self-adsorbed gases and thermal decomposition of active substances in coal.The low-temperature N2 adsorption device.SEM-EDS,and FTIR were used to study the microstructural changes before and after coal oxidation,and the generation mechanism of CO and CO2 gases was inferred.The results showed that after the oxidation at 95?,the surface of coal had no obvious change.After oxidation at 190?,the pore volume of coal became larger,the average pore diameter rose,and the cracks on the surface increased obviously.However,due to the adhesion of oxidation products,some pores were blocked,resulting in a decrease in specific surface area.During the oxidation process,Hydroxy,methyl,methylene and other active groups reacted with oxygen molecules and formed unstable carbon oxygen complexes,such as phenol hydroxyl,carbonyl,carboxyl and ether bond.Besides,CO,CO2 gases were released.TG-DTG curves obtained from the thermo-gravimetric experiment were used to calculate the characteristic temperature points T1?T5.The kinetic parameters of the coal in the oxidation section and combustion section were calculated respectively by Coats-Redfern method.The results showed that the reduction of coal metamorphism degree would lead to the decrease of characteristic temperatures T2?T5 and reaction activation energy of oxidation section and combustion section,which indicated that the reaction resistance was reduced.The reduction of the coal particle size would lead to a decrease in characteristic temperatures T1?T5.But at the same time,there was no obvious change trend between particle size and the activation energy of the oxidation section and the combustion section.Moreover,the coincidence degree of TG-DTG curve for each coal particle size was high,indicating that the particle size had little impact.With the increase of heating rate,the characteristic temperatures T1?T5 became higher,and the activation energy of the oxidation section and the combustion section decreased,which indicated that there was a thermal hysteresis in the reaction.However,the fast heating rate could supply enough heat to the coal particles more quickly and promote the reaction.