Fundamental Study On The Thermokinetics Process Of Coal Oxidation Under Oxygen-depleted Atmosphere

In China,coal fire is one of the major disasters which threaten the pretection and utilization of coal resource.When coal fire happens,numerous coal resources would be destroyed,resulting in enormous economic loss.Meanwhile,toxic and harmful gases,such as CO,CO2,CH4,and NOx,produced by the coal oxidation and combustion would destroy the ecosystem,as well as the surface subsidence caused by underground burning zone.During the evolution of coal fire,oxygen-depleted atmosphere were formed because the supply of oxygen was limited.Focused on the characteristics of coal oxidation in oxygen-depleted atmosphere,this paper investigated the thermal reaction,thermal effects,thermal conduction,and reaction kinetics by combining theoretical analysis and experimental study method.These results were great helpful for bettering understanding the evolution process of coal fire in oxygen-depleted atmosphere.Adopting thermogravimetry-infrared spectrum coupling technology,variations of the characteristic temperatures,characteristic stages,comprehensive decomposition/combustion characteristics,and gaseous products were measured and analyzed.According to the variation of temperature at the same conversion rate,the influence of oxygen concentration on the process of thermal reaction was investigated.Moreover,based on the KAS method and the Malek method,the kinetic parameters and mechanisms were obtained.It was found that the thermal reaction of coal oxidation in oxygen-depleted atmosphere lagged behind that in air atmosphere,and the decrease of oxygen concentration had an obvious influence on the thermal decomposition/combustion stage.In addition,the maximum and the average reaction rate decreased with the decrease of oxygen concentration.The oxygen concentration had slight influence on the apparent activation energy at oxygen-adsorption mass-gain stage,while with the decrease of oxygen concentration,the kinetic mechanism showed the tendency from three-dimensional diffusion mode to one-dimensional diffusion mode.The oxygen concentration had an obvious influence on the apparent activation energy at thermal decomposition/combustion stage,while with the decrease of oxygen concentration,the kinetic mechanism transformed from random nucleation and subsequent growth mode to shrinking sphere mode.Differential scanning calorimetry technology was conducted to study the exothermic characteristics during coal oxidation under oxygen-depleted atmosphere,and the initial temperature of heat release and the amount of heat release were obtained.Besides,by grey relational analysis,the correlation between the variation of functional groups and exothermic rate were investigated.It was found that the heat release of coal oxidation was the result of combined action by various functional groups.The initial temperature of heat release increased with the decrease of oxygen concentration while the amount of heat release decreased.In addition,the oxygen concentration showed greater influence in rapid oxidation stage and main thermal decomposition stage.Moreover,at the same temperature,the decrease in the amount of heat release showed mutational effect with the decrease of oxygen concentration,and the corresponding critical oxygen concentrations were the same as these when the kinetic mechanism transformed.By laser flashing technology,the thermal diffusivity,specific heat capacity,and thermal conductivity during coal oxidation under oxygen-depleted atmosphere were measured and analyzed.It was found that the thermal conduction during coal oxidation under oxygen-depleted atmosphere presented obvious stage characteristics,and the critical temperature increased with the decrease of oxygen concentration.Meanwhile,the thermal conduction and its thermosensitivity were obvious influenced by oxygen concentration when the temperature was more than critical temperature.