Study On The Effect Of Different Convection Mechanisms On The Self-heating Of Loose Coal

The oxidative self-heating behavior of loose coal at room temperature is one of the main hazards in the process of coal storage and transportation,forced convection and natural convection are two heat transfer mechanisms in the process of loose coal oxidation and self-heating,and the study of the characteristics of low-temperature oxidation behavior and its influencing factors under the two convection mechanisms has certain practical significance according to the different storage environments of loose coal.Therefore,by conducting adiabatic oxidation experiments on coal with different degrees of metamorphism and particle size,the variation law of coal oxidation kinetic parameters is obtained,and the oxidation behavior characteristics of coal particles in actual coal piles are further studied on the basis of the influence of particle size and metamorphism on the oxidation kinetic parameters of coal particles under experimental conditions.Based on the oxidation kinetic parameters of coal in actual coal reactors,a multiphysics coupling model of self-heating of coal reactors under forced convection and natural convection mechanisms was established to study the characteristics of oxidative self-heating behavior of coal reactors under different convection mechanisms,and gray correlation degree analysis was carried out for various influencing factors,so as to propose more targeted countermeasures for preventing and controlling self-heating of coal reactors,and provide guidance for the actual project.Small insulation oxidation experiments have limitations on the particle size of coal particles,so the experiment will be carried out at a smaller particle size,since the acceptable temperature of safe storage of coal piles does not exceed 150 °C,and the analysis of the results of the insulation experiment driven by the actual guidance of the project is only considered below 150 °C.Under experimental conditions,it was found that there was a non-Arrhenius phenomenon in the initial stage(<70 °C)and high temperature stage(>150 °C)of coal particle oxidation,and the analysis believed that the physical desorption adsorption and chemical adsorption of coal and oxygen were the reasons for the initial stage,while the restriction of oxygen diffusion was the cause of this phenomenon in the high temperature stage.Experiments show that the apparent activation of coal particles can decrease with the decrease of particle size within the experimental particle size,and its reciprocal number and apparent activation energy within a certain particle size are approximately linear,which is also consistent with the theoretical analysis after simplifying coal particles into spherical particles without internal pores.Based on the determination of oxidation kinetic parameters and variation laws of coal particles,the apparent kinetic parameters of coal reactor oxidation are derived to provide prerequisites for the establishment of self-heating models of coal reactor oxidation under different convection mechanisms.In the study of the oxidative self-heating behavior of coal reactors under forced convection,the following conclusions were found: the influence of wind speed on the self-heating of coal reactors can be divided into low-speed type(0.03～0.09m/s),medium-speed type(0.3～0.9m/s)and high-speed type(3～9m/s),and the growth of the maximum temperature gradually changes from heat dissipation strength constraint to oxygen concentration restriction,and the restriction effect of oxygen concentration in high-speed briquette pile is gradually concentrated in the high temperature stage The distribution of high temperature areas in coal reactors gradually changed from heat dissipation intensity and oxygen concentration to oxygen concentration control;the study of medium-speed and high-speed coal reactors found that the reduction of wind speed when the wind speed was less than 4m/s could significantly improve the safe storage time of coal reactors,and this effect was more obvious when the wind speed was less than 2m/s When the porosity is less than 0.1,the coal pile is difficult to spontaneously combust,and for every 0.5 increase in porosity,the time for the maximum temperature of the coal reactor to reach 150 ° C is 7 days in advance;the coal with small particle size is more conducive to delaying the heating process of the coal pile,and a similar effect can be achieved by covering the corresponding thickness of the small particle size coal;the lower the degree of deterioration,the faster the coal pile heats up,the faster the high temperature area is closer to the surface of the coal pile;the decrease in the height of the coal pile and the angle of the slope will inhibit the increase of the temperature of the coal pile in the high temperature stage and reduce the range of the high temperature area;the size of the influence of each influencing factor on the self-heating of the forced convection coal pile is the particle size in turn,porosity,slope angle,and height.In the study of the oxidative self-heating behavior of coal reactors under natural convection,the following conclusions were found: when the porosity was less than 0.25,the increase in porosity would lead to an increase in the heating rate;after the porosity was greater than 0.25,its increase would lead to an increase in the oxidation range;the reduction of particle size could reduce the heating rate and oxidation range of the coal reactor,and this effect was more obvious the smaller the particle size;the more obvious the coal high temperature area with the lower degree of metamorphism;the lower the coal particle size and porosity,the slower the coal reactor temperature rise,and this effect was more obvious when the particle size was less than 2mm and the porosity was less than 0.2 The higher the slope angle of the coal pile,the greater the thermal buoyancy generated,the more obvious the flow effect of the air flow,and the more oxygen leads to an increase in the heating rate of the high temperature stage.This paper has a total of 109 figures,19 tables,and 110 references.