Experimental study on the characteristics of coal spontaneous combustion under oxygen-depleted atmosphere and re-ignition of its residues
To investigate the processes of coal spontaneous combustion under oxygen-depleted atmos-phere and re-ignition of its residues,the coal samples were oxidized at 200℃,300℃,and 400℃un-der the condition of an oxygen concentration of 5%.The variations of mass and quantity of heat release during spontaneous combustion of raw coal and residues were tested based on synchronous thermal a-nalysis method.Furthermore,the kinetic characteristics was analyzed.The results show that:Compared with 21%oxygen concentration,in the 5%low oxygen environment,the spontaneous combustion process of coal is inhibited,and the characteristic temperature is increased.The maximum reaction rate is reduced from 5.05%/min to 3.12%/min,which is decreased by 38.22%,and the net heat release is reduced from 16 173.73 J/%to 12 647.56 J/%,which is decreased by 21.80%.The dynamic mode shifts from random nucleation and subsequent growth to phase boundary reactions.Compared with 21%oxygen concentration,the apparent activation energy of coal with 5%oxygen concentration de-creases from 91.29 kJ/mol to 81.99 kJ/mol,with a decrease of 10.19%.Compared to raw coal,the oxygen absorption and weight gain process of 5%low oxygen high temperature residue is significantly inhibited.The oxygen absorption and weight gain of residue pairs decrease with the increase of oxida-tion temperature.After undergoing 400℃oxidation,the oxygen absorption and weight gain of residue re-ignition is reduced by 65.99%.With the increase of oxidized temperature,the temperature corre-sponding to the maximum mass first decreases and then increases,while both the ignition point temper-ature and burnout temperature decrease.Meanwhile,the heat release decreases,and the accelerating trend of heat release rate during thermal decomposition gradually disappears.The dynamic mode chan-ges from random nucleation and subsequent growth to a reaction order,and then to a phase boundary reaction.The apparent activation energy first increases from 81.99 kJ/mol to 117.67 kJ/mol and then decreases to 117.77 kJ/mol.These findings provide guiding significance for the scientific management of coal spontaneous combustion hazards.
coal spontaneous combustionresiduescharacteristic temperaturequantity of heat releasekinetics
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