Research To Thermal Relaxation Mechanism Of Spontaneous Combustion In Goaf And Multi Field Coupling Dynamic Numerical Simulation

Coal mine fire is one of the major disasters threatening mine safety production,most of which are caused by spontaneous combustion in goaf.Gangue is the main way to dissipate heat in the goaf,there must be a temperature difference between the inside and outside in the heating process.Previous studies have simplified the gangue by using the lumped parameter method,but it is unknown how much calculation error it will bring.To solve this problem,the effects of oxygen concentration,particle size and coal rank on coal spontaneous combustion are studied,the oxidation reaction parameters used to quantify the degree of coal-oxygen reaction are deduced,the evaluation method of coal spontaneous combustion tendency is put forward based on the standard oxygen consumption rate index regression factor;the heat transfer law between gas-solid medium in goaf is elaborated,the multi-field coupling mathematical model of spontaneous combustion including gangue thermal relaxation process is established and discretized,numerical simulation software is independently developed by using Python programming language,the spatial-temporal distribution of multiple physical fields in the goaf before and after nitrogen injection is simulated;two different temperature observation schemes of goaf are designed,the internal temperature of goaf is monitored by using temperature observation system,the location of the spontaneous combustion risk area is located combined with the field observation and simulation results;the generation and migration law of carbon monoxide in goaf is studied,the effects of thickness of crushed coal,longwall advance rate and ventilation flux on spontaneous combustion in goaf are determined,taking the variable-speed mining process of the working face as an example,a prediction method for evaluating the degree of spontaneous combustion by carbon monoxide in the upper corner is proposed.The results show that the maximum temperature difference inside and outside the gangue is 0.12℃,the lumped parameter method is feasible.If the thermal relaxation process of the gangue is ignored,the calculation error of 7.47℃ will be brought,resulting in the deviation of the prediction results.This study can provide technical guidance and theoretical basis for locating the high temperature area and judging the degree of spontaneous combustion.