Experimental Study On The Fire-fighting Technology Of The Goaf With Dry Ice Phase Change Simulation Driven By Heating

China has always been the world's largest coal producer and consumer.However,spontaneous combustion of leftover coal in the goaf has seriously endangered the normal production of mines and the personal safety of workers.Dry ice treatment of residual coal has the triple functions of cooling and cooling,adsorption inerting and covering oxygen barrier.In this paper,the sublimation of dry ice is studied through theoretical analysis,laboratory experiments and numerical simulation.According to the phase change characteristics of dry ice under natural conditions and the phase change characteristics under heating and driving conditions,the supply and demand relationship suitable for coal mine production is obtained.Firstly,dry ice sublimation experiments with different particle sizes and shapes are carried out by using the established dry ice sublimation model.The dry ice that meets the experimental requirements will be selected for sublimation experiments to simulate the environmental conditions of the goaf,and the sublimation rate of dry ice during the two groups of experiments will be analyzed and calculated.The endothermic rate of sublimation of dry ice,the fastest sublimation rate obtained through experiments is granular dry ice,and the smaller the radius of the dry ice particles,the faster the sublimation rate;through the temperature monitoring during the sublimation of dry ice,it is found that the sublimation of dry ice is obvious in the vertical direction Temperature gradient,and due to the characteristics of CO₂ heavy gas generated by sublimation of dry ice,the gas stays near the sublimation position,and the temperature is lower as the distance from the sublimation surface is closer.Then,in view of the problem that the sublimation rate of dry ice is slow under natural conditions,a dry ice sublimation heating drive device was designed and studied,and the effects of different water-cement ratios and different initial water temperatures of the heating driver on the hydrothermal reaction were studied through experiments.The results show that:when water ash The ratio of 1.8 is the best ratio,which is most conducive to the hydrothermal reaction.The water with different initial temperatures has little effect on the hydrothermal reaction,which provides a later stage for heating and driving dry ice sublimation in the laboratory or in the underground environment.Theoretical basis.In order to prevent the sublimation of dry ice and the rapid decrease of the ambient temperature and the freezing of the water supply pipeline,a certain proportion of salt reagents were added to the water.Through experiments,it was found that 30%Ca Cl₂ solution had the best effect.Finally,the FLUENT numerical simulation method was used to conduct the heating-driven dry ice phase change experiment.In order to obtain the optimal water injection rate in the hydrothermal reaction,first set different water injection flow rates.It was found that when the water-cement ratio is 1.8,the water injection flow rate is less than or equal to 0.000144 L/s,it can accelerate the sublimation of dry ice without heat dissipation to the surrounding environment,and the sublimation rate of dry ice is increased by 5 times compared with that under natural conditions.Under these conditions,the dry ice sublimation experiments with different qualities under heating and driving were performed to obtain the quantitative relationship between the quality of the dry ice thrown in,the amount of CO₂ produced,and the quality of calcium oxide required.The paper has 46 pictures,18 tables,and 77 references.