| Coal fire is burning for a long time and has large burning areas.Some fire-fighting measures still failed to effectively extinguish a large area of coal fire.In order to explore the reasons why coal fire has a long duration and is difficult to extinguish,this paper attempts to apply the theory and method of smoldering to the combustion process of coal,based on underground coal fire shows the phenomenon of smoldering burning.The study found that the continuous combustion of coal is the result of the propagation of coal smoldering,and the difficulty of extinguishing coal is related to the characteristics of coal smoldering combustion.So the idea of cutting off the coal smoldering propagation to control coal fire was proposed.Based on this,a coal smoldering experimental platform was constructed to study the combustion characteristics of coal smoldering,which was applied to the control cases of Open-Pit mine coal fire.The main results and conclusions are as follows:The airflow rate has a great influence on the burning rate of coal,the rate of smoldering propagation and the temperature.Within a certain range,the greater the rate of airflow,the greater the burning rate,the faster the smoldering,and the higher the maximum temperature.The burning rate of coal under vertical smoldering condition increases linearly with the rate of airflow.When the airflow rate is between 0.074 and 1.48 m/min,the rate of smoldering is in the range of 31.03~213.3mm/h,and the temperature range of the smoldering is 450 ℃~1050 ℃.The coal can maintain the smoldering at 500 ℃ with a certain airflow.When the air volume decreases from 2m3 /h to 0.1m3/h,the total smoldering time increases from 11.4h to 146.3h,and the total smoldering time increases exponentially with the decrease of air volume.The minimum air supply rate of the coal smoldering is 0.009~0.013m/min.In practice of coal fire management,regular plugging measures is difficult to ensure that the air leakage rate control below 0.009m/min.It is because the smoldering of coal fire in the low air leakage rate can also be maintained,it leads to fire control measures focused on plugging suffocation failed,causing coal fire is difficult to extinguish.Fire pressure is the power of oxygen supply of the continuous smoldering of coal fire,and is one of the main characteristics of its smoldering combustion.Four kinds of oxygen channel of coal fire were summed up,and the fire pressure model of coal fire was established.The results show that the fire pressure of the smoldering area with the depth of 30 m is 0.1~0.15 Pa at the minimum air supply rate of 0.009~0.013m/min.This model can be used to evaluate the effect of fire plugging,that is,if the fire pressure measured after plugging is much higher than 0.1 ~ 0.15 Pa,it indicates that the fire area is not completely extinguished,to be further taken to strengthen measures.The extinguishment of Open-Pit coal fire should be fire cooling down as the main,plugging suffocation as the auxiliary to reach the purpose of cutting off the smoldering propagation.Taking East Open Pit mine fire as an example,the causes and characteristics of coal fire in open-pit coal mine was analyzed,the treatment technology of this fire was chosen.The heat transfer model of coal mine fire in open-pit mine was established,and it determines the amount of fire extinguishing medium was the half of theoretical model of the calculation estimated results.The practice of the field shows that the foam has the best water use efficiency and the longest cooling effect compared with the water injection and grouting technology.The cooling effect of the foam is remarkable,and it is more effective to prevent the development of the coal mine fire. |
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