Study On Spontaneous Combustion Characteristics Of Pre-oxidized Coking Coal Under Different Oxygen Concentration Environment

Spontaneous combustion of coal seams often occurs in spontaneous combustion dangerous areas such as goaf,closed fire area and open-pit mine area.The oxygen concentration in the area dominated by goaf and closed fire area is 21%lower than the normal atmospheric value,and there is a large amount of pre-oxidized coal.In this regard,in order to understand the influence of pre-oxidation degree and oxygen concentration on the spontaneous combustion characteristics of coal in the process of low-temperature oxidation,this paper takes coking coal as the research object,and studies the changes of physical properties of coking coal after pre-oxidation at 70℃,110℃and 150℃through experimental analysis.The macroscopic spontaneous combustion characteristics and microscopic characteristics of raw coal and pre-oxidized coal at different temperatures in the process of oxidation and heating under the conditions of oxygen concentration of 21%,16%,11%and 6%.The experimental results are expected to provide reference for the prevention and control of coal mine fires in goafs,closed fire areas and other areas.（1）The effects of pre-oxidation at different temperatures on the pore structure characteristics and oxygen uptake of coal samples were studied by high-performance specific surface area and micropore analyzer（BSD-PM2）and coal spontaneous combustion tendency analyzer（ZRJ-1）.The experimental results show that with the increase of pre-oxidation temperature,the pore structure（specific surface area and pore volume）of coal samples increases first and then decreases,reaching the maximum at70℃.The oxygen absorption of each coal sample shows a corresponding relationship due to the change of pore structure.（2）The effects of different temperature pre-oxidation and oxygen concentration on gas concentration,related spontaneous combustion characteristic parameters and crossover temperature during the oxidation and heating process of coking coal were studied by using coal spontaneous combustion characteristic tester GC-4175（ZRJ-1）and gas chromatograph（GC-4000A）.The experimental results show that the critical temperature of raw coal and pre-oxidized coal at different temperatures is between60-80℃,and the dry cracking temperature is between 100-120℃.The pre-oxidation temperature has little effect on the oxygen consumption rate and heat release intensity of coal samples.After pre-oxidation,the cross point temperature of coal samples is lower than that of raw coal.The CO concentration and CO production rate of each coal sample show different size rules due to different pre-oxidation temperatures in the four temperature ranges of 30-60℃,70-110℃,110-160℃,and>160℃.The effect of pre-oxidation temperature on C₂H₄ concentration in the corresponding temperature range is the same as that of CO.When the pre-oxidation temperature is the same,the influence of oxygen concentration on the gas concentration and spontaneous combustion characteristic parameters in the oxidation process of raw coal and pre-oxidized coal begins to gradually appear after the critical temperature,and with the increase of temperature in the oxidation process,the lower the oxygen concentration,the less the gas concentration,and the smaller the spontaneous combustion characteristic parameters.The lower the oxygen concentration,the higher the cross point temperature of the coal sample during the oxidation heating process.Through experimental research,the oxygen concentration in the environment should be reduced as much as possible to prevent the formation of oxidized coal to reduce the risk of coal spontaneous combustion.（3）The solid-liquid two-phase infrared spectrometer was used to study the overall change trend of the content of various functional groups of coking coal after pre-oxidation at different temperatures,and the change rule of the content of main functional groups in the oxidation heating process of raw coal and pre-oxidized coal under different oxygen concentration conditions.The results show that with the increase of pre-oxidation temperature,the content of various functional groups in coking coal shows different increasing and decreasing trends,but the content ratio of various functional groups still has C-O>-OH>aliphatic hydrocarbon>aromatic ring>-COO->substituted hydrocarbon>C=O>aromatic hydrocarbon.The main functional groups in the oxidation heating process of each coal sample have the following rules:between 110-190℃,the-OH content of pre-oxidized coal at 110℃and 150℃decreases,and the-OH content of raw coal and pre-oxidized coal at 70℃decreases during the whole process of oxidation heating.The aliphatic hydrocarbon content of each coal sample increases first and then decreases with the increase of temperature.The higher the pre-oxidation temperature of the coal sample,the temperature at which the peak area turning point occurs is less than or equal to the raw coal or the coal sample with lower pre-oxidation temperature.The aromatic hydrocarbon structure is stable,and its content is not easy to change during low temperature oxidation.When the oxygen concentration is less than or equal to 11%,the C=O content of each coal sample increases first and then decreases at 30℃,110℃and 190℃.Figure[34]Table[10]Reference[106]...