Experimental research on characteristics of coal spontaneous combustion and its influence on lower limits of gas explosion

Most of existing research analyze gas explosion limit from single component gas or parial component mixed gas of coal spontaneous combustion, while analysis of gas explosion limit from mixed gas produced at different stages of coal spontaneous combustion is insufficient, and there are few experimental research on coal spontaneous combustion and gas explosion coupling disaster. In view of the above problems, the characteristic laws of gas generation in process of coal spontaneous combustion were researched by simulating experimental device of coal spontaneous combustion.The 20 L spherical explosion device was used to conduct the experiment about methane mix gas from coal spontaneous combustion at different stages,and effects of coal spontaneous combustion on the lower limits of gas explosion were studied.The experiment results show that main flammable gases of the coal sample spontaneous combustion are CH4, CO, C2H4, C2H6, C2H2， etc. Among these gases, CH4 and CO have the highest volume fraction, and the maximum volume fraction can reach 0.75% and 0.37% respectively. The content of flammable gases produced in different stages of coal spontaneous combustion is increased with the increase of spontaneous combustion time and temperature. CH4 and CO flammable gases are mainly produced at temperatures below 80 ℃ at the initial of coal spontaneous combustion, CO can be used as a marker gas for the slow oxidation stage of coal spontaneous combustion. As the time of spontaneous combustion continues,it starts to produce C2H4 and C2H6 after the temperature exceeds 80 ℃, and then C3H8 gas is gradually produced. At this time, the appearance of C2H4 indicates that the oxidation of coal has entered the acceleration stage. C2H2 is produced on the temperatures of 220 ℃ after the late stage of coal spontaneous combustion, at this point, the coal enters the intense oxidation stage. Low concentration of CO inhibits gas explosion, however, high concentration of CO promotes gas explosion, explosion pressure becomes larger, and lower explosion limit decreases. The mixed gas produced during the spontaneous combustion of coal increases the pressure of gas explosion, decreases the lower explosion limit by 0.55%,so increases the risk of gas explosion.