Experimental study on the characteristics of oxidation kinetics and heat transfer for coal-field fires under axial compression

Abstract

Coal-field fire results in much loss of resource and severe harm for human beings. In order to investigate the oxidation and heat transfer characteristics of coal-field fire under axial compression, the coal samples were heated and loaded by stress within axial compression equipped with a temperature-programmed device. Considering the heat generating rates over temperature in temperature-programmed (TP) device, both the critical temperatures Tc and Tg were obtained to divide the process of TP under axial compression into three stages. (Here, Tc is the critical temperature, it indicates that the coal begins to undergo an intense oxidation reaction. Tg represents the burnout temperature, as the temperature reaches Tg, the oxygen supplied to the furnace is almost exhausted and then fuel molecule of coal reacts with oxygen slowly again.) Stage I (less than Tc) represents the process as the temperature of coal increases slowly, Stage II (Tc ~ Tg) the temperature of coal rises rapidly, and Stage III (more than Tg) the temperature of coal combusts steadily. In Stage I, the smaller the apparent activation energy of coal, the lower the critical temperature Tc. The apparent activation energy of coal is the smallest as the axial compression reaches the critical axial compression (4 MPa), and the thermal conductivity of coal decreases with the increasing temperature. In Stage II, the smaller the apparent activation energy of coal, the lower the Tg, and the thermal conductivity of coal goes up and down as 2, 4, 6 and 8 MPa were loaded in turn. Generally, the results show that the average oxygen consumption rate of coal increases as the porosity increases, while the average porosity of coal increases linearly with the decreasing axial compression. Furthermore, the thermal conductivity changes as a cubic function with the increasing axial compression. The results would be meaningful to explain the spread of coal-field fires and provide guidance for the on-site prevention and control for coal-field fires.