Experimental study on the corresponding relationship between the index gases and critical temperature for coal spontaneous combustion

The critical temperature is a key parameter in coal spontaneous combustion. To acquire variation of the critical temperature and the corresponding relationship between the index gases and critical temperature, we gleaned the coal samples from No. 3 seam in Yanzhou coalfield, Shandong Province, China. Thermogravimetry (TG) was used to analyze the effects of particle size, heating rate, and oxygen concentration on critical temperature. The index gases were determined by 15-t experimental furnace of coal spontaneous combustion. The results showed that the critical temperature measured by TG experiment indicates a trend that is augmented with the increase in particle size. When the heating rate was set up with 5 °C min−1 and the oxygen concentration was 14.9 mass% (13 vol%), the critical temperatures of coal samples with different particle sizes reached the maximal values. When the heating rate rose to 20 °C min−1 and the oxygen concentration was 14.9 mass% (13 vol%), the critical temperatures of coal samples with particle sizes <0.105 mm reached maximums, while they reached minimums when the particle size was >0.105 mm. As the particle was smaller than 0.098 mm, the difference in critical temperatures during two kinds of heating rate tended to first increase, then decrease, and reached a maximum under the condition that the oxygen concentration was 14.9 mass% (13 vol%), while it reached a minimum when the particle size was larger than 0.098 mm and presented a style of “M.” The critical temperature as measured by TG experiment was in the range of 45.4–103.2 °C. The critical temperature is, respectively, achieved in coal spontaneous combustion by the 15-t experimental furnace, in which the concentrations of CO and CO2 increased obviously and the value of CO2/CO reached its maximum.