The critical temperature is a key parameter in coal spontaneous combustion. To acquire variation of critical temperature and the corresponding relationship between the index gases and critical temperature, we gleaned the coal sample from No. 3 seam in Yanzhou coalfield, Shandong province, China. Thermogravimetry (TG) was used to conduct experiments analyzing the influences 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 experimental results showed that the critical temperature measured by TG experiment presents a trend that is augmented with the increase of particle size. When the heating rate was set up with 5 °C min~(-1) and the oxygen concentration was 13%, the critical temperatures of coal samples with different particle sizes reached maximal values. When the heating rate rose to 20 °C min~(-1) and the oxygen concentration was 13%, the critical temperatures of coal samples with particle sizes less than 0.105 mm reached maximums, while they reach minimums when the particle size was greater than 0.105 mm. When the particle was smaller than 0.098 mm, the difference of critical temperatures during two kinds of heating rate tended to first increase then decrease and reached maximum under the condition that the oxygen concentration was 13% while it reached minimum when the particle size was larger than 0.098 mm and presented a style of "M". The critical temperature was 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 CO_2 increased obviously and the value of CO_2/CO reached maximum.
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