ΔP index with different gas compositions for instantaneous outburst prediction in coal mines

In this study we measured the ΔP (initial speed of gas emission) index with different gas concentrations of carbon dioxide (pure CO2, 90% CO2+10% CH4, 67% CO2+33% CH4, 50% CO2+50% CH4, 30% CO2+10% CH4 and pure CH4) of coal samples from the No.2 coal seam in the Yaojie Coal Mine, Gansu province, China. The effect of carbon dioxide concentration, gas composition, coal strength and particle size of coal samples on the ΔP index was investigated. The experimental results show that with gas of various compositions, the ΔP value of three samples were clearly different. The ΔP index of coal samples A, B and C (0.2∼0.25 mm) were 4, 6 and 7 with pure CH4 and 22, 30 and 21 when pure CH4 was used. Carbon dioxide concentration affects the ΔP index markedly. The ΔP index increases with an increase in carbon dioxide concentration, especially for coal B. Hence, the ΔP index and K (another outburst index) values tested only with pure CH4 for prediction of the danger of outburst is not accurate. It is important to determine the initial speed of gas emission given the gas composition of the coal seam to be tested for exact outburst prediction.