An experimental investigation of the roles of water content and gas decompression rate for outburst in coal briquettes

The coal and gas outburst has become a worldwide challenge and is still not fully understood. In this study, an experimental investigation was carried out for outburst evolution. Coal briquettes were fabricated based on less than 0.6 mm pulverized coal particles of Tunliu Coal Mine. CO2 was used to simulate outbursts by saturating coal briquettes in varying gas pressures (0.2, 0.4 and 0.6 MPa). The outbursts of coal briquettes were induced when rapid gas decompression was performed. The results indicate the outbursts depend on the gas pressure, water content and the rate of gas decompression. The differential pressure between the gas inside and outside the coal briquette is essential to outbursts and varies for different water contents while other parameters affect the initiation and intensity of outbursts as well. The higher gas pressure the more intense outburst occurs. It is worth noting that low rate of gas decompression cannot activate any outburst in the experiments even for a high gas pressure. The water content affects the outburst strongly. The critical minimum gas pressure in the coal briquettes with high water content becomes much higher than that in the coal briquettes with low water content. The major energy of the outbursts in the experiments is the expansion energy of the free state gas inside the coal briquettes. This study clearly demonstrates the progressive fragmentation of outbursts due to gas decompression.