Laboratory evaluation of ventilation effect on self-heating incubation behaviour of a high volatile bituminous coal

The concept of a “critical velocity zone” in the longwall goaf environment for the development of a spontaneous combustion event has been supported by numerical modelling. However, there is no experimental data available for Australian coals to show ventilation effects on the self-heating incubation behaviour of broken coal in the longwall goaf. Recent incubation testing has been completed on a high volatile bituminous coal with an R70 self-heating rate value of 3.86 °C/h and a moisture content of 11.3% using flow rates indicative of sluggish ventilation, natural air leakage ventilation and medium ventilation. At the higher medium ventilation flow rate, the coal initially self-heats to approximately 8 °C above mine ambient temperature, before heat loss from moisture evaporation dominates and the coal begins to decrease in temperature. Under the natural air leakage flow rate, the coal self-heats to 28 °C above mine ambient temperature before heat loss again takes over due to moisture evaporation. However, at the sluggish ventilation flow rate the coal is able to incubate to thermal runaway after an extended period indicative of a site equivalent timeframe of approximately 3 years. These preliminary results are consistent with the “critical velocity zone” for hotspot development. They also have implications for the concept of hotspot migration.