Relationship between ash content and R70 self-heating rate of Callide Coal

Borecore samples from the Trap Gully pit at Callide have been assessed using the R70 self-heating test. The highest R70 self-heating rate value was 16.22 °C/h, which is consistent with the subbituminous rank of the coal. R70 decreases significantly with increasing mineral matter content, as defined by the ash content of the coal. This effect is due to the mineral matter in the coal acting as a heat sink. A trendline equation has been fitted to the borecore data from the Trap Gully pit: R70 = 0.0029 × ash2 − 0.4889 × ash + 20.644, where all parameters are on a dry-basis. This relationship can be used to model the self-heating hazard of the pit, both vertically and laterally.