Moisture Content Impact on the Self-Heating Rate of a Highly Reactive Subbituminous Coal

A New Zealand power station has been importing subbituminous coal, which has oocasionally created a spontaneous combustion problem at the port storage facility. Samples of the coal have been tested using an adiabatic oven to determine the self-heating rate of the coal at various moisture contents ranging from asreceived to dry. Initial self-heating rates from room temperature were higher for samples containing up to 75% of the as-received moisture content compared to dry coal. However, the overall time to reach thermal runaway increased with moisture content. This paper clearly shows the highly reactive nature of the subbituminous coal as all tests would have proceeded to ignition, even those performed at close to the as-received moisture content of the coal.