Removal of water from brown coal by treatment with steam

It is known that when low rank coals are subjected to elevated temperatures (200–300°C) under saturated steam conditions, water is removed. The greatest uncertainty associated with the procedure centres around the rate at which this dewatering proceeds. In order to predict the overall removal rate in a proposed continuous thermal dewatering plant, a rate model is required. To do this, the physical properties of moist and dewatered Victorian brown coals were measured. The rate of water removal once dewatering temperatures were reached was also measured and found to be very rapid. The process is thus limited by heat conduction within the particle. A mathematical model for heat transfer within and water removal from a long radially-shrinking coal cylinder of variable properties was set up and tested experimentally. It was found that a non-shrinking, constant property model was a slightly better predictor of dewatering performance.