Drying characteristics of low rank coals in a pressurized flash drying system

•The characteristics of pressurized flash drying of low rank coal were investigated.•The drying ratio mostly increased with temperatures and pressures. But the drying ratio did not increase at high pressure conditions because of increasing boiling temperature.•The empirical equation to predict drying ratio was suggested as follows: Dr=2.82×R0.63×S0.02×P0.28×T0.65. Drying characteristics of low rank coals were examined and determined using a pressurized flash drying system which consisted of a pressurized feeder, rolled tubes (maximum of 6m), a cyclone, and a back pressure regulator. The effect of the operating conditions, such as pressure (maximum of 40bar), gas outlet temperature (maximum of 300°C), particle sizes (212–300 and 300–355μm) and residence time (maximum of 1s) on the drying ratio was investigated and analyzed. The study results show that temperature is a more effective factor than pressure. A correlation equation to predict the drying ratio of coals was suggested based on operation conditions.