2012 Volume 38 Issue 2 Pages 123-128
Fundamental drying behavior of as-mined Loy Yang coal with water content of 56 wt%, a Brown coal from Victoria State, Australia, was investigated. Weight loss due to drying was measured and drying rate was evaluated at a constant temperature of 50–90°C or a constant heating rate of 1–100°C/min. At a constant temperature, the drying rate of Brown coal showed its maximum value in the first period of drying after the heating-up period and decreased gradually. The drying behavior of Brown coal was different from that of wood, one of the best-known materials in drying, which showed two drying periods, the so-called constant-rate and decreasing-rate drying periods. From the measured data obtained at a constant temperature, the drying rate of Brown coal found to be expressed by the equation proportional to (1−X) with drying fraction X and a proportionality constant, in other words, the drying rate constant was proportional to drying temperature. The validity of the proposed drying rate equation was confirmed by comparing the predicted weight loss obtained by the equation with measured one both at a constant temperature condition and at a constant heating rate. The predicted weight loss due to drying was in good agreement with the measured one in the first and middle drying period after the heating-up period, though that in the final drying period was overestimated. Moreover, the times to achieve various drying fractions were estimated from the measured data and the drying rate equation at constant temperature condition. As a result, the time to achieve a given drying fraction increased with a decrease in drying temperature, and the time to achieve a higher drying fraction drastically increased with a decrease in drying temperature.
