Drying of Beulah-Zap lignite

Abstract

Lignite dried in a stream of dry nitrogen at moderate temperatures (20–80 °C) loses water in two distinguishable modes. The first mode represents about 80–85% of the loss of moisture. The second represents the other 15–20% lost under these conditions. The rate follows a unimolecular mechanism (like radioactive decay) for each mode. The activation energy for the first mode is close to the heat of vaporization of water. The rate is dependent upon the gas flow around the sample and the weight (or thickness) of the sample. Work at Amoco Oil Company indicated that the oil yield was higher for the dried coal than for raw or partly dried lignite. Work at Southern Illinois University showed that the mechanism was the same when differential scanning calorimetry was used to follow the kinetics of drying. Other work at the University of Southern Mississippi showed that the physical structure of the lignite (measured by X-ray diffraction) is measurably different for the dried and raw materials.