Hot Water Drying of Subbituminous Coal

This study investigated the reduction of moisture of a Sarpy Creek Montana subbituminous coal when it was heated under pressure in a water slurry. This method of drying is called hot water drying. The temperature range investigated was from 260 C to 360 C. Two particle sizes were studied, namely, 0.4699 cm and 0.0505 cm mean particle diameters. The average initial moisture content of the coal was 26.87 percent. The hot water drying was performed in a cold charge auto-clave. The coal-water slurry was charged, heated to desired temperature and held at that temperature for 15 minutes residence time. It was then allowed to cool to ambient temperature. The moisture reduction for the 0.4699 cm diameter particle averaged at 72.52 percent as drying temperature was increased from 260 to 360 C, while for the 0.0505 cm diameter particle the moisture reduction averaged at 77.26 percent for a similar temperature range. The moisture reduction was found to be independent of both the particle size and the drying temperature. There was significant reduction of sodium content of the coal on hot water drying, and the reduction increased with drying temperature. Sodium reductions of 50 to 75 percent were obtained. Particle size did not have any significant influence on sodium removal. The calorific value of the coal also increased as a function of the drying temperature. The calorific value of the larger hot water dried particles increased from 6098 cal/g dry coal to 6514 cal/g dry coal (average calorific value of the original coal was 5960 cal/g dry coal) as the drying temperature was varied from 260 to 360 C, while the calorific value of the smaller hot water dried coal particles increased from 5544 to 6098 cal/g dry coal (average calorific value of the original coal was 5475 cal/g dry coal). The sulfur removal, though low was found to decrease with increase in drying temperature for both the particle sizes. Reduction in sulfur content and increase in heating value were higher for the larger particle size