Characterization of hydrothermally dried low-rank coals

Over a period of eight years (1989 through 1997) the Mineral Industry Resea rch Laboratory (MIRL) at the University of Alaska, Fairbanks, AK, has inves tigated the effects of temperature, residence time and particle size on the degree of low-rank coal (LRC) upgrading for a nonevaporative, hydrothermal drying process, also known as hot water drying (HWD). The following three Alaskan LRCs were used in this study: Usibelli coal (Seam No. 4) from the N enana Coal Field, Little Tonzona coal from near McGrath, and Beluga coal fr om the Beluga-Yentna field on the west side of Cook Inlet. Replicated facto rial tests were conducted. Experimental results indicate that most of the l ow-rank coal upgrading via HWD occurs rapidly within the first 10 to 20 min of residence time. Thereafter, the upgrading process slot-vs down, and mor e than 100 min of additional residence time is required to produce percenta ge increases equivalent to what was achieved in the first 10 to 20 min. The properties of the hot water dried products were very sensitive to process temperature. Calorific value, carbon and oxygen contents, equilibrium moist ure levels and Hardgrove gindabilities all appear to change linearly with t emperature within the 275 degrees C to 325 degrees C (525 degrees F to 615 degrees F) range.