Upgrading of Low Rank Coal by Advanced Technology

This paper describes the upgrading of low rank coal by hot water drying (HWD), flotation, oil agglomeration and chemical coal cleaning. The coals used were Asam-Asam coal (3.4 db% ash, 73.7 dafb% C) and Beluga coal (8.0 db% ash, 71.5 dafb% C). The HWD treatment was carried out at different temperatures such as 270, 300 and 330 °C. With increasing temperature water content and carboxyl content of the both coals were decreased and their floatability became higher. From the results of float-sink test for Beluga raw coal, it was estimated that a coal concentrate with 4 % ash and 92 % yield is effectively obtained by heavy medium separation for middle size coals(- 1,000 + 425μm) at a specific gravity of 1.45. Combustible matter recovery of the both HWD treated coals by flotation was 20-30 % higher than that of the both raw coals and the ash content of the froth product was lower for the treated coals than the raw coals. By 3 stage flotation of the fine HWD treated Beluga coal(53μm of average size), a clean coal product was obtained with less than 5 % ash and 76 % recovery of combustible matter. Products containing 4.1-4.3 % ash were also recovered by oil agglomeration of the fine HWD treated Beluga coals (9 and 3μm of average sizes). This result is similar to that obtained by 3 stage flotation of 53μm average size coal and it indicated that removal of about 4 % ash is impossible by physical separation method alone. Chemical coal cleaning method of the HWD treated coals with aqueous caustic process leads to a drastic decrease in ash content with a high recovery of combustible matter than that of raw coal. The ultra clean coal with 0.5 % ash and 86 % recovery of combustible matter was produced by a combination of three treatments such as the HWD, 3-stage flotation and chemical cleaning.