低品位炭の改質および高度脱灰に関する研究

Abstract

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.