Pilot-scale studies using a hydrocyclone and froth flotation for the production of beneficiated coal fractions for improved coal liquefaction

Kilogram quantities of coal fractions were produced using pilot-scale density and froth flotation methods. In the density separations a dense-liquid hydrocyclone was used with calcium nitrate solution as the dense medium. Three coals were used in the study: Point of Ayr, Blidworth and Bilsthorpe, and the coal fractions produced were liquefied in a 2 L autoclave using a hydrogenated anthracene oil solvent. For froth flotation, studies were carried out on Bilsthorpe coal using a laboratory flotation column and a Jameson cell and the final concentrates were liquefied in the 2 L autoclave. The hydrocyclone separations showed different yields of overflow and underflow for different coals and hence optimization of the separation density is required for each coal. Digestion in the 2 L autoclave of the overflow samples showed significant increases in overall conversion and oil production compared with the original feed coal. Pilot-scale tests with column flotation and a Jameson cell indicated that they were effective in producing a final concentrate with a vitrinite-rich fraction. These fractions showed increased overall conversion in the 2 L autoclave and increased oil production. For Bilsthorpe coal, the liquefaction products from the final concentrate of the flotation cell were very comparable with those from the hydrocyclone separation. The results show that beneficiation processes such as these could be applied at full scale and that, within the total coal complex, the production of the overflow fraction could be optimized and the much smaller underflow fraction then directed to gasification and combustion reactors.