AN INVESTIGATION OF THE CYCLONE FOR FINE COAL CLEANING

Special Research Report SR-45 The depletion of good quality raw coal and mechanized mining methods, producing more fines, has caused an increase in the percentage of mechanically cleaned coal. As a result the coal industry is faced with the problem of choosing the proper fine coal preparation equipment based on efficiency, economics, and capital and operating costs. The cyclone using only water as medium was investigated for fine coal cleaning. Preliminary work consisted of studies of the water flow rates and a sand suspension flow through the cyclone. Both constructional features of the cyclone and operating variables were considered. A new design feature consisting of a sleeve placed around the vortex finder to aid control of solids distribution was among the cyclone components investigated. Although a three inch cyclone was utilized for practical laboratory reasons, the parameters established may be reasonably transposed to large industrially~ practical units. Washability data indicated that the test coal considered would be very difficult to clean. It contained 51 per cent minus 325 mesh material having an ash content greater than 40 per cent. The clean coal product from the cyclone operation occurred as an underflow which had an ash content near 14 per cent and represented an ash rejection of over 75 per cent. The recovery of l. 45 float material exceeded 80 per cent. The sulfur occurred in particles of such size and gravity that much of it reported to the clean coal, however it is proposed that this sulfur can be effectively removed in subsequent processing stages. Information has been provided on the ability of the cyclone to clean coal efficiently in the extreme fine sizes. From the current work which was actually a classification, it appears that the conventional cyclone using only water and coal feed will be most effective in fine coal cleaning as a unit operation in a multi-stage process. Substantial quality improvement with satisfactory recoveries can be made by treating fine coals in such a process.