Coal Preparation » Fine Coal
This project has generated a large quantity of detailed process efficiency information, on a size-by-size basis, for modern fine coal processing equipment.
This project is complemented by data from a parallel ACARP project (C12050) relating to detailed performance information for large diameter dense medium cyclones.
The Industry was surveyed for recent detailed partition information, on a size-by-size basis. Very few analysis sets were forthcoming. Seven sites agreed to be sampled to cover three different forms of fines processing equipment, namely hydraulic separators, spirals and flotation. Appropriate samples could only be collected from four of the sites, but two of the equipment items were able to be sampled at one of the sites, and two separate sampling runs were collected at another of the sites, leading to six new sets of detailed size-by-size partition information.
The project has identified severe losses and inefficiencies resulting from typical flow sheet configurations. These losses and inefficiencies result from that fact that most processes are “efficient” only for a very limited feed size range. That is not to say that individual processes are not capable of treating a wide range in particle size, but conversely it is advocated that any one process unit can only be metallurgically efficient if exposed to a narrow feed size range.
In order to achieve a high level of metallurgical efficiency, it could be argued that a preparation plant should be configured with at least six or seven different treatment size ranges, e.g. –125+50 mm, –50+12 mm, –12+4 mm, –4+1.4 mm, –1.4+0.5 mm, –0.5+0.2 mm, –0.2 mm. However, reality is that other parameters, namely capital cost, operating cost, process complexity and controllability all need to be taken into account. The overall optimum is always highly dependent on the size-by-size washability of the feed coal(s), since perfect metallurgical separations are not required if there is little near-gravity material around the required cut point(s).
Since operational complexity is generally reflected in operating cost, it is most pertinent to use Net Present Value (NPV) or other appropriate financial assessments to determine the most appropriate trade-off between metallurgical and economic efficiency. In order to undertake meaningful financial analysis, accurate process models need to be developed for each available option for each site, together with detailed washability data for the likely range of feed types, and realistic capital and operating cost estimates for each process option.
Most existing plants work with two or three separate circuits (particle size classes). There is sufficient information generated in this study to provide the basis on which commercial assessment of circuit configuration options could be undertaken. From the information generated in this project, it is possible that plant configurations employing four or five size-based circuits might be justified, based on yield improvements that would more than compensate the additional capital and operating costs.