Coal Preparation » Fine Coal
In many coal preparation plants, beneficiation of the fine coal from the cyclone overflow is deemed uneconomical hence this stream has been sent to the thickener, and then onto tailings. Our objective was to establish a low capital cost solution to generate high value product from the cyclone overflow. Ultimately, we aimed to establish a small, compact, two stage flotation system consisting of Reflux Flotation Cells, capable of generating a clean coal product from the cyclone overflow. The first stage operated as a rougher, receiving 2000 m3/h of flow at 2 to 5 % solids. The goal was to reduce the footprint of the rougher stage to a 3 m diameter vessel. The work in this study indicates that this should be possible using the Reflux Flotation Cell technology.
The objective of this project was to undertake a pilot scale study of Fast Flotation in order to validate the findings from our previous laboratory scale work. This new project successfully verified the scale up of the Reflux Flotation Cell from the laboratory to a study on a lower Hunter Valley mine site. A scale-up factor of ten was achieved. The RFC300 pilot scale unit was operated through a series of Fast Flotation experiments using very high feed fluxes upwards of 9 cm/s. More conventional arrangements operate with fluxes of order 1 cm/s. The separations achieved were quantified with respect to the “ideal” flotation recovery-product ash curve produced by extended tree flotation analysis. In general, both combustible recoveries and product ashes obtained using the RFC300 were in excellent agreement with those predicted by tree flotation analysis over a range of operating conditions, hence confirming the successful scale up from the laboratory to pilot scale.
A strong linear relationship between the liquid split, defined as the ratio of the overflow liquid flux to the feed liquid flux, and product ash was verified, obtaining a reasonable correlation coefficient of 0.94. Greater precision was obtained when examining the bias flux through the cell, which improved the goodness of fit to R2 = 0.97. Through the measurement of the feed, wash water, and underflow flux (or overflow flux), the liquid split or bias flux can be determined and its set point nominated in order to achieve a certain recovery and product ash. Hence, both relationships provide system control options that could be used in a full-scale trial.
This project should lead to the development and commercialisation of new and Fast Flotation cell technology, and to new processing opportunities for plants in both thermal and coking coal operations. The high throughput capacity per unit area of the RFC could lower the overall capital investment required in the installation of large scale flotation cells, perhaps by a factor of 5 or more.