Coal Preparation

Small Coal Washability by Water Fluidisation

Coal Preparation » Fine Coal

Published: July 02Project Number: C10050

Get ReportAuthor: Kevin Glavin | TUNRA, University of Newcastle

Galvin and Pratten (1999) have previously reported the technique of utilizing the density segregation effect of a narrow size range of particles in a fluidised bed to determine washability data. This has been verified with replication of yield density information, but to date there has been no investigation of the performance of the method in generating yield-ash distributions. This project examines the procedure of using water fluidisation for attaining coal washability data with a view to providing a rapid, accurate and safe alternative to the current laboratory method of float-sink testing.

In this study, the primary focus has been on using water fluidisation to obtain data for the particle size range of -4.0+0.25mm. We have identified that separation is a combination of the techniques of fluidisation and particle sizing. This study has shown that the segregation of particles is independent of whether the material is initially sized into narrow particle size ranges for fluidising or if a broad size range is fluidised and then the subsamples sized into individual fractions for analysis. This second option allows a simplification of the analytical technique for obtaining washability data by water fluidisation.

The new method has been tested using a variety of Australian coals. Results indicate good agreement between the particle density distribution data generated by float-sink testing and the new method, although, comparison of particle ash distribution information shows obvious variation mainly in the low ash region. This was especially true for one of the coals tested, which we conclude was atypical. This deviation is due to particle dispersion, which is an integral part of the fluidisation process and cannot be entirely eliminated. The application of a universal correction factor to washability information generated by the new method has been employed to effectively remove any discrepancy with float-sink data.

Although it is desirable to minimise any discrepancy between results produced by floatsink testing and the new method, the wash column data may in fact be an indication of the optimal performance of a particular coal under autogenous separation conditions, similar to jigs, teetered bed separators and spirals processing. The difference may represent the true coal washability performance characteristics that can be expected from a normal plant processing environment, in the same way the tree curve characterises optimum flotation performance.

The major advantage of the new water-based fluidisation technique is the significant reduction in the use of heavy organic liquids utilised in the float-sink procedure, and hence considerable health and environmental benefits. The new method also provides information on a size-by-size basis. Finally, application of the new method to fine particles (-0.250 +0.045mm) has also produced results comparable to the standard laboratory technique of tree flotation.


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