Coal Preparation

Washability Analysis of Fine Coal using a Water-Based Method

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Published: June 14Project Number: C21046

Get ReportAuthor: Kevin Galvin, Simon Iveson & David Hunter | University of Newcastle

The aim of this project was to develop a water-based method for generating washability data and analysing the partition performance of separation operations. Fractionation experiments were performed in a laboratory Reflux Classifier on coal samples in the -0.250 +0.038 mm, - 2.0 +0.25mm and -16 +2.0mm size ranges. For the finest size fraction, using 1.7mm channels, using pure water as the fluidising medium gave a near perfect match to the float-sink curve.


For the coarser samples, the channel spacing had to be increased in order to accommodate the larger particles. This caused a reduction in performance when pure water was used. However, by using glycerol solutions to promote laminar high-shear rate flow, performance was improved, resulting in cumulative yield-ash results that closely matched those obtained by the float-sink method.


This excellent agreement with the float-sink results across a range of sizes from 0.038mm up to 16.0mm means that the laboratory Reflux Classifier fractionation method can potentially be used to analyse feed, product and reject samples to determine the partition performance of separation processes. Three case studies were undertaken to test the method. In each case, samples of the feed, product and reject streams were collected, processed in the batch Reflux Classifier, and then analysed to determine the partition performance. This result was compared to the partition curves calculated from float-sink measurements.


Given the great uncertainty in calculated partition values, we can instead evaluate the laboratory water-based method based on how well it measures the density distribution of material in each flow sample. When the laboratory water-based fractionation ash data was converted into a density distribution, it gave close agreement with the float-sink data. Hence, the method has done as well as can be expected. Small discrepancies in measuring the amount of near-density material amplify uncertainties in partition curves. This applies to any method, and should not be seen as a negative finding against the water-based fractionation method.


The laboratory Reflux Classifier fractionation method has been demonstrated to be able to reliably and accurately measure the yield-ash curve of coal samples varying from 0.038 mm up to as large as 16 mm. Under ideal conditions where the samples are representative and there is a sufficient mass of near cut-point density material, the method has also been proven to be capable of accurately obtaining the partition curve. Even when the coal is fragile, and hence vulnerable to significant breakdown in water, use of the glycerol solution reduces the level of attrition sufficiently to still obtain quite reasonable agreement.


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