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Coal Preparation

Full Scale Gravity - Desliming Using Cascading REFLUX Classifiers

Coal Preparation » Fine Coal

Published: October 18Project Number: C20052

Get ReportAuthor: Simon Iveson, Anthony Price, Kim van Netten, Kevin Galvin | University of Newcastle

Considerable quantities of fine coal are disposed of as part of the tailings from coal preparation plants and there are also large inventories of fine coal in existing tailings dams. The recovery of such coal by flotation is not always possible or economic and the applicable size range of traditional gravity separation devices is generally limited and desliming often ineffective. This project presents the findings of a full‐scale trial of two REFLUX™ Classifiers operated in series which was performed at a CHPP using a custom‐built ACARP‐funded test facility. The purpose of the first 1.4 m diameter unit was to perform gravity separation to produce a clean coal product down to a particle size of about 0.03 mm. The second 2 m diameter unit then deslimed the product with minimal coal loss.

The feed covered the size range 1.0 mm down to 0 mm, a significant size range to cover by gravity separation. Feeds with 30 to 50 wt.% ash at volumetric rates up to 100 m3/h (50 t/h solids) were reliably cleaned to give product ashes less than 10 wt.% with overall combustible recoveries generally in the range 60 to 80 wt.%. When feed rates were pushed to around 200 m3/h (highest was 240 m3/h, 113 t/h solids), product ashes were in the range 8 to 13 wt.% at combustible recoveries of 43 to 67 wt.%. One final run processed 150 m3/h of a very problematic high‐slimes feed with 35 % ‐0.038 mm slimes and a head ash of 52 %, and was able to produce a product with 14 wt.% ash at 56 % combustible recovery.

Tests were performed over a broad range of volumetric feed rates, solids loadings and feed quality. These demonstrated the flexibility and ability of the system to produce clean coal products. The results were also in good agreement with laboratory and pilot‐scale test work carried out previously in project C18037. It is possible to reliably predict full‐scale performance based on laboratory‐scale trials, making this technology suitable for deployment.

Successful production of low‐ash products required the use of low cut points in the first stage gravity unit. This inevitably results in the loss of some combustible material via the gravity unit underflow reject stream. It may be worth installing a scavenger unit to help reclaim some of this misplaced material. This scavenger unit would not require any additional pumps or sumps, as it could be fed by gravity directly from the first stage unit. The product from this scavenger would also not require any significant desliming as the majority of the slimes would have reported to the overflow of the rougher gravity unit. This would give a robust and flexible circuit that could handle a wide range of feed types with low combustible losses.

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