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Coal Preparation

Residual Moisture Reduction Through The Development Of An Air Purge Centrifuge Stage 1 Bench-Scale Feasibility Study

Coal Preparation » Dewatering

Published: March 95Project Number: C3088

Get ReportAuthor: BK Johnston, CJ Veal, SK Nicol | CSIRO Division of Coal and Energy Technology and Novatech Consulting Pty Ltd

This was the first in a series of projects in which the overall objective was to reduce the limiting residual moisture of centrifuge products by 1 wt% absolute basis (or 20 wt% on a relative basis) by injecting a turbulent flow of air or steam through the particulate bed inside the centrifuge.  This project conducted preliminary lab scale experiments.  Two further projects (C4048 and C5448) conducts pilot and full scale tests respectively.

Air or steam purging were thought to have several advantages over alternative methods since no reagents are added (as in surfactant-enhanced dewatering) which may produce adverse downstream reactions, and purging performance should be relatively insensitive to coal type or water quality.  Furthermore the technology should be much cheaper than thermal drying because the water is removed in the liquid phase thereby avoiding the latent energy of evaporation.  

In batch tests involving simultaneous centrifuging and purging with air, moisture reductions of up to 2 wt% absolute basis (40 wt% relative) were achieved, well in excess of the target.  The extent of moisture reduction depended on air purge conditions with a short-duration, high-velocity, air stream proving to be the most effective.  Purge times of 5 - 10 were used.  Coals from two washeries with significantly different reflectance values and implicit surface properties gave almost identical responses to air purging.

Purging with steam proved to be even more effective than with air, moisture reductions up to 2.5 wt% absolute basis (50 wt% relative) being achieved in batch tests involving simultaneous centrifuging/steam purging.  As with air the extent of moisture reduction depended on purge conditions.

A very brief study using a ca 150-350 kg/h pusher centrifuge showed that air or steam purging can be translated from batch to continuous mode.  However more data are needed to substantiate this and derive scale-up factors.  This was investigated further in the subsequent projects.

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