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SCALE INHIBITION IN WASHERS

Mishra, A. Tharumar, M. Barham, S.

Typical Bayer operations require the recovery of valuable caustic via a counter current decantation (CCD) circuit. A major issue with the initial CCD tank, commonly referred to as the first washer, is high rates of scale formation on the tank walls, rake mechanism, feed well and exit piping. This high scaling rate can result in reduced tank life, premature rake failure, increased flocculant consumption, and increased descale turnaround time, all of which ultimately result in a reduction in the efficiency of caustic recovery from the CCD circuit, its primary purpose.

As part of a suite of technologies aimed at improving the overall efficiency of Bayer process operations, Nalco Water has developed ScaleGuard™ technology to mitigate scale formation in the washers (and other) applications. At Hindalco’s Muri Alumina refinery in India, a long-term trial of Nalco Water ScaleGuard technology has been completed. ScaleGuard was applied to the first washer for the purpose of extending the washer life and improving the overall efficiency of caustic recovery.

This paper describes how the ScaleGuard program was applied, how ScaleGuard performance was monitored, the benefits achieved as realized via the extended operational life of the washers, and the overall return on investment (ROI) which justifies the ongoing use of the ScaleGuard program.