New Feedwell Development Significantly Improves Thickener Operation

By: Roymec Technologies  10-04-2012
Keywords: high rate thickener, Mineral processing Thickener, RadFlow Feedwell,

Metallurgical thickeners have evolved over the past century in large technologicalleaps rather than through a slow and steady progression. The first of thesetechnological leaps was the introduction of polymer flocculants in the 1950s,which transformed large diameter conventional thickeners (with flux rates of1-2 t/m/day and a rise rate of 1m/h) into small diameter high ratethickeners (with flux rates of 5-10 t/m/day and a rise rate of 2 -3m/h). The next leap was the development of more efficient closed feedwells inthe 1980s, which better mixed the flocculent and feed and more evenlydistributed the feed into the thickener body. Lastly, was the development of so-called“auto-diluting” systems in feedwells, approximately twenty years ago, whichallowed for feed dilution to take place internally within the thickener.

Roymec Technologies is evolving as a leading sedimentation equipmentsupplier and is well placed to become an international competitor with anextensive installation list and comprehensive design expertise encompassingprocess and mechanical design. Roymec recognizes a growing customer demand forefficiency, safety, and environmental sustainability.

There is still much room for the improvement in thicker design and itis theoretically possible to design smaller, more stable thickeners operatingat higher flux rates. In qualifying this statement, let us first consider howthickeners are sized; flocc settling rates are accurately determined with jar testsor dynamic desktop thickeners and multiplied with a safety factor of four orabove to give the design rise rate. However, logic tells us that a rise rate marginallysmaller than the settling rate will allow for all the floccs to settle out ofsolution. So, where does this excessively large safety factor stem from?

This safety factor is the result of ineffective volumetric energydissipation which arises when changing from low aspect ratio desktop thickenersto high aspect ratio industrial thickeners. This is to say that much of thevolume composing an operational thickener is underutilized because a largetorus shaped volume in the thickener body is effectively stagnant.

By redesigning the feedwell and launder systems, Roymec hasdramatically increased the volumetric efficiency of a thickener which in turnpromises to substantially lower the design safety factor yielding anoperationally stable rise rates exceeding 8 m/hour (material dependent).Associated improvements include small plant footprints and significantly lowerflocculant consumption. With an intensive research and design program,operating for the past two year, using analytical methods, scale modelexperimentation, CFD analysis and pilot field trials, Roymec believes it is onthe forefront of the next generation thickener, the Radflow thickener.

By running a myriad of experiments on a scale model thickener, theadverse effects associated with standard industrial feedwells were determined.These adverse flow effects include swirl recirculation and asymmetry. A highlyefficient feedwell has evolved which evenly and gently introduced the flow intothe thickener body. Similarly, a more stable and robust launder system was designed.

Keywords: high rate thickener, Mineral processing Thickener, RadFlow Feedwell,

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