Outotec introduces ‘Next Generation’ feedwells
Thickening of solids to separate and recover water has been a critical step in mineral processing plants since the late 19th century. Initially, effective dewatering of the solids was required to recover the valuable minerals, but now in the 21st century recovery and re-use of the water is equally important, Richard Triglavcanin explains. Development of flocculants in the early 1960s started a revolution in thickener design and operation eventually leading to the start of high rate thickening in the late 1960s. These thickeners are characterised by a feedwell with a bottom plate to deflect the flocculated feed horizontally into a preformed flocculated bed. Modern high rate thickeners generally incorporate some form of internal dilution into the feedwell to dilute the feed and improve flocculation. Other than some minor design changes, feedwells in high rate thickeners have changed little for nearly 40 years. The feedwell’s Job A thickener feedwell has six basic functions to fulfil:
- Dissipate the energy of the incoming feed
- Introduce dilution water to achieve the optimal density in the feedwell for flocculation of the solids
- Mix the flocculant into the incoming feed
- Retain feed in the feedwell whilst dilution and flocculation occur
- Distribute the flocculated material evenly over the thickener diameter
- Deaeration of the incoming feed.
- Excessive use of flocculant that increases operating costs and can lead to “doughnuts” forming in the thickened bed
- Uneven distribution of feed into the thickener bed leading to possible torque and raking issues
- Poorly flocculated feed exiting the feedwell that forms a plume on the surface of the thickener and results in solids carry over into the clean water launder
- Decreased underflow density
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