Improving the Efficiency of the Tailings Thickener in Coal Prep Plants
Hawk Measurement, which manufacturers the largest range of sonar products to provide optimized performance for all bed level thickener applications, was able to solve a customer’s return water quality problem with an award-winning product.
The customer, a major coal producer, had multiple coal types that they processed through the coal preparation plant.
Some of the coal types produced had different settling characteristics, which affected the tailings thickener efficiency. Also, the “clarometer” automatic flocculent dosing system that tested settling rates in the incoming feedwell failed from time to time, which meant that the floccing rate changed and the suspended solids increased, decreasing the quality of the return water back to the prep plant.
To fix this, Hawk provided a high-powered, three-crystal sonar transducer with automatic scum cleaning impact plate. The two outputs of the sonar system provided BED level (Heavy density compacted interface) and lighter density hindered/fluffy interface layer.
This heavier BED level output was used as one of the input loops to control the underflow pump, in the cascade control loop with the underflow density transmitter, guaranteeing an optimized density being pumped to the tailings dam.
The hindered/fluffy layer was used to monitor the deviation distance between it and the heavier compact bed. As the deviation moved greater than a set distance, flocculent dosing increased. As the deviation decreased, flocculent dosing decreased.
There is a direct correlation between the compact bed level and the lighter hindered/fluffy layer that is affected change in settling conditions caused by ore types; change in settling conditions caused by a change in infeed hydraulics; and change in settling conditions caused by flocculent type and coagulant dosing.
The high powered three-crystal array transducer penetrated the suspended solids, even under poor settling conditions. The hindered/fluffy layer output could also be used in the floc dosing control loop to automate this function if the “clarometer” failed.
Hawks’s ORCA sonar has been awarded two prestigious honors this year – Plant Engineering Magazine’s Product of the Year, and Processing Magazine’s Breakthrough Product of the Year, based on the innovative success in optimizing thickeners and clarifiers.
In March 2008, Hawk introduced a new line of “fourth generation” sonar transducers for improved sensing of Interface levels in tailings, paste, concentrator and Lamella thickeners, settling tanks and CCDs. The new sensors offer big improvements in overall power, penetration and calibration density range. They provide better capability under high suspended solids loading, “sliming” and generally upset process conditions.
The new Hawk array transducer designs include three to seven sonar crystals mounted in a single head. Each sonar array produces a concentrated sonar beam, providing more emitted power and collecting more returned signals. Array transducers yield better penetration, higher sensitivity, and better overall performance in the most difficult environments.
For more information:
Phone: (888) 429-5538
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Web site: http://www.hawkmeasure.com
