SmartDiver real time measurements of thickener interface and mud levels can help to optimize thickener operation and control providing many benefits including an increase in clarity, trim of flocculant addition, control underflow density and prevention of sliming events. In this article, we will focus specifically on quantifying the benefits of using these measurements in the prevention of thickener sliming events.
What are sliming events?
Thickeners separate an incoming feed slurry into clarified liquor going to the overflow and slurry concentrated with solids going to the underflow.
Thickener sliming events occur when solids start reporting to the overflow. These events can reduce production, through:
- direct lost concentrate reporting to the overflow
- indirect reduced mill throughput
- indirect reduced product quality
In addition to the losses in production, sliming events can result in other costs associated with damage to upstream and downstream equipment such as valves and pumps, and direct costs in process water tank cleaning as the solids finally settle in this tank.
How does SmartDriver prevent sliming events?
The SmartDiver allows operators to visualize what is going on inside their thickeners, and see abnormal changes hours before these negative events occur.
Figure 1 shows a trend outputted by the system. The mud (red) and interface (pink) levels are starting to rise at around 4am.
Figure 1. SmartDiver trend – sliming event
The levels continued to increase and at 9:00 am solids started to report to the overflow. The tank was put back under control at 17:00 hours.
This means that during 8 hours, mill throughput was reduced with lost production opportunity. With mud and interface reporting to the overflow, there was also a direct loss of concentrate.
During a site test at a gold plant in Australia, a SmartDiver was installed to capture and document the sliming events occurring. During a period of six months, eight sliming events were identified by the system. These events resulted in a loss of production of 754.7 tonnes, with a total of 4617 g of lost gold production (with an average of 577.12 g lost per sliming event), totaling around US$150,000 over the six-month period. The test was extended and SmartDiver was used in control for three more months with no sliming events.
SmartDiver level measurement trends can be used to identify and monitor thickener sliming events successfully. Such capability allows these outputs to be considered for control logic to prevent sliming events in the future.
In the example described above, the plant could have prevented a loss in production equivalent to USD 150,000 over six months. Thus, capital expenditure for purchasing and installation of SmartDiver is justifiable solely on the basis of the instrument’s capability to prevent sliming events.
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