ENDRESS+Hauser has recently launched a low maintenance, reliable electromechanical system, the FMM 50, which solves the historical shortcomings of other technologies when optimising bed level measurement in thickeners, settlers and clarifiers.
In the mining industry, the waste materials left over after extracting the valuable mineral product are called tailings, and in most processes, tailings consist of a high percentage of water.
With optimum water management now a business imperative for all local industry, any technology that helps reduce water usage is a sound investment. Tailings thickening technologies applied to the separation processes (waster and waste) provide a quick return on investment.
Whether in the thickening or in the final clarification processes, gravity separation aided by flocculant addition results in the solids settling in the bottom of the tank as a mud and the clarified water “overflowing” to the next phase of the process.
The settled mud compacts, and is drawn away as an underflow at a rate that allows its level and density to be maximised whilst maintaining its fluidity.
Key factors for success in the tailings thickening process thus include overflow ‘water’ clarity, underflow high solids percentage, the correct choice of chemicals for flocculant dosing, and a firm and reliable bed level measurement – the ‘bed’ being the interface between the solid material and the clarified water.
Successfully monitoring the bed level during the gravity separation process, which is a direct measure of the efficiency of the settler/clarifier, content can be a particularly delicate and high-maintenance task with numerous technologies already available:
* Theoretical bed level based on the calculation of the average density, using a hydrostatic level sensor, and a non-contact ultrasonic level transmitter.
* Submerged ultrasound sludge blanket transducer to sense reflections from the solid bed
* Turbidity sensor attached to a motorised cable spool which records the light absorption of the sludge.
Because these technologies rely on sophisticated and fine-tuned primary sensing elements, or because of ‘faulty’ theoretical methods, their success has been limited in the demanding thickening environment.
A more robust solution is the buoyancy based electromechanical system, where a sensing weight is lowered on a measuring tape into the thickener or clarifier to detect the level of the dense bed underwater.
Typically the sensing weight is a light weight hollow container filled with the bed level material such that when it is lowered, it ‘floats’ on the bed, and at that point the bed level can be measured.
This more straightforward principle of operation offers a greater ease of operation, but historically often lacked mechanical integrity and was not user-friendly.
Recently, Endress+Hauser released a new, heavy-duty buoyancy electromechanical system called the FMM 50. It was based on the need to minimise price, engineering and maintenance on the one hand, whilst also offering a system that can be set up in the workshop and without the need for specially-skilled personnel.
Easy to follow instructions on set-up and ranging appears in plain English text on the local display.
The electronically controlled motor, although capable of pulling 500N, is easily adjusted for high sensitivity detection to avoid misreading on gradient sludge blankets. The use of 316 stainless steel tape instead of rope, together with four tape wipers guarantees the reliability and longevity of the design.
To overcome issues related to the use of rakes in settling tanks, the measurement cycle of the FMM 50 can be controlled by full remote control so that measurement takes place in between rake rotations.
The FMM 50 has been well proven in Australia, with increasing numbers of mining and sand excavation plant users praising its ease of operation and quick return on investment.
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