Thickeners — or Clarifiers, depending on the application — can be used to recover immediately reusable process water, as well as extract fines and other materials. Thickeners are used by mineral and aggregate producers, as well as by environmental contractors in industries such as wastewater management, to separate solids from liquid in a slurry.
Applications
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The benefits of Thickeners can vary from user to user depending on the producer’s needs and the industry.
For instance, Thickeners can be used in locations where water is in short supply or very expensive, providing immediately reusable process water back to the plant. They can also be used to reduce the size of settling ponds or tailings storage facilities. When combined with other downstream processing equipment, such as a Filter Press, Thickeners can potentially eliminate settling ponds altogether. In some industries, they are used as Clarifiers to remove minerals and fines from process water.
With McLanahan Thickeners, producers can recover up to 90% of their water for reuse to create a more sustainable operation. They are ideal for sites where water is scarce or expensive. McLanahan Thickeners also reduce the amount of material reporting to waste. This allows producers to reduce the size of their settling ponds or tailings storage facilities, which can be expensive and dangerous to maintain, cause permitting issues and potentially cover mineable reserves.
Most McLanahan Thickeners (but not all) incorporate a low profile rake design with or without dewatering pickets, and the rake drive is powered either by a hydraulic power pack or direct coupled electro-mechanical gearbox. A modern feedwell design based on computational fluid dynamics (CFD) modeling ensures minimal flocculant usage. Optional sensors for monitoring bed level, underflow density and overflow turbidity ensure optimal operation.
McLanahan offers a range of thickener types, including High-Rate, Ultra Rakeless, High-Density and Paste, that are tailored to an individual application. They can be used as stand-alone solutions or in conjunction with other equipment.
High-Density Thickeners discharge an underflow mud with a yield stress between 50-100 Pa., which can be pumped with a centrifugal slurry pump. They are commonly characterized by having higher side walls to provide enhanced compression effects, a steeper floor slope to assist with moving the solids to the discharge area and a low-profile rake structure combined with pickets to enhance bed dewatering. High-Density Thickeners are available with on-ground, flat-bottom tanks or elevated tanks, which allow for shorter suction lines and reduced pumping requirements.
High-Rate Thickeners are used by the aggregate and mining industries, as well as environmental contractors, to recover approximately 85% of water for reuse. This high-level of water recovery keeps water consumption at sustainable levels, as well as drastically reduces the slurry volume reporting to waste ponds. They use minimal amounts of flocculant to quickly settle the particles suspended in the slurry, making High-Rate Thickeners environmentally friendly. High-Rate Thickeners can be supplied with flat-bottom, on-ground tanks or elevated tanks, which feature short suction lines that reduce the risk of plugging.
Paste Thickeners achieve the highest possible solids concentration by gravity alone, providing maximum water recovery as high as 90% and discharging a mud with a yield stress greater than 150 Pa. Because of high percentage of solids in the mud, producers can greatly reduce the size of their settling ponds or tailings storage facilities. Paste Thickeners feature tanks with high side walls and steep floor slopes to aid with the compression effects of the mud. A rake and picket system powered by a rugged drive helps create dewatering channels in the mud bed, allowing further compaction of the mud. The Ultra Rakeless Thickeners (ULT) is similar, but features a deeper mud bed and a steeper floor slope to assist in compressing the mud without the use of rakes.
To determine the correct Thickener for an application, the following laboratory tests should be undertaken:
Subsequent to laboratory testing, a pilot plant test can be used to demonstrate viability at a larger scale; however, McLanahan can provide a process warranty on the basis of laboratory test work alone.
A lifting device is a mechanical attachment to the drive head that lifts the Thickener's entire rake mechanism out of the mud bed. While not always necessary, a rake lift is commonly used to provide some insurance against bogging of a Thickener. Should feed or flocculation conditions change and process control tools are either insufficient or inoperative, the rake lift is programmed to activate once a pre-set drive torque is measured. The drive torque is assumed to have increased due to an increase in the thickness of the mud. By lifting the rake mechanism out the thick mud, the operator can buy some time to address the change in conditions prior to the rake drive stalling. Watch How A Thickener Works to see how the rake lifts when torque conditions are high.
The role of the feedwell in a Thickener is to mix the slurry feed and flocculant under the right shear conditions to promote the fastest free settling. It is designed to translate horizontal feed momentum into a gentle vertical motion. Achieving the appropriate velocity and shear conditions are critical to minimize the polymer consumption. The feedwell may incorporate auto or forced dilution of the slurry feed to obtain the optimum solids level as identified in the testing procedure. Watch How A Thickener Works to see how the feedwell mixes and distributes the slurry particles.
Thickener costs vary due to the wide range of duties and styles. Please consult your local McLanahan representative to identify the most cost-effective option for your application.
