Thickeners and Hydroseparators

WesTech thickeners and Hydroseparators are used in many types of processes to separate liquids and solids. In FGD systems they are used to thicken calcium sulfite and gypsum slurries prior to final dewatering. Calcium sulfite slurries normally require a thickener to increase their concentration to 25 - 40 wt.% solids prior to vacuum filtration. Full-scale thickeners are usually 50 to 200 ft. diameter in FGD systems. Hydroseparators for Gypsum

Due to their larger particle size, gypsum slurries thicken much more rapidly than typical calcium sulfite sludges. Consequently, hydroseparators may be used to produce the 30 to 60 wt.% solids required prior to further dewatering.

What is a Hydroseparator?

A hydroseparator is a thickener that is designed to operate like a hydroclone cluster. It produces thickened underflow for filtration or centrifugation. Like hydroclones, hydroseparators produce overflow water containing suspended solids. The amount of solids in the overflow varies with the flow rate and particle size distribution of the feed slurry. Unlike hydroclones, WesTech hydroseparators have the additional flexibility of producing a clear overflow by adding polymer to the feed slurry. The Flocculant ties the fines to the larger particles so that the fines do not return to the scrubber system. Since the fines are not allowed to accumulate in the FGD system, the result is a slurry that can be more easily dewatered to higher concentrations.

Space Requirements

A hydrosparator requires similar space to a hydroclone cluster with its associated tanks and pumps. Because of its small diameter, the hydroseparator can be installed within building, on second and third floors and above filters for gravity feed to the filters. Hydroseparators for full-scale FGD gypsum applications are typically only 10 to 60 ft. diameter.

Flexibility and Performance

• Hydroseparators have the ability to store some thickened solids.
• They are low shear devices, which results in less crystal breakage.
• They have low horsepower requirements.
• They have the ability to use polymer to produce a clear overflow.
• The reduction in the amount of fines returned to the scrubbers results in a larger particle size distribution because new growth occurs on existing larger crystals.
• Hydrosparators have high turndown capability. As flow is reduced, the overflow becomes clearer and the ability to thicken to higher underflow densities is increased.

Cost Comparisons - Hydroseparators Versus Hydroclones

The WesTech hydroseparator also offers lower capital costs when compared to hydroclones for gypsum dewatering. This reduction in capital cost is a result of replacing the hydroclone cluster, underflow tank and overflow tank with a single, small diameter hydroseparator. The pumps required for hydroseparators are less expensive because they do not have the high pressure requirements of hydroclones.

Other Applications

The WesTech hydroseparator can also be used in a ball mill circuit to separate the coarse limestone and return it to the mill for grinding as is being done at the Merom station of Hoosier Energy. In this application the overflow carries the fine, ground limestone out as product to be fed into the FGD system. The coarse solids in the underflow are recycled to the feed of the ball mill for further grinding.

The WesTech PolyBoss is a polymer control system for automatically adjusting the polymer dosage added to a thickener, clarifier or hydroseparator. It samples the flocculated slurry, measures the settling rate and density and adjusts the polymer dosage to set points based on minimum requirements.