High-rate thickeners have shown themselves to be more cost-effective than conventional thickeners in recovering water and cyanide in gold mines, and other. Dorr-Oliver and EIMCO Hi-Rate Thickeners have the highest torque and highest throughput capabilities in the industry. The High-Rate thickeners became popular in the mid 's and are relatively newcomers to the sedimentation line of equipment. As already discussed.


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High Rate Thickeners

They probably high rate thickener produce and handle underflows at as high a solids content as conventional thickeners, and underflows must be much more closely controlled to prevent build-up and overflow of high rate thickener.

This type of unit is strongly counterindicated if scale formation is a problem or if solids tend to hang up and not slide down sloping surfaces. Solids Re-circulation Thickener Solids recirculation units comprise many types.

For feeds in the clarification regime this commonly means mixing into it, one way or another, enough recirculated solids so that the mixed feed will be in the line settling zone settling regime.

Remixing settled solids into new feed increases the thickening load and hence the area demand for thickening. As long as thickening area demand is not controlling, this costs nothing.

High rate thickener area has to be there anyway to satisfy overflow rate limitations. At some amount of recirculation thickeningarea demand will become larger than that for clarification.


The unit size will then increase with increased underflow recirculation. Obviously, the theoretical minimum area needed high rate thickener occur just as this happens, but in practice recirculation control is high rate thickener usually precise and does not appear necessary.

Solids recirculation units can be classified into those having a separate flocculation compartment and those that do not. Solids from settling compartment A return to a flocculating chamber B where they are mixed with new feed.

FLSmidth - Hi-Rate Thickeners

Recycled floccules are maintained in suspension by gentle agitation and augment the rate at which feed fines are collected. The mixed feed then flows to the settling chamber.

Since the solids are fully flocculated, there is no retention time demand, and since the high rate thickener structure is well-formed, it has a high settling rate.

This design, however, relies on a sloping bottom to discharge solids. As noted earlier, such designs become impractical in large diameters.

High rate thickener HR-THK

Settled solids are sucked up from a thickening zone by a turbine impeller atop a draft tube and recirculated to a flocculation compartment or enclosure.

High rate thickener the design of Fig. It was developed originally in Australia for clarifying cane sugar juice.


Usually flocculants are added to hold the resulting mixed feed high rate thickener structure together and to prevent segregation of fines from it.

Where, as in cane sugar juices, the line settling rate of the mixed feed exceeds the overflow rate necessary for simple clarification of unmixed feed, such a unit produces clean overflow at higher rate—in some cases much higher.

Hi-Rate Thickeners

Figure 34 shows an older design using the same principle. So the mechanism is probably just recirculation and mixing of sludge solids into the various feed streams to bring them into the line settling regime. High rate thickener one shown in Fig.

Mixed feed then flows to a settling unit of conventional configuration.

High rate thickener HR-THK

The hydrodynamically rough handling of the underflow stream undoubtedly damages the existing floe structure. Selective Recirculation Thickeners In some operations, thickener underflow is sent on to further processing, from which a certain amount of solids are returned to the thickener.

Obviously such recycling increases the load on the thickener. This condition arises most often when thickener underflow is sent for further dewatering to a device which acts as a classifier.

A solid-bowl centrifuge, for example, acts in almost all high rate thickener as a classifier, in that coarse solids segregate to some degree from fines in the machine, and the fines report selectively to the overflow.

If the centrifuge high rate thickener is then recycled to thickener feed, the recirculating load of fines which forms may in some cases become large enough to overload the thickener. This has happened a number of times in industrial practice.