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drying section of the bowl. The dewatering processbegins at the moment the solids cake, transported by thescrew (scroll), is brought out of the liquid level. If particlesize and “g”-force is sufficiently high, dewatering isinstantaneous as the fluid leaves the capillary system ofthe cake. The surface film will be all that is left aroundeach particle.

Particle size, surface structure and cake thickness greatlyinfluence the final discharged moisture. Finely granulated,incompressible solids have a high filtration resistance.With a thick cake, discharged moisture increases due tothe long filtration paths.

The level of the solids between the screw (scroll) flightsalso influences the dewatering process. Too much mate-rial between the flights inhibits the free filtration of theliquids and causes excess moisture to be transportedwith the solids.

Therefore, a large volume drying section with low solidsloading and a high ”g”-force will definitely have a positiveeffect on the residual moisture. Until now, both criteriacould only be combined in a limited way.

General

The most important design criteria of a solid bowlcentrifuge for the mechanical dewatering of finelygranulated, incompressible solids, is the residual ordischarged moisture.

This residual moisture often increases progressivelywith the increased processed quantity of solids(e.g. PVC, PE, PP, SAN).

In order to reach a desirable final discharged moisture, asolid bowl decanter is designed for heavy loading in theconical (beach) part of the bowl as a last resort.In this case, the centrifuge is completely over-sized inregards to mechanical design and clarificationrequirements.

Until now, all design efforts and even extreme speedincreases have not achieved much of a noticeableperformance improvement. These measures resulted inhigher energy consumption and reduced operating safety.

Dewatering

The dewatering of finely granulated solids is achieved indecanter centrifuges by filtration in the conical beach

TWIN CONE DECANTER -

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The TWIN CONE DECANTER

Using the TWIN CONE DECANTER, it is possible toachieve the requirements for optimum dewatering.The slurry supplied to the feed pipe is accelerated in arelatively small bowl diameter which is sufficient for therequired clarification. Small diameter means low powerconsumption for acceleration.

The sedimented solids of the clarification zone is thickenedin a short cone section (first cone of the TWIN CONEDECANTER). The sump level is variable by an adjustableweir, without influence on drying cone.

The thickened solids are discharged over the rim of thefirst cone into the much larger second drying cone.Here the cake is re-orientated and the solid cake isbroken-up und re-distributed. The larger second coneallows the cake to be situated so that the solids do not fillthe area completely between screw (scroll) flights.

In addition, the larger diameter of the second drying coneyields higher ”g”-forces at relatively low shaft speeds.

This allows any residual moisture and surface moistureto be separated from the solids and the separated liquidis discharged through a second adjustable weir.

The 10 great advantages

Clarification and drying in two separately designedand differently proportioned bowl units.

Separate and therefore optimum adjustmentsof the sump levels for clarification and drying.

No negative compromises between clarification anddrying zones.

Solids loading between scroll flights allows for theliquid to escape, and therefore the washing up ofliquid by an advancing scroll design is eliminated.This allows the use of the proven heavy duty CYCLOgear advancing scroll drive system for differentialspeeds between the bowl and scroll.

The cake is thickened in the first cone, then broken-up and discharged loose in the second drying cone.

The second cone provides a larger volume and lowerscroll flight loading between the flights.

Optimum removal of residual liquids from thethickened cake in the second, high ”g”-force and highvolume drying cone.

The separation of the large liquid loading is achievedin the smaller bowl diameter. As the diameter isproportional to the square of the required power at aspecific acceleration, this results in significant energysavings.

Optional washing possibility in the separate seconddrying cone with separate discharge of the washliquor.

No liquid carry-over from the bowl into the solidsdischarge area during slow down time.

simply logical!In the event that a small amount of solids should becarried out with the liquid discharged at the second coneweir, then this liquid with any small amount of solidsdischarged can be re-introduced into the feed pipe forsubsequent separation (i.e. the solids are not lost, justrecycled).

In the second cone, washing of the solids can now beachieved if desired, and the wash liquor can be keptseparate from the mother liquor.

Another improvement in using the TWIN CONEDECANTER is the elimination of residual liquid flowingfrom the discharge cone when the centrifuge is stopped.This liquid now discharges into the second cone area andis discharged through the second weir.

Screening MachinesProcess Equipmentcircular motion screensdouble counterweight screensround screensjigs

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RESIEBTECHNIK GmbH

Platanenallee 46D - 45478 Mülheim an der Ruhr

Phone +49 (0) 2 08 / 58 01 - 00Fax +49 (0) 2 08 / 58 01 - 300e-mail: sales@siebtechnik.cominternet: www.siebtechnik.com