Decanter Centrifuges

Centrimax supplies used, but refurbished decanter centrifuges made by Flottweg, GEA Westfalia Separator, Alfa Laval, Sharples, Siebtechnik etc.

Thanks to an extensive general overhaul and delivery with a mechanical guarantee, the decanter centrifuges supplied by us fulfil the highest quality requirements.

Centrimax supplies almost all the types of decanter centrifuges available on the market:

The new PLC systems delivered with the decanter centrifuge enable a trouble-free integration in the existing manufacturing process and realise the characteristics of a new machine.

Areas of use for decanter centrifuges

Decanter centrifuges are “solid material oriented” industrial centrifuges which can process liquids / suspensions with high solid material contents (up to ca. 60% by volume).

Typical areas of use are:

  • Clarification of liquids and suspensions
  • Thickening of sludges
  • Dehydration of sludges and suspensions
  • Washing
  • Classification (wet classification of solid materials in a suspension according to grain size)
  • Extraction
  • Separation of 3-phase mixtures (two fluid phases, insoluble in each other, and a solid material phase)
  • etc.

Functional and constructional characteristics of decanter centrifuges

The decanter centrifuge belongs the continuous sedimentation centrifuges with respect to the eduction of fluids as well as the eduction of solid material.

They are horizontally positioned centrifuges with a solid wall drum (therefore also called solid wall screw centrifuges). The drum is cylindrical-conical, it consists of a longer cylindrical part (the so-called clarifying zone) and of a conical part (the so-called dry zone). The material to be processed is fed via a so-called feed tube into the drum, where, due to the centrifugal force the solid material particles sediment on the drum wall.
In the drum there is a screw conveyor rotating at a different speed, which transports the solid material from the cylindrical clarifying zone, via the conical drying zone, to the outlet openings. The difference in rotational speed determines the retention time in the drum. By changing the rotational speed, the dry content of the discharged solid material can be influenced accordingly.
The solid material is then continuously discharged at the outlet openings.
The purified fluid(s) flow through the drum in the opposite direction and are also continuously discharged freely or, as an alternative, under pressure at the end of the drum.

Decanter centrifuge rotor (drum and screw together)

The screw of a decanter centrifuge (solid wall screw centrifuge) serves to discharge the solid material from the drum and can, depending on the application, be performed differently.

Thus, in the event of abrasive media, various forms of wear protection can be added to the screw helix. Furthermore, for sanitary applications or for sticky products, the screw helix can, if necessary, be relief ground.

There are also different versions with respect to the gap of the screw helix (screw pitch) to each other and with respect to the number of screw flights.

In addition there are different designs with respect to the form and position of the holes or slits, through which the medium to be centrifuged is fed into the decanter drum.

Rotor-Geometry

The relevant measurements of a decanter centrifuge, are on the one hand its drum diameter and on the other hand the ratio of the drum diameter to the drum length (D/L). Often the ration drum length to drum diameter (L/D) is specified.

Simplified, one can say that decanters are normally built in the versions D/L = 1:2 or 1:3 or 1:4. The longer version 1:4 is used if, due to the product, a longest possible clarification zone is needed.

Decanter centrifuge drive

There are different types of drive for the decanter centrifuge drum and the screw conveyor.

The simplest version is the drive for drum and screw via a (cyclo or planetary) gearbox which is driven by a belt. In this case the rotational speed of the drum and the screw are constant can only be changed when the decanter is at standstill.

In the event of changeable solid material contents in the suspension being fed in, it can make sense to select a drive type with which the rotational speed difference can be changed during operation. This is, on the one hand, in order to prevent a clogging of the screw or the drum due to a high solid material loading, and, on the other hand, to maintain the dry content of the discharged material as constant as possible. Regarding this, there are different drive systems available (also called “Back drive”). To control the difference in rotational speed in these cases the required torque that the screw has to exert, in order to discharge the solid material, is used.

Decanter housing

On decanter centrifuges one can roughly differentiate between two different types of housings.

For the tunnel construction (e.g. on the GEA Westfalia Separator and Siebtechnik) the housing is constructed as a load bearing shell for the rotor (drum and screw conveyor). This design is very stable and torsion resistant. It has the advantage that, with very little dismantling effort, the complete rotor as well as only the screw conveyor can be withdrawn axially (e.g. for cleaning or inspection purposes).

For the frame construction (e.g. from Flottweg, Alfa Laval (Tetra Pak), GEA Westfalia Separator, Sharples) on the other hand, the rotor is fixed on two pedestal bearings which are connected to each other by a frame. This frame usually bears the motor. Around the rotor the housing is divided into an upper and a lower half. The lower half of the housing is suspended in the frame while the upper half of the housing (usually foldable) is screwed to the lower half of the housing.

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