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Industrial Centrifuge – What is it?
An industrial centrifuge is a machine designed to use the centrifugal force generated by rotation of any mass.
When used for large scale fluid separation applications, it is an industrial centrifuge.
You can think of an industrial centrifuge being a scaled up version of a lab centrifuge (test-tube). Except at a much bigger scale with a flow-through design. That means the separated solids and liquid(s) continuously exit the centrifuge.
Types of Industrial Centrifuges
Industrial centrifuges are available in 2 configurations. These are filtration type and sedimentation (solid bowl) type centrifuges.
Filtration Type Centrifuges
A filtration type centrifuge, uses a rotating ‘basket’ with perforations. This design allows the liquid to pass through while the solids remain in the basket.
A relatively lower rotational speed (lower centrifugal force) is adequate for filtration centrifuges.
They are good for separating large amounts of coarse solids from a liquid. An example would be separation of crystallized sugar from syrup.
Sedimentation or Solid Bowl Centrifuges
A sedimentation type centrifuge has a solid bowl (without any perforations or filter media). In this case the solids accumulate along the bowl wall or periphery. The lighter liquids separate and exit the centrifuge through a liquid outlet passage.
This ‘solid bowl’ feature adds an extra benefit of these sedimentation’ centrifuge. That is 3 phase separation or liquid/liquid/solid separation of any fluid mix.
Solid bowl centrifuges are further sub categorized into 2 types. These are decanter centrifuges and disc stack centrifuges.
More information about decanter centrifuges is on our decanter centrifuge page.
Conical plate (disc-stack centrifuges) are available in 2 main configurations. Self-Cleaning and manual-cleaning types. Summary of design and application of disc stack centrifuges follows.
Self-cleaning Disc Stack Centrifuge (Auto De-sludging)
In a self-cleaning centrifuge, the inlet tube feeds the process fluid into the rotating bowl. The oil phase moves towards the center of the bowl and discharged by a paring disc (4).
The water phase leaves the bowl over the top disc (5) and through a paring disc aka centripetal pump (6). The heavier solids phase collects at the bowl periphery. The bowl discharges the solids automatically (intermittently), as explained below.
A hydraulic system below the separation space in the bowl operates the sludge discharge mechanism. At preset intervals forces the sliding bowl bottom (7) to drop down. This action opens the solids ports (8) at the bowl periphery. Centrifugal force within the bowl ejects the separated solids.
Self-cleaning disc stack centrifuges feature intermittent sludge ejection. These centrifuges are suitable for three-phase separation with solids up-to 5% (%v/v).
Higher solids concentration need frequent sludge ejection cycles, which is not desirable. Proportion of liquid phases may be in any ratio.
Typical applications of a self-cleaning bowl centrifuge
- Separation of machining coolant from tramp oil & sediment.
- Crude oil dewatering & polishing.
- Used engine oil – water & sludge separation.
- Chemical solvent clarification.
- Water & solids removal from diesel fuel.
- Wine and beer clarification.
- Large scale algae cell harvesting.
These types of centrifuges are applicable to a variety of industrial applications. Any high volume fluid separation application with two or three phase separation. The only limitation is fluids with limited solids concentration.
Manual-cleaning Disc Stack Centrifuge (Solid Retaining)
In a manual-cleaning centrifuge the feed is introduced to the rotating centrifuge bowl from the top (1). The distributor (2) accelerates the fluid before entering the disc stack (3). It is between the discs that the separation takes place.
The centrifugal force pushes the water and the heavier solids towards the bowl wall. The solids accumulate on the bowl wall and the water flows over the top disc (4) to an open outlet (5).
The light phase (oil) moves towards the center and exits the bowl through a paring disc (6).
The centrifuge is stopped at intervals for manual cleaning of separated solids. The bowl is mounted on a vertical spindle (7) driven by a horizontally mounted motor. Power transmission is via a worm gear or a pulley and belt drive system.
The solids retaining design of these centrifuge bowls allows for a simpler design. This is due to the absence of the sludge ejection mechanism.
Thus these centrifuges do not need extra operating water system for sludge ejection. This leads to simpler installation and operation.
But this design also limits the applicability of manual-cleaning centrifuges. They are only suitable for liquid/liquid separation with very small amount of solids.