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An industrial centrifuge is a separation machine that uses centrifugal force to separate solids from liquids. A centrifuge exerts a centrifugal force that is thousands of times that of gravity.
This force causes the immediate separation of solids from liquids. And, in the case of immiscible liquids with different densities, it separates the fluids as well.
You can think of an industrial centrifuge is 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.
Industrial centrifuges fall into two main categories: Filtration type and Sedimentation type.
A perforated media allows the fluid to exit the 'screen' bowl in a filtration centrifuge while retaining the solids. The separated liquid collects in the bowl casing and drains out.
A relatively lower rotational speed (lower centrifugal force) is adequate for filtration centrifuges.
They are suitable for separating large amounts of coarse solids from a liquid. An example would be the separation of crystallized sugar from syrup or a chemical precipitate from the supernatant.
There are various mechanisms to collect the separated solids. A description of some of these methods is in the following section.
There are a variety of filtration centrifuges.
A peeler centrifuge has cloth media, which the user 'peels' away with the solids. A basket centrifuge has a perforated 'basket' that retains the separated solids.
Pusher centrifuges have slotted bowls with an articulated pusher arm to 'push' the accumulated solids. A wire mesh 'screens' holds the solids in screening centrifuges.
A sedimentation centrifuge does not use a flow-through or perforated screen or media. This centrifuge uses a solid bowl, which is also known as a 'solid bowl centrifuge.'
The centrifugal force causes the denser solids to collect along the bowl wall. The lighter liquid thus separates from the solids. A liquid pathway allows the separated fluid to exit the bowl.
This 'solid bowl' feature adds an extra benefit to these sedimentation' centrifuge.
The same centrifugal force also causes the differential settling of two immiscible liquids. In this case, the centrifuge separates all three phases, liquid, liquid, and solid. This separator is known as a 3-phase centrifuge.
The primary difference between filtration and sedimentation centrifuges is the bowl design. A filtration centrifuge has a pass-through bowl that allows the liquid to pass through and retains the solids. The sedimentation centrifuge has a solid bowl that uses differential settling to separate the solids from the liquid.
The following summarizes the other differences between these two types of centrifuges.
The particles separated by each centrifuge vary in size primarily due to the centrifuge design.
The perforation size in the filtration type centrifuge defines the particle size separation. Therefore, a filtration centrifuge separates particles that are bigger than the size of the perforation in the bowl wall or screen. This separation ability limits the application of filtration-type centrifuges to the preset size of particles.
The sedimentation centrifuge, however, uses the centrifugal force for separation. The scroll pushes out all the separated solids, regardless of size, out of the centrifuge bowl. Therefore, a solid bowl or sedimentation centrifuge can separate a wide range of particle sizes from the liquid.
Sedimentation centrifuges use the difference between the specific gravity of the solids and liquids to affect separation. Therefore, these centrifuges exert a high g-force for effective separation.
Filtration-type centrifuges need a lower g-force to push the liquid through the bowl perforations.
Typically the sedimentation type centrifuges have centrifugal force from 3,000 Gs to 10,000 Gs, while the filtration type centrifuges have less than 2,000 Gs.
The sedimentation centrifuge ejects the separated solids continuously during sedimentation. A rotating scroll (auger) within the bowl pushes out the separated solids.
A filtration type centrifuge accumulates the separated solids, which a scraper scrapes out of the bowl periodically.
The flow-through bowl of the filtration centrifuge allows the liquid to flow out of the bowl. The separated fluid discharges under gravity from the centrifuge vessel.
The separated fluid in a sedimentation centrifuge rotates at high speed. The built-in pump converts the rotational energy into pressure that discharges the separated liquid under pressure.
A filtration centrifuge, as the name suggests, often uses replaceable filtration media. This media replacement adds to labor and material cost.
A solid bowl sedimentation centrifuge uses the amplified force of gravity to separate the liquid from solids. This type of centrifuge does not require replaceable media, thereby saving cost and time.
There are essential differences between the sedimentation and filtration centrifuges in their design. The following are the key differences between these centrifuges.
The moving parts in this section refer to internal moving parts within the centrifuge. The rotating bowl is a standard moving part in all centrifuges.
The filtration type centrifuge typically has an articulated scraper or blade that periodically scrapes the separated solids from the inside surface of the bowl. The scraped solids then fall out from the bowl by gravity.
A rotating scroll within the sedimentation centrifuge bowl pushes out the separated solids. This solids ejection is a continuous process during which the solids eject out from the rotating bowl due to the centrifugal force.
The filtration type centrifuge has a perforated bowl to allow the separation of liquid from solids and let the separated liquid pass through. The size of these perforations determines the separation particle size.
A sedimentation centrifuge has a solid bowl, and therefore, it is also known as a solid bowl centrifuge. The absence of perforations makes the solid bowl centrifuge more durable with long service life.
Certain areas of the centrifuge bowl are prone to erosion due to the contact with moving abrasive particles. The application of erosion protecting coatings is essential for centrifuge durability.
The solid particles passing through bowl perforations in a filtration centrifuge can wear out the pores expanding the perforation sizes over time. The application of erosion protection to these pores is not always feasible.
The solid scraper or plow in the filtration centrifuge is susceptible to wear. A hard surface coating on the plow edge ensures wear-resistance.
The rotating scroll in the sedimentation centrifuge bowl pushes out the solids. The scroll flights are always in contact with the solids and experience erosion wear. The application of erosion-resistant material, such as tungsten carbide, protects the scroll flights from wear.
An industrial centrifuge capacity (throughput) is the volume of fluid the centrifuge can process in a given time. A decanter-type industrial centrifuge can process 5 to 300+ gallons per minute. An industrial disc centrifuge has a capacity range of 1 to 200+ GPM. The actual processing capacity depends on the process fluid and contaminant level.
The following table lists the capacities of popular sedimentation centrifuges.
|Rated Capacity (Water)||Capacity for 180 cSt Oil|
|Industrial Disc Centrifuge|
|Alfa Laval MOPX 207||32 GPM||12 GPM|
|Alfa Laval WHPX 513||100 GPM||35 GPM|
|Industrial Decanter Centrifuge|
|Alfa Laval NX-314||80 GPM||15 GPM|
|Alfa Laval NX-418||172 GPM||40 GPM|
The cost of an industrial centrifuge is dependent on several factors. The primary factors that determine the cost of industrial centrifuges are as follows.
A small filtration type centrifuge from an established quality manufacturer starts at approximately $30K, while a high capacity unit can cost over $300K. Remanufactured units typically cost 60% of comparable new filtration centrifuges.
Sedimentation type centrifuges have a wider range of costs. A small decanter centrifuge starts at around $50K, while the high-capacity decanters cost over $1M.
Industrial centrifuges find applications in a range of processing and manufacturing industries. See our comprehensive list of centrifuge applications.
Chemical industries use centrifuges to produce coarse and refined chemicals. Sanitary centrifuges find a host of pharmaceutical industry applications, from raw ingredients to finished drugs under hygienic manufacturing processes.
Biotechnology-related companies use disc-stack centrifuges for cell harvesting and reactant recovery methods.
The food industry also has extensive uses for centrifuges. For example, the separation of beer from yeast, orange juice from the pulp, milk from milk-fat, wine from must, flavor extraction all use centrifuges.
The comparison of industrial centrifuges with filters or similar media-based separation methods is quite common. These centrifuges offer several over conventional static separation technologies.
The following is a list of some of the main advantages of industrial centrifuges.
Industrial centrifuges process the fluid continuously for extended periods. They don’t require the downtime associated with filter media replacement.
Continuous operation translates into higher production volume, which leads to increased efficiency.
In the case of filtration, as the filter media accumulates the solid contaminants, the flow-through area (pores) reduces, which in turn reduces the flow volume.
The frequent replacement of filter media is necessary to get higher flow volumes, and this cycle continues with varying flow-rates.
On the other hand, an industrial centrifuge uses mechanical separation to separate and eject the solid contaminants. This purging is a continuous process that allows a centrifuge to process without any reduction in flow-rate.
Industrial centrifuges are heavy-duty machines with an expected life expectancy of 30+ years. Unlike filters, which require constant manual servicing (media replacement), centrifuges are self-operating with fully automatic operation.
The automation practically eliminates service-related downtime, which enhances reliability.
Minimize Product Loss:
The flow-through design feature of industrial centrifuges eliminates the need for manual replacement of filtration media.
Therefore, product losses associated with filter or media replacement are not a concern in centrifugation. Minimized product loss leads to higher productivity and profits.
Low Operating Cost:
The only cost of operating an industrial centrifuge is utilities (electricity, water, air). There are no labor or media costs, which are the main costs related to filters.
Based on the above, the cost per gallon of fluid processed with an industrial centrifuge is negligible. This low operating cost helps the centrifuge owners to recuperate the capital cost remarkably sooner than thought.
Industrial centrifuges are one of the most prolific and understated processing equipment. They have applications in almost all processing industries as described above.
If any type of fluid is handled in a specific industry, chances are there is an suitable application for an industrial centrifuge.