Fluid Separation Technology by Trucent

What is a Solid Bowl Centrifuge?

Trucent Fluid Separation Products

In many industries a solid bowl centrifuge is the tool-of-choice for separating solids from liquids, recovering solids or liquids from slurries, clarifying liquids, and classifying solids.  Fundamentally, this is “clarification centrifuging,” where centrifugal force is used to separate the mixed materials. A mixed liquid or feed slurry is introduced into the centrifuge’s spinning bowl. The high bowl speed accelerates the mixed liquid, creating increased g-forces. These draw denser materials and solid particles out of the liquids, where they collect against the interior of the bowl’s wall.

Some high-speed centrifuges have discharge ports along the outside of this bowl. A solid bowl centrifuge does not—hence the name “solid bowl.” Because it has no discharge ports, the solid bowl centrifuge must periodically be taken out of production, opened up, and scraped out (or, alternately, shifted into “scrape cycle,” where an internal mechanism performs the scrape-and-clean without the operator having to manually dismantle the bowl).

While these separators cannot offer continuous solid-liquid separation or dewatering (because of the need for periodic scraping), their reliance on a somewhat simpler design can be very efficient, making them an extremely cost-effective two-phase liquid-solid separation solution.

Broadly speaking, there are three types of industrial solid bowl centrifuges:

Open-Top Solid Bowl Centrifuge

The open-top solid bowl centrifuge is the most basic industrial centrifuge design, one that people have used for at least a century. They tend to be small and simplistic, with a time-tested design. For that reason they are lower cost to purchase, but only capable of fairly rudimentary two-phase separations. They are most popular in small industrial or agricultural applications.

{TK img “Late 19th/Early 20th century centrifuge battery (separates sugar syrup from the remaining solid particles)” https://commons.wikimedia.org/wiki/File:COLLECTIE_TROPENMUSEUM_Centrifuge-batterij_waarin_suiker_en_resterende_stroopmassa_gescheiden_worden_TMnr_10011795.jpg from the collection of the Museum of the Tropics in Amsterdam, Netherlands}

In an open top centrifuge the mixed stream is introduced into the spinning bowl from the bottom. The centrifugal force generated by the bowl separates out denser particles, leaving the clarified liquid behind. As the mixed stream continues flowing into the bottom of the centrifuge, the clarified liquid phase is pushed up out of the top. Periodically, the operator shuts the centrifuge down and manually scrapes away the collected particles and solids caked to the inside of the bowl. Because everything leaves the centrifuge from the top, these are also sometimes referred to as “top discharge centrifuges.”

A typical use for open-top centrifuges might be in egg production and processing, where they are used to separate out and remove small egg shell fragments and grit during the egg breaking operation.

Scraper Bowl Decanter Centrifuge

A scraper bowl decanter centrifuge can be thought of as an enhanced open-top centrifuge. The fundamental principles are still the same, but a scraper bowl decanter includes an added labor-saving feature: it is equipped with an internal scraper. When the bowl begins to become filled with particles and solids, the operator initiates a “scrape cycle.” (The operator can also pre-program scrape cycles for regular intervals, if that’s preferable.)

During the scrape cycle the feed pump is shut off (preventing new solid-laden liquid from entering the bowl) and that internal blade is brought up against the bowl’s interior, collecting all of the captured solids and particles for quick removal. While this is still time out of production, it is significantly quicker and less labor-intensive than “pump-n-shovel” manual bowl emptying. The downside is that scraper bowl decanter centrifuges tend to be complex; you trade daily labor savings for higher maintenance demands.

Trucent’s CentraSep S-Series of clarifiers stands out among scraper bowl decanters. The CentraSep S-series is the only single-motor vertical-standing self-discharging scraper centrifuge in the world. Chris Clausen, Trucent’s Craft Beverage Industry Manager, has a background in engineering. He explains: 

“Most other solid bowl centrifuges like this are open top. By comparison, the S-Series is inverted, using gravity for drop-out of clarified fluid and scraped cake during the clean-in-place cycle. I love the S-series and, from an engineering standpoint, it’s one of the most elegantly robust systems. I think here we successfully addressed a pretty common problem: how to do the scrape cycle while minimizing wear, tear, and complexity.”

Manual Vertical Disc Stack Centrifuge

A vertical disc stack centrifuge (also called a “conical plate centrifuge”) can be thought of as yet another enhancement of the standard solid bowl separator. In this case, instead of introducing a scraper blade, the centrifuge bowl is filled with a series of fixed conical discs arranged in a vertical stack (and thus they are often called “disc stack” or “disc bowl” centrifuges). These discs increase the amount of available settling surface in the bowl.  This both speeds the separation/sedimentation of liquids and particles and gives you a great deal of fine control over what’s happening inside your centrifuge. The result: more efficient liquid-solid separation.  

But the tradeoff is that the cleaning step with a disc stack centrifuge of this kind is much more labor intensive. The operator must take the entire top end apart to get into the bowl and scrape it. (This is part of the reason that there is a market for self-cleaning/self-discharging disc stack centrifuges like the CentraSep DX Series.)

Solid bowl disc stack centrifuges are best in applications where the solid material is low concentration or very high in value—and the user has human effort to spare. So, for example, manual vertical disc stacks are great for doing a wash on aggregate to mine for gold or other precious metals, or pulling the very fine carbon particulate out of marine diesel while at sea.