Small particles, a big challenge, and a unique approach

Sometimes going back to the drawing board is worth the time and effort. Take the case of how to separate soft, flowing material with high a concentration of very fine particles. Examples include spent yeast from beermaking, algae, sugar syrups. Standard methods involve sending material through two machines: a decanter centrifuge followed by a disc stack separator. But there is also an alternative, hybrid approach. By going back to the basic operating principles of these two machines, Flottweg engineers have solved this separation challenge by combining the strengths of both machines. Keep reading to see how it works and how it’s used in industry.

A technological two-for-one

All decanter centrifuges are based on a simple concept:

• the bowl spins the material
• solid particles are forced out and collect on the sides of the bowl
• a scroll in the center of the bowl turns and its blades convey the solids out
• dry solids and liquid are discharged separately

But products with very fine solids that do not readily compact can be hard to move with the scroll. Due to the small particle size they are slippery and difficult for the scroll blades to grab and move. Another issue is that small particle size requires higher G-forces than decanter can reach to effectively force particles out of the liquid.

Disc stack separators can achieve much higher G-forces than a horizontal centrifuge, making them useful for materials with fine particles. However, they can only handle a low concentration of particles, far lower than those in typical spent yeast, algae, and similar materials. Separators can be prone to clogging and increased cake wetness if the particle concentration is too high.

Flottweg’s Sedicanter® centrifuge combines features of a decanter centrifuge and separator into one machine able to effectively separate these types of materials. Like a decanter it can accommodate large quantities of solids and like a separator it can reach increased  G-forces to force out fine particles. The result is a dry cake and highly clarified liquid phase (i.e. centrate) in a single step.

Another key to boosting separation efficacy comes from the flow of the material and the solid and liquid phases. generally speaking, two options for direction of flow:

• Countercurrent where they flow in opposite directions (typically realized in decanters)
• Cocurrent flow where liquids flow in same direction as the solids

The Sedicanter® especially uses cocurrent flow. This results in less turbulance in the bowl and improved settling of fine particles. An sectional draweing of the Sedicanter® is below.

 

Sectional drawing of a Sedicanter®

Like Flottweg’s other centrifuges, the Sedicanter® operates continuously rather than in batches. Its automatic adjustable impeller regulates the various concentration of the infeed with on-the-fly adjustments, which maintains output results in real time .

Examples in industry

This technology is useful for many applications in the food and beverage, pharmaceutical, and biofuel industries and more. Clean in place (CIP) and hygienic design features make it suitable for applications where safety and cleanliness are critical. Some examples include:

• Beer recovery from spent yeast. Each year, brewers lose an estimated two to three percent of their beer in surplus yeast each year, impacting revenue.
• Fermentation broths for citric acid production. Precencentrated yeast from a nozzle separator averages 15 percent solids. A Sedicanter can increase this to 30 percent dry solids, saving energy in the drying process.
• Algal biomass. Algae is used for pharmaceuticals, biofuels, and more.
• Wheat starch. Effluents and pentosans do not compact easily with standard decanter centrifuge technology due to small particle size.
• Sugar syrup. The adjustable impeller aids clarification by discharging the liquid phase under pressure and applying backpressure.
• Isolated soy protein. , fine fibers, isolated soy protein, esp. very fine particles in protein recovery after wash
• Vitamin B2. High G-forces are needed to separate the high concentration of tiny crystals and bacteria after the fermentation process.

Often there is more than one way to solve a problem. For higher efficiency and easy of operation, the hybrid approach of the Sedicanter® offers a better way. Please contact us to learn more and to discuss your application.