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Reclaim the Profitable Potato Product You Didn’t Know You Had

May 11, 2020

A primary hydrocyclone is one of the first steps in reclaiming potato starch from your recirculating water stream.

A primary hydrocyclone is one of the first steps in reclaiming potato starch from your recirculating water stream.

By:
Jeff Kimpson, Senior Process Project Engineer
Roger Field, Senior Process Engineer

It doesn’t matter how you slice it (chips, strips, or cubes). If you’re not recovering potato starch, you’re dumping money down the drain.

There’s a solution though. By investing in starch recovery process improvements, you’ll achieve both cost savings and profit.

First, we’ll walk you through how a system works, then we’ll help you understand the benefits.

Starch Recovery Systems
How do you choose the right starch recovery system? There are two similar methods to consider.

  1. Decanter Centrifuges: Centrifugal force from the centrifuge’s rotating barrel separates the starch from the water. The discharge consists of a cleaned water stream and wet cake.
  2. Hydrocyclones: Centrifugal force from the pressurized flow into each cyclone separates the starch from the water. The discharge consists of a cleaned water stream and slurry. This is the most commonly used method.

Choosing the right method offers a higher return on investment. Here’s a comparison of the two:

 Decanter Centrifuge Hydrocyclone Bank
Cost  $500,000+ $100,000
Annual  Maintenance  $50,000 to $100,000 $5,000 (includes pump maintenance)
Recirculation Rate  50-75 gallons per minute 1,200+ gallons per minute

 

Hydrocyclones are more commonly used because they are simply cheaper and less maintenance-intensive than decanter centrifuges. This is true from cost, maintenance and resource reduction standpoints.

How Hydrocyclones Work
Step 1: Mechanical cutters or water knife systems cut the potatoes, which release starch. The starch amount is dependent on the specific cut size being produced.

Step 2: The cut potatoes and starch are typically contained or introduced into a recirculating water stream. Additional starch washes from the surface of the cut potatoes as they’re transported. As the product is screened out of the water stream for further sorting and grading, the starch-laden water returns to the main recirculation tank.

Step 3: A slipstream of water, typically 25 percent to 33 percent by volume, is removed from the main recirculation tank. It’s sent through a coarse rotary screen to remove large potato particulate that would plug the starch hydrocyclone assemblies. The screened water then collects in the primary hydrocyclone pump tank.

Step 4: The screened water is pumped through a bank of primary hydrocyclones. The hydrocyclones concentrate the starch (underflow) stream and return the cleaned water (overflow) stream back to the main recirculation tank.

Step 5: The primary hydrocyclone underflow stream passes through a vibratory screen with a fine mesh (100-120 mesh) to remove fine potato fibers. The concentrated starch stream collects in the secondary hydrocyclone pump tank.

Step 6: The concentrated starch stream is pumped through a bank of secondary hydrocyclones for further concentration. The secondary overflow stream flows back to the secondary hydrocyclones to maintain the tank level, while any excess is sent to the primary hydrocyclone pump tank. Since the secondary overflow stream can still contain starch, this allows it to be captured more efficiently than if it were sent back to the main recirculation tank.

Step 7: The concentrated secondary underflow stream runs through a rotary vacuum filter to remove the remaining liquid water (filtrate). This results in a wet cake of starch (see “Sellable Starch Products” below). The small volume of water removed as filtrate typically runs down the drain.

Step 8: To maintain the system’s volume, freshwater is introduced into the main recirculation tank. By managing the recirculation water system in this manner, the entire system can turn over every four to six hours.

Resource Reduction
Now you know how it works, but what benefits does it offer? Starch recovery has an immediate return on investment.

The main recirculation system will operate with fewer potato pieces and starch in the water because the starch is removed as fast as it is being liberated during the cutting process.

By lowering the starch amount that can decompose in the wastewater stream, there’ll be a lower biochemical oxygen demand (BOD) load. This direct relationship will lead to a reduction in wastewater operating costs.

You’ll also see cost savings in both daily water usage and wastewater. Cleaning the starch from the recirculating stream means the water can be recirculated for an extended period, which minimizes freshwater usage in your facility.

Sellable Starch Products
You’ve reduced your operating costs. Now what do you do with your leftover potato starch?

In food manufacturing, potato starch can be a thickener, binder, texturizer and shelf life extender. In glue manufacturing, it can be an adhesive ingredient. Sanitary products, like diapers, utilize its absorption and gelling properties. Starch can strengthen paper products and even function as a glossy paper coating.

With so many applications, your captured starch can be a significant revenue stream. To capitalize on it, you’ll need to provide the starch in a form buyers want. This includes:

Slurry: A concentrated liquid product with a dry solids content of 25 to 32 percent. Slurry is collected and stored in an agitated slurry storage tank (14-18 Baumé) for shipment to a starch processor.

Wet Cake: Slurry can be run through a rotary vacuum filter until the dry solids content reaches about 60 percent. Wet cake is typically stored in supersacks or a live bottom truck for shipment to a starch processor.

Powder: Wet cake can be further processed by running it through a flash or ring dryer until the solids content reaches 90 percent. Dried starch powder is typically stored in supersacks for shipment to a starch processor.

Putting It All Together
If you’re considering a recovery system, there are a few design criteria you’ll want to keep in mind.

Screening: Screening potato particulate prevents hydrocyclone plugging. Screening out ultra-fine potato fibers is essential before final starch product processing.

Consistent Pressure: A steady system flow and feed pressure are key to the hydrocyclone starch recovery process. Constant inlet and overflow pressures are important, as pressure fluctuations can upset the internal flow dynamics. This can cause starch to be rejected out the overflow port of the hydrocyclone.

Open Discharge: A key hydrocyclone component is the “cone spray” discharge pattern. Using an open collection flume to collect the underflow from the hydrocyclones is the most desirable design. In this configuration, the uncovered cyclone tips spray into an open flume. Operators can visually monitor the hydrocyclone discharge for clogged tips and easily correct issues.

So now you think you want to do this, what next? Engaging a trusted engineering design firm is a great step forward. They can help you with improvements or a brand-new starch recovery system.

If you’re ready to put your spuds to work, consider starch recovery and what it can do for you.

About the Authors:

Jeff KimpsonJeff Kimpson, Senior Process Project Engineer
Jeff has been designing starch recovery systems in potato processing facilities since 1988. A Chemical Engineer specializing in process and controls design for food facilities, his experience includes maintenance supervision, process design engineering, and consulting. Prior to joining POWER, he served as a manager and supervisor for engineering divisions of major food processing plants in the western United States. Contact Jeff at jeff.kimpson@powereng.com

 

Roger FieldRoger Field, Senior Process Engineer
Roger has more than 30 years of process and packaging experience for the food industry, with expertise in designing, building, programming, installing, and maintaining automated packaging equipment for large food companies. He is experienced with a wide variety of product types, including high-fat bakery mixes, soups, cereals, and cereal grains. He has also worked in R&D developing scales, baggers and other equipment. Roger is skilled at following a piece of equipment from the initial design stage to installation and startup in production mode. Contact Roger at roger.field@powereng.com