Dual plenum vs single plenum technology

AIR is the sole vehicle for moisture removal within convection dryers. But if it’s not applied with precise control, the texture, taste, quality and safety of a snack product will be in question. Uneven drying or roasting due to improper airflow not only impacts the physical properties of a product, but also has financial implications when considering lost revenue due to food spoilage, decreased yields, and inefficient energy use.

Thermal processing is the science that combines the flow of air and the transfer of heat and moisture to produce optimum product characteristics based on a desired product outcome. Engineers apply the science differently depending on the product and drying application, and they determine the specific variables needed to achieve the optimum conditions. In the end, a consistently even airflow and temperature is obtained for accurate and repeatable results. This is what makes your favourite snacks have the same familiar taste and crunch every time.

Single plenum air flow

Single plenum dryers are used for a variety of snack processing applications. They use a diffuser plate that forces air to spread evenly before moving up through the conveyor bed.

“I describe the effect by comparing it to water running from a garden hose,” said Brian Hinkle, market manager for Bühler Aeroglide in Cary, North Carolina. “When water touches an object,
there’s a splash, and that moves the water into different directions. Similarly, air comes out of a fan in a straight line until something makes it turn. When this happens, we channel the process air, controlling its direction so that it gets evenly distributed.”

The plenum is the chamber located beside the conveyor bed. Mounted fans in the chamber generate airflow that moves through the product bed and alternates from up flow to down flow. The air flowing from the fan creates a trajectory effect, which when contacting the diffuser plate generates back pressure on the fans forcing an even air flow on to the product bed.

Dual plenum air flow

The dual plenum design, with airflow plenums on both sides of the product bed, is a newer design that offers even better process control.

“With dual plenum airflow, the position of the fans takes away the trajectory effect of the air as it is forced to make a 90-degree turn,” said Mr Hinkle. “This, added to the normal resistance of the product on the conveyor, is enough resistance to even out the flow of air without having to use diffuser plates. This provides for a superior product quality, colour, and moisture uniformity.”

Recognised by a higher level of sanitation and more uniform drying, the dual plenum enhances efficiency in two ways – air flow capacity is increased, and it is much easier to clean. The dual plenum dryer is increasingly popular with processors of peanuts, pistachios, almonds, macadamia nuts and sunflower seeds. Nut processors are finding the configuration provides the most reliable heat transfer for destroying harmful bacteria.

“A dual plenum dryer or roaster is especially valuable for nut processing where there’s a critical need for kill steps to remove dangerous microorganisms,” Mr Hinkle explained.

Cleanability and food safety

New export guidelines for food safety are challenging food processors to review cleaning processes and contamination risks for consumers. Therefore, the ability to kill potentially dNike Air Max 97