Peanut butter output capacity doubled at dedicated facility

Two bulk bag dischargers and five flexible screw conveyors have doubled peanut butter production capacity at Once Again Nut Butter’s new 3440 m² dedicated peanut butter facility. The discharger/conveyor system delivers up to 1590 kg/h of raw peanuts to each of two roasters, for a total of 3175 kg/h. The new line provides dust-free operation and improves operator safety.

Founded in 1976 in the US, Once Again Nut Butter processes natural and organic products such as honey, sesame tahini and butters made from peanuts, almonds, cashews and sunflower seeds. As the new plant handles all of the company’s peanut products, the older facility established in 2004 for all nut and seed products will be able to operate peanut-free.

Feeding the new line are two Flexicon BULK-OUT bulk bag dischargers positioned side by side. Both are BFC models equipped with a cantilevered I-beam, hoist and trolley that lift and position the bag in the discharger frame without the need for a forklift. Five flexible screw conveyors, also from Flexicon, move the peanuts through successive steps of the process.

Side-by-side beam-and-hoist-style bulk bag dischargers allow for one frame to discharge material while the other is reloaded.

In the older plant, bulk bags containing peanuts were hoisted above the roaster and emptied directly into it. Compared to direct-emptying, “the bulk bag dischargers in the new plant are safer, automated and improve ergonomics for the operators”, said Peter Millen, Process Engineer at Once Again. The dischargers and conveyors enclose the peanuts, protecting them from contamination while preventing dust from escaping into the facility. Moreover, the new roaster is too tall to suspend a bulk bag above its infeed hopper.

Once Again installed the two bulk bag dischargers side by side, allowing one frame to discharge material while the other is reloaded, and to provide redundancy in the event one of the systems is offline.

The flexible screw conveyors transport the raw peanuts from the dischargers to a gravity separator and a de-stoner that remove foreign matter before the peanuts are discharged into a roaster, improving product quality over the direct-emptying method.

How raw peanuts are processed into peanut butter

Raw peanuts arrive in bulk bags weighing 1000 kg. The operator attaches the bag straps to the lifting frame, and actuates the electric hoist and trolley using a pendant to position the bag in the discharger frame.

The bag’s outlet spout is pulled through an iris valve which closes around the spout, preventing material flow. The operator then unties the drawstring, closes the access door and releases the valve slowly to prevent bursts of peanuts from displacing air and dust from the 156 L capacity hopper into the plant environment. A hinged lid on the hopper also permits manual dumping from handheld sacks.

The hinged lid on the hopper permits manual inspection.

The dischargers are fitted with pneumatically actuated FLOW-FLEXER bulk bag activators, which increasingly raise and lower opposite bottom edges of the bag into a V shape as it empties and lightens, promoting complete evacuation.

Flexible screw conveyors 6.1 m long transport peanuts from each of the discharger’s hoppers at a 45-degree incline before discharging into a gravity separator, which removes any foreign material that is lighter and less dense than peanuts, such as twigs or peanut shell pieces.

From the gravity separator, a third flexible screw conveyor, this one 4.6 m long and inclined at 45 degrees, takes the peanuts to the de-stoner, which removes any material that is heavier and denser than the peanuts, such as pebbles or metal fragments.

Peanuts are then loaded into a silo by a 15 m-long pneumatic conveying line and unloaded from it by another 15 m-long pneumatic conveyor line that terminates at the roaster. Roasted peanuts then proceed via a 21-m long pneumatic conveyor line to a blancher, which removes the peanut skins. Another 21 m-long pneumatic conveyor delivers the blanched peanuts to two holding silos.

From each silo, a 4.6 m-long flexible screw conveyor feeds peanuts to a roasted peanut transfer bin. From each transfer bin, a flexible screw conveyor transports peanuts to a 27 m-long pneumatic conveyor line terminating at the final grinding phase of the process.

All of the flexible screw conveyor tubes measure 114 mm O.D. and house a flat-wire spiral of the same pitch tested to yield optimum efficiency. Each conveyor’s drive motor rotating the screw is controlled by a variable frequency drive. The peanuts discharge from the conveyor below the point where the screw connects to the motor drive, preventing material contact with seals or bearings.

“For cleaning, the flexible screw is removed through a clean-out cap at the lower end of the conveyor tube, after which all components are blown down and/or vacuumed, and wiped clean with a surface sanitiser,” Millen said.

“A bulk bag discharger and flexible screw conveyors from Flexicon have reliably handled sesame and sunflower seeds in the original plant for several years. The equipment was familiar to plant staff, so it made sense to bring that technology over to peanuts.”

As part of specifying the unloading and conveying systems, the company’s peanuts were run on full-size equipment in the supplier’s test laboratory. “This provided data on attributes such as density and flow characteristics in order to establish design parameters, including different angles for running the flexible screw conveyors and product feed rates,” Millen said.