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Solids handling solution helps double peanut butter output

14 January 2019

Two bulk bag dischargers and five flexible screw conveyors have helped to double peanut butter production capacity. 

Once Again Nut Butter has succeeded in doubling production of peanut butter in its new dedicated facility. The plant has been created to handle all of the company’s peanut products to allow its older facility to operate as a peanut-free environment.

Feeding the two new roaster lines with up to 1,590kg/hr of raw peanuts on each line are two Flexicon BULK-OUT bulk bag dischargers positioned side-by-side. Both are equipped with a cantilevered I-beam, hoist, and trolley that lifts and positions the bag in the discharger frame without the need for a forklift. Five flexible screw conveyors, also from Flexicon, then move the peanuts through successive steps of the process.

“Previously bulk bags containing peanuts were hoisted above the roaster and emptied directly into it. Compared to this direct-emptying method the bulk bag dischargers in the new plant are safer, automated, and improve ergonomics for the operators," according to Peter Millen, process engineer at Once Again Nut Butter. The dischargers and conveyors enclose the peanuts, protecting them from contamination while preventing dust from escaping into the facility. 

The two bulk bag dischargers have been positioned 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 removes foreign matter before the peanuts are discharged into a roaster, improving product quality over the direct-emptying method.  

As part of specifying the unloading and conveying systems, 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,” said Millen.

The process
Raw peanuts arrive in bulk bags weighing 1000kg. 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 156l capacity hopper into the plant environment. A hinged lid on the hopper also permits manual dumping from hand-held sacks.

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 6.1m long transport peanuts from each of the discharger 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, with a length of one 4.6m and inclined at 45 degrees, takes the peanuts to the de-stoner, which removes any material heavier and denser than the peanuts, such as pebbles or metal fragments. 

Peanuts are then loaded into a silo by a 15m long pneumatic conveying line, and unloaded from it by another 15m long pneumatic conveyor line that terminates at the roaster. Roasted peanuts then proceed via a 2m long pneumatic conveyor line to a blancher, which removes the peanut skins. Another 21m long pneumatic conveyor delivers the blanched peanuts to two holding silos. 

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

All of the flexible screw conveyor tubes have an outside diameter of 114mm and house a flat-wire spiral of the same pitch tested to yield optimum efficiency. Each drive motor on the conveyor to rotate 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," said Millen. 

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