Conveying upgrades for peanut processor

Peanut processor Nutco is Canada’s biggest supplier of organic peanut butter to the US and also supplies peanut butter in bulk to confectioners and bakers. The company specialises in packaging most of its production for sale under private labels.

Several years ago, Nutco installed two bulk bag unloading systems for incoming peanuts and two flexible screw conveyors to transport peanuts and peanut fines within the plant. Besides improving efficiency, the equipment reduced manual handling and improved plant sanitation, says John Worrell, Plant Manager. “The flexible screw conveyors haven’t needed any maintenance,” he says, “and they require very little sanitation to speak of because they are completely enclosed.”

Two bulk bag unloaders, each with a 7.6 m long flexible screw conveyor, maintain a continuous flow of shelled peanuts to the gas-fired roaster in background. The fully enclosed system enhances plant sanitation and reduces manual handling.

Operator forklift loads bag-lifting frame onto the bulk bag unloader.

Based on its experience with the conveyors, the company now plans to substitute a flexible screw conveyor for a bucket elevator that delivers the peanuts to a hopper from which most of the feed goes for peanut butter production.

In Nutco’s operation, shelled peanuts are roasted, then the skins are removed in a process called blanching. About 80% of the volume goes through an attrition mill that grinds the peanuts into paste for peanut butter. The rest of the peanuts are either packaged as roasted, blanched split peanuts for retail or put through a granulator to obtain chopped peanuts. These are used for crunchy peanut butter or vacuum packed for wholesale distribution.

Nutco receives shelled peanuts in 900-1200 kg bulk bags. Samples from each bag are laboratory tested for mould, then the bags are stored in a cooler until they are needed for processing. At that point each bag is hung on a bag-lifting frame by four loops located at the top of the bag, and each frame is forklift loaded onto a bulk bag discharger.

Bags are unloaded into a 226 L floor hopper from which the peanuts are transported by a flexible screw conveyor to a 283 L surge hopper that feeds the process line. The bulk bag unloading stations, hoppers and flexible screw conveyors were all supplied by Flexicon Corporation.

Worrell explains that two bulk bag unloaders are used in order to maintain a continuous flow of product to the gas-fired roaster, through which the peanuts pass on a conveyor. While a bag is being unloaded at one station, an empty bag can be replaced with a full bag at the other.

Bags are unloaded through a manually operated, 305 mm dia iris valve that is pulled over the bag spout. At the lower end, the valve is sealed to an interface chute in the hopper cover via a dust-tight snap action door. This arrangement minimises dust as well as controls the flow of material. As a bag empties, periscoping extension arms automatically raise the top of the bag, stretching it into a cone shape, thereby promoting complete discharge.

Each flexible screw conveyor empties peanuts (through a discharge adapter and flexible downspout) into a surge hopper from which they are conveyed to the roaster.

Peanuts are discharged from the bulk bag into the receiving hopper through a manually operated 305 mm dia iris valve attached to the bag spout.

Each 7.6 m long flexible screw conveyor consists of a rotating, stainless steel spiral screw, housed in a 115 mm OD polymer tube.

The flexible screw conveyor consists of a rotating, stainless steel spiral screw, housed in a 7.6 m long polymer tube of 115 mm OD. The rotating screw draws in peanuts from the hopper and transports them at a 45° incline to the top of the surge hopper.

A 4 kW electric motor rotates the screw at a variable speed. The motor is located at the top end of the conveyor, above the discharge point, precluding product from contacting the gearbox seals. The stainless steel screw profile not only efficiently moves the peanuts at the required rate, but has been designed to minimise grinding and other damage to the product.

Prior to the installation of the Flexicon equipment, peanuts were received in 50 kg burlap bags. These were loaded onto skids and raised by a forklift onto a mezzanine, where they were lifted two at a time by a jib crane and dumped into the surge hopper.

The bulk bag system has improved efficiency and saved more than AU$110,000 in labour costs, says Worrell. “Previously, it would take two or three workers to unload the 50 kilo bags and load them onto the skids,” he says. “Now, it takes one operator with a fork truck.”

From the surge hopper, the peanuts drop onto a 283 L gravity separator, a perforated table that uses a combination of vibration with up-flowing air to remove dirt, stones and other debris. The peanuts then move by conveyor through the roaster and the blancher, where the skins are removed and the nuts are split by pressing and rolling them between two converging conveyors. The skins are vacuumed from the line and the product is given a final clean-up by an electro-optical sorting machine that rejects peanuts considered too dark, along with any extraneous material.

After passing through the sorter the peanuts fall into a bucket elevator which discharges into a hopper that feeds the attrition mill for making peanut butter. Milling is followed by the addition of ingredients, such as salt and sugar, plus several more process and purification steps to obtain the final product.

About 80% of the peanuts are used for making peanut butter, the other 20% is removed from the hopper through a separate port to be sold as split peanuts or processed into chopped peanuts to be used in the production of crunchy peanut butter.

In the latter case, the peanuts pass through a granulator, then over a vibrating screen that removes the fines. Chopped peanuts pass over the screen and are conveyed by a bucket elevator to the peanut butter operation.

Fines drop through the screen into a 28.3 L hopper. From there the material is moved by a flexible screw conveyor to the bucket elevator that feeds the attrition mill. In this case, the flexible screw conveyor measures 9 m long, with an OD of 90 mm and with a spiral profile screw designed for moving the fines.

Previously the fines were dropped into a drum set on a truck that was pushed away manually when the drum was full. “Now we have an automated process, with no manual handling,” says Worrell. “Before, we had to have someone there all the time, so we are probably saving AU$22,000 in labour costs.”

Next, Nutco plans to install a flexible screw conveyor in place of the bucket elevator that serves the attrition mill. “That bucket elevator is messy and has to be cleaned and sanitised weekly,” says Worrell. “It also requires a great deal of maintenance because of the chains that drive the buckets. We replace about 75 buckets every year, at a cost of AU$55/bucket. Even though it’s a hygienic design it tends to drop peanuts on the floor. Peanut meal and dust stick to the buckets.” Worrell estimates that a flexible screw conveyor will have about a three-year payback, based on savings in maintenance and sanitation.