Long regarded by the general public as a potentially unhealthy, tree nuts (including almonds, pecans and walnuts) have gained a new status as a health food. Many studies have cited the benefit of eating almonds, pecans, walnuts and other tree nuts due to the unsaturated fats they contain. These are thought to prevent blood clots and erratic heart rhythms, among other benefits.1

Production of almonds, pecans, walnuts and other tree nuts in the United States has increased significantly in the past 35 years. Beginning in 1970, when production of almonds, pecans, walnuts and other tree nuts was approximately 305 million pounds (138.3 million kg), U.S almonds, pecans, walnuts and other tree nuts production has grown to over 2 billion pounds (907 million kg) by 2005. Almonds, pecans and walnuts account for the lion's share of the United States' tree nut production.2

Year-over-year tree nut production levels fluctuate. Weather is certainly one factor, but almond, pecan, walnut and other nut trees tend to vary in the production of crop yields, restoring their nutrient reserves by producing fewer nuts one year after yielding a much larger crop.3

Characteristics and Challenges

Most almonds, pecans, walnuts and other tree nuts have an average bulk density of between 30-35 lb/ft3 (481 kg/M3).4

The preparation of almonds, pecans, walnuts and other tree nuts is a labor intensive and costly process. Clean nut "meats" usually comprise about 20 percent of the field weight harvested from orchards. The remainders-twigs, leaves, soil, and in some cases, the hulls, are usually unfit for further processing and must be removed early on.5

The shape and texture of almonds, pecans, walnuts and other tree nuts is crucial when presenting them to consumers. As a result, these products must be handled gently between the orchard and the packaging process. All tree nuts have a high oil content, therefore when they are pushed through a conveying system they will leave a residue that may contaminate the vessels, making a clean-out in between load changeovers necessary.

In the United States, several outbreaks of human salmonellosis associated with raw almonds and detentions of other tree nuts suspected of contamination resulted in mandatory pasteurization rules. This means an additional step in the handling process and increased risk of damage to the shape and texture of almonds, pecans, walnuts and other tree nuts. Gentle, low speed conveying for these materials between any two points is the best method to prevent them from any damage or degradation.

If the almonds, pecans, walnuts and other tree nuts are being pneumatically conveyed into a processing system, the blower used to move them though the convey line must be sized to meet the system. When conveying whole

Tree Nuts

nuts, care must be taken to maintain an airline velocity that does not result in an impact forceful enough to cause damage to them. For ground and mixed nuts, preventing particle segregation during this process is important. Almonds, pecans, walnuts and other tree nuts are usually abrasive, either in full nut or ground form. This means the equipment used to convey them must be able to withstand the potential for abrasion.

If the tree nuts arrive at the processing facility in bulk bags (either as whole nuts or in some pre-processed form including flour or meal), the frames used to discharge these bags should ideally be equipped with additional accessories to completely empty the material from the bag. This includes features such as "periscoping" unloader frames that will stretch the bags, making them rigid and removing any accumulations of material lingering in the bags. Activating devices positioned on the discharger frame closer to the bag spout will promote a better material flow and help ensure complete evacuation of the almonds, pecans, walnuts and other tree nuts from the bags. Some of these bag activating devices also serve as a dust tight seal between the bulk bag and the receiving hopper.

After the bulk bag has been connected to the receiving hopper and the material begins to flow, the air inside the hopper is forced out. Unless this air passes through a filter, airborne dust particles can escape into the surrounding atmosphere. A dust collector mounted on the discharger frame will contain this dust inside the conveyance system. A pneumatic pulse through the filter can remove the dust collected there after the bag has been completely emptied. This reduces the time necessary to perform the routine cleaning and sanitation typically required in most food processing environments.

In whole form, almonds, pecans, walnuts and other tree nuts are generally free flowing and will pass through most processing equipment without the need for flow promotion devices. On the other hand, sliced or ground almonds, pecans, walnuts and other tree nuts tend to interlock in hoppers, impeding flow into downstream processing equipment. To promote a better flow, the feed hoppers may need to incorporate devices such as mechanical agitators or vibrators.

Many orchards prefer to ship whole tree nuts in 50 lb (23 kg) boxes. A dumping station with a dust hood, filtration devices and a pneumatic pulse cleaner is the recommended solution to support the manual unloading of the material. A hopper screen above the receiving vessel will help to prevent the introduction of foreign objects and protects the operators if the nuts are being dumped manually into a hopper that is equipped with agitating devices.

If a flexible screw is being used to convey the almonds, pecans, walnuts and other tree nuts it is important to use a screw that matches the nuts' application requirements. Generally a screw with a wider and rounder profile will be effective in moving a material with the characteristics of tree nuts from the hopper to a filling machine undamaged and with no separation of blended products. For chopped or ground nuts, a wider, flatter, spiral is usually the best option.

Should your almonds, pecans, walnuts and other tree nuts require loading into bulk bags, the bag capacity will be maximized by use of a vibratory densification deck to level the nuts as they fill the bag and by the application of load cells to achieve the desired weight. Seals and other dust containment devices will ensure a dust-tight operation.

Flexicon Applications:
Flexicon's FLEXI-DISC® Tubular Cable Conveyor is particularly suited for gentle conveying of whole almonds, pecans, walnuts and other tree nuts, transferring the material over short or long distances from single or multiple inlets to single or multiple outlets. FLEXICON Flexible Screw Conveyors move tree nut materials short to medium distances, satisfying an exceptionally broad range of applications. Both conveyors are ideal for feeding tree nut packaging lines.

Flexicon also offers bulk bag dischargers, bulk bag fillers, bag dump stations, drum/box/container dumpers and weigh batching systems as stand-alone units or as integrated systems with Flexicon conveyors.

Flexicon's expert design and engineering staff can recommend the best solution for your specific need. Upon your request, Flexicon's test lab can simulate your tree nut handling application using your actual material before building your equipment, and perform Factory Acceptance Testing (FAT) prior to shipment.

About Flexicon:

The ability to move your material efficiently, together with equipment designs and finishes that meet numerous regional and national codes worldwide for chemical, food, dairy and pharmaceutical applications, enables Flexicon to satisfy virtually every aspect of your bulk handling requirement, regardless of material, industry or location worldwide.

In addition to engineering and integrating your system, Flexicon can guarantee its performance, removing the risk and the resources associated with managing multiple vendors.

For performance data on your specific material(s), please contact a Flexicon regional applications engineer.

Related Articles on Almonds, Pecans, Walnuts and Other Tree Nuts:

1 Harvard School of Public Health, The Nutrition Source Nuts for the Heart
2 United States Department of Agriculture, Fruit and Tree Nuts
3 Ibid
4 Powder Bulk Solids Bulk Density Chart
5 US Environmental Protection Agency, Almond Processing

Sources: Where noted. All other information courtesy of Flexicon Corporation.