BULK HANDLING EQUIPMENT & SYSTEMS

Grains

Overview:

Grain is the harvested seed of grasses such as wheat, oats, rice, and corn. Other important grains include sorghum, millet, rye, and barley. Also called cereal, grain is humankind's most important staple food, which is a food that can be eaten fresh or stored long-term for later use. Rice, corn, and wheat are the most common staple foods on Earth.

Almost half of the grain grown around the world is harvested for people to eat directly, as humans get an average of 48 percent of their calories, or food energy, from grain. A third of the world's grain supply is fed to animals. Most domestic animals, from livestock to pets, are fed food rich in grain and grain products. Grain is also used to manufacture cooking oils, cosmetics, and alcohols.

The rest of the world's grain supply is used in the manufacture of industrial products and fuels. Biodiesel is a fuel used for vehicles. One type of biodiesel is ethanol, which can be made from corn. Strong demand for ethanol production has resulted in higher corn prices and increased corn plantings.

Grain is a major component of most national world economies. In the U.S. more than 90 million acres (36 million hectares) of land are planted to corn. Wheat trails only corn in grain plantings, with 63 million acres (25 million hectares) of U.S. land being used to grow this grain. Grain remains the world's largest food yield with more than 2.3 billion metric tons produced annually.

Grain handling facilities include grain elevators, feed mills, flour mills, rice mills, dust pelletizing plants, dry corn mills, facilities with soybean flaking operations, and facilities with dry grinding operations of soy cake. These facilities may receive, handle, store, process and ship bulk raw agricultural commodities such as (but not limited to) corn, wheat, oats, barley, sunflower seeds, and soybeans.

Characteristics and Challenges

Grain dust is the main cause of explosions in grain handling. These explosions are often severe, involving loss of life and substantial property damage. Grain dust is highly combustible and can burn or explode if enough becomes airborne or accumulates on a surface and finds an ignition source. OSHA standards require that both grain dust and ignition sources must be controlled in grain handling facilities to prevent these potentially deadly explosions.

Grain is marketed normally in whole grain form and is considered to be of inferior quality if broken. Breakage may occur from fissures as a result of excessive drying/weathering conditions in the field or during handling. Breakage reduces quality by reducing acceptability and by increasing susceptibility to infestation during storage. This affects milling yield by contributing to weight loss.

Consultation with an experienced material handling systems engineer is recommended when considering a grain conveying solution. Most grain types will have irregular shapes, and bulk shipments usually contain fines. One problem that may be encountered when grain is put in motion is flooding, which could result in expensive and time consuming spillage cleanup efforts. Other problems such as bridging, rat-holing, and convey-line equipment wear can result in greatly reduced processing efficiencies and extensive production line shutdowns. Grain fines are also aeratable, meaning the particles can become airborne and escape into the surrounding atmosphere. This dusting can create highly hazardous conditions.

If the grain is being pneumatically conveyed into a processing system, the blower used to move grain through the air line must be sized to meet the demands of system. The pipes carrying the grain may need grounding to prevent a static
Grains
 
electricity shock. Potential plugging problems must also be considered. Some grain plugs will disperse on their own if no additional grain enters the convey line, but others may require manual cleaning to remove them.

Grain is best handled gently so as not to create fines. Slower speeds are recommended to reduce the risk of damaging the grain.

For grain being unloaded from bulk bags, a secure, dust-tight connection between the bag spout and the equipment inlet is recommended. Flow-promotion mechanisms should be applied to aid in the full evacuation of grain from the bag. These include spring-loaded frames that stretch the top of the bag upward as it empties and elongates, causing grain to flow from the corners of the bag, and pneumatically-actuated flow promotion devices that massage the bag and direct non-free-flowing grain into the bag spout.

To prevent the escape of dust in the event of a leak and/or when incoming grain displaces air, the sealed system can be vented to a dust collector that puts the entire system under vacuum. This provides the added benefit of collapsing empty bags prior to tie-off and removal, preventing dust generation when empty bags are flattened manually.

Feed hoppers should be designed with proper geometry and may need to incorporate accessories such as vibrators to aid in the densifying the grain. A hopper screen above the receiving vessel will help protect the operators if grain is being dumped manually into a hopper that is equipped with agitating devices.

When filling bulk bags with grain, dust can be contained by making secure connections between the material feed source and the bulk bag filler inlet. The sealed system is vented to a filter sock or optional dust collection system to prevent displaced air and dust from entering the plant environment. The use of load cells and vibratory densification decks will greatly maximize the capacity of the bulk bags during the filling process
 
 
Flexicon Applications:

Flexicon's Tubular Cable Conveyor handles friable materials such as grain by gently sliding it through smooth stainless steel tubing using low-friction polymer discs. Several types of grains with disparate size and shapes were conveyed without separation of blends by a Flexicon flexible screw conveyor. A fully automated Flexicon system handling cornmeal paid for itself in seven months. A UK-based dried malt producer overcame a production bottleneck with a trio of Flexicon systems. The handling of three grades of oatmeal was made more efficient and accurate with a Flexicon bulk bag discharging system. Production at a Rice Mill in the Southeastern United States was improved by the introduction of a bulk bag filler.

Due to the highly variable properties of grain, and the limitless permutations of equipment available to load, unload, fill, condition, dump, weigh and convey them, testing the users' actual material in full-scale test laboratories is highly recommended, following a detailed analysis of the application in question by a Flexicon Applications Engineer.

 

 

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