Bulk ingredient storage
May 01, 1996
by Teresa Acklin
Feed manufacturers can enhance efficiency and profits with proper design and use of bulk storage.
Processing feed requires storage of ingredients in either bulk or bagged form. Microingredients such as vitamins or medications are often stored in bagged form, while ingredients such as soybean meal and dicalcium phosphate are stored in bulk form.
Bulk ingredient bins should be used exclusively for one ingredient. For example, soybean meal should not be placed in an empty dicalcium phosphate bin if the soybean meal bin cannot hold all the meal when delivered.
Bulk ingredient storage must be designed, constructed, and installed in a manner that facilitates inspection and clean out of the bins and mill. Proper planning, design and installation of bulk storage will help attain regulatory compliance and enhance the efficiency and profitability of the feed manufacturing operation.
A two- to eight-week supply of bulk ingredients should be maintained in storage. Bulk bins should be sized at a minimum of 125% of the expected purchase increment. If 100 tonnes of meal are purchased at a time, the minimum bulk capacity of the bin should be 125 tonnes.
Allowances also should be made for bad weather, delayed deliveries, and rush seasons. Price advantages from timely, seasonal, or volume purchases of ingredients may result in additional storage space being required.
With proportional mills, volume purchases may reduce the adjustment required in rations. For each new shipment of ingredients, proportional mills require adjustment since moisture, protein, energy, fiber, or other nutrient contents may vary appreciably between purchases.
TYPES OF STORAGE.
Feed ingredients are stored or temporarily held in a variety of structures. The following are normally employed:
ground level, flat-bottom bins with unloading augers are normally used for the storage of grain. Ground-level, flat-bottom bins cost about U.S.$44 to U.S.$55 per tonne capacity, on a turnkey basis;
ground level, hopper-bottom bins are normally used for soybean meal, complete rations and/or grains, such as oats, that are required in relatively small amounts. These bins cost two to three times as much per tonne capacity as flat-bottom bins;
overhead bins normally are used to provide gravity flow to processing or mixing equipment. Because these bins are expensive (about twice the cost per tonne capacity as ground level, hopper bottom bins), their use must be justified by flexibility, efficiency and labor savings in feed preparation.
Overhead bins in high volume systems are sometimes used to temporarily hold complete rations. Overhead bins are called working bins and are not intended for long-term storage.
More than one type of bin may be used for a single ingredient. As an example, large truckloads of soybean meal may be received in a ground level, hopper-bottom bin. The meal can then be transferred to an overhead, working bin as needed for processing.
Hopper-bottoms are probably most justified on those bins emptied and refilled many times and those for which clean out is important. Complete clean out is crucial in bins holding grain or those used for different ingredients at different times. Two bins, or a two compartment bin, for a single ingredient will permit complete clean out of one unit while using from the second, assuring no long carryover of material in the bottom of a bin.
Hopper-bottoms must be steep enough to cause free-flow of the material. Grains require a hopper slope of at least 37°.
Soybean meal is not a free-flowing material, and bins for soybean meal must be designed for the weight and flow characteristics of the material. The slope of the valley angle (shallowest corner angle) in hoppers for soybean meal and other materials that do not flow freely should never be less than 50°, with 60° preferred.
Experience indicates it is better to use large intake openings with reduced or stepped pitch flighting in the loading section on the conveyors removing the product from the bin than to use agitators.
Agitators, or anti-bridging devices, usually are high maintenance items that often lose parts into the product stream and damage equipment. When they fail, it is extremely difficult to discharge a bin, as they cause bridging.
The best mechanical anti-bridge device, either commercial or homemade, consists of rotating vertical pipe with hanging chains. Vibrating devices have not proven to be effective in preventing bridging.
Bins of less than 22-tonne capacity are available with a 70° hopper bottom. Off-center hoppers (hoppered to one corner in rectangular bins or to the side in round bins) also will help to control bridging. Complete rations have somewhat better flow characteristics than soybean meal, but they should be held in 60° hoppers.
With regular use and proper bin and unloading conveyor design, soybean meal and other non-free flowing materials should flow out of the bin. If occasional bridging does occur, use a rubber mallet to bump the bin hopper.
Soybean meal may be purchased either bagged or in bulk. The decision of which to use is based on the labor of handling bags, the cost of bulk storage and the cost of bagged versus bulk product.
Bin sizes for ingredients received in bulk are determined by the expected size of delivered lots. Salt, calcium, and phosphorus sources, milk by-products, and vitamin and trace mineral premixes are normally purchased and stored in bags. In large systems, the labor and expense of handling bags will sometimes justify bulk purchase, handling and storage of truckload lots of all ingredients except vitamin and trace mineral premixes.
Calcium, phosphorus, and salt sources are corrosive and will draw moisture from surrounding materials. These minerals are commonly held in ground level and overhead wooden or steel bins. Corrosion in steel bins can be reduced by coating the inside with epoxy or other coatings. Bins constructed of fiberglass or other noncorroding materials also are available.Handling of Feed Ingredients
Auger conveyors are commonly used to handle grain, soybean meal, and mixed feed. Capacities vary with auger diameter and operating speed.
To save time and labor, augers with diameters of at least 20 centimeters, preferably 25 cm or larger, should be used for placing grain and soybean meal in storage and for load-out and delivery of finished feed. Grain augers are occasionally used to fill ground level bins, but should only be used with nonmedicated ingredients.
It is difficult to avoid residue in augers or drag conveyors, and extensive flushing is required to remove it. Once again, medicated ingredients are best handled in bags to avoid potential problems.
For large feed systems, particularly those that include grain drying and storage, bucket elevators might be appropriate. They cost more than auger systems, but they have a lower power requirement and give longer, more reliable service. A bucket elevator can replace several augers in a system and reduce space required for handling equipment.
Gravity spouts for dry grain must slope at least 37° from horizontal; spouts for wet grain must include at least 45° from horizontal. Gravity spouts for soybean meal must slope at least 60° from horizontal.
Overhead ingredient bins are filled using downspouts from an elevator leg. The downspout angle must be 60° or greater. Since the spout angle is high, most bulk storage bins must be located near the leg.
The distance from the leg is proportional to the height of the leg. Often a second distributor is used to fill the bulk bins allowing better utilization of the main leg distributor. Medicated ingredients should be handled in bags in order to avoid residue problems.
Feeds are often temporarily stored in overhead bins above a driveway prior to delivery to the feed tanks. Medicated feeds may have to pass through the leg and some residue may remain in the leg and in certain locations of the downspouts. This type of feed should be followed by a nursery ration to help flush out the equipment.
It is important to mix enough medicated feed each time to avoid the potential for residue left in the handling system. The clean out or flush ration must be one in which the drug residue that may be picked up will not affect the animals that will be fed.
Bulk bins need to be located near the mixer to minimize the investment in handling equipment. Normally, soybean meal will be added directly to the mixer, assuming it is on scales, or to a weighing/ batching hopper above the mixer. As the distance between bins and the mixer increases, additional handling equipment is required and increases energy and maintenance cost.
Handling ingredients in bulk can reduce purchase cost per ingredient if sufficient quantities can be handled with the equipment and storage. If at all possible, all medicated ingredients should be purchased in bagged form to minimize the potential of carryover and reduce residue problems in the storage structure and handling equipment. If medicated ingredients are purchased in bulk form, a dedicated bulk bin should be used.
All bulk bins should be clearly labeled or numbered to avoid any cross-contamination of ingredients while filling a bin or mixing feed. Proper flushing and sequencing of feeds must follow usage of medicated feed.
This article is based on a paper by Joseph P. Harner III, extension agricultural engineer, Department of Biological and Agricultural Engineering at Kansas State University, Manhattan, Kansas, U.S.; and Fred Fairchild, P.E., extension feedmilling specialist, Department of Grain Science and Industry at K.S.U.