World Grain - December 2012 - 65

FEEDOPERATIONS

center.” A group of cost centers must be used to make each product type, but not all are used for each product. An example of the cost centers required for making each of the types of feed in the preceding product mix is shown in Table 1 (page 64). PRODUCTION RATES Production capacity needs to be based on initial requirements but should also be estimated for future increases or ultimate production goals. Usually the production rate is based on tonnes required and the desired time to produce them resulting in an average “tonnes per hour” capacity. Table 2 (page 66) shows a typical way to determine immediate and future production rates. The initial capacity is 240 tonnes in an eight-hour day. The highest required rate is 48 tonnes per hour (tph), but this is an average. To allow for interruptions in production, an efﬁciency factor not exceeding 80% is recommended. Thus, the actual design capacity should be 48 tph/0.80, which calculates to 60 tph. Although the initial design capacity is only 37.5 tph, the mill should be designed to accommodate the ultimate design capacity of 60 tph. The controlling factor in the design is usually the batching and mixing system. Other cost center equipment may be installed in increments such as grinding or pelleting systems. RECEIVING The system for receiving bulk ingredients should have a minimum capacity of twice the production rate to allow for time variations in truck and rail car arrivals and unloading. The receiving system should have the smallest pit possible that is just steep enough to move the ingredients from the receiving grate opening to the receiving conveyor. Using this design, the bulk material ﬁlls the pit and backs up to the outlet opening on the truck trailer or rail car causing a ﬂood ﬂow condition. Since the only free falling ma-

terial occurs at the initial opening of the vehicle outlet gate, fugitive dust is very minor and a dust control system is usually not needed. Not requiring a dust control system on a bulk receiving pit is a substantial cost savings in installation and operation. The bulk receiving system for the mill we sized above should initially be 30 tph x 2 = 60 tph, but must be able to handle up to 90 tph at maximum capacity. The cost to install a 90-tph system initially may be comparatively small versus replacing the original system or installing a second system later. The bulk receiving system may require higher capacity if hours of operation are less than the hours of production for the facility, or ingredient receiving is done in large quantity over a much shorter time period. An example would be if a truckload of the ingredient is used daily, but that ingredient is received only one day a week. Much higher capacity may also be required if grain or another ingredient is received in unit trains with unloading time limitations. A 110-car grain train requiring unloading in 15 hours or less would need a receiving capacity of approximately 40,000 bushels per hour. For ingredients received by bag or bulk tote, adequate warehouse space must be provided to store the ingredients until they are used. This requires human labor as well as mechanical handling systems such as forklift trucks or bag belt systems. GRINDING Ingredient sizing is accomplished by using a roller mill or a hammermill. A roller mill is one choice for grinding grains to smaller particle sizes. The coarseness and particle size range is determined by the number of roll pairs the product is passed through. For coarse grain grinding, a single pair of rolls may be used, but for ﬁner particles a stand with two or even three pairs of rolls may be used. When using a roller mill to grind to smaller particle sizes, the particle size range will be narrow. A

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World Grain - December 2012

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