Based on these capacities, the mill should be able to ultimately produce 60 tph. Since factors occur that won’t let the mill operate constantly at the rates, I use an 80% efficiency factor. This would make the design capacity required 75 tph.

We now need to list the ingredients needed to produce the feed. Following in Tables 1 and 2 are two typical formulas we will use for this mill design. Each formula shows the ingredients required, amount required, and the source used to add each ingredient to the mix. Overhead bins store those ingredients above a batching scale(s).

**Grain storage requirements**

The amount of ground corn needed is approximately 45% of the formula. This means that at 2,000 tpw, 900 tons of corn would be needed. That converts to 32,143 bushels of corn used per week. At a maximum capacity of 5,500 tpw, nearly 88,500 bushels of corn would be used per week. Let’s assume the mill can get corn on a regular basis, but always wanted to have a two-week supply of corn on hand at all times. Initially 60,000 bushels of corn storage would be needed. At maximum capacity, about 177,000 bushels of corn storage would be needed. The corn storage could initially have 1 to 2 bins but would need added bins to store corn when maximum production capacity is needed. If corn deliveries are not available on a daily basis, then the amount of corn storage needs to be greater so that you don’t run out of corn and still have a minimum of 1 to 2 weeks of corn use in storage.

**Overhead ingredient storage requirements**

Now let’s look at the ingredients to be stored in overhead bins that would be installed in the scaling and mixing tower. Using the two formulas from Tables 1 and 2, Table 3 shows the amount of each ingredient needed in the overhead bins to be able to produce either formula at the amount needed daily initially and finally.

One or more overhead bins will be needed to store each of the ingredients listed in Table 3. Let’s explore the type and size of bins that might be available. Bin capacities are nominally sized by the cross section of the bin times its straight wall height. The hopper volume isn’t normally included as the hopper section is considered to offset the cone or pyramid volume of the product at the top of a full bin.

Square bins are normally used for overhead bins and are built into clusters. These can be metal or slip-formed concrete. Square bins are nominally available in 7-foot x 7-foot, 8-foot x 8-foot and 10-foot x 10-foot cross sections. Metal bins are limited in wall height to about 50 feet, but concrete can be made much taller. Bin capacities are determined by calculating their cubic volume times the density of the ingredient stored in them. Soybean meal has a density of 36 to 40 pounds per cubic foot. If we choose a to use a 10-foot by 10-foot horizontal wall dimensions by a sidewall height of 50 feet, the nominal cubic capacity for the bin would be 10 x 10 x 50 = 5,000 cubic feet. The bin will hold 5,000 feet3 x 40 pounds/feet3 = 200,000 pounds divided by 2,000 pounds per ton = 100 tons of soybean meal. This bin would hold enough for initial production, but a second bin would be needed to hold the soybean meal needed at maximum production.

The number of overhead bins required depends not only on the daily use requirements, but also on whether the ingredient can be replaced within a day. Assume a semi-truck holds 25 tons of meal. If the trucks can deliver daily in the amounts needed, I would size the storage for soybean meal to hold a day’s usage plus at least a half of truck load as a cushion in case the truck is delayed. But if your soybean meal supplier can only deliver two times per week, I would put in bin capacity to hold at least three day’s use of soybean meal plus one-half truckload.

Additional factors enter into the amount of overhead storage needed, including other formulas that might require a higher percentage of one of the ingredients in the initial group of overhead bins or adding other ingredients in overhead bins. The size and number of overhead bins needed requires an understanding of the ingredients needed. Additionally, it is wise to add 2 to 3 bins in the overhead bins as spares.

**Micro-system**

Micro-ingredients are those additives and medications used in producing the required formulas. These are ingredients added in very small amounts. The micro-system can accurately weigh each ingredient and deliver these ingredients to the mixer. It is actually a small batching system.

The ingredients for a micro-system usually come in bags that are manually emptied into the proper compartment in the micro-system. If significant use of an ingredient is required, the use of tote bags that are hung on a stand can be delivered into a specific micro-system compartment. It also is possible to hang the totes on a frame with scale and deliver directly to the mixer.

**Bagged ingredient receiving**

Warehouse space must be provided for pallets of bags, totes, liquids or other materials needed. We will discuss warehouse requirements later.

Liquid storage and handling will be discussed in future articles.

In the next article we will look at receiving and initial process equipment for the mill.