World Grain - April 2019 - 60

FEED OPERATIONS

Creating a batching system
How to size feeders to support required production design capacity

by Fred Fairchild

I have been writing a series of articles on feed mill design
and a specific mill. In the April 2018 issue, we looked at the
amount of feed made per hour and added an 80% efficiency
factor to determine a design capacity of 75 tons per hour was
needed to support the production requirements at the beginning and in the future. It is important that we design the batching and mixing system for current and future needs as a mill
usually has only one main batching and mixing system. Although additional ingredient bins may be added in the future,
the scaling and mixing equipment needs to be designed to
support the ultimate production requirements.
In the May 2018 issue, I introduced two generic feed formulations: one for a Starter/Grower-Broiler (Medicated) feed,
and the other for a Generic 18% Swine Starter Pelleted feed.
I identified which ingredients in each formulation were stored
in overhead bins and batched through the main batching
and mixing system. The smaller dry ingredients were to be
batched and added through a separate micro-ingredient batching system. Each of the formulas were to be produced in a
7,000-pound (3.5-ton) batch.
In this article, I will show how to size the overhead bin
screw feeders to support the 75-tph production design capacity required. First, we need to determine the time allowed to
make a batch. In this design, the mixer used has a complete
drop bottom outlet for quick and complete discharge of a
batch. This requires a surge bin beneath the mixer to hold a
complete mixed batch. Dividing the 75 tons per hour required
production rate by the size of a batch (3.5 tons), we determine
that an average of 24.1 batches need to be produced per hour.
To determine the time needed for making each batch, divide
the number of minutes in an hour (60 minutes) by 24.1 batches per hour and you will get a time of 2.8 minutes required per
cycle. This converts to 168 seconds.
Here, we need to make some assumptions. First, we will allow 10 seconds for the batching scale to completely discharge
into the mixer. Second, it takes the mixer 10 seconds to empty
and be ready for the next batch. And third, the ingredient feeders have 5-second intervals between each ingredient so the
batch scale can confirm the amount of each ingredient in the
scale hopper before the next ingredient is added.
Using the above information, we can determine what I call
a "target time" for charging the ingredients into the scale
60

060_WG_Apr19_Feed Ops.indd 60

A twin shaft mixer manufactured by Hayes & Stolz.
Photo courtesy of Hayes & Stolz.

hopper. Let's assume we are batching five ingredients in the
batching scale for a given formula and we need to determine
the target time (total time) available for the feeders to run.
Target Time for Feeders to Run
Batching Cycle Time in Seconds
=
168 seconds
Deduction Time for Scale Discharge
= (10 seconds)
Deduction Time for Mixer Discharge
= (10 seconds)
Ingredient Intervals five-seconds per Ingredient = (25 seconds)
Feeder Target Time
=
123 seconds
When scaling the ingredients for this formula, the screw
feeders have a total time of 123 seconds to put the ingredients
in the scale. The ingredient intervals time will vary based on
the number of ingredients being put into the batching scale
for each formula. For six ingredients, the target time would
be 118 seconds. With seven ingredients, the target time would
be 113 seconds.
Now we will look at an example of how to select the required feeder size and running time needed for each ingredient, so the total target time isn't exceeded. I normally use
speeds of 105 rpm at two-thirds pitch on feeders and onehalf pitch on smaller feeders. Let's look at the ground corn
April 2019 / World Grain / www.World-Grain.com

4/2/2019 2:06:10 PM

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World Grain - April 2019

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