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Lean on layers to lay off drying cost

03/04/2013 @ 2:51pm

The growth in bin size may be to blame for suffocating grain. Take the 48-foot-diameter bin, for example. This common-size bin is nearly double the diameter of average bins erected a couple of decades ago. Manufacturers are good at equipping such size bins to provide adequate airflow for dry grain.

But start piling up wet grain to the eaves of a 48-foot bin, and you could be asking for a huge electric bill. “The energy required is one of the factors in the drying process that can be manipulated,” says Tom Dorn of the University of Nebraska. “By decreasing the depth of the grain, you can minimize the static pressure necessary and, therefore, the energy costs.”

To understand how this works, you need to understand the relationship between the amount of static pressure and energy use. Regardless of the depth, 1 cubic foot of air per minute per bushel (cfm/bu) is the minimum airflow recommended for grain with 18% moisture. Most fans can push 1.25 to 1.5 cfm/bu through grain. While this number stays the same, the amount of static pressure necessary to move this much air depends on the depth of the grain.

Horsepower escalates

Reducing grain depth can cut horsepower requirements significantly. Dorn provides the following examples using a 48-foot-diameter bin.

» If grain were loaded to a depth of 30 feet in the bin, three 40-hp. centrifugal fans could produce the needed 1.0 cfm/bu to dry the grain.

» If grain were loaded to a depth of 25 feet in the bin, two 40-hp. centrifugal fans could produce 1.0 cfm/bu.

» If grain were loaded to a depth of 18 feet in the bin, then one 40-hp. centrifugal fan could produce the required 1.0 cfm/bu.

Since the airflow remains the same in all three scenarios, the time required to dry the grain would be the same. Dorn notes two fans can dry 83% as much grain per batch as three fans. One fan can dry 60% as much grain per batch as three fans.

Cutting electric costs

Dorn also illustrates how batch drying can cut electric costs using the example of 30- and 36-foot-diameter bins. If both bins were filled with 9,600 bushels of corn, the 30-foot bin would be filled 17 feet deep, while the 36-foot bin would be filled to 11.8 feet. To push 1.25 cfm/bu through these bins would require 3.74 inches of static pressure in the 30-foot bin and 1.55 inches in the 36-foot bin. This means 11.8 hp. will be needed in the first bin, while only 4.9 hp. is required in the larger bin.

Each horsepower required to power a 220-volt single fan draws .93 kilowatts per hour (kWh). If electricity costs 10¢ per kWh, it would cost $15.40 more to dry the smaller bin each day. Because the grain will take 17 days to dry, you can save $262 by drying in the larger bin.

If you dry all your grain this way, you can cut back dramatically on operating costs, Dorn notes.

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