When drying grain, farmers should make sure they have adequate air flow, says a paper by University of Saskatchewan agricultural engineers.
The bioprocess engineering group at the university says depth of grain and the horsepower of the fan are key factors in successful aeration.
Moisture can be removed from grain without adding heat to the aeration during fair October days, but once the temperature drops below 5 C and the humidity is more than 85 percent, little moisture is removed. However, even as the mercury drops, aeration can help by cooling grain to prevent deterioration.
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The paper recommends the maximum depth in bins for economically drying small grains such as wheat, barley, canola, oats and flax is 1.8 metres.
For larger grains, such as peas, lentils and shelled corn, it is 2.4 metres.
“The horsepower required to operate the fan becomes quite large at greater depths and it is generally considered uneconomical for drying,” the paper says.
Even grain on the ground can be dried if piled on top of an air dispersal system attached to a fan. This allows depths 20 percent greater than in the bin.
Drying time varies
For very damp grain, an airflow rate of three to five cubic feet a minute per bushel is recommended for small grains. Drying time varies with the initial moisture level, air temperature, humidity, airflow and the amount of grain to be dried.
Given normal October conditions, grain at 18 percent moisture can be dried in two weeks or less with fans providing 6,000 cubic feet a minute of air flow or more.
However, lower levels of air flow will take too long, stretching the drying period into November when air temperatures will not be high enough to dry the grain.
Edwin Arinze, a member of the team, said that although axial flow fans are popular, they are not necessarily the best.
“The present line of in-line centrifugal fans, which look like axial flow fans, are much better in terms of being able to withstand high operations and give more air supply,” he said.
When drying high moisture grain, the fan should run around the clock, but when moisture drops to about 18 percent for small grains and 14 percent for canola, the fan can be operated during the day generally from 10 a.m. to 7 p.m. when the relative humidity is low.
Adding heat to the aeration can improve its efficiency.
The goal is to reduce humidity in the air by raising the air temperature at least 10 C.
The recommended airflow rates for natural air drying are also used for supplemental heat drying.
Even when it gets too cold for drying, aeration is helpful.
Using aeration, grain that is one to two percentage points above recommended moisture levels can be safely stored.
Normally, much less air flow, only 0.02-0.1 cubic feet a minute per bushel, is needed in this situation. The goal is to prevent moisture from migrating from warm to cold layers.
The aeration system should be turned on periodically during winter to maintain a uniform temperature. It usually takes five to 10 days at 0.1 cubic feet a minute per bushel to cool the grain to the outside temperature, the paper says.
