World Grain - March 2016 - 74

GRAIN OPERATIONS

Aeration, cooling of
stored grain
Without aeration, temperatures can vary greatly,
increasing the chances of mold and insect development
by Susan Reidy

Stored grain problems such as mold, insects, fungi and
spoilage start with or become worse due to improper grain
moisture and temperature.
Temperature differentials in the grain cause moisture to
migrate to the top and center of a stored grain mass, causing
molds to develop and insects to feed and reproduce, according
to an Oklahoma Cooperative Extension Service report written
by Carol Jones, professor, Oklahoma State University.
Aeration keeps the grain cool and maintains uniform
temperatures and moisture in the grain mass. In aeration, a fan
is used to pump outside air through the grain in the storage
facility. Eventually, the grain attains the temperature of the air
traveling through void spaces in the mass, Jones said.
Each type of grain has different storage requirements for
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The time of harvest can have an impact, given the varying
outside temperatures. Oilseeds in general require cooler and
dryer storage conditions than wheat or corn (maize).

Don't confuse grain cooling with natural air drying, which
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natural air grain drying, damp grain is placed in a bin and the
fan is operated continuously for several weeks until all the
grain has dried, she said. Grain cooling includes an initial
period of fan operation to cool grain followed by periodic
operation to maintain even temperatures throughout.
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system will be used. In general, if grain must be cooled
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will be used to prevent moisture migration, only a light
system is needed. If moisture content during storage will
be 1% or 2% above safe levels, a faster aeration system is
desirable, Jones said.
The time required for grain cooling will depend on the
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rate will cut cooling time in half.
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DESIGN CONSIDERATIONS
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'HVLJQLQJ DQ DHUDWLRQ V\VWHP LQYROYHV ¿UVW GHWHUPLQLQJ said, for several reasons:
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aeration goals, Jones said. After the rate is determined, the
against pressure; fans push more mass of cool dense air
air distribution system can be designed and fans selected to
than warm light air;
deliver the required air volume.
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the grain than suction systems;
minute, per bushel of stored grain (CFM/bushel). Rates
x Condensation on top of the grain is visible and
start at 0.05 CFM/bushel and increase as shown in Table 1
usually dries by the end of the aeration cycle. Bottom
(page 78). Light aeration systems (0.1 CFM/bushel or less)
condensation damage caused by suction fans can't be
require long operation times to lower grain temperatures
seen until the bin is unloaded; and
and are suited to cooler climates. Medium and fast systems
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(0.2 to 0.8 CFM/bushel) are used periodically to lower and
vents may freeze over during suction cooling.
equalize temperatures in stored grain.
For high speed grain cooling, 1 CFM/bushel or greater SELECTING FANS
is required, Jones said. Grain can be cooled in one or two
Aeration fans may be either axial (propeller) type or centrifugal
nights of fan operation.
(squirrel-cage) type as shown in Figure 1 (page 76). Axial type
74

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