World Grain - November 2020 - 60

GRAIN OPERATIONS

The above screenshot shows the basic app settings
while the screenshot below shows the air-grain moisture relationships.

It should be noted that during the
evaporative cooling process the heat energy contained within the grain causes
moisture loss of about 0.25 percentage
points for every 5.5°C (10°F) of cooling. Once the grain has cooled, additional moisture loss due to air equilibrium conditions takes much longer than
a temperature change. In the above case
where the air equilibrium conditions
would be driving moisture into the corn
while it is being cooled, 150 hours would
not suffice to increase the entire grain
mass to 17.4% or even 15%. Practically
speaking, grain moisture content may
increase only slightly (0.2 to 0.3 percentage points) over this period, which
would prevent shrink loss and "pay for"
the electricity to run the aeration fans.
Nevertheless, the concern regarding the
potential to trigger mold development in
the bottom grain layers remains.
We can also apply the tool to evaluate
aeration of US corn exported at 14% to
14.5% moisture content under tropical
conditions in a location such as Veracruz, Mexico. However, we need to first
understand the typical local weather
conditions. Figure 1 (page 58) summarizes the monthly temperature and relative humidity values averaged over five
years, and Figure 2 (page 59) represents
the corresponding wet bulb temperatures and EMC values for corn and soybeans determined using this app tool.
A key conclusion is that the narrow
range of relative humidity values of 75%
to 81% throughout the year is above the
safe storage moisture content in equilibrium with 65% to 68% relative humidity in the stored grain mass. Therefore, a
high potential for activating mold spores
exists if this imported corn were aerated
because it would be warmed to an average of 26.6°C (80°F) and increase to
14.8% equilibrium moisture content.
This amount of warming and moisture
increase due to aeration would be costly
and would substantially decrease the
60	

WG_Nov20.indb 60

storability of the imported corn. The recommended best practice is that unless
this corn is utilized within three weeks
of receipt, it should be stored at 13% to
13.5% moisture content and as cool as
possible to prevent onset of spoilage and
insect development, which are slowed
substantially below 20°C (68°F) and an
equilibrium relative humidity of 65% to
68% within the stored grain mass.
AERATION WEATHER FORECAST
This tool will forecast the suitability and
hours of aeration based on a 6- to 10day weather forecast for a specific geographic location. It provides an estimate
of the number of suitable fan run hours
based on historic average and minimum
temperatures for the location and a percentage amount of fan run time the user
can enter. The user can also allow the
app to enter the average and minimum
temperatures based on the geographic
location and weather. The output also
includes a set point recommendation for
a thermostat that could turn the aeration
fans on and off automatically for the
forecast period. The fans could also be
turned on and off manually, or via an
IoT (Internet of Things) switch activated from the user's smartphone.
When we used this app tool for Des
Moines weather conditions during the
recent harvest period and entered for
mid-October the five-year monthly average of 15°C (60°F) and 7.2°C (45°F)
for the average minimum temperature,
the forecast for a 50% fan run time predicted 129 hours of excellent (green)
aeration weather over the following
six days. This was based on a thermostat setting of 15°C (60°F), which the
program sets at that percentage of fan
run time based on the monthly average temperature entered. For the typical
airflow rate of 0.11 m3/min/t (0.1 CFM/
bushel) for a fan (or fans) attached to a
storage silo (or flat storage structure), it
would take a minimum of 150 hours to
move a cooling front through the grain
mass provided it has been cored and unpeaked. Thus, an extra day beyond the
six in this forecast would be required to

November 2020 / World Grain / www.World-Grain.com

11/2/2020 4:15:53 PM


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World Grain - November 2020

Table of Contents for the Digital Edition of World Grain - November 2020

World Grain - November 2020 - 1
World Grain - November 2020 - 1
World Grain - November 2020 - 2
World Grain - November 2020 - 3
World Grain - November 2020 - 4
World Grain - November 2020 - 5
World Grain - November 2020 - 6
World Grain - November 2020 - 7
World Grain - November 2020 - 8
World Grain - November 2020 - 9
World Grain - November 2020 - 10
World Grain - November 2020 - 11
World Grain - November 2020 - 12
World Grain - November 2020 - 13
World Grain - November 2020 - 14
World Grain - November 2020 - 15
World Grain - November 2020 - 16
World Grain - November 2020 - 17
World Grain - November 2020 - 18
World Grain - November 2020 - 19
World Grain - November 2020 - 20
World Grain - November 2020 - 21
World Grain - November 2020 - 22
World Grain - November 2020 - 23
World Grain - November 2020 - 24
World Grain - November 2020 - 25
World Grain - November 2020 - 26
World Grain - November 2020 - 27
World Grain - November 2020 - 28
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World Grain - November 2020 - 30
World Grain - November 2020 - 31
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World Grain - November 2020 - 36
World Grain - November 2020 - 37
World Grain - November 2020 - 38
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World Grain - November 2020 - 40
World Grain - November 2020 - 41
World Grain - November 2020 - 42
World Grain - November 2020 - 43
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World Grain - November 2020 - 58
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World Grain - November 2020 - 60
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