Aeration Best Practices for Grain Storage

Fuji Jian, Ph.D, P.eng

Fuji.Jian@umanitoba.ca Department of Biosystems Engineering, University of Manitoba,

Winnipeg, MB, R3T 5V6. Canada.

What is aeration? ◦ Moving small quantities of air to

modify grain temperature. ◦Airflow rate: 1 to 2 (L/s)/m3 (0.20 to 0.25 cfm/bu).

What is the purpose? ◦ Cool grain. ◦ Eliminate temperature gradients.

Moisture migration due to temperature gradients

Source: unknown

Other purposes?

◦Warm up grain to reduce condensation when grain is unloaded. ◦ Application of fumigants. ◦ Reduce odors from fungi,

insects, and mites.

Principals of Aeration and Drying

ERH A

B

C 100 % RH

1 2

I: Cold and dry ambient air 1: A: Air condition 2: C: Grain condition Drying of grain occurs in both the temp. and moisture fronts A: Zone A B: Zone B A-B: Moisture/drying front C: Zone C B-C: Temperature front

Air RH and T change

How aeration systems work?

Psychometric chart

Duct Aeration With Level Grain

Warm

cool

Warm

cool

cool

cool

cool

How aeration systems work?

Source: modified from Dr. Paul Fields

Temperature front didn’t make it. Molding started before aeration was completed. All points of the temperature front must get all the

way through the grain.

Condition can be corrected by keeping the grain leveled or coring the grain.

Chaff, broken kernels or dirt

Aeration vs natural air drying

Aeration Natural air drying Main objective Modify grain

temperature Modify grain moisture content

Working principle

Heat and mass exchange between grain and air

Air flow rate 0.20 to 0.25 cfm/bu 0.25 to 3.0 cfm/bu Main target Grain is hot (but

dry), to cool grain Grain is wet, to dry grain

Strategy Fan should be stopped when input air is warmer and wet

Fan should not be stopped when input air is wet

Can aeration dry grain? Yes. 1% moisture drop/28℃ drop of

grain temperature. However, aeration is not for drying

grain because airflow rates are too small to reduce the moisture content significantly by using supplied air.

Part of the grain can be over dried.

Do I need a larger fan?

Aeration fans are chosen so that the temperature front moves through the grain bulk before mold and insect growth.

Generally the smallest possible fan is selected.

Larger fans are chosen only if ◦ Grain needs to be cooled quickly. ◦ Several bins are to be cooled with the

same fan.

Which air flow direction should be used?

Upward flow ◦ Fan blows air into the duct (traditional

method).

Downward flow ◦ Fan sucks the air (used under special

conditions).

When to Aerate? Depend on your situations.

Recommendation for Manitobans: Start fan as soon as possible after harvesting and

average outside air temperatures are at least 5°C cooler than the grain in the bin.

Important if large moisture and/or temperature variations.

During the fall and winter; depends on bin size, grain moisture content, and temperature distribution.

Warm grain to 10ºC by mid-June. Ideal grain temperature is 5-10℃ during the entire

storage period.

Is the following statement correct? “Stored Grain on Aeration: Turn your fans OFF in the morning”, recommended by Dr. Ron Palmer .

1)Confusing aeration with natural air drying will result in operation failure at the very beginning because different strategies should be used for drying and cooling grain.

2)Lower than 15℃ air has limited air holding capacity. Therefore, night air will not dry grain, but can cool grain.

3)The best drying condition of the ambient air is decided by the combination of both air temperature and relative humidity. Not only the air temperature.

Comments:

When is the best time for grain aeration or drying at Manitoba?

Why should the fan be sealed when not be used?

Autumn and Winter Spring and summer

condensation

condensation

Chimney effect

Chimney effect

Air volume increase

Questions?