Grain Storage: Aeration Part II

In Part I, we covered the history, basics, and benefits of aeration, along with variables

that impact it, such as grain type and quality, storage design, geography, climate,

and storage duration, and touched on cooling vs. drying. Part II will focus on system

design considerations and provide tips and recommended actions.

Cooling vs Drying

Historically, the primary purpose of aeration was to cool grain, effectively removing heat

generated by harvest or drying processes in preparation for winter storage. While some

moisture removal occurred, the main goal was to achieve a uniform mass of cool grain.

For years some smaller bins had been equipped with “dryeration”, or using heated air

to dry grain in bins rather than using a grain dryer. Expanding this concept the idea was

that if larger amounts of air were passed through the grain mass in the bin, even though

not heated, it would remove more moisture from the grain.

By the 1980s and 1990s, the industry began modifying aeration approaches to not only cool

but also facilitate moisture removal. Grain started to remain in storage well past

traditional spring load-outs, with moisture levels dropping from the conventional 15% to

13.5%–14% at time of unloading. This additional moisture loss, however, raised

handling issues and led to weight loss.

To address this, grain could be stored at moisture levels above 15% while maintaining

quality if bins were equipped to move greater volumes of air (cfm/bu). This necessitated

upgrading from passive roof ventilators to powered roof exhausters, which help remove

warm, moist air from above the grain mass.

With these enhancements, I successfully stored corn at 17.5% moisture in the fall and

retrieved good-quality grain at 15% moisture by late spring or early summer. However,

it's essential to remember that aeration efficiency is limited by the ambient air conditions

at the time of operation, which vary daily, weekly, and seasonally. Management of

system operation and timing is crucial for optimizing conditions.

Volume of Air

The airflow rate (cubic feet per minute per bushel) should match the grain type, storage

structure, and desired storage conditions. Airflow volume requirements have changed

significantly over the years. When I began, wheat storage typically had airflow rates of

1/12 cfm/bu, while corn and bean storage used 1/10. While wheat has remained in that

range due to low drying pressure, corn and soybeans have shifted toward higher air

flows as part of their drying process.

In the late 1980s, the facilities I worked with advanced to 1/8 cfm/bu. By the early

In the 1990s, this increased to 1/7, and by the end of the decade, we were reaching airflow

rates of 1/6 to 1/5 cfm/bu. This increase in airflow allowed us to store higher moisture

grains effectively in temporary storage.

Updraft vs Downdraft

The age-old question is to suck or blow? The debate over whether to use updraft

(positive) or downdraft (negative) aeration systems is ongoing. There is no one-size-fits-

all answers; the choice depends on factors such as commodity type, intended aeration

purpose, bin design, and aeration system layout. Most bins can accommodate either

system.

Many universities advocate for downdraft systems due to their ability to cool the top

layers of grain quickly, especially in cooler weather. Downdraft also tends to remove

warm, humid air effectively and penetrates dense grain layers better. According to Iowa

State University, “Suction airflow should be used in tropical or subtropical humid

climates when cool weather conditions are marginal for insect control." Conversely,

pressure airflow is necessary when loading warm grain onto previously cooled grain,

such as (a) when loading warm grain from a dryer on top of aerated grain in a storage

bin or (b) when loading warm grain delivered to an elevator on top of a bin that has

been previously cooled.

( https://www.extension.iastate.edu/)

Many universities have also discussed the associated hazards of using downdraft air in

cold climates where the top free air vents may freeze over leading to roof collapse.

Personally, I prefer updraft aeration because it introduces a cool air front to push

uniformly throughout the grain mass, rather than pulling warm air down through the

grain mass. I just don’t like the idea of introducing hot air into the grain and have

consistently experienced success with the updraft method.

Roof Exhausters

For optimal aeration, powered roof exhausters are valuable tools. They can run either in

conjunction with main aeration fans or independently. When adequately positioned and

sized, they can effectively exchange warm, humid air above the grain with cooler, drier

air. This helps reduce "crusting" thereby enhancing the aeration system's overall effectiveness.

Other Factors

When designing an aeration system, consider factors such as static pressures, fan

selection and placement, and aeration duct patterns. While I have operational

experience, I do not possess engineering qualifications. Collaborating with

manufacturers, contractors, or agricultural engineering professionals is essential to

ensure you design an effective system. Many Ag Engineering Departments at State

Universities have information on their websites.

Monitoring

An aeration system's effectiveness relies significantly on diligent attention and

management. Grains like corn and soybeans are living entities in a dormant state,

waiting for the right conditions to germinate. The goal of aeration is to maintain this

dormant state and create an unfavorable environment for pests.

Given that ambient air temperature and humidity constantly fluctuate, it’s crucial to

monitor the conditions consistently to prevent the perfect environment for germination

from forming inside the bin. Vital parameters to monitor include:

• Outside Air Temperature & Humidity

• Inside Air Temperature & Humidity

• Grain Temperature & Moisture

These can be tracked manually, as has been done for thousands of years, or through

fully automated grain storage management systems. Long-term storage bins should

also be equipped with temperature cables to aid in monitoring. Additionally, CO2

monitoring can help detect spoilage early, as biological activity (e.g., mold and insect

infestations) releases CO2, allowing for proactive measures to mitigate losses and

improve grain quality.

Various levels of technology are available for automated monitoring of these factors and

more (like energy demand). As an operator, it's essential to conduct a cost-benefit

analysis to determine the level of automation that may be beneficial for your operations.

Recommendations

Based on my experiences, here are some practical recommendations:

• Bin preparation

  • For optimum efficiency empty and clean bins at least once every year.

  • Clean walls as well as floors and be sure to pull the covers off and clean air ducts.

  • Look for any signs of water intrusion and make necessary repairs. Inspect and repair temperature cables as needed.

  • On steel bins be sure to inspect the outside of the bin looking at foundations, anchor bolts, stiffeners, and for any deflection in the bin’s walls. Also, inspect roof panels and roof exhausters as well as any spouting penetrating the rooftop.

  • On concrete for any signs of spalling or disrepair that may lead to leaking.

  • Pay special attention to rooftops and any points of penetration through them.

• Bin filling

  • Avoid Old Crop Overlap: If possible, do not store new crop grain on top of old inventory.

  • Fill Efficiently: Aim to fill bins quickly rather than over several days.

  • Core the Bin: Ensure proper cored filling or consider using a grain spreader.

  • Avoid Overfilling: Do not fill bins so grain touches the roof supports, as this negatively impacts aeration and adds non-designed structural loads.

  • Condition Bin: If filling from a dryer, and if the grain is significantly warmer than ambient air (more than ten degrees), consider using a conditioning bin to allow for cooling and moisture homogenization before transferring to long-term storage.

• Inspect the Fans

  • Ensure all fans are operational and spinning in the correct direction.

  • Inspect ductwork for integrity to prevent moisture ingress into the bins.

• Running the fans

  • Run fans long enough to exchange all air within the bin thoroughly.

  • Optimal operation occurs when the ambient air temperature is at least 10-20 degrees Fahrenheit cooler than the grain.

  • After cooling the grain, consider running roof exhausters periodically on hot days to remove any accumulated warm, humid air beneath the roof.

  • If fans are not in operation for extended periods, cover them to prevent wind-induced air flow if they aren't equipped with automatic louvers.

  • If noise is a concern, consider using sound suppressors on your fans.

Fumigation

If you plan to store grain into the latter part of the year, consider using grain

fumigants. When anticipating long-term storage, I would apply a surface residual

treatment to the bin's walls, floors, and air ducts followed by a fumigant during

filling or after the bin is filled. Given the risks associated with pesticide use,

particularly during bin entries, it’s advisable to engage professionals if you decide

to implement a fumigation strategy.

Monitoring

In the absence of an automated grain storage monitoring system, manual monitoring is

vital. Check every bin frequently; weekly monitoring is acceptable unless you have

concerns. Each time I pass a fan; I would stop to feel the temperature of the exhaust air

and check for any unusual odors. During monthly inventory checks, I would also visually

inspect the bin for crusting and smell for any signs of spoilage. If a possible concern

were detected, I would increase the frequency of inspections as often as needed,

even to a daily level.

When analyzing temperature cable readings, focus on trends rather than just isolated

data points. For insect monitoring, pheromone traps are effective in helping to gauge

stored grain health.

Remember, the most crucial aspect of monitoring is not just data collection but

analyzing that data and TAKING APPROPRIATE ACTIONS to prevent spoilage.

Refrigeration

For certain operations that cater to high-margin markets or specific conditions, investing

in grain refrigeration units or chillers may be worth considering. Although these systems

require additional energy and specialized equipment to operate, they can provide a

consistent supply of cooled air to the grain and may be justified based on your business

model.

Personal Experience

In my career, I’ve been responsible for over 450 million bushels of permanent licensed

storage, alongside an annual intake of 60 to 100 million more bushels in temporary

storage. Through years of trial, and error, and consultation with industry experts, we

developed an effective aeration system tailored for our needs. We rarely faced quality

loss in our bins, and our shrinkage numbers were excellent. This was not a one-size-

fits-all approach; we analyzed each location and adapted our aeration program to meet

its unique requirements. By collecting and analyzing data, we made informed decisions

about system modifications and management practices. We established clear

expectations, provided necessary training, and ensured that our management efforts

received the attention required to protect our valuable grain assets.

Conclusion

Effective aeration of grain in storage is critical for maintaining grain quality and

preventing spoilage. By understanding the nuances of system design, airflow rates,

monitoring, and management strategies, you can significantly enhance the longevity

and quality of your stored grains. Whether through manual inspections or automated

monitoring systems, continuous attention to aeration practices is essential.

Understanding the historical evolution of aeration and its current methodologies equips

us with the knowledge to adapt to changing agricultural landscapes and consumer

demands. The advancements in technology offer unprecedented opportunities to

optimize grain storage conditions, reduce spoilage risks, and enhance overall efficiency.

In an era of heightened demand for quality and safety in agricultural products, effective

aeration practices are a critical practice in maintaining the integrity of the food supply

chain. Thank you for being a part of this journey with us at Grain Guy Fifty; we look

forward to sharing further insights into future posts.