Grain conditioning is the process of increasing the storage life of grain and minimizing grain spoilage and quality loss. The major conditioning operations are in-bin natural drying of grain to reduce the grain moisture, followed by aeration to cool the grain. Sometimes over-dried grain can also be rehydrated to acceptable moisture levels to minimize shrink loss.

Equilibrium Moisture Content (EMC) is the moisture content that grain will attain if exposed to air at a specific relative humidity and temperature for long enough duration of time. If the EMC of the air delivered to the grain—including fan and heater warming—is lower than the grain’s moisture content, moisture will be released from the grain to the surrounding air. If the plenum EMC is greater than the grain’s moisture content, the grain will absorb moisture at a slower rate compared to drying to reach equilibrium with delivered air. Due to its high significance, Integris Pro develops unique and precise EMC/relative humidity/temperature relationships for each grain type/variety and incorporates them in the latest grain curves.

The amount of water vapor in the air is determined by the combination of temperature and relative humidity. Since warm air has the potential to hold more water vapor when it is cooled and humidified in the drying process, it is preferred for drying.

In-Bin Natural Air Drying

Grain bins equipped with a proper aeration system can be successfully used to dry grain using natural air and a small amount of supplemental heat (optional). Natural air in-bin drying is the highest quality and most energy-efficient process. Appropriate and automated fan control strategies are required to optimize the drying performance with uniform drying, energy efficiency and minimum under/over drying.

Continuous fan operation may result in high operating cost (due to excessive energy consumption) and significant spoilage and/or shrink loss, which is where Integris Pro comes in. The system’s advanced fan controls optimize the drying process with accurate estimations of plenum Equilibrium Moisture Content (EMC). It also analyzes psychometric properties of natural air from a locally installed weather station in real-time, and ensures that the fan is operated when the right air quality is available for desired conditioning task (drying, aeration, or rehydration).

Grain Aeration

Grain aeration lowers grain temperature to increase safe storability and protection against mould and insects. Once grain has reached target drying it must be cooled as soon as possible, and should be uniformly cooled to 1.7-4.4°C or 35-40°F for winter holding. Do not freeze the grain as it may result in significant condensation in the following spring/summer.

Integris Pro aeration fan control effectively cools the grain without over-drying or missing the development of hot spots through in-bin temperature sensors. It is important to ensure that grain temperature is uniform throughout the bin to avoid air current movement and potential condensation.

Grain Rehydration

At times, crops such as soybeans and canola arrive from the fields at 2-3% below the maximum acceptable straight grade moisture levels. Physically adding water to the grain is illegal and considered adulteration. However, moisture can be legally added by blowing natural humid air through the grain silo.

This is easily achieved with the Integris Pro NAD fan control by setting the EMC band to a higher EMC and allowing the fan to operate with moist air instead of dry air. Grain can be rehydrated if there is a sufficient airflow rate and the ambient air is not too dry, or with a relative humidity above 80% for at least 8-10 hours of 24-hour daily cycle.

Dryeration

Dryeration is the process of high temperature grain drying and subsequent cooling (aeration). In dryeration, grain from a high temperature dryer is removed with 2-3% higher moisture than desired for safe storage levels and placed in tempering (also referred as heat soaking, steeping, and steaming) bins and then slowly aerated/cooled.

This process has been mainly adopted for corn drying which results in improved grain quality, colour, and reduced kernel damage for an increased storage life. Stress cracks develop when high moisture grain is exposed to high temperatures in the grain dryer and then cooled immediately after drying is finished. Stopping high temperature drying sooner (2-3% above target) also increases dryer capacity and reduces energy consumption and drying cost.

This system consists of free-standing silos which are loaded with grain for drying and storage. A fan—connected to the plenum of the silo through the transition duct—pushes air through the grain to the top of the bin where air leaves the exhaust vents. As the fan pushes the warm, dry air through the plenum, air absorbs the moisture from grain and moves up through the bin. As drying progresses, a drying front is established (a hypothetical layer of 0.5-1.0 m or 1.6-3.2 ft). Once this layer is dry, the front moves to the next layers until the bin is completely dry.

Integris Pro fan control offers several control strategies.

Natural Air Drying (NAD)

NAD fan control operates the fan when plenum EMC are within set windows (upper and lower limits)—restricting the delivery of air that’s either too wet/dry or too cold/hot. The plenum EMC is calculated by using plenum air temperature, relative humidity and grain curve. The system also checks extreme weather using minimum/maximum temperature limits—however, fan control is still weather-dependent, and NAD may still over-dry the bottom layer and leave the top layer unfinished.

Natural Air Drying with Heater (NADH)

For in-bin natural air drying, a small amount of supplemental heat can be added to reduce the relative humidity of air—getting the plenum EMC in the optimal moisture range. A rise of 11°C or 20°F in air temperature can reduce relative humidity by half. Only a small heater (propane or electric) is required to increase the air temperature to 4.5-5.5°C or 8-10°F. By simply passing through the fan, the temperature of the air raises by 1.5-3.5°C or 3-6°F, potentially eliminating the need of a heater. Excessive heat is not required; it will result in over-drying the grain causing shrink and energy loss.

Self-Adaptive Variable Heat (SAVH)

This process automatically adjusts the upper and lower EMC windows throughout the drying process, minimizing run-time hours and over drying costs, as well as moisture non-uniformity.

Understand the capabilities and limitations of your system based on factors such as climate, airflow, length of storage, safe storage period and moisture control objectives.

Airflow Rate

In a typical bin, dry air passes through the grain from the perforated plenum located at the bottom of the bin and absorbs moisture before exiting through exhaust vents located at the top. A higher airflow rate will remove a larger amount of water from the grain, which results in the faster completion of a natural air drying cycle. The recommended airflow rate for natural air drying is 1.0 cfm/bu for 3-5 point moisture removal.

Fans

Fans should be selected specific to the bin size and grain type in order to achieve optimal airflow rate against the airflow resistance caused by the packed grain. Wheat and canola, for example, create higher resistance to airflow (static pressure) compared to corn soybeans at the same grain depth. A fan manufacturer can provide a fan specific performance curve with a rated static airflow deliverable against a given static pressure.

Low speed centrifugal fans deliver maximum airflow (relative to the same horse power axial or high speed centrifugal fan) and are the most efficient for drying. However, these fans cannot be used in tall bins due to the high static pressure of 0.25-0.28 m or 10-11” or greater, and work best in the 0.13-0.20 m or 5-8” static pressure ranges.

High speed centrifugal fans are designed to work against high static pressure of up to 0.51 m or 20”, but they move less airflow. The most efficient drying results are achieved when grain depths are no more than 6.5-7.5 m or 22-25’ and when there are enough vents/exhausts to move the air out of the grain bin. An insufficient ventilation area increases the airflow resistance and reduces airflow rate, risking the grain quality. The recommended ventilation requirement is 1 sq. ft. for every 1,000 cfm delivered by a fan.

Low Temperature Heater

For humid conditions, a small amount of supplemental heat is used with in-bin natural air drying to reduce relative humidity of ambient air and equilibrate plenum air moisture content to desired moisture range.

A rise of 11ºC or 20ºF in air temperature reduces relative humidity to one-half, hence, only a small amount of heat (propane or electric) is required to increase the air temperature by 4.5-5.5ºC or 8-10ºF.

Note: Fan warming raises the plenum air temperature by 1.5-3.5ºC or 3-6ºF (fan warming increases with an increase in static pressure) as ambient air passes through the fan, reducing relative humidity significantly. Therefore, a supplemental heater may not be required.

Excessive heating will result in over-drying of the grain, causing shrink and energy loss. To prevent shrink and energy loss, a heater should not be in continuous operation when ambient air relative humidity is lower and EMC is within desired range. A heater should only be utilized if the plenum EMC is above the target moisture range.

Grain Filling

Grain filling has a significant effect on airflow rate and distribution. Immature, fine, foreign material and broken grain tend to accumulate near the central core of bins and block or reduce the inter-granular space creating airflow resistance at the core. This resistance forces air to move up through the sides of the bin which causes a longer drying front at the core and excessive consumption of energy. Now grain on the sides risks becoming over-dried grain at the side of the bin. Since the airflow rate is higher near the bin wall, the grain near the side wall over-dries due to excessive airflow and longer fan operation, resulting in significant shrink loss.

After filling, the grain bin should be cored and levelled to provide uniform and sufficient airflow throughout. Fill the bin to a shallower grain depth if the moisture content is high or if the airflow rate is less than recommended. Shallower grain depths will reduce the airflow resistance/static pressure and the fan will deliver higher airflow for accelerated drying. Tall bins with small fans should not be used for in-bin natural air drying.

Weather

Favourable weather conditions are essential for successful in-bin natural drying of grain. Running the fan in highly humid, overly dry, rainy or cold ambient conditions will consume excessive energy creating poor drying results.

Integris Pro uses the ambient air temperature/RH from the weather station and rain inputs from the rain sensor for the fan and heater controls. Fans and heaters are only in operation when good quality air with desired temperature and RH levels are available for drying. This ensures optimized energy consumption for efficient, uniform, and fast drying of grain.

Natural air drying is not energy efficient in winter months (mid-November to mid-March) due to cold weather (temperature below 4.4ºC or 40ºF), poor water holding capacity in air and risk of major grain shrink at the bottom of bins from an added heater. Avoid running fans in below freezing temperatures to reduce risk of condensation, vent freeze and high moisture grain freezing together, which would block the airflow leading to potential hotspot development.