Cooling of Grain Storage

Grains generally include wheat, rice, barley, and similar products. To store grains properly according to the storage period, certain precautions must be taken. This text examines the following points:

• The impact of temperature on grain storage
• Temperature control and monitoring
• Short-term and long-term storage goals
• The effect of grain layer depth on storage
• The impact of differential control in improving cooling
• Proper ventilation systems

The Impact of Temperature on Grain Storage:

Temperature Control and Monitoring:

Measure the temperature every few days until the desired temperature is reached, and then check it weekly. Always measure the temperature in the same location. Take measurements where cooling takes the longest or at the farthest point from the ventilation system’s blower fan. It is generally recommended to measure 0.5 meters below the surface and in the center between the ducts. Always use a calibrated temperature probe (thermocouple or thermistor). An increase in temperature may indicate the presence of fungi, sprouting, or weevil development in the grains.

Grain Storage Goals (Short-term and Long-term):

Ideally, cooling should begin as soon as the grains enter the storage facility. This allows grains to be stored at higher moisture levels, effectively extending the safe storage period. Use low airflow (10 cubic meters per hour per ton, equivalent to 6 cubic feet per minute per ton) and start cooling as soon as the air ducts are covered with grains.

• Within 2 weeks of harvest: Reduce the grain temperature to below 15°C to slow insect activity, preventing the complete life cycle of pests like the saw-toothed grain beetle.
• Within 3 to 4 months after harvest: Reduce the temperature to below 12°C to stop insect activity.
• By the end of the year: Lower the temperature to below 5°C to kill adult insects and reduce the number of mites.

The Effect of Grain Layer Depth on Storage:

When grain depth increases, the effectiveness of cooling decreases. As depth increases, the spacing between ducts should decrease according to the following table:

Perforated metal ducts are commonly used for cooling. For oilseeds like canola, due to higher resistance to airflow, reduce the storage depth by 50% to 70%.

The Impact of Differential Control in Improving Cooling:

A differential thermostat controls the cooling fan, turning it on when the ambient air temperature is lower than the grain temperature. Compared to manual control, this method reduces the fan’s operating hours and energy costs while achieving the desired temperature. Place the environmental sensor near the fan inlet, away from the heat generated by the electric motor. Position the probe within the grain mass in a location where cooling takes the longest, and avoid placing it too close to the surface. Blowing air through grains during the winter may increase natural moisture at the grain surface, which can extend up to one-third of the grain depth.

Proper Ventilation Systems:

Common aeration systems are either vertical or horizontal. Vertical systems can be as effective as horizontal systems. The advantages of vertical systems include lower initial investment costs and reduced risk of damage to ducts during unloading in flat storage warehouses. Duct spacing depends on grain depth. In general, placing ducts 4 to 8 meters apart is suitable for a typical flat warehouse. There are also blowing and suction systems, which influence the progress of grain cooling. Vertical aeration systems can operate in suction or blowing modes.

Airflow:

Fans must provide sufficient pressure to overcome resistance from the grain, depth, and duct characteristics (length, local pressure drop, etc.). Ducts should have a large enough diameter and sufficient perforation to minimize resistance. Use an appropriate anemometer in front of or behind the fan. Vertical aeration systems can be used in either sucking or blowing modes.

Conclusion:

For long-term grain storage, several key factors must be considered to protect grain quality and prevent spoilage. Factors such as grain drying, gradual cooling in multiple stages, continuous temperature and humidity control in storage, proper ventilation, pest and insect control, and maintaining a clean warehouse are critical to the successful storage of grains. By following these guidelines and using proper tools for monitoring and controlling conditions, grains can be stored for extended periods without quality degradation or spoilage.