Two Delayed-Cooling Methods

When you need to dry your corn, the grain dryer is often the bottleneck that slows down harvest. Dryeration and combination drying are two delayed-cooling management strategies that can increase the drying rate from your high-temperature (above 120°F.) corn dryer.

With both strategies, the drying process in the high-temperature dryer is stopped at a grain moisture content higher than the final target moisture content. This allows you to push more bushels through your dryer and to increase your overall drying capacity. Plus, with delayed cooling, the grain spends less time in the high-temperature dryer, reducing inputs and increasing energy efficiency.

"Both combination drying and dryeration use a different management style than regular drying," explains Mark Hanna, Iowa State University Extension. "The presence of natural-air drying bins is not as common as it once was, but if the bins are already available, delayed-cooling drying can be an option. In years with much wet corn, this also greatly increases dryer capacity."

How it works
When you dry corn in a high-temperature dryer, the moisture is removed from kernels faster than it can equalize within each kernel. So at the end of drying, the moisture level in the center of the kernel will be higher than the moisture level around the outside.

With delayed cooling, you allow grain to steep or temper, giving the kernel the necessary time for the moisture to equalize. According to Iowa State University (ISU), this can take anywhere from four to 12 hours.

When you cool corn after this resting period, you remove an extra 0.2 to 0.25 points of moisture from the corn for each 10°F. of temperature cooling, which is two to three points of moisture for typical high-temperature dryers. Benefits of delayed cooling include reduced stress cracking of kernels and reduced kernel brittleness.

Designing for dryeration
For dryeration, you need to transfer hot grain from the dryer into a cooling bin where you can keep it for several hours before cooling. Hanna recommends a cooling bin with full-floor aeration. You should avoid using storage bins for delayed cooling, because condensation will occur in cold weather on the bin sidewall and on nearby grain.

The best setup for dryeration is to have two cooling bins. One bin can steep and cool while the other bin is loading. Ideally, each cooling bin is the right size for one day's drying capacity, and the cooling fans should be able to cool the grain in about 12 hours. According to ISU, this requires approximately 1 cubic foot per minute of airflow per bushel of grain to be cooled.

If you are considering adding to your grain drying operation, you should think about adding cooling bins that are up to 1.5 times your current drying capacity so you have some room to expand.

Dryeration how-to
First, transfer hot grain from the dryer at a moisture level two to three points higher than your desired final grain moisture content. Then, let the grain steep in a cooling bin for at least four hours (preferably six to 12 hours) before you start the cooling fan. After you've cooled the grain, move it into your storage bins. Last, monitor the moisture level and adjust drying as necessary.

Hanna advises against immediately starting the cooling fans, because this won't remove as much moisture, and it doesn't provide as much protection from kernels cracking.

Dryeration will require more grain-handling equipment and more management. However, it can provide significant increases in drying capacity and energy efficiency.

Combination drying
If you're interested in delayed cooling but don't have the setup for dryeration, combination drying may be another option. This delayed-cooling method combines high-temperature and low-temperature drying systems, so you must be able to transfer grain from the high-temperature dryer to the low-temperature drying bin.

To start off, you dry corn to a moisture content of 22% or less. Then, you transfer the partially dried corn to the low-temperature drying bin. Start the fans immediately to finish drying.
By immediately cooling in the bin, you reduce the risk of condensation while removing an additional point of moisture, taking the moisture content to no higher than 21%. A moisture content of 21% or less is generally safe for low-temperature drying in Iowa, according to ISU.

You can double or triple drying capacity with combination drying compared with conventional high-temperature drying. However, you will use more electricity instead of natural gas or propane, and a larger drying system investment is required.

Starting place
So which method is better for your farming operation? That will depend on your grain-drying setup.

"Combination drying is generally more attractive than dryeration, at least in Iowa," says Hanna. "Dryeration requires bin space for tempering without airflow before cooling. In practice, this usually means a couple of small bins beyond the dryer with handling systems to move grain on to storage and cooling. Adding the two smaller tempering bins can be challenging in existing systems."

Before you make any changes to your grain-drying system, get an energy audit. This will determine your energy efficiency and will highlight areas where you can improve.

Hanna recommends consulting with a qualified engineer or system planner for assistance in selecting equipment.