Dryeration and In-Storage Cooling for Corn Drying
The typical high-speed drying process rapidly reduces corn moisture content using heated air and then cools the corn rapidly in the dryer before transfer to storage (figure 1). Dryeration (figure 2), a process developed at Purdue University in the late 1960s, modifies this high-speed drying process by transferring the corn hot to a cooling bin, eliminating in-dryer cooling. The hot corn is allowed to “steep” or “temper” in the cooling bin at least 4 to 6 hours before being cooled slowly. After cooling, the corn is transferred to storage. Dryeration provides three advantages over high-speed drying with in-dryer cooling: increased dryer capacity, reduced fuel consumption, and better corn quality (less stress cracking, less fine material, higher test weight).
In-storage cooling (figure 3) is another alternative to in-dryer cooling. Hot corn is transferred directly to the storage bin rather than to a special cooling bin as in dryeration. In-storage cooling eliminates the extra handling step that is sometimes a disadvantage in dryeration. Although dryeration has advantages over in-storage cooling related to energy savings, dryer capacity, and corn quality, elimination of the extra handling step required in dryeration often makes in-storage cooling a feasible alternative. Both dryeration and in-storage cooling are discussed in detail in this publication.
Dryeration
The corn is delivered hot from a high-speed dryer to a dryeration bin where it is allowed to “temper” or “steep” without airflow for at least 4 to 6 hours before being slowly cooled. The capacity of the high-speed dryer is increased because the dryer is not used for cooling. In a batch dryer the cooling time is eliminated. In a continuous-flow dryer a burner can be added to the cooling section, converting the entire dryer column to full heat.
Advantages
Immediately after high-speed drying the inner portions of the kernels are wetter than the outer portions. During the tempering process the moisture equalizes throughout the kernel. During the slow-cooling process following the tempering period two to three percentage points of moisture are removed. By contrast, little water is removed during rapid in-dryer cooling. Since the heat contained in the corn is more effectively utilized for removing water during cooling with dryeration, less fuel is required and more capacity is realized for the high-speed dryer.
The kernel stresses developed in final stages of high-speed drying and rapid cooling also are minimized by dryeration. This improvement in kernel quality produces corn that is less susceptible to stress cracking and damage during subsequent handling operations.
When a high-speed dryer is used for dryeration, the drying air temperature may be increased. This is possible because the corn is discharged at a higher moisture content and is in the dryer for less time. Increasing the drying air temperature increases the dryer capacity and improves the fuel efficiency of the high-speed dryer. When drying air temperature is increased, the corn quality (test weight and stress cracking) should be carefully monitored to insure that satisfactory quality is maintained.
Typically, a 20 to 40 percent savings in energy and a 50 to 75 percent increase in dryer capacity result from dryeration. The actual energy savings and capacity increases depend primarily on the initial corn moisture content. Weather conditions and corn temperature also affect energy use and capacity.
After cooling has been completed, the corn is transferred from the dryeration bin to aerated storage. During the tempering period condensation can build up in the corn next to the bin wall, which can lead to spoilage. As a result, corn that has gone through the tempering period in the dryeration bin should not be left there for storage. If the dryeration bin is to be used for storage of the last corn dried, the recommendations for in-storage cooling should be followed.
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