High temperature batch bin dryers use air heated to temperatures ranging from 120°F to 160°F to dry grain. This type of dryer has a perforated floor and a dryer fan and heater that blows heated air beneath the perforated floor and up through the grain. Heaters can be fueled by natural gas or liquid petroleum gas (LP gas/propane). Grain is loaded at the top of the bin, and distributed via a grain spreader. The optimal drying depth is between 2-1/2 to 4 feet without a stirring device and 6 to 9 feet of grain with stirring device. A wet bin may be needed if grain is harvested faster than it can be dried.
A sweep auger is used to remove grain when unloading, a layer at a time, from the bin. The grain is usually stored in separate bins, however the last batch of dried grain can be stored in the dryer bin as long as bin wall condensation can be controlled. Having adequate venting and a space between the roof and the top of the side wall is important for moisture control and to prevent re-wetting of the grain.
To get the grain at the top of the grain bin dry, the grain at the floor will be over dried unless a stirring device is used. The grain depth should be limited so the moisture variation between the top and bottom is less than 5 percentage points. A stirring mechanism can reduce over drying and increase the efficiency of high temperature bin dryers by 20 to 30%. Vertical augers are used to lift dry grain from near the floor and allow higher moisture grain to replace it. A stirring device should be run continuously when drying in a high temperature bin dryer.
In-bin cooling can also save approximately 15% in energy costs, and increase dryer capacity by about 33%. Dryeration can reduce fuel costs from 20% to 30%, and increase drying capacity by 50% to 70%. Both in-bin cooling and dryeration are only effective if the grain handling system can transfer the grain fast enough that it doesn’t cool off significantly before being unloaded.