Column Dryers
Advantages:
Disadvantages:
·
Dryers require large amounts of fuel which is very expensive
.
Column Batch Dryers
Column batch dryers are completely filled at one time. A common batch dryer configuration is two columns surrounding a plenum chamber. Several circular-shaped batch dryers are also available. Hot air is forced into the plenum from a fan-heater unit and passes through the grain-filled columns and dries the grain. Common batch capacity of batch dryers varies from 80 to 1,000 bushels. Column widths are normally from 10 to 20 inches. High temperatures and high airflow rates characterize batch dryers. The typical operating sequence is fill-dry-cool-unload. Time for one batch varies, but an average may be two to three hours per batch. Control of the drying sequence can be either manual or automatic.
A recirculating device may be added to some batch dryers. This has the effect of reducing the moisture variation across the column of the dryer. For some crops, a higher temperature may be used with a recirculating batch dryer since a kernel of grain will not be next to the heated air for the entire drying cycle and as a result should not get as hot.
Continuous Flow Drying
Wet grain constantly feeds in the top and is dried and cooled in a continuous flow dryer. Dry grain is drawn off the bottom and placed into storage. These dryers are similar to batch dryers in configuration but have a divided plenum chamber. Hot drying air is pushed into the top chamber, and unheated air for cooling is pushed into the lower chamber. Column widths on continuous flow dryers vary from 8 to 20 inches. A sensor controls the discharge rate and consequently the moisture content of the dried grain. Continuous flow dryers use high temperatures and high airflow rates. Airflow rates of 50 to 100 cfm/bushel of grain are common. Continuous flow dryers are available in a large range of sizes. Portable units are available in sizes up to about 1000 bushel per hour capacity, and stationary units of larger capacity are available. The first grain through a continuous-flow dryer generally will need to be cycled through the dryer again for drying to be completed.
Some cross-flow models reverse the airflow through the dryer as the grain progresses down the column to reduce overdrying. Some reverse the air flow in the cooling section to increase energy efficiency. The concurrent airflow in the drying section and counterflow in the cooling section improves energy efficiency and reduces stress cracking in corn. With this system, the heated air enters the grain near the top of the dryer and moves downward in the same direction as the grain. The cooling air moves in the opposite direction as the grain.
Another type of dryer is the mixed flow dryer. In this type, the grain flows over alternating rows of heated air supply ducts and air exhaust ducts. This action provides mixing of the grain and alternate exposure to drying air that is relatively hot, and air which has been cooled by previous contact with the grain. It promotes moisture uniformity and nearly equal exposure of the grain to the drying air.
Other Grain Drying Methods
By