Column Seed Drier Equipped with Direct-fired Heater

The burner should be cut off when drying is completed. The seed should be cooled before it is stored by running the fan at least one-half hour. A few drying bins or units for holding the seed during the drying process have cooling sections, an arrangement that loses no drying time in the cooling process.

The requirements for a good heated-air drier are:

It must be built substantially of proper materials for example, special heat-resisting metals are needed in combustion chambers to give long life.

It must be firesafe. Combustible materials should not be used where temperatures exceed 165 . Combustion chambers on direct-fired driers should have air intakes covered with screen of 1/2-inch mesh to keep out trash. Direct-fired driers that burn oil or coal should have a corrosion-resistant screen of 1/4 inch mesh or some other device to keep burning particles out of the drying bin. Complete control of combustion and high temperature is essential.

It must have an easily adjustable heating unit to provide good regulation from 50 percent to 100 percent of rated capacity.

It must deliver amounts of air for each horsepower of the motor as follows: 3,000 c.f.m. at 1/2-inch static pressure; 2,000 c.f.m. at 1 -inch static pressure; and 1,000 c.f.m. at 2-inch static pressure.

It must operate under all ordinary weather conditions.

It must have overload and low voltage protection on electric motors.

Safety standards have been developed by the National Fire Protection Association. Many insurance companies require that drying installations meet these standards.

SPECIAL DRYING is needed for some seeds because of unusual harvesting, processing, or packaging techniques.

Cucumbers and muskmelons, for example, are threshed wet, but the seed does not separate readily from the surrounding pulp. Fermentation, chemical treatment, or mechanical action is then used to help free the seed. Thereafter, the seed is washed thoroughly and dried without delay.

Where sun drying is possible, seed may be spread in screen-bottom trays placed on racks. Artificial drying is also practiced with various bin-type driers and revolving drum units.

Shallow screen-bottom trays have been used effectively in western Oregon to form the top of a low tunnel. Indirect-heated air is forced down the tunnel and up through the seed-filled trays. This unit can dry 2,000 pounds of cucumber seed in 6 to 8 hours. Seed of consistently high quality is produced, even though drying air temperatures are relatively high-125 130 while free-surface moisture is present on the seed and 100 -120 during the rest of the drying process. Usual recommendations place 100 as the maximum safe temperature while cucumber seed is wet and 110 as the seed becomes drier.

The seeds of watermelon, pumpkin, tomato, and other fruits also require washing in their processing and are later dried like cucumber seed.

WATER can be helpful at times in processing seeds that normally are handled dry. Honeydew, secreted by aphids, sometimes coats seeds, like red clover or alsike clover, and causes them to stick together. Washing with water tends to remove the honeydew; afterwards the seed must be dried. If weather permits, the seed can be spread to dry on large, paved areas, like unused airport runways or roads. Occasional raking or agitating assists drying.

This large-area method is also practiced for many grasses that need drying after harvest. Seed of bluegrass is dried on flat roofs of buildings. Reed canary-grass is spread on dry lake beds. Rye-grass seed may be dried on pavement.

A water separation can be used to recover good onion seed otherwise lost in discard material from the thresher or air-screen cleaner. Some pieces of stalk have the same size or weight as good seed and normally are difficult to remove in dry separations. In water, trash and light material float away from the heavier seed, and pieces of stalks increase in size as they absorb water. A screen separation thus is possible. The seeds can then be spread to sun-dry on racks and canvas or dried artificially.

Seed packaged in moisture-proof containers must be dried to a relatively low content of moisture for safe storage. Special techniques may be needed to dry seeds to the required moisture levels (about 4 percent to 8 percent, depending on the seed) without using damaging temperatures. Recirculation of dehumidified air through bins is practiced successfully for this purpose with some vegetable and flower seed.

THERE ARE many ways of drying harvested seeds, but all are aimed at one goal to help provide seeds that grow vigorously when planted. Drying, whether natural or artificial, must lower the moisture content of seeds so that, through efficient storage, good seeds are available for their important place in agriculture.

N. ROBERT BRANDENBURG is an agricultural engineer in the Harvesting and Farm Processing Research Branch, Agricultural Engineering Research Division, Agricultural Research Service. He is stationed at Oregon State College in Corvallis.

JOSEPH W. SIMONS is principal agricultural engineer, Livestock Engineering and Farm Structures Research Branch in the same Division. He is stationed at the University of Georgia in Athens.

LLOYD L. SMITH is an agricultural engineer, Transportation and Facilities Research Division, Agricultural Marketing Service. He is stationed at the University of Georgia.