Basic Theory of a Furnace Dryer

Composition

• The theory of the dryer begins with its composition. For poorer family farmers — as opposed to much larger corporate mega-farms — the dryer is simple. It contains a combustion chamber, a mode of delivering heat, fans for airflow, a thermostat and a vent. Sometimes it contains a chamber for waste and ash, but many models of the furnace dryer are hand cleaned.

Moisture Equilibrium

• The basic theoretical principle of the action of one of these dryers is called the “Grain Equilibrium Moisture” level. The idea is simple: The agricultural product in question should be dried to the point where the moisture in the product is identical to the level of moisture in the surrounding air. While it is true that some products need to be dried totally, the average grain -- such as oats, wheat or rye -- follows the basic equilibrium idea. In this case, a well dried crop reduces loss and improves grain quality. Corn that is used for human consumption is not dried because each kernel of corn is filled with water.

Drying Theory

• Each kernel of grain needs to be evenly exposed to the hot air. Each grain or kernel needs to be exposed as much as all other grains. This is where the drying technology gets complicated. The general concept is that the higher the temperature, the more rapid the drying. Yet temperatures that are too high can damage the crop. Airflow also must be slow and steady. Rapid airflow can retard the drying process and damage the crop. Hence, in general, moderation must be maintained both with airflow and temperature.

Fuels

• Fuels have become more important as dryer technology has improved. In 2011, many university extension research and furnace manufacturers are promoting bio-mass fueled units. Since each agricultural commodity often produces more waste than the usable product, this means the “husks” can be removed and used as fuel. This saves money, increases efficiency and changes the concept of “agricultural waste.”