Aspects of Kiln Design

The author traces developments in dry kiln design and equipment. The greatest advancement over the early natural-draft type kilns was the power-driven fan circulating system. The external pressure blower type fan systems were the first, but in 1923 they gave way to the much improved internal-fan kiln. The first internal-fan kilns had all fans spaced at about 8-foot intervals along a single shaft that extended the length of the kiln. This system proved inefficient in power consumption and resulted in non-uniform air-flow. The ultimate in fan design and placement was the use of internal kiln motor with fans arranged so that air was blown across the kiln. Overhead placement of fans and heating coils, a heat booster between lumber stacks, a humidification system, and proper placement of exacting dry- and wet-bulb sensors for control of heat, humidity, and venting, has resulted in substantial improvements in kiln design and construction. Further improvements are to be made in schedules and pre-treatments of lumber. Today the most exacting kiln schedules can be followed to dry any species to a uniform final moisture content at highest quality and at lowest cost, both for operation and investment.

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