Dehumidification Drying of Spruce Studs

Spruce studs were dried to an average moisture content (MC) of 16 percent; one charge in a steam heated conventional kiln and three charges by the dehumidification process. Conventional kiln-drying (66 to 82?C: 150 to 180?F) required 56 hours, and the total energy consumption was 2.8 gigajoules (778 kwh). The dehumidification system, at a maximum drying temperature of about 34? (93?F), required 96 hours; however, the total energy consumption was only 0.9 to 1.5 gigajoules (250 to 417 kwh), depending on initial MC of the charge — an energy saving of 68 to 46 percent. Below about 25 percent MC. the drying rates for dehumidification decreased sharply. For charges with similar initial MC, the drying time to 25 percent MC was only 9 hours longer for the dehumidification process, at which point the saving in energy was 67 percent, as opposed to 57 percent at 16 percent MC. The quality of the dry studs was similar for both drying systems, but without a supplementary source of steam the studs dried by the dehumidification process could not be conditioned for stress relief.

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