The objective of this project is to provide the information required by Canadian lumber producers to evaluate the superheated steam/vacuum (SS/V) drying technology as applied to 8/4-inch red oak with respect to drying time, final wood quality, and energy consumption. Two loads of red oak were dried in Forintek’s eastern SS/V kiln with the objective of identifying a suitable schedule with respect to time and quality. The tests involved measurements of drying time as well as wood quality before and after the drying operation, including distortion, drying checks and splits, final moisture content gradient, shrinkage and residual stress (prong test). Energy consumption of the SS/V kiln was also measured.
We were able to develop a schedule to efficiently dry 8/4-inch red oak through the SS/V process. With this schedule, an industrial load of 8/4-inch red oak can be dried in a quarter of the time typically required in conventional kilns. Our results indicate that quality drying is achievable with the SS/V process if the set point temperature is kept relatively low and the relative humidity relatively high while the wood is above the fibre saturation point. 8/4-inch red oak dried by the SS/V process required no conditioning phase to equalize moisture contents at the end of the cycle. Energy consumption measurements indicate that the process used more electrical energy than thermal energy, this being due to the relatively long time required to dry 8/4-inch red oak.