Identification and evaluation of improved drying methods of New Zealand beeches by means of an energy-efficient kiln process (2000)
Type of ContentTheses / Dissertations
Thesis DisciplineChemical Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
AuthorsZhang, Zhengshow all
New Zealand Nothofagus timbers, especially N. fusca (red beech) and N. truncata (hard beech) are among the most refractory timbers in the world to be dried in conventional kilns. The recommended drying method is to air dry these New Zealand beech timbers to about or below their fibre-saturation point before kiln-drying to required moisture contents for end use. Because the air-dry process is an uncontrollable process, due to the weather conditions which may vary from day to day, an alternative strategy is needed. This thesis presents studies on establishing and optimising new drying schedules for New Zealand beech timbers for kiln-drying from green conditions at low temperatures and in dehumidifying drying systems. The studies include: (1) Establishing stepwise drying schedules for drying Nothofagus timbers from green conditions; (2) Using a strain-limited model to optimise the initial step-wise drying schedules into moisturebased schedules. The optimised drying schedules are verified with small-scale experimental drying trials. Work includes the determination of mechanical properties and the drying behaviour of drying N. fagus timbers in their transverse direction. Also the effect of various pre-treatments on the drying rate and the mechanical properties are also determined. Finally, an assessment is made of the energy efficiency of the optimised drying schedules under the proposed dehumidifying drying system.