Mid Sweden University

Modern optimization methods offer tools to create new, and to modify existing wood drying schedules. The total drying time can be minimized, at the sazne time as both the moisture content and the deformation after completed drying are within acceptable limits. The stress levels during drying are also considered.

A method for defining effective schedules for kiln drying of wood is presented. The method is designed in such a way that it proposes an optimized variation of temperature and humidity which yields the minimum total drying time, with the condition that the moisture content and the deformation not exceed specified limits after the drying and that the stress not exceeds a specified level at any time during the drying process in order to avoid crack development. To demonstrate the capability of the optimization method numerical results are presented. It should be noted that ill this first approach, drying starts from moisture content corresponding to the fibre-saturation point, i.e. approximate to 30%).

Optimization with distributed computing is performed on a two-dimensional orthotropic drying model which allows boards with arbitrary outtake of the log and sapwood/heartwood distribution in the cross section. Drying schedules with an optimized variation of temperature and humidity which yields minimized drying time are created at the same time as moisture, stress and deformation levels are considered. A numerical example with distributed computing of a board with a mixture of sapwood and heartwood is presented. Drying starts from the fibre saturation point.