DRYING AT HIGH-TEMPERATURE OF SAPWOOD AND HEARTWOOD - THEORY, EXPERIMENT AND PRACTICAL CONSEQUENCE ON KILN CONTROL

This paper aims to relate the last results obtained in the field of drying theory with the industrial process. It deals particularly with the problem of the difference between sapwood and heartwood that always occurs in the whole stack of an industrial drier. The experimental procedure and the simulation code TRANSPORE are shortly presented. Experiments have been carried out on sapwood and heartwood (Spruce with superheated steam and pine with moist air). The code is used to compare sapwood and heartwood. In the simulations, only the initial moisture content and the permeabilities differentiate both parts of the tree. Once again, the code proves very efficient. For both experiment and theory, the main results are: i) longitudinal liquid migration occurs up to the end of the board only for sapwood ii) the first drying period disappears for heartwood iii) the drying kinetics cross each other at the end of drying These results are of great importance at the time of optimizing the process: among several possible control devices, the temperature loss through the stack seems to be a good choice combining relevant information and easy-to-use measurement.