Impact of various measures to optimize the air velocity in an industrial wood-drying process

Abstract

The relationship between fan speed and electrical energy consumption, and the price of energy, justify studies on the possibilities for reducing air velocity during the wood-drying process. In this study, effects of air velocity were examined to determine when and how much it can be reduced, without affecting the drying rate of the sawn timber. The first experiments were performed in a laboratory kiln, and 36 samples of 50×100 mm boards (2×log) of Norway spruce [Picea abies (L.) Karst.] were dried at 70°C with varying air velocity. Results show that too early or too sharp a reduction in air velocity gives a reduced drying rate and a large variation in moisture content. The next step in the project was a full-scale industrial study in kilns at a Norwegian sawmill. To optimize air velocity conditions, batten spaces were sealed. This had no significant effect on air velocity in the kiln. A reduction in air velocity in the kiln to 60% frequency at 40% moisture content and to 40% frequency at 20% moisture content, without considerable changes in the drying schedule, resulted in an increase in final moisture content.

Keywords:

• Air velocity
• Norway spruce
• wood drying

Acknowledgements

This study was funded by Tørkeklubben (the Norwegian Kiln Drying Club) and The Research Council of Norway. Our thanks to Haslestad Bruk AS for letting us disturb their daily routines with air velocity measurements and Romerike Trelast AS for contributing with material for the laboratory test.