Optimizing radiata pine drying schedules

Abstract

In an era of increased energy costs and concern about profitability, using the best drying schedule is important for softwood drying. The first part of this study looked at the feasibility of finding the combination of dry bulb, wet bulb and air velocity that either minimizes overall drying cost or maximizes profit in a simple radiata pine drying schedule with fixed conditions. A full stack drying model simulation was used to predict drying time and energy costs. Drying parameter constraints were included but drying degrade was ignored. Typical structural and appearance grade set-ups were examined for given energy and fixed cost combinations. It was concluded that significant cost reductions or profit gains are possible by selecting the best schedule. The second part of the study allowed the parameters to vary during the schedule and used a Simplex optimizing algorithm to select the best parameters as the schedule proceeded. The resulting time-varying schedule should be optimal for the given combination of energy and fixed costs. While it was found that such an approach could result in further cost reduction (~10%), it was concluded that a more responsive full stack drying model simulation is required.

Keywords:

• Drying cost
• kiln drying
• kiln drying schedules
• optimal control strategy
• softwoods

Acknowledgements

The data used in this study is from research funded by members of the Scion Wood Drying Multiclient Group. This paper was prepared while employed at Scion, but no specific funding was received for it. The authors wish to acknowledge Richard Dandorff for his computer programming work.