Nonlinear model predictive control of timber drying

There is considerable economic incentive for improved timber drying in terms of reduced total drying time, lower wastage levels and improved product quality. This paper presents simulation results in two areas pertinent to improved timber drying productivity. First, it is shown that timber drying can be posed and solved as a nonlinear model predictive control problem. Recognition of two distinct phases (drying to a set average moisture content, followed by flattening of the moisture content profile) reduces the amount of computation required. It is then shown that the initial moisture content and an on-line measurement of a timber stack's weight provide sufficient information to design a closed-loop control system which achieves significant improvements (relative to standard drying schedules) in both total drying time and final product quality. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.