Kamyr digester chip level poses a difficult control problem, because the chip column dynamics are complex and it is difficult to measure the chip-liquor interface. Control of the chip level is required to smooth digester operation and to stabilize the residence time. Conventional methods rely largely on fixed parameter controllers which are unable to compensate for changes in the process dynamics. Manual controller returning is often required.

An adaptive chip level controller based on Generalized Predictive Control (GPC) is presented. Closed-loop time series identification methods were used to develop the process model and to design the controller. A significant reduction in chip level and P-number variability has been observed since commissioning the controller on an industrial digester in September 1988. The adaptive controller has eliminated the need for manual returning, reduced the need for operator intervention, and demonstrated the potential to predict hang-ups.