Model predictive control of the chip level in a continuous pulp digester, a case study

46 ❘ ❘ ❘ 106:11 (2005) T 239 Pulp & Paper Canada The MPC scheme is straightforward regarding the handling of constraint variables in the control problem. By combining the controlled and constraint variables, it is possible to set-up and tune the MPC controller both to control the level to a set point and to have upper and lower limits to ensure the production level, i.e. to keep the chip level at an average value (set point) but at the same time allow the level to fluctuate within certain limits (as a buffering functionality). The MPC controller is implemented on a continuous digester at the M-real Husum mill, Sweden and has been running since the end of 2003. The digester operators state that digester system has operated more smoothly during this winter period with the updated level control system, compared to last year’s operation. Another purpose of this work is to implement a multivariable model-based controller, such as a MPC controller, on a selected pulp and paper process. The selected process (the digester system) and the MPC controller will be used as a test system for the development of a monitoring and diagnosis system for multivariable and multi-loop control systems.