Recent Experiences with Advanced Control Aimed at Optimizing Product Uniformity, 1991 Process Control, Electrical & Info. Conference Proceedings

Process control in the pulp and paper industry is characterized by a predominant use of proportional integral controllers which most often have default tuning settings and have never been actually tuned. The majority of control practitioners do not use the mathematical principles of control engineering in their jobs relying exclusively on ’feel’ and experience. Audits of pulp and paper mills have shown that many control loops cycle and destabilize product uniformity which is in turn considerably higher than it need be. The opinion is expressed that advanced control strategies can only work in the long term if on-site staff understand the concept - otherwise it is doomed. Hence a major benefit can be achieved if the majority of practitioners can be trained to make effective use of the simple control techniques such as PID. Beyond that, control should be as advanced as necessary to solve the papermaking problem yet to be understood.

The paper describes a number of recent achievements including the following. The use of Lambda Tuning and minimum variance control - both modern concepts in controller tuning and how these have been applied in practice and taught to pulp and paper practitioners in order to minimize product variability. A Kalman Filter based deadtime compensation algorithm that has been implemented in DCS’s to optimize basis weight control. The decoupled control of a multi-plug, multi-fan pump headbox in order to stabilize wet end operation. The implementation, on a DCS, of a linerboard machine automatic grade change strategy. Finally, a DCS implemented groundwood control strategy which controls individual stone specific energy on seven tandem lines in order to optimize pulp quality.