Process Control in Modern Fiber Lines, 1996 Pulping Conference Proceedings

Carl Johan Morell & Roland Åberg

ABB Industrial

Recent and current trends in the chemical pulping industry have changed dramatically the need for advanced information technology tools. The rapid, market-driven, switch to extended delignification in cooking and to new bleaching procedures increases the potential for process control, since the room for mistakes is reduced and the cost for bleaching agents has increased. The introduction of ECF and TCF grades has also increased the number of swings between different grades, since different customers and markets require different pulp properties and pulp production procedures. Altogether, these changes increase the need and benefit from specific measurement technology and process model based control systems, due to frequent grade changes, narrow quality bands and higher cost for wood and chemicals. In addition to the above effects, the current development towards “closure” of the bleach plants and the entire pulping line takes away the last “forgiveness” of the system and thus requires no mistake control. A no mistake control philosophy is not possible to achieve by technology alone, but requires an advanced combination of empowered operators, frequent measurements of relevant process and product variables and process control tools. The paper will describe concepts and technologies for advanced delignification control throughout the fiber line using process model based feed-forward control built on process knowledge and robust measurement devices for pulp and liquors. The process model based controls are kept accurate through dead time compensating adaptation techniques, i.e. using the actual process response for long-term process model corrections. Experience from and comparisons between installations in different parts of the world will be discussed. The powerful combination of process control and operator empowering information technologies such as pulp tracking, on-line predictors and process simulators will be described using examples from control of closed bleach operations and grade change management.