Refiner optimization and control Part III: Natural decoupling in TMP refining processes

Journal article, 2015

In TMP-refining processes, the stabilization of the fiber pad inside the refining zone requires a new control approach. Specific energy control tends to be complex and most often affected by a number of disturbances not so well specified in traditional MPC-concepts. To describe the dynamics in such nonlinear processes is difficult, tedious and requires significant maintenance support. This paper focuses on two important issues related to modeling in mechanical pulping processes: measurements of internal states inside the refining zone and in particular natural decoupling to find a model suitable for future process optimization and improved control concepts of complete refiner lines. The idea is to show how this complex process, with serially linked refiners or refining zones, can be modeled and controlled using a simplified process description. In this series of papers, data from a commercial Twin-refiner and a CD-refiner are available as inputs. As an example of internal state measurements, refining zone temperature profiles and estimated distributed consistency in the refining zone are used. We show that the characteristics of the temperature profile dynamics makes it possible to introduce a decoupling scheme where the anti-diagonal elements in the transfer function matrix describing the process can be eliminated naturally, independent of which refiner is to be controlled.