System Design for Computer Control of the TMP Process

Abstract A computer control system with a generally applicable structure of functions can be defined for the control and optimization of the thermomechanical pulping process. The production lines of the mill can be seen as invariant entireties with respect to their composition and operation and shall therefore be considered as separate control units. The structure of the system can be characterized by three hierarchal categories of functions: The first category includes refiner load control, which is accomplished by digital regulators because of the complexity of the operation. Otherwise, computer-independent control of actuators is preferred. The second category consists of supervising setpoint controls. The immediate aim of these functions is to improve the controllability of the plant by allowing the command of entire refiner lines instead of individual machine units. The concept of command variables has been introduced for this purpose. The third category consists of optimizing functions. They have two purposes, viz. to adjust the operating point of the refiners according to the prevailing restrictions, and to optimize the quality of the pulp produced. The above functions constitute the framework of the computer control system. A significant part of the actual software is aimed at automation of the operation and maintenance of the system. The system was designed in co-operation with several corporations. Experience of organizational matters and documentation of system design are also reviewed in the paper.