The development of a control system for a pulp washing plant through the use of dynamic simulation

Abstract

Pulp is washed in a counter-current, multi-stage process with a high degree of system closure. The system structure gives the process a mixture of fast and slow dynamics. The behaviour of a multi-stage washing plant as a system has so far not been well known. The economic potential of improved control may therefore he estimated to be substantial.In order to develop a control system for a washing plant extensive mill measurements have been performed to gain information about the system. On the basis of the data, collected dynamic models have been developed for individual process elements and for the system as a whole. Through simulations, different control strategies and operating routines have been compared and optimized.In the paper this development work is described as well as general comments concerning washing control. Optimization of a start-up routine for digester and washing plant is shown. The techniques described can also be an advantage in other closed systems to create a better foundation for decisions concerning control, operating routines, process development and reconstruction.