Enhancement studies on operation and control of water usage in paper mills

The ongoing trend in the paper industry is to decrease the environmental impact of a mill by minimising the fresh water intake by closing the white water circuits. This can cause completely new kind of problems at the mill like ac-cumulation of chemical species, problems in wet end chemistry and propagation of disturbances through the in-tegrated flow network. In this paper dynamic behaviour of a closed-cycle paper mill was studied using a detailed com-putational simulation model. This model includes the whole paper mill process starting from the mass towers and ending to the reel. The most important control circuits and parts of mill automation were also included. The model was used in simulation studies including chemical distur-bance propagation analyses, grade change studies and also for operator training purposes to teach new kind of water usage philosophy. For operator training, a real process control system, Valmet Damatic XD, was used to operate the simulator. Simulation runs were performed using the Advanced Paper Mill Simulator (APMS) simulation pro-gram, Dynamic simulation turned out to be a powerful tool for verification of process and automation design as well as for operator training.