Energikartläggning och modellering av pappersmaskin PM 5 Enso Mölndal, samt förslag till energieffektivisering

Papermaking is a process where cellulose fibers suspended in water are dewatered step by step. In the final step, the remaining water is dewatered by evaporation when the paper web is in contact with steam-heated cylinders in the drying section. Even though the drying section only removes approximately 1 % of all the water, it uses as much as 2/3 of all the energy, in form of steam. The drying section of the paper machine PM 5 at Stora Enso Mölndal is divided into three parts, where the first part, the pre-dryer is responsible for the main part of the drying and thus also the main part of the energy consumption. Also being the bottleneck in the production the pre-dryer was the object of the investigation in this project. The aim of this project was to map out the energy flows within and around the pre- drying section and develop a computer model of it. This was done with the purpose of giving propositions of how the machine should be rebuilt to enable increased production and to give lower specific energy consumption. For the development of the computer model the simulation software WinGEMS 4.0 was used, while this program is suitable for simulation of the pulp and paper industries. At first model parameters of the current machine were adjusted, on the basis of measurements done on the machine. This model was then modified to predict the results of different rebuilds. In parallel, pinch analysis was used to investigate the possibilities for heat recovery. The result of the study was that good heat recovery would decrease the specific steam consumption since heat exchange could, to some extent, replace steam for preheating incoming air. The heat exchange is facilitated by a well-designed air system, where air leakage is restricted. Investing in a better air system pays off, as it gives propitious drying conditions and hence somewhat higher production. A more efficient way to increase the production is to expand the pre-dryer with some extra cylinders. Finally, when combining expansion, better air system and better heat exchange the result will be a pre-dryer with increased production and low specific energy consumption