Towards an effluent-free paper mill

The environmental load of the paper industry has been decreased drastically during recent decades. The main emphasis has been on the improvement of external effluent treatment methods. An alternative to the current end-of-pipe technology is internal treatment and the reuse of process waters. VTT Energy is doing research in this field as a part of the CACTUS research programme (Water Management in Papermaking) funded by the Technology Development Centre of Finland (Tekes) and industry. Valmet, UPM Kymmene, Enso, Lappeenranta University of Technology and Åbo Akademi University have been among collaboration partners in this work. This article presents ways to reducing fresh-water consumption in an integrate consisting of a thermomechanical pulping plant and a paper mill. The importance of good water management is illustrated by a simulation study where the concentration of dissolved solids in wire water and in pulp entering bleaching is calculated as a function of fresh-water intake. Topics for further research and problems related to the closing of water circulations are also discussed. The impact on energy balance is analysed using a modified Pinch method.