Framework for water minimisation technology evaluation in papermaking

A framework for evaluating promising water saving concepts is presented. The framework combines process modelling, laboratory and pilot scale experiments and process integration methods. The framework is demonstrated through a study, where technologies for minimisation of water consumption in paper production have been investigated with a paper mill model based on Best Available Technologies as defined in the IPPC-directive. The water use was minimised using a combination of 1) recovery and reuse of cooling and sealing water, 2) increased recycling of process water and 3) internal treatment of contaminated process water. Emphasis was put on modelling of water separation from pulp suspensions and on concentration of washing filtrates with ultrafiltration, nanofiltration and evaporation (MVR and waste heat driven) techniques. The use of papermaking chemicals and the behaviour of dissolved and colloidal substances from wood were included in the model. The parameters for process units as well as chemical behaviour were obtained from laboratory and production scale experiments. These parameters helped us to simulate the effects of reduced water consumption on the chemical composition of process water at various parts of the process, especially at wire pit, bleaching plant and effluent treatment. Also the effects of low water consumption on the energy systems (cooling and heat recovery) and on the overall energy consumption were studied.