The pulp and paper industry is a major polluter of water courses. Public concern and new legislation has led to huge efforts to reduce the pollution load as much as possible, but using conventional technology it appears that the optimum levels have been reached. In particular it has been difficult to reduce the amount of nutrients. A reduction of chlorine compounds can be achieved by converting the bleaching procedure to chlorine free. The modification, however, is costly and has shown to lead to reduced pulp quality. Total evaporation of the effluent and recycling of the water back to the process has been recognised as the best technical solution to the problem. This solution has several drawbacks, the primary ones being high energy consumption, high investment, corrosion problems and fouling of the heat transfer surface.
A novel evaporation technology that has a potential to solve the problems has evolved in Finland during the last few years. The key innovation is a fully plastic plate heat exchanger, where the heat transfer surface is made of high tech polymeric films. The concept gives several benefits, the most important of which are low investment cost, corrosion resistance and exceptionally low energy consumption. The total energy consumption for producing the clean water corresponds to heating up the water by only 7 - 9 C. Several pilot- and demo-runs with the new technology have already been performed, but before reaching full commercialisation and BAT-status (Best Available Technology) of the technology a pilot project at a pulp plant over a reasonably long time span needs to be realised.
This project was concerned with the development of a low cost evaporation unit to eliminate the emission of harmful effluents from process plants, initially in the paper and board industry. The equipment utilised various different grades of plastic film as the bed for the heat exchanger (evaporator) and a range of chemical processes to remove scale. The equipment was tested on a full-scale plant in the paper and board sector and most of the orignal objectives were met with almost continuous operation of the plant and excellent results. The technology has major potential for providing contaminant free evaporated water from the effluent of process plant operations using low cost equipment and low energy consumption.
The project could have a very wide environmental and economical impact on many manufacturing processes all over Europe. Applications for water recycling by waste water evaporation are found not only in the paper and pulp industry, but also almost all branches of industry where water is used as e.g. food industry, chemical industry, metal industry, power production. The production of drinking water from sea water or polluted water resources is also possible. A positive outcome of this project will lead to further application of the technology within these industries. According to one investigation the global market potential would be at least 15 billion Euro during the next 10 years.