In industrial pulp and paper processes, the consumption of fresh water can be reduced by employing counter current water flow arrangements and efficient water separation between the various process stages. The effluent from the processes will then be highly concentrated, but by utilising new evaporation technology, significant cost savings can be achieved. Two evaporation methods, mechanical vapour recompression (MVR) and multi-stage evaporation (ME), are applied to the evaporation process. The operational costs for multi-stage evaporation are low, since low-grade surplus heat from pulping and stock preparation can be used as an energy source. The system is marketed by Hadwaco Ltd Oy of Finland and Andritz AG, who recently signed a co-operation agreement.

In the pulp and paper industry, appropriate water purification technology is becoming increasingly important for many reasons. These include, for example, enhancing production efficiency, improving pulp and paper quality, and simultaneously reducing the environmental load caused by the waste water.
"By utilising the latest vacuum evaporation technology combined with process optimisation through pulp washing stages, water loop closure and counter water flow arrangements, the pulp, paper and fibreboard industry can capitalise on all these advantages at the same time.
In addition, these process improvements and internal water purification of a concentrated effluent stream provide for lower investment and operating costs than, for example, conventional biological effluent treatment," says Peter Koistinen, Marketing and Sales Director of Hadwaco.
When comparing costs all relevant aspects such as production efficiency, fresh water costs, overall electric and thermal energy use, fibre and filler recovery rate and waste water treatment costs must be considered. Effluent treatment efficiency should be evaluated on the basis of the cost per kg of COD (Chemical Oxygen Demand) removed rather than the typical cost per m3 of effluent treated.
Furthermore, the equipment's capability for removing salts and disturbing substances (anionic trash) has to be considered. The low temperature evaporation technology has proven to be the most efficient method to reduce organic load and salts as well as anionic trash. The recovered and recycled distillate is of better quality than - or of the same quality as - chemically treated fresh water. It can be used even at the most critical consumption points of the paper machine. When this purified water is recycled in the process, the demand for fresh water will be significantly reduced.
The evaporation technology developed by Hadwaco utilises large and efficient polymeric heat exchanger surfaces, which means that temperature differentials can be kept very low. Due to the large surfaces, low-grade waste heat can be efficiently utilised in the multi-stage evaporation. In addition, the energy demand of MVR evaporation is lower, when compared with conventional systems.
Energy for the evaporation system can either be obtained by utilising the heat generated in mechanical pulping and stock preparation or in the paper machine. If waste heat is not available, electrical energy can be used for the MVR units.
In the pulp and paper industry, the utilisation of heat from mechanical pulping and stock preparation for vacuum evaporation of the effluent is attractive, since there are literally no extra energy costs. The purified waste water is transferred back to the paper machine at a 25 to 30 °C lower temperature in the form of heated process water or hot distillate.
Hadwaco Ltd Oy is a Finnish specialist in water treatment. The equipment and systems developed by the company are used in a variety of applications, for example, in landfill leachate treatment and purification of effluents from metal surface treatment. Part of the Hackman Group, the company's net sales for 1998 totalled USD 13 million. The company employs some 130 people. The Group's net sales amounted to USD 328 million and it employs approximately 3,200 people.
The Austrian company Andritz AG had net sales of approximately USD 655 million in 1998 and employs about 3,100 people. The company is a specialist in machines for the production of pulp, paper and fibreboard. It commands a significant global market share. The company is owned by The Carlyle Group (US), UIAG (Austria), a private foundation, (Austria) and members of the Andritz AG executive board.

Captions:
1. The Andritz/Hadwaco concept: Counter current water flow arrangements, an efficient water separation between the process stages and treatment of the concentrated effluent fraction by means of a new vacuum evaporation technology.
2. By minimising water demand and employing new evaporation technology for the treatment of concentrated effluents, it is possible to gain significant cost savings. The costs for purification should be evaluated on the basis of the cost per kg of disturbing substances removed (e.g. kg COD) rather than the cost per m3 of effluent treated.

For further information, please contact:

Hadwaco Ltd. Oy
Mr. Peter Koistinen, Marketing & Sales Director
Tel. +358 204 39 5650

Andritz AG
Mr. Heinrich Münster, Vice President, Business Development
Tel. +43 1 81195 5225