Scaling during evaporation of acidic bleach plant filtrates

The potential danger of heat surface scaling during the evaporation of acid ic bleach plant filtrates is discussed. The results of ECF and TCF filtrate evaporation tests are presented. The purity of condensates is analyzed and their potential use to replace fresh raw water in bleached pulp washing is evaluated. No severe scaling was observed on the heat surfaces. The precipitation seem s to happen for the most part in situ in the liquid phase. This means, howe ver that the evaporator should be designed so that it tolerates suspended m atter in the evaporated liquid. When the pH of the filtrate is properly adj usted the purity of the condensates meets, after slight stripping, the requ irements set for the wash water of bleached pulp. (C) 1999 Published by Els evier Science Ltd on behalf of the IAWQ. All rights reserved.