Potassium Kraft Pulping: Possibility or Necessity, 1996 Minimum Effluent Mills Symposium Proceedings

Dr. Walter Ruf

Dr. Johann Zwainz

Patria paper

Rolf Ryham

Jian Er Jiang

Ahlstrom Kamyr Inc.

As kraft pulp and paper mills around the world approach zero effluent discharge along paths set by their different Minimum Impact Mill (MIM tm) strategies, process and non-process elements (PE and NPE) coming with wood supply become accumulated in various parts of a Kraft process. Because of its relatively high content in woods, potassium can be enriched to such a high level that will result in severe problems in chemical recovery operations.

For the past 15 years Patria Papier has been gradually reducing its discharge of effluent volume to 15-25 m3 and COD load to less than 8 kg per ton of paper. As a result, potassium and other PE and NPE are approaching critically high levels, with the K/(Na+K) molar ratio close to 15-16%. It sometimes could reach 30-35%, causing frequent plugging and involuntary shutdowns in recovery boiler operation. Of the four potential solutions identified, one is to convert the current Na-based to a K-based kraft pulping operation. Preliminary laboratory cooking trials demonstrated its technical feasibility. Whether it is a possibility or necessity remains to be seen.