Midpoint Kappa Measurement - New Possibilities in Digester Control, 1999 Pulping Conference Proceedings

Matti Laitinen, Antti Kemppainen, Mats E. Backman

Pulp Kappa number is one of the basic measurements in pulping process control and pulp quality evaluation. Kappa is typically measured after cooking and oxygen delignification as well as after the first alkali stage in the bleach plant. The conventional laboratory analyses have largely been replaced by on-line analyzers that enable quick and efficient process control.

New applications for Kappa measurement have arisen in the digester area. With a conventional continuous digester, the first Kappa result is obtained from the blowline, after the cooking process. The new midpoint Kappa measurement enables analyses right after the digester’s cooking zone, before the washing zone. This measurement detects changes in the cooking process far quicker and corrective action can already be taken in the washing zone.

Mill experiences are promising. Good quality samples are obtained easily and safely; the midpoint measurement has a high correlation to blowline Kappa; and the midpoint results can be combined with blowline Kappa measurement to further improve digester control. The measurement is reliable and quick, it enables faster feedback control and can, moreover, be applied to feed-forward control of the digester’s washing zone.