On-line Alkali Strength Measurement and Control of the Causticizing Process, 1999 Pulping Conference Proceedings

Janne Tolonen, Ossi Tolonen & Jukka Puhakka

Neles Automation

Valmet Automation Kajaani Ltd.

Traditionally the causticizing process has been controlled by using a lime/green liquor ratio-controller, dT-controller, or by conductivity sensors. These control methods have not optimized the causticizing process in the best possible way. Using a Kajaani Alkali Analyzer, an on-line autotitrator, it is possible to optimize the whole causticizing process when two different controls are built up: Green liquor TTA-control and white liquor CE%-control.

Soon after the implementation of this control strategy, a Finnish pulp mill reported results including over 50 % improvement in white liquor quality, more than 50% faster process start-ups after shutdown, and less frequent acid washings of white liquor filter. Improvements were also seen in the other pulp mill departments (digester, bleach plant, evaporation plant and recovery boiler) due to the reduced variability of white liquor quality and higher white liquor strength.