Formation of pirssonite in green liquor handling systems

• Published in: TAPPI Journal
• Main Authors: Zakir, Tasnuva, Tran, Honghi, Papankelakis, Vladimiros G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: TAPPI Press 2013
• Subjects: Canada; Wilcox; Peace River
• Online Access: http://hdl.handle.net/1807/97933; https://doi.org/10.32964/tj12.7.33

The formation of pirssonite is commonly believed to be the cause of hard-scale buildup in green liquor handling systems in kraft pulp mills. The precipitation occurs when the concentration of sodium carbonate in the liquor exceeds the solubility of pirssonite. A laboratory study was conducted to systematically determine the causticizing conditions under which pirssonite precipitates. The results confirmed literature data showing that the solubility of pirssonite increases with temperature but decreases with increased concentrations of sodium carbonate and other sodium salts present in the green liquor. The solubility data obtained were used to create a database for pirssonite formation in OLI, a thermodynamic program for predicting phase stabilities of alkali salts in aqueous solu-tions. The OLI program, with the newly created database, was subsequently used to generate a series of pirssonite solubility curves in terms of saturated total titratable alkali that can be used as operational guidelines to prevent pirssonite precipitation and hard-scale formation in green liquor handling systems. A case study was performed using these solubility curves to explain the occurrence of the pirssonite deposition problem at a kraft pulp mill. This work was conducted as part of the research program Increasing Energy and Chemical Recovery Efficiency in the Kraft Process, jointly supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and a consortium of the following companies: Andritz, Babcock & Wilcox, Boise, Carter Holt Harvey, Celulose Nipo-Brasileira, Clyde-Bergemann, DMI Peace River Pulp, Fibria, Kiln Flame Systems, International Paper, Irving Pulp & Paper, Metso Power, MeadWestvaco, StoraEnso Research, and Tembec.