Evaluation and Control of Pirssonite Scale Formation in Green Liquor Systems of the Kraft Process

• Main Author: Zakir, Tasnuva
• Other Authors: Tran, Honghi
• Language: en_ca
• Published: 2012
• Subjects: Pirssonite; Green liquor Scale; Calcium carbonate; CaCO3; Scale; Deposition; green liquor; Pirssonite solubility; kraft mill scale; Na2Ca(CO3)2∙2H2O; selective dissolution; incongruent dissolution; OLI; 0542
• Online Access: http://hdl.handle.net/1807/33786

Scaling in green liquor handling systems is a persistent problem in many kraft mills. Scaling is commonly believed to be the result of pirssonite (Na2Ca(CO3)2∙2H2O) deposition. In this work, scale characterization was performed by analyzing 12 scale samples obtained from 10 kraft mills. Only 4 samples were identified as pirssonite while the remaining consisted of CaCO3. The predominant presence of CaCO3 in the scale samples was found to be the result of selective dissolution of Na2CO3 from pirssonite scale, leaving CaCO3 behind. Experimental studies were also conducted to study pirssonite solubility under green liquor conditions. Results obtained from these studies were used to create and validate a database for pirssonite in the OLI Systems® software to predict its formation. This database was used to generate a family of pirssonite solubility curves that can be used by the kraft mills as operational guidelines to prevent pirssonite precipitation.