THE SOLUBILITY OF CALCIUM CARBONATE IN GREEN LIQUOR HANDLING SYSTEMS, 2018 PEERS

The formation of hard calcite (CaCO₃) scale in green liquor handling systems is a persistent problem in many kraft pulp mills. CaCO3 precipitates when its concentration in the green liquor exceeds its solubility. While the solubility of CaCO₃ in water is well known, it is not so in the highly alkaline green liquor environment. A systematic study was conducted to determine the solubility of CaCO₃ in green liquor as a function of temperature, TTA, causticity, and sulfidity. The results show that the solubility increases with increased temperature, increased TTA, decreased causticity and decreased sulfidity. The new solubility data was incorporated into OLI Systems Inc. software (a commercially available thermodynamic simulation program for aqueous salt systems) and used to generate a series of CaCO₃ solubility curves for various green liquor conditions. The results help explain how calcite scale forms in the green liquor handling systems. Understanding how CaCO₃ scale is formed helps pulp mills develop viable strategies for mitigating the problem. 

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