Optimization of White Liquor Production: A Comparison of Carbonate Control and TTA Control for Improved Quality

White liquor production is a critical process in the chemical recovery cycle in pulp mills, affecting both operational efficiency and product quality. This thesis investigates the potential for optimizing white liquor production by comparing two control methods: Total Titrable Alkali (TTA) control, which is traditionally used to regulate the process, and carbonate control, an alternative method that has shown promise in other plants but has not yet been tested at Södra Cell Mörrum. The study aims to evaluate how carbonate control affects white liquor quality, with a focus on achieving consistent levels of effective alkali (EA) to minimize process disturbances. Through a combination of theoretical research, practical experiments and data analysis, the project explores the potential benefits of a more stable causticization process, including reduced risks of over- or underliming. Key tasks include literature review, planning and conducting test runs and evaluating the most effective control method. The results showed that carbonate based control reduced variation in several key process steps, particularly in green liquor composition and lime dosing. This contributed to a more stable causticizing process and more predictable operation. The results support that carbonate control is a viable alternative to traditional TTA-based control at Södra Cell Mörrum