Calcite Scale Formation in the Green Liquor Handling System of the Kraft Chemical Recovery Process by Alisha Giglio A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Department of Chemical Engineering and Applied Chemistry University of Toronto ©Copyright by Alisha Giglio 2018 Calcite Scale Formation in the Green Liquor Handling System of the Kraft Chemical Recovery Process Alisha Giglio Master of Applied Science Department of Engineering and Applied Chemistry University of Toronto 2018 Abstract The formation of calcite (CaCO3) scale in green liquor handling systems is a persistent problem in many kraft pulp mills. CaCO3 precipitates when its concentration in green liquor exceeds its solubility. In this work, a laboratory study was conducted to determine the effects of green liquor properties (temperature, TTA, causticity, and sulfidity) on the solubility limits of CaCO3. This new solubility data was used to develop a database of CaCO3 solubility in green liquor using the OLI Systems Inc. software. The second part of this work involved field studies at four kraft pulp mills in Canada and Sweden, to help understand scaling problems affecting the causticizing plants. The results help explain how CaCO3 scale forms in the green liquor handling systems. Understanding how CaCO3 scale is formed helps pulp mills develop viable strategies for mitigating the problem. ii Acknowledgements I would first like to thank my supervisors Professor Honghi N. Tran and Professor Vladimiros G. Papangelakis for their motivation, support, and guidance throughout this project. I will never forget the professional and personal skills they have taught me that will be valuable in my future career. I would like to extend my gratitude to my Reading Committee members, Professor Nikolai DeMartini and Professor Charles Jia for their helpful discussions, feedback, and comments. Many thanks are due to Sue Mao, whose door was always open whenever I had a question or needed guidance with my research, and Dr. Georgiana Moldoveanu who was always there to assist me with laboratory issues. I am also thankful to Nazin Orang for proof-reading this thesis, and my friends and colleagues whom I have worked with over the past two years. This work was conducted as part of the research program on “Increasing Energy and Chemical Recovery Efficiency in the Kraft Process - III”, jointly supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and a consortium of the following companies: Andritz, AV Nackawic, Arauco, Celulose Nipo-Brasileira, Canadian Kraft Paper, Clyde- Bergemann, DMI Peace River Pulp, Domtar, Eldorado, ERCO Worldwide, Fibria, FP Innovations, Georgia Pacific, International Paper, Irving Pulp & Paper, Kiln Flame Systems, Klabin, StoraEnso Research, Suzano, Tembec, Valmet, and West Rock. I would like to thank the consortium members for their financial support as well as valuable discussions and information regarding causticizing plant operations, and scaling problems specific to this work. I would like to personally thank Moise Dion of DMI Peace River Pulp, and Blair Rydberg of Canadian Kraft Paper, for their contributions to the field studies. Finally, I would like to express my sincerest gratitude to Maria Björk and Rickard Wadsborn of Stora Enso, as well as the entire Biomaterials group for hosting me and offering their guidance, friendship, and support during my time in Sweden. Finally, I must express my gratitude to my parents and for providing me with their love and continuous encouragement throughout my years of study and through the process of researching and writing this thesis. This accomplishment would not have been possible without them. iii Table of Contents Acknowledgements ........................................................................................................................ iii Table of Contents ........................................................................................................................... iv List of Tables ............................................................................................................................... viii List of Figures ................................................................................................................................ ix List of Abbreviations ................................................................................................................... xvi Chapter 1 ......................................................................................................................................... 1 1 Introduction ............................................................................................................................. 1 1.1 The Kraft Process ............................................................................................................ 1 1.2 Causticizing Plant ........................................................................................................... 3 1.3 Standard Kraft Pulping Terms ........................................................................................ 5 1.3.1 Total Titratable Alkali (TTA) ..................................................................................... 5 1.3.2 Effective Alkali (EA) and Active Alkali (AA) ........................................................... 6 1.3.3 Causticizing Efficiency (CE) ...................................................................................... 6 1.3.4 Sulfidity ...................................................................................................................... 7 1.3.5 Reduction .................................................................................................................... 7 1.4 Scale Formation in Causticizing Plants .......................................................................... 7 1.5 Motivation and Objectives .............................................................................................. 9 Chapter 2 ....................................................................................................................................... 11 2 Literature Review .................................................................................................................. 11 2.1 Physical Properties of Calcium Carbonate ................................................................... 11 2.2 Calcium Carbonate Scale .............................................................................................. 11 2.2.1 Scale Deposition Mechanism .................................................................................... 12 2.2.2 Calcium Carbonate Phase Transformations .............................................................. 13 iv 2.3 Previous Studies of Calcium Carbonate Solubility ....................................................... 14 2.3.1 Calcium Carbonate Solubility in Water .................................................................... 15 2.3.2 Calcium Carbonate Solubility in Green Liquor ........................................................ 17 2.4 Calcium Carbonate Stability in Green Liquor Systems ................................................ 18 Chapter 3 ....................................................................................................................................... 20 3 Current OLI Models of Calcium Carbonate Solubility ......................................................... 20 3.1 OLI Software ................................................................................................................ 20 3.2 Calcium Carbonate Solubility Using OLI’s MSE Model ............................................. 21 Chapter 4 ....................................................................................................................................... 24 4 Experimental Investigation of Calcium Carbonate Solubility .............................................. 24 4.1 Experimental Procedures .............................................................................................. 24 4.1.1 Apparatus .................................................................................................................. 24 4.1.2 Materials and Methodology ...................................................................................... 25 4.1.3 Solubility Units ......................................................................................................... 26 4.2 Results and Discussion ................................................................................................. 26 4.2.1 CaCO3-Na2CO3-H2O System .................................................................................... 26 4.2.2 CaCO3-Na2CO3-NaOH-H2O System ........................................................................ 35 4.2.3 CaCO3-Na2CO3-Na2S-H2O System .......................................................................... 37 4.3 Solid Sample SEM Analysis ......................................................................................... 39 4.4 Summary ....................................................................................................................... 39 Chapter 5 ....................................................................................................................................... 41 5 Thermodynamic Modelling of Calcium Carbonate Solubility ............................................. 41 5.1 OLI Software ...............................................................................................................