Fundamental Understanding of Warm Lime Softening Process to Improve Steam Assisted Gravity Drainage Produced Water Treatment Performance
Date
2021-01-15
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Abstract
Since the commercialization of the first steam assisted gravity drainage (SAGD) enhanced oil recovery facility in 2001, the warm lime softening (WLS) process has been commonly deployed as part of a SAGD central processing facility (CPF) water treatment plant. The principal process goal of the WLS process is to remove dissolved hardness (e.g. calcium and magnesium ions) and silica by the addition of lime (Ca(OH)2), magnesium oxide (MgO), soda ash (Na2CO3), coagulant, and flocculant. Although the WLS process has been operated for almost 30 years in the oil sands industry, the fundamental electrokinetic properties of the particles generated are not thoroughly investigated. The high temperature, high silica and dissolved organic concentrations also make the WLS unique compared to the traditional cold lime softening process used in municipal water treatment and other industrial water treatment. The understanding of the electrokinetic properties of particle suspensions is of paramount importance as it directly relates to the performance of sedimentation and clarification, as well as the selection of chemicals and doses. Furthermore, the understanding of the impact of feed water chemistry deviations on the charge behaviors of the particle suspensions and on the coagulant dose is of significant practical implications for the WLS operations. This research was undertaken to investigate the surface charges of the two most common softening particles, calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2), under SAGD WLS conditions from zeta potential perspective. A number of experimental conditions (pH, temperature, presence of other ions, additions of other chemicals) were varied to exam the impact on the zeta potential of two softening particles. Visual MINTEQ modelling was utilized to predict chemical speciation under various conditions and was used to assist with data interpretation. High temperature (65°C) jar tests were also performed using synthetic SAGD produced water (PW) samples to simulate the WLS process and assess the impact of feed water deviations (silica, clay, humic acid, Ca(OH)2, MgO, Na2CO3, NaHCO3, CaCl2, and MgCl2) on the dose of a polyamine-based cationic coagulant. The electrokinetic study revealed that pH, and the type of ions and functional groups present in solution are the main impacting factors on the zeta potential of softening particles. The coagulation study revealed that the coagulant dose was significantly influenced by humic acid and silica. The findings of this research can provide insightful knowledge to SAGD operators regarding process monitoring, approaches to onsite chemical optimization, possible controls during an influent water off-specification event.
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Keywords
Steam assisted gravity drainage, warm lime softening, thermodynamic modeling, calcium carbonate, magnesium hydroxide, potential determining ions, coagulation, flocculation
Citation
Zhang, L. (2021). Fundamental Understanding of Warm Lime Softening Process to Improve Steam Assisted Gravity Drainage Produced Water Treatment Performance (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.