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EFFECTS OF MIXING ON SOLVENT ADDITION TREATMENT PROCESSES

  • Author / Creator
    Cheung, Aaron
  • In oil sands extraction, the removal of heavy materials from a bitumen feed is often facilitated by solvent addition treatment processes. These processes mix solvent with bitumen feed to cause the precipitation of heavy products. The settling properties of these heavy products as they separate from the feed can be influenced by the mixing parameters used to combine solvent and feed. Since these properties determine the sizing of settlers and deposition velocity in pipelines, they are important to the overall effectiveness of bitumen recovery operations. Two well known solvent addition treatment processes that have been used in industry for many years are paraffinic froth treatment (PFT) and solvent deasphalting (SDA). While mixing plays a key role in both these processes it is rarely studied making the effects of mixing on solvent addition treatment processes not very well understood. Additionally, both mixing intensity (the rate of energy input) and mixing energy (mixing intensity x mixing time) are major variables in characterizing mixing. Thus, this study aims to to examine how changes to mixing intensity, mixing energy, and mixer configuration influence separation performance in these processes.Paraffinic froth treatment involves mixing a light paraffinic solvent, such as n-pentane or n-heptane, with bitumen froth to precipitate out asphaltene aggregates leaving a diluted bitumen product. In this study, bitumen froth from the Athabasca oil sands was mixed with n-pentane inside a windowed autoclave at 80 °C and 6 bar. Mixing intensity and energy were varied by varying impeller speeds from 700 to 1500 RPM and mixing duration from 2 to 60 minutes. Asphaltene aggregates were sampled and recorded settling inside the autoclave through the window and as individual aggregates in a glass column. From these tests, it was observed that mixing at higher mixing energies formed larger aggregates that were lower density and settled more rapidly. Due to the differences in shearing forces, aggregates formed at lower mixing intensities were also found to settle faster than ones formed from mixing at high intensity. When mixing intensity was kept constant, aggregate settling rate was still found to increase with higher mixing energy. Therefore, it was concluded that the fastest settling aggregates formed at low mixing intensity high mixing time conditions. Solvent deasphalting is traditionally used in refining vacuum residue feeds, but recent interest in partial upgrading technologies has led to exploration of its use with bitumen emulsion feeds extracted from steam-assisted gravity drainage (SAGD). The application of SDA to a bitumen emulsion feed has a potential to result in a three phase mixture of deasphalted oil, pitch, and water. This presents a problem as pitch and water need to flow together but do not readily mix upon settling. This study examined the partial mixing of three phase mixtures to produce a mixture of the bottom two phases while not disturbing the top phase. An analogue alcohol-hydrocarbon-brine mixture was used to simulate SDA phases and test various mixer configurations in a horizontal settler geometry. Ultimately, it was determined that a two-impeller system with a smaller top Lightnin A310 impeller at about 0.8x the diameter of a larger bottom Rushton turbine was the best combination to achieve partial mixing. In order to apply these results to a real process, further investigation of partial mixing with the actual SDA reagents is necessary.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-9tmy-k288
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.