Ice scaling in continuous eutectic freeze crystallization

 

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dc.contributor.advisor Lewis, Alison Emslie en_ZA
dc.contributor.advisor Chivavava, Jemitias en_ZA
dc.contributor.author Jooste, Debora en_ZA
dc.date.accessioned 2017-05-16T07:59:18Z
dc.date.available 2017-05-16T07:59:18Z
dc.date.issued 2016 en_ZA
dc.identifier.citation Jooste, D. 2016. Ice scaling in continuous eutectic freeze crystallization. University of Cape Town. en_ZA
dc.identifier.uri http://hdl.handle.net/11427/24311
dc.description.abstract Eutectic Freeze Crystallization (EFC) is a novel and potentially cost effective technique to treat industrial brines by the simultaneous crystallization of ice and salt under sub-eutectic conditions. Previous research has demonstrated that the formation of an ice scale layer on the cooling surfaces of indirectly cooled crystallizers severely decreases heat transfer. This increases the mechanical energy requirements and overall operational cost of the process. The energy efficiency of EFC as a wastewater treatment and resource recovery technology is, therefore, dependent on effective control of ice scaling. This research focused on determining the induction time, defined as the time between initial nucleation and scale layer formation, where shorter induction times are associated with more severe scaling tendencies. The experimental work was conducted in a hybrid crystallizer-separator with a 2 litre crystallization zone fitted with a mechanical scraping device. The effect of the driving force for heat transfer, scraper speed and the solute type and concentration of inorganic electrolyte impurities in a binary eutectic Na₂SO₄-H₂O system was investigated. Induction time decreased with an increase in the driving force for heat transfer, due to a lower wall temperature and an increased driving force for crystallization as a result of the higher heat flux. An increase in scraper speed resulted in an increase in induction time, due to the more frequent removal of the thermal boundary layer and better distribution of supersaturation and magma throughout the crystallizer. The induction time was found to be specific to dissolved ionic species as a result of unique electrostatic interactions between the cooled wall and ice layer surface. Induction time showed an increase with an increase in concentration of electrolyte impurities, due to the increased mass transfer limitation of solute molecules away from the growing ice front. en_ZA
dc.language.iso eng en_ZA
dc.subject.other Chemical Engineering en_ZA
dc.title Ice scaling in continuous eutectic freeze crystallization en_ZA
dc.type Thesis / Dissertation en_ZA
uct.type.publication Research en_ZA
uct.type.resource Thesis en_ZA
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Engineering & the Built Environment en_ZA
dc.publisher.department Department of Chemical Engineering en_ZA
dc.type.qualificationlevel Masters en_ZA
dc.type.qualificationname MSc (Eng) en_ZA
uct.type.filetype Text
uct.type.filetype Image


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