Graduate Thesis Or Dissertation
 

Fouling Characterization in Hypersaline Wastewater Treatment

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/t722hj027

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  • Water supplies are diminishing worldwide and by 2025 two thirds of the population could be living in regions of water scarcity (local demand for water is greater than water supply). One method to increase available water sources is to use desalination technologies to separate water from saline solutions. While desalination itself isn’t a new idea the process is being expanded to determine how it can be used to treat other contaminated wastewater sources that otherwise wouldn’t be treated which reduces the overall water available. In this aspect a water treatment system is being developed at the Water and Energy Technology Laboratory at Oregon State University to treat hydraulic fracturing wastewater. The SCEPTER (Selective Condensation and Evaporation using Precise Temperature Regulation) system requires a humidification dehumidification (HDH) process to separate different contaminates from the produced water stream. This thesis is part of the research to develop a humidification system that is reliable, low energy, competitive cost, mitigates fouling, and separates contaminants to produce irrigation level water. Two different humidification techniques are reviewed: spray humidification, and a venturi nozzle paired with an evaporator humidification system. Spray humidification while 20-30% less energy intensive than venturi nozzle humidification has a much higher risk of recontaminating the produced water as contaminants can become entrained in the humid air stream and would require additional components to remove them. Whereas the venturi nozzle humidification system is more energy intensive it has a lower risk of contaminating the produced water and is can still be cost competitive with other technologies. As the evaporation zone has the highest risk of fouling due to the high salinity and salt separation a study was done to understand the fouling resistance over time for a highly saline mixture with various surface roughness’. Reducing the surface roughness is beneficial if it is greatly reduced (0.35 µm) but if it is still sufficiently rough (homogeneous 5 µm or 10.5 µm average roughness with microchannels) there is minimal change to the fouling resistance or heat transfer coefficient during pool boiling with 20% saline concentrated seawater. Lastly an evaporation zone was designed to test crystallization fouling in a flow boiling environment and to understand how to mitigate fouling effectively. An electrically heated aluminum pan containing baffles to control the flow path was used to test 10% NaCl and 10% KCl saline solutions at different flow rates (2.3-3.1 g/s) to inform system operating parameters. Maintaining water evaporation rates less than 54% stayed free of fouling (scaling) for 4 hours. If the system operated with a higher water evaporation rate a targeted flush was identified as an applicable fouling mitigation method. Targeted flushing was used on areas where fouling accumulated which allowed the overall evaporation rate to remain unchanged and allowed the system to continue to operate without maintenance. This work can be utilized to estimate the fouling resistance and heat transfer coefficient for a 20% saline mixed salt seawater solution during pool boiling for various surface roughness’ and inform heat exchanger surface roughness design and operation. The evaporation zone work can be utilized when designing other evaporation systems and the operational parameters to avoid fouling can be used to reduce fouling accumulation. In addition, targeted flushing can be a method to mitigate fouling if it does occur in a flow boiling system.
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  • Water and Energy Technology Laboratory-Research Group Website
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  • This work is supported by the US Department of Energy, Advanced Research Projects Agency – Energy (ARPA-E) award number DE-AR-0001000
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