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Date of Award
Campus Access Dissertation
Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)
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Department of Mechanical Engineering-Engineering Mechanics
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Committee Member 4
Shortage of clean water is increasingly becoming a serious global challenge negatively affecting the life quality of billions of people around the world. Water desalination technologies are envisioned as one of potential remedies to freshwater scarcity if their high energy consumptions and negative environmental impacts could be effectively addressed. In addition, the disposal of remaining volume of concentrated toxic brine, which is a typical byproduct of desalination processes, turns into another major drawback of established water purification systems. To resolve the growing concerns of brine disposal and high energy consumption of traditional brine concentration and crystallization, transformational innovations in design of brine evaporative systems should be developed.
This research is about a novel liquid-desiccant-based zero liquid discharge (ZLD) desalination system for fully water and salt recovery in an energy-efficient manner. In contrast to several existing ZLD systems depending on energy-hungry mechanical vapor compression, this liquid desiccant ZLD desalination system relies on the strong hygroscopic properties of liquid desiccant (i.e., water-lithium chloride and water-lithium bromide) solutions to absorb water vapor in the air. Liquid desiccant regeneration units, evaporators, and brine crystallization units function as the core components in the system. The proposed ZLD desalination system can replaces the traditional high-grade-energy mechanical vapor compression process with a low-grade-energy thermal vapor compression process. It exhibits the advantages of low energy requirement, makes low temperature crystallization possible, thus subsequently lowers the component costs and reduces fouling and scaling potential in heat exchanging processes. This merit allows for the integration of renewable energy (i.e., solar energy, a kind of low-grade energy) to the desiccant-based ZLD desalination system, thereby substantially augments the application prospects and market potential of the compact system. A lab-scale ZLD system prototype is firstly developed to validate this feasibility of sorption-based ZLD concept. Systematic tests are performed to comprehensively investigate this liquid desiccant ZLD desalination prototype. The experimental results illustrate that the maximum specific daily water production (SDWP) of the system is 3.96 L/day, together with 59.02 g/h salt crystallization rate, and 26.4% system energy efficiency.
One alternative to improve the brine concentration efficiency and the water and salt recovery ratios is explored and carefully investigated. A novel bi-conductive air gap membrane distillation (AGMD) system is developed to approach a continuous evaporation process through a composite membrane. It demonstrates a hydrophilic high-conductivity characteristic on the feed side and a hydrophobic low-conductivity characteristic on the permeate side of the membrane. The effect of the composite membrane on permeate flux (water production rate) and energy efficiency is studied with different operating parameters. The modified membrane distillation (MD) system achieves maximum water permeate flux () of 9.2 kg/m2-h and has an average of 47 % improvement in gained output ratio (energy efficiency) without applying heat recovery methods. The findings provide new design concepts for commercially available membrane-based thermal water filtration processes, and significantly improve the potential for MD integration in the sorption-based ZLD concept to improve the water recovery ratio in brine concentration process.
Cai, Shiying, "DESALINATION SYSTEM WITH SORPTION-BASED ZERO LIQUID DISCHARGE TECHNOLOGY", Campus Access Dissertation, Michigan Technological University, 2023.