Membrane Distillation Development for Concentrated Solar Thermal Systems

At present, both energy and water are predominantly supplied through the burning of fossil fuels. Going forward, new demand (and the replacement of retiring assets) is increasingly being met by sustainable technologies—largely driven by solar energy. This PhD thesis aimed to address two pressing Sustainable Development Goals, set out by the United Nations, ‘affordable and clean energy’ and ‘clean water’, by developing solar-driven desalination (D) technologies using two different approaches: ‘direct solar-desalination’ and ‘indirect solar-desalination’. The first approach used feedwater heated directly by a solar thermal collector for vacuum membrane distillation (VMD) for a small residential scale. In contrast, the second approach targeted the indirect use of energy from a concentrated solar power (CSP) plant via more well-established desalination processes for large-scale applications. In the first approach, this thesis successfully designed and manufactured the first hollow fiber-based multi-effect VMD that can internally recover the latent heat of the permeate vapor between effects using metallic hollow helical baffles, reducing the energy consumption by more than 60% and producing up to 20 L/h at less than 2 USD per cubic meter of freshwater. In the second approach, detailed numerical simulations found that replacing the power block’s condenser with a multi-effect distillation (MED) system can significantly improve the CSP plant’s payback period by 5% – 13% but at the expense of reducing the thermal efficiency by 7% – 11.5%. Another solution is to utilize some of the generated electricity from the CSP plant to operate reverse osmosis (either on-site or at a facility near the coast); however, this was found to hurt the plant’s revenue since some of the valuable electricity generated is consumed by the RO plant, instead of being sold to the grid. Another CSP-D solution is to replace the conventional steam Rankine cycle with a supercritical CO2 cycle, which can provide the necessary high-temperature waste heat to a MED process without any thermal efficiency reduction. Overall, this thesis examines the potential of utilizing the endless supply of solar energy to produce sustainable clean energy and freshwater that can ‘green-terraform’ arid lands and help water-stressed communities