Date of Award

12-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering

Advisor

Ladner, David

Committee Member

Karanfil, Tanju

Committee Member

Overcamp, Thomas

Abstract

Growing fresh water needs have led to an interest in water desalination using reverse osmosis (RO) membranes. Energy consumption has a large share in the expenses incurred to drive a reverse osmosis desalination system. With depleting fossil fuel reserves, tapping renewable sources of energy is a promising alternative to meet the energy requirements. Wind power coupled to an RO desalination system is a potential means of delivering clean water using sustainable energy. This work investigates modeling of a conceptual wind-energy-driven RO desalination system that is made possible because of an air-pressure energy storage mechanism. Bench-scale experiments were performed on an RO membrane connected to a pressure vessel to validate the models, which were developed based on film theory and solution-diffusion concepts. The models predict water flux and salt concentration through an RO membrane, and were further expanded to predict the performance of a few conceptual full-scale system designs consisting of conventional and air-pressure energy storage wind-RO systems. In the latter design, the energy storage tank serves as a buffer to dampen the variability caused in the discharges and pressures due to the stochastic nature of the wind. The performance of the two systems were compared by varying several input parameters such as the wind patterns, tank volumes, number of RO elements, initial air pressures inside the tank, and the lower pressure limit. The air-pressure energy storage wind-RO system was found to deliver higher water production and better water quality than the conventional wind-RO system demonstrating the usefulness of an energy storage tank for a wind-driven desalination system. Parameters that were important in the design were the initial air pressure and the lower pressure limit (the lowest pressure at which the air tank was allowed to operate). When both the initial air pressure and the lower pressure limit were high, the greatest water productivity was achieved and salt rejection was kept high (98.5 %). These and other parameters are explained in this thesis, giving a framework for thinking about how an air-pressure energy storage system can be integrated with RO to provide renewable-energy desalination.

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