Process Modeling of Forward Osmosis and Pressure Retarded Osmosis Integration with Seawater Reverse Osmosis
pressure retarded osmosis
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PublisherThe University of Arizona.
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AbstractOsmotically driven membrane processes, like forward osmosis and pressure retarded osmosis, may hold key advantages when integrated with reverse osmosis for seawater desalination. The spiral-wound membrane platform in which these processes are applied has inherent disadvantages that need to be explored. Maintaining proper operating pressure in both of the fluid channels of a spiral-wound membrane requires the feed and draw streams to be operated at different flow rates, often as drastic as a 1:10 ratio. This affects the thermodynamic equilibrium of the system and drastically affects potential water and energy recovery. In this work, a model was created to rigorously represent spiral-wound membranes to increase modeling accuracy. A process configuration that features periodic recharging of the stream inside of the envelope is proposed to mitigate the effects of the flow rate difference. The model is used to compare the multi-stage design to single-stage configurations for both forward osmosis and pressure retarded osmosis by testing various feed and draw flow rate ratios, between 1:10 to 1:1, operated by each process as well as important membrane characteristics such as channel height and water and salt permeability. The multi-stage design shows an increase in wastewater utilization from 62.6% to 90% when compared to the single-stage designs for forward osmosis. Additionally, the multi-stage configuration increases the pressure retarded osmosis specific energy recovery from 0.13 kWh/m3 to 0.55 kWh/m3. However, the increased effectiveness of these multi-staged designs comes with a reduction in average water flux and power density, which leads to the requirement of more membrane area and capital investment for potential system implementation.
Degree ProgramGraduate College
Degree GrantorUniversity of Arizona
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Forward osmosis and pressure retarded osmosis process modeling for integration with seawater reverse osmosis desalinationBinger, Zachary M.; Achilli, Andrea; Univ Arizona, Dept Chem & Environm Engn (ELSEVIER, 2020-10)Osmotically driven membrane processes such as forward osmosis and pressure retarded osmosis may hold key advantages when integrated with seawater reverse osmosis to form hybrid FO-RO and RO-PRO systems. In this work, module-scale modeling of these two processes was improved by accurately representing the features of a spiral-wound membrane. The model captures important characteristics such as the cross-flow stream orientation, membrane baffling, and channel dimensions unique to spiral-wound membranes. The new module-scale model was then scaled to the system-level to compare various system designs for FO-RO and RO-PRO systems, most notably, a multi-stage recharge design was defined. Results indicate that the multi-stage recharge design leads to an increase in wastewater utilization, as high as 90%, when compared to the single-stage designs. Additionally, the multi-stage recharge configuration can increase the specific energy recovery of pressure retarded osmosis by over 75%. The multi-stage recharge design is found to be not only advantageous but may be also necessary to the integration of osmotically driven membrane processes with seawater reverse osmosis.
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