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Development of Advanced Compact Energy Recovery Pumping System for Shipboard Seawater Reverse Osmosis Desalination
Navy SBIR 2010.1 - Topic N101-082 ONR - Mrs. Tracy Frost - [email protected] Opens: December 10, 2009 - Closes: January 13, 2010 N101-082 TITLE: Development of Advanced Compact Energy Recovery Pumping System for Shipboard Seawater Reverse Osmosis Desalination TECHNOLOGY AREAS: Materials/Processes ACQUISITION PROGRAM: PMS 501 as well as POM-10 advanced shipboard desalination FNC OBJECTIVE: Develop an advanced compact energy recovery pumping system for use in 2,000 to 12,000 gal/day seawater reverse osmosis (RO) desalination systems found on many current and future Navy surface combatants and submarines. Such a pumping system will provide for reduced energy consumption, improved reliability, less required maintenance, and lower noise emissions of shipboard desalination systems. DESCRIPTION: RO desalination has become the Navy standard for the shipboard production of freshwater since its introduction into the Navy in the late 1980s. In the RO process, high pressure seawater (typically 800 to 1000 psi) is forced through a semi-permeable membrane which allows water passage to the exclusion of salt. To obtain this high operating pressure on current shipboard systems, seawater from the firemain or auxiliary seawater system is filtered through a series of strainers and string wound cartridge filters (down to a nominal filter rating of 3-�m) and then processed in a high pressure pump of rated capacity of 40 gal/min (for the 12,000 gal/day Navy Standard RO plant) or less. The resulting high pressure seawater is then fed into the RO membrane elements, where approximately 20% of the feed water permeates through the membrane as purified fresh water. The remaining concentrated seawater is ultimately sent to a ship overboard system for discharge. Due to minimal pressure drop through the RO elements, the pressure of this concentrate stream is still close to the feed seawater pressure and needs to be reduced before entering most ship overboard systems. Currently, pressure regulating throttling valves are used on shipboard RO systems to reduce the pressure of the concentrate stream. Since the Navy introduced RO plants into the Fleet, improved technologies have been developed that can have a significant ability to lower the energetics and costs of plant operation as well as lessen vulnerability during operation. Energy recovery devices have been developed which can decrease required power by as much as 40% by recovering the energy in the concentrate steam typically lost through the pressure regulating throttling valve and returning it to the high pressure pump. These devices can also improve pump reliability and decrease maintenance requirements, in addition to lowering noise emission, by allowing the use of slower pump speeds. The efficiency of some commercially available recovery devices can exceed 90%.1 The issue for Navy applications is that the existing commercial energy recovery devices have been designed for large capacity RO systems and are extremely limited in availability and efficiency for the flow ranges of smaller capacity desalination plants, typical of most shipboard RO systems.2 The proposed energy recovery system should be able to recover more than 80% of the energy typically lost in the high pressure RO concentrate discharge. The developed system may either be paired to existing high pressure pumps (allowing these pumps to run more efficiently and reduce required maintenance actions on these pumps) or developed as a smaller, lighter integrated pumping system for achieving required feed pressures to the shipboard RO system. GUIDELINES FOR NEW TECHNOLOGY: PHASE I: Demonstration of pumping system efficacy, at a subscale level if necessary, in a laboratory environment, utilizing at least a model seawater mixture of relevant composition (e.g., ASTM synthetic seawater3 or "Instant Ocean") for at least 6 consecutive hours. Longer term and more strenuous testing is of interest to further clarify energy efficiency, reliability, and operational availability. Phase I Option � Produce designs for full-scale device. Perform additional testing on model mixture to determine longer-term operational changes and/or pursue and evaluate changes and improvements to pump. PHASE II: Demonstration of a full-scale device with natural seawater, assembly of full scale pumping system to validate operation. Deliverable will be utilized to prove performance at a Navy natural seawater test facility. Phase II Option � Advanced design to improve reliability and/or reduced system size/weight. PHASE III: Commercialization of device in combination with a Navy-relevant desalination system. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The private-sector will benefit from this technology wherever smaller scale reverse osmosis plants are operated, in the range of 2,000 to 12,000 gallons per day, such as for small municipalities. REFERENCES: 2. "Energy Efficiency in Reverse Osmosis Systems" by Murray Thomson (http://www.adu-res.org/pdf/Loughborough.pdf) 3. ASTM D1141 � 98 (2008) Standard Practice for the Preparation of Substitute Ocean Water. KEYWORDS: energy recovery; high pressure pumps; seawater reverse osmosis desalination
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