Development of Advanced Compact Energy Recovery Pumping System for Shipboard Seawater Reverse Osmosis Desalination

Small RO desalination plants use high pressure up to 1200 PSI to feed sea or brackish water against a semi-permeable membrane. Only a fraction 15-60 % becomes fresh water, while the remaining is a concentrate that has pressure energy being wasted across a dumping valve. For larger plants there have been developed advanced Isobaric Energy Recovery Devices (IERD) able to transfer up to 95-98% back to the feed stream. For small flow capacity units there are several concepts in the market for energy recovery based on discontinuous positive displacement (piston devices), such as Clark or Pearson pumps that have high efficiency. However, these devices involve multiple moving components subject to wear and are inflexible with respect to feed water quality as their recovery ratio must remain fixed. They can not without extensive modifications adapt to advanced modes of operations, such as HP brine recirculation, brine staging or other advantageous flow schemes arising from future anticipated membrane improvements with respect to flux and rejection. Isobaric Strategies Inc. (Isobarix) has under development a second generation ceramic rotary isobaric ERD with only one moving part, which uses a separate booster pump allowing for flexible operation with respect to feed water source or modified flow schemes. The device is based on US patent # 7,306,437. The proprietary design uses Axel Positioning of Rotor (XPR), which offers substantially less engineered manufacturing cost compared to first generation marketed by Energy Recovery, Inc. The latter uses a ducted rotor positioned within a sleeve that subtracts from the most productive flow area, while XPR allows for a full size rotor within a given size pressure vessel. This translates to up to 65% increased flow at same manufacturing cost. It also applies proprietary advanced features to reduce noise level and cavitation potential.