Large diameter spiral wound modules enable significant reductions in reverse osmosis (RO) plant cost. A consortium of membrane manufacturers had identified sixteen inches as the optimum diameter for a new standard. In order to make full use of the cost saving potential of the large diameter, FilmTec's design considerations were based on a scale-up from the proven design of commercially available 8-inch modules. With the same materials and a leaf design as in 8-inch modules, the new 16-inch modules were built with a 4.3 times higher active membrane area and accordingly a 4.3 times higher permeate flow performance. The product water tube was designed for increased physical strength at even less permeate pressure drop. The endcaps feature interlocking technology without interconnectors and with internal brine seals for easier loading. The fiberglass shell was reinforced to resist axial compression arising from pressure drop and increased cross-section area. Sufficient safety margins were verified through extensive testing. A prototype tool for easy element loading and unloading was developed and applied to the demonstration plant at Bedok in Singapore.
This plant is in operation since October 2007 to demonstrate equivalent performance of an 8-inch and a 16-inch RO system running side-by-side on a challenging waste water reuse application. Each system has three 7-element pressure vessels in a 2:1 arrangement and was operated at a constant flux of 17.3 lmh and a recovery of 75%. After some adjustments of the scaling inhibitor dosage the plant had come to a stable operation; at the time of this writing it was approaching 3 months without cleaning or rinsing. The normalized permeate flow of the 16-inch system was 4.3 times higher than the flow of the 8-inch system. A sustainable system flow performance at a fouling factor of 0.85 was demonstrated. The measured system salt rejection indicated an average module salt rejection of 99.65%.
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