| The sand screens and micron filters were | | | | were several reasons the actual value was lower, |
| selected because of the durable and corrosion | | | | the main reason however, was the conservative |
| resistant fiberglass and PVC construction. The | | | | design. Because of some uncertainty in the feed |
| specific model of Eden micron filters was chosen | | | | water quality, the SWRO system was designed |
| to maintain the filter element flux at | | | | with a relatively low flux (approximately 8 gpm |
| approximately 3.3 gpm/per 10" equivalent. | | | | ft2), and a somewhat large hydraulic envelope. As |
| Due to the relative remoteness of the installation | | | | it turned out, the feed water TDS was closer to |
| site, multistage-centrifugal, high-pressure pumps | | | | 36,000 ppm and fairly stable. The lower feed TDS |
| have been selected for their reliability, availability | | | | enabled the system to operate at a lower |
| of parts, economics of operation and easy | | | | membrane feed pressure of 790 psi and a higher |
| maintenance. Centrifugal pumps in general are | | | | permeate flow rate of 120,000 gpd, consequently |
| smoother, quieter, and require less ancillary | | | | using less energy than originally projected and |
| equipment (i.e. pulsation dampeners) than positive | | | | making higher quality permeate. |
| displacement pumps. Hydropro has found that | | | | Conclusion |
| positive displacement pumps are much more | | | | With most of the system assembled, the |
| prone to failure and lengthily downtimes than | | | | installation was fairly straightforward and went |
| high-quality centrifugal pumps. | | | | smoothly. The two units were installed, started |
| The Grundfos Booster Modules were chosen for | | | | up, tested and operator training was completed in |
| several reasons. The inline style helped conserve | | | | less than three weeks. There was, however, a |
| space and provided ease of installation, allowing | | | | problem with the feed water quality and the |
| everything to be mounted on the same skid (with | | | | pretreatment system, which was discovered |
| the exception of cleaning/flush tanks, raw water | | | | after only 24 hours of operation. It immediately |
| booster pumps, and chemical feeds). These | | | | became apparent that the raw water was loaded |
| submersible, multi-stage centrifugal pumps were | | | | with particulate that was quickly fouling the sand |
| also chosen because they are very efficient and | | | | screens and the micron filters. Fortunately, the |
| quiet, and are constructed of corrosion resistant, | | | | feed system could be modified to flow into an |
| 904L super austenitic stainless steel. | | | | existing 250,000 gallon seawater tank from the |
| The high pressure feed and concentrate headers | | | | wells, and the SWRO feed was then drawn out |
| were made of 2205 duplex stainless steel for | | | | of this tank. This settling tank solution worked |
| superior corrosion resistance, and the structural | | | | quite well and provided a feed water with a |
| skid was constructed of FRP for low weight and | | | | pre-filter SDI of 1.25. |
| zero maintenance. ERI´s Pressure Exchanger | | | | There was also one other performance issue that |
| was chosen because of its high energy efficiency, | | | | needed to be resolved. Initially, the permeate |
| dependability, and corrosion resistant materials. | | | | quality was less than what was projected, and it |
| Performance | | | | was not clear why. The system was extensively |
| Values for the projected power consumption | | | | checked ant tested for leaks, and the possibility |
| rates that were presented in the proposal were | | | | that seawater was somehow mixing with the |
| based on a 27ºC feed stream of 45,000 mg/l | | | | permeate was eventually eliminated. It was finally |
| TDS and a permeate flow rate of 100,000 gpd. | | | | determined that the membranes did not meet the |
| The membrane manufactures projection | | | | design rejection required to produce the projected |
| software was used to determine the system | | | | permeate TDS. Once the membranes were |
| parameters at a recovery of 35%, and these | | | | replaced, the system was making plenty of high |
| parameters were subsequently used to determine | | | | quality permeate that was well below the |
| the projected power consumption. The result was | | | | maximum acceptable permeate TDS. |
| an anticipated feed pressure of 900 psi and a | | | | KAJUR and the residents of Ebye have since |
| specific power consumption rate of 3.02 kWh | | | | been enjoying low-cost, high-quality water for |
| m³. | | | | over a year now without any noteworthy |
| Once the system was installed and operating, the | | | | system failures. They are so pleased, in fact, that |
| specific power consumption was calculated based | | | | KAJUR has recently awarded Hydropro another |
| on actual system parameters and the result was | | | | SWRO job utilizing work exchanger energy |
| a much lower value of 2.65 kWh/m³. There | | | | recovery. |