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Three Center Configuration

The three-center configuration consists of an HP pump center, a membrane center, and an ERD center. Ideal with large-scale plants, the three-center configuration allows optimization of equipment size and flexible operation. However, freedom to operate individual membrane arrays at different pressures and recoveries is diminished relative to conventional configurations.
In a three-center configuration:

  • The pump center consists of one or more HP pumps supplying feed water to a header maintained at membrane pressure. Total pump flow approximately equals permeate production.
  • Any number of membrane racks (each equipped with isolation valves) may be connected to the feed header. HP brine is collected in a brine header.
  • The ERD center (consisting of any number of ERDs) draws HP brine from the brine header and uses that energy (plus supplemental hydraulic energy from booster pumps) to pressurize a feed stream approximately equal to the brine flow. This feed stream is directed to the feed header.
  • When using HPBs in the ERD center, the LP feed header to the ERD center is pressurized by a charge pump.

In this regard, the HPB mimics the hydraulic performance of isobaric chambers in the three-center design. However, there are significant operational differences:

  1. The charge pump is upstream of the HPB, thus operating with a low inlet pressure, allowing for the avoidance of expensive pumps typically used for high-inlet pressure operation.
  2. The feed flow rate is varied by changing the discharge pressure of the charge pump. High pressure increases feed flow from the ERD center; conversely, lower pressure decreases feed flow. Thus, another degree of operating flexibility is created realtive to isobaric chambers.
  3. Control of brine flow is quite easy. An HP brine manifold connects the aux nozzle passage of all HPBs. A single regulating valve adjusts the flow, controlling total brine flow.

The VFD on the charge pump is controlled by a signal from the permeate flow meter. The brine valve position is controlled by the brine flow meter. Thus, two signals provide complete regulation of the entire high-pressure section of the RO plant.

The figure below illustrates the full three-center configuration for a mega-scale system:

Three-Center Configuration
















The figure below illustrates the ERD portion of the three-center configuration for a mega-scale system:

ERD Portion in Three-Center