HP-HEMI Series Motor Assisted Energy Recovery Turbocharger

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Six (6) models cover the largest current and anticipated SWRO trains. Standard MOC is Duplex SS 2205 with Super Duplex SS 2507 optional. Brine nozzle valve actuators, flanged connections and other options available.  FEDCO provides the complete HEMI package including motor, VFD and valve actuator.

  1. Brine aux nozzle actuator
  2. HEMI motor
  3. Brine discharge module
  4. Common baseplate

The HEMI control can be integrated into the plant SCADA or FEDCO can provide a stand-alone PLC. Requiring only two process signals, permeate and brine flow, the HEMI control system is easy to install and operation is simple and intuitive.

Hydraulic Energy Management Integration (HP-HEMI)

Feed flows from 400 to 4000 m3/h
Pressure to 83 bar

Every SWRO system must be able to supply a varying pressure to the membrane array to accommodate changes in feed temperature, salinity and membrane fouling. The upper curve in the adjacent graph illustrates a typical annual pressure variation due to seasonal feed water temperature changes.

However centrifugal HPPs cannot provide a variable discharge pressure without use of a very expensive and failure-prone medium/high voltage variable frequency drive (VFD). In addition, the VFD imposes a 3% energy loss from electrical losses.

Ideally, the HPP would only need to produce a constant discharge pressure as depicted by the green line in the adjacent graph. The function of the HEMI is to bridge the gap between the HPP constant-pressure characteristic and the membrane variable pressure requirement.

The HEMI is simply a slightly modified HPB with a motor attached to its rotor. As illustrated by the adjacent figure the motor may be 200 kW and is driven by a standard low voltage VFD. The HPP motor may be 1500kW and may be a direct start or use a soft starter. In this example, the HPP delivers a constant 30 barg discharge pressure while the membrane pressure varies between 50 and 70 barg. At low membrane pressure conditions, the entire energy required for the 20 bar boost is provided by the HPB’s turbine section. At the maximum boost at 40 bar, the turbine provides most of the power while the motor makes up the balance.

Pressure flow too high HEMI VFD reduces rotor speed (reduces feed boost)
Permeate flow too low HEMI VFD increases rotor speed (Increases feed boost)
Brine flow too high Turbine nozzle are reduced (reduces brine flow)
Brine flow too low Turbine nozzle area increased (increases brine flow)

The HEMI can provide entire SWRO control of feed and brine flows by the addition of a basic PLC. The permeate flow meter (FM1) controls the HEMI VFD and the brine flow meter controls the HPB turbine variable nozzle via signals from the PLC. The basic control philosophy is illustrated in the adjacent table.

Typical HEMI PLC Display
HP-HEMI-1000 on Test Stand