FGI FD5000 Series MVD used in Seawater Desalination for Energy Saving
Project Overview
Water shortages have become a key bottleneck restricting economic and social development in coastal areas. Seawater desalination, as a core technology for increasing water supply, is of great significance for ensuring industrial and domestic water use. Reverse osmosis (RO), with its low energy consumption, short construction period, and compact design, is the mainstream process for seawater desalination.
As the core of the RO system, the high-pressure pump pressurizes seawater to 4.0–6.0 MPa, and its energy consumption accounts for more than 60% of the total system energy use.
Customer Needs and challenges
High Energy Costs：Under fixed-speed operation, pressure adjustment relies on valve throttling, wasting a large amount of energy as heat. Under low-load conditions, energy waste can exceed 30%.
Severe Mechanical Stress：Direct start of high-pressure pumps draws 5–7 times the rated current. , impacting the grid and easily causing overheating and aging of transformers, switches, and contactors, as well as tripping.The instantaneous torque shock causes loosening, cracks, and damage to pump shafts, couplings, bearings, and mounts
Poor Control Accuracy：Valve adjustment suffers from lag and poor accuracy; pressure fluctuations easily tear RO membranes or cause brine-side leaks, increasing maintenance costs.
FGI Customized Solution
Correct Sizing & Selection
Considering the characteristics of the seawater desalination system:
First, when seawater temperature rises 1°C above the standard preset temperature, the RO membrane salt rejection rate decreases by about 0.3%, requiring lower operating pressure to ensure product water quality.
Second, when product water load changes, pump speed must be adjusted synchronously to avoid excessive pressure fluctuations that could damage membrane components or pipes.
Finally, the FGI FD5000 series high-voltage drive (model FD5000-6/1250F-1A) was selected, with the following configuration:
Rated voltage: 6kV
Rated power: 1250kW
Rated current: 150A
Control modes: VF control and vector control
Protection rating: IP54 (dust-tight and water-resistant for plant floors)
Core features: Torque control, low-frequency compensation, soft start, Modbus remote communication, and multiple protections (overvoltage, overcurrent, overtemperature)
FGI Solution Advantages
Energy-saving : The MVD adjusts motor speed in real time according to product water load, replacing traditional valve throttling. Energy consumption per ton of water drops by about 10–15%. Maintenance response time is shortened from 2 hours to 15 minutes.
Soft start protection: Starting current is limited to within 1.5 times rated current. It greatly reduces the mechanical and electrical stress of direct starting. Smooth speed regulation avoids severe pump vibration. Equipment overhaul intervals are extended by more than 50%, and maintenance costs are reduced by 30–40%.
Process stability: High-precision pressure closed-loop control keeps inlet pressure fluctuations within ±0.05 MPa. It effectively avoids membrane tearing or brine-side leakage caused by sudden pressure changes. Membrane service life is extended by 1–2 years, and product water quality meets standards (salt content ≤500 mg/L)
Better power quality: The MVD adopts Cascaded H-bridge units topology, keeps input current THDi ≤4%, meeting national standards, reducing grid pollution, and improving power factor to above 0.95.
System Layout
The solution uses a one-drive-one-motor auto bypass design. It keeps the original fixed-speed circuit as emergency backup. This allows installation without stopping normal production. A communication bus connects the drive to the plant DCS. Operators can start, stop, adjust speed, and see alarms remotely.
Performance evaluation
Energy Savings
Before: 3.80 kWh per ton of water; 6,840 kWh per day
After: 3.10 kWh per ton of water; 5,568 kWh per day
Overall energy saving rate: 18.4%
Annual electricity cost saving: ~$37,000 USD (270,000 RMB)
Payback period: ~1.5 years
Equipment Reliability
Equipment failure rate fell 80%
Unplanned downtime decreased by 600 hours per year
Lower Maintenance Costs
Annual spare parts cost fell 80%
Manual inspection frequency dropped 55%
Maintenance efficiency rose 60%
On-Site Photos
Before: Fixed-speed fan control panel at a building materials plant
After: DCS monitoring screen showing intelligent constant pressure control
Customer Testimonial
"This upgrade exceeded our expectations. We save significantly on electricity each month. The pumps run smoothly and bearings last longer. The FGI FD5000 drive is very durable. Their engineers respond quickly. FGI is a reliable partner for industrial energy savings."
— Technical Director, Coastal Machinery Plant
Summary & Contact
This case demonstrates that the precise application of the FGI FD5000 series drive successfully solves the common industry problems of high energy consumption and high maintenance costs in seawater desalination, achieving the triple value of energy saving, quality and efficiency improvement, and cost reduction.
If you have industrial equipment such as fans, pumps, air compressors, conveyors, etc. that need variable frequency retrofit, please contact us for a free energy assessment, customized retrofit plan, and on-site survey.
