How Does an Energy Recovery Device Save Energy in a Seawater Desalination Plant?| Insights by AQUALITEK

Introduction

Seawater reverse osmosis (SWRO) desalination is an energy-intensive process due to its extremely high operating pressure.
However, modern desalination plants are able to operate at surprisingly low energy consumption levels—often below 3 kWh/m³.

The key reason behind this efficiency is the Energy Recovery Device (ERD).

This article explains:

•What an ERD is

•Where the recoverable energy comes from

•How ERDs reuse that energy

•Why ERDs are indispensable in seawater desalination systems

1. Where Does the “Recoverable Energy” Come From?

1.1 High-Pressure Brine: The Hidden Energy Source

In an SWRO system:

•Seawater is pressurized to 55–70 bar

•Only 35–45% becomes product water

•The remaining 55–65% exits the membrane as high-pressure concentrate (brine)

This brine still contains:

•Nearly the same pressure as the feed

•Large amounts of hydraulic energy

Without an ERD, this energy would be wasted through throttling valves.

2. What Is an Energy Recovery Device (ERD)?

An energy recovery device is a hydraulic device that:

•Captures pressure energy from high-pressure brine

•Transfers it back to the incoming seawater

•Reduces the load on the high-pressure pump

ERDs do not create energy—they reuse energy that already exists in the system.

3. How ERDs Save Energy: Step-by-Step Explanation

3.1 Conventional System (Without ERD)

1.High-pressure pump supplies 100% of pressurization energy

2.Brine pressure is dissipated to near zero

3.Energy is completely lost

➡️ Result: Very high power consumption

3.2 System with an Energy Recovery Device

1.Brine exits the RO membrane at high pressure

2.ERD transfers this pressure directly to incoming seawater

3.High-pressure pump only needs to supply the remaining pressure difference

➡️ Result: 40–60% reduction in pump energy demand

4. Main Types of Energy Recovery Devices

4.1 Isobaric Pressure Exchangers (Most Advanced & Mainstream)

How they work:

•Direct pressure-to-pressure transfer

•No conversion to mechanical or electrical energy

•Extremely low losses

Performance:

•Energy recovery efficiency: 95–98%

•Pressure loss: typically < 1 bar

This is the dominant technology in modern SWRO plants.

4.2 Turbines and Turbochargers (Older Technology)

How they work:

•Brine drives a turbine

•Turbine assists the high-pressure pump

Limitations:

•Mechanical losses

•Lower efficiency (70–85%)

•Less suitable for variable flow

5. How Much Energy Can ERDs Actually Save?

5.1 Typical Energy Comparison

➡️ Up to 60% energy savings compared with systems without ERDs.

6. Why Household RO Systems Do Not Use ERDs

Household RO systems:

•Operate at 3–7 bar

•Have minimal pressure energy in concentrate

•Do not generate enough recoverable energy

In contrast, seawater desalination:

•Operates at very high pressure

•Produces large volumes of high-pressure brine

•Makes ERDs economically essential

7. Additional Benefits Beyond Energy Savings

ERDs also:

•Reduce high-pressure pump size

•Lower mechanical stress

•Improve system stability

•Extend equipment lifespan

•Reduce operating costs (OPEX)

•Lower carbon footprint

Conclusion

Energy recovery devices save energy in seawater desalination plants by recycling the pressure energy stored in high-pressure brine instead of wasting it.

In summary:

•High-pressure brine contains valuable energy

•ERDs transfer that energy back to incoming seawater

•Modern ERDs recover up to 98% of this energy

•ERDs reduce SWRO energy consumption by 40–60%

•Without ERDs, large-scale seawater desalination would not be economically viable