Maximizing SWRO’s energy efficiency

How can you reduce your SWRO energy consumption?

Desalination mitigates the risk of water scarcity, but its electricity consumption drives costs and GHG emissions. Energy-efficient SWRO is part of the solution.

High pressure doesn’t have to come at high cost

To produce drinking water, seawater reverse osmosis (SWRO) relies on high pressure, which accounts for about 70% of SWRO’s energy consumption. The more energy-efficiently the SWRO plant produces and uses high pressure, the lower its OPEX and GHG emissions.

While membrane technology and plant design also save energy, the greatest potential to reduce SWRO’s electricity consumption lies in energy recovery devices (ERDs) and the high-pressure pump itself.  ERDs re-use high pressure that would otherwise be wasted to save 60% in energy. The most energy-efficient high-pressure pumps save up to 20% compared to less efficient pumps.

Over an SWRO plant’s lifetime, investments in energy efficiency pay big dividends. OPEX accounts for two-thirds of total costs of ownership, and electrical energy costs represent more than half of all OPEX.

Water scarcity is a growing problem. Desalination can help

Fresh water is a basic human need, but in many places the combination of increased demand and decreased supply has already reached critical levels.

On the one hand, we consume more due to population growth, more agriculture, and increased industrial activity. On the other, there is less fresh water available due to overuse, aquifer depletion, waste, climate change, and pollution.

In many places, desalination is the only way to overcome the growing problem of water scarcity and provide enough water for thirsty populations.

The history of desalination: new technology improves energy efficiency

From condensed steam to SWRO with energy recovery devices

Technological innovations have made desalination significantly more energy efficient over the last 50 years, but much progress can still be made. The financial costs of energy consumption make desalination too expensive for many of those who need it most, but the environmental costs of GHG emissions due to electricity generation are also a growing concern.

Electricity: The biggest share of SWRO’s total cost of ownership

Over a lifetime of 25 years, operating expenditures represent two-thirds of total cost of ownership (TCO) for the average small and medium SWRO plant. Electrical energy accounts for more than half of OPEX, and most of this powers high-pressure pumps for the RO process.

Even small improvements in high-pressure pump efficiency have huge consequences for a plant’s TCO.

All SWRO conditions vary, but pump efficiency needn’t

SWRO operators rely on 2 pump types for high-pressure: either centrifugal (CF) or positive displacement (PD). With energy efficiency rates up to 92%, PD pumps are inherently more energy-efficient than CF pumps, whose efficiencies range between 78-88%. 

But PD pumps have another advantage for SWRO: their flow rates are independent of working pressure. Flow rates vary due to seasonal differences in seawater salinity and water demand.

In CF pumps, pressure and flow rates are interdependent. This difference has crucial consequences for energy efficiency. CF pumps are designed for a narrow best efficiency point at a given flow rate, while PD pumps maintain consistently high efficiency at variable flow rates.

Danfoss high-pressure pumps are ideal for SWRO

Danfoss axial piston pumps are positive displacement pumps specifically designed to save energy in high-pressure SWRO processes.

With their consistently high energy efficiency across variable operating conditions, they save 15-20% in OPEX and GHG emissions compared to centrifugal pumps, and often have a payback period of under two years in retrofits.

Highly efficient pumps and energy recovery devices

Read our cases to learn how end users are saving energy

See how Veolia and Danfoss helped a Spanish municipality reduce energy consumption at its SWRO plant by 57% by retrofitting with iSave ERDs and APP pumps.

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Danfoss is dedicated to engineering high-pressure pump solutions that save energy today and enable a more sustainable tomorrow. Our blog explores issues related to energy and cost efficiency in seawater reverse osmosis (SWRO).