Energy Recovery Devices - Ushering in a sea change in desalination
Updated: Apr 12, 2022
Cross your heart and tell us - as owner or operator of an SWRO, do three questions keep cropping up in your mind or the marketplace:
Is the output water clean and pure?
Is the unit equipped with energy recovery devices?
How effective is process control and transfer efficiency?
The good news is Sea Water Reverse Osmosis has come a long way in the last few years. Backdrop to this transformation is the scrutiny on any activity that requires power consumption, propelled by the global thrust on energy savings, steady depletion in fossil fuels and renewed focus on endowing a greener planet to the next generation.
On the flip side, the challenges of sourcing fresh water from the ground continue to increase, necessitating the development and upgradation of systems that can produce potable water in arid areas or in marine vessels offshore. Let’s take Abu Dhabi as an example: Nine desalination plants accommodate Abu Dhabi's water needs and also supply Fujairah, Umm Al Quwain and Sharjah with clean water. The Emirate accounts for 9% of the desalinated water worldwide and has a production capacity of 1.3 billion cubic metres annually.
A key feature of the world’s most efficient desalination plants, whether serving the needs of four emirates as above, or a lone ship on the high seas, is sustainable technology and optimized power usage.
Always ready for a challenge and ever proactive when the goal is preserving Planet Earth, the desalination industry has embarked on the path of innovation and transformation, and introduced Energy Recovery Devices (ERDs).
On an aside, the energy recovery technology initially developed for sea water treatment has been deployed with equal success in brackish water desalination, industrial wastewater treatment, natural gas processing and well completion.
How do ERDs work? The explanation for a lay person is whenever fluid pressure is reduced through a valve, energy is wasted during the reduction. The recovery device utilizes energy inherent in the process of water treatment, thereby reducing power consumption.
The SWRO process involves high pressure pumping (HPP) to overcome the osmotic pressure in saline feedwater which results in a saline concentrate stream that is highly pressurized. ERDs recover the hydraulic energy and transfer it to the feed stream, reducing both the amount of energy otherwise required by the HPPs and the size of HPP required.
Why are ERDs crucial to achieving carbon neutrality? A research paper published by ‘Frontiers in Sustainable Cities’ states that while Seawater RO offers several advantages over other desalination methods including high efficiency and selectivity, the process requires significantly more energy than alternative forms of potable water treatment.
While conventional surface water treatment requires 0.2–0.4 kWh m−3, and indirect potable reuse (IPR) requires 1.5–2.0 kWh m−3, SWRO desalination needs between 3.5 and 4.5 kWh m−3 to produce the product water, according to a research paper published by Frontiers in Sustainable Cities. Most of the energy consumed by conventional desalination uses fossil fuels, therefore contributing to greenhouse gas emissions.
Reason why the desalination industry has developed ERDs, with the latest devices operating at around 97% efficiency, enabling some plants to achieve SEC of 3 kWh m−3 (around double that of IPR and 10 times that of conventional surface water treatment).
FEDCO, a leader in ERDs, has designed fluid-driven turbochargers and turbogenerators that can handle flows from 30 gpm to 13,000 (7 m3/h to 3,000 m3/h) and pressures from 100 psi to over 2,000 psi (150 bar). The turbocharger recovers energy pressure from the brine stream before recirculating half of the brine back into the feed stream, leading to around 50% recovery.
Danfoss, a leader in innovative and energy-efficient solutions, has launched iSave, the 3-in-1 Energy Recovery Device (ERD) optimized for sea water reverse osmosis applications. iSave captures hydraulic energy from the high pressure reject stream of the SWRO process and transfers the energy back into the system, drastically reducing the energy consumption regardless of flow rate and size of the SWRO system. iSave can be used in almost any SWRO application – land-based or marine, new or retrofit.
Application of Energy Recovery Devices in Projects
Environmentally conscious Water Treatment companies in the UAE such as Advanced Watertek have taken to ERDs, you could say, like a duck to water. To cite a recent example, Advanced Watertek worked with the Emirate of Fujairah to achieve 40% reduction in energy consumption by introducing an Energy Recovery Turbine in the existing SWRO System.
The ERD helped to recover more than 80% of the wasted high pressure brine energy, reduce the size of the high-pressure pump, and lower motor electrical consumption, and turned the tide for an Emirate that relies on SWRO for producing clean water for gardens along the coastline.
If your focus is energy conservation in water treatment, if sustainability is key to your corporate philosophy, if a greener planet is integral to your societal goals, talk to Advanced Watertek. With a track record of 35 years, and installations in 50+ countries and in hundreds of offshore locations and ocean-going vessels, you can expect a holistic solution for SWRO on the coastline or mid seas.
It’s time to make waves with ERD, and usher in a sea change in desalination.