che_february-2025 - 6

Deepwater RO could cut energy use and environmental impact
of seawater desalination
D
esalination of seawater with reverse osmosis
(RO) membranes is a key technology for addressing
water scarcity issues around the globe,
but seawater desalination is energy-intensive
and the brine discharge can create coastal environmental
problems. The company Flocean AS (Oslo, Norway;
www.flocean.green) is among a handful of companies
developing technology for deepwater RO desalination,
an approach that has a number of cost and operational
advantages over conventional seawater RO.
" Terrestrial seawater RO requires high pressures and
is susceptible to bio-fouling of the membranes, as well
as negative environmental impacts associated with
chemical pre-treatment of seawater and discharge of
concentrated brine, "
explains Alexander Fuglesang,
CEO of Flocean. Deepsea RO takes advantage of the
high surrounding hydrostatic pressures, which align
with the osmotic pressure needed for desalination. This
reduces the energy required
to push water through the
membranes by 30 to 50%
compared to land-based RO,
Flocean says.
Installation in deep water
also allows the high-pressure
pump to be placed downstream
of the RO membranes,
on the permeate side, drawing water over the
membranes rather than pushing it through (diagram).
This means energy is focused only on the product
water, unlike in terrestrial seawater RO plants, where
energy is used to pressurize the entire feed stream, the
company states.
Flocean
In addition to the energy savings, the water properties
at depths of 400-600 m offer considerable advantages
for RO. " Seawater at that depth contains minimal algae,
so pre-treatment requirements are reduced, and the temperature,
pressure and salinity are much more consistent
than surface water, which has operational advantages, "
Fuglesang remarks.
Further, because of the energy and operational advantages,
deepwater RO can be economically feasible at
much lower recovery rates than conventional RO (10-
20% water recovery with deepsea, versus 40-50% for
conventional). This alleviates many of environmental impacts
of the brine discharge, as well as reducing biofouling
and scale formation
Flocean has its origins in a Norwegian company with
expertise in building and installing deepsea pumping
systems for the offshore oil and gas sector. The ideas
and concepts for deepwater RO have been around
since the late 1990s, but
with costs of underwater
robotics coming down, and
water scarcity issues growing,
it
makes more sense
now, Fuglesang explains.
Flocean recently announced
a new round of
investment that will further
construction of a demonstration plant on the west coast
of Norway. The company plans to start up the facility in
early 2026. Fuglesang says his company is currently negotiating
commercial " water-as-a-service " contracts for
clients in the Mediterranean Sea and Red Sea regions.
On-demand ammonia production from atmospheric air
N
6
early all ammonia is produced using methane
via the Haber-Bosch process, which requires
high-temperature and high-pressure operation.
A new portable prototype device developed
by researchers from Stanford University (Stanford,
Calif.; www.stanford.edu) and King Fahd University of
Petroleum and Minerals (Dhahran, Saudi Arabia; www.
kfupm.edu.sa) has demonstrated the production of ammonia
from ambient air without any external electricity or
radiation source.
Using wind as its motive force, air is drawn through
a special catalyst mesh consisting of magnetite (Fe3O4)
and Nafion fluoropolymer. Capturing nitrogen from the
air and hydrogen from water-vapor microdroplets, the
catalyst-mesh structure facilitates the reaction to form
an ammonia-rich aqueous solution within the device.
This solution is collected by a condenser plate to separate
it from any unreacted air or water vapor in the reaction
chamber. The performance of the device depends
on many environmental factors, such as humidity and
wind speed, as well as the size, salt content and acidity
of the water droplets. The researchers tested the device
in the field at nine different locations in California's
Bay Area to verify its performance over a wide range of
relative humidities, temperatures and wind speeds. The
device has demonstrated its ability to produce ammonia
solution of sufficient concentration (25 to 120 μM in 1
hour, depending on local relative humidity) for use as a
hydroponic fertilizer.
Other properties that were tuned to improve ammonia
synthesis included the pore size of the mesh and
the size distribution of water microdroplets entering the
chamber. Larger pore sizes led to less-effective catalytic
interaction, while pores that were too small condensed
the gas and water before they could pass through the
mesh and react.
The ability to generate ammonia onsite for fertilizer applications
is extremely beneficial, as it eliminates the need
for storing and transporting materials. The researchers
hope that the device could eventually be integrated with
irrigation systems, enabling localized, on-demand ammonia
production for agricultural sites. They are currently
working to expand the mesh-system size to produce
larger volumes of ammonia.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
FEBRUARY 2025
http://www.flocean.green http://www.stanford.edu http://kfupm.edu.sa http://WWW.CHEMENGONLINE.COM
che_february-2025

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