Drinking water from air humidity
Research News June 2009
Not a plant to be seen, the desert ground is too dry. But the air
contains water, and research scientists have found a way of
obtaining drinking water from air humidity. The system is based
completely on renewable energy and is therefore autonomous.
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Cracks permeate the dried-out desert ground, the landscape bears
testimony to the lack of water. But even here, where there are no
lakes, rivers or groundwater, considerable quantities of water are
stored in the air. In the Negev desert in Israel, for example,
annual average relative air humidity is 64 percent – in every cubic
meter of air there are 11.5 milliliters of water.
Research scientists at the Fraunhofer Institute for Interfacial
Engineering and Biotechnology IGB in Stuttgart working in
conjunction with their colleagues from the company Logos
Innovationen have found a way of converting this air humidity
autonomously and decentrally into drinkable water. “The process we
have developed is based exclusively on renewable energy sources such
as thermal solar collectors and photovoltaic cells, which makes this
method completely energy-autonomous. It will therefore function in
regions where there is no electrical infrastructure,” says Siegfried
Egner, head of department at the IGB.
The principle of the process
is as follows: hygroscopic brine – saline solution which absorbs
moisture – runs down a tower-shaped unit and absorbs water from the
air. It is then sucked into a tank a few meters off the ground in
which a vacuum prevails. Energy from solar collectors heats up the
brine, which is diluted by the water it has absorbed. Because of the
vacuum, the boiling point of the liquid is lower than it would be
under normal atmospheric pressure. This effect is known from the
mountains: as the atmospheric pressure there is lower than in the
valley, water boils at temperatures distinctly below 100 degrees
Celsius. The evaporated, non-saline water is condensed and runs down
through a completely filled tube in a controlled manner. The gravity
of this water column continuously produces the vacuum and so a
vacuum pump is not needed. The reconcentrated brine runs down the
tower surface again to absorb moisture from the air.
“The concept is suitable for various sizes of installation.
Single-person units and plants supplying water to entire hotels are
conceivable,” says Egner. Prototypes have been built for both system
components – air moisture absorption and vacuum evaporation – and
the research scientists have already tested their interplay on a
laboratory scale. In a further step the researchers intend to
develop a demonstration facility.
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