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.