Climate Action 2012-2013

AGRICULTURE, FOOD AND WATER
A low temperature evaporation (LTE)
technology for producing pure water from
seawater by using low quality waste heat has
been developed at BARC. A 30,000 litres/day
low temperature evaporation (LTE) plant for
sea water desalination was integrated into the
nuclear research reactor at Trombay (Figure
3) to make use of part of the waste heat from
the primary coolant water system and produce
desalted water to meet the make-up water
requirement of the reactor.
SOLAR POWERED DESALINATION
Coupling of desalination units with a renewable
energy source is important for climate change
mitigation and adaptation. Use of solar
desalination has been investigated vigorously
earlier, and a few systems set up for water
desalination. The most significant challenges
faced were frequent breakage of glass panes, and
maintenance of the glass surface. With natural sea
water being used as a feed, the concentrate left
over contained fishes and other bio-organisms,
attracting wildlife to cause damage to the
desalination units. However, solar energy can
be applied for very small scale desalination on
individual rooftops. With a few litres of brackish
water, a quantity of drinking water can be
produced for a small household. The concept is
akin to solar water heaters or solar power panels.
The coupling of solar energy and desalination
systems holds great promise. Effective integration
of these technologies will be a step forward to
dealing with water shortage problems with a
domestic energy source that does not produce
air pollution or contribute to the global problem
of climate change. Currently, solar energy may
appear expensive. However, it is predicted that the
unit cost of solar energy will decrease substantially,
while the costs of conventional fuels are expected
to continue to rise.
Solar thermal energy may be used in MSF and
multiple-effect distillation (MED) desalination
plants, while solar photovoltaics (SPV) are
suitable for RO plants. The SPV option is
more attractive than the thermal option in
terms of land requirements (40 per cent less for
SPV). While initial investment costs are high,
improvements in efficiency and production scale
economies can bring SPV plant costs down
substantially in the future. These two factors
are more important than higher government
subsidies for renewable options.
Photovoltaic cell research is concentrating
on increases in efficiency, the reduction of
manufacturing costs and the search for other
suitable materials. Efficiencies higher than 30
per cent (known as ultra high efficiency) have
been reached in cells using gallium arsenide and
its alloys. From the cost reduction point of view,
a three-fold decrease in SPV electricity costs
is required to make it more competitive. SPVpowered
RO plants will become a reality in the
future as it becomes more expensive and less
acceptable to use fossil fuel energy.
Other concepts such as solar ponds, providing
thermal energy for MED and MSF systems,
are also gaining attention. The desalination
units powered by renewable energy systems are
uniquely suited to provide water and electricity in
water scarcity areas.
“Improvements in efficiency
and production scale
economies can bring SPV
plant costs down.”
A promising future technology for thermal solar
desalination is membrane distillation. The water
vapour from the hot feed (brackish or sea water)
permeates across a hydrophobic membrane due
to the thermal gradient, and condenses on the
other side, enabling the collection of relatively
pure water.
Dr. Paramahamsa Tewari has held senior positions
in large engineering and construction organisations,
mostly in Nuclear Projects of the Department of
Atomic Energy, India. He was also deputed abroad
for a year at Douglas Point Nuclear Project, Canada
and is the former Project Director of the Kaiga Atomic
Power Project.
Indian Desalination Association (InDA) was formed
in 1991 in Chennai with the main goal of developing
and promoting appropriate use of desalination and
desalination technologies nation wide in water supply,
water reuse, water pollution control, water purification
and water treatment.
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