Population growth along with limited fresh water
sources has made good quality water a precious commodity today. Towards the alleviation
of acute shortage of fresh water in the costal areas and Island territories of
India, National Institute of Ocean Technology (NIOT), Chennai, an autonomous body
under the Ministry of Earth Sciences has undertaken to establish low temperature
thermal desalination plants to generate the fresh water from the sea surface water
(28-30 0C) and cold deep sea water (9-12 0C). By flash evaporating
the warm sea water under low pressure and condensing the water vapour with the
cold sea water potable water is produced.
This was revealed by Shri Kapil Sibal, Union Minister for Science and Technology
& Earth Sciences at a press conference in New Delhi today.
trials in the laboratory and an experiment on a moored barge off Tuticorin in
400 m water depth, a land based plant was commissioned at Kavarati in Lakshadweep
which is continuously generating good quality water since May 2005. So far more
than 5 crore litres of water has been produced. The availability of high
quality fresh water has drastically reduced dysentery
and other such diseases. Buoyed with this success, eight more such units
are being set up on other islands of Lakshadweep. Towards achieving large capacity plants suitable for mainland requirements
an experimental floating desalination plant of one million litre per day capacity
working on low temperature thermaldesalination plant has been commissioned for
the first time ever in the world at a location 40 km offshore Chennai.
The most complex part of the process
is the drawal of cold water from the ocean which requires a long pipe of 1 m diameter
made up of HDPE. HDPE pipes of such diameter are manufactured in the length of
12 m and these have to be fused together to make a 600 m long pipe weighing 100
tonnes. Since the density of the pipe
is almost equal to saline water, it floats in the water and hence, heavy weight
has to be attached at one end of the pipe to make it straight to reach the depth
of 600 m where cold temperature of 9-12 0C is available.
The deployment and connection of this pipe to the barge is a very challenging
especially with limited offshore
facility available in the country. The 600 m pipe was assembled at Ennore port, then towed to the site and connected
vertically below the barge ‘Sagar Shakti’. The barge is moored to a single point
mooring in deep waters.
that quantity of water, the next difficult task is its storage and transportation
from 40 km offshore point to the shore. For this purpose, water bags of special
material have been designed which can hold and carry 2 lakhs litres of fresh water.
water is lighter than the sea water, it floats and very little power is required
to tow it to the shore.
of the Project
Single point mooring of 1000 m which is of its first kind in
For the first time ever a long pipe was suspended vertically
over the barge in deep waters and cold water of temperature as low as 90C
was pumped up.
Surface sea water has been flash evaporated in low pressure
chamber of 25 millibar (the normal atmospheric pressure is 1000 millibars).
Water of TDS less than 10 ppm has been generated.
Institute is now planning to scale up the capacity of 10 million
litres per day where the cost of water is expected to be below 4 paise per litre.
In this endeavour possibility of collaboration with private industries will also
The technology developed and demonstrated successfully
can readily be adapted for shore based power plants using sea water for cooling.
The sea water used for cooling purposes by thermal power plants attains temperature
of 42-440C and can be used as warm water for evaporation in the flash
chamber of desalination plant. Sea surface water at 28-300C can be
used for cooling the vapour in the condensation plant. It is estimated that the
power plants in Chennai can be configured to provide over 25 per cent of the city’s
requirement of fresh water in this fashion.
(Release ID :26958)