Low-temperature thermal desalination (LTTD) is a
desalination technique which takes advantage of the fact that water evaporates at lower temperatures at low pressures, even as low as
ambient temperature
Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...
. The system uses vacuum pumps to create a low pressure, low-temperature environment in which water evaporates even at a temperature gradient of between two volumes of water. Cooling water is supplied from deep sea depths of as much as . This cold water is pumped through coils to condense the evaporated water vapor. The resulting condensate is purified water.
Using waste heat
The LTTD process may also take advantage of the temperature gradient available at
thermal power plant
A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam ...
s, where large quantities of warm
cooling water
Cooling tower and water discharge of a nuclear power plant
Water cooling is a method of heat removal from components and industrial equipment. Evaporative cooling using water is often more efficient than air cooling. Water is inexpensive and no ...
are discharged from the plant, reducing the energy input needed to create a temperature gradient.
This technique of making use of
waste heat
Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...
is a form of
cogeneration
Cogeneration or combined heat and power (CHP) is the use of a heat engine or power station to generate electricity and useful heat at the same time.
Cogeneration is a more efficient use of fuel or heat, because otherwise- wasted heat from elec ...
.
History
The principle of LTTD has been known for some time, originally stemming from
ocean thermal energy conversion
Ocean Thermal Energy Conversion (OTEC) uses the ocean thermal gradient between cooler deep and warmer shallow or surface seawaters to run a heat engine and produce useful work, usually in the form of electricity. OTEC can operate with a very hi ...
research. Some experiments were conducted in the U.S. and Japan to test low-temperature-driven desalination technology. In Japan, a spray flash evaporation system was developed by
Saga University. In the U.S. state of Hawai'i, the
Natural Energy Laboratory of Hawaii Authority
The Natural Energy Laboratory of Hawaii Authority (''NELHA'') administers the Hawaii Ocean Science and Technology Park (HOST Park). ''NELHA'' was founded in 1974. At , HOST Park is a state-subsidized industrial park for incubator and marginal comm ...
tested an open-cycle OTEC plant with cogeneration of fresh water and electric energy, using a temperature difference of between surface water and water at a depth of around .
Research in India and pilot plants
LTTD was studied by India's
National Institute of Ocean Technology
The National Institute of Ocean Technology (NIOT) was established in November 1993 as an autonomous society under the Ministry of Earth Sciences in India. NIOT is managed by a Governing Council and is headed by a director. The institute is bas ...
(NIOT) from 2004. Their first LTTD plant was opened in 2005 at
Kavaratti
Kavaratti is the capital of the Union Territory of Lakshadweep in India. Kavaratti is a census town as well as the name of the atoll upon which the town stands.
It is well known for its pristine white sand beaches and calm lagoons, which makes ...
in the
Lakshadweep
Lakshadweep (), also known as Laccadives (), is a union territory of India. It is an archipelago of 36 islands in the Arabian sea, located off the Malabar Coast.
The name ''Lakshadweep'' means "one lakh islands" in Sanskrit, though the Lac ...
islands. The plant's capacity is /day, at a capital cost of (€922,000). The plant uses deep sea water at a temperature of .
[Desalination: India opens world’s first low temperature thermal desalination plant – IRC International Water and Sanitation Centre]
. Irc.nl (2005-05-31). Retrieved on 2011-03-20. In 2007, NIOT opened an experimental floating LTTD plant off the coast of
Chennai
Chennai (, ), formerly known as Madras ( the official name until 1996), is the capital city of Tamil Nadu, the southernmost Indian state. The largest city of the state in area and population, Chennai is located on the Coromandel Coast of th ...
with a capacity of /day. A smaller plant was established in 2009 at the
North Chennai Thermal Power Station
North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography.
Etymology
The word ''north'' i ...
(a
coal-fired power plant
A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide, there are about 8,500 coal-fired power stations totaling over 2,000 gigawatts capacity. They generate about a th ...
) to test the concept using power plant cooling water.
The Hindu (2007-04-21). Retrieved on 2011-03-20.
References
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Water desalination