The document discusses various methods for desalination of sea water using solar energy to address global fresh water scarcity. It describes different desalination technologies like solar stills, multi-stage flash distillation (MSF), and multiple effect distillation (MED). While solar desalination is not currently economically viable, further research may help reduce costs. Desalination can provide fresh water for coastal and inland cities but requires substantial investment that may be difficult for poor countries.

1. Biswajit Biswas
Department of Chemical Engineering
Indian Institute of Technology (BHU) Varanasi
DESALINATION OF SEA WATER BY SOLAR ENERGY

2. MILLIONS LACK FRESH WATER AROUND THE WORLD!!
9 Million people without
water access in
developed countries.
36 Million people in
Latin America and
Caribbean.
358 Million people in
Africa.
180 Million people in
South , West and Central
Asia.
186 Million people in
Southeast, East Asia and
Oceania.
Overall about 769
Million people lacks
fresh water all over the
globe.
Source: water.org

3. RELEVANCE TO WATER CRISIS :
Human population is growing at a rate that puts stress on
our current freshwater supply.
Global water use is 9 trillion cubic meters a year and this
rate is expected to increase by approximately 60 billion
cubic meters more per year.
Desalination allows to people to have access to water that
was previously not potable.
Coastal cities can use seawater for their municipal water
supply or landlocked cities can use brackish groundwater for
the same purpose.
Desalination combined with Water recycling are both
integral components of UN’s “water crisis” solution.

4. WHAT IS THE WAY OUT?
In the light of increased water usage and
depleting natural water supplies, the world is
facing an impending water shortage.
To combat this, many countries have turned to
desalination to derive usable water from the
sea.
In this report, we have researched the current
desalination technologies available in order to
provide a comparative analysis of different
methods of solar desalination.
From the research, we have concluded that
although solar desalination is not a viable
option at the present, further research will
make solar desalination most economic.

5. SOLAR STILL
A solar still is a simple way of distilling water, using the heat of the Sun
to drive evaporation from humid soil, and ambient air to cool a
condenser film.
In a solar still, impure water is contained outside the collector, where it
is evaporated by sunlight shining through clear plastic.
In desert environments water needs can exceed 3.8 L per day for a
person at rest, while still production may average 240 mL per day.
Even with tools, digging a hole requires energy and makes a person lose
water through perspiration; this means that even several days of water
collection may not be equal to the water lost in its construction.

6. Multi-Stage Flash Distillation (MSF)
Salt water is heated by solar energy under
extreme pressures and lead through a series of
chambers.
Upon leaving the first chamber the salt water
enters several more chambers each with a
lower pressure than the previous one allowing
even more of the pressurized salt water to
vaporize.
The water that did not vaporize leaves the
system with a higher saline concentration than
when it entered; this is discarded properly as
waste while the distilled water is put into the
municipal water supply as drinkable water.

7. Process of multi stage flash distillation:
Its temperature increases
from sea temperature to
inlet temperature of the
brine heater.
At the outlet of the brine
heater, when entering the
first cell, sea water is
overheated compared to
the temperature and
pressure of stage 1.
Thus it will immediately
"flash" ie release heat, and
thus vapour, to reach
equilibrium with stage
conditions.
The produced vapour is
condensed into fresh
water on the tubular
exchanger at the top of the
stage.
The cumulated fresh water
builds up the distillate
production which is
extracted from the coldest
stage.
Upon leaving the
evaporator, part of the
warmed water is rejected
to the sea, part is used as
the make-up for the plant.
The warmed water may be
used in winter to warm up
the cooling sea-water, thus
enabling the evaporator be
designed for a high
temperature.

8. Multiple Effect Distillation (MED)
Salt water is heated under pressure and and forced
through a chamber.
However, in this system the water vapour from the
first chamber is used to heat the water in the next
chamber.
This produces distilled water (the condensed water
vapor) and more water vapor (the cycle repeats).

9. Process of Multiple Effect Distillation plant:
The steam enters the plant and is used to
evaporate heated seawater. The
secondary vapour produced is used to
generate tertiary steam at a lower
pressure.
The primary steam condensate is
returned to the boiler of the power
station since it is of extremely high
quality that is needed for turbine steam
production.
The MED technique is based on double-
film heat transfer. Latent steam heat is
transferred at each stage by steam
condensation through the heat transfer
surfaces to the evaporated falling film of
seawater.
The process is repeated up to 16 times in
existing plants between the upper
possible temperature and the lower
possible cooling water.
A compressor is used to maintain the
gradual pressure gradient inside the
vessel by removing the accumulated non
condensable gases together with the
remaining water vapour.
The pressure gradient along the MED
effects is dictated by the saturation
pressure of the feed stream and the
saturation pressure of the condensing
steam exiting the last stage.
It is condensed by cooling with
seawater. Typical pressure gradients of 5-
50 kPa across the system (less than 5
kPa/stage) are typical.

10. Future option of Desalination:
Desalination needs to
be implemented in any
ocean bordering
region .
As Saudi Arabia has
demonstrated, water
can be piped inland to
landlocked cities
which means
desalination is not
limited to coastal cities
.
If technology continues to
produce new methods
and better solutions to
the issues that exist
today, there would be a
whole new water
resource for more and
more countries that are
facing water problem.
With complete reliance on
sea water, it would
undoubtedly be at least
an option for many people
struggling to survive or
maintain their standard of
living.

11. COST/ BENEFIT ANALYSIS:
The benefits of desalination are straightforward: more water. The drawback, unfortunately, is the cost.
Regardless most people would avoid paying 3-4 times more for anything if they do not have to . If a
region’s water supply is currently meeting the needs of the people in a sustainable manner, then
switching to desalination, is not an urgent issue.
If the supply is unsustainable and the rate consumption is high, then some action must be taken to
insure that future generations will have access to water.
Desalination will be appropriate if the area is then either rapidly running out of water or if the effort it
would take to make the water supply sustainable is not feasible.

12. SOLUTIONS TO THE ISSUE !!
People must know
what awaits in
future!!
• Countries will have to first do some preliminary
research to make sure that there are locations
within their borders where it is feasible to
construct a desalination plant;
Market
Demand ?
• To address these issues the
respective countries have to
develop an initiative based system
to promote the further use of
desalination.
Organise!!
Co-
operation !!
• If a country meets these qualifications they can apply for the
desalination plant. They will have to determine the most
appropriate way to organize the funds for the construction of
desalination plants on a case to case basis by cooperating with
business, banks, and other resources willing to participate.
Make Blue
Prints !!
• Additionally, drawing up the plans to
implement desalination as well as physically
making the blueprints for a plant will take
another 2-3 years.
• Finally, building the plants themselves would
take anywhere from another 3-4 years . As a
result, they may expect to see the working
effects of desalination as soon as 2023 if they
begin as early as possible.

13. Can a desalination plant be a solution for poor countries affected by
drinking water scarcity?
A desalination plant requires substantial investment towards
building and operation which could be costly and may not be
affordable to poor countries.
Sea-level rise is a major threat to freshwater resources in a number
of countries including small island nations and both developing and
developed countries. One of the options is desalination.Here also
the poor country must look for an alternate solution.
Geography of Desalination is currently used by countries that have
an extreme need for fresh water, have enough money to fund it,
and posses the amount of energy required to produce it.
The technology is expected to spread increasingly, particularly in the
United States, Libya, China, and India. Saudi Arabia is currently the
world’s number one producer of desalinated water.

14. THE INDIAN SCENARIO !!

15. Location of Desalination plant in India
Source: Bhabha Atomic Research Centre

16. Negatives of Solar Desalination
Dumping the wasted high temperature solution back into
the ocean makes the process more complicated.
The energy required to start up and power desalination
plants is a huge expense and is a matter of great concern for
poorer countries.
Within the energy issue, solar energy is potentially the most
cost-effective energy source, but remains largely untapped
due to public opinion.
If regions situated away from the coast or in a high altitude
try to use desalinated water, it is an even more expensive
process.
There are major environmental concerns from desalination,
is related to discharge of brine which can damage the local
ecosystem and biodiversity.

17. SO WHAT TO DO ??
Solar stills were in fact the first method used on a large scale to process contaminated
water and convert it to a potable form.
Of the estimated freshwater being produced a day through desalination processes
worldwide, less than 1% is made using solar energy. The prevailing methods of
desalination are energy intensive and rely heavily on fossil fuels.
Because of inexpensive methods of freshwater delivery and abundant low cost energy
resources, solar distillation has, up to this point, been viewed as cost prohibitive and
impractical.
With the approach of peak oil production, fossil fuel prices will continue to increase as
those resources decline; as a result solar energy will become a more attractive
alternative for achieving the world’s desalination needs.
Environmental implications of desalination regarding safe brine disposal will be
significant by 2050.
It is important for countries to jointly plan and implement national environmental
legislation.
So Solar Desalination is the one of the possible option left in near future to meet the
demand of fresh water.

18. THANK YOU