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Desalination A part of an alternative solution to meet the water in demand?
By Seong Taek BpangMar/07/2011
Table of Contents
• Definition/Back ground
• Operating process
• Types of desalination
• World trend
• Issue of desalination
Current Status of water
• According to IDAo Fresh water is app 3% of
world water deposit
o Less than 30 % of the
water, ground and
surface water, are
available for daily use
within the 3 percent
Increasing demand and unreliable supply • Increasing population and water demand
o The expected population growth is about 2.6 billion in next 45
years, and it would mostly be from developing countries
according to the U.S. Census Bureau.
• Unreliable supplyo Due to the climate change and pollution, traditional method of
collecting water is becoming unreliable.
o Ex- Australia, a country relied on collecting rain fall water is
now looking for alternatives such as desalination due to the
drought and low rain fall
o Ex- Southern California dependence of Colorado river.
Christopher Gasson of Global Water Intelligence (GWI)
• “People do desalination when they run out of opportunities, and the
problem is the world overall is running out of opportunities: groundwater
is overexploited to the extent it’s becoming saline and unusable; rivers are
being drained; new dams are becoming less and less viable [and] long-
distance transfer is expensive and controversial.”
What is Desalination?
Desalination is the process of removing dissolved salt and other minerals from seawater to create freshwater
The fact that desalination requires sea water the construction of a plant is limited by location
Majority of desalination plants are operating and being built in middle eastern country and Pacific island
General Process diagram of Desalination Pant
Pre treatment
Post treatment
Desalination Unit
brine
Water
feed
Fresh
water
Filtering Large particlesScreeningFloatationSedimentation
coagulationChlorinationUV treatmentpH adjustment
CO2 absorptionLimestone (CaCO3)pH adjustmentChlorinationRe-mineralization
Varying post treatment according to application
Drinking water
Irrigation water
Process water
Sodium chloride < 450 mg/L
SAR optimization
minimized
Calcium, Magnesium Hardness 6-
10oDminimized
pH 6.5-8.5
Boron <0.5 mg/L (WHO)<1 mg/L (EU)
Crop dependent
Disinfection Required Not required
Different Types of desalination technology
• Thermal desalination
Multi-stage flash (MSF)
Multiple-effect distillation (MED)
vapor-compression (VC)
• Membrane desalination
Reverse Osmosis (RO)
Electro dialysis reversal (EDR)
Nano filtration
Membrane distillation• Others include Solar , and Geothermal
desalination
Thermal desalination (Conventional)
• Usually requires large amount of energy
• Good combination with Power plant (Dual purpose)o Thermal Desalination plant can use thermal energy (Low grade
energy) that has been exhausted from the power plant.
o For MSF distillation process distillers are coupled with
extraction condensing or back pressure steam turbine
o Most of the desalination plant in middle eastern is dual purpose
desalination plant to achieve low operating cost.
Membrane desalination
• Semi permeable membrane is used for processing water
• Relatively lower energy consumption of Energy compared
to thermal desalination
• Driving force is supplied by a pump (Electricity) o Typical operating pressure of sea water reverse osmosis is
600~1000 psi
o Typical operating pressure of brackish water is 30-250psi
Trend of desalination Plant
Membrane desalination is being favored over thermal desalination
o Development of membrane technology• Increased durability of membrane
– During 1980 and 1990 the life time of membrane was 2~3 y; life time of membrane these days are 7~7.5 y
– Capacity of processing water per membrane • Increased efficiency of membrane
– Typical efficiency of a membrane is reported to be 48%
o Reduced cost of membrane production
Economic side of desalinated of water
• Typical cost of desalinated water (1 m3 =264 gallon)sea water desalting 0.75- 1.25 US $ /m3
brackish water desalting 0.25- 0.60 US $ / m3
• Cost of traditional supply of water0.24-0.66 US $ /m3
• Desalinated water cost component o capital costs 30 - 50 (%)
o energy costs 30 - 50 (%) other costs
o (labor, chemicals, etc) 20 - 30 (%)
• Depending on the location desalinated water can be
competitive with other sources of water
Comparison of the two type
MSF desalinationBenefits: • low operating cost when it
is co-located with power plant
• Relatively low quality of feed water compared to RO.
Cons:• High operating cost when
sources of heat is not available
• High rates of corrosion and scale formation
RO desalinationBenefits:• Low energy intense (Reduced energy consumption)• High quality process water
• Compact plant designCons:• Higher capital cost • Re-mineralization is needed
Comparison in terms of energy usage
Average thermal desalination produce 23.41kgCO2/m3 Average reverse osmosis would produce 1.78kgCO2/m3
Issues and Misconception of Desalination
• Major concerns:o Effects of open water
intake to marine life• Fish eggs• Fish larvae• Plankton
o Pollution due to the
brine• Highly concentrated
brine water is denser than sea water
o Increase in CO2
emission
• Redesigning intake pipe and discharge pipeo Offshore intake
o Sub sea bed intake
o Passive intakes
• Use of an alternative energy sources for desalination planto Majority of the desalination plant in Australia is Wind powered
o Saudi Arabia, a world’s largest producing country is
investigating use of solar powered desalination plant.
• More energy efficient designo Combining technology's of both thermal and Membrane
Efforts in conserving environment
o Outfall pipe
o Multi port diffusor
o Blending with cooling tower water
Growing industry
• As of year 2007, approximately 7,500 desalination plants
are operating world wide.
• 60 % of the plants are located in Middle East
• Desalination industry is growing 10 to 15 % on average
per year
References
• http://www.aboutmyplanet.com/environment/is-desalination-a-solution-to-water-shortages/
• http://www.greenfudge.org/2010/04/01/global-water-woes-mean-desalination-on-the-rise/
• http://maps.grida.no/go/graphic/water-desalination
• http://hbfreshwater.com/desalination-101/desalination-worldwide
• http
://www.idswater.com/Common/Paper/Paper_90/Desalination%20Methods,%20Technology,%20and%20Economics1.htm
• http://www.lenntech.com/processes/desalination/post-treatment/general/desalination-postreatment.htm
• http://www.membranes-amta.org/amta_media/pdfs/6_MembraneDesalinationCosts.pdf
• http://www.mfa.gov.il/MFA/Archive/Communiques/1995/WATER%20DESALINATION
• http://www.oas.org/dsd/publications/unit/oea59e/ch20.htm#TopOfPage
• http://people.uwec.edu/piercech/desalination/MSF.htm
• http://www.treehugger.com/files/2008/06/water-desalination-ottawa-student.php
• http://www.wateradditives.com/Repository/Files/Desalination.pdf
• http
://waterweek.wordpress.com/2007/09/25/power-hungry-seawater-desalination-adds-to-co2-emissions-reverse-osmosis-
at-178kg-of-co2m3-clear-winner-over-thermal-distillation
/
• http://
www.waterworld.com/index/display/article-display/4372157651/articles/waterworld/drinking-water/treatment/desalina
tion/from-seawater_to_drinking.html
• http://www.worldwater.org/data20062007/Table21.pdf