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.

Multi stage flash desalination

Shoaiba MSF desalination plant in Saudi Arabia

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

Reverse Osmosis

• Osmosis

• Reverse Osmosis

Spiral construction of membrane

World largest RO desalination plant in Saudi Arabia

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

World wide desalination water production

Questions?

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