seawater desalination: a sustainable solution to world water shortage
TRANSCRIPT
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Seawater desalinationA sustainable solution to world water shortage
Adelaide Desalination Plant
Jonathon E. BlesingTechnical Director, Aurecon
Con PelekaniPrincipal Process Engineer, SA Water
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• Mid 2013 7,095,217,980 est.• Growth rate 1.14%• Doubling period 61 years
Where will the water come from?• Reduced wastage• Reduced pollution (increase availability)• Recycled water• Better stormwater management
World population
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All are dependent on natural rainfall, which is unlikely to change
Conventional fresh water sources
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Supply is reliant on:• Climatic conditions (seasonal, droughts)• Population concentration (pollution)• Excessive draw-off (increased salinity)
Reduced pollution will increase availabilityWater storage (dams) can attenuate seasonal changeNo solution to an extended drought
We still depend on rain
Fresh water supply
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Nature’s solution is not enough
It’s not enough and it’s not reliable. We need an alternative source of water that is climate independent
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Media reporting and common public perception often considers seawater desalination as:
“…environmentally irresponsible and energy intensive, and described as a very expensive insurance policy for droughts necessary due to mismanagement of our natural resources, rather than a sustainable, environmentally responsible drinking water solution…”
Seawater desalination –Common perception
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To address these common perception issues and achieve a responsible and sustainable plant, the targets need to be:• Minimum impact on the marine,
terrestrial or atmospheric environment• Minimum energy consumption• Minimum impact on local communities• Minimum cost – capital and operating
A tough ask?
Seawater desalination – sustainability
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South Australian conditions
• Driest state, driest continent• Adelaide 1.23M people• Reservoir capacity = 1 year• 40% to 90% from River Murray• River Murray also supplies NSW and
Victoria and is a major food bowl
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Climate impact
Projections show Greater Adelaide would likely have a supply deficit by 2013 in extreme dry year events without a 100GL/a plant
River Murray Drought Years
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• Water security for Adelaide• Expand Mount Bold reservoir?• Stormwater reuse?• Wastewater recycling?• Seawater desalination?• How and where?
Desalination Working Group
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• Desalination plant at Port Stanvac• Capacity 50GL/year, expandable to 100GL/year• Maximum energy consumption <4.5kWh/kL• Low impact on marine environment• Positive impact on terrestrial environment• No impact on local community• Power from renewable energy source
Recommendations
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Concept design phase
• Environmental Impact Statement• Detailed analysis of Gulf St Vincent • Detailed concept design prepared• Pilot Plant set up in December 2008• Tenders called based on the detailed concept design
Contract (Design/Construct) awarded to Adelaide Aqua consortium. January 2009 for 50GL/year plant (later extended to 100GL/year) – AUD$1.82b
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Key Design Factors• Minimum environmental impact – intake system/outfall system• Energy efficient operation – minimum to maximum production• Minimum environmental impact during construction• Positive impact on local terrestrial environment • Minimal impact on local residential community• Power supply from renewable energy supply
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Intake System
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Intake System
• 1.4km offshore• Deep water• Sandy seabed• 4.0m above seafloor• 100mm bar screen• Velocity 0.08m/sec
through screen• Velocity 2.28m/sec
in intake throat
Minimal marine environmental impact
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Outfall Diffusers
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Outfall Diffusers• 1.1km off-shore• Four nozzles• Duckbill valves• Real time monitoring• No disturbance
Minimal marine environmental impact
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Outfall Diffusers
Salinity variations
• Salinity measured 100m from diffusers 0.4ppt to 0.9ppt above ambient
• EPA limit 1.3ppt
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Pre-treatment system
disc filters
• Intake screen in clear water• Band screens 3mm • Disc filters 100micron • Ultra filters 0.04micron (pore size)
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Pre-treatment system
ultra filters
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The result
• Silt density index (measured) – 2.4 average• Reduced fouling of RO membranes• Reduced clean-in-place and chemical usage• Reduced pumping cost• Increased life of membranes• Increased water recovery rate
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Energy recovery – pressure exchange
• 50% of raw seawater is normally rejected to sea but still at high pressure
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Energy recovery – pressure exchange
• 50% of raw seawater is normally rejected to sea but still at high pressure
• Use pressure energy to draw more seawater and supply RO at high pressure
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The result
• 45% of RO pumping energy saved• 24,300kW across whole plant (at full capacity)
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Energy recovery – gravity head
• Main process plant at RL 52.0• Pumping energy penalty from static head• 50% of seawater returned to sea• Two Francis Turbines recover energy
from return pipes
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The result
• A hydro-power system generating 1,290kW at full production
• Generated power supplied directly to the intake pumps
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Permeate recovery
• Unique arrangement of RO racks• First pass racks split (front/rear)• Second pass front – 2 stage• Second pass rear – 2 stage• First pass reject to energy recovery• Second pass reject recycled
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Reverse Osmosis System
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Reverse Osmosis System
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Reverse Osmosis System
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The result
• All water passes through two membranes before transfer to remineralisation stage
• Only first pass reject is returned to sea (via energy recovery)
• Second pass reject is recycled saving pump energy
• Average permeate recovery rate is 48.6%High recovery means less water pumped for given output
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Other systems
• 200kW solar panel array• Variable speed drive main pumping systems • Efficient operation from 30ML/day to 300ML/day
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Specific energy consumption
• SA Government specified 4.5kWh/kLmaximum
• Calculated SEC (based on design data)3.6kWh/kL
• Measured SEC3.47-3.7kWh/kL
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ADP – Site remediation
Creek refurbishment
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ADP – Site remediation
Stormwater retention
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Impact on local community
• Landscaping shields the plant from outside view
• Noise measurements at site boundary rear residential zone show plant is barely audible
• No change to local traffic patterns• Construction phase of significant
benefit to local industries• Buildings blend with local
environment
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Where does the ADP get its power from?
• 20-year agreement with AGL to supply electricity
• 100% from renewable sources
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Cost to power the ADP
1-2 families
How much is 3.6kWh/kL?
1-2 families refrigerators
3.6kWh/day
1.0kL/day
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Cost to power the ADP
Boeing 747 66MW cruising Hydrocarbon fuelNo water
ADP45MWRenewable energyWater for 600,000 people
ADP peak power demand is 45MW at full production
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120Potable water production
The ADP produces 300ML per day
That’s 120 Olympic swimming pools OR…
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Potable water production
2 x 25ML storage tanks 66m diameter x 8m high, filled 6 times per day
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Environmental impact
Will the desalination plant cause the global salinity in the gulf to rise?
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Sustainable seawater desalination
• Climate independent, inexhaustible supply of drinking water
• Minimal impact on the marine, terrestrial or atmospheric environment
• Low energy consumption• Able to run at low capacity when not required• Minimal impact on local community• Positive impact (remediation) on the site• Powered from renewable energy source
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Adelaide Desalination Plant