Water desalination: status, technology, challenges, and potential Noam Lior Life Fellow ASME, Assoc. Fellow AIAA Editor-in-Chief, Advances in Water Desalination Board of Editors Member: Desalination, The International Journal of Desalting and Water Purification, Desalination and Water Treatment – Science and Engineering . The International Desalination & Water Reuse Quarterly, 1997-2003. Chair, Scientific Committee, International Centre for Sustainable Development of Energy, Water and Environment Systems Professor of Mechanical Engineering and Applied Mechanics University of Pennsylvania, Philadelphia, PA 19104, USA [email protected]http://www.seas.upenn.edu/~lior/ 1
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Water desalination:
status, technology,
challenges,
and potential Noam Lior
Life Fellow ASME, Assoc. Fellow AIAA Editor-in-Chief, Advances in Water Desalination
Board of Editors Member:
Desalination, The International Journal of Desalting and Water Purification,
Desalination and Water Treatment – Science and Engineering .
The International Desalination & Water Reuse Quarterly, 1997-2003.
Chair, Scientific Committee, International Centre for Sustainable Development of Energy, Water and Environment Systems
Professor of Mechanical Engineering and Applied Mechanics
Rising population, standards of living and water pollution are diminishing the amounts of naturally available fresh water of good quality while the demand is increasing relentlessly
"Manufactured water" or is making a considerable contribution to the world's potable, industrial, and agricultural water supply.
The technology is improving in cost-performance
and reliability
Desalination processes remain energy intensive and are polluting, needing strong and rapid development
It is increasingly recognized that desalination must be
performed sustainably 2
Noam Lior
The major desalination methods
Distillation (2/3 of market)
multistage flash (MSF; heat)
multi-effect (ME; heat)
vapor compression (VC; mechanical power)
Membrane distillation (MD; temperature (heat), under development)
Membrane Separation (1/3 of market)
Reverse Osmosis (RO, pressure)
Electrodialysis (ED, electrical potential)
Membrane distillation (MD, temperature (heat), under development)
Forward osmosis (FO, under development)
Ion exchange (IE, adsorption, for low salinity waters;
mechanical power)
Freezing (mechanical power and cooling) 3
Noam Lior
Some Desalination Statistics
~ 15,000 large plants
Largest plant (2009?): 880,000 m3/day + 900 MW electricity, Shuaiba III, Saudi Arabia.
A large dual purpose plant (1997): 341,000 m3/day (75 MIGD) multi-stage flash (MSF) Al Taweelah B in Abu Dhabi, United Arab Emirates; dual-purpose plant, produces also 732 MWe of power.
Producing ~65 million m3/d total, globally 0.6% of total or ~3% of municipal/domestic use, abstracted water
Internal: The extremely low price of the product, down to $0.5/ton
now
Corrosiveness of the saline water
Scaling (deposition of precipitates)
Organic fouling
Effect of gases
External: Environmental impact
Some health concerns (preventable) 11
Noam Lior
Desalination Plant
Security
Ingestion into the plant of contaminated saline water feed (oil spills, heavy metals, etc.) affect both product and plant
To avert consequences of poor regional management, accidents, war, and terrorism, it is vitally important to design the plant with robust safeguards against ingestion of undesirably
contaminated saline water
ensure that regional resources' management prevents such contamination
provide for adequate fresh water storage, and
provide adequate plant security.
Kuwait 1991
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Noam Lior
Dual-Purpose plants: synergetic
generation of power and desalination of water
The most economical large scale thermal water desalination systems are dual purpose plants that simultaneously produce electricity and typically MSF (Multi-Stage Flash distillation) seawater distillation.
The original dual purpose plants used a Rankine steam power plant for generating electricity, the turbine of which (having an inlet temperature 500-600 °C) was backpressure or extraction for supplying the heat to the desalination plant.
Higher efficiency and better economics were obtained in later generation systems using a topping gas turbine (inlet temperature ~1200 °C) with a bottoming back-pressure or extraction steam turbine in a combined cycle.
While the prevalent heat source for dual purpose plants is gas or oil, any heat source of sufficient temperature, such as solar, geothermal, nuclear or some type of “waste heat” can be used
RO water desalination plants are currently more efficient than thermal distillation ones, and they use electricity, not heat.
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Noam Lior
DESERTEC: An exciting
plan to solar-generate
electricity in Middle East
and North Africa (MENA)
and transmit it for use in
Europe and MENA, and
also desalt water for
MENA (originally
recommended by the Club
of Rome; from 2009 led by
DII GmbH, an association
of 12 companies,
predominantly German)
14 http://www.dlr.de/tt/trans-csp Noam Lior
ENVIRONMENTAL IMPACTS
All components of the water use cycle
should be considered
source water impacts,
the likely greenhouse and other polluting
gas emissions from the energy
requirements of the desalination process,
embodied materials emissions
potential impacts from concentrate
management approaches,
environmental health considerations in the
product water 15
Noam Lior
Practical energy demand of
desalination plants
R. Semiat, Energy Issues in Desalination Processes. Environmental Science & Technology, Vol. 42,
No. 22, 8193-8201, 2008.
Assuming ηt = 45%
tons of produced fresh waterGained Output Ratio = GOR =
ton of used heating steam
Dual purpose plants (thermal) consume (5.2 to 9.5 kWh exergy)/(m3 produced fresh water)
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Noam Lior
Price of
desalted
water Prices are site and
situation specific
depend much on
government
financing and
subsidies
Depend much on
cost of energy and
its strong
fluctuations
Proper payment for
externalities
In comparison,
municipal water
prices are between
0 and ~$4/m3,
usually < ~$1m3
SW RO SW MSF SW MED
Annualized capital
costs
0.15 0.29 0.22
Parts/maintenance 0.03 0.01 0.01
Chemicals 0.07 0.05 0.08
Labor 0.10 0.08 0.08
Membranes (life not
specified)
0.03 0.00 0.00
Thermal energy 0.00 0.27a 0.27a
Electrical energy
($0.05 k/Wh)
0.23 0.19 0.06
Total ($/m3) 0.61 0.89 0.72 a The costs of thermal energy are likely exaggerated because
offpeak electricity costs, cogeneration, or the use of waste
The new imperative: sustainable desalination The past goal was to produce water reliably at a low enough cost, where
the cost is unfortunately still in many cases based primarily on capital investment in the plant, operating costs for energy, materials and labor, and profit if a private company produces the water.
Desalination based on this approach has recently come under strong criticisms for being unsustainable, and for creating long-term problems which are not considered in the costing and the choice of the entire process, e.g.: Unrealistically low pricing of the energy, as done in many oil-rich countries
Unrealistically low pricing of the water, as done in many countries
Little care of the effluents, which contain highly concentrated seawater (also warm in distillation plants) that may have even far-reaching effects on oceans, various additives that are harmful to the environment and health, heavy metals, as well as the driving power plant emissions
Damage to the eco-system at the plant intake
Desalination allows the development of new regions, which may be unsustainable to begin with.
Legislation already exists in some places about restricting/penalizing such unsustainable attributes, and is likely to results in at least a real added cost (but that is insufficient because the cost is in captive markets likely to simply be passed along to the customer while the abuse continues).
There is urgent need to implement well-analyzed sustainable desalination; also an opportunity to introduce new processes and products to that end.
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Noam Lior
Conclusions, Recommendations,
and Predictions (1/2)
Desalination is vitally important for water-stressed regions that
can not import fresh water and is an important supplement
elsewhere
In reverse osmosis the energy demand has remarkably been
reduced close to the thermodynamic limits, and innovations in
distillation process are leading to lower energy demand
Important goals for desalination in general:
Water cost reduction: reduce plant, supplies and externalities costs and
increase energy efficiency
robustness improvement
developing lower cost, higher life and less polluting materials
understanding the environmental impacts of desalination and developing
approaches to minimize these impacts relative to other water supply
Developing and adopting a rigorous overall sustainable
development approach, including water conservation consideration
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Noam Lior
Conclusions, Recommendations,
and Predictions (2/2)
Membrane processes should be improved by mitigating fouling through pretreatment;
developing high-permeability, fouling-resistant, high-rejection, oxidant-resistant, longer life membranes
Distillation processes can be improved by preventing scale deposition at higher temperatures,
better energy regeneration
higher transport coefficients.
Environmental and social impacts must be understood, recognized, and significantly mitigated
R&D is extremely deficient and governments must invest since the industry has shown little interest