Middle East Desalination

Huntington Beach Proposal

Sources Cited

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Multi-stage Flash

Steam condenses on pipes carrying seawater through a brine heater.

History

Built commercially since the 1950's

The last 10 years have brought improvements because of:

• daily attention to operation

• better training of operators

• automation of controls

• new materials

• anti-scaling research funding

Plant size increases have brought more efficiency to the process

Mechanism

Condensed water heats incoming seawater in a brine heater as it enters the system.  It is then passed on to a series of stages.  Successively lower ambient pressure in the stages causes the seawater to instantaneously boil as soon as it enters without reheating each time.  Incoming seawater cools the vapor on heat exchange pipes and the cycle continues.

Efficiency increases with operation temperature as does detrimental scale formation

     ---scaling is mostly exhibited by calcium sulfate buildup

Plants typically have between 15 and 25 stages

Plant volume can vary between 1 and 15 million gallons per day

Brine heater runs between 70 and 90 degrees Celsius.

image source:http://www.iwra.siu.edu/win/win2000/win03-00/semiat.pdf

Benefits

1) a low operating cost when waste heat is used for the distillation process

2) the quality of the feedwater is not as important when compared with the reverse osmosis system technology 

3) the multi-stage flash system has a high gain output ratio (GOR):
  that is, the ratio of pounds of water produced to pounds of steam condensed in the brine heater

Cons

1) high operating cost when waste heat is not available for the distillation process

2) relatively high rates of corrosion and scale formation due to high operating temperatures

National Science Foundation: Office of Polar Programs. "Sea water desalination system, McMurdo" 1993.

http://www.nsf.gov/pubs/stis1993/opp93104/opp93104.txt

Sources

Buros, O.K. "The ABC's of Desalting" Second Ed. Topsfield, MA  http://www.idadesal.org/ABCs1.pdf

National Science Foundation: Office of Polar Programs. "Sea water desalination system, McMurdo" 1993.

http://www.nsf.gov/pubs/stis1993/opp93104/opp93104.txt

UNEP - International Environmental Technology Centre. United Nations Environment Programme. "Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean" 1997.