In general, where we now have concentration 
ratios of two, Studies indicate that we begin to 
have economic potential if we reach concentration 
ratios of about 5 to 7. The principal chemicals in 
which we are interested are phosphates, chlorine, 
bromine, sodium, and magnesium. 
As a result of continued research in this area, it 
has been demonstrated that it is feasible to raise 
concentration ratios to around four to five. 
e. Long-Range Estimates Long-range estimates 
indicate that by the year 2000 world desalting 
production should be about 30 billion gpd com- 
pared to about 0.10 billion gpd today.** This 
long-range forecast is significant in stating the 
unquestioned need for at least this much addi- 
tional fresh water above and beyond the natural 
supply. The 30 billion gpd capacity, while seem- 
ingly large, is about eight per cent of US. 
domestic consumption today and presumably less 
than one per cent of present world consumption. 
It is within our technical and financial abilities to 
build and put into operation 30 billion gpd 
capacity by the year 2000. An overriding need for 
water suggests that the long-range forecast is 
perhaps conservative. 
B. Techniques of Desalination 
1. Classification 
Figure 63 shows a listing of various major 
techniques of desalination. The processes can be 
divided into four broad categories: distillation, 
crystallization, membranes, and advanced pro- 
cesses in initial development. 
2. Distillation 
a. Multiple-Stage Flash Almost all large desalina- 
tion units now in operation or under construction 
use multiple-stage flash distillation. Incoming sea 
water and recirculated brine are preheated by the 
condensation of product water in a series of stages 
at consecutively higher temperatures. The heated 
sea water is elevated to the maximum operating 
temperature by condensing steam from an external 
source. The hot sea water is allowed to flash to 
38 Water Desalination Report, Vol. IV, No. 1, Jan. 4, 
1968, p. 4. 
Figure 63 
CLASSIFICATION OF DESALTING 
TECHNIQUES 
Distillation 
Submerged Tube 
Film 
Climbing Film 
Multiple Effect 
Falling Film 
Example: Long 
Tube Vertical 
Evaporation 
(LTV) 
Flash 
Single Effect 
Multiple Stage 
Flash (SEMS) 
Combination of film 
and flash 
Example: Multiple 
Effect-Multi-Stage 
Flash (MEMS) 
Vapor Compression 
Crystallization 
Direct or Vacuum 
Freezing 
Secondary Refrig- 
erant Freezing 
Hydrate 
Membranes 
Reverse Osmosis 
Examples 
Ships, Offshore 
Platforms 
Submarines 
OSW Test Bed 
Freeport, Texas, 1961 
1 mgd 
OSW Test Bed 
San Diego, California, 
1962 
1 mgd (36 stages) 
Later transferred to 
Guantanamo Bay 
OSW Test Bed 
(Clair Engle), 
San Diego, California, 
1967, 1 mgd 
OSW Test Bed 
Roswell, New Mexico, 
1963, 1 mgd 
Eilath, Israel, 1963 
240,000 gpd; OSW Pilot 
Plant, North Carolina, 
120,000 gpd 
OSW Pilot Plant, North 
Carolina, 15,000 gpd 
OSW Pilot Plant 
North Carolina 
OSW Pilot Plants: 
Colorado, New 
Mexico, 50,000 gpd 
(Continued on following page) 
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