OSW Test Bed 
Webster, South 
Dakota, 1962 
250,000 gpd 
Electrodialysis 
OSW Mobile Pilot 
Plants 
Advanced Processes as 
lon Exchange 
vapor in a successive series of flash chambers, each 
at a lower temperature and pressure. The flashed 
vapor is condensed by the circulating sea water 
and is collected. A final condenser, using addi- 
tional cooling sea water, maintains the final 
vacuum.?? 
The advantages of this flash method are as 
follows:*° 
—It has been demonstrated satisfactorily in several 
moderate-size plants throughout the world. 
—The equipment configuration and process flow 
are relatively simple. 
—Scale control by acid injection is within present 
technology. 
An OSW demonstration plant was built in San 
Diego in 1962 rated at one million gallons per day. 
It subsequently was transferred to the Guan- 
tanamo Bay Naval Base in Cuba in 1964 and was 
expanded by the Navy to produce 2.1 mgd; it still 
is operating on a day-to-day basis to provide the 
total water requirements of the base. 
b. Multiple-Effect, Falling-Film Multiple-effect, 
falling-film distillation, sometimes referred to as 
vertical tube evaporation, has been used success- 
fully to produce fresh water from sea water in the 
Office of Saline Water Test Facility at Freeport, 
Texas. Sea water is evaporated from a thin film on 
the interior periphery of an evaporator in a series 
of effects. Heat released by the condensation of 
vapor from a previous effect is used to vaporize 
the water, and the condensed vapor is collected as 
the plant product. A large distillation plant now 
under construction in the Virgin Islands will use 
multiple-effect, falling-film distillation. 
3°Mcllhenny, W.F., “Chemicals from Sea Water,” 
Proceedings of the Inter-American Conference on Mate- 
rials Technology, May 1968, p. 125. 
+ Ddorter, J.W., “Water Desalination by Distillation,” 
Ocean Industry, Vol. 2, No. 8: 39-45, 39, August 1967. 
VI-204 
Although somewhat costlier, the process has 
the following important advantages over the multi- 
stage flash concept: 
—Less pumping power required. 
—Less inherent temperature losses. 
—Fewer stages or effects required. 
—The hottest brine is generally more dilute, an 
advantage in scale control. 
—A smaller volume of sea water handled. 
It is anticipated that this technique will be used 
with increasing frequency in the future. 
c. Multiple-Effect, Multiple-Stage Both multiple- 
stage flash and multiple-effect processes have 
certain advantages; some designers now are consid- 
ering various combinations of the two. One is the 
multiple-effect, multiple-stage concept. In this 
design, several stages of a conventional multistage 
plant are grouped into one effect to provide the 
heat input for another group of stages or effects. 
Principal advantages are: (1) It approaches the 
generally more efficient multiple-effect concept 
while retaining most of the structurally simple 
features of the multistage flash design, and (2) the 
brine concentration at the hot end of the plant 
normally approximates that of sea water rather 
than being the double concentrated sea water 
often used in multistage flash plants. 
The Clair Engle OSW Demonstration Facility 
(Figure 64) completed in 1967 uses this technique. 
Figure 64. San Diego saline water test facility, 
Clair Engle Plant. The one-million-gallon-per- 
day desalting plant tests advanced design multi- 
effect, multi-stage flash distillation sea water 
conversion process. (Office of Saline Water 
photo) 
