WSP00451

• File Number: 8273.100
• Description: Colorado River Basin Salinity Control - Federal Agency Reports - BOR
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 11/1/1969
• Title: Cost Analysis of Six Water Desalting Processes
• Water Supply Pro - Doc Type: Report/Study

each stage, brine depth, demisterdesign and placement, condenser tube
spacing, and removal of noncondensables from within the tube bundles.

To operate correctly, each chamber must be in a delicate thermal, fluid

dynamic, and vapor-flow balance. New chamber designs may reduce water
~
~ costs by increasing the ratio of production capacity to capital investment,

eft
~ Seawater represents a very seVere environment for most materials,

and considerable effort is now directed toward the evaluation of con-

struction materials. The problem is one of balancing plant life, ca-

pacity factor, maintenance costs, and capital charges for the lowest

water cost. Experience indicates that metal corrosion of pumps and the

evaporator shell can be a considerable problem. Some of the important

variables in materials selection are: temperature, oxygen level, liquid

velocity, and brine concentration, An additional problem is the time

required to develop accurate corrosion data. A number of lower cost con-

struction materials have been considered, such as prestressed concrete

for the evaporator shell. Present information indicates that the concrete

is leached by the product water and will have to be protected with a

coating. On the other hand, exposure results with concrete have been good
in hot brines below 250oF. The savings that would result from concrete
shell is estimated to be l~/kgal; however, future increases in field con-
struction costs may reduce this savings.

Consideration has been given to increasing the MSF thermal efficiency
by increasing the maximum brine temperature above 250oF. For example,
it has been estimated that with a 30~/106 Btu steam cost, a thermal savings
of 5~/k gal would result from increasing the brine temperature to 350oF.

This savings of course must be balanced against the additional pretreat-

ment of the seawater to prevent scaling, and no economic pretreatment
to permit operation up to 3500F has been found to date, As was mentioned

previously, a higher brine temperature is also possible when using the
MEMS design, and that approach is now being investigated.

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