8 Saline Water Conversion by Flash Evaporation Utilizing Solar Energy DONAT
B. BRICE
Department of Water Resources, State of California, Sacramento, Calif.
Downloaded by CORNELL UNIV on August 20, 2016 | http://pubs.acs.org Publication Date: January 1, 1963 | doi: 10.1021/ba-1963-0038.ch008
In the a p p l i c a t i o n of s o l a r e n e r g y to saline w a t e r c o n v e r s i o n , the c o m b i n a t i o n of a s o l a r heat c o l lector w i t h a process that is c a p a b l e of e n e r g y r e -use m a y
be economically more
direct s o l a r distillation.
attractive
than
A combination plant con-
sisting of a s o l a r heat collector a n d a
multistage
flash e v a p o r a t o r w a s d e s i g n e d to p r o d u c e 3 4 5 10
7
g a l l o n s of
water
annually
when
X
collecting
slightly m o r e t h a n 4 trillion B.t.u. of heat.
The
conversion economics w e r e b a s e d on the i n s o l a tion r e c e i v e d in Southern C a l i f o r n i a . lector a r e a w a s
A large col-
s e l e c t e d , so that the economics
would be representative for supplying a populous area.
The m a x i m u m plant output of 16,500,000
g a l l o n s p e r d a y occurred in J u l y .
The w a t e r p r o -
d u c e d w a s e s t i m a t e d to cost a p p r o x i m a t e l y $ 1 . 1 0 per thousand gallons.
|n applying solar energy to saline water conversion, the combination of a solar heat collector w i t h a process capable of energy re-use may be economically more attractive than direct solar distillation. T h e multistage flash evaporation process can utilize the relatively l o w temperature saline water produced i n a flat-plate solar heat collector more efficiently than most other conversion processes. A combination plant was designed to produce annually 345 X 1 0 gallons of water when collecting slightly more than 4 trillion B.t.u. of heat. A coastal location i n Southern California was assumed for the site of this combination plant; consequently, solar insolation and other meteorological data for that area were used i n making calculations for the solar heat collector. T h e results, however, should be generally applicable to other geographical areas, if corrections are applied for the amount of insolation received. The primary purpose of this study was to optimize the cost of water produced i n a multistage flash evaporator supplied b y brine heated i n a solar heat collector. It was therefore not possible to select both plant capacity and the solar collector area and still permit optimization. I n addition, the brine temperature limitation w o u l d be set b y an economic evaluation of the multistage flash 7
99
Saline Water Conversion—II Advances in Chemistry; American Chemical Society: Washington, DC, 1963.
Downloaded by CORNELL UNIV on August 20, 2016 | http://pubs.acs.org Publication Date: January 1, 1963 | doi: 10.1021/ba-1963-0038.ch008
100
ADVANCES
IN CHEMISTRY SERIES
evaporator and the solar heat collector. Evaporator capital and operating cost estimates from a previous study (4) were used extensively i n this evaluation. Because plant output varies w i t h the time of year, the monthly average of the insolation received at a site along the Southern California coast was used as a basis for calculation. W i t h this known, it was possible to determine the net heat that could be captured b y a solar heat collector w i t h a given number of glazing layers. T h e cost of installing the solar collector was estimated. Then, the relative cost of the solar energy on a monthly average basis for several selected brine temperatures could be determined and the plant could be optimized for a given assumed brine temperature and assumed stage terminal temperature difference i n the flash evaporator. It was first necessary to determine the approximate plant size. B y optimizing the water cost b y month for the minimum solar energy cost for several selected brine temperatures, it was possible to determine the point of m i n i m u m operating cost for the several assumed evaporator plant capacities, and to calculate the area of solar collector required for each condition. As expected, the optimization was heavily weighted i n terms of summer operation when insolation is at a maximum and for the higher brine temperatures when the plant output is relatively greater. Description of Process Figure 1 represents the general flow diagram of the multistage flash evaporation process and the solar heat collector system. T h e process conditions shown are typical for operation w i t h a brine temperature of 1 4 0 ° F . , as w o u l d be the case during M a y , June, and August.
t K K
r
r
\ \
V S O L A R HEAT C O L L E C T O R SINGLE COLLECTOR - 48'xB00' (1080 REO'D) TOTAL COLLECTOR AREA - 80S ACRES APPR. OVER-ALL DIMENSION SISO'x 8260*
MULTISTAGE F L A S H E V A P O R A T O R P L A N T (ONCE-THROU3H CYCLE, FLOWS TYP. FOR AUGUST)
PS
