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LEGAL NOTICE
This report was prepared as an account of
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the use of any information, apparatus,
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his employment with such contractor.
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م 1 زمین
/ - / ا
JUN 1 7 10
AN ASSESSMENT OF CERTAIN AVENUES OF IMPROVEMENT
FOR NUCLEAR DESALINATION TECHNOLOGY
MASTER
by
R. Philip Hammond
Remarks prepared for the
International Atomic Energy Agency
Panel on Use of Nuclear Energy in
Saline Water Conversion
April 27-30, 1964
Vienna, Austria

Facsimile Prices Tela
Microfilm Price s 8 2
Available from the
Office of Technical Services
Deportment of Commerce
Washington 25, D. C.

OAK RIDGE NATIONAL LABORATORY
Oak Ridge, Tennessee
operated by
UNION CARBIDE CORPORATION
for the
U.S. ATOMIC ENERGY COMMISSION
NOT FOR PUBLIC RELEASE OFFICIAL
DISTRIBUTION DAY BE MADE HERACIAL
Bob OUES MAY BE REPORT
CONTAINS MOTH:NG ON PATENT INTEREST.
PROCEDURES ON FILE IN RECEIVINE
SECTION,
AN ASSESSMENT OF CERTAIN AVENUES OF IMPROVEMENT
FOR NUCLEAR DESAL-INATION TECHNOLOGY*
by
R. Philip Hammond
Oak Ridge National Laboratory
Oak Ridge, Tennessee
From the questions which have been asked, I gather that I am
expected to bring you the news of the latest exciting developments
in desalination at the Oak Ridge National Laboratory. However, the
agenda for this meeting does not include reports of unfinished in-
vestigations; moreover, although there are some new ideas afoot at
Oak Ridge, they are aimed toward the very large stations which are
somewhat beyond the scope of the more current interests represented
here. So instead of presenting new developments, I would like today
to talk about where to look for them--to give you some purely analytical
considerations that assess the incentives we have to seek certain im-
provements in this or that portion of the equipment in a dual-purpose
station.
As a preface, may I say that, to me, the most exciting recent
development is the fact that there is sufficient interest and confidence
in nuclear desalting to permit this meeting to be held at all. Only
two years ago I am sure that very few would have considered this topic
worth while, and yet there bas really been no new technical element
except the concept of size. Perhaps we should all take time to realize
that for ordinary-sized plants not much has changed. True, reactor tech-
nology has advanced, the Office of Saline Water has some important
operating data from its demonstration plants, and Oak Ridge has shown
some benefits from better packaging and larger unit sizes, but basically
the technical situation is unchanged from a couple of years ago. At
that time we would have found artificial desalination of sea water in
*Research sponsored by the U. S. Atomic Energy Commission under
contract with the Union Carbide Corporation.
*on loan to Oak Ridge National Laboratory from Los Alamos Scientific
Laboratory, Los Alamos, New Mexico.
small units a marginally useful way to get water. I think we should
all accept the obvious fact that this is stiu true--most water needs
for a time will be best solved by other means, and nuclear desalination,
however glamorous it may sound, will simply not fit. In only a rela-
tively few unusual cases will we find the combination of circumstances
that will justify this new method of water supply which is our subject
here. I do not think that this will be true for very many years,
because I anticipate rapid technological. progress once a few plants are
operating, but at first we will have to rely on every means we can find--
subsidy, large size, special financing, etc.--and still we will find
only a few high-cost areas which can support the first plants we will
build. In a way the situation is similar to that of a jet aircraft,
which is uneconomical and inefficient in small sizes, at low speed and
low altitude. Somehow we must claw our way up through the small sizes
and immature technology of the present to the payoff region; then we
can expect rapid progress through normal commercial incentives, and
both large and small plants will become much cheaper and applicable to
& broad scope of water-supply problems. It is my object today to
mention a few of the areas where such progress may be anticipated.
Dr. Minken has pointed out very vividly the need for consideration
of each plant in its individual environment, with all of its products
and byproducts and their marketing taken together. I concur entirely
in his plea, for such matters as base load and peak load, financing
practice, social and political problems are extremely important, even
determinative, yet they cannot be resolved after a plant is designed.
They are entirely determined by the customer.-by the unique needs of
each situation, and hence must be provided first as input to the design
and optimization of the plant.
Dr. Eshaya bas noted that these input parameters are not the function
of the engineer, but once they are settled upon or taken as arbitrary
variables the rest of the problem--the design of the plant equipment
itself--can be put in a form capable of a wnique engineering solution.
In other words, once the market, financing, and ratio of products
needed are determined, one can present the problem to the engineer,
3
saying, "Here is a black box, out of which flows a certain quantity of
water and a certain quantity of power, and fulfilling these other con-
ditions. Find the best plant to put inside the black box." The rest
of my remarks will be directed toward certain small facets of solving
the problem of the black box.
Consider first the selection of a heat source for an evaporator
plant. If the given parameters dictate that the black box produce
water only, the solution is easy: the cost (s) of a unit of prime
steari must be minimized. If the plant is to produce power only, the
quantity which must be minimized is s/€, where s is steam cost and €
is thermal efficiency. Between these two extremes we have a dual-
purpose plant. What is the optimum condition in this case?
Let us attack this problem by locking first at a 1000-Mw reactor
supplying steam to a power-only plant. Perhaps 330 Mw leaves the
of 100 Mwe to the turbine, we must add about 300 MW to the reactor
capacity and 200 Mw to the heat dum capacity. If the same reactor is
supplying steam directly by throttling to an evaporator, let us see
what happens if we interpose a small noncondensing turbine into the
steam flow and extract 100 Mw of electric power. To accomplish this
without decreasing water output, we must add about 103 Mw to the reactor
capacity. In other words, the effective efficiency of adding electric
output is nearly 100%. Other things being equal, then, we can conclude
that, in a dual-purpose plant, power cost is independent of steam quality
and that both power and water cost are minimized by selecting the heat
conclusion has limits to its validity--it holds only over the range
where the evaporator can receive exhaust steam at the maximum acceptable
temperature and where the resulting ratio of water to power is acceptable.
A more rigorous analysis shows that, although other effects enter in,
prime steam cost is in fact the most important single factor in choice
of reactor for dual-purpose plants over the runge of temperatures and
outputs of most interest.
Turning now to an entirely different problem, let us see what
happens to the black box as we assign different values to the product
ratio, the heat source and steam quality having been fixed. In this
analysis, I shall discuss product ratio in units of millions of gallons
per day of water capacity per megawatt of electric capacity (mga/Mwe)
and assign this ratio the symbol w. Thus, for a power-only plant w = 0,
and for a water-only plant, it would be c.
For the dual-purpose plants of greatest interest, w lies between
0.5 and 1. If multiplied by 41.7, w is converted to gallons per kilowatt-
hour (electric), which is the other form in which product ratio is some-
times expressed.
The first portion of the problem can now be stated as follows:
From a given reactor producing a fixed quality of steam at a given cost,
what is the optimum cross-over temperature (temperature at which steam
exhausts from the turbine and enters the evaporator), and how does this
optimum change with different assigned values of w? We can also ask,
how does the cost of the products vary with w? In particular, we would
like to assess what our incentive is to develop evaporators capable of
higher brine temperatures.
In this study the lower evaporator heat-transfer coefficients and
decreased temperature differences for heat transfer which result at
lower cross-over temperatures were taken into account. Changes in
overall plant pumping power with performance ratio and product ratio
were neglected, as was the effect of plant capacity on unit construction
cost. The former omission is a minor effect, the latter is discussed
separately from the other effects studied here. The study was made
with three different assumptions as to the cost of prime steam: 28,
14, and 7€ per 100 Btu. The 284 figure represents the approximate
cost of steam under municipal financing for a commercially available
reactor such as Oyster Creek; the other figures represent varying degrees
of advance in reactor technology and size but with the same saturated
steam quality (600 psia). Three different evaporator technologies were
also included, representing approximately the single-level flash plant
design by Bechtel Corporation for the Office of Saline Water, a larger
multi-level flash design by Oak Ridge, and a hypothetical advanced evapo-
rator ci the vertical type. (Not all of the nine combinations of these
were included.) Municipal-type financing was assumed. The cross-over
temperatures included ranged from about 130°F to over 330°F. The high-
est demonstrated temperature today 13 250°F in the Point Loma Demonstration
Plant of the office of Saline Water, but in this analysis it was assumed
that higher temperatures could be reached without penalty in construction
cost or operating experience.
Figure I shows the optimum cross-over temperature versus product
ratio for four of the cases. The curve on the right represents the high-
est steam and evaporator cost. An improvement in evaporator technology
tends to lower the optimum cross-over temperature, while reduction in
steam cost has the opposite effect. Figure 2 is corollary to Fig. 1,
giving the e-timum performance ratio, R, versus the turbine exhaust
temperature. This relation is nearly linear.
In Fig. 3 the value of power is taken at a constant (non-subsidy)
of the assigned product ratio, W. Within the acc'ıracy of the work, there
is a constant cost of water for the whole range of product ratios. The
cost level is shifted downward by improvements in either steam cost or
evaporator technology, but there is no preference for either high or low
cross-over temperatures. The conclusion is that within the limits of
feasible operation, the product ratio can be assigned arbitrarily without
affecting the cost of water. There seems to be no incentive to develop
high-temperature evaporators, except to permit higher values of W. Let
us examine this conclusion in the light of other factors. The evaporator
was assumed to cost no more to construct or operate at high temperatures
than at low temperatures. This cannot be strictly true, so that if
there is a preference, it is for a low-temperature evaporator. Also,
at low w, the reactor is larger for a given water ouiput, and would
thus have a lower unit cost. This effect also would tend to favor low
cross-over temperatures, provided the product ratio falls in the range
which can be assimilated.
Finally, the effect of power subsidy should be included, since it
prices. Figure 4 shows the effect on water costs of a l-mill subsidy
from electric power. (The dotted line shows the unsubsidized cost.)
Naturally, as w approacies zero, the subsidy per kilogallon of water
becordes very large, so that once again there is preference for the
lower temperatures and lower values of product ratio. In applying
these conclusions to actual cases, it appears that one should seek
to use the lowest value of w that can be justified. Research leading
to nigher feasible operating torperatures for evaporators should not
be expected to lower water costs, except for water-only plants
(infinite w), but such efforts are justified in making possible higher
product ratios without penalty, so that a wider range of local situ-
ations can be suited.
The results of the study also emphasize the obvious fact that
lower cost steam supply and evaporacor equipment lead to markeäly
lower water costs.
In conclusion, I have two other small comments to offer about
fruitful areas for future development. One of these concerns water-
only plants. Since most reactors turn out their cheapest steam at a
fairly high temperature, and since sea water evaporators are presently
limited to fairly low brine temperatures, there is a severe mismatch.
One alternative to a successful program to develop high-temperature
evaporators would be to employ vapor-compression evaporators. Instead
of driving the vapor compressor with purchased electric power, however,
it could be driven directly with a nonconuensing steam turbine using
the high-temperature reactor steam. The exhaust from the turbine could
be used in an evaporator as in a dual-purpose plant. In a brief pre-
liminary look at this, it appeared that about 60% of the plant out-
put would come from the vapor-compressor evaporator, and the balance
from the exhaust-steam evaporator. With presently foreseeable com-
pressor fans, the water would cost about 5€ per 1000 gallons higher
than that for a dual-purpose plant under the same conditions.
Tae other comment has to do with the buildings required for a
dual-purpose nuclear station. As is well known, reactors are at pres-
ent built into pressure-tight enclosures for safety reasons. Evaporators
are also housed in pressure-tight shells to exclude the atmosphere.
There seems to be no operating reason for not constructing one large
shell to contain both. The cost savings would be substantial, and
various experts in reactor safety have concluded that safety would
be enhanced.
UNCLASSIFIED
ORNL DWG 64-4320
28-8
1A-OR
7-OR
7-A
OPTIMUM TURBINE EXHAUST TEMP., °F

0.4
0.8
1.2
1.6
PRODUCT RATIO w (Mgd/Mwe)
ORNL DWG. 64-4324

28-OR
14-OR
7-A
OPTIMUM PERFORMANCE RATIO
7-OR
150
200
250
300
TURBINE EXHAUST TEMPERATURE, °F
UNCLASSIFIED
ORNL DWG. 64-4322

28-B
HHHH
28-OR
-14-OR
COST OF WATER, &/1000 gol
7-OR (6 +12)
7-A
O
0.2
1.6
1.8
0.4 0.6 0.8 1.0 1.2 1.4
PRODUCT RATIO W (Mgd/Mwe)
UNCLASSIFIED
ORNL DWG. 64-432 1

er
28-OR-
} 14-OR
PRICE OF WATER
(1 mill POWER SUBSIDY) ¢/1000 gal
7-OR
So
0.8
1.6
0.4
1.2
PRODUCT RATIO W (Mgd/Mwe)
.
END



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