WSP00132

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications-Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1980
• Title: Use of Saline Water in Energy Development
• Water Supply Pro - Doc Type: Report/Study

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Feasibility of UaloR Saline Water
---- for Power Plant Cooling
L~]_~r ad uc t ion

A large coal-fired electric generating
plant is truly a staggeringly complex multi-
billion dollar technological marvel requiring
,;I vast aggre~ate of technical expertise to
put it together and make it run. In spite of
the practical complexities the basic princi-
ples of converting coal into kilowatts are
quite sJ.mple. Depicted in Figure 14 is a
f'chematl,c of the epsential elements of a
plant based on the Rankine power cycle. The
working fluid circulates at high pressure
through the boiler where energy is added as
high iemp~tature heat. Leaving the boiler as
a Rurer-heated vapor at high pressure,
the luld expands across the turbine which
drives the generator to emerge as a very low
pressure vapor. This low pressure vapor is
then condensed again to a liquid to be pumped
back up to a high pressure thus completing
the cycle. It is in the condenser that
immense quantities of heat must be rejected
from the power cycle working fluid to a
cooling fluid, usually water. In turn the
heat Ls then rejected to the atmosphere.

Cooling towers are often employed to
enhance the transfer of heat to the atmo-
sphere and permit recycling of the cooling
water. Indicated in Figure 15 are typical
[low rates in the conventional cooling water
l.oop of a power plant producing 1,000
MWe. The makeup water must be provided from
an external source. The blowdown wRter
contains all of the minerals entering with
the makeup water except for small quantities
of salt escaping with cooling tower drift.
Under the total containment philosophy the
blowdown water, in which are concentrated the
Incoming minerals, is not allowed to return
to any waterway and must be disposed of in an

environmentally acceptable manner. It
follows that high quality water with low
concentrations of minerals and ions is
preferable to brackish or saline waters for
power plant cooling au many accounts.
However, under circumstances where fresh
water supplies are l.imited and the pos-
Sibility of using brackish or saline water
exists, the feasibility of doing so should be
closely examined. Power plants recently
built along the East Coast such as Chalk
Point (Washington, D.C.), Turkey Point
(Florida), and Forked River (New Jersey) use
brackish water or seawater directly, ranging
from 7,800 mg/l TDS to 45,000 mg/l TDS before
blowdown, and difficulties they may have
encountered should be studied. Planners
contemplating power plant cooling with saline
water are faced with a variety of questions
such as:

1. What technologies are available for
treating saline water?

2. What are the relative costs of
inlplementin~ various water treatment tech-

nologies? In other words, what are the
relative values of water of various salinity
concentrations used for power plant cooling?

3. Under the total containment phi-
losophy, what are the disposal implications
of using saline waters for cooling? Is
evaporation of brine waters the best option?
How: do evaporative brine ponds perform as a
function of salinity, humidity, solar insols-
t ion, and air temperature?

4,
systems
not ion?

Is mineral recovery from coolin~
using saline makeup water a viable

5, Could reduced fresh water supplies
be effectively supplemented by lower quality
waters in conventional systems under drought
conditions?

6. What are the relative merits of
spray ponds or cooling ponds as opposed to
coolin?, towers where only lower quality
ma~eup water is available?

7. Does dry cooling become preferable
to wet cooling at certain salinity concentra-
tion levels of makeup water and if so, what
are those threshold levels?

The answers to these questions depend In.
part on the particular ions and minerals
making up the salinity. Since this study
could not look at all possible combinations,
the w,ide variety of water chemistries which
might be encountered in the geographical
study area was represented by obtaining
analyses of typical waters from the region.
The particular analyses used are shown in
Table 6. The broad implications of using
these kinds of waters in conventional power
plant cooling are examined. The study has
not considered the option of using saline
groundwaters in a once-through cooling mode
because of the immense quantities of water
that would require.

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Figure 14. Rankine cycle power plant.

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