-------
CONTROL
PROCESS CHANGES
Increased Efficiencies
The adage about prevention and cure applies as well to waste
heat as to anything else. Reduction of waste heat production is
desirable for two reasons: 1) less waste of expensive energy, and
2) fewer problems with or after disposal. Upgrading the efficiency
of operations which produce heat as a by-product is, therefore, a
logical starting point when considering control of thermal pollu-
tion.
Efficiency gains in fossil-fueled, steam-electric stations
have reduced their waste heat discharge rate by approximately one-
half over the past 30 years (Table 3). Such gains have been accom-
plished through a number of refinements in the plant itself and in
operating conditions. Figure 2 presents a schematic diagram of the
basic components of a fossil-fueled steam-electric plant which may
be referred to for a better understanding of plant operation and
efficiency.
The basic steam plant cycle is as follows: the steam drum
furnace combination turns water into high-pressure steam, which
is carried to the turbines at a speed of about 200 miles per hour.
Within l/30th of a second the steam rushes through the turbines,
-------OCR error (C:\Conversion\JobRoot\00000A2W\tiff\2000U49E.tif): Saving image to "C:\Conversion\JobRoot\00000A2W\tiff\2000U49E.T$F.T$F" failed.
-------
53
traveling through a series of stationary nozzles and revolving
buckets which spin the turbine rotor and connected generator shaft
at either 1800 or 3600 revolutions per minute.
Drastic changes occur in the steam as it releases its energy
to the rotating buckets. Steam may enter the turbines at tempera-
tures of over 1000°F and leave at less than 100°F. It enters at a
pressure of 2000 or more psi, expands to a thousand times its en-
trance volume, and leaves at a pressure less than atmospheric.
From the turbine exhaust the expanded, low-pressure steam goes
to the condenser, where it is cooled until it condenses to water.
The process reduces the volume of the steam by a factor of 27,000
in a near-perfect vacuum, thereby returning it to a state in which
it can be easily handled. The water is returned to the boiler
through the feedwater heaters to be used over and over again as the
cycle continues endlessly.
As the cycle repeats, it is necessary to continuously remove
from the condenser an amount of heat equal to that given up in
converting exhaust steam into water. Plant and operational refine-
ments reduce the amount of heat entrained in exhaust steam which,
in effect, increases the overall plant thermal efficiency. Reduc-
tion of exhaust heat is attained through several methods (44):
1) Increasing steam pressure—Elevating the steam pressure at
the turbine entrance reduces exhaust heat by varying increments,
but in general a 100 psi pressure increase will reduce exhaust heat
-------
54
per unit of electricity by 0.4%.
2) Superheating steam—Steam generated in the boiler is heat-
ed even more in a superheat section of the furnace. Each 50°F ad-
ditional temperature rise reduces exhaust heat per unit of electri-
city by about 1.4%.
3) Reheating steam--After the steam has passed through the
high-pressure turbine section it is returned to the furnace reheat
section to absorb additional heat energy. Again, each 50°F increase
here reduces exhaust heat per unit of electricity by about 1.4%.
4) Boiler feedwater heating--A portion of the steam is with-
drawn before it reaches the final turbine exhaust, thereby eliminat-
ing its passage through the condenser. This steam is utilized to
increase the temperature of water entering the boiler. Feedwater
heating can reduce exhaust heat up to 37% per unit of electricity,
depending on the number of heaters used.
5) Reducing exhaust pressure—The pressure in the condenser is
transmitted to the turbine exhaust, i.e., turbine backpressure.
This pressure influences heat rejection to the extent that each 1
psi reduction in pressure reduces exhaust heat per unit of electri-
city by 2.5%.
Modern power plants are designed to make use of these effi-
ciency refinements as much as possible. Through such techniques,
new fossil-fueled plants attain efficiencies near 40%; nuclear-fueled
plants about 33%.
-------
55
Nuclear-fueled plants are inherently less efficient than
fossil-fueled plants even though they too utilize the basic steam
cycle to spin turbines and generate power. The major factor in
the efficiency limitation is that imposed through reduced operat-
ing temperatures. Technological difficulties make it impractical,
uneconomical, or unsafe to produce high-pressure, superheated steam
in a water-cooled reactor system. Whereas modern fossil-fueled
plants utilize steam at temperatures near 1050 F and pressures over
3000 psi, nuclear-fueled reactors of the boiling water or pressur-
ized water types produce steam at about 600 F and about 1000 psi
or 2000 psi, respectively.
Lower temperatures and pressures imply less energy content per
unit volume of steam. Hence, nuclear-fueled plants, compared to
fossil-fueled plants, require larger turbines and condensers for a
given generating capacity in order to compensate for the lower
quality of steam used.
The principal advantage of nuclear fuel is its tremendous energy
density. One ton of uranium has the energy potential of three mil-
lion tons of coal. Present-day reactors convert only about 0.5%
of this energy to usable heat, i.e., combustion efficiency is 0.5%.
Advanced reactor design, i.e., breeder types, will convert much
more energy into a useful form (66). However, while advanced de-
signs will improve fuel consumption, they will not necessarily in-
crease the thermal efficiency to reduce waste heat in steam-electric
-------
56
plant operation.
Reduction of waste heat output from nuclear plants will de-
pend on development of advanced converters which will allow higher
operating temperatures. Such converters will employ a reactor
coolant other than water in the primary flow loop, which circulates
fluid through the reactor core for heat absorbtion. The heat is
then transferred to steam through a heat exchange process in a steam
generator. Systems of this type, still in developmental stages,
are using fluids such as helium, liquid sodium or liquid potassium
for coolants. Reactor outlet temperatures of over 1000°F are pos-
sible.
Because of the vast energy stores in nuclear fuel, its utili-
zation for power production is inevitable. For the next 15 to 20
years, the number of plants in the 30% efficiency class will in-
crease rapidly, which indicates that more efficient systems will
surely lag behind our demands for power. This being the case, our
immediate efforts must focus on waste heat utilization and dissi-
pation while technology is being developed for more efficient power
production methods.
N_ew_Methp_ds_
Gas turbines offer a means of power production without cool-
ing water. Air is taken from the atmosphere, compressed, and sub-
sequently burned with a liquid or gaseous fuel. The resulting
-------
57
high-temperature, high-pressure gases expand through a power tur-
bine and then exit to the atmosphere.
Today's gas turbine efficiencies of less than 25% are not
competitive for power production on a large scale, although some
relatively small turbines are being used for standby and peaking
operation. Future development may achieve higher operating tem-
peratures and increased air flow, which in turn would increase
efficiency to a level near that of fossil-fueled steam plants.
Heat exhausted from gas turbines might possibly be put to use
in a conventional steam-electric plant. Such a combination would
reduce the waste heat discharge rate, although cooling water would
still be used.
Other systems currently under development may offer promise
for future bulk power generation without the need for cooling water.
Two systems receiving much attention lately are fuel cells and
magnetohydrodynamics (MHD), which would convert heat energy directly
into electrical energy (38).
Fuel cells are somewhat similar to conventional storage bat-
teries in that they consist of two electrodes separated by an
electrolyte. The fuel cell does not contain a store of energy; it
generates current as long as fuel and oxidant supply chemical energy
for conversion to electricity.
Individual fuel cells produce very small quantities of power.
Hence, thousands of cells would have to be connected in groups
-------
58
to increase power output to a level which would permit large-
scale production. Predicted eventual efficiencies of 50 to 85%
is a further attribute of the fuel cell system. A prototype and
larger scale central station fuel cell plant are being developed
by Westinghouse under a contract from the Office of Coal Research,
Department of the Interior. Target dates for construction of the
two plants are 1969 and 1973, respectively (38).
MHD generators utilize the principle of passing a conductor
through a magnetic field to produce current. In this system the
moving conductor is an ionized gas. Very high temperatures and
gas velocities must be maintained, which at the present time pre-
sents some major technical difficulties. In theory, the applica-
tion of a MHD generator can be visualized, possibly in combined
operation with a conventional steam plant, but major advances in
materials must be achieved before the future of MHD power generation
can be predicted (38).
ENERGY UTILIZATION
The optimum solution to problems associated with waste heat
disposal would be the use of rejected heat for beneficial purposes.
When dealing with power plant discharges, however, one is con-
fronted with immense quantities of water which are of low quality
when considered as a heat source. Utilization of waste heat in
this form is therefore restricted to only a very few possible
-------
59
applications.
One potential for such utilization is aquiculture, the farm-
ing of plants or animals in fresh or salt water. Aquiculture has
been successfully practiced in Japan and elsewhere. Heated dis-
charges could be used to enhance the environment and increase pro-
duction of commercially valuable species such as pompano, catfish,
shrimp, oysters, and scallops. Research, development, and pilot
studies are in progress to determine the feasibility of such cul-
tivation in American waters (50).
Some nuclear plants could possibly be located to provide bene-
ficial use of heated discharges in keeping shipping lanes free from
ice for extended seasons. A recent journal article (5) contained
specific recommendations for such application to the St. Lawrence
Seaway, proposing extension of the shipping season to the end of
December or even January.
Heated discharges may have application in irrigating and creat-
ing controlled environments for agricultural crops. In this manner,
growing seasons could be lengthened in certain areas for common
crops, and subtropical or tropical varieties might be produced where
they are not normally adaptable.
Cooling water may provide heat to warm swimming areas. Such
use should be guided by the National Technical Advisory Committee
on Water Quality Criteria (76) which recommends: "In primary con-
tact recreation waters, except where caused by natural conditions,
-------
60
maximum water temperature should not exceed 30°C (85°F)."
Thermal discharges may also provide heat for desalination
or other processes, some of which might require higher temperature
water than that normally discharged from steam plants. In such
cases, it may be possible to implement a "trade-off" whereby it
would be economical to alter the usual process for other benefits.
For example, steam from the final turbine exhaust may be 80°F and
0.5 psia. If the steam were tapped off in front of the final tur-
bine stage it may be 250°F and at 10 psig, which might be worth more
for some use other than its final turbine passage. Marketable
steam for use by other industries, for home heating, or for any
other purpose may warrant "trade-off" situations which would help
to reduce waste heat loads to streams and other water bodies.
Creation and application of improved technology for electri-
cal energy conversion is an indirect, but effective, control mea-
sure. The advent of the fluorescent light is a classic example of
getting more useful work from a watt of electricity. Other fertile
areas are the heating, refrigeration, air-conditioning and motor
industries.
COOLING DEVICES
Types
Waste heat rejection to the aquatic environment can be re-
duced through the use of cooling ponds or cooling towers. The most
-------
61
popular devices now in use in this country are various types of
evaporative cooling towers. In the future, large reservoirs used
as cooling ponds may find increased application in some areas.
Any method that provides air-water contact for cooling removes
about 75% of the heat through evaporation and the remainder through
conduction-convection. As water is vaporized, heat is consumed .at
the rate of about 1000 BTU per pound of water evaporated. Almost
all of this heat is taken from the water that remains, thereby
lowering its temperature.
Cooling Ponds
A cooling pond or reservoir is the simplest method of cooling
thermal discharges, although it is the least efficient in terms of
air-water contact. In a flow-through system, warm water is intro-
duced at one end of the pond, cooled through heat dissipation to
the atmosphere, and eventually withdrawn as cold water from the op-
posite end of the impoundment. Since the natural cooling process
is relatively slow without induced air and water movement, surface
area requirements may average about two acres per megawatt output,
depending on local climatic conditions.
Advantages of cooling ponds or reservoirs include:
1. Low construction cost.
2. Serves as a large settling basin.
3. May be beneficial for other purposes, e.g., recreation.
-------
62
Disadvantages are:
1. Low heat transfer rate, necessitating large land area.
2. Possible fogging, icing of nearby roads, etc.
Cooling can be accelerated in a pond by introducing the warm
water through a spray system located 6 to 8 feet above the water
surface. Such a system may reduce the required pond surface area
by a factor of 20 through increased cooling efficiency. This ad-
vantageous savings in land area may be negated through spray system
cost, pumping costs, and increased water loss with its associated
problems.
Cooling Towers
There are many versions of cooling towers. Terminology applied
to towers stems from basic differences in design or operation which
serve to categorize the types.
A tower may be either "wet" or "dry," depending on whether
water is exposed directly to the air; "natural draft" or "mechani-
cal draft," depending on whether fans are employed for air movement;
"cross-flow" or "counter-flow," depending on horizontal or vertical
air flow through the heat transfer section of the tower. In mechani-
cal draft towers, air flow can be either "forced," i.e., pushed
through by fan on bottom, or "induced," i.e., pulled through by fan
on top. See Figures 3, 4, 5 and 6 for schematics (29,41) illustrat-
ing these types.
-------
FIGURE 3
NATURAL DRAFT TOWER
DRIFT
HOT WATER /ELIMINATOR
DISTRIBUTION
COLD WATER
BASIN
WET (Evaporative) COUNTERFLOW
-------
FIGURE 4
NATURAL DRAFT TOWER
HOT WATER
BASIN
FILL I
DRIFT
ELIMINATOR
SHROUD
AIR
INLET
^COLD WATER
BASIN
WET (Evaporative) CROSSFLOW
-------
FIGURE 5
MECHANICAL DRAFT TOWER
AIR OUT
WATER IN
\ ' /' ' ,
.'/ ','•', \'!/
!'. 0:/',^/V,
VII, • Ml ' / "
<•*,/ '"//
WATER OUT
DRIFT
ELIMINATOR
AIR IN
FAN
WET,(Evaporative) FORCED AIR FLOW
-------
FIGURE 6
MECHANICAL DRAFT TOWER
AIR OUT
FAN
WATER IN
WATER OUT
AIR IN
-COOLER
SECTION
AIR IN
DRY, INDUCED AIR FLOW
-------
67
Because it is important to understand the working "language
when discussing cooling towers, the following discussion of signi-
ficant terms is presented.
Dry-Bulb Temperature: ( F, C) Temperature of air read on
an ordinary thermometer.
O ""I
Wet-Bulb Temperature: ( F, C) Obtained by covering the
bulb of an ordinary thermometer with wetted gauze and reading
in moving air. It depends on the dryness and initial tempera-
ture of the air, but is lower than dry-bulb temperature because
some water evaporates from the gauze, removing heat. The wet-
bulb temperature is the theoretical limit to which water can
be cooled through evaporation.
Relative Humidity: (%) The ratio of the amount of water vapor
actually present in the air to the greatest amount it could
hold if saturated at that temperature and pressure. When rela-
tive humidity is 100%, wet-bulb temperature equals dry-bulb
temperature; therefore, the lower the relative humidity, the
greater the difference between wet-bulb and dry-bulb tempera-
tures .
Evaporation Rate: The rate, e.g., gallons per minute, at which
water is being evaporated to cool the circulating water. It
depends on the area of air-water surface contact, length of
time of contact, and difference between wet-bulb temperature
-------
68
of the air and water temperature.
Cooling Range: ( F, C) The temperature difference between
hot water entering a tower and cold water leaving.
Approach: (°F, C) The temperature difference between cold
water leaving a tower and wet-bulb temperature of the surround-
ing air.
Heat Load: (BTU/hr, BTU/min) The amount of heat dissipated
in a cooling tower per unit time. It equals water circulation
rate multiplied by cooling range, i.e.,
) - BTU/mln
Drift, Carry-Over, or Windage Loss: Water carried out of a
tower in mist or small droplet form. It is usually expressed
as a percentage of the circulating water rate. Caused by high
air velocities, it can be almost entirely eliminated through
good design and operation.
t3as_i_n_: The depressed bottom portion of a tower used for col-
lecting and storing cold water.
Slowdown : The continuous or intermittent discharge to waste
of a small portion of circulating water from the tower basin.
It is usually expressed as a percentage of the circulating
water rate. It prevents build-up of dissolved solids left
behind during evaporation.
Makeup: (gpm,cfs) Water required to replace normal system
losses from evaporation, drift, blowdown, and small leaks.
-------
69
Packing or Fill: Material placed in a tower over which water
flows. It increases the air-water surface area and time of
contact and maintains uniform air and water flow distribution.
Packing design dictates the type of flow. Counter-flow towers
usually use film-type packing; cross-flow towers usually use
splash- or droplet-type packing.
Water Distribution System: A network of pipes (usually-) which
spreads incoming hot water uniformly over the packing in a
tower.
Drift Eliminators: Baffles located above the water distribu-
tion system in a tower. As air flows through the baffles in
a curved path, water particles are thrown from the airstream
by centrifugal force.
Natural Draft Towers.--The cooling tower finding frequent ap-
plication to large power plant discharges at the present time is
the wet, natural draft, hyperbolic type. Over 20 of these towers
are now in various stages of operation or construction in this
country.
Hyperbolic towers derive their name from the hyperbolic profile
of the reinforced concrete shell. The largest are almost 450 feet
high and over 300 feet in diameter at the base. The function of
the shell is that of a stack or chimney in providing an enclosure
for air flowing through the packing which is located near the ground
-------
70
either inside or outside of the shell. Air flow through a tower
is created by the difference in density between the internal and
external air. Warm water passing through the packing heats the
air and saturates it with water vapor during evaporative heat trans-
fer. Both processes decrease the air density and cause it to rise
up the tower. More air is drawn in, resulting in the establishment
of a continuous air flow through the tower. External winds moving
across the top of the tower also contribute somewhat to the air
flow by reducing the internal pressure, thereby creating a drawing
effect. However, tower operation is not dependent on external wind-
induced air movement.
Internal packing is located in the bottom 10 to 20 feet of the
tower shell. Warm water distributed above the packing flows down-
ward through it in thin layers, contacting air rising vertically
through the tower. Such opposed flow denotes the counter-flow clas-
sification. (See Figure 3)
Packing may also be located on the outside periphery of a shell.
In this system the water is broken up into droplets by splash-type
packing and allowed to fall downward. Incoming air flows horizon-
tally through the falling water and then travels upward through
the empty tower shell. This case describes the cross-flow classi-
fication. (See Figure 4) Water loading over the packing is from
2 to 4 gpm per square foot of horizontal area (29).
-------
71
Advantages of the evaporative, natural draft type of tower
are (48):
1. Does not have mechanical or electrical components, yet
for a given load it has the same cooling capability as
the mechanical draft type.
2. Low maintenance cost, ijoth in time and money.
3. Independent of wind velocity.
4. Large water loading capacity.
5. For counter-flow design, air and water flows are opposite
in direction, with the driest air meeting the colder
water first, ensuring maximum efficiency.
Disadvantages are (48):
1. Internal resistance to air flow must be kept minimal.
2. Great shell heights are required to produce a draft.
3. Inlet hot water temperature must be hotter than air dry-
bulb temperature to induce air movement.
4. Exact control of outlet water temperature is difficult
to achieve.
Evaporative loss of water through the system amounts to about
1.5% of the flow circulated. Slowdown may require an additional
2 or 3%, depending on the quality of the circulating and makeup
water. Drift is negligible in a well designed tower, not exceed-
ing 0.2% of the circulating flow (41).
-------
72
A fossil-fueled power plant in the 600 MW class or a nuclear-
fueled plant of about 400 MW would discharge about 2500 X 106 BTU's
per hour. Typical design conditions for a hyperbolic, evaporative
tower to handle this heat load may be as follows (41):
Waterflow 450 cfs
Hot Water Temperature 115°F
Cold Water Temperature 90 F
Design Wet-Bulb Temperature 72°F
Design Relative Humidity 50%
Such conditions would require a tower about 400 feet high and 285
feet in diameter for counter-flow design, or about 370 feet high
and 380 feet in diameter for cross-flow design (41).
Care must be exercised when comparing natural draft evaporative
tower requirements at different sites. Each design is necessarily
based on specific conditions—temperature, humidity, etc.--for a
given geographical location. Hence, the size and performance cited
for a tower at one plant site may not apply to another, even though
the plants to be served are quite similar.
Other kinds of natural draft towers depend on air movement
without the use of a chimney or shell.
Atmospheric spray-filled towers, which are really more like
narrow spray ponds, have nozzles located from 6 to 15 feet high
surrounded by a louvered fence which permits air passage but inhi-
bits water loss. Air circulation is dependent mainly on wind velo-
city. Such cooling systems are suited for small refrigeration and
-------
73
engine-water jacket installations, where variations in a relative-
ly small cooling range will not seriously hamper operations. Where
locations permit prevailing winds to flow unobstructed, the system
works fairly well with a minimum of maintenance. Water loading
capacity may be up to 1.5 gpm per sq ft of active horizontal area
with wind blowing at 5 mph (29). Disadvantages may include clog-
ging nozzles, nigh pumping pressures required to atomize water, and
high windage losses.
Atmospheric packed towers are similar to the spray-filled type
except that they are usually larger and contain packing for water
breakup and additional wetted surface exposure. Such systems are
rarely built any more because of their high capital and pumping
costs, and of their dependence on wind for air circulation. Small
mechanical draft towers which handle comparable loads at similar
costs are now preferred.
A final consideration in the natural draft category is the
hyperbolic dry tower. This type also employs a shell for the draft
effect, but utilizes indirect heat transfer instead of evaporation
for cooling. Completely closed cooler sections give up heat through
conduction-convection, hence there is no evaporative loss of heat
or water. The indirect transfer of heat is much less efficient than
the evaporative process so that much larger volumes of air must be
circulated than in a wet tower. Therefore, the shell size must be
larger, which adds to capital cost.
-------
74
Dry towers are also at a disadvantage compared to wet types
because of the lower limit to which water may be cooled. The theo-
retical lower limit in a dry process is the dry-bulb air tempera-
ture; the corresponding limit in a wet process is the wet-bulb
temperature, which is usually appreciably lower (64).
Natural draft dry towers have not been generally used for
large-scale cooling because the capital cost is estimated to be
about three times as much as its wet counterpart (64). However,
the elimination of water loss through the use of such systems may
prove to be a deciding factor in their acceptance in some loca-
tions in the future.
Mechanical, Draft Towers.--Until 1963 when the first hyperbolic,
natural draft evaporative tower was built at the Big Sandy power
plant at Louisa, Kentucky, only mechanical draft towers had been
used in the United States.
Advantages of evaporative, mechanical draft cooling towers
are (48):
1. Close control of cold water temperature.
2. Generally low pumping head.
3. Location is not critical.
4. More packing per unit volume of tower.
5. A smaller approach and greater cooling range are possible.
6. Small land area requirements.
7. Capital cost is less than for a natural draft chimney.
-------
75
Disadvantages include the following (48):
1. High operating costs, including power.
2. High maintenance costs, both in time and money.
3. Subject to recirculation of hot, humid exhaust into
the air intakes.
4. Climatic variation can affect performance because fans
move a fixed volume of air regardless of its density and
related heat transfer properties. Also, efficiency de-
creases as wind speed increases, up to a critical velocity;
at velocities above the critical value the opposite is
true because of less recirculation.
Mechanical draft towers are used over a broad range of heat
loadings because they can be designed specifically for almost any
capacity. Maximum fan sizes limit the capacity of any single cell,
but additional cells may be built to form a bank or unit capable
of meeting the total requirement.
The two air flow designs commonly used in mechanical draft
towers, forced draft or induced draft, were referred to previously
and depicted schematically in Figures 5 and 6.
Forced draft towers, with one or more fans located in the air
intake, are slightly more efficient than induced draft types because
some of the pressure of air velocity is converted to static pres-
sure in the tower and recovered in the form of useful work. Fan
-------
76
location close to solid foundation lessens vibration. Also, locat-
ing fans at the air inlets reduces the possibility of moisture con-
densation on the equipment since most of the air moved is dry.
Recirculation of hot air is common in forced draft towers be-
cause of the proximity of the exhaust to the low-pressure air-intake
region. Hence, efficiency may vary and winter operation often causes
frost and ice formation on equipment or nearby buildings due to the
presence of moisture-laden air near ground level.
Forced draft type fan diameters are limited to 12 feet or less,
compared to nearly 60 feet for the induced draft type, which neces-
sitates more cells for a given capacity (29).
While forced draft towers employ only counter-flow air movement
through the packing, induced draft towers may use either counter-
flow or cross-flow design. The basic differences in packing design
and arrangement, as described previously, apply here also. For
either type of flow, recirculation is generally not a problem because
the top-mounted fan discharges heated air upward, directly away from
the air intake below. Because hot, humid exhaust air moves through
the fan, corrosion of mechanical parts is more pronounced than in a
forced draft system.
Operational pros and cons of cross-flow design versus counter-
flow design are fairly well balanced for operational characteristics.
Physically, cross-flow types can be built lower and provide easier
access to the water distribution system.
-------
77
Mechanical draft systems also may provide air movement in dry
towers, thereby fulfilling the purpose of the hyperbolic shell as
previously discussed. As noted before, large volumes of air are
required because of less efficient heat transfer through conduction
and convection than through the wet evaporative process (64).
Therefore, large fans are required which continuously demand an
appreciable amount of power—about 3% of total electric power pro-
duction (6). Economics related to mechanical draft dry systems
discourage large-scale application at this time.
Side Effects
Concern over possible side effects from cooling devices has
risen along with the projected use of such systems. Primary con-
cern is with potential fogging conditions caused by cooling towers
(14,62), but other possible adverse side effects should be considered.
Because of the large amount of water vapor expelled from eva-
porative towers, extreme climatic conditions may cause condensation,
resulting in ground level fog or drizzle. However, such conditions
are not often encountered in practice (48). A recent investigation
of fogging problems from natural and mechanical draft towers pres-
ently operating in the eastern U.S. supports this conclusion (11).
Reports indicate that natural draft towers did not produce ground-
level fog or drizzle under any weather conditions. Plumes rarely
dropped below the top of the tower for an extended distance, and
-------
78
generally dissipated within a few hundred feet of a tower. Mechani-
cal, induced draft towers reportedly produced substantial amounts
of ground level fog, especially during the winter. The area affect-
ed by the fog was very small, however, extending a maximum of about
one-fourth mile from the towers. Carry-over of some water droplets
was also noted from the mechanical draft type. Resulting precipita-
tion occurred in the immediate vicinity of the towers, causing some
minor icing problems up to 300 feet away.
In general, undesirable meteorologic effects from towers can
be prevented or controlled to a large degree through modern design--
effective drift eliminators, air-flow control, etc. In situations
where problems arise, the area affected is limited to that immediate
to the tower installation (16).
Water circulating through a condenser-cooling tower system may
be treated chemically to prevent corrosion and inhibit biological
growth (21). hence, water extracted for blowdown purposes may con-
tain constituents which would be detrimental to aquatic life in
receiving waters. Such effects may be prevented by treating blow-
down waste separately or, more efficiently, by integrating blowdown
disposal with other plant waste disposal facilities.
-------
79
Cqst^s
An article (41) discussing natural draft, evaporative cool-
ing towers states the following in regard to tower costs:
"Single towers, regardless of design, will cost in the area
of $2.5 to $3.5 million each for the size of towers which have been
utilized to date in the United States.
"The physical size and cost of a tower installation for a
given size generating unit, however, can vary widely with location,
fuel costs, load factors, and with individual practices regarding
capability penalties and capitalization rates. It is possible that
the optimum cooling tower installations for two plants with identi-
cal rated outputs could differ in cost by a factor of two. For this
reason, it is difficult and, indeed, dangerous to generalize when
discussing tower reouirements and costs.'1
The following outlines cooling tower costs as related to each
other, to total plant or production costs, and to consumer costs.
Natural draft evaporative tower capital costs in the eastern
U.S. have been at least 5% of the total capital cost of a power
plant. For a given plant heat load, mechanical draft, evaporative
towers cost approximately two-thirds as much as natural draft;
either natural draft or mechanical draft dry types would probably
cost three to four times more than their wet counterparts.
The indicated savings in initial cost for the mechanical draft,
wet tower is somewhat negated because of power costs for fans, which
-------
80
consume about 0.8% of the power generated by the unit served (44).
For the proposed 540 MW nuclear plant at Vernon, Vermont, the an-
nual cost for production of power to operate fans is estimated to
be about $130,000--about 2% of the initial capital tower cost of
$6 million. Other maintenance costs for the mechanical draft tower
installation are estimated at $60,000 annually--l% of initial tower
costs. For this plant, the initial cost for mechanical draft
towers amounts to 5.1% of the total plant cost of $118 million (19).
In a detailed study for siting 1000 MW nuclear power plants in
the Pacific Northwest (55), natural draft cooling towers were recom-
mended at a number of locations. At all sites the estimated initial
cost of such towers and related appurtenances was about $7.5 mil-
lion, or approximately 5.5% of a total plant capital cost of about
$140 million. Induced draft towers were recommended in one case,
also at a capital cost of about 5.5% of the total plant cost. The
cost of a 2600-acre pond at a location conducive to that type of
cooling system would be about 2.3% of the total plant cost. It
should be noted, however, that the pond location was in an area of
relatively low land value.
These examples indicate that evaporative cooling systems will
increase the capital cost of a power plant by about 5%. An assess-
ment of all fixed and variable costs indicates that power produc-
tion costs are also increased by about 5% (19). It should be noted,
however, that such increases are not carried over to consumer costs
-------
81
in the same proportion because of intermediate fixed costs in-
curred through transmission and administration. According to
Converse (19), production cost is only about one-fifth of consu-
mer cost. In that case, the cost of electricity to the consumer,
because of the use of evaporative cooling towers, would increase
approximately 1%.
TRANSPORT AND BEHAVIOR MANIPULATION
Dispersion and Dilution Techniques
The design of discharge outfalls is, at the present time,
more art than science. Hydraulic model studies, along with other
empirical information, are new the basis for design because theo-
retical equations of fluid motion have not yet reached the stage
of engineering aoplication. Future developments in the area of
mathematical models, hopefully, will place the design of outfall
structures more on a theoretical, rather than empirical, basis.
The physical and hydraulic characteristics of the effluent
and receiving water largely determine the rate of dispersion and
areal extent of dilution. Rate of dispersion is a function of the
existing turbulence of the receiving water, turbulence induced by
the kinetic energy of the effluent, and the density gradient be-
tween the effluent and receiving water. The areal extent of dilu-
tion is a function of the dispersion rate plus the number and
-------
82
orientation of ports in the discharge manifold. Outfalls should
be designed to accomplish specific objectives.
If the objective is to minimize temperature gradients within
the water body, a diffuser designed to maximize induced turbulence
and to distribute the discharge over a broad area is recommended.
The diffuser pipe could be placed in any of the three spacial dimen-
sions of the water body, but common practice is to use a horizontal
diffuser pipe placed across the stream.
A discharge technique which is quite common with TVA is the
use of a discharge channel which floats the warm water on the sur-
face of the receiving stream or reservoir. The objective of this
method is to maximize dissipation of heat to the atmosphere and
minimize the water areas and volume affected by the effluent; mix-
ing is not desired. By forming a warm water wedge over the cool
receiving water, rapid heat loss to the atmosphere is encouraged
by increasing the energy transfer due to evaporation, convection,
and back radiation. Thus, the warm water wedge acts in much the
same manner as a cooling pond. However, this technique results in
sharp temperature gradients near the surface and serious problems
can occur if temperature sensitive organisms are subjected to such
gradients. For example, this technique would not be desirable on
a stream inhabited by a cold-water fishery.
A third alternative discharge technique is to develop a
thermal plume. A single-point discharge below the surface of the
-------
83
receiving water will result in a plume extending in the direction
of the water flow and vertical density gradient. Mixing is oro-
tnoted by both the energy of the receiving water's current and by
the kinetic energy of the discharge. In some streams where plumes
originate near the bed, vertical mixing is rather rapid, but
lateral mixing is slower. For example, plumes from AEC's nuclear
reactors at Hanford, Washington, on the Columbia River exhibit
such characteristics.
A term which has recently been appearing in the literature
regarding thermal pollution is "thermal block." A thermal block
occurs when a warm water mass interferes with fish migration (76,
p. 31). Outfalls should be designed to prevent such a block from
occurring.
A final point must be made concerning the control of heated
discharges by dispersion and dilution. Such techniques cannot be
expected to solve the problems associated with the discharge of
large heat loads into moderate volumes of receiving water. Any
heated discharge which will promote excessive temperature rises
will require the use of cooling devices.
Hater Quality Management
Temperature Prediction
Mathematical and physical models of varying degrees of com-
plexity have been developed to determine the fate and persistence
-------
84
of heat in quiescent waters, flowing streams, estuaries, and the
ocean. The ability to predict water temperatures accurately is
necessary in order to determine the thermal impact of:
1. Proposed waste heat discharges.
2. Changes in the hydraulic characteristics of a water
body or stream—for example, due to the construction
of a dam with its resulting flow regulation.
3. Releases of water from stratified reservoirs with
multilevel outlets.
4. Unusual meteorological conditions.
The following discussion presents the basic approach which
is used to solve temperature prediction problems. However, the
mathematical formulation of the physical heat transfer processes
which occur is not a simple matter. The scope of this guide pre-
vents a presentation of the mathematical derivations leading to
temperature prediction models for all situations. However, a
simplified case is presented in the example problem of the next
section. For information on more sophisticated models, the reader
is urged to consult the technical literature. An excellent basic
reference is the Edison Electric Institute's Publication No. 65-902,
Heat Exchange in the Environment, by J. E. Ldinger and J. C. Geyer,
Department of Sanitary Engineering and Water Resources, The Johns
Hopkins University, June 1, 1965 (27).
-------
85
It is necessary to consider heat transfer mechanisms in
water and between water and the atmosphere in order to describe
temperature regimes mathematically. For localized problems,
e.g., outfalls or plumes, the mechanisms acting in the water
are most important; analysis of conditions throughout larger
systems (rivers, reservoirs, etc.) requires emphasis on the air-
water heat transfer mechanisms as well as those in water. In
either case, specific predictions are desirable so that effec-
tive control or management techniques can be applied.
There are two heat transport mechanisms which occur in
water--advection and dispersion or turbulent mixing. Advection
is the transport of heat by the motion of a mass of water and is
accomplished through ordinary streamflow, utilization of a dis-
charge stream's kinetic energy, or water movement due to density
gradients. Mathematical terms for advection express the rate of
heat energy transfer in terms of the water mass temperature and
velocity along longitudinal, lateral, and vertical axes.
Turbulent mixing or dispersion cause heat interchange through
eddy diffusion or molecular diffusion. Eddy diffusion occurs under
turbulent flow, which depends on fluid velocity and channel
characteristics. Mixing results from the action of small fluid
masses known as eddies, which are random both in size and orienta-
tion. Molecular diffusion is that resulting from random motion
of molecules. Its influence is much less than that from turbulent
-------
86
mixing. Diffusion effects are combined in mathematical expres-
sions, and may be defined along longitudinal, lateral, and
vertical axes.
Heat exchange which takes place between the water surface
and the atmosphere is made up of seven mechanisms.
The mechanisms which are independent of water temperature
are (27):
Qs = Incoming short-wave solar radiation (400 to 2800
BTU/ft2/day).
Q, = Incoming long-wave atmospheric radiation (2400 to
a
3200 BTU/ft2/day).
Qsr Qar = Portions of both short-wave and long-wave
radiation which are reflected or scattered by
the water surface (40 to 200 and 70 to 120
BTU/ft2/day, respectively).
The mechanisms of heat transfer which are dependent on the
surface water temperature include the following (27):
Qbr = Long-wave back radiation from the water to the
atmosphere (2400 to 3600 BTU/ft2/day). It is pro-
portional to the fourth power of the absolute water
surface temperature (AT$), i.e., 0.^ <* (ATS) .
Qc = Heat exchange due to conduction-convection (-300 to
+400 BTU/ft2/day), which is proportional to the wind
speed (W) and the difference between water temperature
-------
87
(T_) and air temoerature (T J, i.e., (1 cc W(TC-T ).
b a c b a
A positive Qc indicates an energy loss.
Qe = Heat loss due to evaporation (2000 to 8000 BTU/ft2/
day), which is proportional to the product of wind
speed (W) and the difference between the water vapor
pressure in saturated air at the water temperature
(es) and the water vapor pressure in the overlying
air (ea), i.e., Qe <* W(es - ea). If ea > es, conden-
sation takes place and the water body gains energy.
The algebraic sum of these surface heat exchange parameters
is equal to the net rate of surface heat exchange. Equilibrium
temperature is reached when this sum is zero.
Micro Models.--In temperature prediction terminology, a micro
model is one which describes or predicts the distribution of heat
in the immediate vicinity of a thermal discharge. The micro models
available at the present time are based on many simplifying assump-
tions which render them less than totally adequate for predicting
local temperature distributions. However, they are useful for
approximating heated discharge dilution rates by receiving waters.
Theoretical work is progressing in areas such as mixing and dis-
persion and will aid in development of generalized micro models
for jets and plumes.
Another factor which adds to difficulties with micro models
is the unique character of many situations. For example, the nature
-------
88
of a stream channel at any location will influence mixing charac-
teristics. Curvature or depth variation may direct discharges into
certain portions of a channel, thereby nullifying the theoretical
description of the length or degree of mixing. Each situation will
therefore require careful description in terms of discharge pumping
rate, river flow, and channel characteristics.
Until generalized micro models can accurately predict local
temperature distributions under various hydraulic conditions, esti-
mates based on simplified models and past experience will be required.
Macro Models.--Macro models are those which describe or pre-
dict temperature regimes in a complete river or river system, lake
or reservoir, estuary, or coastal area. Such models combine heat
transfer mechanisms and water movement on a continual basis with
respect to time. With the current state of the art, technology for
macro-prediction is more reliable than for micro-prediction. This
is possible because of the compensating and averaging effects of
spacial differences in environmental variables.
A macro model maintains an energy budget for the water body
under consideration, i.e., it maintains a heat balance of both the
internal heat exchange and the heat transfer at the water surface.
This heat budget may be expressed as follows:
(Rate of Heat In) - (Rate of Heat Out) + (Rate of Heat
Storage) + (Rate of Heat Exchange at Water Surface) - 0
The rate at which heat flows into and out of the water body is
-------
89
determined from the flow rates and temperatures of inflowing and
outflowing water. These rates require evaluation of the heat
transfer mechanisms in water to define the motion of heat entrained
water masses. The rate of heat storage is determined from the
temperature and volume of the water body in consecutive time
periods. The rate of heat exchange at the water surface is the
algebraic sum of all the water-atmosphere heat exchange rates.
Macro models evaluate terms in the heat budget over specific
time periods, e.g., hourly, daily, weekly, etc. The rate-time
evaluation results in quantitative values for each portion of the
heat budget for each period through the study time span. By super-
imposing flow rates on the time scale, the location of a specific
water mass may be determined at any desired time. For temperature
prediction, a model routes hypothetical masses of water along a de-
scribed course in order to simulate their movement and changes in
thermal properties; temperatures are thereby predicted at specific
locations and points in time.
Thermal Regulation
The need to manage our environment has only recently been rec-
ognized, but we now realize that in order to continue the effective
use of our natural resources, environmental management is a neces-
sity. In terms of thermal pollution control, we can perform water
temperature management through plant siting, coupled with effective
use of regulated river systems. Effective water temperature predic-
-------
90
tion models will enable water resources managers to predict tempera-
tures which will result from combined dam releases and thermal in-
puts to a system. Conditions can then be selected to minimize un-
desirable thermal effects. Such temperature-discharge requirements
can be met through the use of multilevel dam outlets which permit
waters of various temperatures to be selectively released from
stratified reservoirs.
EXAMPLE PROBLEM
This section presents a problem concerning temperature predic-
tion on a well-mixed stream and the sizing of flow-through cooling
ponds. A complete explanation of the methodology is beyond the scope
of this guide, and the reader is urged to consult the literature for
an in-depth review of the many available computational techniques.
The problem solution uses basic methods, all of which can be found in
the publication by Edinger and Geyer (27). As an aid in analyzing the
problem, references to appropriate pages in this reference are given.
The Situation
A 1000 MW electrical output nuclear power plant of 33% effi-
ciency is to be located on a medium-sized river in the temperate
region of the nation. Using applicable hydrologic and meteorologic
data, we wish to compute:
A. Downstream temperature, assuming once-through cooling
and complete mixing in the river.
B. The area of a flow-through cooling pond necessary to
prevent violation of water temperature standards.
-------
91
Part A
Compute the heat energy entering the cooling water as des-
cribed in the "Plant Evaluation" section.
1. For 33% thermal efficiency (r\.}:
•541-3
Heat Rate = ° . 1An - - = 10,340 BTU/KWH
r). v i uu .00
2. Assuming a 5% in-plant heat loss:
Heat to cooling water - (0.95 x Heat Rate - 3413) BTU/KWH
Heat to cooling water - [0.95(10,340) - 3413] BTU/KWH
Heat to cooling water = 6410 BTU/KWH
Total heat to cooling water for the 1000 MW (106 KW) plant
106 KW x 6410 BTU/KWH = 6.41 x IP9 BTU/hr
Compute the temperature rise in the stream, assuming once
through cooling and complete mixing.
Given a design flow in the stream of 3500 cfs, which in terms
of Ib/hr is:
Q = (3500 cfs) (62.4 lb/ft3) (3600 sec/hr)
Q = 7.86 x 108 Ib/hr
Since 1 BTU will raise the temperature of 1 Ib of water 1°F,
AT = AT in river = <6'41 x 10' BTU/h^
r (7.86 x 10B Ib/hr) (1 BTU/lb °F)
AT = 8.2°F
i
-------
92
Equation for computing downstream temperatures.
Downstream temperatures are computed by assuming exponential
temperature decay. This concept is presented mathematically
as:
^= -K(T - E) (27, p. 43)
where -rr = net rate of water surface heat exchange (BTU ft day )
K = energy exchange coefficient (BTU ft day' °F )
T = water surface temperature (°F)
E = equilibrium temperature (°F)
For a well-mixed stream, this equation can be written as:
pCpyu|I = -K(Tx - E) (27, p. 129)
_3
where p = water density (62.4 Ib ft )
C = specific heat of water (1 BTU Ib"1 °F"1)
y = mean stream depth (ft)
U = mean stream velocity (ft day )
TT~ = longitudinal temperature gradient (°F ft" )
x = downstream distance (ft)
Define T = temperature at x = o; then
-Kx )
Pcpyu
Tx = (T - E)e
/\ \J
Kx
By defining a = ^ y ; then
T = (T - E)ea + E
x v o
-------
93
Meteorologic Data
The following data are used in determining K and E:
Time Period
(6 hr intervals)
Midnight - 6 am
6 am - Noon
Noon - 6 pm
6 pm - Midnight
DAILY AVERAGE
For K
1 1
Wind ,u.
Speed w
(mph)
4.0
12.0
12.0
6.0
8.5
1
Net Radiation ,u ,
Input (tV
(BTU ft-* hr-1)
120
290
320
130
215
For E
Air (T ,
Temp 1V
(°F)
65
75
85
70
74
Relative
Humidity
{%}
40
30
20
35
--
Water Vapor '
Pressure of (e )
Ambient Air
(mm Hg)
6.3
6.7
6.2
6.6
6.5
Determination of K
The energy exchange coefficient is computed using a
variation of the equation given on page 48 (27):
K = [15.7 + (0.26 + 3)(bW)]
where W = wind speed (mph)
b = experimental evaporation coefficient (a value of
15 is used in this example)
(3 = proportionality coefficient [See following table]
Range of E g
(OF)(mm Hg op-I)
50 to 60 0.405
60 to 70 0.555
70 to 80 0.744
80 to 90 0.990
-------
94
Thus, for an average daily value of K, using W = 8.5 mph:
K = (15.7 + [0.26 + 3] [(15) (8.5)])
Using appropriate values of 3 for two ranges of E:
i (°F) K(BTU ft"2 day"1 °F"])
60 to 70 120
70 to 80 144
Determination of E
The equilibrium temperature is reached when the rate of change
of energy at the water surface equals zero. Edinger and Geyer
(27) present a method for computing E (pp. 55-59). The method
involves assuming a likely 10°F temperature range for E and by
using the appropriate value for K and the given meteorological
data, computing a value for E. If the computed value of E falls
within the assumed range, the process is complete. However, if
the computed value of E falls outside the assumed range,
another range must be assumed and the process repeated until E
falls within the proper limits. Thus, E is computed by a trial
and error method.
For the stated meteorological conditions and computed values
of K, we can determine a daily average E by the following seven
steps (27):
Step 1. Assumed range of E = 70 to 80°F
-------
95
Step 2. Compute F(K) for use in step 6:
K - 15.7
F(K) =
K
As computed for an E range of 70 to 80°F, K = 144 BTU ft"2 day"1 °F
.'. F(K) - ^ 144 - = °-891
Step 3. Compute E-, for use in step 6:
HD - 1801
E =
-1 K
7 1
From the meteorologic data table, HR = 215 BTU ft hr
or in terms of days, HR = 5160 BTU ft"2 day"1
• - 5160 - 1801 _
Step 4. Compute E? for use in step 6:
(0.26) (Ta)
E2 ~ "(0.26 + 3)
From the meteorologic data table, T = 74°F, and from
a
the table of E range vs. 6, 3 = 0.744
. F _ (0.26) (74) _ ,q
' ' L2 (0.26 + 0.7447 Iy^
Step 5. Compute E~ for use in step 6:
e, - C(3)
a
3 (0.26 + 3)
From the meteorologic data table, e = 6.5 mm Hg. C(3)
a
is related to ranges of E as follows:
Range of E C(3)
(OF) " "(mm Hg)
50 to 60 -11.22
60 to 70 -20.15
70 to 80 -33.30
80 to 90 -53.33
-------
96
Thus for an E range of 70 to 80°F, C(6) = -33.3
. E _ 6.5 - 1-33.3) _ -q fi
' ' 3 (0.26 + 0.744) Jy'D
Step 6. Compute M for use in step 7:
M = E1 + F(K) (E2 + E3)
M = 23.3 + (0.891) (19.2 + 39.6) = 75.7
Step 7. Compute E using the following relationship:
M=E+0.051E2
K
Inserting M and K and setting up a quadratic equation gives:
2 °°
E - 75.7 - 0
.'. 0.000354E2 + E - 75.7 - 0
Solving this equation using the quadratic formula gives:
F = -1 ± [1 - (4) (0.000354) (-75.7)]1/2
t ~ 2 (0.000354)
F = -1 ± (1.10719)172 = -1 ± (1.05223)
0.000708 0.000708
Rejecting the negative value gives:
= n'nnrwna = 73.8°F (This value is acceptable because it
falls within
70 to 80°F.)
falls within the assumed range of
Compute Average Stream Velocity
Q = 3500 cfs
Given an average cross section 800 feet wide and 5 feet deep:
U = S ft) = °'875 ft/sec = ZS^OO ft/day
-------
97
Evaluation of a
-Kx
a =
pCpyU
For x' in miles: a = ( (1) (5) (75,600)
a = -0.0322x'
Solve for T , for x1 = 10, 20, 50 miles
X
Assume unheated river temperature = 74 F
.-. TQ = 74°F + ATR = 74°F + 8.2°F = 82.2°F
TX, = (TO - E)e-°-0322x' + E
For x' = 10 miles
T , = (82.2-73.8)e-(°-0322>(10)+73.8
X
Tx, = (8.4)e'°-322 + 73.8
T , = (8.4) (0.725) + 73.8 = 79.9°F
x
For x' =20 miles
Use same value of a and replace T by T , for x' = 10 miles:
0 X
T , = (79.9 - 73.8) (0.725) + 73.8 = 78.2°F
A
fojlA' = 3°» 40' 50 miles
Following the same procedure:
30 miles, T , - (78.2 - 73.8) (0.725) + 73.8 - 77.0°F
X
40 miles, T , - 76.1°F
A
50 miles, T , = 75.5°F
X
-------
98
These values represent the exponential temperature decay
which is graphically shown on the following plot:
Q 70
Plant
10 20 30
Distance Downstream from Plant
(miles)
50
This graph presents an idealized picture of the downstream
temperatures, since the computations were based on average daily
conditions, and thus no diurnal effect is evident. It also assumes
that the weather data on which K and E are based are indicative
of conditions along the 50-mile stretch of the river. In addition,
no tributary inflows or heated discharges are accounted for in the
50 miles.
-------
99
The diurnal effect may be evaluated by using the six-hour
average meteorologic conditions given previously. Following the
methods described, values of K and E were computed as:
Time Period
(6 hr intervals)
Midnight to 6 am
6 am to Noon
Noon to 6 pm
6 pm to Midnight
K
(BTU ft"2 day"1)
56
196
241
76
E
(°F)
53.8
79.2
84.0
58.1
0
(°F)
71
72
78
76
The values of water temperature (T ) just upstream from the
plant reflect natural diurnal fluctuations.
Using the exponential temperature decay relationship presented
previously and assuming slug flow in the stream, i.e., no longitudi-
nal mixing, the variation in temperature was computed for a parcel
of water which left the plant location at 6 pm. The following
graph demonstrates the effect of diurnal variations in meteorological
conditions on the temperature of the water parcel for a distance of
50 miles downstream. Note that the initial temperature of the
parcel is equal to the natural stream temperature (T ) plus the
temperature increase of 8.2°F caused by the plant discharge.
-------
100
TEMPERATURE OF A WATER PARCEL
85
Q)
3
O
v_
Q)
a
I
E
o
«
+-
to
80
75
I
I
I
10 2O 30 40
Miles Downstream from Plant
50
Time (Military)
0
o
00
o
o
^j-
CM
O
O
(Q
O
O
O
CM
O
O
5j-
CVI
O
O
CM
"™ *
O
o
^-
CM
6 '
o
CM
O
O
CM
-------
101
Part B
Assuming a maximum allowable daily average stream temperature
of 80°F, what flow-through cooling pond area would be required at
the site? The following sketch describes the plant-river-pond lay-
out:
Q! = 1500 cfs
I, = 74° F
RIVER
Q3 = 1500 cfs
T3 = 93°F
COOLING
POND
Q0=3500cfs^)
T0=74°F '
,02= 2000 cfs
1T2 = 74°F
/Q4= 1500 cfs
T4= ?
;= 3500 cfs
-------
102
Temperature Rise Through Plant
Heat to cooling water = 6.41 x 109 BTU/hr
Condenser flow = 1500 cfs = 3.37 x 108 Ib/hr
AT = AT through condenser = - = 19.QoF
C (3.37 x 10b lb/hr)(l BTU/lb °F)
. T = 74°F + 19°F = 93F
Temperature Drop Through Pond
A flow-through cooling pond is assumed to be well mixed
in each cross section, but as in a stream, there is a longitu-
dinal temperature decay. Thus, the equation for predicting the
temperature drop through the pond is equivalent to the exponen-
tial temperature decay equation used on we'll -mixed streams.
Using the temperature subscripts given on the sketch, the
temperature from the pond can be computed by:
T4 = (T3 - E)e'a' + E (27, p. 113)
, , KA
where a = ~r~nr~
pCPQ3
3 -1
Q3 = plant discharge (ft day )
2
A = pond area (ft )
Using an experimental evaporation coefficient (b) of 12, K =
118 and E = 76.9 F. These values are used in the subsequent
cooling pond calculations.
-------
103
Case I - Pond area required for discharge from pond = 80°F.
.'. T = 80°F
Solving the prediction equation for a'
80 = (93 - 76.9)e"a' + 76.9
e~a= (80 - 76.9) / (93 - 76.9)
e"a= 0.193
.-. a' - 1.65
Solving the a' equation for A:
a< = T6274T7lTTi500jT24 hr/dayj73600 sec/hrj
a1 = (1.46 x 10~°)A - 1.65
.'.A = (1.65)7(1.46 x 10~8) - 11.3 x 107 ft2
In acres: A =
(4.36 x 1(T ftVacre)
Ca,se__n_ - Pond area required for mixed river temperature = 80 F.
If a mixing zone is allowed in the stream such that the
mixed river temperature below this zone is equal to or less
than 80°F, a much smaller pond could be used.
-------
104
Referring to the sketch:
Solving for T. :
T T5Q5 - T2Q2 = (80) (3500) - (74) (2000)
4 Q4 1500
. M = 88.0°F
By using the same computational techniques as for Case I
a1 = 0.373
.'. A = (0.373)/(1.46 x 10"8) = 2.55 x 107 ft2
in acres: A = ^55 x 10' ft*> - = 585 acres
(4.36 x 10^ ft /acre) -
-------
REFERENCES
(1) Allen, J. A. 1963. Ecology and functional morphology of
molluscs. Oceano—Marine Biology Annual Review. Harold
Barnes, Ed. 1:253-288.
(2) Amberg, H. R. and J. F. Cormack. 1960. Factors affecting
slime growth in the lower Columbia River and evaluation
of some possible control measures. Pulp and Paper Magazine
of Canada. 61:T-70 to T-80.
(3) Anon. 1966. 1965 National Survey of Fishing and Hunting.
Fish and Wildlife Service, Resource Publication 27.
(4) Anon. 1966. Seventeenth annual electrical industry forecast.
Electrical World. 166(14):113-128.
(5) Anon. 1968. Chemical and Engineering News. June 17.
(6) Stroud, R. H. and P. A. Douglas. 1968. Sport Fishing
Institute Bulletin. No. 191.
(7) Arnold, G. E. 1962. Thermal pollution of surface supplies.
Journal of the American Water Works Association. 54:1332.
(8) Brett, J. R. 1956. Some principles in the thermal require-
ments of fishes. Quarterly Review of Biology. 31(2):75-87.
(9) Brett, J. R. 1960. Thermal requirements of fish--three
decades of study, 1940-1970. Biological Problems in Water
Pollution. Transactions, 1959 Seminar. Robert A. Taft
Engineering Center, Cincinnati, Ohio. Technical Report
W60-3. pp. 110-117.
(10) Brett, J. R., M. Hollands and D. F. Alderdice. 1958. The
effect of temperature on the cruising speed of young sockeye
and coho salmon. Journal of the Fish. Research Bd. of
Canada. 15(4):587-605.
(11) Broehl, D. J. 1968. Field investigation of environmental
effects of cooling towers for large steam electric plants.
Portland General Electric Company. April 1. (unpublished).
(12) Burrows, R. E. 1963. Water temperature requirements for
maximum productivity of salmon. Water Temperature Influences,
Effects, and Control. Twelfth Pacific Northwest Symposium
on Water Pollution Research, Pacific Northwest Water
Laboratory, Corvallis, Oregon, pp. 29-38.
-------
106
(13) Burrows, W. 1959. Textbook of Microbiology. W. B. Saunders
Co., Philadelphia, Pa.
(14) Buss, J. R. 1967. Control of fog from cooling towers. Cool-
ing Tower Institute Meeting, June 26-28.
(15) Cairns, J., Jr. 1956. Effects of increased temperatures on
aquatic organisms. Industrial Wastes. 1(4):150-152.
(16) Christensen, S. R. 1968. Cooling tower plume effects.
Portland General Electric Company. March 4. (unpublished).
(17) Clarke, N., G. Berg, P. Kabler and S. Chang. 1964. Human
enteric viruses in water: sources, survival and removability.
International Conference on Water Pollution Research, London,
1962. Pergamon Press-Oxford, New York. pp. 523-536.
(18) Columbia Basin Interagency Committee. 1966. Columbia River
Water Temperature Conditions and Research Requirements.
Edited by Federal Water Pollution Control Administration,
Portland, Oregon.
(19) Converse-, A. 0. 1967. Thermal Energy Disposal Methods for the
Proposed Nuclear Power Plant at Vernon. Dartmouth College,
Hanover, New Hampshire.
(20) Coutant, C. C. 1962. The effect of a heated water effluent
upon the macro-invertebrate riffle fauna of the Delaware
River. Pennsylvania Academy of Science. 37:58-71.
(21) Cubisino, A. R. 1968. Cooling water treatment specifications.
Cooling Tower Institute Meeting, January.
(22) Dake, J. M. K. and D. R. F. Harleman. 1966. An analytical
and experimental investigation of thermal stratification
in lakes and ponds. Massachusetts Institute of Technology.
Hydrodynamics Report No. 99.
(23) Dondero, N. C. 1961. Sphaerotilus, its nature and significance.
Advances in Applied Microbiology. 3:77-107.
(24) Doudoroff, P. 1942. The resistance and acclimation of marine
fishes to temperature changes: I. Experiments with Girella
nigricans (Ayres). Biological Bulletin. 83:219-244.
-------
107
(25) Doudoroff, P. 1957. Water quality reouirements of fishes
and effects of toxic substances. ln_ The Physiology of
Fishes. M. E. Brown, Ed. Academic Press, Inc., New York.
pp. 403-430.
(26) Dysart, B. C., Ill and P. A. Krenkel. 1965. The effects of
heat on water quality. I_n_ Proceedings of the 1965 Purdue
Industrial Waste Conference.
(27) Edinger, J. E. and J. C. Geyer. 1965. Heat exchange in the
environment. Edison Electric Institute Publication No.
65-902.
(28) Ellis, M. M. 1947. Temperature and fishes. Fish Leaflet
No. 221. U.S. Fish and Wildlife Service.
(29) Elonka, S. 1963. Cooling towers. Power. 107(3):S-1 to S-16.
(30) Federal Power Commission. 1966. Steam Electric Plant Con-
struction Cost and Annual Production Expenses.
(31) Ferguson, R. G. 1958. The preferred temperature of fish
and their midsummer distribution in temperate lakes and
streams. Journal of the Fish. Research Bd. of Canada.
15:607-624.
(32) Fiehn, A. J. 1967. Cooling tower solutions to problems of
power station circulating water system design. Presented
to ASCE Conference, October 1967, New York.
(33) Fish. Bd. of Canada. 1962. Annual Report 1961-62. 206 pp.
(34) Galloway, J. C. 1951. Lethal effects of the cold winter of
1939/40 on marine fishes at Key West, Florida. Copeia.
2:118-119.
(35) Galtstoff, P. S. 1964. The American oyster Crassostrea
virginica Gmelin. U.S. Fish and Wildlife Service, Special
Science Reports—Fish, No. 64. 480 pp.
(36) Gunter, G. 1957. Temperature, Chapter 8, Treatise on marine
ecology and palaeoecology, I. J. W. Hedgepeth, Ed. Geology
Society American Memoirs. 67:159-184.
(37) Gunter, G. and H. H. Hildebrand. 1951. Destruction of fishes
and other organisms on the South Texas coast by the cold
wave of January 28 - February 3, 1951. Ecology. 32(4):731-735.
-------
108
(38) Hauser, L. G. 1968. Advanced methods of electric power
generation. The Cooling Tower Institute Semi-Annual
Meeting, Los Angeles, California. June 24-26.
(39) Hoak, R. D. 1960. The thermal pollution problem. Penn.
Water Pollution Control Assn. Annual Meeting. August
10-12.
(40) Hutchinson, L. 1947. Analysis of the activity of the fresh
water snail Viviparus rnalleatus (Reeve). Ecology. 28(4):
335-345.
(41) Jones, W. J. 1968. Natural draft cooling towers. Industrial
Water Engineering. 5(3):21-24.
(42) King, G. B. and W. E. Caldwell. 1959. The Fundamentals of
College Chemistry. American Book Company, New York.
(43) Kinne, 0. 1963. The effects of temperature and salinity on
marine and brackish water animals, I. Temperature. Oceano-
Marine Biological Annual Review. 1:301-340.
(44) Kolflat, Tor. 1968. Thermal discharges. Industrial Water
Engineering. 5(3):26-31.
(45) Laberge, R. H. 1959. Thermal discharges. Water and Sewage
Works, pp. 536-540.
(46) Major, R. L. and J. L. Mighell. 1966. Influence of Rocky
Reach Dam and the temperature of the Okanogan River on the
upstream migration of sockeye salmon. Fisheries Bulletin,
U.S. Fish and Wildlife Service. 66(1):131-147.
(47) Mathur, S. P. 1967. Thermal pollution from steam-electric
generating plants. Technical Assistance and Investigations,
Robert A. Taft Sanitary Engineering Center, Cincinnati,
Ohio, (unpublished).
(48) McKelvey, K. K. and M. Brooke. 1959. The Industrial Cooling
Tower. Elsevier Publishing Co., New York.
(49) Mihursky, J. A. and V. S. Kennedy. 1967. Water temperature
criteria to protect aquatic life. Symposium on Water Quality
Criteria to Protect Aquatic Life. American Fisheries Society,
Special Publication No. 4. pp. 20-32.
-------
109
(50) Muskie, Edward S. (Chairman) 1968. Thermal Pollution-1968
(Part I). Subcommittee on Air and Water Pollution, U.S.
Congress.
(51) Naylor, E. 1965. Effects of heated effluents on marine and
estuarine organisms. In Advances in Marine Biology.
Sir Fredrick S. Russell, Ed. Academic Press, pp. 63-103.
(52) Nikolsky, G. V. 1963. The Ecology of Fishes. Academic
Press, New York. 352 pp.
(53) Noland, L. E. and E. Reichel. 1943. Life cycle of Lymnaea
stagnalis completed at room temperature without access to
air. Nautilus.
(54) Olson, P. A. and R. F. Foster. 1957. Temperature tolerance
of eggs and young of Columbia River Chinook salmon. Trans.
of American Fish. Soc., 58th Annual Meeting, pp. 203-207.
(55) Pacific Northwest Laboratories. 1967. Nuclear power plant
siting in the Pacific Northwest for the Bonneville Power
Administration. Contract No. 14-03-67868. (Battelle
Memorial Institute, Richland, Washington).
(56) Pennsylvania Department of Health. 1962. Heated discharges--
their effect on streams. Report by the Advisory Committee
for the Control of Stream Temperatures to the Pennsylvania
Water Board, Harrisburg, Pennsylvania. Pensylvania Depart-
ment of Health Publication No. 3. 108 pp.
(57) Phelps, E. B. 1960. Stream Sanitation. Wiley & Sons, New
York. 276 pp.
(58) Prosser, C. L. 1955. Physiological variations in animals.
Biological Review. 30(3):229-262.
(59) Prosser, C. L., F. A. Brown, D. W. Bishop, T. L. John and
V. J. Wulff. 1950. Comparative Animal Physiology. W. B.
Saunders Co., Phila., Pa. 888 pp.
(60) Remirez, R. 1968. Thermal pollution--hot issue for industry.
Chemical Engineering. 75(7):43-52.
-------
no
(61) Renn, C. E. 1957. Warm-water effects on municipal supplies.
Journal of the American Water Works Association. 49:405-412.
(62) Richards, R. T. 1968. Environmental aspects of thermal
station design. Civil Engineering. 38(5):45-47.
(63) Royal, L. A. 1953. The effects of regulatory selectivity
on the productivity of the Eraser River sockeye. Canadian
Fish-Culturist. 14:1-12.
(64) Shade, W. R. and A. F. Smith. 1968. Discussion of economic
considerations in thermal discharge to streams. National
Symposium on Thermal Pollution (II), Nashville, Tennessee.
August 14-16.
(65) Sheridan, W. L. 1960. Relation of stream temperature to
timing of pink salmon escapements in southeast Alaska.
Symposium on Pink Salmon. H. R. MacMillan Lectures in
Fisheries. University of British Columbia, Vancouver, B.C.
pp. 87-102.
(66) Short, Herbert C. (Editor). 1968. Nuclear power buildup
goes critical. Chemical Week. 102(21).
(67) Stangenberg, M. and M. Z. Powlaczyk. 1962. The influence of
a warm-water influx from a power station upon the formation
of biocenotic communities in a river. Water Pollution
Abstracts. 35(3) Abstract No. 579.
(68) Stanier, R. Y., M. Doudoroff and E. A. Adelburg. 1963. The
Microbial World. Prentice-Hall, Englewood Cliffs, N.J.
753 pp.
(69) Talbot, G. B. 1966. Estuarine environmental requirements and
limiting factors for striped bass. A Symposium on Estuarine
Fisheries. American Fish. Soc. Special Publication No. 3.
pp. 37-49.
(70) Tarzwell, C. M. 1957. Water quality criteria for aquatic
life. Biological Problems in Water Pollution. Robert A.
Taft Engineering Center, Cincinnati, Ohio. pp. 246-272.
(71) Technical Advisory and Investigations Branch, FWPCA. 1967.
Temperature and Aquatic Life - Laboratory Investigations -
No. 6. Cincinnati, Ohio. 151 pp.
-------
m
(72) U.S. Atomic Energy Commission. 1967. Nuclear reactors built,
being built, or planned in the U.S. as of June 30, 1967.
Technical Information Division. TID-8200 (16th Review).
(73) U.S. Department of Commerce. 1963 Census of Manufacturers.
U.S. Government Printing Office.
(74) U.S. Department of the Interior, FWPCA. 1968 (January). The
Cost of Clean Water--Vol. II. U.S. Government Printing
Offi ce.
(75) U.S. Department of the Interior, FWPCA. 1968 (February).
Thermal pollution--its effect on water quality. Adminis-
trative Report. Presented to the Water Pollution Control
Advisory Board, Chicago.
(76) U.S. Department of the Interior, FWPCA. 1968 (April). Report
of the Committee on Water Quality Criteria. U.S. Govern-
ment Printing Office. 234 pp.
(77) Wallace, N. W. 1955. The effect of temperature on the growth
of some freshwater diatoms. Notulae Naturae. Academy of
Natural Sciences of Philadelphia. 208:1-11.
(78) Warinner, J. E. and M. L. Brehmer. 1966. The effects of
thermal effluents on marine organisms. International Journal
of Air and Water Pollution. 10(4):277-289.
(79) Wittlinger, P. D., Jr. 1968. Economic aspects of thermal
pollution. Presented at the Cooling Tower Institute Meeting,
New Orleans, January.
(80) Wunderlich, W. 0. and R. A. Elder. 1967. Evaluation of Fontana
Reservoir Field Measurements. TVA Engineering Laboratory,
Norris, Tennessee.
-------
112
OTHER REFERENCES
Colby, B. R. 1963. Fluvial sediments, a summary of source,
transportation, deposition and measurement of sediment dis-
charge. U.S. Geological Survey Bulletin 1181-A.
Dillio, C. C. and E. P. Nye. 1959. Thermal Engineering. Inter-
national Textbook Co., Scranton, Pa.
Ford, G. L. Combined Condenser Cooling Water Systems Increase
Plant Availability. Division of Eng. Design, TVA.
Harleman, D. R. F. and R. A. Elder. 1965. Withdrawal from two-
layer stratified flows. Journal of Hydraulics Div., Proceedings
ASCE 4398, July.
Hogerton, J. F. 1968. The arrival of nuclear power. Scientific
American. 218(2).
McLeod, N. B. 1968. Long-term nuclear fuel costs and working
capital requirements for the pressurized water reactor NUS-450.
For PNW Power Company. April.
Mount, D. I. 1968. Implication for aquatic life of heated
discharges. Statement before Senate Subcommittee on February
13.
Rohrman, F. A. 1968. The possible effects of emissions from
power plants upon water pollution. Cincinnati Water Resources
Laboratory, (unpublished).
Strotzke, V. 1960. Power Station Engineering and Economy.
McGraw-Hill.
U.S. Department of Health, Education and Welfare. 1963. Water
temperature--influence, effect, control. Proceedings, 12th
PNW Symposium on Water Pollution Research. Corvallis, Oregon.
November 7.
Water Resources Council, interagency Subcommittee on Sedimentation.
1963. Determination of fluvial sediment discharge. Report #14.
-------