United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600 7-80-078
April 1980
Wet/Dry Cooling
Tower Test Module
Interagency
Energy/Environment
R&D Program Report
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EPA-600/7-80-078
April 1980
Wet/Dry Cooling Tower
Test Module
by
D.M. Burkart
Southern California Edison Company
P.O. Box 800
Rosemead, California 91770
Grant No. R805220
Program Element No. INE624
EPA Project Officer: Theodore G. Brna
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
In February 1978, a ten-member group of utilities, public
agencies, and private concerns, with Southern California Edison
Company acting as Project Manager, began the field testing of a
single cell wet/dry cooling tower (capable of cooling the waste
heat from a nominal 15 MWe of generation) at a generating
station located in San Bernardino, California. The objectives of
the test program were to:
1. Determine the water conservation aspects of
a wet/dry cooling tower in an arid climate.
2. Determine the operational characteristics
of a wet/dry cooling tower.
3. Develop and verify a mathematical model
of the wet/dry cooling tower.
The test program was successful in achieving the stated
goals of determining the water conservation characteristics,
determining the operational characteristics, and developing and
verifying a mathematical model of a wet/dry cooling tower.
Reduction of the data revealed that the wet/dry tower could
save approximately 19% of the water normally evaporated by an
evaporative cooling tower at the San Bernardino Generating
Station without significantly affecting the normal plant perfor-
mance. This degree of water conservation must be considered to
be very good given the conditions of operation. It is also
indicative of the great potential of wet/dry cooling for achiev-
ing significiant water conservation when the system is optimized
with that goal in mind.
During the testing period of eighteen months there were
several operational problems, the most notable being sticking wet
and dry section dampers, which resulted in design modifications
and revised maintenance and operational procedures.
The mathematical model was developed under EPRI contract by
PFR Engineering (Systems, Inc., and was verified by field test
data obtained from the project.
-ii-
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TABLE OF CONTENTS
Page
Abstract ii
List of Figures iv
List of Tables v
Acknowledgements vi
1. Introduction 1
2. Conclusions and Recommendations 7
3. Operating History 8
4. Test Results 9
5. Mathematical Model 18
Appendices
A. Operational Characteristics 20
B. Method of Determination of Heat Rejection
Rate and Evaporation Rate 35
C. Uncertainty Analysis 37
D. Test Instrumentation 39
E. Description of Damper Control System 47
P. Test Plan 49
G. Table of Conversion Factors 51
-iii-
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LIST OF FIGURES
Number
1 San Bernardino Generating Station Plot Plan 2
2 Operational Schematic of Ecodyne Wet/Dry Cooling Tower 4
3 Dry Section Performance 10
4 Wet Section Performance, Hot Water Temp. = 96°P n
5 Wet Section Performance, Hot Water Temp. = 94°F 12
6 Wet Section Performance, Hot Water Temp. = 92°F 13
7 Wet Section Performance, Hot Water Temp. = 90°F 14
8 Wet Section Performance, Hot Water Temp. = 88°F 15
9 Evaporation Rate 16
A-l Damper Linkage (photograph) 21
A-2 Structural Support Member (photograph) 22
A-3 Damper Blades (photograph) 24
A-4 Biological Growth in Hot Water Basins (photograph) 26
A-5 Floating Scum in Hot Water Basins (photograph) 27
A-6 Top View of Hot Water Basin 29
A-7 Example of Finned-tube Fouling (photograph) 30
A-8 Workman Cleaning Finned Tubes (photograph) 32
A-9 Results of Finned-Tube Cleaning (photograph) 33
A-10 Effect of Finned-Tube Cleaning (photograph) 34
D-l Wet/Dry Cooling Tower Anemometer Locations 4o
D-2 Wet Bulb Temperature and Velocity Map of Stack,
"All Wet" 42
D-3 Wet Bulb Temperature and Velocity Map of Stack,
50% Wet/505? Dry 43
D-4 View of Top of Stack showing Psychrometer Location 44
D-5 Wet/Dry Cooling Tower Instrumentation Schematic 46
E-l Damper Control as a Function of Demand 48
-iv-
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LIST OP TABLES
Number
1 Average Site Meteorological Conditions
A-l Typical Wet/Dry Cooling Tower
Circulating Water Quality
-v-
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ACKNOWLEDGEMENTS
The author acknowledges the time given and patience shown
by the active members of the Coordinating Committee: John Bartz
of EPHI, Ted Brna of EPA, Alex Mailer of DWR, Al Ward of Tucson
Electric, Rudy Alleman of Battelle, Cal Singman of LADWP, Harry
Bishop of WEST, and John Lipnicke of Ecodyne; during the testing
period and the preparation of this report. A special thanks is
given to the personnel at the San Bernardino Generating Station,
especially Jack Severn and Mike Varvis, who, many times, bailed
the project out of trouble. Work done by Ron Moore of Environ-
mental Services Corporation, Dave Stackhouse of Ecodyne, and the
SCE Shop and Test Department in helping to calibrate the tower
instrumentation was invaluable.
Finally, a word of gratitude is given to Bill Vanderford
who worked long, hard, and often alone to keep the project
progressing.
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1. INTRODUCTION
FQRMATION_OF_THE WET/DRY COOLING TOWER TEST MODULE PROGRAM
During 1976, a ten member co-operative was formed for the
purpose of constructing and testing a wet/dry cooling tower. The
membership of this group is as follows:
Southern California Edison Company
Tucson Electric Power Company
Department of Water and Power of the City of Los Angeles
Ecodyne Corporation
Electric Power Research Institute (EPRI)
Western Energy Supply and Transmission Associates (WEST)
United States Department of Energy
United States Environmental Protection Agency
State of California Department of Water Resources
State of California Energy Commission
Southern California Edison Company was designated as Project
Manager of the Wet/Dry Cooling Tower Test Module (Wet/Dry Tower).
Onsite construction commenced in April 1977 and was completed in
December 1977. The test program commenced in February 1978 and
was completed in July 1979.
PROGRAM OBJECTIVES
The objectives of the test program were as follows:
1. Determine the operational characteristics of a
wet/dry cooling tower in an actual generating station
environment.
2. Develop a mathematical model of the wet/dry cooling
tower and verify it with actual data.
3- Determine the water conservation aspects of a wet/
dry cooling tower operating in an arid climate.
TEST LOCATION AND AVERAGE METEOROLOGICAL DATA
The Wet/Dry Tower was sited at the Southern California
Edison Company's San Bernardino Generating Station located in San
Bernardino, California. The generating station consists of two
60 MW oil/ gas fired units cooled by two 10-cell evaporative
cooling towers. The layout of the station is shown in Figure 1.
The Wet/Dry Tower is situated near the north station cooling
tower with a portion of the plant circulating water being by-
passed from that tower to the Wet/Dry Tower by a small circu-
lating pump. The water is returned to the north tower basin by
gravity flow from the Wet/Dry Tower basin.
-1-
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LEGEND :
weather
station
SCALE
N
t
station fence
Wet/Dry Tower
discharge
water
inlet
water
station
cooling towers
Unit 2
boilers
ontrol
room
turbir es
Unit 1
switch-
yard
Figure 1. San Bernardino Generating Station Plot Plan
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The average meteorological conditions recorded at the site
during the test period are as follows:
TABLE 1. AVERAGE SITE METEOROLOGICAL CONDITIONS
Jan Feb Mar Apr May Jun
Mean High Dry Bulb(°F)» 63 66 68 73 78 85
Temperature Wet Bulb(°F) 52 53 53 56 59 61
Mean Low Dry Bulb(°F) 38 40 43 47 51 55
Temperature Wet Bulb(°F) 35 36 38 40 42 45
Jul Aug Sep Oct Nov Dec
Mean High Dry Bulb(°F) 95 94 91 81 71 64
Temperature Wet Bulb(°F) 64 64 63 59 55 54
Mean Low Dry Bulb(°F) 60 61 58 51 43 39
Temperature Wet Bulb(°F) 49 50 49 45 40 36
DESCRIPTION OP WET/DRY COOLING TOWER
As seen in Figure 2, the Wet/Dry Tower (manufactured by
Ecodyne Corporation) is essentially a crossflow evaporative
cooling tower below with a crossflow water-to-air surface heat
exchanger on top. The water flow path is from the hot water
basin atop the tower down through the finned-tube dry section
directly onto the splash-fill wet section. The air flow path is
parallel through both the wet and dry sections with air flow
being controlled independently to each section by dampers. The
amount of heat rejected by either the wet or dry sections is
controlled by these dampers. It is possible to operate the tower
in the all-wet or all-dry modes, or any combination of the two,
by opening or closing the dampers.
The dry section tubes are 1 inch O.D., constructed of
copper-nickel with aluminum fins rolled on the tubes. The
overall diameter of the finned tubes is 2.25 inches; there are 11
fin spirals per inch, and the total length of the tubes is 19
feet, 3 inches. There is a total bare tube surface area of
approximately 20,000 square feet. Operationally, water flows
into the tubes from the hot water basins through flow control
nozzles. The flow control nozzles are of a unique design which
causes the water to spiral down the interior wall of the tube,
* English system units rather than metric have been used through
this report because the English system remains the standard in
the utility industry for which this report is intended. A
conversion table is included as Appendix G.
-3-
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WARM DRY
EFFLUENT
DRY
SECTION
DAMPERS
WET
SECTION
DAMPERS
HEAT
EXCHANGER
NT
INTAKE
LOUVERS
Figure 2
Operational Schematic of Ecodyne
Wet/Dry Cooling Tower
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creating a film flow condition which significantly increases the
heat transfer coefficient over conventional axial flow. There
are 7 basins per side (14 in total) with 273 finned tubes per
basin. The flow to each basin is individually controlled by
butterfly valves.
The water exits the tubes through nozzles which spray the
water directly onto the splash fill in the wet section. Fixed
positon air intake louvers are provided to prevent splash leakage
out of the wet section. The wet section is 29 feet high.
The dampers are actuated by motor drives which are located
on the fan deck at the top of the tower. The drive elements pass
through the deck to torque tubes which connect to the dampers.
The damper positioning is accomplished by a unique damper control
system which automatically controls the distribution of air flow
between the wet and dry sections based on the exiting cold water
temperature. A complete description of the damper control system
is found in Appendix E.
Air flow is provided by a 28 foot diameter fan which has 8
blades. The fan is powered by a 250 horsepower motor and runs at
a constant 135 RPM. The blades are manually adjustable for
pitch angle.
LIMITATIONS OF TEST FACILITY
As can be seen from Figure 1, the Wet/Dry Tower is situated
as a side-stream process to the station's main cooling towers.
During normal testing, the Wet/Dry Tower has a water flow of
approximately 20% of the total circulating water flow. Combined
with the fact that the main towers have a larger cooling range
and a lower approach than the Wet/Dry Tower, this results in the
Wet/Dry Tower having little effect on the condenser circulating
water exit temperature (cooling tower inlet water temperature).
During the summer months this causes no difficulty as the cooling
tower inlet temperature is sufficiently high enough to allow the
tower to develop a full range of cooling, but in the winter a
problem does exist. Because of the lower approach and larger
range of the main towers, the cooling tower inlet temperature is
too low to allow the Wet/Dry Tower to develop a full range in the
all-dry cooling mode. During the winter the station condensers
typically operated with a backpressure in the range of 1.1 to 1.4
inches HgA (mercury, absolute). A backpressure of 4 to 4.5
inches HgA would have been required in order to allow a normal
cooling range in the all-dry cooling mode. Operating at such
high backpressures solely for the purposes of this test could not
be economically justified.
This limitation did not present serious difficulties in
defining the dry section parameters, but did limit the simulation
-5-
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of normal winter operation.
-6-
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2. CONCLUSIONS AND RECOMMENDATIONS
Possibly the most important result of the test program was
the development and verification of the mathematical model. This
will be very valuable in future site selection and preliminary
engineering. Unfortunately, the model at this time is limited to
this particular design of wet/dry cooling tower, which somewhat
limits its usefulness. It is anticipated that additional im-
provements will be made to the model a result of the data taken
during the test program, resulting in a more flexible predictive
tool.
The major goals of the program were achieved and wet/dry
cooling has been shown to be an effective and viable method of
achieving water conservation at an inland generating station
(approximately 19% during the test program). However, during the
test period several areas of investigation, the most notable
being the measurement of the individual wet and dry section air
flow rates, had to be abandoned as unproductive.
The eighteen month period of field operation revealed two
deficiencies which will require further rectification before
this design of wet/dry cooling could be recommended without
reservation for commercial operation. The major concern lies
with the sticking air control dampers; this problem renders
automatic control of the tower impossible. As discussed in this
report, it is recommended that several improvements be made in
order to assure reliable operation:
1. Redesign of the damper drive linkages. Although
this is already being done by the manufacturer,
it will be necessary to field test in order to prove
the design.
2. New motor drives should be selected to provide more
starting torque.
3. The drive linkages for the damper blades should be
positioned on both ends of the blades rather than on
one end only as is presently done.
The other deficiency lies with the fouling of the dry
section finned tubes. Ecodyne has presented and proved one
method of cleaning which is labor intensive and expensive. Some
type of permanently mounted cleaning system which would provide
the option for reduced manpower must now be developed. This
would allow an evaluation of the site to be made, taking into
account such factors as expected cleaning frequency, site
remoteness, cost of labor, and capital expense of the permanent
system, yielding the most economical method of cleaning.
-7-
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3. OPERATING HISTORY
On February 6, 1978, testing was initiated and on July 23,
1979, the test program was completed. During the 532 day test
period, the Wet/Dry Tower was available for testing 80.3% of the
period. Additionally, due to a labor strike which required the
reassignment of some SCE technical and managerial personnel, the
Wet/Dry Tower was unmanned a major portion of the period from May
1, 1978, through July 30, 1978. During this period no testing was
performed although data was collected automatically on an hourly
basis.
The unavailability of the Wet/Dry Tower can be broken down
into the following categories:
Sticking Dampers 10%
Biological Growth in Hot Water Basins 1%
Instrumentation Failures 5%
Fan Drive Shaft Bearing Failure 8/?
Recalibration and Relocation
of Instrumentation J6%
The problems encountered with sticking dampers and biologi-
cal growth in the hot water basins are discussed in detail in
Appendix A. The fan drive shaft bearing failure was due to
faulty maintenance. The instrumention failures occurred solely
with the data acquisition and storage systems. The recallbration
is discussed in Appendix D.
Because of these problems, most notably the sticking dampers
and instrumentation failures, the test plan was not followed
in its entirety as is detailed in Appendix F. However, the
primary objectives of the test plan wera met.
-8-
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4. TEST RESULTS
TOWER PERFORMANCE
Figure 3 shows the dry section performance in degrees
Fahrenheit of water cooling (dry section range of cooling) as a
function of the temperature difference between the inlet hot
water temperature and the inlet air dry-bulb temperature at a
constant water-air mass flow ratio. Two distinct sets of data
are plotted, data taken with the finned tubes heavily fouled and
data taken after cleaning of the tubes (see Appendix A). A
marked difference between the two is obvious. The data taken
with the finned tubes heavily fouled were all taken within a two
month period and, therefore, do not reflect any function of
fouling with relation to time. By calculation, the air-side heat
transfer coefficient was found to be ^5% higher for the clean
tubes over the fouled tubes. The data taken with the clean tubes
were taken during a short period of time and cannot be considered
complete. However, the greatly improved agreement between this
data and the performance predicted by the mathematical model is
very encouraging.
Figures 4, 5> 6, 7 and 8 show the wet section performance
in degrees Fahrenheit of water cooling (wet section range of
cooling) as a function of the temperature difference between the
inlet hot water temperature and the inlet air wet bulb tempera-
ture at a constant inlet hot water temperature and constant
water-air mass flow ratio. Both the performance predicted by the
mathematical model and the measured performance are shown. The
predicted performance is very close to the measured, never
varying more than +3% or -7%. For the mathematical model, water
flow rate and inlet hot water temperature are input values, which
means that the calculated cold water temperatures never varied
from these measured by more than + 3% or -7%.
Figure 9 shows the evaporation rate of the Wet/Dry Tower
as a percentage of the Inlet water flow rate per degree Fahren-
heit of the wet section range of cooling. The evaporation rate
is a function of the difference between the wet section inlet
water temperature and inlet wet bulb temperature at a constant
wet bulb depression. Both the predicted evaporation rates and
the measured evaporation rates are shown. Correlation is
acceptable with the predicted ranging from -H% to -19% of the
measured rate.
The data used in preparing these curves were obtained from
carefully controlled tests in order to minimize error. Data
were taken both at constant air flow rates with varying water
flow rates and at constant water flow rates with varying air flow
rates.
-9-
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Figure 4. Wet Section Performance, Wet Section
Hot (Inlet) Water Temperature = 96°F
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Figure 9. Evaporation Rate
-------
Data collected hourly by the data acquisition system were
used to analyze the Wet/Dry Tower operational modes during
varying atmospheric conditions. During the one-year period of
operation from July 1, 1978, to June 30, 1979, the dry section
dampers were open 41% of the time, creating a water savings of
13%. Because of the fact that the Wet/Dry Tower was down for
repairs and relocation of instrumentation during a large period
extending from October to December 1978, this is not a true
measure of the potential water savings. Based on the performance
of the Wet/Dry Tower and the atmospheric conditions during that
period, it is estimated that the potential water savings during
that period would be approximately 19%. An even more significant
water savings could have been achieved had it been possible to
develop a full range of cooling in the all-dry cooling mode
during the winter months (see Limitations of Test Facility for a
full discussion).
MEASUREMENT OF DAMPER AIR LEAKAGE
One of the unknowns when this program began was the amount
of air leakage which could be anticipated through the dampers.
One method which was tried to measure the leakage was holding a
totalizing anemometer in various locations near the closed
dampers for a specific period of time. The repeatability of data
using this method was very poor. After several other trials, it
was concluded that the air flow rate due to leakage was too low
to be measured by direct means.
The entering and exiting water temperatures of both the wet
and dry sections were then examined. In the case of the all dry
cooling mode with the wet dampers closed, it was found that a
large, easily measured differential existed between the entering
and exiting water temperatures in the wet section. This tempera-
ture differential indicated a significant air leakage. By
calculation, it was determined that the air leakage through the
wet dampers must have been approximately 8 to 9% of the total
measured air flow through the tower in order to cool the water
by that amount. In all, 15 different cases were examined with a
low leakage rate of 8.3% and a high of 9.1%.
The consistency of these results allow a comfortable predic-
tion of the leakage in the wet dampers, but unfortunately this is
not the case for the dry dampers. The temperature differential
that exists in the dry section with the dry dampers closed was
quite small, in most cases being less than the accuracy of the
instrumentation. However, since the design of the wet and dry
dampers is identical, it should be reasonable to assume that the
leakage per unit area of damper would be nearly the same. The
area of the wet dampers is 2474 ft2 and of the dry dampers 1622
ft2. This then would correspond to a dry damper leakage rate
of approximately 5 to 6% of the total air flow through the tower.
-17-
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5. MATHEMATICAL MODEL
As previously stated, one of the three objectives of the
test program was the development and verification of a mathe-
matical model of the Wet/Dry Tower. PPR Engineering Systems
Inc., of Marina del Key, California, was selected to provide the
analysis in the form of a computer program.* The analysis was
performed separately for the wet and dry sections with the water
condition at the exit of the dry section used as input to the wet
section. Each section is treated as a crossflow tower which is
divided into a grid of small increments in both the water flow
direction and air flow direction.
As the wet and dry sections are both served by a common fan
system, neither the total air flow through the system nor the
distribution of air between the wet and dry sections is known.
The program incorporates several convergence calculation loops*
enmeshed in each other, which determine the above unknowns. The
total air flow and its distribution between the wet and dry
sections are initially assumed to allow a first set of calcula-
tions to be made.
The calculation procedure determines the amount of heat and
mass transferred and the pressure drop in each section for the
assumed flows. The pressure drop over each major element in the
flow path is determined including the tube bundle, the fill,
dampers, louvers and any turns encountered by the air. The
heat transfer in the dry section and the heat and mass transfer
in the wet section are calculated on the basis of the physical
principles of the transfer process combined with empirical data
for the properties of the fill.
The first convergence loop checks whether the air side
pressure drop from the inlet to the tower to the exit of the fan
is identical for both the wet and dry sections. If the pressure
drop comparison is not within 1% convergence tolerance, a new
split of the flow distribution is assumed, and the calculation is
repeated until convergence. An outer convergence loop determines
the total air flow rate that corresponds to tower air pressure
and the fan characteristics.
Verification of the mathematical model was done with two
fan pitch angles, 13° and 17°, at various damper settings,
including all-wet, all-dry, and 50/&-wet/50#-dry. Because of the
difficulties experienced with sticking dampers (se=j Appendix A),
less useful data were obtained at the intermediate damper setting
*PFR Engineering Systems, Inc. A Computer Program for the
Performance Simulation of Wet/Dry Cooling Towers. Marina
del Ray, CA. 1977. 48pp.
-18-
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complete discussion of the correlation of predicted and actual
performance is found in Test Results. Briefly, however,
with the exception of the dry section, correlation of actual
data with predicted results fell within acceptable limits.
Additional testing showed the extreme fouling of the finned tubes
to be the chief contributing factor to the poor correlation of
the dry section data, and also pointed out a weakness of the
mathematical model, the need to provide a dry section fouling
factor. PFR has agreed to make the necessary modifications to
the program to provide this factor.
-19-
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APPENDIX A
OPERATIONAL CHARACTERISTICS
The number of operational problems encountered was small-
however, correction of the problems proved to be quite difficult!
Three specific problems (sticking dampers, biological fouling,
and finned tube fouling) accounted for all abnormal maintenance
activities.
STICKING DAMPERS
The most significant problem was that of sticking dampers,
which rendered automatic control of the Wet/Dry Tower impossible!
Sticking was first noted in the wet section dampers in May 1978
less than 5 months after the Wet/Dry Tower commenced operation
and only 3 months after the tower began continuous operation. At
that time a design deficiency was noted in the linkages that
connect the damper panels to the torque tubes (see Figure A-l).
The O.D. of the shoulder bolt and the I.D. of the metal linkage
bushing were nearly identical and did not allow room for the
fiber bushing which was to fit between them. This resulted in
galling which appeared to be causing the sticking. New linkages
were supplied by the manufacturer and installed, but within a
short period the sticking resumed in the wet section dampers.
After a careful review, it was concluded by the manufacturer
that the sticking was due to a misalignment of the damper panels.
Additionally, it was found that the torque tube universal joints
contained hollow pins which were falling out, causing a situation
where the dampers were being partially opened by the torque being
transmitted through the U-joirit dust cover. Following these
repairs, the Wet/Dry Tower operated for a short period withaut
sticking before the tower was shut dov>n for recalibration of the
instrumentation.
When the Wet/Dry Tower resumed operation, the south dry
section dampers jammed in the mid-range position. Individual
damper blades were impacting both structural support members and
structural bolts. The solution was providing additional clear-
ances between the dampers and the structural support members, and
removal of some bolts (see Figure A-2).
Immediately after the tower was returned to service, the wet
section dampers began sticking again. At this point, a panel was
loosened from the torque tube and an attempt was rade to actuate
It manually. It took two men to move the damper through its
complete range of motion. Penetrating oil was then applied to
the 38 pivot points in the panel with the result that the damper
could be moved easily with one hand. With this knowledge, several
linkage arms were removed and sent to the manufacturer for analy-
sis. Extensive corrosion between the brass bushing and the stain-
-20-
-------
Figure A-l
Damper Linkage with Linkage
Shoulder Bolt and
Bushing Shown Circled
21
-------
Figure A-2
Structural Support Member
with Bolt Removed
and Clearances
"Chipped" Away
22
-------
less steel linkage pin was discovered. The solution to this will,
at a minimum, require the complete redesign of the linkages.
Currently, redesigned linkages have been installed in the
Wet/Dry Tower, and an operational test of approximately 3 months
is underway. Results of that test will be issued as an addendum
to this test report.
It is important to note, however, that unless the new
linkages are completely successful, "additional redesign of the
dampers will be required in order to make them suitable for a
commercial utility application. As can be seen in Figure A-3, a
heavy deposit of scale has already built up on the damper blades
after only 18 months of operation. Considering the good quality
of the circulating water at the Wet/Dry Tower (Table A-l), the
reliability of the linkage pivot points with the poorer quality
water typical of the Southwest is questionable. The use of some
form of either sealed or pressure-lubricated joints may ulti-
mately be required. Additionally, the present method of driving
the dampers from only one side only appears inadequate; an
arrangement of driving from each side of the dampers would be
much more suitable for reliable operation. This would result in
the torque being transmitted directly through the area where the
sticking occurs, rather than being reduced by the twisting of the
flexible blades as the torque is transmitted along the length of
the blade. Finally, the size of the motor drives, which is
presently 1/4 horsepower, should be significiantly increased to
provide more starting torque.
BIOLOGICAL FOULING
In mid-summer of 1978, after approximately six months of
operation, a heavy build-up of biological growth was observed in
the hot water basins (Figure A-4). The majority of the growth
occurred at the end opposite the hot water distribution piping
where the lowest water velocities occur. A secondary problem,
the buildup of a foamy scum floating on the surface, was also
observed in the same area (see Figure A-5). The growth is pri-
marily algae, not tenacious in its adherence, and easily removed
with a garden hose stream of water. In fact, it is this quality
which created the worst problem; the algae would break off in
chunks and block the flow control nozzles.
In investigating this problem, a large quantity of sawdust
was discovered to be layered in with the algae. The presence of
the sawdust is due to standard operating procedure at the San
Bernardino Generating Station; sawdust is added to the circu-
lating water to stop small condenser leaks temporarily. It is
probable that the presence of the sawdust acts to accelerate
biological growth by supplying nutrients, but the growth would
most likely still be present and result in operational problems
-23-
-------
Figure A-3
Damper Blades Showing
Heavy Deposition
of Scale
24
-------
TABLE A-l
TYPICAL WET/DRY COOLING TOWER
CIRCULATING WATER QUALITY
Total Hardness as CaC02 100-150 nig/1
Total Alkalinity as CaC02 200-300 mg/1
Total Dissolved Solids 300-400 mg/1
Electrical Conductivity 500-700 umhos
cm
pH 8.2-8.7
Calcium 35 - 55 mg/l
Magnesium 4-8 mg/1
Sodium 50 - 120 mg/1
Potassium 4-6 mg/1
Sulfate 30 - 70 mg/1
Chloride 10 - 50 mg/1
Nitrate 5-15 mg/1
-------
Figure A-4
Build-up of Biological
Growth in Hot Water
Basins
26
-------
Figure A-5
Floating Scum in
Hot Water Basins
27
-------
without the sawdust.
A review of the station's water quality control revealed
that chlorine is used as the only form of biological control.
The injection of chlorine is made near the inlet of the condenser
for a period of 30 minutes per eight-hour shift, and the level of
residual chlorine is maintained below 0.5 pprn at the condenser
outlet. By the time the chlorine travels nearly 1000 feet to the
tower, its concentration level is far too low to be effective for
biological control.
By trial and error the following steps were discovered to
be effective in controlling the problem. Removal of three
flow control nozzles in the outboard row, one from each corner
and one from the middle (Figure A-6), significantly increases the
water flow rate in the otherwise stagnant outboard area. The
benefits from this are threefold: (1) slower build-up of
growth, (2) lessening of flow control nozzle pluggage, and (3)
elimination of the build-up of floating scum. Additionally, the
individual basins are shock treated with sodium hypochlorite on a
quarterly basis by isolating the basin from hot water flow,
adding two gallons of the sodium hypochlorite, and "soaking" for
a period of one hour. The basin is drained and then thoroughly
rinsed before returning to service. This process is performed
one basin at a time with the tower in operation.
FOULING OF FINNED TUBES
Fouling of the finned tubes in the dry section became
obvious after a few months of operation and grew steadily worse
throughout the test program. In discussions with the manufac-
turer, it became apparent that although a fouling factor was used
in determining the heat transfer area required, no one had
anticipated the degree of fouling which occurred (see Figure
A-7). In fairness, the San Bernardino site is possibly a little
unusual in that besides being situated on a dirt and loose gravel
field, the Wet/Dry Tower is also located near the northern and
eastern fence of the station. The land on the other side of
these fences is agricultural and is disked and plowed several
times a year, which puts a considerable amount of dust into the
air. Also, a high degree of pollen and insects exist in the
area. However, dust, pollen and insects are factors which will
exist to some degree at most sites located in the Southwest and
as such must be accounted for in future design.
Another point of consideration is that although no docu-
mentation could be located as to the condition of the tubes
either when they arrived at the site or when they were installed,
a small sample section which was cut for demonstration purposes
does exist. Examination of that section yielded a light machine
oil coating on the fins, most likely left there from the rolling
-28-
-------
Center of Tower
inlet,flow
1
inlet, flow
I
*^ _^ ^ u, -^ x***' ^» " ^ >*.*^ — >—^ -x--»^>*
ooooooooooo
ooooooooooo
ooooooooooo
ooooooooooo
ooooooooooo
ooooooooooo
o o o o o o oo oo o
flow control nozzles removed
Figure A-6. View from top of a hot water basin showing
location of flow control nozzles removed to
aid in control of biological growth
29
-------
Figure A-7. Example of
Finned Tube Fouling. The
Tube Shown is in the
Outermost Row (Row 1).
30
-------
process which attached the fin to the tube. The presence of this
oil on the fins would very likely result in a faster initial
build-up of fouling and possibly a thicker deposit.
Following the completion of the test program and the shut-
ting down of the Wet/Dry Tower, a demonstration cleaning of the
south dry section tubes was performed in order to ascertain the
cost of periodically cleaning the tubes. The cleaning was per-
formed by SERMAC Industrial Cleaning, Inc., with an eight-foot
long "lance" which allowed the operator to reach in approximately
five feet into the dry section (see Figure A-8). A ^5° angle
spray nozzle was used with a flow rate of 8 gpm, a water tempera-
ture of approximately l40°P, and a water pressure of 300 psi
eight inches from the tip. Initially a degreasing agent was
used, but examination revealed that hot water alone was nearly
as efficient in cleaning and greatly reduced the time required.
Results of the cleaning are shown in Figure A-9. By visual
examination, it appears that in excess of 90? of the fouling was
removed.
Figure A-10 shows the effects of the cleaning to a depth of
15 rows of tubes. The number attached to each tube is its row
number counting from the outside in, and there are a total of 25
rows in each basin. Because this was a demonstration cleaning,
it was decided to clean only the exterior half of the south dry
section to limit cost. As can be seen in Figure A-10, good
cleaning was achieved through Row 9, but slight fouling is
observed in Row 12, which is almost the mid-way point of the dry
section. By row 15 the effects of cleaning are not observable.
It is estimated that the cost to perform the entire cleaning job
from both the outside and inside of the two dry sections would be
approximately $3600.
Based upon this experience, it would seem that some form of
in-place cleaning system should be explored for commercial
applications of the tower.
-31-
-------
Figure A-8
Workman using eight foot "lance"
to clean finned-tubes.
32
-------
Figure A-9
Results of finned-tube cleaning. View is
from outermost row (Row 1) inward.
33
-------
Figure A-10
Number^ K* cleaninS Progressing toward center of
show) n tUbe is the row number, with row 1 (not
ing the outmost row away from center of tower.
34
-------
APPENDIX B
METHOD OP DETERMINATION OP HEAT REJECTION RATE AND
EVAPORATION RATE
The method used to calculate the actual heat rejection rate
and evaporation rate of the Wet/Dry Tower is relatively simple.
Based on the data taken, a total tower heat rejection rate can be
calculated for both the water-side (which loses the heat) and the
air-side (which gains the heat). As is shown in Appendix 7.3,
the water-side calculation is the more accurate and is used to
confirm the air-side data for calculation of the evaporation rate.
Qw= Mw Cp (T2 - TI)« (1)
Where
Qw = water-side heat rejection rate (Btu/hr)
Mw = circulating water mass flow rate (Ibs/hr)
CD = constant pressure specific heat of water
(Btu/lb-°P)
T2 = inlet (hot) water temperature (°P)
TI = outlet (cold) water temperature (°P)
The air-side heat rejection rate is calculated as follows:
Qa = Ma (h2 - hi)* (2)
Where
Qa = air-side heat rejection rate (Btu/hr)
Ma = dry air mass flow rate (Ibs/hr)
h2 = enthalpy of air exiting the cooling tower
(Btu/lb of dry air)
hi = enthalpy of air entering the cooling tower
(Btu/lb of dry air)
por these two calculations, T2 and TI are measured directly
and Ma, Mw Cp, h2, and hi are determined from tables.
T~Kreith, Frank. Principles of Heat Transfer, International
Textbook Company, Scranton, PA, 2nd edition, 196?. 620
pp.
-35-
-------
The evaporation rate can be determined using the equation:
E = Ma (Wm2 - Wmi) (3)
Where
E = evaporation rate (Ibs./hr.)
WHIP = weight of moisture per pound of dry air
at tower outlet
Wmi = weight of moisture per pound of dry air
at tower inlet
In this equation Wmi and Wm2 are determined by the
respective wet and dry bulb temperatures and are available in
psychrometric tables.
In expressing the water savings of a wet/dry cooling tower,
the evaporation rate of the wet section is the critical para-
meter. If all of the heat rejection from the water to the air is
assumed to be by release of the latent heat of vaporization (eva-
poration), then it can be said that the evaporation rate varies
directly with the wet section range of cooling (hot water tem-
perature minus cold water temperature) for any particular set of
conditons (tower air flow, tower water flow, ambient air condi-
tions, and tower inlet water temperature). This is true because
the latent heat of vaporization of water is nearly constant for
small changes of temperature such as is experienced in a cooling
tower. From equation (1) it can be seen that the wet section
heat rejection rate must vary directly with the wet section range
of cooling, and since all heat is rejected by evaporation, then
the rate of evaporation must vary directly with the wet section
range of cooling.
Therefore, since the dry section (when in operation) dis-
places a portion of the wet section range of cooling, the water
savings may be expressed as the ratio of dry section range of
cooling to the total tower range of cooling.
Water Savings = —| "_Tj" x 100 (4>
Where T
-------
APPENDIX C
UNCERTAINTY ANALYSIS
The uncertainty In the calculated parameters may be deter-
mined by replacing the measured values with the measured values
plus the Instrument errors and solving for the total error. In
the cases where multiple measurements are made, the probable
error of the instruments is determined by the method of least
squares and substituted for the instrument error. Data taken
from the Wet/Dry Tower consisted of two types: (1) data taken
during controlled testing and (2) data taken hourly by the
automatic data acquisition system. Data taken during controlled
testing are as accurate as possible, with all sources of error
minimized. The data were taken at steady-state conditions, and
several runs of data were taken within a short time of each other
and averaged in order to minimize transients due to changing
barometric conditions, wind, contact resistances, etc. These
data were used for the verification of the mathematical model.
The hourly data describe the operational modes of the Wet/Dry
Tower and were useful in estimating water savings, although the
errors associated with these data must be significantly higher.
The accuracy of the instrumentation used at the Wet/Dry Tower is
as follows:
Hot and Cold Water Temperature, measured by Resistance
Temperature Detectors (RTD) +_ 0.2°P
Stack Psychrometers ~
- Wet Bulb Temperature (RTD) + 0.8°P
- Dry Bulb Temperature (RTD) -f 0.8°P
All Other Psychrometers
- Wet Bulb Temperature (RTD) - 0.2°F,
+ 0.70F*
- Dry Bulb Temperature (RTD) + 0.2°P
Water Plow Meter + i£
Air Plow Rate (Pan Curve from measured Fan KW) +5%
Estimated
Data Acquisition System + 0.1*
The uncertainty expected for the calculated parameters are
as follows:
Waterside Heat Rejection Rate + 4 to 6%
Airside Heat Rejection Rate + 6 to 10%
Evaporation Rate + 6 to IQ%
Wet Section Range of Cooling +_ 3 to 5%
Dry Section Range of Cooling + 10 to 20%
-37-
-------
Where the probable error of each measured value was determined by
Peter's Formula.
r0 = °'8453 Ivil + |v2l + + lvnl)*
n n-1
Where
ro = probable error of the mean
n = number of measurements
v = residual of the observed value In relation
to the mean (I.e., vn = xo - xn)
* Franklin, Phillip. Mathematics. In: Standard Handbook for
Mechanical Engineers, T. Baumeister and L. F. Marks, eds.
McGraw-Hill Book Company, New York, NY, 6th edition, 1967.
pp. 2-32 to 2-3^.
-38-
-------
APPENDIX D
TEST INSTRUMENTATION
AIR PLOW MEASUREMENTS
During the early stages of the testing program, extensive
instrumentation was in place on the exterior of the tower for the
determination of individual air flows through the wet and dry
sections. The instrumentation consisted of eight anemometers per
section (See Figure D-l). The anemometers were propeller-type,
designed to null in a crosswind.
Attempts to calibrate the anemometers were unsuccessful, due
to the prevailing west winds which caused erratic readings.
Several types of shielding were tried with some improvement, but
the readings remained too erratic to be of value. Trials were
made at other locations, including inside the tower, but these
were also unsuccessful. Inside the tower, the problem was the
dampers. Each change in damper angle altered the air currents
and affected the anemometer readings.
Total tower air flow was obtained indirectly from the fan
motor horsepower using a calibrated air flow - fan horsepower
curve for each fan blade pitch angle. The curves were plotted
from equal area traverses which were performed with the dampers
in the all-wet mode, the all-dry mode, and the 50% wet/50!t dry
mode. It is estimated that the curve data are accurate to +_ 5/&.
STACK PSYCHOMETRIC MEASUREMENT
Initial efforts to calibrate the Instrumentation monitoring
the stack exit air temperatures (wet-bulb and dry-bulb) were
unsuccessful, as demonstrated by an inability to balance the
air-side and water-side heat rejection rates. It is essential
that the heat rejection rates balance within the error of the
instrumentation as a check of the validity of the measured exit
air conditions. Prom these conditions the evaporation rate of
the wet section is calculated.
The difficulty lies in correctly determining the location
of the instrumentation under a 28-foot diameter fan with various
structural crossbeams creating eddys and localized high velocity
areas. It was finally determined that it would be necessary to
"map" the stack on a one foot grid for both wet-bulb temperature
and air velocity.
In mapping the stack, it was first determined by measurement
that the north and south halves of the stack were symmetrical.
This allowed the mapping of only one-half of the stack to gain
the required results. The instrumentation, a wet-bulb psychro-
meter and an anemometer, were located on a moveable trolley 1.5
-39-
-------
A 1 f A
A) f A
I
I
I
I
I
I
I
I
I
r
LEGEND: ANEMOMETER
Figure D-l.
Wet/Dry Cooling Tower
Anemometer Locations
40
-------
feet below the fan. The results of the mappings are shown In
Figures D-2 and Figures D-3.
As a result of the mapping exercise, it was learned that
placing fixed location instrumentation in the stack for measuring
exit air conditions does not provide optimum results. Due to the
shifting of the air currents that occur with changes in the
damper settings, the placement of the instrumentation (Figure
D-U) was a compromise. The locations were selected to take
advantage of the symmetry of the stack while still allowing for
effects such as fouling, wind, etc. which might affect one side
of the tower more severely than another.
Because of schedule and budget restraints, a more ideal
system for this test facility could not be installed. Such a
system would consist of a minimum of four packages, each con-
taining a psychrometric station and an anemometer, running on
tracks in the fan stack. Positioning of each package would be
controlled by a mini-processor. Such a system would be capable
of performing an equal area traverse of the stack (based on 10
areas) every half-hour. However, observations indicated a
repeatable error of approximately +_ 0.8°F for the fixed location
instrumentation in both the wet bulb and dry bulb temperatures of
the exiting air, which was considered acceptable.
RECALIBRATIQN AND RELOCATION OF TEST INSTRUMENTATION
All resistance temperature detectors (RTD) were calibrated
to + 0.2°F against an NBS calibrated thermometer. The data
acquisition system was calibrated to + 0.1°F. Both air flow and
water flow were recalibrated by equal area traverses with cali-
brated Pitot tubes.
During this same time period, it was determined that some
relocation of instrumentation would be undertaken to increase
data accuracy. Specifically, two more ambient weather psychro-
metric stations were established in addition to the one existing,
ten RTDs were placed beneath the dry section water discharge to
monitor dry section cold water temperature, and two additional
psychrometric stations were placed in the stack (see STACK
PSYCHROMETRIC MEASUREMENTS in this Appendix) for the measurement
of stack exit air temperatures. Eight of the sixteen psychro-
metric stations on the exterior faces of the tower were removed
to supply the needed instrumentation, with four stations being
relocated and four stations being pirated to supply eight of the
ten required RTDs. The remaining two RTDs were purchased.
LOCATION OF TEST INSTRUMENTATION
As mentioned earlier, some improvements in type and location
of instrumentation were accomplished in order to increase sensi-
-41-
-------
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(68.0)(6&.4)(61.3)(70.2)(71.3)(61.6)
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• • • ••••«
30.4 27.9 32.J 29.6 31.3 30.0 28.9 23.8
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33.3 34.2 36.6 35.4 37.9 35.0 40.8 40.4 33.3
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3*.9 35.4 34.1 35.0 33.3 27.5 31.6 35.8 32.5 41.6 28.3 26.6
Ambient Conditions
wet bulb temperature - 46.5°F
Tower Conditions
inlet water temperature - 79.0°F
discharge temperature - 66.3°F
air flov rate - 1,240,000 CFM
water flow rate - 13800 GPM
3X58.4) '
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(67.3X68.2) (69.1X68.6) (69.5X70.3) (72.0)(73.9X73.4) (73.6) (7^.3X70.7X69.9X6^.6)
3*.2 3*4 28.3 29.1 300 25.0 35.4 36.6 36.6 36.6 400 28.3 *T.6 50-0
(67.4X69.4X70.7X72.1) (74.4)(75.1)(74.8) (70^.6X70.4X6^.8X60.8)
lf.1 2?.S 18.3 18.7 2*.5 26.2 27.5 29.1 40.0 40-8 3*.l
Calculated Results
mean stack velocity
mean wet bulb temperature
velocity - weighted mean
wet bulb temperature
calculated air flow rate
water side heat rejection rate
air side heat rejection rate
heat rejection rate deviation
34 ft/sec.
70.5°F
73.1°F
1,320,400 CFM
1,459,900 BTU/min.
1,647,700 BTU/min.
12.97. (within error
of instruments)
This
contains
fan
and
drive
shaft
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28.3 30.0 24.1 31.2 3*.5 3*. 2 3*. 3 35.0 3*.0 36.6 3*.6
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27.5 32.5 29.1 29.1 25.4 29.1 30.8 31.2 30.0 20.8 30.0
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3*2 31.2 26.6 34.1 36.6 36.6 3*. 1 42.1 4*.6 42.1 3f.6
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(72. 7X73.9) (74. 3X75^.5) (76.1X75.1X70. 7) (65.8)(59.4)
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(70.1X70.4X58.3)
3*. 3 34*. I 2?.8
The numbers in parentheses are the wet bulb
temperatures in degrees Fahrenheit. The
remaining numbers are the air velocities in
feet per second. The data was collected over
a four day period which resulted in a range
of ambient conditions. To account for this,
the wet bulb temperatures have been normalized
to the ambient conditions indicated. The
diameter of the stack is 28.7 feet where the
measurements were taken.
Figure D-2. Wet Bulb Temperature and Velocity
Map of Stack During "All Wet" Mode of Operation
42
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(61.2)(58.4)(58.7)
37.7 38.7 35.6
59.0)(60.5)(63.4)(63.2)(64.8)(66.1)
tt.O 42*.8 F
1.475.700 CFM
1.230.000 BTV/nin.
1.312.000 BTU/mln.
6.71 (within error
of Instruments)
[69^.5) (67.1) (67^7) (68^.7) (74^4) (75^7) (75^.9) (64rf8) (59rfl) (55^.5) (53^.9) (53^8) (51^2) (49^1)
25.8
IJ.y> VO^.O; \jy,t.i \JJ.JI \jj.7; I^J.O,
34".8 26".7 34*5 38.3 42.7 41.1 35.8 37.3 42~.8 51~6
(66,8) (73,5) (74^4) (75.5) (71.9) (66.5) (56^3) (55^3) (53.9) (50.8) (50,1)
22*9 28.1 26*7 2/.3 27\9 25.5 35.2 41.8 47.5 44.C 41.3
(69,3) (72,2) (74,3) (75,6) (76,0) (73,9) (69,5) (60,5) (5J,2) (50^8) (4^9)
24.3 32.6 28.3 25.7 31.3 39.7 41.2 43.8 44.6 43.1 31.7
(70.6)(71.1)(74.0)(75.5)(75.3)(73.3)(59.2)(54.4)(52.0)(51.7)(49.7)
21.6 34*9 32.2 33.1 3«.2 ».« 41.3 40.2 38.7 41.3 43.6
(70.8) 171.8) (73.0) (75.0) (77f 0) (72.4) 160.9) (S4.9) 153.4) (52.1) (49.3)
22*9 32*7 28.3 36.6 37.3 39.4 39.4 42.7 41.6 43.4 44.6
(71^.9) (72.8) (76.4) (77^6) (78.8) (75.3) (65^) (57.2) (54.8) (54.4) (50.1)
25.7 38% 34*.7 35*.3 36*7 40^8 40.4 42.7 41.9 43.7 42.2
(72.4)(72.8)(76.8)(77.6)(77.0)(73.3)(66.5)(57.8)(53.5)(50.3)(50.4)
27*4 32*8 30*0 33?3 33*1 36*1 38% 41*1 43*6 41% 39*7
(72^9) (73^) (74^2) (73^3) (74^5) (69^4) (59^9) (55^6) (53^1) (50^6) (49^3)
35*3 30.1 34.2 24*1 21.7 27.3 34.8 40.0 46.9 40.3 37.3
(71.7)(72.9)(74.3)(74.9)(72.3)(61.2)(50.8)(49.2)(49.0)(50.4)(49.9)
3276 35*6 31T3 39*3 3674 38*5 38T9 43*7 4472 45*8 3770
(72^1) (74^8) (75^2) (73^1 (62^) (55^0) (49^1 (49a) (49^) (49^3) (49.1)
38.6 39^3 32*1 24Tl 4lTl 43T? 42.6 44*2 36% 4*8 26*:
(70^8) (74^) (74.3) (70.3) (61^8) (52.2) (49^8) (50.6) (49.8) (49.4)
42% 42% 42*2 36?2 41*3 41*7 43*3 34?7 39Tl 29?9
(70.8)(72.7)(73.2)(72.6)(69.1)(63.1)(S2.8)(50.3)(49.8)(49.0)
40.0 41.8 39.4 40.2 40.8 42.6 44.7 45.3 43.7 34.
(71^8) (72^) (74^) (72^8) (6742) (58^3) (52^6) (50^2) (50^2)
35.2 37% 36*2 40.9 38.2 41.7 44.2 41.7 29.6
(7149) (73/7) (7^1) (68^) (57.1) (51.1) (50^) (50^)
26.4 40.3 35.5 37.0 42.1 42.9 41.7 31.3
(72.1)(73.7)(64.0)(62.5)(55AB)(52.0)(51.4)
28*3 37*3 38Tl 41% 44.7 42% 39*9
(73.8)(72,0)(62.4)(61.2)(52.6)(51.7)
3177 39*6 41.3 4378 4177 40?2
(75.5)169.2)(74.6)(56.1)(50.7)
38.3 31.7 38.6 41.7 29.7
(64.91(69.71(65.4)
38.6 37.7 31.3
The niabers In parentheses are the wet bulb tempera-
tures in degress Farenhelt The remaining numbers
are the air velocities in feet per aacond The data
was collected over a three day period which resulted
in a range of ambient conditions. To account for
thia, the wet bulb temperatures have been normalized
to the ambient conditions indicated. The diameter
of the stack Is 28.7 feet where the measurements
were taken.
Figure D-3. Wet Bulb Temperature and Velocity Map
of Stack During 50% Wet/50% Dry Mode of Operation
43
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N
Figure D-4.
View from top of stack showing location of stack
psychroraeters. The two tubes shown with each
psychrometer are orificed to provide a weighted
air sample.
44
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tivity or improve data accuracy. The discussion below reflects
the final instrumentation used for the test results.
Figure D-5 depicts the location of the psychrometric sta-
tions, hot and cold water temperature detectors, and other
instrumentation situated on the tower. The location of the
ambient weather stations is shown on Figure 1. In all cases, 100
ohm platinum resistance temperature detectors (RTD) were used.
Water flow measurement created some difficulties which
should be noted. Initially, both inlet and outlet flow was
measured by turbo-probe flowmeters. However, it was discovered
that the sawdust which the station personnel routinely add to the
circulating system to plug small condenser leaks, also worked
well for plugging the flowmeters. After some trials, it was
determined that the flowmeters were inoperable. A differential
pressure cell was then installed to monitor the total developed
head of the circulating pump and a calibrated head - flow curve
was developed from a series of equal' area traverses performed
with a Pitot tube at varying flows.
While this method of flow measurement proved adequate, it
was not totally satisfactory, particularly when it was discovered
that the differential pressure cell had to be recalibrated every
time the pump was shut down. Finally, with the cooperation of
EPRI an "Annubar" flow measuring device was installed which has
performed flawlessly and maintains an error of +1%.
-45-
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Inlet Water Flow
I
Dry Sectiort
I .
///////// \\\\\\v\\
I
(Dry Section
Outlet Water Flow
LEGEND .-
Water temp, detector
Psychrometer
Wattmeter
Flow detector
Figure D-5. Wet/Dry Cooling Tower Instrumentation Schematic
46
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APPENDIX E
DESCRIPTION OP DAMPER CONTrtOL SYSTEM
The damper control system of the Wet/Dry Tower controls
the distribution of air flow between the wet and dry sections.
The temperature of the cold water exiting the tower serves as
the control element. When the cold water temperature is at
setpoint (which in this case was 78°P) or within the deadband
(1.5°F above or below the setpoint), no demand signal is issued
to the control system and the dampers remain in their current
positions. In order to provide stability and prevent "hunting"
of the system, a thermal time delay relay (agastat) is located
between the demand signal and the control system. It was
discovered that a 5-minute setting on this agastat was suffi-
cient to allow the cold water temperature to stabilize after a
change in damper settings. Additionally, another agastat is
provided to limit the period of time the control system may
actuate the dampers after each 5-minute time delay. A 3-second
setting provided 11 degrees of damper movement, which gave
sufficient change without encountering "over-shooting." Figure
E-l shows the basic damper operation as a function of demand.
A key to understanding the operation is the fact that inter-
locks are provided to prevent the operation of either the wet
or dry section dampers unless the other section dampers are
either fully open or fully closed. On a typical cool day, the
operation of the dampers might be as depicted in Table E-l.
TABLE E-l
A) 12 Midnight to 8:00 AM -
8:00 AM -
10:00 AM -
10:30 AM -
12 Noon -
6:00 PM -
7:30 PM -
8:00 PM -
11:00 PM -
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
10056 Open
Fully Closed
10056 Open
Begin to Open
10056 Open
.Complete Opening
Begin to Close
10056 Open
Complete Closing
10056 Open
Begin Opening
10056 Open
Complete Opening
10056 Open
100J6 Open
Begin Closing
100% Open
Complete Closing
-47-
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o
o
i
Jr
oo
I
(open)
100
DRY DAMPERS
C
o
•H
4J
•H
CO
O
a.
o
0 -
©
©
WET DAMPERS
(closed) (A
decreasing
DEMAND
\
Vv®.
increasing
co W
V P
O o
\ © ©
\
\
\
\
\
\
OT *T>
o _*.
p. g;
0 ^
c^^
3
H O
2.9
?M
p
o>
(P
(P C
ct (p
Figure E-l. Damper Control as a Function of Demand
2
o
ct
»•
CD
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APPENDIX P
TEST PLAN
The objectives of the test program, as stated earlier in
this report, were as follows:
1. Determine the operational characteristics of a wet/dry
cooling tower operating in an actual generating station
environment.
2. Determine the water conservation aspects of a wet/dry
cooling tower operating in an arid climate.
3. Develop a mathematical model of the wet/dry cooling
tower and confirm it with actual test data.
The first objective was achieved merely by operating the
Wet/Dry Tower, but the remaining two objectives required a test
plan to follow in order to assure success of the program.
To simplify the plan it is broken into test blocks; however,
because of the need to obtain data over a wide range of ambient
conditions, the test blocks were repeated throughout the test
period.
TEST BLOCK I - START-UP AND CALIBRATION
1. Confirm fan characteristics
2. Confirm pump characteristics
3. Determine velocity and temperature distribution of stack
exit air (see discussion in STACK PSYCHROMETRIC MEASURE-
MENTS in Appendix D)
4. Confirm uniform distribution of water to cooling tower
(This was accomplished by balancing the flows in the two
risers and then equalizing the levels of the hot water
basins.)
5. Determine air velocity distribution entering the Wet/Dry
Tower (see discussion in AIR PLOW MEASUREMENTS in
Appendix D).
6. Calibrate instrumentation within limits (See Appendix C)
TEST BLOCK II - CONSTANT WATER PLOW RATE. VARIABLE AIR FLOW RATE
These tests were run at several constant water flow rates.
Air flow was varied by changing the pitch angle of the fan and by
varying the dampers.
-49-
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TEST BLOCK III - CONSTANT AIR FLOW RATE, VARIABLE WATER FLOW RATE
These tests were run at two constant air flow rates corres-
ponding to fan pitch angles of 13° and 17°. Water flow rate was
varied by use of a valve at the discharge of the circulating
water pump.
-50-
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APPENDIX G
TABLE OP CONVERSION FACTORS
Length:
Area:
Energy:
Pressure:
Plow Rate:
Velocity:
Temperature
1 inch = 2.5*1 centimeters
1 foot (ft) = 0.305 meters (m)
1 ft2 = 0.093 m2
1 horsepower = 1.3^1 kilowatt
1 inch Hg. = 0.013 atmospheres
1 psi = 0.068 atmospheres
1 CFM = 0.472 liters/sec
1 gpm = 0.063 liters/sec
1 ft/sec = 0.305 m/sec
1 °P = 0.556 °C
to convert from °F to °C use this formula
>C =
- 5(°P - 32°)
-51-
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-80-078
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Wet/Dry Cooling Tower Test Module
5. REPORT DATE
April 1980
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
D.M. Burkart
8. PERFORMING ORGANIZATION REPORT NO.
3. PERFORMING ORGANIZATION NAME AND ADDRESS
Southern California Edison Company
P.O. Box 800
Rosemead, California 91770
10. PROGRAM ELEMENT NO.
INE624
11. CONTRACT/GRANT NO.
Grant No. R805220
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES jERL-RTP project officer is Theodore G. Brna, Mail Drop 61
919/541-2683.
16. ABSTRACT The report gives results of an evaluation of the engineering performance
of a single-cell wet/dry cooling tower (about 25 MW) in an 18-month field test at
San Bernardino, CA. Test objectives included determination of the water conserva-
tion and operating characteristics, and verification of a mathematical model for the
wet/dry cooling tower. The crossflow tower had parallel air flows through the wet
and dry sections, and dampers which regulated air flow to allow cooling in either
section, or any combination of the two. Without significantly affecting normal plant
performance, the wet/dry cooling tower could save about 19% of the water normally
avaporated annually by an all-wet tower at the test site. Greater savings could have
Deen achieved by accepting some loss of plant efficiency during the winter months.
rhe mathematical model developed for the tower was verified by test results.
Although some operational problems developed during testing, the major goals of the
test program were achieved.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Pooling Towers
resting
iVater Conservation
Characteristics.
Mathematical Models
Pollution Control
Stationary Sources
Wet/Dry Cooling
Operating Characteris-
tics
13B
13A,07A,13I
14B
12A
3. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
61
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
52
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