EPA-600/7-77-030
U.S. Environmental Protection Agency Industrial Environmental Research EPA-600/7-]
Office of Research and Development Laboratory . _ , . ___
Research Triangle Park, North Carolina 27711 MarCn 1977
ALTERNATIVES TO CHLORINATION
FOR CONTROL OF CONDENSER
TUBE BIO-FOULING
Interagency
Energy-Environment
Research and Development
Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into seven series. These seven broad categories
were established to facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously planned to foster
technology transfer and a maximum interface in related fields. The seven series
are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the effort
funded under the 17-agency Federal Energy/Environment Research and Development
Program. These studies relate to EPA's mission to protect the public health and welfare
from adverse effects of poljutants associated with energy systems. The goal of the
Program is to assure the rapid development of domestic energy supplies in an environ-
mentally-compatible manner by providing the necessary environmental data and
control technology. Investigations include analyses of the transport of energy-related
pollutants and their health and ecological effects; assessments of, and development
of, control technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect the
views and policies of the Government, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161.
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EPA-600/7-77-030
March 1977
ALTERNATIVES TO CHLORINATION
FOR CONTROL OF CONDENSER
TUBE BIO-FOULING
by
H.H.S. Yu, GA Richardson, and W.H. Hedley
Monsanto Research Corporation
1515 Nicholas Road
Dayton, Ohio 45407
Contract No. 68-02-1320
Program Element No. EHE624
EPA Project Officer Fred Roberts
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, N.C. 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, D.C. 20460
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CONTENTS
Figures v
Tables iv
1 Summary 1
2 Conclusions 5
3 Current Practices 10
3.1 Current Chlorination Practices 10
3.1.1 Once-Through Cooling with Marine Waters 11
3.1.2 Closed-Cycle Cooling Using Cooling
Towers with Marine Waters for Makeup 11
3.1.3 Once-Through Cooling with Fresh Waters 12
3.1.4 Closed-Cycle Cooling Using Cooling
Towers with Fresh Water for Makeup 12
3.2 Types of Cooling Systems and Schematic Flow
Diagrams 13
3.3 Seasonal Operating Variables 16
3.4 Chlorine Residual Emissions 18
3.5 Points of Emission 24
3.6 Cost of Current Practices 28
4 Assessment of Alternative Methods 31
4.1 On-Line Mechanical Cleaning 31
4.1.1 Amertap Sponge Ball System 31
4.1.2 M.A.N. Brush System 33
4.1.3 Hot Water Backflush System 33
4.1.4 Economics of Mechanical Cleaning of
Condensers 33
4.2 Chemical Treatments 37
4.2.1 Ozone (O3) 39
4.2.2 Bromine (Br2) 44
4.2.3 Bromine Chloride (BrCl) 47
4.2.4 Iodine (I2) 49
• • •
111
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CONTENTS (continued)
4.2.5 Chlorine Dioxide (C1O2) 50
4.2.6 Hypochlorites (HOC1, MOC1) 52
4.2.7 Other Chemicals 52
4.2.8 Controlled-Release Pesticides 54
4.3 Physical-Chemical Methods of Treatment 58
4.3.1 Ultraviolet Radiation 58
4.3.2 Gamma Radiation 59
4.3.3 Electron Beam Radiation 60
4.4 More Efficient Methods of Present Chemical
Application 60
4.4.1 Serial Dosing Near the Inlet of the
Condenser 60
4.4.2 Addition of Dechlorination Chemicals 62
4.4.3 Slowdown Timing Control 63
4.4.4 Chlorination by Feedback Control of
Residuals 63
4.5 Other Information 63
References 65
Bibliography 68
IV
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FIGURES
Number Page
1 Schematic of nuclear and fissil fuel powerplants. 15
2 Schematic flow diagram of wet cooling system
(fresh water or marine water). 17
3 Typical points of chlorine application and dis-
charge for once-through (or open) cooling system. 20
4 Typical points of chlorine application and dis-
charge for a recirculating (or closed) cooling
system. 22
5 Concentration of total residual chlorine in
cooling-tower blowdown versus time. 23
6 Hypothetical 1,000 MW powerplant water flows
(600,000 gpm) (flows shown in units of
1,000 liters/min). 26
7 Costs of operation, maintenance, and chemical
additions of a once-through cooling system
(1972 dollars). 29
8 Schematic arrangement of Amertap tube cleaning
system. 32
9 Schematic of M.A.N. system reverse flow piping. 34
10 Tube cleanliness versus cost of reduced generating
efficiency. 37
11 Distribution of chemicals added to cooling-water
systems. 3 8
12 Rate of decomposition of ozone. 40
13 Behavior of ozone in saturated solutions at
atmospheric pressures. (An S value of 0.2
is assumed.) 41
14 Schematic cross section of condenser tubes. 56
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TABLES
Number Page
1 Summary of Alternatives to Chlorination of Power-
plant Cooling Water 4
2 Current Applicability of Various Bio-Fouling
Control Techniques 9
3 Use of Various Types of Cooling 14
4 Closed or Recirculating Cooling Systems 16
5 Breakdown on Chlorine Usage for Different Types of
Cooling Systems (1970) 27
6 Comparative Capital Costs of Condenser Cleaning
Systems 34
7 Comparative Annual Costs 34
8 Operating Costs of Ozonating Plants with No
Pretreatment 43
9 Comparison of Ozone Doses Reported in Water and
Wastewater Treatment 44
VI
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SECTION 1
SUMMARY
A majority of power plants in the United States are using chlorine
to control biological fouling in their cooling systems, particu-
larly in the condenser tubes. The use of chlorine has raised ques-
tions regarding the toxicity of chlorinated effluents on aquatic
organisms in the receiving water. In 1972, the reported usages of
chlorine for power plant cooling water treatment alone was 28,600
tons (compared with 256 tons of chlorine for boiler feedwater
treatment).
Although other varieties of biocides (e.g., chlorinated phenols,
acroleins, quaternary ammonium compounds, bromine, etc.) are
employed to control biological fouling in cooling water systems,
chlorine is the most widely used because it is usually the most
economical method of treatment. Chlorination can be applied con-
stantly in low concentrations or intermittently in higher concen-
trations as a shock treatment, although intermittent treatment is
not effective with organisms such as mussels and barnacles that
can rapidly close their shells when conditions are unfavorable and
then open them up when conditions improve.
Current chlorination practice is to provide adequate free chlorine
residual (e.g., 0.5 ppm to 1.0 ppm) at the outlet side of the con-
denser. Recent research has indicated that this free chlorine
could react with a variety of organic compounds to form carcino-
genic compounds, which are of great concern if they enter public
drinking-water systems.
To protect both the public and aquatic life, the Environmental Pro-
tection Agency has established allowable concentrations of free
chlorine in new-plant effluents as an average of 0.2 mg/1 during a
maximum of 2 hours a day (aggregate) and a maximum, during these
periods, of 0.5 mg/1.1 In California, this limit has been set at
only 0.1 mg/1 in undiluted effluent.2 Other states are also enact-
ing similar or more stringent criteria.
1Permissible Chlorine Concentrations in Effluents from New Sources,
Federal Register. Vol. 39, October 8, 1974.
2Collins, H. F. Sewage Chlorination Versus Toxicity—A Dilemma.
Journal of the Environmental Engineering Division Proc. ASCE, 99,
No. EE6, 761-72(1973), December.
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The State of California document entitled Water Quality Control
Plan for Ocean Water of California established the allowable total
chlorine residuals in discharge from ocean plants as a daily aver-
age of 1 mg/1 and a maximum of not more than 2 mg/1 for 10% of the
time. In the mean time, the total chlorine residual shall not
exceed 0.006 mg/1 after three- to five-fold dilution in the receiv-
ing body of water (personal communication with David Deckman,
California State Water Resource Control Board, Sacramento,
California, 916-322-4561). In southern California, the total
chlorine residuals allowed by the local authorities at the dis-
charge end of the condenser are only half of the above numbers.
In the state of Maryland, the allowable total chlorine residuals
vary with the type of receiving body of water. For the effluent
discharging to brackish water, the maximum total allowable chlo-
rine residual is 0.5 mg/1, while the maximum after mixing is
0.02 mg/1 for trout streams and 0.05 mg/1 for other streams (per-
sonal communication with William Chicca, Industrial Permit Section,
Maryland Water Resource Administration, Annapolis, Maryland,
301-269-3821).
In the state of Illinois, there is no state regulation on chlorine
discharge (personal communication with Jeffrey Mill, Permit Sec-
tion, Division of Water Pollution Control, Illinois EPA,
Springfield, Illinois, 217-782-6171).
The EPA has also suggested that continuous exposure of the aquatic
community to chlorine compounds, including chloramines, should not
exceed 0.002 mg/1.3 Chlorination programs to achieve no discharge
of total residual chlorine from recirculating cooling water sys-
tems have been determined to be not fully demonstrated and there-
fore cannot be generally applied by 1983.1*
To decrease passage of ecologically harmful effluents to receiving
waters, viable alternatives to current chlorination practices are
needed. Examples of alternative methods include:
• Use of other chemicals
• More efficient methods of chemical application
• Physical-chemical treatment
• On-line mechanical cleaning, etc.
It should be emphasized that the reasons for chlorinating a cool-
ing tower circuit are precisely the same as those for a
3Environraental Studies Board, National Academy of Sciences, Water
Quality Criteria 1972, EPA-R3-73-033.
^Nichols, C. R. Development Document for Effluent Limitations,
Guidelines, and New Source Performance Standards for the Steam
Electric Power Generation Point Source Category. U.S. Environmen-
tal Protection Agency, NTIS PB 240 853, October 1974. 771 pp.
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once-through cooling system; namely, to control slime growth in
the condenser tubes, not to control algae growth on the tower
structure.
The problem with many of the alternative methods discussed in this
report is the lack of a field test that readily establishes the
efficiency of the processes.
When considering the alternatives to the use of chlorine (or hypo-
chlorite) in cooling water treatment, power plants are presently
left with a limited selection, especially where units that are
already in operation must be included. Effective manual cleaning
is costly and nearly impossible. Mechanical cleaning systems are
relatively expensive, are impossible to retrofit in some instances,
and may often be inadequate without additional chlorination. Ozon-
ation is unproven for power plant cooling water treatment and is
high in both capital and operating costs. Dechlorination with sul-
fur dioxide would result in an additional chemical feed system to
maintain and possible deoxygenation of receiving waters. Use of
bromine chloride may be a viable alternative to chlorine, but fur-
ther R&D is needed. The technical, environmental, and cost
aspects of these alternatives to the use of chlorine in powerplant
cooling water treatment are summarized in Table 1.
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SECTION 2
CONCLUSIONS
From work on this task, it is concluded that:
a. Because of its cost effectiveness, chlorination of
cooling waters (in both recirculating and nonrecirculat-
ing (once-through) cooling systems) is presently the
most widely used technique to control biofouling of con-
denser tubes.
b. The newly established allowable concentrations of
free chlorine in new-plant effluents could be achieved
by means of currently available techniques. By employ-
ing more efficient methods of chemical application,
total chlorine residuals can be cut to well below pres-
ent levels.
c. There are several methods for control of cooling
water biofouling which use chlorine and which are more
efficient and cause fewer problems than continuous chlo-
rination. These include
• Dosing near the inlet of condenser, serially
• Addition of dechlorination chemicals
• Slowdown timing control
• Chlorination by feedback control of chlorine
residuals
Use of one or a combination of the above control tech-
niques would make chlorination systems more complicated
and may require some modifications while having an impor-
tant compensation: The total amount of chlorine used
and discharged chlorine residuals would be reduced to
the practical minimum without impeding the control of
biofouling of condenser tubes and other parts of cooling
water circuits. The size of the chlorination system in
terms of chlorine feed rate would be reduced by a factor
of two, three, or six depending on the number of paral-
lel condensers serving the power plant.
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d. There are several viable alternative methods of
reducing the total residual chlorine in condenser cool-
ing water systems. These include chemical treatment
with other less harmful chemicals and use of on-line
mechanical means of cleaning condenser tubes. Mechani-
cal cleaning is employed in some plants, but its practi-
cability depends on the design configuration of the
existing process piping and structures involved at the
particular plant. Not all existing power plants can be
retrofitted with mechanical cleaning techniques. Mechan-
ical cleaning of condenser tubes, which is widely used
in Europe, deserves to be pursued more actively in the
United States, especially for those power plants using
cooling water with high chlorine demands.
e. Chlorine may still be required, used, and discharged
from systems using mechanical cleaning of condenser
tubes because biological control may also be needed for
other parts of the cooling system or for control of hard-
shelled organisms in marine water circuits.
f. Several other chemicals are potentially attractive
alternatives to chlorine, such as bromine chloride
(BrCl), ozone (03), and chlorine dioxide (C1O2). The
chemical cost of bromine chloride is about three times
that of chlorine, and the cost of ozonation is reported
to be two to ten times higher than that of chlorination.
Chlorination is currently much cheaper than ozonation in
both capital and operating costs. However, it should be
emphasized that the costs of cooling water treatment are
a very small part of total power production costs.
Therefore, it is conceivable that the environmental con-
siderations might outweigh economic considerations if
these chemicals do offer advantages over chlorine gas in
powerplant cooling water treatment.
g. The high cost of ozonation, poor ozone transfer effi-
ciency, lack of residual protection against downstream
contamination for the cooling tower, and lack of field
demonstration probably are reasons why ozonation has not
been practiced in powerplant cooling water systems in
the past. In view of the more rigorous criteria pro-
posed for residual chlorine content in discharging
waters in the future, now is an opportune time for field
testing of ozonation for treatment of cooling water. A
breakthrough in ozone production technology is required,
however, before ozonation can compete economically with
other methods. A new, high-volume, electron-beam, ozone
generator is now expected to produce ozone for about
10 cents/lb, compared with about 16 cents/lb to
20 cents/lb for chlorine. Although ozone is quite effec-
tive in the disinfection of water, the applicability of
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ozone for the bio-fouling control of powerplants is yet
to be field demonstrated.
h. Bromine chloride has been little used until very
recently owing to the lack of commercial availability
and handling technology. Potential ecological and cost
advantages may be gained by substituting bromine chlo-
ride for chlorine. Products of chlorobromination of
water containing ammonia or organic nitrogen are more
easily degraded and less obnoxious than their chlori-
nated analogs; e.g., chloramines. The predominant prod-
ucts formed from several competitive reactions of BrCl
in water are innocuous chloride and bromide salts. In
addition to the fast decay feature, BrCl is less hazard-
ous to marine life than chlorine, while still exhibiting
biocidal activity.5 Although encouraging results were
obtained by field testing at the Public Service Electric
and Gas Company, New Jersey, further research is
required.
i. The chemical cost of chlorine dioxide is very high;
hence, it is not a good candidate for general-purpose
cooling water treatment. However, since it does not
react with ammonia, nitrogenous compounds, or most
organic impurities before oxidizing them, and since its
efficiency is not impared in a high-pH (e.g., pH between
6 and 10) environment, chlorine dioxide could be con-
sidered cost-effective for treatment of cooling water
which has an excessive chlorine demand, such as
secondary-treated sewage effluent used as powerplant
makeup water. Some facts regarding the toxicity of chlo-
rite ion and chlorate, which are formed by disproportion-
ation of chlorine dioxide, are known,6 but further field
testing and demonstration are needed.
j. Use of controlled-release pesticides in nonheat-
transfer surfaces of powerplant cooling systems for bio-
fouling control is a future possibility. The practice
would allow economy in application, and it would reduce
potential hazards stemming from accumulating pesticides
in the environment at a rate higher than that of their
natural degradation, the basic idea is to regulate the
effects of the pesticide or other agent so that the
effects will be felt over a long period of time at a
safe level. For example, one of the approaches is the
5Mills, J. F. The Chemistry of Bromine Chloride in Wastewater Dis-
infection. (Presented at American Chemical Society Meeting).
Chicago, Illinois, August 1973.
6Weber, W. J., Jr. Physicochemical Processes for Water Quality
Control. Wiley-Interscience, New York, New York. 640 pp.
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incorporation of active agents as pendent groups on the
backbone polymer chain. A number of pesticides have
be^en incorporated in vinyl-type monomers and then poly-
merized. Also, by chemically incorporating two or more
organometallic groups along the polymer chain, antifoul-
ing activity can be broadened considerably. The Navy's
work on static testing of acrylic paint containing
organotin compounds shows that such an acrylic coating
(<8 mils thick) is effective up to 4 1/2 years. Use of
coatings for the repulsion of organisms from marine sur-
faces would be particularly attractive for surfaces such
as piping, cooling tower packing, and condenser headers,
where there is no heat transfer. Use of the plastic con-
denser tubes would, however, require substantial design
changes. Further development would be needed because
plastics are inefficient heat transfer media compared to
metal. Establishing the practical feasibility of the
controlled-released pesticides technique for use in
powerplant cooling systems would require considerable
research and development work.
k. Use of radiation techniques (e.g., gamma radiation,
UV radiation) for treatment of powerplant cooling water
is not considered cost-effective at present, nor is it
likely to be in the near future. Radiation techniques
lack the ability to provide any residual disinfecting
capacity in other parts of the cooling system. High-
volume river waters and other sources of high turbidity
and organic and iron content usually cannot be treated
effectively with UV radiation. However, use of nuclear
reactor wastes (instead of gamma radiation from pure iso-
topes, such as cobalt-60) might reduce the operating
cost of cooling-water treatment drastically, making
radiation treatment competitive with other methods in
the future.
1. The development of smooth plastic surfaces that
would not be fouled by microorganisms without using
any chemicals or pesticides may be possible. Based
on some other experience (personal communication with
Dr. E. G. Young, Central Research Department, DuPont
Co., Wilmington, Delaware) on the desalination mem-
brane program, the surfaces could simply be kept
clean by occasional flushing.
m. Current applicability of various bio-fouling control
techniques for existing plants or future new plants are
listed in Table 2. Some of the available control tech-
niques are not easily applied to existing powerplants
because they require extensive modification of installed
equipment before they can be implemented.
8
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TABLE 2. CURRENT APPLICABILITY OF VARIOUS BIO- FOULING CONTROL TECHNIQUES
_ Treatment alternative _ Old plant New plant
Chlorination
Dosing near the inlet of condenser, serially Yes or noa Yes
Addition of dechlorination chemicals Yes Yes
Slowdown timing control (closed cycle) Yes Yes
Chlorination by feedback control of chlorine residuals Yes Yes
Mechanical cleaning Yes or no3 Yes
c c c
Other alternative chemicals
Not applicable to all plants due to design limitations of existing plants.
Chlorine may still be required.
f*
Requires further field testing and demonstration.
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SECTION 3
CURRENT PRACTICES
3.1 CURRENT CHLORINATION PRACTICES
Chlorine is easily the most versatile, the most widely employed,
and in most instances, the most economical chemical for control of
biofouling in cooling waters. In 1972, 25,909 metric tons (28,565
short tons) of chlorine were used in treating the cooling water
for steam electric power plants. This averages to approximately
0.84 metric ton (0.92 short ton) of chlorine per 10 MW of capacity.
Presently, chlorine is the overwhelming choice in the United
States for treatment of cooling water.
The average chlorine residual employed in cooling water systems is
0.5 to 1.0 mg/1 (ppm) , which will control most microorganisms. **
However, to be effective, the chlorine must exist as free avail-
able chlorine (HOC1) and not as combined chlorine (chloramines or
organic chloramines). The combined chlorine is less efficient and
slower in providing biological control in high-volume cooling sys-
tems than is free available chlorine.
Herein lies the difficulty. While chlorination is usually a satis-
factory method overall for control of bio-fouling, biological
growths will gradually build up even when a free chlorine residual
is maintained. In such cases, it is necessary either to increase
the chlorine shock treatment time or the free chlorine residual,
or to use another bio-fouling control agent. Since liquid chlo-
rine is the cheapest source of chlorine, the shock treatment time
of the chlorine and/or the chlorine residual are usually increased.
As a result, chlorine residuals have a greater chance of reaching
the aquatic environment, in which they are toxic. Additionally,
if the cooling water has a high chlorine demand, chloramines,
which are considered as toxic as free chlorine, reach the aquatic
environment.
While some of the free available chlorine is claimed to be aerated
from the cooling water in passing over a tower or spray pond, it
has been shown that the amount of free available chlorine is
reduced by sunlight but not by volatilization. Unless rigid con-
trol of chlorine residuals is maintained, free available chlorine
can reach the aquatic environment through either a closed or a
once-through system.
10
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The chloramines that are formed from water with a high chlorine
demand may also be discharged to the aquatic environment. The
higher chloramines (dichloramine and nitrogen trichloride) can be
removed by aeration. Monochloramine, the most predominant species,
is not subject to consequential losses by aeration. Thus, it is
discharged to the aquatic environment where it is toxic to marine
life.
Current chlorination practices are discussed briefly in this sec-
tion in order to provide a guideline or data base for proposed
alternatives, which will be discussed in the next section.
3.1.1 Once-Through Cooling with Marine Waters7
Bio-fouling of marine cooling water circuits is controlled by two
simultaneous "types" of chlorination: continuous and intermittent.
Continuous, low-level chlorination is used to control the hard-
shelled organisms. Intermittent chlorination is used to control
the "soft forms" and is usually applied ahead of the bar racks.
Gaseous chlorine is introduced in continuous chlorination to give
a free residual chlorine of 0.25 to 0.50 mg/1 (ppm) at the conden-
ser tailpipes. ' In intermittent chlorination, which is universal,
gaseous chlorine is introduced to give 1.0 mg/1 (ppm) free resid-
ual chlorine at the end of 1 hour contact time.
Clean seawater has a 10-minute chlorine demand of approximately
1.5 mg/1 (ppm). Average seawater has a chlorine demand of 2 to 3
m9/l (ppm). This value is somewhat higher if the seawater is con-
taminated with sewage.
Continuous chlorination is usually terminated when the water tem-
perature drops below 4°C (40°F). In the latitudes corresponding
to upper New England and the far Pacific Northwest, chlorination
is discontinued on the average from November 15 to June 10; in the
latitudes of southern New England—New York City—northern
New Jersey area, the average is December 15 to April 1. The bio-
fouling problem is continuous and serious in the South Atlantic
and Gulf coastal waters because the temperature there remains
above 4°C (40°F), and the marine fouling organisms grow the year
around.
-Cycle Cooling Using Cooling Towers wi
for MakeupTTs
3.1.2 Closed-Cycle Cooling Using Cooling Towers with Marine
Waters
Experience with recirculating salt water systems is limited. Bio-
fouling is usually controlled by continuous, low-level chlorina-
tion of the makeup water and standard intermittent chlorination of
7White, G. C. Handbook of Chlorination. Van Nostrand Reinhold
Company, New York, New York, 1972.
BNester, D. M. Saltwater Cooling Tower. Chemical Engineering
Progress. 67(7):49-51, 1971.
11
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the recirculating water as in the case of the once-through cooling
with marine waters. The total amount of chlorine used in inter-
mittent chlorination of recirculating salt water will be less than
that used for a recirculating fresh-water system.
It has been suggested that the makeup water to a salt-water cool-
ing tower should be chlorinated continuously to produce a total
residual chlorine level of 0.1 to 0.2 mg/1 (ppm). However, it has
been reported8 that free residual chlorine levels as high as
1 to 2 mg/1(ppm) were not effective against all forms of marine
life in salt-water cooling towers.
3.1.3 Once-Through Cooling with Fresh Waters'*'7 '9
Data based on experience with existing facilities indicates that
the average chlorine treatment for once-through, fresh-water cool-
ing circuits is from two to three cycles per day. The duration of
the cycle is 30 minutes to 60 minutes to achieve a 0.5 mg/1 (ppm)
free chlorine residual in the condenser tailpipes. In warm cli-
mates, the chlorine cycle frequency is constant (three times per
day). In cold climates, the frequency is two cycles per day in
the winter and three cycles per day in the summer.7 A treatment
duration of between 5 minutes and 2 hours in also reported. **
In the newer systems, chlorination is conducted over a period of
15 minutes to 30 minutes to produce a residual of 1 mg/1 (ppm) or
more at the condenser inlet. Four 30-minute periods a day is not
an ususual program. Dosage is controlled by maintaining a resid-
ual level at the condenser tailpipes of about 0.5 mg/1 (ppm).
Operating data on six typical powerplant chlorination once-through
cooling systems was reported as follows: 1.52 to 7.00 mg/1 (ppm)
chlorine dose gave 0.03 to 1.20 mg/1 (ppm) free chlorine and
0.82 to 2.20 mg/1 (ppm) total chlorine in the discharge and
0.00 to 0.70 mg/1 (ppm) free chlorine and 0.10 to 1.20 mg/1 (ppm)
total chlorine in the effluent. Chlorine treatments varied from
one to five times a day for 20 minutes to 2 hours.9
3.1.4 Closed-Cycle Cooling Using Cooling Towers with Fresh Water
for Makeup1* /7
Data gathered on existing facilities indicates that the average
fresh-water powerplant cooling tower system uses two treatments
per day, each treatment being approximately 10 minutes longer than
the turnover time with the chlorine feed adjusted to produce 'a
free residual chlorine level of 0.5 mg/1 (ppm) in the cooling
water returned to the top of the tower (or at the condenser tail-
pipes) . For most cooling systems, two chlorination cycles per day
9Baker, R., and S. Cole. Residual Chlorine: Something New to
Worry About. Industrial Water Engineering, March/April, 1974.
12
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is adequate. In some cases, three cycles per day may be required
depending on the ambient temperatures and water quality.
Experience has dictated that the chlorination cycle in closed sys-
tems with cooling towers should be at least long enough for one
complete turnover. The turnover times for the various common
tower designs differ so that each cycle has to be tailored to the
specific turnover time.
Some companies believe that the chlorine dose should be sufficient
to produce a 1.0 mg/1 (ppm) free residual chlorine going to the
top of the tower. This residual may dissipate in 1 to 4 hours
depending on the tower design. Generally these power companies
chlorinate once daily until a free residual of 1 mg/1 (ppm) of
chlorine is maintained for 4 hours in the cooling water returned
to the top of the tower.
Although intermittent chlorination is the most common, several
power companies use continuous chlorination. This is based on the
premise that a continuous low level of chlorine residual in the sys-
tem is as effective as an intermittent high level. The free resid-
ual chlorine levels used in the continuous chlorination of closed
systems ranges from 0.30 to 0.5 mg/1 (ppm) at the top of the tower.
3.2 TYPES OF COOLING SYSTEMS AND SCHEMATIC FLOW DIAGRAMS10
Steam electric powerplants, using either nuclear or fossil fuel,
rely on cooling systems to discharge the vast amounts of waste
heat released from condensing steam. On the average, more than
one-half of the heat input is discharged to the cooling water in
the condensing process (33% of the heat input goes to electricity,
and the remainder goes to the stack and within the plant). The
heat added to the water must then be dissipated by some cooling
method. Table 3 shows the extent to which various types of cool-
ing were used by the 695 plants in the United States in 1972.10
As indicated in the table, the majority of the plants providing
the major share of steam-electric capacity employed once-through
cooling using either fresh or saline water. However, there is an
increasing trend away from once-through cooling toward the use of
cooling gonds, cooling towers, and combined systems. Essentially
all towers were of the evaporative type, and little use has been
made of nonevaporative (dry) cooling towers.
The total average withdrawal rates for cooling purposes in 1972
were reported to be:10
10Steam-Electric Plant Air and Water Quality Control Data. Summary
Reports, Federal Power Commission, FPC-S-246, March 1975. 170 pp.
and FPC-S-233, July 1973. 165 pp.
13
-------
TABLE 3. USE OF VARIOUS TYPES OF COOLING10
Percent of total
number of plants
Type of cooling
1969
Percent of total
installed capacity
1970 1971 1972 1969 1970 1971 1972
Once-through, fresh
Once- through / saline
Cooling ponds
Cooling towers
Combined systems
TOTAL
49.8
18.9
5.4
17.2
8.7
100.0
49
18
5
17
8
100
.4
.5
.7
.5
.9
.0
48.1
18.1
6.0
18.1
9.7
100.0
47.2
17.3
6.3
18.6
10.6
100.0
50.5
23.5
5.9
10.9
9.2
100.0
50
22
6
11
9
100
.1
.8
.7
.2
.2
.0
47.
21.
7.
12.
10.
100.
7
5
3
9
6
0
45.4
20.9
8.0
13.4
12.3
100.0
Fresh water: 5,170 m3/s (182,558 cfs)
Saline water: 2,130 m3/s (75,136 cfs)
The freshwater withdrawal rate is equivalent to about 10% of the
average annual runoff of all streams in the continental United
States. The freshwater consumption rate (due to evaporation) is
estimated at 1.56% of the withdrawal rate, 80.5 m3/s (2,843 cfs)
in 1972.
Schematic diagrams using nuclear and fossil-fuel energy of steam-
electric powerplants are shown in Figure 1. Typical condensers
(heat exchangers) contain from 5,000 tubes to 50,000 tubes 2.2 cm
(7/8 in.) or 2.54. cm (1 in.) O.D. by 6 meters to 18 meters (20 feet
to 60 feet) long. Tube material may be stainless steel or brass
alloys, such as admiralty brass, aluminum brass, aluminum bronze,
arsenical copper, 90/10 or 70/30 cupro-nickel. The tubes may be
arranged in one housing or shell or, because of size, may be
arranged in from two shells to six shells for very large units.
In the larger units, each shell may be considered as a condenser.
Steam exhausted from the turbine flows and condenses around the
tubes, while cooling water flows through the tubes extracting heat
from the tube walls which interface with steam. The overall clean-
liness of the tube surfaces is critically important to the effi-
ciency of the condenser and, hence, to the efficiency of the power-
plant. Waterside resistance (consisting of laminar liquid film
and fouling of tube walls) accounts for most of the total resist-
ance to the heat transfer of a tube.
Powerplant cooling-water systems are broadly divided into two main
types—once-through and recirculating—using either fresh waters
or marine waters. In the once-through system, cooling water makes
one pass through the heat exchanger. No evaporation takes place,
and water temperature is increased by about 11°C (20°F). The
present trend is toward the more complex recirculating type, a
14
-------
PRIMARY COOLANT
STEAM
RADIOACTIVE
( a ) nuclear power plant
COOLING TOWER
POND
TACK
STEAM
COOLING TOWER
POND
( b) fossil fuel power plant
Figure 1. Schematic of nuclear and fossil fuel powerplants,
15
-------
cooling tower or spray pond cools the water by evaporation. The
only water losses are from evaporation, windage, and blowdown. A
closed-recirculating (dry) system avoids water losses by using an
air-cooled radiator.
Figures 2-a, 2-b, 2-c, and 2-d show a wet-type cooling water con-
cept of a large, steam, power-generating station utilizing cooling
towers as a helper system. Such a system can be valved so as to
provide the following modes of operation: (a) open cycle (Figure
2-a), (b) helper cycle (Figure 2-b), (c) partial recirculation
(Figure 2-c), (d) closed cycle (Figure 2-d).
A variety of cooling systems (closed or recirculating) are being
used by modern powerplants as listed in Table 4.
TABLE 4. CLOSED OR RECIRCULATING COOLING SYSTEMS
1. Cooling ponds or lakes
2. Spray-augmented ponds
3. Canals with powered spray modules
4. Rotating spray system
5. Wet tower, natural draft/ crossflow
6. Wet tower, natural draft, counterflow
7- Wet tower, mechanical forced draft
8. Wet tower, mechanical induced draft, crossflow
9. Wet tower, mechanical induced draft, counterflow
10. Dry tower, direct
11. Dry tower, indirect
12. Combined wet-dry mechanical draft tower
3.3 SEASONAL OPERATING VARIABLES** •7 •ll
Cooling-water temperature exerts a considerable influence on activ-
ity of microbiological growth and the chlorine dose needed to
achieve a certain level of disinfection.
The effectiveness of chlorine in disinfecting certain cold natural
waters (e.g., in the Pacific Northwest and Alaska) is lower.
Below water temperatures of between 8°C and 12°C, the disinfecting
action of chlorine is dependent only on the diffusion of chlorine
through the cell walls of the mircoorganism since normal metabolic
pathways are generally considered to be closed. The empirical
temperature expression (for the rates of diffusion/or chemical
reaction) is useful for relating temperature with disinfection rate
11Reid, L. C., Jr., and D. A. Carlson. Chlorine Disinfection of
Low Temperature Waters. Journal of the Environmental Engineer-
ing Division, Proceedings of the American Society of Civil Engi-
neers. 100(EE2):339-351, April 1974.
16
-------
OPEN CYCLE
•RIVER, POND, LAKE, OCEAN
(a) open cycle straight-through cooling water system.
HELPER CYCLE
RIVER, POND, LAKE, OCEAN
COOLING
TOWER
I
( b) helper cycle straight-through cooling water system.
PARTIAL RECIRCULATION
RIVER, POND, LAKE, OCEAN
~~U-
r
PLANT
COOLING
TOWER
*
-*-*^
1
^^ -•
(c) partial recirculation of straight-through cooling water system.
CLOSED CYCLE
RIVER, POND, LAKE, OCEAN
SLOWDOWN (-5%)
(d) closed cycle of cooling water system.
Figure 2. Schematic flow diagram of wet cooling system
(fresh water or marine water).
17
-------
= k20e(T 20) (i)
where krp is the rate constant for temperature T, k2Q is the rate
constant for 20°Cf and 3 is an impirical constant.
It should be pointed out that the magnitude of bio-fouling is a
primary function of both chlorine demand and water temperature.
The chlorine demand varies widely throughout the United States.
It can be as low as 2 mg/1 (ppm) and as high as 15 mg/1 (15 ppm) .
In warm climates, the chlorine cycle frequency remains constant
the year around, but in cold climates, the frequency is two cycles
per day in the winter and three in the summer for fresh water.
The duration of the cycle is from 30 minutes to 60 minutes, depend-
ing upon the organism resistance. For a waterway that freezes
over in the winter, the chlorine demand will rise, owing to the
buildup of ammonia in the water. The ice cover prevents the aera-
tion of ammonia. For example, at Duluth, Minnesota, the St. Louis
River has a chlorine demand of 3 to 4 mg/1 (ppm) in the summer and
15 mg/1 (ppm) in the winter. It should also be emphasized that
while algae grow slowly in wintertime in these areas, the slimes
on the condenser tube do grow, and it is only this growth that is
of any concern in the chlorination program.
Artificial lakes also undergo a chlorine demand change with time.
In the initial stages, these lakes may have chlorine demands as
high as 6 to 10 mg/1 (ppm) , tapering off to 2 or 3 mg/1 (ppm)
after 4 or 5 years.
A clean seawater with a chlorine demand of only 1.5 mg/1 (ppm)
will support the growth of mussels, bryozoa, barnacles, sponges,
and slimes so long as the temperature is above 4°C (40°F) . For
control of hard-shelled organisms, continuous low-level [0.25 to
0 . 5 mg/1 (ppm) ] chlorination should begin during the growing sea-
son when the water temperature rises above 4°C (40°F) . The soft-
form organisms can be controlled by intermittent chlorination
every 8 hours to a 1.0 mg/1 (ppm) residual at the end of 1 hour
contact time.
3.4 CHLORINE RESIDUAL EMISSIONS
Consideration must be given to the possible environmental effects
of the chlorine residual in the discharge from condensers or blow-
down from tower systems in the receiving streams. There is consid-
erable doubt as to how far downstream the residual will persist
since it will not only dissipate by dilution, but it will also be
subject to the high chlorine demands usually found in the receiv-
ing waters, such as river or lake bottoms. The most effective
method is to arrange the piping system so that condensers can be
chlorinated individually and so that each condenser discharge will
be diluted by the others not undergoing the chlorination cycle.
18
-------
At those powerplants where once-through cooling is used (Figure 3),
chlorine is usually added to the cool water withdrawn from an
ocean, lake, river, estuary, or ground water source to minimize
biological fouling. Chlorine is applied one or more times a day
over a period long enough to produce a residual chlorine of about
1 mg/1 (ppm) or more at the condenser inlet. Frequency of the
dose and duration of the chlorination cycle is variable, depending
on water quality and temperature. Dosage is controlled by main-
taining a residual level at the condenser outlet at a level of
about 0.5 mg/1 (ppm).
The chlorine demand of cooling waters varies from site to site and
depends upon the source of cooling water and ambient conditions.
It can be as low as 2 mg/1 (ppm) and as high as 15 mg/1 (ppra).7
The popular definition of the term "chlorine demand" is that it is
the difference between dose and residual. To have meaning, it
must be properly expressed in terms of type of residual, tempera-
ture, pH, and time of contact between dosing and residual measure-
ment. It is the time element that is so frequently overlooked and
that poses a problem in very short, time-of-contact situations in
once-through condenser cooling systems. In freshwater circuits
(Figure 3-b), it is impossible to carry free chlorine through a
condenser by putting the points of chlorine application as close
to the condenser water box as possible. Less chlorine is used due
to short residence time (30 seconds to 1 minute) which is insuffi-
cient for the breakpoint reaction to take place between the chlo-
rine and the ammonia or other organic compounds.
Often, sampling and accurate residual determination may consume
much more time than actual contact time. The time interval
between application and sampling may be in the range of 20 seconds
to 30 seconds when chlorine is applied just ahead of the conden-
sers (Figure 3-b) to 3 minutes to 5 minutes when it is applied at
the intake. This error probably accounts for many powerplants
using a larger dosage than necessary in their cooling water.
Substantial savings in chlorine dosage can be achieved by applica-
tion as near the condenser inlet as possible while maintaining con-
trol levels necessary to maintain cleanliness of condensers. This
in turn results in residual chlorine consisting to some major
degree of hypochlorous acid, a form most easily reduced to chlo-
ride by demand of water from adjacent condenser units. For the
past 25 years, with few exceptions, condenser cooling water has
been chlorinated at the intake structure (instead of condenser
inlet) without taking advantage of dilution effects in the dis-
charge canal(s). Generally, new condensers are served by 2 to 6
cooling water flows, with the chlorine control system designed to
treat the unit flows one at a time in sequence. Thus, the chlo-
rine residual in the discharged water will be diluted by a factor
of 1, 3, or 5 depending on the system design.
19
-------
£I2 RESIDUES:
(0.25-0.5 PPM CONTINUOUS
1.0 PPM INTERMITTENT
Cl? APPLICATION POINTS;
0.5 PPM FREE Cl2
CONTINUOUS O40°F)
1.5-4 PPM Cl2 INTERMITTENT, INTAKE (SEA)
ONE AT A TIME
DILUTION
Cl2 MONITOR
<0.3PPM
CONDENSERS
DISCHARGE
(SEA)
( a ) once-through, marine water
CI2 RESIDUES
C\2 APPLICATION POINTS:
[0.5 PPM, 2 -4 CYCLES/DAY I AHEAD OF CONDENSERS INLET, INTAKE (RIVER y^^
' 30 -60MIN /CYCLE (\ ONEATA TIME,1 PPM OR MOREl (C|2 DEMAND: 2-15 PPM)
PUMPS
T3-
CIZ MONITOR
<0.3PPM
CONDENSERS
DISCHARGE
{RIVER, LAKE)
( b ) once-through, fresh water
Figure 3. Typical points of chlorine application and discharge
for once-through (or open) cooling system.
20
-------
The average chlorine treatment for freshwater circuits in power-
plants is from 2 to 4 cycles per day. The duration of the cycle
is from 30 to 60 minutes depending on the organisms's resistance.
However, saltwater circuits must be chlorinated ahead of the bar
racks to prevent fouling from marine organisms (see Figure 7-a).
The hard-shelled, more resistant marine organisms are most effec-
tively controlled by continuous, low-level chlorination [0.25 to
0.5 mg/1 (ppm) free chlorine residue at the condenser tailpipes]
during the growing season when the seawater temperature rises
above 4°C (40°F). The soft forms are controlled by intermittent
chlorination of a 1.0 mg/1 (ppm) residual at the end of 1 hour of
contact time.
The average seawater has 10 minutes chlorine demand of about 1.5
to 3 mg/1 (ppm); it is relatively clean compared to average fresh-
water .
The current trend in the United States is away from large, open,
once-through cooling-water systems (e.g., Figure 3) except those
involving manmade lakes built for that purpose. With closed,
recirculating evaporative cooling systems (e.g.. Figure 4), the
dissolved solids become increasingly concentrated and thus require
continuous blowdown. When operating as a closed cycle, both sides
of the condenser could be chlorinated simultaneously without fear
of too high a residual reaching the receiving waters. The only
chlorine going to the receiving water would be the residual in the
blowdown. The blowdown might be 5% of the recirculating rate. In
a tower circuit, a maximum 1.0 mg/1 (ppm) free chlorine is the
upper limit because of possible wood deterioration at higher
levels over prolonged periods of time. The residual may disappear
in less than one hour on a bright, sunny day with an induced draft
tower. In some hyperbolic, natural draft tower systems, it may
require up to 4 hours before a 1.0 mg/1 (ppm) free residual will
deteriorate to 0.1 mg/1 (ppm) as the result of the lack of sun-
light in this tower design. Figure 5 shows a typical total resid-
ual chlorine in cooling-tower blowdown for the unit which is chlo-
rinated four times a day. At peak values, as much as 65% of the
total residual chlorine was free available chlorine, declining
gradually and disappearing when the total dropped to approximately
0.2 mg/1. The factors involved in the decay rate of the recircu-
lated cooling water after the chlorinated cycle is ended are:
• Blowdown
• Evaporation loss
• Light catalyzed decomposition of free chlorine
• Chlorine demand of the system
• Recirculation rate
• Chlorine demand of the makeup
• Atmospheric contamination
• Decomposition products of basin sediment deposits
21
-------
CI2 RESIDUES
DRIFT,
EVAPORATION
0,25-0.5ppm, CONT.
1.0 ppm, INTERMITTENT
CI2APPLICATION POINTS:
x>0.5 ppm INTERMITTENT
CONDENSERS
CI2 MONITOR < 0.3 ppm
DECHLORI NATION «0.01 ppm CI2)
SLOWDOWN
11 BAR RACKS
n CI2 CONTINUOUS, 0.1-0.2 ppm
MAKE-UP (OCEAN)
(a ) recirculating, marine water
CI2RESIDUES:
,0.5 ppm, 2 - 4 CYCLES / DAY
)-60 MIN/CYCLE
DRIFT, ^
EVAPORATION
CI2 APPLICATION POINTS
AHEAD OF CONDENSERS
INLET/ONE AT A TIME
COOLING
TOWER,
POND
1 ppm
i
i
0
L
- \ L
CL C'
t 2 ^
CJ
Co
~ \ 2
CL C-
t 2 ^
f-
CONDENSERS
PUMPS
CI2 MONITOR,
DECHLORINAT I ON
«0.01ppmCI2)
SLOWDOWN (-5% OF FLOW)
MAKE-UP ( RIVER, LAKE )
(b) recirculating, fresh water
Figure 4. Typical points of chlorine application and discharge
for a recirculation (or closed) cooling system.
22
-------
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
TIME IN MINUTES
Figure 5. Concentration of total residual chlorine
in cooling-tower blowdown versus time.1*
One of these, evaporative losses, has been cited as a possible air
pollution problem. The volatility of chloramines has long been
known to exceed that of free available chlorine. This is particu-
larly true of nitrogen trichloride and, to a slightly lesser
degree, dichloramine. In fact, aeration is frequently used to
remove these compounds following breakpoing chlorination. The
most predominant species, monochloramine, is much less subject to
loss. Free available chlorine is subject to reduction by sunlight
but not by volatilization. Thus it would appear that evaporative
losses of all combined chlorine species, which could be expected
to be nearly all monochloramines in a cooling tower and subsequent
air contamination, are not factors of consequence.
If the blowdown is returned directly to the receiving water, there
are several alternatives.
• Close the blowdown valve during the. chlorination cycles
(i.e., during the period of high, total-residual chlorine
as shown in Figure 5) and set suitable time-delay controls
to match the time-residual characteristics of the system.
• Practice controlled chemical dechlorination of the blow-
down in synchronism with the chlorination program controls
and with time delay.
• Practice split-stream chlorination (splitting the con-
denser flow into separate streams which are chlorinated
one at a time).
23
-------
• Mix the blowdown with another stream which has a high
chlorine demand.
Dechlorination of residual chlorine in cooling-tower blowdown with
automatic addition of sodium bisulfite at the discharge channel is
currently being planned at new powerplants with a sensitivity of
about 0.01 mg/1 (ppm) residual chlorine in the discharge stream.
It should be emphasized that the reasons for chlorinating a cool-
ing tower circuit are precisely the same as those for a once-
through cooling system: to control slime growths in the condenser
tubes, not to control algae growth on the tower structure. Algae
(which are very resistant organisms) are of significance in
cooling-water treatment. Pew algae can be controlled with less
than 1.0 mg/1 (ppm) free chlorine residual and 1 to 2 hours con-
tact time when treated intermittently. The algae growths are sub-
ject to change throughout the year (season to season). The length
of the chlorination cycle should be at least long enough for one
complete turnover of cooling water. Present turnover rates in
both the induced draft and hyperbolic tower system are on the
order of 15 minutes to 20 minutes.
Other technologies potentially available for recirculating cooling-
water systems are split-stream chlorination, blowdown retention,
and intermittent discharge programmed with intermittent chlorina-
tion.
3.5 POINTS OF EMISSION
Points of emission of residual chlorine depend on the cooling sys-
tem employed. In recirculating cooling systems (Figure 4), emis-
sions are mainly from blowdown and wind drift. Water drift losses
from cooling towers and spray are a function of wind speed and
droplet size. Depending on the cooling method employed, drift
losses can range from as low as 0.002% of the cooling flow ("salt-
water" cooling towers) to as high as 5% of the cooling flow (spray
pond). Drift loss is an important consideration when siting a
powerplant in an estuarine environment. In addition to residual
chlorine carried by mist droplets, the impact of salt deposition
from brackish drift loss on the land surrounding a powerplant site
can be quite significant.
The volatility of chloramines has long been known to exceed that
of free available chlorine. This is particularly true of nitrogen
trichloride and, to a slightly lesser degree, dichloramine. The
most predominant species, monochloramine, is much less volatile
than either of these compounds and is therefore much less subject
to loss. It would appear that evaporative losses of combined chlo-
rine, which could be expected to be nearly all monochloramine in a
cooling tower, and the possible resulting air contamination are
not significant. Free available chlorine is subject to reduction
by sunlight but not by volatilization.1*
24
-------
Slowdown from cooling towers is taken from the tower basin ahead
of the point of chlorine application, but this is not the case for
many existing cooling tower systems. If blowdown is used to
sluice ash, the chlorine residual is lost in the ash pond. Simi-
larly, a holding pond could accomplish the same result if the time
of retention is long enough. At the very least, a holding pond
smooths out the peak levels of residual chlorine and reduces the
level to one which can be easily eliminated by controlled chemical
dechlorination. As discussed in the previous section, if blowdown
is returned directly to the receiving body of water, there are sev-
eral alternatives to minimize the direct discharge of residual
chlorine.
In once-through cooling systems (Figure 3), any total residual
chlorine is discharged directly to a receiving body of water, such
as a river, lake, or ocean. To minimize the level of residual
chlorine in the effluent, it is logical to select points of chlo-
rine application and design the control system to take maximum
advantage of dilution effects in discharge canals. Substantial
reduction of total chlorine residual can be achieved by chlorine
application as near the condenser water-box inlet as possible.
The short time of contact minimizes both the chlorine dose
required and the level of combined chlorine residual in the water
as it passes through the condenser. Also, since a large percent-
age of the total chlorine residual in the condenser during each
treatment is free HOC1, the duration of each treatment can also be
reduced. Combined with the chlorine control system designed to
treat the condenser flows one at a time in sequence, the substan-
tial reduction on the total chlorine residual can be achieved in
newer powerplants using a once-through cooling system. For a
marine-water, once-through cooling system, in addition to cyclic
shock treatment of chlorine, the continuous low level of chlorina-
tion is needed for the control of hard-shelled organisms when the
water temperature rises above 4°C (40°F), resulting in continuous
emissions of low-level, total chlorine residual. Removal of low-
level chlorine residual by chemical treatment (e.g., dechlorina-
tion) is available but is not generally practical because of the
additional costs involved to treat the large volumes of water
involved in a once-through system.
It should be emphasized that the discharge of cooling water is
often combined with other sources of wastewaters (e.g., boiler
blowdown, ash-pond overflow, etc.) before being discharged to the
receiving body of water, such as a river. Typical examples are
shown in Figure 6 for a simplified hypothetical case for a recircu-
lating cooling-water system. When the cooling-tower blowdown
water-flow rate is comparable to other sources of wastewaters, the
concentration of the residual chlorine emission in the final dis-
charge stream may be quite different from that of cooling-water
blowdown.
25
-------
INTAKE 2,271
NJ
2,5
23,8
14,4
180,5
METAL
EQUIPMENT
CLEANING
CENTRAL TREATMENT
BOILER
SLOWDOWN 1,
OTHER
LOW-VOLUME
SOURCES
166
BOTTOM ASH
TRANSPORT
180,5
FLY ASH
TRANSPORT
180,5
ASH POND
SLOWDOWN
2,243
COOLING
TOWER
SLOWDOWN 252,8
DRIFT 4,4
EVAPORATION 1,805
OVERFLOW
TREATMENT
DISCHARGE
461
Figure 6. Hypothetical 1,000 MW powerplant water flows (600,000 gpm)
(flows shown in units of cubic meters/min).
-------
As noted in an earlier section, the total average withdrawal rates
of cooling water for the total U.S. steam-electric powerplants
(283,411 MW) are 5,170 m3/s (182,558 cfs) for fresh water and
2,130 m3/s (75,136 cfs) for saline water in 1972. The reported
chlorine additive used for the prevention of biological fouling of
condenser tubes is 25,909 metric tons (28,565 short tons) for the
same year. To show the pattern of chlorine usage, more detailed
breakdowns on the consumption of chlorine for different types of
cooling systems are shown in Table 5.10 (Note: Powerplants with
mixed cooling systems are not included.)
TABLE 5. BREAKDOWN ON CHLORINE USAGE FOR DIFFERENT
TYPES OF COOLING SYSTEMS (1970)10
System
C12 C12/MW
capaciry Metric Short Metric Short
MW % tons tons % tons tons
Once-through cooling
(fresh)
Once-through cooling
(saline)
Cooling ponds
Cooling towers
Combinations
132,000
57,800
14,800
28,000
11,500
54.0
23.7
6.1
11.5
4.7
8,980
8,890
489
1,540
1,110
9,880
9,780
538
1,690
1,220
42.8
42.3
2.3
7.3
5.3
0.068
0.154
0.033
0.055
0.095
0.075
0.169
0.036
0.060
0.105
It is interesting to see (Table 3, 1970) that nearly 70% of the
powerplants in the United States use once-through cooling systems.
Both freshwater and saline-water systems consume about equal ton-
nage of chlorine despite the fact that saline-water systems
account for only about 30% of once-through systems. On a megawatt
basis, a saline-water system consumes 0.150 metric ton
(0.167 short ton) C12/MW per year versus 0.068 metric ton
(0.075 short ton) C12/MW per year for fresh water. This shows
that more than twice the amount of chlorine is consumed for a
saline-water system as for a freshwater system with the same elec-
tric generating capacity. This is expected from the fact that
there is a greater variety of marine organisms (with high-life
forms such as mussels and barnacles) which requires continuous,
low-level chlorination for control of bio-fouling in seawater.
This, in turn, means that there would be more residual chlorine
discharged to the receiving body of water for the powerplant using
once-through marine water instead of fresh water. However, this
does not necessarily imply that the residual chlorine concentra-
tion would be higher for marine-water discharge than that of fresh
water.
27
-------
Chlorination programs to achieve no discharge of total residual
chlorine from recirculating cooling-water systems have been deter-
mined to be not fully demonstrated and therefore cannot be gener-
ally applied by 1983."
In view of the current best control technology available, free
available chlorine discharges in both recirculating and once-
through cooling-water systems are limited to average quantities
reflecting a concentration of 0.2 mg/1 (ppm) during a maximum of
2 hours per day (aggregate) and a maximum of 0.5 mg/1 (ppm).
These limits can be achieved by means of available feedback con-
trol systems presently in use.
3.6 COST OF CURRENT PRACTICES
The treatment technology for once-through condenser cooling-water
systems consists of maintaining the residual chlorine in the efflu-
ent below an established limit by controlling the chlorine added
to the system. The capital costs involved consist of the cost of
a residual chlorine analyzer and feedback controls to adjust the
feed rate. The installed cost of a residual chlorine analyzer and
control equipment is estimated to be about $5,000 regardless of
size of unit (based on 1973 dollars) .**
Besides the installed cost of chlorination equipment, costs of
maintenance, operation, and chemical treatment must be considered.
Figure 7 shows the variation in the costs with powerplant capacity
and once-through cooling flow.12 It is interesting to note that
the cost of chemical treatment is only a small fraction of the
total operation and maintenance costs. Chemical treatment of
recirculating cooling-water systems would be less costly, and the
pollution potential of residual bisulfite chemicals added would be
less significant than with once-through cooling-water systems due
to the smaller wastewater volumes requiring treatment.
The average rate of cooling-water use is 0.028 m3/s to 0.042 m3/s
(1.0 cfs to 1.5 cfs) per MW of installed powerplant capacity.2'11
Therefore, from Figure 7, annual total operation, maintenance, and
chemical cost of a once-through cooling system for a 1,000 MW
powerplant in 1971-1972 was approximately $50,000.
The total operating expenses for cooling-water facilities in 1972
for all of the U.S. powerplants were reported7 to be $35.4 million
for operation and maintenance and $7.0 million for chemical addi-
tives. Chlorine accounts for most of the chemical additives con-
sumed. Assuming fixed charges of 15% on capital costs of cooling-
12Daugard, S. J., and T. R. Sundaram. Review of the-Engineering
Aspects of Powerplant Discharges. Hydronautics, Inc., Laurel,
Maryland. Prepared for Maryland Department of Natural Resources,
U.S. Environmental Protection Agency, Washington, D. C.,
NTIS PB 235 783, October 1973. 115 pp.
28
-------
to
8
1972
OPERATION AND
MAINTENANCE COST
KEY
TOTAL OPERATION AND
MAINTENANCE COST
CHEMICAL COST
OPERATION AND
MAINTENANCE COST
TOTAL OPERATION AND
MAINTENANCE COST
POWER PLANT
MORGANTOWN
WAGNER
DICKERSON
C.P. CROCE
RIVERSIDE
WESTPORT
GOULD ST.
R.P. SMITH
BENNING RD.
POTOMAC RIVER
300 400500 800 1,000
PLANT CAPACITY, MW
2,000
4,000
(a) once through cooling system
operation and maintenance
cost vs. the plant capacity.
4.0
2.0
1.0
0.8
0.6
0.4
0.2
0.1
0.08
0.06
0.04
0.02
0.01
NO. POWER PLANT
01
04
1
2
3
4
5
6
8
9
12
13
14
MORGANTOWN
WAGNER
CHALK PT.
DICKERSON
C. P. CROCE
RIVERSIDE
WESTPORT
GOULD ST.
BENNING RD.
POTOMAC RIVER
POSSUM PT.
TOTAL OPERATION AND
•MAINTENANCE COST
\
\
\
OPERATION AND
MAINTENANCE COST
\«
.,
CHEMICAL \
COST
TOTAL COST OF
OPERATION AND
o MAINTENANCE
CHEMICAL
* COST
OPERATION AND
a MAINTENANCE COST
02
1000
2000
4000 6000800010,000 20,000 40,000
AVERAGE COOLING HOW GALLONS / DAY x 10
(b) total cost of operation and
maintenance and chemical
additions of a once-through
cooling system vs. cooling
flow per day.
Figure 7. Costs of operation, maintenance and chemical additions
of a once-through cooling system (1972 dollars). 12
-------
water facilities of $1,336 (1970), the total expenses for the year
would amount to $242.8 million. This is equivalent to approxi-
mately 0.22 mill per kilowatt hour for the total generation of
1.412 trillion kilowatt hours. Considering the fact that the
nation's total steam-electric generating capacity is 309,861 MW in
1972, the average yearly operation and maintenance cost and chemi-
cal additives cost for a 1,000 MW powerplant in 1972 are as follows;
Operation and maintenance $114,000
Chemical additives 22,600
TOTAL $136,600
This national-average cost reflects all types of cooling systems
(once-through fresh, once-through saline, cooling ponds, cooling
towers, combined systems), and it is about two and one-half times
higher than the cost shown in Figure 6, which represents cost fig-
ures for the Maryland region only.
For reference, the unit costs of the various types of cooling sys-
tems as reported for 1972 are shown in the following tabulation:10
Type of cooling Capital cost/kW
Once-through, fresh $5.06
Once-through, saline 5.00
Cooling ponds 9.31
Cooling towers 7.03
30
-------
SECTION 4
ASSESSMENT OF ALTERNATIVE METHODS
Various chemicals have been used to reduce fouling and restore
tube cleanliness. Acid cleaning is limited to once a year or less.
Fouling can severely affect condenser performance between cleanings.
The use of chlorine is being cut back in many regions by govern-
ment regulations due to environmental considerations.
4.1 ON-LINE MECHANICAL CLEANING
Equipment for automatic on-line mechanical cleaning of condenser
tubes is manufactured primarily by the Amertap Corporation and by
the M.A.N. Corporation of West Germany. By far, most of the suc-
cessful installations in U.S. powerplants have been supplied by
Amertap. In principle, each of the two systems maintains
condenser-tube cleanliness while in operation by mechanical means
rather than chemical means. Some powerplants also use supple-
mental chlorination together with a mechanical cleaning system.
Although chlorination may not be needed for mechanical cleaning of
condensers, chlorine or an equivalent biocide is certainly needed
to prevent excessive growths on the cooling-tower deck and tower
fill for recirculating cooling systems. If the growths are
allowed to proliferate on the decks, the distribution orifices may
become plugged and cause flooding. Excessive growths on the fill
decrease tower efficiency.
4.1.1 Amertap Sponge Ball System1* •l 3
The basic principle of the Amertap system is to circulate over-
sized sponge-rubber balls through the condenser tubes with the
cooling water. These balls, after travelling through the length
of the tube's, are collected at the discharge piping in a basket
arrangement and then repumped continuously to the inlet. This con-
stant rubbing action keeps the walls clean and virtually free from
deposits of all types. Thus, suspended solids are kept moving and
are not allowed to settle. Bacterial fouling is removed quickly.
The number of balls in the system is approximately 10% of the num-
ber of tubes in the condenser. Each tube receives a ball on the
average of every 5 minutes with a normal circulation time per ball
of 20 seconds to 30 seconds.1* A schematic arrangement of the
Amertap system is shown in Figure 8. There are about 2,000 instal-
lations of sponge-rubber cleaning systems in Europe, and about 200
31
-------
to
OUTLET MATER
BOX
COOLING
WATER
OUTLET
STRAINER
SECTION
I
TURBINE EXHAUST
STEAM
fa- KS
\! U ^ "AS
HATCH FOR INSERTING
OR REMOVING BALLS
BALL COLLECTING
KET
BASKET SHUTOFF
HOENSER
IE
BALL
COLLECTOR
,INLET WATER
BOX
-»J
SPONGE,RUBBER
BALLS (TYPICAL)
COOLING WATER
INLET
Figure 8. Schematic arrangement of Amertap tube cleaning system.•*
-------
in the United States. All have achieved a good record of success
in maintaining condenser efficiency and reliability.13
4.1.2 M.A.N. Brush System
The M.A.N. system for on-line mechanical cleaning uses a brush
device about 5 mm long, sized to pass through the condenser tubes
intermittently by reversing the flow of condenser cooling water
each time. Reversing of cooling water forces the brushes through
the tubes to a plastic cage at the opposite end. When the cooling-
water flow is returned to the normal direction, the brushes are
forced to their normal resting position in the cages at the outlet
ends of the tunes. Recycling can be set up automatically for what-
ever frequency of backwash is desired. Twice daily is normal.
The M.A.N. system is reported to be less reliable and tends to
become fouled by leaves, twigs, and even an occasional fish. In
some cases, severe grooving of tubes was found.1* A schematic dia-
gram of the reverse flow piping arrangement of the M.A.N. system
is shown in Figure 9.
4.1.3 Hot Water Backflush System7
Another method which has been tried with varying degrees of suc-
cess in marine-water cooling systems is periodic backflushing of
condensers with hot water. The Southern California Edison Company
has incorporated duplicate intakes in several of its coastal
plants, so that the intake and discharge canals can be used alter-
nately. Current practice is to reverse the canals every 5 weeks
and to raise the water temperature of the discharge water to 49°C
(120°F) for 1 hour after reversing the canals. Since mussels are
very sensitive to heat, they either die or attempt to move, and in
doing so, they are washed out to sea. The heat differential must
be at least 28°C (50°F) to be effective. Since heat treatment
will not affect slime growths, intermittent chlorination must
still be practiced at plants using heat treatment for control of
mussel growths. Slime in saltwater sets up corrosion concentra-
tion cells rapidly, and this will bore a hole in the condenser
tubes very quickly.
4.1.4 Economics of Mechanical Cleaning of Condensers'*
Comparative capital costs of the Amertap system and the M.A.N. sys-
tem are shown in Tables 6 and 7. The costs shown are additional
costs to those that would be required for conventioal chemical con-
ditioning. The costs are revised from the costs reported for a
675 MW1* powerplant by applying the following cost factors:
13Kern, W. I. Continuous Tube Cleaning Improve Performance of Con-
densers and Heat Exchangers. Chemical Engineering. 83(22):139-
144, October 1975.
33
-------
NORMAL FLOW PI PING
BACKWASH FLOW PI PING
OPEN
CLOSED
U)
*»
0
c
I
SECTION OF
CONDENSER BEING
BACKWASHED
FROM INTAKE «-
FROM INTAKE *-
TO OUTFALL -
TO OUTFALL -
FT
Xo Xc
Xc
T
Xo xc
Xo
Xo
c
H'H
i r
Xc Xo
Xo XC
Figure 9. Schematic of M.A.N. system reverse flow piping.
-------
TABLE 6. COMPARATIVE CAPITAL COSTS3 OF
CONDENSER CLEANING SYSTEMS1*
M.A.N. system, baskets and brushes
Amertap system
Tubing
Tube sheet machining
Backwash piping and valves
Miscellaneous piping and valves
Controls
Mechanical construction
Electrical construction
General construction
SUBTOTAL
Indirect costs at 16%
Comparative capital costs3
Amertap
system,
$
_
210,000
Base
Base
Base
13,000
46,000
45,000
29,000
11,000
355,000
57,000
412,000
M.A.N.
system,
$
95,000
1,300
49,000
141,000
Base
8,000
16,000
4,000
Base
214,000
34,000
250,000
Costs shown are increases (or decreases) from the cap-
ital costs of a conventional chemical cleaning system.
Costs are for a 1,000 MW generating unit to be instal-
led in 1979, operating with an open recirculating
cooling system using mechanical draft cooling towers.
TABLE 7. COMPARATIVE ANNUAL COSTS31*
Conventional
chemical Amertap
treatment, system,
$ $
Annual costs of operation
Manual brush cleaning of tubes
Chemicals
M.A.N. system brushes
Amertap balls
Demand 'and energy costs
Comparative costs of operation
Total annual costs
Fixed charges
Costs of operation
Comparative total annual costs
Differential total annual costs
7,400
34,000
Base
41,000
Base
41,400
41,400
Base
30,000
28,000
9,600
67,400
69,300
67,400
136,700
95,300
M.A.N.
system,
$
30,000
23,700
17,900
71,300
42,200
71,300
113,500
72,100
aCosts are for a 1,000 MW generating unit to be installed in 1979,
operating with an open recirculating cooling system using mechan-
ical draft cooling towers. Annual fixed charge rate is 15.0%.
35
-------
Capital costs for 1,000 MW plant
= (1,000/675)°-7 (cost for 675 MW plant)
Operating cost for 1,000 MW plant
= (1,000/675) (cost for 675 MW plant)
The costs in Table 6 are for a 1,000 MW generating unit to be
installed in 1979 which will be equipped with an open recirculat-
ing cooling system using mechanical-draft cooling towers. Table 7
shows the comparative cost of operation and total annual costs for
the same 1,000 MW generating unit. The demand and energy costs
reflect increased circulating water pumping costs for the mechani-
cal systems due to friction of the plastic cages of the M.A.N. sys-
tem and of the strainers of the Amertap system. For the Amertap
system, they also reflect the cost of operating the small pumps
that recirculate the balls. The annual fixed-charge rate is
assumed to be 15.0%.**
Costs of operation shown in Table 7 are based on all cleaning sys-
tems maintaining the same degree of cleanliness. It is expected
that the Amertap system can maintain tube cleanliness at about 95%
if placed in service when the condenser tubes are new and that the
M.A.N. system would not be able to maintain the cleanliness level
as high as the Amertap system. The M.A.N. system operates inter-
mittently, while the Amertap system is a continuous-cleaning system.4
As tube cleanliness decreases, the condenser pressure increases,
which causes the turbine heat rate to increase and the generating
capability to decrease. Figure 10 shows the tube cleanliness fac-
tor plotted against the annual cost of increased fuel and reduced
capability for a 1,000 MW unit. The unit is assumed to operate at
an annual capacity factor of 86.5%, fuel is evaluated at a price
of 47.5 cents/103 Megajoules (45 cents/105 Btu), and generating
capacity is evaluated at an annual cost of $20.80 kW. The costs
plotted in Figure 10 are additional costs as the cleanliness fac-
tor decreases from 100%, which reflects the cleanliness of new
clean tubes.1*
The comparative annual costs shown in Table 6 and in Figure 10 can
be used to determine whether or not a mechanical cleaning system
such as the Amertap or the M.A.N. system can be economically justi-
fied. For a 1,000 MW unit, neither a M.A.N. system with a cleanli-
ness factor of 90% nor an Amertap system with a cleanliness factor
of 95% could be justified unless the cleanliness factor with con-
ventional chemical conditioning is less than 80%. This conclusion
applied only to the case reported here since it is dependent on
such parameters as generator size, capacity factor, and the fuel
cost. It does serve as a general indication of the amount of
improvement in the cleanliness factor that must be achieved in
order to justify an on-line mechanical cleaning system. However,
it should be emphasized that the increased cost is an insignifi-
cant part of the total operation and maintenance costs, and the
36
-------
200
d
5 100
S
GENERATING UNIT-1000MW
FUEL COST - $ 0.45 PER 10* BTU
CAPACITY COST - * 2L 80 / KW / YEAR
ANNUAL CAPACITY FACTOR - 86.5 *
60 70 80 90
CLEANLINESS FACTOR IN PERCENT
100
Figure 10.
Tube cleanliness versus cost of
reduced generating efficiency-1*
advantage of a nonpolluting mechanical cleaning system must not be
ignored.
4.2 CHEMICAL TREATMENTS10/13
Powerplants employ a variety of chemicals in their cooling water
systems in order to prevent fouling. While chlorine is most com-
monly used, other chemicals used are a variety of biocides, caus-
tic soda, alum, sodium dichromate, sulfuric acid, calcium hypochlo-
rite, phosphate, and lime. The type and quantity of chemicals
used in any cooling method are of considerable concern since most
of these chemicals will ultimately find their way into a water
body. Typical distribution of different chemicals used in a power-
plant cooling system for the Maryland region is shown in Figure II.13
Total tonnages of the principal cooling-water chemical additives
used in the U.S. in 1972 and reported by the Federal Power Commis-
sion10 are as follows (excluding the states of Montana, Alaska,
Hawaii, Idaho, Vermont, and Oregon, from which no data were avail-
able) :
Phosphate, tons/yr
Lime
Alum
Chlorine
752.75
16,838.49
1,685.53
28,564.68
37
-------
o
1
u
i
=>
I
Lt-
O
1
11
10
9
8
7
6
5
4
3
2
1
COOLING METHOD :
COOLING
COOLING POND
Figure 11.
Distribution of chemicals added
to cooling-water systems.12
Chlorine is the chemical used in the largest amount, and it
amounts to a national average of about 0.1 ton/yr MW of installed
capacity considering the total steam-electric generating capacity
of 309,861 MW. As discussed in previous sections, other potential
alternative chemicals that may be used to replace chlorine are
ozone, bromine, bromine chloride, chlorine dioxide, etc. Ozone is
the nearest competitor to chlorine as a water disinfectant.
Economics has been a primary factor in the use of chlorine in the
treatment of cooling systems in the United States. It is the
least expensive of the effective biocides. Potentially effective
and feasible biocides have been eliminated from use in cooling-
water systems solely on the basis of economics.
The effect of these chemicals and their potential residuals is of
great concern since most of them will ultimately find their way to
the environment. As in any industrial-scale operation, cost will
remain a primary factor, but the cost in dollars must now be
balanced by compatibility with the environment. Thus the most
desirable control will be the one that is the least expensive in
terms of a combination of cost and versatility and that will also
result in the lowest residuals entering the environment.
There are a number of potential chemicals and several methods that
can be used to control bio-fouling of powerplant condenser tubes.
Some are obviously unacceptable and can be eliminated immediately
because they either change the form of the pollution and do not
solve the pollution problem, or they create more problems than
they solve. Nevertheless, all alternatives except the oxidizable
38
-------
and nonoxidizable biocides (organic compounds) are assessed in
this section. Those that are the most feasible will be assessed
for potential application to control bio-fouling in powerplant con-
denser tubes. All chemical agents are not equally economical and
efficient.
4.2.1 Ozone (03)
In the past, one of the strongest criticisms against ozonation has
been its operational costs. Confusion has been caused by reports
showing a wide variance in cost analysis of ozonation. Ozonation
is favored over chlorination as a disinfectant for a number of rea-
sons:
• It requires shorter contacting time.
• It requires a lower concentration; e.g., 0.024 to
•vO.45 mg/1 (ppm) O3 residual needed for disinfection in
contrast to 0.5 to ^1.0 mg/1 (ppm) of chlorine residual.
• It produces no pollutants in freshwater; in seawater, it
will oxidize bromide ion to bromine.
• It reduces color, odor, BOD, and COD.
• It produces no harmful by-products and inorganic salts.
Ozone is an unstable gas; its half-life ranges from 20 minutes to
30 minutes. Since its half-life is so short, residual O3 dissi-
pates quickly in the ozonated effluent, thus providing no residual
protection against downstream contamination by microorganisms.
Therefore, ozone could provide protection against bio-fouling for
condensers for a once-through cooling system, but it might not be
adequate for simultaneous protection of cooling towers for a
closed-cycle cooling system without additional chlorination.
It has been found1** that ozone requires approximately 5 minutes of
contact as compared to 30 minutes for chlorine. The rate of decom-
position is not appreciable over short contact times. Figure 12
shows the decomposition of ozone with respect to time. Ozone
decomposed 1.44% and 6.25% over periods of 2 minutes and 4 minutes,
respectively.
*
Ozone is a very powerful oxidizing agent. It readily destroys bac-
teria and organic matter, but it also corrodes metals, disinte-
grates rubber, and attacks all plant life. Another serious draw-
back is the interference by iron and manganese. Ozonation in the
presence of either of these metallic ions in water will produce
precipitates, scums, and coloration of water. (Note: A similar
iron and manganese problem occurs with chlorination.)
llfMajumdar, S. B., and O. J. Sproul. Technical and Economic
Aspect of Water and Wastewater Ozonation: A Critical Review.
Water Research, 8:253-260, 1974.
39
-------
o
g
L25
LOO
a 75
a so
a 25
0.25 a so a 75 LOO 1.25
INITIAL OZONE CONCENTRATION, mg/e
Figure 12. Rate of decomposition of ozone.14
Ozone does not undergo dissociation with pH in water as does chlo-
rine, with the resulting loss in disinfection efficiency; nor does
it react with ammonia to form a less efficient disinfectant like a
chloramine. The solubility of ozone in water is a limiting factor
that greatly affects the process of ozonation. The amount of
ozone that will dissolve in water is dependent on temperature and
pressure. A physical relationship between the concentration of
ozone in air and that in water is expressed by:7
C . = S
water
air
(2)
where
cair
S
t
= ozone concentration in water g/m3 of water
= ozone concentration in air, g/m3 of air
= distribution coefficient = 0.588 - 0.0212t + 0.000191t2
= temperature, °C
Figure 13 shows the typical behavior of ozone in saturated solutions
at atmospheric pressure. An increase in the S factor at lower (tem-
peratures indicates that application of ozone is more effective in
a colder climate, although growth of microorganisms is less at
colder water temperatures. The concentration of ozone in the air
is important because of the low solubility of ozone in water.
Increasing the concentration will increase the efficiency of the
process. In present practice, ozone is generated on site at con-
centrations varying from 10 g/m3 to 20 g/m3 of air, which is about
100,000 times above the human tolerance level. It should be empha-
sized that the amount of ozone absorbed by a particular water is a
40
-------
3
CO
0
0
10
20
30
OZONE IN AIR, g/nT
Figure 13. Behavior of ozone in saturated solutions
at atmospheric pressures. (An S value
of 0.2 is assumed.)
From Handbook of Chlorination by Geo. Clifford White,
copyrighted 1972, Litton Educational Publishing, Inc.
Reprinted by permission of Van Nostrand Reinhold Company,
41
-------
function of organic content, which determines the ozone demand and
not the distribution coefficient alone.
The most difficult engineering problem encountered in ozonator
designs is that of efficient mixing in water. In recent designs,
ozonized air (at a slightly positive pressure of 1.2 x 105 Pa
(1.2 atm) in contrast to 6.8 x 101* Pa (10 in. Hg) vacuum for a
chlorinator) is applied to the point of application by means of an
injector system similar to the chlorinator injector system. The
proper mixing at the point of application has long been recognized
as one of the most important factors contributing to the overall
efficiency of the process. Similar to a chlorinator, a minor flow
of water pulls ozonized air into the injector and discharges this
air-water mixture to the total cooling-water flow entering the con-
densers. Entrapment of air bubbles in the condenser chamber must
be prevented. Also, emission of excess ozone in the air must be
minimized. Efficient absorption and mixing of ozone in high-
volume cooling water is difficult to achieve because of the short
rise time of an air-water mixture from diffuser orifices to the
water surface. For a large-volume water flow, it is possible to
achieve better results by two points of application in series
using an injector system. The limiting factor in a single-stage
operation is the gas-transfer efficiency of the injection system
and not the oxidation reactions of ozone. It is not possible to
accurately dose a variable flow of water with the present ozona-
tors because it is difficult to produce ozone proportionally to a
flow rate of water.
Similar to current chlorination practice, shock treatment by ozone
several times a day for a period of about 30 minutes to 60 minutes
may be sufficient to prevent bio-fouling of condensers in a once-
through cooling system, but further field testing and demonstra-
tion is needed to verify that this is effective. For closed recir-
culating systems, additional ozonation of cooling water prior to
entering the cooling tower may be needed due to the fleeting exist-
ence of an ozone residual. For cooling systems using marine water,
continuous ozonation (or chlorination) ahead of the bar racks will
probably still be required. Ozonation of a powerplant cooling sys-
tem has not been reported. However, ozonation followed by chlo-
rination is used in may plants for potable water and wastewater
disinfection. It should be emphasized that most waters and waste-
waters will have a higher ozone demand on a mg/1 basis than the
chlorine demand to accomplish the same degree of disinfection.
The high cost of ozonation and the lack of residual protection
against downstream contamination in the cooling tower probably are
reasons why ozonation is not widely practiced in the United States
for either water or wastewater disinfection. There have been con-
flicting reports regarding capital and operating costs of an ozona-
tion plant. This is because the cost of ozonation is a function
of plant size, place of manufacture, and the quantity and quality
of water to be treated. Typical costs of ozonating plants (water
treatment) with no pretreatment are shown in Table 8:1U
42
-------
TABLE 8. OPERATING COSTS OF OZONATING PLANTS WITH NO PKETREATMENT
Plant capacity: [x 3.8 x 10* mVday
(106 gal/day)] 1 10 100
Type of plant: ozone ozone ozone
Capital cost, $; 202,000 1,080,000 7,460,000
Operating cost, $ [x 3.8 x 103 m3/day
(106 gal/day)]
Amortization
Power
Labor
Maintenance
Oxygen
TOTAL, $ [x 3.8
(106 gal/day)
Operating cost,
(103 gal/day)
(15 yr at 4%)
x 10 3 m3/day
]
$ [3.8 m3/day
]
49.60
36.00
25.60
1.80
24.00
137.00
0.137
26.50
28.80
2.60
1.00
17.80
76.70
0.777
18.31
21.60
0.50
0.67
8.00
49.08
0.043
Extrapolation of these costs to ozonation of 3.8 x 105 m3/day
(109 gal/day), which is about equivalent to a cooling-water flow
rate of a 1,000 MW powerplant, gives:
Capital cost: $9,850,000
Operating cost: $8.7/103 m3/day ($33/106 gal/day)
The operating cost amounts to $12 million a year. Of course, for
powerplant cooling-water treatment, the dosage needed and ozona-
tion period are completely different from that of the water-
treatment plant as shown in the preceding Table 8. A water-
treatment plant requires a continuous high dosage of ozone, while
a cooling-water system requires ozonation for only a few hours a
day and probably at lower ozone dosage. However, a continuous low-
level ozonation is required for marine waters.
In a comparative cost analysis of ozonation versus chlorination of
microstrained secondary effluent, it was reported15 that chlorina-
tion would be much cheaper than ozonation. At an electrical cost
of O.SC/kWh, the operating cost for ozonation was given as 0.46
-------
indicated that, 3.0 mg/1 (ppm) chlorine would accomplish the same
disinfection as the 6.0 mg/1 (ppm) ozone. Ozone will always have
a higher demand than chlorine under the same conditions. This is
because ozone is such a powerful oxidizing agent that it will
attack and degrade almost any organic matter, whereas chlorine
will attack or oxidize only active organic materials or compounds
that are readily substituted. A conventional corona-discharge
ozone system requires 18 to 22 kWh/kg (8 to 10 kWh/lb) of ozone
produced, while a newer electron beam system requires only 6.6 to
11 kWh/kg (3 to 5 kWh/lb).
Ozone dose requirement varies with water sources. Table 9 shows
the comparison of ozone doses reported in water and wastewater
treatment.16 It shows that it requires 2 mg/1 (ppm) to 4 mg/1
(ppm) ozone dosage for disinfection of surface waters depending on
quality of waters.
An EPA study shows capital and operating costs for ozonation at
0.8
-------
TABLE 9. COMPARISON OF OZONE DOSES REPORTED IN WATER AND WASTEWATER TREATMENT16
cn
Dose,
mg/1
Contact
time.
rain
Water/wastewater treated
Objective or
result
1
3
0.5 to
2 to
3 to 4
1.5 to 2
2 to 5
10 to 100
>50
15
82
15
6
7 to 11
5
5
550
92
5 to 10 Good quality ground water
5 to 10 Good quality surface water
5 to 10 Poor quality surface water with filtration
Not given Treated water
5 Treated water
Not given Primary wastewater and stormwater overflow
Not given Secondary wastewater effluent
22 Secondary wastewater effluent
75 Lime-clarified raw wastewater
5 Secondary wastewater effluent
Not given Secondary wastewater effluent
Not given Secondary wastewater effluent
1.6 Tertiary wastewater effluent
<1 Secondary wastewater effluent
90 Innoculated raw wastewater
30 Innoculated autoclaved wastewater
Disinfection
Disinfection
Disinfection
Disinfection
Disinfection
Treatment
Potable quality
Disinfection <200 fecal coliforms/100 ml
COD reduction 55 mg/1 to 35 mg/1
F-2 virus destruction
Oxidation of naturally occuring cyanide
Oxidation of naturally occuring phenol
Complete bacterial disinfection
Disinfection <1,000 coliforms/100 ml
Sterility
Sterility
Reprinted from Journal American Water Works Association, Volume 66, by permission of
the Association. Copyrighted 1974 by the American Water Works Association, Inc.,
6666 West Quincy Avenue, Denver, Colorado, 80235.
-------
residual of 1 ing/1 (ppm) to 2 mg/1 (ppm) . This level of residual
compares to 0.4 mg/1 (ppm) of chlorine to achieve the same quality
pool water.
It is interesting to note that bromides are present in seawater to
the extent of approximately 70 mg/1 (ppm), which is significant.
The..current practice of chlorinating cooling water will convert
the bromides to hypobromous acid as follows:
HOC1 + Br~ H- HOBr + ClT kQ = 2.95 x 103 1/mol-s (3)
Also, chlorination in the presence of bromides will result in a
combination of free and combined chlorine and bromine residuals if
ammonia or nitrogenous material is present.
Bromine, like chlorine, reacts with ammonia to form bromamines,
but the bromamines are better disinfectants, approaching free chlo-
rine and free bromine in this respect. However, the bromamines
are unstable, decomposing rapidly into components that do not have
disinfecting power.' In low-quality surface water, on a dosage
basis, chlorine is far superior to bromine because much of the bro-
mine is utilized in satisfying the halogen demand, and a residual
is difficult to maintain for a significant amount of time to pro-
tect downstream equipment. However, in comparing the efficiency
of chlorine and bromine as disinfectants, since the degree of dis-
infection varies with temperature and pH as well as concentration
of the disinfectant, time of contact, and other factors, it is nec-
essary to compare these agents under a variety of conditions that
may exist in cooling-water systems. For example, the effective-
ness of chlorine increases with decreasing pH, while bromine is
more effective at a high pH. Bromine, unlike chlorine, is an
effective disinfectant (HOBr) at pH values near 9. Although com-
bined chemical species are produced when waters containing organic
amines or ammonia are treated with either chlorine or bromine, the
chloramines have been shown to be ineffective as disinfectants for
cysts, bacteria, and viruses. Bromine, on the other hand, is
available for disinfection of bacteria and viruses whether it
exists as free bromine or as mono- or dibromamine.20 The exten-
sive studies on the halogens as algicides documents the superior-
ity of bromine for a number of species of algae.21 However, the
effectiveness of bromine for controlling bio-fouling in cooling-
water systems is not known. In the past, the use of bromine has
been limited in practice to swimming pools and portable water
treatment.7
20Taylor, D. G., and J. D. Johnson. Kinetics of Viral Inaction by
Bromine. Presented before the Division of Water, Air, and Waste
Chemistry, American Chemical Society, Dallas, Texas, April 1973.
21Kott, Y. Effect of Halogens on Algae. Water Research. 3(4):
256-271, 1969.
46
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Although the cost of bromine is presently twice the cost of chlo-
rine, the use of bromine chloride to generate free bromine in
water is feasible at a lower cost. Bromine is unique in being the
only nonmetallic element which is liquid at ordinary temperatures.
Liquid bromine is corrosive, attacking iron, steel, cast iron,
stainless steel, and copper, either wet or dry. Nickel and monel
resist dry bromine and are used for shipping containers. Other
nickel alloys, including the hastelloys, are less suitable. Tanta-
lum is resistant to bromine, wet or dry, up to 149°C (300°F). Bro-
mine handled in lead, nickel, or monel containers must be dry
(less than 0.003% moisture) and must be protected from ordinary
air, from which it can readily absorb enough moisture to make it
severely corrosive to these materials.
4.2.3 Bromine Chloride (BrCl)
Bromine chloride has been little used until very recently due to
its lack of commercial availability and handling technology. BrCl
is more active than either chlorine or bromine as a bactericide or
viricide in water, and it is less corrosive and more safe to
handle than bromine or chlorine. It has been reported that impor-
tant cost and ecological advantages can be gained by substituting
bromine chloride for either bromine or chlorine.5
Bromine chloride exists in equilibrium with molecular chlorine and
bromine. Commercially available bromine chloride is a liquid con-
taining about 20% molecular bromine and chlorine. Its high reac-
tivity and fast equilibration result in the formation of products
almost exclusively from the reaction of BrCl. Bromine chloride
appears to hydrolyze exclusively to hypobromous acid (HOBr). Any
hydrobromic acid (HBr) formed by hydrolysis of dissociated bromine
would quickly be oxidized by hypochlorous acid (HOCl) to hypo-
bromous acid. (The hypochlorous acid is formed by hydrolysis of
dissociated chlorine.)
In water treatment, the halogen demand of the water must be satis-
fied before reliable disinfection residuals can be obtained.
Because of their higher oxidation potentials, bromine species are
much less stable than chloramine. It is reported that the prod-
ucts of chlorobromination of water are more easily degraded and
less obnoxious than their chlorinated analogs.5 The brominated
derivatives are more readily degraded photochemically and biologi-
cally. The predominant products formed from several competitive
reactions of BrCl in water are the innocuous chloride and bromine
salts.5
Some properties of bromine chloride resemble those of bromine,
while others are unique. Both bromine chloride and bromine yield
hypobromous acid as their major hydrolysis product:
BrCl + H20 -»• HOBr + HC1 (4)
47
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Br2 + H2O t- HOBr + HBr (5)
With respect to efficient usage of bromine, bromine chloride is an
economical method of using bromine. The byproducts of bromine
chloride substitution reactions consist almost entirely of HC1,
whereas a majority of uses of elemental bromine result in a hydro-
gen bromide byproduct. This results in a 50% waste of the total
bromine used. However, it must be remembered that half of the
bromine-chloride molecule is also "wasted" because it is converted
to hydrogen chloride.
Despite the possible advantages of bromine chloride over chlorine
in cooling-water treatment, bromine chloride has never been tested
in a full-scale facility partly due to lack of handling and stor-
age technology and partly due to the unwillingness of the industry
to try new chemicals in the past. The chemical cost of bromine
chloride is about 55
-------
• The extent and rate of decay for the total BrCl residual
was, on the average, greater than that for the total resid-
ual of chlorine for the first minute after the injection.
The decay rates were approximately the same (or slightly
higher) after 3 minutes using a 1:1 dilution.
• The BrCl residuals were significantly lower in the plant
effluent with river dilution.
• BrCl supplies are limited now, and the cost of the chemi-
cal is about three times that of chlorine.
• The results were encouraging, but Public Service Electric
recommended that further research be performed.
Potamic Electric Power Company (PEPCO) at Morgantown is field-
testing bromine chloride in their once-through cooling system.
4.2.4 Iodine (I2)
Iodine has been used to a limited extent in the disinfection of
water and in swimming pools, but it has not proven satisfactory in
cooling-water systems. The use of iodine as a disinfectant for
water has been recognized for a long time, but it has never gener-
ated enough interest to displace the popular use of chlorine. The
high cost of iodine is the main reason for its limited use.
lodination can be used where chlorination or more complete treat-
ment of water is either not possible or impractical.
Elemental iodine (12) and hypoiodous acid (HOI) are two of the
most powerful disinfecting agents among iodine species. At pH 8,
the effective chlorine germicide HOC1 is present at a level of
21.5%, while the ineffective hypochlorite ion is present at a
78.5% level. With iodine, however, the ineffective hypoiodite ion
is present at only a 0.005% level, with elemental iodine at 12%,
and hypoiodous acid at 88%. Therefore, the formation of the in-
effective hypoiodite ion can be ignored. It is less dependent on
pH, temperature, time of contact, and nitrogenous impurities than
chlorine. However, the upper limit for iodine is pH 8 because
higher pH values produce the ineffective iodate and tri-iodide ions,
Iodine is superior to chlorine in swimming-pool applications
because iodine will not react with nitrogenous compounds found in
swimming-pool waters. However, in a closed recirculating cooling-
water system, the primary advantage of iodine becomes a disadvan-
tage because the iodine will not react with nitrogenous compounds
found in cooling waters as does chlorine, and it cannot destroy
these compounds, which serve as nutrients for algae. Iodine is a
notoriously poor algicide, making algae control very difficult,
especially in cooling-tower application.7
49
-------
The cost of iodination is also an important factor against its use
since iodine is at least an order of a magnitude more expensive
than chlorine. It is too expensive to be used on a continuous
basis; e.g., a once-through cooling system. More iodine than chlo-
rine on a weight basis is required to achieve the same rate of dis-
infection of water. However, iodine will not form compounds with
nitrogenous material, so it does not have the potential for dis-
charging toxic materials into a receiving body of water.
4.2.5 Chlorine Dioxide (C1O2)
Chlorine dioxide is being used successfully to assist chlorination
in the control of wastes resulting from the raw water being contam-
inated with phenolic substances and algae. Chlorine dioxide will
not react with ammonia or nitrogenous compounds, and its efficiency
is not impaired (as is that of HOC1) by a high pH environment.
Many other contaminants that will consume chlorine may not react
with chlorine dioxide, making it a superior choice in some cases.
Chlorine dioxide is extremely soluble in water (five times the
solubility of chlorine), but, paradoxically, it is extremely vola-
tile and can be easily removed from aqueous solutions by a minimum
of aeration. The gas explodes when its temperature is raised,
when it is exposed to light, or when it is allowed to come into
contact with organic substances. The exposure of the gas or aque-
ous solution to light results in photochemical decomposition.
Chlorine dioxide must be generated and used onsite. For cooling-
water applications, there are two easily controlled methods of gen-
erating chlorine dioxide in water solution. The first method,
referred to as "chlorine generation," utilizes a standard gas
chlorinator. The two-step reaction is:
C12 + H2O •* HOC1 + HC1
HOC1 + HC1 + 2 NaClO2 -»• 2 C1O2 + 2 NaCl + H2O (6)
The second method, referred to as "3^-Pump Generation," can be used
when gaseous chlorine is unavailable. This method uses
23Wheeler, G. L., and F. Yau. Chlorine Dioxide: A Selective Oxi-
dant for Industrial Wastewater Treatment. Paper Presented on
Industrial Conference & Exposition, Houston, Texas, March 30 to
April 1, 1976.
21fRauh, J. S. Chlorine Dioxide, A Cooling Water Microbiocide.
Presented at the Annual Meeting Water and Wastewater Equipment
Manufacturers Association, Houston, Texas, April 1976.
25Ward, W. J. Chlorine Dioxide, A New Development in Effective
Microbio Control. Annual Meeting Coding Tower Institute,
Houston, Texas, January 19-21, 1976.
50
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hypochlorite and acid as the source of hypochlorous acid. The two-
step reaction is shown below.
2 NaOCl + H2SOn -»• 2 HOC1 + Na2SO^
+ 2 HOC1 + 4 NaCL02 -»• 4 C1O2 + Na2SO!f + 2 NaCl -I- H2O (7)
In both cases, the first reaction step provides hypochlorous acid
in a water stream which carries the reactants to a generator column.
Although chlorine dioxide is readily soluble in water, it does not
react chemically with water as does chlorine. It does not belong
to the family of "available chlorine" compounds, but its oxidizing
power is referred to as having an "available chlorine" content of
263%. However, the oxidizing capacity of chlorine dioxide is not
fully realized in water-treatment practice because the majority of
its reactions with substances in water cause reduction to chlorite,
which may be toxic to humans. Therefore, in actual waterworks
practice, chlorine probably is the better oxidant except under con-
ditions where bad taste and odor are problems.
While the disinfecting power of chlorine dioxide is unaffected
over a wide range of pH (e.g., pH 6 to 10), its efficiency is
reduced at lower water temperatures; e.g., <4°C (40°F) . Waters
having a chlorine demand from substances other than ammonia nitro-
gen will display a chlorine dioxide demand, with a tendency to con-
sume proportionally greater amounts of chlorine dioxide. Chlorine
is an excellent microbiocide under the right conditions. The
advantage of chlorine dioxide is that it offers greater efficiency
in those cases where chlorine is adversely affected by conditions
existing in the water to be treated.
Currently, field trials of chlorine dioxide are underway at two
utilities. A utility on the east coast (PSG&E) uses tidal river
water on a once-through basis, and chlorine dioxide is fed for
10 minutes each 24 hours on one of four large surface condensers.
The other utility is a west-coast municipal station using second-
ary treated sewage effluent as makeup to a'recirculating cooling
system served by a cooling tower. No results are as yet available
from the tests (personal communication with William J. Ward,
Director, Technology & Support, Olin Water Services, Kansas City.
Kansas) .
The chemical cost of chlorine dioxide is from $2.00/lb to $4.00/lb
depending on the quantity used (as quoted by Olin Water Services) .
Because of its high cost and its predominant formation of chlorite,
chlorine dioxide could be considered cost-effective for the treat-
ment of powerplant cooling water with excessive chlorine demand;
e.g., water with high ammonia-nitrogen compound loadings or high
alkalinity.
51
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4.2.6 Hypochlorites (HOC1, MOC1)
The application of hypochlorite in water treatment achieves the
same result as does that of chlorine gas. The active ingredient
is hypochlorous acid (HOC1), which is formed by the hydrolysis of
the hypochlorite ion (OCL~). The only difference between the reac-
tions of hypochlorites [NaOCl or Ca(OCl)2l and chlorine gas is the
side reaction of the end products. The reaction with the hypo-
chlorites increases the hydroxyl ion concentration by the forma-
tion of sodium hydroxide or calcium hydroxide; the reaction with
chlorine gas and water increases the H+ ion concentration by the
formation of hydrochloric acid. Hypochlorite solutions will raise
the pH environment significantly, while aqueous solutions of chlo-
rine gas will lower the pH significantly.
There are conflicting views on the disinfection efficiency of chlo-
rine gas versus hypochlorites. The undesirable side reactions
occurring in the lower pH environment of chlorine gas solution is
the formation of organic chloraminesf which have little or no germ-
icidal efficiency but still appear as part of the total chlorine
residual. In practical application, the aqueous solution of chlo-
rine gas is predominantly undissociated hypochlorous acid with
some molecular chlorine. It has a pH of about 2 at the point of
application. Hypochlorite solutions are buffered to pH 11, and at
this level, the active ingredient is the hypochlorite ion. How-
ever, as soon as the hypochlorite solution becomes diluted with
water, it approaches the pH of the wastewater, and hydrolysis
occurs resulting in the formation of HOC1.
Based on the quantity of available chlorine, the chemical cost of
the hypochlorite is at least double that of liquid chlorine.7 The
metering and feeding equipment for chlorine gas is more expensive
than that for hypochlorite, but the expense of storage facilities
for hypochlorite is far greater and more than offsets the equip-
ment difference. Maintenance of a hypochlorite system requires
more man-hours than does the gas system.
4.2.7 Other Chemicals
4.2.7.1 Acids and Bases—
Inorganic acids and bases become toxic to microorganisms at pH
values below 3 and above 11. The toxicant appears to be the hydro-
gen ion (acid solution) or hydroxide ion (basic solution). It is
not common practice to treat cooling waters by addition of acids
or basis because of the severe corrosion that would result, and
for other reasons. Acids or basis are usually used to adjust the
pH for other toxicants, such as chlorine.
4.2.7.2 Quaternary Ammonium Compounds—
Quaternary ammonium compounds are well-known bacteriocides but are
ineffective against fungi and spores. They are absorbed by
organic matter in water, and they volatilize over a cooling tower,
52
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resulting in loss of effectiveness. They are effective wetting
agents and have been used in recirculating cooling systems with
partial success. In use they are prone to cause foaming. They
are most efficient in slug addition. They would not be feasible
in a once-through system. Their effectiveness is questionable in
a recirculating system.
4.2.7.3 Chlorinated Phenols—
Chlorinated phenols are used for industrial microbiological con-
trol. They are widely used in recirculating water systems primar-
ily for control of organisms that attack wooden cooling towers.
However, they are not easily biodegraded and are toxic to fish and
animals. They have been eliminated on this basis.
4.2.7.4 Fluorine—
Elemental fluorine is the most powerful of all oxidizing agents.
Its capability of oxidizing water (F2 + H20 ~t 2 HF + % O2) renders
it unfeasible for use in cooling-water systems. It is also
extremely corrosive.
4.2.7.5 Hydrogen Peroxide—
Hydrogen peroxide, in a thennodynamic sense, in a stronger oxidiz-
ing agent than oxygen, but it is only a moderately active biocide.
The amounts required and the contact time are inordinate. Even
though hydrogen peroxide is a strong oxidant, it has proven to be
a poor disinfectant.6 Three to four hours is considered the
shortest practical time period for peroxide disinfection with con-
centrations of 1.5% to 5%. Additionally, many bacteria contain
the enzyme catalase, which converts hydrogen perioxide to water
and oxygen. Organisms capable of producing catalase are therefore
able to avoid destruction to the extent that their enzyme produc-
tion can decompose the applied peroxide. In wastewater treatment,
hydrogen peroxide is also an excellent source of dissolved oxygen,
which furthers the activity of aerobic organisms in wastes and
selectively attacks the anaerobic organisms and the filamentous
bacteria. Although hydrogen peroxide is valued for its ability to
oxidize a number of toxic and noxious substances and wastewater
treatment byproducts, hydrogen peroxide is probably not a very-
suitable agent for disinfection of water on a large-scale basis,
such as for use in controlling bio-fouling in cooling systems.
Further research is needed, however, before ruling it out for all
cooling-water applications.
4.2.7.6 Heavy Metals— .
Silver, copper, mercury, cobalt, and nickel deomonstrate signifi-
cant bactericidal properties. Silver has been used to a limited
extent in the treatment of drinking water, but it has not proven
satisfactory in cooling-water systems with respect to economics
and efficacy.
Copper salts are toxic to aquatic organisms and can be eliminated
on this basis. Although copper salts are toxic to bacteria, their
53
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effect is negated by other ions in the water, and they are usually
sensitive to pH. Copper-based biocides have been slug-fed in the
past to control algae in the cooling tower. Ordinarily, other
agents are required in combination with copper for complete con-
trol of bio-fouling.
Organic mercurials are extremely effective biocides. More vola-
tile mercurials have been developed to retain their bactericidal
properties while reducing their toxicity. These compounds, how-
ever, can be aerated over a cooling tower and would enter the atmo-
sphere. Additionally, they would be present in the spray from a
cooling tower or system, and there is danger of human contact.
The organic mercurials can be eliminated on the basis of their
toxicity.
4.2.7-7 Potassium Permanganate—
Potassium permanganate is a powerful oxidizing agent and is an
effective biocide for controlling a wide spectrum of algae and
microorganisms including the slime-forming organisms. The slime
formers grow in any climate and require constant control. Perman-
ganate could be a potential candidate for cooling systems. How-
ever, it acts on all oxidizable material with formation of a man-
ganese dioxide sludge, which presents a removal problem. Further
research and field testing are needed on using permanganate for
controlling condenser-tube bio-fouling.
4.2.8 Controlled-Release Pesticides
A new approach to controlling marine fouling is to use biological
repellents on the marine surfaces, applied either in the form of a
coating or contained within a plastic matrix. For example,
B. F. Goodrich1s "Nofoul" rubber sheet, which contains 6% bis (tri
n-butyltin) oxide in neoprene rubber, is successfully used in sub-
merged marine structures to control fouling by barnacles and other
marine organisms.26 Others include use of the controlled insecti-
cide release from hydrophobia polymer films, use of chloropyrifos
in polyvinyl chloride, or additional polymerization of organometal-
lic monomers with unsaturated comonomers, etc. The basic idea is
to regulate the effects of a pesticide or other agent so that they
will be felt over a long period of time at a safe level. The prac-
tice allows economy in application and reduces potential hazards
stemming from accumulation of pesticides in the enviornment at a
rate higher than that of their natural degradation.
One of the problems with incorporating pesticides in polymer matri-
ces has been the high proportion of inert polymer required when
the release mechanism is simple diffusion from the matrix. One of
the newer approaches to designing controlled-release systems is
26Controlled-Release Pesticides Set for Growth. Chemical and
Engineering News, 53:19, September 1975.
54
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the incorporation of active agents as pendent groups on the back-
bone of a polymer chain, with concentration of the active pesti-
cide as high as 90%.
A number of pesticides have been incorporated in vinyl-type mono-
mers and then polymerized. Also, by chemically incorporating two
or more organometallic groups along the polymer chain, antifouling
activity can be broadened considerably. Use of controlled-release
pesticides may be the way to minimize emissions of pesticides with-
out shocking the environment.
At Southern California Edison, a 3-mil thick epoxy coating (with-
out pesticide, epoxy supplied by Engard Coating Corporation,
15541 Commerce Lane, Huntington Beach, California 92649,
214-431-6553) is presently being applied to the water pump, water
box, tube sheet, and to the first 6-inch length of the condenser
tube entrance section, mainly for erosion and corrosion protec-
tion. The expected life of the coating is about 1-1/2 to 2 years
(shorter life if chemical cleaning is used) (personal communi-
cation with Heinz Holl, Southern California Edison, 213-598-6631).
Also a 2 to 3 mils thick epoxy coating (trade name: SPECOAT)
was applied -in-situ by a patented process to the full 60-foot
length of leaky condenser tubes in one condenser by Specialties
Engineering Corporation (4600 Worth Street, Los Angeles, Cali-
fornia 90063) eleven years ago. The protective coatings were
guaranteed for one year by Specialties Engineering Corporation
but the condenser is still in service today (personal communi-
cation with Jack Monday, president of Specialties Engineering
Corporation, 213-263-4151). Mr. Monday acknowledges that epoxy
has a much lower thermal conductivity compared to bare metal
tube, but he claims that the glass-like smooth epoxy surface
reduces friction, enabling more water to flow through the treated
tubes with the same pressure drop, thus compensating for some
of the loss. In addition, any marine growth is much easier to
flush clean from epoxy-coated condenser surfaces. In view of
the success of this coating, it is possible that other anti-
fouling coatings of similar thickness (less than 3 mils) incor-
porating controlled-release pesticides could be developed.
Further research and development work is needed to investigate
this approach.
At Southern California Edison bio-fouling is controlled by shock
treatment with hypochlorite for a period of about 15 minutes for
4 times a day. During treatment, the total chlorine residual is
maintained below 0.5 ppm at the condenser exit as required by EPA
guidelines (personal communication with John Davis, Southern Cali-
fornia Edison, 213-430-0561). The growth of mussels is controlled
by heat treatment of the condensers; e.g., raising the cooling-
water temperature by 4°C (40°F) by recirculating the cooling water
for a period of 2 hours every 2 months. In addition to bio-fouling
control, manual mechanical tube cleaning by passing rubber balls
55
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through the tubes is performed as a regular maintenance procedure
for preventing scale formation.
The controlled-release pesticides may be used either by coating
the water-side condenser tube surfaces with a controlled-release
pesticide compound or making the condenser tubes of modified plas-
tic. However, the poor thermal conductivity of plastic materials
may hinder performance of condensers and may require enormous-size
condensers to do the same job. One approach to reduce the size
of condensers may be to use thin-walled, small hollow tubes, but
clogging or plugging by other foreign materials would create other
problems.
To assess the effect of thermal conductivity of tube materials,
the thermal transmittance U of the condenser can be written as
(see Figure 14):
U =
hwaterri
£1
(8)
steam
where
water
^steam
*i = condenser tube I.D.
-ri = coating thickness
r3 = condenser tube O.D.
water side film heat transfer coefficient
steam side film heat transfer coefficient
kj = thermal conductivity of coating material
k2 = thermal conductivity of condenser tube
STEAM
Figure 14. Schematic cross section of condenser tubes.
56
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Each term in the denominator represents the thermal resistances of
water-side film, coating, tube wall, and steam-side film. Among
the four terms, the last term connected with condensation heat-
transfer coefficient is negligible compared with other terms due
to the extremely large hsteam- If the water-side controlled-
release pesticide coating is thin [e.g., 0.762 x 10~2 cm (3 mils)],
and if we assume condenser tube I. D. of 1.905 cm (3/4 in.) and
wall thickness of 0.16 cm (1/16 in.), the second term (thermal
resistance of the coating) and the third term would be equal in
magnitude if the thermal conductivity of the tube wall material is
about 20 times that of the coating; i.e., 20 kj = k2)- In general,
the thermal conductivity of polymer coatings is one to two orders
of magnitude smaller than that of metals, which means that the
thermal resistance of the coating cannot be ignored even if the
coating is only 3 mils thick.
Next the case of a metal tube heat exchanger with no coating is
considered. Equation 8 then becomes
U = _± (9)
£2 + £2. in £2. + __±
hwaterri k* rl hsteam
If the water-side film resistance (r2/hwaterri) an<* the tube wall
resistance (r2/r! In r2/ri) are both divided by the outer tube
radius, r2, their relative magnitudes can be compared.
For a 1.905 cm (3/4 in.) I. D. tube and a 0.16 cm (1/16 in.) tube
wall thickness, the two terms become
1 16
.3.1 h
h 4 12
(= 0.016 if h = 1,000 btu/hr/ft2/°F) (10)
3 + L-
1 . T 16 0.08
£ ln —3 k —
4
(= 0.0016 if k = 50 Btu/hr/ft/°F) (11)
From this it is clear that for turbulent waterflow inside met^l
tubes [h = 5,000 kg-cal/hr/m2/°C (1,000 Btu/hr/ft2/°F) and k = 50
to 500 kg-cal/hr/m2/°C (10 to 100 Btu/hr/f t/°F) ] , the water-side
film resistance is almost one order of magnitude greater than the
tube-wall resistance. However, if a plastic tube heat exchanger
(with controlled-release pesticides) is used instead of a metal
tube, the tube wall resistance term would be increased by two
57
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orders of magnitude under the same configuration. Adoption of a
thinner wall and a smaller tube diameter could offset the increase
in the tube wall thermal resistance of the plastic heat exchanger
while maintaining tube rigidity. Much more research and develop-
ment work is needed in developing a practical plastic heat
exchanger for powerplant condenser use.
Using controlled-release pesticides in nonheat-transfer surfaces,
such as in recirculating cooling-tower systems, bar racks, screens,
or concrete canals, is a completely different story. Hot water is
cooled by evaporative cooling and does not involve conductive heat
transfer. Use of controlled-release pesticides, either in the
form of a coating or the structural member itself, would certainly
minimize bio-fouling of cooling towers. The U.S. Navy has succes-
sfully static-tested a variety of coatings (e.g., acrylic base)
with organometallic groups (e.g., organotin) on marine surfaces
for the prevention of marine organism growths. The Navy predicts
that the coating (<8 mils thick) would be effective for 5 years on
a ship hull. The cost of antifouling coatings is $60/gal to
$100/gal (personal communication with Eugene Fischer, U.S. Navy,
Annapolis, Maryland).
4.3 PHYSICAL-CHEMICAL METHODS OF TREATMENT
Radiation treatment of waters is one way to overcome the problems
associated with effluent cleanup due to the gradual tightening of
water quality standards. It is believed, however, that the cost
for radiation treatment will be much higher than that for conven-
tional systems, depending on the methods of treatment employed.
Radiation treatments also provide no post-treatment protection
against recontamination of treated waters. The use of radiation
treatment for powerplant cooling water is not cost-effective at
present due to lack of field-testing experience and its inability
to control bio-fouling of cooling towers for closed recirculating
cooling systems without additional chemical treatment.
In addition to the economic factors, the forms of radiation which
can be seriously considered may conveniently be grouped into two
classes:
• Gamma rays and x-rays
• Beta particles and accelerated electrons
There are other physical-chemical methods of treatment (e.g., elec-
trodialysis, reverse osmosis, freezing, etc.) being considered for
water treatment, but these are not applicable to powerplant
cooling-water treatment because of their high cost.
4.3.1. Ultraviolet Radiation
The radiation energy of ultraviolet rays can be used to destroy
microorganisms. In order to kill, the electromagnetic waves of
58
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ultraviolet must actually strike the organism. The germicidal
effect of ultraviolet energy is thought to be associated with its
absorption by various organic molecular components essential to
the functioning of cells, producing a progressive lethal biochemi-
cal change.
The ultraviolet treatment does not change the water chemically;
nothing is added except energy, which produces heat and results in
a slight temperature rise in the treated water. The only radiant
energy that can be effective in killing bacteria is that which
reaches the bacteria, so that the water must be free of any parti-
cles that would act as a shield. This is one of the main dis-
advantages of the ultraviolet process; other disadvantages are
lack of field testing and its inability to provide any residual
disinfecting capacity.
Effective disinfection of water requires ultraviolet radiation
(2537A) at a dosage of 2,500 to 440,000 microwatt-second/cm2,
depending on the type or organisms, at all points throughout the
water depth, which, in turn, limits the processing of a large vol-
ume of deep-flowing cooling water. However, it is not known
whether ultraviolet could effectively destroy all of the micro-
organisms in cooling water because there is a consensus that
ultraviolet radiation will not kill any organisms that can be seen
with the naked eye.
At present the application of this process is limited to small
water supplies and certain special situations where other methods
are not considered feasible. Based on present technology, the
ultraviolet process is impractical for powerplant cooling-water
treatment because of the cost of the equipment and the power
requirements for operating the germicidal lamp. The cost of the
electric current to operate the lamp is many times that of suffi-
cient chlorine to do the same job.1* Furthermore, most river
waters and other sources of high turbidity and organic and iron
content usually cannot be disinfected at designed capacity.
4.3.2 Gamma Radiation
Gamma radiation has the capacity to destroy microorganisms. It is
expensive,-however, and this coupled with the care required in
applying this method for disinfection purposes would seem likely
to restrict its use at present. Some day nuclear reactor wastes
might be employed for disinfection rather than pure isotopes, such
as cobalt-60 or cesium-137. This could reduce costs significantly.
For example, the first commercial operation using gamma radiation
to treat sewage was initiated in West Germany in 1973. The facil-
ity, designed to use either cobalt-60 or cesium-137, provided
120,000 curies to treat a daily throughput of up to 30 m3- The
radioisotope is encapsulated in a double-walled, corrosion-
resistant steel pipe 8 meters underground. Currently, there is
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considerable debate as to whether radioactive isotopes will emerge
as the preferred method of water treatment. The main dis-
advantages of radioisotopes, such as cobalt-60, are the hazards
inherent in handling large amounts of radioactive material, short-
age of material for wide-spread use, and the high initial and
replacement costs compared with conventional cooling-water treat-
ment. As an example, the initial cost for the source (10 mega-
curies of cobalt-60) to supply 150 kW of gamma radiation would be
$5 million, and the annual replenishment cost (at 12% per year)
would be about $620,000.27 Up to 1.14 x 103 m3 (300,000 gallons)
of sludge can be treated daily. The replenishment cost adds
approximately $5 per 3.8 m3 (1,000 gallons) to the operation with-
out considering capital, operating, and maintenance costs.
The use of radiation for destruction of bacteria has been exten-
sively studied in other areas of technology; e.g., sterilization
of food products. The sterilizing dose is generally accepted as
2.5 mr (millirads), which will handle the most resistant species,
the spore-forming organisms.28 In spite of optimistic predictions,
a realistic figure for radiation-treatment costs is 2.2<=/mr-kg
(IC/mr-lb).18 Thus, if wastewater requires a dose of 1 mr to
achieve the desired objective, the cost will be $83/3.8 m3 (1,000
gallons) (in 1971 dollars)! Against this, the existing proven
technology can completely renovate municipal wastewater to
drinking-quality water for about $0.60/3.8 m3 (1,000 gallons)
(1971 dollars). In view of its prohibitive cost, a major break-
through is needed before radiation treatment of cooling waters
will become economically feasible.
4.3.3 Electron Beam Radiation
A pilot 50 kW high-energy electron-beam source is now being used
to treat sewage and wastewater at Boston's Metropolitan District
Commission Plant. The accelerator provides ionization equivalent
to 3.5 million curies of cobalt-60 or 16 million curies of cesium-
137. Up to 380 m3 (100,000 gal)/day of sludge will flow in a thin,
wide stream under a beam of electrons that swings back and forth
across the moving stream. The electrons provide a radiation dose
of about 400,000 rads, enough to destroy pathogenic organisms pres-
ent in the sludge. An electron accelerator requires running and
maintenance costs, and it does consume large amounts of electric-
ity continuously. At least two accelerators would be needed to
provide continuous service if one failed.
27Irradiation of Sewage Gains Adherents. Chemical and Engineering
News, (53):30, August 1975.
28Ballantine, D. S. Potential Role of Radiation in Wastewater
Treatment. Isotopes and Radiation Technology, 8 (4):415-420,
Summer, 1971.
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Technically, electron-beam radiation is feasible for preventing
bio-fouling of condensers, but it is expensive and does not pro-
vide post-treatment protection of cooling-water systems against
downstream contamination; e.g., algae growth in cooling tower.
Other treatments, such as chemical treatment (e.g., slow-release
biocide in the cooling tower), must be applied simultaneously for
the successful operation of the entire cooling system.
4.4 MORE EFFICIENT METHODS OF PRESENT CHEMICAL APPLICATION
In Section 3, more efficient methods of present chemical applica-
tion are discussed. The advanced application techniques are being
considered in some of the newer powerplants, but they are not prac-
ticed in older powerplants due to design limitations in retrofit-
ting or the lack of need in the past. Established allowable free-
chlorine concentration limitations of an average 0.2 mg/1 and a
maximum of 0.5 mg/1 in effluents (by EPA) are only for new power-
plants.
4.4.1 Serial Dosing Near the Inlet of the Condenser
As discussed earlier in Section 3, for once-through cooling sys-
tems, substantial reduction in chlorine-residual emissions and
savings in chlorine dosages can be achieved by designed chlorine
application as near the condenser inlet as possible without any
loss in condenser performance. This is possible due to the short
contact time (20 seconds to 30 seconds) of the waterflow through
the condensers and due to the fact that most of the added chlorine
still exists as free chlorine (HOCl), instead of less-effective
chloramines formed later on. Often, sampling and accurate free-
chlorine residual determination may consume much more time than
the actual contact time, thus resulting in using a larger dosage
than necessary in the cooling water of many powerplants.
It is reported1* that some powerplants employing once-through
cooling-water systems treat the multiple condensers one at a time,
and discharge from the unit is diluted by that from the other con-
densers not being chlorinated, resulting in the discharge of negli-
gible residual chlorine to the receiving water. The effect of
dilution and exertion of chlorine demand by the unchlorinated
water (fronf the condensers not being treated at the time) occurs
almost simultaneously.
For the past 25 years, with few exceptions, condenser cooling
water has been chlorinated at the intake structure, instead of at
the condenser inlet. The chlorine solution piping system is as
uncomplicated as possible, often being limited to a simple chlo-
rine feed control. For marine-water cooling systems, because of
the growth of shelled organisms, the chlorination equipment and
the diffuser are located ahead of the bar racks, generally several
hundred feet from the condensers.
61
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Generally, most new condensers are served by at least two cooling-
water flows; six are not uncommon. Therefore, if the points of
chlorine application are redesigned and relocated in the piping
system just ahead of the inlet water boxes, and if the chlorine
control system is designed to treat the unit flows one at a time
in sequence, the chlorine residual in the emerged discharged water
would be diluted by factors of two, three, or six depending on the
system design. However, by doing so, the long cooling-water lines
ahead of the condensers and the intake structure would not be pro-
tected in terms of organic fouling or Bryozoa and shelled orga-
nisms if brackish water or seawater is used without additional low-
level, continuous chlorination ahead of the bar racks.
Mechanically or electrically, the chlorination system would become
more complicated, but with compensations. The size of the chlorin-
ation system in terms of the chlorine feed rate would be reduced
by a factor of two, three, or six. This saving in cost would prob-
ably be offset by that for additional solution piping and controls.
However, the total amount of chlorine used and discharged chlorine
residuals would be reduced to the practical minimum for the partic-
ular plant and units. This improved chemical application system
is particularly beneficial to once-through cooling systems, but
the split-stream chlorination of the condenser flow should also be
practiced with recirculating systems with cooling towers.
4.4.2 Addition of Dechlorination Chemicals
Since the current trend in the United States is toward recirculat-
ing cooling-water systems with minimum water intake or discharge
to the environment, the control of blowdown (which amounts to as
high as 5% of the cooling flow) would become increasingly
important.
Dechlorination of the residual chlorine in the cooling-tower blow-
down with automatic addition of dechlorination chemicals can
remove all or part of the total combined chlorine residual. This
treatment is accomplished by the addition of sulfur dioxide or
other sulfur-bearing compounds, such as sodium sulfite or sodium
metabisulfite; activated carbon is also helpful. A dechlorination
facility is being installed in a nuclear powerplant employing cool-
ing towers currently under construction.1* Whenever residual chlo-
rine is present in the discharge channel, sodium bisulfate will be
added in the last chamber of the dilution structure. The addition
of bisulfite must be controlled automatically using a chlorine ana-
lyzer with the sensitivity of about 0.01 ppm residual chlorine.
When sulfur dioxide or related compounds are used, the first reac-
tion is to instantaneously remove the free chlorine (HOCl). The
next reaction is the removal of monochloramine, followed by
dichloramine, nitrogen trichloride, and, finally, the poly-N-
chloro compounds. The total overall reaction time to remove all
of these compounds is never more than a few minutes. The chemical
62
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reaction involved in dechlorination amounts to the conversion of
all of the positive chlorine atoms to the negative chloride atoms,
such as:
S02 + H20 ->• H2S03 + HOC1 -* H2S04 -I- HC1 (12)
NH2C1 4- H2S03 + H20 -»• NH^HSO/, + HCl (13)
Na2S03 + C12 + H20 + NazSOi, + 2 HCl (14)
C + 2 C12 + 2 H20 -»• C02 + 4 HCl (15)
The reaction of sulfur dioxide with both free- and combined-
chlorine residuals is nearly instantaneous, provided there is ade-
quate mixing and rapid contact between them. The speed of the
sodium sulfite reaction is similar to that of sulfur dioxide—a
matter of seconds for completion.
Although dechlorination will remove available free and combined
chlorine, it will not detoxify chlorinated organics (e.g., chloro-
phenols) with the exception of organic chloramines. This would
not pose any problem, since cooling water usually does not contain
appreciable amounts of phenolics as does wastewater.
From an engineering standpoint, the handling of sulfur dioxide is
similar to that of chlorine. Equipment used to meter SO2 is iden-
tical in all aspects to that for metering chlorine. Therefore,
any sulfonator can be used interchangeably between chlorine and
sulfur dioxide. The notable difference between sulfur dioxide and
chlorine gas is in the vapor pressure. This difference is impor-
tant in the withdrawal and handling of the sulfur-dioxide supply
system. Because of possible liquefaction, sulfur-dioxide cylin-
ders and the sulfonator should be heat traced and insulated. The
control of sulfur dioxide to provide the residual in the effluent
acceptable to aquatic life can be accomplished by means of auto-
matic chlorine residual control instrumentation. Approximately
1 mg/1 (ppm) of sulfur dioxide is required to remove 1 mg/1 (ppm)
chlorine residual.
To minimize the requirement of dechlorination, excess total resid-
ual chlorine discharge can be minimized by monitoring free avail-
able chlorine concentrations in the discharge stream and providing
feedback co'ntrol on dechlorination. This type of control system
is not in general use in powerplants at this time but is common
practice in municipal sewage treatment plants.
4.4.3 Slowdown Timing Control
Slowdown from many recirculating cooling-tower systems is continu-
ous. The curve in Figure 5 shows a typical concentration of total
residual chlorine in cooling-tower blowdown versus time, indicat-
ing the cyclic nature of shock treatment and decaying chlorine
residuals. By monitoring the residual chlorine in the effluent,
it is possible to schedule blowdown only at such times when the
63
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residual chlorine is below the established limit. Typical auto-
matic blowdown-control equipment costs for a 1,000 MW fossil-fuel
plant are estimated to be $7,300 including installation (1973
dollars) .**
4.4.4 Chlorination by Feedback Control of Residuals
To minimize the discharge of excess chlorine residuals, technology
is currently available for feedback control of chlorination sys-
tems. By monitoring free-available chlorine discharge in once-
through cooling systems, the chlorinator can be automatically con-
trolled to within the guidelines and limitations. However, it is
yet to be proved that powerplants operating under these guidelines
are capable of controlling bio-fouling of their condensers. If
this cannot be done with conventional chlorination, some other
alternatives discussed in this report might be needed for the con-
trol of condenser bio-fouling.
4.5 OTHER INFORMATION
A significant number of other references containing valuable infor-
mation relative to bio-fouling control for condensers have been
published. A number of these are listed in the bibliography of
this report.
64
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Proc. ASCE, 99, No. EE6, 761-72(1973), December.
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4. Nichols, C. R. Development Document for Effluent Limitations,
Guidelines, and New Source Performance Standards for the
Steam Electric Power generation Point Source Category. U.S.
Environmental Protection Agency, NTIS PB 240 853, October
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5. Mills, J. F. The Chemistry of Bromine Chloride in Wastewater
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65
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12. Daugard, S. J., and T. R. Sundaram. Review of the Engineer-
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66
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25. Ward, W. J. Chlorine Dioxide, A New Development in Effective
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Summer, 1971.
67
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-77-030
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Alternatives to Chlorination for Control of Condenser
Tube Bio-Fouling
5. REPORT DATE
March 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
H.H.S. Yu, G.A. Richardson, andW.H. Hedley
8. PERFORMING ORGANIZATION REPORT NO.
MRC-DA-638
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Monsanto Research Corporation
1515 Nicholas Road
Dayton, Ohio 45407
10. PROGRAM ELEMENT NO.
E HE 624
11. CONTRACT/GRANT NO.
68-02-1320
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 4-10/76
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES j^RL-RTP project officer for this report is Fred Roberts, EPA/
ERL, Corvallis, OR 97330, 51)3/757-4715.
16. ABSTRACT.
The report gives results of a study of methods used to reduce free-chlorine
residuals in power plant effluents. Most U.S. power plants use chlorine (28,600 tons
in 1972) to control biological fouling in their cooling systems, particularly in their
condenser tubes. Using chlorine raises many questions regarding the toxicity of
chlorinated compounds which may enter public drinking-water systems or harm
aquatic organisms in the receiving water. The report considers viable alternatives
to current chlorination practices used to decrease passage of ecologically harmful
effluents to receiving waters. Alternative methods include: use of other chemicals
(BrCl, C1O2, O3, controiled-release pesticides); more efficient methods of chemical
application (serial dosing near the condenser inlet, adding dechlorination chemicals,
blowdown timing control, chlorination by residuals feedback control); on-line mech-
anical cleaning (sponge ball system, brush system, hot water backflush system); and
physical/chemical treatment. Information on advantages, disadvantages, costs, and
applicability for retrofit or new installations of these methods is presented. Pro-
mising approaches to reducing free-chlorine residuals in power plant effluents are
available.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Water Pollution Chlorination
Electric Power Plants
Cooling Systems Aquatic Biology
Condenser Tubes Toxicity
Fouling Prevention Potable Water
Fouling Pesticides
Water Pollution Control
Stationary Sources
Biological Fouling
13B 07C,07B
10B
13A 08A,06C
09A 06T
13H,13J 08H
06F
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
80
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
75
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