EPA-660/2-74-089
DECEMBER 1974
Environmental Protection Technoios
Water Recycle/Reuse Possibilities:
Power Plant Boiler and Cooling Systems
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National Environmental Rastarell CMter
Offict of Research and
U.S. ERvirommntal Protectwn
ConoHis, Qrafoa 97330
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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
five series. These five 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 five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY STUDIES series. This series describes research
performed to develop and demonstrate instrumentation, equipment
and methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the
new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This report has been reviewed by the National Environmental
Research Center—Corvallis, and approved for publication. Mention
of trade names or commercial products does not constitute endorsement
or recommendation for use.
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EPA-660/2-74-089
December 1974
WATER RECYCLE/REUSE POSSIBILITIES:
POWER PLANT BOILER AND COOLING SYSTEMS
Guy R. Nelson
Thermal Pollution Branch
Pacific Northwest Environmental Research Laboratory
National Environmental Research Center
Corvallis, Oregon
Program Element 1BB392
ROAP 21AZU
Task 23
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
For sale by the Superintendent of Documents, U.S. Government Printing Offin
Washington, D.C. 20402 - Stock No. 5501-00971
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ABSTRACT
This report contains the methodology to evaluate, in economic terms,
potential power plant boiler and cooling system water recycle/reuse
programs. Drum type boiler systems and closed cycle cooling systems
are used as the basis for the programs' water requirements. The
evaluations take into account the variable plant characteristics
such as makeup water quality, fuel type, thermal efficiency, capacity
factor and fixed charge rate.
The evaluation methodology is applicable to existing and proposed
power plants, on an individual plant basis—and can be used to
determine the over-all economics of potential recycle/reuse programs.
The report is the first of a series that addresses the water recycle/
reuse potentials of typical power plant processes. This report is
submitted in fulfillment of Task 23 of ROAP 21AZU of the Environmental
Protection Agency. Work was completed as of November, 1974.
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CONTENTS
Page
Abstract ii
List of Figures iv
List of Tables v
Sections
I CONCLUSIONS 1
II RECOMMENDATIONS 3
III INTRODUCTION 4
IV APPROACH 8
V THE BOILER SYSTEM 9
VI THE CLOSED CYCLE COOLING SYSTEM 14
VII TREATMENT TECHNIQUES TO ACHIEVE WATER RECYCLE/REUSE 26
VIII ECONOMIC EVALUATION METHODOLOGY:
COOLING SYSTEM RECYCLE POSSIBILITIES 39
IX REFERENCES 44
X APPENDICES 46
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FIGURES
No. Page
1 Boiler System 10
2 Boiler System Makeup and Discharge Flow Rates 13
3 Closed Cycle Cooling System 16
4 Power Plant Evaporation Requirements 21
5 Power Plant Slowdown Water Quantity Requirements 23
6 Power Plant Makeup Water Quantity Requirements 24
7 Power Plant Recirculating Water Quantity Requirements 25
8 Polymer Addition Costs 33
9 pH Control Costs 34
10 Conventional Side Stream Filtration Costs 35
11 "Rapid Sand" Side Stream Filtration Costs 36
12 Lime Softening Costs 37
13 Brine Concentration Costs 38
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TABLES
No. Page
1 Power Plant Water Requirements 6
2 Boiler System Water Quality 11
3 Recirculating Water Quality Limitations 17
4 Acceptable Cooling System Makeup Water Quality
Characteristics 18
5 Treatment Program Costs 30
6 Hypothetical Power Plant Characteristics 40
7 Boiler System Characteristics 48
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SECTION I
CONCLUSIONS
One potential contribution to meeting the overall goal of environmental
protection in electric power production is to adopt water recycle and
reuse programs within and between power plant systems and processes that
use and/or discharge water. Two such systems that are common to both
nuclear and fossil-fueled power plants are the boiler and cooling systems,
However, before recycle/reuse programs between these two systems can be
adopted, at least two questions must be answered:
1. How can the two processes be categorized as to water quality
and quantity requirements? Once this question is answered, recycle/
reuse programs can be proposed that reduce makeup water requirements
and total plant discharges.
2. Given the broad spectrum of power plant operating conditions,
how can the recycle/reuse programs be monetarily evaluated?
BOILER SYSTEM RECYCLE/REUSE
The boiler blowdown from the flash tank can be recycled to the
pretreatment system and then substituted as a portion of the makeup
water to the boiler. The resultant economics on an individual plant
basis largely depend upon boiler efficiency, percent condensate
return and percent boiler blowdown.
The boiler blowdown can be reused without treatment as a portion of
the makeup to the closed cycle cooling system. While this reuse
scheme has little impact on the water intake requirements, it does
provide a use for a blowdown stream that normally would be discarded,
or require treatment prior to discharge.
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COOLING SYSTEM RECYCLE/REUSE
There are no currently available techniques that allow cooling
system blowdown to be reused as makeup to the boiler system,
because:
1. Direct reuse (without treatment) is not possible because
of the high water quality requirements of the boiler system.
2. Reuse after treatment by such processes as reverse osmosis,
electrodialysis, brine concentration, and demineralization is yet
to be demonstrated on power plant cooling system blowdown.
On the other hand there are recy_cle_ possibilities for the cooling
system that show economic potential. The overall economics for any
recycle scheme depends upon the following power plant characteristics:
1. Fuel type (fossil vs. nuclear)
2. Overall plant thermal efficiency
3. Cooling system cycles of concentration - both before
and after the installation of the recycle program.
4. Plant capacity factor
5. Fixed charge rate for capital expenditures.
6. Percent waste heat dissipated by evaporation in the
cooling system.
7. Capital and 0/M costs of the programs.
8. Makeup and discharge water costs
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SECTION II
RECOMMENDATIONS
This report documents thermal power plant boiler and cooling system
water quality and quantity requirements and the water recycle/reuse
potential of the two systems. Similar efforts are required that
consider other typical plant systems and processes using and/or
discharging water, such as:
1. Ash handling systems
2. Air pollution control devices
3. Coal pile and site drainage systems
4. Water pretreatment processes
5. Condensate treatment systems
With this information in hand, the final task is to refine and
optimize all recycle/reuse applications on a total plant basis.
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SECTION III
INTRODUCTION
To produce electricity, the thermal power generation industry has
significant water quality and quantity requirements. These water
requirements depend upon characteristic plant processes, as shown
in Table 1. As newer, larger power plants come on line, the process
water quantity requirements are increasing. At the same time,
however, the water sources are not increasing. This situation --
an increasing demand for a resource whose supply remains constant —
raises potential economic and environmental problems. One possible
solution to the problems is the practice of water recycle/reuse
between the various power plant processes. The net result of this
practice is a reduction in total, plant-wide water quantity requirements,
Webster defines use (n.) as "The act of employing anything..."
Water reuse then is the use of water by one system that already has
been employed in and discharged from another system. An example of
water reuse is boiler blowdown water being used as makeup water to
a cooling tower.
Reusing Webster , the word, cycle, (not to be confused with cycles of
concentration) is defined as, "A completed course of operations..."
Water recycle is a reuse of water (by a system) that already has
run a complete course through the same system. An example of water
recycle is cooling tower blowdown water being treated and used as
makeup water to the same cooling tower.
The most efficient recycle/reuse programs interpret each water
requiring process as an integral part of the total plant water use
system. This total system interpretation considers factors such as:
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I. water quantity requirements (including process makeup,
blowdown and recirculating water).
2. water quality requirements (including process makeup,
blowdown and recirculating water).
3. plant operating characteristics that affect water requirements.
4. plant site conditions that affect water requirements and/or
supply.
From this interpretation, a well defined "pecking order" emerges that
establishes: firstly, where in the total water use system the recycle/
reuse should be applied; secondly, which process gets a given class of
water (e.g., "first use," recycled, or reused); and finally, which water
streams are to be discharged without further use?
As Table 1 indicates, the number of processes in the "pecking order"
is dependent on the fuel type. Furthermore, in fossil-fueled plants,
fuel quality affects the number of processes. For example, depending
upon ash content, an oil fired plant may or may not have an ash
handling system; or depending on sulfur content, a coal-fired plant
may or may not have an SCL removal device. However, at the very least,
all power plants — nuclear or fossil-fueled -- have a boiler and
cooling system.
Two types of boiler systems and three types of cooling systems are
used by the industry:
i
I. Boiler systems
A. Once through
B. Drum type
II. Cooling systems
A. Once through
B. Closed cycle
C. Combination
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Table 1. POWER PLANT WATER REQUIREMENTS
Fuel
A.
B.
Type
Nuclear*
Fossil
1. Gas
2. Coal
3. Oil
Pretreatment
X
X
X
X
Boiler
X
X
X
X
Cooling
X
X
X
X
Condensate
Treatment
X
X
X
X
Ash
Handling
X
X
Air Pollution
Control
(including S02
X
X
Auxi 1 i ar
removal )
X
X
X
X
*Water requirements for nuclear plant primary loop and emergency coolant supply are not addressed in
this report.
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Some of the more modern power plants and many of those proposed are
using (or will use) drum type boiler systems and closed cycle cooling
systems. The choice of the drum type boiler system is usually one of
operational preference and reliability. The closed cycle cooling
system is chosen generally because of water supply and/or environmental
regulations. This report addresses the water qualities and quantities
that are associated with these two specific systems and their recycle/
reuse potentials.
Digressing for a moment, the reader should recognize that, using the
total system interpretation, any recycle/reuse program, solely between
the boiler and cooling systems, may be altered when fitted into the
"pecking order." However, the programs cited herein are useful in
most cases because (a) the boiler system's characteristics together
with the turbine and condenser design have a significant effect
on the overall thermal efficiency (and, therefore, the amount of
cooling water required); and (b) over 95 percent of the total plant
2
water usage is used for cooling.
Also, this report is only the first of a series which outlines the
water recycle/reuse potentials of typical power plant processes.
Throughout the series, an attempt is made to keep a continuity to
the total system interpretation.
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SECTION IV
APPROACH
This report first discusses each system's water requirements in
two separate sections (titled, appropriately, THE BOILER SYSTEM
and THE CLOSED CYCLE COOLING SYSTEM). Both sections have two
sub-sections.
The first sub-section, WATER QUALITY, details the quality characteristics
of the system's water flows...such as makeup, blowdown, and recirculating
water.
The second sub-section, WATER QUANTITY, describes the amount of water
required for the system's water flows. Also, it identifies the power
plant's operational characteristics that affect the water quantity
requirements.
The report devotes another two sections in describing how recycle/reuse
possibilities can be evaluated.
The first section, TREATMENT TECHNIQUES TO ACHIEVE WATER RECYCLE/REUSE
discusses--
a. The "pecking order" for recycle/reuse
b. The treatment requirements to be applied to water flows
prior to recycle/reuse, and
c. Recycle/reuse economics.
In the final section, ECONOMIC EVALUATION METHODOLOGY: COOLING
SYSTEM WATER RECYCLE POSSIBILITIES, three hypothetical power plant
situations are described. In each situation a cooling system
water recycle possibility is evaluated.
8
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SECTION V
THE BOILER SYSTEM
Figure 1 is a schematic water flow diagram of a typical power plant
boiler system.
WATER QUALITY
Boiler design pressure has the most significant effect on makeup,
boiler feedwater, condensate/steam, blowdown, and flash tank effluent
water quality. Typical power plant boilers operate at or above 100
p
Kg/cm (1500 psig). Table 2 contains maximum values for water quality
parameters in boiler systems with operating pressures above 100 Kg/cm
WATER QUANTITY
The boiler feedwater stream results from the combination of the
condensate return and makeup water flows. The condensate return
flow rate is equal to the steam production rate minus any condensate/
steam leakage. This leakage rate is typically 0 - 2% of steam
production. The steam production rate itself is related directly
to power production; its value is about 3180 Kg steam/MWH (7,000 Ib.
steam/MWH).
The makeup water flow rate (after pretreatment) to the boiler is
equal to the total water loss from the system due to blowdown and
condensate/steam leaks. It is expressed by the equation
M = R[KB + KR]
where: M = makeup water flow rate in Kg/hr
R = steam production rate in Kg/hr
KD = blowdown rate, expressed as a fraction
D
of steam production
KD = condensate/steam leakage rate, expressed
K
as a fraction of steam production
9
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Figure 1
Boiler System
CONDENSATE
RETURN
AFTER
TREATMENT
RAW
WATER
MAKEUP
TREATMENT
MAKEUP
CONDENSATE/STEAM
LEAKAGE
AA/V
BOILER
'FEEDWATER
BOILER
STEAM
TO
TURBINE
AND
CONDENSER
/N
FLASHED
STEAM
SLOWDOWN
FLASH
TANK
LIQUID
EFFLUENT
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Table 2. BOILER SYSTEM WATER QUALITY^
Water Quality
Parameter
Streams
(Typical values in mg/1)
-
Aluminum
Alkalinity
Arrrnonia
Copper
Hardness .
Iron
TDS*
Silica
Feedwater Steam and , ,-
(Makeup and Condensate Slowdown >D
Condensate Return) Return
0.01 Essentially
absent
0.7 pure
0.01
absent water
0.01
0.5 ,- 50
0.02(Wakenhuth°) 3
Flash
Tank 4 5
Effluent*'0
100
6
*Total Dissolved Solids
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Typical blowdown rates are 0.1 - 2%, expressed as a percentage of
steam production. Equation (1) defines the blowdown rate.
\:
B = RKB (1)
where: B = blowdown flow rate in Kg/hr
R = steam production rate in Kg/hr
KB = blowdown rate, expressed as a
fraction of steam production
After the blowdown leaves the boiler, it passes through a flash tank
where part of it is flashed off. The liquid effluent rate from the
flask tank is: H - H
S = RKB[1 - -^ f- ] (2)
where: S = liquid effluent rate, Kg/hr
Hn = heat of liquid water at boiler
Kcal
pressure, ——
Hp = heat of liquid water at flash
Kcal
tank pressure, •
Vp = latent heat of vaporization at
flash pressure,
Figure 2 shows examples of the makeup and effluent rates for the
boiler system as function of power plant size. The figure is
based on the following characteristics:
a. R = 3180 kg Steam/MWH
b. KD = 0.005
2
c. Flash tank pressure =2.0 kg/cm
"»•",• 2
d. Boiler operating pressure = 170 kg/cm
12
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Figure 2
Boiler System
Makeup and Discharge Flow Rates
1500-
Plant
Size
MWE
1000-
500-
R = 3180 kg Steam/MWH
KB~= 0.005
Flash Tank Pressure
=2.0 kg/cm2
Boiler Pressure
= 170 kg/cnr
0
I 1
I I
5.0 IO.O
Flow Rate m^/hr
Liquid Effluent From Flash Tank
•Makeup Water After Pretreafmerit
15.0
13
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SECTION VI
THE CLOSED CYCLE COOLING SYSTEM
An increasing number of new power plants are using or are planning
to use closed cycle cooling systems. The types of closed cycle
systems include:
1. Wet Cooling Towers
2. Spray Cooling Systems
3. Wet/Dry Cooling Towers
4. Dry Cooling Towers
5. Cooling Ponds
Of these, only wet cooling towers, contained spray systems, and the
wet portion of wet/dry towers are amenable to recycle/reuse evaluations
in the context of this report. For this reason, the term cooling
system, as used in the remainder of this report, refers to the above
three types of cooling systems.
Dry cooling towers use only sensible heat transfer to dissipate the
power plant waste heat; thus they have negligible water consumption
rates—hence their exclusion.
Cooling ponds are unique in that:
1. Water requirements are affected by all components of the
energy budget including long wave back radiation.
2. The pond potentially gains and loses water by precipitation,
run-off, and seepage.
3. The pond's large water volume may act as a treatment system
that alters water quality characteristics such as suspended
solids and BOD.
4. Treatment of the recirculating water, except possibly Cl?
ahead of the condenser, is not practical.
14
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WATER QUALITY
Figure 3 is a schematic water flow diagram of a typical cooling system.
Drift, Slowdown, and Recirculating Water
In the recirculating water, constituents (originally in the makeup
water) are concentrated due to the evaporation of the cooling water.
As more evaporation continues, the solubility limits of the consti-
tuents are approached. In addition, temperature changes that occur
in the system effect the solubility of these constituents. If the
solubility limit of one or more of the constituents is exceeded,
cooling system fouling may result. Table 3 provides some recirculating
water quality limitations that are required to minimize this fouling.
The blowdown serves to keep the recirculating water within the limits.
It should be noted that water quality characteristics of the blowdown
and drift are the same as for recirculating water, which is the
source of these system losses.
Makeup Water
Typically, the plant supplies water to the system from the most readily
available water source with little or no pretreatment. Therefore, no
general rule-of-thumb exists for makeup water quality. However, Table
4 contains generally acceptable makeup water quality characteristics
that are available from Juvan.
The quality of the makeup water determines the maximum cycles of
concentration (cycles) at which the system can operate without water
treatment; where cycles is defined as the number of times that
conservative constituents in the makeup water are concentrated
15
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Figure 3
Closed Cycle Cooling System
Q
Condenser
D
4.
Cooling
Device
•M
Where Q = Recirculating Rafe(m3/hr.)
B = Slowdown Rate (m3/hr)
M = Makeup Rate (m3/hr)
E= Evaporation Rato(m3/hr)
D = Drift Rate (m3/hr)
16
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Table 3. RECIRCULATING WATER QUALITY LIMITATIONS1
Characteristic
Limitation
Comment
pH and Hardness
Langelier Saturation
Index =1.0
Langelier Saturation
Index = pH - pHs
where
pH and Hardness
with addition of
proprietary chemicals
for deposit control.
Langelier Saturation
Index = 2.5
pH = measured pH
pHs = pH at saturation
with CaCOQ
8
See Sisson for
nomograph solution.
Sulfate and Calcium
(C$0 ) x (CCa) = 500,000
c
= concentration of
4 S04 in mg/1
= concentration of
Ca in mg/1 as CaCO,
Silica
Csio
C_.n = concentration of
01 VQ
Si02 in mg/1
Magnesium and Silica
V * • 35'000
CM = concentration of
Mg
Mg in mg/1 as CaCO
Suspended Solids4
= 400 mg/1
C = concentration of
ss
ss in mg/1
17
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Table 4. ACCEPTABLE COOLING SYSTEM MAKEUP
WATER QUALITY CHARACTERISTICS
Constituent Concentration (mg/1)
Calcium, as CaC03 40 - 200
Magnesium, as CaC03 10 - 50
M Alkalinity, as CaC03 5-50
Sulfate, as S04 20-140
Chloride, as Cl 10 - 150
Silica, as Si02 2-50
Iron, as Fe 0.2 - 10.0
Manganese, as Mn 0.1-1.0
Oil <1 - 5.0
Suspended Solids 10 - 200
pH 5.5 - 7.5 (pH units)
Specific Conductance, ymhos (18°C) 100 - 500
18
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in the recirculating water. For example, it is possible to have
a makeup water supply with a silica concentration of 50 mg/1 as SiCL.
By definition then, the recirculating water Si02 concentration
is 50 x (cycles). Referring to Table 3, the maximum cycles of
concentration based on silica are: 150/50 = 3.0 cycles. If this
same water has a magnesium concentration of 20 mg/1 as CaCXL, the
magnesium concentration in the recirculating water is 20 x (cycles).
The maximum achievable cycles of concentration based on magnesium
silicate is:
[50 x (cycles)] x [20 x (cycles)] = 35,000
(cycles)2 = 35
cycles = approximately 6.0
After the calculation of the maximum cycles for the other water quality
parameters, if the lowest maximum value for the cycles is three; then
the cycles of the water supply are said to be silica limited.
It logically follows that — with the broad spectrum of water quality
available for cooling water use across the country — a given water
supply can be limited by any of the water quality parameters in Table 3.
WATER QUANTITY
The recirculating water quantity requirement for a thermal power plant
depends upon the plant size, its efficiency, and the temperature rise
across the condenser . The governing equation is:
0 -
Q -
AT)(CP)(P)
3
where Q = Recirculating water flow rate (m /hr)
WH = Waste heat to cooling water (KJ/MWH)
P = Plant size MW
AT = Temperature rise across the condenser (C°)
Cp = Specific heat of water (4.174 KJ/KgC°)
p = Density of water (1000 Kg/m3)
19
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The makeup, evaporation, and blowdown rates are related to the cycles
of concentration by equations (4) and (5) if drift is neglected. The
symbols for the equations are listed in Figure 3.
B = E/(c-l) (4)
M = Ec/(c-l) (5)
where c = cycles of concentration
Two approximate methods for estimating the evaporation rate are
available. One method applies to equation (6).
0.
75(P)(WH)
°
2.319 x 10° KJ/m
Equation (6) is based on 75 percent waste heat dissipation by latent
heat transfer and the approximate latent heat of vaporization value
for water— 2.319 x 106 KJ/m3 (1000 Btu/lb). Equation (6) can be
rewritten:
E1 = E/P = (WH) (0.323 x 10"6) m3/KJ (7)
3
where E1 , in m /hr/MW, is the evaporation requirement per megawatt
hour of plant operating capacity. The value of E1 is directly proportional
to the amount of waste heat rejected to cooling water; therefore, its
value depends on fuel type (fossil vs. nuclear) and over-all plant
thermal efficiency, as shown in Figure 4.
With the substitution of Equations (3), (4) and (5) into equation (7),
the relationships between blowdown/makeup/recirculating water and
the evaporation requirements are expressed:
B = E'P/(c-l) (8)
M = E'Pc/(c-l) (9)
Q = E'P(742)/AT (10)
20
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Figure 4
Power Plant Evaporation Requirements
40-
36-j
Thermal
Efficiency
30-
26-
22-
Nuclear
Fossil Fuel
Basis:
1, 75% of the waste heat is dissipated via
latent heat transfer
2. Latent heat of vaporization = 2,319 x 106 KJ/m3
1.0
1.5
2.0
25
Evaporation Requirement (E<)u
3.0
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Figures 5, 6, and 7 are graphical representations of the above three
relationships. The figures are based on fossil-fueled power plants
operating at 38 percent efficiency. The plant size, P, in the figures
represents the plant output. For example, a 500 megawatt plant
producing at 100 percent capacity and having a cooling system operating
o
at three cycles, has a makeup requirement of 1080 m /hr. A 500
megawatt plant producing at 80 percent capacity has a makeup requirement
o
of 870 m /hr (corresponding to a makeup requirement of a 400 megawatt
plant operating at 100 percent capacity).
The blowdown requirements of Figure 5 also include the drift losses from
the system. State-of-the-art design can control drift losses to a
few thousandths of a percent. Except for the case of very high cycles
of concentration (say above 20 cycles) this drift loss can be neglected
in determining the blowdown rate.
With the development and explanation of equations 8-10, the purpose of
this subsection is accomplished. The reader should be comfortable with
these equations...because they are used in the remainder of the report
to evaluate cooling system recycle/reuse possibilities.
22
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Figure 5
Power Plant Slowdown Water Quantity Requirements
I500H
1000-
ro
CO
Plant
Size
MWcr
500-
C=l.5
Basis: Fossil-fueled Power Plants
with Er = 1.439 m3/MWH
I I
500
i i
1000 1500
Slowdown Flow Rate m3/hr.
2000
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Figure 6
Power Plant Makeup Water Quantity Requirements
1500-
1000-
Plant
Size
MWrr
500-
C=IO C=6.0 /C=4.0
C=3.0
01.5
Basis? Fossil-fueled Power Plants
with E' = 1.439 m3/MWH
i i i
1000 2000
Cooling System Makeup Rate m3 /hr
i i i i i i
3000 4000
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Figure 7
Power Plant Recirculating Water
Quantity Requirements
1500-
1000-
Piant
Size
500-
AT= IO°C
Basis: Fossil-fueled
Power Plants with
E' = 1.439 m3/MWH
i I
50,000 100,000
Water Quantity rrvVhr.
25
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SECTION VII
TREATMENT TECHNIQUES TO ACHIEVE
WATER RECYCLE/REUSE
BOILER SYSTEM
Recycle Possibilities
From Table 2, the water quality and quantity characteristics of
the flash tank effluent indicates that it possibly could be used
as makeup water to the boiler. It could be added to the raw water
prior to pretreatment*; also, the flash tank steam could supply
low grade steam for plant processes. Fuel and water treatment
9 10
cost savings are available with this recycle program ' .Also,
benefits can be realized from the reduction in makeup and discharge
water quantity and from potential savings in disposal costs. For
example, a thousand megawatt fossil-fueled power plant operating
at 80 percent capacity and having the following characteristics,
saves nearly $125,000 per year:
1. Overall boiler efficiency - 0.85
2. Fuel cost - $0.96/106 KJ (1.00 per 106 BTU)
2
3. Water treatment costs - $0.13/m ($0.50 per thousand gallons)
4. Slowdown rate - 0.5 percent
2
5. Flash tank operating at 2 Kg/cm (15 PSIG)
6. 15 percent heat and water loss in the recycle program
The calculations for this savings are in Appendix A. The
dollar figure above does not take into account:
* The flash tank effluent is of higher quality than the raw water.
Generally, raw water quality is the same as cooling system makeup
water quality (see Table 4).
26
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a. any cost for valves and piping.
b. any flash tank effluent pretreatraent costs.
c. any savings in pretreatment systems operation.
d. any savings in waste disposal handling.
Reuse Poss i bi 1 i ti es
The boiler flash tank water quality is better than the cooling system
recirculating water quality (Table 2 vs Table 3); therefore, it can
be used as a portion of the makeup water supply to the cooling tower.
Although this scheme has little overall impact on the power plant's
water supply balance (see example below), it does provide reuse of a
water flow that normally would be discarded.
Example - A 500 MW fossil-fueled power plant, operating within the
boundary conditions for Figures 2 and 6, has a flash tank effluent
rate of 3.7 m /hr. The plant's cooling system makeup rate is 2180
m3/hr @ 2 cycles; 970 m3/hr @ 4 cycles; and 900 m3/hr @ 10 cycles.
COOLING SYSTEM
Reuse Possibilities
In comparing the water quality requirements between the boiler system
and the cooling system, there is no potential for directly reusing
the closed cycle cooling system blowdown as makeup water to the
boiler system.
Pretreatment of the cooling system blowdown (prior to reuse) with such
processes as brine concentration, reverse osmosis, and demineralization
p IT TO
are proposed. * 9 These processes can produce an effluent that is
27
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near boiler water quality. However, the practical potential of the
processes is yet to be demonstrated on large power plant cooling systems
Recycle Possibilities
All closed cycle cooling systems recirculate (and therefore recycle)
water. However, this report's definition of cooling system water
recycle goes beyond the operation of a cooling system. Cooling system
water recycle involves using water treatment methods to increase
the number of times that water recirculates in the system. The result
is a net reduction in the makeup and discharge water quantities.
There are three methods by which the number of recirculations can be
increased:
1. Makeup water treatment programs (makeup programs) -
where all or a portion of the makeup is treated prior to
entering the system. The treatment results in a net
reduction in the makeup and discharge water quantities.
2. Recirculating water treatment programs (recirculating
programs) - where all or a portion of the recirculating
water is treated and recycled back to the cooling system.
The treatment results in a net reduction in the makeup
and discharge water quantities.
3. Slowdown water treatment programs (blowdown programs) -
where all or a portion of the blowdown is treated and
recycled back to the cooling system. Again, the net
result is a reduction in the makeup and discharge water
quantities.
Typically, makeup or blowdown programs involve treatment of all the
makeup or blowdown water flow. On the other hand, recirculating
programs usually involve treating a portion of the recirculating
water flow.
28
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Table 5 contains the capital and operating/maintenance (0/M) costs for some
potential treatment programs. The references contain further information
on the efficiencies and physical descriptions of the programs. In some
specific cases, the cost data can be affected by one or more economic
anomalies, such as extremely high land values, high interest rates (or
other factors affecting the fixed charge rate) and above average installation
charges. Also some recycle programs have additional water treatment costs
or credits associated with the recycled water. To provide guidance for these
anomalies, the costs are based on "normal" conditions of:
1. land values - no greater than 1600 I/hectare (4,000 $/acre).
2. fixed charge rates - 0.10/yr to 0.20/yr.
3. installed cost of capital equipment - no greater than 2.5 times the
basic equipment costs.
4. no water treatment costs/credits given to any recycled water flow.
The following subsection describes the technique that translates the cost
data in Table 5 into their most popular and workable form - a mills per
kilowatt hour (mills/KwH) basis. Once the costs are in this form, they
can be more readily compared with one another and with overall plant costs.
COST CONVERSION TECHNIQUE
Equations 8 through 10 show that blowdown, makeup, and recirculating water
quantities are directly related to the power plant's load variation. That
is, as power production increases or decreases... yea, verily, so do the
water requirements increase or decrease proportionally. The water requirements
are expressed as flow rates (water volume/unit time). For cost analyses
water requirements can be expressed more conveniently in units of water
volume/unit of electricity produced. By the division of the plant size (P)
into both sides of equations 8 10, such expressions are achieved as
follows:
29
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Table 5. TREATMENT PROGRAM COSTS
Treatment Program
Capital Costs
$/m3/hr ($/gpm)
0/M Costs
$/103m3 ($/106 gal)
Reference
GO
o
1. Make-up
Polymer Addition
c
pH Control
2. Recirculating
Sidestream filtration/clarification
Conventional
"Rapid Sand"
3. Slowdown
Lime Softening
Brine concentration
N/A
N/A
352 (80)
110 (25)
330 (75)
38000 (8636)
4-4 -31 (16'7 - 117) from 13
cycles cycles
6.6 (2.5)
8 (30)
8 (30)
15 (57)
230 (871)
13
14
15
13
13
-------
B/P = E'/(c-l) (8a)
M/P = E'c/(c-l) (9a)
Q/P = E'(742)/AT (lOa)
The ratios (B/P, M/P, Q/P) have the units of m3/MWH. For individual plants
the values of these ratios remain constant, even though load variations
occur. With these ratios, the costs in Table 5 can be converted
to a mills/KWH basis by applying the following steps, which are based
on an annual breakdown of cost and performance:
o
1. Convert the capital costs into $/m by: multiplying the
o
capital costs (with the units, $/m/hr) by the fixed charge
rate (with the units (yr)~ and dividing by the capacity factor
(with no units) and the number of hours in a year (8760 hr/yr).
2. Add the result of step 1 to the 0/M costs. The results of this
q
addition are defined as SUM, with the units $/m .
3. Use equations 11, 12 or 13 to determine, respectively, the
blowdown, makeup, or recirculating program's costs in
$/MWH or mills/KWH.
Blowdown Costs = (SUM) x B/P
and from Equation (8a)
Blowdown Costs = (SUM) x E'/(c-l) (11)
Makeup Costs = (SUM) x M/P
and from Equation (9a)
Makeup Costs = (SUM) x E'c/(c-l) (12)
Recirculating Costs = (SUM) x QX/P (102)
and from Equation (lOa)
Recirculating Costs = (SUM) x E'(QX) (7.42)/AT (13)
where Q% is the percent of the recirculating water
being treated.
31
-------
Figures 8 thru 13 illustrate the recycle program costs on a mills/KWH
basis for fossil fueled plants with a 0.15/yr fixed charge rate and
an 0.80 capacity factor.
The costs relationships represented by Equations (11), (12), and (13)
together with the water quality/quantity relationships already developed,
are useful tools for evaluating recycle program economics in both existing
and proposed cooling systems. The next section is devoted to describing,
via the example format, a general economic evaluation methodology that
uses these relationships.
32
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Cycles
of
Concen-
tration
CO
CO
5.0H
Figure 8
Polymer Addition Costs
Basis: Fossil-fueled Power Plants
E' = 1,439 m3/MWH
Capacity Factor =0.8
Fixed Charge Rate = 0.15/yr
1.0
2.0
5.0
3.0 4.0 5.0 6.0
Total Costs (I0~3 Mills/KWH)
7.0
8.0
9.0
based on polymer costs of ($ 0.0308/m3)
-------
Figure 9
pH Control Costs
CO
20-
15-
Cycles
of
Concen- _
tration ,
5.0-
1.0-
I I I I I I
0.01
Basis: Fossil-fueled Power Plants
E1 = 1.439 m3/MWH
Capacity Factor =0.8
Fixed Charge Rate = 0.15/yr
I I I I I I
0.02
i i i r
0.03
Total CostMills/KWH
-------
15-
AT
CO
in
10-
5-
Figure 10
Conventional Side Stream Filtration Costs
Basis:
1% of
Total recirculatirg
water filtered/clarified
Fossil-fueled Power Plants
E1 = 1.439 m3/MWH
Capacity Factor =0.8
Fixed Charge Rate = 0.15/yr
3%
4%
0.05
Total Cost Mills/KWH
0.10
-------
Figure 11
"Rapid Sand" Side Stream Filtration Costs
\S-\
Basis:
AT
CO
5H
Fossil-fueled Power Plants
E' = 1.439 m3/MWH
Capacity Factor =0.8
Fixed Charge Rate = 0,15/yr
0.05
Total Cost Mills/KWH
0.10
-------
10-
Cycles
of
Concen-
tration
5-
Figure 12
Lime Softening Costs
Basis: Fossil-fueled Power Plants
E1 = 1.439 m3/MWH
Capacity Factor =0.8
Fixed Charge Rate = 0.15/yr
0
0.05
Total Cost Mills/KWH
37
-------
Cycles
of 10-
Concen-
tration
CO
00
5-
Figure 13
Brine Concentration Costs
Basis: Fossil-fueled Power Plants
E1 = 1.439 m3/MWH
Capacity Factor =0,8
Fixed Charge Rate = 0.15/yr
T I I it I I I I I l l I I I I l I l i I I I I I I I I I I I I II \
0.5 1.0 1.5 2.0 2.5 3.0 3.5
Total Cost Mills/KWH
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SECTION VIII
ECONOMIC EVALUATION METHODOLOGY:
COOLING SYSTEM RECYCLE POSSIBILITIES
In order to illustrate the method of economically evaluating cooling
system recycle possibilities, three hypothetical power plant situations
are presented. Table 6 contains the pertinent power plant characteristics
for these situations. The reader should keep in mind three premises
that apply to the situation:
1. It is assumed that the biological effects of the total plant
discharges are not compromised by the recycle schemes,
2. It is assumed that the discharges from the recycle schemes
can be treated by the waste handling systems already available
to the plant, and,
1 o
3. Boies et al, state that most cooling systems use an acid or
base for recirculating water pH adjustment; therefore, it is
assumed that the three plants add these chemicals as required
to control pH in the cooling system.
There are conditions where one or more of the premises do not apply. Under
such conditions, the cost of additional treatment systems or lack of
same must be considered in the overall economics.
POWER PLANT #1 - SIDESTREAM FILTRATION AS A RECYCLE POSSIBILITY
This five hundred megawatt plant has a cooling system operating at 1.5
cycles. The system is suspended solids limited (see Table 3). A
consultant advises that, if 1 percent of the recirculating water were
treated by conventional sidestream filtration/clarification, the system
could operate at 3 cycles and be silica limited. What is the
cost of this proposed program? What is the net reduction in water quantity
requirements?
39
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Table 6. HYPOTHETICAL POWER PLANT CHARACTERISTICS
Characteristic
A. Operation
Fuel type
Overall efficiency (%)
Size (MWE)
Capacity factor
Fixed charge rate (yr)~
B. Cooling System
T (C°)
Cycles
Table 4 limit
3
Recirculating rate (m /hr)
Makeup Costs ($/m3)
o
Discharge costs ($/m )
C. Proposed Recycle Program
df
1
Fossil
38
500
0.8
0.15
10.6
1.5
s.s.
50,000
N/A
N/A
Side Stream
Filtration
Power Plant Number
2
Fossil
35
750
0.6
0.11
N/A
2.0
pH and
Hardness
N/A
N/A
N/A
Warm Lime
Softening
3
Nuclear
30
1000
0.8
0.13
N/A
2.5
Calcium and
Sulfate
N/A
0.020
0.379
Polymer
Addition
40
-------
The values of the evaporation requirement (E1), the plant capacity
factor, and the fixed charge rate allow direct use of Figures 6, 9,
and 10. From Figure 10 the sidestream filtration cost is 0.0155 mills
per kilowatt hour. From Figure 9 the savings in pH control cost
for operating at 3 cycles instead of 1.5 cycles is 0.0142 mills
per kilowatt hour. The net cost of the recycle program is therefore:
0.0155 - 0.0142 = 0.0013 mills/KWH
From Figure 6 the reduction in makeup water requirements is 900
3 i
m /hr (3960 gpm).
POWER PLANT #2 - WARM LIME SOFTENING AS A RECYCLE POSSIBILITY
This 750 megawatt station has a cooling system operating at 2 cycles
of concentration. It is pH and hardness limited. The plant
manager, one Mr. Buzz Barr, finds that, by treating the blowdown with
warm lime softening and recycling to makeup, the system can operate
at 5 cycles and be magnesium and silica limited. From the example
calculations shown in Appendix B the cost of a lime softener system
to treat the entire blowdown is 0.0091 mills per kilowatt hour. The credit
in pH control costs for operating at 5 cycles instead of 2 cycles is
0.0082 mills per kilowatt hour. This particular recycle program
results in a net cost of
0.0091 - 0.0082 = 0.0009 mills/KWH
The reduction in water requirements is 947 m /hr (4170 gpm).
NOTE: This reduction in makeup,requirements is not directly attainable
from the water quantity relationships described in section VI. In most
blowdown programs, such as this one, the blowdown is recycled after
treatment and serves as a portion of the makeup requirement (thereby
reducing the overall makeup to the system). The amount that is recycled
depends on several factors, including makeup water quality, treatment
efficiency, and degree of sludge water entrainment. In this example,
a figure of 80 percent blowdown recycle is used.
41
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POWER PLANT #3 - POLYMER ADDITION AS A RECYCLE POSSIBILITY
This 1000 megawatt station has a cooling system operating at 2.5 cycles.
It is calcium and sulfate limited. It is in a water short area where
o
water costs (influent) are $0.02/m° ($25/acre ft). Furthermore, the
station is under a contract—signed by the plant manager—to pay
a local municipality $0.0264/m3 ($0.10/1000 gallons) to handle the
cooling system blowdown in the city's sewage treatment facility.
The power plant engineer proposes a proven water treatment program
calling for the addition of a phosphonate/polymer chemical to the
makeup water. This addition allows the cooling system to operate
at 15 cycles and be magnesium and silica limited. From the example
calculations shown in Appendix B, the cost of the phosphonate/
polymer addition is 0.0055 mills per kilowatt hour. The savings
in payments to the sewage treatment facility is 0.0396 mills per kilowatt
hour. Additionally, the savings in pH control costs are 0.0099 mills/KWH,
Also, the savings in makeup water costs are 0.03 mills/KWH. The
program actually saves 0.074 mills per kilowatt hour. This translates
into an annual savings of $518,592. The reduction in water requirements
is 1200 m3/hr (5282 gpm).
As a result of the above proposal the plant engineer is now the new
plant manager. The former plant manager is now a tour guide at the
St. Louis Zoo working under Marlin Perkins, I think.
SUMMATION
By digesting the information contained in the above examples, the reader
can see there are several factors which affect the economic evaluation
of the treatment programs. The factors include:
1. Fuel type (fossil vs. nuclear)
2. Overall plant thermal efficiency
42
-------
3. Cooling system cycles of concentration both before and after
the installation of the treatment program.
4. Plant capacity factor.
5. Plant fixed charge rate.
6. Percent of the waste heat dissipated by evaporation in the cooling
system.
7. If applicable, influent/effluent surcharges.
The economic evaluation methodology considers these factors on the
total recycle program costs.
43
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SECTION IX
REFERENCES
1. Webster's New Collegiate Dictionary. Second Edition. 1953.
2. Goldman, E. and Kelleher, P. Water Reuse in Fossil-Fueled
Power Stations. In: Complete Water Reuse, Cecil, L. K.
(ed.). New York, N.Y., American Institute of Chemical
Engineers, April 1973. p. 240-249.
3. Water Quality Criteria. National Technical Advisory
Committee. Federal Water Pollution Control Agency.
Washington, D.C. 1968.
4. Personal communication with B. C. Moore. Betz Laboratories,
Inc. Vancouver, WA. December 1973.
5. Personal communication with E. C. Wackenhuth. Public Service
Electric and Gas. Newark, N.J. July 1974.
6. Reviewing Environmental Impact Statements - Thermal Power
Plant Cooling Systems. Thermal Pollution Branch. Con/all is,
Oregon. Rept. No. EPA-660/2-73-016. Environmental Protection
Agency. 1974. 93 p.
7. Juvan, D. 0. Successful Approaches to Once-Through Cooling
System Treatment. Betz Indicator. 43:4 Jan/Feb 1974.
8. Sisson, W. Langelier Index Predicts Waters Carbonate Coating
Tendency. Power Engineering. 77:44. February 1973.
9. Betz Handbook of Industrial Water Conditioning. Betz Laboratories,
Inc. Trevose, PA. 6th Edition. 1962. 427 p.
10. Steam Tables. Combustion Engineering. Winsor, Conn. Third
Edition. 20th Printing. 1940. 38 p.
11. Channabasappa, K. Reverse Osmosis Process for Water Reuse
Application. In: Water-1969. New York, N.Y., American
Institute of Chemical Engineers, 1969. p. 140-147.
12. Heynike, J. and Von Reiche, F. Water Pollution Control in
the Iron and Steel Industry, with Special Reference to the
South African Iron and Steel Industrial Corporation. Water
Pollution Control. 68(5):569-573, September-October 1969.
13. Boies, Levin, and Baratz. Technical and Economic Evaluations
of Cooling System Slowdown Control Techniques. Wapora, Inc.
Washington, D.C. Rept. No. EPA-660/2-73-026. Environmental
Protection Agency. 1974. 73 p.
44
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14. Process Design Manual for Suspended Solids Removal. Burns
and Roe, Inc. Oradell, NJ Rept. on Contract No. 14-12-930.
Environmental Protection Agency. October 1971. p. 11-12.
15. Personal Communication with P. C. Stultz. Baker Filtration
Co. Huntington Beach, CA. December 1973.
45
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SECTION X
APPENDICES
Page
A. Boiler System Recycle Economics 47
B. Cooling System Recycle Economics 49
46
-------
APPENDIX A
BOILER SYSTEM RECYCLE ECONOMICS
Using the plant data from Table 7, the savings in the recycle
program are:
Water from flash tank
Savings = [$^U + $°^- (iJ^)(121 - 15.5)C°(™^)]
nr 10° KJ Kg C° m
[1 - 167° " 5Q8][0.005][3178^-][-m7. ]
_2194 MWH 10 Kg
= 0.00413 mills/KWH
Vapor from flash tank
Savings = (2194 - 65) JS (^ffqi 5°8)(0.005)(3178){^$^—)
Kg ^iy« NWH 1Qb KJ
= 0.01720 mills/KWH
Total savings = 0.02133 mills/KWH
For a thousand megawatt plant with a 0.80 capacity factor, the
annual savings are:
c,.,,•,„„,- _ finnn ^WHwo-zen hr\/n nonoo mi 11S \ / 0 0\ $ lOOOKWH
Savings = (1000 ^-)(8760 —)(0.02133 -^p)(0.8) f'ooQ ^}}s MWH —
= $149,480
A fifteen percent heat and water loss from the recycle scheme results
in a savings of about $125,000 per year.
47
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Table 7. BOILER SYSTEM CHARACTERISTICS
A. Boiler
Steam Production Rate
Operating Pressure
Efficiency
Slowdown Rate
Fuel Costs
Flash Tank Pressure
Water Treatment Costs
Makeup Water Temperature
Flash Tank Temperature
Heat Values (from Betz9'
Slowdown Water
Flash Tank Liquid Water
Flash Tank Heat of Vaporization
Makeup Water
Physical Constants
Heat Capacity of Water
Conversion Factor
3178 Kg/MWH (7000 #/MWH)
170 Kg/cm2 (2415 PSIG)
85 percent
0.5 percent
$0.96/106 KJ ($1.00/106 BTU)
2 Kg/cm2 (30 PSIG)
$0.13/m3 ($0.50/103 gal)
15.5°C (60°F)
121°C (250°F)
1670 KJ/Kg (719 BTU/lb)
508 KJ/Kg (219 BTU/lb)
2194 KJ/Kg (945 BTU/lb)
65 KJ/Kg ( 28 BTU/lb)
4.18 KJ
1000 Kg = 1.0
BTU
Tl
3
(water)
48
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APPENDIX B
COOLING SYSTEM RECYCLE ECONOMICS
POWER PLANT #2 CALCULATIONS (Example)
from Figure 4, E' = 1.662
from Table 5 the cost of the softener is
= r$-057 264 gal $75 4.4 gpm /O.IK yr , 1.662
L -3 o 3 \. Q.eV """" ' ~" "
m/hr •*
= [0.0220] -
T
= 0.0091 mills/KWH
pH control Costs
without softener
r 4- rn nncen 1-662 tr)\ mi 11 s
Costs = [0.0066] / _ \ (2)
= 0.0219 mills/KWH
with softener
[0.0066] - (5)
(5-1) '
= 0.0137 mills/KWH
Net savings in pH control costs
0.0219 - 0.0137 = 0.0082 mills/KWH
49
-------
Water Requirement Savings
Savings = M] - M2 = 1 .662(750) (0.8) [y - ^] = 947 m3/hr
= 4170 gpm
POWER PLANT #3 CALCULATIONS (Example)
from Figure 4, E1 = 2.521
@ 2.5 cycles
pH Control Costs = [0.0066] '
= 0.0277 mills/KWH
Slowdown Costs = [0.0264]
= 0.0444 mills/KWH
Makeup Water Costs = [0.02] 2'5
= 0.084 mills/KWH
@ 15 cycles
pH Control Costs = 0.0178 mills/KWH
Slowdown Costs = 0.0048 mills/KWH
Makeup Water Costs = 0.054 mills/KWH
Polymer Addition Costs = [0.0308]
= 0.0055 mills/KWH
50
-------
Net Savings = 0.0277 + 0.0444 + 0.084 - 0.0178 - 0.0048 - 0.054 - 0.0055
= 0.074 mills/KWH
= $518,592/yr
Water Requirement Savings
Savings = M] - M2 = 2.521 [1000](.8) [^| - }|]
= 1200 m /hr or 5282 gpm
51
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
4. Title
Water Recycle/Reuse Possibilities: Power Plant Boiler and
Cooling Systems
7. Author(s)
Guy R. Nelson
9. organization Thermal Pollution Branch, Pacific Northwest
Environmental Research Laboratory, National Environmental
Research Center-Corvallis, Environmental Protection Agency,
Corvallis, Oregon 97330
10. Project No.
11. Contract/ Grant No.
In-house
15. Supplementary Notes
16. Abstract This report contains the methodology to evaluate, in economic terms,
potential power plant boiler and cooling system water recycle/reuse programs.
Drum type boiler systems and closed cycle cooling systems are used as the basis
for the programs' water requirements. The evaluations take into account the
variable plant characteristics such as makeup water quality, fuel type, thermal
efficiency, capacity factor and fixed charge rate.
The evaluation methodology is applicable to existing and proposed power
plants, on an individual plant basis—and can be used to determine the over-all
economics of potential recycle/reuse programs.
The report is the first of a series that addresses the water recycle/reuse
potentials of typical power plant processes.
na. Descriptors Water, Water Types, Industrial Water*
b. identifiers Boiler Feed Water, Cooling Water, Water Costs, Water Demand*, Water
Reuse*, Water Treatment
(.-. CO
& Group Q5B, 05D
Guy R. Nelson
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
Institution
U.S. GOVERNMENT PRINTING OFFICE: 1974-697-648/67 REGION 10
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