U.S. Environmental Protection Agency Industrial Environmental Research EPA-600/7'78-0313
Office of Research and Development Laboratory .. . -tfi7Q
Research Triangle Park, North Carolina 27711 M&TCn l9/O
THE EFFECT OF FLUE GAS
DESULFURIZATION
AVAILABILITY ON ELECTRIC
UTILITIES
Volume I. Executive Summary
Interagency
Energy-Environment
Research and Development
Program Report
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EPA-600/7-78-031a
March 1978
THE EFFECT OF FLUE GAS
DESULFURIZATION AVAILABILITY ON
ELECTRIC UTILITIES
Volume I. Executive Summary
by
R.D. Delleney
Radian Corporation
P.O. Box 9948
Austin, Texas 78766
Contract No. 68-02-2608
Task No. 7
Program Element No. EHE624
EPA Project Officers:
John E. Williams and Kenneth R. Durkee
Industrial Environmental Research Laboratory Emission Standards and Engineering Division
Office of Energy, Minerals, and Industry Office of Air Quality Planning and Standards
Research Triangle Park, N.C. 27711 Research Triangle Park, N.C. 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
and Office of Air and Waste Management
Washington, D.C. 20460
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TABLE OF CONTENTS
PAGE
TABLE OF CONTENTS ii-iii
LIST OF TABLES iv
LIST OF FIGURES v
1.0 INTRODUCTION 1
1.1 Program Objectives 2
1.2 Definition of Important Terms 3
1.3 Approach 4
2.0 RESULTS AND CONCLUSIONS 6
2.1 Results 6
2.2 Conclusions 8
3.0 AVAILABILITY ASSESSMENT 10
3.1 Generating Unit Component Descriptions 10
3.2 Description of Generating Systems 10
3.3 Utility and Flue Gas Desulfurization
Operating Data 11
3.3.1 Utility Operating Data 13
3.3.2 Flue Gas Desulfurization Operating Data 13
3.4 Effect of Flue Gas Desulfurization Availability
on an Individual Generating Station 17
3.5 Effect of Flue Gas Desulfurization Availability
on Generating Systems 21
4.0 IMPROVEMENTS TO FLUE GAS DESULFURIZATION
AVAILABILITY 28
ii
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TABLE OF CONTENTS (Continued)
PAGE
4.1 Operating Experience for Existing Systems 28
4.2 Measures to Improve Flue Gas Desulfurization
Availability 29
APPENDIX A 31
BIBLIOGRAPHY 33
iii
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LIST OF TABLES
TABLE PAGE
3-1 Percentage Breakdown of System Generating
Capability by Primary Fuel and Equip-
ment--1985 12
3-2 Operating Data for Mature Coal-Fired Units
(390-599 Mw) 14
3-3 FGD Module Performance Data - Average Values -- 15
3-4 The Initial Availability of Seven FGD Systems - 18
3-5 Estimated Effect of Flue Gas Desulfurization
Unit Availability on 1985 Systems 23
3-6 New Coal Generating Capacity in Each System -
1985 24
3-7 Summer Peak Loads - 1985 Projections by NERC -- 25
3-8 Estimate of Megawatts of Additional Generating
Capacity Required to Offset the Effect of
FGD in 1988 and 1998 27
iv
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LIST OF FIGURES
FIGURE PAGE
3-1 Effect of flue gas desulfurization unit
availability on individual generating
station availability at maximum load 19
v
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1.0 INTRODUCTION
This report presents the results of work performed by
Radian Corporation of Austin, Texas, for the Office of Air Qual-
ity Planning and Standards and the Industrial Environmental Re-
search Laboratory of the United States Environmental Protection
Agency. The purpose of this project was to assess the impact of
flue gas desulfurization (FGD) system availability on the ability
of individual coal-fired generating stations* and of generating
systems** to meet consumer demands. Operating information on
utilities and FGD systems from all known sources was analyzed with
the major emphasis on the Edison Electric Institute (EEI) data
base, PEDCo Environmental's Summary Report--Flue Gas Desulfurization
Systems, and contacting utilities with operating FGD systems of
interest to this study.
This project was originally to consider the subject of
reliability and availability. However, during the course of this
investigation it became evident that reliability was not a useful
measure of the ability of an individual unit or a generating sys-
tem to respond to consumer demands for electric power. Further-
more, the term "reliability" was not uniformly defined over the
data bases used in this study. As a result, this study is con-
cerned almost exclusively with the quantification and assessment
of availability, which was defined in a uniform manner.
Almost all commercial applications of flue gas desul
furization on coal-fired boilers use either the Lime Process or
the Limestone Process. Of the other processes of interest in
this study, the Magnesium Oxide and Wellman-Lord Processes are
*Single steam generating plant
**Interconnected pool composed of a mix of numerous generating
plants
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each used at one site while the Double Alkali Process has not
been commercially applied to coal-fired boilers. As a result,
this study concentrates on the operating experience and data
for Lime/Limestone Processes.
At present, many of the measures that lead to a more
reliable FGD system include an economic penalty. An assessment
of these economic penalties was beyond the scope of this study
and is not addressed in this document. As operating experience
and technology developments solve some of the problems, these
economic penalties may be reduced or eliminated.
1.1 Program Objectives
The objectives of this program were identified in the
Work Plan as follows:
To assess the effect of flue gas desulfurization
(FGD) systems on the reliability/availability
of electric utility power generation. A compari-
son of the reliability/availability of existing
FGD units with power plant generating equipment
was included.
To define and assess measures which have been or
can be used to maintain or improve FGD unit
reliability/availability. Emphasis was placed
on operating experience at specific installations.
To report the results of this study in support
of EPA's review of the new source performance
standards for coal-fired steam generators.
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1.2 Definition of Important Terms
Available - The status of a unit or major piece
of equipment which is capable of service, whether
or not it is actually in service.
Availability - The fraction of time that a unit
or major piece of equipment is capable of service,
whether or not it is actually in service.
Forced Outage - The occurrence of a component
failure or other condition which requires that
the unit be removed from service immediately or
up to and including the very next weekend.
Mean Time Between Full Forced Outage - The average
time between each occurrence of a component failure
or other condition which requires that the unit be
removed from service immediately or up to and in-
cluding the very next weekend. The average time
is calculated by dividing the service hours by the
number of forced outages.
. Reliability - The probability that a device will
not fail or that service is continuous in a
specified time period. The term reliability
is not defined as a standard in the utility
industry. The Mean Time Between Full Forced
Outage (MTBFFO) and Loss-of-Load Probability
(LOLP) are sometimes used as measures of
reliability. The MTBFFO and LOLP can be
used to calculate numerical values for
reliability.
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These terms are commonly used in an examination of the
ability of a utility to meet consumer demand. Where possible
these terms are in accordance with the Edison Electric Insti-
tute (EEI) standard definitions.
1.3 Approach
System reliability has been frequently used as an
important measure of the performance of that system. The con-
cept of a system being reliable or dependable is relatively
straightforward. However, the quantification and application
of this concept is relatively complex and is often poorly under-
stood. A reader usually has a preconceived idea of what reliable
or reliability means. These preconceived ideas often inhibit
communication of the results of a system reliability analysis.
As an exmple, assume a system has a reliability of
99 percent for a 1000 hour time period. This statement means
there is a probability of 99 percent that the system will oper-
ate for 1000 hours without a failure. This statement of reli-
ability has three elements: (1) a quality of performance,
(2) the performance is expected over a period of time, and
(3) reliability is expressed as a probability. No information
is provided as to how long the system does not operate when a
failure occurs. The statement of 99 percent reliability for
1000 hours does not mean that the system will operate 990 hours
out of every 1000 hours. Availability, on the other hand, pro-
vides information as to how often a system fails and how long it
does not operate as a result of a failure. Availability data
thus combine the effects of reliability, maintenance, and
repair time and are usually expressed as a percentage.
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Many different organizations reporting reliability/
availability type data use slightly different definitions for
these terms. PEDCo Environmental's measure of reliability in
their FGD status reports is not comparable to the parameters
used by EEI to quantify reliability. Therefore, an evaluation
based on the quantification of "reliabilities" is not possible
in this study. However, the definitions of "availability" used
by EEI and PEDCo are essentially the same. As a consequence of
the preceding discussion, availability was determined to be the
most useful measure of the ability of an individual station or
a generating system to respond to consumer demand.
The steps taken in the completion of this project were
Collect and analyze all available data for utility
and flue gas desulfurization systems.
Determine the effect of FGD units on the avail-
ability of individual generating stations and
generating systems. It was assumed that the
generating station cannot bypass the FGD unit.
The FGD unit availabilities are at the full load
operation of the generating station unless speci-
fied otherwise.
Survey of existing FGD units to determine how
they are meeting or can meet necessary avail-
ability levels.
• Document the operating experience at specific
FGD installations.
Define and assess measures that have resulted
or can result in high levels of FGD unit
availability.
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The following items should be taken into account to
more completely evaluate the effect of FGD availability on
power systems:
Unit use (base load, intermediate load, etc.)
Unit interactions
Coincident outages
Partial outages (generating unit and scrubber)
FGD unit configurations
Network configurations
• Reserve policies
In particular, generating unit use and incidence of coincident
full and/or partial outage will strongly influence the effect
of FGD on system availability and adequacy. Also, in assessing
the effect of FGD on power systems, it is important to recognize
the requirement for excess generating capability above the maxi-
mum demand. Reserve policies, interconnections, and network
state would influence whether or not power was available to
offset these potential effects of FGD. Such an assessment was
beyond the scope of this study.
2.0 RESULTS AND CONCLUSIONS
The effect of FGD availability on power generation
was assessed. The results and conclusions of this study are
given in this section.
2.1 Results
The results of this project are:
1) Mature coal-fired generating unit components
(i.e. boilers, turbines, etc.) are reported to
have an average availability between 80 and 97
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percent. Mature coal-fired generating units are
reported to have an average availability between
70 and 77 percent.
2) The seven FGD units emphasized in this study
have reported average modular availabilities
between 44 and 95 percent. Five of these
have reported average modular availabilities
above 70 percent.
3) An individual base loaded generating station
with an FGD unit cannot meet consumer demand
without FGD module sparing.
4) Generating systems with FGD on new coal-fired
plants can meet a 1985 consumer demand equal
to about 89 percent of the capability without
FGD based on modeling the new coal capacity
in a system as a single generating station
with one FGD unit composed of one module.
However, the systems cannot maintain the
excess generating capability above maximum
demand that is required to insure the ability
to meet demand. Additional generating units
or improvements to the FGD unit availability
would have to offset the reduction in gener-
ating capability due to FGD units.
5) The availability of existing FGD units is
maintained by various combinations of the
following: (a) use of trained operating
and maintenance crews, (b) bringing modules
-------
off-line each night for maintenance, and
(c) inclusion of spare modules.
6) FGD unit components subject to high
failure rates include slurry pumps,
packing gland water systems, nozzles,
valves, fans, mist eliminators, and
reheaters.
7) Maintenance methods, operating tech-
niques, and design concepts were
identified that can or have been used
to produce high FGD availabilities.
8) A preliminary and rudimentary examination
of the relationship between the effect of
FGD and load duration curves was completed.
2.2 Conclusions
The conclusions for this study are:
1) FGD unit availability is a function of
the modular availability, the total
number of modules and the number of
spare modules. The FGD unit avail-
ability is associated with a specific
operating load (percent of capacity)
for the generating unit. The number
of effective spare modules varies
with the operating load since all
modules are not necessarily required
for loads of less than 100 percent
of capacity.
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2) The availability of FGD units has
a significant impact on the ability
of an individual generating station
and a generating system to meet
consumer demand. The reduction in
generating capability for a single
station varies depending on the FGD
unit availability. For a system the
effect of FGD largely depends on the
fraction of new coal plants in that
system. These reductions in capa-
bility must be offset by adding
generating units or by improving
the availability of the FGD units.
3) Use of spare FGD modules dramatically
improves total unit availability.
4) Significant progress has been made in
the last few years in solving the
problems experienced by the existing
FGD units. The problems which present
the greatest challenge to FGD avail-
ability are corrosion, erosion, deposits,
unstable chemistry, and instrumentation.
5) A substantial committment on the part of
a utility to the operation and maintenance
of an FGD unit is required to maintain
high levels of FGD unit availability.
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3.0 AVAILABILITY ASSESSMENT
An assessment of the effect of flue gas desulfuriza-
tion units on the availability of individual electric generating
stations and generating systems was performed. The effect was
quantified by determining the change in the ability of an
individual station or generating system to meet consumer demand.
This section of the report includes a description of generating
unit components and systems (Sections 3.1 and 3.2), a presenta-
tion of utility and flue gas desulfurization operating data
(Sections 3.3 and 3.4), and a determination of the effect of
FGD availability on an individual generating station (Section
3.4) and on generating systems (Section 3.5).
3.1 Generating Unit Component Descriptions
The five major utility equipment component groupings
of interest to this study are boilers, turbines, generators,
condensers, and others (boiler feed water pumps, etc.). These
items are currently used by virtually every utility in the
United States.
There are two basic reasons for selecting these equip-
ment items for study. First, each is generally accepted by the
electric power utility industry as being commercially demonstrated
technology. Second, data has been recorded and in many cases is
available concerning the reliability, availability, and failure
rates of each of these equipment items.
3.2 Description of Generating Systems
Systems of varying mixes of power plant generating
types were examined. The 1985 projections by the National
10
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Electric Reliability Council (NA-35) were the basis for the mix
of generating types specified in these systems. The National
Electric Reliability Council (NERC) consists of nine Regional
Reliability Councils and encompasses essentially all of the
power systems of the United States. The ten systems shown in
Table 3-1 represent the projected mixes for the nine regional
councils and the total projected mix for the NERC for 1985.
The column titled New Coal under Fossil-Fired Steam
Turbines is of particular interest. The New Coal in Table 3-1
represents the percentage of total capacity resulting from coal-
fired steam turbines completed between 1976 and 1985. This New
Coal capacity is assumed to come under EPA's New Source Perfor-
mance Standards. Therefore, control of S02 emissions for this
generating capacity may be required. For this study, all of
this New Coal generating capacity is assumed to use flue gas
desulfurization as the method of S02 control. As a result,
the effect of FGD on each system follows directly from its
effect on the New Coal steam generators in that system.
3.3 Utility and Flue Gas Desulfurization Operating Data
A significant disparity exists between the quality and
quantity of data available for utility systems as compared to
flue gas desulfurization systems. Detailed performance data
for equipment used in the electric utility industry have been
collected on a continuing basis since 1965. There are at least
four data banks for utility systems in the United States. Per-
formance data for operating FGD systems, however, is sparse. At
present the PEDCo Summary Report--Flue Gas Desulfurization Systems
(PE-259) is the primary source.
11
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TABLE 3-1.
l-o
PERCENTAGE BREAKDOWN OF SYSTEM GENERATING CAPABILITY
BY PRIMARY FUEL AND EQUIPMENT--1985
System
Number
1
2
3
4
5
6
7
8
9
10
Fossil-Fired -
By Type of Primary Fuel
Steam Turbines
New Coal
18.4
33.6
3.5
14.5
29.2
4.4
11.7
30.0
13.5
16.0
Total Coal
72.5
37.8
26.4
52.7
58.7
9.9
42.0
36.1
24.5
40.1
Oil Gas
5.0 0.5
10.6 38.1
22.3 0
6.7 0.2
2.0 0.5
37.7 0
11.7 0
11.4 28.4
16.6 1.2
13.8 5.7
Combust.
Turb.
3.4
1.8
14.0
8.1
8.9
8.4
6.5
5.5
5.1
6.4
Comb.
Cycle
0.3
1.3
0.4
0
0.2
0.9
0.6
1.6
2.1
0.9
Nuclear
14.7
8.5
31.5
30.5
21.1
30.0
30.4
13.5
14.9
21.8
Hydro
0.8
0.5
1.5
0.9
8.6
7.8
5.8
3.2
30.6
8.4
Pump
Storage
and
Other
2.8
1.4
3.9
0.9
0
5.3
3.0
0.3
5.0
2.9
Source: NA-325
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3.3.1 Utility Operating Data
There are four primary systems in operation in the
United States which collect and report power system performance
data. These systems are the Edison Electric Institute (EEI) Prime
Movers Committee; the Nuclear Plant Reliability Data Systems (NPRDS)
under the direction of the American National Standards Institute
(ANSI) subcommittee N18-20; the Gray Book I, issued by the Nuclear
Regulatory Commission (NRC Gray Book); and the Federal Power Com-
mission (FPC).
The EEI reports were found to be the best sources of
data that are relevant to this study. Particularly useful was a
special report issued in October 1976 on mature* fossil units cate-
gorized by fuel (ED-059). Data from this report are presented in
Table 3-2.
3.3.2 Flue Gas Desulfurization Operating Data
An initial screening of PEDCo's Summary Report--Flue Gas
Desulfurization Systems (PE-259) for the January to March, 1977.
period identified 16 operational lime/limestone wet scrubbing sys-
tems and 1 operational system using magnesium oxide. No sites
using double alkali or Wellman-Lord were listed. The criteria for
selecting units for inclusion in this study were: (1) the system
treats flue gas from a utility generating station greater than 50
Mw in size, (2) the system has been operating approximately one
year or more, and (3) the system is not a test or demonstration
unit. After application of these criteria to the operating sys-
tems, only 12 lime/limestone units remained. Table 3-3 illustrates
average values for the seven units for which these performance
indicators were available. The average modular availability is
the average of the availabilities of the modules in an FGD system.
*A mature unit has completed the breakin period and has operated
long enough to have a known incidence of outage.
13
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TABLE 3-2. OPERATING DATA FOR MATURE COAL-FIRED UNITS
(390-599 Mw)
Unit
Coal Only
Coal Primary
Boilers
Coal Only
Coal Primary
Turbines
Coal Only
Coal Primary
Condens ers
Coal Only
Coal Primary
Generators
Coal Only
Coal Primary
Other
Coal Only
Coal Primary
Year
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
1972
1973
1974
Units in
Service
32
19
20
36
30
35
32
19
20
36
30
35
32
19
20
36
30
35
32
19
20
36
30
35
32
19
20
36
30
35
32
19
20
36
30
35
Operating
Availability
(%)
75.1
74.3
69.9
74.2
77.3
71.5
79.6
83.0
76.7
79.0
84.0
77.6
86.3
88.4
89.7
86.4
90.6
89.5
96.7
97.4
97.3
96.0
97.6
97.7
91.0
96.3
94.0
90.2
96.1
94.4
95.0
93.3
96.2
94.3
98.0
97.0
Source: ED-059
14
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TABLE 3-3. FGD MODULE PERFORMANCE DATA - AVERAGE VALUES
System
Will County No. 1
La Cygne No. 1
Phillips
Cholla No. 1
Green River
Sherburne County No. 1
Bruce Mansfield No. 1
MW
167
874
413
126
64
720
825
No. of Average Modular
Modules Availability
(0/\
\i°)
2
7
4
2
1
11 (+1 spare)
6
44.2
88.6
60.6
91.5
72. 6b
90.9
77.8°
Utilization3
(%)
33.6
N.A.
49.7
N.A.
62.1
70.9
76.8
Utilization is the hours the FGD unit operated divided by the hours in the
period expressed as a percentage.
Includes two-month outage in March-April, 1977, to reline stack.
Q
Including reduction to half-load from March-July, 1977, due to repairs to
stack lining. Bruce Mansfield reports that the repairs were necessary due
to the improper installation of the original lining.
Sources: AN-184, BE-478, HE-258, KR-115, MU-155, PE-259, PE-267, PE-287, PE-288
-------
The average modular availabilities vary from one unit
to the next. However, five of the seven units have average mod-
ular availabilities greater than 70 percent. Furthermore, three
are greater than 88 percent. Consequently, an average modular
availability in the range of 70 to 90 percent was assumed for
a mature FGD unit. This 70 to 90 percent modular availability
range will receive primary emphasis in evaluating the effect of
the availability of FGD systems on individual generating
stations and on generating systems.
Analysis of the FGD availability data leads to several
conclusions. No correlation between FGD availability and the
size of the generating unit, the type of FGD process, or the
size of the FGD modules was observed. The three systems exam-
ined in this study which have a large number of modules and/or
a spare module (La Cygne No. 1, Sherburne County No. 1, and
Bruce Mansfield No. 1), all have reasonably high modular avail-
abilities. Application on a peaking or intermediate unit rather
than base load allows maintenance to be performed on a more
routine basis and, therefore, enhances reliable operation.
Since FGD units have operated successfully on low sulfur coal
(e.g. Sherburne County No. 1) and high sulfur coal (e.g. La
Cygne), the proper design and operation of the system were
determined to be more important than the sulfur content of the
coal. Historically, inclusion of spare modules and an open
water balance without recycle are additional factors that have
contributed to more reliable operation. The establishment of
a separate operating and maintenance crew that is specifically
trained to work with the FGD unit is a final important factor
in reliable operation. While all of these factors do not
apply to every FGD system, they are all important considerations
in any analysis of system availability.
16
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One comparison of interest is that of the availability
for the initial operating period for older units with the avail-
ability for the initial operating period for newer units. This
comparison is particularly interesting for units by the same ven-
dor. Table 3-4 presents the first year average modular availabil-
ities for the seven FGD units emphasized in this study. This
table points out the substantial improvements in the initial
operating experience of units installed by the same vendor. The
newer B&W and Chemico units show significant improvements rela-
tive to the older units by the same vendor. Furthermore, the
newer units in general show improved average modular availabil-
ities during the initial operating period. These improvements
might be expected as a result of general advances in the state-
of-the-art and particularly due to increased design and operating
experience in the FGD industry. Radian has previously examined
this "learning curve" effect in a study for EPA (DI-R-116).
3.4 Effect of Flue Gas Desulfurization Availability
on an Individual Generating Station
A parametric study was performed to provide an over-
view of the effect of FGD unit availability on an individual
generating station. Availability of the generating plant was
assumed to be 75 percent while the FGD unit availability was
varied from 0 to 100 percent. The results of this parametric
study are shown in Figure 3-1. As can be seen, the FGD unit
availability has a dramatic effect on generating station avail-
ability and, therefore, on the ability of the generating station
to respond to demands for power.
As previously stated, an FGD modular availability in
the 70 to 90 percent range was assumed for a mature FGD system.
The FGD unit availability at full capacity can be calculated
using the modular availability, the number of modules in the
U.S EPA Headquarters Library
Mali code 3404T
17 1200 Pennsylvania Avenue NW
Washington, DC 20460
202-566-0556
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TABLE 3-4. THE INITIAL AVAILABILITY OF SEVEN FGD SYSTEMS
System
Will County No. 1
La Cygne No. 1
Phillips
Bruce Mansfield No. 1
Cholla No. 1
Green River
Sherburne County No. 1
Start-up
2/72
2/73
7/73
4/76
10/73
9/75
3/76
First Year Modular
Vendor Availability (7o)
B & Wa
B & W
Chemico
Chemico
R - Cb
AAFC
CEd
-49
-87*
-36
-80
N.A.
-85
-90
N.A. - Not Available
* - Second year availability is reported because data for
the first year were not available.
«
Babcock and Wilcox
Research Cottrell
Q
American Air Filter
Combustion Engineering
18
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Individual
Generating
Station
Availability
100
90-
13%
10
0
Figure 3-1.
1 77
10 20 30
FGD Unit Availability (%)
100
A - No FGD
B - 6 Modules/I Spare
90% Availability
per Module
C - 5 Modules/No Spares
90% Availability
per Module
D - 6 Modules/I Spare
70% Availability
per Module
E - 5 Modules/No Spares
70% Availability
per Module
Effect of flue gas desulfurization unit availability on
individual generating station availability at maximum load.
-------
FGD unit, and the number of modules required for operation at
full capacity. Assume a five module FGD unit with identical
modules and no spares. With a 70 percent modular availability,
the FGD unit availability at full capacity would be 17 percent.
With a 90 percent modular availability, the FGD unit availability
at full capacity would be 59 percent. The resultant plant avail-
ability for an individual station with an FGD system would then
range from about 13 to 44 percent. For the 13 percent plant
availability (70 percent FGD availability), a reduction of about
62 percent results. With a plant availability of 44 percent
(90 percent FGD availability), the reduction is about 31 percent.
The methodology used in these calculations is given in Appendix A.
Next, assume a spare module is added to the FGD unit
such that five of the six modules can treat the flue gas gener-
ated at full capacity operation of the boiler. The spare module
results in a full capacity availability of 42 percent for the
unit with a modular availability of 70 percent. The unit with
a 90 percent modular availability has a full capacity availability
of 88 percent with a spare module. The resultant plant availabil-
ity for an individual station with an FGD unit would then range
from about 32 to 66 percent. The use of a spare module, there-
fore, improves the availability of the unit dramatically. Unit
availability improves still more with each spare module added but
the economics become less favorable with each spare added.
Previously, the discussion has been limited to opera-
tion of the generating unit at full capacity. During periods of
reduced load on the generating station an FGD module might be
down but the FGD unit could still treat all of the flue gas.
For this reason, the availability of the unit for a range of
boiler loads and the load duration curve for the generating sta-
tion are both important considerations. The effect of a load
duration curve was considered in a rudimentary manner in the
appendix of the Task Report.
20
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3.5 Effect of Flue Gas Desulfurization Availability on
Generating Systems
This study considers the effect of FGD on the nine
NERC regions and on the nation as a whole. The approach to
this examination is the same as that used for an individual
utility generating station in the preceding section. For the
generating systems, however, the FGD units will only affect
the new coal-fired capacity that comes under EPA1s New Source
Performance Standards. As previously stated, all of this new
coal-fired capacity is assumed to use flue gas desulfurization
as the method of S02 control. Therefore, the effect of FGD on
each system is proportional to the new coal-fired steam turbine
generating capacity in that system.
A parametric study of the effect of FGD availability
on 10 utility systems was performed for the year 1985. FGD
unit availability was varied from 0 to 100 percent. The effect
of this availability on the new coal-fired capacity then deter-
mined the overall effect on the system. The new coal-fired
capacity was represented as a single generating plant with one
FGD unit composed of one module. FGD unit availabilities of
70, 80, and 90 percent are emphasized in estimating the impact
of FGD availability on electric generation.
The effect of flue gas desulfurization on a utility
system was estimated as shown below:
% Capacity With FGD - (100% Capacity Without FGD) -
(% New Coal) x (1-FGD Availability)
The system is assumed to be at 100 percent capacity prior to
application of FGD. The reduction in capacity due to the use
21
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of FGD was approximated as the product of the fraction of new
coal capacity in a system and the reduction in availability of
this new coal capacity due to FGD. The fraction of new coal
represents coal-fired plants coming on line between 1976 and 1985.
For example, in 1985 System 4 has 14.5 percent new
coal capacity (Table 3-1). If an FGD availability of 80 percent
is assumed, the effect of FGD is estimated by
100% - (14.57.)(1-. 8) =
1007o - (14. 570 (.2) =
1007, - 2.97o = 97.17o
Therefore, the estimated effect of the use of FGD is a reduction
of generating capacity to 97.1 percent of the capacity without
FGD. The impact of FGD on each system examined using the method
above is shown in Table 3-5 for 1985. Projections were not car-
ried beyond 1985 because data for the systems examined was not
readily available beyond 1985. Additional follow-on work will
be done to carry the projections through 1998 and to also con-
sider other factors such as load demand curves.
The effect of FGD varies from system to system depending
on the amount of new coal capacity and the FGD availability that
is assumed. System 2 shows the greatest impact while System 3 is
the least affected. The percent new coal for each system is shown
in Table 3-6.
The effect of FGD availability on a generating system
is observed to be less dramatic than for an individual station.
This would be expected due to the diluting effect of power genera-
tion with fuels other than coal or with coal units that do not have
FGD systems for S02 control. For a single new coal station the
22
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TABLE 3-5. ESTIMATED EFFECT OF FLUE GAS DESULFURIZATION
UNIT AVAILABILITY ON 1985 SYSTEMS3
FGD Unit Availability (%)b
System
1
2
3
4
5
6
7
8
9
10
70
94
90
99
95
91
99
97
91
96
95
80
96
93
99+
97
94
99+
98
94
97
97
90
98
96
99+
99
97
99+
99
97
98
98+
aEffect is determined by the ratio of system generating
capability with FGD units over system generating capa-
bility without FGD units expressed as a percentage.
One FGD unit composed of one module on a single gener-
ating station representing all new coal capacity.
23
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TABLE 3-6. NEW COAL GENERATING CAPACITY
IN EACH SYSTEM - 1985a
System % of 1985 Total Capacity
1
2
3
4
5
6
7
8
9
10
18.4
33.6
3.5
14.5
29.2
4.4
11.7
30.0
13.5
16.0
aFraction of 1985 total capacity repre-
sented by coal-fired units coming
on-line between 1976 and 1985.
24
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entire station was affected by FGD availability. Conversely,
only the new coal capacity of a generating system is affected
by FGD.
The significance of the 1985 impacts shown in Table
3-5 is difficult to put into perspective until a comparison is
made with consumer demand. The National Electric Reliability
Council (NERC) has projected the 1985 summer total resources
and peak loads in megawatts for the systems examined in this
study (NA-325). The summer peak demand as a fraction of the
total summer resources for each system is presented in Table 3-7
TABLE 3-7. SUMMER PEAK LOADS -
1985 PROJECTIONS BY NERC
System Summer
1
2
3
4
5
6
7
8
9
10 (Nation)
Peak Load (%)a
89
82
78
85
80
71
85
88
76
81
aExpressed as a percentage of the
total summer resources (MW) pro-
jected for 1985 by NERC.
Source: NA-325
25
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Each of the cases presented for 1985 in Table 3-5 can
potentially meet the highest summer peak load projected by the
NERC for 1985 (Table 3-7). However, it is critical to understand
that the primary reason consumer demand can be met in these 1985
example systems is the excess capability above peak loads that
is built into the utility systems. The maximum summer peak load
projected for 1985 is not greater than 89 percent of total re-
sources due to the presence of excess capacity. Table 3-7 indi-
cates that the excess capability above the peak load varies from
11 to 24 percent. The utility industry is required to maintain
these types of excess capabilities to insure their ability to
meet consumer demand, to allow for growth of demand, and to pro-
vide emergency power if a generating unit or units, a transmission
line, or an interconnection should fail.
To maintain this generating capability above maximum
demand, a general reduction in generating capability that occurs
for any reason including the application of FGD must be offset.
The effect of the reduction in generating capability due to FGD
unit availability was estimated assuming that reductions would
be offset by the addition of more generating capacity.
.It is important to note that the data in Table 3-5 are
for 1985. Because lead times for construction of new coal gener-
ating units range from 7 to 10 years, 1985 is probably the first
year that the effects of the NSPS would be seen. Because of the
projected rapid growth in requirements for new coal units brought
on by the energy crisis, it is important to estimate the effects
of a revised NSPS in years beyond 1985. The amount of new coal
26
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generating capability beyond 1985 that would be subject to any
revised new source performance standards has been estimated as
133,800 Mw in 1988 and 386,800 Mw in 1998 (WO-139). The 1988
estimate includes the 1980-1988 projects while the 1998 estimate
includes 1980-1998. The additional generating capacity required
to offset the reduction in generating capability caused by FGD
is thus expected to increase significantly between 1985 and 2000
due to this threefold increase in new coal capacity. Consequently,
the effects of FGD on reliability will probably increase in mag-
nitude in the future. Rough estimates of this effect, obtained
by analyzing all new coal as a single unit with a single scrubber
unit composed of one module, are given in Table 3-8. Average FGD
availabilities of 70, 80, and 90 percent were assumed. These
additional generating requirements are estimates for the entire
United States. They cannot be apportioned or extrapolated to
any specific generating system.
TABLE 3-8.
ESTIMATE OF MEGAWATTS OF ADDITIONAL
GENERATING CAPACITY REQUIRED TO
OFFSET THE EFFECT OF FGD IN 1988
AND 1998
Year
1988
1998
FGD Availability3
70%
40,100 Mw
116,000 Mw
80%
26,800 Mw
77,400 Mw
90%
13,400 Mw
38,700 Mw
aOne FGD unit composed of one module on a single generating
unit representing all new coal capacity.
27
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4.0 IMPROVEMENTS TO FLUE GAS DESULFURIZATION AVAILABILITY
This report has emphasized experience at lime/lime-
stone FGD units. Solutions to some of the problems encountered
by lime/limestone FGD systems have been found. The system
components which are subject to high failure rates have also
been identified. Methods to overcome these high failure rates
such as sparing or maintenance have subsequently been examined.
Certain measures that have resulted or can result in high levels
of system availability have also been defined by the FGD industry,
4.1 Operating Experience for Existing Systems
A similarity in the problems from system to system
is observed. These problems can be generally grouped as fol-
lows: (1) erosion of pumps, seals, and control valves; (2) de-
posits, plugging, or scaling on scrubber internals, nozzles,
strainers, mist eliminators, and in-line reheaters; (3) corro-
sion of fans, reheaters, ducts, and stacks; and (4) vibration
and poor thermal mixing with direct-fired reheaters. Solutions
are also often similar and, therefore, often applicable from
one system to the other. However, any application must be ex-
amined on a case-by-case basis. Resistant materials or coatings
have generally been used in attempts to overcome erosion and
corrosion problems. Careful control of the scrubber operation
and the prevention of solids entrainment in the gas have been
partially successful in preventing deposits buildup, plugging,
or scale. The use of large operating and maintenance crews
in addition to control of the chemistry appears to be the most
dependable solution to plugging and scaling at this time, how-
ever. This approach also applies to erosion and corrosion prob-
lems in some instances. Workable solutions for the direct-
fired reheater problems have not been reported.
28
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4.2 Measures to Improve Flue Gas Desulfurization
Availability
Various measures have been or can be used to main-
tain high levels of FGD availability. These measures which
are discussed below can be grouped into maintenance methods,
operating techniques, and design concepts.
Maintenance Methods
The maintenance methods applied by La Cygne and
Sherburne County have successfully maintained a high system
availability. The important factors in these maintenance
programs are: (1) taking one or more modules off-line each
night for inspection and cleaning, (2) use of a separate
maintenance crew trained to work on the FGD system, and (3)
a general dedication to gaining a better understanding of the
system and how to maintain it better.
Operating Techniques
There are several operating techniques that have been
or can be used to contribute to maintaining a high FGD system
availability. Over and underspray of mist eliminators (de-
misters) removes deposits from the mist eliminators. Operating
with an open loop water balance has historically benefited the
FGD system. Automatic pH and process control result in more
stable operation and tend to prevent major failures such as
massive scaling. Finally, a staff of operators and technicians
to work with the FGD system on a daily basis is very important.
29
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Design Concepts
Each of the FGD systems examined in this study dif-
fers somewhat in design concept. Some of the concepts that
have been or potentially can be successful in enhancing avail-
ability are: (1) dry particulate removal before the FGD system
with an electrostatic precipitator (ESP), (2) dry flue gas
booster fan between the ESP and scrubber rather than a wet fan
after the scrubber, (3) adequate sparing of pumps, valves,
lime/limestone feed systems, packing gland water systems, etc.,
(4) spray tower scrubber configuration, (5) adequate instrumen-
tation for pH, SC>2, additive use, etc. with automatic controls,
(6) indirect reheat of flue gas, and (7) adequate particle
dropout area to reduce solids carryover to the mist eliminators,
The areas of improvement discussed in this section
represent a composite of experience at several specific FGD
units. Future FGD units might be expected to include many of
these imp ro vemen t s .
30
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APPENDIX A
Availability Calculations
31
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The calculations of the availability of the station
with FGD assuming a five module FGD unit without a spare are
shown below. For a FGD modular availability of 70 percent, the
availability of the station with FGD is given by the product
of the FGD unit availability and the station availability.
Availability = (.70)5 (.75)
= (.17) (.75)
= .13
For a FGD modular availability of 90 percent, the availability
of the station with FGD is given by the same calculation.
Availability = (.9)5 (.75)
= (.59) (.75)
= .44
If a spare module is added to the FGD unit, the availability of
the station with FGD is improved as shown below.
Availability = [(. 9) * + 6(. 9) * (. 1)] (.75)
= (.53 + .35) (.75)
= (.88) (.75)
.66
32
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BIBLIOGRAPHY
33
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BIBLIOGRAPHY
AN-184 Anderson, Andy, Private communications. Kentucky
Utilities, 12 May 1977.
BE-478 Beard, J.B., Private communications, Kentucky Utili-
ties Co., Lexington, KY, 12 July 1977.
DI-R-161 Dickerman, James C., et al., Comparison of the avail-
ability and reliability of equipment utilized in the
electric utility industry, draft report. EPA Contract
No. 68-02-1319, Task 12, Radian Project No. 200-045-62.
Austin, TX, Radian Corporation, December 1976.
ED-059 Edison Electric Institute, Prime Movers Committee,
Equipment Availability Task Force, EEI equipment
availability summary report on trends of large mature
fossil units categorized by fuel and in commercial
operation prior to January 1, 1971. N.Y., Oct. 1976.
HE-258 Heacock, Frank A., Jr. and Robert J. Gleason, "Scrubber
surpasses 90% availability", Elect. World 1975 (May
15), 42.
KR-115 Kruger, R.J. and M.F. Dinville, "Northern States
Power Company Sherburne County Generating Plant
limestone scrubber experience". Presented at the
Utility Representative Conference on Wet Scrubbing,
Las Vegas, NV, Feb. 1977.
MU-155 Mundth, Lyman K., Private communication, Arizona Public
Service Co., Phoenix, AZ, 20 July 1977.
34
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BIBLIOGRAPHY (Continued)
NA-325 National Electric Reliability Council, 6th Annual
Review of Overall Reliability and Adequacy of the
North American Bulk Power Systems. July 1976.
PE-259 PEDCo Environmental, Inc., Flue Gas Desulfurization
Systems, Jan., Feb., March 1977, summary report. EPA
Contract No. 68-02-1321, Task No. 28, Cincinnati, OH,
1977.
PE-267 Pernick, S.L., Jr., Private communication, Manager,
Environmental Affairs, Duquesne Light, Pittsburgh, PA,
9 December 1976.
PE-287 Pernick. S.L., Private communication, Duquesne Light,
Pittsburgh, PA, 11 August 1977.
PE-288 PEDCo Environmental Inc., Summary report, Flue gas
desulfurization systems, June - July 1977. EPA
Contract No. 68-01-4147, Task No. 3. Cincinnati, OH,
1977.
35
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TECHNICAL REPORT DATA
(Please read Inunctions on the reverse before completing)
1. REPORT NO.
EPA~600/7-78-031a
2.
3. RECIPIENT'S ACCESSION NO.
4.
TITLE AND SUBTITLE The Effect of Flue Gas Desulfurization
Availability on Electric Utilities
Volume I. Executive Summary
5. REPORT DATE
March 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
R. D. Delleney
8. PERFORMING ORGANIZATION REPORT NO.
78-200-187-07-13
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
P.O. Box 9948
Austin, Texas 78766
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
68-02-2608, Task 7
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
Task Final; 4-12/77
14. SPONSORING AGENCY CODE
EPA/600/13
is.SUPPLEMENTARY NOTES EPA project officers are J.E. Williams (IERL-RTP, 919/541-2483)
and K. R. Durkee (OAQPS/ESED, 919/541-5301).
i6. ABSTRACT The report gives results of an analysis of the effect of the availability of a
flue gas desulfurization system on the ability of an individual power plant to generate
electricity at its rated capacity. (The availability of anything te the fraction of time
it is capable of service, whether or not it is actually in service.) Also analyzed are
its effects on a power generating system (a group of several coal-, oil-, and gas-
fired power plants plus nuclear and hydroelectric plants).
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Flue Gases
Desulfurization
Electric Utilities
Alkalies
Scrubbers
Calcium Oxides
Limestone
Sulfur Dioxide
Dust
Air Pollution Control
Stationary Sources
Alkali Scrubbing
Particulate
Venturi/Spray Towers
Mist Eliminators
13B
2 IB
07A,07D
07B
08G
11G
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
35
20. SECURITY CLASS (This page I
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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