United States Industrial Environmental Research EPA-600 7-79-199a
Environmental Protection Laboratory August 1979
Agency Research Triangle Park NC 27711
Survey of Flue Gas
Desulfurization Systems:
Duck Creek Station,
Central Illinois Light Co.
Interagency
Energy/Environment
R&D Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
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The nine series are:
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This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
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tems. The goal of the Program is to assure the rapid development of domestic
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EPA-600/7-79-199a
August 197S
Survey of Flue Gas
Desulfurization Systems
Duck Creek Station,
Central Illinois Light Co.
by
Bernard A. Laseke, Jr.
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati. Ohio 45246
Contract No. 68-02-2603
Task No. 24
Program Element No. EHE624
EPA Project Officer: Norman Kaplan
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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TABLE OF CONTENTS
Figures
Tables
c
Acknowledgment
Summary
1. Introduction
2. Facility Description
3. Flue Gas Desulfurization System
Background Information
Process Description
Process Design
Process Chemistry: Principal Reactions
Process Control
4. FGD System Performance
Background Information
Operating History and Performance
Problems and Solutions
Removal Efficiency
System Economics
Appendix A, Plant Survey Form
Appendix B. Plant Photographs
Page
iii
iv
vi
vii
1
2
10
10
14
23
36
40
44
44
45
46
50
51
A-l
B-l
11
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LIST OF FIGURES
No. Paqe
1 Overview of Duck Creek Plant Including All Major
Facilities, Accesses, and Waterways 3
2 Major Components of the Coal/Limestone Handling
Network at the Duck Creek Plant 6
3 Simplified Process Flow Diagram of Duck Creek 1
Power Plant and Emission Control System 8
4 Duck Creek 1 FGD Limestone Storage and
Preparation Facility 15
5 Duck Creek 1 FGD System Scrubbing Circuit 17
6 Cutaway View of a Duck Creek 1 FGD Scrubber Module 19
7 Duck Creek 1 Duct Work and Damper Arrangement 22
8 Duck Creek 1 Waste Disposal and Water Return Loop 24
111
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LIST OF TABLES
No. Page
1 Data Summary: Duck Creek 1 ix
2 Characteristics of Coal Fired at Duck Creek 4
3 Design, Operation, and Emission Data: Duck Creek 1 9
4 Duck Creek 1 FGD System Bench-scale Test Results 12
5 Results of the E.D. Edwards Pilot Plant Test Program 13
6 Specifications and Consumption Rates of Duck Creek
Performance Coal 25
7 Design Parameters of Duck Creek 1 ESP 26
8 Design Parameters of Duck Creek 1 FGD System 27
9 Design Parameters and Operating Conditions of Duck
Creek 1 Scrubbers 29
10 Design Parameters and Operating Conditions of
Duck Creek 1 Mist Eliminators 30
11 Design Parameters and Operating Conditions of Duck
Creek 1 Dampers 31
12 Design Parameters and Operating Conditions of Duck
Creek 1 Induced-draft Fans 33
13 Design Parameters and Operating Conditions of Duck
Creek 1 Pumps 34
14 Design Parameters and Operating Conditions of Duck
Creek 1 Tanks 34
15 Design Parameters and Operating Conditions of Duck
Creek 1 Limestone Storage Facilities 36
(continued)
iv
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LIST OF TABLES (continued)
No. Page
16 Design Parameters and Operating Conditions of Duck
Creek 1 Limestone Preparation Facility 37
17 Design Parameters and Operating Conditions of Duck
Creek 1 Waste Disposal System 38
18 Duck Creek 1 D-scrubber Module Performance History 47
19 Results of the D-scrubber Module Test 50
v
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ACKNOWLEDGMENT
This report was prepared under the direction of Mr. Timothy
W. Devitt. The principal author was Mr. Bernard A. Laseke. •
Mr. Norman Kaplan, EPA Project Officer, had primary respon-
sibility within EPA for this project report. Larry Haynes,
Environmental Manager, Central Illinois Light Company, provided
information on plant design and operation.
VI
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SUMMARY
The Duck Creek plant is a new coal-fired power-generating
station owned and operated by the Central Illinois Light Company
(CILCo). It is situated in an unreclaimed strip-mining area near
Canton, Illinois. The current capacity of the plant with one
coal-fired power-generating unit is 416 MW (gross). Duck Creek
1, the existing unit, was placed in commercial service on June 1,
1976. Duck Creek 2, 3, and 4 are three planned additional units
of similar capacity scheduled for commercial operation in 1982,
1989, and 1992, respectively. This will bring the total station
capacity to approximately 2000 MW.
Duck Creek 1 fires a high-sulfur, bituminous-grade, Illinois
coal having maximum sulfur and ash contents of 4.0 and 18.0
percent. To enable the unit to meet Federal New Source Per-
formance Standards, it is equipped with an emission control
system for particulate and sulfur dioxide control.
Primary particulate control is provided by two parallel
electrostatic precipitators (ESP's) with a design removal effi-
ciency of 99.8 percent. The ESP's are supplied by Pollution
Control-Walther. Primary sulfur dioxide control is provided by a
limestone flue gas desulfurization (FGD) system consisting of
four parallel 25 percent-capacity scrubbing modules with a total
removal efficiency of 85 percent. The FGD system is supplied by
Riley Stoker/Environeering.
The utility originally planned to install only one 25 per-
cent capacity (100-MW equivalent) scrubbing module to conduct a
thorough high sulfur coal test program. The data obtained was to
have been used to design the remaining three modules. Approval
of this plan, which was originally granted at the State level,
Vll
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was later revoked by the U.S. EPA, which required the entire
plant to comply with New Source Performance Standards. A consent
decree granted CILCo by the EPA gave the utility a variance to
burn high sulfur coal from July 1, 1976, to April 1, 1977.
During this period, one scrubber module (completed by June 1976)
would remain in the gas path and remove sulfur dioxide from 25
percent of the boiler flue gas. The timetable for the installa-
tion of the remaining modules was accelerated to August 1978.
During the interim period between the end of the variance and the
completion of the remaining modules, low sulfur coal would be
burned in the boiler in order to comply with standards.
The first scrubbing module was placed in service on July 1,
1976, and operated intermittently throughout the remainder of the
year and for approximately one month in early 1977. Several
problems, including plugging, scaling, corrosion, and materials
failure, were encountered during this period. As a result of
this initial operating experience, CILCo and Riley Stoker/Envi-
roneering made some design changes to both the existing and
planned scrubbing modules during the April 1977 to August 1978
period when low sulfur coal was burned. On July 23, 1978, the
three remaining scrubbing modules were completed and all four
modules were placed in the gas path for treatment of high sulfur
coal flue gas.
Central Illinois Light Company reported the total capital
cost of the system to be $37,540,000, including $33,740,000 for
the system and all ancillary equipment and $3,800,000 for the
sludge disposal pond. Based on a unit gross generating capacity
of 416 MW, this amounts to $90.2/kW. Actual annual cost figures
are not yet available; however, based on the limited operation of
one module, CILCo estimates that total annual cost will be
$13,921,000, including $7,539,000 for variable charges and
$6,382,000 for fixed charges. Based on a net unit rating of 400
MW and a capacity factor of 65 percent, this amounts to 6.11
mills/kWh.
Table 1 summarizes data on the facility and the FGD system.
viii
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TABLE 1. DATA SUMMARY: DUCK CREEK 1
Gross rating, MW
Net rating, MW
Fuel
Average fuel characteristics:
Heating value, kJ/kg (Btu/lb)
Ash, percent
Moisture, percent
Sulfur, percent
Chloride, percent
FGD process
FGD system supplier
Application
Status
Startup dates:
Initial5
Commercial
Design removal efficiency, percent
Particulate
Sulfur dioxide
Makeup water, liters/min per MW (gal'/min per MW)
Economics
Capital, $/kW (gross)
Annual, mills/kWh (net)
416
400
Coal
24,523 (10,543)
9.12
18.0
3.30
0.03
Limestone
Riley Stoker/
Environeering
New
Operational
July 1976
August 1978
99.8
85.3
5.65 (1.49)
90.2
6.11
Design fuel specifications for high sulfur Illinois coal.
Boiler and ESP commenced operation in June 1976. One FGD module
commenced operation in July 1976. Full commercial operation with
all four FGD modules commenced in August 1978.
Particulate removal provided by ESP's.
Design makeup water requirements.
IX
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SECTION 1
INTRODUCTION
The Industrial Environmental Research Laboratory (IERL) of
the U.S. Environmental Protection Agency (EPA) has initiated a
study to evaluate the performance characteristics and reliability
of flue gas desulfurization (FGD) systems operating on coal-
fired utility boilers in the United States.
This report, one of a series on such systems, covers the
Duck Creek plant of the Central Illinois Light Company (CILCo).
It includes pertinent process design and operating data, a de-
scription of major startup and operational problems and solu-
tions, atmospheric emissions data, and capital and annual cost
information.
This report is based on information obtained during and
after a plant inspection conducted for PEDCo Environmental per-
sonnel on June 9, 1977, by CILCo. The information presented in
this report is current as of October 1978.
Section 2 provides information and data on facility design
and operation; Section 3 provides background information and a
detailed description of the FGD process; Section 4 describes and
analyzes the operation and performance of the FGD system.
Appendices A and B contain details of plant and system operation,
economic data, and photos of the installation.
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SECTION 2
FACILITY DESCRIPTION
The Duck Creek plant is a new coal-fired power-generating
station owned and operated by CILCo. Located in Fulton County,
Illinois, approximately 65 km (40 mi) southwest of Peoria, the
plant site consists largely of unreclaimed strip-mining land
situated in a relatively flat, rural area. There are no other
major industrial facilities within the immediate area. The
nearest population center is Canton (a town of about 14,000
people), which is approximately 8 km (5 mi) southwest of the
plant.
2
The plant site proper covers an area of approximately 36 km
(9000 acres), approximately 4 km (2.5 mi) from the Illinois
River. Duck Creek, an intermittent stream carrying only the
runoff from the immediate watershed, runs through the site. The
plant's cooling pond was created by constructing an earthen dam
across this creek. The dam, which is a zoned earthwork structure
with a crest length of 520 meters (1700 ft) and a maximum height
of 37 meters (120 ft), forms a reservoir covering an area of
2
approximately 7.36 km (1820 acres). The powerhouse is located
in an unmined section that is capable of withstanding the heavy
loads associated with the powerplant equipment and foundations.
At the present time two coal mines on the site remain active. A
general overview of the Duck Creek plant site, including all
major facilities, accesses, and waterways, is provided in Figure
1.
Duck Creek 1 is equipped with its own steam generator and
turbine. The dry-bottom, pulverized-coal-fired steam generator
is a balanced-draft, front-fired, single reheat unit supplied
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'.
ILLINOIS RIVER
\ EXISTING ROAD '
SECONDARY PLANT ACCESS)
\ rUNIT 4(FUTURE) /LIMESTONE STORAGE ^
^ rUNIT 3(FUTURE/ _-'r _.
IrUNI
UNIT 2(FUTURE)
ASTE STORAG
(UNIT 1)
OrtTH FOUR UNITS
OPERATING) ,
V"
DROP STRUCTURE
HATER CONTROL STRUCTURE(FUTURE\Jfc
Figure 1. Overview of Duck Creek plant, including all major
facilities, accesses, and waterways.
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by Riley Stoker. It produces 1360 Mg (3,000,000 Ibj per hour of
superheat steam at 540°C (1005°F) and 18 MPa (2600 psig), and
1110 Mg (2,450,000 Ib) per hour of reheat steam at 540°C (1005°F)
and 3.3 MPa (481 psig). The turbine generator is a 416-MW
(gross), 17-MPa (2400 psig), 538°C (1000°F), 3.4-kPa (1.0 in.
Hg), 3600-rpm unit supplied by General Electric. The station
also contains one auxiliary boiler, which is used for plant
startups or for powering a house turbine generator. The auxilary
boiler, a shop-assembled unit supplied by Riley Stoker, fires No.
2 fuel oil and produces 23 Mg (50,000 Ib) per hour of steam at
1.8 MPa (250 psig).
The plant burns high sulfur Illinois coal and low sulfur
Colorado coal. Originally, the plant was designed to burn only
a high sulfur bituminous grade of Illinois coal. This coal is
supplied primarily by United Freeman's Crown and Buckheart mines
in Fulton County, near the plant site. The plant also burns a
low sulfur bituminous grade of coal obtained on a spot-purchase
basis from several Colorado mines. It was necessary to find a
low sulfur coal supply source to enable the plant to meet Federal
New Source Performance Standards regarding sulfur dioxide emis-
sions during the interim period between the end of the variance
(April 1, 1977) and commercial operation of the entire FGD system
(August 1, 1978). Table 2 presents average characteristics of
these coals.
TABLE 2. CHARACTERISTICS OF QOAL FIRED AT DUCK CREEK
Source
Characteristics
Value (average)
Illinois
Colorado
Heating value, kJ/kg (Btu/lb)
Ash, percent
Moisture, percent
Sulfur, percent
Chloride, percent
Heating value, kJ/kg(Btu/lb)
Ash, percent
Sulfur, percent
24,523 (10,543)
9.12
18.0
3.3
0.03
24,750 (10,640)
6.97
0.41
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A highly flexible coal-handling system capable both of pro-
viding for the ultimate plant capacity of 2000 MW (net) and of
transporting limestone for the FGD system was developed for Duck
Creek. The flexibility of the coal-handling system was provided
by extending the stacker/reclaimer's travel some 90 m (300 ft),
thereby allowing additional space for limestone storage. A
series of interlocks is included in the system to minimize the
possibility of accidently conveying coal to the limestone area or
limestone to the coal area.
The coal/limestone handling system is designed to accommo-
date deliveries by rail, but it also includes provisions for
truck shipments because of the potential for barge unloading on
the Illinois River. Coal or limestone can be conveyed from the
unloading area to the yard storage area or directly to the plant
at a maximum rate of 1.8 Gg (2000 tons) per hour. Coal or lime-
stone diverted to yard storage is deposited in either live or
dead storage piles. Coal or limestone going directly to the
plant is transported by separate conveyors after passing through
a switch house. Limestone is conveyed on a single 1.8-Gg (2000-
ton) belt to the crushing and milling building, whereas the coal
is transferred to the breaker house and sample house before being
burned in the boiler. Figure 2 illustrates the major components
of the Duck Creek coal/limestone handling network.
To meet Federal New Source Performance Standards, Duck Creek
1 is equipped with an emission control system that includes
electrostatic precipitators (ESP's) and an FGD system. Primary
particulate control is provided by two parallel, cold-side ESP's
supplied by Pollution Control-Walther and designed to remove 99.8
percent of the inlet particulate matter. Primary sulfur dioxide
control is provided by four parallel, wet-limestone, rod-deck
(Ventri-Sorber) scrubber modules supplied by Riley Stoker/En-
vironeering and designed to remove 85 percent of the inlet sulfur
dioxide. All or part of the flue gas can be bypassed around the
scrubber modules by manipulating bypass dampers and module
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(Ti
LIMESTONE SUPPLY FOR I
UNITS 3 AND 4(FUTURE) ,
DEAD STORAGE
(FUTURE)
UNIT 4(FUTUR£)] |l ] ^ /CONVEYOR
j—ffl .HOUSE
UNIT 3(FUTURE)| || j \ *"• BREAKER
HOUSE
UNIT 1
UNIT 2(FUTURE)
EMERGENCY RECLAIM
DEAD COAL STORAGE
DEAD LIMESTONE STORAGE
CONVEYOR
'TRIPPER CONVEYORS
PLANT-SUPPLY CONVEYORS—^
\ LIMESTONE CONVEYOR
\
\
\IMIIIIIIIIII
STACKER/RECLAIMER
TRUCK RECEIVING
•TRAIN POSITIONER
I I II I I I I I
ROTARY CAR DUMPER
LIVE LIMESTONE STORAGE
1 I I I I I I I I I I I I I I I I II I N
Figure 2. Major components of the coal/limestone handling
network at the Duck Creek plant.
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isolation dampers. The bottom ash, fly ash, and scrubbing wastes
are disposed of in an onsite 65-acre sludge pond lined with a
natural impermeable material.
The Federal Clean Air Act of 1972 limits particulate and
sulfur dioxide emissions to 43 ng/J (0.1 lb/10 Btu) and 516 ng/J
(1.2 lb/10 Btu) of heat input to the boiler. Actual particulate
emissions, as measured by the utility during performance tests,
ranged from 47.6 mg/m3 (0.0208 gr/scf) to 191.5 mg/m3 (0.0837
gr/scf).* Actual sulfur dioxide emissions, as measured by the
utility during performance tests, were approximately 252 ppm.
Based on an inlet concentration of 3000 ppm from the combustion
of 3.3 percent sulfur coal, this translates into an FGD system
removal efficiency of 91.6 percent, which is above the 85.3
percent design removal efficiency for 4.0 percent sulfur coal.
Figure 3 provides a process 'flow diagram of Duck Creek 1,
including the power plant, emission control system, reagent
preparation facility, and sludge disposal area. Table 3 presents
data on plant design, operation, and atmospheric emissions.
All measurements are expressed on dry basis.
Performed during single module operation conducted from July
1976 to April 1, 1977.
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00
I 1
cuusirm
FEED
ira
H J
\s
_j
V
kjs ;
y
A
*n
Figure 3. Simplified process flow diagram of Duck Creek 1
power plant and emission control system.
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TABLE 3. DESIGN, OPERATION, AND EMISSION DATA:
DUCK CREEK 1
Generating capacity, MW:
Gross
Net without FGD
Net with FGD
Maximum coal consumption, Mg/h (tons/h)
Maximum heat input, GJ/h (10 Btu/h)
Maximum flue gas rate, m /s (acfm)
Flue gas temperature, °C (°F)
Unit heat rate, kJ/net kWh (Btu/net kWh}
Unit capacity factor, percent (1977)
Emission controls:
Particulate
Sulfur dioxide
Particulate emission rate:
Limit, ng/J (lb/106 Btu)
Actual,mg/m3 (gr/scf)
Sulfur dioxide emission rate:
,6
Limit, ng/J (lb/10
Actual, ppm
Btu)
416
410
400
174 (192)
4,265 (4,040)
668 (1,415,610)
135 (275)
10,380 (9,840)
55 - 60
Electrostatic
precipitators
Rod-deck scrubbers
43 (0.1)
47.6 - 191.5
(0.0208-0.0837)
516 (1.2)
252 a
Measurement obtained during single module operation conducted from
July 1976 to April 1, 1977.
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SECTION 3
FLUE GAS DESULFURIZATION SYSTEM
BACKGROUND INFORMATION
Because environmental constraints prevented expansion of
their existing plants, in the late 1960's CILCo began searching
for locations that were capable of ultimately supporting 2000 MW
of coal-fired capacity and included an onsite pond-treatment
facility for cooling purposes. By early 1970 the search was
narrowed to three possible sites. After determining the Duck
Creek site to be the best of the three, CILCo officials commis-
sioned a thorough feasibility study to determine representative
cost estimates for plant construction, including the use of a
cooling pond. This feasibility study indicated that the Duck
Creek site could support the ultimate plant capacity and that the
use of a cooling pond offered substantial capital and annual cost
savings over mechanical- and natural-draft cooling towers.
Compliance with New Source Performance Standards governing
sulfur dioxide and particulate emissions was also considered at
this stage of development. Investigations revealed that com-
pliance with particulate emission regulations could readily be
achieved with the use of ESP's or scrubbers. Compliance with
sulfur dioxide emission regulations, however, would be more
difficult. Two basic alternatives were considered: burning low
sulfur western coal or burning high sulfur coal and installing
FGD equipment. The former alternative was rejected for several
reasons, including the premium paid for low sulfur coal; higher
transportion costs; the presence of abundant supplies of cheap,
high sulfur coal in mines near the plant site; and the adverse
effect of low sulfur coal on ESP performance.
10
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Two emission control strategies were evaluated for high
sulfur coal application: two-stage particulate and sulfur
dioxide wet scrubbing and an ESP-FGD combination for separate
collection of particulate and sulfur dioxide. The ESP-FGD alter-
native was given primary consideration because it would (1)
result in a capital cost saving of $2,000,000, (2) reduce aux-
iliary power requirements by 10 MW, (3) reduce total annual cost,
(4) offer greater mechanical reliability, and (5) make it pos-
sible to bypass the FGD modules during forced outages without
reducing the boiler load.
In 1972 and 1973 CILCo and Riley Stoker (the boiler supplier
for Duck Creek 1) initiated an intensive program to evaluate
various FGD processes and designs that could be used in conjunc-
tion with an ESP for high sulfur coal service. In late 1972 a
bench-scale program employing a 0.7-m /s (1500-acfm)* laboratory
test unit was conducted. This program involved the use of a new,
patented scrubber design developed by Environeering (formerly
National Dust Collector), a firm later acquired by Riley Stoker.
Originally, Environeering held patents (which expired in early
1972) on a marble-bed design (Marble Bed hydro-filter). Prior to
the expiration of these patents, however, Environeering had
developed a new, patented design using rod-decks in a vertical,
countercurrent spray tower (Ventri-Sorber scrubber). The bench-
scale results (summarized in Table 4) were very encouraging.
Using limestone slurry, this spray tower achieved sulfur dioxide
removal efficiencies in the 80 to 88 percent range on inlet
concentration levels of 2000 to 3000 ppm at pressure drops of 2.1
kPa (8.5 in. H20).
0.5 MW equivalent electrical capacity.
11
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TABLE 4. DUCK CREEK 1 FGD SYSTEM BENCH-SCALE TEST RESULTS
Parameters
Gas flow rate, m /min (acfm)
Liquid flow rate, liter s/s
(gal/min)
Pressure drop, kPa (in. H?O)
Liquid/gas ratio, liter s/m^
(gal/103 acf)
Sulfur dioxide inlet concentra-
tion, ppm
Sulfur dioxide outlet concentra-
tion, ppm
Sulfur dioxide removal effi-
ciency, percent
Test conditions
Block 1
48 (1700)
5.4 (85)
2.1 (8.5)
6.7 (50)
2000
238
88.1
Block 2
48 (1700)
5.4 (85)
2.1 (8.5)
6.7 (50)
3000
555
81.5
As a result of this successful bench-scale test program, a
3
185 m /min (6500 cfm) limestone pilot plant costing over $1
million was installed and operated from March 1973 to December
1973 at CILCo's E.D. Edwards Station. The pilot plant included a
rod-deck scrubber and all the related equipment, which was tied
into the duct work of Edwards 3, a coal-fired unit that included
an ESP for primary particulate control. During the course of
this 9-month test program, the pilot operated over 5100 hours on
boiler flue gas and achieved sulfur dioxide removal efficiencies
above 90 percent on 2 to 3 percent sulfur coal. The most signif-
icant information gained from this plant concerned construction
materials. Originally, the pilot scrubber, including all inter-
nals and rods, was constructed of unlined carbon steel. Wide-
spread corrosion and ultimate failure of the carbon steel shortly
after the outset of the program necessitated replacement of the
internals and rods with Hastelloy G and 316L stainless steel.
The results of the Edwards pilot plant program are summarized in
Table 5.
12
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TABLE 5. RESULTS OF THE E. D. EDWARDS PILOT PLANT TEST PROGRAM
Gas capacity
Nominal, m /min (ft /min)
3 3
Maximum, m /min (ft /min)
Application
Period of performance
Total operation time, h
Coal sulfur, percent
Sulfur dixoide inlet concentra-
tion, ppm
Pressure drop, kPa (in.
H20)
Liquid recirculation rate,
liters/s (gal/min)
Liquid/gas ratio, liters/m
(gal/1000 acf)
Sulfur dixoide outlet concentra-
tion , ppm
Sulfur dioxide removal
efficiency, percent
185 (6500)
193 (6800)
Coal-fired flue gas
Mar. 1973 - Dec. 1973
5100
2.0 - 3.0
2000
2.1 (8.6)
20.5 (325)
6.7 (50)
170
91.5
In November 1974, following the completion of the Edwards
pilot plant test program, CILCo awarded Riley Stoker/Environeer-
ing a contract to supply a limestone FGD system for Duck Creek 1
The contract originally specified that only one module having a
25 percent gas capacity (100 MW) be installed for testing and
evaluation on high sulfur coal. The remaining three modules
would be installed at a later date, and any design modifications
dictated by the module evaluation program would be incorporated.
This approach was eventually rejected by the U.S. EPA, and in
August 1976 CILCo awarded Riley Stoker/Environeering a contract
to supply the remaining three modules for operation by August 1,
1978.
13
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PROCESS DESCRIPTION
The limestone slurry FGD system operating at Duck Creek was
designed, fabricated, and installed by Riley Stoker/Environeering
in accordance with specifications by Gilbert/Commonwealth Asso-
ciates for operating conditions and equipment requirements. The
FGD system consists of four parallel rod-deck scrubber modules
designed to treat the entire boiler flue gas stream of 668 m /s
(1,415,600 acfm) at 135°C (275°F). The FGD system includes
limestone storage, preparation, and handling equipment; a duct
work and damper arrangement; waste disposal and pond water return
equipment; and service water and compressed air equipment.
The Duck Creek FGD system can be conveniently described in
terms of six basic operations: (1) limestone preparation, (2)
limestone slurry handling, (3) gas treatment, (4) mist elimina-
tion, (5) gas bypass, and (6) solids disposal and water return.
Limestone Preparation
Limestone for FGD operations is supplied by the Columbia
Quarry Company in Valmeyer, Illinois, approximately 320 km (200
mi) from the plant site. The limestone is delivered to the plant
by rail as 1.9 cm x 0 cm (3/4 in. x 0 in.) rock containing no
less than 95 percent calcium carbonate. The limestone is stored
in a feed bin with a 24-h supply capacity and transferred to a
wet ball mill, where it is ground by a weigh feeder at a maximum
rate of 36 Mg (40 tons) per hour. The limestone is ground to a
90 percent minus 200-mesh powder and the slurried effluent from
the mill is discharged to a mill slurry tank, which is a collec-
tion sump that serves as a reservoir for the slurry pumps. The
slurry pumps discharge the milled limestone to a classifier at a
rate of 50 liters/s (800 gal/rain). The oversize stone (exceeding
90 percent through 200 mesh) is returned to the front of the mill
for regrinding. Overflow from the classifier returns to the mill
slurry tank. The effluent from the milling system consists of a
35 to 40 percent solids limestone slurry. Figure 4 is a simpli-
fied diagram of the Duck Creek limestone preparation system.
14
-------
LIMESTONE
MAKEUP
HATER
LIMESTONE
FEED
BIN
WEIGH
FEEDER
TO SLURRY
STORAGE TANK
WET BALL MILL
1 OPERATIONAL
1 SPARE
MILL SLURRY
TANK
1 OPERATIONAL
1 SPARE
MILL SLURRY
PUMP
1 OPERATIONAL
1 SPARE
Figure 4. Duck Creek 1 FGD limestone storage and
preparation facility.
15
-------
Limestone Slurry Handling
The ground limestone slurry (35 to 40 percent solids) from
the milling operation is stored in a 301,000-liter (79f500-gal)
agitated storage tank. Two agitators/ one operational and one
spare, maintain slurry suspension and prevent settling. The
slurry is transferred from the storage tank to the pumphouse
through a continuous-feed supply manifold that feeds back to the
storage tank. Taps off the return pipe provide a flow of slurry
to each recirculation tank for use in the scrubbing module or
back to the mill slurry tank.
The limestone slurry tapped from the storage tank return
loop is added to the liquid scrubbing circuit of each module
through a recirculation tank, which'is an agitated, 606,000-liter
(160,000-gal) vessel that receives fresh limestone slurry from
the storage tank, spent solution from the scrubber module, and
return water from the pond. Recirculation-tank slurry is contin-
uously pumped from the base of the recirculation tank through
three 51-cm (20-in.) diameter lines to 12 spray heads located at
the top of each scrubber module. Pumping capacity is provided by
two 497 liters/s (7875 gal/min) operational pumps (one spare per
module). Discharge from the spray heads flows down through the
scrubber module, contacting the gas flowing upward through the
rod decks. Spent solution flows by gravity to the recirculation
tank, where chemical reactions are completed and reaction prod-
ucts and unused reagent are collected. Spent slurry is bled from
the recycle tank by a line off the recirculation pump discharge
header. Figure 5 shows a simplified diagram of the Duck Creek
FGD system liquid scrubbing circuit, including limestone slurry
handling, scrubbing, and recirculation.
Gas Treatment
The flue gas exits the boiler at 1140 m3/s (2,415,000 acfm)
and 446°C (835°F) at full load, then passes through half-size air
preheaters before entering two Pollution Control-Walther ESP's
connected in parallel. Each ESP treats 50 percent of the total
16
-------
MIST
ELIMINATION
SO? ABSORPTION
ZONE
ROD-DECK
SCRUBBER
4 OPERATIONAL
GAS INLET-
LIMESTONE
SLURRY
MAKEUP
WATER
SPRAY
PUMPS
8 OPERATIONAL
4 SPARE
MIST ELIMINATOR
WASHDOWN TANK
4 OPERATIONAL
BLEED TO WASTE
COLLECTION TANK
STORAGE
TANK
SCRUBBER
SLURRY RECIRCULATION
TRANSFER TANK
PUMP 4 OPERATIONAL
1 OPERATIONAL
3 SPARE
RECIRCULATION
PUMPS
8 OPERATIONAL
4 SPARE
Figure 5. Duck Creek 1 FGD system scrubbing circuit.
17
-------
gas flow. The ESP's are designed to remove 99.8 percent of the
inlet particulate when the inlet gas loading is 14.5 mg/m (6.34
gr/scf). The discharge gas from the ESP's enters a manifold
supplying four induced-draft fans. These fans overcome draft
loss in the boiler as well as in the ESP's and FGD system. They
are connected in parallel to a common duct that distributes the
gas to each scrubber module in the FGD system or to the bypass
duct.
Flue gas enters the base of each scrubber module, where it
is quenched to adiabatic saturation conditions. The quenched gas
flows upward through nine successive stages of rod decks, where
it contacts the scrubbing slurry in a countercurrent fashion.
The scrubbing slurry sprayed from the top of each module flows
downward through the rod decks. The rod decks provide intimate
gas/slurry contacting sites that enhance mass transfer of the
sulfur dioxide into the liquid phase, thus promoting sulfur
dioxide removal.
The cleaned, saturated gas stream in each module then exits
the spray zone, turns 90 degrees, and passes through horizontal
mist eliminators, where entrained droplets of moisture and slurry
are removed. The discharge duct from each module feeds gas into
the breeching, through which it enters the stack approximately 20
m (65 ft) above grade. Figure 6 provides a cutaway view of the
rod-deck scrubber and mist eliminator used in the Duck Creek FGD
system.
Scrubbed, saturated gas exits the FGD system and enters the
stack through the breeching section without benefit of reheat.
The "wet stack" is a 150-m (500-ft) chimney with a Cor-Ten steel
flue lined with flake glass. Four bottom hoppers are included in
the stack for collection of moisture and slurry droplets that
fall out of the flue gas because of a difference in the veloc-
ities of the droplets and the gas.
Gas Bypass
The FGD system is equipped with a complex network of ducts
and dampers that allows part or all of the flue gas to bypass any
18
-------
HIST ELIMINATOR
SLURRY
SPRAY HEADS
QUENCH
GAS INLET
ROD DECKS (8)
ROD DECK (1)
SPENT
SLURRY
Figure 6. Cutaway view of a Duck Creek 1 FGD scrubber module.
19
-------
or all of the scrubber modules during outages or emergencies.
The major components are the bypass breeching, control damper,
bypass breeching damper, induced-draft fan isolation dampers, and
scrubber module isolation dampers.
Bypass Breeching—
A breeching section, which can accommodate all or part of
the flue gas flow, is provided for FGD gas bypass. It consists
of a straight duct run extending from the discharge side of the
induced-draft fans to the stack entry point. Flue gas enters and
exits the FGD system via a common inlet and discharge duct, which
routes gas to and from each of the scrubber modules. The common
inlet and discharge ducts exit the bypass breeching downstream of
the discharge side of the induced-draft fans and enter upstream
of the stack entry point. During partial or full load bypass
situations the flue gas can pass directly from the induced-draft
fans to the stack for discharge to the atmosphere.
Two important features of the breeching section are the
materials of construction and an emergency water spray. The
bypass breeching is constructed of Hastelloy G. This material
provides superior corrosion resistance under all gas conditions,
including the hot/dry environment associated with full bypass,
the warm/wet environment associated with partial bypass and
partial scrubbing, and the cool/saturated environment associated
with full scrubbing. The emergency water spray is situated in
the breeching just prior to the stack entry point. The purpose
of this system is twofold: (1) to provide emergency cooling in
the event of a high temperature excursion [exceeding 175°C (350°F)],
which could severly damage the stack liner, and (2) to provide
continuous cooling of the gas bypassing the FGD system so that
the condition of the gas passing through the stack is nearly
constant, thus extending the life of the liner.
Control Damper—
A control damper situated in the common duct downstream of
the discharge side of the induced-draft fans regulates gas flow
20
-------
to the stack so that a maximum of 25 percent of the design gas
flow of 648 m3/s (1,415,600 acfm) at 135°C (275°F) enters each
scrubber. Any gas flow in excess of the design value goes
directly to the stack.
Bypass Breeching Damper—
The bypass breeching is equipped with a single-louver shut-"
off damper that seals off the breeching, permitting flue gas to
enter the FGD system.
Induced-draft Fan Isolation Dampers—
Each of the four induced-draft fans is equipped with double-
inlet control dampers and a double-outlet damper so that any one
of the fans can be isolated from the flue gas path. The outlet
dampers, which are located on the discharge side of the induced-
draft fans, are double-louver, seal-air units that operate in
parallel. A seal-air fan pressurizes the area between the
dampers when they are in the closed position to prevent gas
leakage from the pressurized discharge duct back into the fan.
Scrubber Module Isolation Dampers—
Each of the four scrubber modules is also equipped with a
set of inlet and outlet dampers, so that any one of the modules
can be isolated from the flue gas path. The inlet dampers, which
are located in the inlet duct to each scrubber, are double-
louver, seal-air units that operate in parallel. A seal-air fan
pressurizes the area between the dampers when they are in the
closed position and prevents gas leakage into the scrubber during
maintenance periods or while the boiler is in service. The
outlet dampers, which are located in the outlet duct of each
scrubber, are double slide-gate dampers that operate in parallel.
Two seal-air fans are provided for each set of outlet dampers.
One operates continuously and pressurizes the damper drive mech-
anisms. The other pressurizes the area between the dampers when
both slide gates are in the closed position.
Figure 7 is a simplified diagram of the Duck Creek FGD
system duct work and damper arrangement.
21
-------
EMERGENCY OC
MATER
SPRAYS
ID FAN OUTLET
DAMPERS
ID FAN INLET
CONTROL
DAMPERS
ISOLATION
DAMPERS
Figure 7. Duck Creek 1 duct work and damper arrangement.
22
-------
Solids Pisposajl and Water Return
Spent scrubbing slurry is bled from the scrubber recircula-
tion lines as a 15 percent solids slurry containing reaction
products, unreacted limestone, and collected fly ash. The spent
slurry is transferred to a waste collection tank, where it is
combined with liquid waste streams from plant sumps, and then
discharged to an onsite sludge disposal pond. The pond, which is
lined with a natural impermeable material, covers approximately
2
263,000 m (65 acres). Bottom ash and collected fly ash are also
stored here. The waste solids present in the spent scrubbing
slurry settle out in the pond, and the supernatant is returned to
the plant for reuse. Recycled water is used in the recycle tanks
to maintain liquid levels and for sluicing the bottom ash and fly
ash to the disposal pond. Figure 8 is a simplified diagram of
the Duck Creek waste disposal and water return loop.
PROCESS DESIGN
Fuel
The Duck Creek 1 emission control system is designed to re-
move particulate and sulfur dioxide resulting from the combustion
of a high sulfur bituminous Illinois coal from nearby surface
mines. Table 6 presents specifications and consumption rates of
the performance coal.
Particulate Removal
Primary particulate control is provided by two half-size,
cold-side ESP's situated upstream of the FGD system. These
Pollution Control-Walther ESP's are new units that were installed
as original power plant equipment. Table 7 summarizes the design
parameters.
Sulfur Dioxide Removal
Primary sulfur dioxide removal is provided by a four-module
limestone FGD system situated downstream of the ESP's. Table 8
23
-------
to
SPENT
SLURRY
FRESH
LIMESTONE-
SLURRY
RECIRCULATION
TANKS (4)
PLANT SUNPS
RECYCLE
TO
SCRUBBER
RECIRCULATION
PUMPS (12)
FLY ASH/BOTTOM ASH
WASTE
COLLECTION
TANK
(1)
WASTE TRANSFER
PUMPS (2)
L
WASTE DISPOSAL
POND (1)
f-\ POND WATER
7 RETURN PUMPS
(2)
Figure 8. Duck Creek 1 waste disposal and water return loop.
-------
TABLE 6. SPECIFICATIONS AND CONSUMPTION RATES OF
DUCK CREEK PERFORMANCE COAL
Fuel
Grade
Source
Total raw coal (maximum), kg/h (Ib/h)
Sulfur (maximum), kg/h (Ib/h)
Hydrogen (maximum), kg/h (Ib/h)
Ash (maximum), kg/h (lb/h)°
Moisture (maximum), kg/h (Ib/h)
Volatile matter (maximum), kg/h (Ib/h)
Q
Fixed carbon (maximum), kg/h (Ib/h)
Heat input (maximum), GJ/h (10 Btu/h)
Pulverized coal
Bituminous
Illinois
173,839 (383,249)
7,058 (15,560)
10,430 (22,995)
31,291 (68,985)
39,983 (88,147)
60,844 (134,137)
78,227 (172,462)
4,260 (4,040)
Moisture free.
Moisture and ash free.
As received.
Based on a coal heat content of 24,523 kJ/kg 10,543 (Btu/lb)
25
-------
TABLE 7. DESIGN PARAMETERS OF DUCK CREEK 1 ESP
Number
Arrangement
Type
Supplier
Inlet gas conditions:
Volume, m /s (acfra)
Temperature, °C (°F)
Weight, kg/h (Ib/h)
Pressure, kPa (in. H7O)
3 *
Particulate, g/m (gr/acf)
Outlet gas conditions:
Volume, m /s (acfm)
Temperature, ° C (•F)
Weight, kg/h (Ib/h)
Pressure, kPa (in. H-O)
•> *
Particulate, mg/n {gr/acf)
Removal efficiency, percent
Two
Parallel
Cold side
Pollution Control-'-'alther
717 tl,520,000}
135 (275)
2,107,000 (4,646,000)
4.60 (18.4)
10.5 <4.57)
717 (1,520,000)
135 (275)
2,024,000 (4,463,100)
4.48 (17.9)
0.02 (0.009)a
99.Bb
Maximum guaranteed particulate emission level.
ESP maximum guaranteed removal efficiency based on a coal sulfur
content of 2 percent.
26
-------
TABLE 8. DESIGN PARAMETERS OF DUCK CREEK 1 FGD SYSTEM3
Inlet gas conditions:
Volume, m /s (acfm)
Temperature, °C (°F)
Weight, kg/h (Ib/h)
Pressure, kPa (in. H20)
Sulfur dioxide, kg/h (lb/h)
Particulate, kg/h (lb/h)
Outlet gas conditions:
Volume, m /s (acfm)
Temperature, °C (°F)
Weight, kg/h (lb/h)
Pressure, kPa (in. H_0)
Sulfur dioxide, kg/h (lb/h)
Particulate, kg/h (lb/h)
Sulfur dioxide removal efficiency, percent
€68 (1,415,600)
135 (275)
2,107,000 (4,646,000)
2.5 (10)
14,115 (31,120)
51 (113)
572 (1,211,000)
53 (127)
2,172,000 (4,788,424)
0.5 (2)
2,074 (4,572)
60 (132)
85.3
Maximum performance coal characteristics of 4 percent sulfur
and 18 percent ash.
27
-------
presents inlet and outlet gas conditions and design removal
efficiencies.
Rod-deck Scrubber
The rod-deck scrubber is a proprietary, second-generation
design scrubbing vessel developed by Riley Stoker/Environeering
and marketed under the name Ventri-Sorber Scrubber. The ver-
tical, multistage scrubber is a countercurrent gas-liquid flow
module which contains a series of rod decks arranged vertically
on staggered centers within the vessel. The rods in each rod
deck are 2.5 cm (1 in.) in diameter and spaced 2.5 cm (1 in.)
apart. Table 9 presents design parameters and operating con-
ditions of the scrubber module. Figure 6 presents a cutaway view
of the module, showing the overall arrangement as well as the
internals.
Mist Eliminator
Each scrubber module has a separate set of mist eliminators
arranged in a tilted-vertical position in the horizontal dis-
charge ducts. The mist eliminators are equipped with a fresh-
water wash system which consists of a common wash-down tank and
spray pumps and piping for each mist eliminator. The wash system
is capable of delivering 55 liters/s (885 gal/min) of freshwater
to each mist eliminator. The water is sprayed on the second mist
eliminator, then collected in the wash-down tank and reused on
the first mist eliminator. Table 10 presents design parameters
and operating conditions of the mist eliminators.
Gas Dampers
The flue gas bypass network is comprised of several bypass
dampers, isolation dampers, and seal-air fans which enable the
gas to bypass any or all of the scrubber modules and induced-
draft fans during forced outages without having to shut down the
unit or reduce the load. Table 11 presents design parameters and
operating conditions of the dampers.
28
-------
TABLE 9. DESIGN PARAMETERS AND OPERATING CONDITIONS
OF DUCK CREEK 1 SCRUBBERS
Number of modules
Type
Configuration
Shape
Flow pattern
Dimensions
Length, m (ft)
Width, m (ft)
Height, m (ft)
Number of stages
Number of spray heads
Arrangement of internals:
Number of rod decks
Geometry
Rod diameter (outer), cm (in.)
Rod spacing, cm (in.)
Materials of construction:
Shell
Internals
Rods
Inlet flue gas volume, m /s (acfm)
Inlet flue gas temperature, °C (°F)
Flue gas velocity, m/s (ft/s)
Pressure drop, kPa (in. H_O)
Liquid recirculation rate, liters/s (gal/min)
Liquid to gas (L/G) ratio, liters/m
(gal/103 acf)
Outlet flue gas volume, m/s (acfm)
Outlet flue gas temperature, °C (°F)
Maximum slurry feed rate, kg/min (Ib/h)
Rod deck
Vertical
Rectangular, inverted L
Countercurrent
12 (40)
1.5 (5)
12 (40)
9
12
Vertical, staggered
off center
2.5 (1)
2.5 (1)
Carbon steel
Hastelloy G
316L stainless steel
167 (353,900)
135 (275)
3.9 (13)
2 (8)
994 (15,750)
6.8 (50)a
143 (302,750)
53 (127)
345 (45,600)
a
Approximate L/G value at saturated gas conditions.
29
-------
TABLE 10.
DESIGN PARAMETERS AND OPERATINGv.CONDITIONS
OF DUCK CREEK 1 MIST ELIMINATORS
Number
Number per module
Type
Configuration
Shape
Number of stages
Number of passes
Distance between stages, m (ft)
Distance between vanes, cm (in.)
Materials of construction
Wash system:
Hater source
Point of addition/collection
Hash direction
Frequency
Rate
Pressure
4
1
Chevron
Vertical-tilted 35
degrees fron vertical
plane
Z-shape, 90-deqree bends
2
3
1.2 (4)
6.4 (2.5)
Hastellov G
Fresh (2nd stage); spent wash
from 2nd stage collected
and used for 1st stage
Hash-down tank
1st stage - front and back
2nd stage - front
Continuous
1st stage - 56 liters/s
<885 qal/min)
2nd stage - .49 liters/s
(775 gal/min)a
Low
Approximately 850 liters (225 gal) per min of wash water is lost to
gas stream as entrained moisture droplets. Each stage contributes
half of this water loss. Approximately 2500 liters (660 gal) per
minute of spent wash water from both stages is drained from the
wash-down tank to each recirculation tank.
30
-------
TABLE 11. DESIGN PARAMETERS AND OPERATING CONDITIONS OF DUCK CREEK 1 DAMPERS
Description
Induced-
draft fan
inlet
Induced-
draft fan
outlet
Bypass
breeching
inlet
Scrubber
module
inlet
Scrubber
module
outlet
Number
8
4
1
4
8
Type
Double-
louver
Single-
louver
Double-
louver
Double-
plate
slide-
gate
Manufacturer
Buffalo Forge
American
Warning
and Ventila-
ting
American
Warming
and Ventila-
ting
American
Warning
and Ventila-
ting
Environmental
Elements
Modulation
Open/closed
Open/closed
Open/closed
Open/closed
Seal air
Flow,
mVs(acfm)
Non
1.9S
(4,150)
t'one
1.95
(4.150)
0.57
(1200)
Pressure ,
kPaUn. H20)
e
5.5
(22.0)
5.5
(22.0)
\.
2.5
(10.0)
Service con-
ditions,
°C(»F)/min
370/30
(700)
232/30
(450)
232/30
(450)
232/30
(450)
Torque ,
raPa (psi)
113(16,500)*
276(40,000)
83.6(12,125)*
Comments
Inlet-control
dampers
Isolation dampers
Inlet-control
dampers
Isolation
dampers
Isolation dampers
Per side.
-------
Induced-draft Fans
Four centrifugal induced-draft fans are connected in par-
allel to a common duct with internal baffling promote even gas
flow distribution to the scrubbers and/or bypass breeching.
These fans are designed to operate in tandem with the boiler
forced-draft fans to overcome draft loss in the boiler side and
emission-control side. Each fan is equipped with a water-cooled
oil-lubrication system, complete with pumps and coolers. Table
12 presents the design parameters and operating conditions of the
fans.
Pumps
The FGD system is equipped with 34 pumps covering the liquid
circuit battery limits from limestone preparation to waste solids
disposal. Table 13 presents design parameters and operating
conditions of the pumps.
Tanks
The liquid circuit of the FGD system is equipped with 11
major tanks for storage, transfer, recirculation and collection
of slurry, and addition of makeup water. Table 14 presents
design parameters and operating conditions of the tanks.
Wet Stack
The FGD system has no stack gas reheat system. It is
designed so that the scrubbed gas stream exits the system at
approximately 53°C (127°F) . The bypass duct and stack also
handle the warm and hot flue gas streams associated with partial
and total FGD bypass. The wide variety of operating conditions
has necessitated the incorporation of a number of design fea-
tures, which are summarized as follows:
0 The bypass breeching and discharge ducts are constructed
of Hastelloy G, an exotic, corrosion-resistant alloy.
32
-------
TABLE 12. DESIGN PARAMETERS AND OPERATING CONDITIONS
OF DUCK CREEK 1 INDUCED-DRAFT FANS
Number
Manufacturer
Arrangement
Service
Specifications:
Type
Rating, kW (hp), and rpm
Lube system
Bearings
•Rotation
Performance:
Gas capacity, m /s (ft /min)
Gas temperature, °C (°F)
Gas density, kg/m3 (lb/ft3)
Pressure drop, kPa (in. H-0)
Materials of construction
Buffalo Forge
Parallel
Dry
Centrifugal, double
width, double inlet,
radial tip
2,960 (4,000), 900
Water-cooled, circulating
oil
Self-aligning sleeve type
2 CW8, 2
205 (435,000)
149 (300)
0.785 (0.049)
9.5 (38.0)
Carbon steel
CW = clockwise.
CCW * counter clockwise.
33
-------
TABLE 13. DESIGN PARAMETERS AND OPERATING CONDITIONS OF DUCK CREEK 1 PUMPS
U)
Number
2
4
12
12
2
2
Service
Mill sump
Slurry
transfer and
return
Slurry re-
circulation
Hist elimi-
nator spray
Waste col-
lection
underflow
Fond water
return
Manufacturer
Galigher
Worthing ton
Worthington
Worthington
Barret
Worthington
Tytw
Centrifugal.
•lurry
Centrifugal
•lurry
Centrifugal
slurry
Centrifugal
Centrifugal
slurry
Centrifugal
Materials.
of construction
Rubber-lined
Rubber-lined
Rubber- lined
Rubber- lined
Rubber- lined
Rubber-lined
• Performance
Motor,
Jew (top)
215(290)
26435)
89(120)
Capacity,
liters/a
(gal/min)
50(800)
45(105)
497(7875)
66(1050)
100(1600)
50(800)
Speed,
rpm
1800
1800
770
1800
985
1800
Solids,
percent
55
40-50
15
0
15
0
Operation
1 operational,
1 spare
1 operational,
3 spare
8 operational,
4 spare
8 operational,
4 spare
1 operational,
1 spare
1 operational,
1 spare
TABLE 14. DESIGN PARAMETERS AND OPERATING CONDITIONS
OF DUCK CREEK 1 TANKS
Service
description
Slurry recir-
culation
Slurry
storage
Mist elimi-
nator wash
down
Mill slurry
Number
4
1
4
2
Dimensions,
m {ft)
11 dia. x 6. 7
(37 dia. ,x 22)
7.9 dia. x 6.1
(26 dia. x 20)
1.5 dia. x 3.0
[5 dia. x 10)
Capacity,
liters (gal)
606,000
(160,000)
303,000
(80,000)
11,400
(3,000)
Retention
time, min
10
100
3.5
Agitator
Yes
Yes
No
Yes
Materials of
construction
Rubber- lined
carbon steel
Rubber-lined
carbon steel
Rubber-lined
carbon steel
Concrete
Comments
1 per scrubber
Common
1 per scrubber
1 operational,
1 spare
-------
0 Emergency water sprays are located in the discharge
duct just prior to the stack entry point. The water
sprays provide emergency cooling for stack liner
protection in the event of a high temperature excur-
sion. The water sprays also provide continuous cooling
of the gas bypassing the FGD system so that a constant
gas environment is created within the stack, thereby
extending stack liner life.
0 The 152-m (500-ft) stack is a reinforced-concrete
shell. Its Cor-Ten flue is coated with a sprayed-on
flake-glass liner (Ceilcote 151) for protection from
acid corrosion attack. A venturi throat placed approx-
imately two-thirds of the way up the stack gives the
gas a mechanical boost before it is discharged to the
atmosphere. This boost causes a difference in the
velocity of the gas and the entrained droplets, allow-
ing the latter to fall out of the gas stream and be
collected in four hoppers situated at the base of the
stack.
Limestone Storage and Preparation
Limestone arriving at the plant is either delivered to a
dead storage or live storage area or is transferred directly to
the limestone grinder building. The dead storage area holds 90
days supply and the live storage area, 3 days. Limestone deliv-
ered to the grinder building is stored in a feed bin having a 24-h
storage capacity.
The limestone delivered to the storage bin is 1.9 cm (3/4
in.) and must be ground to a particle size of 90 percent minus
200 mesh. Grinding takes place at 10 kg/s (40 tons/h) in one of
two (one operational, one spare) wet ball mills to which the
stone is supplied by a weigh feeder. Fresh makeup water is fed
to the ball mill at 14 liters/s (220 gal/min) under maximum
conditions (100% boiler load, 4% sulfur coal). The milled lime-
stone is discharged to a slurry tank for collection, then pumped
to a slurry storage tank via a classifier that insures a 90
percent minus 200 mesh product. The effluent from the mill
system, which is a 40 percent solids slurry, is retained in the
slurry storage tank for 100 minutes before it is added to the
liquid scrubbing circuit via the scrubber recirculation tanks.
35
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Tables 15 and 16 present design parameters and operating condi-
tions of the Duck Creek limestone storage and preparation opera-
tions .
TABLE 15. DESIGN PARAMETERS AND OPERATING CONDITIONS
OF DUCK CREEK 1 LIMESTONE STORAGE FACILITIES
Description
Dead storage
Live storage
Feed bin
Number
1
1
1
Capacity, Gg (tons)
39.2 (86,400)
1.30 (2,880)
0.4 (960)
Storage, days
90
3
1
Waste Solids Disposal and Pond-water Return
The spent scrubbing slurry from the recirculation lines of
each module is discharged to a waste collection tank where it is
combined with liquid waste streams from plant sumps and dis-
charged to an onsite sludge disposal pond. The waste collection
tank is situated in a sludge building located approximately half
way between the plant and pond. The sludge disposal pond, which
also accommodates bottom ash and fly ash disposal, has a 3- to 5-
yr service life. It is lined with a natural impermeable material
to prevent contamination of water streams. The inlet waste
stream to the disposal pond consists of a 15 percent solids
slurry containing reaction products, fly ash, bottom ash, and
unreacted limestone. The waste solids settle out in the pond,
and supernatant is returned to the recirculation tanks to main-
tain liquid balance in the FGD system. Table 17 presents design
parameters and operating conditions of the waste disposal system.
PROCESS CHEMISTRY: PRINCIPAL REACTIONS
The chemical reactions involved in the Duck Creek wet lime-
stone scrubbing process are highly complex. Although details are.
beyond the scope of this discussion, the principal chemical
mechanisms are described below.
36
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TABLE 16. DESIGN PARAMETERS AND OPERATING CONDITIONS OF
DUCK CREEK 1 LIMESTONE PREPARATION FACILITY
Weigh feeder:
Number
Manufacturer
Capacity
One
Merrick
45 Mg (50 tons)/h of
1.3 cm (0.5 in.) stone
at 1.5 to 1.8 Mg/m3 (95
to 110 Ib/ft3), 65°C
(150°F), and 15.5 m/min
(50.95 ft/min)
Ball mill:
Number
Manufacturer
Motor drive
Mill speed, rpm
Bearings
Ball charge, Mg (Ib)
Capacity, Mg/h (tons/h)
Slurry solids, percent
Two (one operational, one
spare)
Kennedy Van Saun
Falk/General Electric
18.36
Oil lubricated
67 (148,000)
36 (40)
65
Classifier:
Number
Manufacturer
Dimensions, m (ft)
Lining
Rating
Overflow, Mg/h (tons/h)
Underflow, Mg/h (tons/h)
Inlet flow, liters/s (gal/min)
AP, kPa (psig)
Slurry solids, percent
One
Krebs
0.3 x 1.3 (1.0 x 4.2)
Rubber
90 percent minus 200 mesh
36 (40)
72 (80)
17.7 (281)
245 (20.5)
40
37
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TABLE 17. DESIGN PARAMETERS AND OPERATING CONDITIONS
OF DUCK CREEK 1 WASTE DISPOSAL SYSTEM
Method
Number
Type
Location
Area dimensions, m (acre)
Distance from plant, km (mil
Transportation mode
Pond permeability, cm/s (in./s)
Annual storage capacity:
Ash, Gg (tons)
Reaction products, Gg '(tons)
Volumer a (acre-feet)
Service life, yr
Pond water return rate, liters/s (gal/min)
Pond water return points
Ponding
One
Clay-lined settling
pond
Plant site
263,000 (65)
0,8 (Q.S)
Pipeline
10
-8
no'10,
218 (240,000)
816 (900,000]
328,700 (266.5)
3 to 5
46.6 (738)
Recirculation tanks
38
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The first and most important step in the wet-phase absorp-
tion of sulfur dioxide from the flue gas stream is diffusion from
the gas to the liquid phase. Sulfur dioxide is an acidic an-
hydride that reacts readily to form an acidic species in the
presence of water.
S°2 • S°2(aq.)
S°2(aq.) +H2° ^=* H2S°3
In addition, some sulfur trioxide is formed from further oxida-
tion of the sulfur dioxide in the flue gas stream.
2SO2 + 02 * ». 2S03
This species, like sulfur dioxide, is an acidic anhydride that
reacts readily to form an acid in the presence of water.
S03 « S°3(aq.)
S03(ag.) + H2° * H2S°4
The sulfurous and sulfuric acid compounds are polyprotic
species; the sulfurous species is weak and the sulfuric species,
strong. Their dissociation into ionic species occurs as follows:
< * H+ + ~
+
H_SO. < H + HSO
24 4
< H + SO4
Analogous to the oxidation of sulfur dioxide to form sulfur
trioxide, oxidation of sulfite ion by dissolved oxygen (DO) in
the scrubbing slurry is limited.
2S03= +°2(aq.) ^^ 2S04=
The limestone absorbent, which is 95 percent calcium car-
bonate by weight, is introduced into the scrubbing system as a
slurry with water. At Duck Creek limestone is added to the FGD
system at a stoichiometric rate of 1.5 moles per mole of sulfur
39
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dioxide removed. Limestone is largely insoluble in water, and
solubility increases only slightly as the temperature increases.
In the scrubbing system, the slurry dissolves and ionizes into an
acidic aqueous medium, yielding the ionic products of calcium,
carbonate, bicarbonate, and hydrogen.
CaC03 « CaC03(aq.)
Ca++ + H+ + C03~ < » CaHC03+
CaHCO* •< * Ca++ + HCO3~
The chemical absorption of sulfur dioxide occurs in the
scrubber modules and is completed in the external recirculation
tanks .
Ca++ + SO3= < *" CaSO3
Ca++ + SO,= « * CaSO,
4 4
The calcium sulfite and calcium sulfate reaction products, along
with the collected fly ash and unreacted limestone, are trans-
ferred to the disposal pond. After the sulfur dioxide reaction
products precipitate as hydrated calcium salts and settle out
with the other waste solids, the supernatant is returned to the
recirculation tanks for reuse.
CaS03 + 1/2H20 •
CaS04 + 2H2O < *
PROCESS CONTROL
The Duck Creek FGD system operations are monitored and con-
trolled from a control panel situated in a cubicle in the lime-
stone grinder building. The control cubicle contains the analog
and digital control elements for automatic monitoring and control
of the FGD process inlet and outlet streams. The principal con-
cerns of this control network are flue gas flow, reagent feed,
and slurry solids.
40
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Flue Gas Flow
Gas flow through the scrubber modules is monitored and
controlled to prevent overloading and loss of chemical control.
Control is accomplished by maintaining a constant pressure drop
across the system. Each scrubber module has differential pres-
sure sensors in the inlet and outlet gas ducts. These sensors
relay signals through a differential pressure transmitter to a
controller in the boiler control room. The controller maintains
a constant pressure drop of 2 kPa (8 in. H20) across each module
by adjusting the bypass damper in the bypass breeching through
modulation of an electric drive. This single-louver shutoff
damper can be modulated to any position between fully open and
fully closed to maintain proper gas flow distribution and con-
stant pressure drop.
Another important aspect of this control network is the
operation of isolation dampers. Each scrubber module is equipped
with one double-louver, seal-air damper on the inlet and two
slide-gate, seal-air dampers on the outlet. Each damper is
powered by an electric drive and controlled automatically or
manually from the control cubicle. The automatic control network
is actuated by differential pressure and liquid flow sensors in
the mist eliminator and scrubber recirculation liquid loops.
When below normal values are registered in either of these loops,
the dampers are automatically closed and seal-air fans are
activated to insure complete seal-off.* The dampers reopen when
readings return to normal in both loops. Each damper can be
operated manually from the control cubicle during periods of
reduced load or outages. During manual operation the dampers can
be moved to a closed or intermediate position and reopened only
when readings return to normal.
Reagent Feed
Fresh limestone slurry is continuously added to the FGD
scrubber recirculation tanks to compensate for reagent consumed
One set of seal-air fans operates continuously, pressurizing
the damper drive mechanisms for the outlet slide-gate dampers
of each scrubber module.
41
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in scrubbing operations/ thereby maintaining sulfur dioxide
removal efficiency and chemical integrity. The flow of fresh
limestone slurry into the scrubbing circuit is controlled in an
automatic feed-forward/feedback manner. Primary control is
provided by the feed-forward network, which utilizes the inlet
gas stream's sulfur dioxide concentration and flow rate. Fine
control or "trim" is provided by the feedback network, which
utilizes slurry pH and inlet slurry flow rate. The following
paragraphs summarize the specifics of these control networks.
The flow of sulfur dioxide and boiler gas is measured by
sulfur dioxide gas monitors and boiler load signals originating
in the boiler control room. Sulfur dioxide is measured by six
continuous gas monitors situated at the system inlet duct, at the
system outlet duct, and at each scrubber module outlet. The
signals from all these monitors are recorded and transferred to
an analyzer, which transmits a signal to a computer, indicating
the inlet sulfur dioxide concentration. The boiler load signal
is also transmitted to the computer, indicating the proportional
amount of limestone slurry needed for sulfur dioxide removal.
This output signal enters another computer, which produces four
separate signals that then enter a flow controller. The flow
controller is connected to an actuator that regulates the posi-
tion of a butterfly control valve. Each of these signals can be
biased in relation to the individual scrubber module gas flow.
The flow controller also receives two input signals from pH
monitors situated in the recirculation tanks and from another
computer, which transmits an output signal proportional to slurry
flow rate into the recirculation tanks. The input signals for
this computer are provided by a magnetic flow meter and density
meter located in the storage tank slurry loop and the storage
tank itself.
These three signals (inlet gas flow/sulfur dioxide concen-
tration, slurry pH, and slurry flow) provide the input to the
flow controller that actuates the flow control valves located in
42
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each of the four tap lines, which draw off fresh slurry from the
storage tank return loop. The slurry pH control point is set at
5.5 to 6.0.
Slurry Solids
The solids content of the slurry in the scrubbing circuit is
controlled at the 15 percent level by monitoring the liquid level
of the recirculation tank, the slurry density, the fresh slurry
flow rate, and the spent slurry flow rate. A recirculation
tank level controller and a slurry discharge controller are used
in conjunction with a computer to operate a slurry discharge
flow control valve for each scrubber. Input signals to the
computer and controllers are sent from differential pressure
level transmitters and density meters in the recirculation tanks
and from flow meters in the slurry feed and discharge lines.
Using these signals, the controllers maintain a set ratio between
incoming and outgoing slurry to the recirculation tanks and the
overflow spent wash water from the mist eliminator wash-down
tanks to maintain a 15 percent solids level in the slurry scrub-
bing circuit.
43
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SECTION 4
FGD SYSTEM PERFORMANCE
BACKGROUND INFORMATION
Originally CILCo intended to install one scrubber for the
control of sulfur dioxide emissions at Duck Creek 1, and to
evaluate its effectiveness on high sulfur coal before proceeding
with the design, installation, and operation of the remaining
scrubber modules. It was believed that such a modular approach
would produce sufficient operating data on the scrubbing of flue
gas produced by high sulfur coal so that any drastic design
changes might be made without large capital investments or unit
load reductions.
In 1974 the Illinois EPA approved the modular approach for
the Duck Creek 1 FGD system. Permission was granted for CILCo to
build and operate only one 100-MW equivalent scrubber module
initially, and to build the remaining three modules after this
module had been tested sufficiently. As a result of this ruling,
CILCo awarded a contract to Riley Stoker/Environeering (in
November 1974) for the design and construction of an FGD system
that included only one scrubber module to treat 25 percent of the
total boiler flue gas flow.
In October 1975, the U.S. EPA served a notice of violation,
requiring the entire plant to comply with New Source Performance
Standards governing sulfur dioxide emissions. The utility
obtained a consent decree and elected to move up the expected
completion date of the remaining scrubber modules to August 1,
1978, and on August 26, 1976, awarded Riley Stoker/Environeering
a contract to supply these modules. The utility was also granted
a variance to fire high sulfur coal in the boiler from July 1,
44
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1976, to April 1, 1977, for test purposes. The unit could be
operated at full load during this period with both ESP's and one
scrubber module in the gas path.
The first scrubber module (D-scrubber) was completed in June
1976, placed in service on July 1, 1976, and operated intermit-
tently throughout the fall and winter and for approximately 1
month in the spring of 1977. The purpose of this operation was
to verify process chemistry and design. During this brief period
of service, several problems became apparent, making subsequent
design modifications necessary. The modifications were made and
the remaining modules were installed between April 1977 and July
1978. During this time the utility burned low sulfur coal in
order to meet the sulfur dioxide emission standard of 516 ng/J
(1.2 lb/10 Btu). Initial startup of the entire FGD system
commenced on July 23, 1978.
Because the Duck Creek 1 FGD system has only recently
attained commercial operating status, operating data are limited.
However, the data obtained during the D-scrubber test (removal
efficiencies, problems, solutions, and necessary design modifi-
cations) are discussed in the remainder of this section.
OPERATING HISTORY AND PERFORMANCE
Duck Creek 1 commenced commercial operation on June 1, 1976,
and the D-scrubber module was initially placed in the flue gas
path on July 1, 1976. The limited operation during the balance
of July and August was due primarily to construction deficien-
cies, such as bad welds, faulty pipe hangers, and slurry leaks
in the scrubber. The D-scrubber was taken out of the gas path to
resolve these problems and put back in on September 9. It
operated (intermittently) for approximately 360 hours during the
balance of the month, 385 hours in October, and 24 hours in
November. During these periods a number of major operating
problems were encountered, including massive mist eliminator
scale, spray nozzle and pipe plugging, and materials failure.
45
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The module remained out of service from December through February
because of a scheduled 3-month boiler/turbine overhaul. During
this outage a number of modifications were made to the scrubber
in order to correct the major operating problems encountered.
The unit was placed back in service in mid-March, and the D-
scrubber operated almost continuously for 350 hours during the
balance of the month. During April and May, testing was to
concentrate on operating the automatic control loops; however,
the testing was terminated prematurely because of installation
difficulties, and the D-scrubber was taken out of service. The
unit remained in service with the boiler firing low sulfur
Colorado coal. The ESP's also remained in service, and with the
aid of sulfur trioxide gas injection, removed particulate from
the flue gas generated by the burning of low sulfur coal. The D-
scrubber was placed back in the flue gas path on July 23, 1978,
along with the other scrubber modules. Table 18 summarizes the
performance of the D-scrubber during the July 1976 to April 1977
test period.
PROBLEMS AND SOLUTIONS
The interim testing of the D-scrubber module revealed
several chemical, mechanical, and design-related problems and
prompted a number of modifications to the system. All of the
problems were not directly related to design deficiencies how-
ever; some were caused by operating the scrubber before it was
completely installed. These items are discussed briefly in the
paragraphs that follow.
Chemical Problems
Many of the chemical problems that beset the D-scrubber
module and ancillary equipment were caused or aggravated by an
incomplete instrumentation/control network. The sophisticated
automatic control system could not be put in service during this
early stage of operation.
46
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TABLE 18. DUCK CREEK 1 D-SCRUBBER MODULE PERFORMANCE HISTORY
Period
Jul. 1976
Aug. 1976
Sept. 1976
Oct. 1976
Nov. 1976
Dec. 1976
Jan. 1977
Feb. 1977
Mar. 1977
Apr. 1977-
Jun. 1978
Jul. 1978
Module, Service
8 h
18 h
360 h
385 h
24 h
350 h
Comments
Initial operation of the D-scrubber module for shakedown and debugging
purposes occurred during the month. Limited service time resulted from
bad welds, faulty pipe hangers, and slurry leaks in the module.
Limited operations continued because of continued startup and construction
problems. The module was taken out of the gas path to concentrate on
resolving these problems.
Module restart occurred on September 9. Operation continued throughout
the remainder of the month on an intermittent basis. Major problems
included pipe breaking, pump liner failures, plugging and sealing of mist
eliminators, and some boiler-related problems. The module remained in
service for approximately 15 days of noncontinuous operation.
Total operation time during the month amounted to approximately 16 days
(noncontinuous). The major problem was the continuation of massive scale
development on the mist eliminators, resulting in plugging of the piping
and nozzles to the components spray system.
Sporadic operation resulted from continued scaling problems in the mist
eliminator section. Riley and CILCo initiated modifications to the design
of the module. Specifically, a rod deck was changed in the absorber,
pressure drop across the absorber was increased, piping and pump liner
materials were modified/replaced, and. a freshwater wash system was installed
for the mist eliminator.
The module remained out of service the entire month. During this time, the
boiler fired low sulfur (0.6%) Kentucky coal.
Duck Creek 1 was down throughout the entire period for turbine/boiler over-
haul. During the outage, a number of modifications were made to the scrubber.
Duck Creek 1 returned to service in mid-March. The D-scrubber was placed in
service to test the following modifications made during the preceding outage:
• The mist eliminator spray wash system piping was changed from PVC to FRP
materials, and another spray header was added.
• The slurry circulation system was revamped.
• The original natural rubber liners were replaced with neoprene liners.
Flush/drain systems have been included to minimize solids build up.
• Piping valves were moved closer to the recycle tank.
" Slurry storage tanks were equipped with flush/drain systems.
• Additional mixers were added for greater agitation to promote process
chemistry.
Except for a few minor boiler outages, the module remained in service on a
continual basis during the last part of March.
The firing of Colorado low sulfur coal commenced on April 1 and continued
until July 1978.
Operation of the FGD system with all four scrubber modules in the flue gas
path commenced on July 23, 1978.
-------
Primary difficulties involved frequent scaling and plugging
of the mist eliminators. Although these problems were attributed
primarily to the lack of automatic controls, the wash system was
modified to provide more efficient washing. Specifically, the
polyvinyl chloride materials used in the wash water piping that
feeds water from the wash-down tank to the spray nozzles for each
mist eliminator stage were replaced with fiberglass-reinforced
plastic. Also, an additional spray header was added to the wash
system to provide more thorough rinsing.
Another chemical problem was the widespread corrosion of the
Ceilcote 151 flake-glass liner that was sprayed on the Cor-Ten
steel stack flue to a thickness of 0.5 mm (20 mils). Inspection
of the liner following the D-scrubber test program revealed
blistering and acid corrosion as well as subsequent widespread
corrosion of the flue. The major factor contributing to this
problem seemed to be the intermittent and partial scrubbing load.
This caused the gas conditions to vary widely when passing
through the stack, resulting in premature failure of the liner
because operating conditions exceeded the design conditions
specified for the materials. Two other factors may have contri-
buted to liner failure: the liner material itself (it is no
longer offered by the supplier for stack lining applications) and
the absence of a stack gas reheat system.
The utility has since repaired areas where cracked and
peeled liner exposed bare metal surface, but information on the
success of these repairs is not available. Other U.S. utility
FGD systems using this wet stack approach have met with the same
fate—widespread corrosion of liner, flue, and/or stack, which
ultimately required extended outages for repair and/or modifica-
tion.
Mechanical Problems
Many of the mechanical problems encountered involved pre-
mature pump lining failures and damper leakage. Originally, all
the slurry recirculation and transfer pumps were lined with
48
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natural rubber, and pump cavitation, which occurred frequently,
caused the linings to be stripped from the casings. To rectify
this, CILCo replaced the natural rubber linings in the slurry
recirculation pumps with neoprene linings and the linings in the
remaining slurry pumps with reinforced natural rubber.
The utility also equipped all the slurry pumps with a flush-
out system. Because the circulating fluid is a slurry (15%
solids in the recirculation and discharge lines and 40 to 55% in
the transfer lines), solids settle out when flow is stopped. If
they settle out in the pump, the pump impeller and lining can be
damaged on startup. Therefore, a flush system was installed to
purge the pump with freshwater whenever the system is not in
service.
Design-related Problems
Several design deficiencies were observed either to have
caused or aggravated the chemical and mechanical problems just
discussed. These deficiencies are summarized below.
0 The ceramic spray nozzles in the scrubber spray heads
were originally spinner-vane type. Repeated plugging
of these nozzles prompted replacement with orifices in
the flow lines (open-pipe arrangement) and splash
plates on the top rod deck. The flow orifices reduced
the liquid stream from 10 to 5 cm (2 to 4 in.), and the
splash plates reduced the potential for erosion of the
top rod deck and helped to achieve proper liquid dis-
tribution .
0 Much of the mist eliminator fouling was attributed to
an unexpectedly high carryover of slurry solids in the
gas stream. These solids were eventually deposited on
the mist eliminators, causing fouling, increased pres-
sure drops across the mist eliminators, and ineffi-
ciency of mist eliminator operation. Eventually the
scrubber module had to be shut down to clean the mist
eliminators. This problem was corrected by increasing
the pressure drop across the scrubber by modifying the
rod decks. This modification reduced the entrainment
of slurry solids in the gas stream and reduced fouling
in the mist eliminator.
49
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In addition to the slurry pumps, freshwater flush and
drain systems were added to all the slurry storage
tanks, recirculation tanks, and pipe lines to purge
them of solids that settle out during periods of
inactivity.
Erosion of piping valves in the scrubber recirculation
lines was eliminated by moving the valves closer to the
recirculation tanks. Freshwater flush and drain
systems have also helped to extend valve life.
An improper gas velocity profile in the scrubber con-
tributed to some of the problems. Riley Stoker/
Environeering is now attempting to determine the actual
profile and necessary corrective action.
Additional agitation was added to all the slurry tanks
to maintain solids suspension in the slurry circuit,
minimize solids settling, and promote reaction chemistry.
REMOVAL EFFICIENCY
Because the FGD system has attained its commercial operating
status so recently, sulfur dioxide removal efficiencies for full-
scale operations are not available; however, sulfur dioxide
removal efficiency was measured on the D-scrubber module during
the interim test. The results (summarized in Table 19) indicate
that the removal efficiency was 91.6 percent, which exceeds the
design maximum guarantee value of 85.3 percent.* This measure-
ment was taken for sulfur dioxide inlet concentrations of 3000
ppm.
TABLE 19. RESULTS OF THE D-SCRUBBER MODULE TEST
Gas capacity, m /s (acfm)
Sulfur dioxide inlet concentration, ppm
Pressure drop, kPa (in. H,O)
3
Liquid/gas ratio, liters/m
(gal/103 acf)
Sulfur dioxide outlet concentration,
ppm
Sulfur dioxide removal efficiency,
percent
140 (300,000)
3000
2.2 (8.8)
6.8 (50)
252
91.6
The efficiency guarantee applied to 4 percent sulfur coal.
50
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Particulate removal efficiency measurements taken during the
D-scrubber test program also proved interesting in that the
scrubber was apparently removing as much as 70 percent of the
inlet particulate matter after it had passed through the upstream
ESP's even though scrubbers are not designed to provide any
additional particulate removal capability beyond that of the
emission control system.* The utility and system supplier indi-
cate that this serendipitous phenomenon may be attributed to the
ionization and/or agglomeration of the small particles provided
by passage through the upstream ESP's, which would greatly en-
hance collection of these particles in the downsteam scrubber.
SYSTEM ECONOMICS
The total capital cost of the FGD system reported by CILCo
is $37,540,000. This includes $33,740,000 for the entire system
and all ancillary equipment and $3,800,000 for the sludge dis-
posal pond. Based on a unit gross generating capacity of 416 MW,
this amounts to $90.2/kW. Actual annual cost figures for the FGD
system are not available because of limited operation to date.
However, based on the limited operation of one module, the
utility estimates that the total annual cost of the flue gas
desulfurization system is $13,921,000. This includes $7,539,000
for variable charges and $6,382,000 for fixed charges. Based on
a net unit rating of 400 MW and a capacity factor of 65 percent,
this would amount to 6.11 mills/kWh in total annual cost.
The FGD system is guaranteed not to add any particulate loading
to the discharge gas stream as measured at the outlet of the
ESP's.
51
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APPENDIX A
PLANT SURVEY FORM
A. Company and Plant Information
1. Company name; Central Illinois Light Company
2. Main office: 300 Liberty Street, Peoria, Illinois
3. Plant name: Duck Creek
4. Plant location: Canton, Illinois
5. Responsible officer:
6. Plant manager:
7. Plant contact: Larry Haynes
8. Position; Manager, Environmental Affairs
9. Telephone number: (309)/672-5221
10. Date information gathered; April 1977
Participants in meeting Affiliation
L. Haynes Central Illinois Light Company
B. Laseke PEDCo Environmental, Inc.
J. Tuttle PEDCo Environmental, Inc*
A-l
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B. Plant and Site Data
1. UTM coordinates:
2. Sea Level elevation:
3. Plant site plot plan (Yes, No): Yes
(include drawing or aerial overviews)
4. FGD system plan (Yes, No); Yes
5. General description of plant environs; The plant site
occupies unreclaimed strip-mined land situated in a
flat, rural area.
6. Coal shipment mode(s); Coal is delivered to the plant
site primarily by rail. Provisions have been made to
accommodate truck shipments because of the capability
for barge unloading on the Illinois River.
C. FGD Vendor/Designer Background
1. Process: Limestone
2. Developer/licensor; Riley Stoker/Environeering
3. Address; P.O. Box 547, Wooster, Massachusetts/ 01613
4. Company offering process:
Company: Riley Stoker/Environeering
Address: P.O. Box 547, Wooster, Massachusetts, 01613
A-2
-------
Location:
Company contact; Tom Robinson
Position; Design Engineer
Telephone number:
5. Architectural/engineer:
Company: Gilbert/Commonwealth
Address:
Location: Jackson, Michigan
Company contact: H. W. Sauer
Position; Project Manager
Telephone number:
D. Boiler Data
1. Boiler: Duck Creek 1
2. Boiler manufacturer: Riley Stoker
3. Boiler service (base, intermediate, cycling, peak):
Base
4. Year placed in service; 1976
12,000
5. Total hours operation (date):; .'Capproximate to 1Q/1/781
6. Remaining life of unit; 30-year life span
7. Boiler type; Pulverized-coal, balanced-draft, front-fired
8. Served by stack no. : one
9. Stack height; 152 m (500 ft)
10. Stack top inner diameter:
11. Unit ratings (MW):
Gross unit rating; 416 MW
Net unit rating without FGD; 410 MW
A-3
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Net unit rating with FGD; 400 MW
Name plate rating: 416 MW
12. Unit heat rate:
Heat rate without FGD: 10,130 kJ net/kWh (9600 Btu/net kWh)
Heat rate with FGD; 10/380 kJ/net kWh (9840 Btu/net kWh)
13. Boiler capacity factor, (1977); 55-60%
14. Fuel type: Coal __
15. Flue gas flow rate; 688 m3/s (1,415.600 acfm)
Maximum: 688 m3/s (1,415,600 acfm)
Temperature: 135°C (275°F)
16. Total excess air:
17. Boiler efficiency:
Coal Data
1. Coal supplier(s):
Name(s}: United Freeman
Location(s);Mines are situated close to plant site in
Fulton County near Canton, Illinois.
Mine location(s): Canton, Illinois
County, State; Fulton, Illinois
Seam:
2. Gross heating value: 25,523 kJ/kg (10,543 Btu/lb)
3. Ash (dry basis): 9.12%
4. Moisture: 18.0%
5. Sulfur (dry basis); 3.3%
6. Chloride: 0.03%
7. Ash composition (See Table Al) - Not available.
A-4
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Table Al
F.
Percent weight
Not available
Constituent
Silica, Si02
Alumina, Al_03
Titania, TiO2
Ferric oxide, Fe~G-3
Calcium oxide, CaO
Magnesium oxide, MgO
Sodium oxide, Na-0
Potassium oxide, K2O
Phosphorous pentoxide, PO^C
Sulfur trioxide, SO.,
Other
Undetermined
Atmospheric Emission Regulations
1. Applicable particulate emission regulation
a) Current requirement: 43 ng/J (0.1 lb/106 Btu)
Regulation and section; Federal NSPS _
b) Future requirement: _
Regulation and section:
Applicable SO- emission regulation
a) Current requirement: 516 ng/J (1.2 lb/10 Btu)
Regulation and section No.; Federal NSPS
b) Future requirement:
Regulation and section:
A-5
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Chemical Additives: (Includes all reagent additives -
absorbents, precipitants, flocculants, coagulants, pH
adjusters, fixatives, catalysts, etc.)
1. Trade name: Limestone ______
Principal ingredient; Calcium carbonate (95% minimum)
Function: Absorbent
Source/manufacturer: Columbia Quarry Company
Quantity employed; 152 Gg/yr (168,000 tons/yr)
Point of addition; Scrubber recirculation tanks
Trade name; Carbide lime .
Principal ingredient: Calcium hydroxide
Function: Emergency pH control additive
Source/manufacturer; AIRCo
Quantity employed; Emergency pile maintained at plant
Point of addition: Scrubber recirculation tanks
3. Trade name: Not applicable .
Principal ingredient:
Function:
Source/manufacturer:
Quantity employed:
Point of addition:
Trade name; Not applicable
Principal ingredient:
Function:
Source/manufacturer:
Quantity employed:
Point of addition:
A-6
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5. Trade name: Not applicable
Principal ingredient:
Function:
Source/manufacturer:
Quantity employed:
Point of addition:
H. Equipment Specifications
1. Electrostatic precipitator(s)
Number: Two
Manufacturer; Pollution Control - Walther
Design removal efficiency: 99.8
Outlet temperature; 135°C (275°F)
Pressure drop; 0.13 kPa (0.5 in. H2O)
Mechanical collector(s) - Not applicable
Number: ,
Type:___
Size:
Manufacturer:
Design removal efficiency:
Pressure drop:
3. Particulate scrubber(s) - Not applicable
Number:
Type:
Manufacturer:
Dimensions:
Material, shell:
A-7
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Material, shell lining:
Material, internals:
No. of modules per train:
No. of stages per module:
No. of nozzles or sprays:
Nozzle type:
Nozzle size:
Boiler load capacity:
Gas flow and temperature:
Liquid recirculation rate:
Modulation:
L/G ratio:
Pressure drop:
Modulation:
Superficial gas velocity:
Particulate removal efficiency (design/actual):
Inlet loading:
Outlet loading:
SO2 removal efficiency (design/actual):
Inlet concentration:
Outlet concentration:
4. SO2 absorber(s)
Number: Four
Type; Vertical, rod-deck (Ventri-Sorber scrubber)
Manufacturer: Riley Stoker/Environeering
Dimensions; 12 m x 12 m x 1.5 m (40 ft x 40 ft x 5 ft)
A-8
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Material, shell: Carbon steel
Material, shell lining; Not applicable
Material, internals: 316L SS (rods) and Hastelloy G
No. of modules per train: 1 gpray zone, 9 rod decks
No. of stages per module:
Packing/tray type: Rod deck
2.5 cm (1 in.) rods spaced
Packing/tray dimensions: 2.5 cm Q in.) apart
No. of nozzles or sprays: 12 spray heads
Nozzle type: Open pipe arrangement
Nozzle size; 5 cm (2 in.) flow orifices
Boiler load capacity; 25%*
Gas flow and temperature: 167 m3/s (353,900 acfm) *
Liquid recirculation rate: 994 liters/s (15,.750 gal/min)
Modulation: 50%
L/G ratio; 6.8 liters/m3 (50 gal/103 acf)
Pressure drop; 20 kPa (8.0 in. H?Q)
Modulation:
Superficial gas velocity; 3.9 m/s (13 ft/s)
Particulate removal efficiency (design/actual); 0/75
Inlet loading: Q.Q2 mq/m3 (0.009 qr/acf) (design)
Outlet loading; Q.Q2 mq/m (0.009 qr/acf) (design)
SO- removal efficiency (design/actual): 85.3/91.6
4123 ppm (max. design)/
Inlet concentration: 3000 ppm (actual)
575 ppm (max. design)/
Outlet concentration; 252 ppm (actual)
Wash water tray(s) - Not applicable
Number:
*
Per scrubber module.
A-9
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Type:
Materials of construction:
Liquid recirculation rate:
Source of water:
6. Mist eliminator(s)
Number: Four, one per module
Type: Chevron
Materials of construction: HasteHoy G
Manufacturer; Riley Stoker/Environeerinq
Configuration (horizontal/vertical); Vertical - 35° tilt
Number of stages; TWO
Number of passes per stage; Three
Mist eliminator depth:
Vane spacing; 6.4 cm (2.5 in.)
Vane angles; 90-degree sharp-angle bends
Type and location of wash system; Front and back spray
(1st stage); front spray (2nd stage) .
Superficial gas velocity; 3.6 m/s (12 ft/s)
Freeboard distance:
Pressure drop; 0.25 kPa (1.0 in. H?O)
Comments: Mist eliminator wash-down tanks supply fresh-
water and spent wash water for cleaning; 1st stage -
56 liters/s (885 qpm) and 2nd stage - 49 liters/s
(775 gal/min)
7. Reheater(s): Not applicable - wet stack
Type (check appropriate category) :
A-10.
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in-line
indirect hot air
direct combustion
bypass
exit gas recirculation
waste heat recovery
other
Gas conditions for reheat: Not applicable
Flow rate:
Temperature:
S0~ concentration:
Heating medium:
Combustion fuel:
Percent of gas bypassed for reheat:
Temperature boost (AT):
Energy required:
Comments: The system is not equipped with a stack-gas
reheat system. A wet stack is equipped with hoppers
for collection of entrained droplets.
8. Fan(s) - Service for boiler, ESP's, and FGD system.
Number: Four, induced-draft (with respect to boiler)
Type: Centrifugal, double-width, double-inlet, radial tip
Materials of construction; Carbon steel
Manufacturer; Buffalo Forge
Location: Dry, between ESP's and FGD system
Rating: 2960 kW (4000 hp)
Pressure drop; 9.5 kPa (38.0 in. H20)
A-11
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Recirculation tank(s):
Number: Four
Materials of construction: Rubber-lined carbon steel
Function: Collection of spent solution/limestone makeup
11 m dia. x 6.7 m addition.
Configuration/dimensions; (37 ft dia. x 22 ft)
Capacity: 606,000 liters (160,000 gal)
Retention time: 10 minutes
Covered (yes/no): No
Ag itator: Yes
10. Recirculation/slurry pump(s):
Service
Slurry
recirculation
Slurry
transfer
Number
12
4
Type
Centrifugal
slurry
Centrifugal
slurry
Manufacturer
Korthington
Worth ington
Capacity
497 liters/s
(7875 gal/min)
45 liters/s
(705 gal/min)
Operation
12 total
8 operational
4 spare
4 total
1 operational
3 spare
11.
Thickener(s)/clarifier (s) - Not applicable
Number:
Type:
Manufacturer:
Materials of construction:
Conf iguration:
Diameter:
Depth:
Rake speed:
Retention time:
12. Vacuum filter(s) - Not applicable
A-12
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Number:
Type:
Manufacturer:
Materials of construction:
Belt cloth material:
Design capacity:
Filter area:
13. Centrifuge (s) - Not applicable
Number:
Type:
Manufacturer:
Materials of construction:
Size/dimensions:
Capacity:
14. Interim sludge pond(s) - Not applicable
Number:
Description:
Area:
Depth:
Liner type:
Location:
Service Life:
Typical operating schedule:
Ground water/surface water monitors:
15. Final disposal site(s)
A-13
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Number: One
Description; Clay-lined settling pond
Area: 263,000 m2 (65 acres)
Depth:
Location: On site, 0.8 km (0.5 mi) from plant
Transportation mode; Pipeline
Service life: 3 to 5 years
Typical operating schedule; Continuous flow from waste
collection tank.
16. Raw materials production - Limestone preparation
Number: Two mills (one operational/one spare)
Type: Wet ball mill, oil-lubricated
Manufacturer: Kennedy Van Saun
Capacity: 36 Mg/h (40 tons/h)
Product characteristics; Slurry - 65 percent solids
stream, which is transferred to a mill slurry tank and
then to a storage tank for addition to recirculation tank.
I. Equipment Operation, Maintenance, and Overhaul Schedule
1. Scrubber(s) - Not applicable
Design life:
Elapsed operation time:
Cleanout method:
Cleanout frequency:
Cleanout duration:
Other preventive maintenance procedures:
2. Absorber(s) - Not available
A-14
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Design life:
Elapsed operation time:
Cleanout method:
Cleanout frequency:
Cleanout duration:
Other preventive maintenance procedures:
3. Reheater(s) - Not applicable
Design life:
Elapsed operation time:
Cleanout method:
Cleanout frequency:
Cleanout duration:
Other preventive maintenance procedures
4. Fan(s) - Not available
Design life:
Elapsed operation time:
Cleanout method:
Cleanout frequency:
Cleanout duration:
Other preventive maintenance procedures
Mist eliminator(s) -• Not available
Design life:
Elapsed operation time:
A-15
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Cleanout method:
Cleanout frequency:
Cleanout duration:
Other preventive maintenance procedures:
6. Pump(s)- Not available
Design life:
Elapsed operation time:
Cleanout method:
Cleanout frequency:
Cleanout duration:
Other preventive maintenance procedures:
7. Vacuum filter(s)/centrifuge(s)- Not available
Design life:
Elapsed operation time:
Cleanout method:
Cleanout frequency
Cleanout duration:
Other preventive maintenance procedures:
8. Sludge disposal pond(s)
Design life: 3 to 5 yr
Elapsed operation time:
Capacity consumed:
Remaining capacity:
A-16
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Cleanout procedures:
J. Instrumentation - See text, Section 3, Process Control
subsection.
A brief description of the control mechanism or method of
measurement for each of the following process parameters:
Reagent addition:
0 Liquor solids content:
Liquor dissolved solids content;
Liquor ion concentrations
Chloride:
Calcium:
Magnesium:
Sodium:
Sulfite:
Sulfate:
Carbonate:
Other (specify):
A-17
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Liquor alkalinity:
Liquor pH:
Liquor flow:
0 Pollutant (SO,, particulate, NO ) concentration in
£• X
flue gas:
Gas flow:
Waste water
Waste solids:
Provide a diagram or drawing of the scrubber/absorber train
that illustrates the function and location of the components
of the scrubber/absorber control system.
Remarks: See text of report concerning specific instrumenta-
tion and process control network.
K. Discussion of Major Problem Areas: See text of report con-
cerning problem areas.
1. Corrosion:
A-18
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2. Erosion:
3. Scaling:
4. Plugging:
5. Design problems:
6. Waste water/solids disposal:
A-19
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7. Mechanical problems
L. General comments:
A-20
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APPENDIX B
PLANT PHOTOGRAPHS
B-l
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View of Duck Creek Station. Featured to the right of the
stack are the boiler and turbine houses.
2. View of Duck Creek dead coal storage area. Featured are
the stacker/reclaimer (foreground) and waste disposal pond
(background). Limestone dead storage is maintained at the
far end of the coal dead storage area.
B-2
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3. View of carbide lime supply kept at the plant site for use
during emergency pH control excursions.
4. View of Duck Creek cooling pond. Inverted weir featured
at right allows water to be withdrawn from the deeper,
cooler levels of the pond.
B-3
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5. Discharge canal for cooling water return to cooling pond.
6. View of waste disposal pond. Featured at far end of pond
are fly ash, bottom ash, and scrubbing wastes, which are
discharged to pond for final disposal.
B-4
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7. View of coal transfer houses and conveyor. The coal
transportation network is also capable of handling
limestone.
8. View of Duck Creek ESP. Featured at the left is one of
the four parallel double-inlet induced-draft fans.
B-5
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9. Side view of Duck Creek D-scrubber module. Featured
from right to left are the ESP outlet duct, induced-
draft fan, scrubber module and recirculation tank,
bypass breeching, and stack.
.. -
10. Side view of Duck Creek D-scrubber module
B-6
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11. View of induced-draft fans and discharge duct work.
Double-louver seal-air dampers are featured in discharge
duct near center of photo.
B-7
-------
12. View of top portion of stack. Featured is stack plume
with unit operating at full load and ESP's in service
during low-sulfur coal combustion.
B-8
-------
13. Close-up view of D-scrubber module recirculation tank
14. Mist eliminator PVC wash piping showing solids deposition
incurred during initial operation of D-scrubber module.
B-9
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TECHNICAL REPORT DATA
(Please read Instruction* on tin irio«< bijon rr*»u/>/r/»u''
1. REPORT NO.
EPA-600/7-79-lSga
4. T.TLE AND SUBTITLE
Qf
Systems: Duck Creek Station, Central Illinois
Light Co.
3 RECIPIENT'S ACCESSION NO
5. REPORT DATE
August 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Bernard A. Laseke, Jr.
B. PERFORMING ORGANIZATION REPORT NO
PN 3470-1-C
9. PERFORMING ORGANIZATION NAME AND ADDRESS
PEDCo Environmental, Inc.
11499 Chester Road -
Cincinnati, Ohio 45246
10. PROGRAM ELEMENT NO.
E HE 62 4
11. CONTRACT/GRANT NO.
68-02-2603, Task 24
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 7/78 - 12/78
14. SPONSORING AGENCY CODE
EPA/600/13
16.SUPPLEMENTARY NOTES ffiRL-RTP project officer is Norman Kaplan, Mail Drop 61, 919/
541-2556.
16. ABSTRACT
The report presents the results of a survey of operational flue gas desulfurization
(FGD) systems on coal-fired utility boilers in the United States. The FGD system
installed on Unit 1 at the Duck Creek Station of Central Illinois Light Company
is described in terms of design and performance. The system consists of four
parallel, wet-limestone, rod-deck scrubber modules designed for 25% capacity
each, providing a total sulfur dioxide removal efficiency of 85%. The bottom
ash, fly ash, and scrubbing wastes are disposed of in a sludge pond lined with
a natural impermeable material. The first module of this four module FGD system
was placed in service on July 1, 1976, and operated intermittently throughout the
remainder of the year and for approximately one month in early 1977. On July 23,
1978, the three remaining modules were completed and all four modules were placed
in the gas path for treatment of high sulfur flue gas.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Flue Gases
Desulfurization
Fly Ash
Limestone
Slurries
Ponds
Scrubbers
Coal
Combustion
Cost Engineering
Sulfur Dioxide
Dust Control
Air Pollution Control
Stationary Sources
Wet Limestone
Particulate
13B
21B
07A,07D
11G
08H
21D
14A
07B
18. DISTRIBUTION STATEMENT
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
91
Unlimited
2O. SECURITY CLASS (Thispage/
Unclassified
22. PRICE
EPA Form 2220-1 (t-73)
B-10
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