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 ------- 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- gories were established to facilitate further development and application of en- vironmental technology. Elimination of traditional grouping was consciously planned to foster technology transfer and a maximum interface in related fields. The nine series are: 1. Environmental Health Effects Research 2. Environmental Protection Technology 3. Ecological Research 4. Environmental Monitoring 5. Socioeconomic Environmental Studies 6. Scientific and Technical Assessment Reports (STAR) 7. Interagency Energy-Environment Research and Development 8. "Special" Reports 9. Miscellaneous Reports This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT RESEARCH AND DEVELOPMENT series. Reports in this series result from the effort funded under the 17-agency Federal Energy/Environment Research and Development Program. These studies relate to EPA's mission to protect the public health and welfare from adverse effects of pollutants associated with energy sys- tems. The goal of the Program is to assure the rapid development of domestic energy supplies in an environmentally-compatible manner by providing the nec- essary environmental data and control technology. Investigations include analy- ses of the transport of energy-related pollutants and their health and ecological effects; assessments of, and development of, control technologies for energy systems; and integrated assessments of a wide range of energy-related environ- mental issues. EPA REVIEW NOTICE This report has been reviewed by the participating Federal Agencies, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Government, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. This document is available to the public through the National Technical Informa- tion Service, Springfield, Virginia 22161. ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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. ------- 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 ------- '. 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. ------- 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 ------- 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 ------- (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. ------- 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. ------- 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. ------- 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. ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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. ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 2. Erosion: 3. Scaling: 4. Plugging: 5. Design problems: 6. Waste water/solids disposal: A-19 ------- 7. Mechanical problems L. General comments: A-20 ------- APPENDIX B PLANT PHOTOGRAPHS B-l ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- |