U.S. Environmental Protection Agency Industrial Environmental Research EPA-600/7-78-048d Office of Research and Development Laboratory *%^*» Research Triangle Park. North Carolina 27711 MaTCn 1978 SURVEY OF FLUE GAS DESULFURIZATION SYSTEMS: CHOLLA STATION, ARIZONA PUBLIC SERVICE CO. Interagency Energy-Environment Research and Development Program Report ~ZL ------- 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-600/7-78-0488 March 1978 SURVEY OF FLUE GAS DESULFURIZATION SYSTEMS: CHOLLA STATION, ARIZONA PUBLIC SERVICE CO. by Bernard A. Laseke, Jr. PEDCo Environmental, Inc. 11499 Chester Road Cincinnati. Ohio 45246 Contract No. 68-01-4147 TaskS Program Element No. EHE624 EPA Project Officer Norman Kaplan Industrial Environmental Research Laboratory Office of Energy, Minerals and Industry Research Triangle Park, N.C. 27711 Prepared for U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Research and Development Washington, O.C. 20460 ------- ACKNOWLEDGMENT This report was prepared under the direction of Mr. Timothy W. Devitt and Dr. Gerald A. Isaacs. The principal author was Mr. Bernard A. Laseke. Mr. Norman Kaplan, EPA Project Officer, had primary respon- sibility within EPA for this project report. Information on plant design and operation was provided by Mr. Ed. L. Lewis, Manager, Administration and Technical Services, Arizona Public Service; Mr. Coe Suydam, Mechanical Engineering Department, Arizona Public Service; Mr. Gil Gutierrez, Plant Engineering Department, Arizona Public Service; Milton D. Johnson, Results Engineer, Cholla Steam Electric Station, Arizona Public Service; Aubry Parsons, Assistant Superintendant, Cholla Steam Electric Station, Arizona Public Service; and John Vayda, Utility Gas Cleaning Division, Research-Cottrell. ii ------- CONTENTS Page Acknowledgment ii List of Figures and Tables iv Summary 7 1. Introduction 1 2. Facility Description 2 3. Flue Gas Desulfurization System 6 Process Description 6 Design Parameters 11 Limestone Milling Facilities 14 Process Chemistry: Principal Reactions 14 Process Control 20 4. FGD System Performance 22 Performance Test Run 22 Operation History: Problems and Solutions 23 Design and Operation Modifications 29 Economics 29 Appendices A. Plant Survey Form 35 B. Plant Photographs 56 iii ------- LIST OP FIGURES No. Page 1 Simplified process flow diagram, Cholla 1 FGD system 7 2 Simplified process flow diagram, Module A, Cholla 1 FGD system 8 3 Basic components of flooded-disc FGD system venturi scrubber and cyclonic separator, Cholla FGD system 10 4 Gas flow and damper arrangement, Cholla FGD system 12 LIST OF TABLES No. Page 1 Data Summary: Cholla Unit 1 ix 2A Average Monthly Analyses of Coal Burned in 1975 3 2B Design, Operation, and Emission Data, Cholla Boiler 1 5 3 Data Summary: Particulate and SO- Scrubbers 15 4 Data Summary: FGD System Hold Tanks 15 5 Data Summary: FGD System Mist Eliminators 16 6 Data Summary: FGD System Reheaters 17 7 Typical Pressure Drop Across Components of Particulate Scrubber and Packed Tower 18 8 Results of FGD System Performance Test Runs, October 2 to October 21,1973 24 9 Chemical Analysis of Cholla Station Service Water 28 10 Performance Data for Cholla 1 FGD System: October 1973 to December 1977 30 iv ------- SUMMARY The wet limestone flue gas desulfurization (FGD) system on Boiler 1 at the Cholla Steam Electric Station of the Arizona Public Service Company (APS) was designed and installed by Research-Cottrell (R-C). Research-Cottrell had previously conducted pilot plant operations at the Cholla Station (treating a flue gas slip stream from Boiler 1), but their work on a full-scale FGD system did not begin until January 1971. They prepared preliminary design and submitted a proposal to APS in April 1971 and were awarded the contract in July. Construction and initial testing were not completed until December 3, 1973. Construction was delayed for several reasons: changes in engineering design and material specifications, equip- ment delivery delays, adverse weather conditions, system shake- down problems, and problems with the FGD system at APS's Four Corners Station. Commercial operation of the FGD system commenced on December 14, 1973, and has proceeded on a continuous basis since that time. Cholla Boiler 1 is a base-load unit with a maximum, con- tinuous, net generating capacity of 115 MW when the unit is tied into the FGD system. At full load it consumes pulverized coal at a rate of approximately 49 Mg (54 tons) per hour. The fuel burned in this unit is a low-sulfur, New Mexico coal with the following average characteristics: 23.6 MJ/kg (10,150 Btu/lb) heat content; 0.5 percent sulfur; and 13.45 percent ash. The FGD system consists of two parallel modules (A and B), each designed to accomodate 50 percent of the boiler flue gas. Module A includes a variable-throat, flooded-disc scrubber for particulate control, followed by a packed tower that uses a v ------- limestone slurry for sulfur dioxide removal. The limestone absorbent is purchased primarily from the Superior Company in Phoenix, Arizona. Module B differs from Module A only in that the absorber tower is not packed and limestone slurry is not circulated through it. Module A is designed for 92 percent sulfur dioxide removal efficiency and Module B for 25 percent. This yields a combined sulfur dioxide removal efficiency of 58.5 percent. This efficiency is based on an inlet sulfur dioxide concentration of approximately 400 to 500 ppm. Either or both modules can be bypassed. Gas leakage around each module is approximately 4.5 percent of the volume of the gas being treated. The Munters packing in the Module A tower is 0.6 m (2 ft) thick and constructed of polypropylene corrugated sheets joined together in a crisscross pattern similar to a honeycomb. The mist eliminators are also constructed of polypropylene. The three bundles of shell-and-tube steam reheaters are 316L stain- less steel. The Cholla Steam Electric Station does not have a sludge treatment or fixation system. The sludge and fly ash are pumped to an unlined, pre-existing fly ash pond in a common pipeline. The FGD system operates on an open-water-loop basis that does not require the recycling of water from the pond. Fresh makeup water required to maintain the water balance in the scrubbing system is 0.07 liters/sec per MW (1.04 gpm/MW). According to Research-Cottrell, the particulate and S02 collection efficiencies of Module A were 99.7 and 92 percent during a test run. As of December 1977, APS had not conducted an official acceptance test on the system. Minor modifications were made as a result of initial test- ing, and the system was officially placed in service on December 14, 1973. It operated with a 92.6 percent reliability factor until April 15, 1974, when the system was shut down for approxi- mately 2 weeks for scheduled modifications of the expansion joints. Research-Cottrell repair crews were available during vi ------- most of the first half of 1974, and it is believed that their attention to maintenance was partly responsible for the high system reliability demonstrated during the shakedown period. The performance of the system from the completion o'f final modifications in October 1973 through December 1977 indicates a high degree of mechanical reliability. Shutdowns have occurred primarily during scheduled turbine, boiler, and FGD system over- hauls. The average reliability indexes for the total FGD system in 1974, 1975, 1976, and 1977 were 91, 88, 88, and 95 percent, respectively. Reliability indexes for Module A in the same years were 94, 91, 89, and 93 percent, and for Module B, 88, 85, 89, and 97 percent. Total installed capital cost of the Cholla FGD system to date is approximately $6.5 million or $57/kW (1973 dollars). This cost figure is not final because final performance tests have not been conducted and APS has not yet accepted the system. The capital cost figure includes engineering costs, site prepara- tion, erection, electrical service, limestone handling facili- ties, and pilot plant engineering. Annual operating costs are estimated to be 2.2 mills/kWh. This figure includes a 23 percent charge on capital investment to account for interest, depreciation, taxes, and other fixed char- ges. Also included are labor costs of 0.09 mills/kWh (one full- time auxiliary operator); utility costs of 0.2 mills/kWh (2.8 MW/hr electricity and 18,000 Ib/hr of steam); and material costs of 0.15 mills/kWh (limestone). Maintenance and sludge disposal costs are not included. Arizona Public Service is now in the process of increasing the station's power generating capacity from 115 to 1315 MW. Units 2 and 3, now under construction, are scheduled for com- mercial start-up in June 1978 and June 1979. Each is rated at 250 MW. Units 4 and 5, now in the planning stage, are scheduled for commercial start-up in June 1980 and June 1983. Each of these units is rated at 350 MW. Current emission control reg- ulations require that three of the additional units (2, 4, and vii ------- 5) have FGD-equipped boilers. Research-Cottrell has been awarded two separate contracts to provide additional FGD systems for Units 2 and 4.* Although Unit 5 is still in the preliminary design stage, it is expected to include an FGD system. No FGD system is required on Unit 3; it will have only an electrostatic precipitator (ESP) for particulate control. Table 1 summarizes general data on Cholla Unit 1. viii ------- Table 1. DATA SUMMARY: CHOLLA UNIT 1 Unit rating (net) Fuel Average fuel characteristics' Heating value Ash Sulfur FGD system supplier Process New or retrofit Start-up date Modules Efficiency Particulates Sulfur dioxide Water makeup Sludge disposal Unit cost Capital Annual 115 MW Coal 23.6 MJ/kg (10,150 Btu/lb) 13.45 % 0.52 % Research-Cottre11 Limestone slurry Retrofit October 1973 Twob 99.7 %° 58.5 %d 0.07 liters/sec per MW (1.04 gpm/MW) Unstabilized sludge disposed of on site in pre-existing ash disposal pond. $57/kW 2.2 mills/kWh a Average values of coal burned during 1975 operation. Only one module (A) is equipped with packing and limestone slurry circulation for sulfur dioxide removal. c Total particulate removal efficiency provided by mechanical collectors and venturi scrubbers. d Total system removal efficiency. Module A efficiency is 92 percent; Module B, 25 percent. 1973 dollars. ix ------- SECTION 1 INTRODUCTION The Industrial Environmental Research (IERL) Laboratory 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 Cholla Steam Electric Station of Arizona Public Service Company (APS). It includes pertinent process design and operating data, a description of major start-up and operational problems and solutions, atmospheric emission data, and capital and annual cost information. This report is an update of a previous report based on observations made during an April 2, 1974, plant inspection and on data provided by the utility and the system supplier during that visit. This update report is based on a second plant visit on April 8, 1976, and data obtained since that visit. Informa- tion presented is current as of December 1977- Section 2 presents pertinent facility design and operation data and actual and allowable particulate and sulfur dioxide emission rates; Section 3 describes the FGD system; and Section 4 analyzes FGD system performance. Appendices A and B contain details of plant and system operation and photos of the installa- tion. ------- SECTION 2 FACILITY DESCRIPTION The Cholla Steam Electric Station of APS is in an arid desert region in Navajo County, Arizona, near Joseph City. The terrain surrounding the station is relatively flat and sparsely populated. There is no other major industry in the area. Cholla now operates only one steam turbine generating unit (Boiler 1). This Combustion Engineering (CE) boiler is a dry- bottom, pulverized-coal-fired unit with a net generating capacity of 115 MW. It was put in commercial service in May 1962. Arizona Public Service is in the process of increasing the Station's capacity from 115 to 1315 MW. Units 2 and 3, now under construction, are scheduled for commercial start-up in June 1978 and June 1979. Each is rated at 250 MW. Units 4 and 5, now in the planning stage, are scheduled for commercial start-up in June 1980 and June 1983. Each of these units is rated at 350 MW. All are CE pulverized-coal-fired units. The plant burns low-sulfur subbituminous coal from the McKinley mine near Gallup, New Mexico. It is shipped in by rail. A typical analysis of this coal gives the following values: heating value, 10,400 Btu/lb; sulfur content, 0.5 percent; chloride content, 0.025 percent; ash content, 13.5 percent; and moisture content, 15 percent. Table 2A shows monthly average analyses of the coal burned. Boiler 1 is equipped with mechanical collectors upstream from the FGD system. These R-C multicyclones are designed to remove 80 percent of the inlet particulate. matter. If design efficiency is achieved, loading at the outlet of the mechanical collectors should be approximately 2.2 g/m3 (2.0 gr/scf). ------- Table -2A. AVERAGE MONTHLY ANALYSES OP COAL BURNED IN 1975 CHOLLA STEAM ELECTRIC STATION Month Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Average Sulfur, % 0.56 0.55 0.51 0.52 0.51 0.56 0.55 0.51 0.54 0.49 0.48 0.46 0.52 Chloride (range) , % 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 0.01-0.04 Ash, % 13.51 14.15 22.49 17.69 11.26 12.33 9.76 11.46 9.88 12.40 14.60 11.89 13.45 Heating value, MJ/kg 23.5 22.6 20.9 22.5 23.4 24.1 24.6 23.3 23.7 23.7 23.1 23.7 23.1 (Btu/lb) (10,093) (9.750) (9,970) (9,671) (10,053) (10,352) (10,578) (10,001) (10,199) (9,956) (9,946) (10,178) (10,150) Average moisture, % 15 15 15 15 15 15 15 15 15 15 15 15 15 ------- Arizona State Department of Health Regulation No. 7-1-3.5 limits particulate emissions to 84.27 ng/J (0.196 lb/106 Btu) of heat input to the boiler. Arizona Public Service reports present particulate emissions at Cholla are 11.18 ng/J (0.026 lb/106 Btu). Regulation No. 7-1-4.2 limits SO2 emissions to 430 ng/J (1.0 lb/106 Btu) of heat input to the boiler. The present emission rate, based on a combined PGD removal efficiency of 58.5 percent, is estimated to be 185 ng/J (0.43 lb/106 Btu). Based on limits imposed by current emission regulations, three of the four additional units (2, 4, and 5) planned for this station must be equipped with FGD systems. Arizona Public Ser- vice has already awarded two separate contracts to R-C for limestone slurry TGD systems on Units 2 and 4. "Each system will consist of four modules for the control of particulates and sulfur dioxide. Both PGD systems will have 100 percent capacity, and both are scheduled to go on line simultaneously with the boilers (Unit 2 in June 1978 and Unit 4 in June 1980). Unit 3 will include only an ESP for the control of particulate emis- sions. The emission control strategy for Unit 5 has not yet been determined. Table 2B presents pertinent plant design, operation, and emission data. ------- Table 2B. DESIGN, OPERATION, AND EMISSION DATA, CHOLLA BOILER 1 Total rated generating capacity Boiler manufacturer Year placed in service Unit heat rate Coal consumption Maximum heat input Stack height above grade Design maximum flue gas rate Flue gas temperature Emission controls: Particulate Sulfur dioxide Paritculate emission rates: Allowable Actual Sulfur dioxide emission rates: Allowable Actual 115 MW Combustion Engineering 1962 10,199 kJ/net kWh (9,670 Btu/net kWh) 49 Mg/hr (54 tons/hr 1156 GJ/hr (1096 106 Btu/hr) 76 m (256 ft) 227 m3/sec (480,000 acfm) 136°C (276°F) Mechanical collectors and venturi scrubbers Venturi scrubber and packed-bed absorber 84.27 ng/J (0.196 lb/10 Btu) 11.18 ng/J (0.026 lb/106 Btu) 430 ng/J (1.0 lb/10 Btu) 185 ng/J (0.43 lb/106 Btu) ------- SECTION 3 FLUE GAS DESULFURIZATION SYSTEM PROCESS DESCRIPTION The FGD system consists of two modules, A and B. Each module includes a flooded-disc venturi scrubber, a cyclonic mist eliminator, an absorber tower, and a final mist eliminator. The absorber on Module A includes packing for removal of the sulfur dioxide with circulating limestone slurry. The absorber tower in Module B is a hollow spray tower, and limestone slurry is not circulated through it. Each module treats approximately one-half of the total boiler flue gas. A simplified process flow diagram of the entire FGD system is shown in Figure 1. A simplified process flow diagram of Module A, which provides the primary sul- fur dioxide control, is shown in Figure 2. Gas Circuit Flue gas from the boiler induced-draft (ID) fans is pres- surized by two booster fans to a static pressure of approximately 6.2 kPa (25 in. H~O), then flows downward through the throat of the venturi-type, flooded-disc particulate scrubber. Limestone slurry flows out over the disc and is atomized as it is sheared by the gas stream at the edge of the disc. Slurry is also injected tangentially through nbzzles on the inside wall of the venturi scrubber shell above the tapered throat. The orifice is formed by the annular space between the circumference of the horizontal disc and the wall of the tapered duct section in the throat area. The disc is adjusted in the vertical plane within the tapered duct to increase or decrease the area of the orifice. In this manner gas pressure drop and the resulting particulate scrubbing efficiency are controlled. The saturated, scrubbed flue gas then passes through a cyclonic mist eliminator, where ------- iuvn r , * [tUKi TAH« | I «!»SI TAM ] TO CVA»MATIC!< KKO Figure 1. Simplified process flow diagram, Cholla 1 FGD system. ------- INLET GAS FROM MECHANICAL COLLECTORS BOOSTER FAN BYPASS DAMPER FLOODED DISC SCRUBBER H K* \7 a SLUDGE HOLDUP TANKS 1CYLCONIC MIST ELIMINATOR REHEATER IMPINGEMENT MIST ELIMINATORS *- MAKEUP HATER (FROM WELL) b- PACKING CONICAL SLURRY SEPARATOR FDS DISCHARGE PRE-EXISTING ASH DISPOSAL POND FDS SLURRY TANK LIMESTONE MAKEUP WATER "(FROH UELL) EXIT GAS TO STACK fr- TOWER TANK Figure 2. Simplified process flow diagram of Module A, Choila 1 FGD system. 8 ------- solids from collected fly ash, limestone slurry, and reaction products are separated from the gas stream before it enters the absorber. A diagram of a Cholla flooded-disc venturi and cyclon- ic mist eliminator is provided in Figure 3. Gas from the cyclonic mist eliminator enters the absorber tower near the base. In Module A only, it contacts the limestone slurry on the surface of the wetted-film Munters packing, which is 0.6 m (2 ft) thick. The packed tower section is separated from the cyclonic mist eliminator by a plate containing a conical hat. This arrangement permits the flue gas to leave the cyclonic mist eliminator and enter the packed spray section and yet prevents the spent lime- stone slurry in the packed spray section from combining with the spent scrubbing solution from the flooded-disc venturi (see Figure 2). Thus, fly ash cannot enter the absorber tower. The scrubbed gas then passes through a set of mist elimina- tors (one set per absorber) and is reheated before it is dis- charged to the atmosphere through the main stack. The mist eliminators are slat (special baffle design) impingement type, constructed of polypropylene and arranged horizontally (vertical gas flow) in two stages. Reheat is provided by a set of steam- heated, shell-and-tube heat exchangers (one set per module). Each set of reheaters contains two bundles of tubes, which raise the temperature of the saturated gas stream from 49 °C (120°F) to 71°C (160°F) before it passes through a duct to the brick-lined, concrete stack. Limestone is added to Module A of the FGD system at a rate of approximately 110 percent of the stoichiometric requirement for reaction with the sulfur dioxide in the flue gas. Part of the circulated liquor in the sulfur dioxide absorber is diverted to the flooded-disc scrubber tank (common to both modules) to maintain the pH between 4 and 5 in the particulate control system (flooded-disc venturi). The liquid level in this tank is main- tained by pumping the excess spent liquor to one of two surge tanks (sludge holdup-tanks) before it is discharged to a pre- ------- LIMESTONE SLURRY FLOODED-DISC SCRUBBER HORIZONTAL DISC ORIFICE AREA LIMESTONE SLURRY CYCLONIC MIST ELIMINATOR SPENT SOLUTION DISCHARGE Figure 3. Basic components of the variable-throat, flooded-disc venturi scrubber and cyclonic separator, Cholla FGD system. 10 ------- existing pond. The plant site has no facilities for sludge storage or fixation. Because of the area's light rainfall and a high evaporation rate, wastewater discharge into receiving waters is not a problem. Therefore no liquor is recirculated back to the process. Dampers in the FGD system are arranged so that only Module B can be bypassed, or both Modules A and B can be bypassed simul- taneously. Module A alone can only be bypassed for short periods of time, however, because limestone, which enters the system in the Module A absorber tower tank, is used to control the opera- ting pH of the entire particulate scrubber system to a range of 4 to 6. The inlets to both modules from the booster fans are interconnected through a common suction header. Flue gas flow control to both modules is maintained by balancing the module fans via amperage control. Figure 4 presents a diagram of the Cholla FGD system damper arrangement. DESIGN PARAMETERS The R-C FGD system at Cholla is designed to treat 227 m /sec (480,000 acfm) of flue gas at 136°C (276°F). Actual boiler flue gas flow to both modules (at 115-MW generating capacity) measures approximately 189 m /sec (400,000 acfm). In addition, bypass leakage around the FGD system amounts to 8 m3/sec (17,000 acfm). The flooded-disc particulate scrubbers are constructed of 316L stainless steel and are 1.8 m (6 ft) in diameter by 13.7 m (45 ft) high. Pressure drops on each is 2.5 kPa (15 in. H2O). Each scrubber operates with a liquid recirculattion rate of about 137 liters/sec (2170 gpm) at full load, which is equal to a liquid-to-gas (L/G) ratio of 1.4 liters/m3 (10.1 gal/1000 ft3) at 50°C (l22°F). Two-thirds of the scrubbing solution used in the flooded-disc scrubbers is introduced through the hollow shaft of the flooded disc; the remainder is sprayed through tangential nozzles on the vessel wall. The absorber towers are constructed of 316L stainless steel and are 6.7 m (22 ft) in diameter by 21.3 m (70 ft) high. The 11 ------- INLET LOUVER DAMPER REHEATER SYSTEM GUILLOTINE DAMPER REHEATER STACK GUILLOTINE DAMPER F6D BOOSTER FAN 1 R R Mt "" 1 1 t U- 1 1- - MANUAL J- GUILLOTINE DAMPER 1 t 4 ! 1 *\ -•""". j+ ~V_^~ CROSSOVER DAMPER I GUILLOTINE _^ 17000 ACFM 1 STACK BYPASS LOUVER DAMPERS BOILER ID FAN 1 1 BOILER ID FAN MANUAL GUILLOTINE DAMPER Figure 4. Gas flow and damper arrangement, Cholla 1 FGD system. 12 ------- sulfur dioxide absorber in Module A includes a fixed plate and conical hat separator and packing. The fixed plate and conical hat separator are also constructed of 316L stainless steel. The Munters packing, which consists of a fixed matrix of rigid sheets of polypropylene, has a high specific surface area and low pres- sure drop [0.12 kPa (0.5 in. H2O)]. The superficial gas velocity of the sulfur dioxide absorber is 2.1 m/sec (6.9 ft/sec), and the L/G ratio is 6.5 liters/m3 (48.9 gal/1000 ft3). The mist eliminators in each absorber tower are arranged horizontally in two stages. The first stage is a Chevron-type, two-pass, polypropylene mist eliminator, and in the S02 absorber is approximately 3.7 to 4.6 m (12 to 15 ft) above the packing. The design configuration of the second-stage, four-pass, poly- propylene mist eliminator differs only slightly from that of the first stage. The distance between stages is approximately 1.2 m (4 ft). Vane spacing is 3.8 cm (1.5 in.) in the first stage and 18.1 cm (8.1 in.) in the second stage. On each tower, both stages of the mist eliminator are washed on timed cycle with makeup water from plant wells. A quadrant of each mist elimin- ator stage is sprayed sequentially for 45 seconds every 30 min- utes with 520 kPa (60 psig) makeup water. Flow rate of the makeup water to the mist eliminator is approximately 15 liters/ sec (240 gpm). The set of shell-and-tube heat exchangers on each module raises the temperature of the gas from 50°C (122°F) to 72°C (162°F) before it is discharged to the atmosphere. Each reheater consists of two bundles of 316L stainless steel bare tubes with an outside diameter of 2.5 cm (1.0 in.). The heating medium is high-pressure steam extracted from the boiler steam drum, which is reduced in pressure from 13.2 MPa (1900 psig) to 1.8 MPa (250 psig). The reheater rating is approximately 84 GJ/hr (8 million Btu/hr). Reheater steam power requirements are equivalent to approximately 2 MW of electrical capacity. [Six steam soot blowers are operated 5 minutes during each 8-hour period (once per shift) to clean the tubes.] 13 ------- The reheated, scrubbed gases are discharge'1, through carbon steel ducts to the main stack. The ducts fum each module enter the stack at points directly opposite each other (see Figure 4). The stack shell is constructed of brick-lined concrete. Tables 3 through 7 summarize design and operating parameters for the major components of the Cholla FGD system. LIMESTONE MILLING FACILITIES Most of the ground limestone for the FGD system is supplied by the Superior Company in Phoenix, Arizona. The grade supplied, known as "red wall" limestone, meets size specifications of at least 75 percent by weight less than 200 mesh. Chemical composi- tion specifications call for a minimum calcium oxide content of 52.5 percent, a guaranteed minimum calcium carbonate content of 95 percent, and maximum magnesium carbonate and silica contents of 0.5 and 1.0 percent. The finely ground limestone is stored in a silo on the plant grounds, from which it is discharged at a rate of 9 kg/min (20 Ib/min) into a slurry preparation tank at the base of the silo. The fresh limestone slurry is introduced into the FGD system through the sulfur dioxide absorber recirculation tank. Arizona Public Service is in the process of installing a limestone grinding facility on the plant grounds. This facility will be able to meet present (Unit 1) and future (Unit 2} lime- stone requirements. It will consists of a ball mill capable of grinding 0.6 cm (0.25 in.) limestone rock delivered to the plant by rail to the specified size of 75 percent minus 200 mesh. PROCESS CHEMISTRY: PRINCIPAL REACTIONS The chemical reactions involved in the Cholla wet limestone scrubbing process are highly complex. Although details are beyond the scope of this discussion, the principal chemical mechanisms are described below. The first and most important step in the wet-phase absorp- tion of sulfur dioxide from the flue gas stream is diffusion from 14 ------- Table 3. DATA SUMMARY: PARTICULATE AND SO2 SCRUBBERS Flooded-disc scrubber SO_ absorber tower L/G ratio, liters/m (gallons/1000 acf) Superficial gas velocity, m/sec (ft/sec) 1.35 (10.1) Equipment sizes Equipment internals 1.8 m (6 ft) dia. x 13.7 m (45 ft) Adjustable disc 6.5 (48.9) 2.1 (6.9) 6.7 m (22 ft) dia. x 21.3 (70 ft) 0.6 m (2 ft) fixed matrix packing Table 4. DATA SUMMARY: FGD SYSTEM HOLD TANKS Total number of tanks Tank sizes Retention tine at full load Temperature PH Solids concentra- tion, percent Specific gravity Flooded disc scrubber holdup tank One 3.8 ra (12.5 ft) dia. x 4.3 m (14 ft) 7 min 49°C (121°F) 5.2 15.5 1.102 SO, absorber towers holdup tank One (common) 8.3 ra (27.3 ft) dia. x 8.5 m (28 ft) 5 min 49°C (121°F) 6.5 8.3 1.049 FGD system sludge holdup tank Two 5.6 m (18.5 ft) dia. x 8.2 m (27 ft) 14 hr 49«C (121'F) 5.2 25 Limestone slurry makeup tank Two 32°C (90°F) 20 15 ------- Table 5. DATA SUMMARY: FGD SYSTEM MIST ELIMINATORS Number Materials of construction Type Number of stages Passes/stage Distance between stages Vane spacing Distance between last absorber stage and mist eliminator Wash system: Water Frequency Pressure Capacity Two Polypropylene Chevron (1st stage) Special design (2nd stage) Two Two (1st stage) Four (2nd stage) 1.2 m (4 ft) 3.8 cm (1.5 in.) (1st stage) 18.1 cm (7.1 in.) (2nd stage) 3.7 to 4.6 m (12 to 15 ft) Plant well Intermittent (45 seconds every 30 min per quadrant) 520 kPa (60 psig) 15 liters/sec (240 gpm) 16 ------- Table 6. DATA SUMMARY: FGD SYSTEM REHEATERS Number Type Heating medium Number of tubes per exchanger Tube size, outside diameter Material of construction Heating medium characteristics: Source Pressure Temperature Consumption Rating Soot blowers: Medium Number Frequency Energy requirement, percent of unit output Two Shell-and-tube Steam Two 2.5 cm (1.0 in.) 316L stainless steel Boiler steam drum 1.8 MPa (250 psig) Saturated 9,100 kg/hr (20,000 Ib/hr) 84 GJ/hr (8 million Btu/hr) Steam Six 5 min/8-hr period 17 ------- Table 7. TYPICAL PRESSURE DROP ACROSS COMPONENTS OF PARTICULATE SCRUBBER AND PACKED TOWER Flooded-disc scrubber Sulfur dioxide absorber Mist eliminator Reheater Ductwork Total Pressure drop, kPa (in. H2O) 2.5 (10.0) 0.1 (0.5) 0.1 (0.5) 0.5 (2.0) 1.3 (5.0) 4.5 (18.0) 18 ------- the gas to the liquid phase. Sulfur dioxide is an acidic anhy- dride that reacts readily to form an acidic species in the pre- sence of water S02 J —>• S02(aq.) SO2(aq.) + H2O —*• H-SO^ In addition, some sulfur trioxide is formed from further oxida- tion of the sulfur dioxide in the flue gas stream. 1-+- 2SO. '3 Because conditions are thermodynamically (but not kinetically) favorable, only small amounts of sulfur trioxide are formed. This species, like sulfur dioxide, is an acidic anhydride that reacts readily to form an acid in the presence of water so3 SO (aq.) + H,0 -^-*- H-SO. .3 ^ A TI The sulfurous and sulfuric acid compounds are polyprotic species; the sulfurous species is weak and the sulfuric species is strong. Their dissociation into ionic species occurs as fol- lows: HSO3 H+ + HS03 H+ + HS04 HS04" ±=^ H+ + S04 Analogous to the oxidation of sulfur dioxide to form sulfur trioxide, oxidation of sulfite ion by dissolved oxygen in the scrubbing slurry is limited. ' 2S03= + 02(aq.) ^ 2S04= 19 ------- The limestone absorbent, which is a minimum of 95 percent calcium carbonate by weight, enters the scrubbing system as a slurry with wate*. It is insoluble in water, and solubility n increases only slightly as the temperature increases. When introduced into the scrubbing system, the slurry dissolves and ionizes into an acidic aqueous medium, yielding the ionic pro- ducts of calcium, carbonate, bicarbonate, and hydrogen. CaCO, — >• CaCO- (ag. ) CaCO3(aq.) ^ Ca++ Ca++ + H+ + CO3= ^v CaHCO3+ CaHC03+ ^ Ca++ + HC03~ The chemical absorption of sulfur dioxide occurs in the venturi scrubber and spray tower and is completed in the external recirculation tank. The reaction products precipitate as calcium salts and the scrubbing solution is recycled. The following are the principal reaction mechanisms for product formation and pre- cipitation. Ca + CaS03 _ ++ Ca + CaSO, SO3 — >- CaSO- + 1/2H2O ^CaSi S04~ ^ CaS04 + 2H-O — *- CaSO The hydrated calcium sulfite and calcium sulfate reaction pro- ducts, along with the collected fly ash and unreacted limestone, are transferred to the disposal pond. The supernatant is re- cycled to the process. PROCESS CONTROL The chemistry of the PGD system is maintained by controlling two important parameters of the scrubbing solution, the pH and solids concentration levels. The pH is monitored manually by sampling the scrubbing solution in the tower recirculation tank 20 ------- once per shift. The solids concentration in the scrubbing loop is controlled by the use of nuclear density meters in the FGD recirculation tank. The scrubbing solution pH is maintained at a minimum value of 5.0. Control at this level prevents major pH changes in the scrubber, which may change salt saturation levels and cause solids deposition and scale formation on the scrubber internals. The quantity of limestone used in this pH range is approximately 110 percent stoichiometric, resulting in a limestone utilization rate of 90 percent and a sulfur dioxide removal efficiency of approximately 90 percent in the Module A absorber. The desired solids concentration level in the scrubber circulation loop is 8 to 15 percent. The solids are composed primarily of fly ash, calcium sulfite, calcium sulfate, and cal- cium carbonate. Flue gas loadings and sulfur dioxide concentrations are also monitored and controlled in the scrubbing system. The flue gas that flows into the scrubbing trains is controlled using motor amperage monitoring to balance the ID fans. The measurement of the mass flow of the sulfur dioxide into the scrubbing system is performed by two continuous sulfur dioxide monitors. The FGD system instrumentation is housed in two separate areas. Most of the recording instruments are mounted on a panel in a building housing electrical switch gear, adjacent to the FGD structure. The remaining instruments, primarily for remote control of process operations, are housed in the main boiler con- trol room and are monitored by the boiler control operator. 21 ------- SECTION 4 FGD SYSTEM PERFORMANCE PERFORMANCE TEST RUN Initial testing of the FGD system began on October 2, 1973, as most of the construction had been completed by that time. The system was operated until a scheduled shutdown on October 21. This 3-week test period was used to determine particulate and sulfur dioxide removal efficiencies, mist carryover from the towers, maximum process gas flow rates, and the amount of bypass gas leakage. Module A, which has the packed tower, achieved a sulfur dioxide removal efficiency of 92 percent with average inlet and outlet sulfur dioxide concentrations of 417 and 34 ppm. Arizona Public Service estimates that Module B, which has an empty tower, is capable of removing 25 percent of the inlet sulfur dioxide. Therefore, the combined sulfur dioxide removal efficiency for the two modules was determined to be 58.5 percent [(92 + 25)/2]. No mist carryover from the scrubbing trains was detectable. Solids carryover in Module A were analyzed for calcium ion and showed an average of 0.177 g/m^ (0.05 gr/scf). The appearance of the mist eliminators at the end of the test period, together with the carryover tests, indicated very little entrainment of slurry. Pressure drop buildup across the mist eliminator was less than 0.2 kPa (0.7 in. H2O). The maximum average inlet gas rates during the 3-week opera- tion were 101 m^/sec (214,300 acfm) to Module A and 97 m3/sec (204,600 acfm) to Module B. Air leakage into the system was 9 m3/sec (18,400 acfm) downstream of the flooded-disc scrubbers. Chloride ion concentrations were 1600 ppm in the flooded- disc scrubber recirculation and 575 ppm and in the tower slur- 22 ------- ries. These levels are sufficient to cause pitting corrosion in localized areas when temperatures are greater than 60°C (140°F) and pH is less than 3.0. The chloride content of the coal ranged between 0.01 and 0.04 percent (equivalent to 8 to 32 ppm by weight in the flue gas). The chloride ion concentration was 933 ppm in the boiler water blowdown, which is used as makeup water to the FGD unit. The chloride ion concentration was 144 ppm in the well water, which is used for boiler makeup water and FGD fresh water makeup. Table 8 presents detailed information and data gathered dur- ing the preliminary performance test run. OPERATION HISTORY: PROBLEMS AND SOLUTIONS Start-up and operation of the Choila FGD system have been accompanied by many problems. An analysis of these problems reveals that most were related to process design rather than process chemistry. The utility operators and the FGD system designer have conceived and implemented solutions to many of these problems. The major problems and solutions are discussed in the following paragraphs. 0 Scale accumulated on top of and inside the cavity of the shaft's stuffing box in the flooded-disc scrubber. These scale deposits were discovered early enough to prevent binding of the shaft. Modifying the assembly of the stuffing box and reinstalling it in an inverted position (the cavity at the bottom so it cannot accumu- late solids) delayed binding. Eventually, however, the shaft did freeze and had to be cleaned out. Other minor scale accumulations on top of the shaft dome and around the tangential nozzles of the flooded-disc scrubber did not obstruct the flow of limestone slurry or flue gas through the scrubber. 0 Dilute sulfurous acid condensate caused corrosion in the expansion joints above the reheaters of both FGD modules and on the top row of tubes near the tube sheet on Module B. This corrosion was caused by the accumu- lation of dilute sulfurous acid condensate in stagnant pockets in the reheater and ductwork. To prevent recurrence of this corrosion problem, the carbon steel ductwork upstream of the reheaters in the Modules A and B was insulated with a flake-glass liner (Ceilcote) 23 ------- to *» Table 8. RESULTS OF FGD SYSTEM PERFORMANCE TEST RUNS, OCTOBER 2 to 21, 1973 Participate concentration inlet, g/m3 (gr/scf d) Particulate concentration outlet, gr/scfd S02 concentration outlet, ppm S02 concentration inlet Configuration 2 removal, percent Particulate removal efficiency, percent Gas inlet to PDS, m3/sec -(acfm) Theoretical inlet gas to fOS, m /sec (acfm) Apparent bypass leakage, m /sec (acfm) FDS L/G ratio, liters/m3 (gal./lOOO acf) Tower L/G ratio, liters/m3 (gal./lOOO acf) Gas velocity through tower, m/sec (ft/sec) Hist entrainment from tower, g/m (gr/scf ) Solids entrainment from tower slurry, g/m3 (gr/scf) Pressure drop FOS, kPa (in. H2Q) Pressure drop tower demisters, kPa (in. H2O) Pressure drop reheater, kPa (in. HjO) NA -.Not applicable. A-side 4.569 (1.99S) 0.0190 (0.0083) 34 417 Packed 92.4 99.7 16.9 (214,300) (198,800) 1.35 (10.1) 6.5 (48.9) 2.10 (6.9) 0.000 0.011 (0.005) 3.7 (14.8) 0.0 1.3 (5.15) B-side 5.810 (2.537) 0.0231 (0.0101) 357 409 Hollow 14.4 99.8 96.6 (204,600) 93.8 (198,800) 7.98 ( 16,900) 1.42 (10.6) 2.05 (6.6) 0.000 NA 3.9 (15.7) 0.0 0.6 (2.30) Stack 0.2631 (0.1149) 236 B-side hollow 9.2 99.7 96.4 (204,300) 0.78 (5.8) 2.35 (7.7) NA NA 3.4 (13.5) (Continued) ------- Table 8. (continued) to Ul Temperature tower outlet °C ("Fl AT reheafcer °C <«F) Miat eliminator wash water rate, litera/aec (gpm) Blurry flow to PDS, -litera/aec (gpm) Blurry flow from FOB, liters/sec (gpra) Limestone feed rate, kg/rain (Ib/min) Blurry flow from tower tank to FDS tank, liter a/a (gpm) Blurry flow from PDS tank to eludge holdup tank, litera/aeo (gpm) fewer tank makeup water, litera/aeo (gpra) FOB tank makeup water, liters/sec (gpm) Specific gravity (percent solids tower tank) Speoifie gravity (percent solids FOB tank) Percent aolida PDS tank Tower tank pH FDS tank pH Coal consumption, mg/hr (tona/ht) Coal heating value, MJ/kg (Btu/lb) Atmospheric) pressure, kPa (in. Hg) A-side 49 (121) 36 (65) 0.8 (12.5) 137 (2170) 83 (1317) B-aide with packing 49 (121) 33 (60) 0.9 (14.0) 137 (2177) 94 (I486) 7.5 (16.6) 2.1 (32.5) 4.0 (64.0) 0 NA 1.049 (8.3) 1.102 (14.8) IS. 5 6.5 5.2 49 (54) 23.9 (10,293) 65.4 (25.3) B-side without packing 49 (121) 33 (60) 0.8 (14.0) 88 (1100) NA ------- and the Corten steel expansion joints were replaced with rubber expansion joints. The corroded tube bundle was replaced, and to prevent acid condensate from reaching the new tubes, a trough was installed to divert any condensate away from the tube bundles. It is important to note that corrosion of the reheater by sulfurous acid occurred only in Module B (the module without packing), which has a low sulfur dioxide re- moval efficiency. Presumably, the higher sulfur dioxide removal efficiency of Module A (the packed tower) prevents significant formation of sulfurous acid con- densation. Evidence of chloride attack was noted in the liquid-gas centrifugal separator shell below the absorber. To remedy this problem, R-C coated the interior of the vessel with an epoxy material, which later eroded in spots and had to be repaired. The epoxy material also eroded and disbonded below the scrubber disc. Acid resistant brick was installed in this lower section of the absorber and has held up for more than six months. Evidence of additional chloride attack has been noted on Module B reheater tubes, probably as a result of the chlorides that are introduced in the well water used to prepare makeup slurry. Table 9 presents the results of a March 1976 chemical analysis of the well water. The spray distribution deflector above the flooded disc failed because of stress-corrosion cracking. The deflector was redesigned by R-C, and the new design is holding up. Recently extensive corrosion has occurred in the duct- work leading from the Module B absorber tower exhaust elbow to the reheat tube bundle. The utility has recoated the elbow several times with a Ceilcote liner. An application problem caused repeated failure of the liner. This problem has still not been fully resolved. Harmonic vibrations with deflections of as much as 0.1 cm (0.040 in.) occurred in the reheaters. The vibra- tions were attributed to the vortex effect of an inadequate transition of duct size from the absorber outlet to the reheater shell. To remedy the situation, cross baffles were installed at the reheater entrance. Vibrations also occurred in the Module B booster fan as a result of uneven scale buildup on the fan blades when the unit was idle. The blades were sandblasted, cleaned, and rebalanced to eliminate these vibrations. 26 ------- 0 Sediment built up several times in dead spaces in pipelines and valves of idle pumps and also in process lines. This occured when slurry velocities in the pipe were low (during periods of reduced operating rate). This problem was resolved by redesigning some pipes to eliminate potential dead pockets. To prevent valve freezing due to sediment buildup, some valves were repositioned and flush-out lines were installed. 0 Some pipe liners eroded (e.g., in the absorber tower pump inlet piping). The erosion was sometimes caused by unsatisfactory liner materials and sometimes by high flow velocities through pipes and fittings. The rubber lining in some pipes cracked, primarily because of defects in fabrication. Piping modifications helped to reduce the erosion problem. Burning a lower grade of coal (22 percent ash and 0.7 percent sulfur) in the boiler has been accompanied by some plugging in the mist eliminator and tower packing in Module A. Arizona Public Service has not yet verified whether or not this plugging is related to the lower grade of coal. If this buildup of mater- ial continues, it appears that the life span of the packing and the mist eliminator may be reduced as much as 50 percent. The FGD system is capable of accommodating the boiler down to a 50-MW load level without the system's operation being seriously affected or major problems being encountered. Constant flow is maintained in the liquid circuit to prevent solids depo- sition in the pipelines. A turndown below 50 MW, however, requires that liquid flow be modulated accordingly, and increases the probability_of solids accumulating in the pipelines as a result of the reduced liquid flow velocity. A number of additional minor problems, typical of FGD opera- tions, have been encountered and resolved by normal maintenance and engineering practices. Among these are pump failures; vessel lining failures (requiring recoating); malfunction of solenoid valves in mist eliminator wash system, preventing adequate washing; reheater steam leaks; gas damper adjustments; localized corrosion, erosion, and scaling; liquid leaks in tanks, valves, and pipelines; and expansion joint failures. 27 ------- Table 9. CHEMICAL ANALYSIS OF CHOLLA SERVICE WATER Component Calcium ion Magnesium ion Bicarbonate ion Sulfate ion Chloride ion Sodium ion Total dissolved solids PH Temperature, °C (°F) Concentration, ppm Well No. 1 Well No. 2 126.4 40.0 219.6 132.0 147.0 0 665.0 7.55 18(65) 120.0 34.2 202.5 68.0 127.0 0 551.7 7.50 18(65) 28 ------- Table 10 summarizes the perforraace of the FGD system since start-up. DESIGN AND OPERATION MODIFICATIONS From start-up to the present, FGD operating procedures have been modified somewhat. The most important changes have occurred in the process control area. The continuous pH sensors were eliminated and manual wet techniques were adopted on a once-per- shift basis. The original density meters were replaced with nuclear units. The utility has adopted the practice of water purging of plugged sensing lines. The mist eliminator wash system, originally designed to spray each quadrant with service water for 12 seconds every 8 minutes, has been changed to spray each quadrant 45 seconds every 30 minutes. The only major change in the scrubbing system's design that will be incorporated into the Cholla No. 2 scrubbing system, is the use of Inconel 625 in the fabrication of the reheater tubes (316L stainless steel used in Cholla 1). ECONOMICS In 1973 dollars, the Cholla 1 FGD system cost APS approxi- mately $6.5 million (or $57/net kW). This figure does not include the cost of such items as limestone storage and milling facilities and sludge disposal {a pre-existing ash pond is used). The figure also does not include additional costs in- curred by the system supplier. Cost of the ground limestone is $19.20 to $23.50 per ton, delivered. (Transportation costs included in these figures are $7.07 'to $15.58 per ton, or 37 to 66 percent of the delivered cost.) The annual cost of the system is estimated to be 2.2 mills/ kWh. This figure includes a 23 percent charge on capital in- vestment to account for interest, depreciation, taxes, and other fixed charges. The 1975 and 1976 annual costs of maintenance, including labor and materials, were $183,871 and $216,024. Arizona Public Service believes these maintenance costs are high, 29 ------- Table 10. PERFORMANCE DATA FOR CHOLLA FGD SYSTEM: OCTOBER 1973 TO DECEMBER 1977 Period Oct. Nov. Dec. Jan. Feb. Mar. Apr. Hay June July Aug. sept Oct. Nov. Dec. 1974 Jan. Feb. 73 73 73 74 74 74 74 74 74 74 74 . 74 74 74 74 Avg. 75 75 Reliability, percent Module A Module B System avg. Initial operation and testing initial operation and testing Commercial operation 97 100 100 66 98 100 97 97 95 83 100 100 94 98 96 90 94 66 57 99 100 92 97 99 68 98 100 88 99 99 94 97 83 62 98 100 97 97 97 76 99 10T) 91 98 98 Comments Initial operation and testing of the system and continued for 3 weeks. Particulate and encies, mist carryover, gas flows, and gas The construction and initial testing of the December 3 . Commercial operation began on System performance from December 15, 1973, started on October 2, 1973, sulfur dioxide removal effici- leakage rates wore determined. system were completed on December 14 . to April 15, 1974, was satis- factory. The scrubbing trains were shut down intermittently for replace- ment of corroded Corten steel expansion joints on the reheater bundles . Module B was out of service from April 15 to 28; Module A was out from April 17 to 27. The system was shut down for an annual boiler and FGD system overhaul. 10 o (Continued) ------- Table 10. (continued) Period Har. 75 Apr. 75 Hay 75 June 75 July 75 Aug. 75 Sept. 75 Oct. 75 Nov. 75 Dec. 75 1975 Avg. Jan. 76 Feb. 76 Har. 76 Apr. 76 May 76 June 76 Reliability, percent Module A 88 48 100 97 95 98 84 100 100 91 99 99 76 64 Module B 65 40 100 98 100 97 55 80 100 85 99 98 100 39 System avg. 76 44 100 98 98 98 70 90 100 88 99 98 88 52 Comments Both nodules were out of service most of the month for scheduled repairs and cleaning. A substantial amount of plugging was observed in the Module A absorber tower packing. Some plugging was also noted in the mist eliminators. One forced FGD system outage resulted from flow restrictions in the FDS reciroulation lines because they needed to be cleaned out. Problems recurred with FDS recirculation lines, requiring additional cleanouts . Overhauling of FGD equipment and recoating of vessels accounted for most of the scrubber outage time. Minor problems encountered during this period included recycle pump failure and malfunctioning of the Module B reheater coil. Module A was in service 715 hours, Module B, 654 hours. Some minor valve and plugging was encountered during the period. The FGD system experienced coating failures in the elbow of the exhaust duct leading to the stack. During the month Module A experienced corrosion problems in the reheater tubes. The FDS recirculation lines continued to plug up. The utility shut down the FGD system for inspection, maintenance, and repairs. Ul (Continued) ------- Table 10. (continued) Period July 76 Aug. 76 Sept. 76 Oct. 76 Nov. 76 Dec. 76 1976 Avg. Jan, 77 Feb. 77 Mar. 77 Apr. 77 Hay 77 June 77 Reliability, percent Module A 100 100 100 56 96 98 89 72 99 72 100 87 100 Module B 98 100 100 56 98 100 89 93 99 93 100 87 100 System avg. 99 100 100 56 97 99 89 83 99 83 100 87 100 Comments The utility completed repairs to the coating in the elbow scrubber exhaust duct. The boiler was in service the entire month. Module A and Module B service times were 720 and 679 hours. Boiler, Module A, and Module B service times were 417, 415, and 277 hours respectively. Boiler, Module A, and Module B service times were 720, 682, and 556 hours, respectively. Minor outages were caused by a reheater steam leak and inlet gas damper adjustments. Boiler, Module A, and Module B service times were 744, 742, and 498 hours, respectively. Additional adjustments were made to the Module A inlet gas dampers. Boiler, Module A, and Module B service times were 744, 532, and 684 hours, respectively. Boiler, Module A, and Module B service times were 672, 648, and 591 hours, respectively. The Hunters packing in the Module A absorber was replaced. Minor problems included module vessel plugging, corrosion, liquid piping and gas by-pass dampers. Boiler, Module A, and Module B service times were 744, 532, and 684 hours, respectively. Boiler, Module A, and Module B service times were 638, 635, and 629 hours, respectively. Boiler, Module A, and Nodule B service times were 645, 645, and 645 hours, respectively. The unit was shut down by APS for mid-year inspection, overhaul, and repairs. R-C Initiated a forced oxidation teat program on the system by forcing air into the FDS scrubber tank and converting all the sulfite to sulfate. Boiler, Module A, and Module B service times were 720 hours. to NJ (Continued) ------- Table 10. (continued) U) U) Period July 77 Aug. 77 Sept. 77 Oct. 77 Nov. 77 Dec. 77 1977 Avg. Reliability, percent Module A 97 ' 97 100 100 100 97 93 Module B 99 99 100 100 96 91 97 System avg. 98 98 100 100 99 94 95 Comments Boiler, Module A, and Module B service times were 744, 724, and 734 hours, respectively. Leaks were encountered in the limestone slurry tank and the Module B return line. R-C continued forced oxidation testing . Boiler, Module A, and Module B service times were 744, 723, and 734 hours, respectively. Boiler, Module A, and Module B service times were 720, 718, and 716 hours, respectively. Problems with leaks in the limestone slurry tank and return line to the FDS tank continued to plague the system. Boiler, Module A, and Module B service times were 744, 743, and 743 hours, respectively. Boiler, Module A, and Module B service times were 169, 169, and 142 hours, respectively. Boiler was overhauled during the last half of the month. Minor problems with FGD included venturi leaks and a pump expansion joint failure. ------- and they also believe that the high removal efficiencies and reliabilities listed in the report are the result of considerable financial investment on their part. 34 ------- APPENDIX A PLANT SURVEY FORM A. Company and Plant Information 1. Company name: Arizona Public Service Co. (APS) 2. Main office; Phoenix, Arizona 3. Plant name; Cholla Steam Electric Station 4. Plant location; Joseph City. Arizona 5. Responsible officer; L. K. Mundth 6. Plant manager: Cleo Walker 7. Plant contact; Aubrv Parsons 8. Position; Assistant Plant Manager 9. Telephone number; (602) 288-3357 10. Date information gathered: April 8, 1976 Participants in meeting Affiliation Aubrv Parsons APS Milton Johnson APS H. A. Ohlgren PEDCo Environmental G. 'A. Isaacs PEDCo Environmental B. A. Laseke PEDCo Environmental ------- B. Plant and Site Data 1. UTM coordinates: T 2. Sea Level elevation: Sea level 3. Plant site plot plant (Yes, No) :^ (include drawing or aerial overviews) 4. FGD system plan (yes. No): yes 5. General description of plant environs; Flat and arid desert region, sparsely populated 6. Coal shipment mode; coal is shipped to the plant by rail from the Gallup, New Mexico, area [165 km (100 miles) east of the plant] and the window Rock, Arizona, area [145 km (88 miles) northeast of the plant] . FGD Vendor/Designer Background 1. Process name: Limestone slurry 2. Developer/licensor name; Research-Cottrell, Inc. 3. Address: Box 750. Bound Brook, New Jersey 08805 4. Company offering process: Company name: Research-Cottrell. Inc. Address: P.O. Box 750 36 ------- Location: Bound Brook. NPW Jersey Company contact: James E. McCarthy Position; Manager, Sales Development Telephone number; 201/885-7101 5. Architectural/engineers name: Ebasco. Inc. Address: 2 Rector Street Location: New York. N.Y. 10006 Company contact: Position: Telephone number; 212/785-2200 D. Boiler Data 1. Boiler: 1 2. Boiler manufacturer: Combustion Engineering 3. Boiler service (base, standby, floating, peak): Base 4. Year boiler placed in service: 1962 5. Total hours operation; Approximately 100,000 6. Remaining life of unit: Approximately 16 years 7. Boiler type: Pulverized-coal-fired, wet-bottom 8. Served by stack no.: 1 9. Stack height; 76 m (250 ft) 10. Stack top inner diameter: 11. Unit ratings: Gross unit rating: 124 MW Net unit rating without FGD: 119.5 MW 37 ------- Net unit rating with FGD; 114.3 MW Name plate rating: 12. Unit heat, rate: 10,202 kJ/net kWh (9670 Btu/net kWh) Heat rate without FGD: Heat rate with FGD: 13. Boiler capacity factor, (1974); 85% 14. Fuel type (coal or oil): Coal 15. Flue gas flow: o Maximum: 227 m /sec (480,000 acfm) Temperature: 136°C (276°F) 16. Total excess air; 18 to 20% (3% 02 in flue gas) 17. Boiler efficiency; 86% E. Coal Data 1. Coal supplier: Name: McKinley Mine Location: Gallup, N.M., and Window Rock, Arizona Mine location; Gallup, N.M., and Window Rock, Arizona County, State: McKinley, N.M., and Apache, Arizona Seam: 2. Gross heating value: 23.6 MJ/kq (10,150 Btu/lb) 3. Ash (dry basis): 13.45 avg. 4. Sulfur (dry basis): 0.52 avq. 5. Total moisture; 14.77 avq. 6. Chloride: 0.01 to 0.04 Ash composition (See Table A-l) 38 ------- Table A-l. ASH COMPOSITION OF COAL AT CHOLLA 1 Elemental Constituents Percent by weight Iron 8.10 Aluminum 12.24 Calcium 3.54 Magnesium 2.28 Sodium 0.40 Manganese 0.021 Copper 0.007 Lead 0.001 Nickel 0.001 Chromium 0.007 Zinc 0.010 Barium 0.22 F. Atmo-spheric Emission Regulations 1. Applicable particulate emission regulation a) Current requirement: 84.27 ng/J (Q.196 lb/106 Btu) AQCR priority classification: Arizona State Dept. of Regulation and section No.; Health Regulation No. 7-1-3.5 b) Future requirement (Date: ) : Regulation and section No.: Applicable S0_ emission regulation a) Current requirement; 429.9 ng/J (1.0 lb/10 Btu) AQCR Priority Classification: Arizona State Dept. of Regulation and section No.: Health Regulation 7-1-4.2 b) Future requirement (Date: ) 39 ------- Regulation and section No.s G. Chemical Additives; (Includes all reagent additives - absorbents, precipitants, flocculants, coagulants, pH adjusters, fixatives, catalysts, etc.) 1. Trade name: Limestone Principal ingredient: CaCO^ (95% minimum) Function: Scrubbing agent Source/manufacturer.: Superior Co., Phoenix, Arizona Quantity employed: 110% of stoichiometric Point of addition; Absorber recirculation tank Trade name: NA Principal ingredient: Function: Source/manufacturer: Quantity employed: Point of addition: Trade name: NA Principal ingredient: Function: Source/manufacturer: Quantity employed: Point of addition: 4. Trade name: NA Principal ingredient: Function: Source/manufacturer: Quantity employed: NA - Not applicable 40 ------- Point of addition: 5. Trade name; r Principal ingredient: Function: Source/manufacturer: Quantity employed: Point of addition: H. Equipment Specifications 1. Electrostatic precipitator (s) Number: Manufacturer: Particulate removal efficiency: Outlet temperature: Pressure drop: 2. Mechanical collector(s) Number: Type: Multicvclones (multitube dust collectors) Size: Manufacturer; Research-Cottrell Particulate removal efficiency; 75 to 80% Pressure drop: 3. Particulate scrubber(s) Number: Two Type: Flooded-disc venturi _ Manufacturer: Research-Cottrell Dimensions: 1.8 m $ x 13.7 m (6 ft t> x 45 ft high) 41 ------- Material, shell: 316L stainless steel Material, shell lining; Ceilcote flakeglass (lower portion) Material, internals; None i1 No. of modules: One per module No. of stages; One Nozzle type; See item No. 1, Section M - General Comments Nozzle size: See item No. 1, Section M - General Comments No. of nozzles; See item No. 1, Section M - General Comments Boiler load: 100% Scrubber gas flow: 113 m3/sec (240, OOP, acfm) @ 136°C (276-°F) Liquid recirculation rate: 137 liters/sec (2170 gpm) Modulation: 50% turndown (50 MW) L/G ratio: 1.35 liters/m3 (10.1 gal./lOOO acf) Scrubber pressure drop: 2.5 kPa (10 in. H?O) Flooded-disc controls throat opening Modulation: and pressure drop Superficial gas velocity: Particulate removal efficiency; 99.2% Inlet loading: 70.6 g/m3 (2.0 gr/scf) Outlet loading: SO- removal efficiency: Inlet concentration:_ Outlet concentration: 4. SO, absorber(s) Number: Two (Module A, packed. Module B. hollow) Type: Packed tower absorber (Module A) Manufacturer: Re search-Cottrel1 42 ------- Dimensions : 6.7 m $ x 21.3 m (22 ft $ x 70 ft) Material, shell: 316L stainless steel" Material, shell lining: None Material, internals: Munters Packing No. of modules; Qne No. of stages: Corrugated sheets of polypropylene joined Packing type; jn a fixed matrix, honeycomh Packing thickness/stage; p.g m (2 ft\ Nozzle type: Spinner vane Nozzle size: No. of nozzles: Boiler load: Absorber gas flow; 113 m3/sec @ 136°C (240,000 acfm @ 276°F) Liquid recirculation rate; 567 liters/sec (9000 gpm) Modulation: None L/G ratio: 6.5 liters/m3 (48.9 cral./lOOO acf) Absorber pressure drop: Q.i kPa fO.5 in. H~0) £ Modulation: None Superficial gas velocity; 2.1 m/sec (6.9 ft/sec) Particulate removal efficiency: Inlet loading; _^_____ Outlet loading: 0.353 a/m3 (0.010 ar/scf) SOI removal efficiency: 92% (Module A); 25% (Module B) Inlet concentration; 420 pom (Module A); 420 ppm (Module B) Outlet concentration: 35 ppm (Module AJ; 315 ppm (Module B) 43 ------- 5. Clear water tray(s) Number: None Type: t Materials of construction: L/G ratio: Source of water: 6. Mist eliminator(s) Number: Two, one per Type: Chevron (1st stage)7 special design (2nd stage) Materials of construction; Polypropylene (T-271 and T-41) Manufacturer: Munters Configuration (horizontal/vertical): Horizontal Distance between scrubber bed and mist eliminator: 3.7 to 4.6 m (12 to 15 ft) Mist eliminator depth: Q.3 m (1.0 ft) per stage First stage 3.8 cm (1.5 in.); Vane spacing; second stage 18.1 cm (7.1 in.) Vane angles: 45 degree Type and location of wash system; .intermittent over spray. 15 liters/sec (240 pgm); 45 sec every 30 min/guadrant Superficial gas velocity; 0.1 kPa (0.5 in. H?0) Pressure drop: Comments: Two stages per mist eliminator; two passes in first stage, four passes in second stage. 1.2 m (4 ft) between stages. 7. Reheater(s): TWO Type (check appropriate category): 44 ------- [X] in-line (she11-and-tube heat exchanger, two bundles per exchanger; 316L SS construction) [j indirect hot air (~) direct combustion Q bypass Q exit gas recirculation Q waste heat recovery D other Gas conditions for reheat: Flow rate; 231 m /sec (490,000 acfm) Temperature: 50°C (122°F) SO2 concentration: 35 ppm (Module A); 330 ppm (Module B) Heating medium: Saturated steam Combustion fuel: NA Percent of gas bypassed for reheat: NA Temperature boost (AT): 22°C (40°F) Energy required: 2% Comments ; Saturated gteam extracted from boiler steam dyum at a ressure of 1.8 MPa (250 si) ; consumtion rate is 9000 kg/min (20.000 Ib/hr^; rating is 84 GJ/hr (8 x 106 Btu/hr) . 8. Fan (s) Four: two induced-draft boiler fans and two forced-draft FGD booster fans Type : Forced-draft paddle wheel (FGD booster fans) _ Materials of construction: Mild steel ___ Manufacturers Westinghouse Legation: Upstream of FGD, suction side of boiler ID fan s Fan/motor speed: Motor/brake power: 45 ------- 9. Variable speed drive: Tank(s) Total number of tanks Tank sizes Retiontion time at full load Temperature PH Solids concentra- tion, percent Specific gravity Flooded-disc scrubber holdup tank one 3.8 ra (12 ft) dia. X4.3 m (14 ft) 7 min 49 °C (121 °F) S.2 15.5 1.102 SO. absorber towers holdup tank one (common) 8.3 m (27 ft) dia. xB.5 m (28 ft) 5 min 49°C (121"P) 6.5 8.3 1.049 FGD system sludge holdup tank two 5.6 m (18 ft) dia. x (27 ft) 8.2 m 14 hr each 49°C (121CP) 5.2 25 Limestone slurry makeup tank one 32"C (90°P) 20 10. Recirculation/slurry pump(s) Number 3 3 Description FDS recirculation Absorber recirculation Manufacturer Gould Gould Capacity . liters/sec (gpm) 168 (2670) 587 (9300) Materials Rubber-lined Rubber-lined Service Two operational/ one spare Two operational/ one spare 11, Thickener(s)/clarifier(s) NA Number: None Type: Manufacturer: Materials of construction: Configuration: Diameter: Depth: Rake speed: 12. Vacuum filter(s) NA 46 ------- Number: Type: Manufacturer: Materials of construction: Belt cloth material: Design capacity:_ Filter area: 13. Centrifuge(s) NA Number: None Type: Manufacturer: Materials of construction: Size/dimensions: Capacity: 14. Interim sludge pond(s) Number: One (pre-existing fly ash disposal pond) Description: Solar evaporation and fly ash disposal pond Area: 283,281 to 404>687 m2 (70 to 100 acres) Depth: 1.8 m (6 ft) maximum Liner type; Unlined Location: On plant site Typical operating schedule; Continuous discharge with no recurculation to FGD because of high evaporation rate Ground water/surface water monitors: NA 15. Final disposal site(s) : Pre-existing fly ash disposal pond 47 ------- Number: NA Description: Area: Depth: Location: Transportation mode: Typical operating schedule: 16. Raw materials production: See item No. 2, Section M General Comments Type: None Number: Manufacturer: Capacity: Product characteristics: Delivered 75% < 200 mesh Equipment Operation, Maintenance, and Overhaul Schedule 1. Scrubber (s) Design life: Elapsed operation time: Cleanout method: Cleanout frequency: Scheduled every 6 months Cleanout duration: Other preventive maintenance procedures: Complete with each system shutdown 2. Absorber(s) 48 ------- Design life: Elapsed operation time: Cleanout method: Cleanout frequency: Same as scrubbers Cleanout duration: Other preventive maintenance procedures: Same as scrubbers 3. Reheater(s) Design life: Elapsed operation time: Six steam-operated soot blowers run for Cleanout method;5 roin each 8-hour shift. Cleanout frequency: Cleanout duration: Other preventive maintenance procedures: 4. Scrubber fan(s) Design life: Elapsed operation time: Cleanout method: Cleanout frequency: scheduled every 6 months Cleanout duration: Other preventive maintenance procedures: 5. Mist eliminator(s) Design life: Elapsed operation time: 49 ------- Cleanout method: Cleanout frequency; Every 30 minutes Cleanout duration; 45 seconds, 15 liters/sec (240 gpm) Other preventive maintenance procedures: 6. Pump(s) . Design life: Elapsed operation time: Cleanout method: Cleanout frequency! Scheduled every 6 months Cleanout duration: Other preventive maintenance procedures: 7. Vacuum filter(s)/centrifuge(s) Design life: Elapsed operation time: Cleanout method: Cleanout frequency: Cleanout duration: Other preventive maintenance procedures: 8. Sludge disposal pond(s) Design Elapsed operation time: Capacity consumed: Remaining capacity: 50 ------- Cleanout procedures: J. Cost Data 1. Total installed capital cost; $6.5 million ($57/kW)a 2. Annualized operating cost; 2.2 mills/kwhb 3. Cost analysis (see breakdown: Table A2) 4. Unit costs a. Electricity; p. 2 itiills/kWh (including steam) b. Water: c. Steam: 0.2 mills/kWh (including electricity) d. Fuel (reheating/FGD process); NA e. Fixation cost: NA f. Raw material; 0.15 mills/kWh (limestone)0 g. Labor: 5. Comments a Capital cost figure given in 1973 dollars. Additional capital cost expenditures by APS and R-C not included. Includes a 23% charge for capitalization to account for interest, depreciation, taxes, and other fixed charges. Annual 1975 and 1976 maintenance costs, including labor and materials, were $183,871 and $216,024. CCost of limestone is $19.20 to $23.50 per ton. This includes a transportation cost of $7.07 to $15.58 per ton. . 51 ------- Table A2. COST BREAKDOWN Cost elements A. Capital Costs Scrubber modules Reagent separation facilities Waste treatment and disposal pond Byproduct handling and storage Site improvements Land , roads , tracks , substation Engineering costs Contractors fee Interest on capital during construction B. Annual ized Operating Cost Fixed Costs Interest on capital Depreciation Insurance and taxes Labor cost including overhead Variable costs Raw material Utilities Maintenance Included in cost estimate Yes CZH cm Cm Cm CZD No dD cu CUD cm cm a cm cm cm CZZI cm cm cm Estimated amount or % of total capital cost 23 percenl; 23 percent 23 percent S19.20 - S23.5/tpn limestone 0.2 mills/kWh 5183,871 (1975), $216,024 U976) 52 ------- K. Instrumentation A brief description of the control mechanism or method of measurement for each of the following process parameters: Reagent addition: Liquor solids content: Liquor dissolved solids content: 0 Liquor ion concentrations Chloride: Calcium: Magnesium: Sodium: Sulfite: Sulfate: Carbonate: Other (specify):. 53 ------- Liquor alkalinity: See remarks Liquor pH; See remarks Liquor flow; See remarks 0 Pollutant (SO-, particulate, NO ) concentration in ** X flue gas: See remarks 0 Gas flow; See remarks 0 Waste water See remarks 0 Waste solids: See remarks 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: A thorough description of the instrumentation/ con- trol loop is provided under Process Description in Section 3 of the report. L. Discussion of Major Problem Areas: 1. Corrosion: See Operation Problems and Solutions in Section 4 of the report. 54 ------- 2. Erosion: See Operation Problems and Solutions in Section 4 of the report. 3. Scaling; See Operation Problems and Solutions in Section 4 of the report. 4. Plugging; See Operation Problems and Solutions in Sec- tion 4 of the report. 5. Design problems; See Operation Problems and Solutions in Section 4 of the report. 6. Waste water/solids disposal: See Operation Problems and Solutions in Section 4 of the report 55 ------- 7. Mechanical problems; See Operation Problems and Solutions in Section 4 of the report M. General comments: 1. Two-thirds of the scrubbing solution used in the flooded- disc scrubbers is introduced through the hollow shaft of the flooded disc; the remainder is sprayed through tangential nozzles located on the vessel wall. 2. Arizona Public Service is now installing a limestone grinding facility on the plant grounds. This facility will be able to meet the limestone requirements of Cholla 1 and 2 (Cholla 2 will be put in service in June 1978) . It will consist of a ball mill capable of grinding 0.6 cm (0.25 in.) limestone rock to 75 percent minus 200-mesh product. 56 ------- APPENDIX B PLANT PHOTOGRAPHS Photo No. 1. General view of the FGD system and boiler for the Cholla No. 1 unit. The two parallel scrubbing trains are featured in the foreground. The boiler is featured in the background. The B-side absorber tower is featured closest to the viewer. Photo No. 2. Back view of the A-side scrubbing train. Featured in the photo are the induced draft fans, flue gas ductwork, flooded-disc scrubber, absorber tower, and tank. 57 ------- Photo No. 3. Side view of scrubbing facilities. Featured in the photo from left to right are the coal conveyor, absorber tower, ductwork, slurry recirculation tank, stack, and part of the lime- stone storage silo. Photo No. 4. Closeup view of the scrubbing train. The flooded-disc scrubber, sump, and absorber tower are featured in the photo from left to right. 58 ------- Photo No. 5. Close up view of the base of the shaft which is connected to the flooded-disc located in the throat area of the scrubber. Photo No. 6. Side view of the mechanical collectors and the scrubber induced draft booster fan. 59 ------- Photo No. 7. draft fan. Side view of the scrubber induced Photo No. 8. View of the battery of absorber tower feed pumps. A total of three are employed for service to both scrubbing trains. 60 ------- Photo No. 9. Side view of the twin sludge holding tanks showing the discharge pumps and piping. Photo No. 10. View of limestone silo and lake which provides fresh water to the plant. A work shed is located in the foreground. ------- Photo No. 11. The Cholla station coal receiving, storage and conveying facilities. Photo No. 12. View of the boiler for Cholla No. 2 This unit is currently under construction and is scheduled for start-up in June 1977. 62 ------- TECHNICAL REPORT DATA (Please read Instructions on the reverse before completing) REPORT NO. EPA-600/7-78-048a 2. 3. RECIPIENT'S ACCESSION NO. ,T,TLE AND SUBTITLE Surv?y of Flue Gas Desulfurization Systems: Cholla Station, Arizona Public Service Co. 5. REPORT DATE March 1978 6. PERFORMING ORGANIZATION CODE 7. AUTHOR(S) Bernard A. Laseke, Jr. 8. PERFORMING ORGANIZATION REPORT NO, 9. PERFORMING ORGANIZATION NAME AND ADDRESS PEDCo Environmental, Inc. 11499 Chester Road Cincinnati, Ohio 45246 10. PROGRAM ELEMENT NO. EHE624 11. CONTRACT/GRANT NO. 68-01-4147, TaskS 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 Subtask Final; 1-6/77 14. SPONSORING AGENCY CODE EPA/600/13 15. SUPPLEMENTARY NOTES jERL-RTP project officer is Norman Kaplan, Mail Drop 61, 919/ 541-2556. Report EPA-650/2-75-057a gives first survey results. 16. ABSTRACT The report gives results of a second survey of the flue gas desulfurization (FGD) system on Unit 1 of Arizona Public Service Co. 's Cholla Station. The FGD system, commercially available in December 1973, utilizes a limestone slurry in two parallel scrubbing modules to control SO2 and fly ash from the combustion of low sulfur western coal. (The two-module FGD system is described.) The system's total SO2 removal efficiency is 58. 5% (92% for the SO2 removal module). Either or both modules can be bypassed. The flue gas cleaning wastes are disposed of in an on-site unlined fly ash pond. No water is recycled from the pond to the FGD system. Following a number of modifications of the FGD system by the system supplier and the utility, the system has exhibited a high degree of mechanical reliability while meeting required SO2 and particulate emission control levels. 17. KEY WORDS AND DOCUMENT ANALYSIS DESCRIPTORS b.IDENTIFIERS/OPEN ENDED TERMS c. COSATI Field/Group Air Pollution • Flue Gases Desulfurization Fly Ash Limestone Slurries Scrubbers Coal Combustion Cost Engineering Sulfur Dioxide Dust Control Ponds Air Pollution Control Stationary Sources Wet Limestone Particulate 13B 21B 07A,07D 11G 21D 14A 07B _Q8JL 13. DISTRIBUTION STATEMENT Unlimited 19. SECURITY CLASS (This Report) Unclassified 72 20. SECURITY CLASS (Thispage) Unclassified 22. PRICE EPA Farm 2220-1 (9-73) 63 ------- |