SWEPCO-MU-Ex. 16 WISCONSIN PUBLIC SERVICE WESTON UNIT 4 FLUE GAS DESULFURIZATION FILE NO SYSTEM ANALYSIS

Transcription

1 WISCONSIN PUBLIC SERVICE WESTON UNIT 4 FLUE GAS DESULFURIZATION NO ISSUE DATE AND REVISION NO BLACK & VEATCH CORPORATION WPS

2 NO CONTENTS INTRODUCTION... BRIEF HISTORY OF FGD TECHNOLOGIES First-Generation FGD Systems Second-Generation FGD Systems Third-Generation FGD Systems Current FGD System Design...3 INITIALLY EVALUATED FGD PROCESSES General Wet Limestone-Based Forced-Oxidation FGD Process Wet Lime-Based Forced-Oxidation FGD Process Semi-Dry Lime-Based Spray Dryer Absorber (SDA) FGD Process Altemative Absorber Module Types Systems Selected for Evaluation...17 EVALUATION OF SELECTED FGD TECHNOLOGIES Description of Selected Technologies Comparative Capital and Annual Costs Other Considerations...13 APPENDIX A TABLES Design Criteria Capital and Operating Cost Summary Characteristics of Alternative FGD Systems Economic Evaluation Factors Capital Costs ($1000) Annual O&M Costs ($1000) Operating and Maintenance Staffing Year Accumulative Present Value of Annual Revenue Requirement ($1ooo) Year Accumulative Present Value by Year ($ millions) US EPA Predicted Mercury Removal Rates for Subbituminous Coal TC-1 SWEPCO-MU-Ex. WPS

3 NO FIGURES / Wet Limestone-Based Forced-Oxidation FGD Process Wet Lime-Based Forced-Oxidation FGD Process SDA FGD Process Countercurrent Spray Tower FGD Process Cocurrent Packed Tower FGD Process J-BR FGD Process CDS FGD Process Accumulative Present Value of AQCS Alternatives TC-2 WPS

4 NO : 1.0 INTRODUCTION Wisconsin Public Service Corporation is evaluating the design of the Unit 4 coal-fired generating unit at its Weston Station. This study presents the results of a study into the optimal flue gas desulfurization (FGD) technology for controlling sulfur dioxide (SO2) and particulate matter emissions from this new unit. All of the potential FGD technologies were based on the design criteria in Table 1-1. Parameter Flue gas flow leaving air heater Coal quality Flue gas emission limits Table 1-1 Design Criteria Value 1,832,100 acfm at 280 F and in. H20 Black Thunder coal 8840 Btu/lb 0.30% S (0.68 lb SO~/MBtu) 5.0 % ash 0.12 lb SO2/MBtu (83% removal) lb particulate/mbtu 1-1 SWEPCO-MU-Ex. WPS

5 NO SUMMARY The flue gas desulfurization (FGD) process will be designed to an emission rate of 0.12 pound SO2 per million Btu (83% removal). Based on the required performance and the current state-of-the-art of FGD process design, the four FGD/particulate removal equipment trains were selected for detailed evaluation: Altemative 1 - Lime-based spray dryer absorber (SDA) FGD/fabric filter, the combined fly ash/fgd byproduct is placed in a landfill. Altemative 2 - Two-field ESP/lime-based SDA FGD/fabric filter, fly ash sold off site, FGD byproduct sent to landfill. Altemative 3 - Fabric filter/wet limestone-based, forced oxidation FGD, commercial-grade gypsum byproduct and all fly ash sold off site. Alternative 4 -Same as Alternative 3 except that the FGD gypsum byproduct is placed in a landfill. These altematives provide a good comparison of semi-oh3, and wet FGD technologies with their relative capital and operating costs, and technical advantages and disadvantages. Alternative 2 was included to provide a semi-dry FGD process alternative that retained the potential for off-site fly ash sales. A low-efficiency, two-field electrostatic precipitator (ESP) would be installed upstream of the SDA to remove 80 to 90 percent of the fly ash before it is mixed with FGD byproduct solids and rendered unusable for commercial applications. Although not included in the evaluated equipment trains, the wet lime-based FGD process and the semi-dry circulating chy scrubber (CDS) process are technically and commercially viable FGD processes. They should be considered as wet and semi-dry altematives to the processes evaluated. The capital costs and first-year operating of the four altematives are summarized in Table SWEPCO-MU-Ex. WPS

6 FLUE GAS DESULFURIZATION SYSTEM NO WU Cost Category Alternative 1 SDA + Fabric Filter Capital Cost, $1000 in 2003 Total 69,520 Differential Base Total Annual Costs, $1000 in 2003 Total 5,635 Differential 1,952 Table 2-1 Capital and Operating Cost Summary Altemative 2 ESP + SDA + Fabric Filter Alternative 3 Fabric Filter + Wet FGD Gypsum Sales 90, ,691 21,210 43,171 Alternative 4 Fabric Filter + Wet FGD Gypsum Disposal 112,691 43, ,683 4,401 1,239 Base 718 Accumulative Present Value of Annual Costs, $1000 in 2008 Total 210, , , ,061 Differential Base 21,824 35,670 48,217 The capital costs are budgetary values for comparative purposes only. These costs do not include cost categories that would be relatively equal between the evaluated altematives. These costs were developed using Black & Veatch in-house resources such as vendor quotes on similar equipment at other sites. Review of Table 2-1 indicates that Altemative 1 has the lowest accumulative present value of the four altematives evaluated. The off-site sale of fly ash does not completely compensate of the capital and operating costs of the upstream ESP installed in Alternative 2. In order for the two semi-dry FGD systems to have the same accumulative present value, the total capital cost of the installation of the ESP must be reduced by $13.5 million1. This would represent a cost reduction in the installed capital cost of the ESP of approximately 60 percent. Altemative 2 annual operating costs are based on "selling" the fly ash at S0/ton (i.e., the user hauls the fly ash off site at no cost to WPSC). Alternatives 1 and 2 would also have the same 40-year accumulative present value if the fly ash could be sold for approximately $18.80/ton. Unless otherwise indicated, all costs are expressed in 2003 dollars. 2-2 SWEPCO-MU-Ex. WPS

7 FLUE GAS DESULFUR!ZATION SYSTEM NO. WU The two wet FGD alternatives are more costly than either of the semi-dry FGD altematives; however, the accumulative present value differentials are very sensitive to the estimated capital cost of the wet FGD system. In order for Alternative 3 to have the same accumulative present value as Alternative 1, the total capital cost of the wet FGD system must be reduced by $22.1 million dollars; an approximately 34 percent reduction in the installed cost of the wet FGD equipment. The advantages of off-site sales of gypsum are very evident in Table 5-3. With no significant additional capital cost expenditure, the 40-year accumulative present value of Alternative 3 is nearly $12.5 million less than Altemative 4. In order for lower cost wet FGD alternative, Alternative 3 to have the same 40-year accumulated present value as base cost Altemative 1, gypsum would need to sell of nearly $66.35/ton rather than the assumed $1.00/ton Other factors to be considered in selecting the optimum FGD system for Unit 4 include the following: A semi-dry system would not produce a visible stack plume except in humid or cold weather. The wet FGD systems produce visible and persistent steam plume. The wet FGD systems have no effect on the design or operation of the fabric filter. The fabric filter is an integral part of a semi-dry FGD system. The semidry system reduces the size of the fabric filter by reducing the gas temperature, but also increases the potential for corrosion at poorly insulated locations and around access doors. Unless an ESP is located upstream of the SDA, a semi-dry system would preclude the off-site sale of fly ash from Unit 4. The wet FGD altematives can achieve up to 95 percent removal of SOz removal. The semi-dry FGD altemative can achieve up to 90 percent removal. The semi-dry SDA FGD process would achieve nearly complete removal of sulfur trioxide (SO3) from the flue gas. A wet FGD system would have no significant effect on SO3. Both wet and semi-dry FGD processes achieve nearly complete removal of hydrochloric acid (HCI). 2-3 SWEPCO-MU-Ex. WPS

8 FiLE No Without activated carbon injection, the semi-dry FGD altematives are predicted to achieve less than 25 percent total mercury removal. The wet FGD system alternatives are predicted to achieve on the order of 72 percent removal. With injection of activated carbon, the total mercury removal rates of semi-dry and wet FGD are estimated to be 80 and 85 percent, respectively. The semi-dry FGD process does not generate a wastewater stream. The wet FGD process would generate a chloride blowdown stream of approximately 10 gpm. 2-4 SWEPCO-MU-Ex. WPS

9 NO BRIEF HISTORY OF FGD TECHNOLOGIES 3.1 First-Generation FGD Systems The first generation of FGD systems was installed in the United States and Japan starting in the early 1970s. In the United States, the first generation of FGD systems was installed in response to the Clean Air Act of 1970, which mandated a maximum SO2 emission from new, coal-fired, utility power plants of 1.2 lb SO2 per million Btu (lb/mbtu). These early systems used many different types of FGD processes as shown in the following listing: Lime-based slurry Limestone-based slurry Alkaline fly ash-based slurry MgO-based slurry Sodium-based clear liquor Citrate-based clear liquor Dual-alkali (lime & sodium) Wellman-Lord process A wide variety of absorber types were employed including venturis, vertical countercurrent spray towers, horizontal cross-flow spray towers, and a number of systems using internal structures such as trays, packing, glass marbles, and mobile spheres to improve mass transfer. In general, these first-generation systems achieved SO2 removal efficiencies in the range of 70 to 85%. With a few exceptions, they produced byproduct solids that had no commercial uses and that were sent to disposal ponds or landfills. The MgO, citrate, and Wellman-Lord processes produced commercial-grade sulfuric acid or elemental sulfur. These first-generation systems were characterized as having moderate to high capital costs. Initially, operating and maintenance costs were high, and system reliability was low. Calcium sulfate scaling ofintemals and materials-of-construction failures were prominent problems. As experience with the systems grew, however, process modifications were implemented that reduced the operating and maintenance costs and greatly improved system reliability. 3.2 Second-Generation FGD Systems A second generation of FGD systems was installed starting in the early 1980s. In the United States, additional restrictions were imposed by the Clean Air Act Amendments of 1979, which established a set of new source performance standards that used a combination of minimum removal efficiencies and maximum emission rates for SOz. At the same time, acid rain concerns in Germany resulted in a massive FGD retrofit effort in that country. 3-1 WPS

10 I~1\1 No The second generation of FGD systems installed in response to these requirements differed in several aspects from the first-generation systems. The development and use of spray dryer absorbers (SDAs) were encouraged as a response to the scaling and materials problems in the first-generation systems. Altematives, such as furnace-injection and duct-injection of lime and limestone, were approaching commercial status. Predominately, however, the FGD technologies employed were improved lime-based and limestone-based wet FGDs. The venturi FGDs and absorbers using packing, marbles, and mobile spheres disappeared. Revised spray towers and spray/tray towers were the most frequently seen absorber types. SO2 removal efficiencies varied for the different processes. Lime-based SDA systems were initially able to attain 70 to 80% removal efficiency, with subsequent improvements to over 90% in some cases. Fumace-injection and duct-injection FGD systems were able to achieve 30 to 50% SO2 removal, but at poor reagent utilization rates (i.e., high reagent consumption). As a result of the process improvements and operating experience, second-generation lime- and limestone-based wet FGD systems were able to achieve 90% removal efficiency. Practically all of the second-generation systems in the United States were designed to produce byproduct solids that were disposed of as waste products in ponds or landfills. In Germany and Japan, however, limestone-based wet FGDs began to use forced oxidation of the byproduct solids to produce commercial-grade calcium sulfate dihydrate (CaSOao2H20), commonly called gypsum, which has a number of agricultural and industrial uses. The second-generation FGD systems, and particularly the lime-based and limestonebased wet FGD systems, demonstrated substantial improvements in operating and maintenance costs and in system reliability. 3.3 Third-Generation FGD Systems In 1990, the US Congress again amended the Clean Air Act. The provisions of these amendments provided US electric utilities with more flexibility in their approaches to SO2 emissions control, but also required existing generating units to reduce their current SO2 emissions by January 1, 2000 through one of the following: Switching to lower sulfur coal. Retrofitting FGD systems. Purchase or transfer SO2 emission allowances from another facility. 3-2 WPS

11 NO In the interval between the second and third generations of FGD systems, a number of process improvements were made. The furnace-injection and duct-injection FGD processes, which previously had relatively high reagent requirements and low SO2 removal efficiencies, were further developed; and limestone i_nj ection with _fumace ac fivation (LIFAC) and circulating dry scrubber (CDS) FGD processes evolved from them. The scaling problems that had continued to reduce the availability of lime- and limestone-based systems were nearly eliminated by the widespread utilization of forcedoxidation and inhibited-oxidation process modifications. The maximum SO2 removal efficiency of these wet systems was increased to over 95% through a combination of better tmderstanding of the process chemistry and the use of chemical additives such as dibasic acid (DBA). Many of these process modifications were retrofitted to secondgeneration systems to resolve existing problems. Many of the systems purchased in the United States in response to the 1990 amendments have used the lime- or limestone-based wet FGD process, and most of these systems were designed to achieve 95% or greater SO2 removal. Several limestone-based systems are designed to produce commercial-grade gypsum, and several existing systems in the United States are currently transferring most or all of their byproduct solids to agricultural or industrial users. In Germany and Japan, production of commercial-grade gypsum has become a routine plant operation. The North American Electric Reliability Council evaluated operating data for 111 FGD systems in the United States for the period of 1987 to This data indicated that, for this period, FGD systems were operating extremely reliably and, with a few exceptions, did not significantly contribute to generating unit forced outages. This data covered primarily first- and second-generation FGD systems. The third-generation systems that recently came into service are anticipated to be even more reliable. 3.4 Current FGD System Design The current generation of FGD system design represents further improvements on the advances that were made in the third-generation systems. There has been a significant consolidation among the FGD system vendors and the reduction in the number of qualified suppliers continues. Several FGD system vendors now offer both semi-dry systems, i.e., CDS or SDA systems, and wet systems (lime-based and limestone-based absorbers), and will offer whichever best meets the utility s particular requirements on a site by site basis. As the maintenance requirements of FGD systems have been reduced, the need for installing a spare absorber module has been greatly diminished. Worldwide, the trend has been to increase the volume of flue gas that can be handled in a single absorber 2 "Impact of FGD Systems - Availability Losses Experienced by Flue Gas Desulfurization Systems," North American Reliability Council, July SWEPCO-MU-Ex. WPS-O

12 NO module and to eliminate the use of a spare module. Currently, most FGD system vendors will offer a single CDS / SDA module capable of treating up to 1.0 million acfm and a single wet absorber module capable of treating 2.6 million acfm or more. This is equivalent to volume of flue gas produced by typical 250 and 900 MWe coal-fired boilers, respectively. Availability guarantees of 99 percent over two years are routinely offered. 3-4 WPS-O05850

13 FILI~ General 4.0 INITIALLY EVALUATED FGD PROCESSES Potential altemates for the Unit 4 FGD system were identified for this study as those listed below. All three are commercially available and well demonstrated at the design flue gas flow rate and SO2 removal efficiency. Wet limestone-based, forced-oxidized FGD process. Wet lime-based, forced-oxidized FGD process. Semi-dry, lime-based spray dryer absorber (SDA) FGD process. This section provides a general summary of these technologies. All of the potential FGD processes could be installed in conjunction with either a fabric filter or electrostatic precipitator for particulate matter (fly ash) emission control. Because the low SOz content of the flue gas results in high-resistivity fly ash, a very large precipitator would be required to meet the design emission rate; therefore, a pulse-jet cleaned fabric filter (PJFF) was assumed to be used regardless of the FGD technology selected. 4.2 Wet Limestone-Based Forced-Oxidation FGD Process Numerous suppliers offer FGD processes using limestone slurry as the reagent. Most wet limestone-based FGD processes use a spray tower with countercurrent flue gas flow. Some suppliers include a perforated tray to improve liquid/gas contact. Two experienced FGD vendors, Chiyoda and Mitsubishi, take very different approaches to liquid/gas contact in their absorbers. These altemative absorbers are discussed in Section 4.5. For this study, however, all of these process variations are considered technically equivalent options. A wet limestone-based FGD process using a spray tower is shown in Figure 4-1. The limestone slurry is typically produced from limestone gravel by grinding in wet ball mills. The resulting slurry flows through a classifier to limit the size of the particles suspended in the slurry. The size of the reagent particles is important because higher reagent utilization rates (lower consumption) are generally achieved with smaller reagent 4-1 WPS-O05851

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15 FmL~ No. particles. Limestone slurry and makeup water are added to the reaction tank to maintain the ph, water level, and slurry solids content at the desired value. Slurry from the reaction tank is sprayed into the flue gas flow stream in the FGD module. Sulfur dioxide is absorbed from the flue gas into the slurry liquid where two chemical reactions occur: SO2-1- CaCO3 nt- 1/2 n20 -~ CaSO3 1/2 H20 + CO2 SO2 + CaCO3 + 1/ H20 --~ CaSO4 2 H20 + CO2 Although both reactions occur, most recent wet limestone-based systems use forced oxidation of the byproduct solids to convert practically all of the calcium sulfite (CaSO3 1/2 HzO) to calcium sulfate (CaSO4~ 2 H20), commonly called "gypsum". No separate oxidation vessel is necessary, since the required oxidation air is injected directly into the reaction tank. Slurry is sprayed into the FGD module at a liquid-to-gas (L/G) ratio3 depending on the application and efficiency required. SO~ removal efficiency generally increases with increasing L/G ratio due to increased gas and slurry contact. Sulfur dioxide from the flue gas is absorbed in the slurry liquid and the chemical reactions shown above occur in the liquid phase. The slurry droplets drain into the FGD module reaction tank where the desulfurization reactions are completed. Slurry recirculation pumps return slurry from the reaction tank to the spray nozzles. The desulfurization byproducts formed in a forced-oxidization wet limestone-based spray tower FGD process are discharged via a blowdown slurry stream. This stream contains solids of calcium sulfate, calcium sulfite, unreacted calcium carbonate, and inert impurities from the limestone. The slurry solids are dewatered using hydrocyclones as a primary step, then a vacuum filter or centrifuge as a secondary dewatering step. The filter cake is suitable for landfill disposal. The benefits of forced oxidation include reduction of scaling in the absorber and the production of a byproduct solid with much improved dewatering and handling characteristics. Unlike calcium sulfite solids, which must be mixed with fly ash and lime to produce a material that can be landfilled, calcium sulfate solids are both physically and chemically stable without additional processing steps. The gypsum solids produced by forced oxidation are more chemically pure and dryer than most naturally occurring gypsum deposits. For this reason, gypsum produced by several existing utility FGD systems is currently being used as a raw material for the 3 Liquid to gas ratio is measured in gallons of slurry sprayed per 1000 cubic feet of flue gas. 4-3 SWEPCO-MU-Ex. WPS

16 No production of wallboard and cement. The feasibility of off-site utilization of the FGD system is very site specific and depends on the byproduct quantity, amount available from other local sources, and the local demand for gypsum. Additional study would be required to determine the potential market demand. Most recent FGD systems use a single FGD module to treat the entire flue gas volume from units as large as 1,000 MW. Single-module systems are possible because of their demonstrated high reliability (in excess of 99 percent reliability). Spares can be installed for the components most likely to fail, such as pumps and spray nozzles. Single-module arrangements reduce capital costs and have smaller overall area requirements. Conventional wet limestone-based FGD processes without the use of chemical additives have consistently achieved 90 to 95 percent removal efficiencies over a wide range of coals in the United States. These processes have demonstrated good tumdown capabilities. 4.3 Wet Lime-Based Forced-Oxidation FGD Process Wet lime-based FGD is the generic term for processes using slaked lime as the scrubbing reagent in a spray tower FGD module. This process is offered by a number of FGD suppliers, most of whom use a spray tower with countercurrent flue gas flow. Some suppliers include a perforated tray to improve liquid/gas contact. A process diagram for the system is presented in Figure 4-2. In wet lime-based FGD processes, quick lime (CaO) is slaked to produce a calcium hydroxide [Ca (OH)z] reagent slurry. CaO + H20 --> Ca (OH)2 For a wet lime-based FGD process, the chemical reactions are as follows: 4-4 WPS-O05854

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18 No SO2 + Ca(OH)2 --> CASO3.1/2 H20 + 1/2 H20 SO2 + Ca(OH)~ + 1/ H20 ---> CaSO4o2 H~O Forced-oxidation of lime-based systems is a relatively recent innovation and has much less operating experience than has the limestone-based process. As in the limestonebased forced-oxidation process, practically all of the byproduct solids produced are converted to calcium sulfate. To obtain a fully oxidized byproduct, the solids blowdown is taken from above the reaction tank where the slurry ph is lower. This is necessary since the oxidation step is much easier at lower ph. The oxidation takes place in a separate oxidation tank. The slurry from this tank is dewatered using the same primary and secondary dewatering steps as the wet limestone-based forced-oxidized FGD alternative. The lime reagent slurry reagent may be prepared in detention, paste, or ball mill slakers. Ball mill type slakers are currently the most commonly applied to this application. An inventory of prepared slurry is stored in a slurry feed tank, ready for automatic injection into the FGD module s reaction tank as required to maintain the ph of the reaction tank slurry. The ph of the reaction tank slurry in a wet lime-based FGD process typically ranges between 5.0 and 7.0. Spray towers for wet lime-based FGD processes are essentially identical to those used in wet limestone-based FGD processes discussed in the previous section. The height of the tower and the L/G may be lower than for limestone systems because of the higher reactivity of the lime slurry. Compared to a wet limestone-based FGD system, a wet lime-based system has lower capital costs, lower power consumption, and a shorter absorber module. These advantages, however, are minimized at low inlet SO~ levels such as will be produced by Unit 4. The disadvantages include much higher reagent costs and less operating history for the forced-oxidized process modification. Wet lime-based FGD processes have demonstrated SO2 removal efficiencies as high as 98 percent for a wide range of coals. The process has good tumdown. 4.4 Semi-Dry Lime-Based Spray Dryer Absorber (SDA) FGD Process Spray drying has been used in many industrial process industries since the 1920 s. Since its introduction in the 1970 s, the semi-dry SDA FGD process has been one of the most widely applied FGD technologies. US utilities have installed numerous SDA FGD systems on boilers using low-sulfur fuels. These installations, primarily located in the western US, use either lignite or subbituminous coals as boiler fuel and generally have spray dryer systems designed for a maximum fuel sulfur content of less than 2%. The 4-6 WPS

19 [ NO [ largest installation is at Northem States Power s Sherbume Unit 3 (860 MWe) which bums low-sulfur, subbituminous coal and has been in service since the mid-1980s. There are several variations of this process, but the most prevalent is the installation of one or more spray dry vessels upstream of the particulate control device as shown in Figure 4-3. The SDA absorber vessel is located between the air heater and the particulate removal device, most commonly a fabric filter. Lime slurry is sprayed into the vessel as an atomized mist using either rotary or two-fluid atomizers. Sufficient water is added with the reagent slurry to lower the flue gas temperature to within 18 C (32 F) of the adiabatic saturation temperature. The SO2 is absorbed into the fine spray droplets and reacts with the lime slurry to form both calcium sulfite (-1/3) and calcium sulfate (-2/3). Before the droplet can reach the wall of the atomizer, the heat of the flue gas evaporates the droplet to a dry particle containing the byproduct solids and excess reagent. The byproduct solids and fly ash are collected in the fabric filter. Some additional SO2 removal occurs as the flue gas passes through the dust cake on the bags. The byproducts and fly ash are conveyed pneumatically to the fly ash silo in the conventional manner. These solids are unloaded, conditioned with water, and transported to a landfill. Because of the level of free lime in the byproduct solids, the byproduct/fly ash mixture attains a very high bearing strength and low permeability in the landfill. Unlike the two previously discussed FGD systems, there is currently no commercial use for the byproduct/fly ash. However, some demonstration-scale installations are evaluating the potential to produce a synthetic aggregate from this material. An obvious disadvantage of this system is that the mixing of the byproduct solids with the fly ash eliminates any commercial use of the fly ash. The lime reagent slurry preparation system is identical to that previously described for the wet lime-based forced-oxidation process. However, to reduce lime consumption, a portion of the byproduct/fly ash mixture from the fabric filter is sent to a tank where it is slurried and reused as a supplemental reagent in the SDA. Even with this process feature, an SDA FGD system uses 10 to 20 percent more lime reagent than a wet lime-based system attaining the same SOz removal efficiency. However, its electric power consumption is less, and it has lower initial capital cost. 4-7 SWEPCO-MU-Ex. WPS-O

20 NO Lime Slurry Rotary Atomizer Fly Ash Slurry Reagent Tank Flue Gas From Air Heater Spray Dryer ~ --To Particulate Control Device Ash Lock \. / Feeder ~,~ To Fly Ash Silo Bypass From Boiler Spray ~ Particulate Removal Device To Chimney ID Fan To Fly Ash Silo Figure 4-3 SDA FGD Process 4-8 WPS

21 NO Alternative Absorber Module Types Several suppliers offer lime- or limestone-based FGD processes. Each has standardized on an absorber type they consider best design for this service. The following sections describe the currently available wet and semi-dry FGD absorber types Wet FGDAbsorbers Countercurrent Spray Tower. The countercurrent spray tower has become one of the most widely used absorber types in wet lime- and limestone-based FGD service. Figure 4-4 illustrates the major features of a typical countercurrent spray tower. Flue gas enters at the bottom of the absorber and flows upward. A slurry with 10 to 15% solids is sprayed downwards from higher elevations in the absorber and is collected in a reaction tank at its base. The SO2 in the flue gas is transferred from the flue gas to the recycle slurry. The hot flue gas is also cooled and saturated with water. The recycle slurry is pumped continuously from the reaction tank to the slurry spray headers. Each header has numerous individual spray nozzles that break the slurry flow into small droplets and distribute them evenly across the cross section of the absorber. Prior to leaving the absorber, the treated flue gas passes through a chevron-type mist eliminator that removes entrained slurry droplets from the gas. The mist eliminator is periodically washed to keep it free of solids. In the reaction tank, the SO2 absorbed from the flue gas reacts with the soluble calcium ions in the recycle slurry to form insoluble calcium sulfite and calcium sulfate solids. In forced-oxidized processes, air is bubbled through the slurry to convert all of the solids to calcium sulfate dihydrate, gypsum. A lime or limestone reagent slurry is added to the reaction tank to replace the calcium consumed. In order to control the solids content of the recycle slurry, a portion of the slurry is discharged from the reaction tank to the byproduct dewatering equipment. Depending on the ultimate disposal of the byproduct solids, the dewatering equipment may include settling ponds, thickeners, hydrocyclones, vacuum filters, and centrifuges. The liquid that is separated from the byproduct solids slurry is stored in the reclaim water tank. Process makeup water is also added to this tank to replace water evaporated by the flue gas in the absorber, and water lost with the byproduct solids. The water in the reclaim water tank is returned to the absorber reaction tank as makeup water and used to prepare the reagent slurry. 4-9 SWEPCO-MU-Ex. WPS-O

22 NO To Chimney Mist Eliminators Typical Spray Header Arrangement Water From ID Fans Reagent Makeup Water To Byproduct Handling Equipment Recycle Pumps Figure 4-4 Countercurrent Spray Tower FGD Process 4-10 SWEPCO-MU-Ex. WPS

23 No Cocurrent Packed Tower. The cocurrent packed tower shown in Figure 4-5 uses the same process chemistry as the countercurrent spray tower, but the flue gas and slurry flow cocurrently in the first section of the absorber module. This design is offered by in the US by Advatech (a joint venture of URS Corporation and Japan s Mitsubishi Corporation). In this design, the needed liquid surface area for gas/liquid mass transfer is provided by 3 to 6 feet of open packing. The recycle slurry is evenly distributed across the upper surface of the packing by a few, low-pressure nozzles. Because of the lower nozzle pressure, the solids level in the recycle slurry can be raised to 15 to 25% without resulting in an unacceptable rate of nozzle wear. In another of Advatech s co-current designs, the packing is eliminated and the spray nozzles are turned upward to spray countercurrent to the gas flow. The resulting fountain of slurry falls back down into the reaction tank. This design requires the use of higher-pressure nozzles. Compared to the countercurrent design, the cocurrent packed tower operates as higher flue gas velocity since there is less concern with entrainment of slurry droplets in the flue gas. This altemative also typically uses a horizontal gas flow mist eliminator that can also operate at a higher velocity than the vertical gas flow mist eliminators used in the spray tower design. Jet Bubbling Reactor (JBR). The JBR is a proprietary absorber design by Japan s Chiyoda Corporation. Black & Veatch is the US licensee for this process. This absorber module is unique in the FGD industry because the surface area required for absorption of SO2 from the flue gas is created by bubbling the flue gas through a pool of slurry rather than by recycling slurry through the flue gas as in the other absorber types. Figure 4-6 illustrates the essential features of the JBR. Flue gas is pre-cooled with makeup water and slurry prior to entering the JBR s inlet plenum. The inlet plenum is formed by upper and lower deck plates. The flue gas is directed through multiple, 6-inch diameter, sparger tube openings in the lower deck SWEPCO-MU-Ex. WPS

24 NO.I::ILE From ID Fans ME Wash Water To Chimney Reagent and Makeup Water Mist Eliminators Recycle Pumps Figure 4-5 Cocurrent Packed Tower FGD Process 4-12 SWEPCO-MU-Ex. WPS

25 NO Treated Gas Outlet Gas Outlet Plenum -- Gas Riser -- Inlet Plenum Sparger Pipes Reaction Tank Mist Eliminator Outlet Plenum To Prescrubber ~-~- Chimney From ID Fans Chloride Blowdewn Reagent and Makeup Water To Byproduct Handling Equipment Figure 4-6 JBR FGD Process 4-13 SWEPCO-MU-Ex. WPS

26 NO These tubes are submerged a few inches beneath the level of slurry in the integral reaction tank in the base of the JBR. The bubbling action of flue gas as it exits the sparger tubes and rises through the slurry promotes SOz absorption. The gas then leaves the reaction tank area to the outlet plenum via gas risers that pass through both the lower and upper decks. An external horizontal gas flow mist eliminator removes residual mist carried over from the JBR. The JBR has several advantages compared to the other absorber modules described previously. Because SOz absorption is achieved by bubbling flue gas into the reaction tank, the JBR vessel is relatively compact compared to a conventional spray absorber. Gypsum crystals produced in the JBR have a relatively larger size distribution since there is less attrition due to circulation through slurry recycle spray pumps. Most importantly, the removal efficiency of small particulates (less than 10 ~m) is substantially better in the JBR compare to conventional spray absorbers. This directly increases the removal of condensed SO3 from the system as compared to most other competing wet scrubber designs, which remove practically no SO3. As with any of the absorber types, the advantages of the JBR must be evaluated on a site-specific basis by comparing total annualized costs at the same guaranteed performance levels with those of competing system proposals. Chiyoda has installed over 20 JBR FGD systems around the world treating flue gas from over 10,000 MWe of generating capacity. In the US a 110-MWe JBR FGD system was installed at Georgia Power Company s Plant Yates Unit 1 in 1992 as part of the US DOE CCT program. A JBR has been in operation at the University of Illinois on a 40-MWe facility since The largest North American installation is at Suncor, Inc. in Alberta, Canada. This unit handles flue gas from process boilers (350 MWe equivalent) and has been in operation since Semi-Dry FGD Absorbers Spray Dryer Absorber (SDA). All current SDA designs use a vertical gas flow absorber. These absorbers are designed for co-current or a combination of co-current and countercurrent gas flow. In co-current applications as was shown in Figure 4-3, the gas enters the cylindrical vessel near the top of the absorber and flows downward and outward. In combination-flow absorbers, a gas disperser located near the middle of the absorber directs a fraction of the total flue gas flow upward toward the slurry atomizers. In both cases, the atomizers are located in the roof of the absorber. Both rotary and twofluid nozzles have been applied to this application. The atomizer produces an umbrella of atomized reagent slurry through which the flue gas passes. The SO2 in the flue gas is absorbed into the atomized droplets and reacts with the calcium to form calcium sulfite and calcium sulfate. Before the slurry droplet can reach the absorber wall, the water in the droplet evaporates and a dry particulate is formed WPS

27 NO Some vendors base their designs on a single large rotary atomizer per absorber; others use up to three smaller units. Two-fluid atomizers are always installed as an array of nozzles. All three approaches to spray atomizers have. been successfully applied. The flue gas containing the fly ash and FGD byproduct solids may leave the absorber through the side of the vessel or from the bottom. If the gas leaves through the side, a portion of the fly ash/fgd byproduct solids is collected in a conical hopper at the bottom of the absorber. The solids collected in this hopper are removed by the same pneumatic collection equipment that serves the fabric filter. Circulating Dry Scrubber (CDS). The CDS FGD process is a semi-dr~, lime-based FGD process that uses a circulating fluid bed contactor rather than an SDA. As shown in Figure 4-7, the CDS absorber module is a vertical solid/gas reactor between the air heater and the particulate control device. Water is sprayed into the reactor to reduce the flue gas temperature to the optimum temperature for reaction of the SO2 with the reagent. Hydrated lime [Ca(OH)a] and recirculated dry solids from the particulate control device are injected co-currently with the flue gas into the base of the reactor just above the water sprays. The gas velocity in the reactor is reduced and a suspended bed of reagent and fly ash is developed. The SO2 in the flue gas reacts with the reagent to form predominately calcium sulfite. Fine particles of byproduct solids, excess reagent, and fly ash are carried out of the reactor and removed by the particulate removal device. Over 90% of these solids are returned to the reactor to improve reagent utilization and increase the surface area for SO2/reagent contact. The CDS FGD system produces an extremely high solids load on the particulate removal device due to the recycle of byproduct/fly ash mixture. For this reason, the particulate device is typically an ESP rather than a fabric filter. Most of the recycled material can be collected in the first field of an ESP with minimal effect on the overall ESP sizing. A fabric filter in this same service would require special design features to avoid much more frequent bag cleaning and resulting reduced bag life WPS

28 No CFB Reactor ~--~ To Particulate ~r~ Control Device I Cycl nra~or Wate= Hydrated ~ Lime Flue Gas From Air Heater To Fly Ash Silo CFB Reactor To Chimney From Boiler ID Fan To Fly Ash Silo Figure 4-7 CDS FGD Process 4-16 WPS

29 NO Systems Selected for Evaluation Four FGD/particulate removal equipment alternatives were selected for more detailed evaluation. * Alternative 1 - SDA FGD/fabric filter. Altemative 2 - Two-field ESP/SDA FGD/fabric filter. Altemative 3 - Fabric filter/wet limestone-based, forced oxidation FGD, commercial grade gypsum sold off site. Altemative 4 - Same as Altemative 3 but disposing of gypsum in a landfill. These alternatives were selected to provide a good contrast of initial capital cost, annual operating costs, and byproduct characteristics, as shown in Table 4-1. The wet lime-based FGD system was not used as an alternative plan because its process advantages over the wet limestone-based system are minimized at low inlet SO2 levels and relatively low removal efficiencies. It is however technically feasible and could be considered further if the wet FGD technology is selected for further evaluation. For Altemative 1, the SDA FGD system was selected over the CDS FGD system as the semi-dry lime-based FGD process representative. The two systems are very similar in approach, but the SDA FGD system has more operating facilities and is available from a larger l~umber of vendors. The DCS FGD system could be considered further if the SDA FGD system is selected for further evaluation. Alternative 2 was developed to allow the removal of 80 to 90 percent of the fly ash prior to the SDA FGD system. Collected and handled separately, this ash would be available for off-site sales. This option also substantially reduces the volume of byproduct solids/fly ash mixture that must be disposed of in a landfill. Altemative 3 is based on a spray tower type absorber since this is the most commonly used design. However, the alternative absorber types discussed in Section 4.5 would have the same general advantages and disadvantages compared to the other two alternatives and would have comparable capital and operating costs WPS-O05867

30 No Criteria SO2 Removal Efficiency, % Potential Reagents Capital and Operating Costs Byproduct Disposal Alternatives Fabric Filter Fly Ash Disposal Altematives ID Fans (Not Including Fabric Filter) Flue Gas Ductwork Effect on Chimney Liner Effect On Stack Plume Visibility Changes In Byproduct/Fly Ash Disposal Alternatives Increased Consumption Of Plant Utilities SO3 Removal HCI Removal Total Mercury Removal (PRB Coal) Effects On Wastewater Treatment System Table 4-1 Characteristics of Alternative FGD Systems Alternatives 1 and 2 Alternatives 3 and 4 Spray Dryer Absorber Wet FGD Spray Towers 90+ Lime Relatively lower initial capital costs Relatively higher operating costs Landfill Reclamation Increase in particulate load. Potential for acid condensation. Combined with byproduct solids unless an ESP or fabric filter installed upstream of SDA 4-5 in. wg increase in pressure. Increased potential for buildup ahead of fabric filter. None Visible only during cold or humid weather Byproduct can not be sold. Upstream ESP required for fly ash sales. Uses service water as makeup. Relatively smaller increase in auxiliary power [relative increase = 1.0]. +90% 80 to 100% 8-36% (25% averaged) without powdered activated carbon (PAC) 80% with PAC None 95+ Lime Limestone Relatively higher initial capital costs Relatively lower operatin8 costs Pond Landfill Reclamation Commercial ~gypsum None No effect on fly ash quality 4-6 inwg increase in pressure. Increased corrosion potential for downstream duetwork. Potential for corrosion Potential for acid mist rainout. i Visible under all atmospheric conditions Inhibited oxidation - fly ash required to stabilize byproducts. Forced oxidation - none. Lime- uses service water as makeup. Limestone-uses cooling tower blowdown as makeup. Significant increase in aux power [relative increase = 1.6]. No removal 90 to % (72% average) without PAC 85% with PAC Commercial gypsum - chloride blowdown required. Disposal grade gypsum- if required, smaller than commercial gypsum 4-18 WPS

31 NO EVALUATION OF SELECTED FGD TECHNOLOGIES This section provides a more detailed description of the selected FGD technologies, a comparison of their relative capital and operating costs, and a discussion of other technical considerations. The following four altematives were selected in the previous section. Altemative 1 - Lime-based spray dryer absorber (SDA) FGD/fabric filter, the combined fly ash/fgd byproduct is placed in a landfill. Alternative 2 - Two-field ESP/lime-based SDA FGD/fabric filter, fly ash sold off site, FGD byproduct sent to landfill. Altemative 3 - Fabric filter/wet limestone-based, forced oxidation FGD, commercial-grade gypsum byproduct and all fly ash sold off site. Alternative 4 -Same as Altemative 3 except that the FGD gypsum byproduct is placed in a landfill. 5.1 Description of Selected Technologies Alternative 1 - SDA FGD/Fabric Filter Altemative 1 is a very common air quality control equipment train for low-sulfur coals. This altemative would consist of two 50-percent capacity SDAs, each with an associated multi-compartment fabric filter. The flue gas entering the fabric filter would be cooler than in Alternatives 3 and 4 because the gas temperature has been lowered to within 40 F of the adiabatic saturation temperature. For this reason, the volume of flue gas entering the fabric filter would be smaller, and the fabric filter s capital cost would be slightly less. Lime reagent would be delivered by rail or truck depending upon the location of the lime supply. In either case, the lime would be pneumatically transferred to a storage silo. Slakers would convert the lime to a lime slurry reagent feed. The byproduct/fly ash mixture collected in the fabric filter would be pneumatically transferred to the byproduct storage silo. A portion of the mixture would be recycled as a supplemental reagent and the remainder would be wetted and transferred to a landfill by dump truck. 5-1 WPS

32 NO Because the flue gas is not saturated with water, the chimney flue can be fabricated of carbon steel Alternative 2 - ESP/SDA FGD/Fabric Filter Altemative 2 is identical to Altemative 1 except that a low-efficiency, two-field ESP would be located between the air heater and the SDA modules. The function of this ESP would be to remove 80 to 90 percent of the fly ash before the SDA. This would permit the bulk of the fly ash produced to be suitable of off-site sales and would greatly reduce the volume of byproduct/fly ash mixture requiring landfill disposal. A relatively lowefficiency ESP was selected over a fabric filter in order to minimize capital cost. The estimated cost of this ESP would be approximately half that of a fabric filter handling the same gas volume. Fly ash collected by the ESP would be pneumatically conveyed to the separate fly ash storage silo. If the fly ash is to be sent off-site, it would be unloaded from the silo in a di3 condition and loaded onto trucks or rail cars. If the fly ash were to be landfilled, it would be conditioned with water as it is unloaded and loaded into dump trucks for transport Alternative 3 - Fabric Filter/Wet Limestone-Based, Forced Oxidation FGD/Off-Site Gypsum Sales Altemative 3 consists of a standard, multi-compartment fabric filter followed by a single wet FGD absorber module. The wet FGD system would use limestone reagent and use forced oxidation to produce gypsum suitable for use in the production of cement or wallboard. Limestone reagent would be delivered to the plant site by rail or truck depending upon the location of the nearest suitable quarry. In either case, the limestone would be converted to reagent feed slurry using a ball mill. Byproduct solids produced by the FGD system would be dewatered by hydrocyclones and vacuum filters to produce a filter cake with approximately 10 percent water. The water recovered by the dewatering steps would be returned to the FGD system. The filter cake must be washed with fresh water to reduce the level of chlorides in the gypsum. A chloride bleed stream of approximately 5 to 10 gpm would be required to limit the level of soluble chlorides in the FGD system. The dewatered gypsum can be transported to commercial uses by covered truck or rail car. The fly ash collected by the fabric filter would be pneumatically conveyed to the fly ash silo and handled in an identical manner to the fly ash from the ESP in Altemative SWEPCO-MU-Ex. WPS

33 NO Because the flue gas leaves the FGD system saturated with water, the chimney flue must be fabricated from a corrosion resistant material such as Alloy C-276 or fiberglass reinforced plastic (FRP) Alternative 4 - Fabric Filter/Wet Limestone-Based, Forced Oxidation FGD/Landfill Gypsum Disposal There would be practically no process differences between a system designed to produce disposal-grade gypsum suitable for landfill and a system designed to produce a commercial-grade of gypsum (Alternative 3). The only change would be that the filter cake wash equipment would be eliminated. Transport to a landfill would be by dump truck. 5.2 Comparative Capital and Annual Costs The comparative capital and annual cost of the altematives were evaluated based on the economic factors presented in Table Capital Costs The estimated capital costs of the four altematives in present day (February 2003) are presented in Table 5-2. These costs include, as appropriate, the SDA/fabric filter system (Alternatives 1 and 2), the wet FGD system (Alternatives 3 and 4), a low-efficiency ESP (Alternative 2 only), a stand-alone fabric filter (Alternatives 3 and 4 only), chimney, and balance of plant equipment. The balance of plant category covers the altematives differential costs for the flue gas ductwork, pneumatic ash/byproduct handling equipment (including storage silos), civil construction, and electrical equipment. The cost of each alternative s reagent preparation equipment is included in the alternatives FGD system cost. The cost of the wet FGD system s byproduct dewatering equipment is also included in the FGD system cost. Altematives 2, 3, and 4 would have approximately the same flue gas pressure drop between the air heater and the chimney breeching (-16 inwg).4 The pressure drop for Alternative 1 would be a 3 to 4 inwg less. No differential capital cost was estimated for the induced draft fans resulting from this relatively small increase in the ID fans overall performance requirements. 4 This assumes use of spray tower type wet FGD system. The pressure drop across a CT-121 FGD system would be 4 to 6 inwg greater than a spray tower, which could affect ID fan cost. However, this cost adder would be offset by reduced FGD system capital cost and total electrical power and capacity cost savings. 5-3 WPS