vvEPA United States Environmental Protection Agency Industrial Environmental Research Laboratory Research Triangle Park NC 27711 Technology Transfer Summary Report Sulfur Oxides Control Technology Series: Flue Gas Desulfurization Spray Dry0r Process .- -:-fr'Łtr:5rtiiM*!S!*;i*)g!Si r -7- =Kiiis ^j.itiassS,|nieBrt«*t ••-;, ;"f-A=-:«/ ;1| f ------- ------- Technology Transfer EPA 625/8-82-009 Summary Report Sulfur Oxides Control Technology Series: Flue Gas Desulfurization Spray Dryer Process September 1982 This report was developed by the Industrial Environmental Research Laboratory Research Triangle Park NC 27711 ------- This summary report was prepared jointly by the Radian Corporation of Austin TX and the Centec Corporation of Reston VA. E. D. Gibson, M. A. Palazzolo, and M.; E. Kelly of Radian are the principal contributors. T. G. Brna is the EPA Project Officer. Photographs taken at Argonne National Laboratory are by Al Meyers and Ron Skidmore of the Argonne Graphic Arts Division. ; Comments on or ^questions about this report or requests for information regarding EPA flue gas desulfurization programs should be addressed to: Emissions/Effluent Technology Branch Utilities and Industrial Processes Division IERL, USEPA (MD-61) Research Triangle Park NC 27711 This report has been reviewed by the Industrial Environmental Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park NC, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the U.S. Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. COVER PHOTOGRAPH: Argonne National Laboratory power plant, 500,000-lb/h steam capacity ------- Introduction The Environmental Protection Agency (EPA) is studying spray dryer flue gas desulfurization (FGD) as part of an extensive program of FGD technology development. In this throwaway process (Figure 1), sulfur dioxide (SO2) is removed from the flue gas by an atomized lime slurry [Ca(OH)2] or a solution of sodium carbonate (Na2CO3). The hot flue gas dries the droplets to form a dry waste product while the absorbent reacts with sulfur dioxide in the fliie gas. Dry waste solids—consisting of sulfite (SO3) and sulfate (S04) salts, unreacted ab- sorbent, and fly ash—are col- lected in a fabric filter (baghouse) or electrostatic precipitator (ESP) and are typically disposed of by landfill. By mid-1 981, a total of 12 utility and 11 industrial spray dryer systems had been sold in the. United States. All but three of these systems will use lime as a reagent. One 100-MW utility demonstration (at North- ern States Power Company's River- side Station, Minneapolis, Minnesota) and two industrial sys- tems (atStrathmore Paper, Woronco, Massachusetts; and Celanese Fibers Company's Amcelle Plant, Cumberland, Maryland) were operational as of mid-1981.1 The EPA has been active in sponsor- ing the demonstration and test- ing of spray dryer FGD: From December 1979 to July 1980, pilot tests were performed with various absorbents on a unit treating 20,000 actual ft3/min (570 actual m3/min) at the City of Colorado Springs' Martin Drake Station.2 From May 1980 to December 1980, additional pilot testing was con- ducted on a unit treating 10,000 ac- tual ft3/min (285 actual m3/min) at Public Service of Colorado's Key H^H Flue gas/off-gas H^Bll Cleaned flue gas 1HHJI Absorption feed [P-'-~- '\ Air pollutants H^^H Other systems Cleaned flue gas Lime or sodium carbonate Flue gas Disposal Figure 1. ; Major Components of Spray Dryer FGD Process ------- Comanche Station.3 These tests pro- vided data on key process vari- ables that affect SO2 removal. Emission testing funded by EPA was carried out at Celanese Fibers' Amcelle Plant from May 1980 to December 1980. The Amcelle testing included 23 days of continuous SC>2 monitoring in support of the New Source Performance Standards (NSPS) being developed for indus- trial boilers.4 Spray dryer FGD is currently the only commercially applied dry FGD process. Other dry FGD processes under development include dry injection and combustion of coal- alkali fuel mixtures. Several fac- tors, including mandated and voluntary increases in coal use and the 1979 NSPS for utility boilers, have promoted increased research and development and commercial application of the dry FGD technology. Interest in spray dryer FGD has been spurred primarily by the poten- tial cost savings dry FGD offers over conventional wet FGD, particu- larly for low-sulfur-coal (less than 1.5 percent) applications. Advantages of spray dryer FGD over wet FGD systems include dry waste pro- duction, lower initial capital investment, lower projected operat- ing costs for fuels of moderate sulfur content (up to 3 percent), and less process complexity, which may lead to greater system reliability. Higher absorbent cost is the major disadvantage of spray dryer FGD relative to wet FGD systems. This higher cost results from the higher priced absorbent (lime versus limestone) and the higher Spray dryer exit. Coyote Electric Generating Station, Beulah, North Dakota stoichiometric ratios necessary. Current limits on the applicability of spray dryer FGD stem from a lack of data on installations firing high- sulfur coal, although vendors report high SO2 removal capabilities. This summary report provides a basic description of the spray dryer FGD process. Both sodium carbonate and lime spray drying are dis- cussed, although lime is emphasized because of the higher reagent costs and waste disposal problems associated with sodium carbon- ate and the greater commercial acceptance of lime for dry FGD. ------- Process Description Spray dryer FGD consists of four major steps: • Absorbent preparation • Absorption and drying • Solids collection • Solids disposal Solids disposal is not an integral part of the process but is associated with spray dryer FGD. Figure 2 illus- trates the process flow for a typical spray dryer FGD system. Flue gas exiting the combustion air preheater comes in contact with an alkaline solution or slurry in a spray dryer. The flue gas passes through a contact chamber, and the solution or slurry is sprayed into the chamber with a rotary or nozzle atomizer. The heat of the flue gas dries the atomized droplets while the droplets absorb sulfur dioxide from the flue gas. The sulfur dioxide reacts with the alkaline re- agent to form solid phase sul- fite and sulfate salts. Most of the solids (and any fly ash present) are carried out of the dryer in the exiting flue gas. The rest fall to a hopper at the bottom of the dryer. With spray drying, in con- trast to wet FGD, the flue gas is not saturated with moisture after the absorption step. The gas approaches 20° F to 50° F (11 ° C to 28° C) of the saturation temperature. The solution or slurry sprayed into the dryer is pumped from an absorbent holding tank. Fresh absorbent and dilution water are added to the tank and the con- tents are stirred as needed. In some systems, dilution water is also added to the absorbent feed just up- stream of the spray dryer to improve control of the outlet flue gas temperature. When lime is the absorbent, recycle solids from the spray dryer hopper or downstream solids collection equipment contain unreacted absorbent and are often used to supplement the fresh absorbent feed. Either recycle solids are slurried separately and added to the absorbent feed just up- stream of the spray dryer, or they are added directly to the fresh absorbent in the;holding tank. Flue gas may be reheated after it leaves the spray dryer to prevent con- densation in downstream solids collection equipment. To accomplish reheat, the flue gas from the spray dryer is mixed either with hot flue gas from upstream of the combustion air preheater or with warm flue gas from upstream of the spray dryer. The reheated flue gas then flows to the solids collec- tion device where the dry solids (reaction products, unreacted absorbent, and fly ash) are collected. A fabric filter (baghouse) is the most common solids collection de- vice, but ESP's are also used. When a baghouse is used, significant absorption of sulfur dioxide may occur during solids collection.5 Absorbent in the solids collected on the surface of the bags reacts with sulfur dioxide remaining in the flue gas. The cleaned flue gas leaves the collection device and is exhausted to the atmosphere through a stack. Dry waste solids collected in the spray dryer and the collection device are typically disposed of by landfill. Absorbent Preparation Absorbent solutions or slurries are prepared on site for spray dryer processes. Lime is the most popular reagent, although sodium car- bonate may be used. Other sodium- based reagents, such as nahcolite and trona ore, have also been shown to be effective absorbents for spray drying.2 Sodium carbonate absorbent is pre- pared as a concentrated solution and stirred in a tank. Sodium carbon- ate is more soluble and more reac- tive than lime; however, the leachability of sodium reaction prod- ucts can result in waste disposal problems. ------- Flue gas/off-gas Cleaned flue gas Absorption feed Air pollutants Other systems To disposal Figure 2. Spray Dryer FGD Process Sodium carbonate dissolves in water to produce sodium ions: Na2C03 Za 2Na+ + COg2 (1) In lime systems, pebble lime (CaO) must be slaked to produce a reactive lime slurry (Figure 3a). The slaking reaction can be repre- sented as: Ca(OH)2 (2) Slaked lime dissolves in waterto pro- duce calcium ions: Ca(OH)2 ^ Ca+2 + 20H~ (3) Absorbent utilization can often be improved by recycle of the waste solids, particularly in lime systems, where the unreacted absorbent remaining in the waste solids can be used. Waste solids recycle may not be advantageous for sodium-based systems, however, because the more reactive sodium- based reagent is usually com- pletely consumed during the first pass through the spray dryer. Absorption and Drying Gaseous sulfur dioxide is absorbed from the flue gas in the spray dryer (Figure 3b). As flue gas enters the dryer, it disperses and imme- diately mixes with atomized solution or slurry. Gas phase sulfur dioxide rapidly dissolves into the liquid phase of the droplets and reacts with the absorbent to form solid phase salts; simulta- neously, the solid particles are dried by the heat of the flue gas. Flue gas carrying solid particles exits the spray dryer and flows to a solids collection device. Some S02 absorp- tion also takes place downstream of the spray dryer.6 During absorption, the flue gas in the spray dryer is adiabatically humidified by water evaporated from the solution or slurry. The amount of water injected into the spray atomizer with the absorbent solution or slurry therefore controls the gas temperature approach to the adiabatic saturation temperature. Process variables that affect SO2 removal in the spray dryer include ap- proach to adiabatic saturation temperature, the flue gas residence time in the spray dryer, and the absorbent stoichiometry. These vari- ------- Flue gas/off-gas Cleaned flue gas Absorption feed Air pollutants Other systems »\\ \ / ' i i«» ii'1, ' \ Spray dryer Fresh absorbent holding tank (a) (d) f To landfill Figure 3. '. Lime Spray Dryer FGD with Baghouse: (a) Absorbent Preparation, (b) Absorption and Drying, (c) Solids Collection, and (d) Solids Disposal ables are discussed in the Design Considerations section. The overall SO2 absorption reactions for lime spray drying can be repre- sented as: Ca(OH)2(s) CaSO3 • S02(g) +.H2O(I) ^ + %H2O(I) • 1/2H2O(s) 3/2H2O(l) ^± 2H20(s) (4) (5) For the sodium carbonate process, the overall SO2 absorption reac- tions are: Na2C03{s) + S02,(g) J± Na2SO3(s) + CQ2(g) Na2S03(s)+1/202(g)^± Na2SO4(s) (6) (7) Reaction mechanisms and mathe- matical models have been pos- tulated for the lime spray dryer process.7-8 Equations 8 through 1 3 show the series of reactions that lead to the overall reactions of slaked lime and sulfur dioxide (Equations 4 and 5).8 The sulfur dioxide is absorbed in water and reacts with water to form sulfurous acid (H2SO3) before disso- ciating to form sulfite ions, accord- ing to the following sequence of reactions: S02(g) ;± S02(aq) SO2(aq) + H2O i± H2SO3 H2S03 i± H+ + HS0 J± S03-2 (8) (9) (10) ------- Argonne fly ash hopper system Dissolved lime (see Equation 3) and other alkaline species from re- cycled solids orfly ash neutralize the absorbed sulfur dioxide and thereby drive the reactions in Equa- tions 8, 9, and 10 to completion. Some of the sulfite ions are oxidized by flue gas oxygen to form sul- fate ions: SOT2 + 1/202 (11] The sulfite and sulfate ions then pre- cipitate as calcium salts: Qa+2 -(. SCT2 + M-t-UO ^ CaSO3-VaHzCHs) (12) Ca+2 + SO"2 + 2H20 j± CaS04 • 2H20(s) (13) The quantity of calcium ions avail- able in the liquid phase of the slurry to form the calcium salts is lim- ited by the solubility of slaked lime in water. Theicalcium ions react in the liquid phase of the slurry droplet, and they are replaced with fresh ions from the dissolution of additional solid phase slaked lime (Equation 3). The reactions leading to the overall reactions of sodium carbonate and sulfur dioxide (Equations 6 and 7) are the same as those given for the overall reactions of slaked lime ------- and sulfur dioxide (Equations 4 and 5). The sulfite and sulfate ions precipitate as sodium salts: 2Na+ + SO"2 2Na+ + SO"2 : Na2S03(s) Na2SO4(s) (14) (15) In lime spray dryers, carbon dioxide (CO2) absorbed from the flue gas can react with the slurry to form cal- cium carbonate (CaCO3), thus reducing the availability of calcium ions. C02(g) J± C02(aq) CO2(aq) + H2O J± H2CO3 H2C03 2H+ Ca+2 C032 C032 ±; : CaCO3(s) (16) (17) (18) (19) The importance of carbon dioxide absorption in lime spray drying has not been fully investigated. Pilot plant tests have indicated, however, that the absorbent lost to reaction with carbon dioxide may be recovered by solids product recycle.2 ; Solids Collection Solid particles in flue gas exiting the spray dryer are collected by a baghouse or ESP (Figure 3c). The solid particles consist of reac- tion products, unreacted absorbent, and fly ash. The cleaned flue gas leaves the collection device and is exhausted through a stack. When baghouses are used, SO2 ab- sorption continues during the solids collection step as unreacted absorbent in the solid waste reacts with the sulfur dioxide remain- ing in the flue gas.6 This additional SO2 absorption! can only occur when residual rrioisture remains in the solid particles.9 Solids Disposal Disposal methods for solids collected from spray dryer processes vary with the type of absorbent used. Spray dryer FGD has an advantage over conventional wet FGD in that sludge handling equipment (such as clarifiers, thickeners, vacuum filters, and centrifuges) is not required. Waste solids from spray dryer processes have handling properties similar to dry fly ash and are usually conveyed pneumatic- ally to storage bins and then trucked to landfill sites for disposal (Figure 3d). Integrated System The foregoing steps are part of the integrated system. Figure 3 shows how the four steps—absorb- ent preparation, absorption and drying, solids collection, and solids disposal—relate to form a com- plete lime spray dryer FGD process. ------- Design Considerations Several design elements must be considered in the selection and operation of a spray dryer FGD system: • Absorbent selection and preparation • Spray dryer design and operation • Solids collection • Solids recycle Absorbent Selection and Preparation The selection of an absorbent de- pends mainly on reagent cost and availability, ease of waste dis- posal, and SO2 removal require- ments. Most spray dryers use lime in- stead of sodium-based reagents for three primary reasons: • Lime is generally the less expen- sive reagent. • Lime is the more readily available in most areas. • Lime spray dryer wastes can be disposed of more easily in an environmentally acceptable manner. Sodium carbonate is quite soluble in water. In the spray dryer environ- ment it is highly reactive, which leads to good material utili- zation. The high solubility of the resultant sodium salts, however, cre- ates a waste disposal problem because of the potential for leaching. Lime, on the other hand, has a rela- tively low solubility and is less reactive in the spray dryer. Material utilization is lower :as a result, particularly when high SO2 removal is required. Low utilization can be partly overcome by modifications in the process design; for exam- ple, solids recycle can be used. Lime has an advantage in that the wastes produced can usually be dis- posed of in landfills without special treatment. Absorbent preparation techniques are particularly important in lime sys- tems. Slaking water used to pro- duce lime slurries for spray drying must be of good quality.2 Low- solids water produces small, highly porous, reactive particles. High-solids wastewater, such as cooling tower blowdown, produces large slurry particles that are less reactive and decrease lime utilization. Two types of slakers can be used to prepare lime slurries: ball mill slak- ers and paste slakers.10 Ball mill slakers are more popular because they generally produce a more finely ground absorbent and contrib- ute to a more reactive slurry. Paste slakers offer a potential benefit, however, in that the resulting slurry is somewhat less abrasive than the slurry from ball mills and may reduce wear on pipes and pumps. Slaking temperature, amount of water, and lime purity also affect the quality of the slaked lime slurry.2 Spray Dryer Design and Operation Primary considerations in spray dryer design and operation include the quantity of flue gas to be cleaned, the inlet flue gas temperature and moisture content, the flue gas SO2 content, and the desired SO2 removal efficiency. These fac- tors determine the physical size of the dryer and the amount of absorbent required. Thus, they affect capital and operating costs significantly. The design of the spray dryer contact chamber, the flue gas disperser, and the solution or slurry atomizers is important to efficient removal of sulfur dioxide. Contact chamber volume must provide a flue gas residence time that maximizes SO2 removal and permits ade- quate drying of the absorbent particles. Most lime spray dryers have a flue gas residence time of 10 to 12s. 8 ------- The flue gas disperser and the spray atomizer should provide for inti- mate mixing of the flue gas and the atomized droplets. Complete mixing aids the mass transfer of sul- fur dioxide to the droplets. There- fore, the flue gas disperser should ensure that the gas flow pat- terns within the contact chamber bring all the flue gas in contact with the atomized spray. The atomizer should also produce small droplets to maximize the droplet surface area available for SO2 absorp- tion. If the droplets are too small, however, they may dry out before sufficient S02 absorption has occurred. Atomizer types used in spray dryer FGD processes include rotary atomizers and two-fluid nozzles. Each type has its advantages and disadvantages, although most vendors prefer rotary atomizers.1 Rotary atomizers use a rapidly spin- ning disk (up to 20,000 r/min) to produce a fine droplet mist in the spray dryer. The size of the drop- lets .varies, with the velocity and diameter of the rotating disk and is reasonably independent of the liquid feed rate to the atomizer. Thus, rotary atomizers have one impor- tant advantage in that droplet size can be kept the same regardless of the feed rate of absorbent solution or slurry. This advantage is impor- tant because the required absorbent feed rate varies with fluctuations in the flue gas flow rate and the inlet SO2 concentration. The pri- mary disadvantage is that rotary atomizers are mechanically complex compared with nozzles. A second, potential disadvantage is plugging of the atomizer orifices; many ven- dors minimize this problem through improved disk design.11 Two-fluid nozzles use high-pressure air (or steam) to break up the ab- sorbent solution or slurry into a fine mist of small droplets. These nozzles have two main advantages: they have no moving parts, and large passages for liquid can be used to minimize plugging. Their pri- mary disadvantage is that the change in absorbent liquid feed rate al- ters the droplet size, which varies the SO2 removal efficiency. This problem is somewhat alleviated by multiple nozzles; but more operat- ing problems seem to occur with nozzle atomizers than with rotary atomizers;11 Further commercial experience with spray dryer FGD systems is needed for a full assessment of the drawbacks and benefits unique to each type of atomizer. Design variations in the placement of flue gas discharge points in the spray dryer, the type of gas disperser, and the numberof atomizers are based on vendor experience or preference. Because commercial experience with these varia- tions is lacking,itechnical compari- son is difficult. For example, flue gas discharge points are usually near either trie.top or the bottom of the. spray dryer hopper. Placing the gas discharge point near the top may be advantageous because plugging of the spray dryer hopper would not interfere with gas flow unless the hopper were to become com- pletely filled. More operating experi- ence is needed at full-scale utility FGD units to determine the likelihood of hopper plugging. Several important process or operat- ing variables affect the design and performance of the spray dryer, including: flue gas approach to saturation temperature at the dryer outlet, absorbent stoichiometry, and inlet SO2 concentration.The out- let flue gas temperature is con- trolled by the amount of water injected into the spray atomizer with the absorbent solution or slurry. As this temperature approaches the adiabatic saturation temperature, the residual moisture level in the spray-dried solids increases. The residual moisture aids the mass trans- fer of unreacted absorbent from the center of the particle toward the surface, where it.can react with the absorbed sulfur dioxide. Absorb- ent is utilized more readily at the particle's surface because of the greater area available for SO2 ab- sorption. Thus, SO2 removal rates and absorbent utilization increase as the approach to saturation is narrowed. Most spray dryers are operated with an approach between 20° F and 50° F (11 ° C and 28° C) above the adiabatic saturation temperature.1 The closeness of the approach to sat- uration is restricted by the need to avoid condensation in downstream solids collection equipment. The restriction can be overcome in part if warm or hot gas is bypassed around the spray, dryer to reheat the dryer outlet gas, but the amount of untreated gas used for this purpose may limit removal of sulfur di- oxide in the spray dryer process. Also, an energy penalty is associated with the use of hot gas from up- stream of the combustion air pre- heater because less energy is available for air preheat. Absorbent stoichiometry directly affects SO2 removal in the spray dryer. Stoichiometry for dry scrub- bing has been defined as moles of fresh sorbent introduced to the system divided by moles theoretically required for complete reaction with all the sulfur dioxide entering the system, whether or not all the sulfur dioxide is removed. This definition results in a lower stoichiometric ratio than does the conventional definition for wet scrubbing, which is based on moles of sulfur dioxide removed by the system. For example, a reported stoi- chiometric ratio of 1.2 for a dry sys- tem achieving 80 percent SO2 removal would be equivalent to 1.5 for a wet scrubbing system. The absorbent stoichiometry may be raised by an increase in the amount of absorbent fed to the spray dryer. A higher absorbent stoi- chiometry enhances removal of ------- Coyote soda ash holding tank (left) and control panel (right) sulfur dioxide. This method is limited by two factors, however. First, absorbent utilization decreases with increased stoichiometry, raising absorbent and disposal costs. Second, an upper limit is reached on the solubility of the absorbent or on the percent by weight of absorb- ent solids in the slurry. Decreased absorbent utilization can be partly overcome by operation of the spray dryer at a closer approach to the saturation temperature and by recycle of the collected solids. Preliminary tests at the Northern States Riverside demon- stration system have shown that overall S02 removals of 80 per- cent can be achieved (spray dryer and baghouse) with an absorb- ent stoichiometry of less than 1.2 at an inlet S02 concentration of about 900 ppm.12 The effect of inlet SO2 concentration on spray dryer performance has not been fully investigated; however, over the range of concentrations studied (500-1,500 ppm), increases in concentration only moderately decrease SO2 removal.2'5 The range studied corresponds to the concentrations of sulfur dioxide in flue gas from boilers using low- to moderate-sulfur coals (gen- erally less than 3 percent sulfur by weight). Additional information on the effects of higher SOZ con- centrations will soon be available from testing at one Utility demonstra- tion (Northern States' Riverside Station) and at three industrial sys- tems [Department of Energy's (DOE) Argonne National Laboratory, Argonne, Illinois; Strathmore Paper; and General Motors' Buick Division, Flint, Michigan]. Solids Collection The choice of the paniculate collec- tion device is influenced by SO2 removal during particulate collection and by vendoror customer pref- erence. Fabric filters (or baghouses) are the most widely used collec- tion devices in commercial spray dryer systems sold as of mid- 1 981. Of 23 utility and industrial systems sold, only 1 specifies an ESP. The primary advantage of, baghouses over ESP's is that unreacted alkalinity in the solids 10 ------- collected on the bag surface can re- act with sulfur dioxide in the flue gas. Studies have shown that baghouses can account for 10 per- cent of the total sulfur dioxide removed by a system.2 Baghouses also may be more economical and effective in collecting highly resistive fly ash; they can achieve high particulate removal efficiencies regardless of the type of coal burned, whereas the highly resistive fly ash from low-sulfur western coals may be more difficult and costly to collect using ESP's.11 The ESP's have a potential advan- tage over baghouses because they are less sensitive to condensa- tion and, therefore, the spray dryer can be operated closer to the saturation temperature, which results in higher S02 removals across the spray dryer. The primary dis- advantage of ESP's is that they may not be able to meet stringent particulate emission regulations if the inlet particulate concentrations become too high.13 Future testing of full-scale systems should pro- vide more information on the maximum inlet concentrations that can be expected. Baghouses collecting spray drying solids usually use fiberglass filter bags with pulse-jet cleaning mechanisms in industrial applica- tions and reverse-air cleaning mechanisms in utility applications.1 Solids Recycle \ Recycling waste solids to the spray dryer reduces raw material re- quirements because unreacted absorbent is consumed during recycle. Moreover, if the fly ash is high in available alkalinity, the available alkaline species may aid SO2 absorption by reacting with sulfur dioxide in the flue gas.9'11 The amount of alkalinity available in the fly ash depends; primarily on the type of coal fired. The type of absorbent and the amount of alkalinity available in the fly ash are important in determin- ing the benefits and economics of solids recycle for a particular spray dryer application. Solids re- cycle is particularly beneficial for lime systems because utilization is low for once-through absorb- ent. Solids recycle can increase SO2 removal in 1ime:spray dryers as much as 10 percent at a given absorbent stoichiometry.4 Thus solids recycle can achieve a required SO2 removal with less raw material. As a rule, solids recycle is not bene- ficial in sodium carbonate sys- tems because utilization is relatively high for once-through absorbent. The potential reduction in raw mate- rial requirements may not justify the cost of a waste solids re- cycle system. Maximum benefit from available fly ash alkalinity is pbtained by slurrying the waste recycle solids separately from the fresh absorbent feed. The recycle slurry is then mixed with the fresh absorbent at the point of injection into the spray dryer. If the recycle solids are slurried sep- arately, the alkaline species dissolve more readily and may then react with sulfur dioxide in the flue gas to reduce absorbent requirements.2 As a further benefit, the fly ash in the waste solids recycle may also act as a surface catalyst for absorb- ent utilization by providing an alternative site for precipitation of the absorption reaction products,2'6 thereby decreasing the solid deposits on the absorbent parti- cles. Absorbent utilization is improved because more absorbent sur- face area is available for reaction with sulfur dioxide. 11 ------- Environmental Considerations Important environmental considera- tions in spray dryer FGD include SO2 and particulate removal capabil- ities and dry waste product dis- posal properties. In both pilot- and demonstration-scale testing with low-sulfur fuels, the spray dryer FGD process has consistently shown the ability to meet the NSPS for removal of sulfur dioxide from flue gas exiting coal-fired boilers. Most available data are from pilot- scale applications of-the process because only one utility-size demonstration system and two industrial-size commercial systems are operational. The EPA funded pilot-scale testing at Colorado'Springs' Martin Drake station. These tests [20,000 actual ft3/min (570 actual m3/min)] showed overall SO2 removal effi- ciencies above 75 percent for a lime stoichiometry of less than 1.6 mol lime permol inletsulfurdioxide.2The tests were conducted at inlet SO2 concentrations of 1,500 ppm, without solids recycle, and at an ap- proach to saturation temperature of 20° F (11 ° C). In other tests, fly ash from high-sulfur eastern coals was added to the flue gas along with sulfur dioxide to simulate high- sulfur (about 4 percent) coal appli- cation; SO2 removals greater than 90 percent were measured with a lime stoichiometry of 1.6 mol lime per mol inlet sulfur dioxide.14 These tests were conducted at inlet SO2 concentrations of 4,000 ppm, with 50 percent solids recycle, and at an approach to satur- ation temperature of 20° F (11 ° C). Preliminary tests oh the lime utility- scale (100-MW) demonstration system at Northern States' Riverside Station showed an overall S02 re- moval efficiency of 94 percent at an absorbent stoichiometry of less than 1.4. These tests were conducted at an inlet S02 con- centration of about 840 ppm, at an approach to saturation temper- ature of 18° F (10° C), and with solids recycle.12 ; Test results are also available from two commercial lime spray dryer installations. Compliance test results from the Strathmore Paper system, which treated flue gas produced by combustion of moderate-sulfur coal, show an aver- age S02 removal efficiency of 92 percent.15 With coal averaging 2 percent sulfur,4 an average S02 removal of 70 percent was achieved at the Celanese Fibers sys- stem, based on 23 days of accept- able continuous SO2 monitoring data obtained over a 33-day test period. These tests were con- ducted without solids recycle. Further operating experience will be required to reach optimal S02 removal efficiencies in full-scale spray dryer systems. The available test results, however, have provided data sufficient for the design and sale of 12 utility and 11 indus- trial spray dryer systems. All the spray dryer systems sold to utilities specify low-sulfur west- ern coals or lignite (average sulfur content of 1.5 percent or less). The SO2 removals guaranteed for these systems range from 61 to 87 percent, depending on the coal sulfur content.1 So far, for fuels with more than 1.5 percent sulfur, spray dryer FGD applications have been for industrial boilers. The overall cost effect of the extra absorbent needed for high- sulfur coal application is less severe in these smaller systems than in utilities, which must treat larger quantities of flue gas. Many of the planned and operating industrial spray dryer systems are applied to higher sulfur (up to 3.5 percent) eastern coals. These systems have SO2 removal guarantees from 70 to 90 percent.3 12 ------- High participate removal efficiencies (99 percent or greater) can usually be obtained by ESP's or fabric filter baghouses !n coal-fired applica- tions. In spray dryer systems, both ESP's and baghouses should be capable of achieving high par- ticulate removal. The baghouse may be advantageous, however, in locations where environmental con- siderations require low outlet par- ticulate concentrations, such as 0.01 gr/ft3 (0.02 g/m3). Inlet dust loadings as high as 25 gr/ft3 (57 g/m3) require an ESP efficiency of 99.96 percent—a value that may be difficult to achieve consist- ently with an ESP in a power plant.13 Properly designed baghouses, on the other hand, should be able to meet an outlet emission of 0.01 gr/ft3 (0.02 g/m3), regardless of inlet loading. In addition, the baghouse will usually be more reliable in achieving low opacity.9 Spray dryer FGD systems collect the fly ash together with the FGD reaction products. The composi- tion of the waste solids varies depending on the coal type and the operating conditions of the proc- ess. Waste product from a spray dryer system applied to a boilerfiring low-sulfur coal consists of approx- imately 75 percent fly ash, 1 5 to 20 percent calcium sulfite and sul- fate salts, 5 percent moisture, and less than 5 percent unreacted sorbent.16 Waste solids from spray dryer sys- tems have handling properties similar to fly ash, and are therefore more easily disposed of than wastes from conventional wet FGD systems. The dry waste from lime spray drying exhibits physical properties suitable for on-site land- fill disposal. The waste solids are nonhazardous under current EPA Resource Conservation and Recovery Act guidelines—their leaching characteristics have been determined andlare well within the guidelines set by EPA for definition of a nonhazardous waste.16-17 Fly ash from low-sulfur western coal exhibits cementltious (pozzo- lanic) properties;. Fixation reactions associated with|these properties have been studied to determine the landfill characteristics of wastes from spray dryer systems applied to boilers firing low-sulfur west- ern coals. The addition of about 20 percent water is:reported to give the most desirable landfill disposal properties for solid wastes contain- ing fly ash from low-sulfur western coals.16'17 Another method for disposing of lime spray drying wastes has been de- veloped by Niro, Atomizer, Inc. (patent pending). The dry waste product is combined with 10 to 20 percent water and pelletized to between 2.5 and 3 times its bulk density. The resulting syn- thetic gravel (Nirok) is reported to have a cured density of about 120 Ib/ft3 (1,900 kg/m3) and a compressive strength of over 10,000 Ib/in2 (69,000 kPa). It can be used in concrete mixes, cement founda- tions, and roadbase compositions.16 Solids from sodium-based spray dryer systems are not consid- ered suitable for disposal by conven- tional landfill methods. The sodium salts produced by the proc- ess are highly Water soluble, and a lined landfill is necessary to prevent them from leaching into the ground water.11-18 The Sinterna® Process has been developed to stabilize these wastes by converting the untreated waste material to pellets with reduced leaching poten- tial, but the process.does not appear to be economically desir- able.17 Wastes from lime-based systems are economically and envi- ronmentally preferable, therefore, because they can be landfilled without special treatment. Current and planned disposal methods for spray drying wastes parallel established practices for wet FGD systems. Wastes from the only commercial systems in opera- tion, at Celanese Fibers' Amcelle Plant and Strathmore Paper, are being trucked to landfill, as are the wastes from the demonstration at Northern States' Riverside Station. Tentative waste dispo- sal plans of utilities with con- tracts for commercial systems range from dry landfill to clay-lined ponds for wetted solids. Eight util- ities have reported disposal plans as follows:1 • Natural clay-lined landfill • Landfill lined with PVCa • Landfill with fixation • Wetted transport to landfills (two utilities) • Wetted transport to clay-lined pond • Unspecified landfills (two utilities) Studies by EPA, DOE, the Electric Power Research Institute (EPRI), and many vendors are being con- ducted to characterize further the physical and chemical properties of the dry waste. As more commer- cial systems begin operation, these efforts should gain momentum and result in a broader data base. aPolyvinyl chloride. 13 ------- Status of Development The application of spray drying to FGD developed from earlier commer- cial uses of spray dryers. These devices had been used for many years in a wide range of drying, reac- tion, and purification processes in the chemical industry. Most FGD spray dryer designs are direct adaptations of the standard designs used in other industries, such as the food processing industry.11 Spray dryer FGD also evolved in part from early dry injection FGD studies initiated in the 1 960's. In the systems studied, dry absorbents were injected into the flue gas, and the reaction products were col- lected in fabric filter baghouses or ESP's. Results from many of these early studies were disappointing, but interest in the technology continued because of the potential benefits of such uncomplicated approaches to FGD. Unlike efforts in the development of wet FGD, where the Government has predominated, early efforts in spray dryer FGD were supported pri- marily by industry.^Several com- mercial dry scrubbing systems had been sold before the Govern- ment started to support research and development in this area.18 Early test work included that of Atomics International with its aqueous carbonate process at Southern California Edison's Mohave Station, Laughlin, Nevada, in 1972; testing involved a pilot-scale demonstration of the spray dryer for S02 removal. In 1 974, Niro Atomizer initiated tests of spray drying for FGD applica- tion at its Copenhagen facility, inves- tigating various alkaline sorbents such as lime, limestone, and sodium carbonate. A major impetus to the development of spray dryer FGD occurred in 1977 when the Basin Electric Power Cooperative expanded dry injection studies at its Leland Olds Station to include spray drying. Basin Elec- tric requested bids' for new plants to be fueled with western coal and lignite. Several vendors built and operated small pilot units to prequal- ify as bidders. Test units were operated at Basin Electric's Neal and Leland Olds Stations in North Dakota and at Otter Tail Power Company's Hoot Lake Station in Minnesota. These were the first U.S. applications of the spray dryer for a nonregenerable FGD system, and three contracts were awarded in 1 978 on the basis of the tests. The recipients were Babcock & Wilcox and two joint ventures: Joy Manufacturing Company and Niro Atomizer (Joy-Niro), and Rock- well International and Wheelabrator- Frye, Inc. (Rockwell-WF). In the past few years several com- panies and consortia have become active in dry FGD. Thirteen firms currently offer commercial spray dryer systems, and several have contracted to build commercial units. All the utility units are for lignite or low-sulfur western coal applications, where removal efficiencies and absorbent consump- tion are usually lower than with high-sulfur coals and, in some cases, the alkalinity of the fly ash can supplement the absorbent.11 As of mid-1981, 12 utility systems (totaling over 3,800 MW) and 11 industrial systems had been sold (Tables 1 and 2).1 These systems are mostly lime spray dryer and bag- house combinations. Only two commercial systems, both applied to industrial boilers, were fully oper- ational: the Rockwell-WF system at Celanese Fibers' Amcelle Plant and Mikropul Corporation's system at Strathmore Paper. The first utility system to become opera- tional will likely be another Rockwell-WF system, this one at Otter Tail Power's Coyote Station, Beulah, North Dakota. Startup procedures at Coyote were initiated in January 1 981.1 Two of the most recent industrial systems sold will be applied to boilers firing high- sulfur coal. At least five utilities have specified dry FGD only or are considering either dry or wet FGD for 14 ------- Table 1. Commercial Utility Spray Dryer FGD Process, utility, and station Lime: Basin Electric Power Coop.: Antelope Valley, Beulah ND: Unit 1 Unit 2 Laramie River, Wheatland WY: Unit 3 Colorado Ute Electric Association: Craig Station, Craig CO Unit 3 Marquette Board of Light & Power: Shiras Station, Marquette Ml, Unit 3 Platte River Power Authority: Rawhide Station, Fort Collins CO, Unit 1 Sierra Pacific Power & Light: North Valmy Station, Valmy NV Sunflower Electric Coop.: Holcombe Sta- tion, Hays KS Unit 1 Tucson Electric: Springerville Station, Tucson AZ: Unit 1 Unit 2 United Power Association: Stanton Sta- tion, Stanton ND Sodium carbonate: Otter Tail Power: Coyote Station, Beulah, ND Unit 1 Systems Sold as of FGD units ; Spray dryers; (MW) Atomizers per dryer 430 5° 1 rotary 430 5C 1 rotary' 500 4° 1 2 nozzles 450 NA Nozzlesd 44 1 1 rotary 250 NA Rotaryd : 270 3 3 rotary 310 NA Rotaryd 350 NA Rotaryd 350 NA Rotaryd 65 NA Rotaryd • 41 0 4 3 rotary • Mid-1981 Gas treated actual ft3/min) 2 200 • 2 200 2 810 NA 226 NA 1,200 NA NA NA NA 1 890 Coal Type % Sa subbitu- minous nous Western 0 5 subbitu- minous Western 1 .3 subbitu- minous Subbitumi- 04-1 0 nous Western 1 3 subbitu- minous subbitu- minous subbitu- minous Lignite (a) % SO2 Solids removal collection . u • • i -i • b date (design) device 62 FF 1 982 62 FF 1 985 82 ESP 1 982 87 FF 1983 80 FF 1 982 80 | FF 1983 76 FF 1984 80 FF 1 983 61 FF 1 984 61 ' FF 1984 NA FF 1 981 70 FF 1 981 8Average. ' ' ! bFF = fabric filter; ESP = electrostatic precipitator. : clncludes 1 spare. dNumber not available. i eLow to medium. . . . : • Note.—NA = Data not available. i ; SOURCES: Kelly, M. E., and S. A. Shareef, Third Survey of Dry SO 2Contrbl Systems, EPA 600/7-81-097, NTIS No. PB 81-21 8976, June 1981.Gehri, Dennis, Rockwell International, personal communication, Sept. 25, 1981. 15 ------- Table 2. Commercial Industrial Spray Dryer FGD Systems Sold as of Mid-1981 FGD units Process, company, and station Limo: Argonne National Laboratory, Argonne II ColaneSQ Fibers: Amcelle Plant, Cumber- land MD Fairchild Air Force Base, Spokane WA: Unit 1 Unit 2 Unit 3 General Motors: Buick Division, Flint, Ml University of Minnesota: Unit 1 , Minneap- olis MM Size (1 ,000 Ib/h steam) 170 110 170 110 11O 110 450 85 NA Spray dryers No. 1 1 1 1 1 1 1 1 2 Atomizers per dryer 1 rotary^ rotary, rotary rotary ' rotary' rotary, 1 rotary 4 nozzles 1 single nozzle. Gas volume treated (1 ,000 actual ft3/min) 75 65 NA 46.5 46.5 46.5 167 40 120 Coal Type Illinois bitu- minous Eastern NA NA NA NA Indiana bitu- minous Eastern Subbitu- minous %sa 3.5 1.5-2.5 1.0 1.0 1.0 1.0 1 .0-3.0 2.0-3.0 0.6-0.7 %S02 removal (design) 79 70-85 NA 85 85 85 70-90 75 70 Solids collection device6 FF FF FF FF FF FF FF FF FF Startup date 1981 1980 1981 1983 1983 1983 1982 1979 1981 Sodium carbonate: Calgon, Catlettsburg KY NA University of Minnesota: Unit 2, Minneap- olis MN NA 1 multi- ple nozzle 1 1 rotary, 57 1 1 rotary 120 NA Subbitu- minous 1.0-2.0 0.6-0.7 75 75 FF FF 1981 1981 'Average. bFF - fabric filter. Now.—NA = not available. ! SOURCES: Kelly, M. E.,and S. A. Shareef, Third Survey of Dry SO2 Control Systems, EPA 600/7-81-097, NTIS No. PB 81-218976, June 1 981. Steele, Gone, Niro Atomizer, personal communication, July 1 6, 1981. new units that will go on line before the end of the decade.1 There are also two important full-scale (100-MW) utility demonstrations: theJoy-Niro lime system at Northern States' Riverside Station (now operational) and the Flakt, Inc., lime system adapted for lime or sodium carbonate at Pacific Power and Light Company's Jim Bridger Station, Rock Springs, Wyoming (planned for startup in 1982). Current research and development efforts are examining process variables affecting SO2 removal, as well as application of the tech- nology to high-sulfur coal. Studies by EPA, DOE, EPRI, vendors, and others include assessments of the following:7 • Importance of lime stoichiometry • Effect of flue gas approach to saturation temperature • Effect of waste solids recycle from the spray dryer and baghouse • Refinements of atomization and sorbent preparation techniques • Role of alkalinity in fly ash removal • Need for reheat The technical and economic feasibil- ity of the vendors' approach to design features such as type of atomizer, degree of approach to saturation, particulate collection method, and waste recycle remain to be demonstrated. Current trends 16 ------- suggest that many new systems will use a lime slurry with rotary atom- izers, partial flue gas bypass for reheat, and fabric filter collection. Most of these spray dryer FGD units will likely be limited to low- sulfur-coal conditions, because the cost of lime spray drying relative to wet limestone scrubbing for high- sulfur-coal applications is still uncertain. The rapid growth of spray dryer FGD results partly frorn its potential technical and economic benefits and from the increased use of west- ern coals by utilities, for which spray drying is especially suited. Also important has been the broad base of spray dryer and particu- late collection technology from which spray dryer FGD directly evolved. The April 1981 Dis- trict Court decision upholding the NSPS for utility boilers has been a recent impetus to the technology. The NSPS include a variable percentage SO2 removal provi- sion that requires at least 70 percent S02 removal for boilers firing coal. Spray drying provides a potentially lower cost alternative to wet FGD for low-sulfur-coal applications. 17 ------- Raw Materials and Utilities • Electric energy for auxiliary equip- ment such as agitators/ con. The raw material requirements of veyors, and feed preparation spray dryer FGD processes are equipment for lime or sodium carbonate re- prQcess wgter irements include agent, and the ut.lity needs are dj|ution wgter for absorbent prep. for energy and process water. Energy ^.^ and for sprgy dryer Qut|et f|(je requirements include: ggs temperature control. In lime • Pumping energy to move absorb- spray dryer systems, slaking ent solution or slurry to the water accounts for 10 to 30 per- spray dryer atomizer cent of the total process water • Electric energy forflue gas booster requirements. blowers (forced- or induced- draft fans) Table 3 gives the estimated annual • Electric energy to rotate the raw material and utility requirements atomizers (if rotary type) of sodium carbonate and lime Table 3. ! Estimated Annual Raw Material and Utility Requirements for Lime and Sodium Carbonate Spray Dryer FGD Processes: New 500-MW Coal-Fired Power-Generating Unit , Component Requirement Low-sulfur coal: ; Lime spray dryer system:a'b Raw materials (lime, 1,000 tons) 1 °-> Utilities: '. Fuel (1,000 gal) •• 1 63'8 Process water (106 gal) • • 82-2 Electricity (106 kWh) • •,• • 39-6 Sodium carbonate spray dryer systern:b'° Raw materials (sodium carbonate, 1,000 tons) 18.4 Utilities: Fuel (1,000 gal) 1 65-7 Process Water (10s gal) 70-2 Electricity (106 kWh) • • 41 -2 High-sulfur coal: Lime spray dryer system:d Raw materials (lime, 1,000 tons) • • 112.4 Utilities: Fuel (1.000 gal). ^ Process water (106 gal) 143-6 Electricity (1Q6 kWh) 42'7 Energy for reheat (106 Btu) 137-4 "Warm gas bypass reheat. Stoichiometry of 1.2 mol lime per mol S02 absorbed. Landfill disposal 1 mi from FGD facilities. bCoal with 0.7% S. Meets emission regulation of 1.2 Ib S02/106 Btu with 70% S02 removal. °No gas bypass. Stoichiometry of 1 mol sodium carbonate per mol SO2 absorbed. Lined- pond-disposal 1 mi from FGD facilities. dHot gas bypass reheat. Coal with 3.5% S. Stoichiometry of 1.8 mol lime per mol SO2 absorbed. Includes electrical requirements of fabric filter baghouse. Meets emission regulation of 1.2 Ib S02/106 Btu with 90% S02 removal. Landfill disposal 1 mi from FGD facilities. Notes.—Midwest plant operating 5,500 h/yr. SOURCE- Burnett T X., and K. D.Anderson, Technical Review of Dry FGD Systems and Economic Evaluation of Spray Dryer FGD Systems, EPA 600/7-81-014, TVA EDT-1 27, NTIS No. PB 81 - 206476, Feb. 1981. 18 ------- spray dryer processes for a new 500-MW power-generating unit firing low-sulfur coal.11 System de- sign and operating conditions affect the requirements and must be considered for each specific installation. Absorbent needs vary with the desired SO2 removal, the coal sulfur content, the use of recycle, and (if recycle is used) the available alkalinity in the fly ash. Fuel requirements given are for trucking dry waste solids to the landfill site. The table includes elec- trical needs of the fabric filter baghouse. Spray dryer systems using hot gas bypass (from upstream of the combustion air preheater) to reheat the flue gas incur an energy penalty because of the decrease in energy available to heat air in the preheater. Hot gas bypass will usually be necessary only when high SO2 re- movals (approaching 90 percent) are required, as in higher sulfur coal applications. Hot gas bypass min- imizes the amount of untreated gas that must be bypassed around the spray dryer and thus increases the SO2 removal that can be obtained with a given spray dryer system. Table 3 also gives the estimated raw material and utility requirements of a lime spray dryer process for a new 500-MW boiler firing high- sulfur coal,11 and includes the estimated energy penalty associated with hot gas bypass for this sys- tem. Because data are lacking for full-size spray dryer systems applied to boilers firing high-sulfur coal, these estimates may change considerably after ongoing demonstration-scale studies are completed.1 Reagent requirements are the major cost component of the annual material and utility needs of the spray dryer FGD process. Comparison by weight of the raw material require- ments of lime and sodium carbon- ate spray dryer systems can be somewhat misleading because the molecular weight of sodium car- bonate (106) is nearly twice that of lime (56.1). In molar terms, lime systems usually require more reagent than do sodium carbonate sys- tems because lime is less reactive and therefore has lower material utilization. In terms of weight, how- ever, sodium carbonate sys- tems require more raw material, and the higher cost per unit weight of sodium carbonate usually makes these systems more expen- sive to operate. ;Substituting other sodium compounds for sodium car- bonate may make sodium sys- tems more competitive with lime systems. In particular, trona ore appears to be an attractive alter- native in Western States where it is readily available.19 No commercial spray dryer systems sold as of mid-1981, however, plan to use trona ore as an absorbent. The total utility needs of lime spray dryer systems are generally lower than those of limestone wet scrubbing systems.11 These needs vary, however, with system de- sign and the type of coal burned, which determine the absorbent feed rate requirements and the amount of solids to be disposed of. In low-sulfur-coal applications, lime spray dryer systems have slightly lower energy requirements than wet limestone systems because less energy is needed for pumping. Considerably less solution or slurry must be moved through spray dryer systems. A large part of the associated energy savings, however, is lost to the energy needed for atomizing the solution or slurry. In high-sulfur-cpal applications, the total energy requirements for lime spray dryer systems are much lower than for wet systems because pumping energy needs are re- duced and less ;energy is needed for flue gas reheat.11 Although spray dryer systems on boilers firing high-sulfur coal incur an energy penalty for hot gas bypass, the pen- alty is much less than the energy needed to reheat exit gases from wet scrubbing systems. Installation Space and Land Installation space and total land requirements for spray dryer FGD systems vary depending on the plant size, the spray dryer design, and the type of absorbent used. Installa- tion space requirements for a lime spray dryer system have been estimated from recent Tennessee Valley Authority (TVA) and EPA studies.11-20 The total estimated installation space requirement for a 500-MW lime spray dryer FGD system is about 2.3 acres (0.9 ha), including space for a recycle waste solids slurry system and a process control area (Figure 4). The total area needed for process control, solids recycle, and absorbent preparation and stor- age is estimated at 0.3 acre (0.1 ha). Total installation space requirements for a 500-MW sodium carbonate spray dryer system should not differ significantly from those of the lime system shown in Figure 4. Space requirements for the spray dryer and solids collection equipment would be similar for both systems. Absorbent preparation would require less space in the sodium carbonate system, and space would probably hot be needed for solids recycle storage. Absorb- ent storage, however, would require more space; sodium car- bonate reagent is stored as a saturated aqueous solution, and would need approximately twice the storage space needed for the lime system feed.11 A large additional area is needed for waste solids disposal, on or off site. Assuming a 30-yr lifetime (or 165,000 h of operation), a lifetime 19 ------- Key 260ft Flue gas/off-gas Cleaned flue gas Absorption feed Air pollutants Other "systems ID fan Recycle storage bins Fabric filter baghouse 125ft product tanks ' 340ft i 110ft i Figure 4. Lime Spray Dryer Installation Space Requirements landfill for a 500-MW lime spray dryer system applied to low-sulfur coal (0.7 percent sulfur) would require an area of about 154 acres (62 ha) with an initial depth of 30 ft (9.1 m). A sodium carbonate system would require a clay-lined pond 30 ft (9.1 m) deep with an area of 195 acres (79 ha). These dis- posal area requirements include space for fly ash disposal as well as waste FGD solids. The sodium carbonate system requires more solids disposal area than does the lime system because a greater total volume of waste is; produced. Spray dryer systems need a larger total area for waste disposal than do wet scrubbing systems. For exam- ple, a 500-MW wet limestone scrubbing system would need about 134 acres (54 ha) of disposal land with an initial depth .of 30 ft (9.1 m).11 Spray dryer systems produce more waste because their raw material utilizations are lower. Any disadvan- tages and costs associated with the greater volume of waste are usually outweighed by the advan- tage of a dry waste product, which eliminates the need for dewater- ing equipment and may allow earlier reclamation of land used for FGD waste disposal. 20 ------- Costs Reasonably accurate cost estimates for spray dryer systems can be based on vendor-supplied capital cost information and on operating data from pilot- and demonstration- scale studies. Capital and oper- ating cost estimates for lime and sodium carbonate spray dryer FGD systems have been prepared by TVA for comparison with wet lime- stone scrubbing FGD systems.11 The actual costs of commercial-size spray dryer systems may vary widely from these estimates, de- pending on design and operating developments resulting from full- scale operation in the near future. Tables 4 and 5 give specific compo- nents of annual operating costs Argonne spray dryer, 75,000 actual ft3/min 21 ------- Table 4. Annual Operating Costs for Lime Spray Dryer FGD System on a New 500-MW Coal-Fired Power-Generating Unit Costs Component Annual quantity Unit ($) Annual operating ($1,000) Mills/kWh Direct costs, first yean Conversion costs: ' Operating labor and supervision: i Flue gas desulfurization ;... 25,400 man-hours 15.00/man-hour 381 0.14 Solids disposal ;... 28,152 man-hours 21.00/man-hour 591 0.21 Utilities: ! Fuel 163,750 gal 1.60/gal 262 0.10 Process water ;... 82.2 X106 gal 0.14/1,000 gal 12 0.004 Electricity i... 39.6 X 106 kWh 0.037/kWh 1,464 0.53 Maintenance, labor and materials 2,136 0.78 Analyses 4,191 man-hours 21.00/man-hour 88 0.03 Total conversion costs j... 4,934 1.794 Delivered raw materials (lime) '.... 10,100 tons 102.00/ton 1,030 0.37 Total direct costs J... 5,964 2.164 Indirect costs: Overhead, first year, plant, and administrative .'... 1,717 0.62 Total first-year operating and maintenance costs '-.... 7,681 2.784 Lovehzod capital charges (14.7% of total capital investment) :... 11,336 4.12 Total first-year revenue requirements 19,017 6.904 Lovclizod operating and maintenance costs (1.886 X first-year operating;and maintenance) ;... 14,486 5.27 Levelized capital charges (14.7% of total capital investment) '... 11,336 4.12 Total levelized annual operating costs ',... 25,822 9.39 Notes.—Upper Midwest plant operating 5,500 h/yr. 1984 revenue requirements. 30-yr plant life. 1,346,700 tons/yr western coal burned, 9,500 Btu/kWh. 0.7% sulfur. Warm gas bypass reheat and waste solids recycle. Stoichiometry of 1.2 mol lime per mol S02 absorbed. Meets emission regulation of 1.2 Ib S02/106 Btu with 70%S02 removal. Maintenance costs estimated at 6% of nonlandfill capital investment plus 3% of landfill invest- ment. Landfill disposal 1 mi from plant. Includes investment and revenue requirements for fly ash removal and disposal. Total direct investment, $38,587,000; total fixed investment, $59,369,000; total capital investment, $77,113,000. SOURCE: Burnett, T. A., and K. D. Anderson, Technical Review of Dry FGD Systems and Economic Evaluation of Spray Dryer FGD Systems, EPA 600/ 7-81-014. TVA EDT-127, NTIS No. PB 81-206476, Feb. 1981. and capital charges for a lime and a sodium carbonate spray dryer FGD system. The tabulations assume installation on a new 500-MW power-generating unit burning low- sulfur coal (0.7 percent sulfur). Both FGD systems are designed for 70 percent SC"2 removal. The lime sys- tem, however, uses both untreated warm gas reheat and waste solids recycle, and the sodium carbonate system uses neither. Because all the flue gas must be treated in the sodium carbonate system, this system requires four operating spray dryers. The lime system operates with three spray dryers because by- pass reheating reduces the flow of flue gas to be treated. The annual operating costs for the sodium carbonate system are about 9 percent higher than those for the lime system, primarily because raw material costs and total capital investment are higher for the sodium carbonate system. The higher cap- ital investment results mainly from the costs associated with con- structing an environmentally safe pond for sodium waste disposal. 22 ------- Table 5. Annual Operating Costs for Sodium Carbonate Spray Dryer FGD System on a Generating Unit New 500-MW Coal-Fired Power- Costs Component Annual quantity Unit ($) '. Annual operating ($1,000) Mills/kWh Direct costs, first year: Conversion costs: • ; Operating labor and supervision: ] Flue gas desulfurization ;..... 16,640 man-hours 15.00/man-hour 250 0.09 Solids disposal 28,362 man-hours 21.00/man-hour 596 0.22 Utilities: : • : Fuel 165,700 gal 1.60/gal 265 0.10 Process water !.... 70.2 X106 gal 0.14/1,000 gal ' 10 0.004 Electricity 41.15 X106kWh 0.037/kWh 1,523 0.55 Maintenance, labor and materials ,.... ; 1,863 0.70 Analyses ;• • • • 4,191 man-hours 21.00/man-hour 88 0.03 Total conversion costs I : 4.595 1.694 Delivered raw materials (sodium.carbonate) ; 1 8,350 tons 145.00/ton 2,661 0.97 Total direct costs : I 7,256 2.664 Indirect costs: Overhead, first year, plant, and administrative j. . . . : : 1,475 0.54 Total first-year operating and maintenance costs ;.... 8,731 3.204 Levelized capital charges (14.7% of total capital investment) I. . . . 11,679 4.25 Total first-year revenue requirements .!.... ; 20,410 7.454 Levelized operating and maintenance costs (1.886 X first-year operating and maintenance) .;.-.. 16,467 5.98 Levelized capital charges (14.7% of total capital investment) 11,679 4.25 Total levelized annual operating costs i.... , 28,146 10.23 Notes.—Upper Midwest plant operating 5,500 h/yr. 1984 revenue requirements. 30-yr plant life. 1,346,700 tons/yr western coal burned, 9,500 Btu/kWh, 0.7% sulfur. No gas bypass, no waste solids recycle. Stoichiometry of 1.0 mol sodium carbonate per mol SO2 absorbed. Meets emission regulation of 1.2 Ib SO2/106 Btu with 70% S02 removal. Maintenance costs estimated at 5% of nonlandfill capital investment plus 3% of pond invest- ment. Pond disposal 1 mi from plant. Total direct investment, $40,941,000; total fixed investment, $61,408,000; total capital investment, $79,448,000. SOURCE: Burnett, T. A., and K. D.Anderson, Technical Review of Dry FGD Systems and Economic Evaluation of Spray Dryer FGD Systems. EPA 600/ 7-81-014, TVA EDT-127, NTIS No. PB 81-206476, Feb. 1981. Table 6 gives estimated capital and annual operating costs of 500-MW lime spray dryer systems for four different coals. The costs depend on a number of site-specific factors. Any specific situation should be evaluated for availability and cost of raw materials, utilities, and area for waste disposal. Annual oper- ating costs for spray dryer systems will be most sensitive to the costs of raw materials and electricity. The cost estimates given for lime spray dryer systems were compared with cost estimates for wet lime- stone scrubbing systems.11 For all three low-sulfur-coal applications, the comparison showed that both the capital and operating costs of lime spray dryer systems are lower than those for limestone scrub- bing systems. In the high-sulfur-coal applications, the capital and operating costs for the spray dryer and limestone scrub- bing systems were essentially the same within the accuracy of the cost estimates.11 Further study of spray dryer processes on boilers firing high-sulfur coal should provide data for improved estimates of the relative costs of the two FGD systems in high-sulfur-coal applica- tions. 23 ------- Table 6. j Estimated Capital and Operating Costs for Lime Spray Dryer FGD Process on a New 500-MW Generating Unit „. . . . Total capital System characteristics . b investment C°altyP9° %S _,,- Absorbent n . in %S% stoichi- Operating 6 coal removal ometry* varlables Lignite 07 70 12 Warm gas 826 165 ! bypass reheat, i waste solids recycle Western 07 70 12 Warm gas 771 1 54 ; bypass reheat, waste solids recycle Eastern , 07 70 1 3 Warm gas 75 3 151 ', bypass ; reheat, | no waste solids recycle i pass ! reheat, waste i solids ; recycle , Coal-Fired Power- Annual operating costs0 / $106 Mills/kWh 28 7 1043 25 8 9 39 25 2 918 47 1 1713 'Coal heating values: lignite = 6,600 Btu/lb; western = 9,700 Btu/lb; eastern = 11,700 Btu/lb. Project beginning early 1981, ending late 1983. Average cost for sea ling, mid-1 982. Minimum in-process storage, redundant spray-drying train, pumps are spared. FGD process investment begins at boiler heat exit. Excludes stack plenum and stack; includes only nominal construction overtime. C1984 revenue requirements. '' dMoets emission regulation of 1.2 Ib S02/106 Btu. : *mol S02 absorbed. ; Notes,—Midwest plant operating 5,500 h/yr. 30-yr plant life. Landfill disposal 1 mi from plant. Includes investment and revenue requirements for fly ash removal and disposal. SOURCE: Burnett, T. A., and K. D. Anderson, Technical Review of Dry FGD Systems and Economic Evaluation of Spray Dryer FGD Systems, EPA 600/7- 81-014. TVA EDT-127. NTIS No. PB 81-206476, Feb. 1981. ; 24 ------- References 1 Kelly, M. E., and S. A. Shareef. Third Survey of Dry SO2 Control Systems. EPA 600/7-81 -097, NTIS No. PB 81-218976. June 1981. 2Parsons, Edward L, L. F. Hemen- way, O. T. Kragh, T. G. Brna, and R. L. Ostop. "S02 Removal by Dry FGD." In Proceedings: Sympo- sium on Flue Gas Desulfurization, Houston, Texas, October 1980. Vol. II. EPA 600/9-81-01 9b, NTIS No. PB 81-243-164. Pp. 801-852. Apr. 1981. ! 3Stevens, N. J., G. B. Manavizadeh, G. W. Taylor, and M. J. Widico. "Dry Scrubbing S02 and Particulate Control." Paper presented at U.S. EPA's Third Symposium on the Transfer and Utilization of Particulate Control Technology, Orlando FL, Mar. 1981. 4Kezerle, J. A., S. W. Mulligan, D. P. Dayton, and P. J. Terry. Perform- ance Evaluation of an Industrial Spray Dryer for SO2 Control. EPA 600/7-81-H 43. Aug. 1981. 5Stevens, N. J. "Dry S02 Scrubbing Pilot Test Results." In Proceed- ings: Symposium on Flue Gas De- sulfurization, Houston, Texas, October 1980. Vol. II. EPA 600/9-81-01 9b, NTIS No. PB 81- 243-164. Pp. 777-800. Apr. 1981. 6Hurst, T. B., and G. T. Bielawski. "Dry Scrubber Demonstration Plant Operating Results." In Proceedings: Symposium on Flue Gas Desulfurization, Houston, Texas, October 1980. Vol. II. EPA 600/9-81-01 9b, NTIS No. PB 81-243-164. Pp. 853-869. Apr. 1981. ' 7Downs, W., W. J. Sanders, and C. E. Miller. "Control of S02 Emis- sions by Dry Scrubbing." In Pro- ceedings: American Power Con- ference, Chicago, IL, April 198O. Vol. 42. Pp. 262-271. Chicago IL, American Power Conference, 1 980. 8Getler, J. L, H. L. Shelton, and D. A. Furlong. "Modeling the Spray Absorption Process for S02 Removal." Journal of the Air Pol- lution Control Association, 29(1 2): 1270-1274, Dec. 1979. 9Meyler, J. A. "Dry Flue Gas Scrub- bing: A Technique for the 1980's." Paper presented at the 1 980 Joint Power Conference, Phoenix AZ, Sept. 1 980. 10Kelly, M. E., and S. A. Shareef, Second Survey of Dry SO2 Control Systems. EPA 600/7-81-018, NTIS No. PB 81-157919. Oct. 1980. ; "Burnett, T. A., and K. D. Anderson. Technical Review of Dry FGD Systems and Economic Evaluation of Spray Dryer FGD Systems. EPA 600/7-81 -014, TVA EDT-127, NTIS No. PB 81-206476. Feb. 1981. 12Brown, B., M. Fitzpatrick, C. Sannes, M. Skinner, and A. E. Swanson. "Performance Response of Dry S02 Removal System at Riverside Station." Paper pre- . sented at American Power Confer- ence, Chicago IL, Apr. 1 981. 13The Mcllvaine Company. The Elec- trostatic Precipitation Manual. Vol. III. Ch. IX. Northbrook IL, Mcllvaine, Sept. 1980. 14Gibson, E. D., ed. "Dry FGD Pilot Systems Exceed 90 Percent S02 Removal." FGD Quarterly Report, 5:2, Aug. 1981. 15Surman, J. S., Jr. A Paniculate and Gaseous Emission Study Per- formed for Strathmore Paper Com- pany at the Woronco Mill Power Plant, Woronco, Massachu- setts. Bensonville IL, Mostardi- Platt Associates, May 1 981. 25 ------- ieRasmussen, E. L, J. C. Buschmann, J. R. Donnelly, and S. M. Kaplan. "Disposal of Wastes from Dry SO2 Removal Processes." Paper pre- sented at American Power Con- ference, Chicago IL, Apr. 1981. "Parsons, E. L, V. Boscak, T. G. Brna, and R. L. Ostop. "S02 Re- moval by Dry Injection and Spray Absorption Techniques." Paper presented at the U.S. EPA Third Symposium on the Transfer and Utilization of Paniculate Control Technology, Orlando FL, Mar. 1981. 18Brna, T. G. "Dry Flue Gas Desul- furization in the United States." Paper presented at Third E.C.E. Conference on Desulfuri- zation of Fuels and Combustion Gases, Salzburg, Austria, May 1981. (Available from U.S. Environmental Protection Agency, Industrial Environmental Research Laboratory, Research Triangle Park NC) 19Furlong, D. A., T. G. Brna, and R. L. Ostop. "S02 Removal Using Dry Sodium Compounds." Paper presented at 89th National AlChE Meeting, Portland OR, Aug. 17-20, 1980. 20Drabkin, M., and E. Robinson. "Spray Dryer FGD Capital and Oper- ating Cost Estimates for a North- eastern Utility." In Proceed- ings: Symposium on Flue Gas De- sulfurization, Houston, Texas, October 1980. Vol. II. EPA 600/9- 81-019b, NTIS No. PB 81-243- 164. Pp. 731-760. Apr. 1981. 26 ------- |