EPA-450/3-77-050b December 1977 ENERGY REQUIREMENTS FOR CONTROLLING SO2 EMISSIONS FROM COAL-FIRED STEAM/ELECTRIC GENERATORS - EXECUTIVE SUMMARY U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Air and Waste Management Office of Air Quality Planning and Standards Research Triangle Park, North Carolina 27711 ------- EPA-450/3-77-050b ENERGY REQUIREMENTS FOR CONTROLLING SO2 EMISSIONS FROM COAL-FIRED STEAM/ELECTRIC GENERATORS - EXECUTIVE SUMMARY by W.C Thomas Radian Corporation P.O. Box 9948 Austin, Texas 78766 Contract No. 68-02-2608 Project No. 8 EPA Project Officer: K.R. Durkee Prepared for ENVIRONMENTAL PROTECTION AGENCY Office of Air and Waste Management Office of Air Quality Planning and Standards Research Triangle Park, North Carolina 27711 December 1977 ------- This report is issued by the Environmental Protection Agency to report technical data of interest to a limited number of readers. Copies are available free of charge to Federal employees, current contractors and grantees, and nonprofit organizations - in limited quantities - from the Library Services Office (MD-35) , Research Triangle Park, North Carolina 27711; or, for a fee, from the National Technical Information Service, 5285 Port Royal Road, Springfield, Virginia 22161. This report was furnished to the Environmental Protection Agency by Radian Corporation, P.O. Box 9948, Austin, Texas 78766, in fulfillment of Contract No. 68-02-2608, Project No. 8. The contents of this report are reproduced herein as received from Radian Corporation. The opinions, findings, and conclusions expressed are those of the author and not necessarily those of the Environmental Protection Agency • Mention of company or product names is not to be considered as an endorsement by the Environmental Protection Agency. Publication No. EPA-450/3-77-050b 11 ------- TABLE OF CONTENTS Page 1. 0 BACKGROUND AND PURPOSE 1 2. 0 APPROACH 2 3.0 SUMMARY OF RESULTS 4 3.1 Design Assumptions 4 3.2 Comparison by S02 Control Methods 4 3.3 Comparison by S02 Control Level 11 3.4 Energy Penalty Projections 13 iii ------- 1.0 BACKGROUND AND PURPOSE The existing New Source Performance Standard (NSPS) for S02 emissions from coal-fired steam generators is 0.52 g S02/MJ (1.2 Ib S02/106 Btu) of heat input. Depending on coal sulfur content and heating value, compliance with this standard can be achieved by means of flue gas desulfurization (FGD), coal desul- furization, the use of low sulfur coal, or a combination of these approaches. Since the promulgation of the S02 NSPS in 1971, im- provements have been made in the performance and reliability of FGD processes. Because of these improvements, public interest groups have requested that the EPA promulgate more stringent S02 emission standards. Therefore, the EPA's Office of Air Quality Planning and Standards (OAQPS) has undertaken a program to review the existing NSPS. The study described in this report was done to assist OAQPS in the review by providing information on the en- ergy requirements of S02 control systems. The report answers the following questions. What are the amounts and types of energy required to operate various S02 emission control systems? How do these energy requirements compare to those of steam generators without emission control systems? How do projected energy requirements for emission con- trol compare with projected national energy demands in 1987 and 1997? ------- 2.0 APPROACH The study was based on an EPA model including 102 sys- tems which are combinations of power plants and S02 control meth- ods. The variables considered in the model are level of S02 con- trol, method of S02 control, power plant size, and coal composi- tion. The levels of each variable considered in this study and the combinations of variables were defined by EPA as shown in Table 1. Three levels of S02 control were considered. They in- clude the existing NSPS (0.52 g S02/MJ heat input), 90 percent SO2 removal, and 0.22 g S02/MJ. Control methods considered include regenerable FGD processes, nonregenerable FGD processes, trans- portation of low sulfur coal to the Midwest, and a combination of coal cleaning and nonregenerable FGD processes. Energy requirements for the 102 model systems were cal- culated by extrapolating "base case energy requirements. Base case energy requirements for each S02 control method were calcu- lated from material and energy balances. The base case was 90 percent S02 removal from the flue gas of a 500 MW power plant burning 3.5 percent sulfur coal. Extrapolation factors which de- scribe energy requirements in terms of flue gas rate and S02 re- moved were defined. The extrapolation factors were used to cal- culate energy requirements for all the power plant/S02 control system combinations included in the model. -2- ------- TABLE 1. MODEL S02 EMISSION CONTROL SYSTEMS STUDIED SO2 Control Level Plant Sizes Considered, Mf FGD Processes Considered* Coal 0.52 g SOj/KJ (1.2 Ib S02/10' Btu) 25, 100, 500, 1000 25, 100, 500, 1000 25, 500 25, 500 500 LS, L, MgO. W-L/A, D-A LS, L LS, L 3.5Z sulfur; 27.9 MJ/kg 7.0Z sulfur; 27.9 MJ/kg 0.6Z sulfur; 20.9 MJ/kg western coal transported to a Midwest power plant 0.8Z sulfur; 25.6 MJ/kg western coal transported to a Midwest power plant 2.3Z sulfur; 29.2 MJ/kg** I lo I 90Z S02 Reaoval by FGD 0.22 g S02/MJ (0.5 Ib S02/10( Btu) 25, 25, 25, 25, 25, 25. 25, 25, 100, 500, 1000 100, 500, 1000 100, 500 100, 500 500 500 500 500 LS, LS, LS, LS, LS, LS, LS, LS, L, MgO, W-L/A, D-A L, MgO, W-L/A, D-A L L L L L L 3 7 0 0 0 0 2 4 .5Z .01 .8Z .8Z .81 .81 .3Z .61 sulfur; sulfur; sulfur; sulfur; sulfur, sulfur; sulfur; sulfur; 27. 27. 20. 25. 20. 25. 29. 29. 9 9 9 6 9 6 2 2 MJ/kg MJ/kg MJ/kg MJ/kg MJ/kg MJ/kg MJ/kg** MJ/kg*** *LS - Linestone L - Line MgO - Magnesia Slurry W-L/A - Wellnan-Lord/Allled D-A - Double-Alkali **Physlcally cleaned 3.5Z sulfur; 27.9 MJ/kg coal (40Z sulfur removal) ***Physically cleaned 7.0Z sulfur; 27.9 MJ/kg coal (40Z sulfur removal) ------- 3.0 SUMMARY OF RESULTS The results of the study show how energy requirements depend on SOa control method, level of control, and coal sulfur content. It was found that energy requirements for S02 control systems (expressed as energy required per unit of electrical generating capacity) depend only slightly on plant size. 3.1 Design Assumptions The energy requirements for operating flue gas desulfurization systems were calculated based on the process designs summarized in Table 2. The design assumptions for coal cleaning processes are shown in Table 3. A unit train con- sisting of 100 coal cars and five locomotives was the design basis for coal transportation. Fuel consumption rates, transport distance, train speeds at full and reduced power, and coal dust blow-off losses were specified. Table 4 shows calculated energy requirements for the six processing operations in FGD systems. Particulate/chloride removal, reheaters, and fans account for 65 to 90 percent ot total energy requirements for nonregenerable FGD processes. Sulfur recovery operations account for the majority of energy requirements for regenerable FGD processes. 3.2 Comparison by SOa Control Methods Figure 1 shows the energy required to meet the existing NSPS of 0.52g S02/MJ using different S02 control methods for several coal compositions. The total energy requirements are ------- TABLE 2. PROCESS DESIGN BASES FOR FGD PROCESSES i Ul i FGD Process Process Step Limestone Particulate/Chlorlde Removal Venturi SO 2 Scrubbing Mobile Bed Reheat Indirect Stem Re heater Fans Induced Draft Fans Sulfur Disposal/Recovery Lined Settling Pond Line Venturi Mobile Bed Indirect Steaa Reheater Induced Draft Fan* Lined Settling Pond MgO Venturi Venturi Indirect Steaa Reheater Induced Draft Fans Production of Sulfuric Acid Uellman- Lord/Allied Venturi Valve Tray Indirect Steam Reheater Induced Draft Fans Production of Elemental Sulfur Double-Alkali Venturi Mobile Bed Indirect Steam Reheater Induced Draft Fans Lined Settling Pond •Selection of processing techniques was baaed on data from the open literature which were representative of commercially available systems. ------- separated into the types of energy required, i.e., steam, fuel oil, natural gas, electricity, and coal losses. Nonregenerable FGD processes impose the lowest energy requirements. The combi- nation of coal cleaning and nonregenerable FGD systems requires three times the energy required by the FGD process alone. Trans- portation of low sulfur western coal to the Midwest requires 25 to 100 percent more energy than combusting a high sulfur eastern coal and using a nonregenerable FGD process. TABLE 3. DESIGN ASSUMPTIONS FOR PHYSICAL COAL CLEANING FACILITY 40% sulfur removal 95% energy recovery efficiency The electric power requirements for a 278 kg/s (500 ton/hr) cleaning plant are 2980 kW. The heat duty of a thermal dryer is 534 kJ/kg (230 Btu/lb) of coal dried. One half of the clean coal product (the coal fines) is thermally dried. Heat for the thermal dryers is supplied by burning a portion of the clean coal product. 507o of the ash content of the coal is removed. The average heating value of the clean coal is 29.2 MJ/kg (12,500 Btu/lb). Figure 2 shows the energy required to meet a standard of 90% S02 removal using different S02 control methods for several coal compositions. Figure 3 shows energy requirements for meeting a standard of 0.22 g S02/MJ. The energy requirements for different -6- ------- TABLE 4. ENERGY REQUIREMENTS FOR THE PROCESSING OPERATIONS IN FGD SYSTEMS Energy Requirements for Flue Gas Desulfurization, MJ/s FGD Process Limestone Lime Magnesia Slurry Wellman-Lord/Allled Double- Alkali Coal Sulfur Content 3. 51 7. 01 3. 5* 7.0Z 3.5Z 7. OX 3. 51 7.0Z 3.5Z 7.0* Raw Material Handling and Preparation 2.2 4.4 0.2 0.4 0.5 0.9 0.2 0.3 0.3 0.5 Partlculate/ Chloride Removal 9.0* 9.0* 9.0* 9.0* 3.0 3.0 3.0 3.1 3.0 3.0 S02 Scrubbing 6.8 13.5 6.3 9.4 2.5 5.0 0.9 0.9 2.4 2.4 Reheat 18.3 18.5 18.3 18.3 15.3 IS. 4 16.8 17.3 18.2 18.2 Fans 10.4* 11.1* 10.2* 10.4* 14.7 16.1 18.3 18.8 14.9 14.9 Sulfur Recovery/ Disposal 0.3 0.6 0.3 0.5 41.1 82.8 136 281 0.7 1.3 Total System Energy Requirements** 49.2 57.3 44.3 48.2 77.5 124 176 321 39.8 40.7 *Energy required by fans to overcome pressure drop associated with partlculate removal Is included In the particulate removal operation. "Utilities and Services for the FGD processes account for the discrepancies In system totals. Assumptions 500 MW power plant (net generating capacity) 901 SO: removal Uncontrolled power plant net heat rate - 2640 J/kW-s - Uncontrolled power plant net heat rate - 2640 J/kW-s Steam produced in Magnesia Slurry and Wellman-Lord/Allled process is used within the process. Magnesia Slurry process produces sulfurlc acid as a by-product. Wellman-Lord/Allied process produces sulfur as a by-product. ------- I OIL ON «AS I COAL CLIANINO ANO TNAIN WIMOAM 1.OSHS I STIAM AND ILICTNICITV ) OIIStL FUIL OIL O.ttlULFUN. 20.IMJIX COAL 0.§» SULFUH. tf.t MJ/k« COAL Figure 1. Energy requirements for S02 and particulate control 0.52g S02/MJ control level, 500 MW plant. -8- ------- LtQCNO: | OIL OR «Ai I ITIAM AW ILICTMCITV O i! 3.5% SULFUR ar.auj/kg COAL 7* SULFUR O.t* SULFUR O.t* SULFUR I7.9MJ/k| COAL t0.tMJ/kv COAL tl.VMJ/hf COAL Figure 2. Energy penalties for S02 and particulate control 907o S02 removal control level, 500 MW plant. -9- ------- *.•% SULFU tT.t UJ/h COAL T.0« SULFUR. >?.«MJ/kt COAL Figure 3. Energy requirements for S02 and particulate control - 0.22 g/S02/MJ control level, 500 MW plant. -10- ------- control methods have the same relative variations for the more stringent standards as those for meeting the existing standard. Table 5 summarizes the energy requirements shown in Figures 1 through 3 for combusting a 3.5 percent sulfur coal. TABLE 5. ENERGY PENALTIES ASSOCIATED WITH DIFFERENT METHODS OF CONTROLLING S02 EMISSIONS - 500 MW PLANT, 3.5% SULFUR COAL S02 Control Process Nonregenerable FGD Limestone Lime Double- Alkali Regenerable FGD Magnesia Slurry Wellman-Lord/Allied Coal Cleaning Plus Lime/Limestone FGD Energy Penalty (% Energy Input To Equivalent Uncontrolled Power Plant) Level 0.52g S02/MJ (NSPS) 3.4 3.0 3.0 5.3 11.7 9.8 of SOz Control 90% Removal 0 3.8 3.4 3.0 6.1 13.2 NE .22g S02/MJ NE NE NE NE NE 9.8/10.2 NE = Not Examined 3.3 Comparison by SO; Control Level Figure 4 shows how energy penalties depend on the level of S02 control. Two levels of control are shown, the existing standard and 90 percent SO2 removal. Ninety percent removal is a more stringent level of control than the existing standard. Figure 4 shows that for most control methods the energy penalty for achieving 90 percent removal is about 10-15 percent higher than that required to meet the existing NSPS. -11- ------- 09 I cd c 0) PH bO fc 0) 360 - 340 - 320- 300- 280 - 260 . * ! 180 - 160- 140- 120 - 100- 80- Physical Coal Cleaning and Limestone or Lime FGD © Transporting Low Sulfur Western Coal to Midwest-No FGD Basis: 500 MW plant; 2640 J/kW-s net heat rate; 3.5Z sulfur, 27.9 MJ/kg coal Double-Alkali FGD 0.52 g S02/MJ (NSPS) 90% SO2 Removal Level of Control of SO: Emissions Figure 4. Energy penalties for S02 control of effects of S02 control level. - summary -12- ------- The results of the study also show that for combustion of low sulfur western coal, 90 percent S02 removal requires up to 10 percent more energy than controlling emissions to 0.22 g S02/MJ (0.5 Ib S02/106 Btu) of heat input. For low sulfur coals, 0.22 g S02/MJ is more stringent than the existing NSPS but less stringent than 90 percent removal. For a "bare bones" S02 control system, the energy re- quired for flue gas reheat and particulate/chloride removal is excluded from the limestone and lime systems. This reduces the energy requirements of these systems by 50 to 60 percent. For the double-alkali, magnesia slurry and Wellman-Lord/Allied pro- cesses, the particulate/chloride removal operation is required to prevent buildup of chlorides in the S02 scrubbing liquor. However, excluding flue gas reheat requirements would reduce the energy required by the MgO system by 15 to 25 percent, the W-L/A by about 10 percent and the double-alkali by about 50 percent. 3.4 Energy Penalty Projections The energy penalties associated with S02 controls were compared with projected total U.S. energy consumption for 1987 / and 1997. Depending on control level, method of control, and sulfur content of coal, the energy required to control S02 emis- sions from new coal-fired power plants installed in 1983 through 1987 will be from 0.1 to 0.4 percent of total energy consumption in 1987. For the new capacity installed in 1983 through 1997, the energy penalty ranges from 0.4 to 1.7 percent of projected U.S. energy consumption in 1997. These ranges are based on combusting 0.8 to 3.5 percent sulfur coal and controlling S02 emission to the existing NSPS or effecting 90 percent S02 removal. Assuming the majority of future S02 controls are limestone or lime FGD systems, as is presently true, estimates for 1987 and 1997 would be 0.1 percent and 0.4 percent, respectively. -13- ------- TECHNICAL REPORT DATA (Please read Instructions on the reverse before completing) 1. REPORT NO. EPA-450/3-77-0506b 3. RECIPIENT'S ACCESSION-NO. 4. TITLE AND SUBTITLE The Energy Requirements for Controlling S02 Emissions from Coal-Fired Steam/Electric Generators 5. REPORT DATE January, 1978 6. PERFORMING ORGANIZATION CODE 7. AUTHOR(S) W. C. Thomas 8. PERFORMING ORGANIZATION REPORT NO. 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO. Radian Corporation P. 0. Box 9948 Austin, Texas 78766 11. CONTRACT/GRANT NO. 68-02-2608 12. SPONSORING AGENCY NAME AND ADDRESS Environmental Protection Agency Office of Air Quality Planning and Standards (MD-13) Research Triangle Park, North Carolina 27711 13. TYPE OF REPORT AND PERIOD COVERED Final 14. SPONSORING AGENCY CODE 15. SUPPLEMENTARY NOTES 16. ABSTRACT The report is an executive summary of the main report (EPA-450/3- 77-050a). The main report is an analysis of the energy required by various methods of reducing sulfur dioxide emissions from coal-fired boilers. The energy required for limestone, lime, double alkali, mag- nesium slurry and Wellman-Lord/Allied flue gas scrubbing systems is presented. The variation of energy requirements with coal sulfur content, emission level achieved and plant size is presented. The energy required to transport low sulfur coal to the mid-west or to physically clean sulfur from the coal is presented also. 17. KEY WORDS AND DOCUMENT ANALYSIS DESCRIPTORS b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group 18. DISTRIBUTION STATEMENT Release Unlimited 19. SECURITY CLASS (ThisReportI Unclassified 21. NO. OF ? 18 20. SECURITY CLASS (Thispage) Unclassified 22. PRICE EPA Form 2220-1 (9-73) -14- ------- |