United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park NC 27711 Research and Development EPA/600/S7-85/037 Jan. 1986 v°xEPA Project Summary Primary Sulfate Emission Factors for the NAPAP Emissions Inventory James B. Homolya Primary sulfate emission factors were estimated for Task Group B, Man- Made Sources, of the National Acid Pre- cipitation Assessment Program (NA- PAP), for use in the 1980 and 1985 emissions inventories. Primary sulfate materials consist of SO3, HaSO* or sul- fate salts directly emitted as such from point and area sources. The initial ele- ments in the development of primary sulfate emission factor estimates in- volved an assessment of primary sul- fate formation mechanisms prevalent in combustion processes. The state-of- the-art methodology for primary sul- fate sampling and analysis was reviewed, and the controlled condensa- tion system (CCS) method was deemed to be the best measurement approach. CCS-derived measurement data were abstracted from an inventory of reports including environmental assessment studies, field measurement evaluation experiments, and the U.S./Canadian Work Group 3B inventory. Emission factors with corresponding uncertainty estimates were developed for source categories including external combus- tion, chemical manufacturing, primary metals, wood products, mineral prod- ucts, and petroleum refining. This Project Summary was devel- oped by EPA's Air and Energy Engineer- ing Research Laboratory, Research Tri- angle Park, NC, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report or- dering information at back). Introduction The National Acid Precipitation As- sessment Program (NAPAP) was estab- lished to coordinate and expand re- search relevant to the problems posed by acid deposition in and around the U.S. NAPAP is organized and managed through the Interagency Task Force on Acid Precipitation (ITFAP) and 10 subor- dinate task groups coordinating specific technical areas of research. Task Group B, Man-Made Sources, has prepared a NAPAP emissions inventory implemen- tation plan which is designed to address the needs of the NAPAP research pro- grams being conducted by the other nine task groups within ITFAP. The plan outlines the need for detailed, multi- component point and area source dis- aggregated inventories for defined annual base years to support the devel- opment and testing of atmospheric transport and transformation models to predict acid deposition. Acid deposition model development has centered around the formulation of an Eulerian model which requires high levels of species, temporal, spatial, and sectoral resolution for emissions inven- tory input parameters. Emission inven- tory development is geared to provide data for both the 1980 and 1985 base years which have been targeted for modeling studies. The species require- ments of the 1980 inventory include S02, NOX, VOC, primary sulfate, NH3, CO, and participate matter. Primary sulfate is a generic class of compounds including SO3, H2S04, and sulfate salts. These materials are di- rectly emitted to the atmosphere from many point and area sources and con- tribute to acid deposition processes. This report summarizes an analysis of existing data on primary sulfate emis- sions and presents a tabulation of pri- ------- mary sulfate emission factors appropri- ate for use with the NAPAP emissions inventory. Procedure A summary of the current body of sul- fate emission data was prepared from the findings of a series of sequential as- sessments which included: 1. an evaluation of primary sulfate formation mechanisms; 2. a review of the state-of-the-art for primary sulfate sampling and anal- ysis methodology; 3. a review of existing primary sul- fate inventory factors; and 4. collection, review, and calculation of primary sulfate emission factors from all field test measurement data referenced in the literature. Formation of Primary Sulfates in Combustion Sources Sulfur present in fossil fuels is emit- ted to the atmosphere mainly as S02. However, some of the sulfur is oxidized further in the combustion process and is emitted as primary sulfate compounds. The largest source of primary sulfate emissions (PSE) is from the combustion of coal and oil. The amount of PSE from a particular combustion source is de- pendent on a number of factors includ- ing fuel type and composition, combus- tion equipment design, operating parameters, and emission controls. A significantly higher conversion of fuel sulfur to primary sulfates occurs during oil firing as compared to coal firing. Enhanced PSE from oil combus- tion is due to the low ash, fast burning properties of fuel oil. Also many resid- ual oils contain high levels of vanadium which can catalyze the formation of SO3 in a furnace. Sulfates are formed in combustion processes in both the flame region and downstream in the heat transfer sec- tion. The major primary sulfate forma- tion mechanisms include oxidation of S02 to S03, hydration of S03 to H2S04, corrosion of boiler internals by H2S04, and conversion of metallic oxides in fuel ash to paniculate sulfates. In combus- tion flames, the predominant sulfate formation mechanism is reaction of molecular oxygen to form S03. The final SO3 concentration leaving the flame zone depends on 02 concentration, cooling rate, and the location and rate of mixing of excess air. Increased PSE can be affected by the heterogeneous catalytic oxidation of S02 by metals, metal oxides, and soot suspended in the stream of combustion gases or deposited on boiler internal surfaces. Residual fuel oils from Venezuela and the Middle East contain significant amounts of vanadium which is liberated as V2O5 during combustion. V2O5 has been used extensively in the chemical manufacturing industry, as an oxidation catalyst. The major con- stituents of coal fly ash, SiO2 and AI2O3, are only weak catalysts. Sulfuric acid is formed by reaction of S03 with water vapor in combustion product gases. The acid can adsorb on ash or soot particles, condense on cooler parts of the combustion equip- ment, or be emitted to the atmosphere as a mist. The SO3-to-H2SO4 conversion is temperature- and moisture- dependent. PSE Measurement Methodology The accuracy of PSE factors depends on the ability to accurately measure and characterize sulfate emissions. PSE from combustion sources has been measured on an extractive basis involv- ing sample collection by either absorp- tion or by selectively condensing the S03/H2S04. In the controlled condensa- tion system (CCS) approach, H2S04 is separated from the gas stream by cool- ing the flue gas in a coil below the dew point for H2SO4, but above the dew point of H2O. The resulting H2S04 aero- sol is collected either on the walls of the cooling coil or on a backup frit. The H20 and S02 pass from the coil to an im- pinger system where the SO2 is trapped and oxidized. The use of the CCS is con- sidered to be the best state-of-the-art approach for measuring PSE at fossil fuel combustion sources. Review of Available Primary Sulfate Emission Factor Data Bases Prior to the current need for NAPAP Task Group B to inventory PSE, two en- vironmental program activities included assessments of PSE factors for use in emission inventory development. The Electric Power Research Institute spon- sored a sulfate regional experimental study which included a summary of ex- isting measurements data on primary sulfates and recommended generalized emission factors for a number of source categories. Many of the factors were based on an extrapolation of a limited data set for uncontrolled fossil fuel com- bustion sources along with data con- tained in the EPA Emission Factor Guidelines (AP-42). The United States/Canada Work Group 3B (WG 3B) prepared an emis- sion measurement report in accordance with the Memorandum of Intent on Transboundary Air Pollution of August 1980. The report included an estimate of U.S. and Canadian PSE using factors ab- stracted from the literature along with unpublished emissions data from Cana- dian measurements obtained from the use of a variety of sampling and analy- sis methods. Following review of the ERPI and WG 3B sulfate emissions data sets, an ex- tensive literature review was conducted to include all contemporary PSE mea- surements data in a final analysis and tabulation of emission factors appropri- ate for the NAPAP emissions inventory. Where available, all field measurements using the CCS procedure were consid- ered as the prime data set. Emissions data acquired through the use of meth- ods other than CCS were included only if multiple measurements yielded pre- cise data. Sulfate emission assessments were aggregated for different point sources within the same source cate- gory only if fuel composition and emis- sion controls were similar. PSE factors recommended for use in the NAPAP emissions inventories are listed in Table 1. The factors are re- ported for source classification codes (SCCs) and reflect sulfate emitted as SO4 (molecular weight = 96) based on the chemical analysis of source test samples. Much of the current data set is for fossil fuel combustion in the indus- trial and utility sectors which contribute most of the regional mass emissions of primary sulfates. Table 1 also contains an estimate of the uncertainty for each emission factor. The estimates are based on a qualitative assessment of the representation of available source test data to the assignment of SCC-level factors. ------- Table 1. Primary Sulfate Emission Factors for NAPAP Emissions Inventory Source category NEDS Source classification code (SCO Control device Primary sulfate emission factor" Uncertainty range13 Electric Utilities - External Combustion Eastern bituminous coal Western bituminous coal Lignite Residual oil (>1% sulfur content) Industrial - External Combustion Eastern bituminous coal Residual oil Commercial/Institutional - External Combustion Residual oil (<1% sulfur content) Space Heating - External Combustion Distillate oil Industrial Process - Chemical Manufacturing Industrial Process - Primary Metals Primary copper smelters Primary zinc smelters Primary aluminum smelter Iron production Coke Industrial Process - Wood Products Kraft pulp mill Sulfite pulp mill Wood/bark waste Industrial Process - Mineral Products Cement manufacturing Gypsum manufacturing Industrial Process - Petroleum Industry Fluid crackers Sulfur recovery Claus plants 1-01-002 1-01-002 1-01-003 1-01-004 1-02-002 1-02-004 1-03-004 1-05-001-05 3-01-023 3-03-005-1 3-03-005-2 3-03-005-3 3-03-005-4 3-03-030 3-04-001 3-03-008 3-03-003 3-07-001 3-07-002 1-02-009 3-05-006 and 3-05-007 3-05-015 3-06-002 3-01-032 ESP ESP and FGD ESP ESP and FGD ESP Fuel oil additive Multiclones Multiclones and FGD Multiclones Multiclones and FGD Fuel oil additive Demister Multiclones ESP 0.385 Ib/ton 0.250C 1.290 0.761 1.951 5.439 lb/1000 gal. 2.646 Ib/ton 0.462 5.296 lb/1000 gal. 2.616 25.07 lb/1000 gal." 5.65 lb/1000 gal. 0.100 Ib/ton acid produced 22.5 Ib/ton concentrated ore 1.08 5.76 15.66 55.5 Ib/ton processed 0.5%ofSO2 2.0%ofSO2 0.320 Ib/ton coal charged 3.6 Ib/ton bark g h 15.0 lb/1000 bbl oil 2.8 Ib/ton produced A C B C C B 8 C D D C C B C C D D D D D C C D D D C C 'Metric conversions: 1 Ib = 0.454 kg; 1 ton = 907.2 kg; 1 gal. = 3.7851; 1 bbl = 159.0 i ^Estimated emission factor uncertainty. Assumes that 90% of the values for an individual source lie within the mean uncertainty estimates. Corresponding values are: A = ± 10%; B = ±25%; C = ±50%; D = '±75%; and E = 700%. cEmission factor based on average sulfate scrubbing efficiency of 35%. dEmission factor applicable only to low sulfur content (0.3% s) residual fuel oil. e Total sulfate emissions for kraft pulp mills estimated as 85% of NEDS total paniculate emissions from kraft recovery boilers. f Total sulfate emissions from sodium-base sulfite mills estimated as 70% of NEDS SO2 emissions; for calcium-base sulfite mills estimated as 25% of NEDS SO2 emissions. 9 Total sulfate emissions from cement kilns estimated as 5.6 Ib/ton of cement on an uncontrolled basis. Average paniculate control efficiency from NEDS data assumed to apply in order to calculate actual emissions. h Total sulfate from gypsum plants estimated as 56% as NEDS actual paniculate emissions. ------- James B. Homolya is with Radian Corporation, Research Triangle Park, NC 27709. J. David Mobley is the EPA Project Officer (see below). The complete report, entitled "Primary Sulfate Emission Factors for the NAPAP Emissions In ventory," {Order No. PB 86-108 263/A S; Cost: $11.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air and Energy Engineering Research Laboratory U.S Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 EPA/600/S7-85/037 0000329 PS US ENVIR PROTECTION AGENCY REGION 5 LIBRARY 230 S DEAR80RN STREET CHICAGO IL 60604 ------- |