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-
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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.
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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.
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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
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