United States
                    Environmental Protection
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).

                     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

  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-

PSE Measurement
  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
  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

Table 1.    Primary Sulfate Emission Factors for NAPAP Emissions Inventory
              Source category
NEDS Source
 code (SCO
   Control device
  Primary sulfate
 emission factor"
Electric Utilities - External Combustion
  Eastern bituminous coal

  Western bituminous coal

  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
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










3-05-006 and
   ESP and FGD
   ESP and FGD
  Fuel oil additive
Multiclones and FGD
Multiclones and FGD
  Fuel oil additive
   0.385 Ib/ton
 5.439 lb/1000 gal.
   2.646 Ib/ton
 5.296 lb/1000 gal.
25.07 lb/1000 gal."
                           5.65 lb/1000 gal.
                             0.100 Ib/ton
                           acid produced
                             22.5 Ib/ton
                          concentrated ore
                             55.5 Ib/ton
                            0.320 Ib/ton
                            coal charged
  3.6 Ib/ton bark


15.0 lb/1000 bbl oil
    2.8 Ib/ton



'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
Center for Environmental Research
Cincinnati OH 45268
Official Business
Penalty for Private Use $300

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