B­
1
APPENDIX
B
EMISSION
MODIFICATION
FACTORS
FOR
COAL­
FIRED
UNITS
Mercury
concentrations
in
the
flue
gas
of
coal­
fired
steam
electric
units
are
often
lower
than
the
concentration
levels
contained
in
the
coals
that
they
burn.
This
occurs
because
some
types
of
boilers
decrease
the
amount
of
mercury
entering
the
flue
gas,
or
because
of
the
pollution
control
equipment
already
installed
in
the
units.
Different
boiler
and
pollution
control
equipment
configurations
lead
to
different
changes
in
mercury
emissions
in
the
flue
gas.
EPA
has
calculated
emission
modification
factors
(
EMFs)
that
reflect
these
changes.
The
EMFs
are
calculated
by
dividing
the
amount
of
mercury
exiting
either
the
boiler
or
the
air
pollution
control
device
by
the
amount
of
mercury
entering
the
boiler,
or
control
device.
Mercury
emissions
from
coal
at
specific
boilers
are,
therefore,
calculated
by
multiplying
the
calculated
inlet
mercury
concentrations
in
coal
by
the
EMFs
that
fit
a
particular
boiler/
pollution
control
configuration
(
EPA,
1998).

EPA's
Report
to
Congress
on
hazardous
air
pollutant
(
HAP)
emissions
(
HAP
Study;
EPA,
1998)
1
developed
EMFs
for
specific
boiler
configurations
and
air
pollution
control
devices,
based
on
actual
mercury
emissions
test
data.
The
EMFs
for
coal­
fired
boiler
configurations,
used
in
the
IPM
mercury
analyses,
are
shown
in
Exhibit
B1.

Exhibit
B1
Emission
Modification
Factors
for
Coal­
fired
Boiler
Configurations
Boiler
Type
EMFs1
Circulating
Fluidized
Bed
1.000
Cyclone­
fired
boiler
with
wet
bottom
0.930
Front­
fired
boiler
with
dry
bottom
0.940
Front­
fired
boiler
with
wet
bottom2
0.918
Opposed­
fired
boiler
with
dry
bottom
0.410
Tangentially­
fired
boiler
with
dry
bottom
0.810
Htangentially­
fired
boiler
with
dry
bottom
1.000
Vertically­
fired
boiler
with
dry
bottom
0.780
1
The
1994
EMFs
were
used,
when
the
HAP
Study
reported
separate
EMFs
for
1990
and
1994.
2
The
EMF
for
this
boiler
configuration
was
obtained
from
the
Mercury
Study
Report
to
Congress
(
Mercury
Study;
EPA,
1997),
2
as
the
HAP
Study
has
not
developed
an
EMF
for
this
particular
boiler
configuration.
Source:
EPA
(
1997,
1998)

1
EPA.
1998.
Study
of
Hazardous
Air
Pollutant
Emissions
from
Electric
Utility
Steam
Generating
Units
 
Final
Report
to
Congress.
Volumes
I
and
II.
Office
of
Air
Quality
Planning
and
Standards.
U.
S.
Environmental
Protection
Agency.
EPA­
453/
R­
98­
004a
&
­
004b.
February
1998.
2
EPA.
1997.
Mercury
Study
Report
to
Congress.
Volume
II:
An
Inventory
of
Anthropogenic
Mercury
missions
in
the
United
States.
Office
of
Air
Quality
Planning
and
Standards
and
Office
of
Research
and
Development.
U.
S.
Environmental
Protection
Agency.
EPA­
452/
R­
97­
004.
December
1997.
B­
2
The
EMFs
for
pollution
control
equipment,
used
in
the
IPM
mercury
analyses,
are
shown
in
Exhibit
B2.

Exhibit
B2
Emission
Modification
Factors
for
Pollution
Control
Devices
Pollution
Control
Device
EMFs
FGD
Scrubber
0.660
Fabric
Filter
0.560
Cold­
side
(
CS),
Electro­
static
Precipitator
(
ESP)
0.680
Hot­
side
(
HS),
Electro­
static
Precipitator
(
ESP)
1.000
Particulate
Matter
Scrubber
0.960
No
Control
1.000
Source:
EPA
(
1998)

For
a
boiler
configuration,
with
one
or
more
air
pollution
control
devices,
the
EMFs
are
used
as
multiplicative
factors
(
i.
e.,
the
EMFs
of
the
individual
boiler
configurations
and
the
control
devices
are
multiplied).
For
example,
in
the
case
of
an
opposed­
fired
boiler,
with
a
dry
bottom,
and
with
a
cold­
side,
ESP
and
a
fabric
filter,
the
mercury
emission
reductions
occur
in
three
stages,
which
are
described
below.

Suppose
that
coal
with
one
pound
of
mercury
per
trillion
BTUs
is
fired
in
the
opposed­
fired
boiler,
with
dry
bottom.
 
First,
the
boiler
configuration
(
i.
e.,
opposed­
fired
boiler
with
dry
bottom)
reduces
the
mercury
emissions
to
0.41
lbs
(=
1
lb
*
0.41),
which
indicates
a
mercury
removal
efficiency
of
59%
(=
1
­
0.41).
 
Second,
the
cold­
side,
ESP
further
reduces
those
mercury
emissions
to
0.28
lbs
(=
0.41
lbs
*
0.68),
which
indicates
a
combined
mercury
removal
efficiency
of
72%
(=
1
­
0.28).
 
Third,
the
fabric
filter
reduces
the
remaining
mercury
emissions
to
0.16
lbs
(=
0.28
lbs
*
0.56),
which
indicates
the
total
mercury
removal
efficiency
of
84%
(=
1
­
0.16).
The
combined
EMF
is,
therefore,
calculated
as
follows:
EMF
for
an
Opposed­
fired
boiler
with
dry
bottom
*
EMF
for
a
cold­
side,
ESP
*
EMF
for
a
fabric
filter
(
0.41
*
0.68
*
0.56=
0.156
)

The
HAP
Study
does
not
report
EMFs
for
all
boiler
configurations
and
air
pollution
control
devices
used
in
the
IPM
mercury
analyses.
Therefore,
for
the
purposes
of
this
study,
EPA
developed
EMFs
for
those
boiler
configurations
and
control
devices
for
which
HAP
Study
does
not
contain
data,
using
the
mapping
schemes
outlined
in
Exhibits
B3
and
B4.
B­
3
Exhibit
B3
Default
EMFs
for
Other
Boiler
Configurations
Boiler
Type
Default
Boiler
Configurations
EMF
AFBDRY
Circulating
Fluidized
Bed
1.000
ARCHDRY
Vertically­
fired
boiler
with
dry
bottom
0.780
ARCHWET
Vertically­
fired
boiler
with
dry
bottom
0.780
CFBDRY
Circulating
Fluidized
Bed
1.000
REARDRY
Front­
fired
boiler
with
dry
bottom
0.940
STOKER/
SPRDRY
Unknown
 
(
1)
Tangentially­
fired
with
dry
bottom,
if
the
boiler
came
on­
line
before
1980
(
2)
Opposed­
fired
with
dry
bottom,
if
the
boiler
came
on­
line
in
1980
or
after
0.810
0.410
OTHERDRY
Front­
fired
with
dry
bottom
0.940
TANGENTIALWET
Tangentially­
fired
boiler
with
dry
bottom
0.810
UNKNOWN
Unknown
 
(
1)
Tangentially­
fired
with
dry
bottom,
if
the
boiler
came
on­
line
before
1980
(
2)
Opposed­
fired
with
dry
bottom,
if
the
boiler
came
on­
line
in
1980
or
after
0.810
0.410
VERTICALWET
Vertically­
fired
boiler
with
dry
bottom
0.780
Exhibit
B4
Default
EMFs
for
Other
Air
Pollution
Control
Devices
Pollution
Control
Device
Default
Pollution
Control
Device
EMF
Particulate
Control
Device
­
Unknown
Cold­
side,
ESP
0.680
ESP
Cold­
side,
ESP
0.680
WS
Particulate
Matter
Scrubber
0.960
DRYSCRUB
FGD
Scrubber
0.660
WETSCRUB
FGD
Scrubber
0.660
