Environmental Engineering Reference
In-Depth Information
TABLE 9.1
U.S. NSPS Emission Standards for Fossil Fuel Steam Generators
with Heat Input
>
73 MW (250 MBtu/h)
a
Pollutant
Fuel
lb/MBtu Heat Input
g/GJ Heat Input
SO
2
Coal
1.2
516
Oil
0.2
86
Gas
0.2
86
NO
x
Coal (bituminous)
0.6
260
NO
x
Coal (subbituminous)
0.5
210
NO
x
Oil
0.3
130
NO
x
Gas
0.2
86
PM
c
All
0.03
13
a
Data from EPA, Standards of Performance for New Stationary Sources, Electric Steam Generating Units,
Federal Register,
45,
February 1980, pp. 8210-8213.
b
For power plants built after 1978, Best Available Control Technology (BACT) applies. This means that if the
uncontrolled SO
2
emissions were to exceed 1.2 lb/MBtu, 90 % emission reduction is required by appropriate
control technology (e.g., wet limestone scrubber). For uncontrolled emissions less than 0.6 lb/MBtu, 70 %
emission reduction is required (e.g., dry scrubber). For uncontrolled emissions between 0.6 and 1.2 lb/MBtu,
a specified control technology applies that reduces emissions to a maximum of 0.6 lb/MBtu.
c
PM
particulate matter. For PM emissions an opacity standard also applies, which allows a maximum
obscuration of the background sky by 20 % for a 6-minute period.
=
As an example, Table 9.1 lists the NSPS for fossil-fuel-fired steam generators, including electric
power stations, with a thermal power input of more than 73 MW (250 million Btu/hr). The thermal
power input equals the fuel heating value times its mass rate of consumption. Thus, a power plant
with a 500-MW electrical
output
rating, operating at a thermal efficiency of 33.3%, will have a
1500-MW thermal
input
. Likewise, the NSPS are given in units of pollutant mass per fuel energy
(heating value)
input,
grams/Joule or lb/Btu.
The estimation of the mass emission rate of SO
2
from a fossil fuel fired steam generators is
quite simple. Because practically all sulfur atoms in the fuel burn up to form a SO
2
molecule, all
we need to know is the weight percent of sulfur in the fuel and its heating value. The mass emission
rate
E
SO
2
of SO
2
is
E
SO
2
=
2
×
(
%bywt
.
S
)
E
(
−
2
)
×
FR
(9.1)
where
FR
is the firing rate of fuel in lb/s or g/s. The specific emission rate per unit of fuel energy
input,
e
SO
2
,is
e
SO
2
=
2
×
(
%bywt
.
S
)
E
(
−
2
)/
HV
(9.2)
where
HV
is the heating value of fuel in Btu/lb or J/g. The factor of two arises because SO
2
has
double the molecular weight of S.
The emission rate of NO
x
or CO cannot be computed in that manner, because the formation of
these pollutants is dependent on the combustion process, and not on the weight percent of the atoms
in the fuel. The rate of emission of particulate matter is dependent on the content of incombustible
