Technical Information and References
Gaseous Fuel SO_{x} Emission Factor
(Version 1.0, 1/31/97)
Gaseous Fuel SOx Emission Factor:
Applicability: External Combustion units such as boilers and process
heaters for gaseous fuels (e.g., natural gas, oil field produced gas and
propane).
Equations: Two equations are presented. The first is the fundamental
equation showing how the emission factor is generated. The second is a reduced
form of the basic equation for streamlined use. Finally, a check on the units is
shown.
where:
 EF = SO_{x} emission factor in units of lb/MMBtu (HHV
based, as SO_{2})
 ppmvd S = total sulfur concentration in fuel (as S)
 HHV = higher heating value of the fuel (Btu/scf)
 MM = million
 mol vol = molar volume of the fuel at standard conditions (1
atm & 60 ?F, equals 379 std ft^{3}/lbmole)
 mol ratio = stoichiometric molar ratio for the combustion of
sulfur (1 S + 1 O_{2} 1 SO_{2})
Defaults: Default emission factors can be arrived at by using standard
default values for the heating value and sulfur concentrations for each fuel.
Fuel

ppmvd (as S)

ppmvd (as H_{2}S)

HHV (Btu/scf)

SO_{x} Emission Factor (lb/MMBtu)

PUC Natural Gas

85

80

1,050

0.0137

GPA Commercial Propane

254

239

2,522

0.0170

GPA HD5 Propane

169

159

2,522

0.0113

Produced Gas  South Zone

254

239

1,050

0.0409

Produced Gas  North Zone
 846

796

1,050

0.1362

where:
 PUC Natural Gas: Sulfur concentration based on maximum allowed
total sulfur content of 5 gr/100 scf (as S) per General Order 58A. The
calculations below show how the equivalent concentrations are derived
(depending on the "basis"):
{ppmvd as S = (5 gr S/100 scf)*(10^{6} scf fuel/MM scf fuel)*(lb S/7000
gr S)*(379 scf S/lbmole S)/(32 lb S/lbmole S) = 85 ppmvd as S}
{ppmvd as H_{2}S = (5 gr H_{2}S/100 scf)*(10^{6} scf
fuel/MM scf fuel)*(lb H_{2}S/7000 gr H_{2}S)*(379 scf H_{2}S/lbmole
H_{2}S)/(34 lb H_{2}S/lbmole H_{2}S) = 80 ppmvd as H_{2}S}.
Heating value based on USEPA AP42, Appendix A (Thermal Equivalents of
Various Fuels).
 Propane: Sulfur concentration based on Gas Processors Association
Engineering Data Book (Ninth Edition, 1972), Figure 1550 (GPA Liquefied
Petroleum Gas Specifications, rev. 1979), Commercial Propane = 15 gr/100
scf, HD5 Propane = 10 gr/100 scf (both as S). Same equation as listed in
(a) above for the ppmvd "as S" calculation. Heating value based on Perry's
Chemical Engineers Handbook, Chapter 9, 5th Edition, Table 916.
 Produced Gas: Sulfur concentration based on APCD Rule 311 
Southern Zone limit of 15 gr/100 scf (as H_{2}S) and Northern Zone
limit of 50 gr/100 scf (as H_{2}S). To use in the calculations
(which are based on an "as S" basis), these limits are adjusted to an as
sulfur (as S) basis by use of the equation in note (a) above. This has the
same affect as taking the ratio of the molecular weights (MW_{S}/MW_{H2S})
such that the respective Zone limits are 14.12 gr/100 scf and 47.06 gr/100
scf (as S). Heating value based on USEPA AP42, Appendix A (Thermal
Equivalents of Various Fuels).
 Reporting References: Reporting "as H_{2}S" means the
total sulfur values are converted to an H_{2}S basis by taking the
ratio of the molecular weights (MW_{S}/MW_{H2S}). This is
needed to determine compliance with Rule 311 and permit conditions that
require reporting "as H_{2}S". For PUC and GPA standards and the
emission calculations, sulfur content "as S" is used. "S" in this case is
monoatomic sulfur (MW = 32 lb/lbmole). When reviewing fuel analyses with
diatomic sulfur species, such as CS_{2}, the amount of sulfur from
the compound in question must be doubled to account for the extra mole of
sulfur.
 Permit Condition Limits and Reporting: Since permits require
sulfur content of fuels to be reported "as H_{2}S", the associated
limits for nonRule 311 sulfur concentrations need to be also stated in an
"as H_{2}S" basis so as to minimize the confusion of reporting in
two ways. As such, for PUC natural gas the standard of 85 ppmvd "as S" is
listed in the permit condition as 80 ppmv "as H_{2}S". For GPA
propane/LPG, the standard of 254 ppmvd "as S" is listed in the permit
condition as 239 ppmvd "as H_{2}S".
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