Emission rates from fuel production equipment are estimated from published emission factors, other emissions data, and emission requirements from local and federal rules. In the strictest sense, an emission factor might be considered to be an energy specific emission rate, in g/gal fuel for example, that represents a wide range of equipment and is weighted according to equipment inventory, usage pattern, and other parameters. The term emission factor implies inventory wide applicability and is reserved for published emission rates.
Emissions depend on the location of equipment and the prevailing (and prior) emission standards. Vehicles and combustion equipment in the SoCAB are and will continue to be subject to the strictest emission controls.
SCAQMD limits are as stringent or more so than NSPS and NESHAPS standards. Table 4-1 shows NOx limits on combustion sources in the SoCAB. Boilers and gas turbines have been subject to Best Available control technology (BACT) requirements since the 1980s. All equipment installed since that time would meet NOx levels consistent with Rule 474. More recent installations will need to meet stricter NOx limits under Rule 1134. NOx levels of 9 ppm can only be met with Selective Catalytic Reduction (SCR) and actual emissions with SCR are one-half of the limit.
Emission limits under Rules 474, 1110, 1134, and 1146 are expressed in ppm. These were converted to lb NO2/MMBtu using a fuel factor of 8740 dry scf/MMBtu for natural gas and 9220 dry scf/MMBtu for diesel fuel. These emissions are expressed in lb/Mwh or g/hp-hr for the energy consumption assumptions shown in the table.
4.1 Fuel Extraction, Transportation, and Processing Equipment
Several types of equipment are used repeatedly throughout the estimation of fuel-cycle emissions. For example, diesel powered tanker trucks are used to move diesel, LPG, and methanol fuels from storage locations. Natural gas engines and gas turbines compress natural gas and are used in a variety of fuel industry applications. These engines are used to transmit natural gas feedstock to oil refineries, FT diesel, methanol, and electric power plants. This section summarizes the emissions and estimated usage rates for various types of equipment. The usage rates are related to assumptions for different scenarios.
4.1.1 Engine Emissions
Table 4-2 summarizes the emission and performance characteristics of natural gas turbines used for natural gas transmission, prime movers. Table 4-2 shows estimate of current and future emissions for turbines operating in the SoCAB, California, and the United States. Turbines operating outside of North America are assumed to emit at 1990 United States levels.
Emissions in Table 4-2 are shown in g/bhp-hr. These are converted to g/100scf of natural gas transmitted with usage rates discusses later and the calculation approach in Section 4.4.