4.0 Emissions from Fuel Production and Distribution Processes
This section includes emissions from feedstock extraction, fuel production, and distribution. The emissions sources are covered roughly in order from extraction through distribution with some overlap. Section 4.1 reviews emission rates from equipment used in transporting feedstocks and fuel and in processing operations. Energy usage rates for transportation equipment are also discussed in Section 4.1.
Fuel production emissions and energy inputs are covered in Section 4.2 through 4.8. The allocation of energy use to product fuels is discussed while fuel production processes have a minor or no effect on marginal NMOG or NOx emissions in the SoCAB, they are still analyzed as they affect global CO2 emissions. Fuel processing is defined as the conversion of feedstock material into end use fuel, or fuel production Phase 3. Feedstock input requirements also relate to feedstock extraction requirements in Section 4.1. LPG liquefaction is included Phase 3. Several fuels are processed from a combination of feedstocks and process fuels. Oil refineries and gas treatment plants produce multiple fuel products. Many production facilities import or export electricity and excess heat energy can be exported to other facilities,
Section 4.9 discusses emissions from fuel storage and distribution. These represent the most significant sources of marginal NMOG emissions. Section 4.10 discusses toxic emissions. Since toxic emissions are not measured as frequently as criteria pollutants, these emissions are primarily available from other data sources than those in Section 4.1 through 4.9. Toxic hydrocarbon emissions are estimated as a fraction of NMOG.
Several approaches have been taken towards determining fuel-cycle emissions. Perhaps the simplest approach is to estimate the energy required for each step of the fuel-cycle. Then, "emission factors" can be multiplied by the energy use rate (Jenkins 1979, Unnasch April 1990). There are several negative aspects of relying entirely on this approach. Primarily, energy use expressed in Btu/gal of fuel (or Btu/Btu fuel) is many steps removed from the actual fuel-cycle-processing step.
For example, consider a diesel deliver truck with 7,800 gal of fuel traveling a 50-mi round trip route. A diesel truck fuel consumption of 5 mi/gal is expressed in energy terms as 0.0014 Btu/Btu based on lower heating values (Table 2-1). Expressing all of the fuel processing steps in energy terms allows for a convenient comparison amongst different fuel-cycle emission studies. The emissions in this study are estimated from more fundamental principles. In the case of fuel delivery trucks, a constant mileage is assumed for all fuel types and emissions are calculated from the g/mi emissions and truck fuel capacity to yield g/gal of delivered fuel.
The energy in Btu (HHV) per unit of fuel produced is tracked with the fuel-cycle emissions. Lower heating values are only used to estimate vehicle fuel consumption and are not mixed with higher heating values anywhere in this study.