The new CA_GREET2 includes changes to the emissions from crude oil refining based on the GREET1_2013 model. The GREET1_2013 model uses inputs for oil refining based on the recent papers from ANL. GREET1_2013 models all petroleum fuels with a 1:1 conversion of crude oil to refined product. This assumption under counts the upstream fuel cycle emissions from crude oil refining because it does not take into account the yield from crude oil to refined product.
GREET1_2014 has modified the energy inputs for crude oil refinery emissions. First the fuel share for each refined produce are different with insight based on recent refinery modeling studies. The model now includes a crude oil to refined product yield factor, Y (for example Y = 0.863 for gasoline). The energy inputs for oil refining, E based on the refinery efficiency, and η become:
E = (1/η-Y)
This modification to GREET serves as a proxy to reflect the yield from crude oil to refined product and should be viewed as a more accurate representation of the GHG emissions from oil refining. The merits of this approach require further comparison with other approaches. The term Y, increases the natural gas and other fuel use in the oil refinery when combined with the fuel shares input. The emissions associated with petroleum coke and refinery still gas combustion are not affected by the Y term, even though these fuels are derived from crude oil. The upstream fuel cycle emissions from these fuels should also be included in the GREET calculations. These fuel sources are derived from crude oil; so the emissions should include the upstream fuel cycle component.
If you would like to discuss some of these calculations in more detail, contact us.