4.2.4 Conventional Jet Fuel Results
The life cycle GHG emissions from the production of jet fuel from conventional crude are shown in Table 8. These results incorporate the recovery (crude extraction) and transportation results discussed in Section 4.1 to complete the life cycle GHG inventory. A comparison of the domestic results from this study with the average results presented by Skone and Gerdes (2008) is shown in the far right column of the table. Despite using a different approach to derive the GHG emissions in the processing of feedstock in the baseline case (top-down) from that used in the NETL study (bottom-up approach), similar results were obtained. These results assume average crude oil properties in all three scenarios; hence, they do not include any variation in processing emissions from crude oil quality. In addition, the combustion CO2 equivalent emissions used by Skone and Gerdes are slightly higher than those calculated in this study. This is due to their estimates of CH4 and N2O emissions from jet fuel combustion. These emissions were excluded in this study due to the high level of uncertainty associated with their estimation. Overall, the life cycle GHG emissions of jet fuel from conventional crude obtained by NETL (88.0 gCO2e/MJ) are about 0.7% higher than the baseline results (87.5 gCO2e/MJ) developed herein.
Table 8: Summary of results for jet fuel from conventional crude and a comparison of results to the NETL petroleum baseline study
MIT Conventional Jet Fuel NETL Low Baseline High Baseline Key Assumptions
Crude oil origin US Average Nigeria n/a
Processing Technique Straight
Run Average Hydro-
processed n/a
Refining efficiency (LHV) 98.0% 93.5% 88.0% n/a
Life Cycle CO2 Emissions by Stage
Recovery of feedstock (gCO2/MJ) 3.7 4.2 9.4 4.3
Transportation of feedstock (gCO2/MJ) 0.8 1.5 1.8 1.3 Processing of feedstock to fuel (gCO2/MJ) 1.6 5.5 11.0 5.5
Transportation of jet fuel (gCO2/MJ) 0.8 0.8 0.8 0.9
Combustion CO2 (gCO2/MJ) 73.2 73.2 73.2 73.7
WTT GHG Emissions by Species
WTT CO2 emissions (gCO2/MJ) 7.0 11.9 22.9 12.0
WTT CH4 emissions (gCO2e/MJ) 0.5 2.3 13.0 2.3
WTT N2O emissions (gCO2e/MJ) 0.1 0.1 0.1 0.1
Total WTW GHG Emissions (gCO2e/MJ) 80.7 87.5 109.3 88.0 Life Cycle GHG Emissions Relative to
Baseline Conventional Jet Fuel 0.92 1.00 1.25 1.01
4.3.1 Top-Down Approach (Baseline case)
General Motors et al. (2001) estimated a 2% energy penalty for reducing sulfur content in gasoline and diesel fuel from 350ppm to 5ppm. The baseline assumption in this work assumed the same 2% energy penalty applies for the production of ULS jet fuel compared to conventional jet fuel. Hence, the refining energy efficiency of ULS jet fuel was assumed to be 2% less than that of jet fuel, i.e. 91.5% (LHV). The process fuel shares outlined for conventional jet fuel (Table 3) were also used as inputs to the GREET model for the production of baseline ULS jet fuel.
4.3.2 Bottom-up approach (low and high emissions cases)
The bottom-up approach for ULS jet fuel builds upon that from the baseline case wherein the energy for the processes involved in refining jet fuel was taken from a 2007 Department of Energy sponsored report (Pellegrino et al., 2007). The report provided both a range of refining process energy use and average energy use. The average energy use data for the relevant refining processes were used to calculate the jet fuel refining efficiency.
Straight-Run ULS Jet Fuel
The production of straight-run ULS jet fuel requires crude desalting and atmospheric distillation followed by hydrotreatment to remove sulfur and other impurities. The estimated energy for these processes is shown in Table 9.
Table 9: Energy requirement in the production of straight-run ULS jet fuel
Refining process Energy required (J/MJ product)
Crude desalting and atmospheric distillation 20,055 Hydrotreatment (to S content of ~5ppm) 48,184
Total 68,239
Overall refining efficiency (LHV) 93.5%
Hence, the refining efficiency of straight-run ULS jet fuel is about 93.5% (LHV). This refining efficiency was used in the ULS jet fuel low emissions scenario. The corresponding process fuel shares for the production of straight-run ULS jet fuel are shown in Table 10.
Table 10: Process fuel and fuel shares for the production of straight-run ULS jet fuel Type of process fuel J/MJ of jet fuel Process fuel share (%)
Electricity 3,806 5.6
Natural Gas 42,570 62.4
Refinery Gas 15,235 22.3
Coke 5,603 8.2
Residual Oil 1,025 1.5
Total 68,239 100
Hydroprocessed ULS Jet Fuel
The calculation of the process energy required in the production of hydroprocessed ULS jet fuel is similar to that of jet fuel, except that additional hydrotreating is required to reduce the sulfur content of the fuel from about 500ppm to 5ppm. The energy needed for the refining processes is shown in Table 11.
Table 11: Energy requirement in the production of ULS jet fuel from hydroprocessing Refining process Energy required (J/MJ product) Crude desalting and atmospheric
distillation
20,055
Vacuum distillation 16,379
Hydrotreating (to S content of ~5ppm) 47,578
Hydrocracking 75,092
Total 159,104
Overall refining efficiency (LHV) 86%
The refining efficiency of hydroprocessed ULS jet fuel is about 86% (LHV). This refining efficiency was assumed in the high emissions scenario for the production of ULS jet fuel from conventional crude oil. The corresponding process fuel shares for the production of hydroprocessed ULS jet fuel are shown in Table 12.
Table 12: Process fuel and fuel shares for the production of ULS jet fuel from hydroprocessing Type of process
fuel
J/MJ of jet fuel Process fuel share (%)
Electricity 10767 6.8
Natural Gas 100408 63.1
Refinery Gas 33394 21.0
Coke 12284 7.7
Residual Oil 2251 1.4
Total 159104 100
4.3.3 ULS Jet Fuel Results
The life cycle GHG resulting from the production of ULS jet fuel from conventional crude are shown in Table 13. These results incorporate the recovery and transportation results discussed in section 4.1 to complete the life cycle GHG inventory.
Table 13: Summary of results for ULS jet fuel from conventional crude pathway
Low Baseline High
Key Assumptions
Crude oil origin US Average Nigeria
Processing Technique Straight
Run Average Hydro-
processed
Refining efficiency (LHV) 93.5% 91.5% 86%
Life Cycle CO2 Emissions by Stage
Recovery of feedstock (gCO2/MJ) 3.7 4.2 9.4
Transportation of feedstock (gCO2/MJ) 0.8 1.5 1.8 Processing of feedstock to fuel (gCO2/MJ) 5.5 7.3 13.1 Transportation of jet fuel (gCO2/MJ) 0.8 0.8 0.8
Combustion CO2 (gCO2/MJ) 72.9 72.9 72.9
WTT GHG Emissions by Species
WTT CO2 emissions (gCO2/MJ) 10.9 13.7 25.0
WTT CH4 emissions (gCO2e/MJ) 0.7 2.4 13.2
WTT N2O emissions (gCO2e/MJ) 0.1 0.1 0.1
Total WTW GHG Emissions (gCO2e/MJ) 84.6 89.1 111.2 Life Cycle GHG Emissions Relative to
Baseline Conventional Jet Fuel 0.97 1.02 1.27
In the baseline case, where a refining energy efficiency penalty of 2% was assumed in the production of ULS jet fuel relative to conventional jet fuel, the production of ULS jet fuel results in life cycle GHG emissions about 2% greater than those of conventional jet fuel. In the low
emissions case, the life cycle GHG emissions from the production of ULS jet fuel are decreased by 3% relative to the baseline conventional jet fuel. This effect arises from reduced origin-specific emissions relative to the baseline case and an additional energy intensive hydrotreating step compared to the production of straight-run conventional jet fuel. Conversely, the increase in life cycle GHG emissions between high emissions scenario ULS jet fuel and baseline conventional jet fuel is 27%. The energy penalty in this case results from further hydrotreating the jet fuel from about 500ppm to 5ppm (~2% difference in refining efficiency). The main reason driving the increase are the methane venting and transportation emissions associated with the Nigerian crude oil. In all cases, CO2 emissions from combustion of ULS jet fuel are 0.3 gCO2e/MJ less that conventional jet fuel.
5 Unconventional Petroleum Pathways
This manuscript considers two unconventional petroleum resources, oil sands from Alberta, Canada and oil shale from the Green River Formation in Colorado, Utah and Wyoming. While current production of oil sands is approximately 1.3 million bbl/day, oil shale development is presently limited to laboratory and pilot-plant stages (Hileman et al., 2009). Oil sands are deposits of tar-like petroleum, known as bitumen, within sand or porous rock while oil shale is a solid sedimentary rock that contains kerogen, a mixture of organic compounds, including bitumen, which can be refined to oil. Both of these resources require extensive work to convert the raw resource to a synthetic crude and this results in increased life cycle GHG emissions relative to conventional petroleum. All of the work regarding jet fuel from unconventional crude oil was performed with GREET version 1.8a.