Current Methods for Life-Cycle Analyses of Low-Carbon Transportation Fuels in the United States (2022) / Chapter Skim
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7 Fossil and Gaseous Fuels for Road Transportation
7 Fossil and Gaseous Fuels for Road Transportation
Pages 126-141
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From page 126... ...
, and petroleum and liquid fossil fuels are globally traded fungible commodities, hence no one country's fossil fuels market is truly independent of global market supply and demand considerations.
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) by using renewable electricity to supply energy for electrolysis; subsequently, synthetic fuels can be generated through Fischer–Tropsch synthesis or methanation (Schaaf et al., 2014)
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Downstream of oil extraction, refinery emissions are another important contributor to the life-cycle GHG emissions attributable to liquid fossil fuels. Refinery emissions include hydrogen production emissions used for hydroprocessing, emissions from energy inputs, and onsite emissions (both point source and fugitive emissions)
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In sum, GHG emissions calculations for petroleum fuels include emissions from production, transportation, refining, and combustion. Emissions vary depending on the crude oil, transportation, and refining.
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More than 95 percent of hydrogen is made today via steam reforming, mostly of natural gas, and is called "grey" hydrogen. Six percent of global natural gas production and 2 percent of global coal production is used for hydrogen production, resulting in about 830 million tonnes of CO2 emissions annually.
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LCA methodological issues for evaluating natural gas systems can therefore have wide-ranging implications for the understanding of low-carbon fuels. Natural Gas Global natural gas production has been increasing at a higher rate than oil production, and while there has been a pandemic-caused decline in 2020, it is picking up again and similarly to global oil production, it is projected to keep increasing through this decade.
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in 2010 to 805 BCM in 2020, comprising approximately 78 percent of domestic marketed natural gas production. FIGURE 7-5 Location of shale gas plays in the continental United States.
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to 17 Mg. It is this type of site-to-site variation, which holds for completion along with other stages in the natural gas supply chain, that leads to differing results among natural gas LCA, which may not necessarily show uncertainty.
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CH4 leakage throughout this system contributes to life-cycle GHG emissions of natural gas. There is variability in CH4 emissions throughout the natural gas supply chain depending on the location of natural gas production and the extent to which emissions reductions measures are in place (Alvarez et al., 2018)
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As shale gas grows to comprise a larger share of domestic natural gas production, additional data collection may be necessary to characterize its contribution to natural gas life-cycle emissions more broadly. Another complicating aspect of natural gas LCA is co-product handling.
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Limited supply chain GHG emissions from natural gas systems are relatively straightforward to identify. Extended supply chain and market-mediated effects that influence GHG emissions are more challenging.
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These parameters will evolve as technology advances, data availability increases, and statistical methods may be used to translate the additional data into improved emissions estimates. Recommendation 7-3: Further research on the climate impacts of natural gas production should draw upon real world activity data in part supplied by the natural gas industry and in part from independent studies using satellite and remote sensing technology to improve methane emissions rate estimates; these should be revisited frequently -- at least every five years.
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Attributional LCAs may adopt an average grid CI or assume renewable electricity is used in the production of green hydrogen as a means of comparing the CI of green hydrogen -- assuming it is indeed produced using renewable electricity -- against other fuels. The main factors that influence blue hydrogen GHG emissions are the energy source for steammethane reforming or authothermal reforming and the carbon capture efficiency, along with parameters used to model upstream natural gas production.
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2019. Aggregation and allocation of greenhouse gas emissions in oil and gas production: Implications for life-cycle greenhouse gas burdens.
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2018. Global carbon intensity of crude oil production.
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2020. Quantifying methane emissions from the largest oil producing basin in the United States from space.
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