Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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7.8.3. Historical Trends and Forecasts for Sulfur Content
Other reports in this collection
As mentioned above, surveys show that the sulfur content of most fuels is well below specified limits. All of the surveys show that about 90% of fuels have sulfur
content less than 0.1%. Figure 7-36 shows the historical trends for the U.S. and UK surveys. In the UK, average sulfur level has remained relatively constant since
1988 (Rickard and Fulker, 1997); in the United States, however, the average sulfur content in the NIPER survey has been increasing. This trend conflicts with reports
(Hadaller and Momenthy, 1993) based on projections of increased hydro-treatment to reduce sulfur in gasoline and diesel fuel. However, changes in gasoline
production have not significantly affected jet fuel because there is very little overlap in the boiling range.
The impact of the trend to use low-sulfur diesel fuels is not clear. Many refineries worldwide do not have the hydro-treating capability to make low-sulfur fuels. The API/
NPRA survey for 1996 reported that 46% of the jet fuel blendstock in the United States was straight-run material that was not hydro-treated (API/NPRA, 1997). For
many of these refineries with limited hydro-treating capability, the most economical approach may be to shift blending stocks with higher sulfur content to jet fuel,
saving streams with lower sulfur for diesel fuel.
Without legislation, it is unlikely that average sulfur worldwide will change much from current levels of 0.04-0.06%. The fuel specification certainly could be tightened to
allow no more than 0.1% without any apparent increase in cost or availability, and closer to 0.05% might be possible. There will be areas around the world where the
sulfur will come down on its own, but there will also be pockets where it will stay relatively high. Specific details on future trends of sulfur content do not exist in the
literature; a special survey of worldwide refinery plans would be required to develop a better picture.
Gas-to-liquid conversion processes to produce kerosene (e.g., Fisher-Tropsch processes) yield jet fuel that is almost sulfur-free. Although this approach is attractive in
a few regions where there is an abundance of unused natural gas, it is unlikely that this resource will be significant until well into the next century, as the process
becomes more economically viable (Singleton, 1997). Biomass gasification could also be used to produce the synthesis-gas feedstock for Fisher-Tropsch conversion.
7.8.4. Alternative Fuels to Kerosene
Current aircraft-along with the airport infrastructure for supply, delivery, and storage of fuel-are specifically optimized for the use of current kerosene fuels; any
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