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Ultra-Low Sulfur Diesel Fuels
Issues of ultra-low sulfur in gasoline have created different challenges. In the production of the fuel, the process of sulfur-compound removal left behind extremely aggressive, highly chemically active sulfur that attacked fuel-indication systems. “There were numerous instances around the United States,” says Harrigan, “of the fuel-level sensors inside the fuel tank being contaminated and ceasing to function.” The aggressive sulfur attacked the variable resistance cards and produced a deceptively high resistance. “As luck would have it,” Harrigan notes, “high resistance would show up on the gas gauge as a full tank. So people would be fooled into believing they had a lot of fuel, and then eventually, they would run out.” Harrigan is confident, however, that the industry understands these threats and is equipped with solutions. Standards and ASTM qualification tests have been developed to address concerns as the refineries change over to producing ultra-low sulfur fuels. “I think there’s adequate industry awareness of the potential issues,” says Harrigan, “and also awareness of the preventive techniques and corrective actions that are necessary for things to happen smoothly for the diesel-fuel-using industry, the customers.” An issue that may not have been fully thought out by those in the industry relates to the handling of the ULSD. “They think of it in terms of refining it or of burning it in the combustion chamber of the engine, not what happens in between.” Yet, with a note of optimism, Harrigan adds, “I think that we’re ready. I think that we understand the fuel, with this aggressive sulfur, and that steps have to be taken in the design of the components in the system that could be affected to make them more robust against those types of issues.” In addition, he adds, “We’re still counting on the oil industry to maintain the quality of the fuel coming in.” He anticipates only minimal problems and perhaps the occasional quality breakthrough as the refineries become accustomed to producing the fuel on a day-in-and-day-out basis. Difficulties might arise in terms of handling if the levels of biodiesel in USLD rise. “I don’t believe anyone has any real concerns about the fuel at the two or three percent level, but the biodiesel industry is pushing for 20% fatty-acid methyl ester in the fuel.” Though the issue of higher percentages of biodiesel—the nature of the biodiesel and how its chemistry affects materials in the system—is being actively studied, past examples can demonstrate what happens when caution is abandoned. According to Harrigan, “there have been attempts to rush this into the marketplace with some pretty public embarrassments to the biodiesel industry when things didn’t work out as they intended, especially in the wintertime.” To avoid such incidents from occurring in the future, the industry needs a proactive approach. “It remains for the industry to police itself,” Harrigan concludes, “or run the risk of there being some government regulations added to keep things running smoothly.”
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As the EPA mandate for 100% conversion by 2010 to ultra-low sulfur diesel (ULSD) fuel approaches, stakeholders are on track to resolve or prevent issues that may arise, according to Michael Harrigan of Zen Fuels, LLC, in Ann Arbor, Michigan. “The awareness exists,” says Harrigan, “of what some of the potential issues might be as the oil companies actually produce this fuel.” He cautions that ultra-low sulfur diesel must be forthcoming in order to meet the particulate standards because sulfur fosters the production in the particulate of soot during the combustion process. Key learnings from the run-up to the 80% mandate have proved beneficial in more ways than were anticipated. “We’ve been through the whole business of removing the sulfur and having lubricity issues,” says Harrigan, “but as I understand it, that’s been pretty well addressed, and because of the lubricity-enhancing qualities of biodiesel, or fatty-acid methyl esters, its use provides a kind of a win-win for the biodiesel groups in having at least two or three percent biodiesel in all of the diesel fuels.”