|API-recommended pump label for ULSD.|
Sunday, October 15 marked the official arrival of new ultra-low sulfur diesel (ULSD) in US retail pumps. ULSD contains a maximum of 15ppm sulfur, down from the 500ppm maximum of the low-sulfur fuels it replaces.
ULSD use will immediately cut soot emissions from any diesel vehicle by 10 percent. Combined with a new generation of engines hitting the road in January, it will enable emission reductions of up to 95% percent, according to the Natural Resources Defense Council (NRDC) and the Diesel Technology Forum (DTF).
Diesel is the invisible force that moves the American economy, but until now it has also been a big polluter. Combining the new fuel with cleaner and more energy-efficient engines will mean healthier air and help reduce our dependence on oil.—Richard Kassel, head of NRDC’s Clean Fuels and Vehicles Project
Improvements in both the fuel and the engines are required under new federal rules adopted by the Clinton administration and subsequently endorsed and implemented by the Bush administration. The policy was almost a decade in the making, and involved close collaboration between regulators, oil refiners, engine manufacturers and public health advocates to achieve a cost-effective solution.
The diesel clean-up rivals the removal of lead from gasoline a generation ago. Sulfur hampers exhaust-control devices in diesel engines, much in the same way that lead once impeded the effectiveness of catalytic converters on gasoline cars.
Since the fuel has to end up at the pump with a maximum 15 ppm, refiners are producing it at a slightly lower concentration to allow for some margin of error in production and potential product contamination in the distribution system. ULSD shipped in a pipeline, for example, could pick up an extra couple ppm sulfur.
Refiners have invested in their hydrotreaters—and in additional hydrogen capacity—to produce the fuel.
Conventional hydrotreating puts heated feedstock and hydrogen into a catalyst-laden reactor to separate sulfur from hydrocarbon molecules. The hydrotreatment process can desulfurize streams at multiple points in the refining process: directly following crude distillation (“straight-run” streams); streams coming out of fluid catalytic cracking (FCC) units; and hydrotreating the heavier streams that go through a hydrocracker.
|Catalyst requirements for ULSD production. Click to enlarge. Source: Chevron|
Refineries with hydrotreaters are likely to achieve production of ULSD on straight runs by modifying catalysts and operating conditions. Chevron, as an example, found that producing 10ppm ULSD required about three-times the catalyst volume as did conventional LSD (500ppm). Achieving 3ppm diesel required about 25% more catalyst than for 10ppm, or a reduction in capacity of about 20%.
Desulfurizing the remainder of the distillate streams is expected to pose the greatest challenge, requiring either substantial revamps to equipment or construction of new units.