Higher severity HDT needed for low-sulfur diesel

Most existing mid-distillate hydroprocessing units will have to operate at higher temperatures, lower liquid hourly space velocities (LHSV), or a combination of both, to meet the Environmental Protection Agency's proposed rules to limit sulfur in diesel to 0.05 wt % and total aromatics content to 20 vol %. If current space velocities are maintained, much higher operating temperatures will be required to maintain current diesel output. Higher temperatures will result in much shorter cycle lengths and significantly higher operating costs. Some existing units may not be able to reach the higher temperatures. If space velocities are lowered, refiners may have to consider adding parallel hydroteating units to maintain current production quantities. This could be restricted by the availability of new capital for the additions. A study, that included pilot plant tests, was conducted to determine the ability of existing hydroprocessing units throughout the U.S. to produce diesel fuel at the proposed sulfur and aromatics limits.