Hydrodesulfurization of Diesel Fuel to Meet New EPA Requirements

When the EPA reduced the sulfur content allowable in diesel fuel to 15 ppm in 2010, many refineries had to upgrade their hydrodesulfurization units to meet the new limit. The objective of this project is to design an upgraded catalytic hydrodesulfurization unit that can treat 35,000 barrels per stream day of liquid feedstock containing 1.9 percent sulfur by weight. Performance data from an existing catalytic hydrodesulfurization unit was used to predict the performance of the upgraded unit. ChemCAD software was used for process calculations and the feed was modeled using boiling curve data. The desulfurization reaction kinetics were based on the reduction of dibenzothiophene. The project goals are 99 percent recovery of diesel fuel and a sulfur content below 15 ppm. To achieve these recovery levels the liquid feedstock is run through a catalyst-filled packed-bed reactor, where the sulfur compounds react with hydrogen gas to form hydrogen sulfide gas. The reactor effluent is run through a distillation column to separate the diesel fuel from the naphtha. More volatile and noncondensible compounds, such as butane, propane, nitrogen, and carbon dioxide, are run through an amine process to remove the hydrogen sulfide from the hydrogen recycle stream. Hydrogen is provided from a nearby hydrogen plant.