(420d) A Fischer-Tropsch Fluids Refinery

A preliminary design for a Fischer-Tropsch (FT) fluids refinery was modeled using Aspen Plus software. This project is a part of larger effort to model a coal to liquids plant. The refinery was designed to convert FT fluids into products that meet conventional petroleum product specifications. FT fluids consist primarily of straight chain alkanes, with smaller but significant quantities of alkenes and oxygenates. This composition is similar to a highly paraffinic crude oil. Typically, FT fluids yield high quality diesel fuels but low octane naphthas. The products chosen for this plant were limited to high volume fuels and lubricants. Based on a qualitative examination of product markets and available refining technologies, a total isomerization process was chosen to convert naphtha into an acceptable gasoline blending stock. Kerosene should be usable without further treatment as a jet fuel or as a diesel blending stock. FT diesels are known for high cetane indices, but they may have problems meeting cloud point and pour point specifications during the winter driving season due to the highly paraffinic nature of these diesels. Isomerization or distillation end point control can be used to meet cloud and pour point specifications. FT diesel is expected to be a highly valued blending stock to offset the aromatic nature of diesels produced from heavy oil and bitumen. Most prior FT refining models assume that FT waxes will be converted to naphtha and diesel using a hydrocracking or fluidized catalytic cracking process. In this study, waxes were converted to lubricant base oils using an isomerization process because base oil prices are much higher than fuel prices. A commercial wax isomerization process is available, but this study was hampered by a lack of data in the open literature.