Residual Fuel Oil

Residual fuel oil is generally known as the bottom product from atmospheric distillation units. Fuel oils produced from cracking units are unstable. When used as fuels, they produce smoke and deposits that may block the burner orifices.

The constituents of residual fuels are more complex than those of gas oils. A major part of the polynuclear aromatic compounds, asphaltenes, and heavy metals found in crude oils is concentrated in the residue. The main use of residual fuel oil is for power generation. It is burned in direct-fired furnaces and as a process fuel in many petroleum and chemical companies.

  Due to the low market value of fuel oil, it is used as a feedstock to catalytic and thermal cracking units.  Residues containing high levels of heavy metals are not suitable for catalytic cracking units. These feedstocks may be subjected to a demetallization process to reduce their metal contents. For example, the metal content of vacuum residues could be substantially reduced by using a selective organic solvent such as pentane or hexane, which separates the residue into an oil (with a low metal and asphaltene content) and asphalt (with high metal content).

  Demetallized oils could be processed by direct hydrocatalysis.  Another approach used to reduce the harmful effects of heavy metals in petroleum residues is metal passivation. In this process an oil-soluble treating agent containing antimony is used that deposits on the catalyst surface in competition with contaminant metals, thus reducing the catalytic activity of these metals in promoting coke and gas formation.  Metal passivation is especially important in fluid catalytic cracking (FCC) processes. Additives that improve FCC processes were found to increase catalyst life and improve the yield and quality of products.

  Residual fuels with high heavy metal content can serve as feedstocks for thermal cracking units such as delayed coking. Low-metal fuel oils are suitable feedstocks to catalytic cracking units. Product gases from cracking units may be used as a source for light olefins and LPG for petrochemical production. Residual fuel oils are also feedstocks for steam cracking units for the production of olefins.