Crude Oil Refining

First, a simple overview of the modern crude oil refinery and how it separates and processes crude oil and other feedstocks into liquid fuels and other products - Before arrival at the refinery, a request for crude oil properties is sent to a reputable lab for basic analysis. This may include but not limited to running API, sulfur, water content, sediment, MCR and metals. In some cases even full crude oil assay is requested prior to any refinery process. The crude oil assay run in a lab provides necessary guidance to refinery engineers and other staff to make useful and economically profitable decisions.

At the refinery, crude oil first undergoes physical separation by distillation to yield various boiling range streams. The atmospheric distillation unit usually separates about one half of the crude oil into the desired cut ranges. This is followed by vacuum distillation to yield gas oil fraction and vacuum residue.

The most common fractions of the above Distillations are:
  • Gases or Light Ends (C1-C5)
  • LSR (Light Straight Run Gasoline) (C5-C6)
  • HSR (Heavy Straight Run Naphtha) (C6-C10)
  • Kerosene(C9-C15)
  • AGO (Atmospheric Gas Oil) (C13-C25)
  • Vacuum Residue (C40+)

Crude Oil is mainly a mixture of hydrocarbons and some impurities like sulfur, water & sediments and naturally occurring metals.

There are four main groups of hydrocarbons:
  • Paraffins (Normal & ISO)
  • Olefins
  • Naphthenes
  • Aromatics

The main goal of the refinery is to process the distillation fractions into desired streams that can enable the blenders to make the desired finished products like gasoline, diesel, and jet etc.

In refinery, the fractions undergo several processes, the most common are:
  • Isomerization - Isomerization converts LSR into gasoline.
  • Hydrotreating - Hydrotreating of kerosene gives jet fuels
  • Cat Reforming - Hydrotreating of naphtha together with cat reforming yields gasoline
  • Alkylation - Alkylation of gases gives MTBE and then gasoline
  • Fluid Catalytic Cracking - Fluid cat cracking of atmospheric residue, light & heavy vacuum gas oil gives blending streams of light cycle oil (LCO), heavy cycle oil (HCO). LCO gives #2 fuel oil, HCO gives #6 fuel oil.
  • Hydrocracking
  • Visbreaking
  • Deasphalting
  • Coking - vacuum residue undergoes visbreaking, deasphalting, coking & hydrocracking to make #6 fuel oil. Without these processes vacuum residue gives asphalt
In addition to above processes there are some processes that are essential for meeting the EPA regulated requirements. These are:
  • Desulfurization
  • Hetroatomic Removal (includes nitrogen & oxygen)
  • Process for aromatic/olefin saturation