Crude oil is a very complex mixture of different hydrocarbons and because of this complexity there are multiple methods to distill barrels of crude into their different fuel fractions. The three methods that refineries use are True Boiling Point Distillation (TBP), ASTM Distillation (ASTM) and Equilibrium Flash Vaporization (EFV). These methods, as shown above, are in a decreasing order of significance. This means that the each method produces a different degree of separation with true boiling point being the most efficient.
True Boiling Point is a batch process that uses the physical properties of the different components of crude to separate it into its different fractions with the use of over 100 plates or a reflux ratio of 100. Another positive to distilling crude in this method is that the crude is able to be distilled at a constant temperature (due to the high number of plates) and a crude mixture would be able to be distilled as individual components where temperature is adjusted accordingly.
An ASTM Distillation process is very similar to TBP except that it does not use any plates, and has a reflux ratio of 0. This process condenses the vapors of the crude but because of the lack of plates, the temperatures are not as constant making it less effective to fractionate the crude than that of the TBP method.
The Equilibrium Flash Vaporization process allows for the crude to vaporize separating the components into gas and liquid components. As the gas travels up the stack, it comes in contact with heat exchangers which use a cold fluid to condense the vapors into its separate fuels. Each individual fuel side stream has a decreasing reflux. [1] This method has the lowest crude separation.
Sources:
1. Gary, J. H., & Handwerk, G. E. (2007). Petroleum refining: technology and economics. New York: M. Dekker.