The petroleum industry has adopted as standards a temperature of 60F and a pressure of 14.7 PSI (atmospheric
pressure).
(g) It should be noted that as the density increases, the boiling point increases. This is an
important concept to remember in discussing refinery operations by separation. In other words, the more dense
(the heavier) the hydrocarbon compound, the greater the temperature required to produce vapor from liquid.
2.
Petroleum Refining.
a. Refining is essentially a manufacturing industry, using crude petroleum as its raw material to make
numerous petroleum products. Hundreds of thousands of wells furnish the crude oil to the relatively few
refineries which process the oil into more than 2,500 products which are then distributed through several hundred
thousand markets outlets to millions of customers. To ensure that the entire process runs smoothly and that
demands for petroleum are met, oil is kept constantly on the move from the well to the consumers. Refineries
operate day and night -- a classic example of continuous flow operations.
b. Although many different processes are used in refining, only the major ones are discussed here. The
major processes are separation, conversion, and treatment.
3.
The Separation Process.
Separation processes are physical processes employed to segregate the hydrocarbons in crude oil according to
either boiling range or hydrocarbon types. There are three separation processes: factional distillation, absorption,
and solvent extraction. Distillation is employed in all cases as the first step in refining. Absorption and solvent
refining are secondary steps which may or may not be applied, depending on the end product desired
NOTE: Of all three-separation processes, factional distillation is the most common. At atmospheric temperature,
water boils at 212ƒF.
4.
Fractional Distillation.
The process of distillation is simply heating the crude oil to form vapors and condensing the vapors to liquids.
Since crude petroleum is a mixture of many complex hydrocarbons, all of which have different boiling points, not
one but several distillations are necessary. By the process of distillation, the various hydrocarbon compounds in
crude oil can be separated into groups of hydrocarbons (factions or cuts) having similar boiling ranges. To effect
the separations required in modem petroleum refining, these distillations are carried out as a continuing process in
which a stream of heated crude oil is continuously charged to a fractionating tower and the vapors and liquids
continuously withdrawn.
a. The first distillation takes place at atmospheric pressure. In this process, the light ends (fractions
having the lowest boiling point) are drawn off. This process is frequently referred to as striping because the crude
is stripped of its more volatile components. The first distillation produces fractions used in the following
petroleum products:
Liquid petroleum gases (propane and butane).
Motor gasoline.
Kerosene and jet fuels.
20-3
QM5200
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