(4) Primary distillation occurs in vacuum pipe stills.
Heavy hydrocarbons
will not boil at safe temperatures under atmospheric pressure. To distill them, a
partial vacuum in created within the fractionating column.
The special
fractionators, called vacuum pipe stills, are easily recognized by their short,
thick shape. They will appear very much like large "thermos bottles" sitting next
to a pipe furnace (Figure 2-30). Major recognition features of vacuum pipe still
include:
One or more pipe furnaces
One of more large fractionators
Control building
A small cooling/condensing pond
Possibly an electric substation.
Figure 2-30. Vacuum Pipe Still.
(a)
Pipe furnaces.
First, the crude oil is heated in a pipe furnace
(Figure 2-31).
Here the crude oil is routed into an enclosed structure which
contains a radiator like arrangement of piping and a burner.
Oil is heated to a
high temperature by the burner as it flows through the piping labyrinth. However,
the hydrocarbons are prevented from vaporizing by the considerable pressure at
which they are contained.
IT 0673
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