One to three pipe furnaces, usually two, with one sometimes larger than the
other
A short, thick soaker reactor
Tall thin flash chamber
A taller fractionator
Soaker, flash chamber, and fractionator will be in a line and may be
obscured by a steel framework.
Figure 2-37. Thermal Cracking Unit.
(b)
Fixed bed catalytic cracking unit.
This catalytic cracking method is
still seen in some of the older refineries. In this process, gas-oil is heated in
a pipe furnace and then allowed to vaporize in a reactor/regenerator tank. These
tanks are divided into sections by flat, perforated trays containing bauxite silica
(the catalyst) pellets. The catalyst promotes the breakdown of gas-oil into lighter
hydrocarbons.
During the cracking process, the regenerator must periodically be
shut down and taken off the line by closing the appropriate valves. The carbon is
then burned off the catalyst by firing up the reactor like a furnace. While this
catalyst "regeneration" is being done, other reactor/regenerator tanks take over
the
cracking
operation.
Once
the
carbon
deposits
are
removed,
the
reactor/regenerator can be brought back on line and another taken off to undergo
regeneration. After cracking, the gas-oil is routed to a fractionator where gases,
gasoline, and fuel oils are separated.
Major recognition features of fixed bed
catalytic cracking unit (Figure 2-38) include:
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