(5)
Secondary distillation.
All the products of primary distillation go
through a second distillation process. The secondary distillation units fall into
these categories: catalytic reforming, vapor recovery (light ends), alkylation,
polymerization, cracking, lubricating oil refining, and delayed coking.
(a)
Catalytic reforming.
One of the products of primary distillation is
low-grade gasoline.
Converting this low-grade gasoline into high quality motor
fuel involves a process called catalytic reforming.
The low-grade gasoline stock
is heated in a pipe furnace and then passed through a fractionating column to
remove heavy fuel oil residues and light gases. The fuel oil is passed on to the
treating unit and the light gases. The fuel oil is passed on to the treating unit
and the light gases routed to the catalytic reforming unit (Figure 2-33).
Major
recognition features of catalytic reforming unit include:
Pipe furnaces, most commonly a series of pipe furnaces alternating with
reactors
Three or more short, thin reactor columns
One or two fractionators.
Figure 2-33. Catalytic Reforming Unit.
(b)
The resulting intermediate gasoline is heated again in a pipe furnace
and then routed through a series of reactors containing a catalyst (chemical that
speeds up a reaction).
The catalyst chemically alters the hydrocarbon molecules
creating a high-grade gasoline with a more complex molecular configuration. After
passing through the reactors, the reformed gasoline is introduced into another
fractionating column where more gases are separated.
The reformed gasoline is
unstable and piped to the vapor recovery unit for stabilization (Figure 2-34).
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