Page 23 - Modeling of Chemical Kinetics and Reactor Design

Table 5
Air feed
Component Mole %

Oxygen (O ) 21.0
2
Nitrogen (N ) 78.05
2
Argon (Ar) 0.95

STAGE 1: CATALYTIC REFORMING

After the removal of sulfur, the primary steam reformer converts
about 70% of the hydrocarbon feed into synthesis gas. Methane is
mixed with steam and passed over a nickel catalyst. The main reform-
ing reactions are:

CH +
4 H O [ CO 3+ H 2
2
CO H O [
+ 2 CO + H 2
2
The catalytic steam hydrocarbon reforming process produces raw
synthesis gas by steam reforming under pressure. The reactions are
endothermic, thus the supply of heat to the reformer is required to
maintain the desired reaction temperature. The gases leaving the
reformer are CH , 6 mol/%; CO, 8%; CO , 6%; H , 50%; and H O,
4
2
2
2
30%. The operating pressure is between 20–35 bar, and the gases
leaving the reformer contain about 6% CH . This represents approxi-
4
mately 30% of the original natural gas input. Figure 2 shows the
process flowsheet of catalytic reforming.
In the secondary reformer, air is introduced to supply the nitrogen
required for the 3:1 hydrogen H and nitrogen N synthesis gas. The
2
2
heat of combustion of the partially reformed gas supplies the energy
to reform the remaining hydrocarbon feed. The reformed product steam
is employed to generate steam and to preheat the natural gas feed.
STAGE 2: SHIFT AND METHANATION CONVERSION

The shift conversion involves two stages. The first stage employs
a high-temperature catalyst, and the second uses a low-temperature
catalyst. The shift converters remove the carbon monoxide produced
in the reforming stage by converting it to carbon dioxide by the reaction

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