Environmental Engineering Reference
In-Depth Information
CH
4
Partial recycle
HDS (catalytic unit)
Sulfur removal
Heat
Heat recover
Steam Reformer
High and Low
Shift Reactor
H
2
Separation unit (PSA)
Carbon oxides
Fig. 2.2 Simplified scheme including all main process steps involved in hydrogen production
plants based on methane SR
The array of tubes filled with the catalyst is suspended in a furnace that supplies
heat for the highly endothermic reforming reactions.
In some cases carbon dioxide may replace steam to give a more favourable
H
2
/CO ratio for subsequent reactions of the products [
8
]:
CH
4
þ
CO
2
2CO
þ
2H
2
DH
¼þ
247 kJ/mol
ð
2
:
4
Þ
The product selectivity for all these reactions is controlled predominantly by
thermodynamics, i.e. the final product composition can be foreseen by multi-
component chemical equilibria calculations.
When other hydrocarbons (for example propane) are used as feedstocks, CH
4
is
the favoured product at lower temperatures, while hydrogen is preferred at
temperatures superior to 700-800C[
6
], then the product gas leaves the tubular
reactor at temperatures between 700 and 950C, in dependence of the particular
application. The necessity to operate at these temperatures introduces several
