590 Fuel Cells
of the natural gas–fed POX process. The oxygen fed to the system is sub-
stoichiometric such that both CO and CO
2
are formed in the system. A
water–gas shift reaction can transform the CO from the rst reaction further
into CO
2
. Reactions are
CH
4
+ 1/2 O
2
→ CO + 2H
2
[_H = −247 kJ mol
–1
] (13.6)
CH
4
+ O
2
→ CO
2
+ 2H
2
(13.7)
POX is highly exothermic and raises the reactants to a high temperature.
The resulting reaction products, still in a reduced state, are then quenched
through the introduction of superheated steam. The addition of steam pro-
motes the combined water–gas shift and steam reforming reactions, which
further cools the gas. In most cases, and with sufcient preheating of the
reactants, the overall reaction is exotherm ...