|Carbon Forming Reactions
The following carbon forming reactions are
possible, but are largely prevented by proper
maintenance of Steam/Carbon ratio in the mixed
feed gas to the Reformer:
2CO = C + CO2
CO + H2 = C + H2O
CH4 = C + 2H2
The potentiality for carbon formation in Primary
Reforming is quite complex and depends on
pressure, temperature and composition of the
Reformer mixed feed gas, as well as catalyst
composition. Generally thermodynamic carbon
formation reactions will not occur for Natural Gas
feedstock as long as S/C ratio is maintained
substantially above 1.0. Such risks generally
occur only during plant upset conditions and
properly designed plant trip instrumentation
should largely prevent it.
Nickel has been found to be the most cost-effective active species for Reforming catalysts, although other elements can
work and are more active, including Cobalt, Lanthanum, Platinum, Palladium, Iridium, Rhodium and Ruthenium.
Nickel is combined with various support materials including alpha-Alumina, Calcium-Aluminate, Magnesia-Alumina,
sometimes including Alkali-promoters through proprietary means within an efficient open pore-structure catalyst shape to
overcome gas diffusion limitations, while supporting high catalyst activity.
Reforming catalysts are poisoned primarily by Sulfur, but other compounds can also cause loss of catalyst activity,
including Arsenic, Chlorine and other halogens, Copper, Lead, Silver, Vanadium and Cadmium. Under normal
circumstances only Sulfur and Chlorine present significant threats to loss of Reforming catalyst activity and these effects
on activity are completely reversible when the poisoning contaminant has been removed from the feedstock. Sulfur and
Chlorine concentrations of greater than 0.2 ppmv in the mixed feed (wet basis) or 0.7 ppmv in the hydrocarbon feedstock
can cause significant loss of catalyst activity over the period of a few minutes to a few hours, depending on the
contaminant concentration. Increased levels of Methane and reduced Hydrogen production will take
place until the poisoning is eliminated.
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