2. Fuel processing
Fuel processing technologies convert a hydrogen containing
material such as gasoline, ammonia, or methanol into a hydrogen
rich stream. Fuel processing of methane is the most common
hydrogen production method in commercial use today. Most
hydrocarbon fuels contain at least some amount of sulfur which
poisons the fuel processing catalyst. This presents perhaps the
biggest challenge to reforming. As a result, desulfurization will also
be discussed. In addition, hydrocarbon reforming, plasma reforming,
aqueous reforming, and pyrolysis will also be presented.
2.1. Hydrocarbon reforming
There are three primary techniques used to produce hydrogen
from hydrocarbon fuels: steam reforming, partial oxidation (POX),
and autothermal reforming (ATR). Table 1 summarizes the
advantages and challenges of each of these processes. The reforming
process produces a gas stream composed primarily of hydrogen,
carbonmonoxide andcarbondioxide. Endothermic steamreforming
of hydrocarbons requires an external heat source. Steam reforming
does not require oxygen, has a lower operating temperature than
POX and ATR, and produces the reformate with a high H2/CO ratio
(3:1)which is beneficial forhydrogen production.However, it does
have the highest emissions of the three processes. Partial oxidation
converts hydrocarbons to hydrogen by partially oxidizing (combusting)
the hydrocarbon with oxygen. The heat is provided by the
‘‘controlled’’ combustion. It does not require a catalyst for operation,
has minimalmethane slip, and ismore sulfur tolerant than the other
processes. The process occurs at high temperatures with some soot
formation and the H2/CO ratio (1:1 to 2:1) is favored for the feeds to
hydrocarbon synthesis reactors such as Fischer-Tropsch. Autothermal
reforming uses the partial oxidation to provide the heat and
steam reforming to increase the hydrogen production resulting in a
thermally neutral process. Autothermal reforming is typically
conducted at a lower pressure than POX reforming and has a low
methane slip. Since POX is exothermic and ATR incorporates POX,
these processes do not need an external heat source for the reactor.
However, they require either an expensive and complex oxygen
separation unit in order to feed pure oxygen to the reactor or the
product gas is diluted with nitrogen. Steamreforming is typically the
preferred process for hydrogen production in industry [10–14].
Since all three processes produce large amounts of carbon
monoxide, one or morewater-gas-shift (WGS) reactors – typically a
high temperature reactor and low temperature reactor – are used.
The high temperature (>350 8C) reactor has fast kinetics, but is