Page 279 - Alternative Energy Systems in Building Design

FUEL CELL APPLICATION 253

process that releases significant amounts of carbon dioxide. Therefore, even though
hydrogen fuel used in fuel cells produces clean water as a by-product, the extraction
process remains inefficient and environmentally harmful.
In view of the fact that hydrogen energy production in fuel cells involves the sepa-
ration and recombination of electrons and protons, unlike petroleum or fossil fuels,
hydrogen is not considered an energy source but rather an energy carrier. In essence,
commercial hydrogen is produced from the use of other energy sources, such as petro-
leum combustion and wind-powered solar photovoltaic (PV) energy in hydrolysis.
Hydrogen is also produced from subsurface reservoirs of methane and natural gas by
a combination of steam re-forming referred to as the water-gas shift reaction (from
coal or shale-oil gasification).

HYDROGEN GAS PRODUCTION
Electrolysis requires electricity and high-temperature thermochemical production
(ideal for nuclear reactors), two primary methods for the extraction of hydrogen from
water.

STEAM RE-FORMING
Steam re-forming (also known as hydrogen re-forming or catalytic oxidation) is a
process of producing hydrogen from hydrocarbons. The process, described below, is
the dominant method for producing large amounts of commercial hydrogen gas.

INDUSTRIAL RE-FORMING

Steam re-forming of natural gas, referred to as steam methane re-forming (SMR), is the
most prevalent method used in the production of commercial bulk hydrogen. This
process, which involves the reaction of steam (H O) and methane (CH ) at high tem-
2
4
peratures (700–1100°C) in the presence of a metal-based catalyst such as nickel, is
considered to be the least expensive method of hydrogen gas production.
In this process, steam reacts with methane to yield carbon monoxide and hydrogen:

CH + H O → CO + 3H 2
4
2
Additional hydrogen can be produced from this process by a lower-temperature gas-
shift reaction with the production of carbon monoxide, which can yield carbon dioxide
and hydrogen:

CO + H O → CO + H 2
2
2
This process is also used widely throughout the world in ammonia production, which
requires large amounts of hydrogen gas. Hydrogen gas is also produced as a by-
product of oil refining, which involves the catalytic re-forming of naphtha, also known
as high-octane gasoline.