Environmental Engineering Reference
In-Depth Information
USING HYDROGEN
Before wide-scale use of hydrogen becomes a reality in transporta-
tion, researchers must develop new technologies that can use hydrogen
that is stored or produced, as needed, onboard vehicles.
Hydrogen internal combustion engines can be used to convert hy-
drogen's chemical energy to electricity using a hydrogen piston engine
coupled to a generator in a hybrid electric vehicle.
Onboard reforming for fuel cells depends on catalytic reactions to
convert conventional hydrocarbon fuels, such as gasoline or methanol,
into hydrogen that fuel cells can then use to produce electricity to power
vehicles.
The FreedomCAR Partnership to develop fuel-cell-powered vehicles
commits the U.S. Department of Energy toward a hydrogen-based ener-
gy system by making fuel-cell-powered vehicles available in 2010. The
FreedomCAR program is also sponsoring investigation of ultralight mate-
rials including plastics, fiberglass, titanium, magnesium, carbon fiber and
developing lighter engines made from aluminum and ceramic materials.
These new materials can reduce power requirements and allow other fu-
els and fuel cells to become popular more quickly.
When hydrogen is used as fuel, the main emission from fuel cells
is potable water. Even when using hydrocarbons as fuel, these systems
offer substantial reductions in emissions. Honda's FCX fuel cell vehicle
carries 156.6 liters of compressed hydrogen (about 3.75 kilograms) in two
aluminum tanks. The fuel cell's peak output is 78 kilowatts which drives
the electrical motor that moves the vehicle. An ultra-capacitor acts as a
reservoir when the electrical load during acceleration exceeds the energy
produced by the fuel cell. The ultra-capacitor offers quicker and higher
voltage discharges and recharges than nickel-hydride batteries which are
also used for this purpose. The batteries are slower to charge but hold it
longer.
Solid oxide fuel cell (SOFC) systems can reach electrical efficiencies
of over 50% when using natural gas, diesel or biogas. When combined
with gas turbines there can be electrical efficiencies of 70%, for small in-
stallation as well as large. In a fuel cell system, these efficiencies can be
kept at partial loads as low as 50%. Conventional technologies must run
at close to full load to be most efficient.
NO x and SO x emissions from SOFC systems are negligible. They
are typically 0.06-g/kWhe and 0.013-g/kWhe (kilo-watt hours electrical).
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