Alternative Fuel Sources - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 97

storage tanks that are used in laboratories are able to keep the hydrogen
in a liquid state for several months. It should be possible to build vehicu-
lar storage tanks that would maintain hydrogen in a liquid state for sev-
eral weeks. The small quantity of hydrogen evaporating from such tanks
could also be sent to a fuel cell that would use the hydrogen to generate
electricity. It is also possible to vent the vaporized hydrogen gas to an aux-
iliary hydride system for storage.
This venting of the fuel must be done to keep a fuel tank full when
refueling. In an enclosed space, the vented hydrogen also presents a risk
because of hydrogen's wide flammability limits.
Hydrogen explosions are rare, but any combustible gas in an en-
closed space can be a safety problem. One solution is to burn off the es-
caping hydrogen and use this energy for heating or cooling.
The double-walled vacuum jacketed storage tanks and piping that
are required for liquid hydrogen are expensive compared to conventional
fuel storage tanks. A gasoline tank might cost about $150, while a liquid
hydrogen storage tank could cost up to a few thousand dollars. Because of
the energy density of liquid hydrogen, it requires a fuel tank that is three
to four times as large in volume as required for gasoline or aviation fuel.
Liquid hydrogen fuel systems would require changes in the energy
infrastructure and end use systems, such as stoves, engines and fueling
systems. While disadvantages of liquid hydrogen are substantial, they can
be minimized. A few thousand dollars for a liquid hydrogen storage tank
seems high, but consider that the emissions control equipment required
on gasoline fueled engines adds much to the cost of current vehicles. As
production volumes of cryogenic storage tanks increase, the cost of cryo-
genic tanks are expected to drop below $1,000.
Although cryogenic fuels are difficult to handle, a self-service liquid
hydrogen pumping station was built decades ago at Los Alamos National
Laboratory. It was shown to be feasible for refueling vehicles over an extend-
ed period of time without any major problems. Cryogenic storage is used
by the National Aeronautics and Space Administration (NASA). Liquid hy-
drogen, along with liquid oxygen has been used as a rocket fuel since World
War II. As a fuel for the space shuttle, almost 100 tons (400,000 gallons) are
stored in the shuttle's external tank. To prepare for a shuttle launch requires
fifty tanker trucks to travel from New Orleans to the Kennedy Space Center
in Florida. This represents a great deal of experience in shipping liquid hy-
drogen. Since 1965, NASA has moved over 100,000 tons of liquid hydrogen
to Kennedy and Cape Canaveral by tanker truck.