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Alternative Fuels for Transportation
The weight of the liquid hydrogen system is slightly more than that of
conventional gasoline/diesel storage systems. The liquid hydrogen system
has a volume about 10 times higher than that of gasoline systems for carrying an equal amount of energy. Hydrogen can be delivered to the engine
in cold so that it increases the engine volumetric efficiency, which leads to
increase in power output also. Cold hydrogen reduces acts like a thermodynamic sink and reduces the combustion chamber temperature. This leads to
a reduction in NO x emissions.
The maximum temperature excursions that a storage system would
undergo from an ambient temperature of about 40ºC to the storage temperature of about 13 K amounts to a difference of about 300ºC. This places
high thermal and hence mechanical loads on the pipe-work, flanges and
vessels, and the cool-down has to be controlled to minimize the potential
for leakage due to uneven contraction of the system. Liquefied hydrogen
has the potential problem of causing hydrogen embrittlement of metallic
components in the system. As the liquid is extremely cold, any spillage
rapidly evaporates and cools the ground onto which it falls. This produces a rapid “puff” of expanding vapor that rises rapidly and disperses.
The very high turbulence generated by the sudden expansion of vapor
from the liquid mixes the hydrogen gas with the air, and the gas cloud
typically expands by a factor of five times. Low clouds of dense, cold gas
will spread along the ground, rather than immediately rise and dissipate
(Astbury 2008).
9.13.2 Compressed Hydrogen
In general, hydrogen is produced in the form of gas and also its end use is
in the form of a gaseous state. Hence, it is obvious that most of the industrial
storage is in the form of compressed gas. Natural gas is stored at around
200 bar in strong composite pressure vessels, typically aluminum cylinders
wrapped with fiberglass. However, hydrogen is eight times lighter than
methane per mole, and thus requires a much higher storage pressure to
attain a given volume. As the hydrogen obeys gas law (PV = mRT) at lower
pressure, increase in pressure increases the storage density. However, there
is a slight deviation in the law at higher pressures (Das 1996a).
Hydrogen can be stored as any gas in compressed form in high strength
gas cylinders. One kilogram of hydrogen occupies 11 m 3 of volume at
ambient pressure and temperature. Hence it requires a large volume of gas
to store in its uncompressed form. Hydrogen is stored in compressed gas
cylinders made of aluminum or other high strength materials. Hydrogen
can be compressed up to 550 bar. Hydrogen cylinders (200 bar) weigh nearly
three times more than that of comparable liquid hydrogen. However, the
size of the system can be reduced by increasing the pressure of hydrogen
in cylinders. Compressed hydrogen cylinders require about two times the
volume of gasoline.
Alternative Fuels for Transportation
The weight of the liquid hydrogen system is slightly more than that of
conventional gasoline/diesel storage systems. The liquid hydrogen system
has a volume about 10 times higher than that of gasoline systems for carrying an equal amount of energy. Hydrogen can be delivered to the engine
in cold so that it increases the engine volumetric efficiency, which leads to
increase in power output also. Cold hydrogen reduces acts like a thermodynamic sink and reduces the combustion chamber temperature. This leads to
a reduction in NO x emissions.
The maximum temperature excursions that a storage system would
undergo from an ambient temperature of about 40ºC to the storage temperature of about 13 K amounts to a difference of about 300ºC. This places
high thermal and hence mechanical loads on the pipe-work, flanges and
vessels, and the cool-down has to be controlled to minimize the potential
for leakage due to uneven contraction of the system. Liquefied hydrogen
has the potential problem of causing hydrogen embrittlement of metallic
components in the system. As the liquid is extremely cold, any spillage
rapidly evaporates and cools the ground onto which it falls. This produces a rapid “puff” of expanding vapor that rises rapidly and disperses.
The very high turbulence generated by the sudden expansion of vapor
from the liquid mixes the hydrogen gas with the air, and the gas cloud
typically expands by a factor of five times. Low clouds of dense, cold gas
will spread along the ground, rather than immediately rise and dissipate
(Astbury 2008).
9.13.2 Compressed Hydrogen
In general, hydrogen is produced in the form of gas and also its end use is
in the form of a gaseous state. Hence, it is obvious that most of the industrial
storage is in the form of compressed gas. Natural gas is stored at around
200 bar in strong composite pressure vessels, typically aluminum cylinders
wrapped with fiberglass. However, hydrogen is eight times lighter than
methane per mole, and thus requires a much higher storage pressure to
attain a given volume. As the hydrogen obeys gas law (PV = mRT) at lower
pressure, increase in pressure increases the storage density. However, there
is a slight deviation in the law at higher pressures (Das 1996a).
Hydrogen can be stored as any gas in compressed form in high strength
gas cylinders. One kilogram of hydrogen occupies 11 m 3 of volume at
ambient pressure and temperature. Hence it requires a large volume of gas
to store in its uncompressed form. Hydrogen is stored in compressed gas
cylinders made of aluminum or other high strength materials. Hydrogen
can be compressed up to 550 bar. Hydrogen cylinders (200 bar) weigh nearly
three times more than that of comparable liquid hydrogen. However, the
size of the system can be reduced by increasing the pressure of hydrogen
in cylinders. Compressed hydrogen cylinders require about two times the
volume of gasoline.