Hydrogen
283
A standard pressure vessel of 0.05 m 3 at atmospheric pressure would hold
approximately (0.050/22.4) × 2 = 0.00446 kg of hydrogen, so at 1.4 MPa gauge
(200 psi) a vessel would hold about 0.0625 kg of hydrogen; that is, there is an
increase in storage capacity of about 50-fold compared with storing just the
compressed gas (Guo, Shang, and Aguey-Zinsou 2008).
High strength steel/austenitic steel/aluminum cylinders wrapped with
fiberglass are used as cylinder materials. For the high-pressure cylinders
the cost of materials and safety features are critical issues. The hydrogen
cylinders can be used for hydrogen vehicles as well as fuel cell vehicles.
Hydrogen has a positive Joule–Thompson coefficient and hence a large
reduction in pressure that occurs during a leak from a high-pressure system
results in a rise in temperature, rather than a fall, due to the expansion.
Though compressed hydrogen was suitable for many applications, the use
in automobile applications is limited because of high volume, weight, cost
of compression, and safety aspects. Das (1996b) reported that for 164 atm.
compressed hydrogen gas cylinder compression energy of 12.65 kJ/mol or
4100 kJ for a full cylinder is required. Hence, a lot of energy will be released
under catastrophic rupture situations. This rapid release of hydrogen may
cause backfire.
9.13.3 Solid Hydrogen
Storing hydrogen in metal hydrates has a number of advantages over compressed gas or liquid hydrogen. Solid state hydrogen fuel storage, either
absorption in the interstices of metals and metallic alloys, or adsorption
on high surface area materials such as activated carbons, has been receiving attention for on board hydrogen storage. It is a similar process to the
adsorption of solvent vapors on activated charcoal, in that the adsorption is
accompanied by a release of heat, and the desorption is driven by heating
the metal to release the hydrogen as gas. The heat required for the working
of metal hydrates (about 600 K) can be met by exhaust gases. As the heat of
adsorption would need to be removed, the process of refueling requires the
metal matrix to be connected to an external coolant supply during the filling process. Refueling hydride vehicles is relatively simple. It appears that
hydride vehicles can be refueled in 10 minutes or less. Metal hydride storage
is a safe, volume-efficient, storage method for onboard-vehicle applications.
Metal hydrates storage is suitable for vehicle applications to avoid space
constraints. Metal hydrate should possess the capacity of discharging the
required level of hydrogen to cater to the fluctuating need of the vehicle.
Hence, the proper choice of hydrate is important. The hydrate should be of
high storage capacity with good absorption/desorption characteristics. The
hydrate should be light weight and should have long life with the ability to
withstand engine operation over a prolonged time.
Some of properties of metal hydrates are pressure inside metal hydrates, hydrogen capacity, change in volume, kinetics of reaction, rate of
283
A standard pressure vessel of 0.05 m 3 at atmospheric pressure would hold
approximately (0.050/22.4) × 2 = 0.00446 kg of hydrogen, so at 1.4 MPa gauge
(200 psi) a vessel would hold about 0.0625 kg of hydrogen; that is, there is an
increase in storage capacity of about 50-fold compared with storing just the
compressed gas (Guo, Shang, and Aguey-Zinsou 2008).
High strength steel/austenitic steel/aluminum cylinders wrapped with
fiberglass are used as cylinder materials. For the high-pressure cylinders
the cost of materials and safety features are critical issues. The hydrogen
cylinders can be used for hydrogen vehicles as well as fuel cell vehicles.
Hydrogen has a positive Joule–Thompson coefficient and hence a large
reduction in pressure that occurs during a leak from a high-pressure system
results in a rise in temperature, rather than a fall, due to the expansion.
Though compressed hydrogen was suitable for many applications, the use
in automobile applications is limited because of high volume, weight, cost
of compression, and safety aspects. Das (1996b) reported that for 164 atm.
compressed hydrogen gas cylinder compression energy of 12.65 kJ/mol or
4100 kJ for a full cylinder is required. Hence, a lot of energy will be released
under catastrophic rupture situations. This rapid release of hydrogen may
cause backfire.
9.13.3 Solid Hydrogen
Storing hydrogen in metal hydrates has a number of advantages over compressed gas or liquid hydrogen. Solid state hydrogen fuel storage, either
absorption in the interstices of metals and metallic alloys, or adsorption
on high surface area materials such as activated carbons, has been receiving attention for on board hydrogen storage. It is a similar process to the
adsorption of solvent vapors on activated charcoal, in that the adsorption is
accompanied by a release of heat, and the desorption is driven by heating
the metal to release the hydrogen as gas. The heat required for the working
of metal hydrates (about 600 K) can be met by exhaust gases. As the heat of
adsorption would need to be removed, the process of refueling requires the
metal matrix to be connected to an external coolant supply during the filling process. Refueling hydride vehicles is relatively simple. It appears that
hydride vehicles can be refueled in 10 minutes or less. Metal hydride storage
is a safe, volume-efficient, storage method for onboard-vehicle applications.
Metal hydrates storage is suitable for vehicle applications to avoid space
constraints. Metal hydrate should possess the capacity of discharging the
required level of hydrogen to cater to the fluctuating need of the vehicle.
Hence, the proper choice of hydrate is important. The hydrate should be of
high storage capacity with good absorption/desorption characteristics. The
hydrate should be light weight and should have long life with the ability to
withstand engine operation over a prolonged time.
Some of properties of metal hydrates are pressure inside metal hydrates, hydrogen capacity, change in volume, kinetics of reaction, rate of