Description
Metal hydride tank is a container loading with hydrogen storage alloy powder, heat exchange parts, and gas transport components. The
container body materials are generally aluminum alloy or stainless steel. Our hydrogen storage vessels are based on AB5 metal hydride
alloys. Hydrogen being stored at low pressure in the vessel, they provide a safe and reliable energy storage, particularly for portable
applications, in-house and in-board storage.
Individual vessels can be combined in arrays to reach specific H2 volumes and discharge rates. Contact us for custom-built hydrogen
storage.
Chose your storage depending on the quantity of hydrogen you wish to store. The number in the product name refers to the quantity of
normal liters of gas kept in the vessel (for instance, the MH150 tank can store up to 150NL of hydrogen). Typical uses of the tanks
include fuel cell power, gas chromatography and lab experiments/chemical reactions.
The performance of a metal hydride tank mainly includes the following aspects:
. Capacity — how much hydrogen can be stored, generally indicated as in standard liters NL;
. Releasing rate — the rate that hydrogen is released from the tank. A sufficient heat supply is required for hydrogen releasing. The rate
is determined by the type of metal hydride, efficiency of heat exchange as well as gas transport resistance;
. Recharging time — time that used to refueling the tank;
. Cycle life — the cycle number that the tank can be refueled without a significant degradation in capacity.
The main features of the metal hydride tank:
. High storage density；
. Capability of low temperature releasing
. Quick locking;
. Flexibility in tank size;
. Body materials: stainless steel or aluminum alloy
How to charge your metal hydride tanks
Metal hydride tanks can be filled with hydrogen when connected to a pressurized H 2 source or water electrolysis system, for instance an
industrial H2 bottle obtained from your local gas supplier. Typical input pressure required to charge the tanks varies between 10 to 20
barg depending on the size of the vessel. Lower pressure can be used but charging time is then increase. Contact us to obtain the
charging conditions graphs.
Because of the exothermal reaction when charging the vessels, they must be cooled down during the filling process. Small and medium
size tanks can simply be put into cold/fresh water (in a glass or any other type of reservoir). Large tanks can be equipped with a cooling
circuit.
Charging time is very short compared to the time required to charge a conventional battery. For instance, the small MH10 or MH20 are
fully charged in less than 20 minutes.
Multiple tanks can be charged simultaneously from a single hydrogen source.
Pragma Industries provides accessories like charging sets, connecting devices and can put you in touch with your local gas supplier.
Using good quality hydrogen, with a purity at least equal to 99.99%, ensures a long lasting use of the vessels.
Safety
Metal hydride tanks are ideal for indoor use thanks to their low storage pressure.
However the user should consider the volume of the room where the vessel is stored compared to the volume of hydrogen stored.
Hydrogen has a Lower Flammable Limit (LFL) of 4% diluted in air. We recommend that the uncompressed total volume of hydrogen
stored does not exceed 2% (half of the LFL) of the total volume of the room.
Our tanks are delivered filled with argon to comply with air transportation security rules. Therefore, they need to be charged before being
usable.
How does metal hydride tanks work
Storage Mechanism
Hydrogen is stored in the form of so-called “metal hydride”.
Most metals or alloys can react with hydrogen to form new compounds, which are named as metal hydrides. The formation of metal
hydride is an exothermic process associated with heat releasing. With sufficient heat supply, hydrogen can be released from the asformed metal hydride. Such a reversible reaction process can be expressed as follows:
2/nM + H2 = 2/nMHn +ΔH
where M-metal or alloy; MHn-metal hydride; ΔH-thermal effect associated with the reaction. Pressure and temperature changed, the
reaction will take place alternatively and hydrogen will be absorbed or desorbed.
Atoms of hydrogen, under low temperature or high pressure, can enter the holes of crystalline of the parent metal or alloy, forming solid
solution — α phase; then reaction between hydrogen and metal will continue to form the new phase — β phase. The above figure is the
simple model of hydrogen atoms locating on the grid of metals.
Thermodynamic
From the thermodynamics point of view, the enthalpy associated with the formation reaction of metal hydride reflects the strength of the
metal-hydrogen bond in the metal hydride phase. The relationship among the pressure, temperature and composition is generally
described by a Pressure—Composition—Isotherm plot, namely PCI curve.
In this figure, the sloping part on the left side is for α—phase region. Both α and β phases coexist in the middle region and only β—phase
is present on the right side. The pressure relative to the middle flat region is called the equilibrium plateau pressure.
The relationship between pressure and temperature is described by the Van’t Hoff equation:
LnPH2 = ΔH0/RT – ΔS0/R
Where ΔH0 and ΔS0 are the enthalpy and entropy of the hydrogen absorption reaction, “R” the gas constant and “T” the absolute
temperature. This relationship can be verified experimentally by carrying out PCI measurements on a material at several temperatures.
Adopting the Van’t Hoff relationship and PCI curve, it is possible to determine the enthalpy and entropy of the metal and hydrogen
equilibrium.
Type of metal hydrides
From the engineering point of view, three types of metal hydrides mostly used, which are listed as follows.
– AB type: Ti-Fe-C, Ti-Fe-Ca, Ti-Fe, Ta, Ti-Fe-Mm,…
– AB2 type: Ti-Cr-Fe, Ti-Zr-Cr-Fe, Ti-Zr-Cr-Fe-Mn-Cu, Ti-Mn-V, Ti-Zr-Mn-V-Fe,…
– AB5 type: Ca-Mm-Ni-Al, Mm-Ni-Mn-Co,…