Hydrogen storage systems
Hydrogen is stored in two ways: metal hydrides and compressed gas.
Hydrogen gas can be stored at low pressure through a chemical reaction with an alloy that absorbs hydrogen and which forms a solid metal hydride: various metal alloys (mainly based on magnesium) and intermetallic compounds react with hydrogen to form metal hydrides. In other words, metals can be charged and discharged with hydrogen. These systems take up a very small amount of space and the pressures reached in them vary between 1 and 25 bar; on the down side, they are extremely heavy and need a special cooling system since heat is exchanged when charging and discharging.
Storing hydrogen as compressed gas is done using pressurised, high-strength steel containers. Composite cylinders, lighter than metal ones, are used and operate at pressures between 350 bar and 700 bar (increasing the pressure allows more hydrogen to be stored).
There are four types of container suitable for hydrogen: Type I, Type II, Type III and Type IV, which vary in terms of the constituent material and the gas pressures reached inside them.
A type I tank is more advantageous in economic terms but is extremely heavy. A type IV storage tank can reach 700 bar with a lower weight but costs twice as much as a type I. A key parameter that characterises the storage system are the kilogrammes of H2 stored at the pressure at which you decide to work.
Example of a cylinder bundle.
|TERMS OF SERVICE|
|Hydrogen stored at 500 bar (15°C)||9,5 kg|
|Operating temperature||from -40° C to 65° C|
|Maximum operating pressure||500 bar|
|Maximum filling pressure||500 bar|
|Position of use||Vertical or horizontal|
|Internal volume||300 liters|
|External dimensions||ø49cm x 307 cm (without support)|
|Empty tank mass||260 kg|
|Materials||Type IV – Polymeric liner reinforced with composite material|
|Tip in stainless steel and aluminium||x2|
|Lifepsan||10 years / 5.000 cycles|
|Hydraulic pressure test||750 bar|
|Test in accordance with||EN 12245 – PED 2014/68 / EU to TPED 2010/35/EU|
Example of a technical data sheet for a cylinder containing hydrogen.
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