Different methods of storing, transporting, and distributing Hydrogen
Hydrogen is most commonly stored under compression in pressurized steel or carbon composite cylinders. However, the low volumetric density of hydrogen offers the economic advantage of being compressed into greater densities and thus requiring lower storage capacities.
As a result, the use of liquefaction and the exploration of other chemical carriers such as ammonia have increased in popularity for the storage, and transportation, of hydrogen. Table 1 presents an overview of some of the available storage technologies for hydrogen as detailed by Bruce, et al. (2018).
Storing hydrogen in its gaseous state is achieved through compression inside pressurized tanks that have mechanical devices to control the pressure. Steel tanks can typically store hydrogen at pressures up to 200 bar, while composite tanks can do so up to 800 bar. This form of hydrogen storage is well established, however, may not prove economical for hydrogen on a large scale due to the low volumetric densities of the gas.
Line packing is the process of storing compressed gas within a pipeline network by altering the pipeline pressure. The hydrogen gas can be stored inside a pipeline for days, at a large scale, and then can be distributed when deemed necessary such as during periods of peak demands.
Hydrogen can also be compressed into underground salt caverns through the injection of hydrogen into salt rock, typically intended for long-term storage. However, this storage method is limited by the availability of salt caverns (Bruce, et al., 2018).
Hydrogen can be liquified through the use of a multi-stage process of compression and cooling which is then stored in cryogenic tanks at temperatures of -253 ℃ (Bruce, et al., 2018). Liquified hydrogen has a much greater volumetric density, and therefore provides greater economic advantages in storage capacities.
However, it should be noted that the process of liquefaction typically consumes around 30% of the hydrogen’s energy content. Furthermore, losses of hydrogen are experienced through evaporation, or “boil-off”, and the process itself is expensive (EERE, 2021).
Hydrogen can be converted into ammonia by combining nitrogen and hydrogen using the Haber Bosch Process. The use of green hydrogen creates green ammonia which can be used as a climate-friendly energy carrier, mineral fertilizer, and fuel. Ammonia is much less energy-intensive to liquify than hydrogen and is, therefore, simpler to store and transport (McMahon, 2020).