For the hydrogen economy to work, storing hydrogen at a large scale is necessary. This is a topic of concern because hydrogen is the lightest molecule and hydrogen gas has a very low density. For vehicular applications, this is a necessary step for hydrogen fuelling stations, production and distribution. The storage density needs to be increased to make hydrogen storage economically viable. When hydrogen is being provided to a proton-exchange membrane (PEM) fuel cell, the purity of the delivered hydrogen is crucial; in other applications, like when the hydrogen is being burned with air, it is less critical. There are several technology options for large-scale hydrogen storage because of the various restrictions.
Various technologies can be applied for the storage of hydrogen. (1) Pure molecular hydrogen can be stored as a gas or a liquid without forming physical solid or chemical bonds with other substances. (2) Molecular hydrogen can be adsorbed onto or into a substance and held in place by relatively weak physical van der Waals bonds. (3) Atomic hydrogen can form chemical bonds. Hydrogen can be kept in its purest molecular state as a gas or a liquid. These are the only hydrogen storage methods being used on an extensive basis.
The two primary parts of a condensed hydrogen gas storage system are the storage compartment(s) and the compressors necessary to attain the storage pressure. Compressed hydrogen can be kept in storage either above or below ground. Larger-scale aboveground solutions typically aren’t favored because the investment costs are substantially higher, as is usually the case for gas storage. Hydrogen is already present in significant subsurface storage. Larger quantities of natural gas are currently stored in three different types of metallic tanks :
- Gas containers with storage pressures are just slightly higher than atmospheric pressure.
- spherical Pressure vessels, with maximum storage pressures of up to 20 bar.
- Pipe storage, with 100 bar or so of maximum storage pressure.
Double-walled liquid hydrogen storage tanks most frequently have a strong vacuum applied between the walls. Conduction and convectional heat transfer are reduced by the vacuum . Additional materials, such as alumina-coated polyester sheets, layers of aluminum foil and glass fiber alternated with one another, or aluminum, silica, or perlite particles, are also present in the area between the vessel walls. These substances serve as barriers against radiation-based heat transfer. Boil-off rates are meager for larger spherical tanks, typically below 0.1 percent per day, due to the high degree of insulation and the low surface-to-volume ratio.
Author : Swastika Jha