Present in the atmosphere in a diatomic molecule, hydrogen is the lightest element and the most abundant resource in nature. In an oxygen-rich environment such as Earth's, it burns in a similar way to methane, revealing itself to be a fuel that, unlike all the others, produces no polluting emissions but only water. Among the fuels, it has the highest energy content per unit weight and a very high conversion efficiency, which is more than double that of diesel and petrol . When produced by electrolysis, it can prove to be fundamental in solving the problem of the variability of energy production from renewable sources.
Once produced, hydrogen must be transported. There are several hydrogen distribution strategies, and in recent times, given the growing attention by public and private entities towards this energy vector, transport strategies are also growing.
At the moment, the most common option is that of storing it in large tanks and then transport it by road, rail or sea; however, this solution is quite expensive due to the high gas compression costs.
Instead, the alternative that is gaining ground is to exploit the gaseous state of hydrogen to transport it at low pressures in long pipelines, similar to those used for gas: hydrogen pipelines.
It sounds crazy but the first hydrogen pipelines date back to the 1930s. For example, the Verrés hydrogen pipeline, in the Aosta Valley, built in 1934 to transport hydrogen used in the production of fertilizers; this conduit was capable of transporting up to 24,000 cubic meters of hydrogen in 24 hours. Another is the one located in Germany, in the Rhine-Rurh area, built in 1938 and still functioning to feed the district's industries.
Over the years these infrastructures have multiplied: today there are 1,500 kilometers of hydrogen pipelines in Europe, while in the United States about 900 .
Many companies today are choosing to use existing pipelines to transport hydrogen. The European Hydrogen Bockbone project, which brings together the major gas producing companies in Europe, aims to build 40 thousand km of hydrogen distribution network by 2040, of which more than half obtained from existing gas pipelines. Among other things, the presence of a capillary network can help reduce transport costs and consequently costs for end users as well. However, a criticality of this situation is the interaction between hydrogen and steel in the pipes: hydrogen embraces the metal, reduces its ductility and toughness, and exposes it to the risk of breakage. The pipes must therefore be reinforced and prepared appropriately. The main Italian player in the sector has declared that currently 70% of its total infrastructure is ready for hydrogen distribution.
Another strategy that is generating interest is the transport of hydrogen in existing pipelines used for the distribution of natural gas, together with the latter, in a mixture. In percentages up to 10%, hydrogen should not compromise the piping materials. This solution would allow hydrogen to also reach residential areas, where it could be used for heating or cooking. This system has already been tested in Italy in 2019, first with a mix of 5% hydrogen by volume, then with 10%. In addition, systems are being studied to separate hydrogen from natural gas once it reaches its destination; they are mostly selective membranes. The alternative is to burn the mix of hydrogen and gas together as a single fuel. This solution, however, reduces but does not eliminate the problem of emissions produced by methane. In addition, it requires the presence of control bodies capable of measuring the actual composition of the gas mixtures in the various sections of the network.
Some believe that, before investing in large-scale hydrogen transport, local capillary networks should be built, made up of many short pipelines that connect plants located in close proximity to each other. In fact, producing and using hydrogen locally could really help accelerate decarbonization. This is the case of Arezzo, where 3.5 km of pipes were built in 2008 to supply part of the industrial area.
As proof of the centrality of the issue, the PNRR is also allocating an important part of its resources to the problem of hydrogen transport, investing both in solutions involving compression and in the development of hydrogen pipelines. It has earmarked 160 million euros for research on hydrogen and ways to store and transport hydrogen.
Translated by Simona Taravella