Produzione e distribuzione di elettricità e calore
Hydrogen Transport and Storage
Autors: Marco Cavana, Pierluigi Leone, Stephen McPhail
Production and Distribution of Electricity and Heat
Hydrogen storage and transport are some of the most urgent and challenging solutions to develop safely, reliably, efficiently, and cost-effectively for hydrogen to become a viable universal energy carrier and a possible long term renewable energy storage. In its natural form, hydrogen has a high gravimetric energy density while the volumetric energy density is low. Its low density (the lowest among gases) makes the pressurized storage more difficult. Furthermore, its high flammability and the tendency to generate explosive reaction makes the entire handling of hydrogen more dangerous. There are three typical approaches to store hydrogen: • Physical storage as compressed gas • Physical storage as cryogenic liquid hydrogen • Materials-based storage or solid state storage. The choice of the most suitable storage approach depends on the kind of application (stationary – energy storage – or for mobility), the storage time, the availability of space and the need to move the stored quantities as part of a supply chain. Compressed hydrogen (from 200 to up to 900-1000 bar) is the most common way hydrogen is stored and moved in local transport and distribution supply chain. Compressed storage is also used on board of today’s vehicles fuelled by hydrogen. In fact, one of the rising target market of compressed hydrogen is mobility and refuelling station. In the field of transportations, an alternative (still with relatively low TRL) to pressurized hydrogen is given by hydrogen storage within solid state as a metal hydride. The problem with this kind of storage mean is the high gravimetric density of the system. On the field of seasonal or bulk storage, underground storage in salt caverns is expected to be the more viable solution. However, only R&D projects are done on this field as the hydrogen economy is not sufficiently large to require such amounts of storage. For higher volumes of hydrogen, liquefied hydrogen could be a solution both for stationary storage (at industrial plants where it is used as a feedstock) and transport. The technology are based on the LNG transport and storage area, as cryogenic conditions have to be maintained. The biggest cryogenic tank in the world is at NASA’s facility and it is spherical tank with a volume of 3,220 m3. Ships transport of liquefied hydrogen has only been conceptualized so far, with designs of vessel 200,000 m3 big. In 2020 the first demonstration project has been launched with shipping volumes of around 1250 m3. A valuable alternative to liquid hydrogen is given by the storage and transport of hydrogen in the form of chemical carriers such as Liquid Organic Hydrogen Carriers (LOHC) and/or ammonia. In both cases, these are chemical substances already well known to the industry, thus their supply chain (either global or local) has already been established. The only barriers is on the fact that they have been rarely been employed as a form of hydrogen vector. Storage and transport of hydrogen in this form would mean to chemically bond hydrogen forming molecules (LOHC or NH3), with the advantage of a very stable form of hydrogen storage. On the other hand, energy and capital expenses are needed to run the reaction in a design process plant. In turn, also the recovery of hydrogen from these chemicals would require a dedicated infrastructure and energy consuming transformation steps. However, liquid chemical carriers are believed to be effective for long range shipping transport of hydrogen. For medium to long range transport of hydrogen, the solution that is believed to be the most convenient is the pipeline transport. Hydrogen pipeline have been run since 1930s in Europe to connect industrial areas where it was produced and consumed. At present, about 5000 km of hydrogen pipeline are installed in the world, mainly in the US and Europe.