Some locations are better suited to produce low-carbon hydrogen than others. Specifically, regions with access to natural gas and CO2 storage reservoirs are ideal for producing blue hydrogen, while areas with dependable wind and solar generation and sufficient water resources are favorable for making green hydrogen. National tax credits can also play a role in the location of low-carbon hydrogen projects, with companies seeking to locate their facilities in regions with the most favorable tax incentives. Countries that do not have the resources to support low-carbon hydrogen production may seek to import it from other countries, which, in some cases, could require the long-distance marine shipping of hydrogen. However, since the low-carbon hydrogen market is still emerging, it is unclear what the best method for large-scale overseas transport will be. In this Energy Market Insight, we present four different methods that have been proposed for marine hydrogen transportation and discuss some of the possible pros and cons of each approach.
Low-carbon hydrogen projects produce hydrogen gas, which has a relatively low volumetric energy density at standard conditions (atmospheric pressure and 0° C) and is uneconomic to transport in large quantities. Therefore, hydrogen gas must be compressed, liquefied, or converted into a compound to achieve a higher energy density prior to transport.
Transporting hydrogen as a compressed gas is a relatively straightforward process that involves compressing the gas and storing it at ambient temperatures. While liquid hydrogen offers higher energy densities than compressed hydrogen gas, this method is more energy intensive due to the low temperatures (-253° C) that are required for liquefaction and storage. Liquid hydrogen can also experience boil-off losses, wherein gaseous hydrogen must be released from storage tanks due to the evaporation of liquid hydrogen. Since compressed and liquefied hydrogen do not contain any other substances, they do not require significant processing at the import terminal aside from possible pressure changes.
In addition to being transported as an elemental gas or liquid, hydrogen can also be incorporated into compounds that serve as hydrogen carriers. Liquid ammonia (NH3) is a popular proposed hydrogen carrier since it is nearly 18% hydrogen by weight, can be easily liquified at reasonable temperatures and pressures, and is already globally traded. However, since energy is required at both the export and import terminal for the ammonia synthesis and the reconversion of ammonia back to hydrogen via cracking, respectively, the ultimate energy efficiency of ammonia-sourced hydrogen is less than 50%. Additionally, the final hydrogen product may require additional purification depending on the efficiency of the cracking process and the hydrogen end-use. For example, hydrogen fuel cells typically require fuel that is over 99% hydrogen to function properly. Ammonia itself can also be sold as a fertilizer feedstock and has been proposed as an alternative fuel source for ships and power plants. Therefore, ammonia as an end-product can also serve as a pathway to export low-carbon hydrogen.
Liquid Organic Hydrogen Carriers (LOHC), such as toluene (C6H5CH3), have also been proposed as a means of hydrogen transportation. To use this method, hydrogen is fixed to the LOHC at the export terminal through a process called hydrogenation. The resulting liquid compound is stable at ambient temperatures and pressures and can be transported and stored using existing oil infrastructure. Once at the import terminal, the hydrogen is separated from the LOHC through dehydrogenation and the LOHC can then be recycled and reused to transport more hydrogen. While the hydrogenation process does not require energy inputs, the dehydrogenation process on the import side is energy intensive and, like ammonia, the LOHC method may require additional hydrogen purification. Additionally, LOHCs have relatively low hydrogen concentrations, resulting in a lower volumetric energy density than liquid hydrogen.
As the low-carbon hydrogen market continues to grow and mature, projects will need to start considering their transportation options, factoring in things like production scale, technological maturity, energy inputs on the export and import side, and hydrogen end-use. Due to the wide range of possible hydrogen end uses, e.g., fuel cells, hydrogen turbines, refining, or ammonia products, BTU Analytics suspects that a single overseas transportation method will not be suitable for all projects and that multiple methods will continue to gain traction.
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