Hydrogen is gaining recognition as a clean energy carrier, but its transport presents complex engineering challenges that differ significantly from those for traditional fossil fuels. Its extremely low volumetric energy density requires it to be compressed to high pressures or cryogenically cooled to a liquid. Both methods demand substantial energy input and specialized infrastructure. Developing safe and cost-effective delivery methods is crucial for the global shift toward a hydrogen economy.
Transporting Hydrogen Through Existing Pipeline Infrastructure
Pipeline transport is the most cost-effective solution for moving large volumes of gaseous hydrogen over long distances. Dedicated hydrogen pipelines have historically been used by industrial consumers, with the current U.S. network covering an estimated 700 to 1,300 kilometers. For efficient transport, hydrogen gas must be significantly compressed from its typical production pressure of 20 to 30 bar to much higher pressures, often 180 bar or more.
A major technical obstacle for expanding pipeline use is hydrogen embrittlement. Hydrogen atoms are tiny and can diffuse into the crystalline structure of pipeline steel, reducing the metal’s ductility and fracture resistance. This effect is particularly pronounced in higher-strength steel alloys and must be carefully managed to prevent catastrophic failure, especially when repurposing natural gas lines.
Another challenge relates to the energy density of the gas, even when highly compressed. Hydrogen’s low volumetric energy density means a pipeline transports less energy content per volume compared to a natural gas pipeline of the same size. While blending hydrogen into existing natural gas lines is an option, it raises concerns about pipeline integrity due to embrittlement and complicates accurate metering at the point of use.
Mobile Transport of Compressed and Liquefied Hydrogen
Mobile transport via road, rail, or sea is primarily used for shorter distances or for delivering moderate volumes of hydrogen to decentralized locations, such as fueling stations. This logistics chain relies on two primary forms of pure hydrogen: compressed gas and cryogenic liquid.
Compressed Hydrogen Gas (CH2)
Compressed hydrogen gas is moved in tube trailers, which are truck-drawn platforms fitted with multiple high-pressure cylinders. These trailers typically compress the hydrogen to pressures ranging from 200 bar to 500 bar. Conventional steel tube trailers carry approximately 380 kilograms of hydrogen, though newer composite designs can increase the payload to between 560 and 900 kilograms. This method is flexible but limited in the total mass transported per trip, making it less economical for very large volumes or long haul routes.
Liquefied Hydrogen (LH2)
Liquefied hydrogen is a much denser form, allowing for greater energy content, which is advantageous for long-distance transport. To achieve this liquid state, hydrogen must be cryogenically cooled to an extremely low temperature of -253°C. Specialized, heavily insulated tanker trucks and ships are required to maintain this temperature, and a single tanker can transport around 3,500 kilograms. However, the liquefaction process is highly energy-intensive, requiring between 10 and 20 kilowatt-hours of energy per kilogram of hydrogen. This high energy demand and inevitable boil-off losses mean that liquefied hydrogen is often reserved for routes where the volume advantage outweighs the energy cost.
Using Chemical Carriers for Hydrogen Delivery
For transcontinental or high-volume global shipping, hydrogen can be chemically bound to a carrier molecule, enabling transport as a more manageable liquid. These indirect methods allow the use of existing liquid chemical transport infrastructure, which significantly reduces logistical costs.
Ammonia (NH3) is the leading chemical carrier because it can be liquefied at a mild temperature of -33°C or at moderate pressure. Hydrogen is first converted into ammonia, then shipped using established global ammonia infrastructure, including ports and tankers. Upon reaching the destination, the ammonia is fed into a high-temperature “cracker” unit (600°C to 900°C) and a catalyst to split the ammonia back into pure hydrogen and nitrogen. A drawback is the significant energy loss, costing up to 30 to 40% of the hydrogen’s energy content during the conversion and cracking steps.
Another promising approach involves Liquid Organic Hydrogen Carriers (LOHCs), which are organic liquids like Benzyltoluene. Hydrogen gas is chemically added to the “hydrogen-lean” liquid via hydrogenation, which is safe to handle at ambient temperatures and pressures. The resulting “hydrogen-rich” liquid is then transported using standard liquid fuel logistics. At the delivery point, a dehydrogenation unit uses heat (250°C to 350°C) and a catalyst to release the pure hydrogen gas. The remaining “hydrogen-lean” liquid is shipped back to the source for reuse, creating a closed-loop system.