The need to meet IMO’s greenhouse gas emissions goals for 2030 and 2050 has prompted the industry to investigate several types of alternative fuels that can help vessels lower their carbon footprint. Hydrogen is one of the most promising zero-emission fuel sources being considered.
What are the benefits of hydrogen as a marine fuel?
Hydrogen offers ships a carbon- and sulfur-free fuel option that can eliminate tank-to-wake (TTW) emissions. Hydrogen:
However, there are three major challenges that must be considered for hydrogen to be a fully well-to-wake (WTW) emission-free fuel option: production, transportation and storage, and utilization.
One benefit of hydrogen is near-term availability because it is already produced as part of other land-based industries, though almost entirely by carbon-intensive methods. Hydrogen is typically used for the refining of petroleum, treating metals, processing foods, and producing ammonia or other chemicals. Ammonia is another leading contender as low-emission fuel.
Types of Hydrogen
There are five types of hydrogen in terms of the emissions released during production:
Grey hydrogen represents about 75% of global hydrogen production while brown hydrogen is the second largest source, both of which are very carbon intensive. The high level of emissions can be reduced or abated by implementing CCUS technology (blue hydrogen), but the method is not yet widespread. Green hydrogen, which can potentially be achieved with offshore production powered by renewable energy sources, accounts for only 2% of the global hydrogen supply.
Increased investment in CCUS technology and green hydrogen production is key to reducing or eliminating well-to-tank (WTT) emissions, creating an avenue for hydrogen to be a WTW net-zero carbon solution.
To learn more about how ABS can aid your fleet with carbon accounting and ensuring the sustainability of your fuel choices, see our services below or contact our sustainability team.
The transportation and storage of hydrogen present its own set of challenges, and special considerations are needed during the design stage for hydrogen carriers or any vessels using hydrogen as fuel.
Hydrogen is a gas at ambient temperature and pressure, making it volumetrically inefficient to store and transport at ambient conditions. While industrial hydrogen is typically stored at no more than 200 bar (3,000 psi), the space and materials needed to store an economically viable amount of hydrogen at 200 bar aboard a vessel would be impractical.
To maximize the amount of hydrogen in a given volume, there are three ideal methods of storage:
Liquefied hydrogen offers more stored energy density than gaseous hydrogen, but a large percentage of the energy is required to refrigerate and liquify it. Because hydrogen has a relatively low energy density compared to other marine fuels, this means that vessels using hydrogen as a fuel requires more hydrogen and thus storage space to both power the vessel and maintain liquefication. The additional space for fuel may require larger vessel sizes, decreased cargo space, and more frequent bunkering of the vessel.
The transport of hydrogen as cargo will be necessary to scale the global availability of the fuel. To date, only one pure liquefied hydrogen carrier has been launched as a test bed to prove the viability of transporting hydrogen across large distances. The density of liquefied hydrogen allows carriers to maximize storage onboard and increase trade volume. However, special considerations must be made for the design of hydrogen carriers.
Liquefied hydrogen stored at low pressures can be susceptible to pressure build-up and gas boil-off if stored for long periods of time. Pressure relief valves and proper insulation are critical to protecting against pressure build-up. The boil-off rate is around one to five percent per day for standard land-based liquid hydrogen storage tanks. Improved insulation can reduce boil-off to 0.02 percent per day and energy loss can be almost entirely alleviated if boil-off gas is consumed in an engine or fuel cell.
Another concern for the long-term storage of hydrogen is the potential for hydrogen embrittlement. Because of hydrogen’s small molecular size, it can permeate into the walls of some metal alloy tanks over time. This can lead to a weakening of the structure and contribute to crack formation. Vessels transporting hydrogen must ensure tanks are made of proper materials and have received appropriate surface treatments to prevent embrittlement and premature tank failure.
A potential solution that can alleviate some of the challenges of shipping liquefied hydrogen is to transport it in a carrier substance such as ammonia, methanol, or LOHCs. These fuels do not require the low temperatures or insulation needed to liquefy hydrogen and use less energy. They can also be consumed in some fuel cells, but they may require more energy input to hydrogenate and reform the fuel, making them less efficient overall.
Whether you want to transport hydrogen for trade or use it as a zero-emission fuel, our sustainability experts can guide you through the design considerations to ensure your vessel stores hydrogen safely and efficiently.
Hydrogen fuel cells can be used to generate zero-emission TTW electricity. There are several types of fuel cells with various operational and cost trade-offs, but in general, they consume hydrogen and oxygen and generate heat, water, and electricity.
Proton exchange membrane (PEM) fuel cells are the most common type of fuel cell and consume pure hydrogen. They have been in use for land-based electricity generation for many years. Solid oxide fuel cells (SOFC) are another common type and can accept hydrogen carrier fuels such as LNG, methanol or ammonia. However, SOFCs run at higher temperatures and require fuel reformers.[CB1] Marinized fuel cells are available with a wide range of available power and can be connected in a series to increase output for any size marine power requirement.
Hydrogen mixed with conventional fuels, such as diesel and gasoline, can improve engine efficiency and lower carbon emissions in internal combustion engines, offering a near-term stopgap solution to bridge to eventual fuel cell conversions. For more information on the use of hydrogen in combustion engines, see Hydrogen as Marine Fuel.
If hydrogen is widely adopted as a marine fuel, shipowners and operators could potentially run into availability and cost challenges as energy providers pivot to scale production, especially of green hydrogen, and improve transportation, port and bunkering infrastructure to meet demand.
Despite its challenges, hydrogen as a marine fuel offers one of the clearest paths to zero-emissions TTW operations. Investment in the complete hydrogen value chain, especially in the production of blue and green hydrogen and relevant operational infrastructure, will be key to scaling hydrogen as a true WTW solution.
ABS recognizes the complex challenges facing shipowners and operators as the industry seeks to implement hydrogen as a marine fuel. Connect with our sustainability specialists or explore our solutions below to see how we can assist with all aspects of the hydrogen value chain.
ABS can assist owners, operators, shipbuilders, designers and original equipment manufacturers as they consider the practical implications of the use of hydrogen as marine fuel. Services offered include: