The maritime sector is at a critical juncture, facing the daunting task of decarbonisation in the face of economic and geopolitical crisis. The maritime industry is heavily dependent on fossil fuels and emits more than 1.2 gigatonnes of carbon dioxide equivalents (CO2e) per year, representing about 3% of global greenhouse gas (GHG) emissions. As of early 2023, the average age of a ship was 22.2 years. At the same time, more than half of ships are over 15 years old, many of them either too old to be modernised or too young to be scrapped. Heavy hydrocarbon marine fuels and gasoil have a carbon footprint of 85% of global shipping. Fuel costs account for between 25% and 40% of the cost of operating a vessel. Estimates show that decarbonizing the world’s fleet by 2050 could require $8 billion to $28 billion annually. The infrastructure for 100% carbon-neutral fuels could need an even heftier $28 billion to $90 billion each year. If achieved, full decarbonization could double yearly fuel costs. Switching to another fuel, which can be 50% more expensive, will not happen voluntarily.
The Council of the EU has adopted in July the FuelEU maritime initiative, whic aims to cut GHG emissions from ships operating in Europe by 80% by 2050, as well as increasing the uptake of green hydrogen-based “renewable fuels of non-biological origin” (RFNBOs).
FuelEU requires all ships with a gross tonnage above 5,000 — regardless of what flag they fly — to cut greenhouse gas emissions by 2% from the start of 2025 against a reference emissions intensity of 91.16 grams of CO2 equivalent per MJ of energy used. This progressively rises to 6% from 2030, 14.5% from 2035, 31% from 2040, 62% from 2045, and final 80% from 2050.
A second rule will force operators of seaborne vessels to use at least 1% of green hydrogen-based fuels by 2034. To incentivise the uptake of RFNBOs, FuelEU offers benefit – till 2033 counting of CO2 sequestration twice. If the share of RFNBOs as a share of final energy used by a ship is below 1% for 2031, the EU will introduce a subtarget for RFNBOs to make up 2% of fuels used by ships from 2034. But also FuelEU includes a caveat that if “there is evidence of insufficient production capacity and availability of RFNBOs to the maritime sector, uneven geographical distribution or a too high price of those fuels, the subtarget provided for… shall not apply”.
Also this summer International Marine Organization UN (IMO) has adopted a revised plan to reduce emissions from international shipping. Before this regulator used SOx/NOx levels to stimulate demand for low carbon fuels such as diesel and LNG. New levels of ambition directing the 2023 IMO GHG Strategy are using four main targets.
1. Carbon Intensity of the Ship to decline through further improvement of the energy efficiency for new ships to review with the aim of strengthening the energy efficiency design requirements for ships.
2. Carbon Intensity of International Shipping to decline to reduce CO2 emissions per transport work, as an average across international shipping, by at least 40% by 2030, compared to 2008.
3. Uptake of zero or near-zero GHG emission technologies, fuels and/or energy sources to increase uptake of it to represent at least 5%, striving for 10%, of the energy used by international shipping by 2030.
4. GHG emissions from international shipping to reach n peak as soon as possible and to reach net-zero GHG emissions by or around, i.e. close to 2050, taking into account different national circumstances, whilst pursuing efforts towards phasing them out as called for in the Vision consistent with the long-term temperature goal set out in Article 2 of the Paris Agreement.
Also IMO adopted amendments to MARPOL Annex VI and Annex VI. The recent new regulations laid down by the IMO, contains measurable and reportable levels from each ship that recognize the convention. The EEDI (Energy Efficient Design Index), and the EEXI (Energy Efficiency Existing Ships Index) secure control of the released CO2 and represent the equivalent amount of CO2 that each ship emits, in relation to the amount of cargo carried per mile sailed. Under operation the EEOI (Energy Efficiency Operational Indicator), is explained as the annual fuel consumption divided by transported work. This can be considered as the annual average carbon intensity of a ship in real operational condition. Figures are calculated in a formula with relevant operational data, fuel types and qualities. It is now implemented onboard and managed by the Ship Energy Efficiency Management Plan (SEEMP). In the short term, bunker fuel should play a key role as RFNBOs have to compete with bio-fuels, diesel and LNG, which have gained status of low-carbon fuel.
At the same time, there is a reasoned discussion where market participants and industry experts express doubts about the feasibility of the stated plans. The discussion includes a wide range of scientific, engineering, economic and legal subtopics with interdependent influence. This review focuses only on the physical and chemical properties of hydrogen, its storage and utility as an energy carrier or direct fuel for the merchant fleet. It does not take into account many indirect factors that can significantly affect the future attractiveness of the solutions studied below. The majority cites data from the study “Challenges in the use of hydrogen for maritime applications”, Laurens Van Hoecke et al. 2021 https://pubs.rsc.org/en/content/articlelanding/2021/ee/d0ee01545h It serves enough comprehensive scientific and practical source on the observing topic. The forecast graphs are taken from the most recent report ”The future of maritime fuels” by an independent market participant, Lloyd’s Register, are used for two purposes – to illustrate the scale of supplyp/demand and presents as the one of mass attempts to predict the course of future marine decarbonisation.
When starting the review, it is useful to list the universal features to what makes a low-carbon marine fuel, and a handful that stand out are:
Cost
Energy density
Sustainability
Low-carbon intensity
Safety
Reliability
Ease of use
Compatibility with current fleet and infrastructure.
Hydrogen is gaining a lot of attention as a clean fuel, since it can be generated from renewable energy through electrolysis. In the foreseeable future other methods of water separation and hydrogen extraction at lower costs will obviously reach industrial scale. The potential of hydrogen as a universal energy carrier has no doubt. To use hydrogen as an on-board fuel, a number of demonstration projects have already been initiated, both using hydrogen fuel cells and by using hydrogen-adopted combustion engines.
The most crucial bottleneck with hydrogen as a fuel is likely not the production or the end-point use but rather the storage. By weight, hydrogen is an excellent energy carrier with a lower heating value (LHV) roughly 3 times that of diesel, 33 kW.h/kg compared to 11.39 kW.h/kg. However, hydrogen is such a light gas that under atmospheric conditions the total energy content is only 3.06 W.h/L whereas diesel contains 10.08 kW.h/L, roughly a difference of factor 3000. To deal with this low volumetric energy content at atmospheric conditions several technologies exist to concentrate hydrogen and make storage more efficient. These include: compression, liquefaction and storage in physical or chemical carriers.
Compressed hydrogen
The currently most developed and widely used method to store hydrogen is by compression. Toyota Mirai presents highest rate for compressed hydrogen hydrogen stored in TypeIV tank with pressures 70 MPa. It is only 0.81 kW.h of hydrogen energy; this is a hydrogen density of roughly 26 g//L. The energy penalty for the compression of hydrogen to such a high pressure is about 10% of the energy content of hydrogen (LHV). Compressed hydrogen is used as fuel for most existing ferry and riverboat projects using fuel cells and electric propulsion. Hydrogen can also be combusted in a diesel or a gas engine. The efficiency of fuel cells is almost twice that of combustion engines, but they place high demands on the purity of hydrogen and require regular replacement of expensive membranes. In combustion engines, hydrogen can be the sole fuel in these engines (mono fuel), or it can be used in a dual fuel system. The Belgian ship owner company CMB has developed the Hydroville, the first ever seaworthy passenger vessel that sails on dual-fuel hydrogen combustion engines. The ship owner more recently started a joined venture called BeHydro with an engine manufacturing company, ABC engines. This demonstrates more than anything the interest of ship owners in H2-fuelled engines, as well as their potential. Ships using fuel cells and hydrogen have also been demonstrated but to a smaller extent, examples are the Hydra-ship and the Duffy–Herreshoff water taxi and the Yacht XV 1. On the Scottish Orkney Islands an innovation project called HySeas III is using hydrogen fuel cell powered ships as ferries. A research project at the TU Berlin, investigated the use of hydrogen in a power system for a towboat, called the RiverCell-Elektra. Near Hamburg another ship, the ZemShip Alsterwasser, a small passenger vessel, was also used to showcase the potential of hydrogen as a shipping fuel. Other examples of passenger vessels that were fuelled by hydrogen in recent years include the Nemo H2 in Amsterdam, the Hornblower Hybrid a hydrogen powered high speed ferry operating near San Francisco. However, they have frequent access to refueling infrastructure. Extremely low bunkering speed makes this type of fuel unpromising for large vessels.
Liquid hydrogen
In addition to compression, hydrogen can also be stored in liquefied form. When cooled to -253 °C, hydrogen has a density of 70.8 kg/m3, which is about 775 times the density of gaseous hydrogen under atmospheric conditions. The energy density of liquid hydrogen is about 8.5 MJ compared to 36.3 MJ for diesel fuel, so liquid hydrogen requires a larger volume even without considering the thickness of the insulating material of liquid hydrogen tanks. The shipping industry is gaining experience with cryogenic fuels as liquefied natural gas (LNG) has gained attention as a lower carbon fuel. The challenges of using liquid hydrogen in shipping are greater than with LNG (the liquid is about 90 °C colder, density and specific heat capacity are lower). But much can be learnt and adopted from the processes of developing LNG as a fuel for the use of liquid hydrogen. Cryogenic liquid spills have high risks for the strength of a ship’s hull. They can cause cold fracture of steel, which can lead to hull damage. After a spill of cryogenic liquids, vapour clouds are formed which persist at very low temperatures. Due to the low temperatures, these vapour clouds can pose a serious hazard to people working on board the ship. Clouds of spilled cryogenic liquids contain large amounts of water vapour, so they are heavier than air and therefore do not disperse like gaseous fuels. This late effect increases the risk of suffocation and explosions. The biggest problem with liquid hydrogen refuelling is the low temperature at which the refuelling process takes place and the subsequent vaporisation of the liquid hydrogen. Special insulating materials are required to keep the heat flux into the tank as low as possible. According to NASA, during the launch of the space shuttle, 45% of the acquired liquid hydrogen was lost in the process chain, even before it got into the fuel tank of the shuttle. 12.6% was lost in transit from the trucks carrying the liquid hydrogen to a large storage tank, and 20.6% of the liquid hydrogen was lost from the on-site storage tank to the shuttle’s fuel tank. The fuel on the ship is usually divided into several smaller tanks, but the hydrogen will vaporise in each of these tanks to form partially filled hydrogen tanks. In each of these tanks, it is possible for the liquid hydrogen to churn, causing the stability of the vessel to be compromised. To date, there is no large-scale transport of liquid hydrogen in the maritime industry. At the present stage of the evolution, implantation onboard coastal trade smaller vessels are adapting LH2 feeding of standard fuel cell (FC) for electrical power production. This is presently a promising and evolved consumer of LH2 onboard this type and size of vessels. This consumption gives neither local nor global emission of pollution to air, the only rest product is depleted oxygen and water. Liquid hydrogen is not a common commodity that is transported around the world. Last year Kawasaki Heavy Industries launched the first prototype tanker vessel and terminal in Japan for the carriage of liquid hydrogen. Nevertheless, International Classification Societies have already published requirements for hydrogen-fuelled ships and issued several design and construction approvals. Liquid hydrogen looks like a promising fuel and hydrogen carrier, but not in the short term.
E-ammonia
Ammonia is globally one of the most industrially produced chemicals, with yearly production of over 150 million tons and an even further increased production is expected in the coming years. Gravimetric energy density is 22,5 MJ/Kg and a volumetric energy density of 12,7MJ/l. Ammonia is a crucial chemical in fertilizer production and results from combining hydrogen with nitrogen from air in an industrial process called the Haber–Bosch process. Produced from green hydrogen e-ammonia can serve both as a hydrogen carrier molecule and as a fuel in itself. However, ammonia has severe drawbacks when used in combustion engines; it has a narrow flammability range (15–28 vol%), a high auto-ignition temperature (651 °C) and a low laminar flame velocity (0.015 m2). High temperature fuel cells, or dedicated ammonia fuel cells could also be used to have ammonia as a fuel. Ammonia and liquid hydrogen also have similar energy efficiencies when comparing the storage requirements, which are about 10% lower than those of the other high-density liquid storage methods. Of these two, ammonia production has the lowest energy requirements, and since this process is fully developed already at an industrial scale, the production of green ammonia can serve as a good benchmark figure for the comparison of other hydrogen storage methods. Most global vessel operators excluding Maersk choose e-ammonia as a fuel for decarbonising their fleets. Meanwhile, Maersk is realizing plans to take a share of the ammonia bunkering market. retrofit package for the gradual rebuild of existing maritime vessels by 2025. Big Oil is pushing blue ammonia made with hydrogen produced from natural gas with CCUS.
AE-methanol
Methanol today is a petrochemical product and acts as a competitor to hydrogen and RFNBOs. It has an energy density of 15.8 MJ/LIt is favored by storage and use under normal conditions, high energy density, reduced emissions, widespread industrial use, the presence of infrastructure, proven handling and safety protocol, and also low toxicity for the environment. The disadvantages are high toxicity for humans and a low ignition threshold, which increase the risks of use. Storing methanol on board also offers an interesting advantage over other fuel types; due to its low toxicity to marine life methanol could be stored inside the double hulls of ships. Since methanol poses no danger to marine life there is no environmental risk However, there is renewable e-methanol, which falls into the group of hydrogen-based fuels. The color of methanol is determined by the H2 molecule source. Its geological origin must be legalized by CCUS technology, which is still controversial and does not have a convincingly successful history in the largest existing projects. It is worth noting that the largest logistics operator is betting on methanol. Maersk has launched its first container ship in September 2023. The vessel Laura Maersk has two propulsion systems for diesel and methanol. Company has ordered 24 methanol-fuelled vessels, which will be delivered in 2024-2027. The most famous case of methanol in the shipping industry is the Stena Germanica, a 1500 passenger ferry ship that has an especially adopted four stroke medium speed engine that uses methanol together with MGO as a pilot fuel.
Author Serge Astafurov
Image:MF Hydra, the world’s first ship sailing on liquid hydrogen. screenshot of video of Norled (https://goo.su/nV6sme)
