According to CAI International, “Since the 1960’s, Heavy Fuel Oil (HFO) has been the king of shipping fuels. A byproduct of crude oil, HFO expels 35,000 ppm into the environment and accounts for 8% of the sulfuric dioxide in the air. The arrival of the IMO 2020 fuel regulation in 2019 signaled a formal move toward alternatives to HFO like biodiesel, hydrogen, methanol, and even battery-powered ships. While each of these has been pursued incrementally in the past, the breadth and urgency of a regulated shift is changing the dynamic. Domestic shippers, such as retailers and raw material manufacturers, are tending towards low-sulfur diesel oil alternatives, whereas ocean liner companies are embracing exhaust-cleaning systems known as scrubbers. Even during times of lower fuel demand, we can anticipate ongoing forward motion in alternative fuel adoption.“ (HFO: End of an Era, Hellenic Shipping News, 6-June-2020)
Almost 60% of the respondents in an ABS Survey said they consider Hydrogen and Ammonia as the most attractive fuel choices in the long-term. The survey also reveals that nearly 2/3 of shipowners have no decarbonization strategy. 70% of the respondents selected fuels in the light gas pathway, which includes LNG in the short term, and Hydrogen as a future solution, as the most likely to be adopted. “It is clear that the industry views both Hydrogen and Ammonia as the long-term destination but sees LNG as having a big role to play in addressing the regulatory challenge immediately in front of us,” stated Georgios Plevrakis, Director, ABS Global Sustainability.
A new paper highlights two potential low-emission fuels for long distance international shipping: Hydrogen (H2) and Ammonia (NH3). The January 2020 paper by McKinlay, Turnock, and Hudson titled, “A Comparison of Hydrogen and Ammonia for Future Long Distance Shipping Fuels,” showed findings based on LNG tanker data that Hydrogen and Ammonia are potential future marine fuels for consideration. Using 3-year data, estimates were made for energy requirements based on delivered power, with the maximum consumption for a single voyage at 9270 MWh. Calculations were made for the required volume, mass, and variable cost for several types of fuel such as: LNG, Diesel (HFO), Hydrogen gas, Hydrogen liquid, Metal Hydride, Ammonia, Methanol, and Lithium-ion Batteries.
Hydrogen has significantly higher gravitational energy density than the other fuel options, requiring lesser fuel. The major criticism against Hydrogen as a fuel is the low volumetric energy density. Hydrogen price is also considerably higher than the other fuel options. However, since a vessel will purchase a large quantity of Hydrogen, the commercial price will be lower. Electrolysers can reverse fuel cells and produce clean Hydrogen using only water and electricity. The cost of Hydrogen production is the electricity price. Projections show the cost of electrolysis will fall to 57.6 p/kg by 2025. The energy required to produce 1 kg of Hydrogen will fall from 51 kWh to 44.7 kWh by 2025. Therefore, to produce a delivered power of 9270 MWh, assuming 60% efficiency, about 464000 kg of Hydrogen is required. This equates to a fixed cost of £267,200 plus electricity cost.
Ammonia has several desirable attributes. Its volumetric energy density is similar to LNG, and theoretically increasing the fuel oil tank to 119% with Ammonia could power the tanker for any journey. Ammonia is carbon free, and Ammonia’s price, despite being 3-4 times higher than currently used fuels, is significantly more competitive than Hydrogen and Lithium-ion Batteries. However, the weight of Ammonia is a concern. Powering a tanker from pure Ammonia increases the vessel’s total mass by 2.74% compared to LNG when refueling. Its excess weight increases the overall ship mass by 0.3%-3.7%, decreasing ship performance at sea.
Lithium-ion Batteries require significantly added space and weight considerations. As to cost, the initial capital cost for a battery capacity of 9758 MWh is estimated at £3.9 billion (502 $/kWh). Due a significant increase in global Lithium-ion production, projections show Battery price will drop between 140-620 $/kWh by 2030. However, this lower value would still result in a high cost of £1.04 billion, higher than the alternatives. Recharging time is a big concern. Tesla supercharger’s power rating is 240 kW, therefore, it would take 1000 superchargers 40.7 hours to recharge 9758 MWh, and the local distribution network may struggle to meet this demand. Test results show that using Lithium-ion Batteries to provide the primary power supply for long distance shipping operations is not a viable option. The Batteries would rather be useful for short distance small ferries, or as part of a hybrid power management system, with fuel cells.
CONCLUSIONS. It appears that the shipping industry has no choice but to move away from oil and gas based fuels mainly due to environmental pressures. Decarbonization of the shipping industry is a necessary step to greatly reduce vessel emissions.
Hydrogen (H2) has a low volumetric energy density and this is cited as a major barrier to becoming a mainstream fuel source. “However, the study suggests that volume requirements of either pressurized gas or liquid Hydrogen are not sufficiently high to be considered infeasible.” Hydrogen is high-priced but due to the advancement of electrolysis technology and the decreasing cost of renewable power, it is projected that clean Hydrogen could be competitively priced by 2025. Hydrogen also has significantly high gravitational energy density, and thus requires less fuel.
Metal Hydride requires significantly less volume than other Hydrogen storage methods, and the study concluded that Metal Hydride is not a viable option for transportation application.
Ammonia (NH3) has advantages over Hydrogen, such as less space required for the same energy content, and more competitive current market prices. However, Ammonia has relatively low gravitational energy density and thus requires relatively more fuel. An increase in the vessel’s weight has a detrimental effect on a ship’s performance. Therefore, more energy would be required to complete the same distance.
Methanol (CH3OH) shares similar attributes with Ammonia since their combustion can still produce NOx and carbon emissions, but Methanol is considered the less desirable option.
Lithium-ion Batteries are unlikely to meet the size, weight, and price requirements for long distance shipping. Batteries are bulky, heavy, and costly for long distance international shipping.
Overall, the study finds that Hydrogen and Ammonia show more promising attributes than the other fuel sources, but have significant engineering challenges to meet for viability as clean marine fuels in the foreseeable future for long haul shipping.
That said, it is therefore likely that in the near and medium-term, most green shipowners will choose LNG until Hydrogen, Ammonia, and Methanol have hurdled the engineering tests and become clean marine fuel for long-haul shipping in the future.
