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The shipping industry faces increasing pressure to reduce emissions and meet the International Maritime Organization’s goal of attaining net-zero greenhouse gas emissions from international shipping by 2050. One practical solution to reducing emissions is using alternative fuels like hydrogen-enriched compressed natural gas (HCNG). Currently, no studies are available investigating the potential of HCNG for ship main engines in the maritime industry.

This project evaluates the feasibility of HCNG as an alternative to conventional maritime fuels in short-sea shipping, focusing on technical and economic aspects. It examines HCNG’s potential for CO₂ emission reduction to meet emission regulations and the required modifications for logistics and storage of hydrogen and methane in next-generation ferries. The assessment includes various blending ratios of H₂/CH₄ and suitable locations (on board or at the port) for blending and storage within existing infrastructure.

This project uses the current operations of so-called roll-on roll-off passenger vessel on the Gotland route between the Swedish East Coast and Gotland Island, along with the corresponding port infrastructure, as a case study. The technical assessment explores various blending ratios (H₂/CH₄) and storage opportunities, both in port and on board, addressing their characteristics and challenges. The economic assessment estimates only the costs of the required amount of fuel for different blending ratios (H₂/CH₄) for the case study vessel and routes. The economic assessment gives an idea of how the fuel cost (based on the fuel choice) can affect the economy of the system. Other technical aspects (hydrogen management and logistics, hydrogen facilities and injection systems, etc. are not included as they were out of the scope of the project. However, the economic assessment based on fuel price will provide a sufficient insight into the economic aspects for the stakeholders.

The project also focuses largely on the environmental and climate benefits (performance) of the use of green hydrogen mixed with methane (at different ratios) as a fuel for shipping (using the case study). The environmental analysis focuses on the emission of CO₂ equivalent, in line with the goal of replacing methane with hydrogen as a fuel. As an additionality, the environmental assessment considered the application of renewable methane too i.e., mixing natural gas (fossil methane), renewable methane, and hydrogen with the aim of both cutting down the natural gas share and CO₂ emissions. This goes another step forward where different sources of renewable methane are considered to give a more comprehensive overview over the resulting emissions when renewable methane is used as a fuel.

It has been concluded that the decarbonization potential of HCNG within the investigated blending ratios is marginal due to the decrease in volumetric energy density with higher hydrogen concentrations, necessitating larger fuel volumes to match the energy content of the fuel that is currently used, liquified natural gas (LNG).

Additionally, the technical and economic analysis indicates that currently HCNG may not be a viable option as an alternative to LNG.  This is attributed to the high price of green hydrogen, technical complexity of hydrogen transportation and storage, lack of commercially mature technology. Major cost cut down of green hydrogen and robust regulations against CO₂ emission could potentially pave the way for applications of HCNG. An alternative short-medium term solution would be to use renewable methane in existing infrastructure and vessels.

Regarding the CO₂ emission, while the hydrogen source remains fixed, the choice of methane significantly affects emissions. Fossil-based methane results in the highest emissions, averaging annual 225,000 tons CO₂ equivalent, followed by renewable methane at 180,000 tons. The lowest emissions, annual 64,000 tons CO₂ equivalent, are achieved with bio-methane from manure and biowaste. This highlights that methane source, not just blending ratio, plays a crucial role in emission performance.