A pathway to decarbonize IHC's cable lay vessels with LNG

Annemarie Meijer-Buijs
Annemarie Meijer-Buijs
27 October 2021

Previously, we introduced the inter-array cable lay vessel concept in the offshore market using methanol as a potential clean fuel. More on the subject in our previous blog. Building on this topic, this blog discusses how liquefied natural gas (LNG) can be integrated into the IHC iCLV4000-22 design, and how this enables the decarbonization process of the offshore fleet in the upcoming decade.

Why LNG with fuel cells?

The transition to a climate-neutral society requires that we move away from fossil-based fuels. LNG is seen by many as a transition fuel, being true for fossil natural gas. However, renewable natural gas obtained from renewable energy, with carbon-capturing almost closes the life-cycle emissions.

With LNG being predominantly methane (CH4), it has the lowest carbon emission per unit of energy of all hydrocarbon and alcohol-based fuels. The origin is currently mostly fossil-based, but it may also be produced from biomass (liquefied biogas) and/or from renewable hydrogen combined with captured carbon dioxide (liquid synthetic gas). In combination with an internal combustion engine, LNG gives a significant reduction of nitrogen oxide (NOx), sulfur oxide (SOx), and particulate matter (PM) emissions, about 85%, 99%, and 95%, when compared to diesel. Despite these significant reductions, methane slip could diminish the greenhouse gas (GHG) emissions reduction on a life-cycle basis depending on the applied engine technology. Methane slip can be solved by selecting Solid Oxide Fuel Cell (SOFC) technology as the prime mover. Moreover, the cryogenic storage conditions of LNG could be utilized as a cold medium for future CO2 capturing systems aboard the CLV, although this is a topic excluded from this blog.

Our concept design

The IHC inter-array CLV lays power cables between wind turbines in offshore wind farms, being equipped for this purpose with a total capacity of 4000 ton cable payload in two under-deck basket carousels. This vessel is chosen as the renewable energy related cable lay task put pressure on the environmental impact of this activity. Seeing as wind farms generate renewable energy it is only fitting that the vessels at work in these wind farms also do not impact the environment.  The LNG-fueled CLV concept is designed for an autonomy of 30 days. That being said, LNG cannot be stored in the ship construction tanks like methanol or diesel. By placing a vertical LNG bi-lobe tank and two fuel cell rooms between the accommodation area and the carousels, as presented in the artist impression, it is possible to integrate the LNG fuel storage and prime mover. A battery room is placed adjacent to the thruster room to deal with dynamic power variations belonging to the vessel’s operation and operating limitations of the fuel cells.

Readiness of marine systems and fuel availability

Currently, some barriers limits the availability and operation of this concept CLV. Sufficient power density, costs, and the durability of the SOFC technology are the primary barriers. The power density defines the dimensions of the fuel cell room and thereby possibly having impact on the vessel size. High energy efficiencies make fuel cells very attractive compared to conventional / internal combustion engine technology, though the capacities of fuel cells cannot cover all maritime applications. The SOFC operates at high temperatures (500-1000°C) allowing for fuel reforming in the fuel cell and with enough waste heat for an external reformer if required. The operating conditions of these fuel cells require a steady-state operation, which is challenging in relation to the power variations of these work vessels. Research is currently ongoing worldwide to make the SOFC commercially viable for maritime application in the coming decade.

Where fossil-based LNG is unacceptable in the long term, we predict that LBG (liquefied biogas) and LSG (liquefied synthetic gas) will have a larger share of the gas mix. Synthetic gas can be produced with the methanation of green hydrogen combined with CO2 from carbon capturing, and more efficient technologies such as co-electrolysis are under development. Moreover, the existing and still expanding LNG infrastructure can be used for LBG and LSG as well. However, the origin of LBG is questioned concerning its feedstock in food and land use. Although production technologies are available, the price level of LSG is higher than LNG and LBG. Producing LSG requires a leap forwards in green hydrogen production and carbon-capturing technologies to lower its price level to become viable for the shipping industry. Until then, the concept is ready to use fossil LNG.

Royal IHC’s continued innovation activities

Royal IHC is taking the development of more alternative fueled vessel concepts further to find the most efficient and sustainable solutions for our customers. This LNG fueled inter-array cable lay vessel with solid oxide fuel cells is an example of this as it shows how emissions can be reduced, though effort is required to develop these systems towards commercially-off-the-shelf products. Want to join us on this journey? Let us know!