The choice for alternative fuel depends on the mission profile. Global carbon emissions must be cut significantly in the years to come, including emissions created by the shipping industry. Most of the emissions created by this industry originate from fuel consumption. For all vessel types, it is important to understand and evaluate the operational aspects of the vessel versus the consequences of the choice of fuel types.
The picture is complex. How can you make the best choice?
Designing sustainable vessels, one has to consider both the reduction of energy consumption, the use of greener energy sources and material, more effective vessel operations and the smarter use of energy onboard.
In this article, we are focusing on the use of greener energy sources.
Use of greener energy sources
As ship designers, we evaluate alternative fuels together with our clients and design the power system of the vessel. Studies of power need, range, sailing route and availability of fuel, the realisation timeline combined with the availability and readiness of equipment and technology, the approval process, the customer's expectations and strategies are all aspects that the ship designers will conduct together with the customer. In particular, the volume and energy intensity of the different fuels must be evaluated. This might drive vessel size and operational range/endurance.
This article is based on one of Ulstein's studies on alternative fuels using the typical mission profile of heavy-lift installation vessels used for the foundation installation of offshore wind turbines.
Comparison of different alternative fuels
The setup below is divided into Emissions, and the benefits and/or downsides regarding Safety (flammability and toxicity) and Maturity (technologically, cost of energy and bunkering availability).
Marine Diesel Oil (MDO) is today's widespread choice, but it is also yesterday's choice. The carbon footprint is too large to continue using this fuel as the sole choice for the future.
Looking into alternatives, it is hard to spot which fuel will be the sound choice. There is no single solution viable for all vessel types, and evaluations need to be done of earlier mentioned criteria for each project. Looking into possible future needs and scenarios is also an important part of this.
Alternative fuel study for heavy lift installation vessel design
A heavy-lift installation vessel is a sizeable asset, driven by stability and deck area requirements. Because of its dimensions and layout, there are possibilities to identify available spaces in the vessel to install dedicated tanks for alternative fuels.
Studying the typical mission profile for one of our heavy lift installation vessel designs (the ULSTEIN HX118), we find how much energy is needed for the typical operational modes, and the duration of each mode.
Noting that a typical mission cycle in this example lasts for approx. 14 days and having implemented an alternative fuel tank in this vessel, we can now look at the various fuel options, and the usage of the fuel tank (numbers in green/red).
From the table above it can be concluded that all alternative fuels are theoretically feasible for the Heavy Lift Vessel (if hydrogen is assumed as liquid storage). The calculated mass of the alternative fuels is significant, but controllable, within the loading conditions of the vessel; the expected loss in deadweight capacity is negligible.
The reference full-electric vessel with 14 days operation would require a very large amount of battery: impractical from both weight and cost perspective (very expensive ~200M$). For short periods, full-electric battery operations can be feasible.
But there are other aspects that are not so straightforward. For many of the alternative fuels considered by the marine industry, regulations (and therefore readily available and approved technology) are not yet in place.
LNG:
The most low-hanging fruit with respect to regulations is LNG, where also bunkering infrastructure is currently getting sufficiently in place. The downside is that it still is a fossil fuel.
METHANOL/AMMONIA:
For methanol and ammonia, although regulations are now available, they are still considered as alternative design processes which require risk-based case-to-case approval processes to be performed.
HYDROGEN:
For hydrogen, regulations are not yet set for IMO regulated vessels, and the alternative design process will be even more time-consuming.
When it comes to evaluating the fuels, the real emission reduction is necessary to assess, exemplified in the figure below.
CO2 emissions for a typical mission cycle:
Green = produced from renewable energy and including carbon recapture.
Brown = produced from fossil fuels.
Hydrogen and ammonia result in no or very low local emissions. But for the global emissions, the methanol and hydrogen/ammonia must be green to result in very low emissions. Brown/grey methanol and black hydrogen/ammonia have higher total global emissions than any of the other fuels investigated.
A clear path has not yet been laid for hydrogen, ammonia and methanol. Most likely, only one will be adopted by the market majority, the others will most likely stay in the niche market.
For all the different fuel types, it requires that both the ship and its design, the integrated equipment, systems and technologies, approval of systems, production and availability of the fuel itself, logistics and bunkering are in place. On top of this comes the commercial aspects.
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