STORY Commercial Marine

Technology turnaround: Which fuel for the tugboats of the future?

Posted on December 22, 2021 by Lucie Maluck, Images by Rolls-Royce Power Systems

mtu experts from Rolls-Royce show the way forward to sustainable tugboat operation.
Friedrichshafen, Germany
Will it be hydrogen, methanol, synthetic diesel or ammonia? So far, the fuel scenario of the future has been difficult to estimate. But slowly, the picture is starting to come into focus. One thing is clear however: with IMO rules stipulating that by 2050, CO2 emissions in shipping have to be 50% lower than in 2018, the call is for new fuels, and with them new propulsion concepts. mtu experts at Rolls-Royce have now come up with various configurations for tugboats.  

The fuels of the future will be manufactured using a method known as Power-to-X. The basic principle is as follows: Renewable energy sources such as wind or solar are used to generate electrical power. This is used in electrolysis, in which water is broken down into its components (hydrogen and oxygen). The hydrogen part can be directly used as a fuel or synthesized to produce other fuels such as e-Methane, e-Methanol and E-diesel. If the CO2 needed to synthesize these fuels is derived from the atmosphere or biomass, their combustion can be said to be carbon-neutral because no additional CO2 is being released. Hence they are set to play a decisive role in meeting the IMO's climate targets.

Strong need for dialog in the tech revolution

But which fuel is most suited to marine propulsion and in which applications? “We’ve been talking to our customers about this in detail over the last few months and have now developed various propulsion concepts for tugs,” said Peter Gommeringer, marine applications engineer specializing in new technologies at Rolls-Royce Power Systems. The concepts are based on a hypothetical tugboat of 29m length and 13m width that requires 5,000 kW of driving power and 100 kVA for on-board power.  

Practical advantages of methanol for tugs    

One solution currently favored by many customers is the methanol internal combustion engine. The energy density of methanol is high compared with other sustainable fuels, and since it comes in liquid form, it is convenient to store and tank at ambient temperatures. In many cases, it is even possible to use existing infrastructures with methanol. Methanol tanks can be flexibly accommodated within vessels and demand much fewer safety measures than hydrogen or ammonia.   Due to the safety aspect and fewer complications, the lower investment cost of the methanol tank system presents another advantage.     

Innovative battery/fuel cell combinations

With another concept, the hypothetical tugboat is powered by a combination of fuel cells and batteries, whereby the energy is generated in hydrogen fuel cells and temporarily stored in the batteries. The energy source is liquid hydrogen, which offers high energy density and is stored in a cylindrical tank below deck. “The big advantage that a hydrogen-powered fuel cell has over an internal combustion engine is that it does not generate harmful emissions – neither CO2 nor nitrous gases, nor particulates.” explained Benjamin Oszfolk, fuel cell expert from the mtu PowerLab at Rolls-Royce Power Systems.    

The fuel cell/battery concept offers great flexibility, which is one of its main advantages over the internal combustion engine. With the latter, the driving power needed is delivered solely by the engines, whose output depends on the maximum power requirement of the tug.   Fuel cells combined with batteries, however, open new possibilities. The amount of energy placed at disposal can be tuned to the tug's power requirement at any one time, thereby providing scope to save fuel. If the tugboat mode does not require maximum power or speed, only the number of fuel cells needed is actually switched on. If maximum power output is called for because the tugboat has to travel at high speed or is in tugging mode, all fuel cells are switched on. The energy stored in the batteries will also be used. “That gives our experts the scope to work out the ideal combination of fuel cells and batteries for each application and thus deliver customized drive system solutions,” explained Oszfolk.    

Experts from Rolls-Royce Power Systems know how to calculate the ideal combination of fuel cells and batteries so that a tugboat is operated with maximum efficiency.

Methanol fuel cells

Engineers at Rolls-Royce Power Systems are also considering the use of methanol for fuel cells. Using a ‘methanol reformer’, hydrogen is produced from the methanol which is then used in the fuel cell to generate power. The big advantage of this concept is the fact that methanol has a much higher energy density than hydrogen and therefore permits fuel tanks of more compact dimensions.    

Concepts based on other alternative energy carriers

Experts are even contemplating an electric-only tug in which the power is taken solely from batteries and not generated by on-board fuel cells. “The electric-only system scores the most points for low operating costs,” pointed out Gommeringer, further explaining that it does suffer from a major disadvantage – the low energy density of the batteries, which leads to a very short range. “Electrically powered harbor tugs are certainly an option to be considered, but they will not be able to cover long distances,” he concluded.

The task with each concept is to find the right balance in terms of range, operating and procurement costs and technical feasibility.

Peter Gommeringer, Applications Engineer for new technologies at Rolls-Royce Power Systems

In the near future, mtu experts at Rolls-Royce Power Systems will be engaging with operators, shipyards and owners to discuss these and other concepts in more detail and establish which will be the most efficacious. A concrete study project is currently underway in collaboration with the renowned marine engineering company Robert Allan and towage specialist Svitzer. Other studies are to follow: “The task with each concept is find the right balance in terms of range, operating and procurement costs and technical feasibility,” explained Gommeringer, who is clearly inspired by his mission. “This is a steep challenge, but it's also an opportunity for us to help drive the energy turnaround in the maritime industry and change the face of shipping for good with our innovative propulsion concepts.”  

Commercial Marine

mtu power for new harbor tugs

by Lucie Maluck

Small, but incredibly powerful: Two new harbour tugs soon to tow even the largest container ships into ports in Peru.

Read more

Hydrogen electrolysis on a grand scale

by Wolfgang Boller

Rolls-Royce now developing mtu hydrogen electrolyzer and investing in Hoeller Electrolyzer to produce low-cost hydrogen using green electricity.

Read more

Power Generation

Hydrogen-based energy for the port logistics of the future

by Peter Thomas

Duisburg port is set to become the first inland container terminal in Europe to achieve climate neutrality – thanks to mtu hydrogen-based power solutions.

Read more

Power Generation

Helping data centers towards net-zero

by Silke Rockenstein

Are we on the way to climate-neutral data centers? Experts from Rolls-Royce Power Systems provide an outlook.

Read more

Connect with Us

Customer Assistance Center

We are here to take your Sales & Service questions around the clock, 365 days a year.

Read more

Sales & Service Locator

Find your local partner for Sales & Service.

Read more

mtu Stories

Reports and interviews about mtu products and solutions.

Read more