Alternative fuels such as green methanol are CO2-neutral and can ensure that climate targets are met in shipping. A TU joint project is researching their practicality in detail.
Whether tanker, container ship or cruise liner: Up to now, commercial shipping has been using fossil and mostly polluted heavy fuel oil. This damages the environment and, above all, the climate. The use of exhaust gas purification systems such as scrubbers or catalytic converters can already effectively minimize sulfur, nitrogen oxide or soot emissions on board ships. In order to achieve the climate targets in the transport sector, climate-damaging emissions such as CO2 must also be significantly reduced. Climate-neutral energy sources are therefore needed on ships. These energy sources could be created using power-to-X processes. These are ways of producing various synthetic fuels that are CO2-neutral in the overall balance because the carbon was previously removed from the atmosphere for synthesis. In the E2-Fuels joint research project, the marine engineering group is investigating the use of methanol and oxymethylene ether (OME) as maritime fuels. The focus is on the port infrastructure and bunker interface required on land, as well as on the fuel system on board.
Renewable and synthetic fuel
Thilo Jürgens-Tatje is in charge of the E2-Fuels project in marine engineering. He would like to influence the moving away from diesel or fossil gas and toward climate-neutral propulsion fuels that are suitable for practical use on board. "Electrification as with cars is often not possible; corresponding batteries would be too large and too heavy. The only exceptions could be smaller ferries used for short distances. Therefore, you need hydrogen as a feedstock, which is generated from renewable electricity from wind and sun," the scientist explains. But the use of hydrogen as a marine fuel entails some disadvantages. For example, extreme pressures or temperatures close to absolute zero of minus 273 degrees are required for storage. Therefore, a conversion step to a mobile synthetic fuel is still necessary. This process is called power-to-X. Methanol has already been used on a small scale as a marine fuel for some time, for example, on tankers or ferries. It is a liquid alcohol that can be transported easily. And it has another positive property: In the event of an accident, there is no need to fear a dangerous oil slick; the methanol simply dissolves in the water. It's like tipping a bottle of schnapps into a full bathtub. But there is, of course, a catch: CO2 is needed for production, and this is also released again when the methanol is burned in the engine. In principle, this is not a problem; cement plants or waste incineration plants emit a lot of the unloved gas anyway. Jürgens-Tatje's goal, however, is to make the entire process carbon-neutral. "You could use CO2 from biogas plants. So there would be nothing standing in the way of the closed-loop system.
The big challenge is to produce enough methanol from green hydrogen and green electricity, respectively. To run the whole process economically, people are now relying on hydrogen produced near the equator with the help of solar energy and brought to us by ship," explains the shipbuilder. "Electricity is simply too expensive here in the long term. Nevertheless, we need pilot plants in Europe, too, to solve the chicken-and-egg problem."
But how does the fuel get on board? The TU scientists have developed a solution for that, too: "Refueling terminals where container or cruise ships pick up their fuel are not practical. It simply takes too long. So they investigated the current refueling system, in which so-called bunker ships ensure that the required diesel fuels are transported from large tank facilities on land to the respective ships. The actual refueling then takes place "ship-to-ship" while the ship is taking on or delivering cargo. "Our investigations have shown that the conversion of a conventional bunker vessel is technically and economically feasible. There are also areas in the port that are perfectly suitable for a tank farm on land," Jürgens-Tatje said.
The trick with ignition
Today's diesel engines have to be adapted for the use of methanol. That's because methanol must be ignited like gasoline in order to burn. Unlike diesel, which, if appropriately compressed, will self-ignite. "In large marine engines, however, ignition cannot take place via a spark plug as in a motor vehicle engine. Instead, a small amount of diesel is injected at the right moment with an injector to ignite the methanol," says supervisor Jürgens-Tatje. Project partner MAN has tested an injector designed for this purpose on a test engine. "This is a breakthrough. Soon, conventional diesel engines can be converted relatively easily so that they can also run on methanol," explains the TU scientist. And so methanol could become established as an energy source. The Danish shipping company Maersk is leading the way: It has already ordered 12 new container ships powered by methanol.
Thilo Jürgens-Tatje is a member of the marine engineering group and is responsible for the theory and practice of the E2Fuels project.