The EU-funded HyMethShip project developed a system that innovatively combined a membrane reactor, a CO2 capture system, a storage system for CO2 and methanol as well as a hydrogen-fueled combustion engine to power ships.
The top part of the graphic shows onshore methanol production. The bottom part shows how hydrogen for the engine is obtained from methanol in the reactor (blue arrow). The remaining carbon dioxide is stored in the tank and reused in onshore methanol production. © Fraunhofer
According to the European Environment Agency (EEA), maritime transport is responsible for more than 3% of the total carbon emissions in the European Union. In 2019 alone, emissions reached 144 million tonnes of CO2. Shipping has been one of the fastest-growing sources of greenhouse gas emissions for many years now due to the sharp rise in the trade volume. As a result, shipbuilders and operators around the world are seeking environmentally friendly alternatives to conventional ship engines powered by fuel oil or diesel.
In the HyMethShip project, researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS worked with a number of partners. The Large Engines Competence Center (LEC) in Graz, Austria, was responsible for the overall coordination of the project, while the startup SES-HyDepot e.U. in Innsbruck operated the small-scale testing facility to validate the underlying technical process.
In this concept, the ship is refueled with methanol at port. On board, hydrogen is obtained from the methanol through a steam reforming process and is used for ship propulsion.
The system’s technical centerpiece is the reactor. The methanol is mixed with water, then evaporated by applying heat and fed into the preheated reactor, where the mix of methanol and water is converted into hydrogen and CO2.
The integrated membranes in the module for a reactor separate the hydrogen from the carbon dioxide. © Fraunhofer
When it comes to hydrogen separation and reactor engineering, Fraunhofer IKTS is able to contribute its many years of experience in membrane process technology. The researchers at Fraunhofer developed a ceramic membrane coated with carbon. The hydrogen molecules escape through the extremely fine pores of the membrane, while the larger carbon dioxide gas molecules are retained. In this process, the hydrogen achieves a purity level of more than 90%.
It is then fed into the engine, which it drives by burning in a conventional combustion engine and generates absolutely no exhaust gases that are harmful to the climate.
The process concept used in the project includes two additional design elements that optimize the system. First, the waste heat from the engine is used to heat the reactor, significantly increasing the efficiency of the system. Second, the remaining carbon dioxide is returned to a fluid state downstream of the reactor and fed into the empty methanol tanks. When the ship arrives at port, the CO2 is fed into tanks and can then be used for the next methanol synthesis process.
Methanol is an ideal hydrogen carrier for shipping. Its energy density is twice as high as liquid hydrogen, so the on-board methanol tanks only need to be half the size. It can also be transported safely: Even if a tank leaks, there is no acute environmental risk.—Dr. Benjamin Jäger, IKTS
During development, one of the technical challenges was enlarging the ceramic membranes so that they could be used in the context of the propulsion required for ship engines. The researchers managed to scale the membrane from its original length of just 105 mm to 500 mm, enabling engine propulsion of up to 1 MW. The medium-term goal is to develop propulsion systems of 20 MW and above.
A zero-emission propulsion system would be ideal for ferries that sail fixed routes between two ports, with each port having its own methanol filling station. However, the technology may also be an appealing future solution for container ships and cruise ships.