Hydrogen - how to stay mobile

Far less ideological is the question as to whether fuel cells or liquid fuels are better for propelling ships, trucks and aircrafts. In this instance, liquid fuels have clear advantages, thanks to their high energy density. After all, every ounce of weight counts, especially in aviation, where high performance over long operating times is a necessity.

In NAMOSYN, a project to develop synthetic fuels for sustainable transport, Fraunhofer ISE has teamed up with a host of partners. Tasks include the race to devise a cost-effective method of producing OMEs. This covers the entire value chain, starting with the feedstocks, CO₂ and H₂, and progressing to the development – including all the catalytic and separation processes – of a fuel that complies with current standards. In addition, the research consortium is investigating the in-engine use phase of OMEs, the compatibility of refueling infrastructure, the life cycle over the entire value chain and integration of these new fuels. “At Fraunhofer ISE, we’re looking at six alternative processes and evaluating them in terms of, for example, cost and carbon footprint,” says Dr. Achim Schaadt, head of department at Fraunhofer ISE. Vital to this work is a process simulation platform developed by the research team. This helps to identify the kind of process that would be required to produce a million metric tons of fuel a year. “There’s an interplay here between simulation and experimentation: we learn from the results achieved with small-scale plants and then feed these results into our simulation model,” explains Dr. Ouda Salem, head of the Power-to-Liquids group at Fraunhofer ISE. Another project partner is constructing a modular system with an output of 1 kilogram of OME an hour, while others are busy running engine tests. Incidentally, OMEs can be used not only as fuels but also as highly selective green solvents and CO2 sorbents.

Researchers at the Fraunhofer IKTS site in Hermsdorf, Thuringia, are currently working on a pioneering propulsion system for ships. Partners on the EU project HyMethShip include the shipbuilding company Meyer Werft. “Our method can cut emissions from shipping by as much as 97 percent,” says Dr. Benjamin Jäger from Fraunhofer IKTS, which is coor­dinating a key part of the project – methanol reforming. Such cuts are significant, not least because ships on the open seas still run on heavy fuel oil, which produces emissions such as sulfur compounds. Closer to shore, vessels switch over to die­sel, which in turn releases nitrogen oxides and CO₂ into the atmosphere. All this can be avoided with hydrogen-powered propulsion: sulfur compounds are eliminated, nitrogen oxides cut to almost zero, and any CO₂ is recycled rather than being emitted into the atmosphere along with other exhaust gases. The propulsion system functions as follows: when in dock, the ship refuels with methanol. Unlike hydrogen, methanol is easy to store and does not pose an environmental hazard – even if, in the worst case, the tank were to strike a leak and empty completely. Here, methanol serves as a hydrogen carrier. Onboard, it is reformed, together with water, in a reaction that produces both hydrogen and carbon dioxide. The hydrogen is separated off by means of a membrane and then combusted directly in the ship’s engines to provide propulsion. The reforming process yields more hydrogen than is stored in the methanol, since water also contains hydrogen. Meanwhile, the CO₂ produced in the reaction is stored in tanks until the ship docks. This is then pumped into onshore tanks and reused in methanol production. The heat required for the reforming process is provided by the ship’s engines, which further increases the overall efficiency of the propulsion system. Jäger’s team has been responsible for complete process and reactor design and has also developed the membranes for the system. At the same time, researchers at Graz University of Technology, another project partner, are currently constructing a demonstrator plant designed to supply upwards of 1.6 megawatts of hydrogen power. Initial trials are scheduled to begin early next year, with test operation to follow in the middle of 2021. In addition, the consortium plans to produce a design study for a Scandina­vian ferry fitted with a 20-megawatt propulsion system based on this innovative principle. By way of comparison, an oil tanker is equipped with engines delivering an output of 50 to 80 megawatts.