04/11/2022

Some see hydrogen as the fuel of the future; for others, hydrogen technology is a fire hazard. Where does this fear come from?

Garrit Förster: It’s actually unfounded. Conventional service station logistics has its own risks, too, but they’re generally manageable. Hydrogen is an energy source and, like any energy source, has the potential for an uncontrolled energy release, i.e. a fire or even an explosion. We likely have special respect for hydrogen due to our collective memory of the Hindenburg disaster.

That was a long time ago. Can you briefly bring our younger readers up to speed?

Garrit Förster: The Hindenburg was a German airship, one of the two largest ever built in the world. In 1937, it burst into flames while landing at Lakehurst, New Jersey. 35 people lost their lives. At the time, German airships were filled with hydrogen as a lifting gas because of a lack of access to helium. It was considered harmless at the time: Hydrogen is about ten times lighter than air, so minor leaks from the hull float upward, not down into the passenger cabin, where people were busy smoking. Smoking was not yet looked down on and was considered acceptably safe. The engines, which could also potentially ignite the hydrogen, were also mounted below the hull. It is still not fully clear what led to the disaster during the landing. In any case, the accident put a temporary end to commercial aviation.

Hydrogen has long been used for technical purposes.

Garrit Förster: The gas was discovered and first produced in chemical experiments back in 1766. Hydrogen has been used for technical purposes since the early 20th century, including, as described, as a lifting gas for airships. However, fuel cell technology has also been around since the beginning of the 20th century.

But fuel cells were not rediscovered as a drive technology until just recently. Why did it take so long?

Garrit Förster: Well, this development is not really all that recent. Several mass transit projects are already being successfully tested or implemented. Berlin even had a few hydrogen-powered buses running back in the 1990s. And at Industriepark Höchst, we made it possible to refuel vehicles with hydrogen in front of the South Gate at the turn of the millennium. I believe there are several reasons why fuel cell drives have not really entered the public eye until recently:

• First, pure hydrogen is relatively expensive to produce – more expensive than other fuels, at least for now. At Industriepark Höchst, we have the advantage that hydrogen is a chemical industry byproduct and is produced in large quantities here. It can be stored in Infraserv Höchst's hydrogen center in both highly compressed and unpressurized form.
• Second, hydrogen-powered vehicles still lack a nationwide infrastructure. One will develop, but only in a piecemeal fashion at first. This is an area where we can play a significant pioneering role.

What would this role look like and where do we currently stand?

Garrit Förster: In addition to hydrogen-powered buses running at Industriepark Höchst and the hydrogen filling station in front of the South Gate – which is also open to outside users – Infraserv’s latest project is to fuel mass transit trains with hydrogen. After all, it is only logical to make hydrogen technology widely usable for rail transportation as well.

Before the project began, we integrated all the external partner companies as well as the technical departments at Infraserv and at our mass transit customers using an interface-based, goal-driven approach. The Process and Occupational Safety department’s involvement was particularly noteworthy. It was deeply and regularly involved in all the project routines from the beginning. It has thus always been an integral part of the overall project.

Seeing how you’re emphasizing that fact, is it reasonable to say that safety considerations play a special role in this project?

Garrit Förster: Of course. As I noted at the outset, the risks of hydrogen technology are absolutely manageable. But you have to actually manage them. Hydrogen has unique physical, chemical and thermodynamic properties whose safety impacts have to be considered during use. They include its widely known high flammability and explosiveness as well as characteristics that require careful consideration even though they may not be immediately recognizable as “safety relevant”.

How did you go about it?

Garrit Förster: Our first task was to mobilize existing knowledge from previous and similar projects and evaluate and draw on relevant existing rules and regulations. After all, Infraserv already had extensive experience in handling hydrogen, including storing, compressing and filling it into trailers for transportation on public roads.

We also had to analyze the impact on the project’s licensing status for the future Infraserv Group entity that will be operating the service station. Infraserv itself is classified under hazardous incident law as an upper-tier establishment. That means the project has no additional impact on the overall establishment.

However, it does significantly affect the operator of the service station and the peripheral facilities: By exceeding the IV quantity threshold of the 12th Federal Immission Control Regulation, the peripherals constitute safety-relevant elements of the establishment and are subject to all associated documentary obligations.

What aspects did you have to focus on?

Garrit Förster: Our interdisciplinary safety discussions focused on four safety issues specific to how hydrogen behaves.

1. The storage material: Hydrogen has a low density and high diffusion coefficient and so readily diffuses through materials (e.g. iron and even platinum).
2. The negative Joule-Thomson effect: When the pressure decreases, the temperature increases.
3. Gaseous hydrogen has a low energy density due to its low material density. This is addressed through high storage pressures – 350, 700 or 1,000 bar are common.
4. Explosion hazard: Hydrogen forms an ignitable atmosphere when combined with air.

The choice of materials turned out to pose few problems due to having many years of experience to draw on. It was also fairly straightforward to ensure that hydrogen-carrying plant components were sufficiently gas-tight by using suitable pipe connections and fittings.

So what was the real challenge?

Garrit Förster: It sounds very simple to fill hydrogen from a pressurized storage tank into the tank of a hydrogen-powered vehicle. However, we have to balance the customers’ justified requirements with necessary safety considerations: You want to refuel within a given time and achieve an effectively optimized tank fill level. If the filling parameters are not optimized, you won’t fully utilize the filling volume – in the best of cases. If worse comes to worst, you could impair the tank’s integrity. This is where we see the negative Joule-Thomson effect come into play: Steel tanks can be filled without any problems since they can conduct away heat effectively. However, composite tanks – like the low-weight tanks used in the vehicles we intend to refuel – are poor heat conductors. And that is the limiting factor. Hydrogen heats up during expansion, which manifests itself in rising temperatures. Since temperature and pressure are correlated in thermodynamic systems, you have to consider whether to allow the vehicle tank’s design pressure to be exceeded during refueling or, if too many safety factors come into play, whether to reduce the desired fill level and planned refueling time.

It took many experiments to collect enough data to make these decisions. “Filling curves” were calculated by varying the ambient temperature, initial pressure (residual pressure in the vehicle’s tank), pressure level of the hydrogen storage tank, increase in temperature over time and reported filling time. This information was then stored in the refueling equipment’s control system.

Also, as I mentioned earlier, the hydrogen is kept in storage tanks at different pressure levels. You never want to mix up tanks during the filling and removal processes. To prevent this, we integrated plausibility queries in the control system and implemented “hardware” solutions such as adapters that are specific to each pressure level.

Were there any other challenges?

Garrit Förster: Absolutely. You obviously have to ensure a high security of supply for hydrogen. We have a locational advantage in that hydrogen is a byproduct of production at Industriepark Höchst. However, that comes nowhere near a nationwide infrastructure that can enable ubiquitous hydrogen availability. That’s why we are also testing various alternative and complementary ways of generating and supplying hydrogen in our integrated network at Industriepark Höchst. They currently include:

• Unpressurized on-site production and storage of hydrogen
• Compression and filling into trailer vehicles
• Storage in pressure tanks at different pressure levels
• PEM electrolysis for producing hydrogen in finished modules
• Alternative fueling station on the rail line outside Industriepark Höchst

The proton exchange membrane (PEM) process uses electrolysis to produce hydrogen from water. This process, packaged into pre-assembled ready-made modules, harbors considerable potential to make hydrogen available in places that would otherwise been out of reach for hydrogen due to an unfavorable energy balance or unsurmountable logistics challenges. It essentially meets the initial requirements for rolling out a decentralized supply of hydrogen. “Green hydrogen”, combined with renewable energy, could thus be made available through a nationwide infrastructure.

Your personal conclusion?

Garrit Förster: Our hydrogen train project has made several key advances in putting our experience in hydrogen production, storage and distribution into practice at the requisite scale in a future-proof manner. It represents a valuable contribution to making the widespread use of hydrogen as a transportation fuel economically and ecologically sustainable and thus developing an attractive alternative to fossil fuels in the future.

Infraserv Höchst will draw on the knowledge it has gained to continue acting as a highly capable driver of the further development of hydrogen technology.

Mr. Förster, thank you very much for talking with us today!