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The recent past shows that we cannot get around hydrogen if we want to get to grips with some of the most pressing problems facing humanity. The lightest and most abundant element in the universe has recently emerged more clearly than ever as a key factor in the decarbonisation of the economy and transport - provided the gas can be produced without emitting CO2. But the road to the economic use of green hydrogen is long and rocky, and it is full of technical challenges. For example, safe automated processes require, among other things, specific sensors and, above all, explosion-proof components. These are areas in which the Mannheim-based company Pepperl+Fuchs has always been at home.

And why hydrogen in particular?

Since hydrogen (H) is a very reactive gas that combines preferentially with oxygen (O), by far the largest part of it is bound in water (H2O). And while energy is released when hydrogen and oxygen chemically combine, the same energy is needed to separate them again. "This describes the essential reason why hydrogen is a key element for climate-neutral energy," explains Wolfgang Weber, Global Industry Manager at Pepperl+Fuchs. "We can store green energy by using it to split the H2O molecule. The hydrogen can be temporarily stored in tanks and transported through pipes. When the energy is released again during combustion, only water vapour is produced as exhaust gas. In a fuel cell, electricity can even be generated directly from the oxidation reaction. There are also other climate-friendly uses. For example, it can be used instead of coal to reduce the molten metal in order to produce 'green' steel. The universal element is universally applicable."

From grey to green

At present, however, most of the hydrogen used is not green but grey. That is, it is produced by processes that release CO2. But the green hydrogen economy is being pushed forward with increasing pressure. All over the world, corresponding projects are being promoted with government funds. Large industrial nations like Japan, but also countries like Saudi Arabia, which owe their prosperity almost exclusively to fossil resources, have long been committed to this path. Business is also getting involved on a large scale. Many large corporations have now set their course in the direction of hydrogen.

The principle for obtaining green hydrogen, i.e. electrolysis, is basically simple: you apply a voltage in a water-filled container and the hydrogen moves to the negatively charged pole and the oxygen to the positively charged pole. On a large scale, of course, things are a bit more complex, which is why numerous people around the world are researching to optimise the processes and reduce the costs. It is therefore only a matter of time before green hydrogen can be produced on a large scale and at marketable costs.

It is not called oxyhydrogen for nothing!

What sounds so simple, however, also involves certain risks. Because the most important property of the gas - its enormous reactivity - makes the electrolyser and its periphery a plant with a risk of explosion. As a result, all components involved in storage and transport must be absolutely tight to prevent uncontrolled leakage of the gas. In addition, numerous safety precautions must be taken in the so-called Ex areas, which are specified by laws and standards. "One can apply the same principles that apply to the handling of natural gas. In terms of explosion risk, hydrogen behaves in a similar way to methane, so explosion protection for both gases basically works in the same way," emphasises sales engineer Thomas Schnepf, an expert in this field of application. "Pepperl+Fuchs has a broad portfolio of connection technology components for safe signal transmission in Ex zones. These include intrinsically safe barriers, signal isolators, remote I/O systems and intrinsically safe mobile devices. Our proven technology also works safely and reliably with hydrogen."

Sensors for optimal yield

However, before green hydrogen can be used, green energy must first be produced to generate it. The most important sources for this are known: Hydropower, the sun and, in our latitudes, especially wind. According to a report by the Global Wind Energy Council, wind turbines with a total global capacity of around 740 gigawatts had been installed by the end of 2020. However, many of these wind turbines are located in inaccessible places, mostly offshore, which makes maintenance and adjustment work difficult. To optimise the energy yield, however, the rotor blades must always be positioned precisely into the wind and the angles must be continuously adjusted. In order to ensure the operation of these wind turbines for as long as possible without maintenance and yet effectively, various reliable sensors are required. Encoders, acceleration sensors, vibration sensors and inductive sensors record speed, acceleration and axis position and thus provide the basis for precise control and condition monitoring of the wind turbines.

But there is also a need for measuring devices and sensors for positioning tasks in solar thermal power plants, for example to allow moving mirrors to follow the position of the sun. "Pepperl+Fuchs has a wide range of sensors that are needed for green power generation," explains Wolfgang Weber. "The same applies to the other end of the exploitation chain, such as hydrogen filling stations."

Diversification in the field of electric mobility

Compared to electric charging stations, the number of new installations of hydrogen filling stations is still in its infancy - but their spread is gradually picking up speed. "In heavy-duty transport, battery-based e-mobility can hardly be the optimal solution," Wolfgang Weber explains the background. "Batteries like those in electric cars would simply be too big and too heavy for sensible use there, without being able to guarantee the necessary range. Hydrogen offers a much greater energy capacity in terms of weight and volume, quite comparable to diesel or paraffin." But it is not only well-known truck manufacturers who are working on the development of hydrogen drives; shipbuilding and even the aircraft industry have recognised the signs of the times. In rail transport, they are even one step further: the first hydrogen locomotives are about to be deployed in Germany to replace the previous diesel drives in regular service on non-electrified routes.

Once to the charging station and back - to the tap

One advantage of hydrogen over battery-powered electromobility is particularly obvious: the refuelling process is as quick as with previous fossil fuels, and there is no need for the time-consuming charging process. However, the special properties of the gas require a tank technology that has been adapted in many areas, which, among other things, reliably prevents the super-small molecules from escaping. The refuelling process itself is also somewhat different from the usual and requires more attention, at least initially. In order to nevertheless guide tank customers intuitively through the process, Pepperl+Fuchs offers high-resolution monitors from the VisuNet FLX series, which provide good visibility even in very bright ambient conditions and are suitable for protected outdoor use in hazardous areas. Inductive sensors from the Kurpfälzer company are to provide even more safety during the refuelling process. They monitor whether the connectable H2 filling nozzle, called a dispenser, is firmly and tightly connected to the filler opening. Any collisions with the tank system are detected by acceleration sensors, which also trigger an emergency shutdown if necessary. And the integrated RFID system is supposed to enable automatic accounting of the refuelling process. Together, all these Pepperl+Fuchs solutions should ensure a safe and convenient refuelling experience.

Decarbonisation on a grand scale

In the industrial sector, hydrogen will be able to unfold its beneficial, i.e. decarbonising, effect primarily where high burner capacities are required or the use of a reductive element is a prerequisite. The cement industry alone produces around 2.8 billion tonnes of CO2 emissions worldwide with its kilns. This corresponds to about eight percent of man-made greenhouse gases, which could be largely saved by using green hydrogen as an energy carrier. Comparable figures apply to steam crackers in the petrochemical industry or furnaces in the metal industry and glass and porcelain production. In the steel industry's so-called direct reduction process, hydrogen can also replace the carbon used to remove oxygen from iron ore. Instead of carbon dioxide, only mundane water is released in this crucial step.

Natural gas pipelines become hydrogen pipelines

Of course, such processes require particularly large quantities of hydrogen, which are preferably delivered by tanker or directly via pipeline. "You can use existing natural gas pipelines for this," explains Wolfgang Weber. "A certain percentage of hydrogen is contained in the natural gas anyway, and you can add it up to an additional 60 per cent. The gases are then separated again before use. At some point, only hydrogen could flow through the same pipelines instead of natural gas. However, some precautions would then be necessary to protect the pipelines because hydrogen makes conventional pipe steel brittle - it also likes to react with the carbon in the metal. Basically, however, a very deep infrastructure is already in place here, which will make the transition to a climate-neutral hydrogen economy much easier. Currently, many important steps are being taken in this direction in many places."

All's well that ends well?

Whether green hydrogen will actually be the key element in the energy transition remains to be seen. However, its elementary role in future energy generation and the decarbonisation of industry and heavy-duty transport seems assured. With its many years of experience in the field of explosion protection and industrial sensor technology, Pepperl+Fuchs wants to stand by its customers and partners as a connecting element in the hydrogen chain - from regenerative energy generation, high-pressure compression after electrolysis, transport, storage to large-scale industrial use and hydrogen filling stations.