The green hydrogen economy of the future
One topic of the future is energy generation with hydrogen. Green hydrogen in particular, which is produced using energy from renewable sources, has great potential. There are now many new technologies for producing, transporting and using this energy carrier.
Green hydrogen is hugely important for achieving the Paris climate protection targets. It is produced using power-to-gas technology. In this process, green hydrogen is produced by electrolysis using electricity from renewable energy sources such as wind or sun. This means that green hydrogen is CO²-free.
Hydrogen technologies involve various mechanical or chemical applications for the use of hydrogen. They are intended to help reduce climate-damaging gases such as carbon dioxide or methane. The areas of application range from industrial production and use in goods transportation and traffic to electricity and heat generation. In addition, renewable energies can be stored flexibly with the help of hydrogen technologies.
Technologies for hydrogen production
Green hydrogen must be produced using electrolysis. There are different types of electrolysis, but an electrolyser always consists of several electrolysis cells arranged in a row. Electrical energy from renewable sources is then used to force a redox reaction and split water into its individual components oxygen and hydrogen. The hydrogen can then be stored in various forms.
According to the brochure Hydrogen Technologies from the Fraunhofer Institute for Ceramic Technologies and Systems IKTS, high-temperature electrolysis in particular is a "key technology for the efficient production of hydrogen and synthesis gas". It offers a number of advantages over alkaline and PEM electrolysers. For example, the process does not require any stainless steel components and enables the direct production of synthesis gas. In high-temperature electrolysis with solid oxide electrolysis (SOE), temperatures of more than 750 degrees Celsius are reached during the conversion processes. The electrolyte is used as a solid ceramic material that separates the two half-cells. The water then enters the reaction chambers in the form of steam.
In addition to high-temperature electrolysis, there is also alkaline electrolysis and proton exchange membrane electrolysis. Alkaline electrolysis (AEL) is currently the most widely used electrolysis process, as the investment costs are low and the technology is stable over the long term. AEL uses an OH-conducting liquid electrolyte.
Proton exchange membrane electrolysis (PEM) is operated at low temperatures and is a relatively new technology. Hydrogen can be extracted from industrial and mining waters. The Rodosan process was developed at Fraunhofer IKTS for this purpose. The advantage of PEM is that it can react quickly to fluctuations in the added energy and has good load change behavior. Hydrogen is separated as a usable reaction product during the electrochemical treatment of sulphuric acid and sulphate-free water in the membrane electrolysis cells.
Low-CO² technologies for hydrogen utilization
As a process gas for the production of basic and valuable products, green hydrogen can ensure that no more CO² is emitted. This is because iron ore has to be converted into pig iron in order to produce steel. Coke is used for this in the blast furnace process. In order to make this process almost climate-neutral (CO² reduction of more than 95 percent), hydrogen can be used instead of natural gas in direct reduction processes. According to Fraunhofer IKTS, high-temperature electrolysis is the most suitable method. The existing waste heat can be used effectively and the synthesis gas can be produced.
High-temperature electrolysis is also suitable for ammonia synthesis. Natural gas is currently used for this process, which produces large quantities of CO². If CO² emissions are unavoidable, it is possible to use them as a carbon source. For example, waxes for the cosmetics industry or fuels for air traffic can be obtained. Fischer-Tropsch synthesis is suitable for producing carbon-containing products from CO² and hydrogen. However, for this technology to be particularly effective and efficient, it must be coupled with the (co-)electrolysis process. The co-electrolysis process produces synthesis gas, which makes the production of chemical products particularly efficient.
Green hydrogen also serves as an energy source in the areas of electricity, heat and mobility. Natural gas boilers in buildings can theoretically be operated with hydrogen. In electricity generation, hydrogen can be converted into electricity by means of fuel cells using reconversion. This is done with cold combustion, in which a reaction between oxygen and hydrogen is provoked within the fuel cell. The waste product of the resulting electrical voltage is water, so that no emissions are produced. In the transport sector, hydrogen-powered vehicles, ships and trains are a good complement to electric vehicles. Synthetic fuels based on hydrogen can also be used, particularly in aviation and heavy goods transport.
As part of the Carinthian project "H2 Carinthia", green hydrogen is even to be used twice: in the industrial production of microchips at Infineon and then for refueling means of transport. The green hydrogen is decoupled after production and fed to a PSA (pressure swing absorption) plant at the water filling station, where it is purified for use in transportation. In December 2022, the first five buses powered by recycled green hydrogen were launched on Carinthia's public transport network.
Technologies for storing and transporting green hydrogen
In order to make hydrogen transportable for use elsewhere, it must be stored. This is a major challenge, as it is a light and rather volatile chemical substance. Hydrogen can be stored in various aggregate states above ground in tanks or underground. In liquid form, hydrogen is stored at extremely low temperatures (minus 553 degrees Celsius) in insulated cryogenic tanks, which means that a lot of energy is lost. The cryotanks must be very well insulated so that the hydrogen does not evaporate.
Hydrogen is stored in gaseous form either in pressurized storage tanks or underground cavern storage facilities. This type of storage is used most frequently as it ensures good mobility. Cavern storage facilities in particular have a high storage volume. In addition, no new areas need to be sealed. There are also metal hydride storage facilities, where a lot of hydrogen is stored in solid metal lattice structures (e.g. metals or carbon) and can be released again by heating. However, transportation is made more difficult here due to the high dead weight. Hydrogen can also be absorbed in liquid carrier media such as oil (liquid organic hydrogen carrier). However, a lot of energy is lost due to the catalysts.
The stored hydrogen is then transported by truck, ship or train, for example. For this to be climate-friendly, however, the means of transportation must be electric or powered by green hydrogen. The hydrogen can also be transported in existing or new gas pipelines. The natural gas infrastructure is of particular interest here. The hydrogen can be added to the natural gas in certain proportions. Polyethylene pipes and metal-plastic composite pipes for hydrogen transportation are also being tested at the Bitterfeld-Wolfen Chemical Park.
Thanks to the advancements in Technologies, the hydrogen economy of the future holds great promise for a CO₂-free energy system. For instance, high-temperature electrolysis, as highlighted in the Fraunhofer Institute's Hydrogen Technologies brochure, is a key technology that could significantly contribute to this hydrogen economy thanks to its advantages over other electrolysis methods.
Furthermore, in the future, thanks to Technologies, green hydrogen produced through high-temperature electrolysis could potentially replace natural gas in industries, reducing CO₂ emissions by over 95%, as suggested by the Fraunhofer IKTS in their research.
Source: www.ntv.de
