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Production of hydrogen: process and color theory

Wasserstofftank vor blauem Himmel

Hydrogen production

Hydrogen (H2) is the most common element in the universe, present in very large quantities on Earth and contained in almost all organic compounds. At the same time, it only occurs in bound form - the best-known example of this is water (H2O), which is made up of the elements oxygen (O2) and hydrogen. As hydrogen is a secondary energy, primary energy is always required to produce hydrogen. It can be used to store and transport energy.

The choice of primary energy determines whether the hydrogen is produced in an environmentally friendly way. If electricity from renewable energy sources is used entirely, the end product is sustainable hydrogen. This is also known as green hydrogen, as no carbon dioxide (CO2) is emitted during its production. An overview of the different colour categories of hydrogen can be found further down on this page. But how is hydrogen produced? If you want to produce hydrogen, there are a number of processes you can use: With regard to the production of hydrogen, the reforming process and the water electrolysis are very mature. The Kvæner process, hydrogen production from green algae and the production of biohydrogen are still being trialled.

Hydrogen is a topic with many facets - from production, transport and storage to utilisation. With our expertise, know-how and many years of experience, we are an independent partner for safety and hazard prevention by being able to test, inspect and certify various aspects of hydrogen technology.

Production of hydrogen using the reforming process

In the reforming process, hydrogen is extracted from fossil fuels such as natural gas or coal, but also from sources such as methanol (CH4O) or biomass in a multi-stage process. In industry, the reforming of natural gas is currently the most common method for producing hydrogen. For example, superheated water vapour can be used for the reforming process, which is known as "steam reforming". The by-products include sulphur dioxide (SO2), carbon monoxide (CO) and nitrogen oxides (NOx).

Biohydrogen production

Biohydrogen is produced using a process called "dark fermentation". This involves using biomass, waste water and residual materials as raw materials. The organic compounds they contain are converted into hydrogen and carbon dioxide by microorganisms. Anaerobic conditions prevail, i.e. no oxygen is present. In addition, this conversion takes place during the production of biohydrogen in complete darkness and at temperatures of 30 °C to 80 °C. As it is not possible to utilise all organic compounds in this process, they are subsequently converted into methane (CH4) and carbon dioxide (CO2). In the end, biohydrogen is obtained.

Production of hydrogen with electrolysis

The production of hydrogen at a glance: Electrolysis, vapour gas reforming and pyrolysis as important steps in hydrogen production

Three main procedures

AEL electrolysis: Uses a potassium hydroxide solution as the electrolyte.
PEM electrolysis: Uses a solid polymer membrane instead of a liquid electrolyte.
HTE electrolysis: Works at high temperatures from 100 to approx. 900 °C.
Hydrogen can be produced by water electrolysis, whereby an electric current splits water into hydrogen and oxygen. If renewable energy is used, green hydrogen is produced.
Seawater desalination plant

Seawater desalination: systems for water treatment

The Germany's national hydrogen strategy provides for the import of green hydrogen in addition to its own production - primarily from North and West Africa, as it can be produced very cheaply there from solar and wind power. In 2020, Federal Research Minister Anja Karliczek and her Nigerian counterpart at the time, Yahouza Sadissou, agreed on a package of measures to expand the partnership with West Africa. One of the challenges associated with importing hydrogen is to provide sufficient fresh water for water electrolysis without exacerbating local water scarcity. Seawater desalination technologies make a decisive contribution to protecting the environment in the respective countries, and the water is treated for electrolysis in seawater desalination plants. The long-term development of appropriate infrastructure for seawater desalination is associated with considerable overall social benefits for the producing regions and offers great potential for economic cooperation and development aid.

But how does a desalination plant work? The established processes for desalinating seawater are divided into thermal distillation processes and membrane-based pressure filtration processes. Below you will find descriptions of the two operating modes for desalination plants.

Thermal distillation in seawater desalination plants

  • Multi-stage distillation
    (MED - Multi-Effect Distillation)
  • Multi-stage flash distillation
    (MSF - Multi-Stage Flash Distillation)
  • Vapour compression process
    (TVC - Thermo Vapour Compression)

Thermal distillation in desalination plants is characterised by high energy input: In thermal processes, the water, which is pumped from the sea, is fed through condensation stages in a seawater desalination plant. Heat from power stations in the gas and oil industry, but also from nuclear reactors, is usually used to heat the water to over 100°C. Around 100 kilowatt hours of energy are required per 1,000 litres of water.

Particularly in the dry, sunny regions of North Africa and the Middle East, thermal processes used in seawater desalination plants have been making an important contribution to the supply of fresh water for many years. Today, they can be optimised through hybrid concepts and, for example, enable the transition to a sustainable energy economy in solar/fossil operation.

Seawater desalination plant with membrane-based pressure filtration

  • Reverse osmosis (RO)
  • Nanofiltration (NF)
  • Electrodialysis (ED)

This mode of operation in seawater desalination plants is characterised by efficient energy management: thanks to powerful high-pressure pumps that push seawater through special membranes and efficient energy recovery systems, reverse osmosis has increasingly established itself as the leading technology for seawater desalination. The most modern seawater desalination plants only require around 2.5 kilowatt hours of energy per 1,000 litres of water.

In sunny and windy coastal areas, seawater desalination in special reverse osmosis plants also enables the economical production of green hydrogen. In order to utilise electrolysers, i.e. devices for electrolysis or plants for the production of hydrogen, to a high degree, locations are preferably suitable where wind energy is available at night in addition to high levels of solar radiation during the day. Alternatively, fuel cells can also serve as an energy supplier when there is no wind.

We support you in the planning and construction of seawater desalination plants and carry out all necessary testing activities and fault analyses during the operating phase. To this end, we offer you comprehensive services in the areas of testing, inspection and certification in all phases of the respective project: We are your partner in the concept/planning, production and operation phases of your plant.

Hydrogen colour theory

What color is hydrogen?

Hydrogen is colourless and odourless. The frequently asked question "What colour is hydrogen?" therefore does not refer to a specific colour, but to the amount of carbon dioxide emissions that are produced directly or indirectly during the production of hydrogen.

The respective colour category therefore indicates whether the production of hydrogen is environmentally friendly. A distinction is made between green, blue, turquoise and grey hydrogen.

The individual colours of hydrogen are defined as follows:

Hydrogen colors

Green hydrogen is produced with renewable energies (such as water and wind power or photovoltaics), primarily from water using the electrolysis process. This involves splitting the water molecule into the two elements hydrogen (H2) and oxygen (O2). Producing hydrogen sustainably: If only electricity from renewable energy sources is used for water electrolysis, the hydrogen produced in this way is considered to be free of carbon dioxide and therefore green hydrogen. However, even the production of a wind turbine, for example, is not completely climate-neutral. If you want to produce green hydrogen, you can also gasify and ferment biomass or use biogas reforming biogas. If renewable energies are used in methanol synthesis, i.e. the conversion of hydrogen and carbon dioxide (e.g. from industrial processes) into methanol, then the result is considered "green methanol".

Blue hydrogen is produced using fossil fuels, so it is basically grey hydrogen. However, there is a crucial difference with blue hydrogen: unlike grey hydrogen, carbon dioxide is not released into the atmosphere. Instead, the carbon dioxide is separated, captured and injected into suitable geological formations deep underground, for example. Blue hydrogen is therefore considered carbondioxide neutral in the balance sheet. The corresponding process is known as "carbon capture and storage" (CCS). Potential storage sites include former oil or gas deposits and rock strata containing salt water. So far, this process for producing blue hydrogen has only been used in pilot and test projects in Germany.

When hydrogen is produced via the thermal decomposition of methane or natural gas (some natural gases consist of 98 % methane), it is turquoise hydrogen. This process, known as "methane pyrolysis", produces solid carbon instead of carbon dioxide. If the high-temperature reactor is operated with renewable energy sources and the carbon is permanently bound, this process is carbon dioxide-neutral . A key advantage is that carbon is easier to store than carbon dioxide and can be used in the chemical and electronics industries or in road construction, for example. Compared to the production of green hydrogen using electrolysis, methane pyrolysis is said to require only a fifth of the energy for the production of turquoise hydrogen. However, this hydrogen production process has so far only been trialled on a laboratory scale.

Currently, grey hydrogen still dominates the German market. It is produced from fossil fuels, primarily natural gas and coal. In the production of hydrogen through steam reforming, for example, natural gas is converted into hydrogen and carbon dioxide at temperatures of up to 1000 °C. Depending on the source and electricity mix, the production of one tonne of hydrogen generates around 10 tonnes of carbon dioxide. As it escapes unused into the atmosphere and is not stored in any form, grey hydrogen therefore increases the greenhouse effect.

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