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Ammonia crackingHow ammonia enables the transport of green hydrogen
Ammonia is far more than a raw material for fertilizers. As a carrier for green hydrogen, the chemical could play a key role in decarbonizing industry in the future. Ammonia cracking is what makes the transported hydrogen available again at its destination.
Paving the way for the green transformation
In the future, ammonia could play a decisive role in advancing the green transformation of industry — as a carrier for green hydrogen. Two ships carrying ammonia can transport as much energy as three ships carrying liquid hydrogen. Once it reaches its destination, the ammonia (NH₃) can be split back into its constituent elements, nitrogen (N₂) and hydrogen (H₂). The hydrogen can then be used as a sustainable energy source in industrial processes.
The use of ammonia as a hydrogen carrier is based on the fact that hydrogen is produced in places where renewable energy is abundant and must be transported to places where renewable energy is expensive. Ammonia has a higher energy density than hydrogen, meaning it can store more energy in a small space and is also cheaper and easier to transport.
The key process behind this is known as ammonia cracking. Against the backdrop of climate change and increasingly stringent requirements for sustainable production processes, efficient solutions are needed to make ammonia cracking - and therefore the use of green hydrogen - more attractive for large-scale industrial applications.
To make ammonia cracking both sustainable and economically viable, the process should operate with as little fossil energy as possible. For the centralized production of clean hydrogen through ammonia cracking in large-scale plants, using the ammonia’s own energy is therefore the optimum solution - both for process engineering reasons and to avoid CO₂ emissions.
Plants for every stage of the ammonia process chain
thyssenkrupp Uhde has decades of experience in ammonia production and cracking dating back to the 1950s. Today, the company offers plants for every stage of the ammonia process chain.
There are several factors that affect the efficiency of ammonia cracking:
The slit reactor
“Ammonia cracking is a highly endothermic reaction that is best carried out at elevated temperatures around 600 °C and in a single pass,” explains Renk. For this reason, the mechanical and thermal design of the cracking reactor has a significant impact on the efficiency of large-scale ammonia cracking plants.
The catalyst
Another important factor is the choice of catalyst—an area where research is currently being conducted very intensively. So far, nickel or ruthenium are considered suitable. “While nickel is active at higher reaction temperatures and requires more energy, ruthenium is active even at lower temperatures below 500 °C,” the expert said. “However, ruthenium is scarcer and more expensive.”
The terms and conditions
Process conditions also have a major impact on the efficiency of the cracking process and its suitability for industrial-scale application. “To make the process economically viable, ensure complete reaction, and at the same time avoid negative effects on the material, pressure and temperature must be perfectly balanced,” says Dr. Christian Renk.
thyssenkrupp Uhde has decades of experience in ammonia production. We are now developing the cracking process. Currently, the energy efficiency of our ammonia cracking process is around 80%. The goal is to further increase this figure.
The ammonia cracking process
thyssenkrupp Uhde has set itself the task of developing the ideal cracking process and investigating the various factors that influence it. The focus is on a self-sustaining process in which the required process energy is obtained from the ammonia supplied. One approach under consideration combines a stationary adiabatic pre-reactor with an isothermal reformer.
The self-sustaining process is considered climate-neutral, whereas other process variants - such as those powered by natural gas - generate additional emissions. Nitrogen oxides produced during ammonia combustion (NOₓ, N₂O) are removed at a rate of more than 99.9 percent using the proven Uhde EnviNOx® process.
One thing is certain: Ammonia cracking is an important process step in making tomorrow’s industry more sustainable, advancing the green transformation and closing the green value chain. That is why thyssenkrupp Uhde offers solutions for every stage of this process chain.
Dr. Christian Renk is convinced that carefully engineered solutions like these will make the difference in the future: “This is how we are giving the small ammonia molecule a new role in the 21st century.”