Ammonia cracking: key technology for the green transformation

Ammonia, the small molecule that became well-known in the 19th century through fertilizer production in agriculture, is now one of the most produced chemicals in the world. And it is becoming increasingly important - in future also as a transport medium for hydrogen.

In the future, ammonia could play a key role in driving forward the green transformation of industry - as a transport medium for green hydrogen. “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,” explains Dr. Christian Renk, Head of Technology, Innovation & Sustainability (TIS) - Operating Unit Fertilizer at thyssenkrupp Uhde.

“Ammonia has a higher energy density than hydrogen, so it is able to store more energy in a smaller space and is also cheaper and easier to transport,” explains Dr. Christian Renk. “Two ammonia ships can transport as much energy as three ships carrying liquid hydrogen.” Once it reaches its destination, the ammonia (NH₃) can be broken down into its components nitrogen (N₂) and hydrogen (H₂), with the hydrogen being used as a sustainable energy source in industrial processes.

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The ammonia cracking process is a key technology for the green transformation and can significantly advance the hydrogen economy.

The key process behind this is called ammonia cracking. Against the backdrop of climate change and increasing demands for sustainable production processes, efficient solutions are needed to make ammonia cracking and thus the use of green hydrogen more attractive for large-scale applications.

“thyssenkrupp Uhde has decades of experience in the production of ammonia. Now we are developing the cracking process,” explains Dr. Christian Renk.“The energy efficiency of our ammonia cracking process is currently around 80%. The goal is to further increase this figure.”

To make ammonia cracking sustainable and economical, the process must use as little fossil energy as possible.” For the centralized production of clean hydrogen using ammonia cracking in large-scale plants, the use of the ammonia's own energy is therefore the optimal solution for process engineering reasons and to avoid CO₂ emissions.

null — thyssenkrupp Uhde can draw on many years of experience in the production and cracking of ammonia since the 1950s and today offers plants for all steps along the ammonia process chain.

The efficiency of ammonia cracking is determined by multiple factors.

There are many different factors that influence the efficiency of ammonia cracking:

The cracking reactor
“Ammonia cracking is a highly endothermic reaction that is best carried out at elevated temperatures of around 600 °C and in a single pass,” explains Renk. This is why the mechanical and thermal design of the cracking reactor has a significant influence on the efficiency of large-scale ammonia cracking plants.

The catalyst
Another important factor is the choice of catalyst, an area currently undergoing intensive research. So far, nickel or ruthenium have been considered suitable. “While nickel is active at higher reaction temperatures and requires more energy, ruthenium is already active at lower temperatures below 500 °C,” says the expert. “However, ruthenium is scarcer and more expensive.”

The conditions
The process conditions also have a major influence on the efficiency of the cracking process and its suitability for industrial scale. “In order to make the process economical, ensure a complete reaction and at the same time avoid negative effects on the material, the pressure and temperature must be ideally balanced,” says Dr. Christian Renk.

The ammonia cracking process

thyssenkrupp Uhde has set out to develop the ideal cracking process and to research the various influencing factors. The focus here is on a self-sustaining process in which the required process energy is obtained from the ammonia supplied. The use of a stationary, adiabatic pre-reactor and an isothermal reformer is considered here.

The self-sustaining process is considered climate-neutral, while other process variants, such as the natural gas-fired process, cause additional emissions. The nitrogen oxides (NOx, N₂O) produced during ammonia combustion are purified to over 99.9% using the proven Uhde EnviNOx® process. “This process step is very important and one of our USPs,” says Renk.

One thing is certain: Ammonia cracking is an important process step in making the industry of tomorrow more sustainable, driving forward the green transformation and closing the green chain. That is why thyssenkrupp Uhde offers all steps of the ammonia process chain.

Dr. Christian Renk is certain that it is precisely these well-thought-out solutions that will make a difference in the future: “This is how we give the small molecule ammonia a new task in the 21st century.”

You can find more exciting insights into our research and technologies for ammonia production and splitting in our stories.