Siemens programme manager Ian Wilkinson says the company’s interest in ammonia is partially driven by the fact that “it is based on mature technology and is therefore rapidly deployable at sufficient scale to be useful in meaningful decarbonisation”. Having an existing ammonia industry ensures there is infrastructure in place to store, transport and handle the compound safely from the offset. 

“Because it can be deployed at scale and is relatively easy to transport, ammonia energy storage is likely to be advantageous in situations where you need to store a large amount of energy (i.e. high-capacity applications) and/or want to transport renewable energy a long distance (e.g. over a sea),” Wilkinson said.

While current methods of ammonia production use natural gas or other fossil fuels to provide energy for the synthesis process, the Siemens demonstrator gets its hydrogen supply from water electrolysis and extracts nitrogen from the air, with the two elements then combined in the Haber-Bosch process to make the compound.

According to Wilkinson, “current ammonia production methods account for approximately 1.6% of today’s global CO₂ emissions.” The company estimates that in its use of renewable energy, its demonstrator could potentially save more than 40 million tonnes of CO₂ in Europe alone, and more than 360 million tonnes globally.

The existing ammonia market is huge, with around 180 million tonnes produced each year, and the firm has said that this new ‘green’ ammonia could be applied in the same manner as traditional forms, such as in fertilisers, plastics and food processing.

Another possibility lies in extracting hydrogen from the ammonia, says Wilkinson, as it could act as “a practical hydrogen vector and therefore an enabler for a viable hydrogen economy,” perhaps extending its use to hydrogen vehicles. Wherever possible, the hydrogen will be used directly to minimise energy losses inherent in the process of chemical transformation.

The transition would require modification to only some of the existing equipment he says, as “reciprocating engines can run on ammonia with little modification,” though gas turbine engines would require modification to their fuel and combustion systems.

Ammonia has been used as a fuel source in the past, for instance in municipal buses in Belgium in the 1950s, in the Nasa X programme, as well as in various automotives such as the Marangoni/Toyota Eco Explorer. As such, it is already relatively well established as a fuel source, though this is the first time it has been created in a zero carbon process.

While gas-turbine combustion techniques fuelled with ammonia do not produce any carbon dioxide, the presence of nitrogen in the fuel carries the risk of nitrogen dioxide and nitric oxide emissions – classed together as nitrogen oxides (NOx).

Nitric oxide itself is not hazardous at ambient concentrations; however, nitrogen dioxide is an irritant gas that causes inflammation of the airways in high concentrations. As such, the safety of the process has come under question. 

Despite such doubts, Siemens seems confident that this risk can be easily remedied. According to Wilkinson, researchers at Cardiff University have already proven that a richer air/fuel mixture can significantly lower the NOx emissions, claiming it is more an engineering problem “rather than one of fundamental research”.

“Ultimately, of course, it is possible to scrub NOx from flue gases using, for example, SCR [selective catalytic reduction] techniques which are commercially available today. And the reagent used in SCR? Ammonia (or a derivative thereof, such as urea), of course,” he says.

Since the launch of the demonstrator, Siemens has been working to commission the system and is expected to share results from the project in due course.

If successful, the project would provide huge gains to the firm considering its production of electrolysers, which use electricity to split water into oxygen and use the resulting hydrogen as a building block of ammonia. Additionally, the success of ammonia batteries stands to benefit the energy storage and production industry as a whole by providing a reliable and sustainable means of accessing clean electricity.