Load-flexible Ammonia-Synthesis

Ammonia as Chemical Energy Carrier

Most renewable energy resources are highly intermittent due to their dependency on weather and location. In order to address the resulting seasonal and regional differences in energy supply/demand and to overcome periods of energy shortage, global large-scale energy storage and transportation options are required. In this context, Power-to-X (PtX) concepts for converting renewable electricity via electrolysis and further synthesis processes into green H2-based energy carriers are under intensive investigation. One very promising energy carrier is ammonia (NH3). Compared to H2, NH3 can be liquified at significantly milder conditions for transport and storage. Furthermore, NH3 is a carbon-free molecule, hence energy-intensive carbon-capture processes are not required. This provides unique flexibility regarding potential locations of future renewable NH3 production sites (e.g. off-shore).

NH3 is already one of the most produced inorganic chemicals in the world (e.g. fertilizer production). Today, NH3 synthesis is mainly done in a highly optimized, inflexible steady-state process from H2 and N2 with iron catalysts (Haber-Bosch Process). Due to harsh reaction conditions and usage of fossil fuel-based H2, the process is responsible for 1–2 % each of global energy consumption and CO2 emissions.

Load-Flexible Ammonia Synthesis

By using H2 from renewables via electrolysis, green NH3 production is already technically feasible. However, the intermittent nature of renewable energy supply leads to changing H2 flows induced by the electrolyzer unit. To reduce costly intermediate hydrogen storage, it is essential to develop an ammonia synthesis reactor system capable of operating safely and efficiently across a wide load-range as well as under dynamic conditions. Despite the higher complexity, load-flexible operation can lead to significant improved process performances compared to the steady-state process. Thus, studying and optimizing the dynamic NH3 synthesis are main challenges for efficient utilization of NH3 as a green energy carrier.