(438e) Industry Perspective on Green Ammonia: Current Status and Challenges in Synthesis, Transportation and Utilization

Commercial scale ammonia is synthesized by utilizing the Haber-Bosch process, where hydrogen and nitrogen are exothermically reacted over a catalyst at high temperature and pressure. Nitrogen is sourced directly from air and purified via an Air Separation Unit (ASU). The source of hydrogen, which is more complex and requires energy intensive processes, determines the sustainability of ammonia production. For example, hydrogen produced from steam reforming of light hydrocarbons or gasification of coal to produce synthesis gas typically has an intensive carbon footprint i.e., they release large quantity of carbon dioxide to atmosphere and therefore, the generated hydrogen is brown (coal gasification) or grey (steam methane reforming (SMR) or similar). In contrast, green hydrogen can be produced by using renewable electricity in an electrolyzer to split water into hydrogen and oxygen, where the net carbon dioxide emission is close to zero. One more example of green hydrogen is when it is produced from synthesis gas generated by biomass gasification. Although, this type of process releases carbon dioxide to air, it is that carbon dioxide which is already absorbed into the biomass from air via photosynthesis, creating a carbon dioxide cycle and therefore generating close to net zero carbon dioxide. The corresponding ammonia synthesis using green hydrogen is termed as green ammonia. It should be noted though, that the color-coding of the synthesized ammonia is simply the result of source of hydrogen generation processes that have varying carbon footprints.

The presentation will focus on the electrolyzer-based green ammonia synthesis process (renewable electricity generation used to produce hydrogen in electrolyzers which, along with nitrogen from ASU, feeding to ammonia synthesis), ammonia storage, transportation and its utilization. The discussion will be around the challenges associated with the green ammonia life cycle.

The cyclic nature of the availability of the renewable electricity and difficulties in synchronizing the ammonia synthesis with it, is one example of challenges during synthesis. Water, being the main feedstock for the process, may compete with limited water resources that are typically used for human consumption. The industry normally looks at green ammonia as the carrier of the renewable energy, where it is expected to use ammonia as is, to produce energy or convert it to hydrogen by cracking process and then use the hydrogen to produce energy. The technologies to convert ammonia to energy are still not fully commercialized. The green hydrogen process is capital intensive – especially the electrolyzers. Added to that are the challenges associated with electrolyzer procurement, which makes the green ammonia synthesis process economically unattractive. The need of co-locating renewable electricity source, water availability and easy connectivity to transportation hub may pose hurdles for the location choice of the green ammonia synthesis facility.

All the above issues with green ammonia synthesis will be elaborated and discussed. It is also intended to propose probable solutions or recommend alternatives.