Green ammonia as a vector for intercontinental energy transport

Thesis

Green ammonia is an essential key in the decarbonisation toolkit. For energy systems, it can play a myriad of roles: it is a zero-carbon fertiliser, shipping fuel, hydrogen vector, and dispatchable, portable energy source. Ammonia is already the second-most produced industrial chemical in the world, and yet its production may need to increase five-fold to meet these emerging, green demands.

This thesis provides the first global optimisation of the supply chains that will be needed to deliver green ammonia at such large scales. It considers first the production of ammonia, advancing our understanding of the tools needed to design green ammonia plants, and providing for the first time a viable strategy for operating green ammonia plants without a grid connection. It then explores the constraints on ammonia production, with a focus on land restrictions, which may create a business case for ammonia production on the ocean. Finally, it integrates the results for production and land availability into a supply chain model that incorporates the cost of ammonia transport, and applies the model to two case studies: one focussing on ammonia’s use as a shipping fuel, and one on its application for back-up energy production.

The most significant contribution of this thesis is the global supply chain model, which is a blueprint for an emerging sector of the energy system. In the journey to reaching that blueprint, other interesting outcomes emerge. Of particular interest: (i) connecting to the electricity grid can meaningfully reduce the cost of green ammonia compared to an ’islanded’ system; (ii) Haber-Bosch flexibility is important for producing affordable green ammonia, but may not be as significant as portrayed in some literature; (iii) in land-constrained regions, there is good reason to believe there is a techno-economic case for offshore green ammonia production; (iv) ammonia supply chains optimised on the basis of cost will involve less energy transport than today’s fossil-fuel derived systems.

Authors: Salmon, N

• DOI: 10.5287/ora-g2p2zdkg4
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: renewable energy; linear programming; green ammonia; green fuels; green hydrogen; zero-carbon shipping
• Subjects: Renewable resource integration; Hydrogen as fuel; Engineering