The Role of Ammonia in the Emerging Hydrogen Economy

Green ammonia is a renewable fuel that has the capacity to play an important role in decarbonisation. it is produced from only water, power and air, and can be dispatched on demand as a fertiliser, shipping fuel, hydrogen carrier, or for back-up power supply. Increasingly, ammonia is appearing in national hydrogen strategies as an enabler of the hydrogen economy due to its superior energy density.

Green Ammonia Production

Green Ammonia Production Process

The so-called ‘green‘ ammonia is produced with the HB (Haber Bosch) process, except that the hydrogen feed is sourced via renewable energy. There are several means to produce green hydrogen, but the approach that is envisaged to be the most scalable and cost effective in the long term is water electrolysis powered by wind and/or solar electricity. Energy demand for cryogenic air separation of nitrogen is relatively small compared to the requirements for hydrogen production and is also sourced from renewables for green ammonia.

In the early 1900s, Fritz Haber devised a method of fixing nitrogen by combining atmospheric nitrogen and hydrogen in the presence of a metal catalyst to produce ammonia, commonly known as the HaberBosch pathway. Although process technology has improved over the years, the basic chemistry is identical to the original process developed:

N2(g) + 3H2(g) → 2NH3(g) ΔH = − 92 kJ/mol (− 46 kJ/mol for 1 mol of NH3)

Note: The information presented in this essay has been sourced from scholarly articles titled “A global, spatially granular techno-economic analysis of offshore green ammonia production” authored by Nicholas Salmon and René Bañares-Alcántara from the University of Oxford’s Department of Engineering Science, located at Parks Road, Oxford, OX1 3PJ, UK. and “Optimising renewable generation configurations of off-grid green ammonia production systems considering Haber-Bosch flexibility” authored by Changlong Wang, Stuart D.C. Walsh, Thomas Longden, Graham Palmer, Israel Lutalo, and Roger Dargaville.