Ammonia synthesis is the basis for agricultural fertilizer production and nowadays the Haber-Bosch process is ubiquitous. An estimated 1.8% of the world consumption of fossil energy goes into the production of ammonia and 90% of ammonia production is based on natural gas. The alternative Claude Process based on electrolytically generated hydrogen is proven technology - operated in the 1930's - and if powered by renewable electricity at a sufficiently attractive price, provides two major benefits:
- Displaces the natural gas consumption - and CO2 emissions of Haber-Bosch
- Provides an interruptible electricity demand
The Claude Process. This process is [sic] worked at numerous factories in France and Belgium. The cost of the hydrogen used in the HABER-BOSCH process accounts for about 75 per cent of the cost of the ammonia produced: in the CLAUDE process the hydrogen is made by the electrolysis of water. Some of this hydrogen is burned in air, leaving nitrogen to be used in the ammonia synthesis and synthetic water suitable for the electrolytic cells. The rest of the plant, which works at 750 atmospheres, will be understood from the diagram. To withstand the enormous pressures the converters are made of special steel, and the catalyst is mounted on a gun breech- block device to allow easy withdrawal for replacement. Many variations of the process are possible; in some the nitrogen is obtained from producer-gas, in others from liquid air.
There are several operational and efficiency improvements that spring to mind. Instead of the rather wasteful burning of hydrogen in air to produce nitrogen, the air could be pre-processed e.g. using membrane separation or pressure-swing adsorption to enrich the nitrogen content. The remaining oxygen could then be removed by catalytic reaction with a reduced amount of hydrogen. So if the oxygen content were reduced from 21% to 5%, this would represent ~ 75% saving. Depending on how intermittent the renewable electricity is, gas holders might be provided for both nitrogen and hydrogen. And most of the efficiency improvements developed for the Haber-Bosch process such as better catalysts would apply equally to the Claude process
- A Textbook of Theoretical and Inorganic Chemistry, F.A Philbrick, E.J.Holmyard, 1932