Ammonia could be used to store renewable energy, and as a source of hydrogen for fuel cell-powered vehicles, thanks to a demonstrator developed by Siemens.
The Green Ammonia Energy Storage Demonstrator, developed by Siemens alongside the Science and Technology Facilities Council and the Universities of Oxford and Cardiff, with funding from Innovate UK, is designed to show the complete cycle of renewable power, storage as ammonia, and conversion back to electricity.
Powered by renewable energy, the device first extracts nitrogen from the air and uses electrolysis to separate hydrogen from water, according to Ian Wilkinson, programme manager at Siemens Corporate Technologies.
The two elements are then combined using the Haber-Bosch process, in which hydrogen and nitrogen are reacted under high temperature and pressure in the presence of a catalyst, to produce ammonia.
“We already know how to synthesise ammonia in big quantities, store it, and transport it; the infrastructure is already there,” said Wilkinson.
However, existing techniques to produce ammonia typically rely on the use of natural gas or other fossil fuels, meaning they generate large amounts of carbon dioxide.
The new technique could be used as a means to store excess electricity produced by intermittent renewable energy sources, for use at times when the sun is not shining or the wind is not blowing.
Ammonia could then be burnt as a fuel in gas turbines, where it emits nitrogen and water, but no CO2. “It is chemical energy storage, but it is carbon-free,” he said.
Any NOx in the exhaust gas can be removed by existing catalytic reduction processes.
The fuel can be easily transported, and can also be “cracked” back to nitrogen and hydrogen for use in fuel cells. “Ammonia is a practical and carbon-free hydrogen carrier,” said Wilkinson.
The technique could also be used to produce ammonia for fertiliser, potentially reducing worldwide CO2 emissions by 360 million tons each year.
Suggestion to Siemens: Forget Haber-Bosch and go with production of higher Silanes! Radical idea is the brain child of Peter Plichter of Germany. The chemistry may be somewhat involved, but the basic idea is uptake of hydrogen by silicon compounds (possibly chlorides or fluorides). Silanes all burn utilizing both oxygen and nitrogen without the air separator. Water vapor and silicon nitride are the combustion products. Collect the nitride powder, and later react with steam to produce ammonia, thus you receive a double portion. Same fuel can be utilized for air-breathing spacecraft.
I suspect there might be a cool way to undertake this where a silane fuel cell could be developed, where the nitride product is available, or is by-passed directly to ammonia (and then undergoes another fuel cell reaction).
Ammonia may be practical from a chemistry perspective, but this ignores the safety implications of widespread use of a highly toxic substance as fuel. And to just dismiss NOx control as easily dealt with via existing control technology appears to take no heed of the diesel emissions scandal and the common (but illegal) practice of disabling NOx control on vehicles. When these are taken into account, I suspect the practicality may go away.
There’s a UK company specialising in Ammonia fuel cells who seem like the ideal consumers of this. It’s called AFC energy and they have a fairly large battery in use already and seem to be working hard on all the important issues of longevity and production cost.
Why not just stop at the point you have hydrogen electrolysed from water and use that as a fuel? This could then be burnt in a gas turbine, or used in a fuel cell. What is the overall efficiency of the Siemens process? I don’t see how it can be better than using hydrogen.