SIEMENS will launch a demonstration project in the UK today to showcase the potential of using ‘green ammonia’ for energy storage.
The £1.5m (US$2m) project has been built at the Rutherford Appleton Laboratory at the Harwell Science and Innovation Campus in Oxfordshire in partnership with Oxford University and the University of Cardiff. The project seeks to show that renewable power can be used to split water to produce hydrogen, which can then be combined with nitrogen extracted from the air to make ammonia. This can then be stored and transported for future use as a fuel, and help balance out the intermittency of renewable power.
Ammonia produced in this way avoids the carbon dioxide emissions from conventional production, which uses natural gas as both the source of energy and hydrogen for the synthesis of ammonia. Also, it can be burned as carbon-free fuel, producing only water and nitrogen.
Ian Wilkinson, programme manager at Siemens Corporate Technologies, told The Chemical Engineer that the nitrogen is produced using a pressure swing absorption air separation unit and the hydrogen is made by splitting water using a PEM electrolyser. These are then fed to a bespoke Haber Bosch reactor to produce around 30 kg/d of ammonia, which is stored in a pressurised tank.
Wilkinson said a bespoke reactor is necessary because the scale of the demonstration is too big for lab equipment and too small for industrial kit.
An onsite wind turbine powers the demonstrator and at the other end of the process the resulting ammonia is burned in a three-cylinder spark ignition 30 kW electric generator, with the electricity fed back into the grid.
“One of the big challenges with this is learning about the intermittency. Haber Bosch plants today are run 24/7, 365 days a year,” Wilkinson said. “Here I have a requirement to operate it intermittently because of the intermittency in my electricity supply.”
Fortunately, 90% of the energy required for the demonstration is for the production of hydrogen, and the electrolyser can be switched from standby to full load in less than 10 seconds so this will help the system cope with fluctuations in local wind conditions.
“But it will have some knock-on effect on the Haber Bosch synthesis which obviously state-of-the-art [systems] today are continuous operations so the other point of the demonstration is to start learning about the system operation of a green ammonia plant under the inherently intermittent availability of renewable power.”
Asked about the benefit of the system over other storage technologies currently being developed and applied, Wilkinson said there is no single solution and a suite of technologies is needed to help decarbonise our energy systems.
“Chemical energy storage addresses a different scale in terms of capacity and duration of storage to batteries. So, I think where you’re looking at higher capacities and longer durations, then chemical energy storage is tough to beat.
“Batteries slot in somewhere lower down in terms of capacities and durations. So, it’s a case of choosing the right storage technology for your application. In some cases, batteries will be better, in which case you should use a battery. In some cases, chemical energy storage will be better, in which case you could consider ammonia.”
Wilkinson said to decarbonise society we need technologies that are scalable and can be deployed at scale.
“Ammonia is particularly interesting because as I’m showing with the demonstrator, the technology you need to do it is mature and can be deployed at scale today.
“It’s innovation in the truest sense of the word. I’m not inventing anything – I’m putting together existing technical solutions to solve a new problem – and that new problem here is how do I integrate renewable energy into my energy systems, and make storage work on the kind of scales that we need to really shift the dial on our CO2 emissions.”
Siemens makes the electrolyser used in the project and has a wider interest in how future energy systems might develop. Wilkinson said the company is interested in how sustainable process technologies and industry can be made through electrification.
Other partners in the project include the Sciences and Technology Facilities Council and Innovate UK.