Keeping it in the clay
A 3,500-year-old clay technology may lead to carbon-free electricity. Khai Trung Le reports.
A firebrick system used for over three millennia may offer low-cost storage for carbon-free energy, converting excess electricity collected during low periods of demand and storing it as heat within insulted firebricks that could be fed back into generators for conversion or used directly in industrial processes.
Despite the age of firebrick technology, Dr Charles Forsberg, research scientist at the Massachusetts Institute of Technology (MIT) Department of Nuclear Science and Engineering, USA, sees firebricks as a companion to intermittent renewable energy sources, nuclear plants and unpredictable electricity demand. Forsberg told Clay Technology, ‘In electricity markets such as Iowa, California and Germany, the price of electricity drops to near zero at times of high wind or solar output.’
Forsberg’s Firebrick Resistance-heated Energy Storage (FIRES) system uses clay bricks capable of withstanding extremely high temperatures of up to 1,600˚C that have been linked back to kilns built by the Hittites, ancient Anatolian people from what is now known as Turkey. Altering the chemical composition of the clay allows the FIRES system to adopt a variety of properties – bricks placed at the centre of the assemblage have high thermal conductivity, while bricks on the outside could have low thermal conductivity, creating an insulating shell, retaining heat in the central stack.
While current resistance heaters peak at around 850˚C, Forsberg stated that the clay used in the FIRES system could itself be electrically conductive to act as resistance heaters to both produce and store heat for industrial processes. Silicon carbide has been posited as a potential material, in addition to clay, which is already being produced in large quantities for uses including sandpaper.
The greater engineering problem, converting the stored heat back into electricity, is unlikely to be addressed within this generation of the FIRES system due to the higher temperatures needed to power gas plant turbines.
Forsberg said, ‘While industrial process heat is viable at around 800˚C, the turbines need compressed air heated to at least 1,600˚C. Ordinary resistance heaters can’t go that high, and such systems will also need an enclosed pressure vessel to handle the needed air pressure.’
However, he remains optimistic that the FIRES system could be a feasible replacement. ‘At present, the options for storing excess electricity are essentially limited to batteries or pumped hydroelectric systems. By contrast, the firebrick thermal storage system would cost anywhere from one-tenth to one-fortieth as much as either of those options,’ the scientist said.
Regis Matzie, former Chief Technical Officer at Westinghouse Electric, USA, added his endorsement of the FIRES system. ‘I believe that FIRES is an innovative approach to solve a real power grid problem – a skewed electricity market that produces low or even negative market prices when a significant fraction of electrical energy on the grid is provided by renewables.
‘An economic way to correct this would be to store the energy generated during low electricity market prices, e.g. when the renewables are generating a large amount of electricity, and then releasing this stored energy when the market prices are high. FIRES provided a potential way to do this, but would probably need a demonstration to establish the operability and the economics.’
The team is exploring opportunities among oil refineries with significant wind turbine installations to set up full-scale prototypes by 2020 in a bid to prove the concept in real-world conditions.