Swinkels Family Brewers in the Netherlands recently adopted a new way to heat their brewing process: melted iron. And it’s arguably sustainable. It’s not as weird as it sounds.
Essentially iron dust is set alight, which burns in a contained system and produces heat (which is used to hear water in the brewery). Once burnt, the iron basically becomes rust, which then can be turned back into usable iron using electricity. If electricity is sustainably produced then the whole system is carbon neutral.
If burning metal powder as fuel sounds strange, the next part of the process will be even more surprising. That rust can be regenerated straight back into iron powder with the application of electricity, and if you do this using solar, wind or other zero-carbon power generation systems, you end up with a totally carbon-free cycle. The iron acts as a kind of clean battery for combustion processes, charging up via one of a number of means including electrolysis, and discharging in flames and heat.
As a burnable clean energy storage medium, iron powder’s advantages include the fact that it’s cheap and abundant, the fact that it’s easy to transport and has a good energy density, its high burning temperature of up to 1,800 °C (3,272 °F), and the fact that (unlike hydrogen, for example) it doesn’t need to be cryogenically cooled, or lose any energy during long periods of storage.