Iron fuels the fires of carbon free energy

University researchers working in tandem with the European Space Agency, have tested the use of a new, smokeless, carbon-free energy by burning iron powder. And what better way to assess the potential of this new type of fuel than by brewing beer with all the flavor and less carbon emissions than traditional brews?

First tested in microgravity aboard European Space Agency sounding rockets, a team at McGill University in Canada and Eindhoven University of Technology in the Netherlands have discovered the recipe for igniting iron powder to produce fire.

"The basic idea of burning metal is hardly new, especially in the space field, because solid rockets rely on aluminum particles as fuel – burning many tons within a few minutes," explains Antonio Verga, an ESA engineer who worked on the team's experiments. "But aluminum only burns with very tiny particles – iron is a more practical fuel for controlled combustion, while having a comparable energy density to gasoline."

The combustion process for metal works differently from "conventional" carbon fires, with the burning process transferred between adjacent metal particles by heat radiation, akin to the way neighboring trees can burst into flames during a forest fire.

Known as discrete burning, this occurs when a piece of fuel ignites and burns completely due to the ambient heat radiated by nearby fuel elements.

Unlike traditional fires that burn through their fuel continuously, discrete fires spread by jumping from one fuel source to another.

Furthermore, combustion of aluminum requires heat in excess of 3,000 degrees Fahrenheit (1,649 degrees Celsius), which can only happen through the burning of magnesium. Aluminum powder is a popular ingredient in fireworks such as sparklers, a great example of discrete fire.

The experiments aboard the sounding rockets allowed the iron particles to float freely in a simulated environment of weightlessness as they burned, helping the team to evaluate the optimal size and density of the particles and oxygen levels, to prevent the combustion either burning up too quickly or choking itself out.

"When we burn carbon and oxygen, we produce carbon monoxide or dioxide, but if we burn iron in the place of carbon then no noxious gases are produced at all. Instead, the iron is oxidized – in plain language, it rusts," said Verga.

Confident of this discovery, a student team at Eindhoven University of Technology worked with industrial partners to design a combustion facility to produce steam at Swinkels Family Brewers, a 340-year-old brewery in the Netherlands that produces around 800 million liters (211 million gallons) of beer per year.

Hoping to use a new method to break away from its reliance on fossil fuels and yet continue their brewing operations, Swinkels was willing to collaborate and the students were able to scale up the metal fuel flames of 'percolating reaction-diffusion' waves to a much larger size of 100 kilowatts to produce the steam energy needed for Swinkels brewing process.

"The percolating reaction-diffusion waves experiment, PERWAVES, supported by the Canadian Space Agency and ESA, studies the combustion of metal-particle suspensions in microgravity to investigate the physics of a new type of flame propagation regime," said Jeffrey Bergthorson, associate professor at McGill University's department of mechanical engineering. "Understanding the physics of these metal flames is essential to designing flexible and efficient metal-power systems for carbon-free energy."

Physics aside, PERWAVES is helping Swinkels brew 15 million glasses of beer without the carbon emissions typical of the heat intensive brewing process.

"We are enormously proud to be the first company to test this new fuel on an industrial scale in order to help accelerate the energy transition," said Royal Swinkels Family Brewers CEO Peer Swinkels. "As a family business, we invest in a sustainable and circular economy because we think in terms of generations, not years. Through this innovative technology, we want to make our brewing process less dependent on fossil fuels. We will continue to invest in this innovation."

Currently, the iron burning team is developing an even larger scale system of one megawatt and plans to work towards a five-megawatt pilot peak boiler for the city of Rotterdam in the Netherlands. In another trial system, the researchers are performing experiments toward the reduction of rusted powder back to pure iron using green hydrogen.

According to a professor at TU Eindhoven, there are still many steps to be made but the results look promising.

"Despite all the progress with electric cars, the energy efficiency compared to a traditional petrol-based car is less by a factor of a hundred," said Verga. "If we want to keep the range and power of road transport then we need to look for alternatives."

As iron is one of the most abundant metals on the planet, as well as one of the most-mined minerals in the world, shifting from carbon heavy fuels to produce a smokeless energy comparable to gasoline could potentially mitigate the reliance on fossil fuels. And, if the process of conversion to renewable iron from an oxidized form becomes viable, the renewable energy sector may yet have a new competitor.