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Iron-to-rust cycle tapped by scientists for safe renewable energy transport (interestingengineering.com)
submitted 1 month ago by to c/hydrogen@piefed.social
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...One of the challenges of clean energy is transporting and storing massive amounts of solar and wind power over long distances...

According to the new study, pulverized iron powder could act as a highly efficient, recyclable clean energy storage material...

The concept taps into a beautifully simple chemical loop. When iron powder is combusted, it releases intense heat and turns into iron oxide. In other words, it rusts. To reset it, scientists use green hydrogen generated from excess renewable energy to strip away the oxygen, reducing the rust back into pure iron powder. No carbon dioxide escapes into the atmosphere. The cycle simply repeats...

As it burns similarly to fossil fuels, energy giants wouldn’t need to rebuild their infrastructure from scratch...

The expensive components already in place, such as the steam cycles, massive turbines, heavy generators, and local grid connections, could be fully preserved...

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[–] [S] 1 point 1 month ago (1 child)

Source for claim of 1% mass loss per cycle:
https://research.tue.nl/en/publications/combustion-of-micron-sized-iron-particles-in-a-drop-tube-reactor/

I think the deciding factor between iron and aluminum comes down to exhaust filtration.

Iron oxide in the exhaust can be collected cheaply with a combination of centrifugal and electrostatic forces and it tends to retain is grain size. Aluminum oxide is lighter, more electrically resistive, and tends to break down into too-small nanoparticles.

Yeah, you'd only need to sinter pellets to pump hydrogen through them in a static pile. A fluidized bed reactor can reduce the iron oxide powder as is, and keeping the temperature lower prevents sticky sintering at the cost of taking longer to complete.

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  • [–] 1 point 1 month ago*

    That source only covers losses due to iron evaporation during combustion, it doesn't cover reduction losses back into iron or what the regenerated iron's particle size is, which tells us what milling energy is needed to get back down to sub micron iron. That's the inefficient part of the energy loop, along with reduction efficiency with green hydrogen.

    You need to understand that whatever method is being used for reducing your powder back into iron metal is going to be a mature technology already used for steelmaking. If green energy scientists somehow found a new method for reducing iron into metal it would be global breaking news in the steelmaking industry. That's the extraordinary claim you need to support with sources: how it gets regenerated and at what efficiency, does it need to be milled and to what starting and finishing particle size, consuming what energy, CAPEX, and OPEX? What's the total loop efficiency?

    I really think the overall efficiency is going to be terribly low once you do the math on all steps in the cycle...

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