Supercritical CO2 is dense like water

Sometimes I learn stuff that makes me feel like I’m on the right path with the LFTR concept. I had that feeling today as I listened to a talk by Dr. Steven Wright of Sandia National Labs about a supercritical-carbon-dioxide closed-Brayton-cycle gas turbine.

That’s an awfully large number of adjectives to describe an engine that can turn heat (random kinetic energy) into work (directed kinetic energy) and do it very well. Heat is what we can provide from the fission of thorium (well, actually U233) in a LFTR and work is what we want (in the form of electricity) to provide to customers and users.

SCO2-engines are an interesting variant of the jet engines you see on aircraft. Instead of using air and burning fuel, they use carbon dioxide as their “working fluid” and use the heat from a high-temperature reactor. That reactor could be LFTR, or a pebble-bed reactor, but low-temperature reactors like light-water reactors wouldn’t work for this application. The heat source might not even be a reactor at all, it might be concentrated solar energy.

Dr. Wright talked about a test setup they’ve built to demonstrate the operation of an SCO2-engine. They’re still at the beginning stages but I loved seeing all the pictures of real hardware and actual people having a blast making an exciting new kind of engine.

But this was the part I really got a kick out of:

Supercritical CO2 is a fair fraction of the density of water!

That’s a big deal because usually gases are WAY less dense than liquids. That means that gases need more volume to do the same amount of work. More volume means bigger hardware means more costs.

Dr. Wright talked about how small their compressors and turbines were–for hundreds of kilowatts of power. A few inches in diameter.

Then he talked about how big a 300 MW compressor would be. About a meter in diameter. Amazing.

With technology like this and a heat source like LFTR, we could make nuclear power systems so much smaller than they are now that I think people would scarcely believe it could be done.

Thorium Discussion Forum thread on SCO2-power conversion

V. Dostal, M.J. Driscoll, P. Hejzlar, “A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors”, MIT-ANP-Series, MIT-ANP-TR-100 (2004)

One thought on “Supercritical CO2 is dense like water

  1. I have a question about using super-critical CO2. I've always seen it in association with nuclear power. Can super critical CO2 be used as a stand-alone technology ? Specifically, could it use fossil fuels or other sources of heat ? Or does it work well with nuclear, but not so well with other sources ?

    bob ully, bobully@hotmail.com

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