If they were going to do that, they just wouldn't create them in the first place and keep the higher efficiency numbers. No point capturing the nanotubes out of your exhaust only to burn them.

From TFA:

"They found that the concept is economically feasible and even improves the power plants' energy efficiency."

If that's true, and assuming the CNTs can be sold, sequestered, re-burned, or otherwise disposed of in a way that doesn't ... "exploit" their über-asbestos aspect, I'd think it worth doing on that basis alone.

They seem to be using efficiency to mean cost efficiency here, which is certainly not intuitive when speaking of a power plant. But the article does explicitly say later on that the amount of power produced per metric ton of fuel will decrease, but a bunch of valuable nanotubes will be produced instead - much more valuable than the power output being lost, at least at today's prices.

If that's the case, then why did the sentence I quoted specifically say "energy efficiency"?

It's very difficult to believe the part about "energy efficiency". If it were true then someone can just burn the nanotubes later to produce electricity as proposed in the previous comment.

The new extended electricity plant that produces nanotubes and burn them have the same maximal theoretical electricity output than a traditional electricity plant, but if the "energy efficiency" were true then the new method would produce more electricity.

The traditional method is something like burning the hell of the methane, use the heat to produce electricity and release all the CO2 to the atmosphere

The new method would be, bun the hell of the methane, use the heat to produce electricity, use the CO2 to produce LiCO3, use part of the electricity to produce nanotubes and LiO, burn the nanotubes and use this additional heat to produce electricity and release the CO2 to the atmosphere. The calculations are more complicated because the fumes have different temperatures, and other technical details.

But for me it's unbelievable that an indirect method that transform the CO2 to nanotubes and burns them ads "energy efficiency". I'd guess a 30% energy lost in each step.

Ah, yes. I have no idea what they're talking about then.

Perpetual motion machine detected: Start with some carbon, burn it, collect the carbon nanotubes, repeat.