Comment by gus_massa | Hacker News Reader

Comment by gus_massa | Hacker News Reader

The idea of using this in power plans with natural gas may work. The global reaction is

  CH4 + O2 --> C + 2 H2O + energy

I have to check the calculation, but the research paper looks legit. I'm worried because they use a very indirect process so it's not clear for me that the loss in the intermediate steps are small.

Also, I'd assume that if many power plants start to do this, then the nanotubes price will drop almost to the level of soot. (Would it be much cheaper to just make soot instead of nanotubes?) But they say that the energy production will drop only 10%, so this may make sense with some carbon taxes.

But I really don't like that in the research article they propose to use this in coal plants. They use a complex scheme, (with additional solar panels?), but the global chemical reaction doesn't make sense. They start with coal that is essentially C and the final product is nanotubes that are essentially C, so there is very little room to extract energy.

Has any thought been put into the dangers of literally millions of pounds of carbon nanotubes floating around with nothing to do? CO2 is evil, but some people suspect carbon nanotubes could be the next asbestos if they become widespread.

Wouldn't a substantial pile of such tubes be a serious fire hazard? Aren't they essentially the carbon version of steel wool, ie much more flammable than solid carbon?

TANSTAAFL

I'm guessing that if they are generating nanotubes for sale, their is a collection process that keeps the nanotubes in some sort of container. Since this would take place in a location that also has coal or natural gas, I think they will have the procedures and technology to prevent fires and explosions.

For sale is one thing, but I get the sense that they might do this as a means of reducing CO2 emissions. That would generate truly epic piles of nanotubes, far beyond any concept of containers. For perspective, look at the amount of coal going into a plant. Roughly that much, by volume, would come out again as nanotubes.

If they are flammable, even explosive, nobody has any protocol that could make storage of such volumes safe.

> If they are flammable, even explosive, nobody has any protocol that could make storage of such volumes safe.

Dumb question for a non-engineer: couldn't they feed them back through the power plant again?

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.

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

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"?

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

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.

Some nanotubes have a similar affect to asbestos when inhaled, so I sure hope they're not just leaving piles of it lying around.

Source: http://www.nanotechproject.org/news/archive/mwcnt/

CO2 is not evil and by mass most of life on earth needs it to breathe.

Elevated CO2 from fossil carbon stores (coal/oil etc) is evil. That isn't the same as C02 already in the biosphere.

Lets be precise here: The CO2 from fossil carbon stores is chemically speaking exactly like other C02.

That said, increasing the concentration might not be smart anyways, -I don't know, at this point I'm not really sure. (I used to be very skeptic, now I'm starting to think it might be correct and the proponents just don't get PR.)

>> Lets be precise here:

Do you or do you not believe in the link between the burning of fossil fuels and climate change? If you do not, I am not going to get into a theological debate with a believer.

> Do you or do you not believe in the link between the burning of fossil fuels and climate change?

?

It matters nothing for the chemical properties of CO2.

> If you do not, I am not going to get into a theological debate with a believer.

I am very much a believer, and for technical stuff I believe in experiments, measurements etc : )

From the journal article, re: energy extraction from coal:

"The thermodynamic enthalpy available per CO2 emitted from carbon combustion (−394 kJ/mole) is less than that from methane (−890 kJ/mole) combustion. Coal, compared to natural gas, combustion will generate less excess heat per transformable CO2 to drive CNF [carbon nanofiber] and CNT [copper nanotube] production product is retained within the system at (the electrolysis chamber temperature of) 750 °C, and hence under normal circumstances while a CC [combined-cycle natural gas] CNF plant can co-produce electricity and CNFs, a coal CNF plant will produce only value-added carbon nanotubes, and not surplus electricity."

Annotations in brackets are mine.

my thoughts exactly

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