October 03, 2007
Extraction Of Carbon Dioxide From Atmosphere Seen Possible
Frank Zeman and Klaus Lackner have proposed a way to extract carbon dioxide from the atmosphere in order to prevent global warming, but at what cost?
Removing CO2 from the atmosphere is the subject of a prize announced earlier in 2007 by British entrepreneur Richard Branson. Branson pledged to award $25 million to anyone who can develop a scheme for removing at least one billion tonnes of the gas from the atmosphere every year, for a decade.
So, together with Klaus Lackner, a former colleague at Columbia University, Zeman devised a new way of scrubbing CO2 from air. He has also performed calculations, published in Environmental Science & Technology, which suggest that the new method is efficient enough to justify its use.
The process involves pumping air from the atmosphere through a chamber containing sodium hydroxide, which reacts with the CO2 to form sodium carbonate. This carbon-containing solution is then mixed with lime to precipitate powdered calcium carbonate – a naturally occurring form of which is limestone. Finally, the "limestone" is heated in a kiln releasing pure CO2 for storage.
If the kiln's heat came from a nuclear power plant then no fossil fuels would be needed to make this system work. But I would advice replacing existing coal, natural gas, and oil-powered electric power plants with nuclear power plants before using nuclear power to extract CO2 from the atmosphere.
The lower the cost of non-fossil fuels energy generation falls the more practical and affordable atmospheric CO2 extraction becomes. Nanotech replicators to build solar photovoltaics panels will some day make atmospheric CO2 extraction extremely cheap to do.
If we needed to cool down the planet in a hurry we have much cheaper options.
Agri-char or Bio-char (turning plant matter into charcoal and mixing it with soil) has got to make a lot more sense. Using agri-char provides a structure for micro flora and fauna to live, helps retain water and nutrients in the soil and reduces the need for fertilizer. If we are pulling CO2 out of the air we should do something useful with it.
Strictly speaking, since CO2 extraction is endothermic, that "something useful" could be nothing more than doing it where low grade heat is needed.
Like in my home, in Michigan, this winter.
Interesting idea but not new chemistry. CO2 capture is well understood but there is no sense doing it very inefficiently.
Suppose the device were built. It should be able to remove CO2 from coal plant emissions. Removing CO2 from coal plant emissions is good, right?
Yes, removing CO2 from coal plant emissions is good. Even better, don't the coal at all. Shut that coal plant down and just use the electricity from the nuke plant.
Strictly speaking, since CO2 extraction is endothermic,
Overall, it can be exothermic, if the CO2 can be reacted with silicates to make silica and carbonates. This is the natural reaction that pulls CO2 out of the atmosphere over geologic time (balanced by CO2 reemitted by volcanism).
True, but in order to make the reaction go at any significant rate, you've got to rather finely divide the rock to get surface area, and that tends to consume power by itself. I'd be suprised if anybody came up with an engine that ran off rock and atmospheric CO2, though it would be thermodynamically possible.
It might be worth taking a close look at lichens, to see if any of them get energy from this reaction.
A serious question: From the standpoint of long term atmospheric balance, is it CO2, or carbon, that we want to remove from the atmosphere? After all, it's carbon that's being added; The O2 part of CO2 came from the air in the first place. Are there long term consequences to adding gigatons of carbon, and then removing the O2 it's combined with?
I say this realizing that removing the CO2 is energetically much easier than removing the carbon, and leaving the oxygen behind.
you've got to rather finely divide the rock to get surface area, and that tends to consume power by itself.
Actually, milling of rock to even a fine powder doesn't require all that much energy. Almost all the chemical bonds in the rock are unaffected until the grain size is close to atomic dimensions.
I looked this up some years back (when trying to determine what the energy cost would be for extracting uranium from granite) and was surprised it was low. A single 1 GW nuclear plant could supply enough energy to finely powder, using existing grinding technology, on the order of billions of tons of rock per year.
Interesting; So, how exothermic are weathering reactions? Is this a feasible source of energy, with CO2 extraction merely a byproduct? I'll have to hunt up my CRC this evening.
So, how exothermic are weathering reactions?
95 kJ/mole CO2 for forsterite, 64 kJ/mole CO2 for serpentine.
Is this a feasible source of energy, with CO2 extraction merely a byproduct?
Probably not, the reaction doesn't go very fast. Getting it to go fast enough to be useful is still a subject of research.
A KJ is about a BTU, and the molecular weight of forsterite is about 140; so you're talking about roughly 30 BTU per lb. To heat a typical house might consume a ton of forsterite per hour.
Clearly, it's never going to replace fossil fuels for home heating. :( That's a pretty wimpy reaction, which is, I suppose, why rock doesn't catch fire very often.
That's per mole of CO2. Each mole of forsterite sequesters two moles of CO2.
Oh, and even if it were 1 mole, your calculation should yield about 300 BTU/lb, not 30.
Quoth Brett Bellmore:
Are there long term consequences to adding gigatons of carbon, and then removing the O2 it's combined with?
Perhaps, but the fraction of atmospheric O2 involved is much smaller than the fraction of atmospheric CO2 (because there's so much more oxygen) so they'll be well-hidden.
Are there any waste disposal problems associated with this process??
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If some one thinks really deep he will realise that it is basically not possible to sequester CO2 in any meaningful way other than by a growing tree.
The source of any energy (other non conventional energy like nuclear, thermal, wind , photo voltaic energy etc) basically comes from photosynthesis. Photosynthesis from sugar and all other source of energy ( starch, wood, alcohol, petroleum products etc) come from some or other process of breaking of sugar to carbon dioxide.
So any energy used to block CO2 chemically will ultimately be producing more CO2 somewhere hence not worth even trying.
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