Air capture

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"Air capture"

RealClimate has a good introductory post on air capture, which they explain as:

The idea would be to let people emit the carbon dioxide at the source but then capture it directly from the atmosphere at a separate facility.

This is going to be a relatively expensive and complicated strategy for decades — and, of course, you need a place to put the carbon dioxide. That said, a lot of work is going on to see if one can do air capture driven by heat.

Why does that matter? The world has a LOT of zero carbon waste heat not currently being used for anything. Indeed, U.S. thermal power plants alone throw away in waste heat as much energy as Japan uses for every purpose! That’s more than 20 quads. And that doesn’t even count the heat thrown away in industrial processes. Now the smartest thing to do with that heat for the next few decades is obviously either generate electricity with it or use it for heating buildings or industrial processes.

But we should surely do a fair amount of research on air capture, since, by not later than the 2020s, we’re going to get desperate for emissions reductions, and by the 2030s, we’re going to be very desperate and willing to pursue expensive options we that aren’t yet politically realistic.

Indeed, it seems rather likely to me that something like air capture will be needed by the second half of this century. Assuming we actually seriously try to keep emissions below 450 ppm (currently, a doubtful proposition), we’ll probably need to go back to below 400 by 2100 and 350 by 2150, in my optimistic spin on Hansen’s latest paper.

In summary, air capture is not a near-term or medium-term solution, but possibly a long-term strategy.

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7 Responses to Air capture

  1. Danny Bloom says:

    Joe
    I don’t know how to reach you by email, so I will post this here for now. Feel free to erase if off topic.
    DOT EARTH did a brief post today about polar cities. Take a look and would love to hear your reax pro or con.

    Danny

    http://dotearth.blogs.nytimes.com/2008/03/30/polar-cities-a-haven-in-warming-world/#more-90

  2. elbarto says:

    Joe, from the IPCC special report “Carbon Dioxide Capture and Storage” the principal method for air capture is mineral carbonation. Mineral carbonation using silicate rocks requires 1.6 to 3.7 tonnes of silicate per tonne of CO2 sequestered.

    I estimate that the total world hard-rock mining activity mines about 17-20 Gt/yr of rock producing iron ore, gold, copper etc etc.

    If we were to sequester say 15 Gt/yr of CO2 we would need to mine at least 24 Gt/yr (and up to 55Gt/yr) of silicate rock. More than all the world’s current mining activity.

    Mineral carbonation requires the silicate rocks to be finely ground and reacted with air in pressurised tanks at elevated temperatures in order for the reaction to proceed at a fast enough rate.

    The mining and grinding of the rock would require massive fossil fuel inputs, although heat for the reaction process could theoretically come from power station waste heat.

    Also note that silicate rock often contains asbestos. Thousands of people are now dead or dying from asbestos related disease from the asbestos industry of last century. It’s probably not that great an idea to go and start mining 24 Gt/yr of asbestos containing rock.

    I’m fairly confident that mineral carbonation is yet another “technology blah blah” tactic for delay. Forget “green issues” the word ASBESTOS need only be mentioned for this particular route to face crushing opposition.

  3. Joe says:

    Elbarto — unless they come up with a much better way to store the CO2, I seriously doubt we could store more than 1 GtC or 3.67 GtCO2, probably in deep underground saline aquifers.

    Coal with CCS is probably the only serious CCS we might see before 2050. After that, well, it gets hard to predict.

  4. David B. Benson says:

    Most of the 500 GtC added to the active carbon cycle is probably from coal. Convert the excess carbon dioxide back into coal by hydrothermal carbonization of biomass and bury it back underground.

  5. Jim Bullis says:

    Joe, I liked your campaign to get the O2 back in CO2. Don’t give up. I realize it can be unfair, since it is so often difficult to get a subscript in modern computer technology, and it is easier to say “carbon,” but it has been a sign of incompetence to see it used so simply. Of course, this is in keeping with American dietary data practice, where we started saying “sodium” when we really mean “salt,” and of course, even this is glossing over the different kinds of salt. I noticed a few years ago that European food products actually talk of Na+ ions in foods, where we just say “sodium” on our soda cans. However, I am not certain that Na+ is right criterion for badness in foods either. I have fussed for many years over the danger of drinking water from water softeners, where sodium ions are put in water instead of calcium ions, but I always got the same dismissing blank stares from medical scientists (doctors) as I do from climate scientists on some of my questions. As far as sodium in water goes, it really does not seem to matter.

    Another question Joe: How can I get the report that goes with the recently posted McKinsie chart without buying their subscription?

    David B. Benson: What the heck is hydrothermal carbonization? And is biomass everything from grass clippings to barnyard manure? And if you are going to bury stuff, why does it have to be converted to anything?

  6. Jim Bullis says:

    elbarto: You reminded me of a point I wanted to make about how difficult it is to really get to the truth about things. Maybe Joe will be a little less impatient with questions.

    Asbestos became a villain, as far as I have been able to tell, mostly in the eyes of jurors in the hands of persuasive lawyers. I don’t think the jury pools are exclusively made up of top medical scientists. From all I have been able to find, the thousands of dead and dying from that stuff were mostly shipyard workers that breathed great clouds of the stuff on a daily and continuous basis, and also were smokers. The millions of the rest of us that occassionally brushed an acoustic ceiling seem to be not so badly damaged. My bet is that tobacco is the biggest problem.

  7. Of course, this is in keeping with American dietary data practice, where we started saying “sodium” when we really mean “salt,” and of course, even this is glossing over the different kinds of salt. I noticed a few years ago that European food products actually talk of Na+ ions in foods, where we just say “sodium” on our soda cans. However, I am not certain that Na+ is right criterion for badness in foods either.