Tuesday, December 01, 2009

Hot air (capture)

There's bit of correspondence in Nature Geoscience about air capture, specifically some promotion from RPJr which seems to think that all our problems will be solved by future cost reductions and better technology, and a letter from Andrew Dessler pointing out that the energy cost provides a stiff barrier irrespective of economics.

RP says:
The primary uncertainties surrounding air capture stem more from the lack of large-scale testing rather than scientific or technical concerns.
Dessler replies:
Thus, using today's technology, it takes at least approx0.5 J of energy to capture the emissions generated in producing 1 J of fossil fuel energy. If the energy for capturing carbon comes from fossil fuels, then at least a third of society's fossil fuel energy would have to be diverted to air capture to eliminate all emissions. Alternatively, it would require an increase in the total production of fossil fuel energy of at least a third.
While I would not be surprised to see an engineer claiming that the reciprocal of 1-1/3 is 1+1/3, I would hope most physicists would sum a few more terms in the Maclaurin series and get to 1+1/2 :-) However, a mathematician (me) might point out that the correct numbers based on the energy estimates above are actually 1-1/2 and its reciprocal, 2 :-) That is, half of total power output would have to be devoted to air capture, or alternatively total power output would have to double to reduce net emissions to zero; 2J of total power, with 1J devoted to sequestration, would leave 1J usable.

Of course, the general point (that energy matters irrespective of the economics) is one that has been made repeatedly on RP's previous blog when he has promoted air capture in the past (eg the comment thread here, also here and here). It's unfortunate that Dessler's letter drawing attention to this point actually understates it by such a wide margin. Of course future advances can be expected to reduce that energy cost, but there is a hard lower limit. I vaguely recall it's something in the region of 10% of the total output energy for coal, meaning 25% of the usable power for a 40% efficient power station. But I could be wrong. It may be in the comments linked above.

Andrew Dessler explains via email that he was assuming that the "extra" power would use standard on-site carbon capture and storage at low energy cost - but it seems to me that this still makes the relevant figure for fossil fuel use to be at least a 50% increase rather than the quoted 33%, and probably 60% or more if we use a realistic assumption about CCS.


Martin said...

25% is in the ballpark for claims I have seen. Still, if this could be done at a price that is not absurd (which remains to be shown), colour me happy.

Tom Fiddaman said...

Pielke also can't stop himself from endlessly repeating, "the costs are comparable to more conventional routes of mitigation," even though he knows full well that this is a half truth. In his own assessment, the marginal cost becomes competitive with mitigation only at very deep cuts. The cost (marginal or average) of air capture is dramatically higher until the low-hanging fruit has been harvested.

Hank Roberts said...

Has anyone compared the empty space left by removing petroleum with the volume of carbon dioxide? Where do they imagine _putting_ the CO2?

Even forgetting the amount of subsidence that has already reduced the void spaces.

But of course any program that requires doubling the amount of coal purchased and burned in order to improve the environment has to make sense to those who, well, favor burning more coal.

gravityloss said...

Whoa, what an elementary mistake, spotted it immediately.
If X Joules are produced, you need ½X for air capture and ½X is still available for everything else.
Hence if you want to keep using X for humans, you have to produce 2X, of which X is used for air capture.

And I'm an engineer so there!

crandles said...

>"Where do they imagine _putting_ the CO2?"

deep ocean perhaps?

mineral carbonation perhaps?

or just internalise the cost and let the fossil fuel industry work out the cheapest way
(Yes I am sure the fossil fuel industry will like that and won't lobby against it ;o) )

David B. Benson said...

Sequestration by in-situ peridotite weathering:
would cost around US$10 per tonne of CO2; there is more than enough near-surficial peridotite in Papua New Guinea alone to hold all present + future excess CO2 emissions.

Hank Roberts said...

WHAT'S NEW Robert L. Park Friday, 12 Jun 09 Washington, DC

1. CARBON DIOXIDE: IAP STATEMENT ON OCEAN ACIDIFICATION. At a departmental colloquium 30 years ago the speaker assured the audience that carbon dioxide buildup in the atmosphere would be buffered by absorption in the ocean. I kept waiting for that to happen. Of course, it was happening. According to a statement issued this week by the Interacademy Panel, whose 60-some members range from the Albanian Academy of Science to the Zimbabwe Academy of Science, a quarter of the CO2 produced by human activity in the last 200 years has been absorbed in the oceans. Unfortunately, excessive CO2 in the oceans is no more benign than that in the atmosphere. Marine life that depends on calcium carbonate is particularl. Moreover, ocean acidification is irreversible on a timescale of thousands of years. The only way to mitigate ocean acidification is to reduce CO2 in the atmosphere. Sequestration, that will at best affect the second derivative. We must reduce reproduction.

Hank Roberts said...

Okay, so
-- what will it cost to buy Papua New Guinea, or the right to pump CO2 into all the appropriate rock underneath the whole country?

-- add the unpaid costs of coal now: http://www.nap.edu/catalog.php?record_id=12794

-- add $10/ton

Now, why continue burning coal at those prices instead of spending the same amount of money ramping up development of alternative energy sources?

Why invest in a dead-end technology?

Hank Roberts said...



So it is the net of the gross energy (e.g. barrels of oil, or tons of coal) minus the energy invested in extraction, refinement, and transportation that really counts as usable in the economy.

As I worked more on the paper that Hall and I will co-produce, I began realizing that this is much more significant than anybody seems to have realized. As I outlined in that prior blog, if gross energy is near or at peak (and some say it may be past a theoretical peak; that we are in a bumpy plateau due to the fluctuations in the financial markets) then this means that we are already passed peak net energy. ...

James Annan said...

What everyone said :-)

Also, from my POV, both free-air and point-source capture and storage smack of just kicking the problem down the road and excusing business-as-usual for another decade or two. I don't think there is much chance that either of them (or both together, for that matter) will ever make a big impact on emissions, and it seems to me that renewable energy and/or reduced energy consumption (efficiency, not necessarily recession!) are the best ways forward.

marcus said...

While I like the idea of air capture research, the problem is that basically by definition, the scale of the air capture business will be at least as large as the scale of the fossil fuel industry... every ton of carbon mined and burnt means 3 tons of CO2 in the atmosphere. Whether liquefied and injected or reacted with peridotite, it is likely that more tons of stuff will need to be moved than you had to dig out in the first place. The algae solution is a bit better, in that at least the algae-biofuel can displace some fossil fuels later...

And, as Ken Caldeira noted in a talk, if you are going to build an industry that is as large as the fossil fuel industry to deal with its waste... why not just replace the fossil fuel industry with non-carbon emitting sources instead?

David B. Benson said...

Hank Roberts & all --- Papua New Guinea is not the only location, just the biggest on-shore near surficial perdtite formation (about 1/3 the country). Note the articles refers to Oman. In either location, indeed several others, people might might like to have the (fairly well paid) work, doncha think?

Irrespective of the capture form, do recall that there is already about (44/12)*500 = 1833 gigatons of excess CO2 to be romoved, yes? The sooner the better IMO.

While it is nice to dream of a completely fossil fuel free economy, I'm not expecting this to happen anytime soon.

Chuck said...

I bags watching everyone here who has mixed up New Caledonia and Papua-New Guinea translate between French and Pidgin.

On a more serious note, actual quantitative studies of magnesium silicate mineral carbonation show that most sites take decades to sequester the carbon used in digging them up.

And, of course, the most successful sites are former asbestos mines...

If you put a price on carbon, then nickel miners will earn some extra cash by carbonating their tailings. But assuming that cheap & easy carbon sequestration will magically save us from having to do anything else about emissions is hopeful at best.

David B. Benson said...

Chuck --- Huh? It is true that New Caledonia also has suitable peridotite formations, but Papua New Guinea has vastly more.

EliRabett said...

If you need 0.5J for sequesterization per 1J of energy used, the total is 1.5 J and 33% of that is for sequesterization.

It's the old question of what the markup is, 100% of the store's cost, 50% of customer's cost.

In this case 33% of all energy used is for sequesterization and you need to produce 50% more.

James Annan said...


Well it all depends on whether the additional 0.5J of energy production also produces CO2 that needs sequestered. However even the optimistic viewpoint (that it does not) results in an increase of +50% which is significantly worse than the letter said.

EliRabett said...

Ah, but part of the ju-jitsu is to use intermittent solar/wind/tide for the sequestering.

Chuck said...

They are still nowhere near 1/3 of PNG.

David B. Benson said...

It is the capture, separating the CO2 from the other constiuents of the flue gas, which is energenically expensive, not the sequestration.