CO2 capture

[NetSnake]

I copy/paste the full article cause membership is required and I think it's interesting...

http://www.sciencemag.org/cgi/conten.../315/5817/1371

Science 9 March 2007:
Vol. 315. no. 5817, p. 1371
DOI: 10.1126/science.1139585


Policy Forum
CLIMATE CHANGE:
CO2 Arithmetic


Wallace S. Broecker*

If we are ever to succeed in capping the buildup of the atmosphere's CO2 content, we must make a first-order change in the way we view the problem. Most policies that have been discussed, including cap-and-trade systems and the Kyoto treaty, have treated the problem exclusively in terms of incremental reductions in CO2 emissions. These, however, will not stabilize atmospheric CO2 levels; they only slow the rate of increase. Instead, to actually stop the increase, we must develop the concept of what might be called a "carbon pie." Currently, for each 4 gigatons (Gt) of fossil carbon burned, the atmosphere's CO2 content rises about 1 ppm; including deforestation, we now emit about 8 Gt of carbon per year. Further, this four-to-one ratio will only change slowly in the coming decades. Hence, if we set a desirable upper limit on the extent to which we allow the CO2 content of the atmosphere to increase, then this fixes the size of the carbon pie. If, for example, this limit were to be double the preindustrial CO2 amount (i.e., 560 ppm), then the size of the pie would be 720 Gt of carbon [i.e., 4 (560 - 380)]. Were the limit to be set at 450 ppm, the size of the pie would be only 280 Gt.

Once the size of pie has been established, each of the world's nations would be allocated a slice. In an ideal world, the size of these slices would be based on population. In this case, the world's rich countries would get only about 20% of the pie. If the limit agreed upon were 560 ppm, then the rich nations' share would be about 150 Gt. As these countries together currently consume about 6 Gt of fossil carbon per year, if they continued at this pace, their allotment would be consumed in just 25 years. Faced with this limit, each of these rich nations would be forced to rapidly reduce its emissions (see figure). Poor nations would be able to sell portions of their pie slice to the rich countries and still have enough left to permit them to industrialize.

[netsnake: didn't bother with the figure, just a fancy graph]

If this scenario were to be implemented, I find it highly unlikely that any combination of increased efficiency in energy use, implementation of non-fossil fuel energy sources, and capture of CO2 produced in coal gasification plants would be capable of meeting the required reduction schedule: An additional element would be necessary. The gap (see figure) between actual and allowed emissions would have to be made up either by purchase of CO2 allocated to poorer nations or by burial of CO2 captured from the atmosphere. Stemming the rise in CO2 would require participation of rapidly industrializing nations such as China and India. Under the pie concept, there would be an incentive for them to join for they would have a considerably longer period of time to adjust their CO2 emissions than rich nations. The sooner such an agreement was put into force, the better the situation would be for these nations. Until this is done, the size of the carbon pie will continue to shrink at a rate of 70 to 80 Gt per decade.
Because CO2 sales would serve only as a temporary stopgap, capture of CO2 from the atmosphere would be necessary. CO2 capture from the atmosphere is feasible, but has yet to be implemented, and faces several technological challenges. If the CO2 carried by the air streams used to drive wind turbines were to be captured, then on an energy-equivalent basis, the physical dimensions of the CO2 capture devices would be only 1% of the sweep of the turbines (1). In other words, in a sense, air streams carry 100 times more CO2 than kinetic energy.

In addition to allowing the gap between actual and permissible emissions to be filled, air extraction has other attractive features. (i) It could be done at sites far from population centers and close to the sites of CO2 storage. (ii) Once the rise in CO2 had been stemmed, the CO2 content of the atmosphere could be drawn back down to a level at which the earth's ice caps were stabilized. (iii) It would provide a mechanism by which the thorny issue of compensation for past CO2 emissions by richer nations could be negotiated.

While there is no question that CO2 capture from the atmosphere is doable, the cost is still unknown. Capture would be affordable if it caused the price of fossil fuel energy to increase by 10 to 30%. However, a large fraction of the operating cost would be for the purchase of the energy required to accomplish the capture and burial. If the cost of sufficient fossil fuel to generate this energy is too high, then this strategy would be impractical.

The largest of the costs associated with air-capture will be those associated with the release of the CO2 from the capture material and with the recycling of any chemicals used. As sodium hydroxide, an obvious choice, holds onto CO2 too tenaciously, a better option would be a material that would be able to pick up CO2 but would release it more readily. Regardless of what material is to be used, it is absolutely essential that research on capture and sequestration be carried out to determine whether the energy costs can be brought down to an acceptable level. Capture from coal gasification plants should also be implemented.

In the present political climate, any attempt to achieve an agreement on either the size of a carbon pie or its allocation among the world's nations would be difficult. However, unless we advance beyond thinking only in terms of conservation and alternate sources and begin to think in terms of a carbon pie, we will have no chance to stop the rise in atmospheric CO2.

References and Notes

1. K. S. Lackner, H.-J. Ziock, P. Grimes, in Proceedings of the 24th International Conference on Coal Utilization & Fuel Systems, B. Sakkestad, Ed. (Coal Technology Association, Clearwater, FL, 1999), pp. 885-896.

2. I thank K. Conrad, G. Heal, and K. S. Lackner for discussions.

10.1126/science.1139585

The author is at the Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964-8000, USA. E-mail: broecker@ldeo.columbia.edu

[KRSESQ]

Check my math, please. Carbon has a density of 2267 kg/m3. If I'm correct, 8,000,000,000 tons ( 8 GT?) of the stuff would create a solid cube 152 Meters on a side.

unless I'm misinterpreting the term Giga-Ton.

Sequestoring the carbon shouldn't be a problem, since industrial uses for all that carbon will quickly be found. Super-durable plastics and lubricants based on Fullerenes spun from pure carbon will be two of the great growth industries of the next century. Get in on the ground floor.

Kevin

[Brian Ellis]

Interesting, but like most magazine articles, not thought through. I don't dispute much in the first 4 paragraphs. I'll start by questioning whether it's "doable". Not just economically so, but chemically. However, the key sentence is, I believe, the last one in paragraph 5.

Sodium hydroxide is the "obvious choice" but, as he says, the CO2 cannot be released, so that it is a "one-off" use, meaning that billions of tonnes of chlorine would need to be released into the atmosphere. Not good! Lime is no better. To heat the billions of tonnes of limestone to produce active quicklime and then to reheat it, after use, to discharge the CO2 again would require more energy than we are generating today. Then what would we do with the 9 billion tonnes of CO2 we captured each year just to maintain status quo (this would not reduce it any)? The sheer magnitude of the volume of CO2 we put into the air is something that none of us can easily visualise. Let me try. We emit (round figures) 20 billion tonnes of the stuff from our chimneys and exhaust pipes each year. This takes up a volume of 10,000 billion m3. A hectare is the size of 2 football fields. Let's take 100 football fields or 50 hectares, a sizeable bit of land, 500,000 m². Let's magically park our CO2 on this land. This would give a column of CO2, at ground level pressure, of 20,000 km height, which would take us straight beyond the stratosphere, one-twentieth the distance to the moon. However, this argument is flawed, because the CO2 would not be of constant density because of gravity. If we could contain it into my hypothetical column of ½ million m² cross-section, where would it reach? The moon? The sun? No, it would escape the solar system! (not a bad idea, BTW ).

IMHO, pie in the sky (no pun intended). See here for a complement of information.

[rylan]

Thats carbon though... you'd have to break the bond of the CO2, which would require a lot of energy.
Carbon would have plenty of uses, but I'm not sure what you'd do with captured CO2.

[Brian Ellis]

Check my math, please. Carbon has a density of 2267 kg/m3. If I'm correct, 8,000,000,000 tons ( 8 GT?) of the stuff would create a solid cube 152 Meters on a side.

unless I'm misinterpreting the term Giga-Ton.

Sequestoring the carbon shouldn't be a problem, since industrial uses for all that carbon will quickly be found. Super-durable plastics and lubricants based on Fullerenes spun from pure carbon will be two of the great growth industries of the next century. Get in on the ground floor.

Kevin

I make it 1522 m. You forgot to convert the tonnes to kg???? However, to convert the CO2 to carbon would require more energy than we generated from burning it, in the first place. This is the paradox.

[NetSnake]

well, if there was a way to capture-release-pressurize in real time there wouldn't be much of a space problem...

[GNEP]

Hehe funnily enough I was just putting words in someone's mouth on CCS as this thread started! Cut/paste as follows with various bit taken out to keep you guessing why I'm doing this Too lazy to re-word and fit in the thread (the article is a bit, erm, odd I think).

...support CCS ... in the drive to both reduce the nation’s carbon footprint and to help the world develop a portfolio of techniques with which to combat climate change.

However, we also recognise that there are inherent drawbacks to carbon dioxide capture at source, to liquefaction, to transport and to the subsequent sequestration, which means that the further research and development happening in the UK and internationally is welcome, so that all the potential issues are understood before we commit to widescale use of such technology.

1)Overall energy usage increases – it costs energy to capture, transport and store carbon dioxide, which will most likely come from burning more fossil fuels, thus further reducing the precious resources available to future generations. It is recognised however that there is potential with the use of old coalmines to, over time, form methane after CO2 has been injected, thus increasing supply of accessible and useful fossil fuels in the UK. The argument that CO2 can increase oil and gas recovery from marginal fields largely ignores the fact that in the UK injection of cheap and readily available seawater already achieves this effect.
2)Economics – the government official figures have some problems, and in fact have their origin in a very brief piece of work done for the IPCC. It is our view that they seriously underestimate the costs of CCS on an industrial scale, but getting a better view of these costs in order to create a balanced energy policy is precisely why the further work being done by bright people like your students is absolutely vital.
3)Carbon pricing – given the right carbon pricing framework, it is our belief that the private sector will utilise CCS without further government intervention. However estimated levels of carbon prices would be far in excess of those currently seen under EU ETS or used in the 2006 energy review. At the Stern “social cost” level of £70/tCO2e then we believe that CCS for pulverised coal and gas turbine plants would be economic.
4)Long term storage – whether using depleted oil and gas fields, aquifers, salt caverns or old coal mines, great care needs to be taken that and CO2 pumped down there will remain there, given the temperatures and pressures in these geological formations. Again, this is an area which needs more work.

In conclusion, CCS has the potential to be a very useful medium-term aid in the portfolio of techniques combating climate change, and one in which the UK is positioned to lead the world. However by its very nature it exacerbates sustainability problems which we will have to face at some point in the longer-term future, and have the potential to be seen as some as the “magic bullet” which unfortunately does not exist for a sustainable energy policy. We need to utilise a whole range of technologies and policy frameworks, which include a far stronger drive towards energy efficiency, renewable electricity generation beyond just wind, and extracting as much of the usable energy from those fossil fuels which we will have to burn, for example by combined heat and power from gas on a more distributed basis. CCS together with residual centralised generation capacity is indeed a part of that picture, but there is still much work to be done on CCS before any firm decisions can be made. As such, we fully support the work being undertaken to improve our understanding of its potential and keep a close eye on progress made ...

[Dr Mordrid]

Capturing CO2 by artificial photosynthesis makes more sense. The recent development of new catalysts should help;

http://forums.murc.ws/showthread.php?t=61054

Article....

Artificial photosynthesis moves closer

POTSDAM, Germany, March 12 (UPI) -- German scientists have activated CO2 by using graphitic carbon nitride as a catalyst, moving science closer to artificial photosynthesis.

The achievement was reported by a team led by Markus Antonietti at the Max Planck Institute for Colloids and Interfaces in Potsdam, Germany.

"Chemical activation of carbon dioxide, meaning its cleavage in a chemical reaction, is one of the biggest challenges in synthetic chemistry," said Antonietti.

In contrast to most previous approaches, Antonietti's team worked with metal-free catalysts, turning toward plants for inspiration. Photosynthesis in modern green plants involves an important intermediate step: the bonding of CO2 with nitrogen atoms to form carbamates. The German researchers said they therefore also experimented with nitrogen-rich catalysts with structures that allow them to form carbamates.

"This could make novel, previously unknown chemistry of CO2 accessible," said Antonietti. "It may even be the first step in artificial photosynthesis."

The process is described the journal Angewandte Chemie.

[KRSESQ]

It would be ironic if such carbon sequestration technology turned out to be little more complicated or expensive than existing electrostatic precipitators.

Then there's the possibility that the sequestored carbon turns out to be more of a headache to deal with than the Global Warming was!

Kevin

[KRSESQ]

@ Brian:

I was assuming metric tons - 1000 kg. A cubic meter of pure solid carbon would weigh 2.267 metric tons, correct?

So 8 GT (8,000,000,000 - correct?) of carbon @ 2,267 kg/m3 would have a volume of 3,528,892.8 cubic meters. The cube root of 3,528,892.8 is 152.25. Thus a solid cube of pure carbon would cover half a soccer pitch, correct?

How much greenhouse carbon does an average human body produce in a day?

Kevin

DOH! Incorrect! A soccer pitch is 100 x 50 meters, approximately. So such a hypothetical carbon cube would cover 4 1/2 soccer pitches!

THAT, my friends, is why I am NOT pulling 100k a year in the tech industry! :P

[Dr Mordrid]

Human respiration produces about 450-550 liters of CO2 per day depending on activity etc.

The lower value of 450 liters X 6 billion people comes down to ~2.7 trillion liters/day or 985.5 trillion liters/year. At about 2 g/l thats a lot of CO2; almost 2 billion metric tons. More if you use the higher value.

Now add the respiration of every animal that does.

Flatulence is primarily nitrogen, hydrogen and methane which is also a greenhouse gas.

[Brian Ellis]

@ Brian:

I was assuming metric tons - 1000 kg. A cubic meter of pure solid carbon would weigh 2.267 metric tons, correct?

So 8 GT (8,000,000,000 - correct?) of carbon @ 2,267 kg/m3 would have a volume of 3,528,892.8 cubic meters. The cube root of 3,528,892.8 is 152.25. Thus a solid cube of pure carbon would cover half a soccer pitch, correct?

Sorry, 8E9 tonnes = 3,528,892,809.88 m3 = ~3.53E9 m3 cube root of which is 1522.4609 or 1.52E3 m. If your figs were OK, the density of C would be 8E12 kg / 3.53... = 2.267E6 kg/m3 or 2.267 kg/cm3 which is just slightly on the heavy side.

Anyway, this is still academic, as we don't have enough energy to extract carbon out of CO2 and 8E9 t of C would require 21.92E9 t of CO2 = 10E12 CO2 (first approximation, as we don't emit as much as 8E9 t C. The actual estimate in fossil fuel CO2 is ~19.2E9 m3, containing a tad over 7E9 t C).

I still maintain that the sheer quantities prohibit any form of significant sequestration out of the atmosphere, remembering that the 19.2E9 m3 is EACH year and not just the accumulated total. In fact, significant CCS out of flue gases of power stations is very unlikely as a) the cost would be too high and b) the safe disposal is, as GNEP states, unproven. In any case, this cannot be done with car exhaust gases or central heating boiler flue gases, or open hearth combustion of coal etc.

Significant photosynthetic absorption is impossible, as explained in the ref I cited earlier and nitride adsorption (not absorbtion) is also impossible on the scale required (e.g., not enough natural graphite and synthetic graphite requires far too much energy to manufacture).

[NetSnake]

Significant photosynthetic absorption is impossible, as explained in the ref I cited earlier and nitride adsorption (not absorbtion) is also impossible on the scale required (e.g., not enough natural graphite and synthetic graphite requires far too much energy to manufacture).

OK, I don't know how you define "far too much energy". Do you mean impossible or that more CO2 would be produced than captured? Cause in the latter case that shouldn't be a problem since the synthetic graphite would be reusable, right?

[Dr Mordrid]

I want to know which synthetic graphite Brian is talking about; primary, secondary or fiber? All are made in massive quantities, so I don't understand his supply concerns.

Reusable? It's being used as a catalyst, so wear should be slow & I can't see why it couldn't be recycled.

[Brian Ellis]

OK, I don't know how you define "far too much energy". Do you mean impossible or that more CO2 would be produced than captured? Cause in the latter case that shouldn't be a problem since the synthetic graphite would be reusable, right?

If you want capture billions of tonnes of CO2, you'll need billions of tonnes of the stuff available. Even with a duty cycle of 1 capture process per month, you will still need hundreds of millions of tonnes or more, as I cannot see the weight adsorbed being greater than the substrate weight, most likely very much less. I have no yardstick for this, but metal hydrides store only about 3% of their own weight. The most efficient one I know of is lithium nitride, which can store 12% of its own weight, so I doubt whether it would be significantly more.