September 29, 2008
Low Cost Atmospheric Carbon Dioxide Removal Looks Possible
If carbon dioxide build-up starts causing unacceptable climate change then a cheap way to remove CO2 from the atmosphere might become an option.
University of Calgary climate change scientist David Keith and his team are working to efficiently capture the greenhouse gas carbon dioxide directly from the air, using near-commercial technology.
In research conducted at the U of C, Keith and a team of researchers showed it is possible to reduce carbon dioxide (CO2) – the main greenhouse gas that contributes to global warming – using a relatively simple machine that can capture the trace amount of CO2 present in the air at any place on the planet.
...Keith and his team showed they could capture CO2 directly from the air with less than 100 kilowatt-hours of electricity per tonne of carbon dioxide. Their custom-built tower was able to capture the equivalent of about 20 tonnes per year of CO2 on a single square metre of scrubbing material – the average amount of emissions that one person produces each year in the North American-wide economy.
That 100 kwh per removed tonne of CO2 would be pretty good in terms of energy cost. If the electricity cost only 10 cents per kwh then the cost per tonne would be only $10. Some proposed carbon tax regimes are at $30 per tonne and up. This could be done with photovoltaics once PV becomes cheap enough. The fact that the sun doesn't shine all the time won't matter. Just run the process when the power is available. No need for transmission lines or even expensive circuitry to convert the electricity into AC power. Though materials costs and piping the CO2 somewhere might add substantial costs.
"This means that if you used electricity from a coal-fired power plant, for every unit of electricity you used to operate the capture machine, you'd be capturing 10 times as much CO2 as the power plant emitted making that much electricity," Keith says.
The U of C team has devised a new way to apply a chemical process derived from the pulp and paper industry cut the energy cost of air capture in half, and has filed two provisional patents on their end-to-end air capture system.
The technology is still in its early stage, Keith stresses. "It now looks like we could capture CO2 from the air with an energy demand comparable to that needed for CO2 capture from conventional power plants, although costs will certainly be higher and there are many pitfalls along the path to commercialization."
What I'd like to see: Use sunlight to drive an artificial photosynthesis process that will fix hydrogen from water to CO2 from the atmosphere. The output would be hydrocarbons usable to power cars and for other purposes. All this will come with time.
Update: See the comment by Bruce Dunn. Looks like the energy for the initial CO2 capture is a small fraction of the total amount of energy needed for this method. So this looks like a bad idea.
Um, it seems to me we're just reinventing the wheel here to some extent. Don't plants already capture CO2 and output O2? Sure they also output some CO2 but the there is net capturing of CO2 overall, and no man made electrical energy is required - there ends my memory of school level science/biology. So could the answer be lets grow more plants & protect our forests?
I do however like the idea of fixing hydrogen to CO2 to form hydrocarbons whether we use technology or biology or a combination to do this may open a different debate.
Ideas from a novice....
Hyperion makes a reactor that produces electricity for 5 cents kwh.It has been recently report th that water hydrolysis can be be done at 100% efficiency by use of copper nano particles.There has also been progress in catalytic reactors to convert gases into liquids.So there you have it.Now if only we could find a way to make chocolate for $5 a ton.
I couldn't get the PDF to load at any reasonable speed. But it looks as if their capture of the CO2 is much more complex than the article hints. And once you have it you have to get rid of it. Hence use it or bury it.
Even so, if you really want CO2 then this will get it at less, supposedly, cost than present methods.
I would much rather see nuclear grow to dominate electrical generation. The CO2 problem, whatever its scope, will take care of itself as we reduce fossil fuel use.
What happened to all that recent excitement about the capture of CO2 in cement?
The research group has investigated capturing CO2 using a solution of sodium hydroxide and a reaction tower. The sodium hydroxide is either sprayed into the air, or trickled over a packing, while air is moved through the column with fans. The quoted 100 KWhr of electricity to capture 1 ton of CO2 is only the electricity needed to power the fans and pumps to run the tower. The resulting sodium carbonate solution must then be regenerated to NaOH with the release of CO2. This is the real energy intensive phase. They have examined reactions involving either CaOH or a sodium tri-titanate. Either reaction sequence involves heating solid chemicals to about 850 C and then adding large amounts of energy at that temperature to release the CO2. Their estimate of energy requirements for the sodium tri-titanate procedure is 3 GJ per ton of CO2, which translates into an additional 833 KWhr (note however that this is thermal energy, not electricity). Finally, energy is required to compress CO2 and move it to wherever it is to be stored underground.
Everybody should just breathe *in* for one day and not exhale. Problem solved! Along with over-population and several other BS ecotastrophes.
Sounds like this technology could be sited to work in combination with nuclear and other large power plants that generate large amounts of waste heat. No?
I wonder if this could be used to capture methane gas using less energy than the captured methane could generate in an efficient natural gas power plant? If so, you get a nice twofer. Greenhouse gas reduction and unlimited gas supplies.
If you could scale it way down and speed it up, maybe you could power your car off atmospheric methane. Fun to speculate.
Food for Thought:
Carbon Sequestration in Agriculture and Forestry (http://www.epa.gov/sequestration/faq.html)
4. How much carbon can agricultural and forestry practices sequester?
Carbon sequestration rates vary by tree species, soil type, regional climate, topography and management practice. In the U.S., fairly well-established values for carbon sequestration rates are available for most tree species. Soil carbon sequestration rates vary by soil type and cropping practice and are less well documented but information and research in this area is growing rapidly.
Pine plantations in the Southeast can accumulate almost 100 metric tons of carbon per acre after 90 years, or roughly one metric ton of carbon per acre per year (Birdsey 1996). Changes in forest management (e.g., lengthening the harvest-regeneration cycle) generally result in less carbon sequestration on a per acre basis. Changes in cropping practices, such as from conventional to conservation tillage, have been shown to sequester about 0.1 – 0.3 metric tons of carbon per acre per year (Lal et al. 1999; West and Post 2002). However, a more comprehensive picture of the climate effects of these practices needs to also consider possible nitrous oxide (N2O) and methane (CH4) emissions. (See also FAQ #8)
Carbon accumulation in forests and soils eventually reaches a saturation point, beyond which additional sequestration is no longer possible. This happens, for example, when trees reach maturity, or when the organic matter in soils builds back up to original levels before losses occurred. Even after saturation, the trees or agricultural practices would need to be sustained to maintain the accumulated carbon and prevent subsequent losses of carbon back to the atmosphere.
I know what we need to do:
Plant trees, let them grow for 15 to 60 years, depending upon species, and then harvest the trees.
You then need to store the wood produced to keep it from decomposing and re-emitting CO2 into the air.
One good storage technique is to take the wood and build houses.
Then make sure the houses are left standing for more than twice the harvest timeline to produce a net CO2 air reduction.
Ed Holston has it exactly right. You can take the waste heat from any power generation process, reconstitute and capture the CO2, then use the excess generating capacity at the nuke plant through night hours to react with water and create syngas, which then turns into methanol to run any flex fuel car (see Bob Zubrin's writings). Eventually we will be able operate virtually all medium range (less than 200 miles a day) and local transportation on methanol created out of water and the air.
This is discussed in Nobel laureate George Olah's excellent book "The Methanol Economy". Prof. Olah runs the hydrocarbons institute at USC.
You can also use the CO2 to fertilize oil algae growth adjacent to power plants. There is no reason whatever to look for places to inject CO2 into the ground- it can all be recycled into liquid fuels pretty easily.
Sodium hydroxide is probably a bad absorbant for atmospheric CO2, since the binding energy is too high (making regeneration more expensive).
There is some work on making ionic liquids that are selective for CO2 absorption. Since there are something like 10^18 different ionic liquids that can be synthesized, there's a lot of room in the search space to find ones with binding energy tuned to an optimal value. These liquids are known for having negligible vapor pressures, which would minimize loss to evaporation.
Let's say Dunn is correct - that might mean 1000 kwhr of electricity were required to remove one tonne of CO2 from air and make it ready to be stored somewhere. At 10 cents a kwhr, that's $100 a tonne. A gallon of gas when burned emits 20 lbs of CO2, if you paid $100 a tonne to remove CO2 from the atmosphere and added the cost to a gallon of gas, 2,204 lbs per tonne, that's about 100 gallons of gas, carry the two, etc, you get about $1 a gallon extra. The IPCC Special Report on Carbon Capture and Storage goes into a lot of detail about projected costs of liquifying and piping CO2 to underground storage, and they say its the extraction of the CO2 in the first place where most (90%) of the costs are going to be. Would it be reasonable to expect that if civilization ever woke up to its peril it would pay $1.10 extra per gallon of gas to power itself? I think so. Canadians already pay this much more than US consumers and Canada is still ranked with the US and called a rich country, with a better health care system according to most experts.
And this is just Keith talking about his preliminary work. The recent (September 2009) Royal Society "Geoengineering the climate" study contains this statement about air capture: "Proposals for new methods are still appearing (confidential submissions received) and it is very likely that substantial cost reductions are possible in future" which may refer to the work being done by the company Global Thermostat which is claiming to be building a pilot plant in California that will be operational in the first quarter of 2010. Global Thermostat apparently will be using waste heat of power stations to run their air capture process which they have claimed in the past has the potential to make a coal fired station operate to remove twice as much CO2 as it presently emits, i.e. negative emissions equal to what they are emitting now. The process, so they say, is suitable for solar thermal generators as well. Perhaps just a gleam in someone's eye that won't pan out, but worth paying attention to to see what happens.
**IF** you could capture and concentrate CO2 at a cost which is breakeven at 10 cents per kwh input cost and $10 per ton of CO2
carbon price -- this would be HUGELY important. The really important challenge for you is to
prove this and convince others...
and if it's true, to explain to those who don't know why it is so important.
Just last week, I was in the room when Senator Kerry was lecturing some Republicans and economists,
roughly: "You say that a simple emissions fee for CO2 emissions would be a better market system than my cap-and-trade bill
or what we're proposing at Copenhagen. But let's face it, none of us could get away with charging a carbon fee high enough that
it would do the job." So the House of Representatives passed an act which EPA projects will result in carbon prices which rise to ... $177 per ton, as best I recall, by 2050. Since the US had 6 billion tons of emission per year at last measurement..
a lot of people who can do arithmetic are worried.
BUT... if the people going to Copenhagen understood how a mere $20 per ton emissions fee, world-wide, could actually solve the problem...
this would be huge.
Of course, your $10 (which I hope is true) wouldn't be the whole story. What to do with the CO2? But once it is available and
concentrated enough (30%? 15?), companies like Calera and Aurora and dozens of competitors have good ways to
take care of it, without having to pour liquid CO2 deep into the ground.
The issue here, for the coming century, is not some kind of net energy analysis. It's the economics.
We can do electricity at 10 cents per kwh. Sure, the technology for electricity is in flux itself,
but we can do this.
Maybe it's more expensive than you estimate. But still, it seems more and more likely to me that
we do not need any kind of regime that calls for CO2 prices more than $30-$50 per ton. It would
be a lot easier to get agreement from China if we asked for everyone to pay a carbon fee of $20 per ton
to start than we do in the present approach, asking for quotas or targets they don't yet know how to meet.
Just my personal opinions...
yep sounds like a stupid idea alright, i think we have to rapidly start growing trees all over the world and somehow make wind turbine stations high in the air so all places can get wind energy because the turbines are high in the air and everyone knows its very windy high up. i believe that these two factors would greatly reduce co2 gasses