Ah, Carbon Capture; we hardly knew ye

ResearchBlogging.orgJim Hansen wants to see all coal-fired plants shut down by 2030. Except for any plants that employ carbon-capture and sequestration. Al Gore wants to see the United States generate all its electricity from renewable sources by 2018, which means shutting down all the coal-fired plants. Except for any plants that employ carbon-capture and sequestration. Princeton University's Pacala and Socolow of the "wedge" strategy make CCS an integral part of their future clean energy portfolio. Everybody who's crunched the emissions numbers pretty much agrees that coal has got to go. Unless we can capture all the troublesome carbon dioxide. So can we?

"The technology of sequestration is developing rapidly," write Fred Krupp and Miriam Horn of the Environmental Defense Fund in an optimistic chapter of their optimistic book Earth: The Sequel. But it ain't here yet. Most estimates put affordable equipment at least 15 years in the future. Yes, there are a few pilot projects ;;;; three, I think: one in the North Sea off the coast of Norway, one in Saskatchewan and one in Australia ;;;; but nothing commercial. But let's assume for the sake of an argument that the technology is developing rapidly, and we could start retrofitting coal-fired power plants within the next decade. How effective would that be?

Coal provides about half the electricity in the U.S., so there's no doubt that CCS technology, if it worked, would go a long way toward cutting our greenhouse emissions. But a new peer-reviewed analysis of one of the most promising CCS technologies suggests two big problems are in store.

First, say a trio of researchers from the Copernicus Institute for Sustainable Development and Innovation in The Netherlands, capturing all that carbon dioxide, compressing, transporting and burying it might, if you're lucky, net you a reduction of 71 to 78 % in greenhouse gases, compared to today's coal-fired plants. That's short of the 90 % most informed advocates talk about, even farther from the 100% reduction that popular understanding associates with the process, and it still leaves us with a significant emissions problem.

Second, and just as worrisome, a conventional plant is actually easier on the environment in several other ways, most notably when it comes to "eutrophication, acidification and photochemical oxidation," which means water pollution, acid rain and ozone layer depletion.

"Life cycle assessment of a pulverized coal power plant with post-combustion capture, transport and storage of CO2" appears in the latest issue of the International Journal of Greenhouse Gas Control. The authors set out to detail as best they could, given the lack of a working history of the technology, "a full-chain perspective, from cradle to grave, to assess whether and to what extent the implementation of CCS will increase environmental impacts." They compared one of the most promising candidate technologies, which uses monoethanolamine, a molecule that can absorb CO2 given the right environment, with a standard "sub-critical" coal-fired plant the likes of which dominate the industry today, and a "super-critical" plant, which uses high-temperature furnaces that are only now being introduced around the world.

The bottom-line numbers are fascinating. Per kilowatt-hour, a sub-critical plant produces greenhouse gases that add up to an equivalent of 1,092 grams of CO2. A super-critical plant gets that down to 837 gCO2eq., a not-very-impressive reduction of less than 24%. It might sound like a lot to an engineer, but it's not the kind of technology advance that will justify the extra cost given our need to bring emissions down by at least 80 %.

A CCS plant, meanwhile, scores better, but still not in the necessary ballpark, at 243 gCO2eq. The problem, say the paper's authors, is that CCS involves a lot of steps, each of which requires energy, lowering efficiency at each stage. Here's how Patrick Barry of Science News summarizes the problem:

Captured CO2 must be compressed to about 100 times atmospheric pressure (which takes energy), transported to a suitable underground reservoir (which takes energy) and pumped into the ground (which takes energy). A coal-fired power plant that sequesters its CO2 must burn about 30 percent more coal than conventional plants to cover these energy needs. And that extra coal must first be mined (which has environmental effects) and transported to the plant (which takes fuel) -- the list goes on and on.

Granted, this is just one form of carbon-capture technology. Maybe there are others which can get us closer to a zero-carbon future. But MEA absorption is probably the closest to commercialization, and we can't wait much longer if we want to bring emissions down fast enough to avoid nasty climatological consequences.

And there are no doubt some enthusiasts who, genuinely fearful of what extra greenhouse gases are doing to our planet, see increased acidification and eutrophication and some more skin cancer as the price we will have to pay. Not everyone will agree, though.

The fact is, CCS isn't the only tool at our disposal. There are other ways to generate electricity cleanly. PG&E in California just agreed to buy 800 MW of electricity generated by a massive photovoltaic array to be built (if it clears licensing hearings) in San Luis Obispo County. We don't have to keep burning coal just because it's cheap and easy to find. For one thing, mining coal is bad for your health and the landscape and always will be, no matter how cleanly it's burned. Just drive a few miles off the main highways in West Virginia.

So that just about wraps up the case for carbon sequestration, eh? Well, like anything involving speculative future technologies, we might not want to jump to conclusions. Here's Jim Hansen of NASA's Goddard Institute for Space Studies, addressing that very issue in a conference call I was hooked into last week:

"I think that we have to allow that to be tried. I frankly think that there are very few utilities who want to do it because it will make the electricity much more expensive."

CCS is "probably technically possible," he said, but let's face it ;;;; while every form of power generation has it's problems, but coal has the most.
KOORNNEEF, J., VANKEULEN, T., FAAIJ, A., TURKENBURG, W. (2008). Life cycle assessment of a pulverized coal power plant with post-combustion capture, transport and storage of CO2. International Journal of Greenhouse Gas Control DOI: 10.1016/j.ijggc.2008.06.008


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I don't think carbon capture and sequestration is going to have a huge impact soon, but if you are correct in this article we may as well give up worrying about greenhouse gases.

If a 70% reduction in CO2 from coal electrical plants is no good we are done right now. We will never get better than that in the next 50 years no matter what. What kind of model would say that 70% reductions would not have a large effect? That seems incredible.

In my opinion, the best carbon sequestration is already done: leave the coal under the ground. Way cheaper than burning it and then trying to gather the gases.

I never trusted the idea of "clean Coal". The way I see it, the only thing that would burn cleanly would by hydrogen in oxygen, everyhting else will have a by-product (well I guess even that does too, but ya' know, water). Granted if we can sequester that instead of releasing into our atmosphere it may reduce environmental impacts, but what do you do with the by product? As in CO2, I've heard store it, well what about transportation of the product? How can we be sure we can actually hold on to all of it (brings to mind nuclear wasted, although that's a completely different story). What will we do with our huge tanks of compressed CO2? I'm proud to be a Californian as we've been on the renewable energy kick for a while. The SLO solar farm is just what we need, and PG&E have been working very hard to get us to use less power and find new sources of energy. An interesting thought, which to me seems a little backwards, here in Santa Cruz county they are working on a "Refuse Vaporizor" (I think that's what it's called) where they are taking huge amounts of land fill junk and vaporizing at high temps, apparently it can generate electricity and the major by product is usable ash. I'm not a thermodynamic engineer, but I wonder how they can burn trash at such a temp to vaporize it, capture all the products of the reaching and still be in the positive on energy production.

"capture products of the reaction" not "reaching"

JJ, for some sequestration schemes to work, your coal power plant must be sitting over a pumped-out oil well. Massive government subsidies are also a requirement.

I've recently heard some pretty bad things about the project in Saskatchewan. (Or maybe Alberta?) The conversation went too quickly for me to absorb the details, though.

There is another experimental project that's begun, in northwestern New Mexico. The blurb from DOE sounds promising in this case. (Two active coal plants sitting on the edge of the US's biggest coalbed methane basin. DOE claims that CO2 adsorbs onto coal and frees the methane. Since they're already doing a lot to free the methane (such as pump huge amounts of water out of the rock), this might be one place where sequestration would work.) We'll see, though. Hopefully their monitoring includes paying attention to what is squeezed out of the rock when the CO2 is injected, and monitoring induced earthquakes, and things like that.

Here's DOE's site: http://fossil.energy.gov/news/techlines/2008/08031-San_Juan_Basin_CO2_I… . I'm trying to learn about it to answer student questions, and hoping that DOE is responsible in its pilot study.

It's also important here to distinguish between "pure" CCS and CCS as part of Enhanced Oil Recovery (which is where most of the work is currently being done). Because the whole point of EOR is to produce more oil to burn, you actually end up with more CO2 from that than you inject into the field. CCS for EOR increases CO2 emissions, by making more oil available.