CAN WE BURY THE CARBON PROBLEM?

May 24th, 2007 <-- by Bryan Mignone -->

In this post, I want to focus a bit more on one particular aspect of the carbon and climate problem: Coal. While it’s true that dealing with coal will not, by itself, solve the carbon problem, it is equally true that not dealing with coal will severely limit the opportunities to effectively safeguard the climate.

What exactly is the problem with coal? Well, for starters, coal accounts for about 25% of today’s global energy demand. And because coal contains significantly more carbon per unit energy than either oil or natural gas, it accounts for nearly 40% of all carbon emissions to the atmosphere. In addition, coal is cheap, and both the U.S. and China have enormous domestic reserves, making it even more attractive when concerns over energy security take hold of the political debate.

Of course, it’s not easy to see how we could quickly displace coal when fully 50% of electricity generated in the U.S. comes from coal-fired plants or when China is constructing the equivalent of two 500 MW coal-fired plants each week (roughly the equivalent of the entire U.K. power grid each year). But displacing coal is exactly what must be done if global emissions are to remain on a path consistent with atmospheric stabilization at a “safe” level. There’s simply no way to get from here to there without confronting coal directly.

In theory, emissions from future coal-fired plants could be mitigated in a number of ways (it’s worth having a closer look at a few of the example “wedges” in the Pacala and Socolow piece mentioned in this earlier post). For example, coal-fired plants now on the drawing board could be swapped with nuclear or natural gas-fired plants (burning natural gas releases about half as much carbon as burning coal), with renewable sources such as wind and solar, or by promoting large-scale efficiency improvements that reduce the demand for electricity in the first place.

It turns out that one other alternative may be worth considering as well – carbon capture and storage, or CCS for short. Admittedly, this is an attempt to have our cake and eat it too – a way to continue to burn coal, while limiting emissions to the atmosphere and the ultimate impact on climate. It may sound crazy, but CCS has captured the imagination of the environmental community, the fossil fuel industry and Congress alike.

As the name implies, CCS consists of two distinct activities – capture and storage — that each present a new set of technological challenges. Capture refers to the process of separating CO2 “waste” generated at the power plant. Since we already capture other pollutants, including those that contribute to acid rain and smog, it seems plausible that a similar process could be employed to capture CO2. In fact, American Electric Power (AEP), one of the largest U.S. utilities, recently announced that it would (with help from the Department of Energy) retro-fit two existing coal plants with new “scrubbing” technology designed to do exactly this.

While this option, if demonstrated, will be an important addition to the technology mix, many believe that a newer type of coal-fired power plant, called integrated gasification combined cycle (IGCC for short), when designed explicitly for capture, will ultimately produce power at a lower final cost than conventional coal plants that have been retro-fitted in the AEP manner. The main difference is that IGCC plants separate CO2 (and other pollutants) before combustion, by first gasifying the coal, leading to a relatively pure CO2 stream that eliminates the need for scrubbers at the stack.

In either case, once carbon has been captured, it must be effectively stored for long periods of time to make the project worthwhile. Underground storage in existing geologic (e.g. saline) formations seems to make the most sense because a relatively large amount of suitable pore space is thought to exist in regions where coal plants are now situated. But how can we be sure that injected CO2 will remain sequestered from the atmosphere for long periods of time, and how do we know that the movement of CO2 underground will not threaten drinking water, other natural systems or local communities directly? These are the sorts of questions that need solid answers before we can move ahead with confidence.

Early research is encouraging. The oil industry has extensive experience with similar technology (albeit on a smaller scale) because CO2 is often injected into aging wells to flush out oil that is trapped underground, a process known as “enhanced oil recovery” or EOR. In addition, the three existing “large-scale” (> 1 Mt CO2/yr) injection projects — Sleipner off the cost of Norway, Weyburn in Canada and In Salah in Algeria — have not yet shown any signs of leakage, but then again, the oldest (Sleipner) has only been operating for about a decade, hardly long enough to declare success.

As for the prospects of scaling up these activities in the near future, much will depend on incentives offered by legislation. Several bills have been introduced in Congress to enhance the R&D effort on new coal technologies and to evaluate the prospects for safe underground storage. Future legislation that applies a cap or tax to carbon will further expedite the deployment of CCS, by reducing the cost of carbon-free power relative to conventional alternatives. At this point, the future of CCS seems bright, but we undoubtedly have a long way to go.

Further Reading: For more on coal and CCS, I would recommend the recent MIT report called The Future of Coal.

2 Responses to “CAN WE BURY THE CARBON PROBLEM?”

  1. Calvin Jones Says:

    I would also reccomend that IPCC special report on CCS.

    http://arch.rivm.nl/env/int/ipcc/pages_media/SRCCS-final/SRCCS_WholeReport.pdf

  2. David B. Benson Says:

    This is a proposal which requires no modification to existing coal-firec reactors:

    DoE recently announced that sequestering carbonf dioxide in uneconomic coal seams is praticable. Find one or more not far from a large supply of otherwise uneconomic bio-mass, such as animal wastes, wheat chaff, etc. Put the bio-mass through a fast pyrolysis reactor to produce about 50% carbon dioxide. This will be sequestered. About 40% will be bio-oils, which can be used to self-sustain the pyrolysis and plenty left over to provide energy for the sequestration. (20 MW electric generating stations using a similar process is being constructed in Germany.)

    The remainder of the carbon, about 10%, is biochar, i.e., charcoal powders. These are best sequestered in the soil, about 50% of centuries, to improve poor soils so these will produce even more bio-mass next cropping season.

    My readings suggest that, assuming no value for the bio-char, a fossil carbon tax of $US 37 per tonne of carbon would sustain the bio-mass collection and pyrolysis. Then about $US 50 per tonne ought to be enough to cover the cost of sequestration.

    To read more, besides the obvious search terms, try web trawling on “Shimbir Demon biochar”.

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