The ‘Clean’ in ‘Clean Coal’ Downgraded Again

by Bill Chameides | March 3rd, 2010
posted by Erica Rowell (Editor)

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The problem is that capturing and storing the carbon from coal is a long way from making coal “clean.”

Here’s another reason to call “clean” coal “not-so-clean.”

As the world begins to envision a low-carbon-fueled economy, the future of coal — the most carbon-intensive fossil fuel — becomes as murky as a room full of coal dust.

Not to worry, say coal-industry proponents — we can make coal “clean.” It’s easy, they say; we can just do the CCS thing: capture the carbon dioxide (CO2) produced as a by-product of burning coal and then store it somewhere like in a deep geological formation. Carbon capture and storage — CCS.

It’s not a bad idea, as far as it goes, and research and proof-of-concept tests suggest that it will work. Larger-scale projects to further test the CCS process are now underway (see here and here). Assuming the hurdles of scale as well as public opposition to carbon storage can be overcome — voila, dirty coal becomes clean coal. Full steam ahead, so to speak.

‘Clean Coal’ – Why ‘Clean’ Doesn’t Quite Live Up to Its Meaning

The problem is that capturing and storing the carbon from coal is a long way from making coal “clean.”

•    There are the other toxic gaseous emissions, such as mercury (see here and here), that must be removed from the effluent.

•    There is the problem of what to do with the toxic ash left behind after the coal is burned.

•    And, for coal mined in the eastern United States, there are the enormous environmental costs of mountaintop removal-mining (MTR).

A new paper published in Environmental Science and Technology adds another concern about supposedly clean coal obtained from MTR. Authors James Fox and J. Elliott Campbell, both of the University of Kentucky, carried out a life-cycle analysis of the carbon footprint of electrical power generated from coal obtained by MTR. In addition to the direct emissions associated with burning the coal, they found significant amounts of upstream emissions. The two major sources of these emissions, in their estimation, were:

  1. Extraction and transport: emissions associated with the mining operation itself and with transporting the coal to the power plant.
  2. Emissions of geogenic carbon: emissions associated with the release of carbon that was tied up in coal but left behind in the mining spoil. This spoil is typically compacted back into the soil at the mining site in the reclamation process, exposing the coal in the spoil to the elements and eventual oxidation, leading to the production of carbon dioxide.

Another (relatively small) source of emissions comes from the destruction and oxidation of trees and other organic carbon in the soils removed before mining begins.

Quantifying the Cleanliness of the Cleaner Coal

These upstream sources turn out to be significant but not overwhelmingly so when compared to direct emissions from burning coal.

CO2 emissions from MTR extraction and transport are about five percent of the combustion emissions; this grows to about seven percent if forest destruction is included and to 17 percent if geogenic and soil carbon are included.

But conventional coal is already recognized to be dirty, so why sweat a little more CO2?

And what about so-called clean coal? By the authors’ estimates, conventional coal-burning from MTR leads to emissions of about 302 million metric tons of CO2 per year, if one only accounts for emissions from power plants. The equivalent power-plant emissions from “clean” coal (i.e., using CCS) are only about 39 million metric tons of CO2 annually. That’s a decrease of a factor of almost eight — impressive.

But it should be impressive. After all, using CCS is supposed to fix the CO2 emissions problem, right? Not quite, suggests this new work by Fox and Campbell.

The researchers estimate that upstream CO2 emissions from extraction and transport alone amount to about 50 percent of the plant emissions with CCS. And including all emission sources from MTR, the upstream emissions are estimated to amount to a whopping 170 percent of the CCS power-plant emissions. That’s almost a factor of two larger.

CO2 Emissions: Burning Coal Conventionally Vs. Burning Coal With CCS

By the authors’ estimation, the life-cycle emissions from burning MTR-mined coal in conventional power plants could on an annual basis be:

  • for conventional usage of MTR-mined coal, as large as 354 million metric tons of CO2 and
  • for the same coal burned in CCS plants about 107 million metric tons of CO2.

That’s a decrease of a little more than three, which is a decrease to be sure, but not nearly as large as that factor of eight — or the other claims made (e.g., here, here, and, to an extent, here) about the efficacy of CCS.

So, my question: Does truth in advertising require that “clean coal” be changed to “not-so-clean clean coal.”

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