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Much is being made of the clean coal breakthrough announced at Ohio State this week. The effort utilizes an innovative process called "chemical looping."

Typical coal-fired power plants burn coal to heat water to make steam, which turns the turbines that produce electricity. In chemical looping, the coal isn't burned with fire, but instead chemically combusted in a sealed chamber so that it doesn't pollute the air. A second combustion unit in the lab does the same thing with coal-derived syngas, and both produce 25 thermal kilowatts of energy.

This project sounds promising. But in the official press release there isn't a single mention of waste.

What are the byproducts and how to dispose of/recycle them?

samthebrand
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  • Even if there is no waste from the firing process there is still quite a bit of hazardous waste that results from the the mining of coal. Not to mention there have been a large number of coal slurry dam failures that have literally destroyed ecosystems of the watershed basins they are near. –  Feb 21 '13 at 22:11
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    There's not enough info in the sources linked to make a determination. I wasn't able to find other sources that describe the chemical process or the nature of the byproduct beyond that contains all the CO2. Since we're talking about exothermic reaction theres no reason to presume CO2 actually remains. Who knows what use the byproduct may have, or the external cost of the non-coal inputs. – OCDtech Feb 21 '13 at 22:22
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    I disagree that's there's no mention of waste. The article states the process "chemically converts coal to heat while capturing 99 percent of the carbon dioxide produced in the reaction". CO2 is a waste product. The fact that it's captured will make it easier to pump it under the ground though (which I don't necessarily condone). – Highly Irregular Feb 22 '13 at 00:17
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    @HighlyIrregular - I think the OP is asking about other waste like solid remains(ash) and impurities in the coal that are not consumed by the process. Is the CO2 converted into carbonates or others stable solid, or is it just contained in a natural form? –  Feb 22 '13 at 15:08
  • @Chad, you're probably correct, but actually CO2 disposal may remain the biggest problem of all, so overlooking it would be a mistake. – Highly Irregular Feb 23 '13 at 03:08

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Part of the problem here is what you call "clean." I am in the camp that says "there's no such thing as clean coal technology." I would however like to explain what the problem and disagreement is.

Clean coal technology usually refers to technology to convert coal into heat or electricity in such a way that carbon dioxide can be captured and no coal tar or other pollutants released into the air. That's all well and good but there are really three main problems worth bringing up.

This metric basically is limited to one and only one piece of the supply chain. The pre-processing, mining, etc. isn't considered, and consequently you have the idea that while one piece of the supply chain may be relatively "clean" that doesn't say anything about the overall environmental impact of using the coal.

The second is that the waste still has to be disposed of somehow. It isn't clear what the disposal method is, whether it would be used to produce useful products or just dumped into the earth (again requiring extra energy) and so the disposal portion of the supply chain is a bit of a potential issue too.

Finally there are the complexity costs. What goes into making the equipment and materials for this reaction? How much energy goes into them? What kinds of materials?

Typically when people are talking about the technology being clean they are looking at an idealized environment limited to the use of this coal here.

Interestingly, note that a number of products of coal combustion are utilized in many other ways. We get sulfa antibiotics from the waste of certain forms of coal combustion, for example, the same with a lot of modern dyes (in fact sulfa drugs were an off-shoot of coal dye production). One key element I haven't been able to find information on is what level of re-use of waste products is possible with such a system.

Regardless of how clean it is, however, heavy reliance on non-renewable resources is not sustainable.

Chris Travers
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  • This is really comprehensive. Thanks. I was curious, too, though perhaps didn't explicitly ask about, whether this new technique made disposing of the waste any easier. It seems they got the easy part of "clean coal" down (sequestering waste), but not the more difficult problem of disposal. – samthebrand Feb 22 '13 at 15:26