first of all, thank you for a wonderful and intriguing question! I’ve actually been thinking about this and doing some reading, because I wondered the same thing when I saw the commercials on tv…I was fuming, no pun intended, when I saw the the words “clean” and “coal” be paired together. I had suspected it to be an extreme hyperbole, and sadly after much investigation, I was accurate with my initial assumption.
let’s break this down scientifically, but in a very manageable and understandable way, shall we?
the burning of coal contributes greatly to global warming, and in fact, it is the dirties of fossil fuels (composed mostly of carbons and hydrocarbons). harmful byproducts include ash, sulfur and heavy metals among many others, such as particulate matter, carbon dioxide, nitrogen oxides, sulfur dioxide, and even radionucleotides! meaning, dangerous oxygen radicals that can harm both living organisms and our atmosphere along with radioactivity such as harmful beta particles emitted by radioactive isotopes.
here is the problem: coal is easy to find, and fairly cheap. especially in the US. in fact, coal burning generates a quarter of the world’s electricity. 92% of US coal is burned to generate steam, which runs turbines and generates electricity. the main problem with coal, and why it’s so dirty are the byproducts that arise from the “burning” process.
there are several proposed “methods” termed “clean” that allegedly make the process more environmentally friendly, but let me just say the term “clean” is extremely relative, especially in this case.
various methods of “cleaner” energy generation of coal include: Gasification, wet scrubbers, low nitrogen oxide burners, coal washing, electrostatic percipitators, among several others.
now, scientifically, with regards to “cleaner” burning processes, I must say it is relatively cleaner, and some are very promising, like gasification, which avoids burning all together, but the problem is these methods are deemed the end all be all solution, but they are merely in the preliminary phases, yet they are trying to push these methods as tailor made for right now and ready to use on a large scale.
now, the levels of harmful emissions, or byproducts, are lower, but not significantly lower, relatively. however, the main issue is, they can deal with these harmful substances that still remain once the energy is generated, except these methods are extremely expensive.
a lot of them involve sequestration of these damaging byproducts, by either, for example, injecting them into the ocean, or deep into the surface of the earth and having unreachable beds of coal absorb these byproducts. these processes are extremely expensive and can be time consuming. that’s the kicker, you want a cleaner way, whether a little or a lot, you gotta pay the piper and get rid of the nasty left overs. this leaves the consumer, us the people, paying a significantly greater amount of money, for energy that otherwise should be fairly inexpensive and accessible.
that’s the simplified science behind clean coal technology, to me, still an oxymoron of a term, which to me is not so clean after all, and really expensive to boot. ultimately, this comes down to politics, if you ask me. the coal lobby realizes that a significant part of the american population now subscribes to the theory of global warming (and by theory I mean scientific fact), and so they are trying to better their image using these mirage terms that sugar coat the truth, or most of it, and make things seem a lot better than they actually are. no such thing as “clean” coal…never has been, and this technology doesn’t really exist, at least not yet; nothing available now, in it’s current state, is worth it to be deemed as such.