Clean Coal: An Oxymoron?
To many people who are passionate environmentalists, the words “clean” and “coal” couldn’t be more polarized opposites. The thought of coal directly implies powerplant smokestacks belching carbon dioxide emissions and other pollutants.
Certainly, it is true that coal-burning powerplants have historically been largely responsible for high quantities of sulfur dioxide and nitrous oxide emissions that contribute to acid rain and local air quality non-attainment issues (e.g., haze, surface ozone). And, it remains true that coal powerplants continue to be perhaps the most important single contributor to global warming, by virtue of their high CO2 emissions.
But, is a no-tolerance anti-coal perspective justified on an environmental basis? In my mind, no. In fact, it is theoretically possible to reconcile the concept of zero-emissions coal utilization. This entails the use of an integrated gasifier coal combined-cycle (IGCC), along with carbon sequestration.
This is the vision of the FutureGen Alliance. FutureGen Alliance Announcement This initiative, announced in late 2005, embraces many of the largest and most important parties in coal-fired generation to develop a standardized coal-to-electricity technology that produces no air emissions. The combined-cycle part of the technology is well-understood, having been widely utilized for many years now. In contrast, there are two relatively new technologies that remain to be commercialized for the zero-emissions coal vision to be realized:
The first is gasification technology — converting coal to a synthetic gas (“syngas”) similar to natural gas for use in the combined-cycle. There have been a number of gasification technologies employed for decades, and they work reliably, but none have yet to achieve the holy grail of being deemed “commercially economical”.
The second is carbon sequestration technology — capturing CO2 emissions from the exhaust stream and then injecting it underground. Again, the science is well understood, but the economics of carbon sequestration have always been challenging, particularly because of the intensive energy requirements.
If these two technologies can be commercially improved, making sequestered-IGCC economically-viable, then our future energy and environmental situations are much more assured. We have plenty of coal to last for well more than 100 years, and if we can use it in an environmentally-benign way, it seems like a no-lose resource for us to employ, until we can get to some energy system (solar with storage? hydrogen fuel cells? fusion?) that can realistically serve the human species for millenia.
Yes, if we could use coal cleanly, it would be a nice interim energy solution, but I'd recommend some caution toward FutureGen (and this generation of clean coal in general). Your "no-tolerance anti-coal perspective" is a bit of a straw man, illegitimizing the fact that there are good technical reasons to be skeptical of the "syngas it, scrub it, stuff it" brand of coal-fired electric (or hydrogen) generation.The first is that the compression energy problem is not likely to get solved any time soon. There's no way around the fact that reducing the volume of a gas like CO2 is going to take a significant amount of energy, whether you're making a compressed gas, a liquid, or a diamond. We can certainly compress it and get it underground, but it's going to be expensive to do so.The only way anybody can think of to easily defray this expense is to use the compressed gas as an aid to enhanced oil recovery. However, this is limited to sites where a coal plant exists on top of a sizeable petroleum reservoir – a relatively small portion of the coal plants out there. There are of course other options besides oil reservoirs (salt caves and saline aquifers have been proposed) but these do not offer the opportunity to defray the pumping costs. Without some economic use for this CO2 (soft drinks, anyone?) it's going to be hard for any plant, no matter how efficient it is at converting coal-to-syngas and syngas-to-power, to justify the energy (and revenue) losses of separating the CO2 and pumping it underground. The energy cost of compressing and pumping the CO2 is not likely to go away any time soon. Trying to compress/liquefy gases is not a new problem, and plenty of research has been done, meaning we are not likely to see any big breakthroughs in this area (not impossible, but unlikely).The point is, there are some serious reasons to doubt that this brand of clean coal will ever get far off the ground. It would take regulatory technology mandates ("new plants must capture and store their CO2") to come about, because it won't get economic on its own (unless carbon prices go way up, and then lots of other technologies start to look more attractive). And if we're going to have use technology mandates and/or subsidies, the societal opportunity cost of spending them on a transition technology like clean coal instead of a fully renewable technology seems high.This makes FutureGen and its cousins a good research project, a good PR tool, and a risky investment.