—and “clean coal” is actually a term that's now gaining recognition in the context of two particular technological innovations. One is how you burn it: the pressure, the temperature, and whether it's with or without oxygen. A number of combustion experiments are going on to try to fine-tune how the coal is actually burned.
Of course, coal is not coal, coal, coal; depending on what seam of coal it's taken from, it will have different characteristics, different pollutants, etc., so there's a fine-tuning effort associated with that part of it.
The biggest concern on clean coal is being able to take carbon from the burn, capture it, and store it. We know how to do that technologically. The problem, of course, is that the capture step of that CCS, as it's known, is considerably expensive. Figuring out how to reduce the cost of capturing carbon is an initiative that a number of us are involved in, both inside government among the various departments and among colleagues in other parts of the innovation system.
Clean coal, if it's going to truly be clean, will be burned to as clean as it can be; then the pollutants will be captured, and the carbon dioxide, being the biggest component, will be captured and stored.