Truly clean coal is under-researched and undeveloped

Slate - What the Heck is Clean Coal?

'Clean coal' is a proposed technology that captures the carbon dioxide released by burning coal, compresses it and sends it deep into the earth. Though the technology might be possible, it hasn't actually been developed in a workable manner yet, due to massive increases in the cost to develop the process on a large scale. Furthermore, there seems to be some skepticism about the effects of pumping massive amounts of CO2 into the ground. The coal industry wants to claim that 'clean coal' is just a term for the lowered emissions since regulation and air standards tightened.