Is it "clean coal" or "cleaner coal?"
Is there any process out there whereby coal can be burned as cleanly as nat gas?
It more a matter of efficient burning so there is little left as waste and the carbon dioxide would be captured.
SO2, SO3, NO, NO2, oxidised HG and particulate matter formed when coal is combusted in a power plant boiler, what you and I would think of as pollutants, can be removed, in series, by various technologies. At that point, coal is less expensive on a BTU basis, and just as 'clean', as natural gas. This is true even in the U.S., where natural gas prices are less than one-third those in the U.S.
If one believes that CO2 emissions cause climate change or global warming and therefore supports the EPA's finding that CO2 is a pollutant, then the net cost of removing and selling the CO2, puts coal at a considerable cost disadvantage to natural gas.
In the absence of a belief in a link between CO2 emissions and climate change or AGW, there is no reason to oppose coal-fired power plants.