1. Coal burning power plants produce particulate pollution that directly impacts human health. Modern coal plants pre-treat fuel to minimize pollutants and filter output to remove them from their emissions. The stack of technologies that does this is most of what the industry is referring to when they talk about "clean coal", and it does appear to work.

2. Burning coal releases large amounts of CO2 and contributes to global warming --- about a quarter of the US carbon footprint comes from coal. Supporters of "clean coal" allude to carbon capture and sequestration technology, but it's unclear how effective it is and unclear how widely deployed it will be.

My understanding is that it's reasonable to be skeptical of clean coal as an answer to (2), but not as much for (1). Problem (1) is enormously important: hundreds of people die every year because of PM10 pollution from dirty coal plants. So it's probably best not to adopt the rhetoric that "clean coal" is somehow fake.