Before we begin, let's get one thing out of the way: There's no such thing as "clean coal" technology. It's a pipe dream, sort of like an undefeated Buffalo Bills season capped by a Superbowl win. As long as coal is extracted from the Earth by mountaintop removal and other environmentally harmful means, "clean coal" will remain a buzzword that addresses only one aspect of the problem.
That being said, regarding emissions, one company believes human blood may hold the key to unlocking cheap and effective carbon sequestration for coal-fired power plants. Called Carbozyme, the New Jersey startup is studying how to remove CO2 from noxious smokestack gases — something an enzyme in our blood already does at a rate of 2 pounds of CO2 per day. From Popular Science,
As cells pump CO2 produced during respiration into the blood, the enzyme carbonic anhydrase converts the gas into bicarbonate for easier transport to the lungs. There the same enzyme works in reverse, turning the molecules back into the CO2 gas you exhale. This action could play the critical role of selectively capturing CO2 from mixed gas emissions for later sequestration.
Carbozyme has created a system made up of millions of microscale, porous tubes coated with a synthetic version of the enzyme. The idea is that as smokestack gases pass through the tubes, the enzyme pulls CO2 from the mix and transforms it into bicarbonate and back. This CO2 can then be pumped underground and stored in layers of basalt rock. The process reportedly uses a third less energy than competing CO2 sequestration methods.