clean coal

Short definition from Wiktionary

Noun

1. 1
   Any technology that may mitigate emissions of carbon dioxide and other greenhouse gasses that arise from the burning of coal for electrical power.
2. 2
   anthracite (a cleaner burning variety of coal, which is usually hard and bluish, with fewer impurities; making it acceptable for uses needing cleaner coal)
3. 3
   coke (a coked version of coal, that has been cleaned of many of its impurities, making it acceptable for use in steel-making and other uses needing cleaner coal)