Clean Coal Technologies Coal is the most abundant fossil fuel and also regarded, as the dirtiest not only is coal inherently impure by composition by the fact that it contains ash and sulfur; coal is also difficult to burn completely. Many techniques to combust coal have been developed since the late 1800's. "The first innovation were more concerned with achieving more complete combustion and reducing manual labor than they were with pollution and economic" (Ruzie 1) The history of coal can be dated back around 400 million years ago. "When coal was formed, the earth was covered with swamps. Plants died and the remains settled to the bottom of th