Clean coal technologies reduce emissions either in the combustion cycle or through gasification of the coal. Circulating fluidized-bed combustion (CFB) and supercritical pulverized-coal systems use temperature and pressure in the combustion cycle. Integrated gasification combined-cycle (IGCC) systems convert coal to a gas before combustion. Until recently, all of them have been less reliable than conventional subcritical pulverized-coal (PC) powerplants, the backbone of the U.S. generation fleet. Some also cost more to construct, operate and maintain.