Fluidized bed boiler
Fluidized bed boiler reduces the amount of sulfur emitted in the form of SOx emissions. Sand, limestone etc, which also allows more efficient heat transfer from the boiler to the apparatus used to capture the heat energy. The heated precipitate coming in direct contact with the tubes (heating by conduction) increases the efficiency. Since this allows coal plants to burn at cooler temperatures, less NOx is also emitted. However, burning at low temperatures also causes increased polycyclic aromatic hydrocarbon emissions. Fluidized bed boilers can burn fuels other than coal, and the lower temperatures of combustion (800 °C / 1500 °F) have other added benefits as well.