Blast furnace is a metallurgical furnace, which is used for smelting to produce metals, generally iron. A furnace in which combustion is intensified by a blast of air, especially a furnace for smelting iron by blowing air through a hot mixture of ore, coke, and flux. In a blast furnace, fuel and ore are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions take place throughout the furnace as the material moves downward. The end products are usually molten metal and slag phases tapped from the bottom, and flue gases exiting from the top of the furnace. Blast furnaces are to be contrasted with air furnaces, which are naturally aspirated, usually by the convection of hot gases in the a chimney flue.