The oldest known blast furnaces were built during the Han Dynasty of China in the fourth century B.C.E. Early blast furnace production of cast iron evolved from furnaces used to melt bronze. Iron was essential to military success by the time the State of Qin had unified China (221 B.C.E.). By the eleventh century C.E., the Song Dynasty Chinese iron industry switched from using charcoal to coal for casting iron and steel, saving thousands of acres of woodland.
In a blast furnace, fuel and ore are supplied through the top of the furnace, while air is blown into the bottom of the chamber. The chemical reaction takes place as the material moves downward, producing molten metal and slag at the bottom, with flue gases exiting from the top of the furnace.
The oldest known blast furnaces in the West were built in Durstel in Switzerland,the Markische Sauerland in Germany, and Lapphyttan in Sweden, where they were active between 1150 and 1350 C.E. There have also been traces of blast furnaces dated as early as 1100 found in Noraskog, also in Sweden. These furnaces were very inefficient compared to those used today.
French Cistercian monks, who are known to have been skilled metallurgists, passed on their knowledge of technological advances regarding blast furnaces between the thirteenth and the seventeenth centuries. Iron ore deposits were often donated to them and the monasteries sold their surplus iron as well as the phosphate-rich slag from their furnaces, which was used as an agricultural fertilizer. In 1709 Abraham Darby, a Quaker iron founder in Shropshire, England, used coke instead of charcoal to smelt iron ore in his improved blast furnace. He also processed cast iron into wrought iron and steel.
