Then this iron is further processed to reduce carbon and slag, and to add alloys. There are many alternate methods that has been used throughout history for those two steps.
Air is blown in at the bottom.
The coal burns to CO which reacts with the ore and reduces it. The waste rock in the ore is lighter than iron and floats as slag. The melted iron and slag are tapped at the bottom. Blast-furnaces have been used since the 12th century. Their size has increased.