Blast Furnace

A blast furnace is a tall, continuously operating shaft furnace that smelts iron ore into liquid pig iron by feeding ore, coke and limestone in from the top while a blast of hot air is forced in near the bottom, the coke's combustion providing both the heat and the carbon monoxide that chemically reduces the ore's iron oxide into metal. Furnaces of this basic type developed independently in ancient China by around the fifth century BCE, reaching molten-iron temperatures far earlier than in the West, and separately in medieval Europe from around the fourteenth century, where waterwheel-powered bellows first let furnaces reach the temperatures needed to produce liquid iron rather than the solid bloom of the earlier bloomery. The blast furnace's ability to run continuously and produce iron in much greater volume than a bloomery made it the foundation of large-scale iron and steel production, and its basic principle, however much larger and more automated modern versions have become, still supplies most of the world's primary iron today.