Blast furnaces are gigantic steel furnaces in which iron ore, limestone, and coke are heated to temperatures in excess of 1750 degrees Celsius. The carbon in the coke and the heat within the furnace combine with the iron oxide to form a mixture of iron, carbon monoxide, and slag, and this mixture is known as liquid iron or “hot metal”.
The process of refining iron inside a blast furnace required a tremendous amount of fuel, labor, and resources, and the furnace itself is an impressive behemoth. The largest blast furnaces can reach heights of over 60 meters, with internal volumes of up to 3,500 cubic meters. The temperatures and pressures within these furnaces are immense, with temperatures reaching as high as 2000 degrees Celsius and pressure reaching up to 90 atmospheres.
Once the furnace is preheated and filled with the necessary materials, it is ignited by blowing a stream of sparks into the hearth. In order to maintain the reaction and keep it going, the necessary amount of air and fuel are continuously added to the furnace. The iron ore and the limestone combine with the carbon from the coke to form a molten mixture, which is eventually tapped down into a ‘leaky ladle’. Here, the iron reacts with the oxygen from the air to form the desired pig iron.
The most common type of slag produced in the blast furnace is known as blast furnace slag. This is an impure form of iron which is created as a byproduct of the iron extraction process. This type of slag contains an abundance of useful minerals, such as calcium, magnesium, and phosphorus, which are all beneficial for use in cement production, as a construction material and as a fertilizer.
After the iron has been can be tapped from the furnace, it must be cooled and then processed/worked. Depending on the intended use of the iron, it may need to be further refined, cast into a desired shape, and hardened. The iron is then put through a series of processes to make it suitable for use, such as rolling, drawing, and forging.
The blast furnace process has been used for centuries to produce iron, and has been an integral part of the industrial revolution. It is still an essential component of the steel production process, and continues to be an integral part of the world’s economy.
