Steel is used in many sectors such as the automotive, construction, and household appliances. Steel production requires iron ore, coal, lime and iron-alloys, with gas emissions as a by product as a by product at each process stage.
How is steel made?
Coke production (or coking)
Coke is a grey, hard, and porous fuel with a high carbon content and few impurities, made by heating coal or oil in the absence of air. It is notably used as fuel in blast furnaces as it produces very little smoke when burned, to obtain cast iron which is subsequently transformed into steel.
The manufacturing of coke is accompanied by the emission of certain gases (hydrogen, methane gas, acetylene, ethylene, carbon oxides).
Here, iron is extracted from its ore.
Ore and coke solids are introduces into the top through the blast tube. Hot air at 1200°C, blown into the pot furnace, causes coke combustion. Carbonic oxide will oxidize and form iron oxides (in other words it will absorb their oxygen and thereby isolate the iron), then descends down the furnace to become cast iron.
At the output of furnace, the residue, called blast furnace slag, floats on top of cast iron and is recycled or sent to other industrial sectors (cement works for example).
Blast furnace gas will be channelled through gas pipelines. The risk of explosion must be measured.
This step will help remove the last unwanted elements, such as phosphorus or sulphur.
This step allows for cast iron to be turned into steel: the molten cast iron is poured over a bed of scrap and the unwanted elements (hydrogen sulphide, ammonia) contained in the cast iron are burnt by blowing pure oxygen, which will form carbon monoxide and produce heat.
This is how raw liquid steel, that is still imperfect, is obtained. It will then be refined by removing the remaining impurities.
When the carbon content of the molten bath is at the desired level, the alloying elements are added and the liquid steel is poured into a pre-heated ladle.
The steel gas is made up of 75% CO and 3% hydrogen.
Continuous or ingot casting
The molten steel continuously flows into a bottomless mould. While passing through the mould, it starts to solidify when it comes into contact with walls that are cooled with water. The moulded metal descends, guided by a set of rollers, and continues to cool. When it reaches the outlet, it is solidified and cut at the wanted lengths.
Rolling is used to shape the material.