Blast furnace or electric arc furnace (EAF)
Steel is an alloy primarily composed of iron and carbon, with the addition of small percentages of other elements depending on the type of steel grade is required.
In the case of the Blast Furnace, the raw material is iron ore, which, thanks to high temperatures and the presence of carbon coke, is first transformed into liquid cast iron and then refined to become steel.
In the case of the Electric Arc Furnace, ferrous scrap is melted down until liquid steel is obtained, which is then also processed for refinement.
There are two main methods of producing steel: the Blast Furnace and the Electric Arc Furnace. These two methods are different in several aspects, starting with the raw materials used, the industrial processes involved, their energy consumption and the emissions they produce. Blast Furnaces use iron ore and carbon coke, while EAF furnaces use recycled ferrous materials.
Producing steel with the blast furnace: from cast iron to steel
Once cast iron has been produced from iron ore and carbon coke, excess carbon and impurities are removed in the Blast Furnace to produce steel. Various processes have been tested and developed over the years, and these are the main ones:
- The Bessemer Process
Invented by Henry Bessemer in 1856, it uses a distinctive “pear” shaped furnace. The process begins by introducing air into the lower part of the furnace, creating a high-temperature environment that drives a reaction between the oxygen and carbon in the cast iron. This reaction creates intense flames that consume the excess carbon in the cast iron, which in turn deposits the steel in the furnace.
- Martin-Siemens Process
Originally designed by Carl Wilhelm Siemens around 1850, it was perfected a few years later by the French engineer Pierre-Emile Martin.
This system is based on the separate introduction of fuel gas and air into two separate chambers. This is where the two fluids heat up before meeting in the reaction chamber, known as the laboratory. This is where combustion takes place, generating a temperature of around 1,800°C, which allows the cast iron to be purified and then stripped of its carbon content.
- LD Process
The LD process was invented in 1948 by Swiss engineer Robert Durrer and takes its name from the Austrian cities of Linz and Donawitz, where it was tested and perfected. It is a primary steelmaking method in which a high-carbon molten material is transformed into steel by the insufflation of oxygen, which reduces its carbon content. It is also known as the BOF (Basic Oxygen Furnace) process.
Today, approximately 70 per cent of global steel production is based on blast furnace technology. In Europe, however, production is almost equally divided between the blast furnace and the EAF, with the blast furnace slightly predominant (56%)[1].
Eaf furnace: sustainability and energy efficiency
The manufacturing process of steel has always required the melting of iron, either using the Blast Furnace or the Electric Arc Furnace (EAF). However, the EAF provides several advantages in terms of sustainability and energy efficiency.
The raw elements used in the EAF furnace are recycled ferrous materials, which place steel production in a process of circular economy and reuse of materials, consequently reducing the impact of manufacturing on the environment. In addition, unlike the Blast Furnace, the EAF requires lower temperatures to achieve its output and can be easily shut down once triggered. Electric Arc Furnace facilities are also more flexible and adaptable to production requirements. Energy consumption is also much lower than in blast furnaces, resulting in lower emissions.[2]
