Steel is a highly used material in society today and was developed in the Industrial Revolution as an improvement to iron. Due to its low production cost, steel now represents 90% of the metals consumed by industries.
As one can imagine, steel is a part of everyone’s daily lives, both in homes and offices and in the infrastructure of cities such as buildings, bridges, highways, among others.
Its production happens when iron oxide is mixed with fine sand and coal. This charcoal can be of mineral or vegetable source. So, for the steel to be produced, equipment called a blast furnace is used, where the chemical reaction takes place to separate the iron from its ore. For this to happen, coke is used, which is a reducing agent and comes from mineral coal.
It is important to understand that the coal used in the integrated coking steel industry is called coking coke. In other words, an essential substance in the reduction of iron ore to metallic ore. Thus, the coke will be obtained from the distillation of mineral coal in ovens, without oxygen, and during a certain time.
In this industrial process, coke oven gas, tar, and other chemical products are formed.
Types of steel industrial plants
The plants are classified according to the type of production process, which can be integrated, semi-integrated, and non-integrated.
In these plants, there are three basic phases: reduction, refining, and rolling. These factories have the entire steel production process.
In this type of plant, on the other hand, there are two phases: refining and rolling. So, pig iron, sponge iron, or metallic suction are used, which will be transformed into steel. These raw materials are obtained from third parties to then carry out the steel production process.
Unlike the other two types of plants, non-integrated ones only operate the processing stage. This step can be either lamination or reduction.
Steel production process
Using the example of an integrated plant, which carries out the complete production process, there are some steps that must be respected. These are load preparation, reduction, refining, and rolling.
To start the production process, the load is prepared, which is to make an agglomerate of iron ore using lime and coke fines. This step will result in sinter and coke. Coke is produced when the coal used is processed in the coke oven.
Next, the raw materials are loaded into the blast furnace, which will separate the iron from its ore.
Thus, the reduction of iron ore into liquid metal results in a product called pig iron. In pig iron there is a high content of carbon, which must be refined for steel production to take place.
The next step is the refining of pig iron, where part of the carbon content and other impurities contained in it are removed.
Finally, the rolling of steel takes place in a mechanical forming step. As a result of this step, the steel gains a new profile, reducing its thickness and increasing its length and width.
The transformation of coal into industrial coke
The coke plant is part of the steel industry that is responsible for producing coke. This product is the biggest heat supplier for the blast furnace, being indispensable in the production of steel.
Coke is a material similar to a porous rock, about the size of a fist. It is the carbon source for steel and also influences the blast furnace’s performance.
This coal coking process was what allowed ironmaking to be improved. Consequently, resulting in steel that is produced using coke in steel industries.
Coke oven production process
The coke plant is an essential step in the production of steel, as it is where the coke to be used as fuel and reducing agent in the steel production process is produced.
The first step in the production of coke takes place during the heating of the coal to up to 350 ºC. Thus, there is vaporization of moisture and the beginning of devolatilization.
Then, in the second stage, also known as the plastic phase, the temperature rises and stays between 350 and 500 ºC. Under these conditions, coal decomposes into tar and gases, which are diluted by the liquid formed.
Finally, the third stage consists of a temperature that starts at 500 ºC and reaches 1000 ºC at the end of the production process. It is in this solidification stage that the slurry formed loses even more volatile material, consequently starting to crack to form semi-coke and then coke.
In this transition from semi-coke to coke, the gases generated are characterized by the increase of hydrogen and the reduction of methane, with semi-coke turning into coke only when the temperature gets to a range from 950 to 1000 ºC.
Once formed, the coke remains in the oven until the temperature of the product is homogenized and the physical and metallurgical properties are regulated as well.
It is only after all this process that the coke is ready to be used in steel production, making the final material more interesting and competitive.
Use of coke in the reduction step
During the steel production process, as mentioned above, coke is used as fuel and reducing agent. Considering the second application, coke is the reducing agent precisely in the reduction stage.
And it is at this point in the process that pig iron is produced. Like steel, pig iron is an alloy composed of iron and carbon. However, there are other elements present such as manganese, silicon, and sulfur, in addition to a higher concentration of carbon in pig iron.
Pig iron production is very important for the steel industry, as it accounts for a large part of the cost of steel production.
Thus, it is possible to understand that the use of coke in the steel production process is important and essential to obtain a higher quality product.