Analysis:
Pig iron, ore or processed waste oxygen are the main raw materials.
Steelmaking methods can generally be divided into converter steelmaking, open hearth steelmaking and electric furnace steelmaking. They are introduced as follows:
1. Converter steelmaking The oxidant used in this steelmaking method is oxygen. Blow air into molten pig iron to remove impurities such as silicon oxide and manganese. In the process of oxidation, a large amount of heat is released (containing 1% silicon can raise the temperature of pig iron by 200 degrees Celsius), which can make the furnace reach a high enough temperature. Therefore, converter steelmaking does not need to use additional fuel.
Converter steelmaking is carried out in the converter. The converter is shaped like a pear, with refractory bricks on its inner wall and many small holes (tuyeres) on its side. Compressed air is blown into the furnace from these holes, which is also called side-blown converter. At first, the converter is horizontal. Liquid pig iron at 1300℃ is injected and a certain amount of quicklime is added. Then, air is blown and the converter is rotated to make it stand upright. At this time, the surface reaction of liquid pig iron is fierce, so that iron, silicon and manganese are oxidized (FeO, SiO _ 2, MnO,) to generate slag, and the reaction spreads to the whole furnace through convection between molten steel and slag. After a few minutes, when only a small amount of silicon and manganese remained in the molten steel, carbon began to oxidize, generating carbon monoxide (exothermic), which made the molten steel boil violently. Due to the burning of spilled carbon monoxide, a huge flame appeared at the mouth of the furnace. Finally, phosphorus will also oxidize and further generate ferrous phosphate. Ferrous phosphate reacts with quicklime to produce stable calcium phosphate and calcium sulfide, which together become slag.
When phosphorus and sulfur gradually decrease, the flame recedes and brown steam of ferroferric oxide appears at the mouth of the furnace, indicating that the steel has been refined. At this time, the blast should be stopped immediately, the converter should be turned to a horizontal position, the molten steel should be poured into the ladle, and then the deoxidizer should be added for deoxidation. The whole process only takes about 15 minutes. If the air is blown from the furnace, it is a low-blowing converter.
With the development of oxygen production technology, oxygen top-blown converter (also known as side-blown converter) has been widely used. This converter blows high-pressure industrial pure oxygen, and the reaction is more intense, which can further improve the production efficiency and steel quality.
2. Open hearth steelmaking (also called Martin process)
Oxidants used in open hearth steelmaking are introduced into the air and oxides (scrap iron, scrap steel, iron ore) in the furnace charge. The heat required for the reaction is provided by burning gas fuel (blast furnace gas, producer gas) or liquid fuel (heavy oil).
The hearth of open hearth furnace is a trough made of refractory bricks, and the trough is covered with a top made of refractory bricks. There is a charging port on the front wall of the open hearth furnace, from which the charging machine loads the burden. Close the door caused by the melting of refractory bricks. There are burners at both ends of the furnace, and each burner has two holes for introducing fuel and hot air or leading out furnace gas from the furnace.
The raw materials used in open hearth steelmaking are scrap steel, scrap iron, iron ore and solvents (limestone and quicklime). At the initial stage of smelting, the fuel burns on the surface of the fuel when it meets the introduced hot air, and the temperature is as high as 1800 degrees Celsius. Heat is directly transferred from the flame to the burden, which makes the burden melt quickly (the melting point of iron is 1535 degrees Celsius, and the melting point of steel is slightly lower). At the same time, some molten pig iron generates ferrous oxide, and impurities such as silicon and manganese in pig iron are oxidized by ferrous oxide to produce acoustic slag. Due to too much limestone in the furnace, impurities such as phosphorus and sulfur generate calcium phosphate and calcium sulfide become slag. Secondly, carbon will also be oxidized to produce carbon monoxide, which escapes from molten metal as if the metal were boiling.
At the end of the reaction, deoxidizer is added and slag is scraped regularly. When smelting is about to be completed, it is necessary to check whether the composition of steel meets the requirements according to the analysis before the furnace (rapid analysis can be completed in a few minutes). Technetium-smelting steel flows into the ladle from the tapping hole, and then is injected into the crystallizer from the ladle to be cast into products or ingots.
In order to raise the furnace temperature, the gas fuel should be preheated in the regenerator (as shown in Figures 1, 1, 2, 3, 4 and 4).
In the open hearth furnace, not only liquid pig iron can be added, but also solid pig iron, scrap iron and eroded iron ore can be added. In addition, if 30% oxygen-enriched air is blown into the open hearth and oxygen is blown into the molten metal at the same time, the productivity can be increased by 80%, the smelting time can be shortened by 2~4 hours, and fuel can be saved, and the oxygen-enriched air does not need to be preheated.
3. Steel made by electric furnace can also be smelted in electric furnace with electric energy as heat source. High quality alloy steel can be produced by electric furnace steelmaking. There are many kinds of electric furnaces.
The most widely used is the electric arc furnace.