Desulfurization and Dephosphorization Characteristics in the Process of Top Blowing Converter
Introduction
Removing sulfur and phosphorus from molten iron is a major task in the metallurgical industry. The top blown converter is an important tool for steelmaking, used to desulfurize and dephosphorize the molten iron. The process greatly reduces the sulfur and phosphorus associated with the raw material fed into the converter and helps to improve the quality of the steel produced. This paper will discuss the desulfurization and dephosphorization characteristics of a top blown converter and their importance in the steelmaking process.
Overview of the Desulfurization and Dephosphorization Process
First, molten iron is fed into the top blown converter, which is usually operated in a slightly oxidizing chemical atmosphere. By blowing oxygen-containing gas through the top of the converter and utilizing the combined oxidation and thermal energy that is generated, the sulfur and phosphorus in the molten metal is converted into gaseous oxide compounds. This chemical process results in the formation of volatile oxides of sulfur, such as sulfur dioxide and sulfur trioxide, as well as of volatile oxides of phosphorus, such as phosphorus pentoxide and diphosphorus pentoxide. These volatile compounds are subsequently removed from the converter by the converter’s exhaust gases.
The rate of desulfurization and dephosphorization is determined by the chemical potential and the temperature at which the top blown converter is operated. Typically the converter is operated in a wet chemical atmosphere - where the chemical potential of oxygen is higher than that of the alloy components - that allows for fast oxidation and high oven temperatures, between 1450-1600°C. The process also requires additives such as lime, magnesium, calcium and manganese which serve to remove phosphorus in the form of slag.
Types of Desulfurization and Dephosphorization Reactions in the Top Blown Converter
In a top blown converter, a variety of desulfurization and dephosphorization reactions occur. The most common reactions include:
1. Oxidation of sulfur to sulfur dioxide
At high temperatures, sulfur in the iron is oxidized by oxygen to form sulfur dioxide. This reaction is favored in an oxidizing atmosphere.
2. Oxidation of phosphorus to diphosphorus pentoxide
At high temperatures, phosphorus in the iron is oxidized by oxygen to form diphosphorus pentoxide. This reaction is favored in an oxidizing atmosphere.
3. Hydrogen sulfide to sulfur reaction
At lower temperatures, hydrogen sulfide is oxidized to sulfur. This reaction is favored in a reducing atmosphere.
4. Metals dissolution
At high temperatures, metals such as calcium, magnesium and manganese act as oxidation agents and dissolve any phosphorus present in the iron.
Benefits of Desulfurization and Dephosphorization
The desulfurization and dephosphorization of molten iron in a top blown converter is of immense importance in the steelmaking process as it greatly reduces the levels of sulfur and phosphorus associated with the raw material and helps to improve the quality of the steel produced. By removing these contaminants, the converter helps to avoid chemical imbalances and the formation of unwanted alloys. In addition, reducing sulfur levels increases the corrosion resistance of the steel, improves weldability, and reduces the associated cracking and fissuring. Similarly, reducing phosphorus levels in the steel improves its hardness, strength, and ductility.
Conclusion
In conclusion, desulfurization and dephosphorization of molten iron using a top blown converter is an important step in the steelmaking process. By reactions such as oxidation of sulfur to sulfur dioxide and phosphorus to diphosphorus pentoxide, along with metals dissolution, the process helps to remove contaminants from the raw material, improving the quality of the steel produced. The process also helps to avoid chemical imbalances and the formation of unwanted alloys, as well as increasing the corrosion resistance, weldability and strength of the steel.
