The method of iron desulfurization and its technological development trend
Abstract
The method of iron desulfurization is an important desulfurization process in the production of iron and steel. Iron desulfurization can effectively reduce the sulfur content in the steel and meet the requirements of various specifications. In the steelmaking process, there are many ways of iron desulfurization. In the past, there were traditional physical and chemical methods such as dephosphorization, de sulfurization and steelmaking. With the rapid development of science and technology, the extraction of sulfur from molten iron by vacuum and molten salt became the mainstream method. This paper explains the principle and classification of iron desulfurization, and then introduces the technology development of iron desulfurization, for example, traditional physical and chemical methods, vacuum purification methods, inert gas inert purification methods and molten salt purification methods. Finally, the research direction of desulfurization technology at home and abroad is prospected.
Keywords: iron desulfurization; technological development; purification
1 Introduction
For steel makers, the content of harmful elements like sulfur is a matter of great concern, because sulfur is easy to cause hot brittleness and cold brittleness of steel, so forged steel needs to have a lower sulfur content and heat treated steel needs to have a much lower sulfur content. Therefore, the desulfurization of iron is very necessary in the steelmaking stage. Iron desulfurization is the process of reducing sourness in molten iron by extracting sulfur out of the molten iron.
2 Principle and classification of iron desulfurization
Iron desulfurization mainly removes sulfur from molten iron in a variety of ways to reduce the sulfur content of molten iron and meet the requirements of various specifications. Generally, it can be divided into physical method, chemical method and non-thermal method.
(1) The physical method usually adopts vaporization, boiling, stripping and other methods. In the vaporization method, the melt is injected into the vaporization tower through oxygen lance or air lance to contact with hot air, and the sulfur forms sulfur vapor which is taken away. In the boiling method, the melt is injected into the boiling furnace through oxygen lance or air lance to induce stirring and boiling, and the sulfur vapor is taken away along with the ashes when the melt is discharged.
(2) The chemical method generally uses the reaction between molten iron and certain additives to make sulfur compound, such as sodium sulfide. Sodium sulfide able to react with iron oxide, forming sodium polysulfides, which then react with iron to form iron sulfides. The iron sulfides are then slaggy and sulfur is discharged with the slag. Sodium polysulfide can also be used for iron desulfurization with some iron oxide already in the melt, as in the case of phosphorus removal.
(3) Vacuum method is a kind of non-thermal method, which mainly uses the high vacuum degree of vacuum furnace to absorb sulfur in molten iron into the wall of the tank. The molten iron flows through the bottom and absorbs sulfur into the steel-lined furnace wall during the process of continuous pouring, and the sulfur is taken away with the evacuation.
(4) The inert gas inert purification method is a kind of non-thermal method, it is mainly used nitrogen gas cover of the surface of the molten iron through nitrogen or helium gas, so that sulfur furnace wall containing compounds such as sulfur compounds and sulfur-containing part of the isolation, and then with the removal of nitrogen gas to take away these compounds.
(5) In the molten salt purification method, sodium sulphate, soda and other molten salts are introduced into the molten iron to dissolve the sulfur in the molten iron into the molten salt, and then the sulfide is reduced to hydrogen sulfide gas to achieve the purpose of desulfurization.
3. Technological Development of Iron Desulfurization
(1) Traditional physical and chemical methods
When steelmaking, the traditional physical and chemical methods of dephosphorization and desulfurization are still used today. The method of physical dephosphorization and desulfurization mainly uses the principle of vaporization and boiling. When some furnace gases come in contact with molten iron in the melting furnace, they will take away some sulfur and phosphorus in the molten iron, and the content of sulfur and phosphorus in the molten iron will be reduced to a certain extent.
(2) Vacuum purification method
Vacuum desulphurization technology is one of the most commonly used methods in the steelmaking process. The desulfurization of molten iron by vacuum depends mainly on the generation of a high vacuum degree in a steel shell sealed vacuum furnace. In the process of continuous pouring, part of the sulfur in the molten iron absorbs into the steel-lined furnace wall along the molten iron, and then the absorbed sulfur is taken away with the evacuation.
(3) Inert gas inert purification method
In the inert gas inert purification method, nitrogen or helium gas is used to cover the surface of the molten iron. The sulfur containing compounds in the furnace wall, oxygen containing compounds and some sulfur compounds are isolated, and then are taken away with the removal of nitrogen or helium gas. This method has the characteristics of high efficiency and energy saving, no harmful substances such as nitrogen oxides remaining in the molten iron, and no large amount of dust flying.
(4) Molten salt purification method
The molten salt purification method is mainly used to reduce the sulfur content of molten iron by the method of introducing sodium sulphate and soda into the molten iron to dissolve the sulfur in the molten iron into the molten salt, and then the sulfide is reduced to hydrogen sulfide gas.
4. Research direction of desulfurization technology at home and abroad
At present, with the improvement of environmental protection requirements, the desulfurization technology for molten iron is getting better and better. The current research direction at home and abroad is mainly focused on how to improve the desulfurization efficiency of molten iron and reduce the desulfurization cost. For example, the research direction of vacuum desulfurization also includes research on the development of new vacuum equipment, the improvement of steel shell, the improvement of negative pressure and the improvement of melting speed through the introduction of oxygen-enriched devices. The research of inert gas inert purification also includes the research of injection atomizer, the technology of nitrogen-controlled model, the study of nitrogen and helium gas and so on. The molten salt purification research and development includes the development of sodium sulfate, the study of sodium sodium solution, the optimization of molten salt composition and other aspects of control.
5. Conclusion
The iron desulfurization process is an important desulfurization process in the production of iron and steel. At present, the traditional physical and chemical methods, vacuum, inert gas, stirring and molten salt purification methods are all feasible iron desulfurization methods. The basic principles and methods of iron desulfurization are introduced in this paper, and the development of iron desulfurization technology in recent years is reviewed. It is believed that the continuous improvement of iron desulfurization technology will play an important role in the future production of iron and steel.
