The Increase of Sulphur after Desulphurization in Blow Steelmaking
Abstract
When steelmaking by the converter in steelmaking, it is common to add low-sulphur molten iron after desulphurization, but the low-sulphur molten iron sometimes still brings increase of sulphur in blowing steelmaking. This paper discussed the causes and solutions of the increase of sulphur after desulphurization in blow steelmaking.
Introduction
In the process of steelmaking, the main content of sulphur in molten iron is approximately 1%. The higher sulphur content in molten iron will have an impact on the performance of steel, so it needs necessary desulphurization for the molten iron. The common desulfurization methods are lance smelting and back-decoction desulfurization. After the molten iron is desulphurized, the content of sulfides should be reduced to 0.009-0.02%, which is far lower than the standard of 0.04%. By conventional wisdom, low-sulphur molten iron can bring great benefit to steelmaking.
However, the low-sulphur molten iron sometimes still brings a phenomenon of increasing sulphur when steelmaking by the converter in steelmaking. As for the reasons for this phenomenon, no matter it is undergraduate analysis or the conclusions of many years of practice, as long as the low-sulphur molten iron flows into the converter in steelmaking, the sulphur content of it will still gradually increase. The Sulphur increase of 0.01-0.02%(mass fraction) is more common, but the increase of 0.03-0.04%(mass fraction) is also occasionally occurred.
Discussion
i. Analytical Methods
After many years of research, it is known that the increase of sulphur after introduction of low-sulphur molten iron is caused by two elements of iron and oxygen in molten iron.
(1) Iron
The iron (Fe) in molten iron is the core element of the process of sulphur increase. When adding low-sulphur molten iron to the steelmaking, according to the principles of chemical reaction and oxidation-reduction reaction, the iron particles in the molten iron and the oxygen of air will automatically react to form iron oxide (FeO). The formed iron oxide is easy to combine with sulfur to form sulfide, which will further increase the total sulphur content of the molten iron.
(2)Oxygen
When low-sulphur molten iron is added to the steelmaking, it is impossible to avoid contact with oxygen in the air, so during the process of steelmaking, a certain amount of oxygen will inevitably bring into the converter. Oxygen itself is a necessary element for the sulphur increase of molten iron. It will react with iron to form iron oxide, and then combine with sulphur to form sulfide and increase the total sulphur content of the molten iron.
ii. Countermeasures
(1) Change the process
The increase of sulphur after desulphurization is caused by the combination of iron and oxygen in molten iron. Therefore, the effective way to prevent the increasing of sulphur is to reduce the content of both iron and oxygen. Theoretically, reducing the proportion of the low-sulphur molten iron in the total steelmaking quantity is an effective way to reduce the contact between iron and oxygen. In actual production, we can try to reduce steelmaking by using more scrap steel, which can prevent the contact between iron and oxygen so as to reduce the increase of sulphur.
(2) Use sulphur-containing metal additives
The alkali metal and alkaline earth metal additives is an effective way to reduce the increased sulphur in blow steelmaking. Besides, metal oxides and metal sulfides can also be used as sulphur absorbing agent in blow steelmaking, which can effectively reduce the sulfur increase of the low-sulphur molten iron during steelmaking.
Conclusion
The increase of sulphur after desulphurization in blow steelmaking is due to the reaction between iron and oxygen in molten iron. Reducing the proportion and contact time between iron and oxygen is an effective way to reduce the increase of sulphur. In actual production, we can use metal additives with sulphur content to reduce the sulfur increase of the low-sulphur molten iron during steelmaking.
