Status quo and development prospect of hot metal desulphurization technology

Control and elimination of sulfur steelmaking iron in water are two important conditions of high-quality steel smelting. Since 1965, it has been required to remove more than 99% of the total amount of sulfur from coke and other charge materials in blast furnaces or steelmaking equipment (converters). By the end of the 1970s, many blowing methods had been introduced. Although these injection schemes are different, the basic characteristics are based on the gas sprayed by the spray gun, and most of them use nitrogen as a carrier. Desulfurizers come in two broad categories: calcium carbide based (with lime/ limestone ) and magnesium based (with lime or calcium carbide) mixed desulfurizer. Spray in a torpedo-type iron can or a general ladle. A composite (cooperative) blowing method is employed in which two (or even three) desulfurizing agents are delivered to a spray gun immersed in molten iron by separate injection lines and tanks.
Torpedo jar of hot metal desulphurization <br> This is the most attractive blowing method. Because it can combine the desulfurization of molten iron with its transportation, and the temperature of molten iron can be 30-50 °C higher than that of ordinary hot metal, but it can not avoid the serious slagging of the molten iron in desulfurization. Little research has been done on the slag removal of hot metal cans. This may be because the condition and chemical composition of the slag are difficult to determine and the influence of these two uncertain factors on the total efficiency of hot metal desulfurization is difficult to determine. The higher temperature of molten iron is an advantageous condition for desulfurization with calcium carbide/lime, but it is extremely difficult to shorten the standing time of the molten iron tank after desulfurization to avoid the increase of slagging.
Desulfurization in general hot metal bags <br> There are obvious reasons for this desulfurization method to be promoted. First, a certain amount of sulfur can be taken off to make the molten iron reach the required sulfur content. Second, the blast furnace slag with the molten iron can be removed before the injection (but this is rarely done because the blast furnace slag is not known to be in the desulfurization process). Relationship with desulfurization and its ability to absorb sulfur). Strictly speaking, it is necessary to stabilize the slag brought along with the molten iron before desulfurization. However, it is always impossible to know how much reactant is needed for this purpose, so the selected desulfurizing agent is always used as compensation to stabilize the slag. Then desulfurize again. The ladle has a cover to reduce or even eliminate air ingress, but few are provided for the ladle. The adverse effects of oxygen on desulfurization have been repeatedly demonstrated in many literatures, but new desulfurization devices have ignored this.
The problem of the effect of blast furnace slag on subsequent desulfurization has not received much attention before. The current understanding of this issue has a basic outline. The first is that if the alkalinity of the slag is not proportionate, it will hinder the smooth progress of the desulfurization process. When the blast furnace slag is in the furnace, it should have excellent desulfurization ability, so that the alkali can be fully dissolved, and the viscosity is low and the water solute is excellent.
Injection equipment
The full pneumatic device injection system has matured. It is estimated that there will be no special new methods in the future that will greatly increase the overall efficiency of desulfurization.
A very uniform dosing of the desulfurizing agent is required - this requirement has led to the development of new technologies, and it is now being studied to mechanically distribute the desulfurizing agent to the carrier gas stream. If you can do this successfully, then you can say that this is the best blowing technology.
At present, it is not uncommon to blindly increase the gas flow rate in order to overcome the resistance of the pipeline. This problem has not been fundamentally resolved on most blowing equipment. According to C. Irons' model tests can be imagined that excessive gas flow can cause premature loss of desulfurizers.
The composite blowing system is first used on the blowing of a magnesium-containing desulfurizing agent. This system is very suitable because it reduces the partiality of magnesium particles that could not be overcome in the past. Conventional systems are unable to overcome fluctuations in the composition of the two desulfurizers in a short blowing time. The advent of mechanical powder mixing equipment will certainly alleviate this unevenness. [next]
Desulfurization and refining of steel water in the 1960s and early 1970s began with the use of calcium carbide as a desulfurizer. However, it was soon discovered that in order to improve the exchange of substances, it is necessary to use additives in this desulfurizing agent. Firstly, it is studied whether the "separation" gas or dissociation reaction of CaC0 ₃ in the injection can be the basis for enhancing the potential of desulfurization. However, it was later determined that the amount of "segregated" gas was extremely small and was likely to have no effect in the non-adiabatic expansion of the carrier gas. It is conceivable that the "segregation" gas reduces the oxygen to the interface, and as a result hinders or buryes the secondary oxidation of the sulfide in the slag (and the reverse transformation of sulfur). It should be noted that some steel mills do add a certain amount of CaC0 ₃ in the desulfurization. It was suggested to add desulfurization agent containing more gas in coal; in principle on various other additives to produce a gas that helps to maintain both a reducing atmosphere. In this case, whether the hot metal cover is cumbersome or not remains to be explored (mostly negative).
Lime is added to the calcium carbide-based desulfurizing agent. Initially, the statement that calcium carbide can precipitate a sufficient amount of calcium oxide is likely to be wrong. The conversion of CaC ₂ to CaO occurs only in interaction with air oxygen or oxides in the slag. Added to the calcium carbide in the fluorite will prevent this shift, but would help metal beads fall. Fluorite (melting point of 1418 ° C) does not react fast enough at hot metal temperatures. Tests have shown that the way to increase the overall efficiency of desulfurization is to add a fusible mineral, nepheline syenite, with a melting point of 1250 °C. The addition of this material can significantly reduce the carbide content (for example from 72% to below 55%).
Among the various carbide mixtures described above, lime (CaO) and coal having a low volatile content are added. The future issue is to study the evolution of the addition of nepheline syenite.
Magnesium has become a typical desulfurizer. The use of magnesium depends on the specific conditions of the steel mill and the market price. Although the mixtures and ideas used are different, it should be noted that the use of magnesium as a desulfurizer will encounter certain problems. For example, it has been reported that the slag line is found to be severely rubbed in a torpedo type hot metal tank. This situation is also seen in the open iron ladle, but only to a lesser extent. When using composite blowing, magnesium is sprayed with lime or calcium carbide. At this time, it is more reasonable to decide which method to use according to specific conditions: whether lime or calcium carbide can achieve better results.
The loss of iron has an important impact on the economics of desulfurization. For the iron loss problem, we should first pay attention to the large increase of metal beads in the desulfurization process. At this point, the weight of the slag will at least double. Many steel mills in the United States use a mixed desulfurizer with ~6% fluorite. This on the one hand reduces the loss of iron and on the other hand overcomes some of the disadvantages. The effects of various additives on the weight of the slag under different production conditions are different. Cryolite and a cathode waste (scrap aluminum smelting) can significantly reduce the loss of iron.
The problem of combining blast furnace tapping with hot metal desulfurization has not yet been seriously studied and developed. The existing methods are some of the solutions proposed in the late 1960s, mainly combined with slag and stirred in the iron ditch. The preliminary design of mechanical mixing methods such as the Rhine Steel and Nippon Steel has not been accurately verified. Although these experiments did not leave a deep impression, but let us once again pay attention to this effective desulfurization method, and re-examine its metallurgical conditions. A. More slag regeneration cycle desulfurization has not yet reached the point where practical design and maturity can be achieved. It is currently not possible to treat molten iron by the RH concept with a circulation system, although it has been successfully used in molten steel processing. The use of a unique sliding nozzle to deliver desulfurization agent to molten iron cannot be said to be successful. The same is true for the ISID system, although this method has been used in production experiments, but other parameters have suffered a lot.

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