JP2016084499A - Powdery lime for refining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide powdery lime of refining, when metallic mg is added to quick lime upon injection into a molten metal, improving the capture rate of S by the metallic Mg, and whose conversion into CaS in boundary slag can be promoted.SOLUTION: CaO fired in such a manner that ignition loss is made possible O is made into powdery one of 0.05 mm or lower. In this case, it is fired in such a manner that the purity of the CaO reaches 97% or more, and the ignition loss thereof is made lower than the ignition loss included in the Cao with a purity of 93% or lower. When calcium aluminate powder is further added to a refining agent made of the CAO and metal Mg, it exhibits a reduction action of a slag melting point, and, when floating-up MgS enters the slag in which 12CaO 7AlOis present, the resulfurization of the MgS is suppressed, and its conversion into CaS is suppressed, and its conversion into CaS from the MgS is progressed as well.SELECTED DRAWING: None

Description

  The present invention relates to powdery lime for refining, and more particularly to a lime-based refining agent that reacts with sulfur contained in hot metal or molten steel to desulfurize and promotes the generation of slag.

  Recently, quick lime is frequently used as a refining agent that reacts with it to desulfurize and generate slag in order to remove sulfur contained in molten iron. This is because the coke used during ironmaking contains a large or small amount of sulfur, but if these are left behind, the steel quality deteriorates and the improvement in iron strength is impeded, and the workability is reduced. Impairs malleability and ductility.

CaO as a refining agent is produced by removing carbon dioxide CO ₂ by firing limestone CaCO ₃ . There are cases where the refining agent is poured down on the surface of the molten metal and injected into the molten metal. In the former, the refining agent is a lump of up to about 50 mm, for example, and in the latter case, it is provided as a powder.

  Since CaO reacts with the sulfur content S in the molten metal to produce CaS, if this is slagged and removed from the furnace body, the desulfurized molten iron is purified. When the refining agent is thrown from the furnace toward the molten metal surface, the refining agent with a small specific gravity floats on the molten metal surface, so it cannot be said that there are many opportunities for contact between the refining agent and the molten metal. When the powder is placed on an inert carrier gas by the injection method and blown from an injection lance or from the bottom of the furnace, there are many opportunities to come in contact with S in the molten iron while floating in the molten metal, and thus the refining efficiency is generally high. This is due to the fact that the specific surface area is much larger than that of powdered CaO.

  When adopting the injection method, metal Mg may be added to quicklime. This is because it is known that when CaO reacts with S in the molten metal to produce CaS, it is more active that metal Mg reacts with S than CaO captures S. The process of producing CaS by reacting with CaO when the produced MgS floats on the interface is advantageous for CaO because of high reaction efficiency. As described above, Patent Document 1 discloses that metal Mg powder is mixed and refined when CaO powder is blown from an injection lance.

By the way, CaO is produced by baking limestone at, for example, 900 ° C. to release CO ₂ , but for the metal refining, CaO having a purity of around 92% is provided. The remaining 8% is composed of SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , MgO, the amount of ignition loss, and a very small amount of P. Since SiO ₂ , Al ₂ O ₃ , and Fe ₂ O ₃ are also contained in the molten metal, their presence does not immediately cause a problem, and MgO contributes to an increase in basicity. Most of the other ignition losses are CO ₂ and H ₂ O, which are substances that disappear from quicklime when exposed to further heat.

  If the loss on ignition is to be eliminated when calcining limestone, the degree of calcining needs to be extremely high, and the production cost of quick lime increases. In addition, it becomes unfavorable in refining, such as the occurrence of squeezing and the reduction of the porous property of quicklime, and in practice it is limited to firing that does not harden. As described above, quicklime is used in the form of a lump or in powder form. In the former case, it is desired that the lime is not a sintered product. Accordingly, quick lime that can be used for any purpose is supplied to the market, and is usually up to 92.3% pure.

JP 2010-059518 A

  The use of the above metal Mg is limited to the case where it is applied to the injection method because it is a powder. This metal Mg is so expensive that it cannot be compared with quicklime, and whether or not MgS can be efficiently produced by the metal Mg before the CaS is produced affects the quality of refining. In order to reduce the consumption of metallic Mg, it is indispensable to increase the S content capturing ability, but in reality the relationship with CaO, which makes up most of the input, has not been studied.

  The present invention has been made in view of the above problems, and its purpose is to improve the capture rate of S by the metal Mg and promote the conversion to CaS in the interface slag when using the metal Mg in the injection. It is to provide powdered lime for refining that can be made.

  The present invention is applied to CaO injected into molten metal together with metal Mg powder in order to remove sulfur contained in molten iron. The feature is that it is fired so that the loss on ignition becomes as small as possible in the production process, and is made into powdered CaO of 0.05 mm or less.

  The CaO is baked so that its purity is 97% or more, and its ignition loss is made smaller than the ignition loss contained in CaO having a purity of 93% or less.

Calcium aluminate powder 12CaO · 7Al ₂ O ₃ is added to a refining agent composed of powder of CaO and metal Mg.

A refining agent composed of CaO and Mg metal powder contains 80 to 120 parts by weight of Al ₂ O _{3 and} 24 to 76 parts by weight of Na ₂ O with respect to 100 parts by weight of CaO. Hybrid solid powder may be added.

  In any refining powdered lime, carbon powder is preferably added.

According to the present invention, the CaO is kept at a purity of 97% or higher by using a high firing temperature or a long firing time. Therefore, the remaining CO ₂ and H remaining together with the hybrid such as SiO ₂ , Al ₂ O ₃ , and Fe ₂ O _3. The amount of ₂ O can be kept lower than those contained in CaO having a purity of 92.3% or less. Metal Mg reacts preferentially with CO ₂ or H ₂ O in CaO where it is easy to obtain an oxygen content in the molten metal to produce MgO. As a result, Mg to be reacted with S in the molten metal is consumed. However, CaO that has been treated so that the loss of ignition loss CO ₂ and H ₂ O becomes as low as possible during the production process will not progress to MgO, leaving a large amount of Mg that reacts with S in the melt. Can do.

When calcium aluminate 12CaO · 7Al ₂ O ₃ is added to the refining agent, it exerts an effect of lowering the melting point of slag, and MgS that has floated into the slag in which this calcium aluminate is present Further, sulfite is suppressed, and conversion of CaS from MgS is promoted.

Calcium aluminate soda mixed solid powder containing 80 to 120 parts by weight of Al ₂ O _{3 and} 24 to 76 parts by weight of Na ₂ O with respect to 100 parts by weight of CaO. Is added to the desulfurization action by CaO / metal Mg, the desulfurization action by calcium / aluminate / soda is added, and the desulfurization effect is further improved.

When carbon powder is added, the carbon content removes oxygen content such as Fe ₂ O ₃ in the slag, fosters a reducing atmosphere of the slag, and promotes the generation of CaS.

  Below, powdery lime for refining concerning the present invention is explained in detail based on the embodiment. The CaO to be injected is a powder of about 0.05 mm or less, and an appropriate amount of metal Mg (magnesium) powder is blended. This refining agent in a mixed state is supplied to the molten metal from an injection lance (sublance) or the like. The powder size of CaO is preferably 325 mesh (44 μm) or less, and in some cases, 14 μm or less, and has a specific surface area that is so large that it cannot be compared with lime dropped from the top of the furnace.

  The CaO used here has a purity of 97% or more produced by increasing the degree of firing. This is fired so that the loss on ignition (ignition loss, Ig-loss) becomes as low as possible during the CaO formation process. The thus treated CaO has a loss on ignition less than the loss on ignition contained in CaO having a purity of about 93%. For example, if the purity is 93%, the impurity (hybrid) is 2%, and the loss on ignition is 5%, but the loss on ignition is 5% and only CaO and impurities are present, the purity of the CaO is 93 / (93 + 2 ) = 0.979, ie 98%. Moreover, when 3% of impurities (hybrid) and 4% loss on ignition are lost to 4% of loss on ignition and only CaO and impurities are used, the purity of the CaO is 93 / (93 + 3) = 0.968, ie 97%. In addition,% here is a weight ratio.

Limestone CaCO ₃ exhibits a reaction of CaCO ₃ → CaO + CO ₂ at 825 ° C. or higher, releases CO ₂ and becomes quick lime CaO. Usually, limestone is baked at 900 ° C to 1,100 ° C, or even higher, but in order to produce CaO with a purity of 97% or higher as described above, the baking time should be increased. The firing temperature must be increased. As a matter of course, the fuel consumed for calcination increases, and it is unavoidable that the production cost of CaO increases.

The mined limestone CaCO ₃ is a Meltz furnace that is crushed to a size of ₃₀ to 80 mm and adopts a layered firing method, and a size of 30 mm or less is a rotary kiln that does not need to worry about clogging that hinders gas flow. Is fired. In the latter case, in order to prevent the exhaust gas from being carried out of the furnace on the exhaust gas, a material that is not finer than 1 mm is introduced. Therefore, regardless of which kiln is fired, it will be finely pulverized for injection purposes.

As mentioned above, most of the loss on ignition is CO ₂ and H ₂ O. However, CO ₂ is diffused and H ₂ O is also blown away compared to when CaO 3 having a purity of around 93% is produced from CaCO _3. As a result, it usually approaches the tightened state. That is, the traces of missing CO ₂ or the like remain as fine voids, but the higher the purity, the narrower the voids due to the densification of the structure. Since this CaO is used for injection, it is pulverized to the size described above after firing.

  Since the surface area per unit weight increases as the size of the fine powder of the refining agent decreases, the molten metal contact ratio of CaO increases. Even if it is unavoidable to narrow the voids due to densification, the porous property is not lost at all. As described below, the ability to trap the S content of the molten metal with metal Mg is exhibited, so that it is hardened. Even if it is CaO, if it sees from the whole input refining agent, desulfurization will become a thing improved greatly. Note that metal Mg has been added, focusing on the fact that the melting point is 649 ° C. and the dispersibility in the molten metal is very good and Mg easily forms MgS than CaO becomes CaS. Already mentioned above.

By the way, in the case of a refining agent in which metal Mg is mixed with CaO, it is known that a reaction of Mg + CaO + S → CaS + MgO (the underline indicates what is in the molten metal) is exhibited in the molten metal. However, if there is a loss on ignition in CaO, metallic Mg is a far crab O than from _{SiO 2, Al 2 O 3,} Fe 2 O 3, MgO are impurities in the CaO and CaO in the molten metal It reacts with CO ₂ and H ₂ O, which are easily robbed, to produce MgO. As a result, Mg charged to react with S in the molten metal is consumed unintended, and as a result, the production of MgS is inhibited or suppressed. In the present invention, CaO in which the remaining amount of CO ₂ and H ₂ O is eliminated as much as possible is introduced, so that the amount of metal Mg converted to MgO is remarkably reduced, and MgS is replaced with S in the molten metal. Will greatly increase the opportunity to become.

When MgS generated by Mg + S → MgS in the process of rising after injection reaches the interface slag, it exhibits a reaction of MgS + CaO → CaS + MgO to generate CaS, which is fixed to the slag. As can be seen from this, the present invention focuses on the point that metal Mg reacts with ignition loss CO ₂ and H ₂ O in CaO, and attempts to improve the refining efficiency by eliminating it. That is, it is based on the knowledge of increasing the chance of generating MgS by reducing the generation of MgO. In addition, CaO in the molten metal surface is CaS generation C + CaO + S → CaS + CO (underlined is in the molten metal), but many CaO that floated without becoming CaS is the above formula Like this, CaS is formed by taking S of MgS in the slag.

By the way, MgS is unstable and tends to cause sulfurization, but when it becomes CaS, it becomes a stable property and hardly causes sulfurization. In the interface slag where high-activity CaO that has not yet been converted to CaS is present where MgS has emerged, the replacement with CaS proceeds very smoothly. In addition, the addition amount of metal Mg should just be 0.1-0.3 if it is a grade commensurate with reaction with S in molten iron, ie, lime content is 1. The lime may be salt-baked quicklime, but it goes without saying that the loss on ignition must be minimized as described above. It is important to manage the produced CaO so as not to absorb CO ₂ during storage so as not to cause water contamination during pulverization. If CaO is larger than 0.05 mm, it is not impossible. However, considering the degree of shrinkage, it is natural that the CaO is suitable for injection and can be placed on a carrier gas.

By the way, the above-described refining agent is a powder made of CaO and metal Mg, and calcium aluminate powder 12CaO · 7Al ₂ O ₃ may be added thereto. Calcium aluminate has a melting point of 1,385 ° C. and exhibits the effect of lowering the melting point of slag. When MgS enters slag in which calcium aluminate is present, resulfurization from MgS hardly occurs. Therefore, the CaS in the interface slag promotes the conversion of MgS to CaS and is stably fixed to the slag. The introduction of calcium aluminate also contributes to reducing the consumption of expensive metal Mg. Although not mentioned in detail, this calcium aluminate also acts to increase the deoxidizing ability.

Carbon powder is also added to the mixed powder of CaO and metal Mg or the mixed powder of CaO, metal Mg and calcium aluminate. Carbon removes oxygen from Fe ₂ O _{3 and the} like in the slag to create a reducing atmosphere of the slag, which makes it difficult to cause sulfurization from MgS, and [S] + (CaO) + C → ( The formation of CaS is facilitated by the reaction CaS) + CO 2. In addition, [] means in the molten iron and () means in the slag. The addition amount may be set to 0.1 to 0.03 with lime as 1. If it is less than 0.1 within the range where the effect is produced, the increase in C in the molten metal can be suppressed, and the burden of the subsequent decarburization operation is not increased.

Calcium aluminate soda CaO.Al ₂ O ₃ .Na ₂ O may be added to the refining agent for injection in which metal Mg is added to CaO with a low ignition loss described above. The calcium aluminate soda is a mixed solid of calcium aluminate soda containing 80 to 120 parts by weight of Al ₂ O _{3 and} 24 to 76 parts by weight of Na ₂ O with respect to 100 parts by weight of CaO constituting the calcium aluminate soda. It is a thing, and it is made into a powdered thing and can be used for injection. The desulfurization effect of calcium aluminate soda can be applied to the action of the desulfurization agent made of CaO / metal Mg, and the desulfurization effect is further improved.

This is because it is well known that Na ₂ O constituting a part of calcium aluminate soda has a particularly strong desulfurization action. Sodium carbonate Na ₂ CO ₃ has been widely used as a soda-based refining agent, and this is due to decomposition during refining to produce Na ₂ O. However, sodium carbonate Na ₂ CO ₃ decomposes during refining and white smoke covers the surface of the hot water, obstructing visual inspection during operation. Although contributing Na ₂ O in the desulfurization is generated from Na ₂ CO _3, lowering the contribution to the desulfurization reaction disengaged from the molten metal. Not only that, but Na ₂ O adheres to the furnace wall and the furnace lid, etc., and has some problems such as accelerating the deterioration of the equipment and becoming unable to convert the slag into fertilizer. There is a background that it was replaced.

  By the way, the refining agent of calcium aluminate soda powder is not limited to the case where it is supplied to the molten metal simultaneously with the refining agent obtained by adding metal Mg to CaO. For example, the refining agent obtained by adding metal Mg to CaO in the first half of refining may be fractionated or alternately injected so that calcium aluminate soda powder is supplied in the second half. Metal Mg can also be added to the calcium aluminate soda in the case of this separate supply. In the case of simultaneous supply, the same effect is exhibited that a part of metal Mg can contribute to desulfurization with calcium aluminate soda.

Here, calcium aluminate soda CaO.Al ₂ O ₃ .Na ₂ O will be mentioned (for details, see also Japanese Patent Application Laid-Open No. 2012-012680). The fact that this refining agent has the main fossilizing action is CaO, which is no different from the refining agents described so far. However, it is a calcined product of calcium aluminate soda CaO.Al ₂ O ₃ .Na ₂ O or a mixed solid in the form of a solid solution, and pulverized so that it can be used as a refining agent for injection. Is. Although the manufacturing method will be described later, the configuration is as described above, and the numerical significance thereof is realized by realizing a mixed amount of Na ₂ O which is impossible in Japanese Patent Laid-Open No. 2003-253315 (Japanese Patent No. 4150194). is there. The calcium aluminate soda here takes the form of fixing Na ₂ O to CaO. Then, an excessive ratio of soda is avoided, the adhesion of the furnace wall and the furnace lid of Na ₂ O is cut off, and the conversion of slag to fertilizer is allowed.

Next, a manufacturing method in the case of obtaining a mixed solid of calcium, aluminate and soda as a fired product will be described. The raw materials used are limestone CaCO ₃ for CaO, bauxite (aluminum shale) or aluminum smelting ash for Al ₂ O ₃ , sodium carbonate Na ₂ CO ₃ for Na ₂ O. First, the former two are pulverized to a water kneadable state, for example, 0.2 mm or less, and originally powdered sodium carbonate is added thereto. Then, water and calcium hydroxide for adhesion promotion are added and kneaded.

  The kneaded product is filled into a frame and formed into a block by natural drying or forced drying. When these blocks are allowed to pass through a non-rotating tunnel kiln while being placed on a carriage, a fired product (calcium, aluminate, soda) is obtained by contact with hot gas. Since a kiln in which the furnace body does not rotate is used, the kneading block is not deformed and is not damaged. In addition, the tunnel kiln is fired while slowly moving the object to be fired, so that it is possible to reduce as much as possible the deterioration of quality such as uneven firing.

When obtaining a fired product, the firing speed is slow, but it is placed on a well girder assembled in multiple stages on the carriage, so it contains a much larger amount of processed material than a rotary kiln with a cascading motion. Can be fired. In addition, the reaction of Na ₂ CO ₃ → Na ₂ O + CO ₂ proceeds from when the kiln atmosphere exceeds 400 ° C. CO ₂ becomes kiln exhaust gas, but crystals of Na ₂ O remain in the block. As a result, Na ₂ O must be fixed to CaO. In the case where a flux in which CaO, Al ₂ O ₃ , and Na ₂ CO ₃ are individually mixed in the form of powder or granules is used as a flux, Na ₂ CO ₃ is vaporized at the point of contact with the hot metal to be desulfurized. Some will disappear immediately without contributing, but you don't have to do that.

The fired product thus produced is crushed and ground to obtain a refining flux. Since this injection flux is in a mixed firing state in which CaO, Al ₂ O ₃ and Na ₂ O are integrated, Na ₂ O is restrained by CaO or Al ₂ O ₃ until it is poured into the molten metal and melted. Thus, it is possible to prevent Na ₂ O from disappearing quickly. There is almost no disappearance before the slagging action, such as Na ₂ CO ₃ coming into contact with hot metal having high temperature and high C concentration to cause vaporization loss.

As described above, the remarkable improvement of the desulfurization effect is due to the high manifestation rate of Na ₂ O, but the contribution is high because Na ₂ O is not dissipated before the reaction as described above. That is, it is considered that Na ₂ O is fixed to CaO as a mixed solid of calcium, aluminate, and soda, and poured into the molten metal, and when the refining agent is melted, Na ₂ O is released and activated from that point. As a result of the superposition of the desulfurization action of Na ₂ O and those caused by CaO, it complements such that one side cannot capture, for example, the other part captures sulfa. Needless to say, the desulfurization of the molten metal is promoted at the place where the flux components come into contact, and as a result, if the flux is dispersed, the desulfurization effect of the molten metal is improved accordingly.

By the way, powder metal Mg is mixed in the mixed solid pulverized product of calcium, aluminate and soda so as to improve the desulfurization function, and the amount is equivalent to 10 to 20 parts by weight with respect to 100 parts by weight of CaO before mixing. Metal Mg promotes the production of CaS by the reaction as shown in the formula already shown, and as a result, exhibits a desulfurization action. In this case, MgO produced by combining with a portion of CaO O is a quaternary phase of CaO—SiO ₂ —Al ₂ O ₃ —MgO ₃ together with SiO ₂ contained in a large amount in quicklime, alumina, hot metal, or the like. It becomes a phase state according to it and acts to further promote the melting point decrease of CaO. Not only desulfurization with CaO always exceeding about 30% by weight, Al ₂ O ₃ always exceeding 29% by weight, Na ₂ O always exceeding about 10% by weight, but also desulfurization with metal Mg always exceeding 3% by weight is applied. On the other hand, MgO produced by the reaction also contributes to an increase in basicity, but it cannot be overlooked that slag erosion to magnesia-based refractories is suppressed. In addition, although Mg has extremely high dispersibility in the molten metal, this has already been mentioned.

  Since the metallic Mg is vaporized at 1,090 ° C., the calcium / aluminate / soda mixed solid is pulverized, and then the magnesium is mixed in a metal powder state. The powdery flux thus obtained is very suitable when supplied to the molten metal through a sub lance or from the furnace bottom by an injection operation accompanied with an inert gas.

  Powdered carbon can also be added to the pulverized product of the mixed solid of calcium, aluminate, and soda. This also improves the desulfurization function, but the reaction has already been described. In addition, since carbon disappears when it is baked and does not melt even if it is melted, the calcium / aluminate / soda mixed solid is pulverized and mixed as a powder. The powdery flux obtained in this way is also very suitable when supplied to the molten metal through a sub lance or from the furnace bottom by an injection operation accompanied with an inert gas.

  Next, a method for producing a mixed solid of calcium, aluminate, and soda having the above structure as a solid solution will be described. The raw materials used are limestone and bauxite (boulder shale) or aluminum refined ash and sodium carbonate, which is the same as in the case of calcined products. These are put into a melting furnace such as a flat furnace and melted, and the solid solution obtained by cooling the resulting hybrid melt (calcium, aluminate, soda) is crushed and pulverized to obtain a refining flux. Depending on the degree of pulverization, it can be used as a flux to be poured into the molten metal or as an injection flux.

When obtaining a solid solution, the limestone becomes CaCO ₃ → CaO + CO ₂ at 898 ° C., but the melting point is 2,572 ° C., but the porous and brittle (unburned) quick lime is in a quasi-softened state, Al ₂ O _{3 having} a melting point of 2,050 ° C. is also easily fused when quicklime is formed. On the other hand, the melting point of sodium carbonate is 851 ° C., but CO ₂ is lost from around 400 ° C. to become Na ₂ O, and the melting point is 1,132 ° C. The melted Na ₂ O aggregates CaO and Al ₂ O ₃ , and when the melting or semi-melting progresses over time, it becomes a hybrid state at about 1400 ° C. If this is cooled and crushed, it is a pre-melt product once melted. Therefore, when it is introduced into the molten metal as a refining agent, its melting is easily and rapidly performed.

First, Na ₂ O that forms the surface layer of the refining agent advances the desulfurization action, and CaO from which Na ₂ O has disappeared from the surface takes advantage of its properties to allow the sulfur content to enter and capture the fine pores generated by the porous formation. . CaO and Al ₂ O ₃ also exhibit a behavior similar to calcium aluminate, and promote the desulfurization effect.

Claims (5)

In order to remove the sulfur contained in the molten iron, in the quick lime for refining injected into the molten metal together with the metal Mg powder,
Powdered lime for refining, characterized in that it is fired so that the loss on ignition is as low as possible in the production process to form powdered CaO of 0.05 mm or less.   2. The refining according to claim 1, wherein the CaO is calcined to have a purity of 97% or more, and the ignition loss is less than the ignition loss contained in CaO having a purity of 93% or less. Powdered lime for use.   The powdery lime for refining according to claim 1 or 2, wherein calcium aluminate powder is added to the CaO and Mg metal powder. The CaO / Mg powder contains 80 to 120 parts by weight of Al ₂ O _{3 and} 24 to 76 parts by weight of Na ₂ O with respect to 100 parts by weight of CaO. Powdery lime for refining according to claim 1 or 2, wherein a powder is added.   The powdery lime for refining according to any one of claims 1 to 5, wherein carbon powder is also added to the powdery lime for refining.