JP2008231494A - Desulfurizing agent and method for desulfurizing molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a desufurizing agent which can be produced comparatively simply and, can desulfurize molten iron at high efficiency, even without containing fluorine. <P>SOLUTION: The desulfurizing agent for solving the above problem contains powdery lime having CaO as the main component and a solid-powdery material which mainly contains Al<SB>2</SB>O<SB>3</SB>and SiO<SB>2</SB>and solidifies after previously melting. In this case, the desulfurized efficiency is further improved by making the blending mass ratio of the solid powdery material and the lime (the blending amount of the solid powdery material (mass%)/ the blending amount of the lime) to be 0.05-1.0, and the average grain diameter of the solid powdery material to be ≤15 μm and the basicity (mass% CaO/mass% SiO<SB>2</SB>) of the desulfurizing agent to be ≥3.5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a CaO-based desulfurization agent used for desulfurization treatment of molten iron and a desulfurization treatment method of molten iron using the same.

  In recent years, the demand for higher purity of steel has become stronger than ever, and in accordance with this, technological development for removing impurities in steel has been actively conducted. In today's steel refining process, prior to decarburization refining in a steelmaking furnace such as a converter, a method of removing phosphorus and sulfur contained in the hot metal, that is, pretreatment of the hot metal is generally performed. Yes. In addition, when only the dephosphorization treatment and desulfurization treatment in the hot metal stage cannot be stably reduced to the desired component concentration, dephosphorization treatment and desulfurization treatment are also performed on molten steel discharged from a steelmaking furnace including a converter. Has been done. The dephosphorization treatment and the desulfurization treatment in the molten steel discharged from the steelmaking furnace are referred to as molten steel dephosphorization and molten steel desulfurization, respectively, for the hot metal pretreatment. In the present invention, hot metal and molten steel are collectively referred to as molten iron.

Among these, as a desulfurization agent in hot metal and molten steel, that is, desulfurization treatment of molten iron, a desulfurization agent mainly composed of lime (hereinafter referred to as “CaO”) powder, calcium carbide (CaC ₂ ), calcium aluminum Nate (mCaO.nAl ₂ O ₃ ) and the like are mentioned, but desulfurization agents mainly composed of CaO powder are widely used from the viewpoint of processing cost. The desulfurization reaction in molten iron by the CaO powder is generally represented by the following formula (1).

  In the formula (1), [S] represents sulfur in the molten iron, (CaS) represents CaS in the slag, and [O] represents oxygen in the molten iron. Examples of the method for proceeding the reaction of the formula (1) include a decrease in oxygen potential in molten iron and an increase in basicity of slag.

  Further, the desulfurization rate of molten iron is generally expressed by the following formulas (2) and (3) with the mass transfer of metal and slag as the rate-determining step.

Here, A is the reaction interface area of the metal / slag, V is metal by volume, [% S] sulfur concentration of the metal, (% S) is the sulfur concentration of the slag, k _S is overall reaction rate constant, k _m Metal The mass transfer coefficient on the side, k _slag is the mass transfer coefficient on the slag side, and L _S is the distribution ratio of sulfur between the metal / slag. In order to increase the desulfurization rate, as is clear from the equations (2) and (3), the reaction interfacial area (A) is increased or the mass transfer on the slag side is promoted by promoting the slag hatching (k _slag Increase). Among these, as a means for achieving the latter, a method of controlling the composition of the desulfurizing agent to lower the melting point of the desulfurizing agent is performed.

For example, in Patent Document 1, a mixture of blast furnace slag and CaF ₂ or synthetic slag having a low melting point (Al ₂ O ₃ —CaO—SiO ₂ —CaF ₂ slag) is used as a desulfurizing agent, and hot metal is added to the desulfurization tank. A method of desulfurizing hot metal while continuously supplying is disclosed. Further, Patent Document 2, as a suitable refining flux as desulfurizing agent molten iron and molten steel, a CaO 27 to 37 wt%, the Al ₂ O ₃ 14 to 24 wt%, a SiO ₂ 29-39 mass%, a refining flux containing CaF ₂ 10 to 20 _{wt%, 12CaO · 7Al 2 O 3} , CaO · Al 2 O 3, CaO · 2Al 2 O 3 and the refining flux containing CaO · SiO ₂ is disclosed Has been.

On the other hand, in recent years, the influence of fluorine on the environment has been regarded as a problem, and development of a desulfurization agent containing no fluorine is desired. Conventionally, as a method for accelerating the hatching of a desulfurizing agent without using fluorine and increasing the desulfurization rate, many desulfurizing agents using Al ₂ O ₃ or SiO ₂ as a hatching accelerator for CaO have been proposed. .

For example, in Patent Document 3, a CaO, SiO ₂ and Al source is the main component, the CaO / SiO ₂ ratio is 1.5 to 3.5, and the Al source is a total content of CaO and SiO ₂ of 0. A hot metal desulfurization agent having a ratio of 03 to 0.15 is disclosed. Patent Document 4 includes components of CaO: 30 to 60% by mass, MgO: 3 to 10% by mass, Al ₂ O ₃ : 25 to 50% by mass, SiO ₂ : 5 to 15% by mass, and has a melting point. A calcium aluminate-based desulfurizing agent having a fluidity of 1300 to 1600 ° C. is disclosed.

Further, in Patent Document 5 and Patent Document 6, iron oxide (FeO) and an Al source are contained in a desulfurizing agent mainly composed of CaO, and silicon in hot metal is oxidized with FeO to generate SiO _2. In addition, a method is disclosed in which Al ₂ O ₃ is produced by reacting Al with FeO, and the hot metal is desulfurized with the produced CaO—SiO ₂ —Al ₂ O ₃ semi-molten slag.
JP 52-42411 A JP 2006-257518 A JP 2000-313911 A JP 2002-60832 A JP 2003-253315 A JP 2006-161086 A

  However, the above prior art has the following problems.

That is, the desulfurization agents of Patent Document 1 and Patent Document 2 are desulfurization agents containing CaF ₂ , and when fluorine is present in the slag, the fluorine is eluted into the water during the slag granulation treatment. In addition, since slag is usually used for roadbed materials and cement materials, the fluorine in the slag is eluted into the water due to rain, etc., and the eluted water erodes into the soil, resulting in the environment as described above. Problems can arise.

Since the desulfurization agent according to Patent Document 3 has a low CaO / SiO ₂ ratio, the desulfurization reaction may not actually accelerate. In addition, the calcium aluminate-based desulfurizing agent according to Patent Document 4 is manufactured by mixing various minerals that are raw materials of the desulfurizing agent so as to have a predetermined composition, and melting this in a melting furnace such as an electric furnace. There arises a problem that the manufacturing cost increases. In addition, since the desulfurization agents disclosed in Patent Document 5 and Patent Document 6 contain FeO in the desulfurization agent, when the desulfurization agent is added to the molten iron, the oxygen potential of the molten iron increases, There is a risk of inhibiting progress.

  The present invention has been made in view of such circumstances, and the object of the present invention is that it can be manufactured relatively easily, and enables high-efficiency desulfurization of molten iron even without containing fluorine. It is to provide a desulfurizing agent and a method for desulfurizing molten iron using the desulfurizing agent.

The desulfurizing agent according to the first invention for solving the above problems is a solid powder mainly containing CaO as a main component, Al ₂ O ₃ and SiO ₂ and solidified after being previously melted. And a gaseous substance.

  In the first invention, the desulfurizing agent according to the second invention is the blending mass ratio of the solid powdery substance and the lime (the blending amount of the solid powder substance (mass%) / the blending amount of lime (mass%). ) Is 0.05 or more and 1.0 or less.

  A desulfurizing agent according to a third invention is characterized in that, in the first or second invention, the solid powdery substance has an average particle size of 15 μm or less.

The desulfurization agent according to a fourth invention is the desulfurization agent according to any one of the first to third inventions, wherein the desulfurization agent has a basicity ((mass% CaO) / (mass% SiO ₂ )) of 3.5 or more. It is characterized by.

  A desulfurization agent according to a fifth invention is the desulfurization agent according to any one of the first to fourth inventions, wherein the solid powdery material is slag produced as a by-product when producing hot metal in a blast furnace. Is.

  A desulfurizing agent according to a sixth aspect of the present invention is characterized in that, in any of the first to fifth aspects, the desulfurizing agent does not contain fluorine.

  A desulfurizing agent according to a seventh invention is characterized in that, in any one of the first to sixth inventions, the desulfurizing agent further contains a metal substance for deoxidation.

  According to an eighth aspect of the present invention, there is provided a desulfurization treatment method for molten iron, wherein the desulfurization agent according to any one of the first to seventh inventions is added to the molten iron held in the processing vessel to desulfurize the molten iron. It is characterized by processing.

  The desulfurization treatment method for molten iron according to a ninth aspect is characterized in that, in the eighth aspect, the desulfurizing agent is added over the molten iron from above the bath surface of the molten iron.

  According to a tenth aspect of the present invention, there is provided a molten iron desulfurization treatment method according to the eighth aspect of the present invention, wherein the desulfurizing agent is bathed in molten iron together with a carrier gas through an upper blowing lance disposed above the molten iron bath surface. It is characterized by adding top blowing toward the surface.

  According to an eleventh aspect of the present invention, there is provided a desulfurization treatment method for molten iron according to the eighth aspect, wherein the desulfurizing agent is blown into molten iron together with a carrier gas through an injection lance immersed in the molten iron bath. It is characterized by doing.

  The method for desulfurizing molten iron according to a twelfth aspect of the invention is characterized in that in any of the eighth to eleventh inventions, the molten iron held in the processing vessel is desulfurized while being stirred by a stirring blade. To do.

  According to a thirteenth aspect of the present invention, there is provided a molten iron desulfurization method according to any one of the eighth to twelfth aspects, wherein the molten iron is hot metal.

  According to a fourteenth aspect of the present invention, there is provided a desulfurization method for molten iron according to any one of the eighth to twelfth aspects, wherein the molten iron is molten steel.

According to the present invention, a powdery lime containing CaO as a main component and a solid powdery substance mainly containing Al ₂ O ₃ and SiO ₂ added after being melted once is used as a desulfurizing agent. Therefore, this solid powdery substance lowers the melting point of CaO and promotes the hatching of CaO, and high-speed and high-efficiency desulfurization of molten iron is possible without adding fluorine. Thereby, reduction of desulfurization processing time and reduction of desulfurizing agent basic unit can be expected. Furthermore, since the slag produced | generated by a desulfurization process does not contain a fluorine, the produced | generated slag can be recycled without considering the influence on the environment of a fluorine.

  Hereinafter, the present invention will be specifically described. First, the background to the present invention will be described.

As described above, as one of means for increasing the desulfurization rate, there is a method of promoting hatching of the desulfurizing agent and promoting mass transfer on the slag side. Here, the distribution of the sulfur concentration in the slag after completion of the actual hot metal desulfurization treatment is shown in FIG. As shown in FIG. 1, it can be seen that slag forms CaO aggregates, and sulfur is distributed in a large amount around the aggregated CaO. From this, the composition of the desulfurization agent (hereinafter also referred to as “flux”) is controlled so that liquid phase slag is generated on the slag surface during the desulfurization treatment, and liquid phase slag generation on the slag surface is facilitated. It is necessary to find out the conditions. Fluorite (CaF ₂ ) satisfies these conditions and is an inexpensive substance, but its use is limited from the viewpoint of environmental problems as described above. Therefore, formation of a liquid phase slag is desired within the range of the hot metal treatment temperature without using CaF ₂ .

The inventors conducted a survey in consideration of the above points. As a result, it was found that the ternary slag of CaO—Al ₂ O ₃ —SiO ₂ has a relatively low melting point composition. Therefore, various experiments were conducted using a small melting furnace on the desulfurization characteristics of the CaO-based flux containing Al ₂ O ₃ and SiO ₂ .

  FIG. 2 shows a schematic diagram of a desulfurization experimental apparatus. In the desulfurization experimental apparatus 1, the stirring blade 5 was immersed in the hot metal 6 held in the crucible container 4 while energizing the high-frequency heating coil 2, and the electric motor 3 was used for rotational stirring, and the desulfurization flux was added thereto. Table 1 shows a list of fluxes used in the experiment.

As the flux for desulfurization, lime powder alone (level 1), a mixture of the reagents Al ₂ O ₃ and SiO ₂ at a mass ratio of 1: 1, mixed with 20% by mass of lime (level) 2) A mixture of Al ₂ O ₃ and SiO ₂ in a mass ratio of 1: 1 is melted once, then solidified and then pulverized and powdered (hereinafter, subjected to the above treatment) Three types were used (level 3) in which 20% by mass of lime was called “pre-melt”.

  The amount of desulfurization flux added was 5 kg / t. The desulfurization flux was added all at once before the treatment. Sampling of hot metal 6 was performed every predetermined time, and the desulfurization behavior was investigated. Judging from the experimental results, the desulfurization rate was assumed to be the rate equation shown in the following equation (4), and the desulfurization rate constant Ks (1 / min) was determined based on the experimental results.

FIG. 3 shows the desulfurization rate constant Ks at each obtained test level. The desulfurization reaction was most accelerated by the flux (level 3) in which the materials pre-melted with Al ₂ O ₃ and SiO ₂ were mixed.

  Therefore, the present inventors have focused on slag, that is, blast furnace slag produced as a by-product when producing hot metal in a blast furnace as a result of searching for a material that is premelt and relatively easily available. An example of the composition of blast furnace slag is shown in Table 2.

Some blast furnace slag is cooled and finely ground for cement raw materials. This blast furnace slag powder was mixed with lime at a blending ratio of 20% by mass, and a desulfurization experiment was performed using the desulfurization experiment apparatus shown in FIG. As a result, as shown in FIG. 4, in the flux in which blast furnace slag was mixed with lime at a blending ratio of 20% by mass, the premelt-treated Al ₂ O ₃ and SiO ₂ were mixed with lime at a blending ratio of 20% by weight. A desulfurization rate equivalent to the flux was obtained. Therefore, the present inventors conducted further experiments and investigations on the flux mixed with this blast furnace slag.

  FIG. 5 shows the result of examining the desulfurization rate by changing the mixing ratio of blast furnace slag to lime. As shown in FIG. 5, the desulfurization rate constant is within the range of the blending mass ratio of blast furnace slag and lime (the blending amount of blast furnace slag (mass%) / the blending quantity of lime (mass%)) of 0.05 to 1.0. It was found that Ks increased. Moreover, the desulfurization rate was investigated using the flux which changed the particle diameter of the blast furnace slag powder particle | grains on the conditions which made the mixing | blending mass ratio of blast furnace slag and lime constant. The result is shown in FIG. As shown in FIG. 6, it was found that the desulfurization rate constant Ks increases when the particle size of the blast furnace slag powder particles is 15 μm or less.

Also, using blast furnace slag with different SiO ₂ content, changing the blending mass ratio of blast furnace slag and lime, and changing the basicity of flux ((mass% CaO) / (mass% SiO ₂ )) to desulfurize The speed was investigated. The result is shown in FIG. It was found that the desulfurization rate constant Ks was greatly improved in the region where the basicity of flux ((mass% CaO) / (mass% SiO ₂ )) was 3.5 or more.

The present invention has been made on the basis of the above findings, and the desulfurization agent that enables high-efficiency desulfurization of molten iron according to the present invention includes powdered lime mainly composed of CaO, and Al ₂ O. _And a solid powdery substance mainly containing ₃ and SiO ₂ and solidified after being previously melted. This is because the premelt reduces the melting temperature of the solid powdery substance compared with the case where pure substances are mixed, and accordingly, the melting of lime mainly composed of CaO is promoted, and as a result, the surface of the desulfurized slag This is because the liquid phase slag is easily formed and the desulfurization rate is improved. In the present invention, the solid powdery material mainly containing Al ₂ O ₃ and SiO _2, is that the powdery materials containing Al ₂ O ₃ and SiO ₂ more than 10 wt%, respectively. When the content of Al ₂ O ₃ and SiO ₂ is less than 10% by mass, it is difficult to obtain the above effect.

  In the desulfurizing agent according to the present invention, even if there is no fluorine source, the liquid phase generation on the surface of the desulfurized slag is promoted and the diffusion of sulfur in the desulfurized slag is remarkably increased, so that the desulfurization reaction proceeds sufficiently. Therefore, it is not necessary to add a fluorine source (halide) such as fluorite, and it is preferable not to add it from an environmental measure.

The blending mass ratio of the premelt solid powder substance containing Al ₂ O ₃ and SiO ₂ and lime (solid powder substance blending amount (mass%) / lime blending quantity (mass%)) is: It is preferable that it exists in the range of 0.05-1.0 like the result shown in FIG. 5 mentioned above. The basicity ((mass% CaO) / (mass% SiO ₂ )) of the desulfurizing agent obtained by mixing the solid powder substance and lime is preferably 3.5 or more.

This is preferable because when the basicity of the desulfurizing agent is less than 3.5, the content of SiO ₂ increases, the viscosity of the slag increases, and the desulfurization slag becomes active and the reaction interface area decreases. Absent. Further, when the basicity is low, less than 3.0, the sulfide capacity of the desulfurized slag is lowered, and the desulfurization ability of the desulfurization flux itself is lowered rather than the desulfurization promoting effect by the liquid phase generation. The basicity of 3.5 corresponds to the case where the blending mass ratio of the premelt solid powdery substance containing Al ₂ O ₃ and SiO ₂ to lime is 1.0.

On the other hand, if the blending mass ratio of the pre-melt solid powder substance and lime containing Al ₂ O ₃ and SiO ₂ is less than 0.05, the liquid phase of the desulfurized slag is too small and acts only on the slag aggregation. Therefore, it is not effective because the desulfurization speed is equivalent to that of lime alone.

In the desulfurization agent of the present invention, the particle diameter of the premelt solid powdery material containing Al ₂ O ₃ and SiO ₂ is preferably 15 μm. This is because when the particle diameter is 15 μm or less, the melting of the pre-melt solid powder containing Al ₂ O ₃ and SiO ₂ is promoted when added to the molten iron, and the liquid is applied to the surface of the CaO agglomerated slag. This is because the phase slag can be formed in a short time. At this time, CaO dissolves in the molten slag phase on the surface of the agglomerated desulfurized slag, and a molten slag phase having a saturated CaO concentration is formed on the desulfurized slag surface. Since this molten slag is saturated with CaO, the desulfurization ability can be maintained even if the basicity slightly decreases. On the contrary, if the particle diameter exceeds 15 μm, the melting rate when added to molten iron decreases, so the formation of liquid phase slag is delayed, and the effect of improving the desulfurization rate inherent to the pre-melt solid powdery material is reduced. Therefore, it is not preferable.

The desulfurizing agent according to the present invention can be manufactured at a relatively low cost because it can be manufactured by a relatively simple method of adding and mixing a premelt solid powder material containing Al ₂ O ₃ and SiO ₂ to lime. It is possible. In the present invention, the pre-melt solid powdery substance containing Al ₂ O ₃ and SiO ₂ to be mixed with lime in the present invention is preferably steel slag typified by blast furnace slag. The generated by-product, dust, or waste can be used in a solid state, or after being crushed or classified. Of course, a mixture of silica and bauxite may be produced by melting in an electric furnace or the like. However, in any case, the average particle size is preferably 15 μm or less as described above.

  Moreover, you may add the metal substance for deoxidation to the desulfurization agent which concerns on this invention. This is because when a metal material for deoxidation is added, the oxygen potential of the molten iron is reduced, so that the desulfurization reaction is accelerated. As a metal material for deoxidation, a metal or an alloy containing an element such as Al, Si, or Mg may be used.

  The desulfurizing agent according to the present invention can be applied to a process for removing sulfur contained in molten iron by adding the desulfurizing agent to molten iron held in a processing vessel. At this time, as a method for adding the desulfurizing agent, the desulfurization treatment can be sufficiently performed by adding the desulfurizing agent over the rotating molten iron bath surface. Moreover, the method of adding the top blowing to the molten iron bath surface together with the carrier gas via the top blowing lance can be sufficiently applied. Further, a method may be employed in which an injection lance dipped in molten iron is blown into the molten iron together with the carrier gas. In addition, non-oxidizing gas such as inert gas such as nitrogen and argon and reducing gas such as propane is used as the carrier gas used for the top blowing addition using the top blowing lance and the blowing addition via the injection lance. It is preferable to use it.

  The molten iron to be subjected to the desulfurization treatment using the desulfurizing agent according to the present invention can be applied to both hot metal and molten steel. In particular, as a hot metal desulfurization apparatus, a mechanical stirring type desulfurization tank value in which a stirring blade, also referred to as an impeller, is immersed in the hot metal and rotated to stir the hot metal is preferable because the stirring power is large and the reaction rate is high.

In producing the desulfurizing agent according to the present invention, a sufficient desulfurization effect can be obtained by simply mixing a lime with a premelt solid powder containing Al ₂ O ₃ and SiO ₂ . However, it is preferable to produce the mixture by thoroughly mixing them in a mixer having a closed stirring device. This is because, by mixing with a stirrer, a pre-melt solid powder substance containing Al ₂ O ₃ and SiO ₂ can be physically attached to the surface of the lime particles, so that at the same time as flux addition to the molten iron, Al _The premelt solid powdery substance particles containing ₂ O ₃ and SiO ₂ are melted, and a molten slag phase can be formed on the surface of the solid CaO particles in a fine state. As a result, in addition to the effect of liquid phase generation, the effect of increasing the reaction interface area is further added, and the desulfurization reaction is further improved.

As described above, according to the present invention, the solid pulverized material mainly containing Al ₂ O ₃ and SiO ₂ that has been solidified after being once melted is added to the powdered lime mainly composed of CaO. Since this is a desulfurizing agent, this solid powder material lowers the melting point of CaO and promotes the hatching of CaO, enabling high-speed and high-efficiency desulfurization of molten iron without adding fluorine. Become. Thereby, reduction of desulfurization processing time and reduction of desulfurizing agent basic unit can be expected.

  An example of the hot metal desulfurization treatment using the desulfurizing agent according to the present invention (example of the present invention) will be described. FIG. 8 shows a schematic view of a mechanical stirring desulfurization apparatus embodying the present invention. As shown in FIG. 8, in the mechanical stirring type desulfurization apparatus 7, the stirring blade 10 is immersed in about 300 tons of hot metal 6 held in the hot metal pan 8 for conveying hot metal, and the desulfurizing agent 13 is passed through the dust collecting hood 11. The molten iron was added onto the hot metal bath surface through the charging chute 12 provided in this manner, and the stirring blade 10 was rotated by the electric motor 9 for a predetermined time, so that the hot metal 6 and the desulfurizing agent 13 were rotated and stirred. Moreover, the desulfurization process added by spraying using the top blowing lance (not shown), without using the input chute | shoot 12 was also implemented.

As a raw material for the desulfurizing agent, an Al ₂ O ₃ —SiO ₂ based premelt solid material prepared by melting a mixture of Al ₂ O ₃ and SiO ₂ at a mass ratio of 1: 1 in a heating furnace ( Hereinafter, it was described as “premelt flux”), blast furnace slag, and lime, and these raw materials were pulverized and mixed with a mixer. The amount of desulfurizing agent added was 5.0 kg / t. For comparison, a desulfurization treatment (comparative example) using a desulfurizing agent different from the desulfurizing agent according to the present invention was also performed. Table 3 shows common desulfurization treatment conditions in the present invention example and the comparative example.

  Table 4 shows a list of implementation conditions of the inventive examples and the comparative examples.

  In Example 1 of the present invention, 60% by mass of premelt flux having an average particle diameter of 20 μm was mixed with CaO alone as a desulfurization agent. The desulfurization agent was added from the top of the hot metal bath surface. In Example 2 of the present invention, a desulfurizing agent obtained by mixing 30% by mass of premelt flux having an average particle diameter of 20 μm with CaO alone was used. The desulfurization agent was added in a batch manner from above the hot metal bath surface in the same manner as in Invention Example 1. In Example 3 of the present invention, 20 mass% of a premelt flux having an average particle diameter of 10 μm was mixed with CaO alone as a desulfurization agent. The desulfurization agent was added in a batch manner from above the hot metal bath surface in the same manner as in Invention Example 1.

In Example 4 of the present invention, a blast furnace slag having an average particle size of 10 μm mixed with 20% by mass as a premelt solid powder substance containing Al ₂ O ₃ and SiO ₂ was used as a desulfurizing agent. The desulfurization agent was added in a batch manner from above the hot metal bath surface in the same manner as in Invention Example 1. In Example 5 of the present invention, 20 mass% of blast furnace slag having an average particle diameter of 10 μm was mixed with CaO alone as a desulfurizing agent, and 3 mass% of Al powder was added for deoxidation. The desulfurization agent was added in a batch manner from above the hot metal bath surface in the same manner as in Invention Example 1. In Example 6 of the present invention, a desulfurization agent obtained by mixing 30% by mass of blast furnace slag having an average particle diameter of 10 μm with CaO alone was used. The desulfurization agent is added through a top blowing lance (not shown) placed on the surface of the hot metal bath, with nitrogen gas as the carrier gas and top blowing at a rate of 1.0 kg / min · t. It was.

  In contrast, in Comparative Example 1, CaO alone was used as the desulfurizing agent. The desulfurization agent was added from the top of the hot metal bath surface. In Comparative Example 2, as a desulfurization agent, CaO alone mixed with 20% by mass of silica stone having an average particle diameter of 20 μm was used. The desulfurization agent was added from the top of the hot metal bath surface.

  In both the inventive examples and the comparative examples, sampling was performed from the hot metal before and after the treatment, and the desulfurization rate was investigated. Here, the desulfurization rate was a value defined by the following equation (5).

  Table 5 shows the results of the examples of the present invention and the comparative examples.

  Inventive Examples 1 to 3 were improved in the desulfurization rate than Comparative Example 1. Moreover, the addition yield of the desulfurizing agent was improved. Moreover, compared with the comparative example 2 which added the silica, Examples 1-3 of this invention confirmed the improvement of the desulfurization rate, and the improvement of the addition yield of a desulfurization agent. Here, this invention example 1 whose compounding mass ratio of premelt flux and lime is 1.0 or more, and this invention whose compounding mass ratio of premelt flux and lime is 1.0 or less and 0.05 or more. In comparison with Example 2, the desulfurization rate was improved in Invention Example 2 in which the blending ratio was optimized.

  Further, when the present invention example 2 in which the average particle size of the premelt flux is 20 μm and the present invention example 3 in which the average particle diameter of the premelt flux is 15 μm or less are compared, the present invention example 3 is more desulfurized. It was confirmed that the rate improved.

  Similarly, the present invention example 4 in which blast furnace slag having an average particle size of 15 μm or less was mixed obtained a desulfurization rate equal to or higher than that of the present invention examples 1 to 3, and the desulfurization rate was significantly higher than those of the comparative examples 1 and 2. Improved. In addition, the inventive example 5 to which Al for deoxidation was added had a further improved desulfurization rate than the inventive example 4 because the oxygen potential of the hot metal was lowered. Further, in the present invention example 6 in which the desulfurizing agent was added by top blowing, the desulfurizing agent particles entered directly into the hot metal, so that the yield of addition of the desulfurizing agent was further improved. Compared with Comparative Examples 1 and 2, it was greatly improved.

  An example (invention example) in which a desulfurization treatment of molten steel was performed using the desulfurization agent according to the present invention will be described. FIG. 9 shows a schematic diagram of an RH vacuum degassing apparatus embodying the present invention. As shown in FIG. 9, in the RH vacuum degassing device 14, when the molten steel 19 of about 300 tons held in the ladle 18 for conveying molten steel is subjected to vacuum degassing treatment, A desulfurizing agent was sprayed on the bath surface of the molten steel 19 in the vacuum chamber through the lance 17 to perform desulfurization treatment. Reference numeral 16 in FIG. 9 denotes a dip tube. For comparison, a desulfurization treatment (comparative example) using a desulfurizing agent different from the desulfurizing agent according to the present invention was also performed. Table 6 shows common desulfurization treatment conditions in the present invention and the comparative examples.

  Table 7 shows the working conditions and results of the inventive examples and comparative examples.

  In Example 7 of the present invention, a mixture of CaO alone and 30% by mass of blast furnace slag having an average particle size of 20 μm was used as a desulfurization agent. In Example 8 of the present invention, as the desulfurizing agent, CaO alone mixed with 30% by mass of blast furnace slag having an average particle diameter of 10 μm was used. On the other hand, in Comparative Example 3, CaO alone was used as a desulfurizing agent, and in Comparative Example 4, 20% by mass of silica stone having an average particle diameter of 20 μm was mixed with CaO alone as a desulfurizing agent.

  In both the inventive examples and the comparative examples, sampling was performed from the molten steel before and after the treatment, and the desulfurization rate was investigated. Here, the desulfurization rate was a value defined by the above equation (5). However, in this case, the “sulfur concentration in molten steel” is used instead of the “sulfur concentration in molten steel” in the equation (5).

An implementation result is combined with said Table 7, and is shown. The results were almost the same as in the hot metal desulfurization process. In other words, Examples 7 and 8 of the present invention in which pre-melt solid powders containing Al ₂ O ₃ and SiO ₂ were mixed had a higher desulfurization rate than Comparative Example 3. Moreover, compared with the comparative example 4 which mixed the silica stone, the invention examples 7 and 8 were confirmed to improve the desulfurization rate. Further, when the present invention example 7 in which the average particle size of the premelt solid powder material containing Al ₂ O ₃ and SiO ₂ exceeds 15 μm and the present invention example 8 in which the average particle size is 15 μm or less are compared, Invention Example 8 improved the desulfurization rate.

It is the schematic which shows distribution of the sulfur concentration in the slag after the hot metal desulfurization process completion. It is the schematic of a desulfurization experimental apparatus. It is a figure which compares and shows the desulfurization rate constant Ks in each test level. It is a figure which compares and shows transition of sulfur concentration when using various desulfurization agents. It is a figure which shows the value of the desulfurization rate constant when changing the mixing ratio of blast furnace slag. It is a figure which shows the value of the desulfurization rate constant when changing the particle diameter of a blast furnace slag particle. It is a figure which shows the value of a desulfurization rate constant when changing the basicity of the flux for desulfurization. It is the schematic of the mechanical stirring type desulfurization apparatus which implemented this invention. It is the schematic of the RH vacuum degassing apparatus which implemented this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Desulfurization experiment apparatus 2 High frequency heating coil 3 Electric motor 4 Crucible container 5 Stir blade 6 Hot metal 7 Mechanical stirring desulfurization apparatus 8 Hot metal ladle 9 Electric motor 10 Stir blade 11 Dust collection hood 12 Input chute 13 Desulfurization agent 14 RH vacuum degassing apparatus 15 Vacuum Bath 16 Dip tube 17 Top blowing lance 18 Ladle 19 Molten steel

Claims (14)

A desulfurizing agent comprising: powdered lime mainly composed of CaO; and a solid powdery substance mainly containing Al ₂ O ₃ and SiO ₂ and solidified after being previously melted.   The blending mass ratio of the solid powdery substance and the lime (solid powder substance blending amount (mass%) / lime blending quantity (mass%)) is 0.05 to 1.0. The desulfurizing agent according to claim 1.   The desulfurization agent according to claim 1 or 2, wherein an average particle diameter of the solid powdery substance is 15 µm or less. Basicity of the desulfurizing agent ((wt% CaO) / (wt% SiO _2)), characterized in that is 3.5 or more, the desulfurizing agent according to any one of claims 1 to 3 .   The desulfurization agent according to any one of claims 1 to 4, wherein the solid powdery substance is slag generated as a by-product when hot metal is produced in a blast furnace.   The desulfurization agent according to any one of claims 1 to 5, wherein the desulfurization agent does not contain fluorine.   The desulfurization agent according to any one of claims 1 to 6, further comprising a metal substance for deoxidation.   A method for desulfurizing molten iron, comprising adding the desulfurization agent according to any one of claims 1 to 7 to molten iron held in a processing vessel, and desulfurizing the molten iron. .   The method for desulfurizing molten iron according to claim 8, wherein the desulfurizing agent is added to the molten iron from above the bath surface of the molten iron.   9. The desulfurization agent is added by being blown up toward a molten iron bath surface together with a transfer gas through an upper blowing lance disposed above the molten iron bath surface. Desulfurization method for molten iron.   9. The method for desulfurizing molten iron according to claim 8, wherein the desulfurizing agent is blown into the molten iron together with a carrier gas through an injection lance immersed in the molten iron bath.   The molten iron desulfurization method according to any one of claims 8 to 11, wherein the molten iron held in the processing vessel is desulfurized while being stirred by a stirring blade.   The method for desulfurizing molten iron according to any one of claims 8 to 12, wherein the molten iron is hot metal.   The method for desulfurizing molten iron according to any one of claims 8 to 12, wherein the molten iron is molten steel.

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