JP7400845B2 - Molten iron refining method - Google Patents

Description

The present invention relates to a method for refining molten iron. More specifically, the present invention relates to a technology for applying heat to molten iron in molten iron refining.

In recent years, there has been an increasing demand for expanded use of cold iron sources (scrap) in the steel industry. In order to build a recycling-oriented society, recycling of iron sources is inevitable, and it is also essential to increase the amount of cold iron sources (scrap) used in response to the recent demand for reducing _CO2 gas. Unlike iron ore, which is iron oxide (Fe ₂ O ₃ ), cold iron sources (scrap) do not require a reduction process in the smelting process, making it possible to reduce CO ₂ gas emissions. Even in the law, the amount of cold iron source (scrap) used continues to increase.

In the blast furnace-converter method, iron ore (Fe ₂ O ₃ ), which is a raw material, is charged into a blast furnace together with coke (C source), which is a reducing agent, and the carbon (C) concentration is 4.5 to 5.0% by mass. This is a steelmaking process in which carbon (C), silicon (Si), and phosphorus (P), which are impurity components, are oxidized and removed by melting a certain amount of hot metal and charging the melted hot metal in a converter. When producing hot metal in a blast furnace, approximately 500 kg of carbon source is required per 1 ton of hot metal for reduction of iron ore. On the other hand, when producing molten steel using a cold iron source such as iron scrap as raw material in a converter, the carbon source required for reducing iron ore becomes unnecessary. At that time, even considering the energy required to melt the cold iron source, replacing 1 ton of hot metal with 1 ton of cold iron source leads to a reduction in CO ₂ gas of approximately 1.5 t. From the above, it is essential to increase the amount of cold iron sources (scrap) used in order to reduce greenhouse gas emissions and maintain production activities. That is, in the converter steel manufacturing method using molten iron, increasing the blending ratio of the cold iron source leads to a reduction in the amount of CO ₂ generated. Here, molten iron refers to hot metal and molten cold iron sources.

On the other hand, in order to increase the amount of cold iron source (scrap) used, it is necessary to supply the amount of heat necessary for melting the cold iron source (scrap). Normally, the heat of dissolution of the cold iron source is compensated for by the reaction heat of carbon and silicon contained as impurity elements in the hot metal, but when the blending ratio of the cold iron source increases, the heat of reaction of carbon and silicon contained in the hot metal Carbon and silicon alone do not provide enough heat. In other words, compared to when a cold iron source (scrap) is not used, when a cold iron source (scrap) is used, heat equivalent to the sensible heat of the cold iron source (scrap) is taken away from the hot metal, so heat compensation for that amount is required. becomes. As a known heat compensation technique, it is known to introduce a heating agent such as carbonaceous material or silicon carbide as a heat source.
However, the amount of carbonaceous material that can be used is limited because the sulfur contained therein picks up and adversely affects the components of molten iron. In addition, when using a heating material containing silicon such as silicon carbide, it is necessary to use a certain amount of lime at the same time to ensure basicity. As a result, the amount of lime used increases and the amount of slag increases, resulting in high costs due to industrial waste disposal costs, etc., which is a major disadvantage. From the above, there is a need for a heat compensation technology that picks up less impurity components such as sulfur and is low cost.

From this point of view, for example, in Patent Document 1, a dephosphorization medium mainly composed of powdered lime is conveyed by oxygen gas, passed through a combustion flame by a burner to be heated, and is heated together with the refining oxygen gas on the molten iron bath surface. Techniques have been proposed for spraying and adding. According to this technology, if the burner flame is simply sprayed onto the surface of the molten iron bath, the heat utilization efficiency remains at a few tens of percent or less, but by transferring the heat of the burner flame to the powder, the preheated powder directly enters the hot water. It has been proposed that heat utilization efficiency can be improved by doing so. According to the present technology, heat can be supplied without contaminating the hot metal, the amount of slag does not increase, and the heating cost is low compared to the case where the heat source is input as an auxiliary material with a higher degree of freedom.

For example, in Patent Document 2, regarding the burner technology, a lance with a burner function different from the refining lance is used, and pulverized coal is freely fallen from the center of the lance as a heat source and heat transfer medium, and is preheated in a flame to generate heat. Techniques for compensation have been proposed.

Japanese Patent Application Publication No. 2005-336586 Japanese Patent Application Publication No. 2007-92158

However, the above conventional technology has the following problems. The hot metal dephosphorization treatment method described in Patent Document 1 employs an integrated lance that combines an oxygen supply lance with a burner function. In this integrated lance, there is a discrepancy between the distance from the molten iron bath surface to the nozzle tip (lance height), which is desirable for molten iron refining, and the lance height, which is suitable for heat compensation. That is, with such an integrated lance, it is difficult to achieve both the distance from the molten iron bath surface to the nozzle tip (lance height) suitable for oxygen blowing and the lance height suitable for heat compensation.

For example, in the final stage of decarburization blowing in a converter, it is necessary to reduce the oxygen flow rate to prevent overoxidation of the iron, while applying stirring power to promote the decarburization reaction. For this reason, the lance height is generally lowered to a range where metal adhesion to the lance due to hot metal scattering does not become a problem. Furthermore, even in the early to middle stages of decarburization blowing, where a soft blow jet with a large flow rate and low dynamic pressure is required, it is known that raising the lance height excessively can worsen operations such as slopping. ing.

The reason for this is that the dynamic pressure of the jet becomes lower than necessary, and the oxygen gas supplied from the top blowing lance is blocked by the slag layer existing on the hot metal, leading to overoxidation of the slag. From the above, the height of the refining oxygen lance in the converter is generally within a range of about 2 to 3 m from the molten iron bath surface in most cases. On the other hand, from the viewpoint of thermal compensation, in order to sufficiently transfer the heat of the burner flame to the powder, which is a heat transfer medium, it is required that the powder stay in the burner flame for as long as possible. However, in the case of an integrated lance, the upper limit of the height of the lance is determined by the refining characteristics, and the degree of freedom is small, resulting in poor heat transfer efficiency.

In addition, when the lance height is increased in a free-fall type lance as shown in Patent Document 2, in the converter, the gas blown from the oxygen supply lance to the bath surface is reflected, the CO gas generated from the hot metal, or the stirring Therefore, various high-temperature gases such as bottom-blown gas that are blown in from the bottom of the converter furnace flow out of the converter through the furnace opening. Therefore, there is a problem that the heat transfer medium is scattered and the yield of penetration into the hot metal is deteriorated.

The present invention has been made in view of the above circumstances, and is capable of thermal compensation of a cold iron source even under conditions of a high cold iron source ratio, and has a lance height and height that are particularly desirable for smelting molten iron. The purpose of the present invention is to provide a molten iron refining method that improves the efficiency of heat transfer to molten iron by simultaneously achieving lance heights suitable for heat compensation and ensuring a sufficient yield of the transmission medium.

The molten iron refining method according to the present invention, which advantageously solves the above problems, involves adding powdered auxiliary raw materials to a converter-type vessel charged with molten iron, and supplying oxidizing gas from a top blowing lance. A preliminary treatment blowing or decarburization blowing method, in which one or more burner lances that can be raised and lowered independently are provided in addition to the top blowing lance, and the burner lance is connected to a powder supply pipe and the burner lance. It has an injection hole for blowing fuel and combustion-supporting gas for combustion from the tip, and is formed so that burner flame can be injected. The method is characterized in that a gas is conveyed into the burner flame, passed through the burner flame to be heated, and charged into the converter type vessel, so that the heat of the burner flame is transferred to the hot metal.

Note that the method for refining molten iron according to the present invention is as follows:
(1) The carrier gas is a combustion supporting gas;
(2) The discharge speed of the carrier gas discharged from the tip of the burner lance is 15 m/s or more and 330 m/s or less, where the carrier gas discharge speed is expressed by the following relational expression: Carrier gas discharge speed (m /s) = (1/60) × carrier gas flow rate (Nm ³ /min) / carrier gas discharge hole cross-sectional area (m ² ),
(3) The distance from the tip of the burner lance to the molten iron bath surface is 3.0 m or more;
(4) Setting the oxygen ratio so that the length of the burner flame injected from the tip of the burner lance is 85 to 105% of the distance from the tip of the burner lance to the molten iron bath surface. , where the oxygen ratio is the combustion-supporting gas solid supply oxygen amount/theoretical oxygen amount required for complete combustion.
It is thought that this could be a more preferable solution.

According to the present invention, by making the top blowing lance, which is the lance for oxygen supply, and the burner lance for heat compensation each independent, a degree of freedom is created in the lance height of each lance. Alternatively, it is possible to simultaneously achieve a lance height that is desirable for refining molten iron by decarburization blowing and a lance height that is suitable for heat compensation. Further, according to the present invention, by using a combustion supporting gas that is cheaper than an inert gas as the heat transfer medium carrier gas of the burner lance, it is possible to reduce the cost of the molten iron refining process. Further, according to the present invention, by ensuring the discharge speed of the carrier gas discharged from the burner lance, a sufficient residence time of the heat transfer medium within the burner flame can be ensured. Further, according to the present invention, by setting the burner lance height to 3.0 m or more, it is possible to sufficiently secure the residence time of the heat transfer medium in the burner flame and improve the heat transfer efficiency to the molten iron.

BRIEF DESCRIPTION OF THE DRAWINGS It is a longitudinal cross-sectional schematic diagram which shows the outline of the converter used in embodiment of this invention. FIG. 2 is a schematic diagram of a burner according to an embodiment of the present invention, in which (a) shows a longitudinal cross-sectional view of the lance tip, and (b) shows a bottom view seen from below the nozzle hole.

Embodiments of the present invention will be specifically described below. Note that each drawing is schematic and may differ from the actual drawing. Furthermore, the following embodiments are intended to exemplify devices and methods for embodying the technical idea of the present invention, and the configuration is not limited to the following. That is, the technical idea of the present invention can be modified in various ways within the technical scope described in the claims.

[First embodiment]
FIG. 1 is a schematic vertical cross-sectional view of a converter-type vessel 1 having a top-bottom blowing function used in a molten iron refining method according to an embodiment of the present invention. FIG. 2 is a schematic diagram of the tip of the burner lance showing the structure of the burner lance having a powder supply function, in which FIG. 2(a) shows a longitudinal cross-sectional view, and FIG. FIG.

For example, first, iron scrap as a cold iron source for pre-furnace preparation is charged into the converter type vessel 1 through a scrap chute (not shown). Thereafter, hot metal is charged into the converter type vessel 1 using a charging pot (not shown). The amount of cold iron source charged from the scrap chute shall be 0.15 times or less the sum of the amount of hot metal charged, or it shall not be pre-charged. The source of cold iron to be charged above the furnace is prepared in the above-furnace hopper. As a source of cold iron to be fed into the furnace, small-diameter iron scrap (loose scraps), cut iron scraps (chopper scraps, shredder scraps), small lumps of reduced iron, etc. can be used. Further, it is desirable that large-sized iron scraps, lumps of reduced iron, etc. be cut or crushed so that they can be handled in conveyance equipment such as furnace hoppers and conveyors.

After charging the hot metal, oxygen gas (oxidizing gas) is blown upward toward the molten iron 3 from a top blowing lance 2 configured to blow oxidizing gas upward. An inert gas such as N ₂ is supplied as a stirring gas from a tuyere 4 installed at the bottom of the furnace, and the molten iron 3 is stirred. Then, auxiliary raw materials such as a heating agent and a slag forming material are added, and the molten iron 3 in the converter type vessel 1 is dephosphorized. At this time, a powdered auxiliary raw material 15 such as powdered lime is supplied using a carrier gas from a powder supply pipe provided in a burner lance 5 installed separately from the top blowing lance 2 that top blows the oxidizing gas. FIG. 2 schematically shows the tip of the burner lance 5. A powder supply pipe 11 is arranged at the center, and a fuel supply pipe 12 having an injection hole and a combustion supporting gas supply pipe 13 are arranged in this order around the powder supply pipe 11. Its outside is provided with an outer shell with cooling water passages 14 . Fuel gas 16 and combustion-supporting gas 17 are supplied from injection holes provided on the outer circumference of powder supply pipe 11 to form a burner flame. Then, the powdered auxiliary raw material 15 is heated in the burner flame. By doing so, the powdered auxiliary raw material 15 becomes a heat transfer medium, making it possible to improve the heat transfer efficiency into the hot metal. As a result, it is possible to reduce the amount of heat raising agents such as carbon sources and silicon sources, and it is possible to prevent extension of the dephosphorization treatment time.

In this way, the molten iron refining method of this embodiment employs a lance in which the top blowing lance and the burner lance, which are lances for supplying oxygen, are each independent, so there is flexibility in the lance height of each lance. Therefore, it is possible to simultaneously achieve a lance height that is desirable for molten iron refining and a lance height that is suitable for heat compensation. Therefore, the molten iron refining method of the present embodiment can be suitably applied to pretreatment blowing or decarburization blowing of molten iron.

As described above, according to the molten iron refining method of the present embodiment, the powdered auxiliary raw material is heated by the burner flame, becomes a heat transfer medium, and can transfer heat to the molten iron in the converter. As a result, according to the molten iron refining method of the present embodiment, the heat transfer efficiency to the molten iron is improved, the amount of carbon source and silicon source input as a heating agent is reduced, and the dephosphorization processing time is significantly reduced. It becomes possible to suppress extension and increase in the amount of slag generated.

[Second embodiment]
The molten iron refining method of the second embodiment is characterized in that, in the above embodiment, the carrier gas for conveying the powdered auxiliary raw material to the burner flame is a combustion-supporting gas. In order to minimize heat loss, the inventors adopted a combustion supporting gas as the carrier gas. If an inert gas that does not contribute at all to the reactions that may occur in the converter type vessel 1 is used as the carrier gas, the cost of the inert gas will be extra, and the heat transfer efficiency to the molten iron will be reduced due to the heat removal of the carrier gas. Getting worse.

The molten iron refining method of this embodiment uses the same combustion-supporting gas and carrier gas necessary for fuel combustion, and reduces the amount of gas used in the entire system of the converter type vessel, thereby reducing the amount of heat removed by sensible heat of the gas. It is possible to make it smaller. Additionally, in decarburization furnaces, contamination of molten iron with nitrogen poses a problem. Therefore, when using an inert gas as the carrier gas, it is necessary to use an expensive gas such as argon (Ar), which is disadvantageous in terms of cost.

In addition, in the molten iron refining method of this embodiment, by using the combustion-supporting gas as a carrier gas, it is possible to integrate the system for transporting powdered auxiliary raw materials and the system for supplying the combustion-supporting gas into the same system. becomes. As a result, the structure of the burner lance used in the molten iron refining method becomes simple. Furthermore, the burner lance is lightweight. Furthermore, it leads to a reduction in the cost of manufacturing burner lances and a reduction in the load on equipment required for refining molten iron.

The combustion-supporting gases employed in the molten iron refining method of this embodiment include air, oxygen-enriched air, and oxidizing gases (in addition to pure oxygen, mixed gases of oxygen and CO ₂ or inert gases). can be mentioned. Among these combustion-supporting gases, oxygen is the most desirable in view of the fact that it causes contamination to molten iron, that it complicates exhaust gas management and processing equipment, and that the cost of the carrier gas itself is considered.

As described above, according to the molten iron refining method of the present embodiment, an inexpensive combustion-supporting gas is used as the carrier gas for conveying the powdered auxiliary material to the burner flame, and an inert gas is used as the carrier gas. It is possible to reduce the cost of refining molten iron compared to the case where molten iron is refined.

[Third embodiment]
The molten iron refining method of the third embodiment is characterized in that in the above embodiment, the discharge velocity (discharge flow velocity) of the carrier gas discharged from the tip of the burner lance is 15 m/s or more and 330 m/s or less. Here, the discharge rate of the carrier gas shall be defined by the following relational expression.
Carrier gas discharge speed (m/s) = (1/60) × carrier gas flow rate (Nm ³ /min) / carrier gas discharge hole cross-sectional area (m ² )
In addition, the inventors conducted a burner lance heating test of lime powder (powdered auxiliary raw material), which is a heat transfer medium, by variously changing the carrier gas flow rate and burner lance height in a converter type reaction vessel test. . As a result, from the viewpoint of the powder (powdered auxiliary raw material) reaching molten iron (hereinafter defined as "yield"), it is necessary to charge the powder (powdered auxiliary raw material) by projecting the carrier gas at least 15 m long. It has been confirmed that it is necessary to have a flow velocity of /s or more. The reason for this is that by increasing the discharge flow rate of the carrier gas, the speed of the powder (powdered auxiliary raw material), which is a heat transfer medium, also increases, increasing the molten iron yield rate of the powder (powdered auxiliary raw material) by over 80%. This is because it can be done. Furthermore, the inventors have confirmed that the yield exceeds 90% by setting the discharge speed of the carrier gas to 80 m/s or more. In this embodiment, the upper limit of the discharge speed of the carrier gas discharged from the tip of the burner lance is 330 m/s. The reason for this is that from the perspective of suppressing molten iron scattering when the heat transfer medium collides with the molten iron bath surface, the speed is around the sonic speed (331.5 m/s in air), and the residence time in the flame can be guaranteed to be 0.035 seconds or more. It is from.

In the molten iron refining method of this embodiment, securing the yield is an important issue because if the yield is low, the heat attached to the powder (powdered auxiliary raw material) will not reach the molten iron and will escape from the system together with the exhaust gas. In this embodiment, the yield was evaluated by collecting slag, determining the lime concentration from analysis, and calculating from the mass balance.

As described above, according to the molten iron refining method of the present embodiment, by setting the discharge speed of the carrier gas discharged from the tip of the burner lance to 15 m/s or more and 330 m/s or less, the yield of the heat transfer medium can be increased to 80% or more. As a result, the heat of the heat transfer medium obtained from the burner flame can be efficiently transferred to the molten iron.

[Fourth embodiment]
The molten iron refining method of the fourth embodiment is characterized in that the distance from the tip of the burner lance to the molten iron bath surface is 3.0 m or more in the above embodiment. That is, the molten iron refining method of the present embodiment secures the residence time of the powdered auxiliary material in the burner flame while ensuring the discharge rate (discharge flow rate) of the carrier gas.

From this point of view, in the molten iron refining method of the present embodiment, it is desirable that the distance from the tip of the burner lance to the molten iron bath surface be 3.0 m or more. On the other hand, in the molten iron refining method of this embodiment, the upper limit of the distance from the tip of the burner lance to the molten iron bath surface needs to be equal to or less than the furnace mouth. The reason for this is that when the lance tip is discharged from the furnace mouth, heat from the burner flame is applied to the exhaust equipment, causing damage to the equipment. Since the conditions inside the furnace change from time to time due to wear and tear of the refractories installed in the converter-type container and metal buildup inside the furnace, the bath surface of the molten iron should be inspected periodically using a sub-lance probe. It is desirable to carry out measurements and know the exact height of the molten iron bath surface.

As described above, according to the molten iron refining method of the present embodiment, by setting the distance from the tip of the burner lance to the molten iron bath surface to be 3.0 m or more, the residence time of the powdered auxiliary material in the burner flame can be ensured. As a result, the heat contained in the powdered auxiliary raw material, which is a heat transfer medium, can be efficiently transferred to the molten iron.

[Fifth embodiment]
In the molten iron refining method of the fifth embodiment, in the above embodiment, the length of the burner flame injected from the tip of the burner lance is 85% with respect to the distance from the tip of the burner lance to the molten iron bath surface. It is characterized by setting the oxygen ratio to ~105%. Here, the oxygen ratio is the combustion-supporting gas solid supply oxygen amount/theoretical oxygen amount required for complete combustion.

Further, in the mixed combustion type burner as described in this patent, fuel and combustion supporting gas are mixed after the nozzle exit of the burner lance, and ignited by the furnace temperature to form a burner flame. The length of this burner flame has a correlation with the oxygen ratio. As in the embodiments described above, it is important to ensure the residence time of the powdered auxiliary material within the burner flame in order to ensure heat transfer efficiency.

However, when the length of the burner flame becomes shorter than the set burner lance height (LH), a problem arises in that the residence time of the powdered auxiliary material within the burner flame becomes short. Additionally, if the length of the burner flame is longer than the set burner lance height (LH), the combustion of the fuel may not be completed before the powdered auxiliary material reaches the molten iron bath surface, resulting in poor heat transfer efficiency. This will be a challenge.

In order to solve these problems, we investigated the burner flame length for each burner lance oxygen ratio to be used. As a result, the length of the burner flame from the tip of the burner lance is 85% or more and the ratio of the distance from the burner lance tip to the molten iron bath surface (burner flame length/burner lance height (LH)) is 85% or more and 105% or less. It turns out that it is desirable that In this embodiment, the length of the burner flame refers to the distance until the supplied fuel gas is completely combusted by mixed combustion. Further, the case where the length of the burner flame exceeds 100% of the distance from the tip of the burner lance to the molten iron bath surface means that a part of the fuel gas provided when reaching the bath surface is unburned.

As described above, according to the molten iron refining method of the present embodiment, by setting the length of the burner flame to 85% or more and 105% or less of the burner lance height (LH), the residence time of the powdered auxiliary material in the burner flame is increased. The heat transfer efficiency to the molten iron can be improved.

[Other embodiments]
Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. The structure and details of the present invention can be modified in various ways within the technical scope of the present invention, which can be understood by those skilled in the art. Furthermore, systems or devices that combine the separate features included in each embodiment in any way are also included within the technical scope of the present invention.

Moreover, the present invention may be applied to a system composed of a plurality of devices, or may be applied to a single device. Furthermore, the present invention is also applicable when an information processing program that implements the functions of the embodiments is supplied to a system or device and executed by a built-in processor. A program installed in a computer or a medium storing the program in order to realize the functions of the present invention on the computer is also included within the technical scope of the present invention.

Molten iron was decarburized and refined using a top-bottom blowing converter having a capacity of 340 tons (oxidizing gas top blowing, argon gas bottom blowing) having the same type as the converter type vessel 1 shown in FIG. The top blowing lance 2 for oxidizing gas blowing had five Laval nozzle-type injection nozzles at its tip. The spray angle of the nozzles was 15°, and the nozzles were arranged at equal intervals on the same circumference with respect to the axis of the top blowing lance 2. Note that the throat diameter dt of the injection nozzle is 73.6 mm, and the outlet diameter de is 78.0 mm.

First, 10 tons of iron scrap was charged into the converter 1. Thereafter, 320 tons of hot metal, which had been desulfurized and dephosphorized in advance, was charged into the converter.

Next, while blowing argon gas as a stirring gas into the molten iron 3 from the bottom blowing tuyere 4, oxygen gas is blown as an oxidizing gas toward the bath surface of the molten iron 3 from the top blowing lance 2, thereby decarburizing the molten iron 3. Started refining. The amount of iron scrap charged was adjusted so that the temperature of the molten steel after decarburization was 1650°C.

After that, during decarburization refining, quicklime is introduced as a CaO-based solvent from the burner lance 5 for inputting powdered auxiliary materials as a heat transfer medium until the carbon concentration in the molten iron reaches 0.05% by mass. Decarburization refining was performed. The amount of quicklime added was adjusted so that the basicity ((mass% CaO)/(mass% SiO ₂ )) of the slag produced in the furnace was 3.0. LNG was used as the fuel gas, and the flow rate of oxygen gas, which is a combustion supporting gas for fuel combustion, was controlled so that the air-fuel ratio was 1.2.

<Invention Examples (Test Nos. 2 to 9), Comparative Examples (Tests Nos. 1 and 10)>
Test No. In Nos. 1 to 10, molten iron was dephosphorized using a top-bottom blowing converter with a capacity of 340 tons (oxidizing gas top blowing, argon gas bottom blowing) having the same type as the converter type vessel 1 shown in FIG. Refined. After 20 tons of scrap as a source of cold iron was charged into the converter from the scrap chute, 300 tons of hot metal was charged and dephosphorized. The hot metal conditions were carbon concentration 4.5% by mass, phosphorus concentration 0.140% by mass, and silicon concentration 0.35% by mass. In the dephosphorization blowing, oxygen blowing was carried out so that the amount of oxygen outside the molten metal was 15 Nm ³ per ton of hot metal. The temperature after the dephosphorization treatment was adjusted to 1380°C. The top blowing lance 2 for oxidizing gas blowing had eight Laval nozzle-type injection nozzles at its tip. The spray angle of the nozzles was set to 16°, and the nozzles were arranged at equal intervals on the same circumference with respect to the axis of the top blow lance 2. Note that the throat diameter dt of the injection nozzle is 50 mm, and the outlet diameter de is 54 mm. And test no. In Nos. 1 to 9, during the dephosphorization process, a burner having an injection hole for ejecting fuel and combustion-supporting gas is provided at the tip of a burner lance that is installed separately from the top blowing lance, and the burner is formed by the burner. 5 tons of lime, which is a powdered auxiliary raw material, was added to the furnace as a heat transfer medium so that it passed through the burner flame.

Test No. In steps 1 to 10, a powdery auxiliary raw material supply pipe with a pipe diameter of 0.0619 m and a cross-sectional area of 0.003009 m ² is used to supply powder (powdered auxiliary raw material), which is a heat transfer medium, and smelt molten iron. I did it. Test No. In steps 1 to 10, molten iron is refined by changing the flow rate of the carrier gas for conveying the powder (powdered auxiliary raw material) and the discharge speed of the powder, and the yield of the powder (powdered auxiliary raw material) is calculated. and evaluated it. The results are shown in Table 1. Note that the yield of powder (powdered auxiliary raw material) is defined and calculated as follows.
Yield = weight of auxiliary materials in slag calculated from slag analysis value/total weight of auxiliary materials supplied

In Table 1, the criteria for determining the powder yield are as follows.
◎: Yield is 90% or more.
○: Yield is less than 90% and more than 80%.
×: Yield is less than 80%. The powder (powdered auxiliary raw material) falls freely and the discharge speed of the powder (powdered auxiliary raw material) is insufficient.

As is clear from Table 1, the invention examples (Test Nos. 2 to 9) have improved yields of lime used as a powdery auxiliary material, which is a transmission medium, compared to the comparative example (Test No. 1). Therefore, the efficiency of heat transfer to molten iron is significantly improved. Specifically, as shown in the invention examples (Test Nos. 2 to 9), the carrier gas flow rate of the carrier gas of the transmission medium is set to 3.0 Nm ³ /min or more, and the carrier gas discharge rate (powder velocity ) was 15.0 m/s or more, it was found that the yield of powdery auxiliary raw materials could be increased to 80% or more. In other words, the invention examples (Test Nos. 2 to 9) simultaneously achieved the lance height that is desirable for molten iron refining and the lance height that is suitable for heat compensation, and increased the yield of powdered auxiliary raw materials to 80% or more. This shows that the efficiency of heat transfer to molten iron can be significantly improved. However, in the comparative example (Test No. 10) in which the carrier gas discharge flow rate was 360 m/s and exceeded 330 m/s, the occurrence of spitting became significant.

<Invention Examples (Test Nos. 13 to 15), Comparative Examples (Test Nos. 11 to 12)>
Test No. 11 to 15, the powder discharge speed was set constant to 83 m/s (same conditions as test No. 5), and the burner lance height (LH), which is the distance from the tip of the burner lance to the molten iron bath surface, was ) and refined molten iron. Test No. In Nos. 11 to 15, the residence time of the powder in the burner flame and the heat transfer efficiency (%) to the molten iron were measured and evaluated. The results are shown in Table 2. The heat transfer efficiency (%) is expressed as a percentage (%) of the heat transfer amount (MJ) calculated from the change in the molten iron temperature with respect to the heat input (MJ) due to combustion of the fuel gas.

In Table 2, the heat transfer efficiency (%) was determined as follows.
○: Heat transfer efficiency is 80% or more.
×: Heat transfer efficiency is less than 80%.

As is clear from Table 2, the heat transfer efficiency of the invention examples (Test Nos. 13 to 15) was significantly improved compared to the comparative examples (Test Nos. 11 to 12). Specifically, as shown in the invention examples (Test Nos. 13 to 15), by setting the burner lance height (LH) to 3.0 m or more and ensuring the residence time of the powdered auxiliary material in the burner flame. It has been found that the efficiency of heat transfer to molten iron can be significantly improved. On the other hand, in the comparative examples (Test Nos. 11 to 12), the burner lance height (LH) was set to less than 3.0 m to ensure sufficient residence time of the powdered auxiliary material in the burner flame. It was found that the heat transfer efficiency to the molten iron was less than 80% because of this.

<Invention Examples (Test Nos. 20 to 21), Comparative Examples (Test Nos. 16 to 19)>
Test No. In No. 16 to No. 21, the powder discharge speed was set constant to 83 m/s and the burner lance height (LH) was 3.5 m (same conditions as Test No. 14), and the oxygen ratio was changed. Refined molten iron. Test No. In steps 16 to 21, the length of the burner flame (flame length), flame length/burner lance height (LH), residence time of powder in the burner flame, and heat transfer efficiency to molten iron (%) were measured, and the judgment ( evaluation).

In addition, in Table 3, the determination of heat transfer efficiency is as follows.
○: Heat transfer efficiency is 80% or more.
Δ: Heat transfer efficiency is less than 80% to 40% or more.
×: Heat transfer efficiency is less than 40%.

As is clear from Table 3, the heat transfer efficiency (%) of the invention examples (Test Nos. 20 to 21) was significantly improved compared to the comparative examples (Test Nos. 16 to 19). Specifically, as shown in the invention examples (Test Nos. 20 to 21), the length of the burner flame injected from the tip of the burner lance is 85 mm with respect to the distance from the tip of the burner lance to the molten iron bath surface. It has been found that by setting the oxygen ratio to 105%, the heat transfer efficiency to molten iron can be increased to 80% or more. On the other hand, in comparative examples (test Nos. 16 to 19), the oxygen ratio was set so that the length of the burner flame was 85 to 105% of the distance from the tip of the burner lance to the molten iron bath surface. It was found that the heat transfer efficiency to the molten iron was less than 80% because the heat transfer efficiency was not 80%.

According to the molten iron refining method of the present invention, a lance height that is desirable for molten iron refining and a lance height that is suitable for heat compensation can be achieved at the same time, and the heat transfer efficiency (%) to molten iron is improved. This is industrially useful. Moreover, it is suitable for application not only to the converter type but also to processes that require a heat source.

1 Converter type container 2 Top blowing lance (for oxidizing gas)
3 Molten iron 4 Bottom blowing tuyere 5 Burner lance 10 Burner lance tip 11 Powder supply pipe (powdered auxiliary raw material supply pipe)
12 Fuel supply pipe 13 Combustion-supporting gas supply pipe 14 Cooling water passage 15 Powder (powdered auxiliary raw material)
16 Fuel 17 Combustion-supporting gas 18 Cooling water

Claims (5)

A method for pretreatment blowing or decarburization blowing of molten iron, which is carried out by adding powdered auxiliary raw materials into a converter-type vessel charged with molten iron and supplying oxidizing gas from a top blowing lance,
the molten iron includes a cold iron source;
Separately from the top blowing lance, one or more burner lances that can be raised and lowered independently are provided,
a lance height of the top blowing lance suitable for refining the molten iron;
simultaneously achieving lance heights of the burner lances suitable for heat compensation of the cold iron source;
The burner lance has a powder supply pipe and an injection hole for blowing fuel and combustion supporting gas from the tip of the burner lance, and is formed so as to be able to inject burner flame,
A powdered auxiliary raw material as a heat transfer medium is gas-transported into the burner flame by a carrier gas through the powder supply pipe, passed through the burner flame to be heated, and charged into the converter type container; A method for refining molten iron, comprising transferring heat of the burner flame to the molten pig iron. The method for refining molten iron according to claim 1, wherein the carrier gas is a combustion-supporting gas. The method for refining molten iron according to claim 1 or 2, characterized in that the discharge speed of the carrier gas discharged from the tip of the burner lance is 15 m/s or more and 330 m/s or less.
Here, the discharge speed of the carrier gas shall be defined by the following relational expression.
Carrier gas discharge speed (m/s) = (1/60) × carrier gas flow rate (Nm ³ /min) / carrier gas discharge hole cross-sectional area (m ² ) The method for refining molten iron according to any one of claims 1 to 3, characterized in that the distance from the tip of the burner lance to the surface of the molten iron bath is 3.0 m or more. The oxygen ratio is set so that the length of the burner flame injected from the tip of the burner lance is 85 to 105% of the distance from the tip of the burner lance to the molten iron bath surface. The method for refining molten iron according to claim 4 .
Here, the oxygen ratio is the combustion-supporting gas solid supply oxygen amount/theoretical oxygen amount required for complete combustion.

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