JPH07242926A - Injection lance having double tube structure - Google Patents

Abstract

PURPOSE:To reduce erosion on the tip of an injection lance immersed into molten metal and blows a treating agent by a conveying gas and to prolong its service life. CONSTITUTION:The structure of an injection lance 1 is formed into a double tube constituted of an inner tube 2 and an outer tube 3, the outer tube 3 of the immersing part in which the lance 1 is immersed into the molten metal is produced by a Zr alloy excellent in heat resistance, and furthermore, a flow passage between the inner tube 2 and outer tube 3 is fed with a liquefied petroleum gas. the immersing part of the outer tube 3 is excellent in heat resistance, and furthermore, the tip of the lance is cooled by the decomposition endothermic reaction of the liquefied petroleum gas blown into the molten metal. moreover, the outer peripheral face of the outer tube 3 is covered with refractories 6, so that erosion on the tip of the lance can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an injection lance having a double pipe structure for injecting various treatment agents into a molten metal such as hot metal or molten steel by carrier gas in pretreatment of molten pig iron or ladle refining of molten steel. It is a thing.

[0002]

2. Description of the Related Art For example, in the pretreatment of hot metal, desiliconization, dephosphorization, and desulfurization are performed prior to refining in a converter or the like, thereby reducing the load of the subsequent converter or the like and improving the efficiency of the steelmaking process. The purpose is to improve the iron yield and reduce the basic unit of steelmaking auxiliary raw material. The treatment agents used for such hot metal pretreatment are roughly classified into those of sodium carbonate (Na ₂ CO ₃ ) and those of quick lime (CaO). , In order to improve the dephosphorization efficiency, it is desirable to effectively utilize the process in which the powder of the treating agent floats in the hot metal. Therefore, the powder of the treating agent is introduced into the hot metal together with the carrier gas using an injection lance. Injection method is used.

The hot metal pretreatment by the injection method as described above has the following various problems. That is, in the hot metal pretreatment by the injection method, the injection lance is immersed in the hot metal,
It is usual to blow the pretreatment agent into the hot metal through the lance using argon gas, nitrogen gas, oxygen gas, or a mixed gas of both as a carrier gas.

Since the dephosphorization reaction is an oxidation reaction, a mixed gas having a high oxygen gas mixing ratio or pure oxygen gas may be used as the carrier gas in order to improve the dephosphorization efficiency. However, when the oxygen gas mixing ratio is made higher than when argon gas or nitrogen gas is used or when pure oxygen gas is used, due to the exothermic reaction between the oxidizing gas and various components in the hot metal. The temperature near the tip of the injection lance becomes high and the melting loss at the tip of the lance becomes more severe, resulting in a shorter life. Since the melted lance needs to be replaced, it often happens that the blowing of the processing agent powder must be interrupted during the pretreatment.

In order to solve such a problem, Japanese Patent Laid-Open No. 58-
221210 discloses that prior to decarburizing and refining in a converter, etc.
When immersing the injection lance in the hot metal and blowing the hot metal pretreatment agent into the hot metal through the lance,
The injection lance has a double structure, and the hot metal pretreatment agent is blown into the hot metal from the inner pipe of the lance by using nitrogen gas and / or oxygen gas as carrier gas, and at the same time, the flow between the outer pipe, that is, the outer pipe and the inner pipe. A technique has been proposed in which a hydrocarbon-based gas is blown into the hot metal as a cooling gas from the passage.

[0006]

SUMMARY OF THE INVENTION Stainless steel and plain steel are used for the inner and outer pipes of the double-structured injection lance disclosed in the above publication, and the hot metal dip portion of the outer pipe is coated with a refractory material. I'm supposed to. The hydrocarbon-based gas supplied from the outer pipe is endothermic as the decomposition reaction when it is blown into the hot metal and decomposes at high temperature, so it takes away heat from the tip of the lance. Therefore, even if the carrier gas of the hot metal treating agent blown from the inner pipe is oxygen gas or a mixed gas having a high oxygen gas concentration, it is possible to considerably prevent melting loss due to the temperature rise of the lance tip.

For this reason, it is possible to reduce the situation in which the lance is melted during the hot metal pretreatment and the blowing of the treatment agent powder must be interrupted, but the life may vary depending on the place of use and the type of treatment agent. Is short and the frequency of replacement is high, which is costly and may hinder operation. The present invention has been made in view of the above circumstances, and an object of the present invention is to achieve a longer life of an injection lance having a double pipe structure.

[0008]

In order to achieve the above object, the present invention as set forth in claim 1, is an inner tube which is immersed in a molten metal and blows a treating agent by a carrier gas, and an inner tube having the same axis as the inner tube. In an injection lance having a double-pipe structure composed of an outer pipe for blowing a cooling gas having a core, a heat-resistant metal is used for the outer pipe of the immersion part in which the injection lance is immersed in molten metal, and the inner surface thereof is gas-cooled. It is an injection lance having a double pipe structure characterized by being configured as follows.

According to the second aspect of the present invention, the thermal stress σ = [α · ΔΤ · Ε / 2] generated in the heat-resistant metal used for the outer tube of the immersed portion.
2. The injection lance having a double pipe structure according to claim 1, wherein (1-ν)] is configured to be gas-cooled so that the allowable stress of the refractory metal is within. Where σ: thermal stress (kg / mm ² ) α: linear expansion coefficient (1 / ° C) Ε: Young's modulus (kg / mm ² ) ν: Poisson's ratio ΔΤ: temperature difference between the inner and outer surfaces of the outer tube The present invention uses a functionally graded material capable of preventing thermal stress caused by the temperature difference between the outer peripheral surface and the inner peripheral surface instead of the heat-resistant metal used for the outer tube of the immersion part, and is configured to gas-cool the inner surface. The double-structured injection lance according to claim 1, wherein

In the present invention according to claim 4, the refractory metal used for the outer tube of the immersion part is coated with a refractory material having a thickness such that the outer peripheral surface temperature is within the heat resistant temperature of the refractory metal, or S
The injection lance having a double-tube structure according to claim 1, characterized in that it is coated with an iC / C-based material.

[0011]

In the present invention, a heat-resistant metal is used for the outer tube of the immersion portion where the injection lance is immersed in the molten metal, and the inner surface is gas-cooled, so that melting damage due to temperature rise of the tip of the lance is prevented. You can As the heat-resistant metal used for the outer tube, when the injection lance is immersed in molten steel, it is preferable to use a metal having higher heat resistance than the stainless steel disclosed in the above publication.

A hydrocarbon-based gas is suitable as a gas for cooling the inner surface of the outer tube, and the hydrocarbon-based gas supplied from the flow path between the inner surface of the outer tube, that is, the outer tube and the inner tube is melted. It absorbs heat at the tip of the lance by endothermic decomposition reaction when it is blown into metal and decomposes at high temperature. At this time, a solidified material called mushroom, which is similar to the tuyere of the bottom blowing converter, is formed at the tip of the lance and is protected, so that a further effect of preventing melting damage can be obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. The preferred injection lance structure of the present invention is as shown in FIG. The inner tube 2 as shown in FIG.
In the injection lance 1 having a double pipe structure composed of the outer pipe 3 and the outer pipe 3 having the same axis, the non-immersed portion in the molten steel 7 has cooling water in the flow path between the outer pipe 3 and the outermost pipe 4. It is preferable to allow it to flow and to cool it.

The material of the inner pipe 2 may be ordinary steel or stainless steel as in the conventional case, but the outer pipe 3 is immersed in the molten steel 7 using a heat-resistant metal 5 such as Zn alloy. However, it is preferable to cover the outer peripheral surface with the refractory material 6. Depending on the melting point of the molten metal into which the injection lance 1 is dipped, the refractory 6 may be omitted and the refractory metal 5 may be dipped directly.

When the flux is blown into the molten steel 7 from the injection lance 1, the flux is blown into the molten steel 7 from the inner pipe 2 using argon gas as a carrier gas. Then, propane gas (C ₃ H ₈ ) is supplied as a cooling gas from the gas passage between the outer pipe 3 and the inner pipe 2. In this way, the propane gas blown into the molten steel 7 from the outer pipe 3 absorbs heat at the tip of the lance 1 by the endothermic reaction when decomposing at a high temperature and cools the outer pipe 3 and the inner pipe 2, so that melting loss is caused. Can be prevented. At this time, if mushrooms are formed by cooling the tip of the lance, it is possible to prevent the tip of the lance 1 from directly contacting the molten steel 7, so that the melt loss prevention effect is enhanced.

The thermal stress caused by the temperature difference (ΔT) between the outer peripheral surface and the inner peripheral surface of the refractory metal 5 can be expressed by the following equation (1). σ = α · ΔΤ · Ε / 2 (1-ν) (1) where σ: thermal stress (kg / mm ² ) α: coefficient of linear expansion (1 / ° C) Ε: Young's modulus (kg / mm ²⁾ ) Ν: Poisson's ratio If the allowable stress of the refractory metal 5 is σ _S , the flow rate of the propane gas and the refractory metal thickness may be set so that the temperature difference ΔT such that σ _S > σ is obtained.

When the heat-resistant metal 5 is a Zr alloy, the coefficient of linear expansion: α = 5.94 × 10 ^-6 (1 / ° C) Young's modulus: Ε = 2000 (kg / mm ² ) Poisson's ratio: 0.3 (at 1000 ° C Case) Allowable stress: 3.3 (kg / mm ² ), so the temperature difference between the outer and inner peripheral surfaces of the outer tube 3 is Δ
Τ ≈ 380 ℃. Therefore, it is only necessary to cool with ΔA of propane gas so that ΔΤ falls within 380 ° C.

When a Zr alloy is used as the refractory metal 5 of the outer tube 3, the temperature of the refractory 6 is limited to 1200 ° C. or lower, and the thickness of the refractory 6 is determined accordingly. Further, when the refractory metal 5 has a problem in oxidation resistance, the outer peripheral surface of the refractory metal 5 is covered with the refractory material 6 to improve the oxidation resistance. Using a Zr alloy as a heat-resistant metal in molten steel with a heat size of 250 tons contained in a ladle, and using an injection lance with a 20 mm thick refractory coating on the outer peripheral surface, flux from the inner pipe was 50 kg / min. In addition to supplying 1.0 (Nm ³ / min) of argon gas as the carrier gas, propane gas was supplied from the outer tube and blown into the molten steel. According to the injection lance of the present invention, the life of the lance on average was 10 charges in the conventional single-tube injection lance, but it could be extended to a maximum of 30 charges.

Another preferred injection lance structure of the present invention is shown in FIG. As shown in FIG. 2, when an injection lance 1 having a double-pipe structure composed of an inner pipe 2 and an outer pipe 3 having the same axis is used for pretreatment of the hot metal 8, for example, the outer pipe 3 that comes into direct contact with the hot metal 8 A functionally graded material having excellent oxidation resistance at high temperature and heat resistance due to a temperature difference between the outer peripheral surface and the inner peripheral surface is used for the immersion part. As the functionally gradient material, for example, a ZrO ₂ / Ni-based material can be preferably used.

As the material of the inner tube 2, ordinary steel, stainless steel, or other heat-resistant metal is appropriately used, and various hot metal pretreatment agents from the inner tube 2 are argon gas, nitrogen gas, air, oxygen-enriched air or pure air. Oxygen is blown into the hot metal 8 as a carrier gas. Then, the cooling gas is supplied from the flow path between the outer pipe 3 and the inner pipe 2. If a hydrocarbon-based gas such as propane gas is used as the cooling gas, the effects as described in the above embodiment can be obtained.

In the present invention, since the functionally gradient material is used as the outer pipe 3 of the portion where the injection nozzle 1 is immersed in the hot metal, the heat generated by the surface temperature difference between the outer peripheral surface and the inner peripheral surface of the outer tube 3 is used. In addition to being able to prevent stress, the outer peripheral surface side is made of metal having high heat resistance so that it will not be melted. If a ZrO ₂ / Ni-based material is used as a functionally graded material, it can withstand a high temperature oxidizing atmosphere and can withstand thermal stress due to the temperature difference between the inner and outer surfaces. In addition, for functionally graded materials such as W / Cu and TiB ₂ / Cu, which have problems with oxidation resistance, SiC / C-based materials are chemically vapor-deposited on the surface to improve acid resistance, or refractory materials are used. What was covered may be used.

A hot metal amount of 200 tons / charge was pretreated with hot metal using a dephosphorization and desulfurization facility. Iron oxide (100 kg / min), lime (80 kg / min), soda ash (100 kg / min) as the hot metal pretreatment agent are supplied from the inner tube of the injection lance while supplying argon gas as the carrier gas and propane gas from the outer tube. Then, it was blown into the hot metal to perform hot metal pretreatment.

According to the injection lance of the present invention, the life of the lance in the conventional single-tube injection lance was 4 charges on average, but it could be extended to 300 charges at maximum.

[0024]

As described above, according to the present invention, in the injection lance having the double pipe structure including the inner pipe and the outer pipe, the material of the outer pipe is a metal having excellent heat resistance and the inner surface thereof is Since the gas is cooled, it is possible to prevent melting damage at the tip of the lance. As a result, the life of the injection lance is extended and the molten metal can be treated in a stable state.

[Brief description of drawings]

FIG. 1 is a sectional view showing a tip structure of a preferred injection lance of the present invention.

FIG. 2 is a cross-sectional view showing the tip structure of another preferred injection lance of the present invention.

[Explanation of symbols]

 1 Injection Lance 2 Inner Tube 3 Outer Tube 4 Outermost Tube 5 Heat Resistant Metal 6 Refractory 7 Molten Steel 8 Hot Metal

Claims (4)

[Claims] 1. An injection lance having a double pipe structure comprising an inner pipe for immersing in a molten metal to blow a treatment agent by a carrier gas, and an outer pipe for blowing a cooling gas having the same axis as the inner pipe. 2. The injection lance having a double pipe structure, wherein the injection lance is constructed by using a refractory metal for an outer pipe of a dipping portion in which the injection lance is dipped in a molten metal, and cooling the inner surface of the outer pipe with gas. 2. The gas cooling is performed so that the thermal stress σ = [α · ΔΤ · Ε / 2 (1-ν)] generated in the heat resistant metal used for the outer tube of the immersion part is within the allowable stress of the heat resistant metal. The double-structured injection lance according to claim 1, wherein the injection lance is constructed. Where σ: thermal stress (kg / mm ² ) α: coefficient of linear expansion (1 / ° C) Ε: Young's modulus (kg / mm ² ) ν: Poisson's ratio ΔΤ: temperature difference between the inner and outer surfaces of the outer tube 3. A functionally graded material capable of preventing thermal stress caused by a temperature difference between an outer peripheral surface and an inner peripheral surface is used instead of the heat-resistant metal used for the outer tube of the immersion part, and the inner surface is gas-cooled. The dual-structured injection lance according to claim 1, wherein 4. The refractory metal used for the outer tube of the immersion part is coated with a refractory material such that the temperature of the outer peripheral surface is within the heat resistant temperature of the refractory metal, or is coated with a SiC / C material. The double-tube structure injection lance according to claim 1, 2, or 3.