JP2004169070A - Method for protecting bottom-blown double-tube tuyere in molten metal refining furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for effectively preventing the wear of a tuyere caused by blowing-away of mushroom by suitably keeping the mushroom in a molten metal refining furnace having a double-tube tuyere at the furnace bottom. <P>SOLUTION: When the molten metal is refined by supplying refining gas from the inner tube of the tuyere and gas for cooling the tuyere from a gap between the inner tube and an outer tube, into the molten metal held in the molten metal refining furnace from the double tube type gas blowing tuyere arranged at the bottom of the molten metal refining furnace, a linear flowing velocity of the gas for cooling the tuyere in the gap between the inner tube and the outer tube of the tuyere, is made to be ≤ 220 Nm/sec. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention effectively protects a double-pipe tuyere provided at the furnace bottom of a molten metal refining furnace typified by a bottom-blowing converter or an upper-bottom-blowing converter for steelmaking to reduce wear. How to do it.
[0002]
[Prior art]
A bottom-blowing converter for steelmaking, in which gas is blown below the surface of a molten metal bath in a refining furnace through a concentric double-pipe tuyere (hereinafter simply referred to as "double-pipe tuyere"). Alternatively, top-bottom blow converters are known. The bottom-blowing converter is a molten metal refining furnace in which the entire amount of oxygen gas for refining is blown from the inner tube of the double-tube tuyere. This is a molten metal smelting furnace of the type in which another part is blown in from the inner pipe of the mouth from the top blowing lance.
[0003]
A double-tube tuyere is a tuyere consisting of a metal tube formed in a concentric double tube at a fixed interval. Usually, oxygen or a mixed gas of oxygen and an inert gas (this Gas) is blown into the molten metal, and a cooling gas such as propane gas or inert gas (referred to as “outer tube cooling gas”) is blown from the gap between the inner tube and the outer tube to cool the outer tube. The sensible heat for the gas to reach the temperature of the molten steel and the propane gas are used to cool and protect the tuyere using the decomposition endotherm of the thermal decomposition.
[0004]
Around the tip of the tuyere of such a double tube, a metal mass called mushroom solidified by molten steel is formed. It is known that this mushroom is generated by the balance between the heat received from the high temperature region called the flash point formed by the refining gas blown into the molten steel from the inner pipe, the sensible heat of the outer pipe cooling gas, and the heat removal by the heat of decomposition. (See, for example, Patent Document 1).
[0005]
The mushroom prevents the hot spot and surrounding hot molten steel from coming into direct contact with the tuyere outer tube or surrounding refractory, thereby reducing the erosion of the double tube tuyere and the wear of the refractory around the tuyere. It works to prevent it. Therefore, forming a stable mushroom is effective in reducing tuyere wear. Therefore, conventionally, in a molten metal refining furnace having a double tube tuyere represented by a bottom blown converter or an upper bottom blown converter, an operation for forming a large and stable mushroom has been performed. . Specifically, an outer pipe cooling gas at a certain ratio or more to the refining gas supplied from the inner pipe is supplied to a gap between the inner pipe and the outer pipe.
[0006]
However, according to the findings of the present inventor, as shown in FIG. 2, the outer pipe cooling gas flow path 9 formed in the mushroom 1 is branched like a mesh, and when the mushroom 1 is greatly enlarged, The pressure loss of the outer pipe cooling gas 5 in the mushroom 1 increases extremely. As shown schematically in FIG. 2, the mushroom 1 having a double-tube tuyere that supplies the refining gas 4 from the inner pipe 6 has a high temperature due to the reaction between the refining gas 4 and the molten metal 3 (that is, molten steel) on the inner pipe 6 side. A thick gas flow path 8 is formed due to the influence of the fire point. Therefore, the mushroom 1 and the tuyere are fixed mainly at the inner and outer tube tips (the furnace bottom refractory and the mushroom 1 are in apparent contact with each other, but are not adhered to each other). It has been found that when the pressure loss of the outer pipe cooling gas 5 in the inside 1 increases, the mushroom 1 is blown off during the operation and the tuyere is extremely worn.
[0007]
In particular, in recent years, in the case of converters for steel production (refining furnaces in which molten iron, which is a molten iron-carbon alloy, is decarburized and refined with oxygen to form molten steel), one tuyere is used for high productivity. When the flow rate of the smelting gas flowing through the inner tube is 0.06 Nm ³ / (min · t) or more per tuyere, the mushroom blow-off tends to occur. Is strong. In the case of a molten iron alloy containing 9 to 30% by mass of chromium, such as stainless steel, an operation is performed in which the composition and type of the refining gas and the outer pipe cooling gas are changed stepwise during the decarburization refining. It has become clear that such stepwise gas switching has further triggered the mushroom blow-off.
[0008]
On the other hand, in the case of a converter having a tuyere without oxygen gas blowing, for example, a bottom tuyere having a structure in which a large number of small diameter metal tubes are assembled, as disclosed in Patent Document 2, each tuyere A gas flow meter is installed in each tuyere to calculate the pressure loss of the mushrooms, while each tuyere is equipped with multiple thermocouples at regular intervals inside to measure the temperature, and the pressure loss of these mushrooms and the temperature inside the tuyere It is known that the operation is performed so as to be in a specific stable region.
[0009]
However, since the small-diameter metal tube tuyere disclosed in Patent Document 2 does not blow oxygen as in the above-described double tube tuyere, the mushroom is a tuyere refractory as shown in FIG. It is fixed over the entire surface of the tip, and there is no concern that the mushroom will blow off even if the pressure loss of the gas in the mushroom increases. From this point of view, Patent Literature 2 sets the upper limit of the pressure loss of the mushroom solely in consideration of the decrease in the gas flow rate into the molten steel due to the upper limit, and does not provide any method for preventing the mushroom from blowing off during operation. It did not provide knowledge.
[0010]
[Patent Document 1]
JP-A-63-189873 [Patent Document 2]
JP-A-4-32507 [Patent Document 3]
JP-A-62-147308
[Problems to be solved by the invention]
As described above, in a molten metal refining furnace of the type in which a refining gas is blown into a molten metal (for example, molten steel) from a double tube tuyere, particularly from its inner tube, outer tube cooling flowing into a mushroom from a tuyere outer tube. It has been found that when the gas pressure drop increases, the mushrooms blow off, which was an unexpected phenomenon, which shortened the tuyere life. It did not give a solution.
[0012]
The present invention has been made in view of the above circumstances, and provides a method for appropriately maintaining a mushroom of a molten metal smelting furnace having a double tube tuyere at a furnace bottom, and effectively preventing the tuyere from being worn away due to blow-off of the mushroom. It is intended for that purpose.
[0013]
[Means for Solving the Problems]
The present invention provides a double-pipe gas injection tuyere provided in the furnace bottom of a molten metal refining furnace, into the molten metal held in the molten metal refining furnace, a refining gas from the inner tube of the tuyere, When the tuyere cooling gas is supplied from the gap between the inner pipe and the outer pipe to refine the molten metal, the linear flow velocity of the tuyere cooling gas in the gap between the inner pipe and the outer pipe of the tuyere is set to 220 Nm / The present invention proposes a method for protecting a tuyere of a bottom blown double tube of a molten metal smelting furnace characterized by being made to be no more than sec.
[0014]
The above invention is preferably applied when the flow rate of the refining gas blown into the molten metal from the tuyere inner tube is 0.06 Nm ³ / (min · t) or more per tuyere.
When the molten metal is a molten iron-carbon alloy and oxygen is blown from the inner tube tuyere to perform decarburization refining, the molten iron-carbon alloy further contains 9 to 30% by mass of chromium. In this case, it is preferable to apply the above-mentioned invention because it is more effective.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
The molten metal smelting furnace to which the present invention is applied has at least one gas injection tuyere of a double tube type at the furnace bottom, and a gas supply path for the gap between the inner tube and the outer tube of the tuyere. This is a molten metal refining furnace having a gas supply path for an inner pipe. Specifically, an oxygen bottom-blowing converter and an oxygen top-bottom blowing converter used for refining molten steel are exemplified. In these molten metal refining furnaces, oxygen or a mixed gas of oxygen and an inert gas is blown as molten gas into the molten metal from a tuyere provided at the furnace bottom into molten steel. At that time, oxygen and easily oxidizable components such as C and Si in the molten steel react at the tip of the tuyere to generate heat and generate a so-called high-temperature flash point.
[0016]
Since the tuyere and its surrounding refractory receive heat from this fire point, it is not possible to prevent the tuyere and its surrounding refractory from being damaged without any cooling.
Therefore, at the refining gas injection tuyere, an inner pipe for blowing oxygen or a mixed gas of oxygen and an inert gas and an outer pipe provided so as to form a gap at regular intervals around the inner pipe are provided. An inert gas or hydrocarbon gas is supplied as a cooling gas for the outer tube from the gap between the inner tubes. In particular, a hydrocarbon gas such as propane is advantageous because the tip of the tuyere can be cooled not only by sensible heat but also by decomposition heat absorption. As described above, a metal lump called mushroom is generated around the tip of the tuyere by the action of the outer tube cooling gas, thereby protecting the tuyere.
[0017]
The present inventor has investigated in detail the conditions under which the above-described phenomenon in which the mushroom blows off occurs in the molten metal smelting furnace in which the above-described bottom-blowing tuyere is arranged. As a target heat, a heat for producing molten stainless steel by decarburizing and refining high chromium molten iron containing 9 to 30% by mass of chromium was selected. To confirm the mushroom blow-off phenomenon, specifically, a cable paired with a transmission line and a reception line of an electric pulse is inserted into the tuyere, and from the base of the tuyere by the electric pulse reflection method described in Patent Document 3. The length of the tuyere outer tube up to the tip (ie, the position where it adheres to the mushroom) is continuously measured, and the pressure and linear flow velocity of the outer tube cooling gas are continuously measured to determine the operating conditions and changes in the tuyere outer tube length. Correspondence was made.
[0018]
First, as a preliminary experiment, the furnace was tilted immediately when the tuyere outer tube length was suddenly reduced during operation, and the work of observing the tuyere from the furnace port was repeated, and the tuyere outer tube length was rapidly shortened. When it became, it was confirmed that mushroom 1 had disappeared from the tuyere. In other words, it was presumed that when the tuyere outer tube length was suddenly shortened, the mushroom was blown off immediately before that.
[0019]
Next, the correspondence between the tuyere gas supply conditions and the wear rate of the tuyere outer tube length (this is referred to as the tuyere wear rate) was investigated. Among various conditions, the linear flow rate of the outer tube cooling gas 5 and the tuyere It was confirmed that the wear rate had a relationship as shown in FIG. That is, it has been found that when the linear flow velocity of the outer pipe cooling gas 5 exceeds 220 Nm / sec, the tuyere wear rate rapidly increases.
[0020]
For this reason, in the present invention, the outer pipe cooling gas linear flow velocity is limited to 220 Nm / sec or less. From FIG. 1, the above tendency is more remarkable in the heat in which the inner tube gas flow rate per tuyere is 0.06 Nm ³ / (min · t) or more. Therefore, it has been clarified that the present invention is more effective when applied to heat in which the inner tube gas flow rate is 0.06 Nm ³ / (min · t) or more.
[0021]
The above experiment was carried out in the decarburization and refining of molten iron containing 9 to 30% by mass of chromium. Subsequently, the same investigation was carried out for the decarburization and refining of ordinary steel not containing chromium. It became clear that the tuyere wear rate can be reduced by setting the gas line flow rate to 220 Nm / sec or less.
[0022]
【Example】
As an example of the invention to which the present invention is applied, a chromium-containing molten iron containing 9 to 30% by mass of chromium is formed by a 180 ton top-bottom blowing converter having a furnace capacity of eight double tube type bottom blowing tuyeres. When decarburizing and refining the concentration from 5.5% by mass to 0.2% by mass on average, the refining operation is repeated with the linear flow rate of the outer pipe cooling gas always being 220 Nm / sec or less (195 Nm / sec on average). Was. The inner tube gas flow rate at this time was 0.1 Nm ³ / (min · t) per tuyere. In this way, the tuyere outer tube length was continuously measured by the electric pulse reflection method described above, and the tuyere wear rate was determined. This operation was performed for a total of 100 heats, and the tuyere abrasion rate was calculated. The average was 3.6 mm / heat.
[0023]
As a comparative example, when decarbonizing and refining chromium-containing molten iron containing 9 to 30% by mass of carbon from 5.5% by mass to 0.2% by mass using the same top-bottom blowing converter as the invention example. The operation under the conventional conditions of refining was repeated with the linear flow velocity of the outer pipe cooling gas always exceeding 220 Nm / sec (230 Nm / sec on average). The inner tube gas flow rate at this time was 0.1 Nm ³ / (min · t) per tuyere. The tuyere outer tube length at this time was continuously measured by the aforementioned electric pulse reflection method in the same manner as in the invention example, and the tuyere wear rate was determined. This operation was performed for a total of 100 heats, and the tuyere wear rate was determined. The average was 5.6 mm / heat.
[0024]
As is clear from these examples, according to the present invention, the tuyere wear rate could be reduced to 64% of the conventional one. This has made it possible to extend the bottom life of the top and bottom blown converter by 1.5 times or more.
[0025]
【The invention's effect】
The present invention avoids blow-off of a mushroom at the tip of a tuyere in a molten metal smelting furnace having a double-pipe bottom tuyere at the furnace bottom, particularly in a converter for decarburizing and refining steel. It is possible to reduce the wear rate of the furnace and thereby achieve a longer life of the furnace bottom.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the outer pipe cooling gas line flow velocity and the tuyere wear rate.
FIG. 2 is a schematic diagram showing a mushroom at the tip of a double tube tuyere.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 mushroom 2 furnace bottom refractory 3 molten metal 4 refining gas 5 outer pipe cooling gas 6 inner pipe 7 outer pipe 8 refining gas flow path in mushroom 9 outer pipe cooling gas flow path in mushroom

Claims (4)

From the inner pipe of the tuyere to the refining gas, the inner pipe and the outer pipe into the molten metal held in the molten metal refining furnace from the gas injection tuyere of the double pipe system provided at the bottom of the molten metal refining furnace In supplying the tuyere cooling gas from the gap between the tubes and refining the molten metal, the linear flow velocity of the tuyere cooling gas in the gap between the inner tube and the outer tube of the tuyere is set to 220 Nm / sec or less. A method for protecting a bottom blown double tube tuyere of a molten metal smelting furnace. 2. The bottom blow of a molten metal refining furnace according to claim 1, wherein a flow rate of the refining gas blown into the molten metal from the tuyere inner tube is 0.06 Nm < ³ > / (min.t) or more per one tuyere. How to protect the double tube tuyere. The bottom-blown double-pipe of a molten metal refining furnace according to claim 1 or 2, wherein the molten metal is a molten iron-carbon alloy, and decarburization is performed by blowing oxygen from the inner tube tuyere. How to protect tuyeres. The method according to claim 3, wherein the molten iron-carbon alloy further contains 9 to 30% by mass of chromium.

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