JPH0257631A - Method for cooling submerged tube for molten steel degassing - Google Patents

Abstract

PURPOSE:To effectively cool a submerged tube without accompanying any danger of explosion by fixing with welding a cooling pipe to a core pipe in the submerged tube for uptake, blowing cooling gas from one end of the cooling pipe and discharging the cooling gas into molten steel from the other end as the circulating flow gas. CONSTITUTION:At the time of executing degassing in the molten steel with the vacuum degassing method, the cooling pipe 11 is wound and welded at the circumference of a cylindrical core metal 10 fixed to a flange 15 of the submerged tube 3a for uptake. The gas supplying tube 4 for circulating flow is connected with the lower end of this cooling tube 11 and gas blowing nozzle 12 for circulating flow is connected with the upper end, and in both inner and outer faces of the core 10, brick refractory 13 and monolithic refractory 14 are lined. By this constitution, the cooling gas is supplied into the cooling pipe 11 from a supplying pipe 4 to cool the core metal 10, and blow into the molten steel from the blowing nozzle 12 as the gas for circulating flow. By this method, the service life of the submerged tube 3a is extended and repairing coat is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for cooling a immersion tube for molten steel degassing, in which a immersion tube core used in a molten steel degassing apparatus is cooled with gas.

<Prior art> Vacuum degassing method: The outline thereof will be explained with reference to FIG. In FIG. 5, 1 is a ladle, 2 is a vacuum tank connected to a vacuum pump (the path shown), 3 is two immersion tubes,
It consists of an immersion pipe 3a for ascending molten steel and an immersion pipe 3b for descending molten steel. 4 is a reflux gas supply pipe connected to the rising immersion pipe 3a, and the tip thereof is a gas blowing nozzle 12.

The immersion tube 3 is immersed in the molten steel in the ladle l, the vacuum chamber 2 is depressurized, and an inert gas such as static gas is blown in from the gas injection nozzle 12, and the gas floats up using the blade. After rising into the vacuum chamber 2 from the dipping tube 3a for use and being degassed within the vacuum chamber 2, it is sequentially discharged into the ladle l from the dipping tube 3b for descending.

Generally, the immersion pipes 3a and 3b are composed of an iron core 10 and refractories installed on both the inner and outer surfaces of the core 10, as shown in FIG. 5, and are immersed in molten steel to degas the molten steel. Processing such as component adjustment is being performed.

The temperature of the molten steel is about 1600°C, and the processing time is 20 to 30 minutes, so the temperature of the core metal 10 is low during processing.
Cases in which the temperature reaches a temperature exceeding ooo'c occur repeatedly.

<Problems to be Solved by the Invention> The core metal 10 is for fixing and stabilizing the surrounding refractories, but the linear expansion of the core metal 10 due to temperature rise is larger than that of the surrounding refractories. This leads to the occurrence of cracks at the construction boundary, and on the other hand, the heat deformation of the core metal 10 causes damage to the refractory material, which causes the base metal to penetrate into the refractory material, and furthermore, the core metal 10 is melted by the molten steel, which causes the immersion pipe to be damaged. There was a problem that the lifespan was rate-limiting.

As a conventional technique for solving the above-mentioned problems, for example, Japanese Patent Application Laid-open No. 5
Publication No. 8-96813 proposes a method of welding a cooling pipe to the cored metal, etc., to feed a mixed gas of steam and water and evaporate it in the cooling pipe to cool the cored metal. However, since water is passed through the immersed part of the molten steel to cool it down, there remains the problem that there is a risk of a steam explosion.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art as described above, and to provide a method for cooling a immersion tube that can cool a core metal and extend the life of the immersion tube without the risk of steam explosion. It is.

Means for Solving the Problems> The present invention focuses on the use of gas for cooling without the risk of steam explosion, unlike a steam/water mixture, and firstly, the tip of the immersion tube is castable and fireproof. We performed a heat removal model calculation in which N2 gas is flowed into a cooling pipe buried in an object to cool it.

When the average temperature of N2 gas is 300°C, Brunttle number Pr=0.7. Kinematic viscosity coefficient of fluid v = 0.5x
to-' fluid thermal conductivity λ-0,038 Kcal/m
-h ・'C, Nusocerdo number = 0.023XI? ed
'°"×Pr" (Red: Raynozzle number), and the average thermal conductivity α"' NuIm・λ/d=105.5 (
Kcal/po・h・'c).

Model l As shown in Figure 3, calculate the heat removal when considering only the heat from both sides, ignoring the heat from the top and bottom of the cooling pipe B buried at the tip of the castable refractory: Ll: The heating temperature T of nitrogen gas is as follows.

T1-(λl'T Do+α-L-T,)/(α
-L+λ, )-402°C λl: Heat transfer coefficient of castable refractory = 0.9kcaZ/ +rr h ”CToo: Surface temperature = 1600°C = Thickness from cooling pipe to surface of castable refractory w
o, t m T6=Gas average temperature -300'C Ten-Ichi-I As shown in Figure 4, heat from the top, bottom, and both sides of the cooling pipe B buried at the tip of the castable refractory was considered. Calculate the heat loss when. The heating temperature T of nitrogen gas,
is as follows.

T, = [a-T, -r ・mu (R/r) + λ+-'r
cX, )/(α・“・Z, 1(R/r)+λ,)=97
8°CR: Distance from the cooling pipe to the surface of the castable refractory - 0.1m r: Radius of the cooling pipe = 0.002m According to the heat removal model calculation above, the core metal was removed by nitrogen gas at 40°C.
It was discovered that a cooling effect of 2°C (core metal temperature: 978°C) can be expected, and was obtained as a result of various studies.

In the present invention, a cooling pipe is welded and fixed to a core metal of an immersion tube used for degassing molten steel, and one end of the cooling pipe is connected to a gas supply pipe, and the other end is connected to a gas blowing nozzle for reflux. The cooling gas supplied from the pipe is sent into the cooling pipe to cool the core metal, and then is blown as a reflux gas from the reflux gas blowing nozzle.

<Function> Since the cooling pipe is directly welded to the core metal of the immersion tube, the core metal is efficiently cooled by the cooling gas, preventing thermal deformation of the core metal and cracking of the refractory installed around the core metal. This not only prevents troubles caused by such problems, but also allows the gas used for cooling to be used as reflux gas.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. 1st
As shown in the figure, a cooling pipe 11 is wound and welded around the cylindrical core metal 10 fixed to the flange 15 of the rising immersion pipe 3a, and a reflux gas supply pipe is attached to the lower end of the cooling pipe 11. 4 are connected to each other, and a recirculation gas blowing nozzle 12 is connected to the upper end.

A brick refractory I3 and a monolithic refractory 14 are installed on both the inner and outer surfaces of the core metal lO to which the cooling pipe 11 is welded.

Cooling gas such as inert gas supplied from the reflux gas supply pipe 4 indirectly cools the core metal l by cooling the cooling pipe 11.
While cooling O, it rises, is blown into the rising immersion pipe 3a from the reflux gas blowing nozzle 12, and is used for refluxing the molten steel.

S tJ S vibe is suitable as the cooling pipe 11.
Since the structure is such that the cooling pipe 11 is welded to the outer peripheral surface of the core metal 10, manufacturing is easy.

According to a model calculation when the cooling gas supplied from one side of the cooling pipe 11 is N and the gas is 40ON l/-, it has been obtained that it is possible to sufficiently cool the core metal, and it is actually possible to cool the core metal sufficiently. The amount of gas used as reflux gas is 20
00 to 250 ONp/night, which allows for more than enough cooling.

The diameter of the cooling pipe 11 is 25 mmφ, and the diameter of the reflux gas blowing nozzle is 6 Mφ, and the diameter is 1 mm toward the inner peripheral surface of the rising immersion tube 3a.
It is common to arrange about two.

Static gas is commonly used as a cooling gas, but static gas is expensive, so in addition to Ar gas, N2 gas and CO are used.

Gases are used singly or in combination, and depending on the purpose, island gas, air, hydrocarbon gas (propane), etc. are added.

FIG. 2 shows a rising immersion pipe 3a according to the present invention shown in FIG.
This figure shows a comparison of the temperature changes of the core metal during degassing operations when using a immersion tube with only a core metal without a cooling tube and when using an immersion tube with only a core metal without a cooling tube.

Figure 2 shows that according to the conventional method, the core metal reaches over 1000°C, but according to the method of the present invention, the temperature can be lowered to 700°C or less, although it varies depending on the operating conditions, and the life of the immersion tube can be significantly extended. Can be extended.

<Effects of the Invention> As explained above, according to the present invention, it is possible to efficiently cool the immersion tube core metal by using the reflux gas as a cooling gas without the risk of breaking the immersion tube core metal, thereby extending the life of the immersion tube. is,
It has a great effect on reducing the cost of repair materials for dip pipes.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a rising immersion nozzle according to an embodiment of the present invention, FIG. 2 is a graph showing the temperature transition of the core metal during degassing operation, and FIGS. 3 and 4 are views of the immersion tube. An explanatory diagram showing heat removal model conditions, and FIG. 5 is a longitudinal cross-sectional view showing a conventional vacuum degassing method. Figure 1: Dipping tube, a... Dipping tube for rising, b... Dipping tube for descending, ... Gas supply pipe for reflux, ... Core metal, ... Cooling pipe, ...・Recirculation gas injection nozzle, ... Brick refractories, ... Monolithic refractories. Figure 2 Degassing time (h)

Claims (1)

[Claims] A cooling pipe is welded and fixed to the core metal of the immersion tube used for degassing molten steel, and one end of the cooling pipe is connected to a gas supply pipe, and the other end is connected to a gas blowing nozzle for reflux, and the gas is supplied from the gas supply pipe. A method for cooling a immersion tube for degassing molten steel, characterized in that the cooling gas is fed into the cooling pipe to cool the core metal, and then blown as a reflux gas from the reflux gas blowing nozzle.