JPH05331525A - Method for cooling immersion tube - Google Patents

Abstract

PURPOSE:To safely and effectively cool an immersion tube and to extend the service life of the immersion tube by arranging a passage around a core metal in the immersion tube for treating molten steel and flowing gas mixing fine water drips. CONSTITUTION:The immersion tube 1 for circulating the molten steel into a ladle and a treating vessel in order to execute degassing refining, component adjustment, etc., to the molten steel is constituted by arranging a refractory 3 around the core metal 2. In order to prevent the erosion of the core metal 2 caused by heating with the high temp. molten steel, the development of longitudinal crack to the refractory 3 caused by heat expansion of the core metal 2 and the breakage of the immersion tube 1 caused by contacting with the molten steel, a cooling furnace 4 composed of a half-cutting pipe is formed around the core metal 2, and by introducing cooling medium 5 from an inlet 4a and discharging from an outlet 4b, the immersion tube 1 is cooled. As the cooling medium 5, the gas 10 such as air, etc., and the clean water 9 are supplied into the water drip classifier 7 and the clean water is supplied as the fine water drips having <=30mum together with the air 10 into the cooling passage 4 from a fog generating nozzle 8 through a carrying pipe 6. Apparent sp. heat of the colling medium 5 is increased by mixing the water drips and also, the immersion pipe 1 is effectively cooled with large vaporizing latent heat of the water drips.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cooling a dip pipe used in equipment for degassing molten steel, adjusting the composition of molten steel, refining, and the like, and is intended to realize particularly safe cooling.

[0002]

2. Description of the Related Art In equipment for degassing molten steel, equipment for adjusting the composition of molten steel, refining equipment, etc., a dip tube consisting of a combination of a steel-made tubular core metal and a refractory surrounding it is used. It is customary to carry out treatments such as degassing and component adjustment by immersing in the molten steel. And since the processing temperature of molten steel is around 1600 ° C, in the degassing treatment of molten steel such that the processing time extends to 20 to 40 minutes, the temperature of the core becomes higher than 1000 ° C while repeating the processing. .. Therefore, in the immersion pipe, insertion of the metal into the joint of the refractory due to the high temperature creep phenomenon of the core, melting of the core due to molten steel or vertical cracking of the refractory due to expansion of the core occurs. , Its life is extremely short, and it was necessary to repair it frequently under severe conditions at high temperature.

As an attempt to deal with such a problem, Japanese Patent Laid-Open No.
In the 58-96813 publication, it is arranged near the core metal of the immersion pipe,
A method is disclosed in which a gas body such as air or nitrogen and water as an atomized liquid are fed into a double pipe or a cooling pipe to cool a cored bar.

[0004]

In the above cooling method,
It is possible to improve the cooling capacity by mixing atomized water with gas, but in order to move the atomized water to the lower part of the immersion pipe, the water droplets collide with the inner wall of the cooling pipe and the like. It is necessary to maintain the mist form while adhering. However, as the water droplets repeatedly collide with and adhere to the tube wall, the water droplets grow into larger water droplets, and further, the water droplets aggregate into a water flow, so that the desired cooling capacity cannot be obtained, and The danger of a steam explosion if the cooling medium passages are melted down has not been eliminated.

Therefore, an object of the present invention is to propose a method for cooling an immersion pipe which has a high cooling effect and is free from the risk of steam explosion.

[0006]

Means for Solving the Problems The inventors of the present invention have made various studies on the above-mentioned problems, and found that when atomized water is used as a cooling medium, the water droplet diameter has a suitable range. Came to complete.

That is, according to the present invention, when the cooling medium is supplied to the passage provided around the core of the immersion pipe to cool the immersion pipe, the cooling medium is a gas mixed with water droplets having a diameter of 30 μm or less. It is a method for cooling an immersion pipe, which is characterized in that In practice, it is advantageous to use at least one selected from air, nitrogen and water vapor as the gas.

Now, FIG. 1 shows a cooling device for an immersion pipe used in the present invention. First, the immersion pipe 1 shown has a general structure in which a refractory material 3 is arranged around a core metal 2, and a cooling passage 4 formed by fixing a half pipe to the peripheral wall of the core metal 2 is arranged. The cooling medium 5 is introduced from one opening 4a of the cooling passage 4, the cooling medium 5 is guided by the passage 4 and moves along the cored bar 2, and then is discharged into the atmosphere from the other opening 4b. It On the other hand, the cooling medium 5 passes through the carrier pipe 6,
It is supplied from the water drop classifier 7.

The water drop classifier 7 introduces purified water 9 and gas 10 to a fog generating nozzle 8 disposed inside the fog generating nozzle 8 and atomizes the purified water 9 by the gas 10 at the tip of the nozzle 8. According to the diameter of the water droplet, the classification is performed with a diameter of 30 μm as a boundary, large water droplets are settled in the lower part of the classifier 7, and fogs having a water droplet diameter of 30 μm or less are sent to the carrier pipe 6 as the cooling medium 5. The large-diameter water droplets settled in the lower part of the water droplet classifier 7 are guided to the drain groove 12 by opening the drainage 11.

Here, the classification mechanism of the water drop classifier 7 will be described in detail. The rate at which water droplets with a diameter of 30 μm settle in the atmosphere is about 4 cm / s. Therefore, if the flow rate of the gas rising in the classifier is set to the same level as this, water droplets with a diameter of more than 30 μm will settle in the classifier, and water droplets with a diameter of 30 μm or less will be led out of the classifier together with the rising gas. ..

Further, the fog generating nozzle 8 is not a general one for generating water droplets having an average diameter of about 50 μm, but jet jets enclosing the droplets which are miniaturized by the shearing action of the jet gas are made to collide with each other. It is preferable to use a water droplet having an average diameter of about 6 μm, which is in a form of further miniaturizing the droplet by utilizing mutual shearing action and ultrasonic waves of tens of thousands of hertz generated at that time.

The cooling passage 4 has a structure in which the half-divided pipe shown in FIG. 1 is fixed, a normal cylindrical pipe is fixed, or the core metal itself has a double wall structure, and its inner wall is formed. A cooling passage may be formed between the outer wall and the outer wall.

[0013]

When a mixed fluid of water droplets and gas having a small diameter is used as the cooling medium introduced into the cooling passage of the immersion pipe, the cooling efficiency of the immersion pipe is remarkably improved. However, if the diameter of the water droplets in the cooling medium is large in the process in which the cooling medium travels through the straight portion or bend portion of the cooling passage, it will adhere to or collide with the wall surface of the cooling passage and stay there. Therefore, it is difficult to transport water droplets in a suspended state. Here, there is a risk of cooling efficiency reduction and steam explosion, and in order to avoid these disadvantages, it is necessary to transport water droplets in a suspended state.

Therefore, as a result of studying the diameter of water droplets that can be transported in a floating state regardless of the shape of the cooling passage, it was newly found that the floating state can be maintained if the water droplet diameter is 30 μm or less. That is, since the water droplets having a diameter of 30 μm or less can move along with the airflow and follow the change in the direction of the airflow, the water droplets can be transported in a floating state from the start end to the end of the cooling passage.

A gas containing water droplets having a diameter of 30 μm or less can be expected to have a great cooling effect because the apparent specific heat of the gas increases due to the mixing of the water droplets. It is essentially different from spraying and mist cooling. Furthermore, since almost all water droplets with a large latent heat of vaporization evaporate, only a small amount of water droplets need to be mixed in. The volume expansion of the gas after evaporation is 2 times that of a gas of the same temperature.
It becomes less than double and no sudden volume expansion occurs. Therefore, as compared with water, which is in contact with leaking steel or the like and expands in volume 1000 times to cause a steam explosion, higher safety can be imparted.

The ratio of gas to water droplets in the cooling medium is largely influenced by the characteristics of the fog generating nozzle, but in order to generate fine water droplets with good yield, the jet energy and a predetermined amount of water are required. It is necessary to set the water mixing rate from the balance with the energy required for refining water. For this reason, the water mixing ratio is 1 (kg
-H ₂ O / kg-Air) is preferable.

[0017]

[Example] In a vacuum tank of an RH-type vacuum degassing equipment with a molten steel recirculation velocity of 180 t / min and a processing amount of 285 t per treatment, a core metal with an inner diameter of 1100 mmφ, a thickness of 16 mm and a height of 600 mm was used. When the molten steel is degassed by arranging the immersion pipe (inner diameter: 750 mmφ) of the structure shown in Fig. 1, which is composed of refractory materials, water: 0.5 Nl / min according to the place shown in Fig. 1. And air: 1.2 Nm ³ / min was supplied to the fogg generating nozzle 8 to cool the dip tube using air (fogg) containing 99% by weight of water droplets having a diameter of 30 μm or less as a cooling medium. After performing this process for 62 hours, switch to a process that uses air (mist) that has changed the classification nozzle and changed the average water droplet size to 50 μm (20-100 μm) as the cooling medium, and continue this process for 10 hours. Then, the supply of water to the fog generating nozzle was stopped, the immersion tube was cooled only by air, and 8 hours later, the supply of air was stopped.

The temperature of the core metal after the above (1) fog cooling step, (2) mist cooling step, (3) air cooling step, and (4) cooling stop is shown in FIG. 80m
The results of measurements at m), B (190 mm from the lower end of the core) and C (300 mm from the lower end of the core) are shown in FIG. From the figure, it can be seen that the cooling effect in the cooling using the fog is extremely high as compared with the other steps.

Further, when the treatments to which the cooling steps (1) to (3) are applied are performed for the same treatment time, the cost of the cooling medium used for keeping the temperature of the cored bar at a constant temperature is reduced. ,
(3) Index based on 100 for the air cooling process,
It shows in Table 1. Furthermore, regarding the results of investigating the life until the lower part of the immersion pipe is deformed into a trumpet shape or it becomes unusable due to the limit of vertical crack repair in the treatment applying the cooling process of (1) to (3) above Also, (3) is an index based on 100 in the case of the air cooling step, and is also shown in Table 1.

[0020]

[Table 1]

[0021]

According to the present invention, it is possible to realize the cooling of the dip tube which has a high cooling effect and is free from the risk of steam explosion, and the life of the dip tube can be dramatically improved and at low cost.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating a method for cooling an immersion pipe according to the present invention.

FIG. 2 is a graph showing the cooling effect of the immersion pipe.

[Explanation of symbols] 1 immersion pipe 2 core metal 3 refractory 4 cooling passage 4a opening 4b opening 5 cooling medium 6 carrier pipe 7 water drop classifier 8 fogging nozzle 9 clean water 10 gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobumoto Takashiba 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (no house number) Inside the Mizushima Works, Kawasaki Steel Co., Ltd. (72) Michihiro Kuwayama, Kawashima-dori, Kurashiki-shi, Okayama Prefecture 1-chome (without street number) Inside Kawashima Steel Co., Ltd. Mizushima Steel Works (72) Inventor Masato Mizuto 1-chome (without street number) Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture Kawasaki Steel Co., Ltd. within Mizushima Steel Works

Claims (2)

[Claims] 1. When the cooling medium is supplied to a passage provided around a cored bar of the immersion pipe to cool the immersion pipe, the cooling medium is formed by mixing gas with water droplets having a diameter of 30 μm or less. A method for cooling an immersion pipe, comprising: 2. The method for cooling an immersion pipe according to claim 1, wherein at least one selected from air, nitrogen and water vapor is used as the gas.