JPH0737644B2 - Vacuum degassing device Splashing prevention method in exhaust gas duct - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for preventing attachment of splash in an exhaust gas duct of a vacuum degassing apparatus, and more particularly to an RH vacuum degassing apparatus having an upward blowing lance that hangs down from the center of an upper lid. TECHNICAL FIELD The present invention relates to a method for preventing molten steel splash adhesion in an exhaust gas duct in degassing molten steel by an apparatus.

[Conventional technology]

Recent RH recirculation type vacuum degassing equipment has a large flow rate of blown gas,
In addition to increasing the reflux rate, refining by injecting inert gas and oxygen blowing in a vacuum degassing tank has become popular, and the adhesion of molten steel splash to the inner wall of the tank has become severe. In particular, due to the recent increase in degassing materials for ultra-low carbon steel such as steel sheets for automobiles, the blowing gas is 4000-5000 Nl / m.
The diameter of the immersion pipe has been expanded to increase the in flow rate,
Furthermore, with the aim of increasing the reaction interfacial area, gas is sprayed in the tank, obliquely blown from the wall of the lower tank, and blown laterally.

As shown in FIG. 3, these molten steel splashes adhere and deposit not only on the inner wall 4 of the vacuum degassing tank 2 but also on the exhaust gas duct 6, expansion joint 7, and exhaust gas cooler 9 to reduce the inner diameter of the duct and cause pressure loss. As a result, the operation has become obstructed and the product quality has also deteriorated. In particular, the exhaust gas duct 6 is required to have a high vacuum at an early stage due to the spraying of ultra-low carbon steel. Therefore, a vacuum system having a large exhaust capacity with an extremely short exhaust time is adopted, and the splash 8 is exhausted. It is easily sucked into the gas duct 6. Splatsyu 8
If adhered to and accumulated in the exhaust gas duct 6, the flow path of the duct 6 becomes small and pressure loss occurs, so that a high vacuum degree in the tank cannot be obtained, and also adheres to the exhaust gas cooler 9 to hinder the exhaust gas cooling effect. It is extremely important to take countermeasures because it will cause a major obstacle to the operation such as deterioration of the vacuum exhaust performance. In the past, however, the splash deposit 8A was manually removed, but this work requires high heat and the working environment is poor.

As one of the countermeasures, by increasing the height of the degassing tank 2, the height which was conventionally about 9 to 10 m is recently increased to 11 to 12 m, but there is a limit to this. The current situation is that we are struggling with measures.

As a method for collecting metal in a vacuum degassing tank, Japanese Patent Laid-Open No. 19721/1983
There is a method disclosed in 2. This method blocks most of the pores in the vacuum degassing tank at the time of non-treatment after the degassing treatment, blows in oxygen to melt the deposited metal of the splash 8 and let it flow out through the dipping pipe 10, Although there is a method of receiving it with a ladle or pot installed, it may be effective as a method of removing deposited metal, but as a countermeasure, it is biased towards cleaning and aggressive measures are desired.

[Problems to be solved by the invention]

The object of the present invention is to provide a vacuum degassing tank, in particular oxygen, N ₂ , Ar on top.
The degassing tank with a vertically adjustable lance that blows up gas such as the above reduces the problems of the above-mentioned conventional technology with respect to the adhesion of molten steel splash that occurs during operation, and in particular the adhesion of splash to the exhaust gas duct that most hinders operation. To provide an effective way to prevent.

[Means for solving problems]

The gist of the present invention is as follows. That is, in the method for preventing molten steel splash adhesion to the inner wall of the molten steel at the time of degassing the molten steel by the degassing device for molten steel by the vacuum degassing device having a lance capable of moving up and down to blow gas such as oxygen and argon in the upper part. Injecting an inert gas from the upper blowing lance, the outer peripheral portion of the downward spread angle is the lower end of the exhaust gas duct connection portion of the device,
Alternatively, it is a method for preventing the attachment of the splash in the exhaust gas duct of the vacuum degassing apparatus, which comprises spraying so as to collide with a lower inner wall position.

Prior to the description of the present invention, an outline of a refining method using a vacuum degassing apparatus to which the present invention is applied will be described with reference to FIG.

C: 0.03 to 0.05% of molten steel 12 that was roughly decarburized in a primary refining furnace such as a converter is stored in a ladle 14 and secondarily refined in a vacuum degassing device until an extremely low carbon steel with C ≤ 20 ppm. Decarburized. The vacuum degassing tank 2 has an ascending dip pipe 16 and a descending dip pipe 18 at the lower end, both of which are immersed in the molten steel 12 in the ladle 14, and the surface of the molten steel 12 is tapped together when tapping the converter. It is covered by 13.

A blowing device 22 such as a porous plug for blowing a reflux gas 20 such as Ar is provided on the inner circumference of the lower end of the ascending dip pipe 16, and the vacuum degassing tank 2 is provided with 0.1 to 50 Torr through the exhaust gas duct 6 at the upper part. Since the molten steel 12 in the ladle 14 is sucked up into the vacuum degassing tank 2 by the principle of the gas lift pump, the molten steel 12 decarburized and degassed in the tank is a descending dipping pipe.
Return to the ladle 14 again via 18. Secondary refining is carried out by repeating this process, but an upper blowing lance 2 is provided above the vacuum degassing tank 2 so as to pass through the upper lid 24 and is movable up and down. An inert gas such as N ₂ or Ar is blown in. The upper blowing lance 26 has a triple pipe structure, the outermost double pipe serves as a reciprocating pipe for the cooling water 28, and the central pipe serves as a supply pipe 30 for an inert gas such as O ₂ or N _2. ing. As shown in FIG. 2, a lance seal device 32 is provided and sealed in a penetrating portion of the upper lid 24 of the upper blow lance 26, and a ring provided around the upper blow lance 26 is provided around the seal device 32. An inert gas purge pipe is opened through the pipe 34. Further, the upper lid 24 is provided with an additive alloy charging port 38 and a peep window 40.

In the vacuum degassing apparatus 2 having such a structure, when refining ultra-low carbon steel for decarburization refining by blowing oxygen, etc., as described above, a large flow rate of Ar gas blown from the ascending dip pipe 16 and By blowing oxygen from the blow lance 26,
As described with reference to the conventional apparatus of FIG. 3, the molten steel splash 8 is deposited not only on the inner wall 4 but also on the exhaust gas duct 6 to hinder the operation and deteriorate the product quality.

The present invention adopts the following method as means for solving the above conventional problems. That is, by utilizing the upper blowing lance 26 shown in FIG. 1, the inert gas such as Ar, N ₂ or the like is passed from the oxygen refining lance hole of the upper blowing lance 26 in the direction opposite to the direction in which the splash 8 is rising. Spray downward. By causing a collision between the splash 8 that rises with the exhaust gas by this injection and the inert gas in the degassing tank 2, the large splash 8 that has been conventionally sucked may be dropped, or It is possible to prevent the exhaust gas 6 from being sucked up. In order to magnify this effect, the downward spread angle θ of the gas blown out from the upper blow lance 26 is, as shown in FIG. 2, the outer peripheral portion of the spread angle θ, and the lower end 6A of the connecting portion of the exhaust gas duct 6. Or, it must be sprayed to impinge on the inner wall 4, which is lower than that.

At the same time as spraying the inert gas from the upper spray lance 26,
For the splash 8 that has hitherto hit the upper lid 24,
Purge piping through the ring piping 34 of the lance seal device 32
Spray inert gas downward from 36. Incidentally, the sealing device for the penetrating portion of the upper lid 24 of the upper blowing lance 26 is as disclosed by the applicant in Japanese Utility Model Application Laid-Open No. 63-183256.

The above is the most preferable mode in the case where oxygen blowing is not performed by the upper blowing lance 26, which is the limited direction blowing of the inert gas by the upper blowing lance 26 and the purge pipe 36 around the lance seal device 32. Due to the combination of the downward spraying of the inert gas from the above, the suction attachment of the splash 8 to the conventional exhaust gas duct 6 was significantly reduced.

Next, as in the case of refining ultra-low carbon steel, during the operation of oxygen blowing from the upper blowing lance 26, the upper blowing lance 26 is lowered and positioned directly above the reflux molten steel 12A, so that the inert gas from the purge pipe 36 Only downward spraying.

The gas injected from the upper blow lance 26 and the purge gas blown downward from the purge pipe 36 are not particularly limited as long as they are inert gases, but nitrogen gas is usually used in terms of price.

〔Example〕

The top-blowing lance 26 used in the present invention can have a great effect on the top-blown refining of oxygen during the decarburization operation of ultra-low carbon steel, etc. For prevention, N ₂ gas up to about 1 m ³ / min is used as a purge gas. After the top blowing lance 26 is blown with oxygen, it is used to prevent splashing during other RH operations, especially 1.5 m ³ / min, pressure 7 kg / min to prevent splashing into the exhaust gas duct 6. cm ² G N ₂
The gas was injected according to the method of the present invention, and at the same time, N ₂ gas was blown downward as a purge gas from the purge pipe 36 through the ring pipe 34 of the lance seal device 32. Due to this spraying, the large-sized splashes 8 fall, the splashes 8 can be prevented from entering the exhaust gas duct 6, and the purge gas from the purge pipe 36 also has a flow rate of 1 m ³ / min or more, the upper lid 24 Adhesion to the splash can be significantly reduced compared to the conventional one, and the splash removal work has been performed once for 1,000 vacuum degassing treatments, but by implementing the present invention, it can be significantly reduced to a rate of once every 5000 charges. Natsuta.

(Effect of the invention) The present invention utilizes the opportunity not to carry out the oxygen top-blowing operation of the top-blowing lance attached to the RH vacuum degassing apparatus, and the N ₂ gas from the top-blowing lance is 1.5 m ³ / min, pressure. At 7 kg / cm ² , the outer peripheral part of the downward spread angle is blown so that it collides with the lower end of the exhaust gas duct joint or the inner wall position lower than it, and at the same time, the upper lid piercing part of the upper lid penetrates. By blowing N ₂ at 1 m ³ / min or more also from the purge pipe, the following effects could be achieved.

(A) Since the molten steel splash was almost prevented from entering the exhaust gas duct and accumulating, the pressure loss of the flow passage and the obstruction of the high vacuum degree in the tank as in the past were eliminated, and smooth RH operation became possible.

(B) As for the splashes adhering to the inner wall of the vacuum degassing tank, the large-sized splashes drop according to the present invention, so that the grain size becomes fine and the removal work is facilitated.

(C) In the RH degassing device of 1 charge 275t, the conventional 3
2 workers took 4 hours to remove the splash.
It took only one hour to complete the work, and it was reduced to 1/6.

Moreover, it is now possible to reduce the splash removal work once every 1000 charges to once every 5000 charges, and as a result, it has been possible to improve productivity and significantly reduce work labor.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an apparatus showing a method for preventing attachment of splashing in an exhaust gas duct of a vacuum degassing apparatus (RH-KTB) according to the present invention, and FIG. 2 is an inert gas from an upper blowing lance and a lance seal apparatus. Enlarged sectional view showing the injection situation,
FIG. 3 is a cross-sectional view showing the state of attachment of splashing on the inner wall of a conventional vacuum degassing apparatus. 2 ... Vacuum degassing tank, 4 ... Inner wall, 6 ... Exhaust gas duct, 7 ...
… Expansion joints, 8 …… Splash, 9 …… Exhaust gas cooler, 1
0 …… Immersion pipe (generic name including rising and lowering), 12 …… Molten steel, 12A …… Reflux molten steel, 13 …… Slag, 14 …… Ladle, 16 ……
Ascending dip tube, 18 …… Descent dip tube, 20 …… Reflux gas, 22 ……
Blow-in device, 24 ... Top lid, 26 ... Top blow lance, 28 ... Cooling water, 30 ... Inert gas supply line, 32 ... Lance seal device, 34 ... Ring pipe, 36 ... Purge pipe, 38 …… Additional alloy inlet, 40 …… Peep window

Claims (1)

[Claims] 1. A molten steel splash attachment to the inner wall of a molten steel degassing apparatus by a degassing apparatus for molten steel by means of a vacuum degassing apparatus having a lance capable of ascending and descending to blow gas such as oxygen and argon on the upper part. In the prevention method, an inert gas is jetted from the upper blowing lance and is blown so that the outer peripheral portion of the downward spread angle collides with the lower end of the exhaust gas duct connection portion of the device or the inner wall position lower than that. A method for preventing adhesion of splash in exhaust gas duct of vacuum degassing device, which is characterized in that