JPH02301526A - Method and device for generating fine bubble in molten metal - Google Patents

Abstract

PURPOSE:To efficiently form a large amt. of fine bubbles in molten metal by blowing a subsonic gas from a tuyere opened in the molten metal to generate bubbles and simultaneously allowing a supersonic gas jet to collide with the bubbles from another tuyere set in the tuyere. CONSTITUTION:A gas supply pipe 52 having a refractory 54 and a permeable refractory 56 is dipped in molten metal 50 to form a first tuyere, plural through holes 58 having a small diameter (<=2mm) and piercing the permeable refractory 56 are formed in the permeable refractory 56 to form a second tuyere as the discharge hole 60 for a gas jet. When a subsonic gas 62 is blown from a gas supply pipe 52 and passed through the permeable refractory 56 under such a constitution, the deposited bubbles 66A are spread to a region A slightly away from the surface of the permeable refractory 56. Meanwhile, the gas jet 64 passed through the through hole 58 collides with the inner surface of the deposited bubble 66A to break through the deposited bubble 66A, hence fine bubbles 66B are formed in a region B, and the bubbles are diffused as far as a region C. Consequently, a large amt. of fine bubbles 66B are generated by this simple device, and the efficiency in removing the inclusion and the degasification efficiency are improved.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method and apparatus for generating microbubbles in molten metal, and is effective for promoting metal scouring reactions and removing nonmetallic inclusions. This invention relates to an effective method and device for generating microbubbles using a simple device, and is widely used not only in the steel manufacturing field but also in other metal smelting fields.

[Conventional technology]

It is widely known that metal scouring reactions can be promoted and nonmetallic inclusions can be removed by generating fine bubbles in molten metal. For example, Japan Iron and Steel Institute Lecture Proceedings C
AMP-ISIJ Vol, 1 (19,
88) P, 1161-1164 states that by blowing fine bubbles into molten steel under atmospheric pressure, the removal efficiency of inclusions is dramatically improved, and that the degassing efficiency under reduced pressure due to bubbles is improved. A significant improvement has been reported.

Also, Sumitomo Light Metal G Technical Report Vo1.26, Nn 2 (A
Pril 1985) P, 21-30 reports that the injection of fine bubbles is effective for removing inclusions and degassing even in aluminum smelting. In other words, when processing molten aluminum, the more microbubbles are generated, the larger the contact surface area between the bubbles and the liquid metal, promoting the reaction between gas and liquid. , it is easier to trap inclusions with a large number of fine bubbles, and the separation effect is also greater. Furthermore, when microbubbles are used, there is less turbulence at the interface when the bubbles break on the surface of the molten metal, which reduces the risk of contamination caused by the reaction between slag and molten metal, and floating inclusions. It is reported to have the advantage of less re-entrainment and less splashing.

As a result, the development of technology for generating large amounts of fine bubbles in molten metal has been underway for quite some time. The most
A common prior art technique is to blow gas into molten metal through a porous refractory material called a porous nozzle, but this generally results in poor wettability between the molten metal and the refractory material. Conventionally, the bubbles generated from the micropores on the surface of the refractory coalesce and grow, and it was extremely difficult to obtain fine bubbles in that state.

In order to solve this problem, Japanese Patent Application Laid-Open No. 59-226129
In ``In the case where gas is blown into a molten metal container using an blown plug made of porous refractory provided at the bottom of the molten metal container, and impurities in the molten metal are floated and removed, the amount of blown gas per 100 d of working surface area of the molten metal container. "A method for generating microbubbles using a breathable refractory, characterized by reducing the pressure to 14.2N for 1 minute or less."

Furthermore, Japanese Patent Application Laid-open No. 58-58965 states, ``A porous refractory is attached to the bottom of a molten steel storage container such as a tundish, and an inert gas is injected at a rate of 0.00% per unit contact area between the molten steel and the porous refractory.
While blowing at a rate of 016 to 1.4 NL/win, ci, the molten steel is stirred by an electromagnetic stirring device installed at the bottom of the container, and the molten steel flow rate at the gas injection part is set to 20 am/see or higher.
A method for producing a clean steel with a hardness of less than 80 cm/see is disclosed.

In addition, as shown in Figure 6, in Special Publication No. 63-26169,
A magnetic force is applied to the steel 2 in the lower part of the container by an electromagnetic coil 4 to generate a molten steel flow 6 of 0.8 m/see, and the molten steel flow 6 is passed from a plug 10 through a gas pipe 8. ``Method for cleaning molten steel by adding inert gas.'' Furthermore, as shown in FIG.
In addition to generating a molten steel flow 6 with a flow rate of at least m/see, an immersion agitator 12 is provided, and the immersion agitator 12 is rotated by a motor M. At the same time, a gas body 15 is generated through gas pipes 14A and 14B.
A method for cleaning molten steel by blowing and adding a refining agent 16 at the same time;
' is also disclosed.

Further, in Japanese Patent Application Laid-Open No. 62-192240, as shown in FIG.
Gas discharge part 20 formed of porous refractory material at the tip of 8
, a gas passage 22 formed in the lance body 18 and supplying the gas 15 to the gas discharge part 20, and the lance body 18.
A molten metal bubbling device characterized by comprising a rotating means for rotating the molten metal bubbling device around its axis. ' has been disclosed.

In addition, the Sumitomo Light Metal Technical Report Vol. 1.26 shown above.

Ha 2 shows various embodiments of inert gas nozzles for blowing in for degassing aluminum, and as shown in FIG. Rotating body 26 rotating at high speed
Also shown is a nozzle that generates microbubbles 28 by shearing at .

As described above, in many conventional methods for generating fine bubbles, the flow rate of the molten metal in the gas blowing section is limited to a specific value or more by stirring the molten metal or rotating the blowing device. However, in order to blow in the required amount of gas, a large area of the blowing tuyere operating surface is required, which is impractical in terms of repair costs and equipment life.

Furthermore, as in the prior art described above, in order to generate molten metal flow, an immersed rotating stirrer or an electromagnetic stirring device is naturally required.
In addition to the large size of the equipment, there are disadvantages such as increased wear and tear on the refractories due to the flow of molten metal.

On the other hand, as another method or apparatus for generating microbubbles in molten metal, there is Japanese Patent Publication No. 61-56301 as shown in FIG. This invention is characterized by blowing a gas jet with a flow velocity of about 2 Matsuha number at an angle of 20" or less with respect to the liquid surface of the molten metal, and causing the core of the gas jet to collide with the liquid surface. A method for generating microbubbles in molten metal is disclosed.

In this case, as shown in FIG. 10, gas is blown from a gas blowing pipe 32, a ceramic nozzle 34 having a plurality of small holes of 0.5 to 1 mφ is attached to the tip, and an exhaust port is provided at the top. In addition to 36, a cover 40 is provided to prevent outside air from being drawn in and splash 38.

In addition, JP-A-59-153822 describes, ``In a method for removing inclusions in molten steel in a tundish for iron-making, powder with a diameter of 3 to 100 microns that generates fine bubbles by thermal decomposition is added to the molten steel in the tundish. A method for removing inclusions in molten steel characterized by blowing is disclosed.

However, in the former case, the molten metal is scattered a lot due to the gas jet being blown at a small angle of 20 degrees or less, and there are also problems in maintenance around the nozzle. In addition, the amount of bubbles generated is extremely small compared to the amount of gas used, and as a result, in applications other than removing inclusions, it is not possible to obtain an effect superior to the above conventional technology considering the amount of gas used. The latter invention also requires a device to blow fine powder into the molten metal, and the gas that is blown into the molten metal along with the powder also generates very large bubbles, so the interface between the molten metal, slab, and heat insulating material is disturbed,
It has disadvantages such as causing pollution.

[Problem to be solved by the invention]

An object of the present invention is to solve the problems of the prior art related to the method and device for generating microbubbles in molten metal, and to provide a method and device for efficiently generating a large amount of microbubbles using a simple device. This is what I am trying to do.

[Means to solve the problem]

The above object of the present invention is achieved by the method for generating microbubbles according to the present invention as summarized below. That is, (1) Subsonic gas is injected into the molten metal through a first tuyere opened to generate bubbles, and at the same time, bubbles are generated through a plurality of thin tubes with a diameter of 2I or less provided in or around the first tuyere. A method for generating microbubbles in molten metal, which comprises blowing a gas jet at a speed higher than the speed of sound through a second tuyere and colliding with the bubbles generated from the first tuyere.

Further, the objects of the present invention are all achieved by the microbubble generating device as summarized below. That is, (2) a first tuyere consisting of a gas supply path that opens into the molten metal and has a gas permeable refractory at the open end;
or a second tuyere consisting of a plurality of thin tubes with a diameter of 21 or less arranged on the outer periphery of the tuyere and generating a gas jet at the speed of sound or higher.

(3) a first tuyere consisting of a gas supply pipe that opens into the molten metal and has an average flow velocity of subsonic in the cross section of the tip opening;
A second tuyere consisting of a plurality of thin tubes having a diameter of 211 m or less and disposed within the opening of the tuyere and/or around its outer periphery and generating a gas jet at the speed of sound or higher. Micro bubble generator. It is.

First, an embodiment of a microbubble generating device according to the present invention will be described with reference to FIG.

A gas supply pipe 52 is immersed in the molten metal 50,
The gas supply pipe 52 is lined with a refractory 54 on the outside, and a breathable refractory 56 is attached to the inside of its tip, which forms the first tuyere A according to the invention. A plurality of small-diameter through holes 58 are formed in the breathable refractory 56 , and one through hole 58 serves as a gas jet discharge hole 60 on the surface where the breathable refractory 56 faces the molten metal 50 . The second wing B is formed as a whole. A subsonic gas 62 is supplied to the first tuyere A and a supersonic gas jet 64 to the second tuyere B from different supply sources via headers or the like to the first tuyere A and the second tuyere B.
supply.

The reason why the blowing flow velocity of the gas 62 supplied from the first tuyere A needs to be as low as possible in the subsonic range, and the flow velocity of the gas jet 64 discharged from the second tuyere B is set to be higher than the sonic velocity. When this is caused to collide with the coarse bubbles 66A formed at the first tuyere A.

The splash of molten metal 50 increases at the interface of the jet collision part, and as a result, the interface is disturbed, and as a result, the coarse air bubbles 66A are promoted to become finer, and become fine air bubbles 66B. For this purpose, the flow velocity needs to be higher than the sonic velocity, so the flow velocity of the gas jet 64 is limited to the sonic velocity or higher. Therefore, the size of one through hole 58 is generally set to 2 for removing inclusions and promoting metallurgical reaction.
Onφ or less is required, so the diameters of the plurality of through holes 58 forming the second tuyere B are all limited to 2unφ or less.

Another embodiment of the microbubble generating device according to the present invention will be explained with reference to FIG. In this case, the gas supply pipe 52 forming the first tuyere A opens directly into the molten metal 50. The second tuyere B is formed from a plurality of thin tubes 68 spaced apart by a certain distance on the outer periphery of the first tuyere. For example, as shown in Figure 3,
The lower ends of the double tubes of the inner tube 67 and the outer tube 69 are joined to join the joint 7.
Set it to 0.

The gas supply pipe 52 is an inner pipe 67, and the subsonic gas 6
2 passes through the inside of the inner tube 67, which becomes the first layer A, and the gas 64, which has a speed higher than the speed of sound, is introduced from the gap between the inner tube 67 and the outer tube 69, and flows into a plurality of thin tubes opened at the joint 70 at the lower end. 68, which collectively forms the second tuyere B. In this case as well, the inner diameter of the thin tube 68 is 2 mφ or less, and the gas jet 64 as a whole is discharged at a flow velocity higher than the speed of sound.

Also in this case, the gas 62 supplied from the first wing A and the gas jet 64 discharged from the second tuyere B are supplied from different independent supply sources. The flow velocity of the gas 62 blown from the first tuyere A may be lower than the sonic velocity as long as it can prevent the molten metal 50 from being inserted.
Rather, if it is not necessary to generate a large number of coarse bubbles 66A, it is better to suppress the flow rate as much as possible.

On the other hand, the flow velocity of the gas jet 64 discharged from the second tuyere B needs to be higher than the sonic velocity in order to violently disturb the outer periphery of the coarse bubbles 66A, which are about to expand to the outer diameter of the gas supply pipe 52. It is desirable to make it fast,
In particular, when the flow velocity of the gas jet 64 is set to about Mach 2,
Since the pressure fluctuation of the gas jet 64 extends to a distance of about 10 times the nozzle diameter from the nozzle tip of the group of narrow tubes 68, by colliding with the bubble wall of the coarse bubbles 66A up to this range, turbulence at the interface increases and fine The generation of bubbles 66B can be further promoted.

[Effect]

The structure of the micro-bubble generating device according to the present invention and the reasons for limiting the requirements have been explained with reference to FIGS. 1 and 3, and their effects will be explained respectively.

In FIG. 1, when the subsonic gas 62 is blown from the gas supply pipe 52 and passes through the breathable refractory 56, the flow velocity decreases and becomes sufficiently small, so that the flow rate at A slightly away from the surface of the breathable refractory 56 is Adhesive bubbles 66A are generated in the range up to .

These attached bubbles 66A do not form ism bubbles on the surface of the refractory 56 because the molten metal 50 has poor wettability with the air permeable refractory 56, so the blown gas 62 that has passed therethrough does not form ism bubbles on the surface of the refractory 56, but aggregates and coalesces into coarse attached bubbles. It became 66A. If the attached air bubbles 66A are difficult to float due to the air permeable refractory 56 above as shown in FIG. It may reach an outer diameter of 54 mm. Therefore, some of the bubbles 66A are not miniaturized, but detach from the outer periphery of the attached bubbles 66A, become separated bubbles 66G, and float to the surface.

In order to minimize the amount of this separation bubble 66C,
The flow rate of the gas blown from the tuyere A needs to be as low as possible in the subsonic range.

On the other hand, most of the remaining attached bubbles 66A are made fine by the method according to the present invention. That is, the gas jet 64 that has passed through the through hole 58 collides with the inner surface of the attached bubble 66A.

When the kinetic energy of this gas jet 64 is sufficiently large, it punches out the adhering bubble walls, enters into the molten metal 50 to approximately the area indicated by B in FIG. 1, and then splits to form fine bubbles 66B. The diameter of the fine bubbles 66B at this time is close to the diameter of the depression created when the gas jet 64 collides with the wall of the attached bubble 66A, so in order to obtain the fine bubbles 66B, the gas jet 64 must be discharged. Penetration hole 58
As mentioned above, it is necessary to reduce the diameter of the diameter, and in the present invention, the diameter is limited to 2 mφ or less.

Among the generated bubbles, coarse bubbles 66 such as detached bubbles 66G
A immediately floats up, generating an upward flow of molten metal 50. On the other hand, fine bubbles 66B generated by the present invention
The floating speed of the molten metal 50 is low and it is easily affected by the local flow of the molten metal 50, so it does not float immediately and is dispersed over a relatively wide area as shown by C in FIG.

A case where the present invention shown in FIG. 1 is applied to molten metal contained in a ladle will be explained with reference to FIG. 2.

A micro-bubble generator 76 made of an air-permeable refractory 56 having a plurality of through holes 58 according to the present invention is immersed in the molten metal 50 housed in a ladle 68 at the tip of a lance (gas supply pipe) 52 to generate gas. Subsonic gas 62 is supplied to the first tuyere A, and gas jet 6 at the speed of sound or higher is supplied to the second tuyere B through gas supply channels 72A and 72B having flow rate control valves 71A and 71B.
Supply 4. In this case, if the fine bubble generator 76 at the tip of the lance 52 is immersed as deep as possible in the bottom of the ladle 68 and the respective gases are blown into the ladle 68, the large bubbles 66C generated by the action described above will be immediately removed. Since it floats, a circulating flow 50A of molten metal 50 is generated. Accordingly, the generated microbubbles 66B are accompanied by this upward flow and once rise to near the surface of the molten metal 5°, but are again brought down by the downward flow, circulated up and down in the ladle 68, and are dispersed. . As described above, the dispersion of the microbubbles 66B increases the chance of contact with the nonmetallic inclusions in the molten metal 50, which is extremely effective in causing the nonmetallic inclusions to adhere to the microbubbles 66B and be floated and separated. It is true.

[Application example]

(a) A modification to which the present invention is applied will be explained with reference to FIG. The coarse air bubbles 6 are caused by the gas 62 blown in from the first tuyere A.
Instead of forming micro-bubbles 66B, the gas jet 64 blowing in from the second tuyere B at a speed higher than that of sound fails to form micro-bubbles 66B.
Gas lingering in molten metal 50 can be captured by the device and used to create deposition bubbles 66A. That is, when the apparatus shown in FIG. 4 is immersed in the molten metal 50, the gas that has not formed into fine bubbles 66B and remains is collected in the lower recess 73, so that the second wing on the outer periphery of the recess 73 When gas 64 at a speed higher than the speed of sound is blown from the port B, the collected gas 74 becomes attached bubbles 66A, and then becomes fine bubbles 66B by the gas 64 higher than the speed of sound. In this case, the whole including the second tuyere B and the recess 73 is one part of the first tuyere according to the present invention.
Therefore, the amount of gas collected in the recess 73 per unit time or the amount of gas blown from the second tuyere B is determined by the recess 7.
The value divided by the area of 3 corresponds to the gas blowing speed from the first tuyere A in the present invention. Therefore, the device as shown in FIG. 4 is also effective as a device for capturing residual floating gas in the molten metal 50 and generating fine bubbles.

(b) Next, a special example of how the device of the present invention is used is explained in the fifth section.
This will be explained with a diagram. That is, the apparatus of the present invention can also be used horizontally in molten metal 50, as shown in FIG. In this case, the surfaces of the first tuyere A and the second tuyere B that come into contact with the molten metal 50 are perpendicular to the container such as a ladle, so the attached air bubbles 66 generated by passing through the air-permeable refractory 56
A tends to split upward and float up. Therefore, on the front surface of the first tuyere A, a bubble interface similar to that explained in FIG.
As a result, fine bubbles 66B are generated.

In addition to inert gas, oxygen, air, and other gases can also be used as the gas to be blown into the molten metal depending on the purpose of refining. It is possible to arbitrarily select a type of gas that can be expected to promote physical reactions and improve operation.

〔Example〕

Example 1 An embodiment of the aspect described in FIG. 1 above will be described.

An inner diameter of 0.5 that penetrates the layer of breathable refractory material 56 made of a porous plug with a working part diameter of 100 mφ and a length of 200 nin.
20 through-holes 58 made of 1 mm thin tubes are embedded and different headers are provided from the back side of the permeable refractory 56 and from one end of the thin tube group 58A, respectively, to create a micro bubble generator consisting of a first tuyere A and a second tuyere B. 76 was produced. The sides of the breathable refractory 56 were covered with a non-breathable refractory 74 to prevent gas leakage from the sides. As shown in FIG.
10NIII from each of the porous plug 56 and the capillary tube group 58A.
Ar gas was blown in at a flow rate of /mLn, 10 ONQ/win. At this time, the gas flow velocity is an average of 0.02 m/see on the operating surface of the porous plug 56, and 3 m/see at the outlet of the thin tube 58.
It was 70 m/see.

When the generated bubbles were attached to a steel round bar and the bubble diameter was investigated from the traces left in the solidified layer on the surface of the round bar, many traces of fine bubbles with a diameter of 1 to 2 m were observed.

In order to confirm the effect of the present invention, next, when the blowing of Ar gas from the thin tube group 58A was stopped and only Ar gas of 100 NQ/min was blown from the porous plug 56, the vicinity of the operating surface of the porous plug 56 became undulating. As in the previous case, from the traces left in the coagulated layer on the surface of the round bar, hardly any traces of fine bubbles of 2a++ or less were observed. Therefore, the bubbles generated from the first layer A of the porous plug 56 are transferred to the second layer of the thin tube group 58A.
It was confirmed that fine bubbles 66B were generated by being disturbed by the gas jet 64 from the tuyere B.

Example 2 An embodiment of the aspect described in FIG. 3 above will be described.

As shown in FIG. 3, the gas supply pipe 52 is a steel pipe with an inner diameter of 40++n and whose outer periphery is covered with a refractory material 54.
A micro bubble generator 76 of the present invention was prepared by arranging 10 thin tubes 68 of 1.0 mm in diameter, and immersed in 1600° C. molten steel with the operating surface facing downward in the same manner as in Example 1.
Ar gas was blown at a flow rate of 50 N Q /min from the gas supply pipe 52 and 2 N Q /ll1 in from the gas supply pipe 52, and when the bubble diameter was investigated using a round rod in the same manner as in Example 1, fine bubbles of 1 to 2 mφ were found. Many marks were recognized.

Next, when the blowing of Ar gas from the thin tube group 68 was stopped and Ar gas of 52 N Q /l1 inch was blown only from the gas supply pipe 52, almost no traces of fine bubbles of 2 mφ or less were observed, which was the same as in Example 1. Similarly, the effects of the present invention were confirmed.

〔Effect of the invention〕

The present invention examines the shortcomings of conventional methods and devices for generating microbubbles, and specifically considers the disadvantages of simply injecting gas into molten metal through a group of fine holes in a breathable refractory or a small diameter gas jet blowing hole. Due to the fact that bubbles cannot coalesce and form fine bubbles due to poor surface wettability, the present invention aims to generate bubbles by blowing subsonic gas through a first tuyere opened into molten metal, and A method was adopted in which a gas jet of speed higher than the speed of sound was blown into one tuyere or its outer periphery and collided with the bubbles generated from the first tuyere, and the device was constructed to be compatible with the above-mentioned method for generating microbubbles. We were able to cite the effects of

(b) In the method of the present invention, the gas jet from the second tuyere collides with the inner surface of the bubbles generated by the first tuyere, which changes irregularly, so the shape of the jet entering the molten metal is complex. It is much easier to make bubbles smaller than the conventional technology, which simply impinges a jet on the surface of molten metal.

(b) In the present invention, since even one splash generated is absorbed into the surrounding molten metal, it is possible to omit a means for preventing scattering.

(c) The device according to the present invention is a simple device that can be attached to the tip of a lance for stirring molten metal, does not require special equipment, and can reliably generate a large amount of fine bubbles. .

(d) The present invention is applicable not only to molten steel but also to all other metal refining, and the gas used for the purpose of molten metal refining is not only inert gas but also oxygen, air, and other gases. Therefore, the effect of contributing to the development of many types of molten metal refining using microbubbles is extremely large.

[Brief Description of the Drawings] Fig. 1 is a schematic cross-sectional view illustrating the structure and operation of an apparatus according to an embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view of the micro-bubble generating apparatus according to the present invention applied to molten metal in a ladle. FIG. 3 is a cross-sectional view showing the structure and operation of another embodiment of the present invention, FIG. 4 is a cross-sectional view showing an application example of the apparatus of the present invention, and FIG. 6 to 10 are cross-sectional views showing a special mode of use of the device of the present invention, and FIGS. 6 to 10 are cross-sectional views showing a conventional method or device for generating microbubbles in molten metal. 50... Molten metal 52... Gas supply pipe 54
... Refractory 56... Breathable refractory (porous plug) 58...
Through hole 58A...Thin tube group 60...Gas jet discharge hole 62...Subsonic gas 64...Gas jet at or above the speed of sound 66A...Adhesive bubbles (coarse bubbles) 66B...Fine bubbles 66C・...Separation bubble 68
... Ladle 70 ... Joint part 73 ... Concave part 74 ... Collected gas 76 ... Fine bubble generator

Claims (3)

[Claims] (1) Subsonic gas is injected into the molten metal through a first tuyere opened to generate bubbles, and at the same time a second tuyere consisting of a plurality of thin tubes with a diameter of 2 mm or less provided inside or around the first tuyere A method for generating microbubbles in molten metal, which comprises blowing a gas jet at the speed of sound or higher through two tuyeres to collide with the bubbles generated from the first tuyere. (2) A first tuyere consisting of a gas supply path that opens into the molten metal and has a gas permeable refractory at the open end, and a gas having a velocity higher than the speed of sound that is disposed within the opening of the first tuyere and/or around its outer periphery. A device for generating microbubbles in molten metal, comprising: a second tuyere consisting of a plurality of thin tubes with a diameter of 2 mm or less for generating a jet. (3) A first tuyere consisting of a gas supply pipe that opens into the molten metal and has an average flow velocity of subsonic in the cross section of the tip opening, and a first tuyere that is disposed within the opening of the first tuyere and/or on its outer periphery and that is higher than the velocity of sound. A device for generating microbubbles in molten metal, comprising: a second tuyere consisting of a plurality of thin tubes having a diameter of 2 mm or less for generating a gas jet.