JPH0559778B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is a method for blowing gas into a liquid at a speed close to sonic speed, which eliminates the bottom-struck phenomenon and makes it possible to stabilize the jet. can be,
This makes it possible to carry out gas-liquid reactions extremely advantageously in the steel industry, chemical industry, etc.

BACKGROUND ART Absorption of gas into liquid, reaction of gas with liquid (hereinafter simply referred to as gas-liquid reaction), and stirring of liquid by gas are processes that are frequently performed in the steel industry and the chemical industry. For this purpose, it is well known to blow gas into the liquid through a nozzle.

Problems to be Solved by the Invention In the method of blowing gas into a liquid through a nozzle, in order to improve reaction efficiency and shorten operating time, it is preferable to blow a large amount of gas at as high a speed as possible.

However, in the case of a straight nozzle with a fixed nozzle pipe area, increasing the pressure makes it possible to inject a large amount of gas and maintain a high static pressure at the nozzle outlet, but the speed of sound In order to achieve a flow velocity close to , a large original pressure is required due to the choke phenomenon caused by pipe friction resistance, so it is difficult to flow a large flow rate at low pressure.

On the other hand, a medium-fine nozzle or a tapered-to-widespread nozzle (hereinafter referred to as
If a Laval nozzle is used, it is possible to easily obtain a jet flow close to or supersonic, and it is also possible to blow a large amount of gas at low pressure, but the static pressure at the outlet is small, making the jet unstable. ,
Back attack (bottom hitting phenomenon) is also likely to occur, and the nozzle tip is seriously damaged due to back attack.

Furthermore, in extremely shallow baths, there is also the concern of blow-through.

The present invention provides a method for blowing gas into a liquid through a nozzle in a jet flow, which causes less damage to the tip of the nozzle and enables high-speed, large-volume blowing of gas.

Means for Solving the Problems The present invention provides a method for blowing gas into a liquid through a nozzle at a high velocity of 90% or more of the sonic velocity.
A baffle plate or an equivalent solid surface (hereinafter simply referred to as a baffle plate) is placed in the direction of the tip of the jet flow in the bath, substantially perpendicular to the jet flow. This is a method of instilling.

This will be explained below using the drawings (Figs. 1 and 2).

When gas 2 is blown into the liquid through nozzle 1,
While the flow velocity is low, bubbles are generated at the tip of the nozzle and then separated, which is a repeated process.

As the flow rate increases, the frequency of bubble formation and separation increases, and when the flow rate reaches a high velocity of 90% or more of the sound speed, the gas phase finally enters the gas continuously from the nozzle tip. At this time, the continuous gas phase incorporates the liquid, so that it substantially forms a two-phase flow 3 (there is a core portion 4 containing only the gas phase).

If we define this region as the in-bath jet region, the in-bath jet itself is constantly changing in length and shape in the bath, and is essentially unsteady or unstable.
As shown in Fig. 1, the inside of the liquid and the liquid surface are exhibiting violent movements up and down.

The biggest factor causing this instability is thought to be interaction with the surrounding liquid. That is, the jet in the bath grows and penetrates into the liquid due to the inflow of gas from the nozzle, but as it loses kinetic energy at the tip, it fluctuates under the influence of the movement of the surrounding liquid and also breaks up. In addition, it is often observed in high-speed photographs that the bubble is cut off from the constricted part 5, but this occurs in a region where the pressure has decreased even though the kinetic energy is still high.
This is thought to indicate that the constriction of the bubble leads to cutting.

Cutting in front of the jet causes a discontinuous and sudden volume reduction of the gas phase or mixed phase. Therefore, if a large amount of gas phase is supplied at a constant speed, a sudden pressure increase and accompanying volume expansion will cause the nozzle to It is thought that this phenomenon occurs intensively at the outlet, and as a result, the so-called bottom-striking phenomenon 6 is observed.In order to reduce the frequency of this bottom-striking, the static pressure of the gas phase in the jet (core) must be increased. It is effective to reduce turbulence caused by liquid movement.

On the other hand, the Laval nozzle, which can easily flow a large amount of gas at high speed, has not been put into practical use for blowing gas into liquid. One of the reasons for this is that the pressure is easily converted into kinetic energy and becomes supersonic, so the exit static This is thought to be because it is difficult to maintain high pressure. On the other hand, the commonly used straight nozzle uses a blowing speed close to the speed of sound; however, this type of nozzle cannot theoretically exceed the speed of sound, so the blowing speed increases as it approaches the speed of sound. It can be understood that this method takes advantage of the fact that the jet is relatively stabilized due to the occurrence of the yawking phenomenon and the sudden rise in the gas phase static pressure at the nozzle outlet.

However, it is still not possible to avoid disconnection due to liquid movement in front of the jet and disturbances due to unsteadiness caused by it.

Therefore, if a solid wall 7 is provided below the position where this cutting should occur (from the nozzle) and the jet is made to flow along this wall, the steadiness of the jet flow is guaranteed, and the jet flow is continuous and It transforms into bubbles at fixed locations, stabilizing the entire jet area.

The "baffle" 7 of the present invention assumes this role, bearing the hydrostatic pressure on the jet from above, while at the same time providing a flow path and a location for continuous variation of the jet flow.

Therefore, it is possible to form a stable jet even at relatively low pressures and low flow rates, and the bubbles that separate from the periphery of the baffle plate are extremely small compared to ordinary jet bubbles.

Chemically, this results in an increase in the reaction rate due to an increase in the reaction interface area and residence time, and physically, an increase in stirring power due to an increase in gas hold-up.

This is shown in Figure 2, where the gas 2 ejected from the nozzle 1 collides with the baffle plate 7 located directly above the nozzle, creating an expanding upward bubble flow 8 and a downward ideal circulating flow. form 9. Fine air bubbles 10 are generated on one side of the upper part of the bath and hold up, and the bath surface 11 is quiet.

The shape of the baffle plate is such that it has a surface (flat or curved) that substantially covers the spread of the jet flow. The effect remains the same if the area is too large, but the effect becomes weaker as the area becomes smaller than the spread area.

The position of the baffle plate should be such that it almost covers the spread of the jet flow, and when the nozzle diameter is D and the height of the baffle plate surface from the nozzle is H, 10D≧H≧2D. As mentioned above, the guideline is to bring it closer to the nozzle side than the cut surface of the continuous gas phase.

The specific method for installing baffle boards is as follows: (1) Installed from above independently of the nozzle (Figure 3).

(2) The support frame 12 is integrated with the nozzle (Fig. 4).

(3) Insert it inside the nozzle (Fig. 5).

There are other methods.

Example 1 A water tank with an internal volume of 1.25×10 ⁴ cm ³ was filled with water, and air was blown out from a nozzle (4 mmφ) at the bottom of the tank at a discharge pressure of about 3 to 7 kg/cm ² . The flow velocity at this time is close to the speed of sound, and the volume of the jet region is 2.87×10 ²
cm ³ , the gas hold-up was approximately 0.022 and did not depend much on the discharge pressure. Also, the back attack was intense.

Next, a baffle plate with a surface that almost covers the spread of the jet flow was installed from above at a location 10 mm above the nozzle, and as the air discharge pressure was increased to 3 to 7 kg/cm ² , the gas hold up 0.024 to 0.11
In addition, as the baffle plate was moved closer to the nozzle, and as the air discharge pressure was increased, the back attack was observed to decrease (Figure 6).

Example 2 At the center of the bottom of a converter-like reaction vessel, the inner volume of the furnace was 80 Nm ³ and the distance from the top of the furnace to the bottom brick surface was 6.3 m.
Equipped with one heavy pipe tuyere (inner pipe inner diameter 16 mm, inner pipe outer diameter 16 mm, outer pipe inner diameter 20 mm), and the inner pipe is filled with oxygen gas or
Ar gas, propane gas or N ₂ can be supplied to the gap between the inner and outer tubes.

In addition, from above, there is a lance for blowing acid (tip nozzle shape: 4 mmφ, 6 holes) and an iron cylinder whose tip is coated with refractory (coated portion diameter: 200 mm) 5.3 mm (the area above 6 m from the tip is inside). is water-cooled) is charged into the furnace.

By tilting the furnace, hot metal (C: 4.3%, Si: 0.3%,
1430℃), 12000Nm ³ /hr of oxygen was charged from the top blowing lance, and oxygen was fed from the bottom blowing lance.
By blowing propane at 3000Nm ³ /hr and 50Nm ³ /hr, oxidation refining is carried out, mainly decarburization, and the C content is reduced to 0.3%. Next, the top blowing lance was pulled up to stop the blowing acid, and an iron cylinder whose tip was covered with a refractory was inserted into the furnace, and the tip was lowered to just above the bottom blowing tuyere, under the conditions described above. Continue to use oxygen-propane to reduce C to 0.1%, then keep the charging conditions of the iron cylinder the same and switch both injection gases to Ar (Ar injection amount 2000Nm ³ /hr). Perform blowing for a minute. Final C: 0.0015%, O: 0.08
%, N: 12ppm, H: 2ppm, molten steel at 1580°C is obtained, tapped into a ladle, and after adjusting the composition, is poured.

By placing the refractory-coated tube (equivalent to a baffle plate) directly above the bottom blowing tuyere, the dispersion of O ₂ gas and propane gas blown from the tuyere is promoted.
Promotion of decarburization in the low coal region (and as a result, 1
Strong stirring can be maintained even with this tuyere, and the FeO% of the slag
degassing was realized.

In addition, during Ar injection, bubble dispersion is similarly promoted, which increases the contact effect between Ar and molten steel, resulting in degassing reactions (due to CO reaction and dehydrogenation).
is promoted, the total blowing time is shortened (7 minutes), Ar
It has become possible to reduce gas consumption per unit of production (approximately 40% reduction).

Example 3 In a container lined with a gutter-like refractory with a width of 1.5 m and a length of 12 m, double pipe tuyeres (inner pipe inner diameter 10 mm, inner pipe outer diameter 12 mm, inner pipe outer diameter 12 mm, Provide 5 outer tubes with an inner diameter of 14 mm. In addition, from directly above corresponding to the position of each tuyere, an iron cylinder with a 1.3 m tip covered with refractory (the diameter of the covered part is 200 mm, the inner diameter of the iron tube is 100 mm, the part covered with refractory) The area above 1.5m from the tip of the pipe is water-cooled).

C:1.5% molten steel is continuously charged from one end of this furnace at a rate of 3t/min, and oxygen (from the inner tube) and propane (from the gap between the inner and outer tubes) are fed from each bottom blowing tuyere. were supplied at a ratio of 100:7, and an iron cylinder whose tip was coated with a refractory material was placed directly above each tuyere as a baffle plate.

With this method, bottom-blowing refining can occur stably even though the molten steel depth is small, and low-coal molten steel with C: 0.1% or less can be produced while keeping the degree of peroxidation of the slag low. Ta.

Effects of the Invention As described in detail below, in the present invention, by placing a baffle plate or a solid surface equivalent to the baffle plate at the tip of the jet in the bath, the jet flow collides with this surface and flows along this surface. This means that a (fixed) flow field is ensured for the jet flow, which stabilizes the jet.

The stabilization of the jet produces significant effects as described below.

(1) The bottom-striking phenomenon becomes rare, and damage to the nozzle tip is greatly reduced.

(2) Since there is no concern about blow-through, it is possible to blow a large amount of gas at high speed even in an extremely shallow bath.

(3) It is possible to stably blow a large amount of gas even at a lower pressure than that used with ordinary straight nozzles.

(4) Air bubbles become finer.

As a result, the gas-liquid interfacial area increases, which is extremely advantageous for gas-liquid reactions.

The hold-up amount increases and the residence time of bubbles in the liquid increases, which is advantageous for the gas-liquid reaction.

Increases the stirring effect, especially in shallow baths.

Therefore, the present invention is applicable to steelmaking furnaces, bottom blowing tuyere in steelmaking furnaces, blast furnace casting bed treatment, continuous steelmaking furnaces, gas injection into relatively shallow molten metal flows such as trough-type continuous steelmaking furnaces, and ladle refining. It is applicable to deoxidation, denitrification, dehydrogenation by blowing a large amount of gas, separation of inclusions in tundish, etc., and has great industrial value.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams for explaining the operation of the present invention. 3 to 5 are elevational views illustrating a specific method of installing baffle plates. FIG. 6 is a diagram showing the relationship between nozzle diameter, level, gas discharge pressure, and back attack frequency. 1...Nozzle, 2...Gas, 3...Two-phase flow, 4
...Core, 5...constriction, 6...bottom tapping, 7...
...Baffle plate, 8...Bubble flow, 9...Circulating flow, 10...
...Fine bubbles, 11...Bath surface, 12...Support frame.

Claims (1)

[Claims] 1. In a method of blowing gas into a liquid through a nozzle at a high velocity of 90% or more of the sonic velocity, a baffle plate or a A method of blowing gas at near or supersonic speed into a liquid, which is characterized by placing a corresponding solid surface (hereinafter simply referred to as a baffle plate). 2 When the diameter of the blow nozzle is D, the baffle plate or equivalent solid surface is 2D from the nozzle outlet.
2. A method for blowing gas into a liquid according to claim 1, which is disposed in a distal direction of 10D or more and approximately 10D or less. 3. The method of blowing gas into a liquid according to claim 1, wherein the liquid is a molten metal.