JPS6217463Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Field of Industrial Application) The present invention relates to a bottom blowing nozzle in a top and bottom blowing converter. (Prior technology) In recent years, in order to increase the refining efficiency in steelmaking converters, top-bottom blowing has been introduced, in which oxygen is blown from a top-blowing lance and stirring gases such as CO ₂ , Ar, and N ₂ are blown from a bottom-blowing nozzle below the bath surface. Converter operations are becoming widespread. In order to stably and efficiently operate the top-bottom blowing converter, the bottom-blowing nozzle (hereinafter simply referred to as nozzle) plays an important role. That is,
Since the amount of bottom-blown gas varies greatly depending on operating conditions, the nozzle must have the ability to accurately and accurately blow in a small amount of gas to a large amount of gas. It is also required to have durability against Therefore, nozzles with various structures have been proposed in the past. For example, as shown in JP-A-55-149750, a plug made of refractory material is provided with a plurality of small-diameter through holes to constitute a nozzle, and JP-A-57-1497-
As shown in No. 200533, a structure in which the through hole is made of a tubular body made of a material different from that of the refractory body has been proposed and used. (Problem to be solved by the invention) However, in the conventional nozzle, the number of through holes configured in the plug as a single unit is either a relatively small number of multiple holes, or the technical idea is to provide as many as possible within a predetermined cross section. It was all I could do. For this reason, the blowing control range of the bottom-blown gas mentioned above becomes very limited, or the strength of the nozzle decreases, and its useful life is extremely short, making it difficult to carry out stable operation for a long period of time. It was hot. By the way, it is well known that when the stirring gas is bottom-blown from a nozzle, a pine room is formed directly above the nozzle due to the cooling function of the gas. This pine room is a mushroom-shaped structure in which the molten metal on the nozzle is cooled and solidified by the cooling function of the stirring gas, and prevents direct contact between the nozzle and the furnace bottom refractory and the molten metal that flows violently in the furnace. This is effective in reducing the rate of erosion of the refractory and extending the life of the nozzle. However, the structure of the pine room is extremely fragile, and depending on the situation, it may suddenly disappear, or on the other hand, it may easily become a solidified body, making it difficult to maintain stably and difficult to handle. As a result of repeated research into forming a stable pine room, the applicant has developed a nozzle in which the diameter of the metal pipe buried in the nozzle is 30 mm ² or less, and the collection rate of the metal pipes within the nozzle is within a predetermined range. was invented and filed in Japanese Patent Application Laid-open No. 153818/1983. The present invention further improves the nozzle and provides a nozzle that can more effectively utilize the effects of the pine loom. (Means for Solving the Problems) The present invention provides a bottom-blowing nozzle in which a plurality of small-diameter metal pipes with a cross-sectional area of 30 mm ² or less are buried in a refractory. D ₀ is set within the range based on the following equation (1) using the molecular weight, specific heat, gas decomposition rate, converter furnace volume, and number of installed nozzles as parameters of the bottom-blown gas, and the total cross-sectional area of the buried pipe is , relates to a bottom blowing nozzle in which the cross-sectional area of the collective diameter is 0.8 to 2.8%, and the pipes are evenly distributed and buried within the collective diameter D ₀ . D ₀ : Diameter of buried pipes (mm) M : Molecular weight of bottom-blown gas (Kg/Kmol) W : Volume of converter furnace (Ton/Heat) η : Decomposition rate of bottom-blown gas in the bath N : Bottom-blown gas Number of nozzles Cp; Specific heat of bottom-blown gas (Kcal/Nm ³・℃) (Function) Now, the inventors of the present invention generate a pine room in a nozzle formed by embedding a plurality of the above-mentioned small diameter metal pipes in a refractory material. At the same time, various experiments and research were repeated in order to maintain stability and to blow a predetermined amount of stirring gas (hereinafter simply referred to as gas) from the bottom. As a result, the pine room generated on the nozzle has a large number of pores, and the pores constitute gas passages, and the density of the pores is independent of the size in a normal pine room. It was found that it is almost constant. Further, as the flow rate of the bottom blowing gas is reduced, the pine room gradually melts due to heat received from the molten metal. In other words, it was also found that in order to maintain a stable pine room, it is necessary to maintain an appropriate thermal balance between cooling by the bottom-blown gas and heat received from the molten metal. On the other hand, in a converter, molten steel with various component concentrations,
For example, high carbon steel with a carbon concentration of about 1% to low carbon steel with a carbon concentration of 0.04% or less are manufactured in the same converter.
When producing the above-mentioned high carbon steel, it is necessary to keep the oxygen activity in the slag high in order to facilitate dephosphorization. Therefore, even in the high carbon range (carbon C≧0.4%), it is important to reduce the steel bath stirring power because it is necessary to burn iron and increase the FeO concentration in the slag. In other words, carbon is normally oxidized preferentially in a high carbon region, but by lowering the stirring power, the rate of carbon supply to the flame spot formed by the top-blown oxygen jet is lowered, and the iron is combusted. becomes possible. Such an operation can be carried out by controlling the flow rate of the bottom blowing gas in a decreasing direction and adjusting the stirring force. Figure 3 shows the relationship between the amount of bottom blowing gas and the blow-off phosphorus concentration [P] during the production of high carbon steel with C≧ ^0.4 %.
It can be seen that the dephosphorization ability in the high carbon region can be maintained at a high level by setting the pressure to less than Ton・min (substantially more than 0.01Nm ³ /Ton・min is required to prevent backflow of molten metal). Conversely, in order to economically produce low carbon steel, it is necessary to achieve preferential decarburization in the low carbon range. For this purpose, it is important to increase the stirring power of the steel bath and increase the carbon supply rate to the fire point. Figure 4 shows carbon C
This shows the relationship between the amount of bottom-blown gas and the T・Fe concentration in the slag in the low carbon range of ^0.03 to 0.05%. It becomes possible to reduce Fe. In other words, 0.1Nm ³ /Ton・min or more (substantially 0.1~
It can be seen that preferential decarburization is carried out in the low carbon region by bottom blowing (approximately 0.3Nm ³ /Ton・min). From these findings, in order to differentiate high carbon steel from low carbon steel in the same converter, the amount of gas injected from the nozzle should be at least 0.04 to 0.1, and if it increases, it should be 0.01.
It is necessary to appropriately control the amount of gas within a range of ~0.3 Nm ³ /Ton·min, and there has been a demand for the development of a nozzle that can accurately bottom-blowing such a wide range of gas amounts. The present invention was created as a result of further experiments and research based on the above knowledge. FIG. 1 is a plan view of a nozzle according to the present invention, and FIG. 2 is a partial sectional view showing how the nozzle is installed. In the figure, 1 is a nozzle and 30
Small diameter metal pipes of mm ² or less (hereinafter referred to as pipes)
2, 2a are embedded in a refractory material 3 made of MgO--C or MgO-based material. pipe 2
are evenly distributed and buried within the collective diameter D ₀ set within the range described below. (In the present invention, the buried collective diameter refers to the diameter of the range in which the pipes 2 are buried evenly, and hereinafter simply referred to as the collective diameter.)
is installed on. 7 is a gas supply pipe; gas is supplied from the gas supply pipe 7 to the pipe 2 via a header part 8 provided in the nozzle 1;
It is blown into the furnace. 9 indicates a nozzle holding brick. By the way, in experiments conducted by the present inventors, when a nozzle 1 with a pipe 2 buried in a refractory 3 is used, the pipe 2
It was confirmed that the molten metal adheres to the surface and pine looms are easily formed using this as a starting point, and that pine looms once formed are difficult to peel off. However, regardless of the cross-sectional shape of the individual pipes 2, if the cross-sectional area exceeds 30 ^mm2 , the fifth
As shown in the figure, a relatively large hole 41 is formed in the mash room 4 directly above the pipe 2, so that the upper part of the mash room is left open. As a result, when molten metal infiltrates into the pipe 2 due to fluctuations in the flow rate of the bottom-blown gas, etc., metal plugging phenomenon occurs frequently. When this metal gap occurs, the gas passage in the pine room becomes blocked, and the gas pressure applied to the pine room increases, causing the pine room to peel off, shortening the life of the nozzle, and causing the refractory at the bottom of the furnace to melt. . It is for this reason that the size of the pipe 2 in the present invention is set to be 30 mm ^{2 or} less in terms of cross-sectional area.
Any of the flat hole shapes 2a shown in FIG. b may be used. Now, as mentioned above, the pine room 4 is formed by molten metal adhering starting from the pipe 2, but its shape depends on how much of the refractory 3 the pipe 2 covers.
Much depends on how much is buried. That is, what determines the shape and properties of the pine room is not the diameter D of the nozzle, but the collective diameter D ₀ mentioned above, and is determined by the cross-sectional area of each pipe 2 and the density within the collective diameter. It has been found from the experience of the inventors that this is the case. Next, the means for setting the range of the collective diameter D ₀ will be explained. First, as the amount of bottom-blown gas is reduced, the pine room 4 due to bottom-blown gas
Due to insufficient cooling, the pine room melts. The critical amount of bottom-blown gas at which the pine room starts melting can be determined by applying the pine room heat reception/output balance formula shown in equation (2) below, taking into consideration the heat transfer with the gas within the pine room. Hm・S・Ts=ΔTG・Cp・F……(2) S: Surface area of pine room (m ² ) Hm: Overall heat transfer coefficient between pine room and molten steel (Kcal/Hr・m ²・℃) Ts: Molten steel temperature − Molten steel solidification temperature (°C) ΔTG: Gas rise temperature in the pine room (°C) Cp: Gas specific heat (Kcal/Nm ³・°C) F: Gas flow rate (Nm ³ /Hr) If we rearrange the above equation (2) using S, The following formula (3) is obtained. S=ΔTG・G・F/Hm・Ts ……(3) Here, a normal pine room is approximately hemispherical.

[Table] Now, Figure 6 shows the relationship between the amount of bottom blowing gas (bottom blowing gas in this example is CO ₂ ) required for the pine room not to dissolve, that is, for the pine room to exist, and the aggregate diameter D ₀ . This shows an example of the results obtained. The shaded area above the solid line a is the range where the pine room exists, and from the results of this experiment, the relationship between the amount of bottom-blown gas required for the presence of the pine room and the aggregate diameter D ₀ can be expressed by the following equation (7). It turns out that it can be done. Fmin=9.3×10 ^-6 (Ts/Cp)・D ₀ ² ...(7) Fmin: Minimum gas flow rate (Nm ³ /Hr) Therefore, as mentioned above, the minimum amount of bottom-blown gas required in the converter Since the flow rate is less than 0.04Nm ³ /Ton·min, Fmin per converter can be expressed by the following equation (8). Fmin≦0.04×60×(W/η・N)=2.4(W/η・N
)...(8) Equations (7) and (8) above and Ts are usually up to 200℃ in a converter.
Therefore, by setting the collective diameter D ₀ within the range shown in equation (9) below, it is possible to maintain a normal pine room even for a small amount of bottom-blown gas of 0.04Nm ³ /Ton・min or less. It is. The decomposition rate η of the bottom-blown gas in the bath was expressed as the ratio of the amount of gas effective for stirring in the bath to the amount of gas actually blown into the bath. For example, when a gas such as CO ₂ is blown into the bath, it becomes 2CO and increases the number of gas molecules. Therefore, due to the reaction CO ₂ + C → 2CO, the amount of gas that effectively acts on stirring in the bath is twice the amount of CO ₂ gas actually blown into the bath. An important amount of gas in converter refining is the amount of gas that effectively acts on stirring within this bath. Therefore, in the present invention, the ratio (effective gas amount in the bath)/(bottom blown gas amount), which is determined depending on the type of bottom blown gas, is defined as η. On the other hand, as mentioned above, the pine room has a large number of pores, and since these pores serve as passageways for the bottom-blown gas, the pressure loss inside the pine room is large. Figure 7 shows an example of the results of investigating the relationship between supply pressure and flow rate in order to understand the pressure loss in the pine room.Up to a supply pressure of 15 kg/ ^cm2 , the supply pressure and flow rate have a linear relationship. However, when the pressure exceeds 15 Kg/cm ² , even if the supply pressure is increased, the rate of increase in flow rate becomes low, indicating that the pressure loss in the pine room becomes high. Further, as described above, the pores in the pine room have a substantially constant density regardless of the size of the pine room, so the pressure loss also varies depending on the aggregate diameter D ₀ . Figure 8 shows the results of an investigation of the pressure loss with respect to the aggregate diameter D 0 when bottom blowing was performed at 500Nm ³ /Hr using CO ₂ as the bottom blowing gas.As the aggregate diameter D ₀ increases, _the pressure loss increases. will also decrease. Therefore, the relationship between the pressure loss and the collective diameter D ₀ is expressed by the following equation (10) when the gas supply pressure is 15 kg/cm ² or less. ΔP=B・F/D ₀ (10) However, B is a constant determined by the type of bottom-blown gas, the length, size, degree of bending, wall surface roughness, etc. of the gas flow path. Table 2 shows the results of determining B using the pine room actually generated in a nozzle with a collective diameter D ₀ of 228 mm in a 170-ton converter, and that B is approximately proportional to the molecular weight of the bottom-blown gas. I found out.

[Table] Gas flow rate and pressure loss are generally expressed by equation (11) below. ΔP=4f・(ρu ² /2g)・(l/D) ...(11) f=0.0785/{0.7-1.68logRe+
(logRe) ² } (turbulence) ΔP ; pressure loss (Kg/m ² ) f ; friction coefficient ρ ; gas specific gravity (Kg/m ³ ) u ² ; average gas flow rate (m/sec) g ; gravitational acceleration ( m/sec ² ) l: Length of the pipe in the nozzle (m) D: Diameter of the pipe (m) Re: Ray nozzle number Here, with a normal bottom-blown gas amount, the flow inside the pore is turbulent. Therefore, f can be approximately constant, and ΔP is approximately proportional to ρ. In other words, if the type of bottom-blown gas is different, Δ
It turns out that P is proportional to the molecular weight M of the gas.
On the other hand, it is known that the pressure loss when gas exits from the gas passage is also proportional to the gas specific gravity ρ and the gas average flow rate u ² , and considering this in conjunction with equation (11) above, the relationship between the supply pressure and the gas flow rate is Now, it can be seen that for the same gas flow rate, the supply pressure P is proportional to the molecular weight of the gas. From these findings, P can be approximately expressed by the following formula (12) when P≦15Kg/cm ² . P=0.080・M・F/D ₀ ...(12) As mentioned above, ΔP becomes extremely large when the supply pressure is 15Kg/cm2 or ^more , so the economical blowing condition is P≦15Kg/cm It should be ² . Furthermore, considering the condition that the amount of bottom-blown gas is 0.1Nm ³ /Ton・min or more, which is necessary to economically produce low carbon steel, Fmax≧0.1×60×W ……(13) Therefore, the aggregate diameter D ₀ is determined by the following equation (14). D ₀ ≧3.2×10 ^-2・M・(W/η・N) ……(14) Therefore, the collective diameter D ₀ is obtained from the above equation (9) and (14). It should be set within the range. By the way, even if the collective diameter is within the range of formula (1) above, unless the number of pipes buried within the collective diameter is appropriate, it is not possible to maintain the above-mentioned appropriate mush room. In particular, as mentioned above, the pipe of the present invention has a small cross-sectional area of 30 mm ² or less, so the pressure loss in each pipe is large. For this reason, if a predetermined amount of gas is blown into a small number of pipes, the supply pressure must be increased, which causes the above-mentioned problem. On the other hand, if the number of pipes is too large, the shape of the pores in the pine room becomes complicated, leading to a problem of poor heat transfer during blowing. As a result of repeated various experiments, the present inventors decided to increase the number of buried pipes so that the total cross-sectional area of the buried pipes was in the range of 0.8 to 2.8% of the cross-sectional area of the collective diameter D ₀ . It has been found that the above-mentioned problems can be effectively solved by determining In other words, as mentioned above, the pine loom adheres to the pipe and is strongly bonded, but when the total cross-sectional area of the pipe becomes less than 0.8% of the cross-sectional area of the collective diameter D ₀ , the bonding area between the pipe and the pine loom decreases, causing bottom blowing. When the amount of gas is increased, the pine room peels off. On the other hand, if it exceeds 2.8%, as shown in Figure 9, the pores in the pine room that continue from adjacent pipes will combine and the number of pores will decrease.
When the diameter thereof is 1 mm or more, the contact area between the pine room and the gas inside the pore decreases, resulting in insufficient heat transfer. As a result, the minimum gas amount at the solubility limit of the pine room increases, and the minimum gas amount that maintains the pine room becomes larger than the minimum gas amount determined by equation (2) above, resulting in a narrower flow rate control range. In this invention, the collective diameter is within the range of equation (1), and the total cross-sectional area of the buried pipe is 0.8 to 2.8 of the collective diameter cross-sectional area.
It is for this reason that it is limited to %. (Example) Various nozzles were attached to a 170-ton converter, and the amount of bottom blowing gas, peeling status of pine room, nozzle life, etc. were investigated. Tables 3 and 4 show examples of the survey results.

【table】

【table】

[Table] The present invention is within the collective diameter D ₀ set based on the present invention, and the cross-sectional area of the pipe and the ratio of the total cross-sectional area of the pipe to the collective diameter cross-sectional area are within 0.8 to 2.8%. All of the nozzles had a wide range of bottom-blowing gas volumes, and no peeling of the pine room occurred at all. In addition, we were able to ensure a long nozzle life with an average of 800 to 1000 charges. In Table 3, the life of the nozzle is expressed as an index, with the life of No. 1 based on the present invention being taken as 1. On the other hand, in No. 6, where the ratio of the total cross-sectional area of the pipe to the collective diameter cross-sectional area is outside the above range, there is a lot of peeling of the pine room, and in No. 7, the minimum amount of bottom blown gas is large, that is, a small amount of blown gas As a result, the pine lume melted during blowing of high carbon steel, and the service life was extremely short, ranging from 0.26 to 0.44 mm. In No. 8, the aggregate diameter D ₀ was smaller than the predetermined range, so it was not possible to secure the amount of bottom blowing gas necessary for blowing low carbon steel. On the other hand, in No. 9, the aggregate diameter D ₀ was larger than the predetermined range, so the pine room melted during blowing of high carbon steel and the nozzle life was shortened. In No. 10, the cross-sectional area of the pipe was 30 mm ² or more, so as mentioned above, the pine room peeled off in a short period of time, resulting in an extremely short nozzle life. (Effects of the invention) As detailed above, with the nozzle of the invention, it has become possible to accurately blow bottom-blown gas over a wide flow rate range. In addition, a normally shaped pine room is generated on the nozzle and can be maintained for a long period of time, resulting in a dramatic improvement in the life of the nozzle.

[Brief explanation of drawings]

1a and 1b are plan views of a nozzle based on the present invention, and FIG. 2 is a partial sectional view showing how the nozzle of FIG. 1 is installed. Figure 3 is a chart showing the relationship between the amount of bottom blown gas and the concentration of blow-off phosphorus [P] during the production of high carbon steel, and Figure 4 is the amount of bottom blown gas in the low carbon region and the T/Fe concentration in slag. Figure 5 is a cross-sectional view showing the pine room generated on the nozzle, and Figure 6 is an experimental diagram showing the relationship between the amount of bottom-blown gas required for the existence of the pine room and the aggregate diameter D ₀ . A chart showing an example of the obtained results,
Figure 7 is a chart showing an example of the results of investigating the relationship between supply pressure and flow rate in order to understand the pressure loss in the pine room, and Figure 8 is a graph showing an example of the results of investigating the relationship ^between supply pressure _{and flow rate} in order to understand the pressure loss in the pine room. A chart showing the results of an investigation of the pressure loss with respect to the collective diameter D ₀ during bottom blowing, and FIG. 9 is a sectional view showing another pine room generated on the nozzle. 1... Nozzle, 2, 2a... Pipe, 3... Refractory, 4... Pine room, 5... Tuyere brick,
6... Furnace bottom brick wall, 7... Gas supply pipe, 8... Header section, 9... Nozzle holding brick.

Claims (1)

[Scope of Claim for Utility Model Registration] In a bottom blowing nozzle formed by embedding a plurality of small diameter metal pipes with a cross-sectional area of 30 mm ² or less in a refractory, the collective diameter D ₀ of the buried pipes in the refractory is:
The molecular weight, specific heat, gas decomposition rate, converter furnace volume, and number of installed nozzles of the bottom-blown gas are set as parameters within the range based on the following equation (1), and the total cross-sectional area of the buried pipe is set to the collective diameter cross-section. 0.8~ of area
2.8%, and the pipes are evenly distributed and buried within the collective diameter D ₀ . D ₀ : Diameter of buried pipes (mm) M : Molecular weight of bottom-blown gas (Kg/Kmol) W : Volume of converter furnace (Ton/Heat) η : Decomposition rate of bottom-blown gas in the bath N : Bottom-blown gas Number of nozzles Cp; Specific heat of bottom-blown gas (Kcal/Nm ³・℃)