JPS6151605B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a side-blown converter blowing method in which blowing gas is blown into molten iron through tuyeres provided on the side of the furnace, and a side-blown converter that is most suitable for use in carrying out the blowing method. be. Recently, the pure oxygen bottom-blown converter steel manufacturing method (Q-BOP method) has been attracting attention as a steel manufacturing method that can replace the conventional pure oxygen top-blown converter (LD converter) steel manufacturing method. In this bottom-blowing converter steelmaking method, the gas blown in from the tuyere at the bottom of the furnace stirs the molten iron vigorously as it floats up in the steel bath, so the iron concentration (T.Fe) in the slag is lower than that in the LD converter. As a result, the iron yield is good, and as mentioned above, the high stirring effect results in a high decarburization rate in the low coal region, and the desulfurization ability is also high. It has various advantages over the law. However, the above-mentioned characteristics of the bottom-blown converter steelmaking method also cause phenomena that are disadvantageous compared to the LD converter steelmaking method. In other words, in the bottom-blowing converter steelmaking process, the iron concentration in the slag is kept low, and the iron concentration in the slag does not increase unless the coal is in a considerably low coal range.Therefore, the dephosphorization reaction is low in the early and middle stages of blowing. Good dephosphorization occurs only when the carbon content is suppressed and the carbon content becomes low. On the other hand, in the LD converter steelmaking method, the agitation is weaker than in the bottom blowing converter steelmaking method, and as a result, the iron concentration in the slag becomes considerably high and the iron yield decreases. However, this means that the dephosphorization reaction is accelerated. Moreover, in the LD converter steelmaking process, the iron concentration in the slag can be controlled by setting the position of the top blowing lance, and therefore, the iron concentration in the slag can be controlled before the low coal region where the dephosphorization reaction occurs in the bottom blowing converter steelmaking process. It is possible to carry out the dephosphorization reaction much more actively than in the case of bottom-blown converter steelmaking. This invention was made against the background of the above-mentioned circumstances, and by using a side-blown converter extremely skillfully, the advantages of the bottom-blown converter steel manufacturing method, namely, the improvement of iron yield and the advantages of the top-blown converter steel manufacturing method, were achieved. That is, the object of the present invention is to provide a blowing method that can simultaneously achieve the effect of improving dephosphorization, and a side-blowing converter that is most suitable for carrying out the blowing method. That is, the blowing method of the present invention uses a side-blowing converter in which an appropriate number of upper and lower tuyeres are provided at vertical intervals on the side of the furnace that is immersed in molten iron, At the start of blowing, the blowing gas flow rate at the upper tuyere is set to a large flow rate, and the blowing gas flow rate at the lower tuyere is set to a small flow rate to perform blowing similar to the top-blown converter steel manufacturing method, resulting in decarburization. When the process progresses to a low coal region, the gas flow rate at the upper tuyere is lowered and the gas flow rate at the lower tuyere is raised to perform blowing similar to the bottom blowing converter steel manufacturing process. Further, in the side-blowing converter of the present invention, an appropriate number of upper and lower tuyeres are provided at intervals vertically on the side of the furnace, and a pipe for supplying blowing gas to the upper tuyeres and a pipe for supplying blowing gas to the lower tuyeres are provided. The pipes for supplying the blowing gas to the pipes are separate systems, and the upper tuyere piping system and the lower tuyere piping system are each provided with separate flow rate control devices. The present invention will be described in more detail below with reference to the accompanying drawings. FIG. 1 shows an example of a side-blowing converter for carrying out the blowing method of the first invention, that is, an embodiment of the second invention, in which a steel shell 1 is covered with a furnace wall refractory such as brick. A furnace body 3 is constructed by lining the furnace body 3, and a part of the furnace side 3A of the furnace body 3 that is immersed in the molten iron 4, that is, a position below the surface of the molten iron 4, has vertically spaced The upper tuyere 5 and the lower tuyere 6 are provided substantially horizontally with a distance 1 between them. Therefore, the upper tuyere 5 is located near the slag layer 7 on the surface of the steel bath, and the lower tuyere 6 is located near the bottom 3B of the furnace body 3. Note that a plurality of upper tuyeres 5 and lower tuyeres 6 are usually provided at intervals in the circumferential direction of the furnace body 3. The upper tuyere 5 is connected to a blowing gas supply source 8 through an upper tuyere piping system 7, and the lower tuyere 6 is connected to a blowing gas supply source 8 through a lower tuyere piping system 9, and The upper tuyere piping system 7 and the lower tuyere piping system 9 are respectively provided with a flow control valve 10 and a flow control valve 11 as flow control devices. Therefore, the blowing gas supply piping systems for the upper tuyere 5 and the lower tuyere 6 are separate systems, and the flow rate of the blowing gas supplied to the upper tuyere 5 and the blowing gas supplied to the lower tuyere 6 are separated. It can be controlled independently from the flow rate of the gas used. Note that oxidizing gas such as pure oxygen is often used as the blowing gas, and in this case each tuyere 5, 6 has a double pipe structure similar to that used in pure oxygen bottom-blowing converters, and the inner It is desirable to flow an oxidizing gas for blowing through the tube and to flow a tuyere cooling gas such as a hydrocarbon gas between the inner tube and the outer tube. In this case, the oxidizing gas supply piping system for the inner tube is made into a separate system for the upper and lower tuyere so that the oxidizing gas flow rate in the inner tube of the upper and lower tuyeres can be controlled individually, while the tuyere cooling system on the outer tube side The gas supply piping system may be common to the upper and lower tuyeres, or it may be possible to control both the oxidizing gas in the inner tube and the tuyere cooling gas on the outer tube individually for the upper and lower tuyeres. . In some cases, an inert gas may be used as the blowing gas, and in this case, tuyere cooling gas is not necessary, so it is preferable to use single-tube structures for each tuyere 5 and 6. can. In addition,
The upper tuyere 5 may be exposed above the steel bath if the melting loss of the refractory lining progresses and the surface position of the steel bath is lowered. In that case, the exposed upper tuyere must be closed. If the upper tuyere 5
In this way, even after the upper tuyere on the upper stage is exposed and closed, the upper tuyere on the lower stage can be used to form the upper tuyere at several levels. You can continue blowing. In the converter shown in Fig. 1, a large amount of oxidizing gas is injected from the lower tuyere 6 near the bottom of the furnace, while a small amount of gas is injected from the upper tuyere 5 near the steel bath surface to the extent that molten iron does not leak. By blowing in a large amount of oxidizing gas from the lower tuyere 6 near the bottom of the furnace, the steel bath will be vigorously stirred until it rises to the surface of the steel bath, resulting in the same effect as in the case of a bottom-blown converter. It can achieve the same effects as a bottom-blown converter, such as lowering the iron concentration (T.Fe) in the slag and improving iron yield. On the other hand, if a small amount of gas is injected from the lower tuyere 6 near the bottom of the furnace to prevent molten iron from leaking, and a large amount of oxidizing gas is injected from the upper tuyere 5 near the steel bath surface,
A large amount of oxidizing gas injected from the upper tuyere 5 heats the molten iron to a high temperature near the surface of the steel bath, and the iron oxides generated at that part (flame point) do not have a sufficient reach and reach the steel bath. Since it is fixed in the slag layer on the surface, the iron oxide is not sufficiently reduced by the carbon in the molten iron, and as a result, the iron concentration (T.Fe) in the slag increases. Therefore, the dephosphorization reaction is promoted in the same way as in the LD converter steel manufacturing method. In addition, by adjusting the flow rate of the oxidizing gas blown in from the upper tuyere 5 near the steel bath surface, the iron concentration in the slag can be controlled in the same way as adjusting the height of the top blowing lance in an LD converter. can do. Therefore, in this case, almost the same effect as the conventional LD converter steel manufacturing method can be obtained. As mentioned above, if a side-blown converter as shown in FIG. It is possible to perform blowing which has almost the same effect as the manufacturing method and blowing which has almost the same effect as the conventional LD converter steel manufacturing method. Therefore, by changing the ratio of gas flow rates supplied to the upper tuyere 5 and lower tuyere 6 during blowing, the LD
The advantages of the converter steelmaking method and the advantages of the bottom-blown converter steelmaking method can be obtained at the same time. Blowing under such conditions is the blowing method of the first invention of this application. To explain this blowing method more specifically, at the start of blowing, the gas flow rate supplied to the upper tuyere 5 near the steel bath surface is set to a large flow rate, and the gas flow rate supplied to the lower tuyere 6 near the bottom of the furnace is set to a large flow rate. The flow rate is kept low enough not to leak, and blowing is continued in this state from the early to middle stages of blowing. The C concentration in the molten steel is about 0.25 to 0.35%, preferably 0.3%.
%, the gas flow rate supplied to the lower tuyere 6 is raised to a large flow rate, and the gas flow rate supplied to the upper tuyere 5 is lowered to a small flow rate that does not leak molten iron, and in that state. Bring it to the end of blowing. If blowing is performed in this way, the iron concentration in the slag becomes considerably high in the early and middle stages of blowing, similar to the LD converter steelmaking process, and dephosphorization is promoted. After changing, the steel bath is well stirred as in the bottom blowing converter steelmaking process, and as a result, the iron concentration in the slag increases dramatically at the end of blowing, as in the case of the LD converter steelmaking process. This will be prevented. Therefore, a high dephosphorization rate and good iron yield can be achieved at the same time. Next, examples of the blowing method as described above, reference test examples in which blowing was performed with a fixed gas flow rate in a side-blowing converter shown in Fig. 1, and comparative examples in which bottom-blowing or top-blowing were performed are presented. show. Example: 5 tons of hot metal was charged into a small side-blown converter as shown in Figure 1, and 250 kg of molten metal was charged as an auxiliary material.
CaO was charged and blowing was performed. However, the inner diameter of each tuyere is 13 mm, and the upper tuyere 5 is 400 mm from the hearth bottom.
Six lower tuyeres 6 are provided at equal intervals at a height of 50 mm from the hearth bottom, and the flow rate is controlled individually from the upper tuyere 5 and lower tuyere 6. Pure oxygen gas was blown in under control, and the gas flow rate was changed in the middle of blowing. The depth of the stationary steel bath is 500 mm. Reference test example 1 Using a side blowing converter similar to the above, blowing conditions were set similar to those of a bottom blowing converter, i.e., the gas flow rate at the upper tuyere was fixed at a small flow rate and the gas flow rate at the lower tuyere was fixed at a large flow rate. We performed blowing training. Other conditions are the same as in the example. Reference test example 2 Using a side blowing converter similar to the above, blowing conditions were set similar to those of an LD converter, i.e., the gas flow rate at the upper tuyere was fixed at a large flow rate and the gas flow rate at the lower tuyere was fixed at a small flow rate. I did some blowing. Other conditions are the same as in the example. Comparative Example 1 Pure oxygen bottom blowing was carried out using a small bottom blowing converter having a furnace body profile similar to the side blowing converter shown in FIG. However, the number of bottom blowing tuyeres is six in total, each with an inner diameter of 13 mm. The raw materials charged were the same as in the examples. Comparative Example 2 Pure oxygen top-blowing was carried out using a small-sized top-blowing converter having a furnace body profile similar to the side-blowing converter shown in FIG. However, a four-hole lance was used as the top blowing lance, and the lance height was 600 mm.
The raw materials charged were the same as in the examples. Examples (test numbers 1 to 4), each reference test example, gas flow conditions in each comparative example, C and P concentration analysis values when hot metal and blow-off, C when changing gas flow rate (examples only), blow Table 1 shows the analytical values of iron concentration (T.Fe) in the slag at the time of stopping.

[Table] From Table 1, in the example in which the gas flow rate of the upper and lower tuyeres was changed at around 0.3% C, when the blow-off P concentration was LD converter (Comparative Example 2) It is clear that the iron concentration (T.Fe) in the slag has decreased to a value close to that of the bottom-blown converter (Comparative Example 1). By using the side-blowing converter shown in Figure 1 and fixing the gas flow rate of the upper and lower tuyeres to appropriate values, bottom-blowing converters can be achieved as shown in Reference Test Examples 1 and 2. It is clear that blowing can be carried out with almost the same effects as furnace steelmaking and top-blown converter steelmaking. As is clear from the above description, the blowing method of the first invention of this application can simultaneously promote dephosphorization and improve the iron yield. This method is useful as a new blowing method that combines the advantages of bottom-blown converter steelmaking and top-blown converter steelmaking. In addition, the side-blown converter which is the second invention of this application,
In addition to being optimal for carrying out the blowing method of the first invention, it is also possible to obtain a blowing effect similar to that of a bottom-blown converter or a top-blown converter using the same converter by simply changing the blowing gas flow rate conditions. Since similar blowing effects can be obtained, effects such as optimal blowing depending on the composition of the hot metal to be blown and the type of steel to be finally obtained can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of a side blowing converter used in the blowing method of the first invention, that is, an embodiment of the second invention. 1...Furnace body, 5...Upper tuyere, 6...Lower tuyere, 7...Upper tuyere piping system, 9...Lower tuyere piping system, 10, 11...Flow rate control valve (flow rate control device) ).

Claims (1)

[Claims] 1. An appropriate number of upper and lower tuyeres are provided vertically at intervals in the part of the furnace side of the converter that is immersed in the molten iron, and at the start of blowing, the upper tuyeres are removed. The flow rate of the blowing gas supplied to the lower tuyere is set to a higher flow rate than the blowing gas supplied to the lower tuyere, and during blowing, the gas flow rate supplied to the lower tuyere is set to be larger than the gas flow rate supplied to the upper flow rate. A side blowing converter blowing method characterized by changing the gas flow rate of the upper tuyere and lower tuyere so that the following is achieved, and continuing the blowing in that state until the end of blowing. 2. The blowing gas flow rate of the upper and lower tuyeres is changed when the carbon concentration in the molten iron reaches a value within the range of 0.35 to 0.25%. Blowing method. 3 An appropriate number of upper and lower tuyeres are provided at vertical intervals in the part of the furnace side that is immersed in the molten iron, and piping for supplying gas for blowing to the upper tuyeres and lower tuyeres are provided. A side-blowing converter characterized in that piping for supplying gas for blowing is provided in a separate system, and a flow rate control device is provided in each of the upper tuyere piping system and the lower tuyere piping system.