JPS625969B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a converter operating method, and provides a method that enables efficient converter operation by effectively suppressing slopping occurring in the furnace and stabilizing blowing. As is well known, in a converter, oxygen blown into the molten metal oxidizes impurities in the molten metal and promotes the refining reaction.
During this refining, some iron in the molten metal is also oxidized and mixed into the slag as iron oxide. However, if too much iron oxide is mixed into the slag, it becomes slag, forming the slag, and causing a so-called slopping phenomenon in which the slag overflows from the furnace mouth. This sloping occurs due to operating conditions such as the hot metal blending ratio, slag basicity, and many other factors, and has become a major operational problem. As methods for suppressing the above-mentioned slopping, for example, methods have been proposed, such as a method of injecting a block of inhibitor from an above-furnace bunker when sloping occurs, and a method of blowing inhibitor powder together with blowing gas and carrier gas from a bottom blowing nozzle. The present inventors applied these methods to an actual converter and obtained the following findings. First, with the method of introducing bulk inhibitor from the above-furnace bunker, the timing of introducing the inhibitor is delayed and sloping may not be suppressed.Also, the sloping suppressing effect varies greatly depending on the particle size, so sufficient suppression cannot be achieved. The drawback is that it may not be effective. In other words, the above-furnace bunker is usually installed at a distance from the converter, and if the inhibitor is weighed and introduced after detecting slopping, it will take a considerable amount of time to introduce it into the furnace, making quick action impossible. There was a problem that I couldn't get it. Furthermore, if the particle size of the inhibitor is too fine, the introduced inhibitor will spread and float on the slag forming surface, reducing the slopping inhibiting effect. On the other hand, if it becomes too large, the inhibitor sinks to the slag-metal interface, reducing the inhibitory effect, and the influence of the undissolved inhibitor on the refining reaction cannot be ignored, adversely affecting quality. Furthermore, in the case of block-like inhibitors, there are no lumps of a fixed size and shape, so the reaction varies, and therefore the slopping suppressing effect also varies. On the other hand, as a method of blowing a powdered inhibitor through a bottom blowing nozzle, for example, blowing of limestone powder and carbon powder in Japanese Patent Publication No. 57-5809, carbon injection in Japanese Patent Application Laid-open No. 129617-1974, etc. has been proposed. However, these methods are bottom-blowing operation methods that aim to save costs by melting low [P] steel, adding a heat source, and using inexpensive auxiliary materials, and cannot be expected to be effective in suppressing slopping. . That is, it is thought that this is because the powder is blown into the molten steel due to bottom blowing, so a slag-metal reaction occurs through the molten steel reaction, and it cannot directly suppress the slag properties. In addition, powder blowing from a bottom blowing nozzle has the drawback of high equipment costs and the fact that the tuyere is always in contact with molten steel, making it extremely difficult to manage the tuyere. The present invention was made as a result of various experimental studies to solve the drawbacks and problems of the conventional methods, and it is possible to quickly and reliably perform slopping with simple operations when a slopping phenomenon is detected. This is a converter operating method that makes it possible to suppress blowing and stabilize blowing.The gist of this is that a tuyere is installed on the converter wall at a position where it is not immersed in molten steel during normal operation, and from the tuyere, blowing is made possible to prevent blockage. Gas is injected to prevent tuyere clogging, and when a slopping phenomenon is detected, one or more powders of limestone powder, quicklime powder, coal powder, and coke powder are injected using the anti-clogging gas as a carrier gas. This is a converter operating method characterized by suppressing slopping occurring in the converter and stabilizing blowing. Hereinafter, the present invention will be explained in detail based on Examples. FIG. 1 is a structural diagram of an embodiment in which the method of the present invention is applied to a top-blown converter, where 1 is a converter, 2 is a lining brick,
3 is a top blowing lance, and 4 is a tuyere provided on the furnace wall 5. The tuyere 4 is provided at a position where the furnace wall 5 is not immersed in the molten steel 6 during normal operation. Reference numeral 7 denotes a gas supply device for supplying an anti-occlusion gas to the tuyere 4, which will be described later, and is connected to the tuyere 4 via a flow rate adjustment device 8 and a supply pipe 9. 10 stores powder as a slopping suppressant, which will be described later;
It is also a powder feeding device for supplying powder to the supply pipe 9, and is connected to the supply pipe 9 between the gas supply device 7 and the tuyere 4 via a powder supply device 11 such as a feeder. Accordingly, in the present invention, under normal operating conditions, the minimum necessary gas at a level slightly higher than the furnace internal pressure is continuously ejected from the tuyere 4 into the furnace to prevent the tuyere 4 from clogging. The gas for preventing blockage includes argon (Ar),
Carbon dioxide (CO ₂ ), nitrogen (N ₂ ), etc. can be used.
It may be selected as appropriate, taking into consideration the quality impact on steel, price, ease of handling, etc. For example, Table 1 shows the price index of the gas mentioned above, and from the price point of view, N ₂ , CO ₂
is advantageous.

[Table] On the other hand, N ₂ may slightly increase the [N] level in blown up molten steel. In the experience of the present inventors, for ordinary carbon steel, the adverse effect on quality due to the increase in the [N] level due to N ₂ injection was almost negligible, but for high-grade steels other than the ordinary carbon steel. In this case, the increase in [N] level mentioned above may have a negative effect on quality, and CO ₂ or Ar
It was preferable to use Now, if a slopping phenomenon is detected during the operation (blowing), the powder supply device 11 is driven, the powder from the powder pumping device 10 is supplied to the supply pipe 9, and the blockage prevention gas is is blown into the furnace as a carrier gas. As a powder, limestone powder or quicklime powder has the function of suppressing sloping by reacting with excess iron oxide in slag to generate gas, or by thermally decomposing itself and generating gas. , coal powder, coke powder alone, or two of them.
The above methods are used in combination at an appropriate ratio. In the present invention, as the powder is directly blown into the forming layer 12 as shown in FIG. 1, even if the powder is extremely fine, it will not scatter outside the forming layer. All of the injected particles are dispersed in the forming layer and react directly with the slag of the forming layer 12. Therefore, the functions of the powder can be fully exhibited, and slopping can be suppressed in a short time. The type and amount of powder to be supplied may be determined depending on the furnace capacity, the type of steel to be manufactured, the degree of slopping, etc., and the amount and pressure of the gas blown as a carrier gas are determined according to the amount of supply. The flow rate adjustment device 8 may be adjusted. By the way, known methods can be applied to detect the sloping phenomenon. For example, there is a method in which an operator observes the furnace mouth frame with his own eyes and makes a judgment based on past experience, and a method in which the slag state of slag is detected physically, chemically, as one of the blowing reactions during blowing. Alternatively, it can be estimated quantitatively and qualitatively using a visual method, and then the operator can make a judgment using the output data as an operator guide.
A method of detecting slag formation during blowing, a method of estimating the slag formation state from the sound level in the furnace, vibrations of the furnace body, or lance vibration, and detecting it from the slag formation state; A method of estimating the amount of oxygen using exhaust gas information and detecting the amount of oxygen in the slag can be applied. It is also possible to automatically determine and predict the occurrence of slopping by storing the relationship between the blowing parameters and slopping in, for example, a computing device and inputting the detected values during blowing into the computing device. In the present invention, it is possible not only to detect the actual occurrence of sloping, but also to predict the occurrence of sloping from the blowing parameters and control the blowing of powder based on the predicted information. In the present invention, detecting a sloping phenomenon includes even predicting the sloping. Next, specific examples of the present invention will be described. Example 1 The method of the present invention was carried out in producing low carbon Al killed steel in a 180 ton top-bottom blowing converter. In this example, one tuyere 4 was provided on the furnace wall at a position that is not immersed in molten steel during normal operation (in this example, at a position 6 m from the furnace mouth). 120 Nm ³ /Hr/piece of CO ₂ gas was constantly blown into the tuyere 4 to prevent clogging. Slopping was detected by the method described below, in which the amount of residual oxygen in the furnace was calculated using exhaust gas information, the state of slag sludge was estimated, and the occurrence of sloping was detected from the slag slag state. First, the relationship between the amount of residual oxygen in the furnace and the occurrence of slopping was investigated. Figure 2 is a chart showing the results. In the figure, the horizontal axis shows the time since the start of blowing, and the vertical axis shows the amount of residual oxygen in the slag.In many operations, the occurrence of slopping is detected by observation at the furnace mouth, and the amount of residual oxygen and time at that time are calculated. It has been measured and plotted. From this chart, it was confirmed that on the side where the amount of residual oxygen is higher than the broken line Z, the slopping occurrence rate increases rapidly. Therefore, in this example, when we tracked the fluctuations in the amount of residual oxygen in the furnace during blowing and monitored the occurrence of the slopping phenomenon, we found that the amount of residual oxygen became higher than the broken line Z at point X shown in FIG. An occurrence of slopping has been detected. For this reason, the above-mentioned blockage prevention valve is immediately opened from the tuyere 4.
130 limestone powder with _CO2 gas as carrier gas
It was injected at a flow rate of Kg/mm/piece. Use limestone powder with a particle size of 3 mm or less, and adjust the flow rate of CO ₂ gas.
The pressure was increased to 600 Nm ³ /Hr to allow the limestone powder blown into the furnace to function as a carrier gas. One minute after starting the injection of limestone powder, the amount of residual oxygen in the furnace decreased to point Y shown in FIG. 3, so it was judged that slopping had been suppressed, and the injection of limestone powder was stopped. Along with this, the amount of CO ₂ gas blown from the tuyere 4 was returned to 120 Nm ³ /Hr. Example 2 Similar to Example 1, the type of powder for suppressing sloping and the effect of suppressing slopping were investigated when producing low carbon Al killed steel in a 180 ton top-bottom blowing converter. Table 2 shows the relationship between the type of powder and the success rate of slopping suppression in comparison with the conventional method.

[Table] In the conventional method shown in Table 2, when slopping is detected, 300 lumps of quicklime (particle size 15 to 30 mm) are poured from the furnace mouth.
This is an example in which Kg/time was introduced. Also, in the method of the present invention
Various powders (particle size 3 mm or less) are used for slopping detection using CO ₂ gas as a carrier gas.
Inject 130Kg/mm/piece, and calculate the amount of CO ₂ gas at that time.
It was set to 600Nm ³ /Hr. The criterion for success in suppressing slopping is whether or not sloping is completely suppressed within 1 minute after sloping is detected and injection of powder (in the conventional method, lump quicklime) is started. Success was defined as complete suppression within a certain period of time. From Table 2, it is clear that when the method of the present invention is used, the success rate of suppressing slopping is extremely high compared to the conventional method. Now, FIG. 4 shows a structural diagram of another embodiment of a converter to which the method of the present invention, which makes it possible to select and inject the plurality of gases and powders, is applicable. In this figure, 70a, 70b, 70c are gas supply devices that supply different types of gas, respectively, and are connected to the supply pipe 9 via switching valves 13a, 13b, 13c and flow rate adjustment devices 80a, 80b, 80c. ing. Therefore, the switching valves 13a, 13
Any desired gas can be blown by controlling b and 13c. Also, 10a, 10b, 1
0c is a powder feeding device, and the powder stored in each of the powder feeding devices 10a, 10b, 10c is fed by the powder feeding devices 11a, 11b, 11c, so that the necessary powder can be delivered as a single powder, or , mixed in an appropriate ratio and fed to the supply pipe 9. In the method of the present invention, the powder is blown into the forming layer together with a carrier gas that does not adversely affect the quality of the steel, so it is possible to use fine powder, which is highly reactive but has been extremely difficult to use in the past. There are advantages. In addition, it is possible to directly inject the powder as the suppressor into the forming layer as soon as sloping is detected, which makes it possible to reliably suppress sloping in an extremely short period of time and at a high rate. It has the effect of Stable blowing can be done there. As described above, the practical effects of the present invention are very large.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram showing an example of a top-blown converter to which the method of the present invention can be applied, Fig. 2 is a diagram showing the relationship between the amount of residual oxygen in the furnace and the occurrence of slopping, and Fig. 3 is a diagram showing the relationship between the amount of residual oxygen in the furnace and the occurrence of slopping.
The figure is a chart showing an example of the results of a follow-up investigation of the amount of residual oxygen in the furnace during blowing, and FIG. 4 is a structural diagram showing another embodiment of a top-blowing converter to which the method of the present invention can be applied. 1: converter, 2: lining brick, 3: top-blown lance,
4: Tuyere, 5: Furnace wall, 6: Molten steel, 7, 70a, 7
0b, 70c: Gas supply device, 8, 80a, 80
b, 80c: flow rate adjustment device, 9: supply pipe, 10,
10a-10c: Powder feeding device, 11, 11a-
11c: powder supply device, 12: forming layer, 13a to 13c: switching valve.

Claims (1)

[Claims] 1. A tuyere is provided on the converter wall at a position where it is not immersed in molten steel during normal operation, and an anti-occlusion gas is blown through the tuyere to prevent clogging of the tuyere, and when a slopping phenomenon is detected, the anti-occlusion gas is A converter characterized in that one or more of limestone powder, quicklime powder, coal powder, and coke powder is injected as a carrier gas to suppress slopping occurring in the converter and stabilize blowing. Operating method.