JPH0468363B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method of operating steel refining using a converter. Purpose of the Invention The purpose of the top-blown or top-bottom blown converter operating method is to reduce the carbon contained in the molten metal by oxygen supplied during converter blowing, and to reduce the slag-forming agent introduced into the furnace. The purpose is to cause dephosphorization, desulfurization, etc. to occur through the reaction between the molten slag and the molten metal. In this case, the state of slag slag is a major factor that determines the results of converter operation, and if slag progresses excessively,
This promotes the forming state of slag and eventually causes an abnormal reaction in which slag overflows outside the furnace, i.e., slopping, which causes various problems such as decreased work efficiency, decreased iron yield, deterioration of the working environment, and damage to equipment. . On the other hand, in the case of poor slag formation, the dephosphorization effect and the like deteriorate, making it impossible to obtain steel of desired quality. Therefore, it is desirable to carry out blowing in such a way that excessive slag is formed, and to control the blowing so that sloping does not occur. However, after the middle stage of blowing, when the decarburization reaction actively occurs, the oxygen that is not consumed for decarburization gradually increases, resulting in an increase in FeO in the slag, which reacts with Mn in the molten metal to produce manganese oxide. formation, resulting in a decrease in manganese content,
At this stage, it is desirable to be able to reduce the amount of oxygen in the slag or reduce the amount of slag itself to enrich the slag with Mn. The present invention provides a method that enables the above-mentioned desired operation. Structure and operation of the invention The structure of the present invention is as follows: 1. In a top-blowing or top-bottom blowing converter operating method,
2. A converter operating method, characterized in that blowing is carried out so that the slag always shows a superslag state from the early to middle stages of blowing, and that a forming adjustment operation is carried out when sloping is predicted or detected; and 2. In the top-blown or top-bottom blown converter operating method,
From the early to middle stages of blowing, the slag is always blown so that it shows a state of excessive slag, and when sloping is predicted or detected, forming adjustment operations are carried out, and at the end of the blowing, the amount of oxygen in the slag or A converter operating method characterized by carrying out a Mn enrichment operation using the slag formation status as an indicator. As mentioned above, one of the most important objectives of converter operation is decarburization. The oxygen jet blown from the lance collides with the molten metal surface, is quickly absorbed by the molten metal, reacts with C in the molten metal, and is discharged from the furnace mouth as CO or CO ₂ gas. However, the rate of decarburization reaction in the actual furnace -
dc/dt changes as follows. In other words, early after the start of blowing, the concentration of Si in the molten metal is still high.
Since the molten metal temperature is still low, the decarburization reaction rate gradually increases. When the reaction progresses to a certain extent and the temperature of the molten metal rises, almost 100% of the supplied oxygen is consumed for decarburization, and the reaction rate becomes constant. After that, the concentration of C in the molten metal decreases, and when the diffusion of C in the molten metal to the collision surface between the oxygen jet and the molten metal becomes rate-determining,
The reaction rate gradually decreases. Therefore, considering the change in reaction rate over time based on the supply of oxygen - dc/dO ₂ , or decarbonization efficiency, if the oxygen flow rate per hour is constant, then the change in decarburization efficiency in exactly the same way over time can be calculated as follows: The graph is schematically drawn as shown in Figure 1, and -dC/dO ₂ at a constant reaction rate is usually around 1.08 Kg/Nm ³ . The time period of the flat line in this graph is defined as the middle period of blowing, and the periods before and after that are defined as the early and final stages of blowing, respectively. Of course, the change in -dC/dO ₂ during actual blowing is not as simple as shown in FIG. 1, but the tendency can be considered to be roughly represented by FIG. 1. In the early and middle stages of blowing, Si in the molten metal is oxidized to SiO ₂ by the injected oxygen.
This reacts with a slag-forming agent, such as quicklime, which is introduced into the furnace, to advance slag formation, and together with the reaction between oxygen and molten metal or the generation of (FeO) in the slag by a solvent, dephosphorization is performed. Therefore, it is desirable that slag generation tends to be excessive during this time. For this purpose, for example, the lance height may be increased, the top-blown oxygen jet may be soft-blown, and a blowing operation may be performed to increase the oxygen potential in the slag. Incidentally, the slag slag formation referred to in the present invention is a state in which slag production tends to be excessive as described above, and the oxygen potential in the slag remains high, causing slag formation of the slag-forming agent such as quicklime. This refers to a blowing situation that promotes excessive slag and causes a large amount of slag to exist in the furnace. Therefore, it is possible to determine whether or not there is excessive slagging by checking the amount of oxygen remaining in the furnace during blowing. For example, using the amount of residual oxygen in the furnace as an index, the limit of its temporal change can be patterned and preset in relation to the blowing time based on past results, etc., and can be used as a criterion for determining the excessive slag situation. . That is, by detecting the temporal change in the amount of residual oxygen in the furnace during operation and comparing it with the permissible limit pattern, it is possible to determine whether or not an excessive sludge condition exists. In other words, if the temporal change is below the permissible limit pattern, it can be determined that slag formation is not sufficiently promoted, and if it is above the permissible limit pattern, it can be determined that there is an excessive sludge formation situation. Temporal changes in the amount of residual oxygen in the furnace during blowing can be determined by calculating the flow rate and composition of exhaust gas, the amount of oxygen supplied, the temperature of molten steel, the carbon content, etc., as shown in JP-A No. 57-29519, for example. It can be easily detected by performing arithmetic processing. Further, whether or not the slag is present can also be determined by measuring the slag level. That is, when the oxygen potential in the slag becomes high and the slag becomes excessively slag, it means that an excessive amount of slag is formed. Therefore, similar to the above-mentioned permissible limit pattern of temporal change in residual oxygen amount, the slag level pattern during blowing is set in advance and used as a judgment criterion, and the slag level during blowing can be determined by various means described below. By directly detecting it and comparing it with the set pattern, it can be determined whether the inside of the furnace is in an over-slagging state or not reaching an over-slagging state. However, such blowing with excessive slag always involves the risk of slopping. Therefore, prediction or detection of sloping becomes an extremely important technique. Various attempts have been made to detect the slag level in the past, including the acoustic measurement method
33790), Vibration measurement method (Japanese Patent Application Laid-Open No. 114414/1983),
A method for measuring furnace internal pressure (Japanese Patent Application Laid-Open No. 104417-1982), a microwave measurement method (Japanese Patent Application Laid-open No. 140812-1982), a method for measuring the surface temperature of a furnace body (Japanese Patent Application Laid-open No. 48615-1987), etc. have been proposed. The acoustic measurement method attempts to predict the occurrence of sloping by estimating the slag level by ascertaining changes in the frequency and intensity of the sound generated from inside the furnace during blowing, while the vibration measurement method attempts to predict the occurrence of slopping. This method attempts to predict the occurrence of slopping by estimating the slag level or state by understanding vibration changes and waveform transitions, while the furnace pressure measurement method attempts to predict the occurrence of slopping by understanding changes in the furnace exhaust gas injection pressure during blowing. This method attempts to predict the occurrence of slopping, and the microwave measurement method involves directly projecting microwaves into the furnace during blowing.
This method uses the principle of FM radar to directly measure the slag level and predict the occurrence of slopping.The furnace surface temperature measurement method captures the radiant energy at the top and bottom of the furnace body as temperature, and measures temperature changes and peaks. It attempts to detect the occurrence and amount of sloping from values etc. In response to these, the present applicant first installed an in-furnace light measuring device in a through hole provided in the non-immersed part of the converter wall,
We applied for a patent (Japanese Patent Application No. 37872/1983) for a method for predicting slopping and detecting poor slag formation by observing the intensity and/or wavelength changes of the light in the furnace to detect the forming level. A patent application has been filed for a method for detecting the occurrence of slopping by detecting the light inside the furnace with a light detection device and extracting the proportion of mainly yellowish colors and the fluctuations in that proportion from the obtained color signal. This method can directly and quickly check the situation inside the furnace, especially the slag level. As mentioned above, by comparing the preset slag level pattern and the detected slag level, it is possible to determine whether or not there is excessive slag, and even if there is excessive slag, it is possible to determine whether the slag level is abnormal or not. By setting a level at which the risk of slopping increases, it is possible to accurately predict or detect the occurrence of sloping. Various methods have been proposed in the past for forming adjustment operations to be performed when sloping is predicted or detected. For example, adding a slopping inhibitor, increasing the flow rate of bottom blowing, lowering the lance height, reducing the flow rate of oxygen supply, and adding auxiliary materials are all effective, but the order of priority is as follows: is preferred. Further, when slopping is predicted or detected, if a forming adjustment operation less than the above-mentioned increase in bottom blowing amount is scheduled in advance before the start of blowing, that scheduled operation may be given priority. However, at the final stage of blowing, as mentioned above, FeO in the slag gradually increases and reacts with Mn in the molten metal to become MnO and transfers to the slag, or Mn in the molten metal and MnO in the slag Due to the equilibrium relationship between FeO and FeO, changes occur in which Mn decreases as FeO in the slag increases. Preventing these changes and enriching Mn will make effective use of valuable Mn. This is a valuable operation. In this case, there are two methods: either aiming to reduce the FeO in the slag, or aiming to reduce the formed capacity of the slag itself. The indicator for blowing operations that is closely related to FeO in the slag is the amount of oxygen in the slag, which includes the blowing oxygen flow rate, exhaust gas flow rate, exhaust gas composition, the amount and composition of hot metal charged to the converter, It is determined from the input brand (composition/ingredients) of auxiliary raw materials, input speed of auxiliary raw materials, etc. Therefore, before blowing, especially at the end of blowing, Mn
The permissible limit for the temporal change in the amount of oxygen in the slag should be patterned in consideration of the target enrichment value, and the blowing operation should be performed so that the amount of oxygen in the slag, which is calculated sequentially during operation, falls within the predetermined permissible limit. . Thus, an example of such manipulation is the adjustment of top blown oxygen jets. This is to control the oxygen potential in the slag by changing the stirring power of the top blowing jet to change the stirring state between the slag and metal and the balance of various reactions. Increase in FeO in the slag, and lowering the lance height to create a harder blow will lead to a decrease in FeO in the slag. Another example is the adjustment of bottom blow gas. This is to change the stirring force of the gas by changing the flow rate of the bottom blowing gas, changing the stirring state between the slag and metal and the balance of various reactions, and controlling the oxygen potential in the slag. Stirring results in a decrease in FeO in the slag, and lowering the gas flow rate leads to an increase in FeO in the slag. When attempting to reduce the volume of slag formed, the slag level inside the furnace is measured by detecting the aforementioned light inside the furnace with a photodetector.
Using a pattern of temporal changes in slag level that takes into account the target value of Mn enrichment in advance, as an indicator,
By performing an operation similar to the above-described forming adjustment operation, it is possible to lower the slag level, that is, reduce the formed capacity of the slug. Although the object of the present invention can be achieved by the method described above, further examples will be described and explained. Example 1 A 170T top-bottom blowing converter was used, and the above-mentioned photodetector was used to predict or detect sloping as follows. In other words, the vertical distance below the furnace mouth is 2.5
A through-hole was made in the side wall of the converter of m, and a probe with a built-in optical fiber was placed facing the through-hole to capture the optical image inside the furnace, and a CCD camera was used as a photoelectric conversion device to perform photoelectric conversion. The proportion of the area occupied by the yellowish color in the captured image, that is, the area ratio, is determined and binarized at a threshold level of 50% to obtain a binary signal of the area ratio. In order to know the temporal change in this area ratio, it is passed through a high-pass filter with a cutoff frequency of 5 Hz, converted into a positive value, and then binarized at a threshold level of 50% to obtain a binary signal of the amount of change in area ratio. By combining these, the possibility of sloping was determined as shown in Table 1, and a sloping suppression operation was performed when there was a possibility of sloping. In the early and middle stages of blowing, the lance height of the standard pattern is
The height was set at 200 mm, and the amount of oxygen supplied was kept constant during the entire blowing operation. At the time when it was determined that there was a possibility of slopping, the forming adjustment operations listed in Table 2 were performed in accordance with the priority order shown in Table 2. However, when slopping was predicted or detected, if operations No. 2 to No. 5, which are equivalent to forming operations, were scheduled before the start of blowing, priority was given to them. This kind of operation was carried out 25 times, and the conventional method was carried out 25 times, and the average values and variations of (T-Fe)% in the slag, blow-off [P] x 10 ^-3 %, blow-off [Mn] x 10 ^-2 % were determined. was calculated and shown in Table 3. Example 2 A 170T top-bottom blowing converter was used, and the slopping prediction or detection method was the same as in Example 1, with slag overforming blowing at the beginning and middle of blowing, and slag overforming blowing at the end of blowing.
Mn enrichment blowing was performed. In the early and middle stages of blowing, the lance height is the standard +200mm, the oxygen supply flow rate is the standard amount, at the end of the blowing, the lance height is -100mm, the oxygen supply flow rate is the standard amount, and the bottom blowing gas flow rate is the standard +300Nm ³ /Hr. The operations at the time when it was determined that there was a possibility of slopping were the same as in Example 1. Such operation was carried out 21 times, and the results are shown in Table 4, which is the same table as in Example 1. Example 3 A 170T top-bottom blowing converter was used, and the slopping prediction or detection method was the same as in Example 1, with slag overforming blowing being performed during the early and middle stages of blowing, and slag overforming during the final stage of blowing.
Mn enrichment blowing was performed. The lance height was set to the standard +200 mm during the early and middle stages of blowing, and returned to the standard during the late stage of blowing.The flow rate of oxygen was set to the standard throughout the entire blowing period, and the flow rate of bottom blowing gas was the same as the standard during the early and middle stages of blowing. Standard + in the latter half of blowing training
The pressure was set at 300Nm ³ CO ₂ /Hr. Based on many past operating results, we determined the blowing oxygen flow rate, exhaust gas flow rate, exhaust gas components, the amount and composition of melt cleaning charged to the converter, and the brands of auxiliary raw materials (composition and composition).
As shown in Fig. 2, the permissible limit value for the change in oxygen content in the slag over time was prepared in advance from the input rate of auxiliary raw materials, etc., and was used as a standard for operation. During operation, the sequentially calculated oxygen content in the slag was compared with the pattern of the allowable limit value, but in the early and middle stages of blowing, due to slag hyperformation blowing, the oxygen content in the slag showed changes that were at or above the upper limit value. At the time when the above-mentioned sloping prediction or detection is determined (second
At points X and Y in the figure, forming adjustment operations similar to those in Example 1 were performed. In the later stages of blowing, the aforementioned pattern of increasing oxygen content in the slag occurs;
At Z) in the figure, 0.9 tons of ferromanganese ore was added to cool the slag and increase Mn. Such operation was carried out 18 times, and the results are shown in Table 5, which is the same table as in Example 1. When the blowing ratio of slopping occurrence was calculated for all the examples, it was found to be 3% lower than 28% for the conventional method.

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[Table] Effects of the Invention As detailed above, if the operating method of the present invention is adopted, the operation of the converter will be stable, the variation in the quality of tapped steel will be small, and if the Mn enrichment operation is performed, the It is possible to reduce the amount of ferroalloy added, which is extremely valuable in terms of steelmaking technology.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the change over time in the decarburization oxygen efficiency, and FIG. 2 is a diagram showing an example of the Mn-enriching operation method of the present invention.

Claims (1)

[Claims] 1. In a top-blowing or top-bottom blowing converter operating method,
A converter operating method characterized by blowing so that the slag always shows a slag condition from the early to middle stages of blowing, and performing a forming adjustment operation when slopping is predicted or detected. 2. In the top-blowing or top-bottom blowing converter operating method,
From the early to middle stages of blowing, the slag is always blown so that it shows a state of excessive slag, and when sloping is predicted or detected, forming adjustment operations are carried out, and at the end of the blowing, the amount of oxygen in the slag or A converter operating method characterized by carrying out Mn enrichment operation using the slag status as an indicator.