JPS6154843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dynamic endpoint control of carbon content in steel in converter operation.

In converter blowing, the most important issue is to adjust the temperature and composition of molten steel, especially the carbon content, to target values at the time of blow-off. Therefore, during the blowing process, analyze the exhaust gas from the converter or measure the flow rate, or measure the molten steel temperature and carbon content in the steel using a sublance.
A so-called dynamic end-point control has been developed that determines the carbon content in steel at the time of measurement and adjusts subsequent operating conditions to improve accuracy. In this dynamic end point control method, the end point carbon content can be accurately determined based on the quality of the model that correlates the decarburization rate or the amount of oxygen to be blown from the measurement point to the end point with the carbon content in the steel. whether it can be estimated or not, and the method of expressing the model is concise;
Whether or not the range of application that can be controlled by this model is wide is important in evaluating its practicality. By the way, a model has been proposed in which the decarburization rate is expressed as an exponential function with respect to the carbon content in steel, but it is necessary to identify the model, that is, to calculate the coefficients in the exponential function from actual operation data by multiple regression analysis. It is not easy to make a decision that can accommodate all operating conditions. In addition, in JP-A-52-5613, the relationship between the actually measured carbon content in steel at the final stage of blowing, the amount of oxygen blown from this measurement point to the end point, and the end point carbon content was determined by furnace and steel type based on actual operation data. In addition, the samples are divided into extraction groups according to the fact that the measured carbon content in the steel at the end of blowing is at the same level. In the blowing operation that is to be controlled, the carbon content in the steel is measured at the end of the blowing process, a suitable decarburization curve is selected from the various decarburization curves mentioned above, and the carbon content is calculated from the target end point carbon content. A method is proposed to determine the amount of oxygen that should be injected until the end point. However, in such a method, a decarburization curve is created for each of these various operating conditions and measured carbon content in steel, so the model identification work is extremely complicated and is not practical.

The present invention has been made in view of such circumstances, and it is possible to determine the amount of oxygen to be blown from the time of measuring the decarburization rate or the carbon content in steel at the end of blowing to the end point, and the actual carbon content in steel. The purpose of the present invention is to propose a mathematical formula that correlates the two concisely and accurately, and to provide a method for controlling the end point carbon content based on the mathematical formula.

In the method for controlling carbon content in steel according to the present invention, the oxygen consumption rate at the final stage of blowing in converter operation is expressed by a polynomial of the carbon content in steel, and the polynomial and the appropriate time before the end of blowing are A track record that includes at _least the carbon content C _S in the steel obtained by sublance measurement _at Based on the data, we obtained equation (7) below, which expresses the correlation between these variables, and calculated the carbon content in the steel by sublance measurement at an appropriate point before the end of each blowing process. C _S , the target carbon content in the steel at the end point of blowing is C _E , and by giving at least these to equation (7), the required amount of blown oxygen from the above point to the end point of blowing is ΔO ₂ The method is characterized in that the converter is operated based on the calculation result.

The method of the present invention will be explained in detail below. In order to express the oxygen blowing process mathematically, the decarburization rate V _C is expressed as below (1)
If expressed as in the equation, there exists a relationship between the decarburization rate V _C and the carbon content C in steel that should be expressed as an exponential function as shown in FIG.

V _C = dC/d(O ₂ /W _ST ) ...(1) However, C: Carbon content in steel (%) O ₂ : Oxygen amount (Nm ³ ) W _ST : Estimated from the amount of main raw material charged The molten steel weight (T), that is, V _C is zero when C is zero, and increases as C increases, but this increase in V _C becomes saturated and slows down when C increases to a certain extent. By the way, if the oxygen consumption rate V _O is defined as the reciprocal of V _C as shown in equation (2) below, the relationship between V _O and C should be expressed as a hyperbolic relationship as shown in FIG.

V _O = d(O ₂ /W _ST )/dC ...(2) The relationship between V _O and C is that when C approaches zero, V _O
becomes extremely large, and when C is zero, the apparent V _O
becomes ∞. Further, as C becomes larger, the decrease in V _O becomes saturated and slower, and when C becomes extremely large, V _O approaches a certain constant value. Expressing these mathematically However, a ₀ is a constant, and the formula expressing the relationship between the oxygen consumption rate V _O and the carbon content C in the steel must satisfy the conditions of formulas (3) and (4).

In order to obtain a model formula that appropriately expresses the oxygen blowing process, the inventors of the present application conducted various studies using a large amount of actual operation data, and as a result, the following formula (5) was found to represent the carbon content in steel. It was concluded that this method is appropriate for ensuring accuracy when estimating end point carbon content from measured values.

d( _O2 / _WST )/dC= _a0 + _a1 /C+ _a2 / ^C2
+a ₃ /C ³ ...(5) However, a ₁ to a ₃ are constants. It goes without saying that this equation (5) satisfies the above equations (3) and (4). In addition, the reason why the term on the right side of equation (5) is limited to the -3rd power term of the carbon content C is that even if the -4th power term or higher of C is adopted, no substantial effect in terms of accuracy improvement can be obtained. It is. That is, the oxygen consumption rate V _O
In order for a relationship like the curve shown in Figure 2 to exist between C and the carbon content in steel, the coefficient of C in equation (5) must be
a ₀ , a ₁ , a ₂ , a ₃ , and furthermore, a ₄ of the −4th power term and a ₅ of the −5th power term following the kneading must all have the same sign, but it is necessary to increase the degree of the polynomial. In this case, perform multiple regression analysis using actual operation data to calculate the coefficient of C.
Even if we obtain a ₀ , a ₁ , a ₂ , a ₃ , a ₄ , a _{5 ,} etc., it is almost impossible for all these coefficients to have the same sign, and such a formula cannot be used to express the oxygen blowing process. This is because adopting it as a formula would lack physical significance.

Now, if we apply the above equation (5) to the oxygen blowing process from the time when the carbon content in the steel is measured by the sub-lance at the end of blowing to the end of blowing, the amount of blown oxygen during that period as shown in equation (6) below. can be obtained.

ΔO ₂ /W _ST =∫ ^CS _CE d(O ₂ /W _ST )/dC・dC=a ₀ (C _S −C _E )+a _{1 o} (C _S /C _E ) +a ₂ [(-1/C _S )−(−1/C _E )]+a ₃ [1/2(−1/C _S ² )−1/2(−1/C _E ² )]……(6
) However, ΔO ₂ : The amount of oxygen (N
m ³ ) C _S : Measured value of carbon content in steel by sublance measurement at the end of blowing (%) C _E : Carbon content in steel at the end of blowing (%) Therefore, based on a large amount of actual operation data, ΔO ₂ , C _S
and C _E into equation (6), and by multiple regression analysis,
Once each constant a ₀ to _{a 3} in equation (6) is determined, in the blowing to be controlled, the carbon content in the steel is measured with a sublance at the end of the blowing, and this is set as C _S .
The end point carbon content can be controlled by setting the target end point carbon content as C _E and substituting it into equation (6) to calculate the amount of oxygen ΔO ₂ to be blown from the time of sublance measurement to the end point of blowing.

However, since the molten steel temperature and the amount of auxiliary materials introduced into the steel bath also affect the progress of the decarburization reaction after sublance measurement, the formula for calculating ΔO ₂ is It is practical to adopt the following equation (7), which is obtained by adding K to equation (6).

ΔO ₂ /W _ST = a ₀ ( _CS − _CE ) + a _{1 o} ( _CS / _CE ) + a ₂ [(-1/ _CS ) −(-1/ _CE )] + a ₃ [1/2 (-1/C _S ² )-1/2 (-1/C _E ² )]+K...(7) Here, K is a variable determined by the conditions of converter operation to be controlled, and is expressed as follows ( 8) can be obtained from Eq.

K= _T (T _S - _S ) + _HT (W _HT /W _ST - W _H
T /W _ST ) + _CA (W _CA /W _ST - W _CA /W _ST ) + L...
…(8) However, T _S : Measured value of molten steel temperature by sublance measurement before blowing (°C) _S : Reference value of molten steel temperature at the time of sublance measurement at the end of blowing (°C) W _HT : Sublance measurement after blowing starts Amount of fluorite that has been added during the period up to the point in time (T) _HT : Standard value for the amount of fluorite that should be added during the period from the start of blowing to the time of sublance measurement (T) W _CA : Sublance after the start of blowing Amount of limestone that should be added during the period up to the measurement point (T) _CA : Standard value for the amount of limestone that should be added during the period from the start of blowing to the time of sublance measurement (T) _ST : Standard value for the weight of molten steel (T) _T , _HT , _CA : Constant L: Time-series fluctuation correction term determined from the control performance of multiple charges (for example, 10-odd charges) preceding the controlled object blowing, for example, by increasing the number of times the furnace is used According to
This section (7) is for correcting errors that occur due to damage to the refractories in the furnace and slight fluctuations in the distance between the steel bath surface and the oxygen supply lance due to slight fluctuations in the volume inside the furnace. Multiple regression analysis was performed using actual operation data in the same way as described above for formula (8), and each constant a ₀ ~
Determine a ₃ , _T , _HT , and _CA. Note that the coefficient _T of the molten steel temperature correction term _T ( _TS − _S ) should be negative because the higher the temperature, the higher the decarburization efficiency.

In addition, the reference values _HT , _CA , and _ST are obtained as the average value of the actual operation data when performing multiple regression analysis using a large number of actual operation data. Further, the correction term L is determined as follows. That is, after each charge blowing, the estimated value of ΔO ₂ /W _ST is calculated by setting L = 0 and substituting the actual data on the right side of equation (7), and this and the actual value of ΔO ₂ /W _ST are calculated. The difference between
Let O ₂ /W be the estimated error amount of _ST . Then, let L be the average value of the estimated error amount of ΔO ₂ /W _ST in a plurality of preceding charges.

Based on the above equations (7) and (8), the present invention estimates the amount of oxygen ΔO ₂ that should be blown between the time of sublance measurement and the end of blowing in order to obtain molten steel with the target carbon content. This controls the carbon content at the end point, but in the case of formulas (7) and (8), the validity of this model formula and each coefficient a ₀ ~ Figure 3 shows the validity of a ₃ , _T , etc. as the estimation accuracy of oxygen amount ΔO ₂ .
In other words, in Figure 3, the horizontal axis represents the estimated value of oxygen content, and the vertical axis represents the actual value, each measured per unit weight of molten steel. The value of ±1Nm ³ /T is shown by the broken line. Here, the actual value is the amount of oxygen actually blown in from the time of sublance measurement to the end point of blowing, and the estimated value is the end point carbon content C _E of the molten steel obtained by this blowing. and the measured values C _S and T _S obtained by sublance measurement.
This is the oxygen amount ΔO ₂ calculated by substituting into equations (7) and (8). In short, in order to obtain molten steel with the end point carbon content _CE , the amount of oxygen that should be blown from the time of sublance measurement to the end point of blowing is estimated from (7) and (8),
Compared with the actual value actually injected,
We examined the estimation accuracy of equations (7) and (8). As is clear from the figure ^, the estimation accuracy is extremely high, with 77 out of 86 charges falling within the range of ±1Nm ³ /T.
A high estimation accuracy of 90% was obtained in the range of .

Now, the method of the present invention is carried out as follows after preparing the above-mentioned equations (7) and (8) in advance. That is, to obtain molten steel with a target composition and temperature based on conventional operational experience or by a static end point control method,
Determine the amount of main raw materials and auxiliary raw materials to be charged, as well as blowing conditions such as oxygen supply pattern and blowing time. After starting blowing under the operating conditions determined in this way, the carbon content _C in the steel and the molten steel temperature _T are measured by sublance measurement at an appropriate time before the end of blowing. . Note that the above-mentioned appropriate time point is about 2 minutes ago, but it can be changed as appropriate depending on the oxygen delivery rate and the like. If the time from the time of sublance measurement to the predicted end point of blowing is too long, control will become difficult and accuracy will decrease; if it is too short, the carbon content in the steel has already fallen below the target value, and the end point carbon This is because it is assumed that the content may become uncontrollable. Furthermore, the sublance measurement performed to obtain the carbon content in steel to identify the above-mentioned equations (7) and (8) is also
Of course, this can be done at an appropriate time before the end of blowing.

Then, at an appropriate time before the end point of the blowing, the carbon content in the steel C _S and the molten steel temperature T _S measured by the sublance, together with the target value C _E of the end point carbon content,
By substituting into equations (7) and (8), the required amount of blown oxygen ΔO ₂ from the time of sublance measurement to the end point of blowing is calculated. In this calculation, W _ST is calculated from Equation (9) below.
Calculated based on the charging amount of each main raw material such as _HM .

W _ST = α (W _HM + W _CM ) + βW _SCR + γW _ORE + δW _SCA ...(9) However, W _HM : Hot metal weight (T) W _CM : Cold pig iron weight (T) W _SCR : Scrap weight (T) W _ORE : Iron ore weight (T) W _SCA : Scale weight (T) α, β, γ, δ: Constants Constants α, β, γ, and δ are the yield of pig iron, scrap, iron ore, and scale into molten steel, respectively.
It is obtained by applying multiple regression analysis to equation (9).

The amount of scale etc. to be charged is basically the amount charged at the start of blowing, but if it is added before sublance measurement during blowing to adjust the molten steel temperature, etc. It is preferable to calculate W _ST by adding. The same applies to W _HT and W _CA.

Once the required amount of blown oxygen ΔO ₂ after sublance measurement is determined in this way, by stopping the oxygen supply when this ΔO ₂ amount of oxygen has been blown, the end point carbon content can be adjusted to the target value _CE . It will match.

The oxygen supply pattern is constant throughout the whole blowing period as shown in Figure 4 for molten steel for low carbon steel, and as shown in Figure 5 or 6 for molten steel for medium and high carbon steel. Often in the early stages of blowing,
A pattern such as decreasing the amount from the middle to the end is adopted almost in the same way as the conventional method, but after the sublance measurement, it is preferable not to change the oxygen supply rate, blowing pressure, etc. in order to increase the accuracy rate. Therefore, the amount of oxygen ΔO ₂ that should be blown in after measurement and until the end of blowing, calculated based on equations (7) and (8) by sublance measurement, is substantially determined by the oxygen supply time. In other words, oxygen supply is stopped when the time obtained by dividing ΔO ₂ by the oxygen supply rate at the time of measurement has elapsed from the time of measurement. FIG. 9 is a flowchart showing the control method of the present invention described above. As is clear from the above, this method is roughly divided into two stages: the first stage of identifying model formulas for control, and the second stage of applying them to control in actual operation.
The first step is to obtain equation (5) for the oxygen consumption rate, then determine equations (7) and (8) for the amount of blown oxygen, and then determine the constants in the above equation by regression analysis of actual operation data. Become. The second step is to perform sublance measurement, and calculate ΔO 2 by substituting the measured value and the target value at the end of blowing into equations (7) and (8), and then calculate the oxygen supply of this _{ΔO 2} It consists of steps to perform the following steps.

Figures 7 and 8 are graphs showing the accuracy when applying the method of the present invention, in which the horizontal axis shows the target value (%) of the end point carbon content, that is, _CE , and the vertical axis shows the actual result. It is expressed as a value (%). 7th
The figure shows molten steel for high carbon steel (carbon content 0.51% or more), and Figure 8 shows medium carbon steel (carbon content 0.21% or more).
The solid line in the figure shows the straight line when the target value and actual value match, and the broken line is the solid line in Figure 7 (high carbon steel). Indicates a value of ±0.05% of
In FIG. 8 (medium carbon steel), it is a straight line that shows a value of ±0.03% of the solid line. As is clear from the figure, the accuracy rate is extremely high in all cases; for molten steel for high carbon steel, the accuracy rate within the range of ±0.05% is 37 out of 41 charges, or 90%, and for medium carbon steel. For molten steel, the accuracy within the range of ±0.03% was 40 out of 48 charges, or 83%. In molten steel for medium and high carbon steels, where it is generally difficult to control the end point carbon content and the accuracy is poor, the fact that such a high rate of accuracy has been achieved is due to the effectiveness of the method of the present invention. proves gender.

As described above, the method of the present invention makes it possible to control the carbon content in molten steel at the end point of blowing with extremely high precision, making a great contribution to the improvement of technology for dynamic end point control of carbon content, and preventing reblowing due to component deviation. Alternatively, there are practical benefits such as preventing deterioration of production efficiency due to changes in use, etc., and reducing costs.

It goes without saying that by having a process control computer perform various calculations in the method of the present invention, and further providing this computer with an automatic acid supply stop function, the present invention can be performed almost automatically.

[Brief explanation of the drawing]

Figure 1 shows the relationship between decarburization rate and carbon content in steel.
Fig. 2 is a graph conceptually showing the relationship between oxygen consumption rate and carbon content in steel, Fig. 3 is a graph showing measurement results demonstrating the estimation accuracy of the mathematical formula according to the present invention, Fig. 4, 5, FIG. 6 is a conceptual diagram showing the oxygen feeding pattern, FIGS. 7 and 8 are graphs showing the accuracy of the end point carbon content according to the method of the present invention, and FIG. 9 is a flowchart showing the outline of the content of the method of the present invention.

Claims (1)

[Scope of Claims] 1. The oxygen consumption rate at the end of blowing in converter operation is expressed by a polynomial of the carbon content in the steel, and the oxygen consumption rate obtained by sub-balance measurement at an appropriate time before the end of blowing is expressed by the polynomial and the polynomial of the carbon content in the steel. Based on actual data including at least the carbon content in the steel C _S , the amount of oxygen blown from the above point to the end point of blowing ΔO ₂ , and the carbon content C _E in the steel at the end point of blowing, these variables are determined. Obtain the following formula that expresses the correlation between C S and the carbon content in the steel obtained by sublance measurement at an appropriate time before the end of blowing each time C _S is the target value in the steel at the end of blowing. By setting the carbon content as _CE and inputting at least these into the above formula, the required amount of blown oxygen from the above point to the end of blowing is calculated as ΔO ₂ , and the converter operation is performed based on this calculation result. A method for controlling carbon content in steel, characterized in that: ΔO ₂ /W _ST = a ₀ ( _CS − _CE ) + a _{1 o} ( _CS / _CE ) + a ₂ [(−1/ _CS )−(−1/ _CE )] + a ₃ [1/2 (-1/ _CS2 ) ^-1/2 (-1/ _CE2 )]+K However ^, W _ST : Weight of molten steel _a0 , _a1 , _a2 , _a3 : Obtained from actual data of preceding converter operation. Constant K: Variable determined by the conditions of converter operation to be controlled