JPS6154842B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dynamic end point control of molten steel temperature in converter operation.

In converter blowing, the most important issue is to adjust the temperature and composition of molten steel, especially temperature and carbon content, to target values at the time of blow-off. Therefore, during blowing, the molten steel temperature and carbon content in the steel are measured using a sublance, the molten steel temperature and carbon content in the steel at the time of measurement are determined, and the subsequent operating conditions are corrected using the so-called dynamic end point control. It has been developed to improve the accuracy rate. By the way, in the dynamic end point control method of molten steel temperature, the quality of the model that associates the temperature increase rate or the amount of temperature increase with the amount of oxygen and/or carbon content in the steel that should be blown from the measurement time to the end point,
In other words, in evaluating its practicality, it is important to determine whether the end point molten steel temperature can be estimated accurately from the measured values, and whether the method of expression of the model is simple and whether the range of application that can be controlled by this model is wide. is important. Conventionally, this model displays the amount of temperature increase as a function of the amount of oxygen that should be injected into the molten steel in order to estimate the end point molten steel temperature from the measured value, or the model displays the temperature increase curve (i.e., the temperature at the measurement point) based on actual operation data. It has been proposed to create a relationship between the amount of oxygen to be blown into the steel or the amount of carbon content in the steel and the amount of temperature rise during the period from the beginning to the end point, and to refer to this each time the blowing operation is to be controlled. However, all of these methods have drawbacks such as accuracy and complexity of model identification work, making them impractical.

The present invention has been made in view of the above circumstances, and provides a simple explanation of the temperature increase rate or the amount of temperature increase from the time of measuring the carbon content in steel at the end of blowing to the end point, and the actually measured carbon content in steel. The purpose of the present invention is to propose a mathematical formula that accurately corresponds to the molten steel temperature, and to provide a method for controlling the end point molten steel temperature based on the mathematical formula.

The molten steel temperature control method according to the present invention is such that the temperature increase rate at the end of blowing in converter operation is expressed by a polynomial of the carbon content in the steel, and sub-balance measurement is performed at an appropriate time before the end of blowing in addition to the polynomial. The carbon content in the steel obtained by C _S , the amount of temperature rise ΔT during the period from the above point to the end point of blowing, the amount of coolant W _CL injected into the molten steel during the period, and the amount of coolant in the steel at the end point of blowing. Based on actual data including at least the carbon content C _E of , the following formula (1) expressing the correlation between these variables
For each blowing, the carbon content in the steel obtained by sublance measurement at an appropriate point before the predicted blowing end point is C _S , and the target temperature of the molten steel at the blowing end point is calculated by sublance measurement. The difference between the temperature of the molten steel at the time of measurement obtained at the end of blowing is ΔT, and the target carbon content in the steel at the end of blowing is C _E. The method is characterized in that the amount of coolant to be injected into the molten steel during the period leading to the end point is calculated as W _CL , and operations are performed based on this calculation result.

ΔT=a ₀ ( _CS - _CE ) + a ₁ n ( _CS / _CE ) + a ₂ [(-1/ _CS ) - (-1/ _CE )] +a ₃ [1/2 (-1/ C _S ² )-1/2 (-1/C _E ² )]+f(W _CL )+K...(1) However, ΔT: Amount of temperature rise (℃) during the period from the time of sublance measurement to the end point of blowing 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 (%) W _CL : During molten steel during the period from sublance measurement to the end of blowing (T) f(W _CL ): Function of the above W _CL K: Variables determined by the conditions of converter operation to be controlled a ₀ , a ₁ , a ₂ , a ₃ : Advance rotation Constants Obtained from Actual Data of Furnace Operation The method of the present invention will be described in detail below. First, above (1)
The process of deriving the formula will be explained. Generally, the temperature of molten steel increases due to oxygen blowing, but this is mainly because heat is generated due to the reaction between carbon and oxygen in molten steel, and the rate of progress of the reaction, that is, the carbon content C in steel decreases. If the amount of temperature increase relative to the ratio is expressed as the temperature increase rate V _T as shown in equation (2) below, then the relationship between the temperature increase rate V _T and the carbon content C in the steel is a hyperbolic function as shown in Figure 1. There is a relationship to be expressed.

V _T =dT/dC...(2) However, T: Molten steel temperature C: Carbon content in steel, that is, the relationship between V _T and C, as C approaches zero, V _T becomes extremely large, and when C approaches zero, When , the apparent V _T becomes ∞. Further, as C increases, the decrease in V _T becomes saturated and slows down, and when C becomes extremely large, V _T approaches a certain constant value. Expressing these mathematically Therefore, the formula expressing the relationship between the temperature increase rate V _T and the carbon content in steel must satisfy the conditions of formulas (3) and (4).

In order to obtain a model formula that appropriately expresses the temperature increase process due to oxygen blowing, the inventors of the present application
As a result of various studies using a large amount of actual operation data, we found that equation (5) below is effective in ensuring accuracy when estimating the amount of temperature increase, that is, the end point molten steel temperature, from the measured values of carbon content in steel and molten steel temperature. The conclusion was that it was appropriate.

dT/dC=a ₀ +a ₁ /C+a ₂ /C ² +a ₃ /C
³ ...(5) 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, in order for the hyperbolic relationship shown in Figure 1 to exist between the temperature increase rate V _T and the carbon content C 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, a ₅ of the −5th power term, etc. that follow must all have the same sign, but if the degree of the polynomial is increased In this case, use actual operation data and perform multiple regression analysis 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. As mentioned above, in many conventional methods, the temperature increase process is expressed as a function of the amount of blown oxygen, but the amount of blown oxygen itself is a function of the carbon content in the steel, and in the present invention, the model formula is For the purpose of concise expression, terms related to the amount of blown oxygen are not included.

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 temperature rise during this period is as shown in equation (6) below. can be obtained.

ΔT=∫ ^CS _CE dT/dC・dC=a ₀ (C _S −C _E )+a ₁ n(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) By the way, during the period from the time of sublance measurement to the end point of blowing, molten steel The amount of coolant such as scale added to the molten steel naturally affects the amount of temperature rise. Therefore, when the amount of coolant added to the molten steel is W _CL , the degree to which the molten steel temperature at the end point changes is f( The molten steel temperature at the time of sublance measurement and the sublance charged into the steel bath from the start of blowing to the time of sublance measurement are expressed as a function of W _CL ) and W _CL and added to the right side of equation (6). The amount of raw material also affects the progress of the reaction due to oxygen blowing after the sublance measurement, and therefore changes the amount of temperature rise. Therefore, in order to improve control accuracy, the formula for calculating ΔT is f on the right side
It is practical to employ the above formula (1) in which (W _CL ) and K are added. Here, f(W _CL ) is a term representing the variation in molten steel temperature due to the amount of coolant W _CL injected after sublance measurement, as described above, and is given, for example, as in the following equation (7).

f( _WCL )= _CL ( _WCL / _WST - _WCL / _WS
T )...(7) However, _CL : Standard value for the amount of coolant that should be added to molten steel during the period from the time of sublance measurement to the end of blowing (T) W _ST : The amount of molten steel estimated from the amount of main raw material charged Weight (T) _ST : Molten steel weight standard value (T) _CL : Constant Note that the standard values _CL 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. Also, the coefficient _CL is
As the amount of coolant W _CL increases, the amount of temperature increase decreases, so it should be negative. Further, K is a variable determined by the conditions of the converter operation to be controlled, and is obtained from the following equation (8).

K= _T (T _S − _S ) + _HT (W _HT /W _ST −W _HT /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 at the end of 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 the start of blowing 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 injected during the period up to the measurement point (T) _CA : Standard value for the amount of limestone that should be injected during the period from the start of blowing to the time of sublance measurement (T) _T , _HT , _CA : Constant L: It is a time-series fluctuation correction term determined from the control performance of multiple charges (for example, 10-odd charges) preceding the controlled blowing, and is a correction term for the refractory in the furnace, which is determined from the control results of multiple charges (for example, 10-odd charges), and is used to compensate for damage to the refractory in the furnace due to repeated use of the furnace. However, the standard values _S , _HT , and _CA are used to correct errors caused by slight fluctuations in the heat radiated from the furnace. Obtained as the average value of the data. Further, the correction term L is determined as follows. That is, after each charge blowing, the estimated amount of ΔT is calculated by setting L=0 and substituting the actual data on the right side of equation (1), and
Let the difference between T and the actual value be the estimated error amount of ΔT. Then, let L be the average value of the estimated error amounts of ΔT in a plurality of preceding charges.

In order to determine the constants of equations (1), (7), and (8) obtained in this way, the molten steel temperature T _S and the carbon content in steel C _S that were actually measured by sublance measurement in actual operation, The molten steel temperature T _E and carbon content in steel C _E at the _end point, the amount of coolant introduced after sublance _measurement W _HT , _WCA ), etc., and based on this large amount of actual operation data, C _S , C _E , W _CL and temperature increase amount ΔT (ΔT
= T _E - T _S ), etc., were substituted into equations (1), (7), and (8), and multiple regression analysis was performed to obtain the results expressed by equations (1), (7), and (8). Identify model formulas.

Now, the present invention is carried out as follows after preparing equations (1), (7), and (8) in advance as described above. In other words, based on conventional operational experience or using a static end point control method, blowing conditions such as the amount of main raw materials and auxiliary raw materials charged, oxygen supply pattern, and blowing time are determined in order to obtain molten steel with target composition and temperature. decide. After starting blowing under the operating conditions determined in this way, at an appropriate point before the end of blowing,
The carbon content C _S in the steel and the molten steel temperature T _S are measured by sublance measurement. Note that the above-mentioned appropriate time before the end point of blowing is about 2 minutes before the end point of blowing, but this can be changed as appropriate depending on the oxygen supply rate and the like. If the time from the time of sublance measurement to the end of blowing is too long, control becomes difficult and accuracy decreases; if it is too short, even if the temperature of the molten steel is adjusted by adding coolant, which will be described later, the blowing will be difficult. This is because it is assumed that the temperature will not drop sufficiently by the end of the process. In addition, it goes without saying that the sublance measurement performed to obtain the carbon content in the steel to identify the above-mentioned equations (1), (7), and (8) should also be performed at an appropriate time before the end of blowing. .

Assuming that the carbon content in the steel measured by sublance at an appropriate time before the end of blowing is C _S , the target temperature T _E of the molten steel at the end of blowing and the time of measurement obtained by sublance measurement are calculated. The above formulas (1), (7), and (8) are expressed by assuming that the difference from the molten steel temperature T _S is ΔT (ΔT = T _E - T _S ), and that the target carbon content in the steel at the end of blowing is C _E. Further, by substituting the molten steel temperature T _S at the time of measurement and the amount of auxiliary raw material W _HT that has been input up to the time of measurement, etc., from the time of sublance measurement to the end point of blowing in order to obtain molten steel at the target temperature. Calculate the amount of coolant to be input during the period as W _CL . In this calculation, W _ST is calculated based on the charging amount of each main material such as W _HM from the following equation (9).

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 to the molten steel to adjust the molten steel temperature etc. by the time of sublance measurement, this will be added. It is preferable to calculate _WST by The same applies to W _HT and W _CA.

Once the predetermined coolant injection amount W _CL after the sub-lance measurement is determined in this way, the end point molten steel temperature can be adjusted to the target value by injecting the coolant in the amount of W _CL into the molten steel at an appropriate time after the sub-lance measurement. It will match T _E. FIG. 3 is a flowchart showing the control method of the present invention described above.
As is clear from the above, this method includes a first step of identifying a model formula for control;
It is roughly divided into two stages, the second stage is applied to control in actual operation, and the first stage is obtained by obtaining the temperature increase rate equation (5),
Next, equations (6) [that is, equations (1)], (7), and (8) for the amount of temperature increase are determined, and the constants in the above equations are further determined by regression analysis of actual operation data. In the second step, sublance measurement is performed, and W _CL is calculated by substituting the actual measured value and the target value at the end of blowing into equations (6), (7), and (8). It consists of a step of injecting coolant based on _CL .

Figure 2 is a graph showing the accuracy when applying the method of the present invention, where the horizontal axis shows the target value of the end point molten steel temperature (℃), that is, T _E , and the vertical axis shows the actual value (℃). It is expressed as follows. The solid line in the figure is a straight line indicating the case where the target value and the actual value match, and the broken line indicates the value within ±12°C of the solid line. The accuracy rate within this range of ±12°C was extremely high at 112 out of 116 charges, or 97%, and the fact that we were able to obtain such a high rate of accuracy proves the effectiveness of the method of the present invention. There is.

As described above, the method of the present invention makes it possible to control the molten steel temperature at the end point of blowing with extremely high precision, making a great contribution to the improvement of the technology for dynamic end point control of molten steel temperature, and making it possible to control the temperature of molten steel at the end point of blowing.
There are practical benefits such as preventing deterioration of production efficiency due to cooling work, etc., and reducing costs.

It goes without saying that the present invention can be carried out almost automatically by having a process control computer perform various calculations in the method of the present invention, and by having this computer also control the injection of coolant.

[Brief explanation of the drawing]

Fig. 1 is a graph conceptually showing the relationship between temperature increase rate and carbon content in steel, Fig. 2 is a graph showing the accuracy of the end point molten steel temperature according to the method of the present invention, and Fig. 3 is the content of the method of the present invention. This is a flowchart showing an outline of the process.

Claims (1)

[Scope of Claims] 1. The temperature increase rate at the final stage of blowing in converter operation is expressed by a polynomial of the carbon content in the steel, and the 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. The carbon content in the steel C _S , the amount of temperature rise ΔT during the period from the above point to the end point of blowing, the amount of coolant W _CL introduced into the molten steel during the period, and the carbon content in the steel at the end point of blowing. Based on actual data including at least C _E , the following formula expressing the correlation between these variables is obtained, and the value of the value in the steel obtained by sublance measurement at an appropriate point before the end of blowing each time is calculated. Let C _S be the carbon content, ΔT be the difference between the target temperature of the molten steel at the end point of blowing and the temperature of the molten steel at the time of measurement obtained by sublance measurement, and let C _E be the target carbon content in the steel at the end point of blowing. , by giving at least these to the formula, the amount of coolant to be introduced into the molten steel during the period from the above point to the end point of blowing is calculated as W _CL , and the operation is performed based on this calculation result. Method of controlling molten steel temperature. ΔT=a ₀ ( _CS - _CE ) + a ₁ n ( _CS / _CE ) + a ₂ [(-1/ _CS ) - (-1/ _CE )] +a ₃ [1/2 (-1/ C _S ² )-1/2-(1/C _E ² )]+f(W _CL )+K However, a ₀ , a ₁ , a ₂ , a ₃ : Constants obtained from the actual data of the preceding converter operation K: Variable determined by the converter operation conditions to be controlled f (W _CL ): Function of the amount of coolant W _CL injected from the time of sublance measurement to the end of blowing