JPH0154410B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of controlling AOD furnace operation using computer simulation. In particular, the present invention calculates the progress of the process by knowing the initial values of the temperature, composition, weight, etc. of molten steel, and adjusts the amount of coolant input. The present invention relates to a method for optimizing the decarburization process of molten steel by controlling the input timing, refining gas amount, gas ratio, and gas switching point. In the conventional method of decarburizing molten steel using a computer, it is assumed that Cr% and C% in molten steel, Cr ₂ O ₃ in slag, CO partial pressure, and molten steel temperature are in an equilibrium relationship. Various analyzes have been conducted. For example, a method using a computer to decarburize molten steel is disclosed in Japanese Patent Application Laid-Open No. 1983-52603 (Japanese Patent Publication No. 52-52603
-26212), and the above publication contains the following description. The present invention relates to a method for decarburizing molten steel, and in particular to a method for optimizing the decarburization operation. When steel is decarburized using oxygen, an equilibrium is established between the metal, carbon and oxygen at a certain temperature and pressure. This equilibrium determines the amount of carbon that can be removed from the melt without oxidizing the metals, especially chromium. It is widely recognized that the thermodynamic activity of these elements in the bath and the equilibrium established between these elements and the emitted gas atmosphere can be modified by diluting the oxygen with an inert gas. Elevated temperature limits are determined by practical and economic considerations regarding the effect of high temperatures on the life of the vessel lining and the life of the tuyeres required to inject oxygen and inert gases directly into the molten metal from below the surface. It is based on both considerations. On the other hand, dilution of the blown oxygen with an inert gas also reduces the volume % of the inert gas introduced.
Economic considerations are involved since the steel production rate decreases proportionately. Needless to say, the cost of the inert gas itself is considerable. Hitherto, the main concern has been to reduce the carbon content of the melt to a certain level while minimizing oxidation losses of other elements. Despite the desire to prevent rapid deterioration of refractory materials through careful temperature monitoring, processes to date have been carried out at the expense of relatively low steel production rates and without regard to the amount of inert gas used. Ta. The apparent lack of concern for economics was due to the impossibility of periodically sampling the bath during operation to determine the extent of metal oxidation and the actual bath temperature. I was there. It is better to ensure an acceptable final melt composition than to risk producing a poor quality melt by increasing the production rate and conserving inert gas.
considered far more sensible. At best, over the course of practice, some generalized index can be empirically determined to vary the dilution ratio for a particular melt at regular time intervals and at expected temperature conditions using a given refractory lining composition. It is a position established in The object of the invention is to optimize the decarburization of the molten metal from knowledge only of the initial molten metal composition, weight and temperature, in connection with establishing a given final composition under favorable economic conditions. The aim is to provide programs for Another object of the present invention is to decarburize the molten metal from both a quality and economic point of view in order to consistently produce a final melt composition and temperature in accordance with the desired specifications for a given molten metal at relatively high production rates. The objective is to provide a method for optimizing the The program of the present invention allows oxygen to combine with carbon over a very short period of time, and eventually generate enough carbon monoxide that further oxygen-carbon combinations are prevented due to the selectivity of oxygen toward metal elements. It is based on the theoretical assumption that a pressure is generated in which the reduction of the metal oxide results in a minimum equilibrium partial pressure of carbon monoxide. From this assumption, a theoretical mathematical model was developed to calculate the minimum equilibrium partial pressure of carbon monoxide at certain selected time intervals. From this partial pressure,
A new melt composition, weight and temperature can be determined and readjustments can be made in the dilution ratio to optimize the process, either automatically or through an operator. This mathematical model simulates the complex natural processes that exist in refractory-lined vessels with respect to reaction thermodynamics, heat balance and melt balance, and thus predicts the state evolution of the melt. This mathematical calculation can be done manually, but it cannot be done quickly enough to be of practical use. Therefore, the method of the present invention:
Its practical performance requires a computer. Generally stated, the present invention provides a refractory lined vessel with means for injecting oxygen and diluent gas into the molten metal and adjustable gas flow control means for varying the gas flow ratio. A method for controlling the decarburization of a predetermined mass of molten metal containing carbon and iron is provided. The method of the invention includes: (a) setting said adjustable control means to establish a first flow rate greater than zero for said oxygen and a first flow rate for said dilution gas; (b) Using a calculator to perform the following sequential steps: (1) Defining the thermodynamic activity of each element as a function of its composition in the molten metal from the initial composition, weight, and temperature of the molten metal; calculating a plurality of activity coefficients, each coefficient reflecting the activity of each element in terms of percentage of the element and the dependence of each element on the percentage of other elements in said molten metal; The activity of iron is equal to its molar fraction, and the activity of the oxide of each element has a predetermined value.); (2) The activity coefficient of each element at the predetermined temperature is Step of calculating the theoretical equilibrium partial pressure of carbon monoxide for the oxidation reaction; (3) Step of calculating the absolute maximum partial pressure of carbon monoxide assuming that all the injected oxygen reacts only with carbon; (4 ) selecting the minimum theoretical equilibrium partial pressure of carbon monoxide from (2) and comparing it with the absolute maximum partial pressure of carbon monoxide from (3); (5) said minimum theoretical equilibrium partial pressure is If the magnitude is slightly equal to the absolute maximum partial pressure, further calculating the amount of oxidized carbon and the new metal analysis value and the temperature for its composition from the first gas flow rate; (6) the minimum theoretical equilibrium partial pressure; If the pressure is smaller in magnitude than the absolute maximum partial pressure, further calculate the oxidized carbon and metal, the new metal analysis value, and the temperature for the composition from the theoretical equilibrium partial pressure of carbon monoxide and the first gas flow rate. (7) providing an indication of the new carbon content in the molten metal body; (8) providing an indication of the new carbon content in the molten metal body; (9) If the oxidation amount of the specific element is slightly equal to the predetermined oxidation limit, resetting the gas flow rate control means to increase the proportion of the diluent gas; (c) resetting said adjustable gas flow control means in accordance with the instructions provided in step (9); (d) At predetermined time intervals of not more than 2 minutes, step (7)
Repeating the sequence from step (1) until the carbon content indicated in is reduced to at least the predetermined content. The present invention provides an improved method for optimizing the decarburization of molten steel.
The purpose is to provide a control method for AOD reactors,
According to the present invention, molten steel having a predetermined final composition can be obtained economically by simply knowing the composition, weight, and temperature of the initial molten steel. The present invention provides a predetermined amount of carbon, iron, chromium, manganese, nickel, etc. contained in a refractory-lined container having means for blowing oxygen and diluent gas into molten steel and means for controlling the flow rate of said gases. This invention relates to an improved control method for controlling decarburization of molten steel. In the conventional decarburization operation analysis method disclosed in the above-mentioned Japanese Patent Application Laid-open No. 48-52603, oxygen and carbon combine in a unit time, and eventually further combinations of oxygen and carbon occur, and oxygen is bonded to metal elements. It is based on the theoretical assumption that sufficient CO pressure is generated to be inhibited by selectivity, in which case reduction of the metal oxide results in a minimum equilibrium partial pressure of CO. That is, for example, in refining operations for chromium-containing molten steel, %[Cr]-%
It is based on the assumption that a theoretical equilibrium is maintained between [C] - % (Cr ₂ O ₃ or Cr ₃ O ₄ -) - P _CO - temperature. However, it is difficult to accurately control refining operations by using programs based on such assumptions. According to the conventional method disclosed in the above-mentioned publication, the oxidation of metal is based only on equilibrium theory and no kinetic considerations are made, so changes during the process cannot be calculated. Therefore, it is not possible to accurately calculate the timing to add cold material, and in actual operation, the temperature of molten steel may become too high or, conversely, cool material may be added only after it has become too low, resulting in the oxidation of chromium. There is a risk that this will be promoted. ) The degree of oxidation of Si, Mn, Cr, and Fe is determined by comparing the theoretical equilibrium partial pressure of CO that is in equilibrium with these oxides and the P _CO generated when all oxygen generates CO. According to the example, although these four types of oxides are produced by reacting simultaneously, only CO is produced, or CO and CO are produced simultaneously.
Calculations can only be made for cases in which an oxide of one of Si, Mn, Cr, and Fe is generated. Therefore, if AOD furnace operation is carried out using computer simulation based on the above-mentioned precedent example, it is difficult to carry out proper operation. The present invention aims to provide a control method that eliminates and improves the drawback that it is difficult to accurately control the operation caused by the conventional AOD operation control method using the analysis method based on the equilibrium relationship. This object can be achieved by providing the method described in the claims. The present invention solves the problem of Cr, which has not been subject to conventional analysis.
This is based on the new knowledge that the operation is controlled by a computer, taking into account the oxidation phenomenon that deviates from the equilibrium state of iron and Fe. Next, the process leading up to the invention will be explained. In addition to equilibrium theory and kinetic considerations, the present inventor developed a mathematical model I that more precisely simulates the decarburization phenomenon.
I thought about it. This model will be explained below. This model is for simulating the decarburization process of, for example, chromium-containing molten steel in an AOD furnace. Model: (1) Oxygen-argon mixed gas injected into the refining vessel through multiple tuyeres becomes bubbles, and the oxygen gas immediately reacts with C, Si, Mn, and Cr in the molten steel, producing CO, SiO ₂ , and MnO. , _{producing Cr2O3} . In this case, the amount of oxide produced by the reaction depends on the mass transfer rate of each element to the gas-liquid interface. Equations (1) to (4) show the reaction equations near the tuyere. O ₂ +2 C →2CO (1) O ₂ +4/3 Cr →2/3 (Cr ₂ O ₃ ) (2) O ₂ +2 Mn →2 (MnO) (3) O ₂ + Si → (SiO ₂ ) ( 4) The distribution of oxygen to equations (1) to (4) is shown in equations (5) to (8). O ₂ (C)=(1/2J _C /ΣJ _j )・Γ n _O2 , mol/sec (5) O ₂ (Cr)=(3/4J _Cr /ΣJ _j )・Γ n _O2 , mol/sec ( 6) O ₂ (Mn) = (1/2J _Mo /ΣJ _j )・Γ n _O2 , mol/sec (7) O ₂ (Si) = (J _Si /ΣJ _j )・Γ n _O2 , mol/sec ( 8) Furthermore, the flux J _i from bulk molten steel to the interface is expressed by equation (9). J _j = ρ _n /100M _j・k _j・A _B・(%Cb, j−%Ci, j), mol/sec (9) ΣJ _j =1/2J _C +3/4J _Cr +1/2J _Mo +J _Si , mol/sec (10) where, j: any one selected from C, Si, Mn, and Cr %Cb, j: bulk concentration of j, % %Ci, j: J concentration at the interface, % Γ n _O2 : Amount of oxygen blown into the container, mol/sec ρ _n : Density of molten steel, g/cm ³ k _j : Mass transfer coefficient of j, cm/sec A _B : Surface area of bubbles, cm ² (2 ) Cr ₂ O ₃ and MnO generated in equations (2) and (3) float in the molten steel together with bubbles, and in the process
As shown in equations (11) to (14), C in molten steel
(Hereinafter, C in molten steel will be referred to as C ) and
It is reduced by Si (hereinafter Si in molten steel will be referred to as Si ). 1/3 (Cr ₂ O ₃ ) + C → 2/3 Cr + CO (11) (MnO) + C → Mn + CO (12) 1/3 (Cr ₂ O ₃ ) + 1/2 Si → 2/3 Cr +1 /2( _SiO2
) (13) (MnO) + 1/2 Si → Mn + 1/2 (SiO ₂ ) (14) The reaction rates of equations (11) to (14) are determined by the mass transfer of oxygen in the molten steel in the high carbon region. is,
It is assumed that in the low carbon region, the rate is determined by the mass transfer of carbon in molten steel. Also, equation (11)
Assume that the reaction rate of each of ~(14) also depends on the free energy of each equation. The change in CO concentration in the floating bubble d(CO)/dX and the change in the concentration of Cr, Mn, and Si in the oxides in the bubble d(Cr)/dX, d(Mn)/dX, and d(Si)/dX are They are shown in equations (15) to (18), respectively. d(CO)/dX=J _O・△G ₁₁ +△G ₁₂ /△G _T , mol/cm/sec (15) d(Cr)/dX=−j _O・△G ₁₁ +△G ₁₃ /△ G, 〃(1
6) d (Mn) / dX = −j _O・△G ₁₂ +△G ₁₄ /△G _T , 〃(1
7) d (Si) / dX = −j _O・△G ₁₃ +△G ₁₄ /△G _T , 〃(1
8) Here, △G _11,12,13,14 : Free energy of equations (11), (12), (13), (14), cal j _O : Oxygen flux j _O = ρ _n /1600・A _B /V _B・k _O (%Oi−%Ob), mol/sec (19) d(N ₂ )/dX=ρ _n /2800・A _B /V _B・k _N (%Nb−%N, i ) (20) where, k _O : Mass transfer coefficient of oxygen, cm/sec k _N : Mass transfer coefficient of nitrogen, cm/sec V _B : Rising speed of bubbles, cm/sec %Oi: Cr ₂ O ₃ and Equilibrium oxygen concentration, % %Ob: Oxygen concentration in bulk molten steel, % %Nb: Nitrogen concentration in bulk molten steel, % %N, i: Nitrogen concentration at the interface between bubbles and molten steel, % (3) Floating of bubbles The material balance of molten steel and slag is calculated assuming that oxides that are not reduced during the process enter the slag phase and are not used again. The change in the weight of molten steel dWm/dt is shown in equation (21), and the change in the composition of molten steel d% [Ci]/dt is shown in equations (22) and (23). dWm/dt=−{Σ△Ci・Mi} −ΣdW _SC,l /dt, (g/sec) (21) d[%Ci]/dt=−100Mi/Wm・△Ci−%Ci/Wm・dWm /
dt −Σ%Ci, l/Wm・dW _SC,l /dt, (%/sec) (22
) i: C , Si , Mn , Ni , Cr , d[%N]/dt=-2800/Wm・△N ₂ −[%N]/Wm・dW
m/dt +ρ _nk ′ _N・A/Wm (%N′−%Nb), (%/sec
) (23) Where, △Ci: Oxidation of i, mol/sec Mi: Atomic weight of i, g/mol l: Type of scrap charged into the container W _SC : Type of scrap charged into the container Weight △N ₂ : Amount of denitrification into bubbles, mol/sec ρ _n : Specific gravity of molten steel, g/cm ² k′N: Mass transfer coefficient of nitrogen in molten steel at the free surface, cm/sec N′: Free surface Nitrogen concentration, % A: free surface area, cm ² The change in slag weight dW _S /dt is shown in equation (24), and the change in slag composition d[%M _X O _Y ]/dt is shown in equation (25). . dW _S /dt=M _Cr2O3 /2・△Cr+M _MoO・△Mn+M _SiO2・△Si +M _FeO・△Fe−dW _CaO /dt, g/sec (24) d[%MxOy]/dt=100M _MxOy /W _S・△C _MxOy −%MxOy/M _s・dW _S /dt, %/sec (25) Here, MxOy: Cr ₂ O ₃ , MnO, FeO, SiO ₂ △Cr: Amount of oxidized Cr, mol/ sec △Mn: Amount of oxidized Mn, mol/sec △Si: Amount of oxidized Si, mol/sec △Fe: Amount of oxidized Fe, mol/sec (4) Total reaction heat generated in the refining process , calculate the heat balance by considering the heat radiation loss from the container mouth, the heat loss from the container wall, the heat of fusion of the coolant, and the enthalpy of the gas, and further calculate the temperature change of the molten steel using equation (26). . dT/dt=-ΣQ/(C _p,S W _S +Cp, mWm), ℃/sec (26) Where, C _p,S : Specific heat of slag, cal/℃/g Cp, m : Specific heat of molten steel , cal/°C/g ΣQ: total heat of reaction, heat loss from the container, and other factors, cal/sec Figure 1 shows the results of comparing the mathematical model with the results of actual operation. Note that the operating conditions in actual operation will be described in detail later with reference to Examples. The figure shows the oxidation rate of Cr/mol/with changes in temperature, Cr, and C.
FIG. According to the figure, the solid line, broken line, and dashed-dotted line are calculated values using a mathematical model, and it can be seen that these values agree well with the measured values indicated by Δ, ●, and Γ. At various times A, B, C, and D in the figure, the chromium oxidation rate is A', B', C',
It is shown by point D', and it can be seen that oxidation of Cr occurs at each time point. Table 1 also shows the mathematical model of the present invention and the model of the prior example (Japanese Patent Application Laid-Open No.
The results of calculations regarding the oxidation tendency of Cr at the above points A, B, C, and D using the analytical model disclosed in No. 52603 are shown below. According to calculations based on the previous example, at points A, B, and C, the theoretical equilibrium partial pressure of CO in equilibrium with Cr ₃ O ₄ (P ^e _CO ) _Cr is found from the amount of oxygen blown and the amount of diluent gas blown. Since it is greater than the absolute maximum partial pressure of CO, Cr will not be oxidized. It can be seen that the previous mathematical models based on point equilibrium theory have drawbacks.

【table】

[Table] As mentioned above, according to a mathematical model that simulates the phenomenon in more detail by adding kinetic considerations to equilibrium theory considerations, even in the region where no oxidation should occur when calculated using only equilibrium theory, It can be seen from Table 1 that chromium oxidation occurs. However, since the mathematical model requires a long time, about 4 hours, for calculation by a computer, it is necessary to shorten the time required for the calculation in order to carry out operations based on the mathematical model. Therefore, the present inventor newly invented a mathematical model described below. Next, the mathematical model will be explained. Mathematical model: Macroscopically, the refining reaction of molten steel is expressed by equation (27) ~
(32). {O ₂ }+4/3 Cr = 2/3<Cr ₂ O ₃ > (27) {O ₂ }+2 Mn = 2 (MnO) (28) {O ₂ }+ Si = (SiO ₂ ) (29) { O ₂ }+ C = 2 {CO} (30) N → 1/2 {N ₂ } (31) 1/3<Cr ₂ O ₃ >+Fe=(FeO)+2/3Cr (32) Here, <> : Solid state ( ): Liquid state { }: Gaseous state Cr , Mn , Si , C : Cr, Mn, Si, C in molten steel Calculations can be made assuming that the rate-determining mass transfer of each element to the Perform the following steps sequentially using a computer. (1) Calculate the amount of oxidized metal by the following means. (1-1) Calculate the amount of carbon, silicon, and manganese oxidized within a unit time from the product of the concentration difference of each element and the container coefficient. The container coefficient is determined from the results of calculations using measured data and a mathematical model. (1-2) The amount of oxygen consumed in the oxidation of chromium is the remaining amount after subtracting the amount of oxygen consumed during the oxidation reaction shown in equations (28) to (30) from the amount of oxygen blown into the unit time. Assume that (1-3) As shown in equation (32), Fe in molten steel is oxidized by Cr ₂ O ₃ in slag. Molar ratio in slag calculated from data obtained from actual operation during any of the above reactions.
Assume that Cr/Fe is maintained. (2) When nitrogen is used as the diluent gas or when argon is used, the amount of nitrification or denitrification of the molten steel shown in equation (31) depends on the mass transfer of nitrogen in the molten steel. Therefore, the amount of nitrification or denitrification is calculated by multiplying the vessel coefficient and the nitrogen concentration difference obtained from actual operation and calculation results using a model. (3) Concentration and temperature changes are calculated using the steps below. (3-1) Carbon, silicon, manganese determined in (1) and (2),
Calculate the material balance of molten steel and slag from the amount of chromium oxidation and nitrogen absorption or denitrification. (3-2) From section (3-1), changes in the weight of molten steel, changes in the composition of each of the elements contained in the molten steel, changes in the weight of slag, and changes in the composition of slag are calculated. (3-3) The heat balance of molten steel and slag is calculated from the reaction heat, the amount of heat loss in the container, and the amount of heat of fusion of the cold material shown in equations (27) to (32). Based on these calculation results, the furnace is operated as follows. (a) When the decarburization amount calculated as above becomes smaller than the predetermined decarburization amount, the gas ratio and gas amount of the gas blown into the container are controlled as follows. That is, changing the ratio of oxygen to diluent gas to increase the proportion of diluent gas,
Further, control is performed to change the total amount of mixed gas. (b) Further, control is performed to continue blowing the refining gas until the carbon content in the molten steel determined from the material balance in (3) above becomes equal to the predetermined carbon content. (c) During the above-described control, when the temperature of the molten steel reaches a predetermined maximum temperature, control is performed to inject a required amount of coolant in order to lower the molten steel temperature to a predetermined temperature. The above control is stopped when a predetermined carbon content of the molten steel is obtained. That is, that point is the end point of the refining process. According to the invention, the predetermined time interval of each of said steps is less than 10 seconds and said diluent gas is helium, neon, argon, krypton,
The gas can be selected from nitrogen, xenon, and a mixed gas of any gas selected from them. FIG. 2 is a graph comparing calculated values obtained from a mathematical model. According to FIG. 2, it can be seen that the two calculated values agree well with each other and also match well with the values obtained through actual operation. Figure 3 shows the amount of cold material to be charged into the vessel during calculation operation, the timing of charging the cold material, and the changes in the temperature and composition of molten steel calculated using the model. It is a graph. According to the figure, it can be seen that the calculations using the model agree well with each other. By the way, calculations using said model take about 4 hours to accomplish, while calculations using said model take less than 3 minutes to accomplish. Therefore,
The model can be effectively used as a control program in actual operation. Next, the present invention will be explained with reference to examples. SUS304 stainless steel was refined according to the present invention using a 60 t capacity AOD furnace. The above-mentioned AOD furnaces have 4 and 5 tuyeres, and the refractory inside the furnace is new (the furnace wall is not eroded, so the depth of the steel bath is deeper than that of an old furnace). ) and used furnaces in which the refractories in the furnace have been eroded to some extent (because the furnace walls are eroded, the steel bath depth has furnace characteristics when the refractories in the furnace are shallower than that in new furnaces). ) were used for smelting. Example 1 Figure 1 shows the progress of a computer simulation run using a newly built four-tuyere AOD furnace, showing the steel bath temperature (represented by △) and chromium concentration (●) during the decarburization process. Fig. 3 is a diagram in which carbon concentration (represented by a Γ mark) and carbon concentration (represented by a Γ mark) were investigated over time. In the figure, ~ indicates the timing of input materials,
The types and weights of input materials introduced at each input period were as follows. HCFeCr 1455Kg Iron scrap 2100Kg Iron scrap 2000Kg Stainless steel scrap 2500Kg CaO 620Kg Stainless steel scrap 2000Kg CaO 620Kg The composition and amount of the gas injected during the above refining process are as follows.
Although the changes were made as shown in the table, the period during which the gas was blown with the same gas composition is referred to as one step.In the refining shown in FIG. 1, gas blowing was performed in four steps 1 to 4. Next, Table 2 shows the amount and composition ratio of the blown gas in each step.

[Table] Temperature transition, [Cr]% transition, and [C]% predicted from the results of calculations according to the present invention from Figure 1
It was found that the transition (solid line) and the measured values were in very good agreement with each other, proving that the method of the present invention is superior. FIG. 4 shows calculated values showing changes over time in slag weight, FeO, MnO, and Cr ₂ O ₃ (%) during the operation shown in FIG. 1. It should be noted that actual measurements of the above-mentioned changes over time were not carried out because they are extremely difficult to measure. Example 2 Same procedure using a worn-out AOD furnace with 5 tuyeres.
Refined SUS304 stainless steel. FIG. 2 shows a comparison between simulations based on the mathematical model of the present invention and actual measurements, and the Δ, ●, and Γ marks are the same as those in FIG. 1, respectively. In the same figure, ~
indicates the timing of input materials, and the types and weights of input materials input at each input period are as follows. HCFeCr 1204Kg CaO 390Kg Fe-Ni 2000Kg Iron scrap 810Kg Fe-Ni 2200Kg Fe-Ni 2000Kg CaO 510Kg CaO 500Kg Table 3 shows the composition and composition ratio of the blown gas for each step as well as the amount of each gas.

[Table] Temperature transition, [Cr]% transition, and [C]% predicted from the results of calculations according to the present invention from Figure 2
It can be seen that the trends and the measured values match very well. For example, by adding HCFeCr, Cr
The concentration increases, and Fe-Ni input (,,
), the situation in which the Cr concentration is diluted and lowered is well simulated. FIG. 5 is a graph comparing calculated values and actual measurements of changes in nitrogen concentration during the operation shown in FIG. Since nitrogen was used as the diluent gas in steps 1 to 3, the nitrogen concentration in the molten steel increased, whereas in step 4, argon was used as the diluent gas, so the nitrogen concentration in the molten steel decreased significantly. The calculated values were in good agreement with the measured values indicated by ●. Example 3 A furnace with the same five tuyeres as the operating furnace used in Example 2 was used, but a new furnace with new refractories was used, and the gas amount and gas ratio were operated under the same conditions as shown in Figure 2. did. The results are shown in FIG. In the figure, ~ indicates the timing of input materials, and the types and weights of input materials input at each input time were as follows. Iron scrap 950Kg NiO 786Kg Fe−Ni 1685Kg Iron scrap 510Kg CaO 660Kg Fe−Ni 2272Kg Fe−Ni 2176Kg CaO 500Kg CaO 560Kg NiO 103Kg As can be seen from FIG. were also in good agreement. Table 4 shows the calculated values and actual values for the steel bath temperature and steel bath composition after the completion of decarburization in Examples 1 to 3 shown in FIGS. 1, 2, and 6, respectively. It can be seen that they are in very good agreement.

[Table] Example 4 Figure 7 shows a simulation and actual operation using the molten steel composition and temperature at the time of receiving AOD steel as the initial conditions, but check analysis and temperature measurement were performed on the way, and the simulation was performed again using these as the initial conditions. This shows the results of modifying operations. In the figure, ~ indicates the timing of input materials, and the types and weights of input materials input at each input time were as follows. Fe 820Kg NiO 786Kg Fe−Ni 608Kg CaO 590Kg Fe−Ni 1533Kg Fe−Cr 193Kg CaO 500Kg Fe−Ni 1731Kg Fe−Ni 2476Kg CaO 500Kg The dotted line in the same figure shows the composition when receiving AOD steel.
A simulation was performed using temperature as the initial condition.
This was done through blowing. Check analysis and temperature measurement were performed at the end of the second step. According to this, the molten steel temperature is 15℃ higher than the calculated value, and the C and Cr% are also low, making it a little overoxidized.Thereafter, in order to suppress the temperature rise, the amount of O ₂ was changed from the dotted line calculated at the beginning. The amount was reduced by 15% compared to the case. This calculated value is shown as a solid line, and the operating values are ▲, ●, Γ (temperature,
Cr%, C%). As a result of the modification, it was possible to lower the temperature of the decarburized powder, prevent chromium loss, and avoid overoxidation. Table 5 shows the components and temperatures when receiving AOD steel, the calculated values at the end of the 2nd step using these as the initial conditions, the calculated values at the end of decarburization, the actual measured values of the components and temperatures at the end of the 2nd step, and the re-simulation using these as the initial conditions. The calculated and measured values of the decarburized powder are shown below. Although decarburization is completed in four steps, after that only Ar is injected to accelerate the reaction between excess oxygen and C in the molten steel.
A simulation of decarburization and operational results are also shown.

【table】

[Table] Table 6 below shows the gas composition and injection amount during decarburization refining.

[Table] According to the present invention, the timing and injection of coolant in decarburization refining using an AOD furnace are calculated using an electronic computer, taking into account the oxidation phenomenon that deviates from the equilibrium of Cr and Fe, which was not subject to conventional analysis. It is possible to determine the amount and accurately control the blowing end point.

[Brief explanation of drawings]

Figure 1 shows four tuyeres according to the method of the present invention.
A diagram showing the progress of computer simulation of AOD new furnace operation. Figure 4 shows the slag weight, FeO, MnO, Cr ₂ O ₃ (%) in the operation shown in Figure 1.
Figure 2 is a diagram showing the progress of a computer simulation of an AOD old furnace operation with five tuyeres according to the method of the present invention.
Figure 3 shows the amount of refrigerant to be charged into the vessel during calculation operation, the timing of charging the refrigerant, and the changes in the temperature and composition of molten steel calculated using the model. It is a graph. Figure 5 is a computer simulation diagram showing the progress of changes in nitrogen concentration during operation of an old AOD furnace with five tuyeres, and Figure 6 is a diagram showing computer simulation of changes in nitrogen concentration during operation of a new AOD furnace with five tuyeres according to the method of the present invention. Fig. 7 is a diagram showing the progress of a computer simulation in which actual operation according to the present invention was carried out, check analysis and measurement was performed midway through, and the simulation was performed again using this as an initial condition to correct the operation.

Claims (1)

[Scope of Claims] 1. A predetermined amount of molten metal containing carbon and iron is placed in a refractory-lined container provided with means for blowing oxygen and diluting gases and adjustable control means for controlling the flow rates of each gas. In a method of controlling the operation of an AOD furnace by computer simulation, the decarburization of the AOD furnace is controlled through the respective means, wherein: (a) a first flow rate for the oxygen and a first flow rate for the dilution gas; (b) Setting the amount of oxidation, the amount of nitrogen absorption, the amount of denitrification of the metal, the composition of the molten steel, the temperature, etc. by using the adjustable control means; Calculate: (1) Calculate the amount of metal oxidation using the values obtained from the calculations below. That is, (1-1) The amount of carbon, silicon, and manganese oxidized within a unit time is calculated from the mass transfer rate of each element from the bulk of molten steel to the interface between gas and molten steel. Further, the mass transfer rate of each element from the bulk to the interface is calculated from the product of the difference between the bulk concentration and the interface concentration of each element and the container coefficient. (The vessel coefficient is a coefficient obtained by comparing the result of calculating the model equation using an offline computer with actual operation data within a certain period.) (1-2) Consumption of chromium and iron for oxidation The amount of oxygen is the remainder after subtracting the amount of oxygen consumed for oxidation of each element calculated in (1-1) above from the amount of oxygen blown in within a unit time,
Assuming that all remaining oxygen is consumed for chromium oxidation, the apparent amount of chromium oxidation per unit time is calculated. (1-3) Iron in molten steel is caused by excess Cr ₂ O ₃ in slag.
Cr/Fe in the slag, which is maintained almost constant during operation, is oxidized at a ratio equal to the molar ratio Cr/Fe in the slag calculated from data obtained in actual operation. molar ratio Cr/Fe,
From the apparent amount of chromium oxidation per unit time calculated in (1-2), the true amount of iron and chromium oxidized per unit time is calculated. (2) Calculate the amount of nitrogen absorbed in the molten steel inner tube per unit time or the amount of denitrification by multiplying the nitrogen concentration difference between the bulk metal and gas/metal by the vessel coefficient. (3) Calculate the composition and temperature of new molten steel as follows. That is, (3-1) Calculate the mass balance for the elements from the oxidation amount and nitrogen absorption or denitrification amount of carbon, silicon, manganese, chromium, and iron obtained from (1) and (2) above. (3-2) Calculate the weight of new molten steel, molten slag, and the content of each element in molten steel and slag. (3-3) Calculate the heat of reaction in the oxidation reaction mentioned above, heat loss from the reaction vessel, and heat of melting of the input materials, and at the same time calculate the heat balance of molten steel and slag to calculate the new molten steel temperature. (c) When the decarburization amount calculated as above becomes smaller than the predetermined decarburization amount, the gas ratio and gas amount of the gas blown into the container are controlled as follows. That is, changing the ratio of oxygen to diluent gas to increase the proportion of diluent gas,
Further, control is performed to change the total amount of mixed gas. (d) Furthermore, control is performed to continue blowing the refining gas until the carbon content in the molten steel determined from the material balance in (3) above becomes equal to the predetermined carbon content. (e) During the above-mentioned control, when the temperature of the molten steel reaches a predetermined maximum temperature, control is performed to inject the required amount of coolant in order to lower the molten steel temperature to a predetermined temperature. . A method for controlling AOD furnace operation using computer simulation, characterized by: