Furnace control by atmosphere

Abstract

The present invention relates to a method for adjusting the atmosphere A in a furnace, the atmosphere A being such that a steel strip having a certain composition and an exposed surface area A1 is heated from time T0 to time T S1END A steel strip having a certain composition and exposed surface area is heat treated to a temperature of 1000° C. for a time T S2START From time T N The method includes the following steps: data acquisition, optimization, and injection of H2O.

Description

Technical Field

[0001] The present invention relates to a method for adjusting the atmosphere of a furnace during the heat treatment of a steel strip. More specifically, this method can be used during the annealing of a steel strip.

Background Art

[0002] During the annealing of a steel strip, the steel strip is heated and then maintained above its recrystallization temperature in order to increase its ductility and reduce its hardness. This is done in a furnace where the temperature and dew point of the atmosphere are adjusted. Controlling the atmosphere is crucial for ensuring the quality of the strip.

[0003] The adjustment of temperature is ensured by heating devices (radiant tubes, inductors, etc.) that supply the desired amount of heat.

[0004] The adjustment of the dew point is ensured, for example, by providing water in the form of steam to the atmosphere.

[0005] Each steel grade and type has preferred furnace atmosphere, i.e., preferred process conditions including ranges of temperature and dew point. Therefore, in a continuous production line manufacturing different types and grades of steel strips, it is necessary to adapt the furnace atmosphere to each product. The shorter the time between the atmosphere of one furnace and that of another during product transition, the better the achievable quality of the product.

[0006] To adjust the dew point, existing systems use a proportional-integral-derivative controller (PID controller) which is part of a control loop mechanism combined with a dew point measuring device and a system for injecting water.

[0007] In this system, as shown in Figure 1, the dew point of the atmosphere is measured (DP MEASURED ), and the target dew point is defined (DP TARGET ). Then, an error value, for example, the difference between the measured dew point and the target dew point, is calculated. Thereafter, based on the proportional, integral, and derivative terms calculated by the PID controller, the flow rate of H2O to be injected (H2O INJECTThe H2O flow is determined. Finally, the determined H2O flow is injected into the furnace. This sequence is repeated periodically throughout the heat treatment.

[0008] However, it is important to remember that annealing furnaces typically have a volume that is significant compared to the steam flow that can be injected into the furnace. Therefore, when feeding two types of steel requiring different dew points in succession within a short period of time in the furnace, it is not possible to obtain the optimal dew point over time along the entire length of the coil. This can result in reduced yield or poor belt quality, particularly with respect to the rear of the first belt and the front of the second belt. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The objective of the present invention is to improve the control of H2O injected into the annealing furnace.

[0010] More specifically, the object of the present invention is to provide a preferred annealing atmosphere A for the steel strip S1 in the furnace portion that brings out the optimal quality of the final product. TAR1 Preferred annealing atmosphere A for steel strip S2 TAR2 The goal is to improve transition management. The preferred annealing atmosphere can include a range of values. [Means for solving the problem]

[0011] This objective is achieved by providing the method according to claim 1. The method may also have any of the features of claims 2 to 7.

[0012] Other features and advantages of the present invention will become apparent from the following detailed description of the invention.

[0013] To illustrate the present invention, various embodiments and non-limiting examples will be described with particular reference to the following figures. [Brief explanation of the drawing]

[0014] [Figure 1]Shows an adjustment method known in the prior art. [Figure 2] Shows an embodiment of an adjustment system according to the present invention. [Figure 3A] Shows dew point adjustment known in the prior art. [Figure 3B] Shows steam injection adjustment known in the prior art. [Figure 4A] Shows dew point adjustment according to the present invention. [Figure 4B] Shows steam injection adjustment according to the present invention.

Mode for Carrying Out the Invention

[0015] As shown in FIG. 2, the present invention is a method for adjusting the atmosphere A in a furnace containing H2 and N2, wherein a steel strip S1 having a composition C1 and an exposed surface area A SURF1 is heat-treated from time T0 to time T S1END and a steel strip S2 having a composition C2 and an exposed surface area A SURF2 is heat-treated from time T S2START to time T N and the following steps, namely, A. A data acquisition step, i. At time T0, measure the dew point DP0 of the atmosphere A, ii. Read the target atmosphere A TAR1 of the steel strip S1, and the target atmosphere A TAR1 includes at least a dew point value, iii. Read the target atmosphere A TAR2 of the steel strip S2, and the target atmosphere A TAR2 is a data acquisition step including at least a dew point value, B. An adjustment step, i. N predicted atmospheres A N corresponding to N times T1 to T PRO-1 to A PRO-N are a. The dew point DP0 of the atmosphere measured at time T0, b. The volume of the furnace c. The times T1 to T NThe composition and exposed surface area of ​​the steel strips S1 and S2 in the furnace in each of the above. Steps defined based on, ii. The amount Q of H2O injected at T1 in the furnace. H2O Using a model predictive control controller, the following data, namely, a. Predicted atmosphere A PRO-1 ~A PRO-N , b. The aforementioned target atmosphere A TAR1 and A TAR2 , c. The volume of the furnace and the refresh rates of N2 and H2, d. Composition and exposed surface area of ​​the steel strip S1 in T1 Adjustment steps including the step of estimation using C. Step of injecting the estimated amount of H2O at T1. Regarding methods including

[0016] The furnace is equipped with heating means. The heating means may be, for example, radiating elements such as inductors and / or tubes.

[0017] A furnace may comprise several parts, such as a preheating section, a heating section, a soaking section, and a cooling section. This method can be applied to any part of the furnace. Preferably, the method is applied in the heating section and / or the soaking section.

[0018] Any type of heat treatment is acceptable. However, annealing is preferred, and recrystallization annealing is particularly preferred.

[0019] Steel strips S1 and S2 may have the same or similar composition, corresponding to the same product group. Steel strips S1 and S2 may have different compositions.

[0020] Preferably, the steel strip contains, by weight percent, 0.0001% to 0.50% C, 0.01% to 5.0% Mn, and 0.001% to 5.0% Si.

[0021] The exposed surface area of ​​a steel strip refers to the surface of the steel strip that is inside the furnace and exposed to the furnace atmosphere. The exposed surface area can be expressed per unit area or per volume area.

[0022] T S1END This is the first step in which strip S1 is not inside the furnace. In other words, T S1END is, A SURF1 This is the first time, where the value is equal to zero.

[0023] T S2START This is the first step in which strip S2 is at least partially inside the reactor. In other words, T S2START is, A SURF2 This is the first time period in which the value is not equal to zero.

[0024] In the first step, the data acquisition step, the dew point of the atmosphere is measured, and time T1~T N The target dew point of the steel strip to be heat-treated in either of the following conditions is read out. The target dew point is in target atmosphere A. TAR1 and / or A TAR2 The target dew point range may also be used, so that it includes a range of dew point values.

[0025] The target atmosphere for the steel strip allows for continuous heat treatment to be carried out, ensuring satisfactory product quality.

[0026] The dew point value or range depends on the steel composition. These can be retrieved, for example, from a database.

[0027] In the second step, the adjustment step, the goal is to repeat N times (T1~T N ), that is, determining the required water injection flow rate at each step, and N predicted atmospheres (A) in the case where no water is added to the furnace (e.g., atmosphere). PRO-1 ~A PRO-N The goal is to estimate the atmosphere of the furnace in N steps corresponding to the given conditions.

[0028] Alternatively, N times (T1~T NThe atmosphere of the furnace can be estimated when the amount of H2O injected is different.

[0029] Preferably, N is a positive integer between 2 and 100. More preferably, N is a positive integer between 5 and 50. Even more preferably, N is a positive integer between 10 and 30.

[0030] Preferably, the time T0 to T N Each of these is spaced 5 seconds to 1 minute apart. More preferably, time T0 to T N Each of these will be spaced out by 15 to 45 seconds.

[0031] Preferably, time T0 to T N Each of these is given the same time interval. For example, if N=50 and each of these times is given an interval of 10 seconds, then T0 is at time t=0 seconds, T1 is at time t=10 seconds, T2 is at time t=20 seconds, and T N =T 50 The time t = 500 seconds.

[0032] Predicted atmosphere A PRO-1 ~A PRO-N The definition is the dew point measured in step Ai, the furnace volume, and the time T1 to T N This is done using the composition and exposed surface area of ​​the steel strip in the furnace for each of the aforementioned conditions. Such estimations of the predicted atmosphere are well known to those skilled in the art.

[0033] Alternatively, predictive atmosphere A PRO-1 ~A PRO-N The definition is the dew point measured in step Ai, the furnace volume, and the time T1 to T N This is done using the composition and exposed surface area of ​​the steel strip in the furnace for each of the above, as well as the amount of H2O injected.

[0034] In one or more steps, for example, strips S1 and S2 can be partially in the furnace at the same time, which is especially true when the two strips are welded together. In that case, T S2START is T S1END It happens before.

[0035] In that case, the predicted atmosphere is defined using the composition and surface area of ​​each zone within the furnace.

[0036] In one or more steps, for example, the strip may not be inside the furnace, which is T S2START is T S1END This is especially true when it occurs afterwards.

[0037] The definition of the predicted atmosphere is preferably such that the temperature and pressure of the atmosphere are in steps T1 to T N This is done under the assumption that certain things are constant.

[0038] Preferably, the target atmosphere A TAR1 and A TAR2 This includes at least the minimum and maximum values ​​of the H2 concentration and the maximum value of the CO concentration.

[0039] More preferably, the target atmosphere contains 0.1 to 50 volume% of H2. Even more preferably, the target atmosphere contains 1 to 50 volume% of H2.

[0040] Next, the amount Q of H2O injected into the furnace at T1. H2O This is estimated by using Model Predictive Control (MPC).

[0041] Generally, model predictive control is based on the finite-time leveling optimization of plant model iterations. At time t, the current plant state is sampled, and a cost-minimizing control strategy is calculated for a relatively short time range [t, t+T] in the future.

[0042] For example, in this invention, the definition of the amount of H2O to be injected is carried out by defining a cost function that should be minimized, and the cost function is defined as at least one target atmosphere A TAR and N predicted atmospheres A PROn This represents the difference between [the two values].

[0043] For example, a cost function can have the following structure:

[0044]

number

[0045] The volumes and renewal flow rates of N2 and H2 in the furnace, as well as the composition and exposed surface of the steel strip S1 at T1, allow for the modeling of the dynamics between the amount of H2O injected and the generation of the dew point.

[0046] Alternatively, in step B.ii, the flow of H2O or steam injected at T1 in the furnace can be estimated using a model predictive control controller with the following data. a) Predicted atmosphere A PRO-1 ~A PRO-N b) The target atmosphere A TAR1 and A TAR2 c) The volume of the furnace and the refresh rates of N2 and H2, d) Composition and exposed surface area of ​​steel strip S1 in T1.

[0047] In the fifth step, the amount or flow rate of H2O defined in step B.ii. is injected into the furnace. This injection can be done by directly injecting water into the furnace or by using porter gas.

[0048] According to the present invention, the atmosphere inside the furnace can be brought closer to a set value. The present invention is particularly advantageous when the composition of the band and / or the set point changes inside the furnace.

[0049] Furthermore, the present invention relates to a method for adjusting the atmosphere A inside a furnace containing H2 and N2, wherein the composition C1 and exposed surface area A SURF1 A steel strip S1 having the following characteristics: S1END The heat treatment is performed up to the following step, namely, A. Data acquisition step, i. At time T0, measure the dew point DP0 of the atmosphere A. ii. Target atmosphere A of the steel strip S1 TAR1 The above target atmosphere A is read out. TAR1 This includes a data acquisition step that includes at least the dew point value. B. Adjustment step, i. N time intervals T1~T N N predicted atmospheres A corresponding to each other PRO-1 ~A PRO-N of, a. The dew point DP0 of the atmosphere measured at time T0, b. The volume of the furnace c. The above time T1~T N The composition and exposed surface area of ​​the steel strip S1 in the furnace in each of the above. Steps defined based on, ii. The amount Q of H2O injected at T1 in the furnace. H2O Using a model predictive control controller, the following data, namely, a. Predicted atmosphere A PRO-1 ~A PRO-N , b. The aforementioned target atmosphere A TAR1 , c. The volume of the furnace and the refresh rates of N2 and H2, d. Composition and exposed surface area of ​​the steel strip S1 in the furnace at T1 Adjustment steps including the step of estimation using C. Step of injecting the estimated amount of H2O at T1. Regarding methods including [Examples]

[0050] <Experimental Results> To evaluate the effect of this method on furnace atmosphere control, we model the atmosphere for the transition between two control methods: one using interstitial-free (IF) steel of the type sold by ArcelorMittal and the other using duplex 780 steel of the type sold by ArcelorMittal.

[0051] In the first simulation, the atmosphere is adjusted using a PID controller. In the second simulation, the atmosphere is adjusted using the claimed method.

[0052] In both simulations, the IF steel strip requires a dew point of -30°C and is in the furnace from 0 to 9.5 minutes, while the two-phase 780 steel strip requires a dew point of -15°C and is in the furnace from 9.5 to 20 minutes.

[0053] For each target dew point, the mole fraction of H2O is 5.10 -4 There is a tolerance of ±8°C for the target dew point at 30°C, and ±3°C for the target dew point at -15°C.

[0054] For both simulations, the measured dew point (continuous line), target dew point (thick dashed line), and tolerance (thin dashed line) are plotted in Figure 3A for the first simulation and in Figure 4A for the second simulation. Furthermore, the steam injection is plotted in Figure 3B for the first simulation and in Figure 4B for the second simulation.

[0055] In the first simulation, 14% of the time was spent outside the acceptable range, whereas in the second simulation, according to the claimed method, only 4% of the time was spent outside the acceptable range. Therefore, using the claimed method, the time spent outside the acceptable range is divided by 3.5 in this example.

Claims

1. H ２ and N ２ A method for adjusting the atmosphere A in a furnace containing １ and the exposed surface area A ＳＵＲＦ１ The steel strip S having １ is heat-treated from time T ０ to time T Ｓ１ＥＮＤ and the steel strip S having the composition C ２ and the exposed surface area A ＳＵＲＦ２ is heat-treated from time T ２ to time T Ｓ２ＳＴＡＲＴ and includes the following steps, namely, Ｎ ​ A. Data acquisition step, i. Time T ０ In the above atmosphere A, the dew point DP ０ Measure, ii. The steel strip S １ Target atmosphere A ＴＡＲ１ The above target atmosphere A is read out. ＴＡＲ１ This includes at least the dew point value, iii. The steel strip S ２ Target atmosphere A ＴＡＲ２ The above target atmosphere A is read out. ＴＡＲ２ This includes a data acquisition step that includes at least the dew point value. B. Adjustment step, i. N time intervals T １ ~T Ｎ N predicted atmospheres A corresponding to each other ＰＲＯ－１ ~A ＰＲＯ－Ｎ of, a. Time T ０ The dew point DP of the atmosphere measured ０ , b. Volume of the furnace c. Said time T １ ~T Ｎ The steel strip S in the furnace in each of the above １ and S ２ Composition and exposed surface area Steps defined based on, ii. T inside the furnace １ ~H injected with T N ２ Amount of O Q Ｈ２Ｏ Using a model predictive control controller, the following data, namely, a. Predicted atmosphere A ＰＲＯ－１ ~A ＰＲＯ－Ｎ , b. The aforementioned target atmosphere A ＴＡＲ１ and A ＴＡＲ２ , c. The volume and N of the furnace ２ and H ２ Update traffic, d. T １ The steel strip S in １ Composition and exposed surface area Adjustment steps including the step of estimation using C.T. １ ~T N, the estimated quantity H ２ Step to inject O A method that includes this.

2. The method according to claim 1, wherein the heat treatment is annealing.

3. The method according to claim 1 or 2, wherein the steel strip contains, by weight percentage, 0.0001% to 0.50% C, 0.01% to 5.0% Mn, and 0.001% to 5.0% Si.

4. The method according to claim 1, wherein N is a positive integer from 2 to 100.

5. The aforementioned time T ０ ~T Ｎ The method according to claim 1, wherein each of the is performed at an interval of 5 seconds to 1 minute.

6. In step B. i., the definition is that the temperature and pressure of the atmosphere are at time T. １ ~T Ｎ The method according to claim 1, which is carried out assuming that it is constant for a certain period of time.

7. H ２ and N ２ A method for adjusting the atmosphere A inside a furnace, which includes composition C １ and exposed surface area A １ Steel strip S １ However, time T ０ From time T Ｎ The heat treatment is performed up to the following step, namely, A. Data acquisition step, i. Time T ０ In the above atmosphere A, the dew point DP ０ Measure, ii. The steel strip S １ Target atmosphere A ＴＡＲ１ The above target atmosphere A is read out. ＴＡＲ１ This includes a data acquisition step that includes at least the dew point value. B. Adjustment step, i. n time intervals T １ ~T Ｎ n predicted atmospheres A corresponding to each other ＰＲＯ－１ ~A ＰＲＯ－Ｎ of, a. Time T ０ The dew point DP of the atmosphere measured ０ , b. Volume of the furnace c. Said time T １ ~T Ｎ The steel strip S in the furnace in each of the above １ Composition and exposed surface area Steps defined based on, ii. T inside the furnace １ ~H injected with T N ２ Amount of O Q Ｈ２Ｏ Using a model predictive control controller, the following data, namely, a. Predicted atmosphere A ＰＲＯ－１ ~A ＰＲＯ－Ｎ , b. The aforementioned target atmosphere A ＴＡＲ１ , c. The volume and N of the furnace ２ and H ２ Update traffic, d. T １ The steel strip S inside the furnace in the above-mentioned place １ Composition and exposed surface area Adjustment steps including the step of estimation using C.T. １ ~T N, the estimated quantity H ２ Step to inject O A method that includes this.

Images