Speed and temperature joint control method for annealing furnace

Abstract

The invention discloses a speed and temperature joint control method for an annealing furnace, and the method comprises the following steps: S1, carrying out the modeling of the change relation of the temperature of the annealing furnace along with time through a nonlinear fitting method according to the heating and cooling conditions; s2, according to the obtained nonlinear model of the temperature of the annealing furnace changing along with time, modeling is conducted on speed and temperature control in the process that continuous strip steel passes through a certain furnace subsection; and S3, solving the speed and temperature joint control model by using a particle swarm algorithm. Under the condition that the decision moment is assumed to be fixed, the speed and temperature control problem of the strip steel in the continuous annealing heating furnace in the production process of a 1730 continuous annealing unit in a cold rolling workshop of an iron and steel enterprise is solved.

Description

Technical Field

[0001] The present invention relates to cold rolling continuous annealing production control technology, and more specifically, to a method for jointly controlling the speed and temperature of an annealing furnace. Background Art

[0002] Annealing is a process in the cold rolling production line. It refers to a heat treatment process in which the strip steel is heated to an appropriate temperature, held for a certain period of time, and then slowly cooled to obtain a microstructure close to the equilibrium state. The annealing furnace can be divided into multiple sections from the inlet to the outlet, such as: preheating section, heating section, soaking section, slow cooling section, etc. After the strip steel passes through each section in sequence, the purpose of annealing can be achieved. The most important control problem among them is what transmission speed to adopt and when to set the furnace temperature to what value to meet the annealing requirements of the strip steel in the specified section. In addition, it is also necessary to consider the smooth transition between the furnace temperature setting values of different strip steels to minimize energy consumption.

[0003] Regarding the joint control of speed and temperature, for example, Chinese Patent Application No. 201910312682.2 discloses a furnace temperature control system and method for an annealing furnace, which compares the current temperature value, the temperature preset value, and the output value of the temperature setting ramp function; adjusts at least one of the current temperature value, the temperature preset value, and the output value according to the comparison result and a pre-determined preset strategy. However, when adjusting the current temperature value and the temperature preset value, this method directly makes them equal according to a simple rule, and when adjusting the ramp value, it only adjusts according to a predetermined ratio, which cannot meet the temperature control under complex and variable conditions and does not achieve the joint control of speed and temperature.

[0004] For example, Chinese Patent Application No. 200710052437.X discloses a method for controlling the furnace temperature of a high-temperature annular annealing furnace, which controls the furnace temperature by dividing the output signal of the furnace temperature regulator in the system into two states of furnace door opening and closing. However, this method simply sets the furnace temperature value to a low combustion fixed value or a working condition combustion fixed value in two cases, cannot accurately control the temperature in the furnace in real time, and does not consider the smooth transition of the temperature in the furnace. This method also does not achieve the joint control of speed and temperature. Summary of the Invention

[0005] Aiming at the defects existing in the prior art, the purpose of the present invention is to provide a method for jointly controlling the speed and temperature of an annealing furnace, which solves the problems of speed and temperature control of the strip steel in the continuous annealing furnace of the 1730 cold rolling workshop of iron and steel enterprises under the assumption that the decision-making moment is fixed.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A method for jointly controlling the speed and temperature of an annealing furnace includes the following steps:

[0008] S1. According to the two cases of heating up and cooling down, use the method of non-linear fitting to model the relationship between the temperature of the annealing furnace and time;

[0009] S2. According to the obtained non-linear model of the temperature of the annealing furnace changing with time, model the control of the speed and temperature during the process of continuous strip steel passing through a certain furnace section;

[0010] S3. Use the particle swarm optimization algorithm to solve the above-mentioned speed and temperature joint control model.

[0011] Preferably, the step S1 specifically includes:

[0012] Heat the furnace section of the annealing furnace evenly, sample the data points during the change process of the furnace temperature from zero to the maximum value, and according to the collected data points, model the heating up of the annealing furnace;

[0013] When the furnace temperature of the annealing furnace is heated to the maximum value, stop heating, sample the data points during the change process of the furnace temperature from the maximum value to zero, and according to the collected data points, model the cooling down of the annealing furnace.

[0014] Preferably, the heating up modeling of the annealing furnace adopts an f1(t) function with two variables and marginal effects:

[0015]

[0016] Among them, a1 is the upper limit of the value of f1(t), and b1 controls the speed at which the value of f1(t) reaches the upper limit;

[0017] During the actual heating process of the annealing furnace, record the data points in real time, and then use this function to fit the collected data points to obtain the optimal parameter values of a1 and b1.

[0018] Preferably, the cooling down modeling of the annealing furnace adopts an f -1 (t) function:

[0019]

[0020] Among them, a -1 is the upper limit of the value of f -1 (t), and b -1 controls the speed at which the value of f -1 (t) reaches the upper limit;

[0021] During the actual cooling down process of the annealing furnace, record the data points in real time, and then use this function to fit the collected data points to obtain the optimal parameter values of a -1 and b -1

[0022] ​Preferably, the step S2 specifically includes:

[0023] The optimal set temperature of the strip i is The optimal set speed is If the distance of the strip i from the furnace inlet is d, the time required for the strip i to reach the furnace inlet is

[0024] When the (i - 1)-th coil of strip ends, the temperature of the furnace is

[0025] When the strip i takes time to reach the furnace inlet, the temperature of the furnace is where, w i is a binary variable with values in {-1, 1}, -1 indicates that the furnace needs to be cooled down, 1 indicates that the furnace needs to be heated up, f(·) can take f -1 (·) or f1(·), is the derivative of f(·).

[0026] Preferably, a temperature difference loss is constructed by minimizing the difference between the optimal set temperature of the strip and the temperature that the furnace can actually reach

[0027]

[0028] where, is the initial temperature of the furnace, let

[0029] Preferably, a smoothing loss is established to achieve smooth transition of the optimal temperature of continuous strips The smoothing loss is as follows:

[0030]

[0031] where, is an introduced auxiliary constant,

[0032] Preferably, the temperature difference loss and the smoothing loss need to satisfy the following constraint conditions:

[0033]

[0034] s.t.

[0035]

[0036]

[0037] w i ∈{-1, 1}

[0038] Wherein, W = {w1, w2,..., w L} is the decision variable to be decided; and respectively represent the lower limit and upper limit of the temperature required for the i-th coil of strip steel; V min and V max respectively represent the lower limit and upper limit of the conveyor belt speed.

[0039] A method for coordinated control of speed and temperature for an annealing furnace provided by the present invention makes a coordinated decision on two variables, speed and temperature, so that the furnace temperature meets the strip annealing requirements when the strip enters the annealing furnace. In addition, we also consider the requirement for smooth transition of temperature between continuous strips, which can not only reduce the energy consumption of the annealing furnace but also contribute to extending the service life of the annealing furnace. Brief Description of the Drawings

[0040] Figure 1 is a schematic flow chart of the method for coordinated control of speed and temperature of the present invention;

[0041] Figure 2 is a schematic diagram of the heating and cooling process and the combined function in step S1 of the method for coordinated control of speed and temperature of the present invention. Detailed Embodiments

[0042] In order to better understand the above technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the drawings and embodiments.

[0043] Combined with Figure 1 shown, a method for coordinated control of speed and temperature for an annealing furnace provided by the present invention includes the following steps:

[0044] S1. According to the two cases of heating and cooling, use the method of non-linear fitting to model the relationship between the temperature of the annealing furnace and time, that is, uniformly heat the furnace section, sample the data points of (time, furnace temperature) during the change process of the furnace temperature from zero to the maximum value, and model the furnace heating according to the collected data points; when the furnace temperature reaches the maximum value, stop heating, sample the data points of (time, furnace temperature) during the change process of the furnace temperature from the maximum value to zero, and model the furnace cooling according to the collected data points;

[0045] S2. Based on the obtained non - linear model of the annealing furnace's temperature varying with time, model the control of the speed and temperature during the process of continuous strip steel passing through a certain furnace section; that is, based on the above - mentioned modeling of the temperature varying with time during the furnace heating and cooling processes, considering the case where multiple continuous coils of strip steel have decision - making capabilities for speed and temperature, model the speed and temperature of multiple sections of strip steel to minimize the temperature difference between the optimal temperature and the actual temperature.

[0046] S3. Use the particle swarm optimization algorithm to solve the above - mentioned speed and temperature joint control model.

[0047] The above - mentioned step S1 specifically includes:

[0048] Generally, during the heating process, the temperature first rises rapidly with time, then rises slowly, and finally reaches the temperature upper limit. As shown by curve A in Figure 1 , the heating modeling of the annealing furnace uses an f1(t) function with two variables and marginal effects:

[0049]

[0050] where a1 is the upper limit of the value of f1(t), and b1 controls the speed at which the value of f1(t) reaches the upper limit;

[0051] In order to accurately fit the heating process of the furnace, it is necessary to record data points in real - time during the actual heating process of the annealing furnace, and then use this function to fit the collected data points to obtain the optimal parameter values of a1 and b1.

[0052] The cooling process is opposite to the heating process. The temperature first drops rapidly with time, then drops slowly, and finally the temperature approaches zero. As shown by curve B in Figure 1 , the cooling modeling of the annealing furnace uses the f -1 (t) function:

[0053]

[0054] where a -1 is the upper limit of the value of f -1 (t), and b -1 controls the speed at which the value of f -1 (t) reaches the upper limit;

[0055] Similarly, record data points in real - time during the actual cooling process of the annealing furnace, and then use this function to fit the collected data points to obtain the optimal parameter values of a -1 and d -1 .

[0056] The above - mentioned step S2 specifically includes:

[0057] To simplify the problem, assume that each strip of steel starts to determine the speed and temperature values when it reaches a fixed distance from the furnace inlet. The decision on the strip speed is to meet the different temperature setting requirements of the strip, so that the furnace can just reach the set temperature value through the cooperation of speed within a limited distance.

[0058] Consider L consecutive coils of strip steel. The optimal set temperature of strip i is The optimal set speed is If the distance of strip i from the furnace inlet is d, the time required for strip i to reach the furnace inlet is

[0059] When the (i - 1)-th coil of strip ends, the temperature of the furnace is

[0060] When strip i spends time to reach the furnace inlet, the temperature of the furnace is where, w i is a binary variable with values in {-1, 1}, -1 indicates that the furnace needs to cool down, 1 indicates that the furnace needs to heat up, and f(·) can take f -1 (·) or f1(·), is the derivative of f(·).

[0061] Construct the temperature difference loss by minimizing the difference between the optimal set temperature of the strip and the temperature that the furnace can actually reach

[0062]

[0063]

[0064] where, is the initial temperature of the furnace, let

[0065] Establish the smoothing loss to achieve the optimal temperature smooth transition of continuous strips. The smoothing loss is as follows:

[0066]

[0067] where, is the introduced auxiliary constant,

[0068] The temperature difference loss and the smoothing loss shall satisfy the following constraints:

[0069]

[0070] such that

[0071]

[0072]

[0073] w i ∈ {-1, 1}

[0074] wherein W = {w1, w2,..., w L} is the decision variable to be determined; and respectively represent the lower limit and the upper limit of the temperature required for the i-th coil of strip steel; V min and V max respectively represent the lower limit and the upper limit of the speed of the conveyor belt.

[0075] The above step S3 specifically includes:

[0076] Since T and V are continuous variables respectively, W is a binary integer variable, and the objective function is non-convex, the above minimization problem is a non-convex mixed integer programming problem, which is difficult to solve. Therefore, a heuristic particle swarm algorithm is considered for searching the optimal solution.

[0077] Those of ordinary skill in the art in this technical field should recognize that the above embodiments are only used to illustrate the present invention, rather than to limit the present invention. As long as it is within the scope of the spirit of the present invention, changes and modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for jointly controlling the speed and temperature of an annealing furnace, characterized in that, It includes the following steps: S1. According to the two cases of heating up and cooling down, use the method of non - linear fitting to model the relationship between the temperature of the annealing furnace and time; S2. According to the obtained non - linear model of the temperature of the annealing furnace changing with time, model the control of the speed and temperature during the process of continuous strip steel passing through a certain furnace section; S3. Use the particle swarm algorithm to solve the above - mentioned speed and temperature joint control model.

2. The method for jointly controlling the speed and temperature of an annealing furnace according to claim 1, characterized in that, The specific steps of step S1 include: Uniformly heat the furnace section of the annealing furnace, sample the data points during the change process of the furnace temperature from zero to the maximum value, and model the heating up of the annealing furnace according to the collected data points; When the furnace temperature of the annealing furnace is heated to the maximum value, stop heating, sample the data points during the change process of the furnace temperature from the maximum value to zero, and model the cooling down of the annealing furnace according to the collected data points.

3. The method for jointly controlling the speed and temperature of an annealing furnace according to claim 2, characterized in that, The heating - up modeling of the annealing furnace adopts an f1(t) function with two variables and marginal effects: Among them, a1 is the upper limit of the value of f1(t), and b1 controls the speed at which the value of f1(t) reaches the upper limit; During the actual heating process of the annealing furnace, record the data points in real - time, and then use this function to fit the collected data points to obtain the optimal parameter values of a1 and b1.

4. The method for jointly controlling the speed and temperature of an annealing furnace according to claim 3, characterized in that, The cooling modeling of the annealing furnace uses the f -1 (t) function: Among them, a -1 is the upper limit of the value of f -1 (t), b -1 controls the speed at which the value of f -1 (t) reaches the upper limit; During the actual cooling process of the annealing furnace, data points are recorded in real time, and then the collected data points are fitted using this function to obtain a -1 and b -1 The optimal parameter values.

5. The method for jointly controlling the speed and temperature of an annealing furnace according to claim 1, characterized in that, The specific steps of step S2 include: The optimal set temperature of strip i is The optimal set speed is If the distance of strip i from the furnace inlet is d, the time required for strip i to reach the furnace inlet is When the (i - 1)-th coil of strip ends, the temperature of the furnace is When the strip steel i flower When the time reaches the furnace inlet, the temperature of the furnace is where, w i is a binary variable with values in {-1, 1}, -1 indicates that the furnace needs to be cooled, 1 indicates that the furnace needs to be heated, and f(·) can take f -1 (·) or f1(·), is the derivative of f(·).

6. The method for jointly controlling the speed and temperature of an annealing furnace according to claim 5, characterized in that, Construct the temperature difference loss by minimizing the difference between the optimal set temperature of the strip steel and the temperature that the furnace can actually reach Among them, is the initial temperature of the furnace, and it is set that 7. The method for jointly controlling the speed and temperature of an annealing furnace according to claim 6, characterized in that, Establish smooth loss To achieve the optimal temperature of continuous strip steel Smooth transition, smooth loss As follows: Among them, is the introduced auxiliary constant, 8. The method for jointly controlling the speed and temperature of an annealing furnace according to claim 7, characterized in that, Temperature difference loss Smoothing loss The constraint conditions to be satisfied are as follows: s.t. w i ∈{-1,1} Among them, W = {w1, w2,..., w L} is the decision variable to be decided; and respectively represent the lower and upper temperature limits required for the i-th coil of strip steel; V min and V max respectively represent the lower and upper limits of the conveyor belt speed.

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