JPH06248362A - Method for controlling temperature of material in continuous type heating furnace - Google Patents

Abstract

PURPOSE:To control so as to satisfy the upper limit regulation of temp. fixed as the aim, in which the temp. at each part in a material secures the necessary quality, and also so as not to obstruct the productivity of a heating furnace, in the material temp. control in a continuous type heating furnace. CONSTITUTION:In the material temp. control in a continuous type heating furnace, by using the temp. at each part, in the material and the temp. difference between the above temp. and the upper limit temp. at every moment, such the upper limit value in the setting furnace temp. that the upper limit regulation of the material temp. is satisfied and also, the productivity of the heating furnace is not unnecessarily obstructed, is obtd. at each control period and varied at every moment. Further, in the case of being the fuel flow rate, as the operating quantity, by using a predicting model for furnace temp., the upper limit value in the setting furnace temp. is transformed into the upper limit value in the fuel flow rate and varied at every moment as the same way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material temperature control method for a continuous heating furnace.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a longitudinal cross section (a material advancing direction) of a continuous heating furnace to be controlled and various temperature distributions in the longitudinal direction. In the figure, the heating furnace is divided into 5 zones from the furnace bottom zone to the soaking zone, the horizontal axis is the longitudinal distance, and the graph of the material temperature and the extraction target temperature shows the values related to the material existing at each position. It is a connected curve. In the material temperature control for the plant as shown in the figure, a target temperature rising curve that represents the target pattern of temperature rise of the material average temperature of the material to be heated is provided, and the average material temperature is set to follow the target temperature rising curve. In addition, the method of controlling the fuel flow rate or the furnace temperature (furnace temperature) as the manipulated variable takes into consideration the constraint condition when the quality constraint condition (ripening time etc.) related to the material heating process exists. By setting the target temperature rise curve, it is possible to easily perform the control satisfying the constraint condition.
Optimum control can also be realized by setting a target temperature rise curve so that the temperature rise curve is optimal with respect to a predetermined evaluation function. Therefore, several promising methods for material temperature control have been proposed in recent years. For example, Japanese Patent Laid-Open No. 61-19
In the method described in Japanese Patent No. 9020, the optimum temperature rising curve for each material is determined in advance by some method so that the temperature after Δt time for each material in the furnace becomes a target temperature, that is, a value on the curve. The fuel flow rate set value is controlled as an operation amount.

Further, in Japanese Patent Application Laid-Open No. 2-156017, a target temperature rising curve is determined online at a predetermined cycle so that the temperature rising curve of the material in the furnace is optimum with respect to the evaluation function, and the temperature rising curve is transmitted to the material. The temperature of each part in the material is estimated and calculated from moment to moment using an analysis model that expresses heat, and the fuel flow rate is set so that the average temperature in the material matches the value on the target temperature rise curve after a predetermined time (N ₃ hours). A method of controlling a value as an operation amount is described. The parameter to be optimized is a target heating rate at some points or sections in the furnace, and this value is the same in the same material group. Here, the material group refers to a plurality of materials whose positions in the furnace are continuous, in which portions having similar zonal time, charging temperature, extraction target temperature, etc. are grouped together.

The target temperature rising curve of each material includes the charging temperature for each material, the extraction target temperature, and
Determined by the heat-up time for quality assurance.

The above-mentioned group division copes with the mixture of various materials such as each zone time, charging temperature and extraction target temperature in the furnace, and the number of parameters to be optimized is minimized. This is done in order to reduce and streamline the online optimization process. If the group division is made finer, the optimization processing becomes finer, but the time required for the processing increases. FIG. 6 shows a functional block diagram for explaining the control in this publication.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The above-mentioned conventional techniques (Japanese Patent Laid-Open No. 61-199020 and Japanese Patent Laid-Open No. 2-156).
No. 017), the temperature rise curve of the average temperature of the material is determined. Therefore, the average temperature can be controlled so as to satisfy the predetermined temperature upper limit regulation or temperature lower limit regulation. Almost no consideration is given to the constraint condition regarding the upper limit of the temperature of each part (the temperature of each part including the surface and the inside).

Therefore, in the prior art, in order to satisfy such a constraint condition regarding the upper limit temperature, the upper limit value of the set furnace temperature must be equal to the upper limit value of the material temperature. Therefore, even if the material temperature is considerably lower than the upper limit value, the furnace temperature is suppressed to the material temperature upper limit value or less, and the productivity of the heating furnace is lowered. When the adjustment target (manipulation amount) for controlling the material temperature is not the set furnace temperature but the fuel flow rate set value, for example, the fuel flow rate change and the furnace temperature change as described in JP-A-2-156017. The upper limit of the fuel flow rate set value can be obtained from the set upper limit of the furnace temperature using the furnace temperature prediction model that represents the dynamic relationship of There is a problem of deterioration.

As described above, in the conventional material temperature control method, no consideration is given to the constraint conditions regarding the temperature of the highest temperature part and the lowest temperature part in the material during the temperature rise.

[0009]

According to a first aspect of the present invention, in the material temperature control of a continuous heating furnace, the manipulated variable is a set furnace temperature of each combustion zone (zone in which fuel can be injected), and the control is performed. Plant performance (observed values of each zone temperature, fuel flow rate, etc.) and data on the material to be heated (material thickness,
Width, length, position in the furnace, material, actual charging temperature, etc.) When estimating and calculating the temperature of each part of the material (including the surface and inside) from each material, For each combustion zone (zone in which fuel can be injected), among the materials j to be heated located in the zone and in the vicinity thereof, regarding the material _having the upper limit temperature T _SUj for each part in the material, the material at the current time t internal maximum temperature portion temperature T _SMj (t) and by using the temporal change amount, the predetermined time L only future values T _SMj of _{T SMj (t) (t +} L), T SMj (t + L) Upper limit temperature T _SUj
The difference from _{T SU-Mj (t + L} ) (= T SUj -T SMj (t + L)) and predicts, for each material after accordingly, the temperature difference T _SU-Mj (t +
L) minimum value T _SU-Mj1 (t + L) is _calculated , and the minimum value T _SU-Mj1 (t +
Based on L), the upper limit value of the set furnace temperature of the zone at the current time t is calculated while taking into consideration the furnace temperature distribution in the longitudinal direction of the furnace, and T _SU-Mj1 (t + L) is increased / decreased. The upper limit value is increased / decreased every moment.

The second invention of the present application is that, in the material temperature control of the continuous heating furnace, the manipulated variable is the fuel flow rate set value in each combustion zone (zone in which fuel can be injected), and also in each control cycle. , Plant performance (observed values of each zone furnace temperature, fuel flow rate, etc.), and data on the material to be heated (material thickness,
In case of estimating and calculating the temperature (including the surface and inside) of each part of each material from the width, length, position in the furnace, material, actual charging temperature value, etc., future operation after the present A furnace temperature prediction model that represents changes in each zone furnace temperature due to changes in the amount (fuel flow rate, etc.) is provided, and it is located in the zone and its vicinity for each control cycle and for each combustion zone (zone in which fuel can be injected). Among the materials j to be heated, the maximum temperature T _SMj (t) in the material at the current time t and its temporal change amount are used for the material _having the upper limit temperature T _SUj for each part in the material. , T _SMj (t) of a future value T _SMj (t + L) for a predetermined time L, and a difference T from the upper limit temperature T _{SUj of} T _SMj (t + L).
_SU-Mj (t + L) (= T _{S Uj} −T _SMj (t + L)) is predicted, and then the minimum value T _{SU of the} temperature difference T _SU-Mj (t + L) is calculated for each material. _-Mj1 (t + L) is _{calculated, and based on the minimum} value T _{SU- Mj1} (t + L), the current time t is considered while considering the furnace temperature distribution in the longitudinal direction of the furnace.
Then, the upper limit of the set furnace temperature in the zone is _calculated , and T _SU-Mj1 (t
+ L) increase / decrease the upper limit value according to the increase / decrease, and then use the above-mentioned furnace temperature prediction model so that the future furnace temperature becomes equal to or lower than the upper limit value. It is characterized by changing every moment.

[0011]

According to the present invention, the upper limit value of the furnace temperature can be momentarily changed at an appropriate timing while predicting the future value of the maximum temperature of the material. The temperature is always kept within a predetermined upper limit value, necessary materials are secured, the upper limit value of the furnace temperature is not unnecessarily kept low, and the productivity of the heating furnace is not hindered.

[0012]

FIG. 1 is a flow chart for explaining the principle of the present invention, in which an upper limit value of an operation amount (set furnace temperature or fuel flow rate) for satisfying a material temperature upper limit regulation is calculated for each control cycle. Represents a method. First, in the following description, i is a band number (i = 1, 2, ...
・) And j are material numbers (numbered in the order of loading; j =
, 1), and t represent current times (t = 1, 2, ..., With the control cycle in discrete time control as a unit). Further, the temperature of each part of the material to be heated in the furnace is controlled by a known model formula representing heat transfer on the surface of the material and inside, as described in formula (5) of JP-A-2-156017. Shall be calculated for each.

The purpose of the process of FIG. 1 is to ensure that the upper limit of the temperature of each part in the material is satisfied for each combustion zone.
This is to obtain the upper limit value of the manipulated variable in the material temperature control. At this time, as a material to be considered in each band, as shown in FIG. 2, in addition to the band, a material existing in a range including adjacent bands on both sides thereof by a predetermined distance is used. The furnace temperature near the extraction port and charging port of each zone is greatly influenced by the operation amount of the adjacent zone, so the range was set in this way. In the first process of FIG. 1, among the materials to be heated to be considered in the zone i, the maximum internal temperature T _SMj (t) [° C] of each material j whose upper limit temperature is determined is Future value T for a predetermined time L
_SMj (t + L) [° C] is predicted by the following formula.

[0014]

[Equation 1]

However, L is a positive integer (L = 1, 2, ...), control cycle unit a _M : positive constant [dimensionless]; 0 <a _M <1, and usually 1 such as 0.9 Set to a value close to.

Next, for each material j, the difference T _SU-Mj (t +) between T _SMj (t + L) and the upper limit temperature T _SUj [° C] for that material.
L) (= T _SUj −T _SMj (t + L)) [° C] is the smallest material j
Find one. The material j1 is hereinafter referred to as an i-th band temperature upper limit regulating material.

Next, the predicted maximum temperature value T of the material j1
_Using the value of _SMj1 (t + L) [° C], the upper limit value T _FU , _j1 (t + L) [° C] of the furnace temperature at the future position of the material j1 at the time (t + L)
Is calculated by the following formula.

T _FU , _j1 (t + L) = T _SUj1 + a _TFi · T _{SU- Mj1} (t + L) [° C] (2) Here, T _SU-Mj1 (t + L) = T _SUj1 −T _SMj1 (t + L) [° C] (3) where T _SU-Mj1 (t + L): Predicted temperature difference from the upper limit of the maximum temperature of the material j1 [ ° C] a _TFi : Upper temperature change coefficient of furnace temperature (positive constant for each zone) [Dimensionless] T _SU-Mj1 (t + L) [° C] If it is negative, the value will be smaller than if it is positive.

(To prevent the fluctuation of the furnace temperature upper limit value, that is, the fluctuation of the furnace temperature due to the sign change of the predicted temperature difference value T _SU-Mj1 (t + L) [° C].) FIG. Upper limit of furnace temperature T _FU ,
_In the calculation process of _j1 (t + L) [° C], it represents the relationship between the variables. The reason why the upper limit of the furnace temperature is calculated as a future value by L in the above equation (2) is that the time until the change in the manipulated variable (set furnace temperature or fuel flow rate set value) appears as a change in the actual furnace temperature. This is to take an action such as reducing the operation amount early in consideration of the delay. If L is an inappropriately small value, this time delay between the manipulated variable and the actual furnace temperature causes
The furnace temperature may temporarily exceed the upper limit. The value of L may be equal to or slightly larger than this time delay.

By the processing of the equation (2), the predicted temperature difference value T _SU-Mj1 (t + L) [° from the upper limit temperature of the maximum temperature of the material j1 is obtained.
C] is a large positive value, the furnace temperature upper limit value T _FU , _j1 (t +
The value of L) [° C] is significantly higher than the upper limit value T _SUj1 [° C] of the material temperature and does not hinder the productivity of the heating furnace. on the other hand,
As T _SU-Mj1 (t + L) [° C] decreases and approaches 0,
When the value of the furnace temperature upper limit value T _FU , _j1 (t + L) [° C] approaches T _SUj1 [° C], the material temperature upper limit regulation is satisfied.

Next, the upper limit value of the i-th zone set furnace temperature T _FUi (t)
Calculate [° C]. Here, regarding the actual furnace temperature in the heating furnace, as shown in FIG. 5, there is a temperature distribution in the longitudinal direction of the furnace (the traveling direction of the material). At this time, the set furnace temperature of each zone usually means a set value for the furnace temperature at a predetermined position near the center of the zone (hereinafter, referred to as a representative furnace temperature of the zone). Therefore, the above-mentioned upper limit value T _FUi (t) [° C] is the upper limit value of the i-th zone representative furnace temperature and is calculated by the following equation.

[0022] _{T FUi (t) = T FU} , j1 (t + L) + T Fi (t) -T F, j1 (t / t + L) [° C] ··· (4) where, T _Fi (・): I-th zone representative reactor temperature (actual value or predicted value) [°
C] T _F , _j1 (t / t + L): Actual value of the furnace temperature at the predicted position of material j1 at time (t + L) at the current time t [° C] In the material temperature control, the set furnace temperature is set. When the manipulated variable is set as the _{manipulated variable} , the set furnace temperature T of the i-th zone at the time t is set so as not to exceed the furnace temperature upper limit value T _FUi (t) [° C] calculated by the equation (4).
_{Specify FSi} (t) [° C]. At this time, the fuel flow rate set value is a manipulated variable in the furnace temperature control system, which is a minor loop of the material temperature control system. For example, a universal and well-known PID (proportional + integral + Derivative) Control law. On the other hand, when the fuel flow rate set value is used as the manipulated variable as in the method described in Japanese Patent Laid-Open No. 2-156017, a known furnace temperature prediction model such as the following equation is used.

[0023]

[Equation 5]

Here, ΔT _Fi (τ-1) = T _Fi (τ) −T _Fi (τ-1) [° C] (representative furnace temperature change amount) (6a) ΔF _i (τ-k) ) = F _i (τ-k) −F _i (τ-k-1) [Nm ³ / h] (fuel flow rate change amount) (6b) where τ: time (control cycle unit; τ = 1 2, ...
·) T _Fi (·): i-th band representative furnace temperature Actual value (tau ≦ t) or predictive value (τ> t)] [° C] F i (·): i-th band fuel flow [Actual ( τ ≦ t) or predicted value (τ> t)] [Nm ³ / h] a _Fi : [dimensionless], c _Fk , _i [° C · h / Nm ³ ]: model coefficient (from actual operation data, minimum Determine the value experimentally by using the square method, etc.) m _F : 0 or a positive integer, control cycle unit Note) [Nm ³ / h]: Volume of flow rate per hour when converted to 0 ° C [m ³ ].

Equation (5) is a model equation described in Japanese Patent Laid-Open No. 2-156017. Upper limit value ΔF of variation in the i-th band fuel flow rate set value from the current value such that the furnace temperature upper limit value T _FU , _j1 (t + L) [° C] calculated by the equation (2) is satisfied
_The equation that gives _Ui (t) [Nm ³ / h] is derived from equation (5) and given as follows.

[0026]

[Equation 7]

Note) To derive equation (7) from equation (5),
Obtained by substituting t + 1, t + 2, ..., t + L for τ in the equation
From L equations, T _Fi (t + 1), T _Fi (t + 2), ..., T _Fi
It is sufficient to delete (L-1) variables of (t + L-1). The formula derived by this is the formula (7) in which T _FU , _j1 (.),
Both T _F and _j1 (・) are T _Fi (・), and ΔF _Ui (・) is ΔF
It is an expression that is formally replaced by _i (•).

Through the above processing, the i-th time at the current time t
The upper limit value F _Ui (t) [Nm ³ / h] of the band fuel flow rate set value is obtained by the following equation. F _Ui (t) = F _i (t) + ΔF _Ui (t) [Nm ³ / h] (8) The i-th zone fuel flow rate set value is the upper limit value F _Ui (t) [Nm ³ / h] Not be exceeded. In this way, when the set value is obtained using the furnace temperature change model with the manipulated variable as the fuel flow rate set value, the calculated amount is larger than when the manipulated variable is the set furnace temperature, but The time delay is generally small and faster control is possible.

The upper limit value of the manipulated variable in the material temperature control calculated by the material temperature upper limit regulating method of the present invention is used in the material temperature control system as shown in FIG. 6, for example.

Next, as an embodiment of the present invention, the material j1 having the upper limit of the material temperature of 1250 [° C] and the extraction target temperature of 1230 [° C] is charged into the heating furnace, At the same time, the material j1 has a higher extraction target temperature than the several materials before and after it, is a neck material in the material temperature control (the material that has the largest heat input required per unit area of the upper and lower surfaces), and has no heating furnace. A case where a high load operation (high productivity operation in which the fuel flow rate and the furnace temperature are as high as possible) is requested will be described. At this time, in the material temperature control, the material j1
Regarding the above, it is necessary to raise the average temperature in the material to the extraction target temperature as soon as possible while keeping the upper limit of the temperature. Here, the parameters in the equations (1) and (2) were set as follows.

Control cycle: 2 [min], L = 2 (= 4 [mi
n]), a _M = 0.9, a _TFi = 2.0 (when T _{U- Mj1} (t + L)> 0) 0.8 (when T _U-Mj1 (t + L) ≦ 0) The upper limit of the furnace temperature, which is defined by the constraint condition of 1), is defined as 1340 [° C]. In terms of control, the smaller of this value and the furnace temperature upper limit value calculated by the process of the present invention is used as the actual furnace temperature upper limit value in control.

FIG. 4 shows the average material temperature T _SAj1 (t) [° C] of the material j1 at each time t [min] when the charging time of the material j1 is 0, and the maximum internal temperature of the material ( Surface temperature) T
_SMj1 (t) [° C], furnace temperature T _F , _j1 (t) at the position of material j1
[° C], upper limit of furnace temperature at the same position T _FU , _j1 (t) [° C]
Is a graph in which t is the horizontal axis, and shows the result of the material temperature control including the material temperature upper limit regulation. The solid line in the graph shows the case where the present invention is used, and the broken line shows the case where the furnace temperature upper limit value is simply made equal to the material upper limit value as one of the conventional techniques. Here, the material j1 was conveyed to the extraction side in the furnace at a substantially constant speed.

First, the behavior of each temperature in the present invention will be described below. As can be seen from the figure, the furnace temperature at the position of j1 is low when the material j1 is present near the inlet of the furnace, but then rises rapidly, and at time t ₁ = 30 [min], the upper limit temperature of j1 It exceeds 1250 [° C]. However, at this time, the maximum temperature of j1 is still 150 [°
Since it is lower than C], the upper limit of the furnace temperature for material temperature upper limit is 1500 [° C] or higher, which is very high.

However, thereafter, as the maximum temperature of j1 approaches the upper limit temperature, the upper limit value of the furnace temperature rapidly decreases, and after time t ₂ = 60 [min], the furnace temperature at the material j1 position is suppressed. Is working like. At time t ₃ = 80 [min], the maximum temperature of j1 substantially coincides with the upper limit temperature thereof, and the furnace temperature at the material j1 position and the upper limit thereof also become substantially equal to the upper limit temperature of j1. After that, j
The maximum temperature of 1 is almost constant and j1
Average temperature continues to rise at time t ₄ = 120 [min]
Has reached the extraction target temperature.

On the other hand, in the case of the prior art, the upper limit value of the furnace temperature at the material j1 position is always set equal to the maximum hot part temperature of j1. Therefore, the furnace temperature at the j1 position is also the maximum of j1 after time t _1. It is almost equal to the hot part temperature. For this reason, in the conventional technique, the furnace temperature is unnecessarily suppressed to a low temperature between time t ₁ and time t ₃ as compared with the present invention, and as a result, the temperature rise of the material is delayed, and time t ₄
= 120 [min], the average material temperature of the material j1 has not reached the extraction target temperature. That is, in the prior art, if the material temperature upper limit regulation is attempted, the productivity of the heating furnace is reduced.

[0036]

As described above, according to the present invention, while predicting the future value of the maximum temperature of the material, the upper limit of the furnace temperature is changed from moment to moment at an appropriate timing.
The temperature of each part of the material to be heated is always kept within the specified upper limit, the necessary material is secured, and the upper limit of the furnace temperature is not kept unnecessarily low, and the productivity of the heating furnace is Not hindered.

[Brief description of drawings]

FIG. 1 is a flowchart showing the principle of the present invention.

FIG. 2 is a block diagram showing a range of calculation target materials in calculation of the upper limit values of respective band operation amounts in the embodiment of the present invention.

FIG. 3 is a graph showing the relationship between each variable in the process of calculating the furnace temperature upper limit value at the future position of the material in the embodiment of the present invention.

FIG. 4 is a graph showing temporal changes in material temperature and furnace temperature in one example of the present invention.

FIG. 5 is a block diagram and a graph showing a relationship between a longitudinal cross section of a continuous heating furnace and a longitudinal temperature distribution.

FIG. 6 is a block diagram showing a function of a temperature control system of a continuous heating furnace to which a material temperature control method of a conventional example and the present invention is applied.

Claims (2)

[Claims] 1. The temperature of each material to be heated in the continuous heating furnace is estimated and calculated for each control cycle based on each zone furnace temperature of the continuous heating furnace and the dimension, material and actual charging temperature value of the material to be heated. , In the material temperature control of the continuous heating furnace that adjusts the furnace temperature of each combustion zone of the continuous heating furnace based on the calculated value, for each control cycle and for each combustion zone, Among the materials to be heated, with respect to the material j for which the upper limit temperature T _SUj for each part in the material is defined, the maximum temperature in the material T _SMj (t) at the current time t and its temporal change amount are used to calculate, the predetermined time L only future values T _SMj of _{T SMj (t) (t +} L), the difference between the T _SMj from the upper limit temperature T _SUj (t + L) T
Predict _SU-Mj (t + L), and then for each material,
The minimum value T _SU-Mj seeking (t + L) of the temperature difference _{T SU-Mj (t + L} ), on the basis of the outermost minimum value _{T SU-Mj1 (t + L} ), the longitudinal direction of the furnace temperature distribution of the furnace In consideration of the above, the furnace temperature upper limit value of the zone at the current time t is calculated, and the furnace temperature of each combustion zone is adjusted to be equal to or lower than the calculated furnace temperature upper limit value. Temperature control method. 2. The temperature of each material to be heated in the continuous heating furnace is estimated and calculated for each control cycle based on the temperature of each zone of the continuous heating furnace and the dimension, material and charging temperature actual value of the material to be heated. In the material temperature control of the continuous heating furnace that adjusts the furnace temperature of each combustion zone of the continuous heating furnace based on the calculated value, the furnace that shows the change in each zone furnace temperature due to the future change in the fuel flow rate after the present A temperature prediction model is provided, and for each control cycle and for each combustion zone, among the materials to be heated located in the zone and in the vicinity thereof, regarding the material j for which the upper limit temperature T _SUj for each part in the material is defined, Using the maximum temperature T _SMj (t) in the material at time t and its temporal variation, T
_{Predict a} future value T _SMj (t + L) of _SMj (t) for a predetermined time L and a difference T _SU-Mj (t + L) of T _SMj (t + L) from the upper limit temperature T _SUj , Then, for each material, the temperature difference T _SU-Mj (t + L)
Of the minimum value T _SU-Mj1 (t + L), and the minimum value T _{SU -Mj1} (t + L)
Based on, considering the furnace temperature distribution in the longitudinal direction of the furnace,
An upper limit value of the furnace temperature of the zone at the present time t is obtained, and the upper limit value of the fuel flow rate is calculated using the furnace temperature prediction model so that the future furnace temperature becomes equal to or lower than the upper limit value, and the upper limit value of each combustion zone is calculated. A method for controlling a material temperature of a continuous heating furnace, comprising adjusting a fuel flow rate to be equal to or less than the calculated upper limit value.