JPS60200319A - Controller for furnace temperature - Google Patents

Abstract

PURPOSE:To eliminate the disturbance and to attain the extremely stable and accurate control of furnace temperatures by obtaining both increase and decrease amounts of fuel, then adding these amounts to the feedback control amount when an object to be heated is carried in and out, to obtain a setting signal for a combustion control system. CONSTITUTION:A temperature controller 31 obtains a fuel increase amount DELTAFFin by an increase fuel arithmetic means 34 based on a heat balance system in order to supply the shortage of fuel caused when an object is carried into a control zone. This obtained increase amount is added to the feedback control quantity of a feedback control system in the form of a feedforward control quantity DELTAFFn after receiving a carry-in timing signal from an upper computer 40. While a fuel decrease amount DELTAFFout is obtained in the same way by a decrease fuel arithmetic means 36 in order to remove the excess fuel produced when the object is carried out of the control zone. This decreased amount is added to the feedback control quantity in the form of a feedforward operation amount DELTAFFn after receiving a carry-out timing signal. A signal thus obtained is applied to a fuel control system 50 from a feedback control quantity arithmetic means 39 in the form of a setting signal.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a furnace temperature control device for a heating furnace for steel billets.
In particular, the present invention relates to improvements in furnace temperature control devices that eliminate disturbances in furnace temperature control.

[Technical background of the invention]

As a conventional device of this type, there is a furnace temperature control device for a walking beam type billet heating furnace.

In the control device with
This equipment reheats steel billets to a desired temperature in order to hot roll them (cold charge) or continuously cast steel billets (hot charge). The heating conditions for this steel billet are: (1) heating the steel billet to the target temperature as quickly as possible; (2) heating each steel billet uniformly;
To control the temperature so as not to deteriorate the surface condition of the steel billet,
It is required to reduce the fuel consumption per piece of steel as much as possible.

Previously, constant value control was performed independently for each control zone based on the operator's experience and past operational data. However, as a recent trend, there has been a growing trend toward energy conservation by frequently changing the temperature, a predetermined number of cold charges and hot charges are increasingly being delivered irregularly, and heating furnaces The steel billets have a very wide temperature fluctuation range from room temperature to 700C when they are brought into the furnace, and the steel billets must be kept in the heating furnace for a long time. ,
It was becoming difficult to operate the reactor, relying on the operator's intuition.

Therefore, as a control means that does not rely on the operator's intuition, DDC (Dlrset Dlgi), which directly controls the temperature of the furnace by directly connecting the host computer to the detection end and operation end of the furnace, has been developed.
An automatic combustion control means has been developed that combines the following methods: tal Control) and the like.

Hereinafter, a furnace temperature control device equipped with this combustion control means will be specifically explained. That is, this device has a heating furnace that has a pre-heating zone, a plurality of heating zones, and a control zone divided into two upper and lower zones for each soaking zone.
Although a maximum of 10 pieces of steel pieces are brought in, each piece of steel is brought into the furnace, transported, and taken out using a walking beam, and usually one charge is kept in the furnace for 2 to 4 hours. It is designed to be heated. Charges carried into the furnace are sequentially packed from the control zone on the discharge side and the soaking zone to the preheating zone on the input side and retained therein. 10 pieces x
4 charges) can be retained.

Among the control zones, the preheating zone control zone does not have a burner and is heated by exhaust gas, and is equipped with a furnace temperature detector. The other control zone is equipped with a furnace temperature detector as well as a burner. moreover,
The detected temperature from the furnace temperature detector is sent to the DDC-controlled temperature controller 1 shown in FIG. PID performance using temperature set value SV! (Speed type) The means 3 performs the PID operation η to determine the control opening deviation Δ.
MVn, this deviation ΔMn is the control amount M′v up to the previous time.
n-1 is added to obtain the feedback control amount MV, which is given as the set values sv, , svA of the fuel flow: m: U cylinder needle 4 and air flow rate controller 5. Then, the final operation amount MY, , M
After VA is determined, the furnace temperature set value SV is determined by controlling the fuel flow rate and air flow rate by adjusting the opening degrees of the operating end knob flow control valves 6 and 7 based on this manipulated variable.

I'm trying to get it closer to. Such control is similarly performed for the control zones of the heating zone and the soaking zone.

In the figure, 8 is a switch that is turned on in C mode (commuter mode), and 9.10 is a fuel meteor and air flow rate detector. In addition, in FIG. 1, the air-fuel ratio is controlled by giving the fuel flow rate to the controller 5 and the air flow rate to the controller 5, respectively. [Problems in the Background Art] However, the above-mentioned furnace temperature control device However, there is a disturbance problem in which the steel pieces move in and out of each control zone, disrupting controllability. The degree of disturbance will be explained below using a heat balance equation. Heat balance in a heating furnace applies the law of conservation of energy to the heating furnace and calculates in what form the heat that enters the heating furnace is distributed and where and how it is distributed.

In other words, according to the law of conservation of energy, heat input = heat output + heat storage (
1) holds true. Here, heat input is the amount of heat that enters the area subject to heat balance from outside within a certain period of time, heat output is the amount of heat that goes outside within a certain period of time, and heat storage is the amount of heat that is transferred to the outside within a certain period of time. , means the increase in the amount of heat retained in the relevant part. From a heat accounting perspective, the sum of heat output and accumulation is called heat output, so here we follow that: heat input = heat output.・・・・・・・・・
...(2). Therefore, if we express the heat balance equation of the billet heating furnace based on this equation (2), the upper control zone of the soaking zone (for example, the fourth zone) will not be as shown in equation (3), but the heating zone will still be The upper control zone (for example, the third zone) is as shown in equation (4).

Heat input → mfu, 4・Hf+mfu, 4・Cf・(T,
-T. ) (fuel combustion heat) (fuel sensible heat) +mfu, 4・Bu, 4・Ca・(T, -To)+β4
'M4・HK (air sensible heat) (scale generation heat) = heat output → Qu, 4+λA・Awu, 4・(TGu, 4
”0) (Heat transfer to steel slab) (Wall loss) 10 hsu, 4 (TGLl, 4 Tgw) + m, u, 4°
"g" au, a T, ) (skid loss) (waste gas loss) ・・・・・・・・・・・・・・・(3) Heat input → mfu,
3.Hf +mfu, 5.C2.(Tf-To) (Fuel combustion heat) (Fuel sensible heat) 10 mfu, 3.Bu, 3.Cu.(T, -To) (Air sensible heat) + mgu, 4 ' Cg・(T(lu, 4 ”6)
+β3 ”3 ・Hjc (waste gas heat from the 4th zone)
(Scale formation heat) = heat output → Qu, 3 + λ7・AWu,
5・(TGu, S-T□) (Heat transfer to steel slab) (Wall loss) +Asu, 3・(Tau, 5−Taw) 10 mgu−3・
Cg”Gu,5'r0) (Skid loss) (Waste gas loss) ・・・・・・・・・・・・・・・(4) However, in the above formula, the symbols and subscripts are as shown in Table 1. It has meaning.

Next, in equations (3) and (4), the amount of heat transferred to the steel slab (
Qu, , ) will be specifically explained using formulas.

Generally, heat transfer from the inside of the heating furnace to the steel billet is mostly by thermal radiation. Therefore, the amount of heat transferred by radiation Qj
u (!: shi is determined from the Stefan-Poltzmann law by the following formula.

Qu, j = Σ circle, j, 1 d where, n: number of steel pieces remaining in j zone, heat absorption rate, Tou, j '' j zone upper furnace temperature (tl'), Ts
u(i)'' is the upper surface temperature [C] of the individual steel slabs staying in the j zone, Su: is the upper surface area [m2] of the individual steel slabs staying in the j zone. To the steel slabs in the lower zone The amount of heat transfer QjL can also be expressed by a similar formula.

Therefore, in the heat balance formula described above, the target area in the furnace is divided into control zones and considered individually, but the heat balance is expressed for the entire heating furnace, and the average over a long period of time is calculated for the heating furnace. This is called a heat account (heat settlement). 1.The total amount of heat that entered the furnace and the total amount of heat that came out of the furnace11
: to examine the effective use and amount of loss of a total of 3'l, L and thermal power 1'' respectively.Heat equipment inevitably involves heat loss, but the type of heat loss [(3 ) and formula (4)] and the quantity is clear by heat accounting,
As a result, it is possible to determine whether the furnace is operating properly and whether fuel is being wasted, and it is also possible to take measures to reduce heat loss as much as possible.

In the past, the heat s of the copper material heating furnace shown in Table 2
p2 table was used.

Table 2 In the example of the calorie value 9 table above, it is old as day), so it is extracted @
The sensible heat of heating (the amount of heat added to the steel material from the heating furnace) is 39.
7%, but due to improvements in furnaces and other advances in energy-saving technology, Houkin (1980) found that the average for steel reheating furnaces in the steel industry has gradually increased, and for one major steel manufacturer, the company-wide average has increased to about 7%. In the case of an infant furnace, the sensible heat of the extracted steel material is about 73 cm of the total heat output.

By the way, while considering the above points, let's consider the degree of disturbance caused by the movement of the copper piece in and out of each control zone. When one copper piece is conveyed to the control zone of section j, the amount of heat transferred to the steel piece Qu in equation (5) increases by one as the number of pieces of steel remaining in zone j increases, so the summation term becomes This will increase by one. Therefore, based on this, the ratio of the magnitude of the disturbance given to the j control zone will be estimated. Now, assuming that the heat extracted to the extracted In in the entire furnace is 60%, the amount of heat transferred to the steel material even in the control zone of the J section is on average 60% of the total heat output of the J zone. As mentioned above, up to 10 pieces of steel can stay in the j zone, so the ratio per piece of steel is 96% (60/10). therefore,
In the J ll1lJ zone, one piece of steel causes a heat output of 1%, so the fuel must be increased rapidly by that amount.

On the other hand, as is clear from Table 2, the ratio of fuel combustion heat to heat input is about 90 degrees, and the fuel is in the maximum range of 70 degrees.
%, the fuel shortage on the heat input side due to the sudden increase in heat output by 6 inches is 3.78% (6X0
．． 9X0.7).

Therefore, as described above, in a temperature control system under a fixed seating condition, if one layer of steel slabs are continuously conveyed to the control zone, a considerably large disturbance will occur.
If the furnace temperature was controlled by a normal feed/stock control system, the controllability would be greatly disturbed. It is clear that a similar disturbance occurs when the billet leaves the control zone.

[Purpose of the invention]

The present invention was made with attention to the above points, and it is possible to maintain the furnace temperature extremely stably at the furnace temperature set value as the object to be heated enters and exits each control zone, thereby achieving high furnace temperature control. The object of the present invention is to provide a furnace temperature control device that can control the temperature accurately.

[Summary of the invention]

The present invention calculates the increase in fuel flow rate and the decrease in fuel flow rate using a heat balance formula in order to eliminate the heat profile and excess heat generated when the heated object is carried into and out of the control zone. This is a furnace temperature control device that obtains a set value signal for the combustion control system by adding it to the original feedback control system's foot check control amount in advance at the timing of loading and unloading the heated object.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. FIG. 2 is an overall configuration diagram showing an overview of the furnace temperature control device, and FIG. 3 is a configuration diagram of the DDC temperature controller shown in FIG. 2.

In Fig. 2, No. 2 is a heating furnace, which is divided into a preheating zone A1 a first heating zone B from the direction in which the object to be heated is carried in to the direction in which it is carried out.
1, the second heating zone B2 and the soaking zone C are connected and integrated in this order, and the object to be heated 22. ...is each issue A, Bl,
B2. C is continuously conveyed by a walking beam. Each of the six furnaces A to C is divided into upper and lower control zones with the conveyance path 23 of the object to be heated 22 as a boundary, and the furnace as a whole is composed of eight control zones. There is no burner in preheating zone A, and each other in B1. It is heated by the exhaust gas from B2°C, and each other B1. B2. C has six control zones and the required number of burners (not shown) are provided at desired locations in these zones. In addition, near the furnace inlet and 6
Object surface temperature detectors 24, such as radiation thermometers, for measuring the surface temperature of heated objects 22, . . .
... are installed, and furnace temperature detectors 25. ...is provided.

30 is a DDC, which is provided with a temperature controller 31 specifically shown in FIG. This temperature control! 13
The local furnace temperature set value SV and the higher-level computer furnace temperature set value SVT are inputted to , and the furnace temperature signal pv is inputted from the furnace temperature detector 25 installed in the control zone.
Also, the heated object 22 carried in and carried out from the host computer 40
The object surface temperature signal TTin' TTout and loading and unloading timing signals ST and 5Tout are input.

n This temperature controller 31 is in C mode (heater mode)
A switch 32 that is turned on when the local or upper level calculation
Furnace temperature setpoint SV from Pl & 4o.

and a control 1 calculation means 33 that calculates the control amount deviation ΔJ of the feedback control system by performing PID calculation using the furnace temperature signal pv from the furnace temperature detector 25 of the control zone;
In order to compensate for the lack of heat in the zone due to the delivery of the object 220 to be heated to the control zone, a heat balance method is used to calculate the combustion flow rate using the control zone furnace temperature signal and the object surface temperature signal of the object 22 to be heated. A fuel increase calculation means 34 that calculates the increase, a fuel increase switch 35 that is turned on in response to a control zone import timing signal for the object to be heated 22, and an object to be heated 22
The control zone furnace temperature signal and the discharged object 22 are used to remove the zone excess heat due to the discharge of the
a reduction fuel calculation means 36 which calculates the reduction in fuel flow rate using a heat balance method using the object surface temperature signal; and a fuel reduction switch 37 which is turned on in response to a timing signal for removing the heated object 22 from the control zone. , an output circuit 38 that outputs an increase/decrease signal of the fuel flow rate input through these switches 35 and 37, and a feedback control amount.

Feedback control amount performance that adds the fuel flow rate increase signal or decrease signal ΔFFn to (MVn-1+ΔMvn) to obtain flow rate set value signals for the fuel flow rate adjustment side 51 and air flow rate detector 52 that constitute the combustion control system 5o. Means 39
It's getting stiff. 53 and 54 are fuel flow control valves and air flow control valves, and 55 and 56 are fuel flow rate detection numbers and air flow rate detectors.

On the other hand, the main functions of the host computer 4o include various information processing and management, tracking the positions of all heated objects 22 transferred by the walking beam to obtain the object loading and unloading timing, and complicated operation management. - Calculate the combustion schedule that matches the control zone and its changes; Calculate the furnace temperature set point svT for each control zone based on the optimum heat nolin for the most economical heating and uniform heating; The temperature of each part of the heated object 22 in each control zone is monitored by heat transfer calculation every moment to monitor the baking condition, and to be used in the calculation of equation (5) and equation (6) described later. The surface temperature is actually measured via a temperature detector 24 such as a radiation thermometer, and the heat transfer calculation result of equation (7) described later is corrected each time.

Next, the operation of the device configured as above will be explained.

In other words, this device handles process variables that cause disturbances and changes in those process variables.

The timing of loading and unloading the body is detected, and before the influence of loading and unloading is transmitted to the control system through the delay of Zoroses, a control amount, so-called feedforward control amount, is added to the original feedback controller to cancel out the influence. In addition, the fuel setting value of the combustion control system 50 is set to No. 48, thereby preventing the influence of disturbances and controlling the furnace temperature in each control zone in an extremely stable manner. In addition, each phase is 81°B2.
Since each control zone of C performs similar processing, the control zone of soaking zone C will be explained below.

In the host computer 40, all heated objects 2 in the furnace are usually
Since the 20 positions are tracked using the movement of the walking beam, the timing of each heated object 22 being carried into the control zone is determined every time the heated objects 22 are carried into the control zone.

This object loading timing signal is sent from the host computer 40 to DD.
The temperature vL1 of C is given to the gauge needle. Temperature controller 31
Now, in order to make up for the fuel shortage caused by bringing objects into the control zone, an increase in fuel consumption will be carried out.

The calculation means 34 determines the fuel flow rate increase ΔFF1n based on the heat balance formula, and calculates this at the import timing from the upper calculation Φ4° (receives the rT signal and feeds it to the feedback control amount ° of the feedback control system. ΔFF
Add as n. That is, in the double heat balance equation, when the object to be heated 22 is brought in, the heat transfer to the object 22 rapidly increases on the heat output side.
n is the soaking zone C. However, ' Tsu, 5 is the surface temperature of the upper part of the heated object 22 when it is carried out of the third control zone, that is, the control zone of the second heating zone B2, and K is the upper part of the soaking zone which becomes the control zone F4. Feed forward control dyne (variable during plant field adjustment) in the control zone, B7 is the fuel calorific value.

On the other hand, the fuel increase Δ in the lower control zone of soaking zone C
FFthn is as follows. TsL, 3 is the lower surface temperature of the heated object 22 when it leaves the second heating zone B2, which is the third control zone, and K is the feedforward control gain in the fourth lower control zone F. (variable during plant on-site adjustment). Note that the lower surface temperature of the object T8L, 5, etc. is not measured in Fig. 2, but
As described above, the host computer 40 constantly calculates the temperature of each mesh of the heated object 22 numerically by the object temperature transfer calculation, so this calculation is used to obtain the temperature.

Next, in order to remove excess fuel as the heated object 22 is carried out from the control zone of the soaking zone C, which is the fourth control zone, the reduced fuel calculation means 36 reduces the fuel based on the heat balance formula. The minute ΔFFont is determined and is added to the feedback control claw of the foot knock control system as the feed forward manipulated variable ΔFFn in response to an output timing signal from the host computer 40. That is, in the heat balance equation described above, the decrease ΔFFont in the heat transfer Qu,4 (formula (4)) to the object 22, which rapidly increases on the heat output side when the object 22 to be heated is carried out, is determined by the fourth control zo. Become. here,
T is the temperature of the upper surface of the heated object 22 when it is carried out from the 11u, 44th control zone. Incidentally, the fuel decrease ΔFFout in the lower control zone of the soaking zone C, which is the fourth control zone, is also determined by the same calculation means. In addition, another control zone B1. B
2, a similar feed forward control amount ΔFFn may be determined at each timing when the heated object 22 is carried in and out of the control zone, and added to each feedback control t(MVn-1+ΔMVn). It should be noted that the combustion control system 50 is well known in the art, and a description of its operation will be omitted here.

Therefore, according to the above configuration, in order to satisfy the fuel shortage and excess fuel due to the movement of the heated object 22 into and out of the control zone, the increase in type and the decrease in fuel are calculated based on the heat balance formula. By adding a feed forward control amount to the original feedback control amount in advance based on the timing of loading and unloading the object, the furnace temperature and the surface temperature of the objects being loaded and unloaded are calculated. Regardless of the magnitude of the difference, and even if an arbitrary number of heated objects 22 enter and exit the control zone continuously, a control is always applied to cancel the effect before it is added to the feedback control amount. With a relatively simple configuration, it is possible to prevent the effects of disturbances, and it is possible to control the furnace temperature with much more stability and accuracy than with conventional systems.

In addition, in the above embodiment, a steel piece is used as the object to be heated 22, but the invention is not limited to this.

Alternatively, the output recall 38 may be omitted and the control 1 may be directly input to the deviation performance means 33, where the calculation of the subsequent processing means 39 may be performed.

〔Effect of the invention〕

Therefore, as described above, according to the present invention, it is possible to perform extremely stable and highly accurate furnace temperature control by eliminating disturbances to the control system caused by the movement of heated objects into and out of the control zone. equipment can be provided.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the temperature control system and combustion control system of a conventional equipment. Figure 3 is D in Figure 2.
It is a schematic diagram which specifically shows the temperature hook-tube needle which is a part of DC. 21... Heating furnace, 22... Heated object, 24...
Object surface temperature detector, 25... Furnace temperature detector, 30.
...DDC,, 9J... Temperature controller, 33... Controlled amount deviation calculation means, 34... Increased fuel calculation means, 35.
...Fuel increase switch, 36...Decrease fuel calculation means,
37...Fuel reduction switch, 39...Feet knob control amount calculation means, 40...High-level computer, 50...
...Combustion control system. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (1)

[Claims] In a furnace temperature control device that controls the temperature of a furnace having a plurality of control zones in which heated objects are conveyed, a heated object surface temperature detector and a furnace temperature detector installed in each of the control zones; A feedback control system that calculates a feedback control amount using the furnace temperature output from a furnace temperature detector in the zone and a preset furnace temperature setting value, and a heat amount in the control zone based on the factors of the object to be heated entering the control zone. In order to make up for the shortfall, a necessary increase in fuel flow rate is calculated using a heat balance equation of the furnace temperature model, and this increase in fuel flow rate is added to the feedback control amount in advance according to the timing of bringing the object to be heated into the control zone. In order to remove the excess amount of heat in the control zone due to the cause of the conveyance of the object to be heated to the control zone, a necessary decrease in fuel is calculated using the heat balance equation of the furnace temperature model, and this decrease in fuel is calculated as described above. A furnace temperature control device comprising means for subtracting the feedback control amount from the feedback control amount in advance according to the timing of carrying out the heated object from the control zone, and using the corrected feedback control amount as a set value signal of a combustion control system.