JP2823645B2 - Furnace temperature control method in heating furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a furnace temperature control method in a heating furnace.

<Conventional Technology> Generally, a material to be heated such as a steel sheet that is reheated in a continuous heating furnace such as an annealing furnace is held for a predetermined time in a predetermined temperature region within a soaking zone. The material temperature at that time is measured mainly by a radiation thermometer installed at the outlet of the heating zone and the outlet of the soaking zone. In this case, it is essential to accurately obtain and correct the emissivity ε of the material to be heated. . In order to confirm the soaking time, the calculation for prediction of Atsushi Nobori parameter by, it is essential to determine this case overall heat absorption rate phi _CG. Then, from these emissivity ε and overall heat absorption rate phi _CG is difficult to maintain a high detection accuracy to be identified in real time.

 The reason will be described in detail below.

In normal material temperature measurement, the necessary factors are the surface temperature and the average temperature. The surface temperature is required for evaluating the surface properties of the material, and the average temperature is required for evaluating the internal quality of the material. When a radiation thermometer is used for temperature measurement, the measured value of the surface temperature depends on the emissivity, and the measured value of the average temperature depends on the surface temperature and the heat transfer coefficient of the atmosphere.

On the other hand, there is a method of obtaining the thermal conductivity as a function form of only the average temperature from the actual heating data, but as described above, since the average temperature itself depends on the heat transfer coefficient, another method is used.
For example by radiation equations, it's inevitably determined as a function form of the overall absorption rate phi _CG and surface temperature. Here, in the case of cooling in the atmosphere, becomes that of overall heat absorption rate phi _CG equivalent is immediately emissivity epsilon, also furnace dimensions also epsilon and phi _CG when the ambient heating, the material sizes and furnace wall In any case, φ _CG can be represented by ε, since they are combined as a function of emissivity.

Therefore, if there is a guarantee that the emissivity ε given to the radiation thermometer is a true value, determine the heat transfer coefficient from the measured surface temperature, and further determine the average temperature sequentially using this heat transfer coefficient. Is possible, but at present there is no absolute means for testing the emissivity ε itself.
Therefore, the emissivity and heat transfer coefficient, the surface temperature, and the average temperature do not have a method of giving each of them as a truly correct one in principle, and these four are determined by only one combination. At the same time, it can be said that it is of a nature that should be determined.

Furthermore, it has been clarified that the overall heat absorption rate φ _CG varies depending on the furnace operation conditions, and it is necessary to identify φ _CG, that is, ε in-situ, in-situ, as the first condition for highly accurate material temperature measurement and control. However, there was actually no method for that. Incidentally, slightly, as described in JP-B-61-43649, a method of obtaining by calculation the material temperature while calculating the phi _CG is disclosed.

<Problems to be solved by the invention> However, in Japanese Patent Publication No. 61-43649,
In calculating the material temperature at the time t, the φ _CG value before the time Δt is used, but as described in the detailed description of the invention, “φ
_CG is not necessarily constant even if the material or shape of the slab is the same, and is regarded as an uncertain element that varies depending on the operation state of the furnace (see page 2, column 3, columns 21 to 24).
Line), but such a treatment is inevitable.
Since you are applying the phi _CG which was 20 rows) ", there is a problem with the accuracy, the and theoretically fuel combustion heat, scale formation heat, the heat input from the upstream zone, heat loss from the furnace wall, the exhaust gas the heat balance equation consisting of the loss heat such as a number of uncertain parameters in the grounds for calculating the phi _CG has resulted in limitations on accuracy.

Further, in the heat transfer equation for calculating the material temperature at time t (Equation (3) in the third column), there is no description on how to give the atmosphere heat transfer coefficient α. Therefore, considering that both φ _CG and α are parameters greatly influenced by the furnace operation state, the present invention cannot be said to have been successful. In this regard, if the work of determining φ _CG , ε, α and the material temperature is performed simultaneously,
Very reasonable.

The present invention has been made in view of the above circumstances, and has as its object to provide a highly accurate furnace temperature control method in a continuous heating furnace.

<Means for Solving the Problems> The configuration of the present invention is based on the following procedure, whereby high-precision heat treatment is achieved. This procedure describes a continuous heating furnace divided into a heating zone and a solitary zone as a representative example.

(1) Measure the material surface temperature (T ₀ ) on the inlet side of the heating zone and the furnace temperature (T _FH , T _FK ) of the heating zone and the soaking zone by usual arbitrary means.

(2) The luminance temperature ([ _TH ], [ _TK ]) of the material to be heated is detected by a radiation thermometer at two points, the exit side of the heating zone and the exit side of the soaking zone.

(3) The overall heat absorption rate φ _CG in the heating zone and in the soaking zone is expressed by the following equation, for example, using the deviation ΔT between the furnace temperature and the material surface temperature as a function.

φ _CG = φ ₀ ^{exp (−a / ΔT)} ΔT = _TF −T where φ ₀ ; overall heat absorption rate at the entrance of the heating zone (parameter) T _F ; heating furnace temperature (° C) T; the surface temperature of the heating member (° C.) a; derivative (parameters) (4) gives the emissivity ε of the material to be heated as a function form of phi _CG.

(5) [T _H], epsilon _H and [T _K], material surface temperature in each of the temperature measuring position of the heating home use side and the soaking zone outlet side with epsilon _K T _Ha, converting the T _Ka.

(6) From T ₀ , T _FH , T _FK , φ _CG , heat conduction analysis solution From the heating equation, the material average temperature _Hb , _{Find Kb} . Next, it is converted into the material surface temperatures T _Hb and T _Kb .

(7) Material surface temperature T _Ha , T _Ka determined in step (5)
And the material surface temperature T _Hb, T _Kb obtained in step (6) is a such match within required accuracy respectively, to search for the phi _0.

(8) a, phi ₀ is determined When in step (7), to determine the average temperature of the heated material of the _Hb and _Kb at that time in each heating zone and soaking the delivery side.

(9) The entire heating pattern is identified using the heating calculation result obtained at the same time.

(10) Adjust the temperature distribution in the furnace so as to achieve this heating pattern.

<Operation> The present inventors continuously run a thin steel sheet equipped with a thermocouple in a continuous heating furnace having a heating zone and a soaking zone, and continuously measure the material temperature from the heating zone entrance side to the soaking zone exit side. An experiment was performed. Based on the temperature measurement data obtained at that time, the radiant heat transfer coefficient was back calculated from the heating equation, and the overall heat absorption rate was back calculated from the radiant heat transfer equation. As a result of analyzing the enormous temperature measurement data obtained by variously changing the steel type, thickness, width, running speed, heating zone and soaking zone temperature of the thin steel sheet, the following important findings were obtained. Was.

(1) In the heating zone, the steel grade for the overall heat absorption rate phi _CG is that level, although different by heating conditions, be maintained substantially constant value.

(2) Within the tropics, φ _CG should increase almost in proportion to the furnace time.

These phenomena can be unifiedly interpreted by the difference ΔT between the furnace temperature _TF and the material surface temperature T. In other words, larger level ΔT is usually 200 ° C. greater than the heating zone, phi _CG can be almost regarded as equal to the emissivity of the material in room temperature, whereas, rapid and ΔT is 100 ° C. or less in soaking zone And ΔT gradually approaches 0 with the furnace time. In principle, φ _CG = 1.0 when ΔT = 0, so
In soaking zone it is considered that will continuously increase the phi _CG that ΔT gradually approaches 0. An example of correlation between these ΔT and phi _CG illustrated in Figure 2. From this figure, phi _CG is [Delta] T>
It is almost constant in the region of 200 ° C., and Δ value ≒ 0
It is clear that φ _CG approaches 1.0 at に.

As described above, since φ _CG becomes almost constant in the heating zone and increases almost linearly in the solitary zone, the following equation φ _CG = φ ₀ ^{exp (−a / ΔT)} can be given as φ _CG expression. Was concluded.

Therefore, the surface temperatures T _Ha , T _Ka and T ₀ , φ _{CG of the} material to be heated obtained by converting from [T _X ] and ε _X (where X = H, K)
From the following two equations, which are equivalent to the surface temperatures T _Hb and T _Kb converted from the material average temperatures _Hb and _Kb obtained by the temperature increase calculation, respectively, that is, T _Ha = T _Hb T _Ka = T _Kb It is possible to determine two parameters a and φ ₀ .

By the way, the present inventors have conducted various studies on the relationship between the overall heat absorption rate φ _CG and the emissivity ε, and found that the overall heat absorption rate φ _CG
And emissivity ε are generally found to be combined by a specific relational expression. Thus, the unknown is limited to only φ _CG , and in the end, can be limited to only two unknown parameters a and φ ₀ in the φ _CG expression.

Hereinafter, a basic procedure for identifying a temperature rise pattern in the present invention will be described.

Radiation thermometers are placed on the exit side of the heating zone (that is, on the exit side of the soaking zone) and on the exit side of the soaking zone, respectively, to continuously measure the material surface temperature of the material to be heated, and calculate the measured values by the following procedure. I do.

First, the emissivity [ε] of the radiation thermometer may be set arbitrarily, but it is set to 1.0, which is the simplest in handling, and the detected values of the heating zone emission thermometer and the soaking zone emission thermometer ( That is, the data of the brightness temperature [T _H ] and [T _K ] are logged in real time.

On the other hand, the absorption wavelength λ ₀ of the detection element of the radiation thermometer, the material thickness d, the plate width W, the heating zone time t _H , the soaking zone furnace time t _S , the thermal properties of the material (thermal conductivity λ, Temperature propagation rate a ₀ ), heating zone material surface temperature T ₀ , heating zone furnace temperature T _FH , soaking zone furnace temperature
Enter T _FK etc.

Next, a temporary combination (a ′, φ ₀ ′) of the unknown parameter a and φ ₀ is selected.

The heating zone and the solitary zone are each divided into n small sections, which are divided into 1 to n sections. In the first division, ΔT ₁ from T ₀ and T _F1
= T _F1 −T _0, and, for example, φ _CG (a
φ _CG1 is calculated using the function of (φ ₀ , ΔT).

φ _CG = φ ₀ ^{exp (−a / ΔT)} (1) where ΔT = _TF− T This φ _CG is regarded as the average _CG1 in the first division, and the average heat transfer coefficient ₁ in the first division is For example, α expressed by the following equation (2)
_i (T _i−1 , T _Fi , φ _i ) is converted using a radiant heat transfer coefficient equation that combines the Boltzmann's heat radiation equation and Newton's heat transfer equation.

α _i = _φCGi · σ ｛(T _i-1 +273) ² + (T _Fi +273) ² ｝ · (T _i-1 + T _Fi +546) (k cal / m ² h ° C) …… (2) , Σ: Stefan-Boltzmann constant (= 4.88 × 10 ⁻⁸ kcal / m ² hk ⁴ ) T _Fi : Temperature in the heating zone or each zone of the solitary zone (° C) Furthermore, the average temperature in the material at the exit of the first zone _i indicating _one example by the following equation (3) _{(i-1, t i,} d, T Fi, α i) for prediction calculation by heat conduction analysis KaiNoboru temperature calculation formula.

_i = ( _i−1− T _Fi ) · exp (−k · t _i ) + T _Fi (3) where K = μ ₀ · a ₀ · Y ₂ / 8d ² Y ₂ = f (N, m _{) N = (α i · d} / λ) × 10 -3 μ 0 = 8.889 × 10 3 a 0: temperature propagation rate _{^{(m 2 / h) t i}} : furnace partial wards residence time (s) m: materials shape coefficient Further T _i indicating the material surface temperature T ₁ of the first minute ku outlet for example by the following equation (4) _{(i, α i, d,} T Fi) is converted as a function of.

Where N _i = (α _i · d / λ) × 10 ⁻³ d: material outer diameter λ: thermal conductivity : Average temperature position coefficient In the second section, _CG2 is calculated from the above equation (1) by setting ΔT ₂ = T _F2 −T ₁ , and the average heat transfer coefficient ₂ in the second section and the exit of the second section are obtained in the same manner as described above. Calculate the material average temperature ₂ and the surface temperature T ₂ at.

Repeated successive operations, the average heat transfer coefficient and the average _CGi in all sub-district up to the n partial ku _i, the material average temperature _i and the surface temperature T _i of the total amount ku outlet was calculated and summarized in the two temperature measuring points fever Absorption rate φ _CGH and φ _CGK and material surface temperature T _Hb , T
Extract _Kb .

Next, the emissivity ε _H , ε _K at each temperature measurement position is converted using, for example, a function of ε (φ _CG , W) shown in the following equation (5). Here, W is the plate width of the material to be heated.

First, the emissivity ε of a material is generally expressed by the following equation (5-a).

ε = ｛φ _CG ^-1 +1 -C _F ^-1- (ε _F ^-1 -1) F _M / F _F ｝ ^-1 ... (5-a) where _CF is the material to be heated and the furnace wall This parameter is used to evaluate the state of heat transfer between the elements, and is generally called the view factor.When a furnace having a rectangular cross section completely surrounds a material that does not have a macro concave surface such as a steel plate, C _F ≒ 1.0 Can be considered ε _F is the emissivity of the furnace wall made of brick, usually
Since it is specified in the range of 0.8 to 0.9, it can be given as a constant value. F _M / F _F is the ratio between the surface area of the material and the surface area of the furnace wall, and can be treated as known in advance.

After all, ε can be given as a function of φ _CG and the material size. For example, in the case of a thin plate, the thickness (d) ≪the width (W), so ε is given by the following equation (5). φ _CG and W
Can be calculated by the function

ε = (φ _CG ⁻¹ = b _H · W) ⁻¹ (5) where b _{H is a} positive constant, and then the surface temperature of the material on the exit side of the heating zone and on the level of the tropical zone.
T _Ha and T _Ka are represented by, for example, T _X ([T _X ],
ε _x , λ ₀ ).

T _X = {([T _{X] ^{+273) -1 + λ 0 / C}} 2 · l n ε X} -1 -273 (℃) ...... (6) where, lambda _0: absorption of the detector elements of the radiation thermometer Wavelength (μm) C ₂ : 1.43 × 10 ⁴ (μm · deg) The surface temperatures T _Ha and T _Ka on the heating outgoing side and the solitary outgoing side obtained in the step and the average temperature _Hb predicted and calculated in the above step, Surface temperature converted from _Kb T _Hb , T _Kb
Are compared with each other to determine whether or not the difference is within the allowable error δ, and the selection of the parameters a ′ and φ ₀ ′ of the overall heat absorption rate is repeated until the difference is satisfied.

In addition, for example, the following equation (7) J = (T _Ha −T _Hb ) ² + (T _Ka −T _Kb ) ² ≦ δ (7) may be used as both evaluation functions. Here, δ may be, for example, 1 ° C.

When the difference between T _Ha and T _{Hb and} the difference between T _Ka and T _Kb coincide with each other within required accuracy, a ′ and φ ₀ ′ at that time are respectively identified as a and φ ₀ to be identified, and the surface of the material on the heating exit side is defined. Temperature T _H
(= T _Hb ) and the average temperature in the material _H = (= _Hb ), and the soaking _zone material surface temperature T _K (= T _Kb ) and the average temperature in the material _K (= _Kb ) are determined and output simultaneously.

At the same time, it outputs the heating and heating pattern of the whole area
The furnace temperature distribution is adjusted based on this.

These basic procedures are summarized in a flow chart and shown in FIG.

By using such a procedure, it is possible to detect the material surface temperature and the average temperature in the heating and soaking furnace with high accuracy. Further, since all the arithmetic expressions used here are analytical solutions, the calculation time is extremely short as compared with the case of solving a partial differential equation as described in JP-B-61-43649, and a gradual feedback control is performed. Since it can be performed, it is very advantageous for quick and high-precision material temperature control. Naturally, the accuracy is higher than that of the simple model.

Incidentally, according to a more accurate representation, supra (5) emissivity in the expression total emissivity epsilon, (6) emissivity of formula is the spectral emissivity epsilon _lambda, if a so-called gray body epsilon _lambda = Since it is ε, it can be represented by ε as in this description. However, there are quite a few cases where ε _λ ≠ ε. In this case, assuming that ε _λ / ε =, ε in equation (6) above is replaced by the form of ε, and ε _λ / ε =
Can be used without any problem if the value is determined experimentally and given.

If a pre-tropical zone is attached to the heating zone, the luminance temperature is measured at the three points on the exit side of the pre-tropical zone, the heating zone, and the solitary zone. If used, the method of the present invention can be applied without any problem.

Further, for example, even in the case of an integrated furnace having only a heating zone, the zone may be divided into two zones, and the brightness temperature on the exit side of the split zone may be measured.

Furthermore, it goes without saying that the method of the present invention can be applied to a batch-type heating furnace in which a material to be heated is left standing, similarly to the case of traveling heating.

As is apparent from the above description, the features of the present invention make it possible to simultaneously determine the interrelated overall heat absorption, emissivity, heat transfer coefficient of the heat medium, material surface temperature and average temperature. This is the most preferable method that does not exist at all in the idea of the prior art.

<Examples> Examples of the method of the present invention will be described below.

FIG. 3 is a side view showing an outline when the method of the present invention is applied to a heating / soaking annealing line for a thin steel sheet. In this figure, the surface temperature of the material 1 to be heated is measured, for example, by an Si element type radiation thermometer 5 having an absorption wavelength of 0.9 μm, which is installed on the outlet side of the heating zone 2 (that is, on the inlet side of the soaking zone 3) and on the outlet side of the soaking zone 3.
The temperature measurement signals are measured by a and 5b, and the temperature measurement signals are input to the data collection device 10 together with the heating / soaking zone temperature signals measured by the thermocouples 9a to 9f, and are processed by the processing unit 11. The control signal from the arithmetic processing unit 11 is fed back to the gas flow control valves 7a and 7b of the heating zone 2 and the soaking zone 3 via the control unit 12, and the combustion is controlled. The material to be heated 1 sent out from the pay-off reel 21 passes through the heating zone 2 and the soaking zone 3 sequentially, is heated and soaked, and finally wound up on the take-up reel 22.

In the figures, 4a to 4c are guide rolls installed in the furnace, 6a and 6b are cooling shielding tubes for shielding disturbance light inside and outside the furnace, 8
a and 8b are fuel and air outlets.

Further, the radiation thermometers 5a and 5b installed at the outlet of the heating zone 2 and the exit of the soaking zone 3 according to the present invention are provided with measures for preventing heat, and the set emissivity [ε] is set to, for example, 1.0. Data collection by these radiation thermometers 5a and 5b is performed continuously, taking the following points into consideration. In other words, the two materials are arranged so as to collect the radiation from the central position in the plate width direction of the material to be heated 1 so that two radiation thermometers can measure the same portion of the material.

As the measurement value at the downstream side of the soaking zone 3, the data is sampled with a delay by the required traveling time of the material from the heating zone 2 and the arithmetic processing is performed.

Furthermore, since the surface temperature of the material 1 to be heated on the entrance side of the heating zone 2 is usually as small as less than 50.degree. C. and the tolerance is relatively large as 10 to 20.degree. The surface temperature measured by the radiation thermometer given the rate shall be given.

The material temperature measuring device constructed in this way is applied to a continuous annealing furnace of a heating zone, a soaking zone length of 13 m, a furnace height of 2.6 m, a furnace width of 2.3 m, and a gas that burns directly in the furnace. The surface temperature of a ferritic stainless steel sheet which was continuously heated while traveling at a line speed of 21.2 m / min with a thickness of 1.0 mm and a width of 1030 mm was measured.

A thermocouple was attached to the steel sheet in advance, and the measured value was used as a reference true temperature.

For comparison, a radiation thermometer in which the emissivity of the conventional method was fixed at 0.39 in advance was measured in parallel.

 Table 1 shows the measurement results.

As is clear from this table, in contrast to the method of the present invention in which the emissivity was identified on-line, all of the conventional methods of the fixed emissivity setting method have a large measurement error compared to the measurement value (true temperature) using a thermocouple. You can see that there is. This is because the emissivity preset by the conventional method is higher than the emissivity identified by the present invention method in the heating zone, and conversely lower in the solitary tropics, resulting in such a magnitude relationship of the material temperatures. Things. Therefore, by using the method of the present invention, the measurement accuracy of the material temperature is improved, and it is particularly remarkable in a heating zone having a small emissivity.

As described above, according to the present invention, the overall heat absorption rate can be identified online for each of the heating zone and the soaking zone, and at the same time, the emissivity at the radiation temperature measuring point in the heating zone and the soaking zone can be identified. Measurement of temperature is possible.

Furthermore, by performing furnace temperature control based on the actual measurement value and the deviation from the target material temperature obtained from the temperature increase pattern using normal feedback, the target is reliably reduced and a high-precision annealing process is realized. be able to.

In the present embodiment, the case where the steel sheet is directly heated in the combustion atmosphere furnace is described. However, the present invention is not limited to this, and shapes other than the steel sheet, for example, metals and nonmetals other than round bars and steel, or radiant tubes are used. It goes without saying that the present invention can also be applied to different atmosphere heating methods such as a method.

Although the above embodiment describes a continuous heating furnace divided into a heating zone and a solitary zone, a pre-tropical zone 20 is provided on the entrance side of the heating zone 2 as shown in FIG. In the case of three divisions, a radiation thermometer 5c is attached to the exit side of the pre-tropical zone 20 to measure the luminance temperature of the material to be heated 1 and to measure the furnace temperature by thermocouples 9g to 9i. The brightness temperature at three points, that is, the pre-tropical exit side, the heating zone exit side, and the solitary tropical exit side, is measured, and the measured values at two points are used for calculation. Further, in the case of an integrated heating furnace as shown in FIG. 5, the heating zone 2 is divided into two zones 2a and 2b, and two radiation thermometers 5a and 5b and thermocouples on the exit side of each divided zone are provided. The brightness temperature of the material to be heated and the atmosphere temperature in the furnace may be measured by 9a to 9f. In addition,
This measuring method is the same in the case of a batch-type heating furnace in which the material to be heated 1 is left standing and heated.

<Effects of the Invention> As described above, according to the present invention, emissivity indispensable for temperature measurement using a radiation thermometer is identified online, and overall heat absorption indispensable for temperature rise prediction calculation in atmosphere heating. Because the rate is identified online, the material temperature at the furnace outlet and the heating pattern inside the furnace can be detected with high accuracy.
Target heat treatment based on accurate furnace temperature correction can be performed, resulting in high-level, low-variation product quality, no waste of heat energy, and maximum speed. There are many effects such as high productivity can be maintained by passing through the plate.

[Brief description of the drawings]

FIG. 1 is a flow chart showing a basic procedure according to the method of the present invention.
FIG. 3 is a characteristic diagram showing the correlation between the difference between the furnace temperature and the material surface temperature and the overall heat absorption rate. FIG. 3 is a side view showing an outline of an example of application of the method of the present invention to a two-piece continuous heating furnace. FIG. 5 is a side view showing an example of applying the method of the present invention to a three-piece continuous heating furnace, and FIG. 5 is a side view showing an example of applying the method of the present invention to an integrated heating furnace. 1 ... material to be heated, 2 ... heating zone, 3 ... uniform tropics, 4 ... guide roll, 5 ... radiation thermometer, 6 ... disturbance light shielding tube, 7 ... gas flow control valve, 8 ... ... gas and air vents, 9 ... thermocouple, 10 ... data sampling device, 11 ... arithmetic processing device, 12 ... control device, 20 ... pre-tropical, 21 ... payoff reel, 22 ... take-up reel.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-170023 (JP, A) JP-A-2-73922 (JP, A) JP-A-62-222030 (JP, A) JP-A-1- 184233 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21D 9 / 56,11 / 00 G05D 23/00 G01J 5/00 F27D 19/00

Claims (4)

(57) [Claims] A method for controlling a furnace temperature in a heating furnace for heating a material to be heated, the method comprising dividing the inside of the furnace into a plurality of small sections, measuring the atmosphere temperature in each furnace, and radiating heat of the material to be heated. Energy is measured at at least two different temperature levels, and the temperature of the material to be heated at these radiant heat energy measurement points is predicted and calculated using the overall heat absorption coefficient calculation model and the heat conduction analysis solution temperature calculation model. Based on the heat energy, the parameters of the overall heat absorption coefficient calculation model are determined so that the predicted calculation temperature and the converted temperature become equal to each other, and thereafter, the heating pattern of the material to be heated in the entire furnace is determined. And controlling the temperature distribution in the furnace so as to obtain the heating pattern. 2. The heating furnace according to claim 1, wherein the heating furnace is a continuous heating furnace including a heating zone and a soaking zone, and the radiant heat energy measuring points are on a heating zone and a soaking zone. Furnace temperature control method in heating furnace. 3. The heating furnace is a continuous heating furnace comprising a pre-tropical zone, a heating zone, and a solitary zone, and the radiant heat energy measurement points are three points at respective outlet positions. 2. A method according to claim 1, wherein at least two measured values are used. 4. The furnace temperature control method in a heating furnace according to claim 1, wherein the following equation is used as the overall heat absorption coefficient calculation model. φ _CG = φ ₀ ^{exp (−a / ΔT)} ΔT = _TF −T where φ _CG ; overall heat absorption rate φ ₀ ; parameter (initial overall absorption rate) a; parameter (derivative coefficient) T _F ; heating furnace Ambient temperature (° C) T; Surface temperature of material to be heated (° C)