JP7155988B2 - Method for detecting defective combustion of radiant tube burner - Google Patents

Description

The present invention relates to a combustion failure detection method for a radiant tube burner used in a heat treatment furnace.

A radiant tube burner is used as a heating means in an atmospheric heat treatment furnace for heat-treating a material to be treated in a non-oxidizing or reducing atmosphere. It is important for radiant tube burners to operate under the proper air-fuel ratio. For example, if the ratio of air increases, the amount of exhaust gas discharged to the outside increases, resulting in a significant deterioration in thermal efficiency. Conversely, if the ratio of fuel becomes high, problems such as damage to equipment due to soot, increased environmental load, and waste of fuel due to incomplete combustion of fuel will arise.

Atmospheric heat treatment furnaces employ a configuration in which a large number of relatively low-output radiant tube burners are arranged in the heating chamber in order to achieve uniform temperature distribution in the furnace (heating chamber). Therefore, it is required to accurately detect the presence or absence of poor combustion in these many radiant tube burners.

An important factor in judging the combustion state of the burner is the oxygen concentration in the exhaust gas. For example, in Patent Document 1 below, the exhaust gas discharged from each radiant tube burner is sequentially sent to an oxygen analyzer, the oxygen concentration in the exhaust gas discharged from each radiant tube burner is measured, and the combustion of each burner is performed. It is disclosed that the quality of the condition is determined.

However, in the method of measuring the exhaust gas of a plurality of radiant tube burners while sequentially switching, such as the detection method described in Patent Document 1, the measurement timing of the oxygen concentration is different for each radiant tube burner. Oxygen concentration fluctuations due to factors other than defects are also included in the measurement data. Therefore, it has been difficult to accurately detect the presence or absence of poor combustion.

JP 2017-62096 A

SUMMARY OF THE INVENTION It is an object of the present invention to provide a radiant tube burner combustion failure detection method capable of accurately detecting the presence or absence of combustion failure in a heat treatment furnace equipped with a plurality of radiant tube burners. It was made as

Accordingly, the present invention provides a method for detecting combustion failure of a radiant tube burner in a heat treatment furnace having n (n≧3) radiant tube burners in the same combustion control group, comprising:
Time-series data of the oxygen concentration of the exhaust gas discharged from each of the radiant tube burners is measured and stored, and the degree of variation in the oxygen concentration measured at the same timing in the time-series data corresponding to each radiant tube burner. is obtained, and the combustion failure of the radiant tube burner is detected based on the degree of variation.

When all radiant tube burners in the same combustion control group maintain a normal combustion state, the oxygen concentration of the exhaust gas discharged from each radiant tube burner during operation essentially exhibits the same behavior (waveform). indicates Therefore, combustion failure can be detected by comparing the degree of variation in the oxygen concentration of the exhaust gas discharged from each radiant tube burner.

In the present invention, in order to store the same time-series data (temporally continuous data in the same time zone) for each radiant tube burner, the oxygen concentrations measured at the same timing for each radiant tube burner are extracted. Detection of combustion failure can be performed. That is, it is possible to accurately detect the presence or absence of poor combustion by excluding fluctuations in the oxygen concentration due to factors other than poor combustion.

In the present invention, from the time-series data, set data whose elements are the oxygen concentration x corresponding to the first radiant tube burner and the oxygen concentration y corresponding to the second radiant tube burner measured at the same timing. When at least one of the plurality of extracted sets of data is outside the allowable range defined by the upper and lower allowable values, it can be determined that there is a combustion failure.

Here, the same timing means that the measurement times of x and y are the same, and that there is a slight time difference in the measurement times, taking into consideration the difference in pipe length from the control valve to the oxygen concentration measurement point in each radiant tube burner. It also includes cases where it is provided.

Further, in the present invention, from the time-series data, set data whose elements are the oxygen concentration x corresponding to the first radiant tube burner and the oxygen concentration y corresponding to the second radiant tube burner satisfying a predetermined condition are generated. A plurality of values are extracted, a first correlation coefficient r1 represented by the following formula (1) is obtained, and if the value of the first correlation coefficient r1 is smaller than a predetermined threshold value, it can be determined that there is poor combustion. .
r1=Sxy/(SxxSy) Expression (1)
However, Sx is the standard deviation of x, Sy is the standard deviation of y, and Sxy is the covariance of x and y.

In this way, a set of data whose elements are the oxygen concentration x corresponding to the first radiant tube burner and the oxygen concentration y corresponding to the second radiant tube burner that satisfies predetermined conditions (under specific conditions) is used. Thus, the presence or absence of combustion failure can be detected with high accuracy. Here, the predetermined condition can be defined as, for example, a maximum combustion state in which x and y are measured at the same timing and the opening degree of the control valve for supplying air and fuel is maximum.
Under these conditions, the extracted x and y show a high correlation if the combustion of the target first radiant tube burner and the second radiant tube burner are both normal, so the first correlation If the value of the number r1 is smaller than a predetermined threshold, it can be determined that there is a combustion failure.

Here, in the present invention, the following formula obtained from set data whose elements are the oxygen concentration x corresponding to the first radiant tube burner and the oxygen concentration z corresponding to the third radiant tube burner that satisfy a predetermined condition. The second correlation coefficient r2 represented by (2), and the oxygen concentration y corresponding to the second radiant tube burner and the oxygen concentration z corresponding to the third radiant tube burner satisfying predetermined conditions, and the oxygen concentration z corresponding to the third radiant tube burner. It is possible to further calculate at least one of the third correlation coefficients r3 represented by the following formula (3) obtained from the set data having the elements.
r2=Sxz/(Sx*Sz) Expression (2)
r3=Syz/(Sy×Sz) Expression (3)
However, Sz is the standard deviation of z, Sxz is the covariance of x and z, and Syz is the covariance of y and z.

If the value of the first correlation coefficient r1 is small and it is desired to further specify which of the first radiant tube burner and the second radiant tube burner has poor combustion, the second correlation coefficient It is effective to use at least one of r2 and the third correlation coefficient r3 together.

Further, in the present invention, for each of the radiant tube burners in the same combustion control group, the oxygen concentration of the exhaust gas measured at the same timing is extracted from the time-series data, and an arithmetic mean value of these is obtained,
When the arithmetic mean value is larger than a preset maximum threshold value or smaller than a preset minimum threshold value, it can be determined that there is a combustion failure.
In this way, it is possible to detect the presence or absence of poor combustion caused by upstream control that affects all radiant tube burners in the same combustion control group.

Further, in the present invention, the oxygen sensor for measuring the oxygen concentration can be attached to the upper portion of the elbow portion of the exhaust pipe through which the exhaust gas flows. In order to prevent the oxygen sensor from malfunctioning, the oxygen sensor should be installed at a position where the temperature of the exhaust gas is as low as possible and where contact with water droplets produced by condensation of water vapor in the exhaust gas can be avoided. desirable. Here, the elbow portion is positioned away from the exhaust port of the radiant tube burner, and the upper portion of the elbow portion is suitable as a position that is less likely to come into contact with water droplets. Therefore, by attaching the oxygen sensor to the upper portion of the elbow portion, it is possible to detect the combustion failure with high accuracy.

It is a diagram showing a schematic configuration of a heat treatment furnace used in an embodiment of the present invention. It is the figure which showed the radiant tube burner of FIG. 1 with the peripheral part. FIG. 2 is an explanatory diagram of combustion control in the heat treatment furnace of FIG. 1; FIG. 2 is an explanatory diagram of detection of poor combustion in the heat treatment furnace of FIG. 1; It is an example of time-series data of oxygen concentration measured during operation. FIG. 4 is an explanatory diagram of a first combustion failure detection method;

An embodiment of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a heat treatment furnace used in this embodiment. In the figure, reference numeral 10 denotes a batch-type heat treatment furnace in which a heating chamber 13 is formed inside a box-shaped furnace body 12 . A doorway 14 is formed at one end side in the longitudinal direction of the furnace body 12 , and a workpiece as an object to be processed is loaded into the heating chamber 13 through the doorway 14 by a roller group 15 . The doorway 14 can be opened and closed by a door 17 connected to a driving device 16 .

In the heating chamber 13, heat treatment of the work is performed in a non-oxidizing or reducing atmosphere. The heating chamber 13 is connected to an atmospheric gas supply pipe 19 for introducing atmospheric gas, and is provided with a plurality of radiant tube burners 20 and ceiling fans 22 as heating means along the conveying direction (longitudinal direction). there is

In general, a heat treatment furnace employs a configuration in which a large number of relatively low-output radiant tube burners 20 are arranged in the heating chamber 13 in order to make the temperature distribution in the heating chamber 13 uniform. In this example, the heating chamber 13 is divided into three zones 13a, 13b, and 13c along the conveying direction, and a plurality of radiant tube burners 20 belonging to the same zone are controlled by one system. As shown in FIG. 1, in this example, six radiant tube burners 20 are arranged in the first zone 13a, eight radiant tube burners 20 are arranged in the second zone 13b, and six radiant tube burners 20 are arranged in the third zone 13c. Radiant tube burners 20 are arranged. If combustion control is performed for each zone, control valves for adjusting the amount of fuel gas and combustion air supplied to the radiant tube burner 20 can be shared, and equipment costs can be kept low. In addition, in the batch-type heat treatment furnace 10, the temperature target value during operation is the same for each zone.

As shown in FIG. 2(A), the radiant tube burner 20 includes a pipe-shaped tube body 25 which has a U-shape and extends through the furnace wall 12a from the inside to the outside. A combustion burner 28 arranged in a shape and a heat exchanger 31 arranged in a hollow portion of the other end side 25b of the tube body 25 are provided.

The combustion burner 28 is connected to a fuel branch pipe 42 and an air supply pipe 34 which constitute a part of the fuel supply pipe 40, and converts fuel gas supplied from the fuel branch pipe 42 into combustion air supplied from the air supply pipe 34. mixed with and burned. A pilot burner (not shown) ignites the gas mixture obtained by mixing the fuel gas and the combustion air. High-temperature gas generated by combustion is sent to the other end 25b of the tube body 25 through the turn portion 25c of the tube body 25. As shown in FIG. During that time, the hot gas radiates heat into the heating chamber 13 through the tube wall of the tube body 25 .

The heat exchanger 31 has a substantially cylindrical main body 32 and a hemispherical tip portion 33 , and an air supply pipe 34 for flowing combustion air toward the combustion burner 28 is arranged inside the main body 32 . A vent hole 32a formed in the rear end wall of the main body 32 is connected to an air branch pipe 48 forming part of an air supply pipe 46, and combustion air passes through the air branch pipe 48 and the vent hole 32a. It flows inside the main body 32 . Combustion air that has flowed into the body 32 is preheated by the heat of the high-temperature gas, and then supplied to the combustion burner 28 through the air supply pipe 34 as described above. On the other hand, the exhaust gas (high-temperature gas) after heat exchange with the combustion air passes from the exhaust port 26 formed on the other end side 25b of the tube body 25 to the flue 35a in the exhaust pipe 35. Distributed and discharged to the outside.

As shown in FIG. 2(B), the exhaust pipe 35 includes a horizontal portion 36 extending horizontally with one end communicating with the exhaust port 26, a vertical portion 37 extending vertically upward, and the horizontal portion 36 and the vertical portion. 37 and extends obliquely upward from the horizontal portion 36 toward the vertical portion 37 . In this example, a zirconia oxygen sensor 39 is attached to the elbow portion 38, more specifically to the upper portion 38a of the elbow portion 38. As shown in FIG. Here, the upper portion 38a is an upper portion when the elbow portion 38 is divided vertically along the tube axis.

As shown in FIG. 2(B), the elbow portion 38 is located away from the exhaust port 26 of the radiant tube burner 20, so that the temperature of the exhaust gas to be measured can be lowered to some extent.
Also, the upper portion 38a of the elbow portion 38 is suitable as a position where contact with water droplets produced by condensation of water vapor in the exhaust gas can be avoided. Therefore, by attaching the oxygen sensor 39 to the upper portion 38a of the elbow portion 38, it is possible to suppress failure of the oxygen sensor 39 due to high temperature or water droplets. Further, by activating the oxygen sensor 39 when the temperature inside the furnace is 100° C. or higher, damage to the sensor due to water droplets can be further reduced.

Next, combustion control in the heat treatment furnace 10 will be described. In the heat treatment furnace 10, the inside of the heating chamber 13 is divided into three zones 13a, 13b, and 13c along the transport direction, and combustion control is performed for each zone. A plurality of radiant tube burners 20 in the same zone are controlled using a common control valve as the same combustion control group.

FIG. 3 is an explanatory diagram of combustion control in the first zone 13a. As shown in the figure, a fuel supply pipe 40 through which fuel gas flows is composed of a main pipe 41 and a plurality of branch pipes 42 branched from the main pipe 41 . The main pipe 41 is provided with a flow control valve 43 and an orifice meter 44 for detecting the gas supply amount. An air supply pipe 46 through which combustion air flows is composed of a main pipe 47 and a plurality of branch pipes 48 branched from the main pipe 47 . The main pipe 47 is provided with a flow control valve 49 and an orifice meter 50 for detecting the amount of air supplied. Manual valves 45 and 51 are provided in the respective branch pipes 42 and 48, and their opening degrees are adjusted in advance so that the fuel gas and the combustion air are evenly supplied to the individual combustion burners 28. there is In FIG. 3, only three of the six combustion burners 28 belonging to the first zone 13a are shown, and the remaining three are omitted.

In the figure, 53 is a temperature sensor as temperature detecting means for detecting the temperature in the furnace, and 54 is a combustion control device. The fuel control device 54 controls the thermal power of the combustion burner 28 by increasing or decreasing the opening degrees of the flow control valves 43 and 49 based on the difference between the preset heat pattern during operation and the temperature detected by the temperature sensor 53. . Further, when cooling the inside of the furnace, the supply of the fuel gas is stopped and only the air is allowed to flow through the tube body 25 .

In the second zone 13b, the amounts of combustion air and fuel gas are controlled by a flow control valve arranged in a system different from that of the first zone 13a. As for the third zone 13c, the amounts of combustion air and fuel gas are controlled by a flow control valve arranged in a system different from that of the first zone 13a and the second zone 13b.

Next, the combustion failure detection device 60 provided in the heat treatment furnace 10 will be described. The combustion failure detection device 60 detects combustion failure of the radiant tube burner 20 arranged in the heat treatment furnace 10 . The combustion failure detection device 60 is connected to the combustion control device 54 and the plurality of oxygen sensors 39, as shown in FIG. Operation information is input from the combustion control device 54 , and a signal indicating the concentration of oxygen in the exhaust gas discharged from each radiant tube burner 20 is input from each oxygen sensor 39 via the signal corrector 55 .

The combustion failure detection device 60 includes a storage unit 61 and a combustion failure determination processing unit 62 . The storage unit 61 stores the operation information from the combustion control device 54 and the oxygen concentration time series data from the sensor 39 . The combustion failure determination processing unit 62 determines the presence or absence of combustion failure based on the time-series data stored in the storage unit 61 . The combustion failure detection device 60 can be configured by a computer including a storage device such as a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory) and HDD (Hard Disk Drive). The determination processing unit 62 can be a processor such as a CPU. In this case, a processor such as a CPU executes a control program stored in a ROM or the like. When the combustion failure determination processing unit 62 determines that there is combustion failure, the combustion failure occurrence information can be transmitted to the external terminal 65 or the like connected to the combustion failure detection device 60 .
The combustion failure detection device 60 can also be configured as part of a control unit (not shown) that controls the entire heat treatment furnace 10 or as part of the combustion control device 54 .

FIG. 5 is a diagram showing an example of time-series data of oxygen concentration measured during operation. The heat pattern during operation is mainly divided into temperature rising, soaking, and cooling processes. 54 is finely controlled. Therefore, as shown in FIG. 5, the oxygen concentration in the exhaust gas also changes in a wave-like manner over time. Here, the waveforms of a plurality of radiant tube burners within the same combustion control group ideally have the same or similar shapes. On the other hand, the radiant tube burner in which combustion failure occurs causes a change in the waveform shape.

In this embodiment, time-series data of oxygen concentration during operation (as shown in FIG. 5) is stored in the storage unit 61 for each radiant tube burner, and in the combustion failure determination processing unit 62, each radiant tube burner 20 The presence or absence of combustion failure is detected by comparing and evaluating the degree of variation in oxygen concentration measured at the same timing in the corresponding time-series data.

Specifically, the combustion failure is detected by causing the combustion failure determination processing unit 62 to execute the procedure described below.
(First combustion failure detection method)
First, the first radiant tube burner and the second radiant tube burner are selected from the same combustion control group. Next, from the time series data stored in the storage unit 61, the oxygen concentration _xi corresponding to the first radiant tube burner and the oxygen concentration _yi corresponding to the second radiant tube burner measured at the same timing are calculated. A plurality of set data (x _i , y _i ) as elements are extracted. From the plurality of grouped data obtained in this way, grouped data (x _i , y _i ) distribution (degree of variation) can be obtained.
Here, the allowable range of the degree of variation of the set data (x _i , y _i ) when the combustion of both the first radiant tube burner and the second radiant tube burner is normal is determined in advance by the upper and lower allowable values. With this regulation, it can be determined that there is a combustion failure when at least one of the extracted data sets is outside the allowable range. In FIG. 6, the upper allowable value is represented by y=ax+α, the lower allowable value is represented by y=ax+β, and a, α, and β are constants, respectively.

In this first detection method, if at least one of the extracted set data is lower than the lower limit allowable value, it is determined that the amount of fuel gas supplied to the second radiant tube burner is excessive. guessed. Conversely, if it is higher than the upper allowable value, it is presumed that the amount of fuel gas supplied to the first radiant tube burner is excessive.

(Second combustion failure detection method)
First, the first radiant tube burner and the second radiant tube burner are selected from the same combustion control group. Next, from the time-series data stored in the storage unit 61, the oxygen concentration x _i corresponding to the first radiant tube burner and the oxygen concentration y _i corresponding to the second radiant tube burner satisfying a predetermined condition are elements. A plurality of set data (x _i , y _i ) are extracted. Here, the predetermined condition is a maximum combustion state in which x _i and y _i are measured at the same timing and the opening degree of the control valve for supplying air and fuel is maximum. Specifically, the points indicated by P1, P2, etc. in FIG. 5 correspond to this. Which timing point is the maximum combustion state can be obtained from the operational information sent from the combustion control device 54 .

Then, a first correlation coefficient r1 represented by the following equation (1) is calculated based on the extracted multiple sets of data (x _i , y _i ), and the degree of variation between x and y is obtained.
r1=Sxy/(SxxSy) Expression (1)
Here, standard deviation Sx, standard deviation Sy, and covariance Sxy can be expressed as follows.

Under these conditions, the extracted x and y show a high correlation if both the first radiant tube burner and the second radiant tube burner of interest are normal, so the first correlation coefficient r1 is smaller than a predetermined threshold value, it can be determined that there is combustion failure.

Next, if the value of the first correlation coefficient r1 is smaller than the threshold value and it is desired to further specify which of the first radiant tube burner and the second radiant tube burner has poor combustion, a predetermined _{The following formula (} 2), and the oxygen concentration y _i corresponding to the second radiant tube burner and the oxygen concentration z _i corresponding to the third radiant tube burner satisfying a predetermined condition are used as elements. At least one of the third correlation coefficients r3 represented by the following equation (3) obtained from the paired data (y _i , z _i ) is further calculated.
r2=Sxz/(Sx*Sz) Expression (2)
r3=Syz/(Sy×Sz) Expression (3)
where Sz is the standard deviation of z, Sxz is the covariance of x and z, and Syz is the covariance of y and z.

Here, when the value of the second correlation coefficient r2 is smaller than the predetermined threshold, it is determined that the first radiant tube burner out of the first and second radiant tube burners has poor combustion. can do. Further, when the value of the third correlation coefficient r3 is smaller than the predetermined threshold, it is determined that the second radiant tube burner out of the first and second radiant tube burners has poor combustion. can do.

(Third Combustion Failure Detection Method)
For a plurality of radiant tube burners belonging to the same combustion control group (for example, for the six radiant tube burners 20 belonging to the first zone 13a), the oxygen concentration measurement values of the exhaust gas under predetermined conditions are extracted. Here, the predetermined condition is a maximum combustion state in which the oxygen concentration is measured at the same timing and the opening degree of the control valves for supplying air and fuel is maximum. Specifically, the points indicated by P1, P2, etc. in FIG. 5 correspond to this. Next, the arithmetic mean value of the measured values of the extracted oxygen concentration is determined (the obtained arithmetic mean value is the average oxygen concentration in each burner under maximum combustion conditions). Next, the obtained arithmetic mean value is compared with preset maximum and minimum threshold values, and when the arithmetic mean value is outside the allowable range, it can be determined that there is combustion failure.

Here, when the arithmetic average value is larger than the maximum threshold, it can be estimated that the flow rate of the fuel gas from the main pipe supplied to the target zone (for example, the first zone 13a) is too small. Also, if the arithmetic mean value is smaller than the minimum threshold, it can be inferred that the flow rate of the fuel gas from the main pipe supplied to the target zone is excessive.

Further, it is effective to calculate the arithmetic mean value periodically and store it in the storage unit 61 in association with the information of the measurement time. By finding the amount of change from the initial state, it is possible to know the tendency of the arithmetic mean value to change over time. Even if the most recent arithmetic mean value is within the permissible range, knowing the trend of change over time makes it possible to estimate when to perform maintenance (parts replacement).

Although the embodiments of the present invention have been described in detail above, these are only examples. In the above embodiment, three types of combustion failure detection methods were exemplified, but the first and second detection methods are effective in detecting combustion failure in specific radiant tube burners within the same combustion control group. . On the other hand, the third detection method is effective in detecting combustion failures caused by upstream controls affecting all radiant tube burners in the same combustion control group. Of course, it is also possible to use these detection methods together.

Also, the threshold value (permissible value) that serves as a reference for judging whether the combustion state of the burner is good or bad can be appropriately determined based on operating conditions and the like. Further, the above-described embodiment is applied to a batch-type heat treatment furnace, but the present invention does not deviate from the gist of the present invention, such as being applicable to a continuous heat-treatment furnace. It can be implemented in a form with various changes added within the scope.

10 Heat Treatment Furnace 13a First Zone 13b Second Zone 13c Third Zone 20 Radiant Tube Burner 38 Elbow Part 38a Upper Part 39 Oxygen Sensor r1 First Correlation Coefficient r2 Second Correlation Coefficient r3 Third Correlation Coefficient x, y, z oxygen concentration

Claims (6)

A method for detecting combustion failure of a radiant tube burner in a heat treatment furnace having n (n≧3) radiant tube burners in the same combustion control group, comprising:
measuring and storing time-series data of the oxygen concentration of the exhaust gas discharged from each of the radiant tube burners;
Obtaining the degree of variation in the oxygen concentration measured at the same timing in the time-series data corresponding to each radiant tube burner,
A combustion failure detection method for a radiant tube burner, wherein the combustion failure of the radiant tube burner is detected based on the degree of variation. extracting from the time-series data a plurality of set data whose elements are the oxygen concentration x corresponding to the first radiant tube burner and the oxygen concentration y corresponding to the second radiant tube burner measured at the same timing; 2. The radiant tube burner according to claim 1, wherein when at least one of the extracted set data is outside the permissible range defined by the upper permissible value and the lower permissible value, it is determined that there is a combustion failure. Combustion failure detection method. From the time-series data, a plurality of set data whose elements are the oxygen concentration x corresponding to the first radiant tube burner and the oxygen concentration y corresponding to the second radiant tube burner satisfying a predetermined condition are extracted. 2. A first correlation coefficient r1 represented by the formula (1) is obtained, and if the value of the first correlation coefficient r1 is smaller than a predetermined threshold value, it is determined that there is a combustion failure. The method for detecting defective combustion of a radiant tube burner according to 1.
r1=Sxy/(SxxSy) Expression (1)
However, Sx is the standard deviation of x, Sy is the standard deviation of y, and Sxy is the covariance of x and y. The oxygen concentration x corresponding to the first radiant tube burner satisfying a predetermined condition and the oxygen concentration z corresponding to the third radiant tube burner are represented by the following formula (2) obtained from set data as elements. and the oxygen concentration y corresponding to the second radiant tube burner and the oxygen concentration z corresponding to the third radiant tube burner satisfying a predetermined condition. 4. The method for detecting defective combustion of a radiant tube burner according to claim 3, further comprising calculating at least one of the third correlation coefficients r3 represented by the following equation (3).
r2=Sxz/(Sx*Sz) Expression (2)
r3=Syz/(Sy×Sz) Expression (3)
However, Sz is the standard deviation of z, Sxz is the covariance of x and z, and Syz is the covariance of y and z. For each of the radiant tube burners in the same combustion control group, the oxygen concentration of the exhaust gas measured at the same timing is extracted from the time-series data, and an arithmetic mean value of these is obtained,
Combustion of a radiant tube burner according to any one of claims 1 to 4, characterized in that when said arithmetic mean value is larger than a preset maximum threshold value or smaller than a preset minimum threshold value, it is determined that there is a combustion failure. Defect detection method.
Combustion of the radiant tube burner according to any one of claims 1 to 5, wherein the oxygen sensor for measuring the oxygen concentration is attached to a portion above the elbow portion of the exhaust pipe through which the exhaust gas flows. Defect detection method.

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