JP3524407B2 - Burner combustion diagnostic device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for monitoring the combustion state of burner flames in a combustion furnace of a power plant or the like.

[0002]

2. Description of the Related Art In recent years, in the boiler for thermal power generation, from the viewpoint of environmental measures and the like, it is desired that the combustion apparatus such as the boiler does not generate nitrogen oxides, soot and carbon monoxide as much as possible. In order to form such a combustion state, a burner flame in which the fuel and the air are appropriately mixed in the combustion furnace is formed, and thereby, an extremely high temperature region and an extremely low temperature region are not formed in the combustion furnace. is necessary. In one of such devices for monitoring the combustion state, the combustion state is diagnosed based on the result of spectral analysis (emission spectrum analysis) of light emitted from the combustion flame of the burner at predetermined wavelengths. There is a combustion diagnosis device described in the publication.

FIG. 9 shows a configuration example of a conventional combustion diagnosis device. In the combustion diagnosing device shown in FIG. 9, there are three fields of view (field of view a, field of view b, field of view a, field of view b, attached to the burner 1 and composed of three optical fibers that receive flame emission emitted from three regions of the flame 2 in different axial directions. Optical probe 3 having field of view c), 3-core optical fiber cable 4 for transmitting flame emission received by the optical probe 3, flame emission of each field transmitted by the 3-core optical fiber cable 4 is spectroscopically analyzed for each predetermined wavelength. It mainly includes a spectroscopic analysis unit 101, and a computer 5 that calculates an index for evaluating a combustion state of a fire based on an analysis result of the spectroscopic analysis unit 101 and performs diagnosis.

The optical probe 3 has a different bending angle at the light receiving end.
It consists of two optical fibers, and the function to monitor three areas of different burner flames by the bending angle of this optical fiber (3
Have a field of view). The visual field a monitors the root region of the flame 2, the visual field b monitors the flame central region, and the visual field c monitors the flame tip region.

The combustion diagnosis device calculates the flame temperature from the result of the spectroscopic analysis based on the gray approximation of solid-state light emission due to carbonaceous particles (such as soot) in the flame among the light emission of the flame, By analyzing the state of infrared gas absorption / radiation spectrum intensity due to combustion products such as carbon dioxide, the state of the burner flame is grasped, and the state of combustion is evaluated / diagnosed. FIG. 10 shows an example of spectral radiation characteristics of a pulverized coal combustion flame.

In FIG. 10, a continuous spectrum due to the emission of solid particles of carbonaceous particles (soot, etc.) in the flame can be seen on the longer wavelength side than 0.6 μm. A decrease in emission spectrum intensity due to infrared gas absorption is observed. Carbonaceous particles have emission characteristics similar to a black body and can be generally treated as a gray body having a constant emissivity with respect to wavelength. Since the relationship between the wavelength of the gray body and the monochromatic radiant energy (monochromatic emission spectrum intensity) is given as a function of temperature by Planck's formula, the flame temperature can be calculated from the ratio of the monochromatic emission spectrum intensities of the predetermined two wavelengths from the spectroscopic analysis result. Is (2
According to the principle of color thermometer).

The decrease of the emission spectrum intensity in the vicinity of 1.4 μm is due to the relatively low temperature water vapor in the combustion exhaust gas existing between the optical probe 3 and the flame 2 in a specific wavelength band (1.4, 1.9, 2. (7 μm, etc.) and is a result of absorption of light from the flame. Also, there is gas emission of water vapor in this same wavelength band.
The decrease in the emission spectrum intensity near m is due to the overlap of gas emission due to the high temperature combustion generated steam in the flame and gas absorption due to the low temperature steam in the combustion exhaust gas near the flame (other than this, on the longer wavelength side). There is a similar gas absorption and emission band due to carbon dioxide).

The gas absorption / radiation spectrum intensity of water vapor and the like approximates the value in the gas absorption / wavelength band of the solid emission of the background soot from several wavelengths in the vicinity of the gas absorption / radiation wavelength and not affected by it. Then, from this value and the ratio of the monochromatic emission spectrum intensity in the gas absorption / radiation band, Be
The absorption coefficient is determined according to er's absorption law, and the state of absorption and emission spectrum intensity of gas such as water vapor is quantified and used as an evaluation index of the state of flame.

In the computer 5 of the combustion diagnosing device of FIG. 9, in processing 1, the above-mentioned flame temperature and gas absorption / radiation of water vapor etc. are used as the evaluation value of the flame combustion state from the spectroscopic analysis result of the spectroscopic analysis section 101 of FIG. The state (absorption coefficient) of the spectrum intensity is calculated for each field of view of the optical probe 3, and the process 2
In step 4, the temporal variation of the evaluation value is smoothed by addition average or moving average to obtain the average value level of the evaluation value. In process 3, the deviation from the evaluation value (reference value) in the standard combustion state is analyzed, and in process 4, Whether the target burner flame is abnormal or normal is judged by whether or not there is a significant difference between the current evaluation value and the reference value, and if judged as abnormal, it is based on the database of causal relationships between the evaluation value and combustion conditions. Combustion diagnosis is performed to estimate the cause of abnormality.

[0010]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In a boiler for thermal power generation, which is a multi-burner furnace consisting of a plurality of burners, and each burner flame is also large-scale, it is compared with single and small-scale flames of experimental and research scale. However, the temporal variation of the flame emission state is large, and therefore, the evaluation values such as the flame temperature calculated based on the results of the spectral analysis of the flame emission also vary greatly with time. Especially in the pulverized coal combustion flame, the flame state changes depending on the uneven flow state of the pulverized coal in the coal feeding pipe that feeds the pulverized coal pulverized by the mill to the burner. The fluctuation of the evaluation value such as the flame temperature calculated by the spectroscopic analysis is large.

Further, as a factor of the fluctuation of the amount of light received by the optical probe (flame brightness observed by the optical probe), particularly in pulverized coal burning flame, exhaust gas containing soot produced by combustion is There is an unpredictable fluctuation in the amount of received light that occurs because the light from the flame is blocked by flowing in the field of view of the optical probe.

Conventionally, it is difficult to use instantaneous evaluation values due to this fluctuation, and temporal fluctuation is smoothed by averaging, and the burner flame combustion state is diagnosed based on the smoothed evaluation value. Was going on. However, even with this smoothing, it is easy to suppress fluctuations with short cycles (relatively high frequency fluctuations), but it is not easy to suppress fluctuations with long cycles (low high frequencies), and in general, fluctuations with long cycles Has a larger fluctuation amplitude.

In the burning state of the burner flame, it is important that the flame holding of the flame is kept good so that the combustion air and the fuel such as pulverized coal are appropriately mixed. If the flame holding is poor and the combustion air is not properly mixed with the fuel, the flame becomes diffuse and becomes a factor for the production of environmental pollutants such as CO and dust. In monitoring and diagnosing the combustion state of the burner flame, it is important to judge the quality of the flame holding state.

When the flame holding is deteriorated and the combustion air and the fuel are not properly mixed, the brightness of the flame, the level of the flame temperature, and the like change accordingly, but the spatial and temporal variation of the flame emission state in the visual field. However, the change in flame temperature is buried in the fluctuation level, and the state does not change significantly, or there is a problem that the state change cannot be detected without monitoring for a relatively long time.

As a publicly known example of the flame holding property evaluation of a flame, there is Japanese Patent Laid-Open No. 4-186014, "Flame spectroscopic diagnostic device". JP-A-4-186014 discloses a "flame spectroscopic diagnostic device" which passes an OH radical emission distribution near a flame holder in a gas-fired flame of a gas turbine combustor through an optical filter that selectively transmits only the OH emission wavelength band. After that, measure the image, select a few representative points, measure the time variation of the luminance of the OH radical emission, calculate the cross-correlation between the two points,
The flame holding property is evaluated by determining the fluctuation characteristics of the flame.

In this known example, since the object is a gas-fired flame of a gas turbine combustor, soot generation due to combustion is extremely small as compared with the pulverized coal-fired flame which is the main force in a boiler for thermal power generation. Therefore, the influence of changes in the amount of received light due to contamination of the optical probe's light receiving end that catches flame emission, and random changes in the amount of received light due to the flow of combustion exhaust gas containing black smoke and soot in the observation field of the optical probe are extremely significant. Few.

Therefore, the analyzed luminance (in this known example, the luminance in the OH radical emission wavelength band) is not affected by the disturbance caused by soot or exhaust gas, and the information from the flame can be captured as it is. Since it is unlikely to be affected by disturbances, the calculation result of the cross-correlation coefficient of the temporal variation of the luminance at several measured points is also highly reliable.

On the other hand, in the burner flame of the boiler for thermal power generation, which is the object of the present invention, particularly the pulverized coal flame is strongly influenced by the disturbance due to soot, exhaust gas, etc. By using the fluctuation,
It is difficult to evaluate the state of flame as described in Japanese Patent No. 186,014.

[0019]

To solve the above problems, the present invention mainly adopts the following configurations.

An optical probe having a plurality of fields of view for receiving flame emission emitted from a plurality of regions of a burner flame, and the emission of flames from the plurality of fields received by the optical probe for each field of view. Spectroscopic analysis section for spectroscopically converting the emission of fine particles into monochromatic light of a predetermined number of wavelengths including the wavelengths of the light absorption / emission spectrum band peculiar to combustion products gas and converting it into an electric signal A diagnostic device for diagnosing the combustion state of a burner flame, which comprises a calculation means for calculating the flame temperature and the absorption / radiation spectrum intensity of the combustion product gas for each field of view from the monochromatic light intensity of a predetermined number of wavelengths analyzed by the section. A frequency analysis means for frequency-analyzing the temporal variation of the flame temperature and the light absorption / radiation spectrum intensity of the combustion product gas for each visual field, and the frequency distribution of the variation for each visual field and the Combustion diagnosis apparatus burner flame having an evaluation unit for the difference between the field of view of the wavenumber-distribution as compared to the value when the reference combustion condition to evaluate the combustion state of the burner flame.

In the combustion diagnosis device, the frequency distribution of temporal variation of the flame temperature and the optical absorption / radiation spectrum intensity of the combustion product gas for each visual field and the difference between the visual fields of the varying frequency distribution are flame-ignited. A burner flame combustion diagnosis device having a flame detection function for making a flame extinguishing determination by comparing with a threshold level determined from a time value.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION A burner combustion diagnosis apparatus according to an embodiment of the present invention will be described below with reference to FIGS. Figure 1
FIG. 4 is a diagram showing a flow of processing in a computer that calculates an index for evaluating a combustion state of a flame and makes a diagnosis. That is, FIG. 1 is an improvement of the processing flow in the computer 5 shown in FIG.

In the process 1 of FIG. 1, from the results of the spectroscopic analysis of the burner flame emission, the respective visual fields (visual field a, visual field b, visual field c in FIG. 9: visual field a is the flame root region, visual field b is the flame central region, visual field c is The flame temperature (corresponding to the flame tip region) and the situation of the gas absorption / radiation spectrum intensity (absorption coefficient) are calculated in the same manner as in the prior art. In the present embodiment, the gas absorption / radiation spectrum intensity of 1.4 μ shown in the spectral radiation characteristic of FIG.
The m-band absorption / emission spectrum intensity due to water vapor is used, and hereinafter, this is defined and described as water vapor absorbance.

In process 2-1, the evaluation value of each visual field is smoothed in the same manner as in the prior art to obtain the average value level.
In the process 2-2, the variation status of the evaluation value (flame temperature, water vapor absorbance) of each visual field calculated in the process 1 is FF.
The analysis is performed by the T (Fast Fourier Transform) algorithm, and the frequency spectrum of the evaluation value variation is analyzed.

In process 3, the deviation between the evaluation value (reference value) in the reference combustion state and the current evaluation value (average level of the evaluation value in process 2-1), and the frequency spectrum of the fluctuation of the reference value and process 2 The difference between the fluctuation of the present value analyzed in -2 and the frequency spectrum is analyzed.

In the process 4, whether or not a significant difference is recognized between the average value of the current evaluation values and the reference value, and the significant difference is found between the frequency spectrum of the fluctuation of the current evaluation value and the frequency spectrum of the fluctuation of the reference value. Whether the target burner flame is abnormal or normal is judged depending on whether it is recognized or not.If it is judged to be abnormal, the cause of the abnormality is estimated based on the evaluation value and the database of causal relationships between the fluctuation frequency spectrum and combustion conditions. .

2 to 5 show examples of fluctuation frequency spectra of the evaluation values (flame temperature, water vapor absorbance) analyzed in the process 2-2 of FIG. FIG. 2 is a fluctuation frequency spectrum of the flame temperature when the flame holding is good, and FIG. 3 is a fluctuation frequency spectrum of the flame temperature when the flame holding becomes poor by weakening the swirling of the combustion air.

Similarly, FIG. 4 is a fluctuation frequency spectrum of water vapor absorbance when flame holding is good, and FIG. 5 is a fluctuation frequency spectrum when flame holding is poor. As can be seen by comparing FIG. 2 with FIG. 3 and comparing FIG. 4 with FIG. 5, the swirling force of the combustion air is weakened and the flame holding becomes poor in both the flame temperature and the water vapor absorbance, so that the visual field b (flame central region ), Field of view c (flame tip region)
0.01Hz-0.1Hz of the frequency spectrum of the fluctuation of
Component increases, and there is no change in the visual field a (flame root region). The fluctuation component at a lower frequency close to DC is not significantly different due to the change in flame holding state.

As described above, this is because in the low frequency component close to direct current (corresponding to the average value level of the evaluation value obtained in process 2-1 of FIG. 1), the coal feeding condition of pulverized coal (uneven flow in the coal feeding pipe).
Differences are less likely to appear because they are strongly affected by changes in the overall flame size, but changes in higher frequency regions are strongly affected by the local mixture of fuel and air in the observation field of view, and the flame holding state deteriorates. This is because it will increase with the increase.

Further, since the combustion air is supplied from the outer peripheral direction with respect to the axial direction of the flame, the distribution in the flame axial direction shows that the flame center (field of view b) and tip (field of view a) rather than the flame root (field of view a). Since the fuel is mixed in the field of view c), the influence of the flame holding state is remarkable in the flame center and the tip region (fields b and c) and the field of view a which is the flame root region.
Then it's small.

In process 2-2 of FIG. 1, evaluation values (flame temperature, water vapor absorbance) of each visual field as shown in FIGS.
Analysis of the frequency spectrum of fluctuations in the results and processing 2
The average value level of the evaluation values of each visual field, which is the result of -1, is compared with the reference value in the process 3. In this process 3,
Even if the average value level has a large value variation and no significant difference from the reference value is recognized, the higher frequency component of the frequency spectrum of the variation of the evaluation value (in the present embodiment,
(Between 0.01 and 0.1 Hz band) level b, field c
If there is a difference with the frequency spectrum of the fluctuation of the reference value in the (flame center, tip region) and there is no difference in the field of view a (flame root region), it can be estimated that the flame holding state has changed, and the direction of the difference from the reference value. With (+-), it is possible to diagnose strong flame holding or low flame holding for the flame in the standard state.

When the frequency spectrum of the fluctuation of the field of view a, which is a normally stable flame root region, is significantly different from the frequency spectrum of the fluctuation of the reference value, it is possible to diagnose unstable ignition and formation of a black skirt.

FIG. 6 shows an example of the fluctuation frequency spectrum of the flame temperature when the black skirt is formed. Since the region where the fuel (pulverized coal) is not burned is formed in the root region of the flame, the variation frequency component of the flame temperature in the field of view a becomes small as can be seen by comparing with FIG. However, even when the black skirt is formed, the flame is captured in the optical probe field of view due to the spatial variation in the black skirt region, so the variation component in the low frequency region close to direct current has a relatively high level.

As another effect of the present invention, flame detection becomes possible by frequency spectrum analysis of fluctuations in evaluation values (flame temperature, water vapor absorbance). 7 and 8 show fluctuation frequency spectra of flame temperature and water vapor absorbance when the self-fire is extinguished and the opposing flame is ignited. Even if the self-fire is extinguished, by receiving the opposing flame and radiation from the furnace wall,
The flame temperature shows a value that is not much different from that when the self-ignition is ignited, and the water vapor absorbance is also not so different from that when the self-flame is ignited due to the effects of gas emission by the high temperature steam produced by combustion in the opposing flame and gas absorption by the steam in the exhaust gas in the combustion furnace. Indicates a value.

However, as shown in FIGS. 7 and 8, when the self-flame is extinguished, the variation frequency spectrum of the evaluation value during self-flame ignition shown in FIGS. The conspicuous relatively high frequency (about 0.01 to 0.1 Hz band in this embodiment) fluctuation component is lost, and the distribution between the visual fields (visual fields a, b, c) is lost.

This is because the burner flame exists in the vicinity of the optical probe 3 in FIG. 9 during self-ignition of the flame, so that the light receiving angle of the optical fiber forming the optical probe 3 (the numerical aperture of the optical fiber is about 0.2). The area of the observation field of view is small and the radiation from the partial area of the self-flame can be selectively received.However, when the self-flame near the optical probe is lost, the opposite burner flame or Since the optical probe receives the radiation of the airborne particles in the furnace with a wide field of view,
This is because fluctuations at relatively high frequencies are canceled out, and only fluctuation components at low frequencies close to the DC level such as fluctuations of the opposing flame are detected.

Therefore, a relatively high frequency component (for example, 0.01 to 0.1 Hz) in the fluctuation frequency spectrum of the evaluation value (flame temperature, water vapor absorbance) is lower than the threshold value determined from the level during flame ignition, In addition, if the distribution between the visual fields is lost, it can be determined that a misfire has occurred, and the combustion diagnosis device can also have a flame detection function.

As described above, the embodiments of the present invention include those having the following configurations, functions and operations.

The frequency characteristics of fluctuations in flame temperature and absorption / emission spectrum intensity due to combustion product gas obtained by spectroscopic analysis of flame emission are analyzed, and the flame is determined from the level of a specific frequency band and its visual field distribution (flame axis direction distribution). State of
In particular, the burner flame combustion diagnosis is performed by detecting a change in the flame holding state.

At this time, if the combustion air and the fuel are not properly mixed and the flame holding state of the flame becomes poor, the flame becomes diffusing, so that the spatial and temporal fluctuations of the flame emission state increase. Also, since combustion air is supplied from the outer peripheral direction with respect to the axial direction of the flame, the distribution in the flame axial direction mixes with the fuel at the flame center and the tip region rather than at the flame root, so it depends on the flame holding condition. The fluctuation of the flame emission state is remarkable in the flame center and the tip region.

Although it is theoretically possible to simply use the fluctuation of the brightness of the flame as an index showing the fluctuation of the flame emission state, in the actual apparatus configuration, for example, the bending of the optical fiber like the optical probe 3 of FIG. When the observation field of view is set by the angle, the brightness of the flame received via this optical probe is different from the actual because the transmission loss of light differs depending on the bending angle of the optical fiber, and therefore the field distribution of the brightness fluctuation level is Is also different from the actual situation.

Further, in the pulverized coal burning flame which is mainly used in the recent thermal power generation boilers, dirt on the end face of the optical probe due to adhesion of soot and exhaust gas containing soot flowing in the field of view have a brightness which is difficult to predict. Fluctuation occurs. From this point of view, when considering the device configuration and the actual operation, it is inappropriate to simply use the brightness as an index indicating the variation of the flame emission state.

Therefore, as described in the above-mentioned conventional configuration, calculation is performed based on the monochromatic light spectrum intensity (monochromatic luminance) ratio of a plurality of wavelengths from the result of the spectroscopic analysis of flame emission, and the luminance level itself of the received flame is calculated. It is appropriate to use the fluctuations of the gas absorption / emission spectrum (absorption coefficient) due to the flame temperature and the combustion product gas, which are independent indexes.

The frequency of the observed fluctuation is influenced by the fluctuation of the entire flame size and the fluctuation caused by the local reaction between fuel and air, and continuously exists from the low frequency to the relatively high frequency (frequency Range also depends on the response characteristics such as the sampling frequency of the device). Among these, the fluctuation level at a relatively low frequency close to the DC level is the pulverized coal feeding situation (change in pulverized coal distribution at the burner outlet due to uneven flow in the coal transfer pipe) and fluctuations in furnace pressure, etc. It is difficult to distinguish the fluctuation level under normal conditions from the fluctuation level in the normal state because the influence of the field of view shielding is large due to the fluctuation of the scale and the flow of exhaust gas containing soot in the field of view of the optical probe.

However, the fluctuation level at a relatively high frequency is strongly influenced by the local mixing state of fuel and air in the observation field (the fluctuation on the whole flame scale is remarkable on the low frequency side near DC). , Which is less likely to occur in a relatively high frequency region, so that the fluctuation due to a change in the local mixing state of fuel and air becomes significant in a relatively high frequency region), and increases as the flame holding state deteriorates. . In addition, as described above, the distribution of the field of view in the flame axis direction at the fluctuation level has a distribution in which the difference is small in the flame root region and is large in the flame center and the tip region as the flame holding state changes.

Therefore, the flame temperature obtained from the results of the spectroscopic analysis of the flame emission, the level of the relatively high frequency band of the frequency characteristic of the fluctuation of the gas absorption / radiation spectrum intensity due to the combustion product gas, and its field of view distribution (flame axis direction distribution) It is possible to provide a device capable of diagnosing the quality of the flame holding state of the flame by analyzing.

[0047]

According to the present invention, the fluctuation frequency of the flame temperature and the gas absorption / radiation spectrum intensity by the combustion product gas obtained from the result of the spectroscopic analysis of the flame emission is spectrally analyzed, and its frequency distribution characteristic, in particular, relatively high. By evaluating the state of the burner flame using the level of the frequency band and the observation field distribution that is the flame axis direction distribution, it is possible to provide a device that can diagnose the combustion state such as the quality of the flame holding state.

Further, a flame detection function for making a flame extinguishing determination by the same method can also be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a flow of processing in a computer which calculates an index for evaluating a combustion state of a flame and makes a diagnosis according to an embodiment of the present invention.

FIG. 2 is a diagram showing a frequency spectrum of changes in flame temperature when flame holding is good.

FIG. 3 is a diagram showing a frequency spectrum of changes in flame temperature when flame holding is poor.

FIG. 4 is a diagram showing a frequency spectrum of fluctuations in water vapor absorbance when a flame is good.

FIG. 5 is a diagram showing a frequency spectrum of fluctuations in water vapor absorbance when a flame is defective.

FIG. 6 is a diagram showing a spectrum of changes in flame temperature when a black skirt is formed.

FIG. 7 is a diagram showing a frequency spectrum of variations in flame temperature during burner flame extinction (opposed flame ignition).

FIG. 8 is a diagram showing a frequency spectrum of fluctuations in water vapor absorbance during burner flame extinction (opposed flame ignition).

FIG. 9 is a diagram showing a configuration of a combustion diagnosis device according to a conventional technique.

FIG. 10 is a diagram showing an example of a spectral radiation characteristic of a pulverized coal burner flame.

[Explanation of symbols]

1 burner 2 flames 3 Optical probe 4 Relay optical fiber 5 calculator 101 spectroscopic analysis unit

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Claims (3)

(57) [Claims] 1. An optical probe having a plurality of fields of view for receiving flame emission emitted from a plurality of regions of a burner flame, and the emission of flame from the plurality of fields of view received by the optical probe in a flame for each field of view. A spectroscopic analysis unit that disperses into monochromatic light of a predetermined number of wavelengths including a wavelength for analyzing the emission of carbonaceous particles and a wavelength of a light absorption / emission spectral band peculiar to the combustion product gas, and an electric signal, The combustion state of the burner flame is equipped with a calculation means for calculating the flame temperature and the absorption / emission spectrum intensity of the combustion product gas for each field of view from the monochromatic light intensity of a predetermined number of wavelengths analyzed by the spectroscopic analysis section. A diagnostic device, comprising frequency analysis means for frequency-analyzing temporal fluctuations of the flame temperature and optical absorption / radiation spectrum intensity of combustion product gas for each visual field, and a frequency distribution of the fluctuation for each visual field. Serial combustion diagnosis apparatus of the burner flame, characterized in that it comprises an evaluation means for differences in comparison with the value at the reference time combustion state to evaluate the combustion state of the burner flame across the field of view of the frequency distribution. 2. The combustion diagnostic apparatus according to claim 1, wherein the flame temperature and the frequency distribution of temporal fluctuation of the optical absorption / radiation spectrum intensity of the combustion product gas for each field of view and the field of view of the fluctuation frequency distribution. A burner flame combustion diagnostic device having a flame detection function for making a flame extinguishing determination by comparing the difference between the above-mentioned difference with a threshold level determined by a value at the time of flame ignition. 3. The combustion diagnosing device according to claim 1, wherein the evaluating means relatively compares the frequency characteristics of temporal variations of the flame temperature and the light absorption / emission spectrum intensity of the combustion product gas with respect to each visual field. A burner flame combustion diagnosis device, characterized by diagnosing the quality of a flame holding state by analyzing a level in a high frequency band and a visual field distribution in a flame axis direction.