JPH0629666B2 - Flame detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame detector, and more particularly to a flame detector capable of automatically setting threshold values for flame ignition and extinction.

<Prior art and its problems> A flame detector is a device that determines the ignition and extinguishing states of each burner of a combustion device. For example, in a large-scale boiler for a thermal power plant where a large number of burners are installed, control is required. It is an essential device. This flame detector is roughly classified into an optical flame detector that makes a determination based on the intensity of light emitted from the flame and an ion flame detector that makes a determination based on the ion density in the flame. Among them, the ion-type flame detector uses the electrical properties of the flame to make a flame determination, and it is necessary to bring an electrode rod for guiding an ion current into contact with the flame. For this reason, it is impossible to continuously use the electrode rod for a long time in order to prevent the electrode rod from being burnt out, and the operating range is limited to those for which the operating time is short, such as for an ignition torch (starting burner). That is, long-time use is limited to optical type.

Here, in various combustion devices including the large-scale boiler, a combustion method such as a two-stage combustion method, an exhaust gas recirculation method, or a swirling combustion is often adopted from the viewpoint of reducing air pollutants. There is. Due to this change in the combustion method, the characteristics of the flame have changed, for example, the brightness of the flame has decreased and the flame has lengthened, so that the reliability of the conventional flame detector has become conspicuous. In particular, there is a problem that not only the detection capability for individual flames is deteriorated, but also the light of another burner flame is detected due to a decrease in flame brightness, which causes malfunction of the device.

FIG. 2 shows the structure of a conventional optical flame detector. The optical fiber 12 serves as a light guide section (light receiving section) for receiving and guiding light from the flame, and an optical signal is converted into an electric signal and amplified. The wavelength photoelectric conversion unit 13, the frequency discrimination unit 14 that discriminates only the specific fluctuation frequency component of photoelectric conversion, and the presence or absence of flame by comparing the magnitude of the signal level after discrimination with a predetermined reference value, that is, a threshold value. And the determination result (O
It comprises an output unit 16 for outputting (N, OFF) and a threshold value setting unit 17 for manually setting a threshold value.

In the above conventional device, since the light receiving direction is limited to one direction, it is not possible to sufficiently cope with the change in flame property due to the change in the combustion method described above. Further, since the threshold value is fixedly set, it is difficult to keep up with the reliability because it is not possible to follow the change in flame brightness. That is, the emission wavelength shifts to the long wavelength side due to the change of the combustion method, the flame position to be detected changes due to the flame becoming longer, the light of the strongly swirling flame of the adjacent burner enters the flame detector of the burner of interest, etc. However, it is virtually impossible for the conventional device to maintain high reliability in such a state.

<Object of the present invention> The present invention solves the above-mentioned problems, and an object of the present invention is to provide an apparatus capable of maintaining high reliability of flame presence / absence determination even when the flame state changes.

<Outline of the Present Invention> In short, the present invention is intended for a flame detector that determines ignition or extinction of a combustor (burner) or the like based on the detected light intensity.

Then, the flame detector separates the light-receiving unit that receives the fire from the flame to be detected, the photoelectric conversion unit connected to this light-receiving unit, and the signal output from this photoelectric conversion unit into a predetermined frequency band. Frequency analyzer, an integrator that integrates the signal in the predetermined frequency band separated by the frequency analyzer, and the time average value and standard deviation of the output based on the output from the integrator. Calculates the two thresholds, the ignition threshold and the extinguishing threshold, based on the time average value / standard deviation calculator and the time average value and standard deviation output from the time average value / standard deviation calculator. And a threshold value calculator, comparing the actual value output from the integrator and the output from the threshold value calculator, ignition of the combustor, comprising a comparison determination unit for determining the extinguishing, Ignition threshold and extinction threshold Is configured to be updatable.

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

FIG. 1 shows a signal transmission system of an apparatus showing an embodiment of the present invention, in which light from a flame has different detection angles (for example, horizontal,
Θ ₁ = 15 °, Θ ₂ = 30 °) is received by the three-field optical fiber head 1, and the light that was once received is transmitted through the optical fiber 2 to the visible-near infrared region and the infrared region. It is introduced into the two-wavelength photoelectric conversion unit 3 having sensitivity in the wavelength range. Six types of signals after photoelectric conversion, that is, two wavelengths detected for each field of view are sequentially switched by the switch 4,
It is converted into a digital signal in an analog / digital (A / D) converter 5 in the control device 30. The converted signal is decomposed into frequency components in the frequency analysis unit 6, only the signal in a predetermined frequency band (for example, 50 to 500 HZ) is integrated in the integrator 7, and the value is sent to the comparison and determination unit 8. Here, the threshold calculator 11 determines the magnitude comparison of the actually measured values with a preset threshold value, and sends the determination result to the output unit 9. The output of the integrator 7 is sent to the time average value / standard deviation calculator 10 for calculating the time average value and standard deviation σ by switching. This value is then sent to the threshold value calculator 11, and a threshold value higher than σ, for example, X = −α · σ (ignition threshold value) Y = + β · σ (digestion threshold value) (α, β is a coefficient).

FIG. 3 shows the structure of the three-view optical fiber head 1.

In order to improve the heat resistance, the coating made of the organic resin is removed from the optical fiber, and in order to realize the detection angles Θ ₁ and Θ ₂ , the two optical fibers are heated by heating as shown by reference numeral 18. Bending 19 is performed. When installing the optical fiber head in the burner section, it is desirable to use a protective cylinder made of metal or ceramic that can introduce cooling air. The optical fiber head 1 and the subsequent coated and flexible optical fiber 2 are connected using a three-core collective connector 20. The core diameter of the optical fiber 2 is smaller than the core diameter of the optical fiber arranged in the head 1 so that the light can be transmitted even if the axes of the two fibers are slightly deviated from each other. It is designed to facilitate centering of both fibers.

FIG. 4 shows the structure of the photoelectric conversion element of the two-wavelength photoelectric conversion unit 3. In the figure, this element has a structure in which a silicon (Si) photo diode 21 and a lead sulfide (PbS) photo cell 22 are laminated, and the visible, near-infrared, and infrared regions can be obtained by using a one-view optical fiber. It is configured so that signals in two wavelength bands can be separately extracted. By adopting this element, the number of the optical fibers 2 can be set to three, which is the same as the number of the light receiving side optical fibers.

FIG. 5 shows an example of digital frequency analysis of the signal by the frequency analysis unit 6. In the figure, the shaded area is integrated by the integrator 7, and this value is used for flame determination.

FIG. 6 shows this method more concretely, and shows the results of frequency analysis in a state a in which the burner of interest to the apparatus is ignited and a state b in which the burner is extinguished. Here, it can be seen that the high frequency component increases when the burner of interest is ignited. Since this frequency analysis is performed digitally, for example, the setting of the frequency band as shown by the diagonal lines in FIG. 5 can be made relatively easily by changing the program of the arithmetic unit 30 and can be changed online. It is possible to set the frequency band appropriately and promptly even with respect to the change of, and the reliability of the device is improved.

FIG. 7 shows an example of the change over time of the output signal of the integrator 7, using one of the six types of signals as an example. That is, when the adjacent burners ignite, it can be seen that the output increases like Q ₁ and the influence of the ignition of the other burners occurs. When the burner of interest ignites in this state, the output is Q
Furthermore as ₂ increases, it is possible to determine the presence or absence of the flame irrespective to the operating state of neighboring burner by setting the as threshold dotted a. However, this is not enough to cope with recent changes in the combustion method, and the following threshold values are set. That is, in FIG. 1, the output of the integrator 7 is initially switched and led to the time average value / standard deviation calculator 10, and the time average value when the target burner is in the fire extinguishing state.
_OFF and the standard deviation σ _OFF , the target burner calculates the time average value _ON and the standard deviation σ _ON in the ignition state. Based on these values, the threshold calculator 11 calculates X _ON = _ON −α · σ _ON (ignition threshold) Y _OFF = _OFF + β · σ _OFF (extinguishing threshold) and uses it for flame determination. By calculating this threshold value, if the output is X _ON or more, the probability of ignition is extremely high (99% or more), and if Y _OFF or less, the probability of fire extinguishing is extremely high. Therefore, even if the output increases due to the influence of the adjacent burner, the burner of interest can be reliably determined to be in the fire extinguishing state.

FIG. 8 shows the setting states of the ignition and extinction threshold values. Since these values are initially calculated based on the signal from the actual flame, the reliability of the determination of the ignition / extinguishing state becomes high.
However, when the output shows an intermediate value between X _ON and Y _OFF , the judgment is suspended and the judgment result before this is held.

As described above, when judgment is performed using two threshold values,
Even if the flame shape is unstable and the output fluctuation is large, the correct judgment can be made, and the standard deviation is evaluated to set the threshold value.Therefore, the probability of erroneous judgment due to the unstable output is high. Get lower. In particular, it is extremely effective in preventing erroneous determination due to the influence of other burners. Also, the threshold value can be calculated and set by itself, so that the output shows an intermediate value between X _ON and Y _{OFF for} a certain period of time while the detector is operating. It is possible to change the threshold value by recalculating with the output of. Therefore, it becomes possible to continue the flame determination by following the continuous change of the flame state. FIG. 9 shows the ratio (m ₁ / m ₂ ) of the frequency gradient that should be used as a reference for changing the threshold value. Generally, when the burner of interest is in the ignition state, m ₁ <m _2, that is, m ₁ / m ₂ <1. The calculation of the frequency gradient is not always performed, but is performed by the frequency analysis unit 6 only when the determination is held for a long time.

As described above, since the device of the present invention is a multi-field (three fields of view in the embodiment) dual-wavelength detection system, highly reliable detection is possible even with changes in the flame shape and changes in the emission wavelength of the flame. . Further, since the threshold value used as the judgment reference is set by statistically calculating based on the input signal, it is possible to perform detection with extremely high accuracy. In particular, there are many variations in the output due to the influence of other burners,
By setting the threshold value that takes the standard deviation into consideration, it is possible to exclude the output with a large variation from the target of the judgment, which is very effective in preventing erroneous judgment due to the influence of other burners.

In addition, since it is a method that automatically calculates the threshold value, it is very easy to set the threshold value for many flame detectors, and at the same time, the threshold value can be automatically changed in response to changes in the combustion state. It is possible to quickly respond to changes in the combustion state.

<Effect> As described above, the present invention calculates the time average value and the standard deviation based on the output from the integrator, and calculates the threshold value according to the time average value and the standard deviation. The threshold is updatable. Therefore, accurate flame determination can be continued by sufficiently following changes in the combustion (flame) state due to load fluctuations, for example.

Further, since the flame determination is performed using two thresholds, the ignition threshold and the extinction threshold, the correct determination can be made even if the flame shape is unstable and the output fluctuation is large.

Furthermore, since the standard deviation is used to calculate the threshold,
The probability of erroneous determination due to unstable output is low, and it is particularly effective in preventing erroneous determination due to the influence of other flames.

From the above, it is possible to provide a flame detector with high operational reliability.

[Brief description of drawings]

FIG. 1 is a system diagram showing a configuration example of a detector showing an embodiment of the present invention. FIG. 2 is a system diagram showing a configuration example of a conventional flame detector. FIG. 3 is a partially enlarged view of a three-view optical fiber head which is a light guide portion of the flame detector of the present invention. FIG. 4 is a sectional view of a two-wavelength photoelectric conversion element of the photoelectric conversion unit of the flame detector of the present invention. FIG. 5 is a diagram showing an example of frequency analysis of flame signals. FIG. 6 is a diagram showing a comparison of frequency analysis results in a flame ignition state and a fire extinguishing state. FIG. 7 is a diagram showing an example of a temporal change in flame detector output. FIG. 8 is a diagram showing setting of threshold and extinguishing threshold. FIG. 9 is a diagram showing a signal output gradient. 1 ... Optical fiber head, 2 ... Optical fiber, 3 ... 2-wavelength photoelectric conversion unit 6 ... Frequency analysis unit, 7 ... Integrator 8 ... Comparison judgment unit 10. ...... Time average value / standard deviation value calculator 11. ...... Threshold calculator 30. ... Computing device

Claims (1)

[Claims] 1. A flame detector for determining whether ignition or extinguishing is to be performed based on the intensity of detected light, and a light receiving section for receiving a fire from a flame to be detected, and a photoelectric conversion section connected to the light receiving section. A frequency analysis unit that separates the signal output from the photoelectric conversion unit into a predetermined frequency band, an integrator that integrates the signal in the predetermined frequency band that is separated by the frequency analysis unit, and an output from the integrator. And the time average value / standard deviation calculator that calculates the time average value and standard deviation of the output, and the ignition threshold based on the time average value and standard deviation output from the time average value / standard deviation calculator. A threshold value calculator that respectively calculates two thresholds, a value and a fire extinguishing threshold value, and an actual measurement value output from the integrator and an output from the threshold value calculator are compared, and the combustor concerned is compared. Ignition and extinguishing of A flame detector comprising: a comparison / determination unit, wherein the ignition threshold and the extinction threshold can be updated.