JPH0979571A - Combustion monitor sensor and air ratio control method of combustor using the sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an air ratio to an optimum predetermined value by converting to electric signals incident light from a plurality of optical fiber for receiving radiation light from a flame, and outputting a difference signal between those electric signals as a detection signal. SOLUTION: Near-infrared light incident upon two sets of optical fibers 5a, 5b disposed at a predetermined interval is inputted to a signal processor 28 as a flame detection signal VIR. The flame detection signal VIR outputted from the signal processor 28 is inputted to an arithmetic operation processor 22. In a memory 23 there is stored data indicative of a comparison relation among the flame detection signal VIR, the air ratio, and a combustion load rate, and the data from the memory 23 and the flame detection signal VIR from the signal processor 28 are compared with each other in the arithmetic operation processor 22 and a comparison signal is inputted to an air ratio controller 21 as an air ratio signal. In the air ratio controller 21, the air ratio signal and a set air ratio are compared with each other, and the number of revolutions of a fan drive motor 17 is adjusted such that a difference between them is zero, whereby the so-called PI control of the air ratio is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame detection type combustion monitoring sensor used for combustion monitoring of a combustion device such as a boiler, and an air ratio control method using the same. A non-flame contact type new combustion monitoring sensor consisting of, and this combustion monitoring sensor directly detects the air ratio from the flame, and by the air ratio detection signal,
The present invention relates to a novel air ratio control method for controlling the air ratio of a combustion device to an optimum set value.

[0002]

2. Description of the Related Art As a combustion monitoring sensor used for combustion control of a gas-fired boiler or the like, for example, an electrode-type sensor (frame rod) configured to electrically detect specific ions generated in the process of combustion reaction, Ultraviolet photoelectric tube type sensor (Ultra Vision) that optically detects radical chemical species generated in the process of combustion reaction, micro pressure sensor that mechanically detects pulsation of furnace pressure caused by combustion, etc. Is commonly used until. Similarly,
In oil-fired boilers and the like, photoelectric sensors using a cadmium cell are often used.

However, since the electrode portion of the electrode type sensor is inserted into the flame, deterioration and consumption due to oxidation are severe, and adhesion of various pollutants is unavoidable, which deteriorates the detection performance of the sensor. As a result, it is often necessary to replace or repair the detection unit, which causes an increase in running cost of the combustion monitoring sensor.

Further, the ultraviolet photoelectric tube type sensor and the micro pressure type sensor are expensive in the detecting portion and have a low mechanical strength, so that they lack vibration resistance and impact resistance. As a result, the equipment cost rises and the frequency of maintenance and inspection and replacement of the equipment increases, and the running cost of the combustion monitoring sensor also rises as in the case of the electrode type sensor.

Further, the photoelectric sensor using a cadmium cell can be used only for a luminous flame for oil burning due to the nature of the cadmium cell, and cannot be applied to a flame for gas burning.
Since the signal is taken out by the ON-OFF method, there is a problem that it cannot be used as an air ratio sensor.

In addition, all of the conventional optical combustion monitoring sensors are of a type that observes the flame from the front of the flame, and cannot be applied to a boiler or the like whose burner opening cannot be seen from the front of the flame. Since a device, a glass fiber, a frequency analyzer, an electronic calculator, etc. are separately required, the sensor device itself becomes large in scale, and there is a problem that it is difficult to downsize the sensor device.

On the other hand, in the conventional combustion control of a small boiler or the like, an ideal combustion flame is obtained by adjusting the amount of combustion air (air ratio) supplied to the burner by a flame detection signal from a combustion monitoring sensor. I am trying. However, in the conventional combustion control using the combustion monitoring sensor, the supply air amount (air ratio) changes with the change of the outside air temperature (the temperature of the combustion air). As a result, the residual O ₂ in the combustion exhaust gas varies greatly depending on the season, which causes an inconvenience such as an increase in blower power.

[0008]

SUMMARY OF THE INVENTION The present invention provides a combustion monitoring sensor used for combustion control of a conventional small boiler and the above-mentioned problems in the air ratio control using the same, that is, the durability of the combustion monitoring sensor. In addition to being low, the detection performance deteriorates relatively quickly, it is necessary to replace and repair parts frequently, the combustion monitoring sensor device becomes complicated and large, and the equipment cost rises. There is a problem in that there are restrictions on the mounting position, it is difficult to control the constant air ratio in the air ratio control, and the O ₂ concentration in the combustion exhaust gas fluctuates depending on the outside temperature, resulting in power loss of the blower. Solved, the structure is simple and inexpensive, moreover, the detection part is not in contact with the flame and is highly durable, and the combustion flame of a boiler or the like can be detected not only from the front side of the flame but also from the back side and side surface, Air directly from the flame By detecting and to control the air ratio to the optimum predetermined value, there is provided an air ratio control method for a boiler or the like using a combustion monitoring sensor it.

[0009]

According to the first aspect of the present invention, there are provided a plurality of optical fibers for receiving radiation light from a flame and a plurality of conversion circuits for converting incident light from each fiber into an electric signal. And a signal processing device that outputs a differential signal of those electric signals as a detection signal is a basic configuration of the invention.

The invention according to claim 4 of the present application is an optical fiber for receiving radiated light from a flame, a blue or green filter for passing incident light from the optical fiber, and converting incident light from the filter into an electric signal. A signal processing device having a conversion circuit and outputting the amplified signal thereof as a detection signal is a basic configuration of the invention.

According to a fourth aspect of the present invention, the combustion apparatus has a plurality of optical fibers for receiving the radiated light from the flame and a plurality of conversion circuits for converting the incident light from each fiber into an electric signal. Then, a combustion monitoring sensor including a signal processing device that outputs a differential signal of these electric signals as a detection signal is provided, and the detection signal from the combustion monitoring sensor is input to the air ratio control device as an air ratio detection signal. The basic configuration of the invention is to adjust the supply amount of the combustion air in a direction to reduce the difference from the air ratio set in advance.

According to a sixth aspect of the present invention, an optical fiber for receiving radiant light from a flame, a blue or green filter for allowing incident light from the optical fiber to pass through the combustion device, and an incident light from the filter are provided. Is provided with a combustion monitoring sensor having a conversion circuit for converting the electric signal into an electric signal, and a signal processing device outputting the amplified signal as a detection signal, and the air ratio control using the detection signal from the combustion monitoring sensor as an air ratio detection signal The basic configuration of the invention is to adjust the supply amount of the combustion air in the direction of reducing the difference from the air ratio that is input to the device and set in advance.

Prior to the creation of the invention of the present application, the inventors of the present application produced a small gas combustion type boiler equipped with an all-premixed combustion type multi-port burner as shown in FIG. 17, and used it for combustion. Numerous tests were conducted to obtain basic data on the relationship between flame radiation such as gas emission from a flame and the combustion state represented by the air ratio.

In the boiler 1 of FIG. 17, the fuel gas is city gas (13A), the heat supply amount is 30,000 kcal / h (maximum), 180000 kcal / h (minimum, 60%), and the exhaust oxygen concentration. Is 2 to 8%, the combustion chamber volume is 6.6 × 10 ^-3 m
³ (190 mm × 115 mm × 300 mm), the burner area is set to 6.9 × 10 ⁻³ m ³ (125 mm × 55 mm), and the heat exchanger 3 is provided above the combustion chamber.

FIG. 18 shows an example of the burner plate 2a forming the burner 2, which is 1.2 mmφ-1.
A plurality of 9 mmφ nozzle holes 2b are formed. Further, an optical fiber 5 is provided in the wind box 4 below the burner plate 2a.

[Basic Test 1] In the present invention, in order to realize low NOx control, the combustion state is detected without being affected by external disturbances such as non-flame contact type and fluctuations in the ambient temperature of the wall surface of the boiler and the combustion load factor. The purpose is to make a possible combustion monitoring sensor. Therefore, first, the temperature of each part of the boiler was measured, and the effect of cooling the optical fiber 5 by the mixed airflow flowing into the wind box 4 was investigated.

FIG. 19 shows the measurement results of the temperature at the tip of the optical fiber 5 and the temperature at the center of the lower surface of the burner plate 2a. It was found that the tip temperature of the optical fiber 5 was kept at room temperature. Boiler 1 is 18000k
It was operated for 30 minutes after ignition with cal / hr and O ₂ 4%, and then extinguished the fire and stopped water supply to the boiler.

[Basic Test 2] Next, as shown in FIG. 20, a spectroscope 6 was used to spectrally analyze the emitted light along the central axis of the flame. FIG. 21 shows the measurement result. Radical emission 7 is a band spectrum excellent in the ultraviolet to blue region and should be distributed only at the bottom of the combustion chamber (OH
Radical: 310 nm, CH radical: 430 nm),
The thermal radiation has an excellent band spectrum in the near-infrared region, is distributed throughout the combustion chamber, and is presumed to be the radiation of high-temperature H ₂ O gas. That is, the spectral radiation intensity is relatively high, the near infrared light emitted from the entire combustion chamber is detected,
And so on.

The combustion condition at this time is input: 18000
kcal / h, O ₂ : 6%, and the spectrometer 6 is R446 (wavelength band of 600 nm or less) manufactured by Hamamatsu Photonics KK
And R406 (long wavelength band) were used. In FIG. 21, 7 is radical radiant light, 8 is near-infrared light mainly composed of H ₂ O gas radiant light (hereinafter flame signal), H is the height in the central axis direction of the flame, I ₁ Is the output n of the spectrometer (R406)
A and I ₂ are the output nA of the spectrometer (R446).

[Basic Test 3] Using the boiler 1 shown in FIG.
The temperature distribution on the flame center axis and the time average intensity of the flame signal (near infrared light emission) 8 on the flame center axis were measured using the boiler input and the O ₂ concentration as parameters. The flame signal intensity was measured using the silicon photodiode array 9.

22, FIG. 23, FIG. 24 and FIG. 25 show the measurement results. From the test results, the temperature and flame signal intensity on the flame center axis are both independent of the amount of heat supplied, and It was found to decrease with increasing ratio. The above phenomenon is because the intensity of the thermal radiation light detected as the flame signal is a function of the temperature according to the Planck's thermal radiation.

[Fundamental Test 4] As shown in FIG. 26, a 35-element silicon photodiode array 9 (S4111, Hamamatsu Photonics KK) was installed in the axial direction, and using this, flames at two points in the central axis direction of the flame were used. The correlation properties of the signals were investigated. In the measurement, one measurement position was fixed at H = 70 mm, and the other had a measurement point interval d of -17.6, -8.8,
It was changed to be 8.8 and 17.6. The case of d> 0 indicates that the moving measurement point is above the fixed measurement point. When d = 0, the autocorrelation function of the flame signal at the fixed measurement point is shown. FIG. 27 shows the measurement results, and it can be seen from the cross-correlation function shown in FIG. 27 that the flame signal moves from the lower part of the combustion chamber to the upper part at substantially the same speed.

[Basic Test 5] As shown in FIG. 28, the Si photodiode array 9 was arranged in a direction perpendicular to the flame center axis, and the measurement point interval d was fixed at 4.4 mm. Then, the original signal 11 on one side and the differential signal 12 of both signals are flip-flopped.
Frequency analysis was performed using a T analyzer 10.

FIG. 29 shows the results of the above frequency analysis. The white background shows the original signal 11 and the halftone background shows the differential signal 12.
Is shown. The boiler combustion conditions during the test were input: 18000 kcal / h and O ₂ : 6%.

As is apparent from FIG. 29, in the single sensor signal (original signal) 11, the signal component in the high frequency band (10 Hz or more) increases in proportion to the position H, and in the differential signal 12. It was found that the high frequency component (10 Hz or more) was removed by subtraction processing as a synchronization signal, and the uneven signal perpendicular to the central axis remarkably appeared in the low frequency band.

[Basic Test 6] Next, in order to investigate the behavior of the flame signal detected by the fiber sensor, as shown in FIG. 30, two optical fibers 5a and 5b are provided in the wind box 4 below the burner plate 2a. D is provided separately, one optical fiber 5a is fixed at L = 70 mm, the distance between the other optical fibers 5b is made variable, and each fiber 5a, 5b
The flame signal was detected by and the frequency analysis of the detected flame signal was performed.

FIG. 31 shows the results, where the white background shows the signal (original signal) 14 from the single sensor, and the halftone background shows the differential signal 15. As is clear from FIG. 31, the differential signal 1 is proportional to the increase of the fiber spacing D.
5 increases and exceeds the intensity of the single sensor signal in the vicinity of 40 mm, the flame signal monitored from the wind box 4 through the flame hole is only the low frequency band signal, and the flame center obtained in FIG. It was found that a signal corresponding to the unevenness signal in the direction perpendicular to the axis was selectively detected.

[Basic Test 7] The relationship between the air ratio, the NOx concentration and the heat loss in the boiler 1 shown in FIG. 17 was investigated using the thermal combustion load factor as a parameter. FIG. 32 shows the measurement result, and the heat loss is predicted from the decrease in the adiabatic combustion temperature due to excess air when the air ratio is 1 or more. As is clear from FIG. 32, the air ratio is 1.2 to 1.
It was found that the NOx concentration in the vicinity of 3 was less than 60 ppm and a combustion state with small heat loss was obtained.

From the results of the respective basic tests, the inventor of the present application can install the optical fiber 5 in the wind box 4 below the burner plate 2a, monitor the flame through the nozzle hole 2b, and the two optical fibers 5 .5 is provided at a distance in the direction perpendicular to the flame center axis, and the differential signal of the detection signals of both optical fibers is taken out to cancel the in-furnace heat radiation and external incident light, which are in-phase noise signals. The nonuniformity signal of the infrared light signal (that is, the nonuniformity signal of the radiant light intensity of the H ₂ O gas, and the nonuniformity signal of the near infrared light signal has a high correlation with the combustion gas temperature. We have learned the fact that it has a high correlation with the air ratio during combustion.

The invention of the present application was created by adding the creativity described below to the above findings.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[First Combustion Monitoring Sensor] FIG. 1 is a perspective view showing an example of an embodiment of the present invention. In FIG. 1, 1 is a boiler,
2 is a burner, 2a is a burner plate, 3 is a heat exchanger, 4
Is a wind box, and the external dimensions of the boiler 1 and the structure of the burner 2 etc. are exactly the same as those in the case of FIG.

Further, in FIG. 1, 16 is a fan with a premixer, 17 is a fan driving motor, 18 is a motor controller, 19 is a control valve, 20 is a valve controller, and 2
1 is an air ratio control device, 21a is an air ratio setting device, 21b is an air ratio controller, 22 is an arithmetic processing unit, 23 is a storage device, 24 is the first combustion monitoring sensor of the present invention, and 25 is the second combustion of the present invention. It is a monitoring sensor.

The first combustion monitoring sensor 24 includes two optical fibers 5a and 5b and two Si photodiodes 27.
a, 27b, a signal processing device 28, and the like.

Similarly, the second combustion monitoring sensor 25 is
Optical fibers 5c and 5d, blue and green filters 29a and 29b, and two GaAs photodiodes 3
0a and 30b, and the signal processing device 31 and the like.

The optical fibers 5a to 5d have a diameter of 0.75.
It is four sets of bundled fiber bundled with mm plastic fiber wires and is installed 70 mm away from the plate, and the flame is monitored from below through the flame hole. The tip of the fiber is maintained at room temperature even during boiler operation due to the cooling effect of the mixed air flow. As an optical fiber,
In addition to plastic fiber, glass fiber (core system =
0.75 mm, outer diameter = 1 mm, N · A = 0.2) can be used. It is also possible to use a single core fiber instead of the bundle fiber. Further, it is possible to attach a ball lens or the like to the base end of the fiber so as to increase the amount of light.

FIG. 2 is a block diagram showing the structure of the first combustion monitoring sensor 24, and FIG. 3 is a signal processing device 28 thereof.
2 is an example of a circuit diagram of FIG. With reference to FIGS. 2 and 3, the incident light from the flame incident on the two optical fibers 5a and 5b separated by 40 mm or more and installed in the wind box 4 is sent to the silicon photodiodes 27a and 27b. Then, a current signal proportional to the incident light intensity is generated. The generated current signal is converted into a voltage signal by the current-voltage conversion circuit 32 and then amplified by the differential amplifier circuit 33,
Then, it is input to the subtraction circuit 34. The differential amplifier circuit 33 is intended to remove an excessive signal component at the time of ignition and extinguishment, and a subtraction circuit 34 subsequent thereto.
Is for obtaining only uneven signals such as thermal radiation in the furnace and external incident light which become noise signals as described above. The difference signal of both signals from the subtraction circuit 34 is the follower circuit 35,
It is input to the adder circuit 38 for the offset signal (minute signal) through the secondary high-pass filter (fc = 1 Hz) 36 and the secondary low-pass filter (fc = 10 Hz) 37. The signal to which the offset signal is added is the inverting half-wave rectifier circuit 3
Full-wave rectification is performed by a full-wave rectification circuit (absolute value circuit) 39 including 9a and an inverting adder 39b.

As described above, the band pass filter is for removing direct current disturbance light and high frequency electrical noise from the non-infrared light unevenness intensity signal output from the subtraction circuit 34.

The signal obtained by full-wave rectifying the low frequency (1 to 10 Hz) signal is input to the comparator 40 and compared with a signal from a threshold value setting circuit 41, which will be described later, to determine the full-wave rectified signal. If the value is exceeded, the pulse output generation circuit 42
The pulse output is input to the pulse delay circuit 44 through the pulse inversion circuit 43 in the form of a pulse train. That is, the full-wave rectification circuit 39 and the comparator 40 are the same as the subtraction circuit 34.
This is for removing the signal strength of the output signal from and converting it into a pulse train signal.

In the pulse delay circuit 44, the input pulse train is smoothed according to the pulse time width T from the one-shot trigger circuit 44a and is output as a DC flame detection signal V _IR . That is, the one-shot trigger 44a smoothes the pulse train and sets the response time.
In this embodiment, the electric circuit of the signal processing device 28 has a circuit configuration as shown in FIG. 3, but the signal processing device 28 converts the incident light into an electric signal from at least two fibers. It goes without saying that the circuit configuration may be any one as long as it includes a conversion circuit for performing the above operation and a detection circuit for detecting the operation signals of both electric signals.

By the way, in the first combustion monitoring sensor 24, the optical fibers 5a and 5b are installed with respect to the installation of the sensor.
The problem is the position L, the distance D, and the fiber installation angle φ.
Further, the threshold value setting circuit 41 for the circuit adjustment of the sensor.
The threshold value Vb and the pulse width T of the one-shot trigger circuit 44a become problems. Therefore, these problems will be examined next.

First, the tip positions (L in FIGS. 1 and 2) of the optical fibers 5a and 5b will be examined. Now, the arrangement of the nozzle holes 2b on the burner plate 2a is shown in FIG.
Moreover, it is assumed that the heat radiation from the flame is a point light source that is densely distributed in the combustion chamber. The light emitted from the point light source forms a pattern of illuminance according to the arrangement of the flame holes in the wind box 4 on the back surface of the plate, as shown in FIG. As a result, the flame radiated light that has passed through the plate 2a and radiated into the wind box 4 forms an illuminance distribution as shown in FIG. 5 at the center of a plane where the distance L is constant. Further, the relationship between the installation position L and the illuminance at each point is as shown in FIG. That is, when L = 10 mm, the strength depending on the arrangement of the flame holes appears remarkably, but as L becomes larger, the irradiation area from each flame hole expands and the illuminance is smoothed. Further, when the optical fiber is installed at L of 30 to 50 mm or more, the intensity of the detection signal is not affected by the installation error. Therefore, the installation position L of the optical fibers 5a and 5b is 30
It is desirable that the thickness is 50 mm or more.

Next, the installation angles of the optical fibers 5a and 5b will be examined. When the irradiation light is received by the end face of the optical fiber 5, the received light amount is limited by the numerical aperture N · A which is a characteristic value of the fiber. FIG. 7 shows a model when the light passing through the burner plate 2a is received by the optical fiber 5. “A” indicates a region where the fiber end face can be irradiated with light by passing through the flame hole. Further, b indicates a region that is limited by the numerical aperture and can enter the optical fiber. It can be seen that as the installation angle φ increases, the area shared by a and b decreases and the intensity of the received light signal decreases.

The light receiving area when the installation angle φ is Odeg is shown in black in FIG. In the case of FIG. 8, a = 12 mmφ,
b = 14 mmφ. The area that can be received by the optical fiber exists continuously in the flame center axis direction, but is discrete in the vertical direction. Further, it is considered that the flame signal in the direction perpendicular to the flame center axis was significantly detected due to the discrete light receiving characteristics. FIG. 9 shows the result of examining the relationship between the installation angle θ and the received light signal intensity. The vertical axis represents the ratio to the received light signal intensity when the installation angle θ is Odeg. As a result, larger plastic fibers are less affected by installation angle errors than glass fibers with smaller numerical apertures.

Further, the threshold value Vb and the optical fiber 5
The distance D between a and 5b will be examined. Optical fiber installation angle φ is Odeg, position L is 70 mm, fiber spacing D
When burned at 40mm (input 18000k
FIG. 10 shows the detection signal on the sensor circuit for cal / h, O ₂ = 4%). The low-frequency flame signal generated due to ignition is converted into an AC signal centered on OV by differential processing and filter processing. Determining the presence / absence of this AC signal corresponds to determining the presence / absence of normal combustion flame. FIG. 11 shows an example of the probability density distribution of the signal level that this detection signal can take. The results of the noise signal N during extinguishing and the flame signal P during combustion are shown. That is, these distributions follow a normal distribution. The standard deviation σ _O at the time of extinguishing is 0.29 V, and a signal of 99.99% is included within ± 4 σ _O [1.08 V]. Therefore, the threshold value Vb may be set to 4σ _O or more.

Next, FIG. 12 and FIG. 13 show the results of measuring σ for the flame signal at the time of combustion with respect to the fiber spacing D. As is clear from the figure, as in the case of the flame signal intensity detected from the side, σ does not depend on the change in the supplied heat amount but changes depending on the exhaust oxygen concentration. Further, it increases in proportion to D up to a fiber interval of around 40 mm, but thereafter gradually approaches a constant value.

The width T of the trigger pulse will be examined. The pulse generated in the trigger circuit 44a is binarized to compensate for the time of 0 of the flame signal represented by the 0-1 signal and smooth it. That is, if T is lengthened, the combustion range that can be detected expands to the excess air side, but the detection delay during extinguishing becomes longer. Further, in order to shorten T and widen the detectable range, it is necessary to configure a device having a small noise signal so that the threshold value can be set low. Further, in order to improve the S / N, it is effective to increase the number of fibers, use a device having a large light-receiving surface, and use low noise circuit elements.

In the description of the first combustion monitoring sensor, the near infrared light from the combustion flame is detected by using the two fibers 5a and 5b, but the detection end is formed. The number of fibers 5 may be two or more. For example, the number of fibers 5 may be divided into two groups and the installation positions of the groups may be changed, or the incident light to the two fibers may be used as one original signal and the original signals of the two groups may be You may make it take out a differential signal.

[Second Combustion Monitoring Sensor] Next, an embodiment of the second combustion monitoring sensor 25 will be described. With reference to FIG. 1, the second combustion monitoring sensor 25 detects the intensity signal of the radical emission 7 in FIG. That is, the radical emission 7 has a band spectrum that is excellent in the region from purple to blue and is distributed only in the bottom of the combustion chamber. Specifically, OH radicals (310 μm) and CH radicals (430 μm) are the main constituents.

As a result, the second combustion monitoring sensor 25 concerned
Is composed of optical fibers 5c, 5d installed in the wind box 4, a blue filter 29a made of glass or a green filter 29b made of glass, a signal processing device 31 including GaAs photodiodes 30a, 30b and an amplifier. And a signal proportional to the intensity of radical emission 7 is detected signal V
Send as B, VG.

[Air Ratio Control Method] Next, with reference to FIG. 1, an air ratio control method for a gas fired small boiler using the first combustion monitoring sensor 24 according to the present invention will be described. still,
Although the second combustion monitoring sensor 25 is shown in FIG. 1,
Here, the second combustion monitoring sensor 25 is not operated,
It is assumed that the air ratio control is performed only by the first combustion monitoring sensor 24.

Referring to FIG. 1, the premixed gas 26 jetted into the combustion chamber by the fan 16 with the premixer is the burner 2
A flame group of short flame length is formed in the vicinity of and burns. The combustion flame is monitored through the nozzle holes 2b of the burner plate 2a by the optical fibers 5a and 5b installed in the wind box 4. That is, the near-infrared light incident on the two sets of the bundle fibers 5a and 5b arranged at a predetermined interval, for example, 40 mm or more, receives the silicon photodiode 27a,
27b and the like, a subtraction circuit 34, an amplifier circuit, a filter circuit, and the like, which are input to the signal processing device 28, and the flame detection signal V _IR
Is output as Further, the flame detection signal V _IR output from the signal processing device 28 is input to the arithmetic processing unit 22.

On the other hand, the storage device 23 stores data indicating the correspondence relationship between the flame detection signal V _IR obtained by the pre-caging test and the like, and the air ratio and the combustion load factor. And the flame detection signal V _IR from the signal processing device 28 are compared in the arithmetic processing unit 22,
The air ratio signal is input to the air ratio controller 21. The air ratio control device 21 compares the air ratio signal with the set air ratio, and adjusts the rotation speed of the fan drive motor 17 via an air ratio controller so that the difference between the two is zero. Then, the so-called air ratio PI control is performed.

In the first embodiment, the flame detection signal V _IR from the signal processing device 28 is input to the arithmetic processing unit 22, where the flame detection signal V _IR is corrected by the data from the storage device 23, Is input to the air ratio control device 21 as an air ratio detection signal.
Needless to say, the flame detection signal V _IR from the signal processing device 28 may be directly input to the air ratio control device 21 as an air ratio detection signal by omitting the storage device 23 and the storage device 23.

FIG. 14 shows the relationship between the flame detection signal V _IR from the signal processor 28 and the air ratio in the first embodiment, which was measured by an actual machine with the combustion load factor as a parameter. .

As is clear from FIG. 14, the flame detection signal V _IR takes the maximum value in the vicinity of the air ratio 1, and the signal intensity decreases in the case of incomplete combustion and excess air combustion. Further, the change in the signal intensity with respect to the change in the combustion load factor is sufficiently small, so that the flame detection signal V _IR can directly represent the air ratio in a wide range of the combustion load factor, and the flame monitoring sensor. Also functions sufficiently as an air ratio control sensor.

Next, an air ratio control method using the second combustion monitoring sensor 25 will be described. In the above-described embodiment, the air ratio control using the flame detection signal V _IR using near infrared light as the detection light has been described, but in the present embodiment, the glass filters 29a having different transmission wavelength bands, 29b
And a GaAs photodiode 30a, 30b, a signal processing device 31, etc.
A case where the combustion monitoring sensor 24 is also used will be described.

With reference to FIG. 1, 2 arranged in the wind box 4
As in the case of the first combustion monitoring sensor 24, the flame radiation light is incident on the optical fibers 5c and 5d for forming the second combustion monitoring sensor 25 of the set, as in the case of the first combustion monitoring sensor 24.

The flame radiation light incident on the optical fibers 5c and 5d is passed through the glass filter 29a (blue) or 29b (green) having a different transmission wavelength band to generate the radical emission component 7 (that is, CH Only the radical light and the C ₂ radical light) are GaAs photodiodes 30.
The signal processing device 31 is incident on a and 30b.
After amplification and waveform shaping through a and 31b,
The flame detection signals VB and VG are input to the arithmetic processing unit 22.

In the arithmetic processing section 22, the detection signals V _IR and V B
, VG are used to calculate the air ratio detection signal, which is input to the air ratio control device 21.

Also in this embodiment, the air ratio control can be performed only by the two sets of the second combustion monitoring sensors 26 without using the first combustion monitoring sensor 24.

Further, in this embodiment, the arithmetic processing unit 22
Although the air ratio detection signal is output from the air conditioner to the air ratio controller 21, the radical light detection signals VG and VB from the signal processing devices 31a and 31b are directly transmitted to the air ratio controller. You may input it.

Further, in this embodiment, two sets of the second combustion monitoring sensor 25 are used, but it goes without saying that only one of the second combustion monitoring sensors 25 may be used. .

FIGS. 15 and 16 show the flame detection signal V from the signal processing devices 31a and 31b of the second combustion monitoring sensor.
It shows the relationship between B and VG and the air ratio, and shows the result of measurement using an actual machine with the combustion load factor as a parameter.

As is apparent from FIGS. 15 and 16, the flame detection signals VB and VG in this case have maximum values in the vicinity of the air ratio 1, and the signal intensity increases slightly in proportion to the combustion load factor. Therefore, when used as an air ratio detection signal, it is necessary to slightly correct VB and VG according to the magnitude of the combustion load factor.

In the embodiment of the present invention described above, a small boiler using a premixed combustion type multi-port burner is explained as an example, but the present invention is applicable to not only boilers but also furnaces and the like. It can be applied to all combustion devices, regardless of their capacity.

The present invention also relates to the type of fuel used in the device (L
NG, LPG, low calorie gas, kerosene, heavy oil A, light oil, etc.)
And combustion methods (diffusion combustion, premixed combustion, fluidized bed combustion, etc.) can be applied to all devices.

Furthermore, the present invention is applicable to all devices regardless of the flame detection system (flame front, flame side, flame back, etc.) and device control system (proportional control, ON-OFF control, 3 position control, etc.). Can be applied to.

[0068]

The first combustion monitoring sensor according to the present invention has a plurality of optical fibers for receiving flame radiation light and a conversion circuit for converting the incident light from each optical fiber into an electric signal. The signal processing device outputs a differential signal as a flame detection signal. Therefore, the flame can be monitored in a non-contact state with respect to the flame, and the durability and heat resistance are superior to those of the conventional flame detection sensor, and the repair cost and the like can be significantly reduced.

Further, the structure is simpler than that of the conventional flame detection sensor, and it is possible to downsize the device, simplify the system, and reduce the manufacturing cost.

Furthermore, the flame detection signal V _IR has an extremely accurate correlation with the air ratio, and maintains a substantially constant relationship even if the combustion load factor of the device changes. As a result, the first combustion monitoring sensor can also be used as an air ratio sensor, and when it is used, the air ratio does not change depending on the outside air temperature as in the past, but the air ratio is kept constant. It is also possible to perform low level control and low O ₂ control, which enables energy saving such as reduction of blower power.

Similarly, since the air ratio and CO have a constant relationship, they can also be used as a CO sensor and can also prevent incomplete combustion of the combustion device.

In addition, since the flame can be monitored from the back side of the burner, the installation location can be selected relatively freely without being affected by the structure of the can body, and a plurality of burners are attached. Even in a furnace or the like, the air ratio control of the entire furnace can be performed extremely accurately by detecting the flame of one burner.

In addition, since the respective incident light signals from the plurality of optical fibers are subjected to the differential amplification processing and the subtraction processing in the signal processing device and the differential signals of the respective incident light signals are used as the flame detection signal, the disturbance light, etc. Are canceled out, and a highly accurate flame detection signal V _IR can be obtained.

Similarly, the second combustion monitoring sensor according to the present invention includes an optical fiber for receiving flame radiation light, a blue or green filter, and a conversion circuit for converting the incident light passing through the filter into an electric signal. , A signal processing device for amplifying the electric signal from the conversion circuit and outputting it as a flame detection signal. Therefore, it is possible to obtain substantially the same effect as the first combustion monitoring sensor, and it is possible to further simplify the structure of the flame monitoring sensor.

Also, in the air ratio control method of the present invention, the flame signal from the first combustion monitoring sensor is used as the air ratio detection signal, and the air ratio is set by inputting the air ratio detection signal to the air ratio control device. It is configured to be held in the value.
Thus, the air ratio detection signal of the first combustion monitoring sensor is
As described above, the air ratio in the combustion chamber is displayed very accurately, and it does not change significantly depending on the combustion load factor. As a result, highly accurate and stable air ratio control can be performed when the air ratio is in the range of about 1.0 to 1.4.

Even in a combustion device provided with a large number of burners, the air ratio control of the entire device can be performed with high accuracy by the air ratio detection signal V _IR from the combustion monitoring sensor provided in one burner. .

Furthermore, when the first combustion monitoring sensor and the second combustion monitoring sensor are used together, the detection accuracy of the air ratio detection signal is further improved, and stable air ratio control can be performed. As described above, the present invention has excellent practical utility.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a small gas fired boiler in which the present invention is implemented.

FIG. 2 is a block diagram showing a configuration of a first combustion monitoring sensor of the present invention.

FIG. 3 is a circuit diagram showing an example of a signal processing device of a first combustion monitoring sensor.

FIG. 4 shows an irradiation model of flame synchrotron radiation.

FIG. 5 shows a height position L of an optical fiber and an illuminance distribution of flame radiated light.

FIG. 6 shows the relationship between the installation position L of the optical fiber and the illuminance.

FIG. 7 is a perspective view showing a model when light passing through a burner plate is received by an optical fiber.

FIG. 8 shows a light receivable area when an installation angle θ of an optical fiber is 0.

FIG. 9 shows the relationship between the installation angle θ of the optical fiber and the intensity of the received light signal.

10 is a diagram showing output signal waveforms of respective parts in the signal processing device of FIG.

FIG. 11 shows an example of a probability density distribution of flame detection signal levels.

FIG. 12 shows the relationship between the standard deviation δ of the probability density distribution of the signal level with respect to the flame signal P during combustion and the fiber spacing D, with the boiler input as a parameter.

FIG. 13 shows the relationship between the standard deviation δ of the probability density distribution of the signal level with respect to the flame signal P during combustion and the fiber spacing D, with the oxygen concentration as a parameter.

FIG. 14 shows the relationship between the flame detection signal V _IR and the air ratio.

FIG. 15 shows a relationship between a flame detection signal VB and an air ratio of a second combustion monitoring sensor using a blue glass filter.

FIG. 16 is a diagram showing a relationship between a flame detection signal VG and an air ratio of a second combustion monitoring sensor using a green glass filter.

FIG. 17 shows an outline of a boiler system and sensors used in various tests that form the basis of the present invention.

18 is a perspective view of a burner plate in the boiler of FIG.

19 is a diagram showing a temperature transition of each part of the boiler in the boiler of FIG.

FIG. 20 is an explanatory diagram of a method for spectral analysis of flame synchrotron radiation.

FIG. 21 is a diagram showing the results of spectral analysis of flame synchrotron radiation.

FIG. 22 is a diagram showing a temperature distribution on the flame center axis (input parameter).

FIG. 23 is a diagram showing a temperature distribution on the flame center axis (O ₂ concentration parameter).

FIG. 24 is a diagram showing a time average intensity of a flame signal on a flame center axis (input parameter).

FIG. 25 is a diagram showing the time average intensity of the flame signal on the flame center axis (O ₂ concentration parameter).

FIG. 26 is an explanatory diagram showing a method of testing a spatial correlation characteristic of a flame signal.

FIG. 27 is a diagram showing vertical cross-correlation of flame signals.

FIG. 28 is an explanatory diagram of a method for testing a frequency characteristic of a flame signal.

FIG. 29 is a diagram showing a frequency analysis of a flame signal.

FIG. 30 is an explanatory diagram of a method for testing a frequency characteristic of a flame signal using a fiber.

FIG. 31 is a diagram showing a frequency analysis of a flame signal detected using a fiber.

FIG. 32 is a diagram showing the relationship between air ratio, NOx concentration and heat loss in the boiler of FIG.

[Explanation of symbols]

1 ... Boiler 21 ... Air ratio control device 2 ... Burner 21a ... Air ratio setting device 2a ... Burner plate 21b ... Air ratio controller 2b ... Nozzle hole 22 ... Calculation processing part 3 ... Heat exchanger 23 ... Storage device 4 ... Wind box 24 … First
Combustion monitoring sensor 5 Optical fiber 25 Second
Combustion monitoring sensor 6 ... Spectrometer 26 ... Premixed gas 7 ... Radical radiant light 27a ... Silicon photodiode 8 ... Near infrared light 9 ... Silicon photodiode 27b ... Silicon photodiode array 10 ... FFT analyzer 28 ... Signal processing device 11 ... Original signal 29a ... Blue glass filter 12 ... Differential signal 29b ... Green glass filter 14 ... Original signal 30a, 30b ... GaAs photo 15 ... Differential signal diode 16 ... Fan with premixer 31a, 31b
... Signal processing device 17 ... Fan drive motor 32 ... Current / voltage conversion circuit 18 ... Motor controller 33 ... Differential amplification circuit 19 ... Control valve 34 ... Subtraction circuit 20 ... Valve controller 35 ... Follower circuit 36 ... Bypass filter circuit 40 ... Comparator 37 ... Low-pass filter circuit 41 ... Threshold value setting circuit 38 ... Offset signal adding circuit 42 ... Pulse output generating circuit 39a ... Inverting half-wave rectifying circuit 43 ... Pulse inverting circuit 39b ... Inverting adder 44 ... Pulse delay circuit 39 ... Full wave rectifier circuit 44a ... One shot trigger circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hironobu Uchiyama 3-3-3 Yamate-cho, Suita City, Osaka Prefecture Faculty of Engineering, Kansai University (72) Inventor Satoshi Shibata 600-1, Kuze-Denjo-cho, Minami-ku, Kyoto Company Takuma Kyoto Factory

Claims (6)

[Claims] 1. A plurality of optical fibers for receiving radiated light from a flame and a plurality of conversion circuits for converting incident light from each fiber into an electric signal, and detecting differential signals of those electric signals. A combustion monitoring sensor comprising a signal processing device for outputting as a signal. 2. The number of optical fibers is two, the conversion circuit is a circuit including a silicon photodiode, and the electric signal from each silicon photodiode is made a differential signal through a differential amplifier circuit and a subtraction circuit. Claim 1
The combustion monitoring sensor described in 1. 3. The combustion monitoring sensor according to claim 1, wherein the differential signal is an air ratio detection signal or a CO detection signal. 4. An optical fiber for receiving radiated light from a flame, a blue or green filter for passing incident light from the optical fiber, and a conversion circuit for converting the incident light from the filter into an electric signal. A combustion monitoring sensor including a signal processing device that outputs an amplified signal as a detection signal. 5. The combustion device has a plurality of optical fibers for receiving radiated light from a flame and a plurality of conversion circuits for converting incident light from each fiber into an electric signal, and a difference between the electric signals. Providing a combustion monitoring sensor consisting of a signal processing device that outputs a dynamic signal as a detection signal, input the detection signal from the combustion monitoring sensor to the air ratio control device as an air ratio detection signal, and set the air ratio in advance. A method for controlling an air ratio in a combustion apparatus, wherein the supply amount of combustion air is adjusted in a direction to reduce the difference between the above. 6. A combustion device comprising an optical fiber for receiving radiated light from a flame, a blue or green filter for passing incident light from the optical fiber, and a conversion circuit for converting incident light from the filter into an electric signal. A combustion monitoring sensor including a signal processing device that outputs the amplified signal as a detection signal is provided, and the detection signal from the combustion monitoring sensor is input to the air ratio control device as an air ratio detection signal, and pre-setting is performed. A method for controlling an air ratio of a combustion apparatus, wherein the supply amount of combustion air is adjusted in a direction to reduce the difference from the air ratio.