JPH04324022A - Flame detector of burner - Google Patents

Abstract

PURPOSE:To surely detect an incomplete combustion and flame failure without an effect of fluctuation of flame by a method wherein an integrator obtains oscillating power signals from outputs of an optical sensor that detects combustion flame of a burner, and an integrator having a time constant is connected to the output side of the integrator. CONSTITUTION:In a gas firing radiant tube used for a heat treatment furnace, etc., one end of an optical fiber 17 is faced with the inside of an inner tube 2, and an optical sensor 18 is attached on the other end. Direct current components of outputs of the optical sensor 18 are removed by a coupling capacitor to turn the outputs into alternating current voltage signals and the voltage signals are input to an integrator 21 through an amplifier 19 and a rectifier 20 to obtain oscillating power signals. The output side of the integrator 21 is connected to a lower limit comparator 22 and an upper limit comparator 23 via an integrator 28 in which time constant can be optionally set. When an ON-signal is output either from the lower limit comparator 23 that detects a flame failure or the upper limit comparator 23 that detects an incomplete combustion, a fuel shut-off valve 4 is shut by a logic arithmetic device 26.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame detection device for a burner, which can be applied to a radiant tube burner having a double tube structure and achieve good results.

0002

2. Description of the Related Art In burners that burn liquid or gaseous fuels, it is desirable to maintain optimal combustion conditions during combustion. Conventional techniques for this purpose include capturing the light intensity signal generated by the burner flame as an electrical signal using a semiconductor such as a phototransistor, photodiode, or solar cell, or using an electrode inserted into the flame instead of a light sensor. There is a method that uses these output currents to control combustion by using the integrated value of the power spectrum obtained as a result of frequency analysis of the vibration waveform in the flame. In the former of the above conventional techniques, that is, a method in which the light generated from a flame is captured as an electrical signal and processed by an electric circuit, the optical signal generated by the flame is detected by an optical sensor using a semiconductor such as a phototransistor or a photodiode. As can be seen, there is a problem with the location of this optical sensor, and if the location is not appropriate, good control will not be possible.

[0003] Therefore, the present inventor has developed and proposed a technique to solve this problem (Japanese Patent Application No. 1-312
No. 132). In this technology, an optical sensor detects the oscillating light of the combustion flame, but even if the flame length changes due to turndown, it is necessary to detect the entire turbulent combustion part of the flame. A light sensor is provided at the rear. However, depending on the structure of the furnace, it may not be possible to mount the optical sensor on the opposite side of the burner, and the desired effect may not be expected.

[0004] A technique proposed as a technique that does not have this problem is related to Japanese Patent Application No. 1-312133. In this technique, an electrode is inserted into the flame from the nozzle side of the burner and the flame ion oscillation current is detected, so that it is not limited by the structure of the furnace. However, even when trying to detect the ionic current using electrodes, for example, in burners such as radiant tube burners that form a flame inside a double tube and utilize radiation from the outer tube, continuous combustion cannot be achieved. Since the combustion gas is sucked in from the exhaust port with an ejector etc., the flame point changes due to turndown.
There were cases in which specific parts of the flame could not be detected even with electrodes.

[0005] To solve this problem, we have created a burner that forms a flame within a double tube, such as a radiant tube burner, and uses radiation from the outer tube, and
Fig. 2 shows a burner combustion control device that can obtain good results in combustion control even if the combustion gas is sucked in by an ejector or the like from the exhaust port for continuous combustion.
The following has been proposed (Patent application No. 177816/1999)
issue). To explain this simply, this burner has a double pipe structure consisting of an outer cylinder 1 and an inner cylinder 2. A gas nozzle 3 is provided inside the inner cylinder 2, and a fuel cutoff valve 4 is connected to the gas nozzle 3 in the middle. An inspection port 14 is provided at the base of the inner cylinder 2, and a lens 15 is attached to the inner cylinder 2. An optical fiber 17 is attached with one end facing the lens 15, and an optical fiber 17 is attached with one end facing the lens 15. An optical sensor 18 is attached to the other end of the fiber 17, and a logic operator 26 is connected to the optical sensor 18 via a detection circuit for optical vibration power voltage.
The output side of the fuel cutoff valve 4 is connected to the fuel cutoff valve 4.

The optical oscillation power voltage detection circuit 27 includes an amplifier 19 that amplifies the detection output of the optical sensor 18.
, a rectifier 20 that converts the amplified signal into a DC component, and an integrator 21 that obtains a vibration power signal from the rectified signal.
An upper limit comparator 23 and a lower limit comparator 22 compare the vibration power signal obtained by the integrator 21 with values set in advance for each of the upper and lower limits.

[0007]

[Problem to be Solved by the Invention] With such a configuration, the inside of the inner cylinder 2 can be connected to the lens 15 and the optical fiber 1.
7 and can be monitored by the optical sensor 18. The output of the optical sensor 18 is inputted to the logic operator 26 via the optical oscillation power voltage detection circuit, and the opening/closing of the fuel cutoff valve 4 is controlled by the output signal. This means that the above problem has been solved, but there is one more problem. In the above technology, an optical sensor converts the vibration signal of the synchrotron radiation caused by the fluctuation of the combustion flame into an electrical signal, and the rectified integrated voltage value is used as an indicator of the combustion state. It is difficult to say that the handling of these matters was necessarily appropriate.

[0008] Flame fluctuations cause large variations in the rectified integrated voltage value, so in actual combustion using the above technique, a large time constant (approximately 10
seconds), were smoothed. Therefore, when a misfire occurs, it takes about 10 seconds for the rectified integrated voltage value immediately before the misfire to decay to the lower limit reference voltage value 24 of the lower limit comparator 22 for misfire detection. That is, it takes as much as 10 seconds to detect a misfire, which poses a safety problem. If the time constant is shortened, the detection time becomes faster, but since the dispersion of the rectified integrated voltage value increases, when the average value of the rectified integrated voltage approaches the reference voltage value of the upper limit comparator 23 and the lower limit comparator 22. , even if the combustion is within the normal combustion range, it may be detected as incomplete combustion or misfire due to variations.

The present invention has been made in view of this point, and it is an object of the present invention to provide a burner combustion detection device that does not cause any inconvenience due to variations in the rectified integrated voltage value caused by the above-mentioned flame fluctuations. It is something to do.

0010

[Means for Solving the Problems] As a means for solving the above problems, the present invention provides an optical sensor for detecting the combustion flame of a burner, an amplifier for amplifying the detected output of the optical sensor, and an optical sensor for detecting the combustion flame of a burner. A rectifier that converts a signal into a DC component, an integrator that obtains a vibration power signal from the rectified signal, and an upper limit that compares the vibration power signal obtained by the integrator with preset values for each of the upper and lower limits. a logical operator that performs logical operations on the output signals of the comparator, the lower limit comparator, and the upper limit comparator and the upper limit comparator, and controls the operation of the fuel cutoff valve of the burner based on the result;
and an integrator having a time constant connected at a stage subsequent to the integrator and before the upper limit comparator.

[0011]

[Operation] With this configuration, the integrator with a time constant connected to the stage after the integrator that obtains the vibration power signal from the rectified signal and before the upper limit comparator will respond to flame fluctuations. Since a detection time suitable for detecting incomplete combustion and misfire can be obtained without being affected, the problems of the above-mentioned application can be solved. That is, if the burner misfires for some reason, the flame detector must detect the misfire in a short period of time, shut off the fuel cutoff valve, and stop the supply of fuel into the furnace. On the other hand, the incomplete combustion state generally needs to be detected when incomplete combustion continues for a certain period of time.

[0012] This is the case, for example, when the amount of combustion in a certain burner increases or decreases due to load fluctuations. Especially when the amount of combustion increases, there is often a momentary air shortage, which quickly returns to normal combustion. However, a particularly dangerous situation that the flame detector must detect is when there is a complete lack of air in steady-state operating conditions and incomplete combustion continues to occur. Although the detection time required varies depending on the combustion state, the combustion detection device of the present invention can accommodate this.

[0013]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. In this embodiment, the present invention is applied to a gas-fired radiant tube used in a heat treatment furnace, etc., and 1 is an outer cylinder, and 2 is an inner cylinder provided concentrically inside the outer cylinder. A gas nozzle 3 is provided inside the inner cylinder 2, and a fuel supply pipe 5 with a fuel cutoff valve 4 interposed therebetween is connected to the gas nozzle 3, so that gas 6 is supplied. . The outer cylinder 1 is provided with an exhaust gas jetting part 7 on the insertion side of the inner cylinder 2, and an ejector (not shown) connected to the exhaust gas jetting part 7 causes a flame 8 to circulate from inside the inner cylinder 2 into the outer cylinder 1. It is designed to suck in the combustion gas 9 emitted by the engine.

An air supply pipe 10 is provided in a portion of the inner cylinder 2 that protrudes from the outer cylinder 1, from which air 11 for combustion is supplied into the inner cylinder 2. The gas nozzle 3 is inserted into the inner cylinder 2 for an appropriate length, and a swirler 13 is attached around the tip 12 of the gas nozzle 3 so that the air 11 that flows in is swirled. An inspection port 14 is provided at the base of the inner cylinder 2 near the part into which the gas nozzle 3 is inserted, and a heat-resistant lens (convex lens) 15 is mounted inside the port 14 . An optical fiber 17 is attached to the focal point 16 of the lens 15 with one end thereof facing.

An optical sensor 18 is attached to the other end of the optical fiber 17, and is configured to convert the optical signal input from the optical fiber 17 into an electrical signal. The current obtained by the optical sensor 18 is converted into a voltage, and a coupling capacitor removes the DC component, resulting in an AC voltage signal. This alternating current voltage is then input to an amplifier 19 connected to the next stage, where the amplitude is amplified. amplifier 19
A rectifier 20 is connected to the output side of the converter to convert the signal into direct current.

An integrator 21 is connected to the output side of the rectifier 20 and integrates the rectified signal to obtain a vibration power signal. A lower limit comparator 22 and an upper limit comparator 23 are connected to the output side of the integrator 21 via an integrator 28 whose time constant can be arbitrarily set. The lower limit comparator 22 is turned on when the lower limit voltage is lower than this lower limit voltage, and the upper limit comparator 23 is turned on when the upper limit voltage is exceeded, and the output signal of the integrator 20 is sent to the next stage logical operation unit. It is designed to lead to 26.

In this circuit, the circuit from the amplifier 19 to the stage before the input of the logical operator 26 constitutes an optical power voltage detection circuit 27. The logic operator 26 takes the "OR" of the contact signals of the lower limit comparator 22 and the upper limit comparator 23, and if either signal is on "1", the fuel connected in the middle of the gas supply pipe 5 is shut off. It is designed to shut off valve 4.

This combustion control device constructed as described above operates as follows. The fuel control valve 4 opens and the fuel gas 6 is injected from the gas nozzle 3 into the inner cylinder 2.
When mixed with air 11 from an air supply pipe 10 provided in the inner cylinder 2 and combusted, a flame 8 is generated. In this case air 1
1 is swirled by the swirler 13 and mixed well with the gas 6. Combustion gas 9 generated by the flame 8 is sucked from the exhaust gas jetting section 7 by the operation of an ejector (not shown). The outer cylinder 1 becomes red hot due to combustion, and the radiant heat heats the atmosphere around the burner inserted.

The state of the flame 8 can be monitored through the inspection port 14 provided on the opposite side of the inner cylinder 2 from the flame 8, but if it is detected by the optical sensor 18 in this state, it will be an emergency because it is a non-luminous flame. Since only a weak current is obtained and detection is difficult, detection becomes possible by amplifying the optical density using a circuit after the amplifier 19 connected to the lens 15 and the optical sensor 18. Note that the reason why the lens 15 and the optical sensor 18 are not directly coupled is to protect the optical sensor 18 from high temperatures.

The optical sensor 18 converts the optical vibration of the flame 8 into an electrical signal, and only the alternating current component of the signal is passed through a coupling capacitor (not shown). The amplifier 19 amplifies the amplitude of this alternating current signal, which is then converted into direct current by the rectifier 20. The output signal is integrated by an integrator 21 to obtain a vibration power voltage value. This integrator 21 has a circuit configuration in which the time constant can be changed, and the time constant is set according to the required misfire detection time (usually about 2 seconds). The integrated voltage is output to an integrator 28 provided at the input section of 23. The upper limit comparator 23 in this embodiment is for detecting incomplete combustion of the radiant tube burner, and the integrator 28 provided on the input side of the comparator 23 has a variable time constant circuit configuration like the integrator 21. ing. A time constant is set according to the incomplete combustion detection time required by the combustion equipment used, and the oscillating power voltage is output to the upper limit comparator 23.

In the upper limit comparator 23, the upper limit voltage 25 for determining incomplete combustion is set as a reference voltage, and when the vibration power voltage input from the integrator 28 exceeds the upper limit voltage 25, A contact signal that turns on is output to the logic operator 26. On the other hand, a lower limit voltage 24 for determining misfire is set as a reference voltage in the lower limit comparator 22, and a contact is turned on when the vibration power voltage input from the integrator 21 falls below the lower limit voltage 24. The signal is output to the logic operator 26. The logical operator 26 takes the "OR" of the contact signals input from the upper limit comparator 23 for detecting incomplete combustion and the lower limit comparator 22 for detecting misfire, and determines that either contact signal is on and "1". If this happens, the fuel cutoff valve 4 connected midway through the gas supply pipe 5 is shut off to stop the operation. If both the lower limit comparator 22 and the upper limit comparator 23 are off "0", the fuel cutoff valve 4 is maintained in the open state and the operation is continued.

Here, the relationship between CO, O2 and vibration power voltage in the radiant tube burner is shown in FIGS. 3 and 4.
Shown below. The data shown in these figures were measured using butane as the fuel and with a fixed combustion amount. FIG. 3 shows the relationship between O2 and vibration power voltage after burner ignition, and the horizontal axis shows time. When the amount of air is reduced from a state of excess air after burner ignition, the vibration power voltage increases as O2 decreases, reaching a peak around O2 = 4%, and after that, O2
decreases as .

[0023] Here, when O2 is around 1%, that is, when incomplete combustion occurs, the vibration power voltage increases rapidly. This is because the large-amplitude fluctuations of the low-frequency components of the flame increase due to lack of air. FIG. 4 shows the relationship between the vibration power voltage and CO in section D of FIG. 3, and the horizontal axis indicates time. As is clear from this figure, the oscillation power voltage also increases with the rapid rise in CO (that is, incomplete combustion), and the
There is a correlation between O and the vibration power voltage. Here, the reason why the rise in vibration power voltage is slightly delayed with respect to the rise in CO is (
In A) of FIG. 4, the oscillation power voltage has a large variation and is smoothed by a capacitor, and this is due to the delay caused by the capacitor.

As a result of the above, the vibration power voltage becomes B as shown in FIG.
If it is detected that C is above the upper limit and below the lower limit of C, incomplete combustion and misfire can be detected. Since there is no infrared radiation due to the red heat inside the inner cylinder 2 at the time of a misfire, and there is no vibration component, the vibration power voltage becomes 0, and no malfunction (flame detection) occurs. The voltage output from the integrator 21 is input to the lower limit comparator 22 and the upper limit comparator 23. Therefore, the previous lower limit voltage 24 and upper limit voltage 25 are set as reference voltages, and the upper limit comparator 23 voltage 25
If the lower limit voltage 2 is exceeded, the lower limit comparator 22
A contact signal that becomes "on" when the voltage falls below 4 is led to a logical operator 26.

In addition to the embodiments described above, the present invention can be applied to combustion equipment of other structures, and a plurality of comparators for detecting each state are provided according to the characteristics of each. It goes without saying that each detection time can be adjusted by providing an integrator for setting a time constant on the input side of each comparator.

[0026]

As explained above, the present invention includes an optical sensor that detects the combustion flame of a burner, an amplifier that amplifies the detection output of this optical sensor, and a rectifier that converts the amplified signal into a DC component. an integrator that obtains a vibration power signal from the rectified signal; an upper limit comparator and a lower limit comparator that compare the vibration power signal obtained by the integrator with preset values for each of the upper and lower limits; a logical operator that logically operates the output signals of the upper limit comparator and the lower limit comparator and controls the operation of the fuel cutoff valve of the burner based on the result; and a logical operator that is located after the integrator and before the upper limit comparator Since this burner flame detection device is configured to include an integrator with a connected time constant, it has the advantages of the earlier application mentioned above, as well as the detection required for incomplete combustion and misfire. You will be able to adjust your time. Therefore, it is possible to shorten the misfire detection time, which tends to be long in the prior application.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a prior art embodiment of the present invention.

FIG. 3 is a graph illustrating the operation and characteristics of FIG. 1;

[Figure 4] Vibration power voltage and CO in part D in Figure 3
It is a graph showing the relationship between

[Explanation of symbols]

1 Outer cylinder 2 Inner cylinder 3 Gas nozzle 4 Fuel cutoff valve 5 Fuel supply pipe 6 Gas 8 Flame 11 Air 15 Lens 17 Optical fiber 18 Optical sensor 19 Amplifier 20 Rectifier 21 Integrator 22 Lower limit comparator 23 Upper limit comparator 26 Logic operator 27 Optical power voltage detection circuit 28 Integrator

Claims (1)

[Claims] 1. An optical sensor that detects a combustion flame of a burner, an amplifier that amplifies the detection output of the optical sensor, a rectifier that converts the amplified signal into a DC component, and a vibration power signal from the rectified signal. an integrator for obtaining the oscillation power signal obtained by the integrator, an upper limit comparator and a lower limit comparator for comparing the vibration power signal obtained by the integrator with preset values for each of the upper and lower limits, and the upper limit comparator and the lower limit comparator. a logical operator that performs a logical operation on the output signal of the converter and controls the operation of the fuel cutoff valve of the burner according to the result; and an integrator having a time constant that is connected after the integrator and before the upper limit comparator. A burner flame detection device comprising: