JP5539137B2 - Burner flame monitor - Google Patents

Description

  The present invention relates to a flame monitoring device for a burner.

  As this type of prior art, for example, there is one disclosed in Patent Document 1. That is, Patent Document 1 discloses an ultraviolet discharge tube using a metal photoelectric effect and gas amplification. This ultraviolet discharge tube is formed by sealing a pair of electrodes (anode and cathode) and a special gas in an airtight container made of ultraviolet transmissive glass. When a voltage is applied between the anode and the cathode and an ultraviolet photon emitted from a flame or the like enters the cathode in this state, electrons are emitted from the cathode surface by the photoelectron emission effect. And this discharge of electrons is triggered and discharge is started. The ultraviolet discharge tube has a narrow sensitivity wavelength range of about 160 to 300 nm and does not overlap with the wavelength range of visible light, so it is used as a flame detection device or monitoring device.

Patent Document 1 discloses that in such an ultraviolet discharge tube, the duty ratio between application and non-application of voltage (that is, the ratio between the application time of the first voltage and the application time of the second voltage) is variable. Is described. Further, it is described that the background discharge (dark discharge) can be reduced by adjusting the duty ratio.
On the other hand, Patent Document 2 discloses a device for measuring the discharge of an ultraviolet detector when the shutter is closed and opened as a means for determining the lifetime of the ultraviolet detector.

JP-A-63-13297 Japanese Patent Laid-Open No. 2-97823

  By the way, conventionally, it has been known that the ultraviolet discharge tube has a lifetime, and it has been empirically known that it is proportional to the flame detection time. Further, from such empirical knowledge, it has been considered that the life of the ultraviolet discharge tube is due to the deterioration of the electrode and gas in the hermetic vessel excited by receiving ultraviolet photons emitted from the flame. For the purpose of supporting such considerations, several experiments have been conducted in the past, but these were all experiments using a boiler that repeatedly burns for a short time, and the results of these experiments varied widely. So no clear cause was found.

Therefore, the present inventors conducted experiments using a furnace having a plurality of burners having the same structure as a supply source of combustion heat and continuously operating for 24 hours. In this experiment, a plurality of burners were continuously burned for 24 hours under the same conditions, and an ultraviolet discharge tube having the same structure was assigned to each of the plurality of burners. Further, the period of the voltage applied between the anode and the cathode of the ultraviolet discharge tube (that is, between the electrodes) was set to a different value for each ultraviolet discharge tube. Under such conditions, an experiment was performed to detect the flame of the assigned burner by each ultraviolet discharge tube.
As a result, as shown in FIG. 7, it was found that the life of the ultraviolet discharge tube is substantially proportional to the period of the voltage applied between the electrodes of the ultraviolet discharge tube (that is, almost inversely proportional to the frequency). That is, it has been found that the life of the ultraviolet discharge tube is not due to light reception, but is due to the number of discharges (that is, the number of discharges) generated between the electrodes due to light reception.

Referring to FIG. 7 in more detail, the horizontal axis (X axis) indicates the frequency [Hz] of the voltage applied between the electrodes of the ultraviolet discharge tube, and the vertical axis (Y axis) indicates the lifetime [hr] of the ultraviolet discharge tube. . Each plot in FIG. 7 is an average value of the experimental results at each frequency, and approximate expression (1) was obtained from each plot by the least square method.
Y = 374245 * X- ^0.9013 (1)
The present invention has been made on the basis of such experimental results, and an object of the present invention is to provide a flame monitoring device for a burner that can extend the life of an ultraviolet discharge tube.

  In order to achieve the above object, a flame monitoring device for a burner according to one aspect of the present invention detects and monitors the flame of a burner that burns a fuel containing a compound containing hydrogen as a component with a flame. A monitoring apparatus, an ultraviolet discharge tube in which a plurality of electrodes and gas are sealed in a sealed container that transmits at least ultraviolet rays, a voltage applying unit that intermittently applies a voltage between the plurality of electrodes, and State determination means for determining a flame state, and the voltage application means sets the voltage application period as a first period when the state determination means determines that the flame state is an unstable state. When the state determination means determines that the flame state is a stable state, the voltage application cycle is the second cycle, and the second cycle is longer than the first cycle. And

With such a configuration, when the flame is in a stable state, the number of discharges between the electrodes can be reduced compared to when the flame is in an unstable state, thus extending the life of the ultraviolet discharge tube. be able to. In particular, in a furnace based on continuous operation for 24 hours, most of the combustion period is stable. For this reason, when this invention is applied to said continuous operation furnace, the effect of lifetime extension becomes still more remarkable.
The “voltage applying means” corresponds to, for example, a DC power supply 20, a high-frequency oscillation circuit 31, and a low-frequency oscillation circuit 33, which will be described later. Further, the “state determination unit” corresponds to, for example, a state determination unit 40 described later. Furthermore, as the “first period”, for example, a period T1 described later corresponds. As the “second period”, for example, a period T2 described later corresponds.

  In the above-described burner flame monitoring device, the state determining means determines that the flame is in an unstable state when an elapsed time from the ignition of the burner is less than a predetermined value, When the elapsed time is equal to or greater than a predetermined value, the flame state may be determined to be a stable state. With such a configuration, the state of the flame can be determined accurately and easily. Note that the “predetermined value” is, for example, a relationship between the elapsed time from the time of ignition of the burner and the state of the flame is investigated in advance, and the user can arbitrarily set it based on the result of this investigation. This is a possible value. There is a correlation between the time elapsed since the burner was ignited and the state of the flame. Although the flame state immediately after ignition is an unstable state, the flame state tends to become stable as time elapses.

  In the above-described burner flame monitoring device, the state determining means determines that the flame state is an unstable state when the burner tile temperature of the burner is less than a predetermined value, and the burner tile temperature When is equal to or greater than a predetermined value, the flame state may be determined to be a stable state. Here, the “burner tile” is, for example, a fire-resistant cylindrical member for adjusting the shape of a flame. The burner tile is used in a state where it is arranged on the side of the burner where the flame is ejected. “Burner tile temperature” means the internal temperature of the burner tile, the surface temperature thereof, or the temperature in the vicinity thereof. With such a configuration, the state of the flame can be determined accurately and easily.

  In the flame monitoring device for a burner described above, the burner supplies combustion heat to the furnace, and the state determination means is configured such that the internal temperature of the furnace to which combustion heat is supplied by the burner is less than a predetermined value. When it is, it is determined that the state of the flame is an unstable state, and when the internal temperature is equal to or higher than a predetermined value, the state of the flame is determined to be a stable state. With such a configuration, the state of the flame can be determined accurately and easily.

  In the flame monitoring apparatus for a burner described above, the predetermined value may be a value equal to or higher than the ignition point of the fuel. Here, the “ignition point” means the lowest temperature at which ignition occurs even without a fire source. With such a configuration, when there is a possibility of noncombustion, it is determined that the state of the flame is unstable, and when there is no possibility of noncombustion, the state of the flame is stable. Judgment can be made.

  According to the present invention, the life of the ultraviolet discharge tube can be extended.

The figure which shows the structural example of the flame monitoring apparatus 100 of the burner which concerns on embodiment of this invention. The figure which shows the structural example of the ultraviolet discharge tube. The figure which shows an example of the output waveform of the high frequency oscillation circuit 31 and the low frequency oscillation circuit 33. FIG. The figure which shows an example (the 1) of a state judgment means which judges the state of a flame. The figure which shows an example (the 2) of a state judgment means which judges the state of a flame. The figure which shows an example (the 3) of a state judgment means which judges the state of a flame. The figure which shows the experimental result which the present inventors conducted.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that, in each drawing described below, parts having the same configuration and the same function are denoted by the same reference numerals, and repeated description thereof is omitted.
FIG. 1 is a diagram illustrating a configuration example of a burner flame monitoring apparatus 100 according to an embodiment of the present invention. Here, the burner burns a fuel containing a compound containing hydrogen as a component (for example, hydrocarbons such as methane) with a flame (that is, flame combustion), and the flame monitoring device 100. Detects and monitors the flame of this burner.

As shown in FIG. 1, the flame monitoring apparatus 100 includes an ultraviolet discharge tube 10, a DC power supply 20, a high frequency oscillation circuit 31, a low frequency oscillation circuit 33, a state determination unit 40, a switch element 41, a transistor 51, capacitors 53 and 55, a step-up transformer 58, a diode 54, and a resistance element 57.
Among these, the ultraviolet discharge tube 10 is a detector for detecting ultraviolet rays (ie, UV) emitted from the flame of the burner. As shown in FIG. 2, the ultraviolet discharge tube 10 includes, for example, a sealed container 1 that transmits at least ultraviolet light between an inner side and an outer side, and an anode 3 and a cathode 5 that are arranged and sealed in the sealed container 1. And having. The anode 3 and the cathode 5 are arranged to face each other at a certain distance. Further, a gas (for example, a mixture of rare gases such as argon) 7 is enclosed in the sealed container 1 together with the anode 3 and the cathode 5.

  Returning to FIG. 1, the DC power source 20 applies a voltage to the primary side of the step-up transformer 58, and a high voltage generated on the secondary side is between the anode and the cathode of the ultraviolet discharge tube 10 (that is, between the electrodes). To be applied. As will be described later, the voltage output from the DC power supply 20 is converted into, for example, a rectangular wave when the transistor 51 is repeatedly turned on and off. The converted rectangular wave is applied via a step-up transformer 58 to the anode of the ultraviolet discharge tube 10 and one end of a capacitor 53 arranged in parallel therewith. The value of the secondary side voltage of the step-up transformer 58 is, for example, 300 [V]. The capacitance value of the capacitor 53 is, for example, 20 [pF]. The voltage of the DC power supply 20 is, for example, 5 [V].

  The high-frequency oscillation circuit 31 is a circuit that generates a high-frequency waveform signal. For example, as shown in FIG. 3A, the high-frequency oscillation circuit 31 generates a rectangular wave having a period T1 as a high-frequency waveform signal. The low frequency oscillation circuit 33 is a circuit that generates a low frequency waveform signal. For example, as shown in FIG. 3B, the low frequency oscillation circuit 33 generates a rectangular wave having a period T2 as a low frequency waveform signal. Here, T1 <T2. As an example, T1 is 0.05 [second] and T2 is 0.5 [second] (that is, the high-frequency oscillation circuit 31 oscillates, for example, 20 [Hz], and the low-frequency oscillation circuit 33 For example, oscillation of 2 [Hz] is performed).

In FIG. 1, either a high-frequency rectangular wave output from the high-frequency oscillation circuit 31 or a low-frequency rectangular wave output from the low-frequency oscillation circuit 33 is applied to the base of the transistor 51. The transistor 51 is turned on. For example, a high-frequency rectangular wave and a low-frequency rectangular wave have the same H level, and the L level has the same value. The H level is a value equal to or higher than the threshold voltage of the transistor 51, and the L level is a value lower than the threshold voltage of the transistor 51.
The state determination unit 40 determines that the flame state of the burner is either a stable state or an unstable state based on a predetermined determination material. For example, the state determination unit 40 makes the above determination based on the elapsed time from the time of ignition of the burner, the burner tile temperature, the furnace internal temperature (that is, the furnace temperature), or the like.

  More specifically, as shown in FIG. 4, for example, the state determination unit 40 is connected to the time measuring unit 61 so as to be able to send and receive signals by wire or wirelessly. Here, the time measuring unit 61 measures an elapsed time from when the ignition device (not shown) is operated and the burner 70 is ignited (that is, when the burner 70 is ignited). The state determination unit 40 determines the flame state of the burner 70 based on the signal transmitted from the time measuring unit 61 (that is, information related to the elapsed time). For example, the state determination unit 40 determines that the flame state is stable when the elapsed time from the ignition of the burner 70 is 5 [min] or more, and the elapsed time is less than 5 [min]. If it is, it is determined that the flame is in an unstable state.

  Alternatively, for example, as shown in FIG. 5, a temperature measuring unit 81 is disposed in the burner tile 71, on the surface thereof, or in the vicinity thereof, and the state determination unit 40 communicates signals with the temperature measuring unit 81 by wire or wirelessly. Connected to send and receive. Here, the burner tile 71 is a refractory cylindrical member for stabilizing a flame by returning a part of heat generated by combustion to the flame base. For example, as shown in FIG. 5, the burner 70 is fixed in a through hole that penetrates the furnace wall 91 by a fixing tool 73, and a burner tile 71 is attached to the tip of the burner 70 (that is, a flame injection port). . The tip of the burner tile 71 faces the inside (that is, the inside of the furnace) 92 of the furnace so that the flame can be released toward the inside of the furnace 92 while holding the flame.

  The temperature measuring unit 81 measures the internal temperature of the burner tile 71 or the surface temperature thereof or a temperature in the vicinity thereof (that is, the burner tile temperature), and transmits a signal indicating the measurement result to the state determining unit 40. To do. The state determination unit 40 determines the flame state of the burner 70 based on a signal transmitted from the temperature measurement unit 81 (that is, information related to the burner tile temperature). For example, when the burner tile temperature is 760 [° C.] or higher, the state determination unit 40 determines that the flame state is stable, and when the burner tile temperature is lower than 760 [° C.] Is determined to be unstable. Here, 760 [° C.] is a value equal to or higher than the ignition point of the fuel (for example, natural gas) supplied to the burner 70. The temperature measuring unit 81 is, for example, a thermocouple.

  Alternatively, for example, as shown in FIG. 6, a temperature measuring unit 83 is disposed in the furnace 92, and the state determining unit 40 is connected to the temperature measuring unit 83 so that signals can be transmitted and received by wire or wirelessly. The temperature measuring unit 83 is, for example, a thermocouple. Based on the signal transmitted from the temperature measuring unit 83 (that is, information related to the furnace temperature), the flame state of the burner 70 is determined. For example, the state determination unit 40 determines that the flame state is stable when the furnace temperature is 760 [° C.] or higher, and flame when the furnace temperature is less than 760 [° C.]. Is determined to be unstable.

  Alternatively, the state of the flame may be determined by combining any two or more information of the elapsed time, the burner tile temperature, or the furnace temperature. For example, the state determination unit 40 has an elapsed time of 5 [min] or more from the time of ignition of the burner 70 and a burner tile temperature (or furnace temperature) of 760 [° C.] or more. Determines that the flame is in a stable state, and otherwise determines that the flame is in an unstable state. In other words, the state of the flame is judged by looking at both time and temperature. As another example, the state determination unit 40 determines that the flame state is stable when both the burner tile temperature and the furnace temperature are equal to or higher than 760 [° C.], and otherwise. Judges that the flame is unstable. That is, the state of the flame is determined by looking at the temperatures at a plurality of locations.

  Next, the connection relationship of each element of the flame monitoring apparatus 100 shown in FIG. 1 will be described. The positive electrode of the DC power supply 20 is connected to the collector of the transistor 51 via the primary side of the step-up transformer 58, and the secondary side of the step-up transformer 58 is connected to the capacitor 53 and the ultraviolet discharge tube 10 via the diode 54. Further, the positive electrode of the DC power supply 20 is selectively connected to either the input side terminal of the high frequency oscillation circuit 31 or the input side terminal of the low frequency oscillation circuit 33 via the switch element 41. It has become. The switch element 41 and the state determination unit 40 are connected so that signals can be transmitted and received by wire or wirelessly, and the connection destination of the switch element 41 is switched based on a control signal output from the state determination unit 40. Yes.

  The cathode of the ultraviolet discharge tube 10 is connected to one end of the capacitor 55 and one end of the resistance element 57. The other ends of the capacitors 53 and 55, the other end of the resistance element 57, and the emitter of the transistor 51 are connected to the negative electrode of the DC power supply 20, respectively. Note that the negative electrode of the DC power supply 20 is fixed at, for example, a ground potential. The output side terminal of the high frequency oscillation circuit 31 and the output side terminal of the low frequency oscillation circuit 33 are respectively connected to the base of the transistor 51.

Next, an operation example of the flame monitoring apparatus 100 shown in FIG. 1 will be described.
As described above, when the state determination unit 40 determines that the flame state is an unstable state based on the elapsed time from the time of ignition of the burner, the temperature of the burner tile, the temperature in the furnace, or the like, the switch element 41 Is connected to the high-frequency oscillation circuit 31, and the positive electrode of the DC power supply 20 is connected to the input-side terminal of the high-frequency oscillation circuit 31 via the switch element 41. As a result, the high-frequency oscillation circuit 31 oscillates at a frequency of 20 [Hz], for example, and the transistor 51 is repeatedly turned on and off in synchronization with the frequency of 20 [Hz]. When the transistor 51 is repeatedly turned on and off in synchronization with the frequency of 20 [Hz], the positive electrode and the negative electrode of the DC power supply 20 are short-circuited in synchronization with the frequency of 20 [Hz]. As a result, the voltage output from the DC power supply 20 is converted into a high voltage pulse with a period of, for example, 20 [Hz] by the step-up transformer 58, and the converted voltage is stored in the capacitor 53 via the diode 54, and ultraviolet discharge Applied to the anode of tube 10.

  On the other hand, when the state determination unit 40 determines that the flame state is a stable state, the switch element 41 is connected to the low frequency oscillation circuit 33, and the positive electrode of the DC power supply 20 is connected to the low frequency oscillation circuit 33 via the switch element 41. Connected to the input terminal. As a result, the low-frequency oscillation circuit 33 oscillates at a frequency of 2 [Hz], for example, and the transistor 51 is repeatedly turned on and off in synchronization with the frequency of 2 [Hz]. When the transistor 51 is repeatedly turned on and off in synchronization with the frequency of 2 [Hz], the positive electrode and the negative electrode of the DC power supply 20 are short-circuited in synchronization with the frequency of 2 [Hz]. As a result, the voltage output from the DC power supply 20 is converted into a high voltage pulse with a period of, for example, 2 [Hz] by the step-up transformer 58, and the converted voltage is stored in the capacitor 53 via the diode 54, and ultraviolet discharge is performed. Applied to the tube 10.

  In this way, the state determination unit 40 is released from the excited OH radicals in the flame regardless of whether the state of the flame is determined to be unstable or determined to be stable. As shown in FIG. 2, photoelectrons are emitted from the cathode 5 of the ultraviolet discharge tube 10 and the emitted photoelectrons are accelerated by the voltage between the electrodes, as shown in FIG. Proceed toward. Since this ultraviolet chemiluminescence has high energy peculiar to flames, it can be clearly distinguished from infrared visible light emitted from a red hot furnace wall or the like, so that only the flame can be reliably detected. Photoelectrons traveling while accelerating toward the anode 3 collide with gas molecules enclosed in the ultraviolet discharge tube 10, ionize them, and emit other electrons. As the electrons repeat acceleration and collision in this way, a current (that is, a discharge current) i flows between the electrodes, and the charge stored in the capacitor 53 shown in FIG. 1 is released. Then, a short time pulse voltage is generated at both ends of the capacitor 55 and both ends of the resistance element 57.

  In addition, the electric charge stored in the capacitor 53 is consumed by this discharge, the voltage between the electrodes of the ultraviolet discharge tube 10 falls below the discharge sustaining voltage (that is, the voltage capable of sustaining the discharge), and the discharge stops. The capacitor 53 is charged again when a rectangular wave voltage is applied, and the voltage across the capacitor 53 rises. As a result, the voltage between the electrodes of the ultraviolet discharge tube 10 becomes equal to or higher than the discharge start voltage (that is, the voltage at which discharge can be started), and can be discharged by the incidence of ultraviolet rays. By repeating this, the ultraviolet discharge tube 10 outputs the presence or absence of ultraviolet rays as a pulse voltage. This pulse voltage is output from the output terminal 59. The flame monitoring device 100 detects a flame based on the pulse voltage output from the output terminal 59.

As described above, according to the embodiment of the present invention, when the flame state is stable, the number of discharges between the electrodes can be reduced compared to when the flame is unstable. The life of the ultraviolet discharge tube 10 can be extended. For example, by extending the voltage application period when it is determined to be in a stable state by 10 times from 0.05 [seconds] to 0.5 [seconds], the lifetime during that time can be extended by about 10 times. Thereby, the lifetime improvement of the ultraviolet discharge tube 10 is realizable. In particular, in a furnace based on 24-hour continuous operation, the effect of extending the life is even more remarkable because most of the combustion period is in a stable state.
When the flame is in an unstable state, flame detection is likely to blow out, and unburned gas is generated, increasing the risk of explosion. Measures are necessary.

  On the other hand, when the flame is in a stable state, non-detection of the flame does not directly lead to blow-off. Since there is no unburned gas and there is no danger of explosion, the measure is not urgent. However, the non-detection of the flame when it is in a stable state should be monitored because if the flame is extinguished, hydrocarbons, aldehydes, carbon monoxide, etc. due to incomplete combustion may be produced and the cleanliness of the exhaust may be impaired. Is necessary. Therefore, by changing the voltage application cycle in the stable state to be longer than the application cycle in the unstable state, the burner safety and exhaust cleanliness and the UV discharge tube Longer life can be achieved at the same time.

  In the above embodiment, as the “plurality of electrodes” enclosed in the sealed container, the anode 3 and the cathode 5 are arranged in a state of being opposed to each other. This is just an example. In the present invention, a plurality of anodes 3 and cathodes 5 may be arranged in one sealed container 1. Alternatively, one of the anode 3 and the cathode 5 may be arranged, and a plurality of the other may be arranged. In any case, if the anode 3 and the cathode 5 are arranged to face each other at a certain distance, an ultraviolet photon is incident on the anode 5, thereby causing a current (ie, discharge current) i between the electrodes. Therefore, the same effect as the above embodiment can be obtained.

DESCRIPTION OF SYMBOLS 1 Airtight container 3 Anode 5 Cathode 7 Gas 10 Ultraviolet discharge tube 20 DC power supply 31 High frequency oscillation circuit 33 Low frequency oscillation circuit 40 State judgment part 41 Switch element 51 Transistor 53, 55 Capacitor 57 Resistance element 59 Output terminal 61 Timekeeping part 70 Burner 71 Burner tile 73 Fixing tool 81, 83 Temperature measuring unit 91 Furnace wall 92 Furnace 100 Flame monitoring device

Claims (5)

A flame monitoring device for detecting and monitoring the flame of a burner for burning a fuel containing a compound containing hydrogen as a component with a flame,
An ultraviolet discharge tube in which a plurality of electrodes and gas are enclosed in a sealed container that transmits at least ultraviolet rays;
Voltage application means for intermittently applying a voltage between the plurality of electrodes;
A state determining means for determining the state of the flame,
The voltage applying means includes
When the state determining unit determines that the flame state is an unstable state, the voltage application cycle is the first cycle, and when the state determining unit determines that the flame state is a stable state Is the second application cycle of the voltage,
The burner flame monitoring apparatus, wherein the second period is longer than the first period. The state determination means includes
When the elapsed time from the time of ignition of the burner is less than a predetermined value, the state of the flame is determined to be unstable, and when the elapsed time is greater than or equal to a predetermined value, the state of the flame is stabilized. It is judged that it is in a state, The flame monitoring device of a burner according to claim 1 characterized by things. The state determination means includes
When the burner tile temperature of the burner is less than a predetermined value, it is determined that the state of the flame is an unstable state,
The burner flame monitoring apparatus according to claim 1, wherein when the burner tile temperature is equal to or higher than a predetermined value, the flame state is determined to be a stable state. The burner supplies combustion heat to the furnace,
The state determination means includes
When the internal temperature of the furnace to which combustion heat is supplied by the burner is less than a predetermined value, it is determined that the flame is in an unstable state, and when the internal temperature is equal to or higher than a predetermined value, The burner flame monitoring apparatus according to claim 1, wherein the flame state is determined to be a stable state.   The burner flame monitoring apparatus according to claim 3 or 4, wherein the predetermined value is a value equal to or higher than a firing point of the fuel.

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