JP2913048B2 - Flame detection electrode and flame detection device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a burner used for an oil fan heater, a water heater, or the like, which monitors a flame state by measuring a flame current to detect an abnormality. And a flame detecting device using the same.

[Conventional technology]

In burners such as oil fan heaters and water heaters, there has been a type for detecting a flame current as a sensor for detecting a flame (for example, see Japanese Patent Application Laid-Open No. 57-108519).

As shown in FIG. 9, a flame detection electrode 15 made of a metal bar is arranged on the upper surface side of a metal burner 20, and an AC voltage of about 100 V is applied between the flame detection electrode 15 and the burner 20. An AC power supply 30 is provided so as to apply an electric current. When a flame 50 is generated, a minute flame current of about several tens μA flows through the flame 50, and this current is detected by the ammeter 40. I was

Further, when the flame 50 is incompletely burned, the flame current becomes a low value.
The presence / absence of the generation of 50 and the state of combustion can be detected, and the energization control to the ignition heater 60, the control of the fuel supply amount, and the like are performed according to the value of the flame current.

[Problems of the prior art]

However, since the conventional flame detection electrode 15 as described above requires conductivity, a metal material such as a Kanthal wire or a Ni—Cr wire is used, and the heat resistance is low. Therefore, the surface is easily oxidized and has a short life,
It had to be quite thick to stay within 50. In addition, for example, Si contained in a barber spray or the like adheres, and an insulating layer of SiO ₂ is formed on the surface, which may make it impossible to detect a flame current.

[Means for solving the problem]

In view of the above, the present invention relates to a method of burying a conductor in a ceramic body made of any one of silicon nitride, alumina, mullite, and forsterite, which has a volume resistivity of 10 ⁹ Ωcm or less at a temperature of 800 ° C. or more. It is a detection electrode, and it has been discovered that ceramics, which is originally an insulator, can be used as an electrode for detecting flame current if the volume resistivity at 800 ° C is 10 ⁹ Ωcm or less. is there. Furthermore, the electric conductor can be made to function as an ignition heater by generating heat by energizing the conductor.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 (a) is an exploded perspective view of the flame detecting electrode 10,
Forming a conductor 10c by printing a paste made of a refractory metal such as tungsten or molybdenum, or a carbide, nitride, boride, or silicide of a transition element from group IVa, Va, or VIa on the surface of the unfired ceramic plate 10a. Then, another fired ceramic plate 10b is overlapped so as to cover the conductor 10c and fired and integrated. The conductor 10c has a single linear shape, is led out from the rear end by a lead wire 10d, and has a large area at the front end so that a flame current can easily flow.

Also, as shown in FIG. 1 (b), the ceramic plates 11a, 1a
1b may be a semi-cylindrical shape to constitute a rod-shaped flame detecting electrode 11, or a rod-shaped flame detecting electrode formed by winding a green sheet on which a conductor is printed around an extruded rod-shaped ceramic molded body. Can also be configured. Further, although not shown, a linear body such as a tungsten wire may be embedded as the conductors 10c and 11c.

The ceramic plate 10a, 10b, 11a, as the material of 11b, as a Si ₃ N ₄ main component, periodic table IIb, IIIa, IIIb, IV
Compounds of group b elements, such as silicon nitride ceramics to which a sintering aid such as MgO, Y ₂ O ₃ , Al ₂ O ₃ , ZrO ₂ is added, or SiO ₂ , ZrO ₂ with Al ₂ O ₃ as a main component Alumina ceramics to which CaO, MgO or the like is added is used. These silicon nitride ceramics and alumina ceramics have a large volume resistivity at room temperature of 10 ¹⁴ Ωcm or more, but at 800 ° C, they all fall to about 10 ⁸ Ωcm, and a small flame current flows. It is. In addition to these, mullite (3Al ₂ O ₃ .2SiO ₂ ), forsterite (2MgO.SiO ₂ )
It is also possible to use ceramics such as ₂ ).

Next, a flame detection device using such a flame detection electrode 10 will be described. As shown in FIG. 2, on the upper surface side of the burner 20,
The flame detection electrode 10 and the ignition heater 60 are arranged, and an AC power supply 30 and an ammeter 40 are connected between the flame detection electrode 10 and the burner 20. No current flows at all without the flame 50, but the ignition heater 60 ignites, and when the flame 50 is generated, the flame current flows between the flame detection electrode 10 and the burner 20, so the flame current is detected by the ammeter 40. At this point, ignition is recognized, and a signal to cut off the power supply to the ignition heater 60 is issued. Thereafter, the combustion state is monitored by the current value of the flame current, and control and stop of the fuel supply amount and the like can be performed.

Thus, the use of the flame detection electrode 10 of the present invention allows
The presence or absence of 50 and the state of the flame 50 can be monitored, and since the surface is made of ceramics having excellent heat resistance, the life is long and there is no fear of thermal deformation.

Next, as another embodiment of the present invention, a description will be given of a flame detecting electrode which also serves as an ignition heater.

The flame detecting electrode 12 whose exploded perspective view is shown in FIG. 3 is made of a refractory metal such as tungsten or molybdenum, or a high melting point metal such as IVa, Va, V
A U-shaped conductor 12c is formed by printing a paste made of a carbide, nitride, boride, or silicide of a group Ia transition element, and then another unsintered ceramic plate 12b is laminated and integrally fired. It is. The conductor 12c is U-shaped, and both ends are led out by lead wires 12d and 12e.
Conductor 12c generates heat by energizing between d and 12e,
It can be used as an ignition heater. In this case, when the ceramic plate 12a, 1a
As 2b, those using silicon nitride ceramics having high thermal shock resistance were excellent.

Next, such a flame detection electrode 12 also serving as an ignition heater
A flame detection device using the method will be described. As shown in FIG. 4, the flame detection electrode 12 is arranged on the upper surface side of the burner 20, and the flame detection electrode 12 is placed between the two lead wires 12d and 12e.
When the AC wire 31 is connected through the two switches 70 and 71 and the switch 70 is switched, the AC power supply 30 and the ammeter 40 are connected between the flame detection electrode 12 and the burner 20. Has become. First, the switches 70 and 71 are set to the states shown by solid lines, and the flame detection electrode 12 is energized from the AC power supply 31 to generate heat. At this time, the temperature of the flame detection electrode 12 is 1000 ° C.
The temperature rises as described above, and acts as an ignition heater. Then the flame
When 50 occurs, the switches 70 and 71 are switched to the states shown by the broken lines, and the AC power supply is connected between the flame detection electrode 12 and the burner 20.
The voltage is applied by 30, and the flame current flowing through the flame 50 is detected by the ammeter 40, and the state of the flame 50 can be monitored.

In this case, the timing at which the switches 70 and 71 are switched becomes a problem, but the switching timing may be determined as follows. For example, when the flame detection electrode 12 is operated as an ignition heater, a constant current flows. However, when the flame 50 is generated, the current value decreases rapidly, so that the switches 70 and 71 are switched at this time. Good. In addition, a timer is set in addition to the switch 70, after a certain period of time has elapsed since the start of energization of the flame detection electrode 12 or the start of the supply of vaporized fuel.
7l can be switched.

Another method of using the flame detecting electrode 12 shown in FIG. 3 will be described. As shown in FIG. 5, the flame detecting electrode 12 is disposed on the upper surface side of the burner 20 and two lead wires are provided.
An AC power supply 30 and a switch 70 are connected between 12d and 12e, and this circuit is connected to the burner 20 via an ammeter 40. First, if the switch 70 is closed as shown by the solid line, the AC power supply 30 supplies electricity to the flame detection electrode 12 to generate heat and act as an ignition heater. When the flame 50 is generated, a flame current is generated between the flame detection electrode 12 and the burner 20, and when the current is detected by the ammeter 40, the switch 70 is turned off, and the flame detection electrode 12 acts as an ignition heater. After that, it is sufficient to operate only for detecting the flame current.

As described above, when the flame detection electrode 12 shown in FIG. 3 is used, since it also serves as an ignition heater, it is not necessary to separately arrange an ignition heater, and a simple structure can be achieved.

In the above-described embodiment, one conductor 12c is used for both heat generation and flame current detection, but may be formed separately. That is, the flame detecting electrode 13 shown in FIG. 6A has a similar structure to the flame detecting electrode 12 shown in FIG. 3, but has a linear flame current detecting conductor 13c and a U-shaped. The heat generating conductors 13d are separately formed, and one end of the flame current detecting conductor 13c is led by a lead wire 13e, and both ends of the heat generating conductor 13d are led by lead wires 13f and 13g.

As yet another example, as shown in FIGS. 6 (b) and 6 (c), a flame detecting electrode 14 having a multilayer structure can be formed.
That is, a U-shaped heating conductor 14e is formed on the upper surface of the unfired ceramic plate 14, and a linear flame current detection conductor 14d is formed on the lower surface, and the unfired ceramic plate 14b is formed from the upper surface side.
The unfired ceramic plates 14c are stacked from the lower surface side and fired and integrated, and one end of the flame current detection conductor 14d is led out with a lead wire 14f, and the heat generation conductor 14e.
Are led out by two lead wires 14g and 14h.

Next, a flame detection device using these flame detection electrodes 13 and 14 will be described. As shown in FIG. 7, the flame detecting electrode 13 is disposed on the upper surface side of the burner 20, and the heat generating conductor 13 is provided.
The AC power supply 31 and the switch 70 are connected between the lead wires 13f and 13g from which d is derived, and the AC power supply 30 and the ammeter 40 are connected between the lead wire 13e and the burner 20 from which the conductor 13c for flame current detection is derived. ing. First, the switch 70 is closed, and electricity is supplied to the flame detection electrode 13 to generate heat. When a flame 50 is generated and the flame current is detected by the ammeter 40, the switch 70 is turned off to function as an ignition heater. The operation may be stopped, and thereafter, only the electrode for detecting the flame current may be operated.

In the above embodiment, the burner 20 and the flame detecting electrode 1 were used.
Although the flame current between 0, 11, 12, 13, and 14 is shown, when used for a burner made of a non-conductive material such as a ceramic burner, two flame detecting electrodes are used. To detect the flame current. For example, as shown in a schematic plan view in FIG. 8, a flame detecting electrode 13 having a heating conductor buried on the upper surface side of a burner 20 made of ceramic and a flame detecting electrode 10 having no heating conductor buried therein.
May be arranged at an interval of 1 mm or more, and an AC power supply 30 and an ammeter 40 may be connected between these flame detecting electrodes 10 and 13. In this way, when a flame is generated in the space between the flame detection electrodes 10 and 13, a flame current can be detected. Further, the flame detecting electrode 13 is also used as an ignition heater, and can be ignited by energizing with an AC power supply 31.

In the above embodiment, both of the two flame detecting electrodes are formed by embedding a conductor in a ceramic body. However, one is a conventional flame detecting electrode made of a metal wire, and the other is a ceramic detecting electrode. May be used as a flame detection electrode in which a conductor is embedded.

Experimental Example 1 Here, a prototype of the flame detecting electrode 10 shown in FIG. 1A was actually manufactured, and a use test was conducted with a conventional one made of a Kanthal wire. Both are incorporated in a flame detection device as shown in FIG. 2 and are set so that the AC power supply 30 is set to 100 V and a power supply cutoff signal to the ignition heater 60 is output when a power supply of 10 μA is detected. After energizing the ignition heater 60, the time from when ignition was detected to when the energization of the ignition heater 60 was cut off was measured. The results are shown in Table 1.

The flame detection electrode 10 of the present invention has a width of 3.1 mm,
One using silicon nitride ceramics having a thickness of 1.6 mm and one using alumina ceramics having a width of 6 mm and a thickness of 1 mm were prepared.

From Table 1, it can be seen that even with the flame detection electrode 10 of the present invention using ceramics, the flame current can be detected and a signal to cut off the power supply to the ignition heater 60 can be issued. Incidentally, in the flame detection electrode 10 of the present invention, the time until the energization to the ignition heater 60 is cut off is long, because it takes time until the ceramic layer becomes high temperature and the resistance value decreases. In actual use, there is no particular problem within 30 seconds.

Experimental Example 2 Next, a prototype of the flame detection electrode 12 of the type combined with the ignition heater shown in FIG. 3 was manufactured, and a use test was conducted by arranging it as shown in FIG. As the flame detection electrode 12, a material in which a conductor made of TiN paste was embedded in a silicon nitride ceramic having a cap of 3.1 mm and a thickness of 1.6 mm was used.

When the AC power supply 31 was set to 100 V and the electrode 12 for flame detection was energized, a current of 0.38 A flowed before ignition, but 0.30 A after ignition.
Since the current suddenly drops to 6 A, this current drop point was set as the timing for switching the switches 70 and 71. In this way, it is possible to ignite only with the flame detection electrode 12, and
After the occurrence of 50, the switches 70 and 71 were switched, and the flame current could be detected by the ammeter 40 within one second after the switching.

In this case, since the ceramic layer was previously heated to a high temperature and the resistance was reduced, it is considered that when the switches 70 and 71 were switched, the ceramic layer could immediately function as a flame detection electrode.

Experimental Example 3 Next, a use test was performed on a flame detection device using two flame detection electrodes as shown in FIG. Instead of the flame detecting electrode 10 in FIG. 8, a conventional one made of a metal wire is used, and the other flame detecting electrode 13 has a conductor made of TiN embedded in a silicon nitride ceramic body. , The two flame detection electrodes were arranged in parallel at a height of 6 mm from the burner 20 with an interval of 5 mm.

This flame detection device was able to ignite by the action of the flame electrode 13 also serving as an ignition heater, and was able to detect a flame current within one second after ignition.

Experimental Example 4 Further, the most basic flame detecting electrode 10 shown in FIG. 1 (a) was trial-produced by embedding a conductor made of TiN in a silicon nitride ceramic body, and this was shown in FIG. A test was conducted in which a barber spray was sprayed during combustion with the apparatus incorporated in the indicated flame detector. As a comparative example, a similar test was performed using a flame detection electrode made of a Kanthal wire.

As a result, in the case of the comparative example, when spray was sprayed on the flame detection electrode, an insulating layer of SiO ₂ was formed on the surface, the flame current could not be detected, the fuel supply was stopped, and the flame 50 was extinguished. . In contrast, the flame detection electrode 10 of the present invention
When sprayed, a SiO ₂ layer was similarly formed on the surface, but the flame current could be detected and the fuel state was not stopped. This is because the initial volume resistivity of the Kanthal wire is as small as 10 ° Ωcm, so the resistance value rises sharply by the SiO ₂ insulating layer, making it impossible to detect the flame current. 10 ⁸
This is because, since it has a large volume resistivity of Ωcm, the change in resistance value is small even if an insulating layer of SiO ₂ is generated.

Further, even without spraying, a SiO ₂ layer is formed on the surface of the flame detection electrode during long-term use, but according to the above test results, the flame detection electrode of the present invention has a longer length. It turns out that it becomes available for a period.

〔The invention's effect〕

As described above, according to the present invention, a conductor is embedded in a ceramic body made of any one of silicon nitride, alumina, mullite, and forsterite having a volume resistivity of 10 ⁹ Ωcm or less at a temperature of 800 ° C. or more. Since the surface is made of ceramics by forming the flame detecting electrode in this manner, it has excellent heat resistance, a long life, and is free from deformation. In addition, by using such a substance having a relatively large resistance value, even if an insulating layer such as SiO ₂ is formed on the surface, it is less likely to be adversely affected. Furthermore, if the electric conductor is energized to generate heat, it can also serve as an ignition heater, so that the structure can be simplified and the reaction speed of flame detection can be increased. And a flame detection device.

[Brief description of the drawings]

1 (a) and 1 (b) are exploded perspective views showing a flame detecting electrode according to an embodiment of the present invention, and FIG. 2 is FIG. 1 (a).
It is a schematic side view which shows the flame detection apparatus using the electrode for flame detection shown in (b). FIG. 3 is an exploded perspective view showing another embodiment of the present invention, and FIG.
FIG. 5 and FIG. 5 are schematic side views each showing a flame detecting device using the flame detecting electrode shown in FIG. 6 (a) and 6 (b) are exploded perspective views showing still another embodiment of the present invention, and FIG. 6 (c) is a sectional view taken along line XX in FIG. 6 (b). FIG. 7 is a schematic side view showing a flame detecting device using the flame detecting electrodes shown in FIGS. 6 (a) and 6 (b). FIG. 8 is a schematic plan view showing another embodiment of the flame detecting device of the present invention. FIG. 9 is a schematic side view showing a conventional flame detecting device. 10, 11, 12, 13, 14 ... electrode for flame detection 20 ... burner 30, 31 ... AC power supply 40 ... ammeter 50 ... flame

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F23N 5/12

Claims (4)

(57) [Claims] A silicon nitride, an alumina, a mullite, having a volume resistivity of not more than 10 ⁹ Ωcm at a temperature of 800 ° C. or more;
And an electrode for flame detection in which a conductor is buried in a ceramic body made of any one of the following. 2. A conductor for flame current detection, a conductor for heat generation, or a conductor serving as both, is buried in a ceramics body having a volume resistivity of 10 ⁹ Ωcm or less at a temperature of 800 ° C. or more. A flame detecting device, comprising: a flame detecting electrode formed on the upper surface of a burner. 3. Silicon nitride, alumina, mullite, and the like having a volume resistivity of not more than 10 ⁹ Ωcm at a temperature of 800 ° C. or more.
And a means for measuring a current flowing between the flame detecting electrode and the burner, wherein a flame detecting electrode formed by burying a conductor in a ceramic body made of any one of the flame detecting electrode and the forsterite is disposed on the upper surface side of the burner. Flame detector. 4. A device for arranging two flame detecting electrodes on the upper surface side of a burner, means for measuring a current flowing between these flame detecting electrodes, and at least one of the two flame detecting electrodes. One of which is made of silicon nitride, alumina, mullite, which has a volume resistivity of 10 ⁹ Ωcm or less at a temperature of 800 ° C. or more;
A flame detecting device characterized in that a conductor is buried in a ceramic body made of any one of a ceramic and a forsterite.