JP2576991B2 - Flame detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a flame detection device attached to, for example, an office boiler, and more particularly to prevention of contamination at a light inlet of the device.

[Conventional technology]

It is extremely important to accurately detect the combustion state of various combustion devices such as a large boiler for business use from the viewpoints of safety and economy of the combustion device.

Taking a large boiler for business use as an example, the number of burners installed due to the increase in the capacity of the boiler and the DSS (Daily S
tart Stop) Burner ignition associated with operation,
Due to the adoption of a combustion method for suppressing the generation of nitrogen oxides and changes in combustion behavior accompanying diversification of fuels used, it is desired to further improve the reliability of burner flame detection.

Flame detection methods can generally be broadly classified into an ion flame detection method and an optical flame detection method.

The ion type flame detection method cannot be used continuously for a long time because it uses a flame contact electrode as a sensor.
Usually, it is limited to flame detection for an ignition vaner. On the other hand, the optical flame detection system determines ignition and digestion according to the magnitude of the light emission intensity from the flame, and can be classified into a method of detecting the wavelength used and DC light, and a method of detecting flicker.

2 (a) and 2 (b) are a front view and a cross-sectional view of a tip end of an optical conduit used in a conventional flame detecting device. As shown in FIG. 1, large diameter optical fibers 3, 4, and 5 are mounted inside an optical conduit 1 for detecting an optical signal of a burner flame. The optical signal of the burner flame introduced from the leading end portion is directly extracted to the outside, and is transmitted to a photoelectric converter in a separate cubicle via an optical fiber cable on the way.

At the tip of the optical conduit 1, the radiant heat from the boiler furnace directly hits the light receiving surface of the optical fibers 3, 4, 5 and becomes high temperature, so the optical fibers 3, 4, 5 are stripped off and used in a bare state. It is installed in three directions so that the viewing angles are 0 °, 15 °, and 30 ° as shown in the figure.

Further, in order to prevent a temperature rise due to heat and to prevent dust accompanying the combustion gas from adhering, a primary and a secondary are disposed between the optical conduit 1 and the ceramics cover 9 and between the optical fiber head 2 and the ceramics cover 9. Cooling air 13,1
4 is always flowing.

In the figure, 6 is a head connector, 7 is a connection connector,
8 is an air distribution sleeve, 10 is a cover support, 11 is a contraction nozzle, 12 is cooling air, 17 is a cover slit, and 18 is a gap.

[Problems to be solved by the invention]

In this conventional flame detection device, the air in the atmosphere is pressurized by a centrifugal fan to maintain the differential pressure from the furnace draft, thereby ensuring the cooling air flow rate to the optical conduit 1 and suppressing the temperature rise of the head connector 6. Was.

On the other hand, the light-receiving surfaces of the optical fibers 3, 4, and 5 consist of a small circular polished surface with an outer diameter of 1 mm. If oil drops from the burner or dust in the combustion gas adhere to this light-receiving surface, the amount of transmitted light is significantly reduced. However, it was found that fine dust in the cooling air 12 (primary cooling air 13 and secondary cooling air 14) and fine rust dust in the cooling pipe (not shown) adhered. There was a problem that the amount of light attenuated.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a flame detection device having high reliability over a long period of time.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an optical fiber head for storing an optical signal for introducing an optical signal from a flame, holding the optical fiber in an optical fiber head, and inserting and holding the optical fiber head in a first holding tube with a gap. Further, the first holding tube is connected to the second holding tube.
A flame detecting optical conduit inserted and held in the retaining tube with a gap, and cooling air is supplied from the rear side of the optical conduit, and the cooling air flows through the gaps, respectively. It is intended for a flame detection device to be ejected from the opening side.

A contraction portion such as a contraction nozzle is formed at the tip end opening of the second holding tube, and the tip of the optical fiber is slightly protruded from the optical fiber head by, for example, about 2 mm or more. Features.

〔Example〕

Next, an embodiment of the present invention will be described with reference to FIGS. 1 (a) and 1 (b).

The light pipe 1 is attached to a dedicated seat of the burner assembly, and its tip extends to the vicinity of the burner impeller. The optical fiber head 2 has three optical fibers 3, 4, 5
Are set in directions of viewing angles 0 °, 15 °, and 30 °. The optical signals received by the optical fibers 3, 4, and 5 are transmitted via a head connector 6 and a connection connector 7 having an optical fiber therein, and are extracted to the outside.

The optical fibers 3, 4, and 5 themselves receive the heat from the furnace radiation and the burner flame directly, so the coating is peeled off and attached to the optical fiber head 2 in a bare state, and the ceramic cover 9 applies heat except for the cover slit 17 to the optical fiber head. Is shut off.

On the other hand, a contraction nozzle 11 is provided on the front side of the ceramics cover 9 in order to prevent the dust of the combustion gas and the oil droplets of the burner spray from adhering to the light receiving surfaces of the optical fibers 3, 4, and 5.

The cooling air 12 is pressurized by a centrifugal fan and supplied through an air pipe. The primary cooling air 13 flows through a gap 18 formed outside the ceramics cover 9 by an air distribution sleeve 8 and the inner surface 22 of the ceramics cover 9. Is distributed to the secondary cooling air 14 flowing therethrough, and cools each part by circulation.

The secondary cooling air 14 passes through the cover slit 17 and merges with the primary cooling air 13 before the converging nozzle 11 to form a nozzle slit.
The gas is ejected from the furnace 19 into the furnace, so that dust and spray oil droplets do not enter the inside of the nozzle inner surface 21. The light receiving portions of the optical fibers 3, 4, and 5 are provided with the ceramic cover 9
And has a protrusion 15 of 2 mm or more in a state where a gap is maintained.

Fine particles of cooling air adhering to the light receiving portions of the optical fibers 3, 4, and 5 may reduce the amount of received light in a completely clean state by about 90%. This is because the fine dust that accompanies the cooling air adheres to the tip corners of the optical fibers 3, 4, 5 and grows,
In many cases, it straddles the light receiving surfaces of the optical fibers 3, 4, and 5. That is, the distal end of the optical fiber head 2 has three concave grooves for holding the optical fibers 3, 4, and 5, and the optical fibers 3, 4, and 5 are inserted into the concave grooves, respectively.
Therefore, when the optical fibers 3, 4, and 5 are in contact with the bottom of the groove, the optical fibers 3, 4, and 5 are provided from the bottom side and on the right side of the groove.
, Fine dust tends to adhere from the right side, and it is considered that these are caused by the flow state of the cooling air.

Therefore, it can be said that it is effective to minimize the flow of the cooling air near the light receiving sections in order to minimize the adhesion to the optical fibers 3, 4, and 5 from these phenomena.
For this reason, in the present invention, if the light receiving portions of the optical fibers 3, 4, 5 are made to protrude from the optical fiber head 2 by about 2 mm or more, even if the stagnation of the cooling air occurs at the end face of the optical fiber head 2, even if the optical fibers 3, 4, 5 are generated. , 5 are out of the stagnation, so that there is no adhesion of fine dust, and a decrease in the amount of received light due to the dust can be suppressed.

In addition, it is also possible to install a filter in the cooling air supply system to remove a small amount of fine dust contained in the cooling air.

〔The invention's effect〕

As described above, the present invention first forms the contraction portion at the opening of the tip of the second holding tube, so that dust of the combustion gas, oil droplets sprayed from the burner, etc. can be stored in the second holding tube containing the optical fiber head. Restrict entry into jurisdiction. By further protruding the tip of the optical fiber slightly from the optical fiber head, it is possible to prevent the fine dust adhering to the cooling air from adhering to the receiving surface and growing, thereby providing a reliable flame detection with high detection accuracy. An apparatus can be provided.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are a front view and a cross-sectional view of a light pipe tip according to an embodiment of the present invention, and FIGS. 2 (a) and 2 (b).
FIG. 2 is a front view and a cross-sectional view of a light pipe tip in a conventional flame detection device. 1 ... optical conduit, 2 ... optical fiber head, 3,4,5 ... optical fiber, 8 ... air distribution sleeve, 9 ... ceramics cover, 11 ... contraction nozzle, 12 ... cooling air, 13 ... …
Primary cooling air, 14 ... Secondary cooling air, 15 ... Projection.

Claims (1)

(57) [Claims] An optical fiber for introducing an optical signal from a flame is housed and held in an optical fiber head, and the optical fiber head is inserted and held in a first holding tube with a gap, and further, the first holding tube is connected to the first holding tube. A flame detecting light pipe inserted into and held in the second holding pipe with a gap, cooling air is supplied from the rear side of the light pipe, and the cooling air flows through the gap to form a light beam; In the flame detecting device which is ejected from an end of a conduit, a contraction portion is formed in an opening of a tip of the second holding tube, and a tip of the optical fiber is slightly protruded from the optical fiber head. Flame detector.