JPH0526976Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical conduit for a flame detector, and in particular, to an optical conduit for a flame detector suitable for detecting the flame of a burner using an optical fiber in a boiler furnace. It concerns conduits.

[Conventional technology]

FIG. 2A is a front view of the optical conduit for a flame detector devised by the inventors, and FIG. 2B is a partial sectional view in the axial direction thereof.

In FIGS. 2A and 2B, inside the light pipe 1, a head cover 9 is supported coaxially with the light pipe 1 by a plurality of head cover supports 10, and the inner surface of the light pipe 1 and the outer surface of the head cover 9 are supported coaxially with the light pipe 1. An annular gap 18 is provided between the two. The optical fiber head 2 is inserted inside the head cover 9.

The optical fiber head 2 includes an optical fiber 3 whose detection direction of the flame of the burner is 0° with respect to the horizontal;
An optical fiber 4 having an angle of 15° and an optical fiber 5 having an angle of 30° are arranged in a vertical line. A vertically long slit 17 is provided at the tip of the head cover 9 so that the light from the burner flame enters the optical fibers 3 to 5.

Since the light pipe 1 is provided in the boiler furnace near the burner, it is cooled by the cooling air 12. This cooling air 12 flows through the annular gap 18 between the inner surface of the optical conduit 1 and the outer surface of the head cover 9, and the primary cooling air 13 flows between the inner surface of the head cover 9 and the outer surface of the optical fiber head 2. The secondary cooling air 14 is distributed by an air distribution sleeve 8 to the flowing secondary cooling air 14 . The primary cooling air 13 is blown out from the annular gap 18, and the secondary cooling air 14 is blown out from the vertically long slit 17 in the head cover 9, parallel to the axis of the light pipe 1, into the boiler furnace. ing.

In this way, the end surfaces of the optical fibers 3 to 5 of the light pipe 1 are connected to the vertically long slits 17 of the head cover 9.
, the primary cooling air 13 and the secondary cooling air 14 blowing out from the annular gap 18 and the slit 17.
This protects the boiler from dust contained in the combustion gas in the boiler furnace and from oil droplets sprayed from the burner.

[Problem that the invention attempts to solve]

The above technology is effective when the boiler fuel is LNG, but may not be effective when burning heavy oil with low _NOx . In addition, if the draft inside the furnace fluctuates during normal operation of the boiler or when starting or stopping, unburned carbon contained in the combustion gas and oil droplets sprayed from the burner jump into the head cover 9. It may adhere to the tip surfaces of the optical fibers 3 to 5.

This is a light pipe 1 through which primary cooling air 13 flows.
The shape of the cross section perpendicular to the central axis of the light pipe 1 suddenly changes from an annular shape to a circular shape with the outer circumference of the annular shape as the circumference at the tip of the light pipe 1, so that the primary cooling air 13
The cross-sectional area through which the primary cooling air 13 flows rapidly increases, the flow velocity of the primary cooling air 13 decreases, and the flow becomes turbulent. In addition, as this flow velocity decreases and the secondary cooling air 14 flows through the inside of the primary cooling air 13 whose flow is turbulent, the flow of the primary cooling air 13 is further turbulent and a vortex is generated. This is because unburned carbon and oil droplets are drawn in.

For this reason, the signal level of the burner flame detected by the optical fibers 3 to 5 decreases, resulting in a problem that it is necessary to periodically clean the tip surfaces of the optical fibers 3 to 5.

The purpose of this invention is to create an optical conduit for a flame detector in which unburned carbon contained in combustion gas and oil droplets sprayed from a burner are not caught up in the cooling air and attached to the tip surface of the optical fiber. It is about providing.

[Means for solving problems] The above object is achieved by the following means.

That is, just as the tip of the cylindrical head cover 9 is narrowed from a circular shape to a vertically long slit 17, the tip of the cylindrical light pipe 1 is narrowed from a circular shape to a vertically long slit. Then, the shape of the slit 17 at the tip of the head cover 9 and the shape of the slit at the tip of the light pipe 1 are made similar.

In addition, the inner surface 22 of the slit at the tip of the light pipe 1 and the inner surface 22 of the slit 17 at the tip of the head cover 9
are made parallel to the central axis of the light pipe 1, and the lengths of the inner surfaces of both slits are made longer in the direction of the central axis of the light pipe 1.

[Effect]

By narrowing the tip of the light pipe 1 and the tip of the head cover 9 from a circular shape to a slit shape, the cross-sectional area through which the primary cooling air 13 flows and the secondary cooling air 1 are reduced.
Since the cross-sectional area through which the cooling air 4 flows decreases, both the flow velocity of the primary cooling air 13 and the flow velocity of the secondary cooling air 14 increase. In addition, since the shape of the slit at the tip of the light guide tube 1 and the shape of the slit at the tip of the head cover 9 are almost similar, the inside of the primary cooling air 13 flowing through the slit of the light guide tube 1 is controlled by the head cover 9. Even if the secondary cooling air 14 ejected from the slit 17 flows and the primary cooling air 13 and the secondary cooling air 14 merge, the primary cooling air 13
The flow will not be disturbed or vortices will occur.

Furthermore, the inner surface 2 of the slit at the tip of the light pipe 1 and the inner surface 2 of the slit 17 at the tip of the head cover 9
2 are made parallel to the central axis of the optical pipe 1, and the inner lengths of both slits are made longer in the direction of the central axis of the optical pipe 1, so that the primary cooling air is condensed by both slits. Air 13 and secondary cooling air 14
Neither the flow is disturbed nor the generation of vortices occurs.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1A and 1B. FIG. 1A is a front view of the optical conduit for a flame detector of the present invention, and FIG. 1B is a partial sectional view in the axial direction. The same reference numerals are used, and the explanation will be omitted since it will be redundant.

In Fig. 1 A and B, a cylindrical light pipe 1
Just as the tip of the cylindrical head cover 9 is narrowed from a circular shape to a vertically long slit 17, the tip is narrowed to a vertically long slit 19 to form a contracting flow nozzle 11, which is used for primary cooling. The flow velocity of the air 13 is increased. This contraction nozzle 1
The front shape of the slit 19 in No. 1 is almost similar to the front shape of the slit 17, but since the flame detection direction of the optical fiber 5 is 30° with respect to the horizontal,
The upper edge 20 of the slit 19 is not constricted, and the tube wall of the cylindrical light pipe 1 is extended as it is.

Furthermore, the inner surface 22 of the slit 17 and the inner surface 21 of the slit 19 are both parallel to the central axis of the light pipe 1, and both have a length in the direction of the central axis of the light pipe 1, that is, the depth of the slits 17 and 19. ing. Thereby, the flow of the primary cooling air 13 and the secondary cooling air 14 after contraction is not disturbed, and no vortices are generated. Note that the ratio of the depth of the slits 17 and 19 to the width of the slit in the horizontal direction, depth/width, is preferably 1.5.

Furthermore, the height H of the optical fiber head 2 is reduced, making it easier for the secondary cooling air 14 to pass through. This compensates for insufficient contraction of the primary cooling air 13 due to the upper edge 20 of the slit 19 not being constricted, that is, insufficient increase in the flow velocity of the primary cooling air 13. .

In addition, although the case where the flame of a burner is detected in a boiler furnace has been described, it can also be applied to measures for preventing contamination of a television camera for monitoring the inside of a boiler furnace, an image fiber, etc.

[Effect of idea]

According to the present invention, the flow of the primary cooling air and the secondary cooling air is not disturbed and no vortices are generated, so that unburned carbon and sprayed oil droplets are not caught inside the head cover. Therefore, the end face of the optical fiber does not get dirty and the level of the flame detection signal does not decrease, so there is an effect that there is no need to periodically clean the end face of the optical fiber.

[Brief explanation of the drawing]

Figure 1A is a front view of the light pipe for a flame detector of the present invention, Figure 1B is a partial sectional view in the axial direction, and Figure 2A is a front view of the light pipe for a flame detector devised by the inventors. Figures 2 and 2B are partial sectional views in the axial direction. 1... Optical conduit, 2... Optical fiber head, 3~
5...Optical fiber, 6...Head connector, 7...
...Connection connector, 8...Air distribution sleeve, 9...
...Head cover, 10...Head cover support stand,
11... Contraction nozzle, 12... Cooling air, 13...
...Primary cooling air, 14...Secondary cooling air, 17,
19...Slit, 8...Gap, 20...Top edge,
21, 22...inner side.

Claims (1)

[Scope of utility model registration request] An optical fiber through which light from a flame in the furnace passes is housed in an optical fiber head, the optical fiber head is inserted into a head cover with a gap therebetween, and the head cover is further inserted into an optical conduit with a gap between the optical fiber head and the optical fiber head. cooling air flowing through a gap between the head cover and the light pipe; and cooling air flowing through a gap between the head cover and the light pipe.
In the flame detector light pipes, each of which has a structure in which flame is ejected into the furnace from an opening at the tip of the head cover, the opening at the tip of the head cover and the opening at the tip of the light pipe are shaped like vertically long slits that are substantially similar in shape. The light guide tube has a narrow shape, and is arranged so that the central axis of each of the slit-like openings and the inner surface of the opening are substantially parallel to the central axis of the light pipe. Light conduit for flame detector.