JP2009128011A - Cooling structure for optical-type measuring probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling structure for optical-type measuring probe which can contribute to stable measurement for a long time by efficient cooling and also by preventing staining of an observation window. <P>SOLUTION: The cooling structure for optical-type measuring probe has an inner tube 21, which holds an LDV probe 22 emitting and receiving laser light 4 and makes cooling air circulate in the inside; an outer tube 26 which forms a cooling jacket 27 supplied with cooling water in a space between the inner tube 21 and it; the observation window 30 which is provided in front of the LDV probe 22; a slit part 31 which jets purging air onto the front side of the observation window 30; and a radiation shielding plate 33, which partially covers the observation window 30 and is so formed that the relation between the disposition diameter R of the slit part 31 in the radial direction of the observation window 30 and the diameter r of a hole 33a is R>r. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cooling structure for an optical measurement probe, and more particularly to a cooling structure for an optical measurement probe such as a laser Doppler velocimeter (hereinafter abbreviated as LDV) that measures the behavior of particles in a high temperature field such as a furnace. It is useful.

  Combustion in the furnace of pulverized coal, which is widely used as a fuel for thermal power generation, is a combustion that does not exist in gas combustion or liquid combustion, such as diffusion of pulverized coal particles into the gas phase, release of volatile matter, volatile matter combustion, and char combustion. It is a very complex phenomenon that occurs simultaneously while the processes interact. Therefore, development of combustion technology for pulverized coal at present is often carried out by empirical engineering, which not only involves complicated experiments but also requires a great deal of cost and time.

  For efficient promotion of such pulverized coal combustion technology development, it is necessary to grasp the particle behavior such as the particle velocity in the flame without disturbing the combustion field. There is an LDV as one of the most suitable measuring devices for such applications. This LDV is a device that measures the velocity of particles at a point (focal point) where the laser beams intersect without disturbing the flow using a plurality of laser beams, and the laser beams are emitted from the LDV probe toward the observation target. Therefore, when the distance from the furnace wall to the point at which the particle velocity is measured is longer than the distance (focal distance) from the LDV probe to the focal point of the laser beam, the LDV probe needs to face the furnace in a high temperature field. . For this reason, it is necessary to insert the LDV probe into a high-temperature field such as a furnace while being integrated with some cooling means.

  Note that Patent Documents 1 and 2 can be cited as publicly known documents disclosing similar techniques relating to this type of measurement.

Japanese Patent Laid-Open No. 11-166941 Japanese Patent Laid-Open No. 06-308140

  As described above, the LDV probe applied when observing the behavior of particles during pulverized coal combustion in a furnace is suitable not only for optical components that are vulnerable to high temperatures but also for performing high-precision measurements. Cooling is necessary. Further, in order to continuously and satisfactorily emit and enter laser light, it is necessary to prevent the observation window from being contaminated as much as possible.

  An object of the present invention is to provide a cooling structure for an optical measurement probe capable of contributing to stable measurement over a long period of time by preventing the observation window from being soiled together with efficient cooling.

The first aspect of the present invention for achieving the above object is as follows:
The optical measurement probe that supports the optical measurement probe that emits and / or emits light from the front surface via a support member and distributes the cooling gas introduced from the rear end in the axial direction toward the front end. An inner cylinder that is in contact with the outer peripheral surface of
An outer cylinder that forms a cooling jacket that surrounds the outer peripheral surface side of the inner cylinder and is supplied with a cooling liquid in a space between the outer peripheral surface and the inner peripheral surface;
An observation window of a transparent member disposed in front of the optical measurement probe in the inner cylinder;
A slit portion that faces the front end of the inner cylinder and injects the gas from the outer peripheral side to the front side of the observation window;
An annular member having a hole formed in a central portion for allowing emission or incidence of the light, disposed in front of the slit portion to partially cover the observation window, and in a radial direction of the observation window In the cooling structure of the optical measurement probe, there is provided a radiation shielding plate configured such that the relationship between the arrangement diameter R of the slit portion and the diameter r of the hole satisfies R> r.

The second aspect of the present invention is:
In the cooling structure of the optical measurement probe described in the first aspect,
In the cooling structure of the optical measurement probe, the diameter of the hole of the radiation shielding plate is configured to be slightly larger than the diameter of the emitted or incident light.

The third aspect of the present invention is:
In the cooling structure of the optical measurement probe described in the first aspect or the second aspect,
The slit portion is configured to cool the optical measurement probe, wherein the gas is jetted in parallel to the surface of the observation window.

The fourth aspect of the present invention is:
In the cooling structure for an optical measurement probe according to any one of the first to third aspects,
The optical measurement probe is a laser Doppler velocimeter probe, and has a cooling structure for an optical measurement probe.

  According to the present invention, the optical measurement probe is directly cooled by the cooling gas introduced into the inner cylinder, and the gas is indirectly cooled by cooling the gas through the inner cylinder with the coolant flowing through the cooling jacket. In addition, the optical measurement probe can be cooled. As a result, effective cooling of the optical measurement probe can be performed.

  At the same time, since the cooling gas is jetted to the front side of the observation window through the slit portion, contamination due to adhesion of coal ash or the like to the observation window can be effectively prevented. Here, a radiation shielding plate configured so that the relationship between the arrangement diameter R of the slit portion and the diameter r of the hole is R> r is disposed in front of the observation window, and thus is ejected from the slit portion. The cooling gas is discharged toward the high temperature field through the hole without entraining fouling substances such as coal ash floating in the vicinity of the radiation shielding plate. As a result, fouling substances in the vicinity of the radiation shielding plate can be prevented from adhering to the observation window, and the observation window can be more reliably prevented from fouling. Furthermore, the radiation shielding plate can block part of the radiation from the high temperature field that is not the object of measurement, and effectively prevent the observation window due to radiant heat and the temperature of the optical measurement probe from rising.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. This embodiment is applied to an LDV probe for observing the behavior of pulverized coal particles in a pulverized coal boiler. Of course, the present invention is not limited to LDV to LDV probes. An optical measurement device or an optical measurement probe that involves light emission or incidence can be applied suitably.

  FIG. 1 is an explanatory view conceptually showing a pulverized coal boiler to which a cooling structure of an LDV probe according to the present embodiment is applied. As shown in the figure, the furnace 1 is supplied with pulverized coal as fuel. The pulverized coal supplied into the furnace 1 is burned by the flame 3 formed by the burner 2 to generate steam. An LDV probe (not shown in FIG. 1) housed inside the cooling structure I according to this embodiment is an observation window (not shown in FIG. 1) for observing the behavior of pulverized coal burned by the flame 3. Is directed to the flame 3 so that the tip portion faces the furnace 1 and is disposed on the furnace wall. Accordingly, portions of the cooling structure I and the LDV probe facing the furnace 1 are exposed to a high temperature environment.

  Here, an LDV system to which the cooling structure of the present embodiment is applied will be described. FIG. 2 is an explanatory diagram showing an optical system of the LDV system. As shown in the figure, the optical system includes a light transmitting system lens 5 for introducing laser light 4, a light receiving system lens 6 for scattered light, and scattered light (laser light 4) collected by the light receiving system lens 6. It is comprised with the optical fiber 7 sent out (not shown). Here, the laser beam 4 is separated into two by a beam splitter (not shown) and is condensed by a light transmission system lens 5, and the intersection has a light and dark interference fringe of light intensity. This is point 8. The particles following the flow 9 passing through the measurement point 8 scatter light corresponding to the interference fringes, and the scattered light is transmitted to the measurement unit via the light receiving system lens 6, whereby an electric signal (Doppler burst signal) is obtained. The particle velocity is determined by obtaining the frequency (fd [1 / s]).

  FIG. 3 shows the relationship between the details of the measurement point 8 and the Doppler burst signal. As shown in FIG. 5A, when the polarization planes of the two laser beams 4 and 4 coincide with each other, the measurement volume (elliptical region in the figure) 10 is interfered with the wavefront of the incident laser beam 4. In the horizontal direction, bright and dark interference fringes 11 are formed. The interval (δf [m]) between the interference fringes 11 is geometrically determined by the wavelength of the laser beam 4 and the crossing angle of the two laser beams 4 and 4. On the other hand, as shown in FIG. 5B, the peak portion of the Doppler burst signal corresponds to the bright portion of the interference fringe 11, and therefore, by obtaining the peak-to-peak interval Δt (= 1 / fd). The velocity of the particles 12 can be measured. That is, the velocity V of the particle 12 is given by the following equation.

      V = δf · fd = δf / Δt

  FIG. 4 is an explanatory view showing the cooling structure of the LDV probe according to the present embodiment, which protects the LDV probe for measuring the flow velocity of the particles 12 based on the measurement principle as described above, in a longitudinal section. In this case, the LDV is a backscattering LDV in which the light receiving system is also on the laser side.

  As shown in FIG. 4, the inner cylinder 21 supports the LDV probe 22 via a support member 23, and has an air inlet 25 that passes through a lid portion 24 that closes the rear end thereof and is fixed to the lid portion 24. is doing. The cooling air introduced into the inner cylinder 21 is configured to circulate along the axial direction toward the front end side as indicated by solid arrows in the drawing. As a result, the outer peripheral surface of the LDV probe 22 is cooled in direct contact with the cooling air. Here, the LDV probe 22 emits two laser beams 4 from the front surface so that they intersect at the measurement point 8, and backscattered light at the measurement point 8 is incident from the front surface. Via a measurement unit (not shown).

  The outer cylinder 26 surrounds the outer peripheral surface side of the inner cylinder 21 and forms a cooling jacket 27 in a space between the outer peripheral surface of the inner cylinder 21 and the inner peripheral surface of the outer cylinder 26. Cooling water is supplied to the cooling jacket 27 through a cooling water supply port 28. The cooling water supplied into the cooling jacket 27 circulates through the cooling jacket 27 as indicated by the dotted arrows in the figure, and is then discharged to the outside through the cooling water discharge port 29. As a result, the LDV probe 22 is indirectly cooled by cooling the cooling air through the inner cylinder 21 with the cooling water flowing through the cooling jacket 27.

  The observation window 30 is made of quartz glass, which is a transparent member, and is disposed in front of the LDV probe 22 in the inner cylinder 21. Specifically, the observation window 30 is formed between the support member 32 having a hole 32 a for allowing the cooling air that has circulated through the inner cylinder 21 to flow toward the slit portion 31 and the front end portion of the cooling jacket 27. The outer peripheral part is clamped. As a result, the laser beams 4 and 4 irradiated from the LDV probe 22 are irradiated to the measurement point 8 through the observation window 30 and the observation window as backscattered light reflected by the particles 12 on the flow 9 at the measurement point 8. The light is incident on the LDV probe 22 via 30. The backscattered light incident on the LDV probe 22 is sent to a remote measurement unit (not shown) via the optical fiber 7. At the same time, the observation window 30 also has a function of reducing the temperature rise of the LDV probe 22 by attenuating radiation from a high temperature field (in the furnace) including the measurement point 8.

  The slit portion 31 faces the front end of the inner cylinder 21 and injects cooling air from the outer peripheral side of the observation window 30 to the front side. Thus, fouling substances (coal ash in the case of pulverized coal boilers) floating in a high temperature field such as a furnace are prevented from adhering to the surface of the observation window 30 and fouling the surface of the observation window 30. . That is, the cooling air sprayed through the slit portion 31 is also used as a purge gas for the pollutant. With this structure, the attenuation of the laser beams 4 and 4 at the observation window 30 can be reduced as much as possible.

  Here, the slit part 31 in this embodiment is configured such that cooling air is jetted in parallel to the surface of the observation window 30. By configuring in this way, it is possible to most effectively prevent fouling substances from attaching to the surface of the observation window 30. However, this configuration is not essential. This is because a certain degree of adhesion preventing function to the surface of the observation window 30 can be obtained by injecting air from the outer peripheral side of the observation window 30 to the front side.

  The radiation shielding plate 33 is an annular member in which a hole 33a for allowing the emission or incidence of the laser beams 4 and 4 is formed in the central portion, and is disposed in front of the slit portion 31 so as to cover the observation window 30. It covers the part. Here, the relationship between the arrangement diameter R of the slit portion 31 and the diameter r of the hole 33a in the radial direction of the observation window 30 is configured such that R> r. Thereby, the cooling air sprayed from the slit portion 31 is discharged toward the high temperature field through the hole 33a without involving the high temperature gas in the vicinity of the radiation shielding plate 33 or the like. As a result, it is possible to prevent contamination of the observation window 30 more reliably by preventing contact of the fouling substances such as coal ash and particles 12 in the vicinity of the radiation shielding plate 33 with the observation window 30. Further, the radiation shielding plate 33 can block part of the radiation from the high temperature field that is not the object of measurement and effectively prevent the temperature of the observation window 30 and thus the LDV probe 22 from rising due to radiant heat. Here, the diameter r of the hole 33a is configured to be slightly larger than the diameter of the emitted or incident laser beams 4 and 4. As a result, the radiation shielding by the radiation shielding plate 33 can be performed most efficiently.

  In this embodiment, the LDV probe 22 irradiates the laser beams 4 and 4 and receives the scattered light through the observation window 30. At this time, cooling air is supplied to the inner cylinder 21 inside the cooling jacket 27 so as to flow along the surface of the LDV probe 22 to enhance the cooling effect. The cooled air is jetted from the slit portion 31 to the front side of the observation window 30, thereby preventing fouling substances such as coal ash from adhering to the surface of the observation window 30. Further, the opening portion of the hole 33a of the radiation shielding plate 33 disposed at a position slightly away from the observation window 30 is a final outlet of the cooling air, and its radius r is equal to that of the slit portion 31. It is smaller than the arrangement diameter R. In this way, by restricting the air outlet at a position slightly away from the observation window 30, the entrainment of external gas or the like can be satisfactorily prevented. By preventing such entrainment, adhesion of the coal ash particles 12 to the observation window 30 can also be prevented. In addition, it is desirable for the inner peripheral surface of the part from the slit part 31 to the hole 33a to become the R part for this entrainment prevention effect. This is because it is possible to reduce the generation of vortices in this portion and reliably prevent the entry of pollutants from the outside.

  Furthermore, since the diameter r of the hole 33a of the radiation shielding plate 33 is the minimum radius through which the laser beams 4 and 4 can pass, radiation from a portion unrelated to the measurement object can affect the LDV probe 22. It can be made as small as possible. By reducing the amount of radiant heat from the surroundings entering the LDV probe 22, there is an effect of suppressing the temperature rise of the LDV probe 22. Further, radiation from the surroundings adversely affects the LDV measurement. However, by blocking a part of the radiation with the radiation shielding plate 33, the possible range of LDV measurement can be expanded. Incidentally, the radiation from the surroundings becomes noise when receiving scattered light from the measurement object. In addition, the incidence of radiation inside the LDV probe 22 raises the temperature of the optical components inside the LDV probe 22, causing problems such as the optical axes of the lasers 4 and 4 being displaced and the measurement volume being reduced. However, such a problem can be avoided.

  The present invention can be used in the industrial field of manufacturing and selling measuring instruments for observing the behavior of particles in a high temperature field.

It is explanatory drawing which shows notionally the pulverized coal boiler to which the cooling structure of the LDV probe which concerns on embodiment of this invention is applied. It is explanatory drawing which shows the optical system of a LDV system. It is explanatory drawing which shows the relationship between the detail of the measuring point in a LDV system, and a Doppler burst signal. It is explanatory drawing which shows the cooling structure of the LDV probe which concerns on embodiment of this invention in a longitudinal cross-section.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace 8 Measuring point 11 Interference fringe 12 Particle | grain 21 Inner cylinder 22 LDV probe 23 Support member 26 Outer cylinder 27 Cooling jacket 30 Observation window 31 Slit part 33 Radiation shielding board 33a Hole

Claims (4)

The optical measurement probe that supports the optical measurement probe that emits and / or emits light from the front surface via a support member and distributes the cooling gas introduced from the rear end in the axial direction toward the front end. An inner cylinder that is in contact with the outer peripheral surface of
An outer cylinder that forms a cooling jacket that surrounds the outer peripheral surface side of the inner cylinder and is supplied with a cooling liquid in a space between the outer peripheral surface and the inner peripheral surface;
An observation window of a transparent member disposed in front of the optical measurement probe in the inner cylinder;
A slit portion that faces the front end of the inner cylinder and injects the gas from the outer peripheral side to the front side of the observation window;
An annular member having a hole formed in a central portion for allowing emission or incidence of the light, disposed in front of the slit portion to partially cover the observation window, and in a radial direction of the observation window And a radiation shielding plate configured such that a relationship between an arrangement diameter R of the slit portion and a diameter r of the hole satisfies R> r. In the cooling structure of the optical measurement probe according to claim 1,
A cooling structure for an optical measurement probe, wherein the diameter of the hole of the radiation shielding plate is configured to be slightly larger than the diameter of the emitted or incident light. In the cooling structure of the optical measurement probe according to claim 1 or 2,
The cooling structure for an optical measurement probe, wherein the slit portion is configured to eject the gas in parallel to the surface of the observation window. In the cooling structure of the optical measurement probe according to any one of claims 1 to 3,
The optical measurement probe is a laser Doppler velocimeter probe, and has a cooling structure for an optical measurement probe.