JP2005172636A - Dust meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the influence on a measurement result due to waterdrops formed from a condensed water vapor and attached to a surface of an optical element facing a gas duct, after driving over a long time. <P>SOLUTION: A photocatalyst TiO<SB>2</SB>layer 23 is applied to a surface, exposed to a space which is connected to the gas duct of a collimating lens 8, a reflection plate 14 and a reflecting mirror 10. Light sources 24a, 24b, 26, 28a, 28b are provided in the vicinity of the collimating lens 8, the reflecting plate 14 and the reflecting mirror 10 and turned to the surfaces of these, so as to irradiate an ultraviolet light. Water vapor, attached to the surfaces on the gas duct side of the collimating lens 8, the reflecting plate 14 and the reflecting mirror 10, will not turn into waterdrops, but will turn into a thin film by the action of the photocatalyst layer 23. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dust meter for continuously monitoring the concentration of dust contained in exhaust gas flowing through a flue in a thermal power plant or the like using attenuation of light by dust.

  A dust meter that continuously measures the amount of dust in the flue is equipped with a light projecting / receiving unit composed of a light source and a light detector, and a reflecting mirror placed opposite to the light source across the flue. Using the fact that the light passes through the flue, is reflected by the reflector, and is attenuated by dust in the flue before passing through the flue and entering the photodetector again, A dust meter that measures the amount of dust (concentration) contained in the exhaust gas is known (see Non-Patent Document 1).

In a dust meter, the optical elements of the light transmitting part exposed in the space leading to the flue include optical elements such as a light projecting / receiving part window, a reflecting mirror, and a zero reflecting mirror for obtaining reference light. Purge air is sent from the outside using instrumentation air or blower to prevent dust, fine particles, dust, water vapor including mist from adhering to the road and causing contamination.
VDI (Verein Deutscher Ingenieure) 2066 Part4 Japanese Unexamined Patent Publication No. 7-31155

  However, the dust meter is a device that operates continuously for 24 hours, and there is also water vapor (including dust and sulfuric acid mist components, etc., which also passes through the purge air after a long time). Therefore, when the water vapor condenses and grows, dirt is generated on the surface of the optical element, and as a result, the substantial transmittance of the optical element changes. The principle of the dust meter is to determine the amount of dust from the amount of light reduction that occurs when the passing light beam is absorbed or scattered by dust in the flue, so that dirt adheres to the surface of the optical element through which the measurement light beam passes. If the measurement light beam is scattered or refracted by the dirt component, the apparent transmittance of the flue changes, and as a result, a dust concentration different from the actual dust concentration is output.

  In view of the above, an object of the present invention is to reduce the influence of dirt attached to the surface of an optical element exposed to a space leading to a flue after a long operation on the measurement result.

  The present invention provides a light projecting / receiving unit including a light source and a light detector, and a reflecting mirror that is disposed so as to face the light source through a flue and reflects the light projected by the light source so as to enter the light detector. The light emitted from the light source passes through the flue and is reflected by the reflecting mirror and is detected by the photodetector, and the dust concentration in the flue is measured based on the attenuation of the light. The dust meter is characterized in that a transparent photocatalyst layer is attached to the surface of the optical element exposed in the space connected to the flue with respect to the wavelength band of the measurement light.

An example of the photocatalyst used in the present invention is TiO ₂ . The following points can be mentioned as the catalytic action of TiO ₂ .
(1) Decomposition removal action of organic matter.
(2) A so-called anti-fogging effect that prevents water adhering to the object surface from forming a water droplet as a thin uniform film due to super hydrophilicity.
When the TiO ₂ photocatalyst is applied to the surface of the optical element, the wettability is increased by its anti-fogging action, and the water generated as a result of cooling and dew condensation of the water vapor diffused from the flue does not form water droplets, and a uniform thin film Become.

  In order to enhance the above action, it is preferable to provide a light source for irradiating light of a wavelength that enhances the catalytic function of the photocatalyst toward the photocatalyst layer in the vicinity of the optical element.

  By attaching the photocatalyst to the surface of the optical element exposed to the space leading to the flue, the water vapor that has diffused from the flue is cooled and condensed. Therefore, the measurement light flux is not scattered or refracted by the water droplet, and the measurement of the transmittance in the flue (dust concentration measurement) is not greatly affected.

  If a light source for irradiating light that enhances the catalytic function of the photocatalyst toward the surface of the optical element is provided in the vicinity of the optical element, the action of decomposing and removing the organic matter works, so that the effect of the photocatalyst can be further enhanced.

One embodiment will be described below. FIG. 1 is a diagram showing a configuration of a dust meter according to an embodiment.
Reference numeral 18 denotes a duct that forms a flue therein, and two mounting flanges 16a and 16b are provided on the side wall portion of the duct 18 so as to face each other. , 22b, the light projecting / receiving unit 3 and the reflector head 11 are mounted.

  The light projecting / receiving unit 3 is composed mainly of the light source 2 and the photodetector 4, and the reflecting mirror head 11 is composed mainly of the reflecting mirror 10. The light from the light source 2 is applied to the beam splitter 6, and the light that has passed through the beam splitter 6 is converted into a parallel light beam by the collimator lens 8 and becomes measurement light, reaches the reflecting mirror 10 through the flue in the duct 18, and the reflecting mirror 10 is reflected by the beam splitter 6 again through the flue and reflected by the beam splitter 6. Usually, a glass corner cube is used as the reflecting mirror 10.

  On the other hand, of the light from the light source 2, the light reflected by the beam splitter 6 is guided to the photodetector 4 as a reference light through a space in the light projecting / receiving unit 3 where no dust exists. The measurement light and the reference light incident on the photodetector 4 are guided to the photodetector 4 with their phases shifted from each other.

  The measurement light guided into the duct 18 is attenuated in accordance with the amount of dust existing on the optical path, and as a result, the amount of measurement light incident on the photodetector 4 and the amount of dust existing in the optical path. Has an inversely proportional relationship. By obtaining the difference between the light amount of the measurement light and the light amount of the reference light, the dust amount (concentration) in the light path in the duct 18 can be reduced without being affected by deterioration of the components, changes in voltage or ambient temperature, and the like. It can be measured.

Further, in the light projecting / receiving unit 3, there is a reflecting plate 14 for detecting a zero point (zero dust amount) at every set time and a reference filter 12 for giving attenuation corresponding to a known dust amount. A measurement circuit (not shown) is inserted in the measurement light path so as to be detachable, and the output of the photodetector 4 at the time of insertion is converted into measurement values corresponding to zero dust amount and known dust amount, respectively. ) Is automatically calibrated.
In order to keep the surfaces of the optical elements (lenses, reflectors, windows, etc.) exposed in the space communicating with the duct 18 clean, the light projecting / receiving unit 3 and the reflector head 11 are purged air through purge air inlets 20a, 20b. Is sprayed.

A photocatalyst layer 23 is adhered and solidified on the surface of the collimator lens 8, the reflector 14, and the reflector 10 exposed to the space leading to the flue. As the photocatalyst layer 23, a TiO ₂ layer is adhered and solidified by a method such as coating.

  Light sources 24a, 24b, 26, 28a, and 28b are provided in the vicinity of the collimating lens 8, the reflecting plate 14, and the reflecting mirror 10 so as to irradiate the photocatalyst layer 23 on these surfaces with ultraviolet light. In the reflecting plate 14, the light source 26 is installed so that ultraviolet light is irradiated in a normal retreat position. Since the ultraviolet light emitted from the light source 26 is out of the measurement optical path, the measurement value is not affected. Further, in the collimating lens 8 and the reflecting mirror 10, light sources 24a, 24b, 28a, and 28b are installed so as to irradiate ultraviolet light obliquely from the periphery. The ultraviolet light emitted from these light sources is far away from the photodetector 4, and when a corner cube is used as the reflecting mirror 10, the corner cube has recursion, so the reflected light of the ultraviolet light is It does not enter the measurement light path and does not affect the measured value.

  As a photocatalyst, it is required that the transmittance | permeability with respect to the measurement light beam of visible region 500nm -600nm is high, for example, ST-K211 (product of Ishihara Sangyo Co., Ltd.) is mentioned. As the light sources 24a, 24b, 26, 28a, and 28b, for example, ultraviolet LEDs (for example, NSHU-500 (manufactured by Nichia Corporation)) can be used. Since NSHU-500 can irradiate light having a central wavelength of 370 nm to 380 nm, it is suitable for irradiating the photocatalyst. Since this light source does not emit light having a wavelength of 450 nm or more, if a glass filter (for example, Y-50) that cuts light having a wavelength of 450 nm or less is used as the collimating lens 8, ultraviolet light from this light source is used as measurement light. There is no effect. Further, a normal blue plate glass may be used as the collimating lens 8 and a Y-50 glass filter may be provided immediately before the photodetector.

  Prevents the surface of the collimating lens 8, the reflector 14, and the reflecting mirror 10 exposed in the space leading to the flue from being contaminated by adhering dust, fine particles, dust, water vapor including mist, etc., diffused from the flue. In order to do this, purge air is sent from the purge air inlets 20a and 20b using instrument air or blower, but after a long period of time, there is water vapor that passes through the purge air and adheres to the surfaces of these optical elements. If the water vapor adheres to the surfaces of these optical elements and condenses into water droplets, it causes trouble in measuring the dust concentration.

  In this embodiment, the photocatalyst layer 23 is applied to the surfaces of the collimating lens 8, the reflecting plate 14, and the reflecting mirror 10 to prevent water vapor adhering to these surfaces from condensing and forming water droplets. On the surface to which the photocatalyst layer 23 is applied, the water vapor deposited due to the antifogging effect of the photocatalyst layer 23 does not become water droplets but becomes a thin film, so that the measurement light does not refract and scatter and does not affect the measurement. In addition, even if organic matter adheres to the surfaces together with water vapor, the photocatalytic layer 23 is irradiated with ultraviolet light from the light sources 24a, 24b, 26, 28a, 28b, so that the organic matter decomposition action works and decomposes and removes the organic matter. Has little effect on measurement.

As the photocatalyst layer 23, a layer other than TiO ₂ listed in this embodiment can also be used. For example, a TIO ₂ layer formed by a sol-gel method, or a TIO ₂ layer to which Pt or RuO ₂ is added (see Patent Document 1).
Further, the light source for irradiating the photocatalyst layer with light is not limited to this embodiment.
The configuration of the dust meter shown in this embodiment is merely an example, and can be similarly applied to dust meters having other configurations.

It is a figure which shows the structure of the dust meter of one Example.

Explanation of symbols

2 Light source 4 Photo detector 8 Collimator lens 10 Reflector 14 Reflector 20a, 20b Purge air inlet 23 Photocatalyst layer 24a, 24b, 26, 28a, 28b Light source for photocatalyst irradiation

Claims (3)

A light projecting / receiving unit including a light source and a light detector, and a reflecting mirror disposed so as to face the light source via a flue and reflecting the light projected by the light source so as to enter the light detector; A dust meter for detecting the light reflected by the reflecting mirror through the flue after the light emitted from the light source is detected by the photodetector and measuring the dust concentration in the flue based on the attenuation of the light In
A dust meter characterized in that a transparent photocatalyst layer is attached to the surface of the optical element exposed in the space connected to the flue with respect to the wavelength band of measurement light.   The dust meter according to claim 1, wherein a light source that irradiates light having a wavelength that enhances a catalytic function of the photocatalyst toward the photocatalyst layer is provided in the vicinity of the optical element. The dust meter according to claim 1, wherein the photocatalyst layer contains TiO ₂ as a photocatalyst.

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