EP1508030A1 - Device and method for spectroscopically measuring a gas concentration by determining a single absorption line - Google Patents

Device and method for spectroscopically measuring a gas concentration by determining a single absorption line

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Publication number
EP1508030A1
EP1508030A1 EP03732429A EP03732429A EP1508030A1 EP 1508030 A1 EP1508030 A1 EP 1508030A1 EP 03732429 A EP03732429 A EP 03732429A EP 03732429 A EP03732429 A EP 03732429A EP 1508030 A1 EP1508030 A1 EP 1508030A1
Authority
EP
European Patent Office
Prior art keywords
process gas
laser
shield
beam path
gas
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03732429A
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German (de)
French (fr)
Inventor
Andreas Dietrich
Peter Kasperson
Karl Henrik Haugholt
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Linde GmbH
Original Assignee
Linde GmbH
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Publication date
Application filed by Linde GmbH filed Critical Linde GmbH
Publication of EP1508030A1 publication Critical patent/EP1508030A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/59—Transmissivity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/85—Investigating moving fluids or granular solids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G01N2021/151—Gas blown
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N2021/3129—Determining multicomponents by multiwavelength light
    • G01N2021/3133—Determining multicomponents by multiwavelength light with selection of wavelengths before the sample
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G01N2021/396—Type of laser source
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N21/09—Cuvette constructions adapted to resist hostile environments or corrosive or abrasive materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/02—Mechanical
    • G01N2201/023—Controlling conditions in casing
    • G01N2201/0233—Gas purge

Definitions

  • the invention relates to a device and a method for measuring a concentration of at least one component of a process gas with a laser, the beam path of the laser crossing a volume containing the process gas.
  • Measuring methods and devices are known for determining the concentration of individual components of a gas mixture, which are determined using a laser for laser spectroscopic measurements.
  • the present invention is therefore based on the object of an improved method and an improved device for carrying out laser spectroscopic measurements of the concentration of the components of a
  • the suitability of the invention being particularly important for large volumes of dust-laden process gases.
  • the object is achieved in that the beam path partly leads freely through the process gas and partly shields itself from the process gas, with only the part of the beam path that leads freely through the process gas being provided as a measuring section for a spectroscopic measurement of exactly one absorption line.
  • This has the advantage that, compared to a spectroscopic measurement that measures an area (scanning method), the accuracy of the measurement is significantly increased.
  • a so-called single-line spectroscopy is used. Therefore, a laser is advantageously used, the wavelength of which is fixed or can be fixed to a specific, selected value, which is also precisely observed.
  • an infrared laser with a precisely defined wavelength is used to determine carbon monoxide.
  • scanning lasers that is to say lasers which measure (scan) a wavelength range according to a predetermined sequence, are not suitable for the high accuracy which is an object of the present invention. Due to the definition of only one frequency, continuous automatic calibration of the laser is possible without any other aids. In contrast, scanning lasers require one or more reference gas cells in order to continuously calibrate the laser using these gases.
  • the shielding of the beam path is preferably designed as a hollow body.
  • Means are particularly preferably provided in the area of the shielding for feeding in a purge gas which serves to displace the process gas from the shielding, in particular from the interior of the hollow body.
  • a purge gas which serves to displace the process gas from the shielding, in particular from the interior of the hollow body.
  • Nitrogen for example, is very suitable as the purge gas.
  • Inert gases are also generally considered suitable. The suitability of a gas as a purge gas depends u. a. depending on which component of the process gas the concentration is to be determined.
  • the shield is tubular.
  • the shielding is particularly advantageous as a water-cooled lance executed. This embodiment enables the device according to the invention for measuring the concentration to be used without problems even in process gases which have a very high temperature.
  • the shield has a heat-resistant and / or acid-resistant material.
  • the shield preferably has a ceramic material. These materials also enable problem-free use of the device according to the invention under difficult conditions, for example in the presence of acidic components in the process gas.
  • the shield is attached to the laser at the beginning of the beam path and in front of a detector which is hit by the laser radiation, as a result of which the measuring path is limited by the shield from both sides.
  • This configuration has the advantage, among other things, that any existing edge effects (effects in the edge region of a gas volume) are hidden from the measurement. Disruptive edge effects can occur, for example, in a flowing process gas.
  • the task is solved in that the beam path leads partly freely through the process gas and partly shields itself from the process gas, whereby only the part of the beam path that leads freely through the process gas is referred to as the measuring section and for a spectroscopic measurement of the concentration with the help of the laser, in which exactly one absorption line is determined.
  • the method designed in this way enables a reliable measurement with high accuracy even over large measuring distances and in process gases which are contaminated with dust or are otherwise contaminated or generally mixed with particles.
  • the process gases can easily have a high temperature, since the spectral bands of the water vapor to be expected at higher temperatures do not have a disruptive influence on the measurement of a single absorptine line (single-line spectroscopy) according to the invention.
  • the shield is advantageously flushed with a purge gas.
  • Nitrogen is particularly advantageously used as the purge gas.
  • This is advantageously located inside the Shielding is a clean gas known in its composition, through which the laser beam experiences almost no weakening of its intensity and which behaves neutrally for the concentration measurement, ie does not make a contribution unless the concentration of a nitrogen compound is to be measured.
  • the suitability of a gas as a purge gas depends on which component of the process gas the concentration is to be determined.
  • a purge gas is preferably selected which differs significantly from the gas whose concentration is to be determined with regard to spectroscopy.
  • Inert gases can also advantageously be used as purge gases.
  • the particular advantage of inert gases is that a chemical reaction between the purge gas and the process gas can be excluded.
  • ambient air is drawn in and used as the purge gas. This configuration primarily offers the
  • Process gas nitrogen preferred as purge gas is
  • the invention also has the advantage that a laser with low power can be used to measure the concentration, since the measuring distance is shortened by the shielding according to the invention in comparison to a measurement without shielding.
  • the use of a laser with low power also advantageously reduces the risk of undesired changes in the process gas, which could be triggered by the energy of the laser radiation in the process gas.
  • FIG. 1 a cross section through a volume containing the process gas
  • a tubular volume 1 containing the process gas is shown in the figure, which has on one side a laser 2a and on the opposite side a detector 2b which registers the laser radiation passing through the volume 1 and incident on the detector 2b.
  • the beam path of the laser 2a is partially surrounded by the shield 3, which delimits the measuring section 4 on both sides, both in the direction of the laser 2a and in the direction of the detector 2b.
  • Means for feeding a purge gas such as nitrogen are advantageously provided on the shield 3. These means are not shown in the figure.
  • Volume 1 is filled, for example, with a hot process gas (e.g. the exhaust gas from a steelworks furnace), which has a temperature of 800 ° C or higher and whose content of carbon monoxide is to be determined.
  • a shield 3 is used, which has two water-cooled ceramic tubes 3. Gaseous nitrogen is used as the flushing gas, which displaces the process gas from the interior of the ceramic tubes 3, which are cooled, for example, by tube coils (not shown) carrying cooling water.
  • a shield 3 advantageously has dimensions such that the measuring section 4 is, for example, a length of 10 cm to 30 cm.
  • a measuring section 4 of approximately 20 cm has proven to be particularly advantageous.
  • the laser used is, for example, a tunable laser that is operated according to the invention at a single frequency selected before the measurements.
  • a tunable laser has the advantage that the frequency (or wavelength) that can be well absorbed by the gas component to be determined can be selected from its possible frequency range.
  • the weakening of the selected absorption line is a measure of the concentration of the gas components to be determined in the process gas.
  • a single-mode laser that has a frequency that matches the gas component to be determined.
  • the laser measurements can be carried out with particular advantage as continuous measurements. In a further embodiment of the invention, however, discontinuous measurement methods can also be used successfully.

Abstract

The invention relates to a device and a method for measuring a concentration of at least one component of a process gas by means of a laser (2a), the beam path of the laser (2a) penetrating a volume (1) containing the process gas. The invention is characterized by the fact that one section of the beam path penetrates the process gas in a free manner while another section thereof is shielded from the process gas. Only the section of the beam path, which penetrates the process gas in a free manner, is designated as the section to be measured (4) and is used for measuring the concentration by means of laser spectroscopy, exactly one absorption line being determined for said measurement.

Description

Beschreibung description
Vorrichtung und Verfahren zur spektroskopischen Messung einer Gaskonzentration durch Bestimmung einer einzelnen AbsorptionslinieDevice and method for spectroscopic measurement of a gas concentration by determining a single absorption line
Die Erfindung betrifft eine Vorrichtung und ein Verfahren zur Messung einer Konzentration mindestens einer Komponente eines Prozessgases mit einem Laser, wobei der Strahlengang des Lasers ein das Prozessgas enthaltendes Volumen durchquert.The invention relates to a device and a method for measuring a concentration of at least one component of a process gas with a laser, the beam path of the laser crossing a volume containing the process gas.
Bekannt sind Meßverfahren und -Vorrichtungen zur Ermittlung der Konzentration einzelner Komponenten einer Gasmischung, die unter Einsatz eines Lasers zu laserspektroskopischen Messungen ermittelt werden.Measuring methods and devices are known for determining the concentration of individual components of a gas mixture, which are determined using a laser for laser spectroscopic measurements.
Bei der Anwendung von laserspektroskopischen Verfahren zur Konzentrationsbestimmung von Komponenten in staubbelasteten Prozessgasen (Gasmischungen) sind den bekannten Methoden jedoch durch die auftretendeWhen using laser spectroscopic methods for determining the concentration of components in dust-laden process gases (gas mixtures), however, the known methods are known to occur
Absorption und Reflexion der Laserstrahlung durch die Staubpartikel Grenzen gesetzt. Bei hoher Staubbelastung und größeren Meßstrecken, beispielsweise über einen größeren Rohrquerschnitt hinweg, nimmt die Intensität der Laserstrahlung über die Meßstrecke hinweg so stark ab, dass kein verwertbares Signal am Detektor ankommt. Die bekannten Verfahren sind somit für die beschriebenen Anwendungen nicht geeignet.Absorption and reflection of the laser radiation through the dust particles set limits. With high dust loads and larger measuring sections, for example over a larger pipe cross section, the intensity of the laser radiation over the measuring section decreases so much that no usable signal arrives at the detector. The known methods are therefore not suitable for the applications described.
Der oben beschriebene Anwendungsfall tritt im Bereich der Metallverarbeitung oder der Energiegewinnung und Kraftwerkstechnik vergleichsweise häufig auf, da dort mit Staub verunreinigte (Prozess)-Gase in großen Mengen anfallen, deren Zusammensetzung für den Anlagenbetreiber von großem Interesse ist.The application described above occurs comparatively frequently in the field of metal processing or energy generation and power plant technology, since there are large quantities of (process) gases contaminated with dust, the composition of which is of great interest to the plant operator.
Der vorliegenden Erfindung liegt daher die Aufgabe zugrunde, ein verbessertes Verfahren und eine verbesserte Vorrichtung zur Durchführung von laser- spektroskopischen Messungen der Konzentration der Komponenten einesThe present invention is therefore based on the object of an improved method and an improved device for carrying out laser spectroscopic measurements of the concentration of the components of a
Prozessgases zur Verfügung zu stellen, wobei der Eignung der Erfindung auch für große Volumen staubbelasteter Prozessgase eine besonders wichtige Bedeutung zukommt. Vorrichtungsseitig wird die gestellte Aufgabe dadurch gelöst, dass der Strahlengang teilweise frei durch das Prozessgas führt und teilweise von dem Prozessgas abgeschirmt verläuft, wobei nur der Teil des Strahlengangs, der frei durch das Prozessgas führt als Meßstrecke für eine spektroskopische Messung genau einer Absorptionslinie vorgesehen ist. Damit ist der Vorteil verbunden, dass eine gegenüber einer spektroskopischen Messung, die einen Bereich durchmisst (scanning method), wesentlich erhöhte Genauigkeit der Messung erreicht wird. Erfindungsgemäß kommt eine sogenannte Single-Line-Spektroskopie zum Einsatz. Daher wird vorteilhaft ein Laser eingesetzt, dessen Wellenlänge auf einen bestimmten, gewählten Wert festgelegt oder festlegbar ist, die auch präzise eingehalten wird. Beispielsweise wird zur Bestimmung von Kohlenmonoxid ein Infrarotlaser mit einer genau definierten Wellenlänge eingesetzt. Im Gegensatz dazu sind scannende Laser, also Laser, die einen Wellenlängenbereich nach einem vorgegebene Ablauf durchmessen (scannen) für die hohe Genauigkeit, die ein Ziel der vorliegende Erfindung ist, nicht geeignet. Auf Grund der Festlegung auf nur eine Frequenz ist eine fortlaufende automatische Kalibrierung des Lasers ohne sonstige Hilfsmittel möglich. Scannende Laser benötigen im Gegensatz dazu ein oder mehrere Referenzgaszellen um den Laser anhand dieser Gase fortlaufend zu kalibrieren.To provide process gas, the suitability of the invention being particularly important for large volumes of dust-laden process gases. On the device side, the object is achieved in that the beam path partly leads freely through the process gas and partly shields itself from the process gas, with only the part of the beam path that leads freely through the process gas being provided as a measuring section for a spectroscopic measurement of exactly one absorption line. This has the advantage that, compared to a spectroscopic measurement that measures an area (scanning method), the accuracy of the measurement is significantly increased. According to the invention, a so-called single-line spectroscopy is used. Therefore, a laser is advantageously used, the wavelength of which is fixed or can be fixed to a specific, selected value, which is also precisely observed. For example, an infrared laser with a precisely defined wavelength is used to determine carbon monoxide. In contrast, scanning lasers, that is to say lasers which measure (scan) a wavelength range according to a predetermined sequence, are not suitable for the high accuracy which is an object of the present invention. Due to the definition of only one frequency, continuous automatic calibration of the laser is possible without any other aids. In contrast, scanning lasers require one or more reference gas cells in order to continuously calibrate the laser using these gases.
Bevorzugt ist die Abschirmung des Strahlengangs als Hohlkörper ausgebildet. Besonders bevorzugt sind im Bereich der Abschirmung Mittel zur Einspeisung eines Spülgases vorgesehen, welches zur Verdrängung des Prozessgases aus der Abschirmung, insbesondere aus dem Inneren des Hohlkörpers, dient. Dadurch befindet sich vorteilhaft im Inneren der Abschirmung ein in seiner Zusammensetzung bekanntes, sauberes Gas durch das der Laserstrahl fast keine Abschwächung seiner Intensität erfährt und das sich für die Konzentrationsmessung neutral verhält oder aufgrund der bekannten Zusammensetzung nachträglich aus der Messung wieder eliminiert werden kann. Als Spülgas ist beispielsweise Stickstoff sehr geeignet. Auch Inertgase sind generell als geeignet anzusehen. Die Eignung eines Gases als Spülgas hängt u. a. davon ab von welcher Komponente des Prozessgases die Konzentration ermittelt werden soll.The shielding of the beam path is preferably designed as a hollow body. Means are particularly preferably provided in the area of the shielding for feeding in a purge gas which serves to displace the process gas from the shielding, in particular from the interior of the hollow body. As a result, there is advantageously a clean gas known in its composition inside the shield, through which the laser beam experiences almost no weakening of its intensity and which is neutral for the concentration measurement or can subsequently be eliminated again from the measurement due to the known composition. Nitrogen, for example, is very suitable as the purge gas. Inert gases are also generally considered suitable. The suitability of a gas as a purge gas depends u. a. depending on which component of the process gas the concentration is to be determined.
In einer vorteilhaften Ausgestaltung der Erfindung ist die Abschirmung rohrförmig ausgebildet. Besonders vorteilhaft ist die Abschirmung als wassergekühlte Lanze ausgeführt. Durch diese Ausführung wird ermöglicht, dass die erfindungsgemäße Vorrichtung zur Konzentrationsmessung auch in Prozessgasen, die eine sehr hohe Temperatur aufweisen, problemlos eingesetzte werden kann.In an advantageous embodiment of the invention, the shield is tubular. The shielding is particularly advantageous as a water-cooled lance executed. This embodiment enables the device according to the invention for measuring the concentration to be used without problems even in process gases which have a very high temperature.
In einer vorteilhaften Ausgestaltung der Erfindung weist die Abschirmung ein hitzebeständiges und/oder säurefestes Material auf. Bevorzugt weist die Abschirmung ein keramisches Material auf. Diese Materialien ermöglichen ebenfalls den problemlosen Einsatz der erfindungsgemäßen Vorrichtung unter schwierigen Bedingungen, beispielsweise in Anwesenheit von sauren Komponenten im Prozessgas.In an advantageous embodiment of the invention, the shield has a heat-resistant and / or acid-resistant material. The shield preferably has a ceramic material. These materials also enable problem-free use of the device according to the invention under difficult conditions, for example in the presence of acidic components in the process gas.
Gemäß einer Weiterbildung der Erfindung ist die Abschirmung am Beginn des Strahlengangs beim Laser angebracht sowie vor einem Detektor, auf den die Laserstrahlung trifft, wodurch die Meßstrecke von beiden Seiten durch die Abschirmung begrenzt wird. Diese Ausgestaltung birgt unter anderem den Vorteil, dass eventuell vorhandene Randeffekte (Effekte im Randbereich eines Gasvolumens) aus der Messung ausgeblendet werden. Störende Randeffekte können beispielsweise in einem strömenden Prozessgas auftreten.According to a further development of the invention, the shield is attached to the laser at the beginning of the beam path and in front of a detector which is hit by the laser radiation, as a result of which the measuring path is limited by the shield from both sides. This configuration has the advantage, among other things, that any existing edge effects (effects in the edge region of a gas volume) are hidden from the measurement. Disruptive edge effects can occur, for example, in a flowing process gas.
Verfahrensseitig wird die gestellte Aufgabe dadurch gelöst, dass der Strahlengang teilweise frei durch das Prozessgas führt und teilweise von dem Prozessgas abgeschirmt verläuft, wobei nur der Teil des Strahlengangs, der frei durch das Prozessgas führt, als Meßstrecke bezeichnet wird und zu einer spektroskopischen Messung der Konzentration mit Hilfe des Lasers herangezogen wird, bei der genau eine Absorptionslinie bestimmt wird. Das so gestaltete Verfahren ermöglicht eine zuverlässige Messung mit hoher Genauigkeit auch über größere Meßstrecken hinweg und in staubbelasteten oder anderweitig verschmutzten oder allgemein mit Partikel vermengten Prozessgasen. Die Prozessgase können dabei problemlos eine hohe Temperatur aufweisen, da die bei höheren Temperaturen zu erwartenden Spektralbänder des Wasserdampfs auf die.erfindungsgemäße Messung einer einzelnen Absorptinslinie (single-line-spectroscopy) keinen störenden Einfluss ausüben.On the procedural side, the task is solved in that the beam path leads partly freely through the process gas and partly shields itself from the process gas, whereby only the part of the beam path that leads freely through the process gas is referred to as the measuring section and for a spectroscopic measurement of the concentration with the help of the laser, in which exactly one absorption line is determined. The method designed in this way enables a reliable measurement with high accuracy even over large measuring distances and in process gases which are contaminated with dust or are otherwise contaminated or generally mixed with particles. The process gases can easily have a high temperature, since the spectral bands of the water vapor to be expected at higher temperatures do not have a disruptive influence on the measurement of a single absorptine line (single-line spectroscopy) according to the invention.
Vorteilhaft wird die Abschirmung mit einem Spülgas gespült. Mit besonderem Vorteil wird als Spülgas Stickstoff eingesetzt. Dadurch befindet sich vorteilhaft im Inneren der Abschirmung ein in seiner Zusammensetzung bekanntes, sauberes Gas durch das der Laserstrahl fast keine Abschwächung seiner Intensität erfährt und das sich für die Konzentrationsmessung neutral verhält, d.h. keinen Beitrag liefert sofern nicht die Konzentration einer Stickstoffverbindung gemessen werden soll. Allgemein formuliert hängt die Eignung eines Gases als Spülgas davon ab von welcher Komponente des Prozessgases die Konzentration ermittelt werden soll. In der Regel wird bevorzugt ein Spülgas gewählt, das sich von dem Gas dessen Konzentration bestimmt werden soll im Hinblick auf die Spektroskopie deutlich unterscheidet.The shield is advantageously flushed with a purge gas. Nitrogen is particularly advantageously used as the purge gas. This is advantageously located inside the Shielding is a clean gas known in its composition, through which the laser beam experiences almost no weakening of its intensity and which behaves neutrally for the concentration measurement, ie does not make a contribution unless the concentration of a nitrogen compound is to be measured. Generally speaking, the suitability of a gas as a purge gas depends on which component of the process gas the concentration is to be determined. As a rule, a purge gas is preferably selected which differs significantly from the gas whose concentration is to be determined with regard to spectroscopy.
Auch Inertgase sind vorteilhaft als Spülgase einsetzbar. Der besondere Vorteil besteht bei Inertgasen darin, dass eine chemische Reaktion zwischen Spülgas und Prozessgas ausgeschlossen werden kann.Inert gases can also advantageously be used as purge gases. The particular advantage of inert gases is that a chemical reaction between the purge gas and the process gas can be excluded.
Gemäß einer anderen vorteilhaften Ausgestaltung des Verfahrens wird Umgebungsluft angesaugt und als Spülgas eingesetzt. Diese Ausgestaltung bietet vor allem denAccording to another advantageous embodiment of the method, ambient air is drawn in and used as the purge gas. This configuration primarily offers the
Vorteil niedriger Verfahrenskosten. Jedoch ist die Gegenwart von Umgebungsluft nicht bei allen Anwendungen wünschenswert, beispielsweise bei einer Bestimmung der CO-Advantage of low procedural costs. However, the presence of ambient air is not desirable in all applications, for example when determining the CO
Konzentration in einem Abgas würde Umgebungsluft als Spülgas zu einer Störung derConcentration in an exhaust gas would disrupt the ambient air as purge gas
Messung führen.Measure.
Ebenso ist beispielsweise für Messungen der Sauerstoffkonzentration in einemLikewise, for measurements of oxygen concentration in one
Prozessgas Stickstoff als Spülgas zu bevorzugen.Process gas nitrogen preferred as purge gas.
Die Erfindung weist weiterhin den Vorteil auf, dass zur Messung der Konzentration ein Laser mit geringer Leistung eingesetzt werden kann, da die Meßstrecke durch die erfindungsgemäße Abschirmung im Vergleich zu einer Messung ohne Abschirmung verkürzt wird. Der Einsatz eines Lasers mit geringer Leistung reduziert darüber hinaus vorteilhaft die Gefahr von unerwünschten Veränderungen im Prozessgas, die durch die Energie der Laserstrahlung im Prozessgas ausgelöst werden könnten.The invention also has the advantage that a laser with low power can be used to measure the concentration, since the measuring distance is shortened by the shielding according to the invention in comparison to a measurement without shielding. The use of a laser with low power also advantageously reduces the risk of undesired changes in the process gas, which could be triggered by the energy of the laser radiation in the process gas.
Die Erfindung sowie weitere Einzelheiten der Erfindung werden im Folgenden anhand eines in der Zeichnung dargestellten Ausführungsbeispiels näher erläutert. Hierbei zeigt die einzigeThe invention and further details of the invention are explained in more detail below with reference to an embodiment shown in the drawing. The only one shows
Figur einen Querschnitt durch ein das Prozessgas enthaltendes Volumen Im einzelnen ist in der Figur ein das Prozessgas enthaltendes, rohrförmig begrenztes Volumen 1 dargestellt, das auf einer Seite einen Laser 2a und gegenüberliegend einen Detektor 2b aufweist, der die das Volumen 1 durchquerende und auf dem Detektor 2b auftreffende Laserstrahlung registriert. Der Strahlengang des Lasers 2a ist zum Teil von der Abschirmung 3 umgeben, die die Meßstrecke 4 auf beiden Seiten begrenzt, sowohl in Richtung zum Laser 2a hin als auch in Richtung auf den Detektor 2b zu. An der Abschirmung 3 sind vorteilhaft Mittel zur Einspeisung eines Spülgases wie z.B. Stickstoff vorgesehen. Diese Mittel sind in der Figur nicht dargestellt.Figure a cross section through a volume containing the process gas In detail, a tubular volume 1 containing the process gas is shown in the figure, which has on one side a laser 2a and on the opposite side a detector 2b which registers the laser radiation passing through the volume 1 and incident on the detector 2b. The beam path of the laser 2a is partially surrounded by the shield 3, which delimits the measuring section 4 on both sides, both in the direction of the laser 2a and in the direction of the detector 2b. Means for feeding a purge gas such as nitrogen are advantageously provided on the shield 3. These means are not shown in the figure.
Das Volumen 1 ist beispielsweise mit einem heißen Prozessgas (z. B. dem Abgas aus einem Stahlwerksofen) gefüllt, das eine Temperatur von 800°C oder größer aufweist und dessen Gehalt an Kohlenmonoxid bestimmt werden soll. Dazu wird eine Abschirmung 3 eingesetzt, die zwei wassergekühlte Keramikrohre 3 aufweist. Als Spülgas kommt gasförmiger Stickstoff zum Einsatz, der das Prozessgas aus dem Inneren der Keramikrohre 3 verdrängt, die beispielsweise durch Kühlwasser führende Rohrschlangen (nicht dargestellt) gekühlt werden.Volume 1 is filled, for example, with a hot process gas (e.g. the exhaust gas from a steelworks furnace), which has a temperature of 800 ° C or higher and whose content of carbon monoxide is to be determined. For this purpose, a shield 3 is used, which has two water-cooled ceramic tubes 3. Gaseous nitrogen is used as the flushing gas, which displaces the process gas from the interior of the ceramic tubes 3, which are cooled, for example, by tube coils (not shown) carrying cooling water.
Vorteilhaft weist eine erfindungsgemäße Abschirmung 3 in Abhängigkeit von der Distanz zwischen Laser 2a und Detektor 2b solche Abmessungen auf, dass die Meßstrecke 4 beispielsweise eine Länge von 10 cm bis 30 cm beträgt. Besonders vorteilhaft erweist sich eine Meßstrecke 4 von ca. 20 cm.Depending on the distance between laser 2a and detector 2b, a shield 3 according to the invention advantageously has dimensions such that the measuring section 4 is, for example, a length of 10 cm to 30 cm. A measuring section 4 of approximately 20 cm has proven to be particularly advantageous.
Der eingesetzte Laser ist bespielsweise ein abstimmbarer Laser, der erfindungsgemäß bei einer einzigen, vor den Messungen ausgewählten Frequenz betrieben wird. Ein abstimmbarer Laser hat den Vorteil, dass aus seinem möglichen Frequenzbereich die Frequenz (respektive Wellenlänge) ausgewählt werden kann, die von der zu bestimmenden Gaskomponente gut absorbiert wird. Die Schwächung der gewählten Absoprtionslinie ist dabei ein Maß für die Konzentration der zu bestimmenden Gaskomponete im Prozessgas.The laser used is, for example, a tunable laser that is operated according to the invention at a single frequency selected before the measurements. A tunable laser has the advantage that the frequency (or wavelength) that can be well absorbed by the gas component to be determined can be selected from its possible frequency range. The weakening of the selected absorption line is a measure of the concentration of the gas components to be determined in the process gas.
Es ist jedoch auch möglich einen Singel-Mode-Laser einzusetzen, der eine zu der zu bestimmenden Gaskomponente passende Frequenz aufweist. Die Lasermessungen können mit besonderem Vorteil als kontinuierliche Messungen durchgeführt werden. In einer weiteren Ausführungsform der Erfindung sind jedoch auch diskontinuierliche Meßmethoden mit Erfolg einsetzbar. However, it is also possible to use a single-mode laser that has a frequency that matches the gas component to be determined. The laser measurements can be carried out with particular advantage as continuous measurements. In a further embodiment of the invention, however, discontinuous measurement methods can also be used successfully.

Claims

Patentansprüche claims
1. Vorrichtung zur Messung einer Konzentration mindestens einer Komponente eines Prozessgases mit einem Laser (2a), wobei der Strahlengang des Lasers (2a) ein das Prozessgas enthaltendes Volumen (1) durchquert, dadurch gekennzeichnet, dass der Strahlengang teilweise frei durch das Prozessgas führt und teilweise von dem Prozessgas abgeschirmt verläuft, wobei nur der Teil des Strahlengangs, der frei durch das Prozessgas führt als Meßstrecke (4) für eine spektroskopische Messung genau einer Absorptionslinie vorgesehen ist.1. Device for measuring a concentration of at least one component of a process gas with a laser (2a), wherein the beam path of the laser (2a) passes through a volume (1) containing the process gas, characterized in that the beam path leads partially freely through the process gas and partially shielded from the process gas, only the part of the beam path that leads freely through the process gas is provided as a measuring section (4) for a spectroscopic measurement of exactly one absorption line.
2. Vorrichtung nach Anspruch 1 , dadurch gekennzeichnet, dass die Abschirmung (3) des Strahlengangs als Hohlkörper (3) ausgebildet ist.2. Device according to claim 1, characterized in that the shield (3) of the beam path is designed as a hollow body (3).
3. Vorrichtung nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass im Bereich der Abschirmung (3) Mittel zur Einspeisung eines Spülgases vorgesehen sind, welches zur Verdrängung des Prozessgases aus der Abschirmung (3), insbesondere aus dem Inneren des Hohlkörpers (3), dient.3. Device according to claim 1 or 2, characterized in that means for feeding a purge gas are provided in the area of the shield (3), which means for displacing the process gas from the shield (3), in particular from the interior of the hollow body (3), serves.
4. Vorrichtung nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass die Abschirmung (3) rohrförmig ausgebildet ist.4. Device according to one of claims 1 to 3, characterized in that the shield (3) is tubular.
5. Vorrichtung nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass die Abschirmung (3) als wassergekühlte Lanze ausgeführt ist.5. Device according to one of claims 1 to 4, characterized in that the shield (3) is designed as a water-cooled lance.
6. Vorrichtung nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass die Abschirmung (3) ein hitzebeständiges und/oder säurefestes Material aufweist.6. Device according to one of claims 1 to 5, characterized in that the shield (3) comprises a heat-resistant and / or acid-resistant material.
7. Vorrichtung nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass die Abschirmung (3) ein keramisches Material aufweist.7. Device according to one of claims 1 to 6, characterized in that the shield (3) comprises a ceramic material.
8. Vorrichtung nach einem der Ansprüche 1 bis 7 dadurch gekennzeichnet, dass die Abschirmung (3) am Beginn des Strahlengangs beim Laser (2a) angebracht ist sowie vor einem Detektor (2b), auf den die Laserstrahlung trifft, wodurch die Meßstrecke (4) von beiden Seiten durch die Abschirmung (3) begrenzt wird . 8. Device according to one of claims 1 to 7, characterized in that the shield (3) at the beginning of the beam path at the laser (2a) is attached and in front of a detector (2b), which is hit by the laser radiation, whereby the measuring section (4) is limited from both sides by the shield (3).
9. Verfahren zur Messung einer Konzentration mindestens einer Komponente eines Prozessgases mit einem Laser (2a), wobei der Strahlengang des Lasers (2a) ein das Prozessgas enthaltendes Volumen (1) durchquert, dadurch gekennzeichnet, dass der Strahlengang teilweise frei durch das Prozessgas führt und teilweise von dem Prozessgas abgeschirmt verläuft, wobei nur der Teil des Strahlengangs, der frei durch das Prozessgas führt, als Meßstrecke (4) bezeichnet wird und zu einer spektroskopischen Messung der Konzentration mit Hilfe des Lasers (2a) herangezogen wird, bei der genau eine Absorptionslinie bestimmt wird.9. A method for measuring a concentration of at least one component of a process gas with a laser (2a), the beam path of the laser (2a) crossing a volume (1) containing the process gas, characterized in that the beam path leads partially freely through the process gas and partially shielded from the process gas, only the part of the beam path that leads freely through the process gas is referred to as the measuring section (4) and is used for a spectroscopic measurement of the concentration with the aid of the laser (2a), in which exactly one absorption line is determined.
10. Verfahren nach Anspruch 9, dadurch gekennzeichnet, dass die Abschirmung (3) mit einem Spülgas gespült wird.10. The method according to claim 9, characterized in that the shield (3) is flushed with a purge gas.
11. Verfahren nach Anspruch 10, dadurch gekennzeichnet, dass als Spülgas Stickstoff eingesetzt wird. 11. The method according to claim 10, characterized in that nitrogen is used as the purge gas.
EP03732429A 2002-05-24 2003-05-20 Device and method for spectroscopically measuring a gas concentration by determining a single absorption line Withdrawn EP1508030A1 (en)

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DE10223239A DE10223239A1 (en) 2002-05-24 2002-05-24 Device and method for spectroscopic measurement of a gas concentration by determining a single absorption line
PCT/EP2003/005296 WO2003100392A1 (en) 2002-05-24 2003-05-20 Device and method for spectroscopically measuring a gas concentration by determining a single absorption line

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JP5972760B2 (en) * 2012-11-09 2016-08-17 三菱重工業株式会社 Exhaust gas denitration system, exhaust gas denitration device regeneration method, and exhaust gas denitration device catalyst replacement method
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US3838925A (en) * 1972-12-07 1974-10-01 Baldwin Electronics Inc Photoelectric opacity measuring system
US4076425A (en) * 1976-02-17 1978-02-28 Julian Saltz Opacity measuring apparatus
US4225243A (en) * 1978-06-26 1980-09-30 Measurex Corporation Gas measuring apparatus with standardization means, and method therefor
US4247205A (en) * 1979-02-02 1981-01-27 Measurex Corporation Gas measuring apparatus with standardization means, and method therefor
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