EP0509045A1 - Procede et dispositif de detection des particules dans les milieux en ecoulement - Google Patents

Procede et dispositif de detection des particules dans les milieux en ecoulement

Info

Publication number
EP0509045A1
EP0509045A1 EP19910902809 EP91902809A EP0509045A1 EP 0509045 A1 EP0509045 A1 EP 0509045A1 EP 19910902809 EP19910902809 EP 19910902809 EP 91902809 A EP91902809 A EP 91902809A EP 0509045 A1 EP0509045 A1 EP 0509045A1
Authority
EP
European Patent Office
Prior art keywords
light
rings
detector
particles
laser
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Withdrawn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
EP19910902809
Other languages
German (de)
English (en)
Inventor
Lars Leonardsson
Ake LÄNDIN
Amalendu Parasnis
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.)
ABB Stal AB
Original Assignee
ABB Stal AB
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by ABB Stal AB filed Critical ABB Stal AB
Publication of EP0509045A1 publication Critical patent/EP0509045A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G01N15/0211—Investigating a scatter or diffraction pattern
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G01N2015/0238—Single particle scatter
    • 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
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N2021/4704—Angular selective
    • G01N2021/4711—Multiangle measurement
    • G01N2021/4716—Using a ring of sensors, or a combination of diaphragm and sensors; Annular sensor

Definitions

  • the described device comprises an instrument for the con ⁇ tinuous detection of particles in flowing media.
  • the detec ⁇ tion relates to particles above a certain size or within a certain size interval, the sensitivity increasing with in ⁇ creased size of the particles.
  • a typical field of appli ⁇ cation is the measurement of the erosion capacity of par ⁇ ticles, also called erosiveness, in flue gases for gas tur ⁇ bines .
  • the described phenomenon is an example of Fraunhofer diffraction of light .
  • the pattern created is called diffraction pattern.
  • the magnitude of the angles through which the light is deflected is determined by the size of the particles, which in this case is conside ⁇ rably greater than the light wavelength. At a larger dis ⁇ tance, the pattern is large compared with the cross-section area of the original beam.
  • the non-deflected light will be concentrated at a focal point on the optical axis of the light.
  • the light deflected by a dust particle forms conical surfaces of light which extend from the dust particle and light up the screen with light rings centered around the focus, separated by dark rings.
  • Movement of the light-deflecting particles does not influence the diffraction pattern, since parallel light beams are always focussed on the axis and a given conical angle of deflection always results in the same radial displacement (s) in the focal plane of the deflected light.
  • the angle of deflection is given by s/f, where f is the focal distance of the lens.
  • the state of the art for measuring the size of dust particles is based, inter alia, on the use of a laser beam which is caused to pass the region where a study of the occurrence of particles and particle size is to be carried out.
  • a plate with photo-sensitive diodes is placed in the focal plane of a lens which collects the light to the plate. Fraunhofer diffraction occurs at a large distance from the scattering source, but with the aid of a lens the pattern created may be studied at close hand.
  • Particles of a certain size give rise to light rings with known radii and intensities. The light intensities in different rings are measured with photosensitive diodes.
  • the collected measured values then provide information about the occurrence of particles, the size and quantity of the particles.
  • Known equipment aims at measuring either the total mass or the size distribution of the particles in a flowing medium. Measurement of the total mass of particles in many cases provides insufficient infor ⁇ mation about the composition of particles.
  • Another technique is to make use of square detectors, available on the market, with a large amount of photodiodes collected in a matrix. By collecting the measured values from photodiodes which are located at the same mutual distance from the centre of the detector plate, the same function can be obtained as with the ring detectors described.
  • Simple, reliable instruments for continuous measurements over longer distances for example wide flue gas channels, which are designed to give alarm on the occurrence of particles above a certain size or within a certain size range, do not exist.
  • No general particle measurement instrument is required here, but a device which is able to warn when too high contents of relatively large particles occur.
  • Gas turbines may be used for extracting residual energy from flue gases in power plants fired with solid fuels .
  • an instrument has been produced. This instrument is to warn when large particles above a certain size or within a certain size interval are detected.
  • the measured light power in one single detector ring is a function of the diameter of a light scattering particle according to the formula above. In principle, one ring would be sufficient as such to provide information as to the size of the analyzed particle. The problem is that it is impossible to determine whether the measured light power emanates from one single large particle or from many minor dust grains, each of which scatters light and cooperates to form the measured value of the light power.
  • J ⁇ (x) A + Bx 2 + Cx 4 + ...
  • the received light power may be written as
  • each preceding term is much greater in magnitude than the succeeding term.
  • the light power value Pi is dominated by the term Aid 4 and the light power value for the second detector ring P 2 by the term A 2 d . If the detector rings are formed so that all sub-factors in the constants Ai and A2 are influenced to make Ai and A2 equal, the diffe ⁇ rence in received light power will be
  • Pi - P2 (Bi - B 2 ) ⁇ . d 6 + (Ci - C 2 ) • d 8 + ...
  • the difference signal formed from the two detector rings with the value Pi - P2 is dependent both on the total number and the size distribution of the particles in a manner which makes the measured value of the difference signal a good measure of the total erosiveness of the particles in, for example, a gas turbine.
  • a measure of only the size distribution of the particles independently of the total number of particles within the measuring volume.
  • the invention is based partially on known technique.
  • a laser is mounted on the side of a flue gas channel.
  • the beam from the laser passes a windowed opening into the flue gas channel, extends perpendicular to the flue gas flow and continues at the other side surface of the flue gas channel out through a similarly windowed opening in the channel.
  • the light then hits a lens provided with a small oblique mirror at the front in the centre.
  • the mirror deflects the concentrated, unbroken laser beam to the side, whereas the lens focusses light deflected by the dust particles onto a plate provided with photosensitive diodes, the task of which is to detect incident light powers of the light falling on the diodes.
  • the novelty in this invention resides in the fact that measurement is performed in only a small number of detector rings, which may be achieved by utilizing a difference signal according to the above.
  • the method used provides rapid information about the occurrence of the sought particle size. It utilizes relatively simple components, therefore becomes comparatively inexpensive, and is simple to handle compared with other equipment available on the market.
  • the useful measuring distances for the instrument can be made several times longer than what is technically and economically reasonable with prior art methods.
  • Figure 1 shows the relationship between recorded light power as a function of particle diameter, partly for a detector ring, partly for the difference power from detector rings positioned in pairs, all shown on a logarithmic scale.
  • Figure 2 show curves which illustrate the relationship between received light power as a function of particle size for two detector rings with different diameters but with the same area.
  • SA SE Figure 3 shows a schematic arrangement of all the components included in the device. In addition, the path of the light through the units is also shown.
  • Figure 4 shows an arrangement of the measuring device, in which the output power from the laser is measured in an alternative manner.
  • a preferred embodiment of a device for detection of undesired particles in flue gases will be described with reference to Figure 3.
  • the light from a laser 1 first hits a spatial filter with a beam expander 2 which expands the beam and focusses this at a desired distance beyond the far edge of the flue gas channel, where the beam passes out from the channel through a window 3.
  • a beam stop 4 is applied at the centre of the window 3 or, alternatively, at the centre of the lens 6, to divert the central light beam.
  • the beam stop is formed as a mirror, which deflects the beam for further analysis .
  • a light scattering dust particle 5 diverges the beams which fall upon it.
  • the scattered light is collected in an achromatic double lens 6, passes through an interference filter 7 and thereafter illuminates the detector rings .
  • the generated signals are forwarded to an electronic unit 9 for forming a difference signal, which provides information about the particle size.
  • the somewhat oblique window 10 on the laser side which window is antireflex-coated only on the flue gas side, reflects light to a grey filter 11 which removes 99% of the incident light . After passage through an interference filter 12, this light is allowed to fall on a detector 13, which then provides information about the transmitted light power.
  • Grains of dirt on the glass 10 may also give backscattering. Such light is collected by an interference filter 14 with a lens 15 and is measured with a detector 16. Any fouling of the glass 10 may then be recorded here.
  • Transmitted light power from the laser can also be measured by an alternative arrangement of the equipment according to Figure 4.
  • a beam splitter 21 in the form of a thin glass window is placed in the path of the laser beam at an angle of 45° to this.
  • the reflex from the window, one side of which is antireflex-coated, is allowed to fall on a photodetector 22, which then provides information about the optical output power of the laser.
  • the beam splitter is placed ahead of the spatial filter 2, any disturbances of the laser light from the oblique glass in the beam splitter then being filtered off before it is allowed to penetrate the measuring volume.
  • the concentrated light beam which has been deflected by the beam stop 4 is first allowed to hit an oblique grey filter 17, which reflects a small and variable part of the light to a fiber-optic cable 18.
  • the light from the fibre optics 18 is returned to one of the detector rings 8 to give both of these rings an equal amount of background light.
  • the light which penetrates the grey filter 17 illuminates, after passage through an interference filter 19, a quadrant detector 20.
  • the grey filter has filtered off 99.9% of the original light.
  • the detector 20 gives information about transmitted power in combination with detector 13 or, alternatively, detector 22. Deficient centering and alignment can be read out with a detector 20.
  • Calibration of the measuring equipment is carried out with the aid of a calibration glass which is placed at a definite distance in front of the lens, for example at the numeral 5, in Figure 3.
  • Each calibration glass has been coated with particles of a definite size. This has been achieved by- dropping identical particles of a known size, suspended in a liquid, out onto glass plates. Four or five different sizes of particles which well cover the measuring range are suitable to utilize.
  • the calibration glasses are placed in holders . When specific calibration glasses with known particle sizes are placed in the laser beam, the measuring equipment is trimmed for the best correspondence between measured values and the known particle sizes of each calibration glass.
  • the grey filter may be replaced by a beam splitter, a semi-transparent mirror, etc.
  • mirrors may be used, other light sources than lasers may be utilized, and it is also possible to replace photodiodes with other light-sensitive elements, such as photo-multipliers.
  • the instrument may, of course, incorporate more than one pair of detector rings.
  • the difference signal from, for example, different pairs of detector rings may control electronic units separately, the output signals thereof then being compared or weighed together.
  • the device may be used also for other applications than what has been described here, for example for the detection of suspended particles in liquids or in other fields where it is desired to monitor a corre ⁇ sponding presence of dust particles .

Landscapes

  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Glass Compositions (AREA)
  • Optical Measuring Cells (AREA)

Abstract

On applique un laser (1) au côté d'une voie d'écoulement traversée par un milieu. Le faisceau lumineux provenant du laser (1) traverse la voie d'écoulement. Les particules (5) à l'intérieur du volume de mesure du milieu sont heurtées par la lumière et le défléchissent, ce qui forme des cônes lumineux dirigés vers l'avant. Ces cônes lumieux sont réfractés à l'extérieur de la voie d'écoulement par une lentille (6) et heurtent ensuite une plaque de détection (8). La lumière qui heurte la plaque de détection (8) a la forme d'anneaux lumineux créés par la diffraction. Au moins deux anneaux détecteurs sont disposés sur la plaque de détection (8), lesdits anneaux étant constitués d'éléments photosensibles aptes à mesurer la puissance lumineuse des anneaux lumineux qui les atteignent. Une unité de différentiation électronique (9) crée une différence entre les valeurs mesurées de la puissance lumineuse de deux de ces anneaux détecteurs. On obtient ainsi un signal de différence qui peut s'associer à la distribution granulométrique des particules qui se trouvent dans le milieu en écoulement.
EP19910902809 1990-01-05 1990-12-20 Procede et dispositif de detection des particules dans les milieux en ecoulement Withdrawn EP0509045A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9000039 1990-01-05
SE9000039A SE465338B (sv) 1990-01-05 1990-01-05 Saett och anordning foer detektering av partiklar i stroemmande medier

Publications (1)

Publication Number Publication Date
EP0509045A1 true EP0509045A1 (fr) 1992-10-21

Family

ID=20378173

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19910902809 Withdrawn EP0509045A1 (fr) 1990-01-05 1990-12-20 Procede et dispositif de detection des particules dans les milieux en ecoulement

Country Status (6)

Country Link
EP (1) EP0509045A1 (fr)
AU (1) AU7057291A (fr)
CA (1) CA2072743A1 (fr)
FI (1) FI923094A (fr)
SE (1) SE465338B (fr)
WO (1) WO1991010123A1 (fr)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL9301446A (nl) * 1993-08-20 1995-03-16 Univ Delft Tech Werkwijze en inrichting voor het meten van vormeigenschappen van deeltjes.
US5831730A (en) * 1996-12-06 1998-11-03 United Sciences, Inc. Method for monitoring particulates using beam-steered solid-state light source
DE19912911C2 (de) * 1999-03-22 2001-07-19 Schako Metallwarenfabrik Vorrichtung zur Erkennung von Rauch
DE10136555A1 (de) * 2001-07-27 2003-02-13 Boehringer Ingelheim Int Optimierte Verfahren zur Bestimmung der Aerosol-Partikelgrößenverteilung und Vorrichtung zur Durchführung derartiger Verfahren
CN107941662B (zh) * 2017-11-10 2020-01-21 吉林大学 一种利用强场激光检测火焰内颗粒物分布的装置与方法
EP3588055A1 (fr) 2018-06-21 2020-01-01 Koninklijke Philips N.V. Module de capteur laser avec indication de disponibilité pour utilisation

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4595291A (en) * 1982-10-15 1986-06-17 Tokyo Shibaura Denki Kabushiki Kaisha Particle diameter measuring device
DE3575470D1 (de) * 1985-06-07 1990-02-22 Fritsch Gmbh Geraet zur bestimmung von korngroessen.
GB8624587D0 (en) * 1986-10-14 1986-11-19 North Sea Instr Ltd Particle analysis apparatus
GB2204678A (en) * 1987-03-26 1988-11-16 Joshua Swithenbank Size and velocity measuring instrument for multiphase flows
GB2203542A (en) * 1987-04-14 1988-10-19 Secr Defence Measuring particle size distribution

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9110123A1 *

Also Published As

Publication number Publication date
SE9000039L (sv) 1991-07-06
WO1991010123A1 (fr) 1991-07-11
AU7057291A (en) 1991-07-24
FI923094A0 (fi) 1992-07-03
FI923094A (fi) 1992-07-03
SE9000039D0 (sv) 1990-01-05
SE465338B (sv) 1991-08-26
CA2072743A1 (fr) 1991-07-06

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