FR2464470A1 - ELECTRO-OPTICAL APPARATUS FOR ANALYZING A CARBON GAS - Google Patents

Abstract

THIS APPARATUS ALLOWS SIMULTANEOUS MEASUREMENT OF THE OPACITY, THE CO CONTENT AND THE HYDROCARBON CONTENT OF THE FLUE GASES ALONG A SINGLE MEASUREMENT PATH 14. THE VISIBLE LIGHT EMITTED BY A SOURCE 16 AND CHOPPED BY A WHEEL 18, AS WELL AS THE INFRARED ENERGY FROM A SOURCE 50 AND FILTERED IN 52, ARE DIRECTED ALONG PATH 14 IN A SAMPLE CHAMBER 2, ARRANGED IN THE CHAMBER 4, REFLECTED BY THE MIRROR 10 AND RETURNED TO DEVICES 46, 58 FOR DETECTION OF VISIBLE LIGHT (OPACITY, SOOT) AND INFRARED (CO, HYDROCARBONS). APPLICATION: ADJUSTMENT OF THE FUEL RICHNESS OF THE FUEL MIXTURE OF A BOILER.

Description

The present invention relates to a device

  to measure certain properties of gas from boilers or furnaces (hereinafter referred to as "boiler gas") escaping through a flue. Such measures serve to control the fuel richness of the fuel and air mixture introduced into the boiler in order to minimize the waste of fuel due to the heating of excess air and the subsequent discharge to the boiler. atmosphere of

  this excess air thus heated.

  The modern practice of controlling combustion involves the simultaneous measurement and control of a number of properties of gases escaping from boilers burning fossil fuels. In the usual case, the carbon monoxide content of the gases is measured and adjusted to a predetermined level which constitutes a target or setpoint value. At high air rates compared

  to fuel, that is to say, to low fuel

  The carbon monoxide rate is usually low at about one hundred millionths. When the proportion of oxygen falls just below the level necessary to completely oxidize all the carbon and hydrogen of the fuel, the rate of carbon monoxide begins to increase rapidly. It is at the beginning of this rise in the rate of carbon monoxide that we place

  usually the set point of this rate.

  Under certain conditions, other limitations of decreasing air-to-fuel ratios are achieved before the level of carbon monoxide begins to increase rapidly. In some cases, elemental carbon will precipitate before burning, which increases the smoke opacity in the chimney. In other cases, poor adjustment of the burner or fouling of the end

  this burner can lead to excessive

  high levels of hydrocarbons. So, in order to adjust the

  In the most interesting way, it is important to simultaneously measure carbon monoxide and hydrocarbon levels as well as the degree of opacity.

  gases escaping through the flue.

  There are a number of well-known methods

  to measure the levels of carbon monoxide and hydrocarbons

  bures in flue gases. The preferred method

  call for infrared absorption spectrometry.

  In this method, selected wavelengths of infrared energy are transmitted through a sample of the gas to be analyzed. The rate of infrared energy passing through the gases is then compared with the rate of infrared energy in

  the absence of these gases. The measurement thus obtained of

  energy at these wavelengths gives a qualitative and quantitative measure of the

  gas, in this case carbon monoxide and hydrocarbons.

  There are also well known methods for measuring the opacity of the flue gases. A preferred and well known method is to transmit through the gas to be analyzed the energy (from a source of a photopic light whose wavelength distribution is equivalent to the response of the human eye) and to measure then the amount of light transmitted, the value of the opacity

  defining as the unit minus the transmission.

  It is better to carry directly into the car-

  in the chimney, the measurement of the composition of the gases

  of combustion to eliminate the effects of stratification

  constituents of these gases. To protect the measuring instrument against corrosive and hot combustion gases, special windows isolate the instrument from the gases. After a certain period of time, dirt tends to accumulate on windows and cause errors for flue gas analysis. Similarly,

  variations in energy or light from

  these and the sensitivity of the detectors can lead to errors. One way to reduce such errors is to provide a sample chamber disposed across the flue and which can be periodically purged by air

  clean to allow calibration of the device.

  It is particularly desirable to measure

  simultaneously and, preferably in a single volume of sample

  through the sample chamber, the rates

  carbon monoxide and hydrocarbons as well as opacity

  cited flue gases. Thus, two separate energy beams, one of infrared radiation and the other of visible light, can be transmitted through a single sample chamber, but the size that the sample chamber must thus present to allow the passage of the two beams. then tends to be so large that this sample chamber itself may cause undesirable turbulence that may interfere with the periodic purge. Thus, it has not been possible so far to group these adjustment and measuring devices with a chamber

interesting sample.

  To overcome the disadvantages of prior art,

  The present invention aims to provide an apparatus for simultaneously measuring the opacity, carbon monoxide content and hydrocarbon content of the flue gases.

  and suitable for use with sample chambers

  relatively small and effective, arranged across flues. The invention also aims at providing such an apparatus in which all the measurements are carried out

  along a single measurement path through a flue.

  In the apparatus of the invention, the source of the visible light energy is separated and independent of the source

  infrared energy used for such measurements.

  To achieve the foregoing and other purposes, the present invention provides an apparatus for simultaneously measuring opacity, carbon monoxide content, and flue gas hydrocarbon content along a single path of travel. measuring through a flue. The apparatus comprises a sample chamber disposed across the flue, from one side to the other thereof, and through which the gases of this flue can flow; organs

  defining a single-axis optical path crossing

  longitudinally the sample chamber and which comprise a convergent member adjacent one side of the flue and an optically reflective member adjacent to the other side of the

  flue; a source intended to produce a predefined level

  finished visible light energy; a source for producing a predetermined level of infrared energy and which is independent of the source of the visible light energy;

  a device for detecting the level of

  ble having passed through the sample chamber along the optical path to and from the reflector element; and a device for detecting the level of infrared energy passed through the sample chamber along the optical path to and from the reflector element. The infrared energy source provides this infrared energy at predetermined spectral bands of between about 3 and 5 microns and directs this infrared energy along the single-axis optical path

to the reflector element.

  A particularly preferred embodiment of the apparatus of the invention will now be described, by way of non-limiting example, with reference to the appended drawing in which

  FIG. 1 is an exploded view of the elements constituting

  general purposes of the optical flue gas analysis apparatus according to the present invention; and Figure 2 is a fragmentary side section

  and schematic of the apparatus of the present invention,

in a flue.

  This apparatus comprises a sample chamber 2 disposed across a flue 4 and one side of the flue to the other. When this sample chamber 2 is in the position shown in FIG. 1, the combustion gases, generally indicated by a large arrow 6, can flow through this chamber 2. The chamber 2 is advantageously of the type illustrated in FIG. U.S. Patent Application No. 19,640 filed March 12, 1979 by Howard A. Powers and to which

  refer for a more complete description. Only one

  one end of this chamber 2 is illustrated on the

figure 1.

  One end of the sample chamber 2

  carries a window 8 (represented by an interrupted line) made of a suitable material, transparent to both visible light and infrared radiation, and

  forms a window formed through one side of the flue 4.

  On the outside and directly near this side of the flue 4 is mounted a retro-reflective trirectangular trihedron 10, which comprises an element that can optically reflect the light.

  visible as well as infrared radiation.

  A second window 8 ', also transparent

  infrared radiation and visible light, is also

  It is arranged in the side of the flue 4 situated opposite the window 8. A suitable convergent element, illustrated diagrammatically in FIG. 1 by a lens 12, is disposed near this second window 8 '. Advantageously, the windows 8 and 8 'and the convergent element 12 can be

  made of calcium fluoride or any other

  before transmitting both infrared and visible light.

  The optical axis of the convergent element 12 and the retro-reflector

  10 longitudinally crosses the chamber 2 and defines an optical path for the energy to pass through the chamber

  2 from the convergent element 12 to the retro-reflec-

  10 and to return through the chamber 2 to the convergent element 12. This optical path to a single axis

  is designated by the reference index 14.

  An incandescent lamp or other suitable source of visible light energy 16, which emits at least a significant portion of its energy into the spectral band

  between 500 and 600 nanometers, is preferably

  on the optical path 14, as shown in FIG.

  This source 16 emits its visible light energy towards and along the optical path 14. The portion of the energy emitted by this source 16 towards the optical path 14 meets on its

  a wheel 18, mounted in a conventional manner to be

  born by a conventional device and turn at a speed pre-

  determined. This wheel 18 comprises radially spaced around its axis of rotation and towards its periphery several neutral filters 22, 24, 26 and 28 of predetermined density arranged to cut the optical path aligned on the optical path 14. The wheel 18, to

  role of periodic interruption, also includes several

  cooperating in a conventional manner with an electronic diode

  30 and a phototransistor 32 for transmitting clock signals for indicating when each filter or each space between the filters is aligned with the

  optical path from the light source 16 to the

  14. In the same way, the wheel 18 has an additional hole

  cooperating with an electroluminescent diode 34 and a phototransistor 36 for transmitting a registration signal for identifying which of the filters or spaces between

  the filters that is aligned with the optical path.

  A splitter 38 of the visible light beam, which is advantageously of the type commonly referred to as a dielectric beam splitter and allows about half of the energy of visible light from the source 16 to pass through to the convergent element 12 , is disposed between the wheel 18 and this element 12. Similarly, in the alignment of the optical path 14 and between the resolver of

  beam 38 and the convergent element 12 is arranged a combination of

  beam combiner / splitter 40, which is advantageously made of glass having a light metal coating on the adjacent side of the convergent element 12. This combiner / beam splitter 40 passes most of the visible light energy1 which can so be concentrated by the element 12 and directed along the optical path 14 to the retro-reflector 10 to return through the element 12 and

  the combiner / separator 40 to the splitter 38.

  The inclination of the splitter 38 allows about half of the visible light energy received back from the retro-reflector 10 through the combiner / splitter 40 to be spaced by reflection of the optical path axis 14 to traverse a lens. convergent lens 42 and a photopic filter 44 chosen so that approximately 90% of the energy passing through this filter 44 are in the range

  spectral range of 500 to 600 nanometers.

  From this photopic filter 44, the visible light energy is then directed to a conventional silicon detector 46 which serves as a device for detecting the level of visible light energy having passed through the sample chamber 2 along the optical path 14 and who came back. With its light metal coating arranged on the side directed towards the convergent element 12, the combiner /

  beam splitter 40 can very strongly reflect.

  infrared energy. The inclination of this combiner / sepa-

  40 relative to the optical axis 14 is also such

  that the infrared energy received by this element 40 from

  The nance of the convergent element 12 along the optical axis 14 will also be spaced from the axis 14 and directed along another optical axis 48. On this optical axis 48 is aligned a suitable source 50 of infrared energy covering at

  less the spectral range between 3 and 5 microns.

  Between this infrared source 50 and the combiner / separator

  40, a wheel 52 is mounted in a conventional manner so as to

  see turning under the effect of a conventional workout. FIG. 1 shows this wheel 52 equipped with five filters.

  advantageously contains at least three interfering filters.

  suitable spacers spaced radially about its axis of rotation and towards its periphery and which will selectively transmit the energy of the corresponding spectral band

  with carbon monoxide, the band corresponding to the hydro-

  carbides and a reference band in a region between 3.5 and 4.1 microns. The reference strip is chosen so as to avoid absorption by any constituent of the gases circulating in the flue; it allows a correction to account for variations that are not related to the concentrations

  carbon monoxide and hydrocarbons in the flue.

  The wheel 52 may advantageously also include holes

  cooperating with suitable pairs of electronic diodes

  luminescent and photo-transistors in order to indicate when each filter or space between the filters is in position in front of the infrared source to enable samples to be identified in the manner

  described above about wheel 18.

  An infrared beam splitter 54 includes

  An uncoated germanium window is interposed between the wheel 52 and the combiner / separator 40. About half of the energy from the source 50 can pass through this splitter 54 and be reflected by the combiner / splitter along the optical path 14. passing through the sample chamber 2 to go to the retro-reflector 10 and back to the combiner / separator 40. It is reflected thereon to the splitter 54 which sends by reflection about half of this energy from the combiner /

  separator 40 to a lens 56 of concentration of infra-

  red and a set 58 of infrared detection. This assembly 58 may conveniently comprise a detector

  lead selenide cooled by a thermo-electric device

  that or other suitable device.

  It follows from the above description of the

  that chopped visible light pulses can be directed along optical path 14 to chamber 2

  sample they are going through to return to the

  detector 46, which can measure the level of visible light energy in the spectral range between 500 and 600 nanometers and emit signals processed in a suitable and conventional manner. When the sample chamber 2 is disposed as illustrated in FIG. 1, the flue gases, indicated by the large arrow 6, pass through this chamber and the visible light signal

  will be mitigated by carbon or soot eventually

  held in these gases. When the outer casing of the sample chamber 2 is rotated by 900, for example in the manner described in detail in the aforementioned Patent Application No. 19,640, this chamber 2 will be purged of the exhaust gases and will have no inside. only relatively clean air. During this purge, the visible light source and the detection device can be calibrated and

  standards to provide absolute measures of the opacity

  cited when the flue gases can again pass through chamber 2. Similarly, the absorption of

  the infrared energy emitted by the source 50 in the different

  the spectral bands chosen by the various filters of the wheel 52 by measuring the level of the infrared energy

  received by the detector 58 when the flue gases are

  pour room 2 and also during the purge of this

  chamber for calibration and standardization.

  The particular structure of the apparatus of the present invention is remarkably advantageous in that

  that the device measures along an optical path corresponding to

  single-axis at a time attenuation of visible light and absorption of infrared, and that these measurements are made simultaneously at the same position in the flue. This is advantageous not only for normalizing and adjusting the sampling conditions, but also for allowing the use of a relatively small diameter sample chamber which substantially disturbs the flow of gases in the flue. If certain spectral bands have been indicated above for the various filters, it goes without saying that infrared filters corresponding to many other combinations of spectral bands and neutral filters corresponding to various density levels and that one uses with the visible light source. Various combinations of these filters can be used to meet the rules necessarily applicable for adjustments and which are specified, for example, by an environmental protection agency, such as, for example,

  Rules 40 to 99 concerning the protection of the environ-

  and issued by the C.F.R. Committee.

  different types of furnaces or boilers and different fuels.It is also obvious that the signals generated by

  visible light and by the infrared detector 58 can

  in any suitable manner, preferably by a digital device, in order to obtain the data

wanted in the desired form.

  It goes without saying that, without departing from the

  vention, many modifications can be made to the electro-optical flue gas analyzer,

described and represented.

Claims (8)

  1. An electro-optical gas analyzer for simultaneous measurement of opacity, carbon monoxide content and flue gas hydrocarbon content along a single measurement path through a flue, this apparatus being characterized in that it comprises:   a sample chamber (2) arranged transversally   from one side to the other of the flue (4) and which can be   poured by the flow (6) of the gases flowing through this flue; a device defining a single-axis optical path (14) extending longitudinally through this chamber (2), said device comprising a convergent element (12) disposed in the vicinity of one side of the flue (4) and a reflection element (10) optical device disposed near the other side of this flue (4) and can be used to reflect a beam of radiant energy from this convergent element to   return it along the optical path (14) and make it   pour this element again (12); a source (16) for producing visible light energy and directing it along the optical path (14) to the reflector element (10); a source (50), independent of the source (16), for producing infrared energy at predetermined spectral bands between about 3 microns and 5 microns and for directing this infrared energy along the optical path (14) to the reflective element (10); a device (46) for detecting the level of visible light energy having passed through the chamber   (2) along the optical path (14), through the element   vergent (12) to the reflecting element (10) and returning from this element (10) and through the convergent element (12), and a device (58) for detecting the level of infrared energy having passed through the bedroom (2) along   optical path (14) passing through the convergent element   gent (12) to reach and return to the reflector element (10) to cross the convergent element (12) again; which makes it possible to measure along a single optical path (14) passing through the chamber (2) the energy levels   visible and infrared energy having passed through this chamber.   (2) gas sample. 2. Apparatus according to claim 1, characterized in that it also comprises a device allowing the   to divide the energy of visible light into pulses   of predetermined duration and spacing and periodically applying neutral filters of predetermined density   visible light produced by the source (16) and directed   along the optical path (14).   3. Apparatus according to claim 2, characterized   in that the aforementioned device comprises a wheel (18) for   rotating to periodically interrupt the propagation of the beam and which comprises neutral filters (22, 24, 26, 28) radially spaced about its center of rotation and on the periphery of this wheel.   4. Apparatus according to claim 1, characterized   in that it also includes a device for   divide the infrared energy into pulses of duration,   predetermined spacing and wavelength.   5. Apparatus according to claim 4, characterized in that the device for dividing the infrared energy comprises a rotating element (52) comprising, spaced apart   radially around its center of rotation and at its phérie, several filters.   6. Apparatus according to claim 1, characterized in that it also comprises a beam splitter (38) for passing the energy of visible light from the source (16) to the chamber (2) along the path optical (14) and away from this optical path (14) to a single axis, by reflection, the visible light received back from this chamber (2) for directing this light to the device (46) of   detection of the level of visible light.   Apparatus according to claim 1, characterized in that the source (50) of infrared energy is arranged outside the single-axis optical path (14) and in that the apparatus also comprises a combiner / separator (40). beam which intersects this optical path (14) and is   to let through the visible light energy for the trans-   put and think about the optical path (14) to a single   axis the infrared energy from the source (50).   8. Apparatus according to claim 7, characterized in that it also comprises a beam splitter (54) interposed between the source (50) of infrared energy and the   combiner / separator (40) and intended to pass the energy   infrared source from the source (50) to this combiner / separator (40) and reflect to the device (58) for detecting   infrared the infrared energy received back from the room bre (2).