MEASURING FACILITY AND METHOD FOR THE MEASUREMENT OF AT LEAST TWO DIFFERENT COMPONENTS OF A FLUID

Abstract

In a method for measuring at least two different components of a fluid, the fluid is to a first measuring cell and a second measuring cell. In the first measuring cell, a first component of the fluid is excited by a first excitation to trigger a first light emission, and in the second measuring cell, a second component of the fluid is excited by a second excitation which is different from the first excitation, thereby triggering a second light emission. The first light emission and the second light emission are captured by an optical system facility and guided by the optical system facility in a direction of a detector facility which measures the first light emission and the second light emission.

Claims

1. A method for measuring at least two different components of a fluid, said method comprising: feeding the fluid to a first measuring cell and a second measuring cell; exciting a first component of the fluid hi the first measuring cell by a first excitation to trigger a first light emission; exciting a second component of the fluid in the second measuring cell by a second excitation which is different from the first excitation, thereby triggering a second light emission; capturing the first light emission and the second light emission via an optical system facility; guiding the first light emission and the second light emission in a direction of a detector facility; and measuring by the detector facility the first light emission and the second light emission.

2. The method of claim 1, wherein the first excitation is a laser excitation.

3. The method of claim 1, wherein the first component is nitrogen dioxide.

4. The method of claim 1, wherein the first light emission is a Raman radiation.

5. The method of claim 1, wherein the second excitation is realized by dosing a reactant resulting in a chemiluminescence with the second component of the fluid.

6. The method of claim 5, wherein the reactant comprises ozone and/or the second component is nitrogen monoxide.

7. The method of claim 1, wherein the first light emission is measured using a first bandpass filter and/or the second light emission is measured using a second bandpass filter.

8. The method of claim 1, wherein the first light emission comprises a light emission of the first component and a light emission of a further component different from the first component.

9. A measuring facility for measuring at least two different components of a fluid, said measuring facility comprising: a first measuring cell designed to enable the fluid to be fed to the first measuring cell; an excitation apparatus operably connected to the first measuring cell and configured to generate a first excitation for exciting a first component of the fluid when the fluid is fed to the first measuring cell; a second measuring cell designed to enable the fluid to be fed to the second measuring cell, with the fluid when fed to the second measuring cell causing in the second measuring cell a second component of the fluid to be excited by a second excitation which is different from the first excitation; an optical system facility operably connected to the first measuring cell and configured to capture a first light emission triggered by the first excitation, and operably connected to the second measuring cell and configured to capture a second light emission triggered by the first excitation; and a detector facility operably connected to the optical system facility to enable the optical system facility to guide the first light emission and the second light emission in a direction of the detector facility, said detector facility configured to measure the first light emission and the second light emission.

10. The measuring facility of claim 9, further comprising a further excitation apparatus operably connected to the second measuring cell and configured to generate the second excitation in the second measuring cell,

11. The measuring facility of claim 9, wherein the second measuring cell comprises an inlet for the fluid, an outlet for the fluid, and a further inlet for passage into the second measuring cell of a reactant which chemically reacts with the second component of the fluid and generates a chemiluminescence emission.

12. The measuring facility of claim 9, wherein the optical system facility comprises a first receiving optical system apparatus and a second receiving optical system apparatus.

13. The measuring facility of claim 12, wherein the first excitation excites hi the first measuring cell in the fluid a further component of the fluid which is different from the first component, so that the first light emission comprises a light emission of the first component and a light emission of the further component, said second receiving optical system apparatus being operably connected to the first measuring cell and configured to select the light emission of the further component and to guide it hi the direction of the detector facility, said detector facility being operably connected to the second receiving optical system apparatus and configured to measure the light emission of the further component.

14. The measuring facility of claim 9, wherein the optical system facility comprises a bandpass filtering facility configured to select fluid component-specific light emissions.

15. The measuring facility of claim 9, wherein the optical system facility comprises a first stage and a second stage, with the first stage provided for spatial filtering of the first light emission triggered in the first measuring cell, and with the second stage provided for mapping the spatially filtered first light emission onto the detector facility,

Description

BRIEF DESCRIPTION OF THE DRAWING

[0032] Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

[0033] FIG. 1 shows a schematic representation of a Raman photometer in a perspective view;

[0034] FIG. 2 shows a first sectional representation of the Raman photometer in FIG. 1;

[0035] FIG. 3 shows a second sectional representation of the Raman photometer in FIG. 1;

[0036] FIG. 4 shows a Raman measurement of 960 mg/ma NO.sub.2 with 19.9 vol. % O.sub.2;

[0037] FIG. 5 shows a Raman measurement of synthetic air; and

[0038] FIG. 6 shows a Raman measurement of 100 vol. % CO.sub.2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments may be illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views, In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

[0040] Turning now to the drawing, and in particular to FIG. 1, there is shown a Raman photometer or a Raman scattered light photometer 1, which can correspond to a measuring facility accoridng to the invention. The Raman photometer 1 includes an advantageoulsy pressure-resistant (for example 10 bar), for example cube shaped, first measuring cell 2, through which a fluid 3, for example a gas, in particular an exhaust gas from a combustion, can flow at elevated regulated pressure up to 10 bar absolute. The fluid 3 can enter the first measuring cell 2 via a gas inlet 4 of a gas inlet chamber and leave the cell at two gas outlets 5. Advantageously, the gas outlets 5 are arranged at a right angle to the first measuring cell 2 and lead out of the first measuring cell 2 upwards and downwards in the drawing.

[0041] A laser light apparatus with a laser light source 7 is associated with the first measuring cell 2 and advantageously arranged on the first measuring cell 2 opposite the gas inlet chamber, and advantageously secured.

[0042] As shown in FIG. 1, the measuring facility 1 includes an optical system facility 12,33. The optical system facility 12,33 is likewise associated with the first measuring cell 2 and is adapted to capture light emissions 15, 45 (see FIG. 2 and FIG. 3) triggered in the first measuring cell 2 by way of a laser excitation 6 provided by means of the laser light source 7 and to map them onto a detector facility 29, 43. The optical system facility can include a first receiving optical system apparatus 12 and/or a second receiving optical system apparatus 33.

[0043] Furthermore, it can be seen in FIG. 1 that the first receiving optical system apparatus 12 includes a filter wheel 21 with a plurality of bandpass filters 20 (see FIG. 2 and FIG. 3), 22, 23, 24, 25, 26 for fluid component-specific selection of the emitted radiation.

[0044] FIG. 2 shows a sectional representation of the Rahman photometer 1. The light beam 6 of the laser light source 7 falls for example through a diaphragm 8, via a focusing lens 9 and an interference filter 10 into the measuring cell 2 and penetrates it in the direction of the gas inlet 4, where it is captured for example in a backscatter-free light trap 11. The line segment (beam waist), focused by the lens 9, of the light beam (Gaussian beam) 6 can be positioned in the center of the first measuring cell 2 in order to generate there for example a maximum light yield during the excitation of corresponding fluid components. Furthermore, the center of the first measuring cell 2 can be arranged in a focal point of the entry lenses 16, 36 of the first or second receiving optical system apparatus 12, 33.

[0045] The beam quality and line width of the laser beam 6 can be improved by a diaphragm 8 and an interference filter 10, for example a narrow band one, so the background signal in the first measuring cell 2 can be brought to a low level. The background signal can be greatly reduced, moreover, by the arrangement and configuration of the gas outlets 5 and the light trap 11.

[0046] FIG. 3 shows a further sectional representation of the Rahman photometer 1. The first receiving optical system apparatus 12 and the second receiving optical system apparatus 33 for the Raman photons 15, 45 scattered at the molecules of the fluid 3 can be arranged, advantageously attached, on/to the first measuring cell 2 at a right angle to the laser beam 6. Advantageously, the second receiving optical system apparatus 33 is arranged opposite the first receiving optical system apparatus 12. At this point it should be noted that the use of both receiving optical system apparatuses 12,33 is optional.

[0047] One or more component(s) of the fluid 3 can be excited by the laser 7. A plurality of wavelength-specific light emissions 15, 45 can thus be produced in the first measuring cell 2, and these are triggered by laser excitation 6 of different components of the fluid 3.

[0048] Different fluid components, which can be excited by laser excitation 6, may also be detected solely by the first receiving optical system apparatus 12 in that different bandpass filters 20, 22, 23, 24, 25, 26 are alternately employed,

[0049] The use of the second receiving optical system apparatus 33 is advantageous in order to simultaneously detect the different light emissions 15, 45 from the first measuring cell 2. In this case, different bandpass filters 20, 40 can be used in the first and in the second receiving optical system apparatuses 12, 33, and these are appropriately selected for the respective light emission 15, 45.

[0050] The selection of an appropriate bandpass filter 20, 22, 23, 24, 25, 26, 40 for detection of a corresponding Raman radiation 15, 45 can be summarized hi a table as follows.

TABLE-US-00001 TABLE 1 Selection of the central wavelength of the bandpass filter for different gas components with a laser with a wavelength of 402 nm. Relative Central Raman wavelength of Raman scatter the Raman band Gas shift cross-section with a 402 nm component [cm-1] for N.sub.2 excitation [nm] H.sub.2 (hydrogen) 4155 3.9 483 N.sub.2 (nitrogen) 2331 1 444 CO.sub.2 1285 0.8 424 (carbon 1388 1.1 426 dioxide) 1265 424 O.sub.2 (oxygen) 1555 1.0 429 NO.sub.2 1500 RRS with 402 428 (nitrogen nm excitation dioxide) 1440 RRS with 402 427 nm excitation 1315 RRS with 402 424 nm excitation 3200 RRS with 402 461 nm excitation 3915 RRS with 402 477 nm excitation H.sub.2O 3650 4.5 471 3657 471

[0051] RRS stands for Resonant Raman Scattering in this case.

[0052] From Table 1 it emerges that the measurement of oxygen at 429 nm with a bandpass filter, with a full width of half maximum (FWHM) of 10 nm, of CO.sub.2 (up to 15 vol. % contained in the measuring gas 3) can be disrupted. If the bandpass filter for O.sub.2 cannot be selected to be appropriately narrow, a bandpass filter for CO.sub.2 can also be employed, for example in the filter wheel 21, and a two component determination can be made via a serial measurement (in accordance with the MLR calibration method, matrix inversion in accordance with the method of Multiple Linear Regression). The optimum wavelength for the detection of NO.sub.2 lies at 477 nm, with it being possible to rule out a possible cross sensitivity to hydrogen and water by way of a FWHM of the bandpass filter of 10 nm.

[0053] The receiving optical system apparatuses 12,33 can each have two stages 13, 14, and 34, 35, with the scattered light 15, 45 being focused with the aid of one or more lens(s) 16, 17 onto a rectangular diaphragm 18 in the first stage 13, 34 in each case. The diaphragm 18 can be designed, for example, as a slit diaphragm. The opening 52 can have, for example, a size of approx, 1×4 mm.

[0054] The scattered light 15, 45 can be spatially filtered by the first stages 13, 34, so only those photons, which were scattered from a limited volume around the focused line segment of the laser beam 6, pass into the respective second stage 14, 35. The entry lens 16, 36 of the respective first stage 13, 34 can serve as a pressure-resistant termination or pressure-resistant window of the first measuring cell 2.

[0055] In the respective second stage 14, 35, the scattered light 15, 45 collimated by means of a lens 19, 39 passes through the respective bandpass filter 20, 40. Each of the bandpass filters 20, 22, 23, 24, 25, 26, 40 can be designed in the form of a narrowband (full width of half maximum (FWHM)=5-10 nm for the Raman photons) interference filter or optionally two interference filters located one behind the other. The photons selected gas component-specifically by the respective bandpass filter 20, 40 can be mapped by means of a further lens 21, 41 onto a, for example rectangular, photocathode 28, 42 (for example approx. 1×4 mm in size) of a corresponding photomultiplier 29, 43, by means of which they can be individually detected. Each photomultiplier 29, 43 generates in each case one output signal (for example a Raman signal when the photons from the first measuring cell 2 are detected) 30, 44, which is proportional to the number of photons absorbed by the photocathode 28, 42 per unit of time and is fed to an evaluation facility (processor) 31 for evaluation and ascertaining as well as output 32 of the concentration of the measured fluid components.

[0056] The respective photomultiplier 29, 43 serves to convert the Raman photons generated in only a very small number, in particular also owing to the low laser power, into a sufficiently strong output signal 30, 44. In addition, the measurements can be made in the case of elevated pressure in the first measuring cell 2 of, for example, 5 bar absolute, because the number of generated Raman photons and therewith the Raman signal 29, 43 increase proportionally with the measured gas pressure. A pressure regulator (not shown) can be provided for this purpose at the, optionally merged, gas outlets 5.

[0057] Provision may be made for use of a laser light source 7 with a wavelength appropriate to the electronic transition in the NO.sub.2 molecule in order to allow a sensitive (detection omit below 0.5 ppm (parts per million)) detection of NO.sub.2. For example, a wavelength of a laser diode of around 400 nm, for example 402 nm, in particular 405 nm, can be expedient for this purpose. These short wavelengths can also provide for a good Raman photon yield (proportional to λ¼) in the case of O.sub.2 and further components (CO.sub.2 and N.sub.2) in the measuring gas 3 and do not cause fluorescence. In the Raman scattering of NO.sub.2 it is advantageous that it is possible to make use of the principle of Resonant Raman Scattering (RRS) due to the stimulated emission from the excited electronic energy level. This can result in an approximately 100-fold amplification of the output signal 30, 44 and therewith in an improvement in the detection limit.

[0058] The bandpass filters 20, 40 can be selected such that, for example, nitrogen dioxide and oxygen are simultaneously measured in accordance with the Raman measuring method described above.

[0059] In addition, the laser power can be limited to below 35 mW to satisfy the ex-protection, it being possible to achieve a detection limit for nitrogen dioxide <1 ppm with a measuring duration of one second.

[0060] The Raman photometer 1 also provides a second measuring cell 46. The second measuring cell 46 is, for example, not pressure-resistant The second measuring cell 46 is designed in such a way that it can be fed with the measuring gas 3 and, when the measuring gas 3 is fed in the second measuring cell 46, at least one second component of the measuring gas 3 in the second measuring cell 46 can be excited by a second excitation 47 different from the first excitation 6.

[0061] The second measuring cell 46 can be configured as a chemiluminescence measuring cell. The second component of the measuring gas 3 is, for example, nitrogen monoxide, which is transferred by feeding a reactant, for example ozone 47, into an excited state and emits light—chemiluminescence 48—as a consequence of de-excitation.

[0062] The chemiluminescence 48 of the reaction of nitrogen monoxide (NO) with ozone 47 takes place in a range between about 600 nm to 3,000 nm (see for example: http://teaching.shu.ac.uk/hwb.chemistry/tutorials/molspec/lumin1.htm, retrieved on Dec. 17, 2020). The photomultipliers 29, 43 are advantageously sensitive to about 700 nm. It can thus be expedient for the measurement of the chemiluminescence photons to employ a bandpass filter 22 of 650 nm with FWHM of about 100 nm. The respective photomultiplier 29, 43 also serves to convert the chemiluminescence photons 48 into an output signal (chemiluminescence signal) 30. The output signal can thus be, for example, a Raman or a chemiluminescence signal.

[0063] The concentration 32 of the first and/or the second component, for example of the nitrogen dioxide and of the nitrogen monoxide, can be ascertained on the basis of the output signals 30, 44.

[0064] It may be seen from FIG. 3 that the ozone 47 can be generated in an ozone generator 49. For example, the ozone 47 can be generated either from dry air 50 in a dielectrically hindered gas discharge or be generated with the aid of a UV lamp (for example with an intensity maximum <220 nm). In the case of the UV lamp it is advantageous that no nitrous oxides are generated from the atmospheric nitrogen. The ozone 47 can be fed, for example via a capillary (not shown), to the second measuring cell 46.

[0065] The second measuring cell 46 can be designed as part of the optical system facility 12,33. In particular, the second measuring cell 46 can be configured as an integral component of the first receiving optical system apparatus 12 (FIG. 3) or the second receiving optical system apparatus 33 (not shown),

[0066] As shown in FIG. 3, the second measuring cell 46 can be formed by a space arranged between the first and the second stage 13, 14 of the first receiving optical system apparatus 12 slit diaphragm 18 and the (entry) lens 19 of the second stage 14 of the first receiving optical system apparatus 12. The exit lens 17 of the first stage 13 can be configured, for example, as a focusing lens. The entry lens 19 of the second stage can be configured, for example, as a collimating lens.

[0067] As can be inferred from FIGS. 1 to 3, the first and the second receiving optical system apparatuses 12,33 and, in particular, the stages 13, 14, 34, 35 have, for instance, the shape of a hollow cylinder, with the optically active elements (lenses, diaphragms, bandpass filters) being received in the receiving optical system apparatuses 12,33 and, in particular, in the stage 13, 14, 34, 35. The respective stages 13 and 14 or 34 and 35 can be screwed together. The receiving optical system apparatuses 12,33 can likewise be screwed to the first measuring cell 2.

[0068] It may also be seen from FIG. 3 that the reactant 47 can be fed to the second measuring cell 46 via a chamber 51. The chamber 51 can be formed in the first stage 13 of the first receiving optical system apparatus 12. For example, the chamber 51 can be formed by a space between the exit lens 17 and the slit diaphragm 18. it can be expedient to feed the reactant 47, for example ozone, to the chamber 51 via the capillary.

[0069] During the measuring process, in which at least the second component of the fluid 3, for example nitrogen monoxide, is measured, the measuring gas 3 flows through the second measuring cell 46—by way of gas inlets and outlets (not shown here). At the same time the reactant 47 can be fed to the first chamber 51 in such a way that it passes through an opening 52 of the slit diaphragm 18 into the second measuring cell 46. In this case mixing of the reactant 47 with the fluid 3, which results in the chemiluminescence 48, takes place in the region of the opening 52 of the slit diaphragm 18. It can be expedient to select the opening 52 of the slit diaphragm(s) 18, 38 to be the same size as the cathode(s) 28, 42.

[0070] The opening 52 of the slit diaphragm 18 can be arranged in a shared focal point of the exit lens 17 of the first stage 13 and the entry lens 19 of the second stage 14. In this way the photons 48 produced by the chemiluminescence can be captured particularly easily and mapped onto the cathode 28 of the photomultiplier 29, As discussed above, a bandpass filter 22 of 650 nm with a FWHM of about 100 nm can be employed in the second stage 14 by means of the filter wheel 21 in order to selectively detect the chemiluminescence photons 48.

[0071] The measuring facility 1, as shown in FIGS. 1 to 3, allows simultaneous measurement of nitrogen dioxide (the first component of the fluid 3) and nitrogen monoxide (the second component of the fluid 3). The ozone dosing during the NO.sub.2 Raman measurement need not be interrupted, as would be the case if the fluid 3 in the first measuring cell 2 were excited by the laser light 6 and by ozone 47. With such simultaneous excitation in the same measuring cell, the NO.sub.2 reaction product in the Raman signal would also be measured during the chemiluminescence measurement. In addition, further nitrous oxides (N.sub.2O.sub.5, NO.sub.3), which are not detected in the Raman signal of the NO.sub.2, would be produced in the reaction of the NO with the excess ozone, so a separate measurement of the NO and NO.sub.2 via the two measuring methods is necessary in order to infer the NO concentration 32.

[0072] The afore-described measuring method can be easily calibrated with a range of calibrating gases. The measurement can be carried out on a continuous gas flow, with the result being available every second.

[0073] FIGS. 4 to 6 show exemplary measuring results for simultaneous determination of the concentrations of NO.sub.2 and O.sub.2 by means of the measuring facility 1 shown in FIGS. 1 to 3.

[0074] The Raman photons 15, 45 from the electronically excited NO.sub.2 molecules are counted by the first receiving optical system apparatus 12, fitted with a bandpass filter 20 with a central wavelength (CWL) of 486 nm (or with CWL 477 nm), with the photomultiplier 29.

[0075] The O.sub.2 measurement takes place with a bandpass filtering facility 40. The bandpass filtering facility 40 comprises a bandpass filter at CWL 430 nm. This bandpass filter can also allow Raman photons of NO.sub.2 and CO.sub.2 (carbon dioxide) to pass, however. For compensation of the O.sub.2 measurement an additional bandpass filter with CWL 420 nm was provided for this reason in the bandpass filtering facility 40 in order to compensate the interference components, for example with the aid of an MLR calibration (matrix inversion in accordance with the method of Multiple Linear Regression), CO.sub.2 and NO.sub.2.

[0076] The following bandpass filters (BPF) for example can be employed in the filter wheel 21: [0077] I. Semrock CWL 420 nm FWHM 5 nm [0078] II. Edmund Optics CWL 430 nm FWHM 10 nm [0079] III. Edmund Optics CWL 486 nm FWHM 10 nm

[0080] A test gas with the concentration 960 mg/m.sup.3 NO.sub.2 (rel. measuring uncertainty <2%) was caused to flow through the first measuring cell 2 (1l/min). The test gas also contained 19.9 vol. % O2 for stabilization of the NO2, with the remainder of the test gas being N.sub.2, A minimum detectable concentration of 3 mg/m.sup.3 (corresponds to approx. 1.5 ppm) resulted on the basis of the noise band, of the Raman signal 30, 44 recorded every second. The detection limit of O.sub.2 lies at 0.13 vol. % and of CO.sub.2 at 0.22 vol. % in this measurement.

[0081] FIG. 4 shows a Raman measurement of 960 mg/m.sup.3 NO.sub.2 with 19.9 vol. % O.sub.2. Signal to 240 sec. with the BPF I. then with BPF II. and from 480 sec. with BPF III. Raman signal in signal pulse per second.

[0082] FIG. 5 shows a Raman measurement of synthetic air (80 vol. % N2 with 20 vol. % O.sub.2). Signal to 310 sec. with the BPF (bandpass filter) I., thereafter with BPF II. The measurement with BPF III. is not shown because virtually only the background signal of the BPF III. is present (approx. 470 cps (counts per second)).

[0083] The measuring results in FIG. 4 and FIG. 5 with approximately equal O.sub.2 content of 20 vol. %, exhibit a higher contribution of NO.sub.2 in the case of BPF (bandpass filters) I. and II, caused by the Resonant Raman Scattering. The dark signal of the photomultiplier (when the laser is switched off) is at an almost negligible 10 cps but is deducted from the Raman signals.

[0084] FIG. 6 also shows a Raman measurement of 100 vol. % CO.sub.2. Signal to 240 sec. with the BPF I., then with BPF II. and from 480s with BPF III. with a logarithmic signal scaling.

[0085] In a practical exhaust gas application, it can be expedient to compensate the O2 signal (mainly with BPF II.) with the CO2 signal, irrespective of whether the CO.sub.2 concentration is higher than 15 vol. % or not.

[0086] The combined measuring method for NOx and O.sub.2 determination described in the context of this disclosure can be calibrated with a series of test gases (NO, NO.sub.2, O.sub.2, CO.sub.2, all N.sub.2 in remainder). The influence of CO.sub.2 and H.sub.2O on the chemiluminescence of the NO due to fluorescence quenching can be reduced by the measurement of the specific Raman photons of CO.sub.2 and H.sub.2O. The measurement can be carried out continuously on the gas flow removed by extraction and the concentrations of the individual components can, due to the clock of the filter wheel, be available at the latest every minute. If the oxygen measurement is omitted, the NOx measurement can also be carried out simultaneously with two receiving optical system. A lower detection limit can be achieved by an increase in the laser power and by averaging the measured values.

[0087] The reference characters in the claims serve solely for a better understanding of the present invention and do denote any kind of limitation of the present invention.

[0088] While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0089] What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: