Device for analysing a gas by means of raman scattering and method for operating a device of this type
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-06
- Publication Date
- 2026-03-18
AI Technical Summary
Raman spectroscopy for gas analysis faces challenges with detector saturation due to high light intensities or long exposure times, leading to the 'blooming effect' which distorts measurements and makes it difficult to analyze secondary components accurately, especially when a main component is present in higher concentrations.
The device uses optics to mechanically or optically block or attenuate the Raman scattering of the main component's wavelength range, allowing for extended measurement times or increased pressure to analyze secondary components more precisely, and includes a detector with varying optically active elements or filters to prevent blooming, reducing costs and complexity.
This approach enables more precise analysis of secondary components by preventing detector saturation, improving measurement reproducibility and reducing the risk of blooming effects, while still allowing for the measurement of main components with reduced accuracy.
Smart Images
Figure EP2024062393_14112024_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] title
[0003] Device for analyzing a gas by Raman scattering and method for operating such a device
[0004] State of the art
[0005] The invention relates to a device for analyzing a gas or gas mixture and to a method for operating such a device with features of the respective independent claim.
[0006] Raman spectroscopy can be used to identify and quantify gases in a gas mixture. Each gas exhibits a characteristic Raman spectrum. By analyzing the respective Raman spectrum, the gas can be identified and its concentration in the gas mixture determined. EP 3 961 195 A1 describes a gas measurement device based on Raman spectroscopy.
[0007] Disclosure of the invention
[0008] The problem underlying the invention is solved by a device for analyzing a gas using Raman scattering and a method for operating such a device with the features of the independent claims. Advantageous developments of the invention are specified in the dependent claims.
[0009] One of the advantages of the device according to the invention is that the secondary components of a gas can be analyzed more precisely than was previously possible. It should be noted here that the term "gas" is understood here and below to refer in particular to a gas mixture comprising different components. In such a gas mixture, it is often the case that there is a "main component" that is present in a larger percentage amount than at least one other component, which is therefore referred to as a "secondary component."
[0010] Highly sensitive detectors are required for Raman spectroscopy of gases. CCD detectors with a pixel matrix are commonly used (x-axis: signal versus wavelength, y-axis: signal along the focus spot or measurement spot; the signal is usually summed across all pixels along the y-axis; the y-axis thus represents the quantity or concentration of the gas in the gas mixture). The pixel matrix is read out electronically. Due to high light intensities or long exposure times, the resulting voltage in the pixel accumulates to such a high level that it reaches a maximum in a capacitor of the detector. Further illumination of the pixel area causes an "overflow," the so-called "blooming effect," which increases the charge of the neighboring pixels. This distorts the charge of the neighboring pixels.
[0011] To prevent the blooming effect, edge or bandpass or blocking filters are currently placed in the optical beam path of the Raman spectrometer. These filters attenuate the corresponding spectral ranges and prevent pixel matrix saturation. However, this is associated with high costs. Furthermore, individual Raman spectral ranges cannot be adequately filtered out in this way. Furthermore, the measurement results are not easily reproducible due to manufacturing difficulties.
[0012] All of these disadvantages are avoided in a very simple manner by the invention. In the device according to the invention, the Raman scattering in the wavelength range of the main component and / or the undesired gas fraction is mechanically or optically completely or partially masked out in order to avoid saturation of the detector in this range (typically a range on the x-axis of the detector). This makes it possible, for example, to extend the measurement time or increase the gas pressure in order to be able to analyze the secondary components more precisely. Specifically, a device for analyzing a gas by means of Raman scattering is proposed, which device comprises, among other things, a measuring chamber designed to at least temporarily contain the gas to be analyzed. The measuring chamber can, for example, also be part of a line, so that the gas to be analyzed flows through the measuring chamber.
[0013] The device also includes at least one detector designed to detect Raman scattering emanating from the gas contained in the measuring chamber or flowing through it. A typical detector is designed as a receiver chip (e.g. CCD, CMOS) with a pixel matrix of light-sensitive, i.e. optically active, elements. The device also includes optics arranged in the beam path of the Raman scattering towards the detector and designed such that a first wavelength range of the Raman scattering is directed onto a first region of the detector (along the x-axis of the detector) and a second wavelength range of the Raman scattering is directed onto a second region of the detector (along the x-axis of the detector), wherein the regions are at least approximately adjacent. The different regions of the detector are therefore arranged along the aforementioned x-axis.Different regions of the x-axis correspond to different wavelengths of Raman scattering. Such optics typically include a grating or a prism.
[0014] Finally, the device according to the invention includes an optical device that can at least attenuate the intensity of the Raman scattering directed at the first region. The term "at least attenuate" implies that the optical device is designed such that it transmits a portion of the Raman scattering directed at the first region. However, it also implies that the optical device is designed such that it completely blocks the Raman scattering directed at the first region. This prevents a blooming effect from the first region onto the second region of the detector.
[0015] Alternatively or additionally, it is possible for the detector in the first region to have a smaller number of optically active elements than in the second region, or for at least some of the optically active elements of the detector in the first region to be deactivated. In this case, an additional optical device for attenuating the Raman scattering directed onto the first region may even be dispensed with, thereby reducing the cost and complexity of the device.
[0016] In a further development, the optical device comprises at least one aperture and / or at least one filter. The beam path of the Raman scattering to the detector is thus at least partially covered by an aperture or a filter. This includes the aperture or filter being fixedly positioned in the optical path to the detector, or a partial area of the detector being directly covered or blackened. Thus, a partial area of the detector is no longer illuminated by the Raman scattering, or at least is only illuminated to a lesser extent by the Raman scattering.
[0017] In a further development, it is provided that the transmittance of the aperture or filter and / or the position of the aperture or filter and / or the size of the aperture or filter can be controlled. For example, it is possible to make the aperture and / or filter switchable using piezo or magnetic actuators and to move them into the optical beam path only when needed. With the described piezo actuator technology, even individual CCD pixel rows of a corresponding detector, which typically have a size of 20x20 pm, can be controlled. 2 can be controlled. In addition, a type of slide with "punched out" areas could be inserted in front of the CCD detector.
[0018] If the signal in a certain range is only to be reduced and not completely blocked out, then not an entire CCD pixel row is blocked out, but only a portion of the CCD pixel row in the desired spectral range. Transmittance can also be adjusted electronically, for example. If necessary, a type of control can even be set up that detects blooming and reduces the transmittance to the point where blooming no longer occurs at the detector. The same applies to controlling the size of the aperture or filter. For example, it is conceivable for the aperture or filter to be constructed from multiple elements, with more or fewer elements being introduced into the Raman scattering beam path depending on the current requirements. Overall, this refinement enables the device to be adapted and optimized to different situations.
[0019] In a further development, it is provided that the filter is arranged both in the beam path of the Raman scattering directed at the first region and in the beam path of the Raman scattering directed at the second region, but essentially only attenuates the strength of the Raman scattering directed at the first region. The filter therefore covers at least essentially all of the Raman scattering directed at the first region and the second region. However, the filter only absorbs or attenuates a specific wavelength range of the Raman scattering, namely the wavelength range directed at the first region of the detector. Thus, a partial region of the detector, namely the first region, is illuminated less intensely or not at all. Such a filter can be comparatively large, which makes it easier to manufacture and attach.
[0020] In a further development, the first range corresponds to a wavelength range of Raman scattering that corresponds to a signal from a suspected main component of the gas. This takes into account the fact that the intensity of the Raman scattering of one component in the gas relative to another component in the gas depends on the quantitative proportion of one component relative to the other component. If there is a main component in a gas, i.e. a component that is present in the gas in a significantly larger quantity than the other components, then there is a particularly high risk that such a main component will trigger a blooming effect. Because the Raman scattering of this main component can only hit the first range of the detector in an attenuated form or even not at all, the risk of the blooming effect is reduced from the outset or even eliminated.
[0021] In a further development, the optical device is designed in such a way, or the optically active elements of the detector in the first region are designed in such a way that the strength of the signal generated at the detector of the suspected main component of the gas is of the same order of magnitude as the strength of the signal generated at the detector of at least one secondary component. In this further development, the Raman scattering signal of the main component is thus attenuated such that it is of the same order of magnitude as the Raman scattering signal of the secondary components. In this way, a significantly improved resolution limit for the secondary components can be achieved, while at the same time the main component can still be measured (with reduced accuracy).
[0022] In a further development, the measuring chamber is arranged in the flow path between a process gas line and an outflow line. This allows the components of the gas present in the process gas line to be analyzed with high precision.
[0023] The invention also includes a method for operating a device of the type just described, which comprises the following steps: a. venting a process gas present in the process gas line through the measuring chamber in the direction of the outflow line; b. purging the process gas line with an inert gas via the measuring chamber in the direction of the outflow line until the proportion of the detected process gas at least reaches or falls below a lower limit. This significantly increases process reliability, as it can be determined with high accuracy whether the process gas is only present in such a small proportion in the process gas line that it no longer poses a risk to a user. A typical example of this is a process gas line whose process gas is hydrogen.For maintenance or repair work, the hydrogen must be completely removed from the process gas line and replaced with an inert gas, such as nitrogen, argon, or carbon dioxide. Using the device according to the invention in the process, it is possible to reliably detect even the smallest hydrogen components (minor component) in the process gas line purged with inert gas (main component). Once one gas has been replaced by the other, the filter can attenuate or completely block out the other gas to detect residual traces of one gas in the line.
[0024] In a further development of the method, it is proposed that the method further comprise the following steps: a. introducing process gas into the process gas line; b. flushing the process gas line with the process gas via the measuring chamber in the direction of the outflow line until the proportion of inert gas at least reaches or falls below a lower limit. This is the reverse case described in the previous paragraph. The use of the device according to the invention now allows reliable detection of the complete filling of the process gas line with the process gas (now the main component) and the complete removal of the inert gas (now the secondary component).
[0025] Embodiments of the invention are explained below with reference to the drawings. In the drawings:
[0026] Embodiments of the invention are explained below with reference to the drawings. In the drawings:
[0027] Figure 1 is a schematic diagram of a device for analyzing a gas mixture by means of Raman scattering with an aperture in the beam path of the Raman scattering directed onto a detector;
[0028] Figure 2 is a schematic diagram of a portion of the device of Figure 1;
[0029] Figure 3 is a diagram in which the intensity of an exemplary Raman scattering is plotted against the wavelength;
[0030] Figure 4 is a diagram aligned with Figure 3, in which the signal of a detector of a device for analyzing a gas mixture by means of Raman scattering is plotted against the wavelength, with an exemplary blooming effect (i.e. without the aperture of Figures 1 and 2);
[0031] Figure 5 shows the diagram of Figure 3;
[0032] Figure 6 is a diagram similar to that of Figure 4, aligned with Figure 5, but without the blooming effect (i.e., with the aperture of Figures 1 and 2); Figures 7-13 are schematic diagrams of regions of further embodiments of the device of Figure 1;
[0033] Figure 14 is a schematic diagram of the device of Figure 1 with a measuring chamber arranged in the flow path between a process gas line and an outflow line;
[0034] Figure 15 is a flowchart of a first method for operating the device of Figure 1; and
[0035] Figure 16 is a flowchart of a second method for operating the device of Figure 13.
[0036] In the following, functionally equivalent elements and areas in different figures and embodiments bear the same reference numerals. They are typically explained in more detail only when mentioned for the first time.
[0037] A device for analyzing a gas by means of Raman scattering is designated overall by reference numeral 10 in the figures. It comprises a radiation source, in this case a laser 12. This emits a laser beam 14 in the direction of a deflecting mirror 16. From there, the laser beam 14 passes through a polarizer 18 and a polarization rotator 20 to a beam splitter 22, which has different transmissions for the polarization of the laser beam 14. The laser beam 14 is directed via an objective 24 onto a gas mixture 26, which is located in a measuring chamber 28.
[0038] Energy transfer occurs through inelastic scattering of the laser light 14 by the molecules of the gas 26. The scattered light therefore has a higher or lower frequency than the incident light beam and is specific to the scattering atom or molecule. This scattered light is also referred to as Raman scattering. The Raman scattering emanating from the gas mixture 26 is designated 30 in the figures. It is guided via the lens 24 to the beam splitter 22, and it is deflected by the beam splitter 22, in this case by an example, by 90° in the direction of a detector 32. On the way from the beam splitter 22 to the detector 32, the Raman scatter 30 passes through a grating or prism 34, which refracts the Raman scatter 30 differently depending on the wavelength, a focusing lens 36 and a large-area filter 38 for a specific wavelength range (see Figure 2).
[0039] The detector 32 is, in the present case, by way of example, a CCD detector (a CMOS detector is also possible, for example) with individual CCD pixel rows arranged next to one another perpendicular to the plane of the page, one of which is designated by the reference numeral 40 in Figure 2. A pixel row 40 extends in the x-direction. The direction perpendicular to the plane of the page is the y-direction. An individual pixel, which can also be referred to very generally as an “optically active element,” is designated by way of example by 42 in Figure 2. The grating or prism 34, the focusing lens 36, and the filter 38 are collectively referred to as “optics 44.” The optics 44 are designed such that a first wavelength range of the Raman scattering 30 is directed onto a first region 46a of the detector 32, and a second wavelength range of the Raman scattering 30 is directed onto a second region 46b of the detector 32. The regions 46a and 46b are arranged longitudinally to the x-direction of the detector 32.
[0040] Between the filter 38 and the detector 32, the device 10 comprises an optical device 48, which can at least attenuate the intensity of the Raman scattering 30a directed at the first region 46a. In the present example, the optical device 48 comprises a diaphragm 50, through which the Raman scattering 30a directed at the first region 46a is completely blocked. This is based on the following facts:
[0041] In Figure 3, the intensity I of the Raman scattering 30 is plotted against the wavelength L of the Raman scattering 30 for the gas mixture 26 as an example. It can be seen that different substances in the gas mixture 26 are assigned different wavelength ranges. The ratios of the intensities I approximately reflect the proportion or concentration of the substance in the gas mixture 26. It can be seen here that the intensity I of the two wavelength ranges for hydrogen is significantly higher than the intensities I of the other substances in the mixture. Hydrogen is therefore significantly more strongly represented in the gas mixture analyzed here as an example than the other substances. In the gas mixture 26 analyzed here as an example, hydrogen is thus the main component, whereas the other substances, for example CO2, O2, N2, H2O, etc., are secondary components in the analyzed gas mixture 26.
[0042] In Figure 4, a signal S from detector 32 is plotted against the x-axis of detector 32, but for the case where aperture 50 shown in Figures 1 and 2 is not present. In the present example, the Raman scattering 30a of the hydrogen in gas mixture 26 is directed toward the first region 46a of detector 32, whereas the Raman scattering 30b of the other components is directed toward the second region 46b of detector 32. It can be seen from Figure 4 that in the first region 46a of detector 32, the pixels 42 of detector 32 are saturated, which results in the pixels 42 of detector 32 also being at least largely saturated in the adjacent second region 46b of detector 32. This is called the "blooming effect."This leads to the fact that the secondary components, which are present in the gas mixture 26 only in small quantities compared to the main component hydrogen, cannot be detected or cannot be detected correctly by the detector 32, since the second region 46b is “blinded” by the first region 45a.
[0043] Figures 5 and 6 depict a situation similar to that in Figures 3 and 4, but for the device 10 shown in Figures 1 and 2, which has the aperture 50 in the beam path of the Raman scattering 30 toward the detector 32. The Raman scattering 30a directed toward the first region 46a cannot thus reach the detector 32, but is absorbed by the aperture 50. Accordingly, it can be seen that in the second region 46b, corresponding signals S are generated for all secondary components present in the gas mixture 26. The signal strength S is proportional to the intensity I and thus to the quantity or concentration of the substance in the gas mixture 26.
[0044] The basic principle of absorption of Raman scattering 30a of the main component of the gas mixture 26 by the aperture 50 is shown again in Figure 7. The signal S generated by the detector 32 in the second region 46b is designated 52b in Figure 7. In the embodiment of Figure 8, the aperture 50 is not arranged at a distance from the detector 32, but is applied directly to the pixels 42 of the first region 46a of the detector 32. For example, this can be achieved by blackening the detector 32 in the first region 46a. Alternatively, the pixels 42 of the first region 46a of the detector 32 could also be deactivated.
[0045] In the embodiment of Figure 9, the detector 32 has a smaller number of pixels 42 in the first region 46a than in the second region 46b. In the present example, the first region 46a has no pixels 42 at all.
[0046] In the embodiment of Figure 10, a filter 54 is arranged at a distance from detector 32. This filter selectively attenuates the wavelength range of the main component, i.e., at least substantially only the intensity of Raman scattering 30a directed onto first region 46a, so that its intensity approximately corresponds to the intensity of the secondary components. Accordingly, detector 32 generates a signal 52a whose strength is approximately the same as signal 52b. In this way, a significantly improved resolution limit for the secondary components of gas mixture 26 can be achieved. At the same time, the main component can still be detected, albeit with reduced accuracy.
[0047] In the embodiment of Figure 11, the situation is similar to that of Figure 10, but the Raman scattering 30a directed onto the first region 46a is completely absorbed by the filter 54.
[0048] In the embodiment of Figure 12, a filter 50 is provided which can be electronically controlled, as indicated by an arrow 56. The electronic control can, for example, influence the absorption coefficient of the filter 54. Alternatively or additionally, the position of the filter 54 along the x-axis of the detector 32 can also be influenced by the electronic control. Again alternatively or additionally, the size of the filter 54 can also be influenced by the electronic control. In an embodiment not shown, an aperture is provided instead of a filter, the size and / or position of which can be influenced by an electronic control. In any case, the control can be carried out, for example, by means of piezo or magnetic actuators. With piezo actuators, even individual pixel rows 40 of the detector 32, for example with the typical size of 20 x 20 pm, could be controlled. 2, controlled dimming. In addition, a type of "slide" with "punched-out" areas could also be inserted in front of the detector 32. If the signal in the first area 46a is only to be reduced and not completely faded out, then not an entire pixel row 40 is dimmed in the corresponding area 46a, but only individual pixels 42 of the pixel row 40 are dimmed.
[0049] In the embodiment of Figure 13, the detector 32 has a smaller number of pixels 42 in the first region 46a than in the region 46b.
[0050] Figure 14 shows the device 10, wherein the measuring chamber 28 is fluidically arranged in the flow path between a process gas line 58 and an outflow line 60. The process gas line 58 and the outflow line 60 may belong to a process-engineering system, for example, a hydrogen filling station, an electrolyzer, a gas filling station, a gas trailer, a gas engine, a power plant, or another system that may, for example, be a system operated with flammable gases or gases that are otherwise hazardous to humans or nature.
[0051] In such a process plant, it may be necessary, for example, for maintenance purposes, to completely remove the process gas or gas mixture actually flowing in the process gas line 58 from the process gas line 58. For this purpose, the process gas line 58 is typically purged with an inert gas, for example, nitrogen, argon, or carbon dioxide, thereby removing the process gas or process gas mixture from the process gas line 58.
[0052] In a system in which the device 10 is not installed, as shown in Figure 14, the process gas line is purged without suitable measuring sensors. The duration of the purging process is assumed theoretically depending on the system volume and flow rate. It can therefore happen that an undesirable residual amount of an undesirable gas is still present in the process gas line. In the case of fuel cell applications, for example, this can have particularly negative consequences when the system is restarted. This is avoided by the arrangement shown in Figure 14, since the device 10 can also detect small amounts of secondary components of the gas mixture present in the process gas line 58.
[0053] For this purpose, the process shown schematically by flow diagrams in Figures 15 and 16 is followed. The process of Figure 15 begins in a "Start" function block, designated by reference numeral 62. In a function block 64, the process gas (e.g., hydrogen) present in the process gas line 58 is discharged through the measuring chamber 28 toward the discharge line 60. In a function block 66, the process gas line 58 is purged with an inert gas (e.g., nitrogen, argon, carbon dioxide) via the measuring chamber 28 toward the discharge line 60 until the proportion of detected process gas at least reaches or falls below a lower limit. This lower limit is set so that no danger to persons performing maintenance on the system is posed. The process ends in a function block 68.
[0054] After maintenance has been completed, according to Figure 16, after a start block 70, the process gas (for example, hydrogen) is reintroduced into the process gas line 58 in a function block 72. In a function block 74, the process gas line 58 is then purged with the process gas via the measuring chamber 28 toward the discharge line 60 until the proportion of inert gas reaches or falls below a lower limit. This lower limit is selected to ensure safe operation of the system. The process ends in a final block 76.
Claims
Claims 1. Device (10) for analyzing a gas (26) by means of Raman scattering (30), comprising: a. a measuring chamber (28) which is designed to at least temporarily contain the gas (26) to be analyzed, b. at least one detector (32) which is designed to detect Raman scattering (30) emanating from the gas (26), c. an optic (44) which is arranged in the beam path of the Raman scattering (30) towards the detector (32) and is designed such that a first wavelength range of the Raman scattering (30) is directed onto a first region (46a) of the detector (32) and a second wavelength range of the Raman scattering (30) is directed onto a second region (46b) of the detector (32), characterized in that d.it comprises an optical device (48) which can at least attenuate the strength of the Raman scattering (30a) directed onto the first region (46a), or the detector (32) in the first region (46a) has a smaller number of optically active elements (42) than in the second region (46b) or at least some of the optically active elements (42) of the detector (32) in the first region (46a) are deactivated.
2. Device (10) according to claim 1, characterized in that the optical device (48) comprises at least one aperture (50) and / or at least one filter (54).
3. Device (10) according to claim 2, characterized in that a permeability of the aperture (50) or of the filter (54) and / or a position of the aperture (50) or of the filter (54) and / or a size of the aperture (50) or of the filter (54) is controllable.
4. Device (10) according to at least one of claims 2 or 3, characterized in that the filter (54) is arranged both in the beam path of the Raman scattering (30a) directed onto the first region (46a) and in the beam path of the Raman scattering (30b) directed onto the second region (46b), but essentially only attenuates the strength of the Raman scattering (30a) directed onto the first region (46a).
5. Device (10) according to at least one of the preceding claims, characterized in that the first region (46a) corresponds to a wavelength range of the Raman scattering (30) which corresponds to a signal of a suspected main component of the gas (26).
6. Device (10) according to at least one of the preceding claims, characterized in that the optical device (48) is designed or the optically active elements (42) of the detector (32) in the first region (46a) are designed such that a strength of the signal of the suspected main component of the gas (26) generated at the detector (32) is of the same order of magnitude as the strength of the signal of at least one secondary component generated at the detector (32).
7. Device (10) according to at least one of the preceding claims, characterized in that the measuring chamber (28) is arranged in the flow path between a process gas line (58) and an outflow line (60).
8. A method for operating a device (10) according to claim 7, characterized in that it comprises the following steps: a. venting a process gas present in the process gas line (58) through the measuring chamber (28) in the direction of the outflow line (60); b. purging the process gas line (58) with an inert gas via the measuring chamber (28) in the direction of the outflow line (60) until the proportion of the detected process gas at least reaches or falls below a lower limit value.
9. The method according to claim 8, characterized in that it further comprises the following steps: a. introducing process gas into the process gas line (58); b. flushing the process gas line (58) with the process gas via the measuring chamber (28) in the direction of the outflow line (60) until the The proportion of inert gas at least reaches or falls below a lower limit.