Measuring arrangement for characterising a fuel gas mixture, and method for characterising a fuel gas mixture

Abstract

A measuring arrangement (400) for characterising a fuel gas mixture comprises a carrier structure (410) and components arranged thereon that are able to be exposed to the fuel gas mixture, specifically: a micromechanical resonator (20; 120, 220) having gas-dependent vibration properties; and a thermal conductivity sensor (44; 144); an infrared measuring arrangement (440) having a thermal infrared radiation source (442), an infrared spectroscopic sensor arrangement (444) and an irradiated infrared measurement volume (446) between the thermal infrared radiation source (442) and the infrared spectroscopic sensor arrangement (444); a pressure sensor (430), arranged on the carrier structure (410), in order to sense a static pressure of the fuel gas mixture; a temperature sensor (50; 150) which is configured to measure a temperature value of the fuel gas mixture; and a measuring and operating circuit (600) for receiving signals from the components; and for determining at least one final measured value of a variable characterising the energy content of the gas on the basis of the received signals, wherein the variable characterising the energy content of the fuel gas mixture is selected from fuel value, calorific value, upper Wobbe index of the fuel gas mixture and lower Wobbe index of the fuel gas mixture.

Description

[0001] Measuring arrangement for characterizing a fuel gas mixture and method for characterizing a fuel gas mixture

[0002] The present invention relates to a measuring arrangement and a method for characterizing a fuel gas mixture. Fuel gas mixtures contain, for example, hydrocarbons, in particular alkanes (CnH2(n+i)) and hydrogen, as well as inert gases such as carbon dioxide and nitrogen. European patent EP 3 362 790 B1 discloses the characterization of hydrocarbon-containing fuel gas mixtures based on their density, viscosity, and energy content. The density and viscosity are determined based on the vibration properties of a micromechanical resonator exposed to the fuel gas mixture. The above determination is based on correlations between energy content and density or between the Wobbe index and dynamic viscosity, with these correlations being disturbed by hydrogen and inert gas components such as nitrogen and carbon dioxide.European Patent EP 3 535 581 B1 discloses a further development of the above approach, in which the hydrogen content of the fuel gas is determined using an additional thermal conductivity measurement. Published patent application DE 10 2019 123 874 A1 discloses a suitable measuring arrangement in which a thermal conductivity sensor is integrated into a micromechanical oscillator.

[0003] Depending on the accuracy requirements and the composition of the inert gas, the above methods provide satisfactory results. However, investigations in connection with the present invention have shown that the measurement accuracy is impaired by a high carbon dioxide content. Therefore, the object of the present invention is to remedy this situation.

[0004] The object is achieved by the measuring arrangement according to independent claim 1, the measuring point according to independent claim 11, and the method according to independent claim 14.

[0005] The measuring arrangement according to the invention for characterizing a fuel gas mixture comprises: a support structure; at least one micromechanical resonator arranged on the support structure in such a way that it can be subjected to a fuel gas mixture, wherein the vibration properties of the resonator depend on the applied fuel gas mixture; a thermal conductivity sensor arranged on the support structure, which can be subjected to the fuel gas mixture; an infrared measuring arrangement arranged on the support structure with a thermal infrared radiation source, an infrared spectroscopic sensor arrangement, and an irradiated infrared measuring volume between the thermal infrared radiation source and the infrared spectroscopic sensor arrangement, which can be subjected to the fuel gas mixture;a pressure sensor arranged on the support structure, which has a measuring membrane to which the fuel gas mixture can be applied in order to detect a static pressure of the fuel gas mixture; a temperature sensor arranged on the support structure, which can be applied to the fuel gas mixture, wherein the temperature sensor is configured to detect a temperature measurement of the fuel gas mixture; and a measuring and operating circuit for receiving signals from the resonator of the conductivity sensor, the infrared measuring arrangement, the pressure sensor, and the temperature sensor; and for determining at least one final measured value of a variable characterizing the energy content of the gas based on the received signals, wherein the variable characterizing the energy content of the fuel gas mixture is selected from the calorific value, the heating value, the upper Wobbe index of the fuel gas mixture, and the lower Wobbe index of the fuel gas mixture.

[0006] In a further development of the invention, the infrared measuring arrangement serves to determine the concentration of gas components, in particular of carbon dioxide in the fuel gas mixture on the basis of absorption measurements, wherein the resonator serves to determine the density and viscosity of the fuel gas mixture on the basis of frequency and quality measurements, wherein the measuring and operating circuit is designed to use signals from the same pressure sensor and the same temperature sensor in order to take into account influences of pressure and temperature on the absorption, the density and the quality.

[0007] In a further development of the invention, the infrared measuring length from the thermal infrared radiation source to the at least one sensor arrangement has a length of not less than 10 mm, in particular not less than 15 mm, wherein the measuring and operating circuit is designed to determine the carbon dioxide content of the fuel gas mixture up to a carbon dioxide content of 15 vol.%, in particular up to a carbon dioxide content of 40 vol.%, with an accuracy of 1 vol.%.

[0008] In a further development of the invention, the measuring and operating circuit is designed to carry out the following method:

[0009] Determining a viscosity measurement value and a density measurement value based on vibration properties of the resonator;

[0010] Determining a pressure- and temperature-dependent viscosity measurement, a corresponding temperature measurement, and a corresponding pressure measurement of the flowing gas mixture; Determining a carbon dioxide content based on an infrared absorption measurement using the infrared measuring arrangement;

[0011] Determining a hydrogen content based on a measurement of the thermal conductivity using the thermal conductivity sensor (using the density, viscosity, pressure and temperature measured values);

[0012] Determining a first preliminary value of a first variable characterizing the energy content of the fuel gas mixture using the viscosity measurement value and the density measurement value;

[0013] Determining a second preliminary value of a second variable characterizing the energy content of the fuel gas mixture based on the density measurement value without using the viscosity measurement value; and determining an inert gas content of the fuel gas based on the carbon dioxide content, and a relationship between the first preliminary value of the first variable characterizing the energy content of the fuel gas mixture and the second preliminary value of a second variable characterizing the energy content of the fuel gas mixture; and

[0014] Determining a final measured value of the quantity characterizing the energy content of the fuel gas mixture, using the inert gas content, the hydrogen content and at least one of the preliminary measured values ​​of the quantities characterizing the energy content of the fuel gas mixture.

[0015] In a further development of the invention, a minimum convex envelope exists around the resonator, the thermal conductivity sensor, the infrared measuring volume, the measuring membrane of the pressure sensor and the temperature sensor, wherein the minimum convex envelope has a volume of not more than 1500 pl, in particular not more than 1000 pl, and / or the largest cross-sectional area through the minimum convex envelope is not more than 1000 mm 2 , for example not more than 750 mm 2 , in particular not more than 500 mm 2 and / or the longest diagonal through the minimum convex envelope has a length of not more than 50 mm, in particular not more than 30 mm.

[0016] In particular, the compact arrangement of the sensor components of the measuring arrangement described by the above dimensions justifies the assumption that the spatial variations in the state variables pressure and temperature of the fuel gas mixture in the volume enclosed by the envelope are so small that the measuring and operating circuit is set up to use signals from the same pressure sensor and the same temperature sensor in order to take into account the influences of pressure and temperature on the infrared absorption, the density of the fuel gas mixture and the quality of the resonator. A convex envelope is a surface enclosing a volume, whereby a straight line through any two points on the surface between these points only runs within the enclosed volume including the surface. A minimal convex envelope is the convex envelope for which the enclosed volume is minimal.

[0017] In a further development of the invention, at least one of the sensors and in particular two sensors, selected from a list comprising the temperature sensor and the thermal conductivity sensor, are integrated with the resonator in a chip.

[0018] In a further development of the invention, the thermal infrared radiation source comprises a free-standing, nanostructured, flat filament.

[0019] In a further development of the invention, the thermal infrared radiation source has a power consumption of not more than 500 mW.

[0020] In a further development of the invention, the infrared radiation source is encapsulated in a capsule, wherein the capsule has a window, which comprises, for example, silicon, in particular silicon provided with an anti-reflection coating, or sapphire. In one embodiment of this further development of the invention, the capsule comprises an SMD housing, which, for example, has a base area of ​​no more than 4 x 4 mm 2 , especially about 3x3 mm 2 and has a height of not more than 3 mm, in particular not more than 2 mm.

[0021] In a further development of the invention, the infrared spectroscopic sensor arrangement comprises a first selective infrared sensor for an absorption wavelength of carbon dioxide, in particular 4.26 pm, and / or the sensor arrangement comprises a second selective infrared sensor for a reference wavelength, in particular 3.91 pm.

[0022] In a further development of the invention, the support structure comprises a printed circuit board. The measuring arrangement according to the invention has a relative measurement error of less than 3%, in particular less than 2%, and preferably not more than 1.0% for the calorific value and the Wobbe index.

[0023] The measuring point according to the invention comprises a measuring arrangement according to one of the preceding claims, wherein the measuring arrangement is connected to a fuel gas line of a process plant in order to continuously characterize the fuel gas mixture during operation.

[0024] In a further development of the invention, the measuring arrangement is arranged such that the fuel gas mixture remains in the fuel gas line and flows around the measuring arrangement. Thus, no samples of the fuel gas mixture need to be taken for measurement and discarded after the measurement.

[0025] In a further development of the invention, the fuel gas mixture has a pressure of, for example, 0.5 MPa to 2 MPa when flushing around the measuring arrangement, wherein in particular this pressure corresponds to a current process pressure in the fuel gas line.

[0026] The method according to the invention comprises:

[0027] Determining a viscosity measurement value and a density measurement value based on vibration properties of the resonator;

[0028] Determining a pressure- and temperature-dependent viscosity measurement, a corresponding temperature measurement, and a corresponding pressure measurement of the flowing gas mixture; Determining a hydrogen content of a thermal conductivity measurement using the thermal conductivity sensor, the temperature- and pressure-compensated density and viscosity measurement;

[0029] Determining a carbon dioxide content based on an infrared absorption measurement using the infrared measuring device; determining a first preliminary value of a first variable characterizing the energy content of the fuel gas mixture using the viscosity measurement value and density measurement value compensated for the temperature measurement value and pressure measurement value;

[0030] Determining a second preliminary value of a second variable characterizing the energy content of the fuel gas mixture based on the temperature measurement value and the pressure measurement value compensated density measurement value without using the viscosity measurement value; and

[0031] Determining an inert gas content of the fuel gas based on the carbon dioxide content, and a relationship between the first provisional value of the first variable characterizing the energy content of the fuel gas mixture and the second provisional value of a second variable characterizing the energy content of the fuel gas mixture; and

[0032] Determining a final measured value of the quantity characterizing the energy content of the fuel gas mixture, using the inert gas content, the hydrogen content and at least one of the preliminary measured values ​​of the quantities characterizing the energy content of the fuel gas mixture.

[0033] In a further development of the invention, the variable characterizing the energy content of the fuel gas mixture is selected from calorific value, heating value, upper Wobbe index of the fuel gas mixture and lower Wobbe index of the fuel gas mixture, wherein in particular the relative measurement error for the calorific value and / or the Wobbe index is less than 3%, in particular less than 2% and preferably not more than 1.0%.

[0034] The invention will now be explained in more detail with reference to the exemplary embodiments illustrated in the drawings. In the drawings: Fig. 1: a schematic diagram for determining the viscosity and density of a fuel gas mixture as a function of the quality factor and the resonance frequency of a resonator loaded with the fuel gas mixture;

[0035] Fig. 2: a diagram showing a following from reference data

[0036] Relationship between the upper Wobbe index Wlsup and the viscosity of various gases;

[0037] Fig. 3: a diagram showing a relationship between the calorific value CV and the average molar mass rrimoi of various gases, derived from reference data;

[0038] Fig. 4: a diagram showing a relationship between a correlation value of Wobbe index and calorific value on the one hand and the inert gas content on the other hand, as determined from reference data;

[0039] Fig. 5: a diagram showing a relationship between the thermal conductivity X and the hydrogen content in mol% of various fuel gas mixtures, based on reference data;

[0040] Fig. 6a: a plan view of a first embodiment of a chip with a resonator, a temperature sensor and a thermal conductivity sensor;

[0041] Fig. 6b: a plan view of a second embodiment of a chip with a resonator, a temperature sensor and a thermal conductivity sensor;

[0042] Fig. 7a: a plan view of an embodiment of an inventive

[0043] measuring arrangement;

[0044] Fig. 7b: the view from Fig. 7a with additional dimensions and boundary lines; Fig. 8: a schematic cross-section through an embodiment of a measuring point according to the invention with a measuring arrangement according to the invention; and

[0045] Fig. 9: a flowchart of an embodiment of the method according to the invention.

[0046] The measuring arrangement comprises a resonator which can be supplied with a fuel gas mixture and which has a micromechanical oscillator, in particular a cantilever oscillator. Both the resonant frequency of the resonator and its quality factor depend on the density as well as the viscosity of the resonator, as shown in Fig. 1. The solid lines are curves of the same resonant frequency, with the resonant frequency increasing from right to left from 33.2 kHz to 34.0 kHz. The dashed lines are curves of the same quality factor, with the quality factor increasing from left to right from 60 to 210. Based on the combination of a resonant frequency measurement value Xf and a quality measurement value XQ, a density measurement value X can be calculated from the tuple or intersection point (Xf, XQ). P (Xf, XQ) and a viscosity measurement value X (X f , XQ). Using a pressure measurement XP and a temperature measurement value XT which are recorded during the determination of the resonance frequency measurement value Xf and a quality measurement value XQ, an average molar mass measurement value Xm and a viscosity measurement value X^-ref can be determined from the density measurement value under reference conditions.

[0047] As can be seen from Fig. 2, for alkanes there is a first approximation linear relationship between the viscosity and the upper Wobbe index Wlsup. Furthermore, Fig. 3 shows a linear relationship between the molar mass and the calorific value CV for alkanes. In this respect, the calorific value and / or the upper Wobbe index can be determined with sufficient accuracy for pure alkane mixtures based on the vibration properties of the resonator. However, if fuel gas mixtures contain inert gas components and / or hydrogen, the above linear relationships are disturbed. Therefore, it is necessary to determine the inert gas component and the hydrogen component in order to determine correct values ​​for the calorific value and the upper Wobbe index, respectively. To determine the inert gas component, one approach is to determine a deviation value of one for the ratio of two independently determined values ​​for the calorific value, as explained below.By definition, the following relationship exists between the calorific value and the upper Wobbe index Wlsup:. where M g is the average molar mass of the gas mixture.

[0048] The Wobbe index Wlsup(r|) for alkanes can be determined from the viscosity according to the relationship shown in Fig. 2. Using the above equation, the calorific value CV(WI) is determined as a function of the viscosity-dependent Wobbe index. Furthermore, the calorific value CV(M g ) for alkanes and hydrogen can be determined solely from the average molar mass according to the relationship in Fig. 3. For pure alkane mixtures, these two calorific values ​​CV(WI) and CV(M g ) are essentially the same. To the extent that components other than alkanes are present in the gas mixture, deviations occur that can be quantitatively described with the following deviation value A:

[0049] As shown in Fig. 4, the inert gas fraction IGC correlates well with the deviation values ​​based on reference data for various gas mixtures whose inert gas fraction is dominated by nitrogen. Fig. 4 also contains data from measurements on fuel gas mixtures using the resonator of the measuring arrangement according to the invention and applying a correlation model formed from the reference data.

[0050] The agreement with the actual inert gas content is readily satisfactory if the latter is dominated by nitrogen and if the fuel gas mixture contains little hydrogen. However, as can be seen from Fig. 2, the upper Wobbe index for hydrogen as a function of viscosity does not follow the behavior of the upper Wobbe indices for alkanes, although the calorific value for hydrogen as a function of molecular weight corresponds to the behavior of the calorific value of alkanes. In order to be able to determine the inert gas content with sufficient accuracy, the hydrogen content is first determined by means of a thermal conductivity measurement. The correlation between thermal conductivity and hydrogen content for various fuel gas mixtures is shown in Fig. 5. This correlation can be further improved by taking into account the density and viscosity under reference conditions.Based on the hydrogen content thus determined, the Wobbe index and calorific value for the residual gas reduced by the hydrogen content are determined, as described in EP 3 535 581 B1. Based on these parameters, the inert gas content can then be determined, as described above.

[0051] Figs. 6a and 6b show two embodiments of chips with micromechanical resonators, each having an integrated thermal conductivity sensor. The chip 10 shown in Fig. 6a comprises a cantilever beam 20, which is exposed by preparing a recess 11 using DRIE. A temperature sensor element of a thermal function block 40 is contacted via a first conductor track pair 12 prepared in a first electrode layer. A heating element of the thermal function block 40 is contacted via a second conductor track pair 14 prepared in a second electrode layer. Electrodes of a piezoelectric transducer 30 are contacted via a third conductor track pair 16, each of which has a conductor track in an electrode layer. A reference temperature sensor element 50 in an edge region 22 of the chip 10 and the fourth conductor track pair 52 contacting them are prepared in the first electrode layer.The thermal function block 40 and the reference temperature sensor element 50 together form a thermal conductivity sensor 44.

[0052] The chip 110 shown in Fig. 6b comprises two cantilever beams 120, 220, which are exposed by preparing a recess 111 using DRIE. The cantilever beams each have a thermal functional block 140, 240 and a piezoelectric transducer 130, 230. The following contacting scheme applies to the first cantilever beam 120: A first temperature sensor element of the first thermal functional block 140 is contacted via a first conductor track pair 112 prepared in a first electrode layer. A heating element of the thermal functional block 140 is contacted via a second conductor track pair 114 prepared in a second electrode layer. Electrodes of a first piezoelectric transducer 130 are contacted via a third conductor track pair 116, each of which has a conductor track in an electrode layer.The following contacting scheme applies to the second cantilever beam 220: A second temperature sensor element of the second thermal function block 240 is contacted via a first conductor track pair 212 prepared in the first electrode layer. Electrodes of the first piezoelectric transducer 230 are contacted via a third conductor track pair 216, each of which has a conductor track in an electrode layer. A reference temperature sensor element 150 in the edge region 122 of the chip 110 and the fourth conductor track pair 152 contacting them are prepared in the first electrode layer. The thermal conductivity measurements can be performed with these chips between a thermal function block and the reference temperature sensor element, or, in the case of two cantilevers, between the thermal function blocks of the two cantilevers.In this respect, for example, the first thermal functional block 140 and the reference temperature sensor element 150 together form a first thermal conductivity sensor 144.

[0053] Based on the quality factor and natural frequency of the cantilever beam vibrations, the viscosity and density of the fuel gas mixtures can be determined. Therefore, with the chips, all measurement data required for the steps described so far to characterize a fuel gas mixture can be collected, except for pressure. Further details on the chips are disclosed, for example, in publication WO 2022 008 212 A1.

[0054] For fuel gas mixtures containing alkanes and hydrogen, and possibly nitrogen-dominated inert gas, the mean correlation error (2c>) for determining the inert gas content is approximately 1 mol%. However, if the inert gas is dominated by carbon dioxide, the determination of the inert gas content becomes less accurate. Consequently, the determination of the calorific value or the Wobbe index also loses accuracy. The invention therefore proposes supplementing the measuring system with a carbon dioxide sensor, as explained below.

[0055] The measuring arrangement 400 comprises, as shown in Figs. 7a and 7b, a printed circuit board 410 as a support structure and the components discussed above, which are arranged on the printed circuit board 410, namely a chip 420 with at least one resonator 422, 424 and with a thermal conductivity and temperature sensor (not shown in detail here); as well as a pressure sensor 430 with a measuring membrane 432, the pressure-dependent deformation of which is to be detected, in particular, with a resistive and / or capacitive transducer.

[0056] Furthermore, the measuring arrangement 400 comprises an infrared measuring arrangement 440 arranged on the circuit board 410, which has a thermal broadband radiator 442 and a sensor arrangement 444 with a first selective sensor 444a for measuring at a carbon dioxide absorption line, in particular at a wavelength of 4.26 pm, and a second selective sensor 444b for measuring at a reference wavelength, in particular at 3.91 pm. A suitable thermal infrared radiation source 442 is disclosed, for example, in DE 10 2018 101 974 A1. It has a nanostructured surface, with which a very high emissivity and thus high optical efficiency is achieved.The technology disclosed in DE 2018 101 974 A1 offers, in addition to the high efficiency of the emitter, very good area scalability of the radiating element, so that miniaturized emitters with low power consumption but sufficiently high optical output power can be manufactured to very precisely measure the absorption of heterogeneous gases, in particular CO2, in the smallest possible space. This achieves sufficient signal intensity for measuring the concentration of carbon dioxide in a fuel gas mixture. Suitable radiation sources are available from Infrasolid GmbH under the names HISsmd, HISbasic, and HISpower. The infrared measuring volume 446, which can be exposed to the fuel gas mixture and extends between the broadband radiator 442 and the sensor arrangement 444, has, for example, a measuring path length L shown in Fig. 7b. mof 20 mm. The high radiant power combined with the high sensitivity and spectral selectivity of sensors 444a and 444b are sufficient to achieve sufficient signal dynamics for determining the carbon dioxide concentration from the infrared absorption occurring over the specified measurement path length.

[0057] The circuit board 410 is held by a closure body 450, which is made of stainless steel, for example, and through which a glass feedthrough 452 extends, through which lines (not shown here) run for contacting the aforementioned components of the measuring arrangement 400, for connecting the components to the measuring and operating circuit 600 of the measuring arrangement 400.

[0058] A minimal convex envelope around the resonator, the thermal conductivity sensor, the infrared measurement volume, the pressure sensor's measurement membrane, and the temperature sensor has a volume of no more than 1000 pl. In Fig. 7b, the dotted line 460 encloses the maximum cross-section of the minimal convex envelope, which has an area of ​​no more than 300 mm 2 The longest diagonal D through the minimal convex envelope has a length of no more than 30 mm. The measuring arrangement 400 thus has a compact arrangement of its components, so that the measured values ​​of the state variables temperature and pressure of the fuel gas mixture, which are determined by the temperature sensor and pressure sensor 430 integrated in the chip 420, can be used to take temperature and pressure influences into account in the measurements of the resonator, the thermal conductivity sensor, and the infrared measuring arrangement.

[0059] The measuring point 500 shown in Fig. 8 comprises a pipeline 510 for conveying a fuel gas mixture. The pipeline 510 has a connection opening 512 in which the measuring arrangement 400 belonging to the measuring point 500 is mounted in order to be exposed to the fuel gas mixture conveyed in the pipeline. The measuring arrangement is arranged such that the fuel gas mixture remains in the pipeline and flows around the measuring arrangement. Therefore, no samples of the fuel gas mixture need to be taken for measurement and discarded after the measurement. The fuel gas mixture has a pressure of, for example, 0.5 MPa to 2 MPa when flowing around the measuring arrangement.

[0060] The measuring and operating circuit 600 of the measuring arrangement 400 is arranged outside the pipeline 510.

[0061] An operation of the measuring arrangement 400 according to the invention is reflected in the method shown in Fig. 9, which comprises the following steps:

[0062] Determining a hydrogen content 710 of a thermal conductivity measurement using the thermal conductivity sensor;

[0063] Determining a carbon dioxide content 720 based on an infrared absorption measurement by means of the infrared measuring arrangement;

[0064] Determining a viscosity measurement value 730 and a density measurement value 740 based on vibration properties of the resonator;

[0065] Determining a pressure and temperature dependent viscosity measurement value 740, an associated temperature measurement value and an associated pressure measurement value of the flowing gas mixture;

[0066] Determining a first preliminary value 750 of a first variable characterizing the energy content of the fuel gas mixture using the viscosity measurement value;

[0067] Determining a second preliminary value 760 of a second variable characterizing the energy content of the fuel gas mixture based on the density measurement value without using the viscosity measurement value; and

[0068] Determining an inert gas content 770 of the fuel gas based on the carbon dioxide content, and a relationship between the first preliminary value of the first variable characterizing the energy content of the fuel gas mixture and the second preliminary value of a second variable characterizing the energy content of the fuel gas mixture; and

[0069] Determining a final measured value of the quantity 880 characterizing the energy content of the fuel gas mixture, using the inert gas content, the hydrogen content and at least one of the preliminary measured values ​​of the quantities characterizing the energy content of the fuel gas mixture.

Claims

Patent claims 1 . A measuring arrangement (400) for characterizing a fuel gas mixture, comprising: a support structure (410); at least one micromechanical resonator (20; 120, 220) arranged on the support structure (410) such that it can be subjected to a fuel gas mixture, wherein vibration properties of the resonator (20; 120, 220; 422, 424) depend on the applied fuel gas mixture; a thermal conductivity sensor (44; 144) arranged on the support structure (410) and which can be subjected to the fuel gas mixture; an infrared measuring arrangement (440) arranged on the support structure (410) with a thermal infrared radiation source (442), an infrared spectroscopic sensor arrangement (444) and an infrared measuring volume (446) through which the fuel gas mixture can pass and through which it is irradiated, between the thermal infrared radiation source (442) and the infrared spectroscopic sensor arrangement (444);a pressure sensor (430) arranged on the support structure (410), which can be acted upon by the fuel gas mixture in order to detect a static pressure of the fuel gas mixture; a temperature sensor (50; 150) arranged on the support structure (410), which can be acted upon by the fuel gas mixture, wherein the temperature sensor is configured to detect a temperature measurement value of the fuel gas mixture; and a measuring and operating circuit (600) for receiving signals from the resonator of the conductivity sensor, the infrared measuring arrangement, the pressure sensor, and the temperature sensor; and for determining at least one final measured value of a variable characterizing the energy content of the gas based on the received signals, wherein the variables characterizing the energy content of the fuel gas mixture; Size is selected from calorific value, heating value, upper Wobbe index of the fuel gas mixture and lower Wobbe index of the fuel gas mixture.

2. Measuring arrangement (400) according to claim 1, wherein the infrared measuring arrangement serves to determine the concentration of gas components, in particular of carbon dioxide in the fuel gas mixture on the basis of absorption measurements, and wherein the resonator serves to determine the density and viscosity of the fuel gas mixture on the basis of frequency and quality measurements, wherein the measuring and operating circuit is set up to use signals from the same pressure sensor and the same temperature sensor in order to take into account influences of pressure and temperature on the absorption, the density and the quality.

3. Measuring arrangement according to one of the preceding claims, wherein the infrared measuring volume from the thermal infrared radiation source to the at least one infrared spectroscopic sensor arrangement has a length of not less than 10 mm, in particular not less than 15 mm, and wherein the measuring and operating circuit is designed to determine the carbon dioxide content of the fuel gas mixture up to a carbon dioxide content of 15 vol-%, in particular up to a carbon dioxide content of 40 vol-%, with an accuracy of 1 vol-%.

4. Measuring arrangement according to one of the preceding claims, wherein the measuring and operating circuit is arranged to carry out the following method: Determining a hydrogen content of a thermal conductivity measurement using the thermal conductivity sensor; Determining a carbon dioxide content based on an infrared absorption measurement using the infrared measuring arrangement; Determining a viscosity measurement value and a density measurement value based on vibration properties of the resonator; Determining a pressure and temperature dependent viscosity measurement value, an associated temperature measurement value and an associated pressure measurement value of the flowing gas mixture; Determining a first preliminary value of a first variable characterizing the energy content of the fuel gas mixture using the viscosity measurement value; Determining a second preliminary value of a second variable characterizing the energy content of the fuel gas mixture based on the density measurement value without using the viscosity measurement value; and Determining an inert gas content of the fuel gas mixture based on the carbon dioxide content, and a relationship between the first provisional value of the first variable characterizing the energy content of the fuel gas mixture and the second provisional value of a second variable characterizing the energy content of the fuel gas mixture; and Determining a final measured value of the quantity characterizing the energy content of the fuel gas mixture, using the inert gas content, the hydrogen content and at least one of the preliminary measured values of the quantities characterizing the energy content of the fuel gas mixture.

5. Measuring arrangement according to one of the preceding claims, wherein a minimum convex envelope around the resonator, the thermal conductivity sensor, the infrared measuring volume, the measuring membrane of the pressure sensor and the temperature sensor, wherein the minimum convex envelope has a volume of not more than 1500 pl, in particular not more than 1000 pl, and / or the largest cross-sectional area through the minimum convex envelope is not more than 1000 mm 2 for example not more than 750 mm 2 , in particular not more than 500 mm 2 and / or the longest diagonal through the minimum convex envelope has a length of not more than 50 mm, in particular not more than 30 mm.

6. Measuring arrangement according to one of the preceding claims, wherein at least one of the sensors and in particular two sensors selected from a list comprising the temperature sensor and the thermal conductivity sensor are integrated with the resonator in a chip.

7. Measuring arrangement according to one of the preceding claims, wherein the thermal infrared radiation source comprises a free-standing, nanostructured surface radiator.

8. Measuring arrangement according to one of the preceding claims, wherein the infrared radiation source is encapsulated in a capsule, wherein the capsule has a window which comprises silicon, in particular silicon provided with an anti-reflection coating, or sapphire.

9. Measuring arrangement according to one of the preceding claims, wherein the infrared spectroscopic sensor arrangement has a first selective infrared sensor for a wavelength of 4.26 pm, and / or wherein the infrared spectroscopic sensor arrangement has a second selective infrared sensor for a wavelength of 3.91 pm.

10. Measuring arrangement according to one of the preceding claims, wherein the support structure comprises a printed circuit board.

11. Measuring point comprising a measuring arrangement according to one of the preceding claims, wherein the measuring arrangement is connected to a fuel gas line of a process plant in order to continuously characterize the fuel gas mixture during operation.

12. Measuring point according to claim 11, wherein the measuring arrangement is arranged so that the fuel gas mixture remains in the fuel gas line and flows around the measuring arrangement.

13. Measuring point according to claim 12, wherein the fuel gas mixture has a pressure of 0.5 MPa to 2 MPa when flushing around the measuring arrangement.

14. A method for characterizing a fuel gas mixture, in particular with a measuring arrangement according to one of claims 1 to 10, comprising: Determining a hydrogen content (710) of a thermal conductivity measurement using the thermal conductivity sensor; Determining a carbon dioxide content (720) based on an infrared absorption measurement by means of the infrared measuring arrangement; Determining a viscosity measurement value (730) and a density measurement value (740) based on vibration properties of the resonator; Determining a pressure and temperature-dependent viscosity measurement value (740), an associated temperature measurement value and an associated pressure measurement value of the flowing gas mixture; Determining a first preliminary value (750) of a first variable characterizing the energy content of the fuel gas mixture using the viscosity measurement value; Determining a second preliminary value (760) of a second variable characterizing the energy content of the fuel gas mixture on the basis of the density measurement value without using the viscosity measurement value; and Determining an inert gas content (770) of the fuel gas based on the carbon dioxide content, and a relationship between the first preliminary value of the first variable characterizing the energy content of the fuel gas mixture and the second preliminary value of a second variable characterizing the energy content of the fuel gas mixture; and Determining a final measured value of the quantity characterizing the energy content of the fuel gas mixture (780), using the inert gas content, the hydrogen content and at least one of the preliminary measured values of the quantities characterizing the energy content of the fuel gas mixture.

15. The method according to claim 12, wherein the variable characterizing the energy content of the fuel gas mixture is selected from calorific value, heating value, upper Wobbe index of the fuel gas mixture and lower Wobbe index of the fuel gas mixture.

16. The method according to claim 13, wherein the relative measurement error for the calorific value and / or the Wobbe index is less than 3%, in particular less than 2% and preferably not more than 1.0%.

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