Measuring setup and method for determining a gas content distribution

Abstract

Method for determining a gas content distribution of a multiphase system using a measuring arrangement (10), wherein the measuring arrangement (10) comprises a reaction vessel (12), a plurality of acoustic transmitter and receiver units (14, 16) and an evaluation unit (18), wherein the multiphase system is contained by the reaction vessel (12), wherein the acoustic transmitter and receiver units (14, 16) are connected to the evaluation unit (18) via communication technology and are configured to generate and receive an acoustic signal, and wherein the transmitter and receiver units (14, 16) are arranged such that a measuring section (22) between a transmitter unit (14) and a receiver unit (16) at least partially passes through a volume of the reaction vessel (12), comprising the steps: - generating acoustic signals with the acoustic transmitter units (14) with a frequency and / or with a frequency spectrum in the subcritical range,such that the acoustic signals pass through the multiphase system,- Receiving the acoustic signals after passing through the multiphase system with the acoustic receiving units (16),- Determining the transit times of the acoustic signals using the evaluation device (18),- Determining the gas content distribution in the multiphase system based on the determined transit times using the evaluation device (18) and using tomographic reconstruction algorithms, taking acoustic refraction into account and determining curved acoustic paths.

Description

The invention relates to a measuring arrangement for determining a gas content distribution of a multiphase system.The invention further relates to a method for determining a gas content distribution of a multiphase system by means of the above measuring arrangement.Mixing and stirring operations are widely used in industry and process engineering. Mixing and stirring processes in multiphase systems with a liquid phase and a gas phase in a reaction vessel have particular relevance in process engineering and occur in a multiplicity of different processes. The gas phase can either be formed by direct introduction of gases into the liquid phase in the reaction vessel or can be formed in the interior of the liquid phase as a product in chemical and / or biological reactions, such as, for example, in fermentation processes in biogas reactors. A specific optimization of the plant technology with regard to the stirring systems, baffles, heat exchangers, gas injection devices, supply lines, etc. used and reliable process monitoring have hitherto been made more difficult because of the more difficult access to processes by measurement technology in the reaction vessel.Previously pursued approaches for describing the processes in the reaction vessel have different disadvantages: electrical conductance measurements by means of measuring probes and / or spectroscopic measurements by means of optical probes only provide local values. Although the use of grating sensors, i.e. measuring probes arranged two-dimensionally in the manner of gratings, allows a two-dimensionally resolved measurement in the grating plane, grating probes are unsuitable for use in polyphase systems with a high and / or coarse solids content because of the fine grating-shaped structure.Although the technique of noninvasive computed tomography based on ionizing radiation such as X-rays and / or gamma radiation does offer the possibility of determining the gas content distribution spatially resolved even at a high solids content, the measurement technique is associated with enormous effort, costs and radiation protection and is therefore ruled out for many applications.Electrical resistance and impedance tomography (ERT, EIT) represents a cost-effective, non-invasive alternative to the above-mentioned techniques. It is based on the observation that electrical conductivities differ depending on the nature of the medium. However, when determining the gas content distribution in multiphase systems with a low gas concentration, according to the relationship of Maxwell, only small changes in the electrical conductivity result, so that in these cases the measurement uncertainty usually exceeds the measurement value itself. In particular, when non-uniformity of the liquid phase conductivity occurs, the reliable determination of the gas content distribution becomes impossible in many cases.US 2016 / 0 335 759 A1 describes a tomographic reconstruction at cross sections in the case of polyphase borehole flows or polyphase surface flows which contain water (brine), oil and gas phases. Measurements of digital transmission (or analog attenuation) and signal transit time are made to obtain two views of the same cross-section at a specific location in a flow line. The measurements are then merged to synthesize an image of the polyphase flow in the specific cross section.US 2015 / 0 233 747 A1 describes a system for determining the properties of a polyphase fluid comprising a pipe and a plurality of combined transmitting and receiving units which are arranged around the pipe in the circumferential direction. Each combined transmitting and receiving unit comprises a transmitter and a receiver, wherein the transmitter is respectively oriented such that it transmits a corresponding acoustic signal in the direction of a receiver of a combined transmitting and receiving unit.US 2016 / 0 341 586 A1 describes an apparatus and a method for determining the flow of one or more phases of a multi-phase fluid mixture.US 2007 / 0 157 737 A1 describes a device that determines a property of a multi-phase fluid, such as a ventilated oil and water fluid flowing within a pipe. The apparatus comprises a fluid flow meter, a water fraction meter, and a densimeter, wherein the densimeter determines the density of the fluid stream to determine the gas volume (or void) fraction of the multiphase fluid stream.Accordingly, it is the object of the invention to provide a measuring arrangement and a method for determining a gas content distribution of a polyphase system, wherein the gas content distribution can be determined reliably and with high accuracy, in a spatially resolved manner. In particular, noninvasive determination of the gas content distribution at low gas concentrations and / or at high solids content is also to be made possible.This object is achieved by the features of the independent claims. Preferred refinements are found in the dependent claims.According to the invention, a measuring arrangement for determining a gas content distribution of a multiphase system is therefore provided, comprising a reaction vessel, a plurality of acoustic transmitting and receiving units and an evaluation device, wherein the reaction vessel is configured to accommodate the multiphase system therein, wherein the acoustic transmitting and receiving units can be connected to the evaluation device by communication technology and are configured to generate and receive an acoustic signal, and wherein the transmitting and receiving units are arranged such that a measurement path between a transmitting unit and a receiving unit at least partially passes through a volume of the reaction vessel.The essence of the invention is that the gas content distribution in the multiphase system is determined by permeating the multiphase system with acoustic signals starting from the spatially distributed acoustic transmitting units and detecting the acoustic signals by the spatially distributed acoustic receiving units after passing through the multiphase system.With regard to the measuring arrangement, it is provided that the measuring arrangement comprises the reaction vessel which is designed to accommodate the multiphase system therein. The transmitting and receiving units are arranged in such a way that the measurement path between a transmitting unit and a receiving unit at least partially passes through the volume of the reaction vessel. Thus, the acoustic signal generated by the transmitting unit will at least partially traverse the volume of the reaction vessel before it is received. In particular, the plurality of acoustic transmitting and receiving units define a measurement volume by their arrangement with respect to one another. It is preferably provided that the transmitting and receiving units are arranged relative to the reaction vessel in such a way that there is an overlap between the measurement volume and the volume of the reaction vessel.The multiphase system is preferably a multiphase system having at least one liquid phase and at least one gas phase. In addition to these two phases, further phases can also be present in the multiphase system, for example a solid phase or further liquid phases and / or gas phases. In particular, it is provided that the gas phase is also present as bubbles within the liquid phase.The reaction vessel may be any device which allows the liquid and gas phase of the multiphase system to be incorporated therein. It is thus possible for the reaction vessel to completely delimit a space within which the multiphase system can be located, as in a batch reactor, for example. Alternatively, the reaction vessel can be a flow reactor (flow reactor), wherein the multiphase system can flow through the flow reactor. Reaction vessels in the sense of the invention are also to be understood as meaning plant parts such as pipelines through which flow can take place. Furthermore, it is not necessary for a chemical and / or biological reaction to take place in the reaction vessel. When the multiphase system is present in the reaction vessel, the gas phase of the multiphase system is limited by the volume of the reaction vessel. The liquid phase, within which gas phase in the form of bubbles can likewise be located, is limited by the fill volume of the reaction vessel. If the polyphase system is present in the reaction vessel, it is further preferably provided with regard to the arrangement of the transmitting and receiving units that there is an overlap between the measurement volume and the filling volume of the reaction vessel. Thus, the acoustic signal can preferably also pass through the liquid phase of the multiphase system.The reaction vessel is preferably a reaction vessel which is used as standard in process engineering in the pharmaceutical industry, chemical industry, biogas production and / or wastewater engineering. More preferably, the reaction vessel has a volume between 0.05 m 3 and 20000 m 3. In principle, the shape of the reaction vessel can be arbitrary. Preferably, the shape of the reaction vessel is such that at least a straight distance between two points on the surface of the reaction vessel through the volume of the reaction vessel measures more than 10 cm.Furthermore, it is provided that the measuring arrangement comprises a plurality of acoustic transmitting and receiving units. Within the meaning of the invention, the acoustic transceiver units comprise combined transceiver units, so-called transceivers, in which the acoustic signal can be generated and received by means of the combined transceiver unit, wherein a switch can be made between a transmission mode and a reception mode. Acoustic transmitting and receiving units in the sense of the invention also comprise dedicated acoustic transmitting units and dedicated acoustic receiving units, i.e. separate devices for the transmitting unit and receiving unit. In this case, the transmitting unit is configured to generate the acoustic signal and the receiving unit is configured to receive the acoustic signal. The fact that the measuring arrangement comprises a plurality of acoustic transmitting and receiving units thus means, in the sense of the invention, that a) the measuring arrangement comprises a plurality of transceivers and / or b) the measuring arrangement comprises a plurality of dedicated transmitting units and a plurality of dedicated receiving units. If acoustic transmitting units are referred to below, this is therefore understood to mean the dedicated acoustic transmitting unit and the combined transmitting-receiving unit in the transmitting mode. The same applies analogously to the acoustic receiving units, this thus meaning the dedicated acoustic receiving unit and the combined transceiver unit in the reception mode. In principle, the skilled person will choose the number of transmitting and receiving units to match the volume and / or filling volume of the reaction vessel. However, it is preferably provided that the measuring arrangement comprises at least three transceivers or at least three dedicated transmitting units and three dedicated receiving units. A higher number of transmitting and receiving units has the advantage that the gas content distribution can be determined with a higher spatial resolution.The acoustic transmitting and receiving units can be connected to the evaluation device by communication technology. The evaluation device can be designed as a computer. It is preferably provided that the acoustic transmitting units are designed such that they can generate an acoustic signal on the basis of an input signal of the evaluation device. It is further preferred that the acoustic receiving units are designed such that they can generate data on the basis of the received acoustic signal, which data can be transmitted to the evaluation device. The measuring arrangement can comprise, in addition to the acoustic transmitting and receiving units and the evaluation device, further components for generating the acoustic signal, amplifying the acoustic signal, switching between transmitting mode and receiving mode in transceivers and / or changing between the dedicated transmitting units and dedicated receiving units and data acquisition. These further components are preferably a multi-channel data acquisition device (DAQ), a single- or multi-channel function generator, optionally one or more switching devices for changing between the transmission and reception mode in transceivers and / or for changing between the dedicated transmission units and dedicated reception units, and a signal amplifier. With regard to the acoustic signal generated by the transmitting unit, it is provided according to a preferred development that the transmitting units are monopole emitters and / or kidney emitters. The acoustic signal is thus preferably generated as a spherical wave or as a superposition of a sound field of a monopole radiator and a dipole radiator. Furthermore, it is preferably provided that the transmitting and receiving units are configured to generate and receive an acoustic signal in the frequency range below 16 kHz, particularly preferably in the frequency range from 0.01 to 14 kHz and further preferably from 0.1 to 10 kHz. Furthermore, the transmitting and receiving units can be spherical or flat.Furthermore, it is provided that the acoustic transmitting and receiving units are arranged in such a way that the measurement path between a transmitting unit and a receiving unit at least partially passes through the volume of the reaction vessel. In particular, this means that the acoustic transmitting and receiving units are arranged around the reaction vessel and / or are arranged in the reaction vessel in such a way that the generated acoustic signal can at least partially pass through the volume of the reaction vessel before it is received. In the case of transceivers, this means that the transceivers are arranged to the reaction vessel in such a way that a measurement path which connects two transceivers at least partially runs through the volume of the reaction vessel. In the case of dedicated transmitting units and dedicated receiving units, this means that they are arranged in such a way with respect to the reaction vessel that a measurement path between a dedicated transmitting unit and a dedicated receiving unit at least partially passes through the volume of the reaction vessel. Preferably, all measurement paths, i.e. all possible connection paths between two transceivers, or all possible connection paths between the dedicated transmitting units and the dedicated receiving unit, pass at least partially through the volume of the reaction vessel. Particularly preferably, the measurement paths pass at least partially through the fill volume of the reaction vessel.Such an arrangement can be implemented in several ways. In this context and according to a preferred development of the invention, it is provided that the acoustic transmitting and receiving unitsoutside the reaction vessel,on a wall of the reaction vesselin the wall of the reaction vessel, and / orin the reaction vesselare arranged. The arrangement outside the reaction vessel has the advantage that the transmitting and receiving units are easily accessible and installation and / or maintenance is thus very simple. Furthermore, the transmitting and receiving units do not have to be highly chemical-resistant when mounted outside the reaction vessel, as can be the case when mounted in the reaction vessel. However, the attachment in the reaction vessel can have the advantage that with such an arrangement only the polyphase system is acoustically penetrated and not additionally the wall of the reaction vessel. In other words, in an arrangement in the reaction vessel, the measurement paths are situated completely within the volume of the reaction vessel. Thus, with an arrangement in the reaction vessel, a higher spatial resolution of the gas phase distribution can be achieved. When the transmitting and receiving units are attached to the wall of the reaction vessel, the measurement volume corresponds substantially to the volume of the reaction vessel. On the wall of the reaction vessel, reference may be made to an outer wall of the reaction vessel and / or to an inner wall of the reaction vessel. Alternatively or additionally, it is possible to integrate the transmitting and receiving units directly into the wall of the reaction vessel. This leads to a very robust measuring arrangement.With regard to the distribution of the acoustic transmitting and receiving units, it is provided according to a preferred development that the acoustic transmitting and receiving units are uniform or non-uniformwithin the volume of the reaction vessel,on an enclosure surface,along a line on the enclosure surface, and / oralong a line on the enclosure surface in a planeare arranged. The acoustic transmitting and receiving units can thus be uniformly distributed. Uniformly distributed preferably means that a distance between two adjacent transmitting and receiving units is substantially the same size for all transmitting and receiving units. Alternatively, the transmitting and receiving units can be distributed non-uniformly. For example, the transmitting and receiving units can be randomly distributed. The regular or irregular arrangement of the transmitting and receiving units can relate to the volume within the reaction vessel. For example, the transmitting and receiving units can be uniformly distributed within the volume of the reaction vessel and non-uniformly outside the volume of the reaction vessel. The distribution may also relate to the enclosure surface. The enclosing surface is preferably the surface of a space which encloses the volume and / or the filling volume of the reaction vessel. It can be, for example, the surface of the volume of the reaction vessel. Thus, the transmitting and receiving units can be distributed uniformly on the wall of the reaction vessel, for example. The enclosing surface can also be the surface of the measurement volume which is spanned by the arrangement of the acoustic transmitting and receiving units. A uniform distribution with respect to the surface of the measurement volume can result in the transmitting and receiving units being arranged according to the corners of a regular polyhedron. Further, the uniform or non-uniform distribution may refer to a distribution along a line on the enclosure surface. It is preferably provided that the transmitting and receiving units are uniformly distributed. This also leads to a uniform distribution of the measurement paths. It is further preferably provided that the transmitting and receiving units are located uniformly along a line on the enclosure surface. In particular, it is provided that the transmitting and receiving units, which are arranged uniformly along the line, lie in one plane. For example, in the case of a cylindrical reaction vessel, the transmitting and receiving units can be arranged uniformly along the circumference of the reaction vessel. More preferably, a plurality of such planes are provided parallel to one another. This leads to a construction which is particularly simple to realize.The invention further relates to a method for determining a gas content distribution of a multiphase system by means of the above measuring arrangement, wherein the multiphase system is accommodated by the reaction vessel and the acoustic transmitting and receiving units are connected to the evaluation device by communication technology, comprising the steps:generating acoustic signals with the acoustic transmitting units such that the acoustic signals pass through the polyphase system,receiving the acoustic signals after passing through the polyphase system with the acoustic receiving units,determining propagation times of the acoustic signals by means of the evaluation device,determining the gas content distribution in the polyphase system on the basis of the determined running times by means of the evaluation device.As already mentioned, the essence of the invention is that the gas content distribution in the polyphase system is determined by permeating the polyphase system with the acoustic signals and detecting the acoustic signals by the spatially distributed acoustic receiving units after passing through the polyphase system. In this case, on the basis of propagation times which the acoustic signals require for passing through the measurement paths, wherein the measurement paths pass at least partially through the multiphase system, the gas content distribution in the multiphase system is deduced. The transmitting units thus generate acoustic signals which are designed such that they can pass through the polyphase system in order to be able to carry out a propagation time measurement. The propagation time of the acoustic signal is preferably the time required for the acoustic signal to be transmitted from the transmission unit that has generated the acoustic signal to the reception units that receive the acoustic signal. In the case of transceivers, this means that the time of the acoustic signal is determined for passing through the measurement paths which respectively connect two transceivers to one another. In the case of dedicated transmitting units and dedicated receiving units, this means that the time of the acoustic signal is determined for a pass through the measurement paths which respectively connect a dedicated transmitting unit to the dedicated receiving units. Since the measuring section runs at least partially through the polyphase system, a propagation time measurement is only possible if the acoustic signals are not completely absorbed by the polyphase system. The acoustic signals are preferably designed in such a way that influences of the signal attenuation and signal reflection of the polyphase system and / or of the reaction vessel are reduced. This makes it possible to measure large volumes and thus long measurement paths within the polyphase system.With regard to the configuration of the acoustic signals, it is provided according to a preferred development that the generation of acoustic signals with the acoustic transmitting units such that the acoustic signals pass through the polyphase system comprises generation of acoustic signals with a frequency and / or with a frequency spectrum in the subcritical range. The subcritical range describes signal frequencies below a resonant frequency of the radial pulsations of the bubbles in the polyphase system. The resonant frequency depends on several factors of the polyphase system. These factors include a surface tension of the bubbles, a size of the bubbles, a density behavior of the gas phase and the liquid phase, a compressibility behavior of the gas phase and the liquid phase, a temperature, and a pressure. For example, for air bubbles with a diameter of 2.2 mm in water at an equilibrium pressure close to 1 bar, the resonance frequency is around 3.1 kHz. In this example, the frequency and / or frequency spectrum of the acoustic signals should be below this 3.1 kHz limit. In this context, it is further preferably provided that the method comprises the step of determining the subcritical region of the polyphase system.Furthermore, with regard to the configuration of the acoustic signals and according to a preferred development, it is provided that the generation of acoustic signals with the acoustic transmitting units such that the acoustic signals pass through the polyphase system comprises a generation of acoustic signals with a limited period of time. It is therefore preferably not an acoustic continuous signal, but acoustic signals which are limited in time and preferably are emitted repeatedly. Signals of short duration are preferred in order to increase the measurement rate. Depending on the signal attenuation of the polyphase system, a general signal noise and a signal strength, it may be expedient to increase the signal length in order to realize a more robust runtime determination. The duration of the signal is further dependent on the polyphase system and the frequency of the signal. Preferably, however, the acoustic signal is not longer than 10 seconds. More preferably, the acoustic signal is not shorter than 0.1 milliseconds. The signal duration is particularly preferably between 1 millisecond and 5 seconds.For determining the propagation time, it is advantageous to have a clear autocorrelation behavior of the acoustic signals. In this context, with regard to the configuration of the acoustic signals, it is provided according to a preferred development that the generation of acoustic signals with the acoustic transmitting units such that the acoustic signals pass through the polyphase system comprises a generation of chirp signals and / or pseudo-random sequences. A chirp signal refers to a signal whose frequency changes over time. In this case, the frequency can increase or decrease over time. The frequency change may be linear or nonlinear. A pseudo-random sequence is understood to mean a signal having a pseudo-random binary sequence of individual signals. The pseudo-random sequence is preferably an MLS signal, maximum length sequence. Further preferably, all frequencies or the entire frequency spectrum of the chirp signal and / or of the pseudo-random sequence are in the subcritical range.With regard to a chronological sequence of the method steps, it is provided according to a preferred development that the stepsgenerating acoustic signals with the acoustic transmitting units such that the acoustic signals pass through the polyphase system, andreceiving the acoustic signals after passing through the polyphase system with the acoustic receiving units,The acoustic signals may be repeatedly produced, wherein a time pause is observed between receiving the acoustic signals and re-generating the acoustic signals. Preferably, the measurement volume is transmitted by the transmitting units in chronological sequence and the signals are recorded by the receiving units. After a signal has passed through, the temporal pause can be observed for decaying the acoustic reverberation in order to reduce the noise behavior due to reflections.It can be provided that at a given time only one transmitting unit of the plurality of transmitting units generates an acoustic signal, which is then detected by the plurality of receiving units. Alternatively, it can be provided that two or more transmitting units generate different acoustic signals simultaneously or in a temporally overlapping manner in order to increase the measurement rate. In this case, the different signals should have a low correlation with one another, in order that a clear runtime determination of the different acoustic signals is made possible. In this context, according to a preferred development, it is provided that the step of generating acoustic signals with the acoustic transmitting units such that the acoustic signals pass through the polyphase system comprises simultaneously generating a plurality of different acoustic signals, and the step of receiving the acoustic signals after passing through the polyphase system with the acoustic receiving units comprises receiving the plurality of different acoustic signals after passing through the polyphase system.As already mentioned, the method provides that the gas content distribution in the multiphase system is deduced on the basis of the propagation times of the acoustic signals. In this context, according to a preferred development, it is provided that the determination of the gas content distribution in the multiphase system on the basis of the determined runtimes by means of the evaluation devicedetermining a sound velocity distribution in the polyphase system on the basis of the determined propagation times; anddetermining the gas content distribution in the polyphase system on the basis of the determined sound velocity distribution in the polyphase systemcomprising. The propagation times of the acoustic signals are thus used to determine the acoustic velocity distribution in the polyphase system. The propagation times are preferably converted by means of the evaluation device into a multidimensional scalar field of the speed of sound. Since the speed of sound in polyphase systems is critically dependent on the local gas content, in a further step the multi-dimensional scalar field of the speed of sound can be transferred by means of the evaluation device into a multi-dimensional scalar field of the gas content, which corresponds to the gas content distribution in the polyphase system. The scalar field of the speed of sound and the scalar field of the gas content are preferably a two-dimensional scalar field and particularly preferably a three-dimensional scalar field.In this context, according to a preferred development, it is provided that the determination of the gas content distribution in the multiphase system on the basis of the determined runtimes by means of the evaluation device comprises taking into account correlation parameters of the multiphase system and / or taking into account the measuring arrangement. In the determination of the acoustic velocity distribution on the basis of the propagation times, the measuring arrangement, in particular the arrangement of the acoustic transmitting and receiving units with respect to one another and to the reaction vessel, is preferably taken into account. Further preferably, the correlation parameters of the polyphase system are taken into account when determining the gas content distribution in the polyphase system on the basis of the determined acoustic velocity distribution. The correlation parameters describe the relationship between the scalar field of the speed of sound and the scalar field of the gas content and depend on the polyphase system. In this context, it is preferably provided that the method comprises the step of determining the correlation parameters of the polyphase system. The correlation parameters of the multiphase system can be determined, for example, by means of the measuring arrangement in that the liquid phase of the multiphase system and the gas phase of the multiphase system are measured individually.Likewise in connection with the signal evaluation, it is provided according to a preferred development that the determination of the gas content distribution in the multiphase system on the basis of the determined runtimes by means of the evaluation device comprises a determination of the gas content distribution in the multiphase system on the basis of the determined runtimes by means of tomographic reconstruction algorithms. The evaluation device thus preferably comprises the tomographic reconstruction algorithm. Further preferably, the tomographic reconstruction algorithm determines the speed of sound distribution in the polyphase system on the basis of the determined propagation times. For tomographic reconstruction, algebraic, cell-based algorithms such as simultaneous iterative reconstruction technique (SIRT) or simultaneous algebraic reconstruction technique (SART) can be used. The cell-based tomographic reconstruction algorithms include pixel-based tomographic reconstruction algorithms for two-dimensional scalar fields and voxel-based tomographic reconstruction algorithms for three-dimensional scalar fields. The tomographic reconstruction algorithms thus permit the reconstruction of both two- and three-dimensional velocity distributions. The two- or three-dimensional sound velocity distribution can then be converted into the two- or three-dimensional gas content distribution. In particular in the case of strong non-uniformity in the polyphase system, an extension of the tomographic reconstruction by taking account of the acoustic refraction can be expedient, since the propagation of the acoustic signal in this case does not take place in a rectilinear manner. In this context, it is preferably provided that curved acoustic paths are determined by means of an iterative method, wherein the iterative method starts from straight acoustic paths in a first step and thus determines the scalar field of the speed of sound. In further steps of the iterative method, this scalar field serves as the basis for ascertaining the curved acoustic paths. The curved paths obtained are taken into account in the next step of the iterative method in the renewed determination of the scalar field of the speed of sound. This process is preferably repeated until the result converges.The invention is explained below by way of example with reference to the drawings on the basis of a preferred exemplary embodiment.The drawing showsFIG. 1 shows two schematic representations from different perspectives of a measuring arrangement with dedicated transmitting units and dedicated receiving units, according to a preferred embodiment of the invention, FIG. 2 shows a schematic illustration of a measuring arrangement with combined transmitting and receiving units, according to a further preferred embodiment of the invention, FIG. 3 shows two schematic representations of the transmitting and receiving units, according to a further embodiment of the invention, FIG. 4 shows a schematic structure of the measuring arrangement from FIG. 2, and FIG. 5 shows a flow chart with the steps of a method for determining a gas content distribution of a polyphase system by means of the measuring arrangement, according to a preferred embodiment of the invention.FIG. 1 shows two schematic representations of a measuring arrangement 10 for determining a gas content distribution of a polyphase system from different perspectives. The measuring arrangement 10 comprises a reaction vessel 12, a plurality of acoustic transmitting and receiving units 14, 16 and an evaluation device 18 (not shown here). The reaction vessel 12 is a batch reactor with a 12 m 3 volume, which has a cylinder-like shape, wherein FIG. 1 a ) illustrates the measuring arrangement 10 from above and the reaction vessel 12 is thus circular. The reaction vessel 12 is configured to house therein the multiphase system, in the present case a water-air system. The acoustic transmitting and receiving units 14, 16 are designed to generate and receive an acoustic signal. In the present exemplary embodiment in FIG. 1, dedicated transmitting units 14 and dedicated receiving units 16 are provided as transmitting and receiving units 14, 16. The measuring arrangement 10 comprises twelve transmitting units 14 and twelve receiving units 16, wherein only eight transmitting and receiving units 14, 16 are visible in FIG. 1 a ) on account of the selected perspective. Four transmitting units 14 and four receiving units 16 are arranged within a plane 20 along a circumference of the cylinder-like reaction vessel 12, wherein they are distributed uniformly along the circumference and one transmitting unit 14 is alternated with one receiving unit 16 each. This arrangement within the plane 20 is repeated three times, the three planes 20 being parallel to one another and the planes 20 intersecting the cylinder-like reaction vessel 12 perpendicular to its axis of rotation. In the present case, the acoustic transmitting and receiving units 14, 16 are mounted on a wall 24, here the outer wall of the reaction vessel 12.FIG. 2 shows a schematic illustration of a further preferred embodiment of the measuring arrangement 10. A plane 20 has eight combined transmitting and receiving units 14, 16.Furthermore, measurement paths 22 between the transmitting and receiving units 14, 16 are drawn in in FIGS. 1 and 2. The transmitting and receiving units 14, 16 are arranged in such a way that all measuring paths 22 pass through the volume of the reaction vessel 12. In the case of the dedicated transmission units 14 and dedicated reception units 16 from FIG. 1, the measurement path 22 is always located between a dedicated transmission unit 14 and a dedicated reception unit 16. In the case of the combined transmission and reception units 14, 16 in FIG. 2, the measurement path 22 is located between two combined transmission and reception units 14, 16, so that, despite the same total number (namely eight) of transmission and reception units 14, 16 per plane 20 in FIG. 2, there are more measurement paths 22 than in FIG. 1. sixteen measurement paths 22 are present per plane 20, and twenty-six measurement paths 22 are present per plane 20 in FIG. 2. In the method for determining the gas content distribution of the multiphase system, the steps of which are shown in FIG. 5, the propagation times of the acoustic signal along these measurement paths 22 are determined.FIG. 3 shows two schematic representations of the transmitting and receiving unit 14, 16 according to a further embodiment of the invention. In FIG. 3 a), the combined transmitting and receiving units 14, 16 are shown as monopole radiators. The combined transmitting and receiving units 14, 16 thus generate an acoustic signal in the form of a spherical wave. FIG. 3 b) shows the installation of the acoustic transmitting and receiving unit 14, 16 in a wall 24 of the reaction vessel 12.FIG. 4 shows a schematic structure of the measuring arrangement from FIG. 2, wherein the evaluation device 18, in the present exemplary embodiment a computer, is also depicted. It can be seen in FIG. 4 that the measuring arrangement 10 comprises, in addition to the acoustic transmitting and receiving units 14, 16, as further components, a multi-channel data acquisition device 26, a single-channel function generator 28, and a switching device 30. It can also be seen from FIG. 4 that the acoustic transmitting and receiving units 14, 16 are connected to the evaluation device 18 by communication technology.FIG. 5 shows a flow chart with the steps of the method for determining one of the gas content distributions of the multiphase system by means of the measuring arrangement 10, according to a preferred embodiment of the invention. The method comprises four steps, wherein in the first step the acoustic signals are generated with the transmitting units 14. The acoustic signals are generated to pass through the polyphase system. Tuned to the polyphase system, in the present case the air-water system, the frequency of the acoustic signals is below 3.1 kHz. Furthermore, the duration of the acoustic signals is 500 milliseconds and the acoustic signals are embodied as chirp signals. The acoustic signals are generated in such a way that a single chirp signal of 500 milliseconds duration is generated by a transmission unit 14 and a pause of 300 milliseconds is then observed. Thereafter, a further single chirp signal of 500 milliseconds duration is generated by a further transmission unit 14. The transmitting units 14 thus alternate when generating the signal.In a further step, the acoustic signals are received with the acoustic receiving units 16 after passing through the polyphase system. A single chirp signal of 500 milliseconds duration is thus generated by a transmitting unit 14, which is received by all acoustic receiving units 16. In a further step, the propagation times of the acoustic signals are determined by means of the evaluation device 18, a computer in the present exemplary embodiment.In the last step, the gas content distribution in the multiphase system is determined on the basis of the determined run times. This is implemented by means of a tomographic reconstruction algorithm, in the present case the Simultaneous Algebraic Reconstruction Technique (SART). The tomographic reconstruction algorithm determines a two-dimensional scalar field of the speed of sound on the basis of the runtimes. The tomographic reconstruction algorithm takes into account the measuring arrangement 10, i.e. the arrangement of the acoustic transmitting and receiving units 14, 16 with respect to one another and to the reaction vessel 12. In this case, the evaluation device 18 takes into account previously determined correlation parameters of the polyphase system. The correlation parameters describe the relationship between the scalar field of the speed of sound and the scalar field of the gas content and depend on the polyphase system. In the present case, the gas content distribution within the planes 20 is determined to be two-dimensionally resolved, three of these planes 20 being present.List of reference characters10 Measuring arrangement 12 Reaction vessel 14 Dedicated transmitting unit, combined transmitting and receiving unit 16 Dedicated receiving unit, combined transmitting and receiving unit 18 Evaluation device 20 Plane 22 Measuring path 24 Wall 26 Multichannel data acquisition 28 Function generator 30 Switching devices

Claims

Method for determining a gas content distribution of a polyphase system, by means of a measuring arrangement (10), wherein the measuring arrangement (10) comprises a reaction vessel (12), a plurality of acoustic transmitting and receiving units (14, 16) and an evaluation device (18), wherein the polyphase system is accommodated by the reaction vessel (12), wherein the acoustic transmitting and receiving units (14, 16) are connected to the evaluation device (18) by communication technology and are designed to generate and receive an acoustic signal, and wherein the transmitting and receiving units (14, 16) are arranged in such a way that a measurement path (22) between a transmitting unit (14) and a receiving unit (16) passes at least partially through a volume of the reaction vessel (12), comprising the steps of: - generating acoustic signals with the acoustic transmitting units (14) at a frequency and / or with a frequency spectrum in the subcritical range, such that the acoustic signals pass through the multiphase system, - receiving the acoustic signals after passing through the multiphase system with the acoustic receiving units (16), - determining propagation times of the acoustic signals by means of the evaluation device (18), - determining the gas content distribution in the multiphase system on the basis of the determined propagation times by means of the evaluation device (18) and by means of tomographic reconstruction algorithms, wherein an acoustic refraction is taken into account and curved acoustic paths are determined in this case.The method of claim 1, wherein generating acoustic signals with the acoustic transmitter units (14) such that the acoustic signals pass through the polyphase system comprises generating acoustic signals with a limited amount of time.The method according to any of the preceding claims, wherein generating acoustic signals with the acoustic transmitting units (14) such that the acoustic signals pass through the polyphase system comprises generating chirp signals and / or pseudo-random sequences.Method according to one of the preceding claims, wherein the steps - generating acoustic signals with the acoustic transmitting units (14) such that the acoustic signals pass through the polyphase system, and - receiving the acoustic signals after passing through the polyphase system with the acoustic receiving units (16), are carried out a plurality of times, wherein a temporal pause is observed between receiving the acoustic signals and renewed generation of the acoustic signals.The method of any preceding claim, wherein the step of generating acoustic signals with the acoustic transmitting units (14) such that the acoustic signals pass through the polyphase system comprises simultaneously generating a plurality of different acoustic signals and the step of receiving the acoustic signals after passing through the polyphase system with the acoustic receiving units (16) comprises receiving the plurality of different acoustic signals after passing through the polyphase system.Method according to one of the preceding claims, wherein the determination of the gas content distribution in the polyphase system on the basis of the determined propagation times by means of the evaluation device (18) comprises - a determination of an acoustic velocity distribution in the polyphase system on the basis of the determined propagation times and - a determination of the gas content distribution in the polyphase system on the basis of the determined acoustic velocity distribution in the polyphase system.Method according to one of the preceding claims, wherein the determination of the gas content distribution in the polyphase system on the basis of the determined propagation times by means of the evaluation device (18) comprises taking correlation parameters of the polyphase system into account and / or taking the measurement arrangement (10) into account.Method according to one of the preceding claims, wherein the acoustic transmitting and receiving units (14, 16) are arranged - outside the reaction vessel (12), - on a wall (24) of the reaction vessel (12), - in the wall (24) of the reaction vessel (12), and / or - in the reaction vessel (12).The method according to any of the preceding claims, wherein the acoustic transmitting and receiving units (14, 16) are arranged uniformly or non-uniformly - within the volume of the reaction vessel (12), - on an enclosure surface - along a line on the enclosure surface, and / or - along a line on the enclosure surface in a plane.

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