Radiometric measuring system for measuring the fill material profile

Abstract

The invention relates to a radiometric measuring system for the high-precision determination of the composition of contents (2n) in containers (3) with convex outer walls.The measuring system comprises the following components: - An improved radiation source arrangement, comprising: ◯ an elongated support (10) with a convex segment (100), ◯ a plurality (i) of radioactive radiation sources (11i) arranged along the segment (100) and directed outwards orthogonally to the convex segment (100), wherein the radiation source arrangement (1) is mounted in the container (3) such that the segment (100) is aligned parallel to the convex container wall, - a detector arrangement (4), with ◯ a number (i) of radiation detectors (40i) corresponding to the radiation sources (11i) on the outside of the container (3) to generate a measurement signal (Ii) dependent on the effective measurement height (hi), and - an evaluation unit (5) to create a fill material profile dependent on the effective measurement heights (hi) based on the measurement signals (Ii). A convex arrangement of radiation sources thus enables uniform radiation absorption.This leads to a more accurate detection of phase boundaries, especially in complex separation processes such as oil / water emulsion formation in refineries.

Description

The invention relates to a radiation source arrangement and a corresponding measuring system for radiometric measurement of the fill material profile. In process automation, measuring devices and systems are frequently used to record and / or control process variables. These variables include, among others, fill level, flow rate, pressure, temperature, pH value, redox potential, and conductivity. Depending on the specific process variable, different measuring principles are implemented in the measuring device or system. Actuators, such as valves or pumps, are used to control process variables by changing the flow rate of a liquid in a pipe section or the fill level in a container. The Endress+Hauser Group manufactures and distributes a wide range of such measuring devices and systems. In the case of density or level measurements, measuring systems based on the radiometric method are often used. This method utilizes radioactive radiation (for example, gamma radiation from a cesium or cobalt source) emitted by one or more radioactive sources within the measuring system and passed through the container holding the material to be measured. After passing through the container, the transmitted radiation intensity is recorded by one or more radiation detectors within the measuring system. By evaluating the corresponding measurement signal, the transmitted portion of the emitted radiation intensity is determined by a dedicated evaluation unit within the measuring system. Based on the measured radiation intensity, the density or level of the material is then calculated.The basic operating principle of radiometric density and level measurement is described, for example, in patent EP 2 208 031 B1. Depending on the application, it is relevant to perform height-dependent measurements within the container, as the contents consist of several components layered at different levels. For example, in desalination and separation processes of crude oil refining, the contents of the container are composed of various components such as sand, water, emulsion, oil, and gas, with these components layered at different heights. Accordingly, in such applications, the primary purpose of the radiometric measuring system is to determine the heights of the respective phase boundaries. Precise determination enables efficient separation of the contents, reduces the use of separation chemicals, and minimizes energy costs. A radiometric measuring system that allows such height-dependent measurement of the contents profile is described in patent DE 102019118414 B4. The measuring system described there is based on a plurality of radiation detectors arranged vertically one above the other on a straight support inside the container. In the installed state, the radiation axis of each detector is aligned horizontally with the container wall. Outside the container, a corresponding number of radiation detectors are arranged and aligned at the same height as the radiation axis. However, this arrangement is disadvantageous, particularly for containers with convex outer walls relative to the vertical. Firstly, this design increases the distance between the radiation sources and their corresponding detectors, thereby reducing the measurement resolution. Secondly, calibrating the measuring system becomes more difficult if the beam paths of the individual radiation source / detector pairs are not identical.Particularly in containers with convex outer walls, varying wall thicknesses can lead to different absorption effects, thus distorting the measured radiation intensity. The invention therefore aims to improve the measurement of the fill material profile under such conditions. The invention solves this problem by means of a radiation source arrangement comprising at least the following components: - An elongated support with a segment that extends convexly in the vertical direction corresponding to the container wall, and - a plurality of radioactive radiation sources arranged along the segment, each with a radiation axis that is oriented outwards orthogonally to the convex segment. In the simplest case, the segment and / or support can be designed as a tube, so that the radiation sources are protected within a submerged tube. This protects the radiation sources from external influences and simplifies installation and maintenance. Furthermore, it ensures that the radiation axes are perpendicular to the container wall, resulting in consistent radiation absorption and a uniform measurement distribution. According to the invention, the orthogonal alignment of the beam axes to the convex segment enables the beams from all radiation sources to penetrate the container wall perpendicularly. This ensures that the path length of the radiation through the container wall is the same for all radiation sources, thus eliminating corresponding measurement errors. Based on the radiation source arrangement, a measuring system for radiometric measurement of the fill material profile of fill material compositions in containers can be implemented according to the invention. These containers must have a container wall cross-section corresponding to the convex segment in the vertical direction, or vice versa. For this purpose, the radiation source arrangement according to the invention is to be mounted in the container such that the convex segment of the radiation source arrangement is aligned parallel to the container wall.In addition to the radiation source arrangement, the measuring system comprises a detector arrangement with a number of radiation detectors corresponding to the radiation sources, which are arranged outside the container in the respective radiation axis and aligned concentrically to the radiation source in order to generate a measurement signal that depends on the density of the filling material composition at a corresponding effective measurement height, and an evaluation unit designed to create a filling material profile dependent on the effective measurement heights based on the measurement signals of the individual radiation detectors. In principle, the measuring system according to the invention can be adapted to any convex container shape. Accordingly, the segment of the radiation source arrangement can be designed in an elliptical or circular segment shape in the case of an elliptical or circular segment cross-section of the container wall. For example, containers in which desalination or separation is carried out as part of crude oil processing typically have a circular cross-section. Preferably, the detector arrangement is designed to be concave such that the radiation detectors are each the same distance from the corresponding radiation source. This ensures that the path length of the radiation between the radiation source and the radiation detector is always the same, not only through the container wall but also overall, thus further minimizing measurement errors. To determine the fill material profile of the fill material composition using the measuring system according to the invention, the following method is preferably used: - Providing a list which assigns an effective measuring height to each pair of radiation source and radiation detector or to each corresponding measuring signal, - Emitting radioactive radiation along the radiation axes using the individual radiation sources, - Detecting corresponding measuring signals after passing through the fill material composition using the radiation detectors, and - Creating the fill material profile based on the measuring signals and the respective corresponding measuring heights according to the list. In the simplest case, the list of corresponding assignments can be extracted from the digitally available design documents for the measuring system. The effective measuring heights can then be determined based on the known installation heights of the corresponding radiation detectors and / or radiation sources, the inclination angles of the corresponding beam axes, and the distances along the beam axes, in particular according to [specific examples would be inserted here]. This type of calculation counteracts a "distortion" of the material profile that would otherwise result from the convex arrangement or orientation of the radiation sources. In the simplest case, within the framework of the inventive method, a corresponding density value can be assigned to each of the measurement signals of all radiation detectors, so that a density profile dependent on the effective measurement heights can be created as a fill material profile. The assignment of the measurement signals to the corresponding density values ​​is best carried out on the basis of calibration at the place of use or on the intended container. Instead of creating a simple density profile, the inventive method also makes it possible to create a profile of the contents in such a way that each component of the contents currently in the container is assigned the corresponding effective measurement height – or, in the case of a larger vertical extent of the contents component, the corresponding measurement heights. For this purpose, a table based on relevant literature values ​​must be provided, which assigns a corresponding measurement range of the measurement signals to each component of the contents. For unambiguous assignment, it goes without saying that the individual measurement ranges must not overlap. This allows a comparison to be made after the detection of the measurement signals, in order to determine whether and which of the measurement signals measured by the detectors fall within each of the measurement ranges.Based on this, the table allows the material profile to be created using the comparison and the table itself, such that each component of the material is assigned one or more corresponding effective measurement heights. The vertical resolution of the material profile is determined by the distance between the radiation source / radiation detector pairs. A higher number of corresponding measurement points improves the accuracy of the interpolation, especially in areas with density gradients such as the emulsion layer. For calibration, the measured density values ​​are compared with reference data to ensure that the phase boundaries are determined precisely. A first approximation, with which the height of phase boundaries can be further approximated, consists of: - using the corresponding measurement signals and the previously described table◯ determining those height-technically adjacent radiation detectors and◯ the corresponding effective measurement heights at which the corresponding measurement signals fall into two different measurement ranges, - defining the mean value between these two effective measurement heights as the height of the phase boundary. Thus, in this case, it is assumed that the phase boundary is located halfway between these two effective measurement heights. This approximation can be significantly refined within the scope of the invention by determining, during the calibration, all detectors and their corresponding effective measurement heights whose respective measurement signals lie between two measurement ranges. Subsequently, based on these two measurement signals, the corresponding minimum and maximum range limits of the two adjacent measurement ranges, and the effective measurement height corresponding to the measurement signal, a phase boundary height between the two corresponding components of the fill material is determined. This formula can also be applied if the measurement signal of the next higher radiation detector already falls within the next measurement range, provided there is a continuous transition zone without a sudden change in density. The invention is explained in more detail with reference to the following figures. Figure 1 shows a radiometric measuring system according to the invention on a container with a round cross-section. Figure 2 shows a table which assigns corresponding measuring ranges for the measurement signals of the radiation detectors to the specific components of the contents. Figure 3 shows a detailed view of the measuring system according to the invention in the area of ​​the uppermost radiation source and the corresponding radiation detector. To illustrate the invention, Fig. 1 shows a container 3 with a circular cross-section relative to the vertical, in which crude oil separation takes place as part of the oil refining process. Accordingly, the container 3 contains crude oil as its filling material composition 2, which is not in pure form but comprises various components n layered with respect to the height of the container 3. In the illustrated embodiment, the fill material composition 2n consists of n = five components, which layer according to their density. As the lowest fill material component 2n=1, a layer of sand or sludge settles during crude oil separation, exhibiting a density in the range ΔIn=1 between 1500 and 2500 kg / m³. Above this, a layer of water forms as a further fill material component 2n=2 at a density of approximately 10³ kg / m³.- With a density between 700 and 800 kg / m³, the actual oil layer 2n=4 lies above the water layer 2n=2. - The emulsion layer 2n=3 represents a diffuse transition zone between the water layer 2n=2 and the oil layer 2n=4, with a variable density between 850 and 950 kg / m³. Since the density is not constant but decreases gradually with increasing height of the emulsion layer 2n=3, this leads to a distribution of radiation absorption. This can affect the accuracy of the phase boundary determination, especially if the density gradient is pronounced. - Above the liquid or solid components 2n=1-4, a gas phase 2n=5 exists in container 3, which, depending on its composition, can have a density between 50 and 250 kg / m³. In order to locate the various components of this filling material composition 2n in relation to the height of the container 3, a radiometric measuring system according to the invention is installed on the container 3. For this purpose, the measuring system comprises a radiation source arrangement 1 lowered into the container 3 and a detector arrangement 4 arranged outside the container 3. In the illustrated embodiment, the radiation source arrangement 1 comprises twelve radiation sources 11i=1-12, which are arranged at equal intervals from one another in a dip tube 10 of the radiation source arrangement 1. For delivery and installation of the radiation sources 11i in the dip tube 10, the radiation sources 11i are first housed in a radiation protection container 6 and subsequently attached there to an upper connection of the already installed dip tube 10, such as a flange connection.After the radiation protection container 6 has been attached there, the radiation sources 11i are lowered from here into the immersion tube 10 in order to be positioned there at the intended installation height h11,i. As can be seen from Fig. 1, the immersion tube 10 and the radiation sources 11i are adapted to the circular cross-section of the container according to the invention: The segment 100 of the immersion tube 10 in which the radiation sources 11i are arranged one above the other has a circular segment shape and is parallel to the container wall. The radiation sources 11i are oriented such that the radiation axes are directed outwards towards the container wall orthogonally to the circular segment 100 – and thus at different angles θi to the horizontal. Contrary to the embodiment shown in Fig. 1, this principle according to the invention is also applicable in principle to all other convex cross-sections of the outer container wall, as long as the segment 100 of the immersion tube 10 is designed to be correspondingly convex and the radiation axes 11i are directed outwards orthogonally to the convex segment 100. The detector arrangement 4 comprises twelve radiation detectors 40i = 1-12, corresponding to each radiation source 11i. These are arranged outside the container 3 at corresponding installation heights h40i along the respective radiation axis such that they are aligned towards the radiation source 11i. In the embodiment shown in Fig. 1, the radiation detectors 40i are also arranged such that the distance a' to the corresponding radiation source 11i is always the same for all pairs of radiation detector 40i and radiation source 11i. As a result, the twelve individual radiation detectors 40i primarily detect the radiation intensity of the radioactive radiation transmitted by the associated radiation source 11i through the respective component n of the filling material composition 2n. The intensity of the transmitted radiation depends on the density of the respective filling material component n. Each radiation detector 40 generates a measurement signal Ii, which represents the transmitted radiation intensity and thus the density of the respective component n of the filling material. For this purpose, the radiation detectors 40ials can use a transmission protocol for the measurement signals Ii, for example, "4-20 mA", "PROFIBUS", "HART", or "Ethernet". To determine the filling material profile, the measurement signals Ii are transmitted to a higher-level evaluation unit 5 of the measurement system according to the transmission protocol. In order to create a fill material profile based on the measurement signals, it is necessary to assign a corresponding effective measurement height to each measurement signal or each underlying radiation detector 40i in relation to the bottom of the container. Fig. 3 illustrates an advantageous method for determining the respective effective measurement height using an enlarged view of the uppermost radiation source 11i=12 in the container 3 and the corresponding radiation detector 40i=12: As can be seen from Fig. 3, the measurement height in this case is defined by half the distance 1 / 2 a on the radiation axis between the radiation source 11i and the container wall. This reduces any measurement errors insofar as this value corresponds to the average height at which the underlying radiation penetrates the respective fill material component n for the measurement signals of the radiation detectors 40i. Since the design documents for container 3 and the measuring system typically only specify the installation heights h11 of the radiation sources 11 and h40 of the radiation detectors, as well as the respective angle θ of the radiation axis vi, the effective installation height must be determined according to the geometric relationship. A list can be created and stored in the higher-level unit 5, whereby the corresponding effective installation height is assigned to each radiation source 11 and each radiation detector 40 and the corresponding measurement signal using this list. This allows the material profile to be created by assigning the corresponding effective measurement height to each of the recorded measurement signals from the radiation detectors 40 using the list. To create the material profile in the form of a density profile, an assignment is required that assigns a density value of the material composition to each measurement signal. This allows a vertical density profile to be created based on the acquired measurement signals from the radiation detectors, the assignment to the corresponding density values, and the list of effective measurement heights. The resulting tabular density profile can optionally be converted into a mathematical density function that depends on the height, for example, using splines and the effective measurement heights as support points. A pure density profile does not allow any conclusions to be drawn about the vertical position of the individual components of the fill material. Therefore, in order to be able to deduce the vertical position of the individual components of the fill material from the measurement signals of the radiation detectors 40i, it is necessary to create a table in which the corresponding measurement ranges ΔIn of the measurement signals are assigned to all potential components of the fill material composition 2n, as shown in Fig. 2. The individual, non-overlapping measurement ranges ΔIn are defined by their respective upper and lower limits ΔIn,min and ΔIn,max. Based on the measurement signals from the radiation detectors 40i, whose height-related assignment is determined by the list and the table, it is therefore possible, using evaluation unit 5, to compare the measurement signals 1ida measured by the detectors 40ige to determine whether and in which of the measurement ranges ΔInsie each falls. Thus, a material profile can be output showing at which effective measurement height hi each material component n is currently present. The table and the resulting creation of the material profile can, in turn, be implemented in evaluation unit 5. Based on the table and the current measurement signals Ii, the information content of the material profile can be further extended by calculating and outputting approximate phase boundary heights hn / n-1 between two corresponding material components n, n-1. This is possible by determining, based on the created material profile, specifically those detectors 40i and the corresponding effective measurement heights whose corresponding measurement signals Ii do not fall within any of the specific measurement ranges ΔIn. Using precisely these measurement signals li, the adjacent range limits ΔIn-1,max, ΔIn,less, and the corresponding effective measurement height hi, a phase boundary height hn / n-1 between the two corresponding material components n, n-1 can be approximated. In the event that the measurement signal I of neither of the radiation detectors 40i lies outside the corresponding range limits ΔIn-1,max, ΔIn,min between two components of the fill material n, n+1, then those adjacent radiation detectors 40i, i+1 can be determined whose measurement signals Ii, i+1 fall into two different or adjacent ranges ΔIn, ΔIn+1. The phase boundary height hn / n+1 can then be defined and output as the mean value between the two corresponding effective measurement heights hi,i+1 of the adjacent radiation detectors 40i, i+1. Reference symbol list 1 Radiation source arrangement 2n Filling material composition 3 Container 4 Detector arrangement 5 Evaluation unit 6 Radiation protection container 10 Support or immersion tube 11 Radiation sources 40 Radiation detectors 100 Segment a Distance between the radiation source and the inner wall of the container a' Distance between the radiation source and the radiation detector hi Effective measuring heights hn / n-1 Phase boundary height h11,i Installation height of the radiation sources h40,i Installation height of the radiation detectors Ii Measurement signal i Index of the detector / radiation source pairs n Index of the filling material components vi Radiation axes ΔIn Measuring ranges ΔIn,max Upper limit of the respective measuring range ΔIn,min Lower limit of the respective measuring range Θi Inclination angle of the radiation axes QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature EP 2 208 031 B1

[0003] DE 102019118414 B4

[0005]

Claims

Radiation source arrangement (1) for radiometric filling material profile measurement of a filling material composition (2n) in a container (3), comprising: - an elongated support (10) with a convex segment (100), - a plurality (i) of radioactive radiation sources (11i) arranged along the segment (100), each with a radiation axis (vi) directed outwards orthogonally to the convex segment (100). Radiation source arrangement according to claim 1, wherein the segment (100) and / or the support (10) are / are designed in such a tubular form that the radiation sources (11i) are each arranged one below the other in the immersion tube. A measuring system for radiometric measurement of the fill profile of a fill composition (2n) in a container (3), comprising the following components: - A radiation source arrangement (1) according to claim 1 or 2, - a container (3) having a vertically oriented container wall cross-section corresponding to the convex segment (100), wherein the radiation source arrangement (1) is mounted in the container (3) such that the convex segment (100) is aligned parallel to the container wall, - A detector arrangement (4) with a number (i) of radiation detectors (40i) corresponding to the radiation sources (11i), which are arranged outside the container (3) in the respective radiation axis (vi) and aligned towards the radiation source (11i) in order to generate a measurement signal (Ii) that depends on the density of the fill composition (2n) at a corresponding effective measurement height (hi), and - an evaluation unit (5) designed toto create a fill material profile dependent on the effective measurement heights (hi) based on the measurement signals (Ii) of the individual radiation detectors (40i). Measuring system (1) according to claim 3, wherein the segment (100) and the container wall cross-section are designed in an elliptical segment shape, in particular in a circular segment shape. Measuring system according to claim 3 or 4, wherein the detector arrangement (4) is designed such that the radiation detectors (40i) each have the same distance (a') to the corresponding radiation source (11i). Method for determining a fill material profile of a fill material composition (2n) using the measuring system according to one of claims 3 to 5, comprising the following method steps: - providing a list which assigns an effective measurement height (hi) to each radiation source (11i) and each radiation detector (40i) or each measurement signal (Ii), - emitting radioactive radiation along the radiation axes (vi), - detecting corresponding measurement signals (li) after passing through the fill material composition (2n), and - creating the fill material profile based on the measurement signals (li) and the respective corresponding measurement heights (hi). The method according to claim 5, wherein the effective measuring heights (hi) are determined based on known installation heights (h40,i) of the corresponding beam detectors (40i) and / or (h11,i) of the beam sources (10i), inclination angles (θi) of the corresponding beam axes (vi), and distances (a, a') along the beam axes (vi), in particular according to hi = h11,i + 0.5a * sin(θi) = h40,i − [(a' + 0.5a) * sin(θi)]. to be determined. Method according to claim 5, 6 or 7, wherein the measurement signals (li) of all radiation detectors (40i) are each assigned a corresponding density value, in particular by calibration, and wherein a density profile dependent on the effective measurement heights (hi) is created as the fill material profile. The method according to claim 5, 6 or 7, comprising the following additional method steps: - providing a table that assigns to a plurality (n) of non-overlapping measuring ranges (ΔIn) of the measuring signals (Ii) corresponding fill material components (n = 1, 2, 3, 4) of the fill material composition (2n), - such comparison, ◯ whether and which of the measuring signals (Ii) measured by the detectors (40i) fall into one of the measuring ranges (ΔIn), and - creating the fill material profile based on the comparison and on the table, such that one or more corresponding effective measuring heights (hi) are assigned to the respective fill material component (n = 1, 2, 3, 4). The method according to claim 9, wherein during the calibration the detector(s) (40i) and the corresponding effective measuring heights (hi) are determined whose corresponding measurement signals (Ii) lie between two measuring ranges (ΔIn, ΔIn-1), and wherein, based on these measurement signals (Ii), corresponding range limits (ΔIn-1,max, ΔIn,min) of the adjacent measuring ranges (ΔIn, ΔIn-1), and the effective measuring height (hi) corresponding to the measurement signal (Ii), in particular according to hn / n − 1 = hi [ 1 + ( I i − Δ I n − 1, max ( Δ I n , min − Δ I n − 1, max ) ) ] each phase boundary height (h n / n-1 ) between the two corresponding filling material components (n, n-1). Method according to any one of claims 4 to 9 for use in a desalination process step and / or in a separation process step of a crude oil processing process.

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