Method for determining the particle size distribution of granular material in a delivery flow, and measuring device

Abstract

The invention relates to a method for continuously determining the particle size distribution of solid particles of different particle sizes that are transported in a delivery direction into a delivery flow and in the process collide with an impact element in the form of a waveguide and produce acoustic signals that propagate as structure-borne sound waves in the impact element and are captured using a vibration sensor. The invention also relates to a measuring device for carrying out the method. In order to achieve more accurate results when determining the particle size distribution taking into account a variable flow energy of the delivery flow, it is proposed to reduce the pressure resistance component of the flow resistance of an impact part of the impact element in an inflow direction.

Description

[0001] Method for determining the grain size distribution of granules in a conveying stream and measuring device

[0002] The invention relates to a method for continuously determining the grain size distribution of granules consisting of solid particles with different grain sizes, which are transported in a conveying direction in a conveying stream and collide with at least one impact body configured as a waveguide, generating acoustic signals that propagate in each impact body as structure-borne sound waves. Furthermore, the invention relates to a measuring device for carrying out the method.

[0003] An essential characteristic of granules is their grain size distribution, which is used in all branches of industry as a measurable parameter for process monitoring, quality control, quality management, machine and plant monitoring and machine and plant control.

[0004] Granules are transported during relocation, production or use using different transport systems, whereby the transport usually takes place hydraulically as a conveyed stream, e.g. as a solid-water mixture, pneumatically, e.g. as a solid-air mixture, by means of belt systems or sometimes in free fall. The development of a process and a device that allows grain size analysis in real time in all conveyed streams for a broad grain spectrum from a few micrometers to a few decimeters is of particular importance for a wide variety of industries. A large number of studies and development efforts focus on the use of acoustics for the analysis of granules, mainly in suspension form during hydraulic transport.

[0005] The invention relates to a passive acoustic method, wherein acoustic signals are used for signal processing, which arise during the transport of the granulate by a collision of solid particles of the granulate with a device, such as a probe (impact body), or a part of the transport system, such as a pipe wall.

[0006] Passive acoustic methods are known, for example, from US 5,257,530 B, WO 2014 / 11667 5 A1, US 2008 / 282781 A1, US 10 309 887 B2, US 11 260 399 B2 and EP 3 356 813 B1:

[0007] US 5,257,530 B discloses a metallic probe which is arranged transversely to the conveying direction of a suspension in a line such that the solid particles collide with the probe. An acceleration sensor which records the acoustic signals is attached to the probe outside the line. The amplified acoustic signals are transmitted to a signal processing unit. During signal processing, the concentration of solid particles in the suspension is determined from the signal energy and signal intensity after an FFT analysis (Fast Fourier Transformation). The method is primarily used to determine the concentration and mass of sand in an oil or gas stream. WO 2014 / 116675 A1 discloses an impact body designed as a waveguide which is arranged transversely to the conveying direction of a suspension in a line such that the solid particles collide with the impact body.An acoustic transducer which picks up the acoustic signals is attached to the probe outside the line. The acoustic signals are transmitted to a signal processing unit. The signal processing is used to determine the grain size distribution of the solid particles in the suspension. The acoustic signals are sampled at a sampling frequency of, for example, 250 Hz. For each sampled signal, the frequency spectrum is transformed using a DFFT (Discrete Fast Fourier Transformation) and the PDS (Power Density Spectrum) is generated from this, i.e. the sound power density. A change in the gradient of the signal intensity in the frequency range 100 kHz to 1 MHz and the change in the signal intensity for a preferred frequency in the frequency range greater than 20 kHz are used to determine the grain size of the solid particles in the suspension.

[0008] US 2008 / 282781 A1 discloses a device and a method for monitoring formation sand in pipeline-based oil and gas production streams. The sand causes erosion wear in the pipes, particularly their bends. Erosion wear is usually detected using an electrical resistance sensor. In order to be able to detect the amount of particles and their influence on the erosion wear in addition to the erosion wear, a probe is proposed which has a detector element decoupled from a housing, which has an impact surface, an acoustic sensor coupled to the impact surface, and the electrical resistance sensor for detecting the erosion wear. The acoustic sensor is used to detect the amount of particles by counting the number of collisions between the particles and the impact surface. The probe can also have means for detecting the flow energy.The flow energy of the conveyed stream is measured using a differential pressure transducer. To determine the number of particles in a specific size range impacting the impact surface, the acoustic energy signals of the particles must be correlated with the flow velocity derived from the flow energy, assuming a constant density. The correlation between the acoustic energy signals of the impacting particles and the qualitative changes in flow velocity serves the purpose of correlating the number of particles in the specific size range with the erosion wear for a given velocity profile of the conveyed stream.

[0009] US 10 309 887 B2 and US 11 260 399 B2 disclose passive acoustic measuring methods for continuously determining the grain size distribution of granules in a hydraulic conveying flow of a cyclone. The device comprises a fixed sensor element which is mounted in a process pipe into which a process fluid flows, wherein the fixed sensor element has an impact body which projects into the flow. A double threaded sleeve serves to fasten the impact body. Information about the size of the particles being ground is used for plant control. EP 3 356 813 B1 discloses a passive acoustic

[0010] Method for continuously determining the

[0011] Grain size distribution of granules in a conveying stream, which uses the further knowledge that the characteristics of the acoustic signal depend on the grain size distribution and the flow energy of the conveying stream. The flow energy is determined by the speed and the concentration (mass concentration), or the bulk density, of the solid particles in the granules. In order to obtain reliable measurement results for the grain size distribution in real time, the flow energy of the conveying stream is recorded using at least one force transducer provided in addition to the vibration transducer. The signal processing of the electrical signals from the vibration transducer to determine the grain size distribution is carried out taking the electrical signals from the force transducer into account.

[0012] Based on EP 3 356 813 B1 as the closest prior art, the invention is based on the object of proposing a passive acoustic method with which more precise results can be achieved in real time when determining the grain size distribution of granular solid particles in a conveying flow, taking into account the changing flow energy of the conveying flow. In an advantageous embodiment of the invention, the measurement of the flow energy of the conveying flow using at least one force transducer in addition to the vibration transducer should be dispensed with. Furthermore, a measuring device for carrying out the method should be proposed. The solution to this object is based on the knowledge that the flow resistance of the impact body in the conveying flow, which is composed of the pressure and friction resistance, can adversely affect the signal quality.In particular, a high pressure resistance, also referred to as form resistance, causes the impact body around which the flow is directed to natural vibrations and thus impairs the relationship between the properties of the electrical signals and the grain size distribution.

[0013] Furthermore, the invention in the embodiment of claim 2 is based on the recognition that the recording of the spatial propagation of the acoustic signals in the impact body and the use of the corresponding electrical signals with the aid of a multi-axis vibration sensor with at least three measuring axes leads to an increase in the available electrical signals, from the characteristics of which the grain size distribution can be determined in real time with greater accuracy. In addition to the greater accuracy, the multi-axis vibration sensor offers the further advantage that an additional force sensor is no longer required to record the flow energy of the conveyed stream. To record the flow energy, use can be made of the electrical signals of the at least three measuring axes of the same vibration sensor that records the spatial propagation of the acoustic signals in the impact body.

[0014] In detail, the task is solved by a method for continuously determining the grain size distribution of a granulate consisting of solid particles with different grain sizes with the features of the claim

[0015] 1. A measuring device for carrying out the method results from the features of claim 14.

[0016] The transport of solid particles in a defined conveying direction in a conveying stream is preferably carried out with the aid of a transport system. The transport system is, in particular, a belt conveyor or a flow conveyor that transports the solid particles either pneumatically, i.e., as a solid particle-gas mixture, or hydraulically as a solid particle-liquid mixture in a pipe. In addition, the solid particles can be transported in a conveying direction in a conveying stream in free fall.

[0017] The solid particles collide with the impact body, which is set up as a waveguide, and generate acoustic signals which propagate spatially in the impact body as structure-borne sound waves. The impact body comprises a holding part and an impact part. The impact part can, for example, be streamlined or designed as a flat plate with a longitudinal flow. The impact part of the impact body is exposed to the conveying flow containing solid particles, while the holding part serves to attach the impact body to the transport system, for example to a holder of a belt conveyor or the pipe wall of a flow conveyor. In addition, the preferably multi-axis vibration sensor is arranged in an acoustically conductive manner on the holding part. To ensure undisturbed propagation of the structure-borne sound waves, the impact part and the holding part are made as a single piece from a metallic material.In order to improve the wear resistance of the impact body in the conveying flow, at least the impact part is made of hardened metal, in particular hard metal.

[0018] The shape of the impact part and the flow direction determine the pressure resistance and the frictional resistance.

[0019] The pressure resistance is the force acting on the impacting part of the impact body that is subject to flow, resulting from the pressure difference Ap between its front and rear surfaces. The pressure difference is based on the energy loss of the frictional flow of the discharge stream.

[0020] Frictional drag is caused by the friction of the flow against the surface of the impacting part. The magnitude of this force depends on the size of the affected surface and the flow conditions, especially on whether the adjacent flow is laminar or turbulent. For the same surface size, turbulent flows increase frictional drag, while laminar flows decrease it.

[0021] In the case of circular-cylindrical impact bodies, as used in the known passive acoustic methods, the pressure resistance is approximately 90% and the frictional resistance on the outer surface of the circular cylinder is approximately 10% of the flow resistance when the flow is perpendicular to the longitudinal axis of the circular cylinder. The relatively large frontal area of ​​the impact body, i.e. the area projected into a plane perpendicular to the direction of flow, means that the proportion of pressure resistance is many times higher than the frictional resistance, thereby impairing the accuracy of the measurement of the grain size distribution, particularly in the range of small grain size spectra.

[0022] According to the invention, the shape and flow direction of the impact part are determined such that the pressure resistance is smaller than the frictional resistance, i.e. the proportion of pressure resistance is less than 50% of the flow resistance of the impact part, but preferably less than 30%, particularly preferably less than 10% of the flow resistance. By reducing the pressure resistance, the accuracy of the determination of the grain size distribution and the decoupling from the flow energy of the conveying flow can be further improved.

[0023] For example, in the case of an impact part designed as a disc or flat plate with a flow direction parallel to the surfaces of the disc or plate, the proportion of pressure resistance would approach 0%.

[0024] The flow resistance for a specific impact part can be checked by means of comparative measurements using strain gauges or by experiments. In order to determine the frictional and pressure resistance on a body around which flow occurs, the impact part can, for example, be placed in a flow channel and a flow medium can be moved around the impact part. The resistance is measured by measuring the forces acting on the impact part. In an advantageous embodiment of the invention, both the detection of the propagation of the acoustic signals in the impact body and the detection of the flow energy of the conveyed flow as well as the conversion into electrical signals are carried out with the aid of a multi-axis vibration sensor with at least three measuring axes, which are preferably arranged perpendicular to one another.

[0025] Only the electrical signals from at least three measuring axes of the vibration sensor are used to record both the acoustic signals propagating spatially in the impact body and the flow energy of the conveyed stream, which are required to determine the grain size distribution taking the flow energy into account. To record the flow energy, the ratio of the electrical signals from two measuring axes of the vibration sensor is used. To record the grain size distribution taking the flow energy into account, the electrical signals from at least three measuring axes of one vibration sensor are used.

[0026] Since the acoustic signals from the impact body are transmitted directly to the multi-axis vibration sensor attached to the support member, a multi-axis, particularly a piezoelectric, acceleration sensor is considered as the vibration sensor for detecting the spatially propagating acoustic signals. The acceleration sensor is attached to the support member outside the conveying flow, so that no solid particles from the conveying flow come into direct contact with the multi-axis acceleration sensor.

[0027] The recording of the spatial propagation of the acoustic signals and the recording of the flow energy of the conveyed flow with the aid of only a single multi-axis vibration sensor with at least three, preferably mutually perpendicular measuring axes, means that the recording of the acoustic signals and the flow energy takes place simultaneously and thus in relation to a matching collective of solid particles, so that falsifications of the results of the signal processing are avoided due to a time lag between the recording of the flow energy and the recording of the acoustic signals for determining the grain size distribution taking into account the flow energy.

[0028] With the method according to the invention, it is possible to carry out a more precise grain size analysis in real time with a very broad grain spectrum from a few micrometers to a few decimeters in any type of granular conveying streams with changing flow energy based on a passive acoustic method, without the need to measure the flow energy of the conveying stream using an additional force transducer.

[0029] The pressure resistance of the impact part can be effectively reduced by ensuring that the frontal area of ​​the impact part, i.e. its cross-sectional area projected in the direction of flow onto a surface perpendicular to it, does not exceed 10% of the total surface of the

[0030] impact part is .

[0031] However, the flow resistance of the impact part of the impact body can be reduced not only by the shape and flow direction, but also by increasing the surface quality by reducing the frictional resistance on the surface of the impact part. Preferably, the surface has a roughness depth R t from a maximum of 20 pm to . The roughness depth R t is measured using the stylus method ( DIN EN ISO 25178-601 ) or contactless using conf ocal technology ( DIN EN ISO 25178-602 ) .

[0032] To ensure that the conveying direction of the conveyed stream and the direction of flow of the impact part run parallel to one of the axes of the multi-axis vibration sensor, its measuring axes are arranged in relation to one another in accordance with the x, y and z axes of an orthogonal coordinate system, and the vibration sensor is arranged on the holding part of the impact body in such a way that the x axis of the vibration sensor runs parallel to the direction of flow of the impact part. To determine the flow energy, the ratio of the electrical signals of the two measuring axes in the x and y directions or in the x and z directions of the multi-axis vibration sensor is preferably used.

[0033] In a further embodiment of the method according to the invention, the impact body is held in the conveying stream in a vibration-isolated manner. The vibration isolation between the holding part of the impact body and a mounting, e.g., on the frame of the conveyor belt or on the casing of a pipeline for hydraulic transport, reduces the influence of extraneous vibrations on the impact body and the vibration sensor attached to it; in particular, changes in signal intensity and frequency shifts are largely avoided.

[0034] To further improve signal quality and reproducibility of acoustic signal acquisition, the multi-axis vibration sensor can be detachably connected to the impact body's support element by means of a screw connection. This ensures the best possible permanent contact with the support element.

[0035] The method for continuously determining the grain size distribution requires a prior calibration before starting the regular signal processing of the electrical signals, which is described below for the preferred vibration sensor with three measuring axes:

[0036] In a first step, a normalization function is created by determining a functional relationship (correlation) between the continuously recorded electrical signals from two measuring points of the vibration sensor for determining the flow energy and the concentration or bulk density of the solid particles of the granulate from samples taken at different times during the continuous signal recording. When determining the functional relationship, preferably only a previously defined frequency spectrum of the continuously recorded electrical signals is considered. If the flow energy is recorded using a force sensor which is provided independently of the vibration sensor, as in the prior art, the functional relationship between the electrical signals from the force sensor and the concentration or bulk density of the solid particles of the granulate is determined.Bulk density of the solid particles of the granulate was determined from samples taken at different times during continuous signal acquisition.

[0037] For a hydraulic flow, e.g., a solid particle-water mixture, a sample with a known total volume is taken, and the mass concentration of the sample is determined. The mass concentration ß± is defined as the quotient of the mass m± of a considered mixture component i, here the mass of the solid particles, and the total volume V of the mixed phase taken with the sample.

[0038] When the solid particles are transported on a belt conveyor, the bulk density is determined. The bulk density p Sch denotes the density, i.e., the mass per volume of a mixture of a granular solid, here the solid particles, and a continuous fluid that fills the spaces between the solid particles. In belt transport, the fluid is air.

[0039] In a second step, taking into account the normalization function thus obtained, a calibration function is created for the energy normalization of the signal intensity of the electrical signals for determining the grain size distribution by determining a functional relationship (correlation) between the electrical signals of all measuring axes of the vibration sensor processed with the normalization function and the grain size distribution of the samples taken at different times during the signal acquisition.

[0040] The determination of the grain size distribution of the samples taken at different times is carried out using a known method for determining the grain size distribution, for example by means of a sieve analysis.

[0041] The recording of the acoustic signals of all measuring axes and the determination of the concentration or bulk density as well as the grain size distribution refer to an essentially consistent collective of solid particles from the conveying flow, i.e. the sample is taken in the immediate vicinity of the multi-axis vibration sensor during the recording of the acoustic signals for calibration.

[0042] The control operation of the signal processing of the electrical signals of at least three measuring axes of the vibration sensor for determining the grain size distribution following the calibration then comprises the following steps:

[0043] The electrical signals acquired by at least three measuring axes of the vibration sensor are standardized using the standardization function to eliminate the dependence of the electrical signals acquired by all measuring axes for determining the grain size distribution on the flow energy. During standardization, preferably only the frequency spectrum of the continuously acquired electrical signals, which was previously defined for the creation of the calibration function, is considered.

[0044] Determine the grain size distribution in real time by applying the calibration function to the standardized electrical signals of all measuring axes.

[0045] The control operation of the electrical signal processing in a conventional vibration sensor following calibration is analogous, with only the electrical signal acquired by the vibration sensor being normalized using the normalization function to eliminate the dependence of the signal for determining the grain size distribution on the flow energy. The grain size distribution is determined in real time by applying the calibration function to the normalized electrical signal of the vibration sensor.

[0046] A measuring device for carrying out the method according to one of claims 1-13 results from the features of claim 14.

[0047] The vibration sensor of the measuring device preferably comprises at least three measuring axes. In conjunction with the inventive design of the impact part, the multi-axis vibration sensor develops a synergistic effect with regard to increased accuracy of the measurement results by almost completely decoupling the measurement results from changing flow energy. Shape features of a preferred impact part with reduced pressure resistance are derived from the features of claims 19 and 20.

[0048] Furthermore, tests have shown it to be advantageous for measuring accuracy if the side surfaces of the impact part, which are arranged symmetrically to a plane of symmetry, converge on the underside, i.e. on the side opposite the holding part, to form an edge lying in the plane of symmetry. The edge preferably runs parabolically starting from a profile nose. With a design of this type, the profile nose is preferably formed by an almost point-shaped region on the surface of the impact part, which is the first to come into contact with the solid particles in the conveying stream in the direction of flow. This geometry means that the smallest cross-sectional area of ​​the impact part is in the region of the profile nose, whereby any distortion of the measuring results due to the pressure resistance of the impact part is minimized.

[0049] The method according to the invention and the measuring device are explained in more detail below with reference to the figures.

[0050] Figure 1 shows an example of a

[0051] Flow conveyor arranged measuring device for carrying out the method according to the invention,

[0052] Figure 2 shows a side view of an impact body of the measuring device according to Figure 1 and sections along the lines AA, BB, CC and DD in the side view,

[0053] Figure 3 is a perspective view of the

[0054] Impact body according to Figure 1 ,

[0055] Figure 4 shows a representation of a bracket for the

[0056] Impact body according to Figure 1 ,

[0057] Figure 5 different grain size distributions of a sand-water mixture with four different sands for test series 7- 10 ,

[0058] Figure 6 Signal analyses of test series 1-6 with a state-of-the-art measuring device,

[0059] Figures 7-9 Signal analyses of test series 1-6 with a measuring device according to the invention,

[0060] Figure 10 Signal analyses of test series 1-3 and 7-10 using a state-of-the-art measuring device,

[0061] Figures 11-13 Signal analyses of test series 1-3 and 7-10 with a measuring device according to the invention,

[0062] Figure 14 shows a representation of a normalization function that describes the functional relationship between the electrical signals of two measuring axes of the vibration sensor (calculated flow energy) and the concentration of solid particles (flow energy) of the granulate from samples taken at different times during the signal acquisition,

[0063] Figure 15 shows a representation of a calibration function that describes a functional relationship between the electrical signals of all axes of the vibration sensor, processed with the normalization function, and the grain size distribution of samples taken at different times during signal acquisition.

[0064] Figure 1 shows a measuring device for carrying out a method for continuously determining the grain size distribution of a granulate in a flow conveyor. The measuring device essentially consists of an impact body (4) made of a metallic, wear-resistant material, which is designed to generate acoustic signals through the impact of solid particles of a granulate, which propagate spatially as structure-borne sound waves in the impact body (4). Furthermore, the measuring device has a holder (2) for holding the impact body (4) in a conveying flow in which the solid particles are transported hydraulically through a pipeline (1) in a conveying direction (7).

[0065] The impact body (4) has an impact part (4.1) and a holding part (4.2). The holding part (4.2), which is better seen in Figure 3, comprises a lower section (4.3) which extends vertically from a holding plate (4.4). The lower section (4.3) engages in a slot (10) which is made in the casing of the pipeline (1) parallel to its longitudinal axis (9) (see Figure 1). The lower section (4.3) is flush with the inner wall of the pipeline (1), so that only the impact part (4.1) of the impact body (4) projects into the interior of the pipeline (1).

[0066] The impact part (4.1), whose pressure resistance in the direction of flow (8) of the impact part (4.1) is smaller than the frictional resistance, is streamlined. Further tests have shown that the impact part (4.1) can be designed as a flat plate with longitudinal flow, achieving equally good measurement results but with a significantly simpler geometry.

[0067] As can be seen particularly from the sectional views in Figure 2, the profile of the impact part (4.1) is symmetrical to a plane of symmetry (11). The direction vector of the flow direction (8) lies in the plane of symmetry (11). The greatest length of the profile of the impact part (4.1) in its

[0068] The inflow direction (8) is located directly at the transition to the holding part (4.2). It is at least ten times the greatest thickness of the profile perpendicular to the plane of symmetry (11) (see section AA). Starting from the profile nose (12), the greatest thickness of the profile is located approximately halfway along the greatest longitudinal extent of the profile of the impact part (4.1), and transverse to the inflow direction (8), the greatest thickness of the profile is located at 40-50% of the greatest height of the profile in the plane of symmetry (11).

[0069] It is advantageous for the measurement accuracy if the side surfaces (13) of the impact part (4.1), which are arranged symmetrically to the plane of symmetry (11), converge on a bottom side (14) to an edge (15) lying in the plane of symmetry (11). The edge (15) runs parabolically starting from the profile nose (12), as can be seen in the side view in Figure 2. The profile nose (12) is

[0070] (4.1) is formed by an almost point-shaped area on the surface of the impact part, which is the first to come into contact with the solid particles in the conveying flow in the direction of flow (8).

[0071] The multi-axis vibration sensor (5) designed as an acceleration sensor is mounted on the front side of the holding part

[0072] (4.2) outside the pipeline (1) by means of a screw (6) and thus provides good wave conduction with the

[0073] Impact body (4). The three measuring axes of the multi-axis vibration sensor (5) are arranged according to the x-, y- and z-axes of an orthogonal coordinate system and the vibration sensor (5) is arranged and aligned on the holding part (4.2) in such a way that the x-axis of the vibration sensor is parallel to the

[0074] Flow direction (8) of the impact part (4.1).

[0075] The impact body (4) is attached to the pipeline (1) by means of a bracket (2) designed as a base, which is shown in detail in Figure 4. From sections AA, BB it can be seen that the underside of the bracket (2) is adapted to the contour of the casing of the pipeline (1). The bracket (2) also has a slot (16) which is aligned with the slot (10) in the casing of the pipeline (1). The bracket (2) is attached to the pipeline (1) by means of screw connections. The holding plate (4.4) of the holding part (4.2) is placed on the flat surface of the bracket (2) and screwed to it. A vibration isolation (3) is arranged between the bracket (2) and the holding plate (4.4) (see

[0076] Figure 1) , which also serves as a seal between the retaining plate (4.4) and the bracket (2).

[0077] The acoustic signals converted into electrical signals by the multi-axis vibration sensor (5) are transmitted via a signal line to a signal processing unit (not shown in the figures), for example, a personal computer. The signal processing unit processes the electrical signals from the vibration sensor (5) to determine the grain size distribution from the acoustic signals, taking the flow energy into account. Experiments

[0078] Various tests were carried out using a measuring device for carrying out the method for continuously determining the grain size distribution:

[0079] Experimental setup

[0080] In a hydraulic circuit consisting of a controllable solids pump, a pressure line, a suction line, and a storage container for the granulate, a streamlined impact body (4) according to the invention was installed in the pressure line, and a circular-cylindrical impact body according to the current state of the art was installed at a short distance therefrom. A multi-axis vibration sensor (5) was attached to the streamlined impact body (4) according to the invention, and a single-axis vibration sensor was attached to the cylindrical impact body.

[0081] Experimental procedure

[0082] In an initial test series, only water was pumped at three different solids pump capacities. The tests in this series are labeled Test 1 to Test 3.

[0083] In a second test series, three different tests with different solids concentrations of a sand-water mixture were conducted at a constant solids pump output and maintaining the particle size distribution (specifically, with the particle size distribution of Test 7 in Figure 5), and the corresponding signals were recorded. The tests in this test series are labeled Test 4 to Test 6.

[0084] In a third test series, four different sands with varying grain size distributions (see Figure 5) were tested at a constant solids pump output and maintaining the solids concentration of a sand-water mixture, and the signals were recorded. The tests in this test series are labeled Test 7 to Test 10.

[0085] The recorded electrical signals from Test 1 to Test 10 were subjected to frequency analysis (signal processing). The results are shown in Figures 6-13, with the results of Test 1 to Test 3 (test series with pure water without sand) also documented in each diagram for ease of comparison.

[0086] Figure 6 documents the frequency analyses of the test series Test 1 to Test 6 for the conventional impact body (cylindrical shape). The change in flow energy, whether in the form of an increase in the solids pump performance in Test 1 to Test 3 with water or an increase in the solids concentration in Test 4 to Test 6 with a sand-water mixture, has a direct influence on the signal intensity. From a frequency of 10 kHz, the intensity increases proportionally to the flow velocity and solids concentration of the flow. The signal properties are very dependent on the flow energy (increase in the solids pump performance or increase in the solids concentration). Figures 7 to 9 show the results of the same.

[0087] Test series Test 1 to Test 6 for the streamlined design of the impact body ( 4 ) and the use of a multi-axis vibration sensor ( 5 ) according to the invention are shown.

[0088] The test results show that the use of a streamlined impact body in combination with a multi-axis vibration sensor reduces the influence of the change in flow energy, i.e. the influence of the solid concentration and / or velocity, on the signal properties.

[0089] Figure 10 documents the frequency analyses of the test series Test 1 to Test 3 and Test 7 to Test 10 for the conventional impact body (cylindrical shape).

[0090] The change in the grain size distribution in Tests 7 to 10 leads to a strong increase in the signal intensities across the entire frequency spectrum. However, the order of the intensities for the individual tests in Figure 10 does not correspond to the order of the grain size distribution of the samples (fineness or coarseness). Up to a frequency of 8 kHz, the signal intensities are random and intersect. In a frequency range between 8 and 11 kHz, the signal intensities of Tests 7 and 8 are the same, even though the sand in Test 7 is finer than the sand in Test 8. Then, up to a frequency of 18 kHz, the signal intensity of the finer mixture in Test 7 is even higher than the signal intensity of the coarser mixture in Test 8.Subsequently, up to the frequency 25 kHz, the signal intensity of the finer mixture Test 7 (average grain size 40 micrometers) is even higher than the signal intensity of the very coarse mixture of Test 9 with an average grain size of 100 micrometers.

[0091] Experience has shown that such a signal property, which is very dependent on the flow energy (solids concentration and speed) but very little on the grain size change of the granulate in the conveying flow, does not allow a reliable determination of the grain size distribution of the granulate in a conveying flow in real time.

[0092] Figures 11 to 13 show the results of the same test series Test 1 to Test 3 and Test 7 to Test 10 for the streamlined design of the impact body in combination with the multi-axis vibration sensor according to the invention.

[0093] The influence of the grain size distribution of the samples on the signal intensity in each wave propagation direction varies. Of key importance is the fact that in all wave propagation directions the signal intensity is proportional to the grain size distribution of the samples. The signal intensity of test 7 (average grain size 40 micrometers) is smaller than the signal intensity of test 8 (average grain size 60 micrometers), and the signal intensity of test 8 is smaller than the signal intensity of test 9 (average grain size 100 micrometers), and finally the signal intensity of test 10 (average grain size 180 micrometers) is higher than the signal intensity of test 9.The illustrated streamlined design of the impact body (4) according to the invention reduces the influence of the pressure drag component of the flow resistance on the signal intensity (see second test series) and increases the dependence of the signal properties on the particle size distribution of the flow. In addition, there is the possibility of using different signal properties from three wave propagation directions to determine the particle size distribution of the mass flow.

[0094] Further analyses of the signal properties of the electrical signals recorded when using the measuring device according to the invention show that in a preferred frequency spectrum between the solid concentrations (flow energy) relevant for the flow energy and the signal properties in two

[0095] A functional relationship exists between the wave propagation directions (calculated flow energy), based on which the flow energy in the conveyed stream can be calculated. Figure 14 shows the functional relationship (normalization function). This allows the ratio of the electrical signals from two measuring axes of the multi-axis vibration sensor to be used to determine the flow energy.

[0096] The signal analysis and evaluation of the results further demonstrate that there is a further functional relationship between the energy-normalized signal intensities in the respective spreading directions and the grain size distribution of the samples. This functional relationship (calibration function) is shown in Figure 15.

[0097] The results show that the invention can be used to reliably determine the grain size distribution of the solid particles in a mass flow in real time, even when the flow energy of the conveying flow varies.

[0098]

Claims

Patent claims 1. A method for continuously determining the grain size distribution of a granulate consisting of solid particles with different grain sizes, comprising the steps Transporting the solid particles in a conveying direction (7) into a conveying flow, wherein the solid particles collide with an impact body (4) arranged as a waveguide and generate acoustic signals which propagate in each impact body (4) as structure-borne sound waves, Capturing acoustic signals and converting them into electrical signals, Determining the flow energy of the conveying stream, whereby the flow energy is determined by the speed and concentration or bulk density of the solid particles of the granulate, Determination of the grain size distribution by signal processing of the electrical signals taking into account the detected flow energy, characterized in that the impact body (4) comprises a holding part (4.2) and an impact part (4.1), wherein the impact part (4.1) is surrounded by solid particles of the granulate in a flow direction (8), the flow resistance of the impact part (4.1) around which the flow passes, which is composed of the pressure resistance and the frictional resistance, is determined in such a way that the pressure resistance is smaller than the frictional resistance, the propagation of the acoustic signals in the impact body (4) is detected and converted into electrical signals with the aid of a vibration sensor (5), the electrical signals of the vibration sensor (5) are used to determine the grain size distribution, taking into account the flow energy of the conveying flow.

2. Method according to claim 1, characterized in that the detection of the spatial propagation of the acoustic signals in the impact body (4) and the detection of the flow energy of the conveying flow as well as the conversion into electrical signals are carried out with the aid of a multi-axis vibration sensor (5) with at least three measuring axes.

3. Method according to claim 1 or 2, characterized in that the proportion of pressure resistance is a maximum of 30% of the flow resistance.

4. Method according to claim 1 or 2, characterized in that the proportion of pressure resistance is a maximum of 10% of the flow resistance.

5. Method according to one of claims 1 to 4, characterized in that the flow resistance is reduced by reducing the frictional resistance on the surface of the impact part.

6. Method according to claim 5, characterized in that the surface has a roughness depth of maximum 20 pm.

7. Method according to one of claims 1 to 6, characterized in that the flow resistance is reduced in that the end face of the impact part (4.1), that is to say its cross-sectional area projected in the direction of flow (8) onto a surface perpendicular thereto, amounts to a maximum of 10% of the total surface of the impact part (4.1) around which the conveying flow flows.

8. Method according to one of claims 2 to 7, characterized in that the three measuring axes of the multi-axis vibration sensor (5) are arranged to one another in accordance with the x-, y- and z-axes of an orthogonal coordinate system and the vibration sensor (5) is arranged on the holding part (4.2) in such a way that the x-axis of the vibration sensor (5) runs parallel to the direction of flow (8) of the impact part (4.1).

9. Method according to one of claims 2 - 8, characterized in that the ratio of the electrical signals from two measuring axes of one vibration sensor (5) is used to determine the flow energy.

10. Method according to one of claims 2 - 9, characterized in that the electrical signals of the at least three measuring axes of the one vibration sensor (5) are used to determine the grain size distribution taking into account the flow energy of the conveying flow.

11. Method according to one of claims 1 to 10, characterized in that the holding part (4.2) of the impact body (4) is held in the conveying stream in a vibration-insulated manner.

12. Method according to one of claims 2 to 11, characterized in that before starting the signal processing of the electrical signals for determining the grain size distribution, at least one normalization function is created in which a relationship between the electrical signals of two measuring axes of the vibration sensor (5) for determining the flow energy and the concentration or bulk density of the solid particles of the granulate is determined from samples taken at different times during the signal acquisition, before starting the signal processing of the electrical signals for determining the grain size distribution, at least one calibration function is created in which a relationship between the electrical signals of all measuring axes of the vibration sensor (5) processed with the normalization function and the grain size distribution of the samples taken during the Signal detection is determined from samples taken at different times.

13. Method according to claim 12, characterized in that the signal processing of the electrical signals for determining the grain size distribution comprises the following steps: Normalising the electrical signals recorded by at least three measuring axes of the vibration sensor for determining the flow energy using the normalisation function in order to eliminate the dependence of the recorded electrical signals of all measuring axes for determining the grain size distribution on the flow energy, Determine the grain size distribution by applying the calibration function to the standardized electrical signals of all measuring axes. 14 . Measuring device for carrying out a method for continuously determining the grain size distribution of a granulate consisting of solid particles with different grain sizes, in particular according to one of claims 1 to 13, comprising an impact body ( 4 ) with a holding part ( 4 . 2 ) and an impact part ( 4 . 1 ) around which solid particles of the granulate can flow, with an inflow direction ( 8 ) for the solid particles of the Granules, wherein the impact body (4) is designed to generate acoustic signals by impact of solid particles of the granules on a surface of the impact part (4.1), which propagate as structure-borne sound waves in the impact body (1), the flow resistance of the impact part (4.1), which is composed of the pressure resistance and the frictional resistance, is determined in such a way that the pressure resistance in the flow direction (8) is smaller than the frictional resistance, a holder (2) which is designed to hold the holding part (4.2) of the impact body (4) in a conveying flow of the solid particles transported in a conveying direction (7), a vibration sensor (5) fastened to the impact body (4), which is designed to detect the propagation of the acoustic signals and to convert them into electrical signals, a signal processing unit designed to process the electrical signals of the vibration sensor (5) in order to determine the grain size distribution taking into account the flow energy of the conveying flow.

15. Measuring device according to claim 14, characterized in that a vibration isolation (3) is arranged between the holder (2) and the holding part (4.2) of the impact body (4).

16. Measuring device according to claim 14 or 15, characterized in that the impact part (4.1) is streamlined.

17. Measuring device according to one of claims 14 to 16, characterized in that the flow resistance of the impact part (4.1) composed of the pressure resistance and the frictional resistance is determined in such a way that the pressure resistance in Inflow direction (8) is a maximum of 10% of the flow resistance.

18. Measuring device according to one of claims 14 to 17, characterized in that the flow resistance of the impact part (4.1) composed of the pressure resistance and the frictional resistance is determined in such a way that the pressure resistance in Inflow direction (8) is a maximum of 30% of the flow resistance.

19. Measuring device according to one of claims 14 to 18, characterized in that an end face of the impact part (4.1), that is to say its end face in the direction of flow (8) the cross-sectional area projected onto a surface perpendicular thereto is a maximum of 10% of the total surface of the impact part (4.1) around which the conveying flow flows.

20. Measuring device according to one of claims 14 to 19, characterized in that the profile of the impact part (4.1) is formed symmetrically to a plane of symmetry (11), the direction vector of the inflow direction (8) of the impact part (4.1) lies in the plane of symmetry (11), the greatest length of the profile of the impact part (4.1) in the inflow direction (8) is at least ten times as large as the greatest thickness of the profile of the impact part (4.1) perpendicular to the plane of symmetry.

21. Measuring device according to claim 20, characterized in that the greatest thickness of the profile, starting from a profile nose, is located at 40% - 50% of the greatest length of the profile and at 40% - 50% of the greatest height of the profile of the impact body in the plane of symmetry (11) and transverse to the direction of flow (8).

22. Measuring device according to one of claims 14 to 21, characterized in that the holding part (4.2) and the impact part (4.1) of the impact body (4) are formed in one piece.

23. Measuring device according to one of claims 14 to 22, characterized in that the vibration sensor (5) has at least three measuring axes and is designed to detect the spatial propagation of the acoustic signals and to detect the flow energy of the conveying flow and to convert them into electrical signals.

Images