Heat exchanger comprising an ultrasound sensor for determining the tube wall thickness of a heat exchanger tube of

Abstract

The invention relates to a heat exchanger (1) having a plurality of heat transfer tubes (3) for transporting a first fluid (F1) in order to transfer heat between the first fluid (F1) and a second fluid (F2) via the heat transfer tubes (3). In order to improve usability, ultrasonic sensors (2) are arranged on one or more of the heat transfer tubes (3) for determining the tube wall thickness of the heat transfer tubes (3) in situ, the respective ultrasonic sensor (2) being designed for an operating pressure greater than 30 bar and / or an operating temperature greater than 80 DEG C, wherein the respective ultrasonic sensor (2) is connected to an electronic data acquisition unit (9) for transmitting data in order to transmit measurement data to the electronic data acquisition unit (9) during operation of the heat exchanger (1). The invention further relates to a method for operating a heat exchanger (1).

Description

Technical Field

[0001] The present invention relates to a heat exchanger comprising a heat transfer tube for conveying a first fluid so as to transfer heat between the first fluid and a second fluid via the heat transfer tube, in particular a high-pressure heat exchanger for urea synthesis.

[0002] The invention furthermore relates to a method for operating a heat exchanger. Background Art

[0003] From the prior art it is known to use a heat exchanger for exchanging thermal energy between a first fluid flow and a second fluid flow. A heat exchanger generally comprises a plurality of heat transfer tubes for transporting a first fluid flow so as to transfer heat to a second fluid flow flowing around the heat transfer tubes via the heat transfer tubes or to absorb heat from said second fluid flow via the heat transfer tubes. As part of the urea synthesis, heat exchangers are generally used in which the first fluid flow or the second fluid flow has a high pressure (generally greater than 30 bar) and a high temperature (generally greater than 80° C.). The transport of the first fluid flow through the heat transfer tubes is thus generally associated with the removal of wall material of the heat transfer tubes (in particular corrosive removal and / or erosive removal) or the formation of deposits inside the heat transfer tubes, respectively, so that the wall thickness of the heat transfer tubes changes, in particular decreases, during operation of the heat exchanger. A reduction in the integrity of the wall of the heat transfer tubes may be problematic for the operational safety of the heat exchanger. Therefore, based on chronological maintenance intervals, it is generally necessary to regularly shut down the heat exchanger and measure the wall thickness of the heat transfer tubes.

[0004] For this purpose, measuring probes are usually inserted into the corresponding heat transfer tubes in the non-operating state of the heat exchanger in order to determine the inner diameter or the wall thickness of the heat transfer tubes. Measuring probes comprising ultrasonic sensors, optical sensors or eddy current sensors are known in order to determine the wall thickness.

[0005] Particularly in the case of heat exchangers operating at pressures of the first and / or second fluid flows greater than 30 bar and temperatures greater than 80° C., such service interruptions for determining the wall thickness of the heat transfer tubes are often time-consuming and laborious and are associated with high costs. Summary of the invention

[0006] This is achieved by the present invention.It is an object of the present invention to specify a heat exchanger of the type named at the outset with optimized availability, in particular optimized operation.

[0007] It is also an object of the invention to specify a method for operating a heat exchanger making it possible to optimize the use or operation of the heat exchanger.

[0008] According to the invention, the object is achieved in that, for a heat exchanger of the type named at the outset, ultrasonic sensors are respectively arranged on one or more of the heat transfer tubes for the in situ determination of the wall thickness of the heat transfer tubes, wherein the respective ultrasonic sensor is designed for an operating pressure of more than 30 bar and / or an operating temperature of more than 80° C., wherein the respective ultrasonic sensor is connected to an electronic data acquisition unit for data transmission, so that the measured data are transmitted to the electronic data acquisition unit during operation of the heat exchanger.

[0009] The invention is based on the idea of ​​improving the usability of a heat exchanger designed for high operating pressures and / or high operating temperatures of a first fluid and / or a second fluid, in that the wall thickness of the heat transfer tubes of the heat exchanger is determined in situ, that is, locally on the heat exchanger or the heat transfer tubes, and usually in operation, that is, during operation of the heat exchanger. As a result, operation, in particular process management and / or maintenance of the heat exchanger can be carried out based on the determined wall thickness. In particular, it is not necessary to interrupt the operation of the heat exchanger in order to determine the wall thickness.

[0010] The operation of the heat exchanger means a state in which a first fluid is conducted through a heat transfer tube so as to exchange heat with a second fluid via the heat transfer tube. A high operating pressure and a high operating temperature respectively mean an operating pressure of more than 30 bar and an operating temperature of more than 80° C. of the first fluid and / or the second fluid. In particular, the operating pressure is between 30 bar and 200 bar, preferably about 180 bar, and / or the operating temperature is between 80° C. and 300° C., preferably about 230° C. Typically, the first fluid and / or the second fluid has this type of operating pressure and this type of operating temperature during operation of the heat exchanger, or the heat exchanger is designed for this type of operation. Therefore, it is beneficial if the corresponding ultrasonic sensor has an operating pressure and an operating temperature corresponding to the operating pressure and the operating temperature, respectively. The heat exchanger is preferably a high-pressure heat exchanger.

[0011] It is particularly advantageous if the heat exchanger is a stripper for performing stripping. It is advantageous if the stripper is used for urea synthesis. The stripper can be implemented to synthesize urea by stripping, usually inside heat transfer tubes.

[0012] Typically, the respective ultrasonic sensor is arranged on the respective heat transfer tube so that the ultrasonic sensor is installed in one of the fluids, preferably in the second fluid, during operation of the heat exchanger. It has proven to be effective if the respective ultrasonic sensor is arranged outside the heat transfer tube (typically in the second fluid) during operation of the heat exchanger. Typically, during operation of the heat exchanger, the second fluid has the aforementioned operating pressure and / or the aforementioned operating temperature, or the heat exchanger is implemented for this type of operation. The ultrasonic sensor is typically arranged on the tube wall of the respective heat transfer tube so as to determine the tube wall thickness by emitting an ultrasonic signal into the tube wall. Typically, an ultrasonic signal can be emitted and the reflected ultrasonic signal is detected using an ultrasonic sensor. The heat exchanger typically comprises one, preferably a plurality of ultrasonic sensors of this type. Typically, the heat exchanger or the ultrasonic sensor is implemented for in-situ determination of the tube wall thickness of the respective heat transfer tube and determination in operation, or the tube wall thickness of the respective heat transfer tube is determined in-situ and in operation using an ultrasonic sensor.

[0013] It is expedient if the respective ultrasonic sensor is connected to an electronic data acquisition unit for transmitting data. As a result, measurement data can be transmitted from the ultrasonic sensor to the data acquisition unit during operation of the heat exchanger. For transmitting data, the ultrasonic sensor and the data acquisition unit are usually connected to a signal line, in particular an electrical signal line. Preferably, the signal line is implemented for symmetrical signal transmission. The signal line is usually implemented in the form of a cable. The signal line is preferably a coaxial cable. A plurality of electronic data acquisition units can be provided, wherein different ultrasonic sensors can be connected to various electronic data acquisition units for transmitting data. A plurality of ultrasonic sensors can be connected to the same electronic data acquisition unit for transmitting data. It can be provided that the respective ultrasonic sensors are controlled using the electronic data acquisition unit to which the ultrasonic sensors are connected for transmitting data.

[0014] The heat transfer tube is usually implemented for conducting a first fluid so as to transfer heat between the first fluid and the second fluid through the tube wall of the heat transfer tube. Preferably, it is provided that during operation of the heat exchanger, the second fluid is in contact with the heat transfer tube or the tube wall, in particular directly in contact with the heat transfer tube or the tube wall. The first fluid is usually a first fluid flow conducted through the heat transfer tube during operation of the heat exchanger. During operation of the heat exchanger, the second fluid can be a second fluid flow that usually flows around the heat transfer tube. The second fluid usually has a pressure greater than 30 bar, in particular between 30 bar and 200 bar, preferably about 180 bar, and / or a temperature greater than 80°C, in particular between 80°C and 300°C, preferably about 230°C. The first fluid can have a higher pressure and / or a higher temperature than the second fluid.

[0015] The heat exchanger generally has a fluid chamber for accommodating a second fluid, wherein a heat transfer tube extends inside the fluid chamber. The fluid chamber generally forms a fluid chamber cavity between a fluid chamber wall of the fluid chamber and a heat transfer tube, so as to accommodate the second fluid with the fluid chamber cavity for transferring heat between the first fluid and the second fluid. The heat transfer tube generally extends through the fluid chamber cavity. Generally, it is provided that during operation of the heat exchanger, the second fluid is conducted through the fluid chamber cavity, in particular so that the second fluid flows around the heat transfer tube. Conveniently, the fluid chamber cavity can be implemented in the form of one or more channels, so as to conduct the second fluid using the channel during operation of the heat exchanger. The fluid chamber generally includes at least one fluid chamber inlet and at least one fluid chamber outlet, so as to conduct the second fluid into the fluid chamber (in particular the fluid chamber cavity) via the fluid chamber inlet, and remove the second fluid from the fluid chamber (in particular the fluid chamber cavity) again via the fluid chamber outlet, generally after heat transfer has occurred between the first fluid and the second fluid. The fluid chamber is generally formed so that it comprises the following components, in particular made of the following components: a metal, preferably an iron alloy, particularly preferably a steel alloy, such as an austenitic steel.

[0016] Typically, the heat transfer tubes are at least sectionally spaced apart from one another so that during operation of the heat exchanger a second fluid can flow between the heat transfer tubes for transferring heat thereto. This applies in particular to the interior of the fluid chamber or its fluid chamber cavity.

[0017] Typically, the first fluid and the second fluid are implemented as liquid and / or gaseous. For example, the first fluid and the second fluid can be formed so that they include the following components, in particular made of the following components: liquid water and gaseous water. It can be provided that the first fluid and the second fluid are implemented so that they include the following components, in particular made of the following components: a liquid medium and a gaseous medium, wherein during operation of the heat exchanger, the liquid medium and the gaseous medium of the respective fluid flow through the heat exchanger in opposite directions, typically such that they are in contact with each other. For example, the first fluid can be formed so that it includes a liquid medium and a gaseous medium, wherein in the respective heat transfer tubes, the media flow through the heat transfer tubes in opposite directions, in particular such that they are in contact with each other during operation of the heat exchanger.

[0018] The heat transfer tubes usually extend between a first tube sheet and a second tube sheet, wherein the tube sheet defines a fluid chamber cavity for accommodating a second fluid, wherein the heat transfer tubes terminate in a through opening of the corresponding tube sheet, or are guided through the through opening. Usually, the fluid fed through the through opening of one of the plates is conducted to the through opening of the other plate through the heat transfer tube. The heat transfer tubes are usually connected to the tube sheet in a fluid-tight manner. Usually, the corresponding tube sheet is implemented as a plate shape having a plurality of flow channels oriented transversely (especially orthogonally) relative to the longitudinal extension of the tube sheet, and the flow channels form corresponding through openings. The tube sheet can be implemented as part of the fluid chamber wall of the fluid chamber. The heat exchanger usually includes at least one first tube sheet of this type and at least one second tube sheet of this type. The tube sheets are usually formed so that they include the following components, especially made of the following components: metal, preferably iron alloy, particularly preferably steel alloy, such as austenitic steel.

[0019] In the fluid chamber, one or more fluid guiding surfaces may exist so as to define the flow path of the second fluid using the fluid guiding surface. The corresponding fluid guiding surface is generally implemented as a segmented block of the fluid flow of the second fluid between the heat transfer tubes. The fluid guiding surface may define a flow path having a plurality of deflection curves, along which the second fluid is guided from the fluid chamber inlet to the fluid chamber outlet. For example, the flow path may have a meandering shape. Typically, a plurality of heat transfer tubes pass through the corresponding guiding surface. Typically, a plurality of guiding surfaces intersecting the heat transfer tubes and spaced apart from each other are provided. The corresponding fluid guiding surface is generally oriented transversely (particularly orthogonally) relative to the longitudinal extension of the heat transfer tube. Typically, a plurality of fluid guiding surfaces spaced apart from each other in the longitudinal direction of the heat transfer tube are provided. Typically, the intermediate space between the plurality of heat transfer tubes is substantially closed by the corresponding fluid guiding surface so as to prevent the second fluid from flowing through the intermediate space. The corresponding fluid guiding surface may be implemented as a majority of the intermediate space between the heat transfer tubes closed for the flow of the second fluid in a cross section passing through the fluid chamber. The fluid guiding surface may be formed using a guiding wall arranged in the fluid chamber. The fluid guiding surfaces are usually implemented in plate shape. A fluid chamber usually comprises one or more guiding surfaces of this type.

[0020] Typically, a plurality of heat transfer tubes are interconnected by stabilizing elements in order to stabilize the heat transfer tubes during operation of the heat exchanger. The respective stabilizing elements can be implemented in the form of a plate, wherein the longitudinal extension of the stabilizing elements is typically oriented transversely, in particular orthogonally, relative to the longitudinal extension of the heat transfer tubes connected by the stabilizing elements. Typically, the heat transfer tubes pass through the stabilizing elements. The stabilizing elements are typically referred to as baffles. Typically, a plurality of stabilizing elements spaced apart from one another and connecting the heat transfer tubes to one another are provided along the longitudinal extension of the heat transfer tubes. In particular, the fluid guiding surface can be formed by the stabilizing elements. The stabilizing elements can then be used both to stabilize the heat transfer tubes and to define the flow path of the second fluid.

[0021] It is advantageous if the respective ultrasonic sensor is arranged in an arrangement region on the respective heat transfer tube, wherein the arrangement region (in particular in the flow direction of the first fluid through the heat transfer tube) is defined by one third of the longitudinal extension of the heat transfer tube inside the fluid chamber or inside the fluid chamber cavity. The arrangement region of the respective heat transfer tube extends in particular in the flow direction of the first fluid, usually starting from the entry of the heat transfer tube along the longitudinal extension of the heat transfer tube into the fluid chamber, and has a length of 30%, in particular 20%, preferably 10% of the longitudinal extension of the heat transfer tube inside the fluid chamber or inside the fluid chamber cavity. It has been shown that material removal or wear of the heat transfer tube is generally particularly large in this arrangement region of the respective heat transfer tube, for which reason it is advantageous to position the ultrasonic sensor in said region.

[0022] It is advantageous if the electronic data acquisition unit is arranged outside the fluid chamber, in particular the fluid chamber cavity. As a result, the electronic data acquisition unit is protected from loads, in particular pressure loads and / or temperature loads, in particular of the first fluid and the second fluid. The data acquisition unit typically comprises a microcontroller or can be implemented as a computer. The electronic data acquisition unit is typically implemented to, in most cases, receive measurement data from one or more of the ultrasonic sensors via one or more hardware interfaces. The electronic data acquisition unit can be implemented to process, collect and / or send the measurement data. For example, the measurement data can be sent from the electronic data acquisition unit to an electronic central data unit, which can be implemented to output the data to a user and / or display the data, in particular in a processed manner. Typically, the heat exchanger comprises one or more electronic data acquisition units.

[0023] It has proven to be effective if the corresponding ultrasonic sensor is connected to the data acquisition unit for transmitting data via a signal line, wherein the signal line extends in particular in the fluid chamber, at least in sections inside a protective tube, preferably made of metal, in order to protect the signal line, in particular from loads exerted by the first fluid or the second fluid. It is advantageous if the protective tube forms a volume separated from the first fluid and the second fluid, inside which the signal line extends, in particular through said volume. Conveniently, the protective tube can be connected to the ultrasonic sensor in a corresponding manner. The volume is usually separated from the fluid chamber cavity. Usually, the signal line extends inside the protective tube in the fluid chamber. The protective tube usually extends from the corresponding ultrasonic sensor to a fluid chamber wall of the fluid chamber, in particular of the fluid chamber cavity. It is advantageous if the protective tube is connected to the sensor housing of the corresponding ultrasonic sensor so that the protective tube, preferably together with the sensor housing, defines a volume separated from the first fluid and the second fluid, or a volume separated from the fluid chamber cavity, in which the signal line extends, during operation of the heat exchanger. The protective tube is usually connected to the corresponding ultrasonic sensor, in particular its sensor housing, in a fluid-tight manner. The protective tube can be connected to a fluid chamber wall of the fluid chamber, in particular of the fluid chamber cavity, in a fluid-tight manner, or can be guided through the fluid chamber wall. The fluid chamber can include a signal line guide hole, by means of which the signal line is guided through the fluid chamber wall of the fluid chamber, in particular out of the fluid chamber. Conveniently, the protective tube can be connected to the fluid chamber wall via the signal line guide hole in a fluid-tight manner. Typically, substantially the entire length of the signal line extends inside the protective tube, between the ultrasonic sensor and the fluid chamber or the signal line guide hole.

[0024] The protective tube can be connected to the ultrasonic sensor, in particular its sensor housing, in a force-fit, form-fit and / or material-bonded manner, usually in a fluid-tight manner. The protective tube can be connected to the signal line guide hole or the fluid chamber wall in a force-fit, form-fit and / or material-bonded manner, usually in a fluid-tight manner. It is preferably provided that on one side, the protective tube is connected in a material-bonded manner, in particular welded to the corresponding ultrasonic sensor, in particular its sensor housing, and / or on the other side, the protective tube is connected to the signal line guide hole with which the signal line is guided through the fluid chamber, preferably in a force-fit and / or material-bonded manner by means of a wedge bolt connection. The welded connection enables a load-bearing and space-saving connection to be realized on the ultrasonic sensor. On the fluid chamber wall, or on the signal guide hole, the space requirement for the connection of the protective tube is generally less relevant, for which reason a wedge bolt connection is practical. Alternatively, however, the protective tube can also be connected in a material-bonded manner, in particular welded to the fluid chamber wall or the signal line guide hole. The heat exchanger preferably comprises one or more protective tubes of this type. In particular, a plurality of protective tubes connected to various ultrasonic sensors may be connected to one another such that they form a shared volume in order to guide the corresponding signal lines through the shared volume.

[0025] The protection tube is typically formed such that it comprises metal, in particular consists of metal. Preferably, the protection tube is formed such that it comprises, in particular consists of, a ferroalloy, preferably a steel alloy, preferably an austenitic steel. In this way, an atmosphere, in particular an atmosphere element composition, which is different from the atmosphere in the fluid chamber, can preferably be created inside the protection tube or inside the ultrasonic sensor. The atmosphere, in particular the atmosphere element composition, inside the protection tube or inside the ultrasonic sensor can essentially correspond to the ambient atmosphere of the heat exchanger.

[0026] The corresponding ultrasonic sensor is usually implemented to transmit an ultrasonic signal and receive an ultrasonic signal that is reflected (usually reflected against one or more interfaces). The ultrasonic signal is usually an ultrasonic wave. From the time interval between the transmitted ultrasonic signal and the received ultrasonic signal, in particular the comparison, the distance between the interfaces can be determined. Advantageously, the ultrasonic signal can be transmitted into the corresponding heat transfer tube (in particular its tube wall) using the ultrasonic sensor, and the ultrasonic signal reflected against the interface, in particular the outer wall and the inner wall of the heat transfer tube, can be received using the ultrasonic sensor to determine the tube wall thickness of the heat transfer tube. The corresponding ultrasonic sensor usually includes a piezoelectric crystal for transmitting the ultrasonic signal and receiving the reflected ultrasonic signal. The piezoelectric crystal is usually implemented as part of a piezoelectric element. The actuation of the piezoelectric crystal or the piezoelectric element usually occurs via a signal line. It is beneficial if the piezoelectric crystal is formed so that it includes a lead zirconate titanate ceramic (PZT ceramic), in particular made of PZT ceramic. The piezoelectric crystal can be implemented in plate form and has a thickness of less than 3 mm, in particular less than 1 mm, preferably less than 0.5 mm, particularly preferably between 0.1 mm and 0.15 mm in the emission direction of the ultrasonic signal. The thickness is usually greater than 0.05 mm. The ultrasonic sensor is usually arranged on the heat transfer tube so that the emission direction of the ultrasonic signal is transverse, in particular substantially orthogonal, to the longitudinal extension of the heat transfer tube.

[0027] Typically, the corresponding ultrasonic sensor is implemented and, in particular, arranged on the corresponding heat transfer tube (in particular, its tube wall) so that an ultrasonic signal can be emitted into the corresponding heat transfer tube (in particular, its tube wall); using the ultrasonic sensor and the ultrasonic signal reflected against the outer wall and the inner wall of the heat transfer tube (in particular, its tube wall), the ultrasonic signal can be received using the ultrasonic sensor in order to determine the tube wall thickness of the heat transfer tube. From the time interval, in particular, the comparison between the emitted ultrasonic signal and the received ultrasonic signal, the distance between the inner wall and the outer wall of the heat transfer tube (in particular, its tube wall) can be detected in order to determine the tube wall thickness of the heat transfer tube. The ultrasonic sensor is typically arranged on the heat transfer tube so that the ultrasonic signal is emitted into the heat transfer tube (in particular, its tube wall) using the ultrasonic sensor in a transverse, in particular substantially orthogonal direction relative to the longitudinal axis of the heat transfer tube. Conveniently, the ultrasonic signal can therefore be emitted to the outer wall and the inner wall in a transverse, in particular substantially orthogonal direction relative to the outer wall and / or inner wall of the heat transfer tube (in particular, its tube wall), and in particular can be at least partially reflected against the wall.

[0028] Typically, the inner wall is the inner surface of the tube wall of the heat transfer tube, and the outer wall is the outer surface of the tube wall of the heat transfer tube. Typically, the inner surface is the tube wall surface facing the inside of the heat transfer tube, and the outer surface is the tube wall surface of the heat transfer tube facing away from the inside of the heat transfer tube. This is particularly applicable in the direction orthogonal to the longitudinal axis of the heat transfer tube in the cross section of the heat transfer tube.

[0029] For high accuracy, it has proven effective if, in the corresponding ultrasonic sensor, the transmission and reception of the ultrasonic signal occurs using the same piezoelectric crystal. Typically, the control of the ultrasonic sensor or the piezoelectric crystal switches between a transmission mode, in which the ultrasonic signal is transmitted using the ultrasonic sensor, and a reception mode, in which the reflected ultrasonic signal can be detected using the ultrasonic sensor. Between the transmission mode and the reception mode, there is typically a dead time, during which the reflected ultrasonic signal cannot be detected. Alternatively, it can be provided that the ultrasonic sensor comprises a plurality of piezoelectric crystals, wherein one of the piezoelectric crystals is implemented for transmitting the ultrasonic signal and another of the piezoelectric crystals is implemented for receiving the ultrasonic signal. However, it is preferred if the transmission and reception of the ultrasonic signal occurs using the same piezoelectric crystal.

[0030] Typically, the corresponding ultrasonic sensor includes a damping element, a piezoelectric crystal and a spacer. The damping element is typically coupled to the piezoelectric crystal and implemented to dampen the mechanical vibration of the piezoelectric crystal. The piezoelectric crystal typically rests on the damping element. The spacer is typically arranged downstream of the piezoelectric crystal in the emission direction of the ultrasonic signal toward the heat transfer tube, so as to prevent the ultrasonic signal emitted using the piezoelectric crystal from being reflected against the tube wall of the heat transfer tube during the dead time. The spacer is typically formed of a material suitable for ultrasonic conduction.

[0031] It is advantageous if, in a corresponding ultrasonic sensor, the damping element, the piezoelectric crystal and the spacer are pressed against one another by means of a spring element. In this way, a robust and in particular durable connection can be ensured, even at high operating pressures and / or high operating temperatures. Preferably, the mutual bonding of the damping element, the piezoelectric crystal and the spacer, which bonding is susceptible to loads, can thereby be omitted. The squeezing together is thus usually associated with an elastic deformation of the spring element against the spring force of the spring element. It is advantageous if the spring element is formed by an arrangement of one spring or a plurality of springs, preferably coupled in series with one another. The spring is preferably a disc spring. The spring element is preferably arranged upstream of the damping element in the emission direction.

[0032] The transmission direction generally denotes the direction in which the corresponding ultrasonic sensor is implemented to transmit an ultrasonic signal, in particular towards the heat transfer tube.

[0033] It is advantageous if the damping element is embodied such that it comprises a porous titanium body, in particular is made of a porous titanium body, which is in particular formed such that it comprises sintered titanium. Typically, the titanium body has an average pore size of less than 100 μm, in particular less than 50 μm, preferably between 1 μm and 10 μm, particularly preferably about 5 μm. Thus, a robust ultrasonic signal can be generated. The damping element typically has a thickness in the transmission direction of between 1 mm and 5 mm, preferably about 3 mm.

[0034] The spacer can be formed such that it comprises, in particular consists of, acrylic glass or metal, in particular iron, preferably steel. For a robust ultrasonic signal, it is particularly advantageous if the spacer is formed such that it comprises, in particular consists of, austenitic steel. Preferably, the surface of the spacer is thereby embodied in a polished manner, in particular if the spacer is formed such that it comprises or consists of steel. Typically, the spacer has a thickness in the emission direction of less than 30 mm, in particular between 2 mm and 10 mm, preferably about 5 mm.

[0035] It is advantageous if, in a corresponding ultrasound sensor, a damping element is arranged between the electrical actuation electrode and the piezoelectric crystal, wherein the damping element is embodied as electrically conductive so that electrical actuation of the piezoelectric crystal via the actuation electrode can be achieved by the damping element. The electrical actuation electrode can be pressed against the damping element using the aforementioned spring element. It should be understood that two electrodes are usually present in order to electrically actuate the piezoelectric crystal to transmit and receive ultrasound signals, in particular to apply a voltage to the crystal or to reduce a voltage via the electrodes. The electrodes are usually electrically connected to the piezoelectric crystal on opposite sides of the piezoelectric crystal.

[0036] One of the electrodes can be an actuation electrode and can be electrically connected to the piezoelectric crystal via a damping element, in particular in the manner described above. The other electrode can be electrically connected directly to the piezoelectric crystal, typically on a side of the piezoelectric crystal that is located downstream of the piezoelectric crystal in the emission direction. Alternatively or cumulatively, it is beneficial if, in order to form a piezoelectric element, two piezoelectric electrodes are applied to the surface of the piezoelectric crystal, typically so that they are opposite each other on the piezoelectric crystal, via which the piezoelectric crystal can be actuated to simulate vibrations. The piezoelectric electrodes are typically made of metal, preferably silver. Advantageously, the aforementioned actuation electrode can be provided additionally.

[0037] The corresponding ultrasonic sensor usually comprises a sensor housing which forms an outer sheath of the ultrasonic sensor. Usually, a damping element, a piezoelectric crystal (usually in the nature of a spacer) and / or usually electrodes (in particular actuation electrodes, if necessary) are arranged inside the sensor housing. The sensor housing usually comprises an outlet opening, via which the ultrasonic signal generated using the piezoelectric crystal can leave for measurement using the ultrasonic sensor. The outlet opening is usually isolated in a fluid-tight manner, usually with a spacer.

[0038] It has proven to be effective if the corresponding ultrasonic sensor comprises one or more electrically insulating elements for electrical insulation between the sensor housing of the ultrasonic sensor and the piezoelectric crystal of the ultrasonic sensor and / or the damping element of the ultrasonic sensor and / or one, in particular a plurality of electrodes of the ultrasonic sensor, respectively. The electrically insulating elements are preferably formed such that they comprise zirconium dioxide, in particular are made of zirconium dioxide. The electrically insulating element can completely surround these components. In this way, the risk of short circuits can be minimized even under high loads, in particular pressure loads and / or temperature loads.

[0039] It is advantageous if a coupling component which is formed to include silver, in particular a silver film, is arranged between the respective ultrasonic sensor and the heat transfer tube, or if no coupling component is arranged. This applies in particular during operation of the heat exchanger. The purpose of the coupling component is generally to enable the ultrasonic signal to be coupled into the heat transfer tube in a reflection-reduced manner. It has been shown that at the aforementioned high pressures and / or the aforementioned high temperatures, a sustainable high-quality coupling-in can be obtained if silver is used as a coupling component, or if no coupling component is used. The coupling component is preferably embodied in layers. The coupling component generally has a thickness of between 0.01 mm and 1 mm, in particular of approximately 0.05 mm. The thickness is generally measured in the emission direction.

[0040] The respective ultrasonic sensor can be connected to the respective heat transfer tube in a force-fit, form-fit or material-bonded manner. Conveniently, a retaining device can be provided for this purpose. It is preferred if the respective ultrasonic sensor is connected to the respective heat transfer tube in a force-fit manner, preferably using a clamping connection. In this way, a robust connection between the ultrasonic sensor and the heat transfer tube can be achieved so that the ultrasonic signal can be coupled into the heat transfer tube with low noise, and the measuring object is not significantly damaged as far as the measurement of the tube wall thickness is concerned. It is beneficial if the retaining device includes a spring assembly, wherein the ultrasonic sensor is pressed against the tube wall of the heat transfer tube using the spring assembly with a spring force load. As a result, even under particularly variable pressure loads and / or temperature loads, a strong pressing contact can be ensured. The spring assembly can be formed so that it includes one or more disc springs. Conveniently, a plurality of ultrasonic sensors can be connected to the respective heat transfer tubes using, respectively, separate retaining devices, in particular as described. However, it is also possible to provide that a plurality of ultrasonic sensors are connected to the respective heat transfer tubes using a shared retaining device. Although less preferred, the corresponding ultrasound sensor can alternatively be connected to the heat transfer tube in a materially bonded manner or, in simple cases, in a form-fitting manner.

[0041] It is advantageous if a plurality of ultrasonic sensors are connected to the same electronic data acquisition unit for transmitting data so that the measurement data are transmitted to the electronic data acquisition unit during operation of the heat exchanger. In this way, a compact construction with preferably short signal lines can be achieved. Typically, the electronic data acquisition unit comprises a plurality of hardware interfaces to which signal lines connected to the ultrasonic sensors for transmitting data are connected. One hardware interface can each be assigned to one of the signal lines, respectively. The corresponding ultrasonic sensors can be connected to the electronic data acquisition unit via a single signal line for transmitting data. Alternatively, a plurality of signal lines connected to the ultrasonic sensors can form a shared data bus, via which the measurement data can be transmitted to the electronic data acquisition unit. It is beneficial if a plurality of electronic data acquisition units exist, wherein ultrasonic sensors from different electronic ultrasonic sensor groups are connected to different electronic data acquisition units for transmitting data. This is particularly beneficial for keeping the signal line length short.

[0042] It is advantageous if, for the transmission of data, a plurality of electronic data acquisition units are connected to an electronic central data unit, wherein the electronic central data unit is implemented to collect the measurement data of the electronic data acquisition units and / or to process said data and / or to make said data available for readout by a user. The measurement data may thus have been preprocessed by the electronic data acquisition unit and may be further processed by, for example, the electronic central data unit. In particular, the electronic data acquisition unit and / or the electronic central data unit may be implemented to determine from the measurement data the wall thickness of the heat transfer tube (in particular its wall) measured using a corresponding ultrasonic sensor. For the transmission of data, the electronic data acquisition unit may be connected to the electronic central data unit via a data transmission line, in particular in the form of a data bus. In this way, a compact design may be achieved, in which interference with the measurement data (in particular due to high pressure and / or high temperature conditions in the heat exchanger) may be small. The electronic central data unit typically comprises a microcontroller or may be implemented as a computer. Preferably, the heat exchanger comprises one or more electronic central data units.

[0043] The heat exchanger is usually designed for an operating pressure of more than 30 bar, in particular between 30 bar and 200 bar, preferably about 180 bar, and / or an operating temperature of more than 80° C., in particular between 80° C. and 300° C., preferably about 230° C., or is operated accordingly. It is therefore advantageous if the corresponding ultrasonic sensor is designed for use at this type of operating pressure and / or this type of operating temperature, or has this type of operating pressure and / or this type of operating temperature. The operating pressure and the operating temperature usually refer to the first fluid and / or the second fluid. Preferably, the second fluid has this type of operating pressure and / or this type of operating temperature during operation of the heat exchanger. Usually, the corresponding ultrasonic sensor is arranged inside the second fluid during operation of the heat exchanger. It is therefore advantageous if the corresponding ultrasonic sensor is designed for an operating pressure corresponding to the operating pressure of the second fluid and an operating temperature corresponding to the operating pressure of the second fluid.

[0044] The respective ultrasonic sensor is usually arranged on the tube wall of the respective heat transfer tube, in particular so that it contacts the tube wall. Usually, one ultrasonic sensor is respectively arranged on a plurality of heat transfer tubes of the heat exchanger. A plurality of ultrasonic sensors can also be respectively arranged on a plurality of heat transfer tubes. The heat transfer tubes are usually formed so that they comprise the following components, in particular are made of the following components: metal, in particular an iron alloy, preferably a steel alloy.

[0045] Typically, the electronic data acquisition unit is arranged outside the first and second fluids, or outside a heat transfer space of the heat exchanger, in which heat is transferred between the first and second fluids via heat transfer pipes during operation of the heat exchanger. The heat transfer space may be a fluid chamber, or surround a fluid chamber.

[0046] It is beneficial if in this way the tube wall thickness of the heat transfer tube can be determined during operation of the heat exchanger with an accuracy of less than 0.1 mm, in particular between 0.003 mm and 0.1 mm, typically 0.05 mm. This can be achieved using a heat exchanger according to the present document.

[0047] Another object is achieved by a method for operating a heat exchanger of the type named at the outset, if on one or more heat transfer tubes of the heat exchanger (with which a first fluid is transported in order to transfer heat between the first fluid and a second fluid via the heat transfer tube), ultrasonic sensors are respectively arranged at an operating pressure greater than 30 bar and / or an operating temperature greater than 80° C., wherein the wall thickness of the respective heat transfer tube is determined in situ using the respective ultrasonic sensor, wherein the measurement data from the respective ultrasonic sensor are sent to an electronic data acquisition unit during operation of the heat exchanger. The method can in particular be implemented using the aforementioned heat exchanger. Typically, the wall thickness of the heat transfer tube represents, in a cross section of the heat transfer tube, the distance (in particular radially) between the inner surface and the outer surface of the wall of the heat transfer tube. Typically, the second fluid is arranged outside the heat transfer tube so that heat is transferred between the first fluid and the second fluid via the wall of the heat transfer tube.

[0048] It should be understood that the method for operating a heat exchanger can be implemented according to the features and effects described in this document (especially above) in the context of a heat exchanger. As far as the method is concerned, the same also applies to the heat exchanger.

[0049] It is particularly beneficial if the method for operating a heat exchanger is used for urea synthesis. The heat exchanger can be implemented as a stripper for stripping, in particular for urea synthesis, in which a liquid phase and a gas phase with opposite flow directions are usually provided to be brought into contact with each other, usually inside a heat transfer tube. It is beneficial if a first medium flows through the corresponding heat transfer tube in a flow direction and a second medium flows through the heat transfer tube in a direction opposite to the flow direction so as to react with each other, wherein one of the media is usually liquid and the other medium is gaseous. It usually occurs inside a fluid chamber or a fluid chamber cavity. The first fluid can be formed so that it includes the first medium and the second medium, or is made of the first medium and the second medium. It is beneficial if the orientation of the heat transfer tube and the flow direction of the first fluid flowing through the heat transfer tube is substantially perpendicular, in particular if the heat exchanger is a stripper. The heat exchanger or stripper usually includes a plurality of, in particular more than 10, preferably more than 50, particularly preferably more than 100, particularly preferably more than 1000 heat transfer tubes.

[0050] Typically, a heat exchanger, in particular if the heat exchanger is a stripper, comprises a first inlet via which a first medium can be sent into a heat transfer tube and a second inlet via which a second medium can be sent into the heat transfer tube, so that inside a fluid chamber or fluid chamber cavity, the media flow through the heat transfer tube in opposite flow directions in order to react with each other. With respect to the fluid chamber cavity, the first inlet and the second inlet are typically arranged at different ends of the heat transfer tube so that they are connected to the heat transfer tube in a fluid-conducting manner. The heat exchanger typically comprises at least one outlet for removing a product formed by a reaction between the first medium and the second medium from the heat transfer tube. Practically, the heat exchanger may comprise a first outlet via which a first product can be removed from the heat transfer tube and a second outlet via which a second product can be removed from the heat transfer tube, wherein with respect to the fluid chamber cavity, the outlets are connected to the heat transfer tube in a fluid-conducting manner at different ends of the heat transfer tube. The first product and the second product are typically formed by means of a reaction between the first medium and the second medium or as a result of a reaction between the first medium and the second medium. This is particularly applicable if the heat exchanger is implemented as a stripper.

[0051] For urea synthesis, the first medium is generally formed such that it comprises the following components, in particular is made of the following components: urea, ammonium carbamate and ammonia, and the second medium is formed such that it comprises gaseous carbon dioxide (CO2), in particular is made of gaseous carbon dioxide (CO2). In this way, urea (in particular high-purity urea) can be separated into products, in particular a first product, which is led out of the heat transfer tube, typically at one of the ends of the heat transfer tube or via a first outlet. Conveniently, the process gas formed, typically gaseous ammonia (NH3) and / or gaseous carbon dioxide (CO2), can be led out of the heat transfer tube, typically at the other end of the heat transfer tube or via a second outlet. The second fluid can be formed such that it comprises liquid water and / or gaseous water, in particular is made of liquid water and / or gaseous water. The stripper can be implemented and operated as described in this document, in particular with respect to the heat exchanger.

[0052] It is advantageous if the respective ultrasonic sensor is operated at a frequency greater than 10 MHz, in particular between 10 MHz and 30 MHz, in particular a center frequency, in particular if an ultrasonic signal with a corresponding frequency, in particular a center frequency, preferably of about 15 MHz is emitted from the respective ultrasonic sensor for determining the pipe wall thickness.

[0053] It is advantageous if, for temperature compensation of the ultrasonic velocity of the ultrasonic signal, the thickness of the spacer of at least one of the ultrasonic sensors is used as a reference length and / or the temperature is detected using at least one thermocouple. Since the spacer has a known thickness, changes in the speed of sound of the ultrasonic signal can be taken into account, in particular determined, by ultrasonic measurement with the aid of a corresponding ultrasonic sensor, in particular by detecting the thickness of the spacer with the aid of the measurement signal of the corresponding ultrasonic sensor. The thickness is usually measured in the emission direction. Conveniently, temperature compensation can be performed during each measurement process using the corresponding ultrasonic sensor. Highly accurate measurements are therefore available. Temperature compensation can be taken into account during the determination, in particular calculation, of the pipe wall thickness from the measurement data detected using the ultrasonic sensor.

[0054] Conveniently, the heat exchanger may include one or more (particularly the aforementioned) thermocouples, wherein the thermocouples are implemented for measuring the temperature in the region of the ultrasonic sensor. For example, the corresponding thermocouples may be arranged in the fluid chamber, on one of the heat transfer tubes (particularly in one of the heat transfer tubes), or on the ultrasonic sensor. It is beneficial if the corresponding thermocouples are connected to a data acquisition unit for transmitting data. This can be achieved via a data cable. The data acquisition unit may include one or more hardware interfaces for the corresponding connection of the data cable. Conveniently, the corresponding data cable may extend inside the protective tube, in particular as implemented above. The protective tube can thereby be guided to the corresponding thermocouple. The data cable and the signal line may extend in a shared protective tube.

[0055] High application utility can be achieved if an ultrasonic signal is emitted into the corresponding heat transfer tube (in particular, its tube wall) using an ultrasonic sensor, and the ultrasonic signal reflected against the outer wall and the inner wall of the heat transfer tube is received using the ultrasonic sensor in order to determine the tube wall thickness of the heat transfer tube. The ultrasonic signal is usually emitted using the ultrasonic sensor so that the ultrasonic signal hits the outer wall and the inner wall in a transverse direction, in particular substantially orthogonal direction, relative to the outer wall and / or the inner wall, and is reflected in particular against said walls.

[0056] Determining the wall thickness using a corresponding ultrasonic sensor usually occurs by means of a time-of-flight method. An ultrasonic signal is usually emitted using a corresponding ultrasonic sensor, and the reflected ultrasonic signal is then detected using the ultrasonic sensor. The reflected ultrasonic signal is usually formed by the reflection of the emitted ultrasonic signal against an interface. The interface can be, for example, the outer surface and / or the inner surface of the wall of the heat transfer tube. By detecting the time interval between the emitted ultrasonic signal and the reflected ultrasonic signal, and / or between the reflected ultrasonic signals, the thickness of the wall to which the ultrasonic signal is conducted can be detected. The ultrasonic signal is usually an ultrasonic pulse. Usually, a sequence of reflected ultrasonic pulses corresponding to multiple reflections between the inner and outer surfaces of the wall of the tube, corresponding to the end of the spacer or the outer surface of the tube wall, is detected. The time interval between the detected reflected ultrasonic pulses of the multiple reflections usually corresponds to twice the thickness of the tube wall. The emission time of the ultrasonic signal, the ultrasonic signal reflected against the outer surface of the tube wall, and / or one or more ultrasonic signals reflected against the inner surface of the tube wall can be used as a time mark so as to determine the corresponding tube wall thickness using a chronological comparison of the time marks. By taking into account the speed of sound or propagation velocity of the ultrasonic signal, the wall thickness can be determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Further features, advantages and effects of the invention are derived from the following description of exemplary embodiments. In the accompanying drawings to which reference is made:

[0058] Figure 1 A schematic diagram showing a heat exchanger;

[0059] Figure 2 A schematic diagram showing an ultrasonic sensor in cross section;

[0060] Figure 3 A schematic diagram showing another heat exchanger implemented as a stripper;

[0061] Figure 4 A schematic diagram of another ultrasonic sensor is shown in cross section. DETAILED DESCRIPTION

[0062] exist Figure 1In the figure, a heat exchanger 1 is schematically illustrated, wherein the heat exchanger 1 comprises a plurality of heat transfer tubes 3 and a fluid chamber 4, wherein the heat transfer tubes 3 pass through the fluid chamber 4 so as to conduct a first fluid F1 through the heat transfer tubes 3 and conduct a second fluid F2 through the fluid chamber 4 in a surrounding manner during operation of the heat exchanger 1, so that heat is transferred between the first fluid F1 and the second fluid F2 through the tube wall of the heat transfer tube 3. The fluid chamber 4 forms a fluid chamber cavity 5 between the fluid chamber wall and the heat transfer tube 3 so as to accommodate the second fluid F2, through which the second fluid F2 is conducted. The fluid chamber 4 comprises a fluid chamber inlet 6 for sending the second fluid F2 into the fluid chamber 4, in particular the fluid chamber cavity 5, and a fluid chamber outlet 7 for removing the fluid from the fluid chamber 4, in particular the fluid chamber cavity 5. The second fluid F2 typically has a pressure greater than 30 bar, in particular between 30 bar and 200 bar, and / or a temperature greater than 80° C., in particular between 80° C. and 300° C. Typically, the heat transfer tubes 3 are guided through the fluid chamber 4 so that they are spaced apart from each other so that the second fluid F2 can flow between the heat transfer tubes 3. The first fluid F1 and / or the second fluid F2 can be, for example, liquid water and / or gaseous water. The heat exchanger 1 can be implemented as a stripper. The heat exchanger 1, in particular the stripper, is typically oriented so that the longitudinal extension of the heat transfer tubes 3 is oriented substantially vertically.

[0063] Ultrasonic sensors 2 are arranged on a plurality of heat transfer tubes 3 in order to determine the tube wall thickness of the respective heat transfer tubes 3 in situ and in operation (that is, during operation of the heat exchanger 1) using the respective heat exchanger 1. The respective ultrasonic sensors 2 are arranged inside the fluid chamber 4, outside the respective heat transfer tubes 3, on the heat transfer tubes 3. In order to withstand the high temperatures and / or high pressures in the heat exchanger 1, the ultrasonic sensors 2 are designed for operating pressures greater than 30 bar and / or operating temperatures greater than 80°C. In particular, the ultrasonic sensors 2 are designed to withstand the aforementioned pressures and / or the aforementioned temperatures of the second fluid F2, and have corresponding operating pressures and corresponding operating temperatures. The respective ultrasonic sensors 2 are connected to an electronic data acquisition unit 9 via a signal line 8 in order to transmit measurement data to the data acquisition unit 9 during operation of the heat exchanger 1. The data acquisition unit 9 is arranged outside the fluid chamber 4 so as not to be adversely affected by the high temperatures and high pressures in the heat exchanger 1. The respective signal line 8 is usually implemented as a coaxial cable in order to achieve interference-free transmission of measurement data. The fluid chamber 4 comprises a signal line guide hole 10, via which the signal line 8 is guided out of the fluid chamber 4. The signal line guide hole 10 is usually embodied to be fluid-tight with respect to the fluid chamber cavity 5.

[0064] In order to protect the corresponding signal line 8 from the pressure and temperature of the fluid chamber 4, in particular the second fluid F2, the corresponding signal line 8 extends inside the protection tube 11 in the fluid chamber 4, such as Figure 2. The protective tube 11 extends from the respective ultrasonic sensor 2 to the signal line guide hole 10. Typically, the protective tube 11 is connected, in particular welded, to the respective ultrasonic sensor 2 on one side in a fluid-tight manner and is connected to the signal line guide hole 10 on the other side in a fluid-tight manner, preferably by means of a wedge bolt connection. In this way, a volume separated from the fluid chamber cavity 5, preferably with a different atmosphere, can be formed using the protective tube 11, in which volume the signal line 8 extends. The protective tube 11 is preferably formed of steel, in particular austenitic steel.

[0065] In order to keep the length of the signal line 8 short, it is advantageous if a plurality of electronic data acquisition units 9 are present, wherein the various ultrasonic sensors 2 are connected to different electronic data acquisition units 9 for transmitting the data. Figure 1 A further electronic data acquisition unit 9 is illustrated in FIG. 1 , which is depicted by a dashed line. In a similar manner to that described, the further electronic data acquisition unit 9 can be connected to a further ultrasonic sensor 2 arranged on the heat transfer tube 3 for transmitting data.

[0066] Typically, an electronic central data unit 12 is provided, to which one electronic data acquisition unit 9 or a plurality of electronic data acquisition units 9 are connected for data transmission. The electronic central data unit 12 is implemented to collect the measurement data of the electronic data acquisition units 9 and preferably make said data available for readout by a user. The electronic data acquisition units 9 are typically connected to the electronic central data unit 12 for data transmission via a cable connection 13, in particular a data bus.

[0067] Typically, the heat transfer tubes 3 extend between a first tube sheet 14 and a second tube sheet 15, respectively, wherein the tube sheets are implemented as part of a fluid chamber wall of the fluid chamber 4 or delimit a fluid chamber cavity 5. The respective heat transfer tubes 3 are guided through the first tube sheet 14 and the second tube sheet 15. The fluid chamber 4 comprises a plurality of stabilizing elements 16, which are typically indicated as baffles, which connect the plurality of heat transfer tubes 3 to each other in order to stabilize the heat transfer tubes 3 using the stabilizing elements 16 during operation of the heat exchanger 1. Conveniently, a plurality of stabilizing elements 16 spaced apart from each other along the longitudinal extension of the heat transfer tubes 3 may be present, the stabilizing elements 16 being oriented transversely, in particular orthogonally, relative to the longitudinal extension of the heat transfer tubes 3. It is expedient if the respective stabilizing elements 16 or the fluid guiding surfaces formed thereby insulate the intermediate spaces between the plurality of heat transfer tubes 3 in order to prevent the second fluid F2 from flowing through the intermediate spaces. Typically, a large portion of the intermediate spaces between the heat transfer tubes 3 is closed to the flow of the second fluid F2 through the fluid chamber 4 in a cross section by the respective stabilizing elements 16 or the fluid guiding surfaces.

[0068] It is advantageous if the respective ultrasonic sensor 2 is arranged on the respective heat transfer tube 3 in an arrangement region which is located in one third of the longitudinal extension of the heat transfer tube 3 inside the fluid chamber 4 or fluid chamber cavity 5 in the flow direction of the first fluid F1 through the heat transfer tube 3. Preferably, the ultrasonic sensor 2 is thus arranged between the first tube sheet 14 and the first of the stabilizing elements 16 in the flow direction of the first fluid F1 through the heat transfer tube 3.

[0069] Figure 2 FIG. 2 is a schematic diagram of an ultrasonic sensor 2. Specifically, the ultrasonic sensor 2 is based on Figure 1 The ultrasonic sensor 2 includes a damping element 17, a piezoelectric crystal 18, and a spacer 19. The piezoelectric crystal 18 is arranged between the damping element 17 and the spacer 19 in the transmission direction, and an ultrasonic signal can be transmitted along the transmission direction using the ultrasonic sensor 2. The damping element 17 is implemented to suppress the mechanical vibration of the piezoelectric crystal 18. The spacer 19 is implemented to send the ultrasonic signal generated using the piezoelectric crystal 18 along the transmission direction so that the ultrasonic signal is located inside the spacer 19 during the duration of switching between the transmission mode and the reception mode of the ultrasonic sensor 2. In the transmission mode, the ultrasonic signal can be transmitted using the ultrasonic sensor 2 (particularly the piezoelectric crystal 18). In the reception mode, the ultrasonic signal can be detected using the ultrasonic sensor 2 (particularly the piezoelectric crystal 18).

[0070] The damping element 17 is embodied as electrically conductive and is electrically connected to an actuation electrode 20 upstream of the damping element 17 in the transmission direction S, so that the piezoelectric element can be electrically actuated through the damping element 17 via the actuation electrode 20. The electric cathode usually constitutes the actuation electrode 20. The actuation electrode 20 is electrically connected to the signal line 8 for actuating the ultrasonic sensor 2 or for transmitting data. As previously described, the signal line 8 is connected to the electronic data acquisition unit 9 for transmitting data. The signal line 8 is usually a coaxial cable.

[0071] The ultrasonic sensor 2 comprises a spring element 21, by means of which the actuating electrode 20, the damping element 17, the piezoelectric crystal 18 and the spacer 19 are pressed against each other by means of the spring force of the spring element 21. In this way, a robust connection can be achieved, in particular without adhesive. The spring element 21 can advantageously be implemented using a plurality of disc springs arranged so that they are connected in series. Conveniently, the ultrasonic sensor 2 comprises a sensor housing 22, which forms an outer sheath of the ultrasonic sensor 2. The sensor housing 22 comprises an outlet opening 23 for the ultrasonic signal, wherein the outlet opening 23 is isolated by the spacer 19, in particular in a fluid-tight manner. The spacer 19 is typically connected to the sensor housing 22 in a force-fitting manner, for example using a screw connection.

[0072] Between the sensor housing 22 and the damping element 17 and the actuation electrode 20 , respectively, an electrically insulating element 24 preferably made of zirconium dioxide is arranged, respectively, which normally completely surrounds the damping element 17 and the control electrode in order to prevent electrical contact with the sensor housing 22 .

[0073] In order to protect the signal transmission from the ultrasonic sensor 2 to the electronic data acquisition unit 9 from the second fluid F2, in particular its pressure and / or temperature, the signal line 8 extends inside the protective tube 11, in particular as described above. The protective tube 11 is connected to the sensor housing 22 in a fluid-tight manner, preferably by means of a welded connection, so that the protective tube 11 and the sensor housing 22 define a volume that is separated from the fluid chamber 4 or the fluid chamber cavity 5. In this way, the ultrasonic sensor 2 and the data transmission between the ultrasonic sensor 2 and the electronic data acquisition unit 9 can be protected from the second fluid F2.

[0074] The piezoelectric crystal 18 can be made of lead zirconate titanate ceramic (PZT ceramic). The damping element 17 can be made of titanium sinter, which preferably has an average pore size between 1 μm and 10 μm. The spacer 19 can be made of steel (especially austenitic steel) with a thickness between 2 mm and 10 mm in the transmission direction S. The actuation electrode 20 can be formed so that it includes copper, especially made of copper. The heat transfer tube 3 is generally made of steel (especially austenitic steel). The ultrasonic sensor 2 is preferably implemented to emit an ultrasonic signal, especially an ultrasonic wave, having a center frequency of about 15 MHz.

[0075] Figure 3 A schematic diagram of another heat exchanger 1 implemented as a stripper for stripping is shown. Typically, this type of heat exchanger 1 is used for urea synthesis. The heat exchanger 1 can be configured according to the invention. Figure 1 The heat exchanger 1 in the embodiment of the present invention may be implemented and may in particular include the following: Figure 2 and / or Figure 4Ultrasonic sensor 2 of the description. The heat exchanger 1 is usually oriented so that the longitudinal extension of the heat transfer tube 3 is oriented substantially vertically. For urea synthesis, a first fluid F1 is provided that is formed so that it includes a first medium M1 and a second medium M2 or is made of a first medium M1 and a second medium M2, wherein inside the fluid chamber 4 or the fluid chamber cavity 5, the first medium M1 and the second medium M2 flow through the corresponding heat transfer tube 3 in opposite flow directions. Usually, the first medium M1 is formed so that it includes the following components, in particular is made of the following components: urea, ammonium carbamate and ammonia, and the second medium M1 is formed so that it includes gaseous carbon dioxide (CO2), in particular is made of gaseous CO2. The first medium is usually a liquid. The heat exchanger 1 or stripper usually includes a plurality of, in particular more than 10, preferably more than 50, particularly preferably more than 100, particularly preferably more than 1000 heat transfer tubes 3. The heat exchanger 1 is usually oriented so that the first tube sheet 14 is arranged vertically above the second tube sheet 15. Preferably, the respective ultrasonic sensor 2 is arranged between the first tube sheet 14 and a first one of the stabilization elements 16 .

[0076] The heat exchanger 1 comprises a first inlet 25 through which a first medium M1 can be fed into the heat transfer tube 3 and a second inlet 27 through which a second medium M2 can be fed into the heat transfer tube 3, so that inside the fluid chamber 4 or the fluid chamber cavity 5, the media M1, M2 flow through the heat transfer tube 3 in opposite flow directions so as to react with each other. With respect to the fluid chamber cavity 5, the first inlet 25 and the second inlet 27 are connected to the heat transfer tube 3 in a fluid-conducting manner at different ends of the heat transfer tube 3. For this purpose, the first inlet 25 and the second inlet 27 can be connected to a fluid distribution chamber in a fluid-conducting manner, respectively, wherein the ends of the heat transfer tube 3 are connected to the fluid distribution chamber in a fluid-conducting manner, respectively, so that the first medium M1 and the second medium M2 fed into the corresponding fluid distribution chamber via the first inlet 25 and the second inlet 27 are respectively conducted into the heat transfer tube 3 so that they are distributed to the heat transfer tube 3. The heat exchanger 1 comprises a first outlet 26 and a second outlet 28, through which the first product Z1 can be removed from the heat transfer tube 3, and through which the second product Z2 can be removed from the heat transfer tube 3, wherein the first outlet 26 and the second outlet 28 are connected to the heat transfer tube 3 in a fluid-conducting manner at different ends of the heat transfer tube 3 with respect to the fluid chamber cavity 5, preferably because the first outlet 26 and the second outlet 28 are respectively connected to one of the fluid distribution chambers in a fluid-conducting manner, so that the first product Z1 and the second product Z2 leaving the heat transfer tube 3 can be removed via the corresponding outlets 26 and 28. The first product Z1 is usually urea, in particular high-purity urea. The second product Z2 is usually gaseous ammonia (NH3) and / or gaseous carbon dioxide (CO2). The second fluid F2 is usually formed so that it includes liquid water and / or gaseous water, in particular made of liquid water and / or gaseous water.

[0077] exist Figure 4 In FIG. 1 , a schematic diagram of another ultrasonic sensor 2 is shown in a cross-sectional view. The ultrasonic sensor 2 may have Figure 2 The ultrasonic sensor 2 has the same features and effects as the ultrasonic sensor 2 in FIG. The ultrasonic sensor 2 can be used for Figure 1 and Figure 3 Heat exchanger 1 in. Figure 4 The structure of the ultrasonic sensor 2 in the embodiment basically corresponds to Figure 2 The ultrasonic sensor 2 in FIG. Specifically, the ultrasonic sensor 2 includes a spring element 21, with which the actuation electrode 20, the damping element 17, the piezoelectric crystal 18 and the spacer 19 are pressed against each other by the spring force of the spring element 21. The spring element 21 is arranged between the actuation electrode and a counter-bearing 31, which can be formed by a ring nut. In order to generate an electrical connection between the signal line 8 and the actuation electrode 20, the line and the electrode are connected to each other in a force-fitting manner using a clamping element 30. Figure 2 In contrast to the ultrasonic sensor 2 in the embodiment of the present invention, the ultrasonic sensor 2 comprises a (particularly tubular) connection piece 29 for accommodating the protective tube 11 in a form-fitting manner, wherein the protective tube 11 is inserted into the connection piece 29 in a fluid-tight manner. In this way, a particularly robust connection of the signal line 8 to the ultrasonic sensor 2 can be achieved, for example for use at particularly high pressures in the fluid chamber cavity 5 or at particularly high pressures of the second fluid F2. The connections 29 can be formed so that they comprise steel (particularly austenitic steel) or are made of steel (particularly austenitic steel). Conveniently, Figure 2 The ultrasonic sensor in may also comprise a connection element 29 of this type.

[0078] If, on one or more of the heat transfer tubes 3 of the heat exchanger 1, an ultrasonic sensor 2 designed for an operating pressure of more than 30 bar, in particular between 30 bar and 200 bar, and / or an operating temperature of more than 80° C., in particular between 80° C. and 300° C., is arranged in each case, and wherein the ultrasonic sensor 2 is embodied to transmit measurement data to an electronic data acquisition unit 9 during operation of the heat exchanger 1, the tube thickness of the respective heat transfer tube 3 can be practically determined in situ and preferably in operation. This enables the usability of the heat exchanger 1 to be optimized. In particular, if a signal line 8 for transmitting the measurement signal from the respective ultrasonic sensor 2 to the electronic data acquisition unit 9 runs in a protective tube 11 inside the second fluid F2, and / or if the damping element 17, the piezoelectric crystal 18 and the spacer 19 are pressed against one another in the ultrasonic sensor 2 by means of the spring force of the spring element 21, a particularly high robustness of the in situ determination of the tube wall thickness and generally in operation can be achieved.

Claims

1. A heat exchanger (1), in particular a high-pressure heat exchanger for urea synthesis, the heat exchanger (1) comprising a plurality of heat transfer tubes (3) for conveying a first fluid (F1) so as to transfer heat between the first fluid (F1) and a second fluid (F2) via the heat transfer tubes (3), Features Ultrasonic sensors (2) are respectively arranged on one or more of the heat transfer tubes (3) for in-situ determination of the wall thickness of the heat transfer tubes (3), wherein the respective ultrasonic sensors (2) are designed for an operating pressure greater than 30 bar and / or an operating temperature greater than 80° C., wherein the respective ultrasonic sensors (2) are connected to an electronic data acquisition unit (9) for transmitting data, so that the measurement data are transmitted to the electronic data acquisition unit (9) during operation of the heat exchanger (1).

2. The heat exchanger (1) according to claim 1, Features The heat exchanger (1) comprises a fluid chamber (4) for accommodating the second fluid (F2), wherein the heat transfer tube (3) extends inside the fluid chamber (4), and wherein the data acquisition unit (9) is arranged outside the fluid chamber (4).

3. The heat exchanger (1) according to claim 1 or 2, Features The respective ultrasonic sensor (2) is connected to the data acquisition unit (9) via a signal line (8) for transmitting data, wherein the signal line (8) extends at least in sections inside a protective tube (11) preferably made of metal in order to protect the signal line.

4. Heat exchanger (1) according to claims 2 and 3, Features On one side, the protective tube (11) is welded to the sensor housing (22) of the corresponding ultrasonic sensor (2), and / or on the other side, the protective tube (11) is connected to a signal line guide hole (10), preferably by means of a wedge bolt connection, by means of which the signal line (8) is guided through the fluid chamber wall of the fluid chamber (4).

5. The heat exchanger (1) according to claim 3 or 4, Features The protective tube (11) forms a volume separated from the first fluid (F1) and the second fluid (F2) during operation, and the signal line extends inside the volume.

6. Heat exchanger (1) according to one of claims 1 to 5, Features The corresponding ultrasonic sensor (2) comprises a damping element (17), a piezoelectric crystal (18) and a spacer (19) which are pressed against one another by means of a spring element (21).

7. The heat exchanger (1) according to claim 6, Features The spring element (21) is formed using an arrangement of a plurality of springs, preferably connected in series.

8. The heat exchanger (1) according to claim 6 or 7, It is characterized in that In the corresponding ultrasonic sensor (2), the damping element (17) is arranged between the electrical actuation electrode and the piezoelectric crystal (18), wherein the damping element (17) is implemented to be conductive so that electrical actuation of the piezoelectric crystal (18) via the actuation electrode can be achieved through the damping element (17).

9. The heat exchanger (1) according to one of claims 1 to 8, Features The respective ultrasonic sensor (2) comprises one or more electrically insulating elements for electrical insulation, the one or more electrically insulating elements preferably being formed such that it / they comprise zirconium dioxide between a sensor housing (22) of the ultrasonic sensor (2) and, respectively, a piezoelectric crystal (18) and / or a damping element (17) and / or an electrode of the ultrasonic sensor.

10. The heat exchanger (1) according to one of claims 1 to 9, It is characterized in that Between the respective ultrasonic sensor (2) and the heat transfer tube (3), a coupling component formed such that it includes silver, in particular a silver film, is arranged, or no coupling component is arranged.

11. The heat exchanger (1) as claimed in one of claims 1 to 10, Features The respective ultrasonic sensor (2) is connected to the respective heat transfer tube (3) in a force-fitting manner, preferably using a clamping connection.

12. Heat exchanger (1) according to one of claims 1 to 11, Features A plurality of ultrasonic sensors (2) are connected to the same electronic data acquisition unit (9) for data transmission, so that during operation of the heat exchanger (1) measurement data are transmitted to the electronic data acquisition unit (9).

13. A method for operating a heat exchanger (1), in particular a heat exchanger (1) according to one of claims 1 to 12, It is characterized in that On one or more heat transfer tubes (3), ultrasonic sensors (2) are respectively arranged to have an operating pressure greater than 30 bar and / or an operating temperature greater than 80° C., a first fluid (F1) is transported using the one or more heat transfer tubes (3) so as to transfer heat between the first fluid (F1) and a second fluid (F2) via the heat transfer tubes (3), wherein the wall thickness of the respective heat transfer tube (3) is determined in situ using the respective ultrasonic sensor (2), wherein the measurement data from the respective ultrasonic sensor (2) is sent to an electronic data acquisition unit (9) during operation of the heat exchanger (1).

14. The method according to claim 13, Features The respective ultrasonic sensor (2) is operated at a frequency, in particular a center frequency, greater than 10 MHz, in particular between 10 MHz and 30 MHz.

15. The method according to claim 13 or 14, Features In order to temperature compensate the ultrasonic velocity of the ultrasonic signal, the thickness of a spacer (19) of at least one of the ultrasonic sensors (2) is used as a reference length and / or the temperature is detected using at least one thermocouple.

16. The method according to claim 13, Features The ultrasonic sensor (2) is used to transmit an ultrasonic signal into the corresponding heat transfer tube (3), in particular into its tube wall, and the ultrasonic signal reflected by the outer wall and the inner wall of the heat transfer tube (3) is received by the ultrasonic sensor (2) so as to determine the tube wall thickness of the heat transfer tube (3).

Images