A heat exchanger comprising an ultrasonic sensor for determining the wall thickness of the heat exchanger tubes of the heat exchanger, and a method for operating such a heat exchanger

Abstract

The present invention relates to a heat exchanger (1) comprising 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). To enhance the usefulness, 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), each ultrasonic sensor (2) being designed for an operating pressure exceeding 30 bar (3 MPa) and / or an operating temperature exceeding 80 °C, and each ultrasonic sensor (2) being connected to an electronic data acquisition unit (9) for data transmission in order to transmit measurement data to the electronic data acquisition unit (9) during operation of the heat exchanger (1). The present invention further relates to a method of operating the heat exchanger (1).

Description

Technical Field

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

[0002] The present invention further relates to a method of operating a heat exchanger.

[0003] It is known from the prior art to exchange thermal energy between a flow of a first fluid and a flow of a second fluid using a heat exchanger. The heat exchanger often comprises a plurality of heat transfer tubes, which transport a flow of a first fluid so as to transfer heat to a flow of a second fluid flowing around the heat transfer tubes via the heat transfer tubes or to absorb heat from the flow of the second fluid. As part of urea synthesis, heat exchangers are usually used in which the flow of the first or second fluid normally has a high pressure exceeding 30 bar (3 MPa) and a high temperature normally exceeding 80°C. Thereby, the transport of the flow of the first fluid through the heat transfer tubes is often associated with, respectively, peeling of the wall material of the heat transfer tubes due to corrosion and / or erosion, or the formation of deposits inside the heat transfer tubes, and thus the wall thickness of the heat transfer tubes changes, specifically decreases, during operation of the heat exchanger. The integrity of the tube walls of the heat transfer tubes being impaired can pose a problem in the safety of operation of the heat exchanger. Therefore, it is usually necessary to regularly stop the heat exchanger and measure the wall thickness of the heat transfer tubes based on maintenance intervals over time.

[0004] For this purpose, it is common to insert a measurement probe into each heat transfer tube in a non-operating state of the heat exchanger to determine the inner radius or wall thickness of the heat transfer tube. Measurement probes equipped with ultrasonic sensors, optical sensors, or eddy current sensors are known for determining the wall thickness.

[0005] In the case of a heat exchanger operating at a pressure exceeding 30 bar (3 MPa) and a high temperature exceeding 80 °C of the flow of the first and / or second fluid, in particular, an interruption of this type of operation for determining the wall thickness of the heat transfer tubes is usually laborious and associated with high costs.

[0006] This is addressed by the present invention. The object of the present invention is to define a heat exchanger of the type indicated at the beginning, having optimized usefulness, specifically optimized operation.

[0007] It is also an object of the present invention to define a method of operating a heat exchanger that enables optimized use or operation of the heat exchanger.

[0008] According to the present invention, in a heat exchanger of the type indicated at the beginning, for the in-situ determination of the wall thickness of the heat transfer tubes, one or more ultrasonic sensors are respectively arranged on one or more of the heat transfer tubes, each ultrasonic sensor being designed for an operating pressure exceeding 30 bar (3 MPa) and / or an operating temperature exceeding 80 °C, and each ultrasonic sensor being connected to an electronic data acquisition unit for the transmission of data in order to transmit measurement data to the electronic data acquisition unit during operation of the heat exchanger, whereby the object is achieved.

[0009] The basis of the present invention is the idea of improving the usefulness of a heat exchanger designed for a high operating pressure and / or a high operating temperature of the first and / or second fluid in that the wall thickness of the heat transfer tubes of the heat exchanger is determined in-situ, i.e., locally on the heat exchanger or the heat transfer tubes and usually during operation of the heat exchanger, i.e., the operand. As a result, the operation of the heat exchanger, specifically process management and / or maintenance, can be carried out according to the determined wall thickness. Specifically, there is no need to interrupt the operation of the heat exchanger to determine the wall thickness.

[0010] The operation of the heat exchanger shows a state in which the first fluid is guided into the heat transfer tubes to exchange heat with the second fluid via the heat transfer tubes. High operating pressure and high operating temperature respectively indicate an operating pressure higher than 30 bar (3 MPa) and an operating temperature higher than 80 °C for the first fluid and / or the second fluid. Specifically, the operating pressure is between 30 bar (3 MPa) and 200 bar (20 MPa), preferably about 180 bar (18 MPa), and / or the operating temperature is between 80 °C and 300 °C, preferably about 230 °C. Generally, the first and / or the second fluid has this type of operating pressure and this type of operating temperature during the operation of the heat exchanger, or the heat exchanger is designed for this type of operation. Accordingly, it is beneficial if each 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 beneficial if the heat exchanger is a stripper for performing stripping. It is beneficial if the stripper is used for urea synthesis. The stripper can generally be embodied to synthesize urea by stripping inside the heat transfer tubes.

[0012] Typically, each ultrasonic sensor is arranged on each heat transfer tube such that during operation of the heat exchanger, the ultrasonic sensor is positioned within one of the fluids, preferably the second fluid. It has been found to be effective if each ultrasonic sensor is arranged outside the heat transfer tube, usually within the second fluid, during operation of the heat exchanger. Ordinarily, 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 embodied for this type of operation. The ultrasonic sensor is usually arranged on the tube wall of each heat transfer tube to determine the tube wall thickness by radiating an ultrasonic signal onto the tube wall. Ordinarily, an ultrasonic sensor can be used to radiate an ultrasonic signal and detect the reflected ultrasonic signal. The heat exchanger typically comprises one, preferably a plurality, of ultrasonic sensors of this type. Usually, the heat exchanger or the ultrasonic sensor is embodied to determine the tube wall thickness of each heat transfer tube in-situ and operando, or the tube wall thickness of each heat transfer tube is determined in-situ and operando using an ultrasonic sensor.

[0013] It is advantageous if each ultrasonic sensor is connected to an electronic data acquisition unit for data transmission. As a result, measurement data can be transmitted from the ultrasonic sensor to the data acquisition unit during operation of the heat exchanger. For data transmission, the ultrasonic sensor and the data acquisition unit are usually connected, specifically electrically, to a signal line. Preferably, the signal line is embodied for symmetric signal transmission. The signal line is usually embodied in the form of a cable. The signal line is preferably a coaxial cable. A plurality of electronic data acquisition units may be provided, and different ultrasonic sensors may be connected to different electronic data acquisition units for data transmission. A plurality of ultrasonic sensors may be connected to the same electronic data acquisition unit for data transmission. It may be provided that each ultrasonic sensor is controlled using the electronic data acquisition unit to which the ultrasonic sensor is connected for data transmission.

[0014] The heat transfer tube is typically embodied to direct a first fluid so as to transfer heat between the first fluid and a second fluid through the wall of the heat transfer tube. During operation of the heat exchanger, it is preferably provided that the second fluid is in contact with the heat transfer tube or the tube wall, specifically directly. The first fluid is typically the flow of the first fluid directed to the heat transfer tube during operation of the heat exchanger. During operation of the heat exchanger, the second fluid can typically be the flow of the second fluid flowing around the heat transfer tube. The second fluid typically has a pressure exceeding 30 bar (3 MPa), specifically between 30 bar (3 MPa) and 200 bar (20 MPa), preferably about 180 bar (18 MPa), and / or a temperature exceeding 80 °C, specifically 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 typically has a fluid chamber for containing the second fluid, and the heat transfer tube runs inside the fluid chamber. The fluid chamber typically forms the fluid chamber cavity between the fluid chamber wall of the fluid chamber and the heat transfer tube to contain the second fluid using the fluid chamber cavity for transferring heat between the first fluid and the second fluid. The heat transfer tube typically runs through the fluid chamber cavity. During operation of the heat exchanger, it is typically provided that the second fluid is directed into the fluid chamber cavity, specifically such that the second fluid flows around the heat transfer tube. Advantageously, the fluid chamber cavity can be embodied in the form of one or more channels for directing the second fluid using channels during operation of the heat exchanger. The fluid chamber typically has at least one fluid chamber inlet for directing the second fluid into the fluid chamber, specifically the fluid chamber cavity, through the fluid chamber inlet, and typically at least one fluid chamber outlet for removing the second fluid from the fluid chamber, specifically the fluid chamber cavity, through the fluid chamber outlet after heat transfer has occurred between the first fluid and the second fluid. The fluid chamber is typically formed such that it is made of, specifically made of, metal, preferably an iron alloy, particularly preferably a steel alloy, such as austenitic steel.

[0016] The ordinary heat transfer tubes are at least partially spaced apart from each other, and thus, during operation of the heat exchanger, the second fluid can flow through the space between the heat transfer tubes to transfer heat with the heat transfer tubes. This is particularly applicable inside the fluid chamber or the cavity of the fluid chamber.

[0017] Typically, the first fluid and the second fluid are embodied to be a liquid and / or a gas. For example, the first fluid and the second fluid can be formed such that they contain liquid and gaseous water, specifically such that they are made of them. The first fluid and the second fluid are embodied such that they contain a liquid medium and a gas medium, specifically such that they are made of them, and during operation of the heat exchanger, the liquid medium and the gas medium of each fluid can be provided to flow through the heat exchanger in opposite directions, usually such that they contact each other. For example, the first fluid can be formed such that it contains a liquid medium and a gas medium, and during operation of the heat exchanger, in each heat transfer tube, the media flow through the heat transfer tube in opposite directions, specifically such that they contact each other.

[0018] The heat transfer tubes typically extend between a first tube plate and a second tube plate, which define the boundaries of fluid chamber cavities for containing a second fluid, and the heat transfer tubes terminate at or are guided through passage openings in each tube plate. Typically, the fluid fed through the passage opening of one of the plates is induced through the heat transfer tube to the passage opening of the other plate. The heat transfer tubes are typically connected to the tube plates in a liquid-tight manner. Typically, each tube plate is embodied in a plate-like shape with a plurality of flow channels, specifically oriented transversely, in particular orthogonally, to the longitudinal extension of the tube plate, and the flow channels form each passage opening. The tube plate may be embodied as part of the fluid chamber wall of the fluid chamber. The heat exchanger typically comprises at least one first tube plate and at least one second tube plate of this type. The tube plates are typically formed such that they are made of, specifically, metal, preferably an iron alloy, particularly preferably a steel alloy, such as austenitic steel.

[0019] The fluid chamber may have one or more fluid guiding surfaces for defining a flow path of a second fluid using the fluid guiding surface. Each fluid guiding surface is typically embodied to at least partially obstruct the flow of the fluid of the second fluid between the heat transfer tubes. The fluid guiding surface can 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 run through each guiding surface. Usually, a plurality of guiding surfaces that intersect the heat transfer tubes and are spaced apart from each other are provided. Each fluid guiding surface is typically oriented transversely, specifically orthogonally, to the longitudinal extension of the heat transfer tubes. Usually, a plurality of fluid guiding surfaces spaced apart from each other in the longitudinal direction of the heat transfer tubes are provided. Typically, the intermediate space between the plurality of heat transfer tubes is substantially closed by each fluid guiding surface to obstruct the flow of the second fluid through the intermediate space. Each fluid guiding surface may be embodied to close most of the intermediate space between the heat treatment tubes against the flow of the second fluid in a cross-section through the fluid chamber. The fluid guiding surface may be formed using a guiding wall disposed in the fluid chamber. The fluid guiding surface is typically embodied to be plate-shaped. The fluid chamber typically comprises one or more guiding surfaces of this type.

[0020] Typically, a plurality of heat transfer tubes are connected to each other by stabilizing elements to stabilize the heat transfer tubes during operation of the heat exchanger. Each stabilizing element may be embodied to be plate-shaped, and the longitudinal extension of the stabilizing element is typically oriented transversely, specifically orthogonally, to the longitudinal extension of the heat transfer tubes connected by the stabilizing element. Typically, the heat transfer tubes run through the stabilizing elements. The stabilizing elements are conventionally called baffles. Usually, a plurality of stabilizing elements spaced apart from each other and connecting the heat transfer tubes to each other are provided along the longitudinal extension of the heat transfer tubes. Specifically, the fluid guiding surface may be formed by the stabilizing elements. In this case, the stabilizing elements can function to stabilize the heat transfer tubes and define a flow path for the second fluid.

[0021] Each ultrasonic sensor is arranged in the arrangement area of each heat transfer tube. Specifically, in the flow direction of the first fluid passing through the heat transfer tube, it is beneficial if the arrangement area is defined by the first one-third of the longitudinal extension of the heat transfer tube inside the fluid chamber or the fluid chamber cavity. Specifically, in the flow direction of the first fluid, the arrangement area of each heat transfer tube usually extends along the longitudinal extension of the heat transfer tube for 30%, particularly 20%, preferably 10% of the length of the longitudinal extension of the heat transfer tube inside the fluid chamber or the fluid chamber cavity starting from where the heat transfer tube enters the fluid chamber. Generally, in this arrangement area of each heat transfer tube, it has been shown that material peeling or wear of the heat transfer tube is particularly large. For this reason, it is beneficial to position the ultrasonic sensor in the above area.

[0022] It is advantageous if the electronic data acquisition unit is arranged outside the fluid chamber, specifically outside the fluid chamber cavity. As a result, the electronic data acquisition unit is protected from the loads of the first and second fluids, specifically the pressure load and / or the temperature load. The data acquisition unit usually includes a microcontroller or may be embodied as a computer. The electronic data acquisition unit is usually embodied to receive measurement data from one or more of the ultrasonic sensors via one or more hardware interfaces in most cases. The electronic data acquisition unit can be embodied to process, collect, and / or transmit the measurement data. For example, the measurement data may be transmitted from the electronic data acquisition unit to the electronic central data unit, and the electronic central data unit may be embodied to output the data in a processed manner and / or display the data to the user. Usually, the heat exchanger includes one or more electronic data acquisition units.

[0023] Each ultrasonic sensor is connected to a data acquisition unit for data transmission via a signal line. The signal line is, at least in part, preferably inside a protective tube made of metal, specifically to protect the signal line from the load by the first or second fluid. It has been found to be effective if it runs specifically inside the fluid chamber. It is advantageous if the protective tube forms a volume separated from the first fluid and the second fluid, and the signal line runs specifically through this volume inside the 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 runs inside the protective tube within the fluid chamber. The protective tube usually extends from each ultrasonic sensor to the fluid chamber wall of the fluid chamber, specifically the fluid chamber cavity. During operation of the heat exchanger, it is advantageous if the protective tube is connected to the sensor housing of each ultrasonic sensor so as to preferably define a volume separated from the first fluid and the second fluid together with the sensor housing, or a volume separated from the fluid chamber cavity, and the signal line runs inside the said volume. Usually, the protective tube is liquid-tightly connected to each ultrasonic sensor, specifically its sensor housing. The protective tube can be liquid-tightly connected to the fluid chamber wall of the fluid chamber, specifically the fluid chamber cavity, or guided through the fluid chamber wall. The fluid chamber may be provided with a signal line penetration portion, and the signal line is guided through the fluid chamber wall of the fluid chamber using this, specifically guided to exit the fluid chamber. Conveniently, the protective tube can be liquid-tightly connected to the fluid chamber wall via the signal line penetration portion. Usually, essentially the entire length of the signal line extends inside the protective tube between the ultrasonic sensor and the fluid chamber wall or the signal line penetration portion.

[0024] The protective tube can be connected, usually in a liquid-tight manner, to the ultrasonic sensor, specifically its sensor housing, by means of force fitting, shape fitting, and / or material joining methods. The protective tube can be connected, usually in a liquid-tight manner, to the signal line through-hole or the fluid chamber wall by means of force fitting, shape fitting, and / or material joining methods. On one side, the protective tube is connected, specifically by welding, to each ultrasonic sensor, specifically its sensor housing, in a material joining method, and / or on the other side, the protective tube is preferably connected, preferably by force fitting and / or material joining methods, to the signal line through-hole through which the signal line is guided into the fluid chamber using a wedge / bolt connection. Welded connection enables a space-saving connection that can withstand loads in the ultrasonic sensor. In the fluid chamber wall or the signal line through-hole, the space requirements for connecting the protective tube are usually not very relevant, and for this reason, the wedge / bolt connection becomes practical. However, alternatively, the protective tube may be connected to the fluid chamber wall or the signal line through-hole by a material joining method, specifically by welding. The heat exchanger preferably comprises one or more protective tubes of this type. Specifically, a plurality of protective tubes connected to various ultrasonic sensors may be connected to each other so that they form a shared volume to guide each signal line through the shared volume.

[0025] The protective tube is usually formed such that it contains metal, specifically such that it is made thereof. Preferably, the protective tube is formed such that it contains an iron alloy, preferably a steel alloy, preferably an austenitic steel, specifically such that it is made thereof. In this way, preferably, an atmosphere different from that inside the fluid chamber, specifically the elemental composition of the atmosphere, can be created inside the protective tube or inside the ultrasonic sensor. The atmosphere inside the protective tube or inside the ultrasonic sensor, specifically the elemental composition of the atmosphere, can essentially correspond to the atmosphere surrounding the heat exchanger.

[0026] Each ultrasonic sensor is embodied to typically emit an ultrasonic signal and typically receive an ultrasonic signal reflected from one or more interfaces. The ultrasonic signal is typically ultrasonic. The distance between the interfaces can be determined from the time interval between the emitted and received ultrasonic signals, specifically from a comparison. Advantageously, to determine the wall thickness of the heat transfer tube, an ultrasonic sensor can be used to emit an ultrasonic signal to each heat transfer tube, specifically to its tube wall, and the ultrasonic signal reflected from the interfaces, specifically the outer and inner walls of the heat transfer tube, can be received using the ultrasonic sensor. Each ultrasonic sensor typically comprises a piezoelectric crystal for emitting an ultrasonic signal and receiving the reflected ultrasonic signal. The piezoelectric crystal is typically embodied as part of a piezoelectric element. The operation of the piezoelectric crystal or piezoelectric element typically occurs via a signal line. It is beneficial if the piezoelectric crystal is formed such that it contains lead zirconate titanate ceramic (PZT ceramic), specifically such that it is made therefrom. The piezoelectric crystal is embodied to be plate-shaped and can have a thickness that is less than 3 mm, specifically less than 1 mm, preferably less than 0.5 mm, particularly preferably between 0.1 mm and 0.15 mm, in the direction of emission of the ultrasonic signal. The thickness is typically greater than 0.05 mm. The ultrasonic sensor is typically arranged on the heat transfer tube such that the direction of emission of the ultrasonic signal is transverse to, specifically essentially orthogonal to, the longitudinal extension of the heat transfer tube.

[0027] Generally, each ultrasonic sensor is embodied such that, in order to determine the wall thickness of the heat transfer tube, an ultrasonic signal can be emitted to each heat transfer tube, specifically to its tube wall, using the ultrasonic sensor, and the ultrasonic signal reflected from the outer wall and the inner wall of the heat transfer tube, specifically its tube wall, can be received using the ultrasonic sensor. Specifically, it is arranged on each heat transfer tube, specifically its tube wall. In order to determine the wall thickness of the heat transfer tube, the distance between the inner wall and the outer wall of the heat transfer tube, specifically its tube wall, can be confirmed from the time interval between the emitted and received ultrasonic signals, specifically from the comparison. The ultrasonic sensor is usually arranged on the heat transfer tube such that an ultrasonic signal is emitted to the heat transfer tube, specifically its tube wall, in a direction transverse to the longitudinal axis of the heat transfer tube, specifically in a direction essentially orthogonal thereto, using the ultrasonic sensor. Thus, advantageously, the ultrasonic signal can strike the outer wall and the inner wall in a direction transverse to, specifically essentially orthogonal to, the outer wall and the inner wall of the heat transfer tube, specifically its tube wall, and can be reflected, at least in part, from the above-mentioned wall.

[0028] Generally, the inner wall is the inner surface of the tube wall of the heat transfer tube, and the outer wall is the outer surface. Usually, 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. This is particularly true in the cross-section of the heat transfer tube in a direction orthogonal to the longitudinal axis of the heat transfer tube.

[0029] For high precision, it has been found to be effective if, in each ultrasonic sensor, the emission and reception of ultrasonic signals occur using the same piezoelectric crystal. Usually, the control of the ultrasonic sensor or the piezoelectric crystal switches between a transmission mode in which an ultrasonic signal is emitted 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 usually a dead time during which the reflected ultrasonic signal cannot be detected. Alternatively, the ultrasonic sensor may be provided with a plurality of piezoelectric crystals, and one of the piezoelectric crystals may be embodied to emit an ultrasonic signal and another of the piezoelectric crystals may be embodied to receive an ultrasonic signal. However, it is preferable if the emission and reception of the ultrasonic signal are performed using the same piezoelectric crystal.

[0030] Usually, each ultrasonic sensor includes an attenuation element, a piezoelectric crystal, and a standoff body. The attenuation element is typically coupled to the piezoelectric crystal and is embodied to attenuate the mechanical vibrations of the piezoelectric crystal. The piezoelectric crystal is often supported by the attenuation element. The standoff body is typically positioned downstream of the piezoelectric crystal in the direction of emission of the ultrasonic signal towards the heat transfer tube to prevent the ultrasonic signal emitted using the piezoelectric crystal from being reflected from the wall of the heat transfer tube during the dead time. The standoff body is typically formed from a material that is suitably ultrasonic conductive.

[0031] In each ultrasonic sensor, it is beneficial if the damping element, the piezoelectric crystal, and the standoff body are pressed against each other using a spring element. In this way, even at high operating pressures and / or high operating temperatures, a robust, specifically durable connection can be ensured. Thereby, preferably, the joining of the damping element, the piezoelectric crystal, and the standoff to each other can be omitted, and such joining is prone to loading. Thereby, the pressing against each other is usually associated with the elastic deformation of the spring element against the spring force of the spring element. The spring element is advantageously formed by a spring or preferably an arrangement of a plurality of springs connected to each other in series. The spring is preferably a disc spring. The spring element is preferably arranged upstream of the damping element in the radial direction.

[0032] The radial direction usually indicates the direction in which each ultrasonic sensor is embodied to emit ultrasonic signals specifically towards the heat transfer tube.

[0033] The damping element is advantageously embodied such that it comprises a porous titanium body, specifically such that it is made thereof, and the porous titanium body is formed such that it comprises sintered titanium. Usually, the titanium body has an average pore diameter smaller than 100 μm, specifically smaller than 50 μm, preferably between 1 μm and 10 μm, particularly preferably about 5 μm. Therefore, it is possible to generate a robust ultrasonic signal. The damping element usually has a thickness between 1 mm and 5 mm, preferably about 3 mm, in the radial direction.

[0034] The standoff body can be formed such that it comprises acrylic glass or metal, specifically iron, preferably steel, and is specifically made therefrom. For a robust ultrasonic signal, it is particularly beneficial if the standoff body is formed such that it comprises austenitic steel and is specifically made therefrom. Thereby, specifically, if the standoff body is formed such that it comprises steel or is made therefrom, preferably, the surface of the standoff body is embodied in a polished manner. Usually, the standoff body has a thickness that is less than 30 mm in the radial direction, specifically between 2 mm and 10 mm, preferably about 5 mm.

[0035] In each ultrasonic sensor, an attenuation element is arranged between the electrically actuating electrode and the piezoelectric crystal, and the attenuation element is embodied to be electrically conductive, and thus it is advantageous if the electrical actuation of the piezoelectric crystal can be realized through the attenuation element and via the actuating electrode. The electrically actuating electrode can be pressed against the attenuation element using the aforementioned spring element. It should be understood that usually two electrodes are present to electrically activate the piezoelectric crystal for the emission and reception of ultrasonic signals, specifically to apply a voltage to or reduce the voltage of the said crystal via the electrodes. The electrodes are usually electrically connected to the piezoelectric crystal on both sides of the piezoelectric crystal.

[0036] One of the electrodes can be the actuating electrode and can be specifically electrically connected to the piezoelectric crystal via the attenuation element in the aforementioned manner. The other electrode can usually be directly electrically connected to the piezoelectric crystal on the side of the piezoelectric crystal that is positioned downstream in the radial direction. Alternatively or cumulatively, for forming the piezoelectric element, two piezoelectrodes are usually provided on the surface of the piezoelectric crystal such that they are positioned opposite to each other on the piezoelectric crystal, and it is beneficial if the piezoelectric crystal can be actuated via the piezoelectrodes to promote vibration. The piezoelectrodes are usually made of metal, preferably silver. Advantageously, the aforementioned actuating electrode can be additionally provided.

[0037] Each ultrasonic sensor typically includes a sensor housing that forms the exterior of the ultrasonic sensor. Generally, a damping element, a piezoelectric crystal, usually an essentially stand-off body, and / or usually electrodes, specifically the operating electrodes if necessary, are disposed inside the sensor housing. The sensor housing typically has an outlet opening through which ultrasonic signals generated using the piezoelectric crystal can exit for measurements using the ultrasonic sensor. The outlet opening is often closed in a liquid-tight manner, usually using the stand-off body.

[0038] 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 each of one, in particular a plurality of, electrodes of the ultrasonic sensor, it has been found to be effective if each ultrasonic sensor includes one or more electrical insulation elements. The electrical insulation elements are preferably formed such that they contain zirconium dioxide, specifically are made therefrom. The electrical insulation elements can completely surround these components. Thus, the risk of electrical short circuits can be minimized even under high loads, specifically pressure loads and / or temperature loads.

[0039] It is advantageous if coupling means are arranged between each ultrasonic sensor and the heat transfer tube, formed such that it contains silver, specifically a silver film, or if no coupling means are arranged. This is particularly applicable during operation of the heat exchanger. Generally, the purpose of the coupling means is to enable a coupling that reduces the reflection of ultrasonic signals to the heat transfer tube. It has been shown that a high-quality, durable joint can be obtained when silver is used as the coupling means or when no coupling means are used, at the aforementioned high pressures and / or the aforementioned high temperatures. The coupling means are preferably embodied to be layered. The coupling means often have a thickness between 0.01 mm and 1 mm, specifically about 0.05 mm. The thickness is usually measured in the radial direction.

[0040] Each ultrasonic sensor can be connected to each heat transfer tube by a force fit, a shape fit, or a material joining method. Conveniently, a holding device can be provided for this purpose. It is preferable if each ultrasonic sensor is connected to each heat transfer tube by a force fit method using a clamp connection. In this way, with respect to the measurement of the wall thickness of the tube, a robust connection between the ultrasonic sensor and the heat transfer tube is enabled to allow for a low-noise coupling of the ultrasonic signal to the heat transfer tube without significantly damaging the measurement object thereby. It is beneficial if the holding device comprises a spring component and the ultrasonic sensor is pressed against the tube wall of the heat transfer tube using a spring force load using the spring component. As a result, a strong pressing contact can be ensured, specifically even under variable pressure and / or temperature loads. The spring component may be formed such that it comprises one or more disc springs. Conveniently, a plurality of ultrasonic sensors may be connected to each heat transfer tube respectively using separate holding devices, specifically as described. However, it may also be provided that a plurality of ultrasonic sensors are connected to each heat transfer tube using a shared holding device. Although less preferable, alternatively, each ultrasonic sensor may be connected to the heat transfer tube by a material joining method or, in simple cases, by a shape fit method.

[0041] It is advantageous if a plurality of ultrasonic sensors are connected to the same electronic data acquisition unit for data transmission so as to transmit measurement data to the electronic data acquisition unit during operation of the heat exchanger. In this way, a compact configuration with preferably short signal lines can be achieved. Usually, the electronic data acquisition unit comprises a plurality of hardware interfaces to which the signal lines connected to the ultrasonic sensors for data transmission are connected. One hardware interface can be assigned to each of the signal lines, respectively. Each ultrasonic sensor may be connected to the electronic data acquisition unit for data transmission by a single signal line. Alternatively, a plurality of signal lines connected to the ultrasonic sensors may form a shared data bus and the measurement data may be transmitted to the electronic data acquisition unit via it. It is beneficial if there are a plurality of electronic data acquisition units and different groups of the ultrasonic sensors among the electronic ultrasonic sensors are connected to different electronic data acquisition units for data transmission. This is particularly beneficial for keeping the length of the signal lines short.

[0042] For the transmission of data, a plurality of electronic data acquisition units are connected to an electronic central data unit, and the electronic central data unit is embodied to collect the measurement data of the electronic data acquisition units, and / or process the above data, and / or make the above data available for reading by the user. Thereby, the measurement data may already be preprocessed by the electronic data acquisition units and may, for example, be further processed by the electronic central data unit. Specifically, the electronic data acquisition unit and / or the electronic central data unit may be embodied to determine the wall thickness of the heat transfer tube, specifically its tube wall, measured using each ultrasonic sensor, from the measurement data. For the transmission of data, the electronic data acquisition unit may be connected to the electronic central data unit, specifically via a data transmission line in the form of a data bus. In this way, a compact design with a low likelihood of interference in the measurement data as a result of high pressure and / or high temperature conditions in the heat exchanger, specifically, can be achieved. The electronic central data unit usually comprises a microcontroller or may be embodied as a computer. Preferably, the heat exchanger comprises one or more electronic central data units.

[0043] The heat exchanger is typically designed for an operating pressure higher than 30 bar (3 MPa), specifically between 30 bar (3 MPa) and 200 bar (20 MPa), preferably about 180 bar (18 MPa), and / or an operating temperature higher than 80 °C, specifically between 80 °C and 300 °C, preferably about 230 °C, or is operated accordingly. Correspondingly, it is beneficial if each 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 typically refer to the first fluid and / or the second fluid. Preferably, during operation of the heat exchanger, the second fluid has this type of operating pressure and / or this type of operating temperature. Usually, each ultrasonic sensor is positioned inside the second fluid during operation of the heat exchanger. Correspondingly, it is beneficial if each 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 temperature.

[0044] Each ultrasonic sensor is typically arranged on the tube wall of each heat transfer tube, specifically such that it contacts the tube wall. Usually, one ultrasonic sensor is arranged on each of a plurality of heat transfer tubes of the heat exchanger. A plurality of ultrasonic sensors may be arranged on each of a plurality of heat transfer tubes. The heat transfer tubes are typically formed such that they contain metal, specifically an iron alloy, preferably a steel alloy, and are specifically made of them.

[0045] Usually, the electronic data acquisition unit is arranged outside the first fluid and the second fluid, or outside the heat transfer space of the heat exchanger, where heat is transferred between the first fluid and the second fluid through the heat transfer tubes during operation of the heat exchanger. The heat transfer space may be a fluid chamber or may surround a fluid chamber.

[0046] Thus, it would be beneficial if, during operation of the heat exchanger, the wall thickness of the heat transfer tubes could be determined with an accuracy smaller than 0.1 mm, specifically between 0.003 mm and 0.1 mm, usually 0.05 mm. This can be achieved using the heat exchanger according to this document.

[0047] Another object is one or more heat transfer tubes of a heat exchanger, on which one or more ultrasonic sensors having an operating pressure exceeding 30 bar (3 MPa) and / or an operating temperature exceeding 80 °C are respectively arranged for transporting the first fluid for transferring heat between the first fluid and the second fluid through the heat transfer tubes. The wall thickness of each heat transfer tube is determined in-situ using each ultrasonic sensor, and when measurement data from each ultrasonic sensor is transmitted to an electronic data acquisition unit during operation of the heat exchanger, it is achieved by a method of operating a heat exchanger of the type shown at the beginning. The method can be specifically implemented using the aforementioned heat exchanger. Usually, the wall thickness of the heat transfer tube indicates the distance, specifically in the radial direction, between the inner surface and the outer surface of the tube wall of the heat transfer tube in the cross-section of the heat transfer tube. Usually, the second fluid is positioned outside the heat transfer tube, and thus, heat is transferred between the first fluid and the second fluid through the tube wall of the heat transfer tube.

[0048] It should be understood that the method of operating the heat exchanger can be embodied within the scope of the heat exchanger in accordance with the features and effects specifically described hereinabove. The same also applies to the heat exchanger with respect to the method.

[0049] A method of operating a heat exchanger is particularly beneficial if used in urea synthesis. The heat exchanger may specifically be embodied as a stripper for stripping, in particular for urea synthesis, and it is provided that a liquid phase and a gas phase, usually having opposite flow directions to each other, are normally brought into contact with each other inside the heat transfer tubes. To react with each other, a first medium flows through each heat transfer tube in a certain flow direction, and a second medium flows through the heat transfer tubes in a direction opposite to the said flow direction, and it is beneficial if one of the media is usually a liquid and the other medium is a gas. This is usually carried out inside a fluid chamber or a fluid chamber cavity. The first fluid may be formed such that it contains or is created from the first medium and the second medium. Specifically, if the heat exchanger is a stripper, it is beneficial if the heat transfer tubes and the flow direction of the first fluid through the heat transfer tubes are essentially vertically directed. The heat exchanger or stripper usually comprises a plurality of heat transfer tubes, specifically more than 10, preferably more than 50, particularly preferably more than 100, and especially preferably more than 1000.

[0050] Typically, a heat exchanger, specifically when the heat exchanger is a stripper, comprises a first inlet through which a first medium can be fed to a heat transfer tube, and a second inlet through which a second medium can be fed to the heat transfer tube. Thus, inside a fluid chamber or a fluid chamber cavity, the media flow through the heat transfer tube in opposite flow directions relative to each other so as 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 such that they are connected to the heat transfer tube in a manner that guides the fluid. The heat exchanger typically comprises at least one outlet for removing the product formed by the reaction between the first medium and the second medium from the heat transfer tube. Practically, the heat exchanger may comprise a first outlet through which a first product can be removed from the heat transfer tube, and a second outlet through which a second product can be removed from the heat transfer tube. With respect to the fluid chamber cavity, the outlets are connected to the heat transfer tube at different ends of the heat transfer tube in a manner that guides the fluid. The first product and the second product are typically formed using or as a result of the reaction between the first medium and the second medium. This is particularly applicable when the heat exchanger is embodied as a stripper.

[0051] In urea synthesis, the first medium is typically formed such that it contains urea, ammonium carbamate, and ammonia, specifically such that it is made of them, and the second medium is formed such that it contains gaseous carbon dioxide (CO2), specifically such that it is made of it. Thus, as a product, specifically as a first product, specifically high-purity urea can be separated, and the urea is typically induced out of the heat transfer tube at one of the ends of the heat transfer tube or via the first outlet. Advantageously, the formed process gas, typically gaseous ammonia (NH3) and / or gaseous carbon dioxide (CO2), can be induced out of the heat transfer tube at another end of the heat transfer tube or via the second outlet. The second fluid can be formed such that it contains liquid and / or gaseous water, specifically such that it is made of it. The stripper can be embodied and operated as described in this document specifically with respect to the heat exchanger.

[0052] If each ultrasonic sensor operates at a frequency exceeding 10 MHz, specifically between 10 MHz and 30 MHz, specifically at the center frequency, then, specifically for determining the wall thickness, it is beneficial if ultrasonic signals having corresponding frequencies are emitted from each ultrasonic sensor. The frequency, specifically the center frequency, is preferably about 15 MHz.

[0053] For temperature compensation of the ultrasonic velocity of the ultrasonic signal, it is advantageous if the thickness of the stand-off body of at least one of the ultrasonic sensors is used as a reference length and / or if at least one thermocouple is used to confirm the temperature. Since the stand-off body has a known thickness, the change in the speed of sound of the ultrasonic signal can be considered, specifically determined, by using ultrasonic measurements, specifically by confirming the thickness of the stand-off body using the measurement signals of each ultrasonic sensor. The thickness is usually measured in the radial direction. Conveniently, the temperature compensation can be carried out during each measurement procedure using each ultrasonic sensor. Thus, high-precision measurements can be obtained. The temperature compensation can be considered while determining, specifically calculating, the wall thickness from the measurement data confirmed using the ultrasonic sensors.

[0054] Conveniently, the heat exchanger may comprise one or more, specifically the aforementioned thermocouples, and the thermocouples are embodied to measure the temperature in the region of the ultrasonic sensors. For example, each thermocouple may be arranged in one of the heat transfer tubes, specifically therein, or in the ultrasonic sensor within the fluid chamber. It is beneficial if each thermocouple is connected to the data acquisition unit for data transmission. This can be realized via a data cable. The data acquisition unit may comprise one or more hardware interfaces for connecting the data cables respectively. Conveniently, each data cable can run inside the protective tube, specifically as embodied in the aforementioned. The protective tube can thereby guide to each thermocouple. The data cable and the signal line may run inside a shared protective tube.

[0055] To determine the wall thickness of the heat transfer tubes, if ultrasonic sensors are used to radiate ultrasonic signals to each heat transfer tube, specifically to its tube wall, and the ultrasonic signals reflected from the outer wall and inner wall of the heat transfer tube are received using the ultrasonic sensors, high application practicality can be obtained. The ultrasonic signals are usually radiated using the ultrasonic sensors such that the ultrasonic signals hit the outer wall and inner wall in a lateral direction, specifically in a direction essentially orthogonal to the outer wall and inner wall, and are specifically reflected from the above walls.

[0056] The determination of the wall thickness using each ultrasonic sensor is generally performed using the time-of-flight method. The ultrasonic signals are usually radiated using each ultrasonic sensor, and then the reflected ultrasonic signals are detected using the ultrasonic sensors. The reflected ultrasonic signals are generally formed by the radiated ultrasonic signals being reflected from the interface. The interface may be, for example, the outer surface and / or inner surface of the tube wall of the heat transfer tube. By checking the time interval between the radiated ultrasonic signal and the reflected ultrasonic signal, and / or between multiple reflected ultrasonic signals from each other, the thickness of the tube wall from which the ultrasonic signal is induced can be confirmed. The ultrasonic signals are usually ultrasonic pulses. Usually, an ultrasonic signal reflected from the end of the standoff body or from the outer surface of the tube wall, an ultrasonic signal reflected from the inner surface of the tube wall, and a series of reflected ultrasonic pulses corresponding to multiple reflections between the inner surface and outer surface of the tube wall are generally detected. The time interval between the detected reflected ultrasonic pulses of the multiple reflections generally corresponds to twice the wall thickness. To determine each wall thickness using a time-dependent comparison of time markers, the radiation time of the ultrasonic signal, the ultrasonic signal reflected from the outer surface of the tube wall, and / or one or more ultrasonic signals reflected from the inner surface of the tube wall can be used as the time markers. By considering the speed of sound or propagation speed of the ultrasonic signal, the wall thickness can be determined.

[0057] Additional features, advantages, and effects of the present invention will be understood from the following description of the exemplary embodiments. In the drawings referred to thereby:

Brief Description of the Drawings

[0058]

Figure 1

Figure 2

Figure 3

Figure 4

[0059] In FIG. 1, a heat exchanger 1 is schematically illustrated. The heat exchanger 1 includes a plurality of heat transfer tubes 3 and a fluid chamber 4. The heat transfer tubes 3 run through the fluid chamber 4 so as to guide a first fluid F1 into the heat transfer tubes 3 and to guide a second fluid F2 into the fluid chamber 4 in a surrounding manner during operation of the heat exchanger 1. Thereby, heat is transferred between the first fluid F1 and the second fluid F2 through the tube walls of the heat transfer tubes 3. The fluid chamber 4 forms a fluid chamber cavity 5 between the fluid chamber wall and the heat transfer tubes 3 to accommodate the second fluid F2, and the second fluid F2 is guided into the cavity. The fluid chamber 4 includes a fluid chamber inlet 6 for feeding the second fluid F2 into the fluid chamber 4, specifically into the fluid chamber cavity 5, and a fluid chamber outlet 7 for taking fluid out of the fluid chamber 4, specifically from the fluid chamber cavity 5. The second fluid F2 usually has a pressure exceeding 30 bar (3 MPa), specifically between 30 bar (3 MPa) and 200 bar (20 MPa), and / or a temperature exceeding 80° C., specifically between 80° C. and 300° C. Usually, the heat transfer tubes 3 are guided through the fluid chamber 4 such that they are spaced apart from each other, and thus the second fluid F2 can flow through the space between the heat transfer tubes 3. The first fluid F1 and / or the second fluid F2 may be, for example, liquid and / or gaseous water. The heat exchanger 1 may be embodied as a stripper. The heat exchanger 1, specifically the stripper, is often oriented such that the longitudinal extension of the heat transfer tubes 3 is essentially vertically oriented.

[0060] In-situ and operando, i.e., during operation of each heat exchanger 1 using each heat exchanger 1, ultrasonic sensors 2 are arranged on a plurality of heat transfer tubes 3 to determine the wall thickness of each heat transfer tube 3. Each ultrasonic sensor 2 is arranged inside the fluid chamber 4 outside each heat transfer tube 3 on the heat transfer tube 3. To withstand the high temperature and / or high pressure inside the heat exchanger 1, the ultrasonic sensor 2 is designed for an operating pressure exceeding 30 bar (3 MPa) and / or an operating temperature exceeding 80°C. Specifically, the ultrasonic sensor 2 is designed to withstand the aforementioned pressure and / or the aforementioned temperature of the second fluid F2 and has a corresponding operating pressure and a corresponding operating temperature. Each ultrasonic sensor 2 is connected to the electronic data acquisition unit 9 via a signal line 8 to transmit measurement data to the data acquisition unit 9 during operation of the heat exchanger 1. The data acquisition unit 9 is positioned outside the fluid chamber 4 to avoid being affected by the high temperature and high pressure inside the heat exchanger 1. Each signal line 8 is usually embodied as a coaxial cable to achieve interference-free transmission of measurement data. The fluid chamber 4 is provided with a signal line penetration portion 10, and the signal line 8 is guided out of the fluid chamber 4 through it. The signal line penetration portion 10 is usually embodied to be liquid-tight with respect to the fluid chamber cavity 5.

[0061] As can be seen in FIG. 2, to protect each signal line 8 from the pressure and temperature of the second fluid F2 specifically inside the fluid chamber 4, each signal line 8 runs inside the protective tube 11 in the fluid chamber 4. The protective tube 11 runs from each ultrasonic sensor 2 to the signal line penetration portion 10. Usually, the protective tube 11 is liquid-tightly connected to each ultrasonic sensor 2 by welding on one side and is liquid-tightly connected to the signal line penetration portion 10 using a wedge / bolt connection on the other side. In this way, the protective tube 11 can be used to form a volume separated from the fluid chamber cavity 5, preferably having a different atmosphere, and the signal line 8 runs inside the volume. The protective tube 11 is preferably formed of steel, specifically austenitic steel.

[0062] To keep the length of the signal line 8 short, it is beneficial if there are a plurality of electronic data acquisition units 9 and various ultrasonic sensors 2 are connected to different electronic data acquisition units 9 for data transmission. This is illustrated in FIG. 1 by another electronic data acquisition unit 9 drawn in dashed lines. Similar to the manner mentioned, another electronic data acquisition unit 9 may be connected to another ultrasonic sensor 2 arranged on the heat transfer pipe 3 for data transmission.

[0063] Normally, an electronic central data unit 12 to which the electronic data acquisition unit 9 or a plurality of electronic data acquisition units 9 are connected for data transmission is provided. The electronic central data unit 12 is preferably embodied to collect the measurement data of the electronic data acquisition unit 9 and to make the above data available for reading by the user. The electronic data acquisition unit 9 is usually connected to the electronic central data unit 12 via an electrical cable connection part 13, specifically a data bus, for data transmission.

[0064] The ordinary heat transfer tubes 3 extend respectively between the first tube plate 14 and the second tube plate 15, and the tube plates are embodied to be part of the fluid chamber wall of the fluid chamber 4 or define the boundary of the fluid chamber cavity 5. Each heat transfer tube 3 is guided through the first tube plate 14 and the second tube plate 15. The fluid chamber 4 comprises a plurality of stabilizing elements 16, which are usually shown as baffles, and these connect a plurality of heat transfer tubes 3 to each other in order to stabilize the heat transfer tubes 3 using the stabilizing elements 16 during the operation of the heat exchanger 1. Advantageously, there may be a plurality of stabilizing elements 16 spaced apart from each other along the longitudinal extension of the heat transfer tubes 3, and the stabilizing elements 16 are oriented transversely, specifically orthogonally, to the longitudinal extension of the heat transfer tubes 3. To prevent the flow of the second fluid F2 through the intermediate space, it is advantageous if each stabilizing element 16, or the fluid guiding surface formed thereby, closes the intermediate space between the plurality of heat transfer tubes 3. Most of the intermediate space between the heat transfer tubes 3 is often closed to the flow by the second fluid F2 by each stabilizing element 16 or the fluid guiding surface in the cross-section passing through the fluid chamber 4.

[0065] Each ultrasonic sensor 2 is arranged in the arrangement region of each heat transfer tube 3, and it is advantageous if the arrangement region is located in the first third of the longitudinal extension of the heat transfer tube 3 inside the fluid chamber 4 or the fluid chamber cavity 5 in the flow direction of the first fluid F1 through the heat transfer tube 3. Thereby, preferably, the ultrasonic sensor 2 is positioned between the first tube plate 14 and the first stabilizing element 16 in the flow direction of the first fluid F1 through the heat transfer tube 3.

[0066] Figure 2 shows a schematic diagram of the ultrasonic sensor 2. Specifically, the ultrasonic sensor 2 is embodied according to FIG. 1. The ultrasonic sensor 2 includes an attenuation element 17, a piezoelectric crystal 18, and a standoff body 19. The piezoelectric crystal 18 is disposed between the attenuation element 17 and the standoff body 19 in the radiation direction in which an ultrasonic signal can be radiated using the ultrasonic sensor 2. The attenuation element 17 is embodied to attenuate the mechanical vibration of the piezoelectric crystal 18. The standoff body 19 is embodied to transmit the ultrasonic signal generated using the piezoelectric crystal 18 in the radiation direction, and thus, the ultrasonic signal is positioned inside the standoff body 19 over the time length of switching between the radiation mode and the reception mode of the ultrasonic sensor 2. In the radiation mode, an ultrasonic signal can be radiated using the ultrasonic sensor 2, specifically, the piezoelectric crystal 18. In the reception mode, an ultrasonic signal can be detected using the ultrasonic sensor 2, specifically, the piezoelectric crystal 18.

[0067] The attenuation element 17 is embodied to be electrically conductive and is electrically connected to an operating electrode 20 upstream of the attenuation element 17 in the radiation direction S, and thus, the piezoelectric element can be electrically operated via the operating electrode 20 and through the attenuation element 17. Usually, the electrical cathode constitutes the operating electrode 20. The operating electrode 20 is electrically connected to the signal line 8 for the operation of the ultrasonic sensor 2 or for data transmission. As described above, the signal line 8 is connected to the electronic data acquisition unit 9 for data transmission. The signal line 8 is usually a coaxial cable.

[0068] The ultrasonic sensor 2 is provided with a spring element 21, and using this, the working electrode 20, the damping element 17, the piezoelectric crystal 18, and the standoff body 19 are pressed against each other using the spring force of the spring element 21. In this way, a robust connection can be realized, specifically without an adhesive. The spring element 21 can advantageously be realized using a plurality of disc springs arranged such that the plurality of disc springs are connected in series. Conveniently, the ultrasonic sensor 2 includes a sensor housing 22 that forms the exterior of the ultrasonic sensor 2. The sensor housing 22 includes an outlet opening 23 for ultrasonic signals, and the outlet opening 23 is specifically closed in a liquid-tight manner by the standoff body 19. The standoff body 19 is usually connected to the sensor housing 22 in a force-fitting manner, for example using a screw connection.

[0069] Between the sensor housing 22 and each of the damping element 17 and the working electrode 20, electrical insulating elements 24 preferably made of zirconium dioxide are respectively arranged, which usually completely surround the damping element 17 and the control electrode to prevent electrical contact with the sensor housing 22.

[0070] To protect the transmission of signals from the ultrasonic sensor 2 to the electronic data acquisition unit 9 from the second fluid F2, specifically its pressure and / or temperature, the signal line 8 specifically runs inside the protective tube 11 as described above. The protective tube 11 is preferably connected to the sensor housing 22 in a liquid-tight manner using a welded connection, and thus, the protective tube 11 and the sensor housing 22 define a volume separated from the fluid chamber 4 or the fluid chamber cavity 5. In this way, the transmission of data between the ultrasonic sensor 2 and between the ultrasonic sensor 2 and the electronic data acquisition unit 9 can be protected from the second fluid F2.

[0071] The piezoelectric crystal 18 can be made of lead zirconate titanate ceramic (PZT ceramic). The damping element 17 can preferably be made of a titanium sintered body having an average pore diameter between 1 μm and 10 μm. The standoff body 19 can be made of steel, specifically austenitic steel, having a thickness between 2 mm and 10 mm in the radial direction S. The working electrode 20 can be formed such that it contains copper, specifically such that it is made of copper. The heat transfer tube 3 is usually made of steel, specifically austenitic steel. The ultrasonic sensor 2 is preferably embodied to emit an ultrasonic signal, specifically ultrasonic waves, having a center frequency of about 15 MHz.

[0072] Figure 3 shows a schematic view of another heat exchanger 1 embodied as a stripper for stripping. Usually, this type of heat exchanger 1 is used for urea synthesis. The heat exchanger 1 may be embodied according to the description of the heat exchanger 1 in FIG. 1, and specifically may include the ultrasonic sensor 2 described with respect to FIGS. 2 and / or 4. The heat exchanger 1 is usually oriented such that the longitudinal extension of the heat transfer tube 3 is essentially vertically oriented. In urea synthesis, the first fluid F1 is formed such that it contains or is made of the first medium M1 and the second medium M2, and inside the fluid chamber 4 or the fluid chamber cavity 5, the first medium M1 and the second medium M2 are provided to flow through each heat transfer tube 3 in opposite flow directions. Usually, the first medium M1 is formed such that it contains, specifically is made of, urea, ammonium carbamate, and ammonia, and the second medium M2 is formed such that it contains, specifically is made of, gaseous carbon dioxide (CO2). The first medium is usually a liquid. The heat exchanger 1 or stripper usually includes a plurality of, specifically more than 10, preferably more than 50, particularly preferably more than 100, and especially preferably more than 1000 heat transfer tubes 3. The heat exchanger 1 is usually oriented such that the first tube plate 14 is positioned vertically above the second tube plate 15. Preferably, each ultrasonic sensor 2 is positioned between the first tube plate 14 and the first stabilizing element 16.

[0073] The heat exchanger 1 comprises a first inlet 25 through which a first medium M1 can be fed to the heat transfer tubes 3, and a second inlet 27 through which a second medium M2 can be fed to the heat transfer tubes. Thus, inside the fluid chamber 4 or the fluid chamber cavity 5, the media M1, M2 flow through the heat transfer tubes 3 in opposite flow directions 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 tubes 3 in a manner of guiding the fluid at different ends of the heat transfer tubes 3. For this purpose, the first inlet 25 and the second inlet 27 can be respectively connected to a fluid distribution chamber in a manner of guiding the fluid, and the ends of the heat transfer tubes 3 are respectively connected to the fluid distribution chamber in a manner of guiding the fluid. Thus, the first medium M1 and the second medium M2 fed to each fluid distribution chamber via the first inlet 25 and the second inlet 27 are respectively guided to the heat transfer tubes 3 so that they are distributed to the heat transfer tubes 3. The heat exchanger 1 comprises a first outlet 26 through which a first product Z1 can be taken out from the heat transfer tubes 3, and a second outlet 28 through which a second product Z2 can be taken out from the heat transfer tubes 3. With respect to the fluid chamber cavity 5, the first outlet 26 and the second outlet 28 are connected to the heat transfer tubes 3 in a manner of guiding the fluid at different ends of the heat transfer tubes 3. Preferably, the first outlet 26 and the second outlet 28 are respectively connected to one of the fluid distribution chambers in a manner of guiding the fluid. Thus, the first product Z1 and the second product Z2 exiting from the heat transfer tubes 3 can be taken out via the respective outlets 26, 28. The first product Z1 is usually, specifically, high-purity urea. The second product Z2 is usually gaseous ammonia (NH3) and / or gaseous carbon dioxide (CO2). Ordinarily, the second fluid F2 is formed such that it contains liquid and / or gaseous water, specifically such that it is made of them.

[0074] Figure 4 shows a schematic view of another ultrasonic sensor 2 in cross-section. The ultrasonic sensor 2 can have the same characteristics and effects as the ultrasonic sensor 2 in FIG. 2. The ultrasonic sensor 2 can be used in the heat exchanger 1 of FIGS. 1 and 3. The configuration of the ultrasonic sensor 2 in FIG. 4 essentially corresponds to that of the ultrasonic sensor 2 in FIG. 2. Specifically, the ultrasonic sensor 2 includes a spring element 21, and using this, the working electrode 20, the damping element 17, the piezoelectric crystal 18, and the stand-off body 19 are pressed against each other using the spring force of the spring element 21. The spring element 21 is disposed between the working electrode and a counter bearing 31 that can be formed by a ring nut. To create an electrical connection between the signal line 8 and the working electrode 20, the line and the electrode are connected to each other in a press-fit manner using a clamp element 30. In contrast to the ultrasonic sensor 2 in FIG. 2, the ultrasonic sensor 2 includes a specifically tubular connection piece 29 for form-fittingly accommodating the protective tube 11, and the protective tube 11 is inserted into the connection piece 29 in a liquid-tight manner. In this way, for example, an especially robust connection between the signal line 8 and the ultrasonic sensor 2 can be achieved for use within the fluid chamber cavity 5 or at a particularly high pressure of the second fluid F2. The connection piece 29 can be formed such that it contains or is made of steel, specifically austenitic steel. Conveniently, the ultrasonic sensor of FIG. 2 may also include this type of connection piece 29.

[0075] One or more of the heat transfer tubes 3 of the heat exchanger 1 are each provided with one ultrasonic sensor 2 designed for an operating pressure exceeding 30 bar (3 MPa), specifically between 30 bar (3 MPa) and 200 bar (20 MPa), and / or an operating temperature exceeding 80 °C, specifically between 80 °C and 300 °C. When the ultrasonic sensor 2 is embodied to transmit measurement data to the electronic data acquisition unit 9 during operation of the heat exchanger 1, the wall thickness of each heat transfer tube 3 can be determined in situ and preferably operando. This makes it possible to optimize the usefulness of the heat exchanger 1. Specifically, when the signal line 8 for transmitting the measurement signal from each ultrasonic sensor 2 to the electronic data acquisition unit 9 runs inside the protective tube 11 inside the second fluid F2, and / or when the damping element 17, the piezoelectric crystal 18, and the standoff body 19 are pressed against each other inside the ultrasonic sensor 2 using the spring force of the spring element 21, a particularly high robustness for determining the wall thickness in situ and usually operando can be achieved. [Item 1] A heat exchanger comprising a plurality of heat transfer tubes for transporting a first fluid, specifically a high-pressure heat exchanger for urea synthesis, wherein the plurality of heat transfer tubes are for transferring heat between the first fluid and a second fluid through the plurality of heat transfer tubes, and an ultrasonic sensor is respectively arranged on one or more of the heat transfer tubes for in-situ determination of the wall thickness of the heat transfer tubes, each of the ultrasonic sensors being designed for an operating pressure exceeding 30 bar (3 MPa) and / or an operating temperature exceeding 80 °C, and each of the ultrasonic sensors being connected to an electronic data acquisition unit for data transmission and transmitting measurement data to the electronic data acquisition unit during operation of the heat exchanger. [Item 2] The heat exchanger according to item 1, comprising a fluid chamber for accommodating the second fluid, wherein the heat transfer tubes extend inside the fluid chamber, and the electronic data acquisition unit is arranged outside the fluid chamber. [Item 3] Each of the ultrasonic sensors is connected to the electronic data acquisition unit via a signal line for the transmission of the data, and the signal line extends at least partially inside a protective tube, preferably made of metal, for protecting the signal line, of the heat exchanger according to item 1 or 2. [Item 4] The protective tube is welded on one side to the sensor housing of each of the ultrasonic sensors, and / or the protective tube is connected on the other side, preferably using a wedge / bolt connection, to a signal line penetration part, through which the signal line is guided through the fluid chamber wall of the fluid chamber, of the heat exchanger according to item 2 or 3. [Item 5] The protective tube forms a volume separated from the first fluid and the second fluid during operation, and the signal line extends inside the volume, of the heat exchanger according to item 3 or 4. [Item 6] Each of the ultrasonic sensors includes an attenuation element, a piezoelectric crystal, and a standoff body, and the attenuation element, the piezoelectric crystal, and the standoff body are pressed against each other using a spring element, of the heat exchanger according to any one of items 1 to 5. [Item 7] The spring element is preferably formed using an arrangement of a plurality of springs connected in series, of the heat exchanger according to item 6. [Item 8] In each of the ultrasonic sensors, the attenuation element is arranged between the electrically actuated electrode and the piezoelectric crystal, and the attenuation element is embodied to be electrically conductive, so that the electrical actuation of the piezoelectric crystal via the electrically actuated electrode can be realized through the attenuation element, of the heat exchanger according to item 6 or 7. [Item 9] Each of the ultrasonic sensors includes one or more electrical insulation elements for electrical insulation, and the one or more electrical insulation elements are preferably formed to include zirconium dioxide between the sensor housing of the ultrasonic sensor and each of the piezoelectric crystal and / or damping element and / or electrode of the ultrasonic sensor. The heat exchanger according to any one of items 1 to 8. [Item 10] Between each of the ultrasonic sensors and the heat transfer tube, coupling means formed to include silver, specifically including a silver film, is disposed, or coupling means is not disposed. The heat exchanger according to any one of items 1 to 9. [Item 11] Each of the ultrasonic sensors is preferably connected to each of the heat transfer tubes in a press-fit manner using a clamp connection. The heat exchanger according to any one of items 1 to 10. [Item 12] A plurality of ultrasonic sensors are connected to the same electronic data acquisition unit for transmitting the measurement data to the electronic data acquisition unit during operation of the heat exchanger. The heat exchanger according to any one of items 1 to 11. [Item 13] A method of operating a heat exchanger, specifically the heat exchanger according to any one of items 1 to 12, wherein the first fluid is transported on one or more heat transfer tubes for transferring heat between the first fluid and the second fluid through the one or more heat transfer tubes, and ultrasonic sensors having an operating pressure exceeding 30 bar (3 MPa) and / or an operating temperature exceeding 80 °C are respectively disposed on the one or more heat transfer tubes, and the thickness of the tube wall of each of the heat transfer tubes is determined in situ using each of the ultrasonic sensors, and during operation of the heat exchanger, measurement data is transmitted from each of the ultrasonic sensors to an electronic data acquisition unit. [Item 14] Each of the ultrasonic sensors operates at a frequency exceeding 10 MHz, specifically between 10 MHz and 30 MHz, specifically at the center frequency. The method according to item 13. [Item 15] For temperature compensation of the ultrasonic velocity of the ultrasonic signal, the thickness of the stand-off body of at least one of the ultrasonic sensors is used as a reference length, and / or the temperature is confirmed using at least one thermocouple. The method according to item 13 or 14. [Item 16] To determine the wall thickness of the heat transfer tube, using the ultrasonic sensor, an ultrasonic signal is radiated to each of the heat transfer tubes, specifically to its wall, and the ultrasonic signals reflected from the outer wall and the inner wall of the heat transfer tube are received using the ultrasonic sensor. The method according to any one of items 13 to 15.

Claims

1. A heat exchanger comprising a plurality of heat transfer tubes for transporting a first fluid, specifically a high-pressure heat exchanger for urea synthesis, wherein the plurality of heat transfer tubes are for transferring heat between the first fluid and a second fluid through the plurality of heat transfer tubes, and ultrasonic sensors are respectively arranged on one or more of the heat transfer tubes for in-situ determination of the wall thickness of the heat transfer tubes, each of the ultrasonic sensors being designed for an operating pressure exceeding 30 bar (3 MPa) and / or an operating temperature exceeding 80 °C, and each of the ultrasonic sensors being connected to an electronic data acquisition unit for data transmission, and transmitting measurement data to the electronic data acquisition unit during operation of the heat exchanger.

2. The heat exchanger comprises a fluid chamber for accommodating the second fluid, the heat transfer tubes extend inside the fluid chamber, and the electronic data acquisition unit is arranged outside the fluid chamber. The heat exchanger according to claim 1.

3. Each of the ultrasonic sensors is connected to the electronic data acquisition unit via a signal line for data transmission, and the signal line extends at least partially inside a protective tube, preferably made of metal, for protecting the signal line. The heat exchanger according to claim 1.

4. The protective tube is welded to the sensor housing of each ultrasonic sensor on one side and / or the protective tube is connected to a signal line penetration part on the other side, preferably using a wedge / bolt connection, and the signal line is guided through the fluid chamber wall of the fluid chamber using the signal line penetration part. The heat exchanger according to claim 2.

5. The protective tube forms a volume separated from the first fluid and the second fluid during operation, and the signal line extends inside the volume. The heat exchanger according to claim 3.

6. Each of the ultrasonic sensors includes a damping element, a piezoelectric crystal and a stand-off body, and the damping element, the piezoelectric crystal and the stand-off body are pressed against each other using a spring element. The heat exchanger according to claim 1.

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

8. In each of the ultrasonic sensors, the damping element is arranged between the electrically actuated electrode and the piezoelectric crystal, and the damping element is embodied to be electrically conductive, and thus, the electrical actuation of the piezoelectric crystal via the electrically actuated electrode can be realized through the damping element. The heat exchanger according to claim 6.

9. Each of the ultrasonic sensors includes one or more electrical insulation elements for electrical insulation, and the one or more electrical insulation elements are preferably formed to include zirconium dioxide between the sensor housing of the ultrasonic sensor and each of the piezoelectric crystal and / or damping element and / or electrode of the ultrasonic sensor. The heat exchanger according to claim 1.

10. Coupling means formed to include silver, specifically silver film, is arranged between each of the ultrasonic sensors and the heat transfer tube, or no coupling means is arranged. The heat exchanger according to claim 1.

11. Each of the ultrasonic sensors is preferably connected to each of the heat transfer tubes in a force-fitting manner using a clamp connection. The heat exchanger according to claim 1.

12. A plurality of ultrasonic sensors are connected to the same electronic data acquisition unit for transmitting the measurement data to the electronic data acquisition unit during operation of the heat exchanger. The heat exchanger according to claim 1.

13. A method of operating a heat exchanger, specifically the heat exchanger according to any one of claims 1 to 12, wherein the first fluid is transported on one or more heat transfer tubes for transferring heat between the first fluid and the second fluid via the one or more heat transfer tubes, and ultrasonic sensors having an operating pressure exceeding 30 bar (3 MPa) and / or an operating temperature exceeding 80 ° C are respectively arranged, and the thickness of the wall of each of the heat transfer tubes is determined in situ using each of the ultrasonic sensors, and during operation of the heat exchanger, measurement data is transmitted from each of the ultrasonic sensors to an electronic data acquisition unit.

14. Each of the ultrasonic sensors operates at a frequency exceeding 10 MHz, specifically between 10 MHz and 30 MHz, specifically at the center frequency. The method according to claim 13.

15. For temperature compensation of the ultrasonic velocity of the ultrasonic signal, the thickness of the stand-off body of at least one of the ultrasonic sensors is used as a reference length, and / or the temperature is confirmed using at least one thermocouple, the method according to claim 13.

16. To determine the wall thickness of the heat transfer tube, the ultrasonic sensor is used such that ultrasonic signals are radiated to respective heat transfer tubes, specifically to their walls, and the ultrasonic signals reflected from the outer and inner walls of the heat transfer tube are received using the ultrasonic sensor, the method according to claim 13.

Images