HEAT EXCHANGER WITH ULTRASONIC SENSOR FOR DETERMINING THE PIPE WALL THICKNESS OF A HEAT TRANSFER PIPE OF THE HEAT EXCHANGER AND METHOD FOR OPERATING SUCH A HEAT EXCHANGER

Description

[0001] The invention relates to a heat exchanger, in particular a high-pressure heat exchanger for urea synthesis, comprising several heat transfer tubes for transporting a first fluid in order to transfer heat between the first fluid and a second fluid via the heat transfer tubes. The invention relates to a heat exchanger according to the preamble of claim 1. Such a heat exchanger is known from US 2020 / 388410A.

[0002] Furthermore, the invention relates to a method for operating a heat exchanger.

[0003] It is known from the prior art to use a heat exchanger to exchange thermal energy between a first fluid stream and a second fluid stream. The heat exchanger often has several heat transfer tubes for transporting the first fluid stream, which then transfers heat to or absorbs heat from a second fluid stream flowing around it. In urea synthesis, heat exchangers are typically used in which the first and second fluid streams are at high pressure, usually more than 30 bar, and high temperature, usually more than 80°C.The transport of the initial fluid flow through the heat transfer tubes is often associated with the removal of tube wall material, particularly corrosive and / or erosive processes, or the formation of deposits within the tubes. This results in a change, typically a reduction, of the tube wall thickness during operation of the heat exchanger. Any impairment of the tube wall integrity can compromise the operational safety of the heat exchanger. Therefore, it is usually necessary to shut down the heat exchanger regularly, based on scheduled maintenance intervals, and measure the tube wall thickness.

[0004] For this purpose, it is common practice to insert a measuring probe into the respective heat transfer tube when the heat exchanger is not in operation, in order to determine the inner radius or the tube wall thickness. Measuring probes are known that incorporate an ultrasonic sensor, an optical sensor, or an eddy current sensor to determine the tube wall thickness.

[0005] Especially in the case of heat exchangers that operate with pressures of more than 30 bar and high temperatures of more than 80°C of the first and / or second fluid flow, such an interruption of operation to determine the pipe wall thicknesses of the heat transfer pipes is usually complex or associated with high costs.

[0006] This is where the invention comes in. The object of the invention is to provide a heat exchanger of the type mentioned above, which has optimized usability, in particular enabling optimized operation.

[0007] Furthermore, an objective of the invention is to provide a method for operating a heat exchanger which enables optimized use or operation of the heat exchanger.

[0008] The object of the invention is achieved by arranging an ultrasonic sensor for in-situ determination of the wall thickness of the heat transfer tubes on one or more of the heat transfer tubes in a heat exchanger of the type mentioned above, 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 in order to transmit measurement data 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 heat exchangers designed for high operating pressure and / or high operating temperature of the first and / or second fluid by determining the tube wall thickness of the heat transfer tubes of the heat exchanger in situ, i.e., locally at the heat exchanger or the heat transfer tubes, and usually in operando, i.e., during operation of the heat exchanger. This allows operation, in particular process control, and / or maintenance of the heat exchanger to be carried out depending on the determined tube wall thickness. In particular, it is not necessary to interrupt operation of the heat exchanger to determine the tube wall thickness.

[0010] Operation of the heat exchanger refers to a state in which the first fluid is circulated through the heat transfer tubes to exchange heat with the second fluid via the same tubes. A high operating pressure or high operating temperature is defined as an operating pressure of the first fluid and / or the second fluid greater than 30 bar or an operating temperature greater than 80°C. Specifically, the operating pressure is between 30 bar and 200 bar, preferably around 180 bar, and / or the operating temperature is between 80°C and 300°C, preferably around 230°C. Typically, the first and / or second fluid exhibits such an operating pressure or temperature during heat exchanger operation, or the heat exchanger is designed for such operation. Accordingly, it is advantageous if the respective ultrasonic sensor has an operating pressure or temperature corresponding to the operating pressure or temperature.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 also advantageous if the stripper is used for urea synthesis. The stripper can be designed to synthesize urea by stripping, typically within the heat transfer tubes.

[0012] Typically, the respective ultrasonic sensor is positioned on the heat transfer tube such that, during operation of the heat exchanger, it is immersed in one of the fluids, preferably the second fluid. It has proven advantageous to position the ultrasonic sensor on the outer surface of the heat transfer tube, usually within the second fluid. Generally, during operation of the heat exchanger, the second fluid has the aforementioned operating pressure and / or temperature, or the heat exchanger is designed for such operation. The ultrasonic sensor is typically positioned on a tube wall of the respective heat transfer tube to determine the tube wall thickness by emitting an ultrasonic signal into the tube wall. Typically, the ultrasonic sensor can emit an ultrasonic signal and detect a reflected ultrasonic signal.The heat exchanger typically has one, preferably several, such ultrasonic sensors. The heat exchanger or ultrasonic sensor is usually designed for in-situ and in-operando determination of the pipe wall thickness of the respective heat transfer pipe, or the pipe wall thickness of the respective heat transfer pipe is determined in situ and in operando using the ultrasonic sensor.

[0013] It is advantageous for the respective ultrasonic sensor to be connected to an electronic data acquisition unit for data transmission. This allows measurement data to 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 typically connected by a signal line, preferably an electrical one. The signal line is preferably designed for symmetrical signal transmission. The signal line is typically cable-shaped, preferably a coaxial cable. Several electronic data acquisition units can be provided, with different ultrasonic sensors being connected to different electronic data acquisition units for data transmission. Multiple ultrasonic sensors can also be connected to the same electronic data acquisition unit for data transmission.It may be provided that the respective ultrasonic sensor is controlled by the electronic data acquisition unit to which the ultrasonic sensor is connected for data transmission.

[0014] The heat transfer tubes are typically designed to convey the first fluid, transferring heat between the first and second fluids through the tube walls. Preferably, during operation of the heat exchanger, the second fluid is in contact, particularly direct contact, with the heat transfer tubes or their walls. The first fluid is typically a primary fluid flow circulating through the heat transfer tubes during operation. The second fluid can be a secondary fluid flow during operation, which generally flows around the heat transfer tubes. The second fluid typically has a pressure greater than 30 bar, particularly between 30 bar and 200 bar, preferably around 180 bar, and / or a temperature greater than 80°C, particularly between 80°C and 300°C, preferably around 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 holding the second fluid, with the heat transfer tubes running within this chamber. The fluid chamber usually forms a cavity between its walls and the heat transfer tubes, allowing heat transfer between the first and second fluids. The heat transfer tubes typically pass through this cavity. Generally, during operation, the second fluid is guided through the fluid chamber cavity, specifically by flowing around the heat transfer tubes. Advantageously, the fluid chamber cavity can be configured as one or more channels to facilitate the flow of the second fluid during operation.The fluid chamber typically has at least one fluid chamber inlet and at least one fluid chamber outlet to introduce the second fluid into the fluid chamber, particularly the fluid chamber cavity, via the fluid chamber inlet, and to discharge the second fluid from the fluid chamber, particularly the fluid chamber cavity, via the fluid chamber outlet, generally after heat transfer between the first and second fluids has taken place. The fluid chamber is typically formed with, and in particular made of, metal, preferably an iron alloy, and more preferably a steel alloy, for example, austenitic steel.

[0016] Typically, heat transfer tubes are spaced apart from each other, at least in sections, so that during operation of the heat exchanger, the second fluid can flow between the heat transfer tubes for heat transfer. This applies particularly within the fluid chamber or its fluid chamber cavity.

[0017] Typically, the first fluid and / or the second fluid are liquid and / or gaseous. For example, the first fluid and / or the second fluid may consist of, in particular, liquid and gaseous water. It is also possible for the first fluid and / or the second fluid to consist of, in particular, a liquid medium and a gaseous medium, wherein, during operation of the heat exchanger, the liquid and gaseous components of the respective fluids flow through the heat exchanger in opposite directions, usually in contact with each other. For example, the first fluid may consist of a liquid medium and a gaseous medium, wherein, during operation of the heat exchanger, the media flow through the respective heat transfer tube in opposite directions, in particular in contact with each other.

[0018] The heat transfer tubes typically extend between a first and a second tube plate, with the tube plates defining the fluid chamber cavity for receiving the second fluid. The heat transfer tubes open into or pass through openings in the respective tube plates. A fluid introduced through openings in one plate is usually conveyed through the heat transfer tubes to the openings in the other tube plate. The heat transfer tubes are generally fluid-tightly connected to the tube plates. Each tube plate is typically plate-shaped with several flow channels oriented transversely, and in particular orthogonally, to a longitudinal extent of the tube plate, forming the respective openings. The tube plates can also be formed as part of the fluid chamber walls.The heat exchanger typically has at least one first and at least one second such tube plate. The tube plates are typically made of metal, preferably an iron alloy, and particularly preferably a steel alloy, for example austenitic steel.

[0019] The fluid chamber may contain one or more fluid guide surfaces to define a flow path for the second fluid. Each fluid guide surface is typically designed to partially restrict the flow of the second fluid between the heat transfer tubes. The fluid guide surfaces can define a flow path with multiple bends, along which the second fluid is guided from the fluid chamber inlet to the fluid chamber outlet. For example, the flow path may be meandering. Typically, several heat transfer tubes pass through each guide surface. Generally, several spaced-apart guide surfaces are provided, traversing the heat transfer tubes. The fluid guide surface is usually oriented transversely, and in particular orthogonally, to a longitudinal extent of the heat transfer tubes.Typically, several fluid guide surfaces are provided, spaced apart along the length of the heat transfer tubes. Each fluid guide surface essentially closes the gap between several of the heat transfer tubes to prevent the flow of the second fluid through this space. The fluid guide surface can be designed to close a majority of the gaps between the heat transfer tubes in a cross-section through the fluid chamber, thus preventing the flow of the second fluid. The fluid guide surfaces can be formed by guide walls arranged within the fluid chamber. The fluid guide surfaces are generally plate-shaped. The fluid chamber typically contains one or more such guide surfaces.

[0020] Typically, several heat transfer tubes are connected by stabilizing elements to stabilize them during operation of the heat exchanger. Each stabilizing element can be plate-shaped, with one longitudinal dimension of the stabilizing element usually oriented transversely, and in particular orthogonally, to the longitudinal dimension of the heat transfer tubes connected by it. The heat transfer tubes usually run through the stabilizing element. These stabilizing elements are commonly referred to as baffles. Generally, several spaced-apart stabilizing elements are provided along one longitudinal dimension of the heat transfer tubes, connecting them to one another. In particular, the fluid guide surfaces can be formed by the stabilizing elements.The stabilizing elements can then serve both to stabilize the heat transfer pipes and to define a flow path for the second fluid.

[0021] It is advantageous if the respective ultrasonic sensor is arranged in an arrangement area on the respective heat transfer pipe, wherein the arrangement area, particularly in the flow direction of the first fluid through the heat transfer pipe, is defined by a first third of a longitudinal extent of the heat transfer pipe within the fluid chamber or the fluid chamber cavity. The arrangement area of ​​the respective heat transfer pipe typically extends, particularly in the flow direction of the first fluid, from an inlet of the heat transfer pipe into the fluid chamber along a longitudinal extent of the heat transfer pipe with a length of 30%, particularly 20%, preferably 10% of a longitudinal extent of the heat transfer pipe within the fluid chamber or the fluid chamber cavity. It has been shown that, as a rule, material removal occurs in this arrangement area of ​​the respective heat transfer pipe.Wear and tear on the heat transfer pipe is particularly high, which is why it is advantageous to position the ultrasonic sensors in this area.

[0022] It is advantageous if the electronic data acquisition unit is located outside the fluid chamber, particularly the fluid chamber cavity. This protects the electronic data acquisition unit from stresses, especially pressure and / or temperature stresses, particularly those of the first and second fluids. The data acquisition unit typically includes a microcontroller or can be configured as a computer. The electronic data acquisition unit is generally designed to receive measurement data, usually via one or more hardware interfaces, from one or more of the ultrasonic sensors. The electronic data acquisition unit can be configured to process, collect, and / or forward the measurement data.For example, measurement data can be forwarded from the electronic data acquisition unit to an electronic data center unit, which may be configured to output data, particularly processed data, and / or display it to a user. A heat exchanger typically has one or more electronic data acquisition units.

[0023] It has proven effective to connect the respective ultrasonic sensor to the data acquisition unit via the signal line for data transmission. The signal line, particularly within the fluid chamber, runs at least partially within a protective tube, preferably made of metal, to protect it, especially from damage caused by the first and second fluids. It is advantageous if the protective tube forms a volume separate from the first and second fluids, within which, and especially through which, the signal line runs. The protective tube can expediently be connected to the ultrasonic sensor. This volume is typically separated from the fluid chamber cavity. The signal line usually runs within the protective tube in the fluid chamber. The protective tube generally extends from the respective ultrasonic sensor to a fluid chamber wall, particularly within the fluid chamber cavity.It is advantageous if the protective tube is connected to the sensor housing of the respective ultrasonic sensor in such a way that the protective tube, preferably together with the sensor housing, defines a volume separated from the first and second fluids, or from the fluid chamber cavity, during operation of the heat exchanger, in which the signal line runs. The protective tube is typically connected to the respective 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 the fluid chamber cavity, in a fluid-tight manner, or it can be routed through the fluid chamber wall. The fluid chamber can have a signal line feedthrough through which the signal line is routed through a fluid chamber wall of the fluid chamber, in particular out of the fluid chamber. Advantageously, the protective tube can be connected to the fluid chamber wall via the signal line feedthrough in a fluid-tight manner.Typically, the entire length of the signal line between the ultrasonic sensor and the fluid chamber wall or signal line feedthrough extends within the protective tube.

[0024] The protective tube can be connected, usually fluid-tight, to the ultrasonic sensor, in particular its sensor housing, by means of a force-fit, form-fit, and / or material-fit connection. The protective tube can also be connected, usually fluid-tight, to the signal cable feedthrough or a fluid chamber wall by means of a force-fit, form-fit, and / or material-fit connection. Preferably, the protective tube is material-fitted, particularly welded, to the respective ultrasonic sensor, in particular its sensor housing, and / or the protective tube is connected to a signal cable feedthrough, preferably by means of a force-fit and / or material-fit connection, by means of a wedge bolt connection through which the signal cable passes through the fluid chamber. The welded connection enables a robust and space-saving connection at the ultrasonic sensor. At the fluid chamber wall or...At the signal cable feedthrough, the space requirement for connecting the protective tube is usually less critical, making a wedge bolt connection practical. Alternatively, the protective tube can also be bonded to the fluid chamber wall or signal cable feedthrough by a material bond, in particular by welding. Preferably, the heat exchanger has one or more such protective tubes. In particular, several protective tubes connected to different ultrasonic sensors can be connected to each other to form a common volume, in order to guide the respective signal cables through this common volume.

[0025] The protective tube is usually made of metal, in particular metal. Preferably, the protective tube is made of an iron alloy, more preferably a steel alloy, for example austenitic steel. Preferably, in this way, a different atmosphere, in particular a different composition of atmospheric elements, can be formed within the protective tube or within the ultrasonic sensor than in the fluid chamber. The atmosphere, in particular the composition of atmospheric elements, within the protective tube or within the ultrasonic sensor can essentially correspond to the ambient atmosphere of the heat exchanger.

[0026] The ultrasonic sensor is typically configured to emit an ultrasonic signal and receive a reflected ultrasonic signal, usually at one or more interfaces. The ultrasonic signal is generally an ultrasonic wave. The distance between the interfaces can be determined from the time interval, particularly by comparing, the emitted and received ultrasonic signals. Advantageously, the ultrasonic sensor can emit an ultrasonic signal into the heat transfer pipe, especially its wall, and receive ultrasonic signals reflected at interfaces, particularly an outer and an inner wall of the heat transfer pipe, in order to determine the pipe wall thickness. The ultrasonic sensor typically incorporates a piezoelectric crystal for emitting the ultrasonic signal and receiving the reflected ultrasonic signal.The piezoelectric crystal is typically formed as part of a piezoelectric element. The piezoelectric crystal or piezoelectric element is usually controlled via the signal line. It is advantageous if the piezoelectric crystal is made of, and especially of, a lead zirconate titanate ceramic (PZT ceramic). The piezoelectric crystal can be plate-shaped and, in the direction of transmission of the ultrasound signal, have a thickness of less than 3 mm, particularly less than 1 mm, preferably less than 0.5 mm, and most preferably between 0.1 mm and 0.15 mm. The thickness is generally greater than 0.05 mm.

[0027] According to the invention, the ultrasonic sensor is arranged on the heat transfer pipe in such a way that the direction of transmission of the ultrasonic signal is transverse, in particular essentially orthogonal, to a longitudinal extension of the heat transfer pipe.

[0028] For high accuracy, it has proven advantageous to use the same piezoelectric crystal for both transmitting and receiving ultrasonic signals in the respective ultrasonic sensor. Typically, the ultrasonic sensor or piezoelectric crystal's control system switches between a transmit mode, in which an ultrasonic signal is emitted, and a receive mode, in which a reflected ultrasonic signal can be detected. There is usually a dead time between the transmit and receive modes, during which no reflected ultrasonic signal can be detected. Alternatively, the ultrasonic sensor can be configured with multiple piezoelectric crystals, one for transmitting and another for receiving ultrasonic signals. However, it is preferred that both transmitting and receiving the ultrasonic signals are performed by the same piezoelectric crystal.

[0029] A typical ultrasonic sensor comprises a damping element, a piezoelectric crystal, and a pre-existing section. The damping element is usually coupled to the piezoelectric crystal and designed to dampen its mechanical vibrations. The piezoelectric crystal is often in contact with the damping element. The pre-existing section is generally positioned downstream of the piezoelectric crystal in the direction of transmission of the ultrasonic signal to the heat transfer pipe. This prevents reflection of the ultrasonic signal emitted by the piezoelectric crystal from the pipe wall during the dead time. The pre-existing section is typically made of a material with high ultrasonic conductivity.

[0030] It is advantageous if the damping element, the piezoelectric crystal, and the pre-movement section in the respective ultrasonic sensor are pressed together by means of a spring element. This ensures a robust and, in particular, durable connection even under high operating pressure and / or high operating temperature. Preferably, this eliminates the need for adhesive bonding of the damping element, piezoelectric crystal, and pre-movement section, which is often susceptible to stress.

[0031] The pressing action is typically associated with an elastic deformation of the spring element against a spring force. It is advantageous if the spring element is formed by a single spring or an arrangement of several springs, preferably coupled in series. The spring is preferably a disc spring. The spring element is preferably positioned upstream of the damping element in the transmission direction of the ultrasonic sensor.

[0032] The direction of transmission usually refers to the direction in which a given ultrasonic sensor is designed to transmit an ultrasonic signal, in particular towards the heat transfer pipe.

[0033] It is advantageous if the damping element is formed with, and in particular made of, a porous titanium body, especially one formed with sintered titanium. Typically, the titanium body has an average pore size of less than 100 µm, particularly less than 50 µm, preferably between 1 µm and 10 µm, and most preferably about 5 µm. This allows for the generation of a robust ultrasonic signal. The damping element typically has a thickness of between 1 mm and 5 mm, preferably about 3 mm, in the transmitting direction.

[0034] The pre-wave section can be made of, in particular, acrylic glass or a metal, especially iron, preferably steel. For a robust ultrasound signal, it is particularly advantageous if the pre-wave section is made of, in particular, austenitic steel. Preferably, the surface of the pre-wave section, especially if it is made of or from steel, is polished. Typically, the pre-wave section has a thickness of less than 30 mm in the transmission direction, in particular between 2 mm and 10 mm, preferably about 5 mm.

[0035] It is advantageous if, in the respective ultrasonic sensor, the damping element is arranged between an electrical control electrode and the piezoelectric crystal, wherein the damping element is electrically conductive so that electrical control of the piezoelectric crystal via the control electrode is possible through the damping element. The electrical control electrode can be pressed against the damping element by the aforementioned spring element. It is understood that, as a rule, two electrodes are present to enable the piezoelectric crystal to transmit or receive signals.

[0036] The purpose of a piezoelectric crystal is to electrically control the reception of an ultrasound signal, in particular to apply an electrical voltage or to draw an electrical voltage across the electrodes. The electrodes are usually electrically connected to the piezoelectric crystal on opposite sides. One of the electrodes can be the control electrode and, in particular, be electrically connected to the piezoelectric crystal via the damping element as described above. The other electrode can be electrically connected directly to the piezoelectric crystal, usually on a side of the piezoelectric crystal downstream of the transmitting crystal. Alternatively or cumulatively, it is advantageous to form a piezoelectric element by having two piezoelectric electrodes applied to surfaces of the piezoelectric crystal, usually opposite each other on the piezoelectric crystal, via which the piezoelectric crystal can be controlled to excite vibrations.The piezoelectric electrodes are usually made of metal, preferably silver. Advantageously, the aforementioned control electrode can also be provided.

[0037] Each ultrasonic sensor typically has a sensor housing, which forms an outer casing. The damping element, the piezoelectric crystal (usually essentially the pre-movement section), and / or the electrodes, particularly the drive electrode if applicable, are generally located within the sensor housing. The sensor housing typically has an outlet opening through which an ultrasonic signal generated by the piezoelectric crystal can exit for measurement by the ultrasonic sensor. The outlet opening is usually sealed fluid-tight, often by the pre-movement section itself.

[0038] It has proven effective if the respective ultrasonic sensor incorporates one or more electrical insulation elements for electrical isolation between the sensor housing and the piezoelectric crystal, damping element, or one, and preferably several, electrodes. These electrical insulation elements are preferably made of zirconium dioxide. The insulation elements can completely surround these components. In this way, the risk of an electrical short circuit can be minimized, even under high stress, particularly pressure and / or temperature stress.

[0039] It is advantageous if a couplant formed with silver, in particular a silver foil, or no couplant at all, is arranged between the respective ultrasonic sensor and the heat transfer tube. This applies particularly during operation of the heat exchanger. The purpose of the couplant is usually to enable reflection-reduced coupling of the ultrasonic signal into the heat transfer tube. It has been shown that, at the aforementioned high pressure and / or high temperature, sustained high-quality coupling can be achieved when silver is used as the couplant or when no couplant is used. The couplant is preferably layered. The couplant often has a thickness between 0.01 mm and 1 mm, in particular approximately 0.05 mm. The thickness is usually measured in the transmission direction.

[0040] The respective ultrasonic sensor can be connected to the heat transfer pipe by friction, form-fitting, or material bonding. A holding device can be advantageously provided for this purpose. It is preferred that the respective ultrasonic sensor be connected to the respective heat transfer pipe by friction, preferably with a clamping connection. This ensures a robust connection between the ultrasonic sensor and the heat transfer pipe, enabling interference-free coupling of the ultrasonic signal into the heat transfer pipe without significantly impairing the pipe wall thickness measurement. It is advantageous if the holding device includes a spring component, whereby the ultrasonic sensor is pressed against the pipe wall of the heat transfer pipe by the spring force.This ensures a strong contact pressure even under, in particular, fluctuating pressure and / or temperature loads. The spring component can be formed with one or more disc springs. Advantageously, several of the ultrasonic sensors can each be connected to the respective heat transfer tube by their own mounting device, in particular as described. However, it is also possible for several of the ultrasonic sensors to be connected to the respective heat transfer tube by a common mounting device. Although less preferred, the respective ultrasonic sensor can alternatively be connected to the heat transfer tube by a material bond or, in simpler cases, by a form-fit connection.

[0041] It is advantageous to connect several ultrasonic sensors to the same electronic data acquisition unit (ECU) for data transmission, enabling the transfer of measurement data to the ECU during heat exchanger operation. This allows for a compact design with preferably short signal lines. The ECU typically has multiple hardware interfaces to which signal lines connected to the ultrasonic sensors are attached. Each hardware interface can be assigned to one of the signal lines. Each ultrasonic sensor can be connected to the ECU via its own dedicated signal line. Alternatively, several of the signal lines connected to the ultrasonic sensors can form a common data bus through which measurement data can be transmitted to the ECU.It is advantageous to have multiple electronic data acquisition units, with the ultrasonic sensors from different groups of electronic ultrasonic sensors connected to different electronic data acquisition units for data transmission. This is particularly beneficial for keeping signal cable lengths short.

[0042] It is advantageous if several electronic data acquisition units are connected to a central electronic data unit for data transmission. This central electronic data unit is configured to collect and / or process the measurement data from the electronic data acquisition units and / or make it available for user readout. The measurement data may already be pre-processed by the electronic data acquisition units and, for example, further processed by the central electronic data unit. In particular, the electronic data acquisition units and / or the central electronic data unit may be configured to determine the wall thickness of the heat transfer pipe measured by the respective ultrasonic sensor, specifically its wall thickness, from the measurement data.The electronic data acquisition units can be connected to the central electronic data unit for data transmission via data transmission lines, particularly in the form of a data bus. This allows for a compact design with minimal potential for interference with the measurement data, especially due to the high-pressure and / or high-temperature conditions in the heat exchanger. The central electronic data unit typically includes a microcontroller or can be a computer. Preferably, the heat exchanger has one or more central electronic data units.

[0043] The heat exchanger is typically designed for an operating pressure greater than 30 bar, particularly between 30 bar and 200 bar, preferably around 180 bar, and / or an operating temperature greater than 80°C, particularly between 80°C and 300°C, preferably around 230°C, or is operated accordingly. It is advantageous if the respective ultrasonic sensor is designed for use at such an operating pressure and / or temperature, or has such an operating pressure and / or temperature. The operating pressure and / or temperature usually refer to the first fluid and / or second fluid. Preferably, the second fluid has such an operating pressure and / or temperature during operation of the heat exchanger. Typically, the respective ultrasonic sensor is located within the second fluid during operation of the heat exchanger.Accordingly, it is advantageous if the respective ultrasonic sensor is designed for an operating pressure corresponding to the operating pressure or an operating temperature corresponding to the operating pressure of the second fluid.

[0044] The respective ultrasonic sensor is typically arranged on the wall of the heat transfer tube, in particular in contact with the tube wall. Usually, one ultrasonic sensor is arranged on each of several of the heat transfer tubes of the heat exchanger. It is also possible for several ultrasonic sensors to be arranged on several of the heat transfer tubes. The heat transfer tubes are generally made of metal, in particular an iron alloy, preferably a steel alloy.

[0045] Typically, the electronic data acquisition unit is located outside the first and second fluids, or outside the heat transfer chamber of the heat exchanger, in which heat is transferred between the first and second fluids via the heat transfer tubes during operation. The heat transfer chamber can be the fluid chamber itself or it can enclose the fluid chamber.

[0046] It is advantageous if the wall thickness of a heat transfer tube can be determined in this way 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 with a heat exchanger according to this document.

[0047] The further objective is achieved by a method of the type mentioned above for operating a heat exchanger, in which an ultrasonic sensor is arranged on one or more heat transfer tubes of the heat exchanger, through which a first fluid is transported to transfer heat between the first fluid and a second fluid, at an operating pressure of more than 30 bar and / or an operating temperature of more than 80°C, wherein the wall thickness of the respective heat transfer tube is determined in situ using the respective ultrasonic sensor, and wherein measurement data from the respective ultrasonic sensor is transmitted to an electronic data acquisition unit during operation of the heat exchanger. The method can be implemented, in particular, with a heat exchanger as described above.The pipe wall thickness of a heat transfer pipe typically refers to the distance, particularly the radial distance, between an inner surface and an outer surface of the pipe wall. The second fluid is usually located outside the heat transfer pipes, so heat is transferred between the first and second fluids through the pipe walls.

[0048] It is understood that the method for operating a heat exchanger can be designed according to the characteristics and effects described in this document, particularly those relating to a heat exchanger. The same applies to the heat exchanger with regard to the method.

[0049] It is particularly advantageous if the process for operating the heat exchanger is used for urea synthesis. The heat exchanger, especially for urea synthesis, can be designed as a stripper for stripping, typically involving contact between a liquid phase and a gas phase with opposing flow directions, usually within the heat transfer tubes. It is advantageous if a first medium flows through the respective heat transfer tube in one direction and a second medium flows through it in the opposite direction to react with each other, with one medium typically being liquid and the other gaseous. This usually takes place within the fluid chamber or fluid chamber cavity. The first fluid can be formed from or composed of the first and second media.It is advantageous if the heat transfer tubes or the flow direction of the first fluid through the heat transfer tubes are oriented essentially vertically, particularly if the heat exchanger is a stripper. The heat exchanger or stripper typically has a plurality of heat transfer tubes, in particular more than 10, preferably more than 50, particularly preferably more than 100, and most preferably more than 1000.

[0050] Typically, a heat exchanger, especially a stripper, has a first inlet through which the first medium can be fed into the heat transfer tubes, and a second inlet through which the second medium can be fed into the heat transfer tubes. This allows the media to flow through the heat transfer tubes in opposite directions within the fluid chamber or fluid chamber cavity, reacting with each other. The first and second inlets are usually connected to the heat transfer tubes at opposite ends of the fluid chamber cavity. The heat exchanger typically has at least one outlet for removing the product formed by the reaction between the first and second media from the heat transfer tubes.Practically speaking, the heat exchanger can have a first outlet through which a first product can be discharged from the heat transfer tubes, and a second outlet through which a second product can be discharged from the heat transfer tubes, with the outlets being fluid-conductingly connected to the heat transfer tubes at different ends with respect to the fluid chamber cavity. The first and second products are usually formed by the reaction between the first and second media. This is particularly true if the heat exchanger is designed as a stripper.

[0051] For urea synthesis, the first medium typically consists of, in particular, urea, ammonium carbamate, and ammonia, and the second medium consists of, in particular, gaseous carbon dioxide (CO₂). In this way, urea, especially of high purity, can be separated as the product, particularly the first product, which is usually discharged from the heat transfer tube at one end or via the first outlet. Advantageously, the process gas formed, generally gaseous ammonia (NH₃) and / or gaseous carbon dioxide (CO₂), can usually be discharged from the heat transfer tube at another end or via the second outlet. The second fluid can consist of, in particular, liquid and / or gaseous water. The stripper can be designed and operated as described in this document, particularly in relation to the heat exchanger.

[0052] It is advantageous if the respective ultrasonic sensor is operated at a frequency, particularly a center frequency, of more than 10 MHz, and especially between 10 MHz and 30 MHz, and in particular if ultrasonic signals at a corresponding frequency are emitted by the respective ultrasonic sensor for determining the pipe wall thickness. Preferably, the frequency, particularly the center frequency, is approximately 15 MHz.

[0053] It is advantageous to use the thickness of the feed line of at least one of the ultrasonic sensors as a reference length for temperature compensation of the ultrasonic signal's velocity, and / or to determine the temperature using at least one thermocouple. Since the feed line has a known thickness, determining its thickness via ultrasonic measurement, particularly using the measurement signals from the respective ultrasonic sensor, allows for the consideration and, in particular, the determination of the ultrasonic signal's velocity. The thickness is typically measured in the direction of transmission. Temperature compensation can be conveniently performed with each measurement using the respective ultrasonic sensor. This ensures high measurement accuracy.Temperature compensation can be taken into account when determining, in particular calculating, the pipe wall thickness from measurement data obtained with the ultrasonic sensors.

[0054] Advantageously, the heat exchanger can have one or more thermocouples, particularly those mentioned above, configured to measure temperature in the vicinity of the ultrasonic sensors. For example, the thermocouple can be located in the fluid chamber, on, and especially within, one of the heat transfer tubes, or on the ultrasonic sensor. It is advantageous if the thermocouple is connected to the data acquisition unit for data transmission. This can be implemented via data cables. The data acquisition unit can have one or more hardware interfaces for connecting a data cable. Advantageously, the data cable can run within a protective tube, particularly one configured as described above. The protective tube can extend to the thermocouple. Data cables and signal lines can run within a common protective tube.

[0055] The pipe wall thickness is typically determined using the time-of-flight method with the respective ultrasonic sensor. An ultrasonic signal is usually emitted by the sensor, and the reflected ultrasonic signals are then detected. These reflected ultrasonic signals are generally formed by the reflection of the emitted ultrasonic signal at interfaces. The interface can be, for example, the outer and / or inner surface of a heat transfer pipe wall. By determining the time intervals between the emitted ultrasonic signal and the reflected ultrasonic signals, and / or between the reflected ultrasonic signals themselves, the thickness of the pipe wall into which the ultrasonic signal was introduced can be determined. The ultrasonic signal is usually an ultrasonic wave pulse. Typically, a sensor is located at the end of the supply section or...The system detects an ultrasonic signal reflected from an outer surface of the pipe wall, an ultrasonic signal reflected from an inner surface of the pipe wall, and typically a sequence of reflected ultrasonic pulses corresponding to multiple reflections between the inner and outer surfaces of the pipe wall. The time interval between the detected reflected ultrasonic pulses of the multiple reflections usually corresponds to twice the pipe wall thickness. A transmission time of the ultrasonic signal, an ultrasonic signal reflected from the outer surface of the pipe wall, and / or one or more ultrasonic signals reflected from the inner surface of the pipe wall can be used as time markers to determine the respective pipe wall thickness by comparing these time markers. Taking into account the speed of sound, or...The pipe wall thickness can be determined from the propagation speed of the ultrasound signal.

[0056] Further features, advantages, and effects of the invention will become apparent from the following description of an exemplary embodiment. The drawings referred to therein show: Fig. 1 a schematic representation of a heat exchanger; Fig. 2 a schematic representation of an ultrasonic sensor in a cross-section; Fig. 3 a schematic representation of another heat exchanger, which is designed as a stripper; Fig. 4 A schematic representation of another ultrasonic sensor in a cross-section.

[0057] In Fig. 1 A heat exchanger 1 is schematically depicted, wherein the heat exchanger 1 has several heat transfer tubes 3 and a fluid chamber 4. The heat transfer tubes 3 extend through the fluid chamber 4 to convey a first fluid F1 through the heat transfer tubes 3 during operation of the heat exchanger 1, and a second fluid F2 through the fluid chamber 4 surrounding the heat transfer tubes. Heat is thus 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 walls and the heat transfer tubes 3 to contain the second fluid F2 and through which the second fluid F2 is passed.Fluid chamber 4 has a fluid chamber inlet 6 for supplying the second fluid F2 into fluid chamber 4, in particular the fluid chamber cavity 5, and a fluid chamber outlet 7 for discharging the fluid from fluid chamber 4, in particular the fluid chamber cavity 5. The second fluid F2 typically has a pressure of more than 30 bar, in particular between 30 bar and 200 bar, and / or a temperature of more than 80°C, in particular between 80°C and 300°C. The heat transfer tubes 3 are typically spaced apart and routed through fluid chamber 4 so that the second fluid F2 can flow between the heat transfer tubes 3. The first fluid F1 and / or second fluid F2 can be, for example, liquid and / or gaseous water. The heat exchanger 1 can be designed as a stripper.The heat exchanger 1, in particular stripper, is often oriented such that a longitudinal extension of the heat transfer tubes 3 is essentially vertically oriented.

[0058] Ultrasonic sensors 2 are arranged on several of the heat transfer tubes 3 to determine the wall thickness of each heat transfer tube 3 in situ and in operando, i.e., during operation of the heat exchanger 1. Each ultrasonic sensor 2 is located on the outside of the heat transfer tube 3 within the fluid chamber 4. To withstand high temperatures and / or high pressures in the heat exchanger 1, the ultrasonic sensors 2 are designed for an operating pressure of more than 30 bar and / or an operating temperature of more than 80°C. In particular, the ultrasonic sensors 2 are designed to withstand the aforementioned pressure and / or temperature of the second fluid F2 and / or have a corresponding operating pressure and / or temperature.Each ultrasonic sensor 2 is connected via a signal line 8 to an electronic data acquisition unit 9 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 located outside the fluid chamber 4 to prevent it from being affected by the high temperature or pressure in the heat exchanger 1. The signal line 8 is typically a coaxial cable to ensure interference-free data transmission. The fluid chamber 4 has a signal line feedthrough 10 through which the signal lines 8 exit the fluid chamber 4. The signal line feedthrough 10 is typically designed to be fluid-tight from the fluid chamber cavity 5.

[0059] To protect the respective signal line 8 from the pressure and temperature in the fluid chamber 4, in particular from the second fluid F2, the respective signal line 8 runs inside a protective tube 11 in the fluid chamber 4, as shown in Fig. 2 The protective tube 11 extends from the respective ultrasonic sensor 2 to the signal cable feedthrough 10. Typically, the protective tube 11 is fluid-tightly connected to the respective ultrasonic sensor 2 on one side, preferably by welding, and fluid-tightly connected to the signal cable feedthrough 10 on the other side, preferably by means of a wedge bolt connection. In this way, the protective tube 11 forms a volume separate from the fluid chamber cavity 5, preferably with a different atmosphere, in which the signal cable 8 runs. The protective tube 11 is preferably made of steel, in particular austenitic steel.

[0060] To keep the signal line lengths 8 short, it is advantageous to have several electronic data acquisition units 9, with different ultrasonic sensors 2 being connected to different electronic data acquisition units 9 for data transmission. This is in Fig. 1 This is represented by a further electronic data acquisition unit 9, shown in dashed lines. The further electronic data acquisition unit 9 can be connected, analogously as described, to further ultrasonic sensors 2 arranged on the heat transfer pipes 3 for data transmission.

[0061] Typically, an electronic data center unit 12 is provided, to which the electronic data acquisition unit 9 or units 9 are connected for data transmission. The electronic data center unit 12 is configured to collect the measurement data from the electronic data acquisition units 9 and preferably make it available for readout by a user. The electronic data acquisition units 9 are typically connected to the electronic data center unit 12 for data transmission via an electrical cable connection 13, in particular a data bus.

[0062] The heat transfer tubes 3 typically extend between a first tube plate 14 and a second tube plate 15, the tube plates being formed as part of the fluid chamber walls of the fluid chamber 4 or defining the fluid chamber cavity 5. Each heat transfer tube 3 passes through the first tube plate 14 and the second tube plate 15. The fluid chamber 4 has several stabilizing elements 16, usually referred to as baffles, which connect several of the heat transfer tubes 3 to stabilize them during operation of the heat exchanger 1. Advantageously, several stabilizing elements 16 can be spaced apart along the longitudinal extent of the heat transfer tubes 3, and these stabilizing elements 16 are oriented transversely, and in particular orthogonally, to the longitudinal extent of the heat transfer tubes 3.It is advantageous if the respective stabilizing element 16, or a fluid guiding surface formed by it, closes off a gap between several of the heat transfer tubes 3 in order to prevent the flow of the second fluid F2 through the gap. Frequently, the respective stabilizing element 16, or the fluid guiding surface, closes off a large portion of the gaps between the heat transfer tubes 3 in a cross-section through the fluid chamber 4, thus preventing the flow of the second fluid F2.

[0063] It is advantageous if the respective ultrasonic sensor 2 is arranged in an arrangement area on the respective heat transfer tube 3, which arrangement area lies in the first third of a longitudinal extension of the heat transfer tube 3 within the fluid chamber 4 or the fluid chamber cavity 5 in the direction of flow of the first fluid F1 through the heat transfer tube 3. Preferably, the ultrasonic sensor 2 is located in the direction of flow of the first fluid F1 through the heat transfer tube 3 between the first tube plate 14 and a first of the stabilizing elements 16.

[0064] Fig. 2 Figure 1 shows a schematic representation of an ultrasonic sensor 2. In particular, the ultrasonic sensors 2 are of the Fig. 1 The ultrasonic sensor 2 comprises a damping element 17, a piezoelectric crystal 18, and a pre-transmitting section 19. In a transmission direction in which an ultrasonic signal can be emitted by the ultrasonic sensor 2, the piezoelectric crystal 18 is arranged between the damping element 17 and the pre-transmitting section 19. The damping element 17 is configured to dampen mechanical vibrations of the piezoelectric crystal 18. The pre-transmitting section 19 is configured to transmit an ultrasonic signal generated by the piezoelectric crystal 18 in the transmission direction, such that the ultrasonic signal remains within the pre-transmitting section 19 during the switching between a transmission mode and a reception mode of the ultrasonic sensor 2. In transmission mode, an ultrasonic signal can be emitted by the ultrasonic sensor 2, in particular by the piezoelectric crystal 18.In receive mode, an ultrasonic signal can be detected using the ultrasonic sensor 2, in particular piezoelectric crystal 18.

[0065] The damping element 17 is electrically conductive and is electrically connected upstream of the damping element 17 in the transmission direction S to a control electrode 20 such that the piezoelectric element can be electrically controlled through the damping element 17 via the control electrode 20. The control electrode 20 is typically an electrical cathode. The control electrode 20 is electrically connected to a signal line 8 for controlling the ultrasonic sensor 2 or for data transmission. The signal line 8 is connected, as described above, to an electronic data acquisition unit 9 for data transmission. The signal line 8 is typically a coaxial cable.

[0066] The ultrasonic sensor 2 has a spring element 21 with which the control electrode 20, the damping element 17, the piezoelectric crystal 18, and the pre-section body 19 are pressed together by the spring force of the spring element 21. In this way, a robust connection can be achieved, particularly without adhesive. The spring element 21 can advantageously be implemented with several disc springs arranged in series. The ultrasonic sensor 2 expediently has a sensor housing 22, which forms an outer casing of the ultrasonic sensor 2. The sensor housing 22 has an outlet opening 23 for the ultrasonic signal, wherein the outlet opening 23 is sealed by the pre-section body 19, in particular in a fluid-tight manner. The pre-section body 19 is usually force-fitted to the sensor housing 22, for example, by a screw connection.

[0067] Between the sensor housing 22 and each of the damping element 17 and the control electrode 20, an electrical insulating element 24, preferably made of zirconium dioxide, is arranged, which usually surrounds the damping element 17 or the control electrode completely in order to prevent electrical contact with the sensor housing 22.

[0068] 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, especially as described above, runs inside a protective tube 11. The protective tube 11 is fluid-tightly connected to the sensor housing 22, preferably by means of a welded connection, so that the protective tube 11 and the sensor housing 22 define a volume separate 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.

[0069] The piezoelectric crystal 18 can be made of lead zirconate titanate ceramic (PZT ceramic). The damping element 17 can be made of titanium sinter, preferably with an average pore size between 1 µm and 10 µm. The feed section body 19 can be made of steel, in particular austenitic steel, with a thickness in the transmitting direction S between 2 mm and 10 mm. The control electrode 20 can be made of copper, in particular copper. The heat transfer tubes 3 are usually made of steel, in particular austenitic steel. The ultrasonic sensor 2 is preferably configured to emit an ultrasonic signal, in particular an ultrasonic wave, with a center frequency of approximately 15 MHz.

[0070] Fig. 3 Figure 1 shows a schematic representation of another heat exchanger 1, which is designed as a stripper for stripping. Such a heat exchanger 1 is typically used for urea synthesis. The heat exchanger 1 can be configured according to the explanations for heat exchanger 1 in Figure 1. Fig. 1 trained and in particular ultrasonic sensors 2 as to Fig. 2 and / or Fig. 4 The heat exchanger 1 is typically oriented such that the longitudinal extension of the heat transfer tubes 3 is substantially vertical. For urea synthesis, the first fluid F1 is composed of a first medium M1 and a second medium M2, with the first medium M1 and second medium M2 flowing in opposite directions through the respective heat transfer tube 3 within the fluid chamber 4 or the fluid chamber cavity 5. The first medium M1 is typically composed of, in particular, urea, ammonium carbamate, and ammonia, and the second medium M2 is typically composed of, in particular, gaseous carbon dioxide (CO2). The first medium is usually liquid. The heat exchanger 1, or stripper, typically has a plurality of heat transfer tubes 3, in particular more than 10, preferably more than 50, particularly preferably more than 100, and most preferably more than 1000.The heat exchanger 1 is typically oriented such that the first tube plate 14 is located vertically above the second tube plate 15. Preferably, the respective ultrasonic sensor 2 is located between the first tube plate 14 and a first of the stabilizing elements 16.

[0071] The heat exchanger 1 has a first inlet 25, through which the first medium M1 can be supplied to the heat transfer tubes 3, and a second inlet 27, through which the second medium M2 can be supplied to the heat transfer tubes, so that within the fluid chamber 4 or the fluid chamber cavity 5, the media M1 and M2 flow through the heat transfer tubes 3 in opposite directions to react with each other. The first inlet 25 and the second inlet 27 are fluid-conductingly connected to the heat transfer tubes 3 at opposite ends with respect to the fluid chamber cavity 5. For this purpose, the first inlet 25 and the second inlet 27 can each be fluid-conductingly connected to a fluid distribution chamber, with the ends of the heat transfer tubes 3 being fluid-conductingly connected to the fluid distribution chamber, so that via the first inlet 25 or the second inlet 27, the fluids M1 and M2 flow through the first inlet 25 and the second inlet 27, respectively, to the heat transfer tubes 3.The first medium M1 or second medium M2 supplied to the respective fluid distribution chamber via the second inlet 27 is distributed onto the heat transfer pipes 3 and introduced into the heat transfer pipes 3. The heat exchanger 1 has a first outlet 26, through which a first product Z1 can be discharged from the heat transfer tubes 3, and a second outlet 28, through which a second product Z2 can be discharged from the heat transfer tubes 3, wherein the first outlet 26 and second outlet 28 are fluid-conductingly connected to the heat transfer tubes 3 at different ends of the heat transfer tubes 3 with respect to the fluid chamber cavity 5, preferably by the first outlet 26 and second outlet 28 each being fluid-conductingly connected to one of the fluid distribution chambers, so that a first product Z1 or second product Z2 exiting the heat transfer tubes 3 can be discharged via the respective outlet 26, 28.The first product Z1 is usually urea, especially in high purity. The second product Z2 is usually gaseous ammonia (NH3) and / or gaseous carbon dioxide (CO2). The second fluid F2 is generally formed with, especially from, liquid and / or gaseous water.

[0072] In Fig. 4 Figure 1 shows a schematic cross-sectional view of another ultrasonic sensor 2. Ultrasonic sensor 2 can have the same characteristics and effects as ultrasonic sensor 2 of the... Fig. 2 exhibit. The ultrasonic sensor 2 can be used with a heat exchanger 1 of the Fig. 1 and Fig. 3 be used. The ultrasonic sensor 2 of the Fig. 4 Its structure essentially corresponds to that of the ultrasonic sensor 2 of the Fig. 2 In particular, the ultrasonic sensor 2 has a spring element 21 with which the control electrode 20, the damping element 17, the piezoelectric crystal 18, and the pre-tracking element 19 are pressed together by means of the spring force of the spring element 21. The spring element 21 is arranged between the control electrode and a counter bearing 31, which may be formed by a ring nut. To establish an electrical connection between the signal line 8 and the control electrode 20, these are positively connected to each other by a clamping element 30. In contrast to the ultrasonic sensor 2 of the Fig. 2 The ultrasonic sensor 2 has a connection nozzle 29, in particular a tubular one, for the positive-locking reception of the protective tube 11, wherein the protective tube 11 is fluid-tightly inserted into the connection nozzle 29. In this way, a particularly robust connection of the signal line 8 to the ultrasonic sensor 2 can be implemented, for example for use at particularly high pressure in the fluid chamber cavity 5 or of the second fluid F2. The connection nozzle 29 can be made of steel, in particular austenitic steel. Advantageously, the ultrasonic sensor can also be made of Fig. 2 have such a connecting piece 29.

[0073] If an ultrasonic sensor 2 is arranged on one or more of the heat transfer tubes 3 of the heat exchanger 1, and this sensor is 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, and wherein the ultrasonic sensor 2 is designed 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 tubes 3 can be practically determined in situ and preferably in operando. This enables optimized operational capability of the heat exchanger 1.In particular, if a signal line 8 for transmitting the measurement signals from the respective ultrasonic sensor 2 to the electronic data acquisition unit 9 runs within the second fluid F2 in a protective tube 11 and / or if the damping element 17, the piezoelectric crystal 18 and the pre-section body 19 are pressed together in the ultrasonic sensor 2 by means of a spring force of a spring element 21, a particularly high robustness of the in-situ determination and usually in-operando determination of the pipe wall thicknesses can be achieved.

Claims

1. A heat exchanger (1), in particular a high-pressure heat exchanger for urea synthesis, having several heat transfer pipes (3) for transporting a first fluid (F1), so as to transfer heat between the first fluid (F1) and a second fluid (F2) via the heat transfer pipes (3), wherein a respective ultrasonic sensor (2) for the in-situ determination of pipe wall thicknesses of the heat transfer pipes (3) is arranged on one or several of the heat transfer pipes (3), wherein the respective ultrasonic sensor (2) 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 (2) is connected with an electronic data acquisition unit (9) for data transmission, so as to transmit measured data to the electronic data acquisition unit (9) during operation of the heat exchanger (1), characterized in that a transmission direction of an ultrasonic signal that can be transmitted from the respective ultrasonic sensor (2) is transverse, in particular essentially orthogonal, to a longitudinal extension of the heat transfer pipe (3).

2. The heat exchanger (1) according to claim 1, characterized in that the heat exchanger (1) has a fluid chamber (4) for holding the second fluid (F2), wherein the heat transfer pipes (3) run inside of the fluid chamber (4), wherein the data acquisition unit (9) is arranged outside of the fluid chamber (4).

3. The heat exchanger (1) according to claim 1 or 2, characterized in that the respective ultrasonic sensor (2) is connected with the data acquisition unit (9) via a signal cable (8) for data transmission purposes, wherein the signal cable (8) at least sectionally runs inside of a protective pipe (11), preferably made out of metal, so as to protect the signal cable.

4. The heat exchanger (1) according to claim 2 and 3, characterized in that on the one hand, the protective pipe (11) is welded with the sensor housing (22) of the respective ultrasonic sensor (2), and / or on the other hand, that the protective pipe (11) adjoins a signal cable feed-through (10), preferably by means of a wedge screw connection, with which the signal cable (8) is guided through a fluid chamber wall of the fluid chamber (4) .

5. The heat exchanger (1) according to claim 3 or 4, characterized in that the protective pipe (11) defines a volume separated from the first fluid (F1) and second fluid (F2) during operation, inside of which the signal cable runs.

6. The heat exchanger (1) according to one of claims 1 to 5, characterized in that the respective ultrasonic sensor (2) comprises a damping element (17), a piezo crystal (18) and a lead pipe body (19), which are pressed against each other by means of a spring element (21) .

7. The heat exchanger (1) according to claim 6, characterized in that the spring element (21) is comprised of an arrangement of several springs, preferably in series.

8. The heat exchanger (1) according to claim 6 or 7, characterized in that the damping element (17) is arranged between an electric control electrode and the piezo crystal (18) in the respective ultrasonic sensor (2), wherein the damping element (17) is electrically conductive in design, so that electric control of the piezo crystal (18) can be implemented via the control electrode through the damping element (17).

9. The heat exchanger (1) according to one of claims 1 to 8, characterized in that the respective ultrasonic sensor (2) has one or several electric insulation elements for electric insulation between a sensor housing (22) of the ultrasonic sensor (2) and a respective piezo crystal (18) and / or a damping element (17) and / or an electrode of the ultrasonic sensor, preferably made with zirconium dioxide.

10. The heat exchanger (1) according to one of claims 1 to 9, characterized in that a coupling means made with silver, in particular a silver film, or no coupling means are arranged between the respective ultrasonic sensor (2) and the heat transfer pipe (3).

11. The heat exchanger (1) according to one of claims 1 to 10, characterized in that the respective ultrasonic sensor (2) is connected by force with the respective heat transfer pipe (3), preferably with a clamping connection.

12. The heat exchanger (1) according to one of claims 1 to 11, characterized in that several ultrasonic sensors (2) for data transmission are connected with the same electronic data acquisition unit (9), so as to transmit measured data to the data acquisition unit (9) during operation of the heat exchanger (1).

13. A method for operating a heat exchanger (1), in particular a heat exchanger (1) according to one of claims 1 to 12, characterized in that, at an operating pressure of more than 30 bar and / or an operating temperature of more than 80°C, a respective ultrasonic sensor (2) is arranged on one or several heat transfer pipes (3), with which a first fluid (F1) is transported, so as to transfer heat between the first fluid (F1) and a second fluid (F2) via the heat transfer pipes (3), so that a transmission direction of an ultrasonic signal transmittable from the respective ultrasonic sensor (2) is transverse, in particular essentially orthogonal, to a longitudinal extension of the heat transfer pipe (3), wherein the respective ultrasonic sensor (2) is used for the in-situ determination of a pipe wall thickness of the respective heat transfer pipe (3), wherein measured data are transmitted from the respective ultrasonic sensor (2) to an electronic data acquisition unit (9) during operation of the heat exchanger (1).

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

15. The method according to claim 13 or 14, characterized in that, in order to compensate for the temperature of an ultrasonic velocity of the ultrasonic signal, a thickness of the lead pipe body (19) of at least one of the ultrasonic sensors (2) is used as a reference length and / or a temperature is determined with at least one thermocouple.