Temperature monitoring in electric heaters

Abstract

An electric heater unit (150) is provided that includes at least one heating rod (55) having an electric heating element (60), an optical fiber cable (40), a laser source (10), and an optical sensor (20). The optical fiber cable (40) is attached to a surface of the at least one heating rod (55) and along a length of the at least one heating rod, the optical fiber cable (40) including a plurality of measurement points distributed over a length of the optical fiber cable (40). The laser source (10) and the optical sensor (20) are each coupled to an end of the optical fiber cable (40) for transmitting a laser signal between the laser source and the optical sensor. A controller (30) is operatively coupled with the laser source (10) and the optical sensor (20) and is configured to determine a temperature profile along the length of the heating rod (55) based on the laser signal received by the optical sensor (20).

Description

Technical Field

[0001] The present invention relates to an electric heater unit, which includes at least one elongated electric heating element and a temperature sensor for monitoring the temperature of the elongated electric heating element. Background Technology

[0002] Electric process heaters are used in numerous industries, including food and beverage, pharmaceuticals, and oil and gas, to effectively heat liquid or gaseous fluids. An electric process heater typically comprises a bundle of heating rods that uses electrical energy to heat the fluid flowing around them. The heating rods typically include an electric heating element enclosed in a metal sheath that electrically insulates the heating element from the fluid. In use, the metal sheath is heated by the electric heating element and cooled by the flowing fluid.

[0003] Because the fluid flow through an electric process heater will never be perfectly uniform, temperature differences will indeed occur. Localized overheating can lead to thermal degradation of temperature-sensitive process fluids and / or uneven wear of the heating rods. Tube-wall thermocouples are currently used to monitor the temperature of the heating rods at different locations within the electric heater. However, the wiring and space required for installing thermocouples make it difficult to install and operate a large number of such temperature sensors. Consequently, hot spots formed at points where thermocouples are not installed remain unnoticed, leading to potential heating rod failure and degradation of the heated fluid.

[0004] One object of the present invention is to overcome at least some of the disadvantages of known electric process heaters. Summary of the Invention

[0005] In view of this objective and according to one aspect of the invention, an electric heater unit is provided, comprising at least one heating rod, an optical fiber cable, a laser source, a light sensor, and a controller. The at least one heating rod includes an electric heating element. The optical fiber cable is attached to the surface of the at least one heating rod and extends along the length of the at least one heating rod. The optical fiber cable includes a plurality of measuring points distributed along its length. The laser source is coupled to one end of the optical fiber cable for transmitting a laser signal through the optical fiber cable. The light sensor is coupled to one end of the optical fiber cable for receiving the laser signal from the optical fiber cable. Typically, the laser source and the light sensor are separate units coupled to opposite ends of the optical fiber cable. In other embodiments, the laser source and the light sensor are combined in a single unit having independent connection points for each end of the optical fiber cable. Preferably, multiple optical fibers attached to different heating rods share a single laser source and / or light sensor. In some embodiments, the laser source and the light sensor are jointly coupled to one end of the optical fiber cable, and light from the laser source is reflected at the opposite distal end of the optical fiber cable, then propagates back through the optical fiber cable and is received by the light sensor.

[0006] The controller is operatively coupled to the laser source and the light sensor and is configured to determine the temperature distribution along the length of the heating rod based on the laser signal received by the light sensor. The temperature distribution can be obtained, for example, from spectral analysis of the light received by the light sensor.

[0007] Using fiber optic cables for temperature measurement allows for temperature measurements at multiple points along the length of the heating rod by installing only a single fiber optic cable. A single laser source and a single photodetector can be connected to multiple fiber optic cables and used to determine the temperature at each of the measurement points. Therefore, more temperature measurements can be taken compared to thermocouples previously used. This allows for enhanced monitoring of the heating rod's temperature and significantly reduces the risk of undetected localized hotspots, thus protecting both the heating rod and the process fluid.

[0008] The heating rod may include a thermally conductive sheath to which an optical fiber cable is attached. The sheath is preferably made of a metal capable of withstanding temperature variations that may occur within the electric heater unit and in the fluid flowing through it. A key function of the thermally conductive sheath is to electrically insulate the electric heating element from the process fluid and to effectively transfer the heat generated by the electric heating element to the fluid flowing through the heating rod.

[0009] Similarly, the fiber optic cable may be at least partially enclosed in a protective tube. The protective tube may be made of metal (possibly the same metal used for the thermally conductive sheath). The protective tube protects the fiber optic cable from direct contact with process fluids and allows limited movement of the fiber optic cable relative to the heating rod as the heating rod expands or contracts due to temperature changes.

[0010] In a preferred embodiment, the controller is further configured to control the electric heating element based on the determined temperature distribution. Improved temperature monitoring, achieved through the use of fiber optic cables, allows the controller to react more quickly to small localized temperature rises. Therefore, the controller achieves enhanced temperature control within the heating rod and throughout the heated medium. This enhanced temperature control makes the electric heater unit highly suitable for heating thermistor fluids. Furthermore, reduced wear due to undetected localized hot spots allows for the use of lower-cost materials, which can help reduce the cost of the electric heater unit.

[0011] Typically, at least one heating rod is part of a bundle of substantially parallel heating rods, at least a subset of which have corresponding fiber optic cables attached to the surfaces of the heating rods and along their length. Each corresponding fiber optic cable has multiple measurement points distributed along its length and coupled to a laser source and a photosensitive sensor. A controller is configured to determine a corresponding temperature distribution along the length of each heating rod, each heating rod having one of the fiber optic cables attached to its surface. The use of fiber optic cables allows for easy determination of an accurate and detailed temperature distribution along the entire length of the heating rod. To obtain a useful and reliable temperature distribution also across the entire diameter of the bundle, it may not be necessary to provide fiber optic cables for each individual heating rod.

[0012] Preferably, the controller is further configured to independently control the electric heating element of each individual heating rod according to the corresponding temperature distribution. If the electric heating element is configured to allow independent control of different sections of the heating rod, precise control in all three dimensions will even be possible.

[0013] For example, the measurement points may include fiber Bragg gratings or GaAs crystals to enable temperature measurement by analyzing the refraction of the laser at each individual measurement point.

[0014] The invention described herein primarily provides for use in an electric process heater comprising a housing having a fluid inlet and a fluid outlet, wherein at least one heating rod is positioned within the housing and arranged to heat a process fluid flowing from the fluid inlet through the housing and toward the fluid outlet. However, the invention may also be useful in other devices and systems in which elongated heating elements are used to heat fluids or other media. Attached Figure Description

[0015] Figure 1 An electric process heater is shown, in which an electric heater unit according to the invention can be advantageously used.

[0016] Figure 2 Schematic illustration of the use of Figure 1 The electric heater unit in the electric process heater.

[0017] Figure 3 Schematic illustration of the use of Figure 2 The heating rod in the electric heater unit.

[0018] Figure 4 It shows Figure 2 The cross-section of the electric heater unit.

[0019] These accompanying drawings depict one or more specific embodiments of the teachings by way of example only and not limitation. In the drawings, similar reference numerals denote the same or similar elements.

[0020] Detailed description of the attached figures

[0021] Figure 1 An electric process heater 100 is shown, in which an electric heater unit 150 according to the invention can be advantageously used. The electric process heater 100 includes an inlet 110, a heater compartment or housing 120, and an outlet 130. In use, the electric process heater 100 will be integrated into a larger industrial installation using process fluids. The process fluid enters the heater compartment 120 through the inlet 110. Inside the heater compartment 120, in Figure 2 The electric heater unit 150, shown in more detail, brings the process fluid to the desired temperature, after which the process fluid exits the heater compartment 120 through outlet 130.

[0022] In many industries, such as food and beverage, pharmaceuticals, and oil and gas, process fluids can be heat-sensitive, and precise control of heating processes is crucial. For example, hydrocarbons processed in the oil and gas industry should not crack in the electric process heater 100, but cracking may occur if the membrane temperature is exceeded. This invention provides a novel method for monitoring the heating of process fluids inside the electric process heater 100. By providing a simple method for accurately monitoring the temperature throughout the entire heater compartment 120, this invention offers a more efficient and accurate electric process heater that can be provided at a lower cost.

[0023] Figure 2 Schematic illustration of the use of Figure 1 The electric heater unit 150 in the electric process heater 100. Figure 3 Schematic illustration of the use of Figure 2 The electric heater unit 150 includes at least one such heating rod 55. Preferably, a plurality of such heating rods 55 are provided and arranged in a bundle 50 heating rods 55, which together span a large portion of the diameter of the heater compartment 120. As the process fluid flows from the inlet 110 to the outlet 130 of the electric process heater 100, the bundle 50 heating rods 55 bring the process fluid to the desired temperature.

[0024] The temperature of the electric heating element 60 can be controlled by changing the current flowing through it. The heating rod 55 includes the electric heating element 60, which is controlled by the controller 30. The heating rod 55 may also include a thermally conductive sheath, preferably made of a metal capable of withstanding temperature variations that may occur in the electric heater unit 150 and in the fluid flowing through it. An important function of the thermally conductive sheath is to electrically insulate the electric heating element 60 from the process fluid and to effectively transfer the heat generated by the electric heating element 60 to the fluid flowing through the heating rod 55.

[0025] A temperature monitoring system is provided to monitor the heating process and prevent localized overheating of the heating rod 55 and the process fluid. In this embodiment, temperature monitoring is achieved by measuring the temperature at various points along the length of one or more of the heating rods 55 using fiber optic cable 40, laser source 10, optical sensor 20, and controller 30.

[0026] Similar to the electric heating element 60, the fiber optic cable 40 may be at least partially enclosed in a protective tube. The protective tube may be made of metal (possibly the same metal used for the thermally conductive sheath of the electric heating element 60). The protective tube protects the fiber optic cable 40 from direct contact with process fluids and allows limited movement of the fiber optic cable 40 relative to the heating rod 55 as the heating rod 55 expands or contracts due to temperature changes.

[0027] For example, the fiber optic cable can be attached to the surface of the heating rod 55 using the clamp 70. If both the electric heating element 60 and the fiber optic cable 40 are enclosed in a metal housing, the two housings can be attached to each other by welding or brazing.

[0028] The fiber optic cable 40 includes multiple measurement points distributed along its length, and therefore also along the length of the heating rod 55. For example, the measurement points may include fiber Bragg gratings or GaAs crystals to enable temperature measurement by analyzing the refraction of the laser at each individual measurement point.

[0029] In this embodiment, a laser source 10 is coupled to a first end of an optical fiber cable 40 for transmitting a laser signal through the cable. An optical sensor 20 is coupled to the other end of the optical fiber cable 40 for receiving the laser signal from the cable. In an alternative embodiment, the laser source 10 and the optical sensor 20 are combined in a single unit having independent connection points for each end of the optical fiber cable 40. Preferably, multiple optical fiber cables 40 attached to different heating rods 55 share a single laser source 10 and / or optical sensor 20. In some embodiments, the laser source 10 and the optical sensor 20 are jointly coupled to one end of the optical fiber cable 40, and light from the laser source 10 is reflected at a relatively distant end of the optical fiber cable 40, then propagates back through the cable and is received by the optical sensor 20.

[0030] The controller 30 is operatively coupled to the laser source 10 and the light sensor 20 and is configured to determine the temperature distribution along the length of the heating rod 55 based on the laser signal received by the light sensor 20. The temperature distribution can be obtained, for example, from spectral analysis of the light received by the light sensor 20.

[0031] Temperature measurement using fiber optic cable 40 allows temperature to be measured at multiple measurement points along the length of heating rod 55 by installing only one fiber optic cable 40. A single laser source 10 and a single photodetector 20 can be connected to multiple fiber optic cables 40 and can be used to determine the temperature at each of the measurement points. Therefore, more temperature measurements can be performed compared to thermocouples previously used. This allows for enhanced monitoring of the temperature of heating rod 55 and significantly reduces the risk of undetected local hot spots, thus protecting both heating rod 55 and process fluids.

[0032] In a preferred embodiment, the controller 30 is further configured to control the electric heating element 60 based on the determined temperature distribution. Improved temperature monitoring, achieved through the use of the fiber optic cable 40, allows the controller 30 to react more quickly to small temperature rises. Therefore, the controller 30 achieves enhanced temperature control within the heating rod 55 and throughout the heated medium. This enhanced temperature control makes the electric heater unit 150 highly suitable for heating heat-sensitive fluids. Furthermore, reduced wear due to undetected localized hot spots allows for the use of lower-cost materials, which can help reduce the cost of the electric heater unit 150.

[0033] Typically, the electric heater unit 150 includes a bundle of substantially parallel heating rods 55. At least a subset of the heating rods 55 have corresponding fiber optic cables 40 attached to the surface of the heating rod and along its length. Each corresponding fiber optic cable 40 has a plurality of measuring points distributed along its length and is coupled to a laser source 10 and a light sensor 20. A controller 30 is configured to determine a corresponding temperature distribution along the length of each heating rod 55, each heating rod having one of the fiber optic cables 40 attached to its surface. The use of fiber optic cables 40 allows for easy determination of an accurate and detailed temperature distribution along the entire length of the heating rod 55.

[0034] To obtain a useful and reliable temperature distribution across the entire diameter of bundle 55, it may not be necessary to provide fiber optic cable 40 for each individual heating rod 55. Figure 4 Provided Figure 2The cross-section of the electric heater unit 150 is shown, along with a bundle 50 of 241 heating rods 55, fifteen of which are equipped with fiber optic cables 40. These fifteen fiber optic cables 40 are sufficient to accurately monitor the temperature distribution of the heating rods across the entire diameter of the bundle 50. More fiber optic cables 40 can be added to further improve the accuracy of the temperature monitoring system. Fewer fiber optic cables 40 can be used to further reduce complexity and cost.

[0035] All individual heating rods 55 or groups of individual heating rods 55 can be controlled in parallel to produce the same amount of heat energy. However, preferably, the controller 30 is configured to independently control the electric heating element 60 of each individual heating rod 55 according to the corresponding temperature distribution of each individual heating rod 55. When the electric heating element 60 is configured to allow independent control of different sections of the heating rod 55, even more precise control in all three dimensions will be possible.

[0036] The invention described herein primarily provides for use in the electric process heater 100 as described above. However, the invention may also be useful in other devices and systems in which elongated heating elements are used to heat fluids or other media. While many possible variations of the electric heater have been described above, it will be apparent to those skilled in the art that additional variations and modifications may be made without departing from the scope of the invention as claimed in the appended claims.

Claims

1. An electric heater unit (150), the electric heater unit comprising: - At least one heating rod (55), said at least one heating rod comprising an electric heating element (60); - Fiber optic cable (40), the fiber optic cable being attached to the surface of the at least one heating rod (55) and along the length of the at least one heating rod, the fiber optic cable (40) including a plurality of measuring points distributed along the length of the fiber optic cable (40); - A laser source (10), which is coupled to the end of the optical fiber cable (40) for transmitting laser signals through the optical fiber cable; - Optical sensor (20), the optical sensor being coupled to the end of the optical fiber cable (40) for receiving the laser signal from the optical fiber cable; and - Controller (30), which is operatively coupled to the laser source (10) and the optical sensor (20) and configured to determine the temperature distribution along the length of the heating rod (55) based on the laser signal received by the optical sensor (20).

2. The electric heater unit (150) according to claim 1, wherein the heating rod (55) further includes a thermally conductive sheath, and wherein the optical fiber cable (40) is attached to the thermally conductive sheath.

3. The electric heater unit (150) according to claim 1 or 2, wherein the optical fiber cable (40) is at least partially enclosed in a protective tube.

4. The electric heater unit (150) according to any of the preceding claims, wherein the controller (30) is further configured to control the electric heating element (60) according to a determined temperature distribution.

5. The electric heater unit (150) according to any of the preceding claims. - wherein the at least one heating rod (55) is part of a bundle (50) of substantially parallel heating rods (55); - At least one subset of the heating rods (55) have corresponding optical fiber cables (40) attached to the surface of the heating rod and along the length of the heating rod, each corresponding optical fiber cable (40) having a plurality of measuring points distributed along the length of the corresponding optical fiber cable. - wherein each of the optical fiber cables (40) is coupled to the laser source (10) and the optical sensor (20); and - wherein the controller (30) is configured to determine a corresponding temperature distribution along the length of each heating rod (55), each heating rod having one of the optical fiber cables (40) attached to the surface of each heating rod.

6. The electric heater unit (150) according to claim 5, wherein the controller (30) is further configured to independently control the electric heating element (60) of each heating rod (55) according to the corresponding temperature distribution.

7. The electric heater unit (150) according to any of the preceding claims, wherein one or more of the measurement points comprise fiber Bragg gratings.

8. The electric heater unit (150) according to any one of the preceding claims, wherein one or more of the measurement points comprise a GaAs crystal.

9. An electric process heater (100) comprising an electric heater unit (150) according to any one of the preceding claims and a housing (120) having a fluid inlet (110) and a fluid outlet (130), wherein at least one heating rod (55) of the electric heater unit (150) is positioned inside the housing (120) and arranged to heat a process fluid flowing from the fluid inlet (110) through the housing (120) and toward the fluid outlet (130).

Images