Temperature monitoring in an electric heater

Abstract

This invention provides an electric heater unit (150) comprising at least one heating rod (55) with an electrical heating element (60), a fibre optic cable (40), a laser source (10), and a light sensor (20). The fibre optic cable (40) is attached to a surface of the at least one heating rod (55) and along a length thereof, the fibre optic cable (40) comprising a plurality of measurement points distributed over a length of the fibre optic cable (40). The laser source (10) and the light sensor (20) are each coupled to an end of the fibre optic cable (40) for sending a laser signal therebetween. A controller (30) is operatively coupled with the laser source (10) and the light sensor (20), and configured to determine a temperature profile along the length of the heating rod (55), based on the laser signal received by the light sensor (20).

Description

[0001] TEMPERATURE MONITORING IN AN ELECTRIC HEATER

[0002] Field of the Invention

[0003] This invention relates to an electric heater unit compris ing at least one elongated electrical heating element and a temperature sensor for monitoring a temperature of the elongated electrical heating element .

[0004] Background of the invention

[0005] In many industries , such as the food and drinks industry, the pharmaceutical industry, and the oil and gas industry, electric proces s heaters are used to efficiently heat liquids or gaseous flowing fluids . The electric proce s s heaters typically comprise a bundle of heating rods that use electrical energy to heat the f luid flowing around them . The heating rods typically comprise an electrical heating element , encapsulated in a metal sheath that electrically insulates the heating element from the fluid . In use , the metal sheath is heated by the electrical heating element and cooled by the pa s sing fluid .

[0006] Because the fluid flow through the electric proces s heater will never be perfectly uniform, temperature difference s do occur . Local exces sive heating may lead to thermal degradation of a temperature-sens itive proce s s fluid and / or uneven wear of the heating rods . Tube s kin thermocouples are currently used to monitor heating rod temperatures at different locations inside the electric heater . However , the required wiring and space needed for the installation of the thermocouples make it difficult to install and operate large numbers of such temperature sensors . Consequently, hot spots developing at point s where no thermocouple s are installed remain unnoticed, leading to potential failure of heating rods and degradation of the fluids being heated.

[0007] It is an aim of the current invention to overcome at least some of the disadvantages of the known electric process heaters.

[0008] Summary of the Invention

[0009] In view of this aim and according to an aspect of the invention, an electric heater unit is provided comprising at least one heating rod, a fibre optic cable, a laser source, a light sensor, and a controller. The at least one heating rod comprises an electrical heating element. The fibre optic cable is attached to a surface of the at least one heating rod and along a length thereof. The fibre optic cable comprises a plurality of measurement points distributed over its length. The laser source is coupled to an end of the fibre optic cable for sending a laser signal therethrough. The light sensor is coupled to an end of the fibre optic cable for receiving the laser signal therefrom. Typically, the laser source and the light sensor will be separate units, coupled to opposing ends of the fibre optic cable. In other embodiments, the laser source and light sensor are combined in a single unit separate connection points for each end of the fibre optic cable. Preferably, multiple fibre optic cables, attached to different heating rods, share a single laser source and / or light sensor. In some embodiments, the laser source and light sensor are together coupled to one end of the fibre optic cable and the light from the laser source is reflected at the opposite far end of the fibre optic cable before travelling back through the fibre optic cable and being received by the light sensor.

[0010] The controller is operatively coupled with the laser source and the light sensor, and configured to determine a temperature profile along the length of the heating rod , based on the la ser signal received by the light sensor . The temperature profile may, for example , be derived from a spectral analysis of the light received by the light sensor .

[0011] The use of fibre optic cables for the temperature measurements allows for the temperature to be measured at multiple measurement points along the length of the heating rod by installing j ust one fibre optic cable . A single laser source and a single light detector can be connected to multiple fibre optic cables and can be used to determine the temperature at each of the mea surement point s . As a re sult , far more temperature mea surements can be made than with the thermocouples that have been used previously . Thi s allows for enhanced monitoring of the temperature of the heating rods and significantly reduces the ris k of local hot spots not being detected, thereby protecting both the heating rods and the proces s fluid .

[0012] The heating rod may comprise a thermally conductive sheath , the fibre optic cable being attached to the thermally conductive sheath . The sheath i s preferably made of some metal that can withstand variations in temperature as may be expected in the electric heater unit and the fluid f lowing therethrough . Important functions of the thermally conductive sheath are electrically insulating the electrical heating element from the proce ss fluid and efficiently relaying the heat produced by the electrical heating element to the fluid flowing past the heating rod . Similarly, the f ibre optic cable may, at least partly, be enclosed in a protective tube . The protective tube may be made of a metal , pos sibly the same metal as is used for the thermally conductive sheath . The protective tube protects the fibre optic cable against direct contact with the proces s fluid and may allow for limited movement of the fibre optic cable relative to the heating rod , when the heating rod expands or contract s due to variations in temperature .

[0013] In preferred embodiment s , the controller i s further configured to control the electrical heating element in dependence of the determined temperature prof ile . The improved temperature monitoring realised by the use of the fibre optic cable , allows the controller to react quicker to smaller , local increases in temperature . As a result , the controller achieves an enhanced control over the temperature in the heating rods and throughout the medium being heated . This enhanced temperature control make s this electric heater unit very suitable for heating thermally sensitive fluids . Furthermore , the reduced wear due to undetected local hot spots allows for the use of les s costly material s , which can help to bring down the cost of the electric heater unit .

[0014] Typically, the at least one heating rod is part of a bundle of substantially parallel heating rods , at least a subset of the heating rods having a respective fibre optic cable attached to its surface and along a length thereof . Each re spective fibre optic cable has a plurality of measurement points di stributed over its length, and is coupled to the laser source and the light sensor . The controller is configured to determine a respective temperature profile along the length of each heating rod having one of the fibre optic cable s attached to its surface . The use of f ibre optic cables allows to eas ily determine accurate and detailed temperature profiles along the full length of the heating rods . To obtain a useful and reliable temperature profile acros s the full diameter of the of the bundle too , it may not be needed to provide a fibre optical cable for each separate heating rod . Preferably the controller is further configured to independently control the electrical heating element s of each individual heating rod in dependence of the respective temperature profiles . If the electrical heating element s are configured for allowing independent control of different sections of the heating rods , precise control in all three dimensions will even be pos s ible .

[0015] The measurement points may, for example , include fibre Bragg gratings or GaAs crystals to enable measuring temperatures by analysing the refraction of the laser light at each individual mea surement point .

[0016] The invention de scribed herein is primarily provided for use in an electric proce s s heater compris ing a hous ing with a fluid inlet and a fluid outlet , the at least one heating rod being pos itioned inside the housing and arranged for heating a proce s s fluid flowing from the fluid inlet , through the housing , and towards the fluid outlet . However , the invention may be similarly useful in other devices and systems where elongated heating elements are used for heating a fluid or other medium .

[0017] Brief Description of the Drawings

[0018] Figure 1 shows an electric proces s heater wherein an electric heater unit according to the invention may advantageously be used .

[0019] Figure 2 schematically shows an electric heater unit for use in the electric proces s heater of Figure 1 .

[0020] Figure 3 schematically shows a heating rod for use in the electric heater unit of Figure 2 .

[0021] Figure 4 shows a cros s section of the electric heater unit of Figure 2 .

[0022] These drawings depict one or more implementations in accordance with the present teachings , by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements.

[0023] Detailed Description of the Drawings

[0024] Figure 1 shows an electric process heater 100 wherein an electric heater unit 150 according to the invention may advantageously be used. The electric process heater 100 comprises an inlet 110, a heater compartment or housing 120, and an outlet 130. In use, the electric process heater 100 will be integrated in a larger industrial set up wherein the process fluid is used. The process fluid enters the heater compartment 120 through the inlet 110. Inside the heater compartment 120, the electric heater unit 150, which is shown in more detail in Figure 2, brings the process fluid to the desired temperature, after which it leaves the heater compartment 120 through the outlet 130.

[0025] In many industries, such as the food and drinks industry, the pharmaceutical industry, and the oil and gas industry, the process fluids may be thermally sensitive and precise control over the heating process is essential. For example, hydrocarbons processed in the oil and gas industry should not undergo cracking in the electric process heater 100 but could do so if film temperatures are exceeded. The current invention provides a new way of monitoring the heating of process fluid inside an electric process heater 100. By providing an easier way to accurately monitor temperature throughout the heater compartment 120, the current invention delivers a more efficient and precise electric process heater that can be provided at a lower cost.

[0026] Figure 2 schematically shows an electric heater unit 150 for use in the electric process heater 100 of Figure 1. Figure 3 schematically shows a heating rod 55 for use in the electric heater unit 150 of Figure 2 . The electric heater unit 150 comprises at least one such heating rod 55 . Preferably, a plurality of such heating rods 55 are provided and arranged in a bundle 50 of heating rods 55 , together spanning most of the diameter of the heater compartment 120 . While the proces s fluid flows from the inlet 110 to the outlet 130 of the electric proces s heater 100 , the bundle 50 of heating rods 55 bring the process fluid to the de sired temperature .

[0027] The temperature of the electrical heating element 60 may be controlled by varying an electrical current that runs through the heating element 60 . The heating rod 55 comprises an electrical heating element 60 that is controlled by the controller 30 . The heating rod 55 may further comprise a thermally conductive sheath, which i s preferably made of some metal that can withstand variations in temperature as may be expected in the electric heater unit 150 and the fluid flowing therethrough . Important functions of the thermally conductive sheath are electrically insulating the electrical heating element 60 from the proces s fluid and efficiently relaying the heat produced by the electrical heating element 60 to the fluid flowing past the heating rod 55 .

[0028] A temperature monitoring system is provided for monitoring the heating proce s s and preventing local overheating of the heating rods 55 and the proces s f luids . In this embodiment , the temperature monitoring is achieved by measuring temperatures at various points along the length of one or more of the heating rods 55 , using a fibre optic cable 40 , a laser source 10 , a light sensor 20 , and a controller 30 .

[0029] Li ke the electrical heating element 60 , the fibre optic cable 40 may, at least partly, be enclosed in a protective tube . The protective tube may be made of a metal , pos sibly the same metal as i s used for the thermally conductive sheath of the electrical heating element 60 . The protective tube protects the fibre optic cable 40 against direct contact with the proces s fluid and may allow for limited movement of the fibre optic cable 40 relative to the heating rod 55 , when the heating rod 55 expands or contracts due to variations in temperature .

[0030] The fibre optic cable may, for example , be attached to a surface of the heating rod 55 using clamps 70 . If both the electrical heating element 60 and the fibre optic cable 40 are encapsulated in a metal casing , welding or soldering may be used to attach both casings to each other .

[0031] The fibre optic cable 40 comprises a plurality of measurement points di stributed over its length, and thus over the length of the heating rod 55 too . The measurement point s may, for example , include fibre Bragg gratings or GaAs crystals to enable measuring temperature s by analysing the refraction of the laser light at each individual measurement point .

[0032] In this embodiment , the laser source 10 is coupled to a first end of the fibre optic cable 40 for sending a laser s ignal therethrough . The light sensor 20 is coupled to the other end of the fibre optic cable 40 for receiving the laser signal therefrom . In alternative embodiments , the laser source 10 and light sensor 20 are combined in a single unit with separate connection points for each end of the fibre optic cable 40 . Preferably, multiple fibre optic cables 40 , attached to different heating rods 55 , share a single laser source 10 and / or light sensor 20 . In some embodiment s , the laser source 10 and light sensor 20 are together coupled to one end of the fibre optic cable 40 and the light from the la ser source 10 is reflected at the opposite far end of the fibre optic cable 40 before travelling back through the fibre optic cable 40 and being received by the light sensor 20 .

[0033] The controller 30 is operatively coupled with the laser source 10 and the light sensor 20 , and configured to determine a temperature prof ile along the length of the heating rod 55 , based on the laser signal received by the light sensor 20 . The temperature profile may, for example , be derived from a spectral analysis of the light received by the light sensor 20 .

[0034] The use of fibre optic cables 40 for the temperature measurements allows for the temperature to be measured at multiple measurement points along the length of the heating rod 55 by installing j ust one fibre optic cable 40 . A s ingle la ser source 10 and a single light detector 20 can be connected to multiple fibre optic cables 40 and can be used to determine the temperature at each of the measurement points . As a result , far more temperature measurements can be made than with the thermocouples that have been used previously . This allows for enhanced monitoring of the temperature of the heating rods 55 and significantly reduces the ri s k of local hot spots not being detected, thereby protecting both the heating rods 55 and the proces s fluid .

[0035] In preferred embodiment s , the controller 30 is further configured to control the electrical heating element s 60 in dependence of the determined temperature profile s . The improved temperature monitoring realised by the use of the fibre optic cable 40 , allows the controller 30 to react quicker to smaller increases in temperature . As a re sult , the controller 30 achieves an enhanced control over the temperature in the heating rods 55 and throughout the medium being heated . This enhanced temperature control makes this electric heater unit 150 very suitable for heating thermally sensitive f luids . Furthermore , the reduced wear due to undetected local hot spots allows for the use of les s costly materials , which can help to bring down the cost of the electric heater unit 150 .

[0036] Typically, the electric heater unit 150 comprises a bundle 50 of substantially parallel heating rods 55 . At least a subset of the heating rods 55 have a re spective fibre optic cable 40 attached to it s surface and along a length thereof . Each respective fibre optic cable 40 ha s a plurality of measurement points distributed over its length , and is coupled to the laser source 10 and the light sensor 20 . The controller 30 is configured to determine a respective temperature profile along the length of each heating rod 55 having one of the fibre optic cables 40 attached to its surface . The use of fibre optic cables 40 allows to ea sily determine accurate and detailed temperature profile s along the full length of the heating rods 55 .

[0037] To obtain a useful and reliable temperature profile acros s the full diameter of the of the bundle 55 , it may not be needed to provide a f ibre optical cable 40 for each separate heating rod 55 . As shown in Figure 4 , which provide s a cros s section of the electric heater unit 150 of Figure 2 , shows a bundle 50 of 241 heating rods 55 , of which f ifteen are equipped with a f ibre optic cable 40 . These f ifteen f ibre optic cables 40 may be enough to accurately monitor the temperature profile of the heating rods acros s the full diameter of the bundle 50 . More fibre optic cables 40 may be added for further improving the accuracy of the temperature monitoring system . Fewer optic fibre cable 40 may be used to further reduce complexity and cost . All individual heating rods 55 , or individual groups of heating rods 55 may be controlled in parallel to all produce the same amount of thermal energy . Preferably, however , the controller 30 i s configured to independently control the electrical heating elements 60 of each individual heating rod 55 in dependence of their respective temperature profiles . When the electrical heating element s 60 are conf igured for allowing independent control of different sections of the heating rods 55 , even more precise control in all three dimensions will be pos sible .

[0038] The invention de scribed herein is primarily provided for use in an electric proce s s heater 100 as de scribed above . However , the invention may be similarly useful in other devices and systems where elongated heating elements are used for heating a fluid or other medium . While many pos sible variations of the electric heater have been described above , it will be clear to the s killed person that additional variations and modifications can be made without departing from the s cope of the invention as claimed in the appended claims .

Claims

C L A I M S1. An electric heater unit (150) comprising:- at least one heating rod (55) comprising an electrical heating element (60) ;- a fibre optic cable (40) , attached to a surface of the at least one heating rod (55) and along a length thereof, the fibre optic cable (40) comprising a plurality of measurement points distributed over a length of the fibre optic cable (40) ;- a laser source (10) , coupled to an end of the fibre optic cable (40) for sending a laser signal therethrough;- a light sensor (20) , coupled to an end of the fibre optic cable (40) for receiving the laser signal therefrom; and- a controller (30) , operatively coupled with the laser source (10) and the light sensor (20) , and configured to determine a temperature profile along the length of the heating rod (55) , based on the laser signal received by the light sensor (20) .

2. An electric heater unit (150) as claimed in Claim 1, wherein the heating rod (55) further comprises a thermally conductive sheath, and wherein the fibre optic cable (40) is attached to the thermally conductive sheath.

3. An electric heater unit (150) as claimed in Claim 1 or2, wherein the fibre optic cable (40) is at least partly enclosed in a protective tube.

4. An electric heater unit (150) as claimed in any preceding Claim, wherein the controller (30) is furtherconfigured to control the electrical heating element (60) in dependence of the determined temperature profile.

5. An electric heater unit (150) as claimed in any preceding Claim,- wherein the at least one heating rod (55) is part of a bundle (50) of substantially parallel heating rods (55) ;- wherein at least a subset of the heating rods (55) has a respective fibre optic cable (40) attached to its surface and along a length thereof, each respective fibre optic cable (40) having a plurality of measurement points distributed over its length;- wherein each of the fibre optic cables (40) is coupled to the laser source (10) and the light sensor (20) ; and- wherein the controller (30) is configured to determine a respective temperature profile along the length of each heating rod (55) having one of the fibre optic cables (40) attached to its surface.

6. An electric heater unit (150) as claimed in Claim 5, wherein the controller (30) is further configured to independently control the electrical heating elements (60) of each heating rod (55) in dependence of the respective temperature profiles.

7. An electric heater unit (150) as claimed in any of the preceding Claims, wherein one or more of the measurement points include a fibre Bragg grating.

8. An electric heater unit (150) as claimed in any of the preceding Claims, wherein one or more of the measurement points include a GaAs crystal.

9. An electric process heater (100) comprising an electric heater unit (150) as claimed in any of the preceding claims, and a housing (120) with a fluid inlet (110) and a fluid outlet (130) , the at least one heating rod (55) of the electric heater unit (150) being positioned inside the housing (120) and arranged for heating a process fluid flowing from the fluid inlet (110) , through the housing (120) , and towards the fluid outlet (130) .

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