Temperature sensor and methods of use

A temperature sensing assembly includes a sheath defining an interior space, a first temperature sensor and a second temperature sensor. The first temperature sensor has first and second conductors extending within the interior space of the sheath and joined at a first junction point. The first conductor is constructed of a first material and the second conductor is constructed of a second material that is different than the second material. The second temperature sensor has third and fourth conductors extending within the interior space of the sheath and joined at a second junction point. The third conductor is constructed of a third material and the fourth conductor is constructed of a fourth material that is different than the fourth material. The first material is different than each of the third and fourth materials. The first junction point is adjacent to the second junction point.

FIELD

The present invention relates generally to sensing temperature, and particularly to thermocouples designed to sense temperature at multiple points.

BACKGROUND

Thermocouples are used in a variety of applications to sense temperature at a given location. A typical thermocouple comprises an external sheath and a pair of rod-shaped conductors disposed longitudinally within the sheath. Each conductor is of a dissimilar metallic material, and the two conductors are joined at a distal end within the sheath. An electrical insulation material also is packed about the rods within the sheath. The free ends of the conductors are connected to a detection instrument, such as a voltmeter, that measures the difference in potential created at the junction of the two metals. This difference in potential changes with temperature, thereby readily permitting the accurate detection of temperature at the junction point.

SUMMARY

In one aspect, a temperature sensing assembly includes a sheath defining an interior space, a first temperature sensor and a second temperature sensor. The first temperature sensor has a first conductor and a second conductor extending within the interior space of the sheath and joined at a first junction point to measure temperature. The first conductor is constructed of a first material and the second conductor is constructed of a second material. The first material is different than the second material. The second temperature sensor has a third conductor and a fourth conductor extending within the interior space of the sheath and joined at a second junction point to measure temperature. The third conductor is constructed of a third material and the fourth conductor is constructed of a fourth material. The third material is different than the fourth material. The first material is different than each of the third and fourth materials. The first junction point is adjacent to the second junction point such that a deviation of temperature measurements received from the first and second temperature sensors indicates that one of the first and second temperature sensors has corroded.

In another aspect, a temperature sensing assembly for monitoring temperature of a pressure vessel includes a sheath defining an interior space, a plurality of type K thermocouples, and at least one type N thermocouple. Each of the plurality of type K thermocouples has a junction point. The junction points of each of the plurality of type K thermocouples are spaced throughout the interior space of the sheath. The type N thermocouple has a junction point disposed within the interior space of the sheath.

In another aspect, a method of measuring temperature includes providing a temperature sensing assembly. The temperature sensing assembly includes a sheath defining an interior space, a first temperature sensor and a second temperature sensor. The first temperature sensor has a first conductor and a second conductor extending within the interior space of the sheath and joined at a first junction point to measure temperature. The first conductor is constructed of a first material and the second conductor is constructed of a second material. The first material is different than the second material. The second temperature sensor has a third conductor and a fourth conductor extending within the interior space of the sheath and joined at a second junction point to measure temperature. The third conductor is constructed of a third material and the fourth conductor is constructed of a fourth material. The third material is different than the fourth material. The first material is different than each of the third and fourth materials. The method further includes exposing the temperature sensing assembly to a process or a structure to monitor temperature. The method further includes receiving a first indication of temperature of the process or the structure from the first junction point at a first time. The method further includes receiving a second indication of temperature of the process or the structure from the second junction point at the first time. The method further includes comparing the first indication of temperature to the second indication of temperature.

In another aspect, a temperature sensing assembly includes a sheath defining an interior space, a plurality of temperature sensors, and a rod. Each of the plurality of temperature sensors has a first conductor and a second conductor extending within the interior space of the sheath and joined at a junction point to measure temperature. The first conductor of each of the plurality of temperature sensors is constructed of a first material and the second conductor of each of the plurality of temperature sensors is constructed of a second material. The first material is different than the second material. The rod extends within the interior space of the sheath and is constructed from a third material that is different than both the first and second materials. The third material has a lower electrode potential than both the first and second materials.

DETAILED DESCRIPTION

Referring generally toFIG. 1, an exemplary temperature sensing assembly20is illustrated according to one embodiment. Temperature sensing assembly20includes a sheath22having an enclosed distal end24and an opposed end26from which a plurality of conductor pairs28extend. Each conductor pair comprises a pair of conductors of dissimilar materials, typically metals, that are joined at a junction point30. For example, the dissimilar conductors may be welded together to form the junction. The free ends of the conductor pairs28are connected to instrumentation32, e.g. a voltmeter, that measures the difference in potential created at the junction of the two metals. This difference in potential corresponds to a given temperature.

Sheath22typically comprises an open interior34into which conductor pairs28extend. Within interior34, an insulation material36, such as an electrical insulation material, is disposed about the individual conductors of conductor pairs28. A variety of materials also may be used to form sheath22. For example, stainless steel and Inconel™ are appropriate for use in a variety of applications. In the illustrated embodiment, insulation material36generally fills interior34about conductor pairs28. Although various electrical insulation materials may be used, an exemplary material comprises magnesium oxide (MgO). In some embodiments, sheath22defines an axis27extending along its length, as shown inFIG. 1.

As illustrated best inFIGS. 2A and 2B, temperature may be determined at a plurality of locations along the length of sheath22by forming junction points at selected locations along the sheath. By way of example, the embodiment ofFIG. 2Aillustrates five conductor pairs28A,28B,28C,28D, and28E each having its own unique junction point30A,30B,30C,30D, and30E, respectively. The junction points30A-30E are formed at unique longitudinal locations along sheath22to permit the sensing of temperature at those unique locations. It should be noted that five conductor pairs are illustrated for purposes of explanation and that various numbers of conductor pairs can be utilized. For example, two conductor pairs, three conductor pairs or even up to ten conductor pairs or more can be utilized within sheath22depending on space constraints and the desired application.

Each conductor pair comprises a first conductor38illustrated in solid line and a second conductor40illustrated in dashed line inFIG. 2A. The first conductor38and the second conductor40of each conductor pair28are made of dissimilar conductive materials. Typically, the thermocouple calibration or type is established by the National Bureau of Standards, e.g. J, K, T, E, R or S. The various types typically utilize pairs of dissimilar metallic materials. The following chart provides some examples.

In various embodiments, various combinations of different conductor pair types can be utilized within a single sheath22. For example, in one embodiment, as shown inFIG. 2A, temperature sensing assembly20includes at least one temperature sensor of a first type (e.g., conductor pairs28A-28D), each extending within interior34of sheath22. Each of the thermocouples of the first type include a first conductor (e.g., conductors38A-38D) and a second conductor (e.g., conductors40A-40D) joined at a junction point (e.g., junction points30A-30D) to measure temperature. The first conductor is constructed of a first material and the second conductor is constructed of a second material that is different than the first material.

Temperature sensing assembly20may further include a temperature sensor of a second type (e.g., conductor pair28E) having a third conductor (e.g., conductor38E) and a fourth conductor (e.g., conductor40E), each extending within interior36of sheath22. The third conductor and fourth conductor are joined at a junction point (e.g., junction point30E) to measure temperature. The third conductor is constructed of a third material and the fourth conductor is constructed of a fourth material that is different than the third material. In addition, the first material (i.e., the material of the first conductor of the temperature sensor of the first type) is different than each of the third and fourth materials. In some embodiments, the second material (i.e., the material of the second conductor of the temperature sensor of the first type) is also different than each of the third and fourth materials.

In various embodiments, one of the junction points of the first type of temperature sensor (e.g., junction point30B) is adjacent to the junction point of the temperature sensor of the second type (e.g., junction point30E). For example, in one embodiment, the first junction point (e.g., junction point30B) is less than about 5 mm from the second junction point (e.g., junction point30E) as measured along axis27of sheath22. In another embodiment, the first junction point (e.g., junction point30B) is less than about 10 mm from the second junction point (e.g., junction point30E) as measured along axis27. Because the junction points are adjacent, when installed in a process vessel, the junction points may be positioned within the same level of a process vessel such that the temperature measurements received from the first and second temperature sensors can be compared.

Because the first type of temperature sensor and the second type of temperature sensor have at least one conductor of dissimilar materials, they corrode at different rates. Hence, a deviation of the temperature measurements received from the first and second types of temperature sensors may indicate that at least one of the conductors of either first type of temperature sensor or the second type of temperature sensor has corroded. This may be an indication that corrective action should be taken, as described herein.

In one embodiment, the first type of temperature sensor is a type K thermocouple and the second type of temperature sensor is a type N thermocouple. In another embodiment, the first type of temperature sensor is a type J thermocouple and the second type of temperature sensor is a type E thermocouple.

WhileFIG. 2Aillustrates only one thermocouple of the second type, any number of thermocouples of the second type may be included in temperature sensing assembly100. For example, in some embodiments, there are an equal number of temperature sensors of the first type and of the second type. In other embodiments, a temperature sensor of the second type may be adjacent to every other temperature sensor of the first type.

Although a variety of techniques may be used to join the dissimilar conductors at desired junction points30within sheath22, one technique is to provide conductor pairs28by forming a plurality of rods42that extend into sheath22to distal end24, as further illustrated inFIGS. 3 and 4. For the first type of thermocouple (e.g., conductor pairs28A-28D), the rods42are preformed of the first material, the second material, or a combination of the two. InFIG. 2A, for example, four rods are formed of the second material, one rod is formed of the first material and three rods are formed of a combination of the first material and the second material, with the materials joined at the desired junction point, e.g.30B,30C and30D. When the rods are placed within sheath22, the junction points30A-30D are disposed at desired locations for sensing temperature.

For the second type of thermocouple, the rods42are preformed of the third material, the fourth material, or a combination of the two. InFIG. 2A, for example, one rod is formed of the fourth material and one rod is formed of a combination of the third and fourth materials, with the materials joined at the junction point, e.g.,30E.

Each of the rods42has a distal rod end44, and the appropriate pairs of rod ends are joined together to form conductor pairs28, as best illustrated inFIGS. 3 and 4. Although distal rod ends44may be joined in a variety of ways, the distal rod ends may be fused, e.g. welded, together at a fusion end46. Alternatively, a cross piece or cross rod may be utilized. For example, a cross piece formed of the appropriate conductor material may be welded or otherwise joined to corresponding rod ends. When joined, at least some of the conductors comprise a return segment47(seeFIG. 2A) that returns the conductor from the distal end to a junction point30, e.g.30B,30C,30D,30E within sheath22.

Although various processes may be used to form temperature sensing assembly20, one exemplary methodology includes preparing those rods42with two dissimilar materials (e.g., the first material and second material or the third material and fourth material described above) by, for example, welding the dissimilar conducting materials together at predetermined points. The combination rods42along with the remaining rods42are then passed through insulation36within the open ended sheath22(seeFIG. 3). Insulation36may initially be placed within sheath22in the form of beads. Sheath22is then swaged to compact the insulation36and sheath22.

Following swaging, the insulation, e.g. MgO, is removed at distal end24and the appropriate rods are coupled to form conductor pairs28, as best illustrated inFIG. 4. For example, cross pieces46may be welded across appropriate rod ends44. An appropriate insulation material, such as magnesium oxide powder, is placed around the protruding rod ends and a sheath cap48is attached to the remainder of the sheath by, for example, welding.

In another embodiment, shown inFIG. 2B, temperature sensing assembly20includes a rod49extending within interior34of sheath22. Rod49is constructed of a material that is different than the materials forming conductors38,40. Preferably, rod49is formed of a material that has a lower electrode potential than at least one material forming conductors38,40. In some embodiments, rod49has a lower electrode potential than each of the materials forming conductors38,40. Because rod49has a lower electrode potential than the material of conductors38,40, in use rod49acts as an anode and will corrode prior to corrosion of conductors38,40, as a result of galvanic (or bimetallic) corrosion. This may prevent, or delay, corrosion of conductors38,40and, thereby, extend the useful life of temperature sensing assembly20. In various embodiments, temperature sensing assembly includes a single rod49. In other embodiments, temperature sensing assembly20includes more than one rod49. For example, in at least one embodiment, temperature sensing assembly20includes one rod for each conductor pair28. Rod49can have any appropriate geometry and size and can be rigid or flexible.

In some embodiments, rod49is constructed of pure titanium or a titanium alloy. The alloying material may be chosen based on the type of sensor used in temperature sensing assembly20(e.g., Type J, Type K). In embodiments in which thermocouples of multiple different types are used in temperature sensing assembly20, multiple rods may be included and at least some of the rods may be constructed of different materials than the other rods. For example, one rod of pure titanium and one rod of titanium alloy may be included in temperature sensing assembly20.

Temperature sensing assembly20is readily designed for a variety of applications. For example, one exemplary application utilizes temperature sensing assembly20for sensing temperature at a plurality of locations within an enclosed environment, such as a tank. Temperature sensing assembly20may further include a mounting system designed for attachment to a corresponding flange of a tank (described more fully below). Mounting system50comprises a plate52having a plurality of apertures54utilized in fastening plate52to the corresponding flange by, for example, threaded fasteners. Mounting system50further includes an opening or openings56through which sheath22passes into the container. Sheath22is sealed to plate52at its corresponding opening56by, for instance, a socket weld58.

In the illustrated embodiment, a containment chamber60is formed by a containment wall62connected to a back surface64of plate52. Containment wall62is connected to plate52by, for example, a weld66. At an end opposite plate52, containment chamber60is enclosed by a plate68having one or more plate openings70through which one or more sheaths22extend. Each sheath is sealed within its corresponding opening70by, for example, a socket weld72.

Containment wall62also may include one or more openings74that provide selective access to the containment chamber. For example, in the illustrated embodiment, a pair of bosses76are attached to an exterior surface78of containment wall62proximate openings74. The bosses76may be attached to containment wall62by appropriate welds80.

Each boss76is designed to receive an appropriate instrument, e.g. a valve82. In the illustrated embodiment, one of the valves82is coupled to a T-section84which, in turn, is coupled to a pressure gauge86and an additional valve88. In this exemplary embodiment, the pressure gauge86is attached to determine whether any high pressure fluid leaks into containment chamber60, as described in more detail below. Depending on the application, a variety of instruments may be coupled to containment chamber60.

From containment chamber60, sheath22extends through a support bracket90to which it is attached by appropriate fasteners92, e.g. a bulk head connector. Subsequent to fastener92, sheath22extends to a junction box94having a terminal block96. The various conductor pairs28are coupled to appropriate terminals98of terminal block96. The terminal block may be connected to appropriate instrumentation, such as instrumentation32, to determine the various potential differences, and thereby the temperatures, at each of the junction points30.

Referring generally toFIGS. 6 and 7, a specific application of a temperature sensing assembly is illustrated. In this embodiment, a high pressure chemical reaction vessel100is designed for a desired chemical process. For example, high pressure vessel100may be utilized in the petroleum industry and may comprise a hydrocracker, a hydrotreater, a hydrogen reactor, a catalytic reactor, a catalytic cracker or an ethylene oxide reactor. Vessel100also may be utilized with weld pad or tube skin applications. In an exemplary application, one or more high pressure chemical reaction vessels100are coupled to a manifold pipe102by a connector pipe104. Connector pipe104is disposed in fluid communication with the interior of vessel100generally at an upper portion105of vessel100. Similarly, a second manifold pipe106is coupled to the one or more vessels100by an appropriate lower connector pipe108. Lower connector pipe108generally is connected in fluid communication with vessel100at a lower or bottom portion110. Manifold pipe102and second manifold pipe106can be used to provide ingress or egress of fluids moving to or from high pressure chemical reaction vessel or vessels100.

In a petrochemical application, petrochemicals move into high pressure chemical reaction vessels100in either direction depending on the specific application. For example, flow can be from manifold pipe102downward through vessel100and out through second manifold pipe106. Alternatively, the flow can be in the reverse direction moving from second manifold pipe106upwardly through vessels100to manifold pipe102.

Typically, one or more beds112are deployed within high pressure chemical reaction vessel100at various levels. The number and type of beds vary according to the environment and the types of high pressure and high temperature reactions that take place within the reactor, e.g. high pressure chemical reaction vessel100, for a given application. To sense the reaction temperature at different levels and to control the proper reaction rate, temperature is sensed at various selected levels within vessel100. In some embodiments, two temperature sensors, each being a different type are deployed at a given level. For example, a type N and a type K thermocouple can be deployed at one or more levels within vessel100. When both thermocouples are in good working condition, the absolute temperature measurement of the two thermocouples may be different, however, the temperature readings from the two thermocouples generally correlate with one another as the temperature within vessel100changes. However, as described herein, divergences in the temperature sensed by the different types of thermocouples within a given level may indicate that one of the conductors of one of the thermocouples has corroded. This may indicate that corrective action should be taken or that certain temperature measurements should be disregarded.

One or more temperature sensing assemblies20are deployed to extend downwardly into the interior of vessel100for sensing temperature at a plurality of longitudinal locations within the pressure vessel. It should be noted that one or more systems20also can be deployed from the side (e.g. horizontally) and/or from the bottom of vessel100. As described above, sheath22may enclose a plurality of conductor pairs28designed to sense temperature at a plurality of unique, longitudinal positions along the sheath. However, additional sheaths can be designed to extend into pressure vessel100to provide an even greater number of sensing points for detecting temperature within vessel100. For example, the embodiment illustrated best inFIG. 7shows four sheaths extending downwardly from mounting plate52. Each sheath22may enclose a plurality of conductor pairs28, as described with reference toFIGS. 1-4. In embodiments in which more than one sheath is deployed, a first sheath may enclose thermocouples of a first type and a second sheath may enclose thermocouples of a second type. In such embodiments, divergence of the temperature measurements received from the thermocouples in the first sheath and the temperature measurements received from the thermocouples of the second sheath may indicate that the thermocouples in one of the sheaths has corroded.

The number of conductor pairs28within each sheath and the number of sheaths utilized can be adjusted according to application and design parameters. For example, a single sheath may be able to contain sufficient conductor pairs28to provide temperature sensing capability at all of the desired locations, or the temperature sensing junctions can be divided between additional sheaths. Also, the use of additional sheaths that each contain one or more conductor pairs28permits those sheaths to be bent, curled, arced or otherwise formed to sense temperatures at a variety of other locations within the vessel100.

As illustrated best inFIG. 8, the one or more sheaths22preferably include a relief section114disposed within containment chamber60to facilitate flexing of the sheath due to, for example, thermal expansion. The relief section114of each sheath may comprise an arcuate section116that provides the sheath with sufficient flexibility.

Depending on the application and type of vessel100utilized in the application, the attachment of temperature sensing assembly20to pressure vessel100may vary. However, one exemplary embodiment utilizes a neck118fastened to vessel100by, for example, a weldment. Neck118is deployed around an opening120formed through the outer wall122of vessel100. A flange124is connected to an upper end of neck118to facilitate mounting of temperature sensing assembly20. Flange124typically is welded to neck118. If additional temperature sensing assemblies20are utilized for a given application, a plurality of necks and flanges may be coupled to the pressure vessel as described.

Flange124may include a plurality of apertures126configured for alignment with apertures54of mounting plate52. Appropriate fasteners128, such as bolts, can be inserted through apertures54and126to secure each temperature sensing assembly20to the appropriate high pressure chemical reaction vessel100. As illustrated, the sheath or sheaths22simply are inserted into the interior of vessel100via neck118, and plate52is secured to flange124. Additionally, appropriate seals can be utilized intermediate flange124and plate52to prevent escape of high pressure fluids, depending on a particular application, and as known to those of ordinary skill in the art. It should be noted that numerous types of flanges and other connectors can be utilized in coupling each temperature sensing assembly20to a given high pressure chemical reaction vessel. Additionally, or alternatively, temperature sensing assembly20may also be mounted to a vessel using any of the methods described in U.S. Pat. Nos. 8,870,455; 9,557,225; 9,752,937; and 10,175,117, which are each incorporated herein in their entireties by reference.

The use of multiple conductor pairs able to sense temperature at a plurality of unique locations within a single sheath permits great flexibility in the design of the thermocouple. For example, the sheath may be formed along a contour130, as illustrated inFIG. 9. The multiple conductor pairs28having junction points30separated longitudinally along the sheath22permits detection of temperature at a plurality of unique locations132along contour130. Thus, the temperature detection points are not necessarily disposed linearly along a relatively straight sheath. As described above, a thermocouple of a different type (i.e., comprised of conductors of different material than the other thermocouples) may be provided at, or adjacent to, one or more of unique locations132.

The contour130illustrated inFIG. 9is formed as an arc, however, contour130may comprise a variety of other shapes and arrangements. For example, the embodiment ofFIG. 10utilizes a sheath that is bent downwardly along a relatively straight contour134before transitioning into an arced contour136. Contour136is deployed generally along the arcuate outer wall of a vessel138, as illustrated in bothFIGS. 9 and 10.

A method of measuring temperature is illustrated inFIG. 11. The method includes, at block202, providing a temperature sensing assembly. For example, the temperature sensing assembly may be temperature sensing assembly20described above. The temperature sensing assembly may include a sheath defining an interior space. The temperature sensing assembly may further include a first temperature sensor having a first conductor and a second conductor extending within the interior space of the sheath and joined at a first junction point to measure temperature. The first conductor is constructed of a first material and the second conductor is constructed of a second material that is different than the first material. The temperature sensing assembly also includes a second temperature sensor having a third conductor and a fourth conductor extending within the interior space of the sheath and joined at a second junction point to measure temperature. The third conductor is constructed of a third material and the fourth conductor is constructed of a fourth material that is different than the third material. Further, the first material is different than each of the third and fourth materials.

The method further includes, at block204, exposing the temperature sensing assembly to a process or structure to monitor temperature. For example, the temperature sensing assembly may be deployed in an enclosed environment, such as a tank, as described above. The method further includes, at block206, receiving a first indication of temperature of the process or the structure from the first junction point at a first time. The method further includes, at block208, receiving a second indication of temperature of the process or the structure from the second junction point at the first time. The method further includes, at block210, comparing the first indication of temperature to the second indication of temperature.

The method may further include, at block212, performing a corrective action based on the comparison of the first indication of temperature and the second indication of temperature. The corrective action may include, for example, applying a correction factor to the temperature measurement received from the first or second temperature sensor. Alternatively, or additionally, the corrective action may include disregarding subsequent temperature measurements received from the first or second temperature sensor. The corrective action may also include repairing or replacing one or both of the first or second temperature sensors.

In some embodiments, the method further includes, at block214, receiving a third indication of temperature of the process or the structure from the first junction point and a fourth indication of temperature of the process or the structure from the second junction point, where the third and fourth indications are taken subsequently to the first and second indications. In such embodiments, at block216, the method may further include comparing a first difference between the first and second indications and a second difference between the third and fourth indications. The method may further include, at block218, taking a corrective action based on the comparison of the first difference and the second difference. The corrective action may include, for example, those described above.

It will be understood that the foregoing description is of exemplary embodiments of this invention, and that the invention is not limited to the specific forms shown. For example, the materials utilized in forming the thermocouples may be adjusted according to changes in thermocouple design, advancement of material science, the environment of use, etc. Additionally, the multipoint thermocouples described can be utilized in a variety of applications that may require various mounting structures, support structures and instrumentation. Various applications may or may not require containment chambers, and a variety of vessels ranging from low pressure vessels to high pressure vessels may be utilized for the reaction and/or flow of a variety of substances. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.