Abstract:
A temperature sensing assembly utilizing a multipoint thermocouple. The assembly comprises a vessel, e.g. a chemical reaction pressure vessel, into which a thermocouple is inserted. The thermocouple utilizes an elongated sheath having a plurality of sensors therein. The sensors are arranged to detect temperature at a plurality of unique locations within the vessel.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to sensing temperature, and particularly to sensing temperature at multiple points within a vessel.  
         BACKGROUND OF THE INVENTION  
         [0002]    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.  
           [0003]    In some applications, multiple thermocouples have been combined to permit the sensing of temperature at a plurality of distinct locations or points. For example, sheaths are formed of differing lengths such that the junction point of the internal conductors for each sheath is located at a unique location. This combination of multiple sheaths and conductor pairs can be utilized to sense temperature at multiple locations in a given application.  
           [0004]    The combination of thermocouples can be used, for instance, in high pressure reaction vessels. In certain applications, chemical reactions within the high pressure reaction vessels occur at different rates depending on temperature. Thus, it is desirable to sense the temperature within such reaction vessels to ensure the correct reaction occurs. In applications, such as the refining of petroleum, it can be important to closely monitor temperature at a variety of locations within the pressure vessel to ensure the proper reaction and proper produced material.  
         SUMMARY OF THE INVENTION  
         [0005]    A temperature sensing technique is disclosed. In one embodiment of the technique, a vessel is provided for use in conducting, for example, high pressure chemical reactions. The technique also comprises at least one elongated sheath that extends into the vessel. A plurality of conductor pairs are disposed within each sheath and designed to detect temperatures at unique longitudinal locations along the elongated sheath. An insulation material is disposed about the conductor pairs within each elongated sheath. The invention also relates to a methodology for sensing temperatures at a variety of locations within a pressure vessel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:  
         [0007]    [0007]FIG. 1 is a side view of an exemplary, multipoint thermocouple, according to one embodiment of the present invention;  
         [0008]    [0008]FIG. 2 is a schematic, cross-sectional view of a multipoint thermocouple, according to the present invention;  
         [0009]    [0009]FIG. 3 is a side view of the thermocouple illustrated in FIG. 1 with an end cap of the sheath exploded from the remainder of the sheath;  
         [0010]    [0010]FIG. 4 is an end view taken of the exposed conductor pair ends shown in FIG. 3;  
         [0011]    [0011]FIG. 5 illustrates an exemplary application of the thermocouple of FIG. 1;  
         [0012]    [0012]FIG. 6 illustrates a high pressure reaction vessel combined with a thermocouple, according to an exemplary embodiment of the present invention;  
         [0013]    [0013]FIG. 7 illustrates an exemplary alternate embodiment of the multipoint thermocouple for use in a variety of applications;  
         [0014]    [0014]FIG. 8 is partially cut-away view of a containment chamber utilized with the thermocouple of FIG. 7;  
         [0015]    [0015]FIG. 9 is a schematic illustration of the application of an exemplary thermocouple to sense temperature at a variety of locations or points within a chamber; and  
         [0016]    [0016]FIG. 10 is a schematic illustration showing another exemplary configuration of the thermocouple illustrated in FIG. 9. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0017]    Referring generally to FIG. 1, an exemplary thermocouple system  20  is illustrated according to one embodiment of the present invention. Thermocouple system  20  comprises a sheath  22  having an enclosed distal end  24  and an opposed end  26  from which a plurality of conductor pairs  28  extend. Each conductor pair comprises a pair of conductors of dissimilar materials, typically metals, that are joined at a junction point  30 . For example, the dissimilar conductors may be welded together to form the junction. The free ends of the conductor pairs  28  are connected to instrumentation  32 , 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.  
         [0018]    Sheath  22  typically comprises an open interior  34  into which conductor pairs  28  extend. Within interior  34 , an insulation material  36 , such as an electrical insulation material, is disposed about the individual conductors of conductor pairs  28 . In the illustrated embodiment, insulation material  36  generally fills interior  34  about conductor pairs  28 . Although various electrical insulation materials may be used, an exemplary material comprises magnesium oxide (MgO).  
         [0019]    As illustrated best in FIG. 2, temperature may be determined at a plurality of locations along the length of sheath  22  by forming junction points at selected locations along the sheath. By way of example, the embodiment of FIG. 2 illustrates four conductor pairs  28 A,  28 B,  28 C and  28 D each having its own unique junction point  30 A,  30 B,  30 C and  30 D, respectively. The junction points  30 A- 30 D are formed at unique longitudinal locations along sheath  22  to permit the sensing of temperature at those unique locations. It should be noted that four 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 sheath  22  depending on space constraints and the desired application.  
         [0020]    Each conductor pair comprises a first conductor  38  illustrated in solid line and a second conductor  40  illustrated in dashed line in FIG. 2. The first conductor  38  and the second conductor  40  of each conductor pair  28  are 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:  
                                                                         Recommended   Thermocouple Material       Thermocouple   B&amp;S   Temperature   w/Identifying Characteristics            Calibration   Wire Gauge   Limits F.   Positive   Negative               Type J    8 ga. (.128′′)   0 to 1400   Iron   Constantan ™           14 ga. (.064′′)   0 to 1100   (Magnetic)           20 ga. (.032′′)   0 to 900            24 ga. (.020′′)   0 to 700        Type K    8 ga. (.128′′)   0 to 2300   Chromel ™   Alumel ™           14 ga. (.064′′)   0 to 2000       (Magnetic)           20 ga. (.032′′)   0 to 1800           24 ga. (.020′′)   0 to 1600       Type T   14 ga. (.064′′)   −300 to +700     Copper   Constantan ™           20 ga. (.032′′)   −300 to +500     (Copper Color)           24 ga. (.020′′)   −300 to +400         Type E    8 ga. (.128′′)   −300 to +1600    Chromel ™   Constantan ™           14 ga. (.064′′)   −300 to +1400        (Silver Color)           20 ga. (.032′′)   −300 to +1200        Type R or   24 ga. (.020′′)   to 2700   Platinum 13 Rh   Platinum       Type S           Platnum 10 Rh   Platnum                       (Softer than                       Pt Rh)                  
 
         [0021]    Additionally, various combinations of different conductor pair types can be utilized within a single sheath  22 . A variety of materials also may be used to form sheath  22 . For example, stainless steel and Inconel™ are appropriate for use in a variety of applications.  
         [0022]    Although a variety of techniques may be used to join the dissimilar conductors at desired junction points  30  within sheath  22 , one technique is to provide conductor pairs  28  by forming a plurality of rods  42  that extend into sheath  22  to distal end  24 , as further illustrated in FIGS. 3 and 4. The rods  42  are preformed of the material of first conductor  38 , second conductor  40  or a combination of the two. In FIG. 2, for example, four rods  42  are formed of the material of second conductor  40 , one rod is formed of the first conductor material  38  and three rods are formed of a combination of first conductor material and second conductor material that are joined at the desired junction point, e.g.  30 B,  30 C and  30 D. When the rods are placed within sheath  22 , the junction points  30 A- 30 D are disposed at desired locations for sensing temperature.  
         [0023]    Each of the rods  42  has a distal rod end  44 , and the appropriate pairs of rod ends are joined together to form conductor pairs  28 , as best illustrated in FIGS. 3 and 4. Although distal rod ends  44  may be joined in a variety of ways, the distal rod ends may be fused, e.g. welded, together at a fusion end  46 . 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 segment  47  (see FIG. 2) that returns the conductor from the distal end to a junction point  30 , e.g.  30 B,  30 C,  30 D, within sheath  22 .  
         [0024]    Although various processes may be used to form thermocouple system  20 , one exemplary methodology comprises preparing those rods  42  with two dissimilar materials by, for example, welding the dissimilar conducting materials together at predetermined points. The combination rods  42  along with the remaining rods  42  are then passed through insulation  36  within the open ended sheath  22  (see FIG. 3). Insulation  36  may initially be placed within sheath  22  in the form of beads. Sheath  22  is then swaged to compact the insulation  36  and sheath  22 .  
         [0025]    Following swaging, the insulation, e.g. MgO, is removed at distal end  24  and the appropriate rods are coupled to form conductor pairs  28 , as best illustrated in FIG. 4. For example, cross pieces  46  may be welded across appropriate rod ends  44 . An appropriate insulation material, such as magnesium oxide powder, is placed around the protruding rod ends (see FIG. 2) and a sheath cap  48  is attached to the remainder of the sheath by, for example, welding.  
         [0026]    Thermocouple system  20  is readily designed for a variety of applications. For example, one exemplary application utilizes thermocouple system  20  for sensing temperature at a plurality of locations within an enclosed environment, such as a tank. In the embodiment illustrated in FIG. 5, the thermocouple system further comprises a mounting system  50  designed for attachment to a corresponding flange of a tank (described more fully below). Mounting system  50  comprises a plate  52  having a plurality of apertures  54  utilized in fastening plate  52  to the corresponding flange by, for example, threaded fasteners. Mounting system  50  further includes an opening or openings  56  through which sheath  22  passes into the container. Sheath  22  is sealed to plate  52  at its corresponding opening  56  by, for instance, a socket weld  58 .  
         [0027]    In the illustrated embodiment, a containment chamber  60  is formed by a containment wall  62  connected to a back surface  64  of plate  52 . Containment wall  62  is connected to plate  52  by, for example, a weld  66 . At an end opposite plate  52 , containment chamber  60  is enclosed by a plate  68  having one or more plate openings  70  through which one or more sheaths  22  extend. Each sheath is sealed within its corresponding opening  70  by, for example, a socket weld  72 .  
         [0028]    Containment wall  62  also may include one or more openings  74  that provide selective access to the containment chamber. For example, in the illustrated embodiment, a pair of bosses  76  are attached to an exterior surface  78  of containment wall  62  proximate openings  74 . The bosses  76  may be attached to containment wall  62  by appropriate welds  80 .  
         [0029]    Each boss  76  is designed to receive an appropriate instrument, e.g. a valve  82 . In the illustrated embodiment, one of the valves  82  is coupled to a T-section  84  which, in turn, is coupled to a pressure gauge  86  and an additional valve  88 . In this exemplary embodiment, the pressure gauge  86  is attached to determine whether any high pressure fluid leaks into containment chamber  60 , as described in more detail below. Depending on the application, a variety of instruments may be coupled to containment chamber  60 .  
         [0030]    From containment chamber  60 , sheath  22  extends through a support bracket  90  to which it is attached by appropriate fasteners  92 , e.g. a bulk head connector. Subsequent to fastener  92 , sheath  22  extends to a junction box  94  having a terminal block  96 . The various conductor pairs  28  are coupled to appropriate terminals  98  of terminal block  96 . The terminal block may be connected to appropriate instrumentation, such as instrumentation  32 , to determine the various potential differences, and thereby the temperatures, at each of the junction points  30 .  
         [0031]    Referring generally to FIGS. 6 and 7, a specific application of an alternate thermocouple system is illustrated. In this embodiment, a high pressure chemical reaction vessel  100  is designed for a desired chemical process. For example, high pressure vessel  100  may 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. Vessel  100  also may be utilized with weld pad or tube skin applications. In an exemplary application, one or more high pressure chemical reaction vessels  100  are coupled to a manifold pipe  102  by a connector pipe  104 . Connector pipe  104  is disposed in fluid communication with the interior of vessel  100  generally at an upper portion  105  of vessel  100 . Similarly, a second manifold pipe  106  is coupled to the one or more vessels  100  by an appropriate lower connector pipe  108 . Lower connector pipe  108  generally is connected in fluid communication with vessel  100  at a lower or bottom portion  110 . Manifold pipe  102  and second manifold pipe  106  can be used to provide ingress or egress of fluids moving to or from high pressure chemical reaction vessel or vessels  100 .  
         [0032]    In a petrochemical application, petrochemicals move into high pressure chemical reaction vessels  100  in either direction depending on the specific application. For example, flow can be from manifold pipe  102  downward through vessel  100  and out through second manifold pipe  106 . Alternatively, the flow can be in the reverse direction moving from second manifold pipe  106  upwardly through vessels  100  to manifold pipe  102 .  
         [0033]    Typically, one or more beds  112  are deployed within high pressure chemical reaction vessel  100  at 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 vessel  100 , 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 vessel  100 .  
         [0034]    One or more thermocouple systems  20  are deployed to extend downwardly into the interior of vessel  100  for sensing temperature at a plurality of longitudinal locations within the pressure vessel. It should be noted that one or more systems  20  also can be deployed from the side (e.g. horizontally) and/or from the bottom of vessel  100 . As described above, sheath  22  encloses a plurality of conductor pairs  28  designed to sense temperature at a plurality of unique, longitudinal positions along the sheath. However, additional sheaths can be designed to extend into pressure vessel  100  to provide an even greater number of sensing points for detecting temperature within vessel  100 . For example, the embodiment illustrated best in FIG. 7 shows four sheaths extending downwardly from mounting plate  52 . Each sheath  22  may enclose a plurality of conductor pairs  28 , as described with reference to FIGS.  1 - 4 .  
         [0035]    The use of multiple thermocouples in each sheath facilitates the use of numerous thermocouples with a minimal number of welds at mounting plate/flange  52 . For example, the embodiment illustrated in FIG. 7 only requires four welds about the four sheaths  22 , while multiple thermocouples may be deployed in each sheath. This is advantageous over prior art designs where each thermocouple had its own sheath requiring a separate weld. In many such applications, the relatively large number of welds could not be accommodated at the flange.  
         [0036]    The number of conductor pairs  28  within 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 pairs  28  to 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 pairs  28  permits those sheaths to be bent, curled, arced or otherwise formed to sense temperatures at a variety of other locations within the vessel  100 .  
         [0037]    As illustrated best in FIG. 8, the one or more sheaths  22  preferably include a relief section  114  disposed within containment chamber  60  to facilitate flexing of the sheath due to, for example, thermal expansion. The relief section  114  of each sheath may comprise an arcuate section  116  that provides the sheath with sufficient flexibility.  
         [0038]    Depending on the application and type of vessel  100  utilized in the application, the attachment of thermocouple system  20  to pressure vessel  100  may vary. However, one exemplary embodiment utilizes a neck  118  fastened to vessel  100  by, for example, a weldment. Neck  118  is deployed around an opening  120  formed through the outer wall  122  of vessel  100 . A flange  124  is connected to an upper end of neck  118  to facilitate mounting of thermocouple system  20 . Flange  124  typically is welded to neck  118 . If additional thermocouple systems  20  are utilized for a given application, a plurality of necks and flanges may be coupled to the pressure vessel as described.  
         [0039]    Flange  124  may include a plurality of apertures  126  configured for alignment with apertures  54  of mounting plate  52 . Appropriate fasteners  128 , such as bolts, can be inserted through apertures  54  and  126  to secure each thermocouple system  20  to the appropriate high pressure chemical reaction vessel  100 . As illustrated, the sheath or sheaths  22  simply are inserted into the interior of vessel  100  via neck  118 , and plate  52  is secured to flange  124 . Additionally, appropriate seals can be utilized intermediate flange  124  and plate  52  to 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 thermocouple system  20  to a given high pressure chemical reaction vessel.  
         [0040]    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 contour  130 , as illustrated in FIG. 9. The multiple conductor pairs  28  having junction points  30  separated longitudinally along the sheath  22  permits detection of temperature at a plurality of unique locations  132  along contour  130 . Thus, the temperature detection points are not necessarily disposed linearly along a relatively straight sheath.  
         [0041]    The contour  130  illustrated in FIG. 9 is formed as an arc, however, contour  130  may comprise a variety of other shapes and arrangements. For example, the embodiment of FIG. 10 utilizes a sheath that is bent downwardly along a relatively straight contour  134  before transitioning into an arced contour  136 . Contour  136  is deployed generally along the arcuate outer wall of a vessel  138 , as illustrated in both FIGS. 9 and 10.  
         [0042]    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.