Abstract:
A heat transfer unit includes an inlet manifold; an outlet manifold spaced from the inlet manifold; and a plurality of conduits coupling the inlet manifold to the outlet manifold, wherein at least on the conduits is coupled to the outlet manifold at an oblique angle. In one form, the conduit includes a L-Coil. In another form, the conduit includes a D-Coil. In another form, the conduit includes a coil having two or more C-shaped sections. Each conduit includes a section arranged in an interior space of a heater box, and at least one heater is arranged in the interior space of the heater box.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The disclosure relates to a low pressure drop heat transfer unit for process fluids. 
         [0003]    2. Description of the Related Art 
         [0004]    Various catalytic conversion processes are known in the petrochemical industry. For example, the catalytic reforming of a hydrocarbon feedstream (e.g., a naphtha feedstream) to produce aromatics (e.g., benzene, toluene, and xylenes) is described in U.S. Patent Application Publication Nos. 2012/0277501, 2012/0277502, 2012/0277503, 2012/0277504, and 2012/0277505. The catalytic dehydrogenation of a paraffin stream to yield olefins is described in U.S. Pat. No. 8,282,887. 
         [0005]    Catalytic reforming and catalytic dehydrogenation processes are endothermic and therefore, heat must be added to maintain the temperature of the reactions. U.S. Patent Application Publication No. 2012/0275974 describes the use of interbed heaters to maintain the temperature of reaction in the catalytic reactor of a reforming process. Example heaters for process fluids can also be found in U.S. Pat. Nos. 8,176,974 and 7,954,544. 
         [0006]    Aromatics yield from a catalytic reforming unit and olefin yield from a catalytic dehydrogenation unit increase, while yield of undesirable products from competing cracking reactions decreases, with lessening operating pressure. Thus, it may be advantageous to minimize reaction zone operating pressure. 
         [0007]    The hot residence time of a process stream before the product stream leaves a reactor (also known as hot volume) can also be critical to the catalytic selectivity to desired products for thermally sensitive processes such as catalytic reforming and catalytic dehydrogenation. Hot residence time reduction can be critical in reactor circuit non-catalyst volumes in order to prevent yield loss (aromatics or olefins) from competing thermal cracking reactions. 
         [0008]    Thus, the design of heaters used in catalytic reforming and catalytic dehydrogenation processes to heat the feed upstream of each reactor can be guided by two criteria, pressure drop and hot residence time. While the overall low operating pressure benefits the yields from the processes, it is more beneficial to use the available pressure drop diligently in a reactor circuit. The use of the available pressure drop further upstream in the reactor circuit is least detrimental. The use of higher pressure drop further upstream in the reactor circuit reduces yields to a lesser extent. However, it reduces the hot residence time (thus thermal cracking) in the upstream heaters where the process streams are often more susceptible to thermal cracking than in the downstream heaters. 
         [0009]    Thermal expansion and contraction in heater coils is yet another design consideration. Specifically, the heater coils must be able to withstand high process temperatures and metallurgical changes and mechanical stress. 
         [0010]    Therefore, what is needed is an improved heat transfer unit for process fluids wherein the heat transfer unit provides low pressure drop but also the flexibility to withstand thermal expansion/contraction in the heater coils. 
       SUMMARY OF THE INVENTION 
       [0011]    The foregoing needs are met by a heat transfer unit for process fluids. The heat transfer unit includes an inlet manifold; an outlet manifold spaced from the inlet manifold; and a plurality of conduits coupling the inlet manifold to the outlet manifold, wherein at least one of the conduits is coupled to the outlet manifold at an oblique angle. 
         [0012]    In one version of the heat transfer unit, at least one of the conduits includes a L-Coil. 
         [0013]    In another version of the heat transfer unit, at least one of the conduits includes a D-Coil. 
         [0014]    In another version of the heat transfer unit, at least one of the conduits includes a coil having a plurality of generally C-shaped sections. 
         [0015]    In another version of the heat transfer unit, at least one of the conduits is coupled to the outlet manifold at an angle between about five and eighty-five degrees. 
         [0016]    In another version of the heat transfer unit, at least one of the conduits is coupled to the outlet manifold at an angle between about thirty and sixty degrees. 
         [0017]    In another version of the heat transfer unit, each of the conduits is coupled to the outlet manifold at an oblique angle. 
         [0018]    In another version of the heat transfer unit, each conduit includes a section arranged in an interior space of a heater box and wherein at least one heater is arranged in the interior space of the heater box. 
         [0019]    In another aspect, the invention provides an L-Coil heat transfer unit for process fluids. The L-Coil heat transfer unit includes an inlet manifold; an outlet manifold spaced from the inlet manifold; and an L-Coil coupled between the inlet manifold and the outlet manifold. The L-Coil includes a horizontal leg and a vertical leg, wherein the horizontal leg is coupled to the outlet manifold at an oblique angle such that a flow aperture formed therebetween defines an oblong profile. 
         [0020]    In one version of the L-Coil heat transfer unit, a plurality of L-Coils are coupled to the outlet manifold at an oblique angle. 
         [0021]    In another version of the L-Coil heat transfer unit, the L-Coil is arranged at between about a thirty and sixty degree angle relative to the outlet manifold. 
         [0022]    In another version of the L-Coil heat transfer unit, the L-Coil is arranged at between about a five and eighty-five degree angle relative to the outlet manifold. 
         [0023]    The L-Coil heat transfer unit can further comprise a heater arranged substantially adjacent a bottom of the L-Coil heat transfer unit. 
         [0024]    The L-Coil heat transfer unit can include a section arranged in an interior space of a heater box. 
         [0025]    In another aspect, the invention provides a D-Coil heat transfer unit for process fluids. The D-Coil heat transfer unit includes an inlet manifold; an outlet manifold spaced from the inlet manifold; and a D-Coil coupled between the inlet manifold and the outlet manifold, The D-Coil includes an inlet section and an outlet section, and the inlet section is coupled to the inlet manifold at an oblique angle, and the outlet section is coupled to the outlet manifold at an oblique angle. 
         [0026]    In one version of the D-Coil heat transfer unit, a flow aperture formed between the outlet section and the outlet manifold defines an oblong profile. 
         [0027]    In another version of the D-Coil heat transfer unit, a plurality of D-Coils are coupled to the inlet manifold at an oblique angle and are coupled to the outlet manifold at an oblique angle. 
         [0028]    In another version of the D-Coil heat transfer unit, the inlet section is arranged at between about a thirty and sixty degree angle relative to the inlet manifold, and the outlet section is arranged at between about a thirty and sixty degree angle relative to the outlet manifold. 
         [0029]    In another version of the D-Coil heat transfer unit, the D-Coil includes a section arranged in an interior space of a heater box. At least one heater can be arranged in the interior space of the heater box. 
         [0030]    In a low pressure drop heater design, the heater manifold may account for close to 50% of the total pressure heater pressure drop. The manifold pressure drop is mainly due to the entrance and exit frictional losses from heater tubes to the heater outlet and inlet. 
         [0031]    The invention provides a heat transfer unit with an L-coil design that decreases pressure drop. In one non-limiting example of the heat transfer unit, an angled entrance to the heater outlet manifold is used with the L-coil design. An angled entrance results in an elliptical opening into the manifold. This lowers the inlet velocity and the velocity is in the same direction as the process fluid flow resulting in an additional decrease in a pressure drop. An angled inlet into the heater outlet manifold also provides a longer horizontal arm in an L-heater coil. This in turn gives more flexibility to the heater coil for vertical compression and tension. A longer horizontal arm of the L-Coil can provide better flexibility in vertical movements. 
         [0032]    The invention also provides a heat transfer unit with a D-Coil to integrate the benefits for low pressure drop design with an improved flexibility. A D-coil achieves an added reduction in pressure drop by having an angled entry into and exit from, inlet and outlet manifolds, respectively. In addition, a D-Coil provides a better flexibility for vertical movements in a heater coil. 
         [0033]    The invention demonstrates that an angled connection from heater conduits to the manifold is preferably used and more preferably, an angled connection is used at an outlet manifold connection. This provides pressure drop reduction due to a bigger opening at the connection (thus lower frictional loss) and less turbulence (via same flow direction) with more flexibility for vertical movements. The pressure drop reduction by angled connection may be more at the outlet manifold connection than the inlet connection due to higher designed velocity at the outlet. The pressure reduction benefit can be more prominent in the low pressure drop heater design. The design can also be used for higher pressure drop heater designs. However, yield benefits from reduced heater drop may be less. 
         [0034]    It is therefore an advantage of the invention to provide a low pressure drop heat transfer unit for process fluids. 
         [0035]    It is another advantage of the invention to provide a heat transfer unit for process fluids in a process where pressure drop affects product yields. 
         [0036]    These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings, and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is an end view of a prior art U-Coil heat transfer unit. 
           [0038]      FIG. 2  is a perspective view of the U-Coil heat transfer unit of  FIG. 1 . 
           [0039]      FIG. 3  is a perspective view of a prior art L-Coil heat transfer unit. 
           [0040]      FIG. 4  is a side view of the L-Coil heat transfer unit of  FIG. 3 . 
           [0041]      FIG. 5  is an end view of the L-Coil heat transfer unit of  FIG. 3 . 
           [0042]      FIG. 6  is a top view of the L-Coil heat transfer unit of  FIG. 3 . 
           [0043]      FIG. 7  is a side view of an outlet manifold of the L-Coil heat transfer unit of  FIG. 3 . 
           [0044]      FIG. 8  is a perspective view of an L-Coil heat transfer unit according to one embodiment of the invention. 
           [0045]      FIG. 9  is a side view of the L-Coil heat transfer unit of  FIG. 8 . 
           [0046]      FIG. 10  is an end view of the L-Coil heat transfer unit of  FIG. 8 . 
           [0047]      FIG. 11  is a top view of the L-Coil heat transfer unit of  FIG. 8 . 
           [0048]      FIG. 12  is a side view of an outlet manifold of the L-Coil heat transfer unit of  FIG. 8 . 
           [0049]      FIG. 13  is a perspective view of an L-Coil heat transfer unit according to one embodiment of the invention. 
           [0050]      FIG. 14  is a side view of the L-Coil heat transfer unit of  FIG. 13 . 
           [0051]      FIG. 15  is an end view of the L-Coil heat transfer unit of  FIG. 13 . 
           [0052]      FIG. 16  is a top view of the L-Coil heat transfer unit of  FIG. 13 . 
           [0053]      FIG. 17  is a perspective view of an L-Coil heat transfer unit according to one embodiment of the invention. 
           [0054]      FIG. 18  is a side view of the L-Coil heat transfer unit of  FIG. 17 . 
           [0055]      FIG. 19  is an end view of the L-Coil heat transfer unit of  FIG. 17 . 
           [0056]      FIG. 20  is a top view of the L-Coil heat transfer unit of  FIG. 17 . 
           [0057]      FIG. 21  is a perspective view of a D-Coil heat transfer unit according to one embodiment of the invention. 
           [0058]      FIG. 22  is a side view of the D-Coil heat transfer unit of  FIG. 21 . 
           [0059]      FIG. 23  is an end view of the D-Coil heat transfer unit of  FIG. 21 . 
           [0060]      FIG. 24  is a top view of the L-Coil heat transfer unit of  FIG. 21 . 
           [0061]      FIG. 25  is a perspective view of a D-Coil heat transfer unit according to one embodiment of the invention. 
           [0062]      FIG. 26  is a side view of the D-Coil heat transfer unit of  FIG. 25 . 
           [0063]      FIG. 27  is an end view of the D-Coil heat transfer unit of  FIG. 25 . 
           [0064]      FIG. 28  is a top view of the L-Coil heat transfer unit of  FIG. 25 . 
           [0065]      FIG. 29  is a side view of a Triple C-Coil heat transfer unit according to one embodiment of the invention. 
       
    
    
       [0066]    Like reference numerals will be used to refer to like parts from Figure to Figure in the following description of the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0067]    Catalytic reactor systems may use U-Coil heaters for heating fresh feed and reheating feed between reactors. A U-Coil style heater may be desirable due to low process side pressure drop. An example U-Coil style heat transfer unit  10  is shown in  FIGS. 1 and 2  and includes an inlet manifold  14 , an outlet manifold  18 , a heater box  19 , and a plurality of U-coils  22  arranged for fluid communication therebetween. A number of burners or heaters  26  are arranged adjacent the axial ends of the manifolds  14 ,  18 . The coils in this embodiment and the other embodiments described herein may be formed from a stainless steel (e.g., an austenitic 300 series stainless steel such as 347) or a steel such as 9-Chrome-Moly Steel. 
         [0068]    Alternatively, catalytic reactor systems may use L-Coil heaters for heating fresh feed and reheating feed between reactors. An example L-Coil style heat transfer unit  30  is shown in  FIGS. 3-7  and includes an inlet manifold  34 , an outlet manifold  38 , a heater box  39 , and a plurality of L-coils  42  arranged for fluid communication therebetween.  FIG. 7  shows apertures  46  arranged in the outlet manifold  38  where the outlet manifold  38  couples with the L-Coils  42 . As clearly shown in  FIG. 7 , in this arrangement the apertures  46  are substantially circular. 
         [0069]      FIGS. 8-12  show an L-Coil heat transfer unit  50  according to one aspect of the invention. The L-Coil heat transfer unit  50  includes an inlet manifold  54  arranged to receive a process fluid, an outlet manifold  58  arranged to provide the process fluid to a downstream location, a heater box  59 , and a plurality of L-Coils  62  arranged therebetween. 
         [0070]    The L-Coils  62  are preferably welded to the inlet manifold  54  and the outlet manifold  58  to provide a hermetic seal. As is clearly visible in  FIG. 11 , the L-Coils  62  are arranged at an oblique angle relative to a longitudinal axis A of the outlet manifold  58 . As shown in  FIGS. 3-7 , the current state-of-the-art is to have L-Coils arranged perpendicular to an outlet manifold (i.e., arranged at a ninety-degree angle (90°)). In a preferred embodiment, the L-Coils  62  are rotated relative to the longitudinal axis A by about forty-five degrees (45°). In other embodiments, the L-Coils  62  are rotated relative to the longitudinal axis A by between about thirty and sixty degrees (30-60°). In still other embodiments, the L-Coils  62  are rotated relative to the longitudinal axis A by between about twenty and 70 degrees (20-70°). In still other embodiments, the L-Coils  62  are rotated relative to the longitudinal axis A by between about five and eighty-five degrees (5-85°). 
         [0071]    As shown in  FIG. 10 , the inlet manifold  54  is horizontally spaced from the outlet manifold  58  by a horizontal distance. Additionally, each L-Coil  62  includes a horizontal leg  66  and a vertical leg  70 . Non-limiting example length ranges for the horizontal leg  66  are 0.30 to 7.62 meters (1-25 feet), or 0.61 to 6.10 meters (2-20 feet), or 1.52 to 4.57 meters (5-15 feet). Non-limiting example length ranges for the vertical leg  70  are 6.10 to 24.38 meters (20-80 feet), or 9.14 to 21.34 meters (30-70 feet), or 12.19 to 18.29 meters (40-60 feet), or 13.72 to 16.76 meters (45-55 feet). The oblique arrangement of the L-Coils  62  provides a longer horizontal leg  66  relative to the horizontal distance between the inlet manifold  54  and the outlet manifold  58  as compared with a perpendicular arrangement. This longer horizontal leg  66  allows for more flexibility in the system for better response to thermal and mechanical stresses. 
         [0072]    Turning to  FIG. 12 , the outlet manifold  58  is shown removed from the L-Coil heat transfer unit  50 . L-Coil outlet apertures  74  are clearly visible and provide an oval or oblong or elliptical communication pathway between the L-Coils  62  and the outlet manifold  58 . The L-Coil outlet apertures  74  have a larger sectional area as compared to the apertures  46  shown in  FIG. 7 . 
         [0073]    In one embodiment, the length of the inlet manifold  54  and outlet manifold  58  in the longitudinal direction is about fifteen meters (about 50 feet) or more. In other embodiments, the installation may be smaller or larger, as desired. The L-Coils  62  may be spaced apart by about fifty centimeters (about 10 feet). In other embodiments, more or less spacing may be desirable. The L-Coil heat transfer unit  50  may include up to about eighteen-hundred (1800) L-Coils  62 . In other embodiments, the L-Coil heat transfer unit  50  may include more or less L-Coils  62 , as desired. 
         [0074]    An additional feature of the L-Coil heat transfer unit  50  is the ability to position a burner  78  in a variety of locations and arrangements. As shown in  FIG. 10 , the burner  78  may be arranged near the inlet manifold  54  at the bottom of the heater box  59  and arranged under the L-Coils  62 . The burner  78  may extend the full longitudinal length of the L-Coil heat transfer unit  50 . In other arrangements, two or more burners  78  may be used (see  FIG. 15 ) and may be arranged elevated above the inlet manifold  54 , arranged only at one or two ends of the L-Coil heat transfer unit  50 , or arranged differently, as desired. The L-Coil heat transfer unit  50  provides a significant advantage in the flexibility of how the L-Coils  62  are heated as compared to prior art U-Coil designs wherein hot spots are a significant concern and inhibit the use of burners arranged near the floor or inlet manifold  54 . This flexibility will be readily appreciated by those skilled in the art. 
         [0075]    The L-Coil heat transfer unit  50  provides an advantageous fluid flow pattern (shown in dash lines in  FIG. 8 ) that reduces the fluid friction and therefore reduces the pressure drop through the L-Coil heat transfer unit  50  compared to other heat transfer solutions. In other embodiments, other flow patterns are feasible. For example, the inlet manifold  54  flow may originate on the left (as shown in  FIG. 8 ), or the outlet manifold  58  and the inlet manifold  54  may be switched such that fluid flow is substantially reversed from what is shown. 
         [0076]    Turning now to  FIGS. 13-16 , another L-Coil heat transfer unit  50 ′ is shown. The L-Coil heat transfer unit  50 ′ is substantially similar to the L-Coil heat transfer unit  50  but includes a larger horizontal spacing between an inlet manifold  54 ′ and an outlet manifold  58 ′ and a correspondingly longer horizontal leg  66 ′ on each L-Coil  62 ′. All components of the L-Coil heat transfer unit  50 ′ have been numbered similar to the L-Coil heat transfer unit  50  with prime numbers. An increased horizontal leg  66 ′ length provides an L-Coil  62 ′ with more flexibility with respect to thermal and mechanical stresses. 
         [0077]    Turning now to  FIGS. 17-20 , another L-Coil heat transfer unit  50 ″ is shown. The L-Coil heat transfer unit  50 ″ is substantially similar to the L-Coil heat transfer unit  50  but includes a larger horizontal spacing between an inlet manifold  54 ″ and an outlet manifold  58 ′″, and a correspondingly longer horizontal leg  66 ″ on each L-Coil  62 ″. All components of the L-Coil heat transfer unit  50 ″ have been numbered similar to the L-Coil heat transfer unit  50  with prime numbers. An increased horizontal leg  66 ″ length provides an L-Coil  62 ″ with more flexibility with respect to thermal and mechanical stresses. 
         [0078]    Turning to  FIGS. 21-24 , a D-Coil heat transfer unit  100  includes an inlet manifold  104 , and outlet manifold  108 , a heater box  109 , and a plurality of D-Coils  112  arranged therebetween. The distance between the inlet manifold  104  and the outlet manifold  108  may be in the range of 6.10 to 24.38 meters (20-80 feet), or 9.14 to 21.34 meters (30-70 feet), or 12.19 to 18.29 meters (40-60 feet), or 13.72 to 16.76 meters (45-55 feet). Each D-Coil  112  includes an oblique inlet section  116 , an outlet section  122 , and a transfer section  124  therebetween. Non-limiting example length ranges for the inlet section  116  and the outlet section  122  are 0.30 to 7.62 meters (1-25 feet), or 0.61 to 6.10 meters (2-20 feet), or 1.52 to 4.57 meters (5-15 feet). Non-limiting example length ranges for the transfer section  124  are 9.14 to 13.72 meters (30-45 feet), or 12.19 to 14.68 meters (40-48 feet). 
         [0079]    The illustrated inlet section  116  is arranged at an oblique angle relative to a longitudinal axis of the inlet manifold  104 . In the illustrated embodiment, the inlet section  116  is arranged at about a forty-five degree angle (45°) relative to the longitudinal axis of the inlet manifold  104 . In other embodiments, the inlet section  116  is arranged at between about thirty and sixty degrees (30-60°) relative to the longitudinal axis of the inlet manifold  104 . In still other embodiments, the inlet section  116  is arranged at between about twenty and seventy degrees (20-70°) relative to the longitudinal axis of the inlet manifold  104 . In still other embodiments, the inlet section  116  is arranged at between about five and eighty-five degrees (5-85°) relative to the longitudinal axis of the inlet manifold  104 . 
         [0080]    The outlet section  122  is arranged at an oblique angle relative to a longitudinal axis of the outlet manifold  108 . In the illustrated embodiment, the outlet section  122  is arranged at about a forty-five degree angle (45°) relative to the longitudinal axis of the outlet manifold  108 . In other embodiments, the outlet section  122  is arranged at between about thirty and sixty degrees (30-60°) relative to the longitudinal axis of the outlet manifold  108 . In other embodiments, the outlet section  122  is arranged at between about twenty and seventy degrees (20-70°) relative to the longitudinal axis of the outlet manifold  108 . In still other embodiments, the outlet section  122  is arranged at between about five and eighty-five degrees (5-85°) relative to the longitudinal axis of the outlet manifold  108 . 
         [0081]    As a result of the oblique relation between the D-Coils  112  and the inlet and outlet manifolds  104 ,  108 , the flow apertures formed at the junction between the D-Coils  112  and the inlet and outlet manifolds  104 ,  108  are oval or oblong or elliptical as described above with respect to apertures  74 . 
         [0082]    The D-Coil heat transfer unit  100  provides an advantageous fluid flow pattern (shown in dash lines in  FIG. 22 ) that reduces the fluid friction and therefore reduces the pressure drop through the D-Coil heat transfer unit  100  compared to other heat transfer solutions. In other embodiments, other flow patterns are feasible. 
         [0083]      FIGS. 25-28  show a D-Coil heat transfer unit  100 ′ similar to the D-Coil heat transfer unit  100  and is labeled with prime numbers. The inlet sections  116 ′ and the outlet sections  122 ′ are of decreased length compared to the inlet sections  116  and the outlet sections  122  in the embodiment of  FIGS. 21-24 . 
         [0084]    Turning to  FIG. 29 , a Triple C-Coil heat transfer unit  200  includes an inlet manifold  204 , an outlet manifold  208 , a heater box, and a plurality of Triple C-Coils  210  arranged therebetween. The distance between the inlet manifold  204  and the outlet manifold  208  may be in the range of 6.10 to 24.38 meters (20-80 feet), or 9.14 to 21.34 meters (30-70 feet), or 12.19 to 18.29 meters (40-60 feet), or 13.72 to 16.76 meters (45-55 feet). Each Triple C-Coil  210  includes a generally C-shaped inlet section  216 , a generally C-shaped outlet section  222 , and a generally C-shaped transfer section  212  therebetween. 
         [0085]    The illustrated inlet section  216  is arranged at an oblique angle relative to a longitudinal axis of the inlet manifold  204 . In the illustrated embodiment, the junction of the inlet section  216  is arranged at about a forty-five degree angle (45°) relative to the longitudinal axis of the inlet manifold  204 . See angle C in  FIG. 29 . In other embodiments, the junction of the inlet section  216  is arranged at between about thirty and sixty degrees (30-60°) relative to the longitudinal axis of the inlet manifold  204 . In still other embodiments, the junction of the inlet section  216  is arranged at between about twenty and seventy degrees (20-70°) relative to the longitudinal axis of the inlet manifold  204 . In still other embodiments, the junction of the inlet section  216  is arranged at between about five and eighty-five degrees (5-85°) relative to the longitudinal axis of the inlet manifold  204 . 
         [0086]    The outlet section  222  is arranged at an oblique angle relative to a longitudinal axis of the outlet manifold  208 . In the illustrated embodiment, the junction of the outlet section  222  is arranged at about a forty-five degree angle (45°) relative to the longitudinal axis of the outlet manifold  208 . See angle D in  FIG. 29 . In other embodiments, the junction of the outlet section  222  is arranged at between about thirty and sixty degrees (30-60°) relative to the longitudinal axis of the outlet manifold  208 . In other embodiments, the junction of the outlet section  222  is arranged at between about twenty and seventy degrees (20-70°) relative to the longitudinal axis of the outlet manifold  208 . In still other embodiments, the junction of the outlet section  222  is arranged at between about five and eighty-five degrees (5-85°) relative to the longitudinal axis of the outlet manifold  208 . 
         [0087]    As a result of the oblique relation between the Triple C-Coils  210  and the inlet and outlet manifolds  204 ,  208 , the flow apertures formed at the junction between the Triple C-Coils  210  and the inlet and outlet manifolds  204 ,  208  are oval or oblong or elliptical as described above with respect to apertures  74 . 
         [0088]    The Triple C-Coil heat transfer unit  200  provides an advantageous fluid flow pattern that reduces the fluid friction and therefore reduces the pressure drop through the Triple C-Coil heat transfer unit  200  compared to other heat transfer solutions. In other embodiments, other flow patterns are feasible. 
         [0089]    In one aspect, the invention provides a catalytic dehydrogenation process that includes passing a hydrocarbon feed stream through any of heat transfer units  10 ,  30 ,  50 ,  50 ′,  50 ″,  100 ,  100 ′,  200 , and then passing the heated hydrocarbon feed stream and a catalyst into a reactor thereby creating a product stream. 
         [0090]    In another aspect, the invention provides, a catalytic reforming process that includes passing a hydrocarbon feed stream through any of heat transfer units  10 ,  30 ,  50 ,  50 ′,  50 ″,  100 ,  100 ′,  200 , and then passing the heated hydrocarbon feed stream and a catalyst into a reactor thereby creating a product stream. 
         [0091]    Thus, the invention provides a heat transfer unit for process fluids. While use of the heat transfer unit is not limited to any process, the heat transfer unit can be particularly beneficial in heating process fluids in: (i) the catalytic reforming of a hydrocarbon feedstream (e.g., a naphtha feedstream) to produce aromatics (e.g., benzene, toluene and xylenes) (see, e.g., U.S. Patent Application Publication Nos. 2012/0277501, 2012/0277502, 2012/0277503, 2012/0277504, and 2012/0277505); and (ii) the catalytic dehydrogenation of a paraffin stream to yield olefins (see, e.g., U.S. Pat. No. 8,282,887). 
         [0092]    Although the invention has been described in considerable detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.