Abstract:
A structured packing for a reactor is formed from a metal sheet to promote heat and mass transfer near the wall of the reactor. The structured packing causes lateral flow of fluids flowing through the packing such that jet impingement of at least one reactor wall is promoted. The packing may be used in a cylindrical, annular or plate-type reactor, e.g., a catalytic reactor, or a heat exchanger.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of U.S. provisional application Ser. No. 61/207,170 filed Feb. 9, 2009. The disclosure of the foregoing application is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention pertains to a structured packing for a reactor. The packing may be used in a cylindrical, annular or plate-type reactor, e.g., a catalytic reactor, or a heat exchanger. 
     BACKGROUND OF THE INVENTION 
     Reactors such as chemical reactors and heat exchangers are widely used to promote heat transfer, mass transfer and/or chemical reaction rates. In the case of reactors such as chemical reactors, there is often a need to transfer heat into the reactor (e.g., for endothermic reactions) or to transfer heat from the reactor (e.g., exothermic reactions). In commercial practice, in order to achieve economies of scale, it is desirable to use reactors having large diameters. A high heat transfer coefficient within the reactor is desirable in order to promote transfers of heat between the reactor contents and the environment. A high heat transfer coefficient within the reactor is especially desirable near the outside diameter of the reactor, where the ratio of surface area for radial heat flux to the internal volume is lowest and where the amount of heat to be transferred radially is proportional to the volume internal to the source of the reactor. Friction between fluids and the reactor wall often results in relatively low velocities and accordingly relatively lower heat transfer coefficients near the reactor wall where higher heat transfer coefficients are most desirable. 
     In the case of fixed bed, heterogeneous and catalytic reactors, heat transfer into the reactor wall may limit the reaction rate for endothermic reactions or heat transfer from the reactor may limit the control or safe operation for exothermic reactions. In general, it is desirable to limit the number of internal walls within the reactor to accordingly minimize the number of boundary layers of low velocity and low heat transfer coefficient that heat must pass through in the radial direction. Higher surface area in catalytic reactors provides greater opportunity for acceleration of reactions by providing more sites for catalyst to be effectively deployed. In particular, high geometric surface area near the wall of catalytic reactors increases the available heat for conducting exothermic reactions and the heat sink for endothermic reactions at short distances for heat to travel out of or into the reactors, respectively. 
     THE PRIOR ART 
     It is known that engineered packing consisting of metal substrates can be constructed in a manner so as to contain thinner walls that may be possible in randomly packed beds for catalysis and thereby contain increased geometric surface area at a comparable or lower pressure drop compared to what could be attained in a randomly packed bed. It is also known that engineered packing can be designed to provide desirably high heat transfer coefficients near the reactor wall. 
     U.S. Pat. Nos. 4,882,130, 4,719,090 and 4,340,501 pertain to engineered packing of diverse designs for providing uniform improvements of geometric surface area and heat transfer throughout the volume of the reactor at desirably low pressure drop without differentially superior heat transfer or geometric surface area near the reactor wall. 
     U.S. Pat. No. 4,985,230 discloses an engineered packing suitable for use in annulus or between two walls that provides alternating columns of channels that respectively direct fluid toward the first wall and toward the second wall to induce turbulence of fluid passing through the reactor. Such packing provides desirable heat transfer and geometric surface area near the reactor walls at desirably low pressure drop, but has the disadvantage of being difficult to manufacture. 
     Published patent application US2004/0013580 pertains to a filter body for removing soot particles from diesel engine exhaust. The disclosed structure which is designed to cause fluid to flow through adjacent filter sheets is unsuitable for causing fluid to impinge on and deflect back from a wall to provide desirable heat transfer. 
     PCT Application PCT/US2005/42425 discloses a non-annular reactor containing a core structure near the reactor axis and a casing structure between the core and the reactor wall. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide structured packing for a reactor that will increase the geometric surface area and/or the heat transfer coefficient, especially near the reactor wall, of reactors such as fixed bed heterogeneous catalytic reactors without greatly increasing their pressure drop. 
     It is a further object of the invention to provide structured packing for a heat exchanger that will increase the heat transfer coefficient of heat exchangers without greatly increasing their pressure drop. 
     The foregoing objects and other objects of the invention will be apparent from the details of the invention set forth below. 
     SUMMARY OF THE INVENTION 
     The structured packing of the invention is readily prepared by cutting a sheet and then folding the sheet into a structure comprising alternating columns containing vanes disposed in opposite oblique orientation to the reactor axis for causing fluid to alternately impinge on and return from a wall of the reactor. The columns are separated from each other by substantially straight separating walls. The vanes folded from the same sheet are joined along their sides to the separating walls by webs folded from the same sheet. Preferably, the sheet is metal foil and the structure is preferably formed by progressive blanking folding dies. 
     The structured packing of the invention may be located near the inside diameter of a cylindrical reactor tube or enclosure, in the annulus of an annular reactor, or between two walls of another reactor shape such as between two flat walls in a plate-type heat exchanger. In all cases, the structured packing of the invention will cause fluid to impinge a reactor wall to thereby increase heat transfer through that wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a transverse cross-section of the structured packing of the invention. 
         FIG. 1B  is a longitudinal, radial cross-section of the structured packing of the invention (corresponding to cross-section AA in  FIG. 1A ) showing centripetal vanes. 
         FIG. 10  is a longitudinal, radial cross-section of the structured packing of the invention (corresponding to cross-section BB in  FIG. 1A ) showing centripetal vanes. 
         FIG. 2  is a plan view of a sheet to be formed into the structured packing of the invention. 
         FIG. 3  is a more detailed view of a sheet to be formed into the structured packing of the invention. 
         FIG. 4  is a perspective view of the structured packing of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The structured packing of the invention is utilized in a reactor having an inlet, an outlet and at least one wall and comprises:
         (a) a sheet folded back and forth, thereby forming a row of alternating first and second columns separated from each other by separating walls;   (b) first and second direction vanes located in the respective first and second columns such that at least some of the first vanes are inclined at an oblique angle to the reactor wall and at least some of the second vanes are inclined at an opposite oblique angle to the reactor wall;   (c) webs connecting the at least some of the first and second vanes to the separating walls along at least one lateral side of the at least some of the first and second vanes; and   (d) a multiplicity of gaps between the separating walls and the reactor wall, extending from the inlet to the outlet.       

     Preferably, the structured packing of the invention is formed from a single sheet which may be a metal sheet or foil. The opposite oblique angles referred to in paragraph (b) above may all have the same or different magnitude. The gaps referred to in paragraph (d) above are preferably discontinuous. 
     Typically, the reactor containing the structured packing of the invention will have a cylindrical shape and will contain inner and outer concentric walls and an annulus therebetween. The structured packing of the invention preferably comprises a row of alternating first and second columns with their respective first and second vanes, with the row being disposed in the annulus. It is also preferred that a plate be disposed in the annulus and the packing preferably comprises a row of alternating first and second columns with their respective first and second vanes, with the row being disposed in the annulus. 
     As mentioned above, the reactor may be a chemical reactor, e.g., a catalytic reactor, or it may be a heat exchanger. In the case of catalytic reactors, it is preferred that a catalyst be present on at least a portion of the surfaces of the sheet. 
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring to  FIG. 1A , reactor  1  has a cylindrical wall  2  and structured packing  3 , depicted as a shaded area, resides within wall  1 . The outside diameter  4  of packing  3  corresponds to the inside diameter of wall  1 . Packing  3  has an inside diameter  5  and is divided into longitudinal columns  6  (depicted by shaded and dotted areas), and longitudinal columns  7  (depicted by shaded and cross-hatched areas). Columns  6  and  7  alternate with each other and are separated from each other by radial walls  8 . Reactor  1  has intermittent gaps (not shown) disposed between radial walls  8  and reactor wall  2  along the axial length of the reactor. Fluid flowing along the length of reactor  1  is directed in a centrifugal direction through columns  6  and in a centripetal direction while flowing through columns  7 . 
     Referring to  FIG. 1B  (which is a longitudinal section of reactor  1  through section B-B of  FIG. 1A ), column  6  extends from its outside diameter  4  to its inside diameter  5 . Column  6  is bounded at its outside diameter  4  by reactor wall  2 . The axial length of column  6  contains vanes  9 . Vanes  9  form channels  10  which direct fluid centrifugally as the fluid passes from the top to the bottom of reactor  1 . 
     Referring to  FIG. 10  (which is a longitudinal section of reactor  1  through section A-A of  FIG. 1A ), centripetal column  7  extends from its outside diameter  4  to its inside diameter  5 . Column  7  is bounded at its outside diameter  4  by reactor wall  2 . The axial length of column  7  contains vanes  11 . Vanes  11  form channels  12  which direct fluid centripetally as the fluid passes from the top to the bottom of reactor  1 . 
     Referring to  FIG. 2 , sheet  20  is formed into a structured packing of the invention by cutting and bending columns  21  consisting of repeated shapes  30  forming centripetal vanes, and columns  22  consisting of repeated shapes  40  forming centrifugal vanes. Sheet  20  comprises a ductile, rigid material and is preferably metal foil. 
     Referring to  FIG. 3 , a shape  30  from column  21  of  FIG. 2  and a shape  40  from column  22  of  FIG. 2  are shown in greater detail. Shape  30  is formed from sheet  20  into a vane and its two lateral webs which connect the vane to the sheet from which it is formed. Solid lines depict where the sheet is cut. Dotted lines depict approximately 90° bends in the sheet. Dashed lines depict approximately 180° bends in the sheet. 
     Sheet  20  is cut along lines  31 ,  32  and  33 , wherein horizontal line  33  corresponds to horizontal line  32  for the adjacent shape (not shown) that is similar to and below shape  30  that is shown. The sheet is folded approximately 90° away from the reader along lines  34  and folded approximately 180° toward the reader along lines  35 . The thus-formed vane  9  consists of the essentially flat surface bounded by lines  32 ,  33  and  34 . Vane  9  is attached to the rest of the sheet by webs  37  along the two sides of the vane. Webs  37  are bounded by lines  31 ,  34  and  35 . For an annular or circular packing, vane  9  is preferably wider at its top rather than at its bottom as shown. Vane  9  is a vane creating centripetal channels for fluid flowing from the top to the bottom of reactor  1 . For packing between two flat parallel walls, vane  9  preferably has the same width at its top and bottom. 
     Sheet  20  is cut along lines  41 ,  42  and  43 , wherein horizontal line  43  corresponds to horizontal line  42  for the adjacent shape (not shown) that is similar to and below the shape  40  shown. Sheet  20  is folded approximately 90° toward the reader along lines  44  and folded approximately 180° away from the reader along line  45 . The thus-formed vane  11  consists of the essentially flat surface bounded by lines  42 ,  43  and  44 . Vane  11  is attached to the rest of the sheet by webs  47  along the two sides of the vane. Webs  47  are bounded by lines  41 ,  44  and  45 . For an annular or circular packing, vane  11  is preferably narrower at its top than at its bottom as shown, and vane  11  creates centrifugal channels for fluid flowing from the top to the bottom of reactor  1 . For packing disposed between two flat parallel plates, vane  47  preferably has the same width at its top and bottom. Line  48  represents an axial line along the inside surface of a reactor wall or tube wherein the packing contacts the tube at locations  49  and wherein gaps  50  are between the packing and the wall. The angle between vane  9  and line  49  and the angle between vane  11  and line  49  may be the same or may be different. 
     Referring to  FIGS. 2 and 3 , it is seen that bottom shape  30  in columns  21  is disposed only partially above the lower edge  23  of sheet  20 . Cut edges  31  and  32  for bottom shape  30  of column  21  may result in voids or the absence of packing for such bottom shapes. Similarly, it is seen that top shape  40  in columns  22  is disposed only partially below upper edge  24  of sheet  20 . Upper shapes  40  are accordingly truncated by top edge  24 . 
     The sheet formed as described above is cut into lateral lengths and bent into a ring or annular shape or otherwise inserted near one or two reactor walls. The ends of rings may be joined by welding, adhesive or by interlocking the ends. 
     Referring to  FIG. 4 ,  FIG. 4  is a cutaway perspective view of the structured packing of the invention for a cylindrical or annular reactor in which all items in  FIG. 4  corresponding to the previously-described figures has the same numbering as set forth in the previously-described figures. 
     The reactor walls are not shown in  FIG. 4 . Alternating separating walls  8  of the packing are respectively illustrated with different shading darkness from each other. Note that the vanes and webs are not shaded. Packing  3  arrives at an outside diameter at location  4  and at an inside diameter at location  5 . Centrifugal vanes  9  attached to the separating walls by webs  37  occupy centrifugal columns of the packing. Centripetal vanes  11  attached to the separating walls by webs  37  occupy centripetal columns of the packing. The centrifugal and centripetal columns alternate with each other around the casing and extend along the entire length of reactor  1 , preferably from the reactor inlet to the reactor outlet. 
     In an alternative embodiment, multiple structured packing of the invention may be disposed in series within a single reactor between heat sources and heat sinks. For example, two or more of the structured packing units could be placed concentrically and adjacent to each other in an annular or circular reactor. Two or more of the structured packing units could be placed adjacent and parallel to each other between two plate-shaped reactor walls or between two reactor walls of different geometry. 
     The preceding embodiments are illustrative of the invention. It is, however, to be understood that other expedients known to those skilled in the art or disclosed herein may be employed without departing from the spirit of the invention or the scope of the claims which follow.