Abstract:
The invention disclosed herein is a flow baffle for providing a generally uniform flow to a fluid within a catalytic reactor, which is characterized by a single flow channel. The invention, however, has general application to any single flow channel device. The flow baffle is inserted within the reactor in the single flow channel to cause the fluid flowing in the single flow channel to have a generally uniform flow field, instead of preferentially flowing down a periphery of the channel. The uniform flow field promotes the design optimization of the catalytic reactor.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is generally directed to conditioning a flow within a flow channel having obstructions therein, and more specifically to a baffle plate that is positioned within the flow channel of a catalytic reactor.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention has general utility with respect to flow channels that have obstructions positioned therein and is particularly useful in catalytic reactors having a single catalytic flow channel defined in part by a plurality of tubes. One such catalytic reactor is depicted in U.S. patent application Ser. No. 09/527,708 (hereinafter the &#39;708 application), the disclosure of which is incorporated in its entirety herein by reference. The &#39;708 application has a common inventor with the present application, and is assigned to the assignee of the present invention, namely, Precision Combustion, Inc of North Haven, Conn. However, while the catalytic reactor described and illustrated herein is particularly suitable for use with the present invention, it should be understood that the invention is not limited in this regard as the invention could be used with other structures having a single flow channel.  
           [0003]    The catalytic reactor described in the &#39;708 application employs a single catalytic flow channel created by placing a plurality of tubes within a housing such that the tubes, collectively referred to as a bundle, are separated, one from the other, and from the housing. Each tube has an outside surface a portion of which is within the single flow channel and at least one outside surface has a catalyst positioned on some portion thereof. The single flow channel is defined by the exterior surfaces of the tubes and the housing. More specifically, the housing has an inner surface that defines the periphery of the single flow channel. The structure of the catalytic reactor allows a first fluid to enter the single flow channel and a second fluid to enter the tubes, but prevents the first fluid from entering the tubes and the second fluid from entering the single flow channel.  
           [0004]    A problem with a catalytic reactor configured in the above-described manner is that the tubes are obstructions within the single flow channel. Consequently when a first fluid enters the single flow channel, it has a tendency not to develop a uniform flow distribution across the single flow channel; the first fluid does not enter the bundle uniformly. This causes the first fluid to flow primarily along the periphery of the bundle along the inner surface of the housing causing under utilization of the catalyst.  
           [0005]    This problem is exacerbated the larger the bundle. For example in a seven tube hexagonal-packed catalytic reactor, the flow non-uniformity within the bundle is negligible, thus temperatures of the tubes during operation resulting from catalytic activity are relatively similar. However, when the size of the reactor is increased from 7 tubes to 306 tubes, positioned in 17 rows, the tubes on the outer periphery of the bundle operate significantly hotter than those located toward the middle of the bundle, as a result of the non-uniform flow.  
           [0006]    This non-uniform flow of the first fluid within the bundle can lead to under utilization of the catalyst or even non-uniformity in the catalytic reaction. Where the catalyzed reaction is exothermic, non-uniform flow patterns can cause such undesirable effects as hot spots (local heating to temperatures well in excess of the average reaction temperature). As the hot spot temperature is higher than desired, materials from which the reactor is constructed can be unduly stressed. Therefore, due to material limitations of both the catalyst and the tubes (i.e. the substrate), additional margin in the catalyst and tube material must be incorporated into the reactor.  
           [0007]    Based on the foregoing, it is the general objective of the present invention to provide a reactor that overcomes the problems and drawbacks associated with known reactors.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention resides in one aspect to a catalytic reactor wherein a housing defines an interior area and an inlet in fluid communication therewith. The inlet is adapted to receive a first fluid. A plurality of tubes is positioned in the interior area, each defining an exterior surface and an inlet for receiving a second fluid exclusive of the first fluid. The tubes in cooperation with the interior area define a single flow channel through which, during operation, the first fluid, exclusive of the second fluid, passes. A catalyst is positioned within the flow channel on the exterior surface of at least one of the tubes. The flow baffle is positioned within the interior area upstream of at least some of the catalyst for providing a uniform first fluid flow through any remaining portion of the flow channel.  
           [0009]    In a catalytic reactor of the above-described type, the first fluid must pass over tubes located near the reactor&#39;s inlet before it can contact tubes near the reactor&#39;s center. As a result, there is a tendency for the first fluid to flow primarily along tubes located nearer to the reactor&#39;s inlet, following the path of least resistance. The flow baffle introduces an additional and greater flow resistance, so that all flow paths have similar resistance and the flow of first fluid through the reactor becomes more uniform.  
           [0010]    Preferably, the flow baffle is in the form of a plate that defines a plurality of apertures, each having a peripheral surface extending therethrough. An aperture can have none or one or more tubes passing therethrough. Where a tube or tubes pass through an aperture, if the first fluid is intended to also pass through the aperture then the aperture must be oversized. If the peripheral surface of the aperture engages the tube(s) extending therethrough, passage of the first fluid flowing in the single flow channel through that aperture is prevented. Where all of the apertures have tube(s) passing therethrough, some apertures must be oversized. By properly sizing the apertures, the flow resistance within the single flow channel can be modified to provide a generally uniform flow for a fluid flowing therethrough. A generally uniform flow being defined as one that makes the flow of a fluid over the catalyst generally uniform, such that the reaction at any given location is roughly equivalent to the reaction at any other location.  
           [0011]    The housing is defined in part by an interior area the cross-section of which is modified by the flow baffle and the apertures extending therethrough. Each aperture also defines a cross-section through which the first fluid can flow if not blocked by one or more tubes extending through the aperture. By individual sizing of the cross-sections of the apertures, the cross-sections defined thereby cooperate to make the flow of the first fluid through the single flow channel generally uniform. The size of the apertures is based on the location of the aperture, thus apertures can be sized to varying degrees (i.e. graded) tending to be larger toward the center of the bundle, if desired.  
           [0012]    While the invention has been illustrated with tubes, the invention should not be considered limited to structures having circular cross-sections. It should also be understood that the pattern of the tubes within the housing is for illustration only and is not to be considered a limitation of the invention. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic view generally showing a catalytic reactor with a cut away to show representative tubes inside the reactor.  
         [0014]    [0014]FIG. 2 is a cross-sectional view taken along the longitudinal centerline of the reactor of FIG. 1 with a first embodiment of the present invention positioned therein.  
         [0015]    [0015]FIG. 3 is a section of the reactor of FIG. 2 showing a front view of the first embodiment of the present invention.  
         [0016]    [0016]FIG. 4 is a cross-sectional view taken along the longitudinal centerline of the reactor of FIG. 1 with a second embodiment of the present invention positioned therein.  
         [0017]    [0017]FIG. 5 is a section of the reactor of FIG. 4 showing a front view of the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    As shown in FIG. 1, a catalytic reactor, generally referred to by reference  10 , comprises a housing  12  defining an inner area  14  with a plurality of tubes  16 , collectively referred to as a bundle  18 , positioned therein. The bundle  18  defines a periphery  20 , denoted by dotted lines, having a center region  22 , also denoted by dotted lines. The tubes  16 , each having an inlet  17 , and the housing  12  cooperate to define a single flow channel  24 . The housing  12  defines an inlet  26  and a plurality of passages  28 .  
         [0019]    A tube  16  sealably passes through the passage  28 , such that there is no fluid communication between the outside of the catalytic reactor  10  and the single flow channel  24  through the passages  28 . This structure isolates a first fluid  30  that enters the single flow channel  24  through inlet  26  from a second fluid  32  that enters each tube through entrance  17 . The single flow channel  24  ends at a point where the first fluid  30  and the second fluid  32  can mix (see FIGS. 2 and 4).  
         [0020]    [0020]FIG. 2 shows a baffle plate  34  of the first embodiment positioned spatially downstream, based on the normal flow of a first fluid  30  within the single flow channel  24 , from inlet  26 . The baffle plate  34  is a plate  36  that defines a plurality of apertures  38 , each having a peripheral surface  39 . The tubes  16 , each having an exterior surface  40 , are distributed among and pass through the apertures  38 . While a single tube  16  is shown passing through an aperture  38  this is not required as the aperture  38  could be sized to accommodate more than one tube  16 ; thus the invention should not be considered so limited. FIG. 3 more clearly shows the apertures  38  with the tubes  16  passing therethrough.  
         [0021]    Continuing with FIG. 2, in the catalytic reactor 10 , a catalyst  42  is positioned on at least some of the exterior surfaces  40  of the tubes  16  within the single flow channel  24 . The catalyst  42  is positioned at the surface  40 , therefore other methods such as alloying of the catalyst into a substrate are considered within the scope of the invention. The catalyst  42  need not be on each tube  16 . It is preferred, however, that the baffle plate  34  be positioned within the single flow channel  24  spatially upstream of all the catalyst  42 .  
         [0022]    The tubes  16  are depicted as having a uniform cross section and being uniformly packed (specifically hexagonal) within the inner area  14 . Uniform cross-sections and packing of the tubes  16  should not be considered a limitation of the invention. The term tube as used herein means only a closed structure that confines a flow. In addition, a tube  16  is considered to include a multi-channeled structure.  
         [0023]    In this depiction, all apertures  38  have a cross section that is oversized relative to the tube  16  passing therethrough. This, however, is not required as some apertures  38  could engage the tube  16 , or tubes  16 , passing therethrough. In the case were all apertures  38  have tube(s)  16  passing therethrough, some apertures  38  must be oversized.  
         [0024]    Referring to FIG. 1 and FIG. 2, the size of any particular aperture  38  is determined based on the pressure drop from the periphery  20  to the center region  22  of the bundle  18 . Preferably, the apertures  38  are oversized as necessary to create a pressure drop at least equal to the pressure drop from the periphery  20  to the center region  22 , thereby making it equally desirable for the first fluid  30  flowing through the single flow channel  24  to flow down the periphery  20  or the center region  22  of the bundle  18 . Simplistically, all the apertures  38  could be of the same size; however, it is possible to change the size of, or grade, the apertures  38  to more accurately reflect the pressure gradient within the bundle  18 . The pressure drop from the periphery  20  to the center region  22 , or any other location within the bundle  18 , of any given bundle  18  at the desired flow conditions can be determined by experimentation or calculation.  
         [0025]    Continuing with FIG. 3, the depicted apertures  38  are circular in cross section and concentric with tubes  16 , which also have a circular cross-section, passing therethrough; circular cross-sections of apertures  38  or tubes  16  are merely illustrative and should not be considered a limitation of the invention as other cross-sections regular and irregular and positioning could be employed. It is also not a requirement of the present invention that the apertures  38  have the same or similar cross-section to the tube  16  passing therethrough.  
         [0026]    [0026]FIG. 4 is a second embodiment of the baffle plate  34 . The catalytic reactor  10  is the same as that depicted in FIG. 1 and FIG. 2 except none of the apertures  38  is oversized relative to the tube(s)  16  passing therethrough. Instead, some apertures  38  have no tube  16  passing therethrough. FIG. 5 better shows the distribution of apertures  38  in the plate  35 . This embodiment allows greater flexibility, as aperture  38  placement is independent of tube(s)  16  placement. These apertures  38  can also be of varying sizes.  
         [0027]    As those skilled in the art of reactor design will appreciate, there is a third embodiment of the present invention that is a combination of the first and the second embodiments. In other words, it is possible to use a combination of apertures without tubes passing therethrough and apertures with tubes passing therethrough that are oversized. This embodiment is considered within the scope of the invention.  
         [0028]    Referring back to FIGS. 2 and 4, the catalyst  42  can be any catalyst composition selected to promote the desired reaction of the first fluid  30 , which can either cause an exothermic or endothermic reaction. Those skilled in the art of catalytic reactor design generally know how a given catalyst composition interacts, exothermically or endothermically, with a given first fluid  30 . As those skilled in the art appreciate, there are numerous methods for positioning the catalyst  42  on the surface  40  including but not limited to depositing, such as by dipping or deposition, and incorporation of the catalyst  42  into the tube  16 . It is preferred that the catalyst  42  be positioned on the surface  40  of tube, or tubes,  16  downstream of the flow baffle  34 . It is not a requirement of the present invention, however, that catalyst is positioned on each tube  16 , and the invention should not be considered so limited.  
         [0029]    Although the present invention has been described in considerable detail with reference to certain preferred versions, thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.