Patent Publication Number: US-2016243516-A1

Title: Catalyst support grid

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of conversion of hydrocarbons and, more specifically, of the reforming of hydrocarbon-containing feedstock and ammonia production in a fixed bed catalytic reactor with an improved catalyst support. 
     BACKGROUND OF THE INVENTION 
     Many types of fixed bed catalyst support and retention devices have been used over the decades of chemical plant experience. Many of these devices were small and resulted in a high pressure drop of the reactors in operation. Many of the larger devices were required to be installed in the reactor pressure vessel at fabrication before closure heads were welded into place. Many of the earlier devices were also shaped as straight beams that crossed the lower tangent line of the reactor vessel in a horizontal axis to form a circular disc. 
     There is a need for an improved catalytic reactor with a support having a design that allows supporting of fixed pellet-type catalyst beds within the reactor pressure vessel, to prevent catalyst migration downstream while imposing the minimum possible pressure drop of the reacting fluid passing through the reactor vessel. Also needed is a support grid for a catalytic reactor that may be easily installed through a limited diameter opening in the reactor vessel. Lower catalyst bed support systems that reduce or eliminate empty or dead spaces at the bottom of conventional reactors, as well as catalyst bed support systems that allow refiners to load increasing amounts of catalyst materials into a reactor without resorting to use of inert catalyst support particle beds, which degrade over time and add significant operating costs to the refinery, are also needed. 
     SUMMARY OF THE INVENTION 
     The present invention provides catalytic reactors, catalyst supports, catalyst support grids and systems, collection systems and methods of improving energy efficiency and increasing production in gasoline fraction and/or ammonia production. 
     The catalyst support grid is formed of (i) a center support or support stool in the form of a cylinder; (ii) a support skirt located at the outer circumference of the grid; (iii) a set of radial support arms (rods and brackets) that extend from the center support structure to the support skirt to tie these sections into a rigid frame; and (iv) a disc or grid formed of a plurality of support grid wedges or sections that are supported by the rigid frame. The center support, the support skirt, the set of radial arms, and the disc or grid of the support grid wedges may all be formed of various parts/components that are introduced separately and assembled within the reactor vessel. 
     These and other features and advantages of the present invention will become apparent from the following description of the invention that is provided in connection with the accompanying drawings and illustrated embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an expanded view of a catalyst support grid (bottom support grid assembly) according to an exemplary embodiment of the present invention (illustrating exemplary support grid sections; support skirt sections; outlet collector rods and brackets; outlet collector plate cover; and outlet collector support stool sections). 
         FIG. 2  illustrates a top view of the bottom support grid assembly of  FIG. 1 . 
         FIG. 3  illustrates a side view of the bottom support grid assembly of  FIG. 1 . 
         FIG. 4  illustrates a schematic view of a reactor with the bottom support grid assembly of  FIG. 1 . 
         FIG. 5  illustrates an enlarged top view of the grid with outlet collector assembly of  FIG. 4  (taken from the inside of the reactor vessel). 
         FIG. 6  illustrates a cross sectional view of the assembly of  FIG. 5  taken along line B-B. 
         FIG. 7  illustrates an enlarged view of an exemplary bolt for the grid with outlet collector assembly of  FIG. 4 , and according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides catalytic reactors, catalyst support systems and/or grids, collection systems and methods of improving energy efficiency and increasing production in gasoline fraction and/or ammonia production. 
     The catalyst support system of the present invention is in the form of a support grid for catalytic reactors such as, for example, High and Low Temperature Shifts reactors (HTS and LTS reactors), vertical down-flow reactors, or any other type of catalytic reactor with a bed of solid catalyst particles. 
     In an exemplary embodiment, the present invention provides a catalyst support grid (also referred to as support, support grid, catalyst support system, support assembly, support grid assembly or catalyst bed support grid assembly) for a fixed bed catalyst of a chemical reactor, i.e., for supporting a fixed bed catalyst. The support grid has a robust design to support the catalyst bed (for example, a fixed pellet-type catalyst bed) within the reactor pressure vessel, to prevent catalyst migration downstream while imposing the minimum possible pressure drop of the reacting fluid passing through the reactor vessel. The catalyst support grid may be installed through a limited diameter opening in the reactor vessel. 
     In an exemplary embodiment, and as detailed below, at least one component of the catalyst support grid is modular, i.e., is formed of simple and relatively small parts (sub-parts or sub-sections) that are installed/assembled within the reactor vessel, for example, during a short operating plant shutdown. The repetitive nature of the components (sub-parts, sub-sections or sub-components) forming each component/piece of the support grid assembly allows the installation and assembling of the support grid without the use of welding or similar operations on the assembly itself, eliminating the negative effects of welding on the whole reactor and increasing the reliability of the overall process. Preferably, all components/pieces of the support grid assembly are modular, i.e., each is formed of pieces that can be assembled together and installed within the reactor vessel, independently of the other components/pieces. The assembly components are subsequently assembled together within the reactor vessel. 
     An exemplary support grid of the present invention comprises inter alia (i) a center support or support stool; (ii) a support skirt located at the outer circumference of the grid; (iii) a set of radial support arms (rods and brackets) that extend from the center support structure to the support skirt; and (iv) a grid or disc formed of a plurality of support grid sections or wedges. 
     According to another exemplary embodiment of the present invention, a catalyst support grid comprises inter alia (i) a center support or support stool in the form of a cylinder; (ii) a support skirt located at the outer circumference of the grid; (iii) a set of radial support arms (rods and brackets) that extend from the center support structure to the support skirt; and (iv) a grid or disc formed of a set of support grid wedges or sections that are radial in orientation and are supported by the rigid frame. 
     Another exemplary catalyst support grid of the present invention comprises inter alia (i) a center support or support stool in the form of a cylinder made of parts/areas/regions of a vertical cylinder that are assembled within the reactor vessel; (ii) a support skirt located at the outer circumference of the grid and formed of sections that are assembled inside the reactor vessel; (iii) a set of radial support arms (rods and brackets) that extend from the center support structure to the support skirt to tie these sections into a rigid frame; (iv) a set support grid wedges or sections that are radial in orientation and are assembled inside the reactor pressure vessel to form a disc or grid that is about 80% of the reactor vessel in outside diameter, the support grid wedges being supported by the rigid frame; and (v) a cover plate. 
     Another exemplary catalyst support grid of the present invention comprises inter alia the following modular components or modular structural parts: (i) a center support cylinder made of a plurality of portions/regions/areas of a vertical cylinder, assembled within the reaction vessel on the bottom closure head, the center support cylinder having at least one area that is perforated to allow free passage of the reactant fluid, and being centered over the reactor vessel outlet nozzle; (ii) a peripheral support skirt located at the outer circumference of the grid, the peripheral support skirt being formed of a plurality of components/regions/parts/pieces that are assembled in sections inside the reactor pressure vessel, that sets without welding to bottom closure head of the reactor vessel; (iii) a set of radial support arms (brackets and rods) that extend from the center support structure to the peripheral support skirt to tie these sections into a rigid frame; (iv) a disc or grid formed of a set of catalyst bed support grid wedges or sections that are radial in orientation and are assembled inside the reactor pressure vessel to form a disc that is about 80% of the reactor vessel in outside diameter, the wedges being supported by the rigid frame, and having the mechanical strength to support the weight of the catalyst bed and the resultant force of the pressure drop of reactant fluid as it passes through the catalyst bed in operation, wherein the open area of the support grid wedges is sufficient to impose an insignificant pressure drop on the flowing reactant fluid relative to the pressure drop through the catalyst bed; and (v) a plate cover. 
     As detailed below, the catalyst support grid of the present invention is designed to fit the subject reactor pressure vessel such that it may be fabricated in parts (in a remote manufacturing shop, for example) and transported to the installation site at an ammonia synthesis plant by ordinary truck, marine transportation or any other suitable means. Many or all of the parts are repetitive in design making the fabrication quicker and more economical. The parts may be fabricated of either carbon or alloy steel material, as required by the demands of the particular chemical plant. 
     In an exemplary embodiment, the catalyst support grid assembly may be installed in an ammonia synthesis plant syngas shift converter to restrain the catalyst bed pellets from migration downstream while lowering the overall pressure drop of the reactant syngas fluid through the reactor vessel, as opposed to the traditional design of catalyst retention devices that were small and covered only a limited area over the reactor pressure vessel outlet nozzle. According to the present invention, the new center support (if needed) is taken into the reactor vessel through the limited diameter manway opening at the top of the pressure vessel and the parts are assembled over the existing outlet nozzle by bolting. There is no welding involved on or within the reactor vessel, as the vessel has been post-weld heat-treated at fabrication and as further welding on the vessel is prohibited by recognized pressure vessel codes. The radial support arms are taken into the reactor vessel though the manway nozzle and assembled to the center support by bolting. The arc sections of the peripheral skirt are taken into the vessel through the manway and assembled into a large diameter ring by bolting to each other and outer ends of the radial arms. The catalyst support grid wedges are taken into the reactor vessel through the manway and assembled into a complete disc by bolting to each other with the inner diameter of the disc resting on the center support and the outer diameter of the disc resting on the support skirt. 
     Spring clips or similar structures may be provided and located in the joints between the grid wedges, to keep the joint bolting tight during startups and shutdowns of the ammonia plant as the shift converter reactor undergoes thermal cycling. Several thin layers of inert material of increasingly smaller size may be installed over the catalyst support grid to prevent the small catalyst particles from migrating to the grid face during operation. These thin layers of inert material may be similar to or different from those traditionally used in fixed catalyst bed reactors. The catalyst bed particles are loaded on top of the inert material. 
     Referring now to the drawings, where like elements are designated by like reference numerals,  FIGS. 1-3  illustrate exemplary catalyst support grid  100  (also referred to as catalyst support or assembly or system  100 , catalyst bed support grid or assembly  100 , bottom support grid assembly  100 , or support structure  100 ) of the present invention.  FIGS. 4-7  illustrate an exemplary reactor  200  of the present invention incorporating exemplary catalyst support grid  100  of  FIG. 1 . 
     In an exemplary embodiment, and as detailed below, the catalyst support grid  100  comprises inter alia (i) a center support  10  in the form of a cylinder  10  formed of a plurality of outlet collector support stool sections assembled together; (ii) a support skirt  30  located at the outer circumference of the grid assembly; (iii) radial support arms  50  (rods  50   a  and brackets  50   b ) that extend from the center support structure to the support skirt  30 ; and (iv) a disc or grid  60  formed of catalyst bed support grid wedges or sections  60   a  that are radial in orientation and are supported by the skirt  30 . 
     In an exemplary-only embodiment, the catalyst support grid  100  is formed of (i) an outlet collector  10  in the form of a cylinder  10  (support stool  10 ); (ii) a support skirt  30  located at the outer circumference of the grid assembly and formed of six skirt sections, the six skirt sections being preferably all similar; (iii) twenty four radial support arms  50  (formed of twelve outlet connector rods  50   a  and twelve outlet brackets  50   b ) that extend from the center support structure to the support skirt; and (iv) twenty four catalyst bed support grid wedges or sections  60   a  that are radial in orientation and are supported by the skirt  30 , the wedges forming an outer grid or disc  60 . 
     As illustrated in  FIGS. 1 and 3 , the center support  10  (support stool  10 ) is made of areas/regions of a vertical cylinder that are assembled together and installed within the reactor vessel, on the bottom closure head. The center support  10  is provided in the form of a modular cylinder  10  formed of a plurality of vertical cylinders and of areas or parts of a cylinder, i.e., a multi-part structure formed of pieces/parts (sub-parts or sub-sections) that have similar or non-similar configuration and shape. 
     For example, the specific and exemplary-only embodiment shown in  FIG. 1  illustrates lower part center support  10   a  (lower cylinder section  10   a ) formed of six identical pieces or sub-parts  10   a   1 ,  10   a   2  . . .  10   a   6 , and middle part center support  10   b  (middle cylinder section  10   b ) also formed of six identical pieces or sub-parts  10   b   1 ,  10   b   2  . . .  10   b   6 , which are similar to parts/sections  10   a   1 ,  10   a   2  . . .  10   a   6 . Top cylinder portion  10   c  is formed of six identical pieces or sub-parts  10   c   1 ,  10   c   2  . . .  10   c   6 . All these sub-parts may be installed and assembled together by simple bolting operations and within the reactor vessel, without the need for welding or similar-type procedure. During installation within the reactor vessel, the center support  10  is centered over the reactor vessel outlet nozzle. The center support  10  is also perforated, throughout the whole cylindrical area or only some parts), to allow free passage of the reactant fluid. 
     The peripheral support skirt  30  ( FIGS. 1 and 3 ) is formed of a plurality of support skirt sections  30   a , for example of six similar support skirt sections. The support skirt sections  30   a  have an arcuate configuration. The skirt is located at the outer circumference of the grid, assembled in sections (sub-parts) inside the reactor pressure vessel and without welding, onto the bottom closure head of the reactor vessel. The arc sections  30   a  of the peripheral skirt  30  are taken into the vessel through the manway and assembled into a large diameter ring (i.e., skirt  30 ) by bolting to each other and to outer ends of the radial support arms  50  (i.e., to the connector rods  50   a , as shown in  FIG. 3 ). 
     The set of radial support arms  50  is formed of outlet connector rods  50   a  and outlet brackets  50   b . In an exemplary-only embodiment, the radial support arms  50  consist of twelve similar outlet connector rods  50   a  and twelve corresponding similar outlet brackets  50   b . The arms extend from the center support structure to the support skirt  30  to tie sections  30   a  of support skirt  30  into a rigid frame to support the catalyst bed support grid wedges  60   a , as detailed below. The radial support  50  arms are taken into the reactor vessel though the manway nozzle and assembled to the center support  10  by bolting. In a specific and exemplary-only embodiment, radial support arms  50  are bolted to the middle part center support  10   b , as illustrated in  FIG. 3 . 
     Disc or grid  60  is formed of a plurality of support grid sections or wedges  60   a , for example, of twenty four similar grid sections or wedges  60   a . These sections (wedges or sub-parts) are radial in orientation and are assembled inside the reactor pressure vessel to form disc  60  that is about 80% of the reactor vessel in outside diameter. Grid sections  60   a  (wedges  60   a ) of set  60  have the mechanical strength to directly support the weight of the catalyst bed and the resultant force of the pressure drop of reactant fluid as it passes through the catalyst bed in operation. The open area  63  of the support grid wedges  60   a  is sufficient to impose an insignificant pressure drop on the flowing reactant fluid relative to the pressure drop through the catalyst bed. The catalyst support grid wedges  60   a  are taken into the reactor vessel through the manway and assembled into a complete disc (i.e., into the disc/set  60  of support grid wedges  60   a ) by bolting to each other, with the inner diameter  65  and inner circumferential edge  65   a  of the disc  60  resting on the center support  10 , and with the outer diameter  66  and outer circumferential edge  66   a  of the disc  60  resting on the support skirt  30 . 
     The catalyst support grid  100  may also comprise a plate cover  20  (outlet collector plate cover  20 ) provided over the support stool  10 , as shown in  FIG. 1 . Plate cover  20  is provided with opening  22  (which may have various shapes and geometries, for example, the rectangular shape shown in  FIG. 2 ) and perforations  23  to allow passage of fluid. To permit final assembly, the outer diameter of disc  60  is about equal to the outer diameter of skirt  30 , and the inner diameter of disc  60  is about equal to the outer diameter of plate cover  20 , as shown in  FIG. 3 . 
     An exemplary reactor  200  that may be fitted or retrofitted with the catalyst support grid  100  of the present invention is shown in  FIG. 4 . In fixed-bed hydroprocessing reactors such as reactor  200 , gas and liquid reactants (e.g. hydrogen and a hydrocarbonaceous feedstock) flow downward through one or more beds of solid catalyst extrudates. As the reactants flow downward through the catalyst beds, the reactants react to produce the desired products. Gas phase reactants such as hydrogen are consumed, and heat is generated by the catalytic reactions. 
     Exemplary vertical, down-flow reactor  200  shown in  FIG. 4  includes a reactor vessel  202  with an inner wall  202   a  and having upper and lower catalyst zones  203 ,  204  which abut quench zone  205 , located between the upper and lower catalyst zones  203 ,  204 . A liquid feedstock is introduced into the vessel  202  via a line  206  through inlet  207 . The feedstock is distributed across a distribution assembly  209  adapted to uniformly spray the feedstock across the top of the upper catalyst zone  203 . Reactor  200  also includes support grid assembly  100  that supports catalyst bed  220 , preferably a pellet-type catalyst bed  220 . Catalyst bed  220  may contain packed catalytic extrudates supported on the catalyst bed support  100  of the present invention. The catalyst bed support  100  is affixed to the vessel shell inner wall  202   a . Support center  10  in the form of a vertical cylinder extends in a direction about parallel to longitudinal axis  210  of reactor vessel  202  ( FIG. 6 ) so that, preferably, longitudinal axis  11  of the support center  10  coincides with the longitudinal axis  210  of reactor vessel  202 . 
     The reactor  200  may further include an outlet  231  for discharging product effluent from the reactor  100  during commercial service, and a catalyst drain tube  232  for removing spent catalyst extrudates during turnaround operations. The catalyst drain tube  232  extends downwardly from the bottom of the reactor  200 . 
       FIG. 5  illustrates an enlarged top view of the grid with outlet collector assembly  100  (catalyst support grid  100 ) of  FIG. 4  taken from the inside of the reactor vessel  202 .  FIG. 6  illustrates a cross sectional view of the assembly of  FIG. 5  taken along line B-B. Support center  10  in the form of a vertical cylinder extends in a direction about parallel to longitudinal axis  210  of reactor vessel  202  ( FIG. 6 ) so that, preferably, longitudinal axis  11  of the support center  10  coincides with the longitudinal axis  210  of reactor vessel  202 . Preferably, support skirt  30 , outlet collector arms  50  and disc or grid  60  are assembled within the reactor vessel  202 , and then to the support center  10 , so that these structures are oriented about perpendicular to the longitudinal axis  11  of the support center  10  to form final catalyst support grid  100  (assembly  100 ). 
       FIG. 7  illustrates an enlarged view of an exemplary bolt assembly  300  for the grid with outlet collector assembly of  FIG. 4 , and according to an embodiment of the present invention, showing a threaded stud  323  with nut and washer, a J clip  333 , cover plate  20 , and inspection hatch  322 . 
     Some of the advantages of employing support grid  100  of the present invention in a reactor such as reactor  200  are as follows:
         at least some of the parts (preferably all) of support grid  100  may be fabricated remotely from the installation site and easily shipped using ordinary transport;   the parts are largely repetitive in design and fabrication, thus making engineering and fabrication time minimum. The radial design allows the use of simple structures and design without having to calculate or allow for asymmetric loading of linear beams as in the prior art reactors;   the parts may be introduced through a small diameter manway, as is typical in many catalytic reactor vessels, meaning that the design may be used as an aftermarket improvement to the reactor;   there is no welding required to be performed on the reactor pressure vessel during installation as welding is prohibited by code in most instances. There is no welding required on the grid itself, eliminating the chance of an unintentional arc strike on the pressure vessel during installation;   the repetitive nature of the assembly of relatively small parts means that a small crew may install the grid quickly during a short operating plant shutdown;   the spring clips between the wedges allow the grid to adjust itself during thermal cycling operation. This also limits the amount of rigid bolted joints that can make assembly of the overall support grid more challenging to the field personnel; and   the large open area of the grid means that the overall reactor pressure drop in operation will be substantially reduced from the typical small size retention devices used in the past. This reduction in pressure drop means increased production capacity and/or increased thermal efficiency of the operating chemical unit.       

     In the reactor  200  illustrated in  FIG. 4 , the lowermost or bottom catalyst bed  220  is supported above the outlet using the catalyst support grid  100  which is employed in lieu of a horizontal catalyst tray or a bed of inert material (such as inert ceramic spheres). The horizontal catalyst trays or beds of inert material produce empty or dead spaces at the bottom of the reactor. In addition, the amount of active catalyst that can be loaded into the lower catalyst bed is limited by the static load limits of the horizontal tray. This limitation is significant because available feedstocks are become increasingly disadvantaged, requiring more hydroprocessing which, in turn, necessitates loading more catalyst material into existing reactors. 
     The catalyst bed support grid  100  of the present invention reduces or eliminates empty or dead spaces at the bottom of conventional reactors. In addition, the novel catalyst bed support system of the present invention allows refiners to load increasing amounts of catalyst materials into a reactor, without resorting to use of inert catalyst support particle beds, which degrade over time and add significant operating costs to the refinery. 
     The catalyst support grid  100  of the present invention may be employed in hydroprocessing reactors used in the petroleum and chemical processing industries for carrying out catalytic reactions of hydrocarbonaceous feedstocks in the presence of hydrogen, at elevated temperatures and pressures. Exemplary reactions including hydrotreating, hydrofinishing, hydrocracking and hydrodewaxing, among many others. 
     The support grid of the present invention consists of (i) a center support cylinder, made in areas of a vertical cylinder that is assembled within the vessel on the bottom closure head. The center support cylinder is perforated in some manner to allow free passage of the reactant fluid. The center support cylinder is centered over the reactor vessel outlet nozzle; (ii) a peripheral support skirt located at the outer circumference of the grid, assembled in sections inside the reactor pressure vessel, that sets without welding to bottom closure head of the reactor vessel; (iii) a set of radial support arms that extend from the center support structure to the support skirt to tie these sections into a rigid frame to support the catalyst bed support grid wedges; and (iv) a set of catalyst bed support grid wedges that are radial in orientation and are assembled inside the reactor pressure vessel to form a disc that is about 80% of the reactor vessel in outside diameter; these wedges have the mechanical strength to support the weight of the catalyst bed and the resultant force of the pressure drop of reactant fluid as it passes through the catalyst bed in operation. The open area of the support grid wedges is sufficient to impose an insignificant pressure drop on the flowing reactant fluid relative to the pressure drop through the catalyst bed. 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, embodiments and substitution of equivalents within the scope of the invention. Accordingly, the invention is not to be considered as limited by the foregoing description.