Patent Publication Number: US-11389778-B2

Title: Method of fabricating concentric-tube catalytic reactor assembly

Description:
This application is a continuation of application Ser. No. 15/216,734, filed Jul. 22, 2016, and claims the benefit of U.S. Provisional Application No. 62/196,737, filed Jul. 24, 2015, all of which are incorporated herein by reference. 
    
    
     The present disclosure is directed towards a method of fabricating a catalytic reactor assembly, and more particularly, a method of fabricating a concentric-tube catalytic reactor assembly. 
     Catalytic reactors are devices used in the production of commercial gases through catalytic reforming processes. A catalytic reactor receives feed materials (e.g., a carbonaceous fuel and steam) and guides them through heated passages containing catalysts that convert the feed materials into production gases (e.g., hydrogen, carbon monoxide, carbon dioxide, etc.). Catalytic reactors are sometimes used in conjunction with other devices that consume production gases to drive other processes. For example, catalytic reactors are sometimes used to generate and supply hydrogen to fuel cells that convert the chemical energy of hydrogen into electricity. 
     Some catalytic reactors utilize a tube-in-tube or concentric-tube design in order to reduce the overall size of the reactor or to facilitate specific physical designs and process connection points. Concentric-tube reactors occupy less space by introducing feed materials or reactants through a first tube that is concentric with and fluidly connected to a second tube containing the reactor&#39;s catalyst materials. The compactness of concentric-tube designs improves heat transfer efficiency within the reactor, allowing the reactor to operate at lower temperatures and pressures. At lower temperatures and pressures, the reactor may be simpler in design and construction and may incorporate less expensive materials, thereby reducing the overall cost to construct and operate the reactor. Concentric-tube reactors also enable all process connections to be made at one end of the tube, simplifying construction and enabling designs with low stress under thermal cycling operating conditions. 
     To further improve reactor efficiency and reduce the cost of operation, manufacturers may wish to ensure that all reactants supplied to the reactor are converted into production gases by the catalysts contained in the reactor. However, many catalysts incorporated into reactor assemblies are pre-fabricated with reduced outer diameters and/or increased inner diameters to allow them to be more easily slid between the reactor tubes without being damaged during reactor assembly. This loosening of the fit between the catalyst and the reactor tubes can allow reactants to pass between the catalyst and reactor tubes during operation without being converted into production gases, thereby reducing the conversion efficiency of the reactor. Alternative fabrication methods have involved the use of complicated fixtures and assembly procedures, which may be time consuming and costly. 
     Therefore, there is a need for an improved method of fabricating concentric-tube catalytic reactors that results in a better seal between the catalyst and the reactor tubes. 
     One aspect of the present disclosure is directed to a method of fabricating a catalytic reactor assembly having an outer tube and an inner tube. The method may include inserting a catalyst into the outer tube and inserting the inner tube through the catalyst. The method may further include radially expanding the inner tube against the catalyst. 
     Another aspect of the present disclosure is directed to a method of fabricating a catalytic reactor assembly having an outer tube and an inner tube. The method may include inserting a catalyst into the outer tube and inserting the inner tube through the catalyst, wherein the inner tube is concentric with the catalyst and the outer tube. The method may further include connecting at least a first end of the inner tube to a source of pressurized fluid, directing pressurized fluid from the source into the at least first end of the inner tube, and radially expanding the inner tube against an inner surface of the catalyst using pressurized fluid from the source. 
     Another aspect of the present disclosure is directed to a method of fabricating a catalytic reactor assembly having an outer tube and an inner tube. The method may include inserting a catalyst into the outer tube and inserting the inner tube through the catalyst, wherein the inner tube is concentric with the catalyst and the outer tube. The method may further include connecting a first end of the inner tube to a source of pressurized fluid, sealing a second end of the inner tube, directing pressurized fluid from the source into the first end of the inner tube, and radially expanding the inner tube against an inner surface of the catalyst using pressurized fluid from the source. The method may further include evacuating the inner tube of pressurized fluid. The method may further include installing a cap onto an end of the outer tube and sealing the end of the outer tube. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed. 
    
    
     
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and together with the description, serve to explain the principles of the disclosure. 
         FIG. 1  is a longitudinal cross-sectional illustration of an exemplary disclosed catalytic reactor assembly. 
         FIG. 2  is latitudinal cross-sectional illustration of the catalytic reactor assembly of  FIG. 1 . 
         FIG. 3  is a flowchart depicting an exemplary disclosed method of fabricating the catalytic reactor of  FIG. 1 . 
     
    
    
     Reference will now be made in detail to the present exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Although described in relation to catalytic reactor assembly, it is understood that the methods of the present disclosure may be employed with various types of devices, including, but not limited to catalytic reactors, exhaust purification catalysts, particulate filters, mufflers and sound attenuating devices and heat exchangers. 
       FIG. 1  shows a cross-sectional illustration of a catalytic reactor assembly (“assembly”)  100 , according to an exemplary embodiment. Assembly  100  may comprise an outer tube  110 , an inner tube  120 , and a catalyst  130  disposed in between outer tube  110  and inner tube  120 . Catalyst  130  may be, for example, a toroidal or “donut-shaped” catalyst, a cylindrical catalyst, or an annular catalyst. The catalyst may be in the form of individual pellets or coated onto a metal foil structure. The catalyst may be a single large element (as shown in  FIG. 1 ) or in the form of shorter, individual toroid elements stacked together. Short, individual toroid elements may be stacked tightly or spaced apart from each other. In the embodiment of  FIG. 1 , outer tube  110 , inner tube  120 , and catalyst  130  are concentric about a common axis  140 . For example, assembly  100  may be a concentric-tube reactor or a tube-in-tube reactor. In other embodiments, outer tube  110 , inner tube  120 , and catalyst  130  may be offset from one another. 
     Reactants may flow into one of outer tube  110  and inner tube  120  at a first end  150  of assembly  100 , through catalyst  130 , and into the other of outer tube  110  and inner tube  120  at a closed second end  160  of assembly  100 . Second end  160  may be sealed by a cap  170  (e.g., welded to outer tube  110 ), a compression fitting, or another sealing mechanism. As shown in  FIG. 1 , reactants may flow into first end  150  via outer tube  110 , through catalyst  130 , and into inner tube  120  at second end  160 . After passing through catalyst  130 , the reactants may be converted into products (e.g., product gases) and exit assembly  100  via inner tube  120  at first end  150 . In another embodiment, the reactants may flow into assembly  100  via inner tube  120  at first end  150 , through catalyst  130 , and into outer tube  110  at second end  160 . After passing through catalyst  130 , the reactants may be converted into products and exit assembly  100  via outer tube  110  at first end  150 . Other configurations of outer tube  110 , inner tube  120 , and catalyst  130  may be possible. 
     Outer and inner tubes  110 ,  120  may be formed of a metal or other material configured to withstand the temperatures and pressures at which reactions within assembly  100  are performed. For example, outer and inner tubes  110 ,  120  may be formed of stainless steel and/or other steel or nickel-based alloys, such as those containing one or more of iron, chromium, nickel, niobium, and/or other materials. Outer and inner tubes  110 ,  120  may each have a desired diameter and thickness based on desired operating parameters and conditions of assembly  100 . For example, the diameter of outer and inner tubes  110 ,  120  may be increased to accommodate higher throughputs (i.e., higher quantities and/or rates of production), and the thickness of tubes  110 ,  120  may be increased to accommodate higher operating pressures and/or temperatures. 
     Catalyst  130  may be a pre-fabricated catalyst configured to fit within outer tube  110 . Catalyst  130  may comprise one or more of particulates, pellets, and a coating disposed on a support structure. For example, catalyst  130  may comprise a catalytic coating disposed on structured support (e.g., honeycomb, wall flow, flow-through, fiber, mesh, screen, corrugated foil, stamped foil, metal or ceramic foam, perforated foil, etc.). The structured support may be formed of one or more materials (e.g., silica, alumina, cordierite, zeolite, ceramics, metals, metal alloys, wire mesh, etc.) configured to withstand the desired operating parameters of assembly  100 . Particulates and pellets may be formed of or coated with catalytic materials to form a catalyst bed. 
     Catalyst  130  may incorporate one or more catalytic materials, such as, for example, nickel, cobalt, ruthenium, rhodium, palladium, platinum, and/or other noble metals and mixtures thereof. Catalyst  130  may also or alternatively include catalytic material mixtures comprising, for example, gold, silver, tin, copper, cobalt, molybdenum, iron, gadolinium, boron, etc. Other materials, such as metal oxides (e.g., aluminum oxides and magnesium oxides) and mixed metal oxides may also or alternatively be used. 
     As shown in  FIG. 2 , catalyst  130  may be disposed in an annular space between outer tube  110  and inner tube  120 . The annular space may be defined by an inner diameter D 1  of outer tube  110  and an outer diameter D 2  of inner tube  120 . Catalyst  130  may be pre-fabricated to have a desired outer diameter D 3  and a desired inner diameter D 4 . For example, the outer diameter D 3  of catalyst  130  may be configured to allow catalyst to have a particular fit within outer tube  110 . That is, D 3  may be selected so catalyst  130  fits snuggly, loosely, very tightly, etc., within outer tube  110 . Inner diameter D 4  of catalyst  130  may also be selected to have a desired fit around inner tube  120  (e.g., snug, loose, very tight, etc.) 
       FIG. 3  shows a flowchart depicting an exemplary disclosed method  300  of fabricating assembly  100 . Fabrication of assembly  100  may begin with inserting catalyst  130  into outer tube  110  (Step  310 ). Catalyst  130  may be inserted with outer tube  110  open at first end and second ends  150 ,  160 . Catalyst  130  may be pre-fabricated to have a desired fit when inserted into outer tube  110 . For example, in some embodiments, catalyst  130  may be pre-fabricated to fit snugly or very tightly within outer tube  110  upon insertion. In other embodiments, catalyst  130  may be prefabricated to be less snug upon insertion into outer tube  110  in order to allow for radial expansion against the inside of outer tube  110  when inner tube  120  is installed. 
     Fabrication of assembly  100  may continue by inserting inner tube  120  through the center of catalyst  130  (Step  320 ). Prior to installation, the outer diameter D 2  of inner tube  120  may initially be smaller than the inner diameter of catalyst  130 . In this way, inner tube  120  may be inserted through catalyst  130  without damaging catalyst  130 . By allowing inner tube  120  to be inserted through catalyst  130  after catalyst  130  has been installed in outer tube  110 , the components of assembly  100  may be installed without separating outer tube  110  into longitudinal or latitudinal components. Prior to installation, inner tube  120  may initially be longer than outer tube  110  to allow both ends of inner tube  120  to be accessible during subsequent fabrication steps. 
     In other embodiments, fabrication of assembly  100  may begin with slipping catalyst  130  over or around inner tube  120 . Inner tube  120  may be open at both ends or closed at one end when catalyst  130  is slipped over inner tube  120 . Catalyst  130  may be pre-fabricated to have a desired fit around inner tube  120  upon installation. For example, in some embodiments, catalyst  130  may be pre-fabricated to fit snugly or very tightly around inner tube  120  once installed. In other embodiments, catalyst  130  may be prefabricated to be less snug around inner tube  120  in order to allow for radial expansion of inner tube  120  against the inside of catalyst  130 . 
     In embodiments where catalyst  130  is first slipped over inner tube  120 , fabrication of assembly  100  may continue by inserting inner tube  120  with catalyst  130  as an assembly or sub-assembly into outer tube  110 . Prior to installation, the outer diameter D 3  of catalyst  130  may initially be smaller than the inner diameter D 1  of outer tube  110 , allowing catalyst  130  (alone or in an assembly with inner tube  120  to be inserted into outer tube  110  without damaging catalyst  130 . In this way, assembly  100  may also be fabricated without dividing outer tube  110  into longitudinal or latitudinal components and reassembling them after installation of catalyst  130  and/or inner tube  120 . 
     After inner tube  120  and catalyst  130  are installed, one end of inner tube  120  may optionally be sealed (Step  330 ). For example, one end of inner tube  120  may be welded closed, capped off with a compression fitting, or sealed by another method to allow fluid pressure within inner tube  120  to be increased during subsequent fabrication steps. It is understood that sealing one end of inner tube  120  may be performed before process  300  or at a different point during process  300 . 
     Inner tube  120  may then be pressurized and expanded radially against catalyst  130  (Step  340 ), for example, using a hydroforming process. That is, pressurized fluid may be directed into inner tube  120 , causing the material of inner tube  120  to expand outwardly (i.e., radially) toward catalyst  130 , thereby increasing the outer diameter D 2  of inner tube. For example, in embodiments where one end of inner tube is sealed (i.e., when step  330  is performed), the open end of inner tube  120  may be fluidly connected to a source of pressurized fluid, such as a compressor or a pump. In embodiments where both ends of inner tube  120  are left open (i.e., when step  33  is not performed), both ends of inner tube  120  may be connected to the source of pressurized fluid. The pressure within inner tube  120  may be increased until inner tube  120  expands to a desired size (e.g., a desired outer diameter D 2 ). In this way, the outer diameter D 2  of inner tube  120  may be increased to form a seal with catalyst  130  for preventing the flow of reactants between inner tube  120  and catalyst  130  during operation of assembly  100 . 
     In some embodiments, pressurized fluid may be directed into inner tube  120  to directly cause inner tube  120  to expand. For example, the pressure of a relatively incompressible fluid (e.g., hydraulic fluid, water, etc.) may be gradually increased within inner tube  120  until inner tube  120  expands to the desired size. By controlling the pressure within inner tube  120 , the tightness of the seal between inner tube  120  and catalyst  130  may be controlled. That is, increasing the pressure within inner tube  120  may cause inner tube  120  to expand more and create a tighter seal with catalyst  130 . In some embodiments, the expansion of inner tube  120  may cause the inner diameter D 4  and/or the outer diameter D 3  of catalyst  130  to expand, thereby creating a tighter seal between catalyst  130  and the inside of outer tube  110  and/or the outside of inner tube  120 . 
     In other embodiments, an expansion object, such as a metal sphere or rod, may be forced into inner tube  120 , causing it to expand to the desired size. For example, the expansion object may be driven or drawn through inner tube  120  under the force of pressurized fluid or by a mechanical device until inner tube  120  is sufficiently expanded. Different expansion objects (e.g., balls, bullets, etc.) having different shapes, materials, and/or sizes may be used, as desired and/or depending on the application. 
     Expansion techniques may also or alternatively include internal swaging techniques and/or other tube-expanding techniques adapted for use in expanding inner tube  120 . For example, elastomeric swaging equipment may be adapted to force an expander attached to a drawbolt through inner tube  120 , thereby causing inner tube to expand against catalyst  130 . Other swaging techniques and/or swaging tools (e.g., punches, presses, rotary swages etc.) may also be adapted for expanding inner tube  120 . 
     After inner tube  120  has been sufficiently expanded against catalyst  130 , inner tube  120  may be depressurized (Step  350 ). That is, inner tube  120  may be evacuated of pressurized fluid and/or the expansion object and cleaned out. Inner tube  120  may also be disconnected from the source of pressurized fluid. In embodiments where one end of inner tube was sealed, the sealed end of inner tube may also be reopened based on how it was sealed. For example, a cutting technique may be used to reopen inner tube  120  when it was sealed with a welding process. When a compression fitting was used to seal inner tube  120 , the fitting may be removed. 
     At least one end of inner tube  120  may then be cut to a desired length (Step  360 ). For example, one end of inner tube  120  (e.g., near second end  160 ) may be cut to an appropriate length to allow inner tube  120  to be contained within inner tube  110 . Outer tube  110  may then be sealed at one end (Step  370 ) to encapsulate inner tube  120  within outer tube  110 . For example, cap  170  may be installed on outer tube  110  at second end  160  to seal outer tube  110  and allow fluid to be contained within inner tube  120  during operation of assembly  100 . Cap  170  may be installed using a welding process, compressing fittings, or another method of sealing. 
     Several advantages may be associated with the disclosed method. For example, because inner tube  120  may expand after being inserted through catalyst  130 , inner tube  120  may be sufficiently sealed against catalyst  130  to prevent reactants from bypassing catalyst  130  during operation of assembly  100 . Also, because inner tube  120  may expand after being inserted through catalyst  130 , assembly  100  may have a simple design that is robust, cost effective, and capable of operating at high rates of production. Further, because inner tube  120  may be expanded within catalyst  130  after catalyst  130  has been installed within outer tube  110 , the components of catalytic reactor assembly  100  may be formed and assembled without dividing outer tube  110  into multiple parts and reconnecting them. 
     Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present disclosure being indicated by the following claims.