Abstract:
A new reactor design is presented for a counter-current flowing reactor. The reactor has a catalyst flowing down through the reactor, and over baffles. Gas is admitted under the baffles and flows up through the solid catalyst bed. The design includes slotted plates that extend from the bottom of the baffle in the reactor to a position near the catalyst outlet. The gas flows through the slotted plates and is directed up through the catalyst bed, while directing the flowing catalyst to the catalyst outlet ports.

Description:
FIELD OF THE INVENTION 
     This invention relates to counter-current flow reactors or adsorbers where a fluid flows up through a moving bed of catalyst or adsorbent. In particular, this relates to the internal components for controlling the flow of catalyst or adsorbent through the reactor or adsorber. 
     BACKGROUND OF THE INVENTION 
     A wide variety of processes use counter-current flow reactors to provide for contact between a fluid and a solid. The solid usually comprises a catalytic material on which the fluid reacts to form a product. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation. 
     Counter-current reactors are constructed such that the reactor allows for catalyst, or adsorbent, to flow downward through the reactor, and the gas, or other fluid, flows upward contacting the catalyst. Since catalyst is heavy, and can exert significant force on the reactor internals, the construction has to be with a substantial material, such as thick steel plates. Counter-current reactors provide for continuous processing, with regenerated catalyst entering the reactor and flowing downward though the reactor, to be drawn off. The drawn off catalyst is recycled to a regenerator to refresh the catalyst for reuse. A problem with currently designed counter-current reactors is that the catalyst flows through and is collected in the bottom of the reactor. Significant amounts of the catalyst are bypassed as catalyst sits in the bottom of the reactor waiting to be drawn off for regeneration. In order to reduce the amount of catalyst situated at the bottom of the reactor, the current design is such that a substantial amount of catalyst is retained within the reactor in a non-flowing region. This presents a problem in that the catalyst will eventually be inactivated and is not taken out of the reactor, but creates a dead space where the reactant gas flows and is not processed. 
     Currently, screens for reactors are directed to reactors that have fluidized beds and where the screens prevent the passage of catalyst, or for radial flow reactors where the stresses on the screens are horizontal pressures. Other screens include high velocity flow processes where the solid particles need to be removed from the flow field. These reactors use different types of screens which are not applicable here. 
     The design of reactors to overcome these limitations can save significantly on catalyst that is held up in the reactor and does not flow, as well as catalyst that collects at the bottom of the reactor, and is by-passed by the flowing gas. The catalyst is one of the most significant costs associated with hydrocarbon processing, and reductions in amounts of catalyst used, or by-passed can result in significant savings. Improvements can increase the contact between the catalyst and fluid, and can reduce the amount of non-flowing catalyst. 
     SUMMARY OF THE INVENTION 
     The present invention is a counter-current flowing reactor, where catalyst flows downward with gravity, and a gas, or other fluid, flows upward and over the catalyst. The reactor includes a baffle structure for directing the catalyst in a downward direction, with gas admitted through an inlet and flowing under the baffle to then flow up and contact the catalyst. The reactor further includes a reactor bed plate to direct the catalyst to flow in an annular region for contacting the gas. The reactor also includes a plurality of slotted plates, where the plates extend from the bottom of the baffle to the bottom of the reactor near the catalyst outlet. The plates are arrayed in a circumferential manner to contain catalyst as the catalyst passes below the lower edge of the baffle. The region of inactive catalyst volume is reduced, and the overall amount of catalyst in the reactor is reduced. 
     Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a design for a counter-current flowing reactor; 
         FIG. 2  is a new design for a counter-current flowing reactor; and 
         FIG. 3  is an alternate new design for the counter-current flowing reactor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a counter-current flowing reactor or adsorber, a solid catalyst or adsorbent flows downward through the reactor with the fluid flowing upward over the catalyst or adsorbent. For purposes of this description, a catalyst will be described, but the invention is applicable to an adsorber where the solid particulate material is an adsorbent. The reactor is of a design and the flow conditions are in the range to prevent fluidization of the solid catalyst particles in the reactor bed. 
     In a counter-current flowing reactor, the catalyst flows down by gravity through an opening and gas, or other fluid, is flowing upward through the opening, contacting the catalyst as it flows upward through the reactor. In many applications there is a desire to keep the catalyst flowing. In an annular baffle configuration, as shown in  FIG. 1 , the reactor  10  comprises an outer shell  20 , with a baffle configuration  30  disposed within the shell  20 , and a reactor bed plate  40  sized to direct the flow of catalyst through the reactor  10  and to direct the gas through the catalyst bed. A current design does not have any internal features, such as reactor bed plate  40 , to direct the flow of catalyst out toward the catalyst outlets  38 . The current design allows for the catalyst to flow downward and to collect in the bottom of the reactor. Gas enters the reactor  10  through a gas inlet  22 , flows around the gap  24  between the reactor shell  20  and the baffle  30  and across the catalyst free surface  26 , to flow upward through the catalyst bed  32  and out the gas outlet  34 . Catalyst flows in through a catalyst inlet  36 , through the catalyst bed  32  and out the catalyst outlets  38 . Catalyst can be very heavy, and it is allowed to flow downward through the reactor bed and is collected at the bottom of the reactor  10  where the catalyst flows out the catalyst outlets  38 . 
     A problem exists when the reactor increases in size. The applications have the design desire to keep an outer annular region of catalyst flowing, and the flowing catalyst creates a catalyst free surface  26  between the end of the baffle  30  and the reactor shell  20 . When the reactor  10  is increased in size, the design creates significant no-flow zones  50  for the catalyst, and can be as high as 30% of the catalyst not flowing though the reactor, as well as creating zones where the fluid bypasses significant amounts of catalyst after the catalyst has passed below the bottom of the baffle  30 . The no-flow zone  50  in this type of reactor is that region of catalyst above the bottom of the baffle  30  that is not flowing. Another no-flow zone  51  is the volume of catalyst under the catalyst free surface where catalyst is below a line defined by the angle of repose for the catalyst extending from the catalyst outlet  38 . 
     The current state of the art with the counter-current reactor involves the collection of catalyst at the bottom of the reactor. In this design, there is a significant amount of catalyst in that region which does not flow to the catalyst outlets  38 . 
     The present invention is a cylindrical reactor that allows for more efficient contacting of the catalyst and fluid. The reactor  10 , as shown in  FIG. 2 , includes a reactor housing  20  having a gas inlet  22 , a gas outlet  34 , a catalyst inlet  36  and catalyst outlets  38 . The housing includes an annular baffle  30  having an upper edge  52  and a lower edge  54 , where the upper edge  52  is affixed to the reactor housing  20  at a position above the gas inlet  22 . The lower edge  54  extends below the gas inlet  22  and the baffle  30  creates an annular space  24  between the housing  20  and the baffle  30 . The annular space  24  allows for the distribution of gas circumferentially around the reactor before the gas flows up through the catalyst bed  32 . The reactor  10  includes a reactor bed plate  40  positioned in the reactor, and at a location that is approximately at the level of the lower edge  54  of the baffle  30 . This creates an annular opening for the catalyst to flow through, and the bed plate  40  is sized to direct the rate of flow of catalyst through the reactor  10 , and to maintain a reactor bed  32  residence time for the catalyst. The reactor  10  further includes a plurality of slotted plates  60 . The slotted plates  60  extend from the baffle lower edge  54  to a position proximate the catalyst outlet  38  and arrayed in a circumferential manner around the inside of the reactor housing  20 . By adding the slotted plates  60 , the configuration can be changed to reduce the size of the non-flowing region  50  in the reactor, and reduce the overall amount of catalyst needed in the reactor. 
     In a preferred embodiment, the slotted plates  60  are disposed at an angle at least as great as the angle of repose for the catalyst. The angle of repose is a property of particulate solids. When bulk particles are poured onto a horizontal surface, a conical pile will form, and the angle between the edge of the pile and the horizontal surface is known as the angle of repose. The angle is related to physical properties of the material, such as particle size and shape, density, and the coefficient of friction of the particles. By positioning the slotted plates  60  at an angle at least as great as the angle of repose, the holdup of catalyst is minimized. 
     Optionally, the reactor  10  further includes a plurality of non-slotted plates  62  where the non-slotted plates  62  are arrayed from the edge of the reactor bed plate  40  to a position proximate to the catalyst outlet  38 . This provides for directing the catalyst from the reactor catalyst bed  32  to the catalyst outlet  38  while preventing the accumulation of catalyst in a non-flowing zone  64  below the catalyst bed  32 . The non-slotted plates  62  need to be perforated with openings sufficiently small to prevent the flow of catalyst, but to allow the flow of fluid for pressure testing of the vessel. In this optional design, slotted plates can be used where the non-slotted plates  62  are arrayed. 
     The slotted plates  60  are preferably positioned to have the slots in a vertical orientation. By vertical orientation it is meant that the slots are oriented in the direction of gravity, or the flow of solid catalyst particles. This orientation minimizes abrasion of the catalyst particles over the edges of the slots. The milled plates need to have a sufficient mechanical strength to support the weight of the catalyst against the slotted plates  60  when the reactor  10  is loaded with catalyst and operated with the catalyst moving through the reactor  10 . It is preferred that the plates comprise a steel or alloy that is resistant to corrosion, and of sufficient thickness to support the stress of catalyst on the plates  60 . 
     In one embodiment, the slotted plates  60  have a solid particle side and a fluid side and a plate thickness. The solid particle side comprises a milled plate having solid particle side slots formed therein in a parallel manner. The fluid side comprises a milled plate having fluid side slots formed therein in a parallel manner, and where the fluid side slots intersect the solid particle side slots, thereby allowing fluid to pass through the plates  60 . While the terms ‘milled’ and ‘milling’ are often used to denote standard manufacturing techniques for forming metal plates, it is meant that the terms include any manufacturing method for forming slots, depressions, or holes in metal plates. The terms ‘milled’ and ‘milling’ are used for convenience hereinafter. In this embodiment, it is preferred that the solid particle side slots have a width less than or equal to 1 mm, and more preferably that the slots have a width of less than or equal to 0.7 mm. The fluid side slots will have a width greater than the solid particle side slots. The solid particle side slots are milled to a depth from between 0.05 to 0.5 times the thickness of the plate  60 , and the fluid side slots are milled to a depth from between 0.5 and 0.95 times the thickness of the plate  60 . The slots in the solid particle side are spaced between 2.5 and 5 mm apart from centerline of a slot to the centerline of a neighboring slot. 
     The slots can span the length of the plates  60 , or be segmented to shorter slots aligned longitudinally, or in the vertical direction. The slots preferably are at least 100 mm long and when segmented in the vertical, or longitudinal, direction, have a spacing between them from 5 mm to 30 mm. It is preferred that the slots end at least 20 mm from the end of the plate  60 . This provides sufficient material at the end of the plate  60  for affixing the plate  60  to the lower edge of the baffle  30 , without damaging the slots. 
     In another embodiment, the slotted plates  60  have a solid particle side and a fluid side and a plate thickness. The solid particle side comprises a milled plate having solid particle side slots formed therein in a parallel manner. The fluid side comprises a drilled plate having fluid side holes formed therein, and where the fluid side holes intersect the solid particle side slots, thereby allowing fluid to pass through the plates  60 . While the term ‘drilled’ is often used to denote standard manufacturing techniques for forming holes in metal plates, it is meant that the term include any manufacturing method for forming holes, depressions, or holes in metal plates. The term ‘drilled’ are used for convenience herein. In this embodiment, it is preferred that the solid particle side slots have a width less than or equal to 1 mm, and more preferably that the slots have a width of less than or equal to 0.7 mm. The fluid side holes will have a diameter less than 5 mm, and preferably have a diameter less than 2 mm. The holes are drilled in the fluid side and formed in parallel lines that align and intersect the slots in the solid particle side. The solid particle side slots are milled to a depth from between 0.05 to 0.5 times the thickness of the plate  60 , and the fluid side holes are drilled to a depth from between 0.5 and 0.95 times the thickness of the plate  60 . 
     In another embodiment, as shown in  FIG. 3 , the reactor  10  includes a volume fill element  66 , comprising a conical section having a slope equal to or greater than the angle of repose for the catalyst. The volume fill element  66  occupies space where catalyst becomes inactive due to lack of flow through the reactor  10 . The reactor  10  further includes slotted plates  60 , as described above, where the plates  60  have an upper edge affixed to the lower edge of the volume fill element  66  and a lower edge proximate to the catalyst outlet  38 . This creates a larger void area  68  underneath the volume fill element  66 . The reactor  10  further includes at least one vapor pipe  70  having an inlet and an outlet. The vapor pipe  70  allows the flow of process gas from the reactor inlet  22  to the void area  68  for a better distribution of the process gas flowing through the catalyst bed  32 . The number of vapor pipes  70  can be determined from operating flow conditions, and the desired distribution of fluid into the void area  68 . 
     The invention increases the utilization of catalyst within the reactor, by increasing the relative amount of flowing catalyst, and reducing the volume of inactive catalyst. As can be seen in the two tables comparing the present counter-current reactor design with the present invention, the invention allows changes that reduce the amount of non-flowing catalyst to less than 1% of the catalyst in the reactor. In addition, while keeping the same active volumes of catalyst the total volume of catalyst has been decreased, and the proportion of inactive volume has been substantially decreased. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 current design volumes of catalyst 
               
             
          
           
               
                   
                   
                 Inactive 
                 Active 
                   
                   
                   
                 Active 
                 % 
               
               
                   
                 Inactive 
                 volume 
                 volume 
                   
                   
                 Inactive 
                 non- 
                 of active 
               
               
                   
                 volume 
                 TL to 
                 baffle 
                 Active 
                 Total 
                 volume, 
                 flowing 
                 volume 
               
               
                   
                 head, 
                 baffle, 
                 (approx) 
                 volume 
                 volume 
                 % of 
                 catalyst, 
                 not 
               
               
                 Case 
                 m3 
                 m3 
                 m3 
                 hill, m3 
                 m3 
                 Total 
                 m3 
                 flowing 
               
               
                   
               
             
          
           
               
                 1 
                 0.0449 
                 0.0489 
                 0.396 
                 0.0169 
                 0.507 
                 19 
                 0.0441 
                 11 
               
               
                 2 
                 0.0670 
                 0.0689 
                 0.594 
                 0.0253 
                 0.755 
                 18 
                 0.0666 
                 11 
               
               
                 3 
                 0.1309 
                 0.1390 
                 0.855 
                 0.0495 
                 1.174 
                 23 
                 0.1292 
                 14 
               
               
                 4 
                 0.1991 
                 0.2015 
                 1.277 
                 0.0755 
                 1.753 
                 23 
                 0.1987 
                 15 
               
               
                 5 
                 0.3592 
                 0.3787 
                 1.716 
                 0.1360 
                 2.590 
                 28 
                 0.3553 
                 19 
               
               
                 6 
                 0.5362 
                 0.5368 
                 2.536 
                 0.2031 
                 3.812 
                 28 
                 0.5364 
                 20 
               
               
                 7 
                 1.0472 
                 1.0681 
                 3.811 
                 0.3969 
                 6.323 
                 33 
                 1.0437 
                 25 
               
               
                 8 
                 1.9726 
                 1.9646 
                 6.144 
                 0.7491 
                 10.830 
                 36 
                 1.9763 
                 29 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 new design volumes of catalyst 
               
             
          
           
               
                   
                   
                 Active 
                   
                   
                   
                 Active 
                   
               
               
                   
                 Inactive 
                 volume 
                   
                   
                 Inactive 
                 non- 
                 % of active 
               
               
                   
                 volume 
                 baffle 
                   
                 Total 
                 volume, 
                 flowing 
                 volume 
               
               
                   
                 head, 
                 (approx) 
                 Active volume 
                 volume 
                 % of 
                 catalyst, 
                 not 
               
               
                 Case 
                 m3 
                 m3 
                 hill, m3 
                 m3 
                 Total 
                 m3 
                 flowing 
               
               
                   
               
             
          
           
               
                 1 
                 0.0345 
                 0.3959 
                 0.0170 
                 0.4474 
                 8 
                 0.000793 
                 0.19 
               
               
                 2 
                 0.0626 
                 0.5938 
                 0.0252 
                 0.6816 
                 9 
                 0.001331 
                 0.22 
               
               
                 3 
                 0.1090 
                 0.8549 
                 0.0496 
                 1.0135 
                 11 
                 0.002435 
                 0.27 
               
               
                 4 
                 0.1965 
                 1.2774 
                 0.0756 
                 1.5492 
                 13 
                 0.004069 
                 0.3 
               
               
                 5 
                 0.3095 
                 1.7160 
                 0.1359 
                 2.1614 
                 14 
                 0.006779 
                 0.37 
               
               
                 6 
                 0.5482 
                 2.5361 
                 0.2030 
                 3.2873 
                 17 
                 0.01118 
                 0.41 
               
               
                 7 
                 1.0152 
                 3.8106 
                 0.3970 
                 5.2228 
                 19 
                 0.02109 
                 0.5 
               
               
                 8 
                 2.0632 
                 6.1437 
                 0.7490 
                 8.9558 
                 23 
                 0.04155 
                 0.6 
               
               
                   
               
             
          
         
       
     
     While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.