WO2012173731A2 - Retrofitting radial flow reactors - Google Patents

Abstract

A method is provided for converting a chemical reactor having a single radial flow catalyst bed into a reactor having two serially-arranged radial flow catalyst beds. The method is applicable to radial flow chemical reactors having a reactor tank containing a centrally disposed, fluid permeable pipe, a cover plate assembly disposed between the inlet end of the pipe and the tank inlet, and a fluid permeable wall circumscribing the inner wall of the tank. The method includes removing the cover plate assembly, installing a fluid impermeable obstructer such as a metal plate within a central portion of the pipe; installing a first fluid impermeable cover around the outer wall of the pipe where the obstructer is located, and then installing a second fluid impermeable cover around the inlet end of the pipe. The resulting reactor provides first and second serially-arranged radial flow chambers that can be filled with different catalysts that perform different functions. If the reactor is used to produce para-xylene from ethylbenzene, the upper radial flow chamber may contain a first catalyst that converts ethybenzene to benzene and ethane by dealkylation and the lower radial flow chamber may contain a second catalyst that completes the isomerization of xylenes to an equilibrium mixture.

Description

RETROFITTING RADIAL FLOW REACTORS

PRIORITY CLAIM

[0001] This application claims the benefit of Provisional Application No. 61/497,316, filed June 15, 2011, the disclosure of which is incorporated by reference in its entirety.

FIELD

[0002] This invention relates to retrofitting a chemical reactor having a single radial flow reaction zone into a reactor having two serially-arranged radial flow reaction zones, as well as the modified reactor obtained thereby.

BACKGROUND

[0003] Upgrading chemical processes sometimes involves switching from a single to a multiple step process and hence retrofitting a single zone reactor to a reactor with multiple zones connected in series. One example of such a process is the isomerization of xylenes in a C8 aromatic feed where it is advantageous to dealkylate any ethyl benzene contained in such a feed in a first catalyst bed and then complete the xylene isomerization in a second catalyst bed. By carrying out the reactions in separate catalyst beds, the catalysts can be optimized for the different reactions and the yield of by-products resulting from combining the reactions can be reduced.

[0004] In the case of an axial downflow-type reactor, retrofitting from single to multiple zone operation is fairly straightforward and can, for example, be implemented by simply loading one catalyst layer on top of the other. If desired, a fluid permeable barrier may be installed between the catalyst beds in the reactor to physically separate the first and second catalyst beds.

[0005] In the case of a radial-flow type chemical reactor, it is sometimes possible to convert the reactor into an axial flow reactor having two serial-arranged axial flow catalyst beds. However, such an approach is not always feasible due to the increased pressure drop that the resulting axial flow configuration applies to the flow of product through the tank. To avoid this problem, it is possible to convert the reactor to a multiple zone radial flow reactor by loading the two catalysts into two separate concentric layers of catalyst in the radial flow catalyst bed. As disclosed in, for example International Publication No. WO 99/20384, such concentric loading can be achieved by first removing the cover plate at the upper end of the reactor vessel that directs fluid flow from the inlet of the reactor vessel towards the scalloped, fluid-permeable wall that circumscribes the inner wall of the reactor vessel. Next, the particulate catalyst disposed within the vessel between the center pipe and the fluid permeable wall is removed, and a rigid metal cylindrical shell is lowered into the vessel and concentrically positioned around the center pipe to form an inner and outer annulus for loading the two catalyst beds. Cover plates are used to direct the catalysts into their desired annular sections. The metal cylindrical shell is then lifted, allowing the two catalyst beds to contact each other directly.

[0006] Great care must be taken to position the cylindrical shell concentrically to maintain uniform radial spacing and to avoid mixing the two catalyst layers when the shell is lifted out of the reactor vessel. While such a concentric loading approach is feasible, the quality of the outcome depends greatly on the skill of the personnel conducting the loading procedure. Despite the best of care, the applicant has observed that some degree of mixing always occurs at the interface of the two catalysts using this procedure which interferes with the effectiveness of the catalytic conversion of the feed to the desired products.

[0007] Additional relevant prior art known to the present inventor include EP094172A1, FR1293205A, DE10031347A1, US2004/091404A1, and US 2,683,654.

SUMMARY

[0008] Accordingly, there is a need for a new method of converting a reactor having a single radial flow catalyst bed into a reactor having two serially-arranged radial flow catalyst beds which avoids the intermixing of the catalysts that inevitably occurs with prior art concentric loading techniques and/or avoids the phenomenon of voids being created in catalyst beds or between catalyst bed that allows reactants to flow around the catalyst material to reduce contacting efficiency. To avoid these problems, the method of the invention comprises the steps of removing the cover plate assembly at the upper end of the reactor tank, and installing a fluid impermeable obstructer which is preferably a metal plate within the center pipe at a selected point along a vertical axis that diverts an axial fluid flow into a radial fluid flow through the fluid permeable walls of the pipe. Next, a first fluid impermeable cover is installed around the outer wall of the pipe at the selected vertical point where the obstructer is located. A second fluid impermeable cover is then installed around the inlet end of the pipe to direct all fluid entering the tank inlet through the pipe inlet end, such that a first radial flow chamber is formed between the first and second fluid impermeable covers, and a second radial flow chamber is formed between the first fluid impermeable cover and the tank outlet.

[0009] Preferably, a first solid particulate catalyst is deposited in the bottom portion of the reactor tank in a space defined between the center pipe and the outer fluid permeable wall before the first impermeable cover is installed, and a second solid particulate catalyst is deposited on top of the first impermeable cover in the space defined between the center pipe and the inner fluid permeable wall before the second impermeable cover is installed.

[0010] In operation, fluid entering the inlet of the reactor tank is directed into the inlet end of the center pipe by the second fluid impermeable cover. The fluid obstructer located near the middle of the center pipe directs the fluid flow radially outwardly through the second catalyst, which may for example convert ethylbenzene to benzene and ethane by dealkylation. The outward radial flow of fluid product next flows axially downwardly through the scalloped, fluid-permeable wall that circumscribes the inner wall of the reactor tank to the second radial flow chamber formed between the second fluid impermeable cover and the tank outlet. From there, the fluid flows radially inwardly through the first catalyst, which may for example effect isomerization of xylenes to an equilibrium mixture. Because the first and second catalysts are disposed in separate, serially arranged radial flow chambers, there is no direct interface between the two catalysts where disadvantageous mixing can occur. Additionally, because radial flow is maintained throughout the reactor tank, the pressure drop is only slightly increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1A is a schematic, side cross sectional view of a reactor having a single radial flow catalyst bed.

[0012] Figure IB is a schematic, plan cross sectional view of the reactor shown in Figure 1A viewed along the lines IB- IB in Figure 1A.

[0013] Figure 2 is a schematic cross sectional view of the reactor of Figure 1A partially converted into a reactor having two serially-arranged radial flow catalyst beds.

[0014] Figure 3 is a schematic cross sectional view of the reactor of Figure 1A completely converted into a reactor having two serially-arranged radial flow catalyst beds.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] With reference now to Figures 1A and IB, wherein like reference numerals designate like components throughout all of the several figures, the method of the invention converts a chemical reactor 1 having a single radial flow catalyst bed into a reactor having two serially-arranged radial flow catalyst beds. Chemical reactor 1 includes a reactor tank 3 having an inlet 5 and distributor 6 located in a top wall 7 of the tank 3. The fluid distributor 6 insures a uniform flow of the reagents entering the inlet 5 across the cross-section of the inlet 5. Reactor tank 3 further includes an outlet 9 located in the bottom wall 11 of the tank 3. Cylindrical side walls 13 connect the top wall 7 and bottom wall 11 as shown. A center pipe 15 is concentrically disposed along the axis of the cylindrical side walls 13. Center pipe 15 is fluid permeable. To this end, the walls of pipe 15 may include a large number of uniformly distributed perforations (not shown) and be covered by a screen having a mesh which is large enough to conduct fluid reagents flowing through the tank 3 but small enough to prevent the penetration of particulate catalyst disposed within the single catalyst bed of the reactor. Center pipe 15 includes an inlet end 17 disposed beneath the tank inlet 5, and an outlet end 19 that extends beyond and is surrounded by the tank outlet 9. Although not specifically shown in the Figures, the pipe 15 is surrounded by a split ring socket located above the tank outlet 9 and sealed with ceramic fiber packing such that it forms a continuous channel with the outlet 9 and outlet end 19.

[0016] A cover plate assembly 21 is disposed between the tank inlet 5 and the pipe inlet 17 in order to deflect fluid reagents entering the tank 3 away from the pipe inlet 17 and toward the side walls 13 of the tank. To this end, cover plate assembly 21 includes an impermeable, metallic cover plate 23 surrounded by an impermeable shroud 24 as shown. The circular outer periphery of the shroud 24 is adjacent to a scalloped, fluid permeable wall 26 that is disposed around and spaced apart from the cylindrical interior of the tank 3. Wall 26 may be made permeable by the punching of slots (not shown) in the metal plates forming the wall 26. The slots provide openings large enough to easily conduct liquid or fluid but small enough to confine a particulate catalyst. A plurality of ring-shaped retainers 26.5 retain the scalloped sections of the wall 26 against the inner surface of the cylindrical side walls 13 of reactor 1 as shown in Figure IB. The annular space between the center pipe 15 and the fluid permeable wall 26 defines the single catalyst bed 27 of the reactor 1 which includes a particulate catalyst 28 covered at its top portion by a layer of particulate inert material 29. The scalloped-shaped spaces between the scallops forming the fluid permeable wall 26 and the inner surface of the cylindrical side walls 13 of the tank 3 define a plurality of axial flow paths 30. [0017] In operation, fluid reagents entering the inlet 5 impinge upon the cover plate assembly 21 and are radially directed outwardly into the annular flow path 30. From flow paths 30 the reagents flow radially inwardly through the particulate catalyst 28 in the catalyst bed 27 and are converted to fluid products. The fluid products then flow radially inwardly through the fluid permeable walls of the center pipe 15, and axially through the outlet end 19 of the pipe 15.

[0018] Figure 2 illustrates a reactor 31 that has been partially converted in accordance with the method of the invention. In the position shown, as compared with Figure 1A, the cover plate assembly 21, the particulate catalyst 28, and inert material 29 are all removed from the tank 3. Next, a cut 32 is made in the center pipe 15 in a mid-section thereof. Care should be taken to select a cut location on the pipe 15 that results in the desired relative lengths of the top and bottom catalyst beds. The upper portion of the pipe 15 is then lifted a sufficient distance to allow the installation of a blanking plate 33 over the cut end of the lower portion of the center pipe 15. The metal blanking plate 33 is a solid metal plate which functions as a fluid impermeable obstructor in the pipe 15. After the blanking plate 33 is installed, the two sections of pipe 15 are re-joined as illustrated in Figure 2. Preferably, the installation of the blanking plate 33 and rejoining of the two sections of pipe 15 is accomplished by a welding operation. As is indicated in phantom, the top portion of the fluid permeable wall 26 is trimmed downwardly below the inlet end 17 of the center pipe 15 for a purpose which will become evident hereinafter. Elements 5, 6, 7, 9, 1 1, 13, 19, and 30 in Figure 2 are the same as in Figure 1A, previously described.

[0019] Figure 3 illustrates a reactor 34 that has been completely converted in accordance with the method of the invention. A bottom catalyst bed (Btm) 35 is formed by the installation of a first particulate catalyst 36 in the lower portion of the annular space between the center pipe 15 and the fluid permeable wall 26. Use of a dense loading technique for the catalyst 36 is preferred to minimize the subsequent settling of the catalyst bed 35. The center pipe 15 is covered by a temporary cover and a dense loading machine (not shown) is installed over the tank 3 in a manner known in the art. After the bottom portion of the reactor tank 3 has been filled to the desired level with bottom catalyst 36, a flexible, impermeable bottom cover 37 is installed over the top surface of the catalyst bed 35. In order to prevent the formation of a path for fluid to bypass the bottom catalyst bed 35, the impermeable bottom cover 37 must be flexible enough to remain in contact with the top surface of the bottom catalyst bed 35 as the bed settles. For example, the impermeable bottom cover 37 may be a Texicap®. A Texicap® is made of a ceramic fabric that is highly flexible, resistant to high temperature and impervious to gas flow. A Texicap® is formed from three overlapping, concentric ring-shaped sections of such ceramic fabric, including an outer, center and inner ring (not shown). The inner ring section is fastened to the center pipe 15 by a retainer ring 39. It is not important to seal the outer ring against the permeable wall 26 and cylindrical wall 13 because gas will preferentially flow into the open slots in the scallops at this location.

[0020] Thus one of the discoveries of the present inventor is that even when the precaution is taken to dense load the catalyst to avoid settling, catalysts beds tend to continue to settle in operation at least to some extent. If a rigid structure is used to separate two beds, such settling will cause a void space to form below the gas impermeable divider between catalyst beds. Gas can then flow, such as from the outer wall to the center pipe, without contacting the catalyst. This greatly reduces the contacting efficiency of the catalyst system. However, the use of a flexible material to separate the catalyst beds has been found to be an essential feature to preserve high contacting efficiency between the reactant gas and the catalyst beds.

[0021] After covering the bottom catalyst bed 35 with the impermeable bottom cover 37, a top catalyst bed 43 is installed by the same dense loading technique. After the desired level of top particulate catalyst 44 has been reached within the tank 3, an impermeable top cover 45 is installed. Top cover 45 may be either the previously described cover plate assembly 21 (in Figure 1A) or a Texicap®.

[0022] If cover plate assembly 21 is used it must be modified to include a central opening in the cover plate 23 that circumscribes the inlet end 17 of the center pipe 5. Additionally, the impermeable vertical shroud 24 must be removed from the outer periphery of the cover plate 23 and attached around the inner periphery of the central opening. The outer edge of the cover plate 23 must be sealed against the inner surface of the cylindrical walls 13 of the reactor tank 3, and have the shroud 24 mounted a short distance around the center pipe 15 (previously shown in Figure 2). A layer of seal catalyst 50 and a layer of inert particulate material 52 are loaded several inches to a foot over the top surface of the particulate catalyst 44 to prevent bypassing of the top bed as the catalyst bed settles.

[0023] If a Texicap® is used, it is sealed around the center pipe 15 and the inner surface of the cylindrical walls 13 using retaining rings 47 and 49, respectively. The retaining ring 49 circumscribing the inner surface of the cylindrical walls 13 is preferably supported on top of the permeable wall 26 to minimize the need to weld clips to the inner wall of the tank 3. This is the reason why the upper portion of the permeable wall 26 was clipped down to a level just below the inlet end 17 of the center pipe 15. The scallops forming the permeable wall 26 are often held in place at the top by small diameter retaining rods that are welded to the inner tank walls 13, and these may need to be relocated. The design of the caps on the scallops must also take this into account. The aforementioned layer of seal catalyst 50 and layer of inert particulate material 52 are not required if a Texicap® is employed as the top cover 45 as the flexibility of such a cover allows it to settle along with the catalyst bed.

[0024] In operation, fluid entering the inlet 5 of the completely converted reactor 34 is directed into the inlet end 17 of the center pipe 15, as the impermeable top cover 45 completely blocks any flow through the top surface of the top catalyst bed 43 and the flow path 30. Because of the fluid obstruction provided by the blanking plate 33 welded across the midsection of the center pipe 15, the fluid is then forced to flow radially outwardly through the permeable walls of the center pipe 15 and through the particulate catalyst 44 packed within the top catalyst bed 43. As indicated by the flow arrows in Figure 3, upon leaving the top catalyst bed 43, the fluid next flows vertically downwardly through the annular flow path 30 defined between the permeable wall 26 and the cylindrical walls 13 of the tank 3, where it is forced to flow radially inwardly through the particulate catalyst 36 packed into the bottom catalyst bed 35 and from thence back through the permeable walls of the center pipe 15. As the fluid obstruction provided by the blanking plate 33 prevents the liquid or fluid chemicals from flowing upwardly, the fluid flows downwardly through the outlet end 19 of the pipe 15. In Figure 3, elements 6, 7, 9, 11, and 32 are the same elements described previously in the other figures.

[0025] While the invention has been described in detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention, which is limited only by the appended claims and equivalents thereof.

Claims

Claims:

1. A method for converting a chemical reactor containing a single radial flow chamber into a reactor having first and second radial flow chambers in series, wherein the reactor includes a tank having an inlet and an outlet disposed on top and bottom walls, respectively, a vertically oriented, fluid-permeable pipe having an inlet end disposed beneath the tank inlet and an outlet end extending to the tank outlet, a cover plate assembly disposed between the tank inlet and the pipe inlet end, and a fluid permeable wall that is circumferentially disposed between an inner side wall of the tank and an outer wall of the pipe, the method comprising: removing the cover plate assembly;

installing a fluid impermeable obstructer within said pipe at a selected point along a vertical axis that diverts an axial fluid flow into a radial fluid flow through the fluid permeable walls of said pipe;

installing a first fluid impermeable cover extending between said outer wall of said pipe at said selected vertical point where said obstructer is located and said fluid permeable wall disposed within the tank; and

installing a second fluid impermeable cover extending between the inlet end of the pipe and the inner wall of the tank that directs all fluid entering the tank inlet through the pipe inlet end,

such that a first radial flow chamber is defined between the first and second fluid impermeable covers wherein fluid from said tank inlet flows radially outwardly from said pipe, and a second radial flow chamber is defined between the first fluid impermeable cover and the tank outlet, wherein fluid flows radially inwardly from the first radial flow chamber into said pipe;

wherein at least one of said first and second fluid impermeable covers is formed of a flexible material, preferably a flexible ceramic fabric.

2. The method of Claim 1, further comprising the step of depositing a first solid particulate catalyst into a bottom portion of the tank in a space defined between the pipe and the fluid permeable wall before the first impermeable cover is installed.

3. The method of Claim 2, further comprising the step of depositing a second solid particulate catalyst on top of said first impermeable cover in the space defined between the pipe and the fluid permeable wall before the second impermeable cover is installed.

4. The method of Claim 3, wherein said first and second fluid impermeable covers are each formed from flexible ceramic fabric, and further including the steps of mounting inner and outer edges of the fabric forming the covers around the outer wall of the pipe and inner side wall of the tank, respectively, by means of retaining rings.

5. The method of Claim 3, wherein said first fluid impermeable cover is formed from a cover plate assembly including an impermeable cover plate having a central opening and a vertical impermeable shroud surrounding the central opening, and further including the steps of positioning the central opening of the cover plate around the inlet end of the pipe and sealingly mounting the outer periphery of the cover plate to said inner side wall of said tank.

6. The method of Claim 5, further including the step of depositing a layer of seal catalyst and a layer of inert material over the second solid particulate catalyst to prevent bypassing of the first radial flow chamber due to settling of the second solid particulate catalyst.

7. The method of any one of Claims 3-6, wherein the first and second solid particulate catalysts are different.

8. The method of Claim 7, wherein the solid catalytic compound contained in the first radial flow chamber is selected so as to selectively convert ethylbenzene to benzene and ethane, and the solid catalytic compound contained in the second radial flow chamber is selected so as to selectively isomerize xylenes to an equilibrium mixture.

9. The method of any one of Claims 3-8, wherein the first and second solid particulate catalysts are dense-packed into their respective spaces to avoid settling.

10. The method of any one of the preceding claims, wherein said fluid impermeable obstructer is a plate, and said installation is implemented by cutting the pipe across its cross section, sealingly mounting the plate over the cut end of the pipe, and re-attaching the two cut ends of the pipe.

11. A chemical reactor that provides first and second radial flow chambers in series, comprising:

a reactor tank having an inlet disposed on a top wall and an outlet disposed on a bottom wall;

a vertically oriented, fluid-permeable pipe contained within the tank and having an inlet end disposed beneath the tank inlet and an outlet end extending through the tank outlet; a fluid permeable wall contained within the tank that is circumferentially disposed between an inner side wall of the tank and an outer wall of the pipe;

a fluid impermeable obstructer disposed within said pipe at a selected point along a vertical axis that diverts an axial fluid flow into a radial fluid flow through the fluid permeable walls of said pipe;

a first fluid impermeable flexible cover extending between said outer wall of said pipe at said selected vertical point where said obstructer is located and said fluid permeable wall disposed within the tank; and

a second fluid impermeable flexible cover extending between the inlet end of the pipe and the inner wall of the tank that directs all fluid entering the tank inlet through the pipe inlet end,

wherein a first radial flow chamber is defined between the first and second fluid impermeable covers, and a second radial flow chamber is defined between the second fluid impermeable cover and the tank outlet, and fluid flows from said first to said second radial flow chamber through the space defined between said tank inner wall and said fluid permeable wall.

12. The chemical reactor of Claim 1 1, wherein the first and second radial flow chambers define first and second catalyst beds, each of which contains a solid catalytic compound.

13. The chemical reactor of Claim 12, wherein the catalytic compounds contained in said first and second radial flow chambers are located between the outer wall of the pipe and the fluid permeable wall.

14. The chemical reactor of Claim 13, wherein the solid catalytic compound contained in the first radial flow chamber is different from the solid catalytic compound contained in the second radial flow chamber.

15. The chemical reactor of Claim 14, wherein the solid catalytic compound contained in the first radial flow chamber converts ethylbenzene to benzene and ethane and the solid catalytic compound contained in the second radial flow chamber effects isomerization of xylenes to an equilibrium mixture.

16. The chemical reactor of Claim 1 1, wherein the fluid impermeable obstructer is a plate sealingly mounted across a central portion of the pipe.

17. The chemical reactor of Claim 1 1, wherein said tank and said pipe are cylindrical, and said fluid permeable wall is concentrically disposed between said outer side wall of the pipe and said inner side wall of the tank.

18. The chemical reactor of any one of Claims 11-17, wherein the first and second fluid impermeable flexible covers are formed from a flexible ceramic fabric.

19. The chemical reactor of any one of Claims 1 1-18, wherein inner edge of the flexible ceramic fabric of said first and second impermeable covers is affixed around the outer wall of the pipe by a retaining ring.

20. The chemical reactor of any one of Claims 1 1-19, wherein the outer edge of the flexible ceramic fabric of said second impermeable cover is affixed around the inner side wall of the tank by a retaining ring.