METHOD FOR REVAMPING A CATALYTIC CONVERTER

Abstract

A method for revamping a catalytic converter wherein: said catalytic converter comprises a pressure vessel and a catalytic cartridge containing at least one catalyst bed, the pressure vessel includes a cylindrical shell with a full aperture and includes a removable cover of said aperture, and the catalytic cartridge is removable through said upper aperture, and the method includes: installing an additional shell over the aperture of the original shell, thus obtaining an axially extended shell of the pressure vessel; providing an axially extended catalytic cartridge having an axially extended room for holding catalyst in the so obtained axially extended shell.

Claims

1-16. (canceled)

17. A method for revamping a catalytic converter, the catalytic converter including a pressure vessel with a main axis and a catalytic cartridge containing at least one catalyst bed, wherein the pressure vessel includes a shell with a full aperture and includes a removable cover connected to a flange of the full aperture, the catalytic cartridge being removable through the full aperture; the method comprising: connecting an additional shell to the flange of the full aperture of the original shell, thus obtaining an axially extended shell of the pressure vessel, thereby extending the pressure vessel along the main axis; and providing an axially extended catalytic cartridge having an axially extended room for holding catalyst in the so obtained axially extended shell.

18. The method according to claim 17 wherein providing the axially extended catalytic cartridge includes installing an additional cartridge spool at an end portion of the existing cartridge.

19. The method according to claim 18, wherein the original cartridge has an end flange with a cover; wherein the cover is removed and the additional cartridge spool is connected to the flange of the original cartridge.

20. The method according to claim 18, further comprising forming an additional catalyst bed in an end portion of the modified cartridge which is delimited by the cartridge spool.

21. The method according to claim 20, further comprising: wherein the original cartridge contains one or more baskets for containing catalyst beds; and increasing the axial length of at least one basket of the cartridge.

22. The method according to claim 21, wherein the at least one basket, which is axially extended, includes a last basket of the cartridge.

23. The method according to claim 21, wherein increasing the axial length of the at least one basket of the cartridge includes axially extending the gas-permeable walls of the basket.

24. The method according to claim 17, further comprising a provision in the extended cartridge of an additional shroud or an additional support ring for at least one catalyst bed of the modified catalytic cartridge.

25. The method according to claim 24, wherein the additional shroud or additional support ring are provided to support a catalyst bed which is next to the last catalyst bed.

26. The method according to claim 17, wherein the original cartridge and the modified cartridge include one or more inter-bed heat exchangers.

27. The method according to claim 17, further comprising: removing the original catalytic cartridge from the pressure vessel; and installing a new catalytic cartridge within the pressure vessel, the new cartridge having axial length greater than the original cartridge.

28. The method according to claim 17, wherein the modified cartridge or the new cartridge differs from the original cartridge for at least one of the following features: a number of catalyst beds that can be accommodated in the cartridge; a provision or an arrangement of one or more inter-bed heat exchangers; or a provision or an arrangement of inter-bed quenching means.

29. The method according to claim 17 wherein the additional room for catalyst, provided by the axially extended cartridge, extends over the full diameter of the pressure vessel of the catalytic converter.

30. The method according to claim 17, further comprising adding catalyst into the additional room provided by the axially extended cartridge.

31. The method according to claim 17, wherein the converter includes a horizontal converter or a vertical converter.

32. The method according to claim 17, wherein the converter includes an ammonia converter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG. 1 is a simplified section of a vertical converter according to the prior art.

[0049] FIG. 2 is a simplified section of the converter of FIG. 1 which has been revamped according to an embodiment of the invention.

[0050] FIG. 3 is a detail of the converter of FIG. 2 showing an embodiment for supporting a catalyst bed.

[0051] FIG. 4 illustrates an alternative embodiment for the detail of FIG. 3.

[0052] FIG. 5 illustrates another detail of the converter of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0053] FIG. 1 illustrates a multi-bed vertical converter 1 comprising a pressure vessel having a shell 2 with a bottom closure 3, a full-diameter upper aperture 4 with a removable cover 5. The removable cover 5 is bolted to a top flange 6 of the shell 2.

[0054] The converter 1 has a main axis which in this example is a vertical axis A-A. The shell 2 is substantially cylindrical having the same axis A-A.

[0055] The converter 1 contains a catalytic cartridge 7. The cartridge 7 contains an upper basket 701, an intermediate basket 702 and a bottom basket 703, vertically aligned one above the other. Said baskets hold an upper catalyst bed 704, intermediate catalyst bed 705 and bottom catalyst bed 706 respectively.

[0056] Each of the beds 704 to 706 has a cylindrical annular shape and a radial or axial-radial flow. The radial flow may be directed towards or away from the axis A-A. In the example, the radial flow is directed towards the axis (centripetal flow).

[0057] The cartridge 7 further includes two inter-bed tube heat exchangers 707 and 708 arranged to cool the effluent of the bed 704 or 705 before it enters the next bed 705 or 706, respectively. The tube heat exchangers 707, 708 are accommodated coaxially in a free space delimited by the annular catalyst beds.

[0058] The cartridge 7 further includes means to hold and support the catalyst of the beds 704 to 706 and means to properly direct the gaseous flow to/from the catalyst beds. For example each basket includes an inner gas collector and an outer gas collector. The figure illustrates that the bottom basket 703 has an outer collector (gas inlet) 709 and an inner collector (gas outlet) 710. The inner collector 710 leads to a gas outlet duct 711.

[0059] The cartridge 7 is a self-standing unit which may be removed from the vessel 2 through the upper aperture 4. The upper aperture 4 has substantially the same diameter as the inner diameter of the vessel 2, thus providing full access to the inside of the vessel 2.

[0060] The operation of the converter 1 is basically as follows. A first reaction gas charge R.sub.1 enters at the bottom input 201, is preheated while flowing in an interspace between the shell 2 and the cartridge 7, then enters the first catalytic bed 704 and traverses the catalytic beds 704, 705, 706 sequentially.

[0061] While passing from the top bed 704 to the intermediate bed 705, and from the intermediate bed 705 to the lower bed 706, the effluent gas is cooled in the shell side of the heat exchangers 707, 708. The tube side of the heat exchangers 707, 708 is traversed by a second fresh reaction gas R.sub.2 from the input 202. The preheated gas R.sub.2 leaving the tubes mixes with the first reaction gas R.sub.1 before entering the top catalytic bed 704.

[0062] An additional charge R.sub.3 of fresh reaction gas may be provided at the input flange 203 and mixed with the effluent of the first bed 704, to adjust the gas inlet temperature of the intermediate bed 705.

[0063] The gaseous product effluent P from the lower bed 706 is collected in the duct 711 and leaves the converter 1 via the bottom outlet 203. This way of operation is familiar to a skilled person. Many converters for the synthesis of ammonia from a make-up gas of nitrogen and hydrogen are realized according to the scheme of FIG. 1 or variants thereof.

[0064] FIG. 2 illustrates the converter 1 after a modification according to an embodiment of the invention.

[0065] An additional shell 8 is provided over the upper aperture 4 and secured (e.g. bolted) to the flange 6, thus obtaining an axially extended shell of the pressure vessel. Particularly, the axially extended shell includes the original shell 2 and the additional shell 8, which are secured together and form a unique shell.

[0066] The additional shell 8 has also a full-diameter upper aperture 9 where a cover 10 is fitted. Said cover 10 may be elliptical or spherical or a flat cover according to various embodiments. The cover 10 may comprise a manhole 11. Preferably the aperture 9 has the same diameter as the original aperture 4. The inputs 202 and 203 may be closed (blinded) and replaced by inputs 202a and 203a performing the same function.

[0067] The cartridge 7 is also modified into a modified cartridge 7a by providing a cartridge spool 720 containing a new catalyst bed 721, which replaces the original top bed 704 and becomes the top catalyst bed of the modified cartridge 7a. In this example, the original bed 704 is replaced by a larger bed 721 to maintain a desired load distribution between the catalyst beds.

[0068] The modified cartridge 7a delivers an additional room for adding catalyst. It can be noted that this additional room extends over the full diameter of the converter 1, thanks to the fact that the additional shell 8 is secured to the flange 6 which is a full-aperture flange.

[0069] The cartridge 7 may be re-arranged so that, in the modified cartridge 7a, the two lower beds (intermediate bed and bottom bed) occupy substantially the same volume as the original three beds.

[0070] More in detail, the figures relate to an example where the axial length of the bottom basket 703 is increased. This can be made substantially by replacing or extending the inner collector and outer collector 709, 710. As a result, the modified cartridge 7a includes an axially extended bottom basket 703a. Accordingly, the bottom bed 706a which can be accommodated in the modified basket 703a is also axially extended compared to the original bottom bed 706. It can be said that the bottom basket 703 and bed 706 are axially stretched to a greater length.

[0071] Preferably, also the axial length of the intermediate basket 702 is extended in a similar manner, by increasing the length of the corresponding inner collector and outer collector. As a result, an axially extended intermediate bed 705a may be accommodated in the converter.

[0072] In a multiple-bed embodiment including three or more catalyst beds it is preferred that the last catalyst bed has contains a volume of catalyst substantially equal to the total volume of catalyst contained in the previous catalyst beds.

[0073] Preferably, the total length of the axially extended beds 705a and 706a is substantially equal to the total length of the former three beds. For example, referring to the vertical embodiment of FIG. 2, the top of the intermediate bed 705a is substantially at the height of the flange 6 and of the original aperture 4.

[0074] The bottom intermediate basket 702, as a consequence of the extension of the underlying basket, is also shifted to a higher elevation.

[0075] FIGS. 3 and 4 illustrate, by way of example, two ways of realizing a bottom support of the shifted intermediate basket 702.

[0076] In FIG. 3, an outer collector 722 of the intermediate basket 705 rests on an additional shroud 723 and said additional shroud 723 rests on the existing support ring 724. This embodiment has the advantage of making use of the available support ring 724; the shifted elevation of the intermediate basket is given by the shroud 723.

[0077] In FIG. 4, alternatively, a new support ring 725 is provided. Said new ring 725 may be bolted (as in the figure) or welded to a wall 726 of the cartridge 7a.

[0078] FIG. 5 illustrates an embodiment of the anchoring of the cartridge spool 720 to the structure of the original cartridge 7. In the example, a lower flange 730 of the spool 720 is anchored by means of bolts 731 inserted in pipes 732.

[0079] In the example, the cartridge 7 maintains a three-bed setup before and after the revamping. In other embodiments, however, the number of the catalyst beds and/or the arrangement of inter-bed cooling or quenching means may be varied during the revamping.

[0080] The invention as above described with reference to a vertical converter is also applicable to a horizontal converter.