CA1235887A - Method for removing spent catalyst from a reactor tower and assembly for facilitating same - Google Patents

Abstract

"METHOD FOR REMOVING SPENT CATALYST FROM A
REACTOR TOWER AND ASSEMBLY FOR FACILITATING SAME"
ABSTRACT OF THE DISCLOSURE
A basket is removably inserted in the upper end of each drain tube in those interbed assemblies of a catalytic tower whose catalyst beds are to be removed upwardly by vacuuming. The basket has a grid for a bottom wall, so that catalyst particles thereabove are retained but fluid being treated in the tower can easily pass therethrough. The provision of the baskets makes it possible to downwardly drain spent catalyst from the lower bed sections while simultaneously vacuuming it upwardly from the upper bed sections.

Description

1~35~37 1 ~IELD OF THE`I~VE~TION

2 The present invention relates to a method and apparatus

3 adapted to permit spent catalyst to be simultaneously vacuumed upwardly

4 from the uppermost bed sections of a reactor tower and drained downwardly by gravity from the lowermost bed sections.

7 The catalytic hydrogenation of hydrocarbon feedstock, such 8 as untreated gas-oil, is conventionally conducted in a hydrotreater. Such 9 a hydrotreater is commonly a vertically extending tower whose internal chamber is sub-divided into a plurality of bed sections by horizontally 11 extending grid structures termed 'interbed assemblies' . Each bed 12 section is packed with particulate catalyst, typically in the form oF
13 pellets that might have a length in the order of 15 mm and a diameter 1~ in the order of 3 mm~
An interbed assembly commonly comprises a steel rod grid 16 underlain by a splash tray and a bubble cap tray. The assembly is 17 designed to support a bed of catalyst whilst permitting the fluids in 1~ the reactor to pass therethrough.
19 Each interbed assembly commonly comprises a plurality of vertically disposed, open ended drain tubes which extend through the 21 assembly. These tubes are normally filled with a column of steel balls 22 whereby the catalyst beds are isolated one from another and yet fluids 23 can easily pass from one section to another.

~:35i83~7 1 When the catalyst is spent, it must be removed from the 2 tower to be either discarded or regenerated. This is commonly effected 3 by a combination of two sequentially practised procedures. In accordance 4 with the first procedure, the upper bed sections are first emptied, by inserting a vacuum hose through an aperture in the top of tower and 6 sucking the catalyst upwardly out of the tower. If the second bed 7 section is to be cleaned in the same way, the steel balls are removed 8 from the drain tubes o~ the uppermost interbed assembly and the vacuum 9 hose is extended through one of the drain tubes into the next section.
Once the uppermost bed sections of the tower have been cleaned out in 1l this way, an outlet is opened in the base of the tower. The remaining 12 catalyst and the balls in the tubes then drain downwardly through the 13 drain tubes and bed sections and are removed through the outlet from 14 the tower.
Now, there is a reason why the uppermost bed or beds are 16 recovered separately from lower beds. The catalyst at the top oF the 7 tower, where the hydrocarbon Feed is usually introduced, normally is 18 poisoned and exhausted at a faster rate than the catalyst lower down in 19 the tower. lhus, at the end oF a run, when the catalyst charge as a whole is no longer working at the desired level of efficiency, it is 21 oFten desirable to recover the lowermost catalyst separately, as it may 22 be regenerated and re-used, while the same procedure cannot be practised 23 with success on the uppermost catalyst.
24 Since the uppermost catalyst would d~ain with the lowermost catalyst if both were in the tower and the bottom outlet was opened and 26 removal of catalyst therethrough began, it has heretofore been the practise, 27 as far as I know, to first vacuum out the upper beds -to be discarded, 28 before beginning to drain the bottom beds.

~3~

This sequential technique is time-consuming. By way of 2 example, in a 3-bed, 88 foot tall hydrotreater, having the first interbed3 assenlbly 12 feet from the top, the next 39 feet from the first, and the 4 third 36 Feet from the second, it required a total of 10 shifts to empty the tower using the sequential system. Of this total, two 12-hour 6 shifts were required to vacuum out the upper bed section and eight 12-hour 7 shifts were required to drain out the two lower bed sections. When both 8 of the upper beds were to be vacuumed and only the bottom bed was to be 9 drained, it took nine 12-hour shifts to complete vacuuming and four 12-hour shifts to drain.

11 $UMM~iRY OF THE IIIVEI~TION
12 In accordance with the invention, porous removable baskets 13 are seated in the upper ends oF each oF the drain tubes of those interbed14 assemblies whose supported catalyst beds are to be vacuumed and deliveredupwardly out oF the tower. The baskets are each adapted to retain the 16 column of catalyst thereabove, to prevent the latter from draining down-17 wardly into the next bed section, however, they are capable of permitting18 the reactant fluids moving in the reactor to pass therethrough.
19 As a result of this change, it is now possible to simul-taneously vacuum and drain the bed sections. By way oF comparison, it 21 took eight 12-hour shi Fts to simul taneously vacuum the top bed section 22 and drain the two bottom bed sections of the hydrotreater previously 23 described~ It took nine 12-hour shiFts to simultaneously vacuum the 24 two top bed sections and drain the bottom bed section. In the first case, there was a reduction of two 12-hour shiftsi in the second case5 26 the reduction was four 12-hour shifts. Over the course of a year of 27 operation, this translates into significant increases in plant output.

1 Broadly stated, the invention is, in combination, a 2 catalytic reactor tower having a plurality of interbed assemblies which 3 extend generally horizontally across the tower chamber at vertically 4 spaced apart levels and which sub-divide the chamber into a plurality of catalyst bed sections, one or more of which sections is to be emptied of 6 spent catalyst at the end oF a run by vacuuming said catalyst and delivering 7 it upwardly out of the tower, said interbed assemblies each providing a 8 grid for supporting a bed of particulate catalyst thereon, each such interbed 9 assembly having at least one generally vertical drain tube extending therethrough to enable spent catalyst to be drained by gravity from one 1l section to the next lower section, for remoYal from the base of the tower;
12 and a plurality of removable catalyst baskets, at least one of said inter-3 bed assernblies having at least one drain tube having therein one of said 4 plurality of catalyst baskets, each said basket having an apertured wall, said basket being operative to retain the column of catalyst thereabove, to 16 prevent it from draining downwardly into the next lower bed section while17 permitting fluid to flow Freely therethrough, whereby the bed sections to be 18 vacuumed may be vacuumed at the same time as the bed sections to be drained 19 by gravity are drained.
Another broad aspect of the invention is a method of operating 21 a catalytic reactor tower having a plurality of vertically spaced interbed 22 assemblies, including an uppermost interbed assembly, extending horizontally 23 across the tower chamber to sub-divide it into catalyst bed sections 24 including an uppermost bed section, said interbed assemblies each providing a grid for supporting a bed of particulate catalyst thereon, each such inter-26 bed assembly having at least one generally vertical drain tube extending 27 therethrough for enabling spent catalyst to be drained by gravity from 28 one section to the next lower section. The improvement comprises:
29 placing removable means, before loading the tower with catalyst For a run, in the upper end of each drain tube associated with the uppermost interbed

- 5 ~2~8~
1 assembly, said means being operative to retain thereabove a column of 2 particulate catalyst while permitting fluid to flow freely therethrough;
3 vacuuming spent catalyst upwardly from the uppermost bed section at the 4 end of the run; and simultaneously downwardly draining spent catalyst fromthose bed sections beneath the one or more interbed assemblies fitted with

6 said retaining means.

7 DESCRIPTION OF THE DRAWINGS

8 Figure 1 is a schematic sectional side view showing a

9 catalytic reactor tower with 2 interbed assemblies, the top assembly having baskets in its drain tubes;
1l Figure 2 is a sectional side view showing an interbed 12 assembly in greater detail than Figure 1, with baskets in place in the 3 drain tubes;
4 Figure 3 is a perspective view showing a basket upside down, to illustrate the grid-like bottom wall; and 16 Figure 4 is a perspective view showing the basket of 17 Figure 3 as it would be seated in the drain tube.

1 DESCRIPTION~OF _ E;P~E~ERRED.EMBODTMENT
2 As stated, the invention in one aspect comprises the 3 combination of a conventional hydrotreater or reactor tower 1, having a 4 pluralîty o-f interbed assemblies 2 equipped with drain tubes 3, and removable baskets 4 seated in the upper ends of the drain tubes 3 6 and those interbed assemblies 2 whose particulate catalyst beds 5 are 7 to be removed upwardly by vacuuming.
8 Each basket 4 is generally in the configuration of an 9 inverted hat. It has a cylindrical vertical sidewall 6 and an outwardly extending , horizontal flange 7 at the upper end of said sidewall. A
11 bottom wall 8 extends transversely across the bottom end of the sidewall12 6. The bottom wall 8 is in the form of a grid, formed by spaced apart 3 members 9 and 10. The grid openings are so sized that the catalyst 4 is retained by the grid while fluid movement is readily permitted there-through. The sidewall 6 is adapted to fit snugly within the drain tube 3;
16 and the Flange 7 is adapted to seat on the interbed assembly 2, to 17 maintain the basket 4 in position in the upper end of its associated 18 drain tube 3. The basket 4 is equipped with a handle 12, for easy removal 19 from the drain tube.
The flanged, cylindrical design of the basket 4 allows it 21 to be easily inserted into and removed from the drain tube 3. It can 22 be lifted by the handle 12.
23 Each basket 4 is filled with inert steel balls 11, to 24 further ensure that the catalyst particles cannot si-ft through or clog the basket grid.

1 In another aspect ~f the invention, a method is made 2 available in that the baskets 4 can be placed9 before the hydrotreater 13 is loaded with catalyst, in the drain tubes 3 of those interbed assemblies 4 2 whose catalyst beds 5 are to be removed upwardly by vacuuming. The hydrotreater 1 is then packed with catalyst and a production run proceeded 6 with in conventional fashion. When the run is ended and ihe ca~alyst is 7 to be removed, this is done by:
8 (1) vacuuming spent catalyst upwardly from the uppermost 9 bed;
(2) simultaneously downwardly draining spent catalyst from 11 the beds beneath the one or more interbed assemblies 12 2 fitted with said baskets 4; and 13 (3) if more than one bed is to be vacuumed, removing 14 the baskets 4 from one or more of the drain tubes 3 of the uppermost interbed assembly and then vacuuming 16 spent catalyst from the next lower bed while continuing 17 to drain catalyst from the lower end of the tower if 18 this is appropriate.
19 The scope of the invention is defined by the claims. which now follow.

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In combination:
a catalytic reactor tower having a plurality of interbed assemblies which extend generally horizontally across the tower chamber at vertically spaced apart levels and which sub-divide the chamber into a plurality of catalyst bed sections, one or more of which sections is to be emptied of spent catalyst at the end of a run by vacuuming said catalyst and delivering it upwardly out of the tower, said interbed assemblies each providing a grid for supporting a bed of particulate catalyst thereon, each such interbed assembly having at least one generally vertical drain tube extending therethrough to enable spent catalyst to be drained by gravity from one section to the next lower section, for removal from the base of the tower; and a plurality of removable catalyst baskets, at least one of said interbed assemblies having at least one drain tube having therein one of said plurality of catalyst baskets, each said basket having an apertured wall, said basket being operative to retain the column of catalyst there-above, to prevent it from draining downwardly into the next lower bed section while permitting fluid to flow freely therethrough, whereby the bed sections to be vacuumed may be vacuumed at the same time as the bed sections to be drained by gravity are drained.

2. The combination was set forth in claim 1 wherein each basket comprises:
outwardly extending flange means at its upper end, for seating on the associated interbed assembly to maintain the basket in its position at the inlet of its associated drain tube;

a downwardly extending sidewall adapted to fit snugly in one of said plurality of drain tubes;
and a transversely extending bottom wall apertured as aforesaid.

3. In the method of operating a catalytic reactor tower having a plurality of vertically spaced interbed assemblies, including an uppermost interbed assembly, extending horizontally across the tower chamber to sub-divide it into catalyst bed sections including an uppermost bed section, said interbed assemblies each providing a grid for supporting a bed of particulate catalyst thereon, each such interbed assembly having at least one generally vertical drain tube extending therethrough for enabling spent catalyst to be drained by gravity from one section to the next lower section, the improvement comprising:
placing removable means, before loading the tower with catalyst for a run, in the upper end of each drain tube associated with the uppermost interbed assembly, said means being operative to retain there-above a column of particulate catalyst while permitting fluid to flow freely therethrough;
vacuuming spent catalyst upwardly from the uppermost bed section at the end of the run; and simultaneously downwardly draining spent catalyst from those bed sections beneath the one or more interbed assemblies fitted with said retaining means.