Note: Descriptions are shown in the official language in which they were submitted.
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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.
6 BACKGROUND OF THE INVENTION
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.
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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.
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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.
37
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
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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.
