Method and apparatus for supporting radial reactor centerpipes to accommodate thermal cycling

In a radial flow catalytic reactor, a centerpipe is gravity supported in a central socket member and accommodated as to vertical upward movement within a predetermined maximum distance to prevent unseating of the centerpipe due to thermal cycling of the catalyst and/or the reactor internal members. Such vertical movement of the centerpipe is accommodated by extending the length of the socket member so that it exceeds the expected lift distance of the centerpipe due to such cycling. Desirably, but not necessarily, the centerpipe may include a perforated pipe member axially coextensive with and enclosed within the screen member. The pipe and screen members are independently supported in the socket member by gravity.

FIELD OF THE INVENTION 
This invention relates to radial flow catalytic reactors. More particularly 
it relates to a method of and apparatus for operating a radial flow 
reactor to accomodate vertical movement of a gravity supported, uniformly 
permeable centerpipe due to change of temperature of the centerpipe 
fluids, catalyst and/or portions of the vessel structure during heating 
and cooling of such catalytic reactors. 
DESCRIPTION OF THE PRIOR ART 
It is a particular object of the invention to accomodate vertical movement 
of a centerpipe in a radial flow catalytic reactor over a predetermined 
distance which does not exceed the expected lift distance due to such 
thermal cycling. In general, the "internals" of such radial flow reactors 
are gravity supported in a vertically elongated vessel and all such 
internals are inserted and removed through an enlarged opening, such as a 
manway, in the upper wall of the vessel. ("Internals" as used herein 
refers to the centerpipe, catalyst particles, and catalyst retaining 
screens forming the catalyst bed and providing annular space between the 
outer circumference of the bed and the reactor vessel sidewall including 
any insulating structure.) Where such a radial flow reactor operates at 
elevated temperatures, it is frequently desirable to insulate the interior 
wall of the vessel so that the outer steel wall operates near ambient 
temperature conditions. To avoid heat conduction from the vessel internals 
to the vessel walls, all such internals must be essentially gravity 
supported except for a few low thermal conductivity paths (e.g., thin web 
supports and the like), which may be welded to a vessel nozzle or entry 
pipe in the bottom wall of the vessel. Further, the depth of the socket 
support for the centerpipe is as short as possible while still permiting 
use of the full vertical height of the reactor for radial flow through the 
catalyst bed. 
Additionally, where radial reactors are used for hydroprocessing 
hydrocarbons, hydrogen is used to influence cracking, isomerization or 
reforming of such hydrocarbons. To contain the hydrogen and prevent 
hydrogen embrittlement of the steel vessel walls (due to hydrogen 
interaction with carbon in the steel) it is usually necessary to 
heat-treat such reactor vessels (frequently 60 to 100 feet long and up to 
30 feet in diameter) as a single unit. After such heat treatment it is 
undesirable to affix, as by welding, any portion of the internals to that 
vessel. For this additional reason, such catalyst retaining members are 
gravity supported in the vessel. 
In radial flow reactors, fluid reactant generally enters the top of the 
vessel, flows downwardly in the annular space between the outer catalyst 
retaining screens and the vessel wall, and then passes radially inward 
through the catalyst bed to a perforated centerpipe. Fluid in the 
centerpipe then leaves through an outlet at the bottom of the vessel. 
Alternatively, flow into the vessel may be inverted so that reactant 
enters the bottom periphera of the vessel, flows upwardly in the annular 
space between the vessel wall and catalyst bed, passes through the bed and 
leaves through a centerpipe communicating with a central lower outlet. 
Reverse flow is also possible. In such an arrangement, inlet flow of 
reactant fluids is upwardly in the centerpipe, radially outward through 
the catalyst bed and out of the top of the vessel. 
As mentioned above, conventional radial reactors are usually subjected to 
temperature cycling, an alternate increase and decrease in the temperature 
of the vessel and its contents. The cycles are frequently from 200.degree. 
to 500.degree. C. or more in magnitude. Temperature cycling occurs, for 
instance, when an apparatus is heated and brought into service at an 
elevated operating temperature and subsequently withdrawn from service and 
cooled. Temperature cycling also occurs when contact material in the 
vessel is regenerated at an elevated temperature, or when there is a 
change in feed rate or a power outage. Apparatus employed in catalytic 
hydrocarbon conversion processes such as reforming, isomerization, 
hydrodesulfurization and hydrocracking are especially subject to 
temperature cycling. Because centerpipes of radial flow vessels of 
conventional design are removable, the centerpipe tends to move vertically 
upward in the bed of catalyst material with each temperature cycle. 
The reasons for such net upward movement of the centerpipe is not 
completely understood. Apparently, the centerpipe upon being heated 
expands in an upward direction. But upon being cooled, it contracts from 
both ends toward a center neutral point. Thus, with each cycle, there is a 
net upward movement, frequently up to 1 centimeter or more. Eventually the 
centerpipe will rise enough from its mounting socket, or seat, to allow 
unwanted movement of the contact material. If the centerpipe moves away 
from the seat at the base of the vessel, contact material will flow under 
it, escape from the vessel and enter subsequent vessels such as heat 
exchangers. There the contact material can adversely affect fluid flow 
distribution or contacting efficiency, or shut down flow completely. 
Displacement of the catalyst obstructs flow of the reactant which can 
cause coking and damaging local temperature rises. A further effect of a 
rise of the centerpipe is to decrease the depth of the contact material 
seal above the top perforation in the centerpipe. The decreased seal 
allows some of the feed to bypass the contact material, which leads to 
loss of product quality. 
One arrangement for restraining centerpipe movement is shown and described 
in U.S. Pat. No. 4,244,922, issued Jan. 13, 1981, assigned to the assignee 
of this application. In that patent a horizontal surface is secured to the 
centerpipe in such a position that it carries a portion of the weight of 
the catalyst bed. The horizontal surface is in the form of a disk which 
either is secured to the pipe or rests upon a flange affixed to the 
centerpipe. This arrangement is quite satisfactory to prevent centerpipe 
vertical movement but presents some problems. If the flange is permanently 
fixed to the centerpipe, as by welding, the increased diameter interferes 
with insertion and removal of the pipe through the vessel manway. Further 
it may interfere with visual alignment and landing of the base of the 
centerpipe in the vessel support socket. 
U.S. Pat. No. 4,033,727--Vautarin, issued July 5, 1977; U.S. Pat. No. 
3,167,399--Hansen, issued Jan. 26, 1965 and U.S. Pat. No. 3,027,244--Byrne 
et al, issued Mar. 27, 1962, each discloses radial flow reactors having 
uniform diameter centerpipes which appear to be gravity supported on the 
bottom wall of the vessel, but without means for accommodating upward 
movement of the centerpipe sufficient to prevent unseating and catalyst 
loss from the vessel. 
U.S. Pat. No. 2,997,374--Lavender et al, issued Aug. 22, 1961 discloses a 
radial flow reactor in which the centerpipe is permamently secured to the 
bottom wall of the reactor, vessel. 
U.S. Pat. No. 2,635,989--Bonner, issued Apr. 21, 1953 discloses a radial 
flow reactor in which the centerpipe enters either the top or bottom of 
the reactor and is composed of a vertical series of cones or cylinders of 
decreasing diameter from the inlet to the outlet end of the vessel. The 
centerpipe is permanently affixed to the end wall of the reactor vessel. 
In my prior U.S. patent application Ser. No. 316,522 filed Oct. 29, 1981, 
now U.S. Pat. No. 4,374,094 which is assigned to the assignee of the 
present invention, there is disclosed method and apparatus for preventing 
centerpipe lifting by forming the centerpipe with a uniformly permeable 
frustroconical configuration. The structure is preferably a gravity seated 
rigid screen member against which the weight of the catalyst particles 
bears to resist pipe lift. 
Application Ser. No. 316,547, also filed on Oct. 29, 1981, now U.S. Pat. 
No. 4,374,095 and also assigned to the assignee of the present invention, 
discloses an alternate form of a frustroconically configured centerpipe in 
which an internal pipe is slotted or drilled and openings through the pipe 
are individually covered or the entire pipe is surrounded by screen means. 
SUMMARY OF THE INVENTION 
In accordance with the present invention uniform radial flow through the 
catalyst bed is through a cylindrical centerpipe which is supported in a 
socket, the length of which exceeds the expected axial distance that the 
centerpipe may rise under thermal cycling. Such lifting tendency of the 
centerpipe is also reduced by forming it as a generally rigid screen 
having uniform radial and longitudinal permeability. The centerpipe is 
permitted to lift within a predetermined maximum distance by suitably 
elongating the vessel socket for gravity support of the lower end of the 
centerpipe. 
Preferably, the centerpipe is formed by uniformly permeable screen means in 
the form of vertical bars uniformly spaced apart around the circumference. 
The bars forming said rigid cylindrical screen member are so held by 
internal hoop members bonded to the vertical bars at longitudinally spaced 
intervals of approximately equal distances. In one form a cylindrical pipe 
member of smaller diameter than the centerpipe screen member is enclosed 
within it so that the pipe is radially inwardly spaced from said screen 
member to form a coaxially annular space with the screen member. In one 
preferred form, an upper cap member is secured to the upper end of said 
centerpipe screen to close the top thereof. 
The socket member for the centerpipe also holds said rigid cylindrical 
screen member vertical and coaxial with the walls of the radial reactor 
vessel. Segments, or arcuate sections, of screens disconnectably attached 
to each other are placed adjacent the vessel sidewall to enclose a 
generally cylindrical bed of catalyst particles. Such segments likewise 
extend a desired distance above the centerpipe to assure that the top of 
the pipe is covered by catalyst particles to a desired depth. The top of 
the catalyst bed supports a plurality of arcuate plates, or segments, to 
vertically confine the bed. Further, the vertical screen segments are 
radially spaced inwardly from the vessel sidewall to provide an annular 
flow path along the length and around the circumference of the catalyst 
bed so that reactant may flow uniformly radially to or from the uniformly 
permeable centerpipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, a radial flow reactor vessel 10 supports a 
generally cylindrical bed 12 of catalyst particles. A uniformly permeable 
cylindrical centerpipe, screen member 14, constructed in accordance with 
my invention, extends vertically and axially through bed 12. Flow of 
hydrocarbons to be processed in bed 12 (as indicated by arrows) is from 
inlet distributor 16 in an enlarged central inlet opening 17 designated as 
a "manway" through upper end wall 18 of vessel 10, and into bed 12 from 
the annular space 21 between sidewall 20 of vessel 10 and the retaining 
screen means 22 for bed 12. Centerpipe screen means 14 preferably 
comprises an outer, uniformly permeable, screen means 56 extending from 
the vessel outlet formed by flange 24 in lower vessel end wall 30 toward 
upper vessel end wall 18. If desired, the permeability of screen member 56 
may be increased at the top as compared to its base end. 
Desirably the entire assembly of cylindrical centerpipe screen member 14, 
retainer screen means 22, formed by a plurality of segments 23, catalyst 
bed 12 and cover 26, likewise formed by segments, is supported by gravity 
on lower end wall 30 of vessel 10. In the arrangement of FIG. 1, vertical 
support ring 28 provides a base for screen segments 23. Because vessel 10 
in the present embodiment is intended to operate as a cold wall reactor, 
an internal shell 38 is also mounted on support ring 28 and is spaced from 
outer wall 20 by canted annular rings 39. Rings 39 are vertically spaced 
apart, and as with ring 28, are relatively thin compared to their length 
to form low thermal conductive paths between shell 38 and outer vessel 
side wall 20. The internal reaction volume of vessel 10 is insulated from 
upper wall 18 by a spacer such as annular disc 27. The bottom, side and 
top of vessel 10 is then filled with insulative cement or aggregate 32 to 
provide the necessary insulation. The upper portion 29 of bottom 
insulation is preferably coarse sand, covered with plate means 34, also 
formed in segments. Plate means 34 provides a base for catalyst bed 12. 
As discussed above, it is essential that all portions of the internals 
(apart from the thermal insulation means) of vessel 10 be removable, as 
through manway 17 in upper end wall 18. For this reason cylindrical 
centerpipe screen member 14 must be removable. As will be apparent, the 
diameter of centerpipe screen 14 is somewhat exaggerated to illustrate its 
construction. However, the structure is such that its full diameter will 
readily pass through manway 17. To support centerpipe screen means 14 in a 
vertical position and substantially coaxial with vessel 10, a socket, or 
support seat 25 is supported within bottom outlet flange 24. 
As best seen in FIG. 2, preferably, socket 25 is cylindrical with an 
annular seat 45 for collar 15 formed integral with the lower end of rigid 
centerpipe screen 14. A removable internal collar 41 includes a ring seat 
42 which also rests on annular seat 45. A depending cylindrical skirt 43 
permits internal collar 41 to be anchored in socket collar 25, as by lock 
ring 44, adapted to releasably engage skirt 43 and the inner surface of 
socket 25. For low thermal conductivity support in flange 24, socket 25 
also includes a pair of external mounting collars 46 and 47. A plurality 
of radial ribs 48 are welded to the inner circumference of opening 49 in 
flange 24 of lower wall 30 of vessel 10 to secure socket 25 in place. It 
is to be particularly noted that ribs 48 are thin as compared to their 
radial length and are secured only to opening 49 by welds 53 to assure a 
low heat conductivity path from collars 46 and 47 of socket 25 to flange 
24. 
In the arrangement of FIGS. 1 and 2, desirably the lengths of socket 25 and 
internal collar 41, exceed expected actual lift distance of collar 15 of 
screen 14 due to thermal cycling during operation of vessel 10. Although 
socket 25 may be tapered outwardly a few degrees to assist insertion and 
removal of centerpipe means 14, in general it is preferably cylindrical 
along its length, to frictionally engage the outer surface of collar 15 at 
its lower end. If centerpipe means 14 "creeps" upward under variable 
thermal conditions, or thermal cycling, catalyst particles or fines that 
might enter socket 25 are prevented from reaching the outlet stream by 
removable internal collar 41. Collar 41 is made removable so that seat 45 
may be cleaned if centerpipe member 14 is removed. 
In the arrangemnent of FIG. 1, centerpipe screen means 14 is closed at the 
top by a cap member 11 which extends above the top of bed 12 and catalyst 
bed cover 26. Segments forming catalyst bed cover 26 lie directly on a 
layer of spheres or balls, 40 resting on screen 35. Together this 
arrangement closes off the top of bed 12. Since vertical movement of 
centerpipe means 14 would uncover the upper end of screen member 56 the 
side walls 19 of cap 11 are made sufficiently long so that reactant fluids 
will not bypass bed 12 with accompanying loss of efficiency or degradation 
of products. Top 54 of cap 11 may be provided with a lift eye 55 for use 
in installation or removal of centerpipe 14 through manway 17 by cable and 
lifting hook (not shown). 
A significant advantage of the generally uniform cylindrical shape of 
screen 56 of centerpipe means 14 is to improve radial flow throughout bed 
12. As particularly detailed in FIG. 2, the parallel vertical bars forming 
screen 56 are uniformly spaced and held by hoops 52 equally spaced along 
the ength of screen 56. It has long been appreciated that radial flow 
vessels are subject to considerable variations in flow over various parts 
of the entire cylindrical body of catalyst particles. Under relatively low 
flow conditions and uniform permeability of the catalyst bed, catalytic 
reaction in such reactors is highly efficient. However, with high flow 
rates and non-uniform permeabilities, fluids "channel" or "stratify" 
through selected flow paths, generally those paths with the greatest 
permeability. To accommodate such variations, the width of bars 50 and 
their spacing from each other can be varied as they are assembled and 
welded on hoops 52. 
FIGS. 3 and 4 show a further alternative embodiment of the present 
invention for accommodating centerpipe lifting. As there shown, centerpipe 
means 64 includes screen member 74 which encloses a smaller diameter pipe 
member 65 having slots, or holes, 66 formed therein to control flow of 
fluids throughout the cylindrical body of catalylst 12. As best seen in 
FIG. 3, a preferred form of cylindrical screen 74, (as in FIGS. 1 and 2) 
is a plurality of vertical bar members 60 equally spaced from each other 
and bonded to spaced apart hoop member 62, as by welding. For flow from 
annular space 21 to centerpipe 64, and to restrain catalyst movement 
during fluid flow, bars 60 are generally triangular in cross-section and 
arranged so that their wedge faces are directed inwardly so that there is 
greater clearance for flow at the inner face than at the outer face of 
centerpipe means 64. A specific advantage in such construction is to 
prevent plugging by small particles that may bridge the open spaces 
between the external faces of bars 60. Hoops 62 are spaced apart at 
suitable intervals along the length of centerpipe screen 74 to give 
structural stability against the hydrostatic head of the catalyst bed at 
each level along centerpipe 64. 
Sidewall 67 of cap member 68 is welded to the upper end of screen member 74 
so that cover 69 is above bed 12. Desirably perforated pipe 65 has a 
diameter substantially smaller than the inner diameter of screen member 74 
and terminates in a closed cap 71 whose outer circumference 72 forms a 
slip fit wth the inner surface of sidewall 67 of cap 68. Cap 71 is 
positioned to accommodate differential thermal expansion between screen 
member 74 and perforated pipe 65. The socket end of screen member 74 is in 
the form of a collar 70 secured, as by welding, to the ends of screen bars 
60. 
Although not shown, screen member 74 may be formed by a multiplicity of 
circular members, of the same diameters between base collar 70 and 
sidewall 67 of upper cap 68, to obtain the uniform permeability. The 
circular members are then secured in their axially spaced apart positions 
by radially spaced rods extending between base collar 70 and cap 68. 
In the arrangement of FIGS. 3 and 4, it will be particularly noted that 
socket sidewall 80 is elongated sufficiently to exceed any expected lift 
of collar 70 by screen member 74. Further it will be seen that the lower 
end of perforated pipe 65 includes a ring seat member 81 which lands on a 
radial extension of annular plate 82, formed as a part of socket member 83 
and secured by web 85 so that socket 80 is concentric with vessel bottom 
flange 84. Preferably, the lower end 86 of perforated pipe 65 has no 
openings below the top of socket sidewall 80. 
While only the FIGS. 3 and 4 embodiment of the invention includes a 
perforated pipe, such as 65, the arrangement of FIGS. 1 and 2 may also 
include such a pipe. 
In the arrangements of both FIGS. 1 and 4, if desired, screen member 56 
(FIG. 1) or screen 74 (FIG. 3) may be made up of several cylindrical 
portions of bars 50 or 60 and hoops 52 or 62, respectively, with each 
portion having a decreasing diameter and secured end to end to form a 
stepped, generally conical centerpipe. Such an arrangement may also 
include a perforated internal pipe, if so desired. 
It is frequently desirable to be able to easily remove the catalyst bed 
before attempting regeneration of catalyst, or other servicing of reactor 
10. For example in FIG. 1, catalyst particles may be drained through 
flange 31 which enters vessel 10 through bottom wall 30. Additionally 
flange 33 may be used to extract samples of catalyst particles during 
normal operation, as well as to assist in removing catalyst bed particles. 
After removal of the catalyst, the individual internal elements may be 
removed, (or installed). As shown, to assist in removal or installation of 
centerpipe member 14, a lifting lug or eye 55 is secured to upper end 11 
(FIG. 1) or plate 69 (FIG. 3). Ring 57 holds the several pieshaped 
segments of cover 26 in place on balls 40 over screen 35. 
The present embodiments of the invention have been described in connection 
with flow of hydrocarbons to be reacted in vessel 10 entering through flow 
distributor 16 and with effluent exiting through outlet flange 24. 
However, reverse flow into centerpipe member 14 and then radially 
outwardly through bed 12 to annular space 22 is possible with the 
attendant advantages of accommodating such centerpipe being for thermal 
movement to the extent required, while preventing movement of catalyst 
from bed 12 into the space between the centerpipe and its socket seat. 
While only a few examples of the preferred embodiments of the invention 
have been shown and described, various other modifications or changes in 
both as to the method and apparatus aspects thereof will occur to those 
skilled in the art. All such modifications or changes coming within the 
scope of the appended claims are intended to be included therein.