Apparatus for catalyst replacement

A light-weight and easily manufacturable catalyst support structure is provided, which allows fluid flow into a catalyst bed in uniform distribution. The support structure, used for supporting a moving catalyst bed within a moving bed reactor having an upward flowing fluid phase, is formed in a cone-like shape in which the diameter enlarges upward. The supporting structure comprises a shell-like support member, a first mesh layer comprising thick mesh elements, and a second mesh layer having a mesh size which does not allow catalyst particles to pass through. The first mesh layer overlays the support member, and the second mesh layer overlays the first mesh layer. The shell-like support member includes a circular bottom plate extending perpendicular to the center line of the reactor, and a side wall having a truncated cone shape which extends upward from the edge of the bottom plate. The bottom plate and the side wall are primarily made of perforated plates through which the fluid passes. A plurality of cylindrical flow guides of different diameters are provided underneath the shell-like support member.

Priority is claimed for this application under 35 U.S.C. .sctn.119 based 
upon Japanese patent application 5-172510 filed Jun. 18, 1993. 
FIELD OF THE INVENTION 
The present invention relates to a supporting structure for a catalyst bed, 
the structure having a cone-like shape with a diameter enlarging upward, 
which is used for supporting a moving catalyst bed within a moving bed 
reactor in which fluid flows upward. 
More specifically, it relates to a supporting structure which provides a 
uniform distribution of fluid into a catalyst bed at reduced weight and at 
lower cost. 
BACKGROUND OF THE INVENTION 
The moving bed reactor referred in this specification is described in 
International Patent Publication No. WO91/01359. In the reactor, catalyst 
is charged into the upper portion of the reactor and is drawn off from the 
lower portion of the reactor, when necessary, even during reactor 
operation. It may be used in many kinds of liquid-gas reaction processes, 
for example in hydrodesulfurization of atmospheric distillation residuum 
from crude oil or vacuum distillation residuum from topped crude oil. 
In the moving bed reactor, as shown in the FIG. 4, a two phase fluid 
consisting of a reactant gas (for example, a hydrogen containing gas) and 
a liquid reactant enters into the bottom of reactor A, and flowing upward 
through a catalyst bed B, exits from the top. Wherever necessary, the 
catalyst is charged into the reactor A through a catalyst charge pipe C 
provided in the upper portion and is drawn off through draw-off pipe D 
located above a supporting structure for the catalyst bed. 
In the above-mentioned construction, fresh catalyst charged into the upper 
portion through the catalyst charge pipe C flows downward while catalyzing 
the desired process reactions, loses catalyst activity, and finally is 
drawn off as spent catalyst through draw-off pipe D. The catalyst bed B is 
maintained at a high catalyst activity by charging fresh catalyst to the 
catalyst bed at a rate which balances the removal rate of spent catalyst 
having reduced catalyst activity, so that the desired process reactions 
can proceed effectively even in a small reactor. 
Embodiments of a beam supporting structure are shown in FIG. 5, 6, and 7. 
FIG. 5 is a plan drawing showing the supporting structure for a moving 
catalyst bed (hereinafter referred to as the supporting structure). FIG. 6 
is a sectional drawing showing the section of the supporting structure in 
line Y--Y of FIG. 5, and FIG. 7 is a enlarged drawing showing the section 
of the supporting structure in line Z--Z of FIG. 5. 
Supporting structure 1 is constructed of a framework assembly formed by 
radial beams 3 and transverse members 4 between beams 3, and wire mesh 
layers 5, 6 overlaying the framework, as shown in FIG. 5. As shown in FIG. 
5, FIG. 6 and FIG. 7, the framework consists of 8 beams 3 of a high beam 
height extending radially like spokes towards the upper portion of the 
reactor from an octagonal center plate 2, and having transverse members 4 
between beams 3 to form similar but different sized octagons. 
Spacecloth layer 5 and wire mesh layer 6 overlay the assembly. The 
spacecloth 5 is a woven wire mesh of thick wires, and the wire mesh 6 is 
of a smaller mesh size than the particle size of the catalyst particles. 
The inlet of draw-off pipe D is set above the center plate 2, as shown in 
FIG. 4. The center plate 2 and beams 3 are interconnected with each other 
by adequately sized connecting members, for example octagonal connecting 
member 7, as shown FIG. 6. The supporting structure 10 is connected to the 
reactor A by the reinforcing ring 8. 
As mentioned above, the supporting structure, which comprises a grid-like 
framework of beams and plate members and wire mesh layers overlaid on the 
grid-like frame work, has been developed for moving catalyst bed reactors 
in accordance with the same technical concept as the grid-like supporting 
structures used for conventional fixed catalyst beds. 
However, when, for example, economic factors require an increase in 
throughput, reactors having a large diameter are required to meet the 
throughput requirements. As the diameter of the reactor and the volume of 
catalyst charged to the reactor increases, the size of individual 
structural members in the supporting structure, and especially the size of 
the beams, have to be increased to support the weight load of the 
increased catalyst volume. As the size of individual structural members, 
and especially the size of the beams, increases, they tend to prevent the 
fluid from being uniformly distributed into the catalyst bed. As a result, 
contact between the fluid and the catalyst becomes uneven and variable 
from region to region in the reactor. 
In the beam supporting structures, when a prefabricated polygonal 
supporting structure is installed into a cylindrical reactor, its 
individual members have to be modified mechanically to fit the shape of 
the reactor. However, it is technically very difficult, and requires a lot 
of manpower and time, to make such mechanical modifications in the field, 
and installation costs are high. 
As mentioned above, a supporting structure having large support members 
experience problems with uneven distribution of fluid, and require high 
fabrication and installation costs. Thus, it is expected in the chemical 
or petroleum industries to provide an improved supporting structure 
appropriate to a large reactor. 
In this connection, the purpose of the present invention is to provide an 
easily manufacturable and light-weight supporting structure suitable for 
supporting a moving catalyst bed in a large reactor, while introducing 
fluid into the catalyst bed in a uniform distribution. 
We have found that the increase in weight of the beam supporting structure 
is caused mainly by the construction of the grid-like framework consisting 
of beams and plate members. The grid-like framework is designed 
considering the load of the catalyst bed as a bending stress. These 
members are required to have a section modulus comparable to the bending 
stress. 
As a result of study and experiments, the inventors have completed the 
present invention by adopting a shell-like structure to be designed 
considering the load of the catalyst bed as a membrane stress rather than 
a bending stress. 
SUMMARY OF THE INVENTION 
To achieve the stated objectives, the present invention provides a 
supporting structure forming a cone-like shape, and having a diameter 
enlarging upward, for supporting a moving catalyst bed within a moving bed 
reactor having an upward flowing fluid phase, said supporting structure 
comprising a shell-like support member; a first mesh layer comprising 
thick mesh elements and laid on said shell-like support member; and a 
second mesh layer laid on said first mesh layer and having a mesh size 
such that catalyst particles do not pass through said second mesh layer; 
wherein said shell-like support member comprises a circular bottom plate 
positioned perpendicular to the center line of the reactor, and a 
truncated cone-like side wall extending upward from the edge of said 
circular bottom plate; and wherein said side wall and bottom plate are 
substantially made of plate members provided with many holes. 
It is preferable that the angle (the angle .alpha. indicated in the FIG. 1) 
between the generating line of the truncated-cone and the diameter of the 
moving bed reactor (hereinafter, called the reactor) is larger than the 
angle of repose of catalyst particles, to facilitate the flow of catalyst. 
The thickness of the plate member forming the side wall can be calculated 
in accordance with known membrane stress calculation formulas, based on 
the catalyst weight load to be supported. The diameter, the pitch, and the 
number of the holes are determined based on the allowable pressure drop 
for the reacting gas and the reacting liquid flowing through the 
supporting structure, particle sizes of the catalyst, and the weight of 
the catalyst bed. The materials of the plate members are determined by 
considering corrosion caused by reacting gas and reacting liquid, reaction 
temperature, etc. 
It is preferred that the opening areas of the first wire mesh layer 
overlaying the holes of the plate members be larger than the opening area 
of each hole, and that the diameter of the wire elements is thick enough 
to support the catalyst weight over each of the holes. 
The second wire mesh layer is provided to prevent catalyst particles from 
dropping downward though the supporting structure, and the first wire mesh 
layer is provided to reinforce the second wire mesh layer and to support 
the catalyst weight over the opening area of each hole. The wire mesh 
elements for the first and second wire mesh layers are not necessarily of 
metal wire netting, but may be replaced by any material performing the 
same function as wire netting, for example perforated plates. 
In the preferred embodiment, a supporting structure for a catalyst bed is 
characterized by a plurality of cylindrical flow guides of different 
diameters, concentrically positioned underneath the shell-like support 
member. 
Since the supporting structure for a catalyst bed is formed by plate 
members to support the load of the catalyst in the present invention, the 
weight of the supporting structure can be reduced to a great extent 
compared with a beam supporting structure. Furthermore, since easily 
fabricatable plate members are used as the support members, it is very 
easy to form a truncated-cone and to connect it to a reactor body in the 
field. Since holes are provided in the plate members in uniform 
distribution, the supporting structure according to the present invention 
can introduce fluid into the catalyst bed in a more uniform distribution 
over the whole sectional area of the catalyst bed compared with using beam 
supporting structures. Consequently, efficiency of the reaction process 
becomes higher due to uniform contact between the fluid and the catalyst. 
Thus, the present invention has the process advantage that the fluid can 
be introduced into the catalyst bed in uniform distribution and with small 
pressure drop, and the economical advantages that the weight of the 
supporting structure can be reduced, the fabrication made easier, and 
costs reduced. Furthermore, since diameters and pitches of holes may be 
adjusted according to the specific location, of each hole, the 
distribution pattern of the fluid flow can be adjusted easily. 
In a preferred embodiment, since a plurality of cylindrical flow guides of 
different diameters are provided underneath the shell-like supporting 
member, fluid coming from the lower portion of the reactor can be 
introduced uniformly into the catalyst bed. In the absence of flow guides, 
the fluid flows outwardly along the conical surface of the shell-like 
support member of the supporting structure to be deflected at high 
velocity along the reactor walls. Since the supporting structure according 
to the present invention has the shell-like support member formed by plate 
members, it can be provided with flow guides at optimum locations chosen 
to give a uniform flow distribution, while avoiding holes in the 
shell-like support member. Consequently, a distribution pattern of fluid 
entering into the catalyst bed can be easily adjusted by proper 
positioning of the flow guides.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be explained in detail below based on the 
preferable embodiment, referring to the attached drawings. 
FIG. 1 is a sectional drawing showing the supporting structure for a 
catalyst bed (hereinafter referred to as a supporting structure) in a 
plane containing the centerline of reactor A, and FIG. 2 is a sectional 
drawing of the supporting structure in line X--X of FIG. 1. 
The supporting structure 10 shown in FIG. 1 has been installed in moving 
catalyst bed reactor A (hereinafter referred to as reactor A) shown in 
FIG. 4, where fluid flows upwards from the bottom to the top. The 
supporting structure 10 is positioned such that the centerline of the 
supporting structure 10 is consistent with the centerline of reactor A. 
The supporting structure 10 comprises a truncated cone-like side wall 12, 
having a diameter which enlarges towards the top of the reactor A, and a 
bottom plate 14 located in the center of side wall 12, namely, the lowest 
position of the supporting structure 10, and extending perpendicular to 
the centerline of the reactor A. 
Side wall 12 is shaped as a truncated cone such that angle .alpha. 
indicated in FIG. 1 is larger than the angle of repose of catalyst 
particles. Bottom plate 14, having a nearly circular shape, is connected 
to the edges of the lower portion of side wall 12. A catalyst draw-off 
pipe D, indicated in FIG. 4, is provided such that its inlet is located 
adjacent to and above the bottom plate 14 to facilitate catalyst draw-off 
from the supporting structure 10. 
As shown in FIG. 2, the side wall 12 and the bottom plate 14 both have, as 
a bottom layer, a perforated plate 16 made of plate members to form the 
shell-like support member. A first wire mesh layer 18 overlays the 
perforated plate 16 as a lower layer, and a second wire mesh layer 20 
overlays the first wire mesh layer 18. 
The thickness of the perforated plate 16 can be calculated in accordance 
with known membrane stress calculation formulas, based on the catalyst 
weight load to be supported. Many holes 22 are provided nearly in equal 
pitches to penetrate the perforated plate 16 so that the fluid can be 
introduced into the catalyst bed. The total opening area of the holes 22 
is determined based on the allowable pressure drop for reacting gas and 
reacting liquid entering the catalyst bed. The side wall 12 and the bottom 
plate 14 may not necessarily have holes 22 of the same pitch and of the 
same diameter. For example, holes 22 may be provided in different 
diameters and different pitches depending on location on the support 
structure. 
The first wire mesh layer 18 is made of wire netting with a comparatively 
large mesh size woven using thick metal wires. The second wire mesh layer 
20 is made of wire-netting with a slightly smaller mesh size than the 
particle size of the catalyst. The second wire mesh layer 20 is provided 
to prevent catalyst particles from dropping downward through the 
supporting structure 10, and the first wire mesh layer 18 is provided to 
reinforce the strength of the second wire mesh layer 20 and to support the 
catalyst weight over the opening area of each hole 22. 
Many cylindrical flow guides 24 of different diameters are concentrically 
installed underneath the perforated plate 16 to have their centers on the 
centerline of the side wall 12. The flow guides 24 are made of cylindrical 
members 26, as shown in FIG. 3. 
As per the above-mentioned construction, the flow guides 24 can introduce 
the fluid coming from the bottom of reactor A into the catalyst bed in 
uniform distribution through the supporting structure 10. The supporting 
structure 10 is connected with the body of reactor A by the reinforcing 
ring 30. 
EXAMPLE 
The following is a design example of the supporting structure according to 
the present invention: 
Inside diameter of reactor:4,400 mm 
Weight of catalyst in reactor:220 metric ton 
Angle .alpha.:60.degree. 
Diameter of bottom plate:1,066 mm 
Thickness of perforated plate:22 mm in lower portion of side wall :28 mm in 
upper portion of side wall 
Diameter X Pitch of hole:50 mm.times.75 mm 
First wire mesh layer:metal wire netting having diameter 6 mm, pitch 10 mm 
Second wire mesh layer:metal wire netting having diameter 1.6 mm, 9.times.9 
mesh 
Total weight of supporting:approximately 11 ton structure 
Dimensions of a beam supporting structure designed based on the same design 
conditions as the above design example are as follows: 
Beams:8 solid pieces of 330 mm high, and 150 mm wide 
Transverse member traversing:a number of plate members beams of 300 mm 
high, and 38 mm thick 
Total weight of supporting:approximately 32 ton structure 
Comparing the two cases above, while the beam supporting structure has the 
problem in that it prevents fluid from entering into a catalyst bed in 
uniform distribution due to the wide beams, which cause an uneven and 
non-uniform flow of the fluid, the design example does not cause such 
uneven and non-uniform flow, because of a uniform distribution of the 
holes. While the pressure drop of the fluid through the supporting 
structure becomes great in the beam structure case, in which the flow area 
of the fluid is reduced due to the wide beams, the pressure drop will not 
be so great in the design example, where holes with required diameters can 
be arranged as necessary. Furthermore, power consumption for operating the 
reactor will be reduced. 
The design example can reduce the weight of the required materials to 
approximately 35% of the beam structure and thus can reduce the material 
costs. Since the thickness of the skirt supporting the reactor body can be 
reduced due to the weight reduction of the supporting structure, the 
material cost will be further reduced. Further, since the construction of 
the design example is very simple, compared to the beam structure, the 
manpower required for fabrication and installation can be reduced by 
approximately 30%.