Hydrogenation Reactor Design Considerations

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GBHE Technical Bulletin CTB #10
HYDROGENATION REACTOR DESIGN
Fixed Bed Reactor Internals
The following is designed to give an overview on and some insight in the general
design features of hydrogenation reactors and the impact of the various reactor
internals on performance.
GBHE can offer assistance in the design and alteration of hydrogenation reactors
and their internals to meet specific production and engineering needs. It should
be noted that specific advice can only be given on a case to case basis. For
more information, please contact GBHE
outlet collector
graded catalyst inert
supports
catalyst separation
screens
separation screen
debris collector
void space
inlet distributor
inert balls
catalyst bed
liquid redistributor if
required
catalyst
unloading

INLET DISTRIBUTOR
Reactors operate in different flow regimes within the catalyst bed. In normal
operation, however, there are only three conditions that affect inlet design, viz.
gas phase, liquid phase and mixed phase flow regimes.
With gas flows, inlet velocities are sometimes high and inlet baffles are used to
prevent direct impingement on the reactor bed. These baffles are located on the
reactor centre line and can be as simple as a set of concentric rings with a cover
plate.
Mixed phase flow distributors are more complicated and are covered elsewhere.
The mixed phase flow designs will be the same for the reactor inlet and a
distribution tray. In some high velocity applications it may be necessary to include
both an impingement baffle and a two-phase flow distributor.
DEBRIS COLLECTOR
Reactors contain debris collectors for two reasons:
1. To provide an increased area for fluid flow.
2. To collect trash and any 'tramp material' which can be caught in the
baskets. They will collect millscale from furnaces, storage tanks and
exchangers and still allow the feed stream to pass.
In chemical reactors with clean feed streams these baskets may not be required.
They are typically made from 100 mm diameter baskets of mesh or perforated
plate which is approximately 150 to 200 mm long. They are located triangularly in
an inert bed of alumina balls and are tied together in hexagonal clusters.
As many baskets as possible are fitted into the reactor on a 180 to 200 mm pitch.
Further advice can be given for design of reactor internals if required. Please
contact GBHE

INERT BALLS (top of bed)
It is possible to include a layer of inert ceramic balls directly below the inlet. This
can be a single size or random distribution size material. They protect the
catalyst bed from direct impingement of the inlet feedstock stream. The layer is
usually 0.15 metres in depth unless a greater depth is needed for the inlet debris
collector if used.
The ceramic material is usually alumina. Typically, the balls have a diameter of
12.5 mm. A screen is sometimes included below the layer of inert ceramic
material to prevent the more dense balls from sinking into the catalyst bed during
normal operation.
contact GBHE
CATALYST SEPARATION SCREENS (top of bed)
The separation screen keeps the ballast out of the catalyst bed. The screen is cut
into segments to pass through the manhole and laced together inside to form a
complete circle.
The screen is not attached to the reactor and is free to settle with the bed during
the run. It falls with the catalyst when the latter is unloaded.
Typical screen sizes are given in Table C2
PT-1.
Table C2
PT-1. Screen sizes for Vulcan Series VIG catalysts. Typical values.
VIG-T02 1.2 mm VIG-T03 2.5 mm
Separation Screen Mesh size 18x18 mm
wire diameter 0.58 mm
(0.023")
width of opening 0.83 mm
(0.0326")
34.4% open area
mesh size 12x12 mm
(0.035")
(0.048")
33.2% open area

contact GBHE
CATALYST BED
GBHE VULCAN Series VIG catalysts are HGS shaped catalyst. They can be
dense or sock loaded. When used in existing vessels or in new units, there are
some factors that need to be taken into consideration to make optimum use of
the catalyst activity.
Design of the reactor internals is part of this performance maximization. GBHE
offers to advise wherever possible and make process recommendations for
various options.
Manholes have not been shown in Figure 1. They are, however, an important
factor in new reactors. Further details are available on request.
In general, manholes can be located in the centre line or on the side of the vessel
and can vary in size from 400 to 600 mm.
Similarly, catalyst drop out nozzles are required. Usually, dimensions are
comparable to those for manholes.
contact GBHE
CATALYST SEPARATION SCREENS (bed support)
A fine screen whose opening is less than the catalyst size is sometimes used
between the catalyst and the inert support. It prevents catalyst pieces and fines
generated during normal operation from reaching the outlet and are designed to
have a maximum open surface area and will not seriously affect the total reactor
pressure drop.
The fine mesh is not usually strong enough to span the bed on top of the inert fill.
Any distortion or movement of the screen will allow catalyst to by-pass and may
cause rupture of the fine material. It is therefore necessary to include a second
screen to ensure that weaker screen does not bend and/or rupture. The lower
screen is usually sized to prevent the smallest of the inert balls from passing
through (see also reference for inert support loading).

Table C2
PT -2. Screen sizes for VULCAN Series VIG catalysts. Typical values.
VIG-T02 VIG-T03
Top Screen
(catalyst support)
Mesh size 18x18
(0.023")
Width of opening 0.83 mm
(0.0326")
34.4% open area
mesh size 12x12
(0.035")
(0.048")
33.2% open area
Bottom Screen Mesh size 8 x 8
Wire diameter 1.2 mm
(0.047")
(0.078")
38.9% open area
Mesh size 8 x 8
Wire diameter 1.2 mm
(0.047")
(0.078")
38.9% open area
In some cases, a single bed can be split into two or more sections by separation
screens.
contact GBHE

CATALYST BED SUPPORTS
There are a number of methods for bed supports. These include a grating and
beam arrangement, proprietary screens or inert fill.
The method covered here it the application of inert balls. An outlet collector must
be used when using an inert fill system. The material usually is high purity α-
alumina.
The philosophy is to use a layered fill. The layer directly beneath the catalyst
should be approx. twice the catalyst size. The bottom layer should be approx. 1.3
- 2.5 cm thick (½ - 1"). The balls should cover the outlet collector by a minimum
of 7.6 cm (3") and should be at least 7.6 cm (3") into the straight part of the shell.
Typical support system data for VULCAN Series VIG catalysts are given in table
C2
PT-3.
Table C
2
PT-3
VIG-T02 VIG-T03
Top layer below catalyst bed
(15.2 cm (6") depth)
3.2 mm (1/8") 3.2 mm (1/8")
Next layer below top balls
(15.2 cm (6") depth)
6.4 mm (1/4") 6.4 mm (1/4")
Bottom layer below second
layer (fill rest of the volume)
12.7 mm (1/2") 12.7 mm (1/2")
Where a second bed is used, it may be necessary to use a grating and a beam.
In case alumina balls are used, they should be sized according to the values
given in table C2
PT -2.
Table C
2
PT-4
VIG-T02 VIG-T03
Top layer below catalyst bed
(7.6-15.2 cm (3-6") depth)
3.2 mm (1/8") 3.2 mm (1/8")
Next layer below top balls
(7.6-15.2 cm (3-6") depth)
6.4 mm (1/4") 6.4 mm (1/4")
Bottom layer below second
layer (fill rest of the volume)
12.7 mm (1/2") 12.7 mm (1/2")

contact GBHE
OUTLET COLLECTOR
A gas outlet collector is used whenever an inert fill support material is used. It is
essential that the inert support goes into the straight part of the vessel. The outlet
collector must be submerged in the inert support material and essentially not
protrude into the catalyst bed.
The inert support and outlet collector both keep the liquid/gas flow evenly
distributed across the bottom of the reactor. Without these, the fluid flow would
tend to move toward the outlet nozzle before passing through the whole of the
bed.
The screen and support which make up the collector can take up a large space in
the bottom of the reactor. Therefore, layout and design have to be checked to
ensure optimum design is feasible.
The basic design is a 3x3 mesh with a wire diameter of 2.0 mm. Support bar
spacing is such that it prevents collapse with the design pressure drop.
contact GBHE
LIQUID REDISTRIBUTOR
The liquid redistributor is used to ensure equal loading of liquid and vapour at the
top of the catalyst bed. It is a perforated tray with chimneys and chimney cover.
The principle of a typical redistributor is shown in figure C2
PT-3.
The holes are sized to give a liquid head on the tray. This will depend on the
variation expected to cover the full range of applied liquid flow rates.
The number of chimneys is set by the gas flow. The chimney covers are sized to
overhang the chimney and prevent liquid passing straight down the chimneys.
The distributors are used at the bed inlet as redistributors in a multiple bed
system. An inlet baffle is commonly used to prevent direct impingement.

Figure C2
PT -3
contact GBHE
CATALYST UNLOADING CONNECTIONS
The drop out nozzle is filled with inert support balls. Typically a 15.2 cm (6") pipe
is used as drop out nozzle. It has a removable length which projects into the
vessel. The extended pipe length reaches up to the catalyst bed.
For a bed supported on beams a 30.5 cm (12") manhole is typical. The bottom of
the nozzle is flush with the bottom of the catalyst bed.
Both methods need a protective internal cover which stops if the opening cover is
removed accidentally.
contact GBHE
Perforated Tray

VOID SPACE
The use in void space is allowed in reactor design to allow access to the top of
the reactor. It also avoids direct impingement of the inlet streams onto the
packed surface if no other internals are used.
A void space will also be included if the reactor is split into two beds. This allows
access to both beds.
Typical void spaces depend on reactor diameter and applied internals. Values
can be given after full review of the reactor vessel sketches and process
conditions.
contact GBHE.
Information contained in this publication or as otherwise supplied to Users is
believed to be accurate and correct at time of going to press, and is given in
good faith, but it is for the User to satisfy itself of the suitability of the information
for its own particular purpose. GBHE accepts no liability for loss or damage or
personnel injury caused by or resulting from reliance on this information.
Freedom under Patent, Copyright and Designs cannot be assumed.

Hydrogenation Reactor Design Considerations

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