Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE LNVENTION
Field of the Invention - The present invention relates to
catalytic reaction apparatus and catalyst anti-fluidization
means therefor.
Description of the Prior Art - Catalytic reaction
apparatus for converting hydrocarbon fuels to useful industri-
al gases, such as hydrogen, are well known in the art. In
one type of apparatus, such as apparatus for steam reforming
a hydrocarbon fuel, the process fuel is passed through a tube
containing the catalyst, If the reaction is endothermic the
tube is usually disposed within a furnace which provides the
heat to drive the reaction. If the catalyst filled tube is
vertical and the process gas flows upwardly there~hrough, the
upward force of the fLowîng gas, particularly at higher through-
puts, is usually greater than the weight of the catalyst par-
ticles, resulting in continuous motion of the catalyst parti-
cles relative to each otherO When this condition exists the
catalyst bed is said to be fluidiæed. This continuous motion
results in damage to the particles such as causing them to
break up into smaller pieces or to wear by the friction of the
particles rubbing against each other. Fine size particles
are lost by being carried out of the bed with the reacting
gases; and, over a period of time, the total volume of cata-
lyst within the bed may be reduced to an unacceptable level,
requiring replenishment of the bed,
Anti-fluidization devices are well known in the art.
One common type is a spring loaded perorated member posi-
tioned on top of the bed thereby maintaining the bed under
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compression at all times to prevent fluidization. However,
mechanisms of this type are expensive and it is often diffi-
cult if not impossible to find a suitable spring material
which will withstand the environment ol the apparatus in
which it is to be used.
Complexity and expense are the major disadvantages of
other mechanisms which might be useful in preventing fl~id-
ization, such as the mechanism shown in U. S. Patent
3,374,052 to Liang-tseng Fan et al.
SUMMARY OF THE INVENTION
One object of the present invention is an upflow cata~
lytic reactor having uncomplicated and inexpensive means to
prevent fluidization of the catalyst bed.
According to the present invention an upflow catalytic
reactor includes a vertically extending catalyst bed which
is prevented from fluidizing during operation by a perfo-
,
rated plate which rests on the top sur~ace of the bed by itsown weight and which can move upwardly and downwardly as the
bed expands and contracts while remaining in continuous con-
tact with the top surface, a restraint being disposed above
the plate to limit its travel and thus limit expansion of
the bed to a preselected volume.
- In prior art it is generally taught that in order to
prevent fluidization of a particulate bed, be it a catalyst
bed or any other type of bed, the entire bed must be kept
under compression. We have determined that this is not
true. We have discovered that fluidization does not occur
if only the top layer of particles is prevented from lifting
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o~f the surface o~ the bed, as long as only a small expansion
of the bed is permitted.
The basic problem with upward flow through beds of
particles is the result of a pressure drop through the bed
which exceeds the weight of the particles within the bed.
At this point the top layer of particles in the bed begins
to lift, vibrate, and tumble. As the flow of gas through
the bed is increased this particle activity progresses
downwardly through the bed until large sections of the bed
begin to lift and tumble in a "boiling" fashion. This is
called fluidization. We have found that a perforated plate
or screen which 1) si~ply sits on top of the bed in contact
with the top layer of catalyst particles, 2) is not heavy
enough to prevent expansion of the bed, and 3) is constructed
such that the bed expands without -the me~ber first lifting
off the bed, can prevent fluidization if expansion of the
bed is limited to only a few percent of its nonexpanded
volume. A simple restraining device or stop is positioned
within the reactor whereby the perforated member is limited
in its upward movement by coming into contact with the
restraint.
In accordance with a specific embodiment of the
invention there is provided, in a catalytic reactor for
steam reforming a reformable hydrocarbon fuel including
wall means defining a vertically extending reaction chamber
having a lower end and an upper end, said lower end including
an inlet and said upper end including an outlet, presettled
catalyst particles disposed within said reaction chamber
- forming a vertically extending presettlecl catalyst bed
therein having a top layer of catalyst particles, said
catalyst bed expanding and contracting during operation of
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the reactor, and a perforatea plate resting by its weight
alone atop said catalyst bed and extending thereacross said
perforated plate having weight and pressure drop character-
istics such that said plate is in continuous contact with
the top layer of catalyst particles throughout operation of
said reactor, the improvement comprises: restraint
means fixedly located within said reactor and engageable
with said perforated plate at only a single location, said
single location being at a distance above said perforated
plate which is no more than a few percent of the hei~ht of
said catalyst bed, and wherein the weight of said perforated
plate permits expansion of said bed during operation of said
reactor.
From a different aspect, and in accordance with
the invention, a method for preventing fluidization of a
catalyst bed in a reactor having a vertical column of par-
ticulate catalyst wherein ~ases flow upwardly through said
:; catalyst column and said column of catalyst expands and con-
tracts during operation of the reactor comprises the steps
of: presettling said catalyst column prior to operation of
said reactor; placing atop said presettled catalyst column
at a first vertical location a perforated plate which ex-
tends across the top layer of the catalyst, said perforated
plate having weight and pressure drop characteristics such
that said plate is in continuous contact with the top layer
of catalyst particles in said column and r.ests thereon ~y
its weight alone, said plate being light enough to permit
expansion of said catalyst column during operation of the
reactor, and, by its weight and pressure drop characteristics,
moving downwardly and up~ardly in continuous contact with
said top layer of catalyst as said catalyst column con-tracts
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and expands during operation of the rea~tor~ said plate
preventing the top layer of particles from li~ting off the
bed, and limiting expansion of said catalyst column during
operation to no more than a few percent o~ the nonexpanded
volume of said column by preventing upward movement of said
plate beyond a single fixed, predetermined location~
In accordance with a further embodiment of the
second aspect of the invention, a method for preventing
~luidization in a catalytic reactor having a vertical column
of particulate catalyst which has been presettled prior to
operation of the reactor comprises the steps of flowing
gases upwardly through said catalyst column, permitting said
catalyst column to expand duri.ng said upward flow of gases,
placing atop said presettled catalyst column at a first
: vertical location a perforated plate which extends across
said perforated plate having weight and pressure drop
characteristics such that said plate is in continuous contact
with the top layer of catalyst particles in said column and
rests thereon by its weight alone, said plate being light
enough to permit expansion of said catalyst column during
operation of the reactor, and, by .its weight and pressure
drop characteristics, moving downwardly and upwardly in con-
tinuous contact with said top layer of said catalyst as said
catalyst column contracts and expands during operation of
the reactor, said plate preventing the top layer of particles
from lifting off the bed, and limiting said expansion of
said catalyst column by fixedly losating restraint means
above said plate to stop upward movement of said plate, said
; restraint means bein~ engageable with said plate at a single
. 30 location which is no more than a few percent of the height
of the unexpanded catalyst column above said plate.
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The foregoing and other objects, features and
advantages of the present invention will become more apparent
in the light of the following detailed description of pre-
ferred embodiments thereof as illustrated in the accompanying
drawing.
BRIEF DESCRIPrrION OF rrHE DRAWING
Fig. 1 is a fragmentary, vertical, cross-sectional
view
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of steam reforming reactor apparatus according to the presen~
invention.
Fig. 2 is a cross-sectional view of the apparatus of
Fig. 1 taken substantially along the line 2-2 in Fig. 1.
Fig. 3 is an enlarged view of the upper portion of one
of the reactors of Fig. 1 showing details of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Consider, as an exemplary embodiment of the present in~
LO vention, the catalytic reaction apparatus 10 of Figs. 1-3.
In this embodiment, the apparatus is for the purpose of
steam reforming a reformable hydrocarbon fuel in the presence
of a suitable catalyst in order to produce hydrogen. The ap-
paratus 10 comprises a furnace 12 including burner nozzles
14, a burner fuel manifold 16, and an air manifold 18. Dis-
posed within the furnace 12 are a plurality of tubular reac-
tors 20. In this embodiment there are nineteen reactors ar-
ranged as shown in Fig~ 2.
Each reactor 20 comprises an outer cylindrical wall 22
and an inner cylindrical wall or center tube 24 defining an
annular reaction chamber 26 therebetween. The reaction cham~
ber 26 is filled with steam reforming catalyst particles or
pellets 28 which are supported on a screen 30 disposed a~ the
inlet 32 of the reaction chamber. Any suitable steam reform-
ing catalyst, such as nickel, may be used to fill the reaction
chamber. In accordance with the present invention, antifluid-
ization means 33 is disposed at the outlet 36 (Fig. 3) of the
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reaction chamber and is hereinafter more fully explained in
conjunction with the more detailed view of Fig. 3. The
cylinder which is defined by ~he outer wall 22 is closed at
its upper end 38 by an and cap 40. The center tube 24 has an
upper inlet end 42 and a lower outlet end 44. The inlet end
42 terminates below the end cap 40 such that the center tube
is in gas communication with the outlet 36 of the reaction
chamber 26.
Disposed within the center tube is a cylindrical plug 46
which has an outer diameter somewhat smaller than the inner
diameter of the center tube thereby defining an annular re-
generation chamber 48 ~herebetween having an inlet 49. The
plug 46 may be a solid rod, but in this embodiment is a tube
which is blocked by an end cap 50 at one end thereof such
that reaction products exiting the reaction chamber 26 must
flow around the plug 46 through the regeneration chamber 48.
Spacing between the plug 46 and the center tube 24 is main-
tained by dimpLes 52 in the plug wall. For the purposes of
the present embodiment, the f~mction of ~he regenera~ion
chamber 48 is to return heat from the reaction products leav
ing the outlet 36 back into the catalyst bed of the reaction
chamber 26. The arrangement shown in Fig. 1 provides some
preheating of the process fuel before it enters the catalyst
bed.
Each reactor 20 may be considered to comprise an upper
portion 56 and a lower portion 58. The upper portion 56 is
disposed within what is hereinafter referred to as the burner
cavity 60. The cavity 60 is that voluma of the furnace 12
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within which actual combustion of the fuel and air fed into
the furnace takes place. This volume is characterized by
very high temperatures, considerable radian~ heating as well
as convective heating of the reactors 20, and axial (i.e., in
the direction of the axis of the reactors 20), as well as
radial mixing of the gases therein.
The lower portion 58 of each reactor is surrounded by a
cylindrical wall or conduit 62 spaced outwardly from the wall
22 defining an annular burner gas passageway 64 therebetween
having an inlet 66 and an outlet 67. The outlet 67 is adja
cent th~ inlet 32 of the reaction chamber 26. The passageway
64 is filled with a heat transfer packing material such as
spheres 70 of alumina supported on a screen 68. The space 72
between adjacent conduits 62 is filled with a nonheat conduc-
tive material such as ceramic fiber insulation whieh is sup-
ported on a plate 74 extending a~ross the furnace and which
has holes therein through which the reactors 20 pass. The
plate 74 and the material within ~he space 72 prevents the
furnace gases from flowing around the outside of the conduits
62.
In addition to the plate 74, plates 769 78 and 80 also
extend across the furnace and define manifolds therebetween.
The plate 80 rests on the bottom wall 82 of the ~urnace. The
plates 78 and 80 define a reaction products manifold 84
therebetween; the plates 76 and 78 define a process fuel in-
let manifold 86 therebetween; and, the plates 74 and 76 de-
fine a furnace gas outlet manifold 88 therebetween. The plugs
46 and the center tubes 24 abut the bottom plate 80; the
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outer walls 22 of the reactors abut the plate 78; and, the
conduits 62 abut the plate 74
In operation, a mixture of steam and reformable hydrocar-
bon fuel from the manifold 86 enters the inlet 32 of the reac-
tion chamber 26 by way of the holes 100 in the wall 22; the
manifold 86 is fed by a conduit 102. The mixture immediately
begins to be heated by the furnace gases flowing countercur-
rent thereto through the passageway 64 and begins to react in
the presence of the cataLyst particles 28. As the fuel,
steam and reaction products travel upward within the reaction
chamber 26 they continue to react and pick up additional heat.
The hot reaction products enter the inlet 49 of the regenera-
tion chamber 48. As ~he reaction products traverse the
length of the annular regeneration chamber, heat is trans-
ferred therefrom back into the reaction chamber 26. They
thereupon enter the reaction products manifold 84 through the
holes 104 in the center tube 24, and are carried away from the
reactor via the conduit 106 either for further processing,
storage, or consumption.
Fuel for the furnace enters the manifold 16 via a con-
duit 108 and thereupon passes into the burner cavity 60 by
way of the nozzles 14. Air enters the manifold 18 via a con-
duit 110 and enters the burner cavity 60 via annular passage-
way 112 surrounding each nozzle 14. Burning of the fuel and
air takes place within the burner cavity 60. The hot gases
from the burner cavity travel through the passageways 64 into
the manifold 88 and are exhausted via a conduit 113.
Referring to Fig. 3, the anti-fluidization means 33 is
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comprised of a plate 90 and a restrain~ 92. The plate 90 is
an annulus which simply rests by its own weight atop the cata-
lyst bed in contact with the top layer of catalyst pellets.
The plate is perforated to penmit reac~ion products to pass
therethrough. Its weight and pressure drop characteristics
are such that it will not lift off the catalyst bed but will
maintain continuous contact with the top layer of catalyst
pellets during operation even as the bed expands and contracts.
This prevents the top layer of catalyst pellets from becoming
fluidized, which in turn prevents the catalyst bed from be-
coming fluidiæed, as long as the catalyst bed is not per-
mitted to expand by more than a few percent of its volume
(or axial length, which is directly proportional to volume).
If the bed is permitted to expand too much, pellets or parti-
cles below the top layer will become fluidized, and this
fluidization will be transmitted through the bed until the
entire catalyst bed is fluidized.
The restraint 92 is provided to limit expansion of the
- catalyst bed by stopping upward movement of the plate 90. In
this embodiment the restraint 92 includes an annular plate 91
welded around its inner circumference 94 to the inside surface
of the center tube 24. The plate 91 is perforated with holes
93 therethrough. A cylindrical flange 96 is integral with the
plate 91 and e~tends vertically downwardly therefrom near its
outer edge 98. The plate 91 could have been welded to the
outer cylindrical wall 22 rather than the center tuhe 24;
however, axial thermal expansion of the center tube 24 is less
than that of the outer wall 22 so that it is preferred to fix
the plate to the center tube~
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- As used in this speci~ication and appended claims, the
"weight" of the perforated plate includ~s the weight of any-
thing which may rest on or be attached to or a part o~ the
plate but which moves as one with the plate. For example,
although no~ shown, an annular ring may be secured to the top
surface o~ tbe plate to provide additional weight. Upward
movement of the plate may be stopped when the ring contacts a
suitable restraint.
In practicing the present invention it must be kept in
mind that, even without fluidization, ~he catalyst ~ed will
settle during operation of the reactor due to operational vi-
bration as well as thermal expansion and contraction of the
outer wall 22 relative to the cen~er tube 24. Therefore, it
is desirable to minimize, to the extent possible, settling of
the catalyst bed during operation. This is accomplished by
presettling the catalyst bed, such as by mechanical vibratory
apparatus~ as one fills the reaction chamber 26 during assem-
bly of the apparatus.
By presettling the catalyst bed, adding catalyst parti-
cles to fill the void left by the presettled particles~ pre-
settling the bed again, etc., the reaction chamber can be
filled to the extent desired and settling during operation
(ass~ming fl~dization is prevented) will thereby be mini-
mized. Once the reaction chamber is filled to the desired
level wîth presettled catalyst particles the perforated plate
90 is placed atop the bed and the restraint 92 is wel~ed into
position. Preferably the restraint 9~ is located such that
the flange 96 is in contact with the plate 90 or as close
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` thereto as possible, recalling that the bed expansion will be
the sum of the dis~ance between the plate 90 and the ~lange
96 plus the amount of contraction of the bed due to unavoid-
able additional settling during operation of the reactor.
In one test a reactor constructed in all important re-
spects like the reactor shown in Figs. 1-3 was operated for a
period of 732 hours withou~ any indica~ion that fluidization
of the catalyst bed had occurred. In the apparatus tested
the annular reaction chamber had an outer diameter of 8.75
inches, an inner diameter o~ 6.60 inches, and a presettled
catalyst bed length of 63.0 inches prior to operation of the
reactor. The catalyst was in the form of cylindrical pel-
lets, The plate 90 was made from Incoloy 800 alloy steel
(from International Nickel Co.~ was .125 inch thick, and had
inner and outer diameters of 6.62 inches and 8.55 inches, re-
spectively. It was perforated over its en~ire surface with
.125 inch diameter holes to the extent that the plate was 40%
porous. The annular plate 91 o the res~raint 92 had an outer
diameter of 8.55 inches and was ~0% porous. The flange 96 was
.38 inch long, and prior ~o operation of the reactor it was
; essentially in contact with the plate 90. After 732 hours of
operation and thirty-four shutdown cycles (i.e. the apparatus
is cooled to ambient temperature) settlîng of the bed amounted
to only about 2% of the bed length; no further signi~icant
settling is expected to occur with additional operation.
Thus~ maximum expansion o~ the bed amounted to about 2% of the
bed length and fluidization did not occur~ Increase in bed
pressure drop was limited to less than 4%. I~ is believed
:,
that if the catalyst bed is presettled, restraining the plate
from moving upwardly substantially beyond its initial location
will always prevent fluidization since further settling of the
bed during operation will always be within acceptable limits.
It is not known just how much expansion can be tolerated
without fluidization occurring. From the foregoing example
it is apparent that 2% expansion is acceptable. Perhaps up
to 5% expansion will be acceptable. If, prior to operation of
the reactor, the restraint 92 is located at some dis~ance from
the plate 90 (rather than being located as close to the plate
90 as possibLe) then the amount of expansion during operation
will be that much greater. There is no particular advantage
in keeping the expansion to an absolute minimum as long as
expansion is stopped prior to the onset of fluidization.
It should be apparent that the reactor described in con-
junction with the antifluidiæation means of the present in-
vention is by way of example only. For instance, the instant
invention is as useful for preventing fluidization of a cylin-
drical catalyst bed as it is for the annular bed hereinabove
described. It should also be apparent that the invention is
not limited to use with steam reforming catalyst beds.
Although the invention has been shown and described with
respect to a preferred embodiment thereof, it should be under-
stood by those skilled in the art that other various changes
and omissions in the form and detail thereof may be made
therein without departing from the spirit and ~he scope of
the invention.
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