Note: Descriptions are shown in the official language in which they were submitted.
9694
This invention relates to improved apparatus and
methods for determining the tendency toward attrition and attri-
tion resistance of solid particles, e.g., used to promote
chemical conversions. More particularly, the invention relates
to such improved apparatus and methods for determining the
attrition properties of solid particles used to promote such
conversions wherein mixtures of solid particles and vapor require
separation.
In many instances throughout the process industries,
chemical reactions occur which are promoted by relatively small,
e.g., diameters in the range of about 10 microns to about 500
microns, catalyst particles, for example, in fluidized bed
reactors. One process involving such catalyst particles is
the catalytic cracking of higher boiling hydrocarbons to
gasoline and other lower boiling components which is used
extensively in the petroleum industry. Often, apparatus used
for carrying out such chemical conversion, e.g., cracking,
of a feedstock, e.g., hydrocarbon gas oil, involves a reaction
zone where the relatively small catalyst particles and feed-
20 stock are contacted at chemical conversion, e.g., hydrocarbon -
cracking, conditions to form at least one chemical conversion
product, e.g., hydrocarbons having a lower boiling point than
the hydrocarbon feedstock. Often, while promoting the desired
chemical conversion, the catalyst particles have deposited
thereon material, e.~., carbon, coke and the like, which acts
to reduce the catalytic activity of these particles. Apparatus
which are used to restore the catalytic activity of such
particles often include a regeneration zone where the deposit-
containing solid particles are contacted with oxygen-containing
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vapor at conditions to combust at least a portion of the deposit
material.
Operation of both of the systems referred to above
involves the f~rmation of a mixture of solid particles and
vapor which requires separation. Therefore, both the apparatus
for carrying out chemical conversion and the apparatus for
restoring the catalytic activity of the solid catalyst
particles include a separation zone wherein the mixture of
solid particles and vapor formed in the reaction and regeneration
zones, respectively, are at least partially separated.
Such separation zones often involve conventional cyclone
precipitators.
However, processing solid catalyst particles
through such cyclone precipitators causes increased particle -
attrition. That is, the solid catalyst particles have an
increased tendency to fall apart and/or form fines while
being processed through a separation system, e.g., cyclone
precipitator. The resulting particle "fines" are often of
such a size that they cannot be reused to promote chemical
conversion. Clearly, it is advantageous to provide for
reduced attrition of solid catalyst particles.
In many instances, performing a full scale test
using a conventional cyclone precipitator to determine the
tendency toward attrition and attrition resistance of solid
catalyst particles is impractical from, for example, time,
space and economic considerations and the like. Therefore,
it would be advantageous to have an apparatus to aid in predicting
the attrition properties of a mass of solid particles.
Therefore, one object of the present invention is
to provide apparatus and methods useful in predicting the
attrition properties of a mass of solid particles. Other objects
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1~096~4
and advantages of the present invention will become apparent
hereinafter.
An improved apparatus useful in determining the time
rate of attrition of a mass of solid particles has now been
discovered. ~his apparatus comprises 1) chamber means defined
by substantially opposing first and second end walls and a,
preferably, substantially circular, i.e., cylindrical, sidewall 2)
inlet means, preferably, substantially centrally located, in the
chamber means to provide for entrance of the solid particles into the
chamber means; 3) outlet means located in association with the
chamber means to provide for withdrawing the solid particles from
the chamber means; 4) conduit means providing communication between
the inlet means and the outlet means to allow solid particles with-
drawn from the chamber means in the outlet means to be reintroduced
into the chamber means through the inlet means; 5) impeller means,
preferably located substantially centrally, within the chamber
means to urge the solid particles from the inlet means in the
general direction of the sidewall of the chamber means; and 6)
motor means in communication with the impeller means to provide
for rotation of the impeller means.
This apparatus has been found to provide substantial
benefits, e.g., improved simulation of solid particle attrition ;
in commercially size cyclone separators or precipitators. Such
improved simulation is obtained with a device which is relatively
small, easy to operate and relatively maintenance free. In
certain embodiments of the present invention, as will be
described hereinafter, the present invention may be used to
predict the time rate of attrition or attrition resistance of
a mass of solid particles in a commercially sized cyclone
separator or precipitator.
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In one preferred embodiment of the present invention,
the outlet of the present apparatus comprises a passageway
located substantially tangentially to the sidewall of the chamber.
In another preferred embodiment, the outlet comprises a hopper
in fluid communication with the chamber through at least one
hole in one end wall of the chamber, the hopper having an exit
connected to the conduit. In this embodiment, the hole is
preferably in the bottom end wall of the chamber and, more
preferably, comprises an annular passageway between the chamber
and the hopper.
In a still further preferred embodiment of the
present invention, particularly useful when attempting to predict
the attrition properties of a mass of solid particles in a
commercially sized cyclone separator or precipitator, the
present motor, preferably a variable speed motor,and impeller,
are substantially independent of the chamber. That is, the
motor and impeller rotate without substantially contacting any
components, e.g., end walls and sidewall, of the chamber.
Preferably, the chamber, e.g., end walls and sidewall,
is mounted or supported in such a manner as to be substantially
free to rotate. One convenient way to provide the chamber with
such substantially free rotatability is to suppsrt the chamber
using support means, e.g., a ball bearing attached to a
stationary support member, so that the chamber is substantially
rotatable within the support means, e.g., around the axis of
the ball bearing. This feature is particularly applicable in
circumstances where it is desired to measure the force, e.g.,
torque, created by the circulation of solid particles and vapor
through the present apparatus. Measurement of such forces will
be discussed in detail hereinafter.
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In an additional preferred embodiment, the inlet of
the present apparatus is sized so that the velocity of the solid
particles entering the chamber is substantially reduced relative
to the tip velocity of the impeller, e.g., the impeller blades.
More preferably, the entering velocity is less than about 50~,
still more preferably, less than about 20~ of the tip velocity.
This feature provides that a given solid particle is subjected
to a minimum number of, e.g., no more than one, high velocity
collisions, e.g., with the chamber sidewall, per cycle through
the present apparatus. This closely simulates the movement of a
given solid particle in a commercial cyclone separator or
precipitator.
The present apparatus may be used to determine the
attrition properties of any mass of solid particles. Such
mass of solid particles preferably have a relatively small,
e.g., in the range of about 10 microns to about 500 microns, weight
average diameter. One particular application of the present
invention involves determining the attrition properties of
catalyst particles, such as those useful in catalytic hydrocarbon
cracking, although other types of solid particles may be tested.
The catalyst particles useful in catalytic hydrocarbon
cracking may be any conventional catalyst capable of promoting
hydrocarbon cracking at the conditions present in the reaction
zone, i.e., hydrocarbon cracking conditions. Conventionally,
94
the catalytic activity of such particles is restored at the
conditions present in the regeneration zone. Typical among these
conventional catalysts are those which comprise alumina,
silica, silica-alumina, at least one crystalline alumino
silicate having pore diameters of from about 8A to about 15A
and mixtures thereof. Because of the increased economic
incentive for maintaining the particle size of zeolite-
containing catalyst, it is preferred that the catalyst
particles comprise from about 1% to about 50~, more preferably
from about 5% to about 25%, by weight of at least one
crystalline alumino-silicate having a pore diameter of from
O O
about 8A to about 15A. At least a portion of the alumina,
silica, silica-alumina and crystalline alumino-silicate may
be replaced by clays which are conventionally used in
hydrocarbon cracking catalyst compositions. Typical examples
of these clays include halloysite or dehydrated halloysite
(kaolinite~, montmorillonite, bentonite and mixtures thereof.
These catalyst compositions may also contain minor amounts of
other inorganic oxides such as magnesia, zirconia, etc. When
the catalyst particles contain crystalline alumino-silicate,
the compositions may also include minor amounts of conventional
metal promoters such as the rare earth metals, in particular,
cerium. Such catalyst compositions are commercially available
in the form of relatively small particles, e.g., having
diameters in the range from about 20 microns to about 200
microns, preferably from about 20 microns to about 150 microns.
In general, and except as otherwise provided for
herein, the apparatus of the present invention may be fabricated
from any suitable material or combination of materials o~
construction. The material or materials of construction used
11096~4
for each component of the present apparatus may be dependent
upon the particular application involved. Of course, the
apparatus should be made of materials which are substantially
unaffected, except for normal wear and tear, by the conditions
at which the apparatus are normally operated. In general, such
material or materials should have no substantial detrimental
effect on the feedstock being chemically converted, the chemical
conversion product or products or the catalyst being employed.
These and other aspects and advantages of the present
10 invention are set forth in the following detailed description
and claims, particularly when considered in conjunction with r
the accompanying drawings in which like parts bear like
reference numerals.
IN THE DRAWINGS: ;
Figure 1 is a top plan view of one embodiment of the
present invention taken along line 1-1 of Figure 2.
Figure 2 is a side elevational view, partly in section, ;
of one embodiment of the present apparatus.
Figure 3 is a side elevational view, partly in section, `
20 of another embodiment of the present apparatus.
Figure 4 is a top plan view of the embodiment shown in
Figure 3 taken along line 4-4 of Figure 3.
Referring now to the embodiment of the present apparatus
shown in Figures 1 and 2, the device, shown generally as 10,
includes a substantially circular top end wall 12, a cylindrical
sidewall 14 which has a substantially circular perimeter and
a bottom end wall 16. The bottom end wall 16, which is substan-
tially circular in configuration, does not extend fully to the
sidewall 14, but rather, forms an annular passageway 17 with
sidewall 14 to conical shaped hopper 18. Impeller 20,
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4^
with blades 22 is located within the space defined by top end
wall 12, sidewall 14 and bottom end wall 16. Impeller 20 is
connected through shaft 24 to variable speed motor 26 which is
firmly affixed to support element 28. Shaft 24 is designed not
to contact top end wall 12. Thus, shaft 24 is surrounded by
felt washer 30 which is enclosed in hollow tube 31 which, in
turn, comes into contact with ball bearing 32 and acts to center
shaft 24 so that no contact between shaft 24 and top end wall 12
is made. In addition, this mechanism provides that the impeller 20
is substantially independent of the top end wall 12 or any other
element within the space defined by top end wall 12, sidewall 14
and bottom end wall 16. Further, hollow tube 31, which is attached,
e.g., welded, to top end wall 12, is rotatable around the axis of
ball bearing 32, thus permitting top end wall 12 and sidewall 14 to
be similarly rotatable.
Conical hopper 18 terminates in outlet 34. Bottom end
wall 16 is provided with a centrally located hole 36. One end of
flexible tubing 38 is fitted into hole 36 while the other end of
flexible tube 38 is attached to outlet 34. Flexible tubing 38
provides communication between hopper 18 and the space defined
by top end wall 12, sidewall 14 and bottom end wall 16. Stationary
baffles 40 are attached, e.g., welded, to the sidewall 14 at
substantially the same acute angle from the tangent. The device
10 can also function without baffles 40. For example, a smooth
cylindrical insert can be placed in the chamber, butting up
against the edges of baffles 40.
Top end wall 12 is designed in two sections. Annular
section 13 is permanently affixed to sidewall 14, while circular
hatch section 15, attached to annular section 13 by a series of
studs 21 and wing nuts 19, is removable to provide access to, for
example, impeller 20.
The embodiment shown in Figures 1 and 2 functions as
follows.
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A mass of solid particles, e.g., fluid catalytic cracking
particles, is placed in hopper 18. Variable speed motor 26 is
activated thereby causing impeller 20 to rotate. As impeller 20
rotates, solid particles from outlet 34 pass through flexible
tubing 38 into the space defined by top end wall 12, sidewall
14 and bottom end wall 16. The action of impeller 20 causes these
solid particles to be propelled in a generally outwardly direction
toward sidewall 14. Stationary baffles 40 act to reduce the velo- ~
city of these solid particles as the particles approach sidewall
14. As the particles approach sidewall 14, they fall into the
annular passageway 17 defined by the bottom end wall 16 and sidewall
14 and proceed downward into the hopper 18 where they are recircu-
lated back through outlet 34 and flexible hose 38 into the space
defined by top end wall 12, sidewall 14 and bottom end wall 16.
After a period of time, a given catalyst particle has proceeded
around the apparatus as indicated several times. By determining
particle size distribution both before and after the test period, ~ -
the amount of particle break-up, e.g., attrition, that has occurred
over this period of time can be determined. As will be explained
hereinafter, correlations have been derived based upon, for
example, the speed of the variable speed motor 26, which will aid
in determining the attrition resistance of the solid particles.
Referring now to Figures 3 and 4, an additional embodi-
ment of the present invention is shown generally as 60. The
device 60 includes an internal substantially cylindrically
shaped space defined by top end wall 62, sidewall 64 and bottom
end wall 66. Located within the space so defined is impeller 68
having blades 70. Impeller 68 is centrally located within such
space. Impeller 68 is powered by variable speed motor 72
acting through shaft 74. Variable speed motor 72 is firmly affixed
to support element 73. Felt washer 76 surrounded by hollow tube
77 encompasses shaft 74 and acts to prevent shaft 74 from contacting
bottom end wall 66. In this manner, variable speed motor 72,
shaft 74 and impeller 68 are substantially independent of bottom
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110~6~g
end wall 66, sidewall 64 and top end wall 62. Sidewall 64 has a
substantially tangential exit 78 whereas top end wall 62 is provided
with hole 80. One end of flexible tubing 82 is fitted into hole 80 ~
while the other end of flexible tubing 82 is attached to exit 78.
Flexible tube 82 is supported in place by ball bearing 83 and
support member 84. Ball bearing 83 is designed in conjunction
with support member 84 to support top end wall 62, sidewall 64 and
bottom end wall 66 and, in addition, allow these walls to be
substantially rotatable around the axis of ball bearing 83.
In the embodiment shown in Figures 3 and 4, the bottom end
wall 66 and top end wall 62 extend beyond sidewall 64. Studs 65
in top end wall 62 extend through holes in bottom end wall 66
and are attached thereto with wing nuts 67. In this manner, the
device 60 can be disassembled, for example, for complete removal
of the solid particles being tested.
Device 60 functions as follows. A mass of solid parti-
cles, e.g., fluid catalytic cracking particles, are placed in
the space defined by top end wall 62, sidewall 64 and bottom end
wall 66. Variable speed motor 72 is activated thereby causing
impeller 68 to rotate. The action of impeller 68 causes the
solid particles to be propelled in a generally outwardly direction
toward sidewall 64. As the particles approach sidewall 64, at
least a portion of such particles are caused to flow through exit
78 into flexible tubing 82 and thence into the space defined by
top end wall 62, sidewall 64 and bottom end wall 66. The particles
enter this space at a velocity which is reduced relative to the
top speed of blades 70. After a period of time, a given catalyst
particle has circulated through the device 60 several times and
by determining the particle size distribution of the mass of solid
particles before and after the test period, the amount of particle
attrition resulting during the test can be determined. Correlations,
as noted previously provide an additional measure of the attrition
resistance of such solid particles.
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The following examples clearly illustrate the present
invention. However, these examples are not to be interpreted
as specific limitations on the invention.
EXAMPLES 1 to 4
These examples illustrate certain of the advantages of
the present invention.
A device 10 which propels a mixture of solid catalyst
particles and air was used to simulate the movement of solid
catalyst particles in various separators.
The device 10 involves top end wall 12, sidewall 14
and bottom end wall 16 defining a cylindrical chamber having
an inside diameter of 17 inches. Sidewall 14 has a depth of
3 inches. Centrally mounted in the chamber is an impeller 20
having four blades 22. The impeller 20 has an overall diameter
of 10 inches and a depth of 1.375 inches. The impeller 20 is
driven by a variable speed motor 26 which is mounted above and
outside the chamber as shown in Figure 2. A series of eight baffles
40 surround the impeller. Each of these baffles 40 is 3 inches deep,
6 inches long and is welded to the interior of sidewall 14. Each
of the baffles 40 extend from this surface a substantially uniform
radial distance of 3 inches into the chamber. Also, each of the
baffles 40 is situated at a substantially uniform acute angle
relative to the tangent at the point of attachment to the chamber.
A conical hopper 18, situated directly below the chamber,
is in fluid communication with the chamber by means of annular
p~ssageway 14 definea by sidewall 14 and the outer edge of bottom
end wall 16. Bottom end wall 16 is situated directly below and
is substantially co-extensive with the diameter of the impeller 20
plus blades 22 prevents catalyst particles from failling into the
hopper 18 before the particles are forced out radially beyond the
impeller 20 and blades 22. A piece of flexible one (1) inch
O.D. tubing 38 provides fluid communication between the outlet
34 at the bottom of the hopper and the chamber. This tubing 38
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enters the chamber from below through hole 38 in bottom end wall
16 and terminates in the space at the center of the impeller 20.
This device functions as follows. A quantity of
catalyst particles, of known size distribution, is stored in
the hopper 18. Air, from the surrounding environment is allowed
to mix with the particles. The variable speed motor 26 is
activated and causes the impeller 20 and blades 22 to rotate.
Such rotation creates forces causing the catalyst particles-air
mixture to flow through the tubing 38 into the chamber. The
impeller 20 and blades 22 force the mixture in the chamber
toward the peripheral interior surface of the sidewall 14. At
least a portion of the solid particles strikes this surface.
In any event, substantially all of the solid particles are
returned to the hopper from the chamber and are recycled to the
chamber through the tubing 38. After a period of time of
operation, the solid catalyst particles in the hopper are analyzed
for size to determine the degree of particle attrition which
resulted from operation of the device 10.
In addition, a smooth cylindrical insert can be
placed in the chamber. The perimeter of this insert is
defined by the edges of the baffles 40 away from the interior
peripheral surface of the sidewall 14. The insert has substan-
tially the same depth as the baffles 40. Operation of the
device 10 with this insert in place simulated the operation
of a separator without arresting means, e.g., baffles, vanes
and the like.
Velocities and mass circulation rates within the
test device 10 are determined as follows:
The rotations per minute (rpm) of the variable
speed motor 26 and shaft 24 is accurately measured by a strobe
tachometer, which permits the calculation of the tangential compo-
nent of velocity of the mixture of catalyst particles and air
leaving the impeller 20 and blades 22. The impeller 20 is
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is supported by the variable speed motor 26 and shaft 24, andcontacted the chamber housingl e.g., top end wall 12, only
through a felt washer 30 of negligible friction. The chamber
housing is supported from a ball bearing 32, so that the torque
caused by the circulation of air and catalyst particles can be
measured. A string, having a weight M suspended therefrom, is
attached to the chamber housing, e.g., sidewall 14, tangential
to the outer perimeter of the impeller 20. Force is calculated
from the lateral displacement of the suspended weight using the
following equation-
Force = M
wherein:
X = the lateral displacement of the weightfrom the chamber housing
L = the length of the string
With the variable speed motor 26 in operation, the
air circulation is blocked off by closing the tubing 38 with
pinch clamps, and the force caused by friction and internal
turbulence is measured. Then, the pinch clamps are removed,
and the increase in force caused by circulating air is noted.
Then, the catalyst is added and the incremental force caused
by catalyst circulation is meausred. Circulation rates of both
air and catalyst are calculated from tangential force and
tangential velocity as follows:
Catalyst Circulation Rate (in grams per
second) x Total Catalyst Velocity (in
Force (in grams) = centimeters per sec.)
980
A catalyst particle undergoing radial acceleration by a
rotating blade describes a logarithmic spiral, and will leave
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a rotating blade 22 of the impeller 20 at an angle of 45 to the
tangent so that its radial and tangential velocities are equal,
if it begins near the center and if there is no frictional drag
against the blade 22. In this case, the co-efficient of friction
of the catalyst particles is known from the angle of repose of
a mass of such particles, so this can be used in the calculation
of radial velocity. Tangential velocity of the catalyst parti-
cles is calculated as follows:
Vt = 2~rw; where r is the radius of the blade 22 and
w is revolutions per unit time of the impeller 20. If the
catalyst particles are introduced close to the center of the -
impeller, the radial velocity of the catalyst particles is:
~r = ( ~4 + ~2 _ ~) ~rw;
where ~ is the co-efficient of friction of the catalyst.
The total velocity of the catalyst particles will be the
vector sum of the tangential and radial velocities:
V = ~/ Vt + V2
Using a value of 0.45 for ~, the net velocity is 1.26 times
the tangential velocity.
The catalyst particles used in this test device lO
were obtained from a commercial fluid bed catalytic hydro-
carbon cracking reaction system. These particles had a
composition which included about 15% by weight of alumino-
silicate in a binder comprising silica-alumina. Before
operation of the test device 10, these solid particles had the
following size distribution.
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Size, Microns % By Weight
120+ 12.0
100-120 18.0
80-100 24.0
60-80 23.0
40-60 5.6
20-40 15.9
0-20 1.5
Approximately 20 grams of these catalyst ~ -
particles were placed in the hopper 18 of the test device 10
10 prior to each test.
A series of four (4) tests were run with the second
of the motor set at 2300 rpm. In three of these tests, the
baffles 40 remained uncovered, while in one test the smooth ;~
insert covered the baffles 40, as described above. Results of
these tests were as follows:
RUN Configuration Total Velo- Catalyst Total Incremental
city, Ft./Sec. Circulation,Catalyst Fines-Pro-
gms./sec. Circulated duction
gms. gms.*
1 Baffles 127 9.2 8280 0.13
Uncovered
2 " 12712.8 11540 0.164
3 " 127 6.5 7790 0.15
4 Smooth Insert 127 8.8 7940 0.88
In Place
*Incremental Fines Production is defined as the
net increase in particles 20 microns or less in
size which is apparent in the mass of catalyst
after each test.
These results indicate clearly that the separation
means including arresting means simulated by baffles 40 provides
unexpected and substantial benefits. For example, when the test
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device 10 described above was configured to simulate such a
separation means, i.e , runs 1, 2 and 3, incremental fines
production was less than 20~ the fines production with the
device configured to simulate a smooth wall cyclone separator,
i.e., run 4. Thus, the present apparatus and methods provide
improved simulation of separation means whether or not including
arresting means.
While this invention has been described with respect
to various specific examples and embodiments, it is to be under-
stood that the invention is not limited thereto and that it canbe variously practiced within the scope of the following claims.
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