Apparatus and method for determining the attrition properties of a mass of solid particles

An improved apparatus for determining the time rate of attrition of a mass of solid particles comprising a chamber; inlet and outlet providing for entrance and exit, respectively, to the chamber; a conduit providing communication between the inlet and outlet; an impeller located in the chamber to urge solid particles from the inlet in the general direction of the sidewall of the chamber; and a motor to provide rotation of the impeller. Improved simulation of solid particle attrition in commercial cyclone separators is obtained.

This invention relates to improved apparatus and methods for determining 
the tendency toward attrition and attrition 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 feedstock 
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.g., 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 vapor at conditions 
to combust at least a portion of the deposit material. 
Operation of both of the systems referred to above involves the formation 
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 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. This 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 withdrawn 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. 
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 sidewalls, 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 support 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. 
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 
velocoty. 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, 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 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 of construction. The material or materials of 
construction used 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 invention are set 
forth in the following detailed description and claims, particularly when 
considered in conjunction with the accompanying drawings in which like 
parts bear like reference numerals.

Referring now to the embodiment of the present apparatus shown in FIGS. 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 substantially 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, 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 FIGS. 1 and 2 functions as follows. 
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 velocity 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 recirculated 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 FIGS. 3 and 4, an additional embodiment 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 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 FIGS. 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 particles, 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. 
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 FIG. 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 passageway 14 defined 
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 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 
substantially 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 component of velocity of the mixture of 
catalyst particles and air leaving the impeller 20 and blades 22. The 
impeller 20 is supported by the variable speed motor 26 and shaft 24, and 
contacted the chamber housing, 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: 
##EQU1## 
wherein: X = the lateral displacement of the weight from 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 measured. Circulation rates of both air and 
catalyst are calculated from tangential force and tangential velocity as 
follows: 
##EQU2## 
A catalyst particle undergoing radial acceleration by a rotating blade 
describes a logarithmic spiral, and will leave a rotating blade 22 of the 
impeller 20 at an angle of 45.degree. 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 
particles is calculated as follows: 
V.sub.t = 2.pi.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: 
EQU V.sub.r = (.sqroot.4+ .alpha..sup.2 - .alpha.).pi. rw; 
where .alpha. 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: 
EQU V= .sqroot.V.sub.t.sup.2 + V.sub.r.sup.2 
Using a value of 0.45 for .alpha., the net velocity is 1.26 times the 
tangential velocity. 
The catalyst particles used in this test device 10 were obtained from a 
commercial fluid bed catalytic hydrocarbon 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. 
______________________________________ 
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 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: 
__________________________________________________________________________ 
Total Incremental 
Catalyst 
Catalyst 
Fines-Pro- 
Total Velo- 
Circulation, 
Circulated 
duction 
RUN Configuration 
city, Ft./Sec. 
gms./Sec. 
gms. gms.* 
__________________________________________________________________________ 
1 Baffles 127 9.2 8280 0.23 
Uncovered 
2 " 127 12.8 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 afte 
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 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 understood that the invention is not 
limited thereto and that it can be variously practiced within the scope of 
the following claims.