U.S. patent number 3,627,129 [Application Number 04/792,682] was granted by the patent office on 1971-12-14 for process and apparatus for the separating out of coarse and/or heavy particles from a variable particle size and/or variable particle weight mixture of granular solids maintained in a fluidized state.
This patent grant is currently assigned to Metallgesellschaft A.G.. Invention is credited to Oskar Dorschner, Hans-Werner Gross, Rainer Hartmann.
United States Patent |
3,627,129 |
Hartmann , et al. |
December 14, 1971 |
PROCESS AND APPARATUS FOR THE SEPARATING OUT OF COARSE AND/OR HEAVY
PARTICLES FROM A VARIABLE PARTICLE SIZE AND/OR VARIABLE PARTICLE
WEIGHT MIXTURE OF GRANULAR SOLIDS MAINTAINED IN A FLUIDIZED
STATE
Abstract
Elutriation apparatus and process using apparatus comprising an
upper and a lower member separated by a restricted intermediate
cross section member wherein the lower member has a lesser cross
section than the upper member. The process is carried out by
operating the lower member as a dispersed suspension (known per se)
elutriation apparatus and by operating the upper member as a dense
fluidized bed (known per se) elutriation apparatus with the
intermediate member causing an increase in the velocity, of at
least 1.2 times, of the elutriant passing therethrough from the
lower to the upper members.
Inventors: |
Hartmann; Rainer (Frankfurt am
Main, DT), Dorschner; Oskar (Bad Homburg,
DT), Gross; Hans-Werner (Buchschlag, DT) |
Assignee: |
Metallgesellschaft A.G.
(Frankfurt, DT)
|
Family
ID: |
5681417 |
Appl.
No.: |
04/792,682 |
Filed: |
January 21, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Jan 24, 1968 [DT] |
|
|
P 16 07 648.5 |
|
Current U.S.
Class: |
209/474;
209/502 |
Current CPC
Class: |
B01J
8/0055 (20130101); B01J 8/003 (20130101); C08F
10/00 (20130101); B01J 8/28 (20130101); C08F
10/00 (20130101); B01J 8/44 (20130101); C08F
2/34 (20130101); B01J 2208/00274 (20130101); B01J
2208/00256 (20130101) |
Current International
Class: |
B01J
8/24 (20060101); B01J 8/00 (20060101); B01J
8/44 (20060101); B01J 8/28 (20060101); C08F
10/00 (20060101); B07b 003/02 () |
Field of
Search: |
;209/138,474,139,466,140,141,475,20 ;260/94.9D |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lutter; Frank W.
Assistant Examiner: Hill; Ralph J.
Claims
What is claimed is:
1. Elutriation apparatus comprising a lower chamber, an upper
chamber having a larger cross section than said lower chamber, an
intermediate chamber between said upper and said lower chambers
having a smaller cross section than said upper and said lower
chambers, means for feeding particulate material to said apparatus
for elutriation, means for introducing carrier fluid to said lower
chamber, means for drawing off carrier fluid from said upper
chamber, and means for drawing off coarser grain particles from
said lower chamber, wherein said lower chamber and said
intermediate member have a cross section ratio of at least 1:0.85,
wherein said lower chamber and said upper chamber have a cross
sectional ratio of about 1:2 to 1:15, and wherein the reduction in
cross section of said intermediate member, as compared to said
lower member, is sufficient to increase the velocity of said
carrier fluid to more than 1.2 times as it passes through said
intermediate member as compared to its velocity in said lower
chamber.
2. Elutriation apparatus as claimed in claim 1 wherein said lower
chamber and said upper chamber having cross-sectional ratio of
about 1:3 to 1:10.
3. Elutriation apparatus as claimed in claim 1 wherein said
intermediate member includes a pair of spaced perforated plates
with pipes interconnecting the respective perforations thereof.
4. Elutriation apparatus as claimed in claim 3 including elutriant
supply means connected to the space between said perforated plates
of said intermediate member and communicating with said upper
chamber through bores provided in said upper plate.
5. Elutriation apparatus as claimed in claim 1 wherein said
intermediate member includes an insert element radially spaced from
the juncture of said upper and lower chambers to form an annular
gap.
6. Elutriation apparatus as claimed in claim 5 wherein said insert
element consists at least partially of a conical member having an
axis substantially coincident with the axis of said upper and lower
chambers and having a maximum diameter which is no greater than the
inside diameter of said lower member, which conical member is
axially displaceable.
7. Elutriation apparatus as claimed in claim 1 including elutriant
fluid discharge means disposed below said intermediate member and
elutriant fluid introduction means disposed above said intermediate
member.
8. Process of continuously elutriating a particulate material of
varying grain size which comprises feeding a fluid to and through a
first zone; establishing and maintaining a dispersed suspension in
said first zone; feeding said fluid from said first zone through an
intermediate zone whose cross section is a smaller cross section
with respect to said dispersed suspension zone up to about 0.85
thereof, increasing the velocity thereof to more than 1.2 times the
velocity thereof in said first zone; feeding said fluid from said
intermediate zone to a second zone having a cross-sectional ratio
of about 2:1 to 15:1 with respect to said first zone; establishing
and maintaining a dense fluidized bed in said second zone;
recovering coarser grain particles from the base of said dispersed
suspension zone.
9. The process as claimed in claim 8 including providing said
intermediate zone as a perforated plate and sizing the apertures of
said perforations such that the diameters thereof are about 5 to 20
times the particle size of the coarser grain particles recovered
from the base of said dispersed suspension zone.
10. Process as claimed in claim 8 including providing said
intermediate zone as an annulus between a jacket means and an
insert element which annulus has a gap which is about 2 to 10 times
the diameter of said coarser grain particles withdrawn from said
lower zone.
11. Process as claimed in claim 8 including tapping a portion of
said elutriant fluid upstream of said intermediate zone.
12. Process as claimed in claim 11 including reintroducing said
tapped elutriant fluid to said process downstream of said
intermediate zone.
13. Process as claimed in claim 12 including admixing said tapped
elutriant fluid with fresh elutriant fluid and feeding said
admixture to said process downstream of said intermediate zone.
14. Process as claimed in claim 8 with said elutriant fluid is
gas.
15. Process as claimed in claim 8 carried out at elevated pressure.
Description
It is known that a separation of the constituents can be brought
about in a granular mixture of solids that is composed of particles
of variable size and weight and that is held in a fluidized state
by means of a gas flow, said separation causing heavy or large size
particles to collect in the lower and lighter or smaller size
particles in the upper area.
Large size and/or heavy particles, on the one hand, and small size
and/or light particles, on the other, are differentiated
hereinafter as coarse and fine particles, respectively.
The upwardly flowing gas generating the fluidized condition in the
mixture of solids is referred to hereinafter as carrier gas or
elutrient.
It is known that mixture of solids of variable size or weight of
the individual particles can be sorted out of the fluidized solids
in that the finer particles are upwardly blown or flushed out of
the fluidized solids by means of the carrier gas, with the coarser
particles collecting for instance on the oncoming flow floor for
the carrier gas, designed for instance as a grate, or where the
coarser particles fall out of the spinning mixture, counter to the
flow of the carrier gas, from a grateless, preferably conical
zone.
In this manner it is possible to draw off the fine particles
collecting at the surface of the spinning mixture of solids from a
dense and only slightly agitated fluidized bed, and to remove the
coarse particles depositing on the oncoming flow floor while the
charge mixture is being fed in at medium height of the bed.
Frequently, as a result of the formation of bubbles or tunnels in
fluidized bed agitated more intensively by a carrier gas, a
separation of the mixture of solids into its constituent elements
fails to occur so that the aforementioned method is unsuccessful;
this is the case in particular if the fluidized bed must be heavily
agitated by the carrier gas to prevent, e.g., an agglutination of
wet or glutinous particles.
Such a relatively dense bed can be compared with a boiling liquid
since the carrier gas is apparently forming the dispersed phase
--corresponding to steam bubbles in the liquid. Between the bubbles
and tunnels, the mixture of solids forms coherent areas in which it
is hardly possible for the individual particles to move with
respect to one another.
Contrary to this system is the principle of the dispersed
suspension: in this state, the individual particles can be
considered as the dispersed phase in view of the fact that they are
distributed in the carrier gas in a comparatively low concentration
and can, therefore, move practically independently of one
another.
In operations for the sorting out of coarser particles resulting
from agglomeration, polymerization and the like, by means of
grateless, chambers, one uses, as a rule, a dispersed
suspension.
The granular mixture is held in the grateless chamber in a strongly
agitated and brokenup (aerated) condition. Through the adjusting of
the amount of carrier gas to the amount of solids in the chamber it
is possible to achieve an unstable state of the dispersed
suspension in which solid particles fall out of the lower opening
of the chamber. In the case of a particle mixture, the coarser
particles whose speed of fall is greater than the velocity of the
carrier gas are preferably discharged out of the chamber downwardly
counter to the direction of flow of the gas. On the other hand, the
finer particles contained in the mixture and whose speed of fall is
smaller than the velocity of the carrier gas are carried along by
the carrier gas and discharged upwardly out of the dispersed
suspension.
The use of such devices for the particle separation of fine-grained
solids, e.g., artificial fertilizer, and for the polymerization of
gaseous or vaporous olefins with suitable catalysts is known in the
art. The particular disadvantage in working with a free-flowing,
spinning suspension of solids is that the carrier gas velocity
required for maintaining the desired fluidized state is
substantially above that of a fluidized bed of comparable
diameter.
Moreover, in the case of these grateless chambers known in the art,
the amount of gas required to maintain the desired state of a
suspension increases with changes in the device dimensions to a
greater extent than the square of the diameter of the most narrow
cross section, namely, as is known, by an exponential factor of
about 2.5. Therefore, the enlarging of such equipment to sizes
suitable for industrial applications is subject to rather narrow
limitations.
To obviate this drawback, the carrier medium flow entering the
chamber has been broken up by means of suitable installations into
a plurality of currents of smaller cross section, with the
individual flow paths being designed for instance as Venturi tubes.
However, even this design does not make it possible to achieve any
substantially larger assemblies. Reactors exceeding a diameter of
50 cm. in the most narrow reactor cross sections are thus far
unknown.
To this fact one must add that such reactors are rather critical
with regard to their design. Once the geometric dimensions have
been chosen, the aperture angle of the conical reactor jacket been
determined, and the grain size distribution of the mixture of
solids to be separated has been preset, it is hardly possible to
modify the reactor capacity in any way, and the elevation of the
suspension zone can likewise not be substantially altered in view
of the fact that the amount of gas required to cause the spinning
of the particles present in the maximum reactor cross section
results in such an excessive speed with regard to the most narrow
reactor cross section that the coarse particles can no longer be
made to drop out counter to the flow of the carrier medium.
Therefore, these reactors are sensitive also with respect to
deviations from the preset grain size distribution.
The object of the invention is a process and apparatus for the
continuous separation of a coarse grain fraction, having a close
grain size distribution, out of a mixture of solids having variable
grain sizes, maintained in a fluidized state by means of a carrier
gas, whose grain size distribution can be modified by agglomeration
or polymerization.
It has now been found that it is possible to achieve a clear-cut
separation of a narrow fraction of a given coarsest grain out of
mixture of granular solids in a fluidized state, with any desired
grain size distribution, if one maintains in the upper section of a
fluidized state chamber the state of a comparatively dense
turbulent layer and, in the lower section, the state of a markedly
aerated fluidized suspension, achievable through the selection of
suitable cross sections, and if one increases the velocity of the
carrier gas at the border area between the two states through a
reduction in cross section in such a way that it comes into the
range of incipient delivery, i.e., above the suspension velocity of
the coarser particles.
This process is characterized in that the mixture of solids is
maintained by the carrier gas in the upper area of the reactor at a
greater reactor cross section in a state of a dense fluidized bed
and, in the lower area of the reactor at a smaller reactor cross
section in a state of a dispersed suspension and that in the
boundary cross section between these areas the velocity of flow of
the carrier gas is increased, by means of a reduction in the cross
section, to more than 1.2 times the velocity of flow in the area of
the dispersed suspension.
In view of the fact that the state of incipient delivery is
unstable, coarse grains having a relatively broad grainsize
distribution are discharged out of the upper turbulent layer into
the dispersed suspension situated therebeneath. Within the
dispersed suspension there occurs an intensive sorting of the grain
fraction with the coarsest particles accumulating directly above
the entrance floor for the carrier gas while the finer grain
portions are carried into the upper turbulence layer by the carrier
gas.
What was surprising was the fact that, as a result of the
introduction of an intermediate border area with the ability to
increase velocity, the combination of a dense fluidized layer and a
dispersed suspension layer in a single device was realizable at
all, and that the required amount of carrier gas is practically
independent of the elevation of the turbulent layer. This means
that the conditions of the dense fluidized bed can be computed and
adjusted in accordance with per se known methods and that such a
reactor is operated in its upper section like a conventional
fluidized bed reactor.
The great advantage of the discovered process consists,
furthermore, in that the required velocity of the carrier gas for
any desired suspension state is independent of the diameter of the
selected fluidized bed and that, as a result, based on the instant
invention, it is possible to operate reactors of any engineering
dimensions.
A part of the carrier gas can be shunted off and discharged to the
outside ahead of the reduced border area cross section. This
shunted off part of the carrier medium can be reintroduced in whole
or in part above the narrowed boundary area cross section into the
dense fluidized bed in the upper reactor area; however, it can be
returned also beneath the oncoming flow floor thereby achieving a
cycle of the carrier medium across the area of the dispersed
suspension. In addition to the carrier gas introduced from below
into the reactor, a further amount of carrier gas can be introduced
above the reduced boundary area cross section.
By means of this simple arrangement it is possible to vary with
respect to one another the velocity of flow in the fluidized bed,
in the dispersed suspension and in the reduced boundary area cross
section.
As a result, a device of given dimensions can be readily adjusted
to different particle size distribution charge mixtures.
Furthermore, it thus becomes possible to sort out a mixture of
solids of mixed particle sizes, i.e., to separate it into several
fractions of per se uniform grain sizes. This result can be
achieved in such a way that the coarsest fraction contained in the
mixed charge is separated out first and that, thereupon, the
velocity of flow of the carrier gas in the individual or in more
than two, e.g., three, zones is modified in such a way that the
next grain fraction that has now become the coarsest one is
separated out.
The possibility for an individual change in the velocity of flow of
the carrier gas in a single, in two or in all three zones of the
reactor is advantageous if the grain size distribution of the mixed
charge is being altered during its presence in the reactor, e.g.,
as a result of agglomeration, deposition of solids (e.g., coking)
on the particles, or by means of polymerization. This is
applicable, for example, with regard to the polymerization in the
gaseous phase of olefins through contact with a catalyst-containing
fine-grained polymer held in the fluidized state by means of an
olefin-containing carrier gas (as set forth in one of the following
examples).
A reactor for the execution of the process according to the
invention comprises two superpositioned preferably substantially
coaxial cylindrical jackets, the upper one of which has a wider
cross section than the lower one. The cross section ratio can be
about 1:2 to 1:15, preferably 1:3 to 1:10, between the lower and
the upper cross sections, respectively.
The two cylindrical jackets can be interconnected at their
adjoining extremities by means of an ordinary, annular disk.
However, it is preferred to use a conical spacer as a connecting
element in order to avoid producing blind angles in which solids
are likely to deposit.
As is customary with this type of reactor, the carrier gas is
introduced at the lower end of the lower cylinder via a floor
suitable to receive the oncoming flow, a grate, or the like, and
discharged at the upper end of the cylinder, possibly via a
cyclone.
The granular mixture of solids to be sorted is being introduced
laterally into the upper or lower cylinder. The coarse material
accumulates on the oncoming flow floor or grate whence it is
removed periodically or continuously in a per se known manner via a
central peripheral or lateral removal means.
The fine grain material can, in a per se known manner, be
discharged by the carrier gas current out of the upper cylinder and
be separated out of the gas current in a cyclone, and/or be drawn
off laterally from the level of the dense fluidized bed layer.
In the upper cross section of the lower cylinder there is arranged,
according to the invention, a cross section reduction by means of
which the velocity of flow of the carrier gas is increased so that
maximum velocity of flow within the reactor prevails at this
point.
Such a reduction in cross section can be brought about for instance
by means of a perforated plate, or by means of a concentrically
inserted element, and should have an orifice total cross section
not exceeding 0.85 times the cross section of the lower
cylinder.
The aperture in the perforated plate are preferably dimensioned so
that their individual diameters represent 5 to 20 times the size of
the coarse grain particles to be separated out. In the case of the
use of a concentric insert element, the annular clearance formed by
it with respect to the reactor cross section should have a width of
2 to 10 times the particle size of the coarse grain to be separated
out. These values are preferred and may be adjusted upwardly or
downwardly in given cases. The shape of the grain particles and the
structure of the grain surface, on which the flow properties of a
granular mixture depend to a large extent, have considerable
influence on the dimensioning of said apertures.
The concentric insert element can be connected with the reactor by
means of radial supports. Its shape may be conical or double
truncated conical and it can be movably arranged on a vertical rod
displaceable along the reactor axis.
Above and under the zone with the most narrow reactor cross
section, openings can be arranged in the reactor jacket, which lead
to annular ducts. By means of these annular ducts, partial amounts
of the carrier medium can be drawn off from and/or introduced into
the reactor.
More specifically, a part of the carrier medium can be drawn off
from the lower reactor zone through the lower annular duct ahead of
the reduction in area and be reintroduced into the upper reactor
zone above the reduction in area.
The accompanying drawing illustrates schematically and by way of
example a reactor for the execution of the process according to the
invention and individual components of said reactor.
FIG. 1 schematically shows an axial cross section of a reactor;
FIG. 2 is a cross section along line A--A of FIG. 1 and through the
intermediate perforated plate narrowing down the flow cross
section;
FIG. 3 represents another embodiment of the reduction in cross
section between the two reactor zones by means of a concentric
insert element shown as an axial section;
FIG. 4 represents a horizontal section through FIG. 3 along line
B--B;
FIG. 5 illustrates a variant of the device according to FIG. 4,
with adjustable intermediate area-reducing member;
FIG. 6 illustrates a perforated plate according to FIGS. 1 and 2,
with means for the additional introduction of carrier gas into the
upper reactor zone;
FIG. 7 shows another device for the introduction of additional
carrier gas into the upper reaction zone, in a vertical cross
section;
FIG. 8 represents a horizontal section through FIG. 7 along line
C--C;
FIG. 9 shows a mode of realization of the coarse grain discharge
above the floor suitable to receive the oncoming flow, represented
as a vertical section;
FIG. 10 represents, as an axial cross section, a special design of
the lower reactor zone;
FIG. 11 is the flow diagram of a plant for the execution of the
process according to the invention applied to the polymerization of
gaseous monoolefins.
The reactor 1 schematically illustrated in FIG. 1 substantially
comprises an upper chamber 2 having a larger cross section, a lower
chamber 3 having a smaller cross section, a connecting intermediate
zone 4 having a more narrow cross section, a floor 5 suitable to
receive feed flow of a carrier gas via an air chamber 6, and is
provided with supply lines 7 and 8 for solid material to be
processed, as well as with a discharge line 9 for coarse grain
product that has been separated out, and an outlet 10 for fine
grain product.
The connecting zone 4 is designed as a truncated cone 11. The
reduction in area is by means of a perforated plate 12 illustrated
enlarged as a horizontal cross section in FIG. 2.
Beneath the perforated plate 12 in the jacket of the lower chamber
and above the perforated plate 12 in the jacket of the connecting
zone 4 there have been arranged openings 13 leading outside into
annular ducts 14 and 15, respectively. The annular ducts are
provided with pipe connections 16 and 17 by means of which the
carrier gas can be drawn off or supplied.
In the manner customary with fluidized bed reactors, the upper
reactor zone 2 can be joined via a truncated cone 18 to a
stabilizer chamber 19 from which the carrier gas is drawn off
through a cyclone separator by means of a line (not shown).
As illustrated in FIGS. 3 and 4, the perforated plate 12 can be
replaced by an insert 20, concentrically arranged in the area of
the contact point of the jackets of the lower chamber 3 and the
connecting zone 4, which is fixedly connected to the elutriation
apparatus jacket. The reduction in cross section area is in this
case accomplished by an annular clearance 22.
As illustrated in FIG. 5, the concentrically arranged insert
element 23 may have the shape of a cone and be fastened to a rod 24
displaceable along the apparatus axis. As a result of the vertical
displacement of the element 23 in the area of the connecting zone
4, the cross section area reduction 25 can be altered during
operation. This principle may be applied also with regard to each
individual bore of a perforated plate.
The system for the introduction of additional carrier gas into the
upper reactor zone, consisting of an annular duct 15 with
appropriate openings 13 and a pipe connection 16 (FIG. 1), can be
replaced for instance by a special design of perforated plate 12
illustrated in FIG. 6.
In this case, the perforated plate consists of a plurality of pipes
26 held at their extremities in support elements 27 and 28. The
support elements are connected with a cylindrical housing 29, which
may also be the jacket of the lower chamber 3 (FIG. 1), and which
is provided with a pipe connection 30 for the supply of carrier
gas. In the upper support element 27, bores 31 have been arranged
between the end points of the pipes 26, which lead to the hollow
space between the pipes in the housing, thereby permitting the
carrier gas supplied through a pipe connection 30 to issue through
said bores. Pipes 32 provided with screen covers 33 are shown
inserted in the bores 31.
FIGS. 7 and 8 illustrate another mode of realization for the supply
of additional carrier gas to the upper reactor zone 2. Into a
central bore in the perforated plate 12 there has been inserted a
pipe 34 leading, via a bend 35, to a pipe connection 36 in the
jacket of the lower chamber. The pipe 34 is provided at its upper
end with a porous or perforated gas distribution plate 37.
Furthermore, perforated distributor pipes 38 emanate radially from
the upper pipe end, which can in per se known manner be provided
with screen covers (not shown).
Additional carrier gas is introduced via the pipe connection 36 and
enters into the upper chamber through the openings in the gas
distributor pipe 37 and in the distributor pipes 38.
FIG. 9 illustrates a variant of the coarse grain discharge means.
Whereas in the apparatus according to FIG. 1 the sorted-out coarse
grain accumulated on the floor 12 is being removed via a central
outlet 9 traversing the air chamber 6 and by means of a
bucket-wheel valve, the jacket of the lower chamber can, as shown
in FIG. 9, be expanded at its lower extremity to form a beadlike
annular space 39 constituting a cover over the floor 5 and the air
chamber 6 and can be provided with a delivery pipe 40 comprising a
bucket-wheel valve 41 for the removal of the coarse grain
product.
FIG. 10 illustrates a particular design of the lower reactor zone
3, by means of which the selectivity with regard to the grain size
to be sorted can be improved if need be. Spaced a short distance
above the floor 5 for the feed flow, which comprises a central
aperture for the coarse grain particle outlet 9, there is arranged
a conical insert element 42 attached to the floor for instance by
means of supports 43. The annular edge of this conical insert forms
a narrowed passage 44 with the wall of the lower chamber. The
carrier medium coming in through the oncoming flow floor flows
first under the floor of the cone horizontally with respect to
passage 44 at a velocity of flow somewhat greater than that of the
velocity of the gas in the reactor zone, and generates in this area
a final crosscurrent classification.
This arrangement is of significance in particular in the case of
polymerization processes. For example, in olefin polymerization the
carrier medium comprises a reactant in view of the fact that it
contains the monomer.
The monomer can react with the catalyst still active in the polymer
particles in the area of the lower reaction zone and thus use up
the residual activity thereof while standardizing the grain
size.
FIG. 11 illustrates the application of the process to the gaseous
phase polymerization of ethylene. In an upper part 51 of a reactor
50, designed according to the invention, there is a dense turbulent
fluidized layer formed by polymer and catalyst particles. In the
course of the reaction there occurs a growth in the particles,
owing to the growth of polymer on the catalyst nuclei, which
results in an increase in the volume of the fluidized bed. In order
to prevent a swelling of the bed, the large polymer particles
containing only small amounts of still partially active catalyst
must be flushed out of the process and, to this end, one uses the
process according to the invention.
The coarse particles that have been produced are flushed out of the
process by means of the pipe portions associated with reduced area
intermediate member designed according to FIG. 6 and a coarse grain
particle discharge means 53 and enter a lower reactor part 52 where
the state of an aerated dispersed suspension is formed and
maintained. Here, the particles containing still partially active
catalyst can permit full reaction before they enter the bin 56 by
means of a discharge pipe 54 via a bucket-wheel valve 55.
To replenish the spent catalyst, a mixture comprising fine polymer
and catalyst particles is continuously fed into the upper part of
the apparatus (fluidized bed) bed via a dosing device 57 and input
pipe 58 from a bin 60.
Fine particles can be drawn off at the surface of the dispersed
turbulent layer via a discharge pipe 59 and a bucket-wheel valve
61, as initial preparation of the polymer particle and catalyst
mixture. The carrier gas consisting, substantially, of the monomer
to be polymerized enters a chamber 63 of the reactor via pipe
connections 62 and flows sequentially via a gas distribution grid
64 through the lower part 52, the intermediate reduction in area
member 53 and the fluidized bed 51 of the reactor. In the enlarged
top section of the reactor, particles that have been dragged along
by the elutriant are separated out as a result of the reduction in
the gas velocity. The carrier gas emerges from the reactor at 66,
via line 67, and enters a cyclone 68 where the dust portion taken
up by the carrier gas is separated out and falls into a dust
accumulator 69.
Following cooling in gas coolers (not shown), the dust-free carrier
gas is subsequently fed into a circular gas compressor 70 where it
is compressed to the required pressure. The monomer consumed in the
course of the reaction is replenished via a line 71 and a
pressure-regulating valve 72. In accordance with process
requirements it is possible, as described above, to feed a part of
the current of the carrier gas, via a line 73, into the upper part
of the reactor; a part of the gas current can be drawn off from the
lower reactor part via line 74 and fed via a line 75 into the
upper, fluidized bed, or completely or partially drained out of the
reactor via a line 76. Control of the amount of carrier gas
supplied to the reactor is achieved by means of a bypass valve 77
of the compressor. The olefin polymerization in accordance with the
invention process can also be carried out at elevated pressures up
to about 50 atm. gauge. In the case of propylene polymerization,
for instance, preferred pressures may be around 15 atm. excess
pressure.
The following Examples are illustrative of the practice of this
invention without being limiting thereon.
EXAMPLE 1
For polymerization of ethylene in the gaseous phase, the plant was
operated as illustrated in FIG. 11 and described above.
The upper cylindrical reactor part for accommodating the fluidized
bed had a diameter of 200 mm. and a height of 1.0 meter. The lower
reactor zone had a diameter of 90 mm. and a height of 15 cm. The
two zones were connected by means of a 15 cm. high conical junction
element. The narrowing in the cross section area at the boundary
zone between the lower and the upper parts of the reactor, in
accordance with the invention, was carried out in this case by
means of a concentric rotor according to FIG. 3 and having an
effective cylindrical diameter of 55 mm. The height of the
cylindrical part was 50 cm. while the overall height was 100 mm.
The cone had been displaceably arranged in a manner similar to that
shown in FIG. 5 and, in order to close the 40 mm. diameter central
discharge tube 9 (see FIG. 1), could be moved completely down. For
the purpose of emptying the reactor completely, the cone could be
slidably displaced up to a point in the upper reactor zone.
No use was made of the possibility of draining any carrier gas from
the lower part of the reactor or of feeding additional amounts of
carrier gas into the upper part.
The height of the fluidized bed in the upper reactor part varied
between 400 and 800 mm. The grain size of the spinning material
formed by catalyst and polymer particles was between 0.5 and 4.0
mm.
To maintain a well agitated fluidized state in the upper part of
the reactor, 55 m..sup.3 ethylene had to be fed into the reactor
per hour.
The polymerization reaction was carried out at a slight
overpressure 1.2 atm. absolute pressure.
As a catalyst there was used a suitable Ziegler catalyst which was
applied onto fine-grain polyethylene particles having an average
grain size of approximately 0.5 mm. The catalyst represented 8
percent by weight of the catalyst-polymer mixture. To replenish the
used up catalyst, upon working in continuous operation, 125 g./hour
of catalyst-polymer mixture were fed into the reactor. 5 kg. of
polyethylene particles of a diameter between 2.0 and 3.5 mm. were
discharged per hour from the central discharge tube 9 via the
bucket-wheel valve. In view of the fact that the polymerization is
associated with particle growth, it was not necessary to flush fine
material out of the reactor. The dust resulting from abrasion in
the vortex bed was separated out in a cyclone; it amounted to
approximately 10 g./hr.
The polymer particles discharged in the process exhibited the
following grain spectrum:
Particle size (mm.) Part by Weight (%) up to 1.0 5.2 1.0- 2.0 21.0
2.0- 3.0 44.8 3.0- 4.0 25.8 above 4.0 3.2
EXAMPLE 2
For the purpose of separating out a fraction of coarse grain from
an aggregate of polypropylene particles and for treating the
particles simultaneously with air to deactivate the catalyst
contained in the particles, a device was operated in accordance
with FIG. 1, in which the annular ducts 14 and 15, as well as the
gas inlet and outlet openings 13 had been omitted.
In this case, the ratio of the lower to the upper member diameters
amounted to 0.4 with an upper reactor diameter of 500; the ratio of
the narrowest cross section member to the lower reactor cross
section was 0.45, the narrowest cross section member having been
formed by means of a perforated plate according to FIG. 2 and
having openings of a total diameter of 22 mm.
The overall height of the reactor was 4.5 m., the height of the
fluidized bed was varied between 1.0 and 1.5 m. The velocity of the
carrier gas required to maintain a moderately agitated fluidized
bed was 0.25 m./sec. Polypropylene granulate of the following
composition was fed into the reactor at the rate of 44 kg./hr.,
Particle Size (mm.) Part by Weight (%) up to 0.5 33.3 0.5-1.0 21.4
1.0-2.0 22.4 2.0-3.0 13.0 3.0-4.0 6.1 4.0-5.0 2.1 above 5.0 1.3
There were removed via the central tube in the lower part of the
reactor 15.0 kg./hr. of coarse material having the following
composition:
Particle Size (mm.) Part by Weight (%) up to 1.0 10.0 1.0-2.0 29.0
2.0-3.0 34.1 3.0-4.0 17.6 4.0-5.0 5.5 above 5.0 3.8
The enriched fine material was drawn off from the surface of the
fluidized bed by means of an overflow discharge tube 10.
EXAMPLE 3
To improve the selectivity of the process described in example 2, a
device according to FIG. 10 was mounted into the lower part of the
reactor. The ratio of the diameter of the base of the cone to the
diameter of the lower reactor part amounted to 0.69. The cone had
an angle of 42.degree. and was situated at a distance of 15 mm.
from the oncoming flow floor. The supplying of the charge material
and the discharging of the coarse and fine material was carried out
as in example 2. The hourly yield was 13.5 kg. of coarse material
having the following composition:
Particle Size (mm.) Part by Weight (%) up to 1.0 2.1 1.0-2.0 27.2
2.0-3.0 39.6 3.0-4.0 20.0 4.0-5.0 6.9 above 5.0 4.2
The composition of the fine material was practically unchanged.
EXAMPLE 4
A grain fraction having a greater proportion of coarse material
than that referred to in examples 2 and 3 was treated by performing
the process, in the identical device used in such examples. There
was used as a reduction in area member a perforated plate designed
according to FIG. 6 and having gas outlet bores 31 of a diameter of
2 mm. each, without, however, tubes 32 and cover screens 33. In
view of the fact that the velocity of the carrier gas required to
maintain a moderately agitated fluidized state amounted to 0.3
m./sec. with regard to the granulation of the material in question,
another volume of gas representing approximately 20 percent of that
entering the reactor via the floor receiving the oncoming flow was
introduced additionally into the upper part of the reactor via the
pipe connection 30 and the bores 31.
The charge material supply and volume were the same as in example
1. The discharging of the coarse and fine fractions was carried out
as in example 1. The charge product exhibited the following
composition:
Particle Size (mm.) Part by Weight (%) up to 0.5 10.2 0.5-1.0 27.6
1.0-2.0 32.4 2.0-3.0 18.4 3.0-4.0 7.1 4.0-5.0 1.8 5.0-6.0 1.5 above
6.0 1.0
21.0 kg. of coarse material having the following composition were
separated out per hour:
Particle Size (mm.) Part by Weight (%) up to 1.0 5.4 1.0-2.0 35.1
2.0-3.0 35.4 3.0-4.0 14.9 4.0-5.0 3.9 5.0-6.0 3.2 above 6.0 2.1
* * * * *