U.S. patent number 3,756,569 [Application Number 05/155,362] was granted by the patent office on 1973-09-04 for apparatus for mixing and homogenising bulk material and method of operating the apparatus.
This patent grant is currently assigned to Bayer Aktiengesellschaft. Invention is credited to Arnon Wohlfarth.
United States Patent |
3,756,569 |
Wohlfarth |
September 4, 1973 |
APPARATUS FOR MIXING AND HOMOGENISING BULK MATERIAL AND METHOD OF
OPERATING THE APPARATUS
Abstract
A container with a conical base for the pneumatic mixing of
material in powder or granulated form, and with a gas supply means
at the bottom has at least one riser pipe arranged therein, said
pipe ends in the upper region of the container and is formed with
openings or gaps. At least one opening or gap is formed as an
annular passage, which divides the riser pipe into a lower section
and an upper section. The upper end of the lower section surrounds
and is spaced from the lower end of the upper section, whereby said
gap is defined.
Inventors: |
Wohlfarth; Arnon (Koeln,
DT) |
Assignee: |
Bayer Aktiengesellschaft
(Leverkusen, DT)
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Family
ID: |
5740624 |
Appl.
No.: |
05/155,362 |
Filed: |
June 21, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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49883 |
Jun 25, 1970 |
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Foreign Application Priority Data
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Jul 23, 1969 [DT] |
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P 19 37 374.1 |
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Current U.S.
Class: |
366/106 |
Current CPC
Class: |
B01F
13/0244 (20130101) |
Current International
Class: |
B01F
13/02 (20060101); B01F 13/00 (20060101); B01f
005/12 () |
Field of
Search: |
;259/4,18,95 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jenkins; Robert W.
Parent Case Text
This application is a continuation-in-part of application Ser. No.
49,883, filed June 25, 1970, now abandoned.
Claims
What is claimed is:
1. Apparatus suitable for pneumatically mixing materials in finely
divided form comprising:
a. a vertically extending container having an inlet opening
adjacent its upper end for introduction of finely divided
materials, and an outlet means in the lower end outfitted with
means for selectively closing the outlet, for withdrawal of mixed
materials,
b. a vertically extending riser disposed in the container above and
spaced from the outlet opening and comprising an upper section and
a lower section, said sections being in overlapping, radially
spaced relation defining an annular passage therebetween, with the
upper section terminating above the lower section and the lower
section having its lower end at least as low as the lower end of
the upper section,
c. means for supplying gas for said mixing to the container below
the lower end of the riser for passage of gas into the container
and pneumatic lifting and mixing of the gas and materials in the
riser with the materials filling the container to above the lower
end of the riser.
2. Apparatus according to claim 1, the lower end of the riser lower
section diverging upwardly.
3. Apparatus according to claim 1, and means for adjusting the flow
area of the annular passageway of the riser.
4. Apparatus according to claim 1, and means for selectively
closing the annular passageway of the riser.
5. Apparatus according to claim 1, said means for supplying gas for
said mixing comprising two vertically spaced gas inlet conduits and
valve means for selectively apportioning the flow of gas between
the two conduits.
6. Apparatus according to claim 1, the lower end of the lower
section of the riser terminating below the lower end of the
uppersection of the riser.
7. Apparatus according to claim 1, and a baffle disposed above and
spaced from the upper end of the riser for intercepting the mixture
of gas and particles and separating the particles from the gas.
8. Apparatus according to claim 7, and a gas outlet above the
baffle for discharge of the gas from the container after said
separation by the baffle.
9. Process of pneumatically mixing materials in finely divided form
with apparatus comprising:
a. a vertically extending container having an inlet opening
adjacent its upper end for introduction of finely divided
materials, and an outlet means in the lower end outfitted with
means for selec-tively closing the outlet, for withdrawal of mixed
materials,
b. a vertically extending riser disposed in the container above and
spaced from the outlet opening and comprising an upper section and
a lower section, said sections being in overlapping, radially
spaced relation defining an annular passage therebetween, with the
upper section terminating above the lower section and the lower
section having its lower end at least as low as the lower end of
the upper section,
c. means for supplying gas for said mixing to the container below
the lower end of the riser for passage of gas into the container
and pneumatic lifting and mixing of the gas and materials in the
riser with the materials filling the container to above the lower
end of the riser,
said process comprising:
d. filling the container with finely divided material to a level
between the upper end of the riser lower section and the upper end
of the riser upper section,
e. supplying gas via said gas supplying means for passage therof
into the container and pneumatic lifting and mixing of the gas and
finely divided materials in the riser,
f. said level of the finely divided material being such that finely
divided material during the process flows downwardly through said
annular passageway and into the mixture of gas and finely divided
material rising through the riser, and
g. maintaining the finely divided material at said level during the
process.
10. Process of mixing materials in finely divided form with
apparatus comprising:
a. a vertically extending container having an inlet opening
adjacent its upper end for introduction of finely divided
materials, and an outlet means in the lower end outfitted with
means for selectively closing the outlet, for withdrawal of mixed
materials,
b. a vertically extending riser disposed in the container above and
spaced from the outlet opening and comprising an upper section and
a lower section, said sections being in overlapping, radially
spaced relation defining an annular passage therebetween, with the
upper section terminating above the lower section and the lower
section having its lower end at least as low as the lower end of
the upper section,
c. means for supplying gas for said mixing to the container below
the lower end of the riser for passage of gas into the container
and pneumatic lifting and mixing of the gas and materials in the
riser with the materials filling the container to above the lower
end of the riser,
said process comprising:
d. filling the container with finely divided material to a level
between the upper and lower ends of the riser lower section,
e. supplying gas via said gas supplying means for passage thereof
into the container and pneumatic lifting and mixing of the gas and
finely divided materials in the riser,
f. part of the mixture of gas and finely divided material passing
through the riser leaving the riser pipe via said annular passage,
while periodically another portion of the finely divided materials
rises into the upper section of the riser which portion, after
reaching a certain height, collapses to form a plug of material and
is mixed together with the material transported from the bottom of
the container through the lower section of the riser and discharges
through the annular passage.
Description
BACKGROUND
The invention relates to a container having a conical base for
pneumatically mixing material in powder or granulated form, said
container having at the bottom outlet a gas supply means and having
at least one riser pipe arranged therein, said pipe terminating in
the upper region of the container and having openings or gaps.
The invention is further concerned with two different methods of
operating the mixing container, by means of which the material is
propelled into the riser pipe by gas introduced at the base.
As is know bulk materials which are in a container can be mixed and
homogenised by being carried upwardly by means of a gas stream
through riser pipes arranged inside or outside the container and
being caused to overflow at the upper rim thereof.
It is a disadvantage with these simple arrangements that only
material from a high position in the container is supplied to the
riser pipes at their lower ends. It is true this arrangement
ensures a good transverse mixing of the bed of product disposed at
this height, but it does not provide any sufficient longitudinal
mixing of the layers or beds of product deposited at different
heights in the container.
Apparatus is known in which several riser pipes are arranged inside
(German Patent No. 615771) or outside (German Patent No. 669201) of
the mixing container in order to produce a better longitudinal
mixing, the lower openings forming the supply for the material
being arranged at different heights in the container below the
level of the product.
In another arrangement (U.S. Pat. No. 3,258,252), the riser pipe
arranged in the mixing container is concentrically enclosed by a
second perforated pipe of larger diameter, the lower end of this
pipe being closed by an annular cover. The powder or granulated
material in this case penetrates through the openings in the casing
of the perforated pipe into the annular chamber between the two
pipes, falls due to gravitational force and is carried upwardly
with other material from the bottom of the mixing container by
means of a compressed gas stream through the riser pipe.
A particular disadvantage is that, with the said arrangement, an
improvement in the longitudinal mixing is only to be achieved with
considerable expense in construction. This expense often bears no
relationship to the slight improvement in the quality of the mixing
which is produced thereby and to the insignificantly shortened
mixing time.
In the chemical industry, it is often necessary to carefully clean
a mixer before charging the material to be mixed, because many
mixers have to be used for different types of products. The
standards as regards cleanliness are so thorough that often a man
has to climb the mixer and clean the interior thereof by hand. It
is to be seen from this that all known mixers having complicated
and narrow fittings, small openings, frit-type bottoms, nozzles and
positions which cannot be reached or are only accessible with
difficulty, are unsuitable for the purposes set forth.
Furthermore, with mixers having aeration nozzles, very high gas
velocities are set up locally. The product which is to be mixed and
which frequently consists only of loose agglomerates therefore
often experiences undesirably heavy abrasion.
THE INVENTION
The invention has for an object to provide a simple mixer which can
be easily cleaned and which does not have any complicated fittings,
with which a good longitudinal mixing and a good transverse mixing
and therefore a short mixing time is ensured. A simple riser pipe
without complicated air or product supply means is provided.
Furthermore, low gas velocities are required in the mixing pipe and
at the feeding position, so that the abrasion of the product
remains small.
According to the invention, at least one opening or gap formed as
an annular passage is provided on the riser pipe in the mixing
container, the said gap dividing the riser pipe into the lower
section and an upper section, the upper end of the lower section
being widened and surrounding the lower end of the upper section
while leaving an annular gap.
The mixing gas is supplied to the container at the bottom end of
the mixer housing. Air is advantageously used as mixing gas. The
conical bottom of the mixer housing, which terminates in a
cylindrical end member, is for this purpose provided with an air
supply chamber enclosing the cylindrical end section in annular
form, said chamber also having a conical bottom. The conical bottom
of the air supply chamber in this case serves simultaneously as the
outlet for the product.
A good mixing action of the apparatus as described is only assured
if the gas stream provided for the mixing actually only flows
through the riser pipe provided for it.
A particularly good longitudinal mixing is obtained when the riser
pipe is arranged eccentrically in the container.
It is to be initially assumed that the gas, with the commencement
of the mixing operation, selects its path through the riser pipe
and through the mixing container in an upward vertical direction.
By suitable introduction of the product to be mixed into the mixing
container, for example, through a pneumatic feed pipe with a
tangential inlet into the container, and by fitting a shielding
cone above the upper end of the riser pipe, the container is filled
to a selected level between the bottom and top of the riser. After
the mixing container has been so filled, the level of product in
the annular chamber between the inside wall of the container and
the riser pipe is higher than in the latter. The mixing gas now
flows for the major part through the riser pipe, because there it
has to overcome a smaller flow resistance because of the lower
product level. After the loosening of the product in the riser
pipe, the filling level therein rises, but the bulk weight inside
the riser pipe is then substantially smaller than that inside the
mixing container, and the mixing gas also continues to flow for the
major part through the riser pipe provided for the mixing. The
product to be mixed is raised in the riser pipe by the ascending
gas stream, and when the level to which the container is filled is
above the top of the annular chamber, is caused to overflow at the
upper end thereof. On the conical bottom of the mixer, fresh
product slips down into the gas stream ascending to the riser
pipe.
Because of the construction of the openings in the riser pipe, when
the container is filled as just stated, a part of the product which
is in the container at the level of the annular passage falls from
this position into the riser pipe. In this way, layers of product
from different height positions of the mixing container are
homogenised in the riser pipe.
Consequently, a good longitudinal mixing is assured, in addition to
the transverse mixing. With a mixing test in a mixing container
with a capacity of 3 cubic metres, the mixing time of two hours
with a straight-through riser pipe could be reduced to 20 minutes
with a riser pipe having an additional annular passage. The same
mixing quality was obtained in both tests.
It has proved to be especially advantageous that the annular
passages are to be easily cleaned after the mixing process and that
no deposits of product occur therein.
When the mixer is filled to above the top of the annular passage,
some of the product can naturally drop through the annular passage
into the riser pipe. However, the product level in the riserpipe,
due to the resistance of the material to flow like a liquid, can at
a maximum only reach the height of the lower end of the annular
passage or only a short distance above said height. Since the upper
end of the annular passage in the riser pipe is situated above the
product level in the riser pipe, the difference in the filling
heights and thus also the flow resistance in the container and in
the riser pipe are sufficiently large to produce required gas
flow.
On commencing the mixing operation, the product to be mixed is
disposed in the mixing container and in the riser pipe up to at
least the height of the upper end of the annular chamber in densely
packed form. The mixing gas supplied at the bottom of the mixer has
to force the plug of product beneath the bottom end of the riser
pipe into the said pipe. In this case, very large shearing stresses
have to be overcome at the periphery of the initially still
consolidated plug of product. In addition, the plug is also loaded
by the weight of the product column in the riser pipe. The pressure
necessary for starting up the mixer is usually a multiple of the
pressure required for the continued mixing. By way of example, for
a mixing container having a capacity of 40 cubic metres (height 10
metres, diameter 2-1/2 metres) and filled with synthetic plastic
granulated material (bulk weight: 500 kp/m.sup.3, grain diameter 3
mm.), a starting pressure of more than 20 m. water column is
necessary with a gas quantity of 7,000 m.sup.3 /h (at n.t.p.). For
the actual mixing operation, on the contrary, only a pressure of 2
m water column is required for the same gas throughput.
There are now to be proposed suitable devices by means of which the
pressure necessary on starting the mixer can be lowered.
According to a further development of the invention, the annular
passages can for example change in cross-section or be completely
closed by inflatable, elastic closure elements arranged therein or
by sections of the riser pipe being arranged to be relatively
adjusted in height.
Thus, before starting the mixing operation, the product to be mixed
can be introduced into the mixing container with the annular
passages of the riser pipe closed. The result hereby obtained is
that the introduced product can only penetrate from the bottom of
the mixing container into the riser pipe, so that the level of
product in said pipe only reaches a very small height. The plug of
product between the bottom end of the riser pipe and the bottom of
the container now has only to be moved upwardly against the
shearing stresses at its periphery with supply of the mixing gas,
since the weight of the column of product in the riser pipe by
which it is additionally loaded is avoided.
In this way, the pressure on starting the last-mentioned mixer can
be reduced from 20 m water column to about 2.0 m water column. When
the mixing operation has been initiated, the annular passages in
the riser pipe are also opened again.
According to a further development of the invention, in the conical
lower portion of the mixing container having gas supply chambers at
the bottom end, at least one additional gas supply pipe is
provided, which opens into the conical mixer bottom at or near the
height of the inlet end of the riser pipe.
At the commencement of the mixing operation, the mixing gas can now
initially be introduced into the mixing container from the gas
supply pipe at the higher position. By this means, the product in
the riser pipe is loosened. Thereafter, the gas supply at the
bottom of the conical mixing container is gradually opened and the
upper gas supply is continuously closed to the same extent. It is
still only necessary to loosen the plug of product beneath the
riser pipe by the mixing gas which is now flowing in from the
bottom of the container. Due to the initially relatively long plug
of product inside and outside the riser pipe being loosened in
stages, a reduction of the starting pressure is to be obtained, in
a similar manner as when closing the annular passages in the riser
pipe at the start of the mixing operation.
During the operation of the mixing container, in one embodiment, a
filling level is maintained in the container according to the
invention above the level of the upper end of the annular passage
such that the pressure of the material in the bed in the container
exceeds the mixing gas pressure in the region of the annular
passage and material enters by way of the annular passage into the
riser pipe is mixed with the material introduced at the bottom end
of the riser pipe.
This method can always be carried out when, after the introduction
of the product to the mixing container, the level of product
outside the riser pipe is higher than the upper opening of the
annular passage.
In the case where the filling level in the mixing container is kept
below the annular passage, another method is proposed for the
operation of the mixing apparatus.
The gas introduced at the bottom outlet initially lifts, as before,
the material into the riser pipe. A part of the gas transported
into the riser pipe is caused to overflow through the annular
passage, while periodically another part of the material is lifted
into the upper section of the riser pipe, and after reaching a
certain height, this collapses to form a plug of material and is
mixed together with the material transported from the bottom of the
container through the lower riser pipe section and is carried away
through the annular passage.
Thus, the invention provides apparatus suitable for pneumatically
mixing materials in finely divided form. The apparatus includes a
vertically extending container having an inlet opening adjacent its
upper end for introduction of finely divided materials, and an
outlet means in the lower end outfitted with means for selectively
closing the outlet, for withdrawal of mixed materials. The
vertically extending riser is disposed in the container above and
spaced from the outlet opening, and the riser comprises an upper
section and a lower section. The two sections are in overlapping,
radially spaced relation, defining an annular passage therebetween.
The upper section terminates above the lower section and the lower
section has its lower end at least as low as the lower end of the
upper section. Means are provided for supplying gas for the mixing,
to the container below the lower end of the riser for passage of
the gas into the container and pneumatic lifting and mixing of the
gas and materials in the riser with the materials filling the
container to above the lower end of the riser.
Desirably, the means for supplying gas for the mixing comprises two
vertically spaced gas inlet conduits outfitted with valve means for
selectively apportioning the flow of gas between the two
conduits.
A baffle can be disposed above and spaced from the upper end of the
riser for intercepting the mixture of gas and particles issuing
from the riser, and separating the particles from the gas. A gas
outlet can be disposed above the baffle for discharge of the gas
from the container after the separation by the baffle.
In a preferred construction of the riser, the lower section
diverges upwardly. Further, in a preferred embodiment, the lower
end of the lower section of the riser, terminates below the lower
end of the upper section thereof. Also, as mentioned previously,
means can be provided for adjusting the flow area of the annular
passage, and, desirably, for selectively closing the annular
passage.
One embodiment is hereinafter described by way of example and by
reference to drawings, wherein:
FIG. 1 is a section through the complete mising apparatus, and
FIG. 2 is a section through one embodiment of the riser pipe.
The mixer which is illustrated in FIG. 1 consists of a cylindrical
container 1 having a conical bottom 2 and a removable cover 3. A
riser pipe, which consists of a conical lower section 4, which
diverges upwardly, and a cylindrical upper section 5, is fixed by
stay members 7 a and 7b in the container 1. The two sections of the
riser pipe are fitted one within the other, leaving an annular
passage 6. In order to center the upper section 5 of the riser pipe
in conically widened lower section 6, the upper section 5 is
provided with spacer plates 9 welded radially thereon.
Flanged on the conical mixer bottom 2, which terminates in a
cylindrical end section 10, is a gas supply chamber 11, said
chamber having a conical bottom 12 which serves simultaneously as
the outlet for the product and on which is arranged a bucket wheel
lock chamber or star valve 13 serving as closure member. The mixing
gas delivered by a compressor (not shown) may at will be supplied
to the mixing container through pipe conduit 14 by way of the gas
supply chamber 11 or through the pipe conduit 15 by way of an
opening in the conical mixer bottom 2 and covered by a screen 16.
The pipe conduits 14 and 15 can both be closed by means of shut-off
valves 17.
Fixed on the radial guide plates 18 in the exhaust gas pipe 19 of
the cover 3 of the mixer is the baffle or shielding cone 20 with
the rod 21.
The mixing container is filled through a feed pipe 22 opening
tangentially into the container, said pipe 22 being subsequently
closed by the flap valve 23. The mixing gas is initially supplied
through the pipe 15. At this time, the pipe 14 is closed by the
flap valve 17. Since the level of the product in the mixing
container 1 after the container has been filled is higher than the
level in the riser pipe, the gas chooses the path of lower
resistance through the riser pipe and loosens the product which is
disposed therein. The pipe 14 can now be opened and the pipe 15 can
be closed to the same degree. The mixing gas now enters through the
gas supply chamber 11 and through the cylindrical end member 10 of
the conical mixer bottom 2 into the riser pipe 4 and 5 and thus
carries in a vertically upward direction through the riser pipe the
product which is disposed beneath the lower riser pipe section 4.
The product is then centrifuged radially outwards from the riser
pipe. The mixing gas is discharged through the pipe 19. To the same
extent as product is withdrawn from the bottom of the mixer into
riser pipe, other product slips downwardly from the annular chamber
between the riser pipe and the mixer wall 1. Some of the bulk
material descends through the annular passage 6 into the riser pipe
and is homogenised therein with the product coming from the bottom
of the mixer. The mixing process as described here can however only
be carried into effect when the level of the product in the mixing
container is higher than the upper end of the lower section 4 of
the riser pipe.
If such a small quantity of product is introduced into the mixing
container that the upper end of the lower riser pipe section 4
projects above the level of the product, then as the mixer is
operating, some of the product is discharged with the mixing gas
through the annular passage 6 into the mixing container.
Furthermore, product is also initially raised in the upper section
of the riser pipe 5. As a result, a point is reached at which the
pressure necessary for discharging the product from the upper
section of the riser pipe is higher than that which is necessary
for carrying the product through the annular chamber 6. All the
mixing gas now flows through the annular chamber 6, while the
product still loosened in the upper section 5 of the riser pipe
collapses, with formation of a plug of material. This plug then
slowly slips downwardly and becomes admixed with the product
transported from the bottom of the mixer through the lower riser
pipe section 4. If the plug of material is carried away in this
manner, once again the same pressure conditions prevail as those
which existed on starting up the mixer. The formation of the plug
of product in the upper riser pipe section 5 and the discharge
thereof is thus a process which is periodically repeated throughout
the entire mixing period.
In the constructional form according to FIG. 2, the upper section 5
of the riser pipe is provided with a rubber or synthetic plastic
tube 24 concentrically surrounding the said section. This rubber
tube can be inflated by means of compressed air supplied through
the pipe 25. As a consequence, it is applied to the wall of the
lower riser pipe section 4 and seals off the annular passage 6. In
the Figure, the tube is shown in the inflated state.
If the annular gap 6 of the riser pipe is sealed off before the
product is introduced into the mixing container, then also no
product can fall into the riser pipe during the filling operation.
In this way it is possible considerably to reduce the gas pressure
necessary for starting the mixer. After having been started, the
annular gap is once again opened by reducing the pressure of the
gas which is in the tube 24.
EXAMPLE
A mixer as is shown in the drawing having an overall height 10
meters, and a straight cylindrical section of 7.8 meters in length
and 2.5 meters in inside diameter, is outfitted with a riser as is
shown in FIG. 1, disposed coaxially in the container with respect
to the cylindrical section. The lower end of the riser lower
section is located about 0.4 meters above the outlet 10, and about
0.2 meters above the inlet 16 of conduit 15. The riser lower
section is 440 cm in length, 50 cm in diameter at its lower end and
80 cm in diameter at its upper end. The riser upper section is 550
cm in length and 50 cm in diameter. The over lap of the riser
section is 300 cm. The mixer can be filled to about the level
indicated in the drawing with polyester granulate of particle size
of 3 mm and glass fibers of 0.3 mm diameter and a length of about 5
mm, in the weight proportion of 80 : 20. Using only conduit 15 for
start up, the pressure necessary for starting is 1000 mm of water;
after start up, using conduit 14, the running pressure is also
about 2000 mm of water. Thorough mixing of the batch is completed
in about 60 minutes. Star valve 13 can be operated to empty the
container. In batch operation, the first runnings discharged by the
star valve will not be well mixed and can be saved for use in a
later mixing operation. The equipment can be operated
continuously.
* * * * *