Note: Descriptions are shown in the official language in which they were submitted.
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Distributing device for a fluidizable conveyed material
The invention relates to a distributing device for
distributing a fluidizable conveyed material from a
starting container to a plurality of destination
containers. The distributing device comprises a
conveying pipe having an intake opening for the
conveyed material and a plurality of discharge openings
for the conveyed material. In the conveying pipe there
are arranged pass-through surfaces, through Which a
fluidizing gas stream is introduced into the conveying
pipe.
Distributing devices of this type can be used, for
example, in the production of aluminium. The alumina
which is necessary for the aluminium production must be
fed from a central storage container to the individual
electrolytic cells. According to the size of the
production plant, the alumina supply system is divided
into several levels, the destination containers of the
higher levels respectively forming the starting
containers of the following level. The distributing
device according to the invention is particularly
suitable for the last level, at which the alumina is
distributed from an intermediate container to the
receiving containers of the electrolytic cells.
A distributing device of this type is known, in which
the fluidized conveyed material moves along the
conveying pipe under the influence of gravity, WO
02/074670 Al. A drawback of this distributing device
consists in the fact that the conveying pipe must have
a constant gradient over the whole of its length. In
many cases there are, however, spatial pre-
specifications for the course of the conveying pipe,
which make it difficult to meet the need for a constant
gradient. This applies, in particular, where existing
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plants are to be retrofitted with a new distributing
device.
So-called pneumatic distributing devices are also known.
In these distributing devices, the conveying pipe has a
propellant gas stream passed through it, which is
sufficiently fast that the conveyed material in the
conveying pipe is taken up and entrained by the gas
stream. In order for the conveyed material to be entrained
by the propellant gas stream, the velocity of the
propellant gas velocity must be at least 6 m/s to 7 m/s.
Although such a distributing device is versatile in its
use and it is possible to transport the conveyed material
counter to the force of gravity, the energy consumption is
very high.
The object of the invention is to provide a distributing
device of the type stated in the introduction, which has
low energy consumption and is versatile in its use.
According to this, the distributing device comprises a
propellant gas feed for generating a propellant gas stream
along the direction of conveyance of the conveying pipe.
In one aspect, the invention provides a distributing
device for distributing a fluidizable conveyed material
from a starting container to a plurality of destination
containers, comprising a conveying pipe having an intake
opening for the conveyed material and a plurality of
discharge openings for the conveyed material, and
comprising pass-through surfaces, arranged in the
conveying pipe, for a fluidizing gas stream, wherein a
propellant gas feed is provided, for generating a
propellant gas stream along the direction of conveyance of
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the conveying pipe and wherein the propellant gas quantity
supplied by the propellant gas feed is dimensioned such
that the propellant gas stream through the conveying pipe
has a velocity between 0.5 m/s and 1.5 m/s.
In one embodiment, the fluidizing gas stream and the
propellant gas stream are dimensioned such that a
transport of conveyed material remnants out of the
conveying pipe is possible. In one embodiment, the
discharge openings are arranged on the floor of the
conveying pipe. In one embodiment, the cross-sectional
area of at least one discharge opening is no more than 20%
smaller than the cross-sectional area of the conveying
pipe. In one embodiment, the cross-sectional area of at
least one discharge opening is no more than 10% smaller
than the cross-sectional area of the conveying pipe. In
one embodiment, the cross-sectional area of at least one
discharge opening is no more than 5% smaller than the
cross-sectional area of the conveying pipe. In one
embodiment, the conveying pipe has a portion which rises
in the direction of conveyance. In one embodiment, the
device may comprise destination containers, and wherein a
second destination container is arranged behind a first
destination container in the direction of conveyance of
the conveying pipe, and wherein the second destination
container is arranged higher than the first destination
container. In one embodiment, the destination containers
are sealingly connected to the conveying pipe. In one
embodiment, the device may comprise a starting container,
and wherein the starting container is arranged above the
intake opening. In one embodiment, the intake opening is
freely traversable for conveyed material from the starting
container. In one embodiment, in front of the intake
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opening, conveyed material is arranged in such a way that
the intake opening is sealed off. In one embodiment, a
connecting pipe is arranged between the starting container
and the intake opening.
In one embodiment, the connecting pipe has a length
between 0.8 m and 3 m. In one embodiment, the connecting
pipe has a length between 1.3 m and 2 m. In one
embodiment, the pass-through surfaces are flat. In one
embodiment, the propellant gas quantity supplied by the
propellant gas feed is dimensioned such that the
propellant gas stream through the conveying pipe has a
velocity between 0.7 m/s and 1.0 m/s. In one embodiment,
the specific fluidizing gas stream related to the pass-
through surface ranges between 0.8 m3/(m2.min) and 1.8
m3/(m2-min). In one embodiment, the specific fluidizing
gas stream related to the pass-through surface ranges
between 1.3 m3/ (m2.min) and 1.6 m3/(m2-min).
To begin with, a few terms are explained. By fluidization
is meant a process by which a material existing in
granular form is transformed into a state in which it
behaves similar to a liquid. In the original state, the
particles of the granular material lie one on top of the
other under the influence of gravity. The friction between
the particles is so great that a considerable force is
necessary to move them relative to one another. For the
fluidization, a gas stream is passed from below through
the granular material, so that the gas stream counters the
influence of gravity upon the particles. Given a suitably
chosen fluidizing gas stream, the friction between the
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particles is so small that the granular material
assumes the properties of a liquid. The granular
material thus has the property, for example, of flowing
along a gradient.
As fluidizable is termed any material which can be
transformed into this state by a suitable fluidizing
gas stream.
The pass-through surfaces arranged in the conveying
pipe have the function of introducing the fluidizing
gas stream into the conveyed material such that the
conveyed material assumes the fluidized state. The
pass-through surfaces are thus arranged beneath the
conveyed material, so that the fluidizing gas stream
can act on the conveyed material over a large area.
The conveyed material can be distributed from a
starting container to a large number of destination
containers. Plants are possible in which several
hundred destination containers are assigned to one
starting container. The destination containers, for
their part, can in turn be starting containers for a
subordinate distributing device. In this way, several
levels of distributing devices can be arranged
hierarchically one behind the other.
According to the invention, a propellant gas feed is
provided, which is designed to generate a propellant
gas stream along the direction of conveyance of the
conveying pipe. The propellant gas feed is preferably
arranged at the start of the conveying pipe, i.e. in
front of the intake opening. The generated propellant
gas stream is of such a size that the fluidized
conveyed material moves through the conveying pipe in
the direction of conveyance. At the end of the
conveying pipe, i.e. behind the last discharge opening
in the direction of conveyance, a waste air device can
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be arranged, through which the propellant gas stream
can be evacuated.
When the propellant gas stream enters into the
fluidized conveyed material, the propellant gas stream
mixes with the fluidizing gas stream. The fluidizing
gas stream is deflected in the direction of conveyance,
so that the propellant gas stream together with the
fluidizing gas stream, as a combined gas stream,
support the transport of the conveyed material along
the conveying pipe.
The fact that the fluidized conveyed material is moved
by the propellant gas stream or the combined gas stream
in the direction of conveyance means that the
distributing device according to the invention is
independent of gravity. There is thus a greater freedom
of choice with regard to the conveying track. The
propellant gas stream has merely to be dimensioned such
that the fluidized conveyed material, which is
subjected to low internal friction, is conveyed. Even
though the conveying pipe is fed, apart from the
propellant gas stream, also a fluidizing gas stream,
the gas consumption is considerably less than with a
purely pneumatic distributing device.
Since the distributing device is independent of
gravity, the conveyed material can also be transported
when only a small amount of conveyed material is
present in the conveying pipe. It is also possible to
transport remnants of conveyed material out of the
conveying pipe. The propellant gas stream can be used
to clean the conveying pipe. According to the
invention, this is possible, in particular, even in the
case of horizontal and rising arrangement of the
conveying pipe.
Since the propellant gas stream and the combined gas
stream are forced along the conveying pipe, it is
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possible to deflect the small-radius conveying pipe
without the transport thereby being stopped. A conveyed
material which is moved solely under the influence of
gravity stalls at deflections of this type. The
distributing device according to the invention thus
allows the path of conveyance to be designed more
freely.
It has been shown that a transport of the conveyed
material along the conveying pipe is also possible when
the pass-through surfaces do not extend over the whole
of the length of the conveying pipe. AS a result of the
interaction of the fluidizing gas stream with the
propellant gas stream, the transport is instead
maintained, even when the conveying pipe has portions
in which no fluidizing gas is supplied. Within the
scope of the invention, it is therefore possible to
arrange the discharge openings in the floor of the
conveying pipe. Preferably, the discharge openings are
arranged in those portions of the conveying pipe in
which no pass-through surfaces are arranged. It has
been shown that the combined gas stream of fluidizing
gas and carrier gas transports the conveyed material
such that a part of the conveyed material falls
downwards through the discharge opening, whilst a part
of the conveyed material is transported over the
discharge opening along the conveying pipe. The fact
that at each discharge opening a part of the conveyed
material falls downwards, whilst a part is transported
onward along the conveying pipe, results in the
destination containers filling with conveyed material
at different rates. The destination containers arranged
at the start of the conveying pipe are filled earlier
than the destination containers arranged at the end of
the conveying pipe. This can be countered, for example,
by the discharge openings having different cross
sections or by the discharge openings being provided
with valves, Generally, however, the different filling
speed of the destination containers is tolerated. Once
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the first destination container is fully filled, no
conveyed material can any longer fall into this
destination container and the whole of the conveyed
material is transported over this discharge opening
along the conveying pipe. The distributing device is
operated until such time as the last destination
container is filled, and is then stopped. In order to
determine the time to stop the distributing device, a
fill level sensor can be provided for indicating the
fill state of the last destination container. It is
likewise possible to arrange fill level sensors in all
destination containers.
That a part of the conveyed material falls through the
discharge openings, whilst a part is transported over
the discharge opening, applies even if the discharge
opening extends over the entire width or almost the
entire width of the conveying pipe. The discharge
opening can thus have a cross section of the same size
or almost the same size as the conveying pipe. It is
considered advantageous if the cross-sectional area of
the discharge opening is no more than 20%, preferably
no more than 10%, further preferably no more than 5%
smaller than the cross-sectional area of the conveying
pipe,
Since the transport mechanism is independent of
gravity, the conveying pipe can be configured such that
it has a portion which rises in the direction of
conveyance. The rise can be inclined by 100, preferably
by 200, further preferably by 300, in relation to the
horizontal.
The distributing device according to the invention can
be constituted such that it comprises the destination
containers in which the conveyed material discharged
through the discharge openings is collected. If the
conveying pipe has a rise, then a second destination
container situated further to the rear in the direction
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of conveyance Can be arranged higher than a destination
container situated further forward. Between the first
and the second destination container, the conveyed
material is conveyed counter to gravity. If the
destination containers are arranged beneath the
discharge openings, the conveyed material collects in
the destination containers purely under the influence
of gravity.
For an effective transport of the conveyed material, it
must be ensured that the propellant gas stream and the
combined gas stream move along the track predefined by
the conveying pipe. The gas stream should not be able
en route to escape from the conveying pipe. The
destination containers are therefore preferably
sealingly connected to the conveying pipe, so that an
escape of the gas stream through the destination
containers is not possible.
Furthermore, the starting container can also be
regarded as a component part of the distributing
device. The starting container is preferably arranged
above the intake opening of the conveying pipe, so that
the conveyed material moves into the conveying pipe
purely under the influence of gravity. It is possible
that, at the transition from the starting container to
the intake opening, a lock chamber is provided.
Firstly, the lock chamber can ensure that the gas
stream cannot escape from the conveying pipe out
through the intake opening and the starting container.
Secondly, the lock chamber can ensure that only
measured-off quantities of conveyed material can enter
into the conveying pipe.
Such a lock chamber is not, however, necessary; it is
instead possible within the scope of the invention for
the transition from the starting container through the
intake opening into the conveying pipe to be freely
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traversable for the conveyed material. Such quantity of
conveyed material then passes out of the starting
container into the conveying pipe that the conveying
pipe, in the region below the intake opening, is filled
with the conveyed material. The conveyed material is
fluidized by the fluidizing gas stream and carried away
from the region below the intake opening by the
propellant gas stream. A freely traversable opening is
advantageous, because the conveying pipe is then free
from mechanically moved components,
Through a freely traversable opening, a gas stream can
also, in principle, escape, A resistance is offered
against the gas stream, however, by the fact that it
must penetrate the conveyed material arranged in front
of the intake opening, This resistance is the greater,
the longer the path is through the conveyed material
and the smaller the area is over which the gas stream
can be distributed within the conveyed material.
Preferably, so much conveyed material is arranged in
front of the intake opening that the intake opening is
sealed off. An, in this sense, adequate seal is
proclaimed if only a small part of less than 10% of the
gas stream in the conveying pipe is able to escape
through the intake opening.
The starting container can be arranged in the immediate
vicinity of the intake opening. The sealing of the gas
stream is then taken care of by the conveyed material.
It is advantageous it a connecting pipe filled with
conveyed material is arranged between the starting
Container and the intake opening. The connecting pipe
has a smaller cross-sectional area than the starting
container, so that a greater resistance is offered
against the gas stream. The connecting pipe can have
the same cross-sectional area as the conveying pipe.
For an effective seal, the connecting pipe has a length
between 0.8 m and 3 m, preferably between 1.3 m and 2
m.
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A transport of the conveyed material along the
conveying pipe only takes place when a pressure
difference exists between the start of the conveying
pipe and the end of the conveying pipe. It is desirable
to operate the distributing device with a smallest
possible pressure difference. The sealing of the
starting container and of the destination containers
enables the distributing device to be operated with a
pressure difference between the start of the conveying
pipe and the end of the conveying pipe of no more than
0.2 bar, preferably no more than 0,1 bar.
The cross section of the conveying pipe can have an
optional shape, for example square or rectangular. In a
preferred embodiment, the conveying pipe is round in
cross section. The pass-through surfaces are arranged
in the lower half of the pipe such that they divide the
pipe into two segments in cross section. Through the
lower segment, the fluidizing gas is introduced into
the conveying pipe and distributed amongst the pass-
through surfaces. The fluidizing gas can enter over a
large area through the pass-through openings into the
upper segment of the conveying pipe and can fluidize
the conveyed material in this segment. The conveyed
material is transported through the upper segment along
the conveying pipe.
The pass-through surfaces separating the two segments
can be of flat configuration, which promotes the even
distribution of the fluidizing gas. Furthermore, the
pass-through surfaces are configured such that they
offer as little resistance as possible to the
fluidizing gas, but such that the conveyed material can
nevertheless not fall through the pass-through
surfaces.
Since, in the distributing device according to the
invention, the fluidizing gas moves together with the
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conveyed material through the conveying pipe, the
diameter of the conveying pipe can be smaller than in
known distributing devices. In these, it is namely
always assumed that, above the space necessary for the
conveyed material, further space must be present,
through which the fluidizing gas can be evacuated.
In an advantageous embodiment, the propellant gas feed
is designed such that the propellant gas stream through
the conveying pipe has a velocity between 0.5 m/s and
1,5 m/s, preferably a velocity between 0.7 m/s and 1.0
m/s. The data regarding the propellant gas stream
relate to that portion of the conveying pipe in which
the propellant gas is not yet mixed with the fluidizing
gas, The conveyed material moves through the conveying
pipe with a velocity which is slightly less than the
velocity of the propellant gas stream. At this
propellant gas velocity, up to 12 t/h of conveyed
material can be transported in a conveying pipe of 10
cm diameter.
The fluidizing gas stream which is necessary to
fluidize the conveyed material is generally quoted as
the specific fluidizing gas stream related to the pass-
through surface. Within the scope of the invention,
this fluidizing gas stream can range between 0.8
m3/(m2.min) and 1.8 m3/(m2,mia), preferably between 1.3
m3/(m2.min) and 1.6 ml/(m2.min). The propellant gas
quantity fed to the conveying pipe is independent of
the actual length of the conveying pipe. The fluidizing
gas quantity, by contrast, becomes larger the greater
the length of the conveying pipe, since in a longer
conveying pipe more pass-through surfaces are
necessary.
The invention is described below, by way of example, on
the basis of an advantageous embodiment with reference
to the appended drawings, wherein!
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Fig. 1: shows a schematic representation of a
distributing device according to the
invention;
Fig, 2: shows a cross section through Fig, 1 along
the line A-A;
Fig, 3: shows an enlarged detail from Fig, 1.
An inventive distributing device in Fig. 1 is designed
to distribute a conveyed material from a starting
container 1 to a plurality of destination containers
21, 22, 23, 24. In the illustrative embodiment, only
four destination containers 21, 22, 23, 24 are shown,
whereas in real distributing devices several hundred
destination containers can be present. The connection
between the starting container 1 and the destination
containers 21, 22, 23, 24 creates a conveying pipe 3.
The conveying pipe 3 is made up of a plurality of pipe
segments 31, 32, 33, 341 35. The conveying pipe 3
additionally comprises discharge openings 41, 42, 43,
44 arranged in T-pieces, each discharge opening 41, 42,
43, 44 being arranged above a destination container 21,
22, 23, 24. Under the influence of gravity, conveyed
material can fall out of the conveying pipe 3 through
the discharge openings 41, 42, 43, 44 into the
destination containers 21, 22, 23, 24.
In the lower half of the pipe segments 31, 32, 33, 34,
35, pass-through openings 51, 52, 53, 54, 55 are
arranged, In the region of the discharge openings 41,
42, 43, 44, the conveying pipe 3 is free from pass-
through surfaces 51, 52, 53, 54, 55. As Fig. 2 shows
from the example of the pass-through surface 51, the
pass-through surfaces 51, 52, 53, 54, 55 divide the
pipe 3 into an upper segment 61 and a lower segment 62.
To the lower segment 62, fluidizing gas is fed through
a line 7. The fluidizing gas is distributed in the pipe
segment 62 below the pass-through surface 51 and
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generates a fluidizing gas stream, which enters through
the pass-through surface 51 into the pipe segment 61.
Conveyed material present in the pipe segment 61 and
resting on the pass-through surface 51 is fluidized by
the fluidizing gas stream, which acts from below.
At the start of the conveying pipe 3, a propellant gas
feed 8 is arranged, by which a propellant gas stream is
generated along the direction of conveyance of the
conveying pipe 3. The transport of the fluidized
conveyed material is set in train by the propellant gas
stream and the fluidizing gas stream is deflected, so
that the conveyed material is transported by a combined
gas stream along the conveying pipe 3. A part of the
conveyed material falls through the discharge openings
41, 42, 43, 44 into the destination containers 21, 22,
23, 24, whilst a part of the conveyed material passes
over the discharge openings 41, 42, 43, 44. The
destination containers arranged at the start of the
conveying pipe 3 thereby fill faster than the
destination containers arranged at the end of the
conveying pipe 3. Once all destination containers 21,
22, 23, 24 are filled, the conveyance of the conveyed
material can be suspended, the propellant gas stream
and the fluidizing gas stream can thus be switched off.
The switching on and off of the fluidizing gas stream
and the propellant gas stream is served by valves 9,
10.
In order for the propellant gas stream and the combined
gas stream to effect a transport of the conveyed
material, the gas streams must move along the conveying
pipe 3. In order to prevent the gas streams from being
able to escape from the conveying pipe 3 in another
direction, the destination containers 21, 22, 23, 24
are therefore seal
ingly connected to the discharge
openings 41, 42, 43, 44.
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The starting container 1 is connected by a connecting
pipe 11 to the intake opening 12 of the conveying pipe
3. The connecting pipe 11 and the intake opening 12 are
freely traversable, so that the conveyed material can
fall out of the starting container 1 under the
influence of gravity into the conveying pipe 3. When
the distributing device is out of action, a build-up of
non-fluidized conveyed material 13 forms, as shown in
Fig. 3, in that region of the conveying pipe 3 which is
arranged below the intake opening 12, 8y switching on
the fluidizing gas stream, that part of the conveyed
material which is present in the conveying pipe 3 is
fluidized. The fluidized conveyed material is
transported by the propellant gds stream along the
conveying pipe 3,
The column of conveyed material in the connecting pipe
11 seals off the conveying pipe 3 in the direction of
the starting container 1, The propellant gas stream and
the fluidizing gas stream cannot escape through the
starting container 1, but are forced along the
conveying pipe 3. At the end of the conveying pipe 3,
the combined gas streams of fluidizing gas and
propellant gas are evacuated by a waste air device 13.
The destination containers 21, 22, 23, 24 can, for
their part, be starting containers for destination
containers of a subordinate level. In this way, the
distributing devices can be combined over several
hierarchically arranged levels.
