Note: Descriptions are shown in the official language in which they were submitted.
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Separator For Separating Tobacco Particles
From A Tobacco/Gas Mixture
BACKGROUND OF THE INVENTION
1. Field of the invention
The invention relates to a separator for separating tobacco particles
from a tobacco/gas mixture comprising a hood, a circular deflection space
arranged in the hood, an inlet for the tobacco/gas mixture to be sepa-
rated opening tangentially into the circular deflection space, a down-
wardly directed outlet in the deflection space for the tobacco particles,
an outlet for the tobacco particles at the lower end of the hood, and an
outlet for the gas above the deflection spaceO
In the course of tobacco processing, in particular, however, in the
treatment of expanded tobacco the production of which is apparent for
o~
example from US patent appl~cat~on-~M~ 3~, the tobacco particles
must be separated from the produced tobaccotgas mixture. In particular
for the expansion of tobacco steam or vapour is often used, and conse-
quently hereinafter the term "gas" is intended to cover vaporous media as
well.
The basic principles of particle separation by mass forces will be found,
for example, in "Ullmanns Enzyklopaedie der Technischen Chemie'', 4th edi-
tion, volume 2, Process Technology I. Such "separators" have also al-
ready been used in the tobacco industry. Thus, German Offenlegungsschrift
3,619,816 discloses an apparatus for expanding tobacco which includes,
apart from a cyclone dust separator, a separator having a mesh screen.
The mesh screen permits the passage of the steam/air mixture to an outlet
tube which supplies it to the cycle again, whilst the tobacco particles
are led downwardly to an air lock.
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EuroDean patent application No. 29,588 discloses a method for heating
tobacco impregnated with an expansion agent in which the expanded to-
bacco-containing gas is separated from the tobacco particles by means of
a tangential separator.
A separator as acknowledged above for separating dust particles from a
gas is disclosed in German patent sDecification 639,871. In this case to
the inlet an annular passage is connected from the bottom of which se-
veral passages lead downwardly in helical windings turning in the same
direction as the crude gas supply conduit and terminating with gradual
translation at the chamber wall into a chamber disposed beneath the
annular passage; the radius of curvature of these Dassages is smaller
than the radius of the hood.
This is thus an embodiment of a centrifugal force separator in which the
mixture streams must be conveyed with relatively high speed to obtain the
desired separation caused by the change of movement on passing through
the curved passages.
A disadvantage here is the relatively great constructural requirements
needed for the apparatus for the necessary high transport speed both in
the inlet and in the deflection space and finally in the hood, more-
over, for satisfactory operation of this separator it is absolutely
essential for all areas coming into contact with the dust/gas mixture, in
particular the helically curved passages, to be kept carefully clean be-
cause dew sitions on the walls thereof, in particular encrusted par-
ticles, immediately lead to impairment of the separation efficiency.
Finally, the lower end of the hood must be kept closed, for example, by a
rotary vane lock to ensure the necessary high conveying speeds. There
are, however, many used where the operation can or must be carried out
with an oPen outlet.
SUMMARY OF THE INVENTION
The invention is therefore based on the object of providing a separatorof the type indicated in which the aforementioned disadvantages do not
occur.
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In particular, a separator is to be proposed which in constructionally
simple manner permits the satisfactory separation of gas/tobacco
particles with relatively small conveying speeds~
This is achieved according to the invention by a separator comprising ahood, a circular deflection space arranged in the hood, an inlet for the
tobacco/gas mixture to be separated opening tangentially into the
circular deflection space, a downwardly directed outlet in the deflection
space for the tobacco particles, an outlet for the tobacco particles at
the lower end of the hood, and an outlet for the gas above the deflection
space, in which the deflection space is formed by an upwardly closed and
downwardly open cylinder, wherein the gas is withdrawn from the hood
above the deflection spacej wherein the size ratio of the area (A2) of
the deflection space to the area (Al) of the inlet is between 5 and 30,
and wherein the size ratio of the area (A3) of the hood to the area
(Al) of the inlet is greater than 50.
Expedient embodiments will be apparent from the features of the sub-
sidiary claims.
The advantages achieved with the invention are based on the specific con-
figuration of a centrifugal force separator whose deflection space is
formed by a simple upwardly closed and downwardly open cylinder which is
disposed in another container, hereinafter referred to as "hood", so that
the gas phase emerging downwardly from the deflection space is withdrawn
upwardly over the entire effective flow cross-section of the hood whilst
the tobacco particles fall freely downwardly out of the deflection space
and out of the hood.
The horizontal flow cross-section of the hood must be made so large that
the vertical flow velocity of the gas phase is always less than the
sinking velocity of the tobacco particles to be separated, i.e. the
overall system must be designed taking account of the maximum gas stream
to be expected on the one hand and the minimum sinking speed of the to-
bacco particles to be expected on the other hand.
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To ensure these conditions the size ratio of the area of the deflectionspace to the area of the inlet must lie in the range of 5 to 30; at the
same time, the size ratio of the area of the hood to the area of the in-
let must be greater than 50, in particular greater than 100.
At the inlet of said separator the usual velocities necessary for pneu-matic transport of the mixture tobacco/gas in the region of about 20 m/s
occur whilst the gas discharge velocity at the upper end of the hood is
in the range of about 0.1 to 0.2 m/s.
The necessary pneumatic transport of the mixture terminates practicallyat the wall of the deflection space because there the tobacco particles
fall freely downwardly under the action of gravity whilst the gas is
withdrawn upwardly from the hood by a suction means disposed above the
deflection sDace.
If the separator is operated so that at the lower end of the hood appro-
ximately ambient pressure prevails the hood can be opened downwardly,
i.e. the separator can be operated without a discharge means prone to
trouble, in particular soiling.
In contrast to conventional separators, i.e. cyclones or tangential se-parators, fluctuating throughput rates of the gas and/or tobacco phase do
not have any appreciable influence on the degree of separation because
with the oPen separator described here only a greater or lesser amount of
secondary air is sucked in upon a change of the throughput rate, i.e. the
vertical flow velocity of the gas phase remains approximately constant.
This makes separation of the tobacco particles from the tobacco/gas mix-
ture possible even without using a rotary vane lock, due to the insensi-
tivity explained of the separator to secondary air. Since in contrast to
cyclones or other conventional tangential seParators the gas phase can be
sucked oFf at the greatest cross-section of the hood, the f}ow is made
uniform and the separator relatively very insensitive to the operating
Parameters .
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If, however, in the overall system an inner excess pressure or reduced
pressure exists, the hood must be closed at the bottom by a discharge
means, generally a rotary vane lock or a discharge screw.
With a closed separator the degree of separation improves with decreas-ing gas phase because in this case the difference between the vertical
flow velocity of the gas phase and the sinking velocity of the tobacco
particles becomes greater.
Even if tobacco/gas mixtures causing considerable soiling are to be pro-
cessed, the degree of separation is only slightly impaired and
consequently no excessive demands need be made on the corresponding
tobacco preparation.
The inevitable encrustations at the inner faces of the inlet, deflection
space and hood also influence the separation efficiency only slightly and
consequently the hitherto usual very careful cleaning need only be
carried out at greater intervals of time.
Furthermore, it is now also possible to separate several tobacco/gas mix-
tures in one separator simply by connecting the various two-phase streams
to be separated with each other.
Because of the low flow velocity occurring in the seParator only a low
pressure loss occurs so that in this respect as well the method can be
carried out with reduced energy consumption.
To achieve a uniform flow velocity over the hood cross-section as
necessary for homogeneous separation of the tobacco particles, in the
upDer region of the hood a flow resistor is arranged which as a rule con-
sists of a perforated metal sheet with holes distributed over the sheet
surface.
To prevent tobacco particles from being entrained into the extraction
conduit for the gas a sieve or filter may be arranged beneath the flow
resistor; it is alternatively possible to construct the flow resistor
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itself as sieve or filter.
To facilitate cleaning of the separator an opening closeable by a door
may be provided in the hood and/or the deflection space permitting access
to the interior of the hood or of the deflection space.
If the gas phase contains steam or vapour or other condensing components
then in a preferred embodiment the wall of the hood is provided with a
heating means to prevent condensation and resulting soiling of the walls.
Finally, it is also possible to arrange a plurality of deflection spaces
adjacent each other in a hood and thereby connect a plurality of to-
bacco/gas mixture to be separated with each other, one gas and one to-
bacco particle stream being produced in each case.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in detail hereinafter with reference toexamples of embodiment with the aid of the attached schematic drawings,
wherein:
Fig. 1 is a vertical section through a first embodiment of a
separator,
Fig. 2 is a horizontal section through the separator according
to Fig. 1,
Fig. 3 is a vertical section through another embodiment of the
separator,
Fig. 4 is a vertical section through a further embodiment of
the separator,
Fig. 5a is a vertical section and a plan view of a modification
of the deflection space,
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Fig. 5b is a vertical section and a plan view of a further
modification of the deflection space,
Fig. 5c is a vertical section and a plan view of a further modi-
fication of the deflection space,
Fig. 6 is a vertical section through a separator having two
deflection spaces parallel to each other,
Fig. 7 is a horizontal section through the separator according
to Fig. 6, and
Fig. 8 is a vertical section through an embodiment of the se-
parator with indication of the dimensions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The separator shown in Figures 1 and 2 and denoted generally by the re-ference numeral 10 comprises a vertically arranged downFwardly open hood
12 which has a regular cross-section; as apparent from ~ 2 this
cross-section has a generally rectangular, in particular square, form or
alternatively a circular form as indicated by the dot-dash lines. The
door 24 serves to facilitate inspection and cleaning of the separator 10.
At its upper end hood of the separator 10 is provided with an outlet
hopper 14 having a discharge opening 16 which has a smaller cross-section
than the hood 12. Connected to the outlet opening 16 is a fan (not
shown).
Disposed in the hood 12 is a vertically arranged downwardly open circuit
deflection space 20 to which via a transport conduit 22, generally a
transport pipe, the two-phase mixture to be separated is supplied, that
is, the tobacco/gas mixture. The transport direction is indicated by the
large arrow whilst the flows of the two phases of the tobacco/gas mix-
ture in the conduit 12 are indicated by the two different arrows.
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In this context "circular" means curved and for example, but not ne-
cessarily, round.
The transport conduit 22 opens tangentially into the deflection space 20
which has circular cross-section and as a rule is formed as vertically
disposed cylinder closed at the top and open at the bottom.
The tobacco/gas mixture arriving from the conduit 22 contacts the innerwall of the deflection space 20 tangentially and is guided along a he-
lical path along the inner wall of the deflection space 20 with simul-
taneous retardation to the lower opening of the deflection space 20.
On discharge downwardly out of the deflection space 20 the tobacco
particles fall downwardly as indicated by the arrows whilst the lighter
phase, that is the gas, is sucked off upwardly by means of the fan and
emerges from the outlet opening 16 of the hood 12.
To obtain a uniform flow velocity over the cross-section of the hood 12in the upper region of the latter, i.e. somewhat beneath the hopper 14
but above the deflection space 20, a flow resistor 18 is arranged which
consists of a perforated sheet metal with holes distributed uniformly
over its area.
If the tobacco/gas mixture is supplied to the separtor 10 with adequatepressure the hood 12 can be open at the bottom as can be seen in Figure
1, i.e. in this case the separator 10 can be operated without a trouble-
prone, in particular soiling-prone, discharge means for the separated
tobacco particles.
If, however, in the separator or in the overall system an inner excess
pressure or reduced pressure prevails, then the hood 12 must be closed
downwardly by a discharge means. In the embodiment according to Figure 3
this discharge means is formed by a rotary vane lock 28 which is dis-
posed in the outlet opening in the funnel-shaped lower region 26 of the
hood 12.
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The embodiment of Figure 3 also differs from the embodiment according to
Figures 1 and 2 in an additionally provided screen or sieve 30; said
sieve 30 is disposed in the hood 12 between the deflection space 20 and
the flow resistor 18 and Dreventsentraining of tobacco Darticles into the
extraction conduit connected to the outlet 16.
The horizontal flow cross-section of the hood 12 must be made large
enough to ensure that the vertical flow velocity of the gas phase is
always less than the sinking velocity of the tobacco particles to be
separated, i.e. the separator 10 must be designed taking account of the
greatest gas stream to be expected on the one hand and the smallest
sinking velocity of the tobacco particles to be expeeted on the other.
Figure 4 shows an embodiment of a separator 10 which can be used when the
gas phase consists of steam or vapour or contains condensing components.
In this case the walls of the hood 12 should be provided with a heating
means to prevent condensation and the resulting contamination of the
walls. The heating means is indicated in the wall of the hood 12 by the
zig-zag line.
At the uoper end of the hood 12 the gas Phase consisting of steam or va-
pour or containing condensing components is withdrawn according to the
illustration in Figure 4 to the left and supolied to an exit connecting
piece 32 which is inclined somewhat downwardly in the discharge direction
with respect to the horizontal so that the condensate forming there
collects at the bottom of the exit connecting piece 32 and can be with-
drawn via a conduit 34.
At the end of the conduit 34 a separation of this phase into the down-
wardly emerging condensate on the one hand and the gas on the other is
effected.
Otherwise this embodiment has the construction already described and
therefore need not to be described again.
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Figures 5a to 5c show various embodiments of the deflection space. In the
embodiment according to Figure 5a the cylindrical deflection space 20 is
provided with a closed pointed roof 38 so that no tobacco particles or
impurities can deposit on the deflection space.
Finally, Figures 5b and 5c show embodiments of deflection space 20 which
are open at the top. By appropriate adaptation of the dimensions,
pressures and flow velocities it can be ensured that in this case as well
the gas phase and the tobacco par~icles are withdrawn downwardly from the
deflection space 20. Sediments on the deflection space can be largely
avoided by this modification.
Figure 5b shows an embodiment in which the cylindrical deflection space
20 is followed upwardly by a funnel-shaped region 40 which is pro~ided at
its upper end with a cleaning opening so that the interior of the de-
flection space 20 is freely accessible, in particular for cleaning pur-
poses.
Figure 5c shows an embodiment of the deflection space which has inclined
inwardly extending side walls 42 over its entire height and is likewise
provided at its upper end with a cleaning opening 44. This results in a
smooth inner wall of the deflection space 42 so that the depositing of
tobacco particles or soiling can be largely avoided.
Figures 6 and 7 show an embodiment of a separator which differs from the
embodiments discussed so far in that in the hood 12 two deflection spaces
20 are arranged horizontally adjacent to each other. Each deflection
space 20 is provided with an associated transport conduit 22 for the
supply of the tobacco/gas mixture.
In this manner two separate mixture streams can be processed simultane-
QUSly, one gas stream and one tobacco stream being generated.
Due to the size of the dischargeing transDort systems it may be expe-
dient to taper the hood 12 downwardly as shown in Fig. 6.
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Finally, Figure 8 shows an embodiment of the separator 10 corresp/onding
to Figure 1 and 2 but with a deflection space 20 corresponding to~
5b.
In this Figure the dimensions and the operating conditions implemented in
a production plant have been entered~
1500 kg tobacco per hour was processed with a gas or vapour mass flow of
100 kg/hour. The inlet velocity of the tobacco/gas mixture was of the
order of magnitude necessary for the pneumatic transport at about 20 m/s.
The velocity of the upwardly withdrawn gas was between 0.1 and 0.2 m/s,for which Purpose a reduced pressure of 5 mbar was maintained in the
upper funnel-shaped end region of the hood 12.
The tobacco particles dropped out of the lower open end of the hood 12,maintained at ambient pressure Pu~
The inlet 22 for the tobacco/gas mixture had an area with the size A1 =0.008 m ; the deflection space 20 formed by a cylinder had an area with
the size A~ = 0.1 m2; finally the hood 12 had an area with the size
A3 = 1.4 m .
To achieve the desired gravity separation values other than the latter
may be adopted; however, certain limit values for the area ratios must be
observed, i.e.
5 -~ A2 / A1 ~ 30 and
A3 / A1 2 50
Particularly good results are achieved when the ratio A2 / A1 lies
between 10 and 20 and the ratio A3 / A1 is greater than 100 but less
than 200.
