Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
INSTANTANEOUS SLURRY PREPARATION ON A CONTINUOUS BASIS
This invention generally relates to making sheet from
comminuted tobacco and more particularly to the high speed
preparation on a continuous basis of the slurry therefor.
Up to this time the conventional way to prepare a
shapable tobacco-adhesive slurry has been to combine two
essentially liquid phases; one being a tobacco dispersion
and the other being a baseweb or an adhesive preparation
with additives as may be required. Highly comminuted
tobacco or tobacco powder does not wet very readily and
is further retarded when it is added in a dry state to
a liquid baseweb. To ensure homogeneity of the final
slurry, the vessel of the mixer receiving the two liquid
phases is sufficiently large to provide an extended
residence time.
The extended time that the ground tobacco contacts
the aqueous vehicle has various drawbacks. The extended
time that the tobacco contacts the aqùeous medium pPrmit~
it to swell to its equilibrium state which increases the
yield point of the slurry to be cast, subjects the tobacco
to possible microbiological attac~, and permits total
extraction and interaction of the tobacco solubles which
adversely affects the taste and burn characteristics of
the tobacco sheet. Tobacco dispersions have to be main-
tained at continuous agitation to maintain homogeneity
and this action in combination with the extended holding
time, which is usually in excess of three hours, can
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promote oxidative reactions therein which adversely affect
the taste quality of a tobacco sheet produced therefrom.
Because of the time-dependened swelling character-
istics and resultant yieldpoint of the slurry, more water
needs to be incorporated in the slurry to permit casting
or shaping, thus increasing the energy requirements of
drying. In addition, the complexity of the eo;uipment re-
quired for predispersion of the tobacco and for mixing of
the tobacco dispersion and baseweb result in higher capital
cost and large space and manpower requirements.
Accordingly, an object of the present invention is
to provide means for rapidly preparing on a continuous basis,
a shapable tobacco-adhesive slurry.
Another object of the present invention is to pre-
pare the shapable slurry having a higher solids content than
is available when preparing such a slurry by combining two
or more liquid phases, resulting in lower energy requirements
and higher production rates. Another obje~tive of the pre-
sent invention is to prepare a homogeneous tobacco-adhesive
slurry to be shaped prior to the tobacco arriving at its
equilibrium state.
Still another objective of the present invention
is to provide a cost effective tobacco reconstitution manu-
facturing process characterized by low capital cost and re-
duced space and manpower requirements.
According to the above objects, from a broad aspect,
the present invention provides an apparatus for making a
shapable tobacco/adhesive slurry having a high tobacco solids
content. The apparatus comprises means for continuously pro-
viding a predetermined amount of dry comminuted tobacco.Means is also provided for continuously providing a predeter-
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mined amount of aqueous adhesive proportional to the tobacco
being provided. A high intensity mixing means is provided
and having two inlets, one for receiving tobacco and the
other for receiving adhesives. The high intensity mixing
means has a slurry discharge. Further, the high intensity
mixing means causes a substantially instantaneous homogeneous
slurry of the tobacco and adhesive, and rapidly discharges
the slurry before it arrives at its equilibrium state.
According to a further broad aspect of the present
invention, there is provided a method for making a shapable
tobacco/adhesive slurry having a high tobacco solids content.
The method comprises the steps of: continually providing
proportional amounts of dry comminuted tobacco and aqueous
adhesive to high intensity mixing means, rapidly mixing the
tobacco and adhesive to substantially instantaneously produce
a homogeneous slurry with a high tobacco solids content' and
rapidly discharging the homogeneous slurry from the mixing
means before the slurry arrives at its equilibrium state.
The foregoing and other objects and advanta~es will
appear rnore fully hereinafter from a consideration of
the detailed description which follows, taken together
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with the accompanying drawings wherein several embodiments
of the invention are illustrated by way of example. It is
to be expressly unders~ood, however, that the drawings are
for illustration purposes only and are not to be construed
as defining the limits of the invention.
~ IGURE 1 is a diagrammatic illustration of apparatus
for preparing a slurry in accordance with the present
inventions. FIGURE 2 is a diagrammatic illustration of
apparatus which is a variation of the apparatus of FIGURE
1. FIGURE 3 is an enlarged sectional view o~ the slurry
combining means of FIGURE 1.
FIGURE 4 is an enlarged sectional view of the cover
of the slurry combining means of FIGURE 2.
FIGURE 5 is a sectional view ~aken on line 5-5 of
FIGURE 3.
Referring now to the drawings and particularly to
FIGURE 1, a hopper 10 for comminuted tobacco is provided
with a vibration type feed mechanism 11 which is connected
to a tobacco inlet 22 in the cover 21 of a high intensity
mixing device 20 which will be further discussed. A
reservoir 12 for the baseweb being an adhesive slurry
with any additives desired is provided with pump means
13, which is connected to a second inlet 23 in the
cover 21 of the high intensity mixing device 20.
The drive means for the feed mechanism 11 and the
pump means 13 must be capable of being speed adjustable
to permit proper proportioning of the tobacco and the
baseweb being fed to the mixing means 20. Although not
shown, the drives of the feed mechanism 11 and the pump
means 13 may be provided with any suitable automatic
flow sensing and control means well known in the art.
The high intensity mixing means 20 is provided with
an adjustable variable speed drive as indicated at 29,
which is conventional, and a main casing 24 with a bottom
discharge 25 (see FIGURE 3) which is connected to a slurry
box 14 which provides or distributes a controlled layer
of the final tobacco/baseweb slurry on ~o the casting
belt 19.
A variation of the apparatus of FIGURE 1 is diagram-
matically shown in FIGURE 2. In place of the hopper 10
and the vibration type feed means 11, a modified hopper 15
is provided with a positive type feed 16 having a variable
speed drive which is adjustab.le and.may be provided with
any suitable conventional flow sensing and control means.
A modified high intensity mixing means 20A is substantially
the mixing means 20 of FIGURE 1 with a modified cover 21A
(see also FIGUR~ 4) having inlets 22A and 23A corresponding
to inlets 22 and 2~ of cover 21. The discharge end of the
feed means 16 is connected to the inlet 22A and the pump
13 is connected to the inlet 23A.
As shown to assist in feeding the final slurry to be
cast, a positive feed means 17 with an adjustable variable
speed drive is interposed between the discharge 25 (see
FIGURE 3) of the modified high intensity mixer 20A and the
slurry box 14. When a high solids slurry is prepared with
limited flow characteristics which would appear questionable
to properly deposited from the slurry box 14 on the casting
belt 19, the slurry box 14 may be eliminated and the feed
means 17 may be provided with an extrusion nozzle (not shown)
to extrude the slurry on to the belt 19.
It should be fully understood that the modified
hopper 15 with feed means 16 is totally independent from
the discharge feed means 17. Each may be used in the absence
of the other to modify the apparatus of FIGURE 1.
A typical high intensity mixer 20 being essentially a
grinding mill or comminuting machine is illustrated in
FIGURES 3 and 5. A motor driven rotor 27, rotatable on an
axis transverse to the axis of flow from inlets 22 and 23,
or 22A and 23A, to the dischar~e 25, is provided with a
plurality of series of blades 28 and is operated or rotated
in a total free space which is kept within a reasonable
minimum defined by the housing 24 and cover 21 or 21A of
the mixer 20 or 20A. A screen 26 forms the lower portion
of the actual chamber and extends across the bottom discharge
25, and is spaced closely to the ends of the blades 28 as the
rotor is driven. Each series of blades 28 is so spaced, as
may be seen by referring to FIGURE 3, that all of the blades
provide a wiping action across substantially the full width
of the screen 26 during each revolution of the rotor 27 which
with the centrifugal for.ce inducet.by the high speed rotor
contributes in expelling the slurry from the mixing chamber
defined by the casing 24 and the cover 21 or 21A.
Inasmuch as the tobacco is preground and the baseweb is
a slurry, the mill or the comminuting machine acts as a high
intensity mixer. In the absence of the requirement to grind
the introduced masses of comminuted tobacco and baseweb,
the high speed rotor acting within the chamber provides a
very high energy input acting on a relatively small total
mass, causing substantially an instant homogeneous dispersion
of the two heterogeneous masses into each other to form a
homogeneous mass which is rapidly expelled by the wiping
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action and the centrifugal force of the high speed rotor.
In this manner, the residence time of the slurry in the
mixing device is kept to a minimum, and this slurry is
rapidly fed through the slurry box 14 on to the casting
belt 19.
It is known that the apparent viscosity of aqueous
tobacco dispersion increases with time as the tobacco
progressively absorbs the aqueous medium until the re-
sulting slurry reaches its equilibrium state wherein the
swelling tobacco has absorbed a maximum of the aqueous
medium. It should be quite apparent that if the tobacco
in the dry state and the baseweb slurry can be rapidly
acted on to provide a homogeneous mix which can be cast
prior to the tobacco slurry arriving at its equilibrium
state, the tobacco slurry can contain a higher solids
content with a viscosity which facilitates casting.
Preparation and casting a tobacco slurry in this
manner is attended by various benefits. The short resi-
dence time in the high intensity mixer of limited amounts
of slurry permits rapid start up, shut-down and cleanup
and permits less extraction of the natural soluble in-
gredients of the tobacco which interact with one another
and effect the taste of the resulting product. Also,
microbiological attack of the tobacco caused by holding
tobacco in a slurry form is prevented.
In a typical liquid-liquid system, the slurry composed
of predetermined amounts of baseweb or adhesive slurry and
tobacco dispersion normally will contain a solids content
of from 8 to 11% and have a viscosity of 9 to 13,000
centipoises. 5ince aqueous tobacco dispersions are usually
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quite high in apparent viscosity, it is necessary to
prepare such dispersions having a solids content within
a range of 12 to 17% to maintain flow characteristics.
As an example, to prepare a ~obacco/adhesive or baseweb
slurry with 70% tobacco from a tobacco dispersion with 15.5%
solids and a baseweb with 6.45% solids, the liquid phases
will be combined at a ratio of 1.03 parts of baseweb to
1.00 part of tobacco dispersion and the resulting tobacco/
baseweb slurry will have a 10.9% solids concentration.
The mixing vessel is sized to provide a minimum residence
time of over 10 minutes. However, to ensure homogeneity
of the slurry, in practice the residence time is no less
than 20 minutes.
In the conventional system the residence time of the
tobacco-dispersion/baseweb slurry in the mixer is only of
importance relative to achieving a uniform mix, since the
tobacco is predispersed in water for some time before it
comeæ in contact with the baseweb and thus is preswollen
to its equilibrium state. Since the slurry has a high
liquid content, drying of the slurry is relatively 910w.
In accordance with the present invention, the tobacco
contacts the aqueous medium only after it enters the high
intensity mixer where it has a minimal residence time and
is discharged for substantially immediate casting. Thus,
the homogeneous tobacco/baseweb slurry is mixed and prefer-
ably cast prior to arriving at its equilibrium state.
Thus, the solids content can be higher than the slurry in a
liquid-liquid system and the reduced amount of liquid to
be removed by the drier results in increased production
rates.
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It has been found by way of example, that by uti-
lizing the apparatus of FIGURE 1 or 2, in accordance with
the present invention, having a high intensity mixing means
with a rotor driven at speeds of 3,500 to 5,000 RPM in a
mixing chamber of about 138 cubic inches of free space or
approximately 5 pounds of mass at any given instant, that
the residence time of the slurry in the mixing chamber is
proportional to the sheet production rate as demonstrated
by the following data.
10 Average ~esidence Time (Min.) 0.154 0.13 0.10
Dry Sheet Prod. Rate/Min. 8.2 lbs. 9.6 lbs. 12.3 lbs.
Pounds of Slurry/Min. 32.9 38.4 49.4
% Solids 22 22 22
Pounds of Solids/Min. 7 2 8.4 10.9
Since the limiting factor in such production rates is the
designed efficiency of the dryer it follows that higher
slurry solids permit increased sheet production rates at
which instance the residence time of the slurry in the
mixing chamber is further reduced. This is especially the
case where slurry solids are worked which do not lend them-
selves readily to casting and where extruslon onto the
drying belt constitutes the preferred sheet forming method.
Comparison of the foregoing data with the afore-
noted data for a liquid-liquid system will be illustrative
of the conceptual differences of the conventional liquid-
liquid system and the present invention.
The term '~tobacco" as used herein includes tobacco,
reconstituted tobacco and tobacco waste such as stems or
fines, tobacco substitutes such as cocoa leaves and other
naturally occurring or cultivated vegetation, tobacco-like
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substances, and slmilarly structured synthetic compositions
well known in the art e.g. cellulose or cellulose derivatives.
Although several embodiments of the invention have
been illustrated and described in detail/ it is to be expressly
understood that the invention is not limited thereto.
Various changes may also be made in the design and
arrangement of the parts without departing from the spirit
and scope of the invention as will now be understood by those
skilled in the art.
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