Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TOBACCO EXPANSION PROCESSES AND APPARATUS
Field of the Invention
The invention relates to processes and
apparatus for expanding tobacco. More particularly,
the invention relates to processes and apparatus for
improving throughput and economics of tobacco
expansion.
Background of the Invention
In the past two decades, tobacco expansion -
processes have become an important part of the
cigarette manufacturing process. Tobacco expansion ~ -
processes are used to restore tobacco bulk density
and/or volume which are lost during curing and storage
of tobacco leaf. In addition, expanded tobacco is an
important component of many low tar and ultra-low tar
cigarettes.
U.S. Patent No. 3,524,451 to Fredrickson and
U.S. Patent No. 3,524,452 to Moser et al. describe
processes in which tobacco is contacted with an
impregnant and then heated rapidly to volatilize the
impregnant and expand the tobacco. U.S. Patent No.
3,683,937 to Fredrickson et al. discloses the vapor
state impregnation of tobacco followed either by
heating or rapid pressure reduction for tobacco
expansion.
The use of a carbon dioxide for expanding
tobacco is disclosed in U.S. Patent No. 4,235,250 to
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Utsch; U.S. Patent No. 4,258,729 to Burde et al.; and
U.S. Patent No. 4,336,814 to Sykes et al., among
others. In these and related processes, carbon
dioxide, either in gas or liquid form, is contacted
with tobacco for impregnation and the impregnated
tobacco is subjected to rapid heating conditions for
expansion. In the known carbon dioxide expansion
processes, it is typically necessary to heat the
tobacco excessively in order to achieve substantial and
stable expansion. This excessive heating can harm the
tobacco flavor and/or generate an excessive amount of
tobacco fines. In addition, those processes which use
liquid carbon dioxide for impregnating tobacco
typically result in impregnated tobacco in the form of
solid blocks of tobacco containing dry ice, which must
be broken up prior to heat treatment, thereby
increasing the complexity of the process.
U.S. Patent No. 4,388,932 to Merritt et al.
discloses a process for increasing the post-reordering
filling capacity of previously expanded tobacco.
Previously expanded tobacco having an 'Oven Volatiles'
(OV) content of less than 6 percent is heated to reduce
its OV content to a value said to be well below 3
percent. The OV content of tobacco is said to be
approximately equivalent to its moisture content since
no more than 0.9 percent of tobacco weight is volatiles
other than water. The very low OV content tobacco
recovered from the post-expansion heating step is
subjected to a reordering step for increasing its
moisture content and is said to collapse less during
the reordering step than if it were not heat treated
after expansion. A stiffening of the tobacco during
the heat treatment was proposed to account for the
increased stability of the expanded tobacco during
reordering.
~ .S. Patent No. 4,531,529 to White and Conrad
describes a process for increasing the filling capacity
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of tobacco, wherein the tobacco is impregnated with a
low-boiling and highly volatile expansion agent, such
as a normally gaseous halocarbon or hydrocarbon at
process conditions above or near the critical pressure
and temperature of the expansion agent. The pressure
is quickly released to the atmosphere so that the
tobacco expands without the necessity of a heating step
to either expand the tobacco or fix the tobacco in the
expanded condition. The pressure conditions of this
10 process range from 36 Kg/cm2 (512 psi) and higher with
no known upper limit. Pressures below 142 Kg/cm2 (2,000
psi) were used to produce satisfactory tobacco
expansion without excessive fracturing. ~ -
U.S. Patent No. 4,554,932 to Conrad and White
describes a fluid pressure treating apparatus,
including a cylindrical tubular shell and a spool
assembly mounted for reciprocal movement between a
loading position outside the shell and a treating
position within the shell. When the spool is within
the shell, deformable sealing rings carried in annular
grooves on the cylindrical ends of the spool are forced
radially outwardly for engagement with the interior of
the shell to form a pressure chamber within the shell
between the spool ends. Conduits are provided to
introduce processing fluids into the annular pressure
chamber formed within the shell. The use of this
apparatus for high pressure impregnation of tobacco
with an expansion agent permits easy loading and
unloading of tobacco and avoids the closure and opening
problems associated with conventional pressure sealing
and locking mechanisms, such as pivotable autoclave
lids. This pressure vessel can thus produce time
savings and improve economics in tobacco expansion.
Tobacco expansion processes including
those described above and others, must be conducted in
batch processes when impregnation pressures
substantially above atmospheric pressure are used. The
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batch treating processes require complicated treating
apparatus and long cycle times because of the time
required in opening and closing the vessels and
introducing and removing impregnating agent from the
vessels. Some throughput improvements have been made
by modifying the various apparatus employed to decrease
cycle time; however, substantial throughput
improvements in the known batch systems are available
according to conventional techniques primarily by
increasing volumes of the individual systems and/or
increasing the number of batch systems used
simultaneously.
Summary of the Invention
This invention provides tobacco expansion
processes and apparatus that can be employed for
expanding tobacco at rapid throughput rates employing
high pressure tobacco impregnation conditions. The
processes and apparatus typically involve tobacco
impregnation and expansion cycle times of less than 20
- 30 seconds; the use of preheated, prepressurized
expansion agent such as propane; preheating of tobacco
batches; and/or compression of tobacco within a high
pressure impregnation zone for greatly improving use of
available space in a high pressure impregnation vessel.
In one aspect, the present invention
substantially improves the degree of tobacco filling
capacity increase in tobacco expansion processes using
high pressure impregnation conditions. In other
aspects, this invention provides rapid batch feed
systems for reliably and economically feeding pre-sized
tobacco batches to an impregnation zone and for rapidly
and economically preheating tobacco batches. The
invention also provides apparatus improvements for high
speed/high pressure, spool-and-shell tobacco
impregnation apparatus. Still further the invention
provides an improved accumulator apparatus for the
rapid generation and supply of high temperature/high
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pressure impregnation gasses, including flammable
gasses such as propane. The improved accumulator both
minimizes the mass of such gas present within the
system at any given time and also eliminates costly and
troublesome moving parts required in prior art
accumulators.
Substantial improvement in tobacco filling
capacity increase is obtained according to a first
aspect of the invention by impregnating high moisture
content tobacco with an expansion agent in a high
pressure tobacco impregnation zone, expanding the
impregnated tobacco under conditions to provide
expanded tobacco also having a high moisture content,
and then drying the expanded tobacco following
expansion. Drying of the expanded tobacco is
preferably conducted within a short time period
following expansion, e.g., less than about 5 minutes
after expansion. Although a very high moisture content
in tobacco fed to a high pressure impregnation zone can
cause collapse of the tobacco following expansion in
those processes which do not use heating for expansion,
it has been found that filling capacity increases are
increased with increasing moisture and can be preserved
by drying the tobacco to a moisture content of less
than about 13 percent following expansion.
Advantageously the drying treatment is conducted at a
temperature of 50F (177C)or less and does not reduce
tobacco moisture content to less than about 6-8 wt.
percent so that the tobacco is not stripped of volatile
flavors.
Advantageously, the moisture content of the
tobacco fed to the impregnation zone is greater than
about 20 wt. percent, and preferably is greater than
about 24 wt. percent, in order to provide a substantial
increase in the degree of tobacco expansion.
Preferably, the high moisture content tobacco is
preheated to a temperature greater than about 150F
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(66C) prior to impregnation. Drying following
expansion of the tobacco in accordance with the
invention preserves the high filling capacity level of
the expanded tobacco.
In another aspect of the invention, rapid
feeding and pre-sizing of tobacco batches for tobacco
impregnation and subsequent expansion is achieved.
Apparatus provided according to this aspect of the
invention includes a substantially vertically oriented
metering tube for forming a vertical column of tobacco.
A tobacco column dividing means, which is preferably a
member having a plurality of tines, is associated with
the metering tube and is selectively engageable with
the tobacco column for dividing the column into an
upper portion above and supported by the dividing
means, and a lower portion below the dividing means. A
blocking mem~er spaced below the dividing means is
engageable with the tobacco column for support of the
tobacco column when the dividing means is out of
engagement with the column. The blocking member is
disengageable with the column of tobacco so that when
the dividing means is engaged with the tobacco column,
disengagement of the blocking member results in release
of the lower portion of the tobacco column from the
metering tube. This tobacco is then fed as a batch to
the impregnation zone. The size of the tobacco batch
can be readily controlled by varying the spacing
between the dividing means and the blocking member.
In yet another aspect of the invention, the
vertically oriented metering tube is used for
preheating of tobacco fed to the impregnation zoneO In
accordance with this aspect of the invention, steam is
injected into the metering tube at a location below the
top the tobacco column for heating of the tobacco to a
high temperature, preferably between about 100F (38C)
and about 212F (100C), and the heated tobacco is then
delivered to the impregnation zone. Preferably the
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rapid feeding and pre-sizing system of the invention
discussed above is used for feeding the preheated
tobacco as a batch to the impregnation zone~
Preheating of the tobacco in accordance with this
aspect of the invention is rapid because the steam is
quickly distributed through the tobacco. In addition,
the tobacco above the steam injection zone is preheated
by the rising steam and also functions as an insulator
for the tobacco in the steam injection zone, so that
heating costs can be minimized.
Advantageously, the vertically oriented
metering tube is positioned above an opening in an
upper wall of a horizontally oriented delivery conduit
arranged for delivery of the tobacco batches to the
high pressure impregnation apparatus. A reciprocating
compressing member is mounted in the conduit for moving
the tobacco through the conduit and compressing the
tobacco into the high pressure treating apparatus at
the downstream end of the conduit. The opening in the
conduit communicating with the metering tube is
provided with a pivoting closure member capable of
compressing the tobacco into the conduit. This allows
tobaccos of different densities and batch volumes to be
fed into the impregnation zone without requiring
replacement or modification of the feeding apparatus.
The invention also provides improvements to
the spool and shell apparatus of U.S. Patent No.
4,554,932 to Conrad and White, to impart improved
durability and speed thereto. When used in preferred
embodiments of this invention, the spool and shell
apparatus is operated at a cycle rate of four to five
times per minute or faster. Thus the high pressure
spool and shell apparatus is preferably cycled through
3,000 to 3,600 cycles or more in a 12 hour day.
Although this apparatus improves speed and economics of
tobacco expansion, it has been found that repetitive
outward expansion of the elastomeric sealing rings on
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the cylindrical end members of the spool under high
temperature and high pressure conditions can cause
premature failure of the sealing rings.
The operation and lifetime of the sealing
rings is improved in accordance with the invention by
decreasing the radial gap between the spool member and
the inside surface of the tubular shell at one or more
locations axially adjacent the elastomeric sealing
rings. This is advantageously accomplished by
providing at least one circumferentially enlarged wear
ring on each cylindrical end member of the spool at a
position that is axially adjacent and in contact with
at least a portion of an axial end face of the
elastomeric sealing ring. Preferably the enlarged wear
rings are positioned in contact with both axial end
faces of each elastomeric sealing ring. Because the
wear rings have a greater circumference than the
circumference of the end members of the spool in order
to prevent the spool from scraping the shell, the axial
gap between the spool and the shell is decreased
adjacent the wear members. Positioning of the
elastomeric sealing rings adjacent the wear rings
provides improved axial support to the sealing rings
when these rings are forced radially outwardly under
great pressures. This, in turn, minimizes destructive
axial deformation of peripheral portions of the sealing
rings.
In accordance with another aspect of the
invention, efficiency of the spool and shell
impregnating apparatus is improved by enhancing the
rate of delivery and removal of high pressure, gaseous
expansion agent, to and from the annular high pressure
impregnation zone within the shell. This is
accomplished by enlarging the total cross-sectional
area of the gas delivery and removal ports
communicating between the exterior and interior of the
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shell while also incorporating a particle blocking
means to minimize entry of tobacco into the ports.
In one embodiment of this aspect of the
invention, the high pressure gasses are admitted into
and removed from the cylindrical shell via a plurality
of cooperating ports through the shell that are
circumferentially distributed around the cylindrical
shell. An exterior manifold member surrounds the ports
to contain the processing fluid admitted into the shell
through the peripheral ports. The diameter of each
port at the interior of the shell is less than a
predetermined size in order to prevent tobacco entry
into the ports.
In an alternative embodiment, at least one `
enlarged port having a diameter substantially greater
than tobacco particles is provided through the shell.
An elongate blocking member having an exterior face of
greater width than the port diameter connects
longitudinally between peripheral portions of the end
members of the spool and is aligned radially with the
port opening. When the chamber portion cf the spool,
i.e., the portion between the end members, is moved
through the shell, the blocking member covers the port
so that tobacco in the spool chamber is prevented from
entering the enlarged port. Preferably, at least two
enlarged ports are provided through the shell and a
corresponding number of blocking members are provided
on the spool.
In yet another aspect, the invention provides
improved high pressure accumulators for generating and
storing batches of high temperature, high pressure
gaseous expansion agent, preferably propane at a
temperature above about 250F (121C) and a pressure
above about 2,500 psig. Previously, the supply of
batches of high pressure and high temperature propane
to the impregnation zone at a cycle rate of four to
five times per minute or faster has required either
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storage of a very large volume of high pressure, high
temperature propane; or the use of an accumulator in
the form of a pressure vessel having chambers separated
by a movable member. An inert pressurizing gas was
maintained in one chamber and propane stored in the
other. As propane was periodically added to and
removed from the vessel, the movable member moved
within the vessel, but was sub~ect to failure.
Accumulators according to the present
invention employ a high pressure vessel containing both
the expansion agent and a gaseous pressurizing fluid
within the vessel but with no separating member between
the expansion agent and pressurizing fluid. In one
embodiment, the vessel is maintained at a temperature
above the critical temperature of each of the
pressurizing fluid and expansion agent and under a
sufficiently high pressure that the pressurizing agent
and expansion agent have a high density, near that of
liquid. The pressurizing fluid is selected to have
diffusivity properties relative to the expansion agent
such that the two fluids can be maintained in contact
with only extremely low levels of mass transfer due to
diffusion occurring between the fluids under the
conditions within the vessel. Preferably the
pressurizing gas is nitrogen and the expansion agent is
propane. At pressures above 2,500 psig and
temperatures above about 200F (93C), these two gasses
can be maintained in a vessel substantially separate
from each other so that propane can be cyclically added
to and removed from the vessel with very low loss of
nitrogen to propane.
In another accumulator embodiment, the
expansion agent and a gaseous pressurizing fluid are
maintained within a high pressure vessel which includes
first and second zones arranged for separately
maintaining the two fluids under temperature and
pressure conditions approaching or above supercritical,
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and a third zone in fluid communication with each of
the first and second zones for maintaining a barrier
fluid between the fluids in the first and second zones.
The barrier fluid, which can be water, prevents
substantial mass transfer between the pressurizing
fluid and the expansion agent.
Brief Description of the ~rawings
In the drawings which form a portion of the
original disclosure of the invention:
Figure 1 is a schematic cross-sectional view
of one preferred impregnation apparatus employed in the
invention with various different operating positions
being partially illustrated in phantom;
Figure lA is a schematic cross-sectional view
of an accumulator which can advantageously be used with
the apparatus of Figure 1 for rapidly supplying high
temperature, high pressure impregnating agent thereto,
and which includes first and second zones arranged for
separately maintaining two fluids under temperature and
pressure conditions approaching or above supercritical,
and a zone in fluid communication with each of the
first and second zones for maintaining a barrier fluid
between the fluids in the first and second zones;
Figure 2 is a cross-sectional view of one
preferred tobacco feeding and loading apparatus
including a pair of vertically oriented metering tubes
arranged for feeding a pair of horizontally oriented
conduits positioned upstream of the impregnation
apparatus of Figure 1;
Figure 2A is an enlarged cross-sectional view
of one end of a reciprocating tobacco compacting member
associated with the horizontal conduits in the tobacco
loading apparatus of Figure 2;
Figure 3 is an enlarged cross-sectional view
taken along line 3-3 of Figure 2 and illustrates one
preferred embodiment of a steam injecting apparatus
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associated with the metering tubes in the apparatus of
Figure 2 for introducing steam into a tobacco column;
Figure 4 is an enlarged cross-sectional view
taken along line 4-4 of Figure 2 and illustrates a
different advantageous embodiment of a steam injecting
apparatus associated with the metering tubes in the
apparatus of Figure 2;
Figure 5 is an enlarged cross-sectional view
taken along line 5-5 of Figure 2 and illustrates a
preferred embodiment of a tobacco column dividing means
associated with the metering tubes in the apparatus of
Figure 2;
Figure 6 is partial front view with portions
thereof being broken away, taken along line 6-6 of
Figure 5 showing a lower portion of one metering tube
of the apparatus of Figure 2 and illustrates a
plurality of brushes associated with the tobacco column
dividing means of Figure 5;
Figure 7 is an enlarged schematic cross-
sectional view of a portion of the feeding apparatus of
Figure 2 illustrating the steam injecting apparatus,
the tobacco column dividing means, and a blocking
member for delivering a predetermined volume of tobacco
to the impregnation expansion apparatus of Figure ~;
Figure 8 is cross-sectional view of one end
portion of the spool and shell apparatus of Figure 1
illustrating sealing and wear rings associated with the
end members of the spool, and also illustrates a
plurality of circumferentially distributed ports
through the wall of the shell for introducing a
processing fluid into the impregnation zone;
Figure 8A is a greatly enlarged cross-
sectional view of a portion of the apparatus shown in
Figure 8 and illustrates a preferred cross-section for
the individual ports through the wall of the shell;
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Figure 9 is a schematic cross-sectional view
of a tobacco drying loop employed downstream of the
impregnation apparatus of Figure 1;
Figure 10 illustrates a partial cross-
sectional view of an alternative fluid introducingarrangement for the spool and shell apparatus of Figure
1, the spool being shown in motion between its loading
position and its impregnating position, in which
enlarged ports are provided through the shell, and port
blocking members are positioned on the spool in radial
alignment with the enlarged ports;
Figure 11 is a cross-sectional view taken
along line 11-11 of Figure 10 and illustrates how the
port blocking members, on the spool, block the ports
through the shell as the spool moves through the shell;
Figure 12 is an enlarged perspective view of
one elongate blocking member disassembled from the
apparatus of Figures 10 and 11;
Figure 13 is a graph illustrating tobacco
expansion with varying amounts of moisture and various
degrees of tobacco preheating;
Figure 14 is a graph illustrating how tobacco
expansion can vary with different tobacco densities
during impregnation by expansion agent and with
different impregnation times; and
Figure 15 is a graph derived from a composite
of various expansion data to illustrate the flexibility
of the expansion process and apparatus of the invention
and depicts the total increase in tobacco volume per
hour (in cubic meters per hour) which can be obtained
from the apparatus of Figure 1 as a function of
impregnation time and tobacco compression.
Detailed Description of the Preferred Embodiment
Different process and apparatus embodiments
of the invention are set forth below. While the
invention is described with reference to specific
processes and apparatus including those illustrated in
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the drawings, it will be understood that the invention
is not intended to be so limited. To the contrary, the
invention includes numerous alternatives, modifications
and equivalents as will become apparent from a
consideration the foregoing discussion and the
following detailed description.
Figure 1 schematically illustrates preferred
impregnation processes and apparatus of the invention
including a spool and shell apparatus generally
constructed in accordance with U.S. Patent No.
4,554,932, issued November 26, 1985 to Conrad, the
entire disclosure of which is hereby incorporated by
reference. Various details disclosed in the '932
patent are not repeated herein for the sake of brevity.
However, reference may be had to the '932 patent for
such details.
As illustrated schematically in Figure 1,
tobacco is preferably first treated in a preparation
zone 10 to increase its moisture content to a value
2Q above about 16 percent by weight, preferably above
about 20 percent by weight. The tobacco of increased
moisture content is then passed to a feeding zone 12
wherein the tobacco is heated as described in greater -
detail below and is then fed to a reciprocating spool
and shell high pressure fluid treating apparatus.
The spool and shell high pressure fluid
treating apparatus includes a pressure vessel defined
by a cylindrical shell or enclosure 14 and a spool
assembly 16. The shell 14 and spool assembly 16 can be
made of any suitable materials, including stainless
steel, and the like. The specific construction and
size of the shell and spool will be sufficient to
withstand the pressures contemplated within the
pressure vessel as will be apparent.
The spool assembly 16 includes cylindrically
shaped end members 18 and a connecting rod 20. When
the spool 16 is within the shell 14 as illustrated in
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Figure l, the end members 18, together with the
connecting rod 20 and the shell 14 define an annular
space 22 of predetermined volume constituting a sealed
pressure chamber or zone. The spool assembly 16 is
positioned horizontally and is arranged for
reciprocating movement among a loading position 24,
illustrated in phantom; an unloading position 26, also
illustrated in phantom; and an impregnating position
specifically shown in Figure 1. A fast acting
hydraulic piston or similar motor means (not shown) is
axially attached via a shaft 28 partially shown in
Figure 1 for moving the spool among the three
positions.
The spool is loaded with tobacco at position
24 as discussed in greater detail later and is then
moved to the impregnating position. In the
impregnating position, the spool is sealed within the
shell 14 by radial expansion of elastomeric sealing
rings 30 which are carried in annular grooves formed in
each of the spool end members 18. The construction of
the elastomeric sealing rings 30 is discussed in detail
later in connection with Figure 8.
The sealing rings are formed of deformable
elastomeric material such as vulcanized rubber and are
arranged to receive a hydraulic fluid via fluid lines
32. Hydraulic fluid, such as food grade oil, is forced
through the lines 32 by a hydraulic accumulator 34. The
hydraulic fluid is forced into one end of the spool via
a bore through a connecting rod 36, partially
illustrated in Figure 1, connected to at least one end
of the spool 16. The hydraulic fluid is forced against
the interior of the sealing rings 30 causing them to
expand outwardly and seal the pressure chamber 22
against leaks.
High pressure gas supply and exhaust lines 38
and 40, respectively, communicate through the shell 14
via a plurality of ports 42 discussed in detail later
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in connection with Figure 8. These ports which may be
circumferentially distributed about the periphery of
the shell 14 as shown in Figure 8, or of enlarged
cross-section as shown in Figures 10, 11 and 12, allow
the introduction and removal of high pressure fluid
into and out of the pressure chamber 22 when the spool
member 16 is in the impregnation position. An exterior
manifold 44 surrounds the ports 42 and contains the
processing fluid admitted to the shell 14 via the
circumferential ports 42. The high pressure fluid
flows through the ports 42 and then into the tobacco
loaded and compressed about the spool connecting rod 20
via a plurality of ports and channels in the spool body
shown in Figure 8 and discussed later.
A pair of fast acting valves 46 and 48 are
provided for rapid introduction and release of fluid
into and out of the impregnating chamber 22. These
valves are preferably ball valves having a port size
ranging from 0.5 inch to 1.5 inch in diameter or
greater depending on the size of the impregnation zone
22 to thereby provide for substantially instantaneous
admittance and removal of high pressure fluid to and
from the impregnation zone 22. The valves are
advantageously automatically opened and closed by fast
acting hydraulic actuators, not shown.
On the input side, the high pressure gas line
38 is connected to an accumulator device 50 discussed
in greater detail below. A heater 52 is provided for
heating gas fed to the accumulator 50. Accumulator 50
may also be heated by means not shown to maintain the
fluid within the accumulator in heated condition. A
high pressure pump 54 is provided upstream of heater 52
for feeding high pressure fluid at, e.g., 2,500 psig,
to heater 52 and accumulator 50. Line 40, which is
used to remove high pressure fluid from impregnation
zone 22, is connected to an optional gas recovery zone
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(not shown) for recovery of fluid removed from the
impregnation zone.
The accumulator 50 is used to provide a high
pressure impregnation fluid, such as propane at 2,500
psig, to the impregnation zone in the spool impregnator
shown in Figure 1. The accumulator 50 includes a
tubular vessel 56 formed of a material capable of
withstanding high temperatures and pressures. At the
top and bottom of the accumulator there are ports 58
and 60, respectively, for admitting high pressure
gasses.
An inert high pressure gas, such as nitrogen
at a pressure of above about 2,500 psig, is admitted
through port 58 and, as a result of pressure and
temperature conditions in the vessel, is maintained
substantially separately in the upper portion 62 while
expansion fluid, such as propane, is admitted through
port 60 and is maintained at elevated pressure , e.g.,
above about 2,500 psig, in a lower portion 64 of the
vessel. The vessel 56 is maintained at a temperature
and pressure approaching or above the critical
temperature and pressure of both the pressurizing fluid
and the expansion agent. Under these conditions, and
with selected fluids such as nitrogen as pressurizing
fluid and propane as expansion agent, the diffusivity
of the gasses in the two fluid zones 62 and 64, with
respect to each other, can be sufficiently low that the
two fluids are maintained substantially separately in
the accumulator 50.
When expansion agent gas is discharged from
the accumulator, the pressure loss is sensed by sensor
means (not shown) and a control activates the pump 54
which immediately starts refilling the accumulator with
high pressure expansion agent, preferably propane. The
pressure sensor can be provided in the accumulator or
integrally within the pump 54. The gas accumulator 50
is refilled in a short period of 5 30 seconds, during
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the period employed in the present invention for
impregnating the tobacco in impregnation zone 22 of
Figure 1.
As indicated by arrows 65 in Figure 1, the
level of expansion agent within the accumulator 50
changes cyclicly between a predetermined upper level
and a predetermined lower level as it is added to and
discharged from the vessel. The lower level is
selected to be a certain predetermined distance from
the bottom of the vessel, so that discharge of
expansion agent does not discharqe pressurizing fluid.
Also the lower level is chosen to prevent expansion
agent near the interface of the two fluids from
discharging. For propane and nitrogen gasses, the
lower level for the propane fluid can advantageously
chosen to be about one foot although different levels
can be used depending on the size of the vessel and the
conditions therein as will be apparent.
A level control device, LC, can be employed
to assist in maintaining the expansion agent, e.g.,
propane, level within the predetermined limits
discussed above. Preferably a fluid interface level
sensor or the like is employed to sense the position of
the interface between the expansion agent and the
pressurizing fluid. An integral or separate control
system responds to the level sensor and controls
admission and removal of pressurizing fluid, e.g., ~;
nitrogen, into and out of the accumulator as required
to maintain the maintain the expansion agent between
the upper and lower predetermined levels.
Following discharge of expansicn agent, a
fresh charge of expansion agent is pumped back into the
accumulator until a predetermined upper pressure is
reached. The predetermined upper pressure is chosen
based on: (1) the total combined volume of the
accumulator vessel, the impregnation zone 22 and the
lines 38 between the accumulator 50 and the
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impregnation zone 22; and (2) the desired pressure in
the impregnation zone. Since the pressure in the
accumulator drops as gas is discharged into gas lines
38 and then into the impregnation zone 22 of
impregnator as a result of the increase in volume of
the gas, the upper pressure must be sufficient that the
final pressure of the expansion agent gas reaching the
impregnation zone is at the predetermined pressure for
tobacco impregnation. Thus where the final pressure is
about 2,500 psig, the upper pressure can be, for
example, 2,700 - 3000 psig, depending on the above
factors.
Typically there is some loss of the
pressurizing fluid over time resulting from absorption
of pressurizing fluid by the expansion agent during its
contact with the pressurizing fluid while present in
the accumulator. Although a low gas diffusivity
relationship between the fluids in the accumulator can
theoretically allow them to be maintained substantially
separately, even extremely low gas diffusivity values
for the two fluids in the accumulator can result in a
discharge of a small amount of pressurizing fluid with
each discharge of expansion agent due to some mixing of
the two fluids. However a small level of absorption of
2S pressurizing fluid generally has no substantial
negative impact on tobacco expansion.
When the system includes a recovery system
for expansion agent recycling, the recovery of the
expansion agent following its use will typically result
in the separation and removal of any absorbed
pressurizing fluid so that substantially pure expansion
agent can be recovered for recycling. However the
absorbed pressurizing fluid is typically not recovered,
and in addition, the presence of absorbed pressurizing
fluid in the expansion agent typically decreases the
amount of expansion agent which can be economically
recovered after use. The amount of pressurizing fluid
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-20-
absorbed by the expansion agent is an equilibrium
amount determined based upon the diffusivity values of
the two fluids at the temperature and pressure of the
accumulator 50, and the turbulence within the
accumulator, and is preferably less than about 5 wt.
percent.
An accumulator adapted for minimizing
absorption of pressurizing fluid by the expansion agent
is illustrated in Figure lA. This accumulator 50'
employs a third and more dense fluid such as water, in
a zone separating the pressurizing fluid and the
expansion agent, as a movable liquid barrier between
the two fluids. As seen in Figure lA, the accumulator
50' includes a first zone 62' for receiving a
pressurizing fluid such as nitrogen, and a second zone
64' for receiving and separately maintaining the
expansion agent under high temperature and pressure
conditions. A third zone 61 is in fluid communication
with each of the first and second zones and maintains a
dense fluid media, ~uch as water, as a barrier fluid
between the fluids in the first and second zones.
The barrier fluid shown in the accumulator of
Figure lA minimizes or eliminates commingling of the
pressurizing fluid and the expansion agent even under
conditions of increased turbulence. This feature
reduces the consumption of the pressurizing fluid and
subsequent loss of expansion agent during its recovery,
and can also simplify the design of an expansion agent
recovery system because separation of absorbed fluid is
no longer a substantial consideration. In the
accumulator of Figure lA, the expansion agent such as
propane, will typically absorb a small amount of the
barrier fluid, e.g., water.
Both water and nitrogen make-up are supplied
to the accumulator 50' and, as shown in Figure lA, and
separate interface level detectors LC are preferably
provided in combination with integral or separate
~125 6;~8
-21-
control means for control of water and nitrogen
admitted into the accumulator. These controls are
responsive to the level detectors and provide for the
addition of water in an amount and at a rate sufficient
to maintain the total volume of water in the
accumulator within predetermined upper and lower
control limits. Additionally the control means
provides for the addition and removal of nitrogen in
response to level detector signals to maintain the
height or location of the water-nitrogen interface
within predetermined control limits.
In the accumulator apparatus of Figure lA,
the third zone 64' which maintains the expansion agent
substantially separate, is defined in part by a
partially closed cylinderical chamber located within an
upper portion of the larger pressure vessel. This or a
similar arrangement is particularly advantageous in the
preferred system employing a barrier fluid that is more
dense than either of the pressurizing or expansion
agent fluids. It will be apparent that this
construction and arrangement is only a preferred
construction and that other vessel designs can readily
be provided for providing a movable barrier fluid
separating the other fluids wi~hin the vessel.
Figures 1 and lA illustrate preferred
accumulators of the invention. However, other devices
for providing the substantially immediate delivery of
high pressu~e, high temperature expansion agent can
also be used. For example, a vessel containing only
high density expansion agent maintained above
supercritical temperature can also be used. When the
vessel contains a relatively large mass of expansion
agent compared to the mass of expansion agent removed
in each cycle and maintains the expansion agent at a
high density, the discharge of the expansion agent from
the vessel can be accomplished with only a relatively
small pressure drop in the expansion agent.
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-22-
For example, at 2750 psig, and 300F (149C),
the density of propane is 23.7~ lb/cu.ft. At the same
temperature and a pressure of 2,500 psig, the density
of propane is 22.8 lb/cu.ft. Thus a one cubic foot
vessel of propane fluid maintained at 2,750 psig and
300F (149C) can discharge 0.96 pounds of propane at
300F (149C) to the impregna~ion zone with only a small
decrease in pressure, i.e., from 2,750 psig to 2,500
psig.
In still another embodiment of the invention
a mechanical accumulator can be employed to supply
expansion agent. One presently preferred mechanical
accumulator contemplated for use herein is a 'Metal
Bellows' accumulator available from Parker Bertea
Aerospace, Parker Hannfin Corp., Metal Bellows
Division, Moorpark, California.
Returning to Figure 1, the pressure of the
propane admitted to the impregnation zone 22 is
preferably above 2,000 psig, and more preferably
between about 2,500 psig and 3,000 psig. In accordance
with the present invention, it has been found that
extremely short impregnation times, between about 5 and
about 15 seconds, can be used to impregnate tobacco
when these high pressures are used, while obtaining
extremely desirable increases in tobacco filling
capacity, for examp]e, in excess of 50 to 100% increase
in filling capacity. The temperature of the propane is
advantageously maintained above 280F (138C),
preferably between about 300F (149C) and 400F
(204C), e.g., about 300-315F (149-157C). This
provides excess sensible heat for heating the tobacco
in the impregnation zone.
Referring now to Figure 2, a preferred
tobacco upstream feeding and loading apparatus is
illustrated. Tobacco, in any of various forms
including the form of leaf (including stem and veins),
strips (leaf with the stem removed), cigar filler,
,
2~2~
cigarette cut filler (strips cut or shredded for
cigarette making), or the like, preferably cut filler
tobacco, is moisturized by means known to those skilled
in the art in block 66 to a moisture content of at
least about 13~, and preferably at least about 20%, and
passed through a pneumatic conveying pipe 68 to a
metering device designated generally as 70.
Advantageously, as illustrated, the metering device 70
is formed by two separate metering tubes 72 and 74.
Preferably each of the metering tubes 72 and 74 has a
substantially rectangular cross-section that increases
or diverges slightly in size in the direction of
tobacco flow. As will be apparent, the metering tubes
can have other configurations, such as a circular
cross-section.
The tobacco from pipe 68 enters a feed valve
76 located at the top of the metering tubes and is
distributed between the two metering tubes 72 and 74.
Any of the valves known in the art for feeding a solid
material such as tobacco into a column can be used in
accordance with the present invention. An exemplary
feed valve is a multi-vaned rotary valve as illustrated
in Figure 2. The thus distributed tobacco forms a
substantially vertical tobacco column in each of the
metering tubes 72 and 74. These vertical tobacco
columns are of a predetermined height, which is
monitored in each of the metering tubes by height
sensing means 78. Preferably, the height of the
tobacco column in each of the columns is about three to
four feet. When the height of the tobacco falls below
the predetermined desired height in either of the
tubes, the sensing means actuates the feed valve so
that additional tobacco enters the tube until the
desired height is obtained.
After the tobacco is distributed and fed into
each of the metering tubes 72 and 74, it is subjected
to a steam preheating treatment, which also further
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-24-
moistens the tobacco. Preheating of the tobacco
provides heat for establishing proper short cycle time
conditions in the impregnation zone. Additionally,
extra moisture added to the tobacco plays a role in
providing good exp~nsion results and increases the
pliability of the tobacco. In accordance with this
invention, it has been found that when the tobacco fed
to the impregnation zone 22 has a moisture content
above about 20 wt. percent, preferably between about 24
wt. percent and about 30 wt. percent, and is preheated
to a temperature above about 150F (66C), increased
expansion can be obtained. In the present invention,
the tobacco is preferably both moisturized and
preheated by steam injection into each of the stems of
the metering column. Steam heating is desirable
because heat can be effecti~ely and efficiently
transferred to the tobacco, while at the same time the
mGisture level can be increased. In addition, because
the tobacco is contacted with steam in a metering tube,
the tobacco in the tube above the steam injection zone
or zones can act as an insulator thus increasing the
efficiencies of using stem injection to heat the
tobacco.
Steam is injected into each of the metering
tubes 72 and 74 at a location below the top of the
tobacco column in the tube. Two preferred steam
injectors are designated generally as 80 and 82 in -
Figure 2 and each are described in greater detail
below. These injectors re~uire dry steam which can be
provided by superheat or by external heating of steam
pipes and manifolds to prevent condensation. In
addition, the temperature of the steam injected is
sufficient to heat the tobacco to a temperature above
ambient temperature, preferably above about 125F
(52C), more preferably a temperature of above 150F
(66C), e.g., to a temperature of 150 to about 200F
(66 to about 93C).
. '.:: : , ' . . , . ~ :
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2~5~
-25-
Figures 3 and 4 illustrate two embodiments
for providing steam injection into the tobacco columns.
Figure 3 is a top view taken along line 3-3 of Figure 2
of steam injector 80. Steam is injected through
conduits 84 into an exterior manifold 86 surrounding
the metering tube 72. The manifold is spaced apart
from the exterior wall of the metering tube to form an
annular enclosed space 88. This space contains the
injected steam. The manifold 86 communicates with the
interior of the metering tube via a plurality of ports
90 distributed along opposing faces of the tube. Steam
passing through ports 90 penetrates into the tobacco
column an indicated by the arrows in Figure 3
Figure 4 illustrates another preferred
lS embodiment of a steam injecting apparatus for
introducing steam into the tobacco columns. In Figure
4, the steam injecting apparatus 82 is an insertable
forked member formed by a hollow bridge 92 supporting a
plurality of hollow apertured tines 94. The steam
injecting member 82 is positioned horizontally for
reciprocal movement between a first position outside of
the metering tube 72 and a second position within the
tube. A hydraulic piston or similar motor means is
axially attached via a shaft for moving the steam
injector between the two positions so that the tines 94
penetrate into and out of the tobacco column as
indicated by the direction arrow in Figure 4. When the
tines are inserted into the tobacco column, steam is
injected through a conduit 96 into the bridge and then
into each of the tines of the insertable member. Steam
then exits from the tines through a plurality of ports
98 in each tine member into the tobacco column as
indicated by the arrows.
Although use of both embodiments of the steam
injectors is illustrated in Figure 2, it will be
apparent to the skilled artisan that either of the
steam injectors may be used alone. It can be
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2 8
-26~
advantageous, however, to use a combination of the two
steam in~ectors to insure that the steam is injected
across the entire width of the tobacco column.
The steam injectors of the present invention
are preferably placed at a selected location along the
height of the tobacco column such that substantially
all of the steam injected into the column is condensed
prior to exiting top of tobacco column. The injected
steam travels upwardly within the tobacco column and
heats the tobacco within the tobacco column as it
rises. As heat is gradually lost from the steam, it
condenses onto the tobacco as moisture, until all steam
has condensed.
Following preheating and moistening the
tobacco travels downwardly in the column for dispensing
as a batch to loading conduits 110, shown in Figure 2.
A tobacco column dividing member, designated generally
in Figure 2 as 112, is operatively asociated with each
of the metering columns 72 and 74. Like the tined
steam injectors 82, the tobacco column dividing member
is positioned for horizontal reciprocating movement
between a first position outside of the column and a
second position within the column.
A top view of a preferred embodiment of the
tobacco dividing member is illustrated in Figure 5. As
shown in Figure 5, tobacco dividing member 112
comprises an actuator rod 114, a bridge 116 and a
plurality of closely spaced tines 118. The dividing
members move between the first and second positions to
divide the tobacco column into upper and lower portions
and to thereby measure a predetermined amount of
tobacco which is to be dispensed from the bottom of
each of the tobacco columns. When the tines 118 are
inserted into the tobacco column via an opening
described below, the upper portion of the tobacco
positioned above the dividing means is supported by the
tines. The tines are accordingly closely spaced, e.g.,
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-27-
about one-fourth to one and one-half inches apart. The
lower portion of the tobacco column below the tines is
subsequently dispensed to the loading conduits 110.
The tined tobacco dividing element 112 is
preferably vertically adjustable for selective
engagement with the tobacco column in a pluralit~ of
predetermined vertical locations. Figure 7 illustrates
a range H of heights through which the position of the
tobacco column dividing member can be adjusted. This
provides flexibility in selecting the amount of tobacco
to be dispensed to the loading conduits 110 because
adjusting the position of the dividing member adjusts
the size of the tobacco charge dispensed from the
bottom of the column.
The tines 118 of dividing member 112 access
the tobacco column via a plurality of vertical elongate
slots, which are aligned with the tines 118 through a
double walled portion of the metering tube as best
illustrated in Figures 6 and 7. Figure 6 illustrates a
first outer side wall 120 having elongated vertical
slots 122 formed therein. The outer side wall 120 is
partially broken away in Figure 6 to illustrate a
second spaced apart inner side wall 124 which includes
a second row of vertical slots 126 aligned with
vertical slots 122 and a plurality of horizontal
brushes 128 associated therewith. In addition, a
plurality of brushes 130 are also advantageously
associated with the outer wall 120. The double wall
structure acts as a catch basin to receive tobacco
particles that can adhere to the tines of the dividing
means when the tines are removed from within the
tobacco column. The brushes assist in removing tobacco
particles from the tines. As the tines are withdrawn
from within the tobacco column to a position outside of
wall 120, they contact the two rows of brushes and
tobacco particles are scraped off of the tines and fall
into an opening 132 between the walls. The tobacco
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-28-
particles fall downwardly within the opening 132 to a
lower portion thereof and exit the opening through a
port 134 at the lower end of the opening.
A blocking member preferably in the form of a
rotary valve 140 is associated with the bottom of each
metering tube. The blocking member 140 is engageable
with the tobacco column at a vertical location below
the dividing means 112 for supporting the tobacco
column when the dividing means is out of engagement
with the column. The blocking member 140 is also
disengageahle with the tobacco column for releasing the
lower portion of the tobacco column below the dividing
means 112 to the loading conduits 110.
The blocking member 140 is preferably an air
lock rotary valve. The air lock rotary valve may be
any of the valves known to the skilled artisan, and
advantageously, the valve is an vaneless rotary valve
which is intermittently operated for receiving and
delivering one batch of tobacco at a time as
illustrated in Figure 7. The vaneless rotary valve of
Figure 7 comprises a housing 142 supporting a bucket or
pocket 144 which is rotatable within the housing. A
continuous air lock rotary valve, such as that having a
plurality of vanes, can also be used.
The blocking member 140 is illustrated in
Figure 7 in an emptied, tobacco column supporting
position. When a new a charge of tobacco is to be
dispensed from the bottom of the tobacco column, the
tined dividing member 112 is inserted into the tobacco
column and the blocking member is rotated 180 from its
blocking position to its tobacco receiving position so
that the open end 146 of the bucket 144 is upwardly
positioned in communication with the tobacco column.
In this position the bucket receives the tobacco in the
lower portion of the column and then is moved again
180 to a position dispensing the presized batch of
tobacco to the loading conduits 110. The use o~ an air
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-29-
lock rotary valve as a blocking member is particularly
desirable because in its dispensing position (shown in
Figure 7), the valve blocks and supports the tobacco
column and also provides a seal 148 between the tobacco
column and expansion agent impregnation zone.
The batch dispensing system of the invention
provides a number of benefits. The amount of tobacco
dispensed to the impregnation zone can be easily and
accurately controlled. Thus the dividing members can
be vertically positioned at various positions to
provide any of various predetermined sized batches of
tobacco for impregnation. In addition, the use of
metering tubes provides substantially even distribution
of the tobacco batch across the width of the loading
conduit, below. Batch dispensing of the tobacco charge
is fast, and can provide each tobacco charge to the
impregnation zone in concert with the short
impregnation cycles of the present invention.
Referring now back to Figure 2, the
predetermined amount of tobacco is thus dispensed into
loading conduits 110 for loading onto the spool of the
impregnating apparatus. As illustrated in Figure 2,
separate charges 150 of tobacco are loaded onto the
spool at loading position 24 (Figure 1) by means of a
pair of opposed semi-cylindrical loading and
compressing members 152 which are mounted for
reciprocating movement within horizontal conduits 110.
Preferably, loading conduits 110 have a substantially
rectangular cross-section and are formed of a material
which can withstand wear associated with the repeating
horizontal movement of the loading members within the
loading chambers, such as hardened aluminum. In
addition, advantageously, as illustrated best in Figure
2A, the upper and lower surfaces of the loading and
compressing members are covered with hardened plastic
sleeves 154 which provide lubrication between the
interior walls of the loading chambers and the exterior
. ~ ~ ' ., ' , ~
- 212~2~
-30-
surface of the loading members to prevent ~uckling or
jamming of the loading members. Exemplary materials
us~d to form the sleeves include polyetheretherketone
(PEEK), available from ICI America and RTP Co.
The loading members 152 are connected via
rods 156 to a reciprocating force means such as a
hydraulic piston 157 or the like for cyclic movement
between a retracted position and an extended position.
The tobacco charges are dispensed into the loading
conduits 110 through an opening 158 in the upper wall
thereof. The opening 158 extends substantially across
the width of the loading conduits and is located
between the retracted position of loading members 152
and the extended position thereof. A pivoting closure
member 160 for closing this opening is also provided
and is capable of compressing the tobacco charge into
the loading chamber when in a closed position as
indicated in phantom in Figure 2. Advantageously a
pair of blocking members 162, which may be tined
members, are provided to separate the loading chamber
from the impregnation apparatus. The blocking members
162 are mounted for movement between a first
disengagement position outside of the loading conduits
and a second blocking position within the loading
conduits and prevent tobacco from being blown along the
conduit as the closure member is closed.
To load the tobacco charges onto the-spool
16, the tobacco charges 150 are dispensed from the
rotary valve 140 through opening 158 into loading
conduits 110. The blocking members are inserted into
the conduits 110 and the pivoting closure members 160
are pivoted downwardly to cover the opening 158 and
thus compress if necessary and contain the tobacco
charge within the loading conduits. The semi-
cylindrical loading members 152 are then moved to their
extended position. The tobacco charges are moved
horizontally through loading conduits by the loading
.
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-31-
members 152 and compressed onto spool 16. The opposed
semi-c~lindrically shaped loading members cooperate in
their fully extended positions to form a shell around
the connecting rod 20 of the spool so that the
compressed tobacco is maintained on the connecting rod
of the spool during its movement to the impregnating
position, discussed below. The cylinderical shell
formed by the loading members can also be defined in
part by one or a pair of longitudinal frame members
(not shown~, that can be provided at locations above
and/or below the axis of the spool. Such frame members
are advantageously adapted to mate with the edges of
the semicylinderical loading members to form a closed
cylinderical space around the compressed tobacco.
The loaded spool is moved into its
impregnation position as shown in Figures 1 and 8, and
the sealing rings 30 on both ends of the spool are
forced radially outwardly by hydraulic fluid from fluid
lines 32 for sealing the pressure chamber 22 against
leaks. Advantageously, the sealing rings are
vulcanized or otherwise bonded into annular grooves
formed in the periphery of the spool ends. A
deformable plate or tape 153 is provided at the
interface between each of the elastomeric sealing rings
and the fluid lines 32 so that the sealing rings are
not bonded at this point and can thus be forced
outwardly.
Annular members 160 which may be wear rings,
scraping rings or the like, are also attached in
annular grooves formed in the periphery of each of the
cylindrical end members of the spool and are axially
adjacent to at least one end face of each of the
elastomeric sealing members 30. The wear members have
a circumference greater than that of each of the
cylindrical end members of the spool, which narrows the
annular space or gap between the spool assembly 16 and
the sheli 14. By narrowing this gap, the elastomer of
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'. ~ .. ' : . ~ . ' ' ~
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2 ~ 2 ~
-32-
the elastomeric sealing rings 30 receives better axial
support during the time it is used for sealing. This
minimizes destructive deformation of the sealing rings
resulting from "overflow or extrusion" of the
peripheral edges of the sealing rings into the annular
space between the cylindrical end members of the spool
assembly and the shell.
Preferably, each sealing ring 30 is attached
to a face of a wear member 160 and to surface on the
periphery of tha spool end member. More preferably,
wear members 160 are provided axially adjacent both end
faces of the elastomeric sealing rings 30 and are
attached thereto. The wear members can be attached to
the elastomeric sealing members by welding, adhesive
bonding, vulcanization processes, and the like.
Figure 8 also illustrates a preferred port
construction allowing high pressure gas lines 38 and 40
to communicate through the shell 14 w th rapid delivery
of expansion agent. A plurality of ports 42 are
circumferentially distributed about the periphery of
the shell 14. The enlarged port opening cross-
sectional area provided by ports 42, taken as a group,
provides for an enhanced rate of introduction and
removal of high pressure fluid into and out of the
pressure chamber 22 when the spool member 16 is in the
impregnation position. Advantageously, ports 42 are
diagonally oriented and taper to smaller diameter
openings as illustrated in Figures 8 and 8A to block
entry of particulate tobacco into the ports as the
spool assembly moves from position to position.
An exterior manifold 45 surrounds the shell
14 and forms an annular space around the
circumferentially distributed ports. The ports 42 are
aligned with an annular groove 162 in the spool end
which communicates via a plurality of radial channels
164 and axial channels 166 with grooves 170 formed in
the surface of connecting rod 20. Once introduced
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through gas line 38, the high pressure fluid flows
through the ports 42 into channels 164 and 166 until
reaching grooves 170. Here, the fluid is exposed to
the tobacco loaded and compressed about the spool
connecting rod 22 and flows out of the channels and
into the tobacco as illustrated by the arrows in Figure
8. One or more screens (not shown) surround the
connecting rod 20 to prevent tobacco from clogging the
grooves 170.
Figures 10, 11 and 12 illustrate an
alternative apparatus for improving efficiency of the
spool and shell impregnator by enhancing the rate of
delivery and removal of high pressure, gaseous
expansion agent, to and from the annular high pressure
impregnation zone within the shell. As illustrated in
Figures 10 and 12, the apparatus is shown with the
spool assembly body 16 in motion between a loading
position and an impregnating position~ Thus the spool
assembly 16 is shown partially within, and partially
outside of the shell 14. In this apparatus, each port
42 through shell 14 is advantageously in the form of a
slot of enlarged cross-sectional area, that is
preferably about the same as the cross-sectional area
of the openings through the valves 46 and 48 in the gas
lines 38 and 40 that supply and remove expansion agent
to and from the impregnator. This allows a reduction
in the frictional interaction between the ports and the
expansion fluid with a net result of providing a faster
feed rate for expansion fluid entering into and leaving
the impregnator.
Because the enlarged ports 42 have a diameter
greater than the size of tobacco particles, e.g.
tobacco cut filler, the apparatus of Figures 10-12
includes a port blocking member 260, best seen in
Figure 11, to prevent or minimize entry of tobacco into
the enlarged ports. The port bloc~ing member 260 is an
elongate body having an exterior face 262 of greater
' ' ' ~ ' ' ' .
2~2~62~
-34-
width than the port diameter. As best seen in Figures
11 and 12, the blocking member 260 is joined
longitudinally between peripheral portions of the end
members 18 of the spool assembly 16 and is aligned
radially with the port openings 42 through the shell
(Figure 12).
As illustrated in Figure 11 the blocking
members extends across a portion of the connecting rod
20 of the spool 16 which, in turn forms the 'chamber'
on the spool for holding tobacco. When this portion of
the spool is moved through the shell, the blocking
members 260 cover the ports 42 through the shell 14 so
that tobacco in the spool chamber is prevented from
entering the enlarged ports 42. As best seen in
Figures 11 and 12, the exterior face 262 of the
blocking member 260 is advantageously curved to match
the inside surface of the shell 14. The lower portion
of the blocking member is advantageously tapered in
order to minimize the reduction in space available for
occupation by tobacco.
Preferably, at least two enlarged ports are
provided through the shell and a corresponding number
of blocking members are provided on the spool as seen
in the Figures. A manifold 45 is provided around the
exterior of the shell 14 and defines an annular space
44 that connects to both of the ports 42 so that
expansion agent introduced through the manifold port
38' can communicate with the spool simultaneously
through both shell ports 42. Similarly, expansion
agent removed through manifold port 40' following use
can also exit the shell through both ports 42. This
also increases the rate of feed and removal of
expansion agent from the spool and shell impregnator
allowing a reduction in cycle time.
Returning to Figure 1, following introduction
of expansion agent into the impregnator apparatus, the
compressed and impregnated tobacco is maintained under
,
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2~2~28
-35-
impregnation conditions ~or a short period of time
ranging from 1-2 seconds up to about twenty seconds.
Thereafter the pressure is rel~ased. Preferably,
pressure release is substantially instantaneous, i.e.,
is achieved in about one second or less. This can be
achieved in part by employing a fast acting valve
having a large port ~or rapidly releasing pressure. A
sensor not shown is advantageously provided for sensing
pressure within the impregnator and triggers deflation
of the sealing rings 30 on the spool body when the
pressure therein reaches a predetermined pressure above
ambient pressure, e.g., 5 psig. A second pressure
sensor senses the pressure of the hydraulic fluid in
line 36 which feeds the sealing rings~ Prior to the
time when this pressure reaches ambient, e.g. at 5
psig, this sensor triggers operation of the hydraulic
piston connected to shaft 28 for moving the spool body.
The spool is then moved to unloading position 26
substantially immediately so that tobacco expansion can
be effected.
A pneumatic unloading device such as an oil
free compressor (not shown) is provided in the tobacco
unloading zone and directs fluid such as high pressure
air or nitrogen onto the tobacco surrounding spool 16
when the spool is moved to and from the unloading
position 26. The expanded tobacco removed into the
unloading position 26 expands substantiaIly
instantaneously and as illustrated in Figure 1, is fed
to a recovery chute 172 and then to a conveying
apparatus 174, such as a screw conveyor and the like.
The tobacco which advantageously contains a substantial
amount of moisture, i.e., greater than 13 wt. percent,
is conveyed to a drying zone 176 by conveying apparatus
174.
As best shown in Figure 9 the expanded
tobacco is admitted into a conduit 178 in the drying
zone where it is picked up by upwardly moving heated
,
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-36-
air. Advantageously the heated air has a temperature
of less than about 350F (177~C), and is pr~ferably at a
temperature between about 200F (93C) and about 300~
(149C). The tobacco is conveyed through the drying
zone at a temperature and for a time sufficient to
decrease the moisture content thereof to less than
about 13 percent, and preferably to a value of between
about 6 and about 12 wt. percent. The dried, expanded
tobacco is then passed to a separation zone 1~0. Here
the fluids, including the expansion agent, pass through
a screen 182 or another separating apparatus such as a
cyclone separator and into a recovery loop 18~.
The gas moving through the recovery loop is
preferably primarily nitrogen or another inert gas, and
is injected into the loop as indicated by gas in~ection
zone 186. The nitrogen is heated by a heater 188,
passed through a fan 190 and then continues on in the
loop for picking up the tobacco. A purge stream 192 is
removed continuously from the loop and passed to a
thermal oxidation zone wherein the propane in the
nitrogen is burned.
The tobacco passes from the separation zone
180 to a pair of rotary air lock valves 194 and 196 and
then recovered in a recovery zone 198. The two valves
function to insure that no propane gas is passed
outwardly into the recovery zone. Therefore, inert
gas, such as nitrogen, is admitted between the two
valves. Also, as indicated in Figure 2, nitrogen can
be admitted in other areas of the system for similar
reasons. In this regard, a safety shell 200 in Figure
2 can be provided about the lower portion of the
apparatus, as indicated in phantom. This shell is
provided for the recovery of any propane exiting from
the system during use. Nitrogen is continuously added
to various places in the system. Propane which exits
from various leaks in the system is recovered in the
shell and passed to a thermal oxidizer for burning.
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Returning to the drying treatment, although
when the expansion agent is propane or a similar
expansion agent of the type disclosed in U.S Patent No.
4,531,529 to the White and Conrad, no heating of the
tobacco is necessary in order to fix the tobacco in
expanded form, it has now been found that high moisture
content tobacco can be expanded to a greater degree
than tobacco of normal moisture content. However it
has also been found that some or all of the increased
expansion can be lost as the high moisture tobacco can
collapse. The drying treatment of this invention has
been found to preserve the increased expansion.
Preferably the drying treatment is conducted
rapidly after expansion of the tobacco, e.g., less than
about 5 minutes after expansion, preferably within a
time period of less than about 1 minute following
expansion. Indeed, drying can be conducted
substantially instantaneously following expansion. For
example, the blower used to unload expanded tobacco
from the spool can employ heated nitrogen if desired
and the tobacco can be immediately passed into the
drying zone.
The effect of moisture content on tobacco
expansion is illustrated with reference to Figure 13
which is a graph showing tobacco expansion with varying
amounts of moisture and various degrees of tobacco
preheating. In each case the tobacco was impregnated
for 15 seconds with propane at a pressure of about
2,500 psig and which had been preheated to a
temperature of about 300F (149C). Prior to expansion,
the tobacco had a filling value of about 450 cu.cm/100
g. As can be seen from Figure 13, increasing moisture
content of the tobacco to a level above about 20
percent greatly improves expansion thereof particularly
when the tobacco is preheated to a temperature of about
150F (66C) or higher.
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When propane is used as the impregnating
fluid, the cumulative amount of heat supplied to the
impregnation zone from the heated propane and the
preheated tobacco is advantageously sufficient to
provide impregnation conditions in the impregnation
zone of between about 240F (116C) and about 270F
(132C), preferably about 260F (127"C). It has been
found that impregnation at temper~ture and pressure
conditions of about 260F (127"C) and 2,500 psig can be
achieved in about 5 seconds or even less when the heat
is supplied by both the preheated tobacco and preheated
propane.
The degree of tobacco compression during
impregnation also influences the degree of expansion.
Preferably the tobacco is compressed to a compression
ratio of at least about 1.5:1 during impregnation.
Compression ratio is determined based on the volume of
the tobacco prior to compression. The tobacco volume
prior to compression, or the loose fill volume of the
tobacco, is determined by measuring the tobacco density
in a cubic container of one foot by one foot by one
foot. Tobacco is poured into the cubic container and
weighed to determine the loose fill density of the
tobacco. The loose fill volume of a tobacco charge
prior to compression onto the spool then can be
determined from the weight of the charge and the loose
fill density value of the tobacco. The loose fill
volume of the charge is divided by the compressed
volume of the tobacco charge, i.e., the volume treated
in the impregnation apparatus such as the spool, to
determine compression ratio. All values are determined
at, or corrected to, the actual moisture of the tobacco
charge fed to the impregnation zone. Thus, for a spool
having an impregnation volume of 25 cubic inches,
compressing tobacco having a loose fill volume of 50
cubic inches onto the spool, would result in a
compression ratio of 2:1.
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Advantageously, the tobacco is compressed to
a compression ratio of greater than ~:1, up to ratios
amounts of 3:1 and greater. Compression of the tobacco
increases the tobacco density so that the density of
the tobacco fed into the impregnation zone is
substantially greater than the tobacco density prior to
compression. Those skilled in the art will be aware
that loose fill tobacco densities can vary greatly
depending on whether the tobacco is in leaf form or in
cut filler form; the type of tobacco, the moisture
content of the tobacco, and other factors. Packing
densities of 20-35 pounds per cubic foot, calculated
based on a moisture content of 12% are readily employed
in the present invention. Although increasing the
packing density can, to some extent, increase the cycle
time for achieving identical amounts of expansion,
packing densities in excess of 25-30 pounds per cubic
foot calculated based on 12% moisture and higher have
also been successfully used in the present invention
while achieving impregnation times of below 20 seconds
and filling capacity increases in excess of 50-100%.
Figure 14 is a graph that illustrates how
expansion can be varied by varying tobacco densities
during impregnation and with different impregnation
times. This graph illustrates impregnation of tobacco
samples having a moisture content of 27 percent with
propane at the same conditions described above.
Impregnation times were varied from 4 seconds to 20
seconds. The tobacco samples which had an initial
loose fill density of about 6.2 lb/cu.ft at 12 %
moisture and 76F (24C), were compressed to densities
of 20, 25, 30, and 35 pounds per cubic foot (all
densities calculated at or corrected to 12 percent
moisture). As can be seen from Figure 14, the degree
of expansion increases with increased impregnation time
and with decreasing compression of the tobacco.
However excellent expansion is obtained even at high
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2 ~ 2 ~ 8
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packing densities and short impregnation times of 10
seconds or even less.
Fi~ure 15 illustrates the flexibility of the
expansion process and apparatus of the invention. This
graph is a composite of various expansion data and
illustrates the total increase in tobacco volume per
hour (in cubic meters per hour) which can be obtained
from the apparatus of Figure 1 as a function of
impregnation time and tobacco compression. This data
assumes an available volume of space for occupation by
tobacco of 400 cu. inches, and that the process is
continuously operated at the cycle times shown. As is
apparent, tobacco throughput is increased when cycle
times are shortened and when tobacco compression is
increased. As also seen in Figure 15 the tobacco
volume increase per hour is highest with short cycle
times and increased tobacco compression. This is true
because of the increased throughputs, and despite the
fact that the amount of expansion for each batch of
tobacco was not necessarily as high as could have been
obtained at lower densities and/or with a longer cycle
time. Thus the present invention provides a flexible
process allowing variations in the degree of tobacco
expansion and the degree of tobacco throughput.
The various aspects of the tobacco expansion
processes described herein have been discussed
specifically in connection with the use of propane as
an expansion promoting impregnation agent and the use
of impregnation temperature conditions near or above
supercritical temperature together with conditions of
elevated pressure approaching or above supercritical
pressure, and in connection with preferred apparatus.
It will be apparent that the processes and apparatus of
the invention can be varied by numerous changes; for
example, where recovery of expansion agent such as
propane is not desired, the expansion agent can be
burned following use thereof. In addition various
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~2~28
significant tobacco expansion processes and apparatus
disclosed herein, although particularly suited to
tobacco expansion processes and apparatus employing
high density expansion agent at supercritical
temperatures and using short impregnation times, are
also considered applicable to a wide variety of other
differing tobacco expansion processes, expansion
fluids, and apparatus.
Tobacco filling capacities when referred
to herein, are measured in the normal manner using an
electronically automated filling capacity meter in
which a solid piston, 3.625 inches in diameter, is
slideably positioned in a similarly sized cylinder and
exerts a pressure of 2.6 lbs. per sq. in. for 5 seconds
on a tobacco sample located in the cylinder. These
parameters are believed to simulate the packing
conditions to which tobacco is subjected in cigarette
making apparatus during the formation of a cigarette
rod. Measured tobacco samples having a weight of 50 g
are used for expanded tobacco. Samples having a weight
of 100 g are used for unexpanded tobacco.
Moisture values of tobacco samples are
measured by placing a 100 g sample of tobacco in a wire
mesh basket and then placing the basket into a forced
air oven having an air temperature of about 200 F for
about 3 minutes. The tobacco and wire basket are
weighed prior to and following heating in the oven and
the weight loss expressed as percentage of tobacco
weight prior to heating i5 reported as percent
moisture.
The invention has been described in
considerable detail with reference to preferred
embodiments. However many changes, variations, and
modifications can be made without departing from the
spirit and scope of the invention as described in the
foregoing specification and defined in the appended
claims.
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