Note: Descriptions are shown in the official language in which they were submitted.
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j~~THOD AND APPARATUS FOR LOW RESIDENCE TIME REDRYING OF
TOBACCO
TECHNICAL FIELD
This invention relates to processing of strip tobacco,
and more specifically with the rapid drying, cooling and
reordering of strip tobacco in a tobacco processing plant.
EACKGROUND OF THE INVENTION
Redrying of tobacco leaf material is common in
processing of tobacco material, particularly burley tobacco,
prior to use in cigarettes and after application of a heavy
casing material. In the redrying of tobacco leaf material
control of the moisture content of the tobacco is a goal
pursued due to the stringent requirements of specific
moisture contents of the tobacco leaf needed for further
processing. Processing of the tobacco material including
drying is preferably done at high speeds in order to keep
processing costs down and keep the space required for
processing in the manufacturing plant to a minimum and each
step of the processing of tobacco leaf material requires the
tobacco to be kept at a constant moisture content.
Additionally, time, temperatures, and humidity for drying
tobacco material affects the chemical composition and flavor
of the processed tobacco. Prior to drying, strip tobacco
typically has a moisture content of around 30%. After drying
the moisture content may be as low as 5% and the tobacco is
left very brittle which may cause breakage of the tobacco
leaf during further processing. The breakage is especially
pronounced as the tobacco leaf, after drying, is at around 5%
moisture content. And, so that the chemical composition of
the leaf and subjective flavor remain optimal, the moisture
content after drying must be closely controlled to the ideal
content of about 5%. This close control of moisture content
must be accomplished with as minimal breakage and fluctuation
of the moisture content and chemical composition as possible.
This breakage, or degradation of the tobacco leaf, is
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remedied by the addition of moisture to the leaf material in
a reordering step. Remoistening of the tobacco leaf, or
reordering, raises the moisture content of the leaf material
to around 15g so that the tobacco leaf may be further
processed without further degradation and to keep the tobacco
material at the optimal moisture content for further
processing. Reordering is typically accomplished utilizing
water, steam or a combination of both in combination with
tumbling of the tobacco in a rotating cylinder. This however
often results in additional damage to the tobacco product.
As such, the process and apparatus for drying, cooling and
reordering the tobacco material is very important.
2'ypically, drying of strip tobacco is accomplished using
an apron dryer_ In an apron dryer, air is blown from
LS underneath the conveying means upon which the tobacco is
placed, with the drying air being exhausted from above the
tobacCO product. U.S. patent No. 3,224,452, issued t4
Franklin et al., teaches an apron dryer utilizing three zones
wherein the goal is to equalize the pressure in each zone
2o using pressure sensing means in at least two zones. The
' pressure is equalized in the zones utilizing blast gates, but
the design proves ineffective in providing a high speed
treating apparatus. Additionally, the device teache$
preventing leakage of pressure between zones to ensure equal
25 pressure in each. No attempt is made to vary the treating
conditions or to create a method or apparatus for rapid
redrying and reordering. Alternatively, some dryers may
include drying zones which hare air being blown from the top
of the drying zone through the tobacco material and conveying
30 apparatus and exhausted through the bottom of the dryer.
Diffuser plates are generally used in the conveying means to
even out airflow acro$s the apron conveyor in the updraft
zones. Dryers of this type have inherently high moisture
variation and therefore the tobacco processed therein is
55 susceptible to varying tastes and quality.
Tn addition, the speed at which drying and reordering of
tobacco is done directly affects the overall casts and
AMENDED SHEET
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chemical comppsition of the tobacco processed. Typically,
drying, cooling and reordering Qf tobacco prior to
utilization in a cigarette manufacturing process takes in the
range of 20 to 40 minutes. The time required for
conditioning of the material is Lang because, i,n drying, the
tobacco is treated by passing the tobacco through a tortuous
air flow path, tumbling the tobacco through an airstream, or
the tobacco is passed over jets of a~.r. Passing the tobacco
through a tortuous aix flow path causes hygienic problems,
clogging problems as well as other airflow path problems
AMENDED SHAT
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which must frequently be solved. Passing the tobacco over
air jets also causes great variations in drying of the
tobacco bed. Such inconsistencies create processing problems
down the manufacturing line in that some of the sections of
- 5 tobacco have been kept at appropriate temperatures while
other sections have not. Additionally, the chemical
composition of the tobacco may differ as it has been dried to
differing moisture contents. Thus, a large amount of time is
needed in order to properly and evenly dry the tobacco
material.
Additional problems are also associated with reordering
of the tobacco. If the moisture applied to the tobacco is
only applied at specific points, certain areas of the tobacco
bed will have a higher moisture content than others which
changes the characteristics of the tobacco. It is therefore
required to have drying and reordering of the tobacco without
a great differential in two different samples as well as
keeping the processing time at a minimum.
In particular, drying of the tobacco material directly
effects the generation of pyrazines in the tobacco. Attempts
at changing the drying process with regards to speed and
drying temperature can affect the level of pyrazines in the
tobacco thereby affecting substantive aspects of the
processed material such as flavor and aroma. Any change in
the drying process therefore must not change the composition
of the tobacco as it relates to pyrazines and other
constituent elements.
SUMMARY OF TF~iE INVENTION
The present invention provides a method for low
residence time redrying, cooling and reordering of strip
tobacco material with minimal degradation of the tobacco
during processing. The present invention causes evenly
distributed drying and moistening across the entire bed of
tobacco material processed as well as only requiring a
limited amount of time to fully complete the drying, cooling
and reordering of the tobacco. The present invention
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additionally provides a means for rapid drying and reordering
of tobacco in large quantities which are processed in a short
amount of time and in very little floor space while also
keeping the handling damage of the tobacco to a minimum.
The method of the present invention is comprised of low
residence time drying using fluidized bed technology while
requiring very little processing time, total residence time
being about 10% of the drying time required in prior art
redrying techniques. For redrying of the tobacco material, a
l0 bed of tobacco is formed on a belt conveyor. The tobacco bed
passes through five drying zones, each zone drying the
tobacco using heated air blown from above the tobacco through
a pressure plenum. In each drying zone, heated air is
directed towards the upper surface of the tobacco while also
preventing small fragments of the tobacco from recirculating
through the dryer. The tobacco is then conveyed to a cooler
where the heated tobacco is cooled with ambient air being
directed downwardly onto the tobacco material which is then
conveyed to a reorderer which remoistures the tobacco to an
appropriate moisture content.
The method of the present invention more particularly
comprises passing strip tobacco from a bulker onto a belt
conveyor at a predetermined bed depth. The tobacco passes
through a dryer where heated air is blown onto the tobacco at
between 200°F (93.3° C) to 280°F (137.8°C). The
tobacco is
dried to about 5% moisture content. The tobacco is then
cooled utilizing ambient air to about 80°F (26.67°C). The
tobacco, using vibrational conveying on an upward slope, is
reordered through a steam tunnel. At the exit of the steam
tunnel (reorderer), the tobacco exhibits a moisture content
of about 15% which is the moisture content required for .
utilization in filling cigarettes. The entire time the
tobacco is resident in processing is only about two minutes.
Finally, the present invention comprises a drying
tobacco in a plurality of fluidized bed dryers using heated
air; cooling said tobacco in a fluidized bed cooler using
ambient air; and, reordering said tobacco in a steam tunnel
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in order to raise the moisture content of said tobacco.
Accordingly, one aspect of the present invention
resides in an apparatus for rapid drying, cooling and
reordering strip tobacco, comprising a tobacco dryer for
creating a fluidized bed of tobacco, said dryer having a
plurality of individually controlled heating zones; said
dryer further comprising a first heating zone which subjects
said tobacco to air from above, said air heated to about
22o°F(104.4°C); a second heating zone which subjects said
l0 tobacco to air from above, said air heated to about
240°F(115.56°C); a third heating zone which subjects said
tobacco to air from above, said air heated to about
240°F(115.56°C); a fourth heating zone which subjects said
tobacco to air from above, said air heated to about
240°F(115.56°C); and a fifth heating zone which subjects
said tobacco to air from above, said air heated to about
240°F (115.56°C); a tobacco cooler having a cooling zone; a
continuous conveyor belt extending through said tobacco
dryer and said tobacco cooler; a steam bed transitioning
area at the end of said continuous conveyor; a reorderer
having a steam tunnel formed therethrough; and a vibrating
conveyor adjoining said steam bed transitioning area and
extending through said reorderer.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the invention will be had
upon reference to the following description in conjunction
with the accompanying drawings in which like numerals refer
to like parts and wherein:
Figure 1 is an exemplary view of the processing
apparatus for drying, cooling and reordering the tobacco;
Figure 2 is a block diagram illustrating the processing
required for low residence time drying, cooling and
reordering;
Figure 3 is a front view of a fluidized bed which shows
air directed onto processed tobacco;
Figure 4 is a perspective view of a reorderer; and
Figure 5 is a graph representing the production of
pyrazines in tobacco during drying.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In a preferred embodiment of an apparatus l0 of the
present invention for low residence time drying, cooling and
reordering of strip tobacco is shown schematically in Figure
1. Strip tobacco 12 is fed from a bulker, not shown, onto a
continuous conveyor belt 14. The tobacco 12 is placed onto
belt 14 at a constant depth of about 3 inches along the
entire cross-section of belt 14. Belt 14 passes the tobacco
through each of the drying/heating zones of the dryer 38,
said zones being identified as Zone 1, Zone 2, Zone 3, Zone 4
and Zone 5, respectfully referenced as 22, 24, 26, 28 and 30.
The dryer 38 is comprised of separate independently
controlled heating zones so that the tobacco may be
accurately processed and the drying may be finely controlled.
Each zone can be controlled independently, said controls
including temperature, plenum pressure, and exhaust air flow.
Each zone of the drying process dries the tobacco 12 using
known fluid bed technology, one such dryer being a JetzoneTM
Fluid Bed unit manufactured by Wolverine Corporation. Each
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of the zones 22, 24, 26, 28 and 30 is independently
controlled and has an independent heated air intake and
exhaust, as shown in Figure 1. After drying, tobacco 12 is
then passed into a cooler 32 which again utilizes fluid bed
technology, such as the previously described Jetzone'" Fluid
Bed unit, except without utilizing heated air at the intake.
The tobacco 12 is cooled using ambient air to reduce the
temperature of the tobacco 12 for proper reordering. From
cooler 32 the tobacco 12 passes from continuous belt 14 to a
steam/water bed 36 which accepts the evealy distributed dried
and cooled tobacco 12 With minimal handling damage.
Steam/water bed 36 provides a cushioned drop area created by
steam/water bed 36 where tobacco 12 falls before beginning
the process through reorderer 34. In the reorderer 34 the
bed of dried tobacco 12 is subjected to steam in order to
raise the moisture content of the tobacco 12 to an
appropriate level of about 15% moisture. Using vibrational
conveyance at a slightly upward angle of inclination tobacco
12 passes through steam tunnel 40 of the reorderer 34. This
allows the dried and remoistened tobacco 12 to pass through
the reorderer 34 with no mechanical handling which would
promote damage to the dried tobacco material 12.
Dryer 38, as stated previously, is comprised of five
independent drying zones, 22, 24, 26, 28 and 30 through which
continuous belt conveyor 14 passes. Belt conveyor 14 conveys
tobacco 12 at about a three inch depth (7.62 cm.) and is 7
feet wide (213.3 cm.). The conveyor 14 is a single conveyor
which passes through each of the drying zones as well as the
cooling zone in order to minimize handling damage.
Tobacco 12 enters dryer 38 from a bulker at around 30%
moisture content, as shown in Figure 2. Heated air 50 is
forced into each dryer zone into a pressure plenum 52, shown
in Figure 3, at the following pressures and temperatures:
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ZONE AIR TEMPERATURE PLENUM PRESSURE
HEATING ZONE 1 200F {93.3C) to 2.5 inches water
280F (137.8C) (6.35 cm.)
preferably 220F
(104.4C)
HEATING ZONE 2 200F (93.3) to 2.0 inches water
280F {137.8C) (5.08 cm.)
preferably 220F
(204.4C)
HEATING ZONE 3 200F (93.3C) to 1.5 inch water
280F (137.8C) (3.81 cm.)
preferably 220 F
(104.4C)
HEATING ZONE 4 200F (93.3C) to 1.0 inch water
280F(137.8C) (2.54 cm.)
preferably 220F
(104.4C)
HEATING ZONE 5 200 F (93.3C) to 0.5 inch water
280F (137.8C) (1.27 cm.)
preferably 220F
(104.4C)
COOLING ZONE 1 65F (18.3C) to 0.5 inch water
85F (21.4C) (1.27 cm.)
preferably 75F
(23 . 8C)
Heated air 50 is then forced through a plurality of jet
tubes 54 and impinges upon tobacco 12 at a velocity of
between 1000 to 3000 feet(3.4m. to 914.4m.) per minute. Jet
tubes 54, in flow communication with said pressure plenum 52,
are hollow and about 12 inches long (30.48 cm.). The
temperature of heated air 50 in the pressure plenum 52 of
zone 1 dryer 22 is from 200° F {93.3° C) to about 280°F
(137.8°C), and preferably at about 220°F (104.4°C). As
stated, each zone of dryer 38 is independently controlled
SUBSTITUTE SHEET (RULE 26)
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having its own heated air intake and exhaust, as shown in
Figure 1.
Continuous belt 14 conveys the tobacco product 12 -
through the entire dryer 38 at about 1.3 ft/sec. (39.62
cm/sec). Drying zones 2, 3, 4 and 5, represented by
reference numerals 24, 26, 28 and 30, utilize an air
temperature between 200°F (93.3°C) to about 280°F
(137.8°C),
and preferably at about 240° F (115.56°C) and force the air
5o through pressure plenum 52 at the pressures specified
above. The differing temperatures applied in each drying
zone are used in order to minimize case hardening and leaf
curling which may occur when drying of the tobacco leaf is
attempted under high temperatures. Total residence time of
the tobacco 12 in dryer 38 is only about 60 seconds. Dryer
38 is approximately 80 feet (24.38 m.) in length and, as
previously stated, 7 feet wide (2.13 m.). Tobacco 12, at the
entry of dryer 38, is at about 30% moisture content. Upon
exiting of drying 38, tobacco 12 has been evenly dried to
about 5% moisture content in roughly 10% of the time it would
take to dry the tobacco in a standard commercially available
apron drier.
As shown in Figure 3, the dryer zones 22, 24, 26, 28 and
have a plurality of jet tubes 54 which are in flow
communication with the pressure plenum 52. Jet tubes 54
25 force heated air downward onto the tobacco bed 12 with
minimal disturbance of tobacco 12 yet causing an even drying
of the tobacco throughout the tobacco bed and preventing
deviation of moisture content throughout the bed depth.
Accurate drying of the tobacco material is required because
30 of pyrazine generation, removal of harsh volatiles and
improved machinability of the leaf. Drying of the tobacco
material must be closely monitored due to the drying of the
heavy casing which is applied prior to this process, as
improper drying rnay harden the casing and cause the tobacco
leaf to curl.
As shown in Figure 3, air 50 forced through jet tubes 54
is recirculated back up through each dryer zone 22, 24, 26,
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28 and 30 as well as cooling zone 32 through return channels
58 and 59. In order to keep the dried tobacco material 12
from entering the exhaust return lines 5B and 59 of each of
the dryers, balancing of the intake and exhaust fans is
required for each zone. Heated air 50 is provided in the
pressure plenum 52 through forced air from the plurality of
jet pipes 54. Air 50 is forced against the moving bed of
tobacco 12 at a high rate of speed. Air 50 returns up both
side exhaust vents 58 and 59, shown in Figure 3 for
recirculation back through the independent dryer zone. The
air is recirculated within the dryer or cooler zone creating
a closed system which can be readily balanced by adjustment
of intake and exhaust fans. Tobacco bed 12 requires very
little residence time in dryer 38 in order to properly dry
the material to the requisite level, typically in the order
of around 60 seconds.
As a result of the drying process, pyrazines are
generated in the tobacco. The amount of pyrazines generated
are directly related to the temperature at which the tobacco
is dried as well as the total drying time. Pyrazine
formation in the tobacco affects the flavor and substantive
appeal of the smoked material. As a result, drying of the
tobacco must be closely analyzed to ensure that the chemical
composition of pyrazines in the tobacco remain constant from
process to process. Figure 5 shows a graph of pyrazine
formation using different drying temperatures. Drying the
tobacco 12 using dryer 38 with an air temperature of around
248°F (120°C) causes little or no differential in overall
content of pyrazines. Alteration of total drying time also
affects pyrazine formation and must additionally be
_ controlled. With the method of the present invention,
pyrazine formation remains fairly constant while drying at
about 248°F (120°C) even though the drying time is reduced
from more than minutes to 90 seconds. Thus, a reduction in
total drying time utilizing a process and apparatus such as
described herein may be accomplished while still achieving
uniformity in redrying of the tobacco to about 5% moisture
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content.
After passing through dryer 38, the tobacco is at about
5% moisture content. Because the tobacco is at such a low
moisture content, it is susceptible to damage and breaking so
handling must be kept at a minimum. Also, prior to utilizing '
the tobacco 12 in cigarette production, it must be
remoistened as the requisite moisture content of tobacco in
the final cigarette product is about 15%. To accomplish this
task, the tobacco 12 must pass through cooler 32 which uses
the same jet tubes 54 as are shown in Figure 3. The air 52
used in cooler 32, however, is at ambient temperature,
approximately 75° F (23.8°C), cooling the tobacco in the
tobacco bed 12 to around 80°F 126.6°C). Total residence time
of tobacco 12 in cooler 32 is about 15 seconds and requires
only about 20 feet (6.1 m.) of processing length to reduce
the tobacco to the appropriate temperature.
The tobacco enters the reordering phase in order to
raise--the- uTi°viriture--~c~n~e3'ft ~f the--tobacco--~~--the--
aPpr~przc'~tE'.
levels, from 5% moisture content to around 15% moisture
content. In order for the tobacco to pass from conveyor 14
into steam tunnel 40 of reorderer 34, transitional steam bed
36 is provided. Transfer station 36 is a steam/water bed
which receives the tobacco from conveyor into steam tunnel
40. The height differential between conveyor 14 and
transition station 36 is about 42 inches (106.7 cm.). A
blanket of steam or water is provided under an independent
pressure source at the beginning of the reorderer 34 to
cushion the fall of the tobacco material 12 and to provide an
initial high density moisturizing zone while also insuring
product degradation is kept to a minimum. This drop
zone/steam blanket 34 is located at the infeed of the steam _
tunnel 40. The source of the steam or water, as previously
stated, is under an independent header and can be controlled
independently from the steam tunnel 40. The vibrational
conveying system of the reorderer 34 takes over at this point
and progresses the tobacco material 12 up a slight uphill
gradient through steam tunnel 40. Steam tunnel 40, shown in
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Figure 4, is comprised of bed 60, side walls 64 and 66, and a
plurality of atomizers 62 which are formed in the bed 60 and
wails 64, 66 which are in direct communication with a steam
source. A steam tunnel such as a steam tunnel conditioning
unit manufactured by COMAS may be used. The reorderer 34 is
kept at an upward angle of about 2.5° and moves the tobacco
bed, which is still at about 3 inches depth (7.62 cm.), down
the bed 60 using vibrational conveyance. The plurality of
atomizers 62 utilized in the steam tunnel 40 provide a fine
mist of moisture in order to evenly raise the moisture level
of the tobacco bed without great deviation in any sample
area. Steam tunnel 40 is about 20 feet in length, 7 feet
wide matching the width of dryer 38 and cooler 32. Tobacco
12 has a total residence time within the reorderer of only
about 15 seconds. The moisture content of the tobacco 12
upon exiting reorderer 34 is uniformly 15% throughout.
The apparatus 10, dryer, cooler and reorderer, of the
preferred embodiment of the present invention has a total
length of about 120 feet (36.6 m.) and is 7 feet (2.13 m.)
wide. The handling capacity of the method and apparatus of
the present invention is approximately 14,000 pounds(6350.4
kg.)/hour at the exit of the reorderer. Total residence time
of the tobacco in the dryer, cooler and reorderer is about 90
seconds. This is a marked improvement from prior art dryers
and reorderers which have required a total residence time in
the order of about 20 minutes and encompass more than 200
feet (60.96 m.) in length and have exit reordering capacities
of about 10,000 poundsf4356 kg.)/hour.
The foregoing detailed description is given primarily
for clearness of understanding and no unnecessary limitations
are to be understood therefrom for modifications will become
obvious to those skilled in the art upon reading this
disclosure and may be made without departing from the spirit
of the invention or the scope of the appended claims.
