Note: Descriptions are shown in the official language in which they were submitted.
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TOBACCO DRYING APPARATUS
TECWNTCAL FIELD
S The present invention relates to ati apparatus for drying cut tobacco and
more particularly to
an apparatus for drying tobacco under relatively high humidity dxying
conditions.
BACKGROUND OF TTY rN'VENTION
In the manufacture of cigarettes and like articles, it is the usual practice
co reduce tobacco, the
term being used herein to include both lamina and stems, to a panicle size
appropriate for
manufacturing cigarettes. Tl~e moisture content of the tobacco is generally
increased prior to
this size reduction processing in order to mixziutnize tobacco breakup and
provide a material of
uniform particle size. Furthermore, in order' to process the treated tobacco
tat the
manufacturing of cigarette rods, it is necessary to reduce the l~aoisturc
content of the tobacco
to a level below that which the tobacco is at after treatment by casings,
flavorings and other
additives. The actual drying process has a direct impact upon the quality of
tobacco utilized
during cigarette manufacturing because of the effect the drying process has
upon the tobacco
material itself.
Additionally, drying of tobacco after the addition of flavorings and casinbs
has a direct
impact upon the quality of the tobacco itself. Tt; during drying, the tobacco
is subjected to
rigorous agitation or contact with stationary surfaces, the tobacco material
ea~a be damaged by
breakup thus decreasing the tilling capacity of the tobacco. This unwanted
result is also
acliieved when drying under low humidity conditions. It is therefore necessary
to dry the
moist tobacco under high humidity conditions while also preveneing damaging
contact to the
tobacco material.
3U U.S. Patent No. 4,167,191 teaches a pmcess for high humidity drying of
tobacco m~.~terial in
order to reduce the moisture content of expanded tobacco while mizktxaizzng
yield losses and
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reducing particle lamination while maintaining filling power. The air
temperaitu'e. used to dry
the tobacco is within a range of around 250EF(121.1Ef~ to about 65UEF(343_2EC)
in the
presence of an absolute hutxtidity at a Ieve1 above that which will provide a
wet-bulb
temperature reading of at least about 1 SiIEF(65.6EC),
U_S_ Patent No. 4,315,51. S teaches a tobacco drying apparatus having a
pluraEity of expansion
chambers which cffcxt a drying of the tobacco within a high humidity
environment The
drying chambers are utilized to reduce the velocity of the air flow through
tlt~e apparatus as
well as a dryer means do effect drying of the air entrained tobaveo to the
desirod moisture
level. However, the apparatus requires long extensions of air ducting as well
as several air
redirection areas or elbows which cause the ~tobac;co to come into contact
with the walls of the
ducts tux the air chambers causing tobacco breakup, sanitfuy, cleaning and
other problems
within the apparatus.
SUMMARY OF THE iNVENT1(aN
The present inverilion is for a high humidity tobacco drying apparatus and
more particularly a
high humidity cut tobacco drying apparatus which requires minimal residence
time of the cut
tobacco in the drying and expansion chamber.
2U
Mon particularly, the present invention eoxnprisos a heated air intake duct
which provides air
at a predetermined temperature and humidity level. The air intake duct enters
into a tlrst
arcuate elbow wherein cut tobacco is mixed in the high velocity heated air by
an upwardly
extending trapezoidal inlet The first arcuate elbow rCdirects the air flow
from a horizontal
airflow to a vertical airflow. The outer wall of the intcsrior first elbow has
a water cooled
door which opens outwardly for access to the interior of said drying
apparatus. Tha first
elbow redirects tfte tobacco eatraiztCd air~ow vcrticaiiy ixttb a tong
verricaiiy extending
drying and expansion chamber. The vertically extending drying chamber Cnds at
a second
elbow which redirects the siz~l.ow into a tangential separator. The second
elbow also has a
water cooled door on the interior outer wall thereby preventing buildup of
casings and other
materials on the interior surface of the elbow. The tangential separator
provides a means for
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removing the cut tobacco from the high velocity air stream by reducing the
velocity of the
airflow and allowing the tobacco entrained therein to fall out of the
airstream and into a
rotary airlock. The heated air stream exits the separator frottt both side
walls of the tangential
separator, eacli of said exhausts ezttCriztg a high efficiency cyclone for
further separation sad
removal of any tobacco matexial remaining tux the aurstream_
Finally, the preset inv~tion comprises a high humidity drying apparatus for
drying out
tobacco, comprising: a longitudinally extending bested air intake duct; a
first a~iate elbow
in flow communication with said intake duct and having a downward preselected
angle of
I O eurvatute;, said first elbow having a hinged water-cooled door on an outer
wall; an upwardly
extending tobacco inlet of trapezaidal crass-section in flow communication
with said first
elbow, said upwardly extending tobacco inlet formed an said first elbow at a
point vsihere the
vertical expansion of the Fu~t areuate elbow begins; a verti~lly extending
drying chamber in
flow aammunication with said first elbow; a second arcuatc elbow in flaw
communication
with said vertically extending drying chamber said second elbow having a
binged water
cooled door on any outer wall; a tangential separator in flow communication
with said sccox~d
elbow, said separator having a tobaeca outlet airlock, said separator also
having a first and a
second centrally alignod perpendicular air exhaust on opposed sides, said
first air exhaust
being in flow communication with a first high off cieney cyclone and said
second air exhaust
izx flow communication with a second high effici~.~nCy cyclone.
BRIEF DESCRi~TION Ol~ 'rFIE DRAWINGS
A better understanding of the invention will be had upon reference to thc~
followuig
description in conjunction with the accompanying drawings in which like
numorals refer to
like parts and wherein:
Fig. 1 is a side view of a high humidity drying apparatus of the present
invention;
Fig. 2 is a fmnt view of a vertically extending drying and expansion chamber
of Fig.
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1.;
Fig. 3 is a perspective view of the tangential separator, the two air exhausts
and the
lust and second high eff cicncy cyclone of Fig. 1;
Fig. 4 is a perspective view of the tobacco inlet area;
Fil;. 5 is a side view of the water cooled door on the first arcuale elbow;
Fig. 6 is a side view of the water cooled door on the second arcuate elbow;
Fig. 7 is a side view of the tangartial separator and the watcx cooled door of
its upper
edge; and,
Fig. 8 is a cut away bottom view of the vertically extending drying and
expansion
chamber of Fig. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
~0
As shown in Figure 1, a high humidity drying apparatus 1 U of the present
invention is
cot~aprisGd of multiple duct section.R L 1, 14, 20, 26 and 30. Air far use in
the apparatu.R 10 is
heated is a furnace (not shown). The circulated air, after heating, is raised
to an appropriate
moisture level to create high humidity drying conditions. Moisture is added by
injecting
stcayn into tbc air stream in order to raise the moisture level of the
circulated heated air to the
appropriate level. This also serves to raise the ttmperriurc of the circulated
air within the
dxyaz~.g apparatus itself. The moisture level of the airstream is closely
monitored in order to
provide a wet-bulb temperature of, for example, at least about 210EF(98.9EC)
as that term is
defined in ~U'. S. Patent No. 4,167,191.
i A heated air inlet 15 receives the air from the furnace at a relatively high
velocity such as, for
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example, from 5,000( 1523.9 rtt) to about 8,000(2438.4 m)fa;t per minute. A
heated air intake
duct 11 is disposed in flow communication with and downstream from inlet 15
with
expansion joints 17a and 17b being provided to allow for the heated air intakC
duct 11 to
cxpattd and contract as the air is passed therethrough. The heated sir intake
duct 11 has a
height of about 18 inches and a width or depth of about 66 inches(167.5 cm.).
The average
air temperaiute at the heatod air intake duct 11 is generally maitttaincd at
around
3fi0EF(182.2EC). The sir in the heated aix intake duct 11 has a velocity of,
for example,
about 6300 ft.(1920.2 m~min. as it is accelerated into a narrow entry throat
19 of first arcuate
elbow 14.
IO
The entry throat 19 of first arcuate elbow 14 is tapered inwardly thereby
providing f-u'st
arcuate elbow 14 with an inner diameter less than heated air intake duct 11.
Heated air intake
duct t 1, as shown in Figure 1, has a downward angle of appxoxirna.tely about
12 to 13
does front horizontal before fixst elbow 14 toms upwards to redirect the
airQow
accordingly. After first elbow 14 turns upwards, a trapezoidal inlet airlock
12 is provided aq
the means bo add cut tobacco into the airstream. Inlet airlock 12 is generally
of a trapezoidal
cross-section and is positioned above elbow 14 allowing the tobacco to fall
verticalty into the
airstream flowing through elbow 14 below airlock 12. Inlet airlock 12 has
located therein a
rotary airlock 12a, shown i» Figure 4, for incn,~mental addition of thd cut
tobacco into the
sirslxeam thereby preventing a decr~:ase in the pressure and speed of the
airflow therebelow_
The cut tobacco which enters inlet airlock I 2 usually has casings, flavorings
and other
additives blended therewith and exhibits a tobl maisturc coxttcnt of generally
about 21 °/a to
23% by weight. In a preferred operation, cut tobacco is passed through the
airlock 12 at a
2S rate of, for example, between about 14,()n0 lb(5350 kg)/hr and about 49,000
lb(22226 kg)Ihr.
As shown in p'igure 1, after narrowing along narrow neck portion 19, elbow 14
is provided
with an increasing diamctcx section starring at a position id~~ntifi~d by
vertical expansion line
13 at the juncture with the inlet airlock 12. 'this vertical expansion line 13
,prevents a
negative pressure point forming withizt the inlet airlock I2 and expands along
the interior
angle of curvature of the elbow 14. 'I he incr~sing height of the interior of
the Clbow 14 at
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the vertical expansion line 13 of the airlock 12 causes a zero pressure point
to form just above
the expaztsaon line l 3 of first elbow 14 and within the airlock 12 itself.
This vertical
B~>Z~tflB taffftii T ii~a''iIt cX~iinWui°xu~fi'iS i'v
auv~C't»'iu"ciias~di:io i;uij l~'idt'v'
pressure point within the airlock 12 prevents backflow of the cut tobacco into
the airlock and
keeps the cut tobacxo flowing info the airseream with minimal buildup of the
tobacco in the
airlock. A better diagram of the trapezoidal design of the inlet airlock is
shown in )~igure 4
withixlt which is located a rotary airlock 12a which incrementally allows
tobacco into the
airstream flowing #hcrcbelow under high velocity. Cut tobacco enters the
airlock from a
vibrating conveyor system which pmvidcs the oobacco after fine cutting by a
separate cutting
apparatus. The cut tobacw bass a moisture content of around 21% to 23% as
stated
previously. By implementing the widening of the airlock 12 at expansion line
13, the citt
tobacco is prevented from bacl~lowing into the airlock which can occur when
negative
pressure is formed within the airlock chamber. The trapezoidal cross-sectional
airlock allows
the cut tobacco to be fed into tlxe main aiastreat~a at a relatively high rate
of, for exarrtple,
approximatxly 30,000 pounds(13608 kg~hour on average: ox greater, without
clogging the
airlock portion of the drying apgarxtus or oversaturating the airstream.
The overall design of the present invention creates a double null point
pressure configuration
which is caused directly by the design of the venturi at the tobacco inlet 12_
A first pressure
null point is formed just within inlet area 12 co prevent backflow of the
tobacco in the
tobacco inlet area 12. A second null point is created within tangential
separator 30 j ust below
tlxc air rxhausts 32 and 36 which exit the separator centrally therein. As
stated, this double
null point conrguration aids in transporting the cut tobacco through the
drying apparatus and
ensuring a smooth flow of material throughout the drying apparatus 10.
As shown in Figure 1, first elbow 14 is provided wish a wal;cr cooled exterior
door 16.
Water cooled door 16, shown in Figure 5, provides access to the interior of
the first elbow 14
of drying apparatus 10. Door 16 is provided with a curved interior outer wall
23 which
comes into contact with the cut tobacco and the moist flavorings and casings
added thereon.
Chilled water is circulated through the door 16 within interior channels which
repeatedly
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cross the length of the door 1.6 in back and forth fashion in order to keep a
lay~x of
condensats moisture on interior outer wall 23 which in turn prevents buildup
of the casings
and flavorings. These channels are formed in a back and forth direetio:n in
order to cover as
much surface area of the door 14 as possible. The buildup of material on the
outer wall 23
can present hygiene problems as well as reduce the smooth now of tobacco
material which
comes into contact with the interior outer wall 23- By passing chilled water
through interior
pipes of the door 16, a condensation layer is created on interior outer wall
23 which allows
the cut tobacco to come into contact with the layer of moisturs on the wall
preventing
deposits of any of the casings or flavorings on the interior of the drying
apparatus.
tp
Water cooled door 16 is also attached Lo air cylinder 25 which allows the dour
to be opened
and closed. Door 16 is hinged at point 27 to facilitate: the opening and
closing action. While
interior outer wall 23 of door 16 is curved, a fiat contact surface 25 is
utilized in order to
provide a flat smooth sealing surface. This flat contact surface 25 allows
proper sealing of
the door 16 onto elbow 14 while still providing a hinged access point into the
apparatus. By
providing water cooled door 16, buildup on the interior outer wall 23 is kept
to a minimal
level and access is provided into the interior of the drying apparatus for
inspection and
cleaning when required.
ltetuming to Figure 1, downstream from fiiait arcuate elbow 14 is vertically
extending drying
and expansion chamber 20. And, as best shown in Fignre 2 at the dowx~strc~m
terminating
end of f rst elbow as identified by the numeral 1 R marks the beginning of the
expansion of the
interior of the drying chamber, Vertical drying channber 20 extends upwards
genera3ly about,
for example, 42 feet(12.$ m) to 60 feet (18.3 m) to provide adequate distance
and drying tirtxe
fox the cut tobacco. In order to dry the cut tobacco to the appropriate
moisture level, tobacco
eatrainad within the airslream will remain in the drying chamber 20 until it
reaches a
predetermined moisture content, usually for example, about 13% to 15% by
weight. If the
moisture content of the tobacco is too high, the tobacco will lx. too heavy to
rise to the second
elbow 26. In addition, to ensure the proper flow of tobacco within the
apparatus and
especially in the vertical drying and expansion chamber 20, the walls of the
vertical drying
chamber 20 are rounded at the comers of the chamber, as shown in Figure 8, to
prevent
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contact of the moist tobacco with the interior ducts of the drying apparatus
thereby causing
airflow or liygiene problems. Tlvs ctu'vcd or circular design promotes a
smooth airflow
through the drying apparatus 10 by removing the 90E corners where circulating
air tray
slagnatc and lessen tobacco flow capability. Typically, within the comers of
the ducting,
airflow tends to stagnate or become less active thereby preventing the proper
flow of the
tobacco entrained within the air.
Downstream of the vertical drying chamber 20 and in flow communication
therewith is
second arcuate elbow 26 which, as with first elbow 14, is fitted with an
outwardly oxtending
water cooled door 24. Second elbow 26 is disposed to redirect the air
entrained tobacco from
the vertical direction to horizoni<~.1. Second elbow door 24 baing water
cooled as is th.e first
elbow door 16, prevents buildup of material on outer interior wall surface 31
&hown in Figure
6. This watxsr which is passed through the interior of the door 24, as with
first elbow door 16,
is kept at a controlled temperature of, far example, about 190EF(87.8EC). This
temperature
is optimal in that it is approxita7ately 20EF(-6.67EC). below the appropriate
wet bulb
temperature of the tobaoeo. A fine condensation layer of water is thus formed
on the int~crior
elbow wall 31 allowing the tobacco entrained within the airflow to conbct wall
31 without
leaving residuo on the inner ducts of the drying apparatus. Door 24 is also
hinged at a point
identified by numeral 29 and has au air cylinder 33 attached thereto which
provides means to
raise and lower the door 24.
Downstream from aztd in flow communication with second areuate elbow 26 is
tangential
sGptual~Vr 30 which iu Lutu is iu auw i:ouuuu,uicatiott wiiii duct high
cfLicivuvy uyulm~ ~i0
and 42. As stated previously, the airflow velocity within the drying apparatus
is maintained
at, for example, about 6300 R(1920 m~min. 1n order to remove the tobacco from
the high
velocity airstream, the tangential separator 30 forces the tobacco against an
interior surface or
wall 39 of hinged water Cooled door 38 shown in Figure 7. This reduces the
velocity of the
out mbacco so that it can be removed front the airJ:7aw. And, chilled water
flows through the
interior of hinged door 38 in order to prevent buildup of material oa interior
sur~ce wall 39.
The velocity of the airflow within the drying apparatus 10 is reduced as it
circulates around
the interior of tangential separator 30 thereby allowing, the cut tobacco to
Fall into rotary
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airlock 34. As shown in Figure 3, the heaeed air is exhausted through dual sir
exhaust exit
ducts 32 and 36 whsle the majority ofthe dried tobacco drops out of the
airstream and talc the
rotary airlock 34 for further processing. Each air exhaust 32 and 36 aro
centrally aligned an
on opposite sides of the tangentiai separator and remove air from the
separator 30 through a
multi-vane rotary exhaust located centrally within separator 3U. Each of the
air exhausts 32
and 36 lead to cyclones for the further r~noval of the cut tobacco from the
circulated air
stream. Exhaust from the separator must be properly balanced to each of the
exhausts exit
lines 32 and 36 so that the proper airflow is exhibited within the drier to
prevent buildup of
material in the second elbow 26. The ratio between the drying chamber 22 and
the transition
leading to the separator 3$a, as shown i11 FigurC 1, is approximately 0.4.
A socond zero pressure point is formed within the drying apparatus in the
tangential separator
30 in order to assist in product removal from the interior ducts of transition
area 38a and
second elbow area 24. The moistut'e content of the out tobacco at the airlock
34 is reduced to
about 15% to 17% moisture content and is elevated to a temperature of about
2'1 OEF(98.9EC).
The air exhausted through ducts 32 and 36 will still have small amounts of
tobacco within the
airstn"am. To further filter the air and remove this material, high efficiency
cyclones 40 and
42 arc provided in order to deposit further tobacco dust and material into
removal bins 46 and
48 while allowing the heated air to exhaust through ducts 50 aad 52 and
recirculate back into
the drying apparatus. The drying apparatus 10 can then utilize this heated air
back into the
heated air intake duct 11 for processing of additional cut tobacco. The total
dwell time of the
cut tobacco within the drying apparatus 10 is only about 3 seconds and the
moisture content
is reduced from about 2I% to 23% to about 15% to 17% in that short amount of
time.
Additionally, the drying appan1115 10 reduces breakage of the cut tobacco
thereby increasing
the filling capacity of the material while also reducing the amount of contact
the cut tobacco
has with the interior walls of the apparatus. This not only increases the
filling capacity of the
material but also reduces the maintenance costs of the drying apparatus as the
interior does
riot rexluire extensive and continuous cleaning. To prevent fitxther deposits
of tobaeCO easing
and flavoring material on the interior of the drying apparatus 10 and
specifically within the
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tangential separator 30, back wall 39a of the tangential separator is also
water cooled to
generate a this layer of condensate which buffers the contact of the cut
tobacco on the interior
walls.
Ex~plc 1
,A, test run of the new drying apparatus was conducted under the
specifications outlined
above. The results of the dried cut tobacco were compared with cut tobacco
dried in a prior
art device such as that dcscnibcd i;a U.S.1'atez~t 4,315,515. The results are
shown below. As
can be seen, the moisture coat~t of the cut tobacco remained about the same
while the tatul
drying timeJresident time within the dr~ng apparatus was redtlecd from about 8
seconds to
about 3 seconds. The tobacco dried in the drying apparatus of the present
invention exhibited
a t7auch greater fill value. Moisture from the table is read as the percent
wet weight basis.
hill value is dotamiunc~d ix~. oubic centimeters pex graua. Propylene Qlycal
is measured ~a
percent Particle sip measurcmcnta arc dctcmrincd based upon +9 mesh sievimg
process
where the value disphtyed is the percentage of particles which have a particle
size of +9 or
larger. This value is desired to be as large as possible because it is a good
indication of the
degradation of the tobacco during the drying process. Finally, the -14
particle size
measurement determines the percentage of particles under 14 mesh and is
desirod to be as
small as possible.
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TABLE 1
)?xo a P ccs Tnlcl er E il er Percent t'.:hanac
Average Av_ erase
Moisture Moisture
Moisture Existing 21.8 14.4 NIA
blew 22_ 1 13.5
Fill-Value Existing 4.73 5.03 -~-6
New 4, $4 5.41 +12
Propylt.ne Existins 0.58 0.49 -t 6
~xlycol New 0.59 0.57 -3
+9 ParticleExisting 77.fi 73.7 -5
Size
New 72.9 70.G -3
-14 ParticleExisting 6.S 9.1 +40
size
New 8.4 10.8 +28
'Z'he forcgoixxg det~ilcd description is given primarily for clearness of
understanding and no
S unnecessary linlilations arc Lo be untit.'rstcx~d therefrom for
modifications will beoorne
obvirn~s to those skilled in the art upon jading this disclosure find may be
made without
departing from the spirit of the invention or the scope of the appended
clai~ds.
