U.S. patent number 3,693,631 [Application Number 05/138,039] was granted by the patent office on 1972-09-26 for tobacco expansion process.
This patent grant is currently assigned to Reynold Leasing Corporation. Invention is credited to Arnold G. Moore, Donald A. Newton.
United States Patent |
3,693,631 |
Moore , et al. |
September 26, 1972 |
TOBACCO EXPANSION PROCESS
Abstract
A process of expanding the filling capacity of tobacco which
comprises introducing tobacco and a stream of vapors of a compound
having an atmospheric pressure boiling point between about
-50.degree. and +80.degree. C. into one end of an impregnating zone
wherein the temperature of the tobacco and of the vapors introduced
into said zone are, respectively, below and above the boiling point
of the compound at the prevailing pressure. The tobacco is
impregnated with the compound and the impregnated tobacco is
withdrawn from the impregnation zone and subjected to
vapor-expanding conditions such as immediate treatment with a hot
gas to expand the tobacco. The relative amounts of the compound and
the tobacco introduced into the impregnating zone and in the
impregnated tobacco at the time of expansion is within the range of
about 5 to 200 parts by weight of compound per 100 parts by weight
of tobacco (dry basis). The flow of vapors to the impregnating zone
is controlled with respect to the rate at which the tobacco is
introduced into said zone.
Inventors: |
Moore; Arnold G.
(Winston-Salem, NC), Newton; Donald A. (Clemmons, NC) |
Assignee: |
Reynold Leasing Corporation
(Jacksonville, FL)
|
Family
ID: |
22480163 |
Appl.
No.: |
05/138,039 |
Filed: |
April 28, 1971 |
Current U.S.
Class: |
131/296;
131/901 |
Current CPC
Class: |
A24B
3/182 (20130101); Y10S 131/901 (20130101) |
Current International
Class: |
A24B
3/18 (20060101); A24B 3/00 (20060101); A24b
003/18 () |
Field of
Search: |
;131/14P,17,140 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rein; Melvin D.
Claims
What is claimed is:
1. A process of treating tobacco which comprises introducing
tobacco into a impregnating zone, simultaneously introducing into
said zone and into contact with said tobacco a stream of vapors of
an organic compound having an atmospheric pressure boiling point
between about -50.degree. and +80.degree. C., the temperatures of
said tobacco and said vapor introduced into said zone being,
respectively, below and above the boiling point of said compound at
the pressure prevailing therein, withdrawing the tobacco
impregnated with said compound from said zone, controlling the rate
of vapor introduction into said zone with respect to the rate of
tobacco introduction thereinto such that the weight ratio of
compound in the withdrawn impregnated tobacco is in the range of
about 5 to about 200 parts by weight of compound per 100 parts by
weight of tobacco (dry basis), and suddenly subjecting the
withdrawn impregnated tobacco to vapor expanding conditions whereby
the tobacco is also expanded.
2. The process of claim 1 in which the weight ratio of vapor to
tobacco introduced into said zone is between about 10 and about 100
parts of vapor per 100 parts of tobacco (dry basis).
3. The process of claim 2 in which the vapor expanding conditions
are effected by contacting the withdrawn impregnated tobacco with a
stream of a hot gas.
4. A process of treating tobacco which comprises introducing
tobacco into one end of an impregnating zone, simultaneously
introducing into said one end a stream of vapors of an organic
compound having an atmospheric pressure boiling point between about
-40.degree. and +40.degree. C., the temperatures of said tobacco
and said vapor when introduced into said one end being,
respectively, below and above the boiling point of said compound at
the pressure prevailing in said zone, merging said tobacco and said
vapor stream in said one end and passing the resulting mixture in
contacting, concurrent flow relationship through said zone to
another end thereof whereby said tobacco is impregnated with said
compound, withdrawing the resulting merged stream of tobacco and
compound from said other end, controlling the rate of vapor
introduction into said one end with respect to the rate of tobacco
introduction into said one end such that the weight ratio of
compound to tobacco in the withdrawn stream is between about 10 and
about 100 parts of compound per 100 parts of tobacco (dry basis),
and then suddendly contacting the withdrawn impregnated tobacco
with a stream of a hot gas at a temperature at least 18.degree. C.
higher than the boiling point of the compound at the pressure
prevailing during contact whereby the tobacco is expanded.
5. The process of claim 4 in which said tobacco temperature is not
more than about 20.degree. C. below and said vapor temperature is
not more than about 15.degree. C. above said boiling point at said
prevailing pressure.
6. The process of claim 4 including the steps of separating vapors
of said compound from the expanded tobacco, condensing the
separated vapors to a liquid, continuously flowing a stream of the
condensed liquid to a vaporization zone whereby continuously to
produce the stream of vapors introduced into said one end of said
impregnation zone, and regulating the rate of flow of said
condensed liquid stream to said vaporization zone in response to
the pressure prevailing within said impregnation zone.
7. A process of treating tobacco which comprises flowing a stream
of an organic compound having an atmospheric pressure boiling point
between about -40.degree. and +40.degree. C. in the liquid state to
a vaporizing zone for vaporization therein, flowing a stream of the
resulting vapors from the vaporizing zone into one end of an
impregnating zone, simultaneously introducing tobacco into said one
end of said impregnating zone, the temperatures of said tobacco and
said vapor stream when introduced into said one end being,
respectively, below and above the boiling point of said compound at
the pressure prevailing in said impregnating zone, merging said
vapor stream and said tobacco in said impregnating zone and passing
the resulting mixture in contacting relationship to another end
thereof whereby the tobacco is impregnated with said compound,
withdrawing the impregnated tobacco from said other end,
controlling the rate of flow of liquid to said vaporizing zone in
response to the pressure prevailing within said impregnation zone,
the rate of introduction of said tobacco into said one end being
such that the weight ratio of compound to tobacco in the withdrawn
impregnated tobacco is in the range of about 5 to about 200 parts
by weight of compound per 100 parts by weight of tobacco (dry
basis), and suddenly subjecting the withdrawn impregnated tobacco
to vapor expanding conditions whereby the tobacco is also
expanded.
8. The process of claim 7 in which said tobacco temperature is not
more than about 20.degree. C. below and said vapor temperature is
not more than about 15.degree. C. above said boiling point at said
prevailing pressure.
9. A continuous process of treating tobacco which comprises
continuously introducing tobacco into an impregnating zone at a
predetermined rate, simultaneously introducing into said zone and
into contact with said tobacco a stream of vapors of an organic
compound selected from the group consisting of hydrocarbons and
halogenated hydrocarbons and having an atmospheric pressure boiling
point between about -40.degree. and +40.degree. C. whereby the
tobacco is impregnated with said compound, the temperatures of said
tobacco and said vapor when introduced into said zone being,
respectively, below and above the boiling point of said compound at
the pressure prevailing therein, withdrawing impregnated tobacco
from said zone, controlling the rate of vapor introduction into
said zone with respect to the rate of tobacco introduction
thereinto such that the weight ratio of said compound in the vapor
state and the tobacco introduced into said zone is in the range of
about 5 to about 200 parts by weight of vapors per 100 parts by
weight of tobacco (dry basis), and thereafter suddenly contacting
said impregnated tobacco with a hot gas whereby the tobacco is
expanded.
10. The process of claim 9 in which the organic compound in
trichloromonofluoromethane and the impregnating zone is maintained
under substantially equilibrium temperature and pressure conditions
at a pressure of between about 0 and 30 p.s.i.g.
11. The process of claim 9 in which said tobacco temperature is not
more than about 20.degree. C. below and said vapor temperature is
not more than about 15.degree. C. above said boiling point at said
prevailing pressure.
Description
BACKGROUND OF THE INVENTION
This invention relates to a process of treating tobacco and is
related to the process disclosed in U.S. Pat. No. 3,524,452 of
Glenn P. Moser and Grant M. Stewart issued Aug. 18, 1970. That
patent describes a method of increasing the filling capacity of
tobacco which involves impregnating tobacco with an organic liquid
and then subjecting the impregnated tobacco to a stream of hot gas
whereby the liquid is quickly vaporized with the simultaneous
puffing or expansion of the tobacco particles. This invention
relates to a process which is a modification of, and in certain
respects an improvement over, the process described in said
patent.
An object of this invention is the provision of a tobacco expansion
process in which the amount of impregnating fluid introduced into
the tobacco and present in the tobacco at the time it is subjected
to the expanding conditions may be readily and accurately
controlled.
A further object of this invention is the provision of a process in
which the impregnating fluid is applied to the tobacco in the vapor
state and liquid leaching of soluble constituents normally present
in the tobacco being treated is minimized.
A still further object of this invention is the provision of a
process which permits the use of reduced amounts of impregnating
fluid thereby avoiding the expense incident to the vaporization,
recovering and recycle of excess quantities of impregnant.
Further and additional objects will appear from the following
description and the appended claims.
GENERAL DESCRIPTION OF THE INVENTION
In accordance with one embodiment of this invention, a process is
provided in which tobacco is introduced into one end of an
impregnating zone at a predetermined rate. Simultaneously a stream
of vapors of an impregnating compound having an atmospheric boiling
point between about -50.degree. and +80.degree. C. is introduced
into the same end of the impregnating zone and into contact with
the tobacco whereby the tobacco is impregnated with said compound.
The temperature of the tobacco introduced into the impregnating
zone is below the boiling point of the impregnating compound at the
prevailing pressure and the temperature of the vapor stream is
above said boiling point. The flow of the vapor stream into the
impregnating zone is controlled so that for each 100 parts by
weight of tobacco (dry basis) introduced there are also introduced
at least 5 parts by weight of impregnating compound in the vapor
state. Preferably, rate of vapor flow into the impregnating zone is
in the range of about 5 to about 200 parts by weight of compound
for each 100 parts by weight of tobacco (dry basis) introduced into
the zone. The mixture of compound and tobacco is then moved in
concurrent flow relationship to another end of the impregnating
zone during which time the tobacco becomes thoroughly impregnated
with the compound. After the impregnation has occurred, the merged
stream comprising tobacco and the impregnating fluid, including
vapors and any condensed impregnant, is withdrawn from the other
end of the impregnating zone and suddently subjected to vapor
expanding conditions whereby the impregnant in the tobacco is
vaporized causing the tobacco to expand. Such expanding conditions
are preferably achieved by rapidly increasing the temperature of
the impregnated tobacco by introducing it into a stream of hot gas
in the manner described in said U.S. Pat. No. 3,524,452. A feature
of this invention is the provision of a process in which the rate
of flow of vapors to the impregnating zone is controlled with
respect to the rate of introduction of tobacco into the
impregnating zone.
The tobacco to be treated in accordance with the process of this
invention is preferably a cured tobacco and may be in the form of
shreds, strips, leaves, stems or sheets of reconstituted tobacco.
However, the process is easier to control and the best results are
obtained if tobacco shreds are used. This is for the reason that
usually shreds are relatively easy to handle in continuous
procedures and the final product of the process need not be
subjected to shredding as may be necessary for cigarette
manufacture. Shredding of the final product results in compressing
the product which tends to destroy the ultimate objective of the
process of this invention, namely, to expand the tobacco and
eliminate compressed particles, as may have resulted from prior
treatment including shredding. Any type of tobacco may be used in
the practice of this invention and it is particularly useful for
the processing of burley, flue-cured and Oriental (e.g., Turkish)
tobaccos.
Burley and flue-cured tobaccos used in the manufacture of
cigarettes ordinarily have a moisture content of about 10 to 15
percent by weight. In the practice of this invention, the moisture
content of the tobacco when contacted with the organic vapor is
usually in excess of about 10 percent by weight and preferably
within the range of 10 to 30 percent by weight of the tobacco. The
desired moisture content may be achieved by any suitable procedure
such as sprinkling, spraying, wet steam treatment, or the like, as
is known to those skilled in the art. The presence of the indicated
percentage of moisture is desired since the internal structure of
the tobacco is thereby rendered sufficiently pliable or flexible to
permit the expansion or puffing when the impregnating compound
expands within the tobacco upon heating. If the moisture content is
less than about 10 percent, the process results in the production
of an excess of tobacco fines during the expansion step. A tobacco
having greater than about 30 percent moisture has a tendency to be
mushy or soggy and is difficult to handle in commercial
operations.
In accordance with this invention, the temperatures of the vapor
and tobacco and the rates of flow of each into the impregnating
zone are such that a substantial portion of the impregnating vapor
condenses directly in and on the tobacco thereby providing an
impregnating liquid which vaporizes and expands when the
impregnated tobacco is subjected to the tobacco expanding step. It
is important that the impregnating compound be contacted with the
tobacco in the impregnating zone while the compound is in the vapor
state. The amount of vapors employed and the pressure and
temperature conditions within the impregnator are such that, while
vapor condensation within the tobacco does occur, the accumulation
of separate pools of liquid is avoided. The atmosphere within the
impregnator consists essentially of vapors of the impregnating
compound and under these conditions a condition of substantial
pressure-temperature equilibrium prevails. The pressure within the
impregnating zone may be atmospheric, superatmospheric or
subatmospheric and the pressure-temperature conditions are such
that the only liquid which impregnates the tobacco is that which is
formed by the condensation of the impregnating vapor directly
within the mass of tobacco. The quantity of liquid impregnant that
condenses in and on the tobacco is subject to control and depends
on the relative rates at which the tobacco and vapor are introduced
into the impregnating zone as well as on the temperatures of each.
While some vapor may escape at the points where the tobacco is
entering and leaving the impregnating chamber, it is preferred that
this escape be minimized by conveying the tobacco into and out of
the chamber through suitable vapor locks.
The volatile compound or mixture employed for impregnating the
tobacco is preferably one which is organic in nature, is chemically
inert to the tobacco being treated and has a boiling point at
atmospheric pressure between about -50.degree. C. and +80.degree.
C. Compounds having atmospheric pressure boiling points about
+80.degree. C. do not provide good tobacco expansion and are
difficult to remove completely from the tobacco without adversely
affecting its flavor and aroma. Compounds having very low
atmospheric pressure boiling points (i.e., below -50.degree. C.)
are so volatile under readily obtainable pressures in commercial
operations that the vapors do not readily condense during the
impregnation step and are so fugitive that they are not present as
condensate in the tobacco in the desired concentration at the time
the vapor expanding conditions are applied. Preferably, the
atmospheric pressure boiling point of the compound is between
-40.degree. C. and +40.degree. C. Illustrative inert organic
compounds are: ketones such as acetone and methyl ethyl ketone;
aliphatic or cyclic ethers such as methyl ethyl ether, diethyl
ether, diisopropyl ether, methyl butyl ether, dimethoxymethane,
furan and tetrahydrofuran; aliphatic alcohols such as methanol,
ethanol and 2-propanol; esters such as methyl formate, ethyl
formate and methyl acetate; aliphatic hydrocarbons such as butane,
pentane, isopentane, hexane and the corresponding unsaturated
hydrocarbons; the cyclo aliphatic hydrocarbons such as cyclobutane,
cyclohexane and cyclopentane; the halo-hydrocarbons ethyl chloride,
propyl chloride, isopropyl chloride, sec-butyl chloride, t-butyl
chloride, methyl bromide, ethyl bromide, t-butyl bromide, methylene
chloride, chloroform, carbon tetrachloride, ethylene dichloride,
ethylidene chloride; and the fluorinated hydrocarbons represented
by trichloromonofluoromethane, dichlorodifluoromethane,
monochlorodifluoromethane, 1,1-difluoroethane,
chloropentafluoroethane, octafluorocyclobutane,
1,1,1-trichlorodifluoroethane and 1,2-dichlorotetrafluoroethane.
The organic materials that are preferred are the non-oxygenated
compounds which are relatively non-polar in nature and are
relatively or substantially immiscible in water. These preferred
compounds as a group have a relatively low latent heat of
vaporization and thus require only a low energy input to cause the
impregnant to vaporize and expand within the tobacco. Preferred
materials are the hydrocarbons and the halogenated hydrocarbons of
the types indicated above. Mixtures of vapors of several compounds
may also be used if the boiling points of the liquid mixtures are
within the indicated temperature range. Such mixtures include the
azeotropes such as the trichloromonofluoromethane-isopentane
azeotrope.
The tobacco remains in the impregnating zone for a sufficient time
for condensed impregnating compound to penetrate into the cellular
structure of the tobacco. The time required may vary from a few
minutes to a few hours (e.g., 10 minutes to 2 hours) depending upon
the compound used, the nature of the tobacco and the conditions of
temperature and pressure.
The tobacco withdrawn from the impregnating zone contains about 5
to about 200 parts, preferably about 10 to about 100 parts, by
weight of impregnating fluid for each 100 parts by weight of
tobacco (dry basis). The withdrawn tobacco is next subjected to
tobacco expanding conditions. This may be effected by suddenly
reducing the ambient pressure. However, it is preferred that it be
effected by suddenly subjecting the impregnated tobacco to heat
such as may be imparted by a stream of hot gas as disclosed in said
patent No. 3,524,452. The heat is rapidly applied such that the
temperature of the impregnated tobacco is suddenly elevated to at
least about 18.degree. C. above and preferably about 80.degree. C.
above the boiling point of the impregnating compound at the
prevailing pressures within a period of less than about 10 seconds,
preferably within a period of less than about 4 seconds.
It is preferred that the temperature-pressure conditions within the
impregnating zone be maintained at essentially equilibrium. This
may be readily accomplished when an impregnating compound having a
boiling point within the range of -40.degree. C. to +40.degree. C.
is used and the temperature of the vapor stream introduced into the
impregnator is not more than about 15.degree. C. above and the
temperature of the tobacco introduced is not more than about
20.degree. C. below the boiling point of the compound at the
pressure prevailing in the impregnator. A particular advantage in
operating under these conditions is that the ratio of tobacco to
impregnant in the tobacco to be expanded with the hot gas may be
readily and automatically controlled even though the feed rate of
the tobacco may be intentionally or inadvertently varied. Under a
given set of conditions, the weight ratio of impregnant to tobacco
in the impregnated tobacco withdrawn from the impregnator is
determined largely by the respective temperatures of the tobacco
and impregnating vapors entering the impregnator. Other factors
which may have a considerable influence include the operating
pressures, the boiling point of the impregnating fluid and the
amount of external heat (if any) supplied to the impregnator. When
substantially equilibrated conditions prevail within the
impregnation zone, the ratio of impregnant to tobacco in the
impregnated product is conveniently adjusted by varying the
temperature within the impregnator either by changing the
temperature of the vapor introduced or by changing the amount of
external heat (if any) supplied to the impregnator. Alternatively,
selection of a lower operating pressure results in a lower vapor
temperature with a corresponding decrease in the ratio of
impregnant to tobacco. Accordingly, if the rate of flow of the
cooler tobacco to the impregnator is increased, causing more
condensate to form, the pressure will have a tendency to drop. This
will require more impregnant to maintain the desired equilibrium.
In accordance with one embodiment of this invention, a pressure
responsive sensor is positioned in the impregnation zone and is
arranged to regulate the supply of liquid impregnant to the
vaporizer so that the vapor supply to the impregnator will increase
in proportion to the increase in supply of tobacco. When
trichloromonofluoromethane is used as the impregnant, the pressure
in the impregnator is preferably between about 0 to 30 p.s.i.g.
DESCRIPTION OF THE DRAWING
For a more complete understanding of this invention, reference will
now be made to the accompanying drawing which shows in schematic
form an apparatus in which the process may be carried out. In this
illustrated embodiment, the processing equipment comprises a
tobacco moistener 2, a vapor impregnator 4, an expander 6, a
separator 8, a steam stripper 10, a product reorderer 12, a liquid
recovery unit 14, a liquid storage tank 16, a pressure control
valve 18 and a vaporizer 20. Shredded flue-cured or burley tobacco
is charged via a conveyor 22 to the moistener 2 in which, if
necessary, the water content of the tobacco is adjusted to 10 to 30
percent, suitably to about 18 percent, by weight. If moistening of
the tobacco is not required, the tobacco may by-pass the moistener
via conveyor 24. After moistening, the tobacco is conveyed by
conveyor 25, a star feed valve 26 and duct 28 to one end of the
impregnator 4. The tobacco is discharged into a screw conveyor 30
within the impregnator and is advanced therethrough from left to
right as shown in the drawing. Motor 31 drives the conveyor 30.
Simultaneously the vapors of the impregnating compound are
introduced through vapor line 32 into the impregnator 4 adjacent
the point of introduction of the tobacco. The vapors come into
contact with the tobacco moving in the screw conveyor 30 and at
least a portion of the vapor is condensed in and on the tobacco
particles. The feed rate of vapor passing through line 32 (as
hereinafter described) and into the impregnator 4 is determined by
the pressure within the impregnator which, in turn, is influenced
by the rate at which relatively cool tobacco enters through valve
26. At a given pressure, which is selected on the basis of the
particular impregnating fluid being used, the vapor feed rates are
easily controlled by valve 18 to give an impregnated tobacco
containing between 5 and 200 parts by weight of impregnant per 100
parts by weight of tobacco (dry basis). During the concurrent flow
of tobacco and impregnant in the conveyor 30, the tobacco is
thoroughly impregnated with the compound and a substantial
proportion of the latter condenses on the tobacco due to the fact
that the temperature of the tobacco and vapors introduced into the
impregnator 4 are, respectively, below and above the boiling point
of the impregnating compound.
The tobacco impregnated with the compound in the above-indicated
weight ratio is discharged from the impregnator 4 through duct 34
and a star feed valve 36 into a rapidly moving stream of hot gas
(e.g., steam) in duct 38 and then conveyed to the expander 6. The
hot gas stream in duct 38 has a temperature substantially greater
than the boiling point of the tobacco impregnating compound at the
prevailing pressure so that when the tobacco contacts the hot gas,
the impregnating compound will vaporize or the vapors within the
tobacco will expand to cause the concomitant expansion of the
tobacco. This expansion occurs within the short period (e.g., less
than 10 seconds) during which the gas and tobacco flow through duct
38 and the expander 6. This expansion step is essentially the same
as that described in said U.S. Pat. No. 3,524,452. After expansion,
the tobacco, heating gas and vapors of impregnating compound are
conveyed through conduit 40 to the cyclone separator 8 from which
the expanded tobacco is passed through an air lock 41 to the
stripper 10. Residual impregnating fluid is removed by vaporization
from the tobacco in stripper 10 and the tobacco effluent is passed
to a reorderer 12 in which the product is adjusted to the desired
moisture content, suitably 12 to 14 percent, so that it may be used
in the manufacture of cigarettes. The gases including steam and
vapors of the impregnating fluid are withdrawn from the separator 8
through conduit 42, are heated to the desired extent in a heater 44
and cycled through duct 46 and a fan 48 to duct 38. A side stream
of gases from conduit 42 is taken through line 50, control valve 52
and line 54 to the liquid compound recovery unit 14 for recovering
impregnating fluid, which latter is then passed through line 56 to
storage 16. Vapors from the stripper 10 are passed through line 58
to the recovery unit for salvaging additional amounts of
impregnating compound. Water and air or other non-condensible gases
are removed from unit 14 through line 60 and 62, respectively. In
order to supply impregnating compound vapors for the tobacco,
liquid compound is withdrawn from the storage unit 16 through line
64, pump 65, the pressure control valve 18, line 66, vaporizer 20
and line 32 to the impregnator. A pressure responsive element 68 is
positioned within the impregnator for controlling the amount of
liquid flow through the control valve 18 and hence the flow of
vapors into the impregnator 4. The vaporizer 20 and the impregnator
4 are equipped with outer jackets 70 and 72 through which heat
exchange media may be circulated for appropriate temperature
control.
As previously suggested, the temperature and pressure conditions
for effecting the impregnation and for effecting the expansion may
be varied over wide ranges, depending upon the selection of the
particular impregnating compound, the moisture content of the
tobacco being treated, the ratio of impregnating vapor to tobacco
introduced into the impregnator and in the merged stream withdrawn
therefrom, and the degree of tobacco expansion desired. In any
event, the temperature should be well below those which will
adversely affect the flavor and aroma of the end product but should
be sufficiently high to enable efficient impregnation and expansion
after impregnation.
SPECIFIC EXAMPLE
Reference will now be made to a specific example to illustrate the
process herein-described and claimed. In this example, impregnator
4 is a horizontal steel cylinder 35 feet in length and 42 inches in
diameter mounted at an angle of 20.degree. from the horizontal.
Expander 6 is a round vertical pipe 55 feet high and 58 inches in
diameter. Duct 38 from fan 48 to expander 6 is a horizontal pipe 34
inches wide and 38 inches high.
The impregnating fluid, trichloromonofluoromethane, is drawn from
liquid storage tank 16, through line 64 and into pump 65. This
liquid is pumped into vaporizer 20 jacketed with a hot water-heated
heat exchanger 70. In vaporizer 20 the liquid boils and
trichloromonofluoromethane vapor passes through line 32 to
impregnator 4 at a temperature of about 52.degree. to 55.degree. C.
Vapor flow is regulated, as necessary, by valve 18 to maintain a
pressure inside impregnator 4 of about 14 pounds per square inch
gauge. Impregnator 4 is initially warmed by circulating hot water
through the jacket 72 around the outside wall. Warming of
impregnator 4 is also initially hastened by some condensation of
trichloromonofluoromethane on the inside wall of the impregnator.
After the impregnator has reached an equilibrium temperature,
condensation stops. This equilibrium temperature is about
43.degree. C. (which is the approximate boiling point of
trichloromonofluoromethane at 14 p.s.i.g.), but it could be
slightly lower if there is much air in the impregnator. At this
time all condensate is then withdrawn from impregnator 4 through a
valve (not shown) at the bottom. The equipment is then in a
substantially equilibrated condition and ready to receive
tobacco.
The tobacco used is shredded flue-cured tobacco of moisture content
20.7 percent (equivalent to 26.1 percent moisture based on dry
tobacco). At this moisture level, moistener 2 may be by-passed, and
the shredded tobacco at room temperature, i.e., about 28.degree.
C., is fed directly to conveyor 25 at 50 pounds per minute. The
tobacco drops through star vapor lock 26 into impregnator 4 and is
moved through the impregnator by the screw impeller 30. As the
tobacco is conveyed through the impregnator,
trichloromonofluoromethane is introduced through line 32 at the
rate of about 45 pounds per minute and condenses on the tobacco,
penetrating into the cellular structure of the individual shreds of
tobacco. The total residence time of the tobacco in the impregnator
is about 35 minutes.
The impregnated tobacco then drops into duct 34, through star vapor
lock 36, and down into a rapidly moving stream of heated gas in
duct 38 at approximately ambient pressure. This recycled gas, after
reaching equilibrium operating conditions, contains some air that
is introduced with tobacco, steam from moisture in tobacco, and
vapor of the impregnating compound, trichloromonofluoromethane. The
temperature of this heated vapor at the point tobacco enters duct
38 is about 110.degree. C. and is cycled through the system at the
rate of about 40,000 standard cubic feet per minute. The tobacco
travels with the hot vapor around a gentle bend in duct 38 and is
moved upward through expander 6.
From expander 6 the vapor stream and tobacco pass through duct 40
into cyclone separator 8. Vapor leaves the top of the separator,
through duct 42, and is passed through heater 44, where it is again
heated to about 110.degree. C. by contact with superheated steam
coils. The vapor stream, restored to full heat, is passed through
duct 46 and blown by fan 48 back into duct 38 to contact a fresh
charge of impregnated tobacco. Expanded tobacco drops from the
bottom of separator 8 and through air lock 41 directly to reorderer
12, which is an inclined rotating drum in which a fine spray of
water restores moisture content of the expanded tobacco product to
about 12 to 13 percent moisture. Optional equipment for removing
most of the residual impregnant from expanded tobacco is the steam
stripper 10 between lock 41 and reorderer 12. In the steam
stripper, tobacco remains for a few minutes in a hot, moist
atmosphere that consists of wet steam diluted slightly with ambient
air. In the absence of a steam stripper, expanded tobacco is stored
for several hours at a moisture content of at least 12 percent to
allow residual impregnating fluid to evaporate and escape.
The tobacco heating step in the conduit 38 and expander 6 in the
foregoing operating causes an increase in total quantity of vapor
in the hot, recycled vapor stream. Excess vapor is withdrawn
continuously through line 50 at a rate regulated by valve 52. The
excess vapor is routed to the recovery system 14 which consists
essentially of a condenser. Recovered liquid
trichloromonofluoromethane is passed to a liquid storage tank from
which it is drawn by pump 65 through the valve 18 to the vaporizer
20.
In one operation, a flue-cured tobacco at room temperature (i.e.,
about 28.degree. C.) was charged to the impregnator at the rate of
about 2,500 pounds per hour and the total residence time in the
impregnator was about 35 minutes. At the same time, vapors of
trichloromonofluoromethane were charged through the conduit 32 at a
temperature of 52.degree. to 55.degree. C. and at the rate of about
1900 pounds per hour. The effluent from the impregnator was dropped
into a stream of the hot gas heated to 110.degree. C. in duct 38.
The filling capacity, when measured by the procedure set forth in
said U.S. Pat. No. 3,524,452, increased from about 420 to about 790
milliliters per 100 grams, the tobacco moisture level being 12
percent for both measurements.
It will be apparent that by utilizing vapor in the impregnation
step of this invention, it is possible to accurately control the
amount of impregnating fluid introduced into the tobacco and thus
the degree of expansion. Also, less impregnating fluid is required
than is required in those processes in which the tobacco is first
soaked in liquid before it is withdrawn from the impregnator and
introduced to the expansion zone. Moreover, by eliminating contact
of the tobacco with a liquid pool, extraction and redistribution of
soluble constituents within the tobacco are minimized.
While a particular embodiment of this invention has been
specifically described in the foregoing, it will, of course, be
apparent that other modifications may be made without departing
from the spirit and scope of this invention.
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