GB1559507A - Process and apparatus for increasing the filling capacity of tobacco - Google Patents

Description

(54) A PROCESS AND APPARATUS FOR INCREASING THE FILLING CAPACITY OF TOBACCO (71) We, AMERICAN BRANDS INC., a corporation organized and existing under the state of New Jersey, United States of America, of 245 Park Avenue, New York, N. Y., United States of Ame rica, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process and apparatus for increasing the filling capacity of tobacco.

At present, in the tobacco industry various methods are used for increasing the filling capacity of tobacco. These methods seek to expand compressed and dried tobacco to partially restore the dimensions it had prior to drying and cutting.

Such expansion methods include contacting tobacco leaves and/or stems and/or veins with moisture (in the form of water and/or steam) or a solvent and then exposing the tobacco to heat, vacuum-or freeze-drying so as to increase the filling capacity of the tobacco.

However, none of the prior art methods is entirely satisfactory, for a variety of reasons.

For example, water treatment followed by freeze-drying results in a product which is objectionably tacky because of a hygroscopic film of water-extracted solids which forms on the surface of the tobacco. In many of the heat expansion processes, whilst there is an initial expansion, the expansion disappears upon drying. Solvent expansion is not satisfactory because it adds foreign materials to the tobacco, and because of the cost of the solvents needed.

Furthermore, the prior art methods tend to expand the tobacco so much that if the expanded tobacco were used alone to form rod-like tobacco products, such as cigarettes, the tobacco product would be too prone to collapse, and would thus lack firmness and be of such low quality as to be unsuitable for commercial marketing.

Accordingly, it is currently normal practice to blend such expanded tobacco with non-expanded tobacco. The resulting admixture provides rod-like tobacco products partially formed from expanded tobacco which are sufficiently structurally rigid for commercial sale. However, such blending processes nonetheless fail to produce a completely satisfactory tobacco blend for commercial tobacco products and the necessity for blending expanded and non-expanded tobacco gives rise to the additional drawbacks that an extra blending step is required, as well as separate storage faciiities for the expanded and non-expanded tobaccos. These drawbacks naturally add to the cost of processing the tobacco.

Furthermore, the drying apparatus used during the expansion process often requires a considerable period of time to effect adequate drying. This increases processing time and costs and thus further reduces any cost savings which increasing the filling capacity of the tobacco might produce. Also, there is a tendency for mechanical abuse to occur to the tobacco during drying and such mechanical abuse contributes to break-up of tobacco which results in a less satisfactory end product.

It will thus be appreciated that the prior art tobacco expansion processes cannot achieve, in a simple reliable, rapid and economical manner, an expansion of tobacco materials such that the expanded tobacco can be employed alone for the manufacture of rod-like tobacco products which have the firmness necessary for ordinary use. Accordingly, the present invention seeks to provide a process and apparatus for increasing the filling capacity of tobacco which overcomes or at least mitigates the disadvantages of the prior art techniques.

The invention provides a process for increasing the filling capacity of tobacco, the process comprising a conditioning stage, in which tobacco in shredded form is raised to a temperature of at least 130 F, but below the temperature at which the tobacco will char or discolour, and the moisture content thereof is raised to within the range 15 to 35%, and a drying stage, in which the conditioned tobacco is formed into a thin layer and subjected to treatment for a time intervals not exceeding 5 seconds by entraining the thin layer of conditioned tobacco in a stream of gas whose temperature is greater than that of the conditioned tobacco, whereby the moisture content of the conditioned tabacco is lowered and the filling capacity of the tobacco is increased.

The invention also provides an apparatus for carrying out the process of the invention, the apparatus comprising: a conditioning section having a passage through which tobacco can be passed, a heater capable of raising the temperature of tobacco passing through the passage and a moisture introducing apparatus capable of introducing moisture into tobacco passing through the passage; and a drying section having a gas supply apparatus capable of supplying a stream of gas and a tobacco dispersing means capable of forming tobacco which has passed through the passage into a thin layer for entrainment in the stream of gas provided by the gas supply apparatus, the drying section also incorporating means for rapidly reducing the moisture content of the thin layer of tobacco produced by the dispersing means.

In the following description and claims, all proportions are by weight.

In the process of the invention, in order that the tobacco may not char or discolour, it is preferred that the temperature of the tobacco in the conditioning stage does not exceed 250 F, though the exact upper limit will vary somewhat depending upon the type of tobacco being processed. At the end of the conditioning stage the tobacco preferably has a temperature within the range of from 180 to 200 F, most desirably substantially 190 F, and a moisture content of not less than 20%, the most preferred range of moisture content being 22 to 26%.

The thickness of the layer into which the tobacco is formed during the drying stage of the process is desirably from l/2 to 2 inches, preferably substantially 1 inch, whilst the temperature of the gas employed in this stage is preferably from 300 to 600 F. It is preferred that the duration of the gas treatment not exceed two seconds, that the partial pressure of water vapour in the gas used therein be less than the water vapour pressure within the tobacco and that, in the last part of the drying stage, turbulence be mduced in the flow of gas. The moisture content of the tobacco at the end of the drying stage is preferably from 11 to 16%, which is the moisture content required in most tobaccos for optimum handling during the subsequent manufacturing process.

In the apparatus of the invention, the means for rapidly reducing the moisture content of the thin layer of tobacco preferably comprises a heater capable of heating the stream of gas before it is brought into contact with the tobacco.

Whilst this invention is in no way limited by this belief, it is believed that, during the conditioning stage, some delamination and opening of the shredded tobacco occurs. The elevation of the tobacco temperature to near the boiling point of water permits the water to be rapidly removed when the tobacco enters the drying stage. The high temperature in this stage coupled with the short treatment time not only causes water vapour leaving the tobacco to assert an evaporative cooling action, but also to assert a positive internal pressure such that the expansive effect is greater than in conventional tobacco drying processes. The drying action is facilitated by the intimacy of contact between the tobacco and gas.

Thus, the tobacco shreds are expanded and opened from their original compressed state and are stabilized in that state, resisting the closing back thereof which would otherwise occur during cigarette manufacture. The treated tobacco retains its increase in filling capacity, which can be 5% to 25% greater than conventionally dried tobacco, even during the handling required in cigarette manufacture.

Moreover, since the tobacco enters the drying stage in a thin layer and travels quickly therethrough, there is a diminished tendency for the tobacco to experience mechanical abuse.

A preferred process and apparatus of the invention will now be described, though by way of illustration only, with reference to the accompanying drawings, in which: Figure I is a schematic side elevation of the preferred apparatus of the invention, with some parts broken away for ; Figure 2 is a top plan view of the apparatus shown in Figure 1, again with some parts broken away for clarity ; Figure 3 is an enlarged section along the line 3-3 in Figure 2 and shows the drying section of the apparatus shown in Figure 1 and 2; and Figure 4 is an enlarged section through the moisturizing means shown in Figure 3.

The apparatus of the invention shown in the accompanying drawings is generally designated 10 and is intended to be used for increasing the filling capacity of a blend of different tobaccos and tobacco materials used to make cigarettes, cigars, or other tobacco products formed from shredded tobacco and tobacco materials. This blend of tobaccos is hereinafter referred to as the"total blend"and may include a variety of different types and proportions of tobacco (for example Burley and Bright) and tobacco materials (leaf, stem and veins) depending upon the flavour and other characteristics desired in the end product. In fact, it may include any variety and type of tobacco in any proportions. The total blend can be formed by any conventional procedure, such as admixing the various components and shredding them in a cutter, such as a standard Molins or Legg cutter.

The apparatus 10 comprises a conditioning section (generally designated 12), which raises the temperature and moisture content of tobacco T, and a drying section (generally designated 14) which dries a thin layer of conditioned tobacco T. During its passage through the apparatus 10, the tobacco T is expanded and opened from a crimped, twisted condition and is able to resist the normal tendency to close back to this condition.

The conditioning section 12 comprises a conveyor unit (generally designated 16) and a conditioning unit (generally designated 18). Before entering the conveyor unit 16 the tobacco is shredded and treated by other conventional procedures which cause the tobacco to become compressed and laminated together.

The conveyor unit 16 includes a spreader-feeder 20 and a first conveyor 24 both of which are of conventional construction and will not therefore be described in detail. Structural supports (not shown) are employed to support the two components in their correct positions.

The spreader-feeder 20 has a discharge end 22 positioned above the first conveyor 24 and delivers a controlled amount of shredded tobacco T onto a belt 30 of the first conveyor 24.

The discharge rate from the spreader-feeder 20 and the speed of the belt 30 are adjusted so that a layer of tobacco T of constant thickness is formed.

The conditioning unit 18 (as best seen in Figure 1) includes a heating, ordering, and metering chute 34 having a''hopper"36 and a steaming jacket 38. The hopper 36 is fastened to the discharge end of the first conveyor 24 and forms a tapering inlet to the chute 34. A motor driven doffer 40 is supported by the hopper 36 and a level control 32 is provided to control the height of the tobacco in the chute 34 in order to ensure that proper conditioning is effected. The level control 32 can be an electric eye or an infra-red, sonic beam, fluidic, or other conventional control means and controls the speed of a discharge conveyor 64 (described below) thereby regulating the height of tobacco in the chute 34. The heating, ordering, and metering chute 34 serves to elevate the temperature, moisture content and water vapour pressure of the tobacco T.

As best seen in Figure 2, the chute 34 has a vertical passage 44 through which tobacco can pass. The passage 44 is oval in cross-section to facilitate the movement of tobacco T. The hollow steaming jacket 38 surrounds the passage 44, receives steam through an inlet 48 and distributes the steam into the passage 44 through a plurality of vent openings (not shown) formed in the jacket 38, thus ensuring intimate intermixing of steam with the tobacco T.

The chute 34 also acts as a conventional metering chute to control the discharge of conditioned tobacco therefrom : the tobacco T which descends into the passage 44 tends to accumulate therein and the amount of tobacco T discharged from the chute 34 may be adjusted by varying the speed of a second conveyor 26. The chute 34 may incorporate conventional devices for measuring tobacco temperature and moisture content to permit accurate control of the temperature and moistue content of the tobacco during conditioning.

Sufficient steam is introduced into the jacket 38 to heat the tobacco T to at least 130 F and to increase the moisture content of the tobacco to between 15 and 35%. The time necessary to condition the tobacco can vary from a few seconds to about five minutes, depending upon the exact temperature and moisture content desired and the tobacco blend bemg treated.

After conditioning, the tobacco T leaves the base of the chute 34 and falls onto the second conveyor 26, which comprises a support section 52, a cover 54, the discharge conveyor 64 and a conventional doffer 60. In addition, the second conveyor 26 incorporates an endless belt 56 and a kicker 46 which produces a substantially uniform layer of conditioned tobacco on the belt 56 before the tobacco is passed to the drying section 14.

The support section 52 is connected to the discharge end of the chute 34. Beneath the discharge end 62 of the passage 44 and within the support section 52 is disposed the discharge conveyor 64 and the doffer 60. The downwardly-sloping conveyor 64 serves to provide more uniform delivery of the conditioned tobacco T onto the belt 56 and, in conjunction with the doffer 60, and kicker 46, contributes to the achievement of a uniform layer of tobacco T on the belt 56. To this end, the discharge conveyor 64 slopes downwardly from the discharge end 62 of the chute 34 to the belt 56, and the rates of movement of the conveyor 64 and the belt 56 as well as the discharge rate from the chute 34 must be adjusted so that a uniform layer of tobacco T is carried by the belt 56 to the drying section 14.

The cover 54 above the belt 56 prevents undesirable heat loss from the conditioned tobacco T as it travels from the chute 34 to the drying section 14. Any type of material which will serve this purpose may be used for the cover 54, but the cover 54 must be shaped so that the open top of the conveyor 26 is effectively enclose, in order that the tobacco T may expand properly in the drying section 14. (In some cases, the cover may be omitted.

Also, the conveyor 26 may be eliminated and the chute 34 feed the conditioned tobacco directly into the drying section 14 with appropriate dispersion of the tobacco being effected by means of doffers or similar mechanisms.) The drying section 14 comprises a discharge housing 58 connected to the downsteam end of the second conveyor 26. A doffer 60'is mounted within the discharge housing 58 adjacent the end of the belt 56 and driven at a high speed relative to that of the belt 56 so that the tobacco T is picked or pulled off easily from the belt 56. The doffer 60'not only serves to prevent hang-up of the tobacco T but also provides uniform acceleration of the tobacco T into the remaining parts of the drying section 14.

The drying section 14 further comprises a drier unit (generally designated 70) and a separator (generally designated 74). The drier unit 70 flash dries the tobacco T and comprises a housing 76 and a perforated screen 78. The housing 76 has walls 80 which enclose a chamber and is provided with inlet and outlet openings 82 and 84 respectively.

Also, a hot-gas inlet 86 is formed on one of the sidewalls 80. The perforated screen 78 extends between the inlet and outlet openings 82 and 84 respectively, thus separating a plenum chamber 88 from a tobacco passageway 90. The hot-gas inlet opening 86 communicates with the plenum chamber 88 and allows entry thereinto of hot gas 91, which is supplied from a gas supply means provided with a heater (both not shown). The hot gas 91 is normally hot, moist air having a partial pressure of water vapour therein which is lower than the water vapour pressure of the moisture in the tobacco T, the gas being at a temperature of 300 to 600 F.

The tobacco passageway 90 permits the flow therethrough of a thin layer of tobacco T entrained in the gas. The passageway 90 is of such a size and the velocity of the gas passing therethrough is so regulated as to prevent choking or clogging of the passageway by the tobacco. The screen 78, and hence the passageway 90, are U-shaped since this configuration saves space on the plant floor.

A plurality of louvres or slots 92 are formed in the perforated screen 78 and are arrange in a constant pattern throughout the entire extent thereof. The slots 92 direct streams of hot gas into the tobacco passageway 90 so as to rapidly transport a thin layer of tobacco T through the drying section. The slots 92 are arranged in parallel rows, adjacent rows having the slots 92 staggered with respect to each other to minimize turbulence within the passageway 90 as the thin layer of tobacco T passes therethrough. Consequently, the shredded tobacco passes uniformly and quickly through the housing 76.

The velocity at which the hot gas 91 travels through the slots 92 should be at least sufficient to create a pressure drop across the slots 92 so as to facilitate uniform advancement 9f the hot gas 91 as well as of the tobacco T through the passageway 90. The gas velocity is preferably such that the tobacco will pass through the passageway 90 in less than two seconds.

In the passageway 90 the moisture content of the tobacco T is lowered to near the normal moisture content for cigarette making. For most tobacco blends used in cigarettes, this moisture level lies in the range 11 to 16%. During the lowering of the moisture content, the filling capacity of the tobacco T is increased. For this purpose, it is important that the layer of the tobacco T be relative thin so that there is a greater intimacy of contact of the tobacco surface with the gas 91.

Although it is desirable to have a constant flow rate for the tobacco, the drying section 14 is more adaptable to varying flow rates than conventional drying equipment. The belt 56 can be modulated in speed either in step fashion or proportionally to accommodate a varying input rate of tobacco and the moisture content of the drying gas modulated by proportional water conditioning such that its drying effect is the same for varying rates.

Thus, the disadvantages of the first lot of tobacco into a dryer and the last to come out, as well as normal interruptions in flow, can be instantly compensated.

The drying section 14 is equipped with means for creating turbulance, in the gas stream and rapid acceleration of the gas relative to the tobacco surfaces as they exit from the housing 76. These means take the form of an air-tight venturi member 94 of substantially triangular cross-section. The venturi member 94 is positioned within an outlet duct 97 from the housing 76 so that a narrow space 95 exists between its apex and the opposite wall of the duct 97. For example, if the duct 97 has a width of about six inches, a two-inch space will achieve the desired acceleration of the gas. Other means for increasing the velocity of the gas, such as an orifice or a contraction in the exit duct, can be used in place of the venturi.

The venturi member 94 significantly accelerates the gas 91 so that the velocity of the gas increases relative to the tobacco therein. This rapid increase in velocity creates turbulence so that the gas 91 tends to wipe moisture from the surfaces of the shredded tobacco T; it is believed that such moisture is formed on the surface of the tobacco T by the rapid vapourization of water which occurs through the contact of the gas 91 with the tobacco T in the passageway 90. The continuing intimacy of contact between the gas 91 and the tobacco T adjacent the venturi 94 enables the wiping action there carried out to efficiently remove this surface moisture from the tobacco. By wiping the tobacco surface, it is believed that the removal of moisture and puffing of the tobacco T are more satisfactorily completed.

Naturally, these beliefs in no way limit the invention.

The separator 74 comprises a conventional centrifugal device 96 and an air lock 98. Inlet and outlet ducts 100 and 102 are connected to the centrifugal device 96, which is of a commercially-available type and will not therefore be described in detail. The admixture of puffed tobacco T and gas 91 passes the venturi member 94 and enters the inlet duct 100 which directs the admixture to the centrifugal device 96, where the gas 91 and tobacco T are separated so that the tobacco T descends the outlet duct 102 under gravity whilst the gas leaves via an opening 104 in a duct 106. The gas 91 passing through the opening 104 may be recycled in whole or in part to the housing 76. The air lock 98 is a conventional rotary air lock and discharges portions of the expanded tobacco T onto an output conveyor 108, which advances the tobacco T to further processing, such as cooling and flavouring.

Although the operation of the apparatus 10 is believed to be self-evident the following brief explanation is given. The tobacco T, in shredded form, is conveyed by the first conveyor 24 to the conditioning unit 18 which elevates the temperature of the tobacco T to above 130 F, and the moisture content thereof above 15%. The heating and moisturizing are performed for a time sufficient to permit the tobacco T to open from its compressed condition. The tobacco T then drops onto the second conveyor 26 and is passed to the drying section 14 where its moisture content is rapidly lowered to about its making moisture within 5 seconds so that the tobacco achieves an expanded and opened condition which resists the closing back thereof.

As shown in Figure 4, a spray manifold 110 may be used to introduce moisture back into the tobacco. The spray manifold 110 includes a spray head 112 attached to a duct so as to spray water onto the tobacco as it passes through the inlet duct 100. A tube 114 supplies water to the spray head and a drain 116 and drain piping 118 remove any excess water that is not absorbed by the tobacco but which accumulates at the bottom of the manifold 110.

After treatment by the process of the invention the expanded tobacco may be cooled by any suitable means, as by a current of ambient air, appropriately flavoured and used to form cigarettes, or the treated tobacco may be blended with non-treated tobacco and used to form cigarettes or other tobacco products. The treated tobacco retains its increase in filling capacity, which can vary from about 5 to 25% with no more than the usual loss of filling power during the handling required for cigarette manufacture.

The following examples are now given, though by way of illustration only, to show details of particularly preferred processes of the invention.

Example 1 2500 parts of a commercial filter cigarette blend containing flue-cured, burley, oriental, and by-product tobaccos, in the form of tobacco strip and without finishing flavour or menthol, were shredded with a Molins cutter. The moisture content after shredding was 19. 9%. The tobacco was then passed to the conditioning section of an apparatus of the invention, where its moisture content and temperature was adjusted with steam to a moisture content of 22. 49 and a temperature of 185 F. The conditioned tobacco was conveyed, in a stream of even thickness, using motor driven doffers above an inclined conveyor, to the entrance of a flash drier six feet wide. The gas in the plenum of this section of the apparatus of the invention was at a temperature of 400 F and the air volume was 7,300 s. c. f. m. The tobacco leaving the drier had a moisture content of 13.4%. After conveying and ambient drying, the moisture content was 13. 1% and the filling capacity was 18.5% greater than that of a control shredded sample of tobacco processed in an ADT drier (4.86 cc/gm for the treated sample as compared with 4.10 cm/gm for the control). Tobacco was processed at a rate of approximately 5500 pounds per hour using a gas recycle ratio of 56%. Thereafter the tobacco was conveyed through a flavouring drum where finishing flavour and menthol were incorporated. The filling capacity increase after this additional step was of 15.1% (4.71 cc/gm for treated tobacco as against 4.10 cc/gm for the control.) Cigarettes manufactured from the treated tobacco amounted to 109.5 cigarettes per four ounces of tobacco as compared with 107.5 cigarettes per four ounces of the control. The cigarettes made from treated tobacco compared favourably with the controls for physical properties and smoke composition. Thus, eight cigarettes more per pound of tobacco could be manufactured using tobacco treated in accordance with the present invention.

Example 2 300 parts of a commercial non-filter tobacco blend containing a mixture of flue-cured, burley, oriental and byproduct tobacco shredded in the factory, but without finishing flavour and having a moisture content of 17.9%, were conveyed to a heating and ordering chute forming part of an apparatus of the invention. The tobacco was there conditioned to a temperature of 190 F and a moisture content of 22.3%. The tobacco was then conveyed in an even layer to a 3-foot wide'*U'-shaped flash drier and expanded and dried with hot air at a temperature of 350 F. The air volume was 3600 s. c. f. m. using a gas recycle ratio of 60%. The tobacco came out of a rotary gas lock at 16.4% moisture content and, after passing over a vibrational cooler-shaker conveyor, had a moisture content of 15.2%. The tobacco was finally conveyed to storage containers where it had a moisture of 15. 1%. The filling capacity increase (as determined on a sample drawn from the storage container) was 7.9% (filling capacity 4.10 cc/gm as compared with 3.80 cc/gm for a control sample processed in the conventional manner). The rate of tobacco treatment through the drier was 2750 pounds per hour.

Example 3 Example 2 was repeated, except that a drying temperature of 400 F was used. The moisture content of the tobacco after conditioning was 23.5%, after drying 16.5%, after the vibrational cooler-shaker 14.7%, and at the storage container 14.2%. The filling capacity increase (as determined on a sample from the storage container) was 10.5% (filling capacity 4.20 cc/gm as compared with 3.80 cc/gm for a control).

Example 4 600 parts of a commercial filter blend containing flue-cured, burley, oriental, and byproduct tobaccos shredded or cut in the factory, but without finishing flavour and having a moisture content of 18.2%, were conveyed to the heating and ordering chute mentioned in Example 2. The tobacco was conditioned to a temperature of 204 F and a moisture content of 24.1%. The tobacco was then conveyed in an even layer to the 3-foot wide drier and dried with hot air at 400 F as measured at the plenum. The air volume was 3600 s. c. f. m. using a gas recycle ratio of 60%. The tobacco left the gas lock at a moisture content of 14.7% and after passing over the vibrational cooler-shaker had a moisture content of 15.6%. The tobacco was finally conveyed to storate containers where it had a moisture content of 13.3%. The filling capacity increase (as determined on the samples drawn from the storage containers) was 18.7% (filling capacity 4.. 51 cc/gm as against 3.80 cc/gm for the control). The rate of tobacco treatment through the drier was 2700 pounds per hour.

The filling capacity was measured in all the for

Claims (27)

WHAT WE CLAIM IS:

1. A process for increasing the filling capacity of tobacco, the process comprising a conditioning stage, in which tobacco in shredded form is raised to a temperature of at least 130 F, but below the temperature at which the tobacco will char or discolour, and the moisture content thereof is raised to within the range 15 to 35%, and a drying stage in which the conditioned tobacco is formed into a thin layer and subjected to treatment for a time interval not exceeding 5 seconds by entraining the thin layer of conditioned tobacco in a stream of gas whose temperature is greater than that of the conditioned tobacco, whereby the moisture content of the conditioned tobacco is lowered and the filling capacity of the tobacco is increased.

2. A process as claimed in Claim 1, in which the temperature of the tobacco in the conditioning stages does not exceed 250 F.

3. A process as claimed in Claim 2, in which the temperature of the tobacco at the end of the conditioning stage lies within the range 180 to 200 F.

4. A process as claimed in Claim 3, in which the temperature of the tobacco at the end of the conditioning stage is substantially 190 F.

5. A process as claimed in any of the preceding claims, in which the moisture content of the tobacco at the end of the conditioning stage is not less than 20%.

6. A process as claimed in Claim 5, in which the moisture content of the tobacco at the end of the conditioning stage is not less than 22%.

7. A process as claimed in Claim 6, in which the moisture content of the tobacco at the end of the conditioning stage is not greater than 26%.

8. A process as claimed in any of the preceding claims, in which the thickness of the thin layer is from 1/2 to 2 inches.

9. A process as claimed in Claim 8, in which the thickness of the thin layer is subtantially 1 inch.

10. A process as claimed in any of the preceding claims, in which the temperature of the gas used in the drying stage is in the range 300 to 600 F.

11. A process as claimed in any of the preceding claims, in which the moisture content of the tobacco at the end of the drying stage is in the range 11 to 16%.

12. A process as claimed in any of the preceding claims, in which the duration of the gas treatment does not exceed 2 seconds.

13. A process as claimed in any of the preceding claims, in which the partial pressure of water vapour in the gas used in the drying stage is less than the water vapour pressure within the tobacco.

14. A process as claimed in any of the preceding claims, in which, in the first part of the drying stage the gas flow is non turbulent and in the last part of the drying stage, turbulence is induced in the flow of gas.

15. A process as claimed in any of the preceding claims, in which during the drying stage, the tobacco/gas mixture is passed through a venturi throat.

16. A process as claimed in any of the preceding claims, in which moisture is introduced into the tobaccolgas mixture after the tobacco has passed at least partially through the drying stage.

17. A process for increasing the filling capacity of tobacco, the process being substantially as herein described, with reference to the accompanying drawings and the Examples.

18. An apparatus for carrying out a process as claimed in any of the preceding claims, the apparatus comprising: a conditioning section having a passage through which tobacco can be passed, a heater capable of raising the temerature of tobacco passing through the passage and a moisture introducing apparatus capable of introducing moisture into tobacco passing through the passage; and a drying section having a gas supply apparatus capable of supplying a stream of gas, and a tobacco dispersing means capable of forming tobacco which has passed through the passage into a thin layer for entrainment in the stream of gas provided by the gas supply apparatus, the drying section also incorporating means for rapidly reducing the moisture content of the thin layer of tobacco produced by the dispersing means.

19. An apparatus as claimed in Claim 18, in which the means for rapidly reducing the moisture content of the tobacco comprises a heater capable of heating the said stream of gas before it is brought into contact with the tobacco.

20. An apparatus as claimed in either of Claims 18 and 19, futher comprising a first conveyor which delivers tobacco to the conditioning section and a second conveyor which receives tobacco which has passed through the conditioning section and which forms this tobacco into a thin layer.

21. An apparatus as claimed in any of Claims 18-20 in which the drying section includes an accelerating section capable of increasing the velocity of the gas relative to the tobacco dispersed therein, the acceleration section being disposed adjacent the exit by which tobacco leaves the drying section.

22. An apparatus as claimed in Claim 21, in which the accelerating section comprises a venturi throat.

23. An apparatus as claimed in any of Claims 18-20 in which the drying section further comprises a gas/tobacco separator capable of separating the gas from the tobacco.

24. An apparatus as claimed in Claim 23, in which the gas/tobacco separator includes a gas lock through which separated tobacco can be discharged from the apparatus.

25. An apparatus as claimed in Claim 20, further comprising a first chute down which tobacco can pass from the first conveyor to the conditioning section and a second chute down which tobacco can pass from the second conveyor to the drying section.

26. An apparatus as claimed in any of Claims 18 to 25, further comprising moisturing means capable of introducing moisture into the tobacco after it has been at least partially dried out before it is separated from the gas.

27. An apparatus for carrying out a process as claimed in any of Claims 1 to 17, the apparatus being substantially as herein described, with reference to and as illustrated in the accompanying drawings.