GB2266442A - Apparatus and method for expanding tobacco - Google Patents

Abstract

An expansion apparatus for effecting the expansion of tobacco, the apparatus comprising moistening means (20) for moistening the tobacco with a liquid to a predetermined degree; pre-heating means (20) for pre-heating the tobacco to a temperature in the proximity of, but below, the boiling point of said liquid without non-dielectric heating; and dielectric heating means (40) for heating the tobacco to at least the boiling point of said liquid, thereby to evaporate a portion of the moisture in the cells of the tobacco and thus expand the material. <IMAGE>

Description

APPARATUS AND METHOD FOR EXPANDING CELLULAR ORGANIC SffiTERIAL The present iW.:..%tjon relates to an apparatus and a method for expanding cellular organic material. More particularly, but no nxclusively, the present invention is concerned with the expansion of tobacco.

The economics f the tobacco industry make it desirable to expand the tobacco as much as possible during processing, without the tobacco losing its rigidity.

Furthermore, there is a requirement for theobacco to have a so-called "filling power" so that it is not too loose and then also calls for expansion of the tobacco. The fundamental principle by which expansion is achieved is by rapid heating to cause a sufficiently rapid build-up of vapour within the tobacco cells so as to. exceed the rate at which vapour diffuses through the cell walls. Having thus inflated the cells and partially dried the tobacco, it is then necessary to complete the drying process in such a way as to minimise the subsequent collapse of the cells.

Various prior art methods have been used to achieve rapid cell expansion, including: (1) Heating the product by directly impinging with jets of steam followed by drying.

(2) Impregnation of the product with a low boiling point liquid, followed by rapid heating to evaporate this liquid. In one process, in widespread use, tobacco is impregnated with liquid CO2 at high pressure. A pneumatic conveying dryer is then used to heat the product, driving off the CO2 and moisture. This method can expand the product by more than 100%, but it requires complex plant, and drastically alters the products chemical characteristics some of which adversely affect the flavour of the tobacco.

(3) Drying the moist product in a pneumatic conveying drier at elevated temperatures, allows some expansion to be achieved. The combination of process dwell time and the high temperature causes drastic changes in the product chemical characteristics. Problems with this type of drier include sensitivity to variations in drier load, and there is a tendency for fouling of the heat transfer surfaces, both factors contributing to a degree of fire risk.

The disadvantages of the above cell expansion techniques stem from the need to achieve a high rate of heat transfer into the product. For example, method (2) involving the pneumatic conveying driers, requires a high gas temperature and high conveying velocities. Although the product temperature is not thought to approach that of the conveying gas at the feed point, this method results in a substantial temperature gradient between the surface of each tobacco particle and its centre. This transient effect is more marked at higher drying rates, and causes overheating and chemical changes at the surfaces of the particles, if the temperature gradient is sufficiently great.

The use of dielectric heating such as radiofrequency or microwave heating techniques overcomes the disadvantages of the aforementioned prior art methods by permitting the requisite rapid heat build up in the tobacco cells, but without the extreme temperatures and temperature gradients inherent in the previously described methods. Furthermore, it will be appreciated that dielectric heating allows expansion of all the tobacco cells, rather than just those close to the surface, since it is also able to heat the cells at the centre of the tobacco or other product.

Hitherto, cellular expansion of tobacco based on a dielectric heating approach has not enjoyed widespread commercial exploitation. This is due to the relatively large amount of radio frequency or microwave energy which needs to be used for the tobacco to be heated for expansion and then dried-to its required final moisture content.

It is an object of the present invention to make the dielectric heating approach to the cellular expansion of tobacco a more attractive commercial proposition.

In one aspect the present invention provides a method for the expansion of a cellular organic material, the method comprising the steps of: moistening the material with a liquid to a predetermined degree; pre-heating the material to a temperature in the proximity of, but below, the boiling point of said liquid using non-dielectric heating; and subsequently dielectrically heating the material, thereby to evaporate a portion of the moisture in the cells of the material and thus expand the material.

The step of dielectrically heating the material comprises exposing the material to the dielectric heating for a duration of 0.1 seconds to 10 seconds.

Preferably, the method includes the further subsequent step of drying the material following the dielectric heating step.

If the material is tobacco, the moistening step preferably increases its moisture content in excess of 18%, the tobacco having an equilibrium moisture content of 14%.

Preferably, and most suitably, the liquid is water, in which case the moistening and non-dielectric heating steps may be effected simultaneously by steam. When using water, the non-dielectric heating step -might suitably raise the temperature of the material to in excess of 800C, but less than 100 C.

The method may be carried out under reduced pressure conditions, whereby the above temperatures will be scaled appropriately since the boiling point of the liquid will reduce with pressure.

In another aspect, the present invention provides an expansion apparatus for effecting the expansion of a cellular organic material, the apparatus comprising moistening means for moistening the material with a liquid to a predetermined degree; pre-heating means for pre-heating the material to a temperature in the proximity of, but below, the boiling point of said liquid using non-dielectric heating; and dielectric heating means for heating the material to at least the boiling point of said liquid, thereby to evaporate a portion of the moisture in the cells of the material and thus expand the material.

Preferably, the moistening means and the pre-heating means are both embodied as a steaming station, the steam being used both to moisten and pre-heat the material.

The expansion apparatus may also include a first conveying means for conveying material to the steaming station; and/or a second conveying means for conveying the heated and moistened tobacco to the dielectric heating means. The first and second conveying means are suitably in the form of belt conveyors.

The dielectric heating means may be radiofrequency or microwave heating means.

Preferably, the expansion apparatus also includes a final drying stage, which may be implemented as a cascading rotary drier, a fluid bed drier, or a pneumatic drier.

An exemplary embodiment of the invention is hereinafter described with reference to the accompanying Figure 1, which shows an expansion apparatus for expanding tobacco in accordance with the present invention.

The expansion apparatus includes a steaming station generally denoted 20 having a tobacco inlet 22, a tobacco outlet 24, a steam inlet 26 and a steam exhaust 28. Steam is pumped into steam inlet 26 and flows up the steaming station 20 to the steam exhaust 28, the steaming station 20 being thus operable both to pre-heat and moisten the tobacco which descends the steaming station 20 from tobacco inlet 22 to tobacco outlet 24. A conveyor 10 is located in the mouth of the tobacco inlet 22 and is operable to deliver tobacco to the steam station 20. Disposed adjacent the tobacco outlet 24 is a roller 30. A conveyor 32, having a first end disposed immediately beneath the roller 30, is operable to receive the steamed and pre-heated tobacco exiting the steaming station 20 via the roller 30, and transport it through the expansion station 40 to the drying station 50.The expansion station 40, through which the conveyor 32 passes, includes a dielectric heater in the form of a microwave source 42, operable to irradiate with microwave energy the tobacco being transported. therethrough on the conveyor 32; an exhaust outlet 44 operable to receive and expel the moisture being evaporated from the tobacco; and a conventional mode stirrer 46 operable to prevent the build-up of standing waves.

The drying station 50 is positioned at the second end of the conveyor 32 so as to receive the tobacco which falls from the second end thereof. The drying station 50 is provided with a tobacco inlet 52; an air inlet 54 which receives hot dry air from a heater 60; and a tobacco outlet 56. The heater 60 receives dried air A from an air supply means (not shown), which it heats using electric heating elements 62 rated in this embodiment at 15KW. The drying station 50 is arranged such that the heated dried air from the heater 60 and the tobacco falling from the conveyor 32 come into contact with each other in the drying station 50, whereby the tobacco further dried.

The tobacco outlet 56 of the drying station 50 communicates with a suction pump 70 via a separator 80.

The suction created by the suction pump 70 draws the air and tobacco in the drying station 50 along conduit 64 to separator 80 whereupon the heated air, which at this point also contains water vapour from the tobacco, is directed along conduit 75 to suction pump 70. and finally out of an exhaust outlet 72. The tobacco entering the separator 80 descends into collection device 90. Components 50,70 and 80 collectively constitute a conventional pneumatic conveying drier.

In order to demonstrate the benefits of the present invention, .an example of the operation of the expansion apparatus hereinbefore described is given.

Unexpanded tobacco having an equilibrium content of 14% (wwb - wet weight basis) is conveyed along conveyor 10, to the tobacco inlet 22 of the steaming station 20. In this example, the conveyor delivers 80 Kg/hour of tobacco.

As the tobacco descends from the conveyor 10 into the steaming station 20, it encounters a volume of steam flowing from steam inlet 26 to the.steam outlet 28, which serves to both pre-heat and moisten the tobacco. The steam flow 6 Kg/hour such that the tobacco is pre-heated to temperature of between 80"C and 100"C and its moisture content increased to at least 25% (wwb). The pre-heated and moistened tobacco falls onto conveyor 32 via a metering roller 30 which determines the thickness of the carpet of tobacco on the conveyor 32, which thickness may be in the range of 50-100mm. The conveyor 32, which travels at 0.08 m/s, conveys the moistened and pre-heated tobacco to expansion station 40, where tobacco travelling therethrough is irradiated with microwave radiation produced by the microwave source 42.This causes the temperature of the tobacco to- rise to 1000C whereupon the moisture in the tobacco is rapidly evaporated such that the rate at which evaporation takes place; exceeds the ability of the cell walls within the-tobacco to diffuse the moisture vapour, thereby causing an inflation of the tobacco cells. A portion of the evaporated moisture is expelled via the exhaust outlet 44, in the present example at a rate of 100m3/hour, this corresponding to approximately 1-3% of the overall moisture content of the tobacco. It has been found that a suitable power rating for the microwave source 42 is in the order of- 20 KW per 1000 kg/hour of tobacco flow rate, assuming an equilibrium content of moisture at 14% (wwb).

In order to maximise the expansion of the product, the microwave heating should take place in as short a time as possible, for example the dwell time of the tobacco within the expansion station 40 may be 0.1 to 10 seconds.

On exiting the expansion station the conveyor 32 is conveyed to a final drying stage, which may be of any conventional drier such as, for example, a cascading rotary drier, a fluid bed drier or pneumatic conveying drier. In the present example, the expanded tobacco fails from- the end of conveyor 32 through tobacco inlet 52 into the drying station 50. The 15 kW heater 60 supplies hot dry air to the air inlet 52 of the drying station 50 at a temperature of 1500C (the rate at which dried air is supplied to the heater 60 by air supply means is 240 standard m3/hour). The mixture of heated dry air mixing with the expanded tobacco in the drying station 50 further dries the expanded tobacco thereby to prevent any collapsing of the tobacco cells.

The moisture content of the tobacco, as it is sucked out of the tobacco outlet 56, should be somewhere near to its equilibrium moisture content of 14% (wwb). The moisture containing air which is separated from the expanded and dried tobacco in the separator 80 enters conduit 75 at a temperature of 770C and is subsequently expelled from the outlet 72 of the exhaust fan 70 at a rate of 400m3/hour.

The dried and expanded tobacco accumulates in the collection device 90 ready for further processing.

In an alternative use of the apparatus, the present invention may be carried out at reduced pressure. In addition, liquids other than water may be used to moisten the tobacco.

Thus , it will be appreciated that the contribution the present invention makes to the art lies in pre-heating to a temperature in the proximity of, but below, the boiling point the liquid with which the material is moistened, thereby ensuring that the energy input to the process from the dielectric heating stage is dedicated to achieving rapid evaporation of the moisture contained within the cellular structure of the product. This rapid evaporation is a pre-requisite for expanding the material being processed.

The use of pre-heating by conventional heat sources also minimises the energy input and hence cost of the relatively expensive- dielectric heating stage.

Claims (19)

Claims

1. A method for the expansion of a cellular organic material, the method comprising the steps of: moistening the material with a liquid to a predetermined degree; pre-heating the material to a temperature in the proximity of, but below, the boiling point of said liquid using non-dielectric heating; and subsequently dielectrically heating the material, thereby to evaporate a portion of the moisture in the cells of the material and thus expand the material.

2. The method as in claim 1, wherein the cellular material is tobacco.

3. The method as in claim 2, wherein the moistening step increase its moisture content to a predetermined degree of at least 18%, the tobacco having an equilibrium moisture content of 14%.

4. The method as in any preceding claim, wherein said liquid is water.

5. The method as in claim 4, wherein the moistening and pre-heating steps are effected simultaneously by steam.

6. The method as in claim 4 or 5, wherein the pre-heating step raises the temperature of the material to at least 800C but less than 1000C.

7. The method as in any preceding claim, wherein the step of dielectrically heating the material comprises exposing the material to a dielectric heating for a duration of 0.1 seconds to 10 seconds.

8. The method as in preceding claim, wherein the method further includes the subsequent step of drying the material.

9. The method as in any preceding claim, wherein the aforementioned steps are carried under reduced pressure conditions.

10. The method as in any preceding claim, wherein the dielectric heating is in the form of radio frequency or microwave heating.

11. A method substantially as described herein with reference to the accompanying drawing.

12. An expansion apparatus for effecting the expansion of a cellular organic material, the apparatus comprising moistening means for moistening the material with a liquid to a predetermined degree; pre-heating means for pre-heating the material to a temperature in the proximity of, but below, the boiling point of said liquid without non-dielectric heating; and dielectric heating means for heating the material to at least the boiling point of said liquid, thereby to evaporate a portion of the moisture in the cells of the material and thus expand the material.

13. The expansion apparatus as in claim 12, wherein the moistening means and the pre-heating means are both embodied as a steaming station, operable using steam, to both moisten and pre-heat the material.

14. The expansion apparatus as in claims 13, also including a first conveying means for conveying the material to the steaming station.

15. The expansion apparatus as in claims 12 to 14, further including second conveying means for conveying the heated and moistened material to the dielectric heating means.

16. The expansion apparatus as in claim 15, wherein the first and second conveying means are in the form of belt conveyors.

17. The expansion apparatus as in claims 12 to 16, wherein the dielectric heating means is in the form of radiofrequency or microwave heating means.

18. The expansion apparatus as in claims 12 to 17, the expansion apparatus also including a final drying stage.

19. The expansion apparatus constructed, arranged and adapted to operate substantially as herein before described with reference to the accompanying drawings.