GB2268254A

GB2268254A - Drying tobacco

Info

Publication number: GB2268254A
Application number: GB9313472A
Authority: GB
Inventors: Peter Funke
Original assignee: Koerber AG
Current assignee: Koerber AG
Priority date: 1992-07-01
Filing date: 1993-06-30
Publication date: 1994-01-05
Anticipated expiration: 2013-06-30
Also published as: DE4221573A1; ITMI931359A0; GB2268254B; ITMI931359A1; IT1264882B1; GB9313472D0

Abstract

The total drying energy used drying tobacco in fibrous or leaf form or a similar material is kept low by successively drying in hot steam and another hot gas, preferably hot air, each drying medium performing a partial drying of the tobacco. Part of the moisture-enriched hot steam is superheated again and used for drying, and part of it serves to heat hot air, by which the tobacco is further dried. <IMAGE>

Description

2268254 METHOD AND APPARATUS FOR DRYING TOBACCO The invention relates to a

method of and apparatus for drying tobacco in fibrous or leaf form or a similar material.

It is known, for example from US patent 4 687 007, to dry tobacco, in particular in the form of tobacco fibres which can comprise leaf tobacco or rib-type tobacco, by means of hot steam (that is to say by means of superheated steam) in so-called flow driers, the tobacco being conveyed in the steam flow so that an intensive heat transfer and thus rapid and intensive drying occur.

It is moreover known to dry tobacco by means of a hot gas, in general by means of hot air. This can also be performed in a flow drier such as is known for example from US patent 3 399 462. Another type of hot drying can take place in socalled vibro-fluidized bed driers in fluidized layers. Such driers are described for example in US patent 3 799 176 and US patent 3 877 469.

It is known from DE-OS 33 23 000, for the purpose of saving energy, to supply the vapours of hot-air driers to a heat exchanger in which they warm fresh drying air. The heat exchanger is advantageously operated such that some of the moisture in the vapours which are at the saturation point condenses on cooling. As a result, the condensation heat can be at least partially recovered.

It is moreover known from DE-OS 30 13 703 to supply to a heat pump the moisture-laden drying medium once it has left a drier and thus to recover some of the energy content of the drying medium.

Drying processes which have hitherto been used in practice and which use hot steam operate with vapour compression, or, in multi-step processes, supply the exhaust steam from the previous stage as hot steam. Both processes result in considerable increases in the drying times, since only small temperature or partial pressure differences can be used.

The object of the invention is to better use the energy content of the hot steam. According to the invention, this is achieved in ' that drying is carried out using hot steam and hot gas, preferably hot air, each drying medium performing a partial drying of the tobacco.

Further advantageous embodiments of the process according to the invention can be found in the dependent process claims.

2 The apparatus of the invention is characterized by a hot-steam drier and a hot-gas, preferably hot-air drier, each for the evaporation of part of the tobacco moisture.

The advantage associated with the invention consists in using the heat content of the moisture-laden hot steam partially by superheating and thus re-using it in the flow drier and partially for warming fresh air for the purpose of obtaining hot air. Moreover, the exhaust air quantity can be very greatly reduced in a desirable manner by comparison with pure hot-air driers, since a large proportion of the evaporated water can be recovered as condensate.

The method and apparatus of the invention are particularly suitable for expanding'tobacco, e.g. cut tobacco.

The invention is explained in more detail by way of example with reference to the drawing which is a diagrammatic illustration of one embodiment of the method and apparatus of the invention.

Cut tobacco conveyed along conveying path 3 is supplied at inlet 2 to a hot-steam drier in the form of a flow drier 1 such as is known for instance from US patent 4 687 007, and this cut tobacco leaves the flow drier 1 at outlet 4. In the hot-steam flow drier 1 the tobacco particles are conveyed in superheated steam, as a result of which intensive and rapid drying is achieved. The hot steam (superheated dry steam) is supplied by way of line 6. 7 designates a superheating apparatus which, for example, heats up steam supplied thereto from 1600C to 3000C, The partially dried tobacco, which can for example have lost 40 to 60% of the total moisture to be evaporated, passes from outlet 4 of the hot- steam flow drier together with the steam to an inlet 5 of a separator 8 in which the tobacco is separated from the steam. The separator 8 can be a cellular wheel sluice or a cyclonic separator, -the latter being preferred because of the absence of moving parts. The tobacco leaves the separator 8 at the outlet 9 thereof and passes by way of a conveying path 11 to the inlet 12 of a hot-air drier 13, which can be constructed as a vibro-fluidized bed drier, in accordance with US patent 3 799 176 and 3 877 469. However, the hot-air drier 13 can also be constructed as a flow drier in which the tobacco particles are conveyed in flowing hot air and are at the same time further dried.

3 The tobacco can be dried in the hot-air drier 13 until it reaches its desired final moisture content. It leaves the drier 13 at the outlet 14 thereof and, with the hot air, passes to the inlet 16 of a separator 17 which the dried tobacco leaves at outlet 18. The separator 17 can again be constructed as a cell wheel sluice or as a cyclonic separator. The moisture-laden exhaust air (vapours) leaves the separator 17 by way of outlet 19 and is drawn off by a ventilator 20. Part of the exhaust steam which leaves the separator 8 by way of outlet 21 and which is laden with moisture from the tobacco passes by way of a ventilator 22 and a line 23 to the superheating apparatus 7, in which the moisture taken up from the tobacco (substantially water) evaporates and the exhaust steam is again converted to hot steam which is supplied by way of line 6 to the flow drier 1.

Another part of the moisture-laden exhaust steam passes by way of a line 24 and a choke valve 26 to an inlet 27 of a heat exchanger 28 whereof the other inlet 29 is supplied with fresh air by way of line 31, in which there is a ventilator 32. In the heat exchanger 28 the steam gives off a large part of its heat energy to atmospheric air and leaves the heat exchanger 28 at outlet 33, after which it condenses in a condenser 34. The heated air leaves the heat exchanger 28 at outlet 36 and passes by way of line 37 to the hot-air drier 13. Here, the temperature of the hot air can be about 1OCC. In the hot-air drier the tobacco, which is only partially dried by the hot-steam flow drier 1, is then further dried as described, for example until it reaches its final moisture content.

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Claims

CLAIMS:

1. A method of drying tobacco in fibrous or leaf form or a similar material, characterized in that drying is carried out using hot steam and hot gas, preferably hot air, each drying medium performing a partial drying of the tobacco.

2. A method as claimed in Claim 1, characterized in that the moisture of the tobacco is first reduced using hot steam and then further reduced using hot air.

3. A method as claimed in Claim 1 or 2, characterized in that the steam which has been moisture-enriched in a flow drier is separated from the tobacco and then part of it is superheated again, after which it is returned to the flow drier as hot steam, and another part heats hot air by which the tobacco is further dried.

4. A method as claimed in any one of the preceding claims, characterized in that the hot air further dries the tobacco as it is conveyed in a closed oscillating channel in a vibro-fluidized layer or in a hot-air flow drier.

5. Apparatus for drying fibrous or leaf-form tobacco or a similar material, characterized by a hot-steam flow drier and hot-gas, preferably hot-air drier, each for the evaporation of part of the moisture in the tobacco.

6. Apparatus as claimed in Claim 5, characterized in that the hot-steam flow drier is arranged upstream of the hot-air drier.

7. Apparatus as claimed in Claim 5 or 6, characterized by a superheating apparatus for part of the moisture-laden exhaust steam from the hotsteam flow drier, which is connected to the steam inlet of the hot-steam flow drier, and by a heat exchanger for another part of the moisture-laden exhaust steam from the hot-steam flow drier, to which air is supplied for heating and which is connected to the hot-air inlet of the hot-air drier.

8. Apparatus as claimed in any one of Claims 5 to 7, characterized by a vibro-fluidized bed drier or a flow drier as the hot-air drier.

9. A method of drying tobacco substantially as herein described with reference to the accompanying drawing.

10. Apparatus for drying tobacco substantially as herein described with reference to the accompanying drawing.