Tobacco – Tobacco treatment – Including leaf disintegration
Reexamination Certificate
1999-09-14
2002-05-28
Silverman, Stanley S. (Department: 1731)
Tobacco
Tobacco treatment
Including leaf disintegration
C131S314000, C131S311000
Reexamination Certificate
active
06394098
ABSTRACT:
This invention relates to a method and an apparatus for processing tobacco.
In the tobacco industry, it is well-known that in order to process the tobacco into a suitable form for use in the manufacturing of products, the tobacco leaf has to have the midrib stem removed from the rest of the tobacco leaf (hereinafter referred to as the lamina). This process is generally referred to as threshing.
In the current art, the most common leaf threshing process consists of:
1. Feeding the tobacco leaves into the top of a threshing mill. The leaves are broken up by the action of a rotating element, with radially protruding teeth, until they are small enough to pass through a fixed screen at the bottom of the mill.
2. The threshed leaf is then classified using an air flow in a vertical tower. The lighter, stem free, material rises with the air flow and is removed from the threshing process. The heavier, stem-containing material drops, under the influence of gravity, down the tower, through the air.
3. This heavy, stem containing, material is passed to a second threshing mill, and the process is repeated.
The overall process usually has between four and six stages of threshing and classifying before all the lamina is removed from the midrib stem.
At each stage the aperture size of the screen at the bottom of the mill reduces.
This process is illustrated by means of the flow diagram in FIG.
1
.
It can be observed from this description that it is not possible to reduce the number of threshing stages in use in a process of this form by using a recycle system. The heavy stems would have no means of escaping from the recycle and would accumulate in the process, rapidly overloading it.
GB 740088, U.S. Pat. No. 2,697,439, U.S. Pat. No. 3,046,998 and U.S. Pat. No. 3,513,858 each describe methods of recycling heavy stems with lamina still attached. in each of the processes, an air classification system is used to separate the tobacco into three streams i.e., lamina, clean stems and stems with lamina still attached. The three stream air classification systems are relatively complicated.
U.S. Pat. No. 3,661,159 describes apparatus for stemming tobacco leaves which separates the threshed leaves into light and heavy fractions.
Classification of threshed tobacco leaves into light and heavy fractions is also disclosed in EP-A-0707800, GB-A-2157411 and WO90/05034. The apparatus mentioned in WO90/05034 includes a sieve to separate out the largest size particles after threshing but deals only with improvements in classification systems.
The present invention solves the problem of allowing the use of a recycle system in the processing of tobacco leaves without the need for a complicated three stream air classification system.
According to the present invention, there is provided a method for processing tobacco comprising threshing tobacco leaves in a thresher to form a mixture of free lamina, clean stem pieces from which lamina has been completely or substantially completely removed and unclean stem pieces which have useful pieces of lamina attached thereto, sifting to separate the clean stem pieces from the unclean stem pieces and subjecting the unclean stem pieces to further threshing by recycling the unclean stem pieces to the thresher. The unclean stem pieces are recycled to the same thresher in which they were first produced by threshing tobacco leaves.
The separation of the clean stem pieces from the unclean stem pieces may be carried out at any stage after the threshing step e.g., before or after the conventional separation (or classification) of the lamina from the stem-containing material.
Therefore, in one preferred embodiment, the free lamina is removed from the mixture before sifting. The term sifting is used synonymously with the term sieving in this specification.
In another preferred embodiment, the mixture of lamina, clean stem pieces and unclean stem pieces is sifted to separate the clean stem pieces, and the free lamina is then removed from the unclean stem pieces which are later subjected to additional threshing.
The threshing of the tobacco leaves may be carried out by conventional methods well-known in the art. Sifting of the threshed tobacco may be carried out separately from the threshing step. Alternatively, threshing and sifting may be carried out together in a single piece of apparatus. Such an apparatus for threshing and sifting is described in our related European patent application no. 96309198.8 which is entitled “Apparatus and Process for Threshing Tobacco” and has the same filing date as this application.
Preferably, the free lamina is removed from the mixture or the unclean stem pieces by air classification which is a conventional technique well-known to those skilled in the art.
Sifting to separate the clean stem pieces from the unclean stem pieces (either mixed with or without free lamina pieces) is carried out by the use of a sieve or a similar device. The sieve can be of any type known within the art. Preferably it is a cascade type or rotary type with wiped sides, which are less prone to malfunctioning as a result of screen blocking. The screen size used in the sieve will depend on the size and type of leaves being processed, but commonly the aperture size in the screen will be between 10 and 100 mm.
The type of screen used in the sieve can be of any type known within the art.
The tobacco entering the process may optionally be cut into sections across the stem before threshing, usually referred to as tipping or butting, and the unclean stems may be cut into shorter lengths prior to being threshed with unthreshed tobacco leaves. The shorter stem length improves the sieving of the clean stems after they have been threshed.
The invention also provides apparatus for processing tobacco comprising threshing means for threshing tobacco leaves to form a mixture of free lamina, clean stem pieces from which lamina has been completely or substantially completely removed and unclean stem pieces which have useful pieces of lamina attached thereto, wherein the apparatus further comprises means for sifting to separate the clean stem pieces from the unclean stem pieces and means for returning the sifted unclean stem pieces back to the threshing means. The means for sifting is preferably a sieve. The means for returning the sifted unclean stem pieces back to the threshing means may comprise a conventional conveying device such as a conveyor belt.
By the term clean stem pieces, it is meant that the stem pieces are not attached to useful pieces of lamina i.e., pieces of lamina which could be relatively readily separated from the stem in a threshing process. Similarly, the term unclean stem pieces refers to pieces of stem which do have useful pieces of lamina attached.
The nature of the clean stem pieces will depend upon the aperture size of the screen used in the sieve. Where the aperture size is low, the amount of lamina attached to the stems passing through the screen will be small, typically less than 1% of the total lamina entering the process. Where the aperture size is large, the amount of lamina attached to the stems passing through the screen will be greater, up to 20% of the total lamina entering the process, but is preferably not more than 10% of the total lamina entering the process.
Where the stems produced are clean or contain a very small amount of attached lamina, they can be removed from the threshing process and passed without further processing to a drying stage or other process.
Where the amount of lamina still attached to the stems is greater or where totally clean stems are required for drying or further processing they can be passed first to a final polishing process. The final polishing process can consist of any type of suitable threshing process known within the art. Preferably it consists of a single conventional thresher and classifier or a further single conventional thresher, classifier and sieve with a small aperture screen as described in this application, or carried out using the apparatus described in our related application no. 96309198.8.
The unclean s
Imperial Tobacco Limited
Larson & Taylor PLC
Silverman Stanley S.
Walls Dianne A.
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