IT202000005572A1 - Method of producing homogeneous sheets of nicotine-free plant fibers. - Google Patents

Description

DESCRIPTION

of the invention entitled:

"Method of producing homogeneous sheets of nicotine-free plant fibers?

The present invention relates to a method of producing homogeneous sheets of nicotine-free vegetable fibers.

Both conventional and unconventional methods of producing reconstituted tobacco sheets are known, the latter also referred to as HNB (Heat Not Burn). Generally speaking, reconstituted tobacco? obtained with the use of tobacco by-products and processing scraps (ribs, small pieces of leaves, powder, etc.) which, appropriately shredded until they are practically reduced to powder and mixed with water, glycerin binders and other liquid additives, they allow to obtain an extremely fluid mixture (slurry) having a liquid content of about 70% by weight, which is then poured in the form of a veil on a steel strip and with this transferred to a drying oven. Here the evaporation of the liquid fraction of the dough takes place, so that the solid residue forms a sort of continuous strip of tobacco having approximately the same width as the steel strip. Subsequently, the dried mixture strip is separated from the steel strip and is cut into pieces of various sizes according to the request. These pieces are then transformed into thin filaments which, suitably mixed, are fed to a traditional cigarette packing machine.

Depending on the raw materials used and, in particular, depending on whether shredded tobacco by-products up to a particle size between 20? M and 320? M are used, or whether crushed tobacco leaves with dimensions between 5 and 10 mm are used, reconstituted tobacco is divided into conventional or unconventional.

WO 2016/050469, WO 2016/050470, WO 2016/050471, WO 25 2016/050472 describe known techniques for the production of reconstituted tobacco, which however require large plants and involve high energy consumption to bring the slurry, which when it is product? rather fluid, to the consistency of a sheet of tobacco. ? it is sufficient to point out that a drying oven can? reach even 100 m in length.

Another drawback of the known techniques for the production of reconstituted tobacco with the use of by-products consists in the fact that the formation of the sheet starting from the slurry veil? rather irregular, as the starting products are not homogeneous and their distribution on the steel strip is not? uniform; it follows that the reconstituted tobacco sheet does not allow it to be coiled, n? to be cut regularly.

Purpose of the invention? to use the known technique of production of sheets and strips of reconstituted tobacco in sectors, in which it is not? still been used and at the same time to modify it in order to eliminate the drawbacks that in the specific tobacco sector it currently highlights and would highlight even more? in these new sectors of use. In particular, the invention aims to produce homogeneous sheets and strips of nicotine-free vegetable fibers, in particular potato, hemp, tea, chamomile, mint, sage, rosemary, eucalyptus and others.

Another purpose of the invention? to produce homogeneous sheets of vegetable fibers with plants of much larger dimensions? reduced than those of the well-known reconstituted tobacco production plants.

Another purpose of the invention? to produce homogeneous sheets of vegetable fibers with limited energy consumption.

Another purpose of the invention? to produce homogeneous sheets of vegetable fibers using equipment in part already? available on the market, even if never used in this specific technical sector.

Another purpose of the invention? to produce homogeneous sheets of vegetable fibers with characteristics suitable to satisfy different market demands.

Another purpose of the invention? to produce homogeneous sheets of vegetable fibers by operating at low temperatures and therefore preserving all the aromas of the raw materials used.

According to the invention, all these objects and others that will result from the following description are jointly or separately achieved with a method of producing homogeneous sheets of nicotine-free vegetable fibers according to claim 1.

In particular, the method according to the invention for producing homogeneous sheets of nicotine-free vegetable fibers? characterized by the fact of understanding the execution, in sequence, of the following steps:

- the solid components of the raw materials are crushed with vegetable fibers until they reach a particle size of about 20 - 320? m, preferably about 80-180? m,

- mix the minced product cos? obtained with water, optionally powdered cellulose, at least one binding agent and at least one material for forming an aerosol, until a slurry is obtained with a liquid content of about 30-50%, preferably about 35-40%,

- said mixture is subjected to a first lamination in order to obtain a continuous strip with a thickness of about 1-20 mm, preferably about 1-10 mm, - said strip is subjected already? subjected to said first lamination to a series of further lamination steps, until obtaining a strip having a remarkably constant thickness of about 90 - 280? m, preferably of about 140-200? m, - said strip is dried until its liquid content to about 8-15%.

The present invention is further clarified hereinafter in some of its preferred embodiments reported for purely illustrative and non-limiting purposes with reference to the attached drawings, in which:

Figure 1 shows a schematic general view of a plant for the production of homogeneous sheets of vegetable fibers according to the invention,

figure 2 shows its feeding section in case the sheets of vegetable fibers are obtained from plant leaves,

figure 3 shows its feeding section in case the sheets of vegetable fibers are obtained from stems and branches of plants,

figure 4 shows a partial scheme of the plant with two distinct lines of pre-treatment of the leaves and stems and branches of plants, figure 5 shows its section of grinding, mixing and storage,

figure 6 is a schematic view of a cylinder refiner thereof, figure 7 shows a plan view of its layering section in a particular embodiment.

Figure 8 schematically shows its hot air dryer, and Figure 9 schematically shows its hot air dryer in a different embodiment.

As can be seen from the figures, the method according to the invention for producing homogeneous sheets of nicotine-free vegetable fibers uses a plant comprising more? sections aimed at operating on the incoming raw materials up to transforming them into a continuous belt of vegetable fibers to be sent to subsequent processing or packaging. The raw materials used can consist for example of potato, hemp, tea, chamomile, mint, sage, rosemary, eucalyptus and others.

Pi? particularly, the plant for carrying out the method according to the invention comprises:

- a pre-treatment section of the starting solid products (leaves, stems and branches of the plants) for their preparation for subsequent grinding treatments, - a grinding and storage section awaiting subsequent mixing with suitable treatment liquids,

- a kneading section of solid and liquid materials to obtain a homogeneous dough with a rather dense consistency,

- a section of transformation of the dough, and in particular of a plurality of portions of said mixture, in a continuous belt,

- a rolling line of the continuous strip for its reduction to the desired final thickness,

- drying of the laminated strip.

Conveniently, the preparation and pretreatment section of the solid starting products can? comprise a pre-treatment section of the plant leaves used for the preparation of the sheets of vegetable fibers (fig. 2,4) and / or a section for the preparation and pre-treatment of the stems and branches of the plants (fig.

3.4).

In the case of preparation and pre-treatment of plant leaves (fig. 2,4), the relative section includes a feeding station with a bench 2 for unpacking the bales of vegetable leaves, which generally contain them, and the transfer of these to a grinder 4.

Conveniently, the output of this grinder 4? connected, through a pneumatic conveying line 6, to a cyclone 8, in which the conveying air is separated from the solid product, which is transferred to a vibrating sieve 10 for the separation of the fine parts from the remaining parts of the product. The exit of the fine parts? directly connected to a mill 12, preferably of the cryogenic type, while the output of the remaining parts of the product feeds a traditional twine lever machine 14, which removes any twine previously not removed from the vegetable leaf bales.

The output of the twine lever machine 14 feeds a classification chamber 16 for the separation of any heavy foreign bodies from the vegetable leaves, which through a pneumatic conveyor line 18, a cyclone 20, a belt conveyor 22, equipped with a metal detector 24 for the removal of any metal bodies, a weighing system 26 (master scale), and a pneumatic conveying line 28, are transferred to storage and mixing silos 30, from which they can then be transported, through another? pneumatic transport 32, to the cryogenic mill 12. These silos 30 are sized in order to contain the quantities? of product necessary to form the batches according to the particular recipes to be prepared.

On the other hand, in the case in which the preparation and pre-treatment section is provided to operate on the stems and branches of plants to be used to prepare the sheets of vegetable fibers (fig. 3,4), it comprises an overturning device 34 for containers containing stems and branches of plants, a feeder 36 of these to a vibrating conveyor 38, for the separation of any heavy bodies from them, and a pneumatic conveying line 40 for their transfer to a hammer mill or to a shredder 42, where they are shredded.

The hammer mill or the shredder 42 has the output in turn connected, by means of a pneumatic conveying line 44 equipped with cyclone filters 46, to one or more? storage silos 48.

The exit of the storage silos 48? in turn connected, by means of a screw conveyor 50, to a weighing system 52 (slave scale), which doses the chopped stems and branches in the percentage required by the particular recipe to be prepared, which can then be started, through a pneumatic conveying line 53, to the storage and mixing silos 30, from which they can then be transported, through the pneumatic conveying line 32, to the cryogenic mill 12, which grinds the various products received up to bring them to an average particle size about 20-320? m, preferably about 80-180? m.

There are various types of mills that can be used, even if? pi? It is advantageous to use a cryogenic pin mill, which allows the product to be kept at low process temperatures and therefore to retain the aromas of the raw materials used.

The step mill? in s? traditional and comprises inside a closed structure a fixed disk and a rotating disk or two counter-rotating disks, provided with facing and partially interpenetrating pegs. Being an? Equipment in itself? traditional, it? it has been globally indicated with 12 in fig. 4 and 5 but it is not represented in its internal constructive characteristics n? in its modalities? of operation.

Preferably, the 12? predisposed to carry out a cryogenic grinding, and what? grinding in the presence of liquid nitrogen.

How to ? said, in a plant for the production of plant fiber sheets a cryogenic pin mill 12? somewhat more? advantageous of a traditional mill, essentially for the different modalities? with which the products to be ground are treated. In fact, grinding at room temperature can? lead to obtaining poor quality products? while grinding in the presence of liquid nitrogen allows you to preserve the properties? physical and chemical and organoleptic characteristics of the products.

The quantity of liquid nitrogen used in cryogenic grinding processes? a key part to consider when studying the pros and cons of the process, and can? vary according to the materials processed. Liquid nitrogen at a temperature of -175 ° C is injected onto the product inside the chamber of a screw conveyor 55 which feeds the mill 12 and its residence time in contact with the nitrogen? of about 2 to 5 sec., which? also the transit time of the product inside the auger 55. The temperature of the product leaving the mill 12? advantageously lower than 10 ° C, so that the nitrogen vapors, which are released almost instantly upon contact with the raw material to be cooled, go through the entire feeding system of the mill in countercurrent, carrying out the desired pre-cooling effect. The flow of liquid nitrogen in the pre-cooling system and in the mill is controlled by thermocouples, which make the cryomind process fully automatic.

In summary, the positive factors of cryogenic grinding are:

- higher yields,

- best quality of the final product without breaking or tearing of the molecular structure,

- decrease of the necessary energy,

- best quality of the final product,

- less quantity? waste due to overheating and oxidation,

- final product pi? homogeneous and more? end,

- less quantity? of material to be reprocessed in the grinding system.

Appropriately, the exit of the cryogenic pin mill 12? connected to a fluid bed sieve 54, which has the function of separating the ground product, which comes out of the mill itself and generally has an average particle size of about 20 - 320? m, preferably of about 80-180? m, from pieces larger, inevitably present.

Conveniently, the fluidized bed sieve 54 therefore has the function of classifying the product and of reintroducing into the mill 12 the one with fractions greater than 320? M, after having separated them from those between 20? M and 320? M, which through a pneumatic conveying line 56 are sent to one or more? mixing and storage silos 58.

Advantageously, the outlet of the mixing and storage silos 58? connected, through a pneumatic conveying line 60, with a cyclone filter 62, which has the function of breaking down the dusty air and more? specifically to separate the dust, which is then recovered and reintroduced into the cycle, from the air, which can then? be expelled.

Conveniently, the outlet of the cyclone filter 62 feeds, through a continuous metering system 66, preferably with a screw, a mixer 64, which can be of various types, for example of the horizontal type with overturning or vertical spiral.

The mixer 64? fed with quantity? doses of comminuted raw material, water, at least one binding agent and at least one material to form an aerosol, and configured to obtain at the outlet a mixture with a liquid content of about 30-50%, preferably about 35-40%.

In particular, the values of liquid or humidity, indicated in the present description, are intended to be determined according to the measuring system on a wet basis. In particular, the humidity values? are defined as the percentage of water contained in the total mass of the corresponding product and, in other words, as a percentage ratio between the quantity? d? water and the total mass of the assembly. Conveniently, these values are obtained using the traditional methods envisaged in the literature to measure the quantity? of water in a product, such as those presented in? Tobacco Moisture, Water and Oven Volatiles? A status report of common moisture methods used within the tobacco industry? by Nils Rose ET AL. in? Analytical and bioanalytical chemistry? (1 July 2014, pages 1-16).

Preferably, at least one inlet conduit for water, a material for the formation of aerosols (for example glycerin) and at least one binding agent (binder) is connected to the mixer 64. Conveniently, one or more? inlet ducts for other additives required by the particular recipe to be prepared.

Pi? particularly the plant includes one or more? 68 tanks for the storage of material for the formation of aerosols and one or more? premixers 70, in which pu? said material for the formation of aerosols and, preferably, a plurality of materials can be introduced. of additives dosed in the right proportions to form the liquid to be introduced into the mixer 64.

In order to increase the strength of the finished product sheet and at the same time increase the density? of the product itself? It is preferable that powdered cellulose with a granulometry preferably between 50 and 100 µm in a percentage between 2% and 10% by weight with respect to the comminuted raw material is introduced into the mixer 64 together with the other components of the dough.

This cellulose powder, which before its use? contained in bags or in big-bags, can be introduced directly into the mixer 64 (fig.

1) and in this case, after being poured into a traditional hopper, it is fed to a cyclone filter 72, which through a continuous dosing system 73, preferably of the screw type, introduces it in quantity? dosed in the mixer 64.

Alternatively, powdered cellulose can? be introduced, again through a cyclone filter 72 and a continuous dosing system 73, into the pneumatic conveying line 28 which feeds the mixing and storage silos 30, from which it is then transferred to the mill 12 (fig. 4) through the line of pneumatic conveying 32, together with the other components of the mixture, present in the line itself. From the mill 12 the contents of the mixing and storage silos 30 are then transferred, through the pneumatic conveying line 56 to the silos 58 and from there, through the pneumatic conveying line 60, the cyclone filter 62 and the metering device 66, in the mixer 64.

Examples of preferred materials for aerosol formation (and in particular for the formation of a visible aerosol) include polyhydric alcohols (e.g. glycerin, propylene glycol, triethylene glycol and tetraethylene glycol), aliphatic esters of mono-, di- or polycarboxylic (eg. Methyl-stearate, dimethyl dodecanioate and dimethyltetradecanediate), as well as? their blends. Suitably, glycerin, propylene glycol, triethylene glycol and tetraethylene glycol can be mixed together to form an aerosol-forming material. The material for the formation of the aerosol can? also be provided as a portion of the binding agent (for example, when the binding agent? propylene glycol alginate). Advantageously, suitable combinations of materials for the formation of the aerosol can also be provided.

Preferably, said at least one binding agent (binder) comprises at least one of hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, microcrystalline cellulose, methylcellulose, carboxymethylcellulose (CMC), corn starch, potato starch, guar gum, locust bean gum, pectin and alginates (e.g. ammonium alginate and sodium alginate).

Advantageously, the exit of the premixers 70? connected to an inlet of a hydrator 74, having other inlets connected to a water supply line 76 and to a compressed air supply line 78.

Preferably, the output of the mixer 64 feeds a unit? 80 of forming the dough to obtain a plurality of of portions 82, preferably shaped like loaves / loaves and separated from each other. Conveniently, the unit? 80 comprises a pair of forming cylinders 84, affected by grooves preferably parallel to the axis of the cylinders themselves and intended to take the dough at the inlet and to supply the portions 82 at the outlet. Advantageously, the unit? of forming 80? also? configured to carry out a roughing of the dough and for this purpose, preferably, it comprises a hopper 86 provided inside it with a lump breaker and on the bottom of said pair of forming cylinders 84.

Advantageously, at the exit of the unit? of forming 80? a conveyor belt 88 is provided for transferring the portions 82 to a unit? of first rolling 90.

Preferably, the unit? of first lamination 90 comprises a lobe feeder 92.

Advantageously, along the transfer path from the unit? of forming 80 to the lobe feeder 92 pu? be provided an additional metal detector 94, having the function of removing any metal parts, which could still be present in the mixture and could damage the subsequent units? processing. These metal parts are conveyed along a distinct path before entering the lobe feeder 92 and are collected in a suitable container 96.

The lobe feeder 92 comprises a series of lobed feed rollers, between which the portions 82 (which come out from the forming cylinders 84 of the forming unit 80) are passed so that they are pushed between a pair of cylinders 98, which are configured to form a continuous strip with a thickness of about 1-20 mm, preferably about 1-10 mm.

Conveniently, in a version not shown of the system, downstream of the lobe feeder 92 can? the lamination line 100 can be directly provided. In particular, in this case, the lamination line receives at the inlet the single-layer continuous strip, having a thickness of about 1-20 mm, preferably about 1-10 mm, which comes out of the unit ? of first lamination 90 equipped with lobe feeder 92.

Advantageously, downstream of the unit? of first rolling 90 and upstream of the rolling line 100, pu? be expected a? unit? of layering 102. Preferably, it? configured to have on more? layers the single-layer continuous tape, having a thickness of about 1-10 mm, which comes out of the unit? of first lamination 90, in order to transform it into a multilayer tape with a thickness of about 2-20 mm, which? then sent in input to the lamination line 100.

Preferably, said unit? layer 102 consists of an upstream conveyor belt 104, which has the function of depositing the product belt on an underlying downstream conveyor belt 106, preferably belonging to the rolling line 100, arranging it so that it is stratified on said belt downstream conveyor 106, for example for multiple folding on s? same. Preferably, the upstream conveyor belt 104? raised with respect to the downstream conveyor belt 106 and? equipped with a continuous forward motion with respect to its support structure, and at the same time with an alternating motion with its support structure, parallel to its longitudinal axis.

Conveniently, the unit? of stratification 102 feeds the subsequent and underlying rolling line 100, and depending on the type of plant the upstream conveyor belt 104 of the unit? of layering 102 pu? be arranged parallel or perpendicular to the downstream conveyor belt 106, which advantageously? the inlet belt of the lamination line 100. In particular, if the conveyor belts of the lamination line 100 have a width substantially equal to the width of the product belt that leaves the unit? of layering 102, the upstream conveyor belt 104? arranged parallel to the inlet conveyor belt 106 of the rolling line 100 (fig. 1), while if the conveyor belts of the rolling line 100 are more? wide of the product belt coming out of the unit? of layering 102,? it is preferable that the upstream conveyor belt 104 is arranged orthogonally to the conveyor belt 106 for entering the rolling line 100 (Fig. 7). In this way, the alternating movements of the support structure of the upstream conveyor belt 104 of the unit? layer 102 can distribute the product web over the entire useful width of the rolling line 100.

In both cases, however, the alternating movement of the support structure of the upstream conveyor belt 104 of the unit? of stratification 102 causes a stratification of the product belt, which comes out of the unit? of first rolling 90, on the underlying first conveyor belt 106 of the rolling line 100 and the formation of a stratified belt having a width substantially equal to the useful width of the rolling line itself.

The lamination line 100? formed by more? rolling stations, each comprising a pair of cylinders 108, which delimit an increasingly narrow passage between them. narrow to progressively reduce the thickness of the web of product being processed. In particular, the lamination line 100? configured to progressively bring the continuous strip to a thickness of 90 - 280? m, preferably about 140-200? m.

Preferably, between each lamination station and the next? provided a conveyor belt 110 having a length preferably of about 1.5-2 m, that is to say? sufficient to let the product rest before it undergoes the next lamination step.

Advantageously, the lamination line 100? then completed with one or more? calibration stations, each formed by a pair of calibrating cylinders 112.

? it is advantageously provided that the laminating cylinders 108 and possibly also the calibrating cylinders 112 can be heated, so as to be able to start the drying phase already? during lamination. Conveniently, downstream of the rolling line 100? a dryer 114 is provided, preferably with air recirculation (Fig. 8), to bring the liquid content of said laminated strip to about 8-15%. Advantageously, the dryer 114 can? be divided into two units? 116,118, placed in series with each other (fig. 9). In this case, the unit? 116 upstream? planned to perform the first drying phase and? equipped internally with a steel belt or net belt conveyor for transporting the product leaving the rolling line 100; the unit? 118 downstream? planned to carry out the second drying phase and the subsequent cooling phase and? equipped with a net belt conveyor inside.

Furthermore, the dryer 114? advantageously provided at the inlet and outlet of sensors 120, preferably with infrared rays, which control the product along its entire length.

For the preparation of sheets of vegetable fibers starting from vegetable leaves, the cartons containing said leaves are placed on the undressing bench 2 (fig. 2), where the single bales of vegetable leaves are removed from the cartons and sent to the grinder 4 , which reduces the leaves themselves to a substantially uniform size between 5 and 10 mm.

Appropriately, the product so? shredded is then transferred along the pneumatic conveying line 6 to the cyclone 8, which separates it from the air and makes it fall onto the vibrating sieve 10.

Here is the separation of the pi? fines, which are sent directly to the cryogenic mill 12, from the remaining parts which, after passing through the twine lever machine 14, are sent to the classification chamber 16 for the separation of any heavy bodies from the shredded leaves, which through the pneumatic conveying line 18, the cyclone 20, the belt conveyor 22 equipped with metal detector 24 for the removal of any metal bodies, the weighing system 26 (master scale) and the pneumatic conveyor line 28 are transferred to the storage and mixing silos 30, from which they can then be transported, through the pneumatic conveying line 32, to the cryogenic mill 12.

If sheets of vegetable fibers are to be produced starting from stems and branches of plants, the relative containers are placed on the overturning device 34 (fig. 3), which feeds them to the vibrating conveyor 38 for the removal of any heavy bodies. The stems and branches are then transferred through the pneumatic line 40 to the hammer mill 42, which shreds them to reduce them to a size between 5 and 8 mm.

From here the chopped stems and branches, separated in the cyclones 46 from the transport air, are transferred to the storage silos 48, from which the different types, coming from different qualities, are transferred to the storage silos 48. of vegetables, can be picked up and transferred through the screw conveyor 50 to the dispenser 52, which doses them according to the particular recipe to be prepared.

The stems and branches chopped and dosed in the correct quantities? from here they are transferred through a pneumatic line to the cryogenic mill 12.

If the plant is intended to treat both leaves and stems and branches of plants, the pneumatic conveying line 28 which feeds the mixing and storage silos 30 also enters the pneumatic conveying line 53 which comes from the storage silos 48 ( fig. 4).

Regardless of the type of raw material to be produced, and therefore the nature of the solid parts of this raw material introduced into the unit? of comminution, from the fluid bed sieve 54, fed by the cryogenic mill 12, a ground product comes out which has an average particle size of about 20 - 220 µm, preferably of about 80-180 µm. It is sent to the mixing and storage silos 58, from which the products can then be withdrawn according to the needs and transferred to the mixer 64.

In addition to the ground raw material, any cellulose and in general all the solid products coming from the mixing and storage silos 30, water, at least one binding agent and at least one material are also introduced into the mixer 64. an aerosol. Advantageously, compressed air and other additives can also be introduced.

Conveniently, the whole is then mixed together to form a slurry having a percentage of liquids (humidity) of about 30-50%, preferably about 35-40%, by weight on a wet basis, i.e. a rather thick consistency.

Preferably, the dough so? obtained is transferred to the unit? of molding 80, from which the portions 82, preferably loaf-shaped, come out in succession.

These portions of dough 82, which come out of the unit? of forming 80 are suitably transferred to the unit? first lamination 90 which? configured to output a continuous web with a thickness of about 1-20 mm, preferably about 1-10 mm.

This continuous tape, which comes out of the unit? of the first lamination 90, can? be transferred directly to the rolling line 100 or, in a more? advantageous, can? be folded up on s? itself in its passage through the unit? of layering 102 to be cos? deposited in layered form on the inlet belt of the rolling line 100.

Appropriately, how do you? said, the layering? obtained by dropping the continuous belt on the upstream conveyor belt 104 of the unit? of stratification 102, which is made to advance with respect to its support structure, which is moved by reciprocating motion, so as to arrange on more? layers the product belt on the downstream conveyor belt 106 and that is? at the entrance of the rolling line 100. Depending on the plant and the direction of the alternating movement of the support structure of the conveyor belt 104 of the unit? of layering 102, the product web is arranged on several? layers parallel to the longitudinal direction of the rolling line 100 or orthogonal to it.

Conveniently, at each passage from one station of the rolling line 100 to the other, the product strip undergoes a reduction in thickness, until it reaches the desired thickness in correspondence with the output calibrating cylinders 112, which has a significantly constant value of about 90. - 280? M, preferably about 140-200? M. Advantageously, moreover, at the exit from the rolling line 100 the strip has a liquid content lower than 20% or even 15%, if the laminating cylinders 108 are heated and the removal of the water has already started. during lamination.

The web of product which leaves the rolling line 100 is then subjected to drying in the dryer 114, where its liquid content is brought to about 8-15%.

Conveniently, the dryer 114? with recirculation of air, and compared to the dryers traditionally used in the production of reconstituted tobacco? somewhat more? advantageous both in terms of complexity? in terms of overall dimensions and in terms of energy consumption. There? as traditional plants treat a very fluid and not very stable product (slurry), unlike the product treated by the plant described above, which? much more? dense and much more? stable. Consequently, while the plants that treat slurry require traditional irradiation and conduction dryers, the plant just described can? advantageously to use a recirculating air dryer 114 with a network belt conveyor or a combined system of steel belt conveyors for the first drying phase and network belt conveyors for the second drying phase and for the drying phase. cooling down. In this way they are obtained, at par? of performance, reduced dimensions (about 45 m compared to over 100 m of a traditional dryer) and lower energy consumption given the smaller quantity? of water to be removed (using about 1000 kg / hour of steam / hour compared to over 5000 kg / hour of steam in a traditional dryer).

Conveniently, at the exit of the dryer 114 the product? ready to be wound on a reel or to be cut into sheets or shredded into threads of predetermined dimensions, to be used for the intended uses.

? advantageously provided that the plant can include, as an alternative to the unit? of molding 80 or in addition and upstream of this, a refiner with cylinders 122, which has the task of bringing the solid components of the mixture to a particle size not exceeding 20? m.

The refiner (fig. 6) comprises inside a closed container a plurality of of cylinders 124 arranged in sequence in close proximity to each other, so as to delimit corresponding grinding slots. The lower cylinder 124? ? mounted with the axis outside the plane containing the axis of all the other cylinders 124 and acts as a feeder of the dough, which is taken from the bottom of the container and raised upwards in order to pass between the lower cylinder and the one immediately above and then to follow among all the others. The various pairs of cylinders 124, between which the dough passes, rotate at different speeds, in the sense that the upper cylinder rotates at different speeds. greater than the lower cylinder, with which it cooperates, so as to subject the dough to stretching during the passage between the cylinders 124 of each pair and thus to reduce the size of the particles of the dough itself. Indeed, one of the fundamental parameters for the success of the refining process? just the different speed? of the various cylinders 124, on which the passage of the whole mass of dough which has passed through the grinding slot depends.

The pressure between the cylinders? hydraulically controlled.

All cylinders 124 are cooled with cold water which circulates inside each cylinder and in this way contrasts the heat, which develops from the mixture due to the friction due both to the movement of the cylinders and to the rubbing with the product. In this way the temperature of the product mass is reduced until it reaches 25 ° C.

Thanks to the refiner 122 just described, the friction action, which is exerted on the dough by the cylinders 124 of the latter, develops a considerable binding action of the cellulose fibers contained in the raw material and that involves the double advantage of developing the aromatic components of the product and eliminating the need? to introduce more fiber into the mixture to obtain the required binding effect.

The operation of the plant in this different embodiment provides that the comminuted raw material coming from the preparation and pretreatment stations is fed to the cryogenic pin mill 12 in quantity. proportionally dosed on the basis of the recipe to be obtained, and is brought from this to a particle size of about 20 - 320 µm, preferably of about 80-180 µm.

The product is then transferred with the modality? already? described in the mixer 64, in which a product mixture is formed as described above.

The dough so? obtained is then fed to the cylinder refiner 122, which has the task of bringing the solid components of the mixture to a granulometry not exceeding 20? m. In this way, the friction action exerted on the dough by the cylinders 124 of the refiner 122 develops a considerable binding action of the cellulose fibers contained in the raw material and in particular in the stems and branches of the latter, it entails the double advantage of developing, on the one hand, the aromatic components of the product and, on the other hand, of eliminating the need? to introduce more fiber into the mixture to obtain the required binding effect.

In fig. 1? schematically indicated the position of the refiner 122 between the mixer 64 and the unit? of forming 80, but the invention also provides that the refiner 122 can be an alternative to the unit? of forming 80, and in this case the mixture that comes out of the refiner 122 is transferred directly to the unit? of first rolling 90, for the continuation of the processing cycle according to the modalities? already? described.

The present invention? has been illustrated and described in some of its preferred embodiments, but it is understood that executive variations may be applied to them in practice, without however departing from the scope of protection of the present patent for industrial invention.

Claims (20)

CLAIMS 1. Method for producing homogeneous sheets of nicotine-free plant fibers characterized by the fact that: - the solid components of the raw material containing the nicotine-free vegetable fibers are chopped up to a particle size of about 20 - 320? m, preferably about 80-180? m, - mix the minced product cos? obtained with water, at least one binding agent and at least one material for forming an aerosol, until a slurry is obtained with a liquid content of about 30-50%, preferably about 35-40%, - said mixture is subjected to a first lamination in order to obtain a continuous strip with a thickness of about 1-20 mm, preferably about 1-10 mm, - said strip is subjected already? subjected to said first lamination to a series of further lamination steps, until obtaining a strip having a remarkably constant thickness of about 90 - 280? m, preferably of about 140-200? m, - said strip is dried until its liquid content to about 8-15%. 2. Method according to claim 1, characterized in that the dried continuous web is subjected to winding or transversal cutting or shredding into threads of predefined dimensions. 3. Method according to one or more? of the preceding claims, characterized in that the solid components of said raw material are crushed by grinding. 4. Method according to one or more? of the preceding claims, characterized in that the solid components of said raw material are crushed with a mill. 5. Method according to one or more? of the preceding claims, characterized in that the solid components of said raw material are crushed with a cryogenic pin mill (12). 6. Method according to one or more? of the preceding claims characterized in that powdered cellulose is also mixed with the other substances that form the mixture. 7. Method according to claim 6, characterized in that said slurry is formed with powdered cellulose having a particle size between 50 and 100 µm. 8. Method according to one or more? of the preceding claims characterized in that said mixture is formed with powdered cellulose in a percentage comprised between 2% and 10% of the weight of the raw material. 9. Method according to one or more? of the preceding claims characterized in that before forming said mixture with the comminuted components of said raw material, said comminuted components are mixed with powdered cellulose. 10. Method according to one or more? of the preceding claims characterized in that the mixture formed by comminuted product, possible powdered cellulose, water, at least one binding agent and at least one material is submitted to form an aerosol: - to a roughing step by passing through at least a pair of grooved cylinders (84) and / or - to a refining step by passing through at least a pair of refining cylinders (124,124?) until it reaches a particle size not exceeding 20? m. 11. Method according to one or more? of the preceding claims characterized in that said mixture is subjected to a step of homogenization and forming before subjecting it to said first rolling step. 12. Method according to claim 11 characterized by the fact that said mixture is subjected to a homogenization and shaping step for its transformation into a continuous strip, with a substantially constant width between 100 and 2000 mm and thickness between 1 and 10 mm , to then be subjected to said first lamination step. 13. Method according to claim 11 characterized in that said mixture is subjected to a homogenization and shaping step for its transformation into a sequence of portions (82) to be then subjected to said first rolling step. 14. Method according to one or more? of the preceding claims characterized in that said first rolling of the mixture is carried out with a unit? (90) comprising a lobe feeder (92) and at least one pair of lamination rolls (98). 15. Method according to one or more? of the preceding claims characterized in that at the outlet of said first lamination a single-layer strip with a thickness of about 1-10 mm is obtained. 16. Method according to one or more? of the preceding claims characterized in that, before subjecting said tape, already? subjected to said first lamination, to said series of further lamination steps, it is subjected to stratification until a multilayer tape with a thickness of about 2-20 mm is obtained. 17. Method according to claim 16 characterized in that, in said series of further rolling steps, the dough is left to rest between one rolling station and the next. 18. Method according to one or more? of the preceding claims characterized in that lamination is carried out with pairs of at least partially heated cylinders (108). 19. Method according to one or more? of the preceding claims characterized in that said laminated strip dries by passing through a recirculating air dryer (114). 20. Method according to one or more? of the preceding claims characterized in that vegetable fibers of at least one of the following vegetable substances are used: potato, hemp, tea, chamomile, mint, sage, rosemary and eucalyptus.