EP0546986A1 - Expanding and drying of tobacco - Google Patents

Abstract

A method and an apparatus are described for the expanding and drying of tobacco by means of steam and/or hot gas, according to which method the tobacco is metered into the inner compartment (4), defined at least from two flat jets (3, 3') which flow into the channel from the opposing sources outside the channel walls and are guided into each other at an acute angle, and the tobacco, after the acceleration of speed by means of the flat jets, is deflected by means of a cross-flow, accelerated again, expanded and dried. <??>The device preferably consists of a partially rectangular metering channel section (A-A), which, farther on, is arranged with a gas-permeable channel segment (5) for extracting part of the treatment medium in the channel, the latter, at least in its last section, terminating with a vertical channel (8) connected thereto at 90 DEG , which is surrounded by a wider pipe (9) called a "tower". <IMAGE>

Description

With effective drying and / or expansion, optimal heat transfer plays an important role for good heat utilization and effectiveness. For this purpose, the increased relative speed between the gas-containing treatment medium and the solid, the sudden pressure drop from a higher pressure range to a lower range in various ways have been proposed in general.

Several patents describe the use of the increased relative speed to improve the drying and / or expansion of wet tobacco. DE-PS 30 37 885, for example, proposes deflecting devices which are offset opposite one another in a pneumatic transport pipe, in order thereby to change the direction of movement and the relative speed of the tobacco rib parts with respect to the gaseous heating and transport medium several times. However, these deflection devices lead to deposits of tobacco components on the walls of the pneumatic tube.

According to DE-OS 36 19 816 it is proposed that the hot tobacco should be separated from the steam or gas by a separator consisting of a sieve which extends at an angle of 135 ° to 155 ° to the axis of the transport line at the downstream end thereof. An analogous proposal is described in DE-OS 36 19 015, with the difference that the tobacco drying device consists of two gas flow lines with two separators which are connected to one another and each porous separator arranged at an oblique angle to one another should separate the tobacco from the gas. With this system, the tobacco should be accelerated twice by the gaseous medium.

The tobacco flowing at an oblique angle at high speed in the ascending direction can precipitate on the surface of the gas-permeable separators arranged at an angle to the flow direction or block it.

Flow changes in a pneumatic hot steam tobacco transport channel system lead to undesirable deposits in moist tobacco, especially if the tobacco moisture content is above 35%. These deposits occur to the greatest extent where the flow change is greatest, for example in the bend of a pneumatic transport system. This is also the case with the method described in DE-OS 20 41 874. According to a later patent specification of the same method, the deposit should be reduced by cooling or condensation on the arch.

DE-PS 38 39 529 describes a method and device for the expansion of cut tobacco material, according to which a tobacco gas stream is encased by a separately supplied gas stream, thereby increasing the relative speed between the tobacco material and the gas stream several times. The additional gas flow is supplied through a plurality of slots which are formed at an acute angle as an opening in the channel jacket in the direction of flow.

The further treatment of the tobacco after it exits the treatment channel is only shown schematically, without describing or claiming the type of treatment or drying. No redirection of the flow direction is reported.

According to DE-PS 33 15 274, a tobacco gas mixture flows from a horizontal transport channel through a narrow nozzle at very high speed into a dryer tube provided with bends. In order to be able to transport the tobacco further, the flow rate of the hot gas in the drying tube must be somewhat higher than that of the tobacco gas mixture emerging from the nozzle. This requires an uneconomically high amount of hot gas and involves intensive mixing or dilution of the tobacco with the gas.

When tobacco suddenly enters the nozzle. Hot air environment can cause the heat transfer due to turbulence to expand the tobacco, mainly in the more expandable tobacco fins. For a more significant expansion of tobacco lamina, however, the conditions described in the above patents are not sufficient to produce the desired expansion effect.

The publication DE-OS 26 37 124 describes the use of a venturi nozzle or a reduction in the cross-section of the tobacco transport channel in order to increase the relative speed between the hot gas-containing medium and the tobacco and thus the expansion effect. The expansion effect can of course be further improved by narrowing the cross section of the tobacco transport channel or by using a venturi nozzle for tobacco with a higher moisture content. The patent EP 074 059 is practically based on the same principle. Here it is additionally claimed that the tobacco material should be metered and conveyed in the "base point" of a free jet or nozzle. This could include this ensures that the tobacco dosage is directed directly at the opening of the nozzle, as can be seen from FIGS. 3, 4, 5. The supply of the tobacco or its transport in the "base point" of a nozzle is practically not feasible, since the jet flowing out of the nozzle has such a high speed that it cannot take in the tobacco at this point. It is only after the jet has spread and fills the transport channel that there is a possibility that the tobacco will be embedded in the jet and transported with it. At this point, however, the cross-section of the beam reduces its speed and temperature. In this sense, an optimal use of the heat transfer, which is necessary for a good expansion effect for cut leaf tobacco, is reduced.

According to DE-PS 31 47 846, which is equivalent to this patent, the tobacco should be accelerated in the expansion zone and then transported by an approximately constant speed in a divergent flow under pressure increase be delayed. This embodiment can be ensured by temporarily narrowing the channel cross section, as shown in FIG. 1. Speed acceleration and reduction of a tobacco-steam mixture is described in the previously cited DE-OS 26 37 124 by using a venturi nozzle and in the "PB dispersion dryer" cited in DE-PS 22 53 882, but these statements can be made by the limited possibility of tapering the channel cross-section and mechanical abrasion of the tobacco through the canal wall cannot be regarded as optimal.

It has been shown that the improvement in the tobacco feed metering and the special flow velocity conditions of the tobacco gas stream, the special type of deflection by cross flow, result in an additional improvement in effectiveness.

The aim of the invention is to improve the effect of drying and expansion and to carry this out without the use of gases or liquefied gases at overpressure only by using water vapor and / or air in a simple device in the atmospheric range.

The invention is defined in the main claim and in the associated subclaims. The invention can be further described as follows.

According to the proposed method, the tobacco is supplied from a metering device into a channel of the same diameter after loosening or separating the tobacco fibers, which can be done by using known vibrators and / or needle rollers. This is special In the case of cut leaf tobacco so-called "lamina" is an advantage. If you want to put the tobacco in a steam jet and this jet emerges from a can at high speed, the difficulty can arise that the tobacco penetrates into the barge unevenly or not at all despite the suction effect of the jet.

The supply of the tobacco directly to the nozzle opening or at the "base" of the nozzle cannot be managed because the very high exit velocity of the steam and / or hot gas jet can lead to turbulence or scattering of the results due to the tobacco directed thereon . The tobacco does not reach the base of the nozzle.

According to the invention, it has been shown that an optimal and gentle treatment of the tobacco is made possible if it is in the interior of two laterally widespread surfaces of the flat jets consisting of steam and / or hot gas that flow in from two opposite openings to the channel axis from 5 ° to 60 ° is metered, which intersect in the direction of flow, transported with it at high speed and this is increased again at least by changing the flow direction once by transverse flow by means of a separate gas stream.

The flow velocity of the flat jets enclosing the tobacco from two sides, which preferably flow into the channel from outside each in front of the flat sides of a rectangular channel wall, flows into the channel at the tobacco receiving point of the jets up to their intersection between 300 m / sec. and 100m / sec. is. In this case, the tobacco from the vapor / gas jet surface carrying it does not come into contact with the channel wall mixed into the beam, but at the meeting point of the two beams. This reduces the mechanical abrasion or damage to the tobacco particles and exposes the tobacco to an additional acceleration.

In a preferred embodiment of the method mentioned, the tobacco metering can take place in a vertical channel. The tobacco is preferably metered from the upper opening of a vertical rectangular channel, which falls and is accelerated onto the laterally widespread surfaces of vapor-containing carpets flowing in from the opposite openings, preferably from a flat nozzle. Furthermore, the tobacco is additionally accelerated at the intersection of the two flat jets, after which its flow rate is slowed down by withdrawing part of the transporting steam. This takes place on a section of the transport channel which is designed as a gas-permeable Se segment and can flow out through part of the steam. The steam can be removed through the jacket surrounding the segment or preferably returned to the system after overheating.

The reduction in the flow rate due to steam extraction can then additionally be effected by widening the channel cross section. The tobacco-steam and / or hot gas mixture emerges from the vertical channel at a speed of 3 m / sec. up to 10m / sec. and is in a horizontal channel by means of separate hot gas-containing stream at a speed of 11 m / sec. up to 60 m / sec. deflected by cross flow. This can either be from the horizontal channel by redirection by means of a separate gas flow at a higher speed than that used in the horizontal channel into a vertical one Channel deflected and thereby accelerated again. The tobacco can also be transported through an arch in an extended vertical channel without cross flow. The vertical channel can be covered by a tube with an enlarged cross-section. After exiting the canal, the tobacco is deflected into the tube encasing it by the air resistance and leaves it downward after expansion and drying by gravitation. Another possible embodiment is that the tobacco is dosed through a vertical channel into a horizontal one. In this case, the two flat jets must flow out of openings which are arranged from the opposite side but are offset from one another. The different distance of the two flat jets from the respective nozzle openings to their intersection would cause the two jets to have an uneven speed. To avoid this, the diameter of the individual nozzle openings and the vapor pressures in front of the nozzles would have to be adapted to these requirements.

The use of two flat jets, which surround the tobacco from two opposite sides and mix with it at their cross point, also has the advantage over the use of round jets that the flat jets spread mainly laterally during their flow and not in their overall cross-section , causing their speed to decrease less with distance from the nozzle opening. Due to the high flow velocity in the duct system, the tobacco metered in is deflected from the nozzle opening and falls on the widespread surface of the jet. It is advantageous to have only one flat jet with wider nozzle openings to use, and the position of this outside the channel wall. So the tobacco falls with greater certainty on the surface of the laterally spread steam jets.

In order to further improve the expansion effect, which already arises in the described manner of metering the tobacco from at least one jet consisting of steam and / or hot gas, the deflection of the tobacco-steam mixture by transverse flow is proposed according to the invention.

It has been found that if a jet directed at a tobacco and steam and / or hot gas is penetrated by a cross-directional flow and the jet containing tobacco is deflected, the heat transfer from gas to tobacco and thus the drying and expansion effect are significantly improved . In this case, several components of the effect are likely to lead to the improved effect. The cross flow is dammed up in front of the jet containing solids and therefore a pressure gradient is dammed up in its direction of propagation. It can be assumed that the surprisingly high effect achieved in the practical tests according to the invention can be achieved by the interaction of the two components: pressure build-up or drop in crossflow together with the difference in transport speed between gas and tobacco.

Due to the manner of the deflection according to the invention by transverse flow of the tobacco transport medium, together with the increase in flow speed according to the invention in the tobacco supply and in the deceleration before the deflection, the expansion and Drying effect can be significantly improved. According to the invention, the diversion can take place from horizontal to vertical or from vertical to horizontal direction. A triple redirection can also be used. For example, if the tobacco transport medium mixture is directed from vertical to horizontal and from this to the vertical direction.

When the gas-solid mixture flowing out of a horizontal channel is deflected upwards by a jet, the jet must overcome the resistance caused by the weight of the solid (gravitation), as a result of which it flows before the horizontal jet flows through it the connection space between the horizontal and vertical channels is subjected to a congestion effect and then to a greater pressure drop. The relaxation time, i.e. the time it takes for the particles to adjust to the new flow direction is also greater in this case, which additionally improves the effect of the heat transfer.

The use of a gas-permeable segment in the horizontal channel enables a part to be removed from the transport medium, which can be returned to the system, and at the same time reduces the flow velocity of the jet. This not only prevents an adverse impact of the solid on the wall of the vertical channel, it also achieves an economic advantage. The amount of gas and / or steam required for the additional acceleration can namely be reduced and the diameter of the horizontal and vertical channels can be kept approximately the same.

The section length and the porosity of this section segment is selected such that, for a given tobacco gas flow rate, there is no lateral deviation of the flow bundle and, accordingly, no deposit or blockage on the porous surfaces of the segment.

In the original tobacco-transporting steam and / or hot gas stream, the tobacco steam weight ratio is between 1: 0.7 and 1: 4. The weight ratio between the first tobacco-transporting treatment medium and the deflecting treatment medium in the deflection zone is between 1: 1 and 1: 2.

In the last phase, the tobacco preferably arrives after the corresponding deflection from the channel into a pipe or a "tower" with a larger diameter than that of the channel. To further reduce the flow velocity in the second channel, the cross section at the outlet end of the channel can be expanded. The free space above the centrally arranged second channel is dimensioned such that the tobacco escaping from this into the wider pipe is slowed down by the air resistance and its direction of flow changes. The tobacco will fall in free fall between the outer channel wall and the inner so-called "tower" wall after changing its flow direction at 180 ° onto a conveyor belt and transported away with the desired degree of dryness.

The tobacco falling down in the tube between the outer wall of the relatively short vertical channel and the inner wall of the tube with the tube encasing it can slowly flow in from the bottom upwards additional dry gas, preferably hot gas, can be exposed to an extended residence time.

The inflow rate of a separate gas, which slowly flows upwards from the bottom of the tower in counterflow to the falling tobacco, should be the rate of 1 m / sec. if possible, do not exceed.

This counterflow should be set in such a way that there is no material build-up and the tobacco can leave the drying tower by gravitation.

Due to the repeated increase in relative speed and the change in flow direction, the heat transfer and the use of energy are significantly improved, as a result of which extremely economical drying, expansion or removal of the undesired volatile substances can be achieved.

In the event of a more intensive drying requirement, two treatment units, in particular two so-called tower systems, in which the drying is mainly carried out, can be connected in succession.

The device consists of a tobacco feed channel, from which the tobacco is metered and loosened through a lock (1) and preferably subsequently through a needle roller in a vertical, rectangular transport channel segment. Outside the opposite flat channel walls (A - A), a wide flat nozzle (2,2 ') is arranged at the top, directly after the metering device, from which two flat, carpet-like, laterally widespread flat jets consisting of steam and / or hot gas (3, 3 ') flow downwards and intersect at an acute angle in the tobacco flow direction. The tobacco falls into the interior (4), which is formed by at least two flat streams (3, 3 ') consisting of steam or hot gas, onto the laterally expanded flat jets which accelerate and transport them. To reduce the speed of the tobacco and the steam and / or hot gas, a gas-permeable segment (5) can be provided in the further course, preferably in the round duct (B - B), through which a part of the steam in a double jacket (6) escapes and are returned to the system. (Not shown in the drawing.)

The canal can be extended by an arch in the horizontal direction (7). A better or more effective solution is if the channel opens directly into a horizontal pipe (see FIG. 2) and the tobacco is exposed to separate hot gas for deflection by cross flow. The horizontal channel can also be provided with a gas-permeable segment (5), analogously to that described above. After reducing the flow velocity, the tobacco can be redirected again into a vertical channel (8) and in a wider pipe (8) surrounding it, so-called "tower", change its direction of flow due to the air resistance or due to gravity downwards. The upward steaming hot gas is separated from the tobacco falling by gravity through the sieve (10 ') by means of suction fans (11) and leaves the space between the vertical channel outer wall (8) and the expanded pipe (9) or "Tower" down through the opening (12).

example 1

Sliced Burley tobacco with a moisture content of 27% is dosed into the vertical, rectangular channel (AA) after loosening with a needle roller through a lock (1). Directly below the lock, two flat jet nozzles (2) are arranged outside the channel walls in the opposite position, from each of which a flat jet (3,3 ') consisting of steam - 220 ° C - 250 ° C - flows into the channel downwards in a carpet-like manner and intersect at an acute angle. The tobacco falls on the laterally widespread surfaces in the interior (4) of the two jets and is carried along by them at great speed, transported and accelerated. In addition, the channel can also have a round shape (BB). The channel can be provided with a gas-permeable segment (5), from which steam-containing medium flows into the jacket surrounding it (6). The steam can be returned to the system through a heat exchanger after heating. The tobacco and the steam pass through the horizontal channel (7), which is extended by means of an arc, into a vertical channel (8) connected to it, which is covered with a wider tube (9), the so-called "tower". The tobacco is redirected in the vertical channel from a separate hot gas source by a gas stream at a temperature of 140 ° C - 180 ° C. After exiting the channel, this is moved downward by the air resistance between the channel end and the cover sieve (10 ') of the pipe, or "tower" between the outer channel wall and the expanded pipe, or "tower", so that the tobacco dried through the outlet opening (12) of the tube and this expands at the bottom leaves. The temperature and flow rate of the gas flowing up the channel is regulated so that the tobacco leaves the tube enveloping the channel with a moisture content of 11.5%.

The untreated tobacco and the expanded tobacco are adjusted to 12% moisture after conditioning.

The filling capacity of the tobacco was measured in a Brogwaldt densimeter (20 g tobacco was loaded in a cylinder with 6 cm O with a weight of 3 kg for 30 seconds and the height of the tobacco column was measured after the pressure was released.

Example 2

Virginia cut tobacco was treated as in Example 1.

Claims (12)

Process for expanding and drying tobacco by means of steam and / or hot gas, characterized in that the tobacco is metered into the interior (4), which is formed by at least two flat jets (3, 3 ') consisting of steam and / or hot gas, these flat jets are directed into one another at an acute angle and the expanded tobacco is then fed to the fixation and drying. A method according to claim 1, characterized in that the flow velocity of the tobacco is accelerated by the flat jets and by deflection by means of transverse flow and is reduced at least by steam extraction through the transport channel. Method according to claims 1-2, characterized in that the flat jets from the outside of the opposite channel walls each have a flat nozzle flowing into the channel axis with an angle of 5-60 ° directed flat nozzles. Method according to claims 1 to 3, characterized in that the tobacco is fed into the interior or flat rays enclosing it in a trapezoidal manner on the laterally enlarged surface thereof, and the tobacco and the medium containing steam and / or hot gas are transported in an at least partially rectangular channel. Method according to claims 1-4, characterized in that the steam is removed through the gas-permeable segment of the channel. Method according to claims 1-5, characterized in that the cross-flow of the tobacco in a channel system takes place by diverting the flow direction from vertical to horizontal and from there into the vertical channel connected to it by a separate hot gas-containing medium. Method according to one or more of the above claims, characterized in that the flow velocity of the flat jets which flow into the channel from the opposite sides thereof when in contact with the tobacco between 100 m / sec. and 300 m / sec. and when they start to change flow direction by cross flow into the second channel connected to the first channel at a 90 ° angle between 3 m / sec. up to 10 m / sec. is. Method according to one or more of the above claims, characterized in that the flow rate of the tobacco-containing steam and / or hot gas stream after the deflection by means of a separate gas-containing current in the second channel between 10 m / sec. and 50 m / sec. lies. Method according to one or more of the above claims, characterized in that the tobacco-steam and / or gas mixture is subjected to several deflections, the last change in flow direction from a channel in a vertical channel connected to it at a 90 ° angle by separate gas flow takes place by the channel opening into a tube with an enlarged diameter and the tobacco emerging from the channel between the channel and the tube surrounding it emerges from the bottom through gravity. Method according to one or more of the above claims, characterized in that the transport medium consisting of steam and / or hot gas has a temperature between 180 ° and 300 ° C after the absorption of the tobacco. Method according to one or more of the above claims, characterized in that the shredded tobacco consists of cut, shredded tobacco ribs and / or lamina or tobacco foil. Device for carrying out the method according to claims 1-10, characterized in that it consists of at least one tobacco metering lock (l), a vertical rectangular expansion channel part (AA) connected thereto, in which flat nozzles (2,2 ') a carpet-like, steam-containing jet (3.3') flows in and the two are at an acute angle intersecting rays take up the tobacco in their interior (4), the transport channel continues from vertical to horizontal direction (7), in which the vertical and / or horizontal channel is provided with a gas-permeable segment (5), the horizontal channel (7) in one separate vertical channel (8) opens, which is surrounded by a wider tube (9), from which the tobacco in expanded and dried state downwards (12), the medium containing steam and / or hot gas through a sieve (10) exits with suction (11).

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