Rotary conditioning drum, particularly for drying tobacco

Abstract: The present invention relates to a rotary conditioning drum (1) particularly usable for drying tobacco. The drum (1), which comprises heating means such as a gas or oil burner or steam heating means, has, in the latter case, longitudinal heating units which are constituted by bundles of tubes which are connected to a delivery manifold for injecting steam, and has the peculiarity of comprising at least one conveyor element (11), such as a conveyor belt (11), which is movable axially to the drum (1). The conveyor belt (11) is controlled, in its motion, by an external humidity measurement unit (13,14) and by means for controlling the thermal capacity of the drum (1). The drum (1) finally comprises, in the case of steam heating means, means for collecting and recovering the condensate at the tobacco feed side (9). The presence of the movable conveyor belt (11) allows, if the humidity of the tobacco in output deviates from the desired value, to axially move the belt (11) inside the drum (1) to the point at which the tobacco is at the required humidity. It is thus possible to obtain, in an extremely effective manner, a variation in the "useful" length of the drum (1) with a consequent extremely rapid and precise response during transient periods.

Description: The present invention relates to a rotary conditioning drum, particularly for drying tobacco, according to the preamble of claim 1 (prior art: US-A-3 787 985). One of the most interesting and at the same time critical problems in the field of the tobacco manufacturing industry is currently the drying of shag. The term "shag" defines a blend of various expensive qualities of tobacco, processed appropriately and cut to a specific size. Production facilities are currently known which comprise a drying line the performance whereof, in terms of uniformity and constancy of the degree of humidity reached by the shag, are essential for the optimum outcome of the final product, which is constituted by cigarettes. In order to clarify the disadvantages which can be observed in known facilities, the fact is stressed that in the tobacco industry, the shag, before it can be used to fill the cigarette, must undergo numerous extremely complicated and delicate treatments; in each of said treatment steps, one of the most important parameters to be kept under control is the relative humidity content of the tobacco. Said relative humidity must in fact assume very precise and clearly defined values in every point of the treatment line. Specifically, the humidity must be controlled in an extremely precise manner in two critical points, i.e. prior to shredding and prior to transporting the tobacco to the packaging machines for the final manufacture of the cigarette. In the first case, prior to shredding, the tobacco must have a relative humidity content of approximately 22%; in the second case, prior to transportation, the relative humidity must be approximately 13%. In the latter case, the proposed value must be reached with great precision, since maximum tolerances in the range of 0.1% are required, as packaging machines, which can have a production rate of up to 9,000 (nine thousand) cigarettes per minute, require an extremely stable and uniform product. Otherwise, an excessively humid product would tend to clog the machines, whereas an excessively dry product would tend to crumble, with consequent high waste and a hardly negligible economic damage. In known types of drying facility the humidity of the shag passes from 22% to 13% by means of a drying line which is constituted by a feeder with a gravity tube, a continuous belt weighing machine, a vibrating loading conveyor, a drying drum, a vibrating unloading conveyor, an infrared-ray humidity detector arranged at the inlet of the drum, an infrared-ray humidity detector arranged at the outlet of the drum, and a computerized control system. Specifically, known drying drums are of the rotary type, are inclined by a certain number of degrees toward the outlet and have a variable rotation rate. The rotary drum, which is usually made of stainless steel, is internally provided, in the case of steam heating, with longitudinal heating units which are constituted by bundles of tubes which are connected to a delivery manifold for injecting the steam and to an outlet manifold for discharging the condensate, whereas the inflow of the steam is obtained by means of a special rotating coupling. A hot-air circuit is also provided; according to the type of production, said circuit can be in countercurrent or in current. In said known rotary drying drums it is possible for example to have such a capacity as to be able to dry up to approximately 5,000 (five thousand) Kg/h of shag and therefore simultaneously feed approximately 10-12 high-speed packaging machines, assuming a tobacco content of approximately 0.75-0.8 grams per cigarette. Drums are known which have, for such a capacity, a diameter of approximately 2 meters and a length of approximately 12 meters; this entails, assuming a speed of approximately 1.3 m/min for the product, an internal product passage time of approximately 9 minutes, with an amount equal to approximately 750 kilograms of product stably present inside the drum. In these known types of drum it is thus observed that, upon starting, approximately 9 minutes elapse before the tobacco starts to exit from said drum, and approximately 2 more minutes elapse so that the product may reach a certain uniformity and stability with the consequent possibility of measuring the output humidity. The main disadvantage which is observed in said known types of device therefore consists of the fact that an actual correction can occur only approximately 11 minutes after the starting of the drum. As a partial solution to this disadvantage, it is known to perform an electronic control, which in any case allows, at the most, to stabilize the humidity of the tobacco at the required and preset values only in the second half of the drying drum. These disadvantages produce a considerable amount of inappropriately dried tobacco which constitutes an initial waste which is only partially recoverable: for the above described type of drum, this can be equivalent to the failure to produce approximately half a million cigarettes, with a considerable economic burden. As a partial solution to this disadvantage, it is known not only to redry part of the shag but also to mix it with other tobaccoes: this mixing, however, must occur in large silos in order to achieve uniformity of the humidity content, and at least three silos are required for every drying drum, with consequent cost problems. The current known technology, therefore, does not allow high efficiency in production. As a partial solution, it is known to use a statistical simulation program for controlling the drying line; said program, by interpolating some process data such as the instantaneous mass flow-rate of the tobacco, the relative humidity at the inlet and at the outlet of the drum and the drying temperature, estimates whether the humidity of the tobacco at the outlet of the drum will stabilize within the given tolerance values. The program is therefore such that if the humidity at the outlet is beyond the tolerance range, the actual thermal efficiency of the drum is varied by interacting on a modulating valve in order to increase or decrease the pressure of the steam at the inlet of the drum or by adjusting the valves of the burners in the case of gas or fuel-oil heating. The observable results, however, are generally not acceptable during operation in transient conditions, i.e. for example when the mixture of tobacco to be dried is changed or when the line is emptied completely. The reason which makes this operation unacceptable is the heat inertia of the drum; although the computerized system tries to predict in advance the responses of the machine, a certain time is required in order to adapt to a new condition. The aim of the present invention is therefore to eliminate the disadvantages described above in known types of conditioning drums by providing a drum which allows to lower the relative humidity of the shag to preset values with an optimum maximum tolerance, considerably containing the waste constituted by the excessively dry or excessively moist product. Within the scope of the above aim, an important object of the invention is to provide a drum which allows to have, in output, shag with preset humidity values even during operation in transient conditions, as when the mixture of tobacco to be dried is changed or when the line is emptied completely. Another object of the invention is to provide a drum which associates with the preceding characteristics that of being structurally simple, manufacturable with conventional facilities and known machines, as well as reliable and safe in use. This aim, the objects mentioned and others which will become apparent hereinafter are achieved by a rotary conditioning drum, particularly for drying tobacco, which comprises heating means such as a gas or oil burner or steam heating means, said means comprising, in the latter case, longitudinal heating units constituted by bundles of tubes which are connected to a delivery manifold for injecting steam, characterized in that it comprises at least one conveyor element movable axially with respect to and slidably movable inside said drum and is capable of being actuated by an external humidity measurement unit and by means for controlling the thermal capacity of said drum, said drum comprising, in the case of steam heating, means for collecting and recovering the condensate, said collecting means being arranged at the tobacco feed side. Advantageously, said conveyor element is constituted by a conveyor belt. Further characteristics and advantages of the invention will become apparent from the detailed description of a particular but not exclusive embodiment, illustrated only by way of non-limitative example in the accompanying drawings, wherein: figure 1 is a view of the rotary conditioning drum according to the invention, together with the tobacco feed means; figure 2 illustrates some of the possible arrangements of the conveyor element inside the drum. With reference to the above figures, the reference numeral 1 indicates the rotary conditioning drum, which constitutes a component of a drying line constituted by a silo 2 for storing shag, fed at an adjacent loader 3. An appropriate hopper metering unit 4, unloads said shag from the loader 3 at a belt weighing machine 5. Said weighing machine then deposits the shag at a first vibrating conveyor 6, which unloads the shag inside the rotary conditioning drum 1, wherefrom the dried product is discharged at a second vibrating conveyor 7. The rotary conditioning drum 1 is inclined, with respect to the resting plane 8, so that the feed end 9 is arranged at a greater distance from said resting plane with respect to the distance of the end 10 for unloading the dried shag. The rotary conditioning drum 1 comprises at least one conveyor element 11 which is arranged at the axis of the drum and can slide axially inside said drum. Advantageously, the conveyor belt 11 is mounted on rails or guides 12 and is moved by motor means such as a direct-current motor which allows axial movement of the conveyor element 11 inside the drum 1, to the point at which the shag is at the required degree of humidity. Said degree of humidity is detected by means of a first measurement unit 13, arranged at the belt weighing machine 5, and by a second measurement unit 14, arranged at the end of the second vibrating conveyor 7 opposite to the unloading end 9 of the rotary conditioning drum 1. Said second measurement unit 14, together with means for controlling the drum thermal capacity which are appropriately controlled by an electronic program, allows to control the humidity of the shag, actuating, if said humidity deviates from the desired value, the movement of the conveyor belt 11 inside the drum 1 up to the point at which the shad has the required humidity. This check is very rapid, and adjustment means are provided for controlling the speed of said conveyor belt 11. It is thus possible to consequently have an extremely rapid and precise response even during transient steps for which it is possible to hypothesize, for the conveyor belt 11, an initial position which is fully inside the drum and subsequently its extraction as time elapses until the process stabilizes at canonical values. The drum furthermore has, in the case of steam heating, means for collecting and recovering the condensate. The recovery means are constituted by tubes coiled in a helix inside the drum. The means for collecting the condensate are arranged outside the drum at the feed end 9. This last requirement arises from the fact that in order to insert the conveyor belt 11 inside the drum it is convenient to free from any possible obstacle the unloading end 10 of said drum. It has thus been observed that the invention has achieved the intended aim and objects, a rotary conditioning drum having been obtained which allows to lower the relative humidity of the shag to preset values and with an excellent maximum tolerance even during operation in transient conditions, considerably containing the waste constituted by excessively dry or excessively humid product. The mobility of the conveyor belt 11 inside the drum in fact allows to extract the shag if it has the required degree of humidity in a very rapid manner and with considerable ease in execution. Therefore, instead of varying the thermal capacity of the drum according to the described prior art, the presence of the second measurement unit 14 and of the means for controlling the thermal capacity of the drum allow to activate the movement of the conveyor belt, and said control can be handled by an electronic program which is per se extremely simplified, since it must handle and control a very small number of parameters with respect to what occurred in the prior art. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: Rotary conditioning drum, particularly for drying tobacco, comprising conveyor elements, humidity measurement unit, means for controlling the thermal capacity and heating means such as a gas or oil burner or steam heating means which comprise, in the latter case, longitudinal heating units which are constituted by bundles of tubes which are connected to a delivery manifold for steam injection, characterized in that it comprises at least one conveyor element which is axially movable with respect to and slidably movable inside said drum and is capable of being actuated by the external humidity measurement unit and by the means for controlling the thermal capacity of said drum, said drum comprising, in the case of steam heating, means for collecting and recovering the condensate, said collecting means being arranged at the tobacco feed side. Drum according to claim 1, characterized in that said at least one conveyor element is preferably constituted by a belt which is arranged at the longitudinal median axis of said drum and is movable axially thereto by being mounted on adapted rails or guides and being moved by virtue of an adapted means such as a motor. Drum according to claims 1 and 2, characterized in that said at least one conveyor element is totally or partially insertable within said drum according to presettable movement extents. Drum according to claims 1 and 3, which is interposed between a first vibrating conveyor and a second vibrating conveyor for feeding and unloading the shag, said first conveyor being arranged after a belt weighing machine at which a first tobacco humidity measurement unit is arranged, characterized in that said second conveyor has one end adjacent to the end for unloading the dried tobacco from said drum and has, proximate to the other end, a second humidity measurement unit. Drum according to claims 1 and 4, characterized in that said second humidity measurement unit actuates, together with adapted means for controlling the thermal capacity of said drum which are appropriately handled in combination by a centralized logic unit which actuates said rails, the movement of said at least one conveyor element inside or outside said drum. Drum according to claims 1 and 5, characterized in that it internally comprises, in the case of steam heating means, condensate recovery means which are constituted by a plurality of tubes which are coiled in a helix and are connected to said condensate collection means. Drum according to claims 1 and 6, characterized in that said condensate collection means, in the case of steam heating means, are arranged at the end of said drum from which the shag to be dried is fed.

Inventors: FREGONESE GIORGIO, GASPARINI FABRIZIO, MANTOVANI GIOVANNI, ULBRICH JOACHIM, FREGONESE, GIORGIO, GASPARINI, FABRIZIO, MANTOVANI, GIOVANNI, ULBRICH, JOACHIM
Applicants: GARBUIO SPA, GARBUIO S.P.A.
Application year: 1990
Main classification: A24B3
IPC codes: F26B11, A24B3, F26B25