US 3402479 A
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Sept, 24, 1968 R. HOHM ET AL METHOD AND APPARATUS FOR TREATING TOBACCO v Filed Nov. 17, 1966 t/fluan/ary alum! mi alfll um (ki n/v .1 icidwj United States Patent 3,402,479 METHOD AND APPARATUS FOR TREATING T OBACCO Reinhard Hohm, Hamburg-Bahrenfeld, Guenther Kuehn,
Hamburg-Bramfeld, and Waldemar Wochnowski, Hamburg, Germany, assignors to Hauni-Werke Kiirber & Co., K.G., Hamburg-Bergedorf, Germany Filed Nov. 17, 1966, Ser. No. 595,171 Claims priority, application Luxembourg, Nov. 17, 1965,
9 Claims. (or. 34-66) The present invention relates to a method and apparatus for treating tobacco, particularly for processing diped Burley tobacco having a high moisture content. Still more particularly, the invention relates to improvements in a method and apparatus for expelling nitrogen from and for toasting moist Burley and similar brands of tobacco.
Tobaccos having a high nitrogen content are practically useless for immediate consumption. Therefore, Burley and similar nitrogen-rich tobaccos must be heated to elevated temperature in order to expel nitrogen from the tobacco leaves. However, such heating is complicated by the fact that tobacco and similar hygroscopic substances cannot be heated satisfactorily in the course of actual drying, i.e., when the heating action should bring about expulsion of moisture. Thus, and when a mass of moist tobacco is subjected to elevated temperateures, it as surnes a temperature which is a function of its moisture content and of the temperature of heating medium. The temperature of tobacco will approach the temperature of heating medium with progressing expulsion of moisture.
Heretofore known methods of driving nitrogen out of moist, dipped, Burley and similar brands of nitrogenrich tobacco normally comprise subjecting tobacco having a moisture content of 40-50 percent to the action of dry atmospheric air to reduce the moisture content well below the desired moisture content of l6-l8 percent, normally down to about 3-5 percent. Once the moisture content is reduced to 35 percent, the tobacco can be more readily heated to a temperature in the range of 90110 0., depending on the nitrogen content, whereby the nitrogen leaves the tobacco.
However, and in order to prevent excessive breakage of tobacco during further processing, the thus overdried tobacco (having a moisture content of 3-5 percent) must be subjected to an ordering or wetting treatment with resulting increase in moisture content to between 16-18 percent. Ordering equipment is expensive and the consumption of heat energy during overdrying is very high. Also, overdrying affects the quality of tobacco.
Attempts to bring about expulsion of nitrogen without overdrying of tobacco by resorting to electric highfrequency heating have met with limited success, mainly because such heating is very expensive. Moreover, when subjected to intensive heating, moist tobacco develops internal heat. Also, it is very difficult to withdraw the evaporated moisture from tobacco in presently known treating apparatus.
Accordingly, it is an important object of the present invention to provide a novel and improved method of expelling nitrogen and surplus moisture from Burley and similar tobacco brands in an economic operation and without overdrying.
Another object of the invention is to provide a method of expelling nitrogen from dipped tobacco without reducing the moisture content below a predetermined optimum value.
A further object of the invention is to provide a method of expelling nitrogen from and of simultaneously toasting Burley tobacco in such a way that no ordering is required upon completed expulsion of nitrogen.
An additional object of the invention is to provide an apparatus which can be utilized in carrying out the above outlined method.
A concomitant object of the invention is to provide an apparatus wherein Burley tobacco can be relieved of nitrogen at elevated temperatures while its moisture content decreases but invariably remain above a predetermined minimum value so that the ordering equipment can be dispensed with.
Another object of the invention is to provide a novel method of circulating conditioned air through and along a mass of dipped moist nitrogen-rich tobacco.
Our present invention is based on the discovery that the expulsion of nitrogen can be carried out with greatly reduced consumption of heat energy and without overdrying if the tobacco is caused to exchange heat with a current of air which is in hygroscopic equilibrium with tobacco. In other words, such heating need not result in expulsion of moisture from tobacco. One feature of our invention resides in the provision of a method of treating moist, dipped, nitrogen-rich tobacco by contact with conditioned air. The two essential steps of such method include contacting a mass of tobacco with hot air having a moisture content high enough to establish a hygroscopic equilibrium between air and tobacco, and maintaining the air at a temperature at which the air and tobacco exchange suflicient heat to raise the temperature of tobacco to a value at which the tobacco is relieved of nitrogen and is preferably toasted to retain the substances applied thereto during dipping.
In accordance with a second feature of our invention, the tobacco may be treated by contact with one or more currents of air which expel therefrom surplus moisture whereby such treatment with currents of air precedes and/or follows heating to a temperature which is high enough to expel nitrogen.
The novel features which are considered as characteristic of the invention are set forth in particular in the appneded claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of a specific embodiment with reference to the accompanying drawings, in which:
FIG. 1 is a longitudinal section through the housing of an apparatus for conditioning Burley tobacco which embodies one from of the present invention and comprises a single heating chamber and three drying chambers;
FIG. 2 is a transverse vertical section through the apparatus, substantially as seen in the direction of arrows from the line IIII of FIG. 1;
FIG. 3 is a diagram wherein the curve indicates changes in temperature of tobacco travelling through the apparatus of FIGS. 1 and 2;
FIG. 4 is a diagram showing the variations in temperature, heat consumption and moisture content of tobacco in the apparatus of FIGS. 1 and 2; and
FIG. 5 is a similar diagram showing variations in temperature, heat consumption and moisture content of tobacco in a conventional apparatus.
Referring to FIGS. 1 and 2 in detail, the apparatus comprises a composite housing 50 having five identically dimensioned chambers including a series of three successive drying chambers 86, 88, 90, a heating chamber 92, and a cooling chamber 94. The heating chamber 92 is located upstream of the cooling chamber 94 but downstream of the last drying chamber 90, as considered in the direction of tobacco travel through the housing 50.
The apparatus further comprises a transporting c0n veyor 96 which serves to advance a stream of nitrogenrich, dipped Burley tobacco T having a high moisture content (e.g., between 40 and 50 percent) through the chambers 8694 of the housing 50 whereby successive increments of such tobacco travel from the discharge end of a feed conveyor 98 toward the receiving end of a takeotf conveyor 100. The transporting conveyor 96 comprises an endless perforated or foraminous belt 14 which is trained around rollers 16 and 18. The roller 18 is driven by a suitable variable-speed motor or variable-speed transmission, not shown. The direction of travel of the upper stringer 22 of the belt 14 is indicated in FIG. 1 by arrow 20. This upper stringer is supported from below by a series of supporting rolls 24 so that the stream of tobacco T travels in a preferably horizontal path and is conveyed through the chamber 86, 88, 90, 92, 94 in the just outlined sequence. These chambers are separated from each other by transverse partitions 30, 32, 34, 36 so that each chamber preferably encloses an identical space. The width of the belt 14 is less than the Width of the housing 50 (see FIG. 2) and this housing accommodates a longitudinally extending partition 54 which defines with two perforated walls 38, 40 and elongated duct 52 adjacent to one side wall of the housing 50. The remainder of the housing (at the opposite side of the longitudinally extending partition 54) defines an elongated compartment 53 which also extends above the top wall 38 and below the bottom wall 40 and serves to accommodate various conditioning instrumentalities which will be described hereinafter.
Each of the five chambers 8694 is provided with an inlet 41 connected with a supply conduit 66 for fresh air. Each of these supply conduits may be provided with a suitable valve, not shown. A suction fan 42 serves to draw air through the inlet 41 of the cooling chamber 94 so that such air cools tobacco which has been heated to elevated temperature during travel through the preceding chambers, particularly during travel through the drying chamber 92. The cooling chamber 94 (and more particularly that portion of the compartment 53 which is adjacent to the cooling chamber) need not be provide with a heater.
Though FIG. 2 shows that the housing 50 is of rectangular cross-sectional outline, such outline has been selected for the purposes of illustration because otherwise shaped housings can be used just as well. The numeral 56 denotes in FIG. 2 perforations provided in the belt 22 to enable currents of air to come in intimate contact with tobacco T on the upper stringer 22. The direction in which air currents are circulated through the bottom and top walls 40, 38 and perforations 56 of the belt 14 are indicated by arrow 82.
The compartment 53 accommodates a series of air circulating suction fans 58 which are mounted on brackets 60, 62 and cause the air to flow in the respective chambers 86, 88, 90 and 92 in directions indicated by arrow 82. Each of the first four chambers 8692 is further provided with an outlet connected to a discharge pipe 70 which contains a regulating valve 68. The pipes 70 are connected to separate suction fans 70a or to a common suction fan serving to withdraw moisture-laden air from the respective chambers. Each of the five chambers is preferably provided with a thermometer 72 and a hygrometer 74.
The heating chamber 92 is further provided with a first conditioning device including a wetting or moisturizing unit 76 which can introduce into the circulating air controlled amounts of moisture. In addition, each of the four chambers 86-92 is provided with a second conditioning unit including an electric heater 64 which maintains the temperature of circulating air at a desired value. The partitions 30-36 and the two end walls of the housing 50 are provided with slots which permit passage of the upper and lower stringers of the belt 14 and of the tobacco stream T.
The operation is as follows:
The feed conveyor 98 supplies tobacco T to the lefthand end of the upper stringer 22, and successive increments of such tobacco thereupon advance through the duct 52 by moving from chamber to chamber to issue at the opposite end of the housing 50 and to descend onto the take-off conveyor 100 which supplies nitrogenfree tobacco to a further processing station. During travel through the drying zone accommodating the first three chambers 86, 88, 90, the tobacco stream is subjected to a controlled drying operation by intimate contact with currents of hot air having a relatively low moisture content so that the tobacco and air are not in a state of hygroscopic equilibrium, i.e., the moisture content of air is lower. Air currents in the chambers 86-90 are heated by the respective heaters 64 and the corresponding fans 58 circulate such currents in directions indicated by arrow 82. Thus, each air current fiows upwardly through the respective bottom wall 40, through the lower stringer of the belt 14, through the upper stringer 22, through the mass of tobacco T, through the upper wall 38, and back to the respective heater 64. Each of the heaters is adjustable so that, by observing the thermometers 72, the operator can regulate the air temperature in chambers 3692 independently of each other. The walls 38 and 40 bring about uniform distribution of circulating air. Reheating of air currents in the drying chambers 86-90 is necessary because such currents are cooled in response to expulsion of moisture from the tobacco stream. The fans 70a withdraw a certain amount of moisture-laden air from chambers 86-90, and the supply pipes 66 admit equal amounts of fresh air. Continuous operation of fans 70:: insures that the moisture content of circulating air currents remains within an optimum range to guarantee controlled expulsion of moisture from the tobacco stream. Such tobacco is heated to a certain extent but not sufiiciently to expel requisite amounts of nitrogen. In other words, the primary function of air currents in the drying chambers 86-90 is to expel from tobacco surplus moisture before such tobacco reaches the heating chamber 92.
In the heating chamber 92, the wetting device 76 maintains the moisture content of circulating hot air at a value which is sufiiciently high to insure heating of tobacco to a temperature in the range of 100 C., i.e., to a temperature at which the particles of tobacco are relieved of nitrogen and simultaneously undergo a toasting operation to become impregnated with the flavoring substances applied thereto in the course of a preceding dipping treatment. The operation is preferably such that the wetting device 76 maintains the moisture content of air in the drying chamber 92 at a value which corresponds to moisture content of tobacco leaving the last drying chamber 90 (this is the condition of hygroscopic equilibrium), preferably in the range of somewhat above 1618 percent. The heater 64 of the chamber 92 maintains the temperature of circulating air at about C. whereby such air exchanges heat with tobacco and the temperature of tobacco also rises to about 100 C. Further evaporation of moisture from tobacco will take place only if the moisture content of tobacco exceeds the moisture content of air. Since the two moisture contents are identical or nearly identical, the tobacco stream is heated to requisite temperature and is relieved of nitrogen prior to entering the cooling chamber 94. The thus expelled nitrogen is admixed to circulating air and is withdrawn through the respective discharge conduit 70 by the associated suction fan 70a. At the same time, the inlet 41 of the heating chamber 92 admits equal amounts of fresh air.
Tobacco entering the cooling chamber 94 will normally have a moisture content which exceeds very slightly the desired optimum value. The fan 42 draws cool air from the respective inlet 41 to reduce the temperature of tobacco to room temperature or to another desired value. As the temperature of tobacco in the chamber 94 drops,
such tobacco is relieved of some additional moisture so that the moisture content of the mass leaving the housing 50 is reduced to a predetermined value which is best suited for further processing.
The manner in which the temperature of tobacco varies during travel through the housing 50 is illustrated in FIG. 3. The curve of FIG. 3 shows that, during travel through the first three (drying) chambers 86, 88, 90, the temperature of successive increments of the stream T rises from room temperature (e.g., about 20 C.) to about 50 C. The combined length of time intervals t and 1 shown in FIG. 3 corresponds to the duration of tobacco travel through the drying zone accommodating the three drying chambers. The interval t indicates the duration of travel through the heating zone (chamber 92), and it will be noted that the temperature of tobacco rapidly rises to and then remains in the range of 100 C. which is sufficient to expel nitrogen and to bring about satisfactory toasting. During the last interval t (travel through the cooling zone accommodating the chamber 94), the temperature of tobacco drops to 20 C. or thereabout.
The apparatus of FIG. 1 and 2 can be readily converted to operate in a slightly different way but on the same basic principle. For example, the heating chamber 92 may be placed between the drying chambers 88, 90 or 86, 88 or in front of the drying chamber 86. In other words, heating to a temperature at which the tobacco stream is relieved of nitrogen may take place prior to, simultaneously with, and/or following expulsion of surplus moisture. If the position of the chambers 88 and 92 is reversed, an initial or preliminary drying stage in chamber 86 is followed by heating to about 100 C. and thereupon by two further drying stages in chambers 88 and 90. In the last drying stage, the moisture content of nitrogen-free tobacco is reduced to a value which might be slightly above the desired optimum value, and the remaining surplus of moisture is then expelled in the coling chamber 94. The apparatus may comprise two or more cooling chambers, i.e., not only the drying step but also the cooling step may be carried out in a series of stages. The same hold true for the heating step.
The advantages of our method and apparatus will be even more readily appreciated by referring to FIGS. 4 and 5. The curve 102 of FIG. 5 indicates variations in heat used up by evaporation when the tobacco is treated in accordance with a conventional method. The amount of such heat first increases, thereupon remains constant and finally decreases. The amounts of heat (curve 104) taken up by tobacco first decrease, then remain constant and finally decrease again. The curves 102, 104 converge in the first stage and diverge in the last stage, i.e., the amounts of heat taken up by tobacco increase in comparison with the amounts of heat used up for evaporation as the moisture content of tobacco decreases. The temperature (curve 106) rises in the first stage and thereupon remains con stant to rise again when the amounts of heat admitted into tobacco exceed the amounts used up for evaporation of moisture. The temperature will reach 100 C. when the moisture content of tobacco has been reduced to 5-8 percent, i.e., well below the desired minimum moisture content. This means that the thus treated mass of tobacco must be wetted to raise its moisture content to 16-18 percent; otherwise, the particles would be much too brittle and subsequent treatment would produce too much tobacco dust.
FIG. 4 illustrates the conditions which prevail during treatment of nitrogen-rich tobacco in accordance with our method. The curve 108 indicates that the amounts of heat transferred into tobacco always exceed the amounts of heat (curve 110) which are used up for evaporation. Therefore, the temperature of tobacco (curve 112) rises gradually and continuously until it reaches a desired value, namely, a temperature in the range of 100 C. The temperature will reach 100 C. when the moisture content of tobacco is still in the range of 25 percent which is above the desired ultimate moisture content. If the heating chamber 92 is placed upstream of one or more drying chambers 86-90, the temperature of tobacco will rise to C. while the moisture content is higher than 25 percent.
If the apparatus of our invention is to be used for the sole purpose of expelling nitrogen, the drying chambers 86-90 are not needed at all. However, one or more drying chambers will be used whenever the expulsion of nitrogen should be accompanied by expulsion of surplus mois ture, either before, during and/ or following actual heating to desired temperature. As a rule, the surplus of moisture will be expelled (at least in part) before the tobacco is heated to such temperature which guarantees expulsion of nitrogen.
The transporting conveyor 96 of our apparatus can be constituted by any such conveyor which can guarantee satisfactory exchange of heat between tobacco and conditioned air and satisfactory withdrawal of evaporated moisture.
The air conditioning equipment in the chambers 86-92 is preferably interchangeable. Thus, the heaters 64 of the three drying chambers 86-90 may be of identical design and capacity but the heater in the heating chamber 92 is preferably stronger. The moisturizing unit 76 is needed at the heating station, but each of the drying stations can also use a device which maintains the moisture content .of air in the chambers 86-90 at a desired value.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knoweldge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
What is claimed as new and desired to be protected by Letters Patent is:
1. Apparatus for treating nitrogen-rich tobacco by contact with conditioned air, comprising a heating chamber; conveyor means for transporting tobacco through said chamber; circulating means for maintaining tobacco in said chamber in intimate contact with a current of air; first conditioning means for maintaining the moisture content of said current of air within a range at which a condition of substantial hygroscopic equilibrium is established between air and tobacco in said chamber; and second conditioning means for maintaining said current of air at a temperature at which air and tobacco exchange sufficient heat to raise the temperature of tobacco to a value at which the tobacco is relieved of nitrogen.
2. Apparatus for treating dipped tobacco as defined in claim 1, wherein said second conditioning means is arranged to raise the temperature of tobacco to a value at which the tobacco passing through said chamber is toasted.
3. Apparatus for treating tobacco which contains a surplus of moisture as defined in claim 2, further comprising at least one drying chamber for tobacco transported by said conveyor means, additional circulating means for maintaining tobacco in said drying chamber in intimate contact with a second current of air having a moisture content which is less than the moisture content of tobacco in said drying chamber, and. additional conditioning means for maintaining the second current of air at a temperature high enough to effect expulsion of at least some surplus moisture from tobacco in said drying chamber.
4. Apparatus as defined in claim 3, wherein said drying chamber is located downstream of said heating chamher, as considered in the direction of tobacco travel.
5. Apparatus as defined in claim 3, wherein said drying chamber is located upstream of said heating chamber, as considered in the direction of tobacco travel.
6. Apparatus as defined in claim 3, wherein said cham- 7 bers have identical dimensions and said second and said additional conditioning means comprise heating means for the respective air currents.
7. Apparatus as defined in claim 2, wherein said conveyor means comprises an endless conveying element con- 5 sisting of foraminous material and wherein said circulating means is arranged to induce air flow through said conveying element.
8. Apparatus as defined in claim 2, wherein said first conditioning means comprises a moistening unit for ad- 10 mitting moisture into the current of air in said chamber.
9. Apparatus as defined in claim 2, further comprising at least one cooling chamber for tobacco transported by said conveyor means, said cooling chamber being 10- 8 cated downstream of said drying chamber, as considered in the direction of tobacco travel, and means for circulating in said cooling chamber a current of air at a temperature which is sufficiently low to reduce the temperature of nitrogen-free tobacco to a desired value.
. References Cited UNITED STATES PATENTS 2,714,385 8/1955 Jackson 131-140 3,024,792 3/1962 Touton 131-140 3,202,157 8/1965 Touton 131134 3,224,452 12/1965 Franklin et a1. 131-140 KENNETH W. SPRAGUE, Primary Examiner.