GB2246851A

GB2246851A - Preventing overdrying

Info

Publication number: GB2246851A
Application number: GB9115439A
Authority: GB
Inventors: Carsten Fischer; Peter Schwarz; Bruno Hermsdorf
Original assignee: Koerber AG
Current assignee: Koerber AG
Priority date: 1990-07-17
Filing date: 1991-07-17
Publication date: 1992-02-12
Anticipated expiration: 2011-07-17
Also published as: GB9115439D0; ITMI911781A0; IT1248578B; GB2246851B; DE4022718A1; ITMI911781A1

Abstract

To prevent overdrying of tobacco during start-up and closing-down of a dryer, e.g. one with a rotating inclined drum 1, finely distributed moisture is sprayed onto the tobacco T as it leaves the dryer - the moisture may be a mist of, preferably, hot water droplets, or it may be wet steam. The internal heating of the drum 1 and the application of moisture may be controlled to a conveyor weigher 54 ahead of the drum 1, operating with a monitor of the moisture content of the tobacco entering the dryer. A further monitor may measure the moisture content of tobacco discharged from the dryer. <IMAGE>

Description

Method and apparatus for drying tobacco or a similar material The

invention relates to a method for drying tobacco or a similar material in a drying section through which the tobacco passes.

The invention also relates to an apparatus for drying tobacco or a similar material in a drier through which the tobacco passes, preferably a drying drum.

The term "tobacco" includes tobacco leaves or pieces thereof, torn tobacco, cut tobacco, tobacco sheet, tobacco substitutes or other preferably vegetable material to be dried.

When operating driers of the is inevitable that when reaion of the type, it drier, the initial is over-dried, aforementioned starting-up the tobacco stream since it encounters a hot drier which is not filled with vapours, so that it emits much more moisture than desirable and than is the case when the drier is filled with tobacco. The situation is similar when the drier is stopped, in which the end region of the tobacco stream is overdried, because too much heat is supplied for the drier filled only partly with tobacco.

In order to avoid overdrying at the time of starting-up and stopping a drying drum, it is known to spray water into the drum, in order to produce vapours artificially and thus to avoid excessive drying.

The object on which the invention is based 1 consists of providing a further solution to the afore-described problem of overdrying at the time of starting-up and stopping a drier.

According to the invention this is achieved due to the fact that the initial region and/or the end region of the tobacco stream is sprayed with finely distributed moisture as it emerges from the drying section.

Claims

Improvements and developments according to the invention are disclosed in the subordinate method Claims. The aforementioned apparatus, which serves in particular for carrying out the method, is characterised by the fact that provided at the outlet of the drier is a spray device for applying finely distributed moisture to the tobacco at the beginning and end of the tobacco stream. The term "finely distributed moisture" means mainly moisture in the form of droplets, for example water droplets, which may be hot, so that the hot tobacco leaving the drier absorbs the moisture bettter. The moisture is preferably finely atomized, which may take place with additionally - supplied compressed air. However, it is also possible to spray moist steam, for example saturated steam, onto the tobacco leaving the drier. is possible to introduce a combination and steam, in which case the drops of likewise be hot. Developments of the invention are in the subordinate apparatus Claims. i Finally it of drops water may disclosed 1 i 1 1 1 1 1 i i i i 1 i 1 1 i 1 1 The invention has the advantage that the initial region and/or the end region of the tobacco stream do not need to be separated after leaving the drying section, but can be supplied for further processing, virtually in the same way as the tobacco treated during normal operation of the drier. The invention will be described in detail with reference to the drawings showing one embodiment, in which: Figure 1 is a general view of a d.c. drier in a side view shown partly in section, Figure 2 shows the outlet region of the drier, Figure 3 is a view of the outlet region in the direction of arrow III of Figure 2, Figures 4a and 4b are diagrams for the mass flow of tobacco and associated moisture values as well as the spraying of moisture depending on time for the starting-up operation, Figures 5a and 5b are diagrams for the mass flow of tobacco and associated tobacco moisture values as well as for the spraying of moisture depending on time for the outlet operation. Figure 1 shows a known d.c. drier of' the applicant, such as is described in detail in US-PS 3 429 317. The invention is described in use on this d. c. drier, in which the hot air blown in at the inlet side travels through the drying section in the direction of travel of the tobacco. However, the invention may also be used in so called counterflow driers, in which the hot air is introduced at the outlet of the drier and flows in the opposite direction to that in which the tobacco is conveyed. b The tobacco stream T supplied on a conveyor belt 13, which consists for example of cut tobacco, passes to a conveyor-type weigher 54, which by way of a converter 55 emits a signal corresponding to the mass flow of the tobacco (mass per unit time). The tobacco stream T travels on the latter to a moisture pick-up 16, which is constructed as a HFmeasuring arrangement disposed in a reciprocatingand emits a measurement signal corresponding to the moitture content of the tobacco. By way of a chute 17, the tobacco stream passes into a drum drier 1, which rests on rollers 4 mounted in pedestals 2 and 3 and is set in rotation by a motor 5 by way of a gear and a toothed rim 6 attached to the front end of the drier. Provided at the inlet of the drum drier 1 is a first source of energy in the form of a radiator 7 for heating air, which is introduced into the inside of the drier by means of a fan 8 by way of a delivery line 29. The reference numeral 9 designates an air deflector, upon the opening of which cold air at room temperature can be sucked in by the fan, in order to be able to vary the ratio of room air and hot air, as required. Provided as a second source of energy in likewise known manner within the drum drier 1 are heating coils 10 operated by steam, which coils 10 are connected to a steam pipe 11 with a steam valve 12. The steam valve 12 may be opened to a greater. or lesser extent by way of a serve, drive 48 and thus the supply of heat to the heating coils 10 can be controlled. Upon rotation of the drum drier 1, the heating coils 1 0 act as blades, which entrain and lift the tobacco in the drier and then once more allow it to fall. As a result of the inclination of the drum 1, a conveyance of the tobacco in the direction of the outlet is brought about. plate feeder 1 i 1 i 1 1 i i 0 - Located at the outlet end of the drier for sucking vapours and air out of the drier is an extraction hood 18, in which a sieve drum 20 driven by a motor 19 rotates. Connected to the extraction hood 18 is a suction line 21 provided with a throttle valve 23 and connected to the latter is a fan 22.. The tobacco stream T leaving the drum drier 1 passes by way of a chute 14 onto a conveyor belt 40 and from there' to a further moisture pick-up 41, which emits an electrical signal corresponding to the final moisture content of the tobacco. The moisture pick-ups of moisture meter known in the industry. 16 and 41 may be of the HWK type tobacco-processing The control of the drying drum 1 for the purpose of drying the tobacco stream T supplied and travelling therethrough, takes place in the manner described in detail in US-PS 3 429 317 due to the fact that the signals emitted by the conveyor-type weigher 54 and the first pick-up 16 and corresponding to the initial mass and initial moisture content of the tobacco are combined and control the heat content of the hot air stream supplied at the inlet side from the pipe 29. The signal emitted by the second pick-up 41 and corresponding to the final moisture content of the tobacco controls the supply of steam to the blades 10 by way of the steam valve 12, 48. At the time of starting-up of the drum drier 1, thus when the beginning of the tobacco stream T reaches the drum, the latter is hot and filled with dry air, because the supply of heat is too and the air in the drum becomes saturated vapours. great with expelled water in the form of so calle 1 1 for the first time during drying of the tobacco. Therefore the initial region Ta of the tobacco stream T is overdried very considerably and must be separated, i.e. it must be removed as unusable or re-moistened in a complicated manner. The same is true upon terminating drying, when the end region Te of the tobacco stream T arrives in the drum 1, travels through the latter and in this case is overdried on account of the supply of heat, which is now too considerable, by the blades 10. Therefore, according to the invention, a nozzle 26 is provided in the outlet region of the drum drier 1, to which compressed air and moisture, preferably hot water, can be supplied by way of pipes 27 and 28. The water is atomized by the compressed air and sprayed in the form of a fine mist 31 onto the tobacco stream leaving the drum. The reference numerals 32 and 33 designate a source of compressed air or a water reservoir. Details of the nozzle 26, of the pipes 27, 28 and of the control of a supply of air and water are shown in Figure 2. Disposed in the pipes 27 and 28 are control valves (adjusting valves) 36 or 37, which receive control signals from a time lag member 38. The time lag member 38 receives signals from measured value converter 55 of the conveyortype weigher 54, as soon as the latter ascertains that a minimum value has been exceeded or not reached. This delay time is adjusted so that it corresponds to the travelling time of the of the tobacco stream T or its end the drum 1 as far as the nozzle 26. the initial region Ta region Te through The control of the supply of moisture through the nozzle 26 takes place so that upon the arrival of the tobacco stream T, i.e. when a minimum value of the output signal of the conveyor-type weigher i 1 1 1 i i 1 1 7 - is exceeded, the conveyor-type weigher 54 and the measured value converter 55 send a signal S to the time lag member 38. The signal is delayed until the initial region Ta of the tobacco stream T has arrived in the outlet region of the drum drier 1, i.e. the range of coverage of the nozzle 26, which is possible without difficulties on account of the constant conveying speed of the supply conveyor and of the drum drier 1. When the overdried initial region Ta arrives in the spraying range of the nozzle 26, then the valves 36 and 37 in the pipes 27 or 28 receive an opening signal, so that the moisture is atomized by the compressed air and is sprayed as a mist 31 onto the initial region Ta of the tobacco stream T leaving the drum drier. After a certain time, thus, according to the invention, when the overdried part of the tobacco stream T is moistened and discharged, the valves 36 and 37 are once more closed and the drier and its control operate in the manner described in the aforementioned US-Patent Specification. The time lag member 38 is advantageously constructed so that it emits a control signal whereof the magnitude corresponds to the measuring signal emitted by the measured value converter, so that the mass flow of the moisture, preferably water, delivered by the control valves 36 and 37, corresponds at least approximately to the mass flow of the tobacco, which is conveyed by the drum 1. Figure 3 is a view Perpendicular to the drum 1 with the blades 10, which lift the tobacco in the form of portions T' and allow it to fall back. At the outlet. region, the tobacco portions T' f all through the air onto the discharge belt 40 and are h thus sprayed by the mist 31 from the nozzle 26 (not shown). Figure 4 shows an example of a mass flow T of approximately 5,000 kg/hour. F designates the relative moisture of the tobacco. It will be seen that the initial region Ta of the tobacco stream T (full line) appears after a delivery time t of approximately 3.5 minutes, measured from the delivery of the signal S by the conveyor-type weigher 54, in the outlet region of the drum 1. The moisture curve F' without spraying according to the invention is marked by dots. It can be seen how even a greater part of the tobacco leaves the drier overdried. In comparison therewith, the curve F shown in broken line represents the moisture curve with spraying. It can be seen that virtually the entire initial region Ta of the tobacco stream T is already moistened, so that virtually no losses occur. Figure 4b shows the progress with regard to time of the moisture quantity W (1/hour) supplied. It will be seen that it is advantageous to supply the maximum mass flow of moisture immediately after the expiration of the time lag and then to allow it to decrease. Corresponding control signals may be emitted by a function generator 39 shown in broken line in Figure 2. At the end of the drying process (outlet operation), the pick-up 55 of the conveyor-type weigher 54 sends a signal S to the time lag member 38, when the magnitude of the tobacco stream T falls below a minimum value. After the expiration of the preset time lag, which may differ from that at the start-up, the end region Te of the tobacco stream i 1 1 Z: 1 1 1 1 1 in laa member 38 T passes in the overdried state into the region of the drum drier 1. The valves 36 the lines 27 or 28 are activated by so that the nozzle 26 supplies moisture to the end region of the tobacco. Figure 5a shows the progress of the tobacco stream T after the expiration of the time lag and the moisture without spraying W, represented by a dotted line) and with spraying (F, represented by a broken line). Figure 5a shows that virtually no tobacco is lost or must be remoistened as a result of overdrying. outlet and 3 7 the time Figure 5b shows a curve of the mass flow of the moisture supplied over the time which is brought about by the function generator 39. In place of atomized moisture, moist steam, for example saturated steam, or a combination of both can be used. The use of the invention is not restricted to drying drums, which are operated by d.c. current or a.c. current. It can also be used in other types of driers, in which the tobacco is heated or dried as it passes through, overdrying occurring in the initial and end regions.

1 c i 1 Claims 1. Method for drying tobacco or a similar material in a drying section through which the tobacco passes, characterised in that the initial region and/or the end region of the tobacco stream is sprayed with finely distributed moisture as it leaves the drying section.

2. Method according to Claim 1, characterised in that the mass flow of the initial region and/or of the end region of the tobacco stream is monitored before entering the drying section and a corresponding signal is formed, which is delayed corresponding to the travelling time of the tobacco from monitoring until spraying and controls the moistening of the tobacco (initial region and/or end region) emerging from the drying section.

3. Method according to Claim 2, in that the signal is formed by weighing and conversion into an electrical quantity.

characterised the tobacco

4. Method according to one or more of the preceding Claims, characterised in that the mass flow of the moisture sprayed is controlled depending on the mass flow of the tobacco travelling through the drying section.

5. Method according to one or more of the preceding Claims, characterised in that the progress with regard to time of' the mass flow of moisture sprayed on is predetermined.

1 1 1 i 1 I i 1? 1 Claims, characterised in that the moisture is sprayed i into the tobacco stream leaving the drying section.

6. Method according to one or more of the preceding - 11

7. Apparatus for drying tobacco or a similar material in a drier through which the tobacco passes, preferably a drum drier, characterised in that at the outlet of the drier (1) a spray device (26) is provided for applying finely distributed moisture to the tobacco at the beginning (Ta) and/or end (Te) of the tobacco stream (T).

8. Apparatus according to Claim 7, characterised in that a measuring arrangement (54, 55) is provided for monitoring the beginning and/or the end of the tobacco stream, whereof the output signal is supplied by way of a time lag member (38), whereof the time lag corresponds to the travelling time of the tobacco between the measuring arrangement and spray device, to a control arrangement (36, 37) of the spray device.

9. Apparatus according to Claim 7 and/or 8, characterised in that the measuring arrangement is constructed as a conveyor-type weigher (54), whereof the measurement signal is supplied with a time lag to a control arrangement (36, 37) for the mass flow of the moisture sprayed on.

10. Apparatus according to one or more of Claims 7 to 9, characterised by a programme generator (39) -for the timed sequence of the spray programme at the beginning and/or end of the tobacco stream.

11. Apparatus according to one or more of Claims 7 to 10, characterised in that the spray device sprays the tobacco stream, while it is leaving the drier, for example as a shower.

12 12. A method of drying tobacco or the like substantially as herein described with reference to.the accompanying drawings.

13. Apparatus for drying tobacco or the like substantially as herein described with reference to the accompanying drawings.

Published 1992 at The Patent Office. Concept House. Cardifr Road. Newport. Gwent NP9 I RH. Further copies maybe obtained from v Multiplex techniques lid. St Mary Cray. Keni Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys, Newport. NP l 7HZ. Printed k 1 1 i 1 1 1 i 1 i 1 1 i i