US3624917A - Tobacco curing system - Google Patents

Abstract

A TOBACCO CURING SYSTEM IN WHICH AIR IS FED INTO THE UPPER PART OF A KILN UNDER CONTROLLED CONDITIONS OF TEMPERATURE AND HUMIDITY. A DUCT IS MOUNTED ON A KILN WALL IN COMMUNICATION WITH UPPER AND LOWER OPENINGS IN THE WALL. THE LOWER PART OF THE DUCT IS DIVIDED INTO TWO COMPARTMENTS EACH OF WHICH COMMUNICATES WITH THE OUTSIDE AIR AND THE DUCT. BOTH COMPARTMENTS ALSO COMMUNICATE WITH EACH OTHER. ONE CHAMBER ALSO COMMUNICATES WITH THE LOWER OPENING IN THE KILN TO RECEIVE AIR WHICH HAS PASSED THROUGH THE KILN.

EXTERNAL AIR IS DRAWN INTO ONE COMPARTMENT, HEATED, MIXED WITH THE RECIRCULATED AIR IN CONTROLLED PROPORTIONS AND FORCED THROUGH THE DUCT AND KILN BY A FAN. THE AIR INTAKE IS CONTROLLED BY DAMPERS IN THE HEATING COMPARTMENT AND A DAMPER IS PROVIDED IN THE RECIRCULATED AIR COMPARTMENT TO CONTROL THE INTAKE THEREOF.

Description

. 7, 1971 J. F. MOORE TOBACCO CURNG SYSTEM Filed Nov. 24. 1969 INVLNIUR. JOHN F MOORE United States Patent O 3,624,917 TOBACCO CURING SYSTEM John F. Moore, 100 Hillsdale Ave. W., Toronto 7, Ontario, Canada Filed Nov. 24, 1969, Ser. No. 879,380 Claims priority, application Canada, Nov. 23, 1968,

Inf. cl. Fzab 21/06 U.S. Cl. 34-46 7 Claims ABSTRACT OF THE DISCLOSURE A tobacco curing system in which air is fed into the upper part of a kiln under controlled conditions of temperature and humidity. A duct is mounted on a kiln wall in communication with upper and lower openings in the wall. The lower part of the duct is divided into two compartments each of which communicates with the outside air and the duct. Both compartments also communicate with each other. One chamber also communicates with the lower opening in the kiln to receive air which has passed through the kiln.

External air is drawn into one compartment, heated, mixed with the recirculated air in controlled proportions and forced through the duct and kiln by a fan. The air intake is controlled by dampers in the heating compartment and a damper is provided in the recirculated air compartment to control the intake thereof.

This invention relates to a system for curing tobacco and, in particular, to a system whereby the temperature and relative humidity of the air within the curing kiln may be controlled. In the curing of tobacco it is customary to hang the tobacco in a building or kiln which is substantially enclosed and sealed.

The interior of the 'kiln is heated and over a period of time certain chemical and physical changes take place in the tobacco leaves, resulting in the production of a cured leaf.

In one well known system for curing tobacco, heat is supplied to the building along the oor of the building; the heated air rises through the tobacco leaves and escapes through vents in the roof of the building. This known system, however, suffers from the disadvantage that as the heated air rises through the cooler tobacco leaves, there is a tendency for the heated air to channel or, in other words, to seek the path of least resistance through the tobacco; as a result of this the tobacco leaves are unevenly contacted by the heated air and the curing process is not uniformly carried out.

yIn my `Canadian Pat. No. 640,137, dated Apr. 24, 1962, and entitled Tobacco Curing System, a system which largely overcomes this disadvantage is described. yIn the system described in the above patent heated air is supplied at the top of the kiln, and by means of a closed circuit, forced tiow system the heated air is driven downwardly through the tobacco and out through a vent located at or near the bottom of the kiln, the air being returned from the vent to the circuit after being reheated. The kiln itself is a substantially sealed, enclosed kiln, and means are provided for admitting fresh outside air to the system and exhausting moisture-laden air from the system. The air supply and exhaust means are adjusted in accordance with "ice the humidity within the system, which must be carefully controlled during the curing process.

Now in practice it is extremely difficult to construct a kiln which is air-tight. Because of the very different conditions of temperature and humidity inside and outside the kiln, the doors may warp badly, giving rise to substantial leakage of air which cannot be controlled. Such leakage may in many cases make it difiicult or impossible to control the temperature and humidity within the kiln to the accuracy required.

According to the present invention air at the required temperature and humidity is admitted to the upper part of the kiln from a duct in which the ratio of recirculated air to fresh, outside air is automatically controlled in accordance with the humidity of the air passing from the kiln to the duct. The lower portion of the duct is divided by a partition into first and second compartments to which the recirculated air and the fresh, outside air are, respectively, admitted; the second compartment includes a heater for heating the air admitted to it, and a proportion of the air from the first compartment is also admitted to the second compartment for reheating.

`One embodiment of the invention will now be described by way of example with reference to the accompanying drawing, in which:

FIG. l is a cut away perspective View of the curing system as attached to the outside of the tobacco kiln, and

FIG. 2 is a detailed view of a portion of FIG. l.

Referring now to FIG. 1, a tobacco kiln indicated generally by the reference character 10 consists of a foundation wall (not shown) upon which is constructed a side wall 12 extending upwardly to a roof portion 13. The tobacco kiln, which is generally similar to the kiln described in my Pat. No. 640,137, is enclosed so that there is a minimum leakage of air into or out of the kiln, but any leakage of air which does unavoidably occur is of little importance, as will become apparent hereinafter.

An opening .14 is provided adjacent the top of the wall 12 and a similarly sized opening 15, which is covered by a mesh, is positioned vertically beneath the opening 14, the opening 14 being hereinafter referred to as the first opening and the opening 15 being hereinafter referred to as the second opening.

The opening 14 is located in the wall 12 at a level which is at least partly above the uppermost level at which tobacco may be hung in the kiln so that the air entering the kiln will do so above the tobacco. Similarly the opening 15 is located in the wall 12 at least partly below the lowermost level at which tobacco may be hung so that the air must flow past all of the tobacco before escaping through the opening 15 in the wall 1.2.

A duct .16 is provided externally of the lkiln 10` joining the two openings 14 and 15, and within this duct 16 is contained the mechanism associated with the temperature and humidity control of the curing system. A transverse wall 17 extends across the duct 16 adjacent its lower end, and the transverse wall 17 is provided with a circular central aperture 18 within which is mounted a fan 19 adapted to sweep substantially the entire circular opening. The periphery of the opening 18 is provide with a langed collar 20 to dene the area swept by the fan 19. The fan 19 is mounted on a substantially vertical shaft 21 which is journalled by a support member 22 mounted on a vertical partition wall 23 in the lower part of the duct 16. The shaft 21 is journalled near its upper end by a second support member (not shown) secured to the partition wall l23. The fan 19 is driven by an electric motor 24 by means of a belt and pulley drive 25.

Accordingly, it can be seen that rotation of the shaft 21 by the motor 24 will cause the fan 19 to rotate so as to drive air through the duct 16 in the direction of the arrows 26, through the Afirst opening 14 into the kiln above the uppermost level at which tobacco may be hung, downwardly through the tobacco, and back into the duct 16 through the second opening 1-5.

The transverse wall 17 divides the duct 16 horizontally into a lower portion and an upper portion, the fan 19 being located in the upper portion of the duct. The lower portion of the duct is divided by the vertical partition wall 23 into a rst compartment 27, which communicates with the kiln via the second opening 15, and a second compartment 28 having a bottom wall 29 which extends right across the lower portion and is formed with openings for admitting external air. The circular opening 18 is symmetrically disposed with respect to the compartments 27 yand 28, so that the fan draws air from both compartments and drives the air through the duct.

Below the transverse wall 17 there is provided a source of heat which in the embodiment shown comprises a gas burner 30 having gas supply pipe 31. Combustion air is admitted to the burner 30 by an inlet 32 which extends through the wall 29 of the compartment 28. A chamber 33, having a hinged front panel 34, is located below the second compartment 28, the chamber 33 containing the motor 24 and belt and pulley drive 25, and the fuel supply pipes for the burner 30. lFresh air is readily admissible to the chamber 33 for admission to the compartment 28 and the burner 30.

In operation of the system the fan 19 sweeps the aperture 18 to draw heated air from the compartment 28 and recirculated air from the compartment 27 up into the upper portion of the duct 16. It can be seen, therefore, that a mixture of the heated air from compartment 28 and the recirculated air from compartment 27 is driven through the closed circuit described in the direction of the arrows 26 by being forced by means of the fan 19 through the duct 16, into the kiln through the first opening A14 `above the tobacco, and will then pass downwardly through the tobacco and back into the second compartment 27 of the duct via the second opening 1S.

Suitable means such as a conventional thermostat 35 connected to control means for the burner gas supply, will control the burner 30 and will, accordingly, maintain the temperature of the air mixture within the duct l16 at a desired level. The thermostat 30 may be controlled by any suitable means, which are neither shown nor described, so that the temperature may either rise over a period of time or fall over a period of time as circumstances may require.

During the curing of tobacco it is not only necessary that the temperature be closely controlled, but it is also essential that the humidity of the air within the kiln be controlled. Since the curing of tobacco involves removal of moisture from the tobacco leaf at certain stages, it fis necessary to provide means to exhaust some of the moisture laden air from the -kiln and to admit outside air, the relative humidity of which would be lower than that of the air within the kiln. Moisture laden air passes from the kiln to the first compartment 27 via the opening and a proportion of this air is exhausted via openings 36 in accordance with the total air pressure within the system. The openings 36 (of which only one is shown) are tted with hinged damper doors 37, which are biased towards the closed position by counter Weights 38. A pair of openings 39 are provided in the Vertical partition 23 to allow air to pass from the rst compartment 27 to the second compartment 28, and the ilow of air through these openings is controlled by means of dampers 40, the adjustment of which will be described hereinafter. Besides cooperating with the openings 39,

the dampers 40 cooperate with openings 70 in the floor 29 through which fresh air is admitted to the compartment 28. In one extreme position of the dampers 40, the openings 39 are closed and only fresh air is admitted to the second compartment 28 to be heated therein by the burner 30. 'In the other extreme position of the dampers 40, the lair admission openings in the oor 29 are closed, and only recirculated air is admitted to the compartment 28 to be reheated therein by the burner 30. At any 'intermediate setting of the dampers 40, the ratio of moisture-laden, recirculated air to freshly admitted external air is determined by the setting of the dampers. As illustrated in FIG. 2, the initial setting of the dampers 40 is preset by means of a crank handle 41 mounted at one end of a shaft 42 extending into the chamber 33. The other end of the shaft 42 is connected to a cylinder 43 within which a spring biased piston 44 is splined or keyed so as to rotate with the shaft 42. The piston is connected to a worm wheel 45 which is journaled at 46 for rotation by the handle 41. The damper 40 is pivoted to the partition wall 23 at 47 and is connected by toggle arms 48 to a pinion 49 which engages the worm wheel 45. Connected to the lower toggle arm 48 is a vertical control rod 50, which is secured at its lower end to an expandable bellows 51, the interior of which communicates by means of a tube (not shown) With a bulb contained within an enclosed box 52 (FfIG. l).

The disposition of the fan 19 adjacent the top of partition Wall 23 as previously described will, of course, mean that the fan 19 is subject on its inlet, when inlet damper 40 approaches the vertical side, to two diiferent pressures one below and one above the atmospheric pressure. In compartment 27 the pressure will be reduced with respect to the atmosphere, and in compartment 28, the pressure exceeds atmospheric pressure.

The internal details of the box 52 and associated parts are described in my Patent No. 640,137 and will not be fully described herein. It may be mentioned, however, that the bulb within the box 52 is provided with a wick which lies over its surface and which hangs into a water bath occupying the lower portion of the box 52. The water bath is maintained at a desired level from a reservoir which may conveniently be mounted externally of the duct 16 and connected with the interior of the box by a conduit.

The bulb contains ya material which under normal circumstances exerts a substantial vapor pressure which is capable of actuating the bellows 51 and the control rod l50. Such a suitable material is ethyl chloride. 'Ihe ethyl chloride contained within the bulb 50 is in a liquid-vapor phase and the Vapor pressure of the material, acting upon the bellows 51 will move the control rod `50 and thereby rotate the pinion 49 to operate the damper 40, the minimum opening of the damper is determined by the initial setting of an adjustment mechanism. Thus the piston 44 is spring-biased to a neutral position within the cylinder 43, the setting of the damper 40 having been adjusted by means of a handle 41 through the worm wheel 45 Aand pinion 49. Vertical movement of the control rod 50 superimposes an automatic adjustment of the damper 40 upon the initial adjustment, the worm wheel 45| and pinion 49 acting in such a case as a rack and pinion drive.

The box 52 is provided with an opening which is in communication with a pipe 53 extending vertically within the duct 1'6 to a point adjacent the rst opening 14 where it terminates in an open end 54 to receive air flowing upwardly in the duct 16. A second opening is provided in the box 52 so that air flowing upwardly in the primary duct 16 enters the open end 54, passes downwardly through the pipe 53, ows over the water soaked wick lying on the bulb and returns to the system. Accordingly, the temperature of the material within the bulb will be equivalent to the wet-bulb temperature of the air in the system and the vapor pressure exerted by the ethyl chloride within the bulb will be a function of the Wet-bulb temperature of the air in the system.

If the wet-bulb temperature of the air becomes too high, the vapor pressure of the ethyl chloride will increase and cause the control rod 50 to move upwardly as seen in FIG. 2. This will cause the pinion 49 to rotate clockwise, thereby raising the damper 40 and increase the ratio of fresh air to recirculated air admitted to the second compartment 28.

With the system described, as with the system described in my above mentioned patent, freshly heated air admitted to the duct 16 will be preserved within the system and there will be a minimum of hot air lost due to the exhausting of the humid air through the openings 36 controlled by dampers 37. Since the system described is a forced air system there will be a super-atmospheric pressure within the kiln 10, which will effectively prevent the inward leakage of cold outside air into the kiln. Any leakage of air through the kiln walls will be from the inside of the lkiln outwardly due to the over-pressure which exists within the kiln. As a result there will be no cold air leaking into the kiln to contact the tobacco leaves hanging therein, and accordingly a substantially uniform temperature may Ibe maintained throughout the entire volume of the kiln which, of course, will promote a uniform curing of the tobacco contained therein.

VThe construction of the duct 1,6, as in my previous patent, may be of any suitable material such as sheet metal or composition board. The curing system which has been disclosed is adaptable for use with existing tobacco kilns since the only alterations in those kilns which need to be made would be the provisions of the first and second openings 14 and 15 and the closing of whatever exit vents may exist within the kiln structure. The device is also suitable for use in kilns specially designed to receive it and in such cases the construction of the kiln would need to take into account the fact that the invention proposes that the kiln should be enclosed so as to provide a closed circuit for the forced air system driven by the fan 19.

The source of heat for the air in the second compartment 28 is shown in the drawing as being a gas burner. The fuel to be burned may alternatively be oil, natural gas, synthetic gas, or any other fuel suitable for such an operation, of course.

Although a specific means has been disclosed for controlling the damper 40 in response to the wet-bulb temperature of the air within the system, such means being substantially as disclosed in my Pat. No. 6405137, it is not to be considered that this disclosure is limiting, but is merely illustrative of one form of such a control. There are other suitable controls which could be used and the invention equally contemplates their use. For example, an electrical sensing element could be used in association with the water soaked wick to control an electrical damper motor operating the damper 40. Moreover, a conventional, fast-acting thermostat may be used to control the damper 40 electrically.

In the operation of the curing system described, setting of the dampers 40 to close the openings 39 permits the admission of fresh air into the second compartment 28 through the air admission openings and restricts or prevents air from the kiln entering the compartment 28. The additional air being forced into the kiln forces moist air out through any cracks in the kiln, and when the air admitted to the kiln becomes greater than the air escaping via leaks, the internal pressure builds up to open the dampers 37 and so permit the excess air to escape. The cool, freshly admitted air is prevented from entering the bottom of the kiln, and so condensation of the moist air Within the kiln is prevented.

The procedure for curing the tobacco involves a step for yellowing the tobacco, followed by a step for drying the tobacco. For the yellowing step, the dampers 4f) are preset by means of the crank handle 41 so as to close or nearly close the openings 39, and the thermostat 3S is set to control the desired air temperature. Two alternative methods for performing the drying stepy are available. In the first, the thermostat 35 is set to control the air temperature to a desired value, and the dampers 40 are preset manually to the desired adjustment in accordance with requirements. In this case, the conditions are controlled primarily by the burner. In the second alternative the dampers 4? are first set manually to the closed position to prevent the admission of external air, and the burner thermostat 35 is set at 5 above the desired temperature. The burner operates constantly if the set temperature is not reached, and the dampers 49 are controlled automatically to admit the maximum external air that the burner is capable of heating to the desired temperature, Whatever internal and external air conditions prevail.

What I claim as my invention is:

1. A tobacco curing system comprising an enclosed kiln in which green tobacco may be hung for curing, a first opening in a wall of the kiln above the uppermost level at which tobacco may be hung and a second opening in said wall the lowest portion of which lies below the lowest level at which tobacco may :be hung, a primary duct comprising an upper portion communicating with the kiln via the first opening and a lower portion, said lower portion being divided by partition means into first and second compartments each communcating at its upper end with the upper portion, the first compartment communieating with the kiln via said second opening and the second compartment including means for admitting external air, a source of heat in said second compartment, a fan in said Iupper portion of the duct to draw air from the first and second compartments and drive the air through the duct, through the kiln via the first opening, and into the iirst compartment via the second opening, first damper means to control the admission of external air to the second compartment, second damper means to exhaust air from the rst compartment, temperature responsive means to control the source of heat and means responsive to the temperature of the air supplied to the kiln to control the first damper means.

2. A tobacco curing system as claimed in claim 1 further including at least one opening in said partition means to permit air to flow from the first compartment to the second compartment, said first damper means co-operating with said partition openings to control the ratio of external air admitted to the second compartment from the first compartment, said second damper means controlling the exhaust of air from said first compartment in accordance with the air pressure with the second compartment.

3. A tobacco `curing system as claimed in claim 1 including a wall extending across the primary duct above the source of heat and having a central circular opening therein, the fan being located in the central circular opening for sweeping substantially the whole opening to circulate the air drawn from the first and second compartments.

4. A tobacco curing system as claimed in claim 2 including a Wall extending across the primary duct above the source of heat and having a central circular opening therein, the fan being located in the central circular opening for sweeping substantially the whole opening to circulate the air drawn from the first and second compartments.

5. A tobacco curing system according to claim 1 wherein the source of heat is a fuel burner.

6. A tobacco curing system according to claim 2 wherein the source of heat is a fuel burner.

7. In a tobacco curing system including an enclosed kiln in which green tobacco may be hung for curing having upper and lower openings with the upper opening being above the uppermost level at which tobacco may be hung and the lower opening being below the lowest level at which tobacco may be hung, the improvement comprising: a duct extending between said upper and lower openings to provide communication therebetween; a rst partition having a hole therein extending transversely of said duct to divide said duct into upper and lower portions; a second partition in said lower portion extending upwardly toward said first transverse partition to divide said lower portion into rst and second compartments, a fan disposed in said transverse opening to draw air from said compartments and drive air through said duct; a heat source in said second compartment, said first and second compartments being communicable with each other, with the external air and with the upper portion of the duct, said second compartment further being communicable with the external air, said rst compartment further being in communication with said lower opening; damper means for providing a variable pressure gradient between the air in said rst and second compartment; temperature responsive means to control the heat source; and exhaust means for permitting escape of said moisture laden air adjacent said lower opening level.

References Cited UNITED STATES PATENTS 1,339,374 5/1920 Buensod 34-29 X 2,475,568 7/1949 Moore 131-140 R 3,100,145 8/1963 Moore 34-54 X CARROLL B. DORITY, IR., Primary Examiner U.S. C1. X.R.

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