WO1991000696A1

WO1991000696A1 - Apparatus for the even application of liquid and gaseous fluid to vegetable materials

Info

Publication number: WO1991000696A1
Application number: PCT/GB1990/001066
Authority: WO
Inventors: Victor Albert Montgomery White
Original assignee: GBE International PLC
Current assignee: GBE International PLC
Priority date: 1989-07-11
Filing date: 1990-07-11
Publication date: 1991-01-24
Anticipated expiration: 1992-01-11
Also published as: GB8915824D0

Abstract

An apparatus for applying fluid to vegetable materials, especially tobacco, is provided comprising an elongate substantially horizontally disposed trough (10) of which a substantial portion (11) at the lowermost region is cylindrical, a rotary screw (14) mounted so as to rotate in close proximity to the cylindrical portion (11) of the trough, inlet means (21) for feeding the material to be processed into the trough, inlet means (21) for feeding the material to be processed into the trough, outlet means (22) for delivering the treated product from the downstream end of the trough, and a plurality of steam nozzles (33) arranged in the cylindrical portion (11) of the trough for directing steam into the material from beneath.

Description

APPARATUS FOR THE EVEN APPLICATION OF LIQUID AND GASEOUS FLUID TO VEGETABLE MATERIALS

This invention relates to the even application of fluids to vegetable products with the intention of altering the product's thermal or moisture status. Application examples include: the blanching of vegetables using steam; freezing of products using for example liquid and gaseous carbon dioxide; the conditioning (water and heat application) of tobacco stems so that they can be rendered pliable prior to rolling; the application of heat and water to cut tobacco prior to drying with the objective of achieving volumetric expansion.

In all of these applications it is important that the treatment fluid has near equal opportunity to contact each product particle, that the fluid properties during contact are constant, and that the duration of contact is the same for all particles of product. If these factors are constant each product particle will receive the same process treatment. Conversely as any or all of the factors vary, the spread of treatments received by the particles of product increases. Some particles are over treated while some are under treated. Over treatment may or may not be detrimental. Under treatment usually is detrimental, for example, in freezing or blanching applications. In such instances, under treatment can be reduced by extending or repeating the process. This is inefficient since it requires either more process equipment or the use of more treatment fluid. As an instance where both under and over treatment is detrimental can be illustrated by reference to stem processing in the tobacco industry. Stems are the mid ribs which are removed from tobacco leaves by hand stripping or by mechanical threshing. The liberated lamina and stem fractions are processed separately to render them suitable for use in a s p ing product. Stem pieces are typically from 25-200mm long and from about 3-10mm in diameter. They are received in the process factory in a brittle dry state at about 10 to 14% moisture content. For their satisfactory inclusion in a smoking product they must be converted into a cut product similar to that obtained by cutting the thin lamina portions of the tobacco leaf. To this end the stems are conditioned, that is heat and moisture are added so that they become soft and pliable. Conditioned stems are then passed between rollers which squeeze them to a thickness typically 0.5 to 1.5mm. In this rolled form they are passed to cutting machines to produce thin strands known as cut rolled stem (CRS).

Further heat and moisture is then added to the CRS as a post cutting treatment (PCT) prior to drying to a moisture content suitable for use in the final product. This post cutting treatment stage is employed to cause volumetric expansion of the product and allow the production of a greater volume of smoking product from a given tobacco mass. Prior methods are described in GB Patent 1290613 at the conditioning stage and GB 2138666 at the PCT stage. At both stages treatment uniformity is critical.

At the conditioning stage heat is applied to speed up water absorption. In the past, cold conditioning was used followed by a long storage period during which the water was gradually absorbed into the stem cell structure. More modern processes use heat to encourage the moisture absorption and also use shorter, if any, storage time. Failure to apply sufficient heat to obtain moisture penetration results in some (under treated) stems being presented to the rolling stage in a state where, while the outer cells are over moist, the stem core is too dry. This results in damage to the cell and fibre structure during rolling. This damage has two main detrimental effects which are that damaged cells cannot be fully expanded at the subsequent PCT stage, and also that more waste debris and dust is generated. At the higher temperature extreme, over treated product is hotter. If the product becomes too hot changes occur which cause the product to become less robust and more likely to break up or degrade to smaller particles in subsequent process stages.

During the subsequent post cutting stage, those particles which have received a low heat input are likely to expand less than the average, while those which receive too much heat have an increased risk of subsequent degradation of size.

In the accompanying drawings: FIGURES 1 and 2 show characteristics of filling power and degradation of tobacco for wide and narrow temperature spreads respectively,

FIGURE 3 represents schematically, the cross section of an inclined rotary cylinder used in a known fluid treatment process,

FIGURE 4 is a schematic cross section of a known treatment screw conveyor (e.g. GB Patent No. 1290613),

FIGURE 5 is a schematic cross section of a known vibratory conveyor (e.g. GB Patent No. 2138666),

FIGURE 6 is a side elevation with part section of a

*"**- screw conditioner in accordance with the present invention, and

FIGURE 7 is a section along the line A-A in Figure 6 on an enlarged scale.

Within a situation with constant process time and fluid properties, product temperature is indicative of the heat taken up by the product. This situation is illustrated in Figures 1 and 2. While complete uniformity is not possible, it is clear that a reduction in temperature (heat) spread reduces the quantity of product at risk.

Traditional process methods have included cylinders through which the product transports and in which the product is exposed to fluid sprays and also screw trough conveyors as disclosed in GB Patent 1290613. Here the product lays in and is transported through a trough by the action of a spiral screw. Fluid is presented by sprays mounted above the product. Also, vibratory conveyors are known such as described in Patent 2138666, whereby fluid may be presented by overhead sprays or via jets in the base of the vibrating bed. Each of these methods has disadvantages which detract from the uniformity of heat received by the individual product particles. The three traditional methods are shown diagrammatically in Figures 3, 4 and 5.

Figure 3 represents the cross section of a cylinder. Such cylinders are inclined down from the material entry end and product transports by rolling as the cylinder rotates. The treatment fluid is introduced by one or more sprays arranged to project fluid on to the moving product mass. As the product mass rolls, that material which was exposed at its upper surface layer tends to become the lower surface layer in contact with the cylinder, before emerging again as the upper surface layer. There is little product interchange between the layers. Consequently the outer layers have good presentation to the treatment fluid, but for the treatment fluid to reach the remainder of the product it must have sufficient initial energy to penetrate the interstices between the product particles in successive layers. Also, in order to penetrate the product layers, the fluid must displace the environmental gas (usually air) or become diluted by that environmental gas. Since the lower product boundary is contained by the cylinder wall, environmental gas cannot be expelled in that direction. Most of the upper product boundary is being impacted by the treatment fluid which has penetrated into air gaps between the product. Hence displacement of environmental gasses from the product mass core via its upper surface layers is small. Consequently successive layers have a reduced opportunity to come into contact with a diluted process fluid.

The process treatment fluid sprays can be considered to be point sources of fluid flow origin. They are intended to spread out to cover a sufficiently large proportion of the product upper surface layer. As the fluid spray spreads it will entrain environmental gasses via the well known Coanda effect. Consequently the treatment fluid^"is more dilute at the spray edges than in the centre and as the spray moves away from its source origin the average dilution increases.

The effect of dilution of steam is tabled in various text books which show that while undiluted saturated steam has an expected temperature of 100^*C at atmospheric pressure, 10% dilution with air reduces the temperature to about 97'C, 40% dilution reduces it to about 86^*C and 80% to 60^*C.

The cylinder process method is expected to produce a product with a wide particle to particle temperature because of dilution of the fluid spray presented at the product mass surface treatment primarily of only the surface layers of the product mass and the further dilution of any treatment fluid penetrating the air gaps between product particles.

Figure 4 shows a cross section of a treatment screw conveyor as GB Patent 1290613. The general effects of fluid presentation, dilution and environmental gas displacement are the same as those for the cylinder case. Since in this case the fluid spray origin is closer to the product the effects of dilution as the spray moves towards the product are reduced.

The arrangement shown in Figure 5 serves for steam treatment during vibratory transport of the product. In the disclosure of GB Patent No. 2138668 the detrimental effects of dilution of the treatment fluid is recognised in that steps are taken to prevent air entering the treatment zone. It is further suggested that a possible prevention method could be the use of a conventional cell wheel (sometimes called an air lock). However, some level of dilution is still expected which recommends the use of steam at temperatures of between 126 and 184^*C in order to achieve a product temperature of 103"C to 110"C.

Particles of product are lifted from the base of the vibrator by high temperature high pressure steam jets and come into contact with the upper vibrating surface where they then vibrate towards the conveyor discharge point.

The product is initially subjected to the temperature of the steam at its exit from the jets in the base of the vibrator. This could be a temperature of up to 163^*C. During its transport along the underside of a vibrating lid the inner product gasses are filled with a dilute mixture of treatment fluid and environmental gas and the situation resembles that experienced in the cylinder method. Consequently, the exposed layer which is now the lower product face, receives little new treatment. This situation is represented in Figure 5. The effects of presentation and fluid dilution result in a wide expected final temperature range (as in the case of the cylinder and the traditional screw), but with the additional detriment that the product has also initially been subject to a very high temperature.

The rate at which a product transports a vibratory conveyor is dependent on a number of factors, some of which are constant such as the amplitude of the vibration, some of which are variable such as the density, size and shape of the product. Even with a product type such as tobacco stem or CRS, transport rates are expected to vary. This introduces additional variation into the temperature and time history of the product during treatment.

An object of the present invention is to provide a method which enables the treatment of fluid to displace environmental gas from between the product particles and has a minimal risk of dilution of the treatment fluid by environmental gas. A further object is to enable the product to experience a uniform temperature time exposure.

According to the invention there is provided an apparatus for applying fluid to vegetable materials, especially tobacco, comprising an elongate chamber disposed substantially horizontally, a rotary screw mounted so as to rotate in close proximity to the wall of the chamber, inlet means through which the material to be processed is fed into the chamber,* outlet means for delivering the treated product from the downstream end of the chamber, and a plurality of steam inlets arranged in the wall of the chamber for directing steam into the material from beneath.

Further according to the invention there is provided a method of fluid treatment of vegetable material , especially tobacco, comprising conveying the material to be treated along a chamber by means of a screw rotating in close proximity to the wall of the chamber and passing steam into the material from beneath to fluidise or partially fluidise the material permitting rapid progress of the steam through the material to displace air.

As shown in Figures 6 and 7, the conditioning apparatus comprises a substantially horizontally disposed elongate trough but slightly inclined to the horizontal by 3° shown generally at 10 having a lowermost portion 11 of semi- cylindrical construction surmounted by contiguous side walls 12, 12' to form the uppermost portion of the trough. A lid 13 having interlocking sections encloses the entire trough. A feed screw 14 is mounted at its ends on bearings 15, 16 and is driven through a coupling 17, gearbox 18, and belts 19 by a motor 20. The screw is positioned so as to rotate in close proximity to the cylindrical portion 11 of the trough.

An inlet hopper 21 serving to feed material (tobacco) to be processed to the trough is mounted above the upper end of the screw 14 and an outlet chute 22 provided beneath the lower end of the screw for delivery of the processed material. Beneath the trough in the region between the hopper 21 and chute 22 is arranged a part-cylindrical plenum chamber 23. The latter has a larger diameter than the part cylindrical portion of the trough and is connected in sealing manner (e.g. by welding) along the juncture of the lower portion 11 and the side walls 12, 12'.

The plenum chamber 23 has a steam inlet 24, air vents 25 (only one shown), a condensate drain 26, and is strengthened by one or more stiffening webs 27 having apertures 28.

The lower portion 11 of the trough is provided with steam inlet nozzles 30 arranged in rows longitudinally of the cylindrical portion within a circumferential arc extending over 10-40^* from the vertical. The nozzles are thereby disposed approximately centrally of the material T which rides up on one side of the trough during rotation of the screw.

The nozzles are accessible through a series of removable cover plates 31 mounted on flanges 32 attached to the plenum chamber 23.

The plenum chamber provides heat for heating the whole lower surface of the product as well as a source for the conditioning steam.

A further series of nozzles 33 is mounted on a water feed manifold pipe 34 secured to the inside of the side walls 12'. The nozzles are positioned so as to spray water over the material at the region thereof which is at the highest level .

Washdown water may be provided by way of a spray bar 35.

By the use of steam jets in the screw trough base the carpet of material may be semi-fluidised thus enabling rapid progress of the steam through the product carpet to displace air. However, by keeping the trough less than 30% full, the product is constrained to advance through the screw at the rate dictated by the flight rotation.

AC Tines^may be attached to the flights to circulate the product within itself which ensures that water sprayed on to the upper surface of the carpet is adequately mixed throughout the product.

Since the product has a fixed transit time through the screw and a plurality of jets in the trough base distribution of steam through the product is very even. This means that the range of temperatures and moisture achieved on a particle to particle basis is greatly reduced. When this is considered in the context of the enhancement of controlled steam or similar fluid treatment processes, the ability to obtain a consistent temperature and moisture with little deviation means that:

1. Due to too high product temperatures degradation is reduced.

2. Due to lower product temperatures or moisture under enhancement is reduced. - 12 - The treatment fluid is presented from a wide source near to the product rather than from a distant point or line source and has a defined controlled treatment time.

Claims

- 13 - CLAIMS :

1. Apparatus for applying fluid to vegetable materials, especially tobacco, comprising an elongate chamber (10) disposed substantially horizontally, a rotary screw (14) mounted so as to rotate in close proximity to the wall of the chamber, inlet means (21) through which the material to be processed is fed into the chamber, outlet means (22) for delivering the treated product from the downstream end of the chamber, and a plurality of steam inlets (30) arranged in the wall of the chamber for directing steam into the material from beneath.

2. Apparatus as claimed in claim 1, wherein the chamber is a trough of which a substantial portion at the lowermost region is cylindrical, said inlets (30) being arranged in the cylindrical portion.

3. Apparatus as claimed in claim 1 or 2, wherein the nozzles are disposed approximately centrally in relation to the material which has ridden up on one side during rotation of the screw.

4. Apparatus as claimed in claim 1, 2 or 3, wherein the steam inlets (30) are disposed within a circumferential arc extending 10-40^* from the vertical downstream thereof.

5. Apparatus as claimed in claims 1 or 2, wherein further inlets (33) are provided in the uppermost region of the trough for directing steam or water spray down onto the material .

6. Apparatus as claimed in claim 2, wherein tines (14a) are attached to the screw to circulate the material within itself.

7. A method of fluid treatment of vegetable material, especially tobacco, comprising conveying the material to be treated along a chamber by means of a screw rotating in close proximity to the wall of the chamber and passing steam into the material from beneath to fluidise or partially fluidise the material permitting rapid progress of the steam through the material to displace air.

8. A method of fluid treatment as claimed in claim 7, wherein the steam is passed into the chamber via nozzles arranged approximately centrally of the material which has ridden up due to the rotation of the screw.

9. A method as claimed in claim 7 or 8, wherein the steam is fed into the underside of the chamber at a region defined by a c rcumferential arc extending over 10-40^* from the vertical .

10. A method as claimed in claim 7, 8 or 9, wherein the trough is maintained less than 30% full whereby the material is constrained to advance along the trough at a rate dictated Jby the speed of rotation of the screw.

11. A method as claimed in any of claims 7 to 10, wherein water is sprayed by further nozzles disposed above the material .

12. A method as claimed in any one of claims 1 to 11, wherein the material is circulated within itself by tines attached to the screw to mix the water throughout the material.