DEHYDRATION APPARATUS AND METHOD

FIELD OF THE INVENTION

The present invention is generally in the field of drying techniques, and relates to a dehydration apparatus and method.

BACKGROUND OF THE INVENTION

Various dehydration techniques have been developed. For example, U.S. patent No. 4,479,310 discloses a dehydration apparatus typically used for the dehydration of leaves. Apparatuses similar to said that of U.S. 4,479,310 are known in the market and are used e.g. for the dehydration of parsley.

The capacity of one known in the art apparatus is 2,000 kg parsley per hour, wherein fresh product is fed to the apparatus to be blown by hot air while conveyed via a complex of several floors of stainless steel conveyor grids through which the hot air is blown from the bottom to the top of the apparatus. Fresh product fed to the inlet of the apparatus reaches its outlet about an hour later, with about 5% remaining wet. Through the process, the parsley product loses its fresh-green color. Since the process lasts about an hour, the temperature of hot air should be kept sufficiently low in order to avoid burn damages to the product resulting from its long exposure to heat. The temperature of hot air is thus normally kept in the range of about between 50 and 80 Celsius degrees, a temperature which is too low to cause burn damage, but is also insufficient to destroy undesired microorganisms normally present in the pre-treated product. Accordingly the product typically has to be prepared for dehydration by a

preceding disinfection step in order to destroy bacteria and spores which otherwise will damage product quality and will shorten its shelf life term. In the preceding step, the raw material is to be exposed (in a separate device) for a short period to a temperature of about 150 Celsius degrees or more, believed to be sufficient for destroying any parasite microorganisms accompanying it.

The dimensions of the concerned known device are about 50 meters length, 5 meters width and 4 meters height. Stainless steel conveyor grids are not low priced, so four or five floors of conveyors plus their motors and motion transmission mechanism make the apparatus too expensive. Adding delivery and erection costs, the cost of factory volume occupied by the apparatus, and maintenance expenses involved in keeping in working condition the huge construction of thousands of square meters of conveyor grids and other moving parts, all these factors emphasize the motivation and challenge in developing an alternative device that can address at least part, if not all of the aforementioned drawbacks of the concerned apparatus, to which the present invention is aimed.

SUMMARY OF THE INVENTION

The present invention relates to a dehydration device especially useful for reducing the wetness of leaf vegetables such as parsley. The dehydration device of the present invention comprises a dehydration cell having a product inlet, a product outlet, and a bottom plate with a plurality of apertures forming gas permeable open areas, wherein said apertures are arranged such that the open areas gradually decrease in a direction between first and second ends of the plate along the plate's width such that, when gas is forced into the cell through the plurality of apertures, a plurality of respective separate gas jets eject upwardly from the plate with a gas flow rate decreasing in said direction along the plate thus creating a global directional circulation of the gas throughout the cell and a plurality of local circulations of said gas inside the cell. The local circulations are formed due to the pressure differentiations created either between individual air

jets and the space surrounding them above the respective plate region, or between neighboring jet regions of different flow rate.

In most cases, dehydration will be carried put using hot air for creating circulation and for obtaining the required intensive mass/temperature exchange rates. In some cases, however, it might be preferred to use other fluid types. It should thus be appreciated that the present invention is not restricted to the use of hot air. Other gas types may be used as well, should one so require.

According to a first preferred embodiment of the invention, the gradual decrease in floor plate's open area results from a decrease in the average diameter of the apertures in the respective bottom portions. For example, the diameter of apertures near the first end of the plate may be between about 4 and 5 millimeters and gradually decrease to about 2-3 millimeters for the apertures near the second end of the plate. The average distance between the centers of adjacent apertures is preferably about 30 millimeters, and the apertures are preferably arranged in hexagonal arrays, with a 30 mm distance maintained between each aperture and all the adjacent ones surrounding it. According to the preferred embodiment, the plate width (a distance between the first and second ends) is about 1.7 meters.

It should be appreciated that the width of the device influences the cell quality of sorting between product amounts of different dehydration stages. The length of the device, that is its dimension along an axis perpendicular to the width and along which the flow rate of air flow across the plate remains substantially invariable, is not restricted, and is to be determined according to the required work capacity. For example, a device of 1.7 meters width and having a length of about 5 meters has a dehydration capacity of about 1,000 kg raw product parsley per 1 hour of operation through which the product is dehydrated from about 90% wetness to about 5%. It should be made clear, however, that the average stay of product inside the dehydration cell is approximately only 2-3 minutes, which permits exposing the product to temperatures around 200 Celsius degrees, without damaging the product. Accordingly, it can be appreciated that

the average weight of product present inside the cell at any given moment is about 35 - 50 kg.

According to another embodiment of the invention, the gradual decrease in the plate's open area results from a decrease in the average number of apertures per unit area in respective regions of the bottom plate.

According to yet another embodiment, the gradual decrease in the plate's open area results from a decrease in the average diameter of the apertures and/or reduction in the average number of apertures per unit area.

The cell is delimited at its top by a grid. This may be a net having apertures of about 1-2 millimeters in size. However, in order to prevent blockage of the net by the accumulation of ground-up product particles trapped in the apertures, which may influence the dynamic properties of the device, the device preferably comprise a plurality of parallel rods or wires spaced from one another with a gap of between about 1 and 2 millimeters. By having slots instead of apertures, the accumulation rate of product particles is reduced, and the cleaning (if necessary) of the grid becomes faster and easier.

According to some embodiments of the invention, the cell height from the plate to a top grid delimiting the cell from above, is between 1 and 1.5 meters.

According to some embodiments, the gas is hot air forced through the bottom plate into the cell from a gas supply plenum located underneath the plate (such that the plate serves as a ceiling to the supply plenum). The gas supply plenum accommodates hot air, preferably at an average temperature of about 150-220 Celsius degrees (for parsley, more preferably 200 Celsius degrees), and at an average pressure equivalent to the pressure of about 800 to 1000 millimeters water post.

The hot air supply plenum preferably receives the pressurized hot air from a blower and air (or gas) heater connected to an inlet of the supply plenum; said inlet is located underneath the floor plate.

The hot air may be formed from room temperature air heated by a burner being a part of the gas supply system in gas communication with the supply plenum (which as described is located underneath the plate).

The dehydration cell preferably further comprises a row of horizontally oriented nozzles located near the second end of the plate for injecting pressurized air (or other gas) having flow direction substantially parallel to the plate. This is useful for enhancing the flow of material through the device, by eliminating product accumulation at the corner of the device near the second end of the plate. For two main reasons, the product may tend (in some scenarios) to accumulate on said corner. One reason is that the upwardly oriented air jets erupting from smaller diameter apertures near the second end of the floor plate are of smaller flow rate thus having smaller swept capacity compared to the air jets erupting from the other plate portions. The other reason is that the global directional air circulation in the cell which has downward flowing direction from near the top of the cell towards the second end of the plate, causes certain amounts of product to fall down on the plate. By providing the horizontal air flow directed from said row of horizontally oriented nozzles adjacent and substantially parallel to the plate, the accumulation of product is eliminated and the flow of product throughout the device is enhanced.

The product inlet opening preferably extends above the plate lengthwise of its first end. Furthermore, the product outlet opening preferably extends lengthwise a second end of the top grid, delimiting the cell from above, and remotely from a first end of the top grid which is substantially straight above the first end of the plate. The product outlet opening communicates with an inverted U-shaped tunnel delivering the dehydrated product out of the device. Such arrangement of the inlet and outlet of the product cooperates with the unique air

circulation properties of the cell to generate a fully automated flow of the product from the inlet to the outlet of the cell, wherein a fresh wet product enters the cell through the inlet while dehydrated prepared product exits the cell through the outlet in continuous endless flow without requiring any moving parts or additional conveying mechanism. According to this inlet and outlet configuration, the fresh product is continuously fed to the product inlet at a predetermined rate. Preferably, the product inlet opening has an inlet slope leading the supply of the fresh product from outside of the cell to the inlet opening, simply by a gravity force. When the fresh product enters the cell, it is immediately swept upwardly by means of the highest flow rate air jets erupting from the plate near its first end and where the inlet opening is located, to join the global air circulation in the cell. The swept amount of product clears place for additional fresh product reaching at the opening.

In the cell, the swept product circulates through the global air circulation, while portions of the product diverge from the global circulation to join the local air circulations formed by the air jets injected from the plate in gradually decreasing flow rate from the first end of the plate to its second end.

Since the wet fresh product weighs more than the dehydrated one (and furthermore since partially dehydrated product containing predetermined wet percentage weighs more than partially dehydrated product containing less wet) it is statistically approved that more wet product will sooner diverge by gravity from the global air flow, falling down from its path near the top of the cell to join the local air circulations formed by the upwardly erupting air jet, while less wet product will continue its motion with the global air flow to greater extents along the cell, before falling down to join local circulations. This way, the product amounts of a whole spectrum of wet percentage simultaneously being treated in the cell, are dynamically and automatically sorted according to wetness, such that on average most wet product becomes circulated and most intensively dehydrated by the most flow rate flows of air in the cell, while less wet (or

partially dehydrated) product becomes circulated and further dehydrated by least flow rate flows of air.

During the above described dehydration process, and simultaneously with the amounts of fresh product entering the cell in some average predetermined rate, similar amounts of the prepared dry product automatically exit the cell through the outlet opening. The automatic release of prepared product amounts from the cell is achieved by positioning the outlet opening at the top portion of the cell, near the second end of the top grid which is located substantially straight above the second end of the plate. This location is at a region of the global circulation where the global air flow ends its path segment adjacent to the top of the cell and starts turning down towards the second end of the plate. During normal operation of the device, only lightweight product pieces reach that far with global circulation, while heavier product pieces diverge from the global air flow by gravity and fall down to join the local circulations before they are allowed to reach that far. Said lightweight product pieces, which are the most dehydrated and prepared ones, escape the cell while being carried by a breeze of hot air flowing through the outlet opening.

According to the preferred embodiments of the invention, the outlet opening is adjustable, such that the amount of prepared product escaping the cell is controllable. As will be further described, the adjustment can be made by a pivoting flap determining what thickness extent of the global flow measured from the top of the cell will be allowed to reach the outlet. By this way, only product pieces swept by the uppermost extent of the global flow can escape the cell. By periodically examining the properties (e.g., wetness, color, etc.) of the product pieces thus released from the cell, it is possible to determine whether or not the product stays optimal time inside the cell. In case the product samples are found to be scorched or too dried, the flap (and according to other embodiments, other types of adjustable covers) can be readjusted to increase the product releasing rate, thus shortening the average stay of product pieces inside the cell.

In case the product samples are found to be too wet, the flap can be readjusted to decrease the product releasing rate, thus lengthening the average stay period of product pieces inside the cell.

According to one basic exemplary embodiment, the product inlet opening is arranged lengthwise the entirety of a rear wall of the cell and the product outlet opening is arranged lengthwise along the entirety of a front wall of the cell (the front and rear walls of the cell corresponding to the second and first ends of the plate). The plate extends between the rear wall and the front wall with the plate's open area decreasing gradually from the plate's end near the rear wall to its opposite end near the front wall. The cell further comprises two side walls extending respectively from both sides of the cell between the front wall and the rear wall. Since the cross section of the cell is substantially the same at any vertical plane parallel to the side walls, the flow of product across the cell between the front and the rear wall or vice versa is in paths substantially perpendicular to these walls and substantially parallel to the side walls. This arrangement is especially useful for relatively short cells having the side walls distant from one another a length smaller than a distance between the front and rear walls.

In larger cells whose sidewalls are significantly distant from one another, the product inlet opening and the product outlet opening do not have to extend along the entirety of the rear and of the front walls. Instead, the product inlet opening may be located in the rear wall near one of the side walls, while the product outlet opening may be located in the front wall near the opposite side wall, both openings extending along only short portions of the rear and front walls respectively. As can be appreciated, in this embodiment, the cross section of the cell varies along a vertical plane parallel to the side walls. Actually, three different types of vertical cross section geometry are distinguishable in this cell embodiment. In the first type, taken near the first side wall, the section crosses via the product inlet opening, but not via the product outlet opening (which is

located near the opposite cell's side wall, remotely from the product inlet). In the second type, taken near the second side wall opposite the first side, the section crosses via the product outlet opening, but not via the product inlet opening (which is located near the first cell's side wall, remotely from the product outlet). In the third type, taken at cell's center portion, the section crosses neither the inlet opening nor the outlet opening (which both are located remotely from the center portion, near the side walls).

The above-described asymmetric design of the cell adds to the global air flow circulation in the cell a diagonal flow component resulting from the air swept from the outside of the cell with the product entering through the product inlet and from the air leaving the cell through the outlet opening. Accordingly, the product flow through the cell will also have a diagonal motion component, and the global flow path of product through the cell from the inlet to the outlet will be spiral.

hi order to improve statistics and allow all the product particles to remain inside the cell for substantially the same time periods (thus providing homogenously dehydrated product), the cell may be provided with flow deflectors located near its ceiling. The deflectors, e.g. partitions made of sheet metal plates, can be positioned parallel to one another yet diagonally to the cell walls, with a predetermined gap between each pair of adjacent deflectors. The deflectors partition the cell into a plurality of sub-cells communicating with one another beneath the deflectors where global air circulation is weak while local air circulation is more dominant. Furthermore, the deflectors have a diagonal orientation respective to the cell's walls such that, for each deflector, the end of the deflector at the front wall side is closer to the respective side wall which is near the product inlet than the opposite end of the same deflector. Due to this diagonal orientation, the global flow in each sub-cell is deflected away from the outlet opening, such that the product quantities which were expected to advance with the spiral global flow from the product inlet towards the product outlet in

some hypothetic flow rate (i.e. in case there were no deflectors) will now be delayed due to the deflection so that their actual flow rate will be smaller.

The device may be further provided with a heat exchanging mechanism allowing for gaining heat from hot and wet waste air escaping from above the cell through an air permeable top of the cell (e.g. the aforementioned net or grid) and using it for preliminary heating fresh air to be further heated e.g. by a burner, and then forced through the apertures in the plate into the cell.

A novel dehydration method especially useful for reducing wetness of leaf vegetables such as parsley product is also within the scope of the present invention. The method comprises exposing the product to a plurality of intensive local air circulations formed inside a predetermined dehydration space and having gradually decreasing flow rate from a first end of the space towards a second end of the space remote from said first end, and to a global intensive air circulation formed throughout said space as a result of the gradually decreasing flow rate of the local circulations.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non- limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 is a vertical cross section view of an example of a dehydration device according to the present invention.

Fig. 2 illustrates an example of dynamic equilibrium in the device of Fig. 1, during a dehydration process.

Fig. 3 illustrates a general top view of the device of Fig. 1.

Fig. 4 illustrates a general top view of some portions of the bottom plate of the device of Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 illustrates a vertical cross section view of a dehydration device according to an example of the present invention. The cross section is taken at two remote vertical planes indicated by arrows A-B of Fig. 3.

The device 1 includes a dehydration cell 4 having a product inlet 60, a product outlet 62, and a bottom plate 5. The latter is formed with a plurality of apertures - apertures 6, 7, 8, 9 and 10 being seen in the figure. The apertures form gas permeable open areas, and are arranged such that the open areas gradually decrease in a direction between first and second ends 25 and 26 of the plate along the plate's width. This arrangement of apertures results in that, when gas is forced into the cell through the plurality of apertures, a plurality of respective separate gas jets 16, 17, 18, 19 and 20 eject upwardly from the plate 5 with a gas flow rate decreasing in said direction along the plate, thus creating a global directional circulation (shown by arrows 30-39) of the gas throughout the cell and a plurality of local circulations of said gas inside the cell.

The cell 4 is defined by the bottom plate 5, a top grid 40, front and rear walls 14 and 13, and side walls (90 and 91 in Fig. 3). The device 1 further includes an air supply plenum 2 communicating through a duct 3 with an air blower (not illustrated) for receiving pressurized hot air. The air from the blower is heated on its way to the plenum 2 by means of a burner (not illustrated). The plenum 2 communicates with the dehydration cell 4, through the plurality of apertures forming gas permeable open areas in a top barrier of the plenum being the bottom plate 5 of the cell 4. The open areas of respective portions of the plate decrease gradually from a region near the first end 25 of the plate towards a region near the second end 26 of the plate remote from said first end 25.

According to the illustrated embodiment, the gradual decrease in the plate's open area results from a decrease in the average diameter of the apertures 10, 9, 8, 7, 6, in the respective portions of the plate. For example, a plurality of apertures represented symbolically by the aperture 10, each having a diameter of about 4 millimeters, are arranged in an array (one- or two-dimensional) near the first end 25 of the plate 5. Another plurality of apertures, represented symbolically by the apertures 9, each having a 3.5 mm diameter, are arranged in an array near the first array of the aperture 10. Another array of apertures represented by apertures 8 and having a 3 mm diameter is located between the apertures' array 9 and another array of apertures represented by the apertures 7 having a 2.5 mm diameter.

As described, the apertures become smaller as they approach the second end 26 of the floor plate. Thus, the last array of apertures (closest to the second end 26) represented by apertures 6 comprises apertures of a diameter of 2 mm each. Said gradual decrease in the diameter of the apertures from the first end 25 of the plate 5 towards the second and 26, results in respective gradual decrease in the flow rate of air through the different open area regions in the plate. The air jets injected from the different arrays (or groups) of cross apertures are represented by inverted truncated conic shapes 20, 19, 18, 17, and 16 delimited by respective pairs of inclined dotted lines. The decreasing width and height of the inverted truncated conic shapes 20, 19, 18, 17, and 16 from right to left, emphasizes the decreasing flow rate of air across the plate, from right to left. Due to this unique air flow design, the global air circulation throughout the cell 4 is generated, as described by arrows 30 to 39. As shown by these arrows, the direction of the global circulation in the cell is from above the first end 25 of the plate and upwards towards the top of the cell, then turning left adjacent to the grid 40, and downwards towards the second end 26 of the plate 5, thereafter to the right adjacent the plate 5, and again upwards from the first end 25 of the plate, repeating said path recurrently, hi this figure, the circulatory flow path seems to be parallel to the plane of drawing. This may be true for some

embodiments of the invention. However, as will be explained in detail later on in the description with reference to Fig. 3, the circulation path may further include flow components in directions angled to the plane of drawing. In certain cases, this will result in spiral-like global air flow throughout the cell.

The cell is delimited from above by a grid 40, through which air is constantly released from the cell during operation as to maintain a dynamic equilibrium in the cell while fresh hot air is constantly streamed into it through the bottom plate. Arrows 41 to 52 represent the release of air through the grid. A heat exchanger 56, which may be of any known suitable type, may be useful for saving energy, and is mounted above the cell's top grid 40. The heat exchanger 56 is comprised of an array of air pipes 54 opened at their left end to receive fresh air represented by array of arrows 53. At their right end, the pipes 54 open to a duct 55 in air communication with a blower (not illustrated). The fresh air 53 may be sucked into and through pipes 54 to the blower by the suction power of the blower itself, and alternatively or in order to boost the blower suction, by means of an additional suction device. During the flow of fresh air into the pipes 54 the air is heated by the hot air released from the cell 4 through the top grid 40, the flow of which is indicated by arrows 41 to 48. This way, part of the heat losses resulting from the exhausting of hot air out of the cell, is recoverable. The hot air released through the top opening 57 of the heat exchanger 56 as indicated by arrows 49 to 52, is of a lower temperature than that of the air in the cell since a part of the heat is transferred to the fresh air in pipes 54. The top opening 57 of the heat exchanger 56 preferably communicates with a flue, for delivering the exhausted air out of the plant building.

The cell 4 further comprises a product inlet opening 60 made along the rear wall 13 of the cell 4, through which a fresh product is to be fed into the device for dehydration. According to the illustrated embodiment, the product inlet opening 60 is located at the bottom end of the rear wall 13 of the cell, right above the first end 25 of the plate 5. Further, according to the illustrated

embodiment, a diagonally oriented feeding tray 61 is provided with lower end thereof attached to the lower end of the product inlet opening 60, such that the fresh product may be poured as indicated by arrow 68 from a feeding conveyor to be guided by the inlet slope tray 61 into the cell 4 through the opening 60. When a new amount of fresh wet product is being fed, it is immediately sucked into the cell due to under-pressure near the opening 60 resulting from the high velocity air jets 20 injected from the floor plate 5 near the inlet opening 60, then swept upwardly by the greatest flow rate air jets 20 (and may be also by some of the adjacent air jets 19 of a smaller flow rate) to join the global circulation in the cell indicated by arrows 30 to 39, wherein arrows 32 to 35 indicate an upper part of the global circulation while arrows 37 to 39 and 30 indicate a lower part thereof. Whenever the fresh product is still wet (and thus heavier), greater amounts of it will diverge from the upper part of the global circulation by gravity and fall down as indicated by arrows 70 to 72 and 76 to 78, to join intensive local air circulations resulting from the upwardly oriented air jets injected through the apertures of the plate 5 at the respective regions of fall. As can be appreciated, heavier product will tend to diverge from the global circulation earlier, i.e. it will tend to fall down in the path indicated by arrow 70, while lighter product will tend to keep with the global circulation e.g. as indicated by arrows 33, 34, i.e. it will tend to fall at the regions indicated by arrows 71, 72. This way, the device of the present invention sorts the product automatically for exposing it to heat and mass exchange in correlation with its different wetness degrees during the dehydration process.

As mentioned above, the width of the device influences the sorting quality of the cell between product amounts of different wetness stages. A width of substantially not less than 1.7 meters was found to be substantially appropriate for good sorting quality.

The intensive circulations of the product through both the global and the local hot air flows, result in an intensive heat and mass exchange and in a fast

dehydration process. The actual duration of the dehydration process depends on the specific product and on the parameters and adjustments of the specific device being used. Therefore, optimization of the process, its duration, and the resulting qualities of the prepared product may be achieved based on preliminary experiments to be made by a designer when adapting a specific device to a specific dehydration application. Although two or three minutes process duration (i.e. the average lasting time of individual product item inside the cell) may be typical for a device of the present invention, this time may be shortened or lengthened (even significantly, e.g. to about 15 minutes) if so required. The change may be carried out by changing the parameters of the device, e.g. its dimensions, the air pressure in the plenum, the temperature of the hot air/gas, the open area of the plate, the dimensions of the product outlet opening or any other device parameters.

In order to enhance global circulation in the region adjacent to the second end 26 of the plate 5, where the movement may expected to be less intensive due to the lower flow rate of air jets at this region, there is provided an elevated member 69 lengthwise the second end 26 of the plate 5, with a row of horizontally oriented apertures 66, which inject substantially horizontal air jets 15. Furthermore, one or two rows of apertures are missing at the second end of the plate (i.e. the plate has no apertures near its second end 26), such that there is no interference of upwardly oriented air jets with the effect of the horizontally oriented air jets at this region. Also, the front wall 14 of the cell 4 has an inclined orientation for guiding the product to reach a region of less pressure created by the high velocity air jets 15 injected horizontally from the horizontally oriented apertures 66. By this arrangement, the accumulation of product on the plate 5 at the low flow rate regions is eliminated, and the continuity of the product circulation with the global air circulation in the cell is maintained. According to the illustrated embodiment, the horizontally oriented apertures 66 are of a diameter of between 3.5 and 4.5 millimeters, and preferably of about 4 millimeters diameter. A gap formed between the bottom end of the diagonally

oriented front wall 14 and the elevated member 69 near the second end 26 of the floor plate 5 is utilized to allow access into the cell through a service door 67 formed lengthwise said gap. When the need arises, the service door 67 may be opened allowing the device operator to reach the cell's inside and perform the required treatment (e.g. cleaning the plate or removing stacked product).

The inner surfaces of the cell are preferably smooth, and the corners of the cell are preferably round, in order to avoid product sticking and accumulation. The walls of the device are preferably provided with heat isolation in order to reduce energy loss and also in order to protect surroundings and factory workers from heat damage.

The side walls of the device are preferably provided with transparent windows enabling inspection of the dehydration process.

Due to the comparably short exposure time of the product to the dehydration process, hot air of temperatures of between about 130 to 220 Celsius degrees (and more preferably between 170 and 200 Celsius degrees) may be used without burning or damaging the product. The exposure of the product to such temperatures is sufficient to neutralize any microorganisms, bacteria or spores, suspected to be present in the product, thus improving product quality and extending its shelf life term while eliminating the need for a separate disinfection process. Furthermore, the relatively short process duration reduces the pulverization of the product thus improving the uniformity of the prepared product particles and reducing product loss. With the reduction in weight of the product by losing wetness during the process, its time in the global circulation path becomes longer, while gravity effects it to diverge and fall down increasingly further from the first end of the plate, and increasingly nearer the top of the cell. As a result, when the product is dried and prepared it follows the global circulation throughout the cell with ever growing amounts of it reaching the product outlet opening 62 located near a second end 73 of the top grid 40, and is evacuated from the cell 4 carried by part of the hot air breeze being

continuously released from the cell (along the path indicated by arrows 80 to 82) due to the continuous stream of. new hot air forced into the cell across the plate. An inverted U shaped funnel 65 is attached to the product outlet opening 62 for guiding the prepared product e.g. into a container (not illustrated) being part of an outlet conveying system or of a product weighing and packaging system.

The product outlet opening 62 is adjustable by means of a pivoting flap 63 whose orientation can be determined by a butterfly screw 64 (or alternatively by any other acceptable mechanism). The orientation of the flap determines the dimensions of the gap 75 through which the prepared product may escape the cell. When the gap is adjusted to be small, the rate of release of product is slow, thus on average more product stays in the cell and is exposed to the dehydration process. When the gap is adjusted to be wider, and thus the rate of release of product becomes greater, the product stays on average less in the cell and is less exposed to the dehydration process. Accordingly, by sampling and checking the prepared product it is possible to determine whether or not the flap is adjusted properly, and to optimize the process and in turn the quality of the prepared product by adjusting the flap more accurately, if so required. Furthermore, at the beginning of the dehydration process, wherein a few minutes of dehydration are required before the first amounts of product are prepared, the flap 63 may be adjusted by the butterfly screw 64 to totally close the product outlet, in order to allow build-up of the required dynamic equilibrium inside the cell. After such an initial period, the flap 63 may be opened and adjusted such that there will be substantially equal amounts of prepared product evacuated through the outlet and of fresh product fed through the inlet.

As can be observed, there is a gap between the feeding slope tray 61 and between the plate 5, ending with opening 83. Said gap may be provided with a door, if so desired, and alternatively the height of the feeding slope tray 61 from above the plate 5 may be adjustable such that if so desired the lower end of the tray 61 may be brought to a contact with the end of the plate, thus canceling

the opening 83. The opening 83 is useful for automatic removal of parsley stems from the cell. The inventor has found that during the dehydration process the parsley stems, which become separated from the leaves, tend to accumulate on the plate, and thus by providing said gap and said opening 83, the stems may automatically be removed from the cell propelled by a breeze of hot air being part of the global air circulation in the cell. This way, the prepared product evacuated through the product outlet 62 requires no further sorting for separating stems.

Fig. 2 illustrates an example of dynamic equilibrium in the device of Fig. 1, during the dehydration process.

Fig. 3 illustrates a transverse cross section view of the device of Fig. 1, taken at the horizontal plane marked by arrows C-C of Fig. 1. The device 1 includes an air supply plenum (not seen in this Fig.) located beneath the plate 5 and communicating through the duct 3 with air blower (not illustrated) for receiving pressurized hot air. The air from the blower is heated on its way to the plenum by means of a burner (not illustrated). The plenum communicates with the dehydration cell 4 located above the plate 5, through the plurality of apertures forming gas permeable open areas in the plate 5. As described above, the open areas of respective portions of the plate decrease gradually in a direction along the plate, from near the first end 25 of the plate towards near the second end 26 of the plate remote from said first end 25. Said gradual decrease in the diameter of the plate's apertures results in a respective gradual decrease in the flow rate of air flowing through the different open area regions in the plate. Due to this unique air flow design, global air circulation throughout the cell is generated. The direction of this global circulation in the cell is from near the product inlet above the first end 25 of the plate and upwards towards the top of the cell, then turning left adjacent to the cell ceiling, and downwards from above the second end 26 of the plate towards the plate 5, thereafter to the right adjacent to the plate 5, and again upwards from above the first end 25, repeating said path recurrently.

The cell includes a product inlet opening made along a portion of the rear wall 13 against the product inlet tray 61 through which a fresh product is to be fed into the device for dehydration.

In the example of Fig. 3, a large cell design is used, having side walls 90 and 91 which are significantly distant from one another. In such a large cell, the product inlet opening and the product outlet opening do not need to extend along the entirety of the quite long rear and front walls 13 and 14. Instead, the product inlet opening 60 is located in the rear wall 13 against the inlet tray 61 near the side wall 90, while the product outlet opening (62, not seen in this Fig.) is located in the front wall 14 right above the adjustable flap 63, near the opposite side wall 91. The lengths of the inlet opening and of the outlet opening are substantially similar to the lengths of the inlet tray 61 and of the adjustable outlet flap 62, respectively. It can thus be appreciated according to this figure that both openings extend along only short portions of the rear and front walls respectively.

The cross sections of the cell in this embodiment are not the same along any chosen vertical plane parallel to the side walls 90 and 91. Actually, three different types of such vertical cross sections are distinguishable. In the first type, taken between the lines E-E near the side wall 90 the section crosses via the product inlet, but not via the product outlet opening (which is located near the cell's opposite side wall 91, remotely from the product inlet). In the second type, taken between the lines F-F near the side wall 91 the section crosses via the product outlet, but not via the product inlet (which is located near the first cell's side wall 90, remotely from the product outlet). In the third type, taken between the lines G-G at cell's center portion the section crosses neither through the inlet nor through the outlet (which are both located remotely from the center portion, near the side walls 90 and 91).

The asymmetric design of the cell in this embodiment adds to the global air flow circulation in the cell a diagonal flow component resulting from aix

swept from the outside of the cell with the product entering through the product inlet and from air leaving the cell through the outlet opening. Accordingly, the product flow through the cell will also have a diagonal motion component, and the global flow path of the product through the cell from the inlet to outlet will be spiral.

In order to improve statistics and allow most of the product particles to stay inside the cell for substantially identical time periods (thus providing the homogenously dehydrated product), the cell also includes a plurality of flow deflectors 101 to 105. The flow deflectors are located near the cell's ceiling, leaving a free space between their bottom and the plate, e.g., in case the cell's ceiling is located 150 cm above the plate and the deflectors are of about 25-30 cm height, there will remain a free space of about 120-125 cm between the bottom of each deflector and the plate. The deflectors, which in the illustrated embodiment are partitions made of sheet metal plates, are positioned parallel to one another yet diagonally to the cell walls, with a predetermined gap between the adjacent deflectors. Although the deflectors may extend about only 20% of the cell's height, from the point of view of the product flow they can be thought as partitioning the cell into a plurality of sub-cells. This is because the global flow of product through the cell is divided into a respective plurality of sub flows. Each such sub cell is defined between a pair of neighboring deflectors or between a side wall of the cell and a neighboring deflector. The sub cells communicate with one another beneath the deflectors where the global air circulation is weak while the local air circulations are more dominant. Furthermore, the deflectors have a diagonal orientation respective to the cell's walls such that the near front wall's end 101a-105a of each deflector is closer to the side wall 90 (which is near the product inlet) than the near rear wall's end 101b-105b of the same deflector. Due to this diagonal orientation, the global flow in each sub-cell is deflected away from the outlet opening, such that the product quantities which were expected to advance with the spiral global flow from the product inlet towards the product outlet in some hypothetic flow rate

(i.e. in case there were no deflectors) will now be delayed due to the deflection so that their actual flow rate will be smaller.

The flow of the product throughout the cell is spiral like. When fresh product is fed from a feeding conveyor onto the inlet slope of tray 61, it enters the cell through the inlet opening located in the rear wall 13 against the tray 61. Immediately after a new amount of fresh wet product is fed, it is sucked into the cell due to under-pressure near the opening resulting from high velocity air jets injected uprightly from the floor plate 5 near the inlet opening. The fresh product is then swept upwardly by the air jets adjacent to the inlet (and may be also by some further adjacent less great flow rate air jets) to join the upper part of the global circulation in the cell indicated by arrows 32 to 35 and then join the lower part of the global circulation indicated by arrows 37 to 39 and 30. As can be appreciated, the upper part of the global circulation narrows as it comes closer to the front wall 14, due to the diagonal orientation of the deflectors 101 -105. This causes the product swept by the upper part of the global circulation to deflect and converge toward the side wall 90. The product at the upper part of the global circulation thus becomes denser when approaching the front wall 14. Since the lower part of the cell is not partitioned by the deflectors, the product diverges when reaching the lower part of the global circulation, and thus flows somewhat diagonally as indicated by arrows 106-110. A similar converging and diverging process of the product flow is repeated with respect to each of the deflectors, until the product reaches the cell's end near the side wall 91, and thereafter it is released through the outlet.

Whenever the fresh product is still wet (and thus heavier), greater amounts of it will diverge from the upper part global circulation by gravity and fall down to join the intensive local circulations resulting from the upwardly oriented air jets injected through the apertures in the plate at the respective regions of fall. This way, the device of the present invention sorts the product

automatically, thus exposing it to heat and mass exchange in correlation with the product's different wetness degrees during the dehydration process.

In order to enhance global circulation in the region adjacent to the second end 26 of the plate 5, where the flow is expected to be less intensive due to the smaller flow rate of air jets at this region, there is provided an elevated member 69 lengthwise the second end 26 of the floor plate 5, with a row of horizontally oriented apertures 66, which inject substantially horizontal air jets 15. Furthermore, one or two rows of the apertures are missing at the second end of the plate such that there will be no interference of the upwardly oriented air jets with the effect of the horizontally oriented air jets at this region. Also, the front wall 14 of the cell 4, has a diagonal orientation for guiding the product to reach the low-pressure region created by the high velocity air jets 15 injected horizontally from the horizontally oriented apertures 66. By this arrangement, the accumulation of product on the plate at the regions of a low-rate air flow is eliminated, and the continuity of the product circulation with the global air circulation in the cell is maintained. According to the illustrated embodiment, the horizontally oriented apertures 66 are of a diameter of between 3.5 and 4.5 millimeters, and preferably of about 4 millimeters diameter. The side walls 90, 91 of the device are preferably provided with transparent windows 92 and 93 respectively, making the dehydration process visible.

Fig. 4 illustrates a general top view of some portions of the plate 5 of the device of Fig. 1. A plurality of through apertures 10, 9, 8, 7, 6 is formed in the plate. The apertures are arranged such that the open areas gradually decrease in a direction (as for example indicated by arrow R) along the plate. This decrease can be made by reducing the number of apertures per unit area in a direction along the plate, by reducing the area of each aperture or of groups of apertures in direction along the plate (i.e. without changing the number of apertures per unit area), or a combination thereof (i.e. reducing the number of apertures and their diameters). In the illustrated embodiment the number of

apertures per unit area remains unchanged, and the open areas of the respective plate portions decrease since the apertures are arranged in arrays, each of which contains apertures of greater diameter compared to a neighboring one in a specific direction along the plate.