WO2019166677A1 - Tunnel dehydrator - Google Patents

Abstract

The invention relates to a tunnel dehydrator having a compact and efficient design, for dehydrating all types of products, such as fruits, vegetables or meats, by means of the circulation of heated air. The dehydrator is formed from the usual parts of a tunnel dehydrator: a dehydration chamber (3) and a heating chamber (4); a separation (5) between chambers; a fan (13); a heat source (14); an air inlet (8) and an air outlet (9); trolleys with trays; and openings for the entry and exit of the trolleys. The designs of other dehydrators are improved by introducing: weighing scales (25, 26) to determine the product weight in real time; flow redirectors (31, 33) and a honeycomb panel (35) for achieving a uniform speed-profile distribution in the dehydration chamber, and therefore homogeneity in drying; an air-to-air heat exchanger (39) for using the energy of the air released into the atmosphere; and adjustable motorised air recirculation louvres (46), adjustable motorised air outlet louvres (47) and adjustable motorised air inlet louvres (48) for controlling the amount of recirculated and inlet/outlet air.

Description

TUNNEL TYPE DEHYDRATION TECHNICAL SECTOR

The present invention pertains to the field of dehydration by forced circulation of heated air, and more specifically to the field of tunnel type dehydrators.

The present invention relates to a tunnel-type dehydrating machine for dehydration of all kinds of products that can be dehydrated by the circulation of heated air, commonly fruits, vegetables and other food products. However, the present invention is not limited exclusively to food products and can be used to dehydrate other products whose water content can be extracted by circulation of heated air.

BACKGROUND OF THE INVENTION

Dehydration consists in the partial or total extraction of the water content of a product. Since ancient times dehydration has been used as a method of food preservation. The first forms of dehydration were to take advantage of the sun and wind to dry exposed food outdoors. This method is energy efficient, but it is not a reliable or fast way to get dehydrated products.

To solve the problems derived from the dehydration of products exposed to the sun and the wind, oven-like dehydration systems began to develop. One of these systems is the tunnel type dehydrator. Its main characteristics are described below.

Tunnel type dehydrators are characterized by having a structure that defines a tunnel with two levels: lower and upper. The lower level constitutes the dehydration chamber and the upper level constitutes the heating chamber. Both of them levels are separated by an insulated horizontal wall, with opening in the front and rear to connect the dehydration chamber with the heating chamber.

The admission of ambient air and the expulsion of air into the environment are carried out through openings that can be located in the dehydration chamber or in the heating chamber.

The dehydration chamber has two openings, typically at the ends, one for product introduction (inlet) and another for extraction (outlet). The product is deposited in trays placed in cars that advance in the dehydration chamber. The number of cars depends on the capacity of the dehydrator. These cars can be moved by mechanical means (mobile crane or pusher rails, for example). Another way of moving the product inside the dehydrator is through trays on motorized conveyor belts.

In a conventional tunnel type dehydrator a continuous process of product advance is carried out, that is, when the product of the final end (outlet) has reached its desired humidity level, it is extracted by that end and then fresh product is introduced through the initial end (entry).

Tunnel-type dehydrators can be of two types: parallel flow, where the product moves inside the dehydration chamber in the same direction and direction as the circulated air; and countercurrent flow, where the product advances inside the dehydration chamber in the same direction but in the opposite direction to the circulated air.

The air is circulated by an axial or centrifugal fan typically located in the heating chamber. The air is heated directly or indirectly by gas burner, electric heater or boiler. Depending on the type of energy source for heating the air, it may be located inside or outside the heating chamber.

There are machines similar to that described in the present invention that reflect the state of the art related thereto. The following are the references of some of them:

Document W02006 / 127790A1 refers to a tunnel type dehydrator whose main feature is its dual zone configuration: a counter-current flow zone and another parallel flow zone. Document US2007 / 0240328A1 refers to a parallel flow tunnel type dehydrator whose main feature is to add a door at the product end of the tunnel, force air recirculation by means of an additional fan and add a diverter hood in the chamber heating

These two dehydrators described and other existing ones not described have, among others, the following deficiencies: a) To know when the product has reached its optimum state of dehydration, they are based on the control of the average residence time of the product in the tunnel and in the supervision of an operator. This means obtaining the product with an approximate and inconsistent final humidity level. b) They cannot be used for discontinuous process of product advancement, that is, when the partial or complete loading of the tunnel is introduced and all the introduced load is removed when all of it has reached the desired humidity level. c) They do not provide a homogenous dehydration of the product, so the final product has a different level of humidity depending on the geometric position it occupies within the dehydration chamber. This is due to the non-uniformity of the distribution of the air velocity profile in the dehydration chamber. d) There is an air flow with potentially reusable energy that is expelled directly into the environment. e) They have low energy efficiency and, therefore, high energy consumption and high operating costs. f) High noise during dehydrator operation, mainly due to poor acoustic insulation of the dehydrator walls and configuration of indirect transmission of the motor to the fan by means of a belt or chain, leaving the engine out of the dehydrator.

EXPLANATION OF THE INVENTION

Therefore, the present invention has the task of presenting a tunnel type dehydrator capable of resolving the aforementioned deficiencies, in addition to providing other novelties.

The task is solved with a tunnel-type dehydrating machine according to claim 1. Other advantageous configurations of the apparatus are subject to the dependent claims. The present invention relates to a machine that is composed of the basic parts of a tunnel-type dehydrator: dehydration chamber, heating chamber, horizontal wall separating both chambers with openings at the ends to connect both chambers, openings for admission and expulsion of air from or into the environment, openings in the dehydration chamber for the entry and exit of the product, fan, energy source for air heating, and carts to support and move the product in the dehydrator. The whole body of the dehydrator is properly insulated from the outside thermally and acoustically.

There are two openings in the dehydration chamber, located on one side, typically the largest one. Each opening in the dehydration chamber can be considered as a product inlet or outlet, depending on the type of dehydration process carried out (parallel or countercurrent). Preferably, the opening is of the hinged door type. Each door has a window, with or without the possibility of opening, for product monitoring. This allows the product to be accessed visually or physically without assuming the loss of air from the dehydration chamber, and therefore of energy, which entails opening the door. In addition, although the door has emergency opening means from inside the dehydrator, the window allows you to see if there are people inside. The present dehydrating machine incorporates two weighing means or scales, preferably located in the dehydration chamber under the first car (considered as the car that receives the hottest and driest air from the heating chamber) and under the last car (considered like that car that receives the coldest and wettest air after having passed through the other cars). Thanks to this incorporation, the weight of the product contained in these cars is known at all times. Once the desired level of dehydration is known for a product, the weight to be lost with respect to the fresh product is known and, therefore, the final weight it must reach. In this way, you can know precisely when the product reaches the desired level of dehydration. This avoids having to rely on the residence time of the product in the dehydrator and in the supervision of an operator as indicators of the end of the process.

For a continuous product advance process (either parallel or countercurrent), the scale of the product inlet end is used to introduce the fresh weight contained in the car, that is, the initial product mass. The scale of the product outlet end is used to know the ideal moment for the extraction of the car, based on the final mass that the product must have to reach the desired level of dehydration.

For a discontinuous process of product advancement, the two scales of the input and output ends are used to know the ideal moment for the extraction of all the cars, based on the final mass that the product must have to reach the desired level of dehydration . Starting from a homogeneous distribution of fresh product dough on all trays and all cars, the one previously defined as the first car (the one that receives the hottest and driest air) will be the one that typically dehydrates before. On the other hand, the one previously defined as the last car (the one that receives cooler and wetter air) will be the one that typically dehydrates the last. Once this last car has been dehydrated, it can be affirmed that the cars located between the end cars will have also become dehydrated.

Changes of direction or section in ducts where air or other fluid flows cause a loss of uniformity of the velocity profile distribution in the vicinity of said change of direction or section. In a tunnel type dehydrator this effect is observed since there are changes of direction and section close to the dehydration chamber. The exposure of the product at different air speeds according to the trays it occupies means a difference in the speed of drying between them. To solve the problem of the lack of homogeneity of the level of dehydration of the final product in all trays and trolleys, the present invention incorporates various airflow redirectors located in two 90 ° elbows upstream of the dehydration chamber, and a honeycomb panel in the dehydration chamber (covering its entire section) before the first car. A 90 ° elbow is located at one end of the heating chamber, where the air flow passes from horizontal to vertical. The other 90 ° elbow is in the dehydration chamber, where the air flow goes from vertical to horizontal. The flow redirectors are configurable in shape (typically quarter circumference with or without straight section extension), size and position (they can be attached on rails to allow the movement of each flow redirector along the diagonal of the elbow). The honeycomb panel is configurable in hexagon dimension, sheet thickness and panel thickness. In this way, a uniform distribution of the velocity profile in the dehydration chamber is achieved, exposing the entire product to the same air velocity.

In the first tunnel-type dehydrators, after passing through all the cars, all the air in the dehydration chamber was expelled into the environment. This meant a significant loss of energy, since the expelled air still had drying potential and / or usable thermal energy. Subsequently, tunnels were designed that recirculated a percentage of that flow rate from the dehydration chamber to the heating chamber, mixing it with the air introduced from the environment, thus taking advantage of some of the energy that was previously discarded. However, there was still a flow of air expelled into the environment with potentially usable energy. The present invention, in addition to having means for the recirculation of part of the flow rate of the dehydration chamber, incorporates a means for the energy use of the air expelled into the environment. Said means consists of an air-to-air heat exchanger, without contact between flows. The air in the dehydration chamber that is not recirculated (before being expelled into the environment) and the ambient air (before being heated by the heating battery) are passed through the air-air heat exchanger. With this it is possible to raise the temperature of the ambient air before mixing with the recirculated air. This leads to significant energy savings, greatly reducing fuel consumption. To further increase energy efficiency with respect to other dehydrators, the present invention allows controlling the proportion of air in the dehydration chamber that is recirculated and, therefore, controlling the proportion of that which is renewed. This is achieved through adjustable air dampers: recirculation, inlet and outlet. This allows the renewal (admission of ambient air and expulsion of air into the environment) of the just and necessary amount of air to reduce humidity to the desired level inside the tunnel.

There are stages in the dehydration process in which the air in the dehydration chamber, after passing through the entire product, still has great drying potential and can be completely recirculated. With the adjustable air dampers, the present machine allows the total recirculation of the air, or what is the same, allows not to expel the environment or introduce from the environment. This allows a considerable fuel saving, since, the recirculated air when not mixing with ambient air, it is necessary to provide a lower thermal jump by the source of thermal energy.

The improvement of the energy efficiency of the present invention allows its use at partial loads and at different production rates without energy consumption being strongly affected.

The air is preferably circulated by a single axial fan located inside the heating chamber. To control and modify the speed of rotation a frequency inverter is incorporated. This commercial component allows the dehydrator to select several speeds of rotation, this being directly proportional to the flow of circulated air. The speed of rotation of the fan has a great effect on the consumption of electrical energy. Therefore, in cases where the fan speed can be reduced, energy efficiency will be improved.

The fan is driven by direct drive electric motor, that is, the motor shaft is directly coupled to the fan, without belt or chain. In this way, the motor-fan assembly can be located inside the heating chamber. Thanks to this and the insulation of rock wool the walls of the dehydrator achieves a considerable decrease of the noise captured from the outside of the dehydrator, favoring the health of the operators. The air is indirectly heated by a water-air heat exchanger located in the heating chamber. The source of energy for obtaining hot water is preferably a gas boiler, which can be supported on one side of the dehydrating machine itself.

The operating conditions inside the tunnel are monitored and controlled knowing the physical properties of the air through various temperature and / or humidity sensors located at the appropriate points. Preferably, these points are: point before the air arrives at the product, point after the air passes through the entire product, point in the ambient air, point after the ambient air-to-air heat exchanger passes. All are commercial sensors. To control the value of the sensors, the tunnel operating conditions are modified by adjusting or changing the system parameters that have an effect on these operating conditions: total air flow, recirculated and renewed air flow, and air heating, either individually or in combination. All the operations of reading, control and action are carried out by means of a Programmable Logic Controller, which provides the dehydrating machine with a high speed of response to changes in operating conditions. In addition, the possibility of remote access to the machine from a PC, tablet or mobile device is incorporated, allowing the user to read, control and act on the operating conditions.

The product to be dehydrated is deposited in trays supported on cars that advance manually in the dehydration chamber in one direction or another depending on the dehydration process chosen (parallel or countercurrent). Preferably, the number of cars is four. However, the design of the present invention allows its scaling for a greater or lesser number of cars. When there is a platform scale, an unevenness is created between the inside floor of the machine and the outside floor. Therefore, the introduction and exit of the car is done by installing ramps or other means for lifting the car. It is also possible to bury the machine so that it is at ground level.

The car is composed of a typically metallic structure of a certain number of levels to accommodate the trays on which the product is spread. The trays are typically metal frame and the support surface of the metal mesh product with openings to facilitate air contact with the product. For products with a tendency to adhere to the metal tray, optionally, a non-stick perforated mesh can be superimposed on the tray. Additionally, a tray without openings is incorporated at the lowest level for collecting water or precipitates. There are means for fixing the trays to prevent their exit during the handling of the car. In the upper part of the car there is a roof without openings. On the roof of the dehydration chamber there are curtains without openings, of flexible material, which cover the entire width of the chamber, one for each car. These curtains rest on the roof of the car, thus generating an obstruction to the passage of air in the gap between the roof of the car and the roof of the dehydration chamber. This prevents air from passing through the gap where there is no product.

Various air filters are provided whose purpose is to keep the dehydrator air clean and free of suspended particles to avoid the accumulation of said particles both in the dehydrator components and in the product to be dehydrated. These filters are placed: before the arrival of the air to the product, after passing the air through the entire product and in the admission of ambient air. With this minimum number of filters a circulation of clean air of particles is ensured. In addition, these filters can be washable.

A tray is arranged in the air-to-air heat exchanger for collecting condensates from the air flowing from the dehydrator to the environment. In this tray a large amount of the water extracted from the product is collected. It can be discarded or used.

To facilitate the work of cleaning and maintenance of the heating chamber there are several easily accessible doors.

BRIEF DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, a set of drawings is attached as an integral part of said description, where illustrative and non-limiting nature has been represented. following: Figure 1.- Shows a sectioned front view of the dehydrator of the invention. The air dampers are shown in semi-open position.

Figure 2.- Shows a front view of the dehydrator of the invention. The product entry / exit doors are shown in closed position.

Figure 2.- Shows a rear view of the dehydrator of the invention. Maintenance doors are shown in closed position.

PREFERRED EMBODIMENT OF THE INVENTION

The figures and drawings shown are a mere illustration of the preferred embodiment of the invention and represent one of the many forms of configuration. Although the specific components, materials, configurations and uses are shown, it should be understood that there are possible variations on said components and on the configurations of those components that can be made without changing the scope and function of the present invention.

Figure 1 shows the sectioned front view of the dehydrator (1) of the present invention resting on the exterior floor (2). The main structure of the dehydrator is formed by structural steel tubes of square and / or rectangular section located between the outer enclosure (28) of stainless steel sheet and the inner enclosure (29) that of stainless steel sheet. Among these enclosures is also the insulating material (30) of rock wool. The structure can be executed in such a way that the dehydration chamber (3) and the heating chamber (4) are independent, and can be connected by appropriate anchoring means. The horizontal wall (5) separator of the dehydration chamber (3) and the heating chamber (4) is formed externally by stainless steel sheet and internally by structural steel tube and rock wool insulating material. The dehydration chamber (3) and the heating chamber (4) are connected through the front opening (6) and the rear opening (7).

In the dehydration chamber (3) four carts with wheels are placed: first car (20), second car (21), third car (22) and last car (23). These cars are They are executed with stainless steel tubes and / or structural profiles, with appropriate closing means to prevent movement of trays. The water collection trays (52) are made with tube frame or stainless steel profile and the surface of the tray with stainless steel plate without openings. The product trays (53) are made with tube frame or stainless steel profile and the surface of the tray with stainless steel wire mesh, creating openings to facilitate air-product contact. For products with a tendency towards adhesion on the metal surface of the tray, optionally a mesh of non-stick material of tefloned fiberglass is superimposed, with openings. In the upper part of the car there is a roof (54) made of stainless steel sheet without openings. On said roof rest the curtains (24) of flexible and high temperature resistant material (fiberglass with silicone, for example) that are anchored to the horizontal wall (5). Under the first car (20) there is a scale (25) and under the last car there is another scale (26).

The arrows show the air stream lines (27). The ambient air is introduced into the dehydrator (1) through the intake opening (8) after passing through the washable polyurethane foam filter (38). Its temperature and humidity are measured by the ambient probe (44). The ambient air then passes through the cross-air heat exchanger (39) of cross-type aluminum plates, without contact between flows, where it is preheated by sensible heat exchange with the expulsion air into the environment. It then passes through the motorized intake gate (48) of slats (shown in semi-open position) and the temperature and humidity are measured with the preheated air probe (45). This air is then mixed with the recirculation air and this mixture is sucked by the axial type fan (13) with a direct transmission electric motor, that is, the motor shaft is directly coupled to the fan. The fan is supported on a metal structure that in turn rests on the horizontal wall (5) and / or on the main structure of the dehydrator using rubber anti-vibrators. The electric motor of the fan has adequate characteristics to withstand high temperature and high humidity conditions. The fan drives the air to be heated by the water-air heat exchanger (19) of copper water pipes and aluminum air fins, which receives hot water from the gas boiler (14). Said gas boiler (14) is represented with its chimney (15) of flue gas expulsion and with its defense barrier (16) for possible impacts derived from the movement of cars However, no connection shows the connection of the gas boiler (14) with the water-air heat exchanger (19). Next, the air passes from the heating chamber (4) to the dehydration chamber (3) through the front opening (6) through two 90 ° elbows where the flow redirectors of the heating chamber (31) are located. ) with their respective positioning rails (32) and the flow redirectors of the dehydration chamber (33) with their respective positioning rails (34). The flow redirectors are executed with stainless steel sheet forming a quarter of a width the same as the dehydration chamber (3). The positioning rails are executed with grooved metal profiles, allowing the redirectors to slide. After the flow redirectors of the dehydration chamber (33), the temperature and humidity of the air are measured with the delivery probe (42). Then it goes through the honeycomb panel (35) made of aluminum and the washable drive filter (36) made of polyurethane foam. At this time the air comes into contact with the first car (20), the second (21), the third (22) and the last (23), successively, without passing through the gap between the car roof (54) and the horizontal wall (5) thanks to the curtains (24). After passing through all the cars, the air passes from the dehydration chamber (3) to the heating chamber (4) through the rear opening (7) through the return filter (37) washable polyurethane foam. At this point the air has two paths. On the one hand it is recirculated through the motorized recirculation gate (46) of slats (shown in semi-open position), after measuring temperature and humidity by the return probe (43). On the other hand, it passes through the motorized louver expulsion gate (47) (shown in semi-open position) and through the air-to-air heat exchanger (39) to preheat the ambient air. In this sensitive heat exchange process, the air that comes from the dehydration chamber undergoes condensation, which is collected by the condensate tray (40) and expelled to the outside by the condensate discharge duct (41). After preheating the ambient air, the air is expelled outside through the ejection opening (9).

Figure 2 shows the front view of the dehydrator (1) where you can see the entrance / exit door of access product to the first carriage (10) (shown in closed position) and the entrance / exit door of access product to the last carriage (11) (shown in closed position). Both doors have a window (12) with or without the possibility of opening. The doors can be executed in steel exterior stainless and insulating rock wool insulation, with opening handle from outside and from inside. The window can be executed with double glazing. This Figure 2 also shows the control and protection panel (17) of stainless steel with its screen (55) for the operator's interaction and with its corresponding defense barrier (18) for possible impacts derived from the movement of cars. Inside this table are the common control and command components and especially the Programmable Logic Controller, in charge of controlling and acting on the components of the dehydrating machine (1), and the frequency inverter, which allows modifying the speed of fan rotation

Figure 3 shows a rear view of the dehydrator (1) of the present invention where you can see the maintenance doors (49), (50) and (51) (shown in closed position) that allow access to the heating chamber (4) for maintenance and cleaning operations. These doors are made of stainless steel sheet with rock wool insulating material inside.

Basic or commonly known components of this type of machines are not shown in the figures such as: emergency stop switches, door opening / closing sensors, irrigation signaling, water pipes, lighting, wiring, ramps or other means of access, etc.

Claims

1. Tunnel-type dehydrating machine (1) for the dehydration of all types of products that can be dehydrated through the circulation of heated air, characterized in that it has:  Dehydrator structure that defines at least one tunnel, said tunnel having a lower level and a higher level.  Dehydration chamber (3) on the lower level with openings for product entry and exit (10) and (11).  - Heating chamber (4) on the upper level with one or more openings (8) and (9) in contact with the ambient air outside the dehydrating machine (1).  Means for opening or closing the openings (8) and (9) in contact with the ambient air outside the dehydrating machine (1). - Horizontal wall (5) separator of the dehydration chamber (3) and the heating chamber (4), with insulating material and with opening in the front (6) and opening in the rear (7) to connect the chamber dehydration (3) and the heating chamber (4). Thermal energy source (14) for air heating. - One or more fans (13) air circulators located in the heating chamber (4)  Means for product movement in the dehydration chamber (3).  - Openings for access to the interior of the heating chamber (4). - Means for the protection of the thermal energy source (14) and the control and protection panel (17) against impacts (16) and (18). Means for operator interaction with the dashboard and control panel (55).  Means for weighing the product inside the dehydration chamber (3).  Means for preventing the passage of air through the dehydration chamber (3) through holes where there is no product to be dehydrated.  Means for standardizing the distribution of the air velocity profile in the dehydration chamber (3). - Means for filtering air particles. Means for measuring physical properties of air at various points. Means for preheating the ambient air entering the dehydrator (1) ·  Means for opening or closing the recirculation of the air from the dehydration chamber (3). 2. Dehydrator machine (1) according to claim 1 characterized in that the openings in the dehydration chamber (3) for entry and exit of product are doors (10) and (11) with or without window (12) which in turn can be with or without possibility of opening. 3. Dehydrating machine (1) according to any one of the preceding claims characterized in that the entry of ambient air and exit of air into the environment is controlled by means of air dampers (48) and (47), respectively. These air dampers are motorized with slats. 4. Dehydrating machine (1) according to any of the preceding claims characterized in that the source of thermal energy (14) is a gas boiler. Said boiler heats water, which is transported to the water-air heat exchanger (19) where the air is heated. 5. Dehydrator machine (1) according to any of the preceding claims characterized in that it contains one or more fans (13) with rotation speed controlled by one or several frequency inverters. 6. Dehydrating machine (1) according to any of the preceding claims characterized by containing means for supporting and moving the product by means of a plurality of trays (53) located in one or more carriages (20), (21), (22) and (23). The car contains tray fixing means to prevent movement of them. It also contains a tray for collecting water or precipitates (52) at the bottom, and a roof (54) without openings. The product trays (53) have openings to facilitate product-air contact. 7. Dehydrating machine (1) according to any of the claims Precedents characterized by containing openings for access to the heating chamber through one or more maintenance doors (49), (50) and (51). 8. Dehydrating machine (1) according to any of the preceding claims characterized in that it contains means of interaction of the operator by means of one or several control and protection panels (17) with one or more interaction screens (55). Inside this table are the common control and command components and especially the Programmable Logic Controller, in charge of controlling and acting on the components of the dehydrating machine (1), and the frequency inverter, which allow modifying the speed of fan spin 9. Dehydrating machine (1) according to any of the preceding claims characterized in that it contains weighing means of the product of the dehydration chamber (3) by means of one or several scales (25) and (26) of weighing under the carriages. 10. Dehydrating machine (1) according to any of the preceding claims characterized by containing means to prevent the passage of air through gaps where there is no product by one or several curtains (24) resting on the roofs (54) of the cars . 11. Dehydrator machine (1) according to any of the preceding claims characterized in that the means for standardizing the distribution of the air velocity profile in the dehydration chamber (3) are one or more flow redirectors in the 90 ° elbow of the heating chamber (31) with their respective positioning rails (32), one or more flow redirectors in the 90 ° elbow of the dehydration chamber (33) with their respective positioning rails (34), and panel honeycomb (35) in the dehydration chamber (3). 12. Dehydrating machine (1) according to any of the preceding claims characterized in that the means for air filtration are located: at a point before the product (36), a point after the product (37) and a point before entering the dehydrating machine (38). 13. Dehydrating machine (1) according to any of the preceding claims characterized in that the method for measuring the physical properties of the air is carried out by means of temperature and humidity probes located: at a point before the product (42), a point after product (43), one point before entering the dehydrator machine (44) and one point after the ambient air passes through the air-to-air heat exchanger (45). 14. Dehydrating machine (1) according to any of the preceding claims characterized in that the means for preheating the air introduced from the environment is carried out by an air-to-air heat exchanger (39). For the collection of condensates, a tray (40) and a condensate discharge duct (41) are provided. 15. Dehydrating machine (1) according to any of the preceding claims characterized in that the means for opening or closing the recirculation of air from the dehydration chamber (3) is carried out by means of motorized recirculation gate (46) of slats .