Method for managing a dehydration system and corresponding dehydration system

Abstract

The invention relates to a method for managing a dehydration system suitable for dehydrating a product, comprising a drying device (5) containing an adsorbent material, the method comprising: - phases of water adsorption (S2) by the adsorbent material in order to reduce the partial vapour pressure in a carrier fluid circulating in the system, and - regeneration phases (S3) during which the adsorbent material recovers its adsorption properties; the adsorbent material being such that the water adsorption is exothermic. The method comprises the steps of: - recovering thermal energy (S5) from the drying device (5) during the water adsorption phases (S2), and - using (S6) the recovered thermal energy for: + heating the product (S11); and / or + heating the adsorbent material (S32) in the regeneration phase. The invention also relates to a dehydration system making it possible to carry out this method.

Description

[0001] Method for managing a dehydration system and corresponding dehydration system

[0002] The present invention relates to the field of dehydration and in particular that of dehydration installations.

[0003] Dehydration generally refers to the removal of water from a product. This process can have various objectives, for example, to allow a product to be stored for a long time, or to concentrate certain elements.

[0004] Dehydration includes in particular the processes of drying or desiccation under vacuum.

[0005] These processes include freeze-drying processes. Freeze-drying consists of drying a previously frozen product by sublimation. Freeze-drying is thus carried out by maintaining the product at a low temperature under vacuum. In freeze-drying processes, the water extracted from the products is generally condensed by a system of cold plates and then evacuated from the freeze-drying installation. Other vacuum dehydration processes are known. Dehydrating under vacuum has several main advantages. Lowering the boiling point and therefore working at a lower temperature helps preserve the qualities of the dehydrated product. Dehydrating in the absence of oxygen or in the presence of little oxygen prevents the oxidation of certain molecules.

[0006] However, low pressures imply very large volumes of water vapor, which must therefore be "trapped". There are different ways to trap water: by physiosorption, chemosorption, condensation.

[0007] Vacuum dehydration processes therefore generally involve the use of a water trap containing an adsorbent material. A facility for implementing such processes generally comprises an enclosure that receives tanks of products to be dehydrated and assemblies containing the adsorbent material. A vacuum in the enclosure causes evaporation of the water initially contained in the products and the water vapor thus produced is adsorbed by the adsorbent material.

[0008] The main applications of the dehydration technologies targeted in the present invention relate in particular to the dehydration of food products, cosmetic products, and pharmaceutical products, bio-sourced products (for example wood), or products used in the composition of such food, cosmetic or pharmaceutical products, etc.

[0009] Various dehydration devices have been known in the state of the art for a long time.

[0010] For example, document US2374232 discloses a vacuum dehydration device (in this case freeze-drying), using a desiccant material such as silica gel. The product to be dehydrated is placed in a container which is in communication with a chamber which contains the desiccant material, which allows gas exchange and pressure balance between the container where the product is placed and the enclosure which contains the desiccant material,

[0011] Document FR2805759 relates to a dehydration process in a similar system comprising at least one standard type solid / gas reversible adsorption reactor which contains, in an enclosure, an adsorbent such as zeolite, a tank containing a product to be adsorbed (for example placed on trays); and a fluid connection provided with a valve to allow communication between the enclosure and the tank and a pressure balance between the enclosure and the tank.

[0012] This document recalls in particular that a process for implementing such a device typically comprises the following three successive phases:

[0013] - an adsorption phase, during which the enclosure containing the adsorbent is placed in communication with a tank containing the product to be adsorbed;

[0014] - a regeneration phase, during which said enclosure containing the adsorbent is placed in communication with a condensation system, said enclosure is isolated from said tank, and said adsorbent is heated; and

[0015] - a cooling phase, during which said enclosure is isolated and said adsorbent is cooled.

[0016] The device and method presented in this document relate in particular to the conditions applied to the adsorbent, which can nevertheless be further optimized.

[0017] Document FR1009340 presents a two-stage, low-temperature drying process. Each drying stage takes place in a different dryer, the first operating at 25°C and the second at 13°C. The drying air is drawn in and first passes through a container containing a desiccant. It is then introduced into the second dryer (at 13°C), from where it emerges more humid. In order to maintain its evaporative power, the air is then reheated to 25°C and introduced into the first dryer. The air extracted from the dryers is sent to a container containing a desiccant. Another container contains a desiccant that is being regenerated by circulating air in a closed circuit, heated by external heat. This circuit helps heat the air between the second dryer and the first dryer.

[0018] The installations known to date are therefore not optimized in a global approach to the dehydration process, in order to preserve the properties of the product while allowing efficient implementation of the device.

[0019] In particular, the issue of the energy required to carry out the complete dehydration process is important. Thus, in addition to proposing an efficient dehydration device to preserve the properties of the dehydrated product, for example its taste qualities, it is appropriate to propose a device that has competitive energy consumption compared to existing dehydration solutions.

[0020] The present invention aims to provide an optimized dehydration device.

[0021] Thus, the invention relates to a method for managing a dehydration system adapted to dehydrate a product, the dehydration system comprising a drying device containing an adsorbent material, the method comprising:

[0022] - water adsorption phases by the adsorbent material in order to reduce the partial pressure of water vapor in a carrier fluid circulating in the dehydration system during the dehydration of the product, and

[0023] - vacuum regeneration phases, at a pressure at least 500 millibars lower than atmospheric pressure, during which the adsorbent material recovers adsorption properties; the adsorbent material being such that the adsorption of water is exothermic, the process comprising steps of:

[0024] - recovery of thermal energy at the level of the drying device during the water adsorption phases, and

[0025] - use of recovered thermal energy for:

[0026] + heating the product during its dehydration; and

[0027] + heating of the adsorbent material during the regeneration phase.

[0028] The method further comprises, between the regeneration phase and the adsorption phase, a phase of cooling the adsorbent material, and the thermal energy recovery step comprises the recovery of thermal energy at the level of the drying device during the cooling phase of the adsorbent material.

[0029] A method is thus proposed that makes it possible to significantly limit the energy inputs required to successfully dehydrate products and, more generally, to operate the dehydration system, which includes the dehydration of the product itself and regeneration phases of the adsorbent material used in the system. The adsorbent material used may in particular be or include a zeolite. Regeneration means restoring the activity, i.e. the capacity to adsorb water, of the adsorbent material. For a zeolite, this involves extracting the water by placing it in favorable temperature and pressure conditions. Vacuum regeneration allows for more energy-efficient regeneration (especially since a portion of the energy used for regeneration can be recovered).Vacuum regeneration in this document means regeneration carried out under a pressure of at least 500 millibars below atmospheric pressure (i.e. approximately less than 500 millibars absolute pressure).

[0030] The energy efficiency of the process can be further improved in the following ways.

[0031] The thermal energy recovery step may include the recovery of latent heat of condensation of water vapor present in a gas stream expelled from the adsorbent material during the regeneration phase.

[0032] The thermal energy recovery step may comprise the recovery of thermal energy at a mechanical device of the dehydration system, for example a pump, and the recovered thermal energy may be used for: + heating the product being dehydrated; and / or

[0033] + heating the adsorbent material in the regeneration phase; and / or + maintaining the temperature of a heat transfer fluid. The dehydration system may comprise a second drying device, in which the recovered thermal energy is used at least in part for heating the second drying device in the regeneration phase.

[0034] The method proposed in the invention proves to be particularly relevant and effective in such a configuration. The thermal energy recovered, in whole or in part, from a drying device whose drying material is in the adsorption phase can thus be directly used for the regeneration of the drying material of a drying device in the regeneration phase. The method is thus applicable to a dehydration system comprising several drying devices, in particular two, three, four, five, or even more drying devices.

[0035] The process may include the steps of:

[0036] - placing the product in a dehydration chamber;

[0037] - establishment in the dehydration chamber of a pressure at least 500 millibars lower than atmospheric pressure;

[0038] - establishment between the inlet of the dehydration enclosure and an outlet of the dehydration enclosure of a flow of carrier fluid; and

[0039] - adsorption of water contained in the carrier fluid leaving the dehydration chamber by the adsorbent material contained in the drying device.

[0040] The pressure of the carrier fluid can be raised between the outlet of the dehydration chamber and the drying device, for example by 300 millibars or more.

[0041] Indeed, if a low pressure is favorable to the drying of products, it is unfavorable to the adsorption of water by the adsorbent material.

[0042] To overcome this phenomenon and maximize the energy released due to the exothermic nature of the adsorption, it is proposed to use a system for compressing the carrier fluid between the dehydration chamber and the drying device, in order to place the adsorbent in the most favorable conditions for adsorption.

[0043] However, the maximization of the energy released during adsorption, due to the adsorption of a large amount of water, has the consequence that this large amount of water will have to be removed by desorption during regeneration.

[0044] This is why vacuum regeneration is performed, in order to minimize the energy required for regeneration.

[0045] The product can be brought to and maintained at a temperature between 20°C and 70°C, preferably between 30°C and 40°C, during its dehydration. It is thus proposed to operate the dehydration system under optimal conditions, particularly from an energy point of view, in the different phases of the process. Dehydration is thus carried out under low pressure, well below atmospheric pressure, for example more than 500 millibars below atmospheric pressure (this is referred to as “vacuum” dehydration). The relative humidity of the carrier fluid, at the inlet of the dehydration chamber, is less than 70% and will generally be much lower. The adsorption of water by the adsorbent material is carried out at a pressure higher than the pressure at which the product is dehydrated. The regeneration of the adsorbent material, typically zeolite, is carried out under vacuum.

[0046] Please note that, unless otherwise stated, the expressions "approximately" and "in the order of" refer to the indicated value plus or minus 20%.

[0047] In certain embodiments of the method, since the heating of the adsorbent material in the regeneration phase and the heating of the product during dehydration require a total amount of thermal energy, the recovery of thermal energy in the system covers at least 20%, preferably at least 50%, and more preferably at least 70% of said total amount of thermal energy. As will be shown below, it is possible, in a method according to certain embodiments of the present invention, to limit the inputs of thermal energy necessary for the operation of the dehydration system to a very low level, or even theoretically possible to cancel them.

[0048] The invention also relates to a dehydration system comprising a dehydration chamber in which a product to be dehydrated is placed, and at least one dehydration device comprising a drying device comprising an adsorbent material adapted to adsorb water contained in a carrier fluid which passes through the drying device, the adsorbent material being such that the adsorption of water is exothermic, the dehydration device comprising a flow management module adapted to generate and control a flow of carrier fluid in the dehydration device and in the dehydration chamber, the dehydration system comprising:

[0049] - a device for recovering thermal energy at the level of the drying device and - a device for distributing thermal energy to a means for heating the product in the dehydration chamber, and / or

[0050] - a means of storing thermal energy for use in heating the adsorbent material of the drying device when the latter is in the regeneration phase.

[0051] The system comprises a vacuum source configured to place the adsorbent material at a pressure at least 500 millibars lower than atmospheric pressure during its regeneration, which is then called "vacuum regeneration". The entire thermal energy recovery and distribution function can thus be seen as a recovery module, capable of distributing or storing the recovered thermal energy.

[0052] The device may comprise a second drying device, and the system may then further comprise a means for distributing the recovered thermal energy adapted to distribute to the second drying device all or part of the recovered thermal energy in order to heat the drying material of the second drying device when it is in the regeneration phase.

[0053] The thermal energy recovery device may include a gas / liquid exchanger.

[0054] The energy is thus recovered from a heat transfer fluid, for example oil. This allows it to be stored or, if necessary, transferred, directly or via a liquid / liquid exchanger, to a thermal circuit, comprising a heat transfer fluid, and which allows, for example, the heating of the product which is being dehydrated.

[0055] The thermal energy recovery device may include a heat pump. The heat pump is relevant, particularly more relevant than a gas / liquid heat exchanger for example, when the temperatures of the gases from which thermal energy is to be extracted are relatively low, for example below 120°C.

[0056] The system may further comprise a means of recovering thermal energy emitted by mechanical devices of the system.

[0057] The energy thus recovered, for example by means of heat pumps, can be used in particular in a tracing system (i.e. extended heating) along the system's pipes, in addition to pipe insulation.

[0058] The dehydration chamber of the system may comprise a set of shelves for receiving trays adapted to contain a product to be dehydrated and the means for heating the product may comprise a set of conduits containing a heat transfer fluid heated in whole or in part via one or more exchangers connected to the thermal energy recovery device. This configuration optimizes the ratio between the evaporation surface exposed by the product and the volume of the chamber, as well as the efficiency of the heating of the product.

[0059] Other features and advantages of the invention will become apparent in the description below.

[0060] In the attached drawings, given as non-limiting examples: Figure 1 represents, according to a block diagram, a dehydration system in accordance with one embodiment of the invention; Figure 2 represents, according to a block diagram, an example of a method for managing a dehydration system in accordance with the invention, which can be applied in particular to the dehydration system of Figure 1; Figure 3 represents on a block diagram the sorption curves as a function of pressure for an adsorbent material at two temperature levels; Figure 4 represents sorption results of an adsorbent obtained at a given temperature; Figure 5 represents sorption isotherms obtained at different temperatures for the adsorbent of Figure 4.

[0061] Figure 1 shows, according to a block diagram, a dehydration system according to an embodiment of the present invention. The dehydration system comprises a dehydration device 1 and a dehydration chamber 2 to which the dehydration device 1 is connected.

[0062] In order to dehydrate a product contained in the dehydration chamber 2, a flow of carrier fluid, for example air or advantageously nitrogen, at low pressure and having a low partial pressure of water vapor, is generated in the dehydration chamber 2 by a flow management module 3 of the dehydration device 1. The use of low pressure air as a carrier fluid prevents oxidation of the product being dehydrated. The use of nitrogen as a carrier fluid is even more advantageous in this respect.

[0063] The dehydration chamber 2 is suitable for operating at the target pressure during the dehydration of the products.

[0064] For example, it can have a generally tubular shape and is therefore particularly well suited to systems operating at a high vacuum level.

[0065] Throughout this document, "vacuum" means a pressure at least 500 millibars below atmospheric pressure, and preferably 700 millibars below atmospheric pressure.

[0066] This dehydration chamber 2 may have significant dimensions to allow the dehydration of products on an industrial scale. For example, a tubular chamber with an internal diameter of approximately 2.5 m and an internal length of 5 m may be used. These dimensions are given purely as an example. Systems in which the dehydration chamber 2 has a much larger volume may in particular be considered.

[0067] The dehydration chamber 2 includes a suction pipe allowing the evacuation of the air-laden carrier fluid (typically air and water vapor). The suction pipe is connected to the inlet of the dehydration device.

[0068] The enclosure is equipped with a door allowing the loading and unloading of the products to be dehydrated.

[0069] The products can advantageously be loaded onto trays or bins, suitable for food contact where appropriate. The products treated can be in solid or liquid form (including pasty). The configuration of the dehydration chamber 2 tends to maximize the exchange surface of the products with the carrier fluid, for example with air.

[0070] In order to promote their dehydration, in a dry carrier fluid, the products to be dehydrated can be heated (nevertheless, under vacuum, the dehydration is carried out at low temperature, for example between 30°C and 70°C, which makes it possible not to alter certain qualities of the products treated). The heating of the products in the enclosure can in particular be carried out using a hot heat transfer fluid circulating in conduits 21 integrated into shelves for receiving trays or bins of products arranged in the enclosure 2.

[0071] The temperature of the heat transfer fluid can be controlled by a thermoregulator device 4.

[0072] In particular, according to a preferred aspect of the present invention, the heat transfer fluid can be heated using thermal energy recovered elsewhere in the dehydration system. In various embodiments of the present invention, this recovery of thermal energy can be carried out in various locations, on various heat sources. Primarily, thermal energy from the exothermic adsorption of water by a drying device 5 detailed below can be used to provide the energy necessary to heat the product to be dehydrated to the desired temperature.

[0073] After having circulated in the dehydration enclosure 2, around and / or in contact with the product to be dehydrated, the carrier fluid leaves containing water, i.e. more water than when it entered. The carrier fluid then enters the dehydration device 1.

[0074] The flow management module 3 has the function, in particular, of ensuring the circulation of the carrier fluid in the dehydration system 1 and in the dehydration chamber 2, and of controlling the relative humidity level in the dehydration chamber 2. It can make it possible to control the temperature of the carrier fluid introduced into the dehydration chamber 2. The flow management module 3 thus allows fine control of the dehydration conditions of the product. The flow management module 3 is thus advantageously configured to control vacuum dehydration, a vacuum being applied at the outlet of the dehydration device. Vacuum dehydration makes it possible to carry it out at low temperature, which preserves certain qualities of the product being dehydrated.

[0075] The flow management module 3 also allows the flow rates and pressure in the drying device to be controlled (described below).

[0076] The flow management module 3 may include mechanical equipment, such as a volumetric pump, for example with rotors (roots pump), or any other equipment suitable for operating under high vacuum and for managing the flow rate of the carrier fluid at the outlet of the dehydration chamber and consequently at the inlet of the drying device.

[0077] This equipment also forms a carrier fluid compression device. The compression device allows the pressure of the carrier fluid to be raised between the inlet interface of the dehydration device and the drying device.

[0078] Throughout this document, the concept of upstream and the concept of downstream is understood according to the direction of flow of the carrier fluid.

[0079] Optionally, a buffer tank 6 can be arranged between the mechanical equipment of the circulation module and the drying device 5.

[0080] The buffer tank 6 allows better control and temporal smoothing of the operating conditions of the drying device 5 (pressure and temperature).

[0081] In the exemplary embodiment shown in Figure 1, the system comprises three drying devices 5, 5', 5”.

[0082] Indeed, in the case where the carrier fluid is not recycled in full, or, in general, if it is necessary to provide a supply of carrier fluid into the dehydration system, the carrier fluid introduced may be air or another gas dried in a second drying device 5' of the dehydration device.

[0083] In addition, a third 5” drying device, previously used for dehydrating a product, can be provided, and for example be in the process of being regenerated. It will then be available to be used to adsorb water as soon as the drying device 5 or the second 5' drying device needs to be regenerated. Production without downtime related to regeneration of the drying devices can thus be achieved.

[0084] The flow management device also makes it possible to maintain the desired vacuum level by topping up the vacuum using a vacuum source 7, for example a vacuum pump or a vacuum unit (via a vacuum network).

[0085] In all embodiments, the circulation module may comprise a device for determining the relative humidity of the carrier fluid entering the dehydration device 1, for example a humidity sensor, and use this information to control the flow rates in the dehydration system. The dehydration device comprises, as mentioned above, a drying device 5, intended to capture the water present in the carrier fluid coming from the dehydration enclosure 2.

[0086] The drying device 5 makes it possible to reduce the quantity of water present in the carrier fluid which is present around the drying device or which passes through it. The drying device 5 comprises a material adapted to adsorb a significant quantity of water, called adsorbent material, under appropriate temperature and pressure conditions. This type of drying device 5 is thus commonly called a “water trap”.

[0087] Zeolites are known for their high capacity to adsorb water, without taking up volume, and can therefore be used as an adsorbent material for water traps.

[0088] The adsorbent material may, for example, be installed in a basket or cassette placed in the drying device, so as to be brought into contact with, or even crossed if necessary, the carrier fluid laden with vapour which enters the water trap.

[0089] The adsorption reaction of the adsorbent material used in the context of the present invention being exothermic (as is notably the case with zeolites), the thermal energy produced by the reaction can be recovered and used.

[0090] This heat recovery, during the adsorption phase, can be carried out at the level of the drying device 5, via a first heat recovery device RC1. The first heat recovery device RC1 can be a gas / gas exchanger or a gas / liquid exchanger. In particular, a gas / oil exchanger has been developed to form the first heat recovery device RC1.

[0091] The thermal energy thus recovered can be used to heat the product being dehydrated, and / or to assist in the regeneration of the adsorbent material.

[0092] It is also possible to carry out the regeneration of the adsorbent material immediately after the adsorption phase, in order to take advantage of the temperature acquired by the adsorbent material during adsorption and limit the input of thermal energy necessary for regeneration.

[0093] As regards the heating of the product being dehydrated, if the first heat recovery device RC1 is a gas / liquid exchanger (for example gas / oil), the liquid heated by the heat produced during the adsorption of water by the adsorbent material can be directed to a liquid / liquid exchanger so that the recovered thermal energy is transferred to the heat transfer fluid circulating in the conduits allowing the heating of the product to be dehydrated.

[0094] As regards the use of the recovered thermal energy to regenerate the adsorbent material, this use can be carried out, depending on the system considered and its current use, without delay or in a deferred manner. In a system comprising only one drying device, or in a device comprising several drying devices but no drying device to be regenerated at the time of water adsorption by another drying device, the recovered thermal energy can be stored, for example by storing hot fluid (for example in a heat-insulated tank). In a device comprising several drying devices, the thermal energy recovered at a first drying device whose adsorbent material is in the water adsorption phase can advantageously be used immediately to heat the adsorbent material of a second drying device to be regenerated.

[0095] In fact, when the adsorbent material has adsorbed a significant quantity of water, it must be regenerated by making it desorb the water it contains, so that it recovers its adsorption capacity.

[0096] The dehydration device comprises a regeneration module 8 for this purpose. The regeneration module allows the adsorbent material of the water trap to be placed in temperature and pressure conditions suitable for its regeneration. Regarding the temperature, it is necessary to heat the adsorbent material for its regeneration, all or part of this heating being carried out using thermal energy recovered elsewhere in the system. Regarding the pressure, the regeneration module can in particular be configured to carry out regeneration under vacuum.

[0097] The regeneration module 8 is selected and configured according to the general operating mode of the dehydration device. The latter can advantageously operate in vacuum-assisted adsorption, in particular in vacuum swing adsorption (or VSA according to the English acronym for “Vacuum Swing Adsorption”), in which a low pressure is imposed during regeneration and a relatively higher pressure is imposed during adsorption. Thermal energy which is generally lost, rejected to the atmosphere, in known systems can also be recovered during the regeneration phases. Primarily, this involves recovering the latent heat of condensation of the gas stream (typically the air stream) expelled from the zeolite during the regeneration phase. This hot gas stream has a high relative humidity level, and therefore a high enthalpy.

[0098] Energy recovery is achieved, for example, by means of a second heat recovery device RC2, which may include an exchanger that also allows the recovery of condensed water. The condensed water is itself hot and can be used directly as a heat transfer fluid or to heat a heat transfer fluid in the system.

[0099] More particularly, in the second heat recovery device RC2, the latent heat of condensation can be recovered using a tubular exchanger. The sensible heat of the gas flow during regeneration can be recovered using an exchanger (gas / gas or gas / liquid) or a heat pump. The use of an exchanger is preferred above a certain temperature, for example of the order of 120°C while the use of a heat pump is preferred below this temperature (for example between 70°C and 120°C).

[0100] Thus, energy recovery can be carried out at the level of the drying device not only during the adsorption phase, but also, if necessary, during the regeneration phase to recover part of the energy linked to the initial heating of the zeolite - or more generally of the adsorbent material, and / or part of the energy inputs during regeneration.

[0101] The dehydration device shown in Figure 1 further comprises a cooling module 9.

[0102] The cooling module 9 is a device which allows the zeolite (or other adsorbent material whose water adsorption is exothermic) to be cooled to an optimal temperature after its regeneration (which may have brought it to a very high temperature, for example up to around 280°C for a zeolite).

[0103] The heat taken during cooling can be recovered by a third heat recovery device RC3.

[0104] More particularly, in the third heat recovery device RC3, the sensible heat of the gas flow during cooling can be recovered using an exchanger (gas / gas or gas / liquid) and / or a heat pump. The use of an exchanger is preferred above a certain temperature, for example of the order of 120°C while the use of a heat pump is preferred below this temperature (for example between 70°C and 120°C).

[0105] Finally, a fourth heat recovery device RC4 may be provided to recover thermal energy from the mechanical devices of the system, for example pumps used for circulating fluids in the system. The heat recovery device RC4 may thus comprise one or more heat pumps.

[0106] In Figure 1, the heat recovery devices RC1, RC2, RC3 and RC4 are represented in a functional, global manner. Obviously, many configurations are possible, implementing common or separate exchangers for each drying device, or more generally for each piece of equipment in the system to which it is linked.

[0107] Similarly, the recovery of thermal energy is represented in a general, functional manner, in the form of a recovery module 10, which can ensure the distribution or storage of the recovered thermal energy. Many practical implementations are conceivable for this function.

[0108] Furthermore, in general, the thermal losses of a system according to the present invention can be avoided by insulating the constituent elements of the system: dehydration chamber, drying device(s), system pipes, etc.

[0109] Figure 2 schematically presents a management process that can be implemented in particular for the dehydration system in Figure 2. The solid lines represent the sequence of phases and stages of the process, the dotted lines the possible thermal energy flows.

[0110] A product, for example a food product, is dehydrated in a dehydration step S1. To do this, the product is placed under vacuum, i.e. at a pressure at least 500 millibars lower than atmospheric pressure. In addition, the product is placed under vacuum and heated to a temperature of the order of 30°C to 70°C. A flow of carrier fluid (air or nitrogen for example) at low pressure and low partial pressure of water vapor is established around the product and thus “sweeps” the product to be dehydrated. The dehydration step S1 therefore comprises steps of: heating the product S11, placing the product under vacuum S12 and sweeping S13, which are at least partly simultaneous).

[0111] At the same time as the dehydration step S1, a water adsorption phase S2 by an adsorbent material is carried out. During this phase, water present in the carrier fluid after it has swept the product to be dehydrated is adsorbed by an adsorbent material such as a zeolite.

[0112] Preferably, the adsorption is carried out at a pressure higher than the pressure ("vacuum") used for the dehydration step S1. The adsorption is thus carried out at a pressure as close as possible to atmospheric pressure.

[0113] Once the adsorbent material has adsorbed a certain amount of water, it must be regenerated to regain its adsorption properties. This regeneration can be carried out under vacuum. It requires the input of thermal energy to heat the adsorbent material to a temperature suitable for regeneration.

[0114] The regeneration step S3 thus comprising, simultaneously, a step of placing the adsorbent material under vacuum S31 and a step of heating the adsorbent material S32.

[0115] In order to illustrate the phenomena used for the regeneration of the adsorbent material, the sorption curves as a function of pressure for a typical adsorbent material are shown schematically in Figure 3 (this type of schematic curve is observed in particular for zeolites), at two temperature levels T 1 and T2, with T2>T 1.

[0116] During the regeneration of the adsorbent material, the reduction in pressure causes a release of the water adsorbed by the adsorbent, which corresponds, at a constant temperature T1, to the passage from point P1 to point P2 in the diagram of Figure 3. Thus, the vacuum promotes desorption and this reduces the energy input required during the regeneration phase. Furthermore, heating the adsorbent material, at constant pressure, also causes a release of the adsorbed water. This corresponds to the passage from point P1 to point P4 in the diagram of Figure 3.

[0117] To achieve higher levels of regeneration, it is proposed within the framework of the present invention to combine a reduction in pressure with an increase in temperature, which corresponds to a passage from point P1 to point P3 in the diagram of figure 3.

[0118] The temperature increase is then achieved in whole or in part using the energy recovered during the adsorption phase.

[0119] Thermal energy can be supplied to the adsorbent material using a heated heat transfer fluid, in particular during the phase of water adsorption by the adsorbent material, and during the cooling of the adsorbent material after its regeneration, as explained below.

[0120] It is notable that, when the dehydration system comprises several drying devices comprising an adsorbent material (which constitutes the preferred configuration of the invention), the step of regenerating the adsorbent material can be carried out in parallel with the water adsorption step, on two separate drying devices. During regeneration, hot gas laden with water is extracted from the drying device.

[0121] At the end of regeneration S3, the adsorbent material is very hot; for example, it can be at a temperature of around 280°C for a zeolite. The adsorbent material is then cooled in a cooling step S4.

[0122] The cooling phase is important to achieve a utilization rate of the adsorbent material compatible with industrial use. By actively cooling the adsorbent material, the availability of the drying device for drying is greatly increased.

[0123] Furthermore, the Applicant highlighted the importance of controlling the cooling phase.

[0124] Figure 4 shows the results obtained at a given temperature for an adsorbent (in this case a zeolite). In particular, Figure 4 shows, as a function of time: the weight of the adsorbent (bold line), and the relative humidity of the air around and in contact with the adsorbent (thin line). The samples used in this test were preheated to 300°C beforehand to ensure complete desorption of the water present.

[0125] At the given temperature, Figure 4 shows a significant gain in mass of the adsorbent at 0% relative humidity and between 0 and 15% relative humidity.

[0126] This gain is due to the adsorption of water molecules, which are not, however, eliminated by desorption, despite the relative humidity of the air around the adsorbent being reduced to 0%. This phenomenon is thus interpreted as being an "irreversible" adsorption at the given temperature.

[0127] However, it has been observed that the extent of this irreversibility phenomenon depends on the temperature to which the sample is subjected, as can be seen in Figure 5.

[0128] Figure 5 thus highlights two phenomena that are important for the efficiency of the process that is the subject of the present invention. Figure 5 represents sorption isotherms obtained at different temperatures (TT to T4') for the adsorbent of Figure 4. For a given temperature, the lower curve represents adsorption and the upper curve desorption. At 0% relative humidity, there is a difference between the water content of the adsorbent before adsorption and after desorption, whatever the temperature. This difference corresponds to the irreversibility phenomenon described previously.

[0129] First, the maximum adsorption capacity decreases with increasing temperature. This phenomenon is well known.

[0130] Furthermore, the irreversible nature of part of the adsorption at a given temperature, mentioned above, is noted. This phenomenon does not seem to be mentioned in the literature. It is noted that this "irreversibility" is all the more important as the temperature of the adsorbent is low.

[0131] This information is important for the process that is the subject of the invention. It demonstrates that after a regeneration phase, the adsorbent has a high capacity to re-adsorb water present in the ambient air. Such re-adsorption represents for the following adsorption phase a considerable loss of adsorption capacity, which decreases with increasing temperature.

[0132] The application of active cooling of the adsorbent after regeneration thus makes it possible not only to achieve energy recovery, but also to improve the overall efficiency of the system by maximizing at each cycle the quantity of water adsorbed then released for a given quantity of adsorbent. According to the invention, a thermal energy recovery step S5 is carried out. Primarily, the thermal energy recovery step S5 comprises the recovery of heat from the water adsorption step S2, the adsorbent material being such that the adsorption reaction is exothermic.

[0133] This energy recovery can be achieved using a heat transfer fluid, typically the same heat transfer fluid as that used to heat the adsorbent material during its regeneration.

[0134] Thermal energy recovery is also carried out during the S4 cooling step of the zeolite. Energy recovery during the cooling phase can be carried out using this same heat transfer fluid, which allows for rapid heat recovery.

[0135] Additionally, direct exchange with a low-pressure air flow promotes convection despite the partial vacuum while maintaining the adsorbent material under pressure and temperature conditions where it is unlikely to re-adsorb water.

[0136] However, thermal energy recovery S5 can also include heat recovery during regeneration: latent heat of condensation of the water present in the hot gas (gas stream) extracted from the drying device, and sensible heat of this hot gas. The recovered condensed water can also be a source of calories for thermal energy recovery S5. Similarly, the sensible heat of the gas (typically air) leaving the adsorbent material during its cooling S4 can be recovered.

[0137] Finally, S5 thermal energy recovery may include the recovery of heat from the system's mechanical devices (pumps and other machines).

[0138] The recovered thermal energy is used in a utilization step S6. The utilization S6 may be concomitant with the thermal energy recovery S5, or be carried out later, using a means of storing the thermal energy (for example in the form of a hot fluid stored in a heat-insulated tank).

[0139] The main uses of the recovered thermal energy concern the heating of the product S11 which is being dehydrated S1, and the heating of the adsorbent material S32 which is being regenerated S3.

[0140] The recovered thermal energy can also be used to heat a tracing fluid for the pipes of the dehydration system. Figure 2 is intended as a general representation of a method according to one embodiment of the invention. Obviously, many variants can be envisaged within the scope of the present invention. In particular, the recovery of thermal energy and its use are represented respectively as single steps. It is obvious that the recovery of thermal energy S5 can collectively designate several distinct recoveries carried out within the framework of the method for managing the dehydration system. Similarly, the use S6 of the recovered thermal energy can designate several distinct recoveries carried out within the framework of the method for managing the dehydration system.

[0141] The method and system developed in the invention make it possible to significantly limit the heat inputs required for the system to operate. In practice, the method and system developed in the invention make it possible to dehydrate a product and regenerate the drying devices used by limiting the heat inputs to a low energy input for regeneration. The heat inputs required are all the lower when the conditions of use of the system are optimized in energy terms, in particular by operating at low pressure. No other input is necessary in certain embodiments of the invention.

[0142] The Applicant presents below a comparison between the estimated energy balance of a process according to an embodiment of the invention and that of a comparable freeze-drying process. This balance relates to the thermal energy to be provided in the context of the dehydration of a product and does not take into consideration the energy consumption linked to the operation of mechanical systems such as the pumps used for the circulation of the various fluids in the system.

[0143] To make this estimate we assume that the product to be dehydrated (1 kg of product) is received at 20°C. It is also assumed that this product has the same properties as water (for example the same specific heat capacity).

[0144] The cycle used to dehydrate the product by freeze-drying involves the steps of: cooling the product to -40°C, dehydration by sublimation, capturing the water by condensation, and regenerating the water capturing device by defrosting. The cycle used to dehydrate the product by a method according to one embodiment of the invention (hereinafter referred to as "method according to the invention") involves the steps of: cooling the product to 4°C, dehydration by evaporation, capturing the water by adsorption, and regenerating the adsorbent material.

[0145] For the process according to the invention, cooling down to 4°C serves to preserve the product between its reception and dehydration. Freeze-drying, on the other hand, requires freezing the product and a working temperature of around -40°C.

[0146] Thus, the energy required to cool the product (Q refroidissement) corresponds to: For Freeze-drying:

[0147] Q refroidissement = Q20 →0 °C + Q congélation + Q0→ -40 °C

[0148] Q refroidissement = m Cp eau ΔT + mΔH congélation + m Cp glace ΔT

[0149] Q refroidissement = 497.5 kj

[0150] For the method according to the invention:

[0151] Q refroidissement = Q20 →4 °C

[0152] Q refroidissement = m Cp eau ΔT

[0153] Q refroidissement = 67 kj

[0154] Where AW denotes a variation in enthalpy (or latent heat) of the index element, ΔT denotes a variation in temperature, and Cp denotes a specific heat capacity of the index element.

[0155] The drying or dehydration step consists of a change in the state of the water. This is done by sublimation in the case of freeze-drying and by evaporation in the process according to the invention. For the latter, the energy required to bring the product up to temperature must also be taken into account, as it must go from its storage temperature (here 4°C) to the working temperature during drying (for example 30°C). The energy required for dehydration (Q séchage ) is thus:

[0156] For Freeze Drying:

[0157] Q séchage = Q sublimation

[0158] Q séchage = mΔH sublimation Qdrying = 2809 kj

[0159] For the method according to the invention:

[0160] Q séchage = Q4 → 30 °C + Q évaporation

[0161] Q séchage = m Cp eau ΔT + mΔH évaporation

[0162] Q séchage = 2366 kj

[0163] Since both processes are compared, they operate at very low pressures, and the volumes of steam to be handled are exorbitant. It is therefore necessary to capture the water extracted from the product. In the case of freeze-drying, this is most often done by condensation, using a cold plate. The process according to the invention uses the principle of adsorption, which is an exothermic phenomenon. The energy required to capture the water is therefore:

[0164] For Freeze Drying:

[0165] Q captation = Q condensation + Q solidification

[0166] Q captation = mΔH condensation + mΔH solidification

[0167] Q captation = 2591 kj

[0168] For the method according to the invention:

[0169] Q captation = Q adsorption

[0170] Q captation = mΔH adsorption

[0171] Q captation = 4187 kj

[0172] The adsorption rate of the zeolite is at least 12%, in the hypothesis detailed above this is 18%. Theoretically, a zeolite in optimal and pure condition can reach 27% adsorption rate. Thus, it is assumed that the zeolite is used in the process according to the invention in optimized conditions allowing an adsorption rate of the order of 18%.

[0173] Regeneration of the water catchment system requires:

[0174] For Freeze Drying:

[0175] Q régénération = Q fusion

[0176] Q régénération = mΔH fusion Q régénération 334 kJ

[0177] For the method according to the invention:

[0178] Q régénération = Q désorption + Q refroidissement

[0179] Q régénération =mΔH desorption + m adsorbant CP adsor ΔT

[0180] Q régénération =262 kj

[0181] In a process according to the invention, for desorption (regeneration), a gas stream, typically air, passes through the bed of adsorbent material and serves as a carrier fluid for the water vapor. At the desorption outlet, this air is therefore hot and humid, and therefore has significant energy recovery potential for use in other process steps.

[0182] Similarly, the subsequent cooling of the zeolite is done by a flow of air which heats up in contact with the adsorbent and from which the heat can be recovered.

[0183] In an ideal theoretical case, all the energy needed for regeneration can be recovered.

[0184] The table below summarizes the different needs and potential gains (by recovery) in thermal energy mentioned previously for the two processes (freeze-drying and according to the present invention).

[0185] The energy consumption evaluated by the method described above for freeze-drying (1.73 kWh / kg of water) is in agreement with the bibliographic data, in particular those published by Ademe (French Environment and Energy Management Agency) and by CETIAT (Technical Center for Air and Thermal Industries), which estimate it at 1.8 kWh / kg of water, which corroborates the calculation presented above (“Drying processes in industry”, coordinated by Aude-Claire HOUDON et al.; ADEME Éditions, February 2017, ISBN: 9791029707919).

[0186] Regarding the process according to the invention, 100% energy recovery is obviously only theoretical.

[0187] In practice, a recovery of 40% (or more) of the thermal energy generated during adsorption and a recovery of 50% (or more) of the energy available in the water vapor-rich gas leaving the drying device during the regeneration phase have been achieved by the Applicant. These energy recovery rates can be further improved, in particular by improving the exchangers or heat pumps used and their operating conditions.

[0188] The method for managing a dehydration system according to the invention therefore allows, with these recovery rates, an energy consumption of approximately 0.94 kWh / kg of water, which can be further optimized. This is significantly less than a freeze-drying process and this places the method proposed in the invention at the level of the best hot air drying processes (which require between 0.9 and 1.3 kWh / kg of water), while ensuring minimal degradation, in particular thermal, of the product being dehydrated. An energy-neutral or almost energy-neutral process, except for the operation of machines such as pumps and refrigeration units, seems achievable by a method according to the invention

[0189] Thus, a dehydration system according to the present invention may require only a small single heat input at the regenerating water trap. In the long term, this input may be further reduced or even eliminated.

[0190] All other heat requirements can be covered by thermal energy recovery.

[0191] Finally, in order to limit the overall energy requirements of the dehydration workshop, excess energy under certain operating conditions of the system can be used by other elements of the workshop (heating of domestic water, heating of premises, etc.).

Claims

Claims 1. Method for managing a dehydration system adapted to dehydrate a product, the dehydration system comprising a drying device (5) containing an adsorbent material, the method comprising: - water adsorption phases (S2) by the adsorbent material in order to reduce the partial pressure of water vapor in a carrier fluid circulating in the dehydration system during the dehydration of the product, and - regeneration phases (S3) under vacuum, at a pressure at least 500 millibars lower than atmospheric pressure, during which the adsorbent material recovers adsorption properties; the adsorbent material being such that the adsorption of water is exothermic, characterized in that the process comprises steps of: - recovery of thermal energy (S5) at the level of the drying device (5) during the water adsorption phases (S2), and - use (S6) of recovered thermal energy for: + heating the product (S11) during its dehydration; and + heating the adsorbent material (S32) in the regeneration phase, the method further comprising, between the regeneration phase (S3) and the adsorption phase (S2), a cooling phase (S4) of the adsorbent material, and the thermal energy recovery step (S5) comprises the recovery of thermal energy at the drying device (5) during the cooling phase (S4) of the adsorbent material.

2. Method according to claim, in which the thermal energy recovery step (S5) comprises the recovery of latent heat of condensation of the water vapor present in a gaseous flow expelled from the adsorbent material during the regeneration phase (S3).

3. A method according to claim 1 or claim 2, wherein the thermal energy recovery step (S5) comprises recovering thermal energy at a mechanical device of the dehydration system, for example a pump, and wherein the recovered thermal energy is used for: + heating the product (S11) during dehydration; and / or + heating the adsorbent material (S32) during the regeneration phase; and / or + maintaining the temperature of a heat transfer fluid.

4. Method according to any one of the preceding claims, the dehydration system comprising a second drying device (5'), in which the recovered thermal energy is used at least in part for heating the second drying device (5') in the regeneration phase.

5. Method according to one of the preceding claims, comprising the steps of: - placing the product in a dehydration chamber (2); - establishment in the dehydration chamber (2) of a pressure at least 500 millibars lower than atmospheric pressure; - establishment between the inlet of the dehydration enclosure and an outlet of the dehydration enclosure of a flow of carrier fluid; and - adsorption of water contained in the carrier fluid leaving the dehydration chamber (2) by the adsorbent material contained in the drying device (5).

6. Method according to claim 5, in which the pressure of the carrier fluid is raised between the outlet of the dehydration chamber (2) and the drying device (5).

7. The method of claim 6, wherein the pressure of the carrier fluid is increased by at least 300 millibars.

8. Method according to one of the preceding claims, in which the product is brought to and maintained at a temperature between 20°C and 70°C, preferably between 30°C and 40°C, during its dehydration.

9. A method according to any one of the preceding claims, wherein the heating of the adsorbent material in the regeneration phase and the heating of the product during dehydration require a total amount of thermal energy and wherein the recovery of thermal energy in the system covers at least 20%, preferably at least 50%, and more preferably at least 70% of said total amount of thermal energy.

10. Dehydration system comprising a dehydration chamber (2) in which a product to be dehydrated is placed, and at least one dehydration device (1) comprising a drying device (5) comprising an adsorbent material adapted to adsorb water contained in a carrier fluid which passes through the drying device (5), the adsorbent material being such that the adsorption of water is exothermic, the dehydration device (1) comprising a flow management module (3) adapted to generate and control a flow of carrier fluid in the dehydration device (1) and in the dehydration chamber, characterized in that the dehydration system comprises: - a thermal energy recovery device at the level of the drying device (5) and - a device for distributing thermal energy to a means for heating the product in the dehydration chamber (2), and / or - a means for storing thermal energy for use in heating the adsorbent material of the drying device (5) when the latter is in the regeneration phase, and in that the system comprises a vacuum source configured to place the adsorbent material at a pressure at least 500 millibars lower than atmospheric pressure during its regeneration.

11. System according to claim 10, in which the device comprises a second drying device (5'), and in which system further comprises a means for distributing the recovered thermal energy adapted to distribute to the second drying device (5') all or part of the recovered thermal energy in order to heat the drying material of the second drying device (5') when it is in the regeneration phase.

12. System according to claim 10 or claim 11 in which the thermal energy recovery device comprises a gas / liquid exchanger.

13. System according to one of claims 10 to 12, wherein the thermal energy recovery device comprises a heat pump.

14. System according to one of claims 10 to 13, further comprising means for recovering thermal energy emitted by mechanical devices of the system.

15. System according to any one of claims 10 to 14, in which the dehydration enclosure (2) comprises a set of shelves for receiving trays adapted to contain a product to be dehydrated and in which the means for heating the product comprises a set of conduits containing a heat transfer fluid heated in whole or in part via one or more exchangers connected to the thermal energy recovery device.

Images