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    • 专利摘要:
    Drying chamber (2) for agricultural or marine products comprising: - shelves (3) for supporting agricultural or marine products to be dried, the shelves (3) being arranged parallel to one another inside the chamber of drying (2), - a drying fluid inlet (4) and an outlet of the drying fluid (5) separated by the shelves (3), so as to place the shelves (3) along the drying fluid flow inside the drying chamber (2), the drying fluid inlet (4) being positioned at one end of the drying chamber (2), the drying fluid outlet (5) being arranged at the opposite end of the drying chamber (2). The shelves (3) are positioned to separate the flow of drying fluid from the inlet (4) into a plurality of sub-flows, a sub-flow circulating parallel between two shelves (3). The drying chamber (2) is connected to a solar collector configured to heat the drying fluid before entering the drying chamber (2).
    公开号:FR3040774A1
    申请号:FR1558218
    申请日:2015-09-04
    公开日:2017-03-10
    发明作者:Gatien Fleury；Florian Delrue；Arthur Elie；Jean-Francois Sassi
    申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    Solar dryer for agricultural or marine products.
    TECHNICAL FIELD OF THE INVENTION The invention relates to a solar dryer for agricultural or marine products, and more particularly to a drying chamber for agricultural or marine products. State of the art
    Spirulina (Arthrospira Platensis) is a microalga with a high content of proteins, vitamins, minerals and saturated fatty acids. Proteins represent 60 to 70% of the dry weight of Spirulina. This microalgae therefore has a high nutritional potential and is commonly used for food as a dietary supplement.
    Dried Spirulina can maintain its nutritional qualities for many years. The dehydration of spirulina not only prevents the presence of microorganisms and stops enzymatic reactions, but also reduces the weight and volume of spirulina, which then facilitates transport and storage.
    It is therefore essential to be able to effectively dehydrate Spirulina.
    Several drying techniques currently exist: 1) Freeze-drying (freezing + sublimation drying by means of a vacuum pump), 2) Spray drying (dispersion of the fluid paste in a hot carrier gas), 3) Air drying Convective heat using a primary resource, 4) Direct solar drying, 5) Indirect solar drying.
    Lyophilization and spray drying are drying techniques requiring the use of advanced technologies, and therefore a significant initial investment. In addition, they are particularly energy-intensive (freezing, pump, heating, etc.).
    Convective hot air drying is one of the most widely used processes in the industry: hot air is sent to the product to be dried. The hot air provides the heat necessary for the evaporation of the liquid, present in the product, and drives the vapor formed. Hot air can be obtained by burning natural gas. This technique also requires a lot of energy for the combustion of gas and is therefore not suitable for drying micro-algae in a traditional way.
    To dry small amounts of spirulina, electric dehydrators are often used. The principle is to use the electrical power both for the renewal of the air (convection) and as a source of heat. The best known manufacturers include Stockli and Tribest.
    Techniques 4) and 5) are particularly interesting because they take advantage of solar radiation as a source of heat.
    "Direct" solar drying exposes the material to be dehydrated to solar radiation. For example, the solar dryer is in the form of a tent. The walls of the tent are made of plastic. Foods to dry, such as fish, are placed on the floor of the tent. Air inlets at the bottom of the tent provide air convection and food drying ("Conserving and Transforming Fish", edited by GRET, ISBN: 2-86844-053-3) .
    This drying technique is widely used worldwide because it is simple to set up and requires little investment.
    However, this direct exposure can cause damage such as the cutting of chemical bonds by ultraviolet (UV), or the uncontrolled overheating of the material for example.
    The last technique, indirect solar drying 5), is a technique commonly used for the drying of foodstuffs (fruits, mushrooms, vegetables, etc.) and microalgae.
    In this drying technique, the foodstuffs to be dried are not directly subjected to solar radiation and especially to UV. The temperature of the food is thus much more homogeneous and does not reach any extrema likely to degrade the products: the integrity of the proteins or vitamins is preserved.
    As shown in FIG. 1, the solar dryers comprise a solar collector 1 and a drying chamber 2, in fluid communication. Fluidic communication means that the air can flow from the solar collector 1 to the drying chamber 2.
    The products to be dried are distributed in the drying chamber 2 on different floors, on shelves 3 or racks. The air is heated in the solar collector 1 and then flows to the drying chamber 2. The movement of the air is from top to bottom in the drying chamber 2.
    However, in this type of device, the hot and dry air is introduced from below the product. The air cools and gets wet with the first layers of product. The upper layers are not dried at the same time as the first layers. In addition, the product with the lowest moisture content is in contact with the hottest and least humid air. There is always a risk of damaging temperature sensitive products.
    To ensure good uniformity of drying to overcome this disadvantage, it is possible to stir the product and / or manually move the shelves 2. However, this type of device is not practical to implement.
    OBJECT OF THE INVENTION The object of the invention is to overcome the drawbacks of the prior art and, in particular, to provide a drying chamber for homogeneously and effectively drying the product to be dehydrated.
    This object is achieved by a drying chamber for agricultural or marine products comprising: - shelves for supporting agricultural or marine products to dry, the shelves being arranged parallel to each other within the drying chamber, - a drying fluid inlet and a drying fluid outlet separated by the shelves, so as to place the shelves along the drying fluid stream within the drying chamber, the drying fluid inlet being positioned on one end of the drying chamber, the drying fluid outlet being disposed at the opposite end of the drying chamber.
    The shelves are positioned to separate the flow of drying fluid from the inlet into a plurality of sub-streams, a sub-flow circulating parallel between two shelves.
    This object is also achieved by a solar dryer for agricultural or marine products, comprising: - a drying chamber as previously described, - a solar collector, provided with a drying fluid inlet and a drying fluid outlet the solar collector being configured to heat the drying fluid; a junction system connecting the output of the drying fluid of the solar collector to the drying fluid inlet of the drying chamber.
    BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given by way of nonlimiting example and represented in the accompanying drawings, in which: FIG. , schematically, in section, a solar dryer according to the prior art, - Figure 2 shows in three dimensions, schematically, a drying chamber according to one embodiment of the invention, - Figure 3 shows in three dimensions, schematically, a shelf of a drying chamber according to one embodiment of the invention, - Figure 4 shows in three dimensions, schematically, a solar dryer comprising a drying chamber and a solar collector according to one embodiment of the invention, - Figure 5 shows in three dimensions, schematically, a solar collector according to a embodiment of the invention; FIG. 6 is a graph giving the equilibrium temperature of a solar collector as a function of the emissivity of the surface, in the theoretical case where there would be no cooling by convection and for an incident solar flux of 800 W / m 2; FIG. 7 is a graph giving the power emitted by a solar collector as a function of the emissivity of the surface for the same hypotheses as those of FIG. 6; the line represents the typical solar power at midday in summer in PACA.
    Description of a preferred embodiment of the invention
    The drying chamber 2 is a drying chamber for agricultural or marine products, especially for food applications. The products to be dehydrated can be fruits, vegetables, or even mushrooms.
    It may also be algae, and more particularly microalgae. Preferably, the microalga to be dried is spirulina, a cyanobacterium highly cultivated in the world. The algal biomass is generally obtained, after a filtration step, in the form of a paste comprising more than 80% water. To be dried, the dough is placed in the drying chamber 2 in the form of a thin layer or in the form of spaghetti.
    As illustrated in FIG. 2, the drying chamber 2 for these agricultural or marine products is hollow and comprises an inlet for a drying fluid 4 and an outlet for the drying fluid 5. In the particular example of Figure 2, the drying chamber 2 has substantially the shape of a straight block which comprises an upper wall 6, a bottom wall 7, two side walls, a front wall and a rear wall.
    The upper wall 6 and the lower wall 7 are substantially parallel to each other. The inlet of the drying fluid 4 is disposed at one end of the drying chamber and the outlet of the drying fluid 5 is disposed at the opposite end of the drying chamber 2.
    The so-called front wall corresponds to the front face of the drying chamber 2. The air inlet 4 is positioned on the front wall. The front wall is advantageously perpendicular to the upper and lower walls 6 and 7.
    In the illustrated configuration, the inlet port 4 and the outlet port 5 are configured so that the flow of air, represented by the arrows in FIG. 2, is parallel to the upper and lower walls 6 and 7 over at least part of its path between the air inlet 4 and the air outlet 5.
    A flow of drying fluid can circulate inside the drying chamber 2 from the inlet orifice 4 to the outlet orifice 5. The drying fluid being hot, it tends to rise to the inside the drying chamber. It is therefore particularly advantageous to place the outlet orifice higher than the inlet port when the chamber is in operation.
    The flows of the drying fluid in the various figures are represented by solid arrows. The drying fluid could be a neutral gas, nitrogen type. Advantageously, the drying fluid is air because it is easily accessible. In the remainder of the description, the drying fluid is presented as being air.
    In the illustrated embodiment, the air inlet 4 is positioned on the front wall to best scan the entire internal section of the chamber. The air outlet 5 is arranged so that the air circulates easily and passively between the bottom wall 7 and the upper wall 6, that is to say that the air outlet 5 is arranged higher than the air inlet so that the air enters through the front wall and the air flows between the upper wall 6 and the lower wall 7 to the air outlet 5.
    The air outlet 5 can be positioned at the rear wall, located opposite the front wall. In this configuration, and if the air outlet is at the same level as the air inlet, a fan may be disposed at the air inlet 4 to force, accelerate the movement of air between the air inlet 4 and the air outlet 5.
    The air outlet 5 may be disposed at the lower face 7 of the drying chamber 2. A fan may be used to force the convection. This configuration is advantageous, especially at the beginning of drying since the air can become colder than the ambient air, after passing through the dryer and after being charged with moisture.
    Indeed, hot air gives up its "sensible" heat to compensate for the enthalpy of vaporization of the water contained in the product to be dried, which passes into the vapor phase.
    Preferably, the air outlet 5 is disposed at the upper face 6 of the drying chamber 2. The air leaving the drying chamber, being hotter than the air outside the chamber, in particular at the end of drying, the drying air will tend to rise and will be easily evacuated by the outlet 5 positioned on the top wall 6 of the drying chamber 2. Advantageously, a chimney is positioned above the outlet 5 of the Drying chamber 2 to have a larger draw. Electric assistance can be used to improve the draft.
    According to another alternative, the draft can be improved with a solar chimney device: a solar energy absorbing material is positioned on the chimney to heat the air and thus improve the draft.
    The chamber 2 further comprises shelves 3 for supporting the agricultural or marine products to be dried.
    By shelf is meant a small rack or a small removable tray for supporting the product to be dehydrated. The air inlet 4 and the air outlet 5 are separated by the shelves 3, so as to place the shelves 3 along the flow of air inside the drying chamber 2, and so as to that the surface of the shelves is swept by the air.
    The shelves 3 are arranged parallel to each other inside the drying chamber 2. In parallel, it is meant that the shelves can also be substantially parallel to each other.
    In conventional drying chambers, the shelves 3 are arranged perpendicularly to the air flow (FIG. 1).
    The shelves 3 of the drying chamber 2, according to the invention, are arranged parallel to the flow of air inside the chamber, that is to say that the vector representative of the air flow is parallel to the surface of the rack supporting the material to be dried.
    The shelves 3 are positioned to separate the flow of drying fluid from the inlet 4 into a plurality of sub-flows, a sub-flow circulating parallel between two shelves 3. The inlet port 4 and the outlet orifice 5 are advantageously configured so that the air circulating in the chamber has similar flow rates (temperature and mass flow of air) in the different channels.
    In the configuration illustrated in FIG. 2, the shelves 3 are arranged perpendicularly to the front wall so as to be arranged parallel to the flow of air entering through the air inlet 4. The shelves 3 are arranged parallel to the upper walls 6 and lower 7. The space between two consecutive shelves 3 defines a longitudinal air flow channel 8, also called circulation channel or hydraulic channel. The flow of air flows along these channels 8, parallel to the shelves 3. More particularly, in each channel 8 circulates a sub-flow of air.
    As the hot air circulates parallel to the shelves 3, the product to be dehydrated, distributed on the various shelves 3, receives air having the same degree of hygrometry for each of the shelves.
    At the outlet, the air loaded with moisture, in contact with the products to be dehydrated, is discharged through the outlet orifice.
    This particular arrangement leads to a better distribution of the air flow in the different channels, leading to a better homogeneity of the drying. There is no need for manual intervention to distribute the airflow or move shelves during drying so that the products to be dehydrated dry on average at the same speed.
    As shown in FIG. 3, the shelves 3 are advantageously formed of a support zone 3a which is permeable to air and of a void zone 3b.
    By permeable to air, it is meant that the air can cross, penetrate the support zone. The support zone can support the material to be dewatered while permitting the penetration of air, which facilitates drying of the biomass on both sides.
    The empty zone 3b forms a hole allowing the unobstructed passage of air towards the air outlet 5 of the drying chamber 2.
    The empty zone 3b, configured to allow the passage of air, is at the air outlet 5 of the drying chamber 3b in the case of an outlet orifice formed in the upper wall 6, or in the bottom wall 7.
    The support zone 3a supports the products to be dehydrated. It may be a sieve or a grid, for example nylon. The air circulating both in the air channel located above the shelf 3 and in the air channel below the shelf, the products to be dehydrated are in contact with two air circulation channels and drying is more efficient.
    The shelf 3 may have a length greater than its width. The length of the shelf 3 is the size of the shelf 3 along the axis which connects the air inlet to the outlet and which is substantially parallel to the air flow.
    For example, for a shelf 3 having a length of 75 cm and a width of 57.5 cm, the empty zone 3 b has a dimension of 50 cm x 17 cm and the porous support zone 3 a has a dimension of 50 cm x 50 cm.
    The shelves will, advantageously, all positioned in abutment at the rear face of the drying chamber, so as to have the empty areas 3b of all shelves 3 aligned.
    In the embodiment where the air outlet 5 is on the rear wall, the shelf 3 may not have a void area 3b. It then formed, advantageously, a frame supporting the screen or the grid.
    According to a preferred embodiment, for large shelves in particular, the shelves 3 have a length less than their width, to improve the homogeneity of drying on the same shelf. The products arranged towards the rear face will dry substantially at the same speed as the products arranged towards the front face. The width of the shelf is advantageously twice as large as the length.
    Shelves 3 are advantageously made from a material that can be brought into contact with food products, typically polyethylene. The material must be rigid enough to bear the weight of the products to be dried and, at the same time, have good mechanical properties (tribological, ease of handling, tightness, creep resistance).
    Each shelf 3 comprises, advantageously, handles to facilitate its handling.
    Each shelf is removably mounted in the drying chamber.
    The biomass to be dried is distributed over the various shelves 3. The shelves 3 are then inserted into the drying chamber.
    According to a first alternative, the shelves 3 are inserted by the rear face. The positioning of the air outlet 5 at the top wall 6 is particularly advantageous in the case of loading the shelves by the rear face. This avoids having to disassemble and reassemble the elements arranged at the outlet orifice. According to another alternative, the elements forming the air outlet 5 are integrated in the rear face, to facilitate handling.
    According to another alternative, the shelves 3 can be inserted by one of the two side walls.
    In order to improve the distribution of the air flow, the distance between two consecutive shelves 3 can be modified. The drying chamber comprises means for adjusting the position of the shelves inside the chamber 2 and more particularly the distance between two shelves along an axis passing through the upper face and the lower face.
    Advantageously, the distance between two shelves is increasing from the bottom wall 7 to the upper wall 6 of the drying chamber 2. The section of the hydraulic channels 6 is increasing from the bottom wall 7 to the upper wall 6 of the drying chamber 2 The section of a longitudinal air channel 8 depends on the distance between two consecutive shelves 3 and the distance between the side walls. The section of a channel 8 corresponds to the product of the height between two shelves and the width of a shelf. Advantageously, all the shelves 3 have the same width and the same length.
    According to another preferred embodiment, compatible with the previous embodiment, aperture gradient plates 9 are arranged at the inlet 4 and / or at the outlet 5 of the drying chamber 2.
    In Figure 2, for more visibility, only the aperture gradient plate 9, disposed at the air outlet 5 of the drying chamber 2 is shown. Preferably, aperture gradient plates 9 are present both at the air inlet 4 and at the air outlet 5 of the drying chamber 2.
    The aperture gradient plates 9 are configured to change the hydraulic resistance of the air entering and leaving the chamber.
    The modification of the hydraulic resistance of the channels 8 makes it possible to homogenize the flow of hot air and the temperatures inside the drying chamber 2: the flow in each longitudinal air circulation channel 8 is uniform.
    The aperture gradient plates 9 at the inlet 4 and at the outlet participate in the distribution of the air flow between the shelves 3.
    These plates 9 are provided with openings. The openings can be of any shape. They are advantageously circular. This type of opening is easily achieved by drilling (forests, saws bells).
    The openings have different sizes and / or different opening rates. For an aperture-gradient plate located at the entrance, the apertures closest to the upper wall 6 are smaller than those which are close to the bottom wall 7 and / or they are in a lower density than near the bottom wall. lower wall. For example, the circular openings near the bottom wall 7 have a diameter of 3 cm while those close to the top wall 6 have a diameter of 2 cm. Hot air, having a lower density than cold air, rises naturally. This gradient section allows better distribution of hot air within the drying chamber 2, putting obstacles on the natural path of the hot air, ie by placing smaller openings in the natural passage of the hot air (in the upper part of the drying chamber).
    This opening gradient is particularly advantageous upstream of the drying chamber, that is to say positioned at the air inlet 4 of the drying chamber 2. The opening gradient plate 9 is , advantageously, configured so that the flow is identical between the channels.
    The aperture gradient plate 9 on the front face is advantageously perpendicular to the shelves 3 positioned in the drying chamber 2.
    The aperture gradient plate 9, positioned between the air inlet 4 and the shelves 3, is configured to change the inlet hydraulic resistance in a circulation channel 8 defined by two consecutive shelves.
    The openings of the plate 9 are advantageously positioned below each shelf, or between two shelves, to better control the effective cross section of the longitudinal channel.
    The openings are advantageously distributed homogeneously over the entire width of the shelves. There is, for example, between 5 and 10 openings, advantageously equidistant over the width of the plate 9.
    In the case where the air outlet 5 is at the level of the rear wall, the opening gradient plate 9 will advantageously be perpendicular to the shelves 3 and to the upper wall 6 and / or advantageously parallel to a gradient plate. opening disposed at the entrance of the chamber 2.
    In the case where the device comprises an air outlet 5 at the top wall 6, the opening gradient plate 9 is positioned at the top of the drying chamber 2. It is advantageously parallel at the upper wall 6 and the shelves 3.
    It is advantageous that the input aperture gradient plate has at least the same air inlet surface as the exit aperture gradient plate.
    The drying chamber may comprise a convection system, preferably powered by a photovoltaic panel, possibly connected to a battery, as described in patent BE 1008430. The convection system may be formed of one or more fans. This or these fans can be powered by the battery.
    This forced convection allows a homogenization of the temperature in the drying chamber, a better homogeneity of drying and an acceleration of the dehydration process. This embodiment associating a forced convection and a photovoltaic panel is particularly advantageous, especially in tropical latitudes where the outside air is humid and the solar resource important. The use of one or more batteries (electrochemical accumulators) to power one or more fans, avoids depend on weather conditions for drying, especially in the case of the passage of cloud formations.
    The battery or batteries and possibly a thermostat may be arranged in an electrical cabinet 16 fixed on the supports of the drying chamber 2 (Figure 4).
    Advantageously, it is possible to integrate, in addition, into the control circuit a rain sensor to neutralize forced convection in case of rain, which would result in the rehydration of products.
    Optionally, in the case where the product to be dehydrated is not arranged in a homogeneous manner, it is possible to stir the shelves 3 from time to time manually, or by using a stirring device.
    The drying chamber 2 is advantageously part of a solar dryer for agricultural or marine products. As shown in FIG. 4, the dryer comprises, in addition to the drying chamber 2 previously described: a solar collector 1, provided with an air inlet 12 and an air outlet 13, a system junction connecting the air outlet 13 of the solar collector 1 to the air inlet 4 of the drying chamber 2.
    The solar collector 1 serves to heat the air: the air enters the solar collector 1 where it is heated, then it emerges from the solar collector 1 to be transmitted to the drying chamber 2 via a connector.
    The ambient air temperature is of the order of 15-30 ° C, depending on the seasons and the latitude of use of the invention.
    To dehydrate the products, the temperature of the air entering the drying chamber 2 should preferably be between 20 ° C and 70 ° C, and ideally between 40 ° C and 70 ° C. The temperature at the outlet of said chamber, when the material to be dehydrated is dry, may be close to the inlet temperature. When operating without forced convection, the outlet temperature of the drying chamber is ideally less than 40 ° C.
    Advantageously, the temperature of the air at the outlet of the solar collector will be greater than the temperature of the inlet air of the solar collector from 5 ° C. to 40 ° C. To obtain a solar collector that effectively heats the ambient air up to 20-70 ° C, and ideally up to 40-70 ° C, it is necessary either to use large areas dedicated to the absorption of incident radiation, either to use smaller surfaces and to cover it with a coating, for example a black painted plate, to improve the absorption of incident radiation or to make surface patterns on the plate, such as grooves, for improve heat exchange with the air.
    Another solution is to use a solar collector equipped with solar collection tubes, used for the thermal water heaters (as described in the document CN 103322779). These are glass vacuum tubes in which tubes are inserted with a selective treatment, such as a multilayer deposit.
    However, these solar collectors have either a low solar capture efficiency because the black paint has, in particular, the disadvantage of strongly emitting infrared radiation, or a high investment cost in the case of the use of vacuum tubes.
    In order to heat the ambient air with a high efficiency and a low investment cost, the solar collector 1 forms a heating chamber for the drying fluid and comprises (FIG. 5): an inlet of the drying fluid 12, outlet of the drying fluid 13, o a solar absorber 15 disposed between the inlet 12 and the outlet 13 of the drying fluid and arranged to heat the drying fluid, o a window configured to allow the capture and transmission of incident radiation by the solar absorber.
    In the embodiment illustrated in FIGS. 4 and 5, the solar collector more particularly comprises: a pane forming an upper wall arranged to receive the incident solar radiation, the upper wall being advantageously disposed in parallel to the air flow from the air inlet 12 to the air outlet 13 of the solar collector 1, - a bottom wall 11, - two side walls, - a front wall and a rear wall, - a solar absorber Disposed between the upper wall 10 and the lower wall 11, the absorber 15 being disposed substantially parallel to the upper wall 10.
    This solar collector 1 effectively heats the ambient air to a temperature of 30 ° C to 70 ° C, and ideally 50 to 70 ° C output 13 of the sensor.
    The temperature of the ambient air obviously depends on the weather conditions. The temperature at the outlet of the solar collector 13 depends on the temperature of the air, the incident light intensity and the exposure time of the sensor in the sun. A thermal inertia is present at the beginning of exposure, more or less important depending on the geometry and building materials of said sensor.
    In order for the temperature of the air at the outlet of the solar collector to be of the order of 70 ° C., the corresponding temperature of the absorber is of the order of 100 ° C.
    The temperature is regulated by convection: warmer air circulates faster, which creates a self-regulation of temperatures.
    In the case of the integration of a fan, it is possible to increase the speed of rotation of the fan to limit the residence time of the air in the solar collector, to reduce the temperature of the hot air.
    It is possible to use temperatures above 70 ° C without the product being damaged, as long as the product is wet, because the transfer of water from the product to the air (vaporization) consumes energy (enthalpy) and therefore cool the product.
    Solar radiation enters the solar collector 1 through the glass. The window advantageously limits the convective losses. The window is advantageously made of glass and, more particularly, of translucent glass. Glass is the material that has one of the best transmissions. Even more advantageously, this glass will be coated with an antireflection material to improve the transmission of incident energy.
    Advantageously, the window limits the convective losses, i.e. the convective losses of the air heated by the absorber.
    The solar collector 1 is advantageously inclined at an angle of approximately 15 ° to obtain the best possible effect of the solar radiation on the pane. This angle is however variable depending on the location of the solar dryer. The solar absorber 15 is a metal plate so as to be easily achievable at a lower cost, preferably aluminum, aluminum alloy or stainless steel (for example AISI 430 or 304). The plate has a thickness of a few millimeters, typically of the order of 2 mm. The absorber has substantially the same length and the same width as the heating chamber, and in the example shown, the same length and the same width as the upper wall 10 and lower 11 of the sensor 1 to gain efficiency. The absorber 15 is heated by the incident solar radiation. The absorber 15 is further advantageously covered with an optically selective coating. The selective coating allows a maximum absorption of the incident solar energy while re-emitting the least possible infrared radiation (principle of the black body). In particular, the selective coating absorbs more than 80% of the incident light and reflects less than 25% of the infrared (IR) radiation.
    This coating makes it possible to significantly increase the equilibrium temperature of the solar collector. The equilibrium temperature is the temperature at which the flow of incident solar radiation and the energy flow emitted in IR is at equilibrium, in the presence or absence of a convective air flow.
    The selective coating advantageously covers the entire surface of the solar absorber 15 intended to be exposed to the sun.
    The optically selective coating is, preferably, a paint layer.
    Before using the solar collector in a solar dryer to dehydrate food, the solar collector will preferably be heat treated (typically at 200 ° C for 15 min) to evaporate the solvent contained in the paint.
    Advantageously, this heat treatment leads to a hardening of the surface of the paint, and therefore to a better adhesion of the paint to the metal plate and thus to a greater robustness of the coating during the handling of the absorber.
    The graph of FIG. 6 notably illustrates the variation of this equilibrium temperature as a function of the optical properties of the surface (solar absorption and infrared emissivity of the surface).
    The numerical values were obtained with an incident solar flux of 800 W / m2, and without the plate being cooled by air convection. Under actual real operating conditions, the use of a convection makes it possible not to reach the temperature values indicated in the graph.
    The decrease in emissivity leads to an increase in the equilibrium temperature, which improves the efficiency of the solar collector. The solar energy captured by the absorber is thus transferred to the air and the radiative losses are limited.
    Indeed, the higher the equilibrium temperature of the absorber, the more the air in the drying chamber will be hot and the more the drying will be effective.
    It has also been shown that an absorption of 0.9 significantly increases the equilibrium temperature with respect to an absorption of 0.5. The phenomenon is even more marked with low emissivity.
    FIG. 7 represents the influence of the value of the emissivity of a surface on the power emitted by this surface (W / m2) as a function of its temperature. The power emitted corresponds directly to the power lost. The thermal losses are divided into emissivity of the absorber, convection - particularly losses in the window - and conduction - a priori weak.
    The horizontal line at 800W / m2 represents the typical solar power at midday in the Provence Alpes Côte d'Azur (PACA) region in France.
    When the emissivity is reduced by a factor of 10, especially from 1 to 0.1, thanks to the presence of a surface coating, the infra-red losses of the surface are also reduced by a factor of 10.
    The exchange coefficient between the solar absorber and the air can be improved by texturing the solar absorber. The plate of the absorber can be provided on its surface with macroscopic patterns of millimeter size. It may be, for example, parallelepipeds, 2mm wide and 5mm in length. The parallelepipeds are separated from each other by a distance of 2mm.
    A better exchange coefficient makes it possible to heat the air in the solar collector more efficiently and, advantageously, to reduce the IR losses since the heat absorbed by the plate is transmitted more rapidly to the air.
    The solar collector may include one or more thermal insulators so as to limit thermal losses within the sensor. Advantageously, the insulation not only avoids heat loss by conduction to the outside but also reflects the IR radiation. It may be a material comprising a glass / aluminum fabric, such as that marketed by Winco Technologies under the name of SkyTechPro ® for example.
    The structure of the solar collector is, advantageously, wood which besides its low cost, is a good thermal insulator and avoids heat loss from the inside of the sensor to the outside. In order to ensure good outdoor durability, for example, a layer of paint or stain will be applied to improve its resistance to moisture.
    Advantageously, the section of the air inlet 12 is identical to that of the air outlet 13.
    In order to obtain identical sections, it is possible to equip the air inlet with a pierced plate 14 (FIGS. 4 and 5). The pierced plate 14 comprises at least one opening. The section of the opening of said plate 14 being identical to that of the air outlet 13 of the solar collector 1.
    If the plate 14 has a plurality of openings, the total area of the openings represents the air inlet effective section. This effective section is identical to the air outlet section 13. For example, circular openings 6cm in diameter can be used.
    The air outlet of the solar collector 1 will preferably have the same dimension as the air inlet of the drying chamber 2.
    The junction system advantageously comprises at least one flexible portion, bellows type, so as to change the angle between the solar collector 1 and the drying chamber 2 according to the seasons and sunshine.
    The joining system is, for example, formed of two sleeves and a flexible bellows, each sleeve being in contact either with the solar collector 1 or with the drying chamber 2.
    The solar collector 1 advantageously has a length of at least one meter in order to effectively heat the ambient air, but the collecting surface will advantageously be adapted to the location of implantation and to the quantity of material to be dehydrated. The solar collector 1 is for example in the form of a rectangular parallelepiped whose dimensions are 143cm x 100cm x35cm.
    The sizing of a dryer will depend on its location of use (geographical position), the period during which it is used and the amount of material that it is desired to dry. The first two data are decisive in the evaluation of the daily energy received by the solar collector and therefore the drying capacity of the dryer.
    As a first approach, sizing of the solar collection surface can be done according to the mass of water to be evacuated within the biomass, the number of days required for drying, and the dose of light energy received during of the day, according to the following equation:
    With:
    - S: the surface area of the sensor (m2) - meau: the mass of water to be evaporated (kg) - njmir: the number of days required / wanted for drying - Lv (T): the latent heat of evaporation of l water, function of the temperature and possibly weighted by the activity of the water (kJ / kg) - G *: the measurement of the solar radiation that receives the surface of the sensor in one day (kJ / m2) - η: the solar collector efficiency.
    A solar dryer comprising a non-optimized sensor may have a very low efficiency, that is to say of the order of 0.1 or less. The losses are mainly losses by IR emissivity, conduction at the solar collector, or losses related to the energy cost of the thermosiphon effect.
    The various sizing options (investment / efficiency compromise) will make it possible to increase the efficiency η of the solar collector.
    An optimized solar collector is produced, that is to say a sensor whose output can reach values greater than 0.3. To obtain such a yield, the emissivity of the absorber is preferably less than 0.1 and the bottom and side walls of the sensor comprise a thermally insulating material. This makes it possible to better capture and better conserve solar heat. From the previous equation, and considering that: - 1 kg of Biomass containing 80% of water must be dried (case of spirulina just wrung out of production basin); the biomass once dried must contain 10% residual water (20 g) to be compatible with long-term storage; there is therefore 780 g of water to evaporate, - the solar dryer is installed in the PACA region, - the drying must be done on a sunny day; the average sunshine of a day in October in PACA being 4.7 kWh or 16.92 MJ / m2, - the value of latent heat of evaporation is 3.5 kJ / g; this value is slightly high in order to take into account the activity of the water which becomes weaker and weaker as the matter dehydrates; this value of latent heat of evaporation is coherent with a shaping of Spirulina in the form of spaghetti of 2 mm of diameter for which the activity of the water remains relatively high, the surface of the solar collector absorbing the solar radiation necessary to obtain such a return is:
    Water activity is the pressure ratio between the water vapor at the surface of the product and the water vapor on the flat surface of a liquid at the same temperature. This is the saturation vapor pressure at a given temperature. The activity of water represents the availability of open water around the product. The activity of water A is 1 when the product is in contact with free water. For quality and conservation concerns, the water activity in the product should be lowered to 0.6. When water activity drops (around 20% humidity), more energy will be needed to eliminate. Even overestimating the area of the required solar collector, it is reasonable to assume that a 1 m2 solar collection area will be sufficient to dry the 1kg biomass to a residual moisture content of 10%.
    The biomass is deposited on shelves 3, of the filter cloth type. The biomass is deposited in the form of spaghetti 2mm in diameter. The heart of the product can easily be dehydrated. Such spaghetti is obtained by extrusion of the seaweed paste.
    The product is distributed evenly over the different shelves. For such a quantity, five shelves of 0.25m2 are used. Each shelf supports 200g of product.
    These proportions can be adapted according to the location and the period of use of the dryer (sunshine, temperature, humidity, etc.).
    权利要求:
    Claims (16)
    [1" id="c-fr-0001]
    claims
    1. Drying chamber (2) for agricultural or marine products comprising: - shelves (3) for supporting the agricultural or marine products to be dried, the shelves (3) being arranged parallel to each other inside the drying chamber (2), - a drying fluid inlet (4) and an outlet of the drying fluid (5) separated by the shelves (3), so as to place the shelves (3) along the flow of fluid for drying inside the drying chamber (2), the drying fluid inlet (4) being positioned on one end of the drying chamber (2), the drying fluid outlet (5) being arranged at the opposite end of the drying chamber (2), characterized in that the shelves (3) are positioned to separate the drying fluid flow from the inlet (4) into a plurality of sub-chambers. flow, a sub-flow circulating parallel between two shelves (3).
    [2" id="c-fr-0002]
    2. Drying chamber (2) according to claim 1, characterized in that the drying fluid outlet (5) is positioned on a face opposite to the face containing the drying fluid inlet (4).
    [3" id="c-fr-0003]
    3. Drying chamber (2) according to claim 1, characterized in that the drying fluid outlet (5) is positioned at an upper wall (6) of the drying chamber (2).
    [4" id="c-fr-0004]
    4. Drying chamber (2) according to claim 1, characterized in that the drying fluid outlet (5) is positioned at a lower wall (7) of the drying chamber (2).
    [5" id="c-fr-0005]
    5. Drying chamber (2) according to any one of claims 1 to 4, characterized in that an aperture gradient plate (9) is arranged between the drying fluid inlet (4) and the shelves (3), the aperture gradient plate (9) being configured to change the inlet hydraulic resistance in a circulation channel (8) defined between two consecutive shelves (3), the aperture gradient plate being perpendicular to the shelves (3).
    [6" id="c-fr-0006]
    Drying chamber (2) according to one of the preceding claims, characterized in that an aperture gradient plate (9) is arranged at the drying fluid outlet (5).
    [7" id="c-fr-0007]
    Drying chamber (2) according to claim 3 or 4 and 6, characterized in that the aperture gradient plate (9) arranged at the drying fluid outlet (5) is parallel to the upper wall (6).
    [8" id="c-fr-0008]
    8. Drying chamber (2) according to any one of the preceding claims, characterized in that the section of the longitudinal channels (8) defined by two consecutive shelves is increasing from the bottom wall (7) to the upper wall (6) of the drying chamber (2).
    [9" id="c-fr-0009]
    9. Drying chamber (2) according to any one of the preceding claims, characterized in that the shelves (3) are formed of a zone of breathable material (3a) and a void area (3b). ), the empty zone (3b) being configured to allow the passage of the drying fluid, the empty zone (3b) being at the outlet (5) of the drying chamber (2).
    [10" id="c-fr-0010]
    10. Drying chamber (2) according to any one of the preceding claims, characterized in that it comprises a convection system of the drying fluid, preferably supplied by a photovoltaic panel, optionally connected to a battery.
    [11" id="c-fr-0011]
    11. Solar dryer for agricultural or marine products, comprising: - a drying chamber (2) according to any one of claims 1 to 10, - a solar collector (1), provided with an inlet of the drying fluid (12). ) and an outlet of the drying fluid (13), the solar collector (1) being configured to heat the drying fluid, - a connector connecting the output of the drying fluid (13) of the solar collector (1) to the entering the drying fluid (4) from the drying chamber (2).
    [12" id="c-fr-0012]
    12. Dryer according to the preceding claim, characterized in that the solar collector (1) comprises: o an inlet of the drying fluid (12), o an outlet of the drying fluid (13), o a solar absorber 15 disposed between the inlet (12) and the outlet of the drying fluid (13) and arranged to heat the drying fluid in the heating chamber, said absorber being covered with an optically selective coating - a window configured to allow the transmission of incident solar radiation by the absorber.
    [13" id="c-fr-0013]
    13. Dryer according to the preceding claim, characterized in that the optically selective coating is a paint layer.
    [14" id="c-fr-0014]
    14. Dryer according to one of claims 12 and 13, characterized in that the solar absorber (15) is a plate made of aluminum, aluminum alloy or stainless steel.
    [15" id="c-fr-0015]
    15. Dryer according to the preceding claim, characterized in that the inlet of the drying fluid (12) of the solar collector (1) is provided with a pierced plate (14) comprising at least one opening, the section of the opening said plate (14) being identical to that of the output of the drying fluid (13) of the solar collector (1).
    [16" id="c-fr-0016]
    16. Dryer according to any one of claims 11 to 15, characterized in that the solar collector (1) comprises one or more thermal insulators so as to limit heat losses.
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    同族专利:
    公开号 | 公开日
    FR3040774B1|2018-09-07|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US4501074A|1981-02-17|1985-02-26|Hare Louis R O|Convection powered solar food dryer|CZ308627B6|2019-11-04|2021-01-13|Flexcraft s.r.o.|Solar dryer|
    CN108903022A|2018-09-28|2018-11-30|郑州智锦电子科技有限公司|Drying unit is used in a kind of processing of mushroom|
    CN109539694B|2018-11-13|2020-07-28|新疆泰宇达环保科技有限公司|Natural airing device for cutting silicon slag|
    CN111854346A|2019-04-28|2020-10-30|浙江康居能源科技有限公司|Solar energy inner loop formula high-efficient drying-machine|
    法律状态:
    2016-09-28| PLFP| Fee payment|Year of fee payment: 2 |
    2017-03-10| PLSC| Publication of the preliminary search report|Effective date: 20170310 |
    2017-09-29| PLFP| Fee payment|Year of fee payment: 3 |
    2018-09-28| PLFP| Fee payment|Year of fee payment: 4 |
    2019-09-30| PLFP| Fee payment|Year of fee payment: 5 |
    2021-06-11| ST| Notification of lapse|Effective date: 20210506 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1558218|2015-09-04|
    FR1558218A|FR3040774B1|2015-09-04|2015-09-04|SOLAR DRYER FOR AGRICULTURAL OR MARINE PRODUCTS.|FR1558218A| FR3040774B1|2015-09-04|2015-09-04|SOLAR DRYER FOR AGRICULTURAL OR MARINE PRODUCTS.|
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