Microwave device for continuous extraction and drying of solid organic products

Abstract

Microwave device for the continuous extraction and drying of solid organic products The invention relates to a microwave device (2) for the continuous extraction and drying of solid organic products in the form of plates, comprising a roller conveyor (4) for transporting the products (P) to be treated successively through an extraction chamber and a drying chamber, an extraction chamber (8) comprising a microwave-tight box (10) and inside which a waveguide (12) connected to a microwave generator (14) opens, a drying chamber (32) arranged downstream of the extraction chamber, separated therefrom by a vapor-tight and microwave-transparent separating wall (34), and comprising a hot air inlet (36) and a humid air outlet (38), an inlet sealing airlock (40) which is provided with wave traps (44),and an outlet airlock (42) which is provided with wave traps. Figure for abstract: Fig. 1.,

Description

Title of the invention: Microwave device for the continuous extraction and drying of solid organic products Technical field

[0001] The invention relates to the general field of microwave heat treatment of solid organic products in the form of plates.

[0002] A non-limiting field of application of the invention relates to the extraction and drying by microwave of wooden plates, in particular of wood resulting directly from the first transformation (or sawn timber). Prior art

[0003] In order to be used, the wood must be dry with a maximum water content of 12%. Drying can be done naturally but this requires a very long time, from 6 to 32 weeks or even several years. For this reason, wood manufacturers invest in hot air dryers. The time is reduced to 2 or 3 days but a resting time of about 15 days must be added for the wood.

[0004] These dryers represent significant investments that are difficult for wood manufacturers to bear. Indeed, the selling price of cubic meters of wood does not allow for high drying costs. In addition, current dryers generate mechanical stress in the wood, leading to the boards splitting during drying.

[0005] On the other hand, there is a wood extraction industry. Wood extracts, particularly from softwoods (terpenes, rosin, plant water), have added value for the flavor, cosmetic, pharmaceutical and food industries. This represents an industrial sector in its own right. The wood used for this purpose is an extraction by-product.

[0006] Various methods for extracting and drying wood using microwaves are known from the prior art. Thus, publication FR 2,770,441 discloses a method for drying wood using microwaves at a frequency of 915 MHz. The drying chamber is put under steam pressure (between 2 and 10 bars) to regulate the humidity level in order to prevent the surface of the wood from drying out before core drying is carried out. The water in the wood is rejected at its surface by the action of the microwaves and then evaporated. This air loaded with humidity passes over condensers to extract it. This method describes an evacuation of the exudates to the sewers after treatment, or a possible recovery. This method has the disadvantage of having to be carried out in batches, and not continuously, and of requiring the cavity to be pressurized.

[0007] Publication FR 3,070,869 is also known, which describes a continuous device by conveyor belt allowing the extraction of plant or organic materials. This document describes the presence of extraction chambers allowing the partial pressure of steam. This operation causes the vaporization of water molecules at the heart of the product, which drives the extracts and water towards the surface of the product and induces partial drying. However, this device is unsuitable for wooden boards and does not allow the final drying.

[0008] Publication CN 103789094 is also known, which describes a process for extracting Akila wood using ethanol as a solvent and under vacuum. However, this process is unsuitable for drying.

[0009] Publication US 6,546,646 describes a method for treating flat products by microwaves, heating, drying, disinfection, pasteurization, sterilization or vaporization. This treatment is carried out continuously by selective and differential zones and not homogeneously over the entire surface. The pressure and temperature are controlled. However, the exudates are not recovered.

[0010] Publication US 8,540,924 describes a method for continuously preheating pressed wood particle boards. The magnetrons of this device are arranged on either side of the boards. In theory, this method could allow the boards to be dried but it is not, however, suitable for extraction.

[0011] Publication US2008 / 0104857 describes a continuous multi-stage dryer for fiberboards. Each stage is equipped with rod-type microwave antennas and a humid air evacuation system. This type of antenna does not allow high power to be emitted and is not suitable for industrial use. Statement of the invention

[0012] The object of the invention is to propose a device and a method for combining the extraction and continuous drying of solid organic products in the form of plates.

[0013] According to the invention, this aim is achieved by means of a microwave device for the continuous extraction and drying of solid organic products in the form of plates, comprising: - a roller conveyor intended to transport the products to be treated successively through an extraction enclosure and a drying enclosure, - an extraction enclosure comprising a microwave-tight box and inside which at least one waveguide connected to a microwave generator opens, - a drying enclosure arranged downstream of the extraction enclosure, separated from the latter by a vapor-tight and microwave-transparent separating wall, and comprising at least one hot air inlet and at least one humid air outlet, - an inlet airlock which is positioned at the entrance to the extraction enclosure above the conveyor and which is fitted with wave traps, and - an outlet airlock which is positioned at the outlet of the drying chamber above the conveyor and which is fitted with wave traps.

[0014] The device according to the invention is characterized in particular by the fact that the product to be treated is in the form of plates. The penetration depth of the microwaves being approximately 5cm for a frequency of 2450MHz and 15cm for a frequency of 915MHz, the thickness of the plates will preferably be between 5mm and 100mm.

[0015] The product to be treated is continuously fed, via a microwave-tight inlet airlock, into a first extraction chamber in which the extracts and water from the product are collected in a condenser tank placed at a low point. Then, the product passes into a second drying finalization chamber before exiting via an outlet airlock that is also microwave-tight.

[0016] The invention thus makes it possible to combine the drying and extraction of products in a single operation. This invention makes it possible to find additional value in drying, resulting from energy savings, speed and, most importantly, the valorization of extracts. Indeed, if the drying operation of a product consists of extracting its water, this water can bring fragrances, active ingredients or value-added compounds. No prior art dryer proposes to carry out such a joint extraction operation, the vapours generated being sent into the atmosphere.

[0017] Preferably, the device further comprises a microwave-tight condenser tank which is arranged under the conveyor at the extraction enclosure in order to allow the recovery and condensation of extracts from the products. In this case, the condenser tank may comprise a low point provided with an outlet.

[0018] The conveyor may comprise a plurality of horizontal rollers positioned transversely to the direction of advance of the products to be processed.

[0019] In addition, the extraction enclosure and the drying enclosure may each comprise a plurality of vertical rollers positioned against side walls in order to ensure vertical guidance of the products to be treated.

[0020] The side walls of the extraction enclosure preferably comprise, on an internal face, a double skin allowing the circulation of a fluid during the start-up phases, and on an external face a thermal insulator.

[0021] Also preferably, the extraction enclosure comprises a horizontal wall made of a material transparent to microwaves and intended to be positioned above the products to be treated in order to prevent the extraction vapors from rising into the extraction enclosure.

[0022] Advantageously, the device further comprises a system for moving the products to be processed on the conveyor.

[0023] The invention also relates to a use of the device as defined above for the continuous extraction and drying of wooden boards.

[0024] In this case, the wood may be raw pine wood containing 40% water, 1.26% terpenes and 3.16% rosin. Brief description of the drawings

[0025] [Fig-1] [Fig. 1] is a longitudinal sectional view of a device for extraction and drying according to the invention.

[0026] [Fig.2] [Fig.2] is a view along II of the device of [Fig.l] loaded with wood to be treated.

[0027] [Fig.3] [Fig.3] is a sectional view along III-III of the device of [Fig.l] loaded with wood to be treated.

[0028] [Fig.4] [Fig.4] is a sectional view along IV-IV of the device of [Fig.l] loaded with wood to be treated.

[0029] [Fig.5] [Fig.5] is a sectional view along VV of the device of [Fig.l] loaded with wood to be treated.

[0030] [Fig.6] [Fig.6] shows the detail of the quarter-wave trap of the inlet airlock of the device of [Fig.l]. Description of the embodiments

[0031] The invention relates to the continuous extraction and drying of solid organic products by means of a microwave device 2 such as that shown in [Fig.l].

[0032] The organic products to be treated may be wood, in particular wood directly from primary processing (or sawn timber). For example, it may be raw pine wood containing 40% water, 1.26% terpenes and 3.16% rosin. They are in the form of plates having, for example, a width of 100mm to 1m, a length of 500mm to 6m and a thickness of 5 to 100mm. Depending on the products treated, the thickness of the plates may be even greater.

[0033] For an example of application to wood drying, the product plates to be treated may correspond to the standards from the sawing industry. The challenge is then to reduce the humidity level of fresh wood, generally between 30 and 60% and considered on average at 40%, to a rate of 12% to allow its applications in construction timber and heating wood.

[0034] The device 2 according to the invention comprises in particular a roller conveyor 4 which is intended to transport the products P to be treated successively through an extraction enclosure and a drying enclosure.

[0035] More specifically, the conveyor 4 comprises a plurality of horizontal rollers 6 which are positioned transversely to the direction of advance of the products to be processed through the device.

[0036] These horizontal rollers 6 make it possible to horizontally guide the plates of products P to be treated, the latter being advantageously moved on their edge (several plates moving on the conveyor in parallel can be envisaged).

[0037] The device also comprises an extraction enclosure 8 into which the plates of products P to be treated first penetrate.

[0038] This extraction enclosure comprises a box 10 which is microwave-tight and inside which at least one waveguide 12 opens, connected to a microwave generator 14.

[0039] The number of waveguides 12 of the extraction enclosure depends on the flow rate of products to be treated. It is typically between 1 and 20. In the exemplary embodiment of [Fig.l], four waveguides 12 regularly spaced from each other open into the box 10 of the extraction enclosure.

[0040] The power of each microwave generator 14 may be between 1 and 10 MW. Their frequency is between 100 MHz and 3000 MHz, and preferably 2450 MHz or 915 MHz.

[0041] Windows made of a material transparent to microwaves, for example polytetrafluoroethylene (PTFE), glass, Pyrex® or quartz can advantageously be arranged at the interface between the waveguides 12 and the box 10 (not shown in [Fig.l]).

[0042] The extraction enclosure 8 further comprises a plurality of vertical rollers 16 which are positioned against two side walls 10a of the box 10 (made of electrically conductive material) in order to ensure vertical guidance of the products P to be treated.

[0043] The conveyance of the product plates P to be treated through the rollers 6 and 16 is ensured by a pusher system, for example a jack 18. This system can alternatively be achieved by rollers or motorized casters.

[0044] As shown in [Fig.5], a horizontal wall 20 is arranged along the entire length of the extraction enclosure, just above the passage of the plates of products P to be treated, so as to prevent the extraction vapors from rising into the box 10. This wall is made of a material transparent to microwaves, for example PTFE, a plastic material resistant to a temperature of 120°C or a variety of glass.

[0045] A sufficient height h is provided between the cover 10b of the box 10 and the plates of products P to be treated, so that the multimode propagation configuration allows better homogeneity. This distance h could be, for example, 200 mm.

[0046] Furthermore, the width of the cavity must leave sufficient spacing between each side wall 10a of the box 10 and the product plates P to be treated. This width could for example be between 100mm and 1000mm, and is preferably of the order of 500mm.

[0047] As shown in [Fig.3], the side walls 10a of the box 10 of the extraction enclosure comprise, on an internal face, a double skin 22 allowing the circulation of a hot fluid during the start-up phases.

[0048] Similarly, on their external face, the side walls 10a of the box 10 comprise a thermal insulator 24 so as to limit thermal losses and the risks of burning, the temperature of these walls being able to rise to more than 100°C (see [Fig.5]).

[0049] The microwaves emitted in the extraction chamber 8 make it possible to vaporize certain water molecules at the heart of the plates of products P to be treated and to create a partial vapor pressure carrying the other water molecules and the active ingredients (essential oils, terpenes, resins and other volatile molecules) by percolation and diffusion. These molecules are then carried by the vaporization of the water “wrung out” on the surface of the plates due to the action of the microwaves. A part can be collected directly in liquid form.

[0050] For this purpose, a microwave-tight condenser tray 26 is arranged in the lower part of the extraction enclosure 8. It allows the recovery and condensation of the extracts E obtained.

[0051] Preferably, as shown in [Fig.5], this condenser tank 26 comprises a double skin 28 allowing the circulation of a cold fluid whose temperature is advantageously between 5 and 15°C.

[0052] Also preferably, a horizontal wall 30 allows the steam and liquid extracts to pass through but is impervious to microwaves in order to avoid heating the extracts E by the action of microwaves. This wall 30 is made of perforated conductive material, for example perforated sheet metal or metal grid. This condenser can be thermally insulated to improve its energy performance.

[0053] An evacuation 32 is located at the low point of the condenser tank 26 in order to evacuate the extracts E obtained.

[0054] For wood, this microwave extraction makes it possible to avoid internal residual stresses and to avoid costly step-by-step cooling operations. Depending on the type of wood and extracts desired (for example rosin), it may be necessary to provide an external steam flow to delay the drying point and optimize the extraction efficiency by pushing back the burning threshold. In this case, the horizontal wall 20 of the extraction enclosure will be removed and a steam inlet 30 will be provided on the cover of the box.

[0055] It will be noted that for a given extraction enclosure length, the duration of the extraction operation is given by the feed speed of the product plates to be treated. This duration is between 10 min and 1 h, and is preferably equal to 30 min, which gives for example a feed speed of approximately 13 cm / min for a length of 4 m.

[0056] After the extraction operation, the plates of products to be treated enter inside a drying enclosure 32 allowing their surface drying to be finalized.

[0057] This drying enclosure 32 is arranged downstream of the extraction enclosure 8 with which it is separated from the latter by a separation wall 34 which is vapor-tight and transparent to microwaves.

[0058] The drying enclosure 32 comprises at least one hot air inlet 36 and at least one humid air outlet 38. The hot air preferably has a temperature between 20°C and 120°C, and for example equal to approximately 70°C. The speed of the hot air entering the drying enclosure must be sufficiently high to create a carryaway of the water molecules still present on the surface of the plates of products to be treated by quantity of movement.

[0059] For example, for a wood extraction and drying application with a flow rate of 300 kg / h, a hot air flow rate of approximately 10,000 Nm3 / h of air at 70°C will be recommended.

[0060] The separating wall 34 is transparent to microwaves, which allows a dual action of hot air and microwaves to obtain a very short drying completion time (which may be less than 5 minutes).

[0061] According to an alternative embodiment, the hot air obtained at the outlet may pass into an exchanger in order to transmit part of its heat to the fresh air upstream of the hot air inlet 36.

[0062] The device according to the invention further comprises an inlet airlock 40 which is positioned at the inlet of the extraction enclosure 8 above the conveyor, and an outlet airlock 42 which is positioned at the outlet of the drying enclosure 32 also above the conveyor.

[0063] The inlet airlock 40 is intended in particular to prevent microwave leaks coming from the extraction enclosure 8. It is composed of a guide zone 40a for the plates of products P to be treated, followed by a wave trap zone 40b.

[0064] The guide zone 40a is constituted alternately by rollers 6, 16 and quarter-wave type wave traps 44. The rollers are arranged on the lower face and on the lateral faces of the guide zone 40a.

[0065] As shown in [Fig.5], the vertical rollers 16 pivot around axes 46 fixed on an electrically conductive and microwave-proof structure, for example made of stainless steel. The rollers allow the plates of products to be treated to be guided without friction.

[0066] The wave trap area 40b comprises wave traps 44 which are arranged on the entire upper face of the area, as well as between the rollers of the side and lower faces.

[0067] As shown in [Fig.6], these wave traps 44 may be of the quarter-wave type and consist of series of grooves 44a arranged in planes perpendicular to the advance of the plates of products P to be treated. The depth b of these grooves 44a is determined as a function of the wavelength so that the leakage wave passing between the plate of products P to be treated and the groove enters the groove and is in phase opposition when it leaves it. This makes it possible to physically cancel a large part of the waves circulating towards the outside.

[0068] For a wavelength X, the depth b of the grooves 44a will therefore be: X / 4+k X, k being an integer. For example, for a frequency of 2450 MHz, this length could be 3.06 cm, and for a wavelength of 915 MHz, this length could be 8.20 cm.

[0069] These wave traps 44 can advantageously be covered with a protection 50 so as to prevent the penetration of dust or polluting elements into the grooves 44a. This protection is made of a material transparent to microwaves, for example PTFE, a plastic material resistant to a temperature of 120°C or a variety of glass.

[0070] The outlet airlock 42 has a structure identical and symmetrical to that of the inlet airlock. It consists of a wave trap zone 42a provided with wave traps, for example of the quarter-wave type as described above, followed by a guide zone 42b for the plates of products P to be treated.

[0071] The operation of the device according to the invention can be controlled via a control cabinet 52. This operation can be fully automated via a human-machine interface and allow regulation of the microwave power, adjustment of the feed speed, the air flow rate and its temperature. Temperature and humidity control can be carried out continuously.

[0072] For an example of wood extraction and drying, the drying energy by the process according to the invention is approximately 930kWh per tonne of wood or 0.93kWh per kg of wood. With a conventional process using hot air with a gas burner, the energy required is 1550kWh per tonne of wood. This therefore represents a saving of approximately 40%.

[0073] For example, for a flow rate of 300 kg / h, the microwave power is 300 kW of microwave and the cycle time is 30 minutes. The process according to the invention thus makes it possible to achieve more than 80% extraction yield with a drying rate of 12%. It makes it possible to extract and dry resinous woods (maritime pine, Aleppo pine, etc.) and to recover the water in the wood, the terpenes and the rosins.

Claims

Claims

1. Microwave device (2) for the continuous extraction and drying of solid organic products in the form of plates, comprising: - a roller conveyor (4) intended to transport the products (P) to be treated successively through an extraction enclosure (8) and a drying enclosure (32), - an extraction enclosure (8) comprising a microwave-tight box (10) and inside which opens at least one waveguide (12) connected to a microwave generator (14), - a drying enclosure (32) arranged downstream of the extraction enclosure, separated therefrom by a vapor-tight and microwave-transparent separating wall (34), and comprising at least one hot air inlet (36) and at least one humid air outlet (38), - an inlet sealing airlock (40) which is positioned at the inlet of the extraction enclosure (8) above the conveyor and which is equipped with wave traps (44),and - an outlet airlock (42) which is positioned at the outlet of the drying enclosure above the conveyor and which is fitted with wave traps (44).,

2. Device according to claim 1, further comprising a microwave-tight condenser tank (26) which is arranged under the conveyor (4) at the extraction enclosure (8) in order to allow the recovery and condensation of the extracts (E) from the products.

3. Device according to claim 2, in which the condenser tray (26) comprises a low point provided with an evacuation (32).

4. Device according to any one of claims 1 to 3, in which the conveyor (4) comprises a plurality of horizontal rollers (6) positioned transversely to the direction of advance of the products to be treated.

5. Device according to any one of claims 1 to 4, in which the extraction enclosure (8) and the drying enclosure (32) each comprise a plurality of vertical rollers (16) positioned against side walls (10a) in order to ensure vertical guidance of the products to be to treat.

6. Device according to claim 5, in which the side walls (10a) of the extraction enclosure (8) comprise, on an internal face, a double skin (22) allowing the circulation of a fluid during the start-up phases, and on an external face a thermal insulator (24).

7. Device according to any one of claims 1 to 6, in which the extraction enclosure comprises a horizontal wall (20) made of a material transparent to microwaves and intended to be positioned above the products to be treated in order to prevent the extraction vapors from rising into the extraction enclosure.

8. Device according to any one of claims 1 to 7, further comprising a system (18) for moving the products to be processed on the conveyor.

9. Use of the device according to any one of claims 1 to 8 for the continuous extraction and drying of wooden boards.

10. Use according to claim 9, wherein the wood is raw pine wood containing 40% water, 1.26% terpenes and 3.16% rosin.

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