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Title:
DRYING WOODEN PLANKS
Document Type and Number:
WIPO Patent Application WO/2019/170665
Kind Code:
A1
Abstract:
A drying system (100) for drying wooden planks with a thickness of between 1.8 mm and 8 mm has been described. It comprises a vacuum chamber (110), a vacuum system for generating a vacuum in the vacuum chamber (110) and a plurality of heat exchangers (124) positioned in the vacuum chamber (110), wherein the heat exchangers (110) each extend in a plane and wherein the heat exchangers (110) are configured to, during the drying process, be in contact with the wooden planks to be dried so that a stack of alternating heat exchangers (124) and layers of wooden planks to be dried is formed. The system (100) also comprises a control programmed for controlling the drying system (100) so that during the drying process the pressure in the vacuum chamber (110) is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes.

Inventors:
GERAERTS, Roel (Diepstraat 71, 3511 Kuringen, 3511, BE)
Application Number:
EP2019/055432
Publication Date:
September 12, 2019
Filing Date:
March 05, 2019
Export Citation:
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Assignee:
JAROKA (Senator Alfons Jeurissenlaan 1229, 3520 Zonhoven, 3520, BE)
International Classes:
B27K5/00; F26B5/04; F26B5/10
Attorney, Agent or Firm:
WAUTERS, Davy et al. (DenK iP Leuvensesteenweg 203, 3190 Boortmeerbeek, 3190, BE)
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Claims:
Claims

1.- A drying system (100) for drying wooden planks with a thickness of between 1.8 mm and 8 mm, the drying system comprising

- a vacuum chamber (110),

- a vacuum system for generating a vacuum in the vacuum chamber (110),

- several heat exchangers (124) positioned in the vacuum chamber (110), wherein the heat exchangers (124) each extend in a plane and wherein the heat exchangers (124) are configured to be in contact with the wooden planks to be dried during the drying process so that a stack of alternating heat exchangers (124) and layers of wooden planks to be dried is formed,

- a control programmed for controlling the drying system (100) so that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, and the temperature is between 15°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes.

2.- A drying system (100) according to the preceding claim, wherein the drying system (100) is provided with measuring systems to check whether the heat exchangers (124) make contact with the wooden planks.

3.- A drying system (100) according to the preceding claim, wherein the drying system (100) is provided with a pressure sensor or contact sensor to check whether the heat exchangers (124) make contact with the wooden planks.

4.- A drying system (100) according to any of the preceding claims, wherein the system (100) further comprises one or more measuring systems for measuring one or more of the temperatures, the pressure or the abstracted volume of water, wherein the one or more measuring systems are part of a feedback loop for the control.

5.- A drying system (100) according to the preceding claim, wherein the control is adapted to change dynamically based on feedback received from the feedback loop.

6.- A drying system (100) according to any of the preceding claims, wherein the heat exchangers (124) are based on heating by means of hot water.

7.- A drying system (100) according to the preceding claim, wherein in at least one of the heat exchangers (124) and preferably in several or all of the heat exchangers (124), different channels through which hot water is passed for transferring heat are oriented in different directions.

8.- A drying system (100) according to any of claims 6 to 7, wherein in at least one of the heat exchangers (124) and preferably in several or all of the heat exchangers (124), different channels through which hot water is passed for the transfer of heat are directly fed by a common collector.

9.- A drying system (100) according to any of the preceding claims, wherein the drying system (100) is adapted to transport the entire stack of heat exchangers (124) with the wooden planks in between them in and out of the vacuum chamber (110) by means of a cart and rail system.

10.- A drying system (100) according to any of the preceding claims, wherein the drying system (100) is adapted to be able to place the heat exchangers (124) in a first configuration for loading or unloading wooden planks in the system, the distance between the heat exchangers (124) having a first value greater than 8 mm, and to be able to place the heat exchangers (124) in a second configuration for drying wooden planks in the system, the distance between the heat exchangers (124) being such that contact is made with the wooden planks.

11.- A drying system (100) according to any of the preceding claims, wherein the heat exchangers (124) are configured such that at least 5 layers of wooden planks, for example at least 14 layers of wooden planks, can be dried simultaneously.

12.- A drying system (100) according to any of the preceding claims, wherein the vacuum chamber (110) is more than 600 mm wide, preferably 920 mm or wider.

13.- A drying system (100) according to any of the preceding claims, wherein the heat exchangers (124) form part of a heating system which also comprises one or more of a heating source (120), a hot water storage vessel, pipes, collectors, mixing valves and a circulation pump.

14.- A drying system (100) according to any of the preceding claims, wherein the vacuum system further comprises a condenser for condensing water vapour abstracted from the wooden planks.

15.- A drying system (100) according to the preceding claim, wherein the vacuum system further comprises a discharge conduit for draining water, obtained by condensing water vapour.

16.- A drying system (100) according to the preceding claim, wherein the discharge conduit comprises a gooseneck configuration.

17.- A method for drying wooden planks with a thickness of between 1.8 mm and 8 mm, the method comprising

- contacting several layers of wooden planks with heat exchangers (124), so that a stack of alternating heat exchangers (124) and layers of wooden planks to be dried is formed,

wherein the contact takes place in a vacuum chamber (110) that is brought under vacuum,

the method further comprising checking that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes.

18.- A method according to claim 17, wherein the contacting takes place on both sides of the wooden planks. A control for controlling the drying system (100) according to any of claims 1 to 16, wherein the control is adapted to control the drying system (100) so that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes.

A computer program product for executing, when the computer program product is implemented on a processor, a method according to any of claims 17 to 18.

A drying system (100) for drying wooden planks with a thickness of between 1.8 mm and 8 mm, the drying system (100) comprising

- a vacuum chamber (110),

- a vacuum system for generating a vacuum in the vacuum chamber (110), - several heat exchangers (124) positioned in the vacuum chamber, wherein the heat exchangers (124) each extend in a plane and wherein the heat exchangers (124) are configured to be in contact with the wooden planks to be dried during the drying process, so that a stack of alternating heat exchangers (124) and layers of wooden planks to be dried is formed, the drying system (100) being adapted to be able to place the heat exchangers (124) in a configuration for drying wooden planks in the system where the distance between the heat exchangers (124) is such that contact is made with the wooden planks.

A drying system (100) according to claim 21, wherein the configuration is adapted to provide contact between the heat exchangers (124) and the wooden planks on both sides of the wooden planks during drying.

A drying system (100) according to any of claims 21 to 22, wherein the drying system (100) is adapted to place the heat exchangers (124) in a configuration for loading or unloading wooden planks in the system where the distance between the heat exchangers (124) is greater than in the configuration for drying, so that the heat exchangers (124) are not in contact with the wooden planks.

A drying system (100) according to any of claims 21 to 23, wherein the drying system (100) is adapted to load/unload the wooden planks layer by layer in the drying system (100) by means of a rail system.

A drying system (100) according to any of claims 21 to 23, wherein the heat exchangers (124) are based on heating by means of hot water.

A drying system (100) according to the preceding claim, wherein in at least one of the heat exchangers (124) and preferably in several or all of the heat exchangers (124), different channels through which hot water is passed for transferring heat are oriented in different directions.

A drying system (100) according to any of claims 21 to 26, wherein in at least one of the heat exchangers (124) and preferably in several or all of the heat exchangers (124), different channels through which hot water is passed for the transfer of heat are directly fed by a common collector.

A method for making a top layer for parquet, for example, wherein first a wooden plank is sawn to a thickness between 1.8 mm and 8 mm, and then the wooden plank is dried.

A method according to claim 28, wherein the drying is done by the method according to claims 17 to 18.

Description:
Drying wooden planks

Field of the invention

This invention relates generally to the drying of wooden planks. More specifically, the present invention relates to systems and methods for fast and efficient drying of wooden planks, with for instance a thickness of between 1.8 mm and 8 mm, for example between 4 mm and 6 mm, for use as a top layer.

Background of the invention

Wood top layers are used for the manufacture of, among other things, parquet. Making these top layers comprises, on the one hand, drying the wood and then sawing the wood into thin layers, typically with a thickness of between 1.8 mm and 8 mm.

Existing methods for drying are air drying, dehumidifying drying, and vacuum drying. In the case of air drying, a drying ratio of 1 cm thickness per year is typically achieved if the moisture percentage is to be lowered to about 14%. The waste percentage for the dried product is around 10 to 15 per cent, which is due to the natural nature of the method, with little or no control over the process.

In dehumidifying drying in conventional drying rooms, the typical drying ratio is 1 cm per three weeks and a waste percentage of 7% is obtained. With vacuum drying of thicker wood, the drying time is typically 10 to 30 days and the waste percentage is about 3 to 4%.

So, there is certainly room for improvement.

Summary of the invention

It is an object of embodiments of the present invention to provide good methods and systems for fast and efficient drying of wooden planks. This preferably involves wooden planks with a thickness of between 1.8 mm and 8 mm, for example a thickness of between 4 mm and 6 mm. It is an advantage of embodiments of the present invention that the wood can first be sawn to thickness and subsequently dried.

It is an advantage of embodiments of the present invention that thin planks can be dried immediately after sawing the tree trunk.

It is an advantage of embodiments of the present invention that the duration of drying can be drastically reduced, for example to less than one day, even to less than 2 hours.

It is an advantage of embodiments of the present invention that, due to the short duration of the drying process, less stock of dried wood is needed, since it is possible to respond more quickly to the specific need. It is an advantage of the present invention that a great flexibility in dimensioning can be obtained. In other words, it is an advantage of the present invention that only a limited stock is needed and that it is not necessary to know what dimensions are needed so far in advance in order to use the wood in the production of parquet or other wood products.

It is an advantage of embodiments of the present invention that, despite the accelerated drying, a low percentage of waste for dried wood can be obtained. It is an advantage of at least some embodiments of the present invention that the waste percentage can be reduced to less than 5% waste, for example even less than 2% waste.

The boiling point of the water can be reduced, for instance even to less than 50°C, for example less than 40°C, for example less than 35°C, for example less than 32°C, due to the strong vacuum.

It is an advantage of embodiments of the present invention that drying systems and drying methods are provided that are suitable for drying top layers for use in parquet manufacturing.

It is an advantage of embodiments of the present invention that systems and methods are provided in which wooden planks with a thickness of 1.8 mm to 8 mm can be dried. It is an advantage of embodiments of the present invention that systems and methods are provided in which wooden planks with a thickness of 1.8 mm to 8 mm can be dried to the core of the material. It is an advantage of embodiments of the present invention that, among other things by way of a good selection of the thickness of the planks to be dried, the heat can be transferred quickly into the core of the planks.

It is an advantage of embodiments of the present invention that the heat energy can be evenly distributed over the planks.

It is an advantage of embodiments of the present invention that the temperature and the vacuum are controlled. It is an advantage of the present invention that such monitoring can take place by, for example, constantly adding an adjusted amount of energy.

It is an advantage of embodiments of the present invention that drying techniques can be used which have a relatively low energy consumption. It is an advantage of some embodiments of the present invention that drying does not have to be done via high-frequency techniques, which have a relatively high energy consumption. This object is achieved by a product or a use according to embodiments of the present invention.

The present invention relates to a drying system for drying wooden planks having a thickness of between 1.8 mm and 8 mm, the drying system comprising a vacuum chamber, a vacuum system for generating a vacuum in the vacuum chamber, a plurality of heat exchangers positioned in the vacuum chamber, wherein the heat exchangers each extend in a plane and wherein the heat exchangers are configured to be in contact with the wooden planks to be dried during the drying process, so that a stack of alternating heat exchangers and layers of wooden planks to be dried are formed, and a control programmed for controlling the drying system so that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, for example between 30°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes. It is an advantage of embodiments of the present invention that a drying process is obtained in which the wooden planks have a typical moisture percentage between 85% and 65%, for example approximately 80%, and in which the moisture percentage has dropped to a value between 6% and 10% after the drying process. During the process, the temperature can be between 15°C and 85°C, for example between 30°C and 85°C, for example between 30°C and 32°C. The pressure during the process can be less than 40 mm Hg pressure, for example 35 mm Hg pressure or lower.

It is an advantage of embodiments of the present invention that the wooden planks can have a width of up to 30 cm or wider and that the wooden planks can have a length of up to 300 cm or longer.

The drying system can be adapted to unload the wooden planks layer by layer, by means of a rail system on which the wooden planks between the heating element can be transported in and out of the drying oven and where the heat exchangers can be placed in a configuration for drying wooden planks in the system where the distance between the heat exchangers is such that contact is made with the wooden planks.

The drying system may be adapted to be able to place the heat exchangers in a first configuration for loading or unloading wooden planks in the system, the distance between the heat exchangers having a first value, and to be able to place the heat exchangers in a second configuration for drying wooden planks in the system, the distance between the heat exchangers being such that contact is made with the wooden planks.

It is an advantage of embodiments of the present invention that drying by contact can be achieved, thereby obtaining an efficient way of drying.

The drying system can be equipped with measuring systems to check whether in the second configuration the heat exchangers make contact with the wooden planks.

It is an advantage of embodiments of the present invention that contact drying is possible for different thicknesses of wooden planks and that the system can adapt automatically thereto. Alternatively, the distance between the heat exchangers in the second configuration can also be set manually or in an automated manner by a user.

The drying system can be equipped with a pressure sensor or contact sensor to check whether the heat exchangers make contact with the wooden planks.

The distance between each of the heat exchangers can be greater than 8 mm in the first configuration.

It is an advantage of embodiments of the present invention that the system can be adjusted in an automated manner or in a manual manner to adjust and/or control the distance between the heat exchanger in the configuration for loading or unloading. This means that loading and unloading can always be done in a safe and efficient manner, regardless of the actual thickness of the wooden planks.

The system may further comprise one or more measuring systems for measuring one or more of the temperatures, the pressure or the volume of water abstracted, wherein the one or more measuring systems form part of a feedback loop for the control.

It is an advantage of embodiments of the present invention that accurate monitoring of the drying process can take place.

The control can be adapted to change dynamically depending on feedback received from the feedback loop.

It is an advantage of embodiments of the present invention that the process can proceed in an automated manner, whereby the process can proceed under controlled, for example optimal conditions.

The heat exchangers can be based on heating by means of hot water.

In at least one of the heat exchangers and preferably in several or all of the heat exchangers, different channels through which hot water is fed can be oriented in different directions for the transfer of heat. The homogeneity with which heat is transferred to the wooden planks can thus be high. In at least one of the heat exchangers and preferably in several or all of the heat exchangers, different channels through which hot water is passed for the transfer of heat can be directly fed by a common collector.

The heat exchangers can be configured so that 5 or more layers, for instance 9 or more layers of wooden planks can be dried simultaneously. Alternatively, the system can be adapted to simultaneously dry another number of layers of wooden planks. The vacuum chamber can be more than 600 mm wide, preferably 920 mm or wider. The heat exchangers may form part of a heating system which also comprises one or more of a heating source, a hot water storage vessel, pipes, collectors, mixing valves and a circulation pump. In some embodiments, there may be a plurality of connections per heating source. In some embodiments, there may be between 5 and 19 connections per heating source.

The vacuum system may further comprise a condenser for condensing water vapour abstracted from the wooden planks. The vacuum system may further comprise a discharge conduit for draining water, obtained by condensing water vapour. The discharge conduit can have a gooseneck configuration.

The present invention also relates to a method for drying wooden planks with a thickness of between 1.8 mm and 8 mm, the method comprising contacting different layers of wooden planks with heat exchangers, so that a stack of alternating heat exchangers and layers of wooden planks to be dried is formed, wherein the contacting is done in a vacuum chamber which is brought under vacuum, the method also comprising checking that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, for example between 30°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes. Contacting is preferably done on both sides of the wooden planks. For example, for the various layers of wooden planks, the wooden planks are preferably brought into contact with the heat exchangers for drying, both on the top and on the underside. The method may also comprise a step of loading and unloading where the heat exchangers are brought into a first configuration with the heat exchangers being at a distance greater than the thickness of the wooden planks.

The present invention also relates to a method for making a top layer for, for example, parquet production, wherein first a wooden plank is cut to the thickness of the top layer (between 1.8 mm and 8 mm) and wherein the wooden plank is then dried. The method can further comprise drying according to the above method.

The present invention also relates to a control for controlling the drying system as described above, wherein the control is adapted to control the drying system so that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, for example between 30°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes.

The present invention also relates to a computer program product for executing, when the computer program product is implemented on a processor, a method as described above.

The present invention also relates to a drying system for drying wooden planks with a thickness of between 1.8 mm and 8 mm, the drying system comprising

a vacuum chamber, a vacuum system for generating a vacuum in the vacuum chamber, a plurality of heat exchangers positioned in the vacuum chamber, wherein the heat exchangers each extend in a plane and wherein the heat exchangers are configured to, during the drying process, be in contact with the wooden planks to be dried so that a stack of alternating heat exchangers and layers of wooden planks to be dried is formed, the drying system being adapted to be able to place the heat exchangers in a configuration for drying wooden planks in the system where the distance between the heat exchangers is such that contact is made with the wooden planks. Preferably, contact is made on both sides of the wooden planks, i.e. on both sides of the layer of wooden planks.

In some embodiments, the drying system may be adapted to place the heat exchangers in a configuration for loading or unloading wooden planks into the system with the distance between the heat exchangers having a greater distance, so that the heat exchangers are not in contact with the wooden planks.

In some embodiments, the drying system may be adapted to load/unload the wooden planks layer by layer in the drying system by means of a rail system.

The heat exchangers can be based on heating by means of hot water.

In at least one of the heat exchangers and preferably in several or all of the heat exchangers, different channels through which hot water is fed can be oriented in different directions for the transfer of heat.

In at least one of the heat exchangers and preferably in several or all of the heat exchangers, different channels through which hot water is passed for the transfer of heat can be directly fed by a common collector.

Particular and preferred aspects of the invention are set out in the appended independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. The above and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Brief description of the drawings

FIG. 1 shows a schematic overview of a heating system according to an embodiment of the present invention. FIG. 2 shows an example of a vacuum chamber of a heating system according to an embodiment of the present invention.

FIG. 3 is a schematic representation of the stack of heat exchangers and layers of wooden planks in a configuration for loading and unloading the wooden planks and a configuration for drying the wooden planks, as used in an embodiment of the present invention.

FIG. 4 is a schematic representation of a collector for a heat exchanger, as used in an embodiment of the present invention.

The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes.

Any reference signs in the claims shall not be construed as limiting the scope. In the different drawings, the same reference signs refer to the same or analogous elements.

Detailed description of illustrative embodiments

Although the present invention will hereinafter be described with respect to particular embodiments and with reference to certain drawings, the invention is not limited thereto but is only limited by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the invention.

Furthermore, the terms 'first', 'second' and the like in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms 'top', 'bottom', 'above', 'front' and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noted that the term 'including', used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, values, steps or components as referred to, but does not preclude the presence or addition of one or more other features, values, steps or components, or groups thereof. Thus, the scope of the expression 'a device including means A and B' should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Reference throughout this specification to 'one embodiment' or 'an embodiment' means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification do not necessarily all refer to the same embodiment, but may indeed do so. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly, it should be appreciated that in the description of illustrative embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, there are inventive aspects in less than all the features of a single prior disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some, but not otherfeatures included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by one skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination. In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be carried out without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Where in embodiments of the present invention reference is made to a drying system, reference is made to a drying system for wooden planks. 'Wooden planks' refers to wooden planks such as those that can typically be used as a top layer for a wood product. The wooden planks therefore have a thickness of between 1.8 mm and 8 mm, for example between 4 mm and 6 mm. A typical advantage of this is a wooden plank that can be used as a top layer for parquet. The type of wood is not limiting for the present invention. It can be, for example, oak, beech, etc., but the present invention is not limited by this and can in principle be used for all types of wood.

In a first aspect, the present invention relates to a drying system for drying wooden planks with a thickness of between 1.8 mm and 8 mm. The drying system is based on contact drying in a vacuum. The drying system comprises a vacuum chamber and a vacuum system for generating a vacuum in the vacuum chamber. It also comprises a plurality of heat exchangers positioned in the vacuum chamber, wherein the heat exchangers each extend in a plane and wherein the heat exchangers are configured to be in contact with the wooden boards to be dried during the drying process, so that a stack of alternating heat exchangers and layers of wooden planks to be dried is formed. The drying system further comprises a control programmed for controlling the drying system so that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, for example between 30°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes.

Further standard and optional components will be described with reference to an illustrative drying system, as schematically illustrated in FIG. 1 and FIG. 2. The schematic drying system 100 as shown in FIG. 1 comprises a vacuum chamber 110, also referred to as a 'vacuum drying chamber', a heating system with a heat source 120, for example a heat pump, connected via collectors for supply and discharge 122 with heat exchangers 124, and a vacuum system comprising a vacuum pump 130, a condenser 132 and a reservoir 134. The system typically also comprises a control panel for operating the system. It should be noted that embodiments of the present invention are not limited thereby, but that the illustrative drying system is merely an illustration of one specific embodiment.

The drying system comprises a vacuum chamber in which the wooden planks are dried. In the example, the vacuum chamber has an elongated cylinder shape or a rectangular shape. It should be noted, however, that the specific shape of the chamber is non-limiting and that other forms can also be used. The cylinder shape has the advantage, for example, that relatively few corners and edges are present, so that the airtight sealing of the vacuum chamber becomes easier. The rectangular shape has for example the advantage that the capacity of wood that can be dried can be optimal. The vacuum chamber must be able to be completely sealed in an airtight manner. For this purpose, the appropriate vacuum seals can be provided, both at the location where the different parts of the vacuum chamber touch each other when closing and at the places where there are coupling conduits. This means that the chamber must be able to withstand the air pressure from the outside. The vacuum chamber in the current example is made of stainless steel, although other materials can also be used, provided they can withstand the air pressure. In the present example, the uppermost part of the cylinder can be opened. Various openings are provided in the vacuum chamber to provide the necessary connections to the other components. Firstly, in the current example, openings are provided for the connections with the vacuum pump. In the present example, two openings are provided for the connection with the vacuum pump, although this may also be a different number. Secondly, openings are also provided for the pipes of the heating installation. The dimensions of the vacuum chamber can be adjusted according to the applications and capacities that are intended.

The system also comprises a vacuum pump for creating the vacuum in the vacuum chamber. The required performance of the vacuum pump is to achieve 30 mm Hg vacuum in the vacuum chamber. The size of the volume of water vapour remaining after condensation determines the required capacity of the vacuum pump. If, for example, condensation does not occur, the vacuum pump, in the present example, should be able to remove approximately 560 m 3 of water vapour for the cylindrical chamber and 3800 m 3 of water vapour for the rectangular chamber in a period of, forexample, between 25 minutes and 1 hour. As indicated earlier, it should be noted that the content can be adjusted according to the applications and capacities that are intended. Condensation is of great importance and a critical point since a large volume of watervapour has to be converted. The vacuum pump is preferably chosen such that the part of the pump that is in contact with the water vapour is corrosion- resistant, since the water vapour contains tannic acid (corrosive), which would otherwise cause detrimental effects with respect to the life of the vacuum pump. Suitable vacuum pump systems can be based on a diffusion pump, a rotary pump, a water ring vacuum pump, etc.

The system is adapted to convert the water vapour that is removed into water. A condenser is used for this purpose in the current example. In the current illustrative system, the water, obtained after condensing the water vapour in the condenser, is guided by gravity in the pipes towards the vacuum pump. However, a gooseneck is placed in the line from the condenser to the vacuum pump. At the last point of the gooseneck, a discharge pipe is placed, to drain the water accumulating in the gooseneck under gravity. In the present example, this water is also collected in a reservoir and the amount is measured to determine the speed and the status of the drying. The water can then be drained off, for example discharged after adjusting the pH to a neutral pH level, for example. It should be noted that other embodiments for obtaining drainage of the water vapour converted into water can also be used. In some embodiments, the water vapour could also possibly be drained directly, although this allows for a less easy control of the amount of moisture abstracted from the wooden planks.

All pipes for the vacuum section are made in the present example from thick-walled PVC tubes, with a wall thickness of, for example, 3 to 4 mm. However, it should be noted that other materials can also be used. The pipes from the vacuum chamber to the condenser have a diameter of sufficient size. The pipes from the gooseneck to the part where the water is collected have a smaller but also sufficiently large diameter. All connections are airtight and very well glued.

The drying system also comprises a heating system. In the present example, heating is based on heating by means of a hot water technique, although embodiments of the present invention are not limited thereto. Alternative heating systems are for example by means of hot oil, electric, high frequency, etc. In the present example, where heating is based on heating by means of a hot water technique, the heating system comprises a heating source, a hot water storage vessel and one or more heat exchangers. Furthermore, in the current example, mixer valves, a circulation pump and the necessary pipes and collectors are also provided. The temperature of the water to be circulated is approximately between 15°C and 85°C, for example between 30°C and 85°C, for example between 30°C and 75°C.

The heating source in the present example is a heating boiler. The heating boiler is, for example, a condensing boiler with sufficient capacity. This produces hot water that flows via a pipe to the hot water collection tank. The hot water collection tank is the reservoir that ensures that the required hot water is available to feed the heat exchanger in the vacuum chamber. The feeding is typically done by means of a circulation pump. The hot water collection vessel in the present example is also the reservoir into which the water flows back from the heat exchanger, after it has been used. Typically, this collection vessel is well insulated so that no heat is lost.

The one or more heat exchangers ensure the exchange of heat with the wooden planks. In one example, as used in the present example, the one or more heat exchangers are made up of a number of tubes, for example eighteen aluminium rectangular channels with a diameter of 30 mm x 25 mm, with a wall thickness of 7.5 mm to 20 mm and with a length in the vacuum chamber of 3000 mm long. These tubes are next to each other in the present example and are wrapped in a pleated plate, for example an aluminium pleated plate. The supply of these heat exchangers is done per collector, which ensures a distribution of the heated water, per heat exchanger. For example, each heat exchanger can be fed via a collector. In the present example, each heat exchanger essentially extends in a plane. It is an advantage for evenly drying the wood that the heat exchangers have the same temperature everywhere. The heat is therefore preferably as evenly distributed as possible. The energy released by the heat exchangers must also be sufficient to transfer the required amount of energy in a dosed manner. During the drying process, different heat exchangers are placed above each other with wooden planks in between each time. It is important that the wooden planks and the heat exchangers make good contact with each other. To enable the loading and unloading of the wood between the heat exchangers, different techniques can be used. In one example, a system is provided for systematically unloading different layers of the wood, by moving the various heat exchangers layer by layer out of the drying chamber, for instance sliding them, and removing the planks from them. This can be done, for example, with the aid of a rail system. In another example, the dried wood / wood to be dried is systematically removed from the system, layer by layer, while the heat exchangers remain in the drying chamber. In some embodiments, a system is installed in which more space is created between the heat exchangers during loading and unloading in some embodiments. After loading, the openings must also be able to be closed again so that the heat exchangers are brought back closer together and thus make contact with the wooden planks that have to be dried. In each of the systems, care is taken that there is contact between the heat exchangers and the wood, as this ensures an efficient drying process. The heat exchangers can be placed at a fixed distance from each other for drying during the drying process. However, in some embodiments, contact or pressure sensors may also be used to place the heat exchangers closer together until good contact between the heat exchangers and the wooden planks is obtained. By way of example, a possible configuration of heat exchangers and wooden planks is shown in FIG. 3 during the drying process (A) and during the loading and unloading (B).

In the current illustrative system, the heating is achieved by, during the drying process, circulating water through the aluminium panels with channels with a temperature between 15°C and 85°C, for example between 30°C and 85°C. In the heat exchangers, water can be circulated in different directions. By using heat exchangers where the channels lie in different directions, a more homogeneous heat distribution can take place and the heat transfer can be as uniform as possible. That way there are no cold places. Preferably, the difference of temperature in the water in the heat exchanger is at most 1°C.

The heating system of the present example also includes mixer valves to optionally mix the heated water flowing to the heat exchangers in the vacuum chamber with the return water from the heat exchangers to obtain the required supply temperature. The mixer valves can be part of control equipment for the hot water and are controlled by the central control system.

For circulation, in a specific example, a circulation pump is provided with a capacity between 10 m 3 /hour and 100 m 3 /hour, for example at least 18 m 3 /hour or for example at least 35 m 3 /hour. Preferably, the resistance offered by the circuit is minimised. When the resistance is too great, the capacity of the pump decreases.

In the present example, the heated water leaves the boiler via the pipes to the vacuum chamber, where the water arrives in a collector. This collector distributes the water further to the heat exchangers (also called 'heating elements'). Collectors ensure that each tube of the heat exchanger receives the same amount of heated water and that as much water can be discharged. The pipes and collectors from the current example consist of stainless material. The pipes are preferably provided with sufficient shut-off valves so that the circuit can be formed. As mentioned earlier, it is important that as little resistance as possible is created in the pipes. This can be done by choosing the diameter of the pipes sufficiently large. The connection between the collector to the heat exchanger and the outlet of the heat exchanger must be flexible because it must be possible to place the heat exchangers further and closer to each other mechanically, as described above. The input and output connection between the collector and heat exchangers are thus flexible so that the heat exchangers can be adjustable in height relative to each other. An example of a collector is shown in FIG. 4.

In the current example, a central control is also provided. The control ensures that control can take place according to inputted drying programs. Moreover, the central control can also be provided to gather information about the drying process. The purpose of collecting the data is to gain information about the drying process and to check it. The control can be done locally or can be done remotely over a network, for example over the internet. Maintenance schedules and troubleshooting can also be provided in the control. Measuring and monitoring equipment should also be provided in the system to collect data and compare it with the required parameters and, if necessary, carry out the necessary adjustments. The required parameters include the set values for temperature of the wood and pressure in the drying chamber. The measuring and monitoring equipment may for example comprise one or more of the following: a temperature sensor, software package, control valves and their control, vacuum meter, measuring cup (for the volume of the water), chronometer and a flow meter. In some embodiments, the wood can also be checked before and/or after drying. This can be done automatically or manually. The measuring and control equipment can be adapted for this purpose. Alternatively, these results can also be entered directly in the control. Before this, the quality of the wood can be checked to determine the drying schedule. Afterwards, the wood can be checked for weight for quality control. In a second aspect, the present invention relates to a method for drying wooden planks. The method can be carried out in a preferred manner in a system as described in the first aspect, although this is not necessary.

The method comprises contacting several layers of wooden planks with a thickness of between 1.8 mm and 8 mm with heat exchangers, so that a stack of alternating heat exchangers and layers of wooden planks to be dried is formed, contacting taking place in a vacuum chamber that is brought under vacuum. The method also comprises checking that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, for example between 30°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes. The method may also comprise a step of loading and unloading where the heat exchangers are brought into a first configuration with the heat exchangers being at a distance greater than the thickness of the wooden planks. After the step of loading the wooden planks, the contact of the various layers of wooden planks with the heat exchangers follows by bringing the heat exchangers closer together.

Further standard and optional steps of the method may correspond to the functionality of the elements of the drying system described in the first aspect.

In a third aspect, the present invention relates to a control for controlling a drying system as described in the first aspect. The control is adapted to control the drying system so that during the drying process the pressure in the vacuum chamber is between 15 mm Hg pressure and 80 mm Hg pressure, the temperature is between 15°C and 85°C, for example between 30°C and 85°C, and the drying time of the drying process is between 5 minutes and 240 minutes, for example between 10 minutes and 120 minutes, for example between 10 minutes and 60 minutes. The control can be automated and can be based on feedback from measurement systems for measuring process parameters in the drying system. The control can be programmed according to a predetermined algorithm. The control can be implemented by means of a processor which is coupled to a memory subsystem which comprises at least one form of memory. A storage subsystem may be provided. In particular embodiments, a display system, a keyboard and a pointing device may be provided as part of a user interface subsystem with which a user can manually output information. Ports for inputting and outputting data may also be present, for example for communication with the feedback system. The various elements of the processing system are linked in different ways, for example via a bus subsystem. The present invention thus also relates to computer-implemented controls which are adapted to perform the various method steps of illustrative embodiments as described above. The different steps can therefore also be included as software in a processing system.

The present invention also comprises a computer program product that provides the functionality of each of the methods of the present invention when they are performed on a computer device. Furthermore, the present invention comprises an information carrier such as a CD-ROM, a DVD-ROM or a diskette which stores the computer product in a machine-readable form, and which performs at least one of the methods of the invention when it is executed on a computer device. Nowadays, such software can often be downloaded via the internet or a company intranet site, whereby the present invention comprises the transfer of the computer product according to the present invention via a local or wide area network.

The various aspects can easily be combined with each other, and the combinations thus also correspond to embodiments according to the present invention.