A method of heating wood

Abstract

A method (100) of heating wood (1) in a wood drying compartment (10), the wood drying compartment (10) comprising a first end wall (14) and a second end wall (16) opposite to the first end wall (14), the first end wall (14) comprising an opening (20) and a door (18) for selectively closing said opening (20), and the method comprising: Providing (S101) a stack of wood (1) to the wood drying compartment (10) through the opening (20); circulating (S102) an airflow (AF) through the stack of wood (1); keeping (S103) the relative humidity of said airflow (AF) at 80-100%, such as 90-100%, such as 95-100%; spraying (S104) water (W) into the airflow (AF) to provide a combined air and water flow (CF), and directing (S105) the combined air and water flow (CF) in one single and substantially horizontal direction through the stack of wood (1), from the second end wall (16) towards the first end wall (14).

Description

Field of the Invention

[0001] The present disclosure relates to a method of heating wood. In particular, the disclosure relates to a method of heating wood in a wood drying compartment.Background of the Invention

[0002] Before being used, wood and timber is frequently dried to suitable water content. Drying of wood often is performed in a drying compartment, such as a kiln, where heated air is circulated over the wood subjected to drying.

[0003] The wood is typically stored outside before being provided to the drying compartment, and the temperature of the wood is thus affected by the outside temperature. During the cold season, the temperature of the wood being provided to the drying compartment may therefore be very low, such as below 0 degrees Celsius. The wood may also be completely or partly frozen and / or covered by snow and / or ice. Drying of cold wood may require a large amount of energy. Also for other reasons it is normally preferred that the temperature of the wood, before initiating the drying process, is brought up to approximately the temperature of the drying air used during the drying process.

[0004] Thus, it may be desired to thaw and / or heat the wood to a certain temperature before drying. In some conventional systems, this is achieved by providing the wood to the wood drying compartment and then leaving it there for several hours to allow a successive increase in temperature. However, this requires a lot of time and prolongs the entire procedure, which is undesired from an economical perspective.

[0005] There is also known solutions in which the wood is heated by circulating warm air through the compartment, the direction of the air flow being altered back and forth during the heating for providing even heating. The humidity of the wood may be controlled during the heating by spraying the wood with water. However, this process is also time and energy consuming, since it has to be interrupted for every change of the flow direction.

[0006] There is need for an improved heating method.Summary

[0007] In view of the above, an object of the present disclosure is to provide an improved method for heating of wood in a drying compartment. A further object is to provide a method which is more energy efficient than previously known solutions. A further object is to provide a method which is more time efficient than previously known solutions.

[0008] According to a first aspect of the present disclosure, a method of heating wood in a wood drying compartment is provided, the wood drying compartment comprising a first end wall and a second end wall opposite to the first end wall, the first end wall comprising an opening and a door for selectively closing said opening, and the method comprising: providing a stack of wood to the wood drying compartment through the opening; circulating an airflow through the stack of wood; keeping the relative humidity of said airflow at 80-100%, such as 90-100%, such as 95-100%; spraying water into the airflow to provide a combined air and water flow, and directing the combined air and water flow in one single and substantially horizontal direction through the stack of wood, from the second end wall towards the first end wall.

[0009] The solution builds on the realization that by providing a combined air and water flow to the wood, the air flow having a relative humidity of at least 80%, such as a relative humidity of 100%, the wood may be heated without drying, whereby quality defects may be prevented.

[0010] Furthermore, by providing a combined air and water flow from one single horizontal direction, from the inner wall and towards the door, several benefits may be achieved.

[0011] Firstly, as it is often necessary to press the wood from above during drying, the access to the wood stack from above may be partly impaired by the arrangement for pressing, thus lowering the efficiency when spraying or heating from above. The access to the wood stack from the lateral sides of the compartment is also impaired by the fact that the stickers provided between each layer of wood prevents fluid from lateral penetration into the stack.

[0012] In contrast, the access to the wood stack in the longitudinal direction, from the wall opposite to the opening, that is, from the inner wall of the compartment is typically unhindered, thus increasing the heating efficiency.

[0013] The positioning of the spraying arrangement at the inner wall is also beneficial since it is there protected from mechanical impact, as well as from low temperatures. Damage to the spraying arrangement, as well as freezing of the water in the spraying arrangement during low outside temperatures may thus be prevented by the present disclosure.

[0014] Furthermore, it has been realized that the provision of directing the combined air and water flow in one single and substantially horizontal direction through the stack of wood, allows the combined air and water flow to successively translate into the wood stack, and that this provides for an even heating with low energy losses, while still minimizing the risk of defects in the wood.

[0015] According to one embodiment, the sprayed water comprises condensate water produced during a wood drying process.

[0016] Hereby, water can be saved, as the water is condensate which has been formed through evaporation from the wood during the drying of previous batches of wood. Thus, instead of flushing the condensate out of the compartment after the drying of a wood stack, the condensate water may be saved within the wood drying compartment and reused during the heating of subsequent wood stacks.

[0017] Alternatively or in combination, condensate water used for spraying onto the wood during the heating phase in one compartment may be provided from an earlier or a simultaneous drying phase of wood in a neighboring compartment.

[0018] A further benefit is that energy may be saved, as the condensate typically has a higher temperature than the wood that is to be heated. Thus, the heat contained in the condensate may be reused in the heating of a subsequent wood stack, thus lowering or even avoiding the need of adding additional heat during the heating phase.

[0019] According to one embodiment, at least 85%, such as at least 90%, such as at least 99% of the sprayed water is condensate water.

[0020] Thus, by using almost exclusively condensate water during the heating, a large amount of water and energy may be saved.

[0021] According to one embodiment, the temperature of the water at spraying is 40-90 °C, such as 50-80 °C.

[0022] Hereby, by providing water which already has a higher temperature than the wood which is to be heated, energy may be saved as less or no external heat needs to be supplied to the drying compartment during the heating phase.

[0023] According to one embodiment, the heating is ended when the temperature of the wood reaches 45-90 °C, such as 55-80°C.

[0024] By monitoring the temperature of the wood, the heating phase may be ended when the temperature of the wood is high enough to be able to perform safe and efficient drying. A clear way of determining when to end the heating phase may thus be provided.

[0025] It should be noted that in some cases, such as for some specific types of wood, the heating may be ended at lower temperatures, such as at 25-28°C.

[0026] While the temperature of the wood may be the most relevant parameter for determining when to end the heating phase, it may be hard to measure the wood temperature within the drying compartment.

[0027] Thus, in an alternative embodiment, the heating is ended when the wet bulb temperature within the wood drying compartment reaches 45-90, such as 60-80°C. The wet bulb temperature may be measured or estimated in a variety of ways, for example by a wet bulb thermometer arranged within the wood drying compartment.

[0028] According to one embodiment, the flow rate of the supplied water is at least 0,01 m 3< / h per m 3< of wood, such as 0,03-0,15 m 3< / h per m 3< of wood.

[0029] Hereby, a sufficiently high flow rate for ensuring that the wood may be efficiently and quickly heated while not becoming too dry during the process may be provided.

[0030] According to one embodiment, the water is supplied from a tank during spraying, the tank being arranged inside the drying compartment.

[0031] Water from the drying of a previous or neighboring batch may thus be stored within the wood drying compartment until heating is needed. By arranging the tank within the wood drying compartment, loss of heat from the water may be prevented. Furthermore, by minimizing the distance which the water needs to be transported, energy may be saved.

[0032] In an alternative embodiment, the water may be supplied from a further wood drying compartment, such as an adjacent wood drying compartment. The further wood drying compartment supplying the water may supply water upon conducting the drying, such that the condensate generated during the drying is directly routed to the heating process of the first wood drying compartment. Alternatively, the water may be supplied from a tank within the further wood drying compartment, the tank having been filled by condensate during an earlier wood drying process.

[0033] It would also be possible to use water from several wood drying compartments during the heating.

[0034] According to one embodiment, water is supplied to the tank from a condensing unit, such as from an active condensing unit.

[0035] Thus, the tank has preferably been filled with condense during a previous wood drying cycle, whereby water is saved.

[0036] According to one embodiment, the water is supplied by a plurality of nozzles, the plurality of nozzles being arranged in the horizontal flow path of the combined air and water flow.

[0037] Hereby, by providing the nozzles in the horizontal flow path of the water, such that the water may be sprayed onto the wood horizontally, the combined air and water flow may be allowed to penetrate into the spaces between the wood pieces such that the heat may easily be transported through the entire wood stack, while successively heating the wood.

[0038] According to one embodiment, the stack of wood comprises a plurality of elongate pieces of wood arranged in a plurality of layers, and a plurality of elongate stickers arranged between the layers.

[0039] According to one embodiment, the longitudinal direction of the elongate stickers extend in a longitudinal direction of the drying compartment, between the first and second end walls, and wherein the longitudinal extension of the pieces of wood extends perpendicular to the longitudinal extension of the stickers. By this means, the longitudinal direction of the stickers will lay essentially in parallel with the direction of the combined air and water flow. Hereby, the combined air and waterflow will gain access to and be evenly distributed over all surfaces of the pieces of wood in the stack.Brief Description of the Drawings

[0040] These and other aspects of the present inventive concept will now be described in more detail, with reference to the appended drawings showing an example embodiment of the inventive concept, wherein: Fig. 1 is a schematical cross-sectional side view a wood drying compartment according to an embodiment of the present disclosure. Fig. 2 is a method for heating wood according to an embodiment of the present disclosure. Detailed Description of Example Embodiments

[0041] In the present detailed description, various embodiments of the invention are described.

[0042] Fig. 1 schematically illustrates a wood drying compartment 10 configured for heating and drying of wood 1, the wood 1 being arranged in an inner space 12 of the wood drying compartment 10 during the heating and drying.

[0043] The operation in the wood drying compartment 10 may be divided into two phases, an initial heating phase and a succeeding drying phase. The heating phase may be initiated when the wood 1 provided to the wood drying compartment 10 has a temperature below a predetermined threshold, and thus needs to be heated before the drying phase can be initiated, to avoid damages to the wood 1, and to increase energy efficiency.

[0044] The wood 1 may typically be arranged in at least one stack or bundle containing a plurality of pieces of wood 11, typically arranged side by side with a distance between each other and in a plurality of vertical layers with distance between the layers. The vertical distance between layers of wood may be achieved by arranging a plurality of elongate distance members, so called stickers 13, between each layer. The stickers 13 are preferably arranged essentially perpendicular to the longitudinal extension of the pieces of wood 11. By this means, air may flow comparatively unhindered through the stack of wood 1 and essentially around each piece of wood 11, which allows for efficient drying of the wood 1. A piece of wood 11 may, for example, be a plank, a piece of timbre, a wooden girder, or any suitable type of sawn piece of wood.

[0045] The wood drying compartment 10 comprises a first end wall 14 and a second end wall 16. A door 18 is arranged in the first end wall 14, the door 18 covering an opening 20 for allowing the stack of wood 1 to be transferred into the inner space 12 of the wood drying compartment 10.

[0046] The second end wall 16 is arranged at an opposite side of the wood drying compartment 10 to the first end wall 14. The second end wall 16 is thus the wall furthest away from the door 18 and the opening 20 and may be regarded as the inner wall of the wood drying compartment 10. It is also understood that the wood drying compartment 10 comprises a pair of side walls extending between the first 14 and second 16 end walls and a ceiling extending above the walls, such as to form an enclosed compartment.

[0047] The stack of wood, when received within the compartment, is preferably oriented such that the longitudinal extension of the pieces of wood extends in the lateral direction, between the side walls, of the compartment. Correspondingly, the longitudinal direction of the elongate stickers 13 extend in the longitudinal direction, between the first 14 and second 16 end walls of the compartment.

[0048] The wood drying compartment 10 comprises an air circulation device 22, such as a fan, for creating an airflow AF within the compartment 10. The air circulation device 22 is typically arranged above the wood 1 and is used to recirculate the air after having been transferred through the wood 1. During the heating, the air circulation device is directed such that it draws air from the door-side wall 14 of the compartment 10 and forces it towards the inner wall 16. The same air is thus recirculated during the entire heating phase, and there is normally no supply of fresh air from the exterior.

[0049] A water spraying system 24 is arranged in the wood drying compartment 10, close to the second end wall 16. When a stack of wood 1 is arranged within the inner space 12, the water spraying system 24 is thus arranged between the second end wall 16 and the stack of wood 1.

[0050] The water spraying system 24 is configured to spray water W into the airflow AF from one single and substantially horizontal direction during the heating phase, to provide a combined air and water flow CF.

[0051] The water spraying system 24 comprises a water supply, such as a tank 26, a plurality of vertical pipes 28 fluidly connected to the tank 26, and a plurality of nozzles 30 attached to the plurality of vertical pipes 28. The tank 26 is thus configured to store an amount of water and to supply it to the plurality of vertical pipes 28, from which pipes 28 the water W may be sprayed into the airflow AF and further onto the wood 1 through the nozzles 30.

[0052] A condenser 32 is arranged on top of the compartment 10. The condenser 10 is configured to be used during the drying phase, to condense water from the warm moist air within the compartment by heat exchanging with a cooling medium. The cooling medium may be cooler ambient air from outside of the compartment, such as outside air, which will be warmed in the condenser.

[0053] Further illustrated in figure 1 is a heater 34 arranged for heating the circulating air. As the air passes through the wood stack during the heating phase, it gives off heat to the wood. There may thus be a need to reheat the air before the next passage through the stack of wood. The heater 34 may be of any type suitable to provide heat to the airflow at passage through the heater.

[0054] Fig. 2 illustrates a method 100 of heating wood 1 in the wood drying compartment 10. The method thus relates to the initial heating phase in which the wood 1 is heated, and not to a subsequent drying phase.

[0055] In a first step S101, a stack of wood 1 is provided to the wood drying compartment 10 through the opening 20.

[0056] The wood 1 may be provided to the compartment 10 by a forklift, such as a front-loaded forklift or a side loaded forklift.

[0057] In a second step S102, an airflow AF is circulated through the stack of wood 1 inside the wood drying compartment 10.

[0058] After the air has been forced through the stack of wood 1, it may be recirculated above the stack by a circulation device 22, such as a fan. During the recirculation, the airflow AF may also be heated, such that the temperature is sufficiently high for heating the wood 1 during the next passing through the stack of wood 1. The temperature to which the airflow AF is heated typically depends on the current temperature of the wood. For example, the airflow AF may be heated to a temperature which is a few degrees above the temperature of the wood. Furthermore, the temperature of the airflow AF should preferably not be too low as this may damage the heating coil. For example, the airflow AF may be heated to a temperature of 20-100 degrees Celsius. The temperature of the airflow AF may be regulated based on the wet bulb temperature.

[0059] In a third step S103, which may be performed simultaneously with the second step S102, the relative humidity of said airflow AF is kept at 80-100%, such as 90-100%, such as 95-100%.

[0060] The temperature of the airflow AF may be continuously monitored and controlled such that drying of the wood 1 is substantially avoided during the heating phase. For example, the relative humidity may be controlled by regulating the amount of water W being sprayed into the airflow AF.

[0061] In a fourth step S104, which may be performed simultaneously with the second S102 and / or the third S103 steps, water W is sprayed into the airflow to provide a combined air and water flow CF.

[0062] Most of the water W used during the heating, such as at least 99% of the water W used during the heating, may be water which has been condensed from the recirculating airstream during the drying of one or several previous dryings. The temperature of the condensate may be 60-70 degrees Celsius. Thus, by reusing this warm condensate in the heating of a new stack or batch, both water and energy may be saved.

[0063] The flowrate of the water being sprayed into the airflow AF is at least 0,01 m 3< / h per m 3< of wood, such as 0,03-0,15 m 3< / h per m 3< of wood. After having passed through the wood 1, the water falls to the floor and is discharged through the drain.

[0064] In a fifth step S105, which may be performed simultaneously with the second S102, third S103 and / or fourth S104 steps, the combined air and water flow CF is directed in one single and substantially horizontal direction through the stack of wood 1, from the second end wall 16 towards the first end wall 14. The direction of the spraying of the water W, as well as the direction of the combined air and water flow CF is thus the same during the entire heating phase. The direction of the combined air and water flow CF being from the inner second end wall 16 and towards the outer first end wall 14.

[0065] The combined air and water flow CF is thus configured to pass through the stack of wood 1 in a direction from the second end wall 16 towards the first end wall 14. Once the flow reaches the first end wall 14, the air is recirculated and, if necessary, heated before again being sent through the wood stack 1.

[0066] The temperature of the wood 1 may be monitored during the heating phase, and the heating phase may be ended once the temperature of the wood and / or the wet bulb temperature within the wood drying compartment, reaches a certain threshold, such as 45-90 °C . The exact temperature typically depends on the type of wood being heated.

[0067] Even though the solution has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.

[0068] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Examples

Embodiment Construction

[0041]In the present detailed description, various embodiments of the invention are described.

[0042]Fig. 1 schematically illustrates a wood drying compartment 10 configured for heating and drying of wood 1, the wood 1 being arranged in an inner space 12 of the wood drying compartment 10 during the heating and drying.

[0043]The operation in the wood drying compartment 10 may be divided into two phases, an initial heating phase and a succeeding drying phase. The heating phase may be initiated when the wood 1 provided to the wood drying compartment 10 has a temperature below a predetermined threshold, and thus needs to be heated before the drying phase can be initiated, to avoid damages to the wood 1, and to increase energy efficiency.

[0044]The wood 1 may typically be arranged in at least one stack or bundle containing a plurality of pieces of wood 11, typically arranged side by side with a distance between each other and in a plurality of vertical layers with distance between the layer...

Field of the Invention

[0001] The present disclosure relates to a method of heating wood. In particular, the disclosure relates to a method of heating wood in a wood drying compartment.Background of the Invention

[0002] Before being used, wood and timber is frequently dried to suitable water content. Drying of wood often is performed in a drying compartment, such as a kiln, where heated air is circulated over the wood subjected to drying.

[0003] The wood is typically stored outside before being provided to the drying compartment, and the temperature of the wood is thus affected by the outside temperature. During the cold season, the temperature of the wood being provided to the drying compartment may therefore be very low, such as below 0 degrees Celsius. The wood may also be completely or partly frozen and / or covered by snow and / or ice. Drying of cold wood may require a large amount of energy. Also for other reasons it is normally preferred that the temperature of the wood, before initiating the drying process, is brought up to approximately the temperature of the drying air used during the drying process.

[0004] Thus, it may be desired to thaw and / or heat the wood to a certain temperature before drying. In some conventional systems, this is achieved by providing the wood to the wood drying compartment and then leaving it there for several hours to allow a successive increase in temperature. However, this requires a lot of time and prolongs the entire procedure, which is undesired from an economical perspective.

[0005] There is also known solutions in which the wood is heated by circulating warm air through the compartment, the direction of the air flow being altered back and forth during the heating for providing even heating. The humidity of the wood may be controlled during the heating by spraying the wood with water. However, this process is also time and energy consuming, since it has to be interrupted for every change of the flow direction.

[0006] There is need for an improved heating method.Summary

[0007] In view of the above, an object of the present disclosure is to provide an improved method for heating of wood in a drying compartment. A further object is to provide a method which is more energy efficient than previously known solutions. A further object is to provide a method which is more time efficient than previously known solutions.

[0008] According to a first aspect of the present disclosure, a method of heating wood in a wood drying compartment is provided, the wood drying compartment comprising a first end wall and a second end wall opposite to the first end wall, the first end wall comprising an opening and a door for selectively closing said opening, and the method comprising: providing a stack of wood to the wood drying compartment through the opening; circulating an airflow through the stack of wood; keeping the relative humidity of said airflow at 80-100%, such as 90-100%, such as 95-100%; spraying water into the airflow to provide a combined air and water flow, and directing the combined air and water flow in one single and substantially horizontal direction through the stack of wood, from the second end wall towards the first end wall.

[0009] The solution builds on the realization that by providing a combined air and water flow to the wood, the air flow having a relative humidity of at least 80%, such as a relative humidity of 100%, the wood may be heated without drying, whereby quality defects may be prevented.

[0010] Furthermore, by providing a combined air and water flow from one single horizontal direction, from the inner wall and towards the door, several benefits may be achieved.

[0011] Firstly, as it is often necessary to press the wood from above during drying, the access to the wood stack from above may be partly impaired by the arrangement for pressing, thus lowering the efficiency when spraying or heating from above. The access to the wood stack from the lateral sides of the compartment is also impaired by the fact that the stickers provided between each layer of wood prevents fluid from lateral penetration into the stack.

[0012] In contrast, the access to the wood stack in the longitudinal direction, from the wall opposite to the opening, that is, from the inner wall of the compartment is typically unhindered, thus increasing the heating efficiency.

[0013] The positioning of the spraying arrangement at the inner wall is also beneficial since it is there protected from mechanical impact, as well as from low temperatures. Damage to the spraying arrangement, as well as freezing of the water in the spraying arrangement during low outside temperatures may thus be prevented by the present disclosure.

[0014] Furthermore, it has been realized that the provision of directing the combined air and water flow in one single and substantially horizontal direction through the stack of wood, allows the combined air and water flow to successively translate into the wood stack, and that this provides for an even heating with low energy losses, while still minimizing the risk of defects in the wood.

[0015] According to one embodiment, the sprayed water comprises condensate water produced during a wood drying process.

[0016] Hereby, water can be saved, as the water is condensate which has been formed through evaporation from the wood during the drying of previous batches of wood. Thus, instead of flushing the condensate out of the compartment after the drying of a wood stack, the condensate water may be saved within the wood drying compartment and reused during the heating of subsequent wood stacks.

[0017] Alternatively or in combination, condensate water used for spraying onto the wood during the heating phase in one compartment may be provided from an earlier or a simultaneous drying phase of wood in a neighboring compartment.

[0018] A further benefit is that energy may be saved, as the condensate typically has a higher temperature than the wood that is to be heated. Thus, the heat contained in the condensate may be reused in the heating of a subsequent wood stack, thus lowering or even avoiding the need of adding additional heat during the heating phase.

[0019] According to one embodiment, at least 85%, such as at least 90%, such as at least 99% of the sprayed water is condensate water.

[0020] Thus, by using almost exclusively condensate water during the heating, a large amount of water and energy may be saved.

[0021] According to one embodiment, the temperature of the water at spraying is 40-90 °C, such as 50-80 °C.

[0022] Hereby, by providing water which already has a higher temperature than the wood which is to be heated, energy may be saved as less or no external heat needs to be supplied to the drying compartment during the heating phase.

[0023] According to one embodiment, the heating is ended when the temperature of the wood reaches 45-90 °C, such as 55-80°C.

[0024] By monitoring the temperature of the wood, the heating phase may be ended when the temperature of the wood is high enough to be able to perform safe and efficient drying. A clear way of determining when to end the heating phase may thus be provided.

[0025] It should be noted that in some cases, such as for some specific types of wood, the heating may be ended at lower temperatures, such as at 25-28°C.

[0026] While the temperature of the wood may be the most relevant parameter for determining when to end the heating phase, it may be hard to measure the wood temperature within the drying compartment.

[0027] Thus, in an alternative embodiment, the heating is ended when the wet bulb temperature within the wood drying compartment reaches 45-90, such as 60-80°C. The wet bulb temperature may be measured or estimated in a variety of ways, for example by a wet bulb thermometer arranged within the wood drying compartment.

[0028] According to one embodiment, the flow rate of the supplied water is at least 0,01 m 3< / h per m 3< of wood, such as 0,03-0,15 m 3< / h per m 3< of wood.

[0029] Hereby, a sufficiently high flow rate for ensuring that the wood may be efficiently and quickly heated while not becoming too dry during the process may be provided.

[0030] According to one embodiment, the water is supplied from a tank during spraying, the tank being arranged inside the drying compartment.

[0031] Water from the drying of a previous or neighboring batch may thus be stored within the wood drying compartment until heating is needed. By arranging the tank within the wood drying compartment, loss of heat from the water may be prevented. Furthermore, by minimizing the distance which the water needs to be transported, energy may be saved.

[0032] In an alternative embodiment, the water may be supplied from a further wood drying compartment, such as an adjacent wood drying compartment. The further wood drying compartment supplying the water may supply water upon conducting the drying, such that the condensate generated during the drying is directly routed to the heating process of the first wood drying compartment. Alternatively, the water may be supplied from a tank within the further wood drying compartment, the tank having been filled by condensate during an earlier wood drying process.

[0033] It would also be possible to use water from several wood drying compartments during the heating.

[0034] According to one embodiment, water is supplied to the tank from a condensing unit, such as from an active condensing unit.

[0035] Thus, the tank has preferably been filled with condense during a previous wood drying cycle, whereby water is saved.

[0036] According to one embodiment, the water is supplied by a plurality of nozzles, the plurality of nozzles being arranged in the horizontal flow path of the combined air and water flow.

[0037] Hereby, by providing the nozzles in the horizontal flow path of the water, such that the water may be sprayed onto the wood horizontally, the combined air and water flow may be allowed to penetrate into the spaces between the wood pieces such that the heat may easily be transported through the entire wood stack, while successively heating the wood.

[0038] According to one embodiment, the stack of wood comprises a plurality of elongate pieces of wood arranged in a plurality of layers, and a plurality of elongate stickers arranged between the layers.

[0039] According to one embodiment, the longitudinal direction of the elongate stickers extend in a longitudinal direction of the drying compartment, between the first and second end walls, and wherein the longitudinal extension of the pieces of wood extends perpendicular to the longitudinal extension of the stickers. By this means, the longitudinal direction of the stickers will lay essentially in parallel with the direction of the combined air and water flow. Hereby, the combined air and waterflow will gain access to and be evenly distributed over all surfaces of the pieces of wood in the stack.Brief Description of the Drawings

[0040] These and other aspects of the present inventive concept will now be described in more detail, with reference to the appended drawings showing an example embodiment of the inventive concept, wherein: Fig. 1 is a schematical cross-sectional side view a wood drying compartment according to an embodiment of the present disclosure. Fig. 2 is a method for heating wood according to an embodiment of the present disclosure. Detailed Description of Example Embodiments

[0041] In the present detailed description, various embodiments of the invention are described.

[0042] Fig. 1 schematically illustrates a wood drying compartment 10 configured for heating and drying of wood 1, the wood 1 being arranged in an inner space 12 of the wood drying compartment 10 during the heating and drying.

[0043] The operation in the wood drying compartment 10 may be divided into two phases, an initial heating phase and a succeeding drying phase. The heating phase may be initiated when the wood 1 provided to the wood drying compartment 10 has a temperature below a predetermined threshold, and thus needs to be heated before the drying phase can be initiated, to avoid damages to the wood 1, and to increase energy efficiency.

[0044] The wood 1 may typically be arranged in at least one stack or bundle containing a plurality of pieces of wood 11, typically arranged side by side with a distance between each other and in a plurality of vertical layers with distance between the layers. The vertical distance between layers of wood may be achieved by arranging a plurality of elongate distance members, so called stickers 13, between each layer. The stickers 13 are preferably arranged essentially perpendicular to the longitudinal extension of the pieces of wood 11. By this means, air may flow comparatively unhindered through the stack of wood 1 and essentially around each piece of wood 11, which allows for efficient drying of the wood 1. A piece of wood 11 may, for example, be a plank, a piece of timbre, a wooden girder, or any suitable type of sawn piece of wood.

[0045] The wood drying compartment 10 comprises a first end wall 14 and a second end wall 16. A door 18 is arranged in the first end wall 14, the door 18 covering an opening 20 for allowing the stack of wood 1 to be transferred into the inner space 12 of the wood drying compartment 10.

[0046] The second end wall 16 is arranged at an opposite side of the wood drying compartment 10 to the first end wall 14. The second end wall 16 is thus the wall furthest away from the door 18 and the opening 20 and may be regarded as the inner wall of the wood drying compartment 10. It is also understood that the wood drying compartment 10 comprises a pair of side walls extending between the first 14 and second 16 end walls and a ceiling extending above the walls, such as to form an enclosed compartment.

[0047] The stack of wood, when received within the compartment, is preferably oriented such that the longitudinal extension of the pieces of wood extends in the lateral direction, between the side walls, of the compartment. Correspondingly, the longitudinal direction of the elongate stickers 13 extend in the longitudinal direction, between the first 14 and second 16 end walls of the compartment.

[0048] The wood drying compartment 10 comprises an air circulation device 22, such as a fan, for creating an airflow AF within the compartment 10. The air circulation device 22 is typically arranged above the wood 1 and is used to recirculate the air after having been transferred through the wood 1. During the heating, the air circulation device is directed such that it draws air from the door-side wall 14 of the compartment 10 and forces it towards the inner wall 16. The same air is thus recirculated during the entire heating phase, and there is normally no supply of fresh air from the exterior.

[0049] A water spraying system 24 is arranged in the wood drying compartment 10, close to the second end wall 16. When a stack of wood 1 is arranged within the inner space 12, the water spraying system 24 is thus arranged between the second end wall 16 and the stack of wood 1.

[0050] The water spraying system 24 is configured to spray water W into the airflow AF from one single and substantially horizontal direction during the heating phase, to provide a combined air and water flow CF.

[0051] The water spraying system 24 comprises a water supply, such as a tank 26, a plurality of vertical pipes 28 fluidly connected to the tank 26, and a plurality of nozzles 30 attached to the plurality of vertical pipes 28. The tank 26 is thus configured to store an amount of water and to supply it to the plurality of vertical pipes 28, from which pipes 28 the water W may be sprayed into the airflow AF and further onto the wood 1 through the nozzles 30.

[0052] A condenser 32 is arranged on top of the compartment 10. The condenser 10 is configured to be used during the drying phase, to condense water from the warm moist air within the compartment by heat exchanging with a cooling medium. The cooling medium may be cooler ambient air from outside of the compartment, such as outside air, which will be warmed in the condenser.

[0053] Further illustrated in figure 1 is a heater 34 arranged for heating the circulating air. As the air passes through the wood stack during the heating phase, it gives off heat to the wood. There may thus be a need to reheat the air before the next passage through the stack of wood. The heater 34 may be of any type suitable to provide heat to the airflow at passage through the heater.

[0054] Fig. 2 illustrates a method 100 of heating wood 1 in the wood drying compartment 10. The method thus relates to the initial heating phase in which the wood 1 is heated, and not to a subsequent drying phase.

[0055] In a first step S101, a stack of wood 1 is provided to the wood drying compartment 10 through the opening 20.

[0056] The wood 1 may be provided to the compartment 10 by a forklift, such as a front-loaded forklift or a side loaded forklift.

[0057] In a second step S102, an airflow AF is circulated through the stack of wood 1 inside the wood drying compartment 10.

[0058] After the air has been forced through the stack of wood 1, it may be recirculated above the stack by a circulation device 22, such as a fan. During the recirculation, the airflow AF may also be heated, such that the temperature is sufficiently high for heating the wood 1 during the next passing through the stack of wood 1. The temperature to which the airflow AF is heated typically depends on the current temperature of the wood. For example, the airflow AF may be heated to a temperature which is a few degrees above the temperature of the wood. Furthermore, the temperature of the airflow AF should preferably not be too low as this may damage the heating coil. For example, the airflow AF may be heated to a temperature of 20-100 degrees Celsius. The temperature of the airflow AF may be regulated based on the wet bulb temperature.

[0059] In a third step S103, which may be performed simultaneously with the second step S102, the relative humidity of said airflow AF is kept at 80-100%, such as 90-100%, such as 95-100%.

[0060] The temperature of the airflow AF may be continuously monitored and controlled such that drying of the wood 1 is substantially avoided during the heating phase. For example, the relative humidity may be controlled by regulating the amount of water W being sprayed into the airflow AF.

[0061] In a fourth step S104, which may be performed simultaneously with the second S102 and / or the third S103 steps, water W is sprayed into the airflow to provide a combined air and water flow CF.

[0062] Most of the water W used during the heating, such as at least 99% of the water W used during the heating, may be water which has been condensed from the recirculating airstream during the drying of one or several previous dryings. The temperature of the condensate may be 60-70 degrees Celsius. Thus, by reusing this warm condensate in the heating of a new stack or batch, both water and energy may be saved.

[0063] The flowrate of the water being sprayed into the airflow AF is at least 0,01 m 3< / h per m 3< of wood, such as 0,03-0,15 m 3< / h per m 3< of wood. After having passed through the wood 1, the water falls to the floor and is discharged through the drain.

[0064] In a fifth step S105, which may be performed simultaneously with the second S102, third S103 and / or fourth S104 steps, the combined air and water flow CF is directed in one single and substantially horizontal direction through the stack of wood 1, from the second end wall 16 towards the first end wall 14. The direction of the spraying of the water W, as well as the direction of the combined air and water flow CF is thus the same during the entire heating phase. The direction of the combined air and water flow CF being from the inner second end wall 16 and towards the outer first end wall 14.

[0065] The combined air and water flow CF is thus configured to pass through the stack of wood 1 in a direction from the second end wall 16 towards the first end wall 14. Once the flow reaches the first end wall 14, the air is recirculated and, if necessary, heated before again being sent through the wood stack 1.

[0066] The temperature of the wood 1 may be monitored during the heating phase, and the heating phase may be ended once the temperature of the wood and / or the wet bulb temperature within the wood drying compartment, reaches a certain threshold, such as 45-90 °C . The exact temperature typically depends on the type of wood being heated.

[0067] Even though the solution has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.

[0068] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Examples

Embodiment Construction

[0041]In the present detailed description, various embodiments of the invention are described.

[0042]Fig. 1 schematically illustrates a wood drying compartment 10 configured for heating and drying of wood 1, the wood 1 being arranged in an inner space 12 of the wood drying compartment 10 during the heating and drying.

[0043]The operation in the wood drying compartment 10 may be divided into two phases, an initial heating phase and a succeeding drying phase. The heating phase may be initiated when the wood 1 provided to the wood drying compartment 10 has a temperature below a predetermined threshold, and thus needs to be heated before the drying phase can be initiated, to avoid damages to the wood 1, and to increase energy efficiency.

[0044]The wood 1 may typically be arranged in at least one stack or bundle containing a plurality of pieces of wood 11, typically arranged side by side with a distance between each other and in a plurality of vertical layers with distance between the layer...

Claims

1. A method (100) of heating wood (1) in a wood drying compartment (10), the wood drying compartment (10) comprising a first end wall (14) and a second end wall (16) opposite to the first end wall (14), the first end wall (14) comprising an opening (20) and a door (18) for selectively closing said opening (20), which method comprises the steps of; - providing (S101) a stack of wood (1) to the wood drying compartment (10) through the opening (20), - circulating (S102) an airflow (AF) through the stack of wood (1), - keeping (S103) the relative humidity of said airflow (AF) at 80-100%, such as 90-100%, such as 95-100%, - spraying (S104) water (W) into the airflow (AF) to provide a combined air and water flow (CF), and - directing (S105) the combined air and water flow (CF) in one single and substantially horizontal direction through the stack of wood (1), from the second end wall (16) towards the first end wall (14).

2. The method (100) according to claim 1, wherein the sprayed water (W) comprises condensate water produced during a wood drying process.

3. The method (100) according to claim 1 or 2, wherein at least 85%, such as at least 90%, such as at least 99% of the sprayed water (W) is condensate water.

4. The method (100) according to any of the preceding claims, wherein the temperature of the water (W) at spraying is 40-90 °C, such as 50-80°C.

5. The method (100) according to any of the preceding claims, wherein the heating is ended when the temperature of the wood (1) reaches 45-90 °C, such as 55-80 °C.

6. The method (100) according to any of the preceding claims, wherein the flow rate of the supplied water (W) is at least 0,01 m3 / h per m3 of wood, such as 0,03-0,15 m3 / h per m3 of wood.

7. The method (100) according to any of the preceding claims, wherein the water (W) is supplied from a tank (26) during spraying, the tank (26) being arranged inside the drying compartment (10).

8. The method (100) according to claim 7, wherein water (W) is supplied to the tank (26) from a condensing unit (32), such as from an active condensing unit.

9. The method according to claim 8, wherein the condensing unit (32) is arranged to retrieve condensate water from air circulating in the compartment or a neighboring compartment.

10. The method (100) according to any of the preceding claims, wherein the water (W) is supplied by a plurality of nozzles (30).

11. The method (100) according to claim 10, wherein the plurality of nozzles (30) are arranged in the horizontal flow path of the combined air and water flow (CF).

12. The method (100) according to any of the preceding claims, wherein the stack of wood (1) comprises a plurality of elongate pieces of wood (11) arranged in a plurality of layers, and a plurality of elongate stickers (13) arranged between the layers.

13. The method (100) according to claim 12, wherein the longitudinal direction of the elongate stickers (13) extends in a longitudinal direction of the drying compartment (10), between the first (14) and second (16) end walls, and wherein the longitudinal extension of the pieces of wood (11) extends essentially perpendicular to the longitudinal extension of the stickers (13)

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