Field of invention
[0001] The present invention relates to a method for controlling drying of wood in a compartment.
Technical background
[0002] Before being used, wood and timber is frequently dried to suitable water content.
Drying of wood often is performed in a kiln, where heated air is circulated over the
wood subjected to drying, whereby water from the wood is taken up by the heated air
and removed from the kiln.
[0003] Common problems with such drying of wood include crack formation and deformation
of the dried wood. Further problems relate to inefficient drying and high energy consumption
during drying.
[0004] There is a need for obtaining efficient drying of wood, and drying of wood with minimized
risk of creating cracks or deformation of the wood.
[0005] Further, there is a need for controlling the drying such that dry wood without cracks
or deformations are produced.
[0006] GB648388A discloses a method of drying of a material by eliminating a fluid from the material.
The drying is performed while varying a difference between the vapour pressure of
the fluid to be eliminated in the material and the vapour pressure of the same fluid
in the drying medium, while all other drying factors, such as the temperature of the
drying medium in the drying chamber, the flow of this medium through the drying chamber
and primarily the quantity of the fluid to be eliminated which is removed from the
material per unit of time, are maintained constant.
Summary of invention
[0007] An object of the present invention is to provide efficient drying of wood without
problems of prior art.
[0008] Another object of the present invention is to provide dried wood with high quality.
[0009] Yet another object of the present invention is to provide a method for controlling
drying of wood such that cracks and/or deformation of the dried wood is minimized.
[0010] These and other objects of the invention are at least partly met by the invention
as defined in the independent claims. Preferred embodiments are set out in the dependent
claims.
[0011] According to a first aspect, there is provided a method for controlling drying of
wood in a compartment in accordance with claim 1.
[0012] The controlling may comprise outputting the determined control parameter value.
[0013] The control parameter may be for controlling of heating, of air flow velocity within
the compartment, or of venting of air to or from the compartment, or combinations
thereof.
[0014] The controlling may be controlling of heating, controlling of air flow velocity within
the compartment, controlling of inflow of fresh air to the compartment, or controlling
of outflow of air from the compartment, or combinations thereof.
[0015] The measured value may be an amount of condense water per time unit.
[0016] According to a second aspect, there is provided a computer program product in accordance
with claim 4,
Brief description of drawings
[0017]
Fig.1 is a schematic illustration of a compartment for drying of wood.
Fig.2 is a schematic illustration of a method according to an embodiment.
Detailed description
[0018] The present invention take advantage of the realization that problems with wood subjected
to drying, such as crack formation and/or deformation, is a result of moisture gradients
formed within the wood subjected to drying, with a lower moisture level at the surface
of the wood as compared to further into the wood. The gradients may form tensions
in the wood with resulting crack formation. Too intense drying, such as rapid drying
by high air flows with low relative humidity and high temperature, may be inefficient
and result in cracks in the wood, while too soft drying, such as slow drying, for
example, by lower air flows, with higher relative humidity, and/or lower temperatures,
may result in crack free wood but is time consuming. Therefore, efficient drying may
alter between periods of intense drying and soft drying, to allow the moist gradient
within the wood to level out during the periods of soft drying. The present invention
provides for an efficient way of controlling the drying process and to control the
drying such that high quality wood is produced, with minimized or low degree of crack-formation
and deformation.
[0019] The method of embodiments of the present invention may be used with dryers taking
advantage of condensation of moisture from the air within the dryer. It has surprisingly
been found that the method for drying may be controlled based on measuring the amount
of condense water, to provide efficient drying able to produce dried wood with good
quality. The invention further relies on that the amount of condensed water is linked
to the moisture gradient within the wood being subjected to the drying. For example,
a higher amount of condensed water per time unit may indicate higher levels of moisture
close to or at the surface of the wood, as compared to lower amount of condensed water
per time unit which may indicate that lower levels of moisture close to or at the
surface of the wood, at otherwise similar conditions. Measuring an amount of condense
water, thus, enables efficient control of the drying process with desirable properties
of the dried wood.
[0020] The measurement of an amount of condense water derived from air could be used in
several ways. The amount of condense water could be measured during drying process
for one or more batches of wood to be dried. The measured values could then be compared
to reference values for determining whether the drying process may need to be adjusted
in order to obtain an optimal drying of wood. Control parameter value(s) for controlling
the drying process may thus be set based on such adjustment and these control parameter
value(s) may be used in subsequent drying processes for drying of wood in the compartment.
Hence, the measurements of an amount of condense water derived from air could be used
for setting up of a drying process, which set-up may be performed e.g. when the compartment
is to be taken into use, or at regular intervals or when conditions in the compartment
are changed.
[0021] As an alternative, a control parameter value may be determined in real time during
drying of wood. Thus, based on a measured value of an amount of condense water, a
controller may determine a control parameter value for controlling the drying of wood
during the drying process.
[0022] Control of the drying process may include:
Controlling the fan, thereby allowing performing and altering between intense/hard
drying and soft drying, or intermediate drying there between.
[0023] Controlling the heat supplied to the dryer, thereby controlling the temperature inside
the compartment.
[0024] Controlling the venting out of air from the dryer, thereby allowing air with high
relative humidity to leave the compartment, such as air from an initial stage of the
drying process.
[0025] Controlling inlet of fresh ambient air into the dryer, thereby allowing fresh air
to enter the dryer, or sealing off the dryer from ambient air.
[0026] The present invention will now be described more fully hereinafter with reference
to the accompanying drawings, in which preferred embodiments of the invention are
shown. This invention may, however, be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein; rather, these embodiments
are provided for thoroughness and completeness, and fully convey the scope of the
invention to the skilled person.
[0027] The method according to embodiments take advantage of measuring condensed water during
the drying, and the methods therefore may be used with a dryer that condenses moisture
from the air used for drying. In figure 1, an example of such a dryer suitable for
use with the method of embodiments of the present invention is illustrated. The dryer
comprises a drying compartment 1, comprising at least one air circulator 2, such as
a fan, creating a flow of air within the compartment 1. Wood 6 is arranged inside
the compartment 1 for drying. Although not illustrated, the wood may typically be
arranged in at least one bundle of wood containing a plurality of pieces of wood,
typically arranged several side by side with a distance between each other and in
a plurality of layers with distance between the layers, such that air may flow through
the bundle of wood and essentially around each piece of wood, which allows for efficient
drying of the wood 6. A piece of wood may, for example, be a plank, a piece of timbre,
a wooden girder, or any suitable type of sawn piece of wood. Further illustrated in
figure 1 is a heater 8 arranged for heating the circulating air. A condenser 10 is
arranged in the compartment, such that water is condensed from warm moist air within
the compartment 1 by heat exchanging with a cooler medium. The cooler medium may suitably,
for realising high energy efficiency, be cooler ambient air from outside of the compartment,
such as outside air, which will be warmed in the condenser. The compartment 1 comprises
means for measuring an amount of water condensed by the condenser. For example, the
total volume or mass of condensed water, or a flow rate of condensed water, such as
expressed by mass or volume per time unit, may be measured as an average over a time
period or as a momentary value, or any other suitable way of indicating an amount
of condensed water. Condensed water from the condenser may be collected or transferred
elsewhere by means not illustrated in the figure. The warmed outside air may be transferred
into the compartment 1, for example if it is determined that outside air should be
vented into the compartment 1, or it may alternatively be passed from the condenser
and out of the compartment without being mixed with the atmosphere of the compartment
1. It is realised, that although the condenser 10 is illustrated as being inside of
the compartment, it may alternatively be arrange outside the compartment. The compartment
further may comprises an air outlet 12 for letting air out of the compartment 1, and
an air inlet 14 for letting air into the compartment, the air outlet 12 and the air
inlet 14 may have means for opening, closing or adjusting the passage of air. Further,
a controller 18 may be provided to perform one or more of receiving measured value
indicative of an amount of condense water, determining a control parameter value based
on the measured value, and outputting the determined control parameter value for controlling
the drying of wood, and may communicate with a computer or processor.
[0028] Thus, the condenser 10 may be used to condense water from the moist air of the compartment,
warm an inlet of fresh air from the outside of the compartment 1. It is realised that
the compartment 1 may comprise further or less devices, equipment or arrangements,
and that the compartment 1 is illustrated and discussed as an example of a dryer able
to condense water from the air within the dryer to provide clarity and understanding
to the present invention and embodiments thereof.
[0029] With reference to figure 2 a method 50 for controlling drying of wood according to
an embodiment will now be discussed. The method 50 comprises receiving 52 a measured
value indicative of an amount of condense water derived from air circulating through
the wood during the drying, determining 54 a control parameter value based on the
measured value, and outputting 56 the determined control parameter value for controlling
the drying of wood.
[0030] According to an example, drying of wood in a compartment 1, such as the compartment
discussed with reference to figure 1, is performed. Initially when the water content
is high at the surface of the wood, hard drying is made with air outlet 12 and air
inlet 14 opened such that moist warm air is vented out of and fresh air is vented
in to the compartment 1. Air circulator 2 is run at high efficiency, thus creating
an airflow through the wood at high velocity. Then, when at least a major part of
the water of the surface has been dried, the air outlet 12 and air inlet 14 are closed.
With air outlet 12 and air inlet 14 closed, moist may not be vented out of the compartment,
and the condenser 10 is used for removal of moist from the air within the compartment
1. A combination of venting and condensing may alternatively be used. The method 1
is performed by controller 18 receiving a measured value indicative of an amount of
condense water derived from air circulating through the wood during the drying, in
this case the momentary flow rate measured in cubic metre per second. The controller
18 then determines a control parameter value based on the measured value, in this
case the control parameter adjusts power to the air circulator 2 and is determined
to be 10% of the previous power. The controller 18 then outputs the determined control
parameter value to the air circulator 2 for controlling the drying of wood. In this
example, the amount of condense water was relatively low and had decreased considerably
as compared to previous measurements earlier in the drying due to relatively dry surface
wood of the wood. Therefore, the controller was set to decrease the power to the air
circulator to 10% of the previous power in order to go from hard drying to soft drying.
It is realised, that instead of decreasing the power by 90% in one step, the decrease
may suitably be made in a plurality of steps, using the method of the embodiment.
During the consecutive soft drying, the method is performed a plurality of times,
i.e. by receiving, determining, and outputting as previously described. During the
soft drying the amount of condense water will start to increase, due to water being
transported from the interior of the wood to the surface portion of the wood. As one
result, the controller 18 will output signals to the air circulator 2 which gradually
will increase its power and the drying will be hard drying again. According to this
example, the drying will go over several alternating hard drying and soft drying cycles.
In addition to or alternatively to the adjusting the air flow, the controller may
output signals such that the temperature changes to effect the drying, such as by
signalling to the heater 8 to increase or decrease its power, or, such as when high
flow rate of condense water is determined, to open the outlet 12 and inlet 14, or
any other suitable way of controlling the drying. The method may alternatively be
used to maintain a more even drying, which does not alter between hard and soft drying,
but maintains a suitable degree of drying.
[0031] According to other embodiments, the method may be used to determine if the drying
is finished and thereby for example the heater and air circulator may be turned off.
[0032] It is realized that the condense water may not be the only parameter that controls
the drying. Typically, for example, the temperature, such as the wet bulb temperature
and the dry temperature, the relative humidity and the dimensions of the wood may
also be used in the controlling of the drying.
[0033] The controller 18 may thus be arranged to receive input regarding a plurality of
measurements representing the climate in the compartment 1. The controller 18 may
further be arranged to determine control parameter values based on pre-defined rules
for controlling the drying of wood. The controller 18 may further output control parameter
values for causing an adjustment of the climate in the compartment 1 as previously
described.
[0034] The controller 18 may in one embodiment be implemented as a processing unit, which
is arranged to perform calculations so as to determine control parameter values. The
controller 18 may further comprise an input interface for receiving information from
external units, such as sensors. The controller 18 may thus receive measured values
from the sensors through the input. The processing unit may be connected to the the
input interface for receiving the information. The controller 18 may further comprise
an output for transmitting signals in order to control the climate in the compartment,
such as to alter between soft and hard drying. The processing unit may be connected
to the output for providing appropriate signals based on the calculations performed
by the processing unit.
[0035] The processing unit may be implemented as any type of processor enabling automation
of calculations. The processing unit may thus be a general-purpose computer with special
instructions and may be implemented e.g. as a central processing unit (CPU). The controller
18 may further store a computer program product in memory which may be loaded to the
processing unit for executing the program. The computer program product may also comprise
pre-defined rules for controlling the drying of wood, or such rules may be stored
in the memory of the controller 18. As an alternative, the processing unit may be
a unit that it intended for a specific purpose and may thus be implemented e.g. as
an application-specific integrated circuit (ASIC) or a field-programmable gate array
(FPGA).
1. Method for controlling drying of wood (6) in a compartment (1), the method comprising
subjecting the wood (6) to altering periods of hard drying and soft drying,
repeatedly during drying of wood (6), receiving (52) a measured value of an amount
of condense water per time unit derived from air circulating through the wood (6)
during the drying,
determining (54) a control parameter value based at least on the measured value,
controlling (56) the drying of wood (6) using the control parameter value,
wherein the control parameter is for controlling of heating, of air flow within the
compartment, or venting of air to or from the compartment, or combinations thereof
and wherein the control parameter is for initiating the altering of periods of hard
and soft drying and/or, during altering periods of hard and soft drying, for altering
the drying from hard to soft drying and/or from soft to hard drying.
2. The method of claim 1, wherein said controlling comprises outputting the determined
control parameter value.
3. The method according to any one of the previous claims, wherein the controlling is
controlling of heating, controlling of air flow within the compartment (1), controlling
of inflow of fresh air to the compartment (1), or controlling of outflow of air from
the compartment (1), or combinations thereof.
4. A computer program product comprising a computer-readable medium with computer-readable
instructions such that when executed on a processing unit the computer program product
will cause the processing unit to perform a method comprising
control a circulator (2), a heater (8), an outlet (12) and/or an inlet (14) of a compartment
(1) to subject the wood (6) to altering periods of hard drying and soft drying,
repeatedly during drying of wood (6), receive (52) a measured value of an amount of
condense water per time unit derived from air circulating through the wood (6) during
the drying,
determine (54) a control parameter value based at least on the measured value,
control (56) the drying of wood (6) using the control parameter value,
wherein the control parameter is for control of heating, of air flow within the compartment,
or venting of air to or from the compartment, or combinations thereof
and wherein the control parameter is for initiating the altering of periods of hard
and soft drying and/or, during altering periods of hard and soft drying, for altering
the drying from hard to soft drying and/or from soft to hard drying.
1. Verfahren zum Steuern von Trocknen von Holz (6) in einer Kammer (1), wobei das Verfahren
Folgendes aufweist:
Anwenden von abwechselnden Perioden von Durchtrocknen und sanftem Trocknen an dem
Holz (6),
wiederholt während Trocknens von Holz (6), Erhalten (52) eines gemessenen Werts einer
Menge Kondensationswassers pro Zeiteinheit, der von Luft, die während des Trocknens
durch das Holz (6) zirkuliert, abgeleitet wird,
Bestimmen (54) eines Kontrollparameterwerts basierend zumindest auf dem gemessenen
Wert,
Steuern (56) des Trocknens von Holz (6) unter Verwendung des Kontrollparameterwerts,
wobei der Kontrollparameter zum Steuern von Erwärmung, von Luftstrom innerhalb der
Kammer oder Blasen von Luft in die oder aus der Kammer oder einer Kombination davon
dient,
und wobei der Kontrollparameter zum Initiieren des Abwechselns von Perioden von Durchtrocknen
und sanftem Trocknen und/oder während abwechselnder Perioden von Durchtrocknen und
sanftem Trocknen zum Abwechseln des Trocknens von Durchtrocknen zu sanftem Trocknen
und/oder von sanftem Trocknen zu Durchtrocknen dient.
2. Verfahren nach Anspruch 1, wobei das Steuern Ausgeben des bestimmten Kontrollparameterwerts
aufweist.
3. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Steuern Steuern von Erwärmung,
Steuern von Luftstrom innerhalb der Kammer (1), Steuern von Einströmung von Frischluft
in die Kammer (1) oder Steuern von Ausströmung von Luft aus der Kammer (1) oder Kombinationen
davon ist.
4. Computerprogrammprodukt, das ein computerlesbares Medium mit computerlesbaren Anweisungen
aufweist, derart dass bei Ausführung auf einer Verarbeitungseinheit das Computerprogrammprodukt
die Verarbeitungseinheit dazu veranlasst, ein Verfahren auszuführen, das Folgendes
aufweist:
Steuern eines Zirkulators (2), eines Heizapparats (8), eines Auslasses (12) und/oder
eines Einlasses (14) einer Kammer (1), um das Holz (6) abwechselnden Perioden von
Durchtrocknen und sanftem Trocknen auszusetzen,
wiederholt während Trocknens von Holz (6), Erhalten (52) eines gemessenen Werts einer
Menge Kondensationswassers pro Zeiteinheit, der von Luft, die während des Trocknens
durch das Holz (6) zirkuliert, abgeleitet wird,
Bestimmen (54) eines Kontrollparameterwerts basierend zumindest auf dem gemessenen
Wert,
Steuern (56) des Trocknens von Holz (6) unter Verwendung des Kontrollparameterwerts,
wobei der Kontrollparameter zum Steuern von Erwärmung, von Luftstrom innerhalb der
Kammer oder Blasen von Luft in die oder aus der Kammer oder einer Kombination davon
dient, und
wobei der Kontrollparameter zum Initiieren des Abwechselns von Perioden von Durchtrocknen
und sanftem Trocknen und/oder während abwechselnder Perioden von Durchtrocknen und
sanftem Trocknen zum Abwechseln des Trocknen von Durchtrocken zu sanftem Trocknen
und/oder von sanftem Trocken zu Durchtrocknen dient.
1. Procédé de commande de séchage du bois (6) dans un compartiment (1), le procédé comprenant
de soumettre le bois (6) à des périodes en alternance de séchage fort et de séchage
doux,
de manière répétée durant le séchage du bois (6), de recevoir (52) une valeur mesurée
d'une quantité d'eau condensée par unité de temps dérivée de l'air circulant à travers
le bois (6) durant le séchage,
de déterminer (54) une valeur de paramètre de commande basée au moins sur la valeur
mesurée,
de commander (56) le séchage du bois (6) en utilisant la valeur de paramètre de commande,
dans lequel le paramètre de commande est pour commander le chauffage, du flux d'air
à l'intérieur du compartiment, ou la ventilation de l'air vers ou du compartiment,
ou des combinaisons de ceux-ci
et dans lequel le paramètre de commande est pour lancer le passage de périodes de
séchage fort et doux et/ou durant le passage de périodes de séchage fort et doux,
pour faire passer le séchage de fort à doux et/ou de doux à fort.
2. Procédé selon la revendication 1, dans lequel ladite commande comprend d'émettre en
sortie la valeur de paramètre de commande déterminée.
3. Procédé selon l'une quelconque des revendications précédentes, dans lequel la commande
est la commande de chaleur, la commande d'écoulement d'air à l'intérieur du compartiment
(1), la commande de flux entrant d'air neuf dans le compartiment (1) ou la commande
de flux d'air sortant du compartiment (1) ou des combinaisons de ceux-ci.
4. Produit de programme informatique comprenant un support lisible sur ordinateur avec
des instructions lisibles sur ordinateur de telle sorte que lors de l'exécution sur
une unité de traitement, le produit de programme informatique va faire exécuter un
procédé à l'unité de traitement, comprenant
de commander un circulateur (2), un appareil de chauffage (8), une sortie (12) et/ou
une entrée (14) d'un compartiment (1) pour soumettre le bois (6) à des périodes alternantes
de séchage fort et de séchage doux,
de manière répétée durant le séchage du bois (6), de recevoir (52) une valeur mesurée
d'une quantité d'eau condensée par unité de temps dérivée de l'air circulant à travers
le bois (6) durant le séchage,
de déterminer (54) une valeur de paramètre de commande basée au moins sur la valeur
mesurée,
de commander (56) le séchage du bois (6) en utilisant la valeur de paramètre de commande,
dans lequel le paramètre de commande est pour commander le chauffage, l'écoulement
d'air à l'intérieur du compartiment, ou la ventilation de l'air vers ou du compartiment,
ou des combinaisons de ceux-ci
et dans lequel le paramètre de commande est pour lancer le passage de périodes de
séchage fort et doux et/ou durant le passage de périodes de séchage fort et doux,
pour faire passer le séchage de fort à doux et/ou de doux à fort.