SE540072C2 - Method for controlling drying of wood and a computer programproduct - Google Patents

Abstract

The present invention relates to a method for controlling drying of wood in a compartment. The method comprises receiving a measured value indicative of an amount of condense water derived from air circulating through the wood during the drying, determining a control parameter value based on the measured value, outputting the determined control parameter value for controlling the drying of wood.

Description

METHOD FOR CONTROLLING DRYING OF WOOD AND A COMPUTERPROGRAM PRODUCT Field of inventionThe present invention relates to a method for controlling drying of wood in acompartment.

Technical backgroundBefore being used, wood and timber is frequently dried to suitable water content. Drying of wood often is performed in a kiln, where heated air iscirculated over the wood subjected to drying, whereby water from the wood istaken up by the heated air and removed from the kiln.

Common problems with such drying of wood include crack formationand deformation of the dried wood. Further problems relate to inefficientdrying and high energy consumption during drying.

There is a need for obtaining efficient drying of wood, and drying ofwood with minimized risk of creating cracks or deformation of the wood.

Further, there is a need for controlling the drying such that dry woodwithout cracks or deformations are produced.

Summary of inventionAn object of the present invention is to provide efficient drying of wood without problems of prior art.

Another object of the present invention is to provide dried wood withhigh quality.

Yet another object of the present invention is to provide a method forcontrolling drying of wood such that cracks and/or deformation of the driedwood is minimized.

These and other objects of the invention are at least partly met by theinvention as defined in the independent claims. Preferred embodiments areset out in the dependent claims.

According to a first aspect, there is provided a method for controllingdrying of wood in a compartment, the method comprising receiving ameasured value indicative of an amount of condense water derived from aircirculating through the wood during the drying, determining a controlparameter value based on the measured value, outputting the determinedcontrol parameter value for controlling the drying of wood.

The control parameter may be for controlling of heating, of air flowvelocity within the compartment, or of venting of air to or from thecompartment, or combinations thereof.

The controlling may be controlling of heating, controlling of air flowvelocity within the compartment, controlling of inflow of fresh air to thecompartment, or controlling of outflow of air from the compartment, orcombinations thereof.

The measured value may-leeisan amount of condense water per timeunit.

According to a second aspect, there is provided a compartment fordrying of wood, the compartment comprising a controller performing themethod according to the first aspect.

According to a third aspect, there is provided a computer programproduct comprising a computer-readable medium with computer-readableinstructions such that when executed on a processing unit the computerprogram product will cause the processing unit to perform the methodaccording to any one of claims 1-§8.

Brief description of drawinqs 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 descriptionThe present invention take advantage of the realization that problems with wood subjected to drying, such as crack formation and/or deformation, isa 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 intothe wood. The gradients may form tensions in the wood with resulting crackformation. Too intense drying, such as rapid drying by high air flows with lowrelative humidity and high temperature, may be inefficient and result in cracksin the wood, while too soft drying, such as slow drying, for example, by lowerair flows, with higher relative humidity, and/or lower temperatures, may resultin crack free wood but is time consuming. Therefore, efficient drying may alterbetween periods of intense drying and soft drying, to allow the moist gradientwithin the wood to level out during the periods of soft drying. The presentinvention provides for an efficient way of controlling the drying process and tocontrol the drying such that high quality wood is produced, with minimized orlow degree of crack-formation and deformation.

The method of embodiments of the present invention may be used withdryers taking advantage of condensation of moisture from the air within thedryer. lt has surprisingly been found that the method for drying may becontrolled based on measuring the amount of condense water, to provideefficient drying able to produce dried wood with good quality. The inventionfurther relies on that the amount of condensed water is linked to the moisturegradient within the wood being subjected to the drying. For example, a higheramount of condensed water per time unit may indicate higher levels ofmoisture close to or at the surface of the wood, as compared to lower amountof condensed water per time unit which may indicate that lower levels ofmoisture close to or at the surface of the wood, at othen/vise similarconditions. Measuring an amount of condense water, thus, enables efficientcontrol of the drying process with desirable properties of the dried wood.

Control of the drying process may include: Controlling the fan, thereby allowing performing and altering betweenintense/hard drying and soft drying, or intermediate drying there between.

Controlling the heat supplied to the dryer, thereby controlling thetemperature inside the compartment.

Controlling the venting out of air from the dryer, thereby allowing airwith high relative humidity to leave the compartment, such as air from aninitial stage of the drying process.

Controlling inlet of fresh ambient air into the dryer, thereby allowingfresh air to enter the dryer, or sealing off the dryer from ambient air.

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodiments ofthe invention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to the embodiments setforth herein; rather, these embodiments are provided for thoroughness andcompleteness, and fully convey the scope of the invention to the skilledperson.

The method according to embodiments take advantage of measuringcondensed water during the drying, and the methods therefore may be usedwith a dryer that condenses moisture from the air used for drying. ln figure 1,an example of such a dryer suitable for use with the method of embodimentsof the present invention is illustrated. The dryer comprises a dryingcompartment 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 thecompartment 1 for drying. Although not illustrated, the wood may typically bearranged in at least one bundle of wood containing a plurality of pieces ofwood, typically arranged several side by side with a distance between eachother and in a plurality of layers with distance between the layers, such thatair may flow through the bundle of wood and essentially around each piece ofwood, 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 suitabletype of sawn piece of wood. Further illustrated in figure 1 is a heater 8arranged for heating the circulating air. A condenser 10 is arranged in thecompartment, such that water is condensed from warm moist air within thecompartment 1 by heat exchanging with a cooler medium. The cooler mediummay suitably, for realising high energy efficiency, be cooler ambient air fromoutside of the compartment, such as outside air, which will be warmed in thecondenser. The compartment 1 comprises means for measuring an amountof water condensed by the condenser. For example, the total volume or massof condensed water, or a flow rate of condensed water, such as expressed bymass 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 anamount of condensed water. Condensed water from the condenser may becollected or transferred elsewhere by means not illustrated in the figure. Thewarmed outside air may be transferred into the compartment 1, for example ifit is determined that outside air should be vented into the compartment 1, or itmay alternatively be passed from the condenser and out of the compartmentwithout being mixed with the atmosphere of the compartment 1. lt is realised,that although the condenser 10 is illustrated as being inside of thecompartment, it may alternatively be arrange outside the compartment. Thecompartment further may comprises an air outlet 12 for letting air out of thecompartment 1, and an air inlet 14 for letting air into the compartment, the airoutlet 12 and the air inlet 14 may have means for opening, closing oradjusting the passage of air. Further, a controller 18 may be provided toperform one or more of receiving measured value indicative of an amount ofcondense water, determining a control parameter value based on themeasured value, and outputting the determined control parameter value forcontrolling the drying of wood, and may communicate with a computer orprocessor.

Thus, the condenser 10 may be used to condense water from themoist air of the compartment, warm an inlet of fresh air from the outside of thecompartment 1. lt is realised that the compartment 1 may comprise further orless devices, equipment or arrangements, and that the compartment 1 isillustrated and discussed as an example of a dryer able to condense waterfrom the air within the dryer to provide clarity and understanding to thepresent invention and embodiments thereof.

With reference to figure 2 a method 50 for controlling drying of woodaccording to an embodiment will now be discussed. The method 50comprises receiving 52 a measured value indicative of an amount ofcondense water derived from air circulating through the wood during thedrying, determining 54 a control parameter value based on the measuredvalue, and outputting 56 the determined control parameter value forcontrolling the drying of wood.

According to an example, drying of wood in a compartment 1, such asthe compartment discussed with reference to figure 1, is performed. lnitiallywhen the water content is high at the surface of the wood, hard drying ismade with air out|et 12 and air in|et 14 opened such that moist warm air isvented out of and fresh air is vented in to the compartment 1. Air circu|ator 2is run at high efficiency, thus creating an air flow through the wood at highvelocity. Then, when at least a major part of the water of the surface has beendried, the air out|et 12 and air in|et 14 are closed. With air out|et 12 and airin|et 14 closed, moist may not be vented out of the compartment, and thecondenser 10 is used for removal of moist from the air within thecompartment 1. A combination of venting and condensing may alternativelybe used. The method 1 is performed by controller 18 receiving a measuredvalue indicative of an amount of condense water derived from air circulatingthrough the wood during the drying, in this case the momentary flow ratemeasured in cubic metre per second. The controller 18 then determines acontrol parameter value based on the measured value, in this case the controlparameter adjusts power to the air circu|ator 2 and is determined to be 10% ofthe previous power. The controller 18 then outputs the determined controlparameter value to the air circu|ator 2 for controlling the drying of wood. lnthis example, the amount of condense water was relatively low and haddecreased considerably as compared to previous measurements earlier in thedrying due to relatively dry surface wood of the wood. Therefore, thecontroller was set to decrease the power to the air circu|ator to 10% of theprevious power in order to go from hard drying to soft drying. lt is realised,that instead of decreasing the power by 90% in one step, the decrease maysuitably be made in a plurality of steps, using the method of the embodiment.During the consecutive soft drying, the method is performed a plurality oftimes, 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 surfaceportion of the wood. As one result, the controller 18 will output signals to theair circu|ator 2 which gradually will increase its power and the drying will behard drying again. According to this example, the drying will go over several alternating hard drying and soft drying cycles. ln addition to or alternatively tothe adjusting the air flow, the controller may output signals such that thetemperature changes to effect the drying, such as by signalling to the heater 8to increase or decrease its power, or, such as when high flow rate ofcondense water is determined, to open the outlet 12 and inlet 14, or any othersuitable way of controlling the drying. The method may alternatively be usedto maintain a more even drying, which does not alter between hard and softdrying, but maintains a suitable degree of drying.

According to other embodiments, the method may be used todetermine if the drying is finished and thereby for example the heater and aircirculator may be turned off. lt is realized that the condense water may not be the only parameterthat controls the drying. Typically, for example, the temperature, such as thewet bulb temperature and the dry temperature, the relative humidity and thedimensions of the wood may also be used in the controlling of the drying.

The controller 18 may thus be arranged to receive input regarding aplurality of measurements representing the climate in the compartment 1. Thecontroller 18 may further be arranged to determine control parameter valuesbased on pre-defined rules for controlling the drying of wood. The controller18 may further output control parameter values for causing an adjustment ofthe climate in the compartment 1 as previously described.

The controller 18 may in one embodiment be implemented as aprocessing unit, which is arranged to perform calculations so as to determinecontrol parameter values. The controller 18 may further comprise an inputinterface for receiving information from external units, such as sensors. Thecontroller 18 may thus receive measured values from the sensors through theinput. The processing unit may be connected to the the input interface forreceiving the information. The controller 18 may further comprise an outputfor transmitting signals in order to control the climate in the compartment,such as to alter between soft and hard drying. The processing unit may beconnected to the output for providing appropriate signals based on thecalculations performed by the processing unit.

The processing unit may be implemented as any type of processorenabling automation of calculations. The processing unit may thus be ageneral-purpose computer with special instructions and may be implementede.g. as a central processing unit (CPU). The controller 18 may further store acomputer program product in memory which may be loaded to the processingunit for executing the program. The computer program product may alsocomprise pre-defined rules for controlling the drying of wood, or such rulesmay be stored in the memory of the controller 18. As an alternative, theprocessing unit may be a unit that it intended for a specific purpose and maythus be implemented e.g. as an application-specific integrated circuit (ASIC)or a field-programmable gate array (FPGA).

Claims (4)

1. Method for controlling drying of wood in a compartment, the methodcomprising, performing a plurality of times: receiving a measured value indicative of an amount of condense waterderived from air circulating through the wood during the drying, wherein themeasured value is an amount of condense water per time unit, determining a control parameter value based on the measured value, outputting the determined control parameter value for controlling thedrying of wood.

2. The method according to claim 1, wherein the control parameter is forcontrolling of heating, of air flow within the compartment, or venting of air to orfrom the compartment, or combinations thereof.

3. The method according to claim 1 or 2, wherein the controlling is controllingof heating, controlling of air flow within the compartment, controlling of inflowof fresh air to the compartment, or controlling of outflow of air from the compartment, or combinations thereof.

4. A computer program product comprising a computer-readable medium withcomputer-readable instructions such that when executed on a processing unitthe computer program product will cause the processing unit to perform themethod according to any one of claims 1-3.