EP2005096A1 - Method of drying wood collected in stacks - Google Patents

Method of drying wood collected in stacks

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Publication number
EP2005096A1
EP2005096A1 EP07710530A EP07710530A EP2005096A1 EP 2005096 A1 EP2005096 A1 EP 2005096A1 EP 07710530 A EP07710530 A EP 07710530A EP 07710530 A EP07710530 A EP 07710530A EP 2005096 A1 EP2005096 A1 EP 2005096A1
Authority
EP
European Patent Office
Prior art keywords
wood
drying
gas
stacks
moisture content
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07710530A
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German (de)
French (fr)
Inventor
Kurt Ing. Mühlböck
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Individual
Original Assignee
Individual
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Filing date
Publication date
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Publication of EP2005096A1 publication Critical patent/EP2005096A1/en
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B9/00—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards
    • F26B9/06—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards in stationary drums or chambers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
    • F26B21/02—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
    • F26B21/06—Controlling, e.g. regulating, parameters of gas supply
    • F26B21/10—Temperature; Pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B2210/00—Drying processes and machines for solid objects characterised by the specific requirements of the drying good
    • F26B2210/16—Wood, e.g. lumber, timber

Definitions

  • the invention relates to a method for drying wood stored in stacks with the help of a stack of wood flowing through the drying gas stream, which is performed with removal of moist exhaust gas after the stacks of wood and supply of fresh gas in front of the wood stacks partially circulated through the woodpile, the wood at a moisture content above the fiber saturation is dried faster than at a moisture content below the fiber saturation.
  • a drying gas stream is usually conveyed through the wood stacks, whereby moisture is released from the wood surface to the drying gas, depending on the gas temperature, the gas humidity and the flow rate of the drying gas.
  • the drying gas usually drying air, is thereby partly circulated through the wood stacks, wherein a partial flow is removed from the circulation for the removal of moisture and replaced by heated fresh gas.
  • About the amount of discharged moist exhaust gas and the supplied dry fresh gas the moisture content of the wood stacks supplied drying gas depending on the residual moisture of the wood for a desired drying course will give.
  • shortest possible drying time a comparatively high flow rate for the drying gas stream is selected, which results in a considerable energy input.
  • the discharged amounts of exhaust gas and the supplied fresh gas quantities for the wood stacks are controlled zone by zone independently of each other. This, however, the energy required for the circulation flow of the drying gas remains high.
  • the invention is therefore based on the object, a method for drying wood of the type described in such a way that short drying times can be ensured with a relatively low energy consumption, without damaging the wood to be dried.
  • the invention solves this problem by the fact that the wood before its slower drying with the help of partially recycled in the cycle tion gas stream is dried faster with a drying gas stream consisting at least substantially only of fresh gas.
  • the invention is based on the finding that above the fiber saturation wood can be dried as quickly as desired without being damaged. This means that above the fiber saturation no drying gas flow is required with a certain minimum moisture, so that can be dispensed with a partial circulation of the drying gas flow. If comparatively dry fresh gas is supplied to the wood having a moisture content above the fiber saturation, high drying rates with a low flow rate of the drying gas can be ensured with the advantage that the energy expenditure for maintaining a sufficient drying gas flow is limited in comparison to conventional drying methods. In addition, the gas temperature can be kept low, so that the risk of discoloration due to temperature stresses can be avoided even in hardwoods that are particularly vulnerable to such discoloration.
  • the treatment temperature for the wood can be kept low, at quite economic drying rates.
  • a wood temperature of at most 0 0 C at least during an initial stage of drying with fresh Gas a beneficial in terms of wood color treatment of the wood is possible.
  • the water frozen in this case in the wood evaporates namely at a correspondingly low moisture content of the drying gas, without first liquefying.
  • the drying rate in the range of wood moisture above the fiber saturation can be increased by a moderate heating of the drying gas by the fresh gas after preheating in heat exchange with the sensible waste heat of the exhaust gas discharged before flowing through the wood stack by at least one heating coil is heated, which brings an advantageous utilization of heat energy with it.
  • the illustrated apparatus for drying wood has in a conventional manner a drying chamber 1, in which the wood to be dried is stored in stacks 2 indicated by dash-dotted lines. Above the storage space for the wood stack 2, the drying chamber 1 is provided with a false ceiling 3, which forms an outlet 4 for the drying space flowing through the storage space with the inlet 5 flow channel 6. This flow channel 6 is connected to a cross-flow heat exchanger 7, discharged via the exhaust gas 8 from the storage room and fresh gas 9 is supplied. To promote the drying gas through the storage room 1 distributed fans 10 are provided over the length of the drying chamber.
  • the ratio between the exhaust or fresh gas quantities on the one hand and the proportion of the drying gas circulated via the flow channel 6 can be selected as a function of the drying process.
  • the flow channel 6 In the illustrated closed position of the control flap 11, the flow channel 6 is blocked, so that a circulation flow of the drying gas is suppressed by the drying chamber 1 and sucked on the crossflow heat exchanger 7 fresh gas 9 represents the entire drying gas flow, which after flowing through the wood stack 2 as the exhaust gas 8 again is discharged via the cross-flow heat exchanger 7.
  • a heating register 12 may be provided in the region of the inlet 5.
  • a heating register 13 is arranged in the region of the outlet 4, which is then used when the drying gas flow is occasionally reversed in its flow direction.
  • the drying of stored in the storage room of the drying chamber 1 wood stacks 2 takes place at first closed control flap 11 at least substantially only with the help of the fresh air sucked via the blower 10 9, which has a relatively low moisture content and therefore allows rapid drying of the wood, as long as the wood moisture is above the fiber saturation.
  • a fresh gas usually fresh air is used.
  • exhaust gases from boilers or other equipment can be used advantageously for the wood drying, if these gases are sufficiently dry.
  • the fresh gas 9 can be more or less additionally heated via the heating register 12 in the inlet 5 in order to increase the drying rate, without having to accept any damage to the temperature of the wood.
  • the sensible waste heat of the exhaust gas 8, which dissipates the moisture from the wood surface can be used in the crossflow heat exchanger 7 for the preheating of the fresh gas 9, the amount of heat to be supplied via the heating coil 12 can be comparatively low, especially with regard to the risk of discoloration, especially color-sensitive hardwoods the wood temperature should be limited.
  • the amount of heat to be supplied via the heating coil 12 can be comparatively low, especially with regard to the risk of discoloration, especially color-sensitive hardwoods the wood temperature should be limited.
  • the moisture content of the drying gas is determined solely by the moisture content of the fresh gas 9, which can be kept correspondingly low. Above the fiber saturation even an extremely low gas humidity does not adversely affect the drying process.
  • the low gas humidity caused by the use of essentially only fresh gas allows a considerable reduction in the flow rate of the drying gas through the wood stacks 2, which noticeably reduces the energy input for conveying the drying gas.
  • the missing circulation component of the drying gas flow requires sufficiently large amounts of fresh gas or exhaust gas.
  • the drying chamber 1 is not provided in a conventional manner with individual over the chamber length distributed inlet and exhaust ports, but over the chamber length through openings for the supply of fresh gas 9 and the discharge of exhaust gas 8.
  • the control flap 11 is to be opened, wherein the proportion of the circulation flow can be controlled by the flap position. In the fully open flap position, the exhaust gas or the fresh gas can be blocked, resulting in an exclusive circulation of the drying gas result.
  • the case of an at least partial circulation of the drying gas under certain circumstances greater heat demand can be covered by the heater 13 in the outlet 4.

Abstract

A method of drying wood collected in stacks (2) using a drying gas stream flowing through the wood stack (2) is described which, with removal of moist exhaust gas (8) downstream of the wood stacks (2) and feed of fresh gas (9) upstream of the wood stacks (2), is in part circulated through the wood stacks (2), wherein the wood is dried more rapidly at a moisture content above the fibre saturation than at a moisture content below the fibre saturation. In order to provide advantageous economic drying conditions, it is proposed that the wood, before its slower drying, is dried more rapidly using the in part circulated drying gas stream using a drying gas stream consisting of at least essentially only fresh gas.

Description

Verfahren zum Trocknen von in Stapeln zusammenqefasstem HolzMethod for drying wood stacked in stacks
Technisches GebietTechnical area
Die Erfindung bezieht sich auf ein Verfahren zum Trocknen von in Stapeln gelagertem Holz mit Hilfe eines die Holzstapel durchströmenden Trocknungsgasstromes, der unter Abfuhr feuchten Abgases nach den Holzstapeln und Zufuhr von Frischgas vor den Holzstapeln teilweise im Kreislauf durch die Holzstapel geführt wird, wobei das Holz bei einem Feuchtigkeitsgehalt über der Fasersättigung rascher als bei einem Feuchtigkeitsgehalt unter der Fasersättigung getrocknet wird.The invention relates to a method for drying wood stored in stacks with the help of a stack of wood flowing through the drying gas stream, which is performed with removal of moist exhaust gas after the stacks of wood and supply of fresh gas in front of the wood stacks partially circulated through the woodpile, the wood at a moisture content above the fiber saturation is dried faster than at a moisture content below the fiber saturation.
Stand der TechnikState of the art
Zur Trocknung von in Stapeln gelagertem Holz wird üblicherweise ein Trocknungsgasstrom durch die Holzstapel gefördert, wobei von der Holzoberfläche Feuchtigkeit an das Trocknungsgas abgegeben wird, und zwar in Abhängigkeit von der Gastemperatur, der Gasfeuchtigkeit und der Strömungsgeschwindigkeit des Trocknungsgases. Das Trocknungsgas, üblicherweise Trocknungsluft, wird dabei zum Teil im Kreislauf durch die Holzstapel geführt, wobei zur Abfuhr der Feuchtigkeit ein Teilstrom aus dem Kreislauf ausgeschieden und durch erwärmtes Frischgas ersetzt wird. Über die Menge des abgeführten feuchten Abgases und des zugeführten trockeneren Frischgases kann die Feuchtigkeit des den Holzstapeln zugeführten Trocknungsgases in Abhängigkeit von der Restfeuchtigkeit des Holzes für einen erwünschten Trocknungsverlauf vorge- geben werden. Im Hinblick auf eine möglichst kurze Trocknungszeit wird eine vergleichsweise hohe Strömungsgeschwindigkeit für den Trocknungsgasstrom gewählt, was einen erheblichen Energieeinsatz zur Folge hat.For drying wood stored in stacks, a drying gas stream is usually conveyed through the wood stacks, whereby moisture is released from the wood surface to the drying gas, depending on the gas temperature, the gas humidity and the flow rate of the drying gas. The drying gas, usually drying air, is thereby partly circulated through the wood stacks, wherein a partial flow is removed from the circulation for the removal of moisture and replaced by heated fresh gas. About the amount of discharged moist exhaust gas and the supplied dry fresh gas, the moisture content of the wood stacks supplied drying gas depending on the residual moisture of the wood for a desired drying course will give. With regard to the shortest possible drying time, a comparatively high flow rate for the drying gas stream is selected, which results in a considerable energy input.
Der Umstand, daß die Trocknungsrate von Holz mit einem Feuchtigkeitsgehalt über der Fasersättigung, also von Holz mit einem freien Wasseranteil, im wesentlichen nur von der zugeführten Wärmemenge und erst bei einem Feuchtigkeitsgehalt unter der Fasersättigung, also bei nur mehr in den Holzzellwänden gebundenem Wasser, vom Feuchtigkeitsgehalt abhängt, hat dazu geführt (AT 412 741 B), Holzstapel mit einer unterschiedlichen mittleren Ausgangsfeuchtigkeit oberhalb der Fasersättigung unterschiedlich rasch bis zur Fasersättigung zu trocknen, so daß aufgrund der damit verbundenen unterschiedlichen Trocknungsraten trotz der unterschiedlichen Ausgangsfeuchtigkeit alle Holzstapel gleichzeitig die Fasersättigung erreichen und folglich gemeinsam auf die angestrebte Endfeuchtigkeit unter der Fasersättigung getrocknet werden können, und zwar unter Beachtung eines hiefür vorteilhaften, erheblich langsameren Trocknungsverlaufes. Um die unterschiedlichen Trocknungsraten der Holzstapel mit den unterschiedlichen mittleren Ausgangsfeuchtigkeiten über der Fasersättigung sicherzustellen, werden die abgeführten Abgasmengen und die zugeführten Frischgasmengen für die Holzstapel zonenweise voneinander unabhängig gesteuert. Damit bleibt aber der Energieaufwand für die Kreislaufströmung des Trocknungsgases entsprechend hoch.The fact that the rate of drying wood with a moisture content above the fiber saturation, ie of wood with a free water content, essentially only of the amount of heat supplied and only at a moisture content below the fiber saturation, so only in the wood cell walls bound water, from Moisture content has caused (AT 412 741 B), wood stacks with a different average initial moisture above the fiber saturation to dry faster than fiber saturation, so that due to the associated different drying rates despite the different initial moisture all wood stacks simultaneously reach the fiber saturation and consequently can be dried together to the desired final moisture content under fiber saturation, taking into account an advantageous for this, considerably slower drying process. In order to ensure the different drying rates of the wood stacks with the different average outlet moisture content over the fiber saturation, the discharged amounts of exhaust gas and the supplied fresh gas quantities for the wood stacks are controlled zone by zone independently of each other. This, however, the energy required for the circulation flow of the drying gas remains high.
Darstellung der ErfindungPresentation of the invention
Der Erfindung liegt somit die Aufgabe zugrunde, ein Verfahren zum Trocknen von Holz der eingangs geschilderten Art so auszugestalten, daß kurze Trocknungszeiten unter einem vergleichsweise geringen Energieeinsatz sichergestellt werden können, ohne das zu trocknende Holz zu schädigen.The invention is therefore based on the object, a method for drying wood of the type described in such a way that short drying times can be ensured with a relatively low energy consumption, without damaging the wood to be dried.
Die Erfindung löst die gestellte Aufgabe dadurch, daß das Holz vor seiner langsameren Trocknung mit Hilfe des teilweise im Kreislauf geführten Trock- nungsgasstromes mit einem zumindest im wesentlichen nur aus Frischgas bestehenden Trocknungsgasstrom rascher getrocknet wird.The invention solves this problem by the fact that the wood before its slower drying with the help of partially recycled in the cycle tion gas stream is dried faster with a drying gas stream consisting at least substantially only of fresh gas.
Die Erfindung basiert auf der Erkenntnis, daß oberhalb der Fasersättigung Holz beliebig schnell getrocknet werden kann, ohne Schaden zu nehmen. Dies bedeutet, daß oberhalb der Fasersättigung kein Trocknungsgasstrom mit einer bestimmten Mindestfeuchtigkeit erforderlich ist, so daß auf eine teilweise Kreislaufführung des Trocknungsgasstromes verzichtet werden kann. Wird dem Holz mit einem Feuchtigkeitsgehalt oberhalb der Fasersättigung vergleichsweise trockenes Frischgas zugeführt, so können hohe Trocknungsraten mit einer geringen Strömungsgeschwindigkeit des Trocknungsgases mit dem Vorteil gewährleistet werden, daß der Energieaufwand für die Aufrechterhaltung einer ausreichenden Trocknungsgasströmung im Vergleich zu herkömmlichen Trocknungsverfahren beschränkt bleibt. Außerdem kann die Gastemperatur niedrig gehalten werden, so daß auch die Gefahr von Verfärbungen aufgrund von Temperaturbelastungen selbst bei Laubhölzern vermieden werden kann, die gegenüber solchen Verfärbungen besonders anfällig sind. Die rasche Trocknung des Holzes mit Hilfe von Trocknungsgas niedrigen Feuchtigkeitsgehaltes erfolgt während einer Trocknungsphase, bei der das Holz einen Feuchtigkeitsgehalt oberhalb der Fasersättigung aufweist. Spätestens im Bereich der Fasersättigung muß allerdings die Trocknung auf eine herkömmliche Führung des Trocknungsgases in einem teilweisen Kreislauf umgestellt werden, um Trocknungsschäden zu vermeiden, die erst unterhalb der Fasersättigung in Erscheinung treten.The invention is based on the finding that above the fiber saturation wood can be dried as quickly as desired without being damaged. This means that above the fiber saturation no drying gas flow is required with a certain minimum moisture, so that can be dispensed with a partial circulation of the drying gas flow. If comparatively dry fresh gas is supplied to the wood having a moisture content above the fiber saturation, high drying rates with a low flow rate of the drying gas can be ensured with the advantage that the energy expenditure for maintaining a sufficient drying gas flow is limited in comparison to conventional drying methods. In addition, the gas temperature can be kept low, so that the risk of discoloration due to temperature stresses can be avoided even in hardwoods that are particularly vulnerable to such discoloration. The rapid drying of the wood with the aid of low moisture drying gas occurs during a drying phase in which the wood has a moisture content above the fiber saturation. At the latest in the field of fiber saturation, however, the drying must be converted to a conventional guidance of the drying gas in a partial cycle in order to avoid drying damage, which only appear below the fiber saturation in appearance.
Wie bereits ausgeführt wurde, kann bei einem Verzicht auf einen im Kreislauf durch die Holzstapel geführten Trocknungsgasanteil während eines Feuchtigkeitsgehaltes oberhalb der Fasersättigung die Behandlungstemperatur für das Holz niedrig gehalten werden, und zwar bei durchaus wirtschaftlichen Trocknungsraten. Für besonders farbempfindliche Holzarten hat sich in überraschender Weise herausgestellt, daß bei einer Holztemperatur von höchstens 00C zumindest während eines Anfangsabschnittes der Trocknung mit Frisch- gas eine im Sinne der Holzfärbung vorteilhafte Behandlung des Holzes möglich wird. Das in diesem Fall im Holz gefrorene Wasser verdampft nämlich bei einem entsprechend geringen Feuchtigkeitsgehalt des Trocknungsgases, ohne sich vorher zu verflüssigen.As already stated, if no drying gas fraction circulated through the wood stacks during a moisture content above the fiber saturation is dispensed with, the treatment temperature for the wood can be kept low, at quite economic drying rates. For particularly color-sensitive wood species has surprisingly been found that at a wood temperature of at most 0 0 C, at least during an initial stage of drying with fresh Gas a beneficial in terms of wood color treatment of the wood is possible. The water frozen in this case in the wood evaporates namely at a correspondingly low moisture content of the drying gas, without first liquefying.
Bei der Trocknung weniger farbempfindlicher Hölzer kann die Trocknungsrate im Bereich der Holzfeuchtigkeit oberhalb der Fasersättigung auch durch eine mäßige Erwärmung des Trocknungsgases gesteigert werden, indem das Frischgas nach einer Vorwärmung im Wärmeaustausch mit der fühlbaren Abwärme des abgeführten Abgases vor dem Durchströmen der Holzstapel durch wenigstens ein Heizregister erwärmt wird, was eine vorteilhafte Ausnützung der Wärmeenergie mit sich bringt.When drying less color-sensitive woods, the drying rate in the range of wood moisture above the fiber saturation can be increased by a moderate heating of the drying gas by the fresh gas after preheating in heat exchange with the sensible waste heat of the exhaust gas discharged before flowing through the wood stack by at least one heating coil is heated, which brings an advantageous utilization of heat energy with it.
Kurze Beschreibung der ZeichnungShort description of the drawing
An Hand der Zeichnung wird das erfindungsgemäße Verfahren zum Trocknen von Holz näher beschrieben, und zwar wird eine Vorrichtung zur Durchführung des Verfahrens in einem schematischen Querschnitt gezeigt.With reference to the drawing, the method according to the invention for drying wood will be described in detail, namely a device for carrying out the method is shown in a schematic cross section.
Weg zur Ausführung der ErfindungWay to carry out the invention
Die dargestellte Vorrichtung zum Trocknen von Holz weist in herkömmlicher Weise eine Trocknungskammer 1 auf, in der das zu trocknende Holz in strichpunktiert angedeuteten Stapeln 2 gelagert wird. Oberhalb des Lagerraumes für die Holzstapel 2 ist die Trocknungskammer 1 mit einer Zwischendecke 3 versehen, die einen den Auslaß 4 für das den Lagerraum durchströmende Trocknungsgas mit dessen Einlaß 5 verbindenden Strömungskanal 6 bildet. Dieser Strömungskanal 6 ist an einen Kreuzstromwärmetauscher 7 angeschlossen, über den Abgas 8 aus dem Lagerraum abgeführt und Frischgas 9 zugeführt wird. Zur Förderung des Trocknungsgases durch den Lagerraum sind über die Länge der Trocknungskammer 1 verteilte Gebläse 10 vorgesehen. Mit Hilfe wenigstens einer im Strömungskanal 6 angeordneten Steuerklappe 11 kann das Verhältnis zwischen den Abgas- bzw. Frischgasmengen einerseits und dem Anteil des über den Strömungskanal 6 im Kreislauf geführten Trocknungsgases anderseits in Abhängigkeit vom Trocknungsverlauf gewählt werden. In der dargestellten Schließstellung der Steuerklappe 11 wird der Strömungskanal 6 gesperrt, so daß eine Kreislaufströmung des Trocknungsgases durch die Trocknungskammer 1 unterbunden wird und das über den Kreuzstromwärmetauscher 7 angesaugte Frischgas 9 den gesamten Trocknungsgasstrom darstellt, der nach dem Durchströmen der Holzstapel 2 als Abgas 8 wieder über den Kreuzstromwärmetauscher 7 abgeführt wird. Zur Erwärmung des zugeführten Frischgases 9 kann im Bereich des Einlasses 5 ein Heizregister 12 vorgesehen sein. Gemäß dem Ausführungsbeispiel ist auch im Bereich des Auslasses 4 ein Heizregister 13 angeordnet, das dann zum Einsatz kommt, wenn der Trocknungsgasstrom fallweise in seiner Strömungsrichtung umgekehrt wird.The illustrated apparatus for drying wood has in a conventional manner a drying chamber 1, in which the wood to be dried is stored in stacks 2 indicated by dash-dotted lines. Above the storage space for the wood stack 2, the drying chamber 1 is provided with a false ceiling 3, which forms an outlet 4 for the drying space flowing through the storage space with the inlet 5 flow channel 6. This flow channel 6 is connected to a cross-flow heat exchanger 7, discharged via the exhaust gas 8 from the storage room and fresh gas 9 is supplied. To promote the drying gas through the storage room 1 distributed fans 10 are provided over the length of the drying chamber. With the help of at least one arranged in the flow channel 6 control valve 11, the ratio between the exhaust or fresh gas quantities on the one hand and On the other hand, the proportion of the drying gas circulated via the flow channel 6 can be selected as a function of the drying process. In the illustrated closed position of the control flap 11, the flow channel 6 is blocked, so that a circulation flow of the drying gas is suppressed by the drying chamber 1 and sucked on the crossflow heat exchanger 7 fresh gas 9 represents the entire drying gas flow, which after flowing through the wood stack 2 as the exhaust gas 8 again is discharged via the cross-flow heat exchanger 7. For heating the fresh gas 9 supplied, a heating register 12 may be provided in the region of the inlet 5. According to the embodiment, a heating register 13 is arranged in the region of the outlet 4, which is then used when the drying gas flow is occasionally reversed in its flow direction.
Die Trocknung von im Lagerraum der Trocknungskammer 1 gelagerten Holzstapeln 2 erfolgt zunächst bei geschlossener Steuerklappe 11 zumindest im wesentlichen nur mit Hilfe des über die Gebläse 10 angesaugten Frischgases 9, das einen vergleichsweise geringen Feuchtigkeitsgehalt aufweist und daher eine rasche Trocknung des Holzes erlaubt, solange die Holzfeuchtigkeit oberhalb der Fasersättigung liegt. Als Frischgas wird üblicherweise Frischluft eingesetzt. Es können aber auch Abgase von Heizkesseln oder anderen Einrichtungen vorteilhaft für die Holztrocknung Verwendung finden, wenn diese Gase ausreichend trocken sind. Je nach der zu trocknenden Holzart kann das Frischgas 9 über das Heizregister 12 im Einlaß 5 mehr oder weniger zusätzlich aufgeheizt werden, um die Trocknungsrate zu erhöhen, ohne eine Temperaturschädigung des Holzes in Kauf nehmen zu müssen. Da die fühlbare Abwärme des Abgases 8, das die Feuchtigkeit von der Holzoberfläche abführt, im Kreuzstromwärmetauscher 7 für die Vorwärmung des Frischgases 9 genützt werden kann, kann die über das Heizregister 12 zuzuführende Wärmemenge vergleichsweise gering ausfallen, zumal im Hinblick auf die Verfärbungsgefahr insbesondere farbempfindlicher Laubhölzer die Holztemperatur begrenzt werden soll. Für besonders günstige Behandlungsbedingungen wird in diesem Zusammenhang gesorgt, wenn die Holztemperatur unter 00C gehalten wird. Trotzdem kann eine wirtschaftliche Trocknungsrate sichergestellt werden, weil wegen des Fehlens eines Kreislaufstromes des Trocknungsgases über den Strömungskanal 6 der Feuchtigkeitsgehalt des Trocknungsgases ausschließlich durch den Feuchtigkeitsgehalt des Frischgases 9 bestimmt wird, der entsprechend gering gehalten werden kann. Oberhalb der Fasersättigung nimmt auch eine extrem niedrige Gasfeuchtigkeit keinen nachteiligen Einfluß auf den Trocknungsverlauf.The drying of stored in the storage room of the drying chamber 1 wood stacks 2 takes place at first closed control flap 11 at least substantially only with the help of the fresh air sucked via the blower 10 9, which has a relatively low moisture content and therefore allows rapid drying of the wood, as long as the wood moisture is above the fiber saturation. As a fresh gas usually fresh air is used. However, exhaust gases from boilers or other equipment can be used advantageously for the wood drying, if these gases are sufficiently dry. Depending on the type of wood to be dried, the fresh gas 9 can be more or less additionally heated via the heating register 12 in the inlet 5 in order to increase the drying rate, without having to accept any damage to the temperature of the wood. Since the sensible waste heat of the exhaust gas 8, which dissipates the moisture from the wood surface, can be used in the crossflow heat exchanger 7 for the preheating of the fresh gas 9, the amount of heat to be supplied via the heating coil 12 can be comparatively low, especially with regard to the risk of discoloration, especially color-sensitive hardwoods the wood temperature should be limited. For particularly favorable treatment conditions is in this Ensured when the wood temperature is kept below 0 0 C. Nevertheless, an economical drying rate can be ensured because, due to the lack of a circulation flow of the drying gas through the flow channel 6, the moisture content of the drying gas is determined solely by the moisture content of the fresh gas 9, which can be kept correspondingly low. Above the fiber saturation even an extremely low gas humidity does not adversely affect the drying process.
Die durch den Einsatz von im wesentlichen nur Frischgas bedingte niedrige Gasfeuchtigkeit erlaubt eine erhebliche Herabsetzung der Strömungsgeschwindigkeit des Trocknungsgases durch die Holzstapel 2, was den Energieeinsatz für die Förderung des Trocknungsgases merklich verringert. Der fehlende Kreislaufanteil der Trocknungsgasströmung erfordert allerdings ausreichend große Frischgas- bzw. Abgasmengen. Um einen entsprechenden Volumenstrom sicherzustellen, wird die Trocknungskammer 1 nicht in herkömmlicher Art mit einzelnen über die Kammerlänge verteilten Zu- und Abgasöffnungen, sondern mit über die Kammerlänge durchgehenden Öffnungen für die Zufuhr von Frischgas 9 bzw. die Abfuhr von Abgas 8 versehen werden.The low gas humidity caused by the use of essentially only fresh gas allows a considerable reduction in the flow rate of the drying gas through the wood stacks 2, which noticeably reduces the energy input for conveying the drying gas. However, the missing circulation component of the drying gas flow requires sufficiently large amounts of fresh gas or exhaust gas. To ensure a corresponding volume flow, the drying chamber 1 is not provided in a conventional manner with individual over the chamber length distributed inlet and exhaust ports, but over the chamber length through openings for the supply of fresh gas 9 and the discharge of exhaust gas 8.
Sobald die Holzstapel 2 auf einen Feuchtigkeitsgehalt im Bereich der Fasersättigung getrocknet sind, ist zur schonenden Trocknung des Holzes auf eine Endfeuchtigkeit unterhalb der Fasersättigung ein Anteil des Trocknungsgases in bewährter Weise in einem Kreislauf über den Strömungskanal 6 zu führen, so daß sich für die Trocknungsgasströmung durch die Holzstapel 2 eine höhere Gasfeuchtigkeit einstellt. Zu diesem Zweck ist die Steuerklappe 11 zu öffnen, wobei der Anteil der Kreislaufströmung durch die Klappenstellung gesteuert werden kann. In der vollständig geöffneten Klappenstellung kann das Abgas oder das Frischgas gesperrt werden, was eine ausschließliche Kreislaufführung des Trocknungsgases zur Folge hat. Der bei einer zumindest teilweisen Kreislaufführung des Trocknungsgases unter Umständen größere Wärmebedarf kann durch das Heizregister 13 im Auslaß 4 gedeckt werden. As soon as the wood stacks 2 have dried to a moisture content in the range of fiber saturation, a portion of the drying gas is to be guided in a reliable manner in a circuit via the flow channel 6 for gentle drying of the wood to a final moisture content below the fiber saturation, so that the drying gas flow through the wood stack 2 sets a higher gas humidity. For this purpose, the control flap 11 is to be opened, wherein the proportion of the circulation flow can be controlled by the flap position. In the fully open flap position, the exhaust gas or the fresh gas can be blocked, resulting in an exclusive circulation of the drying gas result. The case of an at least partial circulation of the drying gas under certain circumstances greater heat demand can be covered by the heater 13 in the outlet 4.

Claims

P a t e n t a n s p r ü c h e : Patent claim:
1. Verfahren zum Trocknen von in Stapeln zusammengefaßtem Holz mit Hilfe eines die Holzstapel durchströmenden Trocknungsgasstromes, der unter Abfuhr feuchten Abgases nach den Holzstapeln und Zufuhr von Frischgas vor den Holzstapeln teilweise im Kreislauf durch die Holzstapel geführt wird, wobei das Holz bei einem Feuchtigkeitsgehalt über der Fasersättigung rascher als bei einem Feuchtigkeitsgehalt unter der Fasersättigung getrocknet wird, dadurch gekennzeichnet, daß das Holz vor seiner langsameren Trocknung mit Hilfe des teilweise im Kreislauf geführten Trocknungsgasstromes mit einem zumindest im wesentlichen nur aus Frischgas bestehenden Trocknungsgasstrom rascher getrocknet wird.1. A method for drying stacked wood with the help of a stack of wood flowing through the drying gas stream, which is performed with removal of moist exhaust gas after the stacks of wood and supply of fresh gas in front of the wood stacks partially circulated through the woodpile, the wood at a moisture content above the Fiber saturation is dried faster than at a moisture content below the fiber saturation, characterized in that the wood is dried faster before its slower drying with the help of the partially circulated drying gas flow with a drying gas stream consisting at least substantially only of fresh gas.
2. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, daß das Holz zumindest während eines Anfangsabschnittes der Trocknung mit Frischgas eine Temperatur von höchstens 00C aufweist.2. The method according to claim 1, characterized in that the wood, at least during an initial portion of the drying with fresh gas has a temperature of at most 0 0 C.
3. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, daß das Frischgas nach einer Vorwärmung im Wärmeaustausch mit der fühlbaren Abwärme des abgeführten Abgases vor dem Durchströmen der Holzstapel durch wenigstens ein Heizregister erwärmt wird. 3. The method according to claim 1, characterized in that the fresh gas is heated after preheating in the heat exchange with the sensible waste heat of the exhaust gas discharged before flowing through the wood stack by at least one heating coil.
EP07710530A 2006-04-12 2007-03-23 Method of drying wood collected in stacks Withdrawn EP2005096A1 (en)

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AT0062906A AT503026B1 (en) 2006-04-12 2006-04-12 Method for drying wood arranged in stacks comprises rapidly drying the wood using a circulated drying gas stream with a drying gas stream consisting of only fresh gas before being drying in a slower manner
PCT/AT2007/000141 WO2007115343A1 (en) 2006-04-12 2007-03-23 Method of drying wood collected in stacks

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US20090158615A1 (en) 2009-06-25
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CA2647210A1 (en) 2007-10-18
RU2008144564A (en) 2010-05-20

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