EP2092258B1 - Method for drying wood collected into piles - Google Patents

Method for drying wood collected into piles Download PDF

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Publication number
EP2092258B1
EP2092258B1 EP07845262A EP07845262A EP2092258B1 EP 2092258 B1 EP2092258 B1 EP 2092258B1 EP 07845262 A EP07845262 A EP 07845262A EP 07845262 A EP07845262 A EP 07845262A EP 2092258 B1 EP2092258 B1 EP 2092258B1
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Prior art keywords
drying
wood
gas
piles
moisture
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German (de)
French (fr)
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EP2092258A2 (en
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Kurt Ing. Mühlböck
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B15/00—Machines or apparatus for drying objects with progressive movement; Machines or apparatus with progressive movement for drying batches of material in compact form
    • F26B15/10—Machines or apparatus for drying objects with progressive movement; Machines or apparatus with progressive movement for drying batches of material in compact form with movement in a path composed of one or more straight lines, e.g. compound, the movement being in alternate horizontal and vertical directions
    • F26B15/12—Machines or apparatus for drying objects with progressive movement; Machines or apparatus with progressive movement for drying batches of material in compact form with movement in a path composed of one or more straight lines, e.g. compound, the movement being in alternate horizontal and vertical directions the lines being all horizontal or slightly inclined
    • 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
    • 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 stacked wood, which is dried during a stepwise batch conveyance through a drying channel by means of opposing drying gas streams in successive drying zones to a final moisture content below the fiber saturation, the determined by the number of stacked in the conveying direction wood pile certain Stacking depth of the drying zones increases in the conveying direction.
  • the drying channel forms two drying zones with partially circulated Trocknungsgasströmen, preferably air streams, of which the input side flow against the direction of passage of the wood stack and the output side in the direction of passage through the drying zones.
  • the partial replacement of the two drying gas streams by fresh gas, for which a common inlet is provided in the region of the inlet-side drying gas circulation, is controlled by a common, the output side drying gas cycle associated exhaust flap.
  • This desired independence of the final moisture from the initial moisture is of particular importance, because the moisture content of the individual to dry a stack of combined woods varies greatly, but for the further processing of the dried wood should be a uniform residual moisture.
  • a disadvantage of this known method for drying wood in a drying channel is that the variations in the residual moisture of the dried wood can only be kept within tolerable limits if the drying rate is kept relatively low.
  • the invention is therefore based on the object, a method of the type described for drying stacked wood in such a way that combined to stack woods with very different initial moisture can be dried together in a narrow tolerance range to a predetermined final moisture, with a comparatively low energy consumption.
  • the invention achieves the stated object in that the wood in two input-side drying zones, at least substantially with supplied between these drying zones fresh gas to a moisture content in the fiber saturation region, but substantially above the fiber saturation and then in at least one further drying zone by means of at least partially in the circulation guided, adjustable in terms of its temperature and humidity drying gas stream is dried to the final moisture.
  • the fiber saturation wood can be dried as quickly as desired, without damaging, can be dispensed with a moisture content of the wood above the fiber saturation to a certain minimum moisture ensuring circulation flow of the drying gas, so that the wood with a moisture content above the fiber saturation comparatively dry fresh gas can be supplied.
  • the gas temperature can be kept low, which is especially in connection with a very different moisture content of the individual pieces of wood to be dried stack of importance because the rate of drying of woods with a lower moisture content compared to the wood with a higher moisture content decreases.
  • a drying zone follows in which the drying rate in the conveying direction decreases due to the increasing moisture load of the drying gas flowing in the conveying direction, in particular at a corresponding stacking depth.
  • the stacking depth of the inlet-side drying zone should, however, be kept small in order to ensure a high, not affected by an increasing steam load drying rate despite the low temperature of the drying gas.
  • the rising in the conveying direction moisture content of the fresh gas flow also has a balancing effect on the different moisture contents of the individual woods, so that in the described drying to near fiber saturation has already taken place a substantial adjustment of the moisture content of the individual woods to an average value.
  • 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.
  • the drying is carried out to the final moisture, wherein by a corresponding adjustment of the temperature and humidity of the circulating drying gas and by an advantageous choice of stacking depth, taking into account the respective flow direction for a further moisture compensation the required final moisture uniformly in a small tolerance range can be ensured.
  • the drying of the wood in the range of wood moisture above the fiber saturation can be accelerated by a moderate heating of the drying gas by the fresh gas is heated after preheating in the heat exchange with the exhaust gas from the acted upon with the fresh gas drying zone by at least one heating coil, which is an advantageous utilization the heat energy brings with it.
  • the wood after drying with fresh gas, the wood can pass through additional drying zones to adapt to a favorable average drying process of the individual woods of a stack, in which corresponding drying conditions are ensured by suitable influences on the drying gas flow.
  • the wood can be dried to a moisture content essentially below the fiber saturation in an intermediate zone provided between the outlet-side drying zone in the conveying direction and the two inlet-side drying zones by means of a drying gas stream which is at least partially circulated and adjustable with respect to its temperature and moisture content , so that in the fiber saturation region a gentle transition of the moisture content of a value above the fiber saturation to a value below the fiber saturation results, which is then of increased importance, if not achieved after drying with fresh gas sufficient equalization of the moisture content of the individual woods of a stack could be.
  • the device shown has a housing 1, which forms a drying channel 2, which is provided with a conveyer, not shown for reasons of clarity for gradually through the drying channel 2 to be conveyed wood stack 3.
  • the combined from individual woods stack 3 are successively conveyed by means of the conveyor through individual conveyor zones 4, 5, 6 and 7, wherein the stacking depth, by the number of stacked in the conveying direction 8 wood stack 3 in the drying zones 4, 5, 6 and 7 is determined, increases in the conveying direction 8, which entails a corresponding extension of the residence time of the individual wood stacks in the respective drying zone 5, 7 by itself. Only the residence time of the wood stacks 3 in the intermediate zone 6 between the drying zones 5 and 7 corresponds to the residence time in the drying zone 3, but this is not mandatory.
  • the individual drying zones 4 to 7 are charged with a drying gas, generally air, which is guided in opposite directions through the drying zones 4 to 7, as indicated in the drawing by the flow arrows.
  • a drying gas generally air
  • the drying gas streams consist at least substantially of fresh gas sucked by means of blowers 9 via cross-flow heat exchanger 10 in sections 11 provided above the drying channel 2 flow channel and by a heating coil 12 between the two input-side drying zones 4, 5th is blown into the drying channel 2, so that in the drying zone 4 a drying gas flow against the conveying direction 8 and in the drying zone 5 form a drying gas flow in the conveying direction.
  • the exiting from the stacks 3, loaded with the absorbed wood moisture exhaust gas streams are fed back to the cross-flow heat exchanger 10 via sections 13 of the flow channel above the drying channel 2 to be excreted in the drying process discharged their sensible waste heat to the fresh air sucked. Since the fresh gas has a low moisture content, rapid drying of the wood of the stacks 3 above the fiber saturation can be carried out with the aid of the fresh gas streams in the two input-side drying zones 4, 5. To speed up the drying process, the fresh gas can be moderately heated via the heating register 12. The stacking depth of the drying zone 4 is small in order not to slow the drying by the moisture absorbed by the fresh gases wood moisture.
  • the drying rate can be kept high due to the low moisture of the fresh gases supplied, with the advantage that due the relatively low temperatures of the drying gas streams, the drying rate for woods with a high moisture content fails greater than for woods with a low moisture content.
  • a compensation of the different moisture content of the woods in a stack 3 can be introduced in an advantageous manner with regard to the requirement that the final moisture of all the woods of a stack 3 at the exit of the drying tunnel 2 has a uniform value.
  • the moisture content of the drying air is increased in the conveying direction due to the recorded wood moisture, whereby the drying rate is increasingly lowered and a gentle for the drying course of wood can be set for a further compensation of the different moisture of the individual woods in provides the stacks 3.
  • the stacking depth in the drying zone 5 is correspondingly increased compared to that of the drying zone 4.
  • drying gas is circulated in the drying zone 6 over a section 14 of the flow channel above the drying channel 2, with the aid of a blower 15. The moisture and the temperature of this at least partially circulated drying gas flow can be adjusted according to the respective requirements.
  • a heating coil 12 and on the other hand a device 16 is provided, through which a part of the drying gas flow can be eliminated from the circuit and replaced by fresh gas, so that the moisture of the drying zone 6 supplied drying gas by a mixture of comparatively dry fresh gas with the moist drying gas from the drying zone 6 can be adjusted.
  • the woods After drying the wood of the stack 3 to below the fiber saturation, the woods are dried in an exit-side drying zone 7 to the required final moisture, which must be done gently.
  • the stacking depth of this output-side drying zone 7 is also chosen to be significantly higher than that of the preceding drying zones 5, 6.
  • the conditioning of the drying zone 7 supplied drying gas flow on the one hand again via a heating coil 12 and on the other hand via a separation of a partial stream of the drying gas and a replacement of the excreted drying gas by fresh gas.
  • the circulation flow is maintained by a fan 15 in a portion 17 of the flow channel above the drying channel 2.
  • control of the gas exchange is carried out by means of control valves 18. This represents a design difference with regard to the control of the fresh gas supply in the region of the drying zone 6, because in the device 16, the partial separation of drying gas and the fresh gas supply is made by separate blower.
  • a countercurrent heat exchanger 19 is used in order to use the fillable waste heat of the excreted exhaust gases for preheating the fresh gases, which is not required in the region of the exit-side drying zone 7.
  • the wood stacks 3 are conveyed at a corresponding depth of a stack 3 conveying step at predetermined periods, the output side wood stack 3 of the drying zone 7 taken via an outlet 20 of the device and a new stack through an inlet 21 of the drying zone 4th is abandoned.
  • B. fresh softwood which has within a stack a moisture content of the individual woods between 30% and 200% to a predetermined final moisture, for example between 6% and 20% to dry.
  • the temperature of the drying gases in the area of the input side Drying gases in the region of the input-side drying zones 4, 5 is preferably 30 to 50 ° C and is raised to 65 to 80 ° C in the drying zones 6 and 7.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Drying Of Solid Materials (AREA)

Abstract

The invention relates to a method for drying piles of wood (3), said wood being dried, during a step-by-step transport of the piles through a drying channel (2) by means of drying gas flows flowing in opposite directions in successive drying regions (4, 5, 6, 7), until an ultimate humidity below the fibre saturation is reached, the pile depth of the drying regions, determined by the number of successive wood piles (3) in the direction of transport (8), increasing in the direction of transport. In order to achieve a uniform ultimate humidity with a comparably low energy consumption and advantageous drying rates, in spite of different starting humidities, the wood is dried in two drying regions (4, 5) on the input side at least essentially with fresh gas supplied between said drying regions, until a humidity content in the fibre saturation range is reached, but essentially above the saturation of the fibres, and then in at least one other drying region (7) by means of a drying gas flow at least partially guided in the circuit and adjustable in terms of the temperature and the humidity thereof, until an ultimate humidity is reached.

Description

Technisches GebietTechnical area

Die Erfindung bezieht sich auf ein Verfahren zum Trocknen von in Stapeln zusammengefasstem Holz, das während einer schrittweisen Stapelförderung durch einen Trocknungskanal mit Hilfe gegensinniger Trocknungsgasströme in aufeinanderfolgenden Trocknungszonen auf eine Endfeuchtigkeit unterhalb der Fasersättigung getrocknet wird, wobei die durch die Anzahl der in Förderrichtung hintereinandergereihten Holzstapel bestimmte Stapeltiefe der Trocknungszonen in Förderrichtung zunimmt.The invention relates to a method for drying stacked wood, which is dried during a stepwise batch conveyance through a drying channel by means of opposing drying gas streams in successive drying zones to a final moisture content below the fiber saturation, the determined by the number of stacked in the conveying direction wood pile certain Stacking depth of the drying zones increases in the conveying direction.

Stand der TechnikState of the art

Bei einem bekannten Verfahren dieser Art ( DE 17 29 259 C ) bildet der Trocknungskanal zwei Trocknungszonen mit zum Teil im Kreislauf geführten Trocknungsgasströmen, vorzugsweise Luftströmen, von denen der eingangsseitige gegen die Durchlaufrichtung der Holzstapel und der ausgangsseitige in Durchlaufrichtung durch die Trocknungszonen strömen. Der teilweise Ersatz der beiden Trocknungsgasströme durch Frischgas, für das ein gemeinsamer Zulauf im Bereich des eingangsseitigen Trocknungsgaskreislaufes vorgesehen ist, wird durch eine gemeinsame, dem ausgangsseitigen Trocknungsgaskreislauf zugehörige Abgasklappe gesteuert. Durch ein Konstanthalten einerseits der Temperatur des aus der ausgangsseitigen Trocknungszone abgezogenen Abgasstromes mit Hilfe einer gleichzeitigen Beeinflussung der Temperatur der beiden Trocknungsgasströme und anderseits des Feuchtigkeitsgehaltes des ausgangsseitigen Abgasstromes über die Abluftklappe soll erreicht werden, daß das getrocknete Holz eine vergleichsweise geringe Schwankung hinsichtlich der Restfeuchtigkeit aufweist, und zwar weitgehend unabhängig vom Feuchtigkeitsgehalt vor der Trocknung. Diese angestrebte Unabhängigkeit der Endfeuchtigkeit von der Ausgangsfeuchtigkeit ist deshalb von besonderer Bedeutung, weil der Feuchtigkeitsgehalt der einzelnen zum Trocknen zu einem Stapel zusammengefaßten Hölzer stark schwankt, für die Weiterverarbeitung des getrockneten Holzes aber eine einheitliche Restfeuchtigkeit vorliegen soll. Nachteilig bei diesem bekannten Verfahren zum Trocknen von Holz in einem Trocknungskanal ist allerdings, daß die Schwankungen hinsichtlich der Restfeuchtigkeit des getrockneten Holzes nur dann in tolerierbaren Grenzen gehalten werden können, wenn die Trocknungsgeschwindigkeit vergleichsweise niedrig gehalten wird.In a known method of this type ( DE 17 29 259 C ), the drying channel forms two drying zones with partially circulated Trocknungsgasströmen, preferably air streams, of which the input side flow against the direction of passage of the wood stack and the output side in the direction of passage through the drying zones. The partial replacement of the two drying gas streams by fresh gas, for which a common inlet is provided in the region of the inlet-side drying gas circulation, is controlled by a common, the output side drying gas cycle associated exhaust flap. By keeping constant the one hand, the temperature of the exhaust stream withdrawn from the output side drying zone by means of a simultaneous influence of the temperature of the two drying gas streams and on the other hand, the moisture content of the output side exhaust stream through the exhaust air flap is to be achieved the dried wood has a comparatively small variation in residual moisture, largely independent of the moisture content before drying. This desired independence of the final moisture from the initial moisture is of particular importance, because the moisture content of the individual to dry a stack of combined woods varies greatly, but for the further processing of the dried wood should be a uniform residual moisture. A disadvantage of this known method for drying wood in a drying channel, however, is that the variations in the residual moisture of the dried wood can only be kept within tolerable limits if the drying rate is kept relatively low.

Um hohe Trocknungsgeschwindigkeiten zu erreichen, ohne eine erhöhte Rißgefahr in Kauf zu nehmen, wurde darüber hinaus vorgeschlagen ( WO 90/03543 A1 ), den in zwei Trocknungszonen aufgeteilten Trocknungskanal so zu betreiben, daß die Strömungsrichtung des Trocknungsgases in der eingangsseitigen Trocknungszone im Gegenstrom zur Förderrichtung der Holzstapel verläuft, in der ausgangsseitigen Trocknungszone aber in Durchlaufrichtung. Ziel dieser Maßnahme ist eine rasche Trocknung bis zur Fasersättigung und dann ein allmähliches Absenken des Feuchtigkeitsgehaltes unter die Fasersättigung, wobei die zum Teil im Kreislauf geführten Trocknungsgasströme zwischen den beiden Trocknungszonen mit Hilfe eines gemeinsamen Sauggebläses abgezogen werden, um den vereinigten Abgasstrom nach einem Ersatz eines Abgasteilstromes durch Frischgas zu erwärmen und anschließend wieder in zwei Trocknungsgasströme aufzuteilen. Abgesehen davon, daß aufgrund des vergleichsweise hohen Luftumsatzes die Trocknung einen entsprechend hohen Energieeinsatz erfordert, kann aufgrund der angestrebten hohen Trocknungsgeschwindigkeit während der Trocknung kein ausreichender Feuchtigkeitsausgleich zwischen Hölzern mit in einem größeren Bereich unterschiedlicher Ausgangsfeuchtigkeit erreicht werden, so daß mit stark schwankenden Endfeuchtigkeiten der getrockneten Hölzer gerechnet werden muß.Moreover, in order to achieve high drying speeds without risking an increased risk of cracking, it has also been proposed ( WO 90/03543 A1 ) to operate the divided into two drying zones drying channel so that the flow direction of the drying gas in the input-side drying zone in countercurrent to the conveying direction of the wood stack runs in the output-side drying zone but in the direction of passage. The aim of this measure is a rapid drying to fiber saturation and then a gradual lowering of the moisture content below the fiber saturation, the partially circulated Trocknungsgasströme be deducted between the two drying zones using a common suction fan to the combined exhaust gas stream after a replacement of a partial exhaust gas stream to heat by fresh gas and then split again into two drying gas streams. Apart from the fact that due to the relatively high air turnover, the drying requires a correspondingly high energy consumption, due to the desired high drying rate during drying no sufficient moisture balance between woods can be achieved with in a wider range of different starting moisture, so that with strongly fluctuating final moisture of the dried woods must be expected.

Um vorteilhafte Trocknungsbedingungen bei niedrigen Temperaturen zu erreichen, ist es schließlich bekannt ( US 3 422 545 A ), zwei Trocknungszonen vorzusehen, die mit je einem im Kreislauf geführten Trocknungsgasstrom beaufschlagt werden, wobei in der ersten Trocknungszone die Temperatur und Feuchtigkeit des Trocknungsgasstromes für eine Trocknung oberhalb des Fasersättigungsbereiches eingestellt wird, während der Trocknungsprozess danach in einer zweiten Trocknungszone unter schonenderen Bedingungen fortgeführt wird. Die Behandlung der zu trocknenden Holzstapel oberhalb des Fasersättigungsbereiches mit Hilfe eines im Kreislauf geführten Trocknungsgasstromes setzt allerdings Holzstapel mit einem annähernd gleichmäßigen Feuchtigkeitsgehalt voraus.Finally, in order to achieve favorable drying conditions at low temperatures, it is known ( US 3 422 545 A ), two drying zones are provided, which are each supplied with a circulated drying gas flow, wherein in the first drying zone, the temperature and humidity of the drying gas flow is set for drying above the fiber saturation region, while the drying process is then continued in a second drying zone under more gentle conditions , However, the treatment of the woodpile to be dried above the fiber saturation region with the aid of a circulated drying gas stream requires wood stacks with an approximately uniform moisture content.

Darstellung der ErfindungPresentation of the invention

Der Erfindung liegt somit die Aufgabe zugrunde, ein Verfahren der eingangs geschilderten Art zum Trocknen von in Stapeln zusammengefasstem Holz so auszugestalten, daß zu Stapeln zusammengefaßte Hölzer mit stark unterschiedlicher Anfangsfeuchtigkeit gemeinsam in einem engen Toleranzbereich auf eine vorgegebene Endfeuchtigkeit getrocknet werden können, und zwar mit einem vergleichsweise niedrigen Energieeinsatz.The invention is therefore based on the object, a method of the type described for drying stacked wood in such a way that combined to stack woods with very different initial moisture can be dried together in a narrow tolerance range to a predetermined final moisture, with a comparatively low energy consumption.

Die Erfindung löst die gestellte Aufgabe dadurch, daß das Holz in zwei eingangsseitigen Trocknungszonen zumindest im wesentlichen mit zwischen diesen Trocknungszonen zugeführtem Frischgas auf einen Feuchtigkeitsgehalt im Fasersättigungsbereich, jedoch im wesentlichen oberhalb der Fasersättigung und anschließend in wenigstens einer weiteren Trocknungszone mit Hilfe eines zumindest teilweise im Kreislauf geführten, hinsichtlich seiner Temperatur und seiner Feuchtigkeit einstellbaren Trocknungsgaststromes auf die Endfeuchtigkeit getrocknet wird.The invention achieves the stated object in that the wood in two input-side drying zones, at least substantially with supplied between these drying zones fresh gas to a moisture content in the fiber saturation region, but substantially above the fiber saturation and then in at least one further drying zone by means of at least partially in the circulation guided, adjustable in terms of its temperature and humidity drying gas stream is dried to the final moisture.

Da oberhalb der Fasersättigung Holz beliebig schnell getrocknet werden kann, ohne Schaden zu nehmen, kann bei einem Feuchtigkeitsgehalt des Holzes oberhalb der Fasersättigung auf eine eine bestimmte Mindestfeuchtigkeit gewährleistende Kreislaufströmung des Trocknungsgases verzichtet werden, so daß dem Holz mit einem Feuchtigkeitsgehalt oberhalb der Fasersättigung vergleichsweise trockenes Frischgas zugeführt werden kann. Dadurch können hohe Trocknungsraten mit einer geringen Strömungsgeschwindigkeit des Trocknungsgases und damit ein entsprechend niedriger Energieeinsatz gewährleistet werden. Außerdem kann die Gastemperatur niedrig gehalten werden, was gerade im Zusammenhang mit einem stark unterschiedlichen Feuchtigkeitsgehalt der zu trocknenden Einzelhölzer eines Stapels von Bedeutung ist, weil die Trocknungsrate der Hölzer mit einem niedrigeren Feuchtigkeitsgehalt gegenüber den Hölzern mit einem höheren Feuchtigkeitsgehalt sinkt. Dazu kommt, daß durch die Aufteilung der Trocknung mit Frischgas in eine einlaufseitige Trocknungszone mit einer Frischgasströmung entgegen der Förderrichtung und in eine auslaufseitige Trocknungszone mit einer Frischgasströmung in Förderrichtung der Trocknungszone mit der höchsten Trocknungsgeschwindigkeit eine Trocknungszone folgt, in der die Trocknungsrate in Förderrichtung aufgrund der zunehmenden Feuchtigkeitsbelastung des in Förderrichtung strömenden Trocknungsgases abnimmt, insbesondere bei einer entsprechenden Stapeltiefe. Die Stapeltiefe der einlaufseitigen Trocknungszone soll jedoch klein gehalten werden, um trotz der geringen Temperatur des Trocknungsgases eine hohe, nicht durch eine zunehmende Dampfbelastung beeinträchtigte Trocknungsgeschwindigkeit zu sichern.Since above the fiber saturation wood can be dried as quickly as desired, without damaging, can be dispensed with a moisture content of the wood above the fiber saturation to a certain minimum moisture ensuring circulation flow of the drying gas, so that the wood with a moisture content above the fiber saturation comparatively dry fresh gas can be supplied. As a result, high drying rates with a low flow rate of the drying gas and thus a correspondingly low energy consumption can be ensured. In addition, the gas temperature can be kept low, which is especially in connection with a very different moisture content of the individual pieces of wood to be dried stack of importance because the rate of drying of woods with a lower moisture content compared to the wood with a higher moisture content decreases. In addition, by dividing the drying with fresh gas in an inlet-side drying zone with a fresh gas flow against the conveying direction and in a discharge-side drying zone with a fresh gas flow in the conveying direction of the drying zone with the highest drying speed, a drying zone follows in which the drying rate in the conveying direction decreases due to the increasing moisture load of the drying gas flowing in the conveying direction, in particular at a corresponding stacking depth. The stacking depth of the inlet-side drying zone should, however, be kept small in order to ensure a high, not affected by an increasing steam load drying rate despite the low temperature of the drying gas.

Der in Förderrichtung ansteigende Feuchtigkeitsgehalt des Frischgasstromes wirkt sich ebenfalls ausgleichend auf die unterschiedlichen Feuchtigkeitsgehalte der einzelnen Hölzer aus, so daß bei der geschilderten Trocknung bis nahe der Fasersättigung bereits eine weitgehende Anpassung der Feuchtigkeitsgehalte der einzelnen Hölzer an einen Durchschnittswert stattgefunden hat. 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. In wenigstens einer weiteren Trocknungszone wird daher die Trocknung auf die Endfeuchtigkeit vorgenommen, wobei durch eine entsprechende Einstellung der Temperatur und der Feuchtigkeit des im Kreislauf geführten Trocknungsgases sowie durch eine vorteilhafte Wahl der Stapeltiefe unter Berücksichtigung der jeweiligen Strömungsrichtung nach einem weiteren Feuchtigkeitsausgleich die geforderte Endfeuchtigkeit einheitlich in einem geringen Toleranzbereich sichergestellt werden kann.The rising in the conveying direction moisture content of the fresh gas flow also has a balancing effect on the different moisture contents of the individual woods, so that in the described drying to near fiber saturation has already taken place a substantial adjustment of the moisture content of the individual woods to an average value. 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. In at least one further drying zone, therefore, the drying is carried out to the final moisture, wherein by a corresponding adjustment of the temperature and humidity of the circulating drying gas and by an advantageous choice of stacking depth, taking into account the respective flow direction for a further moisture compensation the required final moisture uniformly in a small tolerance range can be ensured.

Die Trocknung der Hölzer im Bereich der Holzfeuchtigkeit oberhalb der Fasersättigung kann durch eine mäßige Erwärmung des Trocknungsgases beschleunigt werden, indem das Frischgas nach einer Vorwärmung im Wärmeaustausch mit dem Abgas aus der mit dem Frischgas beaufschlagten Trocknungszone durch wenigstens ein Heizregister erwärmt wird, was eine vorteilhafte Ausnützung der Wärmeenergie mit sich bringt.The drying of the wood in the range of wood moisture above the fiber saturation can be accelerated by a moderate heating of the drying gas by the fresh gas is heated after preheating in the heat exchange with the exhaust gas from the acted upon with the fresh gas drying zone by at least one heating coil, which is an advantageous utilization the heat energy brings with it.

Wie bereits ausgeführt wurde, kann nach der Trocknung mit Frischgas das Holz zur Anpassung an einen vorteilhaften durchschnittlichen Trocknungsverlauf der Einzelhölzer eines Stapels zusätzliche Trocknungszonen durchlaufen, in denen entsprechende Trocknungsbedingungen durch geeignete Einflußnahmen auf den Trocknungsgasstrom gewährleistet werden. Zu diesem Zweck kann das Holz in einer zwischen der ausgangsseitigen, in Förderrichtung durchströmten Trocknungszone und den beiden eingangsseitigen Trocknungszonen vorgesehenen Zwischenzone mit Hilfe eines zumindest teilweise im Kreislauf geführten, hinsichtlich seiner Temperatur und seines Feuchtigkeitsgehaltes einstellbaren Trocknungsgasstromes auf einen Feuchtigkeitsgehalt im wesentlichen unterhalb der Fasersättigung getrocknet werden, so daß sich im Fasersättigungsbereich ein schonender Übergang des Feuchtigkeitsgehaltes von einem Wert oberhalb der Fasersättigung auf einen Wert unterhalb der Fasersättigung ergibt, was dann von erhöhter Bedeutung ist, wenn nach der Trocknung mit Frischgas noch keine ausreichende Vergleichmäßigung der Feuchtigkeitsgehalte der einzelnen Hölzer eines Stapels erreicht werden konnte.As already stated, after drying with fresh gas, the wood can pass through additional drying zones to adapt to a favorable average drying process of the individual woods of a stack, in which corresponding drying conditions are ensured by suitable influences on the drying gas flow. For this purpose, the wood can be dried to a moisture content essentially below the fiber saturation in an intermediate zone provided between the outlet-side drying zone in the conveying direction and the two inlet-side drying zones by means of a drying gas stream which is at least partially circulated and adjustable with respect to its temperature and moisture content , so that in the fiber saturation region a gentle transition of the moisture content of a value above the fiber saturation to a value below the fiber saturation results, which is then of increased importance, if not achieved after drying with fresh gas sufficient equalization of the moisture content of the individual woods of a stack could be.

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 weist ein Gehäuse 1 auf, das einen Trocknungskanal 2 bildet, der mit einer aus Übersichtlichkeitsgründen nicht dargestellten Fördereinrichtung für schrittweise durch den Trocknungskanal 2 zu fördernde Holzstapel 3 versehen ist. Die aus einzelnen Hölzern zusammengefassten Stapel 3 werden mit Hilfe der Fördereinrichtung nacheinander durch einzelne Förderzonen 4, 5, 6 und 7 gefördert, wobei die Stapeltiefe, die durch die Anzahl der in Förderrichtung 8 hintereinandergereihten Holzstapel 3 in den Trocknungszonen 4, 5, 6 und 7 bestimmt wird, in Förderrichtung 8 zunimmt, was eine entsprechende Verlängerung der Verweilzeit der einzelnen Holzstapel in der jeweiligen Trocknungszone 5, 7 nach sich zieht. Lediglich die Verweilzeit der Holzstapel 3 in der Zwischenzone 6 zwischen den Trocknungszonen 5 und 7 entspricht der Verweilzeit in der Trocknungszone 3, was aber nicht zwingend ist.The device shown has a housing 1, which forms a drying channel 2, which is provided with a conveyer, not shown for reasons of clarity for gradually through the drying channel 2 to be conveyed wood stack 3. The combined from individual woods stack 3 are successively conveyed by means of the conveyor through individual conveyor zones 4, 5, 6 and 7, wherein the stacking depth, by the number of stacked in the conveying direction 8 wood stack 3 in the drying zones 4, 5, 6 and 7 is determined, increases in the conveying direction 8, which entails a corresponding extension of the residence time of the individual wood stacks in the respective drying zone 5, 7 by itself. Only the residence time of the wood stacks 3 in the intermediate zone 6 between the drying zones 5 and 7 corresponds to the residence time in the drying zone 3, but this is not mandatory.

Die einzelnen Trocknungszonen 4 bis 7 werden mit einem Trocknungsgas beaufschlagt, im allgemeinen Luft, das in gegensinnigen Strömungen durch die Trocknungszonen 4 bis 7 geführt wird, wie dies in der Zeichnung durch die Strömungspfeile angedeutet ist. In den beiden eingangsseitigen Trocknungszonen 4 und 5 bestehen die Trocknungsgasströme zumindest im wesentlichen aus Frischgas, das mit Hilfe von Gebläsen 9 über Kreuzstromwärmetauscher 10 in Abschnitten 11 eines oberhalb des Trocknungskanals 2 vorgesehenen Strömungskanals angesaugt und durch ein Heizregister 12 zwischen den beiden eingangsseitigen Trocknungszonen 4, 5 in den Trocknungskanal 2 eingeblasen wird, so daß sich in der Trocknungszone 4 eine Trocknungsgasströmung entgegen der Förderrichtung 8 und in der Trocknungszone 5 eine Trocknungsgasströmung in Förderrichtung ausbilden. Die aus den Stapeln 3 austretenden, mit der aufgenommenen Holzfeuchtigkeit beladenen Abgasströme werden über Abschnitte 13 des Strömungskanals oberhalb des Trocknungskanals 2 wieder dem Kreuzstromwärmetauscher 10 zugeführt, um unter Abgabe ihrer fühlbaren Abwärme an die angesaugte Frischluft aus dem Trocknungsprozeß ausgeschieden zu werden. Da das Frischgas eine geringe Feuchtigkeit besitzt, kann mit Hilfe der Frischgasströme in den beiden eingangsseitigen Trocknungszonen 4, 5 eine rasche Trocknung der Hölzer der Stapel 3 oberhalb der Fasersättigung vorgenommen werden. Zur Beschleunigung der Trocknung kann das Frischgas über das Heizregister 12 mäßig erwärmt werden. Die Stapeltiefe der Trocknungszone 4 ist dabei gering, um die Trocknung nicht durch die von den Frischgasen aufgenommene Holzfeuchtigkeit zu verlangsamen. Trotz der vergleichsweise niedrigen Frischgastemperaturen kann wegen der geringen Feuchtigkeit der zugeführten Frischgase die Trocknungsrate hochgehalten werden, und zwar mit dem Vorteil, dass aufgrund der vergleichsweise niedrigen Temperaturen der Trocknungsgasströme die Trocknungsrate für Hölzer mit einem hohen Feuchtigkeitsgehalt größer als für Hölzer mit-einem geringen Feuchtigkeitsgehalt ausfällt. Dadurch kann in vorteilhafter Weise ein Ausgleich des unterschiedlichen Feuchtigkeitsgehaltes der Hölzer in einem Stapel 3 im Hinblick auf die Forderung eingeleitet werden, das die Endfeuchtigkeit aller Hölzer eines Stapels 3 am Ausgang des Trocknungstunnels 2 einen einheitlichen Wert aufweist.The individual drying zones 4 to 7 are charged with a drying gas, generally air, which is guided in opposite directions through the drying zones 4 to 7, as indicated in the drawing by the flow arrows. In the two input-side drying zones 4 and 5, the drying gas streams consist at least substantially of fresh gas sucked by means of blowers 9 via cross-flow heat exchanger 10 in sections 11 provided above the drying channel 2 flow channel and by a heating coil 12 between the two input-side drying zones 4, 5th is blown into the drying channel 2, so that in the drying zone 4 a drying gas flow against the conveying direction 8 and in the drying zone 5 form a drying gas flow in the conveying direction. The exiting from the stacks 3, loaded with the absorbed wood moisture exhaust gas streams are fed back to the cross-flow heat exchanger 10 via sections 13 of the flow channel above the drying channel 2 to be excreted in the drying process discharged their sensible waste heat to the fresh air sucked. Since the fresh gas has a low moisture content, rapid drying of the wood of the stacks 3 above the fiber saturation can be carried out with the aid of the fresh gas streams in the two input-side drying zones 4, 5. To speed up the drying process, the fresh gas can be moderately heated via the heating register 12. The stacking depth of the drying zone 4 is small in order not to slow the drying by the moisture absorbed by the fresh gases wood moisture. Despite the comparatively low fresh gas temperatures, the drying rate can be kept high due to the low moisture of the fresh gases supplied, with the advantage that due the relatively low temperatures of the drying gas streams, the drying rate for woods with a high moisture content fails greater than for woods with a low moisture content. As a result, a compensation of the different moisture content of the woods in a stack 3 can be introduced in an advantageous manner with regard to the requirement that the final moisture of all the woods of a stack 3 at the exit of the drying tunnel 2 has a uniform value.

In der Trocknungszone 5 wird aufgrund der Trockengasströmung in Förderrichtung 8 der Feuchtigkeitsanteil der Trocknungsluft in Förderrichtung aufgrund der aufgenommenen Holzfeuchtigkeit vergrößert, wodurch die Trocknungsrate zunehmend gesenkt und ein für das Holz schonender Trocknungsverlauf vorgegeben werden kann, der für einen weiteren Ausgleich der unterschiedlichen Feuchtigkeit der Einzelhölzer in den Stapeln 3 sorgt. Um ein für einen solchen schonenderen Trocknungsverlauf ein geeignetes Trocknungsklima bereitzustellen, wird die Stapeltiefe in der Trocknungszone 5 gegenüber der der Trocknungszone 4 entsprechend vergrößert.In the drying zone 5 due to the dry gas flow in the conveying direction 8, the moisture content of the drying air is increased in the conveying direction due to the recorded wood moisture, whereby the drying rate is increasingly lowered and a gentle for the drying course of wood can be set for a further compensation of the different moisture of the individual woods in provides the stacks 3. In order to provide a suitable drying climate for such a gentler drying process, the stacking depth in the drying zone 5 is correspondingly increased compared to that of the drying zone 4.

Mit der Frischlufttrocknung wird der Feuchtigkeitsgehalt der Hölzer eines Stapels 3 in den Bereich der Fasersättigung, und zwar auf Werte im wesentlichen oberhalb der Fasersättigung abgesenkt. Damit ein schonender Übergang in einem Feuchtigkeitsbereich unterhalb der Fasersättigung erreicht wird, wird in der Trocknungszone 6 Trocknungsgas in einem Kreislauf über einen Abschnitt 14 des Strömungskanals oberhalb des Trocknungskanals 2 geführt, und zwar mit Hilfe eines Gebläses 15. Die Feuchtigkeit und die Temperatur dieses zumindest teilweise im Kreislauf geführten Trocknungsgasstromes kann den jeweiligen Anforderungen entsprechend eingestellt werden. Zu diesem Zweck ist einerseits ein Heizregister 12 und anderseits eine Einrichtung 16 vorgesehen, über die ein Teil des Trocknungsgasstromes aus dem Kreislauf ausgeschieden und durch Frischgas ersetzt werden kann, sodass die Feuchtigkeit des der Trocknungszone 6 zugeführten Trocknungsgases durch eine Mischung des vergleichsweise trockenen Frischgases mit dem feuchten Trocknungsgas aus der Trocknungszone 6 eingestellt werden kann.With fresh air drying, the moisture content of the lumbers of a stack 3 is lowered to the region of fiber saturation, namely to values substantially above the fiber saturation. In order to achieve a gentle transition in a moisture range below the fiber saturation, drying gas is circulated in the drying zone 6 over a section 14 of the flow channel above the drying channel 2, with the aid of a blower 15. The moisture and the temperature of this at least partially circulated drying gas flow can be adjusted according to the respective requirements. For this purpose, on the one hand, a heating coil 12 and on the other hand a device 16 is provided, through which a part of the drying gas flow can be eliminated from the circuit and replaced by fresh gas, so that the moisture of the drying zone 6 supplied drying gas by a mixture of comparatively dry fresh gas with the moist drying gas from the drying zone 6 can be adjusted.

Nach der Trocknung der Hölzer der Stapel 3 bis unter die Fasersättigung werden die Hölzer in einer ausgangsseitigen Trocknungszone 7 auf die geforderte Endfeuchtigkeit getrocknet, was schonend vorgenommen werden muss. Dies bedeutet, daß der wieder in einem zumindest teilweise im Kreislauf geführte Trocknungsgasstrom für ein ausgangsseitiges Trocknungsklima sorgen muß, das die geforderte Endfeuchtigkeit für alle Hölzer eines Stapels 3 sicherstellt. Aus diesem Grunde wird die Stapeltiefe dieser ausgangsseitigen Trocknungszone 7 auch deutlich höher als die der vorausgehenden Trocknungszonen 5, 6 gewählt. Die Konditionierung des der Trocknungszone 7 zugeführten Trocknungsgasstromes erfolgt einerseits wieder über ein Heizregister 12 und anderseits über ein Ausscheiden eines Teilstromes des Trocknungsgases und ein Ersetzen des ausgeschiedenen Trocknungsgases durch Frischgas. Die Kreislaufströmung wird durch ein Gebläse 15 in einem Abschnitt 17 des Strömungskanals oberhalb des Trocknungskanals 2 aufrecht erhalten. Die Steuerung des Gasaustausches wird mit Hilfe von Steuerklappen 18 vorgenommen. Dies stellt einen konstruktiven Unterschied hinsichtlich der Steuerung der Frischgaszufuhr im Bereich der Trocknungszone 6 dar, weil in der Einrichtung 16 das teilweise Ausscheiden von Trocknungsgas und die Frischgaszufuhr durch gesonderte Gebläse vorgenommen wird. Außerdem wird ein Gegenstromwärmetauscher 19 eingesetzt, um die füllbare Abwärme der ausgeschiedenen Abgase für eine Vorwärmung der Frischgase nützen zu können, was im Bereich der ausgangsseitigen Trocknungszone 7 nicht erforderlich ist.After drying the wood of the stack 3 to below the fiber saturation, the woods are dried in an exit-side drying zone 7 to the required final moisture, which must be done gently. This means that the again in an at least partially recycled circulating drying gas flow must provide an output-side drying climate that ensures the required final moisture for all woods of a stack 3. For this reason, the stacking depth of this output-side drying zone 7 is also chosen to be significantly higher than that of the preceding drying zones 5, 6. The conditioning of the drying zone 7 supplied drying gas flow on the one hand again via a heating coil 12 and on the other hand via a separation of a partial stream of the drying gas and a replacement of the excreted drying gas by fresh gas. The circulation flow is maintained by a fan 15 in a portion 17 of the flow channel above the drying channel 2. The control of the gas exchange is carried out by means of control valves 18. This represents a design difference with regard to the control of the fresh gas supply in the region of the drying zone 6, because in the device 16, the partial separation of drying gas and the fresh gas supply is made by separate blower. In addition, a countercurrent heat exchanger 19 is used in order to use the fillable waste heat of the excreted exhaust gases for preheating the fresh gases, which is not required in the region of the exit-side drying zone 7.

Während des Betriebes der dargestellten Vorrichtung werden in vorgegebenen Zeitabschnitten die Holzstapel 3 um einen der Tiefe eines Stapels 3 entsprechenden Förderschritt weitergefördert, wobei der ausgangsseitige Holzstapel 3 der Trocknungszone 7 über einen Auslaß 20 der Vorrichtung entnommen und ein neuer Stapel durch einen Einlaß 21 der Trocknungszone 4 aufgegeben wird. Durch den geschilderten Trocknungsvorgang gelingt es, z. B. frisches Nadelholz, das innerhalb eines Stapels einen Feuchtigkeitsgehalt der Einzelhölzer zwischen 30 % und 200 % aufweist auf eine vorgegebene Endfeuchtigkeit, beispielsweise zwischen 6 % und 20 % zu trocknen. Die Temperatur der Trocknungsgase im Bereich der eingangsseitigen Trocknungsgase im Bereich der eingangsseitigen Trocknungszonen 4, 5 beträgt dabei vorzugsweise 30 bis 50° C und wird im Bereich der Trocknungszonen 6 und 7 auf 65 bis 80° C angehoben.During operation of the illustrated device, the wood stacks 3 are conveyed at a corresponding depth of a stack 3 conveying step at predetermined periods, the output side wood stack 3 of the drying zone 7 taken via an outlet 20 of the device and a new stack through an inlet 21 of the drying zone 4th is abandoned. By the described drying process it is possible, for. B. fresh softwood, which has within a stack a moisture content of the individual woods between 30% and 200% to a predetermined final moisture, for example between 6% and 20% to dry. The temperature of the drying gases in the area of the input side Drying gases in the region of the input-side drying zones 4, 5 is preferably 30 to 50 ° C and is raised to 65 to 80 ° C in the drying zones 6 and 7.

Claims (3)

  1. Method for drying wood collected in piles (3), which wood is dried whilst the piles are conveyed in stages through a drying channel (2) using opposing drying gas streams in subsequent drying zones (4, 5, 6, 7) initially to a moisture content in the fibre saturation range, however substantially above the fibre saturation and then in at least one further drying zone using a drying gas stream, which is at least partially circulated and can be adjusted in terms of its temperature and its moisture, to a final moisture below the fibre saturation, wherein the pile depth of the drying zones determined by the number of wood piles arranged in rows one behind the other in the direction of conveyance increases in the direction of conveyance (8), characterised in that the wood is dried in two input-side drying zones (4, 5) at least substantially using fresh gas supplied between these drying zones.
  2. Method as claimed in Claim 1, characterised in that before it is supplied to the drying zone (4, 5), the fresh gas is heated by at least one damper register (12) after pre-heating in the heat exchange with the exhaust gas from the drying zone (4, 5) subjected to the fresh gas.
  3. Method as claimed in Claim 1 or 2, characterised in that the wood is dried to a moisture content substantially below the fibre saturation in an intermediate zone (6) provided between the output-side drying zone (7), which has a flow passing therethrough in the direction of conveyance, and the two input-side drying zones (4, 5) using a drying gas stream which is at least partially circulated and can be adjusted in terms of its temperature and its moisture content.
EP07845262A 2006-11-21 2007-11-14 Method for drying wood collected into piles Not-in-force EP2092258B1 (en)

Applications Claiming Priority (2)

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AT0192106A AT504578B1 (en) 2006-11-21 2006-11-21 METHOD FOR DRYING WOOD MATCHED IN STACKS
PCT/AT2007/000516 WO2008061264A2 (en) 2006-11-21 2007-11-14 Method for drying wood collected into piles

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EP2092258A2 EP2092258A2 (en) 2009-08-26
EP2092258B1 true EP2092258B1 (en) 2011-07-27

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ATE518106T1 (en) 2011-08-15
AT504578A1 (en) 2008-06-15
WO2008061264A3 (en) 2008-09-18
EP2092258A2 (en) 2009-08-26
AT504578B1 (en) 2009-11-15
WO2008061264A2 (en) 2008-05-29

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