EP0746736B1 - Verfahren und vorrichtung zum trocknen von holz - Google Patents

Verfahren und vorrichtung zum trocknen von holz Download PDF

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Publication number
EP0746736B1
EP0746736B1 EP95911542A EP95911542A EP0746736B1 EP 0746736 B1 EP0746736 B1 EP 0746736B1 EP 95911542 A EP95911542 A EP 95911542A EP 95911542 A EP95911542 A EP 95911542A EP 0746736 B1 EP0746736 B1 EP 0746736B1
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EP
European Patent Office
Prior art keywords
chamber
air
drying
drying air
circulating
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.)
Expired - Lifetime
Application number
EP95911542A
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English (en)
French (fr)
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EP0746736A1 (de
Inventor
Eric BJÖRKMAN
Stefan Ericsson
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PROPAC AB
Original Assignee
PROPAC AB
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Publication date
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Publication of EP0746736A1 publication Critical patent/EP0746736A1/de
Application granted granted Critical
Publication of EP0746736B1 publication Critical patent/EP0746736B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • 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
    • F26B21/08—Humidity
    • F26B21/086—Humidity by condensing the moisture in the drying medium, which may be recycled, e.g. using a heat pump cycle

Definitions

  • the present invention relates to a method and plant for drying wooden elements with the aid of circulating drying air, said elements being stacked in mutually spaced relationship.
  • Wood driers are normally divided into two categories, depending upon their construction, namely circulating air driers and condensation driers. With regard to their construction and working methods, such plants are relatively simple since they need only be provided with means for controlling air speed, air temperature and air humidity in order to achieve a drying function.
  • the elements When wooden elements are to be dried, the elements are stacked in closed spaces, so-called drying chambers, into which warm air and/or steam is delivered from a heating unit with the aid of adjustable fans, the temperature of said spaces being raised to 50-100°C.
  • the warm air is forced to circulate, or flow, through the stacked wooden elements and in so doing takes up, absorbs, moisture from the wood.
  • the warm air is given a dryness and wet temperature status which is suitable to the quality of the wood concerned, by controlling the heat delivered to the air and also the moisture ventilated therefrom.
  • the air becomes saturated with water vapour and is unable to absorb further moisture from the wood, it is necessary to reduce the moisture content of the drying air in order for the drying process to continue. This is either effected by ventilation, i.e. by forced introduction of dry, cold ambient air and the release of moisture-saturated drying air or by cooling and condensing the moisture-saturated air in the chamber.
  • both of these methods require large energy inputs in order to function effectively, since in the case of ventilation, it is necessary to heat the cold ambient air to the relevant drying temperature before introducing the air to the wood located in the drying chamber, and also because energy must be supplied in order to cool and condense the moisture-saturated air in said chamber.
  • this heat recovery in the drying process can be continued until the exhaust air has been cooled to the lowest supply air temperature, wherein most of the enthalpy of the exhaust air is returned to the drying process.
  • this principle is often applied to the economic limit of the heat exchanger with regard to its size, since a large amount of energy is required to dry the wood is large and often corresponds to about half of the total drying costs.
  • the drawback with air circulation drying plants is that they incur high installation costs, requiring well-insulated chambers, and also high operating costs unless provided with advanced heat exchange systems. Such systems are relatively expensive, however.
  • drying plants which operate in accordance with the condensation principle include a condenser for cooling the moisture-saturated drying air and a heating battery for heating the demoisturized air.
  • the cooling effect of the condenser is normally achieved by passing a coolant through the condenser from a compressor cooling unit or by passing a forced flow of cold ambient air through the condenser in a circuit which is closed from the drying chamber.
  • One method of providing an energy lean system for the condensation of moisture-saturated drying air and for heating the demoisturized air is to provide the drying plant with a heat pump whose coolant absorbs heat from the moisture-saturated air (which is therewith cooled) via the condenser, wherein the heat absorbed by the coolant is delivered to the heating battery.
  • a condenser body is forming part of one of the walls of the drying chamber and is being selected from a material having high heat conductivity characteristics.
  • the condenser surface is cooled from outside the chamber by aid of the heat exchange taking place between the air circulating in the chamber and the relatively cold ambient air surrounding the chamber.
  • the drying plant according to said document is not constructed for ventilation of the chamber.
  • From US 3 262 216 is known a drying plant whereby the moisture content of the drying air circulating in the chamber is regulated by passing a condenser surface whereby said surface is arranged for taking advantage of the relatively cold earth on which the drying plant is situated. Further in contrast to the present invention, the drying chamber of said document is not ventilated. Drying air is directed from the drying chamber and passed through a closed system for heating and removing moisture from the air.
  • the present invention is based on the aim to provide a wood-drying plant of the type defined in the introduction which has a low energy consumption and which will condense the drying air rotating in the chamber in the absence of mechanical auxiliaries, such as cooling compressors.
  • a wood-drying plant of the type defined in the introduction which has a low energy consumption and which will condense the drying air rotating in the chamber in the absence of mechanical auxiliaries, such as cooling compressors.
  • Such a plant is constructed on the principle of generating different pressures in the chamber and by effecting exchanges of air in the chamber by causing the warm moisture-saturated drying air that is formed successively in the chamber by being heated to exit from that part of the chamber which exhibits the relatively high pressure, i.e. that part of the chamber which, in accordance with the invention, is located in the region between the stacked wood and the pressure side of respective fans.
  • This replacement air i.e. cold, dry ambient air
  • this replacement air is caused to flow into that part of the chamber which is under the relatively low pressure, through the medium of a heat exchanger which is mounted in the chamber and which forms a wall on which the warm, moist drying air circulating in the chamber condenses. This results in an exchange of heat between the circulating chamber air and the inflowing cold ambient air.
  • the aim of the present invention is realized with a method and plant that have the characteristic features set forth in the following Claims.
  • Fig. 1 and Fig. 2 are respectively schematic vertical sectional and horizontal sectional views of an inventive wood-drying plant; and Fig. 3 and Fig. 4 are respectively schematic vertical sectional and horizontal part-sectional views of a ventilation system intended for use in plants constructed in accordance with the invention.
  • the Figures illustrate an inventive drying plant which comprises typically a housing 1 which includes a drying chamber 2 in which wooden elements (not shown) are stacked in mutually spaced relationship.
  • the drying chamber includes an input port which, when closed, essentially seals the chamber 2 from the outside.
  • the chamber has mounted therein a wall 3 which extends from the floor to the ceiling of the chamber 2 and therewith delimits a corridor from that part of the chamber in which wood to be dried is placed.
  • a fan stand 5 which supports a plurality of stationary fans 4.
  • the fans 4 may conveniently be axial fans which are driven by a variable-speed reversible electric motor 6 through transmission means in the form of power transmission couplings.
  • the motor is placed outside the chamber, so as not to be overheated by the high temperatures that prevail in the chamber.
  • a heating battery 7 which is supplied with hot water and which functions to heat the air circulating in the drying chamber. The air is either pressed or sucked through the heating battery 7, depending on the direction of rotation of the fans 4. It will be understood that a plurality of water nozzles may be arranged in a known manner adjacent the fan-heating battery arrangement for bringing the wooden elements to a state for further treatment.
  • Each heat exchanger includes a heat-transferring, double-walled elongated rectangular body which has provided at its upper end a passageway or air intake 8 for the introduction of dry, cold external air and an air outlet 10 at its bottom end.
  • the air drawn in through the intake 8 constitutes the heat-absorbing medium and flows through the heat exchanger and out through the outlet.
  • Check valves are provided in the air intake 8 or in the air outlet 10, to prevent heated dry air from flowing back through the heat exchanger 9.
  • each heat exchanger 9 includes at least one air-cooling surface 11 which faces in towards the chamber and which forms a wall on which the bypassing drying air condenses.
  • one elongated side of the heat exchangers 9 is placed adjacent the chamber wall.
  • the heat exchangers are preferably disposed with the other longitudinally extending edge of the heat exchangers 9 adjacent the chamber wall so as to form therebetween a gap through which the incoming ambient, replacement air is able to pass.
  • the volume of air drawn in through the air intake 8 by suction is determined by the throughflow area of an adjustable control throttle valve 12 placed in a passageway 13 at the top of the chamber is open.
  • the fan stand 5 is provided at its upper end with a flap 14 which can be swung or flipped between two end positions.
  • the flap 14 and the fan stand 5 divide the corridor into two halves, of which only one half is able to communicate via the fans 4.
  • the area between the stacked wooden elements and the adjacent chamber walls is sealed in a known manner, wherewith the resultant overpressure thus prevailing on the pressure side of the fans 4 will cause the flap 14 to flip so as to provide a free passage from this half of the chamber to the passageway 13.
  • the fans 4 are started up after having placed wooden stacks in the chamber 2 and having closed the intake port.
  • the drying air is heated in the chamber by the heating battery 7, while air is caused to circulate in the chamber 2 by the fans 4, in the arrowed directions.
  • the heated air is caused, in a known manner, to circulate or flow through the stacked wooden elements and continuously absorbs moisture from the wood until the air is fully saturated. It is necessary to demoisturize the saturated air flow in order for the air to again absorb moisture from the wood, which can be achieved by adjusting the extent to which the valve 12 is open.
  • valve 12 When the valve 12 is fully or partially open, warm air which is fully or partially saturated with moisture will flow out through the passageway 13, preferably by virtue of the overpressure prevailing on the pressure side of the fans and also by virtue of a chimney effect.
  • the outflowing air will be replaced with dry, cold ambient air which flows in through the air intake 8 of the heat exchanger 9 located on the suction side of the fans 4, therewith cooling said heat exchanger.
  • the valve 12 While the valve 12 is open and air circulates in the chamber, part of the water vapour in the air flow circulating around the drying chamber will condense as it passes the cooled heat exchanger, by virtue of the heat transfer that takes place between the air flow circulating around the drying chamber and the cold, dry ambient air passing through said heat exchanger.
  • the volume of replacement air taken from outside the drying chamber can vary momentarily even though the air inlet area of the valve 12 has not been changed. For instance, such momentary variations may be due to a change in the pressure conditions in the drying chamber, for instance as a result of an increase or decrease in fan speed.
  • the drying air can be condensed without requiring the provision of separate ventilation fans or cooling compressors that are required in hitherto known drying plants. It will be understood, however, that the inventive plant may also be provided with auxiliary fans for supporting ventilation.
  • the heat exchanger 9 may comprise a single-wall, elongated sheet metal element placed in the corners of the chamber 2.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Drying Of Solid Materials (AREA)
  • Chemical And Physical Treatments For Wood And The Like (AREA)

Claims (8)

  1. Verfahren zum mit zirkulierender Trocknungsluft erfolgenden Trocknen von Holzelementen, die in gegenseitiger Abstandsbeziehung in einer Kammer (2) gestapelt sind, die von außen im wesentlichen abgedichtet ist und in der der Wärmeinhalt und Feuchtigkeitsgehalt der Trocknungsluft reguliert werden kann, dadurch gekennzeichnet, daß der Feuchtigkeitsgehalt der in der Kammer (2) zirkulierenden Trocknungsluft durch Ventilation reguliert wird, wobei ein gesteuertes Volumen von Trocknungsluft aus der Kammer (2) abgegeben wird; und das so abgehende Luftvolumen kontinuierlich durch Frischluftzufuhr von außerhalb der Kammer ausgetauscht wird, wobei in die Kammer (2) eintretende Luft veranlaßt wird, eine oder mehrere Flächen (11) zu passieren, die in der Kammer angeordnet sind und der in der Kammer (2) zirkulierenden Trocknungsluft sowie der in die Kammer eintretenden umgebenden Frischluft gemeinsam sind, und die Flächen so funktionieren, daß sie Wärme zwischen der in der Kammer (2) zirkulierenden Trocknungsluft und der in die Kammer eintretenden umgebenden Austauschluft austauschen, was bewirkt, daß die zirkulierende Trocknungsluft bei ihrem Passieren der Flächen (11) gekühlt und kondensiert wird.
  2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die gesteuerte Abgabe von Trocknungsluft aus der Kammer (2) und der Zustrom von Austauschluft in die Kammer (2) von außerhalb der Kammer über Druckdifferenzen in der Kammer bewirkt werden.
  3. Verfahren nach Anspruch 1-2, dadurch gekennzeichnet, daß jede Luftkühlfläche (11) in einer Ecke der Kammer (2) plaziert ist und so funktioniert, daß sie die in der Kammer zirkulierende Trocknungsluft ablenkt.
  4. Verfahren nach Anspruch 1-3, dadurch gekennzeichnet, daß die gesteuerte Abgabe von Trocknungsluft aus der Kammer (2) und/oder der Zustrom von in die Kammer von außerhalb der Kammer eintretenden Austauschluft durch einen Lüfter unterstützt wird/werden.
  5. Vorrichtung zum mit zirkulierender Trocknungsluft erfolgenden Trocknen von Holzelementen, die in gegenseitiger Abstandsbeziehung gestapelt sind, wobei die Vorrichtung eine Kammer (2) aufweist, in der die Holzelemente gestapelt sind und die von außen im wesentlichen abgedichtet ist, und ferner eine Einrichtung zum Regulieren des Wärmeinhalts und des Feuchtigkeitsgehalts der in der Kammer (2) zirkulierenden Trocknungsluft aufweist, dadurch gekennzeichnet, daß die Vorrichtung zur Ventilation der Kammer durch gesteuerte Abgabe von Trocknungsluft aus der Kammer (2) und Austauschen des abgehenden Luftvolumens durch Frischluftzufuhr von außerhalb der Kammer aufgebaut ist; sowie dadurch, daß in der Kammer (2) eine oder mehrere Flächen (11) angeordnet sind, die durch die in die Kammer von außerhalb der Kammer eintretende Austauschluft gekühlt werden sollen, und die Flächen der in der Kammer zirkulierenden Trocknungsluft und der in die Kammer eintretenden Frischluft gemeinsam sind und so funktionieren, daß sie Wärme zwischen der in der Kammer (2) zirkulierenden Trocknungsluft und der in die Kammer von außerhalb der Kammer eintretenden Austauschluft austauschen, wodurch die in der Kammer zirkulierende Trocknungsluft bei ihrem Vorbeilauf an den Flächen (11) gekühlt und kondensiert wird.
  6. Vorrichtung nach Anspruch 5, dadurch gekennzeichnet, daß die Vorrichtung mittels Druckdifferenzen in der Kammer so wirkt, daß sie Trocknungsluft aus der Kammer (2) abgibt und Austauschluft in die Kammer von außerhalb der Kammer ansaugt.
  7. Vorrichtung nach Anspruch 5-6, dadurch gekennzeichnet, daß jede Kühlfläche (11) in einer jeweiligen Ecke der Kammer (2) plaziert ist und so wirkt, daß sie die in der Kammer (2) zirkulierende Trocknungsluft ablenkt.
  8. Vorrichtung nach Anspruch 5-7, dadurch gekennzeichnet, daß die Vorrichtung einen Lüfter zum Unterstützen der Abgabe von Trocknungsluft aus der Kammer (2) und zum Ansaugen von Austauschluft in die Kammer (2) von außerhalb der Kammer aufweist.
EP95911542A 1994-03-03 1995-03-03 Verfahren und vorrichtung zum trocknen von holz Expired - Lifetime EP0746736B1 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9400745 1994-03-03
SE9400745A SE9400745L (sv) 1994-03-04 1994-03-04 Förfarande och anordning för torkning av virke
PCT/SE1995/000225 WO1995023946A1 (en) 1994-03-04 1995-03-03 A method and plant for drying wood

Publications (2)

Publication Number Publication Date
EP0746736A1 EP0746736A1 (de) 1996-12-11
EP0746736B1 true EP0746736B1 (de) 1999-06-02

Family

ID=20393171

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Application Number Title Priority Date Filing Date
EP95911542A Expired - Lifetime EP0746736B1 (de) 1994-03-03 1995-03-03 Verfahren und vorrichtung zum trocknen von holz

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EP (1) EP0746736B1 (de)
AT (1) ATE180887T1 (de)
AU (1) AU1907295A (de)
DE (1) DE69510042T2 (de)
SE (1) SE9400745L (de)
WO (1) WO1995023946A1 (de)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
PL405932A1 (pl) 2013-11-06 2015-05-11 Amenda Stanisław Zakład Stolarski Instalacja do suszenia, w szczególności do suszenia drewna i sposób suszenia w takiej instalacji

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3262216A (en) * 1963-11-19 1966-07-26 Hardwood Drying & Mfg Co Inc Process for artificially drying lumber
US3866333A (en) * 1971-09-17 1975-02-18 Siemens Elektrogeraete Gmbh Dehumidifier for air utilized in laundry drying
DE2654835A1 (de) * 1976-12-03 1978-06-08 Gerhard Ing Grad Ruedel Kondensator zur regulierung der luftfeuchtigkeit eines innenraumes

Also Published As

Publication number Publication date
DE69510042T2 (de) 2000-01-27
SE9400745D0 (sv) 1994-03-04
EP0746736A1 (de) 1996-12-11
ATE180887T1 (de) 1999-06-15
SE501508C2 (sv) 1995-03-06
DE69510042D1 (de) 1999-07-08
SE9400745L (sv) 1995-03-06
WO1995023946A1 (en) 1995-09-08
AU1907295A (en) 1995-09-18

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