EP0553089B1 - Process and device for drying pourable or bulk materials to be dried - Google Patents

Process and device for drying pourable or bulk materials to be dried Download PDF

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Publication number
EP0553089B1
EP0553089B1 EP91912501A EP91912501A EP0553089B1 EP 0553089 B1 EP0553089 B1 EP 0553089B1 EP 91912501 A EP91912501 A EP 91912501A EP 91912501 A EP91912501 A EP 91912501A EP 0553089 B1 EP0553089 B1 EP 0553089B1
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Prior art keywords
drying
gas
zone
filter
dried
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EP91912501A
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German (de)
French (fr)
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EP0553089A1 (en
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Harald Böhler
Franz Kettenbauer
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Fritz Egger GmbH and Co OG
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Fritz Egger GmbH and Co OG
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B25/00—Details of general application not covered by group F26B21/00 or F26B23/00
    • F26B25/005—Treatment of dryer exhaust gases
    • F26B25/007—Dust filtering; Exhaust dust filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement
    • F26B17/02—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by belts carrying the materials; with movement performed by belts or elements attached to endless belts or chains propelling the materials over stationary surfaces
    • F26B17/08—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by belts carrying the materials; with movement performed by belts or elements attached to endless belts or chains propelling the materials over stationary surfaces the belts being arranged in a sinuous or zig-zag path

Definitions

  • the invention relates to a method and to a plant for drying bulk or free-flowing items to be dried, in particular wood chips or wood fibers, as described in the preamble of claims 1 and 5, respectively.
  • Such a method and such a system are known (DE-C 423 469).
  • wet lignite is dried with hot air in a two-stage process, whereby there is direct contact between hot air and the material to be dried.
  • the advantage of the two-stage process is that not only is the material to be dried dried, but also the drying air laden with impurities or dust through the drying process is filtered, the material to be dried itself forming the porous filter mass and being preheated or pre-dried in this cleaning step. Therefore, additional measures for cleaning the drying exhaust air may be omitted or at least simplified.
  • a lower drying zone and an upper filter zone are arranged within a common housing, to the top of which the material supply and the exhaust gas chimney are connected, while the hot air is supplied to the underside and the dried material is removed.
  • the filter zone is formed by two gas-permeable cylinder walls, which are arranged concentrically and vertically in the housing. As the supplied moist material slides down through the annular space between the two cylinder walls under the effect of gravity, all of the hot air that rises through the drying zone is passed on the underside of the filter zone into the inner cylinder wall, from where it flows essentially radially outward through the two cylinder walls and the material layer located between them, in order to then reach the chimney from the housing chamber formed outside the cylinder wall arrangement.
  • drying system for pressed bodies (pellets) made of hops, in which two air-permeable belt conveyors are arranged one above the other in chambers separated by a horizontal intermediate wall, the material to be dried being fed to the upper belt conveyor, from there to the lower belt conveyor and with it to the Good discharge is transported.
  • Warm drying air first rises through the material layer on the lower conveyor belt (drying zone), is then passed out of the lower drying chamber into a laterally arranged intermediate heater, from which it then flows into the upper chamber and through the drying material on the upper conveyor belt (filter zone ).
  • the entire drying air is passed both through the drying zone and through the filter zone, so that here, too, a possible formation of steam plumes cannot be prevented or can only be prevented by complex additional measures.
  • the invention has for its object to make the generic drying more adaptable to the starting and ambient conditions, so that simple drying is ensured even under unfavorable conditions.
  • Drying air is thus passed through the as yet non-dried material to be acted as a filter medium (filter layer), the pollutants or dust which are taken up and carried along in the drying zone during drying being removed again from the exhaust air.
  • filter layer a filter medium
  • the separated particles do not interfere in the material to be further processed.
  • sticky substances contained in or re-deposited in the shavings are even advantageous and lead to a reduction in the amount of binder to be mixed.
  • Air can advantageously be used as the drying gas if waste heat is available for heating this air within an overall system, for example otherwise difficult to use waste heat in the low temperature range, such as that used in the production of chipboard in the range of approx. 60 ° Celsius to 70 ° Celsius can occur, for example from a washing system for exhaust air from production systems (dryers, presses, etc.).
  • a washing system for exhaust air from production systems dryers, presses, etc.
  • the heat of condensation of water vapor contained in such exhaust air can then be used and considerable energy savings can be achieved.
  • this operating mode of the final dryer can be changed without loss of throughput so that the generation of emissions in the final dryer can be significantly reduced.
  • the system shown has a drying chamber 1 which has a feed 2 with an inlet lock 3 for the material 4 to be dried. This runs inside the drying chamber 1 first over an upper belt conveyor 5 and then over a lower belt conveyor 6, the two belt conveyors 5 and 6 being horizontal and arranged one above the other and connected to each other by an intermediate lock 7. At the discharge end of the lower belt conveyor 6, a discharge 8 with an outlet lock 9 is provided, which is followed by a discharge 10 for the dried material 4 to be dried. This flow path of the material to be dried through the drying chamber 1 is indicated by arrows.
  • the two belt conveyors 5 and 6 each have a rotating conveyor belt 11 or 12, which is porous or air-permeable, but is suitable as its carrier, taking into account the particle size of the drying material 4.
  • the upper run of the upper conveyor belt 11 forms a filter section 13, while the upper run of the lower conveyor belt 12 forms a drying section 14.
  • a filter zone 15 and a drying zone 16 are located above the corresponding sections 13 and 14, through which the material to be dried 4 passes in succession in the form of a layer, as shown in the drawing.
  • the arrow 17 illustrates the supply of air which flows through the drying chamber 1 from bottom to top, as indicated by the sequence of vertical arrows.
  • the air flows in from the outside via an air filter 18.
  • This air is heated in an air heater 19, which is operated by means of low-temperature waste heat, which is supplied, for example, with warm waste water through the heat exchanger line 20.
  • the heated air flows upwards through the drying section 14 of the lower conveyor belt 12 and through the drying material 4 located in the drying zone 16. This is heated and dried, while the air is loaded with moisture and entrains dusty particles 4 from the drying material.
  • the anteroom 25 below the lower belt conveyor 6 and the rear room 26 above the upper belt conveyor 5 are connected by a bypass line 27 to a control flap 28, so that heated air can be metered into the exhaust air 21, which is free of dust and pollutants from the material to be dried 4 is.
  • a bypass line 27 to a control flap 28, so that heated air can be metered into the exhaust air 21, which is free of dust and pollutants from the material to be dried 4 is.
  • Such an admixture of warm air can be particularly advantageous if, at low outside temperatures and without such an admixture of air, undesirable vapor vapor formation occurs due to the water vapor saturation of the exiting exhaust air.
  • a circulation line 29 is provided with a control flap 30 for the exhaust air, which is connected to the chimney 23 between the suction fan 22 and the control flap 24 and opens into the space 31 between the air filter 18 and the air heater 19, so that the recirculated exhaust air also is heated and, if necessary, mixes with outside air supplied according to arrow 17 in order to protect the air heater 19 and possibly also other system parts from frost risk at low outside temperatures.
  • the extent to which the air flowing through the drying zone 16 entrains particles and is loaded with pollutants, and the extent to which these substances are separated in the filter zone 15 depend on several factors, in particular on the properties of the material to be dried 4, its bulk height (layer thickness) and feed rate and the throughput or the flow rate of the air in the two zones 15 and 16. It is therefore provided that the corresponding values can be set or changed in order to achieve optimal results in adaptation to the material to be treated 4 to be treated . In particular, with different air flow velocities be worked in the drying zone 16 and in the filter zone 15, for example by designing these zones with different air flow cross-sections or different lengths with appropriate air guidance.
  • the system could be constructed in a manner not shown in such a way that it can through nozzles or in a fluidized bed or flight dryer, or by mechanical power such as e.g. in a vibration dryer, results in a movement of the material to be dried, which promotes rapid and / or uniform drying. With the goods to be moved in this way, there is an increased and normally disturbing or impermissible entrainment of small particles with the drying air.
  • the drying air in the filter zone being cleaned again, in which a bed height adapted to the behavior of the material to be dried and the flow rate are selected such that, when flowing through the drying air, a separation of particles carried in it is comparable to a deep bed fiber filter results in which these accumulate on the still moist drying material forming the filter layer. Therefore, the exhaust air can possibly be released into the atmosphere or used for other processes, for example also for a recirculation mode in the dryer, without additional exhaust air filters. In such a mode of operation, the system parts, in particular heat exchangers used for reheating, are no longer soiled to an extent that would only allow short operating times without complex cleaning devices.
  • the described passage of the heated drying air through a filter layer formed from material to be dried has the additional advantage that the material to be dried is in the filter layer is heated. It may well be that condensation of moisture from the drying air occurs on the cold material to be dried, which increases its filtering effect.
  • Automatic controls in particular controlled air volume and recirculated air control, can be used to adapt to fluctuating amounts and moisture in the drying material.

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

Abstract

In order to dry materials (4) such as wood chips, the materials are laid in layers on air-permeable conveyor belts (11, 12) and moved forward. Heated drying air (17) is led through the conveyor belt (11 or 12) and the materials to be dried carried thereon within a drying zone (16), then within a filtering zone (15). Dust or toxic substance particles entrained from the drying zone precipitate again in the filtering zone and are deposited on the wet materials to be dried, so that the outgoing drying air (21) is clean.

Description

Die Erfindung bezieht sich auf ein Verfahren und auf eine Anlage zum Trocknen von schütt- oder rieselfähigem Trocknungsgut, insbesondere von Holzspänen oder Holzfasern, wie sie im Oberbegriff der Ansprüche 1 bzw. 5 beschrieben sind.The invention relates to a method and to a plant for drying bulk or free-flowing items to be dried, in particular wood chips or wood fibers, as described in the preamble of claims 1 and 5, respectively.

Ein solches Verfahren und eine solche Anlage sind bekannt (DE-C 423 469). Hier wird nasse Braunkohle in einem zweistufigen Verfahren mit Heißluft getrocknet, wobei es zu einem direkten Kontakt von Heißluft und Trocknungsgut kommt. Der Vorteil der Zweistufigkeit liegt darin, daß nicht nur das Trocknungsgut getrocknet sondern auch die durch den Trocknungsvorgang mit Verunreinigungen bzw. Staub beladene Trocknungsluft gefiltert wird, wobei das Trocknungsgut selbst die poröse Filtermasse bildet und bei diesem Reinigungsschritt bereits vorgewärmt bzw. vorgetrocknet wird. Daher können ggf. zusätzliche Maßnahmen zum Reinigen der Trocknungsabluft entfallen oder zumindest vereinfacht werden.Such a method and such a system are known (DE-C 423 469). Here, wet lignite is dried with hot air in a two-stage process, whereby there is direct contact between hot air and the material to be dried. The advantage of the two-stage process is that not only is the material to be dried dried, but also the drying air laden with impurities or dust through the drying process is filtered, the material to be dried itself forming the porous filter mass and being preheated or pre-dried in this cleaning step. Therefore, additional measures for cleaning the drying exhaust air may be omitted or at least simplified.

Beim bekannten Trockner sind eine untere Trocknungszone und eine obere Filterzone innerhalb eines gemeinsamen Gehäuses angeordnet, an dessen Oberseite die Gutzuführung und der Abgaskamin angeschlossen sind, während an der Unterseite die Heißluft zugeführt und das getrocknete Gut abgeführt werden. Die Filterzone wird von zwei gasdurchlässigen Zylinderwänden gebildet, die konzentrisch und senkrecht im Gehäuse angeordnet sind. Während das zugeführte feuchte Gut durch den Ringraum zwischen den beiden Zylinderwänden unter Schwerkraftwirkung herabgleitet, wird die gesamte Heißluft, die durch die Trocknungszone aufsteigt, an der Unterseite der Filterzone in die innere Zylinderwand geleitet, von wo sie im wesentlichen radial nach außen durch die beiden Zylinderwände und die zwischen diesen befindliche Gutschicht strömt, um dann von der außerhalb der Zylinderwandanordnung gebildeten Gehäusekammer zum Kamin zu gelangen.In the known dryer, a lower drying zone and an upper filter zone are arranged within a common housing, to the top of which the material supply and the exhaust gas chimney are connected, while the hot air is supplied to the underside and the dried material is removed. The filter zone is formed by two gas-permeable cylinder walls, which are arranged concentrically and vertically in the housing. As the supplied moist material slides down through the annular space between the two cylinder walls under the effect of gravity, all of the hot air that rises through the drying zone is passed on the underside of the filter zone into the inner cylinder wall, from where it flows essentially radially outward through the two cylinder walls and the material layer located between them, in order to then reach the chimney from the housing chamber formed outside the cylinder wall arrangement.

Bei dieser bekannten Anlage, bei der die gesamte Heißluft durch die Trocknungszone und die Filterzone strömt, ist die vorgenannte Vereinfachung durch Wegfall oder Verminderung von Nachbehandlungsmaßnahmen eingeschränkt, weil - in Abhängigkeit vom Trocknungsgut und den jeweiligen Betriebsparametern - Zusatzmaßnahmen für eine ordnungsgemäße Abgasabführung ergriffen werden müssen, insbesondere weil die herabgekühlte und mit Feuchtigkeit angereicherte Trocknungsabluft nicht mehr genügend Auftriebskräfte aufweist und die Gefahr störender Dampfschwadenbildung besteht. Dies gilt in besonderem Maße beim Trocknen von Holzspänen oder Holzfasern, wo es zur Bildung des sogenannten "blauen Rauchs" beim Kaminaustritt kommen kann.In this known system, in which the entire hot air flows through the drying zone and the filter zone, the aforementioned simplification is limited by the elimination or reduction of aftertreatment measures, because - depending on the material to be dried and the respective operating parameters - additional measures have to be taken for proper exhaust gas removal, especially because the cooled and moisture-enriched drying exhaust air no longer has sufficient buoyancy forces and there is a risk of disruptive steam vapor formation. This is particularly true when drying wood shavings or wood fibers, where the so-called "blue smoke" can form at the chimney outlet.

Es ist auch bereits eine Trocknungsanlage für Preßkörper (Pellets) aus Hopfen bekannt, bei der zwei luftdurchlässige Bandförderer in durch eine horizontale Zwischenwand getrennten Kammern übereinander angeordnet sind, wobei das Trocknungsgut dem oberen Bandförderer zugeführt wird, von diesem zum unteren Bandförderer gelangt und mit diesem zum Gutsaustrag transportiert wird. Warme Trocknungsluft steigt zuerst durch die Gutschicht auf dem unteren Förderband auf (Trocknungszone), wird dann aus der unteren Trocknungskammer heraus in einen seitlich angeordneten Zwischenerhitzer geleitet, von dem sie dann in die obere Kammer und durch das auf dem oberen Förderband befindliche Trocknungsgut strömt (Filterzone). Auch hier wird trotz der Zwischenentnahme und Zwischenerhitzung der Trocknungsluft die gesamte Trocknungsluft sowohl durch die Trocknungszone wie durch die Filterzone geleitet, so daß auch hier einer eventuellen Dampffahnenbildung nicht oder nur durch aufwendige Zusatzmaßnahmen vorgebeugt werden kann.There is also already known a drying system for pressed bodies (pellets) made of hops, in which two air-permeable belt conveyors are arranged one above the other in chambers separated by a horizontal intermediate wall, the material to be dried being fed to the upper belt conveyor, from there to the lower belt conveyor and with it to the Good discharge is transported. Warm drying air first rises through the material layer on the lower conveyor belt (drying zone), is then passed out of the lower drying chamber into a laterally arranged intermediate heater, from which it then flows into the upper chamber and through the drying material on the upper conveyor belt (filter zone ). Here too, despite the intermediate removal and reheating of the drying air, the entire drying air is passed both through the drying zone and through the filter zone, so that here, too, a possible formation of steam plumes cannot be prevented or can only be prevented by complex additional measures.

Der Erfindung liegt die Aufgabe zugrunde, die gattungsgemäße Trocknung besser anpaßbar an die Ausgangs- und Umgebungsbedingungen zu machen, so daß eine einfache Trocknung auch bei ungünstigen Bedingungen gewährleistet ist.The invention has for its object to make the generic drying more adaptable to the starting and ambient conditions, so that simple drying is ensured even under unfavorable conditions.

Diese Aufgabe wird erfindungsgemäß mit den kennzeichnenden Merkmalen der Ansprüche 1 bzw. 5 gelöst. Zweckmäßige Ausgestaltungen und Weiterbildungen ergeben sich aus den Unteransprüchen.This object is achieved with the characterizing features of claims 1 and 5, respectively. Appropriate refinements and developments result from the subclaims.

Somit wird Trocknungsluft durch das als Filtermittel (Filterschicht) wirkende noch nicht getrocknete Trocknungsgut geleitet, wobei die Schadstoffe bzw. der Staub, die beim Trocknen in der Trocknungszone aufgenommen und mitgeführt werden, wieder aus der Abluft ausgeschieden werden. Auf diese Weise läßt sich eine wirksame Reinigung oder Vorreinigung erzielen. Im weiter zu verarbeitenden Trocknungsgut stören die abgeschiedenen Partikel nicht. Bei der Weiterverarbeitung getrockneter Holzspäne zu Spanplatten sind in den Spänen enthaltene bzw. wieder abgeschiedene klebrige Substanzen sogar vorteilhaft und führen zu einer Herabsetzung der beizumischenden Bindemittelmenge. Der Gefahr der Dampffahnenbildung einschließlich der mehr oder minder sichtbaren Kondensation von Schadstoffen aus dem Abgas, die mit zunehmender Beladung der Trocknungsluft und mit sinkenden Außentemperaturen ansteigt, wird dadurch begegnet, daß dem Abgas ein nicht zur Trocknung verwendeter und daher weder abgekühler noch mit Schadstoffen beladener Teil des heißen Trocknungsgases beigesetzt wird. Ersichtlich lassen sich so kritische Temperatur- und Konzentrationswerte im Abgas vermeiden.Drying air is thus passed through the as yet non-dried material to be acted as a filter medium (filter layer), the pollutants or dust which are taken up and carried along in the drying zone during drying being removed again from the exhaust air. In this way, effective cleaning or pre-cleaning can be achieved. The separated particles do not interfere in the material to be further processed. In the further processing of dried wood shavings into chipboard, sticky substances contained in or re-deposited in the shavings are even advantageous and lead to a reduction in the amount of binder to be mixed. The risk of vapor plumes, including the more or less visible condensation of pollutants from the exhaust gas, which increases with increasing loading of the drying air and with falling outside temperatures, is countered by the fact that the exhaust gas is a part that is not used for drying and is therefore neither cooled nor loaded with pollutants of the hot drying gas is buried. As a result, critical temperature and concentration values in the exhaust gas can be avoided.

Mit Vorteil kann als Trocknungsgas Luft eingesetzt werden, wenn innerhalb einer Gesamtanlage Abwärme zur Aufwärmung dieser Luft zur Verfügung steht, beispielsweise ansonsten schwierig zu nutzende Abwärme im niedrigen Temperaturbereich, wie sie beispielsweise im Rahmen der Spanplattenherstellung im Bereich von ca. 60° Celsius bis 70° Celsius anfallen kann, zum Beispiel aus einer Waschanlage für Abluft aus Produktionsanlagen (Trockner, Pressen etc.) . In einem solchen Konzept läßt sich dann die Kondensationswärme von in solcher Abluft enthaltenem Wasserdampf nutzen und eine erhebliche Energieeinsparung erreichen. Damit verbunden kann zudem, sofern die erfindungsgemäße Trocknungsanlage als Vortrockner einem Endtrockner vorgeschaltet ist, dieser Endtrockner in seiner Betriebsweise ohne Verlust an Durchsatzleistung so geändert werden, daß sich die Entstehung von Emissionen im Endtrockner deutlich reduzieren läßt.Air can advantageously be used as the drying gas if waste heat is available for heating this air within an overall system, for example otherwise difficult to use waste heat in the low temperature range, such as that used in the production of chipboard in the range of approx. 60 ° Celsius to 70 ° Celsius can occur, for example from a washing system for exhaust air from production systems (dryers, presses, etc.). In such a concept, the heat of condensation of water vapor contained in such exhaust air can then be used and considerable energy savings can be achieved. Associated with this, if the drying system according to the invention is connected upstream of a final dryer, this operating mode of the final dryer can be changed without loss of throughput so that the generation of emissions in the final dryer can be significantly reduced.

Ein Ausführungsbeispiel der Erfindung wird nachfolgend anhand einer schematischen Zeichnung näher erläutert. Diese zeigt in einem Vertikalschnitt eine Anlage zur Durchführung des erfindungsgemäßen Verfahrens.An embodiment of the invention is explained in more detail below with the aid of a schematic drawing. This shows in a vertical section an installation for carrying out the method according to the invention.

Die dargestellte Anlage weist eine Trocknungskammer 1 auf, die eine Zuführung 2 mit einer Einlaßschleuse 3 für das Trocknungsgut 4 aufweist. Dieses läuft innerhalb der Trocknungskammer 1 zuerst über einen oberen Bandförderer 5 und dann über einen unteren Bandförderer 6, wobei die beiden Bandförderer 5 und 6 horizontal sowie übereinander angeordnet und durch eine Zwischenschleuse 7 miteinander verbunden sind. Am Abgabeende des unteren Bandförderers 6 ist eine Abführung 8 mit einer Auslaßschleuse 9 vorgesehen, an die sich ein Austrag 10 für das getrocknete Trocknungsgut 4 anschließt. Dieser Strömungsweg des Trocknungsguts durch die Trocknungskammer 1 ist durch Pfeile kenntlich gemacht.The system shown has a drying chamber 1 which has a feed 2 with an inlet lock 3 for the material 4 to be dried. This runs inside the drying chamber 1 first over an upper belt conveyor 5 and then over a lower belt conveyor 6, the two belt conveyors 5 and 6 being horizontal and arranged one above the other and connected to each other by an intermediate lock 7. At the discharge end of the lower belt conveyor 6, a discharge 8 with an outlet lock 9 is provided, which is followed by a discharge 10 for the dried material 4 to be dried. This flow path of the material to be dried through the drying chamber 1 is indicated by arrows.

Die beiden Bandförderer 5 und 6 weisen jeweils ein umlaufendes Förderband 11 bzw. 12 auf, das porös bzw. luftdurchlässig ist, jedoch unter Berücksichtigung der Teilchengröße des Trocknungsguts 4 als dessen Träger geeignet ist. Das Obertrum des oberen Förderbandes 11 bildet einen Filterabschnitt 13, während das Obertrum des unteren Förderbandes 12 einen Trocknungsabschnitt 14 bildet. Über den entsprechenden Abschnitten 13 und 14 befinden sich eine Filterzone 15 bzw. eine Trocknungszone 16, die nacheinander vom Trocknungsgut 4 in Form einer Schicht durchlaufen werden, wie es in der Zeichnung dargestellt ist.The two belt conveyors 5 and 6 each have a rotating conveyor belt 11 or 12, which is porous or air-permeable, but is suitable as its carrier, taking into account the particle size of the drying material 4. The upper run of the upper conveyor belt 11 forms a filter section 13, while the upper run of the lower conveyor belt 12 forms a drying section 14. A filter zone 15 and a drying zone 16 are located above the corresponding sections 13 and 14, through which the material to be dried 4 passes in succession in the form of a layer, as shown in the drawing.

Der Pfeil 17 veranschaulicht die Zuführung von Luft, welche die Trocknungskammer 1 von unten nach oben durchströmt, wie es die Folge senkrechter Pfeile andeutet. Die Luft strömt von außen über einen Luftfilter 18 zu. Diese Luft wird in einem Lufterhitzer 19 erwärmt, der mittels Niedertemperatur-Abwärme betrieben wird, die beispielsweise mit warmem Abwasser durch die Wärmetauscherleitung 20 zugeführt wird.The arrow 17 illustrates the supply of air which flows through the drying chamber 1 from bottom to top, as indicated by the sequence of vertical arrows. The air flows in from the outside via an air filter 18. This air is heated in an air heater 19, which is operated by means of low-temperature waste heat, which is supplied, for example, with warm waste water through the heat exchanger line 20.

Die erwärmte Luft strömt aufwärts durch den Trocknungsabschnitt 14 des unteren Förderbands 12 sowie durch das in der Trocknungszone 16 befindliche Trocknungsgut 4. Dieses wird dabei erwärmt und getrocknet, während die Luft mit Feuchtigkeit beladen wird und aus dem Trocknungsgut 4 staubförmige Partikel mitreißt.The heated air flows upwards through the drying section 14 of the lower conveyor belt 12 and through the drying material 4 located in the drying zone 16. This is heated and dried, while the air is loaded with moisture and entrains dusty particles 4 from the drying material.

Anschließend durchdringt die aufsteigende Luft den Filterabschnitt 13 des oberen Förderbands 11 sowie die in der Filterzone 15 befindliche Trocknungsgutschicht, die als Filtermittel wirksam ist, so daß aus der Trocknungszone 16 mitgeführte Teilchen in der Filterzone 15 wieder abgeschieden werden. Die so gereinigte Abluft 21 strömt über den Saugzugventilator 22 zum Kamin 23. Dieser ist wie dargestellt mit einer Regelklappe 24 versehen.Then the rising air penetrates the filter section 13 of the upper conveyor belt 11 and the drying material layer located in the filter zone 15, which acts as a filter medium, so that particles carried along from the drying zone 16 are separated out again in the filter zone 15. The exhaust air 21 cleaned in this way flows via the induced draft fan 22 to the chimney 23. As shown, this is provided with a control flap 24.

Des weiteren sind der Vorraum 25 unterhalb des unteren Bandförderers 6 und der Nachraum 26 oberhalb des oberen Bandförderers 5 durch eine Umgehungsleitung 27 mit einer Regelklappe 28 verbunden, so daß der Abluft 21 erwärmte Luft zudosiert werden kann, die frei von Staub und Schadstoffen aus dem Trocknungsgut 4 ist. Eine solche Beimischung von Warmluft kann insbesonder dann vorteilhaft sein, wenn es bei niedrigen Außentemperaturen ohne eine solche Luftbeimischung infolge Wasserdampfsättigung der austretenden Abluft zu einer unerwünschten Dampfschwadenbildung kommt.Furthermore, the anteroom 25 below the lower belt conveyor 6 and the rear room 26 above the upper belt conveyor 5 are connected by a bypass line 27 to a control flap 28, so that heated air can be metered into the exhaust air 21, which is free of dust and pollutants from the material to be dried 4 is. Such an admixture of warm air can be particularly advantageous if, at low outside temperatures and without such an admixture of air, undesirable vapor vapor formation occurs due to the water vapor saturation of the exiting exhaust air.

Ferner ist eine Umwälzleitung 29 mit einer Regelklappe 30 für die Abluft vorgesehen, die zwischen dem Saugzugventilator 22 und der Regelklappe 24 an den Kamin 23 angeschlossen ist und in den Zwischenraum 31 zwischen dem Luftfilter 18 und dem Lufterhitzer 19 mündet, so daß die umgewälzte Abluft ebenfalls erwärmt wird und sich ggf. mit gemäß Pfeil 17 zugeführter Außenluft mischt, um bei niedrigen Außentemperaturen den Lufterhitzer 19 und evtl. auch sonstige Anlageteile vor Frostgefährdung zu schützen.Furthermore, a circulation line 29 is provided with a control flap 30 for the exhaust air, which is connected to the chimney 23 between the suction fan 22 and the control flap 24 and opens into the space 31 between the air filter 18 and the air heater 19, so that the recirculated exhaust air also is heated and, if necessary, mixes with outside air supplied according to arrow 17 in order to protect the air heater 19 and possibly also other system parts from frost risk at low outside temperatures.

Ersichtlich ist es auch möglich, anstatt mit zwei Bandförderern 5 und 6 mit einem einzigen Bandförderer zu arbeiten, der den Filterabschnitt und den Trocknungsabschnitt hintereinander in seinem Obertrum aufweist, wenn dafür gesorgt ist, daß die Luft so geführt wird, daß sie die beiden Abschnitte nacheinander durchströmt. Ebenso kann anstelle der Bandförderer 5 und 6 ein anderer luftdurchlässiger Träger verwendet werden, über den oder mit dem das Trocknungsgut 4 vorbewegt wird.Obviously, instead of working with two belt conveyors 5 and 6, it is also possible to work with a single belt conveyor which has the filter section and the drying section one behind the other in its upper run, if the air is made to flow so that it passes the two sections one after the other flows through. Likewise, instead of the belt conveyors 5 and 6, another air-permeable carrier can be used, via which or with which the material to be dried 4 is moved forward.

Das Ausmaß, in dem die durch die Trocknungszone 16 strömende Luft Partikel mitreißt und mit Schadstoffen beladen wird, sowie das Ausmaß der Abscheidung dieser Stoffe in der Filterzone 15 sind von mehreren Faktoren abhängig, namentlich von den Eigenschaften des Trocknungsguts 4, seiner Schütthöhe (Schichtdicke) und Vorschubgeschwindigkeit sowie vom Durchsatz bzw. der Strömungsgeschwindigkeit der Luft in den beiden Zonen 15 bzw. 16. Es ist daher vorgesehen, daß die entsprechenden Werte eingestellt bzw. verändert werden können, um in Anpassung an das zu behandelnde Trocknungsgut 4 zu optimalen Ergebnissen zu kommen. Insbesondere kann mit unterschiedlichen Luftdurcnströmungs-geschwindigkeiten in der Trocknungszone 16 und in der Filterzone 15 gearbeitet werden, beispielsweise indem diese Zonen bei entsprechender Luftführung mit unterschiedlichem Durchströmungsquerschnitt bzw. verschieden lang ausgeführt werden.The extent to which the air flowing through the drying zone 16 entrains particles and is loaded with pollutants, and the extent to which these substances are separated in the filter zone 15 depend on several factors, in particular on the properties of the material to be dried 4, its bulk height (layer thickness) and feed rate and the throughput or the flow rate of the air in the two zones 15 and 16. It is therefore provided that the corresponding values can be set or changed in order to achieve optimal results in adaptation to the material to be treated 4 to be treated . In particular, with different air flow velocities be worked in the drying zone 16 and in the filter zone 15, for example by designing these zones with different air flow cross-sections or different lengths with appropriate air guidance.

Ferner könnte die Anlage in nicht dargestellter Weise so aufgebaut werden, daß sich in ihr durch gezielte Luftführung, wie z.B. durch Düsen oder in einem Wirbelbett- bzw. Flugtrockner, oder durch eingebrachte mechanische Leistung, wie z.B. in einem Vibrationstrockner, eine Bewegung des Trocknungsgutes ergibt, die eine rasche und/oder gleichmäßige Trocknung begünstigt. Bei so bewegtem Trocknungsgut ergibt sich ein erhöhter und normalerweise störender oder auch unzulässiger Mitriß von kleinen Partikeln mit der Trocknungsluft. Dem wird jedoch dadurch abgeholfen, daß die Trocknungsluft in der Filterzone wieder gereinigt wird, in der eine dem Verhalten des Trocknungsguts angepaßte Schütthöhe und die Strömungsgeschwindigkeit derart gewählt wird, daß sich bei der Durchströmung der Trocknungsluft vergleichbar mit einem Tiefbettfaserfilter eine Abtrennung von in dieser mitgetragenen Partikeln ergibt, bei der sich diese an das die Filterschicht bildende noch feuchte Trocknungsgut anlagern. Daher kann ggf. ohne zusätzliche Abluftfilter die Abluft in die Atmosphäre abgegeben oder für sonstige Prozesse verwendet werden, beispielsweise auch für einen Umluftbetrieb im Trockner. Bei einer solchen Betriebsweise werden die Anlagenteile, insbesondere allenfalls zur Nacherwärmung eingesetzte Wärmetauscher, nicht mehr in einem Umfang verschmutzt, der ohne aufwendige Reinigungseinrichtungen nur kurze Betriebszeiten ermöglichen würde. Unter Umständen ist es auch möglich, die ganze Trocknungswärme auf diese Art mittels Umluft vom Lufterhitzer 19 zuzuführen, so daß der Luftfilter 18 entlastet wird oder sogar entfallen kann, der durch die stark staubhaltige Luft in der Nähe von Holzlagerplätzen einen nicht unerheblichen Betriebsaufwand neben ebenfalls wesentlichen Investitionskosten verursacht. Auch im Falle der Mischung der Umluft mit staubhaltiger Außenluft kann der Lufterhitzer 19 (Wärmetauscherleitung 20) nur mit der annähernd staubfreien Umluft beaufschlagt werden.Furthermore, the system could be constructed in a manner not shown in such a way that it can through nozzles or in a fluidized bed or flight dryer, or by mechanical power such as e.g. in a vibration dryer, results in a movement of the material to be dried, which promotes rapid and / or uniform drying. With the goods to be moved in this way, there is an increased and normally disturbing or impermissible entrainment of small particles with the drying air. This is remedied, however, by the drying air in the filter zone being cleaned again, in which a bed height adapted to the behavior of the material to be dried and the flow rate are selected such that, when flowing through the drying air, a separation of particles carried in it is comparable to a deep bed fiber filter results in which these accumulate on the still moist drying material forming the filter layer. Therefore, the exhaust air can possibly be released into the atmosphere or used for other processes, for example also for a recirculation mode in the dryer, without additional exhaust air filters. In such a mode of operation, the system parts, in particular heat exchangers used for reheating, are no longer soiled to an extent that would only allow short operating times without complex cleaning devices. Under certain circumstances, it is also possible to supply all of the drying heat in this way by means of circulating air from the air heater 19, so that the air filter 18 is relieved or can even be omitted, which due to the extremely dusty air in the vicinity of wood storage bins is a not inconsiderable operating expense in addition to essential Investment costs caused. Even in the case of mixing the circulating air with dust-containing outside air, the air heater 19 (heat exchanger line 20) can only be supplied with the almost dust-free circulating air.

Die beschriebene Durchleitung der erwärmten Trocknungsluft durch eine aus Trocknungsgut gebildete Filterschicht hat zusätzlich den Vorteil, daß in der Filterschicht das Trocknungsgut erwärmt wird. Dabei kann es durchaus sein, daß in der Filterschicht eine Kondensation von Feuchtigkeit aus der Trocknungsluft am kalt eingetragenen Trocknungsgut auftritt, wodurch sich dessen Filterwirkung verstärkt.The described passage of the heated drying air through a filter layer formed from material to be dried has the additional advantage that the material to be dried is in the filter layer is heated. It may well be that condensation of moisture from the drying air occurs on the cold material to be dried, which increases its filtering effect.

Bei Trockengut, das nur teilentfeuchtet wird, kann es vorteilhaft sein, die aus der Trocknungszone 16 aufsteigende, meist mit Wasserdampf weitgehend gesättigte Trocknungsluft vor ihrem Eintritt in die Filterzone 15 nachzuerwärmen, um so eine verbesserte Erwärmung des Trocknungsgutes 4 in der Filterzone 15 zu erreichen und eine Kondensation von Wasserdampf am Trocknungsgut 4 in der Filterzone 15 zu begrenzen oder gar zu vermeiden. So kann bereits in der Filterzone 15 eine erste Teilentfeuchtung des Trocknungsgutes 4 stattfinden, die allerdings nur soweit gehen bzw. auf einen unteren Schichtbereich der Filterzone 15 beschränkt bleiben sollte, daß die gewünschte Filterwirkung der Filterzone erhalten bleibt.In the case of dry material that is only partially dehumidified, it can be advantageous to reheat the drying air rising from the drying zone 16, mostly largely saturated with water vapor, before it enters the filter zone 15, in order to achieve an improved heating of the drying material 4 in the filter zone 15 and to limit or even prevent condensation of water vapor on the drying material 4 in the filter zone 15. Thus, a first partial dehumidification of the material to be dried 4 can already take place in the filter zone 15, but this should only go so far or should be limited to a lower layer area of the filter zone 15 that the desired filter effect of the filter zone is retained.

Durch automatische Regelungen, insbesondere durch eine gesteuerte Luftmengen- und Umluftregelung, kann eine Anpassung an stark schwankende Mengen und Eintrittsfeuchten des Trocknungsgutes erfolgen.Automatic controls, in particular controlled air volume and recirculated air control, can be used to adapt to fluctuating amounts and moisture in the drying material.

Claims (10)

  1. Method for drying bulk or pourable material (4), more especially wood chips or wood fibres, in which the material for drying (4) is passed successively through a filter zone (15) and a drying zone (16), and heated drying gas (17) is passed initially through the drying zone (16) and then through the filter zone (15), in which particles carried by the drying gas (17) out of the material for drying (4) are again deposited in the material for drying (4), whereupon the drying gas (17) is removed as exhaust gas (21), characterised in that a portion of the heated drying gas (17) , by-passing the drying zone (16) and the filter zone (15), is mixed with the exhaust gas (21) leaving the filter zone (15).
  2. Method according to claim 1, characterised in that the flow speeds of the drying gas (17) in the drying zone (16) and in the filter zone (15) are selected to be different.
  3. Method according to claim 1 or 2, characterised in that a portion of the exhaust gas (21) leaving the filter zone (15) is again circulated through the material for drying (4).
  4. Method according to one of claims 1 to 3, characterised in that the flow of material for drying and/or the flow of drying gas and/or the supply of heat to the drying gas (17), as well if necessary as the division of the heated drying gas (17) into the drying flow and the mixing flow, and the division of the exhaust gas (21) leaving the filter zone (15) into the flow of removed gas and the circulating flow, are varied manually or by means of automatic control in dependence on the material (4) to be dried and the desired dried product.
  5. Installation for carrying out the method according to claim 1, with a drying chamber (1) having a feed (2) for material for drying, a drying gas feed pipe (at 18), and a removal means (8) for material to be dried, and in which there is disposed a porous carrier (11, 12) for the material (4) to be dried, and from which there emerges a drying gas exhaust pipe (23) separate from the drying material removal means (8), said drying gas exhaust pipe (23) being separated by a drying section (14) and by a filter section (13) of the porous carrier (11, 12) from the drying gas feed pipe (at 18), characterised in that - seen in the direction of flow -the antechamber (25) in front of the drying section (14) of the carrier (11, 12) and the subsequent chamber (26) behind the filter section (13) of the carrier (11, 12) are interconnected by a drying gas by-pass pipe (27) with a regulating valve (28).
  6. Installation according to claim 5, characterised in that the porous carrier (11, 12) is in the form of a driven conveyor belt.
  7. Installation according to claim 6, characterised in that separate conveyor belts (11 or 12) are provided for the filter section (13) and for the drying section (14), said conveyor belts (11 or 12) being disposed one above the other and being interconnected by an intermediate lock (7) for transfer of material for drying.
  8. Installation according to one of claims 5 to 7, characterised in that a heater (19) through which drying gas (17) flows is provided between the drying gas feed pipe (at 18) and the drying section (14) of the carrier (11, 12).
  9. Installation according to one of claims 5 to 8, characterised in that the exhaust gas pipe (23) is provided with a regulating valve (24) in front of which there diverges an exhaust gas circulating pipe (29) provided with a regulating valve (30), said exhaust gas circulating pipe (29) opening into the space (25, 31) in front of the drying section (14) of the carrier (11, 12).
  10. Installation according to claim 8 and 9, characterised in that the exhaust gas circulating pipe (29) opens into the heater (19).
EP91912501A 1990-07-17 1991-07-17 Process and device for drying pourable or bulk materials to be dried Expired - Lifetime EP0553089B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT91912501T ATE103702T1 (en) 1990-07-17 1991-07-17 PROCESS AND PLANT FOR DRYING BULK OR FREE-FLOWING DRYING MATERIAL.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4022702 1990-07-17
DE4022702A DE4022702C1 (en) 1990-07-17 1990-07-17

Publications (2)

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EP0553089A1 EP0553089A1 (en) 1993-08-04
EP0553089B1 true EP0553089B1 (en) 1994-03-30

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EP91912501A Expired - Lifetime EP0553089B1 (en) 1990-07-17 1991-07-17 Process and device for drying pourable or bulk materials to be dried

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EP (1) EP0553089B1 (en)
AU (1) AU8181791A (en)
DE (2) DE4022702C1 (en)
WO (1) WO1992001896A1 (en)

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DE102015113530B3 (en) * 2015-08-17 2016-12-29 Stela Laxhuber Gmbh Belt drying plant with two drying levels
WO2024018430A1 (en) * 2022-07-22 2024-01-25 Imal S.R.L. Plant for wood machining

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DE4217056A1 (en) * 1992-05-22 1993-11-25 Fritz Egger Gmbh Dryer for pourable or pourable goods
DE4305543C2 (en) * 1993-02-20 1999-06-10 Schulz Verfahrenstechnik Gmbh Process for drying a product carried on a belt, in particular a bulk material, and installation for carrying out the process
CN101922858B (en) * 2010-07-02 2012-01-04 张君如 Multi-layer air dryer
PL2650632T3 (en) * 2012-04-13 2016-08-31 Soc General De Aguas De Barcelona S A Multiple product belt drier for drying pasty and/or powdery materials, particularly for drying sludges from treatment plants or biomass
IT201600125377A1 (en) * 2016-12-13 2018-06-13 Imal Srl PLANT FOR DRYING OF UNCERTAIN WOODEN MATERIAL
DE202017005817U1 (en) 2017-11-09 2017-12-01 Augenstein Maschinenbau GmbH Plant for drying a product guided on a belt
DE202018105738U1 (en) * 2018-10-08 2020-01-09 Pfeifer Holz Gmbh Plant for the production of blocks

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DE408857C (en) * 1922-07-15 1925-01-28 Jens Rude Process and device for the recovery of dust in drying and smoldering systems
DE423469C (en) * 1923-03-25 1926-01-04 Louis Gumz Method and device for dedusting exhaust gases from dryers
FR933669A (en) * 1946-09-17 1948-04-28 Improvements to cable driers
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102015113530B3 (en) * 2015-08-17 2016-12-29 Stela Laxhuber Gmbh Belt drying plant with two drying levels
WO2024018430A1 (en) * 2022-07-22 2024-01-25 Imal S.R.L. Plant for wood machining

Also Published As

Publication number Publication date
EP0553089A1 (en) 1993-08-04
AU8181791A (en) 1992-02-18
WO1992001896A1 (en) 1992-02-06
DE4022702C1 (en) 1991-11-28
DE59101294D1 (en) 1994-05-05

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