EP0379657B1 - Sludge drying process - Google Patents

Sludge drying process Download PDF

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Publication number
EP0379657B1
EP0379657B1 EP89120565A EP89120565A EP0379657B1 EP 0379657 B1 EP0379657 B1 EP 0379657B1 EP 89120565 A EP89120565 A EP 89120565A EP 89120565 A EP89120565 A EP 89120565A EP 0379657 B1 EP0379657 B1 EP 0379657B1
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Prior art keywords
sludge
layer
gas
dryer
sand
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EP89120565A
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German (de)
French (fr)
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EP0379657A1 (en
Inventor
Karl Dipl.-Ing. Keller
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Sulzer Escher Wyss GmbH
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Sulzer Escher Wyss GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
    • F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
    • F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
    • F26B3/084—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed with heat exchange taking place in the fluidised bed, e.g. combined direct and indirect heat exchange
    • 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
    • F26B21/04—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure partly outside the drying enclosure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
    • F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
    • F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
    • F26B3/088—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed using inert thermally-stabilised particles

Definitions

  • the invention relates to a method for drying a sludge of the type specified in the preamble of claim 1 (see e.g. DE-A-2245495).
  • All suspensions, sludges, pastes and filter cakes from various dewatering machines can be used for drying.
  • This also includes sewage sludge from municipal or industrial wastewater that comes from sewage treatment plants that are fed with it.
  • sludges are mechanically dewatered. Their further processing, recycling or disposal requires thermal drying. Depending on the degree of dewatering, the pasty sludges contain 40 to 60% water, which impairs handling and the processes for recycling or disposal of the sludge. Thermal drying improves or extends the possibilities for recycling these sludges and / or reduces the amount to be disposed of.
  • a known method uses a direct drum dryer. Depending on the consistency and after pretreatment, the sludge is placed in a rotating drum inclined towards the discharge and migrates to the discharge end by constant rolling in the rotating drum. At the same time, hot air or hot flue gas flows through the drum in countercurrent or cocurrent and absorbs the moisture of the sludge.
  • the system is mechanically and energetically complex, and the moist and polluted exhaust air from the drum dryer requires complex cleaning to limit emissions.
  • Hot air or hot flue gases flow through a layer of sand from the bottom up, which is a Forces fluidization of this sand filling.
  • An inflow floor ensures an even distribution of the inflowing hot gases.
  • Several pumps push the sludge through nozzles directly into the fluidized sand layer. The nozzles are located just above the inflow floor, i.e. in the lower quarter of the sand layer. The sludge releases its moisture to the hot gas flowing through, which has to be cleaned after it has left the dryer.
  • Indirect contact dryers are also known.
  • the sludge is heated indirectly via heating surfaces.
  • these heating surfaces take the form of disks, paddles, rollers, etc.
  • the steam or oil-heated heating surfaces heat the sludge until its moisture evaporates, a ventilator sucks off the vapors and presses them to condense.
  • the sludge is either applied thinly to the heating surfaces and scraped off again, or the heating surfaces are moved or stirred in the product to be dried.
  • the applicant offers a method with an indirect fluidized bed dryer. Overheated vapors flow through a sludge granulate in a circuit from bottom to top in a fluidized bed and thereby fluidize it. An inflow floor with nozzles distributes the gas evenly over the entire dryer surface and ensures balanced fluidization of the granules.
  • Heating surfaces for example heat exchangers, are arranged in this fluidized layer and indirectly transfer the energy required for drying to the granulate.
  • the heating surfaces have different shapes, such as smooth tubes, finned tubes, plates, etc., which are heated with steam or other heat carriers.
  • a granulator creates moist, stable granules by mixing dewatered sludge and part of the already dried sludge.
  • This moist granulate is introduced into the fluidized bed, where its moisture is absorbed by the flowing, overheated vapors.
  • the dried granulate leaves the fluidized bed dryer via an overflow weir or a discharge device. Part of the dried granulate goes back to the granulator, where dewatered sludge is added to the wet granulate.
  • the vapors emerging from the fluidized bed dryer also take fine-grained product particles and dust, which are separated in a cyclone or filter and fed into the granulator. The amount of water evaporated during drying is drawn off as vapors from the circulatory system and condensed or treated thermally.
  • the invention was based on the object of proposing a method of the initially specified type which is more economical than the previously known.
  • a pretreatment of the sludge before drying should not be necessary.
  • the discharge of the dry material from the dryer should be simplified.
  • the energy consumption of the process is to be reduced.
  • the equipment used should be simpler and cheaper, and at the same time largely trouble-free and low-maintenance.
  • the process should be continuously executable.
  • the product should have a high dry matter content and should be easy to manipulate. Environmental pollution should be largely avoided. The environmental impact should be as low as possible.
  • the resulting sludge 1 is a suspension containing organic substances, which is still pumpable with about 40% water and is kept in stock in a silo 12.
  • the drive motor 14 of which can be speed-regulated with a control device 15 the sludge is pumped into a fluidized bed dryer 2 through a line 16, in which a heated sand layer 3 fluidized by means of a gas stream is built up during operation becomes.
  • the sand layer 3 fluidized with a gas stream is heated indirectly by means of stationary heat exchange bodies 5 immersed in the sand layer 3.
  • the pumpable sludge 1 to be dried is introduced under pressure from the pump 13 into the dryer 2 from above onto the sand layer 3 in countercurrent to the fluidizing gas stream.
  • the feed points are provided in the uppermost area of the dryer 2.
  • the fluidized sand entrains the sludge immediately after it emerges from the mouthpieces of a distribution device. During this process, the sludge coagulates and sludge bulbs form which, owing to the fluidization, are distributed in the sand layer 3 and move in floating manner in this.
  • the hot sand and the hot fluidizing gas gradually release the thermal energy to the moist mud tubers, which leads to a steady heating, with water evaporation of the mud tubers, successively layer by layer from the surface to the core.
  • the water vapor is taken up by the gas stream and discharged from the dryer 2 with the exhaust gas stream 6.
  • the fluidized sand constantly rubs against the already dried-up layer of the mud tubers and grinds off the dry mud, its dry substance, as fine dust.
  • This pulverization of the sludge takes place at each sludge tuber until it has completely dried and been ground down to the respective core, until the remaining sludge dry matter has gradually been crushed and has been pulverized in this way.
  • the rising fluidizing gas stream also entrains the pulverized sludge dry matter and the product dust in addition to the water vapor and thus continuously carries the product 4 with the exhaust gas stream 6 out of the dryer 2 as a function of the gas stream speed.
  • the pulverized dry substance 4, ie the sludge dry matter, is continuously separated as a product from the exhaust gas stream 6 in a separation stage, the cyclone 7.
  • a fan 17, downstream of the cyclone 7, sucks off the exhaust gas stream 6 and thus prevents an increase in pressure due to water evaporation and other gas development during the drying process in the dryer 2.
  • the sand in the sand layer 3 and the fluidizing gas stream are heated by means of smooth heat exchange tubes 5, which are arranged horizontally in the provided area of the sand layer 3 in the fluidized state and through which a heat-carrying medium flows.
  • flue gases 8 are the heat-carrying medium, which are generated in a combustion chamber 9 when fossil fuels 10 are burned.
  • necessary air is led through a line 18.
  • At least some of the flue gases are sucked off by a fan 19 after flowing through the heat exchange tubes 5 and led into the combustion chamber 9 with recovery of their residual heat and thus recirculated.
  • the excess part of the flue gases is removed from the circuit via a line 20 and discharged through a silencer 21.
  • the exhaust gas stream 6, from which the product 4 has been separated, is continuously recirculated to fluidize the sand layer 3, the fluidized bed in the dryer 2.
  • the gas still contains all of the water vapor newly generated in the dryer and the other gases developed there. This additional volume of gas must be withdrawn from the gas cycle system in order to keep the pressure in the gas cycle system constant.
  • the gas volume reduced to the amount of gas required for the fluidization of the layer 3 in the fluidized bed dryer 2 is passed through a fan 22, distribution box 37 and inflow base 38 of the dryer 2, which closes the gas circuit.
  • the excess gas quantity is reduced by condensing the condensable excess gas, primarily the excess water vapor in a condenser 11, into which the entire exhaust gas flow is led through a line 23.
  • the condensation takes place by spraying the gas with cooling water, for which a line 24 is provided.
  • the water with the condensate is recirculated via a pump 25 and possibly a cooler 26, an excess being drawn off via a line 27. If there is still an excess volume after the condenser 11 in the circulatory system, a corresponding one becomes Gas amount withdrawn from the circulatory system by opening a valve 28 via a line 29. Water vapor and the gases released during drying remain in the circuit.
  • the gas circuit used for fluidization becomes ever poorer in free oxygen, so that finally the process in and after the dryer 2 takes place in a non-reactive atmosphere, thereby eliminating the risk of burning or explosion.
  • the product dust present in the cyclone 7 has about 90% TS.
  • the pulverized sludge dry mass 4 obtained after the discharge apparatus 30 is fed to a mixer 31, where part of the sludge 1 from the silo 12 is added to the product dust via a speed-controllable pump 32 and a line 33, whereby a desired final moisture content of the product is set becomes.
  • a line 34 leads from the mixer 31 to the cyclone 7, through which the gases produced in the mixer 31 are drawn off.
  • the mixer 31 is provided with a granulator, where the product having the desired moisture content is processed into granules.
  • the end product processed in this way is loaded by means of a transport device 35.
  • a line 36 is also connected to this and, if necessary, serves to empty the dryer 2.
  • the process is suitable for drying a wide variety of suspensions, slurries, pastes and filter cakes from a wide variety of dewatering devices.
  • the process for drying municipal and / or industrial sewage sludge was described here.
  • the sludges no longer have to be structured or granulated before being introduced into the fluidized bed. Since the sand grinds the dried sludge into dust and the dust is discharged with the exhaust gas stream, no complicated discharge mechanism from the dryer is necessary. The recirculation of product for granulation can also be omitted.
  • the fluid bed dryer works in a chemically non-reactive atmosphere, which consists of slightly overheated vapors and the gases contained in the sludge without free oxygen.
  • the sand fluidized in the dryer is an absolutely inert material in the drying process, which does not react chemically with the sludge, moisture or the recycle gas. This prevents inflammation due to overheating in the dryer.
  • the energy for drying the material is indirectly transferred to the material or to the fluidized sand.
  • the heating medium does not come into direct contact with the material or the sand.
  • the evaporated moisture accumulates as water vapor and can be disposed of as such by simple condensation using the waste heat.
  • the horizontal smooth-tube heat exchangers in the fluidized layer carry out an extremely intensive energy exchange with a high specific heat output.
  • An optimal grain distribution of the sand which is selected according to the material to be dried, allows a relatively lower gas velocity and higher heat output than in a fluid bed dryer with a product granulate layer. This reduces the electrical energy required to drive the fans.
  • the fluidized sand layer constantly cleans the immersed heating surfaces during operation, so that their loss of performance due to contamination is excluded.
  • the horizontal smooth tube heating surfaces are stationary and therefore static heat exchangers. They can not only be heated with steam or liquid heat carriers, but also allow heating with hot gases such as air or flue gases.
  • the hot flue gases can be generated as waste heat or from a combustion chamber with direct firing.
  • the dryer Due to the inert sand layer, the dryer remains absolutely insensitive to temperature fluctuations or overheating.
  • the layer of sand also allows rapid heating and enables the system to be started up immediately at nominal output. When the system is switched off, forced reheating for the inert sand filling is absolutely harmless.
  • the dust-like dust product can be adjusted to a desired moisture content of 50% to 90% DM according to a further use.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Microbiology (AREA)
  • Drying Of Solid Materials (AREA)
  • Treatment Of Sludge (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Polysaccharides And Polysaccharide Derivatives (AREA)
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Abstract

A sand layer is fluidized by a gas stream or current in a fluidized bed dryer and indirectly heated by immersed stationary heat-exchanger tubes. The sludge to be dried is continuously fed under pressure in a pumpable conditon from above onto the fluidized sand layer. The sludge is coagulated in the fluidized sand layer to form sludge lumps. Here, the sludge lumps are successively dried from the surface down to the core thereof, and the already dried layers of the sludge lumps are successively abraded by the fluidized sand, whereby the sludge lumps are entirely comminuted and the dry matter thereof is pulverized to form dust. This product dust is continuously discharged together with the exhaust-gas stream from the fluidized bed dryer and continuously separated as a product from the exhaust-gas stream. The gas stream or current freed from dust is partially recycled in a closed circuit back to the fluidized bed dryer for fluidization of the sand layer.

Description

Die Erfindung betrifft ein Verfahren zur Trocknung eines Schlammes der im Oberbegriff des Patentanspruches 1 angegebenen Art (vgl. z.B. DE-A-2245495).The invention relates to a method for drying a sludge of the type specified in the preamble of claim 1 (see e.g. DE-A-2245495).

Zur Trocknung können sämtliche Suspensionen, Schlämme, Pasten und Filterkuchen aus verschiedensten Entwässerungsmaschinen anfallen. Dazu gehören auch Klärschlämme aus kommunalem oder industriellem Abwasser, die aus damit beschickten Kläranlagen stammen.All suspensions, sludges, pastes and filter cakes from various dewatering machines can be used for drying. This also includes sewage sludge from municipal or industrial wastewater that comes from sewage treatment plants that are fed with it.

Diese Schlämme werden mechanisch entwässert. Ihre Weiterverarbeitung, Verwertung oder Entsorgung setzt eine thermische Trocknung voraus. Die pastösen Schlämme enthalten je nach Entwässerungsgrad 40 bis 60% Wasser, was die Hantierbarkeit und die Verfahren zur Verwertung oder Entsorgung der Schlämme beeinträchtigt. Die thermische Trocknung verbessert oder erweitert die Möglichkeiten zur Verwertung dieser Schlämme und/oder reduziert die anfallende zu entsorgende Menge.These sludges are mechanically dewatered. Their further processing, recycling or disposal requires thermal drying. Depending on the degree of dewatering, the pasty sludges contain 40 to 60% water, which impairs handling and the processes for recycling or disposal of the sludge. Thermal drying improves or extends the possibilities for recycling these sludges and / or reduces the amount to be disposed of.

Ein bekanntes Verfahren benutzt einen direkten Trommeltrockner. Der Schlamm wird je nach Konsistenz gegebenenfalls nach Vorbehandlung in eine rotierende, zum Austrag hin geneigte Trommel aufgegeben und wandert durch ständiges Abrollen in der sich drehenden Trommel zum Austragsende. Gleichzeitig durchströmt heiße Luft oder heißes Rauchgas die Trommel im Gegen- oder Gleichstrom und nimmt dabei die Feuchtigkeit des Schlammes auf. Die Anlage ist mechanisch und energetisch aufwendig, und die feuchte und belastete Abluft aus dem Trommeltrockner bedarf einer aufwendigen Reinigung zur Emissionsbegrenzung.A known method uses a direct drum dryer. Depending on the consistency and after pretreatment, the sludge is placed in a rotating drum inclined towards the discharge and migrates to the discharge end by constant rolling in the rotating drum. At the same time, hot air or hot flue gas flows through the drum in countercurrent or cocurrent and absorbs the moisture of the sludge. The system is mechanically and energetically complex, and the moist and polluted exhaust air from the drum dryer requires complex cleaning to limit emissions.

Andere bekannte Vorrichtungen sind direkte Sandwirbelschichttrockner. Heiße Luft oder heiße Rauchgase durchströmen eine Sandschicht von unten nach oben, was eine Fluidisierung dieser Sandfüllung erzwingt. Ein Anströmboden sorgt für eine gleichmäßige Verteilung der einströmenden heißen Gase. Mehrere Pumpen drücken den Schlamm über Düsen direkt in die fluidisierte Sandschicht. Die Düsen sind knapp über dem Anströmboden, also im unteren Viertel der Sandschicht angeordnet. Der Schlamm gibt seine Feuchtigkeit an das durchströmende heiße Gas ab, welches nach dem Austritt aus dem Trockner gereinigt werden muß.Other known devices are direct sand fluid bed dryers. Hot air or hot flue gases flow through a layer of sand from the bottom up, which is a Forces fluidization of this sand filling. An inflow floor ensures an even distribution of the inflowing hot gases. Several pumps push the sludge through nozzles directly into the fluidized sand layer. The nozzles are located just above the inflow floor, i.e. in the lower quarter of the sand layer. The sludge releases its moisture to the hot gas flowing through, which has to be cleaned after it has left the dryer.

Des weiteren sind indirekte Kontakttrockner bekannt. Bei diesen erfolgt die Erhitzung des Schlammes indirekt über Heizflächen. Je nach Trocknerbauart haben diese Heizflächen die Form von Scheiben, Paddeln, Walzen u.ä. Die dampf- oder ölbeheizten Heizflächen erwärmen den Schlamm, bis schließlich seine Feuchtigkeit verdampft, ein Ventilator die entstehenden Brüden absaugt und zur Kondensation drückt. Die Schlämme werden entweder auf die Heizflächen dünn aufgetragen und wieder abgeschabt, oder die Heizflächen werden bewegt, bzw. rühren im zu trocknenden Produkt.Indirect contact dryers are also known. In these, the sludge is heated indirectly via heating surfaces. Depending on the type of dryer, these heating surfaces take the form of disks, paddles, rollers, etc. The steam or oil-heated heating surfaces heat the sludge until its moisture evaporates, a ventilator sucks off the vapors and presses them to condense. The sludge is either applied thinly to the heating surfaces and scraped off again, or the heating surfaces are moved or stirred in the product to be dried.

Die Anmelderin bietet ein Verfahren an mit einem indirekten Wirbelschichttrockner. Ein Schlammgranulat wird mit überhitzten Brüden im Kreislauf von unten nach oben in einem Fließbett durchströmt und dabei fluidisiert. Ein Anströmboden mit Düsen verteilt das Gas gleichmäßig auf die ganze Trocknerfläche und gewährleistet eine ausgeglichene Fluidisierung des Granulates. In dieser fluidisierten Schicht sind Heizflächen, z.B. Wärmetauscher, angeordnet, die indirekt die zur Trocknung erforderliche Energie an das Granulat übertragen. Die Heizflächen haben unterschiedliche Formen, wie Glattrohre, Rippenrohre, Platten usw., die mit Dampf oder anderen Wärmeträgern beheizt werden. Ein Granulator erzeugt durch Vermischen von entwässertem Schlamm und einem Teil des bereits getrockneten Schlammes ein feuchtes, stabiles Granulat. Dieses feuchte Granulat wird in die Wirbelschicht eingetragen, wo seine Feuchtigkeit von den durchströmenden, überhitzten Brüden aufgenommen wird. Das getrocknete Granulat verläßt den Wirbelschichttrockner über ein Überlaufwehr oder über einen Austragsapparat. Ein Teil des getrockneten Granulats geht zurück zum Granulator, wo entwässerter Schlamm zu dem feuchten Granulat zugesetzt wird. Die aus dem Wirbelschichttrockner austretenden Brüden nehmen auch feinkörnige Produktpartikel und Staub mit, welche in einem Zyklon oder Filter abgeschieden und in den Granulator eingegeben werden. Die bei der Trocknung verdampfte Wassermenge wird als Brüden aus dem Kreislaufsystem abgezogen und kondensiert oder thermisch behandelt.The applicant offers a method with an indirect fluidized bed dryer. Overheated vapors flow through a sludge granulate in a circuit from bottom to top in a fluidized bed and thereby fluidize it. An inflow floor with nozzles distributes the gas evenly over the entire dryer surface and ensures balanced fluidization of the granules. Heating surfaces, for example heat exchangers, are arranged in this fluidized layer and indirectly transfer the energy required for drying to the granulate. The heating surfaces have different shapes, such as smooth tubes, finned tubes, plates, etc., which are heated with steam or other heat carriers. A granulator creates moist, stable granules by mixing dewatered sludge and part of the already dried sludge. This moist granulate is introduced into the fluidized bed, where its moisture is absorbed by the flowing, overheated vapors. The dried granulate leaves the fluidized bed dryer via an overflow weir or a discharge device. Part of the dried granulate goes back to the granulator, where dewatered sludge is added to the wet granulate. The vapors emerging from the fluidized bed dryer also take fine-grained product particles and dust, which are separated in a cyclone or filter and fed into the granulator. The amount of water evaporated during drying is drawn off as vapors from the circulatory system and condensed or treated thermally.

Der Erfindung lag die Aufgabe zugrunde, ein Verfahren der anfangs angegebenen Art vorzuschlagen, das gegenüber den bisher bekannten wirtschaftlicher ist. Eine Vorbehandlung des Schlammes vor der Trocknung soll sich erübrigen. Das Austragen des Trockengutes aus dem Trockner soll vereinfacht werden. Der Energieaufwand des Verfahrens soll herabgesetzt werden. Eine eingesetzte Apparatur soll einfacher und billiger und dabei weitgehend störungsfrei und wartungsarm sein. Das Verfahren soll kontinuierlich ausführbar sein. Das Produkt soll einen hohen Trockensubstanzanteil aufweisen und sich leicht manipulieren lassen. Eine Umweltbelastung soll weitgehend vermieden werden. Die Belastung der Umgebung soll so gering wie möglich sein.The invention was based on the object of proposing a method of the initially specified type which is more economical than the previously known. A pretreatment of the sludge before drying should not be necessary. The discharge of the dry material from the dryer should be simplified. The energy consumption of the process is to be reduced. The equipment used should be simpler and cheaper, and at the same time largely trouble-free and low-maintenance. The process should be continuously executable. The product should have a high dry matter content and should be easy to manipulate. Environmental pollution should be largely avoided. The environmental impact should be as low as possible.

Diese Aufgabe ist erfindungsgemäß durch Maßnahmen, die in dem kennzeichnenden Teil des Patentanspruchs 1 angegeben sind, erfüllt.This object is achieved according to the invention by measures that are specified in the characterizing part of patent claim 1.

In den Unteransprüchen sind die kennzeichnenden Merkmale einiger vorteilhafter Ausführungsbeispiele des Verfahrens angegeben.The characterizing features of some advantageous exemplary embodiments of the method are specified in the subclaims.

Im weiteren werden der Erfindungsgegenstand und seine Vorteile näher beschrieben und erklärt. Die Beschreibung bezieht sich auf eine Zeichnung, in der die einzige Figur als Beispiel ein Fließschema einer Anlage zur Durchführung der erfindungsgemäßen Trocknung eines entwässerten Klärschlammes aus einer kommunalen Kläranlage zeigt.The subject matter of the invention and its advantages are described and explained in more detail below. The description relates to a drawing, in which the single figure shows as an example a flow diagram of a plant for carrying out the drying according to the invention of a dewatered sewage sludge from a municipal sewage treatment plant.

Der anfallende Schlamm 1 ist nach einer Entwässerung eine organische Substanzen enthaltende Suspension, die noch mit etwa 40% Wasser in pumpfähigem Zustand ist und in einem Silo 12 im Vorrat gehalten wird. Mittels einer Pumpe 13, deren Antriebsmotor 14 mit einer Steuervorrichtung 15 drehzahlregulierbar ist, wird der Schlamm in einen Fließbett-Trockner 2 durch eine Leitung 16 gepumpt, in welchem beim Betrieb eine erhitzte, mittels eines Gasstroms fluidisierte Sandschicht 3 aufgebaut wird.After dewatering, the resulting sludge 1 is a suspension containing organic substances, which is still pumpable with about 40% water and is kept in stock in a silo 12. By means of a pump 13, the drive motor 14 of which can be speed-regulated with a control device 15, the sludge is pumped into a fluidized bed dryer 2 through a line 16, in which a heated sand layer 3 fluidized by means of a gas stream is built up during operation becomes.

Die mit einem Gasstrom fluidisierte Sandschicht 3 wird indirekt mittels in der Sandschicht 3 eingetauchter, ortsfester Wärmetauschkörper 5 erhitzt. Der pumpfähige zu trocknende Schlamm 1 wird unter Druck aus der Pumpe 13 in den Trockner 2 von oben auf die Sandschicht 3 im Gegenstrom zu dem fluidisierenden Gasstrom eingetragen. Die Aufgabestellen sind im obersten Bereich des Trockners 2 vorgesehen. Der fluidisierte Sand reißt den Schlamm sofort nach dessen Austritt aus den Mundstücken einer Verteilvorrichtung mit. Bei diesem Vorgang koaguliert der Schlamm, und es bilden sich Schlammknollen, die sich aufgrund der Fluidisierung in der Sandschicht 3 verteilen und sich in dieser schwebend bewegen. Der heiße Sand und das heiße Fluidisierungsgas geben sukzessive die Wärmeenergie an die feuchten Schlammknollen ab, was zu einer stetigen Erwärmung unter Wasserverdampfung der Schlammknollen sukzessive Schicht für Schicht von der Oberfläche bis zum Kern führt. Der Wasserdampf wird von dem Gasstrom aufgenommen und mit dem Abgasstrom 6 aus dem Trockner 2 abgeführt. Gleichzeitig reibt der fluidisierte Sand ständig an der bereits abgetrockneten Lage der Schlammknollen und schleift den trockenen Schlamm, seine Trockensubstanz, als feinen Staub ab. Dieses Pulverisieren des Schlammes läuft an jeder Schlammknolle bis zur vollständigen Trocknung und Abschleifen zum jeweiligen Kern ab, bis sich sukzessive und schließlich die verbleibende Schlammtrockenmasse zerrieben hat und auf diese Weise pulverisiert wurde. Der aufsteigende fluidisierende Gasstrom reißt neben dem Wasserdampf auch die pulverisierte Schlammtrockenmasse, den Produktstaub mit und trägt so kontinuierlich das Produkt 4 mit dem Abgasstrom 6 aus dem Trockner 2 in Abhängigkeit von der Gasstromgeschwindigkeit heraus.The sand layer 3 fluidized with a gas stream is heated indirectly by means of stationary heat exchange bodies 5 immersed in the sand layer 3. The pumpable sludge 1 to be dried is introduced under pressure from the pump 13 into the dryer 2 from above onto the sand layer 3 in countercurrent to the fluidizing gas stream. The feed points are provided in the uppermost area of the dryer 2. The fluidized sand entrains the sludge immediately after it emerges from the mouthpieces of a distribution device. During this process, the sludge coagulates and sludge bulbs form which, owing to the fluidization, are distributed in the sand layer 3 and move in floating manner in this. The hot sand and the hot fluidizing gas gradually release the thermal energy to the moist mud tubers, which leads to a steady heating, with water evaporation of the mud tubers, successively layer by layer from the surface to the core. The water vapor is taken up by the gas stream and discharged from the dryer 2 with the exhaust gas stream 6. At the same time, the fluidized sand constantly rubs against the already dried-up layer of the mud tubers and grinds off the dry mud, its dry substance, as fine dust. This pulverization of the sludge takes place at each sludge tuber until it has completely dried and been ground down to the respective core, until the remaining sludge dry matter has gradually been crushed and has been pulverized in this way. The rising fluidizing gas stream also entrains the pulverized sludge dry matter and the product dust in addition to the water vapor and thus continuously carries the product 4 with the exhaust gas stream 6 out of the dryer 2 as a function of the gas stream speed.

Die pulverisierte Trockensubstanz 4, die Schlammtrockenmasse also, wird kontinuierlich als Produkt aus dem Abgasstrom 6 in einer Abtrennungsstufe, dem Zyklon 7 abgetrennt. Ein Ventilator 17, in Stromrichtung hinter dem Zyklon 7 saugt den Abgasstrom 6 ab und verhindert damit einen Druckanstieg infolge der Wasserverdampfung und sonstiger Gasentwicklung bei dem Trocknungsvorgang in dem Trockner 2.The pulverized dry substance 4, ie the sludge dry matter, is continuously separated as a product from the exhaust gas stream 6 in a separation stage, the cyclone 7. A fan 17, downstream of the cyclone 7, sucks off the exhaust gas stream 6 and thus prevents an increase in pressure due to water evaporation and other gas development during the drying process in the dryer 2.

Das Erhitzen des Sandes in der Sandschicht 3 und des fluidisierenden Gasstromes erfolgt mittels glatter, horizontal in vorgesehenem Bereich der Sandschicht 3 im fluidisierten Zustand im Trockner 2 angeordneter Wärmetauschrohre 5, die von einem wärmetragenden Medium durchströmt werden. In diesem Beispiel sind Rauchgase 8 das wärmetragende Medium, die in einer Brennkammer 9 bei Verbrennung fossiler Brennstoffe 10 erzeugt werden. Notwendige Luft wird dazu durch eine Leitung 18 geführt. Mindestens ein Teil der Rauchgase wird nach dem Durchströmen der Wärmetauschrohre 5 über einen Ventilator 19 abgesaugt und in die Brennkammer 9 unter Rückgewinnung ihrer Restwärme geführt und so rezirkuliert. Der überschüssige Teil der Rauchgase wird über eine Leitung 20 dem Kreislauf entnommen und durch einen Schalldämpfer 21 abgeführt.The sand in the sand layer 3 and the fluidizing gas stream are heated by means of smooth heat exchange tubes 5, which are arranged horizontally in the provided area of the sand layer 3 in the fluidized state and through which a heat-carrying medium flows. In this example, flue gases 8 are the heat-carrying medium, which are generated in a combustion chamber 9 when fossil fuels 10 are burned. For this purpose, necessary air is led through a line 18. At least some of the flue gases are sucked off by a fan 19 after flowing through the heat exchange tubes 5 and led into the combustion chamber 9 with recovery of their residual heat and thus recirculated. The excess part of the flue gases is removed from the circuit via a line 20 and discharged through a silencer 21.

Der Abgasstrom 6, von dem das Produkt 4 abgetrennt worden ist, wird kontinuierlich zum Fluidisieren der Sandschicht 3, des Fließbettes im Trockner 2, rezirkuliert. Nach dem Zyklon 7 enthält das Gas noch den gesamten im Trockner neu entstandenen Wasserdampf und die sonstigen sich dort entwickelten Gase. Dieses zusätzliche Gasvolumen muß aus dem Gaskreislaufsystem abgezogen werden, um den Druck in dem Gaskreislaufsystem konstant zu halten. Das auf für die Fluidisierung der Schicht 3 im Fließbett-Trockner 2 erforderliche Gasmenge reduzierte Gasvolumen wird über einen Ventilator 22, Verteilkasten 37 und Anströmboden 38 des Trockners 2 geführt, womit der Gaskreislauf schließt.The exhaust gas stream 6, from which the product 4 has been separated, is continuously recirculated to fluidize the sand layer 3, the fluidized bed in the dryer 2. After cyclone 7, the gas still contains all of the water vapor newly generated in the dryer and the other gases developed there. This additional volume of gas must be withdrawn from the gas cycle system in order to keep the pressure in the gas cycle system constant. The gas volume reduced to the amount of gas required for the fluidization of the layer 3 in the fluidized bed dryer 2 is passed through a fan 22, distribution box 37 and inflow base 38 of the dryer 2, which closes the gas circuit.

Das Reduzieren der überschüssigen Gasmenge erfolgt in dem gezeigten Beispiel durch Kondensieren des kondensierbaren Gasüberschusses, vornehmlich des überschüssigen Wasserdampfes in einem Kondensator 11, in den der gesamte Abgasstrom durch eine Leitung 23 geführt wird. Hier erfolgt die Kondensation durch Besprühen des Gases mit Kühlwasser, wofür eine Leitung 24 vorgesehen ist. Das Wasser mit dem Kondensat wird über eine Pumpe 25 und gegebenenfalls über einen Kühler 26 rezirkuliert, wobei ein Überschuß über eine Leitung 27 abgezogen wird. Falls nach dem Kondensator 11 in dem Kreislaufsystem noch ein Überschußvolumen vorliegt, wird eine entsprechende Gasmenge aus dem Kreislaufsystem durch Öffnen eines Ventils 28 über eine Leitung 29 abgezogen. In dem Kreislauf verbleiben Wasserdampf und die beim Trocknen frei werdenden Gase. Bei dem Kreislaufsystem wird so der zum Fluidisieren benutzte Gaskreislauf immer ärmer an freiem Sauerstoff, so daß schließlich der Vorgang im und nach dem Trockner 2 in nicht reaktionsfähiger Atmosphäre erfolgt, wodurch Brenn- oder Explosionsgefahren eliminiert werden.In the example shown, the excess gas quantity is reduced by condensing the condensable excess gas, primarily the excess water vapor in a condenser 11, into which the entire exhaust gas flow is led through a line 23. Here the condensation takes place by spraying the gas with cooling water, for which a line 24 is provided. The water with the condensate is recirculated via a pump 25 and possibly a cooler 26, an excess being drawn off via a line 27. If there is still an excess volume after the condenser 11 in the circulatory system, a corresponding one becomes Gas amount withdrawn from the circulatory system by opening a valve 28 via a line 29. Water vapor and the gases released during drying remain in the circuit. In the circulatory system, the gas circuit used for fluidization becomes ever poorer in free oxygen, so that finally the process in and after the dryer 2 takes place in a non-reactive atmosphere, thereby eliminating the risk of burning or explosion.

Der in dem Zyklon 7 vorhandene Produktstaub weist ca. 90% TS auf. Die nach dem Austragapparat 30 erhaltene, pulverisierte Schlammtrockenmasse 4 wird zu einem Mischer 31 geführt, wo ein Teil des Schlammes 1 aus dem Silo 12 über eine drehzahl-regelbare Pumpe 32 und eine Leitung 33 dem Produktstaub zugegeben wird, womit eine gewünschte Endfeuchtigkeit des Produktes eingestellt wird. Aus dem Mischer 31 führt zu dem Zyklon 7 eine Leitung 34, durch welche die im Mischer 31 entstandenen Gase abgezogen werden. Der Mischer 31 ist mit einem Granulator versehen, wo das die gewünschte Feuchtigkeit aufweisende Produkt zu einem Granulat verarbeitet wird. Auf diese Weise verarbeitetes Endprodukt wird mittels einer Transportvorrichtung 35 verladen. An diese ist auch eine Leitung 36 angeschlossen, die, wenn nötig, zur Entleerung des Trockners 2 dient.The product dust present in the cyclone 7 has about 90% TS. The pulverized sludge dry mass 4 obtained after the discharge apparatus 30 is fed to a mixer 31, where part of the sludge 1 from the silo 12 is added to the product dust via a speed-controllable pump 32 and a line 33, whereby a desired final moisture content of the product is set becomes. A line 34 leads from the mixer 31 to the cyclone 7, through which the gases produced in the mixer 31 are drawn off. The mixer 31 is provided with a granulator, where the product having the desired moisture content is processed into granules. The end product processed in this way is loaded by means of a transport device 35. A line 36 is also connected to this and, if necessary, serves to empty the dryer 2.

In dem Fließschema sind an einigen Stellen verschiedene Druck- bzw. Temperaturmess- und Steuervorrichtungen normkonform dargestellt, die zur Kontrolle und zum Steuern des Verfahrens angewendet werden. Als bekannt und üblich brauchen sie nicht eigens beschrieben zu werden. Mit ihrer Hilfe läßt sich der Betrieb der Anlage mindestens weitgehend automatisieren.At various points in the flow diagram, various pressure or temperature measuring and control devices are shown that conform to the standards and are used to control and control the process. They do not need to be described as known and usual. With their help, the operation of the system can be automated at least to a large extent.

Das Verfahren eignet sich zur Trocknung von verschiedensten Suspensionen, Schlämmen, Pasten und Filterkuchen aus verschiedensten Entwässerungsvorrichtungen. Beschrieben wurde hier das Verfahren zur Trocknung von kommunalen und/oder industriellen Klärschlämmen.The process is suitable for drying a wide variety of suspensions, slurries, pastes and filter cakes from a wide variety of dewatering devices. The process for drying municipal and / or industrial sewage sludge was described here.

Vorteile des erfindungsgemäßen Verfahrens sind folgende:Advantages of the method according to the invention are as follows:

Die Schlämme müssen nicht mehr vor dem Eintrag in die Wirbelschicht strukturiert bzw. granuliert werden. Da der Sand die getrockneten Schlämme zu Staub zerreibt und der Staub mit dem Abgasstrom ausgetragen wird, ist kein komplizierter Austragsmechanismus aus dem Trockner notwendig. Auch die Rezirkulation von Produkt zur Granulierung kann entfallen.The sludges no longer have to be structured or granulated before being introduced into the fluidized bed. Since the sand grinds the dried sludge into dust and the dust is discharged with the exhaust gas stream, no complicated discharge mechanism from the dryer is necessary. The recirculation of product for granulation can also be omitted.

Der Fließbett-Trockner arbeitet in einer chemisch nicht reaktionsfähigen Atmosphäre, welche aus leicht überhitzten Brüden und aus den in den Schlämmen enthaltenen Gasen ohne freien Sauerstoff besteht.The fluid bed dryer works in a chemically non-reactive atmosphere, which consists of slightly overheated vapors and the gases contained in the sludge without free oxygen.

Der im Trockner fluidisierte Sand ist im Trocknungsverfahren ein absolut inertes Material, welches nicht mit dem Schlamm, der Feuchtigkeit oder dem Kreislaufgas chemisch reagiert. Dadurch sind im Trockner Entzündungen durch Überhitzung ausgeschlossen.The sand fluidized in the dryer is an absolutely inert material in the drying process, which does not react chemically with the sludge, moisture or the recycle gas. This prevents inflammation due to overheating in the dryer.

Die Energie zur Trocknung des Materials wird indirekt an das Material bzw. an den fluidisierten Sand übertragen. Dadurch kommt das Heizmedium nicht in direkten Kontakt mit dem Material, bzw. dem Sand. Durch diese indirekte Beheizung fällt die verdampfte Feuchtigkeit als Wasserdampf an und kann als solcher durch einfache Kondensation unter Ausnutzung der Abwärme entsorgt werden.The energy for drying the material is indirectly transferred to the material or to the fluidized sand. As a result, the heating medium does not come into direct contact with the material or the sand. As a result of this indirect heating, the evaporated moisture accumulates as water vapor and can be disposed of as such by simple condensation using the waste heat.

An den horizontalen Glattrohr-Wärmetauschern in der fluidisierten Schicht erfolgt ein äußerst intensiver Energieaustausch mit hoher spezifischen Wärmeleistung. Eine optimale Kornverteilung des Sandes, welche entsprechend dem zu trocknenden Material gewählt wird, erlaubt eine relativ geringere Gasgeschwindigkeit und höhere Wärmeleistung als in einem Fließbett-Trockner mit Produktgranulatschicht. Dadurch verringert sich der elektrische Energiebedarf für den Antrieb der Ventilatoren.The horizontal smooth-tube heat exchangers in the fluidized layer carry out an extremely intensive energy exchange with a high specific heat output. An optimal grain distribution of the sand, which is selected according to the material to be dried, allows a relatively lower gas velocity and higher heat output than in a fluid bed dryer with a product granulate layer. This reduces the electrical energy required to drive the fans.

Die fluidisierte Sandschicht reinigt während des Betriebs ständig die eingetauchten Heizflächen, so daß ihre Leistungsabnahme durch Verschmutzung ausgeschlossen ist.The fluidized sand layer constantly cleans the immersed heating surfaces during operation, so that their loss of performance due to contamination is excluded.

Die horizontalen Glattrohr-Heizflächen sind ortsfest und damit statische Wärmetauscher. Sie können nicht nur mit Dampf oder flüssigen Wärmeträgern beheizt werden, sondern erlauben eine Beheizung mit heißen Gasen wie Luft oder Rauchgase. Die heißen Rauchgase können als Abwärme oder aus einer Brennkammer mit direkter Feuerung anfallen. Anstelle der bisher bei indirekt beheizten Fließbettapparaten üblichen zwei Wärmeübergängen, vom Rauchgas zum Wärmeträgermedium und vom Wärmeträgermedium zum Produkt, ist hier nur ein Wärmeübergang vom Rauchgas zum Produkt erforderlich. Dadurch erhöht sich der verfügbare Temperaturgradient bzw. erniedrigt sich die Rauchgasaustrittstemperatur und damit die Energieverluste. Es entfällt so auch der bisherige Aufwand für die zweifachen Wärmetauschflächen.The horizontal smooth tube heating surfaces are stationary and therefore static heat exchangers. They can not only be heated with steam or liquid heat carriers, but also allow heating with hot gases such as air or flue gases. The hot flue gases can be generated as waste heat or from a combustion chamber with direct firing. Instead of the two heat transfers that have been customary in the case of indirectly heated fluidized bed apparatuses, from the flue gas to the heat transfer medium and from the heat transfer medium to the product, only one heat transfer from the flue gas to the product is required here. This increases the available temperature gradient or lowers the flue gas outlet temperature and thus the energy losses. This also eliminates the previous effort for the double heat exchange surfaces.

Durch die inerte Sandschicht bleibt der Trockner absolut unempfindlich bei Temperaturschwankungen bzw. Überhitzungen. Die Sandschicht erlaubt auch eine rasche Aufheizung und ermöglicht das Anfahren der Anlage sofort mit Nennleistung. Auch beim Abstellen der Anlage ist ein zwangsweises Nachheizen für die inerte Sandfüllung absolut unbedenklich.Due to the inert sand layer, the dryer remains absolutely insensitive to temperature fluctuations or overheating. The layer of sand also allows rapid heating and enables the system to be started up immediately at nominal output. When the system is switched off, forced reheating for the inert sand filling is absolutely harmless.

Das staubförmige Staubprodukt läßt sich entsprechend einer weiteren Verwendung auf einen gewünschten Feuchtigkeitsgehalt von 50% bis 90% TS einstellen.The dust-like dust product can be adjusted to a desired moisture content of 50% to 90% DM according to a further use.

Claims (9)

1. Method for drying a sludge (1) containing organic substances which is produced after dewatering a suspension, in a fluidised bed dryer (2) with a heated layer of sand (3) which is fluidised by means of a stream of gas, to obtain the dry substance (4) of the sludge (1) as a product, characterised
by indirect heating of the layer of sand (3) by means of fixed heat exchange bodies (5) sunk into the layer (3), by continuous charging of the sludge (1) in a pumpable state under pressure into the dryer (2) from the top onto the layer (3) in a counter-current to the fluidising gas stream for coagulating the sludge to form sludge lumps in the heated fluidised layer (3),
by successive drying of the sludge lumps in the layer (3) with loss of their moisture to the fluidising gas stream and with successive abrasion of the layers of the sludge lumps which have already been dried by the fluidised sand of the layer (3) for powdering the dry substance (4) of the sludge,
by continuously discharging the powdered dry substance (4) from the layer (3) with the stream of waste gas (6) from the dryer (2),
and by continuous separation (7) of the powdered dry substance (4) as a product from the stream of waste gas (6).
2. Method according to Claim 1, characterised in that the heating of the sand layer (3) takes place by means of smooth heat exchange pipes (5) arranged horizontally in the dryer (1), through which pipes a heat-bearing medium flows.
3. Method according to Claim 2, characterised in that flue gases (8) from a combustion chamber (9) in which fossil fuels (10) are burned are used as the heat-bearing medium.
4. Method according to Claim 3, characterised in that after flowing through the heat-exchange pipes (5) at least part of the flue gases is passed back into the combustion chamber (9) to recover their residual heat and is recirculated.
5. Method according to Claim 1, characterised in that the stream of waste gas (6) after the separation (7) of the powdered dry substance (4) is recycled for fluidising the layer (3), the volume of the waste gases being reduced by the excess volume of gas produced during the drying in the dryer (2) to the volume to be used for the fluidising in the dryer (2).
6. Method according to Claim 5, characterised in that the reduction of the volume of waste gas takes place by condensing the condensable constituents in the waste gas, principally the volume of the water vapour additionally produced upon drying, with the non-condensable gas constituents remaining in the circuit, which produces a chemically non-reactive gas mixture of water vapour and the other gas constituents which are released upon drying, which prevents oxidation of the sludge during drying.
7. Method according to Claim 1, characterised in that the dry substance dust (4), which may have approximately 70% dry substance after separation (7), is processed into a mixture of desired humidity by admixing part of the sludge (1) which is produced.
8. Method according to Claim 7, characterised in that the mixture of desired humidity is processed into granules.
9. Method according to Claim 1, characterised in that the sludge (1) which is to be dried is a sewage sludge from domestic or industrial waste water.
EP89120565A 1989-01-27 1989-11-07 Sludge drying process Expired - Lifetime EP0379657B1 (en)

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CA1146813A (en) * 1980-06-30 1983-05-24 456577 Ontario Limited Apparatus and method for treating sewage sludge
DE3047060C2 (en) * 1980-12-13 1985-03-07 Bergwerksverband Gmbh, 4300 Essen Method and device for drying and burning sludge
US4507127A (en) * 1981-12-21 1985-03-26 Nippon Furnace Kogyo Co., Ltd. System for recovering resources from sludge
US4628833A (en) * 1983-04-11 1986-12-16 The Garrett Corporation Fluid bed hog fuel dryer
FI79753C (en) * 1986-01-31 1990-02-12 Valtion Teknillinen Process for drying powdered, granular, particulate or equivalent material
US4787323A (en) * 1987-08-12 1988-11-29 Atlantic Richfield Company Treating sludges and soil materials contaminated with hydrocarbons

Also Published As

Publication number Publication date
EP0379657A1 (en) 1990-08-01
ATE67299T1 (en) 1991-09-15
DE3902446C1 (en) 1990-07-05
CA2006507A1 (en) 1990-07-27
CA2006507C (en) 1994-02-08
FI895755A0 (en) 1989-12-01
DK21590A (en) 1990-07-30
DK21590D0 (en) 1990-01-26
US4970803A (en) 1990-11-20
ES2024707B3 (en) 1992-03-01
JPH02237700A (en) 1990-09-20
NO894789L (en) 1990-07-30
NO894789D0 (en) 1989-11-30

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