EP0434662B1 - Process for bleaching cellulosic materials and plant for carrying out the process - Google Patents

Process for bleaching cellulosic materials and plant for carrying out the process Download PDF

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Publication number
EP0434662B1
EP0434662B1 EP90890325A EP90890325A EP0434662B1 EP 0434662 B1 EP0434662 B1 EP 0434662B1 EP 90890325 A EP90890325 A EP 90890325A EP 90890325 A EP90890325 A EP 90890325A EP 0434662 B1 EP0434662 B1 EP 0434662B1
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Prior art keywords
ozone
bleaching
absorption column
strong water
pulp
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EP90890325A
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German (de)
French (fr)
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EP0434662A1 (en
Inventor
Karl Dr. Schwarzl
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Schmidding-Werke Wilhelm Schmidding & Co GmbH
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Schmidding-Werke Wilhelm Schmidding & Co GmbH
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
    • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone

Definitions

  • the invention relates to a method for bleaching cellulose-containing materials, in particular cellulose, by means of ozone and to a plant for carrying out the method.
  • ozone is an excellent bleach for pulp. So from FR-A-1 441 787 an ozone bleaching is known, wherein ozone-containing gas, which comes from an ozonizer and contains 2.5 to 18 mg O3 per liter, saturated with water vapor and then brought into contact with the pulp to be bleached .
  • the pulp to be bleached is first brought to high consistencies of over 25% and then exposed to the gaseous ozone in flake form.
  • the pulp is placed in a reaction vessel through which an ozone-containing gas flows. The pulp is then washed in order to separate the undesired degradation products that are formed during bleaching.
  • This method has the disadvantage that separate facilities have to be created for the thickening and for the dilution of the pulp.
  • the pulp is bleached unevenly because the pulp flakes have a high consistency.
  • Another method is to bleach pulp at low consistencies of around 3% (low consistency method).
  • Gas containing ozone is passed through a pulp slurry. Because of the large dilution, the process requires the handling of large amounts of liquid and, on an industrial scale, a correspondingly high outlay on equipment.
  • the invention aims to avoid these disadvantages and has as its object to provide an improved method for bleaching cellulose-containing materials, in particular cellulose, by means of ozone.
  • the materials suspended in an aqueous medium contain a solution of ozone in an aqueous medium (strong water) with a content of 30 to 300 gO3, preferably 100 to 150 gO3 per m3 of aqueous medium, is fed under pressure and mixed with the former medium in a mixing device (5), whereupon the mixture is passed through a reaction vessel (7), the bleached material is separated from the bleaching liquor, and any present Residual ozone is destroyed, and the process according to the invention can also be carried out continuously.
  • an aqueous medium strong water
  • ozone is thus first dissolved in an aqueous medium, a concentrated ozone solution being obtained which is referred to as heavy water and which is mixed under pressure with the suspension of the material to be bleached.
  • the ozone-containing gas used being one which contains at least 100 g of ozone / Nm3 of oxygen and where The ozone solution and the remaining oxygen are withdrawn from the column and the remaining oxygen is dried and recycled to produce ozone-containing gas.
  • a preferred embodiment of the process according to the invention is characterized in that an overpressure between 5 and 10 bar is provided in the absorption column, and an overpressure between 2 and 5 bar is provided in the mixing device and in the reaction vessel, the overpressure in the absorption column being higher than in the mixing device and is set in the reaction vessel.
  • the bleaching process according to the invention is best carried out at a temperature below 60 ° C., preferably between 25 and 40 ° C.
  • a further embodiment of the process according to the invention is characterized in that a part of the bleaching liquor is pretreated with ozone after the bleached material has been separated off and is returned to the absorption column for the production of heavy water.
  • the process according to the invention has the advantage that cellulose-containing materials with a higher consistency than is possible with the low consistency process can be bleached, the consistency being up to 15% without a noticeable loss in bleaching quality.
  • the bleach can be used much better, since the required amount of ozone can be calculated precisely.
  • the low-consistency process by which ozone is passed in gaseous form through the pulp slurry inevitably leads to loss of ozone.
  • the invention also relates to a plant for carrying out the method according to the invention, with a device for producing a cellulose suspension, at least one bleaching tower as a reaction vessel, a device for generating an ozone-containing gas, filters, pumps and lines for connecting the plant parts, and is characterized in that the device for generating ozone is connected in terms of line to an absorption column for producing strong water, a mixing device is provided for mixing the pulp suspension with the strong water, the mixing device being connected to the absorption column via a strong water line, and a bleaching tower for receiving the mixture of pulp suspension and heavy water is provided, the absorption column, mixing device and bleaching tower being equipped with devices for generating and adjusting an overpressure.
  • the bleaching tower can be connected to a filter for separating the bleached pulp from the bleaching liquor, which filter is a bleaching liquor line for recycling used Has bleaching liquor in the device for producing the pulp suspension.
  • the bleaching liquor line is expediently connected via a branch to the absorption column, in which branch a heat exchanger is provided, which heat exchanger is also connected to the heavy water line in order to enable heat transfer from the bleaching liquor to the heavy water.
  • Another embodiment of the system according to the invention is characterized in that the absorption column is connected to a return line to the ozone generator in order to return undissolved oxygen from the absorption column to the ozone generator, a dryer preferably being present in the return line.
  • the absorption column 2 is connected via the high-pressure water line 4 via the heat exchanger 22 and the valve 23 to the mixer 5, which in turn is connected to the lower end of a bleaching tower 7 via the feed line 6.
  • an ozone line 8 leads to the residual ozone destroyer 9 and a discharge line 10 via a pump 11 to a filter 12 which is connected to a filter 14 via the bleach liquor line 13.
  • a branch 13a leads from the bleaching liquor line 13 via the heat exchanger 22 to the return water pretreatment 25, which in turn is connected to the top of the absorption column 2 via the return water line 15 and the heat exchanger 24, with supply and discharge lines 24a, 24b for the heat transfer medium is.
  • the method according to the invention is carried out by first filtering e.g. a pulp with a consistency between 10 and 15% is prepared. This pulp is transported by the pump 16 through the pulp line 17 into the mixer 5, where it is intimately mixed with strong water to form a solution with a consistency of between 2 and 5%.
  • the heavy water is formed in the absorption column 2 by return water, which is fed from the return water pretreatment 25 via the return water line 15 into the head of the absorption column 2, having previously been brought to the temperature required for the production of heavy water in the heat exchanger 24 and is treated with ozone-containing gas at an overpressure of up to 8 bar.
  • This gas is produced in the ozone generator 1 from oxygen, contains over 100 g O3 / Nm3 O2 and is introduced in the ozone line 18 from the ozone generator 1 into the lower end of the absorption column 2. Unreacted gas can be fed to the ozone generator 1 via the return line 19 after it has passed the dryer 3.
  • the return line 19 opens into the oxygen line 20, via which the ozone generator 1 is supplied with oxygen.
  • the ozone content of the heavy water can be adjusted between 30 and 300 g O3 / m3 water by a suitable choice of pressure and temperature conditions.
  • the heavy water is removed from the lower end of the absorption column 2 and fed to the mixer 5 via the valve 23 via the heavy water line 4.
  • the valve 23 reduces the pressure, which is between 5 and 10 bar in the heavy water line, so that it is between 2 and 5 bar in the mixer 5 and in the bleaching tower 7.
  • the pulp / heavy water mixture is then introduced into the lower end of the bleaching tower 7 and transported to its upper end over a period of approximately 20 minutes. During this time, the pulp actually bleaches.
  • Any excess ozone present at the head of the bleaching tower 7 can be fed to the residual ozone destroyer 9 via the ozone line 8.
  • the bleached pulp is also applied at the head of the bleaching tower 7 and introduced by the pump 11 through the discharge line 10 into the filter 12 for separating the bleached pulp from the bleaching liquor.
  • the removal of the bleached pulp is indicated at 21.
  • the bleaching liquor can be fed back into the filter 14 to adjust the consistency for further pulp to be bleached.
  • it can also be used for the production of strong water, although it must be pretreated with ozone before being introduced into the absorption column 2. This possible use is indicated in the drawing by the branch line 13a, the return water pretreatment 25 and the return water line 15.
  • the ozone for pretreatment is taken from the ozone line 18.
  • a heat exchanger 22 is expediently provided in the branch line 13a in order to be able to recover heat from the bleaching liquor (approx. 50 ° C.). With this heat, the heavy water in the heavy water line 4 is tempered, preferably to a temperature of about 46 ° C.
  • the process according to the invention can also be carried out with several successive bleaching stages.
  • at least one further bleaching tower is connected downstream of the bleaching tower 7.
  • the pulp suspension is expediently thickened.
  • a pretreated pulp with a consistency of 12% was treated with an amount of 2 kg of ozone per ton of pulp.
  • the ozone solution strong water
  • the ozone solution was mixed into the pulp suspension in a mixer prior to entering the upward bleaching tower.
  • the mixture with the pulp resulted in an ozone concentration of 61.86 g / m3.
  • the initially rapid ozone consumption and the hydrostatic pressure in the bleaching vessel prevented the ozone from rapidly degassing in the initial phase of the bleaching, so that there was no breakdown through the amount of pulp to be bleached.
  • a pre-treated pulp with a consistency of 14% was treated with 4 kg of ozone per ton of pulp.
  • the consistency during bleaching was 2%.
  • the strong water contained 93.3g O3 / m3.
  • the overpressure in the bleaching tower was 4 bar.
  • the treatment with ozone reduced the kappa number by 2 units and also achieved a whiteness gain of 5 points.
  • a pre-treated pulp with a consistency of 14% was bleached with 10 kg of ozone per ton of pulp. In this case, the bleaching was done in two stages.
  • the pulp was brought to a consistency of 2% by adding the ozone solution. After bleaching for 20 minutes in an upward tower under pressure, the suspension was thickened to 5%. Subsequently, the ozone solution was mixed in again to a consistency of 2%. The concentration of the ozone solution was 137.2g O3 / m3.
  • the second bleaching stage was also carried out in a bleaching tower working under pressure. In both cases the bleaching time was 20 minutes. In this case a kappa reduction of 7 units could be achieved with a whiteness increase of 6 points.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Polysaccharides And Polysaccharide Derivatives (AREA)
  • Detergent Compositions (AREA)
  • General Preparation And Processing Of Foods (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

A process for bleaching cellulose-containing materials, in particular pulp, by means of ozone is characterised in that a solution of ozone in an aqueous medium (rich water) containing 30 to 300 g of O3, preferably 100 to 150 g of O3, per m<3> of aqueous medium is fed under pressure to the materials suspended in an aqueous medium and mixed in a mixing device (5) with the latter medium, thereupon the mixture is passed through a reaction vessel (7), the bleached material is separated from the bleaching liquor and any residual ozone which may be present is destroyed.

Description

Die Erfindung betrifft ein Verfahren zum Bleichen von cellulosehältigen Materialien, insbesondere von Zellstoff, mittels Ozon sowie eine Anlage zur Durchführung des Verfahrens.The invention relates to a method for bleaching cellulose-containing materials, in particular cellulose, by means of ozone and to a plant for carrying out the method.

Aus der US-A-4 089 737 ist ein Verfahren zum Bleichen von Cellulose mit Sauerstoff bekannt, der in einer Lauge gelöst wird.From US-A-4 089 737 a method for bleaching cellulose with oxygen is known, which is dissolved in an alkali.

Es ist weiters bekannt, daß Ozon ein ausgezeichnetes Bleichmittel für Zellstoff darstellt. So ist aus der FR-A-1 441 787 eine Ozonbleiche bekannt, wobei ozonhältiges Gas, das aus einem Ozonisator stammt und pro Liter 2,5 bis 18 mg O₃ enthält, mit Wasserdampf gesättigt und anschließend mit dem zu bleichenden Papierstoff in Kontakt gebracht wird.It is also known that ozone is an excellent bleach for pulp. So from FR-A-1 441 787 an ozone bleaching is known, wherein ozone-containing gas, which comes from an ozonizer and contains 2.5 to 18 mg O₃ per liter, saturated with water vapor and then brought into contact with the pulp to be bleached .

An sich wird nach dem sogenannten Hochkonsistenzverfahren der zu bleichende Zellstoff zunächst auf hohe Stoffdichten von über 25% gebracht und dann in Flockenform dem gasförmigen Ozon ausgesetzt. Dazu wird der Zellstoff in ein Reaktionsgefäß eingebracht, das von einem ozonhältigen Gas durchströmt wird. Anschließend wird der Zellstoff gewaschen, um die beim Bleichen entstandenen unerwünschten Abbauprodukte abzutrennen.According to the so-called high consistency process, the pulp to be bleached is first brought to high consistencies of over 25% and then exposed to the gaseous ozone in flake form. For this purpose, the pulp is placed in a reaction vessel through which an ozone-containing gas flows. The pulp is then washed in order to separate the undesired degradation products that are formed during bleaching.

Dieses Verfahren hat den Nachteil, daß für die Eindickung und für die Verdünnung des Zellstoffes eigene Einrichtungen geschaffen werden müssen. Außerdem wird der Zellstoff ungleichmäßig gebleicht, weil die Zellstoffflocken eine hohe Stoffdichte aufweisen.This method has the disadvantage that separate facilities have to be created for the thickening and for the dilution of the pulp. In addition, the pulp is bleached unevenly because the pulp flakes have a high consistency.

Nach einem anderen Verfahren wird Zellstoff bei niedrigen Stoffdichten von etwa 3% gebleicht (Niederkonsistenzverfahren). Dabei wird ozonhältiges Gas durch eine Zellstoffaufschlämmung geleitet. Das Verfahren erfordert wegen der großen Verdünnung die Handhabung großer Flüssigkeitsmengen und großtechnisch einen entsprechend hohen apparativen Aufwand.Another method is to bleach pulp at low consistencies of around 3% (low consistency method). Gas containing ozone is passed through a pulp slurry. Because of the large dilution, the process requires the handling of large amounts of liquid and, on an industrial scale, a correspondingly high outlay on equipment.

Die Erfindung bezweckt die Vermeidung dieser Nachteile und stellt sich die Aufgabe, ein verbessertes Verfahren zum Bleichen von cellulosehältigen Materialien, insbesondere von Zellstoff, mittels Ozon zur Verfügung zu stellen.The invention aims to avoid these disadvantages and has as its object to provide an improved method for bleaching cellulose-containing materials, in particular cellulose, by means of ozone.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß den in wässerigem Medium suspendierten Materialien eine Lösung von Ozon in einem wässerigen Medium (Starkwasser) mit einem Gehalt von 30 bis 300 gO₃, vorzugsweise 100 bis 150 gO₃ pro m³ wässerigen Mediums, unter Druck zugeführt und mit ersterem Medium in einer Mischeinrichtung (5) vermischt wird, worauf die Mischung durch ein Reaktionsgefäß (7) geleitet, das gebleichte Material von der Bleichflotte getrennt, und eventuell vorhandenes Restozon vernichtet wird, wobei das erfindungsgemäße Verfahren auch kontinuierlich durchgeführt werden kann.This object is achieved according to the invention in that the materials suspended in an aqueous medium contain a solution of ozone in an aqueous medium (strong water) with a content of 30 to 300 gO₃, preferably 100 to 150 gO₃ per m³ of aqueous medium, is fed under pressure and mixed with the former medium in a mixing device (5), whereupon the mixture is passed through a reaction vessel (7), the bleached material is separated from the bleaching liquor, and any present Residual ozone is destroyed, and the process according to the invention can also be carried out continuously.

Beim erfindungsgemäßen Verfahren wird somit zuerst Ozon in einem wässerigen Medium gelöst, wobei eine konzentrierte Ozonlösung erhalten wird, welche als Starkwasser bezeichnet wird und welche unter Druck mit der Suspension des zu bleichenden Materials vermischt wird.In the process according to the invention, ozone is thus first dissolved in an aqueous medium, a concentrated ozone solution being obtained which is referred to as heavy water and which is mixed under pressure with the suspension of the material to be bleached.

Es hat sich als vorteilhaft erwiesen, das Starkwasser in einer Absorptionskolonne zu erzeugen, in der ein wässeriges Medium unter Druck mit einem ozonhältigen Gas behandelt wird, wobei als ozonhältiges Gas ein solches verwendet wird, welches mindestens 100 g Ozon/Nm³ Sauerstoff enthält und wobei die Ozonlösung und der restliche Sauerstoff aus der Kolonne abgezogen und der restliche Sauerstoff getrocknet und zur Herstellung von ozonhältigem Gas recycliert wird.It has proven to be advantageous to generate the strong water in an absorption column in which an aqueous medium is treated under pressure with an ozone-containing gas, the ozone-containing gas used being one which contains at least 100 g of ozone / Nm³ of oxygen and where The ozone solution and the remaining oxygen are withdrawn from the column and the remaining oxygen is dried and recycled to produce ozone-containing gas.

Eine bevorzugte Ausführungsform des erfindungsgemäßen Verfahrens ist dadurch gekennzeichnet, daß in der Absorptionskolonne ein Überdruck zwischen 5 und 10 bar, und in der Mischeinrichtung und im Reaktionsgefäß ein Überdruck zwischen 2 und 5 bar vorgesehen wird, wobei der Überdruck in der Absorptionskolonne höher als in der Mischeinrichtung und im Reaktionsgefäß eingestellt wird.A preferred embodiment of the process according to the invention is characterized in that an overpressure between 5 and 10 bar is provided in the absorption column, and an overpressure between 2 and 5 bar is provided in the mixing device and in the reaction vessel, the overpressure in the absorption column being higher than in the mixing device and is set in the reaction vessel.

Das erfindungsgemäße Bleichverfahren wird am besten bei einer Temperatur unter 60°C, vorzugsweise zwischen 25 und 40°C, durchgeführt.The bleaching process according to the invention is best carried out at a temperature below 60 ° C., preferably between 25 and 40 ° C.

Eine weitere Ausführungsform des erfindungsgemäßen Verfahrens ist dadurch gekennzeichnet, daß ein Teil der Bleichflotte nach Abtrennen des gebleichten Materials mit Ozon vorbehandelt und für die Starkwasserherstellung in die Absorptionskolonne rückgeführt wird.A further embodiment of the process according to the invention is characterized in that a part of the bleaching liquor is pretreated with ozone after the bleached material has been separated off and is returned to the absorption column for the production of heavy water.

Das erfindungsgemäße Verfahren hat den Vorteil, daß cellulosehältige Materialien mit einer höheren Stoffdichte, als dies nach dem Niederkonsistenzverfahren möglich ist, gebleicht werden können, wobei die Stoffdichte bis zu 15 % betragen kann, ohne daß ein merklicher Verlust an Bleichqualität eintritt.The process according to the invention has the advantage that cellulose-containing materials with a higher consistency than is possible with the low consistency process can be bleached, the consistency being up to 15% without a noticeable loss in bleaching quality.

Weiters kann durch die Zugabe des Ozons in gelöster Form das Bleichmittel viel besser ausgenützt werden, da die benötigte Ozonmenge genau berechnet werden kann. Beim Niederkonsistenzverfahren, nach dem Ozon in gasförmiger Form durch die Zellstoffaufschlämmung geleitet wird, kommt es unweigerlich zu Ozon-Verlusten.Furthermore, by adding the ozone in dissolved form, the bleach can be used much better, since the required amount of ozone can be calculated precisely. The low-consistency process by which ozone is passed in gaseous form through the pulp slurry inevitably leads to loss of ozone.

Werden beim erfindungsgemäßen Verfahren größere Mengen an Ozon benötigt, so hat es sich als günstig erwiesen, die Bleichung in zwei Stufen durchzuführen. Für diese zweite Bleichstufe wird die Suspension eingedickt und dann nochmals mit frischem Starkwasser nachbehandelt.If larger amounts of ozone are required in the process according to the invention, it has proven advantageous to carry out the bleaching in two stages. For this second bleaching stage, the suspension is thickened and then treated again with fresh strong water.

Die Erfindung betrifft auch eine Anlage zur Durchführung des erfindungsgemäßen Verfahrens, mit einer Einrichtung zur Herstellung einer Zellstoffsuspension, mindestens einem Bleichturm als Reaktionsgefäß, einer Einrichtung zur Erzeugung eines ozonhältigen Gases, Filtern, Pumpen und Leitungen zur Verbindung der Anlagenteile, und ist dadurch gekennzeichnet, daß die Einrichtung zur Erzeugung von Ozon mit einer Absorptionskolonne zur Herstellung von Starkwasser leitungsmäßig verbunden ist, eine Mischeinrichtung zum Mischen der Zellstoffsuspension mit dem Starkwasser vorgesehen ist, wobei die Mischeinrichtung über eine Starkwasserleitung mit der Absorptionskolonne verbunden ist, und ein Bleichturm zur Aufnahme der Mischung von Zellstoffsuspension und Starkwasser vorgesehen ist, wobei Absorptionskolonne, Mischeinrichtung und Bleichturm mit Einrichtungen zur Erzeugung und Einstellung eines Überdruckes ausgestattet sind.The invention also relates to a plant for carrying out the method according to the invention, with a device for producing a cellulose suspension, at least one bleaching tower as a reaction vessel, a device for generating an ozone-containing gas, filters, pumps and lines for connecting the plant parts, and is characterized in that the device for generating ozone is connected in terms of line to an absorption column for producing strong water, a mixing device is provided for mixing the pulp suspension with the strong water, the mixing device being connected to the absorption column via a strong water line, and a bleaching tower for receiving the mixture of pulp suspension and heavy water is provided, the absorption column, mixing device and bleaching tower being equipped with devices for generating and adjusting an overpressure.

Der Bleichturm kann über eine Ableitung mit einem Filter zur Abtrennung des gebleichten Zellstoffes von der Bleichflotte verbunden sein, welches Filter eine Bleichflottenleitung zur Rückführung von gebrauchter Bleichflotte in die Einrichtung zur Herstellung der Zellstoffsuspension aufweist.The bleaching tower can be connected to a filter for separating the bleached pulp from the bleaching liquor, which filter is a bleaching liquor line for recycling used Has bleaching liquor in the device for producing the pulp suspension.

Die Bleichflottenleitung ist zweckmäßigerweise über eine Abzweigung mit der Absorptionskolonne leitungsmäßig verbunden, in welcher Abzweigung ein Wärmeaustauscher vorgesehen ist, welcher Wärmeaustauscher auch mit der Starkwasserleitung in Verbindung steht, um einen Wärmeübergang von der Bleichflotte zum Starkwasser zu ermöglichen.The bleaching liquor line is expediently connected via a branch to the absorption column, in which branch a heat exchanger is provided, which heat exchanger is also connected to the heavy water line in order to enable heat transfer from the bleaching liquor to the heavy water.

Eine andere Ausführungsform der erfindungsgemäßen Anlage ist dadurch gekennzeichnet, daß die Absorptionskolonne mit einer Rückleitung zum Ozongenerator verbunden ist, um nicht gelösten Sauerstoff aus der Absorptionskolonne dem Ozongenerator zurückzuführen, wobei in der Rückleitung vorzugsweise ein Trockner vorhanden ist.Another embodiment of the system according to the invention is characterized in that the absorption column is connected to a return line to the ozone generator in order to return undissolved oxygen from the absorption column to the ozone generator, a dryer preferably being present in the return line.

Eine bevorzugte Ausführungsform der Erfindung wird anhand der Zeichnung näher erläutert, die eine Ausführungsform der erfindungsgemäßen Anlage grob schematisch zeigt.A preferred embodiment of the invention is explained in more detail with reference to the drawing, which roughly schematically shows an embodiment of the system according to the invention.

Mit 1 ist ein Ozongenerator bezeichnet, mit 2 eine Absorptionskolonne und mit 3 ein Trockner. Die Absorptionskolonne 2 ist über die Starkwasserleitung 4 über den Wärmetauscher 22 und das Ventil 23 mit dem Mischer 5 verbunden, der seinerseits über die Zufuhrleitung 6 mit dem unteren Ende eines Bleichturmes 7 in Verbindung steht. Vom Kopf des Bleichturmes 7 führt eine Ozonleitung 8 zum Restozon-Vernichter 9 und eine Ableitung 10 über eine Pumpe 11 zu einem Filter 12, das über die Bleichflottenleitung 13 mit einem Filter 14 in Verbindung steht. Von der Bleichflottenleitung 13 führt eine Abzweigung 13a über den Wärmetauscher 22 zur Rückwasser-Vorbehandlung 25, die wiederum mit dem Kopf der Absorptionskolonne 2 über die Rückwasser-Leitung 15 und den Wärmetauscher 24, mit Zu- und Ableitung 24a, 24b für das Wärmeträgermedium, verbunden ist.1 denotes an ozone generator, 2 an absorption column and 3 a dryer. The absorption column 2 is connected via the high-pressure water line 4 via the heat exchanger 22 and the valve 23 to the mixer 5, which in turn is connected to the lower end of a bleaching tower 7 via the feed line 6. From the head of the bleaching tower 7, an ozone line 8 leads to the residual ozone destroyer 9 and a discharge line 10 via a pump 11 to a filter 12 which is connected to a filter 14 via the bleach liquor line 13. A branch 13a leads from the bleaching liquor line 13 via the heat exchanger 22 to the return water pretreatment 25, which in turn is connected to the top of the absorption column 2 via the return water line 15 and the heat exchanger 24, with supply and discharge lines 24a, 24b for the heat transfer medium is.

Das erfindungsgemäße Verfahren wird durchgeführt, indem zunächst im Filter 14 z.B. ein Zellstoff mit einer Stoffdichte zwischen 10 und 15% bereitet wird. Dieser Zellstoff wird von der Pumpe 16 durch die Zellstoffleitung 17 in den Mischer 5 transportiert und dort mit Starkwasser innig zu einer Lösung mit einer Stoffdichte zwischen 2 und 5 % vermischt.The method according to the invention is carried out by first filtering e.g. a pulp with a consistency between 10 and 15% is prepared. This pulp is transported by the pump 16 through the pulp line 17 into the mixer 5, where it is intimately mixed with strong water to form a solution with a consistency of between 2 and 5%.

Das Starkwasser wird in der Absorptionskolonne 2 gebildet, indem Rückwasser, das von der Rückwasser-Vorbehandlung 25 über die Rückwasser-Leitung 15 in den Kopf der Absorptionskolonne 2 eingespeist wird, wobei es vorher im Wärmetauscher 24 auf die zur Herstellung von Starkwasser erforderliche Temperatur gebracht wurde und bei einem Überdruck bis zu 8 bar mit ozonhältigem Gas behandelt wird. Dieses Gas wird im Ozongenerator 1 aus Sauerstoff hergestellt, enthält über 100 g O₃/Nm³ O₂ und wird in der Ozonleitung 18 vom Ozongenerator 1 in das untere Ende der Absorptionskolonne 2 eingebracht. Nicht umgesetztes Gas kann über die Rückleitung 19 dem Ozongenerator 1 zugeführt werden, nachdem es den Trockner 3 passiert hat. Die Rückleitung 19 mündet in die Sauerstoff-Leitung 20, über welche der Ozongenerator 1 mit Sauerstoff versorgt wird. Der Ozongehalt des Starkwassers kann durch geeignete Wahl der Druck- und Temperaturbedingungen zwischen 30 und 300 g O₃/m³ Wasser eingestellt werden.The heavy water is formed in the absorption column 2 by return water, which is fed from the return water pretreatment 25 via the return water line 15 into the head of the absorption column 2, having previously been brought to the temperature required for the production of heavy water in the heat exchanger 24 and is treated with ozone-containing gas at an overpressure of up to 8 bar. This gas is produced in the ozone generator 1 from oxygen, contains over 100 g O₃ / Nm³ O₂ and is introduced in the ozone line 18 from the ozone generator 1 into the lower end of the absorption column 2. Unreacted gas can be fed to the ozone generator 1 via the return line 19 after it has passed the dryer 3. The return line 19 opens into the oxygen line 20, via which the ozone generator 1 is supplied with oxygen. The ozone content of the heavy water can be adjusted between 30 and 300 g O₃ / m³ water by a suitable choice of pressure and temperature conditions.

Bei einem Druck von 7 bar und einer Ozon-Konzentration im ozonhältigen Gas von 130 g O₃/Nm³ sind je nach Temperatur die folgenden O₃-Konzentrationen im Starkwasser erreichbar: Temperatur (°C) O₃-Konzentration im Starkwasser (g O₃/m³ H₂O) 15 290 20 215 25 195 30 150 35 110 40 70 50 30 At a pressure of 7 bar and an ozone concentration in the ozone-containing gas of 130 g O₃ / Nm³ the following O₃ concentrations can be reached in the strong water depending on the temperature: Temperature (° C) O₃ concentration in heavy water (g O₃ / m³ H₂O) 15 290 20th 215 25th 195 30th 150 35 110 40 70 50 30th

Das Starkwasser wird am unteren Ende der Absorptionskolonne 2 entnommen und über die Starkwasserleitung 4 dem Mischer 5 über das Ventil 23 zugeführt. Mit dem Ventil 23 wird der Druck, der in der Starkwasserleitung zwischen 5 und 10 bar beträgt, reduziert, sodaß er im Mischer 5 und im Bleichturm 7 zwischen 2 und 5 bar beträgt.The heavy water is removed from the lower end of the absorption column 2 and fed to the mixer 5 via the valve 23 via the heavy water line 4. The valve 23 reduces the pressure, which is between 5 and 10 bar in the heavy water line, so that it is between 2 and 5 bar in the mixer 5 and in the bleaching tower 7.

Die Zellstoff/Starkwasser-Mischung wird anschließend in das untere Ende des Bleichturmes 7 eingebracht und während einer Zeitdauer von etwa 20 min zu seinem oberen Ende transportiert. Während dieser Zeit kommt es zur eigentlichen Bleichung des Zellstoffes.The pulp / heavy water mixture is then introduced into the lower end of the bleaching tower 7 and transported to its upper end over a period of approximately 20 minutes. During this time, the pulp actually bleaches.

Etwaig am Kopf des Bleichturmes 7 vorhandenes überschüssiges Ozon kann über die Ozonleitung 8 dem Restozon-Vernichter 9 zugeführt werden.Any excess ozone present at the head of the bleaching tower 7 can be fed to the residual ozone destroyer 9 via the ozone line 8.

Der gebleichte Zellstoff wird ebenso am Kopf des Bleichturmes 7 ausgebracht und von der Pumpe 11 durch die Ableitung 10 in das Filter 12 zur Abtrennung des gebleichten Zellstoffes von der Bleichflotte eingebracht. In der Zeichnung ist mit 21 die Entnahme des gebleichten Zellstoffes angedeutet.The bleached pulp is also applied at the head of the bleaching tower 7 and introduced by the pump 11 through the discharge line 10 into the filter 12 for separating the bleached pulp from the bleaching liquor. In the drawing, the removal of the bleached pulp is indicated at 21.

Die Bleichflotte kann zur Einstellung der Stoffdichte für weiteren zu bleichenden Zellstoff in das Filter 14 rückgeleitet werden. Sie kann aber auch zur Herstellung von Starkwasser verwendet werden, wobei sie aber vor der Einleitung in die Absorptionskolonne 2 mit Ozon vorbehandelt werden muß. Diese Verwendungsmöglichkeit ist in der Zeichnung durch die Zweigleitung 13a, die Rückwasser-Vorbehandlung 25 und die Rückwasser-Leitung 15 angedeutet. Das Ozon zur Vorbehandlung wird der Ozonleitung 18 entnommen.The bleaching liquor can be fed back into the filter 14 to adjust the consistency for further pulp to be bleached. However, it can also be used for the production of strong water, although it must be pretreated with ozone before being introduced into the absorption column 2. This possible use is indicated in the drawing by the branch line 13a, the return water pretreatment 25 and the return water line 15. The ozone for pretreatment is taken from the ozone line 18.

Zweckmäßigerweise ist in der Zweigleitung 13a ein Wärmetauscher 22 vorgesehen, um Wärme von der Bleichflotte (ca. 50°C) rückgewinnen zu können. Mit dieser Wärme wird das Starkwasser in der Starkwasserleitung 4 temperiert, vorzugsweise auf eine Temperatur von etwa 46°C.A heat exchanger 22 is expediently provided in the branch line 13a in order to be able to recover heat from the bleaching liquor (approx. 50 ° C.). With this heat, the heavy water in the heavy water line 4 is tempered, preferably to a temperature of about 46 ° C.

Das erfindungsgemäße Verfahren kann auch mit mehreren aufeinanderfolgenden Bleichstufen durchgeführt werden. Dazu wird mindestens ein weiterer Bleichturm dem Bleichturm 7 nachgeschaltet. Vor der zweiten Zugabe von Starkwasser wird die Zellstoffsuspension zweckmäßigerweise eingedickt.The process according to the invention can also be carried out with several successive bleaching stages. For this purpose, at least one further bleaching tower is connected downstream of the bleaching tower 7. Before the second addition of strong water, the pulp suspension is expediently thickened.

In den nachfolgenden Ausführungsbeispielen wird die Erfindung noch näher erläutert.The invention is explained in more detail in the following exemplary embodiments.

Beispiel 1:Example 1:

Ein vorbehandelter Zellstoff mit einer Stoffdichte von 12 % wurde mit einer Ozonmenge von 2 kg Ozon pro Tonne Zellstoff behandelt. Die Ozonlösung (Starkwasser) hatte eine Konzentration von 80 g Ozon pro m³.A pretreated pulp with a consistency of 12% was treated with an amount of 2 kg of ozone per ton of pulp. The ozone solution (strong water) had a concentration of 80 g ozone per m³.

Die Ozonlösung wurde vor dem Eintritt in den aufwärts arbeitenden Bleichturm in einem Mischer der Zellstoffsuspension zugemischt. Beim Eintritt in den Bleichturm ergab sich durch die Mischung mit dem Zellstoff eine Ozonkonzentration von 61,86 g/m³. Der anfänglich rasche Ozonverbrauch sowie der hydrostatische Druck im Bleichgefäß verhinderten in der Anfangsphase der Bleiche ein rasches Ausgasen des Ozons, so daß kein Durchschlagen durch die zu bleichende Zellstoffmenge auftrat.The ozone solution was mixed into the pulp suspension in a mixer prior to entering the upward bleaching tower. When entering the bleaching tower, the mixture with the pulp resulted in an ozone concentration of 61.86 g / m³. The initially rapid ozone consumption and the hydrostatic pressure in the bleaching vessel prevented the ozone from rapidly degassing in the initial phase of the bleaching, so that there was no breakdown through the amount of pulp to be bleached.

Obwohl die angewandte Ozonmenge nur gering war, konnte dennoch eine Weißesteigerung des Zellstoffes von 4 Punkten erreicht werden. Durch eine herkömmliche Nachbehandlung wurden dann Weißegrade über 80 erreicht. Die Verweilzeit im Bleichturm betrug 20 min. Die Stoffdichte betrug 3 %.Although the amount of ozone used was only small, the pulp's whiteness increased by 4 points. A conventional aftertreatment then achieved whiteness levels above 80. The residence time in the bleaching tower was 20 minutes. The consistency was 3%.

Beispiel 2:Example 2:

Ein vorbehandelter Zellstoff mit einer Stoffdichte von 14 % wurde mit 4 kg Ozon pro Tonne Zellstoff behandelt. Die Stoffdichte während der Bleichung betrug 2 %. Das Starkwasser enthielt 93,3g O₃/m³. Der Überdruck betrug im Bleichturm 4 bar.A pre-treated pulp with a consistency of 14% was treated with 4 kg of ozone per ton of pulp. The consistency during bleaching was 2%. The strong water contained 93.3g O₃ / m³. The overpressure in the bleaching tower was 4 bar.

Durch die Behandlung mit Ozon konnte die Kappazahl um 2 Einheiten verringert werden, und außerdem wurde ein Weißegewinn von 5 Punkten erreicht.The treatment with ozone reduced the kappa number by 2 units and also achieved a whiteness gain of 5 points.

Beispiel 3:Example 3:

Ein vorbehandelter Zellstoff mit einer Stoffdichte von 14 % wurde mit 10 kg Ozon pro Tonne Zellstoff gebleicht. In diesem Fall erfolgte die Bleichung in zwei Stufen.A pre-treated pulp with a consistency of 14% was bleached with 10 kg of ozone per ton of pulp. In this case, the bleaching was done in two stages.

Zunächst wurde der Zellstoff durch Zusatz der Ozonlösung auf eine Stoffdichte von 2 % gebracht. Nach einer Bleichung von 20 min in einem aufwärts arbeitenden Turm unter Druck wurde die Suspension auf 5 % eingedickt. Anschließend erfolgte abermals eine Einmischung von Ozonlösung bis auf eine Stoffdichte von 2 %. Die Konzentration der Ozonlösung betrug 137,2g O₃/m³.First, the pulp was brought to a consistency of 2% by adding the ozone solution. After bleaching for 20 minutes in an upward tower under pressure, the suspension was thickened to 5%. Subsequently, the ozone solution was mixed in again to a consistency of 2%. The concentration of the ozone solution was 137.2g O₃ / m³.

Auch die zweite Bleichstufe wurde in einem aufwärts arbeitenden Bleichturm unter Druck durchgeführt. In beiden Fällen betrug die Bleichzeit 20 min. Es konnte in diesem Fall ein Kappa-Abbau von 7 Einheiten erreicht werden bei einer Weißegraderhöhung um 6 Punkte.The second bleaching stage was also carried out in a bleaching tower working under pressure. In both cases the bleaching time was 20 minutes. In this case a kappa reduction of 7 units could be achieved with a whiteness increase of 6 points.

Claims (10)

  1. A process for bleaching cellulosic materials, in particular pulp, by means of ozone, characterized in that a solution of ozone in an aqueous medium (strong water) having a content of 30 to 300 g O₃, preferably 100 to 150 g O₃, per m³ of aqueous medium is supplied under pressure to said materials suspended in an aqueous medium and is mixed with the latter medium in a mixing means (5), whereupon the mixture is conducted through a reaction vessel (7), the bleached material is separated from the bleaching liquor and possibly present residual ozone is destroyed.
  2. A process according to claim 1, characterized in that the ozone solution (strong water) is produced in an absorption column (2) in which an aqueous medium is treated under pressure with an ozonic gas, wherein a gas containing at least 100 g O₃/Nm³ oxygen is used as said ozonic gas, the ozonic solution and the residual oxygen are withdrawn from the column (2) and the residual oxygen is dried and recycled to the production of ozonic gas.
  3. A process according to claim 2, characterized in that in the absorption column (2) an overpressure of between 5 and 10 bar, and in the mixing means (5) as well as in the reaction vessel (7) an overpressure of between 2 and 5 bar, are provided, the overpressure in the absorption column (2) being adjusted to be higher than in the mixing means (5) and in the reaction vessel (7).
  4. A process according to one or several of claims 1 to 3, characterized in that the process is carried out continuously.
  5. A process according to one or several of claims 1 to 4, characterized in that the temperature during the reaction is maintained at below 60°C, preferably at between 25 and 40°C.
  6. A process according to one or several of claims 1 to 5, characterized in that a portion of the bleaching liquor, upon separation of the bleached material, is pretreated with ozone and recycled into the absorption column (2) for the production of strong water.
  7. A plant for carrying out the process according to one or several of claims 1 to 6, comprising a means for preparing a pulp suspension (14), at least one bleaching tower (7) as a reaction vessel, a means for producing an ozonic gas (1), filters, pumps and ducts for connecting the plant parts, characterized in that the means for producing ozone (1) is in flow-connection with an absorption column (2) for producing strong water, a mixing means (5) for mixing the pulp suspension with the strong water is provided, said mixing means (5) being connected with said absorption column (2) via a strong water duct (4), and a bleaching tower (7) for receiving said mixture of pulp suspension and strong water is provided, said absorption column (2), said mixing means (5) and said bleaching tower (7) being equipped with means for generating and adjusting an overpressure.
  8. A plant according to claim 7, characterized in that the bleaching tower (7) is connected via a discharge duct (10) with a filter (12) for separating the bleached pulp from the bleaching liquor, which filter (12) comprises a bleaching liquor duct (13) for recycling used bleaching liquor into the means for producing said pulp suspension (14).
  9. A plant according to claim 8, characterized in that said bleaching liquor duct (13) is in flow-connection with said absorption column (2) via a branch duct (13a) in which a heat exchanger (22) is provided, which heat exchanger (22) also is connected with said strong water duct (4) in order to enable a heat transfer from the bleaching liquor to the strong water.
  10. A plant according to one or several of claims 7 to 9, characterized in that the absorption column (2) is connected with a return duct (19) to the ozone generator (1) to recycle non-dissolved oxygen from the absorption column (2) to the ozone generator (1), a drier (3) preferably being provided in said return duct (19).
EP90890325A 1989-12-22 1990-12-17 Process for bleaching cellulosic materials and plant for carrying out the process Expired - Lifetime EP0434662B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AT2927/89 1989-12-22
AT0292789A AT393701B (en) 1989-12-22 1989-12-22 METHOD FOR BLEACHING CELLULOSE-CONTAINING MATERIALS, AND SYSTEM FOR CARRYING OUT THE METHOD

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EP0434662A1 EP0434662A1 (en) 1991-06-26
EP0434662B1 true EP0434662B1 (en) 1994-09-21

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DE (1) DE59007258D1 (en)

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Publication number Priority date Publication date Assignee Title
AT395445B (en) * 1991-05-02 1992-12-28 Voest Alpine Ind Anlagen METHOD FOR BLEACHING CELLULOSE-CONTAINING MATERIAL
NO912449L (en) * 1991-06-24 1992-12-28 Norske Stats Oljeselskap MOVABLE PLATFORM FOR SEA.
ZA924351B (en) * 1991-06-27 1993-03-31 Ahlstroem Oy Ozone bleaching process
AT400154B (en) * 1991-12-23 1995-10-25 Voest Alpine Ind Anlagen Process for bleaching cellulosic materials
US6231718B1 (en) * 1992-02-28 2001-05-15 International Paper Company Two phase ozone and oxygen pulp treatment
US5364505A (en) * 1992-12-07 1994-11-15 Kamyr, Inc. Pressurized ozone pulp delignification reactor and a compressor for supplying ozone to the reactor
SE500616C2 (en) * 1993-06-08 1994-07-25 Kvaerner Pulping Tech Bleaching of chemical pulp with peroxide at overpressure
US5645687A (en) * 1995-07-10 1997-07-08 Champion International Corporation Process for manufacturing bleached pulp with reduced chloride production
CN101243369B (en) * 2005-07-07 2010-12-15 Mks仪器股份有限公司 Ozone system for multi-chamber tools

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US2812861A (en) * 1954-02-09 1957-11-12 Maryland Lab Inc Means for ozone treatment of liquids
US2864757A (en) * 1956-02-17 1958-12-16 Air Reduction Ozone concentration and dilution
FR1441787A (en) * 1965-04-30 1966-06-10 Progil Pulp bleaching process
CA902861A (en) * 1969-11-27 1972-06-20 Pulp And Paper Research Institute Of Canada Bleaching of cellulosic pulp
US4089737A (en) * 1974-02-18 1978-05-16 Toyo Pulp Company, Ltd. Delignification of cellulosic material with an alkaline aqueous medium containing oxygen dissolved therein
US3951733A (en) * 1974-11-06 1976-04-20 International Paper Company Delignification and bleaching of wood pulp with oxygen
US4310384A (en) * 1979-01-11 1982-01-12 Weyerhaeuser Company Reducing chemical transfer between treatment stages
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AT393701B (en) 1991-12-10
ATA292789A (en) 1991-05-15
US5133946A (en) 1992-07-28
DE59007258D1 (en) 1994-10-27
ATE111989T1 (en) 1994-10-15
EP0434662A1 (en) 1991-06-26

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