EP0295180A2 - Verfahren zum Bleichen oder zur Delignifizierung eines Zellstoffs mit Sauerstoff, und Anlage zur Durchführung des Verfahrens - Google Patents

Verfahren zum Bleichen oder zur Delignifizierung eines Zellstoffs mit Sauerstoff, und Anlage zur Durchführung des Verfahrens Download PDF

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Publication number
EP0295180A2
EP0295180A2 EP88401393A EP88401393A EP0295180A2 EP 0295180 A2 EP0295180 A2 EP 0295180A2 EP 88401393 A EP88401393 A EP 88401393A EP 88401393 A EP88401393 A EP 88401393A EP 0295180 A2 EP0295180 A2 EP 0295180A2
Authority
EP
European Patent Office
Prior art keywords
suspension
oxygen
steam
vapor
conduit
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP88401393A
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English (en)
French (fr)
Other versions
EP0295180A3 (de
Inventor
Robert Lee
Derek Hornsey
Arthur S. Perkins
Jack A. Davidson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Air Liquide Canada Inc
Canadian Liquid Air Ltd
Original Assignee
Air Liquide Canada Inc
Canadian Liquid Air Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Air Liquide Canada Inc, Canadian Liquid Air Ltd filed Critical Air Liquide Canada Inc
Publication of EP0295180A2 publication Critical patent/EP0295180A2/de
Publication of EP0295180A3 publication Critical patent/EP0295180A3/de
Withdrawn legal-status Critical Current

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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

Definitions

  • the present invention relates to the bleaching or delignification of a cellulose paper pulp.
  • the suspension containing the bubbles is passed into and through a reaction tank which expands the suspension by bringing it to a section in which it takes a relatively slow piston-type flow to allow the bubbles of oxygen dispersed throughout its volume the time to react with the cellulose.
  • the treated suspension is recovered at the outlet of the reaction tank.
  • the bubbles are dispersed in the turbulent liquid suspension by passing the oxygen through a microporous wall under a pressure higher than that of the suspension to bring it into contact with the suspension.
  • the suspension can be preheated by passing it through a steam mixer, on a path going to the pump, and the heated suspension can be deposited in a storage tank upstream of the pump.
  • the smallness of bubbles which are initially produced by diffusing oxygen into the suspension through the porous wall, promotes good dispersion throughout the mass of the dough and, therefore, it therefore promotes the establishment of good contact. , effective for bleaching or delignification, with the fibers of the dough.
  • An object of the present invention is to further improve the contact with oxygen and the dough so as to obtain a better bleaching action with the same amount of oxygen.
  • this result is achieved by injecting oxygen into the mixing diffuser duct as described above but in the form of a mixture of oxygen and water vapor.
  • Small bubbles of oxygen-vapor mixture form momentarily when the mixture leaves the small pores of the wall of the injector but, when each bubble meets the paste, the vapor condenses and releases its oxygen content in the form of 'a smaller bubble.
  • the steam by condensing, brings an additional amount of heat to the dough.
  • the diffuser-mixer Preferably, as large a fraction of the vapor which is necessary to bring the suspension to the reaction temperature, in a single phase, is injected through the diffuser-mixer.
  • the achievement of this result depends on the capacity of the diffuser-mixer. It is therefore possible to inject an additional quantity of heat if necessary into a steam mixer, to bring the suspension to a supply temperature in a preliminary stage, through an injector comprised between the pump and the oxygen-vapor diffuser-mixer. , to bring the temperature to a value closer to the reaction. You can also inject steam to preheat the suspension upstream of the pump.
  • the proportion between oxygen and steam can vary from 20 to 200: 1, by weight, the range from 100 to 150: 1 being preferred. Or, by volume, the proportion between oxygen and vapor can vary from 50 to 500: 1, the range from 300 to 400: 1 being preferred.
  • the oxygen ratio can vary from 80 to 800: 1 by weight, the range from 400 to 600: 1 being preferred. Again, by volume, the oxygen can vary from 200 to 2000: 1, the range from 1200 to 1600 being preferred.
  • the ratio of oxygen to dough can vary from 5 kg to 1 kg per tonne of dry dough. It is therefore desirable to add as much vapor as possible with the oxygen-vapor mixture. Since the amount of steam that can be added is limited by the capacity of the diffuser, it may be necessary to also add steam in an earlier phase, in order to inject enough heat to bring the suspension to the temperature of reaction.
  • the invention makes it possible to obtain the maximum of the potential use of oxygen and of steam in the delignification or bleaching treatment by acting as follows.
  • the total amount of vapor injected into the dough is a controlled amount which will bring the suspension to reaction temperature in the reaction vessel.
  • the proportion of the total quantity of vapor injected with the oxygen-vapor mixture into the diffuser would preferably be substantially the maximum allowed by the injection capacity of the diffuser, or a selected portion quantity, close to this maximum, or 80% or more.
  • the rest of the vapor which is necessary to bring the suspension to the reaction temperature can then be injected into the suspension upstream of the diffuser.
  • the optimal proportion of oxygen to be injected into the dough to obtain good delignification or good bleaching is determined by tests, as is known in the art, and it is chosen according to the particular installation and the conditions which are involved.
  • the injection of oxygen is then regulated so as to continuously supply the suspends the selected oxygen flow.
  • the injection of steam together with oxygen has the effect that oxygen is injected in the form of smaller bubbles than if oxygen was injected alone, which in turn has the effect of creating a larger area of oxygen surface in contact with the paste and ensure better absorption for a given oxygen flow.
  • the invention therefore provides several advantages, namely, the fact that a large quantity of steam used for heating is injected where it is needed, just before the reaction zone and that, at the same time, the injecting oxygen simultaneously with the vapor results in a larger surface area of the injected oxygen and in a better reaction with the paste for a given quantity of oxygen. In this way, the use of oxygen as well as that of steam is substantially increased to the maximum for the particular installation considered.
  • control can be exercised continuously by adjusting the amount of steam introduced into the vapor-oxygen mixture by the temperature of the suspension downstream of the oxygen-vapor diffuser, while keeping the oxygen supply constant, or by having it adjusted by maintaining a certain important variable. If it is necessary to add an additional quantity of oxygen upstream of the diffuser, the temperature adjustment will also ensure the regulation of this injection upstream.
  • the invention is particularly suitable for incremental dosing of the pulp suspension with oxygen. This is done by passing a stream of suspension of cellulose pulp under pressure, arriving from a feed, through a reaction path composed of a plurality of successive stages in each of which the stream is firstly confined to a section in which it has a speed capable of fluidizing it to give it a liquid flow behavior and is then expanded so as to occupy a section in which it has a speed capable of giving rise to a piston type flow.
  • oxygen is injected into the liquid stream under pressure, in the form of a mass of small bubbles, to disperse them throughout the stream, so that most of the oxygen reacts with the paste which is in flow of piston type in this stage.
  • the treated suspension is then recovered at the end of the final stage.
  • the invention also provides for an additional mixing of the suspension leaving the oxygen diffuser obtained by passing it through a pulp fluidizer mixer.
  • This mixer can be placed adjacent to the diffuser or placed some distance downstream. This mixer effectively ensures additional mixing and the dispersion of possible agglomerations of oxygen, so that the oxygen remains in a finely divided form and that it is mixed more intimately with the suspension.
  • a preferred static mixer is composed of a tube whose section decreases towards a constriction followed by a tube which widens to the diameter of the tube in which the suspension of dough circulates. The speed of passage through the throttle will be approximately equal to that observed in the diffuser.
  • the invention also provides means for coordinating the flow of oxygen with the flow of the pulp suspension so as to maintain the appropriate oxygen dosage.
  • a device for measuring the flow rate for example, an orifice plate placed in the path of the suspension, upstream of the diffuser, the orifice plate being connected to a differential pressure cell which is in turn connected to a control device.
  • the control unit sends a signal to an oxygen flow control valve which controls the supply of oxygen to the diffuser.
  • An orifice plate or other device that measures the flow of oxygen is provided in the oxygen supply line.
  • the control mechanism may include a computer that maintains a constant, predetermined and regulated oxygen-to-dough ratio, which is achieved by increasing or reducing the dosage to account for variations in the flow rate of the dough suspension.
  • An installation according to the invention comprises a supply tank for the suspension, an injection and mixing pipe substantially free of obstruction, intended to confine the suspension to a current to determine a substantially free flow in this pipe, a tank having a larger cross section than said duct and which is connected thereto, means for continuously forcing the suspension under pressure from the tank supply to the conduit, and means for adjusting the supply pressure so that the suspension circulating in the conduit has an appropriate speed to create a turbulent liquid flow in this conduit and to cause a piston type flow to take effect to the dough in the reactor.
  • Diffusing means comprise an extended microporous surface which is in contact with the suspension in the duct to diffuse an oxygen-vapor mixture in the suspension under a pressure higher than the pressure for conveying the paste, to form in this way a mass of small oxygen bubbles and mix them throughout the volume of the suspension which circulates in the conduit, so that these bubbles remain in contact with the thick paste over the entire path of the piston-type flow to ensure a delignification or bleaching effect.
  • the control mechanism comprises a supply duct for supplying a mixture of oxygen and steam to the diffusing means and means for controlling the flow of oxygen passing through this duct, a steam duct which leads from a source of steam to said supply duct, and means serving to regulate the flow rate of steam in this duct, the means which serve to regulate the supply of steam responding to the temperature of the suspension when it passes from the mixing duct to the tank of reaction.
  • Means can also be provided for injecting steam into the suspension upstream of the diffusing means.
  • the means for controlling the supply of steam in response to the temperature of the suspension can also control the additional supply of steam.
  • the pulp suspension passes through a primary oxygen diffuser and a plurality of reactors, each of which is preceded by an oxygen diffuser. Any or all of the slurry suspension can be sent to a reaction tower for further extraction with caustic soda.
  • FIG. 1 illustrates a prior method in which steam and oxygen are used jointly for the bleaching of a pulp.
  • a mixture of dough which is normally a thick and heavy mass is continuously passed from a feed source through a steam mixer 15 which preheats it to a temperature ranging from 37.8 ° C to 65.6 ° C, then 76.7 ° C, then 93.3 ° C and then this mixture is sent, via a line 16, to the top of a storage hopper 17.
  • the dough, mixed with steam is discharged, in the form of a suspension, by a pump, and passing through another pipe 21, into an oxygen disperser duct 23 which is shown in more detail in the figure 3.
  • the pressure at which the suspension is discharged is sufficient to circulate this suspension in the conduit 23 at a speed such that it behaves like a turbulent liquid.
  • Steam is sent to the steam mixer 15 by a power source, passing through a tube 25.
  • the steam supply is regulated by a temperature controller 27 which is itself connected to a valve 29 interposed in the tube 25.
  • Oxygen is supplied to a diffusing device contained in the conduit 23, by a conduit 31 which arrives from an oxygen supply source, through a pressure regulating device 33.
  • the diffusing device comprises a microporous wall which forms the interface with the suspension.
  • Oxygen is thus continuously introduced into the suspension of heated dough through the diffuser device, in the form of a mass of small bubbles, at a time when this suspension behaves like a turbulent liquid, so that the bubbles oxygen diffuse in the suspension and mix throughout the volume of the latter.
  • the oxygen-containing suspension passes through a pipe 35 into the bottom of a retention tube 37 fitted with a valve 39 for adjusting the back pressure.
  • the suspension slows down in the tube 37 to take a piston-type flow speed, at which it returns to its thick normal state and it is kept under pressure, so that it gradually absorbs the oxygen which reacts with it.
  • the pulp is retained in the retention tube long enough to allow oxygen to react with the cellulose.
  • the installation according to the invention is implemented as follows.
  • FIG. 2 which illustrates a preferred method according to the invention
  • steam is added to the pipe 131 which sends the oxygen to the diffusing device A (see FIG. 3), which is housed in the dispersing pipe 123, to form an oxygen-vapor mixture.
  • the oxygen supply is controlled by a temperature control member 127 which is connected to the tube 135 at a point between the disperser 123 and the retention tube 137.
  • the vapor is firstly mixed with the oxygen and the oxygen-vapor mixture is then added to the suspension, by the diffusing device A, in the form of a mass of small bubbles.
  • the oxygen-vapor mixture comes into contact with the dough, the vapor condenses into water, thereby bringing heat to the dough, and it leaves the gaseous oxygen inside the dough in the form of bubbles more small (smaller than oxygen-vapor bubbles) which disperse throughout the suspension due to its turbulence.
  • the pressure of the oxygen-vapor mixture, when injected, is about equal to or slightly higher than the oxygen pressure used in the process of Figure 1.
  • the vapor is mixed with the oxygen just before the mixture is injected into the diffuser A and the regulation of the vapor flow is ensured by a control member.
  • temperature 127 which captures the temperature of the dough downstream of the disperser.
  • the dough then enters the pressure retention tube 137, in which it takes a piston-type flow and circulates at a relatively slow speed, under pressure, the oxygen being dispersed throughout the mass in the form of small bubbles to react. with cellulose.
  • the diffuser by means of which the oxygen-vapor mixture is injected into the suspension, in the diffuser A, can take different forms, and which all comprise a microporous wall which forms the interface with the suspension and through which the oxygen-vapor mixture is diffused.
  • This wall is preferably a sintered stainless steel element, as described in Bulletin M 201 of Pall Trinity Micro Corporation, a subsidiary of the Pall Corporation, and in US Pat. No. 2,554,343. Elements of this type are generally used for the filtration.
  • the pore size should be in the range of about 2 microns to 100 microns, and is preferably less than about 10 microns.
  • the porosity must be substantially uniform, the voids having to represent approximately 40% to 50% of the volume of the wall, which has a thickness of between approximately 0.8 mm and approximately 13 mm.
  • FIG. 3 A preferred form of diffuser A is shown in Figure 3.
  • This diffuser is composed of a cap 123 which gives passage to the paste suspension.
  • the cylinder has flanges 63, 64 at its ends, for connection to a pipe.
  • a tube 65 extends transversely to the axis and in a central position across the passage 123 and is held in this passage by a suitable housing 69 formed on the wall of the cylinder 123.
  • the pipe 131 serving to supply the oxygen-vapor mixture to tube 65 leads to diffuser tube 65.
  • the diffuser element may include a conduit or cylinder through which the suspension passes, the cylinder wall defining the flow path.
  • the diffuser element can be part of the cylinder wall, it can take the form of a porous tube which extends transversely to the axis of the cylinder, or it can take the form of a porous tube which s extends along the axis of the cylinder.
  • the path of the suspension is relatively free from obstruction.
  • this tube occupies only a small space, so that the major part of the interior space of the cylinder is occupied by the suspension which circulates there, by coming into contact with the porous diffusing surface.
  • the starting material used in the present process will depend on whether the process is used in the delignification phase or in the bleaching phase of the pulp treatment.
  • the aqueous pulp suspension comes from three or four washing phases which follow the washing phase of the unbleached pulp, the pulp containing a considerable amount of lignin, as indicated by the value of the index.
  • Kappa between 30 and 60, typically between 40 and 50. It contains 10 to 12%, preferably 10 to 12%, by weight, of solids.
  • caustic soda will be added in a proportion of 2 to 4% by weight, typically 3% before delignification.
  • bleaching is usually carried out as soon as the suspension has been washed after the first chlorination phase. Then, it will have a Kappa induce of 3 to 8, typically from 4 to 5. It will contain from 8 to 16%, preferably from 8 to 16%, by weight, of solids. We will again add caustic soda in a proportion from 2 to 4% by weight, typically 3%, to obtain the starting material for bleaching according to the invention.
  • a typical diffuser and mixer duct 123 can vary in cross-sectional area between about 26 and about 110 cm3.
  • the suspension is passed through the conduit at a pressure of about 1.4 to about 14 bar. This gives the suspension a speed of about 0.5 to about 50 meters per second, preferably about 3 to about 10 meters per second.
  • the residence time in the conduit 123 varies between approximately 0.01 and approximately 0.120 seconds.
  • the residence time in the reactor tube 137 varies between approximately 1 and approximately 5 minutes.
  • the surface of the porous wall which forms the interface with the suspension may preferably have an area ranging from approximately 46 cm2 to approximately 186 cm3, covered with pores having a diameter ranging from approximately 10 to approximately 100 micrometers.
  • the oxygen used can be molecular oxygen, such as that which is commercially available and which contains 90% or more and preferably 98% or more oxygen.
  • oxygen can be presented as a gas containing more than 50% oxygen.
  • the starting paste suspension can contain about 10 to about 20% air by volume of the dispersed paste, which dilutes the added oxygen.
  • concentration of the gas containing added oxygen can be at the lower end of the range of oxygen contents and, for a dough containing a lot of air, the added gas may contain oxygen toward the upper end of the oxygen content range.
  • the oxygen content of the exhaust gas which leaves the vent of the final treatment tank is measured. Based on this dosage, we can check if we have obtained a good mixture. Adjustments can be made accordingly and the incremental dosage can be manipulated to obtain the best results.
  • This formula is calculated at the working pressure of this particular phase.
  • the dosage can be proportioned in the same way for each phase or it can be modified so as to adapt to variable conditions such as variations in the nature of the dough or other conditions.
  • the oxygen used must have a volume concentration of at least 90% oxygen, preferably more than 98%, measured under standard conditions.
  • the steam must be saturated steam.
  • the injection pressure of the oxygen-vapor mixture must be approximately 1 to 10 bar higher than the pressure of the pulp suspension.
  • the temperature of the oxygen-vapor mixture, at the time of injection, should be from about 129 ° C to about 198.9 ° C.
  • the injection rate of the oxygen-vapor mixture should be in the range from about 5 kg of oxygen to about 25 kg of oxygen per tonne of dry pulp.
  • the tubes and pipes should be insulated so as to retain the heat.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
EP88401393A 1987-06-08 1988-06-08 Verfahren zum Bleichen oder zur Delignifizierung eines Zellstoffs mit Sauerstoff, und Anlage zur Durchführung des Verfahrens Withdrawn EP0295180A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA539056 1987-06-08
CA 539056 CA1300322C (en) 1987-06-08 1987-06-08 Method of bleaching or delignification of cellulose pulp with oxygen

Publications (2)

Publication Number Publication Date
EP0295180A2 true EP0295180A2 (de) 1988-12-14
EP0295180A3 EP0295180A3 (de) 1989-10-11

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EP88401393A Withdrawn EP0295180A3 (de) 1987-06-08 1988-06-08 Verfahren zum Bleichen oder zur Delignifizierung eines Zellstoffs mit Sauerstoff, und Anlage zur Durchführung des Verfahrens

Country Status (5)

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EP (1) EP0295180A3 (de)
JP (1) JPH0299681A (de)
AU (1) AU613952B2 (de)
CA (1) CA1300322C (de)
FR (1) FR2617877B1 (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993009391A1 (en) * 1991-11-06 1993-05-13 Sunds Defibrator Industries Aktiebolag Heating arrangement
ES2050566A1 (es) * 1991-02-06 1994-05-16 Ingersoll Rand Co "metodo y aparato para el tratamiento de materiales fibrosos con un reactivo gaseoso"
EP0647466A2 (de) * 1993-10-08 1995-04-12 Akzo Nobel N.V. Cellulosische Membranen

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5690786A (en) * 1991-11-26 1997-11-25 Air Products And Chemicals Inc. Process for the treatment of pulp with oxygen and steam using ejectors
US5372679A (en) * 1992-06-08 1994-12-13 Air Products And Chemicals, Inc. Reactor system for treating cellulosic pulp at a constant upward flow velocity

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4177105A (en) * 1973-05-22 1979-12-04 Kamyr, Incorporated Apparatus for delignifying and bleaching cellulose pulp
EP0106460A1 (de) * 1982-09-30 1984-04-25 The Black Clawson Company Verfahren und Vorrichtung zur Sauerstoffdelignifizierung
EP0226495A1 (de) * 1985-11-15 1987-06-24 Canadian Liquid Air Ltd Air Liquide Canada Ltee Verfahren und Vorrichtung zum Bleichen von Papierpulpe

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4177105A (en) * 1973-05-22 1979-12-04 Kamyr, Incorporated Apparatus for delignifying and bleaching cellulose pulp
EP0106460A1 (de) * 1982-09-30 1984-04-25 The Black Clawson Company Verfahren und Vorrichtung zur Sauerstoffdelignifizierung
EP0226495A1 (de) * 1985-11-15 1987-06-24 Canadian Liquid Air Ltd Air Liquide Canada Ltee Verfahren und Vorrichtung zum Bleichen von Papierpulpe

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
JOURNAL OF THE TECHNICAL ASSOCIATION OF THE PULP AND PAPER INDUSTRY, vol. 64, no. 6, juin 1981, pages 87-90, Atlanta, Georgia, US; P.J. KLEPPE: "Oxygen/alkali delignification at medium consistency. Mill-scale trials to commercial installation" *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2050566A1 (es) * 1991-02-06 1994-05-16 Ingersoll Rand Co "metodo y aparato para el tratamiento de materiales fibrosos con un reactivo gaseoso"
WO1993009391A1 (en) * 1991-11-06 1993-05-13 Sunds Defibrator Industries Aktiebolag Heating arrangement
US5479792A (en) * 1991-11-06 1996-01-02 Sunds Defibrator Industries Aktiebolag Heating arrangement
EP0647466A2 (de) * 1993-10-08 1995-04-12 Akzo Nobel N.V. Cellulosische Membranen
EP0647466A3 (de) * 1993-10-08 1996-01-17 Akzo Nobel Nv Cellulosische Membranen.

Also Published As

Publication number Publication date
AU613952B2 (en) 1991-08-15
FR2617877A1 (fr) 1989-01-13
CA1300322C (en) 1992-05-12
FR2617877B1 (fr) 1995-01-06
JPH0299681A (ja) 1990-04-11
EP0295180A3 (de) 1989-10-11
AU2202188A (en) 1990-06-28

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