CA1300322C - Method of bleaching or delignification of cellulose pulp with oxygen - Google Patents
Method of bleaching or delignification of cellulose pulp with oxygenInfo
- Publication number
- CA1300322C CA1300322C CA 539056 CA539056A CA1300322C CA 1300322 C CA1300322 C CA 1300322C CA 539056 CA539056 CA 539056 CA 539056 A CA539056 A CA 539056A CA 1300322 C CA1300322 C CA 1300322C
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- Canada
- Prior art keywords
- oxygen
- slurry
- steam
- pulp
- conduit
- Prior art date
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Classifications
-
- 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
Abstract
METHOD OF BLEACHING OR DELIGNIFICATION
OF CELLULOSE PULP WITH OXYGEN
ABSTRACT
A continuous method of bleaching or delignification of cellulose pulp with oxygen. The pulp in the form of an aqueous slurry is passed through a diffusing and mixing conduit at a velocity at which it behaves as a turbulent liquid and then through a holding vessel at a velocity at which it assumes plug flow. An oxygen-steam mixture is diffused through a microporous wall interfacing with the slurry in the conduit to form a mass of small oxygen bubbles from which the steam condenses imparting heat to the slurry and leaving the oxygen in the form of smaller bubbles dispersed throughout the slurry, presenting a total surface area markedly greater than bubbles resulting from the injection of oxygen alone through the same microporous wall under the same conditions. The oxygen bubbles remain dispersed throughout the slurry when it assumes plug flow, to give time for the oxygen to exert its bleaching effect. Apparatus for carrying out the method.
OF CELLULOSE PULP WITH OXYGEN
ABSTRACT
A continuous method of bleaching or delignification of cellulose pulp with oxygen. The pulp in the form of an aqueous slurry is passed through a diffusing and mixing conduit at a velocity at which it behaves as a turbulent liquid and then through a holding vessel at a velocity at which it assumes plug flow. An oxygen-steam mixture is diffused through a microporous wall interfacing with the slurry in the conduit to form a mass of small oxygen bubbles from which the steam condenses imparting heat to the slurry and leaving the oxygen in the form of smaller bubbles dispersed throughout the slurry, presenting a total surface area markedly greater than bubbles resulting from the injection of oxygen alone through the same microporous wall under the same conditions. The oxygen bubbles remain dispersed throughout the slurry when it assumes plug flow, to give time for the oxygen to exert its bleaching effect. Apparatus for carrying out the method.
Description
13~(~322 BACKGROUND OF TH INVENTION
1. Field of the Invention This invention relates to bleaching or delignification of cellulose pulp.
1. Field of the Invention This invention relates to bleaching or delignification of cellulose pulp.
2. Description of the Prior Art Canadian Patent Application 507,000, Lee, Hornsey, Perkins and Davidson, filed April 18, 1986 contains a bibliography on the use of oxygen in bleaching cellulose pulp slurry.
The Lee et al application discloses a process and apparatus for bleaching pulp in the form of an aqueous slurry having a consistency from 8% to 16~, by introducing oxygen into the slurry, in the form of minute bubbles, at the time the slurry is passing, under pumping pressure, through a diffusing and mixing conduit which confines the slurry to a cross section so that, at the pumping pressure, it moves at a high velocity effective to provide turbulent liquid flow. The phenomenon of the liquid behavior of pulp slurry confined under high velocity is explained in an article entitle "Medium Consistency Technology" appearing in the TAPPI Journal, Vol. 64, No. 6, June 1981, and in the Lee et al application 507,000.
The slurry containing the bubbles is immediately passed from the mixing conduit into and through a reaction vessel which releases the slurry to a cross section at which it assumes relatively slow plug flow, to give the oxygen 1~0()322 bubbles dispersed through it, time to react with the cellulose.
The treated slurry is recovered from the reaction vessel. Dis-persing the bubbles within the turbulent liquid slurry is accomplished by passing the oxygen, under pressure greater than that of the slurry pressure, through a microporous wall into contact with the slurry.
The slurry may be preheated by passing it through a steam mixer, on the way to the pump, and the heated slurry deposited in a storage vessel upstream of the pump.
The minuteness of the bubbles, produced initially by diffusing the oxygen into the slurry through the porous wall, favours good dispersion throughout the mass of the pulp and consequently good bleaching or delignification contact with the pulp fibers.
SUMMARY OF THE INVENTION
It is an aim of the present invention to improve con-tact between the oxygen and the pulp still further so as to achieve enhanced bleaching action with the same amount of oxygen.
This is accomplished, according to the invention, by injecting the oxygen into the diffusing and mixing conduit in the way described above, but as a mixture of oxygen and steam.
Minute bubbles of the oxygen-steam mixture are formed momen-tarily as the mixture passes from the minute pores of the ; 25 injector wall, but as each bubble meets the pulp, the steam condenses and leaves the oxygen content as a smaller bubble.
The condensing steam imparts additional heat to the slurry.
13V03~2 Preferably as much of the steam needed to bring the slurry to reaction temperature as possible is injected, in one stage, through the diffuser-mixer. Whether this can be done depends on capacity of the diffuser-mixer. Therefore, addi-tional steam may be injected, if required, in a steam mixerbringing it to a supply temperature in a preliminary stage, through an injector between the pump and the oxygen-steam diffuser-mixer to raise the temperature closer to reaction.
Steam may also be injected to preheat the slurry upstream of the pump.
So, the invention contemplates:
a) preferably injecting all the steam, in the diffuser-miser, in the form of an oxygen-steam mixture, or b) injecting some of the steam between the pump and the diffuser-mixer to raise the pump to an intermediate temperature, and c) in combination with either a) or b) injecting steam to preheat the pulp upstream of the pump, to preheated supply temperature.
By injecting the oxygen into the liquid-behaving slurry, in an oxygen-steam mixture, as compared with injecting oxygen alone through the same microporous surface, under the same conditions, the effective surface area of the oxygen, in contact with the pulp, may be increased from twice to ten times, with a preferred increase from three to five times. This bring about a corresponding increase in the bleaching effect of the 13Q03~22 of the oxygen and a conse4uent saving of chemical bleaching agent. Heating the slurry with the injected steam, at this stage, is also advantageous.
For bleaching, the proportion of oxygen to steam may range from 20 to 200:1, by weight, with 100 to 150:1 preferred.
Or, in terms of volume, the proportion of oxygen to steam may range from 50 to 500:1 with 300 to 400:1 preferred. For delignification, the oxygen may range from 80 to 800:1, by weight, with 400 to 600:1 preferred. Or, by volume, the oxygen may range from 200 to 2000:1, with 1200 to 1600:1 pre-ferred.
The oxygen to pulp ratio may range from 10 lbs. to 40 lbs. per ton of pulp, measured on a dry basis. Then it is desirable to add as much steam as possible with the oxygen-steam mixture. Since the amount of steam which can be added is limited by the capacity of the diffuser, it may be necessary as well to add steam at an earlier stage, in order to inject enough heat to bring the slurry to reaction temperature.
The invention provides for potential maximum utiliza-tion of oxygen and steam in the delignification or bleachingprocess in the following way. The total amount of steam, injected into the slurry, is a controlled amount that will heat the slurry to reaction temperature in the reaction vessel. Preferably, according to the invention, the propor-tion of the total amount of steam injected with the oxygen-steam mixture in the diffuser would be substantially the maximum allowed by the capacity of the diffuser to inject it . , or a proportional selected amount close to this maximum, say 80%
or more. The remainder of the steam necessary to heat the slurry to reaction temperature may then be injected into it up-stream of the diffuser. The optimum proportion of oxygen to beinjected into the pulp for good delignification or bleaching is determined by tests, as is well known in the art, and selected for the particular plant and the particular conditions involved.
Oxygen injection is then controlled to feed the selected amount continually to the slurry. The injection of steam, along with the oxygen, results in the oxygen being injected in smaller bubbles than if oxygen alone were being injected which, in turn, provides a greater surface area of the oxygen in contact with the pulp and better absorption for a given amount of oxygen.
The invention, therefore, provides several advantages, namely that a large amount of steam used for heating is injected where it is needed just prior to the reaction zone and, at the same time, the injection of the oxygen along with the steam results in greater surface area of the oxygen injected and better reaction with the pulp for a given amount of oxygen. In this way, the utilization of both oxygen and steam is substantially at a maximum for the particular plant.
If all the steam needed to bring the slurry to re-action temperature can be added at the diffuser control may be exerted continuously by regulating the amount of steam fed in the steam-oxygen mixture by the temperature of the slurry down-stream of the oxygen-steam diffuser while keeping the supply of oxygen constant or by control!ing it in keeping with some 130()32Z
relevant variable. If it is necessary to add additional steam upstream of the diffuser the temperature control will also regulate such upstream supply.
The invention lends itself particularly to the incre-mental dosage of the pulp slurry with oxygen. This is done byfeeding of a stream of cellulose pulp slurry under pressure, from a supply, through a reaction path made up of a plurality of successive stages, in each of which the stream is first confined to a cross-section at which it has a velocity such as to fluidize it to liquid flow and is then expanded to a cross-section at which it has a velocity such as to provide plug flow. In each stage, oxygen is injected into the liquid flow under pressure, in the form of a mass of minute bubbles to disperse them throughout, whereby most of the oxygen is reacted with the pulp in the plug flow at that stage. The treated slurry is then recovered from the final stage.
The invention also contemplates a preferred further mixing of the slurry leaving the oxygen diffuser by passage through a pulp fluidizing mixer. This can be located adjacent to the diffuser or positioned some distance downstream. This mixer provides the effective further mixing and dispersing of any agglomeration of oxygen so that the oxygen remains in finely divided form and is more intemately mixed with the slurry. A
preferred static mixer is made up of a pipe tapering down to a choke, followed by a pipe that flares out to the diameter of the pipe in which the pulp slurry is flowing. The velocity through the choke will be about the same as that in the diffuser.
- 130~322 The invention also contemplates means for coordinating the flow of oxygen to the flow of pulp slurry so as to maintain the proper oxygen dosage. This may be accomplished by an appara-tus which includes a flow measuring device, for example, an orifice plate within the path of the slurry, in advance of the diffuser, the orifice plate being connected to a differential pressure cell which, in turn, is connected to a controller.
The controller sends a signal to an oxygen flow con-trol valve controlling the oxygen supply to the diffuser. There is an orifice plate or other device in the oxygen supply line that measures the oxygen flow. The control mechanism may include a computer that maintains a constant, predetermined and set ratio of oxygen to pulp so as to increase and decrease the dosage to keep pace with the differing flow rates of the pulp slurry.
An apparatus, according to the invention, includes a supply vessel for the slurry, a substantially unobstructed injection and mixing conduit for confining the slurry to a stream for substantially free flow therethrough, a reaction vessel having a greater cross-section than said conduit and connected therewith, means for continuously force-feeding the slurry under pressure from the supply vessel to the conduit, and means for regulating the feeding pressure so that the slurry in the conduit has a velocity such as to provide a turbulent liquid flow therethrough and the slurry in the reactor assumes plug flow. There is diffusing means, includ-ing an extensive microporous surface interfacing with the slurry, in the conduit, to diffuse an oxygen-steam mixture into the :
:
) 3,.2 slurry under pressure higher than the pulp feeding pressure thereby to form a mass of minute oxygen bubbles and mix them throughout the slurry in the conduit whereby they remain in contact with the thick pulp throughout the plug flow to pro-vide delignification or bleaching action. The control mechanismincludes a supply conduit for supplying a mixture of oxygen and steam to the diffusing means and means for regulating the flow of oxygen therethrough, a steam conduit leading from a source of steam to said supply conduit and means for regulating the flow of steam therethrough, the means for controlling the steam supply being responsive to the temperature of the slurry passing from the mixing conduit to the reaction vessel.
Means may also be provided for adding steam to the slurry prior to the diffusing means. In this event, the means for controlling the steam supply responsive to the temperature of the slurry may also control the additional supply of steam.
In a preferred apparatus, the pulp slurry flows through an initial oxygen diffuser and a plurality of reactors each pre-ceded by an oxygen diffuser. Any or all may be passed into a reaction tower to allow further extraction with caustic soda.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further explained by reference to the accompanying drawings, in which:
FIG. 1 is a side elevation partly in section through apparatus of the type currently used for steam and oxygen addition to pulp in a bleaching process;
. . . . . ; .. , , , .~, -~ , i3V03ZZ
FIG. 2 is a similar side elevation partly in section through a preferred apparatus effective for carrying out a preferred method, according to the invention; and FIG. 3 is a side elevation, partly in section through a preferred diffusing device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 illustrates a prior method of employing steam and oxygen together in bleaching pulp.
Referring to Fig. 1, a pulp mixture, which is normally a thick heavy mass, is continuously passed from a source of supply through a steam mixer 15 which preheats it to a tempera-ture from 100 to 150F to 170 to 200F and thence through a pipe 16 to the top of a storage chute 17. From the storage chute 17 the pulp, mixed with steam, is pumped, as a slurry, by a pump 19, through another pipe 21 through an oxygen dis-perser conduit 23 illustrated in more detail in Fig. 3. The pressure at which the slurry is pumped is effective to cause it to flow through the conduit 23 at a velocity such that it acts as a turbulent liquid. This phenomenon is described in the Lee et al application 507,000, referred to above. Steam is supplied to the steam mixer 15 from a source of supply through a pipe 25.
The supply of steam is regulated by a temperature controller 27 connected to a valve 29 in the pipe 25.
Oxygen is supplied to a diffusing device within the conduit 23, through a line 31 leading from a source of oxygen supply through a pressure controller 33. The diffusing device 1300~2 has a microporous wall interfacing with the slurry.
Oxygen is thus continuously introduced into the heated pulp slurry through the diffusing device in the form of a mass of minute bubbles at a time when it acts as a turbulent liquid, so that the oxygen bubbles are difFused into the slurry and mixed throughout. The slurry containing the oxygen passes through a pipe 35 into the bottom of a retention tube 37 pro-vided with a back pressure control vaive 39. The slurry slows down in the tube 37 to plug flow velocity at which it reassumes its normal thick condition and is held under pressure so that it gradually absorbs the oxygen whlch reacts with it.
The pulp is retained in the retention tube for suffi-ciently long to allow the oxygen to react with the cellulose.
The parts of the preferred apparatus of Fig. 2 have been given the same tens and digits as in Fig. 1 but have been raised by 100.
Method of the Invention In the apparatus of Fig. 2, illustrating a preferred method, according to the invention, steam is added to the pipe 131 conducting the oxygen to the diffusing device A (see Fig. 3) within the disperser conduit 123 to form an oxygen-steam mixture.
The steam supply is controlled by a temperature con-troller 127 linked to the pipe 135 between the disperser 123 and the retention tube 137. Thus, steam is first mixed with oxygen and the oxygen-steam mixture added to the slurry, through the diffusing device A, in the form of a mass of minute bubbles. When the oxygen-steam mixture contacts the pulp, the i3U~3~ ,~
steam condenses to water vapor, imparting heat to the pulp, and leaving the oxygen-gas within the pulp in the form of smaller bubbles (than the oxygen-steam bubbles) which are dispersed through the slurry by its turbulence. Better sub-division and dispersion of the oxygen is achieved to provide a much greater effective surface area of the oxygen interfacing with the slurry than would occur without the steam. This increases the oxygen transfer rate accordingly and less oxygen need be employed, than otherwise, to obtain the same bleaching effect.
The pressure of the oxygen-steam mixture, as injected, is about the same or slightly higher than the oxygen pressure as in the method of Fig. 1.
In contrast to the prior method, steam is mixed with the oxygen just before injection of the mixture into the diffuser A and the control of the steam flow is carried out by a temperature controller 127 sensing the temperature of the pulp downstream of the disperser.
The pulp then passes into the pressurized retention tube 137 where it assumes plug flow and moves at relatively slow speed, under pressure, with the oxygen dispersed through-out the plug in small bubbles to react with the cellulose.
In the case where several diffusers are used in series, - as for example in the Lee et al Canadian Application 507,000, steam is added to the first stage.
The diffuser through which the oxygen-steam mixture is injected into the slurry in the diffuser A may take various forms, some of which are shown in the Lee et al application 130~322 referred to above all of which include a microporous wall which interfaces with the slurry and through which the oxygen-steam mixture is diffused. This is preferably a sintered stainless steel element as described in Bulletin M 201 of Pall Trinity Micro Corporation, a subsidiary of Pall Corporation and in U.S.
Paent 2,554,343. Such elements are generally used for filtering.
The pore size should be within the range from about 2 microns to 100 microns, preferably less than about 10 microns. The porosity should be substantially uniform with voids making up about 40 to 50% of the volume of the wall, which has a thickness of from about 1/32 of an inch to about 1/2 inch.
A preferred form of diffuser A is shown in Fig. 3. It is made up of a cylinder 123 providing a passage for the pulp slurry. The cylinder has flanges 63, 64 on its ends for connecting into a pipeline. A tube 65 extends transaxially and centrally across the passage 123 and is held in it by a suitable socket 69 formed on the wall of the cylinder 123. The pipe 131 for the delivery of the oxygen-steam mixture to the tube 65 leads to the diffusion tube 65.
The minute streams of oxygen-steam mixture, as the mixture passes through the pores in the tube 65 wall, as they leave the porour surface, are stripped therefrom by the slurry as minute bubbles. The steam condenses from each bubble, immediately it contacts the slurry and leaves a bubbles of oxygen, having a fraction of the size it would have had oxygen alone been injected. While there may be some coalescence, generally speaking, the mass of oxygen bubbles are dispersed 13~0322 throughout the slurry by its turbulence as it passes with great rapidity through the conduit 123 and the bubbles are carried in the slurry into the reaction chamber 137 where it assumes rela-tive slow plug flow. The oxygen therefore has time to react with the pulp and is absorbed as the plug of slurry passes relatively slowly through the vessel 137.
The Diffuser The diffusing element may include a conduit or cylin-der through which the slurry passes, the wall of the cylinder defining the flow path. The diffusing element may form a part of the wall of the cylinder, may take the form of a porous pipe extending transaxially of the cylinder, or may take the form of a porous pipe extending axially of the cylinder. In all cases, the path of the slurry is relatively unobstructed. Where the cylinder has a porous wall, the slurry passes directly through the cylinder without any obstruction. In the case of a pipe within the cylinder, it takes up a minor space so that the major volume of the space in the cylinder is taken up by the slurry moving through it in contact with the porous diffusing surface.
Starting Material The starting material for the present process will depend on whether the method is being employed at the deligni-- fication stage or the bleaching stage of the pulp treatment.
For delignification, the aqueous pulp slurry comes from three or four washing stages following the brownstock washing stage, with the pulp containing considerable lignin, 13~(~322 as indicated by a Kappa number between 30 and 60, typically 40 to 50. It will contain 8 to 16%, preferably 10 to 12%, by weight, solids. Caustic will be added in an amount from 2 to 4%, by weight, typically 3%, prior to delignification according to the present invention.
Bleaching is effected, according to the invention, usually after the slurry has been washed, following the first chlorination stage. Then, it will have a Kappa number from 3 to 8, typically 4 to 5. It will contain from 8 to 16%, preferably 10 to 12%, by weight, solids. Again, caustic will be added in an amount of 2 to 4%, by weight, typically 3%, to provide the starting material for bleaching, according to the invention.
Turbulent Liquid Flow A typical diffusing and mixing conduit 123 may range in cross-sectional area from about 4 to about 17 sq. inches.
To produce turbulent flow, the slurry is fed through the conduit at a pressure from about 20 to about 200 psig. This gives the slurry a velocity from about 0.5 to about 50 meters per second, preferably from about 3 to about 10 meters per second.
The residence time in the conduit 123 will then range from about 0.001 to about 0.120 seconds. The residence time in the reactor tube 137 will range from about 1 to about 5 minutes.
Temperature Steam serves both the function of heating the slurry and as a vehicle for the injection of the oxygen so as to reduce the size of the bubbles of the latter mixed into the slurry.
Typical preferred temperatures are:
~3VV322 a) the starting pulp slurry prior to the mixer 15 will usually have a temperature below around 130F, b) in the mixer 15 the temperature will be raised from 130F to about 140F, c) after the preliminary injection downstream of the pump and prior to the oxygen-steam diffuser mixer to an intermediate temperature between 140F and 160F, d) after the diffuser mixer to a reaction tempera-ture in the range from about 160F to 180F, e) before entry into the retention vessel the pulp should have a temperature within a range from about 160F to about 180F.
Porous Surface The surface of the porous wall interfacing with the slurry may preferably have an area ranging from about 0.05 to about 0.2 sq. feet covered with pores having a diameter within the range from about 10 to about 100 microns.
Oxygen-Steam The oxygen employed may be molecular oxygen, as commer-cially available, containing 90% or more and preferably 98% or more of oxygen. Or, the oxygen can be in the form of a gas con-taining more than 50% oxygen. The starting pulp slurry may con-tain about 10 to about 20% of air by volume of the pulp dispersed which dilutes added oxygen. For a pulp containing little or no air, the concentration of the added oxygen containing gas may be at the lower end of the oxygen content range and for a pulp 13~0~
containing a lot of air, the added gas may contain oxygen toward the upper end of the oxygen range.
In order to control the oxygen dosage to meet require-ments, the oxygen content of off-gas leaving the vent of the final treatment vessel is measured. From this it can be determined whether good mixing is being achieved. Adjustments can be made accordingly and the incremental dosage can be manipulated in order to achieve the best results.
In a multi-stage process, as described, large total amounts of oxygen can thus be added incrementally to a pulp slurry, by adding small amounts at each stage according to the formula:
Volume of oxygen + gas <
Volume (oxygen + gas + pulp + steam) 0.1 This formula is calculated at the operating pressure of that particular stage.
The dosage may be proportioned evenly to each stage or may be varied to suit varying conditions such as changes in the nature of the pulp or otherwise.
The oxygen employed should have at least 90% oxygen content by volume, preferably more than 98% measured under standard conditions.
The steam should be saturated steam.
The oxygen-steam mixture injection pressure should be greater than the pulp slurry pressure from about 15 to 150 psig.
The temperature of the oxygen-steam mixture, at injection, should be from about 265F to about 390F.
~3V(~
The ratejo-f injection of the oxygen-steam mixture should be within the range from about 10 Ibs. of oxygen to about 50 lbs. of oxygen per ton of pulp measured on a dry b~sis.
As will be understood by one skilled in the art, the vessels and piping should be insulated so as to retain heat.
The Lee et al application discloses a process and apparatus for bleaching pulp in the form of an aqueous slurry having a consistency from 8% to 16~, by introducing oxygen into the slurry, in the form of minute bubbles, at the time the slurry is passing, under pumping pressure, through a diffusing and mixing conduit which confines the slurry to a cross section so that, at the pumping pressure, it moves at a high velocity effective to provide turbulent liquid flow. The phenomenon of the liquid behavior of pulp slurry confined under high velocity is explained in an article entitle "Medium Consistency Technology" appearing in the TAPPI Journal, Vol. 64, No. 6, June 1981, and in the Lee et al application 507,000.
The slurry containing the bubbles is immediately passed from the mixing conduit into and through a reaction vessel which releases the slurry to a cross section at which it assumes relatively slow plug flow, to give the oxygen 1~0()322 bubbles dispersed through it, time to react with the cellulose.
The treated slurry is recovered from the reaction vessel. Dis-persing the bubbles within the turbulent liquid slurry is accomplished by passing the oxygen, under pressure greater than that of the slurry pressure, through a microporous wall into contact with the slurry.
The slurry may be preheated by passing it through a steam mixer, on the way to the pump, and the heated slurry deposited in a storage vessel upstream of the pump.
The minuteness of the bubbles, produced initially by diffusing the oxygen into the slurry through the porous wall, favours good dispersion throughout the mass of the pulp and consequently good bleaching or delignification contact with the pulp fibers.
SUMMARY OF THE INVENTION
It is an aim of the present invention to improve con-tact between the oxygen and the pulp still further so as to achieve enhanced bleaching action with the same amount of oxygen.
This is accomplished, according to the invention, by injecting the oxygen into the diffusing and mixing conduit in the way described above, but as a mixture of oxygen and steam.
Minute bubbles of the oxygen-steam mixture are formed momen-tarily as the mixture passes from the minute pores of the ; 25 injector wall, but as each bubble meets the pulp, the steam condenses and leaves the oxygen content as a smaller bubble.
The condensing steam imparts additional heat to the slurry.
13V03~2 Preferably as much of the steam needed to bring the slurry to reaction temperature as possible is injected, in one stage, through the diffuser-mixer. Whether this can be done depends on capacity of the diffuser-mixer. Therefore, addi-tional steam may be injected, if required, in a steam mixerbringing it to a supply temperature in a preliminary stage, through an injector between the pump and the oxygen-steam diffuser-mixer to raise the temperature closer to reaction.
Steam may also be injected to preheat the slurry upstream of the pump.
So, the invention contemplates:
a) preferably injecting all the steam, in the diffuser-miser, in the form of an oxygen-steam mixture, or b) injecting some of the steam between the pump and the diffuser-mixer to raise the pump to an intermediate temperature, and c) in combination with either a) or b) injecting steam to preheat the pulp upstream of the pump, to preheated supply temperature.
By injecting the oxygen into the liquid-behaving slurry, in an oxygen-steam mixture, as compared with injecting oxygen alone through the same microporous surface, under the same conditions, the effective surface area of the oxygen, in contact with the pulp, may be increased from twice to ten times, with a preferred increase from three to five times. This bring about a corresponding increase in the bleaching effect of the 13Q03~22 of the oxygen and a conse4uent saving of chemical bleaching agent. Heating the slurry with the injected steam, at this stage, is also advantageous.
For bleaching, the proportion of oxygen to steam may range from 20 to 200:1, by weight, with 100 to 150:1 preferred.
Or, in terms of volume, the proportion of oxygen to steam may range from 50 to 500:1 with 300 to 400:1 preferred. For delignification, the oxygen may range from 80 to 800:1, by weight, with 400 to 600:1 preferred. Or, by volume, the oxygen may range from 200 to 2000:1, with 1200 to 1600:1 pre-ferred.
The oxygen to pulp ratio may range from 10 lbs. to 40 lbs. per ton of pulp, measured on a dry basis. Then it is desirable to add as much steam as possible with the oxygen-steam mixture. Since the amount of steam which can be added is limited by the capacity of the diffuser, it may be necessary as well to add steam at an earlier stage, in order to inject enough heat to bring the slurry to reaction temperature.
The invention provides for potential maximum utiliza-tion of oxygen and steam in the delignification or bleachingprocess in the following way. The total amount of steam, injected into the slurry, is a controlled amount that will heat the slurry to reaction temperature in the reaction vessel. Preferably, according to the invention, the propor-tion of the total amount of steam injected with the oxygen-steam mixture in the diffuser would be substantially the maximum allowed by the capacity of the diffuser to inject it . , or a proportional selected amount close to this maximum, say 80%
or more. The remainder of the steam necessary to heat the slurry to reaction temperature may then be injected into it up-stream of the diffuser. The optimum proportion of oxygen to beinjected into the pulp for good delignification or bleaching is determined by tests, as is well known in the art, and selected for the particular plant and the particular conditions involved.
Oxygen injection is then controlled to feed the selected amount continually to the slurry. The injection of steam, along with the oxygen, results in the oxygen being injected in smaller bubbles than if oxygen alone were being injected which, in turn, provides a greater surface area of the oxygen in contact with the pulp and better absorption for a given amount of oxygen.
The invention, therefore, provides several advantages, namely that a large amount of steam used for heating is injected where it is needed just prior to the reaction zone and, at the same time, the injection of the oxygen along with the steam results in greater surface area of the oxygen injected and better reaction with the pulp for a given amount of oxygen. In this way, the utilization of both oxygen and steam is substantially at a maximum for the particular plant.
If all the steam needed to bring the slurry to re-action temperature can be added at the diffuser control may be exerted continuously by regulating the amount of steam fed in the steam-oxygen mixture by the temperature of the slurry down-stream of the oxygen-steam diffuser while keeping the supply of oxygen constant or by control!ing it in keeping with some 130()32Z
relevant variable. If it is necessary to add additional steam upstream of the diffuser the temperature control will also regulate such upstream supply.
The invention lends itself particularly to the incre-mental dosage of the pulp slurry with oxygen. This is done byfeeding of a stream of cellulose pulp slurry under pressure, from a supply, through a reaction path made up of a plurality of successive stages, in each of which the stream is first confined to a cross-section at which it has a velocity such as to fluidize it to liquid flow and is then expanded to a cross-section at which it has a velocity such as to provide plug flow. In each stage, oxygen is injected into the liquid flow under pressure, in the form of a mass of minute bubbles to disperse them throughout, whereby most of the oxygen is reacted with the pulp in the plug flow at that stage. The treated slurry is then recovered from the final stage.
The invention also contemplates a preferred further mixing of the slurry leaving the oxygen diffuser by passage through a pulp fluidizing mixer. This can be located adjacent to the diffuser or positioned some distance downstream. This mixer provides the effective further mixing and dispersing of any agglomeration of oxygen so that the oxygen remains in finely divided form and is more intemately mixed with the slurry. A
preferred static mixer is made up of a pipe tapering down to a choke, followed by a pipe that flares out to the diameter of the pipe in which the pulp slurry is flowing. The velocity through the choke will be about the same as that in the diffuser.
- 130~322 The invention also contemplates means for coordinating the flow of oxygen to the flow of pulp slurry so as to maintain the proper oxygen dosage. This may be accomplished by an appara-tus which includes a flow measuring device, for example, an orifice plate within the path of the slurry, in advance of the diffuser, the orifice plate being connected to a differential pressure cell which, in turn, is connected to a controller.
The controller sends a signal to an oxygen flow con-trol valve controlling the oxygen supply to the diffuser. There is an orifice plate or other device in the oxygen supply line that measures the oxygen flow. The control mechanism may include a computer that maintains a constant, predetermined and set ratio of oxygen to pulp so as to increase and decrease the dosage to keep pace with the differing flow rates of the pulp slurry.
An apparatus, according to the invention, includes a supply vessel for the slurry, a substantially unobstructed injection and mixing conduit for confining the slurry to a stream for substantially free flow therethrough, a reaction vessel having a greater cross-section than said conduit and connected therewith, means for continuously force-feeding the slurry under pressure from the supply vessel to the conduit, and means for regulating the feeding pressure so that the slurry in the conduit has a velocity such as to provide a turbulent liquid flow therethrough and the slurry in the reactor assumes plug flow. There is diffusing means, includ-ing an extensive microporous surface interfacing with the slurry, in the conduit, to diffuse an oxygen-steam mixture into the :
:
) 3,.2 slurry under pressure higher than the pulp feeding pressure thereby to form a mass of minute oxygen bubbles and mix them throughout the slurry in the conduit whereby they remain in contact with the thick pulp throughout the plug flow to pro-vide delignification or bleaching action. The control mechanismincludes a supply conduit for supplying a mixture of oxygen and steam to the diffusing means and means for regulating the flow of oxygen therethrough, a steam conduit leading from a source of steam to said supply conduit and means for regulating the flow of steam therethrough, the means for controlling the steam supply being responsive to the temperature of the slurry passing from the mixing conduit to the reaction vessel.
Means may also be provided for adding steam to the slurry prior to the diffusing means. In this event, the means for controlling the steam supply responsive to the temperature of the slurry may also control the additional supply of steam.
In a preferred apparatus, the pulp slurry flows through an initial oxygen diffuser and a plurality of reactors each pre-ceded by an oxygen diffuser. Any or all may be passed into a reaction tower to allow further extraction with caustic soda.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further explained by reference to the accompanying drawings, in which:
FIG. 1 is a side elevation partly in section through apparatus of the type currently used for steam and oxygen addition to pulp in a bleaching process;
. . . . . ; .. , , , .~, -~ , i3V03ZZ
FIG. 2 is a similar side elevation partly in section through a preferred apparatus effective for carrying out a preferred method, according to the invention; and FIG. 3 is a side elevation, partly in section through a preferred diffusing device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 illustrates a prior method of employing steam and oxygen together in bleaching pulp.
Referring to Fig. 1, a pulp mixture, which is normally a thick heavy mass, is continuously passed from a source of supply through a steam mixer 15 which preheats it to a tempera-ture from 100 to 150F to 170 to 200F and thence through a pipe 16 to the top of a storage chute 17. From the storage chute 17 the pulp, mixed with steam, is pumped, as a slurry, by a pump 19, through another pipe 21 through an oxygen dis-perser conduit 23 illustrated in more detail in Fig. 3. The pressure at which the slurry is pumped is effective to cause it to flow through the conduit 23 at a velocity such that it acts as a turbulent liquid. This phenomenon is described in the Lee et al application 507,000, referred to above. Steam is supplied to the steam mixer 15 from a source of supply through a pipe 25.
The supply of steam is regulated by a temperature controller 27 connected to a valve 29 in the pipe 25.
Oxygen is supplied to a diffusing device within the conduit 23, through a line 31 leading from a source of oxygen supply through a pressure controller 33. The diffusing device 1300~2 has a microporous wall interfacing with the slurry.
Oxygen is thus continuously introduced into the heated pulp slurry through the diffusing device in the form of a mass of minute bubbles at a time when it acts as a turbulent liquid, so that the oxygen bubbles are difFused into the slurry and mixed throughout. The slurry containing the oxygen passes through a pipe 35 into the bottom of a retention tube 37 pro-vided with a back pressure control vaive 39. The slurry slows down in the tube 37 to plug flow velocity at which it reassumes its normal thick condition and is held under pressure so that it gradually absorbs the oxygen whlch reacts with it.
The pulp is retained in the retention tube for suffi-ciently long to allow the oxygen to react with the cellulose.
The parts of the preferred apparatus of Fig. 2 have been given the same tens and digits as in Fig. 1 but have been raised by 100.
Method of the Invention In the apparatus of Fig. 2, illustrating a preferred method, according to the invention, steam is added to the pipe 131 conducting the oxygen to the diffusing device A (see Fig. 3) within the disperser conduit 123 to form an oxygen-steam mixture.
The steam supply is controlled by a temperature con-troller 127 linked to the pipe 135 between the disperser 123 and the retention tube 137. Thus, steam is first mixed with oxygen and the oxygen-steam mixture added to the slurry, through the diffusing device A, in the form of a mass of minute bubbles. When the oxygen-steam mixture contacts the pulp, the i3U~3~ ,~
steam condenses to water vapor, imparting heat to the pulp, and leaving the oxygen-gas within the pulp in the form of smaller bubbles (than the oxygen-steam bubbles) which are dispersed through the slurry by its turbulence. Better sub-division and dispersion of the oxygen is achieved to provide a much greater effective surface area of the oxygen interfacing with the slurry than would occur without the steam. This increases the oxygen transfer rate accordingly and less oxygen need be employed, than otherwise, to obtain the same bleaching effect.
The pressure of the oxygen-steam mixture, as injected, is about the same or slightly higher than the oxygen pressure as in the method of Fig. 1.
In contrast to the prior method, steam is mixed with the oxygen just before injection of the mixture into the diffuser A and the control of the steam flow is carried out by a temperature controller 127 sensing the temperature of the pulp downstream of the disperser.
The pulp then passes into the pressurized retention tube 137 where it assumes plug flow and moves at relatively slow speed, under pressure, with the oxygen dispersed through-out the plug in small bubbles to react with the cellulose.
In the case where several diffusers are used in series, - as for example in the Lee et al Canadian Application 507,000, steam is added to the first stage.
The diffuser through which the oxygen-steam mixture is injected into the slurry in the diffuser A may take various forms, some of which are shown in the Lee et al application 130~322 referred to above all of which include a microporous wall which interfaces with the slurry and through which the oxygen-steam mixture is diffused. This is preferably a sintered stainless steel element as described in Bulletin M 201 of Pall Trinity Micro Corporation, a subsidiary of Pall Corporation and in U.S.
Paent 2,554,343. Such elements are generally used for filtering.
The pore size should be within the range from about 2 microns to 100 microns, preferably less than about 10 microns. The porosity should be substantially uniform with voids making up about 40 to 50% of the volume of the wall, which has a thickness of from about 1/32 of an inch to about 1/2 inch.
A preferred form of diffuser A is shown in Fig. 3. It is made up of a cylinder 123 providing a passage for the pulp slurry. The cylinder has flanges 63, 64 on its ends for connecting into a pipeline. A tube 65 extends transaxially and centrally across the passage 123 and is held in it by a suitable socket 69 formed on the wall of the cylinder 123. The pipe 131 for the delivery of the oxygen-steam mixture to the tube 65 leads to the diffusion tube 65.
The minute streams of oxygen-steam mixture, as the mixture passes through the pores in the tube 65 wall, as they leave the porour surface, are stripped therefrom by the slurry as minute bubbles. The steam condenses from each bubble, immediately it contacts the slurry and leaves a bubbles of oxygen, having a fraction of the size it would have had oxygen alone been injected. While there may be some coalescence, generally speaking, the mass of oxygen bubbles are dispersed 13~0322 throughout the slurry by its turbulence as it passes with great rapidity through the conduit 123 and the bubbles are carried in the slurry into the reaction chamber 137 where it assumes rela-tive slow plug flow. The oxygen therefore has time to react with the pulp and is absorbed as the plug of slurry passes relatively slowly through the vessel 137.
The Diffuser The diffusing element may include a conduit or cylin-der through which the slurry passes, the wall of the cylinder defining the flow path. The diffusing element may form a part of the wall of the cylinder, may take the form of a porous pipe extending transaxially of the cylinder, or may take the form of a porous pipe extending axially of the cylinder. In all cases, the path of the slurry is relatively unobstructed. Where the cylinder has a porous wall, the slurry passes directly through the cylinder without any obstruction. In the case of a pipe within the cylinder, it takes up a minor space so that the major volume of the space in the cylinder is taken up by the slurry moving through it in contact with the porous diffusing surface.
Starting Material The starting material for the present process will depend on whether the method is being employed at the deligni-- fication stage or the bleaching stage of the pulp treatment.
For delignification, the aqueous pulp slurry comes from three or four washing stages following the brownstock washing stage, with the pulp containing considerable lignin, 13~(~322 as indicated by a Kappa number between 30 and 60, typically 40 to 50. It will contain 8 to 16%, preferably 10 to 12%, by weight, solids. Caustic will be added in an amount from 2 to 4%, by weight, typically 3%, prior to delignification according to the present invention.
Bleaching is effected, according to the invention, usually after the slurry has been washed, following the first chlorination stage. Then, it will have a Kappa number from 3 to 8, typically 4 to 5. It will contain from 8 to 16%, preferably 10 to 12%, by weight, solids. Again, caustic will be added in an amount of 2 to 4%, by weight, typically 3%, to provide the starting material for bleaching, according to the invention.
Turbulent Liquid Flow A typical diffusing and mixing conduit 123 may range in cross-sectional area from about 4 to about 17 sq. inches.
To produce turbulent flow, the slurry is fed through the conduit at a pressure from about 20 to about 200 psig. This gives the slurry a velocity from about 0.5 to about 50 meters per second, preferably from about 3 to about 10 meters per second.
The residence time in the conduit 123 will then range from about 0.001 to about 0.120 seconds. The residence time in the reactor tube 137 will range from about 1 to about 5 minutes.
Temperature Steam serves both the function of heating the slurry and as a vehicle for the injection of the oxygen so as to reduce the size of the bubbles of the latter mixed into the slurry.
Typical preferred temperatures are:
~3VV322 a) the starting pulp slurry prior to the mixer 15 will usually have a temperature below around 130F, b) in the mixer 15 the temperature will be raised from 130F to about 140F, c) after the preliminary injection downstream of the pump and prior to the oxygen-steam diffuser mixer to an intermediate temperature between 140F and 160F, d) after the diffuser mixer to a reaction tempera-ture in the range from about 160F to 180F, e) before entry into the retention vessel the pulp should have a temperature within a range from about 160F to about 180F.
Porous Surface The surface of the porous wall interfacing with the slurry may preferably have an area ranging from about 0.05 to about 0.2 sq. feet covered with pores having a diameter within the range from about 10 to about 100 microns.
Oxygen-Steam The oxygen employed may be molecular oxygen, as commer-cially available, containing 90% or more and preferably 98% or more of oxygen. Or, the oxygen can be in the form of a gas con-taining more than 50% oxygen. The starting pulp slurry may con-tain about 10 to about 20% of air by volume of the pulp dispersed which dilutes added oxygen. For a pulp containing little or no air, the concentration of the added oxygen containing gas may be at the lower end of the oxygen content range and for a pulp 13~0~
containing a lot of air, the added gas may contain oxygen toward the upper end of the oxygen range.
In order to control the oxygen dosage to meet require-ments, the oxygen content of off-gas leaving the vent of the final treatment vessel is measured. From this it can be determined whether good mixing is being achieved. Adjustments can be made accordingly and the incremental dosage can be manipulated in order to achieve the best results.
In a multi-stage process, as described, large total amounts of oxygen can thus be added incrementally to a pulp slurry, by adding small amounts at each stage according to the formula:
Volume of oxygen + gas <
Volume (oxygen + gas + pulp + steam) 0.1 This formula is calculated at the operating pressure of that particular stage.
The dosage may be proportioned evenly to each stage or may be varied to suit varying conditions such as changes in the nature of the pulp or otherwise.
The oxygen employed should have at least 90% oxygen content by volume, preferably more than 98% measured under standard conditions.
The steam should be saturated steam.
The oxygen-steam mixture injection pressure should be greater than the pulp slurry pressure from about 15 to 150 psig.
The temperature of the oxygen-steam mixture, at injection, should be from about 265F to about 390F.
~3V(~
The ratejo-f injection of the oxygen-steam mixture should be within the range from about 10 Ibs. of oxygen to about 50 lbs. of oxygen per ton of pulp measured on a dry b~sis.
As will be understood by one skilled in the art, the vessels and piping should be insulated so as to retain heat.
Claims (18)
1. A continuous method of bleaching or deligni-fication of cellulose pulp, in which the pulp, in the form of an aqueous stream of slurry, is passed under pressure from a source of supply by pumping means through a diffusing and mixing conduit at a velocity such that it behaves as a turbulent liquid and then through a reaction vessel under pressure at a velocity at which it assumes plug flow, and oxygen is injected, at a pressure higher than that of the slurry, into the slurry in the conduit, through a microporous wall, to form in the slurry masses of minutes bubbles which are dispersed throughout the slurry in which, the oxygen is injected into the stream, through said microporous wall, in an oxygen-steam mixture whereby the steam condenses in and heats the slurry leaving the oxygen as smaller bubbles whereby the effective surface area of the oxygen in contact with the slurry is substantially greater than the surface area resulting from injecting oxygen alone into the slurry under the same conditions.
2. A method, as defined in claim 1, in which the injection of the steam is effective to raise the temperature of the slurry to at least 160°F.
3. A method, as defined in claim 1, in which the steam is also mixed into the pulp, in a preliminary stage, between the pumping means and the oxygen-steam diffuser, to raise the temperature of the pulp from a preheated supply temperature to an intermediate temper-ature below reaction temperature.
4. A method, as defined in claim 1, in which steam is mixed into the pulp, upstream of the pumping means, to bring it to a preheated supply temperature.
5. A method, as defined in claim 1, in which the oxygen-steam mixture is prepared by moving at least a major proportion of the steam employed to heat the slurry to the oxygen just prior to injection into the slurry and continuously regulating the amount of steam mixed with the oxygen in response to the temperature of the slurry.
6. A method, as defined in claim 1, in which there is injected into the slurry a total amount of steam effective to heat the pulp to reaction temper-ature, the steam supplied in the oxygen-steam mixture is adjusted to at least 80% of the maximum steam handling capacity of the diffuser and the remainder of the steam is supplied upstream of the diffuser.
7. A method, as defined in claim 6, in which the oxygen is injected within the range from about 10 to about 50 lbs. per ton of pulp on a dry basis.
8. A continuous method, as defined in claim 1 or 6, in which the proportion of steam to oxygen in the mixture is within the range from about 50 volumes of steam to 1 volume of oxygen to about 400 volumes of steam to 1 volume of oxygen.
9. A method, as defined in claim 1 or 6, in which the pore size of the microporous wall is not greater than 100 microns.
10. A method, as defined in claim 1 or 6, in which the slurry stream is pumped at a pressure within the range from about 50 to about 150 psig through a conduit having a cross section area within the range from about 4 to about 17 sq. inches.
11. A method, as defined in claim 1 or 6, in which the oxygen-steam mixture is injected at a high pressure than that of the slurry, within the range from 20 to 200 psig.
12. A method, as defined in claim 6, in which the reaction temperature of the slurry is regulated by controlling the amount of steam supplied in the oxygen steam mixture in response to the temperature of the slurry downstream of the introduction of the oxygen-steam mixture.
13. A method, as defined in claim 2, in which steam is mixed into the pulp, upstream of the pumping means, to bring the pulp to a preheated supply temper-ature.
14. A method, as defined in claim 1, in which the reaction temperature is within the range from 160°F to 180°F.
15. An apparatus for reacting an oxygen-containing gas with a cellulose pulp slurry having a consistency from 8% to 16% and being, at rest, a thick aqueous dispersion of pulp fibers, to effect delignification or bleaching, comprising, a supply vessel for the slurry, a substantially unobstructed injection and mixing conduit for containing the slurry to a stream for substantially free flow therethrough, a reaction vessel having a greater cross-section than said conduit and connected therewith, means for continuously force-feeding the slurry under pressure from the supply vessel to the conduit, means for regulating the feeding pressure so that the slurry in the conduit has a velocity such as to provide a turbulent liquid flow therethrough and the slurry in the reaction assumes plug flow, diffusing means including an extensive microporous surface interfacing with the slurry in the conduit to diffuse oxygen-containing gas into the slurry under pressure higher than the pulp feeding pressure thereby to form a mass of minute bubbles and mix them throughout the slurry in the con-duit whereby they remain in contact with the thick pulp throughout the plug flow to provide delignification or bleaching action, a gas connection to the diffusing means, means for supplying oxygen to the gas connection, means for supplying steam to the gas connection, means for controlling the oxygen supply, means for controlling the steam supply, and means for recovering treated slurry from the reactor.
16. An apparatus, as defined in claim 15, in which the means for controlling the steam supply is responsive to the temperature of the slurry leaving said mixing conduit.
17. An apparatus, as defined in claim 15, in which there is means for injecting steam into the slurry between the pump and said mixing conduit.
18. An apparatus, as defined in claim 15, in which there is a steam mixer for mixing the slurry with steam upstream of the pump.
Priority Applications (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 539056 CA1300322C (en) | 1987-06-08 | 1987-06-08 | Method of bleaching or delignification of cellulose pulp with oxygen |
| FR8709702A FR2617877B1 (en) | 1987-06-08 | 1987-07-08 | PROCESS FOR BLEACHING OR DELIGNIFYING A CELLULOSIC PASTE WITH OXYGEN, AND INSTALLATION FOR IMPLEMENTING SAME |
| EP88401393A EP0295180A3 (en) | 1987-06-08 | 1988-06-08 | Process for bleaching or delignification of a cellulose pulp with oxygen, and plant for carrying out the process |
| ZA886592A ZA886592B (en) | 1987-06-08 | 1988-09-05 | Method of bleaching or delignification of cellulose pulp with oxygen |
| AU22021/88A AU613952B2 (en) | 1987-06-08 | 1988-09-08 | Method of bleaching or delignification of cellulose pulp with oxygen |
| JP24587888A JPH0299681A (en) | 1987-06-08 | 1988-09-29 | Method of bleaching or delignifying cellulose pulp |
| BR8805312A BR8805312A (en) | 1987-06-08 | 1988-10-14 | CONTINUOUS PROCESS FOR MONEY LAUNDERING OR DE-LENIFICATION OF A CELLULOSIC PASTE AND INSTALLATION TO DO IT |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 539056 CA1300322C (en) | 1987-06-08 | 1987-06-08 | Method of bleaching or delignification of cellulose pulp with oxygen |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1300322C true CA1300322C (en) | 1992-05-12 |
Family
ID=4135839
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 539056 Expired - Fee Related CA1300322C (en) | 1987-06-08 | 1987-06-08 | Method of bleaching or delignification of cellulose pulp with oxygen |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0295180A3 (en) |
| JP (1) | JPH0299681A (en) |
| AU (1) | AU613952B2 (en) |
| CA (1) | CA1300322C (en) |
| FR (1) | FR2617877B1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2046717A1 (en) * | 1991-02-06 | 1992-08-07 | Beloit Technologies, Inc. | Method and apparatus for treating fibrous materials with a gaseous reagent |
| SE469398B (en) * | 1991-11-06 | 1993-06-28 | Sunds Defibrator Ind Ab | HEATING DEVICE FOR EXAMPLE OF CELLULOSAMASSA THEREOF APPLIED BY A MULTIPLE, SCRUBLED LOCATION, TAKEN IN A TRANSMISSION WALL |
| 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 |
| EP0647466A3 (en) * | 1993-10-08 | 1996-01-17 | Akzo Nobel Nv | Cellulosic membranes. |
Family Cites Families (3)
| 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 |
| ZA835925B (en) * | 1982-09-30 | 1984-04-25 | Black Clawson Co | Method and apparatus for oxygen delignification |
| AU595842B2 (en) * | 1985-11-15 | 1990-04-12 | Canadian Liquid Air Ltd. | Pulp bleaching |
-
1987
- 1987-06-08 CA CA 539056 patent/CA1300322C/en not_active Expired - Fee Related
- 1987-07-08 FR FR8709702A patent/FR2617877B1/en not_active Expired - Fee Related
-
1988
- 1988-06-08 EP EP88401393A patent/EP0295180A3/en not_active Withdrawn
- 1988-09-08 AU AU22021/88A patent/AU613952B2/en not_active Ceased
- 1988-09-29 JP JP24587888A patent/JPH0299681A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0295180A2 (en) | 1988-12-14 |
| FR2617877A1 (en) | 1989-01-13 |
| AU2202188A (en) | 1990-06-28 |
| AU613952B2 (en) | 1991-08-15 |
| EP0295180A3 (en) | 1989-10-11 |
| JPH0299681A (en) | 1990-04-11 |
| FR2617877B1 (en) | 1995-01-06 |
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