CA1088361A - Plural stage mixing and thickening oxygen reacting - Google Patents
Plural stage mixing and thickening oxygen reactingInfo
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- CA1088361A CA1088361A CA302,005A CA302005A CA1088361A CA 1088361 A CA1088361 A CA 1088361A CA 302005 A CA302005 A CA 302005A CA 1088361 A CA1088361 A CA 1088361A
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Abstract
ABSTRACT OF THE DISCLOSURE
A method and apparatus for the treatment of fiber material by oxygen bleaching. Digested cellulosic fiber material is treated with oxygen to reduce the Kappa number thereof further to about 15 or below. The reaction products are removed immediately after formation, and during the oxy-gen bleaching process. The fiber material is at a first consistency of about 8 to 15% consistency, and treatment with oxygen is accomplished by mixing the pulp with O2, NaOH
solution, and water to thereby form an integral mixture of pulp with oxygen at a second consistency, thickening the integral mixture to return it to generally its first consis-tency, and repeating the mixing and thickening until pulp of a desired Kappa number (15 or below) is reached. The pulp is then washed and may be subsequently treated to reduce the Kappa number thereof to any desired value. A thickener is used which can thicken pulp at superatmospheric pressures and at a temperature greater than 100°C.
A method and apparatus for the treatment of fiber material by oxygen bleaching. Digested cellulosic fiber material is treated with oxygen to reduce the Kappa number thereof further to about 15 or below. The reaction products are removed immediately after formation, and during the oxy-gen bleaching process. The fiber material is at a first consistency of about 8 to 15% consistency, and treatment with oxygen is accomplished by mixing the pulp with O2, NaOH
solution, and water to thereby form an integral mixture of pulp with oxygen at a second consistency, thickening the integral mixture to return it to generally its first consis-tency, and repeating the mixing and thickening until pulp of a desired Kappa number (15 or below) is reached. The pulp is then washed and may be subsequently treated to reduce the Kappa number thereof to any desired value. A thickener is used which can thicken pulp at superatmospheric pressures and at a temperature greater than 100°C.
Description
BACKGROUND AND S~.~M~RY OF THE INVENTION
In a typical commercial mill for the treatment of cellulosic fiber material to form paper pulp, the fiber mate-rial would typically be digested to a Kappa number of about 35, and the fiber material would be bleached to reduce the Kappa number to any desired value. For instance oxygen bleach-ing could take place to reduce the Xappa number from 35 to 15, and then subsequently chlorine bleaching could be used to further reduce the Kappa number. Conventionally, bleaching takes place either with high equipment and energy penalties and/or with a relatively low pulp yield per ton of fiber mate-rial treated.
Existing equipment for effecting oxygen bleaching presently takes the form of one of a variety of oxygen reactors.
A first type of oxygen reactor such as shown in U.S. Patent No.
3,660,225, utilizes equipment to increase the consistency of the digested pulp ~normally about 8 to 15%) to about 20 to 30%
before treatment, and then the pulp is fed to the reactor for treatment. A second type of oxygen reactor is shown in U.S.
Patent No. 3,832,276, which employs apparatus for thinning the pulp from the normal digester consistency to about 2 to 5~ con-sistency, and then feeding the pulp to the oxygen reactor. A
third approach, such as shown in U.S. Patent No. 3,963,561, em-ploys a different type of oxygen reactor and can treat the pulp at the digester consistency of about 8 to 15%. While all such - . .
.. :: , . ....
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1~8~33~;1 apparatus is effective for achieving the desired resul~s, the capital investment is normally quite high, and the energy penalty associa~ted with treatment - especially where separate dilution and thickening steps must be employed prior and/o~ subsequent to bleaching - is normally quite high, and the Kappa number often cannot be reduced low enough to avoid some chlorine bleaching.
In conventional systems, chlorine is used to reduce the ~appa number from 35 to about 6, with subsequent steps taken to whatever level of brightness is desired.
Chemical cost is greater than for oxygen bleaching, however, and the pollution load increases significantly since the spent chemical solution cannot be returned to the system.
According to the present invention, a method and apparatus are provided which can effect oxygen bleaching at reduced capital cost and at reduced energy penalty compared to existing commercial insulations, with a reduced chemical use and pollution load compared to chlorine bleaching, and with increased yield compared to existing commercial installations.
According to one aspect of the method according to the present invention, digested pulp is treated by ad-ding oxygen and sodium hydroxide solution thereto, to effect oxygen bleaching, reaction products being formed during oxy-gen bleaching, and removing the reaction products substantiallyimmediately after formation thereof, and during oxygen bleach-ing, from the digested pulp. The adding and removing steps . ' . , ' , ' ' ' ' ' .. , ' are consecutively repeated until pulp bleached to desired Kappa numbers produced. Preferably the pulp is at a con-sistency of about 8 to 15~, and the removal step is ac-complished by thickening the pulp to about its original consistency of about 8 to 15%. In this way, digesting can be terminated at a Kappa number of about 70 (instead o~ 35 as conventionally~ with oxygen bleaching effecting the re-- duction of the Kapp~ number from 70 to 15 or even below 15.
According to another aspect of the method ac-cording to the present invention, cellulosic fiber material is treated by digesting the fiber material to produce di-gested pulp having a first consistency of about 8 to 15%, and then the pulp is oxygen bleached by mixing the pulp with
In a typical commercial mill for the treatment of cellulosic fiber material to form paper pulp, the fiber mate-rial would typically be digested to a Kappa number of about 35, and the fiber material would be bleached to reduce the Kappa number to any desired value. For instance oxygen bleach-ing could take place to reduce the Xappa number from 35 to 15, and then subsequently chlorine bleaching could be used to further reduce the Kappa number. Conventionally, bleaching takes place either with high equipment and energy penalties and/or with a relatively low pulp yield per ton of fiber mate-rial treated.
Existing equipment for effecting oxygen bleaching presently takes the form of one of a variety of oxygen reactors.
A first type of oxygen reactor such as shown in U.S. Patent No.
3,660,225, utilizes equipment to increase the consistency of the digested pulp ~normally about 8 to 15%) to about 20 to 30%
before treatment, and then the pulp is fed to the reactor for treatment. A second type of oxygen reactor is shown in U.S.
Patent No. 3,832,276, which employs apparatus for thinning the pulp from the normal digester consistency to about 2 to 5~ con-sistency, and then feeding the pulp to the oxygen reactor. A
third approach, such as shown in U.S. Patent No. 3,963,561, em-ploys a different type of oxygen reactor and can treat the pulp at the digester consistency of about 8 to 15%. While all such - . .
.. :: , . ....
:, . , ', ~ ''' ,. . . .
1~8~33~;1 apparatus is effective for achieving the desired resul~s, the capital investment is normally quite high, and the energy penalty associa~ted with treatment - especially where separate dilution and thickening steps must be employed prior and/o~ subsequent to bleaching - is normally quite high, and the Kappa number often cannot be reduced low enough to avoid some chlorine bleaching.
In conventional systems, chlorine is used to reduce the ~appa number from 35 to about 6, with subsequent steps taken to whatever level of brightness is desired.
Chemical cost is greater than for oxygen bleaching, however, and the pollution load increases significantly since the spent chemical solution cannot be returned to the system.
According to the present invention, a method and apparatus are provided which can effect oxygen bleaching at reduced capital cost and at reduced energy penalty compared to existing commercial insulations, with a reduced chemical use and pollution load compared to chlorine bleaching, and with increased yield compared to existing commercial installations.
According to one aspect of the method according to the present invention, digested pulp is treated by ad-ding oxygen and sodium hydroxide solution thereto, to effect oxygen bleaching, reaction products being formed during oxy-gen bleaching, and removing the reaction products substantiallyimmediately after formation thereof, and during oxygen bleach-ing, from the digested pulp. The adding and removing steps . ' . , ' , ' ' ' ' ' .. , ' are consecutively repeated until pulp bleached to desired Kappa numbers produced. Preferably the pulp is at a con-sistency of about 8 to 15~, and the removal step is ac-complished by thickening the pulp to about its original consistency of about 8 to 15%. In this way, digesting can be terminated at a Kappa number of about 70 (instead o~ 35 as conventionally~ with oxygen bleaching effecting the re-- duction of the Kapp~ number from 70 to 15 or even below 15.
According to another aspect of the method ac-cording to the present invention, cellulosic fiber material is treated by digesting the fiber material to produce di-gested pulp having a first consistency of about 8 to 15%, and then the pulp is oxygen bleached by mixing the pulp with
2' NaO~ solution, and water, thereby forming an integral mixture of pulp with 2 at a second consistency less than said first consistency, thickening the integral mixture to return it to a consistency generally the same as the first consistency, and subsequently mixing and thickening until a desired level of oxygen bleaching is achieved. The oxygen bleached pulp is subsequently washed. The temperature and pressure conditions at which the bleaching is accomplished may be continuous digester conditions - a temperature over 100C. and superatmospheric pressure.
The method, according to the present invention, may be accomplished with minimum capital expenditure by utilizing the apparatus according to the invention, the ., , . .. - . .
1~88~61 apparatus including a plurality of mixing means disposed in series in a line (i.e. digester discharging line) and including first and last mixing means, for mixing digested pulp with 2' NaOH solution, and water; a plurality of 5 thickening means dispos~d in the line in series and includ-ing a first and last thickening means, each thickening means being disposed in the discharge from a mixing means, and means for adding 2' NaOH solution, and water to the mixing means. Means are also provided for washing the pulp dis-10 charge from the last thickening means of the series. Eachthickening means preferably includes an in-line thickner capable of thickening pulp at superatmospheric pressures and at a temperature over 1û0C. such as the thickener shown in U.S. Patent No. 4,041,560 issued August 16, 1977 and U.S.
Patent No. 4,029,579 issued June 14, 1977. Means are provided for recycling back to a previous mixing means in the series, liquid withdrawn from a thickening means to provide the water for mixing in the previous mixing means, and the mixing water for the last mixing means in the series 20 is provided from the washing means, while the separated liquid from the first thickening means in the series is circulated baclc to effect washing in a continuous digester.
The mixing means may comprise fil:~rilizing means for ef-fecting at least partial fibrilizing of the pulp, and means 25 may be provided for separating shives from the pulp dis-charge from the fibrilizing mixing means and for returning the shives to the fibrilizing mixing means while passing the pulp to a subsequent thickening means.
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, ... , , .:: . , lV88361 It is the primary object of the present invention to provide a method and apparatus for treating cellulosic fiber material to obtain a high pulp yield with minimum chemical use and energy penalty, and minimum capital expen-diture, including oxygen bleaching of the pulp. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
__ 1~ FIGU~E 1 is a schematic view showing exem-plary apparatus according to the present invention;
FIGURE 2 is a schematic view showing a portion of the apparatus of FIGURE 1, with fibrilizing and shive removing means;
FIGU~E 3 is a cross-section view of an exem-plary thickener that may be employed in the apparatus of FIGURES 1 and 2; and FIGURE 4 is a cross-sectional view of another exemplary thickener that may be employed in the apparatus of FIGURES 1 and 2.
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1~8~361 DETAILED DESCRIPTION OF THE INVENTION
Apparatus according to the present invention is shown schematically in Figure 1 and includes a continuous digester 10 (such as a Kamyx continuous digester) having a discharge line 12, with means 14 for treating digested pulp in discharge line 12 to effect oxygen bleaching thereof with subsequent reduction of the.Kappa number of the pulp. The pulp is normally discharged into line 12 at a consistency of about 8 to 154. The means 14 - which may be in a line 12 distinct from the digester discharge - includes a plurality of mixing means 16 disposed in iine 12, including a first and last mixing means 16, for mixing digested pulp with 2 NaOH solution, and water so that pulp fed therein at a consistency of about 8 to 15% is discharged at a second consistency less than the first consistency (i.e. about 4 to ~), and a plurality of thickening means 18 disposed in line 12 in series and including a first and a last thickening means 18, each thickening.means 18 being disposed in the discharge from a mixing means 16 so that pulp at the second consistency received by each thickening means 18 is thickened to generally the first consistency. A conventional washing tower 20 or the like is provided as means for washing pulp discharge by the last thic~ening means 18 of the series.
Further treatment means 22 - such as a chlorine bleaching tower or the like (as shown in U.S. Patent ~o. 3,815,386) -is connected to the discharge from washer 20 to effect further :'. ~, ., :' . ', '' ' : ' - ' 83f~.
treatment of the pulp to reduce the Kappa number thereof to any desired value. Means for adding NaOH and 2 to each mixing means 16 includes a common supply 24 or the like, the proper amount being provided to effect controlled oxygen bleaching.
Approximately 90~ of the oxygen bleaching that is to take place upon addition of a given amount of 2 takes place in the first two minutes, therefore the majority of oxygen bleaching takes place in each mixing means 16 and in the portion of the discharge line 12 connecting the mixing means to the subsequent thickening means 18. The mixing means 16 may be of any conventional type for effecting 2' pulp mixing such as the mixer shown in U.S. patent Nos.
The method, according to the present invention, may be accomplished with minimum capital expenditure by utilizing the apparatus according to the invention, the ., , . .. - . .
1~88~61 apparatus including a plurality of mixing means disposed in series in a line (i.e. digester discharging line) and including first and last mixing means, for mixing digested pulp with 2' NaOH solution, and water; a plurality of 5 thickening means dispos~d in the line in series and includ-ing a first and last thickening means, each thickening means being disposed in the discharge from a mixing means, and means for adding 2' NaOH solution, and water to the mixing means. Means are also provided for washing the pulp dis-10 charge from the last thickening means of the series. Eachthickening means preferably includes an in-line thickner capable of thickening pulp at superatmospheric pressures and at a temperature over 1û0C. such as the thickener shown in U.S. Patent No. 4,041,560 issued August 16, 1977 and U.S.
Patent No. 4,029,579 issued June 14, 1977. Means are provided for recycling back to a previous mixing means in the series, liquid withdrawn from a thickening means to provide the water for mixing in the previous mixing means, and the mixing water for the last mixing means in the series 20 is provided from the washing means, while the separated liquid from the first thickening means in the series is circulated baclc to effect washing in a continuous digester.
The mixing means may comprise fil:~rilizing means for ef-fecting at least partial fibrilizing of the pulp, and means 25 may be provided for separating shives from the pulp dis-charge from the fibrilizing mixing means and for returning the shives to the fibrilizing mixing means while passing the pulp to a subsequent thickening means.
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, ... , , .:: . , lV88361 It is the primary object of the present invention to provide a method and apparatus for treating cellulosic fiber material to obtain a high pulp yield with minimum chemical use and energy penalty, and minimum capital expen-diture, including oxygen bleaching of the pulp. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
__ 1~ FIGU~E 1 is a schematic view showing exem-plary apparatus according to the present invention;
FIGURE 2 is a schematic view showing a portion of the apparatus of FIGURE 1, with fibrilizing and shive removing means;
FIGU~E 3 is a cross-section view of an exem-plary thickener that may be employed in the apparatus of FIGURES 1 and 2; and FIGURE 4 is a cross-sectional view of another exemplary thickener that may be employed in the apparatus of FIGURES 1 and 2.
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1~8~361 DETAILED DESCRIPTION OF THE INVENTION
Apparatus according to the present invention is shown schematically in Figure 1 and includes a continuous digester 10 (such as a Kamyx continuous digester) having a discharge line 12, with means 14 for treating digested pulp in discharge line 12 to effect oxygen bleaching thereof with subsequent reduction of the.Kappa number of the pulp. The pulp is normally discharged into line 12 at a consistency of about 8 to 154. The means 14 - which may be in a line 12 distinct from the digester discharge - includes a plurality of mixing means 16 disposed in iine 12, including a first and last mixing means 16, for mixing digested pulp with 2 NaOH solution, and water so that pulp fed therein at a consistency of about 8 to 15% is discharged at a second consistency less than the first consistency (i.e. about 4 to ~), and a plurality of thickening means 18 disposed in line 12 in series and including a first and a last thickening means 18, each thickening.means 18 being disposed in the discharge from a mixing means 16 so that pulp at the second consistency received by each thickening means 18 is thickened to generally the first consistency. A conventional washing tower 20 or the like is provided as means for washing pulp discharge by the last thic~ening means 18 of the series.
Further treatment means 22 - such as a chlorine bleaching tower or the like (as shown in U.S. Patent ~o. 3,815,386) -is connected to the discharge from washer 20 to effect further :'. ~, ., :' . ', '' ' : ' - ' 83f~.
treatment of the pulp to reduce the Kappa number thereof to any desired value. Means for adding NaOH and 2 to each mixing means 16 includes a common supply 24 or the like, the proper amount being provided to effect controlled oxygen bleaching.
Approximately 90~ of the oxygen bleaching that is to take place upon addition of a given amount of 2 takes place in the first two minutes, therefore the majority of oxygen bleaching takes place in each mixing means 16 and in the portion of the discharge line 12 connecting the mixing means to the subsequent thickening means 18. The mixing means 16 may be of any conventional type for effecting 2' pulp mixing such as the mixer shown in U.S. patent Nos.
3,284,055 (Figures 3 and 4) and 3,366,367. The water for mixing by the mixing means 16 preferably is provided for each mixing means 16 from a subsequent stage in the treatment.
For instance, means may be provided for circulating hot water from counter-current washing in washer 20 to the last of the -~
mixing means 16 in the series, such means comprising a line 25, and means are provided for recycling back to a previous mixing means 16 in the series, li~uid withdrawn from at least one of the thickening means 18 to provide water for mixing in the previous mixing means, such recycling means including a line 25' with a pump 26 disposed therein. Pre-ferably a line 25' and pump 26 is provided associated with each of the thickening means, the first thickening means 18 - ,: , ', '. ~ ' ~: '.: ' :; ', .... . ..
in the series having a line 25'' connected back to the digester 10 for providing wash water in the digester 10.
~y recycling the wash media, all the material possible is retained in the system, the withdrawn washing liquid from S the continuous digester 10 being withdrawn by conventional means and passed on to a recovery station.
~here the pulp discharged in line 12 is contem-plated to have a significant number of shives, and/or to effect more intimate mixing, fibrilizing means 16' - shown schematically in Figure 2 - may be provided as at least one of the mixing means for effecting at least partial fibriliz-ing of the pulp. The fibrilizing mixing means 16' may comprise any suitable conventional defibrillator, such as defibrator refiner model L42 lS When a fibrilizing mixing means 16' is provided ther~ is further provided at least one means 27 for separating shives from the pulp discharged from the fibrilizing mixing means 16' and for returning the shives to the fibrilizing mixing . means 16', while passing the pulp to a subsequent thickening means 18. The means 27 includes a conventional cyclone separator 28 or the like, a return line 29 leading from the : separator 28 back to the mixing means 16', and a pump 30 disposed in line 29.
~y mixing and then thickening according to the present invention, the reactive products of the oxygen bleaching are washed out in much the same manner as in known chlorinè displacement bleaching process which utilizes washing _ g _ ..
.; . ' . , : . . :
equipment. Washing equipment would generally be used for liquid systems and could not e~fect the gaseous oxygen bleaching according to the present invention, however, and with the thickeners 18, less chemical can be used, there is better control over the reaction, and less capital investment is necessary; yet the reaction products are removed substantially immediately after formation and during bleaching. Each thick-ener 18 comprises a thickener capable of thickening pulp at superatmospheric pressure and at a temperature of over 100 3C .
so that the pulp in a digester discharge line 12 may be dir-ectly treated without any intermediary steps Preferably, also the thickener is an in-line thickener, which is inexpen-sive and may be inserted directly in the discharge line 12, no accessory vessels being necessary to effect treatment.
Exemplary thickeners 18 that may be utilized to practice the invention and are especially adapted for practicing the in-vention are shown in U.S. Patents No. 4,029,579 issued June 14, 1977 and No. 4,041,S60 issued August 16, 1977, although the invention is not restricted to those particular thickeners.
Such thickeners are illustrated in Figures 3 and 4 of the drawings.
One examplary thickener 18 that is especially use-ful in practicing the invention is shown in Figure 3 (Patent No.4,041,560). The thickener of Figure 3 comprises a generally cylindrical container 31 forming part of discharge line 12 through which the suspension flows in a first direction A, the container having an axis extending generally parallel to the , . . , , . . , ':
: ' ', .. :' , :', . .
1~8~8361 first direction A, screen means 32 for removal of a portion of the liquid from the suspension flowing through the con-tainer 31, the screen rneans 32 having an interior variable volume chamber 33, mechanical means 34 for reciprocating the screen means 32 in the first direction A and in a second direc-tion B opposite to the first direction A so that the volume of the interior cham~er 33 of the screen means 32 is varied, and the discharge line 25, 25'' being connected to the interior chamber 33 of the screen means 32 for expelling liquid separated from the suspension to an area remote from the container 31.
The container 31 may comprise a pipe member of a diameter of about 500 millimeters, having an inlet 36 thereto.
Within the container 31 there is disposed a stationary tubular member 37, supported at one end thereof by a plurality of ra-dially extending arm members 38, at least one of the radiallyextending arm members having an opening 39 formed therethrough.
Mounted for movement over the stationary tubular member 37 is the screen means 32, the screen means comprising a tubular screen member 40 having one end, 41, thereof,closed, and the other end thereof open open, a sealing means 42 being provided at the open end for engagement with the exterior of tubular stationary member 37 during reciprocal movement of the member 40 with respect to the member 37, The interior variable volume chamber 33 is de-fined by the closed end 41, the tubular member 40, and the sta-tionary tubular member 37. The rod 34 is operatively connectedto the tubular screen member 40 at closed end 41 thereof for providing mechanical reciprocation of the screen means in the ,' ' . ' ~883tj~
first direction A and in the second direction B. The rod member 34 is mounted for reciprocation by bushings 43, 44 and 45, the bushing 43 being mounted by a spider member 46 operatively connected to the container 31, the bushing 44 being supported by the stationary tubular member 37, and the bearing 45 extending through the portion 36 of container 31.
The rod member 34 may be reciprocated by any suit-able means such as a hydraulic piston 47 shown in Figure 3.
The hydraulic piston and cylinder 47 is so arranged that during movement of the screen means 32 in the first direction A, the screen means 32 moves with substantially the same velocity as the suspension flowing in direction B in container 31, and dur-ing movement of the screen means 32 in direction B, the screen lS means 32 is moved with a substantially greater velocity. The velocity of the rod member 34 in the second direction B is large enough so that the variable volume intexior chamber 33 of the screen means 32 decreases at a rate with respect to the rate of movement of liquid into the interior chamber 33 through the screen member 40 so that bac~flus~ing,of the screen member 40 takes place. During the backflushing operation, however, liquid will continuously flow throu~h the chamber 48 of the hollow stationary tubular member 37, through opening 39 to a mixing means 16 ~or 16') or digester 10. The hydraulic piston and cy-linder 47 is also arranged so that the rod member 34 may rotatewith respect to the container 31, and means are provided mounted . ' ' , .. ~ .; : ' on screen member 40 that effect rotary movement of the screen member 8 when it is moving in direction B. Such means may take form of a plurality of wing shaped vanes or fins 49 tin dotted line of Figure 3) which can be twisted or angled so that upon relative movement of the membex 40 with respect to the suspension flowing through the container 31 the member 40 is rotated. This relative rotation also facilitates cleaning of the screen 40. Additionally, there is also associated with the screen means 32, means for generating a turbulence in the suspension when the screen means ~2 is moved with respect thereto. The turbulence has a positive influence in that if a plurality of screen means 32 are provided in series in the container 31, different portions of the suspension will be brought into operative association with the succeeding screen means 32. The turbu-lence inducing means may comprise a tooth portion 50 of the closed end 41 of the screen means 32, or a ciruclar edge member of the closed end 41, the means 50 also effecting a shredding or mixing of the suspension.
Liquid that is separated out from the suspension f70wing in container 31 flows into chamber 33 through chamber 48 in stationary tubular member 37, through opening 39, and to line 25', 25''. The line 25 may also have disposed therein conventional pressure resistance devices and flow quantity regulators (not shown).
An exemplary operation of the Figure 3 thickness 18 will be set forth. Suspension to be dewatered, at approxi-mately 8-15% solids concentration, flows in direction A througn , .... . .
- . . .
1~883~;1 elbow portion 36 of container 31 into the container 31.
The rod member 34 is moved upwardly in direction A at substantially the same velocity as the suspension flowing in container 31 by the hydraulic piston and cylinder ar-rangement 47 or the like, and during this upward movementliquid flows through the openings in the tubular ~ovable screen member 40 into the variable volume interior chamber 33 thereof, through interior passageway 48 in stationary tub~lar membex 37, through opening 3g, and into line 25'.
When the screen means 32 has reached its upward limit of travel (as by closed end 41 thereof abutting bushing 43) the hydraulic cylinder moves the rod member 34 downwardly in direction B with a velocity greater than the upward velo-city of the suspension in container 31, and relative rotation of the rod member 34 with respect to the container 31 is ef-fected during this movement in direction B by the force of the suspension acting on fins 49 (the rotation during each downward movement is approximately 120-240). The movement in direction B is with a velocity great enough so that the variable volume of the interior chamber 33 decreases at a rate with respect to the rate of movement of liquid into the interior chamber 33 through the screen means 32 so that back-flushing of the screen member 40 takes place. Turbulence in the suspension is also generated by the means 50 associated with screen means 32. During the downward movement of .he screen means 32 in direction B, liquid is continuously expelled through the opening 39 into line 25'. When the screen means 32 - . . . .,, : . .
1~8~361 reaches its downward limit of travel (as by portion 42 thereof abutting arm members 38) the hydraulic cylinder and piston arrangement 47. is again operated to move the rod member 34 upwardly in direction A, and the process is continued and repeated. The length of the stroke of move-ment of the rod member 34 in either direction is relatively small, for example, 0-100 centimeters, preferably 20-50 centi-meters; the stroke can suitably be approximately 1/2 the length of screen member 40.
Another exemplary thic~ener 18 for use according to the invention is shown in Figure 4 (Patent No. 4,029,579). The apparatus of Figure 4 includes a cylindrical circular cross-section housing 60, having bottom and top flanges 51 and 52, respectively, through which a suspension of comminuted fiber liquid flows in a direction B and having a piston 61 therein.
A fixed hollow piston part 53 is provided, in communication with at least one opening 55 in a plurality of radially ex-t~nding supporting arms 54, the opening 55, through connec-tion 56, leading to a mixing means 16 or digester 10. The movable portion of the piston 61 is shown generally at 58 in Figure 4, and includes a cylindrical body having screen open- -ings 57 disposed along the length thereof. Seals 59 and 70 are provided to allow relative movement o~ the member 58 with respect to the portion 53. First and second piston faces 65, 66, are provided respèctively on cylindrical body 58. Internal chamber 71, 72 of piston 61 communicate with the opening 55 and the interior of container 60 (through screen openings 57). A
~38~36~
valve 68 may be disposed in line 25', as may a pump 63 and accumulator 64, the valve 6e being controlled by remote con- -trol means 69 to provide flow through line 25' in either direction D or direction E.
Operation of the thickener 18 of Figure 4 is as follows: a suspension of comminuted fiber material and liquid ~lows upwardly in direction A into container 60, the suspen-sion acting on first piston face 65 of member 58 to move the member 58 upwardly in direction A from the dotted line position shown in Figure 4 to the solid line position shown in Figure 4.
Since the movement of member 58 is controlled by the velocity of the suspension in container 60, the member 58 moves upwardly substantially with the velocity of the suspension. During move-. ment of the member 58 in direction A, liquid passes through screen openings 57 into chamber 72, while fiber material in the suspension is prevented from passing into chamber 72. The separated liquid flows from chamber 72, through hollow member 53 through outlet 56, and into line 25'. The control means 69 may control valve 68 so that it allows flow of fluid in direc-tion D, to reservoir 62 and ultimately mixing means 16 or di-gester 16. When the member 58 reaches its upward limit of travel in direction A, the control means.69 controls valve 68 so that flow in direction d is prevented and flow in direction E is al-lowed. Separated liquid under pressure of pump 63 and accumu-lator 64 from reservoir 62 then flows .in direction E through out-let 56 into chamber 72, abutting on second piston face 66, and forces the member 58 downwardly in direction B. The pres-sure provided by pump 63 and accumulator 64 can be control-led so that the piston 58 moves downwardly in direction B
much more quickly than it moves upwardly in direction A.
Once the downward limit of travel of member 58 has been reached, control means 69 again activates valve 68 to allow flow in direction D into 16, 10 so that dewatering again takes place. During downward movement of the member 58 in direction B, under the influence of fluid flowing in direc-tion B, some backflushing takes placeO cleaning the openingsin screen 57. It is apparent from an inspection of the ap-paratus of Figure 4 that the movable member 58 can be made relatively light weight, and thereby the forces for initiat-ing action thereof are relatively small.
The apparatus of Figure 4 can be made relatively small and readily installed in discharge line 12, even when line 12 is of relatively small diameter (i.e., 500 milli-meters inside diameter). The "stroke" of the member 58 may be 0-100 centimeters, preferably about 20-50 centimeters. A
plurality of devices 6, 58 may be arranged in series to provide any given amount of dewatering required. Also, while the flow of suspension has been shown in upward direc-tion A, the flow of suspension may be in the downward direc-tion B, suitable modification of the apparatus to accom-modate the suspension movement in the downward direction Bbeing relatively simple.
1~383~i1 The apparatus according to the present invention having been described, the method according to the present invention will now be set forth. Oxygen and NaOH solutions are added to digested pulp to effect oxygen bleaching thereof, reaction products being formed during oxygen bleaching. A
supply 24 provides the oxygen and NaOH solution to effective bleaching. T~is addition may be accomplished by adding water (i.e. from lines 25 or 25') with the 2 and NaOH
solution, and mixing the pulp, water, 2 and NaOH solution (as in mixing means 16). The formed reaction products are removed substantially immediately after formation thereof, and duri~g oxygen bleaching, from the digested pulp. This removal is accomplished by thickening the pulp (as by means 1~) to about its original consistency. The addition of oxygen and removal of reaction product steps are consecutive-ly repeated until pulp bleached to a desired Kappa number (i.e. about 15 or below) is produced. The pulp preferably originally is at a consistency of about 8 to 15% when the oxygen and NaOH solution and water added thereto, the pulp being diluted to about 4 to 8~ consistency and then thick-ened back to the original consistency of about 8 to 15%, but the invention is not limited to these consistency changes.
According to the present invention the digestion of pulp can be stopped at a Kappa number of about 70 (instead of 35 as conventionally), and the oxygen bleaching can be used to reduce the Xappa number further. This results in higher yield compared to digestion of the fiber material to r~' `
1~88361 a Kappa number of about 35. According to the present in-vention the oxJc~en bleaching can be used to reduce the Kappa number from 70 to a Kappa number 15 or even below 15, with reduced chemical use as compared to chlorine bleaching, and a much lower pollution load. Additionally, the oxygen stage effluent can be retained in the system (as by subsequently feeding the discharge from the first thickener to the di- .
gester 10, and subsequent recovery by conventional means).
According to another aspect of the method of the present invention, cellulosic fiber material is treated by the steps of digesting the fiber material by treatment with digesting llquid (in digester 10) to produce digested pulp having a first consistency of about 8 to lS~ and then oxygen bleaching the pulp by (1) mixing the pulp with 2' lS NaOH solution, and water, thereby forming an integral mix-ture of pulp with 2 at a second consistency less than the first consistency (i.e., about 4 to 8%), (2) thickening the integral mixture to return it to a consistency generally the same as the first consistency (i.e., about 8 to 15%), and (3) repeating steps 1 and 2 until a desired level of oxygen bleaching is achieved. Then the oxygen bleached pulp is then washed (in washer 2). The water for mixing the pulp to effect the oxygen bleaching is provided by water removed during a subsequent thickening operation, and all the efflu-ent from the thickeners is retained in the system, and may ultimately be passed to the continuous digested 10 for use as wash media therein. The wash water for the last thickener r - ~
83~1 .. . . .
18 may be provided from the washing means 20. The oxygen bleaching may be accomplished at digester pressure and tem-perature conditions (over 100C and superatmospheric pres-sure).
It will be seen according to the present invention a method and apparatus have been provided having numerous advantages over the prior art for effecting treatment of cellulosic fiber material including oxygen bleaching. While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment thereof, it will be apparent to those of ordinary skill in the art that many modification~ may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and methods.
, . .
For instance, means may be provided for circulating hot water from counter-current washing in washer 20 to the last of the -~
mixing means 16 in the series, such means comprising a line 25, and means are provided for recycling back to a previous mixing means 16 in the series, li~uid withdrawn from at least one of the thickening means 18 to provide water for mixing in the previous mixing means, such recycling means including a line 25' with a pump 26 disposed therein. Pre-ferably a line 25' and pump 26 is provided associated with each of the thickening means, the first thickening means 18 - ,: , ', '. ~ ' ~: '.: ' :; ', .... . ..
in the series having a line 25'' connected back to the digester 10 for providing wash water in the digester 10.
~y recycling the wash media, all the material possible is retained in the system, the withdrawn washing liquid from S the continuous digester 10 being withdrawn by conventional means and passed on to a recovery station.
~here the pulp discharged in line 12 is contem-plated to have a significant number of shives, and/or to effect more intimate mixing, fibrilizing means 16' - shown schematically in Figure 2 - may be provided as at least one of the mixing means for effecting at least partial fibriliz-ing of the pulp. The fibrilizing mixing means 16' may comprise any suitable conventional defibrillator, such as defibrator refiner model L42 lS When a fibrilizing mixing means 16' is provided ther~ is further provided at least one means 27 for separating shives from the pulp discharged from the fibrilizing mixing means 16' and for returning the shives to the fibrilizing mixing . means 16', while passing the pulp to a subsequent thickening means 18. The means 27 includes a conventional cyclone separator 28 or the like, a return line 29 leading from the : separator 28 back to the mixing means 16', and a pump 30 disposed in line 29.
~y mixing and then thickening according to the present invention, the reactive products of the oxygen bleaching are washed out in much the same manner as in known chlorinè displacement bleaching process which utilizes washing _ g _ ..
.; . ' . , : . . :
equipment. Washing equipment would generally be used for liquid systems and could not e~fect the gaseous oxygen bleaching according to the present invention, however, and with the thickeners 18, less chemical can be used, there is better control over the reaction, and less capital investment is necessary; yet the reaction products are removed substantially immediately after formation and during bleaching. Each thick-ener 18 comprises a thickener capable of thickening pulp at superatmospheric pressure and at a temperature of over 100 3C .
so that the pulp in a digester discharge line 12 may be dir-ectly treated without any intermediary steps Preferably, also the thickener is an in-line thickener, which is inexpen-sive and may be inserted directly in the discharge line 12, no accessory vessels being necessary to effect treatment.
Exemplary thickeners 18 that may be utilized to practice the invention and are especially adapted for practicing the in-vention are shown in U.S. Patents No. 4,029,579 issued June 14, 1977 and No. 4,041,S60 issued August 16, 1977, although the invention is not restricted to those particular thickeners.
Such thickeners are illustrated in Figures 3 and 4 of the drawings.
One examplary thickener 18 that is especially use-ful in practicing the invention is shown in Figure 3 (Patent No.4,041,560). The thickener of Figure 3 comprises a generally cylindrical container 31 forming part of discharge line 12 through which the suspension flows in a first direction A, the container having an axis extending generally parallel to the , . . , , . . , ':
: ' ', .. :' , :', . .
1~8~8361 first direction A, screen means 32 for removal of a portion of the liquid from the suspension flowing through the con-tainer 31, the screen rneans 32 having an interior variable volume chamber 33, mechanical means 34 for reciprocating the screen means 32 in the first direction A and in a second direc-tion B opposite to the first direction A so that the volume of the interior cham~er 33 of the screen means 32 is varied, and the discharge line 25, 25'' being connected to the interior chamber 33 of the screen means 32 for expelling liquid separated from the suspension to an area remote from the container 31.
The container 31 may comprise a pipe member of a diameter of about 500 millimeters, having an inlet 36 thereto.
Within the container 31 there is disposed a stationary tubular member 37, supported at one end thereof by a plurality of ra-dially extending arm members 38, at least one of the radiallyextending arm members having an opening 39 formed therethrough.
Mounted for movement over the stationary tubular member 37 is the screen means 32, the screen means comprising a tubular screen member 40 having one end, 41, thereof,closed, and the other end thereof open open, a sealing means 42 being provided at the open end for engagement with the exterior of tubular stationary member 37 during reciprocal movement of the member 40 with respect to the member 37, The interior variable volume chamber 33 is de-fined by the closed end 41, the tubular member 40, and the sta-tionary tubular member 37. The rod 34 is operatively connectedto the tubular screen member 40 at closed end 41 thereof for providing mechanical reciprocation of the screen means in the ,' ' . ' ~883tj~
first direction A and in the second direction B. The rod member 34 is mounted for reciprocation by bushings 43, 44 and 45, the bushing 43 being mounted by a spider member 46 operatively connected to the container 31, the bushing 44 being supported by the stationary tubular member 37, and the bearing 45 extending through the portion 36 of container 31.
The rod member 34 may be reciprocated by any suit-able means such as a hydraulic piston 47 shown in Figure 3.
The hydraulic piston and cylinder 47 is so arranged that during movement of the screen means 32 in the first direction A, the screen means 32 moves with substantially the same velocity as the suspension flowing in direction B in container 31, and dur-ing movement of the screen means 32 in direction B, the screen lS means 32 is moved with a substantially greater velocity. The velocity of the rod member 34 in the second direction B is large enough so that the variable volume intexior chamber 33 of the screen means 32 decreases at a rate with respect to the rate of movement of liquid into the interior chamber 33 through the screen member 40 so that bac~flus~ing,of the screen member 40 takes place. During the backflushing operation, however, liquid will continuously flow throu~h the chamber 48 of the hollow stationary tubular member 37, through opening 39 to a mixing means 16 ~or 16') or digester 10. The hydraulic piston and cy-linder 47 is also arranged so that the rod member 34 may rotatewith respect to the container 31, and means are provided mounted . ' ' , .. ~ .; : ' on screen member 40 that effect rotary movement of the screen member 8 when it is moving in direction B. Such means may take form of a plurality of wing shaped vanes or fins 49 tin dotted line of Figure 3) which can be twisted or angled so that upon relative movement of the membex 40 with respect to the suspension flowing through the container 31 the member 40 is rotated. This relative rotation also facilitates cleaning of the screen 40. Additionally, there is also associated with the screen means 32, means for generating a turbulence in the suspension when the screen means ~2 is moved with respect thereto. The turbulence has a positive influence in that if a plurality of screen means 32 are provided in series in the container 31, different portions of the suspension will be brought into operative association with the succeeding screen means 32. The turbu-lence inducing means may comprise a tooth portion 50 of the closed end 41 of the screen means 32, or a ciruclar edge member of the closed end 41, the means 50 also effecting a shredding or mixing of the suspension.
Liquid that is separated out from the suspension f70wing in container 31 flows into chamber 33 through chamber 48 in stationary tubular member 37, through opening 39, and to line 25', 25''. The line 25 may also have disposed therein conventional pressure resistance devices and flow quantity regulators (not shown).
An exemplary operation of the Figure 3 thickness 18 will be set forth. Suspension to be dewatered, at approxi-mately 8-15% solids concentration, flows in direction A througn , .... . .
- . . .
1~883~;1 elbow portion 36 of container 31 into the container 31.
The rod member 34 is moved upwardly in direction A at substantially the same velocity as the suspension flowing in container 31 by the hydraulic piston and cylinder ar-rangement 47 or the like, and during this upward movementliquid flows through the openings in the tubular ~ovable screen member 40 into the variable volume interior chamber 33 thereof, through interior passageway 48 in stationary tub~lar membex 37, through opening 3g, and into line 25'.
When the screen means 32 has reached its upward limit of travel (as by closed end 41 thereof abutting bushing 43) the hydraulic cylinder moves the rod member 34 downwardly in direction B with a velocity greater than the upward velo-city of the suspension in container 31, and relative rotation of the rod member 34 with respect to the container 31 is ef-fected during this movement in direction B by the force of the suspension acting on fins 49 (the rotation during each downward movement is approximately 120-240). The movement in direction B is with a velocity great enough so that the variable volume of the interior chamber 33 decreases at a rate with respect to the rate of movement of liquid into the interior chamber 33 through the screen means 32 so that back-flushing of the screen member 40 takes place. Turbulence in the suspension is also generated by the means 50 associated with screen means 32. During the downward movement of .he screen means 32 in direction B, liquid is continuously expelled through the opening 39 into line 25'. When the screen means 32 - . . . .,, : . .
1~8~361 reaches its downward limit of travel (as by portion 42 thereof abutting arm members 38) the hydraulic cylinder and piston arrangement 47. is again operated to move the rod member 34 upwardly in direction A, and the process is continued and repeated. The length of the stroke of move-ment of the rod member 34 in either direction is relatively small, for example, 0-100 centimeters, preferably 20-50 centi-meters; the stroke can suitably be approximately 1/2 the length of screen member 40.
Another exemplary thic~ener 18 for use according to the invention is shown in Figure 4 (Patent No. 4,029,579). The apparatus of Figure 4 includes a cylindrical circular cross-section housing 60, having bottom and top flanges 51 and 52, respectively, through which a suspension of comminuted fiber liquid flows in a direction B and having a piston 61 therein.
A fixed hollow piston part 53 is provided, in communication with at least one opening 55 in a plurality of radially ex-t~nding supporting arms 54, the opening 55, through connec-tion 56, leading to a mixing means 16 or digester 10. The movable portion of the piston 61 is shown generally at 58 in Figure 4, and includes a cylindrical body having screen open- -ings 57 disposed along the length thereof. Seals 59 and 70 are provided to allow relative movement o~ the member 58 with respect to the portion 53. First and second piston faces 65, 66, are provided respèctively on cylindrical body 58. Internal chamber 71, 72 of piston 61 communicate with the opening 55 and the interior of container 60 (through screen openings 57). A
~38~36~
valve 68 may be disposed in line 25', as may a pump 63 and accumulator 64, the valve 6e being controlled by remote con- -trol means 69 to provide flow through line 25' in either direction D or direction E.
Operation of the thickener 18 of Figure 4 is as follows: a suspension of comminuted fiber material and liquid ~lows upwardly in direction A into container 60, the suspen-sion acting on first piston face 65 of member 58 to move the member 58 upwardly in direction A from the dotted line position shown in Figure 4 to the solid line position shown in Figure 4.
Since the movement of member 58 is controlled by the velocity of the suspension in container 60, the member 58 moves upwardly substantially with the velocity of the suspension. During move-. ment of the member 58 in direction A, liquid passes through screen openings 57 into chamber 72, while fiber material in the suspension is prevented from passing into chamber 72. The separated liquid flows from chamber 72, through hollow member 53 through outlet 56, and into line 25'. The control means 69 may control valve 68 so that it allows flow of fluid in direc-tion D, to reservoir 62 and ultimately mixing means 16 or di-gester 16. When the member 58 reaches its upward limit of travel in direction A, the control means.69 controls valve 68 so that flow in direction d is prevented and flow in direction E is al-lowed. Separated liquid under pressure of pump 63 and accumu-lator 64 from reservoir 62 then flows .in direction E through out-let 56 into chamber 72, abutting on second piston face 66, and forces the member 58 downwardly in direction B. The pres-sure provided by pump 63 and accumulator 64 can be control-led so that the piston 58 moves downwardly in direction B
much more quickly than it moves upwardly in direction A.
Once the downward limit of travel of member 58 has been reached, control means 69 again activates valve 68 to allow flow in direction D into 16, 10 so that dewatering again takes place. During downward movement of the member 58 in direction B, under the influence of fluid flowing in direc-tion B, some backflushing takes placeO cleaning the openingsin screen 57. It is apparent from an inspection of the ap-paratus of Figure 4 that the movable member 58 can be made relatively light weight, and thereby the forces for initiat-ing action thereof are relatively small.
The apparatus of Figure 4 can be made relatively small and readily installed in discharge line 12, even when line 12 is of relatively small diameter (i.e., 500 milli-meters inside diameter). The "stroke" of the member 58 may be 0-100 centimeters, preferably about 20-50 centimeters. A
plurality of devices 6, 58 may be arranged in series to provide any given amount of dewatering required. Also, while the flow of suspension has been shown in upward direc-tion A, the flow of suspension may be in the downward direc-tion B, suitable modification of the apparatus to accom-modate the suspension movement in the downward direction Bbeing relatively simple.
1~383~i1 The apparatus according to the present invention having been described, the method according to the present invention will now be set forth. Oxygen and NaOH solutions are added to digested pulp to effect oxygen bleaching thereof, reaction products being formed during oxygen bleaching. A
supply 24 provides the oxygen and NaOH solution to effective bleaching. T~is addition may be accomplished by adding water (i.e. from lines 25 or 25') with the 2 and NaOH
solution, and mixing the pulp, water, 2 and NaOH solution (as in mixing means 16). The formed reaction products are removed substantially immediately after formation thereof, and duri~g oxygen bleaching, from the digested pulp. This removal is accomplished by thickening the pulp (as by means 1~) to about its original consistency. The addition of oxygen and removal of reaction product steps are consecutive-ly repeated until pulp bleached to a desired Kappa number (i.e. about 15 or below) is produced. The pulp preferably originally is at a consistency of about 8 to 15% when the oxygen and NaOH solution and water added thereto, the pulp being diluted to about 4 to 8~ consistency and then thick-ened back to the original consistency of about 8 to 15%, but the invention is not limited to these consistency changes.
According to the present invention the digestion of pulp can be stopped at a Kappa number of about 70 (instead of 35 as conventionally), and the oxygen bleaching can be used to reduce the Xappa number further. This results in higher yield compared to digestion of the fiber material to r~' `
1~88361 a Kappa number of about 35. According to the present in-vention the oxJc~en bleaching can be used to reduce the Kappa number from 70 to a Kappa number 15 or even below 15, with reduced chemical use as compared to chlorine bleaching, and a much lower pollution load. Additionally, the oxygen stage effluent can be retained in the system (as by subsequently feeding the discharge from the first thickener to the di- .
gester 10, and subsequent recovery by conventional means).
According to another aspect of the method of the present invention, cellulosic fiber material is treated by the steps of digesting the fiber material by treatment with digesting llquid (in digester 10) to produce digested pulp having a first consistency of about 8 to lS~ and then oxygen bleaching the pulp by (1) mixing the pulp with 2' lS NaOH solution, and water, thereby forming an integral mix-ture of pulp with 2 at a second consistency less than the first consistency (i.e., about 4 to 8%), (2) thickening the integral mixture to return it to a consistency generally the same as the first consistency (i.e., about 8 to 15%), and (3) repeating steps 1 and 2 until a desired level of oxygen bleaching is achieved. Then the oxygen bleached pulp is then washed (in washer 2). The water for mixing the pulp to effect the oxygen bleaching is provided by water removed during a subsequent thickening operation, and all the efflu-ent from the thickeners is retained in the system, and may ultimately be passed to the continuous digested 10 for use as wash media therein. The wash water for the last thickener r - ~
83~1 .. . . .
18 may be provided from the washing means 20. The oxygen bleaching may be accomplished at digester pressure and tem-perature conditions (over 100C and superatmospheric pres-sure).
It will be seen according to the present invention a method and apparatus have been provided having numerous advantages over the prior art for effecting treatment of cellulosic fiber material including oxygen bleaching. While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment thereof, it will be apparent to those of ordinary skill in the art that many modification~ may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and methods.
, . .
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of treating cellulosic fiber material comprising the steps of a) digesting the cellulosic fiber material by treatment with digesting liquid to produce digested pulp having a first consistency of about 8-15%, and b) oxygen bleaching the pulp by practicing the steps consisting of (i) integrally and violently mixing said pulp with O2, NaOH solution, and water, thereby forming an integral mixture of pulp with O2 at a second consistency less than said first consistency, (ii) substantially immediately thickening said integral mixture to return it to a consistency generally the same as said first consistency, and (iii) sequentially repeating steps (i) and (ii) until a desired level of oxygen bleaching is achieved.
2. A method of treating cellulosic fiber material as recited in claim 1 comprising the further steps of, after com-pletion of said step b), washing the oxygen bleached pulp, and subsequently treating the washed oxygen bleached pulp to further reduce the Kappa number thereof.
3. A method as recited in claim 1 wherein the digested pulp originally has a Kappa number of about 70, and wherein the oxygen bleached pulp produced by steps a) and b) has a Kappa number of about 15 or below.
4. A method as recited in claim 1 wherein the digested pulp has a Kappa number of over 15, and wherein said step b) is accomplished until the Kappa number of the pulp has been reduced to about 15 or below.
5. A method as recited in claim 4 comprising the further steps of, after completion of said step b), washing the oxygen bleached pulp, and subsequently treating the washed oxygen bleached pulp to further reduce the Kappa number thereof to any desired value.
6. A method as recited in claim 1 wherein said fiber material is digested at first pressure and temperature conditions, and wherein said oxygen bleaching is effected at substantially said first pressure and temperature conditions.
7. A method as recited in claim 1 wherein water for mixing said pulp in step b) (i) is provided by water removed during a subsequent thickening as provided by step b) (ii.).
8. Apparatus for treating cellulosic fiber material to produce bleached pulp, comprising a) a plurality of mixing means disposed in series in a line including a first and last mixing means, for mixing digested pulp with O2, NaOH solution, and water, so that pulp fed therein at a first consistency is about 8-15% is discharged at a second consistency less than said first consistency, b) a plurality of thickening means disposed in said line in series, including a first and last thickening means, each thickening means being disposed in the discharge from a said mixing means, so that pulp at said second consistency received by each thickening means is thickened to generally said first consistency, and c) means for adding O2, NaOH solution, and water to said mixing means
9. Apparatus as recited in claim 8 wherein said line is a continuous digester discharge line, and wherein each of said thickening means comprises a generally tubular in-line thickener having generally the same diameter as the digester discharge line in which it is disposed.
10. Apparatus as recited in claim 8 wherein said line is a continuous digester discharge line, and wherein each of said thickening means comprises means for thickening pulp at superatmospheric pressures and at a temperature of over 100°C.
11. Apparatus as recited in claim 10 wherein each of said thickening means comprises a thickener including a generally cylindrical container through which suspension to be dewatered flows in a first direction, said container having an axis extending generally parallel to said first direction, screen means for removal of a portion of the liquid from the suspension flowing through said container, said screen means defining an interior variable volume chamber, mechanical means for reciprocating a portion of said screen means in said first direction and in a second direction opposite to said first direction so that the volume of said interior chamber of said screen means is varied by said re-ciprocation, and means connected to the interior chamber of said screen means for expelling liquid separated from said suspen-sion to an area remote frrom said container.
12. Apparatus as recited in claim 10 wherein each of said thickening means comprises a thickener comprising a generally circular cross-section container through which a suspension to be dewatered flows in a given direction, a hydraulic piston mounted generally concentri-cally in said container and having an interior chamber therein for transporting liquid removed from said container to an area remote from said container, means responsive to the fluid pressure of liquid from said suspension for moving said hydraulic piston relative to said container in either a first direction generally cor-responding to the direction of flow of fluid in said container, or a second direction opposite to said first direction, said means including a first and a second piston faces, screen means mounted on said piston for allowing the passage of liquid removed from the suspension through the interior chamber of said piston to the remote area while not allowing removable material suspended in the suspension therethrough, and means for forcing liquid removed from said suspen-sion through said piston chamber to said second piston face to move said piston in said second direction so that no sub-stantial dewatering takes place during movement of said piston in said second direction and so that said piston is moved to a position wherein it may again be moved in said first direction.
13. Apparatus as recited in claim 8 further com-prising means for recycling back to a previous mixing means in said series liquid withdrawn from at least one of said thickening means, to provide the water for mixing in said previous mixing means.
14. Apparatus as recited in claim 8 further comprising means for washing the oxygen-bleached pulp, and means for circulating hot water from said washing means to the last of said mixing means in said series to provide the water for mixing in said mixing means.
15. Apparatus as recited in claim 8 further comprising a continuous digester, said line comprising the digester discharge line, and means for circulating water withdrawn from said first thickening means to said digester.
16. Apparatus as recited in claim 8 wherein at least one of said mixing means comprises fibrilizing mixing means for effecting at least partial fibrilizing of said pulp, and further comprising at least one means for separating shives from the pulp discharged from said fibrilizing mixing means and for returning said shives to said fibrilizing mixing means while passing said pulp to a subsequent thickening means.
17. Apparatus as recited in claim 16 wherein said shive separating and returning means comprises a cyclone separator and a return line from said separator to said fibrilizing mixing means.
18. Apparatus as recited in claim 8 wherein each of said thickening means comprises a thickener including a generally cylindrical container through which suspension to be dewatered flows in a first direction, said container having an axis extending generally parallel to said first direction, screen means for removal of a portion of the liquid from the suspension flowing through said container, said screen means defining an interior variable volume chamber, mechanical means for reciprocating a portion of said screen means in said first direction and in a second direction opposite to said first direction so that the volume of said interior chamber of said screen means is varied by said reciprocation, and means connected to the interior chamber of said screen means for expelling liquid separated from said suspen-sion to an area remote from said container.
19. Apparatus as recited in claim 8 wherein each of said thickening means comprises a thickener com-prising a generally circular cross-section container through which a suspension to be dewatered flows in a given direction, a hydraulic piston mounted generally concentri-cally in said container and having an interior chamber therein for transporting liquid removed from said container to an area remote from said container, means responsive to the fluid pressure of liquid from said suspension for moving said hydraulic piston rela-tive to said container in either a first direction generally corresponding to the direction of flow of fluid in said con-tainer, or a second direction opposite to said first direction, said means including a first and a second piston faces, screen means mounted on said piston for allowing the passage of liquid removed from the suspension through the interior chamber of said piston to the remote area while not allowing removable material suspended in the suspension therethrough, and means for forcing liquid removed from said suspen-sion through said piston chamber to said second piston face to move said piston in said second direction so that no sub-stantial dewatering takes place during movement of said piston in said second direction and so that said piston is moved to a position wherein it may again be moved in said first direction.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA302,005A CA1088361A (en) | 1978-04-26 | 1978-04-26 | Plural stage mixing and thickening oxygen reacting |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA302,005A CA1088361A (en) | 1978-04-26 | 1978-04-26 | Plural stage mixing and thickening oxygen reacting |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088361A true CA1088361A (en) | 1980-10-28 |
Family
ID=4111344
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA302,005A Expired CA1088361A (en) | 1978-04-26 | 1978-04-26 | Plural stage mixing and thickening oxygen reacting |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1088361A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117929300A (en) * | 2023-11-29 | 2024-04-26 | 海南金海浆纸业有限公司 | A method and device for rapid detection of pulp kappa number |
-
1978
- 1978-04-26 CA CA302,005A patent/CA1088361A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117929300A (en) * | 2023-11-29 | 2024-04-26 | 海南金海浆纸业有限公司 | A method and device for rapid detection of pulp kappa number |
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