CA1294396C - Process for decreasing the charge of chemical required in a bleaching extraction stage - Google Patents
Process for decreasing the charge of chemical required in a bleaching extraction stageInfo
- Publication number
- CA1294396C CA1294396C CA000510446A CA510446A CA1294396C CA 1294396 C CA1294396 C CA 1294396C CA 000510446 A CA000510446 A CA 000510446A CA 510446 A CA510446 A CA 510446A CA 1294396 C CA1294396 C CA 1294396C
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- Prior art keywords
- pulp
- washer
- effluent
- chlorination
- extraction
- 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
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF DISCLOSURE
There is provided an improved bleaching process and apparatus for chemical pulp wherein the charge of chemical required in a bleaching extraction stage is decreased by treating the chlorinated pulp with recy-cled extraction effluent.
There is provided an improved bleaching process and apparatus for chemical pulp wherein the charge of chemical required in a bleaching extraction stage is decreased by treating the chlorinated pulp with recy-cled extraction effluent.
Description
1. BACKGROUND OF THE INVENTION
(i) Field of the Invention The present invention relates to an improvement in a bleaching process and apparatus and in particular, relates to an improved method and appartus for decreas-ing the charge of chemical required in a bleaching extraction stage.
(ii) Description of the Prior Art The recycling of some of the extraction effluent during chemical pulp bleaching is a common practice to conserve heat and to displace the acidic chlorination liquor. The recycled extraction stage liquor is added to the chlorinated pulp as it leaves the chlorination stag~ washer via the washer showers and this recycled liquor ls carried with the pulp back into the extrac-tion stage (~-listed, J.~. and Nelson, Jr., G.G. in "The sleaching of Pulp", R.P. Singh, Ed., 3rd Edition, TAPPI
Press, Atlanta, 1979, p. 393; Histed, J.A. and Nicolle, F.M.A., PUlp Paper Mag. Can. 7~ t5) 'rl71 (1974);
Wartiovaara, I., Paperi ja Puu 62 ( 5) 319 ( 1980); and wartiovaara, I., Pulp Paper Can. 81 (7) T167 (1980)).
It is also known in the prior art (Burkart, L.~., Paper Trade J. 156 (2) 33 ~1972) and Azad~ A.M. and Burkart, L.F., Tappi 59 (4) 140 (1976)) to use recycled effluent fortified with sodium hydroxide as the extrac-ting liquor for the first eXtraCtion stage. This is found to decrease the amourlt of sodium hydroxide required in the extraction stage by about 16~.
ti 2. S~MMARY OF THE INVENTI~N
(i~ Aims of the Invention .
It is an object ot the present invention to provide an improved process and apparatus for decreasin~ the amount of chemical required in an extraction stage of a chemical pulp bleaching sequence.
(ii) Statement of the Invention .
According to the present invention, there is pro-vided an additional washing step before the extraction stage begins.
In yreater detail~ in a bleachin~ process wherein a pulp is sequentially subjected to a chlorination, a chlorination washing step, a mixing step with an alka-line solution (usually sodium hydroxide and steam), an extraction step, followed by an extraction stage wash-ing step, there is provided ttle improvement which includes the steps of subjecting the pulp to an addi-tional washing step between the chlorination washing step and the mixiny step. Effluent frorn the extraction stage washing step is recycled to the pulp i~mediately after the chlorination washing step. E~fluerlt from the additional washing step is recycled for use in the chlorination washing step.
There is also provided an improved bleaching appa-ratus which includes an additional washer between a chlorination washer and a mixer for mixing steam and the al~aline solution with the pulp before it enters an extraction tower. There are provided means for direct-ing effluent from the additional washer to the chlorin-ation washer and means for directing the effluent from the extraction washer to the pulp at a point between the chlorination washer and the additional washer.
(i) Field of the Invention The present invention relates to an improvement in a bleaching process and apparatus and in particular, relates to an improved method and appartus for decreas-ing the charge of chemical required in a bleaching extraction stage.
(ii) Description of the Prior Art The recycling of some of the extraction effluent during chemical pulp bleaching is a common practice to conserve heat and to displace the acidic chlorination liquor. The recycled extraction stage liquor is added to the chlorinated pulp as it leaves the chlorination stag~ washer via the washer showers and this recycled liquor ls carried with the pulp back into the extrac-tion stage (~-listed, J.~. and Nelson, Jr., G.G. in "The sleaching of Pulp", R.P. Singh, Ed., 3rd Edition, TAPPI
Press, Atlanta, 1979, p. 393; Histed, J.A. and Nicolle, F.M.A., PUlp Paper Mag. Can. 7~ t5) 'rl71 (1974);
Wartiovaara, I., Paperi ja Puu 62 ( 5) 319 ( 1980); and wartiovaara, I., Pulp Paper Can. 81 (7) T167 (1980)).
It is also known in the prior art (Burkart, L.~., Paper Trade J. 156 (2) 33 ~1972) and Azad~ A.M. and Burkart, L.F., Tappi 59 (4) 140 (1976)) to use recycled effluent fortified with sodium hydroxide as the extrac-ting liquor for the first eXtraCtion stage. This is found to decrease the amourlt of sodium hydroxide required in the extraction stage by about 16~.
ti 2. S~MMARY OF THE INVENTI~N
(i~ Aims of the Invention .
It is an object ot the present invention to provide an improved process and apparatus for decreasin~ the amount of chemical required in an extraction stage of a chemical pulp bleaching sequence.
(ii) Statement of the Invention .
According to the present invention, there is pro-vided an additional washing step before the extraction stage begins.
In yreater detail~ in a bleachin~ process wherein a pulp is sequentially subjected to a chlorination, a chlorination washing step, a mixing step with an alka-line solution (usually sodium hydroxide and steam), an extraction step, followed by an extraction stage wash-ing step, there is provided ttle improvement which includes the steps of subjecting the pulp to an addi-tional washing step between the chlorination washing step and the mixiny step. Effluent frorn the extraction stage washing step is recycled to the pulp i~mediately after the chlorination washing step. E~fluerlt from the additional washing step is recycled for use in the chlorination washing step.
There is also provided an improved bleaching appa-ratus which includes an additional washer between a chlorination washer and a mixer for mixing steam and the al~aline solution with the pulp before it enters an extraction tower. There are provided means for direct-ing effluent from the additional washer to the chlorin-ation washer and means for directing the effluent from the extraction washer to the pulp at a point between the chlorination washer and the additional washer.
3. BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the invention, reference will be made to the accompanying drawings illustrating an embodiment thereof, in Which:
FIGURE 1 is a simplified flow diagram for a recy-cling system in a conventional bleach plant having a chlorination stage followed by an extraction stage.
E'IC~URE 2 is a flow diagram similar to Figure 1 illustrating a verSion of the improved system of the present invention.
Having thus generally described the invention, reference will be made to the accompanying drawings illustrating an embodiment thereof, in Which:
FIGURE 1 is a simplified flow diagram for a recy-cling system in a conventional bleach plant having a chlorination stage followed by an extraction stage.
E'IC~URE 2 is a flow diagram similar to Figure 1 illustrating a verSion of the improved system of the present invention.
4. DESCRIPTION OF PREF~RRED EM~ODIM~N1~
(i) Detailed ~escription of F`i~. 1 and 2 Chlorination dcscribed hereirl includes the various modifications of the chlorination stage where chlorine dioxide replaces some or all o~ the chlorine. Chlorine and chlorine dioxide are examples of oxidising cherni~
cals that can be used before an extraction stage. Any extraction stage preceded by an oxidising Step can be improved ~y the application of this invention.
In greater detail, as shown in Figure 1, a conven-tional chlorination bleaching system having a recycling step includes a chlorination tower 10, piping 12 lead-ing to a chlorination washer 14~ piping 16 leading to a mixer 18 wherein the alkaline solution and steam are mixed with the pulp, a further transport pipe 20 to extraction tower 22 and a transport pipe 24 which leads 3'~3~
to the extraction stage washer 26. Means, 28, are pro-vided for returning effluent from the extraction stage washer 26 to the chlorination washer 14.
In the present invention lll~strated in Figure 2, similar reference numerals are employed for similar components. However, it will be noted that there is provided an additional washer ~o, between chlorination washer 14 and mixer 18. In this instance, the effluent from extraction washer 26 i~ recycled via line 28 to the pulp at a point between washers 14 and 30. A
source of turbulance at this point is beneficial to ensure proper mixing. Effluent from additional washer 30 is recycled to the chlorination washer 14 via line 32.
The liquid used for the showers in the additional washer 30 is introduced via line 34 and may be provided from an extraction effluent or water source (not shown). The washing step is important because it removes Na~C03 an~ C02 formed ~alony Wittl NaCl) in the reaction of chlorinated pulp with extraction efflu-ent. If NaHC03 and C02 remain with the pulp they useLessly consume a large portion of the chemical charge in the extraction stage.
(ii) Examples Illustrating the Practice of the Preferred Embodiments . _ Example 1 illustrates the sodium hydroxide savings that are possible by washing pulp treated with extrac-tion effluent.
1;2~4396 A spruce kraft pulp (Kappa No. 27.5) was chlorina-ted, well-washed and pressed to 20% consistency. It was then diluted to l0~ consistency with effluent from the first extraction stage. This provided 5 mL of recycled effluent for every l g o.d. of pulp. This 5 mL 9-l, however, could have been added by displacing the liquor associated with the pulp or by just simply diluting to lower consistency. The extraction efflu-ent, at 60C, remained in contact with the pulp for 5 minutes. The pulp washed with water and then extracted with aqueous alkali. A second sample was chlorinated, washed well, and pressed to 20% consistency. It was then diluted to 10% consistency with extraction efflu-ent from the first extraction stage. The extraction effluent, at 60c, remained in contact with the pulp for 5 minutes and then alkali was added to it and the extraction completed. A control sample of washed, chlorinated pulp was extracted without any pretreat-ment. All 3 pulps were then further bleached using a DED partial sequence.
As Table I shows, when effluent recycle and wash-ing were used according to the invention, final bright-ness of 89~ was easily obtained even though the chemi-cal consumption in the El stage was decreased by one-third. The conventional type of recycle wherein the recycled effluent is not washed out of the pulp provid-ed no advantages in terms of CE Kappa number or NaOH
usage.
3~
TABLE I
Type of NaOH Charge El in the Effluent Extraction CE ISO Brightness, Recycle Stage, % on Kappa %
o.d. Pulp No.Dl D2 .
No recycle 3.0 5.481.0 89.5 2.0 6.176.7 1.0 9.056.5 8g.6 Conventional 3.0 5.5 81.4 89.6 Recyle 2.0 5.876.6 87.9 (with no wash) 1.0 8.4 60.7 ~5.5 Recycle 3.0 5.182.2 89.9 Followed by 2.0 5.3 81.7 89.6 washing 1.0 5.879.6 88.7 ,. . _., Unbleached pulp: ~lack spruce kraft pulp; Kappa No., 27.5 C-stage : 5.5% C12 on o.d. pulp, 45 min at 25C 3.5~ consistency E-stage : 90 min at 70 C; 10 consistency Dl-stage : 1~ ClO2 and 0.55% NaOH on o.d. pulp; 3 h at 6~C, 10%
consistency E2-stage : 1~ NaOH on o.d. pulp; 1 h at 60C 10~ consistency D2-stage : 0.5% NaOH on o.d. pulp; 3 h at 60'C; 10~ consistency The extraction effluent used foe recyclin9 was produced by extracting the same chlorinated pulp with 3% NaOH on o.d. pulp.
. . .
Table II shows that the alkali savings whiCh were shown to be possible in Example 1 are maintained when the recycling system approaches steady state.
In Run 1, a spruce kraft pulp (Kappa No. 27.5) was chlorinated, well washed and extracted (3.0% NaO~l on o.d. pulp) without any pretreatment. In Run 2, a second sample of the same pulp was chlorinated, washed well and pressed to 20% consistency. It was then diluted with extraction effluent from the extraction lZ9~3~6 stage of Run 1. The extraction effluent, at 60C, remained in contact with the pulp for 5 minutes.
The pulp was washed with water and extracted with only 2% of NaOH on o.d. pulp. In Run 3, a third sample of the pulp was chlorinated, washed well and pressed to 20~ consistency, It was then diluted with extraction effluent from Run 2. Again the pulp was washed with water and extracted with only 2% NaOH on o.d, pulp.
This procedure of using the effluent from the preceding run was repeated. Table II shows that the CE Kappa number is maintained even though the NaOH charge was decreased from 3.0 to 2.0~ on o.d. pulp in Runs 2, 3 and 4.
In Run 5, a sample of the pulp was chlorinated, well wa~hed and extracted with only 2% NaOH on o.d.
pulp. The CE Kappa number was higher than the value value obtained when using effluent recycle and wash according to the invention.
Clearly a charge of 2~ NaOH on o.d. pulp used according to the invention is equal to ~ NaOH used in the conventional manner.
TABLE II
Na~ll Charge Source of in the Type Run Effluen t Ex t rac t ionCE
o~ No. for staye, ~ on Kappa Process ~ecycleo.d. Pulp No.
Conven-tional 1 No recy. ~.0 4.3 Recycle/
Washing 2 Run 1 2.0 4.3 Recycle/
Washing 3 ~un 2 2.0 4.1 Recycle/
Washing 4 ~un 3 2.0 4.0 Conven-tional 5 No Recy. 2.0 5.2 . .
Conditions: As listed in footnote to Table I.
This example illustrates that changes in the time and temperature of treatment of chlorinated pulp with recycled extraction effluent do not effect the outcome of the procedure.
A spruce kraft pulp (Kappa No. 27.5) was chlorina-ted, well washed and presssed to 20% consistency. It was then diluted to 10~ consistency with effluent from the first extraction stage. A time and temperature combination for this reaction between the chlorinated pulp and the recycled extraction effluent was chosen.
The pulp was washed with water and then extracted with 2.0% NaOH on o.d. pulp. The experiment was repeated with different time and temperature combinations for the reaction between the chlorinated pulp and the recycled extraction effluent.
1~¢~ 6 Table III shows that the useful reaction between the chlorinated pulp and the recycled extraction efflu-ent takes place within 30 seconds at temperatures of 25C and higher. The significance of this is that the reaction can be done in a pipeline, and no special reaction vessel would be necessary.
TABLE III
Recycled Extraction Effluent CE
Temperature,Time of Contact, Kappa C min.__ No.
0.5 4.0 1.0 4.0 5.0 4.1 10.0 3.9 c- and E=staye conditions: As in footnote to Table I.
The addition of a small amount o~ chlorine dioxide to the pulp in the chlorination stage is a common prac-tice for minimizing the damage done to cellulose during chlori na t ion .
Table IV shows that the CE Kappa number oE conven-tionally treated pulp is not much affected if 10~
C102 substitution is used. Moreover, by treating the chlorinated pulp according to the invention a reduction in E-stage NaOH to 2.0% or less can be achieved regard-less of whether C102 is used or not.
g 3~6 TABLE~:_ IV
NaOH Charge Cl 2 i n the Type of Substitution Extraction CE
Process in C-Stage Stage, ~ on Kappa % o.d. pulp No.
Conventional o 3.~ 4.3 Recycle/Washing o 2.0 4.2 Recycle/Washing 0 1.5 4.2 Recycle/Washing 0 1.0 4.1 Conventional 10 3.0 4.1 Recycle/Washing 10 2.0 4.0 Recycle/Washing 10 1.5 4.3 Recycle/Washing l0 I.0 4.4 Unbiëached pulp: Black spruce kraft pulp; Kappa No.
27.5 C-stage ~ 5~5~ ~12 on o.d. pulp: 4S min at 25UC; 3.5% consistency CD - ~tage 5.0e C12 and 0.2% C102 on o.d. pulp: 45 min at 25 ~ ~.5 con~istency.
E-Stage : so min at 70~C; 10~ consistency.
The extraction effluent used for recycl.in~ was produced by extracting the same chlorinated pulp with 3~ NaOH on o.d. pulp.
5. SUMMARY
It will be understood that the above-described embodiments are for purposes of illustration only and that changes and modifications apparent to those skilled in the art may be made.
It will also be apparent that a displacement bleaching system could be used to perform the steps of the invention.
The concept of using the extraction ef1uent as described will not be affected by chemical addition to the extraction stage. Oxygen, peroxide or hypochlorite addition to the extraction stage ~,ill not alter the principle of decreasing the sodium hydroxide charye by ` ~I,'~g4~396 washing after recycling and before the extraction s tage .
(i) Detailed ~escription of F`i~. 1 and 2 Chlorination dcscribed hereirl includes the various modifications of the chlorination stage where chlorine dioxide replaces some or all o~ the chlorine. Chlorine and chlorine dioxide are examples of oxidising cherni~
cals that can be used before an extraction stage. Any extraction stage preceded by an oxidising Step can be improved ~y the application of this invention.
In greater detail, as shown in Figure 1, a conven-tional chlorination bleaching system having a recycling step includes a chlorination tower 10, piping 12 lead-ing to a chlorination washer 14~ piping 16 leading to a mixer 18 wherein the alkaline solution and steam are mixed with the pulp, a further transport pipe 20 to extraction tower 22 and a transport pipe 24 which leads 3'~3~
to the extraction stage washer 26. Means, 28, are pro-vided for returning effluent from the extraction stage washer 26 to the chlorination washer 14.
In the present invention lll~strated in Figure 2, similar reference numerals are employed for similar components. However, it will be noted that there is provided an additional washer ~o, between chlorination washer 14 and mixer 18. In this instance, the effluent from extraction washer 26 i~ recycled via line 28 to the pulp at a point between washers 14 and 30. A
source of turbulance at this point is beneficial to ensure proper mixing. Effluent from additional washer 30 is recycled to the chlorination washer 14 via line 32.
The liquid used for the showers in the additional washer 30 is introduced via line 34 and may be provided from an extraction effluent or water source (not shown). The washing step is important because it removes Na~C03 an~ C02 formed ~alony Wittl NaCl) in the reaction of chlorinated pulp with extraction efflu-ent. If NaHC03 and C02 remain with the pulp they useLessly consume a large portion of the chemical charge in the extraction stage.
(ii) Examples Illustrating the Practice of the Preferred Embodiments . _ Example 1 illustrates the sodium hydroxide savings that are possible by washing pulp treated with extrac-tion effluent.
1;2~4396 A spruce kraft pulp (Kappa No. 27.5) was chlorina-ted, well-washed and pressed to 20% consistency. It was then diluted to l0~ consistency with effluent from the first extraction stage. This provided 5 mL of recycled effluent for every l g o.d. of pulp. This 5 mL 9-l, however, could have been added by displacing the liquor associated with the pulp or by just simply diluting to lower consistency. The extraction efflu-ent, at 60C, remained in contact with the pulp for 5 minutes. The pulp washed with water and then extracted with aqueous alkali. A second sample was chlorinated, washed well, and pressed to 20% consistency. It was then diluted to 10% consistency with extraction efflu-ent from the first extraction stage. The extraction effluent, at 60c, remained in contact with the pulp for 5 minutes and then alkali was added to it and the extraction completed. A control sample of washed, chlorinated pulp was extracted without any pretreat-ment. All 3 pulps were then further bleached using a DED partial sequence.
As Table I shows, when effluent recycle and wash-ing were used according to the invention, final bright-ness of 89~ was easily obtained even though the chemi-cal consumption in the El stage was decreased by one-third. The conventional type of recycle wherein the recycled effluent is not washed out of the pulp provid-ed no advantages in terms of CE Kappa number or NaOH
usage.
3~
TABLE I
Type of NaOH Charge El in the Effluent Extraction CE ISO Brightness, Recycle Stage, % on Kappa %
o.d. Pulp No.Dl D2 .
No recycle 3.0 5.481.0 89.5 2.0 6.176.7 1.0 9.056.5 8g.6 Conventional 3.0 5.5 81.4 89.6 Recyle 2.0 5.876.6 87.9 (with no wash) 1.0 8.4 60.7 ~5.5 Recycle 3.0 5.182.2 89.9 Followed by 2.0 5.3 81.7 89.6 washing 1.0 5.879.6 88.7 ,. . _., Unbleached pulp: ~lack spruce kraft pulp; Kappa No., 27.5 C-stage : 5.5% C12 on o.d. pulp, 45 min at 25C 3.5~ consistency E-stage : 90 min at 70 C; 10 consistency Dl-stage : 1~ ClO2 and 0.55% NaOH on o.d. pulp; 3 h at 6~C, 10%
consistency E2-stage : 1~ NaOH on o.d. pulp; 1 h at 60C 10~ consistency D2-stage : 0.5% NaOH on o.d. pulp; 3 h at 60'C; 10~ consistency The extraction effluent used foe recyclin9 was produced by extracting the same chlorinated pulp with 3% NaOH on o.d. pulp.
. . .
Table II shows that the alkali savings whiCh were shown to be possible in Example 1 are maintained when the recycling system approaches steady state.
In Run 1, a spruce kraft pulp (Kappa No. 27.5) was chlorinated, well washed and extracted (3.0% NaO~l on o.d. pulp) without any pretreatment. In Run 2, a second sample of the same pulp was chlorinated, washed well and pressed to 20% consistency. It was then diluted with extraction effluent from the extraction lZ9~3~6 stage of Run 1. The extraction effluent, at 60C, remained in contact with the pulp for 5 minutes.
The pulp was washed with water and extracted with only 2% of NaOH on o.d. pulp. In Run 3, a third sample of the pulp was chlorinated, washed well and pressed to 20~ consistency, It was then diluted with extraction effluent from Run 2. Again the pulp was washed with water and extracted with only 2% NaOH on o.d, pulp.
This procedure of using the effluent from the preceding run was repeated. Table II shows that the CE Kappa number is maintained even though the NaOH charge was decreased from 3.0 to 2.0~ on o.d. pulp in Runs 2, 3 and 4.
In Run 5, a sample of the pulp was chlorinated, well wa~hed and extracted with only 2% NaOH on o.d.
pulp. The CE Kappa number was higher than the value value obtained when using effluent recycle and wash according to the invention.
Clearly a charge of 2~ NaOH on o.d. pulp used according to the invention is equal to ~ NaOH used in the conventional manner.
TABLE II
Na~ll Charge Source of in the Type Run Effluen t Ex t rac t ionCE
o~ No. for staye, ~ on Kappa Process ~ecycleo.d. Pulp No.
Conven-tional 1 No recy. ~.0 4.3 Recycle/
Washing 2 Run 1 2.0 4.3 Recycle/
Washing 3 ~un 2 2.0 4.1 Recycle/
Washing 4 ~un 3 2.0 4.0 Conven-tional 5 No Recy. 2.0 5.2 . .
Conditions: As listed in footnote to Table I.
This example illustrates that changes in the time and temperature of treatment of chlorinated pulp with recycled extraction effluent do not effect the outcome of the procedure.
A spruce kraft pulp (Kappa No. 27.5) was chlorina-ted, well washed and presssed to 20% consistency. It was then diluted to 10~ consistency with effluent from the first extraction stage. A time and temperature combination for this reaction between the chlorinated pulp and the recycled extraction effluent was chosen.
The pulp was washed with water and then extracted with 2.0% NaOH on o.d. pulp. The experiment was repeated with different time and temperature combinations for the reaction between the chlorinated pulp and the recycled extraction effluent.
1~¢~ 6 Table III shows that the useful reaction between the chlorinated pulp and the recycled extraction efflu-ent takes place within 30 seconds at temperatures of 25C and higher. The significance of this is that the reaction can be done in a pipeline, and no special reaction vessel would be necessary.
TABLE III
Recycled Extraction Effluent CE
Temperature,Time of Contact, Kappa C min.__ No.
0.5 4.0 1.0 4.0 5.0 4.1 10.0 3.9 c- and E=staye conditions: As in footnote to Table I.
The addition of a small amount o~ chlorine dioxide to the pulp in the chlorination stage is a common prac-tice for minimizing the damage done to cellulose during chlori na t ion .
Table IV shows that the CE Kappa number oE conven-tionally treated pulp is not much affected if 10~
C102 substitution is used. Moreover, by treating the chlorinated pulp according to the invention a reduction in E-stage NaOH to 2.0% or less can be achieved regard-less of whether C102 is used or not.
g 3~6 TABLE~:_ IV
NaOH Charge Cl 2 i n the Type of Substitution Extraction CE
Process in C-Stage Stage, ~ on Kappa % o.d. pulp No.
Conventional o 3.~ 4.3 Recycle/Washing o 2.0 4.2 Recycle/Washing 0 1.5 4.2 Recycle/Washing 0 1.0 4.1 Conventional 10 3.0 4.1 Recycle/Washing 10 2.0 4.0 Recycle/Washing 10 1.5 4.3 Recycle/Washing l0 I.0 4.4 Unbiëached pulp: Black spruce kraft pulp; Kappa No.
27.5 C-stage ~ 5~5~ ~12 on o.d. pulp: 4S min at 25UC; 3.5% consistency CD - ~tage 5.0e C12 and 0.2% C102 on o.d. pulp: 45 min at 25 ~ ~.5 con~istency.
E-Stage : so min at 70~C; 10~ consistency.
The extraction effluent used for recycl.in~ was produced by extracting the same chlorinated pulp with 3~ NaOH on o.d. pulp.
5. SUMMARY
It will be understood that the above-described embodiments are for purposes of illustration only and that changes and modifications apparent to those skilled in the art may be made.
It will also be apparent that a displacement bleaching system could be used to perform the steps of the invention.
The concept of using the extraction ef1uent as described will not be affected by chemical addition to the extraction stage. Oxygen, peroxide or hypochlorite addition to the extraction stage ~,ill not alter the principle of decreasing the sodium hydroxide charye by ` ~I,'~g4~396 washing after recycling and before the extraction s tage .
Claims (7)
1. In a bleaching process wherein a chlorinated pulp is sequentially subjected to a chlorination wash-ing step, mixed with an alkaline extracting solu-tion, subjected to an extraction step and an ex-traction stage washing step, the improvement com-prising the further steps of subjecting said pulp to an additional washing step between said chlori-nation washing step and said mixing with an alka-line extracting solution, and recycling effluent from the extraction stage washing step to the pulp immediately after the chlorination washing step.
2. The improvement of Claim 1 wherein said additional washing step is carried out using water or an ex-traction effluent.
3. The improvement of Claim 1 wherein effluent from the additional washing step is used in the chlori-nation washing step and is added to the pulp in the chlorination washer.
4. The improvement of Claim 1, 2 or 3 wherein said alkaline extracting solution comprises sodium hydroxide and steam.
5. The improvement of Claim 1,2 or 3 wherein the step of recycling effluent from extraction stage wash-ing step includes the step of providing turbulence at the point of effluent addition to ensure proper mixing.
6. In a bleaching process, the improvement comprising the steps of (a) Subjecting the chlorinated pulp to a chlorina-tion washing step in a chlorination washer;
(b) transporting said pulp to an additional wash-er;
(c) washing said pulp in said additional washer;
(d) mixing an alkaline extracting solution with the pulp after said additional washing (e) subjecting the pulp to an extraction step;
(f) washing the extracted pulp in an extraction stage washing step.
(g) recycling effluent from said extraction stage washing step to the pulp in step (b): and (h) transporting effluent from the additional washing unit in step (c) to the chlorination washer of step (a).
(b) transporting said pulp to an additional wash-er;
(c) washing said pulp in said additional washer;
(d) mixing an alkaline extracting solution with the pulp after said additional washing (e) subjecting the pulp to an extraction step;
(f) washing the extracted pulp in an extraction stage washing step.
(g) recycling effluent from said extraction stage washing step to the pulp in step (b): and (h) transporting effluent from the additional washing unit in step (c) to the chlorination washer of step (a).
7. In a bleaching apparatus which includes a chlori-nation tower, a chlorination washer, a system for mixing steam and an alkaline extracting solution with the pulp, an extraction tower and an extrac-tion washer, the improvement comprising an addi-tional washer between said chlorination washer and mixing system, means for transporting effluent from said additional washer to said chlorination washer and means for transporting effluent from said extraction washer to the pulp between said first chlorination washer and said additional washer.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000510446A CA1294396C (en) | 1986-05-30 | 1986-05-30 | Process for decreasing the charge of chemical required in a bleaching extraction stage |
| SE8702141A SE500585C2 (en) | 1986-05-30 | 1987-05-22 | Pulp leaching with an extra washing step and return of extraction effluent |
| JP62130081A JPS6328993A (en) | 1986-05-30 | 1987-05-28 | Improved bleaching method and apparatus |
| FI872391A FI91289C (en) | 1986-05-30 | 1987-05-28 | Method and apparatus for bleaching the pulp |
| US07/543,924 US5126009A (en) | 1986-05-30 | 1990-06-26 | Process for decreasing the charge of chemical required in a chlorine bleaching extraction stage |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000510446A CA1294396C (en) | 1986-05-30 | 1986-05-30 | Process for decreasing the charge of chemical required in a bleaching extraction stage |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1294396C true CA1294396C (en) | 1992-01-21 |
Family
ID=4133252
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000510446A Expired - Lifetime CA1294396C (en) | 1986-05-30 | 1986-05-30 | Process for decreasing the charge of chemical required in a bleaching extraction stage |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS6328993A (en) |
| CA (1) | CA1294396C (en) |
| FI (1) | FI91289C (en) |
| SE (1) | SE500585C2 (en) |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE445051B (en) * | 1980-04-10 | 1986-05-26 | Sca Development Ab | SET FOR MANUFACTURING MECHANICAL, MAINLY HEART-FREE CELLULOSAMASSA |
-
1986
- 1986-05-30 CA CA000510446A patent/CA1294396C/en not_active Expired - Lifetime
-
1987
- 1987-05-22 SE SE8702141A patent/SE500585C2/en not_active IP Right Cessation
- 1987-05-28 FI FI872391A patent/FI91289C/en not_active IP Right Cessation
- 1987-05-28 JP JP62130081A patent/JPS6328993A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FI91289B (en) | 1994-02-28 |
| SE500585C2 (en) | 1994-07-18 |
| SE8702141L (en) | 1987-12-01 |
| JPS6328993A (en) | 1988-02-06 |
| JPH0415313B2 (en) | 1992-03-17 |
| FI872391A0 (en) | 1987-05-28 |
| FI872391A (en) | 1987-12-01 |
| FI91289C (en) | 1994-06-10 |
| SE8702141D0 (en) | 1987-05-22 |
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