CA1089161A - Bleached kraft pulp mill operation - Google Patents
Bleached kraft pulp mill operationInfo
- Publication number
- CA1089161A CA1089161A CA349,126A CA349126A CA1089161A CA 1089161 A CA1089161 A CA 1089161A CA 349126 A CA349126 A CA 349126A CA 1089161 A CA1089161 A CA 1089161A
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- Canada
- Prior art keywords
- liquor
- condensate
- water
- line
- pulp
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Abstract
ABSTRACT OF THE DISCLOSURE
The BOD level of black liquor condensates in pulp mill wherein bleach plant effluents are introduced to the black liquor re overy operation is decreased to a very low level by combining the most contaminated condensates from the black liquor concentration step and steam stripping methanol from the mixture. The stripped condensate then may be used elsewhere in the mill.
The BOD level of black liquor condensates in pulp mill wherein bleach plant effluents are introduced to the black liquor re overy operation is decreased to a very low level by combining the most contaminated condensates from the black liquor concentration step and steam stripping methanol from the mixture. The stripped condensate then may be used elsewhere in the mill.
Description
108~161 . 1 BLEi~C~lED KRZ~FT PULP MILL OPERATION
This invention relates to a bleached kraft pulp mill operation.
This application is a division of copending Canadian patent application Serial No. 279,885 filed June 6, 1977.
In a liquid effluent free bleached pulp mill, in which bleached pulp is formed by digesting cellulosic fibrous material and bleachin~ and purifying the pulp and in which spent pulping li~uors are subjected to recovery and regeneration to form fresh pulping liquor, liquid effluents from the bleaching and purification operations (bleach plant effluent~ are discharged into the recovery and regeneration operation.
The organic materials content of the bleach plant effluent is burned off in the recovery furnace of the recovery and regeneration operation and the aqueous phase is evaporated in the recovery and regeneration operation.
Owing to the high cost of évaporating water in a pulp mill, in the interests of minimizing operating costs, it is desirable to decrease the total volume of bleach plant effluent which must be discharged into the pulp mill -recovery and regeneration operation and hence minimize the total evaporation load. It is also desirable that any bleach plant effluent volume decrease not significantly adversely affect the pulp quality obtained.
In accordance with-the invention-of the afore- - .
mentioned parent application, there is provided a bleach plant operation in which water conservation is practised by controlling the use of wash water in the bleach plant, controlling the design and operation of washers, deckers and other mechanical devices used in the ble~ch plant, and controlling the inflow of water with chemicalsO
The present invention is concerned with decreasing the BOD level of black liquor condensates resulting from the 35 evaporation of black li~uor prior to furnacing in a pulp -mill of the type wherein bleach plant effluents are intro-duced to the pulp mill recovery operation. The bleach plant operation, such as that of the parent case, produces two liquid effluents, one acid and the other alkaline. These ., :~: : : . - . , :....... : . . ~ . . - :
..
effluents may bc passed to the recovery operation, preferably : in accordance with ~he procedure of our Canadian Patent No. 1,070,908.
In accordance with the present invention, there is 5 provided a bleached kraft pulp mill process, including the steps of: (a~ digesting cellulosic fibrous material in a pulping liquor containing sodium hydroxide and sodium sulphide as the active pulping chemicals to form brown stock and ailute black liquor, washing the resulting ~rown stock 10 with a first wash water, passing the washed pulp through screens and cleaners and thence to a bleach plant; (b) subjecting the pulp to bleaching, caustic extraction and :. washing operations in the bleach plant to result in bleached pulp of the required brightness and purity; Cc~ removing 15 two effluents from the bleach plant consisting of an alkaline effluent and an acid effluent a~d utilizing part of the alkaline effluent as part of the first wash water; (d) passing the dilute black liquor from the digestion step to ~ sextuple effect black liquor evaporators to which heating J 20 steam is fed and recovering condensates from the evaporators;
(el passing concentrated black liquor from the evaporators to : a recovery furnace wherein organic materials present in the , ~oncentrated ~lack liquor are burned and a smelt containing sodium carbonate, sodium sulphide, sodium chloride and 25 sodium sulphate is formed; (f~ forming white liquor contain-~ ing regenerated pulping chemicals from the smelt, separating .: substantially pure solid sodium chloride from the ~hite . liquor by an evaporation procedure, recovering condensed - water from the evaporation, diluting the concentrated white ~: 30. liquor resulting from the evaporation procedure to the required pulping liquor concentration usin~ the remainder of the alkaline filtrate, recycling the latter pulping ~: liquor to the digestion step for use as at least part of : the pulping li~uor therein and discharging the condensed water; ~.gl subjecting~hotwell condensate, flash heat ~- double evaporator condensate and sextuple surface condenser condensate from the sextuple effect evaporators along with !~ ~ turpentine underflow from the digestion step to steam ~: stripping to remove therefrom BOD~causing volatile organic .~- .
, , .:
108~6~
material, recovering the stripped volatile organic material and utilizing the stripped condensate as a source of water for the process; and (h) passing fifth and sixth --evaporator condensate for use in the formation of white liquor from the smelt; and (i~ passing the acid filtrate for use in the formation of white liquor from the smelt, In the procedure of this invention, therefore, the most contaminated condensates are com~ined and steam stripped to remove methanol, which may be used for its fuel value or otherwise, while the less contaminated condensates are used directly without stripping.
The invention is described further, by way of illustration, with reference to the accompanying drawing, which is a schematic flow sheet of a pulp mill recovery and regeneration operation in accordance with one embodiment of the invention.
Referring to the drawing, there is illustrated therein a bleached kraft pulp mill operation in which t~e -~
overall material flow within an effluent-free pulp mill is illustrated. With the elimination of the toxic effect - of bleach plant effluent by introducing the same to the pulp mill recovery operationj such as is descri~ed in the afore-said parent application, ~lack liquor condensates ~ecome the potential dominant effluent. While the total BOD of the black liquor condensates is moderate, typically about 20 l~s of methanol APT of pulp, when compared with that of bleach plant effluent, within the context of an "effluent~
free" pulp milI, the value is quite high.
~;~In the pulp mill operation illustrated in the -drawing, the BOD level of the black li~uor condensates is decreased to a very low level acceptable for discharge from ~ ;
the mill in the "effluent-free" environment. This is achieved ~y combining the most contaminated condensates and thRn steam stripping methanol from this mixture. The methanol removed in this way then may be used for itS
fuel value or otherwise. The stripped condensate then may e used in various locations in the mill.
As seen in the drawing, wood chips are fed by line 51Q to a digester 512 to which white liquor is fed by line 4~ 514 and steaming vessel steam is fed by line 516. Pulp :t, ~" ' ... ~.. '.. . '. ' ' ' ,. ' , - . , ' . , , ' ' . . ' ' '-`` 108~
wash water also is fed to the digester 512 by line 518. The brown stock pulp is fed from the digester 512 by line 520 to a brown stock washer 522 to which wash water is fed by line 524. The washed pulp passes by line 526 through cleaners and screens 528 and line 530 to a bleach plant 532, such as that described in the aforesaid parent application and including an unbleached decker.
Wash water from the bleach plant 532 passes by line 534 to the cleaners and screens 528 and El.stage effluent from the ~leach plant 532 passes by line 536 to join the .
wash water in line 524 passing to the brown stock washer 522. Wire cleaning water also passes to the cleaners and ~.
screens 528 by line 538.
Chlorine chemical preparation 540 provides chlorine .-15 .dioxide and chlorine solutions to the bleach plant 532 by .
line 542 and sodium hypochlorite solution by line 544. The chemical preparation is fed by water in line 545 and all may be produced from a single chlorine dioxide and chlorine generator, for example, using the procedure outlined in 2Q U.S. Patent No. 4,010,112. The latter procedure enables the volume of water entering the bleach plant ~ith the bleaching chemicals to be minimized.
Sodium hydroxide for the bleach plant 532 is fed by line 546 while wash water in the form of pulp machine dryer white water is fed ~y line 548 to the bleach plant. Other inputs for the bleach plant 532 are heating steam by line 550 and ~as~er screen cleaner ~ater by line 552.
The bleached pulp passing out of the bleach plant 532 passes by line 554 to the pulp machine dryer 556. Bleached pulp exits the dryer by line 558 while any excess white water not required in line 546 is passed to sewer by line 560, while some moisture passes to atmosphere through the dryer stack 562~ ~ater for a variety of purposes enters to pu~p machine dryer 556 by line 563, including vacuum pump :. :
35 seaI ~ater, condensate cooler water, trim jet ~ater and ~ ~.
; steam shower ste~m. .
The dilute black liquor and .fla-sh steam ~rom the digester 512 pass by lines 564 and 566 to black liquor evaporators 568. Additional heating steam is fed to the . . :
- ; : : . ......................... - ~ ' .,~ : . - . . . .
10~161 , evaporators 568 by line 570. The black liquor evaporators takes the form of sextuple effect evaporators which produce concentrated black liquor which passes by line 572 to the recovery furnace 574. Various other liquid effluents are produced and these will ~e described further ~elow.
Moisture is lost through weak black liquor oxidation stack 576.
In the recovery furnace 574 all the organic materials are burned and there is formed a smelt in line 578 containing 10 sodium car~onate, sodium sulphide, sodium chloride and ~-sodium sulphate. Stack gases are vented by line 580. Steam is generated in the furnace and the blow down is passed by line 582 to the evaporators 568.
The smelt in line 578 then is passed to liquor preparation 584 wherein white liquor is regenerated. D/C
effluent from the bleach plant 532 passes by line 586 to liquor preparation 584 for kiln scrubbing therein. Smelt spray water is fed to the liquor preparation 584 by line 588. Solid green liquor dregs are removed from the liquor 2a preparation 584 by line 590 as are dregs from the causti-cization ~y line 5~2.
The white liquor resulting from c~emical pr~paration passes to a salt reco~ery process 5q4 by line 596. In the salt recovery process, which typically may be that outlined --in U.S. Patent No. 3,q50,217, solid.sodium chloride is i removed from the white l;quor by an evaporative procedure and recovered by line 598. The concentrated white liquor i is diluted by El filtrate from the bleach plant 532 fed by line 600 to the desired concentration.to the digester 512 by ~:
line 514, as descri~ed.in our a~orementioned Canadian Patent No. 1,070,908. . ~ :
Burkeite ~lso deposited in the salt recovery process 594 passes by line 602 to the liquor preparation 584, while excess condensate from the salt recovery process 5~4 is : : 35 passed to sewer by line 604. Water for salt leaching in the salt recovery process 59.4 is fed by line 605.
: The only liquid effluents being sewered from the system are excess white water in line 56Q and excess conden- ~:
sate from the salt recovery process in line 6Q4. Both of ' ; : .
c these liquors are pure water and hence their discharge is not harmful.
As mentioned above, there are a number of condensates from the black liquor evaporators 568. Those most con-taminated with methanol from the black liquor, the hotwell condensate, the flash heat double evaporator condensate and the sextuple surface condenser condensate pass b~ lines 606, 608 a~d 610 respectively to a methanol stripper 612 along with turpentine underflow from the digester 512 in line 614.
10 In the methanol stripper 612, steam, fed by line 616, strips methanol from the contaminated condensate. The methanol is recovered by line 618 while the purified condensate passes by line 620 to the brown stock washer 522 for use as wash water therein.
Part or all of the purified condensate may be used in a variety of other locations within the mill, for example, in wire cleaning in the cleaners and screens 528, for chlorine dioxide adsorption in chemical preparation 540, or as wash water or make-up water in the bleach plant.
The condensate from the fifth and sixth effect evapor-ators in the black liquor evaporators 568 is passed by line 622 to liquor preparation 584, while condensate rom the second, third and fourth effect evaporators being relatively free of contaminants may be discharged or may 25 join with the purified condensate in line 620 ~y line 624.
The present invention, therefore, provides a bleached kraft mill water utilization system which eliminates noxious a~ueous effluents. Modifications are possible within the scope of the invention. ~ -, : : : : - .
; - , ` . :. , , ~ ~ .
:~ ' ' . - , . .
,.
This invention relates to a bleached kraft pulp mill operation.
This application is a division of copending Canadian patent application Serial No. 279,885 filed June 6, 1977.
In a liquid effluent free bleached pulp mill, in which bleached pulp is formed by digesting cellulosic fibrous material and bleachin~ and purifying the pulp and in which spent pulping li~uors are subjected to recovery and regeneration to form fresh pulping liquor, liquid effluents from the bleaching and purification operations (bleach plant effluent~ are discharged into the recovery and regeneration operation.
The organic materials content of the bleach plant effluent is burned off in the recovery furnace of the recovery and regeneration operation and the aqueous phase is evaporated in the recovery and regeneration operation.
Owing to the high cost of évaporating water in a pulp mill, in the interests of minimizing operating costs, it is desirable to decrease the total volume of bleach plant effluent which must be discharged into the pulp mill -recovery and regeneration operation and hence minimize the total evaporation load. It is also desirable that any bleach plant effluent volume decrease not significantly adversely affect the pulp quality obtained.
In accordance with-the invention-of the afore- - .
mentioned parent application, there is provided a bleach plant operation in which water conservation is practised by controlling the use of wash water in the bleach plant, controlling the design and operation of washers, deckers and other mechanical devices used in the ble~ch plant, and controlling the inflow of water with chemicalsO
The present invention is concerned with decreasing the BOD level of black liquor condensates resulting from the 35 evaporation of black li~uor prior to furnacing in a pulp -mill of the type wherein bleach plant effluents are intro-duced to the pulp mill recovery operation. The bleach plant operation, such as that of the parent case, produces two liquid effluents, one acid and the other alkaline. These ., :~: : : . - . , :....... : . . ~ . . - :
..
effluents may bc passed to the recovery operation, preferably : in accordance with ~he procedure of our Canadian Patent No. 1,070,908.
In accordance with the present invention, there is 5 provided a bleached kraft pulp mill process, including the steps of: (a~ digesting cellulosic fibrous material in a pulping liquor containing sodium hydroxide and sodium sulphide as the active pulping chemicals to form brown stock and ailute black liquor, washing the resulting ~rown stock 10 with a first wash water, passing the washed pulp through screens and cleaners and thence to a bleach plant; (b) subjecting the pulp to bleaching, caustic extraction and :. washing operations in the bleach plant to result in bleached pulp of the required brightness and purity; Cc~ removing 15 two effluents from the bleach plant consisting of an alkaline effluent and an acid effluent a~d utilizing part of the alkaline effluent as part of the first wash water; (d) passing the dilute black liquor from the digestion step to ~ sextuple effect black liquor evaporators to which heating J 20 steam is fed and recovering condensates from the evaporators;
(el passing concentrated black liquor from the evaporators to : a recovery furnace wherein organic materials present in the , ~oncentrated ~lack liquor are burned and a smelt containing sodium carbonate, sodium sulphide, sodium chloride and 25 sodium sulphate is formed; (f~ forming white liquor contain-~ ing regenerated pulping chemicals from the smelt, separating .: substantially pure solid sodium chloride from the ~hite . liquor by an evaporation procedure, recovering condensed - water from the evaporation, diluting the concentrated white ~: 30. liquor resulting from the evaporation procedure to the required pulping liquor concentration usin~ the remainder of the alkaline filtrate, recycling the latter pulping ~: liquor to the digestion step for use as at least part of : the pulping li~uor therein and discharging the condensed water; ~.gl subjecting~hotwell condensate, flash heat ~- double evaporator condensate and sextuple surface condenser condensate from the sextuple effect evaporators along with !~ ~ turpentine underflow from the digestion step to steam ~: stripping to remove therefrom BOD~causing volatile organic .~- .
, , .:
108~6~
material, recovering the stripped volatile organic material and utilizing the stripped condensate as a source of water for the process; and (h) passing fifth and sixth --evaporator condensate for use in the formation of white liquor from the smelt; and (i~ passing the acid filtrate for use in the formation of white liquor from the smelt, In the procedure of this invention, therefore, the most contaminated condensates are com~ined and steam stripped to remove methanol, which may be used for its fuel value or otherwise, while the less contaminated condensates are used directly without stripping.
The invention is described further, by way of illustration, with reference to the accompanying drawing, which is a schematic flow sheet of a pulp mill recovery and regeneration operation in accordance with one embodiment of the invention.
Referring to the drawing, there is illustrated therein a bleached kraft pulp mill operation in which t~e -~
overall material flow within an effluent-free pulp mill is illustrated. With the elimination of the toxic effect - of bleach plant effluent by introducing the same to the pulp mill recovery operationj such as is descri~ed in the afore-said parent application, ~lack liquor condensates ~ecome the potential dominant effluent. While the total BOD of the black liquor condensates is moderate, typically about 20 l~s of methanol APT of pulp, when compared with that of bleach plant effluent, within the context of an "effluent~
free" pulp milI, the value is quite high.
~;~In the pulp mill operation illustrated in the -drawing, the BOD level of the black li~uor condensates is decreased to a very low level acceptable for discharge from ~ ;
the mill in the "effluent-free" environment. This is achieved ~y combining the most contaminated condensates and thRn steam stripping methanol from this mixture. The methanol removed in this way then may be used for itS
fuel value or otherwise. The stripped condensate then may e used in various locations in the mill.
As seen in the drawing, wood chips are fed by line 51Q to a digester 512 to which white liquor is fed by line 4~ 514 and steaming vessel steam is fed by line 516. Pulp :t, ~" ' ... ~.. '.. . '. ' ' ' ,. ' , - . , ' . , , ' ' . . ' ' '-`` 108~
wash water also is fed to the digester 512 by line 518. The brown stock pulp is fed from the digester 512 by line 520 to a brown stock washer 522 to which wash water is fed by line 524. The washed pulp passes by line 526 through cleaners and screens 528 and line 530 to a bleach plant 532, such as that described in the aforesaid parent application and including an unbleached decker.
Wash water from the bleach plant 532 passes by line 534 to the cleaners and screens 528 and El.stage effluent from the ~leach plant 532 passes by line 536 to join the .
wash water in line 524 passing to the brown stock washer 522. Wire cleaning water also passes to the cleaners and ~.
screens 528 by line 538.
Chlorine chemical preparation 540 provides chlorine .-15 .dioxide and chlorine solutions to the bleach plant 532 by .
line 542 and sodium hypochlorite solution by line 544. The chemical preparation is fed by water in line 545 and all may be produced from a single chlorine dioxide and chlorine generator, for example, using the procedure outlined in 2Q U.S. Patent No. 4,010,112. The latter procedure enables the volume of water entering the bleach plant ~ith the bleaching chemicals to be minimized.
Sodium hydroxide for the bleach plant 532 is fed by line 546 while wash water in the form of pulp machine dryer white water is fed ~y line 548 to the bleach plant. Other inputs for the bleach plant 532 are heating steam by line 550 and ~as~er screen cleaner ~ater by line 552.
The bleached pulp passing out of the bleach plant 532 passes by line 554 to the pulp machine dryer 556. Bleached pulp exits the dryer by line 558 while any excess white water not required in line 546 is passed to sewer by line 560, while some moisture passes to atmosphere through the dryer stack 562~ ~ater for a variety of purposes enters to pu~p machine dryer 556 by line 563, including vacuum pump :. :
35 seaI ~ater, condensate cooler water, trim jet ~ater and ~ ~.
; steam shower ste~m. .
The dilute black liquor and .fla-sh steam ~rom the digester 512 pass by lines 564 and 566 to black liquor evaporators 568. Additional heating steam is fed to the . . :
- ; : : . ......................... - ~ ' .,~ : . - . . . .
10~161 , evaporators 568 by line 570. The black liquor evaporators takes the form of sextuple effect evaporators which produce concentrated black liquor which passes by line 572 to the recovery furnace 574. Various other liquid effluents are produced and these will ~e described further ~elow.
Moisture is lost through weak black liquor oxidation stack 576.
In the recovery furnace 574 all the organic materials are burned and there is formed a smelt in line 578 containing 10 sodium car~onate, sodium sulphide, sodium chloride and ~-sodium sulphate. Stack gases are vented by line 580. Steam is generated in the furnace and the blow down is passed by line 582 to the evaporators 568.
The smelt in line 578 then is passed to liquor preparation 584 wherein white liquor is regenerated. D/C
effluent from the bleach plant 532 passes by line 586 to liquor preparation 584 for kiln scrubbing therein. Smelt spray water is fed to the liquor preparation 584 by line 588. Solid green liquor dregs are removed from the liquor 2a preparation 584 by line 590 as are dregs from the causti-cization ~y line 5~2.
The white liquor resulting from c~emical pr~paration passes to a salt reco~ery process 5q4 by line 596. In the salt recovery process, which typically may be that outlined --in U.S. Patent No. 3,q50,217, solid.sodium chloride is i removed from the white l;quor by an evaporative procedure and recovered by line 598. The concentrated white liquor i is diluted by El filtrate from the bleach plant 532 fed by line 600 to the desired concentration.to the digester 512 by ~:
line 514, as descri~ed.in our a~orementioned Canadian Patent No. 1,070,908. . ~ :
Burkeite ~lso deposited in the salt recovery process 594 passes by line 602 to the liquor preparation 584, while excess condensate from the salt recovery process 5~4 is : : 35 passed to sewer by line 604. Water for salt leaching in the salt recovery process 59.4 is fed by line 605.
: The only liquid effluents being sewered from the system are excess white water in line 56Q and excess conden- ~:
sate from the salt recovery process in line 6Q4. Both of ' ; : .
c these liquors are pure water and hence their discharge is not harmful.
As mentioned above, there are a number of condensates from the black liquor evaporators 568. Those most con-taminated with methanol from the black liquor, the hotwell condensate, the flash heat double evaporator condensate and the sextuple surface condenser condensate pass b~ lines 606, 608 a~d 610 respectively to a methanol stripper 612 along with turpentine underflow from the digester 512 in line 614.
10 In the methanol stripper 612, steam, fed by line 616, strips methanol from the contaminated condensate. The methanol is recovered by line 618 while the purified condensate passes by line 620 to the brown stock washer 522 for use as wash water therein.
Part or all of the purified condensate may be used in a variety of other locations within the mill, for example, in wire cleaning in the cleaners and screens 528, for chlorine dioxide adsorption in chemical preparation 540, or as wash water or make-up water in the bleach plant.
The condensate from the fifth and sixth effect evapor-ators in the black liquor evaporators 568 is passed by line 622 to liquor preparation 584, while condensate rom the second, third and fourth effect evaporators being relatively free of contaminants may be discharged or may 25 join with the purified condensate in line 620 ~y line 624.
The present invention, therefore, provides a bleached kraft mill water utilization system which eliminates noxious a~ueous effluents. Modifications are possible within the scope of the invention. ~ -, : : : : - .
; - , ` . :. , , ~ ~ .
:~ ' ' . - , . .
,.
Claims (4)
1. A bleached kraft pulp mill process, including the steps of:
(a) digesting cellulosic fibrous material in a pulping liquor containing sodium hydroxide and sodium sulphide as the active pulping chemicals to form brown stock and dilute black liquor, washing the resulting brown stock with a first wash water, passing the washed pulp through screens and cleaners and thence to a bleach plant;
(b) subjecting the pulp to bleaching, caustic extraction and washing operations in said bleach plant to result in bleached pulp of the required brightness and purity;
(c) removing two effluents from the bleach plant consisting of an alkaline effluent and an acid effluent and utilizing part of said alkaline effluent as part of said first wash water;
(d) passing said dilute black liquor from the digestion step to sextuple effect black liquor evaporators to which heating steam is fed and recovering condensates from said evaporators;
(e) passing concentrated black liquor from the evaporators to a recovery furnace wherein organic materials present in the concentrated black liquor are burned and a smelt containing sodium carbonate, sodium sulphide, sodium chloride and sodium sulphate is formed;
(f) forming white liquor containing regenerated pulping chemicals from the smelt, separating substantially pure solid sodium chloride from the white liquor by an evaporation procedure, recovering condensed water from the evaporation, diluting the concentrated white liquor resulting from the evaporation procedure to the required pulping liquor concentration using the remainder of said alkaline filtrate, recycling said latter pulping liquor to said digestion step for use as at least part of the pulping liquor therein and discharging said condensed water;
(g) subjecting hotwell condensate, flash heat double evaporator condensate and sextuple surface condenser conden-sate from said sextuple effect evaporators along with turpentine underflow from said digestion step to steam stripping to remove therefrom BOD-causing volatile organic material and utilizing the stripped condensate as a source of water for the process; and (h) passing fifth and sixth evaporator condensate for use in the formation of white liquor from the smelt;
and (i) passing said acid filtrate for use in the formation of white liquor from the smelt.
(a) digesting cellulosic fibrous material in a pulping liquor containing sodium hydroxide and sodium sulphide as the active pulping chemicals to form brown stock and dilute black liquor, washing the resulting brown stock with a first wash water, passing the washed pulp through screens and cleaners and thence to a bleach plant;
(b) subjecting the pulp to bleaching, caustic extraction and washing operations in said bleach plant to result in bleached pulp of the required brightness and purity;
(c) removing two effluents from the bleach plant consisting of an alkaline effluent and an acid effluent and utilizing part of said alkaline effluent as part of said first wash water;
(d) passing said dilute black liquor from the digestion step to sextuple effect black liquor evaporators to which heating steam is fed and recovering condensates from said evaporators;
(e) passing concentrated black liquor from the evaporators to a recovery furnace wherein organic materials present in the concentrated black liquor are burned and a smelt containing sodium carbonate, sodium sulphide, sodium chloride and sodium sulphate is formed;
(f) forming white liquor containing regenerated pulping chemicals from the smelt, separating substantially pure solid sodium chloride from the white liquor by an evaporation procedure, recovering condensed water from the evaporation, diluting the concentrated white liquor resulting from the evaporation procedure to the required pulping liquor concentration using the remainder of said alkaline filtrate, recycling said latter pulping liquor to said digestion step for use as at least part of the pulping liquor therein and discharging said condensed water;
(g) subjecting hotwell condensate, flash heat double evaporator condensate and sextuple surface condenser conden-sate from said sextuple effect evaporators along with turpentine underflow from said digestion step to steam stripping to remove therefrom BOD-causing volatile organic material and utilizing the stripped condensate as a source of water for the process; and (h) passing fifth and sixth evaporator condensate for use in the formation of white liquor from the smelt;
and (i) passing said acid filtrate for use in the formation of white liquor from the smelt.
2. The process of claim 1 wherein said stripped condensate is used as part of said first wash water.
3. The process of claim 2 wherein condensate from the second, third and fourth effect evaporators are joined with the stripped condensate.
4. The process of claim 1, 2 or 3 wherein said bleached pulp is dried, at least part of drier white water is returned to the bleach plant and any excess drier white water is discharged with the discharged condensed water.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA349,126A CA1089161A (en) | 1977-06-06 | 1980-04-02 | Bleached kraft pulp mill operation |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA279,885A CA1089157A (en) | 1977-06-06 | 1977-06-06 | Bleach plant operation |
| CA349,126A CA1089161A (en) | 1977-06-06 | 1980-04-02 | Bleached kraft pulp mill operation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1089161A true CA1089161A (en) | 1980-11-11 |
Family
ID=25668520
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA349,126A Expired CA1089161A (en) | 1977-06-06 | 1980-04-02 | Bleached kraft pulp mill operation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1089161A (en) |
-
1980
- 1980-04-02 CA CA349,126A patent/CA1089161A/en not_active Expired
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