CA1273454A - Process for the manufacture of cellulose pulps and cellulose pulps obtained thereby - Google Patents
Process for the manufacture of cellulose pulps and cellulose pulps obtained therebyInfo
- Publication number
- CA1273454A CA1273454A CA000505773A CA505773A CA1273454A CA 1273454 A CA1273454 A CA 1273454A CA 000505773 A CA000505773 A CA 000505773A CA 505773 A CA505773 A CA 505773A CA 1273454 A CA1273454 A CA 1273454A
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- process according
- range
- chemicals
- refined
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000000034 method Methods 0.000 title claims abstract description 66
- 230000008569 process Effects 0.000 title claims abstract description 60
- 239000001913 cellulose Substances 0.000 title claims abstract description 14
- 229920002678 cellulose Polymers 0.000 title claims abstract description 13
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 12
- 239000000126 substance Substances 0.000 claims abstract description 32
- 230000029087 digestion Effects 0.000 claims abstract description 25
- 238000007670 refining Methods 0.000 claims abstract description 23
- 239000000463 material Substances 0.000 claims abstract description 14
- 239000002023 wood Substances 0.000 claims abstract description 11
- 239000000835 fiber Substances 0.000 claims description 12
- 238000005470 impregnation Methods 0.000 claims description 12
- 239000000203 mixture Substances 0.000 claims description 10
- 230000001976 improved effect Effects 0.000 claims description 7
- 210000000988 bone and bone Anatomy 0.000 claims description 5
- 230000009471 action Effects 0.000 claims description 3
- 239000011369 resultant mixture Substances 0.000 claims description 2
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical compound [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 claims description 2
- 239000011236 particulate material Substances 0.000 claims 3
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 abstract description 18
- 235000010265 sodium sulphite Nutrition 0.000 abstract description 9
- 229920001131 Pulp (paper) Polymers 0.000 description 26
- 241000218621 Pinus radiata Species 0.000 description 9
- 235000010980 cellulose Nutrition 0.000 description 8
- 238000004537 pulping Methods 0.000 description 7
- 235000008577 Pinus radiata Nutrition 0.000 description 5
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 5
- 239000005864 Sulphur Substances 0.000 description 5
- 238000007792 addition Methods 0.000 description 5
- 238000010411 cooking Methods 0.000 description 5
- 239000011121 hardwood Substances 0.000 description 5
- 238000010297 mechanical methods and process Methods 0.000 description 5
- 239000011122 softwood Substances 0.000 description 5
- 241000894007 species Species 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 241000006121 Eucalyptus regnans Species 0.000 description 3
- 238000010793 Steam injection (oil industry) Methods 0.000 description 3
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 230000018109 developmental process Effects 0.000 description 3
- 230000005226 mechanical processes and functions Effects 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 238000010025 steaming Methods 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- HLYCTXRRGDDBOW-UHFFFAOYSA-N 2-methylpiperazine-1-carbodithioic acid Chemical compound CC1CNCCN1C(S)=S HLYCTXRRGDDBOW-UHFFFAOYSA-N 0.000 description 2
- 241000963790 Beilschmiedia tawa Species 0.000 description 2
- 238000004061 bleaching Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 230000000366 juvenile effect Effects 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000012216 screening Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229920003043 Cellulose fiber Polymers 0.000 description 1
- 241000196324 Embryophyta Species 0.000 description 1
- 235000005205 Pinus Nutrition 0.000 description 1
- 241000218602 Pinus <genus> Species 0.000 description 1
- 208000036366 Sensation of pressure Diseases 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229940106135 cellulose Drugs 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000002301 combined effect Effects 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 210000001519 tissue Anatomy 0.000 description 1
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
- D21C3/00—Pulping cellulose-containing materials
- D21C3/22—Other features of pulping processes
- D21C3/26—Multistage processes
-
- 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
- D21C3/00—Pulping cellulose-containing materials
- D21C3/22—Other features of pulping processes
- D21C3/26—Multistage processes
- D21C3/266—Multistage processes the same pulping agent being used in all stages
Landscapes
- Paper (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
- Materials For Medical Uses (AREA)
Abstract
ABSTRACT
A PROCESS FOR THE MANUFACTURE OF CELLULOSE PULPS
A process for the manufacture of cellulose pulp from wood material in particulate form comprises the steps of impregnating the material with digestion chemicals in the form of an aqueous sodium sulphite solution and then digesting the treated material. Further digestion chemicals are added followed by mechanically refining the material to predominantly whole fibres. This step is then followed by a further digestion step whereafter the resultant pulp may optionally be further mechanically refined.
A PROCESS FOR THE MANUFACTURE OF CELLULOSE PULPS
A process for the manufacture of cellulose pulp from wood material in particulate form comprises the steps of impregnating the material with digestion chemicals in the form of an aqueous sodium sulphite solution and then digesting the treated material. Further digestion chemicals are added followed by mechanically refining the material to predominantly whole fibres. This step is then followed by a further digestion step whereafter the resultant pulp may optionally be further mechanically refined.
Description
~Z7345~
This invention relates to a process for the manu-facturing of celiulose mechanical pulps and pulps obtained thereby.
S There are many known processes for the manufacture of cellulose pulps and, more particularly, hiyh-yield cellu-lose mechanical pulps. These processes include but are not confined to refiner mechanical processes (RMP), -thermo-mechanical processes (TMP), chemi-mechanical processes 0 (CMP), -thermo-chemi mechanical processes (TCMP) and chemi-thermo mechanical processes (CTMP). These processes which have been developed over the years are essentially developments of the basic RMP process and whilst the differences be-tween processes appear to be small they do represent improvements which lead to the production of improved pulp quality (often but not always coupled with reduced pulp yield). Generally, however, most of the impro-ved processes have been at the expense of an increase in refining energy required to meet the requisi-te paper making or other end use properties.
Mechanical pulp plants typically have a lower specific capital cost to build and mecahnical pulps typi-cally have a high yield and can be cheaper to produce than chemical pulps. In addition mechanical pulps do not provide the pollution problems which are associated with chemical pulps. Generally mechanical pulps have not been of the same high quali-ty as chemical pulps and thus to achieve an end pulp which is of the required quality bu-t at the same time economic to produce it is a well known technique to combine mechanical and chemical pulps. The aforementioned develop-ments in mechanical pulp processes which s-tem from the basic RMP process have led to some mechanical pulps having the characteristics of a chemical pulp and they can thus be used as a replacement, in whole or in part, for chemical pulps in those applications where chemical pulps have traditionally \
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been used.
For example there is disclosed in German patent specifications 1071805, 1145106 and 1145107 to Ontario Paper Company Ltd. processes for the production of mechanical pulps which are claimed -to be useful as substitutes for chemical pulps. These processes require a mechanical pulp of the TMP, RMP, or TCMP type to be treated or mixed with a relatively high charge of digestion chemical, e.g. an aqueous sodium sulphite solution a~Eter the refining stage and the thus treated pulp to be pressure digested with optionally further refining taking place after the diges-tion stage.
In U.S. patent specification 4502918 of McMillan Bloedel Ltd. there is disclosed a pulping process in which wood particles are treated with an aqueous solution of sodium sulphite, the treated particles are then digested and refined following which the resultant pulp is separated in-to an accepts fraction and a rejects or long fibre fraction.
The rejects fraction is then further treated with a sodium sulphite solution, digested and refined whereupon the or at least part of the accepts and rejects fractions are com-bined to form the final pulp.
The present invention has its basis in the suspri-sing discovery that the whole pulp can be subjected to a two stage digestion and refining process with the second addi-tion of an aqueous sodium sulphite solution taking place prior to or with the cellulose material entering or after the first refining s-tage followed by digestion af-ter -the chemical addition. The process can be carried out with sig-nificant savings in energy requirements even though the whole pulp is processed in the two digestion and refining steps whilst increase in many of the desirable properties of -the pulp for end use applications are obtained. The process has particulax application either singly or in combination ' . -.. , .~
- ~ "`;:: ' ;, ' ' "' , ' ~: ;
~Z73454 for pinus radiata corewood and/or pinus radiata slab wood, eucalypts and New Zealand hardwoods but it is believed that it has similar application to other wood types and species.
S Whilst the present invention requires a relatively high total charge of diges-tion chemicals the total charge is split into two separate charges of which the firs-t charge is preferably lower but preferably takes place in an impregna-tion ;
.
: ' ::,.: ' ' ~2~3454 process ra-ther than a simple mixing stage. The resultant pulp is low in fines, has high strength characteristics and is produced with low energy requirements. For example, the total chemical charge in the present invention is in the order of that required in a CMP
process but cloes not require the high energy demands of a CMP process for some wood types particularly plne species and hardwood/softwood blends.
~he object of the present invention is to provide a process for the manufacture of cellulose mechanical pulps which provides a high yield pulp of improved quality which can be used as a substitute for chemical pulps and is achieved without increases or at lesser increases in refining energy inputs.
Broadly, the invention can be said to consist of a process for the manufacturing of cellulose pulp using two or more chemical addition and digestion stages in conjunction with mechanical pulping techniques.
The term "mechanical pulping" as used herein has its normal meaning in the art and refers to the process of disruption of a cellulose substance by mechanical action to yield a product consisting mainly of liberated and separated single cellulose fibres and their fragments and which is suitable for use in the manufacture of paper and other products.
More specifically the invention consists of a process for~
the manufacturing of a cellulose pulp from material in particulate form comprising the steps of impregnating the material with digestion chemicals, digesting the impregnated material, adding further digesting chemicals and mechanically refining the resultant mixture to reduce the material to predominantly whole fibres, digesting the impregnated and refined mixture and then further refining the resulting pulp product, if required.
In the following more detailed description of the . .;, .: . : ,~
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. -.: : : .:
-: -: :: . : ; . : : ::: :
~273~S4 ''"
invention accordin~ to its preferred forms, reference will be made to the accompanying drawing which is a schematic flow diagram of the process.
According to the process, in its preferred form wood chips are washed in washer 10 and conveyed to a surge/pre-steaming vessel 11. In this vessel live steam is added to remove air and preheat the chips to a temperature in the range o~ 80-100C. Discharge of chips from vessel 11 is maintained at a controlled rate to a compression screw feeder 12 wherein excess liquid is removed and the chips are dewatered to over 20% dryness.
In the preferred form the chips are dewatered to over 40~
dryness. The chips are then delivered to an impregnation device 13 (preferably an inclined screw conveyor).
Digestion chemicals are delivered to or between the feeder device 12 and/or the impregnation device 13 with delivery being at a temperature below 100C, preferably under 50C. These delignifying chemicals in aqueous form are of known composition, primarily of the sodium sulphite family, and are added at a level of 0.5 to 5%
active chemical on bone dried fibre. Condensation of steam within the chips causes the liquor to be absorbed into the chips. Retention time within the liquor zone ~
of the impregnation device 13 is 5 to 20 minutes but preferably over 7 minutes.
On leaving the liquor zone of the impregnation device 13 the chips may be subjected to direct steam heating to raise the temperature of the chips to within the range of 80-100C. The impregnated chips are then fed to a primary digester 14 by a pressure sealing device 13a such ; as a compression screw, rotary valve or similar. The residence time within the digester 14 is in the range of 3 to 20 minutes, but preferably 5 to 10 minutes, with heating by direct steam injection to give a vapour phase reaction. The pressure of the primary digester 14 is in . ..
~ - ~:; . . .
, . .: ~ ~ - . :' ~;;- :
- 6 - 2~3~4 the range of 0-800 kPa overpressure, but more preferably 200 to 400 kPa overpressure.
Product from primary digester 14 is by controlled metering in accordance with known procedures and fed via feeder/pressure seal 15 to a primary refiner 16 (such as a disc refiner) operating at 0 to 600 kPa overpressure but more preferably 200 to 300 kPa overpressure.
Further digestion or cooking chemicals of known composition are added to the product feed to the primary reflner 16 for subsequent reaction in the secondary digester 19. The cooking chemicals are mixed with the chip/pulp mixture present in the primary refiner 16 by the r~finer action. Addition of the sulphite based cooking chemicals is in the range of 2 to 20~ active chemical on bone dried fibre preferably 5% to 10% on bone dried fibre.
The pulp and steam generated in the primary refiner 16 are discAarged through a common blowline to a cyclone 17 where water and/or spen-t process liquor s added for consistency control during the subsequent digestion phase. Pulp and liquor is discharged from cyclone 17 by a feeder/pressure seal device 18 (preferably a compression screw) and enters the secondary digester 19.
The residence time within the secondary digester 19 is in the range of 20 to 1~0 minutes but more preferably 30 to 60 minutes at an overpressure in the range of 100 to 800 kPa but more preferably 300 to 600 kPa overpressure.
Discharge from the secondary digester 19 is achieved by injecting water/spent liquor thr~ugh lines 20 and 21 into the base of the secondary digester 19 and mixing this with the pulp. The motive force for discharging the pulp is provided by the internal pressure in the digester. Alternatively the digester may be discharged by screw conveyor or other methods.
. .,-- ~ :. .
: . :. , ~ . , ~2~3454 Discharged pulp is passed to a washer 22, prefer-ably a press washing system, wherein it is washed and pres-sed and passed by a feeder/pressure seal 23 -to a secondary refiner 24. The secondary refiner 24 may operate a-t pres-sure in the range 0 to 600 ]sPa overpressure but preferably200 to 300 kPa overpressure. Steam and pulp are discharged from secondary refiner 24 through a common blowline to a cyclone 25 where they are separated and discharged in sub-stanially the same manner as that from the primary refiner 16.
The resultant pulp may then be treated in accor-dance with accepted pulping practices, such as latency removal, screening, cleaning and bleaching. The resulting pulp product may be dried or used directly or indirectly for its intended end use.
The process as described above is open to modi-fication. For example, either or both the refining stages in refiners 16 and 24 may take place at atmospheric pressure with screws or other discharge and conveying devices; two or more stages of refining may be present prior to or after the secondary digester 19; pulp from the secondary digester 19 may be discharged directly from the pulping process out-lined as being an inter- or post-refining stage; inter-stage washing and dewatering could be included between first stage digesting and first stage refining; a further stage or stages of chemical addition, refining, digesting with or without inter-stage washing and dewa-tering could be added.
Impregnation/cooking chemicals for the first di-gestion stage may be added via a mechanical mixing system, similarly for the second digestion stage they may be added to the cellulose material after the primary refiner in a mechanical mixing system.
:: . .. :
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~;~734~g~
The affect of the in-ter-stage or post-digesting stage is to give a change in fibre properties, improvlng some, but of significance, is a major reduction in refining energy requirements to achieve the desired end use proper-ties The process according to the present inventionresults in a high-yield mechanical pulp of at least a similar but generally improved quality over pulps obtained with similar known process but without increases or at lesser increases in refining energy inputs. High levels of combined sulphur at the same freeness level can thus be achieved without higher power usage as is normally the case with some chemi-mechanical .
:
- 7a -- . ' .~' ' ~ ',. ' ' ~., ","''. . , ~27345~
(CMP) or chemi-thermomechanical (CTMP) processes. The pulp is referred to in the following tables as sulphonated chemi-thermomechanical pulp (SCTMP).
The digestion/refining process treatment allows high sulphonation to be achieved giving better brightness, absorbency, softness and fibre flexibility with a major reduction in refining energy requirements. In addition the process results in clean fibre separation, improved fibre yield with reduced fines and improved bulk, tear index, tensile index, stretch, burst and other wet and dry web properties.
Test runs of the process of the present invention have been carried out and the results of the properties of the process and RMP and CTMP pulp for unbleached screened and cleaned pulp (tested to SCAN standards using a 60 gsm handsheet) are set out below.
The pulp product prior to bleaching stage(s) contains a low quantity of fibre bundles, that is less than substantially 10~ and preferably substantially none.
The process can be used for soft woods, blends of soft woods and blends of softwoods and hardwoods. For the last case superior quality is obtained than when using other high yield processes.
Mesh sizes in the above table are measured according to the Bauer McNett method. Shive content is measured by the Sommerville method. All results in the table are test results for Pinus Radiata slab wood (sawmill residuej chips. All tests are carried out on 60 gsm hand sheets according to I;S.O. standards.
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The following examples of the present invention and conventional chemi-thermomechanical pulp process (CTMP) and refiner mechanical pulp process (RMP) were carried out in a pilot plant using commonly available New Zealand wood species.
Example 1 An RMP process was carried out on softwood chips (Pinus, Radiata, sawmill slab residue) at about 60~ moisture content, the chips being refined with two passes through a double disc refiner at atmospheric pressure. The results are shown in the table in the column headed "RMP" and establish a base for comparison with other pulping processes.
ExamPle 2 A conventional CTMP process was carried out. Blends of chips of different wood species and single species (see first line in the following table) were treated in a steaming vessel for 10 minutes at about 95 degrees centigrade (condensate was drained and the vessel charged with cold impregnation chemical, sodium sulphite, of sufficient concentration to give the desired final sulphur content. The impregnation liquor was heated by recirculation through an external heat exchanger to about 95 degrees centigrade and the liquor then drained. The impregnated chips were digested at about 130 degrees centigrade using direct steam injection for 5 minutes. The digested chips were discharged by screw conveyor and fed to a pressuri~ed double disc refiner operating at about 2 bar overpressure. The resulting pulp was again refined by a second pass through the same refiner under the same pressure conditions.
The results of the processes were listed under the columns CTMP
in the following table ;, . . " ,;
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.
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lZ7;~S~
Example 3 A process according to the present invention was carried out.
slends of chips of different wood species and single species (see first line in the following table) were treated in a steaming vessel for 10 minutes at about 95 degrees centigrade (condensate was drained and the vessel charged with cool impregnation chemical, sodium sulphite, of sufficient concentration to give the desired final sulphur content. The impregnation liquor was heated by recirculation through an external heat exchanger to about 95 degrees centigrade and the liquor then drained. The impregnated chips were digested at about 130 degrees centigrade using direct steam injection for 5 minutes.
The digested chips were discharged by screw conveyor and fed to a pressurized double disc refiner. At the poin-t of feeding the refiner secondary digestion chemical (sodium sulphite liquor) was added at the required concentration to give the desired final pulp sulphur content. The pulp/liquor mixture was conveyed by refiner generated steam (blown) back to the primary cooking vessel and digested at 160 degrees centigrade for about 60 minutes. Digested pulp was discharged and refined for a second time. Both refining stages were pressurized at about 2 bar overpressure.
The results of the processes are shown in columns (marked SCTMP) in the following table.
.' : :' ~ ' . : -.. . : .
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Example 4 The process of Example 3 was carried out. The pulp had further digestion chemicals added at the entry to the second stage refiner and a third stage of digestion was carried out followed by a third stage of refining at atmospheric pressure. The results of this process are shown in the extreme right hand column marked l'SCTMP" in the table which follows.
In the foregoing examples all final pulp was washed and screened through a 0.16mm flat screen prior to property testing to simulate the screening/cleaning function of a typical mechanical pulp mill.
The resultant pulp from the process according to the invention is unexpectedly suitable for further refining development to improve various properties, in particular tensile index, burst, air resistance, that will enhance its performance in its selected end use.
In its undeveloped and developed stage, it is suitable for such end uses as a chemical pulp substitute either directly or in part, in such products as fluffing pulp and various papers such as, but not limited to, tissue, mechanical printing grades, liner board and board.
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PULPING PROCESS RMP CTMP SCTMP CTMP SCTMP SCTMP CTMP SGTMP
Slab P. Radiata, % 100 100 100 50 35 35 Juvenile P. Radiata % 100 100 50 35 35 E. Regnans, % 30 Tawa, % 30 Can. Std Freeness, mls169 389 386 562 435 289 325 235 Tensile Index, Nm/g 31.1 34.2 36.4 20.8 27.4 38.315.9 47.2 Stretch, % 2.1 1.1 2.6 1.5 2.4 2.8 - -Tear Index, Nm sqm/g 8.4 11.7 9.58 8.1 9.32 8.864.85 7.87 Burst Index, kPa sqm/g1.69 1.74 2.11 1.04 1~42 2.250.78 3.14 Sulphur Content, % 0 0.51 0.56 0.41 0.40 0.720.12 0.59 Absorption Capacity, 9/9 10.3 10.1 10.3 10.7 10.i10.3 - -DCM Extractives, % 0.25 0.11 0.28 0.19 0.14 0.180.13 0.14 Bulk, cc/g 2.61 2.75 2.38 3.83 3.06 2.263.65 2.09 Density, kg/cub. m. 383 364 420 261 327 442 274 478 Brightness, %ISO 52.4 49.7 53.2 54.8 57.5 51.647.9 53.8 B.McNett ~48 mesh, %61.1 73.3 71.2 79.6 70.6 68.155.3 65,6 B.McNett -200 mesh, %25.2 19.0 18.8 9.3 17.9 20.621.2 18.4 Sommerville Sh;ve, %0.25 0.12 0.10 0.04 0.02 0.05o.ao 0.07 PFI Minishive, % 0.45 0.30 0.20 0.35 0.10 0.100.07 0.25 Total specific refining1.70 2.27 1.45 2.07 2.22 1.752.05 2~07 energy, MWh/tonne (100) NOTES:
1) Slab P. Radiata: Pinus Radiata sawmill residue; Juvenile P.
Radiata: Pinus Radiata plantation thinnings under 15 years:
E. Regnans: Eucalyptus Regnans plantation grown hardwood;
Tawa: N.Z. native hardwood.
This invention relates to a process for the manu-facturing of celiulose mechanical pulps and pulps obtained thereby.
S There are many known processes for the manufacture of cellulose pulps and, more particularly, hiyh-yield cellu-lose mechanical pulps. These processes include but are not confined to refiner mechanical processes (RMP), -thermo-mechanical processes (TMP), chemi-mechanical processes 0 (CMP), -thermo-chemi mechanical processes (TCMP) and chemi-thermo mechanical processes (CTMP). These processes which have been developed over the years are essentially developments of the basic RMP process and whilst the differences be-tween processes appear to be small they do represent improvements which lead to the production of improved pulp quality (often but not always coupled with reduced pulp yield). Generally, however, most of the impro-ved processes have been at the expense of an increase in refining energy required to meet the requisi-te paper making or other end use properties.
Mechanical pulp plants typically have a lower specific capital cost to build and mecahnical pulps typi-cally have a high yield and can be cheaper to produce than chemical pulps. In addition mechanical pulps do not provide the pollution problems which are associated with chemical pulps. Generally mechanical pulps have not been of the same high quali-ty as chemical pulps and thus to achieve an end pulp which is of the required quality bu-t at the same time economic to produce it is a well known technique to combine mechanical and chemical pulps. The aforementioned develop-ments in mechanical pulp processes which s-tem from the basic RMP process have led to some mechanical pulps having the characteristics of a chemical pulp and they can thus be used as a replacement, in whole or in part, for chemical pulps in those applications where chemical pulps have traditionally \
~; ,;
,;.. . ~
~' :
~Z'734S~
been used.
For example there is disclosed in German patent specifications 1071805, 1145106 and 1145107 to Ontario Paper Company Ltd. processes for the production of mechanical pulps which are claimed -to be useful as substitutes for chemical pulps. These processes require a mechanical pulp of the TMP, RMP, or TCMP type to be treated or mixed with a relatively high charge of digestion chemical, e.g. an aqueous sodium sulphite solution a~Eter the refining stage and the thus treated pulp to be pressure digested with optionally further refining taking place after the diges-tion stage.
In U.S. patent specification 4502918 of McMillan Bloedel Ltd. there is disclosed a pulping process in which wood particles are treated with an aqueous solution of sodium sulphite, the treated particles are then digested and refined following which the resultant pulp is separated in-to an accepts fraction and a rejects or long fibre fraction.
The rejects fraction is then further treated with a sodium sulphite solution, digested and refined whereupon the or at least part of the accepts and rejects fractions are com-bined to form the final pulp.
The present invention has its basis in the suspri-sing discovery that the whole pulp can be subjected to a two stage digestion and refining process with the second addi-tion of an aqueous sodium sulphite solution taking place prior to or with the cellulose material entering or after the first refining s-tage followed by digestion af-ter -the chemical addition. The process can be carried out with sig-nificant savings in energy requirements even though the whole pulp is processed in the two digestion and refining steps whilst increase in many of the desirable properties of -the pulp for end use applications are obtained. The process has particulax application either singly or in combination ' . -.. , .~
- ~ "`;:: ' ;, ' ' "' , ' ~: ;
~Z73454 for pinus radiata corewood and/or pinus radiata slab wood, eucalypts and New Zealand hardwoods but it is believed that it has similar application to other wood types and species.
S Whilst the present invention requires a relatively high total charge of diges-tion chemicals the total charge is split into two separate charges of which the firs-t charge is preferably lower but preferably takes place in an impregna-tion ;
.
: ' ::,.: ' ' ~2~3454 process ra-ther than a simple mixing stage. The resultant pulp is low in fines, has high strength characteristics and is produced with low energy requirements. For example, the total chemical charge in the present invention is in the order of that required in a CMP
process but cloes not require the high energy demands of a CMP process for some wood types particularly plne species and hardwood/softwood blends.
~he object of the present invention is to provide a process for the manufacture of cellulose mechanical pulps which provides a high yield pulp of improved quality which can be used as a substitute for chemical pulps and is achieved without increases or at lesser increases in refining energy inputs.
Broadly, the invention can be said to consist of a process for the manufacturing of cellulose pulp using two or more chemical addition and digestion stages in conjunction with mechanical pulping techniques.
The term "mechanical pulping" as used herein has its normal meaning in the art and refers to the process of disruption of a cellulose substance by mechanical action to yield a product consisting mainly of liberated and separated single cellulose fibres and their fragments and which is suitable for use in the manufacture of paper and other products.
More specifically the invention consists of a process for~
the manufacturing of a cellulose pulp from material in particulate form comprising the steps of impregnating the material with digestion chemicals, digesting the impregnated material, adding further digesting chemicals and mechanically refining the resultant mixture to reduce the material to predominantly whole fibres, digesting the impregnated and refined mixture and then further refining the resulting pulp product, if required.
In the following more detailed description of the . .;, .: . : ,~
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. -.: : : .:
-: -: :: . : ; . : : ::: :
~273~S4 ''"
invention accordin~ to its preferred forms, reference will be made to the accompanying drawing which is a schematic flow diagram of the process.
According to the process, in its preferred form wood chips are washed in washer 10 and conveyed to a surge/pre-steaming vessel 11. In this vessel live steam is added to remove air and preheat the chips to a temperature in the range o~ 80-100C. Discharge of chips from vessel 11 is maintained at a controlled rate to a compression screw feeder 12 wherein excess liquid is removed and the chips are dewatered to over 20% dryness.
In the preferred form the chips are dewatered to over 40~
dryness. The chips are then delivered to an impregnation device 13 (preferably an inclined screw conveyor).
Digestion chemicals are delivered to or between the feeder device 12 and/or the impregnation device 13 with delivery being at a temperature below 100C, preferably under 50C. These delignifying chemicals in aqueous form are of known composition, primarily of the sodium sulphite family, and are added at a level of 0.5 to 5%
active chemical on bone dried fibre. Condensation of steam within the chips causes the liquor to be absorbed into the chips. Retention time within the liquor zone ~
of the impregnation device 13 is 5 to 20 minutes but preferably over 7 minutes.
On leaving the liquor zone of the impregnation device 13 the chips may be subjected to direct steam heating to raise the temperature of the chips to within the range of 80-100C. The impregnated chips are then fed to a primary digester 14 by a pressure sealing device 13a such ; as a compression screw, rotary valve or similar. The residence time within the digester 14 is in the range of 3 to 20 minutes, but preferably 5 to 10 minutes, with heating by direct steam injection to give a vapour phase reaction. The pressure of the primary digester 14 is in . ..
~ - ~:; . . .
, . .: ~ ~ - . :' ~;;- :
- 6 - 2~3~4 the range of 0-800 kPa overpressure, but more preferably 200 to 400 kPa overpressure.
Product from primary digester 14 is by controlled metering in accordance with known procedures and fed via feeder/pressure seal 15 to a primary refiner 16 (such as a disc refiner) operating at 0 to 600 kPa overpressure but more preferably 200 to 300 kPa overpressure.
Further digestion or cooking chemicals of known composition are added to the product feed to the primary reflner 16 for subsequent reaction in the secondary digester 19. The cooking chemicals are mixed with the chip/pulp mixture present in the primary refiner 16 by the r~finer action. Addition of the sulphite based cooking chemicals is in the range of 2 to 20~ active chemical on bone dried fibre preferably 5% to 10% on bone dried fibre.
The pulp and steam generated in the primary refiner 16 are discAarged through a common blowline to a cyclone 17 where water and/or spen-t process liquor s added for consistency control during the subsequent digestion phase. Pulp and liquor is discharged from cyclone 17 by a feeder/pressure seal device 18 (preferably a compression screw) and enters the secondary digester 19.
The residence time within the secondary digester 19 is in the range of 20 to 1~0 minutes but more preferably 30 to 60 minutes at an overpressure in the range of 100 to 800 kPa but more preferably 300 to 600 kPa overpressure.
Discharge from the secondary digester 19 is achieved by injecting water/spent liquor thr~ugh lines 20 and 21 into the base of the secondary digester 19 and mixing this with the pulp. The motive force for discharging the pulp is provided by the internal pressure in the digester. Alternatively the digester may be discharged by screw conveyor or other methods.
. .,-- ~ :. .
: . :. , ~ . , ~2~3454 Discharged pulp is passed to a washer 22, prefer-ably a press washing system, wherein it is washed and pres-sed and passed by a feeder/pressure seal 23 -to a secondary refiner 24. The secondary refiner 24 may operate a-t pres-sure in the range 0 to 600 ]sPa overpressure but preferably200 to 300 kPa overpressure. Steam and pulp are discharged from secondary refiner 24 through a common blowline to a cyclone 25 where they are separated and discharged in sub-stanially the same manner as that from the primary refiner 16.
The resultant pulp may then be treated in accor-dance with accepted pulping practices, such as latency removal, screening, cleaning and bleaching. The resulting pulp product may be dried or used directly or indirectly for its intended end use.
The process as described above is open to modi-fication. For example, either or both the refining stages in refiners 16 and 24 may take place at atmospheric pressure with screws or other discharge and conveying devices; two or more stages of refining may be present prior to or after the secondary digester 19; pulp from the secondary digester 19 may be discharged directly from the pulping process out-lined as being an inter- or post-refining stage; inter-stage washing and dewatering could be included between first stage digesting and first stage refining; a further stage or stages of chemical addition, refining, digesting with or without inter-stage washing and dewa-tering could be added.
Impregnation/cooking chemicals for the first di-gestion stage may be added via a mechanical mixing system, similarly for the second digestion stage they may be added to the cellulose material after the primary refiner in a mechanical mixing system.
:: . .. :
- .: ,. :
~;~734~g~
The affect of the in-ter-stage or post-digesting stage is to give a change in fibre properties, improvlng some, but of significance, is a major reduction in refining energy requirements to achieve the desired end use proper-ties The process according to the present inventionresults in a high-yield mechanical pulp of at least a similar but generally improved quality over pulps obtained with similar known process but without increases or at lesser increases in refining energy inputs. High levels of combined sulphur at the same freeness level can thus be achieved without higher power usage as is normally the case with some chemi-mechanical .
:
- 7a -- . ' .~' ' ~ ',. ' ' ~., ","''. . , ~27345~
(CMP) or chemi-thermomechanical (CTMP) processes. The pulp is referred to in the following tables as sulphonated chemi-thermomechanical pulp (SCTMP).
The digestion/refining process treatment allows high sulphonation to be achieved giving better brightness, absorbency, softness and fibre flexibility with a major reduction in refining energy requirements. In addition the process results in clean fibre separation, improved fibre yield with reduced fines and improved bulk, tear index, tensile index, stretch, burst and other wet and dry web properties.
Test runs of the process of the present invention have been carried out and the results of the properties of the process and RMP and CTMP pulp for unbleached screened and cleaned pulp (tested to SCAN standards using a 60 gsm handsheet) are set out below.
The pulp product prior to bleaching stage(s) contains a low quantity of fibre bundles, that is less than substantially 10~ and preferably substantially none.
The process can be used for soft woods, blends of soft woods and blends of softwoods and hardwoods. For the last case superior quality is obtained than when using other high yield processes.
Mesh sizes in the above table are measured according to the Bauer McNett method. Shive content is measured by the Sommerville method. All results in the table are test results for Pinus Radiata slab wood (sawmill residuej chips. All tests are carried out on 60 gsm hand sheets according to I;S.O. standards.
. ,~ . : . . -:, .
:~Z~ 4S~L
The following examples of the present invention and conventional chemi-thermomechanical pulp process (CTMP) and refiner mechanical pulp process (RMP) were carried out in a pilot plant using commonly available New Zealand wood species.
Example 1 An RMP process was carried out on softwood chips (Pinus, Radiata, sawmill slab residue) at about 60~ moisture content, the chips being refined with two passes through a double disc refiner at atmospheric pressure. The results are shown in the table in the column headed "RMP" and establish a base for comparison with other pulping processes.
ExamPle 2 A conventional CTMP process was carried out. Blends of chips of different wood species and single species (see first line in the following table) were treated in a steaming vessel for 10 minutes at about 95 degrees centigrade (condensate was drained and the vessel charged with cold impregnation chemical, sodium sulphite, of sufficient concentration to give the desired final sulphur content. The impregnation liquor was heated by recirculation through an external heat exchanger to about 95 degrees centigrade and the liquor then drained. The impregnated chips were digested at about 130 degrees centigrade using direct steam injection for 5 minutes. The digested chips were discharged by screw conveyor and fed to a pressuri~ed double disc refiner operating at about 2 bar overpressure. The resulting pulp was again refined by a second pass through the same refiner under the same pressure conditions.
The results of the processes were listed under the columns CTMP
in the following table ;, . . " ,;
- :,: .
.
. : ~::: . : .
lZ7;~S~
Example 3 A process according to the present invention was carried out.
slends of chips of different wood species and single species (see first line in the following table) were treated in a steaming vessel for 10 minutes at about 95 degrees centigrade (condensate was drained and the vessel charged with cool impregnation chemical, sodium sulphite, of sufficient concentration to give the desired final sulphur content. The impregnation liquor was heated by recirculation through an external heat exchanger to about 95 degrees centigrade and the liquor then drained. The impregnated chips were digested at about 130 degrees centigrade using direct steam injection for 5 minutes.
The digested chips were discharged by screw conveyor and fed to a pressurized double disc refiner. At the poin-t of feeding the refiner secondary digestion chemical (sodium sulphite liquor) was added at the required concentration to give the desired final pulp sulphur content. The pulp/liquor mixture was conveyed by refiner generated steam (blown) back to the primary cooking vessel and digested at 160 degrees centigrade for about 60 minutes. Digested pulp was discharged and refined for a second time. Both refining stages were pressurized at about 2 bar overpressure.
The results of the processes are shown in columns (marked SCTMP) in the following table.
.' : :' ~ ' . : -.. . : .
1~73~5~
Example 4 The process of Example 3 was carried out. The pulp had further digestion chemicals added at the entry to the second stage refiner and a third stage of digestion was carried out followed by a third stage of refining at atmospheric pressure. The results of this process are shown in the extreme right hand column marked l'SCTMP" in the table which follows.
In the foregoing examples all final pulp was washed and screened through a 0.16mm flat screen prior to property testing to simulate the screening/cleaning function of a typical mechanical pulp mill.
The resultant pulp from the process according to the invention is unexpectedly suitable for further refining development to improve various properties, in particular tensile index, burst, air resistance, that will enhance its performance in its selected end use.
In its undeveloped and developed stage, it is suitable for such end uses as a chemical pulp substitute either directly or in part, in such products as fluffing pulp and various papers such as, but not limited to, tissue, mechanical printing grades, liner board and board.
~ . ......
~Z734S~
PULPING PROCESS RMP CTMP SCTMP CTMP SCTMP SCTMP CTMP SGTMP
Slab P. Radiata, % 100 100 100 50 35 35 Juvenile P. Radiata % 100 100 50 35 35 E. Regnans, % 30 Tawa, % 30 Can. Std Freeness, mls169 389 386 562 435 289 325 235 Tensile Index, Nm/g 31.1 34.2 36.4 20.8 27.4 38.315.9 47.2 Stretch, % 2.1 1.1 2.6 1.5 2.4 2.8 - -Tear Index, Nm sqm/g 8.4 11.7 9.58 8.1 9.32 8.864.85 7.87 Burst Index, kPa sqm/g1.69 1.74 2.11 1.04 1~42 2.250.78 3.14 Sulphur Content, % 0 0.51 0.56 0.41 0.40 0.720.12 0.59 Absorption Capacity, 9/9 10.3 10.1 10.3 10.7 10.i10.3 - -DCM Extractives, % 0.25 0.11 0.28 0.19 0.14 0.180.13 0.14 Bulk, cc/g 2.61 2.75 2.38 3.83 3.06 2.263.65 2.09 Density, kg/cub. m. 383 364 420 261 327 442 274 478 Brightness, %ISO 52.4 49.7 53.2 54.8 57.5 51.647.9 53.8 B.McNett ~48 mesh, %61.1 73.3 71.2 79.6 70.6 68.155.3 65,6 B.McNett -200 mesh, %25.2 19.0 18.8 9.3 17.9 20.621.2 18.4 Sommerville Sh;ve, %0.25 0.12 0.10 0.04 0.02 0.05o.ao 0.07 PFI Minishive, % 0.45 0.30 0.20 0.35 0.10 0.100.07 0.25 Total specific refining1.70 2.27 1.45 2.07 2.22 1.752.05 2~07 energy, MWh/tonne (100) NOTES:
1) Slab P. Radiata: Pinus Radiata sawmill residue; Juvenile P.
Radiata: Pinus Radiata plantation thinnings under 15 years:
E. Regnans: Eucalyptus Regnans plantation grown hardwood;
Tawa: N.Z. native hardwood.
2) All tests carried out to ISO standards on 60 gsm handsheets.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the manufacture of cellulose pulp from wood material in particulate form comprising the steps of impregnating the material with digestion chemicals, digesting the impregnated material, adding further digesting chemicals and mechanically refining the resultant mixture to reduce the material to predominantly whole fibres and further digesting the impregnated and refined mixture.
2. The process according to Claim 1 wherein the pulp product resulting from the second digesting step is further refined by mechanical action.
3. The process according to claim 1 wherein digestion chemicals are added by impregnation to the particulate material at a temperature of below 100°C
with the level of active chemical being in the range of about 0.5 to 5% on bone dried fibre.
with the level of active chemical being in the range of about 0.5 to 5% on bone dried fibre.
4. The process according to Claim 3 wherein the impregnation of the particulate material takes place over a time period of about 5 to 20 minutes.
5. The process according to Claim 3 wherein the impregnated particulate material is fed, at a temperature in the range of about 80 - 100°C, to a first digester wherein it is heated by direct steam at an overpressure in the range of about 0 - 800 kPa for a period of about 5 to 10 minutes.
6. The process according to Claim 5 wherein the product issuing from the first digester is refined in a primary refiner with further digestion chemicals added to the said product from the digester, said digestion chemicals being sulphite based with the active chemical therein being in the range of about 2 to 20% on bone dried fibre.
7. The process according to Claim 6 wherein the further digestion chemicals are added prior to the product being refined in the primary refiner.
8. The processing according to Claim 6 wherein the further digestion chemicals are added to the product within the primary refiner.
9. The process according to Claim 6, 7, or 8 wherein the pulp and liquor from the primary refiner is digested at an overpressure in the range of about 100 to 800 kPa for a period of time in the range of about 30 to 60 minutes.
10. A cellulose pulp with improved bonding ability, long fibre fraction and lower fines content with satisfactory yield and lower specific energy concumption obtained from the process according to claim 1, 2 or 3.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NZ211684A NZ211684A (en) | 1985-04-04 | 1985-04-04 | Manufacture of cellulose pulp: second digestion step follows initial digestion and refining steps |
| NZ211684 | 1985-04-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1273454A true CA1273454A (en) | 1990-09-04 |
Family
ID=19921155
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000505773A Expired - Lifetime CA1273454A (en) | 1985-04-04 | 1986-04-03 | Process for the manufacture of cellulose pulps and cellulose pulps obtained thereby |
Country Status (15)
| Country | Link |
|---|---|
| EP (1) | EP0199481B1 (en) |
| JP (1) | JPS61282491A (en) |
| KR (1) | KR930003394B1 (en) |
| AR (1) | AR243623A1 (en) |
| AU (1) | AU585331B2 (en) |
| BR (1) | BR8601558A (en) |
| CA (1) | CA1273454A (en) |
| DE (1) | DE3667515D1 (en) |
| ES (1) | ES8705940A1 (en) |
| FI (1) | FI83238C (en) |
| MY (1) | MY102502A (en) |
| NO (1) | NO167159C (en) |
| NZ (1) | NZ211684A (en) |
| PT (1) | PT82341B (en) |
| ZA (1) | ZA862454B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103410036A (en) * | 2013-08-15 | 2013-11-27 | 齐鲁工业大学 | Production method for high-yield hardwood pulp |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| USH1672H (en) * | 1988-03-28 | 1997-08-05 | Kimberly-Clark Corporation | Tissue products made from low-coarseness fibers |
| FI126694B (en) * | 2005-12-02 | 2017-04-13 | Metsä Board Oyj | Chemical-mechanical pulp and process for producing chemical-mechanical pulp |
| CN102561094B (en) * | 2012-01-06 | 2015-04-15 | 黑龙江浩源生物科技有限公司 | Method for making pulp and paper by using cornstalk xylose residue |
| CN104928958A (en) * | 2015-05-25 | 2015-09-23 | 张家港市欣发包装有限责任公司 | Method of producing corrugated paper with straw |
| AT518800B1 (en) | 2016-06-17 | 2019-09-15 | Andritz Ag Maschf | METHOD FOR PRODUCING FIBROUS MATERIAL |
| CN112342814B (en) * | 2020-11-19 | 2023-03-31 | 横县东糖糖业有限公司纸业分公司 | Method for producing high-strength natural-color paper pulp by taking eucalyptus bark as raw material |
| CN113481741B (en) * | 2021-07-27 | 2023-05-09 | 中福海峡(平潭)发展股份有限公司 | Fungus grass chemical machine pulp and preparation method and application thereof |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1145106A (en) * | 1980-07-11 | 1983-04-26 | Alan C. Shaw | Procedure for improving properties of mechanical wood pulps |
| US4502918A (en) * | 1981-06-10 | 1985-03-05 | Macmillan Bloedel Limited | Two-stage chemical treatment of mechanical wood pulp with sodium sulfite |
| AU570034B2 (en) * | 1983-04-20 | 1988-03-03 | Process Evaluation And Development Corp. | Continuous pulp digester |
-
1985
- 1985-04-04 NZ NZ211684A patent/NZ211684A/en unknown
-
1986
- 1986-04-03 CA CA000505773A patent/CA1273454A/en not_active Expired - Lifetime
- 1986-04-03 NO NO861307A patent/NO167159C/en not_active IP Right Cessation
- 1986-04-03 ZA ZA862454A patent/ZA862454B/en unknown
- 1986-04-04 AR AR86303572A patent/AR243623A1/en active
- 1986-04-04 ES ES554182A patent/ES8705940A1/en not_active Expired
- 1986-04-04 AU AU55650/86A patent/AU585331B2/en not_active Ceased
- 1986-04-04 JP JP61079058A patent/JPS61282491A/en active Pending
- 1986-04-04 BR BR8601558A patent/BR8601558A/en not_active IP Right Cessation
- 1986-04-04 EP EP86302491A patent/EP0199481B1/en not_active Expired
- 1986-04-04 FI FI861453A patent/FI83238C/en not_active IP Right Cessation
- 1986-04-04 DE DE8686302491T patent/DE3667515D1/en not_active Expired - Lifetime
- 1986-04-04 KR KR1019860002568A patent/KR930003394B1/en not_active IP Right Cessation
- 1986-04-04 PT PT82341A patent/PT82341B/en not_active IP Right Cessation
-
1987
- 1987-10-10 MY MYPI87002889A patent/MY102502A/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103410036A (en) * | 2013-08-15 | 2013-11-27 | 齐鲁工业大学 | Production method for high-yield hardwood pulp |
Also Published As
| Publication number | Publication date |
|---|---|
| PT82341B (en) | 1988-12-15 |
| BR8601558A (en) | 1986-12-09 |
| FI861453A0 (en) | 1986-04-04 |
| FI83238B (en) | 1991-02-28 |
| NZ211684A (en) | 1989-07-27 |
| AR243623A1 (en) | 1993-08-31 |
| NO167159B (en) | 1991-07-01 |
| PT82341A (en) | 1986-05-01 |
| MY102502A (en) | 1992-06-30 |
| AU585331B2 (en) | 1989-06-15 |
| NO167159C (en) | 1991-10-09 |
| ZA862454B (en) | 1986-11-26 |
| ES554182A0 (en) | 1987-06-01 |
| ES8705940A1 (en) | 1987-06-01 |
| NO861307L (en) | 1986-10-06 |
| EP0199481A1 (en) | 1986-10-29 |
| KR860008339A (en) | 1986-11-14 |
| FI861453A (en) | 1986-10-05 |
| KR930003394B1 (en) | 1993-04-26 |
| AU5565086A (en) | 1986-10-16 |
| FI83238C (en) | 1991-06-10 |
| EP0199481B1 (en) | 1989-12-13 |
| JPS61282491A (en) | 1986-12-12 |
| DE3667515D1 (en) | 1990-01-18 |
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