CA1164704A - Method for improving the washing of cellulose pulps - Google Patents
Method for improving the washing of cellulose pulpsInfo
- Publication number
- CA1164704A CA1164704A CA000394153A CA394153A CA1164704A CA 1164704 A CA1164704 A CA 1164704A CA 000394153 A CA000394153 A CA 000394153A CA 394153 A CA394153 A CA 394153A CA 1164704 A CA1164704 A CA 1164704A
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- Prior art keywords
- pulp
- washing
- stage
- press
- screw
- 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
- D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D1/00—Methods of beating or refining; Beaters of the Hollander type
- D21D1/20—Methods of refining
- D21D1/40—Washing the fibres
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
- Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
- Investigating Or Analysing Biological Materials (AREA)
- Investigating Or Analysing Materials By The Use Of Chemical Reactions (AREA)
- Peptides Or Proteins (AREA)
Abstract
METHOD FOR IMPROVING THE WASHING OF CELLULOSE PULPS
ABSTRACT OF THE DISCLOSURE
An improved method is provided for washing cellulose pulps, which enables more chemicals and more combustible organic material to be recovered from the waste washing liquors, washing the chemically cooked and optionally mechanically defibrated pulp suspension in a plurality of stages while supplying water; subjecting the pulp to at least one mild mechanical treatment between twin interdigitated rotating screws in between two or more washing stages, after the pulp has been partially washed, thereby obtaining a pulp having a lower extractives content and Kappa number, and improved dewatering properties, and a washing effluent containing less contaminants.
ABSTRACT OF THE DISCLOSURE
An improved method is provided for washing cellulose pulps, which enables more chemicals and more combustible organic material to be recovered from the waste washing liquors, washing the chemically cooked and optionally mechanically defibrated pulp suspension in a plurality of stages while supplying water; subjecting the pulp to at least one mild mechanical treatment between twin interdigitated rotating screws in between two or more washing stages, after the pulp has been partially washed, thereby obtaining a pulp having a lower extractives content and Kappa number, and improved dewatering properties, and a washing effluent containing less contaminants.
Description
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SPE CIFICATION
In the chemical pulpin~ of lignocellulosic material there is obtained a chemical pulp which contains inter alia inorganic chem-cals and dissolved o. ganic su~stances, ~ainly li~nin and 5 mulor quantitie~ of cellulose, toge~er wi~ extractive substances, such as res3n. The ur~esirable residual material is washed out ~f -the pulp~ The waste pulping liquor and washing liquids obtained normally are evaporated and burned, so that ~eir chemicals content can be recovered. In order to fac~litate recovery of the 10 chemicals, the washing effluent should have the highest possible ~ollds concentratlon a~d ~e least possible amount oE water, which mea~s that the amowlt of water used during the washing should be kept to a mLnlmum.
When producing cellulose pulps wi~h a yleld in e~ccess of 15 abo~t 55%, the wo~d chlps are normally mechanically deEibrated to separate and free the fibers before washing and/or screening the pulp. During screening the pulp7 the screens collect nondefihrated wood residues, referred to as rejects or tailings, which are normall~ defibrated in a separate stage to separate and free ~le , ~`
., j~ .
fibers which are ~en returned to the pulp flow.
In order to obtain the purest possible pulp, efforts are made to wash ~e greatest possible amount of contaminants from the pulp suspension after deligni~ication, i. e., such contaminants as 5 inorganic chem ical residues and dissolved organic substances. The washing techniques a~plied hitherto, however, leave significant qua~tities of residual chemicals and undesirable organic substances in the pulp.
lhere are a number of d~fering washing methods ~at can 10 be used. Tn the oldest method, the pulp suspension is washed in so~
- called diffusers, whivh give a displacement wash which is carried out batchwise ill large vesse~s. Ano~er method, which is commonly used nowadays, washes ~e pulp suspension on drum filters, normally in several stages. The number of drum filters may vary, 15 although normally from three to four filters a~e used. Tn a more recent method, the washed pulp ls compressed In presses, whlch remave larger volumes of liquid than can be done with filters, resultlng ln a more efflcient recovery of chemicals and organlc substances.
These washing technlques all leave slgnificant quantlties of resldual chemlcals and unde#lrable organlc substances in the pulp. When the pulp Is to be subsequently bleached, these chemlcals and organlc substances compete for and thus glve an unnecessarlly high consumptl~ of bleaching chemicals, and al80 I-ad to dlscharge ..
1.~61:~7~
o an undesk~bly high quantity of substarlces harmful to the environ-ment. ~n the waste liquors. An increase ill the reco~ery ol chemicals used in the cellulose processes is highly desirable, bo~ froxn an economic and environmental aspect.
In Canadi~n a1pplication Se~ial No. 360, 196, filed ~eptember 12, 1980, to 30nas Arne Irlgvar Lindahl, a process and ~pparaLus are provided for the deres~ation of cellulose pulp, by a~ljusting th~ pulp concentration to with~ the range from a~out 15 to about 35~/c; add~
sufficient alkali to the pulp to bri~; -~e amount of alkali, calculated 10 as NaOH, wi~in the range f~om about 2 to about 1~ g/kg of water accompanying the pUL~; ~ubjecting ~e pulp to a mild, mechanical working in the bite of twin interdigitated ~otating sc~ews at all energy input of from 8 to 100 kWh per to~ of pulp, removing and reacting the pulp with the added alkali for from about 0.1 to about 15 five hoùrs, and then washing out dissolved resirl from the pulp.
In Canadian application Serial No. 391, 674, filed December 7, 1981, to Jonas A~ne Ingva~ Lindahl, a process a~d apparatus are provided for. the deresillation and brightness improvement of cellulose p1llp, by adjusting ~e pulp concentration to within ~e 20 range from about 15 to about 35%; adding sufficient allcali to the pulp to b~ing th~ amount of alkali, calculat~d as NaO~I, within the range f~om about 0. 5 to about 17 g/kgr of water accvmpan~rinlr the pulp; adding sufficient o:~idizing bleaching agent to the pulp to bring the amount of oxidizing bleaching gent to w~in the range Irom -7~'~
about 0.2 to about 22 g/kg of water; subjecting the pulp to a mild, mechanical working in the bite of twin interdigitated rotating screws at an energy input of from 8 to 100 kWh per ton of pulp; removing alld reacting the pulp with the added alkali and bleaching agent for 5 from about 0.1 to about five hours; and then washing out dissolYed resin rom the pulp.
The present invention provides a method for washing cellulose pulps produced from lignocellulosic material more effective-ly than lmown washing techniques, so as to improve the recovery of 10 chemicals and combustible organic materials from the wa~te liquors.
The invention is applicable to chemical pulps, semimechanical pulps, and chemimechanical pulps, produced from both softwood and hardwood.
In the process of the invention, unbleached cellulose pulp 15 produced from lignocellulosic material in a pulping process including a chemical pulping stage and, optionally, a mechanLcal defibrating stage, is washed with water or an aqueous solution In a plurality of stages, and in between at least two washing stages is subjected to a mild mechanical working between two interdigitated rotating screws 20 at an énergy input of from 7 to 200 kWh per ton of pulp.
VVhen applying the method according to the InventLon, the cleansing effect obtained has been found to be partlcularly good when at least 10~C of the impurities originally present in the pulp sus-pension are removed in at least one washing stage preceding the 25 mild mechanical working. Tn other words, at least 10~C of the 3-~4~
solids content of the waste pulping liquor should be washed out prior to subjecting the pulp suspension to the mild mechanical working It h~s also been found particularly suitable to increase ~e solids content of the pulp suspension prior to the mild mechanical 5 treatment to a pulp concentration between 10~C and 50~7c, preferably between 14~C and 40~c, and suitably between 20~C and 35~c- Upon completion of the mild mechanical worldng, ~e pulp suspension is diluted to a pulp consistency of between 0. 5 and 13 %, in conjunction with mixing wi~ wash liquid in the su~sequent washing step. ~en 10 the pulp is washed on filters, the most suitable input pulp consistency lies between 0. 5 and 6~c, while washing-dewatering in, for example, a press is suitably per$ormed at an input pulp consistency of between 2 and 13~c.
The present invention also provides apparatus for improving 15 the washing of unbleached cellulose pulps comprising, in coznbination, means for adjusting the pulp concentratlon to withln the range from about 10 to about 50~c, preferably from about 14 to about 40~c;
washlng means for washing cellulose pulp with water or an aqueous solution, and separating the waste wash water or aqueous solution;
20 means $or subjecting the pulp to a mild mechanical treatment in the bite of twLn interdigitated rotating screws at an input energy of from 7 to 200 kWh per ton of pulp; means for adjusting the pulp concentration to within the range from 0. 5 to 13~c; and means for washing the cellulose pulp at substantially the same pulp consistency.
~ ~61~71~4 There can be several washing stages before and/or after the mild mechanical working, and ~ere can be several mild mechanical working stages, each preceded by and followed by a washing stage.
In a preferred embodiment, there is means for adjusting pulp concentration after each washing stage which comprises a dewatering device preferably including a press; ~e twin interdigitated rotating screws comprise a screw defibrator; a screw feeder is inc.luded for transferring the pulp from the dewatering device to the 10 screw defibrator andbetween each washing stage; and there is means for transferring the pulp from the last washing stage to a pulp container or to the next processing stage.
The Figure shows schematically apparatus embodying the meff~od according to the invention applied in the Examples in washing 15 blrch sulfate pulp and chemimechanical spruce pulp in three stages, each of the washing stages beLng equipped with a press, 4, 14, 18.
Installed between the first and second washing stages is a screw defibrator 10 of the kind sold under the trade mark FROTAPULPER6'.
The washing process of the invention is preferably carried 20 out on unbleached cellulose pulp, after the lignocelluloslc material has been digested to cellulose pulp, as Ln a dLgester with digesting chemlcals recovered from spent digestLon liquor, and then ~e pulping liquor washed out in a washing stage.
7~
As ~e wash liquid, water is normally used and is preferred.
However, waste aqueous wash liquids such as are obtained in de-watering stages in ~e washing process of the invention can be used, for example, waste press liquor used in the Examples herein, as 5 well as acidic and alkaline waste liquors from o~er pulp treating processes in the plant or pulp mill, such as pulping and bleaching waste liquors, w~ich may desirably be diluted with water before use.
The pulp can be dewatered in one or more stages to a relatively high pulp concentration within the range from about 10 to 10 about 50~ in any conventional dewatering device, such as a drum washer, belt washer, roll press or screw press.
A suitable apparatus for the mild mechanical working treatment is a screw defibrator (screw refiner)j and especially sultable is the screw defibrator sold by MoDoMekan AB under the 15 trademark FROTAPULPER~. This screw defibrator has two rotatlng Interdigitated screws which are arranged in parallel to each other in a housing provided with an inlet and an outlet for pulp The screws are interdigitated or engage each other for kneadlng the pulp and at lea~t some of the screw flights are 20 provided wi~ serrations or indentations on their outer periphery.
Such a screw deflbrator is described In U . S patents Nos 3,054, 532, patented September 18, 1962, 3,064,908,patented November 20, 1962, 3,533,563, patented October 13, 1970, and 3,724,660 patented Aprll 3, 1973.
3 ~ 7~
~ nother type of ~crew defibrator that can be used is described inU.S. patentNo, 4,284,24~, patentedAugust 18, 1981, to Erik Folke Eriksson.
The pulp mi~ed wi~ water is subjected to shearing and 5 kneading forces in the screw defibrator in the form of pulsating pressure loads. As a result OI this treatment, a very effective washing of the pulp with ~e water is obtained. As for the pulp fibers, the treatment is mild, since the fibers are not shortened (which is the case in beating or milling) or adversely affected in 10 any other way.
~ e treatment in the screw defibrator usually is carried out at atmospheric pressure, but it can also be carried out at super-atmospheric pressures of ùp to 500 kPa. During the mechanical treatment, the temperature of the pulp increases, due to liberation 15 OI heat, sLnce at least 60~C of the energy input is transformed to heat. I~e hlgher the input of energy, the greater is the temperature Increase durLng the work.
The mild mechanical working ac~ording to the invention can be carried out at any desired temperature, as normally used in 20 practlce. However, a particularly suitable temperature range Is between about 20 and about 110C, while a preferred range is between about 35 to about 90C.
By "mild mechanical working" is meant a working in which pulp suspensions of the aforementioned solids concentration or pulp 7 !r~ 4 consistency are subjected to a repeated pressing, kneading and shearing at an input of electrical energy for carrying out said treatment within the range from aloout 7 to about 200 kWh per ton of bone dry pulp, and prefera~ly wi~in the range from about 10 to about 100 kWh per ton OI bone dry pulp.
After ~le mild mechanical treatment the pulp is transferred by means of a suita~le device, such as a pump, screw feeder or belt conveyor to another washing apparatus for continued washing with water or an aqueous solution.
Thereafter, the washed pulp may be carried directly to bleaching and drying or final treatment, for example, to manufacture of paper of different qualities. The mel~od according to ~e invention ls prlmarily applicable to the manufacture of washed unbleached or sllghtly bleached cellulose pulp. However, it is also possi~le to apply the method to ~e manufacture of pulp which is bleached to a varylng extent, lncluding bleachLng to a final brI~htness exceedlng ~0~; ISO. Usually the pulp after it has been treated according to the Inventlon ls bleached In one or more bleachlng stages In any selected bleachlng sequence.
The novel washing method according to the Inventlon, In whlch 1he pulp suspenslon Is mechanlcally treated ln a mlld fashlon between two or more of the stages of a washlng sequence, has been surprisingly found to provide a cleaner pulp and to result In a higher chemlcal recovery, a lower dlscharge of Impurlties In the 7~, 4 waste water or aqueous solution effluent, and a higller solids concen-tration in the effluent than was previously the case, when applying conventional washing techniques.
Thus, ~e present invention affords the important advantage 5 cf yielding a purer pulp. This is manifested, inter alia, by a considerable lowering of the extractives content of the p~lp, and of its Kappa number.
The advantages afforded by the method according to ~e invention also include the possibility of increasing the solids concen-10 tration o~ the waste washing liquor from the pulp washing stage, i. e.,~e concentration of organic materials contained in said liquor, and also the concentration of inorganic chemicals contained therein.
This increases the fuel value of the waste washing liquids, representlng a valuable savlng In energy. Because more contamlnants 15 are brought to e~aporation and burning, and a greater amount of chemLcal8 are recovered,the amount of envlronmentally harmful 8ubstances contained in the effluent is less than would otherwlse be the case, whlch is an important advantage, and also desirabLe from an envlronmental aspect. Consequently, the cost involved In the 20 treatment and destructlon of envIronmentally harmful substances In ~e effluent can be reduced when applylng the Inventlon.
~ fur~er advantageous and surprLslng effect afforded by the invention is that the consumption of bleachlng chemi cals, such a8 chlorine, chlorine dioxide, hypochlorite, hydrogen peroxide and oxygen gas, is markedly reduced when bleaching the washed pulp.
Ano~er surprising effect obtained by the inclusion of the mild mechanical treatment process according to the invention is 5 that the dewatering of ~e resultant pulp suspension is markedly improved, a fact which affords decisive advantages when fur~er treating the pulp.
The advantages afforded by the method according to ~e invention are fur~er illustrated by ~e Examples which follow.
Ille Examples set ~orth preferred embodiments of ~e l~lvention carried out in parallel, In which birch sulfate pulp and chemimechanical spruce pulp were washed in three stages, incorpor-atlng the mild mechanlcal treatment process between the first and second washing stages (Examples 1 and 2), in comparison wi~
15 Control8 ~ and 2, In which the pulp suspensions were not subjected to any form of mechanlcal treatment between the dlferent stages of the washLng se~uence.
The apparatus illustrated in the Figure was utilized in all the E~camples, and hence the reference numerals refer to correspond-20 ing references in the Flgure.
Unble~ed and un~ashed birch sulfate p~llp was introducedthrough the line 1 into ~e tank 2 of the processing system shown in the Figure. In the tank 2 the pulp suspension was diluted with press 5 was$e liquor supplied through the line 22, until the pulp consistency was about 8~c. The pulp suspension was then passed through line 3 to the first washing stage 4, including a press in which the pulp suspension was compressed to a dry solids content of 33. 3~c,and then passed through the line 5 to the screw feeder 6, arranged to 10 feed the pulp suspension ~rough the lines 7 and 8 (line 9 was closed) to the screw defibrator 10 provided with two rotating screws whose bla~les had concave portions and in which the pulp suspension was sub3ected to a mild mechanical treatment, after which the sus-pension passed throu~ line 11 to the second screw feeder 12. The 15 ternperature of the pulp suspension at the inlet to the screw de-fibrator 10 was 68C, and at the outlet of the defibrator was 71C.
The amount of electrical energy consumed by the mild mechanlcal treatment in the screw defibrator 10 was 15 kWh per ton o bone-dry pulp.
The treated pulp suspension was diluted in the screw feeder 12 to,a pulp consistency of 8%, by introduclng press waste liquor to the feeder through line 21,the wastellquor mixing effectively with ~e palp suspension during its transport through the feeder 12.
The diluted pulp suspension was then passed through the line 13 to a second washing stage 14, including a press similar to that used in the first washing stage 4. The pulp suspension was washed alld agaill thic'~ened in the press 14 to a dry solids content of 33. 3~c-Waste liquor obtained from the press 14 was recycled through ~e 5 line 22 to the tank 2, where it was used to dilute incoming pulp suspension. The pulp suspension after being washed and thickened ill the second washing stage was then passed through the line 15 to ~e screw feeder 16, and then through the line 17 to a ~ird washing stage 18 equipped with a press similar to the presses used in the two 10 preceding washing stages 4, 14.
The pulp suspension was diluted aIld mi~ed in ~e screw feeder 16 in a manner similar to that in the preceding screw feeder 12, although in this case with pure water supplied through the line 20, to a pulp conslstency of 8%. After washing the pulp suspension and 15 compresslng lt to a dry sollds content of 33. 3~c in ~e press 18, the wa~hed pulp suspenslon was remo~ted through a llne 19.
Samples of the press waste lLquors were removed from the Ilne# 21 and 22 for analysis purposes. Samples of the washed pulp were also taken from the line 19. The analysls results are shown 20 in Table 1.
Waste llquor from the presæ in the flrst washlng stage 4 was taken through a llne 23 and passed to a recovery plant (not shown In ; the drawîng), where the waste llquor was evaporated and burned.
Because the washlng llquid was passed ln counterflow to the flow 7~
of pulp suspension, and because of the mechanicaL treatment to whi~h the pulp suspension was subjected, the press waste liquor had a high organic substance content (about 13~c) and7 at the same time~
ahigh fuelvalue.
As a control, a birch sulfate pulp taken from the same batch as the pulp used in Example 1 was washed a~d treated in ~e same apparatus, but with ~e dlfference ~hat the pulp suspension was not subjected to a mUd mechanical treatment between ~e first a~
seccnd washing stages. Thus, all flow of pulp suspension through 10 the line 8 was stopped, and line 9 was opened, so that ~e pulp suspension passed directly through the line 9 to the second screw feeder I 2.
~ fter washing and compressing the pulp suspension in the press 1~ of the second washing stage, the pulp obtained had a dry 15 sollds content of 2B~c. ~fter washing and thickenlng the suspenslon In the press of the third washing stage 18, the pulp also had a dry fiolids content of 26/~C. Tt will be noted that the conslstellcy of the pulp suspenslon at ~e inlets to stages 14 and 18, respectively, was also 8~c in this test, and that the pressure exerted by the presses 20 was the same as that in Example 1.
Samples for analysls were removed in this control run at the sa~ne locations as in the run accordlng to Example 1. The analysls results are shown in Table I below:
3 ~7~4 TABLE I
Exampie % Dry sol-ids content of pulp suspension Control .
Subsequent to passulg ~e press of the second washing stage 14, ~c 26.0 33.3 Subsequent to passing the press of the thirdwashingstage18, ~c 26.0 33.3 1~ Amount of press waste liquor obtained from:
The press of the second washing stage 14,m3/ton 8. 65 9 50 The press of the thlrd washu~g stage 18, m3/ton 8 . 65 9. 50 Dry solids content of press waste liquor from:
The press of ~e second washing stage l4, 3Zc 3. 503. 70 The press of the third washing stage 18, ~c 1. 621. 89 Sodium content of ~e press waste liquor from:
The press of ~e second washing stage 14, g~l Na 6. 55 7. 02 The press of the thlrd wa~hing stage 18, g/l Na 2. 83 3. 38 Totally washed from the pulp suspenslon ln 20 the second and ~lrd washing staces:
As dry sollds, kg/ton bone dry pulp 450. 0532. 0 As Na, kg/ton bon~ dry pulp 80.9 98. 5 Propertles of finally washed pulp Extractlves content (according to SCAN-C7: 62) 0. 34 0.18 25 DCM (dlchloromethane), %
Vlscoslty (accordlng to SCAN-C15:62) cm3/g 972 969 Kapp~ number (according to SCAN-C1: 59) 17. 514. 7 'Irg~
As seen from the Tal~le, the method according to the inven-tion -gives quite surprisingly a considerably better washing ~an can be obtained when wash-ng in accordance wLth l~own techniques.
Despite the fact that the mild mechanical treatment was carried out 5 on a pulp suspension which had only been partially washed, the method according to the invention surprisingly resulted in a pulp with a much lower extractives conte~t than can be obtained when corlventionally washing pulp without mechanically treating the pulp l~etween washing stages.
One important advantage with respect to energy afforded by the increased extent to which organic substances are washed ~rom the pulp is that the fuel value of the waste liquor is also increased Fur~er, a higher percentage of the cooking chemicals are recovered.
3 ~ 7;~
Unl~leached and unwashed chemimechanical spruce pulp cooked to a yield of 73% based on the dxy wood was introduced through the line 1 into the tank 2 of the processing system shown in 5 the Fi,?ure. In the tank 2 the pulp suspension was diluted with press waste liquor supplied ~rou~h the line 22, untll ~e pulp consistency was about ~c. The pulp suspension was then passed through line 3 to ~e first washing stage 4, including a press in which the pulp suspension was compressed to a dry solids content of 33 . 3~c ,and 10 then passed ~rough the line 5 to the screw feeder 6, arranged to feed the pulp suspension through the lines 7 and 8 (line 9 was closed) to the screw defibrato~ 10 provided with two rotating screws whose blades had concave portions and in which the pulp suspension was subjected to a mUd mechanical treatment, after which the sus-15 penslon paæsed throu~ line 11 tothe second screw feeder 12. Thetemperature of the pulp suspension at the Lnlet to the screw de-flbrator 10 was 68C, and at the outlet of the defibrator was 71C.
The amount of electrical energy consumed by the mild mechanical treatment in the screw defibrator 10 was 15 kWh per ton of bone-dry 20 pulp.
The treated pulp suspenslon was diluted In the screw feeder 12 to a pulp consistency of 7%7 by introduclng press waste liquor to the feeder through line 21, the waste liquor mixing effecti~ely wi~
~e pulp suspensi~n durlng its transport ~rough the feeder 12.
25 The diluted pulp suspension was then passed through the line 13 to a second washing stage 14, including a press similar to that used in the first washulg stage 4. The pulp suspension was washed and again thickened in ~e press 14 to a dry sollds content of 34~c Waste liquor obtained Irom the press 14 was recycled ~rough ~e 5 line 22 to the tank 2, where it was used to dilute incomlng pulp suspension. The pulp suspension after being washed a~d $hickened in the second wash~g stage was then passed fflrough the line 15 to the screw feeder 16, and then ~rough the line 1~ to a third washing stage 18 equipped with a press similar to the presses used in the two 10 preceding washing stages 4, 14.
The pulp suspension was diluted and mixed in ~e screw feeder 1~ in a manner similar to that in the preceding screw feeder 12, althou~h in this case with pure water supplied through ~e line 20, to a pulp conslstency of 7~c- After washing the pulp suspension and 15 compresslltg It to a dry sollds content of 34~c In the press 18, the washed pulp suspensLon was remoYed through a line 19.
Samples of the press waste liquors were removed from the llnes 21 and 22 for analysLs purposes. Samples of the washed pulp were also taken from the line 19. The analysls results are shown 20 ln Table IT.
Waste liq,uor from the press in ~e flrst washing stage 4 was taken throug~ a llne 23 and passed to a recovery plant (not shown ln the drawlng), where the waste llquor was evaporated and burned.
Because the washlng llquid was passed in counterflow to the flow , 7~r~
of pulp suspension, and because of the mechanical treatment to which ~e pulp suspension was sub3ected, the press waste liqu~r had a high organic sub~tance content (about 13%) and, at the same time, a high fuel value.
As a control, a chemimechaJlical spruce pulp taken from the same batch as the pulp used in Egample 2 was washed and treated in the same apparatus, but wLth the difference that the pulp sus-pension was not subjected to a mild mechanical treatment between 1he first and second washing stages. Thus, all flow of pulp sus-10 pension throu~h the line 8 was stopped, and line 9 was opened, so that the pulp suspension passed directly through the line 9 to ~e second screw feeder 1~.
After washing and compressing the.pulp suspension in the press 14 of the second washing ætage, the pulp obtained had a dry 15 solids content of 30~c After washlng and thickening the suspension ln the press of the thlrd washing stage 18, the pulp also had a dry solldfi content of 30%. It will be noted that the consIstency of the pulp suspension at the Inlets to stages 14 and 18, respectively, was also 7~c ln thls test, and that the pressur~ exerted by the presses 20 was the same as that in Example 2.
Samples for analysls were removed ln this control run at the same locatlons as ln the run accordlng to Example 2. The anal~sls results are shown ln Table II below:
3.~ 7~
TABLE: 11 Example ~c Dry solids content of pulp suspension Control 2 Subsequentto passing ~e press of the 30 34 second wash~ng sta~e 14, ~c Subse~uent to passing ~e press of the 30 34 third washing stage 18, ~c Amount of press waste liquor obtained from:
.
The press of ~e second washing stage 14,m3/ton 10. 95 11. 34 The press of the third washing stage 18, m3/ton 10. 9G 11. 34 ~0 Dry solids content of press waste liquor from:
The press of the second washing stage 15, ~c 0. 77 0. 80 ', The press of the third ~vashing stage 18, ~c 0. û9 0.12 Sodium content of ~e press waste liquor from:
-The press of the second washing stage 14, g/l Na 1. 62 1. 87 The press of the thiTd washing stage 18, g/l Na 0. 45 0. 47 Totally washed from the pulp suspension in20 e second and thlrd washin~ sta~es:
As dry solids, kg/ton bone dry pulp 94. 2 104. 3 A~ Na, l~g/ton bone dry pulp 22. 7 24. 3 Properties of finallg washed pulp:
Extractlves content (according to SCAN. C7: 62) 0. 62 0.12 25 DCM (dlchlorome~ane), ~c
SPE CIFICATION
In the chemical pulpin~ of lignocellulosic material there is obtained a chemical pulp which contains inter alia inorganic chem-cals and dissolved o. ganic su~stances, ~ainly li~nin and 5 mulor quantitie~ of cellulose, toge~er wi~ extractive substances, such as res3n. The ur~esirable residual material is washed out ~f -the pulp~ The waste pulping liquor and washing liquids obtained normally are evaporated and burned, so that ~eir chemicals content can be recovered. In order to fac~litate recovery of the 10 chemicals, the washing effluent should have the highest possible ~ollds concentratlon a~d ~e least possible amount oE water, which mea~s that the amowlt of water used during the washing should be kept to a mLnlmum.
When producing cellulose pulps wi~h a yleld in e~ccess of 15 abo~t 55%, the wo~d chlps are normally mechanically deEibrated to separate and free the fibers before washing and/or screening the pulp. During screening the pulp7 the screens collect nondefihrated wood residues, referred to as rejects or tailings, which are normall~ defibrated in a separate stage to separate and free ~le , ~`
., j~ .
fibers which are ~en returned to the pulp flow.
In order to obtain the purest possible pulp, efforts are made to wash ~e greatest possible amount of contaminants from the pulp suspension after deligni~ication, i. e., such contaminants as 5 inorganic chem ical residues and dissolved organic substances. The washing techniques a~plied hitherto, however, leave significant qua~tities of residual chemicals and undesirable organic substances in the pulp.
lhere are a number of d~fering washing methods ~at can 10 be used. Tn the oldest method, the pulp suspension is washed in so~
- called diffusers, whivh give a displacement wash which is carried out batchwise ill large vesse~s. Ano~er method, which is commonly used nowadays, washes ~e pulp suspension on drum filters, normally in several stages. The number of drum filters may vary, 15 although normally from three to four filters a~e used. Tn a more recent method, the washed pulp ls compressed In presses, whlch remave larger volumes of liquid than can be done with filters, resultlng ln a more efflcient recovery of chemicals and organlc substances.
These washing technlques all leave slgnificant quantlties of resldual chemlcals and unde#lrable organlc substances in the pulp. When the pulp Is to be subsequently bleached, these chemlcals and organlc substances compete for and thus glve an unnecessarlly high consumptl~ of bleaching chemicals, and al80 I-ad to dlscharge ..
1.~61:~7~
o an undesk~bly high quantity of substarlces harmful to the environ-ment. ~n the waste liquors. An increase ill the reco~ery ol chemicals used in the cellulose processes is highly desirable, bo~ froxn an economic and environmental aspect.
In Canadi~n a1pplication Se~ial No. 360, 196, filed ~eptember 12, 1980, to 30nas Arne Irlgvar Lindahl, a process and ~pparaLus are provided for the deres~ation of cellulose pulp, by a~ljusting th~ pulp concentration to with~ the range from a~out 15 to about 35~/c; add~
sufficient alkali to the pulp to bri~; -~e amount of alkali, calculated 10 as NaOH, wi~in the range f~om about 2 to about 1~ g/kg of water accompanying the pUL~; ~ubjecting ~e pulp to a mild, mechanical working in the bite of twin interdigitated ~otating sc~ews at all energy input of from 8 to 100 kWh per to~ of pulp, removing and reacting the pulp with the added alkali for from about 0.1 to about 15 five hoùrs, and then washing out dissolved resirl from the pulp.
In Canadian application Serial No. 391, 674, filed December 7, 1981, to Jonas A~ne Ingva~ Lindahl, a process a~d apparatus are provided for. the deresillation and brightness improvement of cellulose p1llp, by adjusting ~e pulp concentration to within ~e 20 range from about 15 to about 35%; adding sufficient allcali to the pulp to b~ing th~ amount of alkali, calculat~d as NaO~I, within the range f~om about 0. 5 to about 17 g/kgr of water accvmpan~rinlr the pulp; adding sufficient o:~idizing bleaching agent to the pulp to bring the amount of oxidizing bleaching gent to w~in the range Irom -7~'~
about 0.2 to about 22 g/kg of water; subjecting the pulp to a mild, mechanical working in the bite of twin interdigitated rotating screws at an energy input of from 8 to 100 kWh per ton of pulp; removing alld reacting the pulp with the added alkali and bleaching agent for 5 from about 0.1 to about five hours; and then washing out dissolYed resin rom the pulp.
The present invention provides a method for washing cellulose pulps produced from lignocellulosic material more effective-ly than lmown washing techniques, so as to improve the recovery of 10 chemicals and combustible organic materials from the wa~te liquors.
The invention is applicable to chemical pulps, semimechanical pulps, and chemimechanical pulps, produced from both softwood and hardwood.
In the process of the invention, unbleached cellulose pulp 15 produced from lignocellulosic material in a pulping process including a chemical pulping stage and, optionally, a mechanLcal defibrating stage, is washed with water or an aqueous solution In a plurality of stages, and in between at least two washing stages is subjected to a mild mechanical working between two interdigitated rotating screws 20 at an énergy input of from 7 to 200 kWh per ton of pulp.
VVhen applying the method according to the InventLon, the cleansing effect obtained has been found to be partlcularly good when at least 10~C of the impurities originally present in the pulp sus-pension are removed in at least one washing stage preceding the 25 mild mechanical working. Tn other words, at least 10~C of the 3-~4~
solids content of the waste pulping liquor should be washed out prior to subjecting the pulp suspension to the mild mechanical working It h~s also been found particularly suitable to increase ~e solids content of the pulp suspension prior to the mild mechanical 5 treatment to a pulp concentration between 10~C and 50~7c, preferably between 14~C and 40~c, and suitably between 20~C and 35~c- Upon completion of the mild mechanical worldng, ~e pulp suspension is diluted to a pulp consistency of between 0. 5 and 13 %, in conjunction with mixing wi~ wash liquid in the su~sequent washing step. ~en 10 the pulp is washed on filters, the most suitable input pulp consistency lies between 0. 5 and 6~c, while washing-dewatering in, for example, a press is suitably per$ormed at an input pulp consistency of between 2 and 13~c.
The present invention also provides apparatus for improving 15 the washing of unbleached cellulose pulps comprising, in coznbination, means for adjusting the pulp concentratlon to withln the range from about 10 to about 50~c, preferably from about 14 to about 40~c;
washlng means for washing cellulose pulp with water or an aqueous solution, and separating the waste wash water or aqueous solution;
20 means $or subjecting the pulp to a mild mechanical treatment in the bite of twLn interdigitated rotating screws at an input energy of from 7 to 200 kWh per ton of pulp; means for adjusting the pulp concentration to within the range from 0. 5 to 13~c; and means for washing the cellulose pulp at substantially the same pulp consistency.
~ ~61~71~4 There can be several washing stages before and/or after the mild mechanical working, and ~ere can be several mild mechanical working stages, each preceded by and followed by a washing stage.
In a preferred embodiment, there is means for adjusting pulp concentration after each washing stage which comprises a dewatering device preferably including a press; ~e twin interdigitated rotating screws comprise a screw defibrator; a screw feeder is inc.luded for transferring the pulp from the dewatering device to the 10 screw defibrator andbetween each washing stage; and there is means for transferring the pulp from the last washing stage to a pulp container or to the next processing stage.
The Figure shows schematically apparatus embodying the meff~od according to the invention applied in the Examples in washing 15 blrch sulfate pulp and chemimechanical spruce pulp in three stages, each of the washing stages beLng equipped with a press, 4, 14, 18.
Installed between the first and second washing stages is a screw defibrator 10 of the kind sold under the trade mark FROTAPULPER6'.
The washing process of the invention is preferably carried 20 out on unbleached cellulose pulp, after the lignocelluloslc material has been digested to cellulose pulp, as Ln a dLgester with digesting chemlcals recovered from spent digestLon liquor, and then ~e pulping liquor washed out in a washing stage.
7~
As ~e wash liquid, water is normally used and is preferred.
However, waste aqueous wash liquids such as are obtained in de-watering stages in ~e washing process of the invention can be used, for example, waste press liquor used in the Examples herein, as 5 well as acidic and alkaline waste liquors from o~er pulp treating processes in the plant or pulp mill, such as pulping and bleaching waste liquors, w~ich may desirably be diluted with water before use.
The pulp can be dewatered in one or more stages to a relatively high pulp concentration within the range from about 10 to 10 about 50~ in any conventional dewatering device, such as a drum washer, belt washer, roll press or screw press.
A suitable apparatus for the mild mechanical working treatment is a screw defibrator (screw refiner)j and especially sultable is the screw defibrator sold by MoDoMekan AB under the 15 trademark FROTAPULPER~. This screw defibrator has two rotatlng Interdigitated screws which are arranged in parallel to each other in a housing provided with an inlet and an outlet for pulp The screws are interdigitated or engage each other for kneadlng the pulp and at lea~t some of the screw flights are 20 provided wi~ serrations or indentations on their outer periphery.
Such a screw deflbrator is described In U . S patents Nos 3,054, 532, patented September 18, 1962, 3,064,908,patented November 20, 1962, 3,533,563, patented October 13, 1970, and 3,724,660 patented Aprll 3, 1973.
3 ~ 7~
~ nother type of ~crew defibrator that can be used is described inU.S. patentNo, 4,284,24~, patentedAugust 18, 1981, to Erik Folke Eriksson.
The pulp mi~ed wi~ water is subjected to shearing and 5 kneading forces in the screw defibrator in the form of pulsating pressure loads. As a result OI this treatment, a very effective washing of the pulp with ~e water is obtained. As for the pulp fibers, the treatment is mild, since the fibers are not shortened (which is the case in beating or milling) or adversely affected in 10 any other way.
~ e treatment in the screw defibrator usually is carried out at atmospheric pressure, but it can also be carried out at super-atmospheric pressures of ùp to 500 kPa. During the mechanical treatment, the temperature of the pulp increases, due to liberation 15 OI heat, sLnce at least 60~C of the energy input is transformed to heat. I~e hlgher the input of energy, the greater is the temperature Increase durLng the work.
The mild mechanical working ac~ording to the invention can be carried out at any desired temperature, as normally used in 20 practlce. However, a particularly suitable temperature range Is between about 20 and about 110C, while a preferred range is between about 35 to about 90C.
By "mild mechanical working" is meant a working in which pulp suspensions of the aforementioned solids concentration or pulp 7 !r~ 4 consistency are subjected to a repeated pressing, kneading and shearing at an input of electrical energy for carrying out said treatment within the range from aloout 7 to about 200 kWh per ton of bone dry pulp, and prefera~ly wi~in the range from about 10 to about 100 kWh per ton OI bone dry pulp.
After ~le mild mechanical treatment the pulp is transferred by means of a suita~le device, such as a pump, screw feeder or belt conveyor to another washing apparatus for continued washing with water or an aqueous solution.
Thereafter, the washed pulp may be carried directly to bleaching and drying or final treatment, for example, to manufacture of paper of different qualities. The mel~od according to ~e invention ls prlmarily applicable to the manufacture of washed unbleached or sllghtly bleached cellulose pulp. However, it is also possi~le to apply the method to ~e manufacture of pulp which is bleached to a varylng extent, lncluding bleachLng to a final brI~htness exceedlng ~0~; ISO. Usually the pulp after it has been treated according to the Inventlon ls bleached In one or more bleachlng stages In any selected bleachlng sequence.
The novel washing method according to the Inventlon, In whlch 1he pulp suspenslon Is mechanlcally treated ln a mlld fashlon between two or more of the stages of a washlng sequence, has been surprisingly found to provide a cleaner pulp and to result In a higher chemlcal recovery, a lower dlscharge of Impurlties In the 7~, 4 waste water or aqueous solution effluent, and a higller solids concen-tration in the effluent than was previously the case, when applying conventional washing techniques.
Thus, ~e present invention affords the important advantage 5 cf yielding a purer pulp. This is manifested, inter alia, by a considerable lowering of the extractives content of the p~lp, and of its Kappa number.
The advantages afforded by the method according to ~e invention also include the possibility of increasing the solids concen-10 tration o~ the waste washing liquor from the pulp washing stage, i. e.,~e concentration of organic materials contained in said liquor, and also the concentration of inorganic chemicals contained therein.
This increases the fuel value of the waste washing liquids, representlng a valuable savlng In energy. Because more contamlnants 15 are brought to e~aporation and burning, and a greater amount of chemLcal8 are recovered,the amount of envlronmentally harmful 8ubstances contained in the effluent is less than would otherwlse be the case, whlch is an important advantage, and also desirabLe from an envlronmental aspect. Consequently, the cost involved In the 20 treatment and destructlon of envIronmentally harmful substances In ~e effluent can be reduced when applylng the Inventlon.
~ fur~er advantageous and surprLslng effect afforded by the invention is that the consumption of bleachlng chemi cals, such a8 chlorine, chlorine dioxide, hypochlorite, hydrogen peroxide and oxygen gas, is markedly reduced when bleaching the washed pulp.
Ano~er surprising effect obtained by the inclusion of the mild mechanical treatment process according to the invention is 5 that the dewatering of ~e resultant pulp suspension is markedly improved, a fact which affords decisive advantages when fur~er treating the pulp.
The advantages afforded by the method according to ~e invention are fur~er illustrated by ~e Examples which follow.
Ille Examples set ~orth preferred embodiments of ~e l~lvention carried out in parallel, In which birch sulfate pulp and chemimechanical spruce pulp were washed in three stages, incorpor-atlng the mild mechanlcal treatment process between the first and second washing stages (Examples 1 and 2), in comparison wi~
15 Control8 ~ and 2, In which the pulp suspensions were not subjected to any form of mechanlcal treatment between the dlferent stages of the washLng se~uence.
The apparatus illustrated in the Figure was utilized in all the E~camples, and hence the reference numerals refer to correspond-20 ing references in the Flgure.
Unble~ed and un~ashed birch sulfate p~llp was introducedthrough the line 1 into ~e tank 2 of the processing system shown in the Figure. In the tank 2 the pulp suspension was diluted with press 5 was$e liquor supplied through the line 22, until the pulp consistency was about 8~c. The pulp suspension was then passed through line 3 to the first washing stage 4, including a press in which the pulp suspension was compressed to a dry solids content of 33. 3~c,and then passed through the line 5 to the screw feeder 6, arranged to 10 feed the pulp suspension ~rough the lines 7 and 8 (line 9 was closed) to the screw defibrator 10 provided with two rotating screws whose bla~les had concave portions and in which the pulp suspension was sub3ected to a mild mechanical treatment, after which the sus-pension passed throu~ line 11 to the second screw feeder 12. The 15 ternperature of the pulp suspension at the inlet to the screw de-fibrator 10 was 68C, and at the outlet of the defibrator was 71C.
The amount of electrical energy consumed by the mild mechanlcal treatment in the screw defibrator 10 was 15 kWh per ton o bone-dry pulp.
The treated pulp suspension was diluted in the screw feeder 12 to,a pulp consistency of 8%, by introduclng press waste liquor to the feeder through line 21,the wastellquor mixing effectively with ~e palp suspension during its transport through the feeder 12.
The diluted pulp suspension was then passed through the line 13 to a second washing stage 14, including a press similar to that used in the first washing stage 4. The pulp suspension was washed alld agaill thic'~ened in the press 14 to a dry solids content of 33. 3~c-Waste liquor obtained from the press 14 was recycled through ~e 5 line 22 to the tank 2, where it was used to dilute incoming pulp suspension. The pulp suspension after being washed and thickened ill the second washing stage was then passed through the line 15 to ~e screw feeder 16, and then through the line 17 to a ~ird washing stage 18 equipped with a press similar to the presses used in the two 10 preceding washing stages 4, 14.
The pulp suspension was diluted aIld mi~ed in ~e screw feeder 16 in a manner similar to that in the preceding screw feeder 12, although in this case with pure water supplied through the line 20, to a pulp conslstency of 8%. After washing the pulp suspension and 15 compresslng lt to a dry sollds content of 33. 3~c in ~e press 18, the wa~hed pulp suspenslon was remo~ted through a llne 19.
Samples of the press waste lLquors were removed from the Ilne# 21 and 22 for analysis purposes. Samples of the washed pulp were also taken from the line 19. The analysls results are shown 20 in Table 1.
Waste llquor from the presæ in the flrst washlng stage 4 was taken through a llne 23 and passed to a recovery plant (not shown In ; the drawîng), where the waste llquor was evaporated and burned.
Because the washlng llquid was passed ln counterflow to the flow 7~
of pulp suspension, and because of the mechanicaL treatment to whi~h the pulp suspension was subjected, the press waste liquor had a high organic substance content (about 13~c) and7 at the same time~
ahigh fuelvalue.
As a control, a birch sulfate pulp taken from the same batch as the pulp used in Example 1 was washed a~d treated in ~e same apparatus, but with ~e dlfference ~hat the pulp suspension was not subjected to a mUd mechanical treatment between ~e first a~
seccnd washing stages. Thus, all flow of pulp suspension through 10 the line 8 was stopped, and line 9 was opened, so that ~e pulp suspension passed directly through the line 9 to the second screw feeder I 2.
~ fter washing and compressing the pulp suspension in the press 1~ of the second washing stage, the pulp obtained had a dry 15 sollds content of 2B~c. ~fter washing and thickenlng the suspenslon In the press of the third washing stage 18, the pulp also had a dry fiolids content of 26/~C. Tt will be noted that the conslstellcy of the pulp suspenslon at ~e inlets to stages 14 and 18, respectively, was also 8~c in this test, and that the pressure exerted by the presses 20 was the same as that in Example 1.
Samples for analysls were removed in this control run at the sa~ne locations as in the run accordlng to Example 1. The analysls results are shown in Table I below:
3 ~7~4 TABLE I
Exampie % Dry sol-ids content of pulp suspension Control .
Subsequent to passulg ~e press of the second washing stage 14, ~c 26.0 33.3 Subsequent to passing the press of the thirdwashingstage18, ~c 26.0 33.3 1~ Amount of press waste liquor obtained from:
The press of the second washing stage 14,m3/ton 8. 65 9 50 The press of the thlrd washu~g stage 18, m3/ton 8 . 65 9. 50 Dry solids content of press waste liquor from:
The press of ~e second washing stage l4, 3Zc 3. 503. 70 The press of the third washing stage 18, ~c 1. 621. 89 Sodium content of ~e press waste liquor from:
The press of ~e second washing stage 14, g~l Na 6. 55 7. 02 The press of the thlrd wa~hing stage 18, g/l Na 2. 83 3. 38 Totally washed from the pulp suspenslon ln 20 the second and ~lrd washing staces:
As dry sollds, kg/ton bone dry pulp 450. 0532. 0 As Na, kg/ton bon~ dry pulp 80.9 98. 5 Propertles of finally washed pulp Extractlves content (according to SCAN-C7: 62) 0. 34 0.18 25 DCM (dlchloromethane), %
Vlscoslty (accordlng to SCAN-C15:62) cm3/g 972 969 Kapp~ number (according to SCAN-C1: 59) 17. 514. 7 'Irg~
As seen from the Tal~le, the method according to the inven-tion -gives quite surprisingly a considerably better washing ~an can be obtained when wash-ng in accordance wLth l~own techniques.
Despite the fact that the mild mechanical treatment was carried out 5 on a pulp suspension which had only been partially washed, the method according to the invention surprisingly resulted in a pulp with a much lower extractives conte~t than can be obtained when corlventionally washing pulp without mechanically treating the pulp l~etween washing stages.
One important advantage with respect to energy afforded by the increased extent to which organic substances are washed ~rom the pulp is that the fuel value of the waste liquor is also increased Fur~er, a higher percentage of the cooking chemicals are recovered.
3 ~ 7;~
Unl~leached and unwashed chemimechanical spruce pulp cooked to a yield of 73% based on the dxy wood was introduced through the line 1 into the tank 2 of the processing system shown in 5 the Fi,?ure. In the tank 2 the pulp suspension was diluted with press waste liquor supplied ~rou~h the line 22, untll ~e pulp consistency was about ~c. The pulp suspension was then passed through line 3 to ~e first washing stage 4, including a press in which the pulp suspension was compressed to a dry solids content of 33 . 3~c ,and 10 then passed ~rough the line 5 to the screw feeder 6, arranged to feed the pulp suspension through the lines 7 and 8 (line 9 was closed) to the screw defibrato~ 10 provided with two rotating screws whose blades had concave portions and in which the pulp suspension was subjected to a mUd mechanical treatment, after which the sus-15 penslon paæsed throu~ line 11 tothe second screw feeder 12. Thetemperature of the pulp suspension at the Lnlet to the screw de-flbrator 10 was 68C, and at the outlet of the defibrator was 71C.
The amount of electrical energy consumed by the mild mechanical treatment in the screw defibrator 10 was 15 kWh per ton of bone-dry 20 pulp.
The treated pulp suspenslon was diluted In the screw feeder 12 to a pulp consistency of 7%7 by introduclng press waste liquor to the feeder through line 21, the waste liquor mixing effecti~ely wi~
~e pulp suspensi~n durlng its transport ~rough the feeder 12.
25 The diluted pulp suspension was then passed through the line 13 to a second washing stage 14, including a press similar to that used in the first washulg stage 4. The pulp suspension was washed and again thickened in ~e press 14 to a dry sollds content of 34~c Waste liquor obtained Irom the press 14 was recycled ~rough ~e 5 line 22 to the tank 2, where it was used to dilute incomlng pulp suspension. The pulp suspension after being washed a~d $hickened in the second wash~g stage was then passed fflrough the line 15 to the screw feeder 16, and then ~rough the line 1~ to a third washing stage 18 equipped with a press similar to the presses used in the two 10 preceding washing stages 4, 14.
The pulp suspension was diluted and mixed in ~e screw feeder 1~ in a manner similar to that in the preceding screw feeder 12, althou~h in this case with pure water supplied through ~e line 20, to a pulp conslstency of 7~c- After washing the pulp suspension and 15 compresslltg It to a dry sollds content of 34~c In the press 18, the washed pulp suspensLon was remoYed through a line 19.
Samples of the press waste liquors were removed from the llnes 21 and 22 for analysLs purposes. Samples of the washed pulp were also taken from the line 19. The analysls results are shown 20 ln Table IT.
Waste liq,uor from the press in ~e flrst washing stage 4 was taken throug~ a llne 23 and passed to a recovery plant (not shown ln the drawlng), where the waste llquor was evaporated and burned.
Because the washlng llquid was passed in counterflow to the flow , 7~r~
of pulp suspension, and because of the mechanical treatment to which ~e pulp suspension was sub3ected, the press waste liqu~r had a high organic sub~tance content (about 13%) and, at the same time, a high fuel value.
As a control, a chemimechaJlical spruce pulp taken from the same batch as the pulp used in Egample 2 was washed and treated in the same apparatus, but wLth the difference that the pulp sus-pension was not subjected to a mild mechanical treatment between 1he first and second washing stages. Thus, all flow of pulp sus-10 pension throu~h the line 8 was stopped, and line 9 was opened, so that the pulp suspension passed directly through the line 9 to ~e second screw feeder 1~.
After washing and compressing the.pulp suspension in the press 14 of the second washing ætage, the pulp obtained had a dry 15 solids content of 30~c After washlng and thickening the suspension ln the press of the thlrd washing stage 18, the pulp also had a dry solldfi content of 30%. It will be noted that the consIstency of the pulp suspension at the Inlets to stages 14 and 18, respectively, was also 7~c ln thls test, and that the pressur~ exerted by the presses 20 was the same as that in Example 2.
Samples for analysls were removed ln this control run at the same locatlons as ln the run accordlng to Example 2. The anal~sls results are shown ln Table II below:
3.~ 7~
TABLE: 11 Example ~c Dry solids content of pulp suspension Control 2 Subsequentto passing ~e press of the 30 34 second wash~ng sta~e 14, ~c Subse~uent to passing ~e press of the 30 34 third washing stage 18, ~c Amount of press waste liquor obtained from:
.
The press of ~e second washing stage 14,m3/ton 10. 95 11. 34 The press of the third washing stage 18, m3/ton 10. 9G 11. 34 ~0 Dry solids content of press waste liquor from:
The press of the second washing stage 15, ~c 0. 77 0. 80 ', The press of the third ~vashing stage 18, ~c 0. û9 0.12 Sodium content of ~e press waste liquor from:
-The press of the second washing stage 14, g/l Na 1. 62 1. 87 The press of the thiTd washing stage 18, g/l Na 0. 45 0. 47 Totally washed from the pulp suspension in20 e second and thlrd washin~ sta~es:
As dry solids, kg/ton bone dry pulp 94. 2 104. 3 A~ Na, l~g/ton bone dry pulp 22. 7 24. 3 Properties of finallg washed pulp:
Extractlves content (according to SCAN. C7: 62) 0. 62 0.12 25 DCM (dlchlorome~ane), ~c
2~0 17~J~4 As seèn from the T~le, the method according to the in~ren-tion gives ~uite surprisingly a considerably better ~ashing than can be obtained when washing in accordance with ~mown techniques.
Despite the fact ~at ~e mild mechanical treatment was carried out 5 on a pulp suspension which had only been partially washed, ~e method according to the invention surprisingly resulted in a pulp with a much lower extractives content ~an can be obtained when conventionally washing pulp without mechanically treating ~e pulp between washing stages.
One important advantage with respect to energy afforded by ~e Increased extent to which organic substances are washed from the pulp iS that the fuel value of the waste liquor is also increased.
Fur~er, ahigher percentage of the cooking chemicals are recovered.
A comparison of washing the pulp in accordance with known 15 technlques and washing the pulp in accordance with the present Invention shows that more water is removed and more chemicals recovered when uslng the method according to the invention This Is shown by the fact that the volume of waste liquor recovered when applying the present invention was greater, despite the fact that the 20 consistencies of the pulp suspensions entering the presses, in both tests, were maintalned constant ~t 7%.
Accordlng to measurements taken, the washlng water in ~cample 2 also contained slightly larger quantities of dry solids than the wa~hlng water in the Control. Thus, it can be establiæhed that ~e fuel values of the liquors obtained when applying the method according to the invention are higher than ~e fuel Yalues of corres-ponding liquors obtained when washing chemimechanical pulp in accordance with conventional techniques.
Despite the fact ~at ~e mild mechanical treatment was carried out 5 on a pulp suspension which had only been partially washed, ~e method according to the invention surprisingly resulted in a pulp with a much lower extractives content ~an can be obtained when conventionally washing pulp without mechanically treating ~e pulp between washing stages.
One important advantage with respect to energy afforded by ~e Increased extent to which organic substances are washed from the pulp iS that the fuel value of the waste liquor is also increased.
Fur~er, ahigher percentage of the cooking chemicals are recovered.
A comparison of washing the pulp in accordance with known 15 technlques and washing the pulp in accordance with the present Invention shows that more water is removed and more chemicals recovered when uslng the method according to the invention This Is shown by the fact that the volume of waste liquor recovered when applying the present invention was greater, despite the fact that the 20 consistencies of the pulp suspensions entering the presses, in both tests, were maintalned constant ~t 7%.
Accordlng to measurements taken, the washlng water in ~cample 2 also contained slightly larger quantities of dry solids than the wa~hlng water in the Control. Thus, it can be establiæhed that ~e fuel values of the liquors obtained when applying the method according to the invention are higher than ~e fuel Yalues of corres-ponding liquors obtained when washing chemimechanical pulp in accordance with conventional techniques.
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1, A process for washing unbleached cellulose pulp produced from lignocellulosic material in a pulping process including a chemical pulping stage, which comprises washing the pulp with water or an aqueous solution in a plurality of stages, and in between at least two washing stages subjecting the pulp to a mild mechanical working between interdigitated rotating screws at an energy input of from about 7 to about 200 kWh per ton of pulp,
2. A process according to claim 1, in which at least 10% of the solids content of the pulp suspension is removed in at least one washing stage preceding the mild mechanical working.
3. A process according to claim 1 which comprises increasing the solids content of the pulp suspension prior to the mild mechanical working to a pulp concentration between about 10% and about 50%, and then, upon completion of the mild mechanical working, diluting the pulp suspension to a pulp consistency of between about 0.5 and about 13%, in conjunction with mixing with wash liquid in the subsequent washing step.
4. A process according to claim 1 which comprises washing the pulp on filters at an input pulp consistency of between about 0.5 and about 6%.
5. A process according to claim 1 which comprises washing the pulp in a press at an input pulp consistency of between about 2 and about 13%.
6. A process according to claim 1 in which the energy input is within the range from about 10 to about 100 kWh per ton of pulp.
7. Apparatus for improving the washing of unbleached cellulose pulps comprising, in combination, means for adjusting the pulp concentration to within the range from about 10 to about 50%; washing means for washing cellulose pulp with water or an aqueous solution, and separating the waste wash water or aqueous solution; means for subjecting the pulp to a mild mechanical treat-ment in the bite of twin interdigitated rotating screws at an input energy of from 7 to 200 kWh per ton of pulp; means for adjusting the pulp concentration within the range from 0. 5 to 13%; and means for washing the cellulose pulp at substantially the same pulp consistency.
8. Apparatus according to claim 7 in which the means for adjusting the pulp concentration comprises a drum washer.
9. Apparatus according to claim 7 in which the means for adjusting the pulp concentration comprises a screw press.
10. Apparatus according to claim 7 in which the means for adjusting the pulp concentration comprises two stages, a drum washer and a screw press.
11. Apparatus according to claim 7 in which the means for subjecting the pulp to a mild mechanical treatment is a screw defibrator.
12. Apparatus according to claim 11 in which the two rotating interdigitated screws are arranged in parallel to each other in a housing provided with an inlet and an outlet for pulp, and at least one of the screw flights is provided with serrations on its outer periphery.
13. Apparatus according to claim 11 in which the screw defibrator is adapted for operation at superatmospheric pressures up to 500 kPa.
14. Apparatus according to claim 11 including a screw feeder for transferring the pulp from the means for adjusting pulp concentration to the screw defibrator and between each washing stage; and means for transferring the pulp from the last washing stage to a pulp container or to the next processing stage.
15. Aparatus according to claim 7 in which heat from the twin interdigitated rotation screws is captured and utilized in a following treating stage.
16. A process according to claim 1, in which the pulping process includes a mechanical defibrating stage.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8100179A SE443383C (en) | 1981-01-14 | 1981-01-14 | PROCEDURE FOR WASHING CELLULOSAMASSA |
| SE8100179-4 | 1981-01-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1164704A true CA1164704A (en) | 1984-04-03 |
Family
ID=20342871
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000394153A Expired CA1164704A (en) | 1981-01-14 | 1982-01-14 | Method for improving the washing of cellulose pulps |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0056263B1 (en) |
| JP (1) | JPS57139591A (en) |
| AT (1) | ATE14762T1 (en) |
| AU (1) | AU548277B2 (en) |
| CA (1) | CA1164704A (en) |
| DE (1) | DE3265116D1 (en) |
| FI (1) | FI69656C (en) |
| NO (1) | NO160219C (en) |
| SE (1) | SE443383C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4971658A (en) * | 1986-12-17 | 1990-11-20 | A. Ahlstrom Corporation | Method of intensifying the washing of a fiber suspension |
| US5554259A (en) | 1993-10-01 | 1996-09-10 | Union Camp Patent Holdings, Inc. | Reduction of salt scale precipitation by control of process stream Ph and salt concentration |
Families Citing this family (14)
| 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 |
| FI81136C (en) * | 1987-11-11 | 1990-09-10 | Ahlstroem Oy | Method and apparatus for treating pulp |
| US6572697B2 (en) | 2000-03-14 | 2003-06-03 | James Hardie Research Pty Limited | Fiber cement building materials with low density additives |
| JP5089009B2 (en) | 2000-10-04 | 2012-12-05 | ジェイムズ ハーディー テクノロジー リミテッド | Fiber cement composites using sized cellulose fibers |
| EP1574614B1 (en) | 2000-10-17 | 2015-11-11 | James Hardie Technology Limited | Method for reducing impurities in cellulose fibers for manufacture of fiber reinforced cement composite materials |
| AU9690401A (en) * | 2000-10-17 | 2002-04-29 | James Hardie Res Pty Ltd | Method and apparatus for reducing impurities in cellulose fibers for manufactureof fiber reinforced cement composite materials |
| ES2284820T3 (en) | 2001-03-09 | 2007-11-16 | James Hardie International Finance B.V. | FIBER REINFORCED CEMENT COMPOUND MATERIALS USING CHEMICALLY TREATED FIBERS WITH IMPROVED DISPERSABILITY. |
| US7993570B2 (en) | 2002-10-07 | 2011-08-09 | James Hardie Technology Limited | Durable medium-density fibre cement composite |
| CN100402455C (en) | 2003-01-09 | 2008-07-16 | 詹姆斯哈迪国际财金公司 | Fiber cement composite materials using bleached cellulose fibers |
| US7998571B2 (en) | 2004-07-09 | 2011-08-16 | James Hardie Technology Limited | Composite cement article incorporating a powder coating and methods of making same |
| NZ571874A (en) | 2006-04-12 | 2010-11-26 | Hardie James Technology Ltd | A surface sealed reinforced building element |
| DE102007036377A1 (en) * | 2007-07-31 | 2009-02-05 | Voith Patent Gmbh | Use of washing and screw presses for raw material and pulp washing |
| US8209927B2 (en) | 2007-12-20 | 2012-07-03 | James Hardie Technology Limited | Structural fiber cement building materials |
| SE538262C2 (en) * | 2014-06-26 | 2016-04-19 | Valmet Oy | Arrangements for feeding and washing lignocellulosic material and two-stage analysis system comprising the arrangement |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2451963A1 (en) * | 1979-03-22 | 1980-10-17 | Creusot Loire | PROCESS AND INSTALLATION FOR PREPARING AND WASHING A PAPER PULP FROM A LIGNOCELLULOSIC MATERIAL REDUCED IN PIECES |
-
1981
- 1981-01-14 SE SE8100179A patent/SE443383C/en not_active IP Right Cessation
-
1982
- 1982-01-04 FI FI820005A patent/FI69656C/en not_active IP Right Cessation
- 1982-01-05 AU AU79175/82A patent/AU548277B2/en not_active Ceased
- 1982-01-08 AT AT82100102T patent/ATE14762T1/en not_active IP Right Cessation
- 1982-01-08 DE DE8282100102T patent/DE3265116D1/en not_active Expired
- 1982-01-08 EP EP82100102A patent/EP0056263B1/en not_active Expired
- 1982-01-13 NO NO820095A patent/NO160219C/en unknown
- 1982-01-14 CA CA000394153A patent/CA1164704A/en not_active Expired
- 1982-01-14 JP JP57004819A patent/JPS57139591A/en active Granted
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4971658A (en) * | 1986-12-17 | 1990-11-20 | A. Ahlstrom Corporation | Method of intensifying the washing of a fiber suspension |
| US5554259A (en) | 1993-10-01 | 1996-09-10 | Union Camp Patent Holdings, Inc. | Reduction of salt scale precipitation by control of process stream Ph and salt concentration |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS63557B2 (en) | 1988-01-07 |
| FI69656B (en) | 1985-11-29 |
| NO820095L (en) | 1982-07-15 |
| EP0056263B1 (en) | 1985-08-07 |
| EP0056263A1 (en) | 1982-07-21 |
| JPS57139591A (en) | 1982-08-28 |
| DE3265116D1 (en) | 1985-09-12 |
| SE443383C (en) | 1987-07-14 |
| SE8100179L (en) | 1982-07-15 |
| FI820005L (en) | 1982-07-15 |
| AU548277B2 (en) | 1985-12-05 |
| NO160219B (en) | 1988-12-12 |
| FI69656C (en) | 1991-12-24 |
| ATE14762T1 (en) | 1985-08-15 |
| AU7917582A (en) | 1982-07-22 |
| SE443383B (en) | 1986-02-24 |
| NO160219C (en) | 1989-03-22 |
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