CA1065560A - Process for manufacturing improved high-yield pulps - Google Patents

Abstract

PROCESS AND APPARATUS FOR PREPARING
HIGH-YIELD CELLULOSE PULP

ABSTRACT OF THE DISCLOSURE

Process and apparatus are provided for the preparation of improved high-yield cellulose pulps, such as semichemical, chemimechanical, thermo-mechanical, and mechanical pulps, which comprises mechanically defibrating a mixture of particulate ligcocellulosic materials which have been partially pulped and softened to different extents. Part of the raw lignocellulosic material in particulate form is washed, moistened with steam, impregnated with pulping chemicals and pulped to a yield of from about 65 to about 92%.
Another part is treated in similar manner but either not pulped at all or, if pulped, pulped to a lesser extent, The two parts are mixed with-out intermediate washing, after which the mixture is heated to a temperature within the range from about 90 to about 200°C under pressure to obtain softening of the lignin, and delignification, after which the resulting product is mechanically defibrating to form cellulose pulp.

Description

~ss~0 SPE~IF tC~TION

Using lmowll teclmiques it is possible to prepare from Scandinavian softwoods such as spruce, stroll~ chemimechanical cellulose pulps in high yields o about 85C/cc These pulps are however quite difficult to bleach.
5 Moreover, the pulp fibers are extremely resistant to further refining or beating, and hence it is difficult to improve their mechanical strength for the preparation of paper. The paper produced from such pulp also has a rough surface, which renders it less suitable for use as writing and prir~ting paper.
- ~ addition, the paper has a low opacity.
When the yield is increased using known techniques~ to approxi~tely 90tc or higher, a cellulose pulp is obtairled that is more suited for the n~anu-facture of paper, and that ca~ be bleached comparatively easil~. However, th0 mechanical strength is so reduced ~hat unless a stronger cellulose pulp is mi~ed with it, such softwood pulp is unsuitable for the mamlfacture of 15 writing and printing paper.
High-yield cellulose pulps can be produced from hardwoods at a pulp yield of appro~ima~ely 90~c or more. A readily bleached but extremely weak pulp is obtained A~ a pulp yield of approximately 85% or less, a strong pulp is obtained) whlch is less dificult to beat, and which can be 20 readily bleached with a lignin-preserving bleaching agent such as hydrv~en peroxide .
Accordingly, it has been proposed that cellulose pulps from softwoods and cellulose pulps from hardwoods be mixed, in order to im-prove the properties of each, and ovel~come their disadvarltages. However, this 25 is not practical, because such diEferent pulps must be manufactured by ' Inpletely difEerent methods and then mixecl together, whlch i9 not an economic procedure, since it requires doubling the e~uipment and space requirements.
To avo:id thi~, it has been proposed that such high~
yield pulps be prepared by pulp:Lng mixtures of raw particulate hardwood and softwood. This however is unsatisfactory, because the two kinds of woods really require different pulping conditions.
It has been -found difficult to obtain pulps of high strength, which give papers of good surface smoothness.
In one particular aspect the present invention provides a process for preparing cellulose pulps having a yield within the range from about 70 to about 93% from raw lignocellulosic material which comprises heatlng under pressure a mixture of at least two portions of particulate lignocellulosic material, at least one of which is unpulped and the other is partially pulped, and subjectlng the heat-treated mixture, of which one portion is softer than the other, to mechanical defibration.
In another particular aspect the present invention provides apparatus for preparing high-yield pulp from raw particulate lignocellulosic material comprislng, in combination, first and second pressure digester vessels, at least one having an impregnating vessel in flow communication therewith for impregnating particulate lignocellulosic material with pulping chemicals; a steam-moistening vessel having a steam inlet line for steam-moistening particulate lignocellulosic material; dewatering feeder means for conveying steam-moistened lignocellulosic material from the steam-moistening vessel to the impregnating vessel; feeder means for conveying digested particulate lignocellulosic material from the first digester vessel to the second digester vessel; a mechanical defibrator; and feeder means for conveying digested particulate lignorellulosic material from the second digester to the mechanical defibrator.

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The process of the in-vention includes a number of permutations in optional process steps.
~owever before heating under pressure, one portion of lignocellulosic material :is always:
~) washed b) moistened with steam c) impregnated d) partially pulped 2a-` ` 106SS6(~
while allotller portion of lig~locelllllosi(: material is always:
a) washed alltl, in additic)ll, b) either:
(i) moistened with steam or:
(ii) rnoistened with steam ancl impregrlated This portion is never separately pulped.
The separation of the particulate Egnocellulosic material may:
take place:
a) be~ore the washing . b) after $he washing c) after the washing and steam-moistening In one embodiment of the process of the invention, one portion of the raw lignocellu~sic material in particulate form is wash~d, ms)ist-ened with steam~ impregnated with pulping chemicals, then pulped to a .
yield ~vîthin the range from about 65 to about 92~, preferablg from about ~: 78 to ab-~ut 88~/o, and then mix~d without intermediate washing with an~ther porti~n ~f lignocell llosic material which has been impregna$ed with pulp-ing chemicals but not pulped. The mi~ure is hea-ted to a temperature within the ~ange from about ~0 to about 200 S:~, preferably from about 10~ $o about 185C7 under pressure, to o~tain a second partial deligni-fication and s~ftening ~ the first portiun of lignocellulosic material, . after which the partially deligni~ied mixture of chips is mechanically defibrated.
~ a preferred embodiment of the inventiorl, the second pvrtion of lignocellulosic rnaterial is als~ moistened with steam at a temperature within the range from ab~ut 90 C ts) ab~ut 11ûC for at least fi~
- minutes, and impregnated with pulping chemicals, so that a certain 3L~6556~
delignification and sof-tening is obtained after mixt~1re with the first portion during heating oE the mi~h1re of the materials uncler pressure.
The heating under pressure is effectecl so that the final yielcl of the first portion of lignocellulosic material is within the ran~e from about 60 to about 88~, preIerably from about 73 ~o about 85~, and the yield of the second portion of lignocellulosic is within the range from ab~ut 85C/o to about lOO~o~ preferably from about 90 to about 96%. In order to achieve yields within these ranges, the rnaterial mi.~ture should be heated under pressure for a~out l to about 20 minutes, and preferably frvm about 2 to about lO minutes.
The yield is a good measure of the extent oP deligmf1cation and is cletermined with an accuracy of ~ . The yielcls o~ the two portions can be determined after they have been mixed using the following procedure, exemplified for a l: l mixture:
(1) Each portion, the first and the second, is processed separately through all the stages" and the yiel~ls are determined:
. . for the first portion:. . (l) after the digestion 2) after the heating under pressure for the second portion: (l) before the heating under pressure ~ - (2) a~ter the heating under pressure ~ The total yield is then calculated using 50% of the first portion yield and 50% of the second portiorl yield. This separate processing of the first and second portions is then repeated using minimum aud ma~imum treatment conditions and different types of raw materia1s. Finally the ~irst and second portions are processed according to the invention, i. e. g iS56~
the first and secorld portions ~re IMixed 1:1, and lhe proceq~ c~rried out on the mixture. Yield determillations are c~rried out as above. Tlle results ol~tainecl correspond to those previo-lsly ol~tainecl and to the calculatecl ones. The results are thereEore considerecl to be correct 5 and dependable.
Prior to the pulping of the firs~ portlon of lignocellulosic material, it is particularly suitable to impregnate the material with pulping chemicals, and to remo~re the excess pulping chemicals prior to the second pulping under pressure.
After the mixture of particulate materials has been partially dellgnified under pressure, the reslllting product is mechanically defibrated, and optionally subjected to an additional mechanical defi- :
bration or refining process~ and optionally also to a bleaching process, pre~erably with a lignin-preservin~ bleaching agent such as hydrogen 15 peroxide.
The process of the invention is appllcable to any k}n~ of wood. In r generaI, hardwood such as beech and oak is more costly than so~vood, such ~s spruce and pine, but both types of wood can be pul~ed satisfactorily usin~
this process. Exemplary hardwoods which can be pulped include birch, 2~ beech, poplar, cherry, sycamore, hickory7 ash, oak, chestnut, aspen, maple~ alder and eucalyptus. Exemplary softwoods include spruce, fir~ ~
pine, cedar, juniper~ and hemlock.
~ the process of the invention, mixtures of two or more hardwoods and softwoods, of two or more hardwoods, and o~ two or more 25 softwoods, can be processed to form cellulose pulps o~ superio~ paper-m~ing properties.

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In ~e case of wood, it is pr~Eerr~3d that the material be in the form of small piecesO Subdivision o~ th~ wood into chip orm can be done in a chipper, which should provide chips having a size within the range from about 15 to 30 mm by from about 20 to 40 mm, with a thickness of Erom 5 about 0. 5 to about 10 mm. The use o~ thill chips having a thickness from about Q.5 and about 5 mm is particularly suitable, since this facilitates the penetration of the pulping chemicals into the lignocellulosic material .
In accordance with the irlvention, the particulate lignocell~llosic material is washed at least once prior to treatment wi~ steam in order to 10 - remove contaminants, such as pieces of metal, stones, dirt, etcO, which may be attached to the chips. During washing, elevated temperatures can be ~ ,, . . , ,, , . . . . _ . . . . .
used. In a pulp mill, surplus heat from the pulp manufacturing process and friction heat from the refiners can be used to heat the waæhing liquid or for other purposes outside the mill. Washing the chips at elevated 15 temperatures give a mvre effective wash, and the heated chips do not require as long a residence time in the subsequent steam treatment stage.
~n equalization o~ the moisture content of the chips is also obtained, which in turn results in a pulp of more aniform quality.
~ollowing the washing, at least one portion of the chips is 20 steam treated. - Another portion can be, but need not be. At least one of -the portions of chips is always impregnated with pulping chemicals sub-sequent to washing and steam-mvis~ening and then pulped and passed to the common pressure ~essel~ ~nother portion of chips may bè passed to the common pressure ve~sel dlrectly subsequent to its washing or subsequent 25 to washing and steam-moistening. AlternatiYelyg this second portion after washing and steam-moistening also may be impregnatecl witb pulping cilemicals prior to bein, passec~ to the common pressure vessel. Thi~
second portion of cllips is, however, not subjected to ~ny separate pulpillg operation. In the commoll pressur~ vessel one portion o~ the mai;erial, the one previou~ly clige~ted, may optionally be fu~ther clelignified ancl another portion may here be delignified for the first time on its route through the stages of the process. One portion of chips is th~us pulped ~o a lesser or greater extent than the ~ther, so that the two portions are not at the same pulping stage when leaving the common pressure ve~el;
one is harder than the other.
lû The separate pulping of the first portion ls carriecl out at a temperatùre wi-thin the range from about 100 to about 180C~ for from about 2 to about 24Q minutes.
In the impregnation stages any pulping chemicals can be used, for example, chemlcals for a sulfate or sulfite pulping, or an oxygen gas/aLkali pulping, such as aqueous sodium hydrosulfide solution~ aqueous sodium hydroxide, aqueous sodium p~lysulfide solution, having a pN
from ab~ut 2 to about 13, preferably from about 5 to about 9.
The pulping liquor employed for ehe first and second partial àigestions o~ the chips in accordance with the invention accordingly can comprise any alkaline material as the alkali, including not only sodium hydroxide but also sodium bicarbonate,~mmonium hydroxide, and magnesium hydroxide The pulping can be carried out using sul:Eur dioxide? or oxygen gas .. . ~, .. . .. ~ . .. ...
and aIkali, ~if desired. The proportion~ of the pulping chemicals in the liquor is likewise n~ critical, and can be varied as desired. The chips are impregnated to about 100~ by weight of pulping chemicals solution.

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Following the first pulping stage, without an interroecliate washirlg, the t~o portions of material, of which at l~ast one is partially plllped~ are then combined, after which the.mixhlre is subjected to a partial p~lping stage by treatin~ at a supe:ratmosplleric pressure within the range from about 1 to about 11 at.mospheres" prefer~bly within the range from about 1. 5 to about 9 atmospheres~ at a temperature within the range from about 90 to about 200C, preferably from about 100 to about 185C, for from about :l to about 20 minutes.
If desired, the portion of lignocell~llosic material not partially digested can be impregnated with pulping chemicals prior to being combined and subjected to the cornmon pulpillg stage.
In ~he drawings: -Figure 1 is a flow sheet which shows the various steps in the process af the invention;
_gure 2 is a schematic view in longitudinal section showing apparatus for carrying out the process of the invention; and Figure 3 is a cros~ectional view taken along the line 3-3 of Figure 2.
The following Examples are illustrative of pre:Eerred embodiments in accordance with the inventlon~
The difficlllties in obtaining pulps o~ high strength which give papers of acce~able surface smoothness from hardwood and softwood and mixtures thereof when using the processes known prior to this invention are illustrated by the experiments described below as Controls 1, 2, and 3O

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CO~T ROI, l _ _ ___ Digestion oE the same type of softwnod (long fiber wo_) to clifferent yields.
Spruce chips having a length of approxi~nately 30 mLn~ a width of approximately 15 mm, and a thickness of apprc)~imately 3 mm were 5 washed ~nd moistened with steam at atmospheric pressure or ten minutes.
The chips were then pressed in a laboratory press, and allowed to e~pand by absorption of aqueous pulping liquor comprisillg 50 g/l sodium hydroxi~e calculated as Na20, and sulEur dioxide SC)2 in an amount of 65 g/l. The pH
of this solution was 6~ OD The chips absorbed 1, 000 ml of this solution ` per 1, 000 g of dried chipso The impregnated chips were then charged to a digester, and heated with saturated steam to 170C and a pressure of 8.4 kplcm2 to obtain a partlal digestion.
The first batch (A) of chips was digested for S minutes at 170C .
The second batch (B) was digested for 25 minutes at 170C. Each of these digestion times can be considered- as the total digestion time, since the time needed to reach maximum digestion temperature was less than 1 minute. The chips in batches A and B were defibrated separately in a disc refiner under digester pressure, with the simultaneous addition forming an aqueous pulp 20~, suspension in dilution water of the defi~rated pulp from the refiner.
.. ..... . . . . . . .
The d~fibratecl pulp was then blown to a hydrocyclone, to separa~e steam from the pulp suspension~ The consistency of the resulting pulp suspension -was approximately 30~c, and the temperature was 87C. The defibrated pulp was then refined in a second disc refiner. Dilution water was added in 25 the second disc refiner to a pulp consistency of approximately 23~7c during .
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the reining. Thc reEined pulp was then cleaned and dewa-terecl to ~ pulp consistellcy o approximately 35~/c, after which it ~vas bleached with 3~/c hydrogen peroxide and 008G/c sodium dithionite. The pulp suspension was theri beaten 1, 000 re~olu~i~ns in a laboratory P F 3 mill, and formed 5 into laboratory sheets in order to test the properties of the pulp and its suitability for the manufacture of paper. The Eollowing results were obtained:
TABLE I
Pulp Batch A Pulp Batch B
Pulp yield ~c 9102 84 Degree o$beating, Schopper-3~iegler 56.5 15 Brightness after bleaching, SCAN, ~c 77.4 70.7 Breaking length, meters 4200 6800 Tear Eactor 72 84 Light scattering coef~icient, rn2~g 36.7 21 4 Air permeability, SCAN P26:68, ml/min 980 - 2300 The results show that 13atch A had a higher ~egree of beating and brigh~ess than Batch B, demonstrating that the pulp of Batch A is more readily beaten and bleached. The pulp of Batch A also had a be~er opacity~ -20 which is determined by measuring the lighl scattering coefficlent~ and IS

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directly proportional thereto. On the okher halld? the pulp of Batch B had a higher mechanical strength.
The paper from Batch B had an unacc eptable writing surface, as shown by the high permeabilityD
5 ~ ONTROL 2 Digesting I:he same type of hardwood (short fiber wood) to different yielcls.
Control 1 was repeated, with the difference that birch chips were used instead of spruce. All other processing conditi~ns were the same.
The following results were obtained:
TABLE II
Pulp Batch A Pulp Batch B
Pulp yield ~ 93.0 84.2 Degree of beating,- ~ch~pp&r-Riegler 1205 18 Brightness after bleaching, SCAN ~/c 81.5 8007 Brea~ing length, meter~3 270 4900 Tear factor 13 63 Light scattering coefficient, m2~g 37.5 31D3 Air permeability SCAN-P26:68, ml/min ~3000 1173 The res- lts sh~w that hardwood treated in accordance with the 20 conventional procedure at a high yield provicles a pulp which although readil~
bleached has an extremely low ~nechanlcal strength. When the pulp yield is reduced to 8402~G, as in Batch B the strength of the pulp is improved considerably, while the pulp is still readily bleached, and less difficult to beatO The papers from each batch were not acceptable for wriiting, as shown 25 by the high permeability.

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Dîg~esting mixtures of softwood ~lld hard~vood to high yisld.
.
Batch ~, a mixture of 50~/c bi:rch chips ~nd 50'7c spruce chips by weight, the chips ha~ring the same dimensions as given in Control 1 except 5 that the chip thiclmess was 2 mm, was moistened with steam and impregnated with pulping liquor in the manner recited in Control 1. The mixture of chips was then pulped at 16~C for 20 minutes. The partially delignified chips were defibrated, refined, and bleached, as described in Colltrol 1. The pulp obtained was beaten 500 revolutions in a laboratory PFI mill, ancl lû laboratory sheets then formed~. The sheets were tested to determine their paper properties.
The second Batch B of chips was a mi~ture of 50% birch and 50~c pine chips. This batch was treated under exactly the same conditions.
The following results were obtained:
TABLE llI

Batch ~ Batch B
Spruce Chips Pine Chips Pulp yield ~G 8900 89.5 Degre~ of beating, Schopp~r-:Riegler 40 5 14.5 - ~0 Brightness after bleaching, SCAN % 7804 7~.5 ~3re~ leng~5 meters - 390û 3100 Tear factor 68 63 Lig~ht scattering coefficient, m2/kg 36.1 33.4 Air permeability, SCAN~P26:68 1560 ~3000 .

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The results show that bolh pulps were readily bleachecl, and had good light-scattering properties. The mechanical strength of the pulp was lower however than that of a pulp produced solely Erom softwood, i.e., spruce chips, Control i, at a corresponding yield. The surface smoothness 5 o ~aper produced from this pulp would be unacceptably low, as apparent from the high permeability. These pulps gave a hard and brittle paper, having poor stretch an~; straill properties.
The effectiveness of the process and apparatus o~ the present invention in overcoming the disadvantages of the known pulps as described 0 above is illustrated in the following ExamplesO

The manuEacture of chemimechanical pulp from two difierent types o~ wood~
birch and spruce, of ~hich the birch chips a~e ~tllped m~re7 usin~ the pr~cess of Figure 1.
Technical grade birch chips having ~n approximate size of 30 by 15 mm and a thickness of 5 mm (designated chip stream A in the flow sheet of Figure 1) were washed in a chip washer 1, and moistened with steam in a steam-moistening vessel 2 at atmospheric pressure and a temperature o~
100C for ten minutes. The steam- moistened chips were then passed to an 20 impragnating vessel ~ by way of a screw feeder 3, so constructed that the chips were compressed while they were being transported to the vessel 4, so that en route they were dewatered from a moisture content of appro~imately 6$ck to a moisture content of approximately 50'~c. Subsequent to the passage through ~e screw feeder, the chips were allowed to expand in the impreg-25 nating vessel 4~ while they were absorbing pulping liquor. The pulping )6SS~

liquor was passed to the vessel ro~n a chemical preparation stage 5, andmaintained at constant level in the vessel 4. As the chips swelled in the impregnation Yessel, they absorbed approximately one liter of digestion liquor :Eor each l~ilogram o chips. The pulping liquor co.mprised sulfur 5 dioxide in admi~ture with sodium hydroxide, the amo~mt of sodium hydroxide being 50 g/17 calculated as Na2O and the amount of sulfur dioxide being 65~ g/I. The pulping liquor had a pH of 6. 0.
The impregnated chips were then passed to the digester 6~ in which they were subjected to a vapor phase pulping process by supplying lû steam directly thereto at a superatmospheric pressure of 7. 5 kpjcm2 through the line 7, giving a pulping temperature of 170C in the digester 6. The chips were held in the digester 6 for twenty min~rtes.
Following the digestion, the chips were fed to the pressure vessel ~ by means of a screw feeder 8, whlch was of the same construction 15 as the screw :Eeeder 3, and which e~pressed surplus p.ulping liquor and steam from the chips~ The pulping liquor thus recovered could be used for impre~ating the second stream of spruce chips, designated as B in Figure 1 in an impregnating vessel 23, or for preparing fresh pulping liquor in the chemical preparing stage 5, or passed directly to an apparatus 10 for 20 recovery of spent pulping chemicals~
After the digestion the chip stream A from the digester 6 had a pulp yield of 83~
The stream of spruce chips designated as B in Fig~re l was of chips having the same dimensions as the birch chips of stream A. The 25 chips were passed directly to the common pressure vessel 9, after being .

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washed in the chip w~sher llo The chips in stream B were mixed in the pressure ~essel 9 with the chips from stream ~ in equal proportions by ~,veightO
Excess steam was fed to th~ pressure vessel 9 through the line 12 from the screw feeder 8 at a superatmos~leric pressure o 2.5 kpfcrn3.
In the pressure vessel 9, the mixture of chips ~ and B were subjected to a deligni~ication in the vapor phase at a temperature o 125C for three l~inutes. Under these conditions, the stream o.E chips B was brought to a pulp yield o appro~imatel~ 95%0 The resulting steam-heated mixture of p~rtially delignified chips A and only very slightly delignified chips B was then passed to a defibrator 14, a disc reiner, by means of a screw feeder 13 at the bottom of the pressure vessel 90 The chips were - defibrated in the defibrator 14 at a superatmospheric pressure o.~ 2 kp/cm2.
at a temperature of appro~imately 120C~Co The defibrated pulp was then passed to the hydrocyclo~e 15, for separating steam from the pulp cooling water being passed to the hydrocyclone through the line 16~
From the cyclone, the pulp was ~ed to a further disc refiner 1~, whare the pulp was further refined at atmospheric pressure, and at a temperature of approximately 85C and a pulp concentration of 25~ZC. The pulp was then screened whlle beirlg diluted with water in a pressure screen 18 a~ a l~Zc pu~p consistency. The screened pulp was then cleaned in a vortex cleaner 19.
The rejects fraction from the pressure screen 18 and the vortex .
c~è~ner 19 was dewatered to a pulp consistency of 20~/c, and ~en refined in the refiner 200 The refined reiects fraction pulp was returned to the pressure screen 18D

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The accepts 1action rom the pressure ~;creen l8 and the vortex cleaner l~ was dewatered to a pulp c~nsistency (1~ 20~., and bleached with hydrogen peroxide.
The total yield of pulp thus obtained was 87~/c, and the brightness, 5 78/c SCANo The strength and optical properties of the pulp were such that the pulp c:ould be usecl for the manuacture of writing ancl printing paper.
EXAMPLE 2 .
The manufacture of chemimechanical pull? from five different types sf wood~
o which birch-aspen-beech chips are pulped more, using the process of :Figure 1.
A mixture of birch chips, aspen chips, and beech chips in the proportion of 40: 40: 20 designated chip stream ~ in the flow sheet of ~igure 1 was washed in a chip washer l and moistened with steam in a ~team-moistening vessel 2 at at.mospheric pressure and a temperature of 100C for ten minutes. The steam-moistened chips were 15 then passed to an impregnating vessel 4 by way of a screw feeder 3, so constructed that the ch ips were compressed while they were being transported to the vessel 4, so that they were dewatered from a moisture content of approximately 65~c to a moisture content of approximately 50~7co .Subsequen~
to ~he passage through the screw feeder, the chips were allowed to expand 20 in the impregnating vessel 4, while they were absorbing pulping liquor. The pulping liquor was passed to the vessel from a chemical preparation stage 5, and maintained at constant level in the vessel 4. As the chips swelled in the impregnation vessel1 they absorbed approximately one liter of digestion li~or for eachkilogramof ~hips The pulping liquor comprised sulfur dioxide 25 in adm~ure with sodium hydroxide, the amount of soclium hydroxide being 50 g/l,calculated as Na20,and the amo~mt o sulfur dioxide being 65 g/lo The pulping liquor had a p~I of 6. 0~

' OGT 2 9 1~75 1~65S~
The impreg,nated chips were then fed to ~ligest0r 6, in which they were subjected to a vapor p~lase pulping process by supplying ~he steam directly thereto at ~ superatmospheric pressure of 7 . S kplcm~ through the line 7, giving a pulping temperature of 170C in the digester 6~ The chips 5 w~re held in the digester 6 for twenty minutes~ .
Follow~g the digestion, the chips were fed to the pressure vessel 9 by means oP a screw feeder 8, which was of the same construction as the screw feeder 3, and which expressed surplus pulping liquor and steam from ~: the chipso The pulping liquor thus recovered could be used for impregnating 10 ~ the second stream of chlps, designated as B in Figure 1, in an Impregnàting vessel 23, or for preparing fresh pulping liquor in the chemical l?reparing stage 5, or passed directly to an apparatus 10 for recovery o spent pulping chemicals . :
fter the digestion, the chip stream A from the digester 6 had 15 a pulp yield OI 83~G.r The stream o-~ chips designated as B ~n Figure 1 was a mixture of pine and spruce chips in the proportion 60: 40, the chips having the sarn.e dimensions as ~he chips of stream A. The chips were passed directly to ~
the common pressure vessel 9, after being washed in the chip washer 11 D The 20 ~ chips in stream B were mixed in the pressure vessel 9 with the chlps from stream A,: in eqùal proportions by weightO
Excess steam was fed to th~ pressure vessel 9 through the line 12 from the screw ~eeder 8 at a superatmospheric pressu:re o:E 2 . 5 kp/cm2.
~ the pressure vessel 9, the mixture of chips A and B were 25 sub~ected to adelignificati3n in the vaE)or phase ~t a temperatur6~ of .

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125C for three minutes. Under tllese conclitions, the stream of chips :B
was brought to a pulp yield oE approximately 95~rtc- The resulting steam heated ~ixture o partially delignified chips A and only very slightly delignieied chips B were then passed to a clefibratc~r 14, a disc refiner, by 5 ~eans of the screw feeder 13 at the bottom of the pressure vessel 9. The chips were defibratecl in the de~ibrator 14 at a superatmospheric pressure of 2 kp/cm2 at a temperatùre of approxirnately 1~0C. The defibrated pulp was then passed to the hydrocyclone 15, for separating steam from the pulp, cooling water being passed to the hydrocyclone through the line 16.
10From the cyclone, the pulp was led to a further disc refiner 17 where the pulp was further re:fined at atmospheric pressure at a temperature of approximately 85C and a pulp concentration o:E 25~C~ The pulp was then screened while being diluted with water in a pressure screen 18 at a 1~c pulp consistency. The screened pulp was then treated in a vortex cleaner 19.
15~ The rejects fraction from the .~ressllre scre~n 18 and the v~rte~
cle`aner-~ was dewatered to a pulp consistency oi: 20'3~c and then ref~ned in the refiner 20~ The re~vned xejects fraction pulp was returned to the pressure screen 180 The accepts fraction from the pressure screen 18 and the vortex 20 cleaner 19 was dewatered to a pulp consistency of 20%, and bleached with ` ~ hydrogen peroxideO
The total yield of: pulp thus obtained was 87~c~ and the brigh~ess, 77~c SCAN. The strength a~d optica1 properties of the pulp were such that ~he pulp could be used for the manufactllre of writing and printing paper and ~5 cardboardO

106SS~0 E~AMPL:E 3 The manufacture of chemin~echanical pulp from one type of wood, spruce, using~ the process of Figure 1.
Technical gracle spruce chips having an approximate size of 5 30 by 15 mm and a thiclmess of 5 mm (designated chip stream A in the flow sheet of Figure 1) were washed in a chip washer 1 and moistened with steam in a steam moistening vessel 2 at atmospheric pressore and a temperature of 100C for ten minutes. The steam~moistened chips were then passed to an :
impregnating vessel 4 by way of a screw feeder 3, so constructed that the 10 chips were compressed while they were being transported to the ~v~ssel 4, so that they were dewatered from a moisture content of approximately 65~k to a moisture content of approximately 50 YC . Subsequent to the passage through the screw feeder, ~he chips were allowed to expaIId in the impregnating vessel 4 while they were absorbing pulpingi:liquor. The pulping li~uor was 15 passed to the vessel from a chemical preparation stage 5, and maintained at constant level in ~he vesssl 4. As the chi~s swelled in the impregnation vessel, they absorbed approximateb one liter of digestion liquor for each kiloD~ram of chips. The pulping liquor comprised sulfur dioxide in admixture with sodium hydroxide, the amount of so~ium hydroxide being 5~ g/l ;
.
~0 calculated as Na20, a~d the amount of sulfur dioxide being 65 gllo The pulping liquor had a pH of 6. 0.

The impregnated chips were then fed~ to the digester 6, in which - they were subjected to a vapor plhase pu~q?ing process by supplying the steam :~ ~ directly thereto at a superatmospheric pressure oP 7.5 kp/cm2 through the line 25 77 giving a pulping temperature of 170C in the digester 6. The chips were held in the digester 6 for twenty r~linutes.
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:

, ~06556~

Following the digestion, the chips were fed to the pressure ves~el 9 by means of a screw feeder 8, which was ~f the same construction as the screw eeder 3, and which en route pressed surplus pulping liquor and steam :Erom the chips. The pulping liquor thus removed could be used for impreg-5 nating the second stream of spruce chips, desigrlated as B, in Figure 1 in animpregllating vessel 2~, or for preparing fresh pulping liquor in the chemical preparing stage 5, or passed directly to an apparatus 10 for recovery of spent pulping chemicals.
A-fter the digestion, the chip stream ~ from the digester 6 had a lO ;: pulp yield of 83~
The stream of chips designated as B in Figure 1 was spruce chips having the same dimensions as the spruce chips of stream Ao The chips were p~ssed directly to the common pressure vessel 9, after being washed in the chip washer llo The chips in stream B we:re mixed irl the pressure 15 ~ vessel 9 with the chips from stream ~, in equal proportiorls by weigh~.
Excess steam was fed to the pressure ~essel 9 through the :~ .
line 12 from~the screw îeeder 8 at a superatmospheric pressure of 2.5 kp/cmZ.
In the; pressurg vessel 9, the mixture of chips ~ and B was su~Jected to a deligniQcahon in the vapor phase at a temperature of 20 1 25C for three minutes. Under these conditions the stream of chips B was : brought to a pulp yield of approximately 95~c- The resulting steam-heated ~: mixture of partially delignified chips A and only very slight~y ~eli~nified ~: ~ chips B were then passed to a defibrator 14, a disc refiner, by means of a screw feeder 13 at the bottom of the pressure vessel 9. The chips were 25 defibrated in the defibra~r 14 at a superatmospheric pressure of 2kp/cm3.
' ~ ' ' ' . .

. ~ 20 .
. ~
.

i n~;s.~6~
at a temperature of appl~oximately 120C . The defibrated pulp was then passed to the h~drocyclolle 15 for separating steam from the pulp, cooling ~vater being passed to the hydrocyclone throu~h the line 16.
From the hydrocyclone, the pulp was led to a further disc refiner 17, where the pulpwas further reEined at atmospheric pressure, and at a temperature of appro~imately 8~C and a pulp concentlation oE 25~c.
The pulp wa then screened while being diluted with water in ~ pressure screen 18 at a l~c pulp consistency. The screened pulp was then treated in a vorte~ cleaner 19.
The rejects fraction from the pressure screen 18 and the vortex c~eaner was dewatered to a pulp consistency of 20~C and then refined in the refiner 200 The refined rejects fraction pulp was returned to the pressure screen 18.
- The accepts fraction from the pressure screen 18 and the vortex :
15 ~ cleaner 19 was dewatered to a pulp consistency of 20/c~ and bleached with hydrogen pero~ide. The total yield of pulp thus obtained was 89~cl and the brightness, 78% SC~N. The strength and uptical properties of the pulp were such that the pulp could *e used for the manufacture of writing and p~inting paper, cardboard, arld soft tissue paper~
~ , .

The manufacture of chemi~nechanical pulp from a batch of chips comprising one type of wood, birch, divided into two str0ams, both of which were . .
partially pulped, using the process of Figure 1.
Technical grade birch chips having an appr~imate si~e of 30 by 15 mm and a thickness of 3 mm (designated chip stream A in the flow ~ .

~6556~

sheet o~) were washed in ~ chip washer 1, and moistell~d with ste~
in a steam-moistening vessel 2 at atmospheric pressure and a temperature of 100C for ten minutes. The steam-moistened chips were then passed to an impregnating vessel 4 b~7 way of a screw feeder 3, so constructed that the 5 chips were compressed while they were being transported to the vessel 4 so that they were dewatered from a moisture content of approximately 65yC to a - moisture content of approximately 50~Zco Subsequent to the passage through the screw feeder, the chips were allowed to expa~d in the impregnating ves~el 4 while they were absorbing pulping liquor. The pulping li~uor was passed to the vessel from a chemical preparation stage 5, and m.sintained at constant level in the vessel 4. As the chips swelled in the impregnation vessel, they absorbed approximately one liter of digestion liquor for each kilogram of chips. The pulping liquor comprised sulfur dloxide in admhYture with sodium hydroxide, the amount of sodium hydroxide being 50 g/l calcula~ed as Na2O and the amount of sulfur dioxide being 65 g/1. The pulpillg llquor had a p~I of 6~ 0.
The impregnated chips were then led to a digester 6, in which~
.
t hey were subjected to a vapor phase pulping process by suppl~ing the .
- steam directly thereto at a su~eratmo~pheric pressure of 7. 5 kplcm2 through the line 7, giving a pulping temperature of 170C in the digester 6. The ; chips ~were held in the digester 6 for twenty minutes~
Following $he digestion, the chips were fed to the pressure vessel 9 by means of a screw feeder 8, which was of the same construction as the screw feeder 3, and which e~pressec~ surplus pulping liquor and steam 2~ from the chips en rou~:e. The pulping liquor thus removed could be used -.

1~65S60 for impreg~ating the se~oncl strealll o chips, designated as B in Fi~ure 1, in all impregnating vessel 23, or for preparing resll pulping liq~lor in the chemical preparing stage 5, or passed directly to an apparatus lO for recovery oE spent pulping chemicals.
Tlle stream of chips B comprised birch chips having the same dimensions as the birch chips of stream ~. The stream B was washed in a chip washer ll, and moist~ned with steam in the ~tearn moistening vessel 21 ~t atmospheric pressure at a temperature of 100C for 10 minutes. The steam-moistened chips were then passed to the impregnating vessel 23 by means of the screw feeder 22, which was of the same type as th~ screw feeder 3. In the impregnatingvessel 23, the chips were impregnated with the same kind of pulping liquor as used in the impregnating vessel 4. The impregnated chip6 were then passed from the impregnating vessel 23 directly to the pressure vessel 9, where the chips were mi~ed with the chip stream A
in the proportion 30: 70 by weight.
.
The mixture of chips was then treated with direct steam at a superatmospheric pressure of 6.5 kp/crh~. The steam was admitted through the line 24. At this pressure, the temperature of the steam was 160Co The steam digestion process was continued for 15 minutes. I~ this way, the total mixture was partially delignifled, and the yield o~ the chips of stre~m A
was approximately 79~c, while the yield of the chips af stream B was approximatel~ 90~c ` The chips were defibrated in the defibrater 14 at a superatmos-pheric pressure o~ 2 kp/cm~ at a temperature of approxim~tely 12ûC`C. The 25 de-fibrated pulp was then passed to the hydrocyclone 15 for separatillg steam , .

106556~t from the pulp~ co~ling water being passed to the hydrocyclone through the line 16.
From the hydrocyclone, the pulp was led to a further disc x efiner 17, where the pulp was further re:Eined at atmospheric pressure, and at a 5 temperature o.E approximately 85 C and a pulp concentratioll of 25~CD The pulp was then screened ~vhile being diluted with water in a pressure screen 18 at a 1~/c pulp consistency. The screened pulp was then treated in a ~ortex cleaner l9o The re~ects fraction frorn the pressure screen 18 and the vortex 10 cleaner 19 was dewatered to a pulp consistency oE 20~, and then refined : in the refiner 20D The refined rejects fraction pulp was returned tothe pressure screen 18.
The accepts fraction from the pressure screen 18 and the vorte~
cleaner 19 was dewatered to a pulp consistency of 20%, and bleached with 15 hydrogen peroxideO The total yield of pulp thus ob$amed was 85~ andthe brightness,, 81~C SC~No The strength and optical properties of the pulp were such that the pulp could be used for the manufacture of writing and printing p~per, cardboard and similar productsO

20 : The manufacture of chemimechanical pulp from three diEferent types of wood, .
birch, aspen, and spruce, the birch and aspen being pulped more, and the . . .
spruce pulped less, u~ng the process of Figure lo : A mLxture of birch and aspen chips in the proportion 50: 50 by - weight having the appro~imate size of 50 by 15 mm and a thic~mess of 1 mm 25 (designated chips stream A in the flow sheet of Figure 1) was washed in a ~06~56~

chip washer 1 and moistened with steam in a steam-moistenin~ vessel ~ at atmospheric pressure and a temperature of 100C for ten minutes. The steam-moistened chips were then passed to an impregnating vessel ~ by way of a screw feeder 3, so constructed that the chips were compressed while 5 they were being transported to the vessel 4, so that they were dewatered from a moisture content of appro~imately 65~ to a moisture content OI ap-proximately 5û~c. Subsequent to the passage through the screw feeder, the ~chips were allowed to expand ~ the impregnating vessel 4 while they were absorbing pulping liquorO The pulping liquor was passed to the vessel from 10 a chemical preparation stage 5, and maintained at contant le~el in the vessel 4. ~s the chips swelled in the impregnation vessel, they absorbed approximate~r one liter of digestion liquor for each kilogram of chips. X'he pulping liquor comprised sulfur dioxide in admixture with sodiu~n hydroxide, the amount of sodium hydroxide being 50 g/l calculated as Na20 and the 15 amount of sulfur dioxide being~65 g/l~ The pllping liquor had a pH of 6Ø
The impregnated chips were then fed to the digester 6, in which ;; ~ they were sul~jected to a vapvr phasa pulping process b~ supplying steam direcM~ ~ereto at a supera~mospheric ~ressure of ~.~ kp/cm2 through the line 7, giving a pulping temperature of 170C in the digester 6. The chips 20 were held in the digester 6 for twenty minutes.
, FQllowing the digestion, the chips were fed to the pressure , . .
vessel 9 by means of à screw feeder 8, which was of the same construction as the screw feeder 3, and which e~pressed surplus pulping liquor and steam ` ~ from the chipso The pulping liquor thus ramoved could be used for impreg-25 nating the second stream of chips, desigllated as 13 in Figure 1, in an :1~655~

impregnatirlg vessel 23, or for preparing ~resh pulping liquor in the chel~lic~l preparing stage 5, or passed dlrectlg to an apparatlls 10 for recovery of spent pulping chemicals.
The stream of chips B comprised spruce chips having the same 5 dimensions as the birch alld aspen chips of stream Ao The stream B was washed in a chip washer 11 and moistened with steam in the steam-moistening vessel 21 at atmospheric pressure at a temperature of 100C for 10 minutes.
The steam-moistened chips were then passed to the impregnating vessel ~3 by means of the ~crew feeder 22, which was of the same type as ~he screw 10 feeder 3O ~ the impregnating vessel 23, the chips were impregnated with the sarne kind of pulping liquor as used in the impregnating vessel 4. The impregnated chips were then passed rom the impregnating vessel 23 directly to the pressure vessel 9, where the chips were mixed with the chip stream A
in the proportion 30: 70 by weight.
15~ The mixture of chips was then treated with direct steam at a superatmospheric pressure of 6.5 kp/cm2. The steam was admitted through the line 24. At this pressure, the temperature oE the steam was 160Co ;~ The steam~igestion process w~s continued for 15 minutes. In this way, the total mixture was partially delignified, and the yield of the chips of 20 ~tream A was approximately 79~c, while the yield of the chips of stream B
was approximately 90~;.
The chips were defibrated in the defi~rater 14 a~ a superatmospheric pressure of 2 kp/cma at a temperature of approximately 120C. The defibrated pulp was then passed to the hydrocyclone 15for separating steam from the 25 pulp, cooling water being passed to the hydrocyclone through the line 160 ' 06~56~

Frolll the hyclrocyclone, the pulp was led to a further disc refiner 17, where the pulp was further refined at atmospheric pressure, and at a temperatlre of approximately 85~C ancl a pulp concentration of 25~c. The pulp was then screened while being diluted with water in a pressure screen 18 5 at a 1~; pulp consistency. The screened pulp was then treated in a vortex cleaner 19..
: The rejects fraction from the pressure ~creen 18 and the or~ex~cleaner .19 was dewatered to a pulp consistency of 20% and then refined in the refiner 20. The refined rejects fraction pulp was returned 10 to the pressùre screen 18~
The accepts fraction from the pressure screen 18 and the vorteæ cleaner 19 was dewatered t~ a pulp consistency ~ 20%, and bleached with hydrogen peroxide. The total yield of pulp thus obtained was 84a/C and the brightness, 79~Yc SCANo The strength and optical properties ~f the pulp 15 were such that the pulp co~ ld be used ~or the maml:facture of writing and pr~nting paper, cardboard and s~ft tissue paper.

, ~ - : . .
The pulping process can be carried out in the digester in the liqu~d phase or in the vapor phase In the liquid phase pulping, a less concentrate: pulping liquor can be used When the pulping is effected ~n 20 the liquid phase? the chips are passed directly from the steam-moistening . ~
vessel 2 to the digester 6 through the line 26, while the pulping chemicals - are passed to the digester 6 from the chemical preparation stage 5 by way , of line 27~ In this event, the temperature for the pulping can be within the range from about 100 to about 180~C at a superatmospheric pressure 25 : within the range from abbut 0.5 to about 13 kp/cm2. A suitable pulping time .

' .

2~

~06SS~;O

is from about 2 to 240 mirlutes.
When the chip stream ~ is pulped or deligni:fied in the digest~r 6, there IS ol~tained in accordallce with the inventioll a pulp yield of rom about 65 to about 92C/C, al~d preferably :Erom about 78 to about 880/C.
S The chip stream B subsequent to washing in the chip washer 11 can be passed directly to the pressure vessel 9, and mixed therein with the chip stream A~ It is also possible subsequent to the ste2rn-moistening step 21 to impregnate the chip stream B with a small amount of pulping chemicals, prior to feeding this stream to the pressure vessel.

The residence time of the chip mixt-lre in the pressure vessel - .
9 is not more than 20 minutes. A preferred residence time is from about 2 to about 10 minutes. In the pressure -~eb.~el 9, the superatmos-pheric pressure Is preferab~y held within the range from about 0. ~ .~o about 9 kp/cm8.
~ The chips treated in the pressure vessel 9 anà passed to the ~ ~ ~ defibrator 1~ may also be de~ibrated at atmospheric pressure, and the : ~ ~ defîbratlng means may comprise a conical refiner or a screw defibrator~
A suitable type is that marketed under the trademar~ FROTAPUI~PEl~.
When two defi~rators are used, part of the chip stream from the 2û pressure vessel 9 can be defibrated without subjecting the chips to ~ressure, while the remaining chips are defi~rated under pressureO When the chips are defibrated without pressure, the chips from the pressure vessel must first pass through hydrocyclone 2~ to separate the steam from the chipso If desired, diluting and cooling liquids can be passed to the hydrocyclone 2 5 ~ by way of a line 16, as can also liquids containing bleaching agents, such as ~L~655~(~

bleaching waste liquors, for example. Subsequent to being defibrated, the pulp may conveniently be subjected to a further defibra~ion or beating step, - for exampl~, in a disc refiner, conical lllill or screw defibrater 17, or in any other suitable form of defibrater refining or beating apparatus.
The two chip streams may also be defibrated separately~ in which case each of the separate streams of chips may be subjected to a subsequent refining operation. The two~ pulps obtained subsequent to the defibration can also be rnixed together, and processed in a common refiner.
The chips which are defibrated under pressure n~ay subsequently be beaten individually, while the chips defibrated 'dt atmospheric pressure may also be beaten individually. One advantage afforded by beating puip - batches separately after defibration is th~t the different batches can be-subjected to different degrees of beati-ag. When using two defibrators downstream of the pressure vessel, the defibrators may be set to different levels of defibration.
~- ~ Since the beaten pulp mag contain incompletely defibrated chip pieces called shnes, it may be necessary to screen the pulp to separate ~he shives and recycle them. In this way there is obtained a fraction com-prising coarse pulp and shives. This fraction is called reject pulp, aIld is normally dewatered to a relatively high pulp consistency? preferably from about 15 to a~out 30~c~ and is processed ~ suitable beating means, m which the shives are defibrated to single fibers. The reject fibers are then normally passed to the flow ~f pulp passing to the pulp screening apparatus.
The screened pulp is dewatered, preferably on filters, and can then be bleached or dried directly. In an integrated cellulose processing factory, ~3L065S60 the bleached or unbleached pulp is passed to the paper m1ll directly after passing the scl~eening apparatus, or after being subjected to an intermedi~t~
dewatering process~
Suitable bleaching agellts for bleaching the pulp obtained include the so-called lignin-preserving bleaching agent, such as peroxides and dithionite. Other bleaching agents include the borohydrides, peracetic acid, thioglycolic acid and hydroxyl amine.
For the purpose of comparing the products o~tained in acGordance with the invention witb those obtained using known procedures, a number of comparative laborator~7 ruals we~e carried out, and the results are shown in ~the follow7ng Examples E~AMPLE~ 6 . ~
The process of the invention compared with Batch ~, Control 3O
~ ~ ~- Spruce chips having a length of appro~imately 30 mm, a width of approximately 15 mm, and a thickness of appro~imately 2 mm, designated chip streàm B, were washed and then moistened with steam at atmospheric pressure for ten minutes. The chips were pressed in a Llboratory press, and were permitted to swell in an aqueous pulping liquor of pH 6.0 comprisingr :::
~ ~ ~ 50 g!l sodium hydroxide ~NaO~I) calculated as Na8O, and S()2 65 g/l. The~
.
` 20 amount o~ pulping solution absorbed by the chips during this impregnation ; ` ~ was 1, 000 ml per l, 000 g of dry chips.
A stream oE chips designated as chip stream A comprising birch chips having the ~ame dimensions as the spruce chips was treated in a ` parallel stream in exactly the same manner as the chips stream Bo In accordance with the invention, the birch chips were then pulped , ~06S56C~
separately for 10 minutes, after which the chips were mixed together in a pressure vessel with the illlpregnated, but not pulped, spruc:c chips, in the proportion of 1:1 by weight. The resl~lting chip mixture wa~ pulped in the vapor phase at a temperature of 160C correspondin~ to a superatmospheric pressure of 6. 5 kp/cm2 for 10 minutes . The total coo~ing time Eor the stream of birch chips was 20 m~nutes, including the 10-minute pulping period during which the chips were pulped separately, and the 10-minute period during which they ware pulped together with the spruce chips.
The mixture of partially digested chips was then defibrated in a disc refiner under digester pressure while simultaneously adcling diluting water. The defibrated pulp blown to a hydrocyclone for separatillg steam from the pulp suspension. The con5istency of the suspension was approxi-mately 30~c, and the temperature was 87C. The defi~rated pulp was then refined in a second disc refiner, and diluting water was added so tha~ the - 15 chips were refmed at a pulp consistency o~ approximately 23'~c. The refined ~; pulp was then screened and dewatered to approxlmately 35~7c pulp consistency, ; and then bleached with 3~G hydrogen peroxide and 0. 8~/c sodium dithionite .
The bleached pulp was beaten 500 re~rolutions in a laboratory ~ mill, and ~ormed into laborator~7 sheéts for evaluation of its paper pr~perties.
- ~The table below compares the resuits obtained with the results - ~ from the pulp design~ted Batch A, Control 3. The difference between Example 6, the pulp obtained and in the process of the inYentionJ and . .
Batch A, Control 3, is that the birch chips in the process accorclin~ to the invention were cool~ed separately for 10 minutes at a temperature of 160C
and together with the spruce chips for 10 minutes ~t a temperature of 1~0~C, ~' ' ' .

- .

while the birch and SpI uce portions of the pulp of Batch A, Control 3, w~re cooked together for 20 minutes at 160Co The results obtained are shown in the :Eollowing Table:
TABLE IV
Control 3 ]Batch A . E~AMPLE 6 Pulp yield, ~c . 89. 0 88. 7 Degree of beating, Schopper-~iegler 40.5 42.0 Brightness after.bleaching, SCAN ~c 80O4 80.2 ~ Breaking length, meters 3900 ~ 4800 .
.
~: ~ Tear factor 68 76 Light sca~tering coeEficient, m2/~g 36.1 34.8 Air permeability SCAN P26:68 ml/min 1560 1110 Elongation, ~c 3 4 4 . :
Double fold number 6 18 The results shown. in the Table demonstrate that the process according to the invention provides a stronger paper than the process of : Control 3j while retaining the remaining desirable properties o the pulp.
Thus, the process of the invention produces a pulp which gi~res a strong 20 ~ paper having a uni:Eorm and smooth surface, and good stretchal3ilityO

The process accor~ing to the invention compared with Batch B, Control 3.
.. .._.~ . _ Pine chips having a length of approximately 30 mm, a width of approximately 15 mm, and a thickness of approximately 2 mm, designated - 25 chip stream B, were washed and then moistened with steam at atmospheric .

1~655~0 pressure for tell ~inutes. The chips were pressed in a laboratory press, and were permitted to swell in a pulping liquor of pH 6. 0 compsising 50 g/l sodium hydro2~ide ~NaOH), calculated as Na20, and SO2, 65 g/lo The amount o pulping solutioll absorbed by the chips during the impregnation was 1, 000 ml 5 per 1, 000 g of dry cllips .
A stream of chips designated as chip s-tream A comprising birch chips having the same dimensions as the pine chips was treat~d in a parallel stream in exactly the same manner as the chip stream B.
- ~ accordance with the invention, ` the birch chips were then 10 pulped separately for 10 minutes, after which the chips were mi~ed to~ether in a pressure vessel with the impregnated, but not pulped, pine chips in the proportion of 1:1 by weight. The resulting chip mixture was pulped in the vapor phase at a temperature of 160C corresponding to a superatmospheric pressure of 6.5 kp/cm2 for 10 minutesD The total pulping time for Ithe stream l5 of birch chips was 20 minutes, including the 10-minute pulping period during which the chips were pulped separately, and the 10-minute period during which they were pulped together with the pine chips.

.
The mixture o partially digested chips was then ~e~ibrated in a disc refiner~ under digester pressure while simultaneously adding diluting 20 water. The def~ibrated pulp was blown to a hydrocyclonefor separati~g steam ~ : .
from the pulp suspen~ion. The consistency of the suspen~ion was approximately 30C,~C, and the temperature was 87~Co The defibrated pulp was then reE~led in a second disc rPfine~and diluting water was added so that the chips were refined at a pulp consistency o~ approximately 23~ZC. The refil~ed pulp was 25 ~then screened and dewatered to appro2~imately 35C,~c pulp consistency7 and ~en . J L

:

~Q~;~;iS~O

bleached with 3~/c hydrogell p~roxide and 0. 8C,7C sodium dithionite.
The bleached pulp was beaten 500 revolutions in a laboratory mill, and formecl into laboratory sheets for eval-lation of its paper properties~ The Table below compares the results obtained with the 5 pulp clesignated as Batch B, Control 3. The difference between the pulp obtained in the process of the invention and that obtained in Batch B, Co~rol

3, is that the birch chips in the process according to the invention were coo}~ed separately for 10 minutes at a temperature of 160C and together ~vlth the pine chips for 10 minutes at a temperature Df 160C, while the birch and 10 pine portions OI the pulp of Batch :13, Control 3, were cooked together for 20 minutes at 160C.
The results of the experiments are shown in the follo~ving TableO

TABLE V
(:~ontrol 3 ~ Batch B E~A~qPLE 7 Pulp yield, C,~C 89 . 5 89 . O
Degree~vf beàting, Schopper-Riegler 1405 26.0 Brigh~ess aEter bleaching, SCAN ~/c 77.5 77.8 Breaking length, meters 3100 3900 Tear :factor 63 70 Light scattering coe-Eficient, l$L2/~g 33.~ 33.6 - ~.4ir permeability, SCAN-P26:68 ml/min ~3000 1820 ` Elongationy ~c ~ 2 . 7 3 0 3 : Double fold number ~ 7 The d~ta in the Table show that the pulp pr.oduced in accordance with the invention yields a stronger paper exhibiting good surface smoothness~

~L~)SS~i60 good elollgation, and a high toug~h~ess, while retainillg good ~ptical prop-erties. Using a mixture of pine chips and birch chips, a considerably higher degree of beating is obtainecl in the pulp in accorclance with the invention than in the pulp produced in accs)rdance witll Batcll B, Control 3.
- - ~
EXAM:PLE 8 The process of the invention compared with a miYture of mechanical and .. . . ~ .. .
chemical pulpo - .
In the manufacture of paper7 mechanical pulp is often m~xed with chemical pulp to produce wood paper, the chemical pulp giving the 10 papèr its strength, while the mschanical pulp mostly contributing to good formation, l.e., a good ~miform distribution oE the fibers in the paper, and a high degree of opacity.
A control r-rh w~s carried out in which there was produced a : ` ~ mixture of 35~G peroxide bleached mechanical pulp having a brightness of 15 ~ 80~o SCAN and 65~ chemical pulp having a brigh~ness ~ 91% S~AN. This J ~ ~ mixture was beaten'500 revolutians 'in a labol ator~' mill~ after ;which . . .
laboratory sheets were formed; These`sheets were tested for paper prbp- ~
~ ~ , erties, and the r~sults were compared with the results obtained v7ith the - paper produced in accordance with the invention in Example 6.

~ The results obtai~ed àre compared in the Table below:

' ~ ' , . . .

.

TABLE VI

Mechanical/chemical pulp E~AMPLE 6 Pulp yield, ~k 65 88.7 Degr~e of beating, Schopper.-:Rieg~er 31 42 Brightness, after bleaching, SCAN ~c 83 ~0.2 Breaking length, meters 3200 4800 Tear factor 76 76 ~. Llght scattering coefficient, m~g 41.2 34~8 Air permeability SCAN P26:68, ml/min 1150 1110 The results show that the tensile strength of paper rmanufactured from the pulp produced in accordance with the invention is higher than the tensile strength o:E a conventlonal wood cellulose paperO The only properties which were somewhat impaired were the opacity and ~he brightness. Thus, 15 USillG the process according to the invention, it:is possible to produce a : high quality paper exhiblting properties equivalent to those obtained by mixing mechanical and expensive chemical pulps~ and this at a total pulp yield, which is approximately 24~C higher. ~.
t is not at present understood why ~e process of the invention 20 gives a pulp which, in addition to being readi3~ bleached and readily beaten .: ~and e~ibiting favorable optical properties, also.has such a high mechanical strength that it ca~ be used for the manufacture of writing and printing paper without the addition of reinforcing pulp o~ high mecharlical strength~ It ma~r be that the beatixlg process carried out in the process according to the 25 invention is more efficient7 since two kinds of chips that have been delignifled to different degrees or not at all delignified are defibrated and refined together;

5S~
the chips that are pulpe~ less, or unplllped, which are hardcr, a~si9t in defibrating th~ chips which are pulped mvre, and are so~ter. Th~ harder chips may also assist in fibrillating the indi~iclual ~ibersg and fibrillatit)n may occur at an earlier stage of the defibralîng and refining process than ~vh~n relatively so~t chips are beaten separately.
A further ~actor contributing to the favorable results may be that the softer chips fill the the disc pattern in the disc reEiller more rapidly than do the hard chips. When the discs are filled rapidly~ the energy applied by the refiner is ùsed more eIfectively, and a larger working area and a longer residence tlme are obtained during passage o~ the pulp through the grinder. It is also possible that different types of fibers coming into intimate contact with each other during the defibration p~ocess develop binding potentials between the fibers, which is not possible when the chips are deIibrated and beaten separa~ely.
An important advantage of the process of the invention is that it produces a high pulp yield, which is important ln view oE the scarcity ~E wood i n comparison to the mounting demand. Thus, each expedient that makes it possible to recorer a larger percentage of the pulp from natural wood is of ~eat significance.
~ By the process of the invention, it is possible to produce a high~
yield pulp which provides paper e~fhibiting good mechanical strength, good surface smoothness, good elongation, low brittleness, and good optical properties. In addition, the pulp is also readily beaten and bleache~
certain cases, the process according to the invention produces a pulp with lower energy input than other known processesO Since, in accordance with SS~O

the invelltion, cliEferent t~pes of wood can be coml:~:irlecl to advantage, tlleinvention also allows an effective recovery o:E available raw materials in forest stallds o:E several types of wood, ancl t}liS even when the various typesare present in small amounts. ~nother advantage a:E:Eorded by the invention is that the cooking waste liquor obtainecl has a higher solids con-tent, therebyimproving heat economy in recovery of the pulping chemicals. The pulping llquor also has a higher extract content than the pulping liquors used in joint cooking processes, which results in a lower e~kract content ~ the finlshed pulp.
Tn the process of the invention, the same e~uipment can to a very large extent be used :Eor the separate process steps, as opposed to other processes, in which dif:eerent types of pulp from different mills are mixed together. The chemical prep~ration plantl the comrslon pressure vessel, and the disc refiners are examples o~ apparatus which are commonly used in the different process steps. Other apparatus which are used in common in the process of the inventiQn are the screening~plant, the pulp drying system, and the chemicals recovery systemO
The apparatus for carrying out the process of the invention shown in Figures 2 and 3 comprises two vertical pressure ~essels 36, 38, withm.
the Ip~er portion of which ~ere is arranged an impregnating vessel 32, 44, which is provided with a solution ir~let line 33, 46 and vertical conveyer ,~ screws 34, 47, into which chips can be fed via a dewatering screw feeder 30, 43 fr~m a steam-m~istening vessel 28, 41 with steam inlel~ line ~9, 42, and intowhich a stream ~, B of chips to be pulped is passed ~ .
~ Arranged ~l ~he~bottom o~ the presæure vessel 36, 38 is a screw : , 3~

~ss~

con~eyer 39, 5~ for conveying material under pressure from the bottom of the press-~e vessel, from vessel 36 to vessel 38~ ànd from ~essel 38 to a de-fibrator 51.
Operation o~ the apparatus is as follows:
~ Particulate lignocellulosic material such as wood chips are washed and then divi~led into two streams A and B,, which are fed into the ;~ . apparatus as streams A and B in Figure a.
The chip.~stream A passes to the steam-moistening vesse~ 28, in which the chips are treated with stea~ conveyed to the vessel through .
:the line 2~ The steam-moistened chips are then transported to the Impregnating chamber 32 by the screw :Eeeder 30, while simultaneously being dewatered thereby. The water squeezed out from the chips is collected and recycled by way of the line 31.
`~ ~ ; An aqueous solution contain~ng the impregnating pulping chemicals is passed to the impregnating chamber 32 by way ~f the line 33.
The impregnated chi~s are passed through the impregnat~ng pulping liquor : ~ by means o~ vertically~extending convey~r screws 34. The impregnated chips then pass over the upper edge 35 of the impregnating chamber 32, and .
descend through the digester 36. The positioning of the impregna~ing - .
chamber 32 and the two vertical conYe~r~r screws 34 in the digester 36 is more clearly shown in~ igure 3, which is a cr:oss-sectional view OI the digester 36 taken along the line 3-3 of Figure 2.
Steam is passed to the digester 36 throu~h the line 37, for heating the chips during the digestionO To enaure that the chips have been digested to the desired e~tent when the chips `reach the bottom o the vessel, the 1~55ÇiC) dwell time of the chips which are cont~luously descending thl ough the clig~ester 36 is adjusted by the speed of rotation of the screw ~eeder 39 which draws the chips fl om the cligester 36 to the press~u~e vessel 38~ During their passage through the screw eeder 3g, a portion of the cooking liq.uor 5 is squeezed from the partially digested and softened chips~ The cooking waste liquor squeezed from the chips is recovered by way o~ line 40, and recycled after regeneration ~nd chemicals recovery.
The chip stream A is mixed in the pressure vessel 38 with the chip stream B~ The chip stream B passes through a s$eam-moistening , 10 vessel 41, to which steam is passed through a line 42, and the chips are conveyed to an impregnating chamber 44 by means of a dewatering~ screw feeder 43. The water squeezed from the chips is led off by the line 45, ~nd recycled. The impregnating chamber 44 may contain impregnating pulping chemicaIs~ or only water, as desired. The impregnating liquor, whether 15 water or pulping liquor, is ~assed to the chamber 44 by the line 4~.
The chips are conveyed througll the-impregnating chamber 44 by means of two vertically extendi~g con~Teyer screws 9;7, similar to those shown in Figure 3O
After passing through the impregnating chamber 44, the chips 20 ~ are carried over the upper edge 48 of the chamber and then desceQd through the common pressure ~essel 38~ where they are mixed with the chips of chip stream A~ which are subjected to a further partial digesti~n during ` ~ ~ - tr~verse of vessel 38 .
Steam is supplied to the pressure vessel 38 through the line 49, 25 and the ~ ture ~Ç chips is treated with heat under press~lre. After the pressure treatment the partially cligested chips are passed ~ the screw ' ~

i5S6~
--~ feeder 50 to the defibratnr 51. The dwell time in vessel 38 is adjusted by the feed rate of the screw fee~ler 50. The pulp from the defibrator is passed tllroug~h a hydrocyclnne (not sh~wn) to sep~rate steam from the pulp, after which the pulp may opti~nall~ be refinecl in a further refining stage, alld is then screened and bleaclled.
At the ends of the screw feeders 30 and 43 coImected to the digester 36 ancl the pressure vessel 38, respecti~vely, sealing means are provided, which ma~e it impossible for steam to escape from the screw feeders, but these seals are not shown in Fi~ure 2.

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Claims (27)

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. A process for preparing cellulose pulps having a yield within the range from about 70 to about 93% from raw lignocellulosic material which comprises heating under pressure a mixture of at least two portions of particulate lignocellulosic material, at least one of which is unpulped and the other is partially pulped, and subjecting the heat-treated mixture, of which one portion is softer than the other, to mechanical defibration.

2. A process according to claim 1, in which the unpulped and the partially pulped portions of lignocellulosic material are of the same type.

3. A process according to claim 1, in which the unpulped and the partially pulped portion s of lignocellulosic material are of different types .

4. A process according to claim 1, in which a first portion of raw lignocellulosic material in particulate form is washed, moistened with steam, impregnated with pulping chemicals, partially pulped to a yield within the range from about 65 to about 92%, mixed without intermediate washing with a second portion of lignocellulosic material which has been washed or washed and moistened with steam but not pulped, the mixture is heated to a temperature within the range from about 90 to about 200°C, under pressure, to obtain a second partial pulping and softening of the first portion of ligno-cellulosic material, and the pulp mixture is then mechanically defibrated.

5. A process according to claim 4, in which the unpulped and partially pulped portions of lignocellulosic material are of the same type.

6. A process according to claim 4, in which the unpulped and partially pulped portions of lignocellulosic material are of different types.

7. A process according to claim 4, in which the second portion of lignocellulosic material prior to mixing with the first portion is also impregnated with pulping chemicals subsequent to being washed and moistened with steam at a temperature within the range from about 90 to about 110°C
for at least five minutes, and then partially pulped, so that a partial pulping and softening of the second portion is obtained after mixing with the first portion during the heating of the mixture of the materials under pressure.

8. A process according to claim 4, in which the heating under pressure is effected for from about 1 to about 20 minutes so that the final yield of the first portion of lignocellulosic material is within the range from about 60 to about 88%, and the yield of the second portion of lignocellulosic material is within the range from about 85% to about 100%.

9. A process according to claim 4 in which, prior to the second pulping of the first portion of lignocellulosic material, the excess pulping chemicals are removed and recycled.

10. A process according to claim 4, in which the partial pulping is effected with pulping chemicals selected from at least one of the groups consisting of chemicals for sulfate pulping; chemicals for sulfite pulping, and chemicals for oxygen gas/alkali pulping.

11. A process according to claim 1, in which the mechanically defibrated mixture is subjected to bleaching.

12. A process according to claim 11, in which the bleaching is effected with lignin-preserving bleaching agents.

13. A process according to claim 1, in which at least two of the portions of lignocellulosic material are both softwood.

14. A process according to claim 1, in which at least two of the portions of lignocellulosic material are hardwood.

15. A process according to claim 1, in which at least two of the portions of lignocellulosic material are softwood.

16. A process according to claim 1, in which at least one of the portions of lignocellulosic material is hardwood, and another is softwood.

17. A process according to claim 1, in which the lignocellulosic material is in the form of chips having a size within the range from about 15 to 30 mm by from about 20 to 40 mm, with a thickness within the range from about 0.5 to about 10 mm.

18. A process according to claim 1 in which the mechanically defibrated mixture is subjected to an additional mechanical defibration.

19. A process according to claim 18 in which the mechanically defibrated mixture is subjected to bleaching.

23. A process according to claim 1, which comprises heating at a pressure within the range from about 1 to about 11 atmospheres.

21. Apparatus for preparing high-yield pulp from raw particulate lignocellulosic material comprising, in combination, first and second pressure digester vessels, at least one having an impregnating vessel in flow communi-cation therewith for impregnating particulate lignocellulosic material with pulping chemicals; a steam-moistening vessel having a steam inlet line for steam-moistening particulate lignocellulosic material; dewatering feeder means for conveying steam-moistened lignocellulosic material from the steam-moistening vessel to the impregnating vessel, feeder means for conveying digested particulate lignocellulosic material from the first digester vessel to the second digester vessel; a mechanical defibrator; and feeder means for conveying digested particulate lignocellulosic material from the second digester to the mechanical defibrator.

22. Apparatus in accordance with claim 21, in which the dewatering feeder means is a dewatering screw feeder.

23. Apparatus in accordance with claim 21, in which the feeder means is a screw feeder.

24. Apparatus according to claim 21, in which the impregnating chamber is provided with feeder means for feeding impregnated lignocellulosic material to the digester.

25. Apparatus according to claim 21, comprising a second steam-moistening vessel, and means for conveying steam-moistened particulate lignocellulosic material therefrom to the second digester vessel where it is blended with digested particulate lignocellulosic material from the first digester vessel.

26. Apparatus according to claim 21 comprising a second impreg-nating vessel, and means for conveying impregnated particulate lignocellulosic material therefrom to the second digester vessel where it is blended with digested particulate lignocellulosic material from the first digester vessel.

27. Apparatus according to claim 21, in which the vessels and feeder means are arranged in direct flow connection for continuous operation so that particulate lignocellulosic material can continuously be fed into the system at the steam-moistening vessel, and removed as defibrated lignocellulosic material after the mechanical defibrator.