Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 7 ~
~O91/06700 ~ ~; PCT/~E90/00721
A METHOI) OF PRODUCING CELLULOSIC PULP
The present invention relates to a method of producing
mechanical or chemimechanical cellulosic pulp, in par-
'' ticular paper pulp, with a low energy input, by disin~
tegrating and beating (refining) wood material in atleast one stage. ..
.. . .
An object of the present invention is to effect the
disintegration and beating of the wood material in a
0 manner,which substantially decreases the total energy
consumption, as described in more detail here below.
.
A reduction in energy consumption or an improvement in
the paper forming properties of the pulp produced is
achieved when applying the present invention to
present-day manu~acturing processes using high pulp
consistencies, and also.when applying manufacturing
processes at lower pulp consistencies, ~or instance in
accordance with the method of manu~acturing mechanical
and.,chemimechanical pulps.described.in.Swedish Patent.
Application,.No.--8801731-4, publishedlon November 6,.,-
1989:. -. : ~...~.~ . .,,.. I,~ - - :
The,beating of cellulosic material at~low.pulp consis.
tencies is a method which has long been~used to~improve
the paper forming properties of the fibres. This, how-
~eyer,japplies solely to,,,.li.gnin-free,or,j.substantially,;
lignin,~ree.~ibre , such,ast,fibres produced;in.accor-
~dance~-with.,the:-.sulphateior,$ulphite.methods....As,;:,to.,~ s
mechanically produced-!pulpsj..as.~e.g..;thermomechanical
~Ç PU1PL ,(T~P).~orr,,chemimechanical,pulp (CTMP~j~,it;has~?no~,
bee~,considered,~hat refining.at-,low consistency,~,~ol,~
c:alled~after.-beating,.~,,can:!be~;used)for other objects ~J,~.
than to i~prove~;the,ilight scattering ~apacity of the
pulps and to slightly shorten the ~ibre length, there~
with improving:the,~ormation.wh~n producing paper. ,--
,
.
', '1"` `, ':.,`;
WO9l/06700 20 ~30 4 8 Pcr/sEgo/oo721 ~
Investigations have earlier been carried out to explore
the possibility of subjecting TMP produced at high
consistencies to a subsequent beating process at lower
consistencies.'For instance, Scan Research Report
409/1984 reports work carried out with respect to
energy consumptions when after-beating pulps at low
concentrations as compared with rsfining tpe pulps at
high concentrations. The results of this investigation
show that the freeness of TMP can be lowered by `'
10-30 ml without impairing the strength properties of
the pulp to any substantial extent, and that energy
savings of 50-150 kWh/tonne can be achieved. The total
energy consumed, however, was quite considerable, in
the order of'magnitude of 1600 to 2300 kWh/tonne.
Pulp and Paper Magazine of Canada, Vol. 81, No. 6, June
1980, pages 72-80 (N. Hartler) reports attempts to
reduce the energy consumption of chip refining pro-
cesses. One proposal made in this report is that the ~ ' -
chemical environment around the fibres is changed by ~
adding chemicals. It was found,tha~ energy consumption
coul~ be reduced by 30%,'by adding~sodium'hydroxide,' '
although the total consumption still remained in the'
region of about 1300 kWh/tonne. A poorer yi~ld was
obtained with-these tests, however,'and the brightness
was impaired considerably.
In'an~articlé~published in Svensk Papperskidning,,1982,
pages;R 132-139~(P' Axelson~andiR. Simonson),'-there'jis
a report on the~effect'of~;impregnating~!chips with~
sulphite~during~the r~fining stage, inter alia-on -~ ''' ,
energy consumpt'ion~ The~energy-diagram''showed a minimum
subsequent-to-the~absorption of a given'~quantity~ofl '
sulphité.rThe-ltotal''energ~consumption;~howev'er, was;"
still'at a'high-level~of 2000 kWh/tonne.~
Attempts have'also been made'to t:reat thermomechanical
';` 20~`30~8
WO9l/06700 PCT/SE90/00721
pulp with fibre-modifying chemicals. It has been found
that the energy consu~ption can be reduced by at most
30%, when the defibred pulp is treated with ozone in a
two-stage method,.prior to the refining process. This
can only be achieved, however, at the cost of the
yield.
It has now been found possible, in accordance with the
'present invention, to produca mechanical paper pulp at
a considerable reduction in energy input.
It has not been possible until very recently to reduce
khe energy consumed when producing mechanical pulps, by
defibring the wood material by beating at low consi-
stencies. The reason for this is,because it was notknown how to avoid~,fibre cutting and therewith an
excessively.low'tensile and tear index of the resultant
mechanical.pulp and, at the same time, improve the pulp
bonding properties. This manufacture of pulp at low
energy inputs is achieved by.disintegrating and beating
wood material in~at:;least two stages.- The material-is
coarsely disintegrated:in-a ~irst stage ~t a.consis- -
tency e,xceeding 20~,:wherein acid groups in the wood
? material are,,neutralized and the material thinned to a
consistency.of,l-10%,:and..then beaten in one or.more
stages.-~' ~ 3''' ' .'''~ , ' :: r: -
It~:hasibeen found that::the.energy..input~can"be~:further~~reduced by-means~`,ofnthe pre~ent inventionj..which~.~,is:
~-;characterized.'by.adding to,.thef~ood:material prior,.to
the beating process an agent which has,,the ahility-,to
~orm complexes with polyvalent (2 valences or more)
metal'~;ion~,~~particularly~,cal~ium,ions, so-.called com-
~lexingl,(sequestering):f.agent,~:so~,that the.~cont~nt-;of.
: calcium''~and polyvalent~7~(~.~alences.:or..more),ions~in~n,the ,~:
wood-*o the ~ajor-,part,are:,replaced-by sodium-ions.,The
aim-~with th2~ion exchang~ to.sodium ~orm in this manner
.
WO91/06700 PCT/SE90/00721
is to provide as good conditions as possible to obtain
elektrolytic swelling by causing charged group~, as
e.g. carboxylic and/or sulphonic acid groups, to repel
each other.-Said swelling contributes to the fact that
the fib~e material can be delaminated (fibrillated)
more easily and leniently at refining and beating.
According to a first embodiment of the invention,.the
disintegrating and beating processes are carried out in
one and the same stage, wherein a complexing agents and
preferably also sodium hydroxide for the purpose of
neutralizing released acid groups are added to the wood
material, preferably after steaming. Surplus liquor:is
then pressed from the wood, before beating is com-
menced. The advantage with this embodiment is that it
can be utilized directly in a number of present-day-
- operational mills which produce mechanical and -:.
chemimechanical pulps. . .
. .
.. . ......... , . - .
In a second, more suitable embodiment.which affords a
-greater..:reduction in-energy input,.the coarse disin-
tegration and beating processes..are~carried.out.:in .
mutually different stages...In this~regard, the :...
- . complexing agent,~and.also the preferably.added sodium
hydroxide,- can:be introduced prior to coarsely dis=:
integrating the wood or subsequent thereto. It may.~be
advantageous to effect both additions prior to the
-.coarse:disintegration stage,.par.ticularly in~*he!case
of.~chemimechanical:pulp,;..and therea~ter.ipress~.excessive
oliquid.frQm~lthe.:.suspension.priori.to said~.coarse~disin~
.tegration stage. ..~ t
~:-.r;~ ,r ~- J~r ^:: r~ Jr-~7 ~ ~ J~
^The complexing agent is no~mally.addedfto theiwood~
materialr3in~.~an amount:corresponding..to the-.amount.ofj
~:'polyvalent~metaljionsJin-.the)wood~material.- This~amount
..--ican~:correspond to 8-l30~mmolf:per~kg o~:wood,~ suitably
:::15-50 ~mol.per kg.of:wood. A con~on amount of poly-:
.
20~30~8
~ WO91/06700 '''` ' PCT/SE90/00721
~... ~
valent metal ions in Swedish spruce chips is 20-30 mmol
of wood, for instance 25 mmol. The complexing agent
will preferably be one in the alkali metal form, and
then particularly in the sodium form. A complexing
agent in'the potassium form can also be used in certain
instances with'respect to economy, whereas the remain-
ing alkali metal forms would be too expensive in normal
operation. ' ~
.,
The amount of complexing agent required can also be
calculated on'the basis of the amount of calcium and
other polyvalent metal ions present in the wood mate-
rial, and determining the molar quantity of these ions
and adding the complexing agent in a quantity corres-
ponding to -~ 50% of this molar quantity. A suitable
range is ~ 30%. Substantially equimolar quantities can
also be use'd, of course.
In the case of one particularly suitable embodiment,
the pulp'is produced by disintegrating and beating wood
material in at~-least two stages. The material is
coar'sely~di's`inte`grated~in tXe first~stage andrth'e acid '~
groups present in the~wood'polymers are neutralized,
either completely or partially,'' suitably by the addi-
tion of sodium hydroxide. The material suspension is
thin'ned'prefexably'with a water at a temperakure cor~-
responding''''to"'thêS;softening~temperature of-the,lignin,
i.e:-a-temperaturë' of!40-9~C~valid at~'a refining fre-
~ quency~''o~'about~l~Her~z.rForlhigher loading~frequencies
~;(e~g~'"a'round'1O4 Hertz)'-'like the frequencies~occurring
during-;technical'refining~"a:~higher~temperature~range.
Said thinning water suitably have an ion strèngth (de-
fined as the total content of cations expressed as
mol7 1 r ( litrej)r~of'tat'?most r 0'~ 05~qmol~per~ilitre-.fThetmate-
~3rial L iS ~ then ~éaten-''in-~one or~more~stages-atia
consistency of preferably l-10% and an energy input`
which is normally in total at most 500 kWh per tonne of
WO91/06700 2 0 7 3 0 ~ 8 PCT/5E90/00721 ~
i,.,,,, ,," .
material. In this case, the complexing agent is added
prior to the beating process and can even be added
prior to the first stage. In the case of chemimechani-
cal pulp, it is preferred to add the complexing agent
and also to press surplus liquid from the material
suspension prior to coarsely disintegrating the
material. In the case of mechanical pulp, the complex-
ing agent is normally added to the suspension between
the coarsely disintegrating stage and the first beating
stage. Appropriate parts of the method described in
Swedish Patent Application No. 8801731-4 can be applied
in this case and these parts of the known method are
incorporated here as a
reference.
The suspension consistency during the coarse disinte-
grating stage will therefore preferably be high, e.g.
above 20%. It is also suitable to use a low energy
input.during the coarse disintegrating stage,.e.g. an
. .input.of at most 800.kWh.per.tonne wood material, and
the sodium hydroxide is(preferably added in an amount
- which-wi-ll no~-appreciably exceed the.-amount required
to.neutrali2e.the acid groups present in the wood poly-
mers,.at most 225 mmol.per kg.
The complexing agent will~preferably be a substance
~cbapable of.forming.complexes-lwith pol~valent metal~.
- ions,;primarily::.calcium~ions. The complexing agen is
~ prefe~ably;-usediiin:~its~alkali~:metalrform,-~primarily.its
~rsodium form;n-~so-as ~o.deliyer sodium ionsrlto-~the~wood i~.
and-itake-up:.calcium..and.other polyvalent~-metal .ions..
~from~,the-wood. ~ s.~ ,` t~::;2
-~,..`Suitable.groupsiofjcomplexingJagents and3examplesiof
specific complexingtagents~iare~given in thei~following ~-
Table~ ?.~
, : .
~;WO91/06700 2 ~ 73 ~ ~ ~ PCT/SE90/00721
Amines-ethyl amines, iminea_tcarboxvlates, ~hosphona-
tes, sulphonates):
Desiqnation
DTPA
Diethylene triamine-pentaacetic acid .
EDTA
Ethylene-diamine-tetraacetic acid
HEDTA
Hydxroxy ethyl ethylene-diamin~-triacedic acid
NTA Nitrilo triacetic acid
DHEG
N,N-di(2-hydroxy ethyl) glycine
: TEA Triethanol amine
NTP Nitrilo-trimethylene.phosphonic acid
MIDA
N-methyl imine-diacetate
IDA Imine diacetate : - .
HEIDA~
Disodium-hydroxy-ethyl imine-dia~etate - --
DTPMPA
~~Diethylene-triamine-pentam~thylene-phosphonic acid
`; ~ ("De~uest")~
EACDA .~
Ethyl amine-cyclopentene-l~dithiocarboxylic acid
CDTA~
~~''t''?~ 'CyclohexyIe'ne-diamine-triaceticiacid- ;~
3 o . t ~ r~l t ~ r ~
Poly~-carboxylates (including poly-phosphonate and poly-
~sulphonate):~f~ n;~ '3 :.`..,, ,ii .~.i ~., ~ ~ ,, " ' ~1; ~,
PQC~iPs:~ly-(hydroxycarboxylate) ,rM~iup~to rabout,~6000
Polyvalent carboxylate:
., .,. ~ ., .. , ~ ., . , ~ . . ..... . . ..
- . :
,
. , - , . . .
.- : , , : ~
WO91/06700 - , ~, s Q` :~; PCT/SE90/00721
- Na-citrat
- Gluconicacid alacton
- Na-tartrate
Pol~valent phosphate: ~ -
STPP
Na-tripolyphosphate
Remainder:
M~PP
Bis-phosphonyl methyl phosphonic acid
- Poly (sodium-a-hydroxyacrylate)
. .i :
The invention will now be described in more detail with
reference to working embodiments and also with ree-
rence to the accompanying drawing, in which
Figure 1 is a flow sheet illustrating an inventive
embodiment for producing a pulp o~ the CTMP-type with
high consistency refining asi-a first stage; --;
~, . .
`~ Figure 2 is a.flow:sheet illustrating an inventive
embodiment for producing pulp of the TMP-type with high
consistency refining as the first stage; and
Figure 3 is a flow sheet which illustrates another;
inventive embQdiment~for.:producing TM~ this embodiment
using an extruder as the first disintegrating stage.
" S~ qci ~
Figure 4 is a flow sheet illustrating another~embodi-
ment according to the invention ~or producing CTMP,
this'~embodimentiusing a:,plug"scre~ s.first-jdisinte-
grating stageO
Figure 5 is a flow sheet illustxating an embodim~nt
' ' ' , ' ' . ~ ':
,
.' ~
~ WO91/06700 2 0 7 3`; ~ 4i8 PCT/SE90/00721
similar ~o that according to ~igure ~, but for produc-
ing TMP.
Example 1
The flow sheet shown in Figure 1 relates to the produc-
tion of chemithermomechanical pulp. Spruce chips were
steamed in a first stage and then impregnated with a
solution containing a'^givèn quantity of complexing
agent, in this instance Na4EDTA 25 mmol/kg wood, corre-
sponding to the amount of polyvalent metal ions present
in the woodj of which 20 mmol/kg wood were calcium
ions. The solution also contained sodium sulphite-
corresponding to about 160 mmol/kg wood. Subsequent to
impregnation, the-wood material was pressed in a plug
screw to a dry content of about 50%. The pulp was then
de~ibred at-high pulp consistencies and with:an energy
consumption of 500'kWh/t, whereafter the suspension of
defibred wood material was thinned with water having a
temperature of 60C'and an ion strength of 2.0 mmol/l,
so`as to obtain a pulp con'sistency of-3%.
~'The''pulp was then beaten at this pulp concentration at
a specific edge load of 0.5 Ws/m'and a-net energy
consumption of 120 kWh/t corresponding to a gross
"~ enèrgy consumption'of''200''~Wh'~t'to'a'freeness of 250 ml
''CSF'ànd~à mean-fi~e lëngth'(P~L)~of"2.0 mm, i'~e. equal
''?to~a~'s~ght~y~morë rëspectivëiy~than is'normal:in the
conventionai~mani~facturê 'of~CTMP with an emergy~~con-
su'mption o~ q650' k~X/~ JS ~
`'Thus,jwhën-'practicing'~the inven~ivé'method,ienergy-:
`consumption is'reduc'èd--fro'm'i650'-kWh/t'in the cas~.,of
the~convéntionàl met~od-'to 700r'kW~/t',t which'is~also
7~~'si'ightly'lower tha'n"`thé'Ievel achievéd with~the'method
taught'`by the'Swedish~ Pakent''Application No. 8801731-4
'-'' which émpioys a'similar technique but'in which no ion
-, : : ...
:. :
: : - , ~' : ~ .: ,
'
'
WO91/06700 2 0 i ~ ~ 4 8 :`` PCT/SE90/00721
exchange takes place with the aid of complexing agents.
Example 2
Figure 2 is a flow chart which illustrates the manufac- .
ture of TMP for use in newsprint. Spruce chips are
steamed in a ~irst stage, whereafter the chips are
impregnated, preheated and coarsley refined while
adding lOO-mmol NaOH/kg wood (corresponding to the
content of acid groups having protonic form in the
wood) at a pulp concentration of 35% in a pressurized
refiner with an energy consumption of 600 kWh/t. The
coarsely refined pulp stock.was then thinned to a.pulp
:concentration of 10% with a solution, temperature.80C,
containing a complexing agent, in the.present case
Na4EDTA 25 mmol/kg wood, in an amount corresponding to
the-amount of polyvalent metal ions present in the
wood,.in the-illustrated case 25 mmol/kg wood,.of which
:. 20.mmol/kg wood were calcium ions. Subseq~ent to
.thinni~g the stock, the wood material was pressed.in a
pulp press to a dry conten~ of about 40%.~The defibred
pulp stock was then thinned with water at a temperature
: ~of:80C.and an.ion strength of 2.0 mmol/l to obtain.a
pulp.concentrationjof 3%. . .-
2 5
..... .;. The pulp was then beaten at.this~pulp.concentration at
..~s,a~sp2cific edge load of 0.5,Ws/m..and a;net energy,con-
~fsumption.!of 150 kWh/~t,.~correspondlng to a grossrenergy
consumption of 250 kWh/t, toj.a.freenessi of~
150 ml CSF and a mean fibre length"~PML? ~ 2.0 mm~
i.e. respectively equal to and slightly more than is
normal -n the-case;o~,.TMP which~can.be.produced.in.!the
.least energy xequiringrtechniq~e;known;at..pr,esent with
an~ener~y~consumption of 1650;kWh/~ (single st~age~.
~ ~efining;with;double;disc.re~iners)..Two stage proc~es-
--~ses, which are~at present. the most..co~mon processes
.!:used in the manufacture of TMP., often require an energy
-, .
'
.
.' '~ ' ' ' ' , " .
~ WO91/06700 2 0 7 3 0 ~ 8 PCT/SE90/00721
input of more than 2000 kWh/t in order to obtain a pulp
having a freeness of 150 ml CSF.
As will be seen from the aforegoing, the inventive
method was effective in reducing energy consumption
from the level'of 1650 kWh/t required in the conven-
tional process to a level of ~50 kWh/t, which is also
slightly lower than the level achieved with the method
taught by the aforementioned Swedish Patent Application
No. 8801731-~, in which similar tecnique is used but
where no ion exchange takes place with the aid of
complexing agents.
Exam~le 3
-
The flow sheet in Figure 3 illustrates a method of
manufacture of ~MP for use'as newsprint. Spruce chips
were steamed in a first stage and then charged to a
BiVis-machine.
.. . . . . .
` - "`' ' '-
As the chips-were defibred in''th machine, there was
added thérëto-a solution-containing~firstly a-quantity
of complexing agents; here Na4EDTA'~25 ~mol/kg wood,
corrësponding to'the'content of'-'polyvalent metal:-ions,
~of which 20 mmol/kg''~wood'`were calcium ions, and the
~ ~ r r r.... , " ~ ,
solution~secondly also contained sodium'hydroxide in an
amount~corrësponding ~o~iOO mmol NaOH/kg wood.'~The~-
chemiciàl solution~'containing Na4EDTA and'NaOH was in-
''~Stro,duced~in courltér'flo~ to~!the'3'wood'`flow~via:the,.~,...~r
/ ? ~ ' rr ~ r ... .1 . ~ . .. . . .
^' repéated-pressing/diluting~'method applied~in~a;BiVis.'
-The~matériai;passedith'ro'ugh~'the~four compression;~zones
~'-''iof~'the machi~é~and the'~'élect'rical~energy consumed'was
' about;300'' kWh~j ~ wocd ' ~ fSu~se'q'uént'ltoibeing~discharged
f'rom the~BiV'i~ the~'~wood~'ma'té'riâ'l"su'spension'was thinn-
;'~ e~w~ith watér~to a'dryrc'ontent':of'about~i4%. The water '`'had a temperatûré-'of 80C an~'an~ion strength of-2.0
''immoijl. The`pulp was''th'en béaten at this pulp concent-
: . . . . .
- , . . . .
.
.. , . .
.. . . .. .
.
,
.
W O 91/06700 2 0 7 3 0 4 8 ; PC~r/SE90/00721
12 ;'
ration at a specific edge load of 0.5 Ws/m and a net
energy consumption of 200 kWh/t, corresponding to a
gross energy consumption of 330 kWh/t to a freeness of
150 ml CSF and a mean fibre length (PML) of 2.0 mm.
When proceeding in accordance with this method, de- ,
fibring and refining of the pulp required a total
electrical energy input of 630 kWh/t, which is lower
than that achieved in the preceding Example (Example 2)
with TMP, where the energy consumed in achieving a j'
freeness of 150 ml CSF was 850 kWh~t.
Example ~
The flow sheet in Figure 4 illustrates the manufacture
of chemithermo~echanical pulp while using a complexing
agent-for,the exchange of calcium and other polyvalent
ions to sodium ions,acting as counterions to the acid ' 1,
groups present in the wood.
...
Spruce chips were steamed in a first stage and then
impregnated with a~ solution containing a quantity of
complexing-,agents,.-in~.-the.~illustrated case Na4EDTA ,
25 mmol/kg wood, corresponding to.the~polyvalent, , .
.metalion,content of the wood, in this case.25 mmol/kg
wood,--of which 20 mmol/kg wood were calcium ions. The
, solution,also.!contains sodium sulphite,~in~;,an amount
corresponding,.rabout 150~;mmol/Xg wood.,.Subsequent,!to.
-~impregnating,~lthe.~chips, thel~chips were..pressedijin,a
plug-screw~to,-aldry~content~iof,about,~,50%...;The.~pulp.jwias
.then~preheated iand refined atS,a highOpulp concientrajtion
e-~.in-one',stage,,to CSF-levels,between;200..and 700~ml.CSF
.? with;,aj~speçific~e,leckr,icaljene,rLgy,consumptlon which,was '
about,-~-20,~:~ lower~A than ,that, obtained;.,ln~:the(absenc,e of
~ nion:exchange,.with~ithe aid,l,of,~complexing agents. The~
35 -.tensile strength~iof,;the pulps.in the;CSF-rangej.examined ;1-
~was'more than 20%,greater,than when not..using. -
.complexing agents for ion exchange to sodium form.,When -
I
2073~8
WO91tO6700 ~' ; PCT/SE90/00721
13
the pulp was refined in one stage to 500 ml CSF and
then in a second stage to 200 ml CSF at a pulp consis-
tency of 30%, slightly more electrical enérgy was con-
sumed than in the aforementioned case, although the
energy consumption was still about 20% lower than the
energy consumed with a corresponding reference where no
ion exchange was effected where no ion exchange was
effected with the aid of complexing agents.
~.. . . ..
. ; . :
Exam~le 5
The flow sheet in Figure 5 illustrates a method of
manufacturing TNP for use in the production of news-
print, while using complexing agents to exchange cal-
cium ions and other polyvalent ions tio sodium ionsacting as counter ions to the acid groups present in
the wood.
Spruce chips were steamed in a first stage and then
impregnated~by pressing the chips in a plug screw and
allowing the chips to expand in an impregnation vessel
containing a solution of complexing agents, in the
present case Na EDTA 25 mmol/kg wood, in an amount cor-
responding to the polyvalent metal-ion content of the
wood, in the present casé!25-~mmollkg wood, of`which
20~mmol/kg wood~were calcium~ions. The complexing agent
was then removed~andi~he ion-exchanged chips preheated
and-refined-~whilel~simultaneously,-adding sodium hyd~
roxide in an.amountc.corresponding to.. lOO.mmol.NaOH/kg f
wood at a pulp consistency of 35~ in a pressurized ~-
refiner. The energy consumption was about 15% lower
than when`the same procedure was carried~out;~ut with-
out--an ion exchàngétw~lt~the"aid oficomplexing agents.
~`i~.^'
I ;'`'~''
.
~. ` '
.
