Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
,.. , 2~..:~~'l.. "~u',14~45 MRRf<S & :CLERK MiC 861 88A 1142 .; . , . _. ,.
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WO 9110211 PCT/GB9U/01176
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TREATTd~~HT OF FIBROUS MA2'~RIA1;8
The present invention relates to the treatment of
fibrous materials (particularly but not exclusively
cellulosic fibres) which aze used in the production of
paper".
The term paper as used herein is generic to
paper, paperboard, and like fibrous sheet materials
which are generally (but not necessarily) of a
ce11u1Qsic nature.
In essence, the process for manufacturing paper
comprises preparing a suspension of fibres (usually
cellulose fibres) from which the paper is to be
produced and then passing this suspension along
suitable conduit to a papermaking wire or fozmer
(hereinafter referred to generically as a wire) on
whichw the suspension is deposited. A vacuum is
applied to that side of the wire opposite to the side
on which the suspension is deposited so that water is
drawnWhrottgh the wire to leave a sheet of the fibres
which may then be further dried and processed as
required .
Various additives are required for this process.
In particular, paper sizing agents are frequently
added to the suspension. Examples of such paper
sizing, agents are rosin emulsions which .are used in
conjunction with aJ.um (or other simple or polymeric
aluminium salts). Further examples are cationic
polymer and rosin emulsion, mixtures, see for example
~GB=A-x,11,751. Other aombina~t~.ons of sizes and
fixers axe also used. .
So far as the sizing of fibres 'wia~h a rosin
emulsion in conjunction with alum (ie. a~:uminl.um
sulphate) is concerned, the alum is effective under
.' acid conditions to break down the emulsion arid cause
the rosin to be deposited on the particulate material
28.,Jf~N. .' g~_, _.14~ 46 MARKS & , CLERK .M!C, 061. 834 1142 , , , . .. , f
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WO 9~ ~~2119 PCr/GB90~01176
z
which constitutes the furnish (i.e. fibres and any
filler present). Conventional practice is for the ,
rosin emulsion (pH ca 7} and alum solution (pH less ..
than 3) to be added sepazately to the suspension of .
cellulose fibres from which the paper is to be
prepared.
Conventionally, the additions of rosin and alum
solution are made at separate locations along a pipe
through which the f~.brous stock is flowing. zn
p~.rticular, the alum solution is normally added to the
pipe considerably upstream of the rosin emulsion.
The amount of alum solution added will generally
be such as to provide a pH of 5 to 5.5 in the
suspension prior to the addition of the rosin
emulsion. This degree of .acidity is required in the
suspension so that the rosin is deposited and retained
on the cellulose fibres.
However, this acidic pH may cause problems if the
fibrous stock has been produced at least partly from
waste paper Which incorporates calcium carbonate or
when calcium carbonate is added as a filler. In this
case, the calcium carbonate gives rise to deposits of
calcium sulphate. Such deposits build up over a
period of time cause blockage of the various lines in
the plant and, more importantly, in the apertures of
the foraminous wire on which the paper is formed.
The process must therefore be periodically shut down
so that the blockages may be cleared. Obviously this
is a considerable disadvantage. The use of pH
conditions close to neutrality is not possible k~gcause
the rosin is not sufficiently deposited or retained on
the fibres. This is a signifscant disadvantage of
sizing with rosin emulsions.
The formation of calcium sulphate deposits may be
avoided by the use of reactive sizes, for example,
alkyl ketene dimer (AKb) sizes, in place of the rosin
and alum. However, ATCb szzes are not the idea.
;2$"JAN_,'.9~.~4:,46 MRRKS & CLERK MiG 061".834,..1142 ., . , " P.10 .
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solution when it is desired to produce paper on a MG
(machine glaze) machine s.~nre MG cylinder adhesion is
frequently lost and furthermore AKD produces only a
. poor finish an such macha:nes.
we now believe that the abovementioned
limitations of rosin-alum sizing result from the way
in which the rosin and alum and introduced into the
fibre suspension in the prior processes, and that
these limitations are overcome by using the procedures
set out below which ~.nvolve rapid mixing of rosin
emulsion and alum solution streams and the
~.ncorporation of a localised zone (of relatively high
concentration) in the fibre suspension. The rosin
emulsion/alum solution system is an unstable system in
that a mixture of these two components will normally
flocculate, but using the rapid mixing procedures set
out below a rosin emulsion/alum solution mixture may
readily be incorporated in the suspension without
problamc rcs»J t i nr,J from f 1 t~cculatiOn . These
procedures wild. tnererore also pe appiic:azra~ Lv m.~
incorporation into f ibxe suspensions (for use in
preparing paper) of additive mixtures which give rise
to an unstable system,' e.g. a mixture of cationic
polymer and anionic rosin, emulsion.
According to a first aspect of the present
invention there zs provided a method of providing a
mixture of additives in an aqueous suspension of
fibres to be used fox the manufacture of paper, the
method comprising providing within the suspens~.on a
localised zone of a freshly prepared mixture of
discrete liquid streams of the additives, and causing
the freshly prepared mixture to be dispersed within
the suspension.
According to a~ second aspect of the present
invention there is provided papermaking apparatus
compr~.sing suspension preparation means for preparing
a suspension of fibres, a foraminous wire on which the
28 JRN. ' ~2. .14.~ 4~. MARKS, & CLERK MiC , 061 834 1142 ; ~ y . . . , . P :
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suspension is deposited for preparing the paper, and
conduit for conveying the suspension between the
suspension preparation means and the wire wherein
provided along the conduit is a mixing assembly having
two inlets into which separate streams of additives to
be mixed are supplied and having an outlet region in
the conduit at which the localised zone of a mixture
of the additives is provided.
The method of the first aspect of the invention
is particularly applicable to the treatment of fibre
suspensions with a mixtuxe of additives which together
give an unstable system, i.e. one which flocculates on
admixture of the two additives. Using the method of
the invention, the two additives are rapidly mixed and
introduced at relatively high concentrations into the
fibre suspension before flocculation problems occur.
A pazticular example of such an additive system is a
mixture of a rosin emulsion and an aluminium salt
solution, and a further example is a mixture of
cationic polymer (e. g. DAbMA.C) and anionic rosin
emulsion.
The method of sizing fibres using rosin
emulsion/aluminium salt solution is an important
aspect of the present invention in its own right and
therefore according to a third aspect of the present
invention there is provided a method of sizing fibres
in an aqueous suspension thereof, the method
comprising providing within the. suspension a zone of
a freshly 'prepared mixture of discrete streams o~ a
rosin emulsion and of an aluminium salt resulting in
a mixture which is at an acidic pH '(i.e. less than 7)
less than that of the suspension, and causing the
freshly prepared mixture to be d~.spersed with~.n the
suspension whereby the mixture undergoes a pH
transition which is effective to cause ros~.n to be
deposited on the fibres.
The fibres to be treated will generally' be
. , 28 JRN ,'92 14: 48 MRRKS ;& CLEF2K, MiC 061 834 .1.142 . . " , ",. .. , .
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!Y0 91I02I 19 PCT/GB94/03176
cellulose fibres and the invention will be
specifically described with reference to such fibres.
It should however be understood that the invention is
also applicable to the sizing of other types of fibres
from Which paper may be prepazed.
The following description is directed
particularly to the third aspect of the invention.
Generally the fibre suspension will itself be a
flowing stream and the localised zone of the freshly
mixed solution of the aluminium salt and rosin
_. .. . ,, . . . . , , ~ , _.. _ ~ _ _ _ s _.. ..~ ~......, i.".
the methods described in mote detail below. 7Che
localised zone is distributed within such a fibre
suspension stream by the flow thereof. The pH of the
localised zone in the suspension may as a matter of
practice be difficult to measure. However the pH of
the suspension itself (prior to mixture with the rosin
emulsion (aluminium salt solution) is easy to measure
and it is simply necessary to ensure that a mixture of
the rosin emulsion/aluminium salt solutions will be of
an acidic pH less than that of the fibre suspension.
In this Way, it is ensured that the localised zone of
the mixed rosin emulsion/aluminium salt solution will
. be at an acidic pH less than that of the fibre
suspension. For preferance, the pH of the fibre
suspension.after the rosin emulsion aluminium salt has
been~d'ispersed therethrough is above 6.5, preferably
above 6~.7. This ensures that no substantial calcium
sulphate deposits (for the case where the fibrous
stock has been produced at least partly from Calcium
carbcinate as a filler). Furthermore, operation at
these pH values improves~drainage through the w~:re of
the papex making machine.
" We have discovezed that, it is: possible :to use
rosin :emulsions and solutions of aluminium salts to
. effect sizing of cellulose fibres which are in aqueous
suspension provided that the rosin emulsion and
28 JH(y; ' 92, 14: 48 MRRKS & CLERK . ~1iG 061,. 834 .1142 .. ; . .. . . , . ,
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aluminium salt solution are continuously provided in
the suspension as a freshly mixed localised zone which
is at a pH less than that of the suspension. As this
zone is distributed throughout the suspension, the
resin emulsion/alum mixture undergoes a pH transition
Which is effective to cause the rosin to be deposited
on the fibres.
We do riot wish to be bound by any particular
theory as to the chemical mechanism of the sizing
process of the invention but we believe that the pH
transition causes the formation of po~.ynuclear
aluminium species and probably also some aluminium
hydroxide precipitate (which may well be amorphous at
this stage since the crystallisation process takes
some considerable time) and' that it is the polyriucledr
complexes, possibly with' some contribution from
precipitated aluminium hydroxide, which are
responsible for the effectiveness of the invention.
The method of the invention is most preferably
carried out with cellulose.f fibre suspensions at a pH
(before admixture with, the rosin emulsion/aluminium
salt) of greater than 6 particularly in the range 7 to
8. The invention is also.operative at virtually any
normal acid pH for rosin sizing and up to say 9.5,
This should be contrasted with the prior art process
where rosin emulsion and' alum solution, added at
separate locations in the paper making process, are
not effective f or sizing cellulose fibres which are in
a suspension at a pH greatex' than 6..
The invention thus provides the significant
advantage that it may be used' for the s~.zing, with
rosin emulsion, of cellulose. fibre suspensions which
contain calcium carbonate 'and which are at a pH above
6. With such suspensions, the method of the invention
does not give rise to unacceptable deposits of calcium
sulphate, calcium aluminium sulphate, and related
compounds in the paper machine. Any deposits formed
28 JRN '92 14:49 MRRKB &.CL~RK:M~C,061 834 .1142 P.,14,:. , , ,
W0 9l/OZl'!9 ' PCT/G890/t» 176
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are lzkely to be of a very small crystal size and are
probably included in the final paper.
Zn contrast to the use of reactive sizes (eg. AKD
sizes) which have heretofore been required for sizing
suspensions with a pH above 6, the method of the
invention produces paper having an excellent finish on
a MG (machine glaze) machine and also an increase in
running speed as compared to that obtained with AKD
.sizes .
The aluminium salt used in the method of the
invention should preferably be an acidic salt and is
most preferably alum. Tt is however possible to use
other aluminium salts that will give rise to
polyhydraxy aluminium ions and/or A1(OH)3, eg.
polyhydroxy aluminium salts such as the compound known
as polyaluminium chloride. The amount of the alum
solution used will preferably be such as to provide 1-
4% by weight of alum (expressed as Alz(SO4)3.18Hz0) dry
basis on the f ibxes. Other aluminium salts may be
used in appropriate amounts. For example, we have
found that the amount of polyaluminium chloride used
in the process~may be about 1/St" of the corresponding
amount of alum required . .
At least in the case where the aluminium salt is
alum, the pH of a mixture of the alum solution strearit
and the rosin emulsion stream should for preferance be
below A, more preferably about 3.8.
The method of the invention works effectively
with a wide variety of rosins, eg, tall oil rasin and
gum rosin. The rosin~will usually have a melting
paint of 70-85° C. The rosin emulsion will generally
comprise 20-50% solids and be used in an amount so as
to provide 0.1-2% by weight (dry basis) on the fibres.
The inventian will be described further with
specific reference to alum as the aluminium salt,
.' although it will be appreciated that other alumina.um
salts may be substituted thexefor.
", 28 JRN , ' 92y 111,: 49 : MRRKS . & CLERK MAC 061 $34 ~ 1142 . . _ . . ~, :
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In the preferred method of carrying out the
invention, the ceaJ.ulose fibre suspension flows
through a conduit and the localised zone of the
mixture of rosin emulsion and alum solution is
provided in the conduit at a location past which the
cellulose fibre suspension flows. The flow of the
suspension is effective to cause the rosin
emulsion/alum solution in 'the localised zone to be
distributed within the suspension and thereby undergo
the pH transition.
In one preferred method of carrying out the . ,
invention, the alum solution and rosin emuhsion are
intensively mixed together ~.mmediately prior to the
infection of the mixture into the conduit along~which
the suspension of cellulose fibres is flowing.
Conveniently, the mixing is effected by passing the
rosin emulsion and alum s.olu.tion in opposite
directions, and under turbulent fhow conditions,' along
a tube which has intermediate its ends an outlet
communicating with the interior of the conduit. This
mixing: tube may, for example, comprise a T-piece with
the rasii~ emulsion and alum sohutions being, difeeted
(prefera.bly under turbulent flow conditions) in
appasi.te dixection,s along the "bar" of the T and the
resultant mixture being passed.along the "stem" of the:
T into.the conduit.
In, another preferred way of carrying out the
method: of the invention, the rosin emulsion and alum
solution are introduced as separate streams into the
cellulose f~.bre suspensions flowing along the conduit
and mixed xn situ within the. suspension. xn. this
case, the points at which the aluminium solution and
rosin emulsion are discharged into the cellulose fibre
suspension flowing along the conduit must be ..
sufficiently close to each other to create a mixing ,
zone before either the. rosin .emuls,ion or alum solution
is diluted too much.
. .,28 JfIN ,'9~, 14:50 MRRKS & CLERK hiiG 061 834 1,1A2 ; , . . , , .. ..P.16
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Using the abovedescribed methods, the rosin
emulsion/alum solution mixture is, able to be
incorporated in the fibre suspension without
flocculation problems occurring.
It is preferable that the localised zone of the
mixture of rosin emulsion and alum solution is
provided in a cellulose fibre suspension which is in
th'e form of so-called thick stock, ie. a suspension
which generally contains about 3~ by weight of the
cellulose fibres rather than the thin stock (which
will generally comprise about ~.% by weight of the
fibres), although this does depend on the degree of
dilution in going from thick to thin stock. The
invention is however applicable to the treatment of
fibre suspensions containing greater or lesser amounts
of fibres. however, fox preferance the suspension
will comprise 0.1$--10$ by .weight of fibres, more
preferably 0.2-5~.
The invention will be further described by any of
example only with reference to the accompanying
drawings, in which:
Fig. 1 is a daagram~ of aluminium hydroxide
solubility as a function'of pH; and
Fig. 2 is a schematic diagram of a papexznaking
process; and
Figs . 3 to 15 diagrammatically illustrate various
types of mixing apparatus which may be used in the
method of the invention.
Fig. 1 is a plot of' total dissolved aluminium
(At) vs pH and shows the stability region of freshly
precipitated Al(OH)j based on the assumption that the
only other species present are'Al(OH)4-,:A1(OH)2*, its
dimer Al2(OH)Z°*, A113(OH)~a5+, and A17(OH)m"+, as well
' as the uncomplexed iorr Alj*. ~ Fig. 1 is a thermodynamic
diagram and may be thought of as~ corresponding to
.' equilibration times longer than those normally
encountered in the sizing px~oaess in a pager mill.
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In the method of the invention, the mixture of
rosin emulsion~and alum solution which forms the
localised zone in the cellulose fibre suspension
preferably has a pH less than 4. The alum stocks in
many paper mills contain of the order of 8% A1z03(M.Wt
101.96), ie. approx. 0.78 mol dm-3. Thus for the
maaority of stock found in a paper mill, the aluminium
conceritxation is normally greater than 10-' mol dm-'
.a.nd thus greater than the, minimum value of A1.~ at
which Al(OH)3 precipitate will form. Altering the pH
fxom its value of less then 4 to above 6 causes a move
to the right on the diagram so that the system enters
the insoluble region causing the formation of
polyriuclear. complexes and precipitating some, arid
maybe quite a lot , of A1 ( (7~T ) 3 , probably in a
gelatinous form. It is though;. (R. Counter, M.J.
Jaycock and J.T~. Pearson, Svensk Papperstidning ?8,
333 (1975)) that one or bath of the latter two species
are necessary for satisfactory sizing. Since
aluminium is being precipitated from solution, the
move on the diagram from the lower to the higher pH is
in fact a downward diagonal move. Depending on the
precise mill conditions, the final position on the
solubility diagram may : be inside the region
cor7Cesponding to A1 ( OH ) 3 or in the A1 ( OH) 4- region,
where the concentration of~polynuclear complexes will
be vanishingly small, and there would be no
precipitated A1(OH)3. However, in the latter
situation, if the point at which the localised zone of
rosin emulsion/alum solution mixture is provided is
moved near to where the sheet is formed, it is
believed that there will not be time for the A1(OH)3
to redissolve or for the ~polynuclear species to be
converted to A1(pH)4', so that satisfactory sizing
performance can be achieved. In this respect, it
should be borne in mind that Rig. 1 is a thermodynamic
(and not a kinetic) diagram representing the position
28 JAN..'92 14~51 MRRKS & CLERK MiG.861 834.1142 P.18
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et eguilibrium which may take some time tv achieve.
_ Thus, in the case just described, the A1(OH)3 and
polymeric aluminium hydroxy species ( initially formed')
persist long enough for sizing to take plaee.
Some idea of the relative lability of the
polynuclear complexes can be gained from the work of
R.W. Smith reported in "Nonequilibrium Systems in
Natural. Water Chemistry", Advances in Chemistry Series
ACS, No. 106, p. 250 (1971).' mhis paper states that
the fastest acting species are the mononuclear ones
such as A1''', A1(OH)x'' and A1(OH)z'. The polynuclear
species in the reported experiments had lifetimes up
to one hour, and the aged precipitate A1(OH)3 much
longer. This work offers some support for the
~eontention that it is the polynuclear aluminium
species that are important in the process of the
present invention, and henoe the need to go through
the relevant formation pH range in the mixing zone.
Fig. 2 is a very schematic illustration of'the
basic steps involved in papermaking. within a tank
100 there is prepared a suspension of cellulose fibres
which are then passed along conduit 101 to a head box
102 from Which the suspension is deposited on a wire
103 of a Foudrinier machine Vacuum boxes- 104 serve
to draw water from the layer of fibres on the wire.
It should be understood that the conduit 101
shown in k'ig. 2 is intended very schematically to
represent the connection between the tank 100 and the
head box lOZ. In practice,. the conduit arrangement 5.s
likely to be rather more complicated that that
illustrated and may include a thick stock line arid a
thin stock line as well as pumps far moving the
suspension.
' However, whatever the conduit arrangement, there
is provided a mixing arrangement 105 at some paint
.' alone the conduit 'for providing therein a localised
zone of freshly mixed streams of rosin emulsion and
28 JAN '92 14:52 MRRKS &' CLERK .M.%C. X761 .834 1142 1
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1.2 yr~
alum solution. various examples of such mixing
arrangements are illustrted in Figs. 3-15.
Figs. 3-15 show various mixing arrangements for
providing the localised zone of 'the mixture of rosin
emulsion and alum solution in a conduit 1 along which
an aqueous cellulose fibre suspension is flowing in
the direction of arrow A. The conduit 1 will for
preference be the thick stock pipe. In each of Figs.
3-15 the rasin emulsion: is considered to be supplied
in the direction of arrow B along a pipe, or pipe
section, referenced as 2 and the alum solution is
supplied in the direction of~arrow C along a pipe, or
pipe section, referenced as 3.
The mixing device of ~'ig. 3 is the preferred
device for use in the invention and is a T-piece
arrangement in which the rosin emulsion and alum
solution streams impinge upon each other so that the
mixture exits in the direction of arrow D along the
stem of the T which is provided in the centre of the
conduit 1. The mixture enters conduit 1 as a
localised zone at a pH of less than 4, which then
beoomes dispersed throughout the cellulose fibre
suspension and thus undergoes the necessary pH
transition. By way of example, and as illustrated in
the drawings, the pH of the ffiber suspension up stream
of the T-piece may be about 7-~8 whereas down stream of
the T-piece (and after distribution of the rosin
emulsion/alum solution in the suspension (the pH may
be about 6.7.
Ideally, the flow of rosin emulsion and alum
solution along the respective pipe sections ~ and 3
will be turbulent flow as this will promote more
intensive and rapid mixing of the two streams.
Whether the flow inside the mixer is laminar or
turbulent is dependent on the Reynolds' number (Re).
For a long smooth straight pipe~the critical value of v
(Re) is usually taken as 2000, and this value may be
2,8vrvRxuviaiy.'S2: MRRKS & CLERK MiC 051,;834 1142 . . . ' . . . , ,..
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used as a rough guide in calculating the diameters
needed to produce the preferred turbulent flow
conditions inside the mixer- A more detailed
consideration of the conditions governing turbulent
flow is given an Appendix a, and the design of a T-
piece for mixing rosin emulsion and alum solution is
given in Appendix b.
Fig. 4 shows a modification of Fig. 3 in Which
the . stem of the ~ T is omitted and the rosin
emulsion/alum solution mixture simply issues through
an orifice 4 into the conduit 1.
the mixing devices shown in Figs. 3 and 4 may be
manufactured from tubing which is of a diameter
specifically selected (or produced) to give the
. required turbulent flow conditions. The T-piece can
however also be made from standard size tubing and
have its bore reduced by means of znserts 5 as shown
in Figs. 5-7. These inserts 5 may be bored With
either the right sized holes. to foam T-piece type
configurations~~.(Figs. S and 6) or bored to form a
-. device similar~to the Hartridge-Roughton, mixer as
shown in Fig. 7. In the latter figure the; rosin
emuision/alum solution flows are injected ,using
opposite pairs of semi-tangential.jets (2'+.2 " and 3'
and 3'' ); the tube for the merging flow being at:. right
- angles to the plane of the paper. The inserts may be
kept iw place by using a push-tit or crimped, glued.,
screwed, p~.nned or welded (conventionally or
electrically) in position or retained in, place by
means of f langes .
Fig. 8 shows a further embodiment o~ T-piece type
mixing device. In this case, a T-piece connector has
internally threaded ends such that tubes.2 and 3 for
supplying rosin emulsion, arid alum solution
respectively may be mounted therein as shown. Also,
a tube may be mounted in the stem of the T through
which the mixture of alum solutzon and rosin-emulsion
~8 JRN '92 1.4:53 MARKS .& GLERK MiG.061 834 1142 - p..21.. _.
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exits into the suspension of cellulose fibres. The
length of this latter tube may be selecaed having ,
regaxd to the length of time for which it is desired
to keep the alum solution and rosin emulsion in
ccintact with each other ~ before they enter the
cellulose fibre suspensi,on.~ If desired, or necessary,
inserts S may be provided in the T-piece connector as
shown. The illustrated insert may be formed from' a
single' piece of tubing (one end of which .is closed)
simply by boring a hole transversely through the tube
adjacent its closed end to obtain the configuration
shown. This insert may then simply be inse7:ted into
the T-piece connector along the stem thereof.
As an alternative to mixing the xosin emulsion
and alum solution together prior to their injection
into the conduit 1, it is possible to create a mixing
zone inside the main flowing stream of the cellulose
fibre suspension, but outside the injecting pipes Z
and 3. The essence of the idea in this case is that
the discharge points f rom the pipes 2 and 3 must be
sufficiently close to each other. to create a mixing.
zone before either injected stream is diluted very
much. Figs. 9-13 show what may be considered as
virtual T-pieces, where the,mixing zone is created by
the injections streams, and; the pipe work is somewhat
curtailed. Fig. 9 shows the two angled pipes 2 and 3
with their ends one behind the other so that the
mixing zone occurs around the end of the downstream
pipe. Straight pipe~entry (see Fig. 10) into the
cellulose fibre stream works just as well.
Fig. 11 shows the two pipes 2 and 3 at right
angles to the walls of the conduit 1 injecting into
the middle of the cellulose fibre stream so that the
injected flows impinge on each other. Fig. 12 shows
a similar arrangement fox produeing impinging streams ' .
but in which the pipes 2 and 3 are angled relative to
each other. However, the arrangements of Figs.ll and
28 JPN.' 2 24:53 NRRKS & CL~RK.M!c 061 834 1142 . f'.22..
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12 are believed to be less efficient in mixing, as
might be expected, and less effective from the paint
of view of sizing paper making performance than the T°
piece of Figs. 3 and 4.
In the arrangement of Fig. 13, the end of pipe 3
locates within the end of pipe 2 so as to provide a
mixing annulus.
In the mixing devices of Figs. 3 to 13 the
mixture of rosin emulsion and z~lum solution is
produced within the bounds of the conduit 1. It is
however possible to mix the rosin emulsion and alum
streams externally of the conduit 1 and to inject the
mixture either at the periphery of the conduit 1 or
more preferably into the middle thereof, Such an
arrangement is shown in Fig. 14, The mixing process
and use of inserts is covered by similar
considerations to those described above for the T-
piece of Fig. 3.
Fig. 15 is a madif ication of the arrangement
shown i:n Fig. J.4 but in which a cross-piece is
provided instead of a ~'-piece. As previously, rosin
emulsion is supplied along pipe section 2 and alum
solution along pipe section 3. Water is supplied
along the addi~ional p7.pe section referenced as 4.
The advantage of this arrangement is that when the
flaw of alum and size stops, the water from pipe
section 4 keeps the line clear. Additionally the
. necessary minimum (Re) f or turbulent flow can be
achieved by adjusting the water flaw. Furthermore the
concentration of the alum/size mixture passing to the
stock line may be adjusted.
It is also poss~.ble to use other commercial
mixing devices other than the simple pipe arrangements
shown in Figs. 3-1.5; but such, other devices may be
more expensive. ~iowever, they may offer, dependent
upon the specific design equivalent performance to the
Hartridge-Roughton mixer when the problem of very low
~~.JRN '92_1Q:54 MARKS & CLERK MiC 06~ 834 11A2 P.23
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flow rates is encountered, and achieving (Re) > 2000
may become difficult in straight pipes whilst
.retaining reasonable dimensions. -
The invention has been specifically described in
relation to the sizing of fibres using a mixture of
rosin emuJ.sion and aJ.um solution. However, other
additives may be mixed us~.ng the procedure of the
first aspect of the invention for the treatment of the
fibre suspension. For example, the additives mdy
comprise a stream of a cationic polymer (e. g. DAriMAC)
and a anionic rasin~emulsion. A mixture of these two
components is known to "invert" in that it goes from
an anionic sizing system to:a cationic sizing system.
Streams of these two components may be mixed in, a T-
piece (or other mixing device) in which the inversion
takes place prior to introduction of the mixture into
the fibre suspension. '
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APPENDIX a
CONDITIONS GOVERNING THE TRANSITION FROM LAirdINAR TD
Ti3RHULENT FLOW
The parameter used to assess, in a particular
case, the flow regime for a fluid flow in a
cylindrical pipe or annulus is known as Reynolds'
Number, (Re). This can be considered as a
dimensionless group of parameters defined by:-
(Re) = dVL/n ..................(~1)
where d = density of the fluid, which in S°I has
the units kg m 3
v = f low velocity ( average ) , ~m s!'
L = characteristic length, m'
n = viscosity, kg xri 1 s~l.
Therefore (Re) = kg' m j. m sYl. m which is unitless.
kg m i s-i
There are prob7.ems over the definition .of the
'characteristic length' in particularcases. For d
cylindrical pipe many texts suggest that the ra3lus be
employed for flow in a cylindrical pipe [1]. However
a standard work on fluid flaw recommends the use of
diameters, for example in the case of an annulus {2].
This choice will obviously make a difference in value
of (Re) defin~.ng the transition point from laminar to
turbulent flow, the different choices making a
w difference of 2x in the appropriate value.
Ref erence { 1 ] suggests turbulent f low occurs when
(I~e).is greater than 1000, ox 2000 if the diameter is
used for the characteristic length.. There has also
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been suggested that there should be considered to be
a transitional region above this value, with true
turbulence only being guaranteed when (Re) i.s greater
than 2000 (based on z~ = radius).
When considering the effects of pipe radius
changes in a practical plant situat~.on, then the
linear average flaw velocity is not normally constant,
usually it is the volume flow velocity, v, that is
kept constant. These two velocities are related, fox
a cylindrical pipe, by:-
v = rtrZv . . . . . . . . . . . ( 2 )
which on substitution in (1) gives:-
(Re) = dvL/(r~r2n) ......(3)
Thus considering equations,(1) and (3), then:-
(a) if v (the linear flow velocity) is constant then
increasing the radius of the~pipe increases (Re)
and increases the chance of turbulence, but
(b) if v (the volume flow vel~city) is constant then
increasing the size of the pipe decreases the
value of (Re) and decreases the chance of
turbulence.
The relevance of this fax the T-piece mixer is
obvious, since volume flow rates are fixed, and
therefore constrictions in the mixing zone increase
the value of (Re), the probability of turbulence and
efficient rapid mixing.
The other factors that should be remembered are
that these critical values of (k~e) are far a long,
smooth bore, cylindrical pipe. Irregularities in the
walls and dirt in the pipe are likely to decrease the
critical value of (Re). Thus for (Re) values greater
than 2000 turbulence is virtually guaranteed, but
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considerably lower values. of (F2e) than 100 (say about
S00) might be necessary to confidently predict laminar
flow.
REFERENCES
[1] "physics", SGStarling & A.7WOOdall; Longmans,
Green & Co. (1950) p. 96.
j2] "Internal Fluid Flow", AJWard-Smith, Clarendon
Press (1990) p. 274.
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annt~'rnTV t.
DESIGN FOR' T--PIECE FOR MzXx:NG.~EMULSION' & ALUM BEFORE
INJECTION .
The following flow rates are assumed:-
1, Size emulsion flow = 7.50 - 400 1 hr 1
2. Liquid Alum flow - 150 - 370 1 hr''
and that this is injected into a backwater stream
flowing at a rate in excess of 600 1 hr''.
The Reynolds Number. (Re) of the flow is given
by:-
Re ) = av~.
n
where d - density, V - flow velocity, n --
viscosity, and
L = characteristic length (eg. the tube diameter)
Tf we work in SI units, then taking the solutions
to have a viscosity slightly higher than water, we
have n = 1 centipo~.se.= 0.001 N s m-1. The density is
about 1 g cry-3 - 1000 kg m ', and ~.f we assume the
internal diameter of the pipe to be 0.5 in = 0.0125 m
then L = 0.0125 rn. The total minimum flow is 300 1
hr-~ T 300 x J.0-3 rn' hr" 1 , hence : -
v = 300 x 10'' / (60 x b0~) m' s''
300 x 10'3 x 4 / ( 60 x 60 x n x 0. 01252 )
0 . 068 m s '
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in the 0.5 in diameter stainless pipe. There~ore:-
(Re) = (1000 x 0.68 x. 0.0125) / 0.001 = 8500
which is considerably above the transition region
limit of 2000~and well into the turbulent flow region.
This means that the ~law would also be turbulent even
in the approaches to the combination of the flows in
the mixing. zone of~tlxe t-piece, wheze (Re) - 4250.
