Note: Descriptions are shown in the official language in which they were submitted.
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ARRANGEMENT FOR MIXING FLOWS IN PAPERMAKING PROCESS
[0001] The invention relates to a method of mixing flows with each
other in a papermaking process, according to which method a first flow is fed
through a tube; and one or more second flows is/are fed into the first flow
via a
feed opening which is in connection with the space limited by said tube; and
the first flow is conveyed in the tube to a mixing zone, which mixing zone
comprises at least one form part on the inner periphery of the tube, the
control
surfaces of which form part extend a predetermined distance from the inner
periphery of the tube towards the middle of the tube, and which control
surfaces together with the inner periphery of the tube define the inner
surface
of the tube; and turbulence is generated in the first flow by means of said
control surfaces; and the second flow is fed to the mixing zone portion into
the
first flow through one or more feed openings positioned on the inner surface
of
the tube.
[0002] The invention further relates to a mixer comprising a tube,
through which a first flow of the papermaking process is conveyed; and a feed
opening which is in connection with the space limited by the tube and with a
feed channel for mixing a second flow into the first flow through the feed
opening; and a mixing zone formed in the tube, which mixing zone comprises
at least one form part on the inner periphery of the tube, and which form part
comprises control surfaces extending a predetermined distance from the inner
periphery of the tube towards the middle of the tube for generating turbulence
in said flow in the mixing zone of the tube; and the inner periphery of the
tube
and the control surfaces of the form part define the inner surface of the tube
in
the mixing zone; and the mixer comprises in the mixing zone portion on the
inner surface of the tube one or more feed openings, which is/are in
connection with the feed channel and through which the second flow is
feedable into the first flow.
[0003] The invention further relates to feeding equipment of a head
box of a paper machine, comprising a tube through which a first flow is
conveyed to the head box; and a feed opening which is in connection with the
space limited by the tube and with a feed channel for feeding a second flow
into the first flow through the feed opening; and a process component, such as
a pump or screen, which is arranged in said tube before the head box; and a
mixing zone in the tube, extending from the nearest process component
preceding the head box to the head box, and which mixing zone comprises at
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least one form part on the inner periphery of the tube, and which form part
comprises control surfaces extending a predetermined distance from the inner
periphery of the tube towards the middle of the tube for generating turbulence
in said flow in the mixing zone of the tube; and that the inner periphery of
the
tube and the control surfaces of the form part define the inner surface of the
tube in the mixing zone; and that in the portion of the mixing zone, the inner
surface of the tube is provided with one or more feed openings, which is/are
in
connection with the feed channel and through which the second flow is
feedable into the first flow.
[0004] There is a plurality of objects in different papermaking
processes in which other pulp flows or various additives, such as coloring,
filling and retention agents, are mixed into the main flow formed of liquid
and
pulp. It is typical to mix retention chemicals that bind solid matter
particles into
the fiber suspension flow headed for the head box of a paper machine, which
retention chemicals allow improvement of the retention of fines and filler
agents in the wire section of the paper machine. The mixing of different
components can be performed with what are called tube mixers. Thus, the
additive is conveyed into the pulp flow through tubes or nozzles arranged on
the side of the pulp tube. However, the arrangement has not brought about a
mixing result that would be sufficiently good. Attempts have also been made to
feed a jet of additive at a very fast rate into the pulp flow, whereby the
desired
effect would have been for the additive jet to better penetrate into the pulp
flow. Unfortunately, the problem here is that some additives, such as a
retention agent, adheres to the surface of the fiber or other solid matter in
an
unpreferred manner when being fed at a fast rate, which results in what is
called flat conformation, for example, and the additive no longer has the
desired retention relative to the filling agent or fines. Further, the result
may be
unpreferred degradation of the retention agent because of too great shear
forces. Due to these aspects, the final product is subjected to detrimental
variation of the profile.
[0005] Further, in order to improve the mixing, injection nozzles can
be used that extend some distance into the inside of the pulp tube. The
problem is, however, that the ends of the nozzles inside the pulp tube gather
impurities, which makes the feed of the additive more difficult and
deteriorates
the quality of the final product.
[0006] An object of this invention is to provide a novel and an
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improved arrangement for mixing two separate flows in a tube.
[0007] The method according to the invention is characterized by
the second flow being fed into the first flow through the feed opening
positioned in the form part.
[0008] Further, the mixer according to the invention is characterized
in that the at least one form part comprises at least one feed opening, and
that
the feed opening is in connection with the feed channel outside the tube.
[0009] Further, the feeding equipment according to the invention is
characterized in that the at least one form part comprises at least one feed
opening, and that the feed opening is in connection with the feed channel
outside the tube.
[0010] The essential idea of the invention is that the first flow of the
papermaking process is conveyed in a tube which is provided with one or
more form parts arranged on the inner periphery of the tube. The form parts
comprise control surfaces which extend a predetermined distance from the
inner periphery of the tube towards the middle of the tube. The form parts
control the flow flowing in the tube and generate turbulence in the flow. The
zone that begins in the flowing direction after the nearest process component
preceding the form part, i.e. after a pump or screen, for instance, and that
ends after the form parts at the point where the mixing effect of the
turbulence
generated by the form parts has essentially weakened is in this application
called the mixing zone of the tube. The inner periphery of the tube and the
control surfaces of the form parts define together the inner surface of the
tube
in the mixing zone, i.e. the surface that contacts the flow flowing through
the
mixing zone. In accordance with the idea of the invention, the mixing part
comprises one or more feed openings on the inner surface of the tube, which
openings are in connection with the feed channels outside the tube. From said
feed openings, at least one second flow is fed into the first flow flowing in
the
tube. The form parts function as mechanical mixing members, and the
turbulence generated by them mixes the flows efficiently with each other.
Owing to the form parts, the penetration of the second flow into the first
flow is
improved. The rate of the flow flowing through the mixing zone can be kept
relatively slow, and yet, good mixing can be achieved. Owing to the mixing
that
is better than previously, problems resulting from poor mixing can be avoided
in the manufacturing stages after the mixer. The invention enables
manufacture of products of more uniform quality. In addition, since the mixing
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is good, expensive additive chemicals can be used in amounts smaller than
previously. Earlier, it has been necessary to compensate for the poor mixing
by feeding an excessive amount of additive chemicals into the pulp flow.
(00111 The essential idea of a preferred embodiment of the
invention is that at least one of the form parts in the mixing zone comprises
a
feed opening which is in connection with the feed channel. Through the feed
opening in the form part, a second flow is fed from the outside of the tube
into
the first flow flowing in the tube. The form parts allow the flow to be fed
closer
to the middle of the flow flowing in the tube, which makes the mixing of the
flows more efficient. Since the feed opening is at the same level as the
control
surface of the form part, and further, since the form part is designed to
remain
easily clean, the form part and the feed opening arranged in it do not gather
impurities.
[0012] The essential idea of a second preferred embodiment of the
invention is that the first flow is a mixture of liquid and solid matter used
in
papermaking, for example a mixture of fibers and water, and the second flow
is paper making chemical, such as a retention agent.
[0013] The essential idea of a third preferred embodiment of the
invention is that the tube mixer is arranged on the feeder line headed for the
head box of a paper machine, after a mechanical screen. Thus, the first
component of a two-component retention agent is at first fed via the feed
openings in the mixing zone into the first flow flowing in the tube, and the
flocs
made by the first component are formed as desired by means of form parts
after the feeding point, after which the second retention agent component is
fed either from the point where the form parts form the flocs as desired or
thereafter. In this way, the shear forces required for the formation of the
flocs
as desired are achieved by means of form parts, and not with mechanical
screens, as previously. Hence, the rejecting effect of screens and the
degradation of the chemical in the screen can be avoided, and in this the
consumption of expensive retention agents can be reduced.
[0014] The invention is described in greater detail in the attached
drawings, in which
[0015] Figure 1 shows a schematic and perspective view of a tube
mixer;
[0016] Figures 2 to 4 show a schematic view of mixers according to
the invention, seen from the side and being cut out;
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[0017] Figure 5 shows a schematic view of a mixer according to the
invention, seen from the longitudinal direction and as a cross-section;
[0018] Figures 6a to 6c show a schematic view of applications
according to the invention; and
[0019] Figure 7 further shows a schematic view of an application
according to the invention, seen from the side and being cut out.
[0020] Figures are greatly simplified for the sake of clarity. The
reference numerals of the figures correspond to each other.
[0021] Figure 1 shows the basic structure of a tube mixer without
equipment relating to the feed of an additive or the like. The mixer comprises
a
tube 1, through which a first flow V~ is conveyed; the flow can be a mixture
of
liquid and solid matter, such as a mixture of fiber and water, or it can be
mere
liquid. Form parts 4a to 4c are arranged on the inner periphery 3 of the tube
1,
the cross-section of the tube being wave-like at this point. The form parts
protrude from the inner periphery of the tube and form control surfaces 5, by
means of which the flow V~ is controlled and turbulence is generated in the
flow. The number, form and dimensioning of the form parts and their positions
relative to each other are designed in a case-specific manner. Preferably,
there are at least three form parts arranged on the inner periphery 3 of the
tube at even distances from each other and in the direction of the
longitudinal
axis of the tube substantially at the same point. One preferred shape of form
parts is indicated in Figure 1. Seen from the direction of flow, the area of
the
wedge-shaped form part is at first approximately zero, because its front edge
is a line-like surface in the direction of the periphery. When proceeding
towards the direction of flow, the line-like surface grows in the direction of
the
radius into a cross-section in the form of a sector of a circle. At the same
time
as it is growing in the direction of the radius of the tube 1, the form part
begins
to diminish in the direction of the periphery, and the rear edge of the form
part
becomes line-like again. Hence, the solids in the flow, such as fibers, do not
adhere to it, but the form is substantially without stagnation points and
remains
thus easily clean. The form parts similar to those shown in Figure 1 can also
be arranged in the way opposite to what is shown, i.e. in such a way that the
sharp edge of the radius is directed forwards. Combining a desired number of
form parts having an appropriate shape and dimensioning at the mixing point
of the tube allows an appropriate mixer to be tailored for each purpose.
[0022] Later, in Figures 2 to 5 and Figure 7, the form parts are
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illustrated for the sake of clarity in a simplified manner as wedge-like
parts. In
addition, figures only illustrate a part of the form parts of the mixer.
[0023] Figure 2 shows a preferred application of the invention. The
form parts 4a to 4b are here provided with a transverse boring 6. The first
end
of the boring is in connection with the feed channel of the additive component
or another feed channel 7 outside the tube 1, and at the second end of the
boring 6 there is a feed opening 8, which is in connection with the space
limited by the tube 1. Thus, the second flow V2 can be fed from the feed
channel 7 into the first flow V~, whereby the flows mix with each other owing
to
the turbulence caused by the form parts. The second flow V2 can be liquid or a
mixture of liquid and solid matter. The second flow V2 is for example a
mixture
of water and fiber pulp, a papermaking chemical, such as a retention or
coloring agent, or it may be for example a filler agent, dilution water or a
paper
machine filtrate, e.g. clear or cloudy water. Further, the second flow may be
for
example wire water or head box pulp. Furthermore, the second flow may be a
combination of an appropriate gas and solid matter.
(0024] In connection with the feed opening 8, there may be a
nozzle 9, which feeds the second flow V2 into the first flow V~ in the desired
manner. The nozzle allows control of the flow rate of the flow V2 and thus
also
the penetration into the first flow V~. In the same way, the nozzle allows
generation of turbulence in the second flow to be fed, which improves the
mixing of the flows with each other. Further, for instance the additive can be
fed together with the feed water through the nozzle, whereby the dosing of the
additive can be affected by the control of the flow and pressure of the feed
water. As can yet be seen when observing the lower form part in the figure,
there may be several feed openings in one form part. Either different
substances or, as the figure shows, a single substance can be fed from the
several feed openings in a single form part.
[0025] Figures 2 and 3 show the mixing zone S of the tube, where
one or more second flows V2 is/are mixed into the first flow V~, the second
flow
being led from the feed channel 7 outside the tube 1. The mixing zone S can
begin as early as before the front edge of the first form part. The mixing
zone
begins as early as after the nearest process component 18 preceding the form
part in the flowing direction, for instance a pump or screen, because in this
case, too, the form part can contribute to the uniform distribution of the
additive. The mixing part S ends after the form parts at the point where the
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mixing effect of the turbulence generated by the form parts has substantially
weakened.
(00261 Example
[0027] The diameter of the tube was 350 mm, the greatest
dimension in the radial dimension of the tube was 120 mm, and the length of
the form part in the direction of the axis of the tube was 200 mm. Pulp having
the flow rate of 3m/s in the tube was conveyed in the tube to the head box of
a
paper machine. The mixing turbulence weakened at a distance of 1,100 mm
from the rear edge of the form part.
[0028] In the solution of Figure 3, the form parts 4a and 4b are
hollow, whereby one or more injection tubes 10 is/are conveyed through at
least some of the form parts, along which injection tubes the second flow V2
is
fed from the feed channel 7 into the inside of the tube 1. The outermost ends
of the injection tubes 10 thus form a feed opening 8, which is at
substantially
the same level as the outer surface of the form part in such a way that no
stagnation points gathering impurity are brought about in the form part. The
outermost end of the injection tube can be provided with an appropriate
nozzle. Further, additives or other flows can be fed into the first flow V1
even
before the form parts 4a and 4b. Thus, nozzles 11 arranged on the inner
periphery of the tube 1 can be used, or alternatively, second form parts 12a
and 12b are arranged on the inner periphery of the tube 1, through which parts
the additive component can also be fed. Also the second form parts 12a, 12b
achieve turbulence in the flow V~ and improve the mixing. The solution
according to Figure 3 enables the use of two-component additives. Thus, the
first additive component L~ is fed before the form parts 4a, 4b, the second
additive component L2 being fed later through the form parts 4a, 4b and/or
after the form parts for instance via a nozzle 30. This enables the feed of
both
components of the two-component retention agent only after the machine
screen. Together with the solids of the pulp mixture, the first retention
agent
component forms what are called flocs, which are degraded by means of the
shear force provided by the form parts 4a, 4b of the mixer. Then, the second
retention agent component is fed via the feed openings 8 in the form parts
and/or via the nozzle 30, which component re-forms the flocs as desired. This
solution allows a substantial reduction in the consumption of the retention
agent compared with the solutions presently in use, in which the first
retention
agent component is dosed before the machine screen, in which case, typically,
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part of the expensive retention agent mixes with the reject separated by the
screen.
[0029] As can be seen from Figures 2 and 3, the feed openings can
be directed in a desired manner, either perpendicularly relative to the first
flow,
upstream or downstream, depending on the situation.
[0030] Figure 4 shows a mixer having hollow form parts 4a, 4b.
Thus, for example, an additive component is fed from the feed channel 7 into
the hollow space 13 of the form parts, which additive component is dosed into
the space limited by the tube 1 through one or more feed openings 8 formed
on the control surface 5 of the form part. The number, form and position of
feed openings can be selected according to the situation. The feed openings
can be formed on the control surface of the form part in accordance with a
predetermined pattern.
[0031] Figure 5 shows a mixer according to the invention, seen
from the end of the tube 1. In this case, the form parts 4a to 4d have a
curved
control surface 5. Through each form part, a different flow is conveyed into
the
inside of the tube 1. Further, a flow can be fed into the first flow through
one or
more feed openings 40 positioned between the form parts.
[0032] Figure 6a shows an application according to the invention. A
pulp component is fed with a pump 16 along the primary line 17 to the
machine screen 18, after which the pulp component is conveyed in the tube 1
to the head box 50 of the paper machine. In this case, the mixing zone S
begins after the nearest process component preceding the head box, i.e. after
the screen 18. Form parts have been arranged in the tube portion between the
screen 18 and the head box 50, and additive flows required are supplied to the
mixing zone in the manner according to the invention. The screen 18 can be a
screen structure known per se, such as a slotted basket screen or hole basket
screen. In the application according to Figure 6b, the pulp line is divided
into at
least two secondary lines 19 after the screen 18, along which the pulp
component is conveyed to the head box of a wire section functioning with a
separate web arrangement of the paper machine, i.e. to a multilayer head box
20, which doses a web having two or several layers to the wire section of the
paper machine. At least one of the secondary lines 19 comprises a mixer 21
according to the invention, which mixer enables for instance the feed of a two-
component retention agent after the machine screen. The mixing of each
secondary line and the addition of additives can be controlled separately.
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[0033] The solution shown in Figure 6c substantially corresponds to
the one shown in Figure 6b, except that here the nearest process component
preceding the head box (20) is a pump (16). Thus, the mixing zone (S)
extends from the pump (16) to the head box (20).
[0034] Owing to the improved penetration and mixing, additives can
be fed from one or more smaller feed conduits, whereby in the paper machine,
the variation of the web profile in the machine direction and cross-direction
is
reduced. In other words, the web profile is thus more even and there is not so
much need for fixing. When the scale of mixing is reduced in the way
described above, the mixing result is better. Thus, the formation, i.e. the
small-
scale basis weight variation is improved, in other words the formation reading
is reduced. Owing to the reduction in the profile variation and the basis
weight
variation, the feed point of the retention agent, for example, can be
positioned
closer to the head box. Thus, chemicals can be saved, because the effect of
some retention agents weakens as the effective time increases. The cross-
machine profile of the filling agent cannot be fixed in the paper machine.
Weak
or uneven feed of retention agent results in a poor filling agent profile. The
feed of the retention agent can be improved by means of the invention,
whereby the filling agent retention is more even, and therefore also the
filling
agent profile is more even.
[0035] The upper embodiment of Figure 7 illustrates a mixer in
which a mixture of two different components L~ and L2 is fed through the form
part 4. Thus, for example some filling agent or fiber pulp can be fed via the
first feed channel 7, and for example some chemical can be fed via the
second feed channel 31, whereby the components are mixed with each other
before the mixture formed thereof is dosed into the flow V~. If the first
component to be mixed is a mixture of liquid and solid matter, for example a
paper machine filtrate, and the second component is a retention agent, the
time of the pre-mixing of said components is fixed in such a way that the
retention agent does not have time to react in an undesired way with the
solid'
matter particles in the first component. A solution of this kind enables
dilution
of a retention agent and other chemicals also with impure liquids containing
solid matter before they are fed into the first flow.
[0036] In the lower solution of Figure 7, the mixer comprises three
successive form parts in the longitudinal direction of the tube. The additive
L~
is fed through the first form part 12 and a second additive L2 is fed through
the
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third form part 32. The second, i.e. the middlemost, form part 4 functions as
a
static mixing member. A solution of this kind is well applicable to the dosing
of
two-component chemicals.
[0037] The drawings and the related specification are only intended
to illustrate the idea of the invention. The details of the invention can vary
within the scope of the claims. Thus, the shape of the form part can be
selected according to the need. The form part can thus be wedge-shaped or
pyramid-shaped, a part comprising curved surfaces, or otherwise appropriately
designed. What is essential is that the form part comprises control surfaces
which achieve a sufficient turbulence in the pulp flow for the purpose of
mixing.
In addition, it is essential that the form parts remain clean in the flow of
pulp
components. Further, the form parts can be arranged to be adjustable,
whereby their position relative to the tube (on the periphery of the tube and
in
the longitudinal direction of the tube) and/or their shape can be adjusted to
achieve the desired mixing. The control surfaces of the form parts can be
controlled to extend a desired distance from the periphery of the tube towards
the inner part of the periphery of the tube, for example.
