Note: Descriptions are shown in the official language in which they were submitted.
CA 02413210 2002-12-16
METHOp AND SYSTEM FOR IMPROVING THE DRYING CAPABILITY
OF A PAPER WEB
F ~~~gf the invention:
This invention refers to a method according to the introductory part of claim
1.
Having passed the water extradlon means of a paper making machine the paper
web
passes into the drier group of the paper making machine with a water content
of
approx. 5o%. The drier group consists of a plurality of drying cylinders made
from
Steel which in their interior are supplied with hot steam and which generally
are
arranged in two planes one above the other and are staggernd relative to each
other sa
that the paper web to be dried passes between the drying cylinders
successively
embracing said cylinders over part of the cylinder surface. Passing the
cylinders the
paper web is pressed against the surfaces of the cylinders by means of a
follower fabric
web as well in the upper as in the lower group of drying cylinders,
CA 02413210 2002-12-16
Z
~~jk;grou d of the Invention:
Modem paper making machines operate with speeds of approx. 1000 - 2200 meters
per minute. With increasing production speed the paper web during its free
running
phase which means within the transient sections between two adjacent drying
cylinders each is to be supported in order to avoid fluttering, instability
and finally
breaking of the paper web. This results in a system which instead of two
separate drier
webs uses one drier fabric only for the upper and the lower group of drying
cylinders,
which drier fabric is continuously in contact with and supports the paper web.
For drying a continuous running sheet of paper having an upper row of drier
roils and a
lower roll of drier rolls staggered with respect to the rolls of the upper row
and a paper
sheet passing successively around the drier rolls according to US 3,378,936 A
a pair of
double mesh screens maintained under tension and adapted to firmly contact the
top
and bottom of the paper sheet and support it throughout substantially the full
extent of
the drier are known. The upper row of drier rolls and the lower row of drier
roils are so
positioned in relation to each other that the distance which the paper must
travel
between rolls is decreased to a minimum.
Furthermore, from US 4,850,121 a drier section of a paper making machine with
horizontal upper and lower groups of drier rolls is known, which form
triangular
pockets between an upper and a lower cylinder each. An endless drier felt is
trained to
run a paper web sinuously sucessively and in direct contact on the upper
perimeter
areas of the upper and cower drier roils. Broke is ejected downwardly from the
pocket.
To facilitate such broke ejection, drier felt roll wrap enhancing felt rolls
in the pockets
are provided, which define a respective brokeyreceiving and ejecting subpocket
under
the upper drier rolls at each pocket.
A system of this type is known as the UNO RUN System with which the paper web
is
supported along the exposed section between the drying cylinders, and the
upper or
CA 02413210 2002-12-16
the lower group of drying cylinders is heated. The output of a system of this
type is
increased by reducing the stopping period of the machines. This results in a
reduction
of the drying capacity of the group of drying cylinders and in an increase of
the specific
steam consumption.
ThP"lnvention:
it is an object of this invention in view of the known systems to avoid the
danger of
fluttering and thus the damage of the web to a considerable extent by
maintaining the
stability of the paper web during its transition from one group of drying
cylinders to the
other, increasing the heat transfer from the drying cylinders onto the paper
web and in
this manner making available more heat energy, obtaining an improved mass
transfer
of waterlair within the web sections, in which during the passage of the web
evaporization of the humidity from the paper web is obtained, and improving
the
effectivity of the drier section in view of the specific steam consumption.
According to the subject invention this object is solved by the features of
the
characterizing part of claim t . Further embodiments are the subject of the
subclaims.
This proposal according to the invention allows to increase the degree of
embracing
the heated drying cylinders forming the plane of the upper cylinders
considerably so
that an increased and more intense heat transfer from the upper drying
cylinders on to
the paper web to be heated will be obtained. Furthermore, this allows to
increase
considerably the length of the section of the paper web, which between two
adjacent
heated cylinders extends in free air, and to increase considerably the mass
transfer of
water/air by evaporizing the humidity within the paper web, because the paper
web
when passing the free section between two adjacent heated cylinders compared
with
common geornetries passes a section of extended Length for discharging
humidity,
which is set free by heating up the cylinders. Choosing the geometry of the
drying
cylinders with deflection rollers mainly depends on the framing
characteristics of the
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4
machine so that corresponding embodiments of the invention will be adapted to
the
spatial situation according to the framing of the plant.
The angle over which the paper web embraces the heated drying cylinders with
conventional plants is approx. 2 x 170° = 340° (with upper and
lower heated
cylinders), with a plant according to the UNO RUN System it is approx.
210°, and
with a system according to the invention it is approx. T60°. The latter
figure compared
with the figure of conventional UNO RUN machines is considerably higher so
that a
substantially larger heat amount is transferred from the heated cylinders onto
the paper
web. The even higher figure with conventional machines is caused by the fact
that as
well the upper as the lower drying cylinders are heated.
Practice has proven that with a diameter D of the heated drying cylinders the
section of
the paper web which is in contact with the surrounding air, which means the
free
section between two or three adjacent heated cylinders, is about 2,0 D with
conventional systems, about 3,5 D with a system UNO RUN, and about 4,15 D with
a
system according to the subject invention so that with a system according to
this
invention considerably more humidity of the paper web can be removed from the
section between two adjacent heated cylinders compared with prior art systems;
among others, this results from the fact that in view of the longer section
more time is
available for evaporization.
The various embodiments of the subject invention allow the designer to
consider a
number of other criterions, such as the spatial conditions in accessing the
pockets,
considering the framing geometry, choosing the positioning of the web
stabilisators,
etc. The designer also will be in a position to combine elements of different
embodiments of the invention with each other for special cases, for example to
bring
c!ifferent groups together, make alterations concerning the framing geometry,
and the
like.
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~speciaily, when n~-designing already existing plants and machines it is
useful in view
of already available web stabilisators, blowing boxes, etc. to have the
possibility of
alterations in order to be able to use existing components to an optimum
extent.
According to the invention with choosing among different embodiments existing
components, for example guide rollers, ball bearings, etc., can be used for
higher web
tensions without any reinforcement.
The higher mass transfer of water/air which can be obtained with the subject
invention,
has the result that the paper web will arrive at the subsequent heated drying
cylinders
at a lower temperature than with conventional systems, for example an UNO RUN
System. This has the effect that the heat transfer will be correspondingly
increased.
Based on the higher values of the heat transfer the steam consumption of the
plant will
be decreased.
Altogether, according to the proposal of the subject invention the efficiency
of the
system compared with a known system UNO RUN can be increased by approx. 25 -
30%.
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6
In the following the Invention wiN be described by way of examples with
reference to
the accompanying drawings, in which:
Fig. 1 shows a known embodiment of a common drier group of a paper making
machine in schematic representation,
Fig. 2 shows an embodiment of a known drier group which is called UNO RUN
System,
Fig. 3 is an embodiment of a drier group of a paper making machine according
to the
subject invention,
Fig. 4 is a further embodiment of a drier group according to the invention,
Fig. 5 is a further variation of a known embodiment of a drier group called
"SINGLE
FELT System",
Fig. 6 is a further embodiment of the subject invention which has been
Improved
over a drier group according to Fig. 5,
Fig. 7 is another variation of a known embodiment of a drier group,
Fig. 8 shows another embodiment according to the invention which has been
improved in view of a drier group according to Fig. 7, and
Fig. 9 is a variation of an embodiment according to Fig, 8 of the subject
invention,
Detailed Description of Embodiments:
The embodiment according to fig. 1 shows a geometry with an upper group of
heated
drying cylinders 1, 3, 5, 7 and a lower group of heated drying cylinders 2, 4,
6 which
are staggered relative to each other in a zigzag formation in two parallel
planes. An
upper drying fabric 8 is passed over the upper drying cylinders 1, 3, 5, 7 and
over
guide rollers 9, 10, 11 between the drying cylinders 1 and 3, 3 and 5, 5 and 7
and
rests upon a section A-$ /E-F /etc. ... (heating sections). Upstream of the
drying cylinder
i and downstream of the drying cylinder 7 additional guide rollers 1 ~, 13 are
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7
provided, and in the further course of the fabric web 8 additional tensioning
rollers,
guide rollers, etc. can be positioned in a manner known per se.
In correspondence with the upper fabric web 8 a lower fabric web 14 fs passed
over
the lower section of the heated drying cylinders 2, 4, 6 which web is pressed
against
the drying cylinders 2, 4, 6 by means of guide rollers 15, 16, 17, 18 within
section C-D
/etc. ... (heating sections). The wet paper web which on passing through the
drying
group discharges humidity is marked by 19. It extends over the drying
cylinders 1 - 7
alternately with the upper and the lower section of the group of drying
cylinders in a
zigzag formation between the fabric webs 8 and 14 one after the other, and its
sections
B-C, D-E /etc. (steaming sections), which means the transient areas each from
the upper
onto the lower drying cylinders and vice versa are not supported. With this
type of
system the speed of passage is limited.
Fig. 2 shows a further development of the system according to Fig. t, namely
the so-
called UNO RUN geometry with which the fabric web 20 and the paper web 19
together are guided in a zigzag formation over the drying cylinders 1 - 7,
whereby the
fabric web 20 presses the paper web 19 in the area A=B' lE'-F' /etc. (heating
sections)
against the upper group of heated drying cylinders 1, 3, 5, 7. Because the
fabric web
?.0 at the drying cylinders 1, 3, 5, 7 is arranged resting upon the paper web
19, the
association of paper web and fabric web at the lower drying cylinders 2, 4, 6
is vice
versa, which means that the fabric web 20 is arranged between the paper web 19
and
the drying cylinders 2, 4, 6. In this manner the fabric web at the lower
drying cylinders
is exposed to the heat of the drying cylinders the surface of which may be
heated by
steam, contrary to the paper web to be dried so that heating the lower drying
cylinders
prevents the transfer of heat onto the paper web, Therefore, in practice the
lower group
of drying cylinders is no longer heated, and accordingly, section B'-E' forms
the
evaporization section. At the transition from the upper to the lower drying
cylinders
web stabilizers 21, 22, 23 are provided which receive and discharge the amount
of air
taken along with the fabric web 20 which air would cause an air barrier in
front of the
CA 02413210 2002-12-16
cylinder 2. Reference numerals 24, 25, 26 point to scrapers known per se which
act
upon the surface of the drying cylinders 1, 3, 5 and 7.
The system according to Fig. 3 shows an embodiment of the invention which is
an
improvement of the system according to fig. 2. The drying cylinders 1 - 7 are
arranged
according to the drying cylinders 1 - 7 of Flg. 2, the paper web 19 and the
fabric web
za are equivalent to webs 19 and 20 of Fig. 2. The lower drying cylinders 2,
4, 6 can
be unheated, whereas the upper drying cylinders ~, 3, 5, 7 are heated. The
route of the
webs is extended in length in the running direction compared with the
rectilinrar
passage and is designed between cylinders 19, 20 by inserting a guide roller
27,
between cylinders 4 and 5 by inserting a guide roller 28, and between
cylinders 6 and
i by inserting a guide roller 29 so that the drying cylinders 3, 5, 7 are
embraced over a
larger section K-t_ (heating section) of the peripheral surface of the
cylinder, and thus
results In a considerably longer heat transfer section compared with the
system
according to fig. 2. In this manner a longer section G-K compared with Fig. 2
(namely
B'-E') is available for evaporating the humidity which section combines the
embracing
section H-I at the unheated cylinder 2 and the free web section G-H and I-K
deflected
by the guide roller 27.
In view of the shifting and deflection within the geometry according to Fig. 3
of the
rectilinear (in Fig. 2) transient passage of the webs from one drying cylinder
3 to the
succeeding cylinder 4 an Increased heat transfer from the drying cylinders to
the paper
web is achieved because the paper web embraces the heated drying cylinders 3,
5, 7
over a larger section K-l.. On the other hand in view of the larger free
running section
G-K of the paper web 19 between leaving the upper drying cylinder 1 and
reaching the
next upper drying cylinder 3 the corresponding paper web section covers a
longer
distance and accordingly, there is more tune available for intensive
evaporization of
the humidity within the paper web so that an improved evaporization of the
humidity
will be obtained. Also with this embodiment similar to the arrangement
according to
Fig. 2 web stabilizers 21 and scrapers 24 can be provided.
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9
With the embodiment according to fig. 4 the deflection of the paper web 19 and
the
fabric web 20 supporting said paper web contrary to the embodiment of Fig. 3
is
achieved in such a manner that by inserting guide rollers 30, 31, 32, 33 the
corresponding heated drying cylinders 1, 3, 5, 7 of the upper group are
embraced at a
larger angle and over a longer section K'-L' (heating section) compared with
the
embodiment according to Fig. 2 and in relation to the drying cylinder 1
according to
Fig. 3 so that in this manner a higher amount of heat transfer from the drying
cylinders
to the paper web will be obtained. At the same time, in view of the extension
of the
free, unsupported section G'-K' of the web resulting from the deflection of
the route of
the web a larger evaporization section between two subsequent, heated drying
cylinders 1, 3 or 3, 5 or 5, 7 is achieved so that the paper web is allowed
more time for
discharging humidity.
Fig. 5 shaves another known embodiment of a group of heated drying cylinders
34, 35,
36, 37 with interposed deflection rollers 38, 39, 40 in a different design of
the drier
group, which is known as a "SINGLE FELT System". With this type of system the
lower
group of heated or unheated drying cylinders, which are substituted by mini-
cylinders
or deflection rollers 38 - 40 is lacking. The heating section N-0 corresponds
substantially with the geometry according to Fig. 2, and the evaporation
section O-P is
considerably shorter than that of the geometry according to Fig. 2, because
the mini-
cylinders are positioned at a small distance from the drying cylinders 34, 35,
36, 37,
and in addition thereto have a substantially smaller diameter.
Fig. 6 shows a system which Is a further development of the system according
to Fig. 5,
and which is part of the invention. The paper web 19 and the fabric web 20 are
passed
in common over the heated drying cylinders 34 - 37 in such a manner that both
webs
embrace the surface of the cylinder periphery to a greater extent than with
the system
according to Fig. 5. The heating section N'-O at the drying cylinder 35
extends from
the position N' across the cylinder periphery to the position O so that the
paper web
19 embraces the cylinder periphery aver a longer section of the drying
cylinder than
with the known embodiment, with the result that mare heat is transferred from
the
CA 02413210 2002-12-16
1~
drying cylinder 35 onto the paper web 19. This results from the fact that in
addition to
the deflecting rollers 38, 39, 40 a further guide roller 49, 42, 43 each is
added, and the
web section O-P' between two adjacent drying cylinders 35, 36 is substantially
extended so that in view of such increased evaporation section an improved
evaporation, which means an increased mass transfer of water/air, is obtained.
Fig. 7 shows a known geometry of a drying system consisting of upper and lower
heated cylinders, equivalent to the drawing of Fig, 1, however, in the form of
intermediate groups with groups separated from each other. With this type of
design
blast suction boxes are required for ventilating the pockets. The geometry of
the drier
system according to Fig. 7 is dependent on the framing of the machine. The
drying
cylinders 1 - b of a group are separated by a preceeding cylinder 58. The
drying
cylinders are all heated. Associated to them are guide rollers 44, 45, 46 and
47, over
which the upper fabric web 48 is passed, and guide rollers 49, 50, 51 and 52,
over
which the lower fabric web 53 is passed. Furthermore, blast suction boxes 54,
55, 56,
57 are provided, which mainly are used as paper web stabilizers. The shown
drying
cylinders 58 and 60 are part of a preceeding or a succeeding drier system.
With this
type of parts of the geometry of the paper web 19 predetermined sections
between an
upper and a lower guide roller each or between a guide roller and a drying
cylinder are
not supported and thus are not guided. Heating section and evaporating section
correspond with the geometry of the drier group according to Fig. 1.
This type of known design has been developed according to Flg. 8 In an
improved
man»er so that the web is ventilated very well, which means that blast suction
boxes
can be dispensed with, and that the paper web 7 9 is supported by the fabric
web 62
along its entire route. Paper web 19 and fabric web 62 are passed along the
drying
cylinders 1 - 6 during their passage in such a manner that the heated drying
cylinders
1, 3, 5 are embraced by the webs to a by far further extent than the heated
drying
cylinders 1, 3, 5 of the system according to Fig. 7, and that accordingly the
heati»g
section T-U is considerably increased. This is achieved by the fact that the
free section
of the web between an unheated and a succeeding heated drying cylinder 2, 1;
4, 3 is
CA 02413210 2002-12-16
11
substantially increased, as the webs 56 and 62 are passed around the guide
rollers 50,
51, 52 in a loop, and accordingly, the evaporiaation section U-V also has a
substant(allly greater length.
With the passage of the web according to flg. 8 the evaporation section U V
joining the
heating section T-U is extended or alternatively deflected by means of the
deflection
rollers 50, 51 or 52 before the web reaches the corresponding heated drying
cylinder
1, 3, 5, whereas that part of the web leaving the crorresponding drying
cylinder 1, 3, 5
is passed in a straight Line, which means at the shortest distance to the
drying cylinder
4or6.
The variation according to fig. 9 Is designed so that the web section V W
running-up at
the corresponding drying cylinder 1, 3, 5 extends in a straight line from the
preceeding
drying cylinder 2, 4, 6 to the drying cylinder 1, 3, 5, and the leaving web
section W-X
is passed opposite to the dir~ectian of the web passage around the
corresponding
deflection roller 50', 51' or 52', before it reaches the corresponding
subsequent drying
cylinder 4, 6, 60 so that the evaporation section W-X is substantially longer
than the
preceeding section joining the extended heating section V W.
This variation considers structural conditions of available paper machine
drier groups
so that structural groups of an existing machine can be used if the plant is
to be
modified.
Separating the groups of these two variations has been provided with a known
NL1CK-
OOWN Geometry" structure by using the embodiments according to the invention
so
that also with the separations within the groups the support of the web is
guaranteed
during the entire operation.
