Note: Descriptions are shown in the official language in which they were submitted.
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Distribution unit in an inlet box for a dewatering press
The present invention relates to a distribution unit for adding a fibre
suspension to an
inlet space of a dewatering press, an inlet box comprising one or more of said
distribution units, a twin-wire press with said inlet box and a use of said
distribution
unit or inlet box for a twin-wire press.
Dewatering presses for dewatering of a fibre suspension and forming of a
continuous
web thereof are previously known. One example of a known dewatering press is a
twin-wire press. Dewatering of the pulp is usually done from an inlet pulp
concentration of 3-8 percentages by weight to an outlet pulp concentration of
30-50
percentages by weight. According to the state of the art, such twin-wire
presses
comprises lower rolls, an endless lower wire running in a path around the
lower rolls,
upper rolls, and an endless upper wire running in a path around the upper
rolls. The
two wires co-operate with each other along dewatering sections of said paths,
in which
the wires forms a wedge-shaped dewatering space for the fibre suspension
between
each other. During displacement of the wires along said dewatering sections,
the wires
thus successively compresses the fibre suspension in the wedge-shaped space,
whereby the fibre suspension is initially pressed and dewatered and formed to
a
continuous fibre web between the wires.
An inlet box provides for supply of fibre suspension to the wedge-shaped
dewatering
space between the wires. The known twin-wire press further comprises two
dewatering
tables supporti:ng the respective wire in said dewatering sections of the
path, such that
the wedge-shaped dewatering space is formed between the wires, and a roll
arrangement situated after the dewatering tables, as seen in the direction of
movement
of the wires, for finally pressing and dewatering of the fibre web between the
wires, so
that the fibre web will get a desired dryness. Alongside the longitudinal
direction of
the wires, in the wedge-shaped dewatering space, there are perforated
dewatering
elements that are arranged against the wires outside the dewatering space.
Formed
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filtrate flows through the wires and the perforated dewatering elements and is
lead
away to upper and lower outlet boxes, respectively, arranged at the dewatering
tables.
The upper and lower outlet box, respectively, may be divided into several
chambers
whereby a filtrate that flows through the upper and lower dewatering elements,
respectively, may be divided into partial filtrate in two or more chambers in
the
respective outlet box.
In the traditional twin-wire press the geometry for the inlet box, for adding
of the fibre
suspension to the wedge-shaped dewatering space between the wires, is very
difficult
to set to obtain correct and desired suspension flow. Said geometry is
carefully tested
through numerous tests and trial-runs for a long time before the twin-wire
press is
placed in production. The geometry for the inlet box is hence fixed.
The fibre suspension is fed from a container, though gravity or with pump, via
inlet
pipes in to a distribution unit at the inlet box. When entering into the
distribution unit
the fibre suspension meets a first distribution sheet, whereby the fibre
suspension is
distributed over the entire width of the distribution unit in a slit and the
fibre
suspension is thereafter re-linked around the distribution sheet to the next
slit and on to
an outlet for further feeding to the wedge-shaped dewatering space between the
wires.
Different kinds of disturbances to the production can occur in the process,
whereby
problems arise with the inlet box. In the inlet box formation of so called
plugs,
consisting of fibre suspension that is locally thickened resulting in that the
fibre
suspension stands still, can occur, resulting in that the inlet box has to be
opened for
cleaning. Malfunction on the propelling motor, system errors or an emergency
halt of
the machine can also led to occasional problems with the inlet box, which
means that it
has to be opened for control and occasional repair. It also happens that the
inlet box
needs to be opened for performing of normal maintenance on the inlet box.
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A traditional inlet box consists of a number of metal sheets which are joined
with a
large number of bolted joints. Opening the inlet box to make room for cleaning
or
perform repairs on the inner of the inlet box, such as the slits, is time
consuming and
complicated. Large parts of the inlet box have to be disassembled.
Straightness of the
metal sheets and the tolerances in general for the slits are precise, to get
as good
distribution of the fibre suspension as possible. Since the slits, which are
formed from
inner metal sheets in the inlet box, has an extensive spreading over large
surfaces with
few supports, the load on the slit sheets are relatively large. The slits,
which are
formed from the metal sheets, is therefore very sensitive for rapid increases
in
pressure. It is enough with a few bars overpressure to damage the metal sheets
and
make unacceptable changes in the slit tolerances. If the pressure gets far too
high the
inlet box could be damaged and in worst case collapse.
A conventional inlet box comprises one or more distribution units for adding
of a fibre
suspension to an inlet space at a dewatering press. Since the tolerances of
the slits of
each distribution unit are carefully determined, usually multiple distribution
units is
required for one inlet box at a dewatering press, since it otherwise becomes
far too
large surfaces and difficult to maintain the set tolerances in the slits.
In a conventional inlet box, comprising one or more distribution units, it is
prior
known to use pressure sensors, placed inside of respective distribution unit
in the inlet
box, which when sensing an exceeding pressure sends a signal to the control
system of
the press for shutting down the feeding of the fibre suspension to the inlet
box.
However such a shut down happens via the control system with some delay. It is
also
known that there are explosive members connected to the control system, which
are
mounted in the distribution units in the inlet box so that the bolted joints
can be blasted
and the joined metal sheets separated, at a signal from the control system, so
that the
increased pressure inside of the distribution units in the inlet box can be
removed, to in
such a way prevent permanent damages to the inner parts of the distribution
units of
the inlet box. Naturally there are some damages to the bolted joints and outer
metal
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sheets which require extensive repairs. Maintenance, control and repairs of a
conventional distribution unit or inlet box resulting in long stoppage of
production,
which means lost production time, and hence a cost.
The purpose of the present invention is to at least partially eliminate the
disadvantages
associated with the state of the art mentioned above. A general purpose in
accordance
with the present invention is to achieve an improved distribution unit and an
inlet box
respectively, comprising one or more distribution units. More precise the
purpose is to
achieve a distribution unit and an inlet box respectively with longer life
span and/or to
achieve a simpler and faster maintenance in a dewatering press, such as a twin-
wire
press. Yet another purpose is, to a larger extent, to be able to even out the
increased
pressures in the distribution unit in the inlet box or to stop the feeding of
the fibre
suspension well in time before the risk of damages to the distribution unit or
the inlet
box arise. Furthermore, a purpose is to reduce the cost of repairs, control
and
maintenance of an inlet box for a dewatering press such as a twin-wire press.
This purpose is achieved with a distribution unit for adding of a fibre
suspension to an
inlet space at a dewatering press, in accordance with the present invention,
which
distribution unit comprise a distribution housing, which forms at least one
distribution
slit. The distribution slit is intended to be coupled to the inlet space of
the dewatering
press. The inlet box comprise at least one inlet member for adding of fibre
suspension
to the distribution slit, so that the fibre suspension passes through the
distribution slit
while spreading in the slit. The distribution housing is equipped with at
least one
opening to the distribution slit and a hatch belonging to the opening for
shutting
thereof. The hatch is hinged to the distribution housing in such a way so that
it is
pivotable relative to the distribution housing between a first position, in
which the
hatch seals the opening, and a second position, in which the hatch exposes the
opening. The distribution unit is arranged to enable the hatch to move at
least
somewhat towards an open position under influence of a pressure, exceeding a
predetermined value, in said distribution slit.
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Repairs and inspection becomes less complicated in comparison to the
construction in
accordance with the traditional distribution units in an inlet box. In
accordance with
the present invention the cost of repairs and inspection is reduced, as well
as
assembling and replacing since the duration of the production halts can be
considerably reduced, in comparison to the traditionally used distribution
units in an
inlet box. Damages to the distribution unit and the inlet box, respectively,
can be
avoided to a larger extent.
Thanks to the fact that the distribution unit is arranged to enable movement
of the
hatch to at least a somewhat more open position under the influence of a
pressure,
exceeding a predetermined value, in said distribution slit, the hatch can
consequently
be automatically opened in case of a increased pressure inside of the
distribution unit,
whereby damages to, among other things, the distribution slits in the
distribution unit
can be minimized to a larger extent.
According to one embodiment of the present invention, a hydraulic cylinder is
arranged to move the hatch between said first and second positions.
The pressure in the hydraulic cylinder can be adapted to essentially
correspond to the
load that the pressure by the maximum allowed pressure in the distribution
slit creates.
The present invention also relates to an inlet box for adding of a fibre
suspension to an
inlet space at a dewatering press, comprising one or more distribution units,
which
have been described above in accordance with the present invention.
The present invention also relates to a use of a distribution unit or an inlet
box, which
have been described above in accordance with the present invention, for a twin-
wire
press.
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The present invention also relates to twin-wire press comprising an inlet box,
which
have been described above according to the invention.
Additional preferred features, advantages and preferred embodiments according
to the
invention are evident from the dependent claims, and also from the following
description of examples of embodiments.
The present invention shall now be described in more detail by examples of
embodiments, with reference to the accompanying drawings, without restricted
interpretation of the invention thereof, where
Fig. lA shows, schematically in a partial view, a cross-section of a
distribution
unit comprising a hatch, according to one embodiment of the present invention,
in a
first position with the hatch closed,
Fig. 1B shows, schematically, in a partial view, a cross-section of the
distribution unit, according to Fig. lA, in a second position with the hatch
open,
Fig. 1 C shows schematically, in a perspective view, a part of the
distribution
unit, according to Fig. lA-B, with the hatch in the open position,
Fig 1D shows schematically, in a perspective view, a part of an inlet box,
comprising a plurality of distribution units with a respective hatch,
according to the
distribution unit in Fig. lA-C, at an inlet part of a dewatering press, and
Fig. 2 shows, schematically in an overview, a longitudinal cross-section
through a twin-wire press according to an embodiment of the present invention
that
can comprise the inlet box with the embodiment shown in Fig. 1D.
In Fig. lA-C the distribution unit 1 is shown according to one embodiment of
the
present invention. The distribution unit 1 comprises a distribution housing 2
that forms
at least a first distribution slit 4 and a second distribution slit 4'. The
distribution unit 1
comprise at least one inlet member 6 for adding of fibre suspension to the
distribution
slit. The distribution housing 2 comprise an outlet opening 5 via which the
fibre
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suspension passes after passage through the distribution slit 4, 4'. The fibre
suspension
passes through the distribution slit while spreading in the slit. The
distribution housing
2 is equipped with at least one opening 8 to the distribution slit 4, 4' and a
matching
hatch 10 for sealing of the opening 8. The hatch 10 is hinged to the
distribution
housing 2, in a first pivot 11, so that the hatch is pivotable relative to the
distribution
housing 2 between a first position P 1, in which the hatch 10 seals the
opening 8, and a
second position P2, in which the hatch 10 exposes the opening 8. Consequently,
easier
and faster maintenance can be achieved in a dewatering press, such as a twin-
wire
press. Furthermore the increased pressures in the distribution unit 1 can to a
larger
extent be evened out. Feeding of the fibre suspension 1 can also be aborted
well in
time before risks of damages to the distribution unit arises. This can take
place through
that the hatch 10 is automatically opened, at least partially at a to large
pressure inside
of the distribution unit 1 and if it is decided that, by the process control
system or an
operator, there is risk of damages to the distribution unit 1 if the running
is continued,
the feeding of the fibre suspension is aborted. A pressure that should affect
the
opening of the hatch should be above a predetermined value, in said
distribution slit 4,
4', before the hatch automatically can be opened.
The distribution unit 1 can comprise at least one hydraulic cylinder 12,
arranged to
move the hatch 10 between said first and second positions P 1, P2. The
hydraulic
cylinder can be arranged in front of the front end of the hatch 13. The
cylinder 14 of
the hydraulic cylinder 12 is preferably arranged to the distribution unit 1,
at the
underside 15 (see Fig. 1D) of the distribution unit. The outer end 16 of the
piston bar
18 of the hydraulic cylinder is hinged to the hatch in a second pivot 20. As
shown in
Fig. lA-D, a link arm 22 can be fixedly fastened to the top of the hatch 24.
The link
arm 22 is in its first end 26 hinged on the distribution housing 2 in the
first pivot 11
and in the second end 28 is the link arm 22 arranged to the piston bar 18. As
illustrated in Fig. lA-D, preferably two hydraulic cylinders 12 are arranged
at a hatch
10 to move the hatch between the positions P 1, P2.
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The pressure that is provided by the hydraulic fluid, such as oil, in the
hydraulic
cylinder 12 can be adapted to essentially correspond to the load that the
maximum
allowed pressure in the distribution slit 4, 4' creates. Calculation of the
maximum
allowed pressure in the distribution slits 4, 4' of the distribution units 1,
with regards
to a certain safety margin, can preferably be done at the construction,
installation or
assembly of the distribution units 1. An inlet box 30 preferably comprises
several
distribution units 1. The pressure in the distribution slits 4, 4' can
preferably be
measured with a pressure sensor arranged in a common inlet pipe (not shown),
for
adding of fibre suspension to the distribution slits 4, 4' at the distribution
units 1, to
which inlet pipe all of the inlet members 6 are connected. The hydraulic
cylinder 12
can be provided with a pressure limiting member, such as a non-return valve.
The
pressure in the hydraulic cylinder 12 can also be measured using a manometer.
Fig. 1C shows a distribution unit 1 comprising the hatch 10. As is clear from
Fig. 1D,
an inlet box 30 is shown, according to one embodiment of the present
invention, with a
number of distribution units 1 according to Fig. lA-C, comprising a plurality
of
hatches 10. The inlet box 30 is shown in Fig. 1D arranged at a dewatering
press, such
as a conventional twin-wire press 50. The twin-wire press 50 shows a
dewatering
space (not shown in Fig. 1D), an endless lower wire 54 and an endless upper
wire 56.
The dewatering space has en inlet space 52, situated at and around the inlet
box 30.
The distribution slit 4, 4'of respective distribution unit 1 at the inlet box
30 is intended
to be connected to the inlet space 52 of the dewatering press and the inlet
box 30 is
hence arranged for adding of a fibre suspension to the inlet space 52 of the
twin-wire
press 50. Again with referral to Fig. lA-C, the fibre suspension is added via
the
distribution slit 4, 4' and de-linking takes place under spreading in at least
one
distribution slit 4 in the distribution housing 2. The fibre suspension passes
after
passage through the distribution slit 4, 4' via the outlet opening 5 at the
distribution
housing 2 to the inlet space in the dewatering press.
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Fig. 2 shows schematically in an overview a longitudinal cross-section through
a
conventional twin-wire press 50 according to an embodiment of the present
invention
which can comprise the inlet box 30 with a plurality of distribution units 1
according
to the embodiments shown in Fig. 1A-D. Corresponding conventional features and
parts is denominated with the same reference numbers for the twin-wire press
50
shown in Fig. 2 as for the distribution unit 1 and the inlet box 30,
respectively, with the
embodiments according to the present invention shown in Fig. lA-D.
The conventional twin-wire press 50 shows a dewatering space 58 with an inlet
space
52 in the area at and around the inlet box 30. The fibre suspension to be
dewatered is
added from the inlet box 30 to the dewatering space 58 limited between the
endless
lower wire 54 and the endless upper wire 56 under movement of the wires 54,
56.
Perforated dewatering elements (not shown) have contact with the wires outside
of the
dewatering space. The filtrate flows through the wires 54, 56 from the
dewatering
space and is collected in outlet boxes 60, 62. The lower outlet box 60,
arranged in a
lower dewatering table, receives filtrate that flows from the dewatering space
through
the lower wire 54 and lower dewatering element, while the upper outlet box 62,
arranged in an upper dewatering table, receives filtrate that flows from the
dewatering
space through the upper wire 56 and upper dewatering element.
The twin-wire press 50 comprises three lower rolls, one drive roll 100, one
control roll
102 and one tension roll 104. The said endless lower wire 54 runs in a path
around the
lower rolls 100, 102, 104. In the corresponding manner said endless upper wire
56
runs in a path around three upper rolls, one drive roll 106, one control roll
108 and one
tension roll 110. Said upper outlet box 62 in the upper dewatering table that
supports
the upper wire 56, and said lower outlet box 60 in the lower dewatering table,
that
supports the lower wire 54, forms the dewatering space 58 between the wires
54, 56.
The twin-wire press comprises one common roll arrangement 112 according to the
state of the art.
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In operation of the twin-wire press 50 according to Fig. 2, the transportation
of the
wires 54, 56 takes place under rotation of the rolls 100-110. The fibre
suspension to be
dewatered is fed to the oblong dewatering space 58 via the inlet box 30 at the
inlet
space 52 thereof. The fibre suspension is dewatered in the dewatering space 58
under
movement of the wires, so that a filtrate flow from the dewatering space 58
through
the wires 54, 56 and the perforated dewatering elements is formed. The
filtrate that
flows from the dewatering space through the wires is collected in the outlet
boxes 60,
62.
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