Note: Descriptions are shown in the official language in which they were submitted.
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A PRESS FOR DEWATERING A SUSPENSION
Field of technique
The present invention relates to a press that comprises a distribution device
arranged to receive a liquid suspension of solid biological material and
distribute said suspension horizontally by means of a dewatering drum, a
.guide plate and a trough.. arranged below the dewatering drum, which =. plate
and trough are arranged at a distance from said dewatering drum for forming -
a gap between the dewatering drum on one side and the guide plate and the
trough on .the other. side, into which gap liquid can. be pressed from the.
suspension. upon operation of the the press- in order to-produce. dewatered.
pulp from the solid biological material, and a feed channel arranged to lead
.the liquid suspension from the distribution device to said gap.
-15
The present invention also relates to a method of cleaning a press of the
above mentioned type.
Technical background
Processes aiming ' at dewatering a liquid suspension of solid biological
material often utilize a press wherein water is pressed out of the suspension
into a drum, -whereby a relativeley -dry pulp is obtained from the biological
material. An example of such a process is .production of papermaking pulp
from cellulose fibers, .which process often comprises one or more presses
where the pulp is dewatered and possibly washed. That kind of presses that
are often referred to as dewatering presses or washing presses, depending
on whether the pulp is only dewatered or also.washed, often comprise at least
one rotaring drum against which the pulp is pressed. As -the. pulp is pressed
against the drum, the water is pressed into the interior of the drum while the
dewatered pulp. remains on the outer side of the drum and is- scraped off
therefrom for instance by means of a so-called scraper. The pressing of the
pulp is effected by means. of .a trough and a guide plate_surrounding the
drum.
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Between the trough and the guide plate, on one side, and the drum on the
other side a gap is formed, which converges in the rotating direction of the
drum.
During dewatering of a liquid suspension in the above mentioned type of
press in. order to produce a dewatered pulp it sometimes happens that the
pulp sticks in said gap, in devices feeding the liquid suspension to the
press,
or in devices discharging the dewatered pulp from the press. In such a case
the press has to be stopped and the pulp remaining therein has to be
removed. EP1035250 describes a press wherein the lower part of the trough
can.be lowered for access to possible pulp therein. Further, the side part of
the trough can be tilted outwards and downwards as a. baffle for access to yet
another part of the drum.
Summary of the invention
An object of the present invention is to provide a press for dewatering a
liquid
suspension of solid biological material, which press provides' a way of
removing material that has stuck inside the press in a simpler way than in
prior art technique.
This object is achieved with a press comprising a distribution device arranged
to receive a liquid suspension of solid biological material and to distribute
the
suspension horizontally by means of a dewatering drum, a guide plate and a
trough arranged under a dewatering drum, which plate and trough are
arranged at a distance from the dewatering drum for forming a gap between
the dewatering drum on one side and the guide plate and the trough on the
other side, in which gap liquid can be pressed from the suspension during
operation of the press for forming a dewatered pulp of the solid biological
material, and a feed channel arranged to lead the liquid suspension from the
distribution device to said gap, said press being characterized in that the
guide plate is rotatable around a horizontal shaft arranged at a first end of
the
guide plate, whereby a transfer member is connected to the guide plate at a
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second end of the guide plate opposite the first end of the plate for
adjusting a
distance of the guide plate from the dewatering drum.
An advantage of this press is that the construction thereof is compact and
simple, while providing a simple access to possible pulp that has stuck
between the drum and the guide plate, so that the press can quickly be
cleaned at possible shut-downs.
According to an embodiment the first end of the guide plate is positioned
above the other end of the guide plate, seen in vertical direction. An
advantage of this embodiment is that the lower part of the guide plate can be
.transfered from the drum,, so that pulp that has stuck between the drum and
the guide plate can fall down and out of the gap under gravity, possibly
assisted also by some instrument.
According to an embodiment the guide plate is arranged below said feed
channel. An advantage of this embodiment is that the pulp is led from the
feed channel and downwards towards the guide plate, which reduces the risk
of pulp sticking or being squeezed between the guide plate and the drum, and
simplifies the removal of the pulp in case that would happen anyway.
Preferably the guide plate has a pressing surface provided for forming,
together with the dewatering drum, said gap, whereby the feed channel has a
nozzle end arranged to communicate with the upper end of the pressing
surface while the press is running. An advantage of this is that during
removal
of pulp that has stuck in the gap between the guide plate and the drum good
access is provided, as the guide plate extends up to the feed channel.
According to an embodiment, a sealing strip is arranged between the upper
end of the pressing surface and a lower feed plate comprised in the feed
channel. An advantage of this is that good access to the gap between the
guide plate and the drum is achieved in combination of only a minor risk of
leakage of the liquid suspension during operation of the press.
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According to an embodiment the guide plate is located at least partly on the
same horizontal plane as the distribution device. An advantage of this
embodiment is that a compact press is provided.
According to an embodiment the guide plate is located at least partly between
the distribution device and the dewatering drum. This embodiment provides a
'highly compact construction, as the distribution device and the guide plate
share a common space beside the dewatering drum. Further, no space or
very little space is required at the side of the press for the guide plate.
More
preferably the central part. of the guide plate is located between the
distribution device and the dewatering drum.
According to a preferred embodiment the transfer member is a hydraulically
steered transfer member. That kind of transfer members are simple to steer
and they provide high force when pressing the pulp in the gap between the
drum and the guide plate.
According to a preferred embodiment the transfer member is arranged to
operate 'in an essentially horizontal direction. This provides a very compact
and flexible embodiment of the transfer member.
Another object of the present invention is to provide a flexible way of
cleaning
a press for dewatering a liquid suspension of solid biological material.
This object is achieved with a method of cleaning a press for dewatering a
liquid suspension of solid biological material, said press comprising a
distribution device arranged to receive a liquid suspension of solid
biological
material and to distribute the suspension horizontally by means of a
. dewatering drum, a guide plate and a trough arranged below the dewatering
drum, which plate and trough are arranged at a distance from the dewatering
drum for forming a gap between the dewatering drum on one side and the
guide plate and the trough on the other side, in which gap liquid can be
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pressed from the suspension during operation of the press for obtaining a
dewatered pulp of the solid biological material, and a feed channel arranged
to lead the liquid suspension from the distribution device to said gap, which
method is characterized in that the guide plate is rotatable around a
horizontal
5 shaft that is arranged at a first end of the guide plate, whereby a transfer
member is. connected to the guide plate at a second end of the guide plate
opposite the first end of the plate for adjusting a distance of the guide
plate
from the dewatering drum, whereby during the cleaning of the press the
second end of the guide plate is transferrred by means of said transfer
member in a direction away from the dewatering drum, so that the space
between the guide plate and the dewatering drum will be accessible for
cleaning.
An advantage of this method is that access to and removal of material that
15. has stuck between the guide plate and the drum becomes very flexible and
simple.
Other advantages and characteristics of the invention become obvious from
the following description and the appended claims.
Brief description of the drawings
In the following, the invention will be described by means of exemplary
embodiments and with reference to the appended drawings.
Fig. 1 is a perspective view and illustrates a press for dewatering and
possible washing of a fiber suspension according to an embodiment of the
present invention.
Fig. 2 is a cross-sectional view and illustrates the press of Fig. 1 along
section
II-II.
Fig. 3 is a cross-sectional view and illustrates an enlargement of the guide
plate of Fig. 1 and 2.
Fig. 4 is a cross-sectional view and illustrates the guide plate of Fig. 3
during
operation of the press.
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Fig. 5 is a cross-sectional view and illustrates the guide plate of Fig. 3 at
a
maintenance state.
Description of preferred embodiments
Figures 1 and 2 illustrate schematically a press 1 for dewatering a liguid
suspension of cellulose fibers for production of e.g. paper. Figure 1
illustrates
the press 1 in perspective view with some parts shown in detail and some
covers lifted aside, and Fig. 2 illustrates the press 1 shown along along
section II-II of Fig. 1.
The press 1 is, as best illustrated in Fig. 1, provided with a longitudinal
first
distribution screw 2. The distribution screw 2 has a centrally placed inlet 4
for
a liquid suspension of solid biological material in form of cellulose fibers.
The
. weight percentage of the cellulose fibers in the liquid suspension is
typically
3-15 weight-%. The liquid suspension also includes possible impurities,
usually no more than approximately 1 weight-%, and the rest, i.e. 84-96
weight-% is water. An inlet conduit 6 is arranged for introduction of the
liquid
suspension to the inlet 4 from a source of liquid suspension (not shown). e.g.
from a pulper.
The first distribution screw 2 distributes the liquid suspension received via
a
point-formed inlet 4, along a first dewatering drum 8. The dewatering drum 8
has a liquid-permeable layer, such as a perforated plate or a filter cloth,
which
allows the cellulose fibers, in form of dewatered pulp, to remain on the
surface of the drum 8 during pressing of the suspension against the outer
periphery of the drum 8, while the liquid is pressed into the interior of the
drum 8 and led away.
The distribution screw 2 extends essentially along the whole length of the
dewatering drum 8, which in practice means that the active length LF of the
distribution screw 2, which active length LF is the length along which the
distribution screw 2 introduces liquid suspension to the dewatering drum 8,
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typically approximately 75-120%, more typically 80-110% of the active length
LT of the dewatering drum 8, which active length LT is the length along which
the dewatering drum 8 receives and presses pulp. It is.understood that in
addition to the above described active lengths LF and LT illustrated in Fig.
1,
both the distribution screw 2 and the drum 8 have, among others, bearings
and end pieces not shown in Fig.-1 that are included in their respective total
lengths, but not in the active length, which, as mentioned, is the length
along
-which the liquid suspension is distributed, respectively pressed to produce a
still dryer pulp.
As becomes obvious from Fig. I and 2, the press I is also provided with a
second distribution screw 10, a conduit 11 arranged for introducing the liquid
suspension to the second distribution screw 10, and a second dewatering
drum 12. From Fig. 2 it becomes obvious that the press 1 is essentially
symmetrical around its central part. For this reason, mainly the right-hand
part
of the press 1, as shown in Fig. 2, is described, while it is understood that
the
left-hand part of the press 1 has an essentially corresponding form, only
mirror-inverted.
20, The distribution screw 2 has, as becomes obvious from the detailed
enlargement of Fig. 1, a casing 14 inside which a screw 16 is arranged to
rotate under operation of the discribution screw 2. Thanks to the screw 16,
the central part of which is conical in both directions, seen from the centre
of
the screw 16, the liquid suspension fed via the point-form inlet 4 is
distributed
evenly along the active length LT of the dewatering drum 8. A feed channel
18 extends essentially horizontally from the upper part of the feed screw 2,
approximately aft 11 o'clock seen along the circumference of the housing 14,
towards the dewatering drum 8, as shown in Fig. 2. From Fig. 1 it becomes
obvious that the feed channel 18 has an active length LI that is essentially
the
same as the active length LF of the distribution screw 2, more precisely the
lenght LI is usually 80-110% of the length LF.
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Under operation of the press 1, the liquid suspension is fed via conduit 6 to
the inlet 4. The liquid suspension can e.g. come from fiber washing or from a
pulper connected to another press that is similar to the press 1 and in
process
view is located upstream thereof. The suspension is distributed by screw 16
of the distribution screw 2 and led via the feed channel 18 to a gap 20 that
is
formed between the dewatering drum 8 on one side and a guide plate 22 and
a trough 24 on the other side. As becomes obvious from Fig. 2 the gap 20
has, seen from the feed channel 18 and further in the rotational direction R
of
the drum 8, a converging width. As a result, liquid will be pressed out from
the
liquid. suspension and into the drum 8 when the liquid suspension is pressed
by the drum 8 first against the guide plate 22 and later the trough 24 in a
converging gap 20, whereby the cellulose fibers remaining on the outside of
the drum 8 will form a further dewatered pulp of cellulose fibers. The
dewatered pulp, with a dry solids content of e.g. 15-55 w-%, more typically
20-50.w-%, is then released from the drum 8, approximately at 9 o'clock seen
along the periphery of the drum 8 in accordance with Fig. 2, and transported
away by means of a shedder screw 26 for further treatment, such as washing
and/or drying.
The press 1 can be provided with one or more washing devices 28, by means
of. which washing liquid, such as clean water or filtrate or condensate water
from another process stage can be introduced into the pulp while the pulp
remains in the gap 20, in order to wash away impurities from the pulp.
During operation of the press 1, pulp can stick in the gap 20. This results in
shut-down of the press 1, and the trough 24 has to be lowered vertically
downwards, as shown by an arrow N in Fig. 2, for access to the drum 8 so
that it can be cleaned of the pulp. In accordance with the present invention
and in a way presented in the following in more detail the guide plate 22 can
also be lowered in a flexible way.
Fig. 3 illustrates the guide plate 22 according to an embodiment of the
present invention in a ready for operation state, i.e. a state when liquid
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suspension can be introduced into the distribution screw 2. The guide plate
22 is rotatable by means of a horizontal shaft 30. As becomes obvious from
Fig. 1 the guide plate 22 extends, seen in a horizontal direction, along
essentially the whole active length LT of the drum 8, i.e. the guide plate 22
.5 has an active length LP that is typically 80-120% of the active length LT
of the
drum 8. The shaft 30 is bearing-mounted in the press 1 at its respective ends,
and can also be bearing-mounted in the press 1 in one or more further
positions along the length LP of the guide plate 22.
The guide plate 22 is located, as seen in Fig. 3. at least partly on the same
horizontal. level as the distribution screw 2, and the central part C of the
guide
plate 22 is located between the distribution screw 2 and the dewatering drum
8.
The feed channel 18 has, as best illustrated in Fig. 3, an upper feed plate 32
and a lower feed plate 34. The guide plate 22 has a pressing surface 36 that
is provided for, together with the drum 8, forming a gap 20. The upper end 38
of the pressing surface 36 is via a sealing strip 40 in contact with a nozzle
part 42 of the lower feed plate 34, at which nozzle part the feed channel 18
discharges into the gap 20. The guide plate 22 has in its upper end 44 a
notch 46, in which the horizontal shaft 30 is fixed, e.g. by means of welding.
The guide plate 22 extends from a position on the level of the upper part of
the distribution screw 2 to a position below the lower part of the
distribution
screw 2. At its lower end 48 the guide plate 22 is connected to a hydraulic
piston 50. The hydraulic piston 50 is fixed in the press 1 and is, as seen in
Fig. 3, arranged under the distribution screw 2. The hydraulic piston 50 is
arranged to operate in an essentially horizontal position. As becomes obvious
from Fig. 1, a number of hydraulic pistons 50 can be arranged along the
length LP of the guide plate 22. The hydraulic pistons 50 can be connected to
a source 52 of pressurized hydraulic liquid, shown in Fig. 1. A control unit
54
controls the amount of pressurized hydraulic liquid being introduced to the
hydraulic pistons 52 from said source 52, whereby the transition point of the
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hydraulic pistons 50 in horizontal direction can be adjusted. During
adjustment of the transition point of the hydraulic pistons 50, the control
unit
54 controls the feed of pressurized hydraulic liquid to the pistons 50 from
the
source 52 of pressurized hydraulic liquid.
5
As becomes obvious from Fig. 3, a mechanical arrester 56 is provided on the
press in order to limit the horizontal transition point of the hydraulic
piston 50
in horizontal direction. The piston of the hydraulic piston 50 is provided
with a
chuck 58, which in the position of the hydraulic piston 50 of Fig. 3 is
pressed
10 against the arrester 56. Thereby the hydraulic piston 50 and the guide
plate
22 reach a first end position that provides a desired width of the gap 20
between the guide plate 22 and the drum 8. Preferably the piston of the'
hydraulic piston 50 is provided with a threaded adjusting device for fine
adjustment of the width of the gap 20 when the chuck 58 of the hydraulic
piston 50 is pressed against the arrester 56.
In the operation-ready state of Fig. 3 the hydraulic piston 50 has thus
transfered the lower part 48 of the guide plate 22 in the direction towards
the
drum 8 for providing the width of the gap 20 desired for operation. The
hydraulic piston 50 is preferably provided with a mechanical fastener known
per se, by means of which the hydraulic piston 50 is fixed in the position
illustrated in Fig. 3 also after pressure of the hydraulic system has been
released. As an alternative for such mechanical fastening in the hydraulic
piston 50 itself, the trough 24 can, according to an alternative embodiment,
be
provided with a pin, illustrated as an upwards directed pin 60 in Fig. 3,
which
locks the guide plate 22 in the operating position. This pin 60 is pushed into
the lower part 48 of the guide plate 22 when the trough 24 is pushed
vertically
upwards to its operating position and locks the guide plate 22 in its
operating
position. When the trough 24 is lowered for cleaning, which is described in
more detail with reference to Fig. 5, the pin 60 follows therewith downwards
and is drawn out from the guide plate 22, which is thus released. A further
alternative embodiment is to keep the hydraulic piston 50 constantly
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pressurized under operation of the press, so that the guide plate 22 is
thereby
kept in its operating position.
Fig. 4 illustrates the guide plate 22 shown in Fig. 3 during the operation of
the
press 1. In the position shown in Fig. 4 the hydraulic piston 50 thus keeps
the
guide plate 22 in the position that provides the desired width of the gap 20.
As
becomes obvious from Fig. 4, liquid suspension is led in via the inlet 4 and
further. to the distribution screw 2. The distribution screw 2 distributes the
liquid suspension along the active length LT. of the drum 8, shown in Fig. 1,
and then leads the liquid suspension further to the feed channel 18. Via the
feed channel 18 the liquid suspension reaches the gap 20 and is pressed
between the drum 8 and the pressing surface 36 of the guide plate 22 under
rotation of the drum 8, which rotation is illustrated with an arrow R, during
production of still dryer pulp. After being pressed between the pressing
1.5. surface 36 of the guide plate 22 and the drum 8, the pulp is further
pressed to
a higher, dry solids content between the drum 8 and the trough 24 as is partly
.illustrated in Fig. 4, but becomes best obvious from Fig. 2.
Fig. 5 is a cross-sectional view and illustrates the guide plate 22 of Fig. 3
according to an embodiment of the present invention in a maintenance
position. The maintenance position is used e.g. when pulp has stuck in the
gap 20. In that kind of situations, the trough 24 illustrated in Fig. 1 and 2
will
be lowered vertically downwards, in accordance with arrow N shown in Fig. 2,
which allows access to the lower part of the drum 8 for cleaning. Such a
vertical lowering of a trough is known per se and described e.g. in the right-
hand column of Fig. 1 of EP 1035250. Again, with reference to Fig. 5 of the
present invention it becomes obvious that the trough 24 is not anymore in its
operating position. The guide plate 22 is released from the trough 24, as the
guide plate 22 is mounted on the press 1 itself and not on the transferrable
trough 24. Thereby, the guide plate 22 does not follow the vertical lowering
downwards of the trough 24. In addition to lowering of the trough 24
downwards, also the hydraulic piston 50 becomes activated, according to the
method of an embodiment of the present invention, as the control system 54
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of Fig. 1 controls the source 52 of pressurized hydraulic liquid in order to
draw
back the guide plate 22 from the drum 8, i.e. the hydraulic piston 50 draws
the
lower end 48 of the guide plate 22 in a direction B away from the drum 8,
whereby the guide plate 22 is rotated around the horizontal shaft 30 in a
direction towards the distribution screw 2. In the position shown in Fig. 5
the
hydraulic piston 50 draws the guide plate.22 towards the mechanical arrester
56, whereby the hydraulic piston 50 and the guide plate 22 reach another end
position. As the hydraulic piston 50 draws the lower end 48, the guide plate
22 will at its upper end 44 be rotated around the symmetrical axis of shaft
30.
By this movement, the gap 20 is widened and a longest distance, illustrated
with S in Fig. 5, is formed between the drum 8 and the pressing surface 36 of
the guide plate 22 at the lower end 48 of the guide plate 22. As a result,
pulp
that has stuck between the pressing surface 36 and the drum 8 either is
released by itself and falls downwards, out of the gap 20, and/or an operator
can simply insert a cleaning instrument, or just his hand, in the gap 20,
which
due to the hydraulic piston 50 drawing back the lower end 48 of the guide
plate 22 has been widened to an accessable width, and release the stuck
pulp. As becomes obvious from Fig. 5 the gap 20 will be widened the whole
way up to the upper end 44 of the guide plate 22, i.e. up to the inlet into
the
feed channel 18, with the result that an operator can simply get access to
pulp that has stuck in the gap 20 up to the position where the feed channel 18
discharges into the gap 20, which is an essential advantage compared to
prior art, e.g. EP 1035250, in which it is very difficult to get access to and
release pulp that has stuck in the vicinity of a corresponning inlet. Further,
the
guide plate 22 has according to the present invention, a remarkably simpler
construction than the baffle shown in EP 1035250. A further advantage is that
the guide plate 22 in its backdrawn position illustrated in Fig. 5 does not
require any space at the side of the press, unlike the solution presented in
EP
1035250. Therefore, a press 1 with a guide plate 22 according to the present
invention can be placed in locations with limited space.
When the gap 20 has been cleaned off pulp the guide plate 22 can be
returned by means of the hydraulic pistons 50 to the operation-ready state
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shown in Fig. 3, and the trough 24 can be returned to the position-shown in
Fig. 1, so that fiber suspension can again be fed, via inlet 4, the
distribution
screw 2 and the feed channel 18 to the gap 20.
It will be appreciated that many variants of the embodiments described above
are conceivable within the scope defined by the appended claims.
In the above it has been described how the press 1 is utilized for dewatering
a
liquid suspension comprising cellulose fibers. It is understood that the press
1 can also be utilized for dewatering of suspensions of other types of solid
biological material. Examples of such materials include various types of
biomasses to be dewatered, and possibly washed, before using for
production of fuel, e.g. via an ethanol production process, a biogas
production
process, or a fuel pellet production process. It is also possible to utilize
the
press for dewatering a biomass prior to combustion thereof. Examples of
biomasses that can be dewatered in the above described press include straw,
bagass, other annual plants, grass, vegetable tops, leaves, coniferous litter,
algae, moss etc. The liquid in the suspension can be water, but also other
liquids, e.g. various organic or inorganic solvents can be present in the
suspension to be dewatered.
It has been described in the above that the press 1 is provided with one or
more washing devices 28. It is understood that the press can also be
designed devoid of these devices, if the material to be dewatered does not
require washing.
It has been described in the above how the hydraulic pistons 50 connected to
a source 52 of pressurized hydraulic liquid can be utilized for controlling
the
positions of the guide plate 22. It is understood that other transfer members
operating in horizontal direction can be utilized. For instance, the hydraulic
pistons can be replaced with usual hydraulic lifters that are manually pumped
to a desired position for the guide plate 22. Another possibility is to
utilize as
transfer members threaded rods with adjusting bolts, which run under the
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distribution screw 22 and the transfer position of which can be adjusted by
means of a stationary key.
In the above it has been described a press 1 having two oppositely rotating
dewatering drums 8, 12. The present invention can also be applyid in presses
having a single dewatering drum.
