Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a separator for a stock
suspension.
As is known, separators have been used to clean the
stock suspensions fed to the stock inlet of paper machines.
5~ Generally, these separators have been constructed in t,he form
of tanks which receive the stock suspension. These tanks have
been equipped with feed lines which deliver the stock suspen-
sions, strainer elements to strain out impurities, discharge
lines to remove strained suspension and withdrawal lines to
lO. remove the impurities retained by the strainer elements. In
many cases, special damping devices, for example in the fashion
of expansion tanks, have also been incorporated in these sepa-
rators in order to obviate vibrations which occur in the feed
lines to the stock inlet and which have an adverse effect on
15- the paper production. Apart from the fact that such installa-
tions are relatively complicated and occupy considerable space,
they do not operate completely satisfactorily in every case.
Accordingly, it is an object of the invention to
eliminate the need for special vibration dampers in stock
20. suspension separators.
It is another object of the invention to provide a
stock suspension separator of improved construction which
achieves a vibration damping effect and an improved cleaning
action.
25. It is another object of the invention to provide a
stock suspension evaporator which eliminates the need for a
separate vibration damper while providing a better vibration
damping effect.
Briefly, the invention provides a separator for
30~ stock suspension wherein a tank which receives the suspension
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within a closed chamber contains a free gas space above the level of stock
suspension in the fashion of an expansion chamber. For example~ in additibn
to the tank, the separator includes a strainer element within the chamber,
a feed pipe communicating with the interior of the strainer element for
delivering the stock suspension into the interior of the strainer element7
a discharge pipe connected to the tank at a lower end of the chamber for
remo~ing strained stock suspension and a withdrawal pipe in communication
with the interior of the strainer element for removing impurities strained
from the suspension. Any suitable means may be used to maintain the free
space in the chamber above the level of the suspension. For example~ a
control system may be used which feeds a pressurized air flow into the free
space above the suspension level while maintaining the air pressure in the
free space within a predetermined range.
The invention further provides a method of separating impurities
from the stock while damping vibrations without the need of special vibration
dampers. To this end, the method comprises the steps of feeding the stock
suspension into and through a strainer element within a tank to strain im-
purities while maintaining a le~el of strained suspension in the tank with a
free space above the level of the suspension in the tank. In order to
maintain the free space, the method includes the steps of introducing a
pressuri~ed air flow into the space while maintaining the air pressure in
the space with a predetermined range sufficient to maintain a free suspension
level. In addition, the method includes the steps of removing the strained
suspension from the tank and of removing the impurities from the strainer.
In addition to the cleaning action, a separator so
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constructed gives very intensive damping of the vibrations
occurring in the feed duct (i.e. the discharge pipe from the
separator) to the stock inlet. This is due to the cooperation
of the strainer element with the gas space since it has been
5. found that the strainer element itself has a damping action
due to the turbulence of the component currents passing through
the strainer apertures. In this way, vibration energy is dissi-
pated with the proximity of the gas space having a very favor-
able effect in this regard.
10. It has been found that the damping action of the
strainer element increases in inverse proportion to the size of
its apertures, i.e. the finer the strainer the better the
damping action. With fine strainers, however, there is a risk
of clogging so that cleaning blades must be provided which
15- exert a pressure pulse on the strainer to lift the impurities
adhering thereto. To this end, the strainer element may have
the form of a body of revolution and be provided with a rotor
having cleaning blades.
The separator is constructed so that the feed pipe
20. leads into the interior of the strainer element with the rotor
and cleaning blades located within the strainer element. This
improves the damping action of the strainer element because
the stock flows through the strainer element in an outward
direction and is rendered turbulent in the larger tank area.
25. If the cleaning blades are disposed in the strainer element,
the pressure waves formed by the blades are intensely attenua-
ted when they are transmitted to the tank area and they are
not propagated in the stock feed pipe.
Very good results are obtained if the orifices of the
30- feed pipe and of the withdrawal pipe are disposed on the axis
4.
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of the strainer element~ To this end, the feed pipe may lead
into the tank from above with an orifice situated beneath the
level of the stock liquid while the discharge pipe is connected
to the base o the tank. This gives an axis-symmetrical arrange-
ment of the pipes on the one hand with no propagation of thecleaning blade pressure pulses in the conduits while, on the
other hand, the movement of the impurities retained on the
strainer is assisted ln the direction of the discharge pipe.
The means for maintaining the free space in the tank
may be in the form of a means for controlling the level of stock
liquid in the tank~ A means may also be provided to control
the feed of stock to the tank in dependence on the pressure in
the discharge pipe.
These and other objects and advantages of the invention
will become more apparent $rom the following detailed descrip-
tion and appended claims taken in conjunction with the accompanying
drawings in which:
Fig. l diagrammatically illustrates a cross-sectional
` view of a first embodiment of a separator according to the
invention;
Fig. 2 illustrates a corresponding sectional view to
Fig. l showing another embodiment of a separator according to
the invention; and
Fig. 3 illustrates a partial view taken on line III-
III of Fig. l.
Referring to Fig. l, the stock separator includesa tank l which has a base and a ceiling which, in part, define
a closed chamber. The tank is of any suitable cross-sectional
shape for example the peripheral boundary of the tank may be
formed by a cylindrical wall. A strainer element 2 is mounted
5.
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on the base of the tank 1 within the closed chamber. As shown
in Fig. 3, the strainer element 2 is of circular cylindrical
shape with a solid bottom and top and a perforated sidewall.
The strainer element 2 houses a rotor 5 with cleaning blades 6.
This rotor S is secured on a shaft 7 which is rotatably mounted
in bearings 8 at the top and bottom and driven via a belt pulley
10 .
A feed pipe 3 communicates with the interior of the
strainer element 2 for delivering a stock suspension into the
strainer element interior. As shown, the feed pipe 3 extends
through the base of the tank 1 and has an outlet orifice 4
situated on the axis of the strainer element 2. he feed
pipe 3 is coincident with the rotor 5 such that the rotor
shaft 7 passes into the feed pipe 3 with one bearing 8 being
disposed in an enlargement of the feed pipe 3.
A discharge pipe ll communicates with the tank cham-
ber exteriorly of the strainer element 2 for removing strained
stock from the tank l for delivery to a stock inlet (not
shown) of a paper machine. As shown, the discharge pipe 11
is connected to the tank l at a lcwer end of the tank chamber
sIightly above the base.
A withdrawal pipe 9 is in communication with the
interior of the strainer element 2 for removing impurities
strained from the suspension. As shown, this pipe 9 contains
a control valve and passes through the base of the tank l up-
.
wardly into the bottom of the strainer element 2.
A means is also provided for maintaining a free space12 during operation in the tank chamber above the level of
suspension E. This means includes a compressed air line 13
containing a control valve V which leads into the tank 1
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near the ceiling to com~unicate with the air space 12. A line
14 also leads out of the tank 1 near the ceiling to exhaus-t
air. This line 14 includes a control valve 15 which is actuated
via a controller 16 which receives signals from measuring sen-
5- -sors 17, 18 which are respectively located above and below the
level E of suspension in the tank 1. Thus, the means also con-
trols the level E of stock suspension in the tank 1.
The feed pipe 3 and withdrawal pipe 11 are also pro-
vided with a means for controlling the feed oE stock suspension
1~. into the tank 1 in dependence on the pressure or rate of with-
drawal in the discharge pipe 11. This means includes a pres-
sure sensor 20 disposed in the discharge pipe 1, the signal of
which is fed to a controller 21 which actuates a control valve
in the feed pipe 3.
15. In operation, stock suspension is fed at a controlled
rate vla the feed pipe 3 into the strainer element 2, is
strained upon passing into the tank 1 proper, fills the tank 1
to a level E and is discharged via the discharge line 11 to
flow to a stock inlet tnot shown) of a paper machine. During
20- this time, pressurized air is delivered via the line 13 into
the tank 1 to maintain a free space 12 above the suspension
level E while the rotor 5 is rotated to cause a cleaning of im-
purities from the wall o~ the strainer element 2. At suitable
times, the strained impurities are drawn off via the withdrawal
line 9 in any suitable manner.
Referring to Fig. 2, wherein like reference characters
indicate like parts as above, the separa-tor may have a feed
pipe 3' which extends downwardly through the tank ceiling and
air space 12 to a point below the level E of stock suspension
30- in ~he tank chamber. As above, the orifice 4' of the feed
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pipe 3' is coaxial with the axis of the strainer element 2
which, as shown, is mounted on the end of the pipe 3' in spaced
relation to the base and ceiling of the tank 1. In addition,
the discharge pipe 11' communicates with the chamber coaxially
below the strainer element to remove the strained stock suspen-
sion. As shown, the orifice 30 of the discharge pipe 11' is
situated on the axis A of the strainer element 2 so that the
flow of stock from the feed pipe 3' into the discharge pipe ]1'
is symmetrical with respect to the axis A~ Thus, the pressure
10. pulses of the cleaning blades 6 cannot be propagated in the
pipe 11' and hence in the stock inlet. Also, in this embodiment,
in which the stock flow is in the upward direction, the move-
ment of the particles retained on the strainer element 2 and
along the strainer element into the pipe 9 is assisted.
15. As shown, the rotor 5 passes through the discharge
plpe 11' which is at the ~ottom of the tank 1 and is supported
in three bearings 8. The level E of the stock suspension and
the feed of stock suspension may also be controlled in the same
manner as above described with respect to Fig. 1.
Referring to Fig. 1, during operation the pressure
sensors 17, 18 fed pressure signals to the controller 16 repre-
sentative of the air pressure in the free space 12 and the water
level E. Should the level E fall, the signal from the sensor
18 decreases correspondingly. As a result, assuming the signal
25. from the sensor 17 remains constant, the controller 16 opens the
valve 15 so as to reduce the air pressure in the space 12.
As -the pressure on the suspension then decreases, the flow
through the discharge pipe 11 decreases such that the suspen-
sion level E rises. Suitable values are applied to the sensors
17, 18 and controller 16 as well as the pressure sensor 20 and
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controller 21 so as to maintain the level E constant or at
least within a predetermined ran~e. Of course, other varia-
tions of these parameters may also be used to maintain the
level E constant.
5.
10 .
15.
20.
25.
30.
