FILTRE-TAMBOUR POUR L'EXTRACTION DU FILTRAT D'UNE SUSPENSION FIBREUSE

DRUM FILTER ASSEMBLY FOR EXTRACTING FILTRATE FROM A FIBER SUSPENSION

Abrégé anglais

Abstract of the Disclosure
Mode of eliminating the drawbacks caused by
the sealing and by leakages of sealing in filter
wishers or sedimenters or equivalent, in which the
fibre suspension is fed from a feeder box (4) or feeder
component onto the filtering member (5), which moves in
relation to the feeder box or feeder component.
The suspension leaking through the sealing
between the filtering member (5) and the feeder box (4)
or feeder component is passed back to the supply flow of
the filter washer or sedimentary or equivalent.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A drum filter assembly for extracting filtrate from
a fiber suspension comprising a cylindrical rotary drum
filter a feed box adjacent said filter, an enclosure
surrounding said filter, a first portion of the enclosure
being a basin adjacent said filter, a second portion of the
enclosure having an opening for receiving the feed box and a
third portion providing an outlet for the fiber suspension
from which filtrate has been extracted, non-leakproof means
between the feed box and the rotary drum filter to permit an
amount of mixture of filtrate and fiber suspension to pass
directly from the feed box to the basin without passing
through the rotary drum filter so as to allow the absence of
leakproof seals between the rotary drum filter and the feed
box, means for maintaining a portion of the filtrate in a
hollow interior of the rotary drum filter free of fibers, a
filtrate collecting tank, filtrate pipe means connected
between the interior of the rotary drum filter and the
collecting tank for removing filtrate from the filter to the
collecting tank, a first pipe for removing filtrate from said
collecting tank including a first valve means, an inlet feed
pipe for feeding the mixture of filtrate and fiber suspension
to the feed box, a drain pipe for draining the mixture of
filtrate and fiber suspension from the basin, and a second
pipe including a second valve means connected between the
collection tank and the feed pipe for returning a portion of
the filtrate to the inlet feed pipe, said drain pipe being
connected to said second valved pipe to return the mixture of
filtrate and fiber suspension to the inlet feed pipe.
2. A drum filter assembly as set forth in claim 1 and
further comprising means for maintaining said basin and the
interior of the drum at a substantially equal pressure and
means for maintaining the area above said drum at a pressure

higher than the pressure in said basin and the interior of
the drum.
3. A drum filter assembly as set forth in claim 1,
wherein said inlet feed pipe means for feeding the mixture of
filtrate and fiber suspension is provided with the mixture in
a range of 0.5 to 8% fiber suspension.
4. A drum filter assembly as set forth in claim 1,
wherein said inlet feed pipe means for feeding the mixture of
filtrate and fiber suspension is provided with the mixture in
a range of 1 to 5% fiber suspension.

Description

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The present invention is concerned with an assembly
which eliminates the drawbacks caused by the sealing and by
leakages of sealing in filter washers or sedimenters or equiva-
fonts, in which the fibre suspension is fed from a feeder box
or feeder component onto the filtering member, which moves in
relation to the feeder box or feeder component.
For filtering or thickening and washing of fibre sup-
pensions, in particular of cellulose fibre suspensions or pulp
stock, filters are used in which the fibre suspension is semi-
minted either on various revolving drums or on other filtering
members, such as, for example, a wire or equivalent.
The fibre suspension is passed into the filter feeder
box, basin or equivalent diluted to the appropriate consist
Tunis. The fibre suspension is sediment Ed by means of a differ-
once in pressure onto the filtering face, which moves relative
to the stationary feeder component and carries the sediment Ed
suspension further. In the prior art, the problem of sealing
the slot between the mobile filtering member and the edge of
the stationary feeder component has been resolved by using some
dragging members or a small play. Dragging members cause Abram
soon of the filtering member, and the small play is readily
blocked, causing damage on the filtering member. Nor is it posy
sidle to make the play so little that no leakages at all should
occur.
An object of the present invention is to eliminate
the above problem of sealing. The invention is characterized
in that the suspension leaking through the sealing between -the
filtering member and the feeder box or feeder component is
passed back to the supply flow of the filter washer or semi-
mentor or equivalent. Thus, according to the invention, it is
not even attempted to make the said zone leak-proof, but a fee-
son able leakage is permitted and the leaking fibre suspension

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is returned under control in the process upstream to the point
of the process at which the fibre suspension is diluted before
being fed onto the filter. The leaking suspension is not mixed
together with all of the filtrate, but only with the part of
the Filtrate what is used for diluting the fibre suspension
Burr the cementer.
In accordance with one embodiment of the present
invention, there is provided a drum filter assembly for extract-
in filtrate from a fiber suspension comprising a cylindrical
rotary drum filter, feeding means adjacent the filter, an enclo-
sure surrounding the filter, a first portion of the enclosure
being a basin adjacent the filter, a second portion of the
enclosure having an opening for receiving the feeding means and
a third portion providing an outlet for the fiber suspension
from which filtrate has been extracted, non leakproof means
between the feeding means and the rotary drum filter to permit
an amount of mixture of filtrate and fiber suspension to pass
directly from the feeding means to the basin without passing
through the rotary drum filter so as to allow the absence of
leakproof seals between the rotary drum filter and the feeding
means, means for maintaining a portion of the filtrate in a
hollow interior of the rotary drum filter free of fires, a lit-
irate collecting tank conduit means connected between the
interior of the rotary drum filter and the collecting tank for
removing filtrate from the filter to the collecting tank, a
first valved conduit means for removing filtrate from the got-
looting tank, an inlet feed conduit for feeding the mixture of
filtrate and fiber suspension to the feeding means, a drain con
dull for draining the mixture of filtrate and fiber suspension
from -the basin, and a second valved conduit means connected
between the collection tank and the feed conduit for returning
a portion of the filtrate to the inlet feed conduit, the drain
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conduit being connected to the second valved conduit means to
return the mixture of filtrate and fiber suspension to the
inlet feed conduit.
In a preferred embodiment of the present invention,
the drum filter assembly further comprises means for maintain-
in the basin and the interior of the drum at a substantially
equal pressure and means for maintaining the area above the
Crimea at a pressure higher than the pressure in the basin and
the interior of the drum.
Preferably the mixture of filtrate and fiber suspend
soon in the supply line is in the range of 0.5 to 8% fiber sup-
pension, more preferably in the range of 1 -to I fiber suspend
soon.
The invention will now be described in more detail in
the following, as applied to a drum washer and with reference
to the attached drawings, wherein:
FIGURE 1 shows a flow diagram in accordance with an
embodiment of the present invention;
FIGURE 2 is a sectional view of the principle of
implementation of the mode described above, in a sedimentary-
washer; and
FIGURE 3 shows a section taken along the line A-A in
Figure 2.
According to Fig. 1, the fibre suspension, e.g. pulp
stock, is introduced, e.g., from a blow-off tank at a higher
consistency (e.g., 5%) than the consistency of feeding onto the
washer-filter (e.g. I The pulp stock is diluted in the
feeder pipe system between points 1 and 2 before the pulp
reaches the feeder box 4. In the feeder box, the pulp stock is
pressed, by means of the difference in pressure between the
interior of the drum and the outside as well as by means of the
liquid pressure, against the filtering wire-faced drum 5,
whereat the filtrate ends up inside the drum. The pressure

I
prevailing outside the upper portion of the drum is higher than
the pressure in the interior of the drum. On the other hand,
the pressure prevailing in the basin 6 outside the lower port
lion of the drum is equal to the pressure inside the drum. The
S direction of rotation of the drum 5 in the figure is clockwise.
Through the slot 12 between the feeder component 4 and the
drum 5, part of the pulp to be fed leaks into -the basin portion
it. The width of -the slot may be, e.g., 1 to 30 mm. The leak-
in pulp stock and the filtrate required for the dilution, come
in into the basin 6 out of -the drum 5 interior r are mixed in
the basin, and the mixture is passed via pipe 7 to the inlet
side of the pump 8 and further through -the dilution pipe 9 so
as to dilute the pulp to be fed in. The filtrate free from
fires is passed by means of a separate pipe 10 from inside the
drum into a filtrate tank 11, from which it can be also pumped
further to any such position of the process at which a fibre
content in the filtrate is detrimental, e.g., to the evaporate
in plant, to the washing jets of the preceding washer-filtex,
or to any other, equivalent purposes.
The interior of the drum and the basin 6 are isolated
from each other in a way known in the prior art by means of
interlaced seals 13, whereat -the filtrate can flow through the
wire backwards into -the basin, but the fires have no access
into the drum.