Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WO 97/13026 PCT/SE96/01226
APPARATUS FOR DEWATERING/PRESSING IN COMBINATION WITH WASHING OF
PAPER PULP.
The present lnvention relates to an appararus for dewatering, pressing
and washing treatment of material such as paper pulp etc.
Pulp factories uses washing of fiber pulp partly after the cooking pro-cess for washing out of cooking chemicals and dissolved organic substan-
ces, partly between different stages in the bleach plant for washing out
of reaction products and remaining chemicals. With the present-days in-
creased claims for the environment and using of a closed process in the
mill, the claims for an effective washing of the pulp in increased too.
Up to now different kinds of filters normally are used for washing of the
fiber pulp. The washing process is here carried out partly through dilu-
tion/compressing/dewatering of the fiber pulp, partly through displace-
ment by adding of spray water to the pulp web. The disadvantage with these
filters is that the incoming consistency must be low - about 1 percent -
and the outgoing consistency limitid for about 12-15 percent. This means
that large quantities of water is circulated in the washing system, and
due to the low outgoing consistency the washing out of the chemical reac-
ted products are limitid.
Furthermore filter washers needs a big vertical space and the energy con-
sumption is high. Not least depending of a considerable pump energy is
necessary.
Presses are also used present-day for washing of pulp, and these installa-
tions has increased considerably tlle last years. These types of presses
works either as pure dewatering machines or they are equipped with an ex-
tra device for adding of washwater. The washing process is here consequen-
tly carried out either merely by d:iluting/pressing or this in combination
with displacement.
Presses works with incoming consistency for about 4 percent and outgoing
consistency for about 30-35 percent. These figures means big advantages by
using of presses in comparison wit~l filters.Less circulat1ng liquid qllan-
tity, less diluting of the pulp, less volume for the machine, higher was-
hing out effect of the fiber pulp etc.
Presses for washing of pulp are today normally roll presses. These machi-
nes are expensive, they have high :Loading on their foundation, they are
sensitive for variation in consistency and freeness of the incoming pulp
and the incoming consistency is limitid to maximum 4 percent.
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Screw presses, as are used very much today for pure dewatering/squeezing
of fiber pulp, are simple and cheap machines. The problem is that we to-
day have not an effective screw press construction with separate washlng
zone for adding of liquid for more effective washing process.
The object of the present invention is to produce a screw washing presswhere the advantages for the screw press construction itself is used and
in comination with an effective washing zone. Incoming pulp suspension
at consistency normally 4-10 percent is dewatered/squeezed in a first de-
watering zone up to about 12-20 percent. After this washing llquid is ad-
ded in a zone where the fiber pulp is allowed to expand. No dewateringexist in the washing zone but on the other hand an effective mixing to
distribute the washing liquid in the fiber pulp.
After the washing zone the fiber pulp is once more comprimated between a
straight screen cylinder and a divergent core of the screw. In the final
part of the press exist dewatering out through the screen cylinder as well
as inwards through a perforated core of the screw. Throttle devise is used
at the outlet of the cylinder to regulate the final dryness of the press-
ed pulp.
Fig. 1 lS a section through one embodiment of the invention.
The apparatus shown in fis. 1 includes an inlet section 1 for the pulp, a
first dewatering zone 2, a washing section 3 for diluting/adding of wash-
ing liquid, a final pressing zone 4 and an outlet zone 5 for the washed
and comprimated pulp.
In the outer case 6, formed like a through, is section 1 separated fromsection 2 by means of a wall 7, section 2 from section 3 by means of a
wall 8, section 3 from section 4 by means of a wall 18 and section ~ from
section 5 by means of a wall 9.
A press screw with divergent core 10 hav a length through all the embodi-
ment and shaft journals have conventional bearings 13 and 14 (not showed).
On the journal 12 is placed a gear motor for drive of the screw.
In zone 2 the converging screw flights 15 is surrounded by a screen cylin-
der 16. In zone 3 are bars 17 welded on the screw core for an effective
mixing of the fiber pulp with washing liquid 39 added through pipe 41 and
screen holes 40. In zone 4 the cylindrical screw flights 19 are surronded
by a screen basket 20. The rear part of screen basket 20, zone 37, is not
perforated. In the forward part of the press screw 10 is also the core per-
forated 22 for draining inwards of squeezed liquid.
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WO 97/13026 PCT/SE96101226
At the pulp outlet 23 is connected a throttle devise 24 and this can be
regulated in horizontal directior-. The compressed pulp fall down through
the outlet chamber 25. The pulp ~s fed to the press through a pipe 26
and the squeeced liquid is drained out through pipes 27 and 28 and the
squeezed liquid through holes 22 is drained out through the channel 29.
The apparatus operates in the following way.
The material to be dewatered and washed is fed from a pump or level box
through a pipe 26 and further by the screw flight 15 in to the zone 2.
The pulp is here dewatered throuclh compression and self draining. The water
is pressed through the holes 36 and further through pipe 27. Thr compres-
sing ratio counted as a flight volume 30/flight volume 31 is in a magni-
tude of 2,0:1 to 4,0:1, preferably 2,5:1 to 3,5:1. At the putlet 38 from
zone 2 has the pulp a possibility to expand at the same time as washing
liquid is added through pipe 41 and screen holes 40. The ratio of diame-
ter 32/diameter 33 is in a magnitude of 1,1:2,5, preferably 1,5:2,0. Thebars 17 on the screw core 10 gives an effective mixing of the added liquid
into the fiber pulp. In the zone 37 the screen basket 20 is not perforated.
In the zone 4 the fiber pulp i successively compressed between a screen
basket 20 and a diverging screw core 10. The compression ratio counted as
a flight volume 34/flight volume 35 is in a magnitude of 2,0:1 to 4,0:1
preferably 2,6:1 to 3,2:1.
In the final part of the zone 4 the screw core 10 change from a diverging
to a cyndrical form. The cyndrical part is perforated 22 for transport in-
wards of the squeezed liquid. At the pulp outlet 23 is applied a throttle
devise 24 for a final regulating of the dryness of the pulp. Through ho-
les 21 squeezed water is distributed through pipe 28 and through holes 22
squeezed water through channel 29. The washed and compressed pulp fall
down through the outlet chamber 25.
Due to an initial dewatering in zone 2 from consistencies 2-10 percent up
to 12-20 percent and then adding of washing liquid and effective mixing
down to consistencies 6-12 percent and fianlly dewatering/squeezing up to
25-35 percentis received an effective washing treatment in only one mach-
ine wich has in itself undoubted advantages in comparison with for example
roll presses etc.
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In the present invention is several possibilities to regulate the wash-
ing effect through variation of the revolution for the screw lO, through
variation of the quantity of added washing liquid 39 and variation of the
power for the throttle devise 24.
For a further effective washing process this apparatus can be designed as
a pressure vessel at wich the fiber pulp can be dewatered/washed at over-
pressure and raised temperature. This means lower viscosity of the fluid
and by that better washing out of the rest products in the pulp suspen-
sion.
A variation of the apparatus of the present invention is showed in Fig.2.
Here is the screen cylinder prolonged for connection with the wall 8. The
washing liquid 39 is added and distributed through pipe 18 and further
through nipples 40.
