APPARATUS FOR DEWATERING/PRESSING IN COMBINATION WITH WASHING OF PAPER PULP

Abstract: A feed and dewatering device for dewatering/squeezing/washing of fiber pulp etc. comprising one section (1) for inlet, one section (2) for dewatering/squeezing, one section (3) for adding and mixing of washing liquid, one section (4) for the final dewatering/squeezing and one section (5) for outlet of treated material. The dewatering in zone (2) exists between a converging screen basket and a diverging screw core and dewatering in zone (4) between a cylindrical screen basket and a diverging screw core.

Description: APPARATUS FOR DEWATERING/PRESSING IN COMBINATION WITH WASHING OF PAPER PULP. The present invention 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/dewateπng 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 the 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 diluting/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 with filters.Less circulating liquid quan¬ 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 freeπess of the incoming pulp and the incoming consistency is limitid to maximum 4 percent. 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 washing zone for adding of liquid for more effective washing process. The object of the present invention is to produce a screw washing press where the advantages for the screw press construction itself is used and in cominatioπ 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 liquid is ad- ded in a zone where the fiber pulp is allowed to expand. No dewatering exist 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 compπmated 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 is a section through one embodiment of the invention. The apparatus shown in fig. 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 and an outlet zone 5 for the washed and compπmated pulp. In the outer case 6 , formed like a through, is section 1 separated from section 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 4 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. At the pulp outlet 23 is connected a throttle devise 24 and this can be regulated in horizontal direction. The compressed pulp fall down through the outlet chamber 25. The pulp is 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 through 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/flιght 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/dιameter 33 is in a magnitude of 1,1:2,5, preferably 1,5:2,0. The bars 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 l successively compressed between a screen basket 20 and a diverging screw core 10. The compression ratio counted as a flight volume 34/flιght volume 35 is in a magnitude of 2,0:1 to 4,Oil 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 cyndπcal 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. In the present invention is several possibilities to regulate the wash¬ ing effect through variation of the revolution for the screw 10, 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.

Claims: CLAIMS. 1. An apparatus for dewatering, squeezing and at the same time washing of material in form of paper pulp etc. including an inlet and an outlet for the material and a feeding device comprising a longitudinal feed screw with diverging screw core and the screw surrounding mantle which in a first section (2) is formed as a screen basket with in the feed direction coverging form, in a second section (3) is formed as a device for adding dilute liquid and a third section (4) formed as a cyndπcal screen basket C H A R A C T E R I Z E D in that the proportion between diameter outlet converging screen basket (16) zone (2) and diameter cy¬ lindrical screen basket (20) zone (4) is of a magnitude of 1:1,1 to 1:2,5 and preferably 1:1,5 to 1:2,0. 2. Apparatus according to claim I C H A R A C T E R I Z E D in that within zone (3) and at the beginning zone (4) are on the feed screw (10) applied units (17) for agitating and mixing the material fed out from zone (2) with the diluting liquid added to zone (3). 3. Apparatus according to claim I C H A R A C T E R I Z E D in that the drive unit for the screw (10) has variable revolutions. 4. Apparatus according to any of the claims 1-3, C H A R A C T E R I Z E D in that core of screw (10) is perforated at the outlet position (23) for draining also inwards of the squeezed liquid. 5. Apparatus according to any of the claims 1-4, C H A R A C T E R I Z E D in that at the outlet(23) for the material are applied throttle device (24) for final regulating of the dryness of the treated material. 6. Apparatus according to any of the claims 1-5, C H A R A C T E R I Z E D in that the apparatus is designed as a pressure vessel at which the mate¬ rial can be dewatered/washed at overpressure and by that raised tempe¬ rature.

Inventors: BERGGREN TORSTEN LENNART, BERGGREN, TORSTEN, LENNART
Applicants: BERGGREN TORSTEN L, BERGGREN, TORSTEN, LENNART
Application year: 1996
Main classification: D21C9
IPC codes: B01D29, B30B9, D21C9