WO1979000512A1

WO1979000512A1 - Apparatus for pressing liquid out of material containing liquid

Info

Publication number: WO1979000512A1
Application number: PCT/SE1979/000009
Authority: WO
Inventors: H Andersson
Original assignee: Saeffle Gjuteri & Mekaniska Verkstad AB; Saeffle Gjuteri & Mekaniska Ve
Current assignee: Saeffle Gjuteri & Mekaniska Verkstad AB; Saeffle Gjuteri & Mekaniska Ve
Priority date: 1978-01-16
Filing date: 1979-01-15
Publication date: 1979-08-09
Anticipated expiration: 1980-07-16
Also published as: FI70801C; FI70801B; NO147981B; FI790098A7; NO790112L; NO147981C

Abstract

An apparatus for pressing liquid out of suspensions containing liquid, comprising a screw feeder (5) adapted to feed the suspensions towards a dewatering zone (2) in which there are disposed two converging endless filter members (20, 21) adapted to be driven round a pair of back and front breaking rollers (18a, 18b). The pressing angle ((Alpha)) between the filter members can be varied as can the speed of the filter members in relation to the material which is fed forwards in order to achieve an optimum flow resistance for each suspension. In certain cases, this can be very high. A worm wheel (13) is provided to prevent material from retreating in the screw thread (11). According to one form of embodiment, two or more dewatering zones are disposed in series one after the other, thus further increasing the possibilities for achieving optimum dewatering conditions.

Description

APPARATUS FOR PRESSING LIQUID OUT OF MATERIAL CONTAINING LIQUID

TECHNICAL FIELD

The present invention relates to an apparatus for pressing liquid out of material containing liquid, primarily fibrous suspensions, comprising a screw feeder adapted to feed the material in the axial direction towards a zone where the liquid is pressed out of the material and two converging endless filter members are adapted to be driven round a back and a front breaking roller. For the sake of simplicity, the expressions "to dewater" and "dehydrations" are used, but this does not mean any restriction of the application of the invention to material containing water only. The invention can be used to advantage for materials containing other liquids than water, for example, oils, emulsions etc.

BACKGROUND ART

It has long been known, for example through the German Patent Specification 317 788, to dewater and concentrate for example sispensions containing fibre by means of a substantially tubular, conically ending filter through whixh the suspension is fed with a screw. Apparatuses the method of working of which is based on this principle are still manufactured to a considerable extent, among others by Saffle Gjuteri & Mek. Verkstads AB and are marketed under the trade name DESICCATOR. A disadvantage of these known apparatuses, however, is that the dewatering zone does not offer the optimum flow resistance to different kinds of suspension. Various methods of varying the flow resistance have therefore been proposed. Among others it was previously proposed through French Patent Specification 572 324 to vary the pressing angle and to exchange the substantially tubular, conical filter for two converging endless filter members adapted to be driven round a back and a front drive roller. This type of apparatus has been further improved, French Patent Specification 1 130 181, but has nevertheless not acquired any importance in comparison with dewaterers of the DESICCATOR type. One reason for this may be the circumstance that the optimum flow resistance cannot be used if this is high, because the material then tends to retreat into the thread of the feed screw.

STATEMENT OF INVENTION A first object of the invention is therefore to provide an apparatus of the kind referred to at the beginning, with which the flow resistance in the dewatering zone can be regulated, while at the same time material is prevented from retreating into the screw thread eve when the flow resistance in the dewatering zone is comparatively high.

Other objects of the invention are to produce a robust construction with low installation and maintenance costs and with low power consumption.

These and other objects can be achieved in that at least the one filter member is variably adjustable to vary the pressing angle, that is to say the angle between the converging filter members, between 0º and 30º, preferably between 0º and 25º, and that said filter member is adapted to be able to be driven round in its path round the breaking rollers at variable speed, including a speed which is lower than the speed of the dewatered material, with the object of achieving an optimum flow resistance the use of which is rendered possible, even when the flow resistance is high, by means of a worm wheel with such a shape that at least one of its teeth always lies in sealing engagement with the feed screw, in its thead, as a result of which material is prevented from retreating into the thread because of the high flow resistance in the dewatering zone. The filter member may appropiriately comprise a filter cloth with a perforated supporting base.

An object of one form of development of the invention is to further improve the possibilities for regulating the flow resistance in the dewatering zone. This can be achieved in that the suspension or other material which is to be dewatered is exposed to ever harder pressing pressure in two or more following, converging filter members. By this means, the possibilities are improved for selecting a suitable pressing angle for each suspension. Moreover, in an introductory dewatering zone, the suspension can be given a more careful treatment, while a more intensive pressing of the material is first effected in a following zone, which further improves the regulating possibilities. This can also involve lower reject losses. Lower reject lossed can likewise be obtained as a result of the fact that the filter cloth in an introductory dewatering zone is denser than in a later zone.

The pressing angle in the first zone may be fixed, while the pressing angle in the final zone is preferably variable. According to an alternative form of embodiment, however, the pressing angle in the introductory stage may likewise be variable.

According to another aspect of the invention, the speed of the filter cloth is different in different dewatering zones. Thus the speed of the filter cloth may be higher in an introductory zone, for example, than in a later zone.

According to another aspect of the invention, the apparatus comprises a plurality of similar, series-coupled filter members, as a result of which the apparatus can be built up of a number of modules, which can reduce the cost of manufacture and stock-keeping considerably.

Other features and aspects of all the advantage of the invention will be apparent from the following description of two preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following discription of the preferred forms of embodiments, reference will be made to the accompanying drawings in which

Figure 1 is a vertical longitudinal section through an apparatus according to a firs preferred embodiment of the invention;

Figure 2 is a horizontal section II-II in Figure 1; and

Figure 3 is a horizontal section through an apparatus according to another preferred from of embodiment of the invention. In the figures, only those details have been shown - in certain cases only diagrammatically - which are required for an understanding of the invention, while other details have been omitted so that what is essential may be better emphasized.

DESCRIPTION OF PREFERRED FORMS OF EMBODIMENT

The apparatus illustrated in Figures 1-2 consists of two main parts, namely a feed part 1 and a dewatering part 2 in a dewatering zone. The feed part 1 and the dewatering part 2 are separated from one another by a partition 3. The feed part 1 comprises a cylindrical feed housing 4 and a feeder screw 5 mounted in this. The feed housing 4 is bounded at the back by an end wall 6. The shaft 7 of the feeder screw extends with a sealing action through the end wall 6 and is mounted in double bearings in a bearing housing 8. The feed part has an inlet 9 for the material which is to be dewatered. In the normal case, this is constituted by a fibre suspension, for which reason this is referred to hereinafter. The inlet 9 comprises a front gable 10 which is set obliquely like the thread pitch of the feeder screw 5. The feed screw 5 has a cylindrical thread 11 with an even pitch with a rounded bottom.

Disposed under the feeder screw is a worm housing 12 which is tightly fitted to the feed housing 4. The worm housing contains a worm wheel 13 which is mounted with a sealing action in a worm-wheel-chamber 14 in the worm housing 12, so that material cannot pass the worm wheel through the worm housing. Furthermore, the teeth 15 of the worm wheel have a circular cylindrical shape, which is selected so that at least one of the teeth always lies in tight engagement against the feeder screw 5, in its thread 11. By this means, material is prevented from retreating into the thread 11.

The feed housing 4 is tightly connected to the partition 3 as well as a stand 16 in the dewatering part 2. The stand 16 constitutes a holder for a reject liquid trough 17 and for two pairs of vertically mounted, standard drilled breaking roller 18a and 18b respectively. The reject liquid trough 17 is covered by a plate 17' which is perforated with a dewatering hole 19. Mounted over the back and frontbreaking rollers 18a and 18b respectively in each pair of breaking rollers is a vertically disposed endless filter cloth or wire 20. The parts of the wire which face on another are supported by a perforated supporting plate 21. All the breaking rollers are rotatable about their respecive axes.

Two rubberized rollers 22 are driven via gear wheels 23 and 24 or by other means by means of a change speed gear and a geared motor. The rubberized rollers 22 are pressed against the wires 20 with reference to the back breaking rollers 18a so that the wires 20 are conveyed forwards in the direction of the arrows 25. The speeds of the two wires 20 are equally great but preferably lower than the speed of the dewatered filter cake. By this means, an extra variable flow resistance is created. The back breaker rollers 18a are also adapted to be able to be positively driven by means of a chain drive or correspondingly via the gearwheel 23. Above the vertically disposed wires is a horizontal cover plate 26 which is parallel to the cover 17' of the reject tank 17. An outlet for the dewatered and pressed filter cake is designated by 28 while a pair of blast nozzles for cleaning the wires is designated by 30.

As can be seen from Figure 2, the filter members - which consist of the wires 20 with the supporting plates 21 behind them - are arranged so that they converge towards one another in the feed direction of the suspension. According to the invention, the two front breaking rollers 18b can be moved away from and towards one another along a circular line the centre of which coincides with the centre of the axes of the back breaking rollers. In order to guide this displacement, slots 29 or corresponding guide means are provided in the cover 17' of the reject-liquid trough 17 and in the cover plate 26. In Figure 2, the front breaking rollers 18b are shown brought together to the maximum which gives the maximum flow resistance. The separation of the front breaking rollers 18b is counteracted by restraining members, not shown, which may consist of mechanical springs, for example. It is also possible to adjust the nip between the end positions which are determined by the slot 29 or a corresponding guide member. This can be effected manually or hydraulically, for example. According to the form of embodiment, the pressing angle α can be varied in this manner between 0º and 18º. The invention is not, however, restricted to 18º as a maximum pressing angle. Thus by adjusting the pressing angel between the filter members, an optimum flow resistance can be obtained, which can be used even when it is high because the suspension is prevented from retreating into the thread by means of the worm wheel 13.

In Figure 3, the details which correspond to those in Figures 1 and 2 have been given the same references. The feed part 1 of the apparatus is completely identical with that which is shown in Figures 1-2 and therefore comprises a feed housing 4 with a feeder screw 5, a worm wheel 13 and an inlet 9 for the suspension or other material which is to be dewatered.

The feed part 1 is separated by a partition 3 from a dewatering part 200 which comprises two series-coupled dewatering zones 2' an 2''. The dewatering part 200 is connected, in a sealing manner to the partition 3 and like the dewatering part 2 in the apparatus of Figures 1-2 comprises a stand, not shown and a reject liquid trough disposed under a horizontal cover plate 260.

The components illustrated in Figure 3 in the introductory zone 2' in the dewatering part 200 comprise a pair of endless wires 20' with perforated supporting plates 21' situated behind them. The drainage hole in the cover plate 260 is designated 19'. Upper and back breaking rollers for the wires 20' are designated by 19a' and 18b' respectively, while a pair of rubberized rollers pressed against the wires 20' are designated by 22' and a pair of driving gearwheels are designated by 23'.

Corresponding details in the final dewatering part 2'' have been provided with the same references as in the first dewatering part 2' but with a ' ' sign instead of a ' sign. An outlet for dewatered filter cake is designated by 28. Disposed between the two dewatering zones 2' and 2' ', more specifically between the back breaking roller 18b' in the first zone 2' and the front breaking roller 18a' in the next zone 2' ' is a pair of guide plates 30 for the partially dewatered material.

According to this form of embodiment, the pressing angle 06' in the first zone is fixed which means that the back breaking rollers 18b in this zone cannot be displaced. On the other hand, the back breaking roller 18'' in the final zone 2'' can be displaced in the slot 29'' so that the pressing angle α ' ' in this zone can be varied.

The first wires 20' preferably have a smaller size of mesh than the following wires 20 ' '. Furthermore, the speed of the front wires 20' is preferably greater than the speed of the later wires 20' '.

Claims

1: An apparatus for pressing liquid out of material containing liquid, particularly fibrous suspensions, comprising a screw feeder adapted to feed material in the axial direction towards a dewatering zone in which there are disposed two converging endless filter members adapted to be driven round a back and a front breaking roller, c h a r a c t e r i s e d in that at least the one filter member is variably adjustable to vary the pressing angle (α), that is to say the angle between the converging filter members (20, 21) are adapted to be able to be driven round in their path round the breaking rollers (18a, 18b) at variable speed, including a speed which is lower than the speed of the dewatered material, all with the object of achieving an optimum flow resistance, the use of which is rendered possible even when the flow resistance is high, by means of a worm wheel (13) of such a shape that at least one of its teeth (15) always lies in sealing engagement with the feeder screw (5) in its thread (11), as a result of which material is prevented from retreating into the thread as a result of the high flow resistance in the dewatering zone (2).

2. An apparatus as claimed in claim 1, c h a r a c t e r i s e d in that the filter members comprise a filter cloth (20) with a perforated, supporting base (21).

3. An apparatus as claimed in one of the claims 1 and 2, c h a r a c t e r i s e d in that at least the one filter member is variably adjusted as a result of the fact that the front breaker roller (18b) can be displaced along a circular line, the centre of which coincides with the centre of the back breaking roller (18a).

4. An apparatus as claimed in one of the claims 1-3, c h a r a c t e r i s e d in that the thread of the feeder screw has a rounded bottom and that the teeth (15) on the worm wheel (13) have a corresponding circular cylindrical shape.

5. An appartus as claimed in one of the claims 1-4, c h a r a c t e r i s e d in that the filter mambers are disposed vertically.

6. An apparatus as claimed in one of the claims 1-5, c h a r a c t e r i s e d in that at least two pairs of converging filter members (20', 21', 20'', 21'') are disposed in series in successive dewatering zones (2', 2").

7. An apparatus as claimed in claim 6, c h a r a c t e r i s e c in that the pressing angles ( α', α'') are different in the series-coupled dewatering zones.

8. An apparatus as claimed in claim 7, c h a r a c t e r i s e d in that the pressing angle ( α ' ' ) is greater in a following dewatering zone (2'') than in the immediately preceding zone (2').

9. An apparatus as claimed in on of the claims 6-8, c h a r a c t e r i s e d in that the filter cloths (20'') in a following zone have a greater size of mesh than in a preceding zone.

10. An apparatus as claimed in one of the claims 6-9, c h a r a c t e r i s e d in that the speed of the filter cloth is lower in a following dewatering zone than in the immediately preceding zone.

11. An apparatus as claimed in one of the claims 6-10, c h a r a c t e r i s e d in that the number of dewatering zones is two.

12. An apparatus as claimed in one of the claims 6-11, c h a r a c t e r i s e d in that the number of dewatering zones is more than two.

13. An apparatus as claimed in one of the claims 11 and 12, c h a r a c t e r i s e d in that the series-coupled filter members are alike.

14. An apparatus as claimed in one of the claims 6-13, c h a r a c t e r i s e d in that the pressing angle in the first dewatering zone is fixed and variable in the final dewatering zone.