EP0635309A1 - Double pusher centrifuge - Google Patents

Abstract

The invention concerns double pusher centrifuges which have a rotating sieve drum (6) and separate a mixture (17) into fluid and into a solid component (40) in the form of filter cakes (14, 15). A centrally arranged pusher floor which moves backwards and forwards along the axis (10) of a sieve drum (6), pushes away outwards, on alternate sides, with its outer annular area the filter cake (14) which has been formed since the last time the drum area was cleared. In this process, the pusher floor has at the level of the filter cake a plurality of axial through-openings (12) which are each supplied with mixture via radial feed openings (13) associated with them. The diversion into the axial through-openings takes place forcibly in response to the resistance at the outlet which on the ejecting side is large in comparison with the filter cake (14) present there while on the opposite side a cavity (16) is produced behind the pusher floor which comes away, into which cavity (16) the mixture can flow. Distribution takes place forcibly, there being sufficient pressure, as a result of the high circumferential speed in the through-openings (12), to compensate slight differences in the levels on each side. <IMAGE>

Description

The invention relates to a double-shear centrifuge with a rotating sieve drum in order to separate the mixture of liquid and solids in the form of filter cake, with a centrally arranged moving floor device which moves back and forth along the axis of the sieve drum to alternate the filter cake with a push the outer ring area away, and with a central feed unit to feed new mixture into empty spaces that arise behind the returning outer ring area.

Double push centrifuges have the advantage that during the ejection movement that the push floor device makes in one direction to eject the filter cake, an empty space is created on the rear side of the push floor in which the fresh mixture can be fed for filtering. With correct reversal of the feed with mixture on the opposite side of the moving floor device, it is possible to feed continuously. For example, EP 0 068 095 shows double-push centrifuges with a central through-hole on the moving floor device, the edge of which is used as a control edge, in order to inevitably, depending on the position of the moving floor, the mixture of a stationary radial feed on the front or rear to switch. A friction disc is connected on both sides to the actual moving floor in order to form a rotating annular space in which the mixture is accelerated towards the screening drum. It is essential that the two drum halves in front of and behind the moving floor are loaded with the same amount of solids. The axial position of the radial feed must therefore be set exactly, whereby the position must be sought experimentally by measuring the two solid mass flows. In the case of wearing products, long-term changes in the geometry of the inlet pipe can lead to uneven distribution. Furthermore, fluctuations in the amount of food are passed on as an uneven distribution. In theory, such fluctuations in quantity can be reduced by increasing throttling at the outlet of the radial feed. On the one hand, the necessary inlet height must be available for such a restriction and, on the other hand, there is a risk of backflow and blockage if the outlet opening is reduced.

The object of the invention is to simplify the distribution of mixture in double-shear centrifuges. This object is achieved in that a plurality of axial passage openings are provided on both sides in the outer ring area of the moving floor device, which can each be fed from the center via associated radial feed openings within the moving floor device and which redirect the mixture on both sides in the axial direction in order to counteract the ejection movement of the moving floor device to the drum side on which the moving floor is currently running away from the filter cake.

The invention has the advantage that the axial distribution of the mixture directly in the pressure field on the surface the sieve drum takes place through the axial passage openings by distributing the radially entering mixture according to the outlet openings differently delimited by the filter cake on the side that runs away from the filter cake. The condition of the filter cake on the moving floor therefore inevitably controls the distribution of the mixture, while the individual radial feeding of several axial passage openings ensures that the mixture has the same peripheral speeds and pressures in the passage openings. The radial feed openings branch off from an annular space which, despite its axial movement, can easily be supplied with a mixture by the central feed unit. A breakthrough of the moving floor device located in the axis can be used exclusively for the passage of washing and washing liquid if, for example, a support tube penetrates the central feed device and has a deflector to the rear area. This creates a simple, non-clogging infeed system and more space for product washing on the back of the drum. There is enough space there for a ring channel that runs along with the moving floor but is axially adjustable, which deflects and accelerates the rinsing and washing liquid to the filter cake.

In order to effectively eject the filter cake axially and still feed it through axial through openings in the moving floor, annular gap sections and intermediate webs must alternate. Depending on the design of the common annular space from which the radial feed openings branch off, the axial passage openings in the outer annular area of the moving floor can be designed quite differently. With a double-walled moving floor, the two walls of which form the common annular space, spikers can be used that distribute to the axial passage openings. If the axial passage openings are open towards the periphery, then the intermediate webs must be kept wider in order to achieve the same ejection effect on the filter cake as an outer ring surface with a closed circumferential band. In order to make the ejection effect on the filter cake adjustable on the one hand and to make the axial outlet height for the mixture of the axial passage openings adjustable relative to the inner circumferential surface of the sieve drum, wear rings can be attached in the outer ring area.

Another possibility for producing a double-walled moving floor is to make the axial through-bores on the actual moving floor and to mill their radial feed openings in the form of channels, a cover which is put on later covering the channels and at the same time forming the annulus common to them. Such channels, for example milled in, have the advantage that they can be advanced in the direction of rotation with respect to the center of an annular gap section in order to apply mixture to the axial passage opening more uniformly over its share of the circumference.

Fig. 1

schematisch einen Längsschnitt durch eine Doppelschubzentrifuge;

Fig. 2

schematisch die Ansicht einer Schubbodeneinrichtung mit axialen Durchtrittsöffnungen und radialen Anspeiseöffnungen in Form von Taschen;

Fig. 3

schematisch einen Längsschnitt durch eine Schubbodeneinrichtung entsprechend Fig. 2, bei der ein Deckel zur Bildung eines Ringraums und zur Abdeckung der Taschen vorgesehen ist;

Fig. 4

einen vergrösserten Ausschnitt des eigentlichen Schubbodens aus Fig. 3 an seiner Peripherie zur Siebtrommel;

Fig. 5

schematisch die Ansicht einer doppelwandigen Schubbodeneinrichtung, die ein Abschlussband zur Siebtrommel aufweist;

Fig. 6

schematisch einen Längsschnitt durch eine Schubbodeneinrichtung entsprechend Fig. 5 mit einem axial verschiebbaren Ringkanal zum Auffangen und Verteilen von Waschflüssigkeit;

Fig. 7

schematisch die Ansicht einer doppelwandigen Schubbodeneinrichtung, deren axiale Durchtrittsöffnungen zur Siebtrommel hin offen sind;

Fig. 8

schematisch einen Längsschnitt durch eine Schubbodeneinrichtung entsprechend Fig. 7; und

Fig. 9

einen Ausschnitt eines eigentlichen Schubbodens entsprechend Fig. 4, bei dem Verschleissringe eingesetzt sind.

In the following, the invention is explained on the basis of exemplary embodiments. Show it:

Fig. 1

schematically shows a longitudinal section through a double-shear centrifuge;

Fig. 2

schematically the view of a moving floor device with axial passage openings and radial feed openings in the form of pockets;

Fig. 3

schematically shows a longitudinal section through a moving floor device according to Figure 2, in which a lid is provided to form an annular space and to cover the pockets.

Fig. 4

an enlarged section of the actual moving floor of Figure 3 on its periphery to the screening drum.

Fig. 5

schematically the view of a double-walled moving floor device, which has an end band to the screening drum;

Fig. 6

schematically shows a longitudinal section through a moving floor device according to FIG 5 with an axially displaceable annular channel for collecting and distributing washing liquid.

Fig. 7

schematically the view of a double-walled moving floor device, the axial passage openings are open to the screening drum;

Fig. 8

schematically shows a longitudinal section through a moving floor device according to FIG. 7; and

Fig. 9

a section of an actual moving floor according to FIG. 4, in which wear rings are used.

In the figures, double-shear centrifuges with a rotating sieve drum are shown, which separate from a mixture in liquid and in solids in the form of filter cakes. A centrally located moving floor, which moves back and forth along the axis of a screening drum, alternately pushes with its outer ring area since the last release of the Drum area attached filter cake to the outside. The moving floor at the level of the filter cake has a plurality of axial passage openings, each of which is supplied with a mixture via the radial feed openings associated with them. The deflection in the axial through openings is inevitable in accordance with the resistance at the outlet, which is large on the ejecting side compared to the filter cake, while on the opposite side there is an empty space behind the moving moving floor into which the mixture can flow. The distribution is inevitable, but due to the high peripheral speed in the passage openings there is enough pressure to compensate for nuances in the bilateral level.

In FIG. 1, a sieve drum 6 is supported on one side via bearings 24 in a housing 1, which in a central region intercepts the liquid 39 centrifuged with the sieve drum 6 in a filtrate housing 4, while the filter cakes 14, 15 are each moved along by an axially oscillating moving floor device 5 the drum jacket surface can be pushed outwards into a corresponding solid housing 3. On the bearing side, a plurality of outlet openings 22 for the rear filter cake 14 are made in the sieve drum. The push floor device 5 itself is connected via bolts 26 and a push hub 25 to a piston rod 23, which in turn is axially movable in the axis 9 of the sieve drum in order to make an axially oscillating movement during rotation with the sieve drum 6, which is from the actual push floor is transferred to the filter cake 14, 15 at its periphery. The housing 1 is closed with a housing cover 2. A feed unit 11 in the form of a tube for a mixture 17 is attached to the housing cover and is coaxially pierced by a support tube 20 at its outlet, the support tube having a deflector 33 carries, which deflects the mixture 17 in the radial direction. The support tube 20 reaches the rear space of the screening drum 6 through a central opening 34 in the sliding floor device 5 and enables flushing and / or washing liquid 21 to be introduced into the rear space via one or more internal tubes 19.

FIGS. 2, 3 and 4 show an embodiment of the moving floor device 5, in which an annular space 18 is generated by a cover 29 placed on the front side, from which a plurality of radial feed openings 13 each merge into axial passage openings 12, which pass in an outer ring area 10 of the moving floor device 5 are arranged in the area of the filter cakes 14, 15. During the to-and-fro movement of the sliding floor device 5, mixture 17 is introduced radially in the area between the extended lid edge and the actual sliding floor and further accelerated by the friction on the walls in an annular space 18 in which baffles in the form of pockets 28 are attached to to bring the mixture in the pockets 28 to peripheral speed. Between the cover 29 and the pockets 28, the radial feed openings 13 are cut out, through which the mixture 17 reaches axial through openings 12, which connect the front and rear spaces of the screening drum 6. The surface of the sieve drum consists of a sieve 7, which is held by a perforated support cylinder 8. The mixture 17 tries to distribute itself axially and in the circumferential direction at the outlet from the passage openings 12, the offset filter cake 14 to be pushed out being opposed on the side in the direction of the ejection movement 27, while an empty space 16 is formed on the opposite side in the the mixture 17 can flow in to separate it from the liquid portion. After the reversal of movement, the amount of solid that has settled in the meantime becomes with it subsequent filter cake is not ejected by quite a stroke, while the solid content is deposited on the back.

4 shows axial passage openings 12 which occupy an entire annular gap section 30 in order to achieve a good level compensation for the filter cakes 14, 15 also in the circumferential direction. The pockets 28 are offset in the direction of rotation 32 in order to bring about a more uniform inflow in the annular gap cross section 30. The cover 29 is supported in the actual moving floor by a recess 31 with a shoulder, which at the same time forms a boundary for the radial feed openings 13 in the region of the pockets 28. In the area of the axial passage openings 12, annular recesses are made on both sides, into which wear rings 38 can be inserted according to FIG. 9.

FIGS. 5 and 6 show a double-walled moving floor device 5 as a welded construction, in which the feed unit 11 feeds the mixture 17 in the middle of a hollow moving floor. The two side walls are connected at their periphery via an end band 35. The axial passage openings 12 are separated from one another by spikes 36, the spits 36 simultaneously forming the radial feed openings 13 from the annular space 18. A funnel-shaped ring channel 37 for washing liquid 21a can be fixed in various axial positions on the bolt 26 in order to collect and distribute the washing liquid introduced via the pipe 19 and the support pipe 20 in the rear space of the screening drum 6. Via an additional pipe 19 projecting further in the axial direction, rinsing liquid 21b can be introduced into the rear space of the sieve drum 6 in order to remove the filter cake 14 and to clean the sieve covering 7.

FIGS. 7 and 8 show a welded construction analogous to FIGS. 5 and 6, in which the outer end band has been omitted. The axial passage openings 12 are open towards the sieve, so that care must be taken to ensure that the distance between two spots 36 is small enough to maintain a continuous ring shape for the filter cakes 14, 15 when they are ejected.

FIG. 9 shows a section of the sliding floor 5 with attached wear rings 38. The wear rings can be used to keep the wear away from the passage openings 12. It is also possible to adapt the axial outlet height to the product properties. The locking ring can be designed as a whole part or from several radially displaceable segments. The radial overflow height can be adjusted continuously as sliding segments.

Claims (10)

Double-shear centrifuge with a rotating sieve drum (6) to separate the mixture (17) into liquid (39) and the solids content (40) in the form of filter cake (14, 15), with a central moving floor device (5), which extends lengthways the axis (9) of the sieve drum (6) to and fro to push the filter cake (14, 15) alternately with an outer ring area (10), and with a central feed unit (11) to new mixture (17) in empty spaces (16) which arise behind the returning outer ring area (10), characterized in that on both sides in the outer ring area (10) of the moving floor device (5) there are several axial passage openings (12), each of which comes from the center via associated radial feed openings (13) can be fed within the moving floor device (5) and which divert the mixture (17) on both sides in the axial direction in order to counter the ejection movement of the moving floor to guide (5) to the drum side on which the moving floor is currently running away from the filter cake. Double-shear centrifuge according to claim 1, characterized in that the radial feed openings (13) branch off within the moving floor device (5) from a common annular space (18) which can be supplied with mixture (17) from the central feed unit (11). Double-push centrifuge according to claim 1 or 2, characterized in that the push floor device (5) has an opening (34) in the center for a stationary support tube (20) in which at least one axially Slidable tube (19) allows the introduction of washing and / or rinsing liquid. Double-push centrifuge according to claim 3, characterized in that the support tube (20) penetrates the central feed device (11) and has at least one deflector (33) for mixture (17) at the opening (34) within the moving floor device. Double-shear centrifuge according to one of claims 1 to 4, characterized in that the passage openings (12) in the outer ring region (10) have the shape of annular gap sections (30). Double-shear centrifuge according to one of claims 2 to 5, characterized in that the annular space (18) is formed from a double-walled sliding floor device (5). Double-shear centrifuge according to claim 6, characterized in that the push-floor device (5) is double-walled in the outer ring region (10) and is formed with an end band (35). Double-shear centrifuge according to one of Claims 2 to 5, characterized in that the annular space (18) is formed by a cover (29) fitted in the moving-floor device (5). Double-shear centrifuge according to one of claims 1 to 8, characterized in that wear rings (38) can be attached in the outer ring area (10), with which the axial outlet height from the axial passage openings (12) can be adjusted relative to the inner circumferential surface of the sieve drum. Double-shear centrifuge according to one of claims 1 to 9, characterized in that there is an axially displaceable ring channel (37) parallel to the moving floor device (5) for collecting and distributing washing liquid (21a).

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