EP0322516A2 - Solid bowl centrifuge - Google Patents

Abstract

In a solid bowl centrifuge, in particular for separating media with different density or their mixtures and/or suspensions, which are difficult to separate into a comparatively lighter and at least one heavier phase, having a drum which is rotatably mounted on a shaft and forms in itself a settling basin, and having elements for feeding in the media to be separated and for discharging the separated phases, it is proposed that the discharge element (8) for the lighter phase (14) be led to an overflow (8a) on a drum end wall (16) and the discharge element (9) for the heavier phase (13) be constructed, starting from the lowest region (17) of the settling basin (3), with a conveying device (18) and be arranged so as to open into the discharge-side part of the hollow shaft (43b) of the expulsion body (6). In this arrangement, the conveying device (18) can be constructed as a compressed-air liquid syphon (37). <IMAGE>

Description

The invention relates to a full-fledged centrifuge, in particular for separating media of different densities or their mixtures and / or suspensions that are difficult to separate into a comparatively lighter and at least one heavier phase, with a drum rotatably mounted on a shaft and a cylindrical clarifying pond in itself and with Organs for entering the media to be separated and for discharging the separated phases.

There are centrifuges of this type, for. B. from DE-OS 33 17 047 known, in which along the clarification pond at a distance from the inner wall of the drum a rotatably mounted with a hollow shaft and extending in the direction of the axis of rotation arranged displacement body, and the centrifuge is designed with means for operation in direct current , wherein the entry element for the medium to be separated is arranged at the inflow area of the clarification pond and the discharge elements for the separate phases are arranged starting from the discharge area.

Although the technical sector assigned to the centrifuges has been a specialist area that has been mature for decades, the increasing development of microbiology for the treatment of wastewater and / or liquid manure places ever increasing demands on the separability of centrifuges, since the resulting gel-like sludge is unwilling to sediment and therefore great difficulties in phase separation.

Various methods and devices have become known for dewatering such predominantly viscous sludges, which, however, have so far not been able to solve the problem satisfactorily.

For example, German utility model 84 60 004.7 proposes an overflow separation centrifuge for the separation treatment of sludge with a liquid discharge tube protruding into the drum and having a sleeve at the free end, the sleeve being adjustable to skim off a phase at different depths in the sedimentation pond.

Such a device is very difficult to operate and also prone to failure.

Another known centrifuge according to DE-OS 26 51 657 has a clear liquid overflow at a point between the inlet and the solids discharge, the overflow member consisting of a plurality of tubes projecting radially from the outside into the clarification chamber. The accumulation height can be adjusted by letting the tubes protrude more or less far into the clarification room.

The disadvantage of this design is that energy is lost with the peripherally carried out clarification phase and the liquid which is thrown out produces a very undesirable foam formation, for the control of which foam-suppressing agents are occasionally used, which cause costs and also contaminate the clear phase.

Even this known device cannot satisfy the problem at hand.

For this purpose, according to DE-OS 33 17 047, a solid-bowl screw centrifuge of cylindrical design for separating suspensions which are difficult to separate has been proposed, which has a separating disc at the end of the separating space and clear-phase channels arranged in front of the separating disc and sediment channels behind the separating disc. Both discharges lead out of the centrifuge drum in the area of the center thereof. A measuring cell for determining the dry matter content is arranged in the sediment discharge and controls a quantity control element in the clear phase discharge line in accordance with the constant solids content in the sediment.

The known device requires a supply of the suspension with pressure between 0.4 to 0.6 MPa and thus a sealing of the bearings.

Such seals are very complex in their design; but they are also sensitive to maintenance, very susceptible to wear and therefore prone to failure. This known centrifuge can therefore also not be technically satisfactory.

Based on the prior art mentioned, the object of the invention is to provide a centrifuge of the type mentioned, in which the phases separation difficult to separate z. B. sewage sludge largely avoiding energy losses and without a complicated design of the centrifuge as well as avoiding overpressure operation and with a simple control of the solids content in phases containing different solids, and which can be created with as little effort as possible in manufacturing, assembly and maintenance costs and with economic energy expenditure is operable.

The problem is solved in a solid bowl centrifuge of the type mentioned with the invention by a configuration according to the features of the main claim.

It is a great advantage of the synergistic interaction of these features that, in direct current operation, the suspension to be separated is guided precisely with regard to maximum selectivity. The arrangement of the displacement body ensures that a large surface of the clarification pond corresponding to the diameter of the displacement body is retained in the sedimentation area, whereas the entry and the discharge area of the media is comparatively closely associated with the center of rotation. This saves drive energy and ensures energy-efficient operation.

The arrangement of a conveying element in the discharge element for the sedimentation phase does not require any pressure operation, therefore it avoids seals and their maintenance problems and it is very economical from the point of view of the required energy expenditure.

One embodiment provides that the conveying device is designed as a compressed air liquid lifter based on the principle of the so-called mammoth pump and is connected to a compressed air line which is guided through the hollow shaft into the interior of the drum.

The compressed air liquid lifter advantageously has a very simple embodiment, requires no moving parts, is uncomplicated, effective in terms of the conveying effect and, in particular, controllable within predetermined limits with regard to the conveying capacity.

Further expedient refinements of the centrifuge are provided in accordance with the features of claims 4 to 9. The invention is shown in schematic drawings in a preferred embodiment.

• Fig. 1 eine Vollmantelzentrifuge in rein schemati­scher Darstellung und im Schnitt entlang einer vertikalen, durch die Rotationsachse verlaufenden Ebene,
• Fig. 2 einen Funktionsstammbaum einer Schlammein­dickanlage mit der Vollmantelzentrifuge nach Fig. 1.

The drawings show in detail:

• 1 is a full jacket centrifuge in a purely schematic representation and in section along a vertical plane extending through the axis of rotation,
• 2 shows a functional family tree of a sludge thickening system with the solid bowl centrifuge according to FIG. 1.

1 shows the solid bowl centrifuge (40) with a drum (2) mounted on hollow shafts (41a, 41b) on both sides in the bearing blocks (42a, 42b). Inside the drum (2) there is a hollow displacement body (6) immersed in the clarification pond (3). This is also rotatably supported on both sides on the hollow shafts (43a) and (43b) in the bearing blocks (42a) and (42b). The centrifuge (40) suspension, indicated by the arrow (44), is fed through the hollow shaft (43a). The suspension (44) exits through the openings (45) in the hollow shaft (43) and enters the interior of the drum (2) and forms the clarification pond (3) there during operation.

The hollow shaft (41a) of the drum (2) has a V-belt pulley (26) for driving and the hollow shaft (43a) of the displacement body has a V-belt pulley (25). 2, in cooperation with the V-belt sweater (27) of the drive motor (28), form a differential V-belt drive (24) for the centrifuge (40).

The jacket (1) of the drum (2) is preferably formed with a conical extension (4) in the flow direction of the clarifying pond (3). As a result, the suspension entering the artificial gravity field through the openings (45) on the left-hand side according to FIG. 1 becomes an acceleration component for the content particles of the heavier phase in the flow direction (10) granted. The particles obviously have the tendency to migrate to the right in the clarification pond (3) to the area of the largest drum diameter and thereby sediment. The centrifuge (40) works in direct current while maintaining optimal separation sharpness conditions, the displacement body (6), designed as a smooth truncated cone, not causing disturbing eddies or a counterflow field at any point in the clarifying pond (3).

As further shown in FIG. 1, the discharge element (8) for the light phase (14) leads to an overflow (8a) on the drum end wall (16) and the discharge element (9) for the heavier phase (13) from the deepest area ( 17) of the clarification pond (3), starting with a conveying device (18), and arranged to open into the hollow shaft (43b).

This conveying device (18) is designed as a compressed air liquid lifter (37a, 37b) and connected to a compressed air line (19) which is guided through the hollow shaft (43b) into the interior of the drum (2). The arrangement is surprisingly simple, at the same time functionally reliable and energetically economical.

The conical widening (4) of the jacket (1) of the drum (2) with an opening angle (α 1) between 1 ° and 8 °, preferably between 3 ° and 5 ° and the ver is advantageous thrust body (6) with a rotationally symmetrical jacket (20) in the form of a truncated cone with an opening angle (α 2) which essentially corresponds to the opening angle (α 1) of the drum shell (1).

This results in a clarification pond (3) with a comparatively large surface area in the area of the displacement body (6), which results in sedimentation conditions with optimal parameters.

An expedient embodiment of the centrifuge further provides that the displacement body (6) has clearing elements (21).

It is known that a solid bowl centrifuge on the inner wall (5) of the jacket (1) can lead to solid build-up, which causes the flow of the heavier phase (13) in the direction (10) to the deepest area (17) of the clarification pond (3) complicate or prevent. Such batches are preferably formed during the dewatering of viscous, pasty sludge, in particular sewage treatment plant sludge.

The clearing elements (21) are two clearing strips standing vertically opposite one another on the jacket (20) in the embodiment shown as an example. Through this the accumulation of the solid-liquid mixture Solids in the area of the inner drum wall (5) kept in motion so that they cannot get stuck.

Each broach (21a, 21b) can be designed as a helix with a very large pitch with a pitch angle (β) with respect to the axis of rotation (x-x) of the system between 0 and 10 °, preferably between 3 and 5 °. This measure supports and evenens the transport of the solids in the centrifuge drum (2) to the solids discharge end (15).

Advantageously, the small difference in rotational speed between the displacement body (6) with clearing elements (21a, 21b) compared to the drum (2), in contrast to the transport of solids by means of a helix, requires only a negligibly small amount of drive energy.

Therefore, this drive can be designed very simply, preferably as a V-belt drive.

In the system of this V-belt drive (24), the hollow shaft (43a) of the displacement body (6) has a first V-belt pulley (25) and the hollow drive shaft (41a) of the drum (2) has a second V-belt pulley (26). This results in cooperation with the V-belt sweater (27) common drive motor (28) with appropriate dimensioning an intended rotational differential speed between drum (2) and displacement body (6) - Fig. 2.

A further reduction in the drive power required for the system of the centrifuge (40) can also be achieved by arranging flow guide elements (51, 52) in the interior of the drum (2), for example in the form of curved blades in the manner of a radial pump or turbine impeller are through which kinetic energy is converted into potential energy, and vice versa. This known arrangement improves the economic operation of the centrifuge.

As can be seen from the process diagram of a thickening plant according to FIG. 2 with a solid jacket centrifuge (40), the discharge (31) of the heavier phase (13) can be assigned a measuring device (29) for determining the solids content and via a signal line (30) and a computer unit (35) and a control line (36) can be assigned to a quantity control element (32a, 32b) in the compressed air line (19) of the compressed air liquid lifter (37), which is connected to the control element (32a) of the compressed air quantity regulator (32b) via the control line (36) is. The compressed air generation system has a compressed air pump (38) with a motor (38a). Via the control device (29, 35, 32) the discharge amount of the solid phase (13) is influenced in accordance with a predetermined delivery characteristic of the compressed air liquid lifter (37) so that its solids content remains constant.

On the side of the suspension (44) to be supplied, a coarse material separator (34) is connected upstream of the entry element (43a, 45).

This expediently has two units (33a, 33b) in tandem arrangement. The suspension (44) is, for example, from a storage container (39) with the line (48) through the feed pump (49) and a switchable valve bank (50a, 50b) alternately through filter (33a) or filter (33b) into the centrifuge (40 ) fed. The tandem arrangement enables two-way operation, whereby the filter that is not in operation can be cleaned without interrupting operation and then switched on again in the inlet.

Claims (9)

1. Solid bowl centrifuge, in particular for the separation of difficult to separate media of different densities or their mixtures and / or suspensions in a comparatively lighter and at least one heavier phase, with a drum rotatably mounted on a shaft and a cylindrical clarifying pond in itself and with organs for Entering the media to be separated and for discharging the separated phases, a displacement body, which is mounted rotatably with a hollow shaft and extends in the direction of the axis of rotation and is arranged along the clarification pond at a distance from the inner wall of the drum, and the centrifuge is designed with means for operation in direct current, wherein the entry element for the medium to be separated is arranged at the inflow area of the clarification pond and the discharge elements for the separated phases starting from the discharge area thereof, characterized in that the discharge element (8) for the easier phase (14) leads to an overflow (8a) at one drum end wall (16) and the discharge member (9) for the heavier phase (13) from the deepest area (17) of the clarifying pond (3) starting with a conveyor (18) and formed in the discharge-side part of the hollow shaft (43b) of the displacement body (6) is arranged to open out. 2. Centrifuge according to claim 1, characterized in that the jacket (1) of the drum (2) in the flow direction (10) of the clarifying pond (3) is formed with a conical extension (4). 3. Centrifuge according to claim 1, characterized in that the conveyor (18) for the discharge members (9) of the heavier phase (13) as a compressed air liquid lifter (37) according to the principle of the so-called mammoth pump and to one through the hollow shaft (43b) in the inside of the drum (2) guided compressed air line (19) is connected. 4. Centrifuge according to claims 1 to 3, characterized in that the compressed air line (19) through the discharge-side part of the hollow shaft (43b) and with branches along the discharge elements (9) of the heavier phase (13) in the inlet-side area of the compressed air liquid lifter ( 37a, 37b) is led into the mouth. 5. Centrifuge according to one of claims 1 to 4, characterized in that the conical extension (4) of the jacket (1) of the drum (2) has an opening angle (α 1) between 1 ° and 8 °, preferably between 3 ° and 5 °, and the displacement body (6) is formed with a rotationally symmetrical jacket (20) in the form of a truncated cone with an opening angle (α 2) which corresponds to the opening angle (α 1) of the drum shell (1) corresponds. 6. Centrifuge according to one of claims 1 to 5, characterized in that the jacket (20) of the displacer (6) for transporting the heavier phase (13) has clearing members (21), and these preferably as helices with a very large slope angle (β) with respect to the axis of rotation (xx) of the system are formed between 0 ° and 10 °, preferably between 3 ° and 5 °. 7. Centrifuge according to one of claims 1 to 6, wherein the drum (2) and the displacement body (6) can be driven by a cooperating drive (24) with a differential gear, characterized in that the differential gear is designed as a V-belt drive and the V-belt pulleys (25 or 26, 27) are dimensioned so that the drum (2) is driven relative to the displacement body (6) at a differential speed. 8. Centrifuge according to one of claims 1 to 7, characterized in that the discharge (31) of the heavier phase (13) is assigned a measuring device (29) for determining the solids content and via a signal line (30) a quantity control element (32) in the Compressed air line (19) of the compressed air liquid lifter (37) is connected. 9. Centrifuge according to one of claims 1 to 8, characterized in that a coarse material separator (34) is connected upstream of the entry member (43a, 45) for the medium to be separated (44).

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