EP0423461B1 - Solid bowl decanter centrifuge - Google Patents

Description

The invention relates to a solid-bowl screw centrifuge for the continuous separation of a solid-liquid mixture, consisting of an elongated centrifuge drum which is rotatably mounted about its longitudinal axis and which surrounds a coaxially arranged screw conveyor rotating at a different speed, the screw spirals of which are attached to a screw drum , Means for feeding material to be separated into the drum along its axis and openings for the discharge of the separated light and heavy materials are provided.

From WO 87/06856 a screw centrifuge is known in which, by arranging the discharge openings for the light phase in the vicinity of the drum shaft axis, the centrifuge drum can be filled with light phase to such an extent that the screw conveyor, which is hollow and of particularly low weight, can be filled is floating self-centering in the light phase. This enables high speeds and high throughputs, but means that the centrifuge must always be completely filled, which requires a particularly high monitoring effort.

From German Offenlegungsschrift 33 17 047, a cylindrical solid-bowl screw centrifuge of the above type for separating suspensions is known, which has a cutting disc with an annular gap between the cutting disc and centrifuge drum at the end of the separation space. Clear phase channels are arranged radially on the screw body at a distance in front of the cutting disc and open into an axially arranged clear phase discharge line. Immediately behind the cutting disc is a radially extending sediment channel, which opens into a sediment discharge line arranged coaxially with the clear phase discharge line. A disadvantage of this known solid-bowl screw centrifuge, however, is that, owing to the risk of clogging of the discharge channels, it can only be used to separate thin media, and that these media must not only be supplied to the centrifuge under excess pressure, but also that the centrifuge only under excess pressure can be operated. In order to accomplish this, the centrifuge must be provided with special seals, in particular mechanical seals, both in the feed area and in the discharge area of the separated media, which not only have to be replaced frequently due to the rapid wear and tear, but which also have a relatively complicated design and are therefore very expensive to buy. In addition, the liquid discharge through the centrifuge hollow shaft is required a special hollow shaft gear for the worm drive, which is also relatively expensive and associated with correspondingly higher acquisition costs. The same disadvantages also apply to the solid-bowl screw centrifuge known from US Pat. No. 4,566,873, which is basically of the same design.

The object of the invention is to provide a solid-bowl screw centrifuge which, while avoiding the disadvantages mentioned above, is not only distinguished by its simple structural design, but which, even with high separation performance and very low energy consumption, continuously separates solid-liquid mixtures, in particular the drainage of thick sludge.

This object is achieved by the features of the characterizing part of claim 1. Advantageous embodiments of the invention are specified in the subclaims.

The design of the centrifuge according to the invention not only enables a pressure-free feeding of the solid-liquid mixture into the separating space of the centrifuge and the discharge of the separated substances from the centrifuge without special mechanical seals, but also a radial deflection of the Liquid separated from the solid reached laterally to the liquid discharge and thereby recovered a large part of the kinetic energy, which is in the suspension in the separation chamber of the centrifuge. The centrifuge according to the invention is therefore distinguished from known centrifuges of a similar design by its relatively simple construction and by its significantly lower energy consumption with high separation performance.

The arrangement of the pump-like guide elements in the inlet area very advantageously results in a particularly uniform distribution of the solid-liquid mixture in the separation space of the centrifuge, while the arrangement of the turbine-like ones Guiding elements in the discharge area for the lighter substances enable a particularly energy-saving discharge of the lighter substances from the separation area of the centrifuge.

In a further embodiment of the invention, a further considerable saving in kinetic energy is also very advantageously achieved in that the turbine or pump-like guide elements or their flow channels are arranged or formed radially or at an oblique angle as well as straight or curved.

Further details, features and advantages of the invention result from the following explanation of solid bowl screw centrifuges schematically shown in the drawing figures.

Fig. 1:

eine Gegenstrom-Vollmantel-Schneckenzentrifuge mit an der Förderschnecke angeordneten Leitelementen gemäß der Erfindung im Längsschnitt;

Fig. 2:

eine Gleichstrom-Vollmantel-Schneckenzentrifuge mit an der Förderschnecke angeordneten Leitelementen gemäß der Erfindung im Teillängsschnit;

Fig. 3:

eine Gleichstrom-Gegenstrom-Vollmantel-Schneckenzentrifuge mit an der Förderschnecke angeordneten Leitelementen und mittigem Feststoffaustrag gemäß der Erfindung im Teillängsschnitt.

It shows:

Fig. 1:

a countercurrent solid bowl screw centrifuge with guide elements arranged on the screw conveyor according to the invention in longitudinal section;

Fig. 2:

a direct current solid bowl screw centrifuge with guide elements arranged on the screw conveyor according to the invention in partial longitudinal section;

Fig. 3:

a cocurrent-countercurrent solid-bowl screw centrifuge with arranged on the screw conveyor Guide elements and central solids discharge according to the invention in partial longitudinal section.

As shown in Fig. 1, the solid bowl screw centrifuge consists of a cylindrical solid shell part (1), which is followed by a conical solid shell part (2) tapering in the direction of the discharge of the heavy substances. The cylindrical-conical drum casing (1, 2) is mounted in a housing (3) so that it can rotate. A screw conveyor (4) with a screw drum (4 ') and a screw helix (5) arranged thereon are rotatably mounted coaxially in this cylindrical-conical solid jacket. On the left outside there is a drive (6) for the screw conveyor (4) and on the right outside there is a drive (6 ') for the centrifuge drum (1, 2). A feed tube (7) axially leading into the centrifuge drum (1, 2) is also arranged on the right side. The material inlet pipe (7) opens into a distributor chamber (8) arranged on the screw drum (4 '), to which a plurality of pump-like guide elements, which are arranged in the between the The screw drum (4 ') and the centrifuge drum (1, 2) separating space (10) open. Turbine-like guide elements in the form of flow channels (11) are provided on the conveyor screw (4) on the left-hand side Divert liquid (arrow 13) separated from the solid matter (12) radially inwards laterally towards the liquid discharge opening (15 ').

In the liquid discharge area in the end wall of the centrifuge drum (1) discharge openings (15 ') are provided for the light substances, which on the one hand have a smaller radial distance (r₁) from the centrifuge drum axis (a) than the largest radial distance (r₂) of the outer circumference the worm drum (4 ') from the centrifuge drum axis (a), and which on the other hand have a greater radial distance (r₁) from the centrifuge drum axis (a) than the outer circumference (r₃) of the centrifuge drum shaft (16'), that is are arranged outside the centrifuge drum shaft. This embodiment of the solid-bowl screw centrifuge according to the invention not only very advantageously enables a completely pressure-free supply of the solid-liquid mixture into the separation space of the centrifuge and the discharge of the separated substances from the centrifuge without special mechanical seals, but it also makes a particularly large proportion of the kinetic Energy that is in the suspension in the centrifuge separation area can be recovered with high separation performance. It is also of not insignificant advantage that the radial distance (r₄) of the discharge openings (15) for the heavy substances from the centrifuge drum axis (a) is smaller than the greatest radial distance (r₂) of the outer casing of the screw drum (4 ') .

In operation of the solid bowl screw centrifuge shown in FIG. 1, the screw conveyor (4) is driven at different speeds in relation to the centrifuge drum consisting of the solid bowl parts (1) and (2) and the solid-liquid mixture to be separated from the centrifuge is fed via the feed pipe (7). supplied from outside without pressure. Under the action of the centrifugal forces, the solids or thick matter is separated from the liquid in the separating space (10) of the centrifuge, the discharge for the heavy substances at the end of the centrifuge drum opposite the discharge for the light substances or the liquid (arrow 13) (1, 2) takes place. The liquid separated from the solid (12) is diverted to the liquid discharge opening (15 ') via the flow channels, which first run parallel to the worm shaft and then radially inwards, and are discharged from the centrifuge drum, while the solids (12) felt by the screw helix (5) and transported inwards via the conical drum shell part (2) and discharged from the centrifuge drum via lateral openings (15). As a result of the fact that the guide elements (9) designed as flow channels, according to the invention, deflect the solid-liquid mixture radially emerging from the feed pipe (7) into an axial flow in the separating space (10) of the centrifuge, the solid discharged from the feed pipe (7) is Liquid mixture formed by the flow channels which also rotate with the screw conveyor (4) Turbine or pump-like guide elements (9) are detected and accelerated by them with a high degree of efficiency and very low frictional losses to the high peripheral speed of the rotating separation space required in the direction of rotation. In the separating chamber (10), the predominantly radial direction of flow of the solid-liquid mixture is diverted without loss of energy into the axial direction of flow, where it moves in spiral and / or axially oriented paths over a large radius towards the discharge end of the centrifuge drum and under the influence of the Centrifugal force separates the heavy components (solids) from the lighter components (liquid). The liquid separated from the solid is guided by the turbine or pump-like radial, oblique, straight or curved guide elements (11) practically without loss of energy to the smallest possible radius and passes next to the drive shaft (16) of the screw conveyor (4) through the openings (15 ') from the centrifuge drum without pressure. The solid (12) separated from the liquid is also conveyed to the smallest possible radius by means of the screw conveyor (4) via the conical jacket part (2) and discharged from the centrifuge drum with very little kinetic energy through the side openings (15). The radial distance (r₄) of the discharge openings (15) for the heavy substances from the centrifuge drum axis (a) is advantageously less than the largest radial distance (r₂) of the outer shell of the screw drum (4 '). To support the transport of solids in the conical drum casing part (2), additional other transport aids, such as, for example, can also be used very advantageously. B. the pressure effect of the clear phase in connection with a baffle plate and negative pond height can be used. Furthermore, the bearings (17) and (18) of the screw conveyor (4) are very advantageously arranged with a smaller radial distance from the drum axis (a) than the outlet openings (15, 15 ') for the solids (12) and the liquid ( 13), whereby the bearings (17, 18) are safely protected against splashing water and dirt.

The solid bowl screw centrifuge according to the invention can, as shown in FIG. 2, possibly also be carried out very advantageously as a direct current centrifuge. In this case, guide elements (20, 22) are arranged on the outside of the hollow screw shaft (19), through which the liquid, which is conducted in the separating space (21) in cocurrent and separated from the solid, directs an inward radial deflection via the guide elements (20, 22) formed Flow channels reach the liquid discharge openings (23 ') arranged outside the centrifuge drum shaft and are discharged from there to the outside. Here, too, turbine or pump-like guide elements (24) according to the invention are very advantageously arranged on the hollow screw shaft (19) in the feed inlet area, which guide elements contain the solid-liquid mixture radially emerging from the feed pipe (25) deflected into an axial flow in the centrifuge separation space (21) without loss of energy.

Finally, as shown in FIG. 3, the solid bowl screw centrifuge according to the invention can also be very advantageously designed as a cocurrent and countercurrent centrifuge. The centrifuge drum (26) and screw conveyor (27) are cylindrical, and the solids discharge (28) is very advantageously carried out in the center of the centrifuge drum (26). Here too, turbine or pump-like guide elements (31, 32, 33) according to the invention are arranged on the screw conveyor (27), which direct the solid-liquid mixture emerging radially from the feed pipe into a flow in the centrifuge separation chamber, which runs axially parallel to the screw conveyor and deflect the liquid separated from the solid in the discharge area radially inwards laterally towards the liquid discharge opening (34), which are arranged outside the centrifuge drum shaft (35). Also in this co-current and countercurrent solid bowl screw centrifuge shown in FIG. 3, the arrangement according to the invention of turbine or pump-like guide elements on the screw conveyor achieves the same advantages as in the solid bowl screw centrifuges shown in FIGS. 1 and 2.

The turbine or pump-like guide elements can very advantageously run radially or at an oblique angle, straight or also curved, in particular also spiral running, arranged or designed so that they act like a pump or turbine impeller during operation of the centrifuge. The cross section of the flow channels formed by the guide elements can, depending on the need and depending on the solid / liquid mixture to be separated in each case, also be very advantageously round or angular in order to thereby ensure operation that is as smooth as possible. If necessary, the guide elements acting like a pump wheel can be arranged on the centrifuge drum with the same advantages instead of on the screw conveyor. In case of need, it is also very easy to provide separate discharges for more than two substances separated from one another in the centrifuge on the centrifuge drum. It is essential here that the component in the centrifuge which is separated in terms of quantity and is guided as far as possible inwards and discharged from there without pressure in order to be able to operate the centrifuge according to the invention with significantly less energy and cost compared to previously known centrifuges.

The energy saving achieved by the solid-bowl screw centrifuge designed according to the invention in comparison with the centrifuges known hitherto results from the following calculation:

Hierbei bedeutet:

m

die Durchsatzleistung (t/h).

D

den Durchmesser der Zentrifugentrommel (m).

n

die Trommelumdrehung pro Minute (U/min.)

η

den Wirkungsgrad der Zentrifuge.

In order to bring the suspension up to the peripheral speed required in the separation area of the centrifuge, the acceleration power can be calculated using the following empirical formula:

$${\text{P}}_{\text{B}}\text{= 3.81 x 10⁻⁷ x}\frac{\text{1}}{\text{η}}\text{xmx D² x n² (kW)}$$

Here means:

m

the throughput (t / h).

D

the diameter of the centrifuge drum (m).

n

the drum revolution per minute (rpm)

η

the efficiency of the centrifuge.

Dieser Berechnung liegt ein Wirkungsgrad η von 0,80 und reduzierte Zulauf- und Absprifzradien von etwa 1/3 x Trommelinnendurchmesser D zugrunde.The efficiency η in known centrifuges is generally around 50%. Due to the inventive design of the solid bowl screw centrifuge, namely by the arrangement of the turbine or pump-like guide elements or flow channels, the energy expenditure is reduced drastically to about 1/6 of the previously required energy with otherwise the same separating effect of the centrifuge:

${\text{P}}_{\text{B}}\text{= 0.7 x 10⁻⁷ xmx D² x n² (kW)}$

This calculation is based on an efficiency η of 0.80 and reduced inflow and spray radii of around 1/3 x inner drum diameter D.

In addition to this very low energy consumption for the centrifuge drive, the centrifuge according to the invention is not only characterized by its simple and reliable machine construction and the very low product damage or flake and cell destruction, but also due to their insensitivity to coarse substances or individual heavy particles in the feed material. In addition, the centrifuge designed according to the invention eliminates both mechanical seals for the screw bearings and hollow shaft gears for the screw drive, as a result of which a particularly strong reduction in investment and operating costs is achieved. The noise level, ie the noise level of the centrifuge according to the invention, is also considerably lower compared to known centrifuges and the throughput and separation performance are significantly higher.

Claims (4)

1. A solid-bowl screw centrifuge for continuously separating a solid-liquid mixture, comprising an elongate centrifuge drum mounted for rotation around its longitudinal axis and surrounding a coaxially-disposed conveying screw which rotates at a different speed, the screw turns being secured to a drum, there being devices for supplying material for separation to the drum along the axis thereof as well as openings for discharging the separated light and heavy substances, characterised by a number of turbine or pump-like guide elements (9, 11, 20, 22, 24, 31, 32) in the form of flow ducts uniformly distributed around the periphery and disposed on the outside of the conveyor screw (4, 19, 27), wherein

   (a) the guide elements (9, 24, 31) serve to convert the gas-liquid mixture emerging radially and without pressure from the material feed pipe (7, 25, 29) into an axial flow,

   (b) the guide elements (11, 20, 22, 23) serve for the transport of the liquid (light phase) separated from solid parallel to the conveying screw (4, 19, 27) in the direction of the outlet opening (15', 23', 34) for the light phase, and

   (c) the guide elements (11, 20, 32) serve for deflection of the light phase radially inwards towards the discharge opening for the light phase (15', 23', 34), and

   (d) the flow ducts formed by the guide elements as per (a), (b) and (c) are interconnected,

   and by outlet openings (15', 23', 34) for the light phase disposed outside the centrifuge-drum shaft (16', 35, 56) on an end wall of the centrifuge and at a smaller radial distance from the centrifuge axis a than the greatest radial distance between the centrifuge axis a and the outer jacket of the screw drum.
2. A solid-bowl screw centrifuge according to claim 1, characterised in that the turbine or pump-like guide elements (9, 11, 20, 22, 24, 31, 32) are disposed or formed radially, or at an oblique angle, or are straight or curved.
3. A solid-bowl screw centrifuge according to claim 1 or 2, characterised in that the outlet for heavy substances is disposed at the end opposite the outlet for light substances or in the middle of the centrifuge drum (1, 2, 26).
4. A solid-bowl screw centrifuge according to any one of the preceding claims, characterised in that separate outlets are provided for more than two substances separated from one another in the centrifuge.

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