EP0806245B1 - Screw centrifuge with centrifugal-force operated valve - Google Patents

Abstract

The screw centrifuge for the separation of solids and liquids from a mixture comprises a rotating drum (10) and a coaxial screw (11), rotating at a different speed, with a liquid exit (13) and a solids exit at the other end. Apart from the liquid drain (13), a further drain (16) is provided which is closed by a spring loaded piston (19) at high rotational speeds and opened at low speeds. The piston acts in a radial direction and at right angles to the drain.

Description

The invention relates to a centrifuge, in particular a screw centrifuge for the separation of solid-liquid mixtures with a rotatable drum jacket and one with a different one Speed rotatable screw conveyor and in the front wall of the Centrifuge drum arranged liquid discharge openings and with solids discharge openings at the other end of the centrifuge drum.

Solid-bowl screw centrifuges have a facility for the central Feed the solid-liquid mixture to be separated into the Centrifuge drum and outlet openings for the discharge of each other separate light and heavy fabrics. To the expiry of The liquid freed from solids is in the front wall of the Centrifuge drum several liquid discharge openings distributed around the circumference arranged, and the other, mostly tapered The end of the drum also points around the circumference at its periphery distributed discharge openings through which the from the screw conveyor transported within the drum and from the liquid largely freed solid is discharged.

Such as B. from Fig. 1der DE-OS 40 33 070 well formed when operating such a screw centrifuge inside the centrifuge drum a liquid ring, the inside diameter of the radial arrangement of the circumference of the drum front wall evenly distributed liquid drain openings or from the Height of radially adjustable weir washers is determined by their Adjustment the liquid level or the pond depth can be changed can. When switching off the screw centrifuge (shutdown process) the speed of the centrifuge drum decreases until it stops and thus the centrifugal force also decreases. It will then a speed is reached when the centrifuge drum runs out, where the centrifugal force becomes lower than the gravitational force with the result that the developing in the centrifuge drum Liquid ring collapses and the liquid level inside the centrifuge drum through the solids discharge openings extends so that at these openings, even if only for a short time, Liquid is also discharged in an undesirable surge becomes.

But also when proposed as in DE-OS 40 33 070 the weir discs of the Liquid drain openings can be adjusted radially outward to reduce the pond depth of the liquid ring as quickly as possible, there is still a significant amount of liquid left in the Centrifuge drum, d. H. the one remaining on the inside of the drum Liquid ring suddenly collapses before the shutdown and he can undesirably drum on the Leave the solids discharge side. Conversely, increased when starting again the screw centrifuge is the one remaining in the centrifuge drum Fluid the moment of inertia of the rotor and complicates thus the acceleration of the masses to be set in rotation.

The object of the invention is therefore to overcome these disadvantages avoid and create a screw centrifuge when starting and shutdown no more problems that occur of the one located or remaining in the centrifuge drum The amount of fluid stems, especially the problem of leakage of liquid at the solids discharge openings during the shutdown process. This object is achieved according to the invention with the measures of Labeling part of claim 1 solved. Advantageous configurations are specified in the subclaims.

The invention is based on the idea of the above in screw centrifuges liquid ring described or remaining in the centrifuge, the during the start-up and shutdown process of the centrifuge leads to problems in the start-up and shutdown phase to disappear bring to. In the screw centrifuge according to the invention is namely in the drum end wall radially outside the liquid drain openings at least one drum discharge opening arranged, preferably are radially outside of the liquid drain openings several drum discharge openings evenly distributed around the circumference arranged around the centrifuge drum to be able to completely empty any remaining liquid. This Drum discharge openings arranged in the drum end wall are each crossed radially by a hole in the a centrifugal valve is inserted with a spring-loaded Valve body or closure body in such a way that the closure body at high drum speed (operating speed) the drum discharge opening each closed and at low drum speed the drain opening opens. The centrifugal valve of the The screw centrifuge according to the invention thus works in exactly the opposite direction such as B. return valves used in plate separators, which at high speed of the separator due to high centrifugal force and product load open the discharge openings for the difficult phase, while exactly the opposite in the screw centrifuge according to the invention with high centrifugal force, the integrated centrifugal valve closes.

According to a special feature of the invention, the closure body of the centrifugal valve consist of a piston valve that into a radially inside the drum discharge opening the drilled end wall blind bore is insertable and in this under the influence of the force of a spring and that in centrifuge operation built-up centrifugal force can be moved back and forth like a piston and thereby clearing the crossing drum discharge opening or closes. The spring is preferably one in the drum end wall arranged radially outside the drum discharge opening preloaded compression spring, e.g. B. helical springs whose Clamping force, which builds up the counterforce to centrifugal centrifugal force, is matched to the opening speed at which the valve spool is moved radially inwards and the respective Piston emptying opening opens when the centrifuge is shut down.

During the shutdown process of the screw centrifuge, d. H. from reaching a certain reduced speed of the centrifuge drum up to to a standstill the centrifugal force on the breech body is reduced of the centrifugal valve acts, so that the closure body due to the force of the tensioned compression spring moved inside and thereby the drum emptying opening or the um several openings distributed more or less the circumference abruptly releases, so that the centrifuge drum of remaining Amount of liquid is emptied and the risk of undesirable Sloshing out of this remaining amount of liquid the solids discharge openings no longer exist. Vice versa during the start-up process, the drum emptying openings are under Action of the spring-loaded centrifugal valve body until it is reached a certain operating speed kept open so that starting the screw centrifuge or accelerating the rotor due to a remaining amount of liquid in the drum is not disabled.

The invention and its further features and advantages are based on of the embodiment shown schematically in the figures explained in more detail.

Fig. 1:

den Längsschnitt durch eine Schneckenzentrifuge zur Trennung von Feststoff-Flüssigkeitsgemischen ausschnittsweise im Bereich des Trommelendes, an welchem die von den Feststoffen befreite Flüssigkeit (Zentrat) aus der Zentrifugentrommel abläuft;

Fig. 2:

vergrößert herausgezeichnet aus Fig. 1 das in der Peripherie der Stirnwandung der Zentrifugentrommel angeordnete Fliehkraft-Ventil zur Trommelentleerung in geschlossener Ventilstellung;

Fig. 3:

das Fliehkraft-Ventil der Fig. 2 in der die Trommel-Entleerungsöffnung freigebenden Ventilstellung, und

Fig. 4.:

ausschnittsweise den Querschnitt längs der Linie IV-IV der Fig. 2.

It shows:

Fig. 1:

the longitudinal section through a screw centrifuge for the separation of solid-liquid mixtures in sections in the region of the drum end at which the liquid (centrate) freed from the solids runs out of the centrifuge drum;

Fig. 2:

enlarged drawn from Figure 1, the centrifugal valve arranged in the periphery of the end wall of the centrifuge drum for emptying the drum in the closed valve position;

Fig. 3:

2 in the valve position releasing the drum emptying opening, and

Fig. 4 .:

sections of the cross section along the line IV-IV of FIG. 2nd

As shown in FIG. 1, the screw centrifuge according to the invention has a drum shell 10 with coaxially arranged therein with snail spirals 11 provided screw conveyor, in the same direction of rotation like the centrifuge drum 10, but with a different one Speed rotates. The solid-liquid mixture to be dewatered such as B. the sewage sludge is in the centrifuge drum introduced through the central feed pipe 12. When operating the Screw centrifuge is formed under the influence of the centrifugal force within the centrifuge drum 10 from a liquid ring from which the heavy materials with the help of the screw conveyor 11 to the right transported and over the mostly conical drum end to the in 1 not shown solid discharge openings are promoted, while the liquid (centrate) freed from the solids the centrifuge drum runs through liquid drain openings 13, the drum end wall attached to the left end of the drum 14 are evenly distributed around the circumference. The Inner diameter of the formed in the centrifuge drum 10 Liquid ring is due to the height of the liquid drain openings 13 weir washers 15 partially covering the outside certainly.

After the screw centrifuge has shut down, it remains inside the Centrifuge drum 10 in any case, a residual liquid considerably Quantity that applies both when moving off and when starting again the screw centrifuge the problems described above prepares.

These problems are eliminated in that in the invention Screw centrifuge in the drum end wall 14 radially outside the liquid drain openings 13 at least one, preferably several drum discharge openings distributed around the circumference 16 are arranged, each radially from a bore 17 are crossed, in each of which a centrifugal valve 18 is inserted with a spring-loaded closure body in such a way that the closure body at high drum speed (operating speed) the Drum discharge opening 16 closes and at low drum speed the emptying opening 16 opens. In Fig. 1 is the centrifugal valve 18 in its closing the drum emptying opening 16 Position drawn, and in this position is the valve Drawn out enlarged in Fig. 2. In Fig. 3 is the centrifugal valve 18 in its opening the drum discharge opening 16 Position drawn out.

As can be clearly seen in FIGS. 2 to 4, there is the closure body of the centrifugal valve 18 from a piston valve 19, the after position in Fig. 2 in its bottom dead center and according to Fig. 3 in his top dead center is struck. The spool 19 is in a radially inside the drum discharge opening 16 to this blind hole 17 insertable in the drum end wall and in this under the action of the force of a spring 20 and that in the centrifuge mode built-up centrifugal force can be moved back and forth like a piston, having the crossing drum emptying opening 16 according to FIG. 3 releases or closes according to FIG. 2.

As can be clearly seen in FIGS. 2 and 3, the spring 20 is according to this Embodiment radially in the drum end wall 14 biased arranged outside the drum discharge opening 16 Compression spring, the tension force, which the counterforce to Centrifugal centrifugal force builds up, is matched to the opening speed, in which the valve spool 19 moves radially inward and the drum emptying opening 16 during the shutdown process the centrifuge releases. That is: when parking the Screw centrifuge reduces the speed of the centrifuge drum 10 to a standstill and the centrifugal force is also reduced. It then becomes when the centrifuge drum 10 runs out reaches a speed at which the centrifugal force becomes lower than the gravitational force with the result that that in the centrifuge drum forming liquid ring breaks down. This collapsing Liquid ring creates in the invention Screw centrifuge no longer has the problems described above because at this stage of the centrifuge operation, the piston slide 19 centrifugal valves distributed around the circumference moved radially inwards and thus the drum discharge openings distributed around the circumference 16 release, via which the centrifuge drum runs out 10 is completely emptied of liquid. This open position the centrifugal force valves 18 arranged according to the invention shows the Fig. 3. Conversely, the spool 19 only move from one certain drum speed radially outward and close it only then the drum emptying openings 16 when restarting the centrifuge.

2 and 3 also show that the piston rod 21 of the piston valve 19 engaging valve spring 20 with its radial outer end in a cap-shaped screw plug 22 is supported, in the end face of the drum end wall 14 from Circumference radially to the centrifuge axis is screwed. The radially outer head of this cap-shaped locking screw advantageously has a through hole 23 for liquid discharge and for self-cleaning of the centrifugal valve with self-cleaning of the Coils of the coil spring 20 on.

The piston slide 19 of the centrifugal valve 18 has both in the lower Dead center (Fig. 2) and in top dead center (Fig. 3) a safe Stop, so that both when closed as A stable valve position even when the valve is open sets. In addition, the cylindrical part in the exemplary embodiment of the sliding body 19 by the prevailing in the centrifuge drum 10 Pressure against the guide surface, so that the remaining Residual gap 24 between piston slide 19 and wall of Blind hole 17 is practically reduced to zero, as shown in FIG. 4 well reveals.

Basically, there is also the possibility of the liquid drain openings 13 and the drum emptying openings 16 together Centrifugal valves 18 to combine or combine.

Claims (6)

1. A centrifuge, especially a screw centrifuge for the separation of solid-fluid mixtures with a rotatably mounted drum casing (10) and a conveyor screw (11) in it which can rotate at a different speed of rotation and with fluid run-off openings (13) arranged in the end wall (14) and with solids extraction openings at the other end of the centrifuge drum, characterised in that in the end wall (14) of the drum radially outside the fluid run-off openings (13) at least one drum emptying opening (16) is arranged which is crossed through radially by a boring (17) in which a centrifugal valve (18) is introduced with a spring loaded closing element (19) in such a manner that the closing element closes the drum emptying opening (16) at high drum rotation speed, i.e. at operating speed, and opens the emptying opening at low drum speeds of rotation.
2. A centrifuge according to Claim 1, characterised in that the closing element of the centrifugal valve (18) comprises a piston valve (19) which can be introduced into a blind boring (17) adapted to the latter in the drum end wall (14) within the drum emptying opening (16) and in this can travel to and fro like a piston under the influence of the force of a spring (20) and the centrifugal force built up by the operation of the centrifuge and thereby opens or closes the crossing drum emptying opening (16).
3. A centrifuge according to Claim 2, characterised in that the spring (20) is a pre-tensioned compression spring arranged in the drum end wall (14) radially outside the drum emptying opening (16), whose tensional forced which builds up the opposing force to the centrifugal force of the centrifuge, is determined by the opening speed of rotation at which the valve piston valve (19) is moved radially inwards and thereby opens the drum emptying opening (16) in the running down of the centrifuge.
4. A centrifuge according to Claim 2 or Claim 3, characterised in that the radially outer lying end of the spring (20), which engages with the piston rod (21) of the piston valve (19), is supported in a cap shaped closing screw (22), which is screwed into the end of the drum end wall (14) from the circumference radially to the centrifuge axis.
5. A centrifuge according to Claim 4, characterised in that the radially outer lying head of the cap shaped closing screw (22) has a through boring (23) for the outflow of fluid and for the self cleaning of the centrifugal valve (18).
6. A centrifuge according to one of the Claims 1 to 5, characterised in that several drum emptying openings (16) and centrifugal valves (18) are arranged symmetrically distributed around the circumference in the end wall (14) of the drum.

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