Sludge Centrifuge

Abstract

Spaced around the periphery of the centrifugal rotor are permanently open nozzles for discharging sludge separated from the liquid fed to the separating chamber of the rotor. To remove the sludge cushions accumulating on the peripheral wall of this chamber between the permanently open nozzles, the rotor periphery has at least one sludge outlet which is alternately opened and closed by an axially movable piston valve.

Description

The present invention relates to centrifuges for separating a sludge-containing liquid and in which the rotor is provided along its periphery with circumferentially spaced nozzles which are permanently open to discharge sludge separated in the separating chamber of the rotor.

A difficulty with centrifuges of this type is that the nozzles are easily clogged if the sludge contains particles larger than the inner diameter of the nozzles. The sludge concentration obtained in the separation depends upon the number as well as the inner diameter of the nozzles, since a reduced number of nozzles requires an increased inner diameter of the nozzles. If, in order to avoid this clogging of the nozzles, their inner diameter is increased and consequently their number is reduced correspondingly, the sludge cushions formed between the nozzles will grow faster radially inward toward the periphery of the disc set and into the latter, due to the bosh angle of the sludge. This means that the centrifuge must be stopped more often for cleaning than when using the smaller nozzles. Each cleaning of the centrifuge rotor requires dismounting of the rotor and consequently troublesome and time-consuming work. Different methods have been attempted for clean-flushing the centrifuge rotor while keeping it in rotation, without reaching any satisfactory solution of the problem.

According to the present invention, which aims at eliminating this difficulty, the separating chamber of the centrifuge rotor has the afore-mentioned nozzles, and the rotor is provided along its periphery with one or more sludge outlet openings arranged to be opened and closed by an axially movable piston valve. When using a single sludge outlet opening, this opening can extend continuously along the entire periphery of the rotor. The opening and closing movements of the piston valve can be effected in a manner which is conventional in the art.

The invention is described more in detail below with reference to the accompanying drawing, in which the single illustration is an axial sectional view of the left-hand half of an example of the new centrifuge.

In the drawing, a centrifuge rotor 1 comprises an upper part 1a and a lower part 1b which are clamped together by a lock ring 2. In the rotor wall is a sludge outlet opening 3 and similar openings (not shown) spaced around the periphery of the rotor, these openings being opened and closed in a conventional manner by a valve piston 4. The latter has a plurality of holes passing radially through the piston at its upper annular portion and spaced therearound to form permanently open sludge outlet nozzles, one of these holes being shown at 5. Alternatively, such holes may be formed in the upper part 1a of the rotor body, as shown with dash-dotted lines at 5a. The holes 5 or 5a open into the openings 3. When separating bacteria from milk, the holes 5 can have a diameter of 0.4 mm; and when separating baker's cottage cheese from sour coagulated skim milk, these holes can have a diameter of 1.0 mm.

The rotor 1 is carried and driven by a hollow shaft 6, through the central channel of which liquid to be separated is supplied to the separating chamber of the rotor. The liquid enters this chamber past the lower edge of a distributor 7. Separated sludge is thrown outwardly through the holes 5; but between these holes (reckoned peripherally) sludge deposits are eventually formed as indicated at 8. Purified liquid flows through a disc set 9 inwardly toward the axis of the rotor and thence, via an overflow outlet 10, into a paring chamber 11. The latter is provided with a stationary parting disc 12 connected to an outlet pipe 13.

Assuming that baker's cottage cheese is to be separated from sour coagulated skim milk, the skim milk is fed through the shaft 6 to the separating chamber of the rotor and is divided into whey and baker's cottage cheese. The whey passes inwardly and is discharged by the paring disc 12, while the cheese passes outwardly toward the periphery of the rotor for discharge through the holes 5 and the openings 3. Despite this discharge through the holes 5, some of the cheese deposits on the inner surface of the rotor periphery at its regions located between the circumferentially spaced holes 5, so that these deposits eventually form substantially conical cushions each having its apex extending inwardly toward the periphery of the disc set 9. These cheese cushions, however, must not be allowed to grow into the disc set, since they would then impair the separation efficiency of the centrifuge. To avoid such impairment without having to stop the centrifuge rotor in order to dismount and clean it, the openings 3 are opened by downward actuation of the valve piston 4 without stopping the centrifuge rotor. Due to the centrifuge force, the cheese cushions are then thrown out directly through the openings 3; and after the valve piston 4 is returned to its closing (upper) position as illustrated, the separation can be continued.

In those cases where bacteria are separated from whole milk, a layer of impurities settles along the inside of the rotor periphery, and through this layer extend radial channels which are formed just opposite the holes 5 and which remain open during the separation course. Bacteria separated from the milk are thrown out through these channels, as long as the sludge layer does not build up sufficiently to reach the periphery of the disc set. To avoid this build-up, the sludge layer may be discharged in the afore-mentioned manner at suitable intervals (for example, 1 hour).

After a separation course has been completed, the centrifuge rotor can be cleaned by opening the valve piston 4 while keeping the rotor in continued rotation.

In the illustrated embodiment, the valve piston 4 is actuated conventionally by varying the feed rate of an operating liquid from a stationary duct 15 into an annular space 4a between the valve piston 4 and the lower bowl part 1b, this liquid entering the space 4a near the rotor axis. To keep the piston 4 in its raised position as shown, the space 4a is maintained completely filled with the operating liquid despite a continual bleeding thereof through a peripheral outlet 4b. Thus, the pressure of the operating liquid is sufficient to hold the upper edge of the piston against the opposing edge of the upper bowl part 1a, as shown at 16, thereby preventing discharge directly through the openings 3. By sufficiently reducing the flow rate from duct 15, the operating liquid drains from space 4a through outlet 4b until the upward pressure on piston 4 is diminished enough to allow lowering thereof under the pressure exerted by the contents of the separating chamber, whereupon the openings 3 are unblocked for direct discharge therethrough independently of the holes 5. Piston 4 is returned to its raised (closing) position by increasing the feed rate from duct 15 so as to re-fill the space 4a.

Claims

I claim:

1. In a centrifuge for separating a sludge-containing liquid, the combination of a centrifugal rotor having a separating chamber and including a peripheral portion, said chamber having permanently open nozzle means leading outward from the chamber periphery for discharging sludge separated therein, said peripheral portion having a sludge outlet opening, and a piston valve movable in the rotor axially thereof between a first position for preventing sludge discharge from said peripheral portion of the chamber except through said nozzle means and a second position for discharging sludge through said outlet opening independently of said nozzle means.

2. The combination according to claim 1, in which said nozzle means are in the piston valve.

3. The combination according to claim 1, in which said nozzle means are in said peripheral portion of the rotor.