Sludge Centrifuge

Abstract

The centrifugal rotor has a level-maintaining outlet for clean-separated liquid, a peripheral outlet at the greatest radius of the inside of the rotor wall, and a conical screw operable in the rotor to convey separated sludge for discharge from a region of the rotor remote from said outlets. A valve coacting with the peripheral outlet is associated with control means operable by the action of liquid discharged from the level-maintaining outlet to maintain the valve in condition to close the peripheral outlet, the valve being operable in response to interruption of the liquid discharge from the level-maintaining outlet to open the peripheral outlet and thereby effect removal of deposits on the conveyor screw.

Description

The present invention relates to a sludge centrifuge equipped with a liquid-level-maintaining outlet for clean-separated liquid as well as with a conical screw coaxial with the centrifuge rotor and feeding separated sludge to an outlet located closer to the axis of rotation of the centrifuge rotor than said liquid outlet, the centrifuge also having an outlet which can be opened intermittently and is located at the greatest radius of the inside of the wall of the centrifuge rotor. A centrifuge of this kind is disclosed in the Swedish patent specification 310,624.

A centrifuge of the above-mentioned kind is of special interest for the separation of a sludge-containing liquid which, in addition to sludge with a higher specific gravity than the liquid, contains sludge with a lower specific gravity than the liquid. As in the case of certain waste waters, this lighter sludge may consist of sticky substances, such as fat, which deposit on the screw and fill its threads, whereby a further running of the centrifuge is made impossible. By opening the outlets which can be opened intermittently and interrupting the supply of the liquid to be separated, but otherwise allowing the centrifuge to run, the rotor can be emptied of liquid through these outlets. After the liquid has discharged from the rotor, the deposits on the screw are thrown outwardly by the centrifugal force and fed by the screw to the sludge outlet.

In the centrifuge according to the Swedish patent specification 310,624, it is necessary for removal of deposits on the screw to take steps to open the outlets through which the rotor is emptied of liquid, in addition to an interruption of the supply of the liquid to be separated. The present invention relates to an improvement of this centrifuge whereby the discharge of liquid from the rotor is effected automatically by an interruption of the supply to the centrifuge of the liquid to be separated. Consequently, in this way an appreciable simplification of the operation of the centrifuge is effected. More exactly, the new centrifuge is characterized by a valve inserted in said outlet which can be opened intermittently, said valve being arranged to be kept closed under the action of liquid discharged from the levelmaintaining outlet.

A number of different embodiments are possible within the scope of the present invention. A first such embodiment is characterized in that the valve-controlled outlet has a radially outer opening forming a valve seat and that a double-armed lever, arranged on the outside of the centrifuge rotor, is journalled so that a valve body carried by one end of the lever is movable radially relatively to said valve seat, the other end of the lever being arranged to be actuated by liquid discharged from the level-maintaining outlet.

A second embodiment is characterized in that the valve-controlled outlet has a radially outer opening forming a valve seat for a radially movable valve body and that a channel, provided with a drainhole, leads from the level-maintaining outlet to the radially outer end of the valve body.

A third embodiment is characterized in that the valve-controlled outlet opens into a vortex fluidistor, located radially outside this outlet, the tangentially arranged inlet for the control liquid of the fluidistor communicating with the level-maintaining outlet.

A fourth embodiment is characterized in that the valve-controlled outlet has an axially directed, outer opening forming a valve seat for a valve body which is axially movable in a chamber as a piston, the chamber thus having an axially inner and an axially outer end, there being a channel leading from the level-maintaining outlet to the outer end of the chamber, and each end of the chamber being provided with a drainhole.

The invention is described more in detail below with reference to the accompanying drawings in which

FIGS. 1 through 4 are axial sectional views of parts of four different embodiments, chosen by way of example, of the rotor of the present centrifuge. Corresponding details in the different figures have the same reference numerals.

In FIG. 1, reference numeral 1 designates a centrifuge rotor having a horizontal axis of rotation 2. A conventional conical screw 3 feeds sludge, deposited on the inside of the rotor, to the left to the usual outlet (not shown) which is located closer to the axis of rotation than an outlet 4 for clean-separated liquid. The liquid to be separated is supplied through the usual inlet (not shown). The outlet 4 is formed by a hole located eccentrically in a disc 5 which is inserted in the right-hand end wall of the rotor and which is adjustable by being rotated. Thus, the distance of the liquid outlet 4 from the axis of rotation 2 can be varied in a desired manner. At the greatest radius of the inside of the rotor there is a hole 6 passing radially through the rotor wall. A double-armed lever 7 is journalled on a bracket 7a on the outside of the rotor wall. The left-hand end of the lever carries a valve body 8, the hole 6 opening into a valve seat for the valve body 8. The right-hand end of the lever has the shape of a scoop 9, which catches liquid discharging from the overflow outlet 4. As will be readily understood, the valve 6, 8 is kept closed as long as liquid discharges through the overflow outlet 4 (i.e., as long as rotor 1 continues to receive a supply of the liquid to be separated).

When it is desired to clean the screw 3, the liquid supply to the rotor is interrupted without the centrifuge being stopped. Liquid then ceases to act upon the scoop 9, and the valve 6, 8 opens under the pressure of the liquid 10 present in the rotor. The latter is then emptied of all liquid through the hole 6, and the fat or similar sticky, light material stuck in the threads of screw 3 is thrown from the latter by centrifugal force and hits the inside of the rotor's peripheral wall, whence the screw feeds the material to the sludge outlet. After this cleaning has taken place, the supply to the rotor of the liquid to be separated is resumed, the supply rate appreciably exceeding the discharge rate which is possible through the hole 6.

In FIG. 2, 11 designates an annular chute arranged on the outside of the end wall and catching a part of the liquid discharging from the overflow outlet 4. The main part of the liquid from the outlet 4 flows over the edge of the chute 11. A channel 12 leads from this chute to the radially outer end of a radially guided valve body 13, for which the hole 6 serves as a valve seat. The channel 12 has a drain hole 14. A recess 16 is provided in the annular member 15 in which the channel 12 and chute 11 are formed. As long as the supply of the liquid to be separated is uninterrupted, the valve 6, 13 is kept closed by means of the liquid pressure acting against the radially outer end of the valve body 13. When the supply of the liquid to be separated is interrupted, the supply of liquid to the chute 11 ceases and the channel 12 is emptied of liquid through the drain hole 14. The valve body 13 is thus thrown radially outwards by the centrifugal force, the liquid 10 being discharged through the hole 6 and the recess 16. The screw 3 therefore becomes cleaned, as previously described.

FIG. 3 shows a variation of the embodiment according to FIG. 2, in that the valve body in FIG. 2 has been replaced by a vortex fluidistor whose cavity 17, as seen in radial direction, has a circular shape. The channel 12 opens tangentially into the fluidistor, as indicated at 18, and supplies control liquid from the chute 11. As long as control liquid is supplied to the fluidistor from the chute 11, the whirl formation in the fluidistor cavity 17 generates such a great flow resistance against discharge of liquid through the hole 6 that the outflow through the latter is small. However, as soon as the supply of the liquid to be separated is interrupted, the chute 11 is drained through the passage 12, 18, 14, whereupon the whirl movement in cavity 17 ceases and the flow resistance in the passage 6, 17, 14 is strongly reduced so that the centrifuge rotor 1 is emptied through the hole 14.

In FIG. 4, 19 designates a valve housing secured to rotor 1 and in which there is arranged an axially movable valve body 20 provided with a labyrinth seal. In the rotor end wall there is arranged an axial channel 21 in which a tube 22 is inserted, this tube serving as a valve seat for the valve body 20. The chute 11 is like the chutes 11 in FIGS. 2 and 3. The space 23 in which the valve body 20 moves has a liquid inlet 24 from the chute 11 and two drain holes 25 and 26, one at each end of the space 23. As long as liquid flows into the space 23 from the chute 11, the valve 20 - 22 is kept closed, since the right-hand end of the valve body 20 has a greater surface area acted upon by liquid than its left-hand end. However, as soon as the supply of liquid from the chute 11 ceases, the valve body 20 is pressed to the right and the liquid 10 is emptied through the drain hole 25.

It will be understood that screw 3 is rotated at a different speed than the rotor 1, in order to convey the separated sludge to the left toward the sludge outlet. Those details of the centrifuge not illustrated are well known in the art, as disclosed, for example, in U.S. Pat. Nos. 3,447,742 and 3,506,187 dated June 3, 1969, and Apr. 14, 1970, respectively.

Claims

We claim:

1. In a sludge centrifuge, the combination of a centrifugal rotor for receiving a sludge-containing liquid to be separated, the rotor being mounted for rotation about an axis and having a liquid-level-maintaining outlet for clean-separated liquid, the rotor also having a peripheral outlet located at the greatest radius of the inside of the rotor wall, a conical screw mounted in the rotor coaxially thereof and operable to convey separated sludge for discharge from the rotor at a region thereof remote from said outlets, a valve coacting with said peripheral outlet for opening and closing the same, and control means associated with said valve and operable by the action of liquid discharged from said level-maintaining outlet to maintain the valve in condition to close said peripheral outlet, said valve operating to open said peripheral outlet in response to interruption of the liquid discharge from the level-maintaining outlet.

2. The combination of claim 1, comprising also a seat for said valve and at least partly defining said peripheral outlet, said control means including a double-armed lever mounted on the outside of said rotor and carrying said valve on one arm of the lever, the other arm of the lever being in position to be actuated by liquid discharged from the level-maintaining outlet.

3. The combination of claim 1, comprising also a seat for said valve and located at the outer end of said peripheral outlet, said valve being movable radially to and from said seat and having a radially outer end, said control means forming a channel provided with a drain hole and leading from the level-maintaining outlet to said outer end of the valve.

4. The combination of claim 1, in which said control means include a vortex fluidistor located radially outside said peripheral outlet and into which said peripheral outlet opens, the fluidistor having a generally circular cavity and a passage leading from the level-maintaining outlet and opening tangentially into said cavity.

5. The combination of claim 1, comprising also a seat for said valve and through which said peripheral outlet opens in a direction parallel to said rotation axis, said control means forming a chamber in which the valve is reciprocable parallel to said axis, said chamber having an inner end adjacent said peripheral outlet and having an outer end remote from the peripheral outlet, said control means also forming a channel leading from the level-maintaining outlet to said outer end of the chamber, each end of said chamber having a drain hole.