Centrifuge for separating solids from liquids

A centrifugal rotor having peripheral outlets for intermittent sludge discharge includes two axially united and interconnected parts forming between them the separating chamber. One of the rotor parts is a bowl formed in one piece and provided with an edge portion directed radially inward, the other rotor part having a substantially smaller diameter than the bowl part and being connected therewith at said edge portion. The portion of the bowl part surrounding the separating chamber, and including said edge portion, has a form which, as seen in an axial section through the rotor, is substantially the axial section form of a hollow conical body.

The present invention relates to a centrifugal separator of the type in 
which the rotor comprises two axially united and interconnected parts 
forming between them a separating chamber, the rotor having a central 
inlet for a mixture of liquid and solid particles, a central outlet for 
separated liquid, and several peripheral outlets for separated solid 
particles, the last-mentioned outlets being constituted by channels 
extending through the rotor body from the radially outermost part of the 
separating chamber to the outside of the rotor body. A separator of this 
type also has means arranged to be displaced axially during operation to 
and from sealing contact against the outside of the rotor body around the 
peripheral outlet channels, the sealing surfaces of said means and the 
outside parts of the rotor body surrounding the outlet channels being 
arranged so that the sealing is effected by a sealing force acting 
substantially parallel to the rotor axis. 
A centrifugal separator of this kind is disclosed in German Pat. No. 
582,587 issued in the year 1931. 
At the end of the nineteenth century, the continuously operating 
centrifugal separator was invented. Originally, it had a rotor with an 
unbroken surrounding wall, i.e., there were no peripheral outlets for 
solid particles separated in the rotor. At the beginning of the twentieth 
century, the so-called nozzle separator was invented, the rotor of which 
is provided with narrow outlet openings at its periphery, through which 
separated solid particles are thrown out during the operation of the 
separator. Later, various valve means were invented for enabling 
intermittent opening of the peripheral outlet openings of nozzle 
separators during operations. One valve means of this kind is shown in the 
above-mentioned German Pat. No. 582,587. Valve means of this kind were 
desired because the peripheral outlet openings thereby could be made 
larger, and in this way clogging thereof could be avoided. About the year 
1930, there was invented a centrifugal separator of the kind used today. A 
centrifugal separator of this kind is characterized in that the rotor is 
provided with a number of peripheral outlet openings which can be closed 
and opened during operation by means of an annular slide arranged to be 
brought into sealing abutment against the rotor body radially inside the 
peripheral outlet openings. A centrifugal separator of this kind is shown, 
for instance, in German Pat. No. 652,292 issued in 1934. 
Since the last-mentioned invention was made, substantially all development 
in the field of centrifugal separators, concerning intermittent discharge 
of solid particles separated in the centrifuge rotor, has proceeded within 
the scope of that invention. The so-called nozzle separator with 
continuous discharge of separated solid particles during operation has 
been developed along with the new kind of centrifugal separator but has 
become less and less important. The largest part of the market has been 
taken over by centrifugal separators with intermittently opening 
peripheral outlets for separated solid particles. 
Since the development of centrifugal separators started, there has been a 
constant desire for improved separation efficiency. This desire has been 
especially concerned with centrifugal separators having intermittently 
opening peripheral outlets for separated solid particles, and it has been 
fulfilled by different means. One such means has been making the 
centrifugal separators larger, another means being the use of higher 
speeds of rotation. Serious problems as to strength have been encountered, 
however, and these problems to a large extent have been caused by the 
principle of construction of centrifugal separators with an internal 
annular slide arranged to be brought into sealing contact against the 
centrifuge rotor body radially inside its peripheral outlet openings for 
separated solid particles. 
The present invention involves a departure from the development course 
followed during the last forty years concerning centrifugal separators 
with intermittently opening peripheral outlets for separated solid 
particles, and it aims at fulfilling the desire for better separation 
efficiency without obstacles due to the conventional problems as to 
strength. 
The invention is characterized for this purpose in that a centrifugal 
separator of the initially described kind, which has been known since at 
least the year 1931, is modified so that one part of the rotor is 
constituted by a bowl formed in one piece and provided with a radially 
inwardly directed edge portion, the other part of the rotor having a 
substantially smaller diameter than the bowl-formed rotor part and being 
connected therewith at its said edge portion, the surrounding portion of 
the bowl-formed rotor part, including said edge portion, having a form 
which, as seen in an axial section through the rotor, is substantially 
like the axial section form of a hollow conical body. 
By this invention, it is possible to form a centrifuge rotor, of the kind 
having means for intermittent opening of peripheral outlets during 
operation, in a favorable manner seen from the technical strength point of 
view, so that at least twice as large centrifugal forces as before may be 
achieved within the separating chamber without change of the diameter of 
the centrifuge rotor. It has thus proved possible in practice to obtain a 
centrifugal force of about 13,000 g, in contrast to about 6,000 g for 
conventional centrifugal separators having the same diameter and 
intermittently opening peripheral outlets. 
It has also proved possible by the invention to remove from the centrifuge 
rotor, during operation, separated solid particles having a dry substance 
content higher than that previously obtainable. This is believed to be due 
to the fact that a substantially higher pressure can be obtained now than 
previously within the radially outermost part of the separating chamber. 
Owing to the resulting pressure difference between this part of the 
separating chamber and the atmosphere surrounding the rotor, such large 
shearing forces will be obtained in the mass of the separated solid 
particles within the separating chamber, when the peripheral outlets of 
the rotor are opened, that the particles can flow out through the 
relatively small outlets in spite of the fact that the particle mass has a 
very large dry substance content. 
It has been possible also by means of previously known centrifugal 
separators, having intermittently opening peripheral outlets, to obtain a 
high dry substance content of a particle mass within the separating 
chamber, this result being accomplished by causing the separation to go on 
for a relatively long time. It has not been possible, however, to 
discharge a firmly compressed mass of particles thus obtained through the 
relatively small outlets in the surrounding wall of the rotor. Therefore, 
it has generally been necessary to accept a substantially lower dry 
substance content of the particle mass discharged from the centrifuge 
rotor than the one really desired. 
An important consequence of the invention is that centrifugal separators 
with intermittently opening peripheral outlets can now be given a 
substantially more simple construction than previously. Because the 
peripheral outlets of the centrifuge rotor may be made relatively small, 
the force influencing the operating means due to the pressure of the 
content of the separating chamber, and which must be overcome when said 
outlets are to be closed, is relatively small. The arrangement necessary 
for providing this closing force, and for removal of the same, may 
therefore be given small dimensions. A centrifugal separator according to 
the invention may thus be made more simple and less expensive and yet more 
effective than previous centrifugal separators with intermittently opening 
peripheral outlets. 
In a preferred embodiment of the invention, the radially inwardly directed 
edge portion of the bowl-formed rotor part has an inner diameter that is 
slightly larger than the outer diameter of the conical disc set normally 
arranged within the separating chamber. In this way the rotor body may be 
given the most favorable form, seen from the technical strength point of 
view, and still the disc set may be mounted within the rotor in the most 
simple manner.

As shown in FIG. 1, the centrifuge rotor comprises two parts 1 and 2 which 
are held together by means of a lock ring 3. The rotor defines a 
separating chamber 4 in which a conical disc set 5 is arranged. Within the 
rotor there are also a conical distributor 6 having radial distributor 
wings 7, and a stationary inlet pipe 8 extending into the distributor. The 
inlet pipe 8 supports on its outside a paring disc 9 with paring channels 
10 opening into an outlet chamber 11 for separated liquid. 
From the radially outermost parts of the separating chamber 4 a number of 
channels 12 extend parallel to the rotor axis through the lower rotor part 
2. In the openings of the channels 12 at the outside of the rotor are 
small sleeves 13 which extend some distance downward from the outside of 
the rotor body. Small members 14 for closing the openings of the sleeves 
13 (and thereby the openings of the channels 12) are fastened on an 
annular plate 15 arranged concentrically with the rotor axis, and movable 
axially relative to the rotor. Annular sealing members 16 and 17 are 
arranged so that a substantially closed space 18, extending around the 
rotor axis, is confined between the plate 15 and the lower part 2 of the 
rotor. The space 18 remains substantially closed also during axial 
movement of the plate 15 relative to the rotor part 2. The plate 15 is 
pressed towards the rotor part 2 by means of a large number of springs 19 
supported by plate 20 connected with the rotor part 2. 
The entire rotor is supported by a rotatable shaft 21 having an axial 
channel 22. This channel 22 communicates at its upper end through several 
crossing channels 23 in the shaft 21, and through the same number of 
channels 24 in the rotor part 2, with the space 18 between the plate 15 
and the rotor part 2. The channel 22 also communicates with a device 25 
arranged to supply pressurized air intermittently to the channel 22 and 
thus subject the space 18 to overpressure. 
As shown in FIG. 2, the separating chamber contains filler pieces 26 
located at the periphery of the rotor part 2. These filler pieces form 
together with the rotor part 2 funnel-shaped pockets 27 in the separating 
chamber, the chamber 12 extending from the radially outermost parts of 
these pockets. 
In the operation of the centrifugal separator, liquid containing particles 
to be separated is supplied into the centrifuge rotor through the inlet 
pipe 8, from which it flows in the distributor 6 between the distributor 
wings 7 and thence into the separating chamber 4. In the latter, the solid 
particles are separated by the centrifugal force and are collected in the 
funnel-shaped pockets between the filler pieces 26 (FIG. 2), while liquid 
freed from particles flows toward the axis of the rotor to the outlet 
chamber 11 and thence from the rotor via the paring channels 10. 
When separated solid particles are to be removed from the separating 
chamber 4 after a certain period of time, the device 25 is activated so 
that the channels 22-24 and the space 18 are subjected for a short moment 
to overpressure. The plate 15 is thus forced away from the rotor part 2 
against the action of the springs 19, whereby the channels 12 are opened. 
Due to the high pressure prevailing within the separating chamber 4 as a 
consequence of the rotation of the rotor, separated solid particles are 
forced out from the rotor through the channels 12. The particles are 
thrown by the centrifugal force away from the openings of the sleeves 13 
without coming into contact with the outside of the rotor. 
As soon as the pressure in the channels 22-24 and the space 18 returns to 
normal (generally atmospheric pressure), the plate 15 is pressed by 
springs 19 back to its starting position where the members 14 close the 
openings of the sleeves 13. 
Of course, a sludge-sensing device of a known type (not shown) may be 
provided for automatically sensing when the centrifuge rotor must be 
emptied of separated solid particles. In that case, the sensing device 
would be arranged to separate automatically, in a conventional manner, the 
above-mentioned device 25 for the supply of pressurized air to the 
channels 22-24 and the space 18. 
The cross-sectional area of the channels 12 may be varied with regard to 
the kind of solid particles to be separated in the centrifugal separator. 
For instance, when yeast particles are to be separated in connection with 
production of beer, it has proved suitable to use channels 12 having a 
diameter of about 10 mm. Further, the filler pieces 26 may be formed with 
regard to the kind of particles to be separated. The angle formed by the 
funnel-forming surfaces of the filler pieces with a radius of the 
centrifuge rotor is thus chosen with regard to the relevant angle of 
repose for the separated particles. 
With the above-described centrifugal separator, pressurized air is used for 
opening the channels 12. If desired, liquid could be used, of course, as 
the pressure fluid. A number of throttled drainage channels would then 
have to extend from the radially outermost part of the space 18. The 
device 25 in such a case need not generate any substantial pressure by 
itself. Owing to the centrifugal force obtained by the presence of liquid 
within the space 18, there would automatically be created a necessary 
pressure for forcing the plate 15 away from the rotor part 2. 
If desired, the present invention may be used with centrifugal separators 
of the kind comprising constantly open nozzles at the periphery of the 
centrifuge rotor. During operation of centrifugal separators of this kind, 
a high viscosity mass of separated particles is continuously removed from 
the separating chamber through these nozzles. In certain cases it has 
proved desirable to provide the rotor of such a centrifugal separator with 
further outlets for separated solid particles. These outlets should 
normally be closed but should be opened intermittently for rapid removal 
of an excess of particles separated in the separating chamber. An 
arrangement of this kind, comprising continuously open outlets as well as 
intermittently opened outlets, may be used for preventing an excessive 
increase in the particle concentration of the particle mass leaving the 
separating chamber through the constantly open outlets. 
The intermittently opening outlets may be constituted by peripheral outlets 
12 according to the present invention. Because of the simplicity of the 
construction shown in the drawing, these outlets may be opened and closed 
with high frequency without substantial wear of the centrifuge rotor and 
without substantial reduction of the speed of rotation of the centrifuge 
rotor in connection with the opening actions. 
The intermittently opening outlets are preferably situated farthest from 
the axis of rotation in the separating chamber, while the inlet parts of 
the constantly open nozzzle channels are situated somewhat radially inside 
the intermittently opening outlets in the separating chamber. This 
prevents the nozzle channels, which are very narrow, from being clogged by 
large solid particles present in the centrifuged liquid. Preferably, the 
inlet parts of the nozzle channels are directed so that they turn their 
openings radially outwards, i.e., away from the rotor axis. Clogging of 
the nozzle channels in this way may be practically avoided. 
As will be noted from FIG. 1, the rotor part 2 is constituted by a bowl 
formed in one piece and provided with an upper edge portion 2a directed 
radially inward. The other rotor part 1 has a substantially smaller outer 
diameter than the bowl part 2 and is connected thereto at the edge portion 
2a by means of the locking ring 3. As shown, the edge portion 2a has an 
inner diameter slightly larger than the outer diameter of the disc set 5.