US2591396A

US2591396A - Centrifugal separator

Info

Publication number: US2591396A
Application number: US703347A
Authority: US
Inventors: Bergner Nore Einar
Original assignee: Separator AB
Current assignee: Alfa Laval Holdings Amsterdam AB
Priority date: 1945-11-02
Filing date: 1946-10-15
Publication date: 1952-04-01
Anticipated expiration: 1969-04-01
Also published as: FR1002923A; GB626500A

Description

April 1, 1952 N. E. BERGNER CENTRIFUGAL SEPARATOR 4 Sheets-Sheet l Filed Oct. l5, 1946 l Igl 1 INVENTOR. MJRE EJNAR .BERGNER BY 'H7 y L u S a ORYFY April 1, 1952 N. E. BERGNER CENTRIF'UGAL SEPARATOR Filed Oct. l5, 1946 /N VE/v TOR IVORE EJNAR, BERGNER April 1, 1952 N. E. BERGNER CENTRIFUGAL SEPARATOR 4 Sheets-Sheet I5 Filed Oct. l5, 1946 S \\\\\\\\\\\\\\\\\\\\\\\\\mmv" 37 z5 FIG. 6

10b 1Gb l N VEN TOR. ,ii/ORE EENAR BERGNER April 1, 1952 N. E. BERGNER CEr-ITRIFUGAL sEPARAToR 4 Sheets-Sheet 4 Filed Oct. l5, 1946 EG. I0

ze 7b 36| 37 Hall' Y /N VEA/TOR MRE 511m ERGME-R Patented Apr. 1, 1952 CENTRIFUGAL `SEPABATQR,

Nore Einar Bergner, Appelviken, Sweden, assigner toAktiebolaget Separator, Stockholm, Sweden,

a corporation of Sweden Application (lctober 15, 1946, Serial No. Aiililg347 In Sweden November 2, l194:5

25 Claims.

This invention relates to apparatus for separating particles from a fluid `by rotating the mass of fluid and particles in a separating chamber. yMore particularly, the invention has reference to a novel centrifuge for this purpose which ai- `fords improved results, as compared with prior vcentrifugesby reason `of its inclusion of a helical Worm so arranged in the separating chamber that itcoacts with the rotating mass to discharge the particles separately fromthe fluid.

As the invention maybe used to particular advantage for separating .dust or other particles from a .gasffor exam-ple, to purify the gas, it will :be described herein as a gas centrifuge. It will be understood, however, that the invention is not limited to such use.

Cyclones are constructed so that the axis of rotation `of the gas mass will be vertical, and the lparticles separated from the gas are discharged from the separating chamber in such a way that, due to the force of gravity, `they will settle to the bottom of .the cyclone where they are collected. This method of discharge sets a limit to the `applicability of such cyclones, owing to the fact that the particles most diiiicult to separate, and which are separated out in the vicinity `of the gas outlet, have low falling speeds, thus being easily sucked away by the escaping gas. The separating power of a cyclone cannot, therefore, be -raised very much, as the highest angular speeds cannot be utilized.

The present invention, therefore, is directed to the provision of an improved centrifuge which eliminates the disadvantage above mentioned and which, in addition, `provides other advantages l I unobtainable with prior apparatus of this cha-r- ,acteiz As inthe ca se of cyclones, the new apparatus discharges 4the particles in the axial direction. However, this discharge is eliected forcibly by a worinshaped as a spiralspring and specially adapted Afor the purpose. the worm being prefer ably rotated on. an axis coinciding with the longitudinal .axis of the rotation-,symmetrical sepa rating chamber. The operation may `be readily controlled by proper adjnstment of the relation =between the angular speeds of the gas and of the worm in the separating chamber at the radias where a certain discharge speed is` desired. In order that the `friction,against the wormshall not unnecessarily reducergthe 4angular speed of the gas, the worm is preferably caused to rotate in the same direction as the `gas in the separating chamber.

For a more complete understanding of the-invention, ,reference may be had to the `following 2 description, talen in conjunction with the 4accompanying drawings in which Fig. 1 is `a sectional view `of `one form of the new apparatus, the section ,extending `alone" the axis of rotation on the line I-l in Fig. 2,;

Fig. 2 is a sectional view Von the line.2 2 in Fig. 1, with `parts Abroken away;

Fig. Slis a sectional View similar to Fig. `2 but emerged and showing only the ,manner `0f :mounting an inner supporting ring for the worm on its rotating shaft;

Fig. f1 is a View similar' to Fig. 3 v` but showing an alternative supporting arrangement for the worm:

Fig. 5 is a perspective view of still another arrangement for Vsupporting the worm on the shaft, and

Figs. 6 to 4Ill, inclusive, Aare ,sectional views. taken along the axis ofrotaton, showing parts o .modediorms Qf .the apparatus- In the following description, `the expression "direction of displacement is intended to denote the `direction `in which-the particles are provided with an axial movement in the separating chamber bythe relative movement :between the rotatingV gas and thezworm.

The ,mode of vOllllltiin o f the separator depends `upon the variablerelattve uspeeds, oi theguas andthe worm. The `inlet speed rof the gas irnmcf- `diatelv :berend .the inlet to the separating chamber iS Changed to perinheralxspeed .0f the ses r,1'0- tation in the chamber so `that `this inlet speed will determine the `angular speed, i. e. the separating `power and the orienter-pressure.

If the peripheral speed of the `gas at the louter edge ofthe worm is lower `than the speedof the worm at its outeredge, the gas is displaced there by the Worm inan `axial direction which depends upon the `direction of the worm thread. If the inlet speed of the `gas is increased, and assuming the rate of rotation of the worm to be unaltered, the speed 0f .discharge is diminished; and ,the` dis charge ceases when the angular speeds ofthe gas aridof theworrnare equal. I n case the gas speed is fur-ther increased, thefdirectionof discharge :is reversed. During its ,movement toward itsoutlet, which is nearer the axis fof` rotation than the inlet, thegas willfbe rotating .mo1'eguickly, Vwhile the angular `Speed 0f the worm remains @existant Thisrfact accounts for two instances of g-S movement whichl can be distinguished.

In the first instance, the worin rotates everywhere.` at a higherangular,speedthan the gas, i.e. even at the smallest radii, .and the speed of discharge of the particleldecreases with reduced radial distance from the axis of rotation. The di-` rection of movement for such gas particles as will enter at the side surfaces of the gas inlet, is indicated by dotted arrows in Fig. '1.

In the second instance, when the peripheral speed of the gas is greater than that ofthe worm at; its outer edge, the relative movement will increase f the more the gas is approaching the outlet. The direction of discharge is here the reverse of that in the former case, and the discharge speed increases towards the outlet. The gas particles will thus move according to the dotted arrows in Fig. 6. i n

In a transitionary instance. the peripheral speed of the worm is greater than that of the gas at the inlet, but smaller than that of the gas at the outlet. The discharge direction of the particles is then changed at a certain radial distance from the axis, and it will be understood that in this Ycase easily separated particles will be discharged in the one direction at great radii, and particles difllcult to separate will be discharged in the opposite direction at small radii.

The gas separator illustrated in Figs. 1 and 2 operates according to the aforementioned transitionary case. It comprises a separating chamber l surrounded by a pipe 2 which, in turn, is surrounded by a housing 3. In the space 31 between the latter, the gas is introduced. The pipe 2 is provided with one or more generally rectangular orices 4 extending between

walls

5b and 5d which constitute the side surfaces of the gas inlet. The pipe 2 is rotatable so that the slot 6, which is limited by the housing 3 and an edge of the pipe dening the orice 4, can be made narrower or wider. By this or any other arrangement having the same effect, it is possible to change the tangential inlet speed of the gas at a certain capacity, or change the capacity for constant inlet speed. This adjustment may be made in the course of the separation, by any suitable means (not shown), such as an adjustment handle outside the housing for rotating the pipe 2.

In the separating chamber I is the worm 1 which brings about the axial discharge. The separate gas leaves the separating chamber I at the inner edges of the worm 1 at both ends of the separating chamber, and passes between the worm shaft 8 and pipes 9a and 9b, respectively, to gasdischarge chambers Illa and 10b. Secured to each side of the housing 3, that is, near each end of the separating chamber l, are side pieces lla and l lb providing sludge spaces |2a and 12b as well as the gas discharge chambers lila and 10b, respectively, the side pieces serving also to support bearings 13a and 13b for the worm shaft B. The bearings may, if desired, be supported by elastic and/or shock-absorbing elements, such as rubber rings I4 or buffers, like the top bearings of separators.

The worm 1 is provided at its ends with covers 15a and I-Sb, respectively, the outer sides of which may also serve'as ventilator wheels. The sludge or -dust dischargedby the worm is brought to the right (Fig. y1) at the radii where the peripheral speed of theworm is greater than that of the gas, if the right-hand'threaded worm is rotating in the direction of the arrow. At smaller radii, where the peripheral speed ofthe worm is less than that of the gas, the dust is discharged in the opposite direction. When the dust has reached the covers 15a and |5b, it is conveyed to the corresponding sludge spaces through slots i111 and Hb, respectively. As shown, the slot Ha is formed between the outer edge portion of cover 15a and a ring l9a on the worm, while the slot I1b is formed at the inner edge portion of cover 15b between the latter and the hub of an adjacent cover i8. In order to facilitate this radially directed movement, the slot |112 may serve as an inlet to a fan formed by vanes 18h between the covers 15b and it, and the slot 11a may serve as an outlet from a fan formed by vanes [8a between the edge of the ring ISa and the cover I5a.

The separated gas is led away through diffusor-like'outlets 33a and 33h at opposite ends of the worm. The speed of the discharging gas can thus be reduced, the kinetic energy of the gas then being transformed into pressure. The diffusors 33a and 331) may be spiral-shaped if desired, it being understood that their purpose is to transform energy of rotation as well as energy emanating from the axially directed movement of the gas, into pressure energy.

The worm 1 is supported by outer supporting rings ld and l9b, and by inner supporting rings formed by the pipes 9a and 9b and an intermediate pipe Sic, which are centered in relation to the shaft 8 by spokes or wings 20 connected to the shaft. The outer supporting rings I9a and I9b may be provided with internal grooves into which the outer edges of the worm are threaded and/or fixed, as by soldering or welding. In order that the spokes or wings 2D shall cause as little resistance as possible to the gas flow, they may be made of steel wire or of thin plate, or they may be stream-line shaped, thus offering little resistance to an axially directed flow `and/or a, rotational flow. As shown in Fig. 3, six spokes or wings 2) are formed by U-shaped plates 20a tted at their intermediate portions in longitudinal slots in the shaft 8, the sides of adjacent plates converging and being secured at their ends to the inner supporting ring for the worm. In the modication shown in Fig. 4, three spokes are provided by a triangular plate 20h fixed to the shaft 8a, the corners of the plate being secured to the inner supporting ring.

In operation, a certain difference in pressure will always prevail between the gas discharge chambers lila, leb and the sludge spaces I2a, I2b. The pressure in the sludge spaces is equal to the difference between the initial pressure of the in-going gas in the space 31 and the head obtained immediately beyond the inlet slot 6. In the central parts of the gas discharge, i. e. in the inlet of the diffusors 33a and 33h, a low pressure (subatmospheric) prevails, the magnitude of which depends upon constructional details as well as upon throughput rate and inlet pressure. The high speeds of the gas, mainly directed tangentially in the plane of rotation and which cause this low pressure, are reduced in the diifusors 33a and 33D and are thus transformed into pressure. Accordingly, if the gas were able to pass through the separator without loss, the final pressure of the gas in the outlet lil would be the same as its initial pressure. f

The wings 20 in the-gas outlet pipes 9a and 9b may be shaped in such a way as to transform the gas energy intov mechanical work which is absorbed by the rotor shaft 8, or suitable turbine devices inthe gas outlet may serve this purpose. In such a case, the pressure in the gas discharge chambers Illa and Ib will naturally be lower the more energy is taken from the gas by these means. I Y

Ignoring such an energy transformation by l`wings or blades, and assuming that a slit 32 is formed `between the rotor and the stationary part of each diffusor 33a, 33h at its inner portion, as shown in Fig. 1, a higher pressure will always prevail in the sludge spaces I2d, I2bl than at these slits. Consequently, it is necessary to provide means for preventing dust-mixed gas from leaking out through the slits from the sludge spaces to the discharging purified gas. Instead of the usual type of tightening or sealing means for such purposes, a ventilator or turbine may be used, or any other device which can overcome this drop in pressure. If the device affords a somewhat higher difference in pressure between its inlet and outlet than exists between the sludge space I2a or I2b and the slit 32, a certain limited quantity of pure gas may escape'through the slit from Athe `gas outlet to the sludge space I2@ or 42o. `In the embodiment of the invention shown in Fig. l, the tightening devices are constituted by fan wheels loa and IED on the rotor. i

As the fans iSd and lob are to create a pressure equal to or somewhat greater than the pressure fall in the separating chamber I, their rate of rotation must increase if this pressure fall increases. The rate of rotation ofthe fans, i. e., ,of the rotor, therefore depends upon the initial pressure of the gas being separated, upon the gas speed in the inlet slot 5, and upon the throughput rate. If desired, the use of the tightening fans IGa and I 6b may be avoided by locating each slit 32 at a part of the diusor in which the pressure lhas become as great as or somewhat greater than that in the sludge space I2a or IZb, as shown at 32u. in Fig. 9. As friction losses cannot be avoided, it is necessary that the diameter `of the slit 32u, be greater than that of the worm, if the pressure at the slit is to be identical with or greater than the pressure in the sludge space. The slit 32a may be dimensioned and located in this manner by modifying the diffuser as shown at 33e (Fig. 9), the modification including an outwardly flared end piece 39a secured to and forming a continuation of pipe sa.

By changing the inlet speed of the gas through slot 6, the speed and direction of the discharge may be controlled. The operation of the separator shown in Fig. l is such that easily separated particles are discharged to the right in the outer portion of the separating chamber i and escape to the sludge space I2ct through the slits 22a and Ila. Lighter particles are separated nearer to the axis of rotation and are discharged to the left (Fig. 1).

`They escape through the slit I'llr to the sludge space I 2b. Thus, the separator not only rids the gas of dust but also separates more and less easily separated particles from each other and leads them to different sludge spaces. By properly controlling the inlet speed of the gas in relation to the angular speed of the worm l, it is possible, therefore, to distribute the dust particles at will, according to their separability, between the sludge spaces I2a and |26.

The invention is not limited to the form shown" `in Fig. l but may, for example, take either of the forms shown in Figs. 6 and 7. The separator l illustrated in Fig. 6 is intended for large throughputs. Because of strength factors, the rotational speed of the worm l is limited and reduced, the greater its diameter' is made. Accordingly, if a high degree of separation is desired at a large throughput rate, it is preferable to choose a speed of the ingoing gas lwhich is higher than the peripheral speed of :the worm. All .of the .out-separated particles4 will then -move in the `same axial direction, although at varying speeds, and are collected in a number of generally annular slits 23 formed in a cover 23a rotating with the worm. In Fig. 6, only three lslits 23 are shown, in order to simplify the disclosure. The out-separated particles are -conveyed to the sludge space I2 through fans or ventilators 24. If all of the fans 24 (Fig. 6) open into a common sludge space, they must have varying outer diameters or in any case be so designed that their outlet pressures will be nearly equal. For practical reasons, the fan 24 having its inlet nearer to the shaft 8 is dimensioned so as to give a somewhat higher outlet pressure than the next fan, the .gas inlet of the latter being situated on a greater radius. This reduces the risk of particles difficult to separate being exposed to such gas speeds as may cause previously separated particles to be blown into the gas outlet. Should the outlets vfrom slits 23 open into different sludge spaces, the latter can be tightened or sealed from each other in any suitable manner. The outer diameters of the fans 24, in a separator of this type, should generally be greater than that of the worm l.

In the Fig. 6 embodiment, the pitch of the worm thread preferably decreases toward the gas outlet (to the left in Fig. 6) so that the discharge speeds are reduced in the parts of the separating chamber I located closer to the particle outlets 23. The length of the -worm may also be reduced in this manner. At the opposite end of the worin, where no particle discharge takesy place, the iinal turn of the worm is suitably xed and centered, this nal turn being in a plane at right angles to the rotating shaft at a cover 25. The cover 25 is shaped and xed to the shaft 8 in such a Way that the cover also -serves as support for radially directed forces and for turning and bending moments. The worm is surrounded by a tube 26 at the side of the gas inlet near the particle outlets 23, and opposite the gas inlet the inner edge of the worm is xed to a tube 2l. The separator parts may be so dimensioned and arranged that the tube 21 extends'partly into the tube 26, whereby these tubes include between them more than one thread of the worm, preferably more than two threads. Thus, each tube is rigidly xed to the other, so that the whole rotor will be resistant to the forces incident to operation of the separator, especially to transverse forces of inertia.

The embodiment shown in Fig. 7 is adapted primarily for small capacities. The lperipheral speed of the worm 'I in this instance is considerably greater than the inlet speed of the gas so that, if the direction of the worm rotation and of the worm thread is the same as in Figs. l and 6, the gas will move to the right in Fig. 7. Also, in this instance the discharge speed decreases as the gas approaches the outlet. The particles escape to the sludge space I2c through slits 28 and fans or ventilators 29 formed in a cover 28a rotating with the worm at the right-hand end thereof. Otherwise, the separator is in principle like that shown in Fig. 6. It may be desirable in the Fig. 7 embodiment to increase the pitch of the worm toward its right-hand end located nearer to the outlet. As the fans 29 rotating with the worm (especially at the large radii) have a considerably greater angular speed .than the gas, they can be made with an external diameter smaller than thatgof the worm. The external diameters of the -fans 29 may decrease the nearer to the axis of rotation their `inlets,arelocated.

assises ing chamber I in directions .toward the covers Ia and I5b (Fig. 1) presupposes that the gas has at the same time an axial movement. As the separated gas near the covers flows centrally in its discharge. i. e. in a direction toward the shaft and not parallel with it, care must be taken that Vgas from the sludge spaces IZa, I2b circulates at the ends of the separating chamber. On the side of the cover ItlaI facing the separating chamber are ventilator vanes I8a. (not absolutely necessary), which produce at the inner edge of thel ring I9a`. a pressure higher than that of the gas being separated at the same radius. Therefore, gas will be fanned out through the slitv IIa to'the'sludge space IZa'and pass back from there, at about the outer radius of the separating chamber, through the slit 22a. When entering the slit 22a., the gas has a low speed of rotation and is therefore caused to move towards the cover Ila by the worm. Gas will thus circulate around the ring I9a, and it is important for the proper functioning of the separator that the gasA escaping outwards through the* slit Ila. has a higher particle content than the gas entering through the slit 22a.. This may be the case without any special arrangements being provided, but fulllment of this condition may be assured by introducing a filter in or near the slit 22a (for instance, a cloth, a net, or the like) allowing the gas'but not the particles to pass through it. The same arrangement may, of course, be used at the slit 22D as Well.

In order to ensure that the gas has sufficient angular speed when passing through the slit 22a, and as high a speed as possible after passing v.through the slit 2217,'Y it may be desirable to provide a system of wings in these slits. Thus, the slit 22a may be provided with a system of suitably shaped wings orblades, either stationary or rotating with the rotor. The'air passing through the slit 22h may be introduced by similar means to obtain the desired speed as it enters the separating chamber.

The wings as well as the filters above nientioned may be incorporated in the separators shown in Figs. 6 and '7. In Fig. 6, I have shown rotating wings 30 in the outlet slit from sludge space I2, and in Fig. 7 I have shown stationary wings 3I in the outlet slit from the sludge space During its passage through separating chamber I from the inlet to its outlet. a gas particle moves along a surface of rotation whose shape is determined by the pitch and rotationalveloeity of the worm, and by the gas speed. Gas particles entering at the two end surfaces of the inlet B, that is, at the Surfaces or edges extending parallel to the shaft 8 and along the inlet, will move along such surfaces of rotation whose shape, however, will differ somewhat from that of other particles, due to the friction against gas masses located at the periphery of the separating chamber proper, and against rotor parts. By the separating chamber proper is meant that portion of the chamber I located between the two extreme or limiting surfaces of rotation along which particles from these two end surface-s of the gas inlet are moving. If the gas is considered as moving without friction. its angular speed outside this separating chamber .proper will be constant, but within this chamber the gas particles will be moving at diiferent angular speeds. A great difference in speed between these gas masses may cause certain difculties in the discharge vof the particles, Ibut these'dlfilculties may be avoided by discharging the particles'exactly vat these limit surfaces of rotation, as in the embodiments shown in Figs. 10 and 1l.

In Fig. l0, I have shown part of a worm 1a,

one end portion of which is surrounded by a shell 26 fitting tightly to the outer edges of the worm surfaces, the shell being shaped according to the limit surface. The shell 26 is provided at different radii with annular slots 34 forming outlets for vthe separated particles and which, as in the embodiments of Figs. 6 and 7, form the inlets to discharge fans 35 for the particles entering the sludge space I2d. l

- Instead of providing the particle outlet slots in the shell '26, they may be formed in the worm by making the worm sunfaces double, as shown at Ib in Fig. ll. Near the end of the worm, the internal surface of the worm facing the direction from which the discharge is effected has a spiralshaped slot 36 extending along the above-mentioned limit surface of rotation. In other words, the slot 36 has a gradually decreasing radius from the axis of rotation as it extends along the Worm toward the direction of discharge, and the slot serves as an outlet for the particles leading into the outwardly facing space between the double walls of the worm. In this outwardly facing space between the two worm surfaces lying closer together are wings 35a, between which the particles are transported to the sludge space I2e. The radial distances from the shaft to the outer edges of these wings, which thus act to discharge the particles, preferably vary in the same manner as in the ventilators 24 fand 29 shown in Figs. 6 and 7. It will be apparent that in the Fig. 1l embodiment, instead of enclosing the separating chamber proper in a shell as shown in Fig. l0, the shell is in effect arranged at the outer edges of the worm. The outlines of the shell and. of the limit surface may then differ from each other, as sholwn in Fig.-l1.

The discharging gas has a great kinetic energy which may be utilized and transferred to the shaft 8 by the use of turbine arrangements at the gas outlet. The spokes 26 may for that purpose be shaped as turbine blades. Moreover, special turbine arrangements rotating with the shaft 8 may be provided at the gas outlet, for example, as shown in Fig. 8. These turbine arrangements may comprise two or more series of turbine blades including stationary guide blades 40 and adjacent rotating blades 4 I, the blades lbeing arranged radially in planes at right angles to the shaft, yand also obliquely to such planes, or cylindrically. Thus, if the fan or compressor supplying the separator with gas of the required pressure is coupled to the rotor shaft 8, its power consumption will be considerably reduced because of the turbine arrangements.

In order to obtain a good separation with the new apparatus, it is important that .the gas move as freely as possible in the separating chamber. Accordingly, the worm should always be extended a certain minimum length in the direction of feed reckoning from the side surfaces olf the gas inlet 6, that is, from the inlet surfaces nearest the side pieces IIa, IIb. The covers 23a and 28a in Figs. 6 and 7, and the covers ISa and I5b in Fig. l, must therefore be located at such distances from the inlet 6 that they do not intercept the main paths of flow of the gas to the gas outlets (do not intersect the dotted arrows in Figs. 6 and 7). It appears that the minimum length indicated should beat least asgreat as the height-'of :the wonnmeasuredzradially, i. e. `the difference :betweenthe :,outerrand :inner radii of the worm.

It will be observed that the length of the sepaarating .chamber proper is not greater than the Awidth-of the gas inlet 6 between the limit sur- :faces a and 5b (Fig. 1). The radial gas speeds will decrease as this chamberismade wider, and consequently ahigher degree of separation will Abe obtained. The minimum length of the worm determined principally by the width of the gas .inlet A(i and is limited only by Arequirements of jphysi'cal strength. The practical lower limit for the length of the worm will generally correspond to a measure somewhat smaller than its outer diameter.

The relation between the outer and the inner radii of .theworm should be loiw for several reasons. A great radius ratio means among other `things alarge outer diameter of the worm, whereby therate of rotation of the worm must be kept ,low because of strength factors. Also, the increase in speed of the gas inthe separating chamber becomes very great, so that with a large radius ratio the inner friction of the gas may cause great losses of energy. Furthermore, the worin would have to be relatively long, involving mechanical diiliculties in construction.

If, on `the other hand, the radius ratio of the 'wormis too small, there is a risk that the rotavtion in the separating chamber will not have time to become fully developed, due to the diiicultyin `bringing about a completely tangential and shock-free introductionof the gas. It :appears `thatradius ratios between 1 to 1.5 and l to 6 are .particularly Vfavourable and that values above Y1 yto .1.0 and ,below `1 to 1.2 are unsuitable.

`An .excessively great pitch of the worm will .provide too great a discharge speed. This discharge speed should be .less than the tangentially directed peripheral speed of the gas, for if they are of the same magnitude, great shock .losses may ensue at the inlet i6. As a general rule, theupper limit for the pitch of the worm should be smaller than the outer diameter of the worm.

In Fig. l, I have shown only one outlet slit at each of the covers I5a or i512, through which the particles are discharged from the separating chamber. .It is evident that in some cases it may be desirable to provide several outlet slits for the particles, as in the case of the slits 23 in Fig. 6, orthe slits 28 in Fig. '7.

The sludge space i2a or i213, or both, may be 'provided with openings' which can b e shut by covers or valves, and through which the separated particles can `be discharged. Furthermore, special pockets or collecting vessels for `the particles may be connected to these openings, and the `openings can be closed by the valves, or the like, `-when the pockets are to be emptied orexchanged.

It is often desirable that the particles accumulated in a sludge space be discharged out of it continuously. This can be achieved by passing the discharge from the sludge space through a suitable mechanical device such as a filter or, when the particles are 4not diflcult to separate,

through an ordinary cyclone which has no moving parts. Such a cyclone may be connected to thesludge space and supplied from there with Vgas containing particles, the pressure of the gas thus being about equal to the inlet pressure in the separating chamber l of the separator. The cyclonepuried gas, which has a degree of purity less than that ofthe purified gasrfroni the sep- .able manner.

varator, constitutes but va small portion of the separated gas quantity, and it may if necessary kbe led back to a nozzle in the gas pipe supplying the separator. In this case, the kinetic energy of the gas from the cyclone should be transformed into pressure energy, which `may be done .in any suit- If the gas passes through the cyclone with moderate losses, the area in that part of the nozzle where the gas is reintroduced into the pipe suppling the separator, need only be slightly smaller than the area at the inlet 6 of the separator.

In separators having rotors which cannot be reinforced by pipes 26 or 2l (Figsf and 7), for example, aseparator as shown in Fig. 1, it may be necessary to `introduce several .supports to centre the worm, possibly along the whole of its length. The worm ls, in fact, generally similar to `a spiral spring, that is, rather weak transversally, and this may cause certain difculties at high or critical speeds. Such supports may consist ofspokes attached to the inner edge of the worm and to the shaft. The supports may be shaped in such a way and/or spaced at such a distance that a small elastic change of shape during the rotation can be permitted by them. In those cases where it is not necessary to consider any relative speed between the gas and the rotor at the gas outlet from the separating chamber, the spokes may be replaced, `as shown in Fig. 5, by supporting ribs 2l extending along the entire length of `the worm. The ribs will stiffen `the rotor considerably, but if the critical rotational speed of the rotor-need not be great, theribs -ZI may be divided into` shorter lengths which are attached to each other.

As the coarsest sludge particles are thrown at a high speed against the pipe 2, the latter may be arranged so that it is `easily replaceable, or it may be made of a durable material, or its surface may be provided with a protective coating.

The nature, temperature, etc. of thegas to be separated may make it necessary 'to protect the `shaft bearings inlsome way, for instance, by enoutlet for the purified fluid, means for directing the mixture tangentially into the chamber `through said inlet to cause the mixture to .rotate yaround the chamber, a rotary helical worm inthe chamber disposed substantially coaxially therewith and operable to discharge from the chamber particles suspended in the'uid, said mixture inlet being located near the outer edge portion ofthe worm, and said puried iiuid` outlet being located near the inner edge portion of the worm, and means for rotating the worm at a predetermined angular speed relative to the angularspeed of particles suspended in the fluid adjacent the worin, to effect said dischargeof the particles `in a direction generally Vparallel to the rotation axis of the worm.

`2. Apparatus as defined .in claim l, in which the pitch of the worm is smaller than the outer diameter of the worm.

3. Apparatus as defined in claim 1, in which the axial length of the worin is at least as large as` said inlet but projects axially beyond at least one side of the inlet for a distance at least as great as the radial dimension of the Worm from its inner edge to its outer edge.

5. Apparatus as defined in claim 1, in which said purified fiuid outlet is displaced from the mixture inlet in the direction of the axis of ro tation of the mixture in the chamber.

6. Apparatus as defined in claim 1, in which said last means rotate the Worm in the direction of rotation of the mixture in the chamber and at a rate such that the peripheral speed of the worm is less than the speed of the mixture at the inlet, said outlet being displaced from the inlet in the direction of the axis of rotation, the pitch of the Worm decreasing from the region of the inlet to the region of the outlet.

7. Apparatus as defined in claim 1, in which said last means rotate the worm. in the direction of rotation of the mixture in the chamber and at a rate such that the peripheral speed of the worm is greater than the speed of the mixture at the inlet, said outlet being displaced from the inlet in thedirection of the axis of rotation, the pitch of the Worm increasing from the region of the inlet to the region of the outlet.

8. Apparatus as defined in claim 1, in which the ratio between the outer diameter and the inner diameter of the worm, as measured in a common plane at right angles to the axis of the worm, is less than 6 to 1 but greater than 1.5 to 1.

9., Apparatus as defined in claim 1, in which said last means rotate the worm in the direction of rotation of the mixture in the chamber and at a rate such that the peripheral speed of the worm is greater than the speed of the mixture at the inlet but less than the speed of the fluid at said outlet.

10. Apparatus as defined in claim 1, in which said chamber has a limit surface provided with discharge openings for particles separated from the fluid.

11. Apparatus as defined in claim l, in which the'chamber has two outlets for separated particles, one particle outlet being located at each side of the mixture inlet reckoning in the direction of the axis of rotation of the mixture in the chamber, one of said particle outlets being disposed near the outer edge of the worm and the other near the inner edge of the worm.

12. Apparatus as defined in claim 1, in which Ythe chamber has a 'plurality of annular outlet openings arranged coaxially with the axis of rotation of the mixture in the chamber and at different radial distances from said axis, through which particles of varying separability are discharged from the chamber, easily separated particles being discharged through one of said annular openings located at a relatively great radial distance from said axis, and particles diiiicult to separate being discharged through an annular opening nearer said axis.

13. Apparatus as defined in claim 1, comprising also areceptacle for receiving particles separated in said chamber, the chamber having a plurality of particle outlets communicating with the receptacle and located at different radial distances from the axis of rotation of the mixture in the chamber, and means for inhibiting vcirculation of Valso a receptacle for receiving particles separated in said chamber, the chamber having a pluralityV of particle outlets communicating with the receptacle and located at different radial distances from the axis ofrotation of the mixture in the chamber, and means for inducing a small circulation of fluid through the receptacle from a particle outlet located at a relatively small radial distance from said axis to a particle outlet at a greater radial distance from said axis.

l5. Apparatus as defined in claim 1, comprising alsoa shaft in the chamber for rotating the worm, and means for supporting the Worm on the shaft and shaped to offer only a small resistance to the movement of theefluid at said fiuid outlet.

16. Apparatus as defined in claim l, comprising alsoV a shaft for rotating the worm, and turbine means for transmitting to the shaft energy from vthe speed of rotation and of translation of the fluid at said fluid outlet.

17. Apparatus as defined in claim Vl, comprising also a shaft in the chamber for rotating the VWoriruand spokes in the form of Wings for supportingthe worm on the shaft and shaped as turbine blades.

18. Apparatus as defined in claim 1, comprising also a shaft for rotating the Worm, and turbine means for transmitting to the shaft energy from the speed of rotation and of translation of .the fluid at said fiuid outlet, the turbine means including a generally ring-shaped rim of turbine blades rotating with the shaft, and an adjacent stationary rim of guide blades.

19. Apparatus as defined in claim 1. in which said last means rotate the worm about the axis of rotation of said mixture in the chamber, a receptacle for receiving particles separated in the chamber and communicating with the chamber at a greater radius from said axis than the purified fiud outlet, and means for preventing fluid from leaking to said fluid outlet from the receptacle. Y

20. Apparatus as defined in claim 1, in which said last means rotate the worm about the axis of rotation of said mixture in the chamber, a receptacle for receiving particles separated in the Vchamber and communicating with the chamber at a greater radius from said axis than the purified fluid outlet, there being a clearance space adjacent part of the rotating structure and extending between the duid outlet and the receptacle, and means for creating across said clearance space a drop in pressurergreater than that between the fluid outlet and the receptacle and Y defining a generally annular slit coaxial with the axis of rotation of the worm and located ata radial distance from said axis which is at least as great as the radial distance from said axis to the outer edge of the Worm.

22. Apparatus as defined in claim l, comprising also adjustment means for varying the minimum area of said mixtureinlet. Y

23. Apparatus as defined in claim 1, comprising also supporting members to which theV ends of the worm are fixed.

24. Apparatus as defined in claim 1, comprising also a generally annular member rotatable with the Worm and through which the purified fluid flows from the separating chamber, a second generally annular member rotatable With the Worm and surrounding the first member in spaced relation thereto, said members dening an outlet from the chamber for particles separated n the chamber, and a receptacle for the particles communicating with said particle outlet along one end of said second annular member and also communicating with the chamber along the other end of said second member.

25. Apparatus as dened in claim 1, in which the `chamber has near each end of the worm an outlet for the purified fluid, the chamber also having near at least one end of the Worm an outlet for particles separated in the chamber, said particle outlet being located at a greater radial distance from the axis of rotation of said mixture in the chamber than the adjacent fluid 15 14 REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 948,062 Morgan Feb. 1, 1910 1,274,058 Kutsche July 30, 1918 2,147,671 Pratt Feb. 21, 1939 FOREIGN PATENTS Number Country Date 507,711 Germany Sept. 19, 1930 491,112 Great Britain Aug. 26, 1938