A centrifugal separator Technical field The present invention relates to a centrifugal separator for separating solid and/or liquid particles suspended in gas media, comprising a rotor which is provided with deposit means, said rotor being rotatably mounted in a surrounding, stationary housing and having a central inlet for the gas medium to be cleaned, said housing having, firstly, an outlet for cleaned gas, which, when passing through the deposit means in the rotor, has been freed of solid and/or liquid particles, and, secondly, an outlet for the solid and/or liquid particles first deposited on the deposit means and thereafter transferred, by centrifugal force, to a lateral wall of the housing, the out- let for the solid and/or liquid particles having the form of at least one through-hole in the lateral wall of the housing The background of the invention In order to achieve effective purification of gases from solid or liquid particles sus- pended therein with the aid of a centrifugal separator, the rotor is provided with de- positing means in the form of a large number of tightly stacked plates, such as coni- cal discs, or a plurality of curved axial plates, or some other form of depositing means having an equivalent function. The gas to be purified flows into a central in- let well in the rotor, whereafter the particles in the gas are caused to precipitate and be deposited onto the depositing means as the gas flows radially out of the rotor.

The deposited particles then slide outwardly along the depositing means and are fi- nally thrown out onto the surrounding stationary housing wall as a result of the cen- trifugal forces. The particles caught on the housing wall are then transported in heli- cal rivulets along the wall towards a collection device due to the axial and tangential flow components of the gas in the housing. The collection device can have the form of a circumferential gutter, in which the particle flows (rivulets) are collected in a

ring shape, and whereafter the particle ring is drained out via drain holes from the gutter. As a result of the high peripheral speed of the plates causing a high tangential flow velocity of the gas in the housing, high shear stresses are created in the ring of liquid or particles collected in the gutter. This increases the risk that the liquid or particles on the wall will be transported in an undesired direction and be broken up and returned to the exiting gas flow. This is particularly true in and in the vicinity of the collection gutter, where the collected liquid and particle ring can be broken up and be entrained with the gas flow. One cause of this is the powerful gas turbulence in the gutter.

The purpose and solution of the invention It is a purpose of the present invention to remove the above mentioned disadvan- tages and to select a device, where the arrangement at the outlet for the liquid/partic- les is such that the separated liquid and/or solid particles are subjected to a substan- tially reduced shear effect from the gas where the liquid/particles are drained off to thus reduce the risk of return to the gas flow.

For this purpose the device described by way of introduction is characterized in that it has those defining features which are disclosed in the characterizing clause of the attached claim 1. The inwardly directed baffle ledge creates on its upstream side a vortex which generates an air cushion. The air cushion forms a barrier for rivulets flowing towards the outlet and drops of liquid or solid particles so that they are formed into a stationary ring upstream of the baffle ledge. By placing one or more outlet holes or slots at the location for this annular collection of liquid or particles, it is possible to divert in an undisturbed manner the liquid/particles from the centri- fugal separator housing without remixing into the purified gas.

Further features and advantages of the device according to the invention will be evi- dent in more detail below with reference to the accompanying drawings.

Brief description of the drawings Fig. 1 is a schematic side view of a centrifugal separator according to the invention; Fig. 2 is a view similar to Fig. 1 with the rotor unit removed, showing schematically the direction of flow of the gas in the housing and the liquid or particle flow en- trained to the inside of the housing wall; Fig. 3 is a fragmentary enlarged side sectional view of the area of the separator housing closest to the outlet for the separated liquid or particles; Fig. 4 is a view similar to Fig. 3 showing an alternative embodiment of a baffle ledge; Fig. 5 is a schematic perspective view from inside of the area shown in Fig. 3 but where the outlet holes are exemplified with an essentially axial slot and where a rib on the inside of the housing steers the particle flows towards the slot; Fig. 6 is a cross section through the housing with radial holes, as seen from above; and Fig. 7 is a view similar to Fig. 6 but with tangentially directed holes.

Detailed description of preferred embodiments In Fig. 1, a centrifugal separator according to the invention is generally designated 10. The separator is used for separation of solid and/or liquid particles suspended in gas media, e. g. for cleaning air containing an oil mist or other verifying particles. In order to meet increasingly strict environmental requirements for industrial buildings, it is often necessary to remove dirty air or other gases via long pipe systems to big external cleaning devices. The centrifugal separator 10 according to the invention is so compact that it can be placed directly on the machine which produces a polluted gas medium, and makes it possible to purify such polluted air so effectively that it can be released into the room directly at the process machine or machines in ques- tion.

The centrifugal separator 10 comprises a rotor 12 with a plurality of depositing means mounted thereon in the form of disc plates 14. The disc plates 14, onto which solid and/or liquid particles suspended in the gas are to be deposited, can have the form shown in Fig. 1, viz. conical disc elements stacked on each other with a small axial space therebetween. The rotor 12 is driven by a motor 16 via a shaft 18. A sta- tionary, conically shaped housing 20 surrounds the rotor 12 and has a connection piece 22 for inlet of the gas to be cleaned. The connection piece 22 is directly cen- tred at the inlet well 26 of the rotor 12.

The conical lateral wall 28 of the housing 20 has on its interior surface a radially inwardly directed annular flange or baffle 30 at a level somewhat below the bottom end of the portion of the rotor 12 containing the disc plates 14. Beneath the baffle ring 30 there are outlet openings 32 for the cleaned gas in the lateral wall 28. Spaced above the baffle ledge 30 there are exit holes 34 for the solid particles or liquid separated from the gas. These holes are disposed in the lateral wall 28 of the hous- ing 20. These holes 34 can be made radially (Fig. 6) or tangentially in the gas vortex direction of the housing (Fig. 7). Even if it is possible to use a single such exit hole 34, it is preferable to have a number of such holes distributed about the periphery of the housing 20 to increase capacity. The exit holes 34 can have circular cross sec- tional shape or take the shape of elongated slot-shaped openings extending essen- tially axially, as is shown in Fig. 4. The holes 34 can have a constant cross-sectional area through the housing wall 28 or can have increasing cross-sectional area in the flow direction (Figs. 6 and 7).

During operation, the gas to be cleaned flows into the central inlet well 26 in the rotor 12 and the particles in the gas are then caused to be deposited on the disc plates 14 as the gas flows radially out of the rapidly rotating rotor 12. The deposited particles then slide along the plates 14 and are finally thrown over onto the sur- rounding stationary housing wall 28 by the centrifugal forces. As can be seen in more detail in Fig. 2, the solid and/or liquid particles, due to the axial and tangential

flow in the housing, have a helical flow direction along the inside of the housing wall 28, forming drops or rivulets of liquid or solid particles, as indicated by the arrows in Fig. 2. As the gas flows past the baffle ledge 30 towards the lower gas outlets 32, an eddy 36 creating a gas cushion is created, as shown in Fig. 3, on top of the ledge 30. This annular gas cushion 36 forms a barrier which stops the obliquely downwardly flowing rivulets of liquid or solid particles so that a ring 38 of collected liquid/particles is formed around the inside of the housing wall 28. The outlet holes 34 are placed level with the ring 38 formed on the housing wall 28. This provides for smooth drainage from the housing of the liquid/particles collected on the hous- ing wall 28, providing effective removal of collected liquid/particles.

Fig. 4 shows a conceivable alternative design of the baffle. In this case, the baffle 30 is provided with an inner upwardly directed edge 39, or the like, to form a gutter, in which remaining liquid/solid particles can be collected when the centrifuge is stopped. During the actual operation, liquid/particles are prevented from reaching the baffle, since otherwise they would have a tendency to move radially inwards on the baffle and, when overflowing over the inner edge of the baffle, be re-dispersed in the gas flow. The gutter can have a salable drain for removal of residual liquid when the centrifuge is standing still.

As can be seen in Fig. 5, the inside of the housing wall 28 can be arranged with rib- like elements 42 which can guide the flow of liquid or particles on the housing wall 28 directly to the outlet holes 34. Furthermore, it is conceivable to make the axial extent of the outlet holes 34 and the vertical position of the holes above the baffle 30 adjustable in a manner not shown in more detail here, to adapt a single centrifu- gal separator to different operating conditions.

Even if the stationary housing in the most preferred embodiment shown in the drawings is conical with diameter increasing towards the outlet holes 34, it is possi-

ble to make the lateral wall of the housing circular cylindrical or reverse conical, i. e. with shortening diameter towards the outlet holes.

It is also conceivable to arrange in a single housing two or more baffle elements on the inside of the housing with associated outlet holes located upstream of the holes, for example, if the airflows downstream of the rotor are allowed to flow to either end of the housing.

The solution suggested according to the invention makes it possible to achieve an effective and continuously gas-cleaning centrifugal separator with so compact di- mensions that it can be placed directly on the machine or equipment producing the gas which must be cleaned, without the need to use filters coupled thereafter.