Abstract:
In a centrifugal separator, the rotor of which is adapted to be driven by means of a gaseous driving fluid, the rotor itself supports a ring of turbine blades extending around the rotational axis of the rotor. A stationary nozzle is adapted to direct a flow of the driving fluid towards the ring of turbine members. After the driving fluid has passed between the turbine blades and has influenced them for driving of the centrifugal rotor, it enters a reversing chamber formed by a stationary reversing member. In the reversing chamber the driving fluid is caused to change its direction and is then conducted again towards the ring of turbine members in order to be utilized a second time for driving of the centrifugal rotor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/SE01/02284 filed on Oct. 19, 2001, which designates the United States of America and was published in English as PCT International Publication No. WO 02/34408 A1 on May 2, 2002, and Swedish Patent Application No. 0003915-6 filed on Oct. 27, 2000. The disclosures of these patent applications are incorporated by reference herein in their entireties. 
     FIELD OF THE INVENTION 
     The present invention relates to a centrifugal separator having a rotor and a driving means for rotation of the rotor about a rotational axis by means of a gaseous driving fluid. 
     BACKGROUND OF THE INVENTION 
     About 100 hundred years ago pressurised steam was sometimes used for driving centrifugal rotors. A steam turbine was coupled to the driving shaft of a centrifugal rotor in one way or another, usually through a gear device. Since then rotors of high speed separators usually have been driven by means of electrical motors. 
     Lately, driving of a centrifugal rotor by means of a gas turbine has sometimes been suggested. A gas turbine operated centrifugal rotor is suggested for instance in U.S. Pat. No. 5,779,618. However, no efficient and compact arrangement for gas turbine operation of a centrifugal rotor has been seen. 
     The present invention has for its object to provide an efficient and compact driving means for the rotor of a centrifugal separator by means of a gaseous driving fluid. 
     SUMMARY OF THE INVENTION 
     This object can be obtained by means of a driving means including 
     turbine members connected with the rotor and arranged in a ring around and at some distance from said rotational axis, 
     at least one supply member adapted to direct said driving fluid towards the ring of turbine members in a way such that the rotor is brought into rotation about said rotational axis by successive actuation of the turbine members by said driving fluid, and 
     at least one reversing member, which is adapted to receive at least part of said driving fluid having passed through the ring of turbine members and conduct it back towards the ring of turbine members in a way such that the rotor once more is actuated in its rotational direction by such returned driving fluid. 
     A driving means of this kind can be made efficient, because the energy of the driving fluid can be utilised in an advantageous way, and also be made compact because the driving means can be integrated with the rotor itself. 
     Even if it is possible to arrange the supply member for the driving fluid so that it directs the driving fluid axially towards the turbine members, it is assumably most advantageous to arrange one of the supply member and the reversing member radially outside the ring of turbine members and the other one of the supply member and the reversing member radially inside the ring of the turbine members. It is assumed that the available space would be utilised most effectively if the supply member is arranged radially outside and the reversing member radially inside said ring of turbine members. 
     If two or more supply members and reversing members are used, it is suitable that these are distributed evenly around the ring of turbine members, so that a balanced loading of the rotor is obtained from the forces to which this is subjected by the driving fluid. If only two supply members and reversing members, respectively, are used these are, thus, arranged at diametrically opposite sides of the ring of turbine members. This is advantageous for the life time of the bearings, through which the rotor is suspended in a stationary support device, e.g. a housing surrounding the whole rotor. 
     In order to make possible the most efficient utilisation of the energy of the driving fluid it is suitable that the ring of turbine members is arranged at the radially largest portion of one axial end wall of the rotor. Thus, if the rotor at one axial end has a first portion surrounding the rotational axis and situated at a first radial distance therefrom and a second portion surrounding the rotational axis and situated at a second distance therefrom, said second distance being greater than said first distance, the ring of turbine members should be arranged adjacent to and at the same distance from the rotational axis as said second portion. Preferably, the ring of turbine members is carried directly by said second portion. 
     The invention may be used in a centrifugal rotor intended for liquid cleaning as well as a centrifugal rotor intended for gas cleaning. When it is used in connection with gas cleaning, the centrifugal rotor is preferably surrounded by a stationary housing having a receiving chamber and an outlet for cleaned gas coming from the centrifugal rotor. If so, the housing is preferably shaped in a way such that gas having been used for driving of the centrifugal rotor is introduced into said receiving chamber and, thus, may leave the centrifugal separator together with the cleaned gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is further described in the following with reference to the accompanying drawing, in which 
         FIG. 1  shows an axial section through a centrifugal separator according to a preferred embodiment of the invention, and 
         FIGS. 2 and 3  show cross sections along the lines II—II and III—III, respectively, in  FIG. 1 . The axial section in  FIG. 1  is taken along the line I—I in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The centrifugal separator shown in the drawing includes a stationary housing  1  consisting of an upper part  2 , an intermediate part  3  and a lower part  4 . The parts are kept together by means of clamping members  5  and  6 . The upper housing part  2  forms an inlet  7  for a gas or a gas mixture to be cleaned by means of the centrifugal separator. The lower housing part  4  forms both an outlet  8  for gas having been cleaned and an outlet  9  for material having been separated from the gas. 
     The intermediate part  3  of the stationary housing forms a surrounding wall, surrounding a space in the housing, and has at its upper end an annular end wall  10  extending a distance inwardly from the surrounding wall. The annular end wall  10  supports within the housing a central sleeve  11 , the interior of which communicates with the aforementioned gas inlet  7 , that is formed by the upper housing part  2 . A gasket  12  is adapted to seal between the upper housing part  2  and the sleeve  11 . 
     The sleeve  11  supports in its said interior, by means of several supporting members  13  (see  FIG. 2 ), a central hub  14 . The supporting members  13  are distributed around the periphery of the sleeve and leave between themselves several passages  15  which at their upper ends communicate with the aforementioned gas inlet  7 . 
     On its inside the hub  14  supports a bearing sleeve  16 , which in turn supports through bearing balls  17  a vertically extending shaft  18 . The shaft  18  extends downwardly into the housing  1  and supports therein a rotor  19 . The rotor is rotatable in the housing  1  about a vertical rotational axis R. 
     The rotor  19  includes a substantially conical or bowl formed upper end wall  20  and a similarly formed lower end wall  21 . Both of the end walls  20  and  21  turn their concave sides upwardly towards the gas inlet  7  of the stationary housing. Between the end walls there is arranged a stack of conical separation discs  22  (only part of the stack is shown in  FIG. 1 ), which between themselves delimit thin interspaces forming through flow passages  23  for gas to be cleaned in the centrifugal separator. The end walls  20  and  21  and the separation discs  22  are kept axially compressed on the shaft  18  by means of a screw  24  and a spring  25 .  FIG. 3  shows a separation disc  22  seen from above with respect to  FIG. 1 . The disc has a conical outer portion  26  and a central portion  27  connected therewith. The central portion has a large number of through holes  28  situated at some distance from the centre of the disc and distributed around it. In the assembled rotor  19  (see  FIG. 1 ) these holes  28  form together with the interspaces between the central disc portions  27  a central space  28   a  communicating with the aforementioned through flow passages  23  between the discs  22 . Furthermore, the central portion  27  has a central non-round, in this case hexagonal, opening through which the aforementioned shaft  18  is to extend. As can be seen from both  FIG. 1  and  FIG. 3 , the shaft  18  is surrounded by a sleeve  29  extending axially between the rotor end walls  20  and  21 . The sleeve  21  has a circular inner cross section but a hexagonal outer cross section, so that the outside of the sleeve may be in rotational engagement with the separation discs  22  as well as the end walls  20  and  21 . 
     On the upper side of each disc  22  there are several rib like protuberances  30  which are evenly distributed around the centre of the disc and which extend across the conical portion  26  of the disc from the central portion  27  to the peripheral edge of the disc. The protuberances  30  serve as spacing members between adjacent separating discs  22  in the rotor and also as flow guiding members during operation of the centrifugal separator, as will be explained later. The rib like protuberances extend on each separating disc in a way such that they form an angle with generatrices of the conical portion  26  of the separation disc. 
     The upper end wall  20  of the rotor has a radially inner portion  31 , that is formed in one piece with a central sleeve  32  surrounding the shaft  18 , and a radially outer portion  33 . The radially inner portion  31  of the end wall  20  has several through holes  31   a  distributed around the central sleeve  32  and forming a central inlet of the rotor  19  for gas to be cleaned. The holes or inlet  31   a  communicate with the gas inlet  7  in the stationary housing part  2  through the interior of the stationary sleeve  11 . The radially inner portion  31  of the end wall  20  further has an annular axial flange  31   b , which surrounds an end portion of the stationary sleeve  11  in a way such that the smallest possible interspace is formed between the flange  31   b  and the sleeve  11 . If desired, a sealing may be arranged in this interspace. 
     The radially outer portion  33  of the end wall  20  supports on its upper side a ring of turbine blades  34 , which extends concentrically with the rotational axis R of the rotor (see  FIG. 2 ). The blades  34  are situated in a downwardly facing annular groove on the underside of the end wall  10 , formed between two downwardly directed annular, concentric flanges  35  and  36 . The ring of turbine blades are, thus, supported on the radially outermost portion of the rotor. 
     As can be seen from  FIG. 2 , the two said flanges  35  and  36  do not extend circularly all the way around the rotational axis R. Thus, the outer flange  35  has two interruptions or gaps  37  and  38 , whereas the inner flange  36  has one interruption or gap  39 . Supported by the intermediate part  3  of the stationary housing a nozzle  40 , that extends into the first mentioned interruption or gap  37 , is adapted to receive a pressurised gas and to direct a flow of this gas towards the ring of turbine blades  34  from the outside of the ring. The nozzle  40  is directed in a way such that the gas flow causes the blades  34  and, thereby, the whole of the rotor  19  to rotate around the rotational axis R, counter clockwise with respect to  FIG. 2 . 
     The blades  34  are somewhat arcuate, as can be seen, which is not really necessary, and conducts the gas stream supplied between adjacent blades to the inside of the ring of blades, where the gas flow enters a small reversing chamber  41 . This reversing chamber  41  is delimited between on one side a reversing member  42 , that is constituted by part of the stationary end wall  10 , and a plate  42   a , that is fixed to the underside of the end wall  10 , and on the other side the ring of turbine blades  34 . The reversing chamber is formed in a way such that the gas entering thereinto from the interspaces between the turbine blades  34  is conducted without substantial pressure loss in a curved path a distance forwardly in the rotational direction of the turbine blades to a certain position and after that, again in between the turbine blades  34  situated at this position. The pressurised gas is utilised in this way once more for driving of the ring of turbine blades  34 . 
     When the pressurised gas has again passed through the ring of turbine blades  34 , it flows radially outwardly through the interruption or gap  38  in the flange  35  to an annular space  43  in the intermediate part  3  of the stationary housing (see  FIG. 1 ). This space  43  communicates directly with a receiving chamber  44  that surrounds the rotor  19  in the stationary housing  1 . 
     As can be seen from the drawings, the part of the housing  1  surrounding the rotor  19  is substantially rotational symmetric and it has a form substantially adapted to the outer shape of the rotor. The outlet  8  for cleaned gas is situated in a conical portion of the housing part  4  at the same axial height as the lower rotor end wall  21 . The outlet  9  for material having been separated from supplied contaminated gas is situated centrally below the rotor  19  aligned with the rotational axis R of the rotor. 
     As can further be seen from the drawing (see particularly  FIG. 2 ) the reversing member  42  is formed in one piece with and at substantially the same axial level as the sleeve  14 , which on its inside supports the bearing  16 ,  17  for the rotor shaft  18 . The reversing member  42  thereby is situated radially seen between the bearing  16 ,  17  and the turbine blades  34 . This gives the centrifugal separator a very compact construction with respect to the arrangement for driving and journalling of the rotor. 
     The above described centrifugal separator operates in the following manner. 
     For rotation of the rotor  19  the nozzle  40  is charged with pressurised gas, e.g. compressed air, from a source that is not shown. A flow of gas is directed by the nozzle  40  from a gas supply area, formed by the gap  37  in the flange  35  radially outside the ring of turbine blades  34 , towards the outside of this ring, so that the gas flows between the blades and causes these and, thereby, the rotor  19  to rotate counter clockwise with respect to  FIG. 2 . 
     Driving gas exiting from the blade interspaces on the inside of the blade ring enters the reversing chamber  41 , in which it is deflected forwardly in the rotational direction of the blade ring and, thereafter, again is directed towards the blades  34  for renewed driving thereof. After having been used twice for driving of the turbine blades the gas exits through the gap  38  in the flange  35  into a space  43  (see  FIG. 1 ), from where it flows further on out into the receiving chamber  44  surrounding the rotor  19 . 
     A contaminated gas to be cleaned from solid and/or liquid particles suspended therein is supplied through the gas inlet  7  in the stationary upper housing part  2 . The gas flows further through the passages  15  and the rotor inlet  31   a  into the central space  28   a  in the rotor  19 . From the central space  28   a  the contaminated gas flows further through the flow passages  23  between the conical portions  26  of the separation discs  22 . 
     Between the separation discs  22  the contaminated gas is brought into rotation by the rotor, particles present in the gas and having a density larger than that of the gas being separated as a consequence of the centrifugal force and being brought into contact with the upper sides of the conical portions  26  of the separation discs. In contact with these portions of the separation discs the particles move as a consequence of the centrifugal force radially along generatrices of the portions  26 , the particles or coalesced liquid particles being collected by the inclined ribs  30 . The separated particles move by means of the centrifugal force further along the ribs  30  to the peripheral edges of the separation discs, from where they are thrown away from the discs and hit the surrounding wall  3  of the housing. 
     The gas being gradually freed from particles flows between the adjacent separation discs  22 , guided by the ribs  30 , towards the peripheral edges of the discs and leaves the rotor at these edges. Via the receiving chamber  44  the cleaned gas flows out of the housing  1  through the outlet  8 . This outlet  8 , as can be seen, is situated below the level at which particles having been separated from the gas are thrown away from the rotor  19  towards the surrounding wall  3 . Even the gas having been used for driving of the rotor  19  leaves the stationary housing through the outlet  8 . 
     As a consequence of the fact that the contaminated gas enters the central space  28   a  in the rotor  19  substantially without rotational movement, whereas the cleaned gas leaves the rotor under rotation at a radius larger than the radius of the central space  28   a , an underpressure will be formed in the central space  28   a . Hereby, the contaminated gas need not be supplied to the rotor at an overpressure. Instead, it may be sucked into the rotor from the gas inlet  7  of the stationary housing  1 . 
     The particles separated from the gas, solid and/or liquid, move downwardly along the inside of the surrounding wall  3  and further along the conical lowermost portion of the housing  1  and out through the outlet  9 . By the shape of the outlet pipe forming the outlet  8 , shown in  FIG. 1 , i.e. by the fact that this outlet pipe extends a short distance into the interior of the housing  1  and is provided with a flange, it is avoided that separated particles are entrained by cleaned gas out through the outlet  8 .