Abstract:
The invention concerns a turbine structure for the expansion of gas and vapour, comprising a body or casing with a peripheral work fluid transit volute from an entrance to an exit passage, at least a first stator and possible subsequent stators, a turbine shaft rotating around an axis and carrying at least a first rotor and possible subsequent rotors working together downstream of the first stator and subsequent rotors, respectively, an external tube member jutting out frontally from said body or casing and coaxial to the rotating turbine shaft, and where between the tube member ( 18 ) and the turbine shaft ( 15 ) is positioned a supporting unit ( 19 ) extractable en bloc from said external tube ( 18 ) except for the shaft.

Description:
FIELD OF THE INVENTION 
       [0001]    These invention refers to the field of turbines for the expansion of gas and vapour section in particular with a high molecular mass, and chiefly concerns improvements to the general structure of a turbine with one or more stages. 
       STATE OF THE TECHNIQUE 
       [0002]    The turbines for the expansion of gas and vapour of the type taken into consideration essentially comprise a fixed body or casing having an entrance passage and an exit passage of the work fluid, at least a first stator and possible subsequent stators respectively of a first and possible subsequent turbine stages, a turbine shaft rotating around an axis and carrying at least a first rotor and possible subsequent rotors respectively associated with the first stator and with subsequent stators, and a system for assembling and supporting said turbine shaft on the body or casing. 
         [0003]    It is well known that, in order to reach a high efficiency, the play between the fixed part, that is the body or casing, and the rotating part, that is each rotor of the turbine, must be greatly reduced in relation to certain points where the blow-by of fluid can become an important loss factor: in particular in labyrinth seals and in the space included between the apex of the vanes and the fixed ring skimmed by the vanes themselves. 
         [0004]    The maintaining of limited play is made possible by the fact that the access temperatures of the flu id are relatively modest (typically falling between 80-300° C.), so the variation of the dimensions due to dilations is limited, in particular the diameters of the rotating devices that are involved, during the starting transient and during the normal operation of the machine at different loads. 
         [0005]    Analogously, the maintaining of limited play is made possible by the fact that also the mechanical stress in the rotating parts is modest; consequently there is a limited variation in their dimensions, in particular the diameters, during the starting transient and the normal functioning of the machine. 
         [0006]    As regards to the above, the use of rolling bearings is often preferable for the sustentation of the shaft of the turbine: in fact the rolling bearings can be made without intrinsic play so that the radial position of the shaft coincides when the machine is stopped and in rotation. Furthermore, the rolling bearings are less expensive than the plain bearings, and are tolerant should there be a brief lack of lubrication, that would on the other hand rapidly damage the plain bearings. In addition the rolling bearings are not damaged by the presence of frequently repeated stops and starts, on the contrary to the plain bearings. 
         [0007]    However, both with rolling bearings and with plain bearings, it is important for the change of bearings to be trouble-free and rapid, in the same way as the change of the turning seal (should they be, as is known, flat face mechanical seals, gas seals, labyrinth or some other type) that block the passage of the work fluid from the internal volume of the turbine into the atmosphere and vice versa, should the internal pressure of the work fluid be less than the atmospheric pressure, preventing the entrance of air in the internal volume of the expander. 
       OBJECTIVES AND SUMMARY OF THE INVENTION 
       [0008]    This invention has been developed based on the considerations and specific needs mentioned above and referring to a turbine for the expansion of a fluid in a gas or vapour state, chosen in particular between work fluids with a high molecular mass to be used in the field of systems for the production of energy from power sources and/or with moderate temperatures. 
         [0009]    It is in fact one objective of this invention to propose a turbine structure for the expansion of gas and vapour including improvements both in the configuration of its body or casing, and in the combination and distribution of the components in said body, in order to simplify the assembly, to define and always maintain a secure seal of the fluid between the parts in rotation and those fixed. 
         [0010]    Another objective of the invention is also to perfect the supporting system of the turbine shaft, to make dismantling easy and to facilitate maintenance operations. 
         [0011]    The invention therefore proposes a turbine structure for gas and vapour expansion according to the preamble in claim  1 , and in which the body or casing comprises a transit volute of work fluid from the entrance to the exit passage through rotors and stators, a shield that extends radially from said volute towards the axis of the turbine shaft and an external tube fixed in front of said shield and designed to carry the shaft of the turbine with the interposition of a support unit. 
         [0012]    According to a further characteristic aspect the support unit of the shaft is axially extractable in block from the external tube, the shaft remaining where it is, and said support unit essentially comprising a concentric internal sleeve to the turbine shaft and carrying inside it some bearings and sealing means operating on the shaft. 
         [0013]    Advantageously, the external tube and internal sleeve join concentrically through two peripheral reciprocal support zones with limited axial extension, provided between the internal surfaces of the tube member and outside of the sleeve, and also through a reciprocal conical support zone between said two components near their ends facing towards the rotors of the turbine. All together, the two radial supports and the conical one are basically the same as an isostatic system having a hinge on the side of the conical support zone in combination with a first contiguous radial support, and a carriage on the distant radial support on the side of the other radial support zone. 
         [0014]    The invention consequently proposes technical solutions that correspond efficiently to the requirements indicated beforehand, that is to reach an excellent concentricity of the fixed and rotating parts, avoiding the onset of loads on the bearings due to the deforming of the mechanical structures, and to allow a secure confinement of the work fluid at least in the operating phases and also an easy exchange of the bearings and rotating seals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention will furthermore be described in detail with reference to the enclosed schematic drawings, in which: 
           [0016]      FIG. 1  shows an exploded view and a cross section of the components of a part of the dual stage turbine; 
           [0017]      FIG. 2  shows, also in cross section, some of the components in  FIG. 1  assembled, and others still separated; 
           [0018]      FIG. 3  shows, once more a cross section of a part of the assembled turbine; 
           [0019]      FIG. 4  shows a front view according to the arrow F of the whole in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The description that follows refers to an axial turbine, that is to say a turbine in which the transport of mass from the input to the output of the fluid mechanics path in which the expansion takes place is predominantly due to the axial components of the speed of the fluid, but the invention is also applicable to turbines with diagonal flow or also only locally radial. 
         [0021]    In the example represented the turbine, although only partially shown, is however the axial type and comprises two stages. It basically has: a body or casing  11  with an entrance path of the fluid  12  and an exit path—not shown—; a first stator  13  and a second stator  14 ; a turbine shaft  15  rotating around an axis X and carrying a first rotor  16  and a second rotor  17  positioned downstream of the first stator  13  and of the second stator  14 , respectively; and a system for the assembly of said shaft on the body or casing  11 , made up of a tube member  18  and by a support unit  19  inside the tube member. 
         [0022]    Starting from the most external part, the body or casing of the turbine  11  has a volute  20  and a frontal ring-like shield  21 . The volute  20  defines a duct through which the fluid that arrives from the entrance passage  12  is carried to the stator  13  of the first stage and on to the stator in the second stage and to every possible stage following on. The ring-like shield  21  extends radially from the volute  20  towards the axis X of the shaft  15 . The volute  20  and the shield  21  can be an integral part, as shown in the drawings, or made up of two respective parts fixed between them either by welding or by means of a flanged connection. 
         [0023]    Then, preferably, the shield  21  is not flat but, seen in a meridian cross-section, has a corrugated shape, defined by a succession of cylindrical or also conical parts joined by radial sections, defining loops and protrusions. This configuration is such as to allow deformations of the shield  21  turned to absorb the radial expansion and to limit the stresses caused by the differences in temperature between the inside and outside of the turbine so that they do not influence the coaxiality of the system. 
         [0024]    The stator  13  of the first stage of turbine is made up of a respective first plurality of statoric vanes  22  attached towards the outside to a first statoric ring  23 . This ring is fixed overhanging inside the volute, or to a flange connected to it, so that the ends of said blades  22  rest against the internal surface  24  of a part of the volute  20  just upstream of the rotor  16  of the first stage, directly, or by means of an interposed calibrated ring—not shown—which could be returned to the internal surface of the volute and which would in this case be easier to work. 
         [0025]    The first rotor  16  is made up of a relative disc  25  fixed to the turbine shaft  15  and provided with radial blades  26  facing towards and skimming said statoric ring  23  with reduced play and/or with the possible interposition of a peripheral ring, continuous or segmented, attached to the same blades. 
         [0026]    In the same way the stator  14  of the second stage of turbine is made up of a relative second plurality of statoric blades  27  supported externally by a second statoric ring  28  that is fixed in the same way as the first statoric ring  23 , or together with it, inside the volute  20 , so that the ends of said second blades  27  rest against an interstage diaphragm  29  just upstream of the second rotor  17 . Also this second rotor is made up of a relative disc  30  fixed to the turbine shaft  15  in the same way as the disc  25  of the first rotor  16  and is provided with radial blades  31  facing towards and skimming said second statoric ring  28 . 
         [0027]    The interstage diaphragm  29  is static, positioned between the discs  25 ,  30  of the two rotors  16 ,  17  with the interposition of labyrinth sealing means  32 , which in the drawing—FIG.  3 —are schematically represented as spire shaped annular elements. 
         [0028]    As a whole, the support of the statoric blades, in particular those of the first statoric ring which are less extended radially, to the internal surface of the volute directly or indirectly, ensures the concentricity between the rotation axis of the rotors  16 ,  17 , obviously coincident with the axis X of the turbine shaft  15 , and the external statoric rings  23 ,  28  when the turbine is in function, a condition that would not exist if said coaxiality were entrusted only to the internal side of the volute, larger and connected to the tube member with a longer run and subject then to greater thermal expansion and variations in diameter. 
         [0029]    The turbine shaft  15  has a preset diameter, and at its end facing towards the inside of the body or casing  11  has at least one head  15 ′ preferably made integrally together with the shaft—FIG.  1 —. As shown, the discs  25 ,  30  of the rotors  16 ,  17  are fixed on opposite parts of the head  15 ′ of the shaft  15 , for example both by means of a teethed system and/with screw stays or the like  33 . 
         [0030]    The tube member  18  of the assembly system of the turbine shaft  15  is connected coaxially to the shield  21  and protrudes from the front of the casing  11  according to the axis X of said shaft. The connection can be carried out by welding or by flanging. In this second case, the tube member  18  has a peripheral flange  118  that is fixed, by means of screws  121 , to a counter flange  120  provided along the internal margin of the shield  21 , and between the flange and counter flange are inserted some spacers  34 . These spacers are preferably made up of washers that can have different widths and be superimposed in different numbers so as to establish a correct connection and radial play between the ends of the rotoric blades and the corresponding statoric ring of the first stage, at least the contiguity between said rotoric blades and the respective external ring becomes defined by a conical surface—that is to say not cylindrical—as in the case represented. 
         [0031]    In addition, the tube member  18  and the turbine casing  11  or, better, the front of the volute  20 , can also be connected by a support  118  for example of the spider or dial type as shown in  FIG. 4 , designed to prevent axial deviations, vibrations or oscillations of the tube member so as to ensure the coaxiality of the latter relatively to the body or casing  11 . The support  122  can have an annular part  122 ′ encircling the tube member  18  and some radial arms  122 ″ that connect to the volute using appropriate means  123  so as to allow a certain degree of radial freedom. 
         [0032]    The support unit  19  of the turbine shaft  15  comprises components that are assembled when they are installed in the tube member around the shaft and which are then axially extractable all together from the tube member  18  except for the shaft  15 . 
         [0033]    In particular, the support unit  19  comprises a sleeve  35  that has an external diameter compatible with the internal diameter of the to be member  18  and which holds inside, with the help of spacers, bearings  36 , preferably roller, and a sealing system  40  operating on the shaft. 
         [0034]    It is important that the radial connecting of the support unit with the tube member  18  takes place so that it does not cause deformations of the inside of the sleeve  35  and neither variations in its coaxiality compared with the turbine shaft. This purpose is reached advantageously by an isostatic type of coupling between the external tube member  18  and internal sleeve  35 . According to the invention this isostatic type of coupling is carried out by creating two circumferential support zones A, B, however with limited surface extensions and separated in parallel, between the internal surface of the tube member  18  and the external surface of the sleeve  35 , and a conical, that is spherical, support zone C always between the tube member  18  and sleeve  35  near their end facing towards the head  15 ′ of the turbine shaft  15 , that is to say towards the rotors  16 ,  17 — FIG. 3 . 
         [0035]    These ways of radially and conically supporting is comparable from the cinematic point of view to a support on a line more than on a wide surface, which from the side of the conical or spherical support zone C, combined with the radial support zone A contiguous to it, is equivalent to a hinge with centre in O, whereas from the side of the extreme radial support zone B, it is equivalent to a carriage, so the system tends not to transmit to the inside sleeve  3 , improper deformations in the meridian plane of the external tube member  18 . 
         [0036]    The support unit  19  is held axially in the tube member  18  by a ring nut  19 ′ screwed to the shaft  15 . At the free external end of the tube member  18  is fixed a head flange  38 . At the free end of the shaft  15  is fixed, using any appropriate means, a head joint  55  to connect it to a device—not shown—to transmit a drive torque. On the other side, between the head flange  38  and the sleeve  35  of the support unit  19  can be arranged some selected pressure springs  39  operating in the direction to ensure physical contact of the two coaxial components—tube member/sleeve—in the conical support zone C, winning against both the load due to possible unbalance of the turbine and the one due to the thrust of the work fluid. 
         [0037]    Between the tube member  18  and the support unit  19  of the turbine shaft  15  will also be provided, although not shown, an appropriate lubrication system. 
         [0038]    The abovementioned sealing system  40  can be a mechanical type and positioned between the internal end of the sleeve  35  and the head  15 ′ of the turbine shaft  15  so as also to be extractable together with other components of the support unit  19 . Between the sleeve  35  of the support unit  18  and the tube member  18  at least a sealing gasket  18 ′ can be positioned the same applying to another sealing gasket  36 ′ that can be placed between the mechanical sealing device  40  and the turbine shaft  15 . Frontally, at the internal end of the tube member  18  is assembled on the other hand a sealing gasket  41  facing towards the head  15 ′ of the turbine shaft  15 . 
         [0039]    Furthermore, the housed tube member  18  and the sleeve  35  are radially connected to each other by a screw or key  38 ′ so as to define the insertion position and to prevent rotation of the sleeve in the to be member. As shown in  FIG. 3  the screw or key  18 ′ operate in an extended seat  35 ′ so as to allow small axial movements of the support unit  19  compared with the shaft  15  and the tube member  18 . 
         [0040]    Thanks to this placing, the support unit  19 , thrust by the springs  39  can normally hold itself in an advanced contact position on a level with the conical support C, but also retract slightly depending on the axial position of the shaft head of the turbine so as to be able to adjust/regulate the position of the rotor group inside the body or casing of the turbine.