Abstract:
A blade ring for an axial turbomachine is provided, having an outer surface that is arranged on an outer ring and faces radially inwards, and an inner surface that is arranged on an inner ring and faces radially outwards, the surfaces being arranged concentrically and parallel to one another and delimiting an annular flow channel that tapers in the main flow direction of the axial turbomachine, as well as at least one adjustment blade that is arranged so as to be displaceable, in the flow channel, parallel to a surface line of one of the surfaces by a guiding device, and that is able to be fixed, in a predetermined position, to at least one of the rings.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2012/071992 filed Nov. 7, 2012, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP12153630 filed Feb. 2, 2012. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a blade ring for an axial turbomachine, an axial turbomachine having the blade ring and a method for adjusting the maximum flow rate of the blade ring. 
       BACKGROUND OF INVENTION 
       [0003]    In order to achieve economical operation of a steam turbine, it is important that a maximum possible process steam mass flow rate from a boiler, for example of a power plant, can be expanded in the steam turbine. The maximum process steam mass flow rate which can be fed through the steam turbine is one of the decisive variables in the configuration of the steam turbine and is termed the maximum flow rate of the steam turbine. The guide blade rings of the steam turbine have a multiplicity of guide blades which are arranged evenly distributed around the circumference, blade ducts being formed between the guide blades. Radially, the blade ducts are delimited on the hub side by a hub contour and on the housing side by a housing contour. The maximum flow rate of the steam turbine is decisively influenced by the maximum flow rate of the first guide blade ring, which is substantially determined by the totality of all the effective cross sections of the blade ducts of the first guide blade ring. 
         [0004]    The maximum flow rate of newly manufactured steam turbines is subject to certain imprecisions on account of manufacturing tolerances and assembly tolerances of components of the steam turbine. Further, the maximum flow rate changes on account of ageing of the components. It is thus often necessary to correct the maximum flow rate of the steam turbine in order to once again be able to operate the steam turbine in the rated state. To that end, guide blades which are in operation are exchanged for new guide blades with an improved profile with respect to the maximum flow rate of the steam turbine. Generally, all the guide blades of an affected blade ring are exchanged, which is however very laborious and cost-intensive. As an alternative, the trailing edge of the guide blades can be shortened. However, the maximum flow rate of the guide blade ring can only be increased thereby, and the shortening often leads to worse aerodynamic properties and to lower mechanical strength of the guide blades. 
       SUMMARY OF INVENTION 
       [0005]    The invention is based on an object of providing a blade ring for an axial turbomachine, the axial turbomachine having the blade ring and a method for adjusting the maximum flow rate of the blade ring, with the abovementioned problems being overcome and in particular the maximum flow rate of the axial turbomachine being changeable in a correcting manner. 
         [0006]    The blade ring according to the invention for an axial turbomachine has an outer face which is arranged on an outer ring and is oriented radially inward, and an inner face which is arranged on an inner ring and is oriented radially outward, which faces are arranged concentrically and parallel with one another and delimit an annular flow duct which tapers in the main flow direction of the axial turbomachine, and at least one adjustment blade which is arranged such that it can be displaced, in the flow duct, parallel to a side line of one of the faces by a guiding device, and which can be secured in a predetermined position on at least one of the rings. 
         [0007]    A side line is distinguished by the fact that it is arranged on one of the two faces and is directed toward the imaginary tip of the respective face. 
         [0008]    The diameter of the flow duct decreases in the direction of the tapering of the inner face and of the outer face. If the at least one adjustment blade is displaced in the tapering direction with the aid of the guiding device, its distance in the circumferential direction to the blades which are arranged adjacent thereto in the blade ring decreases, by which the closure of the flow duct, for the fluid flowing through the flow duct, increases and the maximum flow rate of the blade ring decreases accordingly. Similarly, the maximum flow rate can be increased by displacing the at least one adjustment blade, with the aid of the guiding device, counter to the tapering direction. The maximum flow rate of the blade ring can thus advantageously be simply changed by actuating the guiding device. This can for example be necessary if the maximum flow rate of the blade ring changes on account of ageing of components of the axial turbomachine or if the maximum flow rate has to be matched to parameters which themselves are changing, such as a change in process steam mass flow rate. Furthermore, the maximum flow rate can be corrected in order to compensate for manufacturing tolerances or assembly tolerances of a newly manufactured axial turbomachine. It is conceivable that the inner ring is formed as a disk. 
         [0009]    The outer face and the inner face are preferably conical faces. Alternatively, the outer face and the inner face preferably have, in segments along the respective side line, identical radii of curvature in every cross section perpendicular to the axis of the flow duct such that, when the adjustment blade is displaced, the radial gaps between the adjustment blade and the faces remain constant. In this context, each of the cross sections of the outer face and of the inner face is preferably in each case formed, perpendicular to the axis of the flow duct, from a polygon or from a plurality of circle segments which are arranged immediately adjacent to one another. 
         [0010]    The blade ring is preferably a diagonal stage of the axial turbomachine. The diagonal stage advantageously has the flow duct which is delimited by the two conical faces. The blade ring is preferably a guide blade ring having static, non-rotating guide blades and a static, non-rotating inner face and outer face. 
         [0011]    In a preferred embodiment, the blade ring has a plurality of blades, wherein the blades are, in alternation, the adjustment blades and blades which are securely attached to the outer face and/or to the inner face. Each of the securely attached blades is preferably made in one piece together with the inner ring and the outer ring or in one piece together with a segment of the inner ring and a segment of the outer ring. This advantageously results in high stiffness of the blade ring. By virtue of the fact that every second blade is securely attached, the blade ring is advantageously easily accessible for a production tool during production of the blade ring. 
         [0012]    It is preferred that the guiding device has a sliding groove in the inner ring and/or in the outer ring, and a peg on the radial outer side and/or on the radial inner side of the adjustment blade, wherein the peg engages in the sliding groove. The guiding device preferably has, in at least one of the sliding grooves downstream in the main flow direction of the axial turbomachine, an endstop by which the adjustment blade can be secured in the predetermined position. In this context, when the axial turbomachine is in operation, the adjustment blade is pressed against the endstop by the fluid flowing in the flow duct, thus securing the adjustment blade. The position of the adjustment blade in the flow duct may be defined, for example, by introducing a spacer against the endstop. The spacer can for example be securely attached to the outer ring and/or the inner ring by grub screws and/or welding points. 
         [0013]    The guiding device is preferably set up such that the at least one adjustment blade can be exchanged for another adjustment blade. Thus, the at least one adjustment blade can be exchanged for the other adjustment blade having different aerodynamic properties. In addition, the maximum flow rate can be adapted by a suitable swap, in that for example the other adjustment blade has a profile having a shorter or longer chord length. 
         [0014]    The axial turbomachine according to the invention has the blade ring according to the invention. The maximum flow rate of the axial turbomachine is preferably determined by the maximum flow rate of the blade ring. 
         [0015]    The method according to the invention for adjusting the maximum flow rate of the blade ring has the following steps: predetermining a setpoint value for the maximum flow rate of the blade ring; determining the actual value of the maximum flow rate of the blade ring; comparing the actual value of the maximum flow rate of the blade ring with the setpoint value for the maximum flow rate of the blade ring; displacing the at least one adjustment blade by the guiding device parallel to the side line such that the setpoint value for the maximum flow rate is the same as the actual value of the maximum flow rate; securing the adjustment blade with the guiding device. If the maximum flow rate of the axial turbomachine is defined by the maximum flow rate of the blade ring, the maximum flow rate of the axial turbomachine can be changed by displacing the at least one adjustment blade. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention will be explained in more detail below with reference to the appended schematic drawing. 
           [0017]    The FIGURE shows a longitudinal section through an axial turbomachine having a preferred embodiment of the blade ring according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0018]    As is shown in the FIGURE, an axial turbomachine  1  has a housing  22 , a shaft  21  and a plurality of blade rings  11  to  13 . A fluid  25  can be made to flow within the housing  22 , in a main flow direction  17 . 
         [0019]    The FIGURE shows a first guide blade ring  11 , a rotor blade ring  12  and a second guide blade ring  13  which are arranged in this order in the main flow direction  17  of the fluid  25 . 
         [0020]    The first guide blade ring  11  has an outer conical ring  24  which is attached to the housing  22  and has a radially inward-facing conical outer face  2  and, within the outer conical ring  24 , an inner conical ring  23  which has a radially outward-facing conical inner face  3 . The conical outer face  2  and the conical inner face  3  are arranged concentrically with one another, have an identical taper angle  18 , are arranged parallel to each other in every axial section and delimit an annular flow duct  4 . As shown in the figure, the inner conical ring  23  and the outer conical ring  24  are frusta. It is however also conceivable for the inner conical ring  23  to include its cone tip. 
         [0021]    The cone axes  26  of the conical outer face  2  and of the conical inner face  3  coincide with the shaft axis  27 . The conical faces  2 ,  3  are oriented such that the outer diameter  28  (the figure shows half the outer diameter  28 ) of the flow duct  4  decreases in the main flow direction  17 . 
         [0022]    Alternatively, the inner conical ring  23  and the outer conical ring  24  are modified such that the conical inner face  3  and the conical outer face  2  have, in segments along the respective side line  6  and along the breadth of the adjustment blade  7 , identical radii of curvature in every cross section perpendicular to the shaft  21  such that, when the adjustment blade  7  is displaced, the radial gaps between the adjustment blade  7  and the conical faces  2 ,  3  remain constant. It is for example conceivable for the radii of curvature to be of infinite size, such that each of the cross sections of the conical faces  2 ,  3  perpendicular to the shaft  21  in each case forms a polygon, one blade being arranged on each of the straight line segments of the polygon. The length of each of the straight line segments of the polygon becomes shorter downstream in the main flow direction  17 . 
         [0023]    It is also conceivable that each of the cross sections perpendicular to the shaft  21  is formed from a plurality of circle segments. The radii of curvature of the circle segments can in this context be either greater or less than the radii of the flow duct  4 . Downstream in the main flow direction  17 , the extent of each of the circle segments becomes shorter, whereas the radius of curvature remains constant in each case. 
         [0024]    Not only straight lines or circle segments are conceivable for the cross sections of the conical faces  2 ,  3 , but also other shapes whose cross sections do not change along the side line  6 . Equally conceivable is the provision of different shapes for the conical outer face  2  and the conical inner face  3 , for example a polygon for the conical outer face  2  and circle segments for the conical inner face  3 . 
         [0025]    An adjustment blade  7  is arranged within the flow duct  4  and is arranged with its radial outer side  9  on the conical outer face  2  and with its radial inner side  10  on the conical inner face  3 . The adjustment blade  7  has a peg  15  both on its radial inner side  9  and on its radial outer side  10 , the pegs  15  respectively engaging in a sliding groove  14  in the inner conical ring  23  and in the outer conical ring  24 . The sliding grooves  14  are arranged mutually parallel and run in each case along a side line  6  of the conical faces  2 ,  3  such that the adjustment blade  7  can be displaced parallel to the side lines  6 . If the adjustment blade  7  is displaced in the main flow direction  17 , the distance in the circumferential direction between the adjustment blade  7  and the blades arranged adjacent thereto in the first guide blade ring  11  is reduced, whereby the closure for the fluid  25  in the first guide blade ring  11  increases. As a consequence of the increasing closure, the maximum flow rate of the first guide blade ring  11  is reduced. Conversely, the maximum flow rate can be increased by the adjustment blade  7  being displaced upstream in the main flow direction  17 . The greatest possible displacement path  8  of the adjustment blade  7  is limited by the length of the flow duct  4  in the main flow direction  17  and the length of the sliding grooves  14 . In order to change the maximum flow rate, it is also conceivable that the adjustment blade  7  is replaced by another adjustment blade having a shorter or longer chord length. 
         [0026]    Various shapes are conceivable for the sliding grooves  14  and the pegs  15  such as a T-shape or a dovetail. The sliding groove  14  in the conical inner face  3  is limited in the main flow direction  17  by an endstop  29 , i.e. it does not continue as far as the downstream end  5  of the flow duct  4  such that, when the axial turbomachine  1  is in operation, the adjustment blade  7  is pressed against the endstop  29  by the flow of the fluid  25 . It is also possible to limit the sliding groove  14  in the conical outer face  2  in the main flow direction  17  by an endstop, or to limit both sliding grooves  14  by an endstop. Upstream in the main flow direction  17 , the sliding grooves  14  are not limited, such that the adjustment blade  7  can be removed from the flow duct  4  and exchanged for another adjustment blade. 
         [0027]    As shown in the figure, spacers  16  are provided in the sliding grooves  14  in order to fix the position of the adjustment blade  7 . The spacers  16  are arranged both on the downstream side of the pegs  15  and on the upstream side of the pegs  15 . It is in principle possible not to provide any spacers  16  on the upstream side as, in operation, the adjustment blade  7  is pressed against the downstream spacers  16  or against the end of the sliding groove  14 . The smallest possible maximum flow rate for the adjustment blade  7  is reached when none of the spacers  16  is provided on the downstream side. 
         [0028]    All the blades in the first guide blade ring  11  are formed as the adjustment blades  7  and are thus of displaceable design. Alternatively, the blades could alternately be formed as the adjustment blades  7  and securely attached to the conical faces  2 ,  3 . Is it conceivable here that the inner conical ring  23 , the outer conical ring  24  and the securely attached blades are made out of a single piece. It is equally conceivable that, in each case, a securely attached blade is made out of a single piece together with in each case a segment of the inner conical ring  23  and of the outer conical ring  24  and thus the first guide blade ring  11  is composed of a multiplicity of segments. 
         [0029]    It is conceivable that the adjustment blades  7  are equally provided for a rotor blade ring. In this case, the inner conical ring  23  is securely connected to the shaft  21  and the adjustment blade  7  is displaceably arranged, by its radial inner side  10 , on the inner conical ring  23 . The inner conical ring  23  and the adjustment blade  7  are thus rotating components of the axial turbomachine  1 . A gap could be provided between the radial outer side  9  of the displaceable blade  7  and the conical outer face  2 . The adjustment blade  7  could also be in engagement, via its radial outer side  9 , with the outer conical ring  24 . In this last case, the outer conical ring  24  would also be a rotating component. 
         [0030]    Adjusting the maximum flow rate of the first guide blade ring  11  is performed as follows: predetermining a setpoint value for the maximum flow rate of the blade ring  11 ; determining the actual value of the maximum flow rate of the blade ring  11 ; comparing the actual value of the maximum flow rate of the blade ring  11  with the setpoint value for the maximum flow rate of the blade ring  11 ; displacing the at least one adjustment blade  7  by the guiding device parallel to the side line  6  such that the setpoint value for the maximum flow rate is the same as the actual value of the maximum flow rate; securing the adjustment blade  7  with the guiding device. 
         [0031]    Although the invention has been illustrated and described in more detail by means of the preferred exemplary embodiments, the invention is not limited by the disclosed examples and other variations may be derived herefrom by a person skilled in the art without departing from the scope of protection of the invention.