Abstract:
A turbomachine having a rotor is provided, wherein the rotor comprises a central holding element and rotor elements which are arranged thereon, is intended to permit faster start-up without reducing the lifetime of the rotor, while permitting better predictions relating to the remaining lifetime of the rotor. To this end, a contact element is arranged in a region of the rotor between the holding element and the rotor element, wherein the contact element comprises a temperature measurement device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2012/065098 filed Aug. 2, 2012, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP11179152 filed Aug. 29, 2011. All of the applications are incorporated by reference herein in their entirety 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a turbomachine having a rotor, wherein the rotor comprises a central retaining element and rotor elements arranged thereon. 
       BACKGROUND OF INVENTION 
       [0003]    A turbomachine is a fluid energy machine in which energy is transferred between fluid and machine in an open space by means of a flow according to the laws of fluid dynamics via kinetic energy. Energy is normally transferred by means of rotor blades which are shaped such that the flow around them produces a pressure difference between the front and back sides (wing profile). A turbomachine typically consists of a rotating part, the rotor, and a stationary part, the stator. 
         [0004]    A gas turbine is a turbomachine in which a gas under pressure expands. It consists of a turbine or expander, a compressor connected upstream thereof, and a combustor connected between the two. The working principle is based on the cyclic process (Joule process): this compresses air by means of the blading of one or more compressor stages, then mixes this air with a gaseous or liquid fuel in the combustor and ignites and combusts the mixture. In addition, the air is used for cooling, in particular of components subjected to high thermal stresses. 
         [0005]    This produces a hot gas (a mixture of combustion gas and air) which expands in the subsequent turbine part, wherein thermal energy is converted to mechanical energy and then drives the compressor. In a shaft engine, the remaining portion is used to drive a generator, a propeller or other rotating loads. In a jet engine, by contrast, the thermal energy accelerates the hot gas stream, producing thrust. 
         [0006]    The rotor of a turbomachine, particularly in the case of gas turbines, is a component which is subjected to high thermal and mechanical stresses. It conventionally consists of a central retaining element, a shaft or axle, to which are attached the remaining rotating elements such as disks and rotor blades. In particular in the case of a cold start of the turbomachine, the rotor disks are in this case subjected to very high stresses. On one hand, the rotors experience considerable heating in the region of the blade roots, and on the other hand cooling air flows through the rotor so that the temperature of the material does not exceed the strength limits. 
         [0007]    The flow structures and heat transfer effects which appear inside the rotor are extremely complex and have for decades been the subject of university research the world over. This applies first and foremost to the transient processes when starting up or shutting down the machines. 
         [0008]    In practice, the temperatures occurring in the rotor—and in particular the temperature gradients which give rise to thermal stresses—are currently estimated conservatively, i.e. on the safe side. This often involves FEM (finite element method), a numerical method for solving partial differential equations, with which solid-body simulations can be carried out. In this case, the boundary conditions are determined using individual prototype measurements. Sample measurements of the temperature of individual rotor components are also carried out here in part. 
         [0009]    The data obtained in this manner are used, on one hand, to estimate the maximum number of start cycles that a rotor can withstand before it has to be replaced and, on the other hand, to estimate a rotor preheat time, which is necessary in certain cases in order to reduce thermal stresses to an acceptable level and to keep the number of permitted start cycles high enough. However, waiting a certain time before commencement of operation of the rotor always implies increased energy consumption and a longer startup time for the turbomachine, which is undesirable, particularly for example in the case of gas turbine and steam turbine power plants, as these often have to cover peak power requirements of the electrical grid at short notice. 
       SUMMARY OF INVENTION 
       [0010]    It is therefore an object of the invention to indicate a turbomachine which allows faster startup without this reducing the lifespan of the rotor, and at the same time allows better prediction of the remaining lifespan of the rotor. 
         [0011]    This object is achieved, according to the invention, by a contact element being arranged in a region of the rotor between the retaining element and the rotor element, wherein the contact element comprises a temperature measurement device. 
         [0012]    The invention thus proceeds from the consideration that faster startup and better estimation of the lifespan would be possible in particular if especially precise and up-to-date data on the temperature behavior of the rotor of a turbomachine for generating power were made available. To that end, it is possible, for example based on the adaptation to transient temperature profiles from FEM models, to derive analytical temperature formulae by means of which the material temperature can be estimated on the basis of measured operational data. An estimation of this kind must, however, always be conservative with respect to operational safety and lifespan. This can for example have the consequence that, during startup, there is an unnecessarily long wait for the corresponding temperature conditions or even that the process of starting the turbomachine is locked, even though the required material temperature has been reached, as the temperature formula has estimated the temperature as too low. 
         [0013]    For this reason, the temperature must be determined still more precisely. This can be achieved by directly measuring the temperature in that region of the rotor which is of interest. This is however problematic in that certain regions of the rotor, in particular the disk hubs subjected to particularly high thermal stresses, are arranged inside the turbomachine and access to these is therefore difficult. Hence, a means should be found to measure the material temperature using an appropriate arrangement of a temperature measurement device. This can be achieved by the temperature measurement device being arranged in a contact element between the rotor element to be measured and the retaining element of the rotor. This can be effected with the aid of temperature converters such as resistance sensors or thermocouples. The contact element is then pressed against the retaining element by centrifugal force during rotation of the rotor, thus ensuring good contact and good heat transfer. 
         [0014]    In this case the central rotor element is a tie rod and/or the rotor element is a rotor disk, i.e. the contact element is located between the tie rod and the rotor disks attached thereto. Contact elements can thus be attached to all disks over the entire axial length and the temperature of these can thus be detected. At the same time, this means that the rotor of a stationary turbomachine designed for industrial power generation is particularly stable and of simple construction. 
         [0015]    Advantageously, said region of the rotor is the region which is subjected to the highest thermal loads in comparison to other regions. Indeed, not all regions of the rotor of the turbomachine are subjected to the same level of load in operation. Thus, for example, the disk hubs of the rotor are comparatively highly loaded parts. In order that a temperature measurement does not need to be carried out in all regions, it should be ensured that in every case the highly loaded regions which are critical for calculating the lifespan are precisely measured. 
         [0016]    Thus, determining the lifespan of the rotor is improved while reducing expenditure. 
         [0017]    In a further advantageous configuration, the contact element is mounted rotatably on an axle, wherein the axle is attached to the central retaining element. This means that the contact element is configured as a pawl which is attached to the central retaining element, in particular the tie rod. By virtue of the rotatably mounted axle, this pawl moves, under the effect of centrifugal force, outward on the side facing away from the axle and wedges the surrounding rotor component, in particular the rotor disk. The pawl thus serves two purposes: on one hand to attach and centrally and symmetrically secure the rotor disk, and on the other hand in the chain of transmitting the signal of the disk temperature to the pawl temperature, data transmission and monitoring. The pawls may also be used to damp oscillations in the rotor. An advantageous embodiment of the pawl is in this case such that even at turning rotational speed, i.e. when the turbomachine is started up, it bears against the disk with sufficient force and such that at operating speed it allows a relative expansion of the rotor components. 
         [0018]    The contact element advantageously comprises a thermally conductive material on its side facing the rotor element. This ensures a particularly good transfer of heat from the region to be measured on the rotor disk to the temperature measurement device, which improves the quality of the temperature determination. 
         [0019]    In a further advantageous configuration, the contact element comprises an insulating material on its side facing the central retaining element. This prevents an input of heat or a loss of heat in the direction of the central tie rod. This also improves the quality of the temperature determination. 
         [0020]    The central retaining element advantageously comprises, in the region of a bearing assigned to it, a transmitter connected to the temperature measurement device on the data side and serving to transmit the temperature data. The data line from the temperature measurement device thus runs on or in the central retaining element, e.g. the tie rod to the bearing, which is typically arranged in an outer region. The transmitter can for example be designed according to the inductive principle or by means of sliding contacts and thus allows signals to be transmitted to the stationary components. An embodiment of this type can be operationally active for long periods of operation. For reasons of good accessibility, positioning the transmitter on a bearing also makes it possible to carry out maintenance without dismantling the rotor. 
         [0021]    In an advantageous configuration, a plurality of contact elements is arranged symmetrically about the central retaining element. This avoids imbalances and allows temperature measurement over the entire circumference. 
         [0022]    The turbomachine is advantageously a gas turbine. Specifically in gas turbines, whose components, in particular the rotor, are subjected to the highest thermal and mechanical stresses, the described configuration is of considerable advantage with respect to determining lifespan and reduces the startup time without sacrificing operational safety or lifespan. 
         [0023]    A turbomachine of this type is advantageously used in a power plant. 
         [0024]    The advantages achieved with the invention are in particular that, by virtue of measuring over the entire lifespan of the turbomachine, up-to-date data on the temperature behavior of the rotor are available. With the aid of these data, substantially more precise lifespan estimates for rotors can be made, and the number of permissible starts, corresponding to physical actualities, can be adapted in an up-to-date manner. This is an immediate industrial advantage for the operator, in particular in the case of installations with frequent cold starts. At the same time, continuous temperature measurement permits a better estimation of the rotor lifespan and a shortening of the startup process without reducing the lifespan. In addition to the time saving and thus increased flexibility, less energy is also used for startup. Direct temperature measurement, together with the signal line in the region of the bearings, further presents a particularly maintenance-friendly system for continuous temperature measurement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The invention is described in more detail with reference to a drawing, in which: 
           [0026]      FIG. 1  shows an axial section through a gas turbine, 
           [0027]      FIG. 2  shows an axial section through a partial region of the rotor of the gas turbine of  FIG. 1 , and 
           [0028]      FIG. 3  shows a radial section through a contact element of the gas turbine. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0029]    In all figures, identical parts are given the same reference signs. 
         [0030]    A gas turbine  101  as shown in  FIG. 1  is a turbomachine. It has a compressor  102  for combustion air, a combustor  104  and a turbine unit  106  for driving the compressor  102  and a generator (not shown) or a work machine. To that end, the turbine unit  106  and the compressor  102  are arranged on a common turbine shaft  108 , also termed the turbine rotor, to which the generator or, as the case may be, the work machine is also connected, and which is mounted rotatably about its central axis  109 . These units form the rotor of the gas turbine  101 . The combustor  104 , which is embodied as an annular combustor, is equipped with a number of burners  110  for burning a liquid or gaseous fuel. 
         [0031]    The turbine unit  106  has a number of rotary rotor blades  112  which are connected to the turbine shaft  108 . The rotor blades  112  are arranged in a ring shape on the turbine shaft  108  and thus form a number of rotor blade rings or rows. The turbine unit  106  further comprises a number of stationary guide vanes  114  which are attached, also in a ring shape, to a guide vane carrier  116  of the turbine unit  106  so as to form guide vane rows. The rotor blades  112  serve in this context to drive the turbine shaft  108  by impulse transfer from the working medium M which flows through the turbine unit  106 . The guide vanes  114  serve, on the other hand, to guide the flow of the working medium M between in each case two successive—as seen in the direction of flow of the working medium M—rotor blade rows or rotor blade rings. A successive pair, having a ring of guide vanes  114  or a guide vane row and of a ring of rotor blades  112  or a rotor blade row, is in this context also termed a turbine stage. 
         [0032]    Each guide vane  114  has a platform  118  which is arranged as a wall element for fixing the respective guide vane  114  to a guide vane carrier  116  of the turbine unit  106 . The platform  118  is in this context a component which is subjected to comparatively high thermal loads and which forms the outer limit of a hot gas channel for the working medium M which flows through the turbine unit  106 . Each rotor blade  112  is, in analogous fashion, attached to the turbine shaft  108  by means of a platform  119 , also termed the blade root. 
         [0033]    A ring segment  121  is in each case arranged on a guide vane carrier  116  of the turbine unit  106  between the spaced apart platforms  118  of the guide vanes  114  of two adjacent guide vane rows. The outer surface of each ring segment  121  is in this context also exposed to the hot working medium M flowing through the turbine unit  106 , and is separated in the radial direction from the outer end of the rotor blades  112  located opposite by a gap. The ring segments  121  arranged between adjacent guide vane rows serve in this context in particular as covering elements which protect the interior housing in the guide vane carrier  116 , or other integrated housing parts, from thermal overloading caused by the hot working medium M which is flowing through the turbine  106 . 
         [0034]    In an exemplary embodiment, the combustor  104  is configured as what is termed an annular combustor, wherein a multiplicity of burners  110 , arranged around the turbine shaft  108  in the circumferential direction, open into a common combustor space. To that end, the combustor  104  is configured in its entirety as an annular structure which is positioned around the turbine shaft  108 . 
         [0035]    In order to permit a better prediction of the lifespan of the rotor and the requisite possible preheat times, the gas turbine  101  is configured for a temperature measurement in the rotor. This is shown in  FIG. 2 , which represents an enlarged section through the rotor of the gas turbine  101 . 
         [0036]    This shows the more detailed construction of the rotor in axial section: the already-described rotor blades  112  of the turbine unit  106  are in each case attached, together with the platforms  119 , to one rotor disk  122  per rotor blade row. The rotor disks  122  are attached to a tie rod  124 . A pawl  126 , which is rotatably attached to an axle  128  by means of nuts  130 , is arranged in the region subjected to the greatest thermal load. A data line  132  leads to a temperature measurement device  134  in the pawl  126 . 
         [0037]      FIG. 3  shows a radial section through the rotor, wherein the shape of the pawl  126  can be seen. The temperature measurement device  134  is arranged in the region facing the rotor disk  122 . A material with good thermal conductivity is applied on top of it and an insulator underneath it. The data line  132  leads from the temperature measurement device  134  to a bearing (not shown) of the rotor, where it leads into a transmitter which transmits the temperature data to stationary components. 
         [0038]    When the tie rod  124  rotates with the rotor, the pawl  126  is pressed against the rotor disk  122  such that there exists a good transfer of heat to the temperature measurement device  134 . The pawl  126  thus fulfills multiple functions: on one hand it secures the rotor disk and provides radial equalization, on the other hand it serves as a transmission member in the temperature measurement. In addition, the pawl  126  serves to damp oscillations. 
         [0039]    By means of the temperature measurement, the startup time of the gas turbine  101  is on one hand reduced. On the other hand, temperature data for the rotor are available, which permits particularly precise predictions with respect to the lifespan of the gas turbine  101 .