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(11) | EP 1 760 269 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Stationary blade of a steam turbine |
| (57) The invention relates to a stationary blade (1) of a steam turbine comprising a blade
(8) having a leading edge (10) and a trailing edge (12), wherein said blade (8) in
a region (16) in proximity of said trailing edge (12) is equipped with a number of
drip-off elements (14).
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TECHNICAL FIELD
[0001] The present invention relates to a stationary blade of a steam turbine comprising a turbine blade having a leading edge and a trailing edge. Furthermore, it relates to a steam turbine equipped with a number of blades of this kind.
BACKGROUND ART
[0002] In the region of the last stages of steam turbines, in particular in low pressure steam turbines, components such as stationary blades or in particular moving blades may be subject to an erosive wear caused by impinging water droplets, also referred to as droplet impact erosion. In particular, in the region of the ultimate stages of a steam turbine or even before that the expansion of steam typically will have progressed to an extent that the saturation temperature is reached and partly condensation of the steam occurs. Accordingly, so-called wet steam or steam which is mixed with comparatively small droplets of condensed water is generated.
[0003] The presence of condensate in the steam may contribute to erosive wear on the turbine components such as turbine blades, in particular at their leading edges and trailing edges of the blade. Under adverse conditions of use, the maximum permissible stripping of material caused by droplet impact erosion may be reached quickly so that the useful life of the blade and consequently the service life of the turbine as well as efficiency are reduced considerably. It is accordingly a general desire to minimize the negative effects of erosive wear on turbine blades or other components caused by impinging water droplets. In order to minimize this type of erosion, various components such as moving blades of the steam turbines may be manufactured in a way such that their resistance against impinging water droplets is increased. In particular, the leading edge and parts of the blade surface of moving blades of the last stages of steam turbines may be hardened (flame-hardened or laser-hardened) as a function of the calculated thermodynamic conditions of use. The purpose of such hardening is to improve the material properties by changing the structural state in such a way that stripping off caused by impinging water droplets is reduced. However, approaches of that kind trying to minimize the effects of erosive wear involve additional effort in manufacturing and designing turbine systems and do not yield satisfactory results with respect to desired life time of the turbine components.
DISCLOSURE OF THE INVENTION
[0004] It is accordingly an object of the present invention to provide a stationary blade of the steam turbine, in particular for use in the wet steam region of the last stages of steam turbines, that contributes to minimizing the undesired effects of erosion wear due to impinging water droplets.
[0005] According to the present invention, this object is achieved by providing a number of drip-off elements to the blade surface of the stationary blade.
[0006] The concept of the present invention is based upon the recognition that the water droplets generated in the wet steam region due to condensation effects - the so-called primary droplets - typically are of comparatively small size. Due to this small size, these primary droplets, when directly impinging on stationary or moving blades of the turbine, do not cause significant damage and accordingly do not contribute too significantly to erosive wear. However, these relatively small size primary droplets, after hitting stationary blades of the turbine, may stay on the blade surface and together with other incoming droplets may form a condensate film on the respective turbine blade. The condensate in this condensate film due to the flow dynamics and pressure conditions in the respective turbine stage will be moved towards the rear of the turbine blade and accumulate in the respective surface region of the blade. After sufficient accumulation of condensate, comparatively large size water droplets will be formed and will drip off from the trailing edge of the respective blade. These comparatively large size, so-called secondary droplets will cause significant damage when impinging on other stationary or moving blades positioned further downstream and accordingly will contribute significantly to erosive wear.
[0007] Accordingly, the invention is based upon the concept to reduce the particle size of secondary droplets in order to minimize the effects of erosive wear. In order to achieve this design goal, according to the present invention the stationary blade in a region in proximity to the rear end or trailing edge of the blade is equipped with a number of drip-off elements. These drip-off elements, by proper design, shape and/or other structural properties are configured such that dripping off of the condensate film of the respective stationary blade is facilitated and occurs in earlier stages as compared to conventional stationary blades. As a result, less accumulation of condensate material occurs until the respective droplet finally drips off, and accordingly the droplet size is significantly lowered.
[0008] In a preferred embodiment, the drip-off elements have an elongated shape with relatively small effective diameter, therefore keeping the local surface area the condensate might adhere to relatively small. Preferably, the drip-off elements may have a spike-like or a needle-like shape.
[0009] In another preferred embodiment, the drip-off elements are formed by brush hairs, in particular of the kind that may be used in brush gaskets or seals.
[0010] With the concept according to the invention, considerable minimization of erosive wear due to droplet impact erosions in the wet steam region of a steam turbine may be achieved. Consequently, the life time of other components such as moving blades may be increased even without specific protection measures for these components. The concept of the invention may be applied to new or existing turbine blades and in particular may also be applied to turbine blades already in use during service or maintenance activities. The effect on the flow dynamics and other working conditions in the steam turbine is comparatively low, such that no significant changes in the blade design or the like are necessary for applying the drip-off elements.
[0011] The stationary blade according to the invention preferably is used in a steam turbine, in particular in the last stages of a low pressure steam turbine.
BRIEF DESCRIPTION OF THE DRAWING
[0013] As shown in a perspective view of a stationary blade 1 of a steam turbine according to FIG 1, a main body forming the blade 8 extends between an outside shroud 2 and an inside shroud 4. The blade 8 has a leading edge 10 oriented in upsteam direction of the steam flow, i. e. exposed to the incoming flow medium within the steam turbine. It also has a trailing edge 12 oriented in downstream direction of the steam flow, i. e. towards the outlet region of the steam turbine.
[0014] The stationary blade 1 as shown in FIG 1 is specifically designed for early and easy drip-off of condensate accumulating on the surface of the blade 8. In order to achieve this effect, a number of drip-off elements 14 is provided in a region 16 on the surface of the blade 8 in proximity to the trailing edge 12. The drip-off elements 14 that may be formed by spikes, brush hairs or other needle-like, comparatively thin, elongated objects, are designed such that condensate accumulating on the surface of the blade 8 is guided towards their individual tips. In the tip region of the respective drip-off element 14 the condensate accumulates further until it reaches a size that no longer adheres to the relatively small surface area in the respective tip region of the drip-off element 14.
[0015] According to this relatively small surface area in the tip region of the respective drip-off element 14, the formed droplet drips off at a comparatively early stage in its build-up phase, and accordingly the typical size of the resulting droplet is kept comparatively small. Consequently, the so-called secondary droplets generated by dripping off of condensate of the blade 8 of the stationary turbine blade 1 is kept comparatively small, and accordingly erosive wear due to droplet impact erosion in the steam turbine equipped with the stationary blade 1 is minimized.
[0016] The drip-off elements 14 may be soldered or welded to the trailing edge 12 of the blade 8 or may be fastened by other appropriate methods. The distance between neighboring drip-off elements 14 preferably is chosen larger than typical droplet sizes whereas their individual length as an example may be in the range of 2 to 10 mm. The diameter of the drip-off elements referably is less than 0.2 mm.
1. Stationary blade (1) of a steam turbine comprising a blade (8) having a leading edge
(10) and a trailing edge (12), wherein said blade (8) in a region (16) in proximity
of said trailing edge (12) is equipped with a number of drip-off elements (14).
2. Stationary blade (1) according to claim 1, in which at least one of said drip-off
elements (14) is formed by a spike attached to said blade (8).
3. Stationary blade (1) according to claim 1 or 2, in which at least one of said drip-off
elements (14) is formed by a brush hair.