Steam introduction device in a power plant

Details Steam introduction device in a power plant Steam introduction device in a power plant

1999-04-24

2001-02-20

Smith, Duane S. (Department: 1724)

Gas and liquid contact apparatus

Contact devices

Atomizer type

C261S118000, C261SDIG001

Reexamination Certificate

active

06189871

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a steam power station with a boiler, a steam turbine, a condenser and a bypass line which bypasses the steam turbine by leading directly from the boiler to the condenser. It relates, in particular, to a steam introduction device between the bypass line and the condenser and to the first of two steam passage diaphragms in this steam introduction device.
2. Discussion of Background
During the startup and rundown of a steam power plant and during steam turbine load shedding due to a shutdown of the plant, the steam is not led from the boiler to the steam turbine, since said steam contains too much water and would consequently damage the turbine blading. Instead, the steam is led directly from the boiler into the condenser through a bypass line and a steam introduction device. The steam introduction device serves for expanding the steam and cooling it before it enters the condenser for condensation. The steam flowing in via the bypass line has, on the one hand, a high flow velocity and, on the other hand, a temperature of up to 600° C. By contrast, the temperature prevailing in the condenser is around 40° C. It is therefore expedient to lower the temperature of the steam and its velocity sharply. This also means that the components of the steam introduction device are exposed to a high temperature gradient.
According to publication number CH-T 080 273 of the Brown Boveri Companie, a bypass regulating valve is followed by a two-stage steam introduction device which is arranged in the condenser. The first stage of the steam introduction device consists of a steam passage diaphragm, specifically a perforated diaphragm which is frustoconical and by means of which the hot steam stream is sprayed and fanned out. Downstream of the perforated diaphragm, the latter enters an expansion or cooling chamber. Here, it is cooled by means of cool condensate which is sprayed into the fanned-out steam stream by a plurality of nozzles. In the second stage of the steam introduction device, the steam flows through a second perforated diaphragm, by means of which the steam is distributed in the condenser neck and over the cooling tubes of the condenser.
A perforated diaphragm of the first stage of the steam introduction device is manufactured from a plurality of plane components, specifically a part for the envelope of the cone frustum, a closure part for the vertex of the cone and a transitional part for connection to the end of the bypass line. The orifices in the perforated diaphragm are drilled into the still plane part of the cone envelope, said part subsequently being hot-formed into a cone and welded together. The closure part for the vertex of the cone is then welded to the cone frustum and the transitional part is welded to the end of the bypass line.
In order to ensure that the cone, which has a multiplicity of drilled orifices, has sufficient mechanical stability, relatively large wall thicknesses are necessary. The larger the wall thickness, the higher the thermal stresses. As mentioned, this perforated diaphragm is exposed to a very high temperature gradient. During use, therefore, the considerable temperature gradient from one side of the perforated diaphragm to the other leads, in the case of large wall thicknesses, to correspondingly high thermal stresses, with the result that cracks may form in the material. As early as during the hot-forming process, too, small cracks may form, and these may subsequently increase in size during operation and ultimately lead to a material fracture. Such susceptibility to cracks or fractures is detrimental to the operating reliability of the power plant, since damage to the perforated diaphragm can be rectified only by a repair, with the entire plant being shut down. Furthermore, the cost-intensive production of the perforated diaphragm is a disadvantage. On the one hand, the manufacture of the plurality of individual parts and the welding work for assembling these necessitate a high outlay in terms of fabrication and cost. On the other hand, while the perforated diaphragm is being formed into the cone, the geometry of the drilled orifices is distorted, so that, where appropriate, the orifices have to be remachined.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel perforated diaphragm for a steam introduction device in the bypass line of a steam power plant, said device possessing increased operating reliability due to improved thermal stability and necessitating a lower outlay in terms of fabrication and cost, as compared with the prior art described.
The object is achieved by means of a steam introduction device having a perforated diaphragm of which consists of a single spherical part.
The main advantage of a perforated diaphragm of this type is the increased mechanical stability and thermal load-bearing capacity of the perforated diaphragm and the consequently achieved operating reliability of the steam introduction device. The operating reliability of the entire power plant is also increased thereby, since a longer operating time of the device without any repairs is ensured.
As compared with a conical shape, a spherical shape is mechanically more stable per se. The selected shape of the diaphragm thus affords increased mechanical stability, as compared with the prior art. By virtue of this increased shape-induced stability, the diaphragm according to the invention has a smaller wall thickness than the conical diaphragm, the stability necessary for the diaphragm being nevertheless ensured. Moreover, a smaller wall thickness affords the advantage that the thermal stresses in the material, which are caused by the temperature gradient, are lower. As a result, the thermal load-bearing capacity is appreciably increased and the susceptibility of the diaphragm to fractures is reduced.
In a preferred version, the orifices of the perforated diaphragm are arranged in such a way that each orifice is equidistant from each orifice next to it. This likewise brings about a uniform material thickness and thermal stability of the diaphragm.
The one-part spherical diaphragm is produced by means of a pressing operation. After the desired shape has been obtained, the workpiece is reannealed and is cooled and stress-relieved in a controlled manner. The final product has minimal material stresses due to this method of manufacture, this being conducive to the thermal load-bearing capacity of the diaphragm during operation.
A second advantage is the reduction in the cost of fabricating the perforated diaphragm. This is achieved primarily by the reduction in the number of parts to a single part and in the number of machining steps. Only one pressing operation is necessary in order to manufacture the diaphragm, and welding operations are no longer required. There is no need for the separate manufacture and fitting of a closure part, as was the case with the conical perforated diaphragm, or, in particular, also of a transitional piece between the perforated diaphragm and the end of the bypass line. The spherical perforated diaphragm has a straight rim, the diameter of which is adapted to the diameter of the bypass line. During assembly, the perforated diaphragm is welded directly onto the end of the bypass line without the aid of a separately manufactured transitional piece.
Finally, the drilling of the orifices in the perforated diaphragm is carried out by means of a numerically controlled machine after the operation of pressing the diaphragm. Remachining of the orifices, as in the prior art, is no longer necessary, thereby avoiding further outlay in terms of fabrication.


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patent: 4278619 (1981-07-01), Tiefenthaler
patent: 4474477 (1984-10-01), Smith et al.
patent: 5338496 (

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