Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-06-12
2001-10-23
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039780
Reexamination Certificate
active
06305155
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the field of applied thermodynamics. Specifically, the present invention relates to a method for cooling a structural part of a gas turbine plant and to a corresponding gas turbine plant. The gas turbine plant has a turbomachine shaft, a compressor and a cooling device. The cooling device is formed with a first duct for a main air stream and a second duct for a partial air stream. The cooling device thereby utilizes the main and the partial air streams which are compressed by the compressor of the gas turbine plant. One end of the first duct of the cooling device opens directly or indirectly into a compression region of the compressor. The term “compression region” as used herein means, in particular, respective stages of a turbocompressor. According to the instantly disclosed invention, however, the “compression region” also includes the region downstream of the compressor in the direction of flow, such as the outlet diffuser.
In order to effectively increase the efficiency and the power of gas turbines, it is an object of continuous development to raise the turbine inlet temperature. The highly heated gas which enters the first turbine stage and flows out of the combustion chamber subjects this stage to particularly severe attack. Highly heat-resistant metallic materials allow inlet temperatures of about 600° C. in stationary gas turbine plants, and in the case of aircraft engines they may even be about 900° C. If higher working temperatures are required, at least the first turbine stage must be cooled. This is all the more necessary because the turbine stage itself also undergoes corrosion stresses due to the aggressiveness and oxygen content of the hot combustion gas and due to the centrifugal stress on the turbine rotor. To cool the first guide blades and moving blades of the gas turbine, it is therefore known to extract a partial mass air stream from the compressed main mass air stream downstream of the compressor, and, by passing the combustion chamber, feed the the partial mass air stream directly to cooling ducts of the guide blades via the housing and to the moving blades of the first rows through the rotor. The blades can then be cooled by convection cooling, film cooling or else transpiration cooling to such temperatures as ensure that the blades have an acceptable useful lifetime.
Of course, the partial mass air stream branched off from the main mass air stream causes the efficiency of the gas turbine plant to be impaired. The size of the branched-off partial mass air stream must therefore be dimensioned in such a way, that on the one hand, sufficient cooling, but, on the other hand, also high efficiency is achieved. For this purpose, it is also necessary for pressure losses to be minimized. For example where the partial air stream is concerned, a pressure loss occurs because delivery conduit losses and pressure losses due to cooling ducting occur. It is therefore necessary, after cooling, to feed the partial mass air stream back to the hot working gases, then flowing out of the combustion chamber, in such a way that the pressure of the partial mass air stream can still be utilized by the turbine.
It is also known that, in the case of large stationary plants, there is an additional external compressor which compresses the partial mass stream intended for cooling, in order to compensate pressure losses. However, the additional compressor likewise requires drive energy in the form of electrical current. The calculation of an efficiency of the gas turbine plant must then take this energy into account accordingly. The greater it is, the lower the efficiency of the gas turbine plant becomes.
German published patent application DE 33 10 529 A1 discloses the cooling of a gas turbine by means of compressor air which is further compressed by a centrifugal compressor. The centrifugal compressor is formed essentially by a rotating flow duct. The concept of compression by means of a centrifugal compressor necessitates considerable radial distances over which the air to be compressed must be ducted. Such radial distances are achieved with rotor discs which are typical of jet engines. U.S. Pat. No. 3,936,215 also describes a centrifugal compressor of an engine.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a system for compensating for the pressure losses due to cooling ducting in a gas turbine plant, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which is maximized in terms of energy and efficiency.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of cooling a structural part of a gas turbine plant, which comprises:
compressing a main mass air stream in a compressor;
branching off a cooling partial mass air stream from the main mass air stream compressed in the compressor;
ducting the cooling partial mass air stream in a closed,
spatially stationary duct to a structural part to be cooled; and
additionally compressing the cooling partial mass air stream independently of the main mass air stream in a radial stage disposed concentrically on an outer circumference of an axial stage.
In other words, the method according to the invention cools a structural part of a gas turbine plant by means of the partial mass air stream (after having been compressed together with the main mass air stream, by a compressor of the gas turbine plant). The “cooling” partial mass air stream is thereafter branched off from the main mass air stream and subsequently ducted, in a closed, spatially stationary duct, to the structural part to be cooled. The partial mass air stream undergoes, independently of the main mass air stream, additional compression which is carried out by utilizing the rotational energy of a turbomachine shaft of the gas turbine plant. The additional compression is derived from the radial stage disposed concentrically on the outer circumference of an axial stage of the compressor. Since the duct is spatially stationary, this utilization does not take the form of centrifugal compression. Additional compression by means of the turbomachine shaft which is rotating in any case is a way of making it possible to compensate pressure losses particularly advantageously in energy terms. That turbomachine shaft of the gas turbine plant which is utilized for additional compression may be that of the turbine, that of the compressor which has compressed the main mass air stream or, for example in the case of a “split-shaft” plant, even the shaft of the compressor additionally belonging to the gas turbine plant. Since a high energy is available by virtue of the inertia forces of the rotating shaft which take effect in any case, the utilization of this rotational energy for the additional compression of the partial mass air stream is also advantageous on account of the existing energy density.
The rotational energy of the turbomachine shaft may be utilized in various ways. Advantageously, the additional compression is carried out by means of blading on the turbomachine shaft. The step is recited as guiding the cooling partial mass air stream through a turbine blade and thereby cooling the turbine blade. This is advantageous particularly because the know-how and technology from hitherto conventional bladings can be transferred to this blading. However, the rotational energy may also be converted into pressure, for example, by other suitable means, such as guide plates, which are arranged adjacent to the branch-off of the partial mass air stream from the main mass air stream. The compensation of the pressure loss of the cooling-air ducting of the partial mass air stream by the suitable utilization of the rotational energy of the turbomachine shaft may be so great that the partial mass air stream can also be guided through a blade. A blade of this type is, for example, a guide blade or moving blade of the first turbine inlet stages. These can thus also be cooled to sui
Casaregola Louis J.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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