Power plants – Utilizing natural heat
Reexamination Certificate
2000-07-07
2001-08-21
Nguyen, Hoang (Department: 3748)
Power plants
Utilizing natural heat
C060S643000, C417S150000
Reexamination Certificate
active
06276140
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for the generation of electrical energy.
BACKGROUND OF THE INVENTION
Fluid-flow machines, of which, in the heat-engine category, the gas turbine constitutes a widespread energy-converting unit, are used for the generation of energy. Gas turbines are operated with liquid and/or gaseous fuels. A typical recuperator gas-turbine construction has an air compressor, also called turbocompressor, which draws in fresh air, which is typically compressed to a pressure of 4 to 8 bar and, in certain circuits, is forced into a heat exchanger, in which it is preferably preheated by still hot combustion gases flowing from the turbine. In plants without a recuperator, the pressure at the end of the compressor is typically 12-30 bar. Finally, the preheated and compressed supply air passes together with fuels into a combustion chamber, in the course of which hot or combustion gases higher than 1200° C. are produced. These combustion gases flow at high velocity into the turbine and drive the latter, which is normally coupled to a generator for the generation of electricity.
A multiplicity of efforts are made to improve the operation of gas turbines with regard to their power density and their efficiency. The efficiency of a gas turbine depends in principle on the ratio of the energy input into gas turbine to the energy converted by the gas turbine, which energy can be converted into electrical energy by means of a generator. It is thus necessary to reduce the proportion of energy which is theoretically made available to the gas turbine by the combustion gases but is not converted into electrical energy.
A large proportion of the losses of a gas turbine is connected with the relatively high temperatures at the turbine outlet. So that as high a percentage as possible of the heat supplied in the combustion chamber can be converted into mechanical power by the turbine, the pressure ratio of the gas turbine must be selected to be as high as possible.
However, high pressure ratios have the disadvantage that the compressed air is very hot. The result of this is that, at a fixed turbine outlet temperature, with increasing pressure ratio, an ever decreasing amount of heat per kilogram of air can be directed into the combustion chamber. In addition, it is no longer possible to preheat the air, since the air temperature downstream of the compressor, at a high pressure ratio, becomes higher than the exhaust-gas temperature downstream of the turbine.
A further important source of losses in gas turbines is connected with the fact that about ⅔ of the mechanical power of the turbine has to be applied for driving the compressor. Since the turbine and compressor have component efficiencies which are less than
1
, the power output of the turbine to the compressor leads to a product efficiency which corresponds to the product of the component efficiencies and is therefore markedly lower than the component efficiencies.
The abovementioned reasons lead to a compromise. The maximum power density of a gas turbine is achieved at a lower pressure ratio than the maximum efficiency. As a rule, the pressure ratio of the gas turbine is therefore selected such that an optimum compromise between power and efficiency is achieved. In addition to the improvement of the abovementioned aspects with regard to the power density and the efficiency of gas turbines, the thermal loading capacity of the individual components which are necessary for the operation of gas turbines is also increasingly important for the conception and design of such plants. Not least for reasons of competition, it is necessary to design gas-turbine plants in such a way that they are not too complicated and consequently not too costly, but on the other hand it is necessary to offer durable and high-quality products.
Thus, for example, conventional compressor stages in each case consist of a rotor and a stator, which are fitted with moving and guide blades and by means of which the air flowing through the compressor stage is heated by the compression from ambient temperature up to above 500° C. Such high temperatures put a considerable strain on the materials used in the compressor stage, and this has a lasting harmful effect on the service life of the individual components involved, so that complicated and extensive cooling measures have to be taken in order to increase the resistance of the materials in the compressor region to the high temperatures which occur. In addition, since the cooling air is very hot, the cooling is difficult and uses a great deal of cooling air.
SUMMARY OF THE INVENTION
The object of the invention is to design an apparatus for the generation of energy by means of a fluid-flow machine in such a way that the power density and the efficiency as well as the service life of the components of the fluid-flow machine, in particular its thermally loaded components, are to be increased.
According to the invention, an apparatus for the generation of energy by means of a fluid-flow machine, preferably a gas turbine, for the drive of which a compressor arrangement for compressing a compressible medium, preferably air, is provided, which medium, via a feed-line system, can be fed to the fluid-flow machine directly or after the interposition of a combustion chamber, in which the compressed medium can be ignited with the addition of fuel, is designed in such a way that the compressor arrangement provides at least one compressor stage in which the medium can be compressed isothermally.
The idea underlying the invention is to convert air into a precompressed state in the course of an isothermal compression in which the air can be compressed to a comparably high degree, as is also possible in the case of conventional air-compressor stages, but without reaching high compression temperatures, so that this air, in the extreme case while avoiding a conventional air compressor section and thus dispensing with the need to drive the air compressor by the gas turbine, is directly available for the drive of the gas turbine. The decisive advantage of isothermal compression lies in the fact that the maximum possible heat supply does not decrease with increasing pressure ratio. Thus the power density remains high even at a high pressure ratio. In addition, recuperation is always possible. Furthermore, the decisive advantage of an open cycle operated with an external isothermal compressor consists in the fact that no efficiency products occur.
Furthermore, it is possible according to the invention to direct isothermally precompressed air to a conventional high-pressure precompressor stage, by means of which the air density is increased to a fixed desired value. In this way, the temperature of the highly compressed air, after passing the high-compression compressor unit, is reduced from normally 555° C. to below 300° C. The low temperature level of the highly compressed air inside the compressor unit helps in particular to ensure that any components present in the compressor unit, such as, for example, moving blades on the rotor and guide blades on the stator, are subjected to lower thermal loads, so that cooling measures can be completely or at least partly dispensed with, as a result of which the arrangement becomes simpler to maintain and becomes more cost-effective. In addition, the cooling-air consumption of the rotor and the turbine, on account of the low air temperature, can be greatly reduced, a factor which considerably increases the power density and efficiency of the plant.
Finally, a gas turbine having the upstream isothermal compression according to the invention offers improved properties with regard to the utilization of the waste heat of the exhaust gases discharging from the gas turbine, especially since, as described above, the temperature level of the highly compressed air, after discharge from a high-pressure precompressor stage arranged downstream of the isothermal compression, is lower than in compressors of conventional gas-turbine plants, and therefore an improved he
Keller Jakob J.
Keller-Schärli Maria A.
Wettstein Hans
ABB Alstom Power ( Schweiz) AG
Burns Doane Swecker & Mathis L.L.P.
Keller-Schärli Maria A.
Nguyen Hoang
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