Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2000-08-25
2003-05-13
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S782000, C060S806000, C060S728000, C060S736000
Reexamination Certificate
active
06560966
ABSTRACT:
FIELD OF THE INVENTION
This application claims priority under 35 U.S.C. §§ 119 and/or 365 to Patent Application No. 199 40 174, filed in Germany on Aug. 25, 1999; the entire content of which is hereby incorporated by reference.
The invention relates both to a method for operating a power plant, and to a power plant for employing the method. The power plant in question has at least one gas turbo group with at least one compressor, at least one combustor, and at least one gas turbine, whereby one part of the air compressed in the compressor is branched off, cooled in a cooling air cooler, and used as a coolant for the gas turbo group. The heat removed from the compressed air is used at least in part for generating superheated steam that is introduced at least in part at a suitable place into the gas turbo group.
BACKGROUND OF INVENTION
Many variations of gas turbine power plants and methods for operating such power plant systems are known. In a simple, open gas turbine process, the system essentially consists only of a compressor and a combustor followed by a gas turbine. In order to operate the system, processed (for example filtered, de-iced, heated or cooled), ambient air is introduced into the compressor. The compressed air is then conducted further into the combustor where the enthalpy of the compressed air is increased by combustion. The resulting combustion gases are expanded in the gas turbine, whereby the released energy is returned through a rotor shaft to the compressor and also to a generator.
The exhaust gases of the first gas turbine in principle still contain sufficient oxygen to be usable as preheated air for a second combustion. In order to increase the efficiency of such a system, a second combustor and a second gas turbine are therefore positioned behind the first gas turbine for so-called “sequential combustion.” The gas enthalpy increases again in this second combustor, and the resulting combustion gases are expanded in the second turbine.
The first turbine is the high pressure turbine and the second turbine a low pressure turbine. Both turbines are usually installed on a common shaft.
In combination systems, the waste gases from one or more gas turbines that have been expanded almost to atmospheric pressure are used in a waste heat steam generator for generating steam. This steam is used in a separate, closed steam cycle for generating additional mechanical or electrical energy to operate a steam turbine. Part of the steam in the steam cycle also can be used as process steam or for a remote heating system, or the like.
One problem in the operation of such power plant systems is cooling. The blades of the shaft and housing of the gas turbines are in constant contact with hot combustion gases from the combustion chambers. Depending on their position and the material of the various parts, cooling is necessary to ensure mechanical integrity during operation. For the cooling of these components, several systems that use coolants such as air, steam, or other coolants are known.
In a method to which the invention at hand is also related, compressed air is removed from the compressor and is supplied to the turbines for cooling. By using part of the compressed air for turbine cooling, the amount of air involved in the thermodynamic working process of the gas turbine is automatically reduced. This results in lower gas turbine output power and efficiency. The cooling air also could result in an increase in gas turbine energy losses, for example because of the so-called dilution effect, i.e., due to the mixing losses caused by the cooling air entering the turbine gas stream.
During the construction of high-performance gas turbines, it is therefore necessary to minimize the amount of cooling air. On the one hand, this can be achieved by using more exotic materials and special temperature protection coatings for the components to be cooled, which, however, is associated with higher investment costs. An alternative for minimizing the amount of cooling air amount is to reduce the temperature of the compressed air externally, before the air is used for turbine cooling. This results in a higher heat exchange since the temperature differential between the coolant and the metal surface of the parts to be cooled is increased. An equivalent cooling therefore requires a smaller amount of cooling air. The gas turbine performance is increased by this since less air bypasses the thermodynamic gas turbine process.
Various methods to cool the compressed cooling air externally are known.
On the one hand, there are so-called quench coolers in which the compressed air is cooled by injection of water. However, this method is associated with a high thermal stress of the air coolers. The gas turbine cooling air also could be contaminated by contaminants in the water, which could lead to catastrophic consequences. To prevent this, large amounts of highly purified water are required for this method. In addition, strict control of the air temperature after mixing is extremely difficult. However, a highly accurate determination of the cooling temperature is necessary in order to prevent damage to the gas turbine.
In another method for cooling the compressed air, cooling elements are used. The removed heat is released into the atmosphere, for example, the coolant used in a heat exchanger is re-cooled by air fans. With this method, the removed heat is lost to the gas turbine process.
DE 195 08 018 A1 furthermore shows another cooling method in which the removed heat can be reused. In the system described in DE 195 08 018 A1, which is hereby incorporated by reference in its entirety, there is a combination system with a gas turbine cycle and a complete, closed water steam cycle. In this method suggested there, the air is cooled in air coolers that are integrated into the water steam cycle. Part of the steam generated in a waste heat steam generator is used as a coolant for the air cooler, whereby the heat removed from the cooling air is used to superheat the steam. The superheated steam then can be returned into the water steam cycle, for example, into the waste heat steam generator, or can be used for injection into the gas turbine. Unfortunately, this method requires a combination cycle with a closed water steam cycle, which again is associated with high investment costs. This method also cannot be used during the times in which the components of the water steam cycle, for example, the steam turbine or waste heat steam generator, are unavailable. It is furthermore not suitable for the phased concept of a system which only functions as a combination system in the last upgrade phase.
EP 0 519 304, which is hereby incorporated by reference in its entirety, furthermore describes how, in a cooling air cooler, steam generated by indirect heat exchange is introduced into a combustor of a gas turbo group and is expanded in a turbine while supplying useful power. However, especially when a gas turbo group is used whose combustion chamber is operated with contemporary premix burners with a lean premixed combustion for minimizing noxious substances, it is not easy to add larger amounts of steam into the combustor. This may lead to a destabilization of the flame in connection with a significant increase in emissions of partially burned and unburned substances and dangerous fluctuations in combustor pressure. In addition, the addition of large amounts of water steam to the hot gas increases the heat transfer to the components to be cooled, which therefore has a counterproductive effect in that it again increases the cooling air requirement. EP 0 519 304 explicitly discloses a further heating of the generated steam in a waste heat steam generator; according to the generally known state of the art, this step in the process certainly could be eliminated.
SUMMARY OF THE INVENTION
The invention is therefore based on the task of creating an alternative to known method in which the required cooling air is effectively cooled, and the heat removed hereby used again, while avoiding the above mentioned disadvantages.
Fetescu Mircea
Liebig Erhard
Rickli Jean-Pierre
Stirnimann Franz
Alstom
Burns Doane Swecker & Mathis L.L.P.
Kim Ted
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