Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-04-17
2001-06-12
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039182
Reexamination Certificate
active
06244035
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a gas and steam-turbine plant having a heat-recovery steam generator that is connected downstream of a gas turbine on the flue-gas side and has heating areas which are connected in a water/steam circuit of a steam turbine. The invention also relates to a method of operating such a gas and steam-turbine plant.
In a gas and steam-turbine plant, heat contained in an expanded working medium (flue gas) from the gas turbine is utilized to generate steam for the steam turbine. The heat transfer is effected in a heat-recovery steam generator, which is connected downstream of the gas turbine on the flue-gas side and in which heating areas are disposed in the form of tubes or banks of tubes. The latter in turn are connected in the water/steam circuit of the steam turbine. The water/steam circuit normally includes a plurality of pressure stages, for example two pressure stages. Each pressure stage has a preheating and an evaporator heating area.
The steam generated in the heat-recovery steam generator is fed to the steam turbine, where it expands to perform work. In this case, the steam turbine may include a number of pressure stages, which are adapted in their number and layout to the structure of the heat-recovery steam generator. The steam expanded in the steam turbine is normally fed to a condenser and condenses there. The condensate resulting during the condensation of the steam is fed again as feedwater to the heat-recovery steam generator, so that a closed water/steam circuit is obtained.
The condenser of such a gas and steam-turbine plant, like a heat exchanger, can normally be acted upon by a cooling medium, which extracts heat from the steam for the condensation. In that case, water is normally provided as the cooling medium. As an alternative, however, the condenser may also be constructed as an air condenser, to which air is admitted as the cooling medium.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a gas and steam-turbine plant that has an especially high plant efficiency during various operating states and a method of operating such a gas and steam-turbine plant with which an especially high plant efficiency can be achieved, that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a gas and steam-turbine plant, comprising a gas turbine receiving intake air and having a flue-gas side; a steam turbine having a water/steam circuit; a heat-recovery steam generator connected downstream of the gas turbine on the flue-gas side, the steam generator having heating areas connected in the water/steam circuit; a main condenser associated with the steam turbine; and a further condenser having a water/steam side connected in parallel with the main condenser, the further condenser to be cooled by the intake air.
The invention is based on the concept that, for an especially high plant efficiency, heat which develops in the plant process should be utilized to the greatest possible extent. At the same time, the heat extracted from the steam during its condensation should also be returned, at least partly, into the plant process. Due to the temperature level of the steam of about 60° C. during its condensation, the transfer of the heat extracted in the process into the intake air to be fed to the gas turbine is especially favorable.
The total mass flow of fuel/air mixture which can be fed overall to the gas turbine per unit of time is reduced by the preheating of the intake air of the gas turbine, so that the maximum power output attainable by the gas turbine is lower than if the preheating of the intake air were dispensed with. It has been found, however, that the fuel consumption drops to a greater extent than the maximum attainable power output during the preheating of the intake air by feeding of condensation heat, so that the overall efficiency increases.
In this case, the condenser, like an auxiliary condenser, may be acted upon by bleed steam from the steam turbine. In such a configuration, the condenser can be utilized in an especially favorable manner for providing a rapid power reserve which, for example, may also be required within a shorter reaction time to back up the line frequency of an electric network fed by the gas and steam-turbine plant. In this case, in order to activate the power reserve, the steam feed to the condenser is interrupted, so that the entire steam flow is directed through the main condenser. Therefore, a preheating of the intake air for the gas turbine does not occur, which leads to a rapid increase in the maximum output delivered by the gas turbine.
A compressor to which the intake air for the gas turbine can be fed through an intake-air line is normally assigned to the gas turbine. In accordance with another feature of the invention, the condenser is connected directly in the intake-air line on the cooling-medium side. In such a refinement, the condenser is expediently constructed as an air condenser. Losses as a result of conversion processes are kept especially low due to the single-stage heat transfer from the condensing steam to the intake air.
In accordance with a further feature of the invention, in an alternative development, the condenser is connected to a heat exchanger on the cooling-medium side through an intermediate cooling circuit, and the heat exchanger is in turn connected on the secondary side in the intake-air line connected upstream of the gas turbine. In such a configuration, the transport of the heat transferred during the condensation to a medium directed in the intermediate cooling circuit is also possible over large distances in a comparatively simple manner.
In accordance with an added feature of the invention, a steam-quantity ratio between the steam flows to be directed to the condenser and the main condenser is expediently adjustable, preferably as a function of the load state of the gas and steam-turbine plant. During operation of such a plant, the steam flow directed through the main condenser is condensed in a conventional manner with the use of an external cooling medium. At the same time, due to the adjustability of the steam-quantity ratio between the steam flows, the operating parameters of the steam flow directed through the condenser can be kept approximately constant in an especially simple manner, so that such a plant can be operated in an especially reliable manner. In addition, for every operating state of the plant, the intake air can thereby also be preheated to the maximum attainable temperature for the respective operating state.
In accordance with an additional feature of the invention, the main condenser has a condensate preheater connected downstream thereof, and condensate flowing off from the condenser, as viewed in the direction of flow of the condensate, can be fed downstream of the condensate preheater into the water/steam circuit of the steam turbine. Therefore, the residual heat remaining in the condensate after the condensation of the steam can be introduced into the water/steam circuit in an especially favorable manner.
With the objects of the invention in view, there is also provided a method of operating a gas and steam-turbine plant, which comprises preheating the intake air to be fed to the gas turbine with heat extracted during condensation from steam flowing off from the steam turbine.
In accordance with a concomitant mode of the invention, in the process, condensate obtained during the condensation is advantageously admixed to preheated condensate directed in the water/steam circuit of the steam turbine.
The advantages achieved with the invention reside in particular in the fact that, due to the transfer of the heat extracted during the condensation of the steam to the intake air for the gas turbine, this heat can be utilized for the plant process. Such a gas and steam-turbine plant therefore has an especially high plant ef
Casaregola Louis J.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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