Power plants – Motive fluid energized by externally applied heat – Process of power production or system operation
Reexamination Certificate
1999-10-21
2001-05-01
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Process of power production or system operation
C060S656000, C060S657000, C060S679000
Reexamination Certificate
active
06223536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of starting up a steam system having several different pressure stages, at least one container for receiving a medium circulating in the plant being arranged at each pressure stage.
Furthermore, it relates to a drum-type heat-recovery boiler and a steam system containing a drum-type heat-recovery boiler for carrying out the method and also to a combined-cycle power station having such a steam system.
2. Description of the Prior Art
During the cold start of a thermal power station having a steam turbine and, for example, a drum-type heat-recovery boiler having several different pressure stages, the steam generated in the individual pressure stages is in each case drawn off via a bypass, when the cooling system is in operation, by the condenser, which is assigned to the steam turbine and through which cooling water flows, until the generated steam meets the requirements of the steam turbine and the further conditions for the start-up of the steam turbine have been fulfilled. However, a heat quantity transferred to the steam in the heat-recovery boiler is thus dissipated to the environment via the condenser or its cooling system. The bypass operation is therefore affected by losses. In addition, the heating surfaces, in particular at the boiler end on the exhaust-gas side, remain cold for a prolonged period.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel method of the type mentioned at the beginning in which, during start-up operations, in particular cold starts, the heat in the region of the steam system and in particular in the region of the boiler can be retained and this heat is utilized for heating the heating surfaces, in accordance with the temperature profile over the entire steam system including the heat-recovery boiler.
According to the invention, this is achieved in that the medium, as heat transfer medium, is transferred from a respective container of a higher pressure stage to a respective container of a lower pressure stage for heating the same and its contents.
A drum-type heat-recovery boiler for carrying out the method is distinguished by the fact that a respective evaporator drum of a higher pressure stage is connected to an evaporator drum of a respective lower pressure stage via a water line.
A steam system containing a drum-type heat-recovery boiler for carrying out the method is distinguished by the fact that, from a respective container of a higher pressure stage of the heat-recovery boiler or the further components of the steam system, the medium, as a rule water, is transferred as heat transfer medium to a respective container of a lower pressure stage of the further components of the steam system for heating the same and their contents.
A combined-cycle power station having such a steam system comprises a gas turbogroup, by means of whose exhaust gas the heat-recovery boiler is heated, and a steam turbogroup, to which the steam generated in the heat-recovery boiler is fed.
Owing to the fact that, during the start-up of the steam system, no heat is dissipated from the system by cooling and the circulating medium is already utilized as heat transfer medium before the evaporation, i.e. in the liquid state, the start-up time of the steam system and thus the period up to the availability, for example, of a steam turbine can be considerably shortened.
A container of a higher pressure stage of the steam system is to be understood as a drum, but also as an economizer, an evaporator or a superheater. A container of a lower pressure stage, apart from being understood as the abovementioned units, which then work at a lower pressure stage, is also to be understood as a feedwater tank/deaerator or a condenser/hot well.
Depending on the state of the plant, the term medium refers in general to a liquid or the corresponding steam.
In the case of a heat-recovery boiler or steam power station, the media, in quite general terms, are water and steam. However, the water also normally contains additives, so that the medium cannot be designated as chemically pure water but rather as consisting mainly of water.
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patent: 5477683 (1995-12-01), Persson
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patent: 4132315C2 (1994-03-01), None
patent: 4432960C1 (1995-11-01), None
patent: 4447044C1 (1996-04-01), None
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Nguyen Hoang
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