Liquid heaters and vaporizers – Circulation – With start-up operations
Reexamination Certificate
2000-02-07
2001-06-26
Wilson, Gregory (Department: 3749)
Liquid heaters and vaporizers
Circulation
With start-up operations
C122S00100C, C122S45100R
Reexamination Certificate
active
06250258
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and apparatus for operating a steam generation plant having a steam turbine, and more specifically to a method and apparatus for starting up a once through heat recovery steam generator which is connected to a steam consumer within a working-fluid-cycle.
BACKGROUND OF THE INVENTION
The invention relates, further, to a once through heat recovery steam generator connected to a steam consumer within a water steam cycle and having an evaporator and at least one superheater section for carrying out the method.
In power stations having a steam generation plant and a steam turbine, the aim in the first place is generally to achieve short start-up times, irrespective of whether a steam power station pure and simple or a combined cycle plant is concerned. What is critical is the duration until steam meeting the requirements of the steam turbine is available under stable conditions at the boiler outlet. Known designs of boilers conform to these requirements only inadequately.
The start-up of the boiler and steam turbine in connection with combined cycle power stations utilizing the exhaust-gas heat of the gas turbine for steam generation in the heat recovery steam generator is particularly important. Gas turbines are nowadays capable of running up from the cold state to the rated-load mode in markedly less than one hour.
Heat recovery steam generators with a circulation-type drum evaporator can often follow such rapid thermal loading to only a restricted extent because of the thick-walled components of the drum. Heat recovery steam generators on the principle of the once-through evaporator, with a separator between the evaporator and superheater, can achieve stable operating states even at medium pressures of up to about 80 bar. However, due to the superheaters connected downstream of the separator, the temperatures at the outlet of the heat recovery steam generator are too high for rapid start-up of a steam turbine.
The time for starting up a steam turbine nevertheless depends essentially on the steam temperatures. The lower the steam temperature can be maintained during start-up, the more rapidly the steam turbine can be started up. The object, for this reason, is to develop heat recovery steam generators, in combination with water steam cycles, which follow the gas turbine without delay during start-up, reach stable operating states quickly and supply the steam turbine at an early stage with steam at low temperatures for the start-up.
BRIEF SUMMARY OF THE INVENTION
The object on which the invention is based is to provide a method of the type initially mentioned which allows a short start-up time for a steam consumer. Another object is to provide a once through heat recovery steam generator or a water steam cycle for carrying out the method.
According to the invention, this is achieved by the arrangement of a separator within the heat recovery steam generator downstream of the at least one superheater section or in the working-fluid-cycle, said separator making it possible that, prior to the start-up, the heat recovery steam generator or the working-fluid-cycle is filled with the working medium in the liquid state up to the separator, that the liquid phase of the working medium is loop-circulated in the heat recovery steam generator or in the working-fluid-cycle and the supply of heat is subsequently initiated, and that, after the formation of steam has commenced, separation is carried out between the vaporous phase and the liquid phase of the working medium downstream of said superheater section in the separator, the liquid phase is further loop-circulated and the steam is conducted to a tank. When the requirements of the steam consumer are achieved, the supply of the steam to said tank is prevented and the steam is supplied to the steam consumer.
According to the invention, the superheater heating surfaces, which otherwise remain dry for a long time and therefore uncooled, may be used at least partially for preheating and evaporating the heat transfer medium during the start-up.
A once through heat recovery steam generator, connected to a steam consumer and having at least one superheater section, and a corresponding water steam cycle, for carrying out the method, are distinguished by a separator which is arranged downstream of the at least one superheater section in the direction of run of the working medium flowing through the heat recovery steam generator or the water steam cycle.
REFERENCES:
patent: 3120839 (1964-02-01), Glahe
patent: 3259111 (1966-07-01), Koch
patent: 4262636 (1981-04-01), Augsburger
patent: 4290390 (1981-09-01), Juzi
patent: 4487166 (1984-12-01), Haller et al.
patent: 5839396 (1998-11-01), Franke et al.
patent: 1228623 (1966-11-01), None
patent: 1230037 (1966-12-01), None
patent: 1290940 (1969-03-01), None
patent: 1299642 (1969-07-01), None
ABB Alstom Power ( Schweiz) AG
Burns Doane Swecker & Mathis L.L.P.
Wilson Gregory
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