Liquid heaters and vaporizers – Industrial – Port
Reexamination Certificate
2001-09-13
2002-11-19
Wilson, Gregory (Department: 3749)
Liquid heaters and vaporizers
Industrial
Port
C122S00100C, C122S406400
Reexamination Certificate
active
06481386
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of power generation. The invention relates to a continuous-flow steam generator having a combustion chamber for fossil fuel that is followed on the fuel-gas side, through a horizontal gas flue, by a vertical gas flue. The containment walls of the combustion chamber are formed from vertically disposed evaporator tubes gastightly welded to one another.
In a power plant with a steam generator, the energy content of a fuel is utilized for evaporating a flow medium in the steam generator. In such a case, the flow medium is normally carried in an evaporator circuit. The steam supplied by the steam generator may, in turn, be provided, for example, for driving a steam turbine and/or for a connected external process. If the steam drives a steam turbine, a generator or a working machine is usually operated through the turbine shaft of the steam turbine. Where a generator is concerned, the current generated by the generator may be provided for feeding into an interconnected and/or island network.
The steam generator may, in this context, be configured as a continuous-flow steam generator. A continuous-flow steam generator is disclosed in the paper “Verdampferkonzepte für Benson-Dampferzeuger” [“Evaporator concepts for Benson steam generators”] by J. Franke, W. Köhler, and E. Wittchow, published in VGB Kraftwerkstechnik 73 (1993), No. 4, p. 352-360. In a continuous-flow steam generator, the heating of steam generator tubes provided as evaporator tubes leads to an evaporation of the flow medium in the steam generator tubes in a single pass.
Continuous-flow steam generators are conventionally configured with a combustion chamber in a vertical form of construction. As such, the combustion chamber is configured for the heating medium or fuel gas to flow through in an approximately vertical direction. In such a case, the combustion chamber may be followed on the fuel-gas side by a horizontal gas flue, a deflection of the fuel-gas stream into an approximately horizontal direction of flow taking place at the transition from the combustion chamber into the horizontal gas flue. However, in general, because of the thermally induced changes in length of the combustion chamber, such combustion chambers require a framework on which the combustion chamber is suspended. The suspension necessitates a considerable technical outlay in terms of the production and assembly of the continuous-flow steam generator, and the outlay is even greater when the overall height of the continuous-flow steam generator is larger. The increase is true, particularly with regard to continuous-flow steam generators that are configured for a steam power output of more than 80 kg/s under full load.
A continuous-flow steam generator is not subject to any pressure limitation, so that fresh-steam pressures well above the critical pressure of water (P
cri
=221 bar), where there is still only a slight density difference between the liquid-like and steam-like media, are possible. A high fresh-steam pressure is conducive to high thermal efficiency and, therefore, to low CO
2
emissions of a fossil-fired power station that can be fired, for example, with hard coal or else with lignite in solid form as fuel.
A particular problem is presented by the construction of the containment wall of the gas flue or combustion chamber of the continuous-flow steam generator in terms of the tube-wall or material temperatures that occur there. In the subcritical pressure range down to about 200 bar, the temperature of the containment wall of the combustion chamber is determined essentially by the height of the saturation temperature of the water, when wetting of the inner surface of the evaporator tubes can be ensured. Such wetting is achieved, for example, by using evaporator tubes that have a surface structure on their inside. Consideration is given, in particular, to internally ribbed evaporator tubes, of which the use in a continuous-flow steam generator is present in the prior art, for example, from the paper quoted above. These so-called ribbed tubes, that is to say tubes with a ribbed inner surface, have particularly good heat transmission from the tube inner wall to the flow medium.
Experience has shown that it is not possible to avoid the situation, when the continuous-flow steam generator is in operation, where thermal stresses occur between adjacent tube walls of different temperature when these are welded to one another. Such stresses occur, in particular, with regard to the portion of the combustion chamber connecting the combustion chamber to the horizontal gas flue following the combustion chamber, in other words, between evaporator tubes of the outlet region of the combustion chamber and steam generator tubes of the inlet region of the horizontal gas flue. These thermal stresses can markedly reduce the useful life of the continuous-flow steam generator and, in an extreme case, may even give rise to tube cracks.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a fossil-fired continuous-flow steam generator that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that requires a particularly low outlay in terms of production and assembly and, moreover, during the operation of which, keeps low temperature differences at the connection of the combustion chamber to the horizontal gas flue following the combustion chamber. The features apply particularly to the mutually directly or indirectly adjacent evaporator tubes of the combustion chamber and steam generator tubes of the horizontal gas flue following the combustion chamber.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a continuous-flow steam generator, including a combustion chamber for combusting fossil fuel, the combustion chamber having a fuel-gas side, an outlet region, burners, and containment walls formed from vertically disposed evaporator tubes welded to one another in a gastight manner, a horizontal gas flue having an inlet region and being disposed level with respect to the burners of the combustion chamber, a vertical gas flue connected to the fuel-gas side of the combustion chamber through the horizontal gas flue, a connecting portion forming the outlet region of the combustion chamber and the inlet region of the horizontal gas flue, a plurality of the evaporator tubes respectively acted upon in parallel by a flow medium, and a number of the evaporator tubes formed in a loop in the connecting portion.
The continuous-flow steam generator has a combustion chamber with a number of burners disposed level with the horizontal gas flue. A plurality of the evaporator tubes is respectively acted upon in parallel by flow medium. A number of the evaporator tubes are acted upon in parallel by flow medium being led in the form of a loop in a connecting portion that is made of the outlet region of the combustion chamber and the inlet region of the horizontal gas flue.
The invention proceeds from the notion that a continuous-flow steam generator capable of being set up at a particularly low outlay in terms of production and assembly should have a suspension structure capable of being executed in a simple way. At the same time, a framework capable of being set up at a comparatively low technical outlay for the suspension of the combustion chamber can be accompanied by a particularly low overall height of the continuous-flow steam generator. A particularly low overall height of the continuous-flow steam generator can be achieved by the combustion chamber being configured in a horizontal form of construction. For such a purpose, the burners are disposed level with the horizontal gas flue in the combustion chamber wall. Thus, when the continuous-flow steam generator is in operation, the fuel gas flows through the combustion chamber in an approximately horizontal main direction of flow.
Moreover, when the continuous-flow steam generator with the horizontal co
Greenberg Laurence A.
Mayback Gregory L.
Siemens Aktiengellschaft
Stemer Werner H.
Wilson Gregory
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