Liquid heaters and vaporizers – Steam treatment
Reexamination Certificate
2001-07-18
2002-12-31
Wilson, Gregory (Department: 3749)
Liquid heaters and vaporizers
Steam treatment
C122S00600B
Reexamination Certificate
active
06499440
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a steam generator with a combustion chamber for fossil fuel. A horizontal gas flue and a vertical gas flue are provided downstream of the combustion chamber.
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. For the evaporation of a flow medium, the steam generator has evaporator tubes, the heating of which leads to the evaporation of the flow medium carried in them. The steam supplied by the steam generator may, in turn, be provided, for example, for a connected external process or else for driving a steam turbine. When the steam drives a steam turbine, a generator or a working machine is normally operated via the turbine shaft of the steam turbine. In the case of a generator, the current generated by the generator may be provided for feeding into an interconnected and/or island network.
In this context, the steam generator may be configured as a continuous-flow steam generator. A continuous-flow steam generator is known from 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 the evaporation of the flow medium in the steam generator tubes in a single pass.
Steam generators are conventionally configured with a combustion chamber in a vertical form of construction. This means that the combustion chamber is configured for the heating medium or fuel gas to flow through in an approximately vertical direction.
At the same time, the combustion chamber may be followed on the fuel-gas side by a horizontal gas flue, the fuel-gas stream being deflected into an approximately horizontal flow direction at the transition from the combustion chamber into the horizontal gas flue. However, because of the thermally induced changes in length of the combustion chamber, combustion chambers of this type generally require a framework on which the combustion chamber is suspended. This necessitates a considerable technical outlay in terms of the production and the assembly of the steam generator, this outlay being the greater, the greater is the overall height of the steam generator.
The configuration of the containment wall of the gas flue or combustion chamber of the steam generator presents a particular problem with regard to the tube-wall or material temperatures which occur there. In the subcritical pressure range up to about 200 bar (20 MPa), the temperature of the containment wall of the combustion chamber is determined essentially by the level of the saturation temperature of the water when wetting of the inner surface of the evaporator tubes can be ensured. This is achieved, for example, by the use of evaporator tubes which have a surface structure on their inside. In particular, internally ribbed evaporator tubes come under consideration in this respect, of which the use in a continuous-flow steam generator is known, for example, from the abovementioned paper. 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 containment walls of the combustion chamber being heated to a differing extent. As a result of the different heating of the evaporator tubes, therefore, the outlet temperatures of the flow medium from evaporator tubes heated to a greater extent are substantially higher than in the case of evaporator tubes heated normally or heated to a lesser extent. This may give rise to temperature differences between adjacent evaporator tubes, leading to thermal stresses which may reduce the useful life of the steam generator or even cause pipe cracks.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a steam generator for fossil fuel which overcomes the abovementioned disadvantages of the heretofore-known steam generators of this general type and which requires a particularly low outlay with respect to its production and its assembly and in which, at the same time, temperature differences between adjacent evaporator tubes, when the steam generator is in operation, are kept particularly low.
With the foregoing and other objects in view there is provided, in accordance with the invention, a steam generator, including:
a combustion chamber for fossil fuel, the combustion chamber having a fuel-gas side;
a horizontal gas flue;
a vertical gas flue connected, via the horizontal gas flue, on the fuel-gas side to the combustion chamber;
the combustion chamber having burners provided substantially on a level with the horizontal gas flue;
the combustion chamber having containment walls formed from vertically disposed evaporator tubes welded to one another in
a gastight manner;
a number of the evaporator tubes being subdivided into a first group and a second group, the first group and the second group of the evaporator tubes to be acted upon in each case in parallel by a flow medium;
the second group being provided in series with the first group and downstream of the first group as seen in a direction of flow of the flow medium;
the containment walls of the combustion chamber being subdivided into a first region and a second region along a main flow direction of a fuel gas flow;
the first region being formed from evaporator tubes of the first group and the second region being formed from evaporator tubes of the second group; and
the second region being provided, on the fuel-gas side, between the first region and the horizontal gas flue.
In other words, the object of the invention is achieved by a steam generator with a combustion chamber for fossil fuel, which is followed on the fuel-gas side, via a horizontal gas flue, by a vertical gas flue, the combustion chamber including a number of burners provided on a level with the horizontal gas flue, wherein the containment walls of the combustion chamber are formed from vertically disposed evaporator tubes welded to one another in a gastight manner, a number of the evaporator tubes are subdivided into a first group and a second group, the first group and the second group of the evaporator tubes can be acted upon in each case in parallel by a flow medium, and the second group follows the first group of the evaporator tubes in series in the direction of flow of the flow medium, and in which the containment walls of the combustion chamber are subdivided into a first region and a second region in the main direction of flow of the fuel gas, the first region is formed from evaporator tubes of the first group and the second region from evaporator tubes of the second group, and the second region is provided, on the fuel-gas side, between the first region and the horizontal gas flue.
The invention is based on the idea that a steam generator which is to be set up at a particularly low outlay in terms of production and assembly should have a suspension structure which can be implemented in a simple manner. A framework to be set up at a comparatively low technical outlay for the suspension of the combustion chamber may, in this case, be accompanied by a particularly low overall height of the steam generator. A particularly low overall height of the steam generator can be achieved by the combustion chamber being configured in a horizontal form of construction. For this purpose, the burners are provided on a level with the horizontal gas flue in the combustion chamber wall. The fuel gas therefore flows through the combustion chamber in an approximately horizontal direction when the steam generator is in operation.
Moreover, when the horizontal combustion chamber is in operation, temperature differences between adjacent evaporator tubes should be particularly low in order reliably to avoid premature material fatigue. Where a horizontal combustio
Franke Joachim
Kral Rudolf
Greenberg Laurence A.
Locher Ralph E.
Siemens Aktiengesellschaft
Stemer Werner H.
Wilson Gregory
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