Liquid heaters and vaporizers – Steam treatment – Boilers with superheaters
Reexamination Certificate
2001-07-18
2002-09-10
Wilson, Gregory (Department: 3749)
Liquid heaters and vaporizers
Steam treatment
Boilers with superheaters
C122S459000, C122S00600B
Reexamination Certificate
active
06446584
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a steam generator having a first and a second combustion chamber with a respective number of burners for fossil fuel.
In a power plant having a steam generator, the energy content of a fuel is utilized for evaporating a flow medium in the steam generator. The steam generator has evaporator tubes which are heated, leading to evaporation of the flow medium conducted therein in order to evaporate the flow medium. Steam provided by the steam generator may in turn be used, for example, for a connected external process or for driving a steam turbine. If the steam drives a steam turbine, a generator or a driven machine is normally operated through a turbine shaft of the steam turbine. In the case of a generator, the current generated by the generator can be provided for feeding into an interconnected and/or separate network.
In that case, the steam generator may be constructed as a once-through steam generator. A once-through steam generator has been disclosed by a paper entitled “Verdampferkonzepte fur Benson-Dampferzeuger” [Evaporator Concepts For Benson Steam Generators] by J. Franke, W. Köhler and E. Wittchow, published in VGB Kraftwerkstechnik 73 (1993), No. 4, pages 352-360. In a once-through steam generator, the heating of steam-generator tubes provided as evaporator tubes leads to evaporation of the flow medium in the steam-generator tubes in a single pass.
Once-through steam generators are normally constructed with a combustion chamber in a vertical type of structure. That means that the combustion chamber is constructed for a throughflow of a heating medium or heating gas in an approximately vertical direction.
In that case, a horizontal gas flue can be connected downstream of the combustion chamber on the heating-gas side. The heating-gas flow is deflected into an approximately horizontal flow direction at a transition from the combustion chamber into the horizontal gas flue. However, due to temperature-induced changes in length of the combustion chamber, the combustion chamber generally requires a framework on which the combustion chamber is suspended. That necessitates a considerable technical outlay during the manufacture and installation of the once-through steam generator, which becomes larger as the overall height of the once-through steam generator becomes larger.
Fossil-fuel-fired steam generators are normally constructed for a particular type and quality of fuel and for a certain output range. That means that the combustion chamber of the steam generator, in its main dimensions, that is length, width and height, is adapted to combustion properties and ash properties of the predetermined fuel and to the predetermined output range. Therefore, each steam generator, with its fuel and output range associated therewith, has an individual structure of the combustion chamber with regard to the main dimensions.
If the combustion chamber of a steam generator is to be reconstructed, for example for a new output range and/or a fuel of a different type or quality, recourse may be had to planning documents of already-existing steam generators. With the aid of the documents, the main dimensions of the combustion chamber are then normally adapted to the requirements of the steam generator to be reconstructed. However, despite that simple measure, the structure of a steam generator for newly predetermined boundary conditions, due to the complexity of the systems taken as a basis, still involves a comparatively high design cost. That applies in particular when the respective steam generator is to have an especially high overall efficiency.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a fossil-fuel-fired steam generator, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which has a concept for a combustion chamber that permits an especially simple structure for a certain type and quality of fuel and for a predetermined output range and which requires especially little outlay in terms of manufacture and installation.
With the foregoing and other objects in view there is provided, in accordance with the invention, a steam generator, comprising a modular combustion space including a first module having at least one first combustion chamber and a second module having at least one second combustion chamber. The at least one first and at least one second combustion chambers each have a respective number of burners for fossil fuel and define a substantially horizontal main flow direction for heating gas. A common horizontal gas flue is provided, into which the at least one first and at least one second combustion chambers lead. A vertical gas flue is disposed downstream of the common horizontal gas flue on the heating-gas side.
The invention is based on the idea that a concept for the combustion chamber of the steam generator should permit an especially simple construction for a certain type and quality of fuel and for a predetermined output range of the steam generator. This is the case if a modular type of construction of the combustion chamber is provided. In this case, modules of the same kind prove to be especially simple to handle and permit an especially high degree of flexibility with regard to a desired rating of the combustion chamber. In addition, it should be especially simple to increase or reduce the size of the combustion chamber through the use of the modules.
However, a combustion chamber constructed for a throughflow of the heating gas in an approximately vertical direction requires a framework which is technically very complicated to construct. That framework would also have to be appropriately adapted with considerable outlay if the steam generator was retrofitted. In contrast thereto, a framework which is to be constructed with comparatively little technical outlay can be accompanied by an especially low overall height of the steam generator. A combustion chamber given a horizontal type of construction and having a first and a second combustion chamber therefore offers an especially simple concept for a steam generator with a modular construction. In this case, the burners, in both the first and the second combustion chambers, are disposed at the level of the horizontal gas flue in the combustion-chamber wall. The heating gas therefore flows through the combustion chambers in an approximately horizontal main flow direction during operation of the steam generator.
The burners are advantageously disposed on an end wall of the first combustion chamber and on an end wall of the second combustion chamber, that is on that containing wall of the respective first and second combustion chambers which is opposite the outflow opening to the horizontal gas flue. A steam generator with such a construction can be adapted to the burn-out length of the fuel in an especially simple manner. The burn-out length of the fuel in this case refers to the heating-gas velocity in the horizontal direction at a certain average heating-gas temperature, multiplied by a burn-out time t
A
of the fuel. In this case, the maximum burn-out length for the respective steam generator is obtained during full load, that is the “full-load operation” of the steam generator. The burn-out time t
A
is in turn the time which, for example, a pulverized-coal grain of average size requires in order to burn out completely at a certain average heating-gas temperature.
In order to keep material damage and undesirable contamination of the horizontal gas flue, for example due to a yield of molten ash at a high temperature, at an especially low level, a length L of the first and the second combustion chambers, which length is defined by a distance from the end wall to an inlet region of the horizontal gas flue, is advantageously at least equal to the burn-out length of the fuel during full-load operation of the steam generator. This horizontal length L of the first combustion chamber and of the second combustion chamber will generally be larg
Franke Joachim
Kral Rudolf
Greenberg Laurence A.
Mayback Gregory L.
Siemens Aktiengesellschaft
Stemer Werner H.
Wilson Gregory
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