Liquid heaters and vaporizers – Industrial – Port
Reexamination Certificate
2001-06-18
2002-09-10
Wilson, Gregory (Department: 3749)
Liquid heaters and vaporizers
Industrial
Port
C122S00100C, C122S406300, C122S460000
Reexamination Certificate
active
06446580
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the fields of thermodynamics and power generation. The invention relates, more specifically, to a continuous-flow steam generator having a combustion chamber for fossil fuel, which is followed on the fuel-gas side, via a horizontal flue, by a vertical gas flue, the containment walls of the combustion chamber being formed from vertically arranged evaporator tubes welded to one another in a gastight manner.
In a power plant with a steam generator, the energy content of a fuel is utilized for the evaporation of a flow medium in the steam generator. The flow medium is thereby conventionally 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. When the steam drives a steam turbine, a generator or a working machine is normally operated via 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 network and/or an isolated network.
The steam generator may thereby be designed as a continuous-flow steam generator, also referred to as a once-through generator. A continuous-flow steam generator is known from the paper “Verdampferkonzepte fur Benson-Dampferzeuger” [“Evaporator concepts for Benson steam generators”] by Franke, Köhler, and Wittchow, published in VGB Kraftwerkstechnik 73 (1993), No. 4, pages 352-60. 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 designed with a combustion chamber in a vertical form of construction. This means that the combustion chamber is designed for the heating medium or fuel gas to flow through in an approximately vertical direction. The combustion chamber may thereby be followed on the fuel-gas side by a horizontal gas flue, a deflection of the fuel-gas stream into an approximately horizontal flow direction taking place at the transition from the combustion chamber into the horizontal gas flue. However, in general, on account of the thermally induced changes in length of the combustion chamber, combustion chambers of this type require a scaffold on which the combustion chamber is suspended. This necessitates a considerable technical outlay in terms of the manufacture and assembly of the continuous-flow steam generator. The outlay is all the greater, the greater the overall height of the continuous-flow steam generator. This occurs particularly in the case of continuous-flow steam generators which 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 it is possible to have live-steam pressures well above the critical pressure of water (p
cri
=221 bar) where there is still only a slight density difference between liquid-phase and steam-phase medium. A high live-steam pressure is conducive to high thermal efficiency and therefore to low CO
2
emissions of a fossil-fired power station which may be fired, for example, with (hard) coal or else with lignite (brown coal) as fuel.
A particular problem is presented by the design of the containment wall of the gas flue or combustion chamber of the continuous-flow steam generator with regard to the tube-wall or material temperatures which occur there. In the subcritical pressure range up 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 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. For this purpose, in particular, internally ribbed evaporator tubes may be considered, for 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 transfer from the tube inner wall to the flow medium.
Experience has shown that it is not possible to avoid the situation where the containment wall of the combustion chamber is heated to a differing extent. Due to the different heating of the evaporator tubes, the outlet temperatures of the flow medium from evaporator tubes heated to a greater extent may therefore, in the case of continuous-flow steam generators, be generally higher than where evaporator tubes heated to a normal or lesser extent are concerned. Temperature differences between adjacent evaporator tubes may thereby arise, leading to thermal stresses which may reduce the useful life of the continuos-flow steam generator or may even cause tube cracks.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a fossil-fired continuous-flow steam generator of the abovementioned type which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and which requires a particularly low outlay in terms of manufacture and assembly and, moreover, during the operation of which temperature differences between adjacent evaporator tubes of the combustion chamber are kept particularly low. It is a further object to provide a continuous-flow steam generator which is especially easy to produce and assemble.
With the above and other objects in view there is provided, in accordance with the invention, a continuous-flow steam generator, comprising:
a combustion chamber having a plurality of burners for fossil fuel and having a fuel-gas side;
a horizontal gas flue substantially at a level with said burners and a vertical gas flue following said combustion chamber on said fuel-gas side;
said combustion chamber having containment walls formed from substantially vertically arranged evaporator tubes welded to one another in a gastight manner, and including a plurality of evaporator tubes each formed with inner ribs defining a multiple thread;
a common inlet header system for a flow medium connected in common to a number of said evaporator tubes of said combustion chamber and a common outlet header system connected in common to said evaporator tubes, such that the number of said evaporator tubes can be acted upon in parallel by the flow medium;
wherein a quotient formed from a steam power output (given in kg/s) under full load of the continuous-flow steam generator and a sum (given in m
2
) of an inner cross-sectional area of said number of said evaporator tubes capable of being acted upon in parallel by the flow medium is smaller than 1350 (given in kg/sm
2
).
In other words, the object of the invention are achieved with the continuous-flow steam generator that has a combustion chamber with a number of burners arranged level with the horizontal gas flue and designed in such a way that, in each case for a number of evaporator tubes capable of being acted upon in parallel by flow medium, the quotient formed from the steam power output M (given in kg/s) under full load and the sum of the inner cross-sectional areas A (given in m
2
) of these evaporator tubes capable of being acted upon in parallel by flow medium is smaller than 1350 (given in kg/sm
2
.)
The invention proceeds from the notion that a continuous-flow steam generator capable of being produced at a particularly low outlay in terms of manufacture and assembly should have a suspension structure capable of being executed by simple means. A scaffold to be produced at a comparatively low technically outlay for the suspension of the combustion chamber may at the same time 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 designing the combustion chamber in a horizontal fo
Franke Joachim
Kral Rudolf
Wittchow Eberhard
Greenberg Laurence A.
Locher Ralph E.
Stemer Werner H.
Wilson Gregory
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