Liquid heaters and vaporizers – Plants – Feed water heaters
Reexamination Certificate
1999-06-14
2001-02-20
Leo, Leonard (Department: 3743)
Liquid heaters and vaporizers
Plants
Feed water heaters
C122S00700A, C165S145000, C165S146000
Reexamination Certificate
active
06189491
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a steam generator.
In a gas and steam-turbine plant, the heat contained in the expanded working medium or heating gas from the gas turbine is utilized for the generation of steam for the steam turbine. The heat transfer is effected in a waste-heat steam generator, which is disposed down-stream of the gas turbine and in which a number of heating areas for the water preheating, the steam generation and the steam superheating are normally disposed. The heating areas are connected in the water/steam circuit of the steam turbine. The water/steam circuit normally contains several, e.g. three, pressure stages, in which case each pressure stage may have an evaporator heating area.
For the steam generator disposed as a waste-heat steam generator downstream of the gas turbine on the heating-gas side, a number of alternative configuration concepts are suitable, namely the configuration as a once-through steam generator or as a circulation steam generator. In the case of 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. In contrast, in the case of a natural or forced-circulation steam generator, the circulating water is only partly evaporated when passing through the evaporator tubes. The water that is not evaporated in the process is fed again to the same evaporator tubes for further evaporation after separation of the generated steam.
A once-through steam generator, in contrast to a natural or forced-circulation steam generator, is not subject to any pressure limitation. Therefore, live-steam pressures well above the critical pressure of water (P
cri
=221 bar), where there is only a slight difference in density between a medium similar to a liquid and a medium similar to steam, are possible. A high live-steam pressure promotes a high thermal efficiency and thus low CO
2
emissions of a fossil-fired power station. In addition, a once-through steam generator has a simple type of construction compared with a circulation steam generator and can therefore be manufactured at an especially low cost. The use of a steam generator configured according to the once-through principle as a waste-heat steam generator of a gas and steam-turbine plant is therefore especially favorable for achieving a high overall efficiency of the gas and steam-turbine plant in a simple type of construction.
A once-through steam generator may in principle, be made in one of two alternative constructional styles, namely in upright type of construction or in horizontal type of construction. Here, a once-through steam generator in a horizontal type of construction is configured for a throughflow of the heating medium or heating gas, for example the exhaust gas from the gas turbine, in an approximately horizontal direction, whereas a once-through steam generator in an upright type of construction is configured for a throughflow of the heating medium in an approximately vertical direction.
A once-through steam generator in the horizontal type of construction, in contrast to a once-through steam generator in the upright type of construction, can be manufactured with especially simple means and at an especially low production and assembly cost. In the case of a once-through steam generator with horizontal type of construction, however, the steam-generator tubes of a heating area, depending on their positioning, are subjected to heating that differs greatly.
In particular in the case of steam-generator tubes leading on the outlet side into a common discharge collector, however, different heating of individual steam-generator tubes may lead to the funneling of steam flows having steam parameters differing greatly from one another and thus to undesirable efficiency losses, in particular to comparatively reduced effectiveness of the relevant heating area and consequently reduced steam generation.
In addition, different heating of adjacent steam-generator tubes, in particular in the region where they lead into a discharge collector, may result in damage to the steam-generator tubes or the collector.
Summary of the Invention
It is accordingly an object of the invention to provide a steam generator which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is suitable for a horizontally configured construction and in addition has the advantages of a once-through steam generator. Furthermore, the steam generator is to make possible an especially high efficiency of a fossil-fired power station.
With the foregoing and other objects in view there is provided, in accordance with the invention, a steam generator, including:
a heating-gas duct; and
at least one once-through heating area is disposed in the heating-gas duct through which a flow is conducted in an approximately horizontal heating-gas direction, the at least one once-through heating area formed from a number of approximately vertically disposed steam-generator tubes connected in parallel for a through flow of a flow medium, the steam-generator tubes are configured such that a steam-generator tube of the steam-generator tubes heated to a greater extent compared with a further steam-generator tube of the steam-generator tubes has a higher flow rate of the flow medium compared with the further steam-generator tube.
Here, the expression once-through heating area refers to a heating area that is configured according to the once-through principle. The flow medium fed to the once-through heating area is thus completely evaporated in a single pass through the once-through heating area or through a heating-area system containing a plurality of once-through heating areas connected one behind the other. At the same time, a once-through heating area of such a heating-area system can also be provided for the preheating or for the superheating of the flow medium. In this configuration, the once-through heating area or each once-through heating area may contain a number of tube layers, in particular like a tube nest, which are disposed one behind the other in the heating-gas direction and each of which is formed from a number of steam-generator tubes disposed next to one another in the heating-gas direction.
The invention is based on the idea that, in the case of a steam generator suitable for an embodiment in a horizontal type of construction, the effect of locally different heating on the steam parameters should be kept especially small for a high efficiency. For especially small differences between the steam parameters in two adjacent steam-generator tubes, the medium flowing through the steam-generator tubes, after its discharge from the steam-generator tubes, should have approximately the same temperature and/or the same steam content for each steam-generator tube allocated to a common once-through heating area. Adaptation of the temperatures of the flow medium discharging from the respective steam-generator tubes can be achieved even during, different heating of the respective steam-generator tubes by each steam-generator tube being configured for a medium throughflow adapted to its average heating, which depends on its position in the heating-gas duct.
For an especially favorable adaptation of the flow rate of the flow medium to the heating of the respective steam-generator tube in the case of a steam generator configured for a full-load pressure at a superheater discharge of more than 80 bar, the steam-generator tubes of at least one once-through heating area are advantageously configured or dimensioned on average for a ratio of friction pressure loss to a geodetic pressure drop at a full load of less than 0.4, preferably less than 0.2. In the case of a steam generator having a pressure stage that is configured for a full-load pressure at the superheater discharge of 80 bar or less, the steam-generator tubes of the at least one once-through heating area of this pressure stage are advantageously configured on average for a rati
Franke Joachim
Kral Rudolf
Wittchow Eberhard
Greenberg Laurence A.
Leo Leonard
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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