Title of Invention

STEAM GENERATOR

Abstract A steam generator, on the one hand, is to be suitable for a horizontal type of construction and, on the other hand, is to have the advantages of a once-through steam generator. To this end, the steam generator, according to the invention, comprises - an entry collector - a discharge collector - a healing gas duct and at least one once-through heating area arranged in the heating - gas duct through which flow can occur in an approximately horizontal heating - gas direction, wherein once-through heating area is formed from a number of approximately vertically arranged steam - generator tubes connected in parallel for throughflow of a flow medium and the once through heating area is designed in such a way that a steam - generator tube heated to a greater extent compared with a further steam - generator tube of the same once-through heating area has a higher flow rate of the flow medium compared with the further steam - generator tube.
Full Text -1A-
Description
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 arranged downstream 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 arranged. The heating areas are connected in the water/steam circuit of the steam turbine. The water/steam circuit normally comprises several, e.g. three, pressure stages, in which case each pressure stage may have an evaporator heating area.
For the steam generator arranged as a waste-heat steam generator downstream of the gas turbine on the heating-gas side, a number of alternative design concepts are suitable, namely the design as a once-through steam generator or the design 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 which 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, so that live-steam pressures well above the critical pressure of water (pkri = 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

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pressure promotes a high thermal efficiency and thus low C02 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 designed according to the once-through principle as a waste-heat steam generator of a gas- and steam-turbine plant is therefore especially favourable 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 horizontal type of construction is designed 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 upright type of construction is designed for a throughflow of the heating medium in an approximately vertical direction.
A once-through steam generator in horizontal type of construction, in contrast to a once-through steam generator in 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 in horizontal type of construction, however, the steam-generator tubes of a heating area, depending on their positioning, are subjected to heating which 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 funnelling 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.

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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.
The object of the invention is to specify a steam generator which is suitable for a design in horizontal type of construction and in addition has the said 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.
This object is achieved according to the invention by a steam generator in which at least one once-through heating area is arranged in a heating-gas duct through which flow can occur in an approximately horizontal heating-gas direction, which once-through heating area is formed from a number of approximately vertically arranged steam-generator tubes connected in parallel for the throughflow of a flow medium and is designed in such a way that a steam-generator tube heated to a greater extent compared with a further steam-generator tube of the same once-through heating area 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 which is designed 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 comprising 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 arrangement, the once-through heating area or each once-through heat ing area may compri se a number of tube layers, in particular like a tube nest, which are arranged one behind the other in the heating gas direction and each of which is formed from a number of steam-generator tubes arranged next to one another in the

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heating-gas direction.
The invention is based on the idea that, in the case of a steam generator suitable for an embodiment in 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 designed for a medium throughflow adapted to its average heating, which depends on its position in the heating-gas duct.
For an especially favourable 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 designed for a full-load pressure at the superheater discharge of more than 80 bar, the steam-generator tubes of at least one once-through heating area are advantageously designed or dimensioned on average for a ratio of friction pressure loss to geodetic pressure drop at full load of less than 0.4, preferably less than 0.2. In the case of a steam generator having a pressure stage which is designed for a full-load pressure at the superheater discharge of 80 bar or less, the steam-generator tubes of at least one once-through heating area of this pressure stage are advantageously designed on average for a ratio of friction pressure loss to geodetic pressure drop at full load of less than 0.6, preferably less than 0.4. This is based on the knowledge that different heating of two steam-generator tubes leads to especially small temperature differences and/or differences in the steam content of

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the flow medium at the outlets of the respective steam-generator tubes when heating of a steam-generator tube to a greater extent leads on account of its design to an increase in the flow rate of the flow medium in this steam-generator tube.
This can be achieved in an especially simple manner by a friction pressure loss which is especially low compared with the geodetic pressure drop. Here, the geodetic pressure drop indicates the pressure drop on account of the weight of the water column and steam column relative to the area of the cross-section of flow in the steam-generator tube. The friction pressure loss, on the other hand, describes the pressure drop in the steam-generator tube as a result of the flow resistance for the flow medium. The total pressure drop in a steam-generator tube is essentially composed of the geodetic pressure drop and the friction pressure loss.
During especially intense heating of an individual steam-generator tube, the steam generation in this steam-generator tube becomes especially high. The weight of the medium which has not evaporated in this steam-generator tube therefore decreases, so that the geodetic pressure drop in this steam-generator tube likewise decreases. However, all steam-generator tubes connected in parallel inside a once-through heating area have the same total pressure drop on account of their common inlet-side connection to an entry collector and their common outlet-side connection to a discharge collector. If there is a geodetic pressure drop in one of the steam-generator tubes which is especially low compared with the steam-generator tubes connected in parallel with it on account of its especially intense heating, an especially large quantity of flow medium then flows for a pressure balance through the tube heated to a greater degree if the geodetic pressure drop is on average the dominant portion of the total pressure drop on account of the design of the once-through heating area.
In other words: a steam-generator tube heated

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more intensely compared with the steam-generator tubes connected in parallel with it has an increased flow rate of flow medium, whereas a steam-generator tube heated to an especially low degree compared with the steam-generator tubes connected in parallel with it has an especially low flow rate of flow medium. By a suitable specification of the ratio of friction pressure loss to geodetic pressure drop due to the design of the steam-generator tubes, in particular with regard to the selected mass-flow density in the steam-generator tubes, this effect can be utilized for automatic adaptation of the flow rate of each steam-generator tube to its heating.
In the design of the steam-generator tubes with regard to the ratio of friction pressure loss to geodetic pressure drop, the relevant variables can be determined according to the relationships specified in the publications Q. Zheng, W. Kohler, W. Kastner and K. Riedle "Druckverlust in glatten und innenberippten Verdampferrohren", Warme- und Stof fiibertragung 26, pp. 323-330, Springer-Verlag 1991, and Z. Rouhani "Modified correlation for void-fraction and two-phase pressure drop", AE-RTV-841, 1969. Here, for a steam generator designed for a full-load pressure at the superheater discharge of 180 bar or less, its characteristic values are to be used for the full-load operating state. On the other hand, for a steam generator designed for a full-load pressure of more than 180 bar, its characteristic values are to be used for a part-load operating state at an operating pressure at the superheater discharge of about 180 bar.
As extensive tests have shown, the automatic increase in the flow rate of flow medium when the steam-generator tube is heated to a greater degree, which increase is the intention of the design criterion for the steam-generator tubes, also occurs within a pressure range above the critical pressure of the flow medium. In addition, in the case of a once-through heating area to which a water/steam mixture flows in the design case, the

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intended automatic increase in the flow rate when a steam-generator tube is heated to a greater degree also occurs when the friction pressure loss in the steam-generator tube is on average about five times higher than in the case of a steam-generator tube of a once-through heating area to which merely water flows in the design case.
Each steam-generator tube of a once-through heating area is expediently designed for a higher flow rate of the flow medium than each steam-generator tube arranged downstream of it in the heating-gas direction and belonging to the same once-through heating area.
In an alternative or additional advantageous development, a steam-generator tube of the once-through heating area or of each once-through heating area has a larger inside diameter than a steam-generator tube arranged downstream of it in the heating-gas direction and belonging to the same once-through heating area. This ensures in an especially simple manner that the steam-generator tubes in the region of comparatively high heating-gas temperature have a comparatively high flow rate of flow medium.
In a further alternative or additional advantageous development, a choke device is connected upstream of a number of steam-generator tubes of the once-through heating area or of each once-through heating area in the direction of flow of the flow medium. In this arrangement, in particular in the design case, steam-generator tubes heated to a lower degree compared with steam-generator tubes of the same once-through heating area can be provided with the choke device. The flow rate through the steam-generator tubes of a once-through heating area can therefore be controlled, so that an additional adaptation of the flow rate to the heating is made possible. In this case, a choke device may also be connected in each case upstream of a group of steam-generator tubes.
In a further alternative or additional advantageous development, in each case a plurality of

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entry collectors and/or a plurality of discharge collectors are allocated to the once-through heating area or to each once-through heating area, each entry collector being commonly connected upstream of a number of steam-generator tubes of the respective once-through heating area in the direction of flow of the flow medium or each discharge collector being commonly connected downstream of a number of steam-generator tubes of the respective once-through heating area. Thus an especially favourable spatial arrangement of the steam-generator tubes in their region adjoining the entry collectors is possible.
For especially high heat absorption, the steam-generator tubes expediently have ribbing on their outside. In addition, each steam-generator tube may expediently be provided with thread-like ribbing on its inner wall in order to increase the heat transfer from the steam-generator tube to the flow medium flowing in it.
The steam generator is expediently used as a waste-heat steam generator of a gas- and steam-turbine plant. In this case, the steam generator is advantageously arranged downstream of a gas turbine on the heating-gas side. In this circuit, supplementary firing for increasing the heating-gas temperature may expediently be arranged behind the gas turbine.
The advantages achieved by the invention consist in particular in the fact that a steam generator which is especially favourable for achieving an especially high overall efficiency of a gas- and steam-turbine plant can also be made in horizontal type of construction and thus at an especially low production and assembly cost. In this case, material damage to the steam generator on account of the heating of the steam-generator tubes, which is spatially inhomogeneous to an especially high degree, is reliably avoided on account of the fluidic design of the steam generator.
Exemplary embodiments of the invention are explained in more detail below with reference to a

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accompany drawing, in which:
Figures 1, 2 and 3 each show in simplified representation a longitudinal section of a steam generator in horizontal type of construction.
The same parts are provided with the same reference numerals in all figures.
The steam generator 1 according to Figures 1, 2 and 3, like a waste-heat steam generator, is arranged downstream of a gas turbine (not shown in any more detail) on the exhaust-gas side. The steam generator 1 has an enclosing wall 2 which forms a heating-gas duct 3 through which flow can occur in an approximately horizontal heating-gas direction indicated by the arrows 4 and which is intended for the exhaust gas from the gas turbine. A number of heating areas which are designed according to the once-through principle and are also designated as once-through heating areas 8, 10 are arranged in the heating-gas duct 3. In the exemplary embodiment according to Figures 1, 2 and 3, in each case two once-through heating areas 8, 10 are shown, but merely one once-through heating area or a larger number of once-through heating areas may also be provided.
The once-through heating areas 8, 10 according to Figures 1, 2 and 3 comprise a number of tube layers 11 and 12 respectively, in each case like a tube nest, which are arranged one behind the other in the heating-gas direction. Each tube layer 11, 12 in turn comprises a number of steam-generator tubes 13 and 14 respectively, which are arranged next to one another in the heating-gas direction and of which in each case only one can be seen for each tube layer 11, 12. In this case, the approximately vertically arranged steam-generator tubes
13, connected in parallel for the throughflow of a flow
medium W, of the first once-through heating area 8 are
connected on the outlet side to a discharge collector 15
common to them. On the other hand, the likewise
approximately vertically arranged steam-generator tubes
14, connected in parallel for the throughflow of a flow
medium W, of the second once-through heating area 10 are
14,
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connected on the outlet side to a discharge collector 16 common to them. The steam-generator tubes 14 of the second once-through heating area 10 are fluidically arranged downstream of the steam-generator tubes 13 of the first once-through heating area 8 via a downpipe system 17.
The flow medium W can be admitted to the evaporator system formed from the once-through heating areas 8, 10, which flow medium W evaporates on passing once through the evaporator system and is drawn off as steam D after discharge from the second once-through heating area 10. The evaporator system formed from the once-through heating areas 8, 10 is connected in the water/steam circuit {not shown in any more detail) of a steam turbine. In addition to the evaporator system comprising the once-through heating areas 8, 10, a number of further heating areas 2 0 indicated schematically in Figures 1, 2 and 3 are connected in the water/steam circuit of the steam turbine. The heating areas 20 may, for example, be superheaters, intermediate-pressure evaporators, low-pressure evaporators and/or preheaters.
The once-through heating areas 8, 10 are designed in such a way that local differences in the heating of the steam-generator tubes 13 and 14 respectively only lead to small temperature differences or differences in the steam content in the flow medium W discharging from the respective steam-generator tubes 13 and 14. In this case, each steam-generator tube 13, 14, as a result of the design of the respective once-through heating area 8, 10, has a higher flow rate of the flow medium W than each steam-generator tube 13 or 14 arranged downstream of it in the heating-gas direction and belonging to the same once-through heating area 8 or 10 respectively.
In the exemplary embodiment according to Figure 1, the steam-generator tubes 13 of the first once-through heating area 8, which are connected on the inlet side to an entry collector 21, are designed in such a way that, during full-load operation of the steam generator 1, the ratio of friction pressure loss to

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geodetic pressure drop within the respective steam-generator tube 13 is on average less than 0.2. On the other hand, the steam-generator tubes 14 of the second once-through heating area 10, which are connected on the inlet side to an entry collector 22, are designed in such a way that, during full-load operation of the steam generator 1, the ratio of friction pressure loss to geodetic pressure drop within the respective steam-generator tube 14 is on average less than 0.4. In addition, each steam-generator tube 13, 14 of the once-through heating area 8 or 10 respectively may have a larger inside diameter than each steam-generator tube 13 or 14 arranged downstream of it in the heating-gas direction and belonging to the same once-through heating area 8 or 10.
In the exemplary embodiment according to Figure 2, a valve, as choke device 23, is in each case connected upstream of each steam-generator tube 13, 14 of the once-through heating areas 8 and 10 respectively in the direction of flow of the flow medium W in order to set a flow rate adapted to the respective heating. This helps to adapt the flow rate through the steam-generator tubes 13, 14 of the once-through heating areas 8, 10 to their different heating.
In the exemplary embodiment according to Figure 3, a plurality of entry collectors 26 and 28 respectively and a plurality of discharge collectors 30 and 32 respectively are in each case allocated to each once-through heating area 8, 10, as a result of which a group formation is possible in an especially simple manner. In this case, each entry collector 26, 28 is commonly connected upstream of a number of steam-generator tubes 13 and 10 of the respective once-through heating area 8 or 14 in the direction of flow of the flow medium W. Each discharge collector 30, 32, on the other hand, is commonly connected downstream of a number of steam-generator tubes 13 and 14 of the respective once-through heating area 8 or 10 in the direction of flow of the flow medium W. In the exemplary embodiment

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according to Figure 3, the steam-generator tubes 13, 14 of the once-through heating areas 8 and 10 respectively are again designed in such a way that, during operation of the steam generator the ratio of friction pressure loss to geodetic pressure drop in the respective steam-generator tube 13, 14 is on average less than 0.2 or 0.4 respectively. A choke device 34 is in each case connected upstream of the tube groups thus formed.
With regard to the design of its once-through heating areas 8, 10, the once-through steam generator 1 is adapted to the spatially inhomogeneous heating of the steam-generator tubes 13, 14 as a result of the horizontal type of construction. The steam generator 1 is therefore also suitable for a horizontal type of construction in an especially simple manner.

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1. Steam generator (1) in which at least one once-through heating area (8,10) is
arranged in a heating-gas duct (3) through which flow can occur in an
horizontal heating-gas direction, which once-through heating area (8,10) is formed from a number of vertically arranged steam-generator tubes (13,14) connected in parallel for the throughflow of a flow medium, characterized in that the once-through heating area (8,10) is designed in such a way that a steam-generator tube (13,14") heated to a greater extent compared with a further steam-generator tube (13,14) of the same once-through heating area (8,10) has higher flow rate of the flow medium compared with the further steam-generator tube (13,14).
2. Steam generator (1) as claimed in Claim 1, wherein the steam-generator tubes
(13,14) of at least one once-through heating area (8,10) are designed on
average in each case for a ratio of friction pressure loss to geodetic pressure
drop at full load of less than 0.4, preferably less than 0.2.
3. Steam generator (1) as claimed in Claim 1 or 2, wherein each steam-generator
tube (13,14) of a once-through heating area (8,10) is designed for a higher
flow rate of the flow medium than each steam-generator tube (13,14)
arranged down-stream of it in the heating-gas direction and belonging to the
same once-through heating area (8,10).

4. Steam generator (1) as claimed in one of Claims 1 to 3, wherein a steam-generator tube (13,14) of the once-through heating area (8,10) or of each once-through heating area (8,10) has a larger inside diameter than a steam-generator tube (13,14) arranged downstream of it in the heating-gas direction and belonging to the same once-through heating area (8,10).
5. Steam generator (1) as claimed in one of Claims 1 to 4, wherein a choke device (23) is in each case connected upstream of a number of steam-generator tubes (13,14) of the once-through heating area (8,10) or of each once-through heating area (8; 10) in the direction of fiow of the flow medium.
6. Steam generator (1) as claimed in one of Claims 1 to 5, wherein in each case a plurality of entry collectors (26, 28) and/or discharge collectors (30, 32) are allocated to the once-through heating area (8,10), or to each once-through heating area (8,10), each entry collector (26, 28) being commonly connected upstream of a number of steam-generator tubes (13,14) of the respective once-through heating area (8,10) in the direction of flow of the flow medium.

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7. Steam generator (1) as claimed in Claim 6, wherein a choke device (34) is
connected upstream of at least one entry collector (26, 28);
8. Steam generator (1) as claimed in one of Claims 1 to 7, wherein a gas turbine
is arranged upstream on the heating-gas side,
Dated This 6th Day Of November 1997


A steam generator, on the one hand, is to be suitable for a horizontal type of construction and, on the other hand, is to have the advantages of a once-through steam generator. To this end, the steam generator, according to the invention, comprises
- an entry collector
- a discharge collector
- a healing gas duct and
at least one once-through heating area arranged in the heating - gas duct through which flow can occur in an approximately horizontal heating - gas direction, wherein once-through heating area is formed from a number of approximately vertically arranged steam
- generator tubes connected in parallel for throughflow of a flow medium and the once
through heating area is designed in such a way that a steam - generator tube heated to a
greater extent compared with a further steam - generator tube of the same once-through
heating area has a higher flow rate of the flow medium compared with the further steam -
generator tube.


Documents:

02103-cal-1997-abstract.pdf

02103-cal-1997-claims.pdf

02103-cal-1997-correspondence.pdf

02103-cal-1997-description (complete).pdf

02103-cal-1997-drawings.pdf

02103-cal-1997-form-1.pdf

02103-cal-1997-form-2.pdf

02103-cal-1997-form-3.pdf

02103-cal-1997-form-5.pdf

02103-cal-1997-gpa.pdf

02103-cal-1997-priority document others.pdf

02103-cal-1997-priority document.pdf

2103-CAL-1997-(04-10-2012)-FORM-27.pdf

2103-CAL-1997-CORRESPONDENCE 1.1.pdf

2103-CAL-1997-FORM-27.pdf

2103-CAL-1997-PA.pdf


Patent Number 194463
Indian Patent Application Number 2103/CAL/1997
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date 24-Jun-2005
Date of Filing 06-Nov-1997
Name of Patentee SIEMENS AKTIENGESELLSCHAFT
Applicant Address WITTELSBACHERPLATZ 2, 80333 MUENCHEN.
Inventors:
# Inventor's Name Inventor's Address
1 EBERHARD WITTCHOW SCHRONFELD 96, D-91054 ERLANGEN
2 JOACHIM FRANKE KLOSTERBERGSTR. 9, D-90518 ALTDORF
3 RUDOLF KRAL WEINHOFER STR. 27, D-90518 ALTDORF
PCT International Classification Number F28F27/02,F22B1/18
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 19651678.1 1996-12-12 Germany