EP1512906A1 - Once-through steam generator of horizontal construction and method of operating said once-through steam generator - Google Patents

Abstract

The throughflow steam generator (1) has an evaporator throughflow heating surface (8) in a hot gas channel (6) through which gas can flow approximately horizontally with a number of steam generator tubes (12) in parallel and a heating surface segment (26) that can carry an opposite flow of the flowing medium and has an outlet (16) positioned so that the saturated steam temperature at the outlet of the evaporator throughflow heating surface deviates by less than a maximum value from the hot gas temperature at the heating surface segment outlet position in the operating case. An independent claim is also included for the following: (a) a method of operating an inventive throughflow steam generator.

Description

The invention relates to a continuous steam generator, wherein in one in an approximately horizontal heating gas direction durchströmbarem Heizgaskanal an evaporator Durchlaufheizfläche is arranged, which a number of to flow through a flow medium connected in parallel steam generator tubes includes.

In a gas and steam turbine plant is in the relaxed Working fluid or fuel gas contained in the gas turbine Heat used to generate steam for the steam turbine. The heat transfer takes place in one of the gas turbine downstream Heat recovery steam generator, in which usually a Number of heating surfaces for water pre-heating, for steam generation and are arranged for steam overheating. The heating surfaces are connected in the water-steam cycle of the steam turbine. The water-steam cycle usually includes several, z. B. three, pressure levels, each pressure level one Evaporator can have.

For the gas turbine as a heat recovery steam generator on the heating gas side Downstream steam generators come several alternative Design concepts, namely the design as a continuous steam generator or the design as a circulating steam generator, into consideration. In a continuous steam generator, the heating leads from intended as evaporator tubes steam generator tubes an evaporation of the flow medium in the steam generator tubes in a one-time pass. In contrast, will in a natural or forced circulation steam generator in circulation Guided water in one pass through the evaporator tubes only partially evaporated. The unevaporated water is after a separation of the generated vapor for a further evaporation supplied to the same evaporator tubes again.

In contrast to a natural or forced circulation steam generator, a continuous steam generator is not subject to any pressure limitation, so that fresh steam pressures are possible far above the critical pressure of water (P _Kri ≈ 221 bar) - where there are only slight differences in density between liquid-like and vapor-like medium. A high live steam pressure promotes a high thermal efficiency and thus low CO ₂ emissions of a fossil-fired power plant. In addition, a continuous steam generator in comparison to a circulating steam generator a simple construction and is thus produced with very little effort. The use of a designed according to the flow principle steam generator as heat recovery steam generator of a gas and steam turbine plant is therefore particularly favorable to achieve a high overall efficiency of the gas and steam turbine plant with a simple design.

Special advantages in terms of production costs, but also with regard to required maintenance work a heat recovery steam generator in horizontal construction, in which the heating medium or heating gas, ie the exhaust gas from the Gas turbine, in approximately horizontal flow direction the steam generator is guided. In a continuous steam generator in horizontal design, the steam generator tubes a Heating surface, however, depending on their positioning a strong be exposed to different heating. Especially at on the output side connected to a common collector Steam generator tubes can be a different heating individual Steam generator tubes to a merger of steam streams with strongly divergent steam parameters and thus to undesirable efficiency losses, in particular to a comparatively reduced effectiveness of the affected Heating surface and thereby reduced steam generation, to lead. A different heating adjacent Steam generator tubes can also, in particular in the junction area from collectors, to damage to the steam generator pipes or the collector. The desirable use a laid in horizontal construction continuous flow steam generator as a heat recovery steam generator for a gas turbine can thus considerable problems with respect to a sufficiently stabilized Flow guidance with it.

From EP 0 944 801 B1 a steam generator is known which is suitable for a design in horizontal construction and also having the said advantages of a continuous steam generator. For this purpose, the known steam generator in terms of his Evaporator Durchlaufheizfläche designed such that a compared to another steam generator tube of the same Evaporator continuous heating surface more heated steam generator tube a higher compared to the other steam generator tube Having flow rate of the flow medium. The evaporator continuous heating surface the known steam generator thus shows in the nature of the flow characteristic of a natural circulation evaporator heating surface (Natural circulation characteristic) when occurring different heating of individual steam generator tubes a self-stabilizing behavior without the requirement external influence to an alignment of the exit side Temperatures also at differently heated, flow medium side connected in parallel steam generator tubes leads. However, this design concept requires that the well-known steam generator for a feed with flow medium provided with comparatively low mass flow density is.

The invention is therefore based on the object, a continuous steam generator of the above mentioned type, too at a Feeding with flow medium with comparatively large mass flow densities a particularly high operational Security guaranteed. Furthermore, a particularly suitable Method for operating the steam generator of the above be specified type mentioned.

With respect to the continuous steam generator, this object is achieved according to the invention solved by the one in the flow medium Counterflow to the Heizgaskanal flow-through Heizflächensegment includes, the flow-medium-side outlet in Seen heating gas direction is positioned so that the in the operating case at the outlet of the evaporator Durchlaufheizfläche adjusting, pressure-dependent saturated steam temperature by less than a given maximum deviation from the Operating case at the position of the exit of the Heizflächensegments deviates from the prevailing heating gas temperature.

The invention is based on the consideration that in the Feeding the evaporator Durchlaufheizfläche with comparatively large mass flow densities a locally different Heating individual pipes, the flow conditions such could affect that of less heated and more heated pipes less heated pipes flowed through by more flow medium become. More heated pipes would be worse in this case cooled as underheated pipes, so that the occurring Temperature differences would be amplified automatically. To this Fall even without active influence on the flow conditions To be able to respond effectively, the system should be for a fundamental and global limitation of possible temperature differences be designed suitable. This is the knowledge usable, that at the exit from the evaporator Durchlaufheizfläche the flow medium at least substantially saturated steam temperature given by the pressure in the steam generator tube must have. On the other hand, the flow medium but have the maximum temperature, the heating gas at the Exit point of the flow medium from the evaporator Durchlaufheizfläche Has. By a suitable vote this both limiting the possible temperature interval at all Limit temperatures can therefore also on each other the maximum possible temperature imbalances suitably limited become. By the division of the evaporator Durchlaufheizfläche in an exit-side countercurrent segment and this heating gas and media side upstream another segment is the outlet in Heizgasrichtung freely positionable, so that an additional design parameter is available. One particularly suitable means for adjusting the two limit temperatures the targeted positioning is one another the exit of the evaporator Durchlaufheizfläche in Flow direction of the fuel gas seen.

Advantageously, the positioning of the exit is the Evaporator continuous heating surface in relation to the temperature profile of the heating gas in the throttle cable selected such that a maximum deviation is maintained at about 50 ° C, so in terms of on available materials and other design parameters ensures a particularly high level of operational safety is.

A particularly simple and thus also robust construction is achievable by the heating surface especially with regard to Collection and distribution of the flow medium particularly easy is executed. Here is the heating surface for the implementation from all process sections of the complete evaporation, So from preheating, evaporation and at least partial overheating, in a single stage, so without intermediate components to collect and / or distributing the flow medium, suitably formed. Advantageously, therefore, includes a number of the steam generator tubes in each case a plurality of flow medium side alternately cascaded riser pipe sections and downpipes.

A heating takes place both in the riser and in the downpipe pieces instead. Such a circuit of the steam generator tubes, in the case of a heating from the downside durchströmten pipe sections takes place, however, contains in principle a risk for the occurrence of flow instabilities. As it turned out, as one of these possible Causes an occurrence of vapor bubbles in downward flowed through steam generator tubes are considered. If namely, in a downwardly flowed steam generator tube Steam bubbles should form, so these could be in the Rising steam generator tube water column rise and thus a movement counter to the flow direction of the flow medium perform. To such, the flow direction the flow medium opposite movement consistently suppress any existing vapor bubbles, should by a suitable specification of the operating parameters a forced entrainment of the vapor bubbles in the actual Flow direction of the flow medium ensured become. This is achievable by the feeding of the Evaporator Durchlaufheizfläche takes place such that the flow rate the flow medium in the steam generator tubes the desired deadweight on the possibly causes existing vapor bubbles. A comparatively high flow velocity already flowed through in the first down Steam generator tube can be particularly simple Way by a comparatively strong heating of the steam generator tubes at the flow medium side entrance and thereby Conditional rapid increase of the vapor content in the flow medium achieve. For this purpose, the flow medium side is advantageously Entry of the evaporator continuous heating surface designed as a riser pipe and so close to the hot gas side Inlet of the evaporator continuous heating surface arranged, that during operation, the steam generator tubes flowing through Flow medium at the inlet of the first downcomer piece a flow rate of more than a predetermined one Minimum speed has.

The first riser and downcomer pieces preferably form a further heating surface segment arranged in DC circuit, also referred to below as DC segment, which is advantageously arranged in countercurrent circuit Heizflächensegment, in the following also countercurrent segment called upstream flow medium side is connected. By a such arrangement of the segments in the heating gas channel is largely get the advantage of a pure countercurrent circuit, the To transfer heat of the exhaust gas effectively to the flow medium and at the same time a high, inherent security against Dangerous temperature differences on the flow medium side Outcome achieved.

In an alternative advantageous embodiment, the other Heizflächensegment but also in countercurrent to Heizgasrichtung be switched.

Conveniently, the steam generator is used as a heat recovery steam generator a gas and steam turbine plant used. there is the steam generator advantageously heizgasseitig one Gas turbine downstream. In this circuit may suitably behind the gas turbine an additional firing to increase be arranged the heating gas temperature.

With regard to the method, the stated object is achieved by the flow medium in Heizgasrichtung seen at a Position removed from the evaporator Durchlaufheizfläche at which the heating gas temperature prevailing during operation less than a given maximum deviation from the during operation due to the pressure loss in the evaporator continuous heating surface adjusting saturated steam temperature differs.

Advantageously, the flow medium before its exit from the evaporator Durchlaufheizfläche in countercurrent led to the fuel gas, with additional or alternative advantageous embodiment, a maximum deviation of about 50 ° C is specified.

To the emergence of possible flow instabilities consistently To prevent, the flow medium is advantageously already at or immediately after entering the Evaporator continuous heating surface of such a strong heating exposed to it in a first downer of the respective steam generator tube a flow velocity of more than a predetermined minimum speed.

Advantageously, the minimum speed is for taking along generated in the respective first downpipe piece Steam bubbles required flow rate specified. The feeding of the evaporator Durchlaufheizfläche takes place thus such that the comparatively high flow rate already in the first downflowed steam generator tube the desired deadweight on the possibly causes existing vapor bubbles. flow instabilities due to a movement of rising vapor bubbles contrary to the flow direction of the flow medium can thus safely avoided.

The advantages achieved by the invention are in particular in that by the now provided, to the temperature profile the heating gas in the throttle cable adapted positioning the flow-medium-side outlet of the evaporator Durchlaufheizfläche the total in the evaporation of the flow medium Achievable temperature interval between saturated steam temperature of the flow medium and heating gas temperature the exit point is narrowed comparatively narrow, so that regardless of the flow conditions only small outlet-side temperature differences are possible. Thereby can be a sufficient approximation of the temperatures of the flow medium be ensured in any operating condition. In addition, however, it is also ensured that the possible Exit temperatures limited in their absolute height are, so that given by the material properties permissible limit temperatures remain safely below.

An embodiment of the invention will be described with reference to a Drawing explained in more detail. Therein, the FIG shows simplified in Representation in longitudinal section a continuous steam generator in lying construction.

The continuous steam generator 1 according to the FIG is in the manner of a Heat recovery steam generator of a not shown Gas turbine downstream on the exhaust side. The continuous steam generator 1 has a surrounding wall 2, the one in a approximately horizontal, indicated by the arrows 4 Heizgasrichtung x throughflowable gas channel 6 for the exhaust gas from the gas turbine forms. In the heating gas channel 6 is one each Number of heating surfaces designed according to the flow principle, Also referred to as evaporator Durchlaufheizfläche 8, arranged. In the embodiment according to the FIG is only an evaporator pass-through heating surface 8 is shown, but it can also a larger number of evaporator Durchlaufheizflächen be provided.

The evaporator through-flow 8 formed evaporator system is acted upon by flow medium W, the with a single pass through the evaporator Durchlaufheizfläche Evaporates 8 and after exiting the evaporator Durchlaufheizfläche 8 discharged as vapor D and usually superheater heating surfaces supplied for further overheating becomes. The formed from the evaporator Durchlaufheizfläche 8 Evaporator system is in the water-steam cycle, not shown a steam turbine switched. In addition to the evaporator system are in the water-steam cycle of the Steam turbine a number of others, not closer in the FIG switched shown heating surfaces. At the heating surfaces These may be, for example, superheaters, medium-pressure evaporators, Low pressure evaporator and / or act to preheater.

The evaporator passage heating surface 8 of the continuous steam generator 1 according to the FIG. Comprises in the manner of a tube bundle Plural of parallel to the flow of the flow medium W switched steam generator tubes 12. It is in each case a plurality of steam generator tubes 12 in Heizgasrichtung x seen side by side. It is only each one of the juxtaposed steam generator tubes 12th visible, noticeable. The steam generator pipes arranged next to each other 12 is flow side before its entry 13th in the heating gas 6 each have a common inlet collector 14 before and after their exit 16 from the Heizgaskanal. 6 a common outlet header 18 downstream. The Steam generator tubes 12 include a number of the flow medium W in upwardly flowed through riser pieces 20 and downflow through downpipes 22, in each case by flowed through in a horizontal direction overflow 24 are interconnected.

The continuous steam generator 1 is for a particularly high operational Security and consistent suppression of Also referred to as temperature imbalance significant temperature differences at the exit 16 between adjacent ones Steam generator tubes 12 even with a feed with comparatively designed high mass flow densities. Includes the evaporator Durchlaufheizfläche 8 in its flow medium side seen rear area a Heizflächensegment 26, which is connected in countercurrent to the direction of the heating gas x. A Number of each interconnected by overflow 24 Riser pipe pieces 20 and downpipe pieces 22 form In addition, another, in DC to Heizgasrichtung x switched Heizflächensegment 28, which is the Heizflächensegment 26 is connected upstream. Through this circuit is the positioning the outlet 16 seen in Heizgasrichtung x selectable. This positioning is in the continuous steam generator. 1 chosen such that in the case of operation in the evaporator Durchlaufheizfläche 8 adjusting pressure-dependent saturated steam temperature of the flow medium W by less than one predetermined maximum deviation of about 50 ° C from that in the operating case at the position or at the height of the outlet 16 of the Heizflächensegments 26 prevailing heating gas temperature deviates. Since the temperature of the flow medium W at the outlet 16 must always be at least equal to the saturated steam temperature, on the other hand, not higher than that prevailing at this point Heating gas temperature can be, are the possible temperature differences between differently heated pipes even without further countermeasures to the given maximum deviation limited by about 50 ° C.

The arranged in Heizgasrichtung x far ahead in the heating gas duct 6 Another heating surface segment 28 is thus on the heating gas side and flow medium side which is also of a number of each interconnected by overflow 24, in the Counterflow to Heizgasrichtung x flowed through riser pieces 20 and downpipe pieces 22 formed Heizflächensegment 26 downstream.

An arrangement of downwardly flowed pipe sections as the downcomers 22 within the Heizgaskanals 6th is basically only possible if by appropriate measures the stability of the flow within the steam generator tubes 12 is ensured. A heating from downwards namely, through-flow pipe sections can generally for the formation of vapor bubbles in the flow medium W lead, if, due to their low specific Weight against the flow direction of the flow medium W rise, the stability of the flow and thus the operational Safety of the continuous steam generator 1 impair could. On the other hand, a circuit of the Steam generator tubes 12, in which only a heating of the in the upward direction flowed through pipe sections, so the riser pipe pieces 20, takes place, with a high constructive Effort connected.

A particularly simple and therefore robust construction of the Continuous steam generator 1 can be reached by the evaporator Durchlaufheizfläche 8 especially with regard to collection and distribution of the flow medium W particularly simple is and on additional components such as unheated manifolds is omitted. Instead The steam generator tubes 12 each comprise a plurality of flow medium side alternately connected in series Riser pipe pieces 20 and downcomers 22 which within the Heizgaskanals 6 laid, so a heating by the fuel gas are exposed.

The inlet 13 is at the gas inlet of the evaporator Durchlaufheizfläche 8, ie in Heizgasrichtung x far ahead in the heating gas channel 6, arranged. By the arrangement of the entrance 13 in the region of the Heizgaskanals 6, in which the Heating gas has the highest temperature, is a very fast Heating and thus evaporation of the flow medium W achieved in the steam generator tubes 12. Because the flow velocity a water-steam mixture at the same Mass flow rate is higher, the greater the vapor content and thus the specific volume of the mixture is reached the flow medium W in this arrangement of the inlet collector 14 comparatively fast a high flow velocity.

This is particularly favorable to the stability of the in the Steam generator tubes 12 held to ensure flow. An important, the stability of the flow in crucial Dimensionally disabling factor is namely the occurrence of vapor bubbles in the steam generator tubes 12. Due Their low specific weight can be used in steam generator pipes 12 rising steam bubbles rise upwards and thus in the downward flow-through downpipes 22nd perform a movement against the flow direction. There such a movement the stability of the flow crucial the ascendant needs to make better Steam bubbles in the steam generator tubes 12 consistently prevented become. An important criterion for the stability of the Flow is the flow velocity of the flow medium W. It already flowed through in the first down Pipe, so in the first downpipe piece 22, a value, which is at least as high as that for carrying vapor bubbles required speed, so these are with the Flow entrained and a rise contrary to the flow direction safely prevented. By positioning the Entry 13 at the hot gas entrance and the consequent high velocity of the flow medium W already in first downpipe piece 22 is the desired entrainment effect for forming steam bubbles at the same time low constructive Effort ensured.

Claims (15)

Continuous steam generator (1), in which in an approximately horizontal heating gas direction (x) can be flowed through Heating gas duct (6) arranged an evaporator Durchlaufheizfläche (8) is that a number of to flow through a Flow medium (W) connected in parallel steam generator tubes (12), and one of the flow medium (W) in countercurrent heating surface segment (26) through which the heating gas channel (6) can flow includes, the flow-medium-side outlet (16) is positioned in the direction of heating gas (x) in such a way that that in the operating case at the outlet of the evaporator Durchlaufheizfläche (8) adjusting the saturated steam temperature less than a given maximum deviation from that during operation at the position of the exit (16) of the Heizflächensegments deviates from the prevailing heating gas temperature. Continuous steam generator (1) according to claim 1, wherein a Maximum deviation of not more than 70 ° C is specified. Continuous steam generator (1) according to claim 1 or 2, at a number of the steam generator tubes (12) each one Plural of flow medium side alternately connected in series Including riser (20) and downpipe pieces (22). Continuous steam generator (1) according to one of claims 1 to 3, in which the flow-medium-side inlet (13) of the evaporator Durchlaufheizfläche (8) so close to the hot gas side Entry of the evaporator Durchlaufheizfläche (8) arranged is that in the case of operation that the steam generator tubes (12) flowing through flow medium (W) a flow velocity of more than a predetermined minimum speed having. Continuous steam generator (1) according to one of claims 1 to 4, whose evaporator passage heating surface (8) another, the Heizflächensegment (20) strömungsmediumseitig upstream Heating surface segment (22). Continuous steam generator (1) according to claim 5, wherein the another heating surface segment (22) in countercurrent to the direction of the heating gas (x) is switched. Continuous steam generator (1) according to claim 5, wherein the further heating surface segment (22) in the DC to Heizgasrichtung (x) is switched. Continuous steam generator (1) according to one of claims 1 to 7, the heating gas side is preceded by a gas turbine. Method for operating a continuous-flow steam generator (1) with one in an approximately horizontal Heizgasrichtung (x) throughflowable Heizgaskanal (6) with an evaporator Durchlaufheizfläche (8) containing a number of Flow through a flow medium (W) connected in parallel Steam generator tubes (12), wherein the flow medium (W) in Heizgasrichtung (x) seen at a position off the evaporator Durchlaufheizfläche (8) is discharged, at the the heating gas temperature prevailing during operation by less as a predetermined maximum deviation from that in the operating case at the outlet of the evaporator continuous heating surface (8) deviating saturated steam temperature deviates. The method of claim 9, wherein the flow medium (W) before exiting the evaporator continuous heating surface (8) is conducted in countercurrent to the heating gas. A method according to claim 9 or 10, wherein a maximum deviation of not more than 70 ° C is given. Method according to one of claims 9 to 11, wherein the Flow medium (W) already at or immediately after the Entry into the steam generator tubes (12) of such a strong Heating is exposed to it in a first downpipe section (24) of the respective steam generator tube (12) a Flow rate of more than a predetermined minimum speed having. Method according to Claim 12, in which the minimum speed the to take with in the respective first downpipe piece (22) generated vapor bubbles required flow rate is given. Method according to one of claims 9 to 13, wherein the Flow medium (W) after its entry into the evaporator Durchlaufheizfläche (8) guided in countercurrent to the heating gas becomes. Method according to one of claims 9 to 13, wherein the Flow medium (W) after its entry into the evaporator Durchlaufheizfläche (8) in cocurrent to the fuel gas becomes.

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