EP2324285B1 - Heat recovery steam generator - Google Patents

Description

The invention relates to a heat recovery steam generator with a number of evaporator tubes connected in parallel on the flow medium side, through which a number of superheater tubes are connected via a water separation system, wherein the water separation system comprises a number of water separation elements, each of which downstream of a number of evaporator tubes and / or a number of superheater tubes upstream, wherein each of the Wasserabscheideelemente comprises a connected to the respective upstream evaporator tubes Einströmrohrstück, seen in its longitudinal direction merges into a Wasserableitrohrstück, wherein in the transition region a number of Abströmrohrstücken branches, which are connected to an inlet header of the respective downstream superheater tubes.

A heat recovery steam generator is a heat exchanger that recovers heat from a hot gas stream. Heat recovery steam generators are used, for example, in gas and steam turbine power plants, in which the hot exhaust gases of one or more gas turbines are conducted into a heat recovery steam generator. The steam generated therein is then used to drive a steam turbine. This combination produces electrical energy much more efficiently than gas or steam turbine alone.

Heat recovery steam generators can be categorized by a variety of criteria: based on the flow direction of the gas flow, heat recovery steam generators can be classified, for example, into vertical and horizontal types. Furthermore, there are steam generator with a plurality of pressure stages with different thermal states of the water-steam mixture contained in each case.

Steam generators can generally be designed as natural circulation, forced circulation or continuous steam generators. In a continuous steam generator, the heating of evaporator tubes leads to a complete evaporation of the flow medium in the evaporator tubes in one pass. The flow medium - usually water - is supplied to the evaporator tubes downstream superheater tubes after its evaporation and overheated there. The position of the evaporation end point, d. H. the point of transition from a flow with residual moisture to pure steam flow, is variable and mode-dependent. During full load operation of such a continuous steam generator, the evaporation end point is, for example, in an end region of the evaporator tubes, so that the overheating of the evaporated flow medium already begins in the evaporator tubes.

In contrast to a natural or forced circulation steam generator, a continuous steam generator is not subject to any pressure limitation, so that it can reach steam pressures far above the critical pressure of water (p _crit ≈ 221 bar) - at which water and steam can not occur simultaneously at any temperature and therefore no phase separation is possible - can be designed.

In order to ensure reliable cooling of the evaporator tubes, such a continuous steam generator is normally operated with a minimum flow of flow medium in the evaporator tubes during low-load operation or during start-up. The operationally provided minimum flow of flow medium in the evaporator tubes is thus not fully evaporated during startup or during low load operation in the evaporator tubes, so that in such a mode at the end of the evaporator tubes still unevaporated flow medium, d. H. a water-steam mixture are present.

Since the evaporator tubes downstream of the continuous steam generator superheater tubes usually not for a relatively large flow unvaporized flow medium are designed continuous flow steam generators are usually designed so that even when starting and during low load operation excessive water ingress into the superheater pipes is safely avoided. For this purpose, the evaporator tubes are usually connected to the superheater tubes connected downstream via a Wasserabscheidesystem. The water separator causes a separation of the emerging during the start or in low load operation of the evaporator tubes water-steam mixture in water and in steam. The steam is fed to the superheater tubes connected downstream of the water separation system, whereas the separated water can be returned to the evaporator tubes, for example via a circulation pump, or removed via a decompressor.

The Wasserabscheidesystem can include a variety of Wasserabscheideelementen that are integrated directly into the tubes. In this case, in particular each of the parallel-connected evaporator tubes may be assigned a Wasserabscheideelement. The Wasserabscheideelemente can continue to be designed as a so-called T-piece Wasserabscheideelemente. In this case, each T-piece water separation element in each case comprises an inflow pipe piece connected to the upstream evaporator pipe, which, as seen in its longitudinal direction, merges into a water drainage pipe piece, wherein an outflow pipe piece connected to the downstream superheater pipe branches off in the transition region.

By this construction, the T-piece Wasserabscheideelement is designed for a Trägheitsseparation of the flowing from the upstream evaporator tube in the Einströmrohrstück water-steam mixture. Because of its comparatively higher inertia, namely, the water content of the flow medium flowing in the inflow pipe piece flows preferably further in the axial extension of the inflow pipe piece at the transition point and thus passes into the water diverter pipe piece and from there usually continues into a connected collecting container. The vapor content of the inflow pipe section flowing water-steam mixture, however, can better follow a forced deflection due to its relatively lower inertia and thus flows through the Abströmrohrstück to the downstream superheater pipe section. A designed for continuous operation heat recovery steam generator of this type is for example from the EP 1 701 090 A1 and the EP 1 701 091 A1 known.

In a continuous steam generator with such a designed Wasserabscheidesystem can be done by the decentralized integration of the water separation in the individual tubes of the pipe system of the continuous steam generator water separation without prior collection of effluent from the evaporator tubes flow medium. Thus, a direct transfer of the flow medium in an inlet header of the downstream superheater tubes is possible.

Due to the design, the transfer of flow medium to the superheater tubes is not only limited to steam, but now a water-steam mixture can be continued to the superheater tubes by the Wasserabscheideelemente be fed. As a result, the evaporation end point can be pushed into the superheater tubes as needed. Thus, a particularly high operational flexibility can be achieved even in start-up or low load operation of the continuous steam generator. In particular, the live steam temperature can be controlled in comparatively large limits by influencing the feedwater quantity.

However, it should be noted in such systems that, due to the integration of the water separation function into the individual tubes, a comparatively high number of individual tube pieces or elements is required, especially in the region of the separation system.

The invention is therefore based on the object to provide a heat recovery steam generator of the type mentioned above, while maintaining a particularly high operational flexibility a comparatively low design and repair costs brings with it.

This object is achieved according to the invention by arranging a distributor element on the steam side between the respective water separation element and the inlet header of the subsequent heating surface.

The invention is based on the consideration that the decentralized separation of water, which takes place separately in each of the parallel-connected evaporator tubes in the construction described above, a comparatively large number of T-piece Wasserabscheideelementen can lead to design problems in large-scale application. Due to the space problems that may be associated with the need to accommodate such a large number of water separation elements, such a construction may also entail significant additional costs and restrictions on the heat recovery steam generator's geometric parameters due to the high design effort involved.

A reduction in the design cost of the heat recovery steam generator could be achieved by simplifying the design of the water separation system. For this purpose, the number of Wasserabscheideelemente used can be reduced. However, in order to obtain the advantages of decentralized water separation, such as the possibility of feeding with water-steam mixture, the basic construction in the form of T-piece water separation elements should be maintained. The combination of the two aforementioned concepts can be achieved by a collection of the flow medium from a plurality of evaporator tubes in each case a Wasserabscheideelement.

Due to a reduced number of tee-Wasserabscheideelementen direct steam-side forwarding to the inlet header of the downstream superheater tubes, however, to inhomogeneities in the distribution to the various Conduct superheater pipes. Therefore, in order to achieve a uniform distribution to the downstream superheater tubes after the exit of the steam or water-steam mixture from the T-piece Wasserabscheideelement, a distributor element is arranged on the steam side between the respective Wasserabscheideelement and the inlet header.

Advantageously, the geometric parameters of a number of outlet pipes are chosen such that a homogeneous flow distribution is ensured on the inlet header of the respectively downstream superheater pipes. As a result, a homogeneous entry is already achieved in the inlet header, which continues accordingly in the downstream superheater tubes. The outlet tubes can, for example, have the same diameter and be guided at equal intervals parallel to one another in the inlet header.

In an advantageous embodiment, the distributor element is designed as a star distributor, d. H. it comprises a baffle plate, an inlet tube arranged perpendicular to the baffle plate, and a number of outlet tubes arranged in a star shape around the baffle plate in the plane thereof. The inflowing water impinges on the baffle plate and is distributed in a symmetrical manner perpendicular to the inflow direction and directed into the outlet tubes. In this case, the baffle plate in a particularly advantageous embodiment is circular and the exit tubes arranged concentrically to the center of the baffle plate at equal intervals to the respective adjacent outlet tubes. In this way, a particularly homogeneous distribution is ensured on the different outlet pipes.

It is advantageously provided between 5 and 20 outlet pipes per distribution element. With a smaller number, a sufficient homogenization of the entry of steam or water-steam mixture in the inlet header could no longer be guaranteed, while a higher number problematic in the geometric configuration of the distributor element may be, especially if this is designed as a star distributor.

In one embodiment of the water separation system as a T-piece separator there is the possibility of overfeeding, d. H. Forwarding of water-steam mixture in the superheater pipes. Any irregular flow created in the evaporation process will thus continue in the T-piece water separator elements and the downstream superheater tubes.

Such turbulent flows can occur in particular in the form of so-called slugs, which are caused by the different flow velocities of vaporized and unevaporated flow medium in the tubes. The result is a wave-like movement that causes a pulsating mass flow, which can lead to mechanical and thermal loads on the Wasserabscheideelemente and also the downstream superheater tubes. To avoid this, measures should be taken against the further propagation of the turbulence from the evaporator tubes into the T-piece water separator elements and the downstream superheater tubes. This should be done before the water-steam mixture in the T-piece Wasserabscheideelemente. For this purpose, in each case a flow turbulence damper is provided in the inflow pipe sections of a number of water separation elements in an advantageous embodiment.

Among other things, the turbulences in the pipe system arise because two different phases of the flow medium flow through the pipe system parallel to one another. At the interface of the two phases, vortices occur at widely differing flow velocities, resulting in a rapid local displacement of the interface between the two phases in the form of a wave-like motion.

With particularly strong turbulent flow, these waves can become so large that they cover the entire pipe cross-section Close, and there are so-called slugs, ie areas with non-vaporized flow medium and large mass, in alternation with mainly filled by steam areas, with a much lower mass. These slugs generate a pulsatile mechanical load on the entire pipe system. In order to deliberately destroy these slugs and to restore a uniform flow, the flow turbulence dampers in an advantageous embodiment each comprise a number of bulkheads, each of which closes a part of the pipe cross section. The slugs break at the bulkheads, some of the water is held back and distributed to the area following the slug, mainly dominated by steam. Thus, the waves are smoothed and pulsation-free operation is achieved by smoothing the wave motions.

In order to functionally arrange the components necessary for the refraction of the slugs in the tubes arranged upstream of the water separation elements, the direction of oscillation of the wave movements entering the flow turbulence absorbers should be known and predictable. In particular, possible swirling movements of the inflowing water-vapor mixture should be suppressed, as these could hinder the operation of the flow turbulence damper. For this purpose, the flow turbulence dampers on the tube inner wall advantageously comprise a number of guide profiles aligned in the main flow direction of the flow medium. Through the guide profiles a possible swirling motion of the water vapor mixture is stopped and the water vapor mixture is introduced in such a geometric position in the flow turbulence damper that they can fulfill their task appropriately.

In order to allow a particularly simple construction of the flow turbulence dampers, the flow turbulence dampers can be introduced directly during the production of the tubes. For this purpose, the flow turbulence dampers are advantageously made of a material having the same material as the tube or similar composition. This also prevents too high a mechanical stress on the pipes, which would arise with different materials for pipes and flow turbulence dampers and / or the guide profiles by the different thermal expansion properties.

The advantages achieved by the invention are in particular that a uniform distribution of the flow medium is achieved on the superheater tubes by the vapor-side arrangement of an additional distribution element between the respective Wasserabscheideelement and the inlet header of the superheater heating even at a much lower number of Wasserabscheideelementen. These measures make it possible to reduce the number of water separation elements in the first place. This means a much lower production cost and a comparatively lower complexity of the pipe system of the heat recovery steam generator and it is a particularly high operational flexibility even in start-up or low load operation achievable.

FIG 1

den Verdampfer eines Abhitzedampferzeugers mit horizontalem Rauchgaspfad in seitlicher Ansicht,

FIG 2

den Verdampfer eines Abhitzedampferzeugers aus FIG 1 in der Aufsicht,

FIG 3

den Verdampfer eines Abhitzedampferzeugers aus den FIG 1 und 2 in Richtung des Rauchgaspfades gesehen,

FIG 4

den Verdampfer eines Abhitzedampferzeugers mit vertikalem Rauchgaspfad in seitlicher Ansicht, und

FIG 5

ein T-Stück-Wasserabscheideelement.

An embodiment of the invention will be explained in more detail with reference to a drawing. Show:

FIG. 1

the evaporator of a heat recovery steam generator with horizontal flue gas path in lateral view,

FIG. 2

the evaporator of a heat recovery steam generator FIG. 1 in the supervision,

FIG. 3

the evaporator of a heat recovery steam generator from the FIG. 1 and 2 seen in the direction of the flue gas path,

FIG. 4

the evaporator of a heat recovery steam generator with vertical flue gas path in a side view, and

FIG. 5

a tee water separator.

Like parts are given the same reference numerals to all figures.

The FIG. 1 shows the schematic representation of a heat recovery steam generator 1 with horizontal flue gas path. The flow medium M is fed into the pipe system by an upstream feed pump not shown in detail. Initially, it flows into a number of evaporator inlet collectors 2, which ensure the distribution of the flow medium M to four evaporator heating surfaces with evaporator tubes 4, in which then an evaporation of the flow medium takes place. Optionally, further evaporator heating surfaces may be connected upstream or the heating surfaces may be arranged in different geometrical configurations in the heating gas channel.

In each case, a number of evaporator tubes 4 opens into a via a first evaporator outlet header 6 and a second outlet header 8 in a common transition pipe section 10, which is the T-piece Wasserabscheideelement 12 downstream. The T-piece Wasserabscheideelement comprises a Einströmrohrstück 14, which is seen in its longitudinal direction merges into a Wasserableitrohrstück 16, wherein in the transition region, a Abströmrohrstück 18 branches off. The Wasserableitrohrstück 16 opens into a Abschlämmleitung 20, which is arranged downstream of a collecting tank 22 arranged outside the flue gas duct. To the collecting tank 22, an outlet valve 24 is connected, via which the separated water can either be discarded or re-fed to the evaporation cycle.

In the T-piece water separation element 12, flow medium M enters through the inflow pipe piece 14. The proportionate water W flows due to its inertia in the longitudinal direction following Wasserableitrohrstück 16. The vapor D, however, follows due to its lower mass imposed by the pressure ratios deflection in the Abströmrohrstück 18. The Abströmrohrstück 18 are the superheater tubes 26 in two Überhitzerheizflächen over a superheater inlet collector 28 downstream. The superheater tubes 26 eventually open in a superheater outlet header 30. The vapor D is collected there and fed through the steam outlet 32 for its further use; Usually one is in the FIG. 1 not shown in detail device such as a steam turbine provided.

If necessary, the outlet valve 24 can be closed and thus an overfeed of the T-piece Wasserabscheideelemente 12 be brought about. In this case, still unevaporated water W enters the superheater tubes 26, so that they can still be used for further evaporation, d. h., The evaporation end point can be moved into the superheater tubes, which allows a relatively higher flexibility in the operation of the heat recovery steam generator 1.

In order to allow a particularly simple construction of the heat recovery steam generator 1, a comparatively smaller number of T-piece water separation elements 12 should be used. In order to compensate for the resulting inhomogeneities in terms of distribution to the superheater tubes and thus to allow such a configuration in the first place, the T-piece Wasserabscheideelementen distribution elements 34 are interposed in the manner of star distributors. These provide for a pre-distribution of the flow medium M in the event of over-feeding of the T-piece Wasserabscheideelemente 12 on the superheater inlet collector 28th

The operation of the distribution elements 34 in the form of star distributors is in the plan of the heat recovery steam generator 1 according to FIG. 2 seen. Also recognizable are the first and second evaporator outlet collectors 6, 8, furthermore the T-piece water separation elements 12, the drainage line 20 and the collecting container 22.

In the distributor elements 34 designed as a star distributor, the flow medium M impinges on a circular baffle plate and bounces from there into star-shaped, concentrically-symmetrically arranged outlet tubes 36 Arrangement of the output shown in the embodiment eight output tubes 36 is assigned to each output tube 36 about the same amount of flow medium M. These open at equal intervals in the superheater inlet header 28, so that there is already a pre-distribution of the flow medium M to the entire width of the superheater inlet header 28.

The further introduction from the superheater inlet header 28 into the superheater tubes 26 is based on FIG. 3 clearly showing the heat recovery steam generator 1 from the direction of the flue gas inlet. Visible are the second evaporator outlet header 8, further the T-piece Wasserabscheideelemente 12, the Abschlämmleitung 20, the sump 22 with the outlet valve 24, further the distributor elements 34 with the discharge pipes 36, which open into the superheater inlet header 28.

FIG. 3 shows clearly the advantages of the pre-distribution: Through the distribution elements 34, the flow medium M is already distributed over the eight outlet pipes in each case homogeneously over the entire width of each superheater inlet collector 28. In a direct introduction of the flow medium M via a single line per T-piece Wasserabscheideelement 12, the flow medium M in the superheater inlet collectors 28 could not be evenly distributed, as these due to the width of the superheater heating not for such a homogeneous distribution of, for example, a single supply are suitable.

FIG. 4 shows an alternative embodiment, namely a heat recovery steam generator 1 with vertical flue gas direction in a side view. The components and their function are substantially identical to that in the 1 to 3 shown steam generator, only the evaporator tubes 4 and the superheater tubes 26 are arranged horizontally. The evaporator tubes 4 are repeatedly guided in turns through the Heizgaskanal.

Due to the smaller number of T-piece Wasserabscheideelementen 12 each of these elements is relatively larger dimensions. In order to avoid a comparatively high mechanical load on these T-piece water separation elements and the superheater tubes 4 downstream of them at such a higher admission with flow medium M, flow turbulence dampers 38 are provided in an area upstream of the T-piece water separation elements 12. These may for example be mounted in an outlet region of the evaporator tubes 4, in the illustrated embodiment, they are introduced in the inflow pipe section 14 of the T-piece Wasserabscheideelements 12, which separately in FIG. 5 is shown.

For example, the flow turbulence dampers 38 may include a number of bulkheads or guide profiles that may be fabricated from the same material as the inflow tubing 14. With regard to their geometric parameters, they can furthermore be adapted to the local flow conditions provided during operation.

By the flow turbulence damper 38 slugs and other turbulent flows are reduced and reduces the mechanical load on the downstream components. In particular, in the vertical kinking areas of the Abströmrohrstücks 18 and the Wasserableitrohrstücks 16 thus a pulsation-free operation even with a comparatively large dimensioning of the T-piece Wasserabscheideelemente 12 is possible.

Claims (8)

1. Waste heat steam generator (1) with a number of evaporator tubes (4) connected in parallel on the flow medium side, downstream of which is connected a number of superheater tubes (26) via a water separation system, wherein the water separation system comprises a number of water separation elements (12) upstream of each of which is connected a number of evaporator tubes (4) and/or a number of superheater tubes (26), wherein each of the water separation elements (12) comprises an inflow tube section (14) connected to the respective upstream evaporator tubes (4) which, when seen in its longitudinal direction, extends into a water evacuation tube section (16), wherein a number of outflow tube sections (18) branches off in the transitional area,
   characterised in that the outflow tube sections (18) are connected to an inlet collector (28) of the respective downstream superheater tubes (26) and wherein a distributor element (34) is arranged on the steam side between the respective water separation element (12) and the inlet collector (28).
2. Waste heat steam generator (1) according to claim 1, in which the respective distributor element (34) comprises a baffle plate, an inlet tube arranged at right angles to the baffle plate and a number of outlet tubes (36) arranged in a star shape around and level with the baffle plate.
3. Waste heat steam generator (1) according to claim 2, in which the baffle plate is circular in shape and the outlet tubes (36) are arranged concentric to the centre of the baffle plate equally spaced from the respective adjacent outlet tubes (36).
4. Waste heat steam generator (1) according to one of claims 1 to 3, in which the respective distributor element (34) comprises between five and 20 outlet tubes (36).
5. Waste heat steam generator (1) according to one of claims 1 to 4, in which a flow turbulence damper (38) is provided in each of the inflow tube sections (14) of a number of water separation elements (12).
6. Waste heat steam generator (1) according to claim 5, in which the flow turbulence damper (38) comprises a number of bulkheads in each case which each close off a part of the tube cross-section.
7. Waste heat steam generator (1) according to claim 5 or 6, in which the flow turbulence damper (38) on the inner wall of the tube has a number of guide profiles aligned in the main flow direction of the flow medium.
8. Waste heat steam generator (1) according to one of claims 5 to 7, in which the flow turbulence damper (38) is made of a substance with a composition the same as or similar to the tube material.

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