EP2324285A2

EP2324285A2 - Waste heat steam generator

Info

Publication number: EP2324285A2
Application number: EP09782665A
Authority: EP
Inventors: Jan BRÜCKNER; Joachim Franke; Holger Schmidt; Frank Thomas
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2008-09-09
Filing date: 2009-09-07
Publication date: 2011-05-25
Anticipated expiration: 2029-09-07
Also published as: RU2011113827A; WO2010029033A3; CN102171513B; EP2204611A1; PL2324285T3; ES2614155T3; CN102171513A; WO2010029033A2; US8701602B2; US20110162594A1; EP2324285B1

Abstract

The invention relates to a waste heat steam generator (1) having a plurality of evaporator tubes (4) which are connected in parallel on the flow medium side, a plurality of overheating tubes (26) being mounted downstream of the evaporator tubes by means of a water separation system. Said water separation system comprises a number of water separating elements (12), each water separation element being respectively mounted downstream of a plurality of evaporator tubes (4) and/or upstream of a plurality of overheating tubes (26). Each water separating element (12) comprises an inlet pipe (14) which is respectively connected upstream to the evaporator tubes (4), said inlet pipe extending into a water evacuation pipe when seen in the longitudinal direction. A plurality of outflow pipes (18) branch off in the transitional area, said pipes being connected to a inlet collector (28) of the overheating tubes (26) which are respectively connected downstream. The aim of the invention is to provide said type of waste heat steam generator which is characterised in that it has a particularly high level of operational flexibility with comparatively low construction and reparation complexity. As a result, a distribution element (34) is arranged on the steam side between the respective water separating element (12) and the inlet collector (28).

Description

description

heat recovery steam generator

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, ie 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 located, for example, in an end region of the evaporator tubes, so that the overheating of the vaporized 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 at any temperature at the same time, and thus 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 when starting or in the

Low load operation in the evaporator tubes is not completely evaporated, 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 superheater tubes connected downstream of the evaporator tubes of the continuous-flow steam generator are usually not suitable for a relatively large flow of unvaporized flow. are designed medium, continuous steam generators are usually designed so that even when starting and during low load operation excessive water ingress into the superheater tubes is safely avoided. For this purpose, the evaporator tubes are usually connected to the superheater tubes connected downstream via a water separation system. 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 downstream of the Wasserabscheidesystem

Superheater tubes supplied, whereas the separated water can be supplied to the evaporator tubes again, for example via a circulation pump or discharged via a decompressor.

The Wasserabscheidesystem may include a plurality of Wasserabscheideelementen that are integrated directly into the tubes. In this case, in particular each of the evaporator tubes connected in parallel can be assigned a water separation element. 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, viewed 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 for inertial separation of the flowing from the upstream evaporator tube in the Einströmrohrstück water-steam mixture is designed. Because of its comparatively higher inertia, namely, the water content of the flow medium flowing in the inflow pipe section at the transition point preferably continues in the axial extension of the inflow pipe section and thus enters the water diverter pipe section and from there usually further into a connected collecting tank. 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 waste heat steam generator of this design designed for continuous operation is known, for example, from EP 1 701 090.

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. This also allows a direct transfer of the flow medium into an inlet header of the downstream superheater tubes.

In addition, 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 water separation elements are over-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 design 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 the water-steam mixture from the T-piece Wasserabscheideelement, a distributor element is arranged on the steam side between see 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-vapor mixture in the inlet header can no longer be guaranteed, while a higher number is problematic in the geometric design of the distributor ment, 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.

The turbulences in the pipe system are caused, among other things, by two different phases of the flow medium flowing parallel to one another through the pipe system. 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 create 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 movements.

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 turbine damper, the flow turbulence dampers can be introduced directly during the production of the pipes. 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 in the case of different materials for pipes and flow turbulence dampers and / or the guide profiles as a result of 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 even at a much lower number of Wasserabscheideelementen by the vapor-side arrangement of an additional loan distribution element between the respective Wasserabscheideelement and the inlet header of the superheater. These measures will reduce the number of

Wasserabscheideelementen ever enabled. This means a considerably lower production outlay and a comparatively lower complexity of the pipe system of the heat recovery steam generator, and a particularly high level of operational flexibility can also be achieved, even during start-up or low-load operation.

An embodiment of the invention will be described with reference to a

Drawing explained in more detail. Show:

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

2 shows the evaporator of a heat recovery steam generator

1 in the plan view, FIG. 3 shows the evaporator of a heat recovery steam generator from FIGS. 1 and 2 in the direction of the flue gas path,

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

5 shows a T-piece Wasserabscheideelement.

Like parts are given the same reference numerals to all figures. 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 provide for 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 can also be connected upstream or the heating surfaces can be arranged in different geometrical configurations in the heating gas duct.

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. An outlet valve 24 is connected to the collection container 22, via which the separated water can either be discarded or re-supplied to the evaporation circulation.

In the T-piece water separation element 12, flow medium M enters through the inflow pipe piece 14. Due to its inertia, the proportionate water W flows into the water drainage pipe piece 16 which follows in the longitudinal direction. The steam D, on the other hand, follows the diversion into the outflow pipe piece 18 due to its lower mass. The overflow pipe piece 18 is superposed in two superheater heating surfaces downstream of a superheater inlet collector 28. 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, a device not shown in detail in FIG. 1, for example a steam turbine, is 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, unevaporated water W enters the superheater tubes 26 so that they can still be used for further evaporation, ie. 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 with regard to the distribution to the superheater tubes and thus to enable such an embodiment in the first place, distribution elements 34 are interposed in the manner of star distributors to the T-piece water separation elements. These provide for a pre-distribution of the flow medium M in the event of over-feeding of the T-piece Wasserabscheideelemente 12 to the superheater inlet collector Δ O QO.

The mode of operation of the distributor elements 34 in the form of star distributors can be seen in the plan view of the heat recovery steam generator 1 according to FIG. 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 clear from FIG. 3, which shows 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 clearly shows the advantages of the pre-distribution: Through the distributor elements 34, the flow medium M is already distributed homogeneously over the entire width of each superheater inlet collector 28 via the respective eight outlet tubes. 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.

4 shows an alternative embodiment, namely a heat recovery steam generator 1 with a vertical flue gas direction in a side view. The components and their function are essentially identical to the steam generator shown in FIGS. 1 to 3, 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 can be mounted, for example, in an outlet region of the evaporator tube 4, in the exemplary embodiment shown they are introduced into the inflow pipe section 14 of the tee water separation element 12, which is shown separately in FIG.

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 Abströmrohr- piece 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

claims

A heat recovery steam generator (1) having a number of evaporator tubes (4) connected in parallel on the flow medium side, with a number of superheater tubes (26) connected downstream via a water separation system, the water separation system comprising a number of water separation elements (12) each downstream of a number of evaporator tubes (4) and / or upstream of a number of superheater tubes (26), wherein each of the Wasserabscheideelemente (12) connected to the respective upstream evaporator tubes (4) Einströmrohrstück (14), in its longitudinal direction seen in a Wasserableitrohrstück (16) merges, wherein in the transition region a number of Abströmstromstücken (18) branches off, which are connected to an inlet header (28) of the respective downstream superheater tubes (26), and wherein the steam side between the respective Wasserabscheideelement (12) and the inlet header (28) a distributor element (34) angeo rdnet is.

2. heat recovery steam generator (1) according to claim 1, wherein the geometric parameters of a number of outlet pipes (36) of the respective distributor element (34) are selected such that a homogeneous flow distribution on the Eintrittssamm- ler (28) of the respective downstream superheater tubes (26 ) is guaranteed.

3. heat recovery steam generator (1) according to claim 1 or 2, wherein the respective distributor element (34) comprises a baffle plate, arranged perpendicular to the baffle input tube and a number of star-shaped arranged around the baffle plate in the plane of the output tubes (36).

4. heat recovery steam generator (1) according to claim 3, wherein the baffle plate is circular and the outlet tubes (36) are arranged concentrically to the center of the baffle plate at equal intervals to the respective adjacent outlet tubes (36).

5. heat recovery steam generator (1) according to one of claims 1 to

4, in which the respective distributor element (34) comprises between five and 20 outlet tubes (36).

6. heat recovery steam generator (1) according to one of claims 1 to

5, wherein in the Einströmrohrstücken (14) a number of Wasserabscheideelementen (12) each have a flow turbulence damper (38) is provided.

7. heat recovery steam generator (1) according to claim 6, wherein the

Flow turbulence damper (38) each comprises a number of bulkheads, each closing a part of the pipe cross-section.

8. heat recovery steam generator (1) according to claim 6 or 7, wherein the flow turbulence damper (38) on the pipe inner wall comprises a number of aligned in the main flow direction of the flow medium guide profiles.

9. heat recovery steam generator (1) according to one of claims 6 to

8 wherein the flow turbulence dampeners (38) are made of a material having a similar or similar composition to the tubing.