EP2184536A1 - Steam generator pipe, accompanying production method and once-through steam generator - Google Patents

Abstract

A steam generator tube (10), in whose tube interior (22) at least one tube insert (18, 18 ', 18 ") is arranged to form a swirl-producing inner profile, is intended to have a particularly favorable heat transfer behavior in the case of simple and cost-effective production and a wide range of different operating conditions For this purpose, according to the invention, the tube insert (18, 18 ', 18 ") is formed by a profile wire (20) wound on the tube inner wall (24) in the manner of a helical spring.

Description

The invention relates to a steam generator tube, in which tube interior at least one tube insert is arranged to form a swirl-producing inner profile. It further relates to a continuous steam generator with such steam generator tubes. The invention further relates to a method for producing a steam generator tube provided with a swirl-producing inner profile.

In the combustion chamber walls of a continuous steam generator, gas-tightly welded steam generator tubes are usually used with one another via webs to form a throttle cable surrounding the combustion chamber, which are connected in parallel for the flow of a flow medium. Instead of tubes with separate, separate flat iron bars in between, it is also possible to use tubes which are already factory-equipped with molded fins. The steam generator tubes can be arranged vertically or obliquely. For a reliable operating behavior of the continuous steam generator, the steam generator tubes are generally designed such that sufficient cooling of the steam generator tubes is ensured even at low mass flow densities of the steam generator tubes flowing medium.

An important design criterion is the heat transfer properties of a steam generator tube. A high heat transfer allows a particularly effective heating of the medium flowing through the steam generator tube with simultaneous reliable cooling of the steam generator tube per se. The heat transfer behavior of a steam generator tube can be affected by the occurrence of so-called boiling crises in fossil-heated steam generators, which are operated at subcritical pressures. The pipe wall is no longer affected by the liquid flow medium - usually water - wetted and thus insufficiently cooled. Due to the higher material temperatures, the strength values of the pipe wall could then be reduced.

To improve the heat transfer behavior usually steam generator tubes are used, which have as a result of a deformation process (eg cold drawing) on its inside a surface structure or an inner profile in the form of helically wound ribs. Due to the shape of the ribs, a swirl is impressed on the medium flowing through the steam generator tube, so that the heavier liquid phase collects on the tube inner wall as a result of the acting centrifugal forces and forms a wetting liquid film there. This ensures a sufficiently high heat transfer from the pipe inner wall to the flow medium even at comparatively high heat flux densities and low mass flow densities.

A disadvantage of the known internal finned steam generator tubes that they are relatively expensive to produce due to the limited deformability of the pipe material. In particular, in high-temperature steels with high chromium content, the deformability is severely limited. Such materials are playing an increasingly important role in steam generator tubes today, since they permit - at least in principle - a design of a steam generator for particularly high steam parameters, in particular for high live steam temperatures, and consequently particularly high efficiencies. Due to the material-related limitations in processing, however, it is not possible in practice or only with considerable effort to produce internally ribbed tubes with the desired, fluidically advantageous rib profiles in the context of a deformation process of smooth tubes. In particular, sufficiently steep flank angles and sharp-edged transitions in connection with large rib heights are difficult to produce. In addition, the height of the ribs is manufacturable only within a narrow frame. In addition, results There is only a slight flexibility with regard to the profile design along the pipe.

For these reasons, only the use of plain tubes, ie without internal ribbing, is currently being considered for the design and conception of modern steam generators with so-called ultra-high steam conditions. Due to the comparatively poorer heat transfer conditions in these smooth steam generator tubes against innenberippten pipes must therefore be selected in the design of the steam generator, a comparatively high mass flow density for the flow medium to ensure a sufficiently high heat transfer and thus reliable cooling of the steam generator tubes. Accordingly, in order to be able to keep the number of steam generator tubes suitably low for the same overall throughput, a bore in the form of a helical winding must be used for the design of the steam generator mentioned instead of a so-called vertical bore, in which the steam generator tubes are essentially vertically guided and form the enclosing walls of the combustion chamber the steam generator tubes are selected in the combustion chamber walls. As a result, however, the combustion chamber construction becomes undesirably more complex and complex, and due to the geometry-related larger pipe lengths, higher pressure losses must be accepted.

Alternatively, various types of swirl-producing components have already been proposed for subsequent installation in a steam generator tube. These include, in particular, the so-called "twisted tapes": strips made of a metal strip that are twisted or twisted. However, the tube fittings known hitherto have the disadvantage in common that on the one hand they obstruct the (originally) free cross section in the center of the tube and therefore lead to very high pressure losses, and on the other hand they divert the entire flow extremely strongly and in some cases "overdrive". , A simple twisted tape z. B. leads to accumulation at higher vapor contents in the two-phase flow the water phase in the gusset between the pipe wall and the tape with simultaneous drying and thus insufficient cooling of the inner wall areas leeward of the tape. Steam generator tubes with inserts in the type of twisted tapes are therefore not equally suitable for all operating conditions usually occurring in steam generators.

Alternatively, a steam generator tube is known in the tube interior to form a swirl-producing inner profile at least one tube insert is arranged. This comprises at least one sheet metal frame with a number of large-area recesses, wherein the insert is twisted in the longitudinal direction. The recesses allow the trouble-free passage of the flow medium in the longitudinal direction of the steam generator tube.

The invention is now based on the object of specifying a still further improved steam generator tube of the type mentioned, which has a particularly favorable heat transfer behavior in a simple and inexpensive held production and a wide range of different operating conditions. Furthermore, a production method suitable for the production of such a steam generator tube as well as a continuous steam generator are to be specified, which has a particularly simple design with high operational safety and high efficiency.

With respect to the steam generator tube, the object is achieved according to the invention by the tube insert is formed by a wound in the manner of a coil spring, guided on the tube inner wall profile wire.

The invention is based on the consideration that the design of the tube insert to form the swirl-producing inner profile should consistently comply with the basic design criteria for use in the steam generator tube, namely in particular both the provision of a suitable swirl-producing inner profile by recourse on the screw contour as well as a substantial avoidance of unnecessary pressure losses, as they could arise by blocking the central flow path in the steam generator tube. To be able to provide a reliable surface structure against this background with particularly simple means, the design of the tube insert is essentially provided as a helical spring.

The tube insert and thus the profiled wire forming this can extend over the entire length of the steam generator tube away. Alternatively, in a preferred embodiment, but also a piece or sectional introduction of the swirl-producing tube insert may be provided, preferably in particular in those zones of the steam generator tube in which the operation of the steam generator due to design is expected to be particularly high heat input due to particularly high local heating , appropriate pipe inserts are provided.

In order to allow a comparatively simple introduction of the tube insert into the tube interior of the steam generator tube, preferably by inserting, the dimensions of the individual components are advantageously selected correspondingly suitable. In particular, the helical spring formed by the profile wire in the load-free state, ie in the mechanically and thermally unloaded state, has an outer diameter that is at least 1 mm smaller than the inner diameter of the tube. This allows a comparatively simple introduction of the tube insert into the tube interior under normal working conditions, wherein, in addition, effects of induced changes in length can be suitably compensated in this way. As has been found out, during the steam generator operation, a temperature difference of up to 100 K and more may arise between the actual steam generator tube and the profile wire serving as the inner profile. The resulting difference in length between the steam generator tube and the profile wire can be absorbed by elastic deformation of the helically wound profile wire.

In a particularly advantageous embodiment, the components of the steam generator tube are designed such that after introduction of the tube insert in the tube interior compared to conventionally used innenberippten tubes as far as possible comparable flow and operating characteristics are obtained. For this purpose, the profile wire advantageously has a substantially rectangular cross-section, so that after introduction of the profile wire into the tube interior, a contour similar to that of an ordinary innenberippten tube is formed. Moreover, it is particularly advantageous that, in contrast to conventional finned tubes, which are produced by using considerable deformation forces by a deformation process of smooth tubes, a great flexibility in terms of flow-related parameters, such as number of turns, width of the edge webs (corresponding to the rib height in finned tubes), Flank angle and sharp edge exists. These parameters can be adapted in particular by suitable cross-sectional specifications for the profile wire to the respective design case. With regard to conventional tube dimensions, the profile wire advantageously has a quadrangular cross section with side lengths of at least 1.5 mm in each case.

For fixing the tube insert in the tube interior of the profile wire is supported in a particularly advantageous development over a number of arranged at respectively associated support points spring elements on the tube inner wall. The spring elements, which are preferably designed as flat-shaped springs, are expediently positively or positively and materially connected to the profile wire. The longitudinal axis of the spring elements expediently forms an angle of about 90 ° to the pitch angle of the profile wire. The respective spring element is formed in a further advantageous embodiment as a flat shape spring and has a spring leg with a length of more than the pitch of the formed by the profile wire coil spring, so that each leg is pressed laterally outwardly to the inner tube wall through the subsequent Windungsgang the coil spring and can cause a fixation there. In order to further favor the fixation while the diameter of the imaginary circle formed by the outer edges of the spring legs, before assembly of the steam generator tube is greater than its inner diameter, so that when assembling the steam generator tube with the tube insert, the spring legs of the spring elements bent inwards and be curious. This creates a frictional connection between the tube insert and the steam generator tube.

At a helical turn of the profile wire, which forms a circular ring as seen perpendicular to the longitudinal axis of the steam generator tube, can be arranged a single spring element or a plurality of spring elements. In the arrangement of one or two spring elements of the profile wire is thereby non-positively connected to the inside of the steam generator tube, wherein the side of the steam generator tube on which the helical part formed by the profile wire frictionally rests against the tube inner wall, preferably facing the strongest heating should. With three or more spring elements, the profile wire can be fixed at approximately the same distance from the inside of the steam generator tube.

The inner profile formed by the profile wire for swirl generation can be designed in the manner of a single-spring coil spring. In an advantageous embodiment, however, the replica of a two- or multi-start coil spring is provided, this being achievable by a plurality of guided into each other, forming in its entirety a multi-start coil spring profile wires. Adjacent profile wires are advantageously connected in places by means of spacers, so that seen in the longitudinal direction of the steam generator tube results in a uniform inner profile. The spacer (s) can be integrated into said spring elements in a further advantageous embodiment, so that both the fixing function on the spring effect and the positioning function on the setting of the desired distance can be ensured with a single component.

In a particularly advantageous embodiment, the provided with the pipe insert to provide a swirl-producing inner profile steam generator tube in a special way aerodynamically designed in view of the purpose in the steam generator. In this case, in a particularly advantageous embodiment, the effect can be exploited that, by using a separate component independent of the production of the actual steam generator tube to provide the swirl-producing inner profile, comparatively many degrees of freedom can be used in the presetting and selection of individual characteristic parameters. By using these degrees of freedom, the steam generator tube can be configured in a streamlined manner with respect to the desired phase separation, without causing inadmissible deformation forces during its production, as in the case of an internally ribbed steam generator tube. Thus, it has been found that the phase separation caused by the swirl is particularly great in the evaporation of water when the pitch angle of the helically wound profile wire, relative to a plane perpendicular to the tube axis of the steam generator tube, is less than 50 °. Advantageously, therefore, said pitch angle highest 45 °, preferably highest 40 °, more preferably at most 35 °, in a particularly advantageous embodiment at most 30 °.

Furthermore, it is desirable for a comparatively long, extending over the entire height of the boiler steam generator tube to provide along its longitudinal extent depending on the location different guide profiles in the tube interior, the spatial development or variation of both the vapor content and the heating profile Take into account. Such a concept can be advantageously realized in that a plurality of inserts is introduced into the steam generator tube, which are arranged in separate pipe sections, wherein the respective insert with its geometric parameters to the provided during operation local heating and / or to the local flow conditions is adjusted. Since it has also been found that the swirl is retained after a single generation even with a two-phase flow over at least a flow path of five pipe diameters, no complete, complete assembly of the tube is necessary. Rather, the inserts can be installed spaced apart from each other in the steam generator tube.

Conveniently, the steam generator tubes described here are used in a fossil-heated continuous steam generator. Due to the swirl-producing inner profile of the pipes and the associated improvements in the heat transfer behavior, a sufficient heat transfer to the flow medium and thus cooling of the pipe walls is ensured even in boiler designs with a vertical pipe arrangement ("vertical pipe"). A vertical pipe with a higher number of tubes and with relatively short pipe lengths allows due to the opposite obliquely or spirally arranged pipes lower flow rates and lower mass flow densities operation of the steam generator with reduced pressure loss and reduced minimum flow rate. Thus, the steam generator comprehensive power plant can be designed for a lower minimum load. The separation effects known from inclined steam generator tubes, in which water and steam only flow stratified when falling below a minimum flow velocity or a minimum load so that partial regions of the tube walls are no longer wetted, do not occur in the case of vertical bore. In addition, eliminates complex, associated with extensive and costly welding work supporting structures for the boiler, as a boiler wall with vertical pipe can usually be designed self-supporting.

Furthermore, the above-mentioned tube installations can also result in convective heating, such as is present in waste heat boilers of combined cycle power plants, due to the improved heat transfer to a reduction of the heat exchanger surface and thus to significant cost savings.

With regard to the manufacturing method, the above-mentioned object is achieved by introducing a tubular insert formed from one or more profiled wires wound in the manner of a single or multi-start helical spring into the tube interior, by inserting the tube insert centrally by means of a number of support points via associated gripper elements in each case a screw thread of the coil spring engaging mounting rod is pulled into the pipe interior. As has been found out, the production of said steam generator tube is a particular problem, since on the one hand for the assembly process, so the introduction of the tube insert into the pipe interior, a certain play between the pipe wall of the steam generator tube and the pipe insert must be present and roundness of the steam generator tube taken into account On the other hand, the tube insert in the later steam generator operation should be non-positively connected to the pipe inner wall of the steam generator tube. In order to pull the tube insert into the steam generator tube, the outer diameter of the helical part formed by the profile wire is smaller than the inner diameter of the steam generator tube. The spring elements that are to produce a frictional connection between the tube insert and the steam generator tube, during the assembly process due to friction exert a force on the profile wire in the direction of the tube axis, which can lead to an elongation of the helical spring tube insert. To counteract this, it is intended to use an assembly aid. This consists expediently of a long rod on which perpendicular to the rod axis a number of rotatable webs are arranged, which engage between the helical turns of the profile wire. Thus, the tube insert can be drawn into the steam generator tube, without causing elongation of the tube insert. After installation, the mounting aid is rotated slightly about its longitudinal axis and pulled out in the opposite direction from the pipe interior.

The advantages achieved by the invention are in particular that by the introduction of a wound in the manner of a coil spring, guided on the tube inner wall of the steam generator tube profile wire in a particularly simple manner and with particularly simple means a Innenberippung for the steam generator tube can be provided without this the comparatively complex and material-consuming cold deformation steps of the tubular body would be necessary. This makes it possible to provide pipes with a swirl-producing inner profile even for pipe materials which can not readily be processed per se, as are used, in particular, in steam generators for high steam conditions. Due to the helical winding of the profiled wire, the axial flow in the tube interior receives a twist, with which a water content contained in the steam core flow is transported to the tube wall, where it forms a water film during the entire evaporation process, thereby ensuring a particularly good cooling of the steam generator tube. The advantageous for the heat transfer ring flow is not disturbed appreciably, since due to the basic structure of the tube insert in the center of the steam generator tube no internals are required. The shaping of the profiled wire also increases by vortex formation, the turbulence of the flow near the wall and thereby avoids the formation of larger vapor bubbles.

FIG 1

einen Durchlaufdampferzeuger in vereinfachter Darstellung mit vertikal berohrter Brennkammerwand,

FIG 2

einen Rohreinsatz,

FIG 3

den Rohreisatz nach FIG 2 in seitlicher Ansicht,

FIG 4

den Rohreinsatz nach FIG 3 im Querschnitt,

FIG 5

ein Dampferzeugerrohr mit einem darin eingebrachten Rohreinsatz nach FIG 2 im Längsschnitt,

FIG 6

das Dampferzeugerrohr nach FIG 5 im Querschnitt,

FIG 7

einen vergrößerten Ausschnitt des Rohreinsatzes nach FIG 2,

FIG 8

einen mehrgängig ausgeführten Rohreinsatz,

FIG 9

den Rohreinsatz nach FIG 8 im Querschnitt,

FIG 10

ein Dampferzeugerrohr mit integriertem Rohreinsatz nach FIG 8,

FIG 11

das Dampferzeugerrohr nach FIG 10 im Querschnitt,

FIG 12

einen Rohreinsatz in dreigängiger Ausführung,

FIG 13

den Rohreinsatz nach FIG 12 im Querschnitt,

FIG 14

ein Dampferzeugerrohr mit darin integriertem Rohreinsatz nach FIG 12,

FIG 15

das Dampferzeugerrohr nach FIG 14 im Querschnitt,

FIG 16, 17, 18

jeweils ein Federelement,

FIG 19

eine Montagehilfe zur Einbringung eines Rohreinsatzes in ein Dampferzeugerrohr in seitlicher Ansicht,

FIG 20

die Montagehilfe nach FIG 19 in Austragsposition, und

FIG 21

die Montagehilfe nach FIG 19 in Draufsicht.

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

FIG. 1

a continuous steam generator in a simplified representation with vertically annotated combustion chamber wall,

FIG. 2

a pipe insert,

FIG. 3

after the pumice FIG. 2 in lateral view,

FIG. 4

the pipe insert FIG. 3 in cross section,

FIG. 5

a steam generator tube with a tube insert inserted therein FIG. 2 in longitudinal section,

FIG. 6

the steam generator tube after FIG. 5 in cross section,

FIG. 7

an enlarged section of the tube insert after FIG. 2 .

FIG. 8

a multipurpose pipe insert,

FIG. 9

the pipe insert FIG. 8 in cross section,

FIG. 10

a steam generator tube with integrated tube insert after FIG. 8 .

FIG. 11

the steam generator tube after FIG. 10 in cross section,

FIG. 12

a tube insert in three-speed design,

FIG. 13

the pipe insert FIG. 12 in cross section,

FIG. 14

a steam generator tube with integrated therein tube insert after FIG. 12 .

FIG. 15

the steam generator tube after FIG. 14 in cross section,

FIGS. 16, 17, 18

one spring element each,

FIG. 19

an assembly aid for introducing a tube insert into a steam generator tube in a lateral view,

FIG. 20

the mounting aid after FIG. 19 in discharge position, and

FIG. 21

the mounting aid after FIG. 19 in plan view.

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

In FIG. 1 schematically a continuous steam generator 2 is shown with a rectangular cross section, the vertical throttle cable is formed by a Umfassungsungs- or combustion chamber wall 4, which merges at the lower end in a funnel-shaped bottom 6.

In a firing range V of the throttle cable, a number of burners for a fuel in each case an opening 8, only two of which are visible, mounted in the combustion chamber wall 4 composed of steam generator tubes 10. The vertically arranged steam generator tubes 10 are gas-tightly welded together in the firing zone V to form an evaporator heating surface 12.

Above the firing range V of the accelerator cable there are convection heating surfaces 14. Above this there is a flue gas outlet channel 16, via which the flue gas RG produced by combustion of a fossil fuel leaves the vertical throttle cable. The flowing in the steam generator tubes 10 flow medium is due to the radiant heat of the burner flames and convective heat transfer from the flue gas RG heated and evaporated. The flue gas RG serves as a heating medium for the flow medium flowing into the steam generator tubes 10. As the flow medium water or a water-steam mixture is provided in the embodiment.

In addition to the in FIG. 1 Of course, one-turn boilers (so-called tower boilers) are also further boiler configurations, eg. B. in the manner of a two-pass boiler, possible. The steam generator tubes to be described below can be used in all these variants, both in the firing area and in the rest of the flue gas duct. A use in a heat recovery steam generator is conceivable.

The continuous steam generator 2 is designed for operation at particularly high steam conditions, which are associated with comparatively high material stress. Accordingly, the steam generator tubes 10 are made of comparatively high strength, high alloy steel materials. In order to ensure a particularly good heat transfer to the guided in the steam generator tube 10 flow medium even with such materials that are usually not suitable for the otherwise used in tube forming techniques such as cold drawing in particular during production, the steam generator tubes 10 to produce a comparatively low mass flow density Dralls in the flow medium designed as internally ribbed tubes. With regard to the choice of material, which does not allow the application of such a Innenberippung recourse to the usual method for this internal Innenberippung in the steam generator tubes 10 by a separate component, in particular a tubular insert 18, realized, which introduced into the tube interior of the respective steam generator tube 10 is.

The tube insert 18, the in FIG. 2 in lateral view and in FIG. 3 is shown in longitudinal section, is formed by a wound in the manner of a helical spring profile wire 20, which after its introduction into the steam generator tube 10 whose Internal ribbing should form. Starting point for the production of the steam generator tube 10 is thus a smooth tube into which the tube insert 18 formed by the profile wire 20 is inserted. The tube insert 18, which in cross section in FIG. 4 is shown, as shown in the illustration in FIG. 5 can be seen, introduced into the tube interior 22 of the respective steam generator tube 10, wherein the spiraling in the manner of a helical spring profile wire 20 is guided in the vicinity of the tube inner wall 24 along. The assembled steam generator tube 10 is in cross section in FIG. 6 shown.

In order to ensure a comparatively simple introduction of the tube insert 18 provided as profile wire 20 in the tube interior 22 of the steam generator tube 10, the helical spring formed by the twisted profile wire 20 is dimensioned such that its outer diameter d in cross section in the load-free state, ie in particular in the cold, unheated state and in the mechanically relaxed, undeformed state, compared to the tube inner diameter D of the steam generator tube 10 slightly, namely at least 1 mm in the embodiment, is smaller. For an unproblematic insertion of the helical spring formed by the profile wire 20 in the tube interior 22 of the steam generator tube 10 is made possible.

The profile wire 20 is intended to provide in the introduced into the steam generator tube 10 state of its inner ribbing for producing particularly favorable flow conditions and in particular a reliable swirl flow. To take this into account, the profile wire 20 is designed in terms of its dimensioning and contouring, so in particular with regard to its cross-sectional profile on the one hand and in view of the characteristic parameters of the coil spring, in particular on the pitch L, on the other hand suitable.

In the choice of the cross-sectional profile for the profile wire 20 is particularly considered that the phase separation of the flow medium is particularly particularly large when the profile wire 20 has a substantially square or rectangular cross-section, preferably with side lengths of 1.5 mm or more. The rectangular cross-section of the profile wire 20 is in the exemplary embodiment, in particular in the partial illustration in FIG FIG. 7 recognizable. Alternatively, the profiling of the profiled wire 20 may also be carried out in such a way that the flow medium causes a particularly large heat transfer as a result of additional flow turbulence generated via the wire profile. For this purpose, the angle formed by the inflow side of the profiled wire 20 with the tube inner wall 24 of the steam generator tube 10 is preferably greater than 90 °, wherein the angle formed by the outflow side of the profile wire 20 with the tube inner wall 24 of the steam generator tube 10 is smaller than 90 ° , Such a configuration or profiling of the profiled wire 20 produces demolition edges, which promote vortex formation and thus tear the boundary layer against the tube inner wall 24 of the steam generator tube 10. This additional improvement of the heat transfer can be achieved by the manufacturing process in the production of the profile wire 20 - the wire cross section can be twisted in particular something - or by a suitable shaping of the wire cross section.

With regard to the fundamentally provided dimensioning of the tube insert 18 in relation to the inner diameter D of the steam generator tube 10, a mechanical fixation of the tube insert 18 in the steam generator tube 10 is advantageous. For this purpose, the profile wire 20 is supported on the pipe inner wall by way of a number of spring elements 30 arranged at respectively assigned support points. The respective spring element 30 is formed as a flat shape spring and has a spring leg 32 with a length of more than the pitch L of the helical spring formed by the profile wire. This ensures that when the spring element 30 is hooked on one turn of the profiled wire 20, the spring leg 32 protrudes beyond the next thread, so that it, such as the representation in FIG. 7 is removed, is pressed by the further turn with a suitable attachment to the outside and thus in the direction of the tube inner wall 24 of the steam generator tube 10. Thus, the spring elements 30 bend during insertion of the tube insert 18 into the respective steam generator tube 10, are thereby tensioned and exert a force perpendicular or at an angle to the tube axis on the inner wall 24 of the steam generator tube 10. This then serves to fix the tube insert 18 in the steam generator tube 10th

As the cross-sectional views in 4 and FIG. 6 can be removed, seen in cross-section, three or more spring elements 30 may be evenly distributed around the tube circumference, so that a uniform support of the tube insert 18 can be made in all directions. Alternatively, as per section of the steam generator tube 10 seen but also less, so in particular only one or two spring elements 30 may be provided, so that the tube insert 18 is supported by the profile wire 20 itself and on the other hand by the one or more spring elements 30 relative to the tube inner wall 24.

In the embodiment according to FIG. 8 an alternative tube insert 18 'is shown, in which two profile wires 20 are executed nested in the manner of a nested winding. This results in a comparatively high longitudinal density of the ribs with at the same time a particularly suitable pitch angle of the profiled wires 20 FIG. 10 is shown in longitudinal section a provided with such a double-threaded winding of profile wires 20 Dampfzeugerroh 10. As the associated cross-sectional views in FIG. 9 respectively. FIG. 11 can be removed, in this case, the support of the tube insert 18 'relative to the tube inner wall 24 of the steam generator tube 10 per per cross-section only two spring elements 30 accomplished, at a suitable third fixation point the tube insert 18' forming profile wires 20 directly against the tube inner wall 24. Another alternative Embodiment is in the embodiment of the FIGS. 12 to 15 3, in which a further alternative tube insert 18 "in the form of a three-flight design is formed from three suitably nested profile wires 20. Otherwise, the other components correspond to the illustration according to FIGS FIGS. 12 to 15 the previous ones.

In order to ensure a uniform ribbing in the embodiment of the tube insert 18 ', 18 "in the manner of a multi-flighted helical spring with profiled wires 20 nested in one another, the respective profile wires are suitably connected to one another via suitable spacers 40 in the longitudinal direction of the steam generator tube 10. Exemplary embodiments of such spacers 40 for attachment between adjacent profile wires 20 are in cross section in the FIGS. 16 to 18 shown. The spacer 40 may, as FIG. 16 removable, be arranged as a simple spacer between the adjacent profile wires 20. Advantageously, however, the spacer 40 is also designed in the manner of an integrated component as a spring element 30 for fixing the tube insert 18, 18 ', 18 "to the tube inner wall 24. In its lower portion, the spacer 40 has the spring leg 32 already mentioned. Such a combined or integrated design is in FIG. 17 for a zweigängiges structure, so the nesting of two profile wires 20, and in FIG. 18 for a three-flighted structure comprising three profile wires 20.

For mounting the steam generator tube 10, so in particular for the introduction of the insert 18, 18 ', 18 "in the tube interior 22, a special tool, namely an assembly aid 50, is provided, as in the embodiment in the FIGS. 19 to 21 is shown. It is particularly considered that there is a particular problem in the production of said steam generator tubes 10, since on the one hand for the assembly process a certain amount of play between the tube inner wall 24 of the steam generator tube 10 and the tube insert 18, 18 ', 18 "must be present, as well as out of roundness of the steam generator tube 10 must be considered, on the other hand, the tube insert 18, 18 ', 18" in the later steam generator operation should be non-positively connected to the tube inner wall 24 of the steam generator tube 10. To be able to draw the tube insert 18, 18 ', 18 "into the steam generator tube 10, on the one hand, the outer diameter d of the helical spring formed by the respective profile wire 20 is smaller than the inner diameter D of the steam generator tube 10. The spring elements 30, the force-locking connection between The tube insert 18, 18 ', 18 "and the steam generator tube 10 can thus exert a force on the profile wire 20 in the direction of the tube axis during the assembly process due to friction, which can lead to a local or global elongation of the tube insert 18. To avoid this, the mounting aid 50 is provided.

This consists of a long rod 52, on which a number of rotatable webs 54 is arranged perpendicular to the rod axis, which, if necessary, between the helical turns of the respective profile wire 20 engage. In the form of barbs, the webs 54 are designed to be tiltable such that upon loading of the mounting aid 50 in the pulling direction, that is, in the embodiment upwards, the webs 54 engage in the wire windings and thus take them along. In a movement of the mounting aid 50 in the opposite direction, however, the webs 54 fold away, so that the mounting aid 20 can be guided in the appropriate direction through the pipe insert 18. Thus, the tube insert 18, 18 ', 18 "can be drawn into the tube interior 24 of the steam generator tube 10, without that it can lead to an elongation of the tube insert 18, 18', 18".

Claims (10)

Steam generator tube (10), in the tube interior (22) to form a swirl-producing inner profile at least one tube insert (18, 18 ', 18 ") is arranged, wherein the tube insert (18, 18', 18") of a in the manner of a coil spring wound, on the tube inner wall (24) guided profile wire (20) is formed. Steam generator tube (10) according to claim 1, wherein the helical spring formed by the profile wire (20) in the load-free state has an outer diameter (d) which is at least 1 mm smaller than the inner tube diameter (D). Steam generator tube (10) according to claim 1 or 2, wherein the profile wire (20) has a substantially rectangular cross-section. Steam generator tube (10) according to one of claims 1 to 3, whose profile wire (20) via a number of respectively associated support points arranged spring elements (30) on the tube inner wall (36) is supported. Steam generator tube (10) according to claim 4, wherein the respective spring element (30) is formed as a flat shape spring and a spring leg (32) having a length greater than the pitch of the formed by the profile wire (20) coil spring. Steam generator tube (10) according to one of claims 1 to 5, in the tube interior (22) is arranged a plurality of one another, in its entirety a multi-start coil spring forming profiled wires (20). Steam generator tube (10) according to claim 6, wherein the adjacent profile wires (20) are connected in places via spacers (40). Steam generator tube (10) according to any one of claims 1 to 7, wherein the pitch angle of the respective helically wound profile wire (20), with respect to a plane perpendicular to the tube longitudinal axis, at most 45 °, preferably at most 40 °, particularly preferably at most 35 °, in particular advantageous embodiment is at most 30 °. A continuous steam generator (2) comprising a number of steam generator tubes (10) formed according to any one of claims 1 to 8. Method for producing a steam generator tube (10) provided with a swirl-producing tube insert (18, 18 ', 18 "), in which a tube insert (18, 18) formed from one or more profiled wires (20) wound in the manner of a single or multi-start helical spring is formed ', 18 ") in the tube interior (22) is introduced by the tube insert (18, 18', 18") by means of a centrally guided, engaging at a number of support points via associated gripping elements in each case a helical coil of the coil spring mounting rod into the tube interior (22) is retracted.

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