EP1957865A2

EP1957865A2 - Steam generator pipe, associated production method and continuous steam generator

Info

Publication number: EP1957865A2
Application number: EP06830084A
Authority: EP
Inventors: Joachim Franke; Oliver Herbst; Holger Schmidt
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2005-12-05
Filing date: 2006-11-22
Publication date: 2008-08-20
Also published as: TW200732598A; ZA200710581B; KR20080081805A; RU2411410C2; WO2007065791A2; EP1793163A1; BRPI0619421A2; CN101223402A; AU2006324058B2; AU2006324058A1; US20090050307A1; CN100567813C; JP2009518611A; AR058847A1; CA2632313A1; RU2008127383A; WO2007065791A3

Abstract

The invention relates to a steam generator pipe (10) which can be produced in a simple and economical manner and which has particularly good heat transitional behaviour having a large band width with various operational conditions. According to the invention, at least one insert (22) is arranged in the inner chamber of the pipe (18) in order to form a swirl-generating inner profile. The insert (22) comprises at least one lamination frame (24) having a number of large recesses (26). The insert (22) is drilled in the longitudinal direction and rests at least partially on the pipe inner wall (36) with the longitudinal edges thereof (30).

Description

description

Steam generator tube, associated manufacturing process and continuous steam generator

The invention relates to a steam generator tube with a swirl-generating inner profile. It also relates to a once-through steam generator with such steam generator pipes. The invention further relates to a method for producing a swirl-generating inner profile

Steam generator tube.

In the combustion chamber walls of a once-through steam generator are usually employed with one another via webs welded gas-tight steam generator tubes to form a combustion chamber surrounding the gas flue, which are connected in parallel for the flow of a flow ^¬ medium. Instead of tubes with ^¬ as intermediate, separate flat bar webs may also pipes are used, which are factory equipped with angeform- th fins. The steam generator tubes can be arranged vertically or at an angle. The steam generator tubes are typically designed so that even at low mass flow density of the steam generator tubes by the flowing medium a sufficient cooling of the steam generator tubes is ensured for a si ^¬ cheres performance of the once-through steam generator.

An important design criterion, the heat transfer ^¬ properties of a steam generator tube. A high heat transfer enables a particularly effective heating of the medium flowing through the steam generator tube with reliable cooling of the steam generator tube itself. The heat transfer behavior of a steam generator tube can be impaired in conventional steam generators that are operated at subcritical pressures by the occurrence of so-called boiling crises. The pipe wall is no longer wetted by the liquid flow medium - usually water - and is therefore only insufficiently cooled. As a result of Drying out early could then reduce the strength values of the pipe wall.

In order to improve the heat transfer behavior, steam generator tubes are usually used which, as a result of a deformation process (eg cold drawing), have a surface structure on the inside or an inner profile in the manner of helically wound ribs. The shape of the ribs which is the steam generator tube Menden throughflow medium is to swirl, so the heavy ^¬ re liquid phase that due to the centrifugal forces acting on the tube inner wall collects and forms there a wetting liquid ^¬ keitsfilm. This ensures reliable heat transfer from the inner pipe wall to the flow medium even with comparatively high heat flow densities and low mass flow densities.

A disadvantage of the known steam generator tubes is that they are comparatively complex to produce due to the limited deformability of the tube material. The formability is severely restricted, particularly in the case of high-temperature steels with a high chromium content. Such materials play an increasingly important role in steam generator tubes nowadays, since - at least in principle - they allow a steam generator to be designed for particularly high steam parameters, in particular for high fresh steam temperatures, and the associated high efficiency. Due to the material-related restrictions in processing, it is not possible in practice, or only with considerable effort, to produce internally finned tubes with the desired, aerodynamically advantageous finned profiles as part of a deformation process from smooth tubes. In particular rea ^¬ accordingly steep flank angles and sharp-edged transitions in connection with large fin heights are difficult to be manufactured. In addition, the height of the ribs can only be manufactured within a narrow frame. In addition, only a small Flexi ^¬ gives stability with respect to the tread pattern along the pipe. Alternatively, various types of swirl-generating built-in parts for retrofitting in a steam generator tube have already been proposed. These include, in particular, the so-called "twisted tapes": tapes made from a metal strip that are twisted or twisted. However, the previously known pipe internals have the disadvantage in common that on the one hand they have the (originally) free cross-section in the center of the pipe block and therefore lead to very high pressure losses, and that they also redirect the entire flow extremely strongly and partially

Z "over plump". A simple twisted tape. B. leads hö ^¬ heren steam contents in the two phase flow to an accumulation of the water phase in the gusset between the pipe wall and the tape at the same time drying out and therefore inadequate cooling of the inner wall portions leeward of the tape. Steam ^¬ generator tubes with internals in the manner of twisted tapes are therefore not for all in steam generators commonly occurring defects ^¬ Tenden operating conditions alike. the invention is therefore based on the object, a vapor ^¬ generator tube to indicate the at simple and inexpensive held manufacture of the aforementioned type and has a particularly favorable heat transfer behavior in a wide range of different operating conditions. Furthermore, a production method suitable for the production of such a steam generator tube and a continuous steam generator are to be specified which, with high operational safety and be i has a particularly simple structure with high efficiency.

With respect to the steam generator tube, the aforementioned object is achieved according to the invention by an insert disposed in the tube interior to form a drallerzeu ^¬ constricting the inner profile at least, the use of at least men a Blechrah- comprises a number of large-area cutouts, wherein the insert is twisted in the longitudinal direction, and the longitudinal edges of the respective sheet metal frame at least partially abut the inner tube wall. The invention proceeds from the consideration that the multiphase flow is to have a swirl within a steam generator tube to improve the heat transfer ^¬ te, so that the liquid phase due to the rotation of the inner pipe wall is guided and wets uniformly as possible. Suitable flow-guiding elements should therefore be arranged in the interior of the tube for the targeted production and maintenance of such a swirl flow. As has been found, the flow guidance is particularly bene- ficial if one hand does not "over-twisting" still too much pressure drops along the flow path occurring defects th ^¬, on the other hand, the swirl effect is still intense enough to the liquid phase of the flow medium on the ge ^¬ to lead the entire pipe circumference to the inner pipe wall.

To avoid high pressure drops, resulting in a high energy requirements for the feed water pump, and to ensure the steam discharge inside the tube, the flow-guiding elements are substantially in the manner of a home should be nenprofils arranged on the inner tube wall and the tube ^¬ cross-section not in the center, or only block slightly. In order to avoid the manufacturing limitations associated with the finned tubes of conventional design, the swirl-generating inner profile should be realized by means of tube internals or inserts, which can be manufactured in the desired shape independently of the steam generator tube and are subsequently drawn into the tube.

For this purpose, a twisted in the longitudinal direction of sheet-metal frame is disposed in the tube interior with the concept presented here, at least partially, before ^¬ preferably, however, completely abuts with its longitudinal edges on the tube inner wall. In an alternative variant, a built-in body formed from a plurality of sheet metal frames and twisted in the longitudinal direction is arranged in the interior of the tube, each of the twisted or twisted sheet metal frames resting with its two longitudinal edges on the inner tube wall. This embodiment, after ^¬ following in more detail in the description of the figures explained. In contrast to the previously known twisted tapes, the respective sheet metal frame is, however, with a number of large recesses which, for. B. can be punched out or cut out of the sheet material, provided. With a large surface area is meant here that the all recesses total covered area of at least 50%, preferably depending ^¬ but at least 80%, of the base makes each sheet metal frame from ^¬ so that after insertion into the tube interior, a substantial part of the tube cross-section in the center free remains. So that the steam inside the tube can undisturbed akkumu ^¬ lose and flow out.

In contrast to the closed twisted tapes, the twist generation is caused by the sections near the edge, i.e., the edge webs that surround or enclose the recesses, each of which winds helically along the inner wall of the tube and has a shape and function similar to the fins of conventional finned tubes. The contiguous with the "over-twisting" negative effects of conventional twisted tapes can be avoided. Instead, it is achieved with liquid flow means also at moderate swirl intensity and at a comparatively low pressure loss, a uniform wetting of the Rohrin ^¬ nenwand. The end-side gen transverse webs and the transverse webs optionally between two in each case arranged one behind the other in the longitudinal direction

Recesses are provided, only have a support function for the tube insert and only insignificantly disturb the swirl flow in the center of the steam generator tube. A particular advantage of the new concept that contrast in the Ge ^¬ to the finned tubes, the considerable using deformation forces are produced ^¬ tubes by a deformation process of smooth, great flexibility respect ^¬ Lich the flow-related parameters, such as number interturn, Width Edge webs (corresponding to the fin height for finned tubes), flank angle and sharp edges exist. Corresponding design specifications can be implemented particularly simply and precisely when implemented as an insert component because, as a rule, only one or more suitably punched-out or cut-out sheets or metal strips have to be provided and inserted into a smooth pipe that is comparatively easy to manufacture by twisting.

Advantageously, the tube insert is seated at the intended operating temperature of the steam generator tube due to the tension of the drill ^¬ or the sheet metal frame / s non-slip in the tube interior. The sheet metal material and the twisting tension are thus matched to the geometric conditions in such a way that creeping or slipping of the insert in the interior of the pipe is prevented.

Although the tube insert relatively firmly and securely seated already due to its geometrical dimensions and its drill voltage in the steam generator tube, an additional fixing is preferably provided, wherein each or at least a sheet metal frame at least one place, preferably in the vicinity was ^¬ ner both ends, with the Inner pipe wall is firmly connected. The fixed connection is advantageously a highly heat-resistant welded connection. A variant which is somewhat more complex to produce, but which ensures particularly secure fixation, comprises a plurality of spot welds distributed over the longitudinal edges of the sheet metal frame. The welding fixation can be produced particularly well if the sheet metal frame or frames is / are made from a material with a composition similar to the tube material.

Furthermore, it is precisely the case of a comparatively long one, which extends over the entire height of the steam boiler

Steam generator tube desirable along its length depending on the location, different guide profiles in Rohrin ^¬ Neren provide that carry the spatial development or variation of both the vapor portion and the heating profile calculation. Such an approach can be advantageous ^¬ way legally realized by that a plurality of inserts introduced into the steam generator tube, which are arranged in separate tube sections, where the respective insert is adapted with its geometrical parameters to the intended operating local heating and / or len to the Loka ^¬ flow conditions. As has also forth issued ^¬ that the swirl is maintained after a single generation even with a two-phase flow at least over a flow distance of five pipe diameters, not a complete, uninterrupted insertion of the tube is notwen ^¬ dig. Rather, the inserts by gaps vonein ^¬ other spaced be built into the steam generator tube.

Conveniently, the Dampferzeu ^¬ gerrohre described herein are used in a fossil-fired-through steam generator. Due to the swirl-generating inner profile of the pipes and the associated improvements in heat transfer behavior, this is also the case for boiler designs with

Tube assembly ( "vertical Tubing") a sufficient Wär ^¬ meübertragung to the flow medium or a cooling of the tube walls ensured. A Senkrechtberohrung with a higher number of tubes, and with relatively short lengths of pipe made possible due to the over obliquely or spirally arranged tubes lower flow rates and lower mass flux operation of the steam generator with reduced pressure loss and with reduced minimum throughput. Thus, the power plant comprising the steam generator can be designed for a lower minimum load. The separation effects known from inclined steam generator pipes, in which water and steam only flow in layers if the flow rate falls below a minimum flow rate or a minimum load vertical sections of the pipe walls are no longer wetted, and there is no need for time-consuming, extensive and costly welding Supporting structures for the steam boiler connected to ice work, since a boiler wall with vertical pipes can usually be designed to be self-supporting.

Furthermore, due to the improved heat transfer, the aforementioned pipe internals can also be closed with convective heating, such as is present in the waste heat boiler of combined cycle power plants a reduction of the heat exchanger surface and to interpret thus lead ^¬ handy cost savings.

With regard to the manufacturing process, the above-mentioned object is achieved by a biased by twisting

Installation body, which consists of one or more interconnected sheet metal frames, is introduced into the interior of the pipe, the installation body being relaxed after insertion until it is at least partially in contact with the longitudinal edges of the pipe inner wall. In other words, the sheet metal frame (s) is / are prestressed by twisting and drawn into the steam generator tube with a reduced diameter in this state. After its partial relaxation, the installation body presses itself against the inner pipe wall. The remaining drill voltage is chosen so that s can take place of or the plate frame / at the intended operating temperature of the evaporator tube and no slipping no building facing on the desired degree ^¬ rising untwisting. In addition, the installation body is advantageously welded to the inner tube wall at least at one end.

The advantages achieved by the invention are, in particular, that the new pipe inserts result in a flexible flow guidance in the pipe interior which can be used for all pipe materials and which can be adapted according to the need for ^{improving the} heat transfer. Due to the design flexibility brought about by the largely freely configurable geometric parameters, a swirl profile which varies over the length of the evaporator tube can be set and which is exactly adapted to the respective local heating. The production limitations of the traditional finned tubes are avoided. Especially in the case of new power plant developments with higher design values for the steam parameters, the production of finned tubes is becoming more and more complex due to the higher chromium content of the new materials required for higher temperatures and pressures. Here, the new swirl-generating internals can replace the finned tube or enable such applications in the first place. An embodiment of the invention is based on a

Drawing explained in more detail. In it show:

1 shows a once-through steam generator in a simplified representation with the combustion chamber wall in vertical contact,

FIG 2 is a sectional view of a steam generator tube with a swirl-generating internal profile ausbil ^¬ Denden insert which consists of a single twisted sheet metal frame,

3 shows a provided to form a tube insert

Tin frame in its original state before its twisting,

4 shows a sectional view of a steam generator tube similar to that in FIG. 2, the insert however consisting of two sheet metal frames oriented at an angle to one another,

5 shows a cross section through an insert, which is constructed similarly to the insert from FIG. 4, in two successive production phases before the twisting, and

6 shows a cross section through a tube insert according to an alternative embodiment, likewise in two successive manufacturing phases before the twisting.

Identical parts are provided with the same reference symbols in all the figures.

1 shows schematically a once-through ^steam generator 2 with a rectangular cross section, the vertical gas train of which is formed by a surrounding or combustion chamber wall 4 which merges into a funnel-shaped bottom 6 at the lower end. In a firing area V of the throttle cable, a number of burners for a fuel are installed in an opening 8, only two of which are visible, in the combustion chamber wall 4 composed of steam generator tubes 10. The vertically arranged steam generator tubes 10 are gas-tightly in the approximate range Befeue ^¬ V to an evaporator heating surface 12 are welded together. Above the firing region V of the gas flue are Konvektionsheizflachen 14. In a flue gas outlet channel is 16, the flue gas produced by combustion of a fossil fuel RG vertical gas ^¬ train leaves over the. The flow medium flowing in the steam generator tubes 10 is heated by the radiant heat of the burner flames and by convective heat transfer from the flue gas RG and thereby evaporated. The flue gas RG serves as a heating medium for ^¬ flowing into the steam generator tubes 10 flow medium. Water or a water-steam mixture is provided as the flow medium in the exemplary embodiment.

In addition to the example shown in FIG 1 A-train boiler (so-called tower boiler) are of course also other boiler ^¬ configurations such. B. in the manner of a two-pass boiler. The steam generator tubes to be described below can be used in all of these variants, both in the lighting area and in the rest of the flue gas duct. Also a use in a Abhitzedampferzeu ^¬ ger is conceivable.

2 shows in a sectional view a detail of the tubing of the combustion chamber wall 4 of the continuous ^¬ steam generator 2 steam generator inserted pipe 10. In the pipe inner space 18 of a smooth tube 20 is accommodated an insert 22 mono-, which forms a swirl-generating internal profile for improving the heat transfer behavior. In the exemplary embodiment, the insert 22 comprises a sheet metal frame 24, which is twisted in the longitudinal direction, ie around the tube axis, and has a plurality of large-area recesses 26. The width B of the sheet metal frame 24 shown in FIG. 3 before it is twisted is slightly larger than the tube diameter of the smooth tube 20 provided for receiving it. The rectangular recesses 26 are formed in the longitudinal direction. hen arranged in a row one behind the other and separated by narrow crossbars 28. In the transverse direction the recesses ^¬ erstre CKEN 26 almost over the entire width B of the sheet metal frame 24 and are separated from the two longitudinal edges 30 by narrow edge webs 32nd

The sheet metal frame 24 is now twisted about its longitudinal axis 34 and, in this prestressed state, is introduced into a smooth tube 20 provided as a steam generator tube 10. The width B of the sheet metal frame 24 is sized in relation to Rohrdurchmes ^¬ ser, the sheet metal frame that 24 can partially relax, such that the edge webs 32 in Montageendzu ^¬ stood along a given helical line on the pipe inner wall 36 along winds. The remaining residual voltage fixes the sheet metal frame 24 while securely in the tube interior 18. In addition, the edge webs 32 of the sheet metal frame 24 is welded at meh ^¬ eral points with the inner pipe wall 36th

Like the tube wall 38 of the smooth tube 20 receiving it, the sheet metal frame 24 is made of a heat-resistant metallic material with a high chromium content. Of course, other suitable materials known to those skilled in the art can also be used. Due to the fact that the sheet metal frame 24 is manufactured separately from the smooth tube 20, the height and width of the edge webs 32 and the pitch angle of the helical lines formed by the longitudinal edges 30 can in particular be set as desired. In a first approximation, the geometric parameters are generally chosen in a manner similar to that of the fins of conventional finned tubes. In addition, but also a location-dependent adaptation and optimization can take place, the chamber wall on the course of the heating profile along the Brennkam ^¬ takes 4 consideration.

FIG 4 also shows a sectional view of a steam generator tube 10 with an insert 22 which consists of two connected mitein ^¬ other and angularly aligned

Sheet metal frame 24 is made. Each of the two sheet metal frames 24 has, similar to the sheet metal frame 24 shown in FIG. recesses 26 on. The edge webs 32 of the two sheet metal frames 24, each of which winds helically along the inner tube wall 36, form a swirl-generating inner profile in the manner of a four-start screw thread. Compared to that in the manner of a two-course

Screw thread internal profile of the insert 22 formed ge ^¬ Mäss FIG 2 may be one for the uniform wetting of the inner tube wall 36 with a liquid-sigkeitsfilm leading swirl flow produced thereby, particularly with comparatively large internal pipe diameters even more effective way.

In FIG 5, a particularly simple and convenient Ferti ^¬ is a transmission method shown for such use 22nd For this purpose, as can be seen in a cross-sectional view in the left part of FIG. 5, two similar sheet metal frames 24, each of which is designed similarly to the sheet metal frame 24 shown in FIG ^¬ other welded (spot weld 40). The two sheet metal frames 24 are then bent in the manner shown in FIG. 5 by approximately 90 ° along their longitudinal axis 34, so that the cross-sectionally cross-shaped structure shown in the right part of FIG. 5 is formed. The insert 22 is finally twisted in the longitudinal direction and drawn into a smooth tube 20.

Similarly, if necessary, an existing three mitein ^¬ other connected sheet metal frame 24 insert 22 can be manufactured (FIG 6), which forms a swirl-generating internal profile in the form of a six-hand screw thread by twisting and introduction into a smooth pipe 20th

Claims

1. steam generator tube (10), in which at least one insert (22) is arranged in the tube interior (18) to form a swirl-generating inner profile, the insert (22) having one or more sheet metal frames (24) with a number of large-area recesses (26 ), and wherein the insert (22) is twisted in the longitudinal direction and its longitudinal edges (30) at least partially abut the inner tube wall (36).

2. Steam generator tube (10) according to claim 1, wherein the respective recess (26) from the two longitudinal edges (30) of the sheet metal frame (24) is spaced apart by a narrow edge web (32).

3. Steam generator tube (10) according to claim 1 or 2, in which a plurality of longitudinally one behind the other in the sheet metal frame (24) arranged recesses (26) are spaced apart by narrow crossbars (28).

4. Steam generator tube (10) according to one of claims 1 to 3, in which the insert (22) due to its drilling tension at the intended operating temperature non-slip inside the tube

(18) sits.

5. Steam generator tube (10) according to one of claims 1 to 4, in which the insert (22) at at least one point, preferably in the vicinity of its two ends, is firmly connected to the inner tube wall (36).

6. steam generator tube (10) according to claim 5, wherein the fixed connection is a welded joint.

7. steam generator tube (10) according to any one of claims 1 to 6, wherein the insert (22) made of a material with a

Pipe material similar composition is made.

8. steam generator tube (10) according to one of claims 1 to 7, with a plurality of inserts (22) which are arranged in separate pipe sections, the respective insert (22) with its geometric parameters to the local heating provided in operation and / or is adapted to the local flow conditions.

9. continuous steam generator (2) comprising a number of steam generator tubes (10) which are formed according to one of claims 1 to 8.

10. A method for producing a steam generator tube (10) provided with a swirl-generating insert (22), in which an insert (22) formed from one or more sheet metal frames and biased by twisting is introduced into the tube interior (18), the insert being used (22) is relaxed after insertion until the longitudinal edges (30) of the sheet metal frame (s) (24) lie at least partially against the inner tube wall (36).

11. The method according to claim 11, wherein the insert (22) is welded to the inner tube wall (36) at least at one end after its partial relaxation.