AU2006200834A1 - Fast assembly method for large steam generators - Google Patents

Description

P001ool Section 29 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Fast assembly method for large steam generators The following statement is a full description of this invention, including the best method of performing it known to us: FAST ASSEMBLY METHOD FOR LARGE STEAM GENERATORS The invention relates to an assembly method for the fast erection of steam generators and a corresponding steam c- generator.

Large steam generators are designed nowadays almost without 00 exception as tube-wall steam generators, the boiler wall whereof is formed by inclined or vertically arranged tubes connected to one another. The boiler wall surrounds a gas S pass, for example in the form of a duct standing upright.

c-q Arranged in the upper part thereof are internal components such as economisers, reheaters, superheaters and other heating surfaces. The boiler wall is provided on its outside with buckstays and wall boxes, which include headers arranged on cross-bars. The lower end of the boiler wall is followed by a boiler hopper, which hangs over a socalled boiler floor. The whole boiler, to which the aforementioned elements belong, is arranged suspended in a boiler structural steelwork. The boiler structural steelwork stands on a base bordering the boiler floor and has several boiler columns braced together by means of cross-bars and bracings, said boiler columns carrying a boiler structural steelwork roof. The boiler structural steelwork roof carries the boiler, which is provided with a boiler roof at the top beneath the boiler structural steelwork roof.

For the fast erection of larger steam generators of this kind, DE 100 14 758 C2 proposes a method which makes it possible to erect simultaneously the upper part of the boiler wall and the internal components to be provided there. For this purpose, the boiler structural steelwork roof is divided into an outer roof section and into an inner roof section. The boiler structural steelwork is first erected with the outer roof section. The latter is designed in such a way that it offers access from above to the volume enclosed by the boiler structural steelwork. By means of a crane, therefore, parts for the erection of the boiler wall, in particular the upper boiler wall, can be lifted in from above through an opening left in the outer c- roof section. This enables the assembly of the upper boiler wall by means of a suitably large crane. At the same time, there can be erected on the boiler floor, or just above the OO latter, the inner roof section of the boiler structural steelwork roof. The latter is held for example by traction ropes, the hoisting systems whereof are anchored in the boiler structural steelwork, e.g. to the outer roof section (1 of the boiler structural steelwork roof. The necessary internal components are now erected beneath the inner roof section of the boiler structural steelwork roof, whereby the inner boiler structural steelwork roof can accordingly be raised step by step. The assembly of the upper boiler wall and the assembly of the internal components thus run in parallel in terms of timing. Because both assembly procedures are in each case very time-intensive, a large amount of building time can thus be saved by the parallel assembly. When the upper boiler wall and the internal components are each completed, the internal components including the inner boiler structural steelwork roof are taken upwards and fixed and connected at their installation point.

This method has been tried and tested for the erection of larger steam generators. It does however have its limitations with particularly large steam generators, the boiler structural steelwork roof whereof has at least one, but preferably a plurality of undivided main beams spanning the gas pass.

The problem of the invention is to provide a method and a steam generator which also permits the rational erection of particularly large steam generators.

This method is solved by the method according to claim 1 N and the steam generator according to claim 8.

It is presupposed in the method according to the invention c- that the outer roof section has a plurality of main beams, whereof at least one extends transversely over the gas pass, whereby beam intermediate spaces are present between 0O the various main beams. The beam intermediate spaces serve as an access opening, through which components to be assembled in the upper part of the gas pass, such as Cbuckstays, wall boxes or boiler wall parts, can be guided c-q to their point of installation by means of a crane. The crane can guide the parts in a suspended fashion through the beam intermediate spaces.

While the upper part of the boiler is largely erected and completed in this way, it is possible at the same time, in a construction area lying vertically below the aforesaid, above the boiler floor, to assemble the inner roof section of the boiler structural steelwork roof and, beneath the latter, the boiler roof and the internal components. The parts concerned can be held at the respective desired height and connected together, for example by means of a suitable auxiliary device. It is also possible to erect the inner boiler structural steelwork roof by suitable means and to assemble suspended therefrom the boiler roof to be assembled thereunder and the internal components. The inner roof section of the boiler structural steelwork roof can also be suspended on strands or traction ropes which are attached to suitable cable hoisting systems. The cable hoisting systems include, for example, hydraulic lifters, which can be set up on the main beams of the outer boiler structural steelwork roof. The main beam extending transversely over the gas pass can in particular be used for the suspension of the inner boiler structural steelwork roof or roof modules into which the inner boiler structural steelwork roof is divided.

(I4 The design proposed in this regard permits the application of the principle of the simultaneous erection of the upper boiler wall and the built-in compartments at assembly c, points vertically spaced apart from one another and the subsequent bringing-together, whereby the inner roof section with internal components suspended therefrom is OO raised upwards, also in the case of very large steam generators with which an inner roof section covering (1 virtually the whole gas pass and an outer roof section Cstanding completely outside of the gas pass would lead to c-i uneconomical solutions. With the division of the boiler structural steelwork roof in the proposed manner, whereby at least one main beam of the outer roof section runs transversely across the gas pass, gas passes of, for example, 30 m x 30 m cross-section can be bridged without problem. The main beams are preferably designed free from interruption, which offers static and dynamic advantages and leads to a reduction in highly loaded points of separation. With the proposed design, very large boiler structural steelwork roofs can also be divided into an inner and outer roof section and can subsequently be brought together after the assembly of the upper boiler wall and the internal components at the various points.

It is possible to design the inner roof section as singlepiece or multi-piece, e.g. divided into roof modules. The inner roof section can be erected on the boiler floor or can be brought there in the form of prefabricated units.

The boiler roof to be assembled thereunder and internal components can then be assembled suspended from it, whereby the inner roof section remains at the same, sufficient height or is raised step by step proceeding from a lower height.

If the inner roof section is designed in one piece, it will in any event be moved upwards as a whole with the internal kO IND components suspended thereunder, when the upper boiler wall is complete and the internal components suspended on it are ready assembled. If, however, the inner roof section is divided into roof modules, two different assembly c- procedures can alternatively be carried out, i.e. in the first place synchronous raising of all the roof modules with the internal components suspended thereunder to the O0 assembly point or in the second place raising of the roof modules with the internal components suspended individually beneath the respective roof module one after the other, i.e. at different times. In the latter case, the boiler c-q roof must also be designed multi-piece, so that each inner roof module has its own boiler roof section assigned to it.

Whilst the first-mentioned procedure has the advantage that internal components can simultaneously be carried by a plurality of roof modules, i.e. can occupy an area that is larger than that of a single roof module, the secondmentioned procedure has the advantage that the erection of the upper boiler wall and the erection of the internal components can be linked to one another more closely in terms of procedure and timing. If, for example, a very large steam generator with four boiler walls is being erected, said walls being orientated for example to the north, east, south and west, and if the northern boiler wall and, around the adjoining corners, a part of the eastern and the western boiler wall are already completed, the roof module adjacent to the northern boiler wall can already be raised, whilst further roof modules with internal components lying thereunder are still being erected over the boiler floor and the eastern, western and southern boiler walls are still being completed. This procedure also improves the accessibility to the internal components to be erected. Welding and assembly work, for example, is facilitated. The achieved flexibility with regard to the organisation of the production sequence permits the latter to be compressed so as to achieve the shortest possible building times for large steam N generators.

The corresponding advantages are obtained with the steam c- generator according to claim 8. The preferably undivided main beam of the outer boiler structural steelwork roof spanning the gas pass endows the boiler structural OO steelwork with particular stability and offers a suspension point for the inner boiler structural steelwork roof or the c-i modules thereof. The result is a statically favourable Cconstruction combined with the aforementioned advantages as c-i regards the erection of the steam generator.

Although it is not essential, it has proved advantageous to align the beams of the outer boiler structural steelwork roof parallel to one another. This produces a clearly arranged structure. Furthermore, the main beams are preferably undivided. They can be already erected in a previous construction phase in which the boiler wall has not yet been completed. The intermediate spaces between the main beams are designed sufficiently large to permit boiler wall sections and other parts to be lifted from above into the boiler structural steelwork.

The main beams are preferably designed as box-section beams. A sufficient stability under load is achieved with the latter, especially during the construction phase in which they freely span the gas pass, so that the main beam spanning the gas pass in particular can also serve as a support for the cable hoisting systems for raising the inner boiler structural steelwork roof.

Further details of advantageous embodiments of the steam generator are the subject-matter of the drawing, the description and sub-claims.

Examples of embodiment of the invention are illustrated in the drawing. In the figures: Figure 1 Figures 2 to 5 Figure 3 Figure 4 Figure 5 shows an essentially completely assembled steam generator in a diagrammatic perspective view, show the steam generator in various construction stages, whereby figure 2 illustrates a partially erected outer boiler structural steelwork and the inner boiler structural steelwork roof already erected as well as an assembly crane, illustrates a subsequent construction stage of the boiler structural steelwork with buckstays and wall boxes already partially assembled, illustrates a construction stage, in which the boiler structural steelwork with the outer boiler structural steelwork roof is erected and the boiler walls are being assembled, whilst ancillary heating surfaces are being assembled at the same time above the boiler floor, and illustrates a building stage in which the ancillary heating surfaces, after their preliminary assembly, have been raised together with the inner boiler structural steelwork roof into their installation position and fixed in the latter, Figure 6 Figures 7 to 9 Figure 10 shows a simplified embodiment of a steam generator according to the invention in a diagrammatic simplified plan view, show different configurations of the divided boiler structural steelwork roof in a diagrammatic vertical sectional view and shows an embodiment of the steam generator according to the invention during a building stage in a simplified perspective view.

Figure 1 illustrates a steam generator 1 in the manner of a tower construction, which is carried by a boiler structural steelwork 2. Boiler structural steelwork 2 includes vertically arranged boiler columns 3 which rest on suitable foundations. Boiler columns 3 erected in a square and arranged vertically are connected to one another by horizontal boiler structural steelwork bars 4 which are arranged in tiers. Bracings 5 are provided for the purpose of reinforcement. At the top, boiler structural steelwork 2 carries a boiler structural steelwork roof 6, which is divided into an outer roof section 7 and an inner roof section 8. In the present example of embodiment, outer roof section 7 is formed by three main beams 7a, 7b, 7c, which rest in parallel and spaced apart from one another on boiler structural steelwork 2. At least one of main beams 7a, 7b, 7c, in the present example middle main beam 7b, spans a central free space in boiler structural steelwork 2, in which a gas pass is to be erected. All main beams 7a, 7b, 7c, but at least middle main beam 7b, are preferably designed undivided viewed over the length. Main beams 7a, 7b, 7c can be divided along longitudinally running jointing planes into part-beams. There are however no continuous transverse joints.

Inner roof section 8 is carried by outer roof section 7 and c- is connected to the latter. The outline, i.e. the maximum external dimensions, of inner roof section 8 is at least somewhat smaller than the clear width of the space 0O surrounded by a boiler wall 19 in steam generator 1, at least in its upper section 9. In this section, illustrated steam generator 1 is preferably provided with vertical 0 tubing (boiler wall 19a in the upper section).

c-i Provided in section 9 of steam generator 1 are internal components, including economisers, reheaters and superheaters. These are formed in each case by horizontally arranged tube bundles, which extend transversely through the gas pass defined by steam generator 1 and the connections whereof are led through boiler wall 19, in particular its section 19a. The latter is surrounded externally by buckstays 12, which support boiler wall 19 externally and are carried by the latter. These buckstays are connected to one another at boiler corner regions as well as to boiler wall 19. Moreover, the buckstays formed by horizontal, rigid beams are connected to one another by vertical beams, so-called struts.

Inner roof section 8 of boiler structural steelwork roof 6 is formed by one or, as illustrated in figure 1, two roof modules 8a, 8b, which are carried by main beams 7a, 7b, 7c.

Modules 8a, 8b are preferably held at the same height and for their part carry boiler roof 19c shown in figure 7, which terminates the gas pass to the top, as well as the internal components suspended beneath the boiler roof. Roof modules 8a, 8b are screwed or welded to main beams 7a, 7b, 7c. However, roof modules 8a, 8b form independent units which are pre-assembled independently of main beams 7a, 7b, 7c and are subsequently fixed to the latter.

(I4 Section 9 of the boiler is followed below by a further section 10 of the boiler with a boiler wall section 19b, which is provided with tubing vertically or obliquely.

Buckstays 14 support boiler wall section 19b from the exterior and are carried by the latter. There follows below a boiler hopper 11 which is also provided with buckstays.

OO

Steam generator 1 illustrated in this regard is erected in (1 the sequence illustrated in figures 2 to kO IND c-i According to figure 2, the assembly of boiler structural steelwork 2 is started first. Boiler structural steelwork columns 3 and boiler structural steelwork bars 4 as well as bracings 5 are erected stage by stage. A crane 16 can be used for the assembly. Other suitable means are also possible.

At the same time, roof modules 8a, 8b are pre-assembled on the boiler structural steelwork floor or are positioned at this point in a pre-assembled state. They preferably lie more or less precisely vertically beneath the location they will subsequently occupy in the installed position. The overall cross-section of the outline, which is defined by roof modules 8a, 8b, is somewhat smaller than the internal clear width of the gas pass.

A further work step is illustrated in figure 3. With continuing progress on boiler structural steelwork 2, the assembly of individual buckstays 12 and wall boxes 15 it started here. The latter are lifted with crane 16 as preassembled buckstays and wall boxes 12', 15' from above into or onto boiler structural steelwork 2 and are provisionally placed or installed there.

When buckstays and wall boxes 12, 15 are assembled and boiler structural steelwork 2 has reached its desired height, outer roof section 7 is erected, whereby main beams CI 7a, 7b, 7c are assembled on upper boiler structural steelwork bars 4. They can moreover be connected to one another by connecting beams, as for example by connecting beam 7d, which is arranged outside the outline defined by boiler wall 19. Connecting beam 7d supports main beams 7a, 7b and prevents the latter from having to take up OO excessively large tilting loads. If roof modules 8a, 8b are 00 respectively divided or split up still further, further CI connecting beams can also be arranged above internal space kO 13 surrounded by boiler wall 19, e.g. parallel to existing c-i connecting beam 7d. Accordingly, four roof modules arranged in a square, for example, would then be worked with.

On outer roof section 7, there is now arranged, for example, a cable hoisting system 17, which includes several cable hoisting devices whose traction rope bundles 18 are each attached to the corners of roof modules 8a, 8b. The cable hoisting systems can be positioned both on main beams 7a, 7b, 7c and on the connecting beams, for example on connecting beam 7d.

The erection of boiler structural steelwork 2 is essentially completed with this building stage. The simultaneous assembly of boiler wall 19a in upper section 9 and the erection of internal components beneath roof modules 8a, 8b is now commenced. This procedure is illustrated in figure 4. For the erection of boiler wall 19a, individual boiler wall parts 20 and, as mentioned, also buckstays and other parts, as required, are introduced from above using crane 16 into interior space 13 and secured, for example suspended on outer roof section 7.

Boiler wall 19a is thus erected as in a register from top to bottom. The gas pass bounded by the latter and already emerging in its upper section 9 still has a free crosssection, which is bridged solely by main beam 7b.

At the same time as the installation of parts 20 for the I erection of boiler wall 19, the internal components are erected beneath this construction point. For this purpose, cable hoisting system 17 raises inner roof modules 8a, 8b in each case to a height, and holds them at this height, which is such that the internal components can be erected step by step. When roof modules 8a, 8b have been raised to OO a first height, the boiler roof is first erected beneath them and secured in a suspended manner. Roof modules 8a, 8b CI are then raised to the next assembly height, so that a Cfirst economiser heating coil 21 can be run beneath the c-i boiler roof and secured with carrying pipes 28 to roof modules 8a, 8b. A further economiser heating coil 22 follows after further lifting. Roof modules 8, 8b are now each raised step by step and, as illustrated in figure 4, a first reheater coil 23 and a second reheater coil 24 are installed one after the other, suspended on carrying pipes.

After further raising of roof modules 8a, 8b, a superheater coil 25 arranged at the lowermost point can be installed.

Roughly at the same time as the completion of the aforementioned internal components 21 to 25, boiler wall 19a has in the meantime also been completed. In the next step illustrated in figure 5, construction unit 26 comprising roof modules 8a, 8b and internal components 21 to 25 is raised and thus guided upwards between boiler walls 19a to its installation point. Roof modules 8a, 8b are raised into the intermediate spaces present between main beams 7a, 7b, 7c and connected there to main beams 7a, 7b, 7c. Main beams 7a, 7b, 7c thus carry roof modules 8a, 8b and the loads suspended from the latter. Internal components 21 to 25 can now be connected.

Boiler wall 19b and boiler hopper 11 are subsequently assembled in order to obtain the finished steam generator according to figure 1.

Figure 6 illustrates a modified embodiment of a steam generator 1 in a diagrammatic and simplified plan view.

Insofar as agreement exists with the details described above, the same reference numbers are used and reference is c- made to the above description. A total of three main beams 7a, 7b, 7c span here the internal space defined by boiler wall 19, whereby main beams 7a, 7c are again arranged O outside the gas pass defined by boiler wall 19. Main beams 7a, 7ab, 7b, 7bc, 7c are arranged at uniform distances and parallel to one another and are preferably designed Cundivided. Main beams 7ab, 7b, 7bc in particular have no c-q point of separation in the immediate vicinity of boiler wall 19 inside interior space 13. They are assigned to outer boiler structural steelwork roof 7 and not to inner boiler structural steelwork roof 8.

Inner boiler structural steelwork roof 8 comprises here of a total of four roof modules 8a, 8aa, 8bb and 8b. In plan view, the latter each have an approximately rectangular outline and pass into the intermediates spaces defined by main beams 7a to 7c. Their length is somewhat smaller than the spacing of the opposite-lying boiler walls, which run transversely to main beams 7a to 7c. Their width corresponds to the main beam spacing. Roof modules 8a to 8b can be raised together essentially synchronously into the installation point. Roof modules 8a to 8b can hang loosely beside one another or also be connected between each other by struts subsequently running beneath main beams 7a to 7c or also be connected together by the internal components. A common closed boiler roof can for example be carried by all four roof modules 8a to 8b. It is however also possible to separate roof modules 8a to 8b completely and to raise the latter one after the other into their installation point between main beams 7a to 7c. This enables, as the case may be, a further rationalisation of the assembly process.

Figure 7 illustrates the arrangement of roof modules 8a to l 8b in the installed position between main beams 7a to 7c, which form outer roof section 7. As can be seen, at least boiler roof 19c and internal components (not illustrated in c- detail) are suspended with suitable carrying pipes from roof modules 8a to 8b, which form inner roof section 8.

Main beams 7a to 7c are designed for example as a box- OO section and corresponding beams of roof modules 8a to 8b are flanged-mounted on the latter laterally.

(NO

S Roof modules 8a to 8b of the inner roof section can, as c-i illustrated in figure 8, also be arranged suspended, if need be, beneath main beams 7a to 7c. Roof modules 8a to 8b can abut against one another laterally or, as illustrated in the figure 8, maintain a spacing with respect to one another.

Diverging from this, individual roof modules 8a, 8aa and/or 8bb can be connected to roof section 8 which is then formed in one piece, said roof section being fixed suspended beneath main beams 7a to 7c. Inner roof section 8 can, as shown, have beams designed continuous. However, if need be, points of separation can also be provided. Such points of separation can lie beneath individual main beams or also between the latter. Such optional points of separation 27, 28 are drawn dashed in figure 9. Points of separation 27, 28 are bridged by connection means. Depending on the desired production sequence, the corresponding connection means can already be fitted during the pre-assembly of inner roof section 8 beneath the subsequent installation point. Alternatively, it is possible to raise the individual parts of inner roof section 8 simultaneously or one after the other to their installation point until they lie adjacent to main beams 7a to 7c and then to close the points of separation 27, 28 with suitable connection means.

D Figure 10 illustrates a large steam generator with an outer CI boiler structural steelwork roof section 7 and an inner boiler structural steelwork roof section 8, which essentially correspond to the construction according to figure 8. The previous description on the basis of the same reference numbers applies to figure 10, with the exceptions explained below. Two outer main beams 7a, 7c are provided which lie outside the gas pass, as well as four main beams 00 S 7ab, 7b, 7bb, 7bc which extend transversely over the gas kO CI pass and which, as already described above, are not divided S at least vertically above boiler wall 19 or inside the q region bordered by boiler wall 19.

Inner boiler structural steelwork roof section 8 consisting for example of three roof modules 8a, 8b, 8c is illustrated lying on the boiler floor. Roof modules 8a, 8b, 8c each have a grid structure with beams 29, 30. Whereas beams 29 are fixed beneath main beams 7ab, 7b, 7bb, 7bc transversely to the latter and suspended thereon, beams 30 lie parallel to main beams 7ab, 7b, 7bb, 7bc and thus between the latter on beams 29. Main beams 7ab, 7b, 7bb, 7bc can be arranged at uniform or different distances from one another.

For the rational erection of large steam generator 1, a boiler structural steelwork 2 is first erected with an outer roof section 7, which includes a plurality of main beams 7a to 7c. At least one, e.g. main beam 7b, bridges the gas pass to be erected. When main beams 7a to 7c have been assembled, the erection of upper boiler wall 9a commences, whereby the corresponding parts are lifted between main beams 7a to 7c from above into the boiler structural steelwork and positioned. The erection of inner roof section 8, in one piece or divided into roof modules 8a, 8b, suspended beneath its subsequent installation point inside the space bounded by boiler columns 3, begins immediately. Internal components 23 to 25 are fixed to roof modules 8a, 8b. Construction unit 26 thus erected is raised upwards all in one piece or roof module by roof module and l assembled between main beams 7a, 7b, 7c or beneath the same. The production method proposed in this regard permits a further shortening of the construction times of steam c- generators, in particular when their gas pass has a large cross-section which exceeds the dimensions 15 m x 15 m.

00 c-i

Claims (11)

1. A method for the assembly of a steam generator (1) with a gas pass bounded by a boiler wall whereby the steam generator has a boiler structural steelwork with a divided boiler structural steelwork roof whereby the boiler structural steelwork roof (6) has an outer roof section which includes a OO 00 plurality of main beams (7a, 7b, 7c) mounted on the boiler structural steelwork at least one of which (-i ND main beams extends transversely over the gas pass and Cbetween which main beams there are beam intermediate spaces present, and a one-piece or multi-piece inner roof section which is carried by the main beams (7a, 7b, 7c), whereby the method includes the following steps: cable hoisting systems from which traction ropes (18) extend downwards, are positioned on the main beams (7a, 7b, 7c), regions of the boiler wall (19) are pre-assembled as in a register and introduced from above through the beam intermediate spaces into the boiler structural steelwork and fixed there, during the erection of the boiler wall the internal components (25) are pre-assembled with the inner roof section in a lower region of the boiler structural steelwork (19) and connected with the traction ropes (18), the inner roof section and the internal components are then raised by means of the cable hoisting systems (17) upwards to their installation point in an upper region of the gas pass and connected, and the inner roof section is connected to the outer roof section (7)

2. The method according to claim 1, characterised in that the one-piece or multi-piece inner roof section is erected on the boiler floor and is connected with the traction ropes (18). 0 3. The method according to claim 1, characterised in that the one-piece or multi-piece inner roof section is IN raised step by step and that the internal components are erected suspended beneath the inner roof section

4. The method according to claim 1, characterised in that the inner roof section comprises roof modules (Sa, 8b) not connected together, which are raised simultaneously upwards to their installation point after erection of the internal components The method according to claim 1, characterised in that the inner roof section comprises roof modules (8a, 8b) not connected together, which are raised upwards one after the other to their installation point in each case after the erection of the internal components (25) connected to them.

6. The method according to claim 4 or 5, characterised in that the roof modules (8a, 8b) are fixed between the main beams (7a, 7b, 7c).

7. The method according to claim 4 or 5, characterised in that the roof modules (Sa, 8b) or the roof section (8) formed in one piece are arranged beneath the main beams (7a, 7b, 7c) and connected to the latter. S 8. A steam generator in particular for the c-i generation of steam by means of fossil fuels, in particular large steam generators, with a boiler structural steelwork with boiler walls (19) which are carried by the boiler structural steelwork and which are designed as OO 0 tube walls and bound a gas pass, c-i IN with a boiler structural steelwork roof which is Scarried by the boiler structural steelwork and is divided into an outer and an inner roof section (7, whereby the inner roof section can be transported during assembly upwards through the gas pass to the outer roof section already erected there and is connected in the assembled state to the outer roof section with internal components (25) which are arranged in the gas pass and are carried by the boiler structural steelwork roof and a boiler roof (19c) which is carried by the boiler structural steelwork roof characterised in that, the outer boiler structural steelwork roof (7) contains a plurality of main beams (7a, 7b, 7c), at least one of which spans the gas pass.

9. The steam generator according to claim 8, characterised in that the beams (7a, 7b, 7c) belonging to the outer boiler structural steelwork roof are arranged at intervals parallel to one another. O 10. The steam generator according to claim 8, characterised in that at least the main beam (7b) belonging to the outer boiler structural steelwork roof and bridging the gas pass is designed continuous over its length.

11. The steam generator according to claim 8, Scharacterised in that the main beams (7a, 7b, 7c) are OO 0 arranged at uniform intervals from one another. (N ND 12. The steam generator according to claim 8, Scharacterised in that the main beams (7a, 7b, 7c) are designed as box-section beams.

13. The steam generator according to claim 8, characterised in that the inner roof section is formed by a single roof module, which is arranged beneath the main beams (7a, 7b, 7c).

14. The steam generator according to claim 8, characterised in that the inner roof section is formed by a plurality of roof modules, which are not rigidly connected between one another. The steam generator according to claim 14, characterised in that the roof modules (8a, 8b) are arranged beneath the main beams (7a, 7b, 7c).

16. The steam generator according to claim 14, characterised in that the roof modules (8a, 8b) are arranged between the main beams (7a, 7b, 7c).

17. The steam generator according to claim 13, 14, 15 or 16, characterised in that the roof module (8a) or the roof modules (8a, 8b) are carried by the main beams. Dated this 27th day of February 2006 ALSTOM TECHNOLOGY LTD WATERMARK PATENT TRADE MARK ATTORNEYS 290 Burwood Road Hawthorn, Victoria 3122