Helical Baffle for Once-Through Steam Generator

Abstract

A steam generator includes a shroud and an annular stepwise helical baffle extending along at least part of a length of the shroud. There is a riser located in a central region of the steam generator. The helical baffle is made up of at least one annular sector of flat plates. The edges of the flat plates may be straight or corrugated.

Claims

1. A steam generator comprising: a shroud having a top and a bottom; an annular stepwise helical baffle extending along at least part of a length of said shroud; a riser located in a central region of said steam generator; a tube bundle region within said steam generator, said tube bundle region comprising a plurality of tubes; wherein said helical baffle comprises an annular sector comprising flat plates, each of said flat plates having at least one side edge.

2. The steam generator of claim 1, wherein said annular stepwise helical baffle extends from said bottom to said top of said shroud.

3. The steam generator of claim 1, wherein said annular stepwise helical baffle comprises single helix.

4. The steam generator of claim 1, wherein said annular stepwise helical baffle comprises multiple helices.

5. The steam generator of claim 1, further comprising a shelter enclosing said central region.

6. The steam generator of claim 1, wherein said plate side edges are straight. The steam generator of claim 1, wherein said plate side edges are corrugated.

8. The steam generator of claim 1, wherein said plate side edges are arranged such that none of said tubes lay along said plate side edges.

9. The steam generator of claim 1, wherein said an annular sector of plates forms a complete 360 annulus.

10. The steam generator of claim 1, wherein at least two of said plate edges are connected by a vertical plate.

11. The steam generator of claim 1, wherein at least two of said plate edges are mechanically fastened.

12. The steam generator of claim 1, wherein at least two of said plate edges are welded together.

13. The steam generator of claim 5, wherein said shelter comprises a plurality of straight panels inserted along said tube bundle, said panels positioned such that said tube bundle is divided into an outer tube bundle region and a central tube bundle central region.

14. The steam generator of claim 13, wherein said central tube bundle region further comprises at least one single-segmental baffle.

15. The steam generator of claim 13, wherein said central tube bundle region is equipped with double segmental baffles.

16. The steam generator of claim 1, wherein said tube bundle region is spaced from said shroud to form a said gap between said tube bundle region and said shroud, said gap being sealed by vertical baffles.

17. The steam generator of claim 16, wherein said vertical baffles are fixed to said shroud.

18. The steam generator of claim 16, wherein said vertical baffles are fixed to said shroud said flat plates.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the accompanying drawings, forming a part of this specification, and in which like reference numbers are used to refer to the same or functionally similar elements:

[0017] FIG. 1 is a front view of a prior art OTSG arrangement;

[0018] FIG. 2 is a front view of a prior art SMR arrangement;

[0019] FIG. 3 is a front view of the OTSG according to the present invention;

[0020] FIG. 4 is a cross sectional view of the OTSG, taken along line 4-4 of FIG. 3;

[0021] FIG. 5 is a cross sectional view of the OTSG, showing an embodiment of the invention in which an inner shelter is employed;

[0022] FIG. 6 is a front view of the OTSG showing the use of single segmental baffles and double segmental baffles; and

[0023] FIG. 7 is a cross sectional view of the OTSG, showing the use of vertical baffles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Referring now to drawing FIGS. 3-7, which depict an OTSG 300 embodying the annular stepwise helical baffle 302 according to the present invention, a preferred embodiment of the present stepwise helical baffle 302 is shown. In certain embodiments, the helical baffle 302 extends from bottom to the top of the shroud 304. In other embodiments, it can be limited to a specific region of the tube bundle 306. Embodiments of the invention may have single or multiple helices. In some embodiments, the central region 308 is occupied by the central riser 310 in the SMR design. In others, it is enclosed by inner shelter 312 for normal full circular bundle.

[0025] The helical baffle 302 is made of an annular sector of drilled only flat plates 314. The segment extends from the central region 310 to the shroud 304. The side edges of the annular sector plates 314 can be straight 314a or corrugated 314b. An important feature is that edges of the sector plate 314 follow the tube drill pattern such that no tube lays along the edges of the annular sector plates 314. FIGS. 4 & 5 show twelve annular sector plates 314 that form a complete 360 annulus. However, the number of sector plates 314 that form the 360 annulus can change depending on the configuration. Those sector plates 314 are positioned side by side and offset axially along the tube bundle 306 direction to form the helical baffle 302. The offset between consecutive sector plates 314 depends on the design. The gap between consecutive sector plates 314 can be sealed depending on the allowable leakage. If an offset bigger than the thickness of the annular sector plate 314 is designed, a vertical plate 316 should be used to connect the edges of the consecutive sector plates. Groups of sector plates 314 can be mechanically fastened or welded together as single part to facilitate assembly.

[0026] With reference to FIG. 5, it is also within the scope of the invention for a central shelter 312 to be formed from straight panels that are inserted along the tube bundle 306. The shelter 312 divides the bundle 306 into outer annular region 318 and central region 320. It is within the scope of the invention for the space between tubes (not shown) on both sides of the shelter 312 to be increased to accommodate situations in which thick panels are specified or required for a particular application or situation. The central region 310 of the bundle 306 can be equipped with single segmental baffles 322a or double segmental baffles 322b depending on the requirements of a particular application or situation. The baffles 322a, 322b should be designed to ensure that the pressure drop on both sides of the shelter 312 is the same for an evenly split flow rate.

[0027] The gap 324 between the tube bundle region 306 and the shroud 304 is, in certain embodiments, sealed using vertical baffles 326 located at different orientations along the circumference. The vertical baffles 326 are preferably fixed to the shroud 304 or the vertically aligned annular sector plates. Also, the gap 328 between the tube bundle region 306 and the central region outer boundary 330, is in certain embodiments, sealed with vertical baffles 332 that are similar to vertical baffles 326. However, the vertical baffles 332 may extend for a short distance as perforated plates inside the bundle 306 region to introduce additional hydraulic resistance to the flow near the inner radius of the bundle 306. This additional resistance, if required, ensures that the velocity radial distribution does not increase significantly near the inner radius of the bundle 306.

[0028] The present invention can be applied to any OTSG. Multiple parameters of the presently disclosed invention can be changed to satisfy different steam generator sizes and bundle arrangements. Such parameters are the number of annular sector plates 314 per 360, the axial offset between consecutive plates 314, number of helices, the region along the bundle 306 where this design is used, and the size of the central region and the use of baffles 326, 332 in the central region.

[0029] The present invention provides many advantages. The present design introduces helical support plates 314 to the tube regions of the OTSG. This new arrangement can be manufactured following the procedure of the current state of the art of the industry. Introducing helical support plates 314 streams the flow to follow support plate 314 orientation which generates cross flow component of the velocity. The presently-disclosed design provides enhancement of heat transfer rate under a wide variety of operating conditions. The cross flow enhances the heat transfer coefficient on the tubes outside surface and consequently the heat transfer rate. Improving the bundle heat transfer rate allows an increase of the thermal duty of the OTSG for the same tube bundle 306 size or reduces the tube bundle 306 size for the same heat duty. This results in a reduction in the NPP capital cost per megawatt.

[0030] While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. It will also be understood that the present invention includes any combination of the features and elements disclosed herein and any combination of equivalent features. The exemplary embodiments shown herein are presented for the purposes of illustration only and are not meant to limit the scope of the invention. Thus, all the features of all the embodiments disclosed herein are interchangeable so that any element of any embodiment may be applied to any of the embodiments taught herein.