Steam generator

Abstract

A steam generator comprising a vessel having an inlet and an outlet, and in use a primary fluid flow enters the vessel through the inlet and exits the vessel through the outlet. A plurality of modules are connected in series and at least partially housed within the vessel, and each module comprises at least one tube. The modules are arranged such that at least one tube of one module is coaxial with at least one tube of an adjacent module so as to define a conduit through which a secondary fluid can flow from one module to an adjacent module.

Claims

1. A steam generator comprising: a vessel having an inlet and an outlet, wherein in use, a primary fluid flow enters the vessel through the inlet and exits the vessel through the outlet; and a plurality of modules connected in series and at least partially housed within the vessel, wherein each module comprises: a plurality of tubes, and a flange plate positioned at an axial end of the plurality of tubes, wherein the modules are arranged such that each of the plurality of tubes of one module is coaxial with one of the plurality of tubes of an adjacent module so as to form a conduit bundle comprising a plurality of conduits through which a secondary fluid can flow from one module to an adjacent module, and wherein adjacent modules of the plurality of modules are connected together via the flange plates of the adjacent modules, and wherein an intermediate plate is positioned between adjacent flange plates of the adjacent modules, the intermediate plate comprising a plurality of holes, each hole receiving one of the plurality of tubes of each of the adjacent modules, and the axial end of the plurality of tubes of the one module and the axial end of the plurality of tubes of the adjacent module are both located within the intermediate plate.

2. The steam generator according to claim 1, wherein each flange plate comprises a plurality of holes, each hole receiving one of the plurality of tubes.

3. The steam generator according to claim 1, wherein the intermediate plate and two flange plates are bolted together.

4. The steam generator according to claim 1, wherein the intermediate plate and the flange plates are welded together.

5. The steam generator according to claim 1, further comprising a seal between adjacent flange plates and the intermediate plate.

6. The steam generator according to claim 1, wherein the flange plates are formed as a separate component to the tubes.

7. The steam generator according to claim 6, wherein one or more of the plurality of flange plates are integrally formed with the vessel.

8. The steam generator according to claim 1, wherein the conduit is U-shaped.

9. The steam generator according to claim 1, wherein the conduit is helical.

10. The steam generator according to claim 9, wherein one tube defines one turn of the helical conduit and an adjacent tube defines an adjacent turn of the helical conduit.

11. A steam generator system comprising the steam generator according to claim 1; a primary fluid flow channel connecting to the inlet of the vessel and for connection to a heat source; and a secondary fluid flow channel connecting to the outlet of the vessel and for connection to a turbine.

12. A steam generator comprising one or more tube bundles, the steam generator being configured to receive a secondary flow through the tube bundles and a primary flow outside the tube bundles; wherein each tube bundle comprises a first sub-bundle connected in series to a second sub-bundle, wherein each of the first and second sub-bundles comprise a plate including a plurality of holes, each hole receiving one of a plurality of tubes of the respective first or second sub-bundle, and wherein the plate of the first sub-bundle connects to the plate of the second sub-bundle with an intermediate plate positioned between the plates of the first and second sub-bundles, the intermediate plate comprising a plurality of holes, each hole receiving one of the tubes of each of the first and the second sub-bundles, an axial end of the plurality of tubes of the first sub-bundle and an axial end of the plurality of tubes of the second sub-bundle are both located within the intermediate plate, and the first and second sub-bundles and the intermediate plate are arranged such that the tubes of the first sub-bundle are substantially coaxial to the tubes of the second sub-bundle, such that in use, fluid flows from the first sub-bundle to the second sub-bundle.

13. The steam generator according to claim 1, wherein each of the plurality of holes of the intermediate plate include a chamfered axial end.

14. The steam generator according to claim 1, wherein the vessel is configured to receive the primary fluid as a pressurized liquid.

15. The steam generator system according to claim 11, wherein the heat source is a nuclear reactor.

16. A nuclear power plant steam generator comprising: a vessel having an inlet and an outlet, wherein in use, a primary fluid flow from a nuclear reactor of the nuclear power plant enters the vessel through the inlet and exits the vessel through the outlet; and a plurality of modules connected in series and at least partially housed within the vessel, wherein each module comprises: a plurality of tubes, and a flange plate positioned at an axial end of the plurality of tubes, wherein the modules are arranged such that each of the plurality of tubes of one module is coaxial with one of the plurality of tubes of an adjacent module so as to form a conduit bundle comprising a plurality of conduits through which a secondary fluid can flow from one module to an adjacent module, and wherein adjacent modules of the plurality of modules are connected together via the flange plates of the adjacent modules, and wherein an intermediate plate is positioned between adjacent flange plates of the adjacent modules, the intermediate plate comprising a plurality of holes, each hole of the plurality of holes of the intermediate plate receiving one of the plurality of tubes of each of the adjacent modules, and the axial end of the plurality of tubes of the one module and the axial end of the plurality of tubes of the adjacent module are both located within the intermediate plate.

Description

DESCRIPTION OF DRAWINGS

(1) The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 illustrates a cross section of a steam generator;

(3) FIG. 2 illustrates a cross section through a connector between two conduit modules of the steam generator of FIG. 1;

(4) FIG. 3A and 3B each illustrate a cross section through alternative connections between two conduit modules; and

(5) FIG. 4 illustrates a tube of a conduit module of an alternative steam generator;

DETAILED DESCRIPTION

(6) Referring to FIG. 1 a steam generator is indicated generally at 10. The steam generator includes a conduit bundle 12 partially contained within a vessel 14. The vessel 14 includes an inlet 16 and an outlet 18. In the present embodiment, the vessel is formed using conventional methods and design, so will not be described in more detail here. In use, a primary fluid flow (indicated by arrow 20) enters the steam generator through the inlet 16, flows through the vessel 14 and exits the steam generator though outlet 18.

(7) The conduit bundle 12 includes a plurality of conduits 22. The conduits are arranged so that an inlet of each conduit connects to an inlet header 24 and an outlet of each conduit connects to an outlet header 26. In use, a secondary fluid flow (indicated by arrow 28) flows through the conduit bundle, entering each conduit of the bundle at the inlet header 24 and exiting each conduit of the bundle at the outlet header 26.

(8) As will be understood by those skilled in the art, the pressure of the primary fluid flow 20 will be greater than the pressure of the secondary fluid flow 28. As will be discussed later, during use of the steam generator 10 it is important that the secondary fluid flows through the conduits 22 and the primary fluid is external to the conduits.

(9) In the present embodiment, each of the conduits 22 are an inverted U-shape and so form an inverted U-shaped conduit bundle 12.

(10) The conduit bundle 12 is formed as a modular arrangement, In the present embodiment, to form the U-shaped conduit bundle, two end modules for connecting to the inlet header 24 and the outlet header 26, four straight tubed modules and two arcuate modules are provided. However, the conduit bundle may comprise any number of modules (e.g. two or more modules) depending on the requirements (e.g. size and heat transfer requirements) of a given steam generator, and the modules may take any suitable form.

(11) Each module comprises a plurality of tubes 30 (only one set of tubes labelled for improved clarity), and a plate 32a, 32b, 34a and 34b (only four plates labelled for clarity) associated with at least one axial end of the tube (a plate is associated with both axial ends of the tubes for all modules except the two end modules that connect to the headers 24, 26).

(12) Considering the modules indicated at 36 and 38 in FIG. 1. Module 36 is connected in series to module 38 and modules 36 and 38 are positioned so that the tubes of module 36 are coaxial with the tubes of module 38. A plate 32a is positioned at one end of the tubes of one module 36 and another plate 34a is positioned at an opposite axial end of the tubes of the module 36. Similarly, a plate 32b is positioned at one axial end of the tubes of the module 38 and another plate 34b is positioned at an opposite end of the tubes of the module 38.

(13) Referring now to FIG. 2, the plates include a series of holes dimensioned to receive each of the tubes 30 of the respective module. That is, as illustrated in FIG. 2, the plate 34a receives each of the tubes of the module 36 and the plate 32b receives each of the tubes of the module 38. In this way, the plates 34a, 32b support the tubes and define the spacing therebetween.

(14) An intermediate plate 40 is provided between the plates 34a and 32b of the modules 36, 38. The intermediate plate 40 includes a plurality of holes and receives tubes from both the module 36 and the module 38. The axial ends of each hole in the intermediate plate are chamfered (in the region 46 indicated for one hole) to reduce the likelihood of mechanical interference between the tubes of each module and the intermediate plate. In the present embodiment, the tubes are a close fit to the holes in the intermediate plate.

(15) In the present embodiment, the flange plates 34a, 32b include a recess within which the intermediate plate is seated. An O-ring seal 44 is provided around the edge of the intermediate plate to improve sealing between the intermediate plate and the two flange plates 34a, 34b.

(16) The two flange plates 34a, 34b and the intermediate plate 40 are connected together using a fastener 42. In the present embodiment the fastener is a bolt and nut, but any suitable fastener may be used.

(17) The flange plates 34a, 34b have two main functions: as a tube sheet and as a mechanical interface with another conduit module 12. As a tube sheet, the flange plates provide a mechanical location for the tubes. As a mechanical interface, the flange plates provide a means of aligning and attaching an adjacent module.

(18) The thickness of the flange may be minimised so as to reduce weight. However, the thickness of the flange will also be selected so as to allow for tube expansion and to maintain structural integrity (e.g. to avoid unacceptable bending or distortion of the flanges). The flanges may be clad to improve structural integrity.

(19) An exemplary use of the steam generator 10 is in a pressurised water reactor (PWR). In such an exemplary embodiment, the inlet 16 of the vessel 14 receives a primary fluid flow (e.g. liquid water) from a reactor. By way of illustration only, the absolute pressure of the fluid entering the inlet 16 may be about 15 MPa, but the skilled person will understand that this can vary depending on reactor design and reactor loading. The primary fluid flow circulates through the vessel and exits through the outlet 18 where it re-circulates to the reactor.

(20) The inlet of the conduit bundle 12 receives a secondary fluid flow (e.g. liquid water) from a condenser. By way of illustration only, the absolute pressure of the fluid entering the inlet of the conduit bundle may be about 6 MPa, but the skilled person will understand that this can vary depending on reactor design and reactor loading. The secondary fluid flows along each conduit of the conduit bundle flowing from one tube of one module to a coaxial tube of an adjacent module. The secondary fluid flow then exits the conduit bundle at the outlet header 26, for example as saturated steam. The secondary fluid then flows to a turbine and back to the condenser. The turbine is generally connected to a generator to generate electricity.

(21) During operation of the steam generator, the pressure differential between the lower pressure fluid inside the conduit bundle and the higher pressure fluid outside the conduit bundle ensures that the flange plates remain connected and there is no leakage between the primary fluid flow and the secondary fluid flow.

(22) The modular arrangement of the conduit bundle means that large steam generators can be manufactured as smaller individual modules, which eases transportation and installation of steam generators because the component parts are smaller. Further, maintenance of the described steam generator may be eased because a single module can be inspected and/or replaced as required. The modularity of the conduit may also provide the following benefits: Size limitations within a supply chain can be removed; Larger steam generators can be manufactured; An increased choice of materials and material suppliers for the tubes; and Production, validation and manufacture of steam generators can be eased.

(23) Generally, tube supports are provided to support the conduits of the conduit bundle in the vessel. The construction of the described embodiment means that in some steam generator designs it will be possible to eliminate tube supports, for example if the tube length is selected to be below that where significant vibration would occur. Alternatively, it may be possible for the tube supports to become part of the module structure.

(24) It will be appreciated by one skilled in the art that, where technical features have been described in association with one or more embodiments, this does not preclude the combination or replacement with features from other embodiments where this is appropriate. Furthermore, equivalent modifications and variations will be apparent to those skilled in the art from this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting.

(25) For example, the flange plates of each conduit bundle may be connected using an alternative arrangement, for example the arrangements shown in FIGS. 3A and 3B. In FIGS. 3A and 3B similar reference numerals are used for similar features as the previously described embodiment, but a prefix 1 or 2 is used to distinguish between embodiments.

(26) In the arrangement shown in FIG. 3A, an intermediate plate 140 is positioned in a recess and between the flange plates 134a, 132b, similar to the previously described embodiment, such that an edge region of the two flange plates abuts against each other. However, instead of using an O-ring and a fastener, the flange plates are welded together in a region 148 along an abutment interface between the two flange plates.

(27) In the arrangement shown in FIG. 3B, an intermediate plate 240 is provided similarly to the arrangement shown in FIG. 3A, but in the arrangement shown in FIG. 3B the intermediate plate extends the full width of the flange plates, i.e. no recesses are provided in the flange plates for receiving the intermediate plate. The intermediate plate is then welded to each of the flange plates in a region 248a and 248b along an abutment interface between the intermediate plate and the flange plates.

(28) The example shown in FIG. 1 includes inverted U-shaped conduit bundles, but in alternative embodiments the conduit bundles may take any suitable form. For example, the conduit bundles may be helical (or coiled). In such embodiments, each module may define one or more of the loops of the helical conduit, FIG. 4 illustrates a tube 330 from a module of a helical conduit.

(29) In another alternative embodiment, the flange plates may not be a distinct component from the vessel and may instead be integrated with the vessel (e.g. with the wall/shell of the vessel).

(30) In a further alternative, the steam generator may include a single conduit and corresponding single conduit modules, as an alternative to conduit bundles.