Vapor generator with integral economizer

BACKGROUND AND SUMMARY OF THE INVENTION

This is a continuation-in-part of application Ser. No. 782,555, filed Dec. 10,1968, now abandoned.

The present invention relates in general to vapor generators in which heat extracted from a hot primary fluid flowing through tubes extending within a pressure vessel is used to vaporize a secondary liquid that is introduced into the vessel.

More particularly, the invention is directed to a steam generator of the foregoing type which has an economizer chamber integrally contained within the vessel enclosing a portion of the tubular heat exchange surface for the purpose of preheating feedwater that is introduced directly into the economizer chamber, to flow therethrough, and exit therefrom into the residual vessel volume.

While steam generators having integral economizers are known, as exemplified by U. S. Pat. No. 3,356,135 issued to R. K. Sayre, the vapor generator construction of the instant invention has many advantageous features not to be found in any prior art.

In my vapor generator, the a economizer chamber is positioned in spaced-apart relation to the vessel to define therewith an annular downcomer passage that communicates with one or more of the riser passages extending through the chamber. Such an arrangement prevents thermal shock to the vessel by providing thermosyphonic circulation of the heated liquid around the outside of the economizer chamber.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In The Drawing:

FIG. 1 is a schematic elevation view, partly in section, of a vapor generator constructed in accordance with a preferred embodiment of the invention.

FIG. 2 is a cross-sectional plan view of the vapor generator showninFIG. 1 as taken alongline 2-2 therein.

FIG. 3 is a schematic elevation view, partly in section, of a vapor generator constructed in accordance with another embodiment of the invention·

FIG. 4 is a cross-sectional plan view of the vapor generator shown in FIG. 3 as taken along line 4-4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

As exemplified by FIGS. 1 and 2, the vapor generator 10 has a vertically elongated, generally cylindrical pressure vessel 11 in which is installed an upper tubesheet 12 and lower tubesheet 13, being enclosed on its outside face by hemispherical heads 15 and 16 respectively to form a unitary structure.

A plurality of parallel heat exchanger tubes 17 are disposed within the vessel 11 with their opposite ends secured in the tubesheets 12 and 13. Hemispherical head 15 forms a plenum 18 above the upper tubesheet 12 and has an inlet nozzle 19 for admitting hot fluid, such as the primary coolant from a nuclear reactor core (not shown), which flows downwardly through the tubes 17 and collects in a plenum 20 formed by hemispherical head 16 and lower tubesheet 13. The primary fluid exits plenum 20 through an outlet nozzle 21 provided in head 16.

Within vessel 11 is disposed an economiier chamber 22 that is supplied with feedwater to be preheated, which feedwater enters economizer chamber 22 directly through through thermally shielded conduits 23 that extend through nozzles 24 provided in vessel 11.

Economizer chamber 22 is positioned in spaced-apart relation to vessel 11 so as to define therewith an annular downcomer passage 25, and is positioned in spaced-apart relation to the lower tubesheet 13 to define therewith a flow space 39 that is in communication with the bottom of passage 35 and a centrally located riser passage 40 defined by an open ended tubular conduit 30. Economizer chamber 22 encloses a portion of the heat exchange surface of some ofthe tubes 17 such that the feedwater entering chamber 22 is preheated by heat transferred from the hotter primary fluid flowing through the tubes in that portion of the heat exchange surface with the lengths of tubes 17 within chamber 22. The feed liquid thus absorbs heat in flowing through chamber 22 and exits therefrom through outlet 25 provided at the top thereof. This heated liquid that is discharged into the residual vessel volume is further heated and a portion is vaporized and superheated by heat transfer from the hotter primary fluid as it flows around the tube surface located outside economizer chamber 22.

In the particular embodiment shown in FIGS. 1 and 2, the vapor generator 10 is constructed as a once-through steam generator in which the steam generation rate over substantially the entire operating load range is such that a clearly defined water level does not exist within the vessel 11. Rather there exists a bubbling and boiling disengaging space 38 above the top of economizer chamber 22, within which the steam as it is generated separates by thermosyphonic action from the saturated liquid. The steam in traveling upwardly in heat transfer relation is superheated as it flows about the tube surface located in the vessel volume zone 36 above the disengaging space 38. The residual saturated liquid remaining in the disengaging space 38 after separation from the steam flows outwardly and down through annular passage 35, sweeping across the lower tubesheet 13 and then flowing upwardly through the riser passage 40. It should be noted that to promote thermosyphonic circulation within the vapor generator 10, the conduit 30 contains heat exchange tubes 17 to impart heat to the upwardly flowing fluid in riser passage 40.

Baffle 28 is provided inside the vessel 11 and spaced from the inside wall of the vessels to form an annular flow passage 37 which opens into the vapor space in the upper portion of the vessel, above disengaging space 38. Thus baffle 28 is so arranged that annular passage 37 is open at its upper end and closed at its lower end whereby the path of the exiting steam is separate and distinct both from the steam within space 36 and from the vapor and liquid in disengaging zone 38, the exiting steam leaves the passage 37 via a plurality of spaced nozzles 27 located in the vessel 11 wall near the lower extremity of baffle 28. The baffle 28 extends downward toward the top of the economizer chamber 22 as far as possible without interfering with the circulation of liquid through downcomer passage 35 so the vessel 11 wall will be maintained at substantially the same temperature as the exiting steam to minimize the thermal stresses in the tubes 17. The stress is a function of the differential mean temperature of the tubes 17 and the vessel 11 wall, and by sweeping a large portion of the vessel 11 wall with superheated steam, as occurs where baffle 28 is extended to terminate near the top of economizer chamber 22, the mean vessel 11 wall temperature can be maintained very close to the mean temperature of tubes 17 and hence tube thermal stresses can be minimized.

It should be noted that the economizer chamber 22 has a generally annular configuration and can be simply constructed using an outer cylindrical sheet 29, a tubular conduit 30, and an annular bottom plate 31 connected along its outer edge to cylindrical sheet 29 and connected along its inner edge to the lower end of conduit 30.

Within economizer chamber 22 are provided a plurality of annular disc baffles 32 and 33 arranged in generally parallel, vertically spaced relation to One another and to the bottom plate 31. The baffles 32 and 33 are arranged in alternate sequence over the height of economizer chamber 22, the baffles 32 being connected along their outer edges to cylindrical

3,547,084 sheet 29 for support thereby, and the baffles 33 being connected along their inner edges to tubular conduit 30 for support thereby. Thus, the baffles 32 and 33 form within economizer chamber 22 a sinuous flow passage for the feedwater being preheated as it flows generally upward through chamber 22 from the entry locations of nozzles 24 to the outlet 25. Baffles 32 and 33 within economizer chamber 22 offer the advantage of increasing the effective heat exchange flow path of the feed liquid through chamber 22, although they may be omitted, if desired.

It should be noted that the tubes 17 pass through bottom plate 31 and such baffles 32,33 as they individually encounter in their upward extension through economizer chamber 22. To accommodate these extensions, the bottom plate 31, and the baffles 32,33, are provided with suitably sized holes 34 to perniit the tubes 17 to pass upwardly through the plate 31 and baffles 32, 33 and thence into the upper tubesheet 12 where they are secured. The lower extremities of tubes 17 are similarly secured in lower tube sheet 13.

The economizer chamber 22 geometry exemplified in vapor generator 10 is designed to provide fluid flow and temperature conditions that are in general symmetrical in distribution with respect to the central longitudinal axis of vessel 11. This can be readily seen from FIGS. 1 and 2 which show the annular outlet 25 of economizer chamber 22 positioned in generally coaxial relation to the annular downcomer passage 35 and the single riser passage 40 defined by conduit 30 centrally located with respect to outlet 25 and downcomer passage 35 and extending lengthwise generally parallel to downcomer passage 35.

FIGS. 3 and 4 illustrate a vapor generator 10’ generally similar to the vapor generator 10, but having an economizer chamber 22' of somewhat different design in that it has a plurality of riser passages 41A, 41B, 41C and 41D defined by corresponding open ended conduits 42A, 42B, 42C and 42D supported by a bottom plate 43 substantially in the same manner as bottom plate 31 supports conduit 30 in FIGS. 1 and 2.

Bottom plate 43 is positioned in parallel spaced-apart relation to the tubesheet 13 to define therewith a flow space 39' so downcomer passage 29' will be in communication with the riser passages 41A—D.

The conduits 42A—D are preferably arranged so that the riser passages 41A—D are generally parallel to the downcomer passage 29'.

While in accordance with the provisions of the statutes there is illustrated and described herein a specific embodiment of the invention, those skilled in the art will understand that changes may be made in the form of the invention covered by the claims, and that certain features of the inven4 tion may sometimes be used to advantage without a corresponding use of the other features.