US3547084A

US3547084A - Vapor generator with integral economizer

Info

Publication number: US3547084A
Application number: US884688A
Authority: US
Inventors: Theodore S Sprague
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1969-12-12
Filing date: 1969-12-12
Publication date: 1970-12-15
Anticipated expiration: 1987-12-15

Description

United States Patent VAPOR GENERATOR WITH INTEGRAL ECONOMIZER 6 Claims, 4 Drawing Figs.

U.S. Cl.. 122/32 Int. Cl F22b l/06 Field ot'Search 122/32, 33,

Primary Examiner-Kenneth W. Sprague Attorney-J. Maguire ABSTRACT: A vapor generator including a pressure vessel, a plurality of heat exchanger tubes extending within the vessel to convey therethrough a hot primary fluid, and an economizer chamber integrally contained within the vessel and enclosing a portion of the tubular heat exchange surface to effect preheat of a secondary liquid which flows through the chamber. The economizer chamber is positioned in spacedapart relation to the vessel to define therewith an annular downcorner flow passage that communicates with one or more riser passages, the latter extending through the chamber to accommodate the heated riser flow, with the riser discharge therefrom subsequently entering the residual vessel volume.

PATENTEU DEC] 5 I970 sum 1 OF 2 IINVENTOR. T Theodore S. Sprague AT ORNEY PATENTED nt cl 519701 35471084 "sumanr v 1 VAPOR GENERATOR WITI-I INTEGRAL ECONOMIZER BACKGROUNDIAND SUMMARY OF TIIE INVENTION This is a continuation-impart of application Ser. No. 782,555,filedDec. 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 liquidthat 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 thatis 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. i i

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 preventstherrnal 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: 1

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 ofthe vapor generator shown in FIG. I as taken along line 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 a vertically elongated, generally cylindrical pressure vessel 11 d 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 economizer chamber 22 that g 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 of the 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 theresidual 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 tubesurface 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 rangeis 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 l3 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 22as 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 baflle 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 the advantage of increasing the effective heat exchange flow path of the feed liquid through chamber 22, although they may be omitted, if desired.

lt=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 permit 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 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 withrespect 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 4lA-D.

The conduits 42AD are preferably. arranged so that the riser passages 4lA-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 inven tion may sometimes be used to advantage without a corresponding use of the other features.

I claim:

1. In a vapor generator having a pressure vessel and a plurality of heat exchanger tubes extending within said vessel to accommodate the flow therethrough of a hot primary fluid, the improvement which comprises an economizer chamber disposed within said vessel in spaced-apart relation thereto to define therewith an annular downcomer passage, said economizer chamber enclosing a portion of the heat exchange surface of said tubes to preheat by heat transfer therethrough from the primary fluid a second liquid introduced into the economizer chamber, said economizer chamber having an outlet for discharging into the residual vessel volume heated secondary liquid to be vaporized by heat transfer from the primary fluid through tube surface area outside the economizer chamber and means defining at least one riser passage extending through said economizer chamber said riser passage being in communication with said downcomer passage to accommodate the circulation outside the economizer chamber of the heated secondary liquid discharged therefrom.

2. The improvement according to claim 1 wherein said economizer chamber is positioned in spaced-apart relation to a tubesheet associated with said heat exchanger tpbes to define with said tubesheet a flow space communicating said annular downcomer passage with each riser passage.

3. The improvement according to claim 1 where said economizer chamber has an annular outlet positioned in generally coaxial relation to said annular downcomer passage, and including an open conduit defining a single riser passage centrally located with respect to said outlet and downcomer passage.

4. The improvement according to claim 1 including a plurality of open conduits supported by said economizer chamber and extending therethrough to define a plurality of riser passages generally parallel to said downcomer passage.

5. The improvement according to claim 1 wherein at least one heat exchanger tube extends through said riser passage to facilitate thermosyphonic circulation of said heated secondary liquid.

6. The improvement according to claim 1 including conduit means disposed for connection outside said vessel to a source of secondary liquid and extending into the vessel to communicate said economizer chamber with said source for introducing said liquid into the economizer chamber, and baffle means disposed within said economizer chamber to increase the effective heat exchange flow path of said secondary liquid through the economizer chamber.