US3661123A

US3661123A - Steam generator feedwater preheater

Info

Publication number: US3661123A
Application number: US103188A
Authority: US
Inventors: Nicholas D Romanos
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1970-12-31
Filing date: 1970-12-31
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09
Also published as: CA933056A

Abstract

Feedwater preheating apparatus for a shell and tube type vapor generator is disclosed incorporating a plurality of nozzles arranged to discharge cold feedwater into a collector conduit disposed in a region of the unit containing heated fluid. Inductor means are provided to aspirate heated fluid into the collector conduit for mixing with the feedwater whereby the latter is heated.

Description

United States Patent Romanos May 9, 1972 [54] STEAM GENERATOR FEEDWATER PREHEATER [72] Inventor:

[73] Assignee:

Nicholas D. Romanos, Chattanooga, Tenn.

Combustion Engineering Inc., Windsor, Conn.

[22] Filed: Dec. 31, 1970 [21] Appl.No.: 103,188

[52] U.S. Cl ....122/34, 122/438 [51] Int. Cl ..F22b 1/16 [58] Field olSearch ..l22/32,34,438

[56] References Cited UNITED STATES PATENTS 2,862,479 12/1958 Blaser et al. ..122/34 Coykendall 122/438 X Sprague 122/32 Primary Examiner-Kenneth W. Sprague Attorney-Carlton F. Bryant, Eldon H. Luther, Robert L. 01- son, John F. Carney, Richard H. Berneike, Edward L. Kochey, Jr. and Lawrence P. Kessler [57] ABSTRACT Feedwater preheating apparatus for a shell and tube type vapor generator is disclosed incorporating a plurality of nozzles arranged to discharge cold feedwater into a collector conduit disposed in a region of the unit containing heated fluid. Inductor means are provided to aspirate heated fluid into the collector conduit for mixing with the feedwater whereby the latter is heated.

14 Claims, 4 Drawing Figures PATENTEDMAY 9 I972 SHLET 2 OF 2 VEN T02 N/CHOI. AS A? ROM N0 5 A Tree/v5 Y STEAM GENERATOR FEEDWATER PREI'IEATER BACKGROUND OF THE INVENTION In the operation of shell and tube .vapor generators vaporizable liquid is placed in indirect heat exchange relation with a heated fluid. Conventionally, the heated fluid is conducted through tubes that are housed within a pressure shell with the vaporizable liquid being admitted to the shell in a manner to immerse most or all of the tube surface. In units of the prior art a cylindrical baffle is disposed about the bundle of tubes to divide the shell interior to an annular downflow passage with which the vaporizable liquid supply means communicates and an axially disposed evaporator chamber containing the bundle of tubes.

Because the feed liquid that is admitted to the downflow passage is at a considerably lower temperature than the vaporizable fluid flowing in the evaporator chamber and still lower than that of the heated fluid conducted by the tubes, means must be provided to counter the affects produced by the admission of this cold liquid. These affects include instabilities in the generation of vapor in local areas of the evaporation chamber, the creation of thermal gradients in critical areas of the tube-sheet-to-shell welded joints, and the aggravation of thermal expansion differential between the tubes and the cylindrical baffle.

It is well known that such problems can be alleviated by preheating the feed liquid prior to admitting it to the vapor generator and, particularly, prior to passing it to the evaporation chamber thereof. Such preheating has, in the past, been accomplished by the use of separate heat exchangers located externally of the unit to heat the feed liquid prior to its admission to the shell. Alternatively, reliance has been made upon the mixture in the downflow passage of the incoming feed liquid with liquid being recirculated through the unit, the latter being at about saturation temperature, for preheating purposes.

Neither of these alternatives has been found to be completely satisfactory. The first-mentioned considerably increases the equipment costs of the vapor generating plant in that supplementary heat exchange apparatus is required while the latter suffers from the deficiency of disuniformity of preheating due to variances occuring in the amount of liquid recirculated at different levels of unit operation.

It is to the solution of these problems, therefore, that the present invention is directed.

SUMMARY OF THE INVENTION According to the invention, apparatus that is integral with a shell and tube vapor generator is provided for preheating the feed liquid admitted to the same by the transfer of heat from the vapor-liquid mixture generated within the vapor generator. The invention contemplates providing a plurality of feedwater discharge nozzles disposed in a region of the vapor generator containing heated vapor-liquid mixture. The nozzles are arranged to discharge feedwater into a collector conduit and inductor means that cooperate with the nozzles are provided to aspirate a portion of the vapor-liquid mixture into mixed relation with the feedwater within the collector conduit whereby the latter is heated by the transfer of heat between the two fluids.

The invention also contemplates a novel baffle arrangement for conducting the heated feedwater from the collector conduit to the downflow passage in a manner whereby it will be distributed substantially uniformly about the periphery of the downflow passage.

For a better understanding of the invention its operating advantages and the specific objectives obtained by its use, reference should be made to the accompanying drawings and descriptions which relate to the preferred embodiment.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational section 'of shell and tube type vapor generator incorporating the present invention;

FIG. 2 is a partial elevational section of a portion of the vapor generator shown in FIG. 1;

FIG. 3 is a section taken along line 3-3 of FIG. 2; and

FIG. 4 is a section taken along line 4-4 of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT In FIG. 1 of the drawings there is shown a shell and tube type vapor generator 10 incorporating feedwater preheating apparatus constructed according to the present invention. The vapor generator 10 comprises a vertically elongated pressure vessel defined by a lower cylindrical shell 12 and an enlarged diameter, upper cylindrical shell 14 that is integrally connected to the lower shell by means of a frusto-conical transition member 16. The ends of the vessel are closed, at the bottom by means of a hemispherically-formed closure head 18 and at the top by a dome shaped closure 20 containing a vapor outlet nozzle 22. The interior of the pressure vessel contains an axially elongated cylindrical baffle 24 that is concentrically spaced from the wall of the lower shell 12 to define an inner evaporation chamber 30 and an external, annular downcomer flow passage 32. The lower end of the baffle 24 is spaced from the bottom of the vessel interior in order to establish fluid communication between the downflow passage 32 and the evaporation chamber 30. The bottom of the vessel interior is defined by a tube sheet 34 that extends transversely of the axis of the vessel and connects with the wall of the shell 12. The tube sheet 34 contains a plurality of openings to fixidly secure the ends of U-shaped heat exchange tubes 38 that are arranged to form an axially extending bundle substantially filling a transverse section of the evaporation chamber 30. The tube openings extend through the tube sheet 34 to place the tubes 38 in fluid communication with a heating fluid chamber 42 that occupies that region of the vessel enclosed by the closure head 18 and the tube sheet 34. This chamber 42 is divided into inlet and outlet portions, 44 and 46 respectively, by means of a divider plate 48 that extends transversely of the chamber and is weldedly attached to the tube sheet 34 and the inner surface of the closure 18. The tubes 38 of the tube bundle are arranged such that their opposite ends communicate with one of the respective portions of the chamber 42 whereby the circulation of heating fluid through the tubes is effected. lnlet and outlet nozzles, 50 and 52 respectively, communicate with the

respective chamber portions

44 and 46 and connect the same to a source of heating fluid (not shown) in order to effect continous circulation of heating fluid between the vapor generator and the source.

According to the invention, novel means are provided for supplying feedwater to the vapor generator 10 and for preheating the same prior to its discharge into the downflow passage 32 for ultimate entry into the evaporation chamber 30. Such means comprises a feedwater inlet nozzle 54 that penetrates the upper vessel shell 14 and an inlet duct 56 that communicates therewith, the latter extending horizontally across the interior of the vessel as shown in FIG. I. The duct 56 is disposed within a region of the vapor generator termed the vapor collection plenum 58 that is formed in the upper region of the vessel interior in open communication with the evaporation chamber 30. The plenum is defined by an enlarged diameter cylindrical baffle 60 which is concentrically spaced from the upper end of the downflow baffle 24 thus to form concentric spaces therebetween indicated as feedwater discharge space 62 and separated liquid recirculation passage 64. The top of the plenum 58 is closed by a horizontally disposed closure plate 66. The plate 66 contains a plurality of mutually spaced openings 68 to which are attached centrifugally operated vapor-liquid separating apparatus 70 of wellknown construction. The plenum-forming members are secured at their upper and lower ends to the interior surface of shell 14 and to the bafile 24 respectively by

appropriate slip joints

72 and 74 that are capable of accommodating relative thermally-induced radial and axial expansion and contraction of the respective members.

Adjacent its lower end the vapor collection plenum 58 is provided with an annular distribution channel 76 formed of concentric annular plates that are arranged to separate the channel from the remainder of the plenum. These plates include a frusto-conical plate 78 forming the inner peripheral side of the channel and a top closure plate 80 extending from the top of plate 78 to the annular wall of baffle plate 60. The lower end of the channel is provided with concentrically spaced, axially disposed

plates

82 and 84 and, together with horizontally arranged closure plates 86 and 88, form a wierlike tortuous passage that communicates, at 90 with the feedwater discharge space 62.

As shown in the drawings the feedwater inlet duct 56 may be flared at its outer end and attached, as by means of welding, to the inner wall of the nozzle 54. The duct 56 is preferably formed of a lesser diameter than the nozzle wall to extend spacedly therethrough to provide a thermal shield for protecting the shell against undue stressing that would otherwise be caused by the impingement of the incoming cold liquid upon the hotter metal members. The duct 56, whose inner end is closed by a closure cap 92, extends diametrally across the plenum 58 terminating short of baffle 60 and extending through openings 94 provided in frusto-conical channel-forming plate 78 for reasons hereinafter described. An enlarged diameter feedwater collection conduit 96 surrounds the feedwater duct 56 in eccentric relation thereto. The conduit is substantially extensive with the duct through the plenum 58 having its ends supportedly attached, as by welding or the like, to the baffle 78 and plate 80.

A plurality of upstanding discharge tubes or nozzles 98 are axially spaced along the length of duct 56. These tubes extend upwardly from the duct and through the accommodating openings 100 provided in the conduit 96 to locate the upper, discharge ends of the tubes within the vapor collection plenum 58. inductor caps 102 spacedly enclose, by means of radial struts 104, the discharge end of each tube 98. Each inductor cap 102 is, as shown, a generally cylindrical member having a hollow interior that spacedly encircles the upper end of the tube to form an annular passage 106 thereabout. The base 107 of the interior of the cap 102 is provided with a spherical or equivalent shape to smoothly redirect the stream of feedwater issuing from the tube downwardly through the passages 106 and thence through the openings 100 into the feedwater collector conduit 96. The passage 106 between the upper end of each discharge tube and the wall of its associated cap is sized to create a relatively high velocity flow of liquid from the passage into the conduit interior thereby creating a region of low pressure adjacent each conduit opening 100 that is effective to aspirate amounts of heated vapor-liquid mixture from the plenum 58 into the conduit. Within the conduit interior the inducted higher temperature heated fluid is intimately -mixed with the cold feedwater thereby increasing the temperature of the latter.

As in the disclosed arrangement, a liquid difiusor plate 108, here shown attached to each tube 98, may be provided to obstruct the flow of liquid entering the interior of conduit 96 causing the liquid stream to be diffused into droplets by impinging on the plate. in this way the liquid can be dispersed into small droplets thereby presenting a greater amount of surface area to the other heat exchange medium by which heat transfer between the two will be enhanced.

The operation of the hereindescribed vapor generating apparatus is as follows. A high temperature high pressure heating fluid flows from its source through the inlet nozzle 50 into the inlet portion 44 of the chamber 42 and then is conducted by means of the tubes 38 through the evaporation chamber 30 emerging therefrom through the outlet portion 46 of the chamber 42 and nozzle 52. At the same time, feedwater is conducted to the interior of the vessel through inlet nozzle 54 and inlet duct 56. The feedwater, after having been preheated as described hereinafter, is conducted downwardly through the down flow passage 32, entering the evaporation chamber 30 at the bottom thereof, and being caused to flow upwardly through the chamber 30 in heat exchange relation with the heating fluid conducted through tubes 38 due to the thermal siphonic action occuring therein as a result of the difference in density of the fluid in the downflow passage 32 and the evaporation chamber 30. In flowing through the evaporation chamber 30 the liquid is heated and a portion thereof transformed into vapor. The so-created vapor-liquid mixture rises into the vapor collection plenum 58 and is subsequently caused to flow through the several separating apparatus 70 where the component parts of the mixture are separated by centrifugal action. The separated vapor rises from the separator 70 into the upper region of the vessel and is conducted therefrom through the vapor outlet nozzle 22. The separated liquid, on the other hand, is discharged downwardly into the liquid recirculation passage 64, ultimately entering the downflow passage 32 and recirculated through the unit.

The feedwater that enters the unit through the inlet duct 56 is preheated as hereinbefore more fully described by mixing in the feedwater collection conduit 96 with a portion of the vapor-liquid mixture that is aspirated from the vapor collection plenum 58 into the conduit by means of the action of the inductor caps 102. The heated feedwater is conducted from the opposite ends of the conduit 96 into the annular distribution channel 76 within which the liquid is dispersed annularly about the periphery of the channel due to the presence of the wier-like structure presented by the plate member 82 through 88. The liquid is discharged downwardly from the channel 76 through the annular opening into the feedwater discharge space 62 where it will be caused to comingle with the separated liquid flowing through the passage 64 prior to entering the downflow passage 32. in mixing with the separated liquid which exists at saturation temperature, the heated feedwater, if still subcooled, will have its temperature further raised before entering the passage 32. The combined flows of fresh feedwater and recirculated liquid enters the evaporation chamber 30 at the bottom of the downflow passage 32 and circulates through the unit in the manner heretofore described.

By means of the present invention, therefore, there is provided a effective means for preheating feedwater supplied to shell and tube type vapor generators thus to ameliorate the deficiencies in vapor generator operation attendant with supplying unheated feedwater to such apparatus. The preheating equipment is simple in configuration and requires little, if any, change in the design of present day vapor generators to accommodate its use. Moreover, the apparatus can be constructed at little expense using components that are readily available.

It will be understood that various changes in the detail, materials, and arrangement of parts have been herein described and illustrated inorder to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. In a vapor generator wherein vapor is produced by the transfer of heat between a fluid heating medium and a vaporizable liquid and wherein the vapor produced is contained in a vapor collection plenum, the improvement comprising apparatus for preheating feedwater supplied to said vapor generator prior to passing it in heat exchange relation with said heating medium, said apparatus including:

a. a mixing chamber disposed in, but substantially isolated from, said vapor collection plenum;

b. an inlet duct connected to a source of feedwater;

c. a plurality of discharge tubes emanating from said duct and arranged to discharge incoming feedwater into said mixing chamber;

d. inductor means operated by the flow of feedwater from said discharge tubes for aspirating heated vaporizable liquid from said vapor collection plenum into said mixing chamber in mixed relation with said feedwater; and

e. means for conducting heated feedwater from said mixing chamber into heat exchange relation with said heating medium.

2. Apparatus as recited in claim 1 wherein the outlet ends of said discharge tubes are disposed externally of said mixing chamber in said vapor collection plenum and the wall of said mixing chamber contains means forming openings to receive the feedwater discharge from said discharge tubes.

3. Apparatus as recited in claim 2 wherein said mixing chamber comprises a horizontally disposed, transversely extending conduit enclosing said inlet duct and said discharge tubes extend from said duct through the mixing chamber wall openings to dispose their outlet ends in said vapor collection plenum, and inductor means operative to aspirate heated vaporizable liquid into said mixing chamber by directing the flow of feedwater from the outlet ends of said discharge tubes through said conduit opening.

4. Apparatus as recited in claim 3 wherein said inductor means comprise annular hollow caps spacedly enclosing the outlet ends of said discharge tubes, the interior wall of said caps defining a flow directing surface for conducting the discharged feedwater through said conduct openings.

5. Apparatus as recited in claim 4 wherein the interior of said inductor caps is formed of a substantial U-shaped section.

6. In a vertically disposed shell and tube vapor generator comprising:

a. generally cylindrical sell means defining a pressure vessel having a lower vapor generating portion and a vapor collection plenum disposed in open communication thereabove;

b. a vapor outlet from said vapor collection plenum;

c. an axially extending conduit concentrically spaced from the wall of said shell to define an annular downflow passage about said vapor generating portion;

d. means for circulating fluid heating medium through said vapor generating portion;

e. means for circulating vaporizable liquid seriatim through said downflow passage, said vapor generating portion and said vapor collection plenum;

f. the improvement comprising feedwater preheater apparatus including:

i. a horizontally disposed conduit traversing said vapor collection plenum defining a mixing chamber;

ii. means forming a plurality of longitudinally spaced openings in said conduit communicating said mixing chamber with said vapor collection plenum;

iii. a plurality of feedwater discharge tubes having their outlet ends arranged to discharge feedwater through said openings into said mixing chamber;

iv. inductor means operated by the flow of feedwater from said discharge tubes for aspirating heated vaporizable liquid from said collection plenum into said mixing chamber; and

v. means for conducting heated feedwater from said mixing chamber into said downflow passage.

7. Apparatus as recited in claim 6 including:

a. a feedwater inlet nozzle penetrating said shell;

b. an inlet duct having one end communicating with said nozzle, said duct being enclosed by said mixing chamber conduit and substantially coextensive therewith; and

c. said feedwater discharge tubes connecting with said duct and having their outlet ends extending through said conduit openings into said vapor collection plenum.

8. Apparatus as recited in claim 7 wherein the periphery of said conduit openings is concentrically spaced about the surface of the respective feedwater discharge tubes.

9. Apparatus as recited in claim 8 wherein said inductor means each comprise:

a. generally cylindrical, hollow cap spacedly enclosing the outlet end of an associated feedwater discharge tube;

b. the interior of said cap defining a flow directing surface for directing feedwater from said discharge tube through said concentric conduit opening.

10. Apparatus as recited in claim 9 wherein said inductor cap is substantially U-shaped in section.

11.A aratus as recited in claim6including: a. b e means defining an annular distribution channel about said vapor collection plenum, said baffle means including concentrically spaced baffles defining a tortuous path;

b. means defining an annular opening connecting said channel with said downflow passage; and

c. means connecting said mixing chamber in fluid communication with said distribution channel.

12. Apparatus as recited in claim 11 wherein the opposite ends of said mixing chamber conduit are open and connect with said baffle means, said baffle means including openings to connect the ends of said mixing chamber conduit in fluid communication with said distribution channel.

13. Apparatus as recited in claim 11 including:

a. an annular plate concentrically spaced from said shell to define said vapor collecting plenum on its interior and an annular recirculating liquid-flow passage thereabout;

b. a horizontal plate closing the top of said plenum;

c. a plurality of separators mounted upon said horizontal plate in fluid communication with said plenum. and arranged to discharge separated liquid into said recirculating liquid flow passage.

14. Apparatus as recited in claim 13 wherein the lower end of said annular plate cooperates with said concentric baffles to concentrically space said distribution channel opening from said recirculating liquid flow passage, said plate terminating short of said downflow passage to place said opening and said liquid flow passage in fluid communication with said downflow passage.

Claims

1. In a vapor generator wherein vapor is produced by the transfer of heat between a fluid heating medium and a vaporizable liquid and wherein the vapor produced is contained in a vapor collection plenum, the improvement comprising apparatus for preheating feedwater supplied to said vapor generator prior to passing it in heat exchange relation with said heating medium, said apparatus including: a. a mixing chamber disposed in, but substantially isolated from, said vapor collection plenum; b. an inlet duct connected to a source of feedwater; c. a plurality of discharge tubes emanating from said duct and arranged to discharge incoming feedwater into said mixing chamber; d. inductor means operated by the flow of feedwater from said discharge tubes for aspirating heated vaporizable liquid from said vapor collection plenum into said mixing chamber in mixed relation with said feedwater; and e. means for conducting heated feedwater from said mixing chamber into heat exchange relation with said heating medium.

6. In a vertically disposed shell and tube vapor generator comprising: a. generally cylindrical sell means defining a pressure vessel having a lower vapor generating portion and a vapor collection plenum disposed in open communication thereabove; b. a vapor outlet from said vapor collection plenum; c. an axially extending conduit concentrically spaced from the wall of said shell to define an annular downflow passage about said vapor generating portion; d. means for circulating fluid heating medium through said vapor generating portion; e. means for circulating vaporizable liquid seriatim through said downflow passage, said vapor generating portion and said vapor collection plenum; f. the improvement comprising feedwater preheater apparatus including: i. a horizontally disposed conduit traversing said vapor collection plenum defining a mixing chamber; ii. means forming a plurality of longitudinally spaced openings in said conduit communicating said mixing chamber with said vapor collection plenum; iii. a plurality of feedwater discharge tubes having their outlet ends arranged to discharge feedwater through said openings into said mixing chamber; iv. inductor means operated by the flow of feedwater from said discharge tubes for aspirating heated vaporizable liquid from said collection plenum into said mixing chamber; and v. means for conducting heated feedwater from said mixing chamber into said downflow passage.

7. Apparatus as recited in claim 6 including: a. a feedwater inlet nozzle penetrating said shell; b. an inlet duct having one end communicating with said nozzle, said duct being enclosed by said mixing chamber conduit and substantially coextensive therewith; and c. said feedwater discharge tubes connecting with said duct and having their outlet ends extending through said conduit openings into said vapor collection plenum.

9. Apparatus as recited in claim 8 wherein said inductor means each comprise: a. generally cylindrical, hollow cap spacedly enclosing the outlet end of an associated feedwater discharge tube; b. the interior of said cap defining a flow directing surface for directing feedwater from said discharge tube through said concentric conduit opening.

11. Apparatus as recited in claim 6 including: a. baffle means defining an annular distribution channel about said vapor collection plenum, said baffle means including concentrically spaced baffles defining a tortuous path; b. means defining an annular opening connecting said channel with said downflow passage; and c. means connecting said mixing chamber in fluid communication with said distribution channel.

13. Apparatus as recited in claim 11 including: a. an annular plate concentrically spaced from said shell to define said vapor collecting plenum on its interior and an annular recirculating liquid flow passage thereabout; b. a horizontal plate closing the top of said plenum; c. a plurality of separators mounted upon said horizontal plate in fluid communication with said plenum and arranged to discharge separated liquid into said recirculating liquid flow passage.