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US3900010A - Method and apparatus for reverse circulating nuclear steam generator secondary fluid - Google Patents

Method and apparatus for reverse circulating nuclear steam generator secondary fluid Download PDF

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Publication number
US3900010A
US3900010A US462270A US46227074A US3900010A US 3900010 A US3900010 A US 3900010A US 462270 A US462270 A US 462270A US 46227074 A US46227074 A US 46227074A US 3900010 A US3900010 A US 3900010A
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US
United States
Prior art keywords
gas
annular
fluid
downcomer passage
passage
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US462270A
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English (en)
Inventor
Fred Zwald Stiteler
Ronald Louis Honigmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Combustion Engineering Inc
Original Assignee
Combustion Engineering Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Combustion Engineering Inc filed Critical Combustion Engineering Inc
Priority to US462270A priority Critical patent/US3900010A/en
Priority to CA219,352A priority patent/CA1026539A/en
Priority to DE19752515268 priority patent/DE2515268A1/de
Application granted granted Critical
Publication of US3900010A publication Critical patent/US3900010A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B37/00—Component parts or details of steam boilers
    • F22B37/02—Component parts or details of steam boilers applicable to more than one kind or type of steam boiler
    • F22B37/48—Devices or arrangements for removing water, minerals or sludge from boilers ; Arrangement of cleaning apparatus in boilers; Combinations thereof with boilers
    • F22B37/483—Devices or arrangements for removing water, minerals or sludge from boilers ; Arrangement of cleaning apparatus in boilers; Combinations thereof with boilers specially adapted for nuclear steam generators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B1/00—Methods of steam generation characterised by form of heating method
    • F22B1/02—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers
    • F22B1/023—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers with heating tubes for nuclear reactors, as long as they are not classified according to a specified heating fluid, in another group
    • F22B1/025—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers with heating tubes for nuclear reactors, as long as they are not classified according to a specified heating fluid, in another group with vertical U shaped tubes carried on a horizontal tube sheet

Definitions

  • Such systems typically involve a once-through flow of the cleaning solution and thus require large supply and waste storage tank capacities, and as a result also require large quantities of the chemical cleaning solution. Also in order to install such systems in steam generators not originally equipped, additional penetrations of the steam generator vessel may be required. In addition, when preparing such a system for actual use, time consuming removal of the steam dryers and steam separators from the interior of the steam generator vessel is required.
  • a second need for steam generator secondary fluid reverse circulation is during periods of reactor shutdown. During such periods it is necessary to maintain circulation of the steam generator water in order to maintain chemistry specifications of the secondary fluid in order to minimize corrosion and other undesirable chemical reactions occurring in the steam generator during the shutdown period.
  • Such an arrangement also requires a pumping system of relatively large capacity as well as the associated piping, controls and other related hardware.
  • a method of inducing reverse circulation of steam generator secondary fluid which employs the principle of natural circulation due to a difference in fluid density.
  • This method may be used in any steam generator of the type including an outer annular downcomer passage and an inner cylindrical riser section into which a bundle of inverted U- tubes whose ends are secured to a lower tube sheet extend upwardly thereinto.
  • the steam generator may be envisioned as a U-tube with one leg being the inner riser section which contains the tube bundle and the other leg the downcomer passage.
  • the secondary fluid density in the annular downcomer is reduced by injecting nitrogen or other suitable gas into the downcomer annulus adjacent to the lower end of the annulus.
  • the gas bubbling up the downcomer produces a void fraction or a fluid-gas mixture of lower density than that in the tube bundle.
  • a fluid density differential is established between the inner riser section and the downcomer and a natural circulation of fluid is induced from the inner riser region upwardly through the annular downcomer passage.
  • the gas is introduced into the downcomer annulus through an annular gas distribution pipe which includes a plurality of holes along its length from which the gas issues to provide a uniform gas injection around the entire annulus.
  • Spent gas rising from the surface of the fluid in the steam generator is vented at the top of the steam generator, collected and recirculated.
  • Such a technique may be used both to induce natural circulation of the existing secondary fluid to maintain chemical specifications, or may be used to induce circulation of a suitable cleaning fluid which has been placed into the steam generator in place of the secondary fluid in order to chemically clean the secondary surfaces.
  • the system of the disclosed invention thus exhibits numerous advantages over prior art techniques for accomplishing reverse circulation of steam generator secondary fluid. Among these advantages are the following: (1) The system is simple and does not require use of pumps to circulate steam generator fluid. (2) It minimizes the quantity of cleaning solution required for chemical cleaning. This in turn reduces radiological hazards, minimizes cleaning solution supply and waste storage tank capacity, and solution feed pump capacity required is also minimized. (3) The system may be built into new steam generator systems as a permanent feature without interfering with normal operational requirements of the steam generator. (4) The system can be installed on existing steam generators without the need for additional penetration of the steam generator vessel.
  • FIG. 1 is a sectional elevation of a nuclear steam generator employing secondary fluid circulation apparatus according to the present invention
  • FIG. 2 is a sectional view taken along line 22 of FIG. 1;
  • FIG. 3 is a sectional elevation, similar to FIG. 1 on a reduced scale, of a nuclear steam generator showing an alternate means for introducing gas into the annular downcomer passage.
  • FIG. 1 of the drawings there is shown a nuclear operated steam generator 10 comprising an upright, generally cylindrical vessel I2 having dome shaped upper and lower closure caps, 14 and 16 respectively.
  • a tube sheet 18 is provided in the lower end of the vessel dividing its interior into a lower heating fluid chamber 20 and an upper vapor generation chamber 22.
  • the heating fluid chamber 20 is separated into inlet and outlet portions, 24 and 26 respectively by an upstanding partition plate 28, and appropriate connections are provided for circulating heating fluid into and out of the vessel.
  • the vapor generation chamber 22 contains an annular baffle means 30 dividing the chamber into an outer annular downcomer passage 32 and an inner riser section 34.
  • a bundle of inverted U-tubes 36 whose ends are secured to the tube sheet 18 in communication with the inlet 24 and outlet 26 portions of the heating fluid chamber 20 is provided in the riser section 34 for passing heating fluid in heat exchange relation with vaporizable liquid that enters the vessel through an inlet 37.
  • the vaporizable liquid admitted to the vessel is circulated downwardly through the downcomer passage 32 and thence upwardly into the riser section 34, in the latter of which a portion thereof is transformed into vapor.
  • the upper end of the riser section 34 is closed by a horizontally disposed baffle plate 38 which, together with baffle means 30, defines a vapor liquid mixture collection plenum 40.
  • the baffle plate 38 is provided with a plu rality of openings (not shown) to which are attached upstanding connecting pipes 42 for mounting separator apparatus 44 in communication with the collection plenum 40.
  • a second baffle plate 46 Overlying the separator apparatus 44 is a second baffle plate 46 extending across the full cross section of the cylindrical vessel 12, this plate is also provided with a plurality of openings to which are attached upstanding steam dryer modules 48. Steam generated in the riser section 34 passes upward through the steam separators 44 and dryers 48 to a vapor plenum 50 in the upper end of the vessel.
  • a vapor outlet nozzle 52 communicates with the vapor plenum 50 for conducting the processed vapor through steam line 54 and shutoff valve 56 to a point of use.
  • annular gas distribution pipe 58 which is positioned about midway between the outside of the baffle means 30 and the inner wall of the cylindrical vessel 12.
  • This annular gas distribution pipe 58 is provided with a plurality of uniformly spaced gas openings 60 on the upper side thereof and also communicates with a gas supply pipe 62 which passes through an already existing handhole penetration 64 in the cylindrical pressure vessel 12.
  • a gas vent 66 is provided in the upper closure cap 14 through which gas which has bubbled up through the downcomer annulus 32 may be vented from the vapor plenum 50 in the upper end of the cylindrical vessel 12.
  • the gas thus vented is passed through recirculation line 68 and passes to a nitrogen storage tank 70 and from there is drawn as needed by nitrogen gas supply pump 72 which recirculates the gas via the gas introduction line 62 back to the gas distribution pipe 58 in the lower end of the downcomer annulus 32.
  • the existing secondary fluid is first pumped or drained from the interior of the cylindrical vessel 12.
  • the vessel is then filled with a suitable cleaning fluid which may be any of a number of commercially available acid solutions designed specifically for the cleaning of steam generators.
  • the level of the cleaning fluid in the steam generator should be below the position of thenitrogen gas vent 66, and at least as high as the elevation of the baffle plate 38. However, if it is desired to clean the separators 44 and dryers 48 the fluid level should be above the upper level of the steam dryers 48 in order to insure flow of cleaning fluid through this apparatus.
  • the steam valve 56 is shut off, and other penetrations are sealed to insure that the cleaning fluid is confined to the interior of the vessel 12.
  • the nitrogen pump 72 is then activated and caused to introduce nitrogen gas into the gas distribution annular pipe 58 from which gas issues through openings 60 to provide a uniform gas injection around the entire downcomer annulus 32.
  • the nitrogen gas thus introduced tends to bubble uniformly up through the downcomer annulus 32 to produce a void fraction or a fluid-gas mixture of lower density than that of the fluid in the tube bundle region 34.
  • a natural circulation of cleaning fluid is established due to the density differential between the tube bundle region 34 and the annular downcomer passage 32.
  • the cleaning fluid thus flows downwardly through the tube bundle region 34, passes around the lower end of the baffle 30 and thence upwardly through the annular downcomer passage 32.
  • the cleaning fluid flowing through the downcomer annular passage continues moving upward into the vapor plenum region 50 in the upper end of the vessel.
  • the nitrogen gas contained in the cleaning fluid passes from the cleaning fluid in this region and is vented from the top of the steam generator through the gas discharge vent 66.
  • the vented gas is then collected in nitrogen tank 70, and in turn recirculated back to the lower end of the downcomer passage 32 via nitrogen pump 72 and nitrogen introduction line 62.
  • the cleaning fluid which has passed into the vapor chamber 50 then passes downwardly through the steam dryer apparatus 48 and through the steam separator apparatus 44 into vapor liquid mixture collection plenum 40 and from there passes down through the tube bundle region 34 and is again caused to recirculate upward through the downcomer passage following the same route as has just been described.
  • the cleaning fluid flow at a velocity of about 0.5 to l ft/sec through the tube bundle region of the steam generator. This velocity corresponds to a volume flow of approximately 33,000 gals/min (GPM). In order to induce a flow of this volume it is necessary to introduce approximately 1500 standard cu. ft./min of nitrogen gas through the annular gas distribution pipe 58. The entire cleaning operation is ideally carried out at a temperature of approximately 250F.
  • nitrogen gas as the circulation gas for the reason that nitrogen possesses the advantages that it is inert to any of the chemicals present in the secondary fluid, it serves to purge undesirable gases such as oxygen from the system and is also relatively inexpensive; other suitable gases could be used with equal success in achieving the circulation desired.
  • gases such as oxygen from the system and is also relatively inexpensive; other suitable gases could be used with equal success in achieving the circulation desired.
  • oxygen in place of nitrogen to aid in oxidizing copper deposits.
  • Another application of the present invention is to induce a circulation of the existing secondary fluid in the steam generator during periods of shutdown in order to maintain uniformity of the chemistry and maintain chemistry specifications throughout the steam generator for purposes of reducing corrosion and other undesirable chemical reactions during the shutdown period.
  • all that is necessary is that sufficient steam generator fluid be added to the steam generator vessel to bring the fluid level above the baffle plate 38.
  • the nitrogen pump 72 is then actuated and introduces nitrogen gas into the annular gas distribution pipe 58 located adjacent to the lower end of the annular downcomer passage 32. Natural circulation is then induced in the same manner as described in connection with the cleaning operation, thus causing a circulation up through the downcomer passage down through the openings in the steam separator apparatus 44 and downward through the tube bundle region.
  • FIG. 3 a second embodiment of the apparatus for introducing nitrogen gas into the lower end of the downcomer annulus 32 is shown.
  • an annular nitrogen gas introduction header 74 is positioned near the upper end of the downcomer annulus 32 just underlying the region in which the steam generator fluid is introduced through inlet penetration 37.
  • the nitrogen supply line 62 passes through a penetration 76 in the cylindrical vessel 12 and communicates with the distribution header 74.
  • Extending downwardly from the annular distribution header 74 are a plurality of smaller diameter nitrogen supply lines 78, these lines extend downward through the annular downcomer passage 32 and terminate at a point just above the lower end of the downcomer baffle 30.
  • each of these downwardly extending nitrogen distribution lines 78 is provided with a T-type fitting 80 which extends through a horizontal segment of the downcomer annulus.
  • Each of the T-fittings 80 is provided with a plurality of nitrogen discharge openings (not shown) on the upper side thereof.
  • This second described embodiment will have particular application in a steam generator structure wherein the size of the downcomer annular passage 32 and the required rate of flow of secondary coolant fluid through the annular downcomer passage makes the positioning of an annular pipe in a region of narrow flow cross section undesirable as it would tend to increase the flow resistance of the secondary fluid in this region.
  • This problem is overcome in the second embodiment by positioning the annular gas distribution header 74 in a region above the downcomer annulus which is substantially larger in cross section than at the lower end of the downcomer where the nitrogen gas is introduced.
  • a method of inducing fluid circulation on the secondary side of a steam generator of the tupe including an outer vessel and a vapor generation chamber having an annular baffle means dividing the chamber into an outer annular downcomer passage and an inner riser section, wherein the fluid level is said steam generator is above said annular baffle means, comprising the step of: introducing gas into the lower end of the annular downcomer passage, whereby said gas bubbles up the downcomer passage creating a region of fluid density in the downcomer passage less than the fluid density in the inner riser section, the density differential therebetween inducing a natural circulation of the fluid down the inner riser section and into and up through the downcomer passage.
  • a method according to claim 1 including venting out of the outer vessel gas which has risen through the annular downcomer and passed from the fluid into the region above the fluid level.
  • a method according to claim 2 including collect ing the gas which is vented from the outer vessel and re-introducing said gas into said annular downcomer passage in said introducing step.
  • a method of cleaning the secondary side of a steam generator of the type including an outer vessel and a vapor generation chamber having a annular gaffle means dividing the chamber into an outer annular downcomer passage and an inner riser section comprising the steps of:
  • Apparatus for inducing fluid circulation on the secondary side of a steam generator of the type including an outer vessel and a vapor generation chamber having an annular baffle means dividing the chamber into an outer annular downcomer passage and an inner riser section, wherein the fluid level is above said annular baffle means, comprising: means for introducing gas into the lower end of the annular downcomer passage, whereby said gas bubbles up the downcomer passage creating a region of fluid density in the annular downcomer passage less than the fluid density in the inner riser section, the density differential therebetween inducing a natural circulation of the fluid down the inner riser section and into and up through the downcomer passage.
  • said means for introducing gas comprises and annular gas distribution pipe disposed within and at the lower end of said annular downcomer passage, said annular gas distribution pipe including a plurality of gas discharge openings on the upper side thereof; and gas supply means in flow communication with said annular gas distribution pipe.
  • Apparatus according to claim 6 including means for venting out of the outer vessel, gas which has risen through the annular downcomer and passed into the region above the fluid level.
  • Apparatus according to claim 8 including means for collecting the gas vented from the outer vessel by said venting means; and means for re-introducing said collected gas into said annular downcomer passage through said means for introducing gas.
  • annular downcomer passage has a region of larger cross sectional flow area adjacent the upper end thereof and wherein said means for introducing gas comprises: an annular gas distribution within said region of larger cross sectional flow area; and a plurality of gas distribution pipes extending vertically downward through said annular downcomer passage to a position adjacent the lower end thereof, each of said vertically extending gas discharge pipes including a gas discharge fitting at the lower end thereof, each of said fittings containing a plurality of gas discharge openings on the upper side thereof.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Cleaning By Liquid Or Steam (AREA)
  • Structure Of Emergency Protection For Nuclear Reactors (AREA)
US462270A 1974-04-19 1974-04-19 Method and apparatus for reverse circulating nuclear steam generator secondary fluid Expired - Lifetime US3900010A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US462270A US3900010A (en) 1974-04-19 1974-04-19 Method and apparatus for reverse circulating nuclear steam generator secondary fluid
CA219,352A CA1026539A (en) 1974-04-19 1975-02-04 Method and apparatus for reverse circulating nuclear steam generator secondary fluid
DE19752515268 DE2515268A1 (de) 1974-04-19 1975-04-08 Verfahren und anordnung zur umkehr der umlaufrichtung eines mediums auf der sekundaerseite eines waermeaustauschers insbesondere fuer kraftwerke mit kernreaktoren

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US462270A US3900010A (en) 1974-04-19 1974-04-19 Method and apparatus for reverse circulating nuclear steam generator secondary fluid

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CA (1) CA1026539A (de)
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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4261300A (en) * 1978-12-26 1981-04-14 Combustion Engineering, Inc. Nuclear steam generator
US4479459A (en) * 1982-07-13 1984-10-30 International Telephone And Telegraph Corporation Sequencing blow down valve mechanism
US4488513A (en) * 1983-08-29 1984-12-18 Texaco Development Corp. Gas cooler for production of superheated steam
US4638768A (en) * 1985-04-04 1987-01-27 Westinghouse Electric Corp. Steam generator tubesheet/channel head/centerstay assembly
US4756770A (en) * 1986-02-11 1988-07-12 Arkansas Power And Light Company Water slap steam generator cleaning method
US5257296A (en) * 1991-10-25 1993-10-26 Buford Iii Albert C Steam generator chemical solvent mixing system and method

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3114353A (en) * 1959-06-25 1963-12-17 Babcock & Wilcox Co Vapor generating unit and method of operating same
US3245460A (en) * 1962-05-02 1966-04-12 Aqua Chem Inc Art of removing scale in multiple unit evaporator systems
US3468293A (en) * 1968-05-10 1969-09-23 Whiting Corp Multi-stage forced circulation evaporator and method
US3766892A (en) * 1972-04-21 1973-10-23 Combustion Eng Split feed economizer

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3114353A (en) * 1959-06-25 1963-12-17 Babcock & Wilcox Co Vapor generating unit and method of operating same
US3245460A (en) * 1962-05-02 1966-04-12 Aqua Chem Inc Art of removing scale in multiple unit evaporator systems
US3468293A (en) * 1968-05-10 1969-09-23 Whiting Corp Multi-stage forced circulation evaporator and method
US3766892A (en) * 1972-04-21 1973-10-23 Combustion Eng Split feed economizer

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4261300A (en) * 1978-12-26 1981-04-14 Combustion Engineering, Inc. Nuclear steam generator
US4479459A (en) * 1982-07-13 1984-10-30 International Telephone And Telegraph Corporation Sequencing blow down valve mechanism
US4488513A (en) * 1983-08-29 1984-12-18 Texaco Development Corp. Gas cooler for production of superheated steam
US4638768A (en) * 1985-04-04 1987-01-27 Westinghouse Electric Corp. Steam generator tubesheet/channel head/centerstay assembly
US4756770A (en) * 1986-02-11 1988-07-12 Arkansas Power And Light Company Water slap steam generator cleaning method
US5257296A (en) * 1991-10-25 1993-10-26 Buford Iii Albert C Steam generator chemical solvent mixing system and method

Also Published As

Publication number Publication date
DE2515268A1 (de) 1975-10-30
CA1026539A (en) 1978-02-21

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