US2821966A - Vapor generator - Google Patents

Description

Feb. 4, 1958 F. G. RAYNOR 2,821,966

VAPOR GENERATOR Filed March 25. 1954 'TELE'.ZJ-

1"VPOR :GENERATOR r'orrest G. .Raynor, flaldwin, N. Y-Mlaissignor to The iBabcollr za'vvllilcoxCompany,` New York, NY., a corporation -f New 'Jersey .'Aplctin'MarchS, 1954, Serial No. 41183661 .5\ClaimS. (Cl. 122-408) Thistrinventi'onf relates Ltoui'd. heat exchangey apparatus, ande-the inventioniis:consideredasexempledxin a' vapor ;generatinglunitofhighacapacity.

yMany :modern vapor :generating :units fozrerateu at .l high :'Suid-:pressures'.ofwtheorder of 1600+250() :p.-.s. i. and it lis :evident Athat these cunits,l in order to -vvithstand.;sueh i-pressuresrover: a long life, imustzhave their pressure corn- `piments oft considerable :wall` thickness. vThis lis .particuwlrly true f tof l the vapor 1*aridxliquid:drums of the i pertilnentmnits. Someiofrthese drums Ihave-a lengthfofthe forderaof 1.5.0-60 ifeetwandaudiameter of .the order .off4-6 lifeet. Underwsuchwconditions,'the r:wall-thickness of the flsteel-.drum wall-:must be -great. -It is, .in many eases, ytof.theworderotelO inches,-and,\in some cases, jsome sect-ions of :the .dr-ums are of much. greater -wall thick- Amess. Thisiispparticularlly trueinV the drum`zoue vinfwhich downcomerseareconnectedto .tl1e.-1iquid spaceof the drum. In order that .t-hedrums ofthe pertinent'units may effectively'operate over a long period, considerable attention must be apaid sto :the .metal `stresses `in -the rdrums. Y.Infmariyi-.cases `.the drums aresubject toiprestressing-in their fabrication.in.order thatthe operative stresses .due to huid, .pressures ..of. normal operation 1 may i.be .of.an.optimrum.character. y

Inthe manufacturerofany suchdrums, itis .obviously important that .the many .downcomer tubesandfrisertubes connected to the drum mustbe; join'edftherewithfin pres- `sure-tight condition `,This`involves contact .of .the con- `nected tubes and the 'drum` metal over large areasandit in'volves stressing of the 'drum metal.

All ofthe above conditionsmustbe taken intofcon- `sideration .in'the starting up 4of a large capacity yvapor @generating unit, and particular attention Vmust be paid to'the method of starting upithe unit in order that addi- "tional and undesired'stresses inthe tdrum metal may'be Iavoided. "Toa'ttain thisendthe starting up of suc'h aunit Imust "beginv'vith a"l0w heat inpt and the increments "of `heatinput'niustbe"srr1all V.and they'must be effective over `considerable1period-softimeinorder that the tem- ;perature"'gradients in "the metal, `and particularly' thedrum "metal, may belkept within'al1owable'limits. `For`these reasons, complicated and `extensive time-temperature schedules 'mustbe carefullyfolloweldin the starting up of the unit.

This invention deals with a unitto be started up under "the-above'conditions, andmore` particularly, witha unit finwhichffthere-is 4a row of downcomerftubes leading frorrr-'thebottOmof 4the drum along its straight section. Inu many -suclr4 units the drum ends, with their dished or "convex end-portions, must project substantially `beyond fthe zone of the 'downcomersand this arrangement leaves "aconsiderablefbody'of liquid within 'each of the pertifnent end portions=andfdisposed to one side of the main stream oflliquid enteringthe-end downcoiners. Thereifo'regthe increasei-inliquidtemperature involved in the zstartin'giupoftheunit-is not uniform. The attendant `heatinputis.-=less fetectiveriny the bodies of the liquid iat .the adrum ends f than =in .the rz/.one immediately Aadjacent ICC lthe 'downeomers A-This'invention'involves lfl'uiddlovv' directing means so associated with the 'end downcomers and the drum ends so-as to overcome thepertinentdiiculty and maintain substantially constant temperatures in thedrum'metalduring starting up. Y

The-inventioniisiconcisely set'forth in 'thefappe'nded claims, but forfaclearer understanding of 'the invention, its .l uses I and advantages, Jrecourse Ashould be tha'd to the 2a'cco'mpany'iangi` description `which refers, lby. like l reference characters, ztorth'e @accompanying idrawing in which #a rpreferredfembodimentloftthefinvention is illustrated.

f In thezdrawings:

`Fig. i1 ,isaa'rsidefsectional view indicating avtype :of

high pressurelvapor generating unit to 1which:the inven-y `tionza'pplies;

iFig. I1.2 isza transverse verticalnsectionofthe vapor and :liquid idrum rofitherpertinent vapor .generating unit;

iFtig. 3'is aipartial-verticalsection through thefFignZ ;drum-showingf thetillustrative liquid flow directing 'means leadingafromtheidrumfend portion `to the inletsof the adjacent.downcomersyand 4 Fig. f41is-a plan -section of-.one endof .the drum, on

.the section line `but ofLF ig. 2.

The .inventioneis applicable to the vaporandtliquid `separatingffdrumsltly'of the Fig. .1 high pressure vapor ...generating unit. .This .unit includes .a vertically Melone fgated combustion-chamber 12 dened by .upright vapor l generating ywall .tubes,.some of .which are.indicated rv*at `ll4..as leadingzfrom bottom header lvto the top .header Theyfluid flows .continue .thence.throughrooftubes .20 to the vaporaandliquid.inlet..chamber.22 of the .drum

V 1li). `longthe .oppositewall of.the..combustionchainber .other vapor. .generating tubes .24 .lead V.upwardly.-.frorn thelowerlheaders.'26 andZS. V'These .tubeshave'intermediate portions .30 upwardly inclined .toward 'therear wall`32 of the convection gas pass 3`4. `Bey`ondthe.upf per Iends of these'inclined portions the Ytubes arebent to form a tubular screen 36'disposed across'thegasilt of the gas `pass'i34l 'Beyond the upper portion f `this screen the vtubes are disposed in alignment tov 'define the rear wall 3'8 of the combustion chamber. These tbes are.risers"having,theiruppenpai'ts 4'0 connected "to the 'vapor an'd lliquid mixture inlet 'hamber 122V of 'thedrum The remaining walls ofthe combustion cha'mberare similarly defined by upright vapor generating tubes icon nected by appropriate headers andotherconnections to the vapor and liquidrnixture'charnber 22. There may "be,'at" the opposite'side of the drum"10,"a"similarvapor 'and' liquid-mixture chamber 42 connected'with the'rnixture chamber 22 byinverted channel connections, such as 44, which, tthrou'ghoutl'a lsubstantiz'ilpart'of thel-eng'th of the drum, lvare disposed "between'ithe downcom'ers Fig. ""2 indicates vapor and liquidi separators 50having whirl `chambers having 'substantially "tangential linlets 'communicating `with -the upper parts of' thevapor and liquid mixtureI chambers 22 and L42, respectively. There `wouldpreferably*be-afrowof 'such separators at-each `'the disclosure 'of the Fletcher' Land `Rowand lsllatent '525289,970 of July 314, 1942. `iEachseparatordischarges separated liquid downwardly into 'the 'drum space'between the chambers'fZZ and -1 42 l-where a-norml water flevel is `maintained as at 54. YSeparatedvaporis'discharged from ther tops of ythe-separators and subsequentvly .passesfrorntthe drumlvap'or space .throughVcircula-l tors :56 to ra-..superheater which 'maylincludethe :banks of tubes such. as-1 thosedndicatedat r'53; and :60, in the Ilp- 3 ow gas pass 34 of the vapor generator. Downcomers 46--48 and 62-64 are indicative of a row of downcomers communicating with the water space of the drum and leading downwardly along the rear wall of a gas pass 34 to headers 26-28.

As indicated in Figs. 3 and 4 the endmost downcomers are considerably spaced from the adjacent end of the drum. This is a situation in which there will be a large body of liquid disposed within each of the drum ends and beyond the zone immediately adjacent the inlets of the downcomers. This situation causes a liquid temperature difference between the liquid in the drum ends and the main body of liquid immediately adjacent the inlets of the downcomers which would promote undesirable metal stresses in adjacent portions of the drum when the vapor generating unit is being started up, and such thermally created stresses are apt to be particularly darnaging in the vapor and liquid drums of vapor generating units operating at very high pressures and temperatures. Under such conditions the thickness of the drum walls may range anywhere from 4-6" to l5", and the undesirable effects of these pertinent stresses increase as the thickness of the drum metal increases. These undesirable effects may also be augmented by the welded construction of the drums. To prevent these undesirable stress effects the applicant provides ow directing means such as the inverted channel or tunnel member 66 at each end of the drum. The inlet 68 of this member is in direct communication with the inlets of one or more of the end downcomers, such as 62-64. Fig. 3 indicates the outlet end of the channel member 66 as having a closure 72. Thus, the liquid within the drum and adjacent the drum ends will circulate freely with the remaining body of the circulating liquid and the metal temperatures at the drum ends will be maintained at substantially the same value as the temperature of the other parts of the drum. The members 66 may also be considered as a part of conduit means of a tubular nature establishing separate fluid flows from the drum ends to the downcomers.

The conduit means including the members 66 have a free ow area greater than that of the downcomers directly associated therewith. As to the further details relative to the pertinent type of vapor generating and superheating unit, it is indicated that this unit is intended to be more of the type shown in detail in the common assignees pending application Ser. No. 291,686, led June 4, 1952.

What is claimed is:

1. In a natural circulation vapor generating unit, a metallic pressure vessel in the form of a thick-walled metallic vapor and liquid drum of large diameter, a multiplicity of downcomers distributed in a narrow zone extending longitudinally of the drum and joined to the drum at its lowermost part in pressure-tight relationship, the drum end portions extending longitudinally beyond the zone of the downcomers, a row of vapor generating tubular risers similarly joined with the drum in pressuretight relationship at positions substantially circumferentially spaced from the row of downcomers, and conduit means within the drum forming tubular passages leading lengthwise of the drum from the projecting end portions of the drum into the inlets of the endmost downcomers, said conduit means establishing separate free ow of liquid from the drum end portions to the said endmost downcomers, the tubular passages formed by the conduit means being closed at their ends most remote from the end portions of the drum.

2. In a natural circulation vapor generating unit, a

pressure vessel in the form of a cylindrical vapor and liquid drum having a large diameter and thick walls, a multiplicity of tubular downcomers distributed throughout a circumferentially narrow zone extending longitudinally of the midsection of the drum and joined to the 4 drum at its lowermost part in pressure-tight relationship, the end portions of the drum extending beyond the zone of the arrangement of downcomers, a row of tubular risers joined to the drum in pressure-tight relationship at positions substantially circumferentially spaced from the zone of the downcomers, and conduit means of a tubular nature forming tubular passages leading longitudinally of the drum from the projecting end portions of tht drum into the inlets of the endmost downcomers next adjacent the pertinent end portions, each of said conduit means covering the inlets of a plurality of downcomers, said conduit means establishing free ow of liquid from the drum ends to the said endmost downcomers.

3. ln a high pressure vapor generating unit, a pressure vessel in the form of a thick-walled metallic drum having hollow cylindrical straight mid-section and outwardly dished end portions at the ends of the mid-section, a furnace, means firing the furnace, vapor generating riser tubes subject to the heat of the furnace and joined with the drum in pressure-tight relationship thereto at levels above the level of the lowermost portion of the drum, a multiplicity of downcomer tubes distributed longitudinally of the mid-section of the drum and joined with the lower part of the drum in pressure-tight relationship, means establishing communication between the downcomers and the lower ends of the riser tubes, and means including a part of the drum wall between the inlets of downcomers nearest the end portions of the drum and forming conduits of a tubular nature disposed within the drum, each conduit leading from a space within a dished end portion of the drum to a plurality of inlets of the next adjacent downcomers, the conduits being closed at their ends remote from their ends within the dished end portions of the drum.

4. In a high pressure vapor generating unit, a pressure vessel in the form of a thick-walled metallic drum having a straight hollow cylindrical main-section and outwardly dished sections closing the ends of the mainsection, a furnace, means firing the furnace, vapor generating riser tubes subject to the heat of the furnace and joined in pressure-tight relationship with the drum at levels above the lowest level of the drum, a multiplicity of downcomer tubes having their upper ends joined with the lowermost part of the drum at positions longitudinally distributed throughout the main section of the drum and confined to a circumferentially narrow zone of the drum, means establishing communication between the downcomer tubes andthe lower ends of the risers, and straight conduit means of a tubular nature disposed within the drum entirely below its normal water level and forming tubular passages leading from the spaces within the dished end portions of the drum to positions wherein each passage communicates with the inlets of the downcomers next adjacent the pertinent end portions, each tubular passage terminating inwardly in a closed end at a position remote from the midpoint of the drum length so as to leave the intermediate downcomers free of the conduit means, the conduit means having a free ow area greater than that of the downcomers directly associated therewith.

5. In a high pressure vapor generating unit, a pressure vessel in the form of a thick-walled metallic drum having a straighthollow cylindrical mid-section and .outwardly dished end portions at the ends of the midsection, a furnace, means firing the furnace, vapor generating riser tubes subject to the heat of the furnace and having their upper ends joined with the drum in pressure-tight relationship thereto over portions of the drum at levels above the lowermost level of the drum, a plurality of downcomer tubes distributed in a narrow zone extending longitudinally of the drum mid-section and having their upper end joined with the lowermost part of the drum inpressure-tight relationship thereto, means establishing communication between the downcomers and the lower ends of the riser tubes, and means including parts of the drum wall forming conduits of a tubular nature disposed within the drum and leading longitudinally of the drum from the spaces within the dished end portions of the drum to the inlets of the next adjacent downcomers, the conduits being closed at their ends most remote from the pertinent dished ends of the drum.

1,655,057 Hawley Jan. 3, 1928 6 Rowand et al. July 14, 1942 Hardgrove Apr. 20, 1943 Fletcher Apr. 18, 1944 Fletcher Jan. 30, 1945 Waeselynek Oct. 14, 1952 FOREIGN PATENTS Germany Aug. 14, 1903 Sweden Oct. 2, 1906

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