US2729430A - Heat exchanger - Google Patents

Description

Jan. 3, 1956 E. N. SIEDER ET AL 2,729,430

HEAT EXCHANGER Filed May 10, 1954 ROBERT M CHURCH EVERETT N. 51505;?

IN V EN TORj AFTO NEY nited States Patent HEAT EXCHANGER Everett N. stead, mascara, snandben M. Chn enwest. field, N. Y., assignors to AleoProductginc New York, N. 53., a corporation ofNew York Application May 10, -1 954,-Serial'No. 428,134 renting. 61.257 32 This invention relates to heat exchangers and 1 particularly to feed water heaters equipped with su'bco'oler'sections.

The subco'oler sec-tibn of a feed water heater of the horizontal two-pass "type operates most efiiciently when it is maintained full of'condensate. In the-normal operation'of this typeof heat'e'r,the steam passing' through the main body of the'shell condenses asit 'conta'c'tsthe tubes and falls into the 'bo-ttom'of the shell where'it collects in a =pool. The pressure of the unemdensed steam {in the shell above the pool forces condensate fr om the'poolinto the subcooler unit which in one known "construction en velopes the inlet endportions of "the -tube's et the list pass. A tight seal is required bt'ween such -a 'subcooler and the "remainder'ofthe --steaii1-'filled shell"so that the relatively high pressur'e ste ahi and airwill not leak into the subco'oler and dimihish its fiieiency. Effective s'eals have been diiiicult fodesi'gn.

Various structures *have been conceived for this pur pose as, for example, the one described in U. S. Patent '#2,666,625 to W. M. *By'erly. Inthis const'ruetion, the

enveloping bathe structure or 'shroudhf the stibcooler is made in two telescoping 'portioris, thefloverlapping'joint being-equipped with 'aninterleavedtype of seal. The outer or downstream portion of the shroud is "secured to the fixed tube sheet and the ihherdr upstream'pbi'tion isfse cured to an interior tube plate. LThe-tube's are"exp'ancled or rolled into the openingsfprovided in the interior tube "plate whereby fluid tight "connections are ensured. As

the tubes may expand thermally, the interior tube plate moves with them a dcarrie's the inner pbrtioh of the shroud with it. The Byerlyh'ealis designed to compensate subcooler to function with a low'level condensate .pool

in the shell thus providing for theexposure'of the surface of nearly all of the tubes outside the subcooler 'to the steam in the shell with a --consequent ihcrease in the efficiency of operation "of the apparatus. Another object is to provide such a seal which will function effectively "despite the differential thermal expansion btween the subcooler and the tubes "e xtndiii'g t'liefe't hrough. Still another object is to provide a "novel seal which permits relatively "easy removal and tplaidhieht "of defective tubes.

.2 be apparent from the following description, the accom- .panying drawings, 'and the appended claims.

In the drawings,

Fig. l is-a partial longitudinal sectional view through an exchanger showing only as much of the heat exchanger as is necessary to understand the invention. The figure omits some of the tubes for clarity;

Fig. 2 is a partial sectional view taken "on line 2-2 of Fig. 1; and,

Pig. 3 is a view similar to Fig. 2 of an alternate con struction.

in Fig. 1 there is shown a portion of a conventional feed water heater including ashll -10 provided with a header or waterbox l'l'which is divided by the transverse partition 12 into inlet and outlet compartments 13 and l t. Wafer inlet nozzle 15 and outlet n'e'zzle 16 communicate with compartments 13 and 14 respectively. A plurality oftubes17 (only a few'being'shown for clarity) extend longitudinally of the shell and transfer the water to 'beheated frorncompartm'ent --13 to compartment 14 through the interiorof theshell where they are subjected to steam supplied through inlet nozzle '18. The tubes are fixedly supported-at their outer ends by conventional rolling into the fixed tube sheet 19.

The'tubes may be of the U-type, as shown in the Byerly patent supra, ortheymay be of the conventional straight typeextending between-fixedand floating tube sheets as illustrated in the U. s. Pateht#2,381,006 to N. A. Scott lr. The first heatingpass is etfe'c'ted as the feed water moves-through the tubes 17 in the lower portion of the shell and thesec'ond pass is'eife'ct'ed as the water returns thrdugh the tubes'in'theupper p'ortion of the shell. The heated water passes out'oftheshell into compartment 14 and thence throug lrnozzle16to apoint of use.

Preferably secured to the tube "sheet 19 and extending into the interior of the shell to enclose the tubes of the first pass 'forapredetermined portion of their length is a sub'oooler unit generally indicated as 20. I This unit includesa "water shroud having a top'wall 21 and a con- -taihihg'w'all 22attached thereto. a Wall 22 is preferably arcuat'e in cross section as best shown in Fig. 2. The outer end of the 'subcooler is formed by tube sheet 19 which serves as anend closure for the unit. The inner endof thes'ubcoole'r has an end support plate 23 apertured topermit a sliding'fit of the tubes therethrough. The

top wall -2'1"and-th'e containing "wall 2-2 project inwardly beyond the end plate 23 anda're clo'sed'by an apertured closure support'plate 24 which is spaced from end plate 23 to form a separate' condehsing 'chainber 25. It is int- -port'ant -to'note that tubes 17 have a'clearance lit in plates 23 and 24. Hence, dilfer'ential expansion between the tubes and the shroud and relative-movement between the two is permitted. No prior art device,'of which applicant is aware, has this arrangement.

A condensate inlet nozzle 26 is formed in the bottom of the-containing wall 22 adjacent-endiplate '23 andpreferably extends downward therefrom'so that the mouth of the nozzle is spaced as'hort distance from the-shell.

-An outlet-nozzle 2.7 -for the condensateisprovidedin the containing wall 22 nearthe tube sheet-19 an-dpreferably near the top oftheunit. A port 28 is provided in the bottom edge of'end plate-23 adjacent'inletnozzle 26 to establish communication between chamber 25 and the interior of the subcooler proper. Conventional baffies 29 secured preferably in staggered relation within the condensing section of the shell are provided to lengthen the path of the -flow of steam 'thus'to-incr'ease the impingement of steam against the condensing surface of the :tubes. Spaced throughout the =subcooler unitare addition'al staggered baffles 50 to lengthen the pathof'fiow of Disposed within the subcooler near top wall 21 is an open ended vent pipe 31, the purpose of which will be shortly described. One end of the pipe is in communication with chamber 25 and the other end is positioned in a lower pressure zone. Since a subcooler inherently has such a zone adjacent its outlet, in a preferred embodiment the other end of the vent pipe is placed adjacent the outlet nozzle 27 as illustrated in Fig. 1.

The operation of the device is as follows: Steam enters inlet nozzle 13 and follows a course through the main body of the shell as guided by the baffles 29. The steam is condensed as it contacts the tubes 17 and the condensate drops to the bottom of the shell to form a pool, the surface of which is maintained at a level slightly higher than the mouth of the nozzle 26. The pressure of the steam within the shell forces condensate from the pool upward through nozzle 26 into the subcooler to fill the same, the course of condensate flow to the outlet nozzle 27 being controlled by the bafiies 30. All of this is con ventional in the art.

As the condensate enters the subcooler proper, a portion of it is bypassed through port 28 to fill chamber 25 whence it is supplied to pipe 31. Because of the flow of condensate through the subcooler, the pressure at the condensate outlet nozzle 27 is lower than the pressure at the condensate inlet nozzle 26. This pressure diflerential is transmitted through pipe 31 to chamber 25 and causes a part of the condensate entering nozzle 26 to be continuously drawn through port 28 into chamber 25 to keep the latter flooded and to supply the pipe with a continuous flow of the condensate. It should be here observed that the by-pass flow just described and the flooded condition of the subcooler are both continuously maintained even though the level of the shell pool is only slightly higher than the mouth of the nozzle 26. The surface of nearly all of the tubes outside the subcooler are thus entirely exposed to steam. Consequently, little or no loss results from the immersion of the tube surfaces in the pool of condensate.

When the apparatus is in operation, the pressure of the steam in the main body of the shell is higher than the pressure of the condensate in chamber 25. The result is that the condensate can not leak from the chamber into the main body of the shell through the clearances between tubes 17 and the apertures in the closure plate 24. More important, however, is the fact that any steam passing through the clearances from the main body of the shell into chamber 25 is condensed in chamber 25. Likewise the pressure of the condensate within the main body of the subcooler is higher than the pressure of the condensate in the chamber. But in this case any leakage from the main body of the subcooler through the clearances around the tubes in the end wall 23 passes into the fluid in chamber 25 and is carried through the pipe 31 back into the main body of the subcooler. A fluid seal is thus produced by the condensate in chamber 25 which positively prevents steam from passing into the main body of the subcooler. Furthermore, no water within chamber 25 can leak either way because of pressure dilferentials. At the same time full freedom of expansion by the tubes and the subcooler construction is permitted.

In Fig. 3 is shown an alternate construction embodying the invention. In this embodiment the subcooler comprises a top Wall 21a extending completely across the shell to make a fluid tight seal therewith by suitable sealing means 32. The end plate 23a in this case is shaped to conform with and is sealed to the shell. It serves as a confining wall of the subcooler. Closure plate 24a, likewise shaped and sealed, is spaced therefrom to form a condensing chamber corresponding to chamber 25 in Fig.

-l. The port 28a for entrance of the condensate into the subcooler in this embodiment is in the bottom edge of closure plate 23a. A corresponding port is formed in the lower edge of end plate 24a opposite port 28a to 4 l provide for the flow of condensate into the main body of the subcooler.

The operation of the alternate construction corresponds to the operation of the preferred embodiment, as previously described.

It is to be noted that while pipe 31 utilizes the heat exchanger itself and receives its low pressure effect at outlet 27, the pipe may obviously obtain the low pressure efiect from any other suitable source and the operation will be the same.

Similarly, while port 28 is shown in plate 23 in the preferred embodiment in Fig. 1, any opening into the lower portion of chamber 25 will suflice as, for example, through the containing wall itself into the chamber between plates 23 and 24.

Thus a positive seal is ensured to keep the steam and air out of the subcooler and keep the subcooler flooded while, at the same time, permitting a clearance fit between tubes 17 and plates 23 and 24 to accommodate expansion and facilitate tube removal.

While there have been hereinbefore described approved embodiments of this invention, it will be understood that many and various changes and modifications in form. arrangement of parts and details of construction thereof may be made without departing from the spirit of the invention, and that all such changes and modifications as fall within the scope of the appended claims are contemplated as a part of this invention.

What we claim is:

i. In a heat exchanger of the horizontal shell and tube type in which fluid passing through the tubes is heated by steam supplied to the shell and condensed therein, a structure enveloping a portion of the tubes to form a subcooler, inlet means for the flow of condensate from the shell into the subcooler in response to the pressure of steam in the shell, means for the outlet of such condensate from the subcooler, aperture means in said structure through which the tubes extend to permit differential expansion between the tubes and the subcooler structure, means on the subcooler structure forming a chamber to enclose said aperture means, inlet means for the flow of condensate into said chamber in response to the pressure of steam in the shell, and condensate conducting means leading from said chamber to a zone of pressure lower than the pressure of the condensate in the chamber whereby a continuous flow of condensate through the chamber is produced thus to form a fluid seal.

2. In a heat exchanger of the horizontal shell and tube type in which fluid moves through the tubes in two passes and is heated by steam supplied to the shell and condensed therein, in combination, a transverse wall arranged above the tubes of the first pass and extending axially of the shell a portion of their length, means secured to said wall and enveloping a portion of the tubes of the first pass for a portion of their length, and an end plate secured to said wall and to the enveloping means to define a subcooler structure; inlet means for the flow of condensate from the shell into the subcooler structure in response to the pressure of steam in the shell; means for the outlet of such condensate from the subcooler structure; aperture means in said plate through which the tubes extend to permit differential expansion between the tubes and the subcooler structure; means adjacent the plate forming a chamber to enclose said aperture means; inlet means for the flow of condensate into said chamber in response to the pressure of steam in the shell; and a condensate conducting pipe leading from said chamber to a zone of pressure lower than the pressure of the condensate in the chamber whereby a continuous flow of condensate through said chamber is produced thus to form a fluid seal.

3. A combination, according to claim 2, in which the means secured to the transverse wall to envelop the tubes of the first pass is a portion of the shell.

4. A combination, according to claim 2, in which the means secured to the transverse wall to envelop the tubes of the first pass is a wall, arcuate in cross section, spaced from the shell.

5. In a heat exchanger of the horizontal shell and tube type in which fiuid moves through the tubes in two passes and is heated by steam supplied to the shell and condensed therein, in combination, a transverse wall arranged above the tubes of the first pass and extending axially of the shell a portion of their length, wall defining means secured to the transverse Wall and enveloping the tubes of the first pass for a portion of their length, and an end plate engaging the transverse wall and the enveloping wall means to define a subcooler structure, said end plate being apertured to provide for the extension of the tubes therethrough so that difierential expansion between the tubes and the subcooler structure is permitted; inlet means for the flow or". condensate from the shell into the subcooler structure in response to the pressure of steam in the shell; means for the outlet of such condensate from the subcooler structure; a second plate spaced from the first and apertured to provide for the extension of the tubes therethrough; means connecting the first and second plates to define a chamber; inlet means for the flow of condensate into said chamber in response to the pressure of steam in the shell; and a condensate conducting pipe leading from the chamber into the subcooler structure to a zone of pressure lower than the pressure of condensate in the chamber whereby a continuous flow of condensate through said chamber is produced thus to form a fluid seal.

6. In a heat exchanger of the horizontal shell and tube type in which fluid moves in two passes through tubes secured to a fixed tube sheet and is heated by steam supplied to the shell and condensed therein, the tubes of the first pass being enclosed throughout a portion of their length by a subcooler structure supplied with a flow of condensate from the shell in response to the pressure of steam in the shell, means sealing the subcooler structure to the fixed tube sheet, aperture means in the subcooler structure through which the tubes of the first pass extend to permit the tubes of the first pass to move axially in relation to the subcooler structure in response to difierential expansion between the tubes and the subcooler structure, inlet means for the flow of condensate from the shell into the subcooler structure in response to the pressure of steam in the shell; means for the outlet of such condensate from the subcooler structure: and a fluid seal to receive condensate leaking from the subcooler structure through said apertures, such seal comprising a structure defining a chamber in communication with the aperture means in the subcooler structure, inlet means to permit the flow of condensate from the shell into said chamber in response to the pressure of steam in the shell, and a pipe extending from said chamber to a position in the subcooler adjacent the subcooler outlet where the pressure of the condensate is less than the pressure of the condensate in the chamber, such pipe thus providing means for the continuous flow of condensate through the chamber to form a fluid seal.

7. In a heat exchanger of the horizontal shell and tube type in which fluid moves in two passes through tubes secured to a fixed tube sheet and is heated by steam supplied to the shell and condensed therein to form a pool at the bottom of the shell, the tubes of the first pass being enclosed throughout a portion of their length by a subcooler structure supplied with a flow of condensate from the pool of condensate in the shell in response to the pressure of steam in the shell, means securing the subcooler structure to the fixed tube sheet, aperture means in the subcooler structure through which the tubes of the first pass extend to permit the tubes of the first pass to move axially in relation to the subcooler structure in response to differential expansion between the tubes and subcooler structure, inlet means for the flow of condensate from the shell into the subcooler structure in response to the pressure of steam in the shell; means for the outlet of such condensate from the subcooler structure; and a fluid seal to receive condensate leaking from the subcooler structure through said apertures, such seal comprising a structure defining a chamber in communication with the aperture means in the subcooler structure, inlet means extending into the pool of condensate to permit the flow of condensate from said pool of condensate into said chamber in response to the pressure of steam in the shell, and a pipe extending from said chamber to a position in the subcooler adjacent the subcooler outlet where the pressure of the condensate is less than the pressure of the condensate in the chamber, such pipe thus providing means for the continuous flow of condensate through the chamber to form a fluid seal.

References Cited in the file of this patent UNITED STATES PATENTS 2,299,455 Bowman et al Oct. 20, 1942 2,392,638 Bowman et a1. Jan. 8, 1946 2,666,625 Byerley Jan. 19, 1954

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