US1992504A - Surface condenser - Google Patents

Description

Feb. 26, 1935. A. l.. PENNIMAN SURFACE coNDENsER Filed April 1o, 1933y AQN K,

A ORNEYS.

Feb- 26,1935. A. L. PENNIMAN SURFACE CONDENSER Filed April 1o, 193s s sheets-sheet 2 RNEYS.

Pefented Feb. ze, '193s 1,992,504

SURFACE ooNnnNsnn Abbou L. reimlmm, Baltimore, Ma. Appueauen Api-n 1o, 193s, sel-m N. 665,413 comme. 'Y (c1. 251-43) They present invention relates to conlapse due to the relatively large stresses set up densers, and more particularly to conin thetubesheets on account of the difference densers of the surface type. This application is in pressure on the two sides of the sheets. This a continuation in part of applicant's prior apmethod of securing the tubes has caused con-- 5 pllcation, Serial No. 279,720, filed May 22, 1928, siderable trouble not only in the operation of the 5 entitled "Surface condensers." condenser, but also in the operation of the asso- The changes in temperature taking place in ciated power plant elements.

a condenser during operation necessitate ilexl- One serious disadvantage of packing the tubes bility of the structure due to the presence of arises because, in many instances, the packing,

lo relatively long parts lof such condenserstx'ucafter a comparatively short period of condenser l0 ture, which parts consist of different metals and operation, becomes compacted to such a degree possess diiferent coeflicients of expansion; Therev as to prevent the movement of the tubes. 'Ihus is considerable range of variation under operthe packing loses its function and the condenser ating conditions which consequently necessitate cannot be safely operated until the packing is l5 flexibility of structure in order to compensate for renewed. The renewal of the packing means a l5 those variations. Some of the conditions which shut-down in the operation of the condenser and give rise to the necessity for ilexibility of structhe associated engine orturbine and power plant ture are discussed immediately below. accessories. Moreover, it is diillcult to ascertain Thus during starting up periods, the air pumps the condition of the packing and, unless the pack- AUNL'llaz-D STATES `MT1-:Nij OFFICE are not able to take care of the air leakage at ing is renewed with a frequency providing for a 20..

the shaft vglands of modern turbine installations. great-factor of safety, the useless or harmful v A similar condition exists when the air pump condition oi' the packing may not be ascertained fails to function properly, during the operation until after serious trouble has occurred. of the condenser. In either case, the steam tem- Another diilculty with packing lies in the fact 23 perature in the condenser and, accordingly the that there is leakage of circulating water into 25 temperature of the shell, rises considerably and the condenser, even when the packing is in exmay approach or even'exceed 212 F. while the cellent condition. As is.well known to those tubes retain a temperature close to that of the concerned with the design or operation of concirculating cooling medium. The result is a densers, 'leakage has a serious eil'ect upon the lengthening of the shell, as compared with the operation of steam boilers because the presence 30 tube bundle, or a relative shortening of the tube of even a small amount of dissolved or suspended bundle. l material causes priming and foaming and solids Failure of the pumps which circulate the coolare carried over into the superheater and turing medium through the tubes will cause a rapid bines, clogging the superheater tubes and eroding rise of the temperature of all parts of the conthe turbine blades. 35. denser, including tubes and shell. Since the These diillculties which arise in-connectlon tubes are usually made of non-ferrous metal -and`with the use of the packing of tubes have led have a larger coeiilcient of expansion than the to attempts at solution of the problem byl ex ferrous shell,. the result of this condition is a pending, or'otherwise rigidly'securing the tubes' do relative lengthening of the tube bundle, as comat both ends of the tube sheets. -In one such 40 pared with the shell. method, the needed iiexibility'is obtained by the The features described immediately above will use of so-called iloating tube sheets. One apillustrate the necessity for exibility of structure plication of this method attempts to compensate in these surface type condensers, 'particularly for expansion by floating the tube sheet at one i steam condensers. In practical application, two end of the condenser upon a rubber expansion 46 types to secure exibility of structure have been joint. This construction has not proved particgenerally employed. One expedient employed ularly satisfactory, because some tubes, being in the prior art is the use Vof-p'ackingl and the colder than others, hold kthe floating tube sheets tubes oi surface condensers have been secured from movement suiilciently great to follow the to the tube sheetsin a manner as by packing at expansion of the warmer tubes. The result is -50 one or both ends, to permit expansion and cona loosening ofthe tube sheets, resulting in leakage traction with change of temperature. When of the circulatingwater, and theconsequent cone either or` both ends of the tube are placed so tamination of the condensate. However, the rubas to be free to expand, it is necessary to stay ber expansion joint is a further source of trouble: 17 i the tube sheets suiilciently to prevent their colfor this joint soon loses its leak-proof qualities.

The present invention has for its object means of securing flexibility of structure to compensate for variations due to temperature changes without the utilization of packing and/or floating tube sheets. The flexibility is secured by deflection of the tubes in a predetermined manner as set forth hereafter, with or without deflection of the tube sheets.

The objects and advantages will appear from the detailed description set forth below, it being understood, however, that this detailed description is given by way of illustration only, and not by way of limitation, since various changes therein may be made by those skilled in the art without departing from the scope and spirit of the present invention.

In connection with that more detailed descrip'- tion, there is shown in the drawings, in

Figure l, a longitudinal section of a two-pass condenser having the present invention embodied therein, in

Figure 2, a fragmentary sectional view on an enlarged scale of a single tube expanded at both ends in the tube sheets and passing through intermediate tube supporting sheets; in

Figure 3, a fragmentary view illustrating the deflection of the tube secured in accordance with the present invention; in

Figure 4, a fragmentary sectional view on an enlarged scale of one of the tube sheets as mounted on the shell; in

Figure 5, a modified form of structure of tubesheet as mounted on the shell; in

Figure 6, afragmentary view in cross section of the condenser; and in Figure "l, a fragmentary detail view of a baille and slip joint therefor.

In accordance with the present invention, the condenser is constructed with` the tubes expanded at both ends in the tube sheets, or otherwise rigidly secured to said -tube sheets. Both tube packing and floating tubesheets are eliminated. Compensation for variations due to temperature changes are effected in the present construction by deflection of the tube bundles with or without deflection of the tube sheets. This construction eliminates the-major cause of leakage of circulating water into the condenser. Installation of tubes is simplified. And as thereis no packing to dry out or any diaphragm expansion joint to be affected, the condenser may be permitted to dry out during shut-down periods, and can be baked to remove scale. Other advantages will also be apparent to those skilled in the art from the further description set forth b'elow.

The present invention is concerned with condensers having condenser tubes of a length which require' some means for compensating for the variations that take place with change of temperature. In order to obtain the desired flexibility it is necessary to have tubes which behave asv long slender columns. For purposes of the present invention, such tubes are defined to have a length resulting in a ratio of slenderness of 200 or more. The ratio of slenderness is equal to the length divided by the radius of gyration. This inventibn enables the use of tube condensers having relatively long tubes as described above, and makes possible the practical use of such tubes, both ends of which are expanded into the tube sheets. In accordance with the present invention, the slenderness of the long tubes causes the relative lengthening of the tube bundle, as compared with thevsh'ell, to be compensated mainly by deection of the-tubes,

which stresses the metal of the tubes and tends to loosen the expanded joints of the tubes in the sheets, be Ikept as smallas' possible. 'Iy'he following analysis of the conditions to be considered in this respect shows and indicates the progress in the vart which is obtained by the use of the present invention.

For satisfactory operation, it is necessary 'that the support plates, during deflection, serve mainly as guides for the tubes only, and that they do not take up any appreciable bearing pressures resulting from the defiection. Such pressures de- 4 crease the service life of the tubes, ontaccount of wear caused by friction and vibration, and, in addition, void the mathematical determination of the shape of the tubes to be taken lon expansion because the combination of pressure and friction causes the tube sections located in the support plate holes to act in a way similar to fixed points, more or less, and, therefore, eliminates free deflection. In addition, the introduction of such fixed points either increases the thrust to be taken up by the fixed ends of the tubes or makes it necessary to provide for movement of the ends by deflection of the sheets.

Several methods are provided by the present invention for obtaining the conditions outlined above. One is to avoid the use of any means of support in the center or near to it as would be obtained with the utilization of one support plate only or any other uneven number ofsupports. The use of one support plate in the center of the condenser results in causing a fixed point in the center of the tube, on expansion, with either half v of the tube free to defiect in any direction. The defiection, therefore, is not under control. The

use of three support plates, with one support in the center, limits the movement of the center section of the tubes, on expansion. This condition results not only in excessive tube wear at the center support plate, but also in a corresponding increase of the end thrust since it cuts the effective columnar length in half. In addition, the pressure forces the deection between support plates into directions whichY cannot always be 'calculated. This identical condition appears with the use cf any uneven number of support plates.`

The proper guidance of deflection on expansion necessitates the presence of certain curvatures of the tubes on installation. Any expansion with the'endsxed tends to increase the curvature of all sections which are already curved. Accordingly, if the support plate holes are intended to serve as guides only, the tubes mu'st be substantially straight in the sections passing through the holes. Since more or less all of a slender tube takes a part in the deflection on expansion, the-condition can be obtained only by changing directions of curvings and locating the reversing points' at the support plates. 'Ihe use of a'single bow throughout the tube eliminates straight sections and reversals and the expansion 70 tion, with reversing points at the tube support plates and withperfectdrainage of the tubes when the condenser is emptied since no part of the tube, excepting when it ishot, is lower than the ends. The elevation of the holes in the support plates, above the holes in the tbe sheets, may be chosen only large enough to insure good drainage of the tubes or slightly larger though it should be considered that increasing elevation increases the ilexibility of the structure. The holes in the support plates must be tapered, with the diameter increasing from the center to the outside, to allow good bearing support for the tubes at any angle they may assumeduring deection. These angles can be determined either by experiment or by calculation and depend on various factors, as length of intermediate sections and elevation of the holes in the support plates above the axis of A the component holes-in the tube sheets.

Since the supports are to serve as guides and since this condition demands the use of compound curves with points of reversal at the supports, further limitations appear in regard to the arrangement of the support plates; The most favorable conditions are obtained with two supports especially when the center section is made longer than the end sections, preferably the distance between the tube sheets and the support plates giving tube sections having a length corresponding to a ratio of slenderness of not less than 65. The use of two supports is satisfactory with all tube lengths employed so far. With four supports, bearing pressures at the supports cannot be eliminated, but can be kept down by making the center section and the endsections long and the two remaining sections as short as possible. In such constructions using four supports, desirably ithe center sections of the tubes between the tube supports are made longer than the end sections of the tubes, and the end sections of the tubes have a length Vcorresponding to a ratio of slenderness of not less than 65. The remaining tube sections should be kept as short as possible. 'I'he tubes will'be essentially straight in these two sections, with pronounced bending effects at the supports unless the openings through which the tubes pass in these supports are sufciently large especially in the direction of bend'I ing of the .tubes. With six supports, the center section should again be longer than either one of the other sections; each of these sections shouldlates to various means of making the tube sheet' sufficiently flexible to deflect to the extent needed.

The desirability of using flexible tube sheets in I combination with long tubes has not been previously recognized in the prior art. Flexibility is obtained by the use of unstayedsheets, only sumciently thick to secure satisfactory expansion of the tube ends, and is increased by providing a space between the periphery of the tube bundles Aand the rigidly xed surface of the sheets, such space being sufciently large to allow for deflection of the tube sheets within the limits of elastic deformation of the metal. This condition may be aided by thinning v the tube sheet outside of the tube bundle. Thekpace can be obtained either by spacing the periphery of the tube bundle a corresponding amount from the shell, in which case bales must be employed to force all of the steam to enter the space within the tube bundle, or by providing a special off-set ange section, as s hown for example in Figure 4 and Figure 5.

Turning to a, consideration of the condenser structure illustrated in the drawings, exemplifying the invention discussed above, the condenser comprises a shell 10 having a steam inlet 11 and a condensate outlet 12. A circulating water inlet-outletI header 13 is bolted to the shell 10 at one end thereof, and a water reversing header 14 'is bolted to the shell a t the other end. Tube sheets 15 and 16 are rigidly secured between the ends of the shell 10 and the headers 13 and 14, respectively. Tubes 17 are expanded at both ends in the tube sheets 15 and 16 and extend through support plates 1'8 and 19 suitably secured to the condenser shell. A baille plate 20 causes a more even distribution of the steam within the shell and is illustrative of many devices including tube arrangements providing steam lanes, for eiecting `a good steam distribution within the condenser.

As shown in Figure 2, the tube supporting plates 18 and 19 have holes 21 and 22 respectively for the passage of each tube'1'7 therethrough. These holes in the supporting plates are out of line in a vertical plane' with the.corres ponding holes 23 and 24 in the tube sheets 15 and 16, in which the respective tubes are rolled or expanded. In a condenser tted with 1 inch outer diameter Admiralty tubes 'eighteen feet long, the holes 2 1 and tion of the holes in the tube sheets and tube sup-' porting sheets tending to guide the direction of deection. The present invention is concerned with the use of two or other even number of support plates, two being used as illustrativein the drawings, since it is the usual practice to use two plates with condenser tube lengths of from 12 to 26 feet, and this represents by far the bulk of condensers in service at the present time. It is also obvious that the greater the misalignment of the holes in the support plates with respect to the tube plates, the greater the tendency for.v

the tubes to deiiect. There is, however, a definite disadvantage in having the tube support plates misaligned-to too great an extent in that it makes the problem of renewing tubes particularly difficult. It, therefore, becomes necessary to determine a distance which the holes in the tube support plates should be oiset that will provide satisfactory operation ofthe condenser without an unreasonable amount of difliculty in replacing the tubes. By experimentation, it has been determined that in a condenser using tubes varying in length from 16 to 26 feet, if the vertical misalignment of the tube holes in the tube support plates with respect to the tube sheets was 1 inch,

the condenser performed satisfactorily, and that itV was not unreasonably troublesome to replace the tubes.

Instead of calculating the most desirable location of the support plates and of the relative location of the holes, for the best combination of .low thrust at the tube ends and easy replacement of tubes, a full scale experimental apparatus may be set up.

Figure 3 illustrates an experimentalapparatus which was set up, and shows the behavior of tubes installed according to the present invention, and illustrates a record obtained photographically of such experimental installation as a result of double exposure. The tube, in this case, Was 18 feet long. With an elevation of the holes in the intermediate support plates of one inch above the holes in the supports representing the sheets, the cold tube A showed a very slight curvature only. The increase of curvature, as caused by expansion on account of heating,v shows plainly the compound nature of the curvature which is a fundamental characteristic of structures produced in accordance with the present invention. Thus the hot tube is shown in position B in Figure 3, and definitely shows the compound curvature resulting by controlling the'character of deflection of the tubes in accordance with the present invention in order to compensate for variations due to temperature changes.

As pointed out above, the exibility of the condenser structure may be increased by flexibility of the tube sheets especially when the initial curvature of the tubes is smalLyWhen the tubes are stressed in tension 'on account of the shell becoming hotter than the tubes,'the stresses have to be taken up first by straightening of the tubes as far as possible, secon`d`by deformation of tubes and/or tube sheets. It is obvious that if a tube is attached to the tube sheets directly adjacent to the point of support of the tube sheet at its perinreter, all of the stress set up in the tube resolvsfitself as tension in the tube and shear in the tube sheet. Since the possible non-destructive shear deformation is small, and.

the force required to cause such shear deformation is'large, the stresses will result in elastic stretchingof the tube metal followed by loosening of thef ends in the sheets or by permanent stretchingV of the tubes if the stresses are not sufliciently relieved by the elastic deformation.

The present invention provides a distance between the periphery of the tube bundle and the perimeter of the tube sheet at the point of attachment to the shell. This distance is to be calculated in such a way that the stresses resulting from the relative expansion of the shell can be taken up by a combination of elastic stretching of the tubes and elastic bending of the tube sheet, including the space located between the periphery'of the tube bundle and the point of attachment, in such a way that th'e stress within the tube remains below that' necessary for loosening the joints in the tube sheets or exceeding the elastic limit of the tube metal.

The necessary distance between tube bundle and point of attachment of the tube sheet to the shell may be procured by spacing the tube bundle a corresponding distance from the shell in which case it is necessary to provide batlles to 17, expanded at 24 in the tube sheet 16 represents the outside tube of the .tube bundle. An olf-set design of the flange connections of shell and header securing the tube sheet provides the space required for deflection of the sheet. For this purpose the flange 40 of the shell and flange 41 of the header are extended sulliciently to provide off-set portions or shoulders 38 and 39 respectively.

A further means of securing flexibility of the tube sheets is shown in Figure 5.- In this case, the tubes 17 are expanded as shown at 24 in the tube sheet 16', the latter having an outermost portion F of reduced thickness. This thinner section of the tube sheet 16' lying between the tube bank and the shell, assists in the deflection which may take place in the tube sheet and provides a greater flexibility therein. Both the lconstruction of Figure 4 and Figure 5 may be utilized simultaneously, a method whose advantage is indicated by a comparison of Figure 4 and Figure 5; however, one or the other is usually sufficient to provide for the necessary flexibility of the tube sheet.

For example, the free distance of the tube sheet between the periphery of the tube bundle and the side of the shell in the condensers built in accordance with this invention was approximately 4 inches in condensers which were equipped with approximately 735078 inch outer diameter tubes, the tube sheets being 12 feet in diameter at the point of attachment to the shell.

The use of individual plates or tube supports, as outlined above, is the simplest and cheapest means of taking care of supporting and guiding the tubes. However, the present invention is not limited tosuch means, but covers any means of support which obtain the desired end, that is to" force a compound curving of the tubes with reversals or straight sections at or near the points of support.

Ballles may be required for various purposes within the condenser and are attached to the shell, the tube supporting sheets, and the tube sheets. Means devised to obtain flexibility of structure by deflection of the sheets include methods to permit flexibility'in the fastening of these baille plates as described immediately below.

The general path of the steam is across the tubes in substantially a vertically downward direction. The saturated noncondensible gases which tend to collect in the bottom of the condenser are drawn across a part of the tube bank designated generally by the reference character 26 as shown more clearly in Figure 6. This section of the tube bank is separated from the rest of the tubes by a rain plate 27 which maybe in sections 27a, 27h, and 27c extending longitudinally of the condenser shell, and which are supported between the tube sheets and tube supporting plates, as may be necessary, as shown more clearly in Figure 1. In order that the tube sheets may deflect, it is necessary that those sections of the rain plate 27 located between the tube sheets 15 and 16 and the adjacent supporting plates be -attache'd to either the tube sheet or the adjacent supporting plate by means permitting the rain plate sections to slip with respect to the tube sheet or tube supporting plate. As here shown, the rain plate section 27a has one end thereof rigidly secured to the tube supporting plate 19 while the other end thereof -is secured to the tube sheet 16 by the clamping plates 28 and 29 which form a slip joint. 'Ihe rain plate section 27h may be rigidly secured at both ends to the tube supporting plates 18 and 19.

The rain plate section 27e may have one end rigidly secured to the tube supporting plate 18, and while its other end is secured to the tube sheet by means of the slip joint comprising clamping plates 30 and 31. The construction of the slip joint is shown more clearly in Figure 7. 'I'he rain plate section 27a, for example, is clamped between the plates 28 and 29 which are rigidly secured to the tube sheet 16 by means of the bolts 32. The rain plate is attached tightly 'to the wall of the condenser in any suitable manner, as by the rivets 27', as shown more clearly in Figure 6.

' by reason o! the fact that unless the non-concessive by-passing of the steam around the tubebundle, bailles as represented by plate 34 may be used.

' In the prior art standard surface condenser with packed tube ends, baille plate 34, of course, is not used; however, rain plate 27, or some substitute for it, must be used and it has been a well known fact that one of the most prolific causes of poor condenser perfomance has been due to leakage past rain plate 27, thereby'allowing the air pump to become overloaded.- Therefore, the baille plates are supported in sections between the tube sheets and tube support plates, and must be fastened against the tube sheets, tube support plates, and the condenser shell in such a manner as to be substantially vapor tight, despite the fact that the two tube sheets must be able to breathe each toward one another or away from one another,

depending upon the stresses set up by the rela'.- tive temperatures of the several parts of the condenser. It is, therefore, obviously desirable to t both of these bailies with some form of slip joint at the point where .they are attached to the tube sheets. L

It will be understood that condensers employing the present invention may be generally of any well known type, the construction being modified to permit of the embodiment presented by the present invention. The tube sheets may be rigidLv secured in any suitable manner as alternative to the construction illustrated. Instead of The tight-joints are necessary' expanding the tubes in the tube sheets they may be similarly associated therewith by any suitable arrangement preventing relative movement therebetween and assuring a leak-proof joint. As 'indicated above, an even number of tube supporting sheets must be used, but the exact numthe more specific description of the invention as set forth above, this disclosure should not be interpreted as limited by those theories of operation, since those considerations have been given merely by way of explanation and not as limitations on the structure herein disclosed.

Having thus set forth my invention, I claim:

1. A surface condenser comprising a shell, two approximately vertical tube sheets rigidly supported in said shell, two approximately vertical xed tube supports placed intermediate said tube sheets, tubes expanded at both ends into horizontal holes in said tube sheets, the centers of the holes in said 4tube supports being located above the axis of the corresponding holes in said tube sheets.

2. A surface 'condenser comprising a shell, two approximately vertical tube sheets rigidly supported in said shell, two approximately vertical xed tube supports placed intermediate said tube sheets, tubes expanded at both ends into horizon-g tal holes in said tube sheets, the centers of the holes in said tube supports being located above the axis of the corresponding holes in said tube sheets, said holes in said supports being enlarged from the center section to the outsides to permit angular displacement of the tubes.

3. A surface condenser comprising a shell, tub sheets rigidly supported in said shell or attached thereto, an even number of fixed tube supports placed intermediate said tube sheets, tubes expanded at both ends into holes in said tube sheets, the holes being substantially at right angles to the tube sheet's, and the centers of the holes in the tube supports being located outside of the line joining the centers of corresponding holes in the tube sheets.

4. A surface condenser comprising a shell, tube sheets rigidly supported in said shell or attached thereto, an evennumber of xed tube supports placed intermediate said tube sheets, tubes expanded at both ends into holes in said tube sheets, the holes being substantially at right angles to the tubesheets, and the centers of the holes in the tube supports being located outside of the line joining the centers of corresponding holes in the tube sheets, the holes in said tube supports being enlarged from the center section-to the outsides to permit angular displacement of said tubes.

A ABBO'I'I L. PENNIMAN.

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