US2720259A - Gas venting of heat exchangers - Google Patents

Description

Oct. 11, EI JACQBY GAS VENTING OF HEAT EXCHNGERS 2 Sheets-Sheet 1 Filed April 14, 1950 lNvEm-oR Hamid E. .fco f oct. 11, 1955 H, E, JACOBY 2,720,259

GAS VENTING OF HEAT EXCHANGERS Filed April 14, 1950 2 SheetsSheet 2 INVENTOR Hamid E. .fazcov ATTO mixture `tends to increase.

' core `or cone of gas that is relatively inactive.

United States Patent Oiice 2,720,259 Patented Oct. 11, 1955 2,720,259 GAs VENTING oF HEAT EXCHANGERS Harold E. Jacoby, Brooklyn; N. Y., assigner, by mesne assignments, to Chicago Bridge & Iron Company, New

York, N. Y., a corporation of Illinois` Application April 14, 1950, Serial No. 155,843 8 Claims. (Cl. 159-27) `This invention relates to heat exchangers and more particularly to improved means for removing non-condensible gases from a heat exchanger, e. g., the heating element of a tubularevaporator. This application is a lcontinuation-in-part of my copending application, SeralMNo. 712,810, led November 29, 1946, now abandoned. t

Heat exchangers of the type with which the present invention is concerned normally comprise a plurality of tubesgarranged in a tube bundle and mounted at their ends in a pair` of tube sheets. The tube bundle and associated tube sheets are encased in a shell or other suitable housing. The medium which is to be heated is caused to flow through the interior of the tubes `and a heating medium comprising a condensible vapor is introduced into the shell and is caused to condense on the external surfaces of the tubes thereby delivering heat to the tubes and through the tube walls to the heated medium within the tubes. Heat exchangers of this type are commonly referred to as tube-in-shell `heat exchangers and may be separate self-contained units or they may be heating elements incorporated in process equipment such as evaporators, crystallizers, re-boilers, wasteheat boilers, andthe like.

The steam `or` other condensible heating medium used int such a `heat exchanger normally contains a small proportion of non-condensible gas and as the condensible vapors condense,` the proportion of gas in `the vapor-`gas If this non-condensible gas is `not removed it tends to produce gas binding of the h"e`atin`gxsurface,` i. e., it tends to blanket portions of the heating surface in suchmanner as to prevent fresh high quality steam from coming in contact with those surfaces. Hence it is essential for eflicient operation that this non-condensible gas be eifectively removed.

It hastherefore been the practice to introduce the steam orothier condensible heating medium at one point on the periphery ofthe shell of theheat exchanger and to attempt to remove non-condensible gases at another point on the periphery of the shell spaced from the point of admission of the heating medium. For example,` 'in cases where the heat exchanger is arranged with its `tubes in `verticall position, steam has been admittedto the shell or casing ofthe heat exchanger at a point near the top of the tube bundle and non-condensible gas mixed with steam has been removed at a point on the periphery of the heat exchanger opposite the lower endof "thettube bundle. This previous practice is "objectionable from several points of View. Since the noncondensible gases are withdrawn at the periphery of the tube bundle there will be within the tube bundle a central This inactive core of non-condensible gas will accumulate `around the central tubes `of the heat exchanger and thus substantially reduce the effective heating surface `available for heat transfer.

A further disadvantage of the usualV venting `arrangenient is that it permits theinooming vapors to owdirectly from their point of admission to the point of venting. Normally the shell or housing of the heat exchanger is appreciably spaced from the tube bundle and there is thus an annular space between the inner surface of the shell and the tube bundle which offers relatively little resistance to the ow of vapors. Since vapors will tend to flow at a higher rate through channels that offer less resistance to flow, an appreciable proportion of the incoming heating medium may flow through this annular space directly to the fixed gas vent and thereby bypass the heating surfaces of the heat exchanger. Thus the steam content of the vented gas is increased and the heating efficiency of the heat ex changer reduced.

In order to overcome this diiculty it has been proposed that the center tube of `the exchanger be omitted and that xed gases be withdrawn at a point on or near the axis of the tube bundle. However, when the center tube is omitted a space is left at the center of the tube bundle through which channeling of the vapors can occur and hence, an excessive amount of steam is withdrawn from the heat exchanger with the fixed gases.

lt is accordingly an object of the present invention to provide an improved method of removing non-condensible gases from a heat exchanger. It is another object of the invention to provide lixed-gas removal means which when incorporated in the heat exchanger increases the eilciency of heat transfer therein. It is still another object of the invention to provide fixed-gas removal means that minimizes steam losses with the fixed gas. Other objects of the invention will be in part obvious and in part pointed out hereinafter. t

The many objects `and advantages of the present invention may best be appreciated by referring to the accompanying drawing which illustrates apparatus incorporating a preferred embodiment and a modification of the invention and wherein:

Figure 1 is a vertical sectional View of a self-contained heat exchange unit incorporating the apparatus of the present invention;

Figure 2 is a vertical sectional view of an evaporator having incorporated therein a heat exchanger'embodying a modification of the present invention;

Figure 3 is an enlarged detailed View of the xed-gas removal tube shown in Figure 2; d

Figure 4 is a view similar to Figure 3 but showing a tube having a section that is detachable .for cleaning;

Figure 5 is a vertical section of an evaporator body similar to that of Figure 2 but having a heat exchanger with three spaced tube bundles; and

Figure 6 is a horizontal section taken on theline 6 6 of Figure 5 and illustrating the central arrangement of the vent tube in each of the several tube bundles.

Referring to the drawings, and more particularly to Figure 1 thereof, the numeral 10 designates a tube bundle comprising a plurality of tubes (only a few of which are shown in Figure 1) arranged in a cylindrical bundle and mounted at their upper ends in the tube sheet 12 and at their lower ends in the tube sheet 14. Surrounding the tube bundle 10 and tube sheets 12 and 14 there is a shell or casing 16 that extends beyond the ends of the tube bundle to form with the lower tube sheet 14 an inlet chamber 18 and with the upper tube sheet 12 an outlet chamber 20. The iluid to be heated is admitted through the inlet pipe 22 to the chamber 18 and flows through the tubes of tube bundle 10 wherein it is heated by condensation of a condensible heating medium outside the tubes. The heated fluid then flows into outlet chamber 20 and leaves the exchanger through outlet pipe 24. d

Steam or other condensible vapor is admitted to the exchanger through an inlet pipe 26 and flows into contact with the tubes of tube bundle 10 and in a generally down ward direction alongv the tubes in such manner that it condenses on the tube surfaces and gives up its latent heat which is transferred to the heating medium within the tubes. In the upper part of the exchanger there is provided a cylindrical baie 27 mounted on an annular plate 29 fixed to the inner surface of the shell 16. The bafiie 27, plate 29 and shell 16 cooperate to define an annular passage through which the inlet steam may flow before coming into contact with the tubes of the tube bundle. The baflie 27 operates to prevent inlet steam from impinging directly on the tube bundle and to improve the distribution of steam around the periphery of the tube bundle. Condensate is removed near the bottom of the tube bundle through condensate pipe 28.

As previously pointed out the condensible heating medium normally contains a small proportion of noncondensible gases. To effect removal of such gases the tube bundle is provided at its center with a vent pipe 30 which extends between the tube sheets 12 and 14 in a manner similar to the other tubes of the tube bundle but is blauked off at one end (in this case the upper end) so that gases may iiow from only one end of the tube. The open end of vent tube 30 passes through the tube sheet 14, chamber 18 and shell 16 out of the exchanger. At a point near the lower end of the tube bundle the vent tube 30 is provided with one or more holes 32 through which gas may flow into the vent tube and thence out of the heat exchanger.

In order to regulate the removal of condensible gas an automatic controller 34 is provided which may be of the conventional pneumatic type and may comprise a temperature responsive element 36 located in a thermometer Well 38 near the point at which the non-condensible gases enter the vent tube 30, a pneumatically operated regulating valve 40 and the controller 34 proper, which positions the valve to maintain the exit gases at a predetermined temperature. Since the temperature of the exit vapors varies in accordance with the steam content thereof the temperature controller may be so adjusted as to maintain the steam content of the exit vapors at a desired predetermined value and thus minimize the steam losses in the vented gas.

With the construction shown in Figure l, bypassing of steam from the steam inlet to the vent gas outlet is precluded since all of the steam must necessarily come in contact with the tube bundle before it reaches the vent gas outlet. Furthermore, there is no chance for an inactive core of non-condensible gas to build up within the exchanger as would be the case if the vent gas were removed from the periphery of the exchanger rather than at a point near the longitudinal axis of the exchanger. Also since the spaces between the vent pipe 30 and adjacent heating tubes are substantially the same as the spaces between adjacent heating tubes, there is no reduced pressure drop path through which channeling of steam can occur to increase the proportion of steam in the vent gas and thereby reduce the heating efliciency of the exchanger.

Referring now to Figure 2 of the drawings, there is illustrated in this ligure an evaporator of the generaltype disclosed in my co-pending U. S. application, Serial No. 650,468, filed February 27, 1946, now Patent 2,544,885, but provided with a vent tube constructed and arranged in accordance with the present invention. y The evaporator of Figure 2 is provided with a tube bundle 50 similar to the tube bundle 10 of Figure l, and extending between the upper tubesheet 52 and lower tube sheet 54. The medium to be heated, e. g., a solutionthat is to be evaporated, enters at the bottom of the evaporator through a connection 56 and passes through a chamber 58 and the tubes of the tube bundle 50 to a vapor disengaging space 60 defined by the shell 62 and upper tube sheet 52, thence out of the evaporator through a connection 63. Concentrated liquor leaves the evaporator body through a discharge connection 64. Condensible vapor, which may be either steam or water vapor that has been vaporized in a 4 v previous effect, enters the heat exchange portion of the evaporator through a tangential connection 66 and comes into contact with the tubes in the tube bundle 50. The vapor iows over the top of a baffle 68 and along the tubes of the tube bundle in a generally downward direction and condenses to give up its latent heat to the fluid within the tubes. Condensate is removed near the bottom of the tube bundle through the connection 70.

As in the structure of Figure l, as the vapors condense fixed gas tends to accumulate in the lower central portion of the tube bundle. T o remove this ixed gas a central tube 72 is provided that extends between and is mounted at its ends in the tube sheets 52 and 54. The upper end of tube 72 is connected by a conduit 74 extending through the vapor space 60 to the exterior of the shell 62.

Referring now to Figure 3, the lower end of tube 72 is closed by a plug 75 which acts as a guide and anchor to secure the lower end of the vent tube in desired position with respect to the tube sheet. Formed in the side wall of tube 72 near the lower end thereof, there -is a drain slot 76 through which any condensate forming within the tube 72 will drain into the vapor space of the heat exchanger and be removed through the connection 70. The lower portion of tube 72 is also provided with vertically spaced pairs of aligned openings 78, alternate pairs of openings being located at right angles to one another. Fixed gases pass through the openings 78 and thence through conduit 74 to the exterior of the evaporator body. The pairs of aligned openings are arranged at right angles to one another to provide more uniform removal of the fixed gas. The vertical spacing of the openings is such that fixed gas may iiow to the interior of the tube 72 even though a certain amount of sludge and/or condensate has accumulated at the bottom of the tube bundle. Removal of the iixed gas through tube 72 may be manually regulated by means of a valve 80 in the conduit 74.

In certain cases, as for example, where the heat ex change portion of the evaporator is boiled out to remove accumulated solids from the outer surfaces of the tubes of the tube bundle, the quantity of solids collecting at the bottom of the tube bundle may be sufficient to plug up the holes 78 and in such cases it is desirable to provide some means whereby at least a portion of the vent tube may be removed for cleaning. A structure adapted to accomplish this purpose is shown in Figure 4. Referring to Figure 4, the vent tube 72 is formed in two telescoping sections comprising an upper section 82 that is mounted in upper tube sheet 52 and a lower section 84 supported from the lower tube sheet 54. The lower section 84 is provided with drain slot 76 and vent holes 78, as in Figure 3, and rests on the inner surface of a cap 86 threaded onto a nipple 88 secured to the lower tube sheet 54. When it is desired to clean the holes 78 the cap 86 is removed and the section 84 is withdrawn from the tube bundle. After cleaning the section 84 and cap 86 are replaced. The lower end of upper section 82 is ared outwardly to facilitate re-insertion of section 84 therein. It will be noted that in the embodiment of Figure 2, the vented gas is withdrawn through the upper end of the vent tube, whereas in Figure 1 the vent gas is withdrawn through the lower end of the vent pipe. Removal of the vent gas through the upper end of the vent pipe is usually preferable since it precludes accumulation, in the fixed gas removal conduit, of a body of condensate which may interfere with a smooth flow of the withdrawn vent gas.

From the foregoing description it will be seen that the apparatus of the present invention increases the efliciency of utilization of the heating surface within a heat exchanger and reduces steam losses due to venting of the non-condensible gases from the heat exchanger. By locating the vent gas outlet near the center of the tube bundle dead spaces within the heat exchanger are eliminated and there is no chance for a core or cone of noncondensible gas to build up and blanket the heating sur- `face of the tube bundle. Furthermore, all of the entering condensible vapors must pass through some portion of the tube bundle before they reach the vent gas outlet and therefore bypassing of steam directly to the vent gas outlet is` reduced. Also the special arrangement of the vent pipe in the tube bundle is such thatthere is no reduced pressure drop path between the vapor inlet and vent gas outlet permitting bypassing or channeling f the condensible vapor. Removal of the vent gas may be controlled by a temperature controller as disclosed or by a controller directly responsive to the water content of the vapors or in other suitable ways to minimize steam losses through the vent line. The present vent systemis particularly useful in vertical tube bundles, although it may also be used in horizontal tube bundles as well.

It is to be understood thatthe foregoing description is illustrative only and that various modifications maybe madewithin the scope of the invention. For example, the tubes within the heat exchangermay be arranged in a number of individual bundles instead of a single bundle and the individual bundles may be separated from one another by a baffle or wall or merely by an open passage. In such a case it is desirable that vent gas pipes be provided near the central longitudinal axes of the separate bundles within the exchanger.

This modification is illustrated in Figures and 6 of the drawings. Referring to these figures, the heat exchanger 100 of the evaporator body there shown is composed of three spaced tube bundles 102, 104 and 106 that are supported at their ends in the tube sheets 108 and 110. It is evident that the exchanger 100 may be composed of any number of tube bundles greater than one and three are shown for illustrative purposes only.

Near the center of each of the tube bundles 102, 104 and 106 are the vent tubes 112, 114 and 116 respectively which are similar in construction to each other and to the tube 72 of Figure 2. The three vent tubes are closed at their lower ends and connected at their upper ends to the pipes 118, 120 and 122 respectively which lead through the evaporator body and are provided externally thereof with regulating valves 124, 126 and 128 respectively. If desired the three vent tubes can be connected within the evaporator body to a manifold 130, shown in dotted lines in Figure 5, which is provided outside the evaporator with a regulating valve 132.

It is evident that the vent tubes 112, 114 and 116, due to their central location within their respective tube bundles, function in the same manner as tube 72 of Figure 2. In order to reach the vent tube in each bundle, condensible vapor must pass through the other tubes of the bundle and hence by-passing of condensible vapor to the Vent is avoided. Moreover the vent tubes extend from one tube sheet to the other and hence channeling of the condensible vapors along the axes of the tube bundles is eliminated. Other modifications within the scope of the invention will be apparent to those skilled in the art.

What is claimed is:

l. In heat exchange apparatus of the tube-in-shell type, in combination, a pair of spaced tube sheets, a plurality of tube bundles mounted in said tube sheets and each having a length substantially greater than its diameter, a shell encasing said tube bundles, a vapor inlet connection near one end of said shell and remote from the other end thereof for introducing into said shell condensible vapor to ow along said tubes and be condensed on the exterior surface thereof, said vapor containing a small proportion of fixed gas, a condensate removal conduit in said shell, fixed-gas removal tubes located one each near the centers of each of said tube bundles and extending substantially from one of said tube sheets to the other tube sheet, the walls of said gas removal tubes at the ends of said tubes most remote from said inlet connection being provided, within said shell, with one or more openings and a conduit connecting one end of each of said gas removal tubes with the exterior of said shell, whereby nieu gas may pass through said tubes and conduit to the exteriorl of said shell.

2. In heat exchange apparatus of the tube-in-shell type, in combination, a tube bundle having tubes mounted in a pair of spaced tube sheets and having a length substantially greater than its diameter, a shell encasing said tube bundle, a vapor inlet connection near one end of said shell and remote from the other end thereof for introducing into said shell a condensible vapor to flow along said tubes and be condensed on the external surfaces thereof, said vapor containing a small proportion of fixed gas, a condensate removal connection in said shell, a` fixed gas removal tube located at the longitudinal axis 'of said tube bundle and extending substantially from oneof said tube sheets to the other tube sheet, the wall of said` tube near the end most remote from said inlet connection being provided, within said shelLwith one or more openings, a conduit connecting one end of said tube with theexterior of said shell, whereby fixed gas may pass through said tube and conduit to the exterior of said shell, and means responsive to the temperature of said condensible vapor near said opening for controlling the rate of removal of said fixed gas.

3. In heat exchange apparatus of the tube-in-shell type, in combination, a tube bundle having tubes mounted in a pair of spaced tube sheets and having a length substantially greater than its diameter, a shell encasing said tube bundle, a vapor inlet connection near one end of said shell and remote from the other end thereof for introducing into said shell a condensible vapor to flow along said tubes and be condensed on the external surfaces thereof, said vapor containing a small proportion of lixed gas, a condensate removal connection in said shell, a iixed gas removal tube located near the center of said tube bundle and extending substantially from one of said tube sheets to the other, said gas removal tube being formed in two sections and the section more remote from said inlet connection being provided, within said shell, with one or more openings, the gas removal tube section containing said openings being detachable from said tube bundle for cleaning, and a conduit connecting one end of said gas removal tube with the exterior of said shell.

4. An evaporator body comprising in combination a tube bundle having vertically arranged tubes mounted in a pair of spaced horizontal tube sheets, the length of said tube bundle being substantially greater than its diameter, a shell encasing said tube bundle and dening with the upper of said tube sheets a vapor disengaging space, a vapor inlet connection to said shell near the upper end of said tube bundle and remote from the lower end thereof for introducing into said shell a condensible vapor to flow downwardly along said tubes and be condensed on the exterior surfaces thereof, said vapor containing a small proportion of fixed gas, a condensate removal connection in said shell near the lower end of said tube bundle, a fixed gas removal tube located near the center of said tube bundle and extending substantially from one of said tube sheets to the other, said gas removal tube being formed in two sections and the lower section being provided with one or more openings, said lower section being removable through said lower tube sheet for cleaning, and a conduit connected to the upper end of said gas removal tube and extending through said vapor disengaging space to the exterior of said shell whereby fixed gas may pass through said gas removal tube and conduit to the exterior of said shell.

5. In heat exchange apparatus of the tube-in-shell type, in combination, an elongated tube bundle having tubes mounted in a pair of spaced horizontal tube sheets, anv

elongated shell encasing saiditube bundle, a vapor inlet connection in said shell near the upper end of said tube bundle for introducing into said shell a condensible vapor to flow axially along said tubes and be condensed on the exterior surfaces thereof, said vapor containing a small proportion of fixed gas, a condensate removal connection in said shell nearthe lower end of said tube bundle, a fixed gas removal tube located at the longitudinal axis of said tube bundle and extending from one of said tube sheets to. the other tube sheet, the lower end only of said gas removal tube being provided within said shell with one or more openings andaconduit connecting one end of said gas removal tube with the exterior of said shell, whereby xed gas may pass through said tube and conduit vto the exterior of said shell.

6. Heat exchange apparatus according to claim 5 and wherein said conduit connects the upper end of the gas removal tube with the exterior of said shell.

7. Heat exchange apparatus according to claim 6 and wherein the lower end of the gas removal tube is closed and provided within said shell with a drain slot for removal of condensate therefrom and the lower portion of the wall of said tube above said drain slot is provided with vertically spaced pairs of horizontally,alignedvopenings with alternate pairs of openings being located at right- ;angles to one another. I

References Cited in the le of this patent UNITED STATES PATENTS 1,049,425 Webre ]an.7, 1913 1,399,710 Justus Dec. 6, 1921 1,586,814 Leonard Junel, 1926 1,622,918 Merlis Mar'. 29, 1927 1,638,697 Merlis Aug. 9, 1927 2,090,985 Peebles et al Aug. 24, 1937 2,204,497 Hunter June 11,7194() 2,350,936 Smith .Tune 6, 1944 2,544,885

Jacoby et al. Mar. 15, 1951

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