US3212571A

US3212571A - Tube bundle for shell and tube type heat exchanger formed of spirally wound coil segments

Info

Publication number: US3212571A
Application number: US248371A
Authority: US
Inventors: Nicholas D Romanos
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1962-12-31
Filing date: 1962-12-31
Publication date: 1965-10-19
Anticipated expiration: 1982-10-19

Description

Oct. 19, 1965 N. D. ROMANOS 3,212,571

TUBE BUNDLE FOR SHELL AND TUBE TYPE HEAT EXCHANGER FORMED OF SPIRALLY WOUND COIL SEGMENTS 2 Sheets-Sheet 1 Filed Dec. 31, 1962 o ooU INVENTOR. NICHOLAS D. ROMANOS BY WWJQW ATTORNEY Oct. 19, 1965 N. D. ROMANOS 3,212,571

TUBE BUNDLE FOR SHELL AND TUBE TYPE HEAT EXCHANGER FORMED OF SPIRALLY WOUND COIL SEGMENTS Filed Dec. 31. 1962 2 Sheets-Sheet 2 FIG. 3

FIG. 4

INVENTOR. NICHOLAS D. ROMANOS Byg ATTORNEY United States Patent 3,212,571 TUBE BUNDLE FOR SHELL AND TUBE TYPE HEAT EXCHANGER FORMED 0F SPIRALLY WOUND COIL SEGMENTS Nicholas D. Romanos, Chattanooga, Tenn., assignor to Combustion Engineering, Inc., Windsor, Conn., a corporation of Delaware Filed Dec. 31, 1962, Ser. No. 248,371 9 Claims. '(Cl. 165163) This invention relates to heat exchangers for the generation of vapor wherein a heating fluid is directed through a vessel which houses tubular elements adapted to conduct a vaporizable fluid in such a manner that heat is given up by the gases and transferred to the vaporizable fluid whereby the latter is transformed into vapor. More particularly, the invention relates to a novel tube bundle design for heat exchangers of the tube and vessel type.

Heat exchangers of the tube and vessel type have found popular application in installations where space limitations exist. Organizations have been devised in the past which enable a large amount of heating surface to be exposed to the heating medium flowing through the vessel such that an efficient generation of vapor can be effected. These organizations normally comprise vessels having positioned therein tube bundles constructed of a large number of closely arranged tubes. The tubes employed in the construction of the tube bundles have assumed several diverse forms such as straight, U-shaped and helically wound tubes, the object being to position as many tubes as possible within the limited confines of the vessel in such a manner that the hot gases are free to contact the surface of the tubes whereby a transfer of heat can take place.

In heat exchangers employing straight tubes, the tubes extend along lines parallel to the axis of the vessel and have their ends attached to tube sheets which are located at each end of the vessel. In order to make for a compact installation, the tubes are arranged closely adjacent one another and substantially fill the vessel. Vapor generators employing U-tubes in the construction of their tube bundles are formed in much the same way with the exception that the tube ends are attached to a single tube sheet located at one end of the vessel. In these installations the straight legs of the U-tubes extend into the gas filled portion of the vessel along lines which are parallel to the axis thereof, and the U-bends, which join the straight legs of the tubes, are positioned at the opposite end of the vessel from the tube sheet. Where helically wound tubes are employed in the tube bundle, each of the tubular elements is normally wound in the form of a helix having a constant diameter. Several elements are employed, each being formed of a slightly smaller diameter such that all of the helices can be telescopically arranged in nested relation to arrive at a tube bundle having a given capacity.

In each of the above mentioned organizations the tubular elements, in traversing the length of the vessel, remain equidistantly spaced from the axis of the vessel and this, due to the non-homogeneity of the gas flow within the vessel, renders it virtually impossible to approach a uniformity of vapor generation within all of the tubes. This non-homogeneity of gas flow is brought about by the fact that those gases which flow adjacent the wall of the vessel give up a portion of their heat to the exterior thereof thus causing the temperature of the gases to become progressively cooler the closer they come to the wall. The result is that those gases which flow through the center of the vessel are much hotter than those which flow adjacent the wall with the gases flowing 3,212,571 Patented Oct. 19, 1965 along intermediate paths being cooler by an amount which is proportionate to their distance from the axis of the vessel. Since the amount of vapor generated in each tubular element is dependent upon the temperature of the gases with which that tubular element comes in contact, there will therefore be a greater amount of vapor generated in the tubes extending through the center of the vessel than is generated in the tubes extending closer to the wall.

In order to overcome this deficiency, some vapor generators have been devised in which the tube bundle comprises flat spiral coils in which a number of coils are placed in stacked relation within the vessel thereby causing the fluid flowing through each coil to traverse the entire transverse section of the vessel and thus contact substantially all of the gas flow therewithin. While tube bundles of this type enable the fluid to extract heat from all of the gas paths existing within the vessel, they are still unable to render a uniformity of vapor generation in all of the tubes due to the fact that the gases, which flow parallel to the axis of the coils, give up a portion of their heat to each of the fluid bearing tubular coils as they come in contact with it, therefore, the further downstream a coil is located the cooler the gases with which it comes in contact and thus the lesser the amount of vapor generation that takes place therewithin. The result remains a non-uniformity of vapor generation throughout the generator.

According to the present invention there is provided a heat exchanger having a tube bundle incorporating tubular elements so formed as to enable the tube circuits which they comprise to exhibit more uniform vapor generation because of the fact that they wind back and forth across the entire transverse section of the vessel while at the same time extending along the length of the vessel thereby enabling the total amount of heat transfer to be substantially the same in each circuit. The tube bundle comprises a number of parallelly connected tubular circuits which, in turn, are made up of tubular coils wound in spiral fashion and each having a determinate axial length. By means of this arrangement each tube not only traverses the entire transverse section of the vessel, but it also extends along the axial length thereof thereby enabling the amount of heat given up to each circuit by the gases to be more uniform to thus effect a more uniform generation of vapor in each circuit.

An important feature of the present invention is that the design of generators employing this form of tube bundle is rendered much simpler. The coil segments are all identical in size and dimension and form the elements of a tube bundle of given capacity. To construct heat exchangers of greater or less capacity, all that is required is to increase or decrease the number of coil segments which comprise the tube bundle. Furthermore, the overall capacity of the tube bundle is limited only by the size of the vessel which will contain it since coils can be connected in series, ad infinitum, thereby repeating the structure of the coil over and over again throughout the length of the vessel until a tube bundle having the desired capacity is achieved.

Another important feature of the segments which make up the tube bundle in the instant heat exchanger is that the coils are so wound as to eliminate the possibility of gases flowing through the vessel without contacting part of the heating surface of the tube bundle. This feature is achieved because the coils are so formed that the turns on one side of the axial midpoint of each coil segment are of a size to place each in alignment with the spaces existing between the turns located on the opposite side of the midpoint thereby substantially filling the transverse portion of the vessel With tubular heating surface. The end result of this structure is that a more eflicient transfer of heat can be effected between the gases and the vaporizable fluid thereby increasing the thermal efliciency of the generator.

It is therefore an object of the present invention to provide a heat exchanger capable of generating vapor that is characterized by compactness of form and efficiency of operation.

Another object of the invention is to provide a heat exchanger of the tube and vessel type capable of generating vapor wherein the amount of vapor generation in all of the tubes is substantially uniform.

Still another object of the invention is to provide a heat exchanger of the tube and vessel type capable of generating vapor that is characterized by simplicity of design which permits the construction of subsequent heat exchangers whose capacity varies from that of the norm by merely increasing or decreasing the number of elemental parts which comprise the heating surface thereof.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein:

FIGURE 1 is a longitudinal section of a heat exchanger constructed in accordance with the terms of the present invention;

FIGURE 2 is a transverse section taken along line 2--2 of FIGURE 1;

FIGURE 3 is an illustration of a typical tubular coil segment employed in the heat exchanger shown in FIG- URE 1; and

FIGURE 4 is an end view of the tubular coil segment shown in FIGURE 3.

While the invention will be described as a vapor generator employing hot gases as the heating medium and with water passing through the tubular coils, it is to be understood that this is intended to be merely illustrative and not restrictive of the invention and that the heat eX- changer may be employed for uses other than the generation of steam and that the heating fluid may flow through the tubular coils rather than around them with the fluid to be heated then flowing around the coils rather than through the same.

Referring now to the drawings wherein like reference characteristics are used throughout to designate like elements, there is shown in FIGURE 1 the simplest form of a preferred embodiment of the present invention. In this figure is shown a heat exchanger comprising a cylindrical member 12 having its ends capped by means of dome-shaped members 14 which are Welded to the ends of the cylindrical member to form a substantially closed vessel. Each of the dome-shaped members contain a central opening which provides for the admission and discharge of heating fluid into and out of the vessel, the opening 18 designating the hot gas inlet and 16 the hot gas outlet.

Mounted within the vessel is a tube bundle generally designated as 20 which is composed of a number of tubular coil segments 22 one of which is shown in detail in FIGURES 3 and 4. Each of the coil segments 22 comprises a pair of tubes which are helically wound in the form of a spiral so as to achieve a shape generally in the form of a cone and then joined at their apices by means of a connecting member. As shown in FIGURE 3, that section of the segment positioned at the left of the axial midpoint29, having its turns designated as 24, is spirally wound in a clockwise direction while that to the right of the axial midpoint, having its turns designated as 26, is spirally wound in the counter clockwise direction. To complete the coil segment the ends of the two tubes which form the apices of the thus-formed conical shapes are joined by means of a U-shaped conduit member 28 to thereby form a spirally wound tubular coil conforming generally to the shape of a double cone having a median vertex wherein the radial dimension of the turns becomes progressively smaller closer to the midpoint 29.

In order to increase the thermal efliciency of heat exchangers employing this structure, the spacing of the turns 26 is such that they fall into longitudinal alignment with the spaces existing between the turns 24. The resultant structure, as best shown in FIGURE 4, presents a heating surface which substantially fills the entire transverse section of the vessel thus preventing any of the gases which flow through the vessel from flowing through the tube bundle, without contacting some portion of the heating surface thereof.

The manner of constructing a vapor generator embodying the instant invention is as follows. A plurality of tubular coil segments 22 which in number are equal to that necessary to produce the desired generator capacity are arranged in concentric, nested relation. The coil segment structure shown in FIGURES 3 and 4, and as described above, is such that they can be arranged in a close compact fashion substantially filling the vessel. As shown in FIGURE 1, the segments 22 are placed within the vessel with like turns of adjacent coils positioned closely adjacent one another such that the plurality of circuits formed thereby wind through the vessel in substantial parallel alignment. The terminal ends of each of the circuits are connected to headers 32 or equivalent manifold structures, which are located at both the inlet and outlet ends of the tube bundle, by means of connecting conduits 30. Openings 31 are provided in the wall of the vessel to permit passage of the conduits 30 to the exteriorly lo cated headers 32. Lining the openings 31 are thermal sleeves 34 which are attached to the openings and welded at their outer ends to the conduits.

The size of the tube bundle is dictated by the desired capacity of the generator and the volume of the vessel.

The factors affecting the size of the tube bundle are the number of parallelly connected circuits employed and the number of serially connected coil segments that make up each circuit. The tube bundle illustrated employs eleven circuits wherein each circuit is formed between its inlet and outlet ends by four coil segments connected in series.

Connecting the segments in fluid circulation are U-shaped conduits 36. When it is desired to construct a vapor generator having greater or less capacity, all that is necessary would be to increase or decrease the number of serially connected coil segments in each circuit until the desired amount of heating surface is achieved. By the same token, the capacity of the tube bundle can also be increased or decreased by the number of parallelly connected circuits employed in the construction thereof.

When all of the coil segments 22 are assembled to form the tube bundle, an axial opening or void 37 is caused to exist along the axis of the tube bundle. This void 37 is filled by means of a baffle 38 whose shape conforms to that of the void thereby preventing the heating fluid from flowing anywhere but around the heating surface of the tube bundle.

To position and support the tube bundle within the vessel 12, a number of elongated flat plates 42 are welded- 1y attached to the inner wall of the vessel along circumferentially spaced lines thereabout. The inner edge 44 of these plates 42 is scalloped to receive the outermost turns of each coil segment 22. Support bars 46 welded at one end 48 to the plates 42 and having their other end 50 in abutting engagement with the surface of the 'bame 38 extend obliquely along lines defined by spaces between adjacent turns of the coil segments 22 which comprise the tube bundle. Such bars 46 emanate from longi tudinally spaced points along each of the fiat plates 42 and are so arranged as to permit the adjacent turn of a coil segment to rest upon it.

in operation the heat exchanger, when employed as a vapor generator, has hot gases admitted through the inlet opening 18 into the vessel containing the tube bundle 22 and out through the outlet opening 16. At the same time, water is admitted to the tube bundle 22 by way of the inlet header 32 where it is distributed to the various circuits which comprise the tube bundle by means of the conduits 30. In flowing through the circuits heat from the gases is imparted to the water to transform it into vapor before the fluid leaves the tube bundle through the outlet header 33.

The quality and/ or temperature of the fluid leaving the tube bundle 22 depends upon the temperature of the gases flowing through the vessel and/ or the amount of vaporizable fluid admitted to the tube bundle. If the steam generator is designed to have the fluid leaving the bundle contain a mixture of liquid and vapor, a separator can be installed in the outlet line downstream of the outlet header 33 to separate the mixture into its component parts of liquid and vapor. On the other hand, if the steam generator is designed to have the fluid emerging from the vessel in the form of vapor, such vapor may be superheated and passed directly to a vapor operated work producer.

By means of the present invention there is provided a tubular structure which permits the construction of an extremely compact heating surface for use in a vapor generator of the shell and tube type. There is also provided an arrangement whereby a more uniform generation of vapor is effected within each circuit of a multi-circuit installation due to the traversal of the entire transverse section of the vessel by all of the tubular elements which form the heating surface of the unit. This uniformity of vapor generation within each circuit makes it possible to more easily determine the amount of heating surface necessary to construct a vapor generator of any given capacity so that construction thereof can be effected by merely adding or subtracting the required number of serially connected tubular coil segments or by varying the number of circuits employed within the generator.

While there has been illustrated and described a preferred embodiment of the invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. The invention therefore is not to be limited to the precise details set forth herein but shall avail itself of such changes as fall within its purview.

What is claimed is:

1. A heat exchanger for the indirect transfer of heat from a heating fluid to a fluid to be heated comprising a substantially closed vessel; means for passing one of said fluids through said vessel; a tube bundle disposed within, and substantially filling the transverse section of said vessel, said tube bundle including a plurality of fluid circuits comprising co-axially internested, spirally Wound tubular coils of equal tube length; each of said tubular coils being identically formed and comprising a plurality of continuous spiral turns extending from a major radial dimension adjacent the wall of said vessel to a minimum radial dimension adjacent the axis thereof and defining a pair of opposed conical sections that conform generally to the shape of a double cone; each turn of one conical section of said tubular coils being in longitudinal alignment with spaces between adjacent turns of the other conical section thereof, said spaces between adjacent turns, as measured normal to the axis of said coils, being no less than the diameter of the coil-forming tube; said coils being assembled within said vessel with their turns of equal radial dimension in close-adjacent, longitudinally aligned relation; header means connecting said fluid circuits for parallel fluid flow; and means for passing the other of said fluids through said fluid circuits.

2. The organization of claim 1 wherein said fluid cir- 6 cuits each comprise a plurality of said tubular coils connected in series flow relation.

3. The organization of claim 1 wherein aligned turns of minimum radial dimension of said coils define an axial opening through said tube bundle; and axially extending baffle means disposed in and substantially filling said opening.

4. A heat exchanger for the indirect transfer of heat from a heating fluid to a fluid to be heated comprising a substantially closed vessel; means for passing one of said fluids through said vessel; a tube bundle disposed within, and substantially filling the transverse section of said vessel, said tube bundle including a plurality of fluid circuits comprising co-axi-ally internested, spirally wound tubular coils of equal tube length; each of said tubular coils being identically formed and comprising a plurality of continuous spiral turns extending from a major radial dimension adjacent the wall of said vessel to a minimum radial dimension adjacent the axis thereof and defining a pair of opposed conical sections that conform generally to the shape of a double cone having a median vertex; each turn of one conical section of said tubular coils being in longitudinal alignment with spaces between adjacent turns of the other conical section thereof, said spaces between adjacent turns, as measured normal to the axis of said coils, being no less than the diameter of the coilforming tube; said coils being assembled within said vessel with their turns of equal radial dimension in close-adjacent, longitudinally aligned relation; header means connecting said fluid circuits for parallel fluid flow; and means for passing the other of said fluids through said fluid circuits.

5. The organization of claim 4 wherein said fluid cir cuits each comprise a plurality of said tubular coils connected in series flow relation.

6. The organization of claim 4 wherein aligned turns of minimum radial dimension of said coils define an axial opening through said tube bundle; and axially extending baffle means disposed in and substantially filling said opening.

7. A heat exchanger for the indirect transfer of heat from a heating fluid to a fluid to be heated comprising a substantially closed vessel; means for passing one of said fluids through said vessel; a tube bundle disposed within, and substantially filling the transverse section of said vessel, said tube bundle including a plurality of fluid circuits comprising co-axially internested, spirally wound tubular coils of equal tube length; each of said tubular coils .being identically formed and comprising a plurality of continuous spiral turns extending from a major radial dimension adjacent the wall of said vessel to a minimum radial dimension adjacent the axis thereof and defining a pair of opposed conical sections that conform generally to the shape of a double cone having a median vertex; each turn of one conical section of said tubular coils being in longitudinal alignment with spaces between adjacent turns of the other conical section thereof, said spaces between adjacent turns, as measured normal to the axis of said coils, being no less than the diameter of the coil-forming tube; said coils being assembled within said vessel with their turns of equal radial dimension in close-adjacent, longitudinally aligned relation; header means disposed externally of said vessel connecting said fluid circuits for parallel fluid flow; and means for passing the other of said fluids through said fluid circuits.

8. The organization of claim 7 wherein said fluid circuits each comprise a plurality of said tubular coils connected in series flow relation.

9. The organization of claim 7 wherein aligned turns of minimum radial dimension of said coils define an axial opening through said tube bundle; and axially extending baflle means disposed in and substantially filling said opening.

(References 011 following page) 7 & References Cited by the Examiner 2,300,634 11/42 Schoenfeld 122--250 Hardlng 61; a]. 1 g g ggi g CHARLES SUKALO, Primary Examiner. ac strom 5 Glenn 5 L. JR., Examzner.

2,227,293 12/40 Bobo 122-250

Claims

1. A HEAT EXCHANGER FOR THE INDIRECT TRANSFER OF HEAT FROM A HEATING FLUID TO A FLUID TO BE HEATED COMPRISING A SUBSTANTIALLY CLOSED VESSEL; MEANS FOR PASSING ONE OF SAID FLUIDS THROUGH SAID VESSEL; A TUBE BUNDLE DISPOSED WITHIN, AND SUBSTANTIALLY FILLING THE TRANSVERSE SECTION OF SAID VESSEL, SAID TUBE BUNDLE INCLUDING A PLURALITY OF FLUID CIRCUITS COMPRISING CO-AXIALLY INTERNESTED, SPIRALLY WOUND TUBULAR COSTS OF EQUAL THE TUBE LENGTH; EACH OF SAID TUBULAR COILS BEING IDENTICALLY FORMED AND COMPRISING A PLURALITY OF CONTINUOUS SPIRAL TURNS EXTENDING FROM A MAJOR RADIAL DIMENSION ADJACENT THE WALL OF SAID VESSEL TO A MINIMUM RADIAL DIMENSION ADJACENT THE AXIS THEREOF AND DEFINING A PAIR OF OPPOSED CONICAL SECTIONS THAT CONFORM GENERALLY TO THE SHAPE OF A DOUBLE CONE; EACH TURN OF ONE CONICAL SECTION OF SAID TUBULAR COILS BEING IN LONGITUDINAL ALIGNMENT WITH SPACES BETWEEN ADJACENT TURNS OF THE OTHER CONICAL SECTION THEREOF, SAID SPACED BETWEEN ADJACENT TURNS, AS MESURED NORMAL TO THE AXIS OF SAID COILS, BEING NO LESS THAN THE DIAMETER OF THE COIL-FORMING TUBE; SAID COILS BEING ASSEMBLED WITHIN SAID VESSEL WITH THEIR TURNS OF EQUAL RADIAL DIMENSION IN CLOSE-ADJACENT, LONGITUDINALLY ALIGNED RELATION; HEDER MEANS CONNECTING SAID FLUID CIRCUITS FOR PARALLEL FLUID FLOW; AND MEANS FOR PASSING THE OTHER OF SAID FLUIDS THROUGH SAID FLUID CIRCUITS.