US3431893A - Single-tube forced-circulation heat transfer devices - Google Patents

Description

11, 1969 1.. F; H. M. FOUCHE ETAL 3,431,893

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SINGLE-TUBE FORCED-CIRCULATION HEAT TRANSFER DEVICES FiledNov. 8. 1966 Sheet 8 of 8 Luamu Fame-me new; roman. 131m United States Patent 3,431,893 SINGLE-TUBE FORCED-CIRCULATION HEAT TRANSFER DEVICES Lucien Frdric Henri Marcel Fouch, Neuilly-sur-Seme, and Marc Roger Armand, Saint-Germain-en-Laye, France,, assignors to Fives-Penhoet, Paris, France, a French body corporate Filed Nov. 8, 1966, Ser. No. 592,852 Claims priority, application6France, Nov. 8, 1965,

Us. Cl. 122-32 11 Claims Int. Cl. F22b 1/08 ABSTRACT OF THE DISCLOSURE It is the essential object of the present invention to provide a single-tube forced-circulation heat-transfer device, preferably of the steam-generator type, comprising clusters of straight vertically disposed tubular elements through which a fluid to be vaporized is circulated, said tubular elements being housed in at least one casing in which a heat-bearing fluid circulates in countercurrent relationship to the fluid to be vaporized.

A heat transfer device of this character is intended more particularly for use in a nuclear plant wherein the heat transfer device lies within an enclosure containing the nuclear reactor. In a plant of this type the heat bearing fluid to be cooled consists as a rule of carbon dioxide constituting the reactor coolant, the fluid to be heated consisting of water.

It is known that the water circulating in the heat transfer is in succession, as it flows through said straight tubular elements, in the liquid state in a first, so-called economizer section, in the state of a water and vapour mixture in a second, so-called vaporizer section, and finally in the vapour state in a third, so-called superheater section.

The fact that these heat transfer devices must be housed within an enclosure containing a reactor is attended by serious inconveniences, due to the reduced space available, notably in connection with the fitting of the various water-supply and steam delivery pipelines which do not partake directly in the heat transfer cycle, since the greatest possible number of tubular heat transfer elements must be accommodated in order to obtain the maximum efficiency. Similar difliculties are experienced in connection with the accommodation of the supporting structure.

On the other hand, these heat transfer systems were hardly accessible during the reactor operation, thus precluding any repair works during the actual service time, and therefore asymmetric conditions must be avoided in the cooling of the heat-bearing fluid in case some of the tubular elements were not supplied with water.

It is the primary object of the present invention to provide a heat transfer device particularly adapted to the various requirements to be met in the equipment of nuclear plants, and remarkable notably in that it consists of identical superposed unitary panels comprising a number of identical tubular elements, said panels being grouped into separate identical units constituting each an elementary heat transfer unit, said units being so assembled as to have the shape of a polygonal annulus in a plane at right 3,431,893 Patented Mar. 11, 1969 angles to the axes of said tubular elements, and to leave on the one hand between the outer contour of said annulus and the wall of the enclosure in which said units are housed, and on the other hand in the central portion of said annulus, free spaces adapted to receive the supporting structure and permit the passage of the watersupply and steam-outlet pipes.

This arrangement also permits more particularly of obtaining a perfectly homogeneous distribution of a very considerable number of heat-transfer tubular elements in the enclosure containing the reactor while preserving the passages necessary for the access to the upper portion of the heat transfer system. Thus, a high filling coefficient is obtained, with a corresponding increment in the heat transfer efliciency and a rational utilization of the space available in the enclosure.

A ccording to another feature of this invention the aforesaid units are assembled with a view to have the general configuration of a hexagonal annulus.

This hexagonal shape is particularly advantageous if the enclosure has a circular contour.

According to a further feature of this invention each unitary panel aforesaid consists of a sheet of tubular elements each having its axis disposed in a common plane and connected at either ends to a single header having its axis coplanar with the axes of said tubular elements.

With this distribution of the tubular elements into flat panels adapted therefor to be easily juxtaposed the manufacture and mounting of the heat transfer device are considerably simplified.

According to another feature characterizing this invention, the tubular elements of each panel are connected to at least one of said headers by means of flexible connecting tubings having their axes coplanar with the axes of said tubular elements, the pitch of the connections between said tubings and the relevant header being smaller than the pitch of the tubular elements.

The fact of providing flexible tubings permits of compensating differential expansions likely to take place between the various tubes of a same panel and the fact that these flexible tubings (which partake only accessorily in the heat transfer process) may consist of simple pipe sections having a diameter smaller than that of said tubular elements, permits of disposing the connecting points at a shorter relative spacing than that permitted by a direct connection of the tubular elements. Under these conditions, headers having a length inferior to the panel length may be used, and thus space is saved which may advantageously be used for the passage of the various inlet and outlet pipes.

According to another advantageous feature of this invention, the aforesaid units are of polygonal configuration When seen in a section taken at right angles to the axes of the tubular elements.

These units may have a rectangular, square, lozenge, parallelogram, hexagonal or regular or nonregular polygonal cross-sectional configuration, or these cross-sectional shapes may be selected as a function of the room available for the heat transfer device in the enclosure containing the nuclear reactor.

According to a specific form of embodiment of the invention, the aforesaid units are of lozenge configuratron in cross-section.

This lozenge-shaped cross-sectional contour permits of obtaining an equilateral triangular pitch for the tubular cluster, which is advantageous in that it affords a better uniformity in the distribution of the heat-bearing gas; moreover, in case the enclosure in which the heat transfer device has a circular configuration, the use of lozengeshaped units affords an optimum utilization of the space available therein.

Still according to this invention, a plurality of separate circuits for the fluid to be heated, for example four circuits, are provided, every fourth panel of a same unit being connected to each circuit aforesaid.

Thus, four completely separate but mutually imbricated heat transfer devices are actually obtained, whereby in case of faulty supply of one or a plurality of these heat transfer devices any extremely detrimental asymmetry in the cooling of the reactor coolant is definitely avoided.

Other features and advantages of this invention will become apparent as the following description proceeds with reference to the accompanying drawings illustrating diagrammatically by way of example various forms of embodiment of the invention which should not be construed as limiting the scope of the invention. In the drawings:

FIGURE 1 illustrates in diagrammatic form a heat transfer device constructed according to the teachings of this invention, as seen from above, with a partial section taken upon the four sectors A, B, C, and D in order to show various component elements of the heat transfer device which lie at different levels;

FIGURE 2 is an elevational view With parts broken away to illustrate one portion of the heat transfer device which comprises a unitary panel;

FIGURE 3 is a detail section taken on a larger scale along the line IIIIII of FIGURE 2;

FIGURE 4 is a fragmentary elevational view of the heat transfer device showing two units consisting of juxtaposed unitary panels, one of these units being shown in external view and the other in section;

FIGURE 5 is a fragmentary view showing on a larger scale the upper portion of a unit of the type shown in FIGURE 4;

FIGURE 6 is an elevational view showing the superposed sheets of tubes feeding the water headers of a unitary panel;

FIGURE 7 is a section taken upon the line VII-VII of FIGURE 6;

FIGURE 8 is a section taken upon the line VIII-VIII of FIGURE 6;

FIGURE 9 is a plane view from above of a unit showing in diagrammatic form the steam headers and the steam outlet tubes connected to these headers;

FIGURE 10 is a perspective view showing on a larger scale the mounting of the steam headers on the flanges of the supporting structure;

FIGURE 11 is a plane view from above of the supporting structure of the heat transfer device, and

FIGURE 12 is a section taken upon the line XII-XII of FIGURE 11.

The attached drawings illustrate a typical form of embodiment of the present invention which consists of a single-tube heat-transfer forced-circulation steam generator housed in an enclosure containing a nuclear reactor and intended for cooling the gaseous cooling fluid of this reactor, the circulation of this cooling fluid taking place in the downward direction and the fluid to be heated, water and water vapour, is circulated in the opposite or upward direction.

This heat transfer device is illustrated diagrammatically in FIGURE 1 in order clearly to show the relative arrangement of its various component elements.

To this end, FIGURE 1 is divided into four sectors A, B, C and D corresponding to three sections taken in three different planes (A, B, C), and to a plane view from above (D). Sector A corresponds to the lower portion of the heat transfer device. Sector B shows the sheets of tubes supplying water to the water headers. Sector C shows the water headers located at the lower portion of the unitary panels. Finally, sector D shows the steam outlets tubes.

This heat transfer device consists essentially of plane unitary panels 1 (see FIGURE 2) comprising each a number of vertical straight tubular elements 2 constituting a sheet of tubes having coplanar axes, and two headers 3, and 4, header 3 being at the lower portion of the panel for supplying liquid water thereto, the other header 4 being disposed at the upper portion of the panel to receive the outgoing steam; the axes of these headers are coplanar with those of the tubular elements. These panels 1 are juxtaposed to constitute separate, lozenge-shaped units designated by the reference numeral 5. Each unit constituting a complete elementary heat transfer device, is fed with liquid water from a cluster of bent tubes designated as a whole by the reference numeral 6 and disposed beneath the water header 3. Each unit further comprises above the steam headers 4, clusters of water steam outlet tubes designated as a whole by the reference numeral 7.

FIGURE 1 also shows the water-feed and steam outlet bulbs 8 which are no part of the present invention, together with the water supply pipes 9 (connected to the clusters 6) and the steam delivery pipes 10 (connected to tubes 7).

The lozenge-shaped units 5 are assembled with a view to constitute a hexagonal annulus 11 leaving on the one hand a central free space 12 and on the other hand, several free spaces 14 between the external sides of the hexagonal annulus 11 and the wall 13 of the circular enclosure. Through these spaces 12 and 14 access may be had to the upper portion of the heat transfer device; they permit the passage of the downwardly extending steam outlet pipes 10 connected to the steam outlet tubes 7, and also of the various pipe lines connected to the reactor: sheath failure detector, CO filtration means, etc. These spaces are also used for disposing the structure elements supporting the units 5, notably the posts carrying the upper framework 15 such as the column 16 disposed centrally of the enclosure.

The number of tubes constituting each unitary panel 1 is relatively high and selected as a function of the network pitch limiting the diameter of the headers, the perrnissible length of these headers, the maximum permissible dimensions of each panel, these dimensions being subordinate primarily by the space available in the enclosure in which the heat transfer device is to be housed, and also by the inherent handling and transport problems. In the case illustrated the panel 1 comprises thirty-two tubular elements 2.

The tubular elements 2 are connected to the water header 3 by means of flexible tubings 17 capable of absorbing differential thermal expansions likely to take place between the various tubular elements of a same panel. These tubings 17 are so disposed that their axes are coplanar with those of the tubular elements 2 and also with those of the headers 3 and 4 (see FIGURE 3).

Each tubing 17 comprises two successive and oppositely directed bends 18a, 18b and consists therefore of three substantially rectilinear sections 19a, 19b, 19c. These tubings 17 are disposed symmetrically with respect to a plane P normal to the panel which is disposed centrally of the headers 3 and 4. In the left-hand half of the panel (as seen in FIGURE 2) the end tubing has its first section 19a inclined from right to left, its second section 1% inclined from left to right, and finally its third section inclined again from right to left. Of course, the sections 19a, 18b and 19c of the end tubing of the right-hand half panel are inclined in opposite directions.

The tubings 17 in which water in the liquid state circulates require a smaller cross-sectional passage area than the tubular elements 2. Advantage will be taken of this narrower cross-sectional dimension for considerably reducing the relative pitch of the connections between these tubings 17 and the water header 3 with respect to the pitch of the tubular elements themselves. Thus, the header 3 may be given a length considerably smaller than the relative spacing of the two endmost tubular elements of the panel. This pitch difference is compensated by gradually modifying the inclination of the third section 190 of each connecting tubing 17. Whilst the angular value of the bend between the first section 19a and the secend section 19b remains unchanged in all the tubings 17, whether in the first or left-hand half-panel or in the second or right-hand half-panel, the angle between the second section 19b and the third section 190 increases gradually from the tubing remotest from the aforesaid plane of symmetry P to the tubing nearest thereto, this third section in the specific case of the two central tubings, being substantially coextensive with the tubular element to which they are connected.

This symmetrical arrangement of tubings 17 with respect to said plane of symmetry P permits of disposing these tubings within the space bounded by the two endmost tubular elements of the panel.

The tubular elements 2 may consist of ribbed or finned tubes, or plain tubes, and if desired internal means may be provided therein for increasing the coefiicient of heat transfer. These tubular elements have waisted end portions (see FIGURES 3 to 5) to eliminate welding steps. These waisted portions 20' are as long as possible so that each tubular element can be connected directly to the relevant header. These waisted portions are obtained for example by removing the external fins of the tubular element at the ends thereof.

All the unitary panels 1 thus obtained are identical in that they comprise the same number of tubular elements having the same length; only the upper waisted portions of these tubular elements have different lengths, in the case of juxtaposed panels, so that by properly offsetting the steam headers 4 to each other in the vertical direction the best use can be made of the space available at the upper portion of each unit the space left free between the waisted portions of two odd order tubular elements being adapted for example, to receive the headers of evenorder panels. As a result, the steam headers 4 constitute two rows disposed at different levels, the headers of one row corresponding to the gaps formed between the headers of the other row (see FIGURES 3 to 5).

The aforesaid unitary panels are so juxtaposed as to constitute units having, in the case illustrated, a lozenge configuration which, in the case of a circular enclosure, afiords, the best possible filling and which, while permitting on the other hand the distribution of the tubular elements according to an equilateral triangular pitch arrangement, ensures an optimum distribution of the heatbearing gas.

It should be noted that to avoid the transport of unduly heavy and cumbersome units, these lozenge-shaped units may be divided in turn into a plurality of parallelograms corresponding each to a subunit.

Each unit 5 constitutes a partial elementary heat transfer device comprising its inherent water supply pipes and steam outlet pipes, as well as its casing 22 constitut ing a passage for the downwardly flowing heat-bearing gas.

The pipes supplying water to the lower headers 3 of each unit are bent to a hairpin configuration (see FIGURES 6 and 7) to constitute fiat sheets 6a, 6b, 6c, 611 to which an external contour corresponding to that of the unit with which said supply pipes are associated, that is, a lozenge configuration in the specific case contemplated herein. These sheets of supply pipes extend at right angles to the circulation of the heat-bearing gas, and furthermore they are superposed to one another. Thus, a cluster of tubes 6 is obtained which takes an active part in the heat transfer process and due to its position at the end of the gas path, therefore where the highest temperature diiferences are obtained, it enables this cluster to homogenize these temperatures.

These superposed sheets 6a, 6b, 6c, 6d are advantgeo-usly so oriented that the rectilinear sections of the tubes extend parallel to the various sides of the quadrilateral bounding the heat transfer unit; thus, in the case illustrated, the various sheets are alternately parallel to the sides of the lozenge. Thus, a squ ared cluster particularly efiicient for gas mixing purposes is obtained.

Moreover, the fact of bending these water supply pipes imparts a sufiicient flexibility thereto to take up lpossible expansions and distortions.

It is known that, as a rule, it is advantageous to provide in a heat transfer system not a single water circuit but a plurality of completely independent water circuits. Each unit of the heat transfer device according to this invention is connected to four separate feed circuits to which the unitary panels are connected. In order to ensure the maximum possible homogeneity, these heat transfer units are i'mbricated into each other by disposing the panels in such a manner that any pair of adjacent panels are connected to two separate circuits. In the case illustrated, each circuit supplies every other four panels in each unit. FIGURE 8 shows the manner in which the headers 3 and the sheet of tubes 6 are interconnected. As these headers are juxtaposed in the order 3a 3b, 3c, 311, 3a, 3b, etc., all the headers bearing the same index are connected to one of the sheets bearing the same index.

With this arrangement the gaseous streams are homogeneously cooled even in case a plurality of panels connected to a same circuit were not fed with water whilst the adjacent panels are still supplied with water.

The steam outlet tubes 7 connected to headers 4 are so disposed as to constitute flat sheets arranged preferably horizontally. Each tube 7 corresponds to one of the separate circuits and is connected to every four steam headers by means of connecting pipes 21 opposite to the tubular elements 2, that is emerging from the upper portion of the headers 4 (see FIGURES 4 and 5).

FIGURE 9 shows the manner in which the headers 4 are connected to the sheets of tubes 7. All the headers 4a (corresponding to the water headers 3a) are connected to a same steam tube 7a by means of pipe lines 21a. Similarly, the headers 4b, 4c, 4d are connected to the tubes 7b, 7c, 7d by means of pipe lines 21b, 21c and 21d, respectively.

The casings 22 surrounding each unit extend from the steam headers 4 to the clusters of water feed pipes. The function of these casings is to guide the flow of heat bearing gas about the tubular elements 1. This casing is adapted to receive a detachable cover or like end member at each upper and lower end so as to constitute a fluidtight enclosure adapted to be filled with an inert gas or connected to an air-conditioning circuit in order to protect the tubes against the detrimental action of moisture and dust during transport and storage periods, until the plan is actually put into service.

The structure supporting the units 5 comprises an upper horizontal framework 15 consisting of crossed beams or girders 25 forming lozenges corresponding to the sectional configuration of the units, plates 24 being mounted on these beams of girders. This framework is supported in turn by the central post 16 received in the recess 12 (FIGURE 1), and on brackets or like members 28 secured to the skirt 29 supporting the reactor proper. Each unit is supported at its upper portion by plates 24 on which it bears through the medium of elements supporting the unitary panels. In the case illustnated, each panel 1 is supported by the steam headers 4. The plates 24 have notches 26 formed therein, these notches 26 being adapted to be firmly engaged by the correspondingly shaped end pieces 27 secured to the ends of headers 4 (see FIGURE 10). The notches 26 are so spaced as to ensure the distribution of headers 4 in two superposed rows as mentioned hereinabove; the difference in depth between any pair of successive notches corresponds to the diiference in level between these two rows, The plates supporting the unitary panels of a same unit constitute the upper portion of the casing of this unit.

Although the heat transfer device illustrated is designed for an upward water circulation, it is obvious that this device could be disposed upside down, if desired, so that a downward water circulation be obtained, the heat hearing gas circulating in the upward direction.

Many modifications may be brought to the form of embodiment illustrated without inasmuch departing from the scope of the invention. Thus, for example, the flexible connecting tubings 17 may be mounted on the steam outlet side, that is, between the headers 4 and tubes 7. Similarly the central post 16 may be replaced by several posts, for example six posts disposed at six corners of the inner hexagonal space 12, and the brackets 28 may be replaced by posts disposed at the periphery of the hexagonal annulus 11.

Of course, the invention is not limited by the form of embodiment described and illustrated which is given by way of example only.

What we claim is:

1. A single-tube forced-circulation heat transfer device constituting preferably a steam generator comprising a substantially cylindrical vertical enclosure Within which a heat-bearing fluid is circulated in axial direction, identical juxtaposed plane unitary panels located within said enclosure and within which a fluid under pressure to be heated is circulated, each one of said panels comprising a number of identical straight vertically disposed tubular elements constituting a sheet of tubes having coplanar axes an upper header and a lower header the axes of said headers being coplanar with those of said tubular elements, each one of said tubular element having its upper end connected to said upper header and its lower end connected to said lower header, said panels being grouped into separate identical units constituting each an elementary heat transfer device, a separate casing member for each one of said units, a supporting structure for said units and said casing members, water supply and steam outlet pipes for supplying water to said units and evacuating steam therefrom, said units being so assembled as to have in a plane at right angles to the axis of said tubular elements the form of a polygonal annulus having an outer contour and a central portion and to leave on the one hand between said outer contour and said enclosure and on the other hand in said portion, free spaces for receiving said supporting structure as well as said water-supply and steam-outlet pipes.

2. Device according to claim 1, wherein said annulus is a hexagonal annulus.

3. Device according to clairn 1, wherein said tubular elements of each panel have a constant pitch and wherein flexible connecting tubings having their axes coplanar to those of the tubular elements are provided for connecting each one of said tubular elements to one at least of said headers, said connecting tubings comprising two successively oppositely directed bends and being disposed symmetrically in relation to a plane of symmetry norm-a1 to the plane of the coplanar axes of said tubular elements and passing through the center of said headers, the connections between said connecting tubings and the corresponding header having a constant pitch, said pitch being inferior to the pitch of the tubular elements.

4. Device according to claim 3, wherein each one of said connecting tubings comprises, in the direction of circulation of said fluid to be heated, first, second and third substantially rectilinear sections, the angle formed between said first and second sections being substantially the same in all the tubings of a same half panel, the angle between the second and third sections increasing in each half panel from the tubing remotest from the plane of symmetry to the tubing nearest to said plane of symmetry.

5. Device according to claim 4, wherein the third section aforesaid of each one of the two connecting tubings connected to the two central tubular elements are substantially in axial alignment with said tubular elements.

6. Device according to claim 1, wherein said units have a lozenge configuration in section.

7. Device according to claim 6, wherein said lozengeshaped units consist of subunits having the shape of parallelograms inscribed in each lozenge.

8. Device according to claim 1, wherein said supporting structure comprises an upper horizontal framework consisting of crossed beams on which plates or like members are mounted which constitute the upper portions of said casings and supporting said unitary panels.

9. Device according to claim 8, wherein said plates are provided with notches or the like engageable by said upper headers.

10. Device according to claim 8, wherein said crossed beams are supported by brackets or posts, disposed at the periphery of said annulus.

11. Device according to claim 8, wherein said supporting structure comprises a single supporting post coaxial to said annulus.

References Cited UNITED STATES PATENTS 3,018,764 1/1962 Huet 122-34 3,104,652 9/1963 Tillequin et al. 122-32 3,117,559 1/1964 Fouehe 122-32 3,294,070 12/1966 Bell 12232 3,254,634 6/1966 Vorkauf 122235 KENNETH W. SPRAGUE, Primary Examiner.

US. Cl. X.R. 1225l0

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