Shell and tube heat exchanger with a shell having a polygonal section

Abstract

Heat exchanger comprising a tube bundle (1) and a shell (2) which surrounds said tube bundle, said tube bundle comprising tubes (3) arranged with a square or triangular pitch, wherein said shell (2) has a cross-section, in a plane perpendicular to said tubes, having the form of an irregular polygon; said irregular cross-sectional polygon has a number of sides which is a multiple of three or multiple of four for tube bundles with a triangular or square pitch, respectively; the sides of said cross-sectional polygon are parallel to the directional lines of the tubes.

Claims

1. A heat exchanger comprising a tube bundle and a shell which surrounds said tube bundle, said tube bundle comprising tubes arranged with a square or triangular pitch, wherein: said shell has a cross-section, in a plane perpendicular to said tubes, having the form of an irregular polygon; said cross-sectional polygon has a number of sides which is a multiple of three when the tubes have a triangular pitch and is a multiple of four when said tubes have a square pitch, the sides of said cross-sectional polygon of the shell are parallel to directional lines of the tubes of said bundle; wherein the heat exchanger comprises a central duct, wherein the tubes of the bundle are arranged in a ring between said shell and said central duct.

2. The heat exchanger according to claim 1, wherein the tubes of the bundle have a square pitch, and said directional lines of the tubes are straight lines in a plane perpendicular to the axis of the tubes, having directions spaced at angles of 45 degrees.

3. The heat exchanger according to claim 1, wherein the tubes of the bundle have a triangular pitch, and said directional lines of the tubes are straight lines in a plane perpendicular to the axis of the tubes, having directions spaced at angles of 60 degrees.

4. The heat exchanger according to claim 1, wherein said central duct also has a cross-section, in a plane perpendicular to said tubes, having the form of an irregular polygon, and wherein: said cross-sectional polygon of said duct has a number of sides which is a multiple of three when said tubes have a triangular pitch and is a multiple of four when said tubes have a square pitch, and the sides of said cross-sectional polygon of the duct are also parallel to directional lines of the tubes of said bundle.

5. The exchanger according to claim 4, wherein the number of the sides of the cross-sectional polygon of the duct is smaller than the number of sides of the cross-sectional polygon of the shell.

6. The exchanger according to claim 1, wherein the tube bundle is extractable from the shell.

7. The exchanger according to claim 1, wherein the tube bundle comprises baffles for supporting the tubes and for preventing vibrations.

8. The heat exchanger according to any claim 1, for use as an internal exchanger of pressurized apparatus or chemical reactors.

9. A pressurized apparatus, such as a chemical reactor and preferably a catalytic reactor for the synthesis of ammonia or methanol, comprising a heat exchanger according to claim 1.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic cross-sectional view of a tube apparatus according to a first embodiment of the invention.

(2) FIG. 2 shows a detail of FIG. 1.

(3) FIG. 3 is a schematic cross-sectional view of a tube apparatus according to a second embodiment of the invention.

(4) FIG. 4 shows a detail of FIG. 3.

(5) FIG. 5 shows a schematic cross-sectional view according to a third embodiment.

(6) FIG. 6 shows a schematic cross-sectional view of a tube apparatus according to a further embodiment, with a central duct.

(7) FIG. 7 shows a detail of FIG. 6.

(8) FIG. 8 is an axonometric view of a portion of a tube bundle according to one of the various embodiments of the invention.

DETAILED DESCRIPTION

(9) FIG. 1 shows schematically a cross-section of a tube bundle 1 with a shell 2. The bundle 1 comprises a plurality of tubes 3 arranged with a square pitch.

(10) As can be noted from the detail shown in FIG. 2, the axes of four adjacent tubes 3 are arranged in the manner of the vertices of a square. Owing to the square pitch arrangement, the tubes 3 are arranged along directional lines 3.1, 3.2, 3.3 and 3.4 spaced at 45. For example, taking as a reference a straight line coinciding with the directional line 3.1, the directional lines of the tubes are defined by angles of 0, 45, 90 and 135.

(11) The shell 2 has a cross-section of an irregular polygon. The cross-section is understood as being viewed in a plane perpendicular to the tubes 3, i.e. perpendicular to a longitudinal axis of the tube bundle (corresponding to the plane of FIGS. 1 and 2).

(12) The number n of the sides of said irregular polygon is a multiple of the parameter p which expresses conventionally the arrangement of the tubes 3. Said parameter p is equal to 3 for a triangular pitch and 4 for a square pitch.

(13) In the example shown in FIG. 1 with tubes having a square pitch, the shell 2 is substantially a prism comprising 24 faces. The polygon viewed in cross-section therefore appears as an irregular polygon with 24 sides.

(14) The sides of the cross-sectional polygon of the shell 2 are parallel to directional lines of the tubes. Each side is parallel to one of the directional lines: in FIG. 2 it can be seen for example that the side 2.1 is parallel to the directional line 3.1; the side 2.2 is parallel to the directional line 3.4; the side 2.3 is again parallel to the directional line 3.1; the side 2.4 is parallel to the directional line 3.4; the side 2.5 is parallel to the directional line 3.3.

(15) In other quadrants, as can be noted from FIG. 1, the cross-sectional polygon comprises sides parallel also to the other directional line 3.2.

(16) Looking at FIG. 1 it can be seen that the stepped shell 2 is able to surround a bundle of tubes with a square pitch, such as the bundle 1 shown, without leaving any major bypass areas around the peripheral tubes, unlike a conventional cylindrical shell.

(17) FIGS. 3 and 4 show a variation of embodiment with tubes having a triangular pitch. For the sake of simplicity the same reference numbers as those in FIG. 1 are used.

(18) The shell 2 has a cross-section of an irregular polygon with 18 sides. The directional lines of the tubes 3.1, 3.2 and 3.3 in the cross-sectional plane are spaced at angles of 60, i.e. for example are oriented at angles of 0, 60 and 120 degrees with respect to a reference direction parallel to the direction 3.1. In the detail shown in FIG. 3 it can be seen that the side 2.1 is parallel to the directional line 3.1, the side 2.2 is parallel to the directional line 3.3 and so on.

(19) FIG. 5 shows a detail of a shell 2 with a greater number of sides, in particular 60 sides with a triangular tube pitch. It can be seen that the stepped shell 2 closely matches a cylindrical shell, the cross-section of which is indicated by the broken line 4 in the figure. The stepped shell, however, has the advantage that it does not leave bypass areas such as for example the zone indicated by 5.

(20) FIG. 6 shows an embodiment in which the apparatus also comprises a central duct 6. The tube bundle 1 therefore is arranged in a ring between the shell 2 and the duct 6. Advantageously, the duct 6 also has a stepped cross-section with sides parallel to the directional lines of the tubes, in accordance with that described above.

(21) The sides of the cross-sectional polygon of the internal duct are also multiples of the parameter which expresses the pitch of the tubes and are parallel to the directional lines of the tubes. The number of sides (i.e. faces) of the internal duct is not necessarily equal to the number of sides of the outer shell; preferably it is smaller.

(22) For example in FIG. 7 two sides 6.1, 6.2 of the duct 6 are shown. The duct 6 has a cross-section with 12 sides, while the shell 2 has a cross-section with 24 sides.

(23) The design of the internal duct 6 also with a stepped cross-section has the further advantage of allowing a certain number of additional tubes to be accommodated. This advantage is shown in FIG. 7: it may be noted that, owing to the stepped form of the duct 6, a useful volume 8 for housing three tubes may be recovered.

(24) The illustration in FIG. 6 is provided purely by way of example and the advantage of displacing the tubes from the periphery to the centre may be more evident in the case of apparatus provided with a larger number of tubes.

(25) FIG. 8 shows a simplified axonometric view of a tube bundle with a triangular pitch, provided with a shell 2 according to the invention. The figure also shows the axis 9 of the tube bundle (which is parallel to the tubes 3); the cross-sections shown in FIGS. 1-7 are cross-sections along planes perpendicular to said axis 9.