PLATE EXCHANGER FOR CHEMICAL REACTORS WITH AUTOMATICALLY WELDABLE COLLECTORS

Abstract

Plate heat exchanger for internals of isothermal chemical reactors, said plate heat exchanger comprising a plurality of heat exchange plates (1) having an essentially rectangular shape, wherein each plate comprises two walls (2, 3) which are joined together along their perimeter, and wherein each plate comprises a respective first collector for feeding a heat exchange medium to the plate and a respective second collector for receiving said medium form the plate, said first collector and second collector being fixed to opposite sides of said plate, and at least one (10, 30) of said first collector and second collector comprises edge surfaces which are planar and parallel to respective planar end portions (12, 13) of said plate, to provide plane and parallel surfaces for automated welding.

Claims

1. A plate heat exchanger for internals of isothermal chemical reactors, said plate heat exchanger comprising a plurality of heat exchange elements in the form of plates, each plate having an essentially rectangular shape, wherein each plate comprises two walls which are joined together along their perimeter and spaced apart, so as to form an internal passage for a heat exchange medium, and wherein each plate comprises a respective first collector for feeding said medium to said passage and a respective second collector for receiving said medium from said passage, said first collector and said second collector being fixed to opposite sides of said plate, wherein: at least one of said first collector and second collector of each plate extends along a plate edge and comprises edge surfaces which are planar and parallel to respective planar end portions of said plate, in such a way that said edge surfaces of said at least one collector and said end portions of said plate form parallel and plane matching surfaces, which are welded together.

2. The heat exchanger according to claim 1, wherein said at least one collector is in the form of a clamp.

3. The heat exchanger according to claim 2, wherein said collector is C-shaped comprising two flanges which parallel overlap with said end portions of the plate.

4. The heat exchanger according to claim 1, said at least one collector being connected to a feeding or receiving pipe and having a cross-section which decreases in a direction away from said pipe.

5. The heat exchanger according to claim 4, wherein said at least one collector has a trapezoidal or triangular shape with a zone of maximum height in the proximity of said pipe, and the height decreases in a direction away from said pipe.

6. The heat exchanger according to claim 1, wherein said at least one collector has a sandwich-like structure, comprising two walls which are sandwiched together, said walls having welding end portions parallel to the end portions of the plate.

7. The heat exchanger according to claim 6, wherein a first wall of said two walls of said at least one collector is formed by a portion of a wall of the plate which extends beyond a peripheral edge of said plate.

8. The heat exchanger according to claim 7, comprising a cover which is applied onto said plate and forms the remaining second wall of said sandwich collector.

9. The heat exchanger according to claim 8, comprising welds which close said cover of the sandwich plate and which are performed on a same side of the assembly formed by plate and collector.

10. The heat exchanger according to claim 6, wherein said collector comprises a plurality of reinforcing and spacing inserts between the respective two walls.

11. The heat exchanger according to claim 1, wherein the plates have a pressed plate body or a sandwich plate body.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0035] FIG. 1 is a schematic cross-section through an isothermal chemical reactor containing a heat exchanger.

[0036] FIG. 2 is a view of a portion of a heat exchange plate and associated collector, according to an embodiment of the invention.

[0037] FIG. 3 is a cross-sectional view of the plate and collector according to FIG. 2.

[0038] FIG. 4 shows a plate with sandwich design according to another embodiment.

[0039] FIG. 5 shows a front view of a collector and part of the plate according to FIG. 4, with internal reinforcing strips.

[0040] FIG. 6 shows a variation of the embodiment of FIG. 5, with reinforcing discs instead of the strips.

[0041] FIGS. 7 and 8 are cross-sectional views of two further embodiments of plates with a sandwich design.

DETAILED DESCRIPTION

[0042] FIG. 1 shows a schematic cross-section of a heat exchanger 100 for a chemical reactor. The exchanger 100 is immersed in a catalytic bed 102 and comprises heat exchange plates 1 which in the example are arranged radially in the direction r around a central axis. The exchanger has an annular structure.

[0043] FIG. 1 relates to a radial-flow or axial-radial flow reactor in which the catalytic bed and the exchanger are bounded by two cylindrical walls 103 and 104. In an axial-flow reactor the outer wall is the vessel of the reactor, while the inner wall is a central tube generally having the function of a manhole.

[0044] FIGS. 2 and 3 show a first embodiment of the invention in which a heat exchange plate 1 is formed essentially by a first wall 2 and by a second wall 3; the second wall 3 is welded to the wall 2 along the perimeter and at separate points corresponding to welding spots 4 using a construction method which is known per se.

[0045] The walls 2, 3 are formed by metal sheets, preferably of austenitic steel or duplex steel.

[0046] The inside 5 of the plate 1 is passed through by a heat exchange fluid, such as water, steam, water/steam mixtures or a gas, supplied and received by collectors welded to two sides of the plate itself. FIGS. 2 and 3 show a collector 10.

[0047] The plate 1 may also comprise a series of spacers 6 between the walls 2 and 3 and arranged in the region of the collector 10.

[0048] The collector 10, in the embodiment of FIGS. 2-3, has a substantially C-shaped cross-section which clamps the peripheral edges of the plate 1. More in detail the C-shaped collector 10 has two walls 11 extending parallel to end portions 12, 13 of the walls (metal sheets) 2 and 3.

[0049] Accordingly, parallel and plane surfaces for automated welding are available, i.e. the end portions 12 and 13 of the metal sheets 2 and 3, and the tips of the walls 11 of the collector 10.

[0050] The welds, which are indicated by the arrows W in FIG. 3, are provided between said planar surfaces of the walls 11 and the end portions 12, 13 and, thanks to the parallel and plane surfaces, can be performed automatically, for example using laser technology.

[0051] The collector 10, referring for example to a feeding collector, operates as follows. The fluid is supplied into the chamber 14 defined between the collector 10 and the plate 1 and flows through the inside 5 of the plate 1, if necessary passing through apertures between the spacers 6. On the other hand, when the collector 10 is a receiving collector, the fluid passes from the inside 5 of the plate to the chamber 14 of the collector.

[0052] The collectors have a cross-section which is generally greater than passing-through cross section of the plate body. In order to ensure a suitable strength, the collectors are made preferably with metal sheets thicker than the metal sheets of the plate. Referring to FIGS. 2-3, the distance between the two sheets of the C-shaped collector 10 is greater than the distance between the sheets of the plate since the collector grips the plate body externally.

[0053] In some embodiments, the necessary flow cross-section requires apertures such that the collector is not strong enough, despite a reasonable increase in thickness of the collector itself. In order to solve this problem, it is possible to provide reinforcements, for example intermediate spacing strips or spacing discs or reinforcing welding spots.

[0054] FIGS. 4-6 show an embodiment of a collector 30 having, in a front view, a triangular shape. The triangular collector 30 has a maximum height close to a feeding or receiving pipe 35. Accordingly, the cross-section available to the flow inside the collector 30 decreases in a direction away from said pipe 35.

[0055] More in detail, the FIGS. 4 and 5 show a collector 30 which has a sandwich structure, essentially formed by two walls 31, 32. Preferably, said two walls 31 and 32 are parallel to the walls 2, 3 of the plate 1. In some embodiments one of the walls 31, 32 may be formed by a portion of one of the walls 2, 3 of the plate.

[0056] Advantageously, the collector 30 also comprises a series of intermediate spacers (for example spacing strips) 33 to define channels 34 for the fluid and space the walls 31, 32. Preferably said spacers 33 have a full cross-section, for example square or rectangular so as to provide a suitable pressure resistance.

[0057] The arrows in FIG. 4 show the flow path of the fluid passing for example form the feed pipe 35 into the channels 34 and then flowing in the inside of the plate 1, between the walls 2 and 3.

[0058] Said sandwich design is particularly advantageous with radial plates. FIGS. 4-6 also illustrate the radial direction r, oriented from the axis towards the outside of the heat exchanger. Said radial direction r is also shown in FIG. 1.

[0059] The collector 30 has a trapezoidal or triangular shape, with a height decreasing in the radial direction away from the feeding pipe (generally situated on the outer periphery) and therefore towards the axis of the reactor. The pipe 35 is located in the zone of maximum height opposite to the axis. In this way the zone close to the axis is a zone of minimum height and the flow cross-section decreases away from said pipe 35, towards the axis where the plates converge, adapting to the flowrate which is the greatest close to the pipe 35 and diminishes at the inner end 15 (FIG. 5) of the plate.

[0060] FIG. 6 shows an embodiment wherein the plate is reinforced by tabs 33 which perform a function similar to strips 33.

[0061] FIGS. 7 and 8 show two further embodiments of a heat exchange plate with a sandwich collector according to the invention.

[0062] In FIG. 7 a wall 31 of the collector 30 coincides with the wall 2 of the plate 1, which extends beyond the plate edge zone 7 forming a base of the sandwich collector 30. A cover 32 is applied onto the end portions 12, 13 of the walls 2 and 3, to form the opposite wall of the collector 30.

[0063] The collector 30 is closed by a series of welds 36 which join the cover 32 to the aforementioned end portions of the walls 2 and 3 and to the tops of the spacers 33 (if provided) creating intermediate fixing points.

[0064] It should be noted that said welds 36 can be performed from the same side (for example from the top). Working from one side only is an advantage for the manufacturing process because it avoids turn over and reposition of the workpiece on the automatic welding machine, reducing the production costs.

[0065] The welds 37 at the base of the spacers 33 and the spacer 6 may be performed manually or automatically through the outer surface (in the figure the bottom surface) of the sheet 31. The invention is however advantageous since it allows the welds 36which are the most costly and main responsible for the leak-tightness of the collector/plate assemblyto be performed automatically and on the same side.

[0066] Preferably, the wall 2 of the plate, which is common to the collector, has a greater thickness than that of the wall 3.

[0067] The variant according to FIG. 8 (similar to FIG. 7) provides welds on both sides, it has however the advantage to perform automatically all welds, including the welds which fix the spacers 33.

[0068] FIG. 8 relates to a preferred embodiment wherein the collector also comprises an L-shaped spacer 38 which compensates for the different height between the cover 32 of the collector and the top wall 3 of the plate 1 and allows simplification of the form of the cover 32, which may be made for example using a flat metal sheet. Also the welds of the spacing strips 33 (or the tabs 33) can be performed automatically.

[0069] From FIGS. 7 and 8 it can also be understood how the sandwich collector structure is suitable to resist to high pressures, owing to the spacers 33 (or tabs 33) which reinforce the structure and reduce the apertures between adjacent support points of the sheets.