ISOTHERMAL TUBULAR CATALYTIC REACTOR

Abstract

Isothermal catalytic reactor (1) comprising a catalytic bed (2) and a tubular heat exchanger immersed in said catalytic bed, wherein the exchanger is formed by straight tubes connected to a distributor (6) and to a header (7) formed by preferably toroidal bodies which support the said tubes, and wherein the catalytic bed is of the type crossed by an inward radial flow.

Claims

1. Isothermal catalytic reactor comprising at least one catalytic bed and a heat exchange tube bundle immersed in said catalytic bed, said tube bundle comprising tubes which are substantially straight and internally passed through by a heat exchange fluid, wherein: the reactor comprises a distributor and a header for the heat exchange fluid, and each of said tubes has opposite ends connected respectively to said distributor and to said header, the reactor being devoid of tube plates; the reactor also comprises a distributor and a header for the shell-side gases, which are arranged so as to ensure an essentially radial inward flow across the catalytic bed, and at least one of said distributor and said header comprises a plurality of straight or curved cylindrical elements closed at both ends, said elements being distributed along at least two concentric circumferences.

2. The reactor according to claim 1, wherein at least one of said distributor and said header comprises a substantially toroidal body.

3. The reactor according to claim 1, wherein at least one of said distributor and said header comprises a body having a shape of spherical portion or ellipsoidal portion.

4. The reactor according to claim 3, wherein the reactor is vertical and said distributor and said header are formed by a top body and a bottom body, respectively at the top and bottom ends of the tubes, and the top body comprises said plurality of cylindrical elements, and the bottom body comprises said body with a spherical or ellipsoidal form.

5. The reactor according to claim 1, wherein said gas distributor comprises a cylindrical wall which is at least partially perforated, and said gas header comprises a central tube which is at least partially perforated and coaxial with said cylindrical wall, and said catalytic bed and said heat exchange tubes are housed inside the annular space between said wall and said central tube.

6. The reactor according to claim 1, wherein said gas distributor comprises scallops which ensure the external containment of the catalytic bed.

7. The reactor according to claim 1, wherein the tubes are connected to the distributor and to the header by means of shaped end connectors.

8. The reactor according to claim 1, comprising anti-vibration supporting and mounting baffles for the tubes, said baffles being arranged on planes perpendicular to the axis of the tubes, and the reactor comprises a series of baffles where adjacent baffles support the tubes in different directions, and the baffles have a predefined repetition periodicity.

9. The reactor according to claim 8, wherein said baffles comprise supporting elements of the tubes which are parallel to directrices of the tubes and wherein two adjacent supporting elements of the tubes are spaced by a pitch which is a multiple of the pitch (p) of the tubes and is more than twice the pitch of the tubes.

10. The reactor according to claim 9, wherein the pitch between said supporting elements is three times the pitch of the tubes, and the baffles are arranged with a periodicity equal to six baffles.

11. The reactor according to claim 8, wherein said supporting elements of the tubes are formed by rods.

12. The reactor according to claim 1, wherein at least one between said distributor and said header comprises a manhole.

13. Use of a reactor according to claim 1, as a catalytic reactor for ammonia or methanol synthesis or for a shift reaction.

Description

DESCRIPTION OF THE FIGURES

[0032] FIG. 1 is a schematic longitudinally sectioned view of an isothermal reactor according to a first embodiment of the invention;

[0033] FIG. 2 is a schematic longitudinally sectioned view of an isothermal reactor according to a second embodiment of the invention;

[0034] FIG. 3 is a schematic longitudinally sectioned view of an isothermal reactor according to a third embodiment of the invention;

[0035] FIG. 4 is a cross-section through the reactor according to FIG. 3;

[0036] FIG. 5 is a diagram showing a tube bundle with square pitch and supporting rods according to the prior art;

[0037] FIG. 6 is a diagram showing a tube bundle with square pitch and an arrangement of the supporting rods according to an embodiment of the invention;

[0038] FIG. 7 is a diagram similar to FIG. 3 for tubes with a triangular pitch.

DETAILED DESCRIPTION

[0039] FIG. 1 shows a vertical reactor 1 comprising a catalytic bed 2 and a tubular heat exchanger immersed in said catalytic bed.

[0040] The catalytic bed 2 is contained in a substantially annular space between a cylindrical wall 3 and a central tube 4 coaxial with said wall 3. Both the cylindrical wall 3 and the central tube 4 have at least part of the surface perforated so as to allow the passage of the reagents and gaseous products. The catalytic bed is supported by a basket (not shown) according to the art known per se. The lines 18 and 19 indicate the volume filled with catalyst during conditions of normal use; below the line 18 there is usually inert material.

[0041] The tubular heat exchanger comprises essentially a straight tube bundle 5. The tubes 5 are housed inside the annular space between the wall 3 and the central tube 4.

[0042] The ends of the tubes are connected to two bodies 6 and 7 which act as a distributor and a header for a heat exchange fluid. Each tube 5 is connected to the distributor 6 and the header 7 by means of suitably shaped end connectors 8. It should be noted that the tubular exchanger thus formed is without tube plates. The distributor 6 and the header 7 in fact structurally support the tubes 5, in addition to supplying and collecting the heat exchange fluid.

[0043] The main inlets and outlets of the reactor 1 comprise: a reagent inlet 9, an outlet 10 for the reaction products; an inlet 11 and outlet 12 for the heat exchange fluid. The reactor is also provided with at least one opening 14 for emptying (drop-out) of the catalyst.

[0044] The wall 3 and the central tube 4 form respectively a distributor and a header for the shell-side gases, which ensure an inward radial flow across the catalytic bed. In greater detail, the reagents entering via the inlet 9 flow into the space 13 around the perforated wall 3 (between the wall 3 and the outer shell 15) and cross the catalytic bed 2 with a substantially radial flow; inside the bed 2 the desired chemical conversion takes place and the reaction products are collected inside the central tube 4 which is in turn in communication with the outlet 10.

[0045] The heat exchange fluid may supply heat or remove heat depending on the type of reaction, i.e. endothermic or exothermic, and may undergo a phase change. FIG. 1 for example refers to a reactor configuration for exothermic reaction (for example ammonia or methanol synthesis) in which the reaction heat is used to produce steam. The fluid supplied to the inlet 11 is water which evaporates at least partially inside the tubes 5.

[0046] FIG. 1 shows an embodiment in which the distributor 6 and the header 7 are formed by toroidal bodies 60, 70.

[0047] FIG. 2 shows an embodiment in which one between the distributor and the header, in the example the distributor 6, is formed by an ellipsoidal body 61.

[0048] FIGS. 3, 4 show an example in which one between the distributor and the header, in the example the header 7, is formed by a plurality of straight or curved cylindrical elements 71 which are closed at both ends by end-plates 72. Said cylindrical elements 71 are distributed alternately along two concentric circumferences with radius r1 and r2 (FIG. 4) in order to maximise the use of the space available, in particular of the cross-section of the shell of the reactor

[0049] The elements 71 have preferably a length of not more than 1 meter so that it is possible to reach the welds of the central tubes also without entering inside them, after removal of one or both the end-plates 72. This constitutes an advantage in terms of dimensions (diameter) of the headers and in case the welding operations require preheating of the materials where access by the workman would be impossible.

[0050] The embodiments shown in FIG. 1, FIG. 2 and FIGS. 3 and 4 may be combined with each other for the distributor 6 and the header 7, respectively.

[0051] As mentioned above, the tube bundle 5 is without tube plates, since the ends of the tubes are connected solely to the distributor 6 and header 7. In order to ensure the stability of the tubes and in particular prevent vibrations, the reactor 1 advantageously comprises a plurality of baffles for supporting the tubes, distributed along the tube bundle at suitable intervals.

[0052] A preferred embodiment of said baffles is shown schematically in FIG. 6. The baffles are formed by supporting elements such as rods 16 parallel to the directrices 17 of the tubes. Said directrices 17 are lines joining together the centres of said tubes. The ends of the rods 16 may be fixed to a suitable support frame or housing.

[0053] Advantageously, the rods 16 are spaced with a greater pitch than the rod-baffles of the prior art which is shown, for comparison purposes, in FIG. 5.

[0054] According the prior art the rod-baffles have a distance which is twice the pitch of the tubes. The figure shows the conventional embodiment with pitch p between tubes 5 and pitch 2p between the rods 16.

[0055] FIG. 6 shows instead the bars with expanded pitch according to the invention, for example with a pitch 3p. This arrangement of the rods at a greater distance has proved to be advantageous because it allows the tubes to be conveniently supported, but at the same time it increases the free space in the bed 2 for filling/emptying of the catalyst and for settling it.

[0056] The periodicity of the baffles is therefore equal to six baffles, namely groups of six baffles with different orientation of the rods are arranged alternately along the reactor axis, and the sequence of six baffles is repeated periodically, if necessary, until occupying the length of the entire tube bundle.

[0057] FIG. 7 refers to tubes with a triangular pitch. The rods 16 are arranged along directrices inclined of 0, 120, 240 and form a rhomboid-like grid. The periodicity of the baffles is equal to six. The rods 16 are spaced by a pitch 3p and with a periodicity of six baffles indicated by the letters A-F. More specifically, the first baffle comprises the rods A, the second baffle comprises the rods B, and so on, until the sixth baffle which comprises the rods F. In the figure it can be seen that the pitch between two rods of a baffle (for example between two rods A) is three times the pitch of the tubes.