Multi-bed catalytic converter with inter-bed cooling

Abstract

A multi-bed catalytic converter comprising at least a first catalytic bed, a second catalytic bed and a heat exchanger arranged between said first bed and said second bed, wherein said heat exchanger is arranged to transfer heat from the hot effluent of the first bed to a cooling medium; said heat exchanger comprises a plurality of stacked round plates, wherein adjacent plates define gaps therebetween, and the effluent of the first catalytic bed and the cooling medium are respectively fed into alternate gaps.

Claims

1. A multi-bed cylindrical catalytic converter, comprising: a first catalytic bed; a second catalytic bed; a heat exchanger arranged between said first catalytic bed and said second catalytic bed, said heat exchanger being arranged to transfer heat from a first medium to a second medium; an input and an output for the first medium; and an input and an output for the second medium; wherein the first medium is the hot effluent of the first catalytic bed before admission into the second catalytic bed, and the second medium is a cooling medium; wherein said heat exchanger comprises a plurality of stacked round plates, said plurality of stacked round plates being full circular plates or annular plates, and adjacent plates of the plurality of stacked round plates define gaps therebetween; wherein the hot effluent of the first catalytic bed and the cooling medium pass respectively through alternating ones of the gaps between the plurality of stacked round plates; wherein said first catalytic bed is a hollow cylinder comprising a cavity and said heat exchanger is arranged coaxially to the first catalytic bed inside said cavity.

2. The multi-bed cylindrical catalytic converter according to claim 1, wherein said plurality of stacked round plates are stamped plates obtained mechanically by metal sheet pressing.

3. The multi-bed cylindrical catalytic converter according to claim 1, wherein at least one of the input or the output of at least one of the first medium or the second medium includes a plurality of nozzles disposed on a cylindrical shell around the plurality of stacked round plates of the heat exchanger.

4. The multi-bed cylindrical catalytic converter according to claim 3, wherein said cylindrical shell comprises a first plurality of input nozzles for distributing the first medium and a second plurality of output nozzles for collecting the first medium after cooling.

5. The multi-bed cylindrical catalytic converter according to claim 4, wherein said first plurality of input nozzles and said second plurality of output nozzles being diametrically opposed, so that said first medium traverses the gaps between the plurality of stacked round plates with a flow that is substantially parallel to a passage-through direction from said first plurality of input nozzles toward said second plurality of output nozzles.

6. The multi-bed cylindrical catalytic converter according to claim 1, wherein at least one of the input or the output of at least one of the first medium or the second medium includes a passage made on a top cover or a bottom plate of the heat exchanger, being respectively above or below the plurality of stacked round plates.

7. The multi-bed cylindrical catalytic converter according to claim 6, wherein said passage has a shape of a sector of a circle or sector of an annulus extending over an angle of 60° to 300°.

8. The multi-bed cylindrical catalytic converter according to claim 6, wherein one of the top cover or the bottom plate has a first passage for distributing the first medium and the other one of said top cover or said bottom plate has a second passage for collecting the first medium after cooling.

9. The multi-bed cylindrical catalytic converter according to claim 8, wherein said first passage and said second passage are diametrically opposed such that: the first medium flows through said gaps with a flow substantially parallel to a first direction, which is a passage-through direction; and said first medium enters and leaves the heat exchanger with a flow in a second direction that is substantially perpendicular to said first direction.

10. The multi-bed cylindrical catalytic converter according to claim 8, wherein said first passage includes a first set of input nozzles for said first medium, and said second passage includes a second set of output nozzles for collecting said first medium after cooling.

11. The multi-bed cylindrical catalytic converter according to claim 1, wherein said plurality of stacked round plates comprise a port or a plurality of ports for the input and/or the output of at least one of the first medium or the second medium.

12. The multi-bed cylindrical catalytic converter according to claim 11, wherein said plurality of stacked round plates comprise one input port and one output port for the cooling medium, said input port and said output port being diametrically opposed to each other.

13. The multi-bed cylindrical catalytic converter according to claim 11, wherein said plurality of stacked round plates comprise a plurality of input ports and a plurality of output ports for the cooling medium, said plurality of output ports being arranged in a more peripheral position than said plurality of input ports.

14. The multi-bed cylindrical catalytic converter according to claim 13, wherein: said plurality of input ports are arranged along an inner rank and said plurality of output ports are arranged along an outer rank; and said inner rank and outer rank are circular, the inner rank having a first radius and the outer rank having a second radius, the first radius being smaller than the second radius.

15. The multi-bed cylindrical catalytic converter according to claim 13, wherein said plurality of input ports are radially aligned with corresponding outputs ports of the plurality of output ports.

16. The multi-bed cylindrical catalytic converter according to claim 11, wherein: said heat exchanger is delimited by a cylindrical shell comprising an inlet opening for said first medium, said inlet opening extending over a segment of the cylindrical surface of said cylindrical shell, said segment extending over an angle from 10 to 45°; said heat exchanger comprises a collecting port for collecting said effluent after cooling; and said inlet opening and said collecting port being diametrically opposed, so that said first medium traverses the gaps between the plurality of stacked round plates with a flow that is substantially parallel to a given direction from said inlet opening toward said collecting port.

17. The multi-bed cylindrical catalytic converter according to claim 1, further comprising sealing strips arranged to seal a possible by-pass path of the first medium or the second medium around the plurality of stacked round plates, said sealing strips having a V cross-section.

18. The multi-bed cylindrical catalytic converter according to claim 1, wherein said plurality of stacked round plates are annular and said heat exchanger comprises a central manifold for collecting one of said first medium or said second medium after the heat transfer, for collecting the first medium after cooling, said central manifold being annular.

19. The multi-bed cylindrical catalytic converter according to claim 1, wherein at least one of the first medium or the second medium traverses the heat exchanger with a radial flow.

20. The multi-bed cylindrical catalytic converter according to claim 1, wherein said heat exchanger comprises weldings between the plurality of stacked round plates arranged to respectively feed the effluent of the first catalytic bed and the cooling medium into alternating ones of the gaps.

21. The multi-bed cylindrical catalytic converter according to claim 1, configured for the synthesis of ammonia or methanol.

22. The multi-bed cylindrical catalytic converter according to claim 1, wherein said gaps have a width from 1 mm to 10 mm.

23. The multi-bed cylindrical catalytic converter according to claim 22, wherein said width is from 2 mm to 6 mm.

24. A method for revamping a multi-bed catalytic converter, wherein the multi-bed catalytic converter includes: a first catalytic bed, a second catalytic bed, and a heat exchanger arranged between said first bed and said second bed; said heat exchanger being arranged to transfer heat from the hot effluent of the first catalytic bed before admission into the second catalytic bed to a cooling medium; said heat exchanger being a tube bundle heat exchanger; the method comprising: replacing said tube bundle heat exchanger with another heat exchanger comprising a plurality of stacked round plates, wherein adjacent plates of the plurality of stacked round plates define gaps therebetween, and the effluent of the first catalytic bed and the cooling medium are respectively fed into alternating ones of the gaps; wherein said first catalytic bed is a hollow cylinder comprising a cavity and said new heat exchanger with stacked round plates is arranged coaxially to the first catalytic bed inside said cavity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a simplified scheme of a multi-bed inter-cooled converter according to the invention.

(2) FIG. 2 shows the first catalytic bed and the first inter-bed cooler of the converter of FIG. 1 according to an embodiment of the invention.

(3) FIG. 3 shows a top view of the inter-bed cooler of FIG. 2.

(4) FIG. 4 shows a variant of FIG. 2.

(5) FIG. 5 shows a plate heat exchanger with a radial flow configuration according to a further embodiment of the invention.

(6) FIG. 6 shows the counter-current flow of the fluids circulating between the plates of the heat exchanger of FIG. 5.

(7) FIG. 7 shows an alternative to the plate heat exchanger of FIG. 5.

(8) FIG. 8 shows a variant of FIG. 7.

(9) FIG. 9 shows a variant of FIG. 8.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(10) FIG. 1 illustrates a multi-bed converter 1, for example an ammonia or a methanol converter, including a vessel 2 and a catalytic cartridge 3 comprising three adiabatic catalytic beds 4, 5, 6 arranged in series, two inter-bed plate heat exchangers 7, 8 and, optionally, a bottom heat exchanger 9.

(11) Each bed 4, 5, 6 is traversed by a radial inward or mixed axial-radial flow and has an annular cylindrical shape with a central axial cavity 10.sub.A, 10.sub.B, 10.sub.C. The plate heat exchangers 7, 8, 9 are arranged, respectively, in said central cavities 10.sub.A, 10.sub.B, 10.sub.C to provide inter-bed cooling of the gaseous products evolving from one catalytic bed to another.

(12) A fresh make-up gas (MUG) is fed to the converter 1 through the gas inlet 11 and enters the first bed 4; the effluent of the first bed 4 is cooled while flowing through the plates of the first inter-bed exchanger 7; the cooled effluent enters the second bed 5. Similarly, the effluent of the second bed 5 is cooled in the second inter-bed heat exchanger 8 before entering the third bed 6, and the effluent of the third bed 6 is cooled in the bottom heat exchanger 9 before leaving the converter 1 via the outlet 12.

(13) According to the example of FIG. 1, the catalytic beds 4, 5, 6 are adiabatic since they contain no cooling means. In other embodiments, one or more of said catalytic beds 4, 5, 6 may be isothermal, i.e. contain heat exchange bodies (e.g. tubes or plates) immersed therein.

(14) FIG. 2 illustrates in greater detail the first catalytic bed 4 and the first inter-bed plate heat exchanger 7 of the converter 1 of FIG. 1, according to an embodiment of the invention.

(15) Said catalytic bed 4 is delimited by a gas distributor 13 and a gas collector 14, which are represented by an outer cylindrical wall and an inner cylindrical wall, respectively. Said outer and inner cylindrical walls are permeable to gas and able to retain the catalyst, comprising e.g. slots of a suitable size.

(16) Said gas collector 14 internally defines the above mentioned central cavity 10.sub.A, which accommodates said first plate heat exchanger 7.

(17) As shown in FIG. 2, said heat exchanger 7 comprises a plurality of stacked full circular plates 15. Adjacent plates define gaps 16 therebetween for the passage of the hot gas HG leaving the first catalytic bed 4 and for the passage of a cooling medium (not shown in FIG. 2). In particular, adjacent plates 15 are welded in such a way to allow the passage of the hot gas HG through first gaps 16 and the passage of the cooling medium through second gaps 16, said first and second gaps being alternated.

(18) The plate heat exchanger 7 has a cylindrical shell 17, which comprises an opening 18 for feeding the hot gas HG into the heat exchanger. Said opening 18 extends over a segment of the cylindrical surface of said cylindrical shell 17. According to the example shown in FIG. 3, said segment extends over an angle α of 30°.

(19) The plate heat exchanger 7 also comprises a porthole 19 for collecting the cooled gas CG after passage through the respective gaps 16 (i.e. the above referred first gaps) between the plates. Said porthole 19 is advantageously opposite to the opening 18.

(20) As a result of the relative position of the inlet opening 18 and the collecting porthole 19 of FIGS. 2 and 3, the flow of the hot gas HG through said first gaps is essentially directed along a diametral direction from the inlet opening 18 toward the collecting porthole 19.

(21) In greater detail, after traversing the gas collector 14, the hot gas HG spreads into the central cavity 10.sub.A and enters the plate heat exchanger 7 through the inlet port 18. The hot gas HG is supplied to alternate gaps between the plates 15 and the resulting cooled gas CG then converges into the porthole 19, from which it is directed to the subsequent catalytic bed.

(22) The embodiment shown in FIG. 4 is preferred when a pipe 20 must be accommodated inside the central cavity 10.sub.A. Accordingly, the plates 15 are annular.

(23) FIG. 5 illustrates an embodiment of a plate heat exchanger 7 traversed by a radial flow of the hot gaseous effluent HG.

(24) According to this embodiment, the plate heat exchanger 7 comprises stacked annular plates 15 and a central annular manifold 21 for collecting the cooled gas CG after passage through respective gaps 16. The hot gas HG is fed to the heat exchanger 7 along the entire peripheral surface of the heat exchanger 7 and is collected into the central manifold 21, thus generating a radial inward flow.

(25) The plates 15 comprise a plurality of input ports 22 and a plurality of output ports 23 for the passage of a cooling medium CM. Said input ports 22 are arranged along a first circular rank having a first radius and said output ports 23 are arranged along a second circular rank having a second radius, wherein said first radius is smaller than said second radius. Preferably, said input ports 22 are radially aligned with corresponding outputs ports 23.

(26) As a result of the above described position of said input and output ports 22, 23, the cooling medium CM traverses alternate gaps 16 with a radial outward flow, thus resulting in counter-current with respect to the hot gas HG.

(27) Accordingly, the embodiment of FIG. 5 provides for a heat exchange between fluids in counter-current, as further shown in FIG. 6.

(28) FIG. 7 shows a variant of the plate heat exchanger 7, wherein the plates 15 comprise one input port 22a and one output port 23b for the passage of the cooling medium CM. Said ports 22a and 23a are diametrically opposed. As a result, the cooling medium CM traverses alternate gaps 16 between the plates 15 with a flow which is substantially parallel to a given direction, i.e. from the input port 22a to the output port 23a, as can be seen in FIG. 7 (dotted arrows). The hot gas HG has a radial inward flow, similarly to the embodiment of FIGS. 5, 6.

(29) FIG. 8 shows a variant of FIG. 7, wherein the hot gas HG and the cooling medium CM traverse alternate gaps 16 between the plates 15 with a counter-current parallel flow.

(30) The cooling medium CM is fed to the plate heat exchanger 7 through the input port 22b and leaves the exchanger 7 through the output port 23b. In another embodiment (not shown), the cooling medium CM enters and leaves the exchanger 7 through one or more input nozzle(s) and one or more outlet nozzle(s), respectively.

(31) The hot gas HG is fed to the plate heat exchanger 7 through a first set of shell nozzles (input nozzles) disposed on the cylindrical shell 17 (see FIG. 2). Preferably said input nozzles are diametrically opposite to the input port 22b.

(32) The cooled gas CG leaves the exchanger 7 through a second set of nozzles (output nozzles) of the shell 17. Preferably said output nozzles are diametrically opposite to the output port 23b. The embodiment of FIG. 8 also comprises sealing strips 24 for sealing a possible by-pass path of the hot gas HG around the plates. It can be appreciated that the embodiment of FIG. 8, and variants thereof, provides a counter-current parallel flow pattern of hot gas and cooling medium.

(33) The central cavity of the annular plates 15 houses a pipe 20 traversed by a further medium (third medium) which is not involved in the heat exchange process of said plate heat exchanger 7.

(34) The configuration of the plate heat exchanger 7 illustrated in FIG. 8 allows a better arrangement of the heat exchanger inside the converter.

(35) FIG. 9 is a variant of FIG. 8, wherein the hot gas HG enters and exits the plate heat exchanger 7 via respective input nozzles and output nozzles (not shown) with a flow which is substantially perpendicular to the flow of the hot gas HG into the gaps 16. This arrangement allows a more compact design of the plate heat exchanger 7. Said input nozzles are distributed over an input area 25 of a top cover of the heat exchanger 7. Said output nozzles are distributed over an output area 26 of a bottom cover. Preferably said input area 25 and said output area 26 have an angular opening of 180° or around 180°.