Process and reactor comprising a plurality of catalyst receptacles

Abstract

A reactor having a shell comprising one or more reactor tubes located within the shell, said reactor tube or tubes comprising a plurality of catalyst receptacles containing catalyst; means for providing a heat transfer fluid to the reactor shell such that the heat transfer fluid contacts the tube or tubes; an inlet for providing reactants to the reactor tubes; and an outlet for recovering products from the reactor tubes; wherein the plurality of catalyst receptacles containing catalyst within a tube comprises catalyst receptacles containing catalyst of at least two configurations.

Claims

1. A reactor having a shell comprising: one or more reactor tubes located within the shell, said reactor tube or tubes comprising a plurality of catalyst receptacles containing catalyst; means for providing a heat transfer fluid to the reactor shell such that the heat transfer fluid contacts the tube or tubes; an inlet for providing reactants to the reactor tubes; and an outlet for recovering products from the reactor tubes; wherein the plurality of catalyst receptacles containing catalyst within a tube comprises catalyst receptacles containing catalyst of at least two configurations, wherein the catalyst receptacle comprises: an annular container, said container having a perforated inner container wall defining an inner channel, a perforated outer container wall, a top surface closing the annular container and a bottom surface closing the annular container; a surface closing the bottom of said inner channel formed by the inner container wall of the annular container; a carrier outer wall extending from the bottom surface of said container to the top surface; a seal extending from the container by a distance which extends beyond the carrier outer wall; said carrier outer wall having apertures located below the seal.

2. The reactor according to claim 1 wherein the catalyst receptacles containing catalyst differ in the type of catalyst within the receptacle, the amount of catalyst within the receptacle, the amount of heat removed from the receptacle or combinations of these.

3. The reactor according to claim 1 wherein the catalyst receptacles containing catalyst allow, in use, the temperature of the reaction to be within 100° C. of the equilibrium temperature at a given conversion level.

4. The reactor according to claim 1 wherein there are three, four, five, six, seven, eight, nine, or ten different configurations of catalyst receptacles containing catalyst.

5. The reactor according to claim 1 wherein the at least two configurations of catalyst receptacles containing catalyst comprises the use of different catalysts.

6. The reactor according to claim 1 wherein the at least two configurations of catalyst receptacles comprises a change in the amount of catalyst loaded in the catalyst receptacle.

7. The reactor according to claim 6 wherein the change in the amount of catalyst loaded in the catalyst carried is achieved by altering the amount of catalyst loaded into the catalyst receptacle and filling the receptacle with inert material.

8. The reactor according to claim 6 wherein the change in the amount of catalyst loaded in the catalyst receptacle is achieved by altering the length of the receptacle.

9. The reactor according to claim 1 wherein the at least two configurations of catalyst receptacles comprises altering the diameter of the carrier such that when it is loaded into a tube, the annular space between the catalyst receptacle and the reaction tube into which it is to be inserted is altered.

10. A reactor system comprising a reactor according to claim 1 used in combination with one or more conventional adiabatic beds.

11. The reactor system according to claim 10 wherein the system is configured such that a bulk reaction can be carried out initially in a conventional adiabatic bed before being passed to a reactor of claim 1.

12. A process for carrying out an equilibrium limited reaction comprising providing reactants to the reactor of claim 1, allowing reaction to occur, and recovering product.

13. The process according to claim 12 wherein the process is the oxidation of sulphur dioxide to sulphur trioxide, the manufacture of ammonia, the synthesis of methanol from carbon monoxide and hydrogen, the water-gas shift reaction, the reverse water-gas shift.

14. A process for carrying out an equilibrium limited reaction comprising providing reactants to a reactor system according to claim 10, allowing reaction to occur, and recovering product.

15. The process according to claim 14 wherein the process is the oxidation of sulphur dioxide to sulphur trioxide, the manufacture of ammonia, the synthesis of methanol from carbon monoxide and hydrogen, the water-gas shift reaction, the reverse water-gas shift.

16. A process for carrying out an equilibrium limited reaction comprising providing reactants to a reactor system according to claim 11, allowing reaction to occur, and recovering product.

17. The process according to claim 16 wherein the process is the oxidation of sulphur dioxide to sulphur trioxide, the manufacture of ammonia, the synthesis of methanol from carbon monoxide and hydrogen, the water-gas shift reaction, the reverse water-gas shift.

Description

(1) The present invention will now be described, by way of example, with reference to the accompanying drawings in which:

(2) FIG. 1 is a chart illustrating the equilibrium constant dependence on temperature for the reaction of sulphur dioxide oxidation to sulphur trioxide in a conventional reaction;

(3) FIG. 2 is a graph illustrating a typical temperature profile for the oxidation of sulphur dioxide in a prior art process including intermediate cooling;

(4) FIG. 3 is a schematic representation of a prior art reactor system;

(5) FIG. 4 is a schematic representation of a reactor in accordance with the present invention;

(6) FIG. 5 is a perspective view of one example of a catalyst receptacle for use in the reactor of the present invention;

(7) FIG. 6 is a cross section of the catalyst receptacle of FIG. 5 viewed from the side;

(8) FIG. 7 is a perspective view of a second example of a catalyst receptacle for use in the reactor of the present invention;

(9) FIG. 8 is a perspective view of the catalyst receptacle of FIG. 7 viewed from below;

(10) FIG. 9 is a partial cross-section of the catalyst receptacle of FIG. 7 viewed from the side;

(11) FIG. 10 is a schematic representation of the catalyst receptacle of FIG. 7 in place in a tube illustrating the flow path;

(12) FIG. 11 is a schematic representation of a plurality of catalyst receptacle of FIG. 7 located in a reactor tube;

(13) FIG. 12 is an enlarged portion of part A of FIG. 11; and

(14) FIG. 13 is a graph illustrating the benefits of the present invention.

(15) It will be understood that the drawings are diagrammatic and that further items of equipment such as reflux drums, pumps, vacuum pumps, temperature sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks, and the like may be required in a commercial plant. The provision of such ancillary items of equipment forms no part of the present invention and is in accordance with conventional chemical engineering practice.

(16) One example of the reactor of the present invention is illustrated in FIG. 4. The reactor comprises a shell 30 having an inlet 31 for reactants and an outlet 32 for products. The reactor includes a plurality of tubes 33. Any number of tubes may be used. The number of tubes selected will determined by the production capacity of the plant. A commercial sized plant may comprise thousands of individual reactor tubes. For ease of illustration, 5 tubes have been illustrated. The reactor will include means for mounting the tubes in position but for simplicity these have been omitted from the drawing. Similarly means for distributing the reactants throughout the tubes and collection means in the bottom of the reactants to collect the products and allow them to be collected in the outlet 32.

(17) In use the tubes will be surrounded by a heat transfer fluid 35. Means for introducing and removing the fluid will generally be included but these have been omitted from the windows. Where the reaction to be carried out is an exothermic reaction, the heat transfer fluid will be a cooling fluid. Thus the heat transfer fluid may be any of those typically used including boiling water on the shell side raising high pressure, typically up to 100 bara, steam, heat transfer fluids such as Dowtherm or molten salt cooled reactors. Where the reaction is an endothermic reaction, the heat transfer fluid will be a heating fluid.

(18) Each tube 33 will include a plurality of catalyst carriers which for the purposes of this application will be referred to as receptacles 34. The stack of receptacles 34 in each tube 33 will include at least two different configurations.

(19) One example of a catalyst receptacle 34 which can be placed in the, or each, tube is illustrated in FIGS. 5 and 6.

(20) The receptacle 34 comprises an annular container 41 which has perforated inner and outer container walls 42, 43. The perforated wall 42 defines an inner channel 44. A top surface 45 closes the annular container at the top. It is located at a point towards the top of the inner and outer container walls 42, 43 of the annular container 41 such that a lip 46 is formed. A bottom surface 47 closes the bottom of the annular container 41 and a surface 48 closes the inner channel 44 formed by the inner container wall 42. The surface 48 is located in a higher plane that that of the bottom surface 47.

(21) A seal 49 extends from the upper surface 45 and an upstanding collar 50 is provided coaxial with the inner channel 44.

(22) A cap 51 closes the top of inner channel 44. Apertures 52 in the cap allow for fluid ingress.

(23) A carrier outer wall 53 surrounds the container 41. Apertures 55 allow fluid egress from the catalyst receptacle.

(24) The catalyst receptacle 34 is located in a reactor tube 54. The flow of gas is illustrated schematically in FIG. 6 by the arrows.

(25) Further details of this catalyst receptacle can be found in GB1417462.7 filed 2 Oct. 2015, the contents of which are incorporated by reference.

(26) One alternative catalyst receptacle is illustrated in FIGS. 7 to 9. This receptacle 34a comprises an annular container 41a which has perforated inner and outer container walls 42a, 43a. The perforated wall 42a defines an inner channel 44a. A top surface 45a closes the annular container 41a. It is located at a point towards the top of the inner and outer container walls 42a, 43a such that a lip 46a is formed. A bottom surface 47a closes the bottom of the annular container 41a and a surface 48a is located in a lower plane than that of the bottom surface 47a. Spacer means in the form of a plurality of depressions 56 are located on the bottom surface 47a of the annular container 42a. Drain holes 57 and 58 are located on the bottom surface 47a and the bottom surface 48a.

(27) A seal 49a extends from the upper surface 45a and an upstanding collar 59 is provided coaxial with the inner channel 44a. A corrugated upstanding skirt 53a surrounds the annular container 41a. The corrugations are flattened in the region L towards the base of the receptacle 34a.

(28) When the plurality of catalyst receptacles 34 of this arrangement are located within a reactor tube 54 as illustrated in FIG. 11 the interlock. The effect on the flow path is shown in FIGS. 6 and 7. Further details of the catalyst receptacle of this arrangement are illustrated in FIG. 12 and described in WO2011/048361, the contents of which are incorporated by reference.

(29) Whatever the arrangement of catalyst receptacle used, the present invention provides that along the length of the tube there will be at least two and usually more configurations of the catalyst receptacle itself and/or the catalyst located within the receptacle. In one arrangement, the length of the receptacle and hence the size of the annular container 41 or 41a containing catalyst will be increased. In a second arrangement, the thickness of the annular container 41 or 41a may be altered. This can be achieved by adjusting the position of the perforated inner 42, 42a and outer 43, 43a container walls. In a still further arrangement the radial size of the receptacle can be changed such that the size of the gap with the tube wall will alter at different points in the tube.

(30) It will be understood that whilst the catalyst receptacles have been described with particular reference to a use in a tube of circular cross-section the tube may be of non-circular cross-section for example, it may be a plate reactor. Where the tube is of non-circular cross-section, the receptaclewill be of the appropriate shape. In this arrangement, in the embodiment described in which an annular monolith is used it will be understood that the monolith will not be a circular ring and this term should be construed accordingly.

(31) The present invention will now be described by way of example with reference to the production of sulphur trioxide by the oxidation of sulphur dioxide.

Comparative Example 1

(32) In this example, the reactor tubes are loaded with identical catalyst receptacles. The selection of the design of the receptacle has to be a compromise between ensuring sufficient reaction takes place to achieve the desired conversion whilst ensuring that the discharge temperature from the tubular reactor is sufficiently low to meet the equilibrium temperature that determines the overall conversion of SO.sub.2 to SO.sub.2.

(33) In this example, a target conversion of 99.5% was selected. Since the equilibrium temperature to achieve this conversion is around 390° C., the gas discharging from the reactor must be at a lower temperature than this if the desired conversion is to be achieved.

(34) Based on this the following inlet conditions were set for the tubular reactor: Inlet temperature 420° C. Inlet pressure 1.4 bara Inlet SO.sub.2 concentration 11% vol SO.sub.2 conversion to SO.sub.3 99.5% Required catalyst volume 36 m.sup.3 Reactor Design Number of zones 1 (Each zone is defined as containing the same design of catalyst receptacle) Reactor diameter 7 m Tube Length 30 m (Due to limitations on overall tube length this is likely to require a minimum of 2 or possibly 3 reactors in series) Average deviation from MRL 90° C. (This is defined below) Max. deviation from MRL 120° C.

(35) As discussed above, for equilibrium limited reactions, it is possible to calculate the optimum reaction pathway that maximises the reaction rate as the conversion progresses. This is typically plotted as conversion versus temperature so as the conversion progresses the operating temperature that gives the maximum kinetic reaction rate can be read from such a chart (this is shown in FIG. 13 as a dashed line). This optimum temperature is known as the Maximum Rate Locus (MRL).

(36) There may be different means of characterising the efficiency of the reaction in terms of how well the catalyst is utilised. The maximum efficiency would be achieved if the reaction temperature through the reaction ideally matched the MRL. In reality there will always be some catalyst operating at temperatures above and below the MRL and this will represent an efficiency loss since the kinetic reaction rate per unit volume of catalyst will reduce the further away from the MRL that the catalyst is operated.

(37) For the catalyst receptacles there is an inlet temperature to each catalyst bed within the receptacle and an exit temperature, it is therefore necessary to adopt as a measure of catalyst utilisation efficiency the average of the absolute value of deviation of the inlet and exit temperature for each catalyst bed from the optimum temperature determined by the MRL.

(38) Thus, where a single design of catalyst receptacle is used throughout the reactor, the average deviation of the absolute values of the inlet/exit temperatures (on an absolute basis) from the optimum value relevant to the conversion at that point in the reactor is 90° C.

(39) As illustrated in FIG. 13, the diagonal lines which show the operating temperature versus the conversion could be +/−90° C. Again the maximum temperature for a given conversion will be limited by the equilibrium temperature and the difference between MRL and equilibrium temperature may be lower than 90° C., so depending on position in the reactor the temperature deviation may be +30° C./−120° C. for example.

Example 2

(40) Example 2 is similar to Comparative Example 1 except that the reactor contains several zones of catalyst receptacles, the design of receptacle in each zone is optimised to ensure that the temperature rise per catalyst bed and the temperature drop achieved during the heat transfer to the shell-side of the reactor are such that the catalyst volume required is optimised by ensuring that the catalyst operates as close to the optimum temperature as possible.

(41) The following inlet conditions were set for the tubular reactor:

(42) TABLE-US-00001 Inlet temperature 420° C. Inlet pressure 1.4 bara Inlet SO.sub.2 concentration 11% vol SO.sub.2 conversion to SO.sub.3 99.5% Required catalyst volume 19 m.sup.3 Reactor Design Number of zones 4 (Each zone is defined as containing the same design of catalyst receptacle) Reactor diameter 7 m Tube Length 7 m (This will be possible in a single tubular reactor) Average deviation from MRL  26° C. Max. deviation from MRL  80° C.

(43) It can therefore be seen how operating much closer to the MRL achieves greater utilisation of the catalyst and therefore reduces the required catalyst volume for a certain production volume.

(44) The table below details the design of catalyst receptacles in a tube used in Example 2

(45) TABLE-US-00002 Inlet Exit Zone 1 2 3 4 Catalyst 125 150 150 150 receptacle length (mm) Catalyst volume 10 20 40 100 (cm.sup.3) Number of cans 5 5 10 20 Annulus in 3 5 8 8 catalyst receptacles (for heat transfer) (mm)