REFORMING REACTOR COMPRISING REFORMER TUBES WITH ENLARGED OUTER SURFACE AREA AND STRUCTURED CATALYST

Abstract

A reforming reactor for an endothermic process including a plurality of reformer tubes allowing a flow of hydrocarbons and at least one further fluid inside the tubes is provided. Wherein the reformer tubes contain in their interior a catalyst for the conversion of the hydrocarbons and the at least one further fluid to synthesis gas, and a means for heating the reformer tubes. Wherein at least a portion of the plurality of reformer tubes is provided with one or more elements for enlarging the outer surface area of a reformer tube, and the catalyst includes a structured catalyst. Also an endothermic process for the production of synthesis gas, including allowing a flow of hydrocarbons and at least one further fluid inside a plurality of reformer tubes, and heating the plurality of reformer tubes to convert said hydrocarbons and the at least one further fluid to synthesis gas.

Claims

1.-23. (canceled)

24. A reforming reactor for an endothermic process, the reforming reactor comprising: a plurality of reformer tubes allowing a flow of hydrocarbons and at least one further fluid inside the tubes, wherein the reformer tubes contain in their interior a catalyst for the conversion of said hydrocarbons and said at least one further fluid to synthesis gas; means for heating the reformer tubes, wherein at least a portion of the plurality of reformer tubes is provided with one or more elements for enlarging the outer surface area of a reformer tube, and the catalyst comprises a structured catalyst.

25. The reforming reactor according to claim 24, wherein the reforming reactor is configured such that a normalized space velocity at an inlet of a reformer tube is from 1 Nm.sup.3/(s*m.sup.3) to 5 Nm.sup.3/(s*m.sup.3).

26. The reforming reactor according to claim 24, wherein the reforming reactor is configured such that a normalized space velocity at an inlet of a reformer tube is from 1.9 Nm.sup.3/(s*m.sup.3) to 3.2 Nm.sup.3/(s*m.sup.3).

27. The reforming reactor according to claim 24, wherein the means for heating the reformer tubes are burners, wherein the reformer tubes are arranged in rows within the reforming reactor, each row of reformer tubes thereby defining a reformer tube row, wherein the burners are arranged in rows within the reforming reactor, wherein a plurality of inner burners is arranged between and parallel to two reformer tube rows, thereby defining an inner burner row, and wherein a plurality of outer burners is arranged between and parallel to a reformer tube row and a reforming reactor wall, thereby defining an outer burner row.

28. The reforming reactor according to claim 27, wherein the elements for enlarging the outer surface area of a reformer tube are distributed heterogeneously along the circumference of a reformer tube, wherein the circumferential surface of a reformer tube has a first partial surface and a second partial surface, wherein the first partial surface corresponds to the surface with which reformer tubes within a reformer tube row face one another, and the second partial surface corresponds to the surface with which reformer tubes face a row of inner burners or a row of outer burners, and wherein the number of elements for enlarging the outer surface of a reformer tube arranged on the first partial surface is larger than the number of elements for enlarging the outer surface of a reformer tube arranged on the second partial surface.

29. The reforming reactor according to claim 24, wherein the structured catalyst is selected from the group consisting of monoliths, open cell foams, stacked wire meshes and structured packing.

30. The reforming reactor according to claim 24, wherein the structured catalyst comprises a supporting structure and a catalytic active species fixed to said supporting structure.

31. The reforming reactor according to claim 24, wherein a flowed-through area of the reformer tube comprises a circular cross-section or an annular cross-section.

32. The reforming reactor according to claim 24, wherein the structured catalyst comprises one type of structured catalyst or a plurality of structured catalysts within the same reformer tube.

33. The reforming reactor according to claim 24, wherein an element for enlarging the outer surface area of the reformer tube is made from the same material as the reformer tube.

34. The reforming reactor according to claim 24, wherein an element for enlarging the outer surface of the reformer tube is substance bonded to the material of the reformer tube.

35. The reforming reactor according to claim 24, wherein an element for enlarging the outer surface area of the reformer tube is selected from at least one element of the group consisting of fins, blades, rips, slats and lamellae.

36. The reforming reactor according to claim 35, wherein the element for enlarging the outer surface area of the reformer tube is a fin.

37. The reforming reactor according to claim 24, wherein an element for enlarging the outer surface area of the reformer tube extends in the longitudinal direction of the reformer tube.

38. The reforming reactor according to claim 24, wherein the number of elements for enlarging the outer surface area of the reformer tube is larger in the area of the inlet of the reformer tube than in the area of the outlet of the reformer tube.

39. The reforming reactor according to claim 24, wherein the number of elements for enlarging the outer surface area of the reformer tube on the circumference at any height along the reformer tube is comprised between 0 (zero) and 50.

40. The reforming reactor according to claim 24, wherein the heat flux from an outer part of the reformer tubes to an inner part of the reformer tubes is from 50 kW/m.sup.2 to 200 kW/m.sup.2 on average along the length of the tube.

41. The reforming reactor according to claim 24, wherein the reformer tube provided with one element or a plurality of elements for enlarging the outer surface area of said reformer tube comprises an outside surface area which is at least 10% to 60% higher than a comparable reformer tube without elements for enlarging the outer surface area.

42. An endothermic process for the production of synthesis gas, comprising: allowing a flow of hydrocarbons and at least one further fluid inside a plurality of reformer tubes, whereby the reformer tubes contain in their interior a catalyst for the conversion of said hydrocarbons and said at least one further fluid to synthesis gas; heating the plurality of reformer tubes to convert said hydrocarbons and said at least one further fluid to synthesis gas; wherein at least a portion of the plurality of reformer tubes is provided with one or more elements for enlarging the outer surface area of a reformer tube, and the catalyst comprises a structured catalyst.

43. The endothermic process according to claim 42, wherein a normalized space velocity at an inlet of a reformer tube is from 1 Nm.sup.3/(s*m.sup.3) to 5 Nm.sup.3/(s*m.sup.3).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0109] The invention will now be detailed by way of exemplary embodiments and examples with reference to the attached drawings. Unless otherwise stated, the drawings are not to scale. In the figures and the accompanying description, equivalent elements are each provided with the same reference marks.

[0110] In the drawings:

[0111] FIG. 1 depicts a reformer tube 100 equipped with one fin for enlarging the outer surface area of a reformer tube,

[0112] FIG. 2 depicts a reformer tube 200 with tube-in-tube configuration, comprising an outer tube and an inner tube,

[0113] FIG. 3 depicts a reformer tube 200 with tube-in-tube configuration, comprising an outer tube and an inner tube, wherein the inner tube comprises a rod,

[0114] FIG. 4 a top view of a section 400 of a reforming reactor, showing two reformer tubes of one reformer tube row and three burners of each burner row adjacent to the reformer tube row.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0115] FIG. 1 depicts a reformer tube 100 equipped with one fin for enlarging the outer surface area of a reformer tube. However, only one fin is shown for the sake of simplification. For most of the cases, the reformer tube 100 will be equipped with a plurality of fins.

[0116] The reformer tube 100 comprises a reformer tube 101 to which a fin 102 is attached by welding. Both the reformer tube and the fin are made of a refractory alloy, preferably the same refractory alloy. The reformer tube 100 is also equipped with a structured catalyst in its interior (not shown). The fin 102 has the shape of a plate with rectangular cross-sectional shape having a length (l), a width (w) and a thickness (t). The fin 102 extends in longitudinal direction over the entire length (l) of the reformer tube 101 to which it is attached. The reformer tube 100 is flown through from top to bottom by process gas (dotted arrow), which contains mainly methane as hydrocarbon component and steam as a further fluid. The reformer tube 100 is heated from the outside with burners (not shown). The process gas is converted to hydrogen and carbon monoxide (synthesis gas) at the structured catalyst (solid arrow). Carbon dioxide is usually produced as a by-product.

[0117] FIG. 2 depicts a longitudinal section of a reformer tube 200 with tube-in-tube configuration, comprising an outer tube 201, an inner tube 202 and fins 203 as elements for enlarging the outer surface of the outer reformer tube 201.

[0118] The reformer tube 200 as shown in FIG. 2 has a so-called tube-in-tube configuration, where this configuration is defined by an outer tube 201 and a tube 202 inside the outer tube. Between the wall of the outer tube 201 and the inner tube 202 is a structured catalyst (indicated by the hatched area). The inner tube 202 is free of catalyst, i.e. free to flow through. The flow to the reformer tube 200 is from below, whereby the process gas containing methane and steam first flows through the outer, catalyst-filled outer tube 201. The reformer tube 200 is heated from the outside with burners (not shown). Thereby, methane and steam are converted into synthesis gas at the catalyst arranged in the outer tube 201 of reformer tube 200. The reformer tube 200 is closed at the top, whereby the synthesis gas then inevitably flows through the inner tube 202 from top to bottom and exits the reformer tube 200 on the same side where the process gas enters the reformer tube. The synthesis gas flowing downwards heats the endothermic reaction taking place in the outer tube 201 and cools itself in the process.

[0119] The reformer tube 200 comprises a plurality of fins 203 as surface enlarging elements for the outer reformer tube 201. As a longitudinal section of reformer tube 200 is depicted in FIG. 2, only two of the plurality of fins are shown. The fins 203 are attached to outer reformer tube 201 by welding. The reformer outer tube 201, the reformer inner tube 202 and the fins 203 are made of a refractory alloy, preferably are made of the same refractory alloy. The fins 203 have the shape of a plate with rectangular cross-sectional shape having a length (l), a width (w) and a thickness (t). In terms of the thickness (t), the fins 203 extend perpendicular to the drawing plane of FIG. 2. The fins 203 extend in longitudinal direction over the entire length (l) of the outer reformer tube 201 to which they are attached.

[0120] FIG. 3 depicts a longitudinal section of a reformer tube 200 with tube-in-tube configuration, comprising an outer tube 201, an inner tube 202, fins 203 as elements for enlarging the outer surface of the outer reformer tube 201 and a rod 204 arranged within the inner tube 202. By the rod 204, the velocity of the reformed syngas in the inner tube is increased. Otherwise, the same explanations apply to FIG. 3 as to FIG. 2.

[0121] FIG. 4 depicts a top view of a section 400 of a reforming reactor (or reforming furnace), showing two reformer tubes 402a and 402b forming a part of a reformer tube row. Further depicted are three burners 401a, 401b and 401c, forming a part of an inner burner row and three burners 404a, 404b and 404c, forming a part of a further inner burner row. Each of the inner burner rows is adjacent to the reformer tube row. The reformer tubes 402a and 402b are each equipped with ten fins 403 and filled with structured catalyst (not shown).

[0122] In a reforming reactor, of which a section is shown in FIG. 4, the inner burner row with burners 401a, 401b and 401c, the inner burner row with burners 404a, 404b and 404c, and the reformer tube row with reformer tube 402a and 402b extend in the y-direction of the drawing plane. Reformer tube rows and inner or outer burner rows alternate in the x-direction of the drawing plane. Inner burner rows are arranged between two reformer tube rows and outer burner rows (not shown) are arranged between an outer wall of the reforming reactor and a reformer tube row. Due to this arrangement, one reformer tube row is always fired by the burners of two burner rows.

[0123] The fins 403 are distributed heterogeneously along the circumference of the reformer tubes 402a and 402b. The circumferential surface of the reformer tube 402a comprises a first partial (circumferential) surface 405 and a second partial (circumferential) surface 406. The first partial surface 405 is divided into two sub-surfaces (indicated by solid lines). The two sub-surfaces of the first partial surface 405 each face a neighbouring reformer tube (reformer tube 402b for the lower sub-surface and reformer tube not shown for the upper sub-surface). The second partial surface 406 is divided into two sub-surfaces (indicated by dotted lines). The two sub-surfaces of the second partial surface 406 each face a neighbouring burner tube row (the left sub-surface faces the inner burner row with burners 401a, 401b and 401c; the right sub-surface faces the inner burner row with burners 404a, 404b and 404c). Six fins 403 in total are arranged on the first partial surface 405, and only four fins in total are arranged on the second partial surface 406. So the number of fins arranged on the first partial surface, facing another reformer tube, is larger than the number of fins on the second partial surface, facing the burners of the inner burner rows.

[0124] The reformer tubes 402a and 402b see an increased temperature in particular on the side facing the burners, i.e. the second partial surface 406. In this area, the external heat transfer from the combustion zone of the reforming reactor to the outer wall surface of the reformer tubes 402a and 402b and the internal heat transfer from the inner wall surface of the reformer tubes 402a and 402b to the structured catalyst is favoured. As a consequence, a lower number of fins 403 is attached to the reformer tubes 402a and 402b in the areas facing the burners, i.e. the areas referred to as the second partial (circumferential) surface 406 of a reformer tube 402a or 402b. On the sides of a reformer tube 402a or 402b, where the reformer tubes face each other, referred to as the first partial (circumferential) surface 405, the aforementioned heat transfer is impaired, resulting in lower temperatures. To improve the heat transfer in those areas of the reformer tubes 402a and 402b, the number of fins 403 is larger there.

EXAMPLES

[0125] Further features and embodiments of the invention are described in the following examples. The examples do not represent a limitation of the claimed invention.

[0126] For the examples of tables 1a, 1b and 2 (single pass reformer tubes), a Catacel structured catalyst obtained from Johnson Matthey was used. The characteristics of the catalyst (pressure drop, heat transfer coefficient) were modelled in a proprietary reforming simulation environment based on supplier data and the results of test campaigns on steam methane reformers that were equipped with said catalyst.

[0127] For the examples of Table 3 (tube-in-tube reformer tubes), a ZoneFlow structured catalyst obtained from Zoneflow Reactor Technologies was used. The characteristics of this catalyst were again modelled in a proprietary reforming simulation environment based on supplier data and tests on pilot plants.

[0128] For the overall steam methane reforming (SMR) simulation, AspenPlus, a process simulation software package from aspentech, was used. The proprietary simulation tool mentioned above solved the mass, momentum and energy conservation equations in the combustion chamber and reforming tubes. It uses inputs from the global SMR simulation in AspenPlus, and its results are fed back to Aspen in an iterative process until the simulation has converged.

[0129] Fluent from ansys was used to model the impact of fins on the reformer tubes. A simplified model of the fins was inferred from the CFD simulations with Fluent, which was then integrated in the solver of the proprietary simulation tool.

[0130] The width (w) and thickness (t) of the fins was selected such that they would yield 90% of the heat flux (or heat transfer) gains that a fin with infinite width would produce.

[0131] The fins were not positioned in the 1.sup.st meter of length of a reformer tube after the inlet, to avoid damage from the burner flames.

[0132] The fins, extending in longitudinal direction of the reformer tubes, were disposed in such a way that there would be no shadowing effect from one fin to another, i.e. the minimal distance between two fins along the circumference of the tube was at least equal to the width of the fin.

[0133] The fins were distributed heterogeneously along the circumference, primarily in the region where the tubes face each other, which is where the tube wall temperature is the lowest (see FIG. 4), and away from the portion of the tubes facing the burners. As mentioned before, this setup provides a significant increase in heat flux while limiting the increase in the tube wall temperature, so that the tube thickness does not need to be increased, which would be detrimental to the costs and efficiency of the reformer.

[0134] In the following, the design of the fins is given for each of the tables.

[0135] Tables 1a, 1b and 2single pass tubeslow steam export (Table 1a and 1b) and high steam export (Table 2) [0136] Fins dimensions: [0137] 5 mm (t)20 mm (w)500 mm (l); [0138] Number of fins: [0139] 8 along circumference, disposed as 4 on each side facing another tube, with a spacing of at least 20 mm across the circumference between 2 fins, and 21 segments of 500 mm along length of tube (for a total of 10.5 m), with no fins in 1.sup.st meter after the inlet (to avoid damage from the burner flames); [0140] Tube inner diameter: [0141] 4 inch=101.6 mm, tube thickness 8.5 mm, external diameter=118.6 mm; [0142] Tube external surface=4.471 m.sup.2 [0143] Fins external surface per tube=810.5 m(20 mm+5 mm)=2.100 m.sup.2 [0144] Increase of external surface=47.0%

TABLE-US-00001 TABLE 1a Low steam export SMR - single pass tube configuration Comparative examples comp. comp. comp. comp. comp. comp. comp. example example example example example example example 1a 1b 1c 1d 1e 1f 1g Setup catalyst catalyst catalyst catalyst structured structured | structured pellets pellets + pellets + pellets + catalyst catalyst catalyst tubes tubes tubes with fins with fins with fins Maximum 921 921 921 921 921 921 921 tube wall temperature [ C.] Heat flux 98 99 118 137 99 118 138 [kW/m2] * Normalized 1.80 1.74 2.14 2.55 1.75 2.12 2.52 space velocity at SMR inlet [Nm3/s/m3] CH4 79.4 82.8 80.5 77.9 82.5 81.0 79.0 conversion [%]** Reformer 47.6 50.0 48.6 47.3 48.5 47.0 45.5 efficiency (%) No of tubes 100.0 100.0 83.3 71.4 100.0 83.3 71.4 in reformer*** Total NG 100.0 99.3 99.8 100.3 99.4 99.7 100.1 consumption (feed + fuel)*** pressure 2.45 2.37 3.43 4.72 2.37 3.40 4.65 drop [bar] reformer 19.4 21.1 14.2 10.0 20.5 13.8 9.8 efficiency/ pressure drop (KPI 1) reformer 47.6 50.0 58.3 66.2 48.5 56.4 63.7 efficiency/ no. of tubes (KPI 2) * Surface of fins not considered in calculation **in reformer only, pre-reformer not considered ***Reference case value normalized at 100
(Specifications equally applicable for tables 1b, 2 and 3)

TABLE-US-00002 TABLE 1b Low steam export SMR - single pass tube configuration Examples (invention) example 1a example 1b example 1c example 1d example 1e Setup tubes with tubes with tubes with tubes with tubes with fins + fins + fins + fins + fins + structured structured structured structured structured catalyst catalyst catalyst catalyst catalyst distribution of hetero- hetero- hetero- homo- hetero- fins geneous geneous geneous geneous geneous Maximum tube 921 921 921 921 921 wall temperature [ C.] Heat flux 122 142 163 157 106 [kW/m2] Normalized 2.01 2.39 2.82 2.95 1.66 space velocity at SMR inlet [Nm3/s/m3] CH4 conversion 87.3 85.4 83.1 77.9 88.73 [%] Reformer 49.8 48.5 47.1 46.3 51.0 efficiency (%) No of tubes in 83.3 71.4 61.9 61.9 100 reformer Total NG 98.5 99.3 99.4 100.3 98.2 consumption (feed + fuel) pressure drop 3.19 4.37 6.10 6.10 2.24 [bar] reformer 15.6 11.1 7.7 7.6 22.8 efficiency/ pressure drop (KPI 1) reformer 59.8 68.0 76.1 74.8 51.0 efficiency/no. of tubes (KPI 2)

TABLE-US-00003 TABLE 2 High steam export SMR - single pass tube configuration comparative examples examples comp. comp. comp. comp. (invention) example example example example example example 2a 2b 2c 2d 2a 2b Setup catalyst catalyst catalyst catalyst tubes tubes pellets pellets + pellets + pellets + with with tubes tubes tubes fins + fins + with fins with fins with fins structured structured catalyst catalyst Maximum 921 921 921 921 921 921 tube wall temperature [ C.] Heat flux 107 109 130 150 156 116 [kW/m.sup.2] Normalized 1.98 1.92 2.35 2.81 2.63 1.82 space velocity at SMR inlet [Nm.sup.3/(s*m.sup.3)] Methane 75.4 78.7 76.5 74.0 81.1 84.3 (CH.sub.4) conversion/% Reformer 45.4 48.0 46.7 45.4 46.6 49 efficiency/% Number of 100 100 83.3 71.4 71.4 100 tubes in reformer (normalized) Total NG 100 99.6 100.1 100.6 99.5 98.5 consumption (process gas and fuel gas) pressure 2.55 2.46 3.57 4.91 4.53 2.33 drop [bar] reformer 17.8 19.5 13.1 9.2 10.3 21.0 efficiency/ pressure drop (KPI 1) reformer 45.4 48.0 56.0 63.5 65.2 49.0 efficiency/no. of tubes (KPI 2)
Table 3tube-in-tube configuration of reformer tube

Examples 3a and 3b

[0145] Fins dimensions: [0146] 5 mm (t)20 mm (w)500 mm (l) [0147] Number of fins: [0148] 8 along circumference, disposed as 4 on each side facing another tube, with a spacing of at least 20 mm across the circumference between 2 fins, and 21 segments of 500 mm along length of tube (for a total of 10.5 m), with no fins in 1.sup.st 1 m after the inlet [0149] Tube inner diameter: [0150] 5 inch=127 mm, tube thickness 15.5 mm, external diameter=158 mm [0151] Tube external surface=5.956 m 2 [0152] Fins external surface per tube=810.5 m(20 mm+5 mm)=2.100 m.sup.2 [0153] Increase of external surface=35.3%

TABLE-US-00004 TABLE 3 Low steam export SMR - tube-in-tube configuration Comparative examples compara. compara. compara. compara. Invention example example example example example example 3a 3b 3c 3d 3a 3b Setup catalyst structured structured structured tubes tubes pellets catalyst catalyst catalyst with with fins + fins + structured structured catalyst catalyst Maximum tube 921 921 921 921 921 921 wall temperature [ C.] Heat flux [kW/m.sup.2] 66 68 101 132 102 137 Normalized space 1.09 1.02 1.61 2.34 1.55 2.14 velocity at SMR inlet [Nm.sup.3/(s*m.sup.3)] Methane (CH.sub.4) 79.3 85.5 80.3 76.3 82.7 80.8 conversion/% Reformer 59.2 60.8 57.2 52.7 59.8 56.7 efficiency/% Number of tubes 100.0 100.0 66.7 50.0 66.7 50.0 in reformer (normalized) Total natural gas 100.0 99.1 99.4 100.8 98.9 99.3 consumption (process gas and fuel gas) reformer 59.2 60.8 85.8 105.4 89.7 113.4 efficiency/No. of tubes (KPI 2)

[0154] For the sake of comparability, each individual case within the same simulation type (low steam export single pass; high steam export single pass; tube-in-tube configuration) was designed such that the same amount of hydrogen and export steam is produced. Furthermore, the simulations were carried out in such a way that the same maximum wall temperature of a reformer tube, in this case 921 C., is obtained for each case.

[0155] For all examples according to the invention (setup with structured catalyst and fin) a heterogeneous distribution of fins along the circumferential surface of a reformer tube is assumed, with the exception of example 1d. According to example 1d, the fins are uniformly or homogeneously distributed along the circumferential surface of a reformer tube.

[0156] Table 1a shows the results of the simulations for comparative examples according to the respective setup mentioned in the table (low steam export SMR; single pass tube configuration; catalyst pellets 1a; catalyst pellets and tubes with fins 1b-1d; structured catalyst without fins 1f+1g). All comparative examples involving fins used the advantageous heterogeneous distribution of the fins to limit the increase in maximum wall temperature.

[0157] Table 1b shows the results of the simulations for examples according to the invention and the respective setup mentioned in the table (low steam export SMR; single pass tube configuration; structured catalyst with fins 1a-1e, for 1d with homogeneous distribution of the fins, otherwise heterogeneous distribution).

[0158] Table 2 shows the results of the simulations for comparative examples and examples according to the invention and the respective setup mentioned in the table (high steam export SMR; single pass configuration; catalyst pellets comparative example 2a; catalyst pellets with tubes with fins comparative examples 2b-2d; structured catalyst and tubes with fins examples 2a+2b).

[0159] Table 3 shows the results of the simulations for comparative examples and examples according to the invention and the respective setup mentioned in the table (low steam export SMR; tube-in-tube configuration; catalyst pellets comparative example 3a; structured catalyst comparative examples 3b-3d; structured catalyst and tubes with fins examples 3a+3b).

[0160] The tables 1a, 1b, 2 and 3 show the synergistic effects of using a combination of a surface-enlarging element, such as fins, on the reformer tube and the simultaneous use of a structured catalyst. The non-inventive comparative examples show performance parameters of reformer tubes with either catalyst pellets and reformer tubes with or without fins, or with structured catalyst and reformer tubes without fins.

[0161] Tables 1a and 1b refer to a low steam export steam methane reforming case with single pass tube configuration (as shown in FIG. 1), for instance in Western Europe, with relatively expensive natural gas. Table 2 refers to a high steam export steam methane reforming case with single pass tube configuration, for instance on the US Gulf coast, with relatively inexpensive natural gas. Table 3 refers to a steam methane reforming case with tube-in-tube configuration (as shown in FIGS. 2 and 3) and low steam export. The process gas is first reformed in the outer tube, and the reformed gas then flows back through the inner tube and exchanges heat counter-currently with the feed gas. Therefore, the heat for the reactions comes from the combustion chamber of the steam reformer as well as the reformed gas flowing in the inner tube.

[0162] A setup with reformer tubes with surface-enlarging elements, such as fins, will yield a reformer efficiency comparable to that of a conventional design (without fins), albeit with fewer tubes, thereby generating capital investment (CAPEX) savings. However, various adverse effects are observed, as fins are added to the reformer tubes and the number of tubes is decreased. For a given reformer duty and fewer tubes, the maximum wall temperature increases, which may impact the lifetime of the reformer tubes. The mass flux per tube increases, with the consequence that the pressure drop and approach to equilibrium increase.

[0163] As external fins are added to reformer tubes with catalyst pellets (see comparative examples 1a and 1b; comparative examples 2a and 2b), the higher heat exchange surface leads to a higher reformer efficiency and lower natural gas consumption (comparative example 1 b; comparative example 2b). As the number of reformer tubes is decreased (comparative examples 1c and 1d; comparative examples 2c and 2d), the additional surface of the fins offsets the decrease in the number of tubes, with the consequence that the natural gas consumption stays largely unchanged relative to the reference comparative cases 1a and 2a. The smaller steam methane reformer, i.e. the steam methane reformer with fewer tubes, has a higher impact on the production price of Hydrogen in the scenario of Table 2 (US gulf coast), where natural gas is cheaper and the weight of capital investment in the price of Hydrogen is more pronounced.

[0164] In comparative cases 1c and 2c, the increase in maximum wall temperature must be addressed. One solution would consist in increasing the reformer tube wall thickness. In typical cost-efficient reformer designs, however, the maximum tube wall thickness has already been reached. The reforming temperature must then be reduced to avoid exceeding design limits on the maximum wall temperature, which in turn affects the thermodynamic equilibrium of the reforming reaction adversely and limits the reformer efficiency. As the number of tubes is further decreased (comparative examples 1d and 2d), the reforming temperature must be decreased further until the reformer efficiency falls beneath or is equal to that of the reference comparative examples 1a and 2a. The capital investment savings linked to a reformer with fewer tubes now need to be weighed against an increase in natural gas consumption.

[0165] For a given reformer size and number of tubes, a design with structured catalyst will yield a slight improvement in reformer efficiency over a conventional design with catalyst pellets.

[0166] As structured catalyst is substituted for conventional pellets (comparative example 1e; comparative example 3b), the reformer efficiency increases, with a corresponding reduction in natural gas consumption. Similarly to a design of reformer tubes with fins, however, the benefits of structured catalyst are maximized by reducing the number of tubes in the reformer and aiming for a reformer efficiency close to that of the conventional design, which results in capital savings (comparative example if; comparative example 3c). As the number of tubes is decreased, the maximum wall temperature increases. The reforming temperature must once again be decreased to avoid exceeding design limits on the maximum wall temperature, which affects the thermodynamic equilibrium of the reforming reaction adversely and leads to a higher consumption of natural gas. As the natural gas in the feed increases, so does the pressure drop. As the number of reformer tubes is decreased under a certain limit (comparative example 1g; comparative example 3d), the heat transfer benefits from the structured catalyst no longer compensate the loss in heat exchange surface from the reduction in number of tubes. The reformer efficiency decreases significantly, with the consequence that the natural gas consumption increases sharply and is now higher than for the reference comparative cases 1a and 3a. At the same time, the additional heat available in the flue gas of the reformer leads to higher steam production. If it is assumed that the steam export capacity is constrained by local requirements the steam-to-carbon ratio or some other plant parameter have to be modified compared to the reference comparative cases 1a and 3a. This leads to a further degradation of plant economics. The steam-to-carbon ratio is defined as the molar ratio of steam to carbon excluding carbon from carbon monoxide and carbon dioxide.

[0167] Enlarging the outer surface of reformer tubes, for example with fins, helps overcome the heat transfer resistance from the combustion chamber of a steam reforming furnace to the reformer tubes. Structured catalysts help to overcome the internal heat transfer resistance in the tube. The combination of both features thus enhances both the external and internal heat transfer coefficients.

[0168] However, the synergistic effects of structured catalysts and tubes with enlarged outer surface go further. As noted above, and evidenced by comparative examples 1d and 2d, as fins are added to the reformer tubes and the number of reformer tubes is decreased, the wall temperature increases, with the consequence that the reforming temperature has to be decreased and the reaction equilibrium is degraded. The addition of structured catalyst yields higher heat transfer coefficients from the tube wall to the reforming gases, thereby providing a larger heat sink and reducing the tube temperature. Furthermore, the higher geometric surface area (GSA) and lower pressure drop of the structured catalyst allows to operate at higher mass flux while maintaining a reasonable conversion and pressure drop (comparative examples 1 d and 2d). The normalized space velocity in Tables 1a to 3 is defined as the normalized volume flow rate at 0 C. (zero degree Celsius) and 1 atmosphere, divided by the total volume of the reformer tube, i.e. reactor, filled with catalyst and including the space used by the catalyst. The increase in convection encourages the heat transfer further, and the increased amount of reaction provides a surprisingly even larger heat sink, which allows to increase the reforming temperature and recover a high reformer efficiency (example 1a; example 2) or to decrease the number of tubes further (example 1b), depending on the relative weights of natural gas and capital investment.

[0169] Conversely, starting with a design involving structured catalyst, and by decreasing the number of reformer tubes beyond a certain limit (comparative examples 3c and 3d), the loss in heat exchange surface becomes predominant, leading to a degradation of the reformer efficiency, and a corresponding increase in natural gas consumption. The addition of surface-enlarging elements, such as fins, enhances the reformer efficiency, resulting in more natural gas savings (example 3a versus comparative example 3c; or example 3b versus comparative example 3d), or allowing for a further decrease in reformer size whilst maintaining the natural gas consumption (example 3b versus comparative example 3c), depending on the relative weights of natural gas and capital investment.

[0170] By increasing the heat flux between the combustion chamber of the reforming reactor and the tubes, the surface-enlarging elements, such as fins, allow for a decrease in the number of tubes without compromising on the reformer efficiency or increasing the firing duty. The structured catalyst enhances the internal heat transfer and limits the wall temperature increase linked to the higher heat flux from the fins, thereby enabling to increase the reforming temperature or reduce the number of tubes in the reformer further. The combination of both surface-enlarging elements, such as fins, and structured catalyst yields synergies, allowing for a more compact and efficient reforming reactor, i.e. reformer, than with either surface-enlarging elements, such as fins, or structured catalyst only.

[0171] The synergistic effect based on the combination of structured catalyst and the use of fins is also illustrated by the following fact. As described above, the performance of the reforming reactor can be very well described by two different key performance indicators. One is the quotient of the reformer efficiency and the pressure drop (hereinafter referred to as KPI 1) and the other is the quotient of the reformer efficiency and the number of reformer tubes in the reforming reactor (hereinafter referred to as KPI 2). If one compares the respective comparative examples with the examples according to the invention for the same number of reformer tubes in the reforming reactor, it can be seen that the two KPIs are higher in each case when a combination of structured catalyst and fins is used. For example, KPI 1 according to example 1a (number of tubes normalised 83.3) is 15.6, while KPI 1 according to comparative Example 1c (fins and catalyst pellets) is only 14.2 and according to comparative Example 1f (structured catalyst, no fins) is only 13.8. KPI 2 according to Example 1a is 59.8, while KPI 2 according to Comparative Example 1c (fins and catalyst pellets) is only 58.3 and according to Comparative Example 1f (structured catalyst, no fins) is only 56.4. The same observation results from the comparison of Example 1 b (number of tubes normalised 71.4) with KPI 1=11.1 and KPI 2=68.0 and Comparative Examples 1d with KPI 1=10.0 and KPI 2=66.2 and 1g with KPI 1=9.8 and KPI 2=63.7. This observation can be transferred to all other cases in tables 1a, 1b, 2 and 3 with the appropriate adjustments. In all cases, the combination of structured catalyst and fins with the same number of tubes results in a higher KPI 1 and KPI 2. The synergistic effect from the use of surface-enlarging elements and structured catalyst established according to the invention therefore enables the construction of more compact reforming reactors with a reduced number of reformer tubes with the same efficiency.

[0172] However, further unexpected effects can be derived from the data in the tables. In Table 1 b, only example 1e has a normalised space velocity below 2 Nm.sup.3/s/m.sup.3. In examples 1a to 1d, the normalised space velocities are in the range of approximately 2 to 3. KPI 1 is higher in example 1e than in examples 1a to 1d, but KPI 2 in example 1e is lower than in all examples 1a to 1d. This is because the high pressure drop according to examples 1a to 1d, which is reflected in KPI 1, is significantly overcompensated by a resulting higher KPI 2 due to the drastically reduced number of reformer tubes in examples 1a to 1d compared to example 1e. Also, most of the performance data in examples 1a to 1d (natural gas consumption, natural gas conversion, etc.) are comparable to the performance data of example 1e. Thus, it is surprisingly found that by setting comparatively high space velocities and simultaneously using structured catalyst and fins, the number of reformer tubes in the reforming reactor can be drastically reduced without any loss in the key performance data of the reforming reactor. The same observations can be made for the cases in Table 2. KPI 1 is lower in the case of example 2a (normalised space velocity above 2) than in the case of example 2b (normalised space velocity below 2). However, this effect is overcompensated by the significantly higher KPI 2 of example 2a, as the number of reformer tubes was reduced by 28.6% according to this example compared to example 2b. The same observation can be made with the corresponding adjustments for examples 3a and 3b of Table 3.

[0173] Another surprising effect can be derived from the comparison of examples 1c and 1d. The arrangement of the fins according to example 1c corresponds to a heterogeneous distribution as showed in and described for FIG. 4. The arrangement of the fins according to example 1d corresponds to a homogeneous distribution, whereby the number of fins corresponds to the number according to example 1c and the fins have the same surface area, but the distribution of the fins along the circumferential surface of the reformer tube is uniform with equal spacing between them. KPI 1 and KPI 2 are both higher for the same number of reformer tubes in examples 1c and 1d, but with heterogeneous arrangement of fins according to example 1c. The heterogeneous arrangement of the fins thus enables further optimisation of the reforming reactor with regard to its efficiency and the possibility of building the most compact reformers possible.

LIST OF REFERENCE SIGNS

[0174] 100 reformer tube with fins [0175] 101 reformer tube [0176] 102 fin [0177] 200 reformer tube with fins [0178] 201 outer reformer tube [0179] 202 inner reformer tube [0180] 203 fin [0181] 204 rod [0182] 400 section of reforming reactor [0183] 401a, 401b, 401c burner [0184] 402a, 402b reformer tube with fins [0185] 403 fin [0186] 404a, 404b, 404c burner [0187] 405 first partial (circumferential) surface [0188] 406 second partial (circumferential) surface

[0189] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.