Reforming reactor burner

Abstract

FIELD: burner for reforming reactor.SUBSTANCE: burner for a reforming reactor, in particular for a secondary reformer. Burner (1) for reforming process gas which includes an oxidizer pipe (4) located coaxially with an annular channel (5) of the process gas relative to the vertical axis (A-A) of the burner, wherein the oxidizer pipe extends beyond the end section (9) of the annular channel of the process gas and is a cylindrical pipe with an end nozzle (10) expanding to form a bell-shaped end wider than the pipe. The nozzle (10) of the oxidizer pipe (4) has an edge (16) with a wave-shaped profile with periodically alternating crests and valleys relative to the said axis, wherein the said wave-shaped profile has upper and lower sections relative to the vertical height.EFFECT: reduction of thermal stresses along the edge of the nozzle.13 cl, 3 dwg

Description

[0001] Technical field

[0002] The invention relates to a new design of a burner for a reforming reactor, in particular for a secondary reformer. Prior art

[0003] The reformer burner is used to introduce process gas and oxidizer into the combustion chamber. The process gas is a combustible gas, such as partially oxidized gas obtained in the preceding primary reforming stage. The oxidizer can be air, enriched air, or pure oxygen.

[0004] In a secondary reformer, the burner is mounted vertically at the top of the high-pressure vessel. The vessel contains a catalytic bed for the reforming reaction and a combustion chamber above the catalytic bed, where the process gas and oxidizer are combined and combustion occurs, resulting in the gas mixture reaching the temperature required for the catalytic reaction (e.g., approximately 1000-1200°C).

[0005] The burner is used to supply process gas and oxidizer into the combustion chamber, while premature contact between the two streams is prevented. EP 1680355, in particular, describes a burner in which an oxidizer tube is located coaxially within an annular process gas duct and has an expanded end section (nozzle) with a flared mouth. In a preferred embodiment, the oxidizer tube includes a swirler that imparts a swirling motion to the oxidizer upon its contact with the process gas around the nozzle.

[0007] The generally recognized advantages of this shape include good mixing of the oxidizer and process gas, the formation of a diffuse flame at the outlet of the oxidizer pipe, the absence of the possibility of backfire into the gas channel, and uniform distribution of feed across the catalytic layer.

[0008] A diffuse flame forms immediately behind the nozzle edge. The distance between the nozzle edge and the flame depends on the velocity of the two streams, the mixing rate, and the ignition delay time. Typically, in a secondary reformer burner, the distance between the flame and the burner edge is a few millimeters.

[0009] The nozzle flare edge reaches its maximum temperature and is subject to significant thermal stress. During normal thermal cycles in this type of equipment, thermal stress can lead to the formation of radial cracks and reduce the reliability and service life of the torch.

[0010] DE 2010 005022 discloses an oxidizer pipe nozzle having an edge with a wave-shaped profile in a plane perpendicular to the axis.

[0011] Disclosure of the essence of the invention

[0012] The invention is based on ongoing efforts to improve the burner design described above. Specifically, the invention aims to alleviate thermal stresses along the nozzle edge.

[0013] The Applicant found that, firstly, the distance between the flame and the edge is the primary factor determining the edge temperature. Furthermore, the invention is based on the unexpectedly strong influence of edge shape on the reduction of thermal stress. Specifically, the Applicant found that deviating the edge shape from the typical flat (circular) shape and imparting it a characteristic periodic curvature leads to a strikingly significant reduction in thermal stress.

[0014] Accordingly, the above-described problem is solved by a burner according to claim 1. Preferred features are set forth in the dependent claims. Other features of the invention include a gas reforming reactor and a reforming method according to the claims.

[0015] Disclosure of invention

[0016] The edge of the oxidizer tube's end nozzle has a wave-shaped profile with alternating crests and valleys in the axial direction of the burner. This direction is usually vertical, for example, when the burner is installed on top of a reforming reactor.

[0017] This profile lies on a surface parallel to the torch axis. This surface is preferably cylindrical. The line corresponding to the nozzle edge lies on this surface. Accordingly, the axial position of the edge point can vary according to the alternation of crests and troughs. In a vertical torch, this may refer to the upper and lower sections of the wave profile, where the terms "above" and "below" refer to the position relative to the vertical height.

[0018] In a preferred embodiment, the maximum amplitude of the edge wave profile is from 1 mm to 15 mm, preferably from 2 mm to 8 mm. The maximum amplitude is measured relative to a reference plane perpendicular to the axial direction of the torch. The number of edge waves in a preferred embodiment can be from 4 to 36, preferably from 6 to 24. The term "waves" refers to waves that form a full oscillation period, including a positive and negative plane relative to the reference plane.

[0019] The ratio of the number of edge waves to the diameter of the oxidizer pipe in millimeters is preferably from 0.016 / mm to 0.144 / mm, more preferably from 0.024 / mm to 0.096 / mm. In particular, when using a wider range of 0.016 / mm to 0.144 / mm and assuming a pipe diameter of 200 mm, the number of waves can range from 4 to 28. Typically, the pipe diameter is from 100 mm to 300 mm. The specified pipe diameter is the inner diameter of the cylindrical portion of the pipe.

[0020] Similarly, the maximum wave amplitude can be determined as a function of the oxidizer tube diameter. In a preferred embodiment, the ratio of the maximum amplitude of the wave-shaped edge profile relative to the reference plane perpendicular to the axial direction of the burner to the oxidizer tube diameter is from 0.004 to 0.06, preferably from 0.008 to 0.032.

[0021] The wavy edge profile may be any profile that can be mathematically represented by a periodic function, in particular a sinusoid, a symmetrically or antisymmetrically repeating polynomial function, a symmetrically or antisymmetrically repeating shape, or a combination thereof. If the wavy profile is formed by a polynomial function, this function must be symmetrically or antisymmetrically repeating to ensure periodicity. In a preferred embodiment, the edge has a sinusoidal profile, where the term "sinusoidal" means a profile that can be described by a sinusoidal function.

[0022] A highly preferred embodiment includes a swirler in the oxidizer tube upstream of the nozzle. The swirler is adapted to impart rotation to the oxidizer flow around the axis of the oxidizer tube, which is located vertically in the preferred embodiment. Upon exiting the oxidizer tube, the flow diverges radially, following the flared profile of the nozzle.

[0023] The oxidizer tube, or at least a portion thereof, in particular the nozzle, is preferably manufactured using 3D printing, such as additive manufacturing. The advantage of 3D printing is that it eliminates internal stress in the material.

[0024] An application of particular interest concerns the secondary reforming of partially oxidized gas previously obtained in the primary reforming stage. This can be implemented, for example, in the reforming of hydrocarbon feedstock to produce hydrogen-containing gas, particularly makeup gas for ammonia synthesis. The primary reforming stage can be performed in a fired furnace (primary reformer) or, in some embodiments, in a gas-fired reformer (GFR).

[0025] Another feature of the invention is a reactor for reforming process gas, comprising a combustion chamber and a burner installed above the combustion chamber, in which:

[0026] The burner includes an oxidizer tube located coaxially inside the annular channel of the process gas;

[0027] The burner is positioned vertically so that the oxidizer pipe and the annular channel are positioned vertically;

[0028] The oxidizer tube projects below the end section of the annular channel into the combustion chamber below;

[0029] The oxidizer tube is a cylindrical tube with an expanding end section that forms a socket wider than the tube;

[0030] wherein the edge of the end section of the oxidizer pipe has a wave-shaped profile with alternating ridges and valleys in the axial direction.

[0031] The embodiments of the burner described above are also applicable to the reactor according to the invention.

[0032] Preferably, the reactor according to the invention is a secondary reformer comprising a catalytic bed below the combustion chamber.

[0033] Another feature of the invention is a method for reforming hydrocarbon feedstock to produce a hydrogen-containing gas, in particular makeup gas, for example, a method comprising a step of primary reforming of the feedstock in the presence of steam, to produce a primary reforming effluent, and a step of secondary reforming this effluent in the presence of an oxidizing agent, when the secondary reforming is carried out in a reactor according to the above description.

[0034] Without being bound by theory, the applicant has found that the inventive design allows the flame to be maintained at a greater distance from the edge of the nozzle flare. A wave-shaped profile, particularly a sinusoidal one, can be defined relative to a plane representing the "zero position" of a conventional profile. Relative to this plane, the inventive profile can have a maximum amplitude of 2⋅d, where d is the wave amplitude, representing the vertical distance from this plane to the highest points of the crests and the lowest points of the troughs (or "depressions").

[0035] The number of waves around the edge circumference can also vary in different embodiments.

[0036] The wave profile according to the invention moves the flame away from the nozzle edge. The displacement is on the order of a few millimeters, which may seem insignificant, but it is comparable to the typical distance between the flame and the edge, and therefore has a significant impact on the temperature field. Importantly, the observed synergistic interaction between the wave profile and the creation of a vortex motion in the oxidizer flow, for example, by means of a swirler installed in the oxidizer tube, is also observed.

[0037] An additional factor contributing to the reduction in maximum temperature (and, therefore, thermal stress) is that the lowest parts (troughs or depressions) of the wave curve face the region of maximum oxygen flow velocity, compared to the highest parts (crests). Accordingly, cooling of the lower parts of the edge, which may be closer to the flame, is improved.

[0038] Another advantage is the increased elasticity of the edge due to the wave shape, which accordingly reduces thermal stress.

[0039] In short, the wave-shaped profile of the invention unexpectedly offers several advantages as a result of the combined positive effects: the flame is formed at a greater distance from the nozzle edge; certain parts of the nozzle are better cooled by the oxidizer flow; and the elasticity of the nozzle edge and its response to stress are improved. A particularly preferred embodiment is the combination with a swirler in the oxidizer channel, where the swirling motion of the oxidizer flow enhances the above-described advantages.

[0040] Description of drawings

[0041] The invention is discussed in more detail below with reference to the accompanying drawings, in which:

[0042] Fig. 1 shows a schematic section of a secondary reformer equipped with a burner in accordance with the invention;

[0043] Fig. 2 shows the nozzle of the burner oxidizer pipe;

[0044] Fig. 3 shows another image of the nozzle profile.

[0045] Fig. 1 illustrates the following main elements:

[0046] 1. Burner;

[0047] 2. Combustion chamber;

[0048] 3. Secondary reforming catalyst;

[0049] 4. Oxidizer pipe;

[0050] 5. Annular process gas channel;

[0051] 6. Gas distributor;

[0052] 7. Gas inlet pipe;

[0053] 8. swirler;

[0054] 9. End section of annular channel 5;

[0055] 10. Oxidizer pipe nozzle 4;

[0056] 11. Burner flame (diffuse flame);

[0057] 12. Process gas flow;

[0058] 13. Oxidizer flow;

[0059] 14. Wall of the upper part of combustion chamber 2.

[0060] Fig. 1 shows a reactor R with a burner 1 installed therein. Process gas 12 and oxidizer 13 are fed into the reactor. By means of the burner 1, the process gas and oxidizer 13 are combined in the combustion chamber 2, and as a result of combustion, the gas temperature rises to the catalytic reaction temperature in zone 3 of the catalyst.

[0061] Process gas 12 may be the effluent from a primary reformer, such as a fired furnace. Process gas 12 may be obtained by steam reforming a hydrocarbon, particularly methane. Oxidizer 13 may be air, enriched air, or oxygen generated by an air separation unit.

[0062] The process gas 12 and the oxidizer 13 reach the combustion chamber 2 through the vertical pipe 4 and the annular channel 5 around the pipe 4. The pipe 4 and the channel 5 are separated so that the oxidizer and gas cannot mix inside the burner 1 until they enter the combustion chamber 2.

[0063] At the end of section 9, the process gas enters the upper zone of combustion chamber 2. Preferably, the upper zone has a conical wall diverging toward the underlying catalytic layer, as shown in the drawing.

[0064] At the outlet of channel 5, process gas 12 can meet with oxidizer 13. Pipe 4 passes below end section 9 (i.e., into combustion chamber 2) so that oxidizer nozzle 10 is located below end section 9. Here, diffuse flame 11 is formed. Recirculation flow is also created, but the location of nozzle 10 prevents backfire into channel 5.

[0065] The oxidizer flow exiting pipe 4 has a vortex character caused by swirler 8. Nozzle 10 expands radially outward toward wall 14, forming a bell-shaped end / crown 15 (Fig. 2), from which the vortex flow diverges radially, mixing with the gas. Accordingly, the diameter of the outlet end section of nozzle 10 is larger (i.e., lies on a larger circumference) than the diameter of pipe 4.

[0066] Next, Fig. 2 shows that the edge 16 of the pipe 4 has a sinusoidal profile with several waves 17, each of which has a crest 18 and a trough 19 in the direction of the axis A-A, which runs vertically, since the pipe 4 is installed vertically in the reformer R above the combustion chamber 2.

[0067] Fig. 3 shows a sinusoidal profile of the edge 16 relative to the reference plane 20. This plane 20 denotes the position of a flat edge (circular edge) according to the prior art. The figure shows the deviation of the sinusoidal edge 16 proposed in the invention from a conventional flat edge, along the vertical coordinate Z (positive direction - upward). In particular, Fig. 3 shows that the ridges 18 are located above the plane 20 at the Z-coordinate +d, while the troughs 19 are located below the plane 20 at the Z-coordinate -d. The ridges 18 can be considered as the "peaks" of the edge 16, and the troughs 19 as the "minima".

[0068] Figure 2 also shows the diameter D of the pipe 4, which can serve as a reference dimension for determining the number and / or amplitude of the waves 17 in accordance with some embodiments. This diameter D is the inner diameter of the cylindrical portion of the pipe 4, in front of the flared bell at the end.

[0069] Each wave 17 in edge 16 can be considered to include a positive portion of the wave cycle above reference plane 20 and a negative portion of the wave cycle below that plane.

[0070] The ridges 18 are somewhat further removed from the flame 11 (which generates thermal stresses primarily through radiation), while the valleys 19 are somewhat closer to the flame but benefit from better cooling due to the higher flow velocity. As a result, the sinusoidal edge 16 is less susceptible to stress than a flat edge under the same conditions.

[0071] The figures show that the wave-shaped profile of the edge 16 lies on a cylindrical surface parallel to the vertical axis A-A of the burner 1. This wave-shaped profile is located vertically in the direction of the coordinate axis Z.

[0072] Gas dynamic calculations showed a reduction in the maximum edge temperature by approximately 10°C and a reduction in maximum thermal stresses by approximately 40% to 70% of the original level.

[0073] The figures show a sinusoidal edge 16, however, generally speaking, other periodic profiles can be used within the scope of the invention.

Claims

1. A burner (1) for reforming a process gas, including an oxidizer pipe (4) located coaxially with an annular channel (5) of the process gas relative to the vertical axis (A-A) of the burner, wherein the oxidizer pipe extends beyond the end section (9) of the annular channel of the process gas and is a cylindrical pipe with an end nozzle (10) expanding to form a bell-shaped end that is wider than the pipe; characterized in that the nozzle (10) of the oxidizer pipe (4) has an edge (16) with a wave-shaped profile with periodically alternating crests and valleys relative to the said axis, wherein said wave-shaped profile has upper and lower sections relative to the vertical height.

2. The burner according to claim 1, in which the ratio of the maximum amplitude of the wave-shaped edge profile relative to the reference plane (20), perpendicular to the axial direction of the burner, to the diameter of the oxidizer tube in millimetres is from 0.004 to 0.06, preferably from 0.008 to 0.

032.

3. A burner according to claim 1 or 2, wherein the ratio of the number of edge waves to the diameter of the oxidizer tube in millimetres is from 0.016 / mm to 0.144 / mm, preferably from 0.024 / mm to 0.096 / mm.

4. A torch according to any one of the preceding claims, wherein the wave-like edge profile can be represented mathematically by a periodic function, such as any of: a sine function; a symmetrically or antisymmetrically repeating polynomial function; a symmetrically or antisymmetrically repeating shape; or a combination thereof.

5. The burner according to claim 1, wherein the edge has a sinusoidal profile.

6. The burner according to claim 5, wherein the amplitude of the sinusoidal profile is from 1 to 6 mm, and the period is from 4 to 24 waves.

7. A burner according to any of the preceding paragraphs, including a swirler (8) located in the oxidizer tube in front of the nozzle.

8. A burner according to any of the preceding claims, wherein at least the nozzle of the oxidizer tube is made by 3D printing, preferably by additive manufacturing technology.

9. Reactor (R) for reforming the supplied gas (12), including: combustion chamber (2); a burner (1) according to any one of paragraphs 1-8, wherein the burner (1) is installed above the combustion chamber (2) so that the oxidizer pipe (4) and the annular channel (5) of the process gas are located vertically, and the oxidizer pipe (4) protrudes below the end section (9) of the annular channel of the process gas, passing into the combustion chamber.

10. A reactor according to item 9, adapted for secondary reforming of process gas obtained after primary reforming of hydrocarbon feedstock with steam.

11. A method for reforming hydrocarbon feedstock to produce hydrogen-containing gas, comprising a stage of primary reforming of the feedstock in the presence of steam to produce a primary reforming effluent, and a stage of secondary reforming of this effluent in the presence of an oxidizing agent, wherein the secondary reforming is carried out in a reactor according to paragraph 9 or 10.

12. The method according to claim 11, wherein a diffuse flame is formed at the end of the oxidizer pipe where the oxidizer is combined with the process gas.

13. The method according to claim 11 or 12, wherein the oxidizer is any gas from air, oxygen-enriched air and oxygen.

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