Burner for reforming reactor

Abstract

A burner (1) for a reforming reactor comprising an oxidant tube (4) coaxially arranged within an annular process gas channel (5) wherein a nozzle (10) has a trumpet-shaped shape and a lip (16) of the nozzle has a waveform or sinusoidal profile.

Description

Technical Field

[0001] The present invention relates to a new design of burners for reforming reactors, in particular for secondary reformers. Background Art

[0002] The burner for the reforming reactor is designed to introduce process gas and oxidant into the combustion chamber. The process gas is a combustible gas such as, for example, partially oxidized gas produced by a previous primary reforming step. The oxidant can be air, enriched air or pure oxygen.

[0003] In a two-stage reformer, for example, the burner is mounted vertically on top of a pressure vessel. The vessel contains a catalytic bed for the reforming reaction and a combustion chamber above the catalytic bed, wherein the process gas and oxidant contact so that combustion occurs and the gas mixture reaches the desired temperature for the catalytic reaction (e.g., about 1000-1200°C).

[0004] The burner is designed to supply process gas and oxidant to the combustion chamber, thereby avoiding premature contact between the two streams.

[0005] For example, EP 1680355 describes a burner having an oxidant tube coaxially arranged in an annular channel for process gas, wherein the oxidant tube has an enlarged end section (nozzle) of trumpet-like shape. In a preferred embodiment, the oxidant tube comprises a swirler so that the oxidant has a swirling motion when contacting the process gas around the nozzle.

[0006] Recognized advantages of this shape include good mixing between oxidant and process gas, formation of a stable diffusion flame at the outlet of the oxidant tube, avoidance of flashback in the gas channels, uniform feed to the catalytic bed.

[0007] The diffusion flame forms just downstream of the trumpet-shaped nozzle edge. The distance between the sharp edge of the nozzle and the flame depends on the speed of the two streams, the mixing speed and the ignition delay time. Typically, in the burners of the secondary reformer, the distance between the flame and the burner tip is in the order of millimeters.

[0008] The lip of the trumpet nozzle reaches the highest temperature and is subject to considerable thermal stresses. For typical thermal cycles of such equipment, thermal stresses can lead to the formation of radial cracks and reduce the reliability and life of the combustor.

[0009] DE 202010005022 discloses a nozzle for an oxidant tube having a lip with a corrugated profile, wherein the corrugated profile lies in a plane perpendicular to the axis. Summary of the invention

[0010] The present invention results from a continuing effort to improve the above-mentioned design of burners. In particular, the present invention aims to solve the problem of how to relieve the thermal stresses on the lip (circumferential edge) of the nozzle.

[0011] First, applicants have recognized that the distance between the flame and the lip is a key parameter in controlling the temperature of the lip. Furthermore, the present invention is based on the very unexpected discovery that a modified shape of the lip is effective in reducing thermal stresses. In particular, applicants have discovered that the deviation of the lip from a traditional flat (circular) configuration to a generally periodic curve results in a surprisingly significant reduction in thermal stresses.

[0012] The above problem is therefore solved by a burner according to claim 1. Preferred features are described in the dependent claims. Further aspects of the invention are a reactor for reforming gas and a reforming method according to the claims.

[0013] The lip of the end nozzle of the oxidant tube has a corrugated profile with a series of peaks and troughs in the axial direction of the burner. Said direction is usually the vertical direction, for example when the burner is mounted on top of a reforming reactor.

[0014] The wave profile is located in a surface parallel to the burner axis. The surface is preferably a cylindrical surface. The line corresponding to the lip of the nozzle is located in the above-mentioned surface. Therefore, the axial position of the point of the lip can vary according to the continuity of the peaks and troughs. In vertically mounted burners, reference can be made to the higher and lower parts of the wave profile, wherein the terms "higher" and "lower" refer to the vertical height.

[0015] In a preferred embodiment, the peak amplitude of the wave profile of the lip is 1 mm to 15 mm, preferably 2 mm to 8 mm.The peak amplitude is measured relative to a reference plane perpendicular to said axial direction of the burner.

[0016] In a preferred embodiment, the number of waveforms of the lip may be 4 to 36, preferably 6 to 24. The term waveform denotes a waveform along a full period, thus comprising positive and negative planes according to a reference plane.

[0017] Preferably, the number of waves of the lip is 0.016 / mm to 0.144 / mm, more preferably 0.024 / mm to 0.096 / mm, relative to the diameter (mm) of the oxidant tube. For example, by applying the wider range of 0.016 / mm to 0.144 / mm above and assuming that the tube has a diameter of 200 mm, the number of waves may range between 4 and 28. Typically, the diameter of the tube is 100 mm to 300 mm. The diameter of the tube is the inner diameter of the cylindrical portion of the tube.

[0018] Similarly, the peak amplitude of the waveform can be determined based on the diameter of the oxidizer tube. A preferred embodiment provides that, relative to a reference plane perpendicular to the axial direction of the burner, the peak amplitude of the waveform profile of the lip is 0.004 to 0.06, preferably 0.008 to 0.032 relative to the diameter of the oxidizer tube.

[0019] The wavy profile of the lip can be any profile that can be mathematically represented by a periodic function, such as a sine function, a polynomial function that repeats symmetrically or antisymmetrically, any one of a symmetrical or antisymmetrical repetition of a shape, or a combination thereof. If a polynomial function is used to construct the wavy profile, the function must repeat symmetrically or antisymmetrically to provide periodicity. In a preferred embodiment, the lip has a sinusoidal profile, wherein the term sinusoidal refers to a profile that can be represented by a sine function.

[0020] A highly preferred embodiment comprises a swirler in the oxidant tube upstream of the nozzle. The swirler is adapted to rotate the oxidant flow around the axis of the oxidant tube, which in a preferred arrangement is a vertical axis. Upon discharge from the oxidant tube, the flow opens radially along the widening (trumpet-shaped) profile of the nozzle.

[0021] The oxidant tube or at least a portion thereof (such as a nozzle, etc.) is preferably made by 3D printing (eg by additive manufacturing). Manufacturing using 3D printing has the advantage of not generating internal stresses in the material.

[0022] An application of particular interest relates to the secondary reforming of partially oxidized gases previously produced in a primary reforming step. This can be carried out, for example, in the case of reforming a hydrocarbon feedstock for the production of a hydrogen-containing gas, such as a make-up gas for ammonia synthesis, etc. The primary reforming step can be carried out in a combustion furnace (primary reformer) or, in some embodiments, in a gas heated reformer (GHR).

[0023] Another aspect of the present invention is a reactor for reforming process gas, the reactor comprising a combustion chamber and a burner mounted above the combustion chamber, wherein:

[0024] The burner includes an oxidant tube coaxially arranged within the process gas annular passage;

[0025] The burner is arranged vertically so that the oxidant tube and the annular channel are vertical;

[0026] An oxidant tube extends below the end section of the annular passage and into the combustion chamber below;

[0027] The oxidant tube is a cylindrical tube in which the end section widens to a tip that is larger than the tube, thereby having a trumpet-like shape;

[0028] Therein, the lip edge of the end section of the oxidant tube has a wave profile having a series of peaks and troughs in the axial direction.

[0029] The embodiments of the burner described above are also applicable to the reactor of the present invention.

[0030] Preferably, the reactor of the present invention is a secondary reformer comprising a catalytic bed below the combustion chamber.

[0031] Yet another aspect of the present invention is a process for reforming a hydrocarbon feedstock to produce a hydrogen-containing gas such as an ammonia make-up gas, for example, the process comprising the steps of primary reforming the feedstock in the presence of steam to obtain a primary reforming effluent and the step of secondary reforming the effluent in the presence of an oxidant, wherein the secondary reforming is carried out in a reactor as described above.

[0032] Without being limited by theory, applicants have found that the design of the present invention is able to maintain the flame at a greater distance from the lip of the trumpet-shaped nozzle. The waveform profile, such as a sinusoidal profile, can be described with reference to a plane identifying the "position zero" of a conventional profile. From this plane, the profile of the present invention can have a peak amplitude of 2*d, where d is the amplitude of the wave, i.e., the vertical distance of the highest peak point and the lower peak point (or "trough") from the plane.

[0033] The number of undulations on the circumference of the lip may also vary depending on the embodiment.

[0034] The wave profile of the present invention shifts the position of the flame away from the lip of the nozzle. This shift is in the order of a few millimeters, which may seem small, but it is comparable to the typical distance between the flame and the lip, and the effect on the temperature field is significant. Interestingly, it has been found that the wave profile is particularly synergistic with the provision of a swirling motion of the oxidant flow, for example by means of a swirler installed in the oxidant tube.

[0035] An additional effect that helps reduce the maximum temperature (and therefore thermal stress) is that the lowest parts of the wave profile curve (toughs or valleys) are exposed to areas of higher velocity of the oxidant stream than the highest parts (peaks). Therefore, the lowest part of the lip (which may be closer to the flame) benefits from enhanced cooling.

[0036] Yet another advantage is that the corrugated shape increases the elasticity of the lip, which in turn reduces thermally induced stresses.

[0037] In summary, in a very unexpected manner, the wave profile of the invention benefits from the positive effects of the following combination: the flame is formed at a greater distance from the lip of the nozzle; certain parts of the nozzle receive better cooling from the oxidant flow; the elasticity of the lip and its behavior under stress are improved. A particularly preferred embodiment is the combination with a swirler located in the oxidant channel, wherein the swirling motion of the oxidant flow enhances the above advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention will now be explained with the aid of the accompanying drawings, in which:

[0039] Figure 1 is a schematic cross section of a secondary reformer equipped with a burner according to the invention.

[0040] Figure 2 The nozzle of the oxidizer tube of the burner is shown.

[0041] Figure 3 The outline of the nozzle is further illustrated.

[0042] Figure 1 The following key features are illustrated:

[0043] 1 Burner

[0044] 2 Combustion chamber

[0045] 3 Catalysts for secondary reforming

[0046] 4 Oxidant tube

[0047] 5. Process gas annular channel

[0048] 6 Gas distributor

[0049] 7 Gas inlet pipe

[0050] 8. Cyclone

[0051] 9 End section of the annular channel 5

[0052] 10 Nozzle of oxidant tube 4

[0053] 11 Burning flame (diffusion flame)

[0054] 12 Process gas flow

[0055] 13 Oxidant Flow

[0056] 14 Wall of the upper part of the combustion chamber 2 DETAILED DESCRIPTION

[0057] Figure 1A reactor R equipped with a burner 1 is shown. The reactor receives a process gas 12 and an oxidant 13. With the help of the burner 1, the process gas and the oxidant 12 are contacted in the combustion chamber 2 so that combustion brings the gas to a suitable temperature for the subsequent catalytic reaction in the catalyst zone 3.

[0058] The process gas 12 may be the effluent of a primary reformer, such as a combustion furnace. The process gas 12 may be produced by steam reforming of hydrocarbons, such as methane, etc. The oxidant 13 may be air, enriched air or oxygen provided by an air separation unit.

[0059] Process gas 12 and oxidant stream 13 reach combustion chamber 2 via vertical tubes 4 and annular channels 5 surrounding said tubes 4. Tubes 4 and channels 5 are spaced apart so that oxidant and gas cannot mix inside burner 1 and before they enter combustion chamber 2.

[0060] At the end section 9, the process gas 12 enters the upper region of the combustion chamber 2. Preferably, the upper region has conical walls diverging towards the catalyst bed below, as shown.

[0061] When leaving the channel 5, the gas 12 may come into contact with the oxidant 13. The tube 4 extends below the end section 9 (i.e. inside the combustion chamber 2), so that the oxidant nozzle 10 is actually below the end section 9. Here, a diffusion flame 11 is formed. A recirculation flow is also generated, but the position of the nozzle 10 avoids flashback in the channel 5.

[0062] The oxidant flow leaving the tube 4 has a swirling motion caused by the swirler 8. The nozzle 10 widens radially towards the wall 14, thereby forming a flared tip 15 ( Figure 2 ), the swirling flow radially protrudes from the top end 15 to mix with the gas. Therefore, the outlet end section of the nozzle 10 is larger than (ie, located on a larger diameter) the diameter of the tube 4.

[0063] Still reference Figure 2 The lip 16 of the tube 4 has a sinusoidal curve with a plurality of waveforms 17 , each waveform 17 having a peak 18 and a trough 19 in the direction of the axis AA, which is the vertical direction when the tube 4 is vertically installed in the reformer R above the combustion chamber 2 .

[0064] Figure 3 The diagram shows the sinusoidal curve of the lip 16 relative to a reference plane 20. The plane 20 represents the position of a planar lip (circumferential lip) according to the prior art. The diagram shows the deviation of the sinusoidal lip 16 of the invention from a conventional planar lip according to the vertical coordinate Z (positive upward). In particular, Figure 3It is illustrated that the peak 18 is located at a Z coordinate of +d on the plane 20, while the trough 19 is located at a Z coordinate of -d on the plane 20. The peak 18 may be considered the "highest level" of the lip 16, while the trough 19 is the "lowest level".

[0065] Figure 3 Also illustrated is the diameter D of the tube 4, which according to some embodiments may be a reference for determining the number and / or amplitude of the waveforms 17. The diameter D is the inner diameter of the cylindrical portion of the tube 4 before the flared end.

[0066] Each waveform 17 in the lip 16 may be considered to include a positive period above a reference plane 20 and a negative period below said plane.

[0067] The crest 18 is slightly further away from the flame 11 (which causes thermal stress mainly by radiation); the trough 19 is slightly closer to the flame, but takes advantage of better cooling due to the higher flow rate. In summary, under the same conditions, the sinusoidal lip 16 has less stress than the flat lip.

[0068] These figures illustrate that the wavy profile of the lip 16 is located in a cylindrical surface parallel to the vertical axis AA of the burner 1. The wavy profile is arranged vertically according to a reference direction Z.

[0069] CFD calculations have revealed that the maximum temperature of the lip is reduced by about 10°C and the maximum thermal stress is reduced to about 40% to 70% of the original value.

[0070] These figures illustrate a sinusoidal lip 16, but more generally other periodic profiles may be used within the scope of the invention.

Claims

1. A burner (1) for reforming a process gas, the burner comprising an oxidant tube (4) which is arranged coaxially with respect to an axis (AA) of the burner in a process gas annular channel (5), wherein: The oxidant tube extends further relative to the end section (9) of the process gas annular passage, and the oxidant tube is a cylindrical tube having an end nozzle (10) which widens to form a larger top end than the tube, thereby having a trumpet-like shape; Characterized in that the nozzle (10) of the oxidant tube (4) has a lip (16) having a wave-shaped profile with a periodic sequence of peaks and troughs according to the axis.

2. The burner according to claim 1, wherein: Relative to a reference plane perpendicular to the axial direction of the burner, the peak amplitude of the wave profile of the lip is 0.004 to 0.06, preferably 0.008 to 0.032, relative to the diameter of the oxidant tube.

3. The burner according to claim 1 or 2, wherein: The number of waves of the lip is 0.016 / mm to 0.144 / mm, preferably 0.024 / mm to 0.096 / mm, relative to the diameter of the oxidant tube.

4. A burner according to any one of the preceding claims, wherein: The wave-shaped profile of the lip may be mathematically represented by a periodic function, such as any of a sinusoidal function, a symmetrically or antisymmetrically repeated polynomial function, a symmetrically or antisymmetrically repeated shape, or a combination thereof.

5. The burner according to claim 1, wherein: The lip has a sinusoidal profile.

6. The burner according to claim 5, wherein: The sinusoidal profile has an amplitude of 1 mm to 6 mm and a period of 4 to 24 waves.

7. A burner according to any one of the preceding claims, comprising a swirler (8) in the oxidant duct upstream of the nozzle.

8. A burner according to any one of the preceding claims, wherein: At least the nozzle of the oxidant tube is made by 3D printing, preferably by additive manufacturing.

9. A reactor (R) for reforming a gas feed (12), comprising: Combustion chamber (2); A burner (1) according to any one of claims 1 to 8; The burner (1) is installed above the combustion chamber (2) so that the oxidant tube (4) and the process gas annular channel (5) are arranged vertically, and the oxidant tube (4) extends below the end section (9) of the process gas annular channel, thereby extending into the combustion chamber.

10. The reactor according to claim 9, adapted for secondary reforming of a process gas produced after primary reforming with steam of a hydrocarbon feedstock.

11. A method for reforming a hydrocarbon feedstock to produce a hydrogen-containing gas, the method comprising the steps of primary reforming the feedstock in the presence of steam to obtain a primary reforming effluent and secondary reforming the effluent in the presence of an oxidant, wherein: The secondary reforming is carried out in a reactor according to claim 9 or 10.

12. The method according to claim 11, wherein: A diffusion flame is formed at the top end of the oxidant tube where the oxidant contacts the process gas.

13. The method according to claim 11 or 12, wherein: The oxidant is any one of air, oxygen-enriched air or oxygen.

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