FIELD

[0001] The present disclosure relates to the field of catalytic steam reforming reactors, and more specifically to improved design of bayonet steam reforming reactors.

SUMMARY

[0002] In a first aspect, a bayonet steam reforming reactor comprises an outer tube having an inside diameter, an inner tube disposed at least partially within the outer tube to define an annulus between the inner tube and the outer tube, and a structured packing containing a catalyst disposed within the annulus, wherein the inside diameter of the outer tube is less than 90 mm.

[0003] In some embodiments, the inside diameter is less than 80 mm.

[0004] In some embodiments, the inside diameter is less than 70 mm.

[0005] In some embodiments, the reactor is operable at a process gas pressure of at least 40 bar and a peak temperature of at least 900° C.

[0006] In some embodiments, the reactor is operable at a process gas pressure of at least 50 bar and a peak temperature of at least 930° C.

[0007] In some embodiments, the reactor is operable at a process gas pressure of at least 55 bar and a peak temperature of at least 950° C.

[0008] In a second aspect, a bayonet steam reforming reactor comprises an outer tube having an inside diameter and a wall thickness, an inner tube disposed at least partially within the outer tube to define an annulus between the inner tube and the outer tube and a structured packing containing a catalyst disposed within the annulus, wherein a ratio of the wall thickness to the inside diameter is at least 0.080.

[0009] In some embodiments, the ratio is at least 0.100.

[0010] In some embodiments, the ratio is at least 0.120.

[0011] In some embodiments, the reactor is operable at a process gas pressure of at least 40 bar and a peak temperature of at least 900° C.

[0012] In some embodiments, the reactor is operable at a process gas pressure of at least 50 bar and a peak temperature of at least 930° C. [0013] In some embodiments, the reactor is operable at a process gas pressure of at least 55 bar and a peak temperature of at least 950° C.

[0014] In a third aspect, a bayonet steam reforming reactor comprises an outer tube having an inner diameter and a wall thickness, an inner tube disposed at least partially within the outer tube to define an annulus between the inner tube and the outer tube, and a structured packing containing a catalyst disposed within the annulus, wherein the inside diameter is less than 90 mm and a ratio of the wall thickness to the inside diameter is at least 0.080.

[0015] In some embodiments, the inside diameter is less than 80 mm.

[0016] In some embodiments, the inside diameter is less than 70 mm.

[0017] In some embodiments, the ratio is at least 0.100.

[0018] In some embodiments, the ratio is at least 0.120.

[0019] In some embodiments, the reactor is operable at a process gas pressure of at least 40 bar and a peak temperature of at least 900° C.

[0020] In some embodiments, the reactor is operable at a process gas pressure of at least 50 bar and a peak temperature of at least 930° C.

[0021] In some embodiments, the reactor is operable at a process gas pressure of at least 55 bar and a peak temperature of at least 950° C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 schematically depicts a longitudinal cross section of an example reactor in accordance with the present technology.

DETAILED DESCRIPTION

[0023] The steam reforming process presents an opportunity to provide small molar flows of high-pressure water and feedstock at minimal compression cost and convert them to larger molar flows of high-pressure products. The typically 10-38 bar outlet gas from the steam reforming reactor can be compressed to 50-150 bar for downstream ammonia or methanol synthesis reactors. For its transportation or use in the refining of petroleum, hydrogen typically must be at pressures much higher than those of conventional steam reforming. Product compression is a major cost of the production of ammonia, methanol, and hydrogen. It is therefore desirable to intensify the steam reforming process to operate at higher pressure at acceptable conversion of the reactants to products.

[0024] The steam reforming reaction is thermodynamically favored by lower pressure and higher temperature. However, because syngas or hydrogen produced from a steam reforming reactor at higher outlet pressure can be more valuable for downstream processing, it may be desirable to operate at both the highest feasible pressure and temperature. Historically, the peak or outlet gas temperature from a steam reforming reactor was constrained to about 870° C to accommodate the strength of the outlet system metallurgy. To attain acceptable conversion of the reactants at this upper temperature limit, the maximum steam reforming pressure is conventionally limited to about 38 bar or less. Although higher reforming pressures could be accommodated by increasing the tube wall thickness, such alterations to existing steam reforming reactors without raising the peak reforming temperature would have undesirably resulted in lower feedstock conversion.

[0025] In some steam reforming reactors, the temperature of the gas can be lowered from the peak reforming temperature before the gas enters the outlet system, but bayonet reactors have rarely been used or attempted to be used. A major reason for their failure is that catalyst pellets used in steam reforming reactors must be strong enough to avoid crushing upon thermal cycling of the tube. The pellets typically also have high geometric surface area to promote reactivity, resulting in large, non-spherical particles such as cylinders with axial holes and flutes along their lengths. Particle sizes of about 15 mm in diameter have proved most effective to provide both sufficient crushing strength and surface area at acceptably low pressure drop. To attain good heat transfer to avoid tube failure by overheating and to provide plug flow that avoids bypass that causes both loss of reactivity and carbon deposition on the outer pellets, the reactor tube inside diameter should be at least 10 or 20 times the particle diameter. Tube inside diameters are normally 100-130 mm in commercial practice, which is small for plug flow with such large particles. Larger tube diameters lower the surface area to volume in a reactor constrained by heat transfer from the tube to the process gas and require thicker walls, which further impede heat transfer and increase the thermal stress due to the temperature gradient within the tube wall. Because the ratio of particle diameter to tube diameter is generally less than about 6 to 1, poor flow pattems ensue, permitting tube failure by overheating and carbon deactivation and spalling of the pellets, process intensification itself is constrained.

[0026] The problems are only compounded in a bayonet configuration, where the annulus width, being much smaller than the tube diameter, requires smaller particles for plug flow, where smaller particles would have higher pressure drop and lower crushing strength. Further, to pass the process gas through only a portion of the tube cross section and the return gas through another portion of the tube cross section entails higher pressure drop than a conventional single pass tube having flow only in one direction through a reactor which occupies the full tube cross section. To apportion even a very high portion of the tube cross section to an annular reforming reactor and a small portion of the cross section to the return gas results in very small inner tubes with limited heat transfer surface area for the return gas to be cooled from the peak reforming temperature to the maximum acceptable outlet system temperature. Hence, for multiple reasons the use of bayonet reactors has been delayed until some design constraints could be eliminated by new discoveries.

[0027] It is desirable to intensify the steam reforming process by enabling reforming to higher pressures and temperatures than have been previously possible with acceptable conversion of the reactants and tube service life. It is also desirable to improve heat management of the steam reforming process and lower the cost of tubes, reactors, and extraneous heat exchangers per unit of production of syngas or hydrogen.

[0028] It has now been discovered that structured packings can be effectively substituted for pellets in the annulus of a bayonet steam reforming reactor to provide sufficient geometric surface area and acceptably low pressure drop and to substantially prevent process gas from bypassing catalytic surfaces while occupying a smaller portion of the of the tube cross than was previously possible with pellets. It has further been determined that a 10-15 mm wide annulus can be adequate for sufficient reactivity and sufficiently low pressure drop for the flow rate commensurate with the amount of heat that can be transferred from the tube to the process gas at that given flow rate. In some cases, within a bayonet tube with a structured packing, heat transfer can be promoted by introducing such devices in portions of the tube length outside a heated furnace to increase the heat transfer between the annulus gas and return gas, rather than promoting heat transfer between the gas in the annulus and the gas in the return gas tube along the hottest length of the bayonet tube or not within a heated furnace.

[0029] It has further been discovered that the use of a bayonet reactor with a reduced tube diameter (e.g., an outer tube having a relatively smaller inside diameter) relative to conventional bayonet reactors, but without substantially reducing the thickness of the outer tube, can permit effective steam reforming at higher temperatures and pressures than previous possible. In some cases, such benefits are realized in conjunction with configurations in which the bayonet reactor is partially disposed within a furnace such that one end and a portion of the length of the bayonet reactor are disposed outside of the furnace while the opposite end and a portion of the length of the bayonet reactor are disposed within the furnace.

[0030] Accordingly, in some embodiments, a bayonet reactor is provided with a structured packing containing a catalyst in its annulus wherein the outer tube has an inside diameter less than 90 mm. Such inside diameters are smaller than those of conventional bayonet reactors and have been discovered to advantageously permit steam reforming at higher temperatures and pressures relative to conventional bayonet reactors, while still resulting in acceptable conversion of feedstock.

[0031] In some embodiments, a bayonet reactor is provided in which the outer tube has a ratio of wall thickness to inside diameter at least 0.08. Such wall thickness to inside diameter ratios are larger than those of conventional bayonet reactors and have been discovered to advantageously permit steam reforming at higher temperatures and pressures relative to conventional bayonet reactors, while still resulting in acceptable conversion of feedstock.

[0032] The catalyst may contain a platinum group metal such as platinum (Pt), palladium (Pd), rhodium (Rh), and rhenium (Re).

[0033] Novel reactors disclosed herein in accordance with the present technology can operate at process gas pressures of at least 40 bar and at temperatures of at least 900° C. In some cases, the reactor may be suitable for operation at pressure at least 50 bar or at least 55 bar. The reactor may be suitable for operation at a peak temperature of at least 930° C or at least 950° C. The reactor in some embodiments operates at a steam-to-carbon (S/C) ratio less than 6.0, and in some cases less than 3.0. Example reactors in accordance with the present technology will be described in greater detail herein with reference to Figure 1.

[0034] A bayonet catalytic reactor, or simply a bayonet reactor as used herein, can be a reactor comprising a first, outer tube and a second, inner tube disposed within the first tube, wherein both tubes are open at a first end, and the first tube is closed and the second tube is open at the second or opposite end. Fluid enters the first end into an annulus defined between the first and second tubes, flows to the second end, flows from the annulus into the second tube at the second end, returns within and along the length of the second tube, and exits the first end of the second tube. The annulus can contain a catalyst for reacting the fluid within the annulus.

[0035] The steam reforming reaction includes those chemical reactions between steam or carbon dioxide and a feedstock containing carbon and hydrogen, such as methane for example, to produce a syngas containing hydrogen and oxides of carbon.

[0036] Pressures referred to in units of bar herein refer to absolute pressure.

[0037] A steam-to-carbon ratio or S/C ratio of a mixed feed corresponds to the moles of steam divided by the moles of carbon contained in the mixed feed.

[0038] Referring now to Figure 1, an example bayonet catalytic reforming reactor 1 comprises a first, outer tube 2 shown with hatched lines, and a second, inner tube 3, shown as dark, solid lines, disposed within the outer tube 2 such that a first annulus 6 is formed between an inner surface of the outer tube 2 and an outer surface of the inner tube 3. The outer tube 2 and the inner tube 3 have corresponding first ends 4 and second ends 5. The first ends 4 of the outer tube 2 and the inner tube 3 are preferably proximate each other, and the second ends 5 of the outer tube 2 and the inner tube 3 are proximate each other. The outer tube 2 and the inner tube 3 are open at the first end 4 so as to accommodate inflow of fluid into the outer tube 2 and outflow of fluid from the inner tube 3 at the first end 4. The outer tube 2 is closed at the second end 5 and the inner tube 3 is open at the second end 5 so as to accommodate flow of fluid from the first annulus 6 into the inner tube 3 at the second end 5. The first annulus 6 formed between the outer tube 2 and the inner tube 3 contains a catalytic reactor 7, shown with cross hatched lines, in the form of a structured packing. [0039] In some embodiments, an inside diameter of the inner surface 8 of the outer tube 2 is preferably less than 90 mm, more preferably less than 80 mm, in some cases less than 70 mm, and in some cases less than 60 mm.

[0040] In some embodiments, the ratio of the wall thickness of the outer tube 2 to the inside diameter of the inner surface 8 of the outer tube 2 is at least 0.080, more preferably at least 0.100, and in some cases at least 0.120.

[0041] The void space within the inner tube 3 and the void space within the first annulus 6 are in fluid communication with each other at the second end 5 and may not communicate with each other at any other location along the length of the reactor 1. Suitable fittings of any form are provided at the first ends 4 of the tubes 2, 3 to isolate the inlet 11 of the outer tube 2 from the outlet 12 of the inner tube 3. For example, such a fitting 13 may be a T-fitting, and fitting 14 may be an L-fitting or a T-fitting. Various arrangements may be substituted for fittings 13 and 14 illustrated in Figure 1.

[0042] The outer tube 2 and the inner tube 3 are shown to penetrate a wall 15 (shown as a dotted area) of a furnace 16. The first ends 4 of the outer tube 2 and the inner tube 3 can be outside the furnace 16, and the second ends 5 of the outer tube 2 and the inner tube 3 are inside the furnace 16. Vertical portions of the tubes and furnace are omitted from the drawing, shown as blank spaces, as the reactor 1 can have a variety of lengths without departing from the scope of the present technology.

[0043] The substrate of the catalytic reactor 1 (e.g., the materials disposed within the first annulus 6) according to the present technology may include metal, ceramic, and/or other materials.

[0044] In some embodiments, the catalyst in the first annulus 6 is at least partly disposed outside the furnace 16 and is suitable for promoting the steam reforming reactions at temperatures less than 600° C. The catalyst may contain any of various metals such as, for example, nickel (Ni), platinum (Pt), palladium (Pd), rhodium (Rh), and/or rhenium (Re).

[0045] Other devices such as turbulators and/or packings for enhancing heat transfer between the inner tube 3 and gas within the inner tube 3, insulation, and/or a second catalytic reactor within the inner tube 3 may also be included to enhance performance.

[0046] The inner tube 3 and any devices within the inner tube 3 may be constructed of materials that are resistant to metal dusting corrosion as are well known in the literature, such as corrosion-resistant alloys, materials having corrosion-resistant coatings such as aluminum, or the like.

[0047] Other advantages and other embodiments of the current invention will be obvious to those skilled in the art. Their omission here is not intended to exclude them from the claims advanced herein.

[0048] Although the present invention has been described in terms of certain preferred embodiments, various features of separate embodiments can be combined to form additional embodiments not expressly described. Moreover, other embodiments apparent to those of ordinary skill in the art after reading this disclosure are also within the scope of this disclosure. Furthermore, not all the features, aspects and advantages are necessarily required to practice the present technology. Thus, while the above detailed description has shown, described, and pointed out novel features of the present technology as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the apparatus or process illustrated may be made by those of ordinary skill in the technology without departing from the spirit or scope of the present disclosure. The present technology may be embodied in other specific forms not explicitly described herein. The embodiments described above are to be considered in all respects as illustrative only and not restrictive in any manner.