A reactor and method of carrying out an endothermic reaction

Abstract

In a reactor comprising a cylindrical combustion chamber, at least one burner, and a circular array of tubes containing a catalyst, an annular baffle extending into the combustion chamber is provided on a wall opposite to the burner, the annular baffle redirecting the combustion gases around the combustion chamber to achieve a more uniform heat distribution and an increase in overall heat transfer.

Description

Technical Field

[0001] The present invention relates to the field of reactors, and more particularly to reactors for producing, for example, hydrogen by steam reforming a hydrocarbon feedstock, such as natural gas, or by cracking (or "dissociation") an ammonia feedstock in an endothermic catalytic reaction. Prior Art

[0002] An "endothermic" reaction requires energy (usually heat) from the environment to provide the activation energy for the reaction to occur. Examples of endothermic reactions include the cracking (or "dissociation") of ammonia into hydrogen (H2) and nitrogen (N2) and the steam reforming of hydrocarbons to form synthesis gas containing H2 and carbon monoxide (CO). The endothermic nature of these reactions necessitates the use of a fired reactor or furnace.

[0003] The ammonia cracking reaction is represented by the following reaction formula: 2NH 3⇌ 3H 2+ N 2

[0004] The standard heat of reaction (per mol of ammonia) at 1 bar and 0°C is 45.47 kJ / mol. The process is usually carried out over a catalyst.

[0005] Steam reforming, or steam methane reforming (SMR), is a process used to produce a mixture of H₂ and CO by reacting a hydrocarbon feedstock with water. Natural gas is typically used as the feedstock, but other hydrocarbons such as liquefied petroleum gas (LPG) and naphtha can also be used. The SMR reaction is represented by the following equation: CH 4 + H 2O ⇌ CO + 3H 2

[0006] The reaction is strongly endothermic (ΔH SR = 206 kJ / mol) and is generally carried out over a catalyst.

[0007] Because these reactions are equilibrium reactions, the product gas typically contains a small amount of reactants. The amount of residual reactant in the product gas (often referred to as "slip" of the reactant(s)) can be varied by changing the temperature and / or pressure at which the reaction occurs, with higher temperatures and / or higher pressures favoring conversion and thus reducing slip.

[0008] Shell-and-tube reactors for carrying out endothermic reactions are well known in the art. Examples of such reactors include those disclosed in GB1004234A, US2007 / 0187079A, US6808689A, and CN202036974A. Typically, these reactors have a cylindrical shell containing a plurality of catalyst-filled tubes. Hot gas circulates in the space between the shell and the tubes, and the gas to be processed travels through the tubes. The hot gas provides the heat required for the endothermic reaction to occur. The reactors described in these references also have plate baffles positioned horizontally within the reactor to divert the hot gas around the tubes, thereby expanding the flow pattern and increasing mixing between the hot and cold gases.

[0009] This annular reactor can also be constructed as a cylindrical shell with one or more burners ignited from the top or bottom surface. Process gas flows through catalyst-containing tubes circumferentially arranged within the cylinder. The hot combustion gases provide heat to the tubes primarily through radiation and then exit through dedicated ports designed to evenly distribute the flow. The reactor tubes themselves may contain additional tubes internally, allowing heat exchange to occur between the innermost tube and the annulus between this innermost tube and the hot combustion gases. Examples of this type of reactor are disclosed in US Pat. No. 6,835,360A, EP4,025,333A, EP2,223,739A, KR20220096295A, EP2394735A, and US Pat. No. 2022152576A.

[0010] US6835360A discloses an endothermic catalytic reaction apparatus comprising a combustion chamber containing a plurality of tubular reaction chambers arranged concentrically around an axially extending radiant burner centrally located within the chamber.

[0011] Each tubular reaction chamber is defined as an annular space between an outer tube and an inner tube coaxially positioned within the outer tube. This annular space is filled with catalyst. Reactant gases enter the reaction chamber through an inlet, travel through the catalyst bed in the annular space, then travel through the inner tube and exit through an outlet. The gases traveling through the inner tube transfer heat to the reactant gases traveling through the reaction chamber.

[0012] The radiant burners deliver radiant energy uniformly across a 360-degree arc to the surface of the outer conduit. Each tubular reaction chamber has a convection chamber. Combustion gases exiting the radiant burners are directed into the convection chamber, which is concentrically positioned around a portion of the outer conduit near the end of the tubular conduit containing the reactant gas inlet. After providing heat to the outer conduit through convection, the combustion gases exit through an outlet.

[0013] Compared to typical SMRs or cracking furnaces, annular reactors of the type disclosed in US Pat. No. 6,835,360A are typically designed for smaller capacities and often rely on premix burners to provide heat. Low-momentum flames successfully achieve smooth heat distribution within the relatively small reactor volume. However, when the fuel has a high hydrogen content, premix burners cannot always be used and may result in higher NOx emissions. To overcome these limitations, non-premix burners similar to those used on larger furnaces can be installed. Using such burners typically results in higher velocities of combustion gases entering the reactor. Due to the small size of the reactor, the combustion gas momentum cannot be dissipated. If the hot gases directly impinge on the tubes, this can lead to uneven heat distribution and localized overheating of the tubes.

[0014] There is a general need for more efficient combustion reactors, and in particular, a need for smaller annular reactors using non-premixed burners with improved heat transfer. Summary of the Invention

[0015] According to a first aspect of the present invention, a reactor is provided, for example, an endothermic reactor, comprising: an insulating cylindrical sidewall having a first end and a second end opposite the first end, the insulating cylindrical sidewall being closed at the first end by a first insulating end wall and at the second end by a second insulating end wall, the cylindrical sidewall and the end walls defining a combustion chamber having an inner diameter, an inner height, and a longitudinal axis parallel to the cylindrical sidewall; at least one burner centrally positioned in the first insulating end wall; a plurality of catalyst-containing tubes extending through one of the insulating end walls into the combustion chamber and toward the opposing insulating end walls, the tubes being parallel to the insulating cylindrical sidewall and configured to mate with the combustion chamber. a circular array coaxial with the longitudinal axis of the combustion chamber; at least one outlet for combustion gas, the at least one outlet extending through the insulating end wall, the plurality of catalyst-containing tubes extending through the insulating end wall, the at least one outlet being positioned adjacent the tubes; and an annular baffle located on and extending from the second insulating end wall into the combustion chamber, the annular baffle being coaxial with the longitudinal axis of the combustion chamber, wherein the circular array of the plurality of catalyst-containing tubes is positioned between the annular baffle and the insulating cylindrical sidewall, and wherein the annular baffle has an inner diameter in the range of about 55% to about 90% of the inner diameter of the combustion chamber and a height in the range of about 5% to about 30% of the interior height of the combustion chamber.

[0016] The inventors have determined that an annular baffle of appropriate height and positioned at an appropriate location on the wall opposite the burner(s) redirects the combustion gases from the burner(s), forcing the gases to recirculate within the combustion chamber of the reactor before reaching the catalyst-containing tubes. Recirculating the combustion gases increases the residence time of the combustion gases within the combustion chamber and provides more uniform heat distribution, thereby increasing overall heat transfer by up to about 10% and / or reducing the tube wall temperature near the second end wall by up to about 100° C., for example, to up to about 80° C. or up to about 70° C., and / or increasing the temperature of the gases upon exiting the catalyst-containing tubes, thereby reducing the amount of unreacted gases, such as ammonia or methane, in the feed.

[0017] The present invention enables upgrading of an existing annular combustion reactor by retrofitting the reactor with a new, low NOx burner using an annular baffle.

[0018] According to a second aspect of the present invention, a method for performing an endothermic reaction is provided, the method comprising: burning a fuel and an oxidant gas in (multiple) burners to heat catalyst-containing tubes of a reactor as described in the first aspect; and passing a feed gas through the catalyst-containing tubes to produce a synthesis gas.

[0019] According to a third aspect of the present invention, there is provided the use of the reactor as described in the first aspect for carrying out an endothermic reaction, such as ammonia cracking or steam reforming of a hydrocarbon feedstock.

[0020] The present invention is particularly applicable to the endothermic reactor disclosed in US6835360A. Simple diagram description

[0021] Figure 1 depicts the movement of combustion gases within a conventional annular reactor having a non-premixed burner;

[0022] Figure 2 depicts the movement of the combustion gases within the reactor having a non-premixed burner according to the present invention;

[0023] Figure 3 depicts a cross-section of a first embodiment of a reactor according to the present invention (wherein the cylindrical side wall is omitted);

[0024] Figure 4 depicts a partial cross-section of a second embodiment of the reactor according to the present invention;

[0025] Figure 5 depicts a partial cross-section of a third embodiment of the reactor according to the present invention;

[0026] Figure 6 is a computational fluid dynamics (CFD) model of the movement of combustion gases in a combustion chamber of an annular reactor having a non-premixed burner but no annular baffle;

[0027] FIG7 is a CFD model of the movement of combustion gases in the combustion chamber of a comparative reactor having an annular baffle having an inner diameter that is 50% of the inner diameter of the combustion chamber; and

[0028] FIG. 8 is a CFD model of the movement of combustion gases in the combustion chamber of a reactor according to the present invention. Implementation Method

[0029] Throughout this specification, unless otherwise stated, any reference to pressure is to absolute pressure.

[0030] A reactor according to the present invention includes an insulating cylindrical sidewall having a first end and a second end opposite the first end. The insulating cylindrical sidewall is closed at the first end by a first insulating end wall and at the second end by a second insulating end wall. The insulating cylindrical sidewall, together with the two insulating end walls, defines a combustion chamber having an inner diameter, an inner height, and a longitudinal axis parallel to the insulating cylindrical sidewall.

[0031] The insulation on the sidewalls is typically of at least substantially uniform thickness. Thus, the combustion chamber is also substantially cylindrical. The term "internal diameter" is intended to refer to the diameter of the cylindrical combustion chamber measured from the inner surface of the insulation.

[0032] The insulation on the first and second end walls also typically has at least substantially uniform thickness.The term "internal height" is intended to mean the height of the combustion chamber measured at any point from the inner surface of the insulation on the opposing walls.

[0033] Insulation is typically made of refractory ceramic materials, such as carbides, nitrides, and oxides of elements such as silicon, aluminum, magnesium, calcium, boron, chromium, and zirconium. Specific examples include oxides of aluminum (alumina), silicon (silicon dioxide), magnesium (magnesium oxide), and calcium (lime). As is known in the art, ceramic materials can be cast into bricks or spun into fibers.

[0034] The present invention is particularly applicable to reactors in which the inner diameter of the combustion chamber is equal to, but preferably greater than, the internal height of the combustion chamber. In such reactors, the momentum of the combustion gases generated by non-premixed burners tends not to dissipate by the time the gases reach the opposing walls, resulting in uneven heat distribution.

[0035] The ratio of the combustion chamber's inner diameter to its inner height is typically at least 1:1. Furthermore, the ratio of the combustion chamber's inner diameter to its inner height is typically no greater than 2:1, for example, no greater than 1.5:1. Thus, the ratio of the combustion chamber's inner diameter to its inner height is typically in the range of about 1:1 to about 2:1, or about 1:1 to about 1.5:1, for example, about 1.1:1, about 1.3:1, or about 1.4:1. The ratio of the combustion chamber's inner diameter (D) to its inner height (h) can be referred to as the chamber's "aspect ratio."

[0036] The reactor further includes at least one burner centrally located on the first end wall. In embodiments having a single burner, the burner is positioned on or along the longitudinal axis of the combustion chamber. In embodiments having more than one burner, for example, two, three, or four burners, the burners are typically arranged symmetrically about the longitudinal axis of the combustion chamber.

[0037] The reactor can be top-fired or bottom-fired. In a top-fired reactor, the first insulating end wall forms the top wall (or roof) of the reactor's combustion chamber. In a bottom-fired reactor, the first insulating end wall forms the bottom wall (or bottom) of the reactor's combustion chamber. In a preferred embodiment, the reactor is a top-fired reactor.

[0038] The burner is typically a non-premix burner, or if more than one burner is present, each burner is typically a non-premix burner. In a premix burner, the fuel and oxidant are mixed before entering the furnace and igniting. However, in a non-premix burner, the fuel and oxidant are fed through separate ports and mixed in the furnace. To achieve the high degree of mixing required for stable combustion and low emissions, the fuel and oxidant typically leave the non-premix burner at a relatively high velocity, and the combustion gases tend to carry "high momentum" into the furnace. For this reason, non-premix burners typically generate combustion gases with greater momentum than those generated in premixed or radiant burners, such as those used in US Pat. No. 6,835,360A.

[0039] Burners can be defined by their "swirl number." The intensity of swirl imparted to the fluid as it leaves the burner is quantified by the swirl number (S), which is defined as the ratio of the axial flux of the fluid's angular momentum (Gφ) to the product of the fluid's axial thrust (Gx) and the burner nozzle's exit radius, R. Since S = Gφ / GxR, high-momentum burners typically have low swirl numbers due to the fluid's high axial thrust (Gx).

[0040] The present invention is particularly applicable to reactors having one or more burners having a swirl number not greater than about 0.7 or not greater than about 0.6, for example, in the range of about 0.1 to about 0.5. Those skilled in the art will recognize such burners as high momentum burners.

[0041] The non-premixed burner(s) may be referred to as a "low NOx" burner, ie, a burner that generates relatively small amounts of NOx.

[0042] The reactor also includes a plurality of catalyst-containing tubes extending through one of the insulating end walls into the combustion chamber and toward the opposite insulating end wall. The tubes are parallel to the insulating cylindrical side wall and arranged in a circle or circular array coaxial with the longitudinal axis of the combustion chamber.

[0043] The tube may extend through the first insulating end wall and toward the second insulating end wall. In such embodiments, the tube extends through the end wall on which the burner(s) are positioned. In preferred embodiments, the tube extends through the second insulating end wall and toward the first insulating end wall. In such embodiments, the tube extends through the end wall opposite the end wall in which the burner(s) are positioned.

[0044] The reactor further comprises at least one outlet for combustion (or flue) gas, the at least one outlet extending through the end wall through which the plurality of catalyst-containing tubes extend, i.e., the end wall opposite the burner(s). Thus, while the outlet(s) may extend through either the first insulating end wall or the second insulating end wall, in a preferred embodiment, the outlet(s) extend through the second insulating end wall.

[0045] The at least one outlet is positioned adjacent to or in close proximity to the tubes. The outlet(s) are typically positioned around the section of the tube extending through the end wall. In a preferred embodiment, each tube has an annular outlet that surrounds the portion of the tube extending through the second end wall. However, other embodiments are also contemplated. In this regard, the arcuate outlet may surround the portions of two or more tubes extending through the end wall. Indeed, a single outlet in the form of a circular slit may encompass the portions of all tubes extending through the end wall. In other embodiments, the outlet may be in the form of a ring of holes in the second end wall positioned near the periphery of the end wall. In yet further embodiments, there may be a plurality of non-concentric holes for the flue gases exiting the combustion chamber.

[0046] The reactor includes an annular baffle, which is positioned on the second insulating end wall and extends from the second insulating end wall into the combustion chamber. The annular baffle is coaxial with the longitudinal axis of the combustion chamber.

[0047] The term "baffle" as used herein refers to a surface such as a wall, blade, or panel that directs or blocks the flow of a fluid.

[0048] A circular array of catalyst-containing tubes is positioned between the annular baffle and the insulating cylindrical sidewall. There is typically a space between the circular array of tubes and the cylindrical sidewall. In a preferred embodiment, the circular array of tubes is adjacent, that is, immediately adjacent to the sidewall but not adjacent to it.

[0049] Annular baffle

[0050] The inventors have observed that the location of the annular baffle is critical to the present invention. In this regard, the inventors have determined that if the annular baffle is too close to the center of the combustion chamber, a stagnant zone will form within the baffle ring, and the flow of combustion gases will not be directed back toward the first insulating end wall. In this case, the gases in the combustion chamber near the first insulating end wall will remain cooler, the residence time will remain low, and hot spots may form on the tubes. Therefore, the inventors have determined that the annular baffle must have an inner diameter that is at least approximately 55% of the inner diameter of the combustion chamber. In a preferred embodiment, the inner diameter of the annular baffle is at least approximately 60% of the diameter of the combustion chamber, for example, at least approximately 65%.

[0051] The inventors have determined that if the ring is too close to the tube, the momentum of the combustion gas flow will be dissipated, and recirculation of the gas toward the first end wall will not occur or will be less stable. In this regard, the inventors have determined that the annular baffle must have an inner diameter that is no greater than about 90% of the inner diameter of the combustion chamber. In a preferred embodiment, the inner diameter of the annular baffle is no greater than about 85% of the inner diameter of the combustion chamber, for example, no greater than about 80%.

[0052] The inner diameter of the annular baffle can be in the range of about 65% to about 80% of the inner diameter of the combustion chamber, for example, about 65% to about 75%. In some embodiments, the annular baffle has an inner diameter in the range of about 68% to about 72% of the inner diameter of the combustion chamber, for example, about 70%. In other embodiments, the annular baffle has an inner diameter in the range of about 75% to about 85% of the inner diameter of the combustion chamber, for example, about 78%.

[0053] The inventors have also observed that the height of the baffle is also critical to the present invention. In this regard, the inventors have determined that if the annular baffle is too tall, the desired recirculation pattern of the combustion gases to the tubes becomes inhibited. Therefore, the inventors have determined that the height of the annular baffle must be no greater than 30% of the internal height of the combustion chamber. In a preferred embodiment, the height of the annular baffle is no greater than approximately 25% of the internal height of the combustion chamber.

[0054] The inventors have also determined that if the annular baffle is too low, it will not redirect the combustion gases back toward the first end wall, allowing some gases to bypass the baffle and reach the outlet directly. In this regard, the inventors have determined that the annular baffle must have a height of at least about 5% of the interior height of the combustion chamber. In a preferred embodiment, the height of the annular baffle is at least about 8%, for example, at least about 15%, of the interior height of the combustion chamber.

[0055] The height of the annular baffle may be in the range of about 8% to about 25% of the interior height of the combustion chamber. In some embodiments, the height of the annular baffle is in the range of about 8% to 12% of the interior height of the combustion chamber, for example, about 10%, or in the range of about 18% to about 22%, for example, about 20%.

[0056] The inventors have also determined that, when the inner diameter of the baffle is at least 75% of the inner diameter of the combustion chamber, the height of the baffle is, in a preferred embodiment, at least 15% of the inner height of the combustion chamber.

[0057] In some embodiments, particularly where the aspect ratio of the combustion chamber is in the range of about 1.3:1 to about 1.5:1, the inner diameter of the annular baffle is in the range of about 68% to 72% of the inner diameter of the combustion chamber, e.g., about 70%, and the height of the annular baffle is in the range of about 8% to about 22% of the inner height of the combustion chamber, e.g., about 10% or about 20%.

[0058] In other embodiments, particularly where the aspect ratio of the combustion chamber is in the range of about 1.3:1 to about 1.5:1, the inner diameter of the annular baffle is in the range of about 75% to about 85% of the inner diameter of the combustion chamber, and the height of the annular baffle is in the range of about 15% to about 25% of the inner height of the annular baffle.

[0059] For all embodiments, the annular baffle is typically a circular strip extending perpendicularly from the second insulating end wall. Such a strip typically has an at least substantially rectangular cross-section. However, other configurations may be suitable, including a regular polygonal strip; annular baffles with angled or curved walls, i.e., with a concave or convex cross-section, as appropriate; or annular baffles with a tapered cross-section, i.e., with a base that is wider than the top.

[0060] The annular baffle is also usually not perforated.

[0061] The annular baffle typically has a thickness ranging from about 0.1 centimeters (cm) to about 15 cm, for example, about 0.25 cm to about 10 cm. One factor in determining the thickness of the annular baffle is the material from which it is made. In this regard, the annular baffle may comprise or be made of a metal alloy or a refractory ceramic material. If made of a ceramic material, the material may be the same as or different from the ceramic material of the insulation.

[0062] Suitable metal alloys include heat-resistant steels, such as 1.25Cr-0.5Mo steel.

[0063] Where the annular baffle comprises or is made of a metal alloy, it may have a thickness in the range of about 0.25 cm to about 2 cm.

[0064] Suitable refractory ceramic materials for the annular baffle include carbides, nitrides, and oxides of elements such as silicon, aluminum, magnesium, calcium, boron, chromium, and zirconium. Specific examples include oxides of aluminum (aluminum oxide), silicon (silicon dioxide), magnesium (magnesium oxide), and calcium (lime).

[0065] Where the annular baffle comprises or is made of a ceramic material, it may have a thickness in the range of about 2.5 cm to about 10 cm.

[0066] The annular baffle can be cast together with the second insulating end wall. In other embodiments, the annular baffle is made of refractory ceramic bricks, for example, alumina.

[0067] The annular baffle is typically the only baffle in the reactor. However, in some embodiments, the reactor further includes at least one other baffle, such as an annular plate baffle, positioned on the insulating cylindrical sidewall and extending generally vertically from the sidewall into the combustion chamber, typically up to (and generally not exceeding) the plurality of catalyst-containing tubes. If present, the annular plate baffle is typically positioned at a point within the midsection of the cylindrical sidewall, for example, at about 30% to about 50% of the interior height of the combustion chamber as measured from the first end wall.

[0068] Tube containing catalyst

[0069] In some embodiments, each catalyst-containing tube is formed from a single tube filled with catalyst. In these embodiments, the tubes extend through the first and second insulating end walls of the reactor, and a feed gas is passed from an inlet at one end of each tube through the catalyst to form a product gas that exits each tube through an outlet at the opposite end of the tube.

[0070] In other embodiments, each catalyst-containing tube comprises an inner tube coaxially positioned within an outer tube, defining an annular space between the outer and inner tubes, the annular space being filled with catalyst. In some of these embodiments, feed gas flows from an inlet at one end of each tube through the catalyst in the annular space, and then product gas flows countercurrently with the feed gas flow in the annular space through the inner tube and exits the tube through a product gas outlet at the same end of the tube as the feed gas inlet. However, in other embodiments, the feed gas flows in opposite directions, i.e., first through the inner tube and then over the catalyst in the annular space between the inner and outer tubes.

[0071] The ends of the tubes opposite the ends with the feed gas inlet / product gas outlet may not reach the opposite end wall. Thus, in these embodiments, a gap may exist between these ends of the catalyst-containing tubes and the end wall. However, in other embodiments, the ends of the tubes opposite the feed gas inlet / product gas outlet ends may extend through the opposite end wall to provide improved access to the interior of the tubes.

[0072] The or each combustion gas outlet includes a shroud extending from the second insulating end wall away from the combustion chamber and defining an annular convection space around or encircling the section of the catalyst-containing tube(s) outside the combustion chamber. The combustion gases transfer heat to the tubes in the convection space, improving overall heat transfer. The section of the catalyst-containing tube(s) outside the combustion chamber typically ranges from about 30% to about 50%, for example, about 40%, of the length of the tube(s).

[0073] The catalyst in the tubes can be any catalyst suitable for endothermic reactions. Such reactions include steam reforming of hydrocarbon feedstocks, such as methane, natural gas, liquefied petroleum gas (LPG), and naphtha, and cracking of ammonia.

[0074] In some preferred embodiments, the catalyst is an ammonia cracking catalyst, such as a nickel-based catalyst, a ruthenium-based catalyst, or an iron-based catalyst.

[0075] The term "nickel-based catalyst" refers to a catalyst containing nickel as the sole (or at least the primary) catalytically active metal, i.e., the metal responsible for catalyzing the cracking reaction. Nickel may be the sole metal in the catalyst, or alternatively, one or more other metals may be present, for example, in a nickel-supported material, such as a metal oxide, e.g., silica (SiO₂), alumina (Al₂O₃), zirconium oxide (ZrO₂), or a mixed metal oxide support, such as calcium aluminate or spinel (MgAl₂O₄), perovskite (CaTiO₃), or zeolite. The loading of the catalytically active metal(s) on the support may range from about 0.1% to about 70% by weight. The terms "ruthenium-based catalyst" and "iron-based catalyst" are intended to be interpreted accordingly.

[0076] Many examples of suitable ammonia cracking catalysts are known to those skilled in the art, including US 2015 / 0217278A, Masel et al. (Catalyst Letters, vol. 96, Nos. 3-4, July 2004), Lamb et al. (Int. J. Hydrogen Energy, 44 (2019) pp 3726-3736), and Boisen et al. (J. Catalysis 230 (2005) pp 309-312).

[0077] In other preferred embodiments, the catalyst is a steam reforming catalyst, such as a nickel-based catalyst, for example, a nickel-alumina catalyst. Nickel-based catalysts may have an alkali metal promoter, such as potassium or magnesium. Steam reforming (or SMR) catalysts are well known in the art, and any of these known catalysts may be used with the present invention. Examples of commercial reforming catalysts suitable for use with the present invention include the KATALCO™ series of catalysts (Johnson Matthey) and the ReforMax LDP series (Clariant).

[0078] method

[0079] Reactors are typically used to carry out endothermic reactions. Therefore, in a second aspect, the present invention provides a method comprising: burning a fuel and an oxidant gas in a burner(s) to heat catalyst-containing tubes of a reactor as described in the first aspect; and passing a feed gas through the catalyst-containing tubes to produce a product gas.

[0080] The feed gas may be a hydrocarbon feedstock or ammonia.

[0081] In the case where the feed gas system is ammonia, the catalyst is an ammonia cracking catalyst, and the product gas system is a cracked gas, which contains hydrogen, nitrogen, and residual ammonia.

[0082] In the ammonia cracking reaction, the ammonia feed to the reactor typically contains at least 98 mol% ammonia and is typically at a pressure in the range of about 5 bar to about 60 bar and at a temperature in the range of about 400° C. to about 800° C. The flow rate of the ammonia feed is typically in the range of about 200 kilograms per hour (kg / h) to about 3500 kg / h.

[0083] The composition of the cracked gas will depend on the composition of the ammonia feed, as well as the temperature and pressure of the cracking reaction, which determine the amount of ammonia slip. In this regard, ammonia slip is typically in the range of about 0.1 mol% to about 5 mol%. The temperature of the cracked gas leaving the catalyst bed is typically in the range of about 500°C to about 700°C, and the pressure of the cracked gas is typically in the range of about 30 bar to about 40 bar.

[0084] In the case where the feed hydrogen is a hydrocarbon feedstock, the catalyst is a steam methane reforming catalyst, and the product gas system comprises a synthesis gas of hydrogen and carbon monoxide gas.

[0085] In steam reforming reactions, the hydrocarbon feedstock is typically mixed with steam at a pressure ranging from about 8 bar to about 40 bar and a temperature ranging from about 400°C to about 600°C. Steam is present to provide a steam-to-carbon atom (associated with the hydrocarbons) ratio ranging from about 2:1 to about 6:1. The flow rate will depend on the characteristics of the hydrocarbon feedstock. For natural gas, the flow rate is typically from about 70 kg / h to about 15,000 kg / h, for example, from about 140 kg / h to about 1,500 kg / h.

[0086] The composition of the product gas will depend on the composition of the hydrocarbon feedstock, as well as the temperature and pressure of the steam reforming reaction, which determine the amount of residual reactants in the product gas. For steam methane reforming, methane slip is typically in the range of about 0.25 mol% to 5.0 mol% on a dry basis. The temperature of the product gas leaving the catalyst bed is typically in the range of about 750°C to about 950°C, and the pressure of the product gas is typically in the range of about 5 bar to about 40 bar.

[0087] The combustion process in the reactor can be at least partially fueled internally using waste gas generated during hydrogen recovery from the product gas. Preferably, the combustion process in the furnace is fueled internally, i.e., the fuel is ammonia or waste gas generated during hydrogen recovery from the cracked gas, or a mixture of the two. In other words, trimming fuels such as LPG, naphtha, ammonia, natural gas, or methane (preferably derived from biogas or methanation of renewable hydrogen) can be used to supplement the main fuel.

[0088] When fed to the burner(s), the fuel is typically at a pressure in the range of about 1 bar to about 3 bar and at a temperature in the range of about -20°C to about 250°C, for example, about 40°C to about 250°C for off-gas generated during hydrogen recovery, and about -20°C to about 250°C or about -20°C to about 40°C for natural gas. The flow rate will depend on the characteristics or composition of the fuel used. Where the primary fuel is off-gas generated during hydrogen recovery from the product gas, the total flow rate can typically be in the range of about 30 kg / h to about 3,600 kg / h. The flow rate of trim fuel is typically no greater than about 150 kg / h, for example, about 10 kg / h to about 100 kg / h for natural gas.

[0089] The oxidant gas is typically air, but may also be an oxygen-enriched gas, such as oxygen-enriched air or pure oxygen, as appropriate.

[0090] In embodiments where the oxidant gas is air, when fed to the burner(s), the air is typically at a pressure in the range of about 0.9 bar to about 1.2 bar, and at a temperature in the range of ambient temperature (which may be as low as -20°C) to about 250°C, and has a flow rate in the range of about 150 kg / h to about 5400 kg / h. The excess air will be in the range of about 5% to about 80%.

[0091] The composition of the combustion (or flue) gas from ammonia cracking applications will depend on the characteristics of the fuel and oxidant gas. However, when the fuel is waste gas from a hydrogen recovery process supplemented with natural gas product gas, and the oxidant gas is air, the combustion gas typically contains nitrogen (70%-80%), argon (0.5%-1.0%), oxygen (1%-5%), carbon dioxide (1%-5%), and water (10%-20%). If hydrogen, ammonia, or cracked gas is used as the trimming fuel, the flue gas will contain no carbon dioxide, other than that absorbed with the combustion air. Although the majority of the nitrogen comes from the PSA waste gas, since it contains all the nitrogen atoms present in the feed ammonia, the proportions of oxygen and argon are determined by the proportion of excess air used in the combustion, as is the case with nitrogen. Excess air should be kept to a practical minimum to maximize process efficiency. The practical minimum is determined by the proportion required for stable combustion.

[0092] In SMR applications, the flue gas will have the same components but in different proportions, namely, carbon dioxide (10%-20%, e.g., 13.5%), oxygen (3%-15%, e.g., 6.75%), 64.5% nitrogen (60%-70%, e.g., 64.5%), water (10%-20%, e.g., 15.3%), and argon (0.5%-3.0%).

[0093] For either application, the pressure of the combustion gas is typically in the range of about 0.8 bar to about 1.1 bar, and the temperature is typically in the range of about 400°C to about 650°C.

[0094] The furnace load of the reactor (based on the LHV of the fuel) may be in the range of about 90 kilowatts (kW) to about 4500 kW, and the tube load may be in the range of about 4 kW / tube to about 60 kW / tube.

[0095] The number of tubes in the reactor is typically in the range of 12 to 72, and the number of burners is typically one, but more may be used, for example, up to three.

[0096] The combustion chamber typically has an internal height in the range of about 0.9 meters (m) to about 4 m and an internal diameter in the range of about 1 m to about 5 m.

[0097] In some embodiments, the ratio of the inner diameter to the inner height of the combustion chamber of the reactor is in the range of about 1.3:1 to about 1.5:1, the inner diameter of the annular baffle is in the range of about 65% to about 75% of the inner diameter of the combustion chamber, and the height of the annular baffle is in the range of about 8% to about 25% of the inner height of the combustion chamber. Additionally, the reactor typically has a single non-premixed burner.

[0098] In some embodiments, where the reactor has a single non-premixed burner and the ratio of the inner diameter to the inner height of the combustion chamber of the reactor is in the range of about 1.3:1 to about 1.5:1, the inner diameter of the annular baffle is in the range of about 75% to about 85% of the inner diameter of the combustion chamber, and the height of the annular baffle is in the range of about 15% to about 25% of the inner height of the combustion chamber.

[0099] Aspects of the present invention include:

[0100] #1. A reactor comprising: a. an insulating cylindrical sidewall having a first end and a second end opposite the first end, the cylindrical sidewall being closed at the first end by a first insulating end wall and at the second end by a second insulating end wall, the insulating cylindrical sidewall and the insulating end walls defining a combustion chamber having an inner diameter, an inner height, and a longitudinal axis parallel to the cylindrical sidewall; b. at least one burner centrally positioned in the first insulating end wall; c. a plurality of catalyst-containing tubes extending through one of the insulating end walls into the combustion chamber and toward the opposing insulating end walls, the tubes being parallel to the insulating cylindrical side wall and arranged in a circular array coaxial with the longitudinal axis of the combustion chamber; d. at least one outlet for combustion gas, the at least one outlet extending through the insulating end wall, the plurality of catalyst-containing tubes extending through the insulating end wall, the at least one outlet being positioned adjacent the tubes; and e. an annular baffle located on the second insulating end wall and extending from the second insulating end wall into the combustion chamber, the annular baffle being coaxial with the longitudinal axis of the combustion chamber,

[0101] wherein the circular array of the plurality of catalyst-containing tubes is positioned between the annular baffle and the insulating cylindrical sidewall, and

[0102] The annular baffle has an inner diameter within a range of about 55% to about 90% of the inner diameter of the combustion chamber, and a height within a range of about 5% to about 30% of the inner height of the combustion chamber.

[0103] #2. The reactor of aspect #1, wherein the burner is a non-premixing burner, or if there is more than one burner, each burner is a non-premixing burner.

[0104] #3. A reactor as described in Aspect #1 or Aspect #2, wherein the inner diameter of the annular baffle is in the range of about 65% to about 85%, or about 65% to about 75%, or about 75% to about 85% of the inner diameter of the combustion chamber.

[0105] #4. A reactor as described in any one of Aspects #1 to #3, wherein the height of the annular baffle is in the range of about 8% to about 25% of the interior height of the combustion chamber, for example, about 8% to about 12% or about 18% to about 22%.

[0106] #5. A reactor as described in any one of Aspects #1 to #4, provided that when the inner diameter of the annular baffle is at least 75% of the inner diameter of the combustion chamber, the height is at least about 15% of the inner height of the combustion chamber.

[0107] #6. A reactor as described in any one of samples #1 to #4, wherein the inner diameter of the annular baffle is in the range of about 68% to about 72% of the inner diameter of the combustion chamber, for example, about 70%, and the height is in the range of about 18% to about 22% of the internal height of the combustion chamber, for example, about 20%.

[0108] #7. A reactor as described in any one of samples #1 to #5, wherein the inner diameter of the annular baffle is in the range of about 75% to about 85% of the inner diameter of the combustion chamber, and the height is in the range of about 15% to about 25% of the internal height of the combustion chamber.

[0109] #8. A reactor as described in any one of aspects #1 to #7, wherein the annular baffle is a circular band extending vertically from the second insulating end wall.

[0110] #9. The reactor of any one of aspects #1 to #8, wherein the annular baffle has a thickness in the range of about 0.1 cm to about 15 cm.

[0111] #10. The reactor of any one of aspects #1 to #9, wherein the annular baffle has a thickness in the range of about 0.25 cm to about 10 cm.

[0112] #11. A reactor as described in any one of samples #1 to #10, wherein the annular baffle comprises a metal alloy or a ceramic material.

[0113] #12. A reactor as described in any one of Aspects #1 to #11, wherein the annular baffle is made of alumina refractory bricks.

[0114] #13. A reactor as described in any one of aspects #1 to #11, wherein the annular baffle comprises a metal alloy, or is made of a metal alloy and has a thickness in the range of about 0.25 cm to about 2 cm.

[0115] #14. A reactor as described in any one of samples #1 to #11, wherein the annular baffle comprises a ceramic material or is made of a ceramic material and has a thickness in the range of about 2.5 cm to about 10 cm.

[0116] #15. A reactor as described in any one of Aspects #1 to #14, wherein the annular baffle is cast together with the second insulating end wall.

[0117] #16. The reactor of any one of aspects #1 to #15, wherein the ratio of the inner diameter (D) to the inner height (h) of the combustion chamber is in the range of about 1:1 to about 2:1.

[0118] #17. A reactor as described in any one of aspects #1 to #16, wherein the plurality of catalyst-containing reactor tubes extend through the second insulating end wall and toward the first insulating end wall.

[0119] #18. A reactor as described in any one of aspects #1 to #17, wherein the plurality of catalyst-containing tubes extend through both the first insulating end wall and the second insulating end wall.

[0120] #19. A reactor as described in any one of samples #1 to #18, wherein each catalyst-containing tube comprises an inner tube coaxially positioned within an outer tube, an annular space defined between the outer tube and the inner tube, and the annular space is filled with the catalyst.

[0121] #20. A reactor as described in aspect #19, wherein there is a gap between the ends of the catalyst-containing tube and the opposing insulating end walls.

[0122] #21. A reactor as described in any one of aspects #1 to #20, wherein the circular array of the plurality of catalyst-containing tubes is positioned adjacent to the insulating cylindrical sidewall.

[0123] #22. A reactor as described in embodiments #1 to #21, wherein the outlet or each outlet includes a shield extending from the second insulating end wall away from the combustion chamber and defining an annular convection space around or surrounding a section of the catalyst-containing tube(s) outside the combustion chamber.

[0124] #23. The reactor of aspect #22, wherein the section of the catalyst-containing tube(s) outside the combustion chamber is in the range of about 30% to about 50%, e.g., about 40%, of the length of the tube(s).

[0125] #24. A reactor as described in any one of Aspects #1 to #23, wherein the catalyst is an ammonia cracking catalyst or a steam methane reforming catalyst.

[0126] #25. A method for performing an endothermic reaction, comprising: a. Combusting a fuel and an oxidant gas in (a plurality of) burners to heat the catalyst-containing tubes of the reactor as described in aspects # 1 to # 24; and b. Passing a feed gas through the catalyst-containing tubes to produce a product (or "synthesis") gas.

[0127] #26. The method of aspect #25, wherein the feed gas is ammonia, the catalyst is an ammonia cracking catalyst, and the product gas is a cracked gas, wherein the cracked gas comprises hydrogen, nitrogen, and residual ammonia.

[0128] #27. A method as described in aspect #25, wherein the feed gas system is a hydrocarbon feedstock selected from the group consisting of methane, natural gas, LPG, and naphtha or mixtures thereof, the catalyst is a steam methane reforming catalyst, and the product gas system comprises synthesis gas of hydrogen and carbon monoxide gases.

[0129] #28. Use of a reactor as defined in any one of Aspects #1 to 24 for performing an endothermic reaction.

[0130] #29. The use as described in aspect #28, wherein the endothermic reaction is ammonia cracking or steam methane reforming of a hydrocarbon feedstock.

[0131] The present invention will now be described, by way of example only, with reference to the accompanying drawings.

[0132] FIG1 depicts a 20° section of an annular reactor (2) according to the present invention. This section has two catalyst-containing tubes (however, as depicted, the second tube is largely hidden behind the first tube). It will be understood that the reactor (2) will actually have 18 such sections, and therefore a total of 36 tubes.

[0133] According to Figure 1, the reactor (2) has an insulating cylindrical side wall (not shown), an insulating first end wall (4), and an insulating second end wall (6) that define a combustion chamber (8). The combustion chamber (8) has an inner diameter (not shown), an inner height (h), and a longitudinal axis (10).

[0134] In this configuration, the first end wall (4) forms the top of the combustion chamber (8) and the second end wall (6) forms the bottom of the combustion chamber (8). For convenience, the first and second end walls (4, 6) will be referred to as the top (4) and bottom (6) respectively.

[0135] The non-premix burner (12) is centrally located, ie coaxially with the longitudinal axis (10) of the combustion chamber (8), in the top portion (4).

[0136] Although only two tubes are shown, a plurality of catalyst-containing tubes (14) extend through the bottom (6) into the combustion chamber (8) and toward the opposite top (4). The tubes (14) are parallel to the cylindrical sidewall (not shown) and are arranged in a circular array coaxial with the longitudinal axis (10) of the combustion chamber (8). The catalyst can be an ammonia cracking catalyst such as a ruthenium-based catalyst or a nickel-based catalyst, or a steam reforming catalyst such as a nickel-based catalyst.

[0137] There is an annular outlet (16) for the combustion gases, which extends through the bottom (6) adjacent to and around each tube (14). A tubular shroud (18) is positioned around the section of each tube (14) extending away from the combustion chamber (8). An annular space (not shown) between the outer surface of the tube (14) and the inner surface of the shroud (18) forms a convection space (not shown) in which heat transfer from the hot combustion gases to the tube (14) occurs.

[0138] As indicated by the arrows within the combustion chamber (8), hot combustion gases are generated by the burner (12) and flow generally downward from the top (4) to the bottom (6) of the combustion chamber (8). The gases are then deflected by the bottom (6) and tend to move radially toward the cylindrical sidewall (not shown). The inventors have determined that a significant portion of the combustion gases then exit the combustion chamber (8) directly through the combustion gas outlet (16), with only the remainder of the gases circulating around the chamber (8).

[0139] This flow pattern results in a "hot band" (generally indicated at 20) around the wall of each tube (14), near the outlet (16), which can compromise the integrity of the tube (14) at that point. A cold zone (22) also develops in the section of the tube (14) toward the top (4) of the combustion chamber (8). Uneven heat distribution adversely affects the efficiency of the catalytic reaction within the tube (14).

[0140] The section of the reactor (2) depicted in FIG2 is identical to the section of the reactor (2) depicted in FIG1 , except for the annular baffle (24) described further below. Features common between FIG1 and FIG2 are given the same reference numerals. Only the distinguishing feature(s) are discussed below.

[0141] An annular baffle (24) is positioned on the bottom (6) of the combustion chamber (8) and extends into the combustion chamber (8). The annular baffle (24) is positioned coaxially with the longitudinal axis (10) of the combustion chamber (8) and has a substantially rectangular cross-section. A circular array of a plurality of catalyst-containing tubes (14) is positioned between the annular baffle (24) and the cylindrical sidewall (not shown).

[0142] In this configuration, the annular baffle (24) has an inner diameter that is approximately 70% of the inner diameter of the combustion chamber (8) and a height that is approximately 20% of the inner height of the combustion chamber (8).

[0143] As indicated by the arrows in the combustion chamber (2), the annular baffle (24) has the effect of diverting and recirculating the combustion gases around the combustion chamber (8), thereby increasing the residence time of the combustion gases in the chamber (8) and providing a more uniform heat distribution to the tubes (14). Overall heat transfer is improved by up to about 10%, and the tube wall temperature near the combustion gas outlet (16) is reduced by up to about 100°C, for example, to about 70°C.

[0144] FIG3 is a cross-section of a reactor according to the present invention having 36 tubes, 18 of which are depicted. The reactor has a first insulating end wall (4) or top and a second insulating end wall (6) or bottom opposite the first insulating end wall (4). A non-premixed burner (12) is positioned in the middle of the first insulating end wall (4), and catalyst-containing tubes (14) extend in a circular configuration through the second end wall (6) to the first end wall (4). A shield (18) surrounds the portion of each tube (14) that extends beyond the second end wall away from the combustion chamber. An annular baffle (24) is positioned on the second end wall (6) and extends into the combustion chamber. The insulating cylindrical sidewalls are not shown.

[0145] It will be appreciated that although the reactor in FIG3 is depicted as being comprised of a plurality of 20° segments having two tubes as the segments depicted in FIG2, in practice the reactor would not be divided into segments in this manner.

[0146] Figure 4 is a partial cross section of another reactor (2) according to the invention of the type depicted in Figures 2 and 3. A person of ordinary skill will understand that only the left side is depicted, and the right side is simply a mirror image of the left side.

[0147] Features that are common between Figures 2 to 4 are given the same reference numerals. Only the distinguishing features will be discussed below.

[0148] The tube (14) is depicted in cross section. Thus, it can be seen that the tube (14) has an outer tube (28) and an inner tube (30) coaxially positioned within the outer tube (28). The catalyst fills the annular space (32) defined by the outer and inner tubes (28, 30). In this embodiment, a plug (34) of catalyst is located at the top of the tube (14), covering the opening of the inner tube (30). The outer tube (28) extends through the top (4) of the combustion chamber (8) and is closed first with an insulating plug (35) and then with a gasket (36) that provides access to the catalyst.

[0149] A feed gas stream (38), in this case ammonia, travels over the catalyst in the annular space (32) where it is cracked to form a cracked gas comprising hydrogen, nitrogen, and residual ammonia. The cracked gas travels through the inner tube (30) where heat is transferred through the walls of the inner tube to the gas being cracked on the catalyst in the annular space (32) before exiting the reactor (2) as stream (40) through an outlet (not shown).

[0150] The combustion gases exit the combustion chamber (8) via the outlet (16) and travel through the convection shroud (18) where they transfer heat to the gases being cracked on the catalyst in the annular space (32) before exiting the reactor (2) as a flue gas stream (42).

[0151] Figure 5 depicts an alternative to the reactor (2) depicted in Figure 4. Features that are common between Figures 4 and 5 are given the same reference numerals. Only the distinguishing feature(s) are discussed below.

[0152] The difference between the reactor (2) of Figure 5 and the reactor (2) of Figure 4 is that the tube (14) does not extend all the way through the combustion chamber (8), but there is a gap between the end cover (37) and the top (4) of the combustion chamber.

[0153] Examples

[0154] CFD simulations were performed using Ansys Fluent software (version 2023) to model the flow of combustion gases in a tube reactor comprising a single non-premixed burner and a combustion chamber with an aspect ratio (inner diameter to inner height) ranging from 1.3:1 to 1.5:1, for cracking ammonia using a nickel-based catalyst.

[0155] As described below, the same simulations were performed for a reactor without annular baffles and for reactors with annular baffles of varying heights and internal diameters.

[0156] The model is constructed from multiple fluid (furnace and internal process tubes) and solid (tubes, shroud, and refractory walls) volumes. All volumes are solved simultaneously, and the heat transfer between them is modeled using the conjugate heat transfer method.

[0157] To reduce computational workload, most simulations were performed on a 1 / 18th section of the reactor, which has 36 tubes. Therefore, this section has two tubes. Simulations with eight tubes were also performed to ensure that the observed flow patterns were not due to simplified models. Multiple meshes were tested to ensure a mesh-independent solution. For the two-tube model, the final mesh consisted of approximately 5 million volumes.

[0158] For the furnace side, the following models are included:

[0159] Turbulence Modeling

[0160] Turbulent combustion interaction

[0161] Simplified combustion dynamics based on the default Fluent model of a H2-rich flame

[0162] Radiative heat transfer in participating media

[0163] Gas emissivity according to temperature and composition

[0164] The flow model on the pipe side includes:

[0165] Turbulence Modeling

[0166] Definition of porous media based on catalyst data

[0167] Customized to enhance heat transfer based on the Nimvari 2003 model

[0168] The kinetics of ammonia cracking over ruthenium-based catalysts were modeled using rate equation 9 based on Lamb et al. (Int. J. Hydrogen Energy, 44 (2019) pp 3726-3736)

[0169] The tube, shroud, and refractory wall are modeled as gray bodies with emissivity and material properties provided by the manufacturer.

[0170] Boundary conditions:

[0171] The two surfaces parallel to the tube that bound the reduced volume are modeled as periodic boundaries

[0172] At the burner inlet, we specify the mass flow, composition, pressure, and temperature of air and fuel (main fuel of hydrogen recovery waste gas and natural gas trimming fuel) within the above range.

[0173] At the process tube inlet, we specify the process gas mass flow, composition, pressure, and temperature within the above ranges.

[0174] At the furnace and pipeline outlets, we specify the pressure within the above range.

[0175] For the outer surface of the furnace, "mixed" boundary conditions are used to simulate the effects of natural convection and radiation in the atmosphere.

[0176] The furnace load and tube load are within the ranges identified above.

[0177] The simulation is conducted on the following aspects:

[0178] (a) Reactor without annular baffles;

[0179] (b) a reactor having an annular baffle having an inner diameter that is 50% of the inner diameter of the combustion chamber and a height that is 15% of the inner height of the combustion chamber; and

[0180] (c) A reactor having an annular baffle having an inner diameter that is 70% of the inner diameter of the combustion chamber and a height that is 20% of the inner height of the combustion chamber.

[0181] The problem being solved is confirmed by simulation (a). In this regard, FIG6 clearly depicts the clockwise flow of the combustion gases, which directly impinge on the section of the tubes near the second insulating end wall (6) before circulating back to the top of the reactor, resulting in the formation of a hot zone on the tube walls at the bottom of the furnace. A large portion of the hot combustion gases also exits through the shroud (18) without being recirculated. This flow pattern reduces heat transfer per tube and increases ammonia slip. The inventors have recognized that this problem can be solved by using annular baffles.

[0182] However, the annular baffle (24) in simulation (b) did not solve this problem. In this regard, Figure 7 shows that a stagnant zone is formed within the annular baffle (24), resulting in clockwise top recirculation of the combustion gas, which again leads to higher tube wall temperatures, lower heat flux, and higher ammonia slip. The inventors determined that the inner diameter of the annular baffle is too small.

[0183] The inventors observed that the larger annular baffle (24) in simulation (c) in FIG8 redirects the flow of the combustion gases, causing a counterclockwise top recirculation, which reduces the temperature of the tube wall at the bottom of the reactor and improves the heat flux, thereby reducing ammonia slip.

[0184] It will be understood by those skilled in the art that the clockwise flow of combustion gases depicted in Figures 6 to 8 is actually counterclockwise on the opposite side of the combustion chamber. Similarly, the counterclockwise flow depicted in Figure 8 will actually be clockwise on the opposite side of the combustion chamber.

[0185] The results of simulations (a) and (c) are confirmed in Table 1 below. simulation Heat transfer per tube Ammonia slip Tube wall temperature at the bottom of the furnace (a)-without annular baffle 25 kW 4% 680℃ (c)-Annular baffle 27 kW 1.6% 610℃ Table 1

[0186] According to the data in the table, the use of annular baffles in simulation (c) improved heat transfer per tube by 8%, thereby reducing ammonia slip by approximately 60%. In addition, the tube wall temperature was reduced by 70°C.

[0187] While the invention has been described with reference to the preferred embodiments depicted in the drawings, it will be understood that various modifications are possible within the spirit and scope of the invention as defined in the following claims.

[0188] In this specification, unless expressly indicated otherwise, the word "or" is used in the sense of an operator that returns a true value when one or both of the stated conditions are met, as opposed to the operator "exclusive or," which requires only one of the conditions to be met. The word "comprising" is used in the sense of "include" and is inclusive of "consisting of," rather than exclusively referring to "consisting of."

[0189] The publication of any prior document herein is not an admission or representation that the teachings of that document were common general knowledge in Australia or elsewhere as of the date of its publication.

[0190] 2: Reactor 4: Insulate the first end wall / top 6: Insulate the second end wall / bottom 8: Combustion Chamber 10: Longitudinal axis 12: Non-premixed burner 14: Tube containing catalyst 16: Ring exit 18: Shield 20: Tropical 22: Low temperature zone 24: Annular baffle 28: External tube 30: Inner tube 32: Ring Space 34: Catalyst Plug 35: Insulation plug 36: Washer 37: End cap 38: Feed gas flow 40: Flow 42: Flue gas flow

Claims

1. A reactor comprising: an insulating cylindrical sidewall having a first end and a second end opposite to the first end, the cylindrical sidewall being closed at the first end by a first insulating end wall and at the second end by a second insulating end wall, the cylindrical sidewall, the first insulating end wall, and the second insulating end wall defining a combustion chamber having an inner diameter, an internal height, and a longitudinal axis parallel to the cylindrical sidewall; at least one burner centrally positioned in the first insulating end wall, wherein each of the at least one burner is a non-premixed burner; a plurality of catalyst-containing tubes extending through one of the first and second insulating end walls into the combustion chamber and toward the other insulating end wall opposite to the first insulating end wall, the plurality of catalyst-containing tubes being parallel to the insulating cylindrical sidewall and configured in a circular array coaxial with the longitudinal axis of the combustion chamber; At least one outlet for combustion gases, the at least one outlet extending through the plurality of catalyst-containing tubes through the one insulating end wall, the at least one outlet being positioned adjacent to the plurality of catalyst-containing tubes; and an annular baffle located on and extending from the other insulating end wall into the combustion chamber, the annular baffle being coaxial with the longitudinal axis of the combustion chamber, wherein the circular array of the plurality of catalyst-containing tubes is positioned between the annular baffle and the insulating cylindrical sidewall, and wherein the annular baffle has an inner diameter in the range of about 55% to about 90% of the inner diameter of the combustion chamber, and a height in the range of about 5% to about 30% of the internal height of the combustion chamber.

2. The reactor as claimed in claim 1, wherein the inner diameter of the annular baffle is in the range of about 65% to about 85% of the inner diameter of the combustion chamber.

3. The reactor as claimed in claim 1, wherein the inner diameter of the annular baffle is in the range of about 65% to about 75% of the inner diameter of the combustion chamber.

4. The reactor as claimed in claim 1, wherein the inner diameter of the annular baffle is in the range of about 75% to about 85% of the inner diameter of the combustion chamber.

5. The reactor as claimed in claim 1, wherein the height of the annular baffle is in the range of about 8% to about 25% of the internal height of the combustion chamber.

6. The reactor as claimed in claim 1, wherein the annular baffle is a circular band extending vertically from the second end wall.

7. The reactor as claimed in claim 1, wherein the annular baffle has a thickness ranging from about 0.1 cm to about 15 cm.

8. The reactor as claimed in claim 1, wherein the annular baffle is made of a metal alloy and has a thickness ranging from about 0.25 cm to about 2 cm.

9. The reactor as claimed in claim 1, wherein the annular baffle is made of ceramic material and has a thickness ranging from about 2.5 cm to about 10 cm.

10. The reactor as claimed in claim 1, wherein the annular baffle is cast together with the second insulating end wall.

11. The reactor as claimed in claim 1, wherein the ratio of the inner diameter (D) to the inner height (h) of the combustion chamber is in the range of about 1:1 to about 2:

1.

12. The reactor as claimed in claim 1, wherein the plurality of catalyst-containing reactor tubes extend through the second insulating end wall and toward the first insulating end wall.

13. The reactor as claimed in claim 1, wherein the plurality of catalyst-containing tubes extend through both the first insulating end wall and the second insulating end wall.

14. The reactor as claimed in claim 1, wherein each of the plurality of catalyst-containing tubes includes an inner tube coaxially positioned within an outer tube, and an annular space is defined between the outer tube and the inner tube, the annular space being filled with the catalyst.

15. The reactor as claimed in claim 14, wherein a gap exists between the ends of the plurality of catalyst-containing tubes and the other insulating end wall.

16. The reactor as claimed in claim 1, wherein the circular array of the plurality of catalyst-containing tubes is positioned adjacent to the insulating cylindrical sidewall.

17. The reactor as claimed in claim 1, wherein the at least one outlet or each of the outlets includes a shroud extending from the other insulating end wall away from the combustion chamber and defining an annular convection space around a section of the plurality of catalyst-containing tubes outside the combustion chamber.

18. The reactor as claimed in claim 17, wherein the section of the plurality of catalyst-containing tubes outside the combustion chamber is within about 30% to about 50% of the length of the plurality of catalyst-containing tubes.

19. A method for carrying out an endothermic reaction, the method comprising: burning a fuel and an oxidant gas in (a plurality of) burners to heat a catalyst-containing tube of a reactor as claimed in claim 1; and passing a feed gas through the catalyst-containing tube to produce a synthesis gas.

20. The method of claim 19, wherein the feed gas system is ammonia, the catalyst is an ammonia cracking catalyst, and the syngas system is a cracked gas containing hydrogen, nitrogen, and residual ammonia.

21. The method as claimed in claim 19, wherein the feed gas system is selected from the group consisting of natural gas, LPG and naphtha, the catalyst is a steam reforming catalyst, and the synthesis gas comprises hydrogen and carbon monoxide.

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