WO2026013372A1

WO2026013372A1 - Device for hydrogen production

Info

Publication number: WO2026013372A1
Application number: PCT/GB2025/050028
Authority: WO
Inventors: Christopher Maurice TIMS; Robert Harrison; George Michael CARINS; Toby SCOBELL; Sotiris ALEXANDROU; Michael Edward Rendall
Original assignee: AFC Energy PLC
Current assignee: AFC Energy PLC
Priority date: 2024-07-09
Filing date: 2025-01-08
Publication date: 2026-01-15
Anticipated expiration: 2027-01-09

Abstract

A hydrogen production device for producing a hydrogen rich gas from ammonia comprising a first chamber comprising an inner wall and an outer wall defining an internal volume, wherein the first chamber contains an ammonia decomposition catalyst disposed between the inner wall and the outer wall, the first chamber having one or more ammonia gas inlets and one or more raw cracked gas outlets, wherein said one or more ammonia gas inlets and one or more raw cracked gas outlets are arranged such that the ammonia flows through the first chamber from the one or more ammonia gas inlets to the one or more raw cracked gas outlets and contacts the ammonia decomposition catalyst; and one or more heat sources for heating the ammonia decomposition catalyst; wherein the first chamber has one or more fins, said one or more fins disposed between the inner wall and the outer wall of the first chamber, wherein the first chamber has an internal surface area, wherein the internal volume is between 10 ml and 100 litres and wherein the ratio of the internal surface area in mm² to the internal volume in mm³ is between approximately 1 :2 and 1 :6.

Description

DEVICE FOR HYDROGEN PRODUCTION

Background

Hydrogen gas is a promising clean fuel with a significant role to play as part of the global effort to reduce climate change. It can be readily combusted, as well as being used to generate electrical energy using specialized devices such as fuel cells. There are a number of methods of generating hydrogen, for example steam reformation of natural gas or water electrolysis. However, one promising method of generating clean hydrogen is the catalytic breakdown (commonly referred to as ‘catalytic cracking’ or simply ‘cracking’) of ammonia gas into hydrogen and nitrogen according to the following reaction:

2NH₃ ^ N₂ + 3H₂

Devices for producing hydrogen by this means are commonly referred to as ‘ammonia crackers’ and involve providing a heated chamber containing catalyst through which ammonia gas flows. Upon contact with the catalyst, the ammonia is cracked and the hydrogen and nitrogen gas are produced. Such devices are known in the art (see, for example, W02009098452A2).

The basic premise is to pass heated ammonia gas over an ammonia decomposition catalyst at the correct temperature range to catalytically convert the ammonia into hydrogen and nitrogen. The output gas is typically a mixture of hydrogen, nitrogen, and a residual amount of uncracked ammonia due to the cracking reaction being an equilibrium between ammonia and cracked gas. Further filtration steps are required to purify the hydrogen (i.e. the use of a gas separator such as a palladium filter or a pressure-swing-adsorption device) if the desired output is to be free of Nitrogen or Ammonia.

In order to optimize the reaction conditions in the reaction chamber of such a device, the incoming gas flow rate, pressure and residency within the reactor must be carefully managed to maximise the decomposition of ammonia as efficiently as possible without compromising the longevity of the device. In addition, good heat transfer is required to minimize the volume of the reactor and to maximise the utilization of the catalyst.

Applicants have discovered a reaction chamber architecture which addresses the drawbacks of the prior art devices to optimize the decomposition of ammonia into nitrogen and hydrogen.

Summary of the Invention

In a first aspect, the invention provides a hydrogen production device for producing a hydrogen rich gas from ammonia comprising a first chamber comprising an inner wall and an outer wall defining an internal volume, wherein the first chamber contains an ammonia decomposition catalyst disposed between the inner wall and the outer wall, the first chamber having one or more ammonia gas inlets and one or more raw cracked gas outlets, wherein said one or more ammonia gas inlets and one or more raw cracked gas outlets are arranged such that the ammonia flows through the first chamber from the one or more ammonia gas inlets to the one or more raw cracked gas outlets and contacts the ammonia decomposition catalyst; and one or more heat sources for heating the ammonia decomposition catalyst; wherein the first chamber has one or more fins, said one or more fins disposed between the inner wall and the outer wall of the first chamber, wherein the first chamber has an internal surface area defined as the area of the internal volume facing surface of the inner wall and each surface of the one or more fins, wherein the internal volume is between 10 ml and 100 litres and wherein the ratio of the internal surface area in mm² to the internal volume in mm³ is between approximately 1 :2 and 1 :6.

In some embodiments, at least one of the one or more heat sources are proximal to the inner wall or proximal to the outer wall.

In some embodiments, the one or more heat sources comprise at least two heat sources, preferably wherein at least one of which is proximal to the inner wall and at least one of which is proximal to the outer wall.

In some embodiments, at least one of the one or more fins are attached to and/or extend from the inner wall.

In some embodiments, at least one of the one or more fins and the inner wall are a one-piece construction.

In some embodiments, at least one of the one or more fins is attached to the inner wall by mechanical interference fit or mechanical fasteners. In some embodiments, at least one of the one or more fins are attached to the inner wall by a bonding. In a further embodiment, the one or more fins are made of a different material to the inner or outer wall of the first chamber. In a further embodiment, the bonding is a weld or a braze.

In some embodiments, the one or more fins comprise a plurality of fins. In a further embodiment, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of the plurality of fins are attached to and/or extend from the inner wall. In another embodiment, the plurality of fins are attached to and/or extend from the inner wall, In a further embodiment, the plurality of fins are disposed as one or more spirals through the length of the first chamber.

In some embodiments, the plurality of fins are disposed as one or more rows, each fin of each row being parallel with each fin of the same row on a plane substantially perpendicular to the length of the first chamber.

In some embodiments, each fin of the plurality of fins has an angle which is the same as each other fin.

In some embodiments, at least one fin of the plurality of fins has an angle which is different to at least one other fin. In a further embodiment at least one fin of the plurality of fins having a different angle to at least one other fin is in the same row as the at least one other fin. In an embodiment, the plurality of fins are disposed as at least two rows, and the at least one fin of the plurality of fins having a different angle to at least one other fin is in a different row to the at least one other fin.

In some embodiments, the angle of each fin is chosen from the group consisting of: substantially perpendicular to the length of the first chamber, substantially parallel with the length of the chamber, and/or angled between substantially perpendicular and substantially parallel with the length of the chamber.

In some embodiments, at least one of the one or more fins has a planar profile.

In some embodiments, at least one of the one or more fins has a varied profile through its length. In a further embodiment, wherein at least one of the one or more fins comprises one or more apertures and/or one or more protrusions and/or one or more depressions on a surface of the at least one fin. In some embodiments, at least one fin of the one or more fins may be a hollow fin which comprises a subchamber defined by one or more fin walls and an internal baffle, wherein the one or more fin walls comprise one or more entry apertures on a face of the fin, and one or more exit apertures on an opposite face of the fin. In some embodiments, at least one of the one or more fins comprises an indent proximal to the inner and/or outer wall.

In some embodiments, the device further comprises a plurality of rows wherein at least one row of the plurality of rows is disposed such that one or more fins of the at least one row are not wholly overlapping with the one or more fins of at least one other row of the plurality of rows through the length of the first chamber.

In some embodiments, the device further comprises a plurality of rows, with a distance (d) between each pair of adjacent rows, wherein the distance (d) is the same through the length of the first chamber.

In some embodiments, the device comprises a plurality of rows, each with a distance (d) between each pair of adjacent rows, wherein the distance (d) differs between at least two pairs of adjacent rows through the length of the first chamber.

In some embodiments, at least one of the one or more fins are connected to the outer wall of the first chamber by mechanical interference fit or mechanical fasteners.

In some embodiments, at least one of the one or more fins is a one-piece construction with the outer wall.

In some embodiments, at least one of the one or more fins are attached to the outer wall by a second bonding.

In some embodiments, the second bonding is welding or brazing.

In some embodiments, the inner wall further defines a second chamber within the first chamber, the second chamber having one or more fins disposed therein.

In some embodiments, the one or more fins extend from the first chamber into the second chamber.

In some embodiments, the inner wall and/or the outer wall have the shape of a cylinder, with the inner wall being disposed within the outer wall, and the volume between the inner wall and the outer wall being the first chamber, the first chamber having an annular shape.

In some embodiments, the inner wall and/or the outer wall each have a prismatic shape, with the inner wall being disposed within the outer wall, and the volume between the inner wall and the outer wall being the first chamber.

In some embodiments, the inner wall and the outer wall are concentric.

In some embodiments, the inner wall and/or the outer wall each have an irregular prismatic shape, with the innerwall being disposed within the outer wall, and the volume between the innerwall and the outer wall being the first chamber.

In a second aspect, the invention provides a hydrogen production device for producing a hydrogen rich gas from ammonia comprising: a first chamber comprising outer wall defining an internal volume of the first chamber, wherein the first chamber contains an ammonia decomposition catalyst disposed within the first chamber, the first chamber having one or more ammonia gas inlets and one or more raw cracked gas outlets, wherein said one or more ammonia gas inlets and one or more raw cracked gas outlets are arranged such that the ammonia flows through the first chamber from the one or more ammonia gas inlets to the one or more raw cracked gas outlets and contacts the ammonia decomposition catalyst; wherein two or more inner walls are disposed within the internal volume, defining two or more inner chambers within the first chamber, wherein the two or more inner chambers each comprise a heat source for heating the ammonia decomposition catalyst; wherein the two or more inner walls have one or more fins, said one or more fins extending from the two or more inner walls and disposed in the internal volume of the first chamber; wherein the first chamber has an internal surface area defined as the area of the internal volume facing surface of each of the two or more inner walls and each surface of the one or more fins, and wherein the ratio of the internal surface area in mm² to the internal volume in mm³ is between approximately 1 :2 and 1 :6.

In some embodiments, the two or more inner walls each have the shape of: a cylinder; a prism; and/or an irregular prism, wherein each of the two or more inner chambers are defined as the internal volume defined by at least one of the two or more inner walls.

In some embodiments, the two or more inner chambers are fluidly connected to a combustion chamber, and/or wherein the two or more inner chambers are combustion chambers having an oxidation catalyst disposed therein.

In some embodiments, the minimum distance between each of the two or more inner chambers is twice the minimum distance between any of the two or more inner chambers adjacent to the outer wall and the outer wall.

In some embodiments, at least one of the two or more inner walls having one or more fins extending therefrom have a one-piece construction.

In some embodiments, at least one of the one or more fins is attached to at least one of the two or more inner walls by mechanical interference fit or mechanical fasteners. In some embodiments, at least one of the one or more fins are attached to at least one of the two or more inner walls by a bonding, optionally wherein the one or more fins are made of a different material to the two or more inner walls or the outer wall, further optionally wherein the bonding is a weld or a braze.

In some embodiments, the one or more fins comprise a plurality of fins.

In some embodiments, the plurality of fins are disposed as one or more spirals through the length of the first chamber.

In some embodiments, at least one fin of the plurality of fins has an angle which is different to at least one other fin. In a further embodiment, the at least one fin of the plurality of fins having a different angle to at least one other fin is in the same row as the at least one other fin or wherein the plurality of fins are disposed as at least two rows, and the at least one fin of the plurality of fins having a different angle to at least one other fin is in a different row to the at least one other fin; optionally wherein the angle of each fin is chosen from the group consisting of: substantially perpendicular to the length of the first chamber, substantially parallel with the length of the chamber, and/or angle between substantially perpendicular and substantially parallel with the length of the first chamber.

In some embodiments, at least one of the one or more fins has a planar profile.

In some embodiments, at least one of the one or more fins has a varied profile through its length; optionally wherein at least one of the one or more fins comprises one or more apertures and/or one or more protrusions and/or one or more depressions on a surface of the at least one fin.

In some embodiments, at least one fin of the one or more fins may be a hollow fin which comprises a subchamber defined by one or more fin walls and an internal baffle, wherein the one or more fin walls comprise one or more entry apertures on a face of the fin and one or more exit apertures on an opposite face of the fin.

In some embodiments, at least one of the one or more fins comprises an indent proximal to at least one of the two or more inner walls or the outer wall.

In some embodiments, the device comprises a plurality of rows wherein at least one row of the plurality of rows is disposed such that one or more fins of the at least one row are not wholly overlapping with the one or more fins of at least one other row of the plurality of rows through the length of the first chamber.

In some embodiments, the device comprises a plurality of rows, with a distance (d) between each pair of adjacent rows, wherein the distance (d) is the same through the length of the first chamber. In some embodiments, the device comprises a plurality of rows, each with a distance (d) between each pair of adjacent rows, wherein the distance (d) differs between at least two pairs of adjacent rows through the length of the first chamber.

In a third aspect, the invention provides a system for producing purified hydrogen comprising one or more devices according to the first aspect or the second aspect and any of its embodiments, further comprising a gas separator for separating hydrogen gas from other gases in fluid communication with the one or more devices.

In a fourth aspect the invention provides a system for producing electrical energy comprising the system of the third aspect, further comprising a fuel cell.

Brief Description of the Drawings

Figure 1 shows a cutaway view of an exemplary device according to the invention. Figure 1 A shows a side cutaway view. Figure 1 B shows a top down cutaway view.

Figure 2 shows an internal view of a section of an exemplary device according to embodiments of the invention. Figure 2A shows a 3D view. Figure 2B shows a side- on view. Figure 2C shows a top-down view.

Figure 3 shows an internal view an alternative section of an exemplary device according to embodiments of the invention. Figure 3A shows a 3D view. Figure 3B shows a side-on view. Figure 3C shows a top-down view.

Figure 4 shows exemplary fins according to the invention. Figure 4A shows a side on view of a fin having a planar profile. Figure 4B shows a side on view of a fin having a varied profile. Figure 4C shows a top-down view of a fin having two indents proximal to the inner wall.

Figure 5 shows an exemplary hollow fin according to embodiments of the invention. Figure 5A shows a 3D cutaway view. Figure 5B shows a top-down view. Figure 5C shows a side on cut-away view.

Figure 6 shows an internal, side on view a section of an exemplary device according to embodiments of the invention having non-overlapping fins.

Figure 7 shows an internal side on view of two sections of an exemplary device according to embodiments of the invention. Figure 7A shows a device where the rows are all an equal distance apart from their adjacent row. Figure 7B shows a device where the rows are different distances apart to their adjacent row.

Figure 8 shows a side-on, cutaway view of an exemplary device according to some embodiments of the invention having a second, internal chamber and one or more internal fins disposed inside said second chamber.

Figure 9 shows an alternative section of an exemplary device according to embodiments of the invention as a side-on view.

Figure 10 shows a side-on, cutaway view of an exemplary device according to some embodiments of the invention having a second, internal chamber and one or more internal fins disposed in the first chamber and extending from the inner wall only. Figure 11 shows a side-on, cutaway view of an exemplary device according to some embodiments of the invention having a second, internal chamber and one or more internal fins disposed in the first chamber and second chamber and extending from the inner wall only into both chambers.

Figure 12 shows a system comprising a device according to the invention as part of a system including a gas separator and a hydrogen fuel cell.

Figure 13 shows a top down, cutaway view of a cross section of the device demonstrating exemplary shapes the chambers of the device can take.

Figure 14 shows a cross-sectional view across the width of a device according to an aspect of the invention, and then a three-dimensional view of said device.

Detailed Description

In a first aspect, the invention provides a hydrogen production device (a device) for producing a hydrogen rich gas from ammonia comprising: a first chamber comprising an inner wall and an outer wall defining an internal volume, wherein the first chamber contains an ammonia decomposition catalyst between the inner wall and the outer wall, the first chamber having one or more ammonia gas inlets and one or more raw cracked gas outlets, wherein said one or more ammonia gas inlets and one or more raw cracked gas outlets are arranged such that the ammonia flows through the first chamber from the one or more ammonia gas inlets to the one or more raw cracked gas outlets and contacts the ammonia decomposition catalyst; the device further comprising one or more heat sources for heating the ammonia decomposition catalyst; wherein the first chamber has one or more fins, said one or more fins disposed between the inner wall and the outer wall of the first chamber, wherein the first chamber has an internal surface area, wherein the internal volume is between 10 ml and 100 litres and wherein the ratio of the internal surface area in mm² to the internal volume in mm³ is between approximately 1 :2 and 1 :6.

US 2003/0232224 A1 relates to a process for producing hydrogen from gaseous ammonia and recycling a portion of said hydrogen to heat the reaction. A conventional tubular ammonia cracking apparatus is shown (cf. Figure 3 therein), but there is no disclosure of the advantageous architecture of the present invention.

US 4430304 A disclose a catalytic ‘slab’ reformer where pins and fins are shown extending through all inner walls of the device (cf. Figure 4 therein). There is no disclosure in US 4430304 A of the advantageous architecture of the present invention.

US 2578193 A discloses an apparatus for producing hydrogen from gaseous ammonia, intended for home use. This is a conventional ammonia cracking device and the document discloses none of the advantageous architecture of the present invention.

US 2023/118083 A1 relates to a generic ammonia cracking device. There is no disclosure therein of the advantageous architecture of the present invention. US 2004/ 154223 A1 relates to a generic ammonia cracking device. There is no disclosure therein of the advantageous architecture of the present invention.

GB 1 336 375 A relates to an old generic reaction chamber architecture. There is no disclosure therein of the advantageous architecture of the present invention.

CN 111 170273 A relates to a generic ammonia cracking device as part of a ship power system. There is no disclosure therein of the advantageous architecture of the present invention.

Turning to the present invention, the first chamber comprises an outer wall and an inner wall which defines an internal volume where the decomposition of ammonia reaction takes place. The first chamber is gas tight with respect to the outside atmosphere, except for the one or more ammonia gas inlets and the one or more raw cracked gas outlets. It can take any shape, depending on the specific requirements for its installation and the envisioned use case. Inside the chamber, there is an ammonia decomposition catalyst which catalyses the conversion of ammonia into a raw cracked gas including nitrogen and hydrogen when the ammonia gas flows from the one or more ammonia gas inlets through the chamber before exiting via the one or more raw cracked gas outlets. The one or more ammonia gas inlets and the one or more raw cracked gas outlets are arranged such that, in use, ammonia gas flows through the internal volume and contacts or interacts with the ammonia decomposition catalyst. This can be achieved in any number of ways apparent to the skilled person. For example, the one or more ammonia gas inlets may be disposed at a first end of the first chamber, with the one or more raw cracked gas outlets disposed at the second end of the first chamber, the second end being opposite end of the first chamber. In such an example, each end means the opposite ends of the chamber lengthwise. The raw cracked gas consists essentially of a mixture of hydrogen gas, nitrogen gas, and ammonia gas. The ammonia gas in the raw cracked gas is the ammonia which did not decompose into nitrogen and hydrogen as it passed through the first chamber. Many suitable catalysts are known in the art. For example, supported monometallic catalysts (e.g. Fe, Ru, Cu, Ni, Ir, Co, Mo, Pt and Pd) multimetallic catalysts or alloy catalysts (e.g. Ni-Pt, Ni-Co, Ir-Ni, Co- Mo, Fe-Co, Fe-Mo, Cu-Zn), nitride and carbide catalysts (e.g. Carbides and nitrides of Mo, Fe, Co, Ni, Ti, V, Mn and Cr), and metal amide/imide catalysts (e.g. LiNH2, NaNH2, KNH2) may be used in the present invention. The catalyst is between the inner and the outer wall of the first chamber. It may be deposited directly upon an internal face of the chamber and/or it may be deposited on a suitable substrate which is then placed inside the chamber. In one embodiment, the ammonia decomposition catalyst is coated on an internal surface of the inner wall and/or the outer wall. To be clear, the internal surface is the surface which is inward facing and may include the entire surface of the one or more fins. It may be the surface of the inner wall facing into the first chamber and the one or more fins and/or the surface of the outer wall facing into the first chamber. In another embodiment, the ammonia decomposition catalyst is provided on a separate substrate which at least partially fills an internal volume of the first chamber. In a further embodiment, the ammonia decomposition catalyst is both coated on the internal surface of the inner wall (including the surface of the fins) and/or the outer wall (including the surface of the fins), as well as being provided on a separate substrate which at least partially fills the internal volume of the first chamber. The one or more ammonia inlets, one or more raw cracked gas outlets, and the ammonia decomposition catalyst are arranged so that, in use, the ammonia gas flows into the one or more ammonia inlets, flows through the device such that the ammonia gas contacts the ammonia decomposition catalyst such that it is converted into the raw cracked gas comprising hydrogen and nitrogen, and the raw cracked gas comprising hydrogen and nitrogen flows out of the one or more raw cracked gas outlets. Where the term ‘ammonia gas’ is recited throughout this specification, this means a gas mixture comprising ammonia in its gaseous form. In other words, it is an ammonia-containing gas. Such a gas may have any other number and/or ratio of other constituents, provided it comprises ammonia in its gaseous form.

The ammonia decomposition reaction, being an equilibrium, is favoured at lower pressures and higher temperatures; however these conditions are at odds with designing and building efficient and commercially viable ammonia crackers whereby a compromise set of conditions are selected to give sufficient ammonia conversion at the lowest temperatures and pressures that are suitable for the downstream processes. For example, the reaction may be at a temperature of 400 to 950 degrees Celsius and the pressure anywhere from 0.1 to 40 barg. Typically one or more heat sources are provided to heat the device to the optimal temperature for the chosen pressure. For example, the one or more heat sources may be an additional hot gas stream, an electrical induction heater, a radiative heater, a resistive electrical heater, a combustion heater, or any of the above in combination. In order to provide good heat transfer throughout the internal volume of the first chamber, the chamber has one or more fins disposed therein between the inner wall and the outer wall, as will be described below. The one or more heat sources can heat the device from the inside (in other words they are proximal to the inner wall). Additionally or in the alternative they can heat the device from the outside in (in other words they are proximal to the outer wall). A combination approach can also be taken. Regardless of the arrangement of the one or more heat sources, the one or more fins function to conduct the heat throughout the internal volume of the first chamber. The one or more heat sources heat the inner wall, the outer wall, and the fins, and ultimately heat the ammonia decomposition catalyst and ammonia gas to the required temperature to decompose the ammonia gas flowing through the first chamber. Where the ammonia decomposition catalyst is disposed on a separate substrate which at least partially fills the internal volume, the heat is transferred from the inner wall, the outer wall, and the one or more fins, to the substrate so that the reaction can proceed.

An exemplary device according to the invention is shown in Figure 1 having an annular structure, with an inner wall 102 forming a first cylinder, and an outer wall 103 forming a second cylinder with the first cylinder disposed inside the second cylinder, such that a reaction chamber is formed between the inner wall 102 and the outer wall 103. The first chamber is the reaction chamber where ammonia gas is at least partially decomposed into nitrogen and hydrogen upon contact with the ammonia decomposition catalyst therein. Figure 1 A shows a cutaway view from the side. Figure 1 B shows a cutaway top-down view. As shown, the device 100 is annular, and has an inner wall 102 and an outer wall 103 defining a first chamber 101 . The inlets and outlets are not shown in the cutaway diagram. An ammonia decomposition catalyst 104 is disposed within the first chamber as a coating on the internal face of the inner wall and the outer wall. Additionally, there are one or more fins 105 extending from the inner wall and the outer wall, though in other embodiments the one or more fins may extend from the inner wall only. A heat source 106 is provided and arranged to heat the ammonia decomposition catalyst in the first chamber.

The inner wall and the outer wall can comprise or be constructed of any suitable material, though a metal is preferred in some embodiments. The chamber is preferably constructed of Austenitic stainless steels or high Nickel Chromium content superalloys. These materials are resilient at the temperature and pressure at which the decomposition occurs and have excellent thermal conductivity. In some embodiments the one or more fins can be constructed of the same material as the inner wall and/or the outer wall. In some embodiments, the one or more fins may be made from a different material to the inner and/or the outer wall. This is an advantage where, for example, the fins need to have better thermal conductivity than the inner or outer walls of the first chamber. In one embodiment, at least one of the one or more fins are attached to and/or extend from the inner wall. This means the fins are physically connected to and/or in physical contact with the inner wall. In one embodiment, the one or more fins and the inner wall are a one-piece construction. This means that there is no defined material border between the inner wall and the one or more fins. For example, if the inner wall and the one or more fins are made by die-casting, they would be a one-piece construction. This has the advantage of excellent heat transfer between the inner wall and each of the one or more fins, as there will be negligible imperfections in the join between the two structures. In some embodiments, the one or more fins are manufactured as a separate entity and attached to the inner wall of the first chamber. For example, they may be attached as a mechanical interference fit, or using mechanical fasteners like clips, rivets, and the like. In some embodiments, the one or more fins are attached to the inner wall by a bonding. This means that the one or more fins are manufactured separately and bonded to the inner wall, for example by welding or brazing. In some embodiments, the fins may extend through the width of the first chamber such that they contact the outer wall of the first chamber. In some embodiments, the fins may only extend part way through the width of the first chamber such that they do not contact the outer wall. This is advantageous as it prevents heat loss through the outer wall to the environment.

In some embodiments, as shown in Figure 1 , there are a plurality of fins. The skilled person will envisage that the chamber could have a single fin which runs the length of the first chamber and provides a heat transfer surface, a substrate for the ammonia decomposition catalyst, and may influence gas flow. However, having a plurality of fins allows for further customization of the flow paths of the gas passing through the first chamber and is thus advantageous. The first chamber has an internal volume, and an internal surface area. The internal surface area is defined by the inside-facing surface of the inner wall of the (first) chamber, as well as each surface of the one or more fins. In other words, this means the area of the face of the inner wall of the first chamber facing the internal volume of the first chamber and the area of each of the one or more fins facing the internal volume of the first chamber combined. The internal volume of the (first chamber) ammonia cracker is between 10 ml to 100 litres (optionally 10 ml to 40 litres) and the ratio of the surface area of the inward face of the inner wall and the one or more fins (in mm²) to the internal volume (in mm³) is between 1 :2, and 1 :6, preferably approximately 1 :2, 1 :3, 1 :4, 1 :5 or 1 :6.

Applicants have surprisingly discovered that for ammonia cracking reactors operating at volumes of 10 ml to 100 litres, a particular surface area to volume ratio is particularly advantageous. In some embodiments, the internal volume of the ammonia cracker is between 10 ml and 100 litres, preferably 10 ml and 40 litres, more preferably between 1 litre and 30 litres, more preferably between 1 litre and 20 litres, more preferably between 2 litres and 5 litres, wherein the ratio of the internal surface area (in mm²) to the internal volume (in mm³) is between approximately 1 :2 and 1 :6. Preferably the ratio is approximately 1 :2, 1 :3, 1 :4, 1 :5 or 1 :6. Such a ratio has the effect of maximizing the heat transfer from a heat source to the catalyst substrate and/or ammonia decomposition catalyst.

In alternative embodiments, the internal surface area may be defined by the insidefacing surface of the inner and outer wall of the (first) chamber, as well as each surface of the one or more fins. In other words, this means the area of the face of each of the inner wall and outer wall facing the internal volume of the first chamber, and the area of each of the one or more fins facing the internal volume of the first chamber combined. In such embodiments, the internal volume of the ammonia cracker is between 10 ml and 100 litres, preferably 10 ml and 40litres, more preferably between 1 litre and 30 litres,, more preferably between 1 litre and 20 litres, more preferably between 2 litres and 5 litres and the ratio of the internal surface area (in mm²) to the internal volume (in mm³) is between approximately 1 :0.8 and 1 :6. Preferably the ratio is approximately 1 :0.8, 1 :0.9, 1 :1 , 1 :2, 1 :3, 1 :4, 1 :5 or 1 :6. As before, such a ratio has the effect of maximizing heat transfer from the heat source to the catalyst substrate and/or ammonia decomposition catalyst.

In some embodiments, the plurality of fins are disposed as one or more spirals through the length of the first chamber. Figure 2 shows a small section of such an arrangement, in 3D without the outer wall shown (A), including side on (B) and top down (C) views. In such an arrangement, the fins 205 are not aligned in the horizontal axis, instead they spiral down the inner wall 202 in the direction of the length of the first chamber. In some embodiments there could be two or more such spirals of fins, further altering the gas flow characteristics. A spiral arrangement as shown has the advantage of increasing the path length of the gas flows through the reactor as well as attributing some additional turbulence thus increasing the residency of the gas, as it tends to flow in a spiral, following the fins through the first chamber the gas is able to pick up further heat from the external heat source. In some embodiments, the one or more fins may be arranged as two spirals down the length of the first chamber, one of which spirals in a clockwise direction and the other in an anticlockwise direction. This arrangement has the advantage of increasing turbulence in the gas flow thus slowing the flow and increasing gas residency time in the first chamber. The skilled person will appreciate that in some instances a combination of the two approaches may be taken, by providing one section structured as a single spiral of fins to speed up gas flow in one section of the first chamber and providing a further section structured as two spirals, one arranged in a clockwise direction and one in an anticlockwise direction to slow the gas down.

In some embodiments, the plurality of fins are disposed on the inner wall as one or more rows, each fin of each row being parallel with each fin of the same row on a plane substantially perpendicular to the length of the first chamber. Figure 3 shows a small section of such an arrangement in 3D without the outer wall shown (A), including side on (B) and top down (C) views. As shown, there are three rows of fins 305 disposed on the inner wall 302, each row being defined by the alignment of the fins of that row along a plane h which is perpendicular to the flow of gas in use (indicated with an arrow). Having such an ordered structure allows for uniform control of gas flow through a section of the first chamber.

In some embodiments, each fin of the plurality of fins has an angle which is the same as each other fin, as shown for example in Figure 3. As shown in Figure 4, the angle a is that angle which is between the plane h which is perpendicular to the flow of gas in use and the lowermost face of the fin. (A) shows a fin 405 disposed on the inner wall 402, the fin having a planar (i.e. flat) profile, and (B) shows a fin 405 disposed on the inner wall 402 having a varied profile through its length. Where the fin has a varied profile, the angle a is measured as an average over the length of the fin. In some embodiments, at least one fin of the plurality of fins has an angle which is different to at least one other fin. By adjusting the angle of any one fin, the effect it has on the gas flow path can be adjusted, thus enabling a fine degree of control over the gas flow through the first chamber. In some embodiments, the at least one fin of the plurality of fins having a different angle to at least one other fin is in the same row as the at least one other fin. In some embodiments, the plurality of fins are disposed as at least two rows, and the at least one fin of the plurality of fins having a different angle to at least one other fin is in a different row to the at least one other fin. In an exemplary embodiment, each row of fins in the plurality of fins has an angle which is opposing the angle of the fins in its adjacent rows. An example arrangement is shown in Figure 9. In this arrangement, the angle of the fins of the first and third row 905 orient the face of the fins in one direction, and the angle of the fins of the second row 914 orientate the fact of the fins in an opposing direction. Such an arrangement increases the gas residency time. Of course, a combination of these two approaches can be taken, such that the angle of any fin can vary with respect to the other fins on its row or on different rows. This customizability of the device allows for optimal engineering of gas flow for any given installation or use case. For example the angle of each fin can be chosen from the group consisting of substantially perpendicular to the length of the first chamber (i.e. along the plane has defined previously), substantially parallel with the length of the chamber (i.e. perpendicular to plane h as defined previously), and/or angled between substantially perpendicular or substantially parallel with the length of the chamber (in other words, between the two prior angles). As mentioned previously and shown in Figure 4, each fin can have a substantially planar or a varied profile through its length. Different shaped fins offer a further degree of control of the localized gas flow characteristics and so allow very fine control of gas residency time and velocities. Any combination of fin shapes are envisaged alone or in combination for the purposes of this invention. In some embodiments, at least one of the one or more fins comprises one or more apertures, and/or one or more protrusions and/or one or more depressions on its surface. These variations increase the overall surface area of the fin, increasing the reaction surface when the fin is coated with catalyst, and allowing further fine control of local gas flow. The fins could be etched, engraved, or roughened to create the protrusions and/or depressions. In some embodiments, each fin may be shaped to provide a flow channel proximal to the inner and/or outer wall. This is achieved by removing a portion of the fin proximal to the inner and/or outer wall, thus allowing gas to flow proximal to the inner and/or outer wall. Such a shape may be described as a fin with an ‘indent’. An exemplary fin of this embodiment is shown in Figure 4C, with the fin 405 having two indents 407 proximal to the inner wall 402.

In some embodiments, at least one fin may be a hollow fin which comprises a subchamber defined by one or more fin walls with an internal baffle, wherein the one or more fin walls comprise one or more entry apertures on a face of the fin, and one or more exit apertures on an opposite face of the fin. An exemplary hollow fin 505 is shown in Figure 5, with Figure 5A showing a 3D cutaway of a fin, Figure 5B showing a top-down view, and Figure 5C showing a side-on cutaway view. In this exemplary embodiment, the one or more fin walls 508 of the subchamber define a subchamber volume 509 with the internal baffle 510 therein. Gas flows into the one or more entry apertures 511 , through the subchamber volume 509 around the internal baffle 510, and then exits via the one or more exit apertures 512. In some embodiments, the hollow fin extends substantially the width of the first chamber, such that it is almost in contact either the inner wall 502 (when attached to the inner wall) or the outer wall 503 (when attached to the inner wall), so that the flow of gas must occur through the subchamber volume 509 of the hollow fin. Such hollow fins provide further control of gas residency time and create a turbulent flow by forcing the gas down a defined path, which is advantageous in the present invention.

In some embodiments, the device comprises a plurality of rows of fins, wherein at least one row is disposed such that one or more fins of the at least one row are not wholly overlapping with the one or more fins of at least one other row of the plurality of rows through the length of the first chamber. Figure 6 shows an exemplary embodiment of such a device. In the shown section, there are three rows of fins 605 disposed on the inner wall 602, but they are not wholly overlapping with each other. As the gas flows through this section, it is forced to go around the fins, as there is no flow path leading directly from the inlet side to the outlet side of the chamber. This provides a further customization of flow paths within the device, thus allowing further fine control of gas velocity and residency in any one section of the first chamber. To further provide turbulent flow, the one or more fins of each row can be set an angle which is substantially perpendicular to the one or more fins of an adjacent row, such that the turbulence of gas increased. This is demonstrated in Figure 9, though it is envisaged that at least one row is disposed such that one or more fins of the at least one row are not wholly overlapping with the one or more finds of at least one other row of the plurality of rows through the length of the first chamber in addition to the one or more fins of each row being at an angle substantially perpendicular to the one or more fins of an adjacent row. Indeed, each adjacent row may be angled and offset in this way compared to its neighbouring rows.

In some embodiments, the device comprises a plurality of rows with a distance, d, between each pair of adjacent rows, and this distance remains the same through the length of the first chamber. In some embodiments, the device comprises a plurality of rows, each with a distance (d) between each pair of adjacent rows, wherein the distance d differs between at least two pairs of adjacent rows through the length of the first chamber. Figure 7 shows a section of the inner wall 702 with three rows of fins 705 disposed thereupon, with a distance d calculated as the distance between each row of fins in the gas flow direction which is indicated by an arrow. In Figure 7A, the distance d is the same between each pair of rows. In Figure 7B, the distance d differs between the first pair of rows, and the second pair of rows. Spacing the rows in this way provides further control over the gas velocity and gas residency time in any one section of the device. Applicants have found that having a section of the chamber towards the one or more ammonia gas inlets where the rows are closer together (i.e. the distance d is smaller) compared to the downstream section provides an improved device. In any event, having different distances between the rows of fins allows for multiple designs to suit particular functions for the first chamber.

In some embodiments, at least one of the one or more fins are connected to the outer wall of the first chamber by mechanical interference fit or mechanical fasteners. In some embodiments, at least one of the one or more fins is a one-piece construction with the outer wall. In some embodiments, at least one of the one or more fins are attached to the outer wall by a second bonding, preferably welding or brazing. Any combination of the above can be used, along with any combination of connecting one or more fins to the inner wall as described earlier, in order to put the invention into effect.

In some embodiments, the inner wall of the device defines a second chamber, and the second chamber has one or more fins disposed therein. These fins can have any of the characteristics described above alone or in combination. In an embodiment of the invention, the one or more fins extend from the first chamber into the second chamber. This provides optimal heat transfer characteristics between the first chamber and the second chamber. As shown in Figure 8, a heat source can be provided in or through the second chamber 813 and having one or more fins 805 disposed in the second chamber 813 and the first chamber 801 improves the transfer of heat from the second chamber 813 into the first chamber 801 . In some embodiments, at least one of the one or more fins are attached to and/or extend from the inner wall. In some embodiments, at least one of the one or more fins extend from the inner wall into the volume of the first chamber. In some embodiments, where the device comprises a plurality of fins, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of the plurality of fins are attached to and/or extend from the inner wall. Such fins will optimize heat transfer from the inner part of the device to the ammonia decomposition catalyst residing in the first chamber. In some embodiments, the one or more fins are attached to and/or extend from the inner wall. That is to say, all of the fins extend from said inner wall into the volume of the first chamber. Such a device is shown in Figure 10. The device has a first chamber 1001 and a second chamber 1013, wherein the second chamber provides heat which is conducted through the inner wall 1002 shared between the first chamber 1001 and the second chamber 1013 via the one or more fins 1005. In some embodiments, the one or more fins which are attached to and/or extend from the inner wall extend partially across the width of the first chamber towards the outer wall. In such embodiments, each of the one or more fins has a leading edge which is the edge of each fin closest to the outer wall, and there is a gap between the leading edge and the outer wall. In such embodiments at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of the one or more fins may extend partially across the width of the first chamber towards the outer wall. In some embodiments all of the one or more fins extend partially across the width of the first chamber towards the outer wall. In effect, in such embodiments, the stated proportion of the one or more fins each have a leading edge which is the edge of each fin closest to the outer wall, and each have a gap between the leading edge and the outer wall. In some embodiments, one or more fins may additionally extend into the volume of the second chamber from the inner wall. In such embodiments the one or more fins are attached to or extend from said inner wall. Where the one or more fins comprises a plurality of fins, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of the plurality of fins are attached to and/or extend from the inner wall. Such a device is shown in Figure 11. The device has a first chamber 1101 and a second chamber 1113, wherein the second chamber provides heat which is conducted through the inner wall 1102 shared between the first chamber 1101 and second chamber 1113, and the one or more fins 1105 extending from the inner wall assist in this transfer of heat into the volume of the first chamber 1001 . This is particularly advantageous where the heat source is in the second chamber as described above, or otherwise the heat is provided proximal to the inner wall as it maximizes heat transfer from the inner wall of the device and minimizes heat loss through the outer wall of the device.

Though the device has been shown to be an annular device in the Figures, the skilled person will appreciate that other geometries will achieve the effect of the invention with no substantial modification required. Exemplary embodiments of the general shape of the first chamber are provided below, though the skilled person will appreciate that there are no limitations on the shape of the first chamber other than the recited volumes and internal surface area to volume ratio outlined herein to achieve the advantages of the invention.

In one embodiment, the first chamber is annular, formed of the inner wall and an outer wall, both the inner wall and outer wall having a generally cylindrical shape or profile. This is exemplified in the figures. In other words, the cross-sectional shape of the first chamber across the width of the device is annular. The volume defined between the outer wall and the inner wall is the first chamber, and the one or more fins extend from the inner wall into the first chamber. Such a device is shown, for example, in Figure 1 . In all embodiments, the first chamber will be an enclosed volume except for any inlets or outlets, such as the one or more ammonia gas inlets and one or more raw cracked gas outlets. In some embodiments, the inner wall and outer wall are (i.e. have the general shape of) concentric cylinders. The advantage of this is that the length between the inner wall and outer wall is equal (uniform) and so heat transfer from the inner wall to the outer wall will be even throughout the volume of the first chamber. Likewise any heat transfer from the outer wall to the inner wall will be even. In such embodiments, the heat source may be within the volume defined by the inner wall alone (i.e. a second internal volume or the inside volume defined by the inner wall), the inner wall being a cylinder. Such a device is shown, for example, in Figure 10.

Less optimal embodiments of the invention which still enjoy advantages over the devices of the prior art are similar to the device formed of two cylinders described above. In such embodiments, the inner wall and/or outer wall may be any three- dimensional prismatic shape. For example, the inner wall and/or outer wall may have the shape of a triangular prism, rectangular prism, pentagonal prism, hexagonal prism, or any other prism. Example cross sectional views of devices are shown in Figure 13 without the one or more fins being shown. In such embodiments, the volume between the inner wall 1302 and the outer wall 1303 defines the first chamber 1301 . In some embodiments, the internal volume defined by the inner wall defines a second chamber 1313 which may comprise heat source for heating the first chamber 1301. As the distance between the inner wall and outer wall varies in such devices, there will be an associated loss of efficiency due to non-uniform heat transfer from the inner wall into portions of the first chamber volume. However, such devices will still enjoy advantages associated with the volumes and internal surface area to volume ratio of the invention. Similarly to the abovementioned embodiment, further embodiments involving an inner wall and an outer wall having differing cross- sectional shapes are also envisioned. For example, in one embodiment the inner wall is the shape of a triangular prism and the outer wall is the shape of a cylinder. In another embodiment, the inner wall is the shape of a cylinder and the outer wall is the shape of a triangular prism. In another embodiment, the inner wall is the shape of a rectangular, pentagonal, hexagonal, or any other prism, and the outer wall is the shape of a cylinder. In another embodiment, the inner wall is the shape of a cylinder and the outer wall is the shape of a rectangular, pentagonal, hexagonal, or any other prism. In another embodiment, the inner wall is the shape of a prism, and the outer wall is the shape of a different prism.

Depending on the space allotted for the device, for example in an engine bay, the first chamber may be an irregular prismatic shape to fit into the available space. This would be achieved by the inner wall and/or outer wall having an irregular prismatic shape. Keeping the internal surface area to volume ratio as required by the invention means that such devices maintain the advantages associated with the invention compared to devices which do not have said ratio.

In a further aspect, the invention provides a hydrogen production device for producing a hydrogen rich gas from ammonia comprising a first chamber comprising an outer wall defining an internal volume of the first chamber, wherein the first chamber contains an ammonia decomposition catalyst disposed within the first chamber, the first chamber having one or more ammonia gas inlets and one or more raw cracked gas outlets, wherein said one or more ammonia gas inlets and one or more raw cracked gas outlets are arranged such that the ammonia flows through the first chamber from the one or more ammonia gas inlets to the one or more raw cracked gas outlets and contacts the ammonia decomposition catalyst; wherein two or more inner walls are disposed within the internal volume, defining two or more inner chambers within the first chamber, wherein the two or more inner chambers each comprise a heat source for heating the ammonia decomposition catalyst; wherein the two or more inner walls (optionally each) have one or more fins, said one or more fins extending from (at least one of) the two or more inner walls and disposed in the internal volume of first chamber; wherein the first chamber has an internal surface area defined as the area of the internal volume facing surface(s) of each of the two or more inner walls and each of the internal volume facing surfaces of the one or more fins, (optionally wherein the internal volume is between 10 ml and 100 litres) and wherein the ratio of the internal surface area in mm² to the internal volume in mm³ is between approximately 1 :2 and 1 :6.

The internal surface area is defined by the inside-facing surface of the inner walls of the first chamber, as well as the area of each surface of the one or more fins. In other words, this means the area of the face of the inner walls of the first chamber facing the internal volume of the first chamber and the area of each of the one or more fins facing the internal volume of the first chamber combined. In some embodiments, the internal volume of the first chamber may be between 10 ml and 100 litres (optionally 10ml to 40 litres). In some embodiments, the ratio of the internal surface area to the internal volume is between 1 :2 and 1 :6, preferably approximately 1 :2, 1 :3, 1 :4, 1 :5 or 1 :6.

In an alternative embodiment, the internal surface area is defined by the area of the internal volume facing surface of each of the two or more inner walls and the outer wall, each surface of the one or more fins. In other words, this means the area of the face of the inner walls and the outer wall of the first chamber facing the internal volume of the first chamber and the area of each of the one or more fins facing the internal volume of the first chamber combined. In some embodiments, the internal volume may be between 10 ml and 100 litres. In some embodiments, the ratio of the internal surface area in mm² to the internal volume in mm³ is between approximately 1 :0.8 and 1 :6. Preferably the ratio is approximately 1 :0.8, 1 :0.9, 1 :1 , 1 :2, 1 :3, 1 :4, 1 :5 or 1 :6. As before, such a ratio has the effect of maximizing heat transfer from the heat source to the catalyst substrate and/or ammonia decomposition catalyst.

A device according to this aspect is shown in Figure 14 as a cross-sectional view across the width of the device in the upper panel, and a three dimensional view in the lower panel, with the first chamber 1401 being the internal volume defined by the outer wall 1403, and the two or more inner walls 1402 disposed within said internal volume and defining two or more inner chambers 1413, each inner chamber 1413 comprising a heat source for heating the ammonia decomposition catalyst within the first chamber. The volume of the first chamber is the internal volume defined by the outer wall minus the (inner chamber internal) volume of each of the two or more inner chambers and the two or more inner walls. Each of the two or more inner walls 1402 has one or more fins 1405 extending therefrom, disposed in the internal volume of the first chamber 1401 (the fins are not shown in the three dimensional view of Figure 14). The one or more ammonia gas inlets and the one or more raw cracked gas outlets are arranged such that, in use, ammonia gas flows through the internal volume and contacts or interacts with the ammonia decomposition catalyst. This can be achieved in any number of ways apparent to the skilled person. For example, the one or more ammonia gas inlets may be disposed at a first end of the first chamber, with the one or more raw cracked gas outlets disposed at the second end of the first chamber, the second end being opposite end of the first chamber. In such an example, each end means the opposite ends of the chamber lengthwise. In such a device, the minimum distance between any one of the two or more inner walls 1402 and the outer wall 1403 may be (optionally approximately) half that of the distance between any one of the two or more inner walls 1402 and an adjacent inner wall. In other words, the minimum distance between each of the two or more inner chambers 1413 may be (optionally approximately) double that of the minimum distance between any of the outermost inner chambers (i.e. those inner chambers closest to the outer wall) and the outer wall 1403. This provides optimal efficiency of heat transfer between the inner chambers and the first chamber volume. Whilst the outer chamber is shown as a rectangular prism, and each of the inner chambers is shown as a cylinder, the skilled person will understand that each chamber can have a shape which suits a particular application of the technology or installation site. As such, the outer wall may be any three dimensional shape such as but not limited to a cylinder, a rectangular prism, a triangular prism, a pentagonal prism, a hexagonal prism, or any other regular prism. The outer wall may be an irregular prism having a variable cross-sectional profile through its length. In addition, each of the two or more inner chambers may be any three dimensional shape such as but not limited to a cylinder, a rectangular prism, a triangular prism, a pentagonal prism, a hexagonal prism, or any other regular prism. Each of the two or more inner chambers may be an irregular prism having a variable cross-sectional profile through their length. Indeed, in some embodiments, at least one of the two or more inner chambers may have a three dimensional shape which differs from the other inner chambers. Every combination of the abovementioned shapes for the outer wall and each of the two or more inner chambers are envisaged as embodiments of this aspect of the invention. Alternatively, the shape of each of the two or more inner chambers may be substantially the same as each of the other inner chambers. The volume of each of the two or more inner chambers may be the same or different. Having each volume be the same may provide for a uniform heating through the internal chamber.

Alternatively, the volume of each inner chamber may be varied so as to reduce heat transfer in any hot spots in the first chamber in use. Provided the surface area to volume ratio according to the invention is maintained, the device will enjoy the advantages associated therewith over known devices.

Each of the two or more inner chambers comprise a heat source for heating the ammonia decomposition catalyst. In other words, heat is provided into an (inner chamber) internal volume of each of the two or more inner chambers and transfers through the two or more inner walls (and the one or more fins) into the internal volume of the first chamber to heat the ammonia decomposition catalyst. In some embodiments, the two or more inner chambers are fluidly connected to a heater, such that a heat transfer medium (such as hot gas) flows from the heater to the two or more inner chambers. Each of the two or more inner chambers may be fluidly connected to one or more heaters and may be connected to the same or to different heaters. In some embodiments, the two or more inner chambers are fluidly connected to a combustion chamber. Each of the two or more inner chambers may be fluidly connected to one or more combustion chambers and may be connected to the same or to different combustion chambers. Each combustion chamber combusts a fuel gas with an oxygen rich gas to produce a hot flue gas which carries heat from each combustion chamber to the two or more inner chambers. Alternatively or in addition, the two or more inner chambers may themselves be combustion heaters, wherein an oxidation catalyst is disposed within the two or more inner chambers such that when a fuel gas and an oxygen rich gas are mixed within the two or more inner chambers, it combusts proximal to the oxidation catalyst and produces heat proximal to the two or more inner walls which is transferred by said inner walls (and the one or more fins extending therefrom) and into the first chamber to heat the ammonia decomposition catalyst. In such embodiments the two or more inner chambers will have an inlet for fuel gas and oxygen rich gas, and an outlet for exhaust gas.

In some embodiments, each of the two or more inner walls having one or more fins extending therefrom have a one piece construction. In other words, the fins are integral and thus part of each of the two or more inner walls, and are constructed of the same material with no boundary between the material of the inner wall and the fin. As previously stated, this has the benefit of providing excellent heat transfer from the two or more inner walls to the one or more fins extending therefrom. In some embodiments, at least one of the one or more fins is attached to at least one of the two or more inner walls by mechanical interference fit or mechanical fasteners. As stated previously, this means that the one or more fins are manufactured separately to the two or more inner chambers and attached thereto afterwards with, for example, clips, rivets and the like. In some embodiments, at least one of the one or more fins is attached to at least one of the two or more inner walls by a bonding. This bonding may be a weld or a braze, and this has the advantage of allowing the attachment of fins made of different materials to the two or more inner walls to affect how heat is transferred from the two or more inner chambers via the one or more fins. In some embodiments, the one or more fins comprise a plurality of fins. The plurality of fins may be disposed as one or more spirals through the length of the first chamber as shown previously for the prior aspect in Figure 2. The plurality of fins may be disposed as one or more rows, each fin of each row being parallel with each fin of the same row on a plane substantially perpendicular to the length of the first chamber, as shown in Figure 3. Each fin of the plurality of fins has an angle which is the same as each other fin, in some embodiments, as shown in Figure 3B. In some embodiments, each fin of the plurality of fins has an angle which is different to at least one other fin as exemplified in Figure 9. The at least one fin of the plurality of fins having a different angle to at least one other fin is in the same row as the at least one other fin or the plurality of fins are disposed as at least two rows, and the at least one fin of the plurality of fins having a different angle to at least one other fin is in a different row to the at least one other fin as exemplified in Figure 9. The angle of each fin may be chosen from the group consisting of: substantially perpendicular to the length of the first chamber, substantially parallel with the length of the chamber, and/or angle between substantially perpendicular and substantially parallel with the length of the first chamber. With reference to Figure 4, the angle a is that angle which is between the plane h which is perpendicular to the flow of gas in use and the lowermost face of the fin. (A) shows a fin 405 disposed on the inner wall 402, the fin having a planar (i.e. flat) profile, and (B) shows a fin 405 disposed on the inner wall 402 having a varied profile through its length. Where the fin has a varied profile, the angle a is measured as an average over the length of the fin.

In some embodiments, at least one of the one or more fins has a planar profile as shown in Figure 4A. In some embodiments, at least one of the one or more fins has a varied profile through its length as shown in Figure 4B. In some embodiments, at least one of the one or more fins comprises one or more apertures and/or one or more protrusions and/or one or more depressions on a surface of the at least one fin as described for the prior aspect. These modifications to a fin increase its surface area and so are useful in tuning the overall internal surface area to volume ratio of the first chamber of the device.

In some embodiments, at least one fin of the one or more fins may be a hollow fin which comprises a subchamber defined by one or more fin walls and an internal baffle, wherein the one or more fin walls comprise one or more entry apertures on a face of the fin, and one or more exit apertures on an opposite face of the fin, as shown for the prior aspect and exemplified Figure 5.

In some embodiments, at least one of the one or more fins comprises an indent proximal to one of the two or more inner walls and/or the outer wall, as shown for the prior aspect and exemplified in Figure 4C.

In some embodiments, there are a plurality of rows of fins on at least one of the two or more inner walls, wherein at least one row of the plurality of rows is disposed such that one or more fins of the at least one row are not wholly overlapping with the one or more fins of at least one other row of the plurality of rows through the length of the first chamber, as shown in Figure 6.

In some embodiments, there are a plurality of rows of fins on at least one of the two or more inner walls, with a distance (d) between each pair of adjacent rows, wherein the distance (d) is the same through the length of the first chamber as shown in Figure 7A. In some embodiments, there are a plurality of rows, each with a distance (d) between each pair of adjacent rows, wherein the distance (d) differs between at least two pairs of adjacent rows through the length of the first chamber, as shown in Figure 7B. It will be appreciated that each of the two or more inner walls defining each of the two or more inner chambers may have either the same distance (d) for the plurality of rows of fins extending therefrom, or a differing distance (d) between each of at least two pairs of adjacent rows. One or more of the one or more fins may extend into the inner volume of one or more the two or more inner chambers. For the avoidance of doubt, any of the embodiments disclosed for the device of the first aspect of the invention may be applied to the device of this second aspect of the invention.

The abovementioned embodiments alone or in combination provide the benefits of the present invention, and all combinations of the abovementioned embodiments are envisioned as part of the invention.

The exact shape, size, and number of fins will depend on the size of the required device. Likewise, the number of rows of fins required will vary depending on the device requirements, and upon the particular application of the device of the invention.

In a further aspect the invention provides a system for producing purified hydrogen comprising one or more of the device of the first aspect or the second aspect and any of their embodiments, and further comprises a gas separator for separating hydrogen gas from other gases in fluid communication with the one or more devices. The gas separator may be a pressure swing adsorption device and/or a palladium filter, which are known in the art for separating hydrogen from nitrogen and ammonia, though any suitable gas separation device may be used. For example, see US6340382B1 and GB969673A (incorporated by reference herein).

In a further aspect the invention provides a system for producing electrical energy comprising the system of the previous aspect, further comprising a fuel cell. Such a system allows the hydrogen produced by the one or more devices of the first aspect to be used to generate electrical energy. Suitable fuel cells are known in the art. For example, see GB2508649A (incorporated by reference herein).

Figure 12 shows a system having a device according to the present invention 1200 in fluid communication with a gas separator 1215 via a common raw cracked gas flow conduit 1216, The gas separator is in fluid communication with a hydrogen fuel cell 1217 via a common purified cracked gas flow conduit 1218. The flow of gas is indicated with arrows, showing an ammonia gas entering the ammonia cracker 1200 via an inlet, the ammonia gas is decomposed into a raw cracked gas comprising nitrogen gas and hydrogen gas, and the raw cracked gas exits the ammonia cracker into the common raw cracked gas flow conduit 1216 and flows through an inlet into a gas separator 1215 where the nitrogen and any other impurities are removed from the raw cracked gas, producing a purified cracked gas consisting essentially of hydrogen. The purified cracked gas exits the gas separator via an outlet and is conveyed to a hydrogen fuel cell 1217 via the common purified cracked gas flow conduit 1218 where the hydrogen is used along with oxygen gas to generate electricity.

In a further aspect of the invention, the device for producing hydrogen could be a steam reformer, for example a hydrocarbon steam reformer, or other thermocatalytic decomposition reactor having any of the features and embodiments of the first or second aspect.

Claims

1 . A hydrogen production device for producing a hydrogen rich gas from ammonia comprising: a first chamber comprising an inner wall and an outer wall defining an internal volume, wherein the first chamber contains an ammonia decomposition catalyst disposed between the inner wall and the outer wall, the first chamber having one or more ammonia gas inlets and one or more raw cracked gas outlets, wherein said one or more ammonia gas inlets and one or more raw cracked gas outlets are arranged such that the ammonia flows through the first chamber from the one or more ammonia gas inlets to the one or more raw cracked gas outlets and contacts the ammonia decomposition catalyst; and one or more heat sources for heating the ammonia decomposition catalyst; wherein the first chamber has one or more fins, said one or more fins disposed between the inner wall and the outer wall of the first chamber, wherein the first chamber has an internal surface area defined as the area of the internal volume facing surface of the inner wall and each surface of the one or more fins, wherein the internal volume is between 10 ml and 100 litres and wherein the ratio of the internal surface area in mm² to the internal volume in mm³ is between approximately 1 :2 and 1 :6.

2. The device according to claim 1 , wherein at least one of the one or more heat sources are proximal to the inner wall or proximal to the outer wall.

3. The device according to claim 1 or claim 2, wherein the one or more heat sources comprise at least two heat sources, preferably wherein at least one of which is proximal to the inner wall and at least one of which is proximal to the outer wall.

4. The device according to any one of the preceding claims, wherein at least one of the one or more fins are attached to and/or extend from the inner wall.

5. The device according to any one of the preceding claims, wherein at least one of the one or more fins and the inner wall are a one-piece construction.

6. The device according to any one of the preceding claims, wherein at least one of the one or more fins is attached to the inner wall by mechanical interference fit or mechanical fasteners.

7. The device according to any one of the preceding claims, wherein at least one of the one or more fins are attached to the inner wall by a bonding.

8. The device according to claim 6 or claim 7, wherein the one or more fins are made of a different material to the inner or outer wall of the first chamber.

9. The device according to claims 7 or 8, wherein the bonding is a weld or a braze.

10. The device according to any one of the preceding claims, wherein the one or more fins comprise a plurality of fins.

11 . The device according to claim 10, wherein at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of the plurality of fins are attached to and/or extend from the inner wall.

12. The device according to claim 10, wherein the plurality of fins are attached to and/or extend from the inner wall.

13. The device according to claim 10, wherein the plurality of fins are disposed as one or more spirals through the length of the first chamber.

14. The device according to claim 10, wherein the plurality of fins are disposed as one or more rows, each fin of each row being parallel with each fin of the same row on a plane substantially perpendicular to the length of the first chamber.

15. The device according to any one of claims 10 to 14, wherein each fin of the plurality of fins has an angle which is the same as each other fin.

16. The device according to any one of claims 10 to 14, wherein at least one fin of the plurality of fins has an angle which is different to at least one other fin.

17. The device according to claim 16, wherein the at least one fin of the plurality of fins having a different angle to at least one other fin is in the same row as the at least one other fin.

18. The device according to claim 16, wherein the plurality of fins are disposed as at least two rows, and the at least one fin of the plurality of fins having a different angle to at least one other fin is in a different row to the at least one other fin.

19. The device according to claims 15 to 18, wherein the angle of each fin is chosen from the group consisting of: substantially perpendicular to the length of the first chamber, substantially parallel with the length of the chamber, and/or angled between substantially perpendicular and substantially parallel with the length of the chamber.

20. The device according to any one of the preceding claims, wherein at least one of the one or more fins has a planar profile.

21 . The device according to any one of the preceding claims, wherein at least one of the one or more fins has a varied profile through its length.

22. The device according to claim 21 , wherein at least one of the one or more fins comprises one or more apertures and/or one or more protrusions and/or one or more depressions on a surface of the at least one fin.

23. The device according to any one of the preceding claims, wherein at least one fin of the one or more fins may be a hollow fin which comprises a subchamber defined by one or more fin walls and an internal baffle, wherein the one or more fin walls comprise one or more entry apertures on a face of the fin, and one or more exit apertures on an opposite face of the fin.

24. The device according to any one of the preceding claims, wherein at least one of the one or more fins comprises an indent proximal to the inner and/or outer wall.

25. The device according to any one of claims 14 to 24, comprising a plurality of rows wherein at least one row of the plurality of rows is disposed such that one or more fins of the at least one row are not wholly overlapping with the one or more fins of at least one other row of the plurality of rows through the length of the first chamber.

26. The device according to any one of claims 14 to 25, comprising a plurality of rows, with a distance (d) between each pair of adjacent rows, wherein the distance (d) is the same through the length of the first chamber.

27. The device according to any one of claims 14 to 25, comprising a plurality of rows, each with a distance (d) between each pair of adjacent rows, wherein the distance (d) differs between at least two pairs of adjacent rows through the length of the first chamber.

28. The device according to any one of the preceding claims, wherein at least one of the one or more fins are connected to the outer wall of the first chamber by mechanical interference fit or mechanical fasteners.

29. The device according to any one of the preceding claims, wherein at least one of the one or more fins is a one-piece construction with the outer wall.

30. The device according to any one of the preceding claims, wherein at least one of the one or more fins are attached to the outer wall by a second bonding.

31 . The device according to claim 30, wherein the second bonding is welding or brazing.

32. The device according to any one of the preceding claims, wherein the inner wall further defines a second chamber within the first chamber, the second chamber having one or more fins disposed therein.

33. The device according to claim 32, wherein the one or more fins extend from the first chamber into the second chamber.

34. The device according to any preceding claim, wherein the inner wall and/or the outer wall have the shape of a cylinder, with the inner wall being disposed within the outer wall, and the volume between the inner wall and the outer wall being the first chamber, the first chamber having an annular shape.

35. The device according to any one of claims 1 to 33, wherein the inner wall and/or the outer wall each have a prismatic shape, with the inner wall being disposed within the outer wall, and the volume between the inner wall and the outer wall being the first chamber.

36. The device of claim 34 or claim 35, wherein the inner wall and the outer wall are concentric.

37. The device according to any one of claims 1 to 35, wherein the inner wall and/or outer wall each have an irregular prismatic shape, with the inner wall being disposed within the outer wall, and the volume between the inner wall and the outer wall being the first chamber.

38. A hydrogen production device for producing a hydrogen rich gas from ammonia comprising: a first chamber comprising outer wall defining an internal volume of the first chamber, wherein the first chamber contains an ammonia decomposition catalyst disposed within the first chamber, the first chamber having one or more ammonia gas inlets and one or more raw cracked gas outlets, wherein said one or more ammonia gas inlets and one or more raw cracked gas outlets are arranged such that the ammonia flows through the first chamber from the one or more ammonia gas inlets to the one or more raw cracked gas outlets and contacts the ammonia decomposition catalyst; wherein two or more inner walls are disposed within the internal volume, defining two or more inner chambers within the first chamber, wherein the two or more inner chambers each comprise a heat source for heating the ammonia decomposition catalyst; wherein the two or more inner walls have one or more fins, said one or more fins extending from the two or more inner walls and disposed in the internal volume of the first chamber; wherein the first chamber has an internal surface area defined as the area of the internal volume facing surface of each of the two or more inner walls and each surface of the one or more fins, and wherein the ratio of the internal surface area in mm² to the internal volume in mm³ is between approximately 1 :2 and 1 :6.

39. The device according to claim 38, wherein the two or more inner walls each have the shape of: a cylinder; a prism; and/or an irregular prism, wherein each of the two or more inner chambers are defined as the internal volume defined by at least one of the two or more inner walls.

40. The device according to claim 38 or claim 39, wherein the two or more inner chambers are fluidly connected to a combustion chamber, and/or wherein the two or more inner chambers are combustion chambers having an oxidation catalyst disposed therein.

41 . The device according to any one of claims 38 to 40, wherein the minimum distance between each of the two or more inner chambers is twice the minimum distance between any of the two or more inner chambers adjacent to the outer wall and the outer wall.

42. The device according to any one of claims 38 to 41 , wherein at least one of the two or more inner walls having one or more fins extending therefrom have a one- piece construction.

43. The device according to any one of claims 38 to 42, wherein at least one of the one or more fins is attached to at least one of the two or more inner walls by mechanical interference fit or mechanical fasteners.

44. The device according to any one of claims 38 to 43, wherein at least one of the one or more fins are attached to at least one of the two or more inner walls by a bonding, optionally wherein the one or more fins are made of a different material to the two or more inner walls or the outer wall, further optionally wherein the bonding is a weld or a braze.

45. The device according to any one of claims 38 to 44, wherein the one or more fins comprise a plurality of fins.

46. The device according to claim 45, wherein the plurality of fins are disposed as one or more spirals through the length of the first chamber.

47. The device according to claim 45, wherein the plurality of fins are disposed as one or more rows, each fin of each row being parallel with each fin of the same row on a plane substantially perpendicular to the length of the first chamber.

48. The device according to any one of claims 45 to 47, wherein each fin of the plurality of fins has an angle which is the same as each other fin.

49. The device according to any one of claims 45 to 47, wherein at least one fin of the plurality of fins has an angle which is different to at least one other fin.

50. The device according to claim 49, wherein the at least one fin of the plurality of fins having a different angle to at least one other fin is in the same row as the at least one other fin or wherein the plurality of fins are disposed as at least two rows, and the at least one fin of the plurality of fins having a different angle to at least one other fin is in a different row to the at least one other fin; optionally wherein the angle of each fin is chosen from the group consisting of: substantially perpendicular to the length of the first chamber, substantially parallel with the length of the chamber, and/or angle between substantially perpendicular and substantially parallel with the length of the first chamber.

51 . The device according to any one of claims 38 to 50, wherein at least one of the one or more fins has a planar profile.

52. The device according to any one of claims 38 to 51 , wherein at least one of the one or more fins has a varied profile through its length; optionally wherein at least one of the one or more fins comprises one or more apertures and/or one or more protrusions and/or one or more depressions on a surface of the at least one fin.

53. The device according to any one of claims 38 to 52, wherein at least one fin of the one or more fins may be a hollow fin which comprises a subchamber defined by one or more fin walls and an internal baffle, wherein the one or more fin walls comprise one or more entry apertures on a face of the fin and one or more exit apertures on an opposite face of the fin.

54. The device according to any one of claims 38 to 53, wherein at least one of the one or more fins comprises an indent proximal to at least one of the two or more inner walls or the outer wall.

55. The device according to any one of claims 47 to 54, comprising a plurality of rows wherein at least one row of the plurality of rows is disposed such that one or more fins of the at least one row are not wholly overlapping with the one or more fins of at least one other row of the plurality of rows through the length of the first chamber.

56. The device according to any one of claims 47 to 55, comprising a plurality of rows, with a distance (d) between each pair of adjacent rows, wherein the distance (d) is the same through the length of the first chamber.

57. The device according to any one of claims 47 to 55, comprising a plurality of rows, each with a distance (d) between each pair of adjacent rows, wherein the distance (d) differs between at least two pairs of adjacent rows through the length of the first chamber.

58. A system for producing purified hydrogen comprising one or more devices according to claims 1 to 57, further comprising a gas separator for separating hydrogen gas from other gases in fluid communication with the one or more devices.

59. A system for producing electrical energy comprising the system of claim 58, further comprising a fuel cell.