Catalytic reactor with combustion chamber
Background
Catalytic reaction chambers are used for many industrial production processes. For example, ammonia crackers and/or steam reformation devices are routinely used in the production of hydrogen gas for use as a fuel. Typically, such devices have a chamber comprising a catalyst which, when heated to an appropriate temperature, will readily catalyze the breakdown of a hydrogen rich gas (e.g. ammonia for an ammonia cracker or methanol, ethanol or hydrocarbons for a steam reformation device) into hydrogen gas and other reaction product gases. The catalytic breakdown of ammonia into hydrogen and nitrogen gas proceeds as an endothermic reaction as follows:
2NH3 ^ N2 + 3H2 AH° = +46.22 kJ. moh1
The ideal temperature for this reaction to proceed efficiently depends on the pressure of the system and the catalyst used, but generally ammonia cracking devices require heating in order to sustain the reaction of ammonia gas into nitrogen and hydrogen. The same is true of the reaction for steam reformation of methanol, ethanol, and hydrocarbons. The reactions can be represented as follows:
CH3OH + H2O CO2 + 3H2 AH0 = +49.2 kJ. moh1
CH3CH2OH + H2O 2CO2 + 6H2 AH0 = +173.3 kJ. moh1
CxHy + 2XH2O XCO2 + (0.5y + 2X)H2 AH0 = Enthalpy of reaction at standard state
Again, the ideal temperature for this reaction depends on the catalyst used and the pressure of the system.
Currently, there are several types of devices for these endothermic reactions which provide heat in a variety of ways. For example, some known devices use electrical heating (either resistive, radiant, or induction) to heat the reaction chamber to an appropriate heat for catalytic decomposition reactions to occur (see e.g. W02009098452). A downside of electrical heating systems is that they require power. In off-grid systems, such as a ship’s power system, the electricity will be generated by the engine or an ancillary power system such as a fuel cell. Efficiency losses result in wasting energy when converting chemical energy into electrical energy. In the case of induction heating, large auxiliary components are required which generate losses and consume space. Induction coils are typically water-cooled which removes heat from the reactor. Heat is removed by this water-cooling process, resulting in a more pronounced temperature gradient across the reactor, lowering efficiency. Alternatively, some known devices use combustion furnaces which combust either a fuel gas (such as methane) or off-gases produced by the catalytic reactor itself (see, e.g. WO2017015569A1 ). A major drawback of current combustion heaters (also known as ‘burners’) for hydrogen/ammonia reactor systems is high NOx formation. For hydrocarbon combusting heaters, the generation of CO2 is a major drawback. Such burners often rely on hot flue gases to heat the reactor or radiant heat from the flame, instead of the heat of combustion itself, which is the highest grade heat. An additional drawback of present combustion heating architectures for these types of catalytic reactors is that it is difficult to achieve uniform heating on a surface of the device due to the dynamics of heating using gaseous fuels. Another approach is to use catalytic combustion burners to generate heat. One form of catalytic combustion heater is a so-called ‘base burner’, which typically have a ceramic coated in a catalyst. A combustible mixed gas is introduced to the catalyst and combusted, and heat is transferred from the flue to a reactor. The disadvantage is that the heat is generated far from the reactor, resulting in loss of high-grade heat energy which would otherwise be available to the reactor. An alternative approach to catalytic combustion heaters is to catalyse the reactor wall by directly applying oxidation catalyst on a wall for heat transfer to the reactor, to make use of the high grade heat energy and transfer more energy to the reactor. The known systems provide a premixed mixture of reactant gases (capable of combusting) which enters the combustion chamber. This has the disadvantage of creating the conditions for ‘flashback’, where combustion can occur in other parts of the system than the combustion chamber due to the gas being premixed. In order to prevent this, such systems run with a gas mixture having an inefficient ratio of hydrogen in a hydrogen containing gas compared to oxygen in an oxygen containing gas. This ratio is typically set to 3x the stoichometric ratio or greater. A lambda of 1 is the stoichometric air to fuel ratio.
What is needed is a catalytic reactor having an improved heating system to ensure maximal efficiency in the production of hydrogen containing product gases from fuel gases. Applicants have discovered such a device, which provides uniform heating on a surface whilst operating at lambdas at or below 1 , optimizing the device for use in the production of a hydrogen containing product gas. This device is especially useful for catalytic reactions which are endothermic in nature and require heating in order to proceed, for example but not limited to the decomposition of ammonia into hydrogen gas, or the reformation of methanol, ethanol and hydrocarbons into hydrogen gas.
Summary of the invention
In a first aspect, the invention provides a device for hydrogen production comprising: a reaction chamber containing one or more catalysts disposed therein, a fuel gas inlet, and a hydrogen-rich gas outlet; a first reactant gas chamber having a first reactant gas inlet for conveying a first reactant gas and being in fluid communication with an exhaust; and a second reactant gas chamber having a second reactant gas inlet for conveying a second reactant gas; wherein the reaction chamber and the first reactant gas chamber share a first wall therebetween, the first wall comprising a thermally conductive substrate having a reaction chamber face and a first reactant gas chamber face, wherein the first reactant gas chamber face of the first wall has a reaction surface which is coated with a reactant gas decomposition catalyst; wherein the first reactant gas chamber further comprises a second wall opposite the first wall defining a volume therebetween, the second wall being shared between the first reactant gas chamber and the second reactant gas chamber; wherein the second wall comprises one or more apertures disposed in an aperture-containing area along a length and width of the second wall such that the second reactant gas chamber and the first reactant gas chamber are in fluid communication with one another, wherein the aperture-containing area has a first section, a second section, and a third section, the first section being a third of the aperture-containing area distal to the fuel gas inlet and the third section being a third of the aperture-containing area proximal to the fuel gas inlet, the second section being a third of the aperturecontaining area of the second wall between the first section and the third section, wherein the total cross-sectional area of the one or more apertures disposed in the first section is less than the total cross-sectional area of the one or more apertures disposed in the third section, wherein the total cross-sectional area of the one or more apertures disposed in the second section is greater than the total cross- sectional area of the one or more apertures disposed in the first section and less than the total cross-sectional area of the one or more apertures disposed in the third section, wherein the cross-sectional area of the second reactant gas chamber is greater than the total cross-sectional area of the one or more apertures.
In some embodiments, each of the reaction chamber, the first reactant gas chamber, and the second reactant gas chamber are cylindrical, wherein the second reactant gas chamber is disposed within the first reactant gas chamber, and wherein the first reactant gas chamber is disposed within the reaction chamber, wherein the width of the second wall is the circumference of the second wall, optionally wherein the one or more apertures are disposed along the length and circumference of the second wall.
In some embodiments, the one or more apertures comprise one or more of the following: a helical aperture spiraling down the aperture-containing area of the second wall having a first helical portion disposed in the first section, a second helical portion disposed in the second section, and a third helical portion disposed in the third section of the aperture-containing area of the second wall, wherein the cross-sectional area of the first helical portion is less than the cross-sectional area of the third helical portion, and the cross-sectional area of the second helical portion is greater than the cross-sectional area of the first helical portion and less than the cross-sectional area of the third helical portion; and/or one or more linear apertures disposed down the length of the aperture-containing area of the second wall each having a first linear portion in the first section, a second linear portion disposed in the second section, and a third linear portion disposed in the third section, wherein the cross-sectional area of the first linear portion is less than the cross-sectional area of the third linear portion, and the cross-sectional area of the second linear portion is greater than the cross-sectional area of the first linear portion and less than the cross-sectional area of the third linear portion; and/or a plurality of apertures comprising a first group of apertures, a second group of apertures and a third group of apertures, the first group of apertures being disposed within the first section of the second wall, the second group of apertures being disposed within the second section of the second wall, and the third group of apertures being disposed within the third section of the second wall wherein the total cross-sectional area of the first group of apertures is less than the total cross-sectional area of the third group of apertures, and wherein the total cross-sectional area of the second group of apertures is greater than the total cross-sectional area of the first group of apertures and less than the total cross-sectional area of the third group of apertures.
In some embodiments, each of the one or more apertures are configured to eject the second reactant gas such that it mixes with the first reactant gas and combusts upon contact with the reactant gas decomposition catalyst.
In some embodiments, the first wall comprises one or more heat transfer structures comprising metal extending into the reaction chamber.
In some embodiments, the first reactant gas comprises hydrogen and the second reactant gas comprises oxygen. In some embodiments, the first reactant gas comprises oxygen and the second reactant gas comprises hydrogen.
In some embodiments, the exhaust is proximal to the second reactant gas chamber.
In some embodiments, the exhaust is cylindrical and is disposed within the second reactant gas chamber.
In some embodiments, the device further comprises an insulating chamber disposed between the exhaust and the second reactant gas chamber, wherein the insulating chamber and the second reactant gas chamber share a first insulating chamber wall therebetween, and the insulating chamber and the exhaust share a second insulating chamber wall therebetween, the second insulating chamber wall disposed opposite to the first insulating chamber wall and defining an insulating volume therebetween.
In some embodiments, the insulating chamber comprises a single aperture such that the insulating chamber is in fluid communication with the first reactant gas chamber.
In some embodiments, the second wall comprises one or more auxiliary apertures, said one or more auxiliary apertures being disposed between the second reactant gas inlet and the first section of the second wall, wherein the total cross-sectional area of said one or more auxiliary apertures for a given area is greater than the total cross-sectional area of the one or more apertures in an equivalent area of the first section of the second wall.
In some embodiments, the one or more auxiliary apertures comprises one or more of the following: a helical auxiliary aperture spiraling down the length of the second wall between the second reactant gas inlet and the first section of the second wall; and/or one or more auxiliary linear apertures disposed down the length of the second wall between the second reactant gas inlet and the first section of the second wall; and/or a plurality of auxiliary apertures disposed in the second wall between the second reactant gas inlet and the first section of the second wall.
In some embodiments, the device is an ammonia cracker for the production of hydrogen, wherein the one or more catalysts are ammonia decomposition catalysts.
In some embodiments, the device is a methanol, ethanol or hydrocarbon reformation device for the production of hydrogen, wherein the one or more catalysts are steam reforming catalysts, partial oxidation catalysts, or autothermal catalysts.
In a further aspect, the invention provides a system for generating electricity comprising the device of the first aspect or any of its embodiments, a gas separator, and a fuel cell.
Brief description of the drawings
Figure 1 shows a cross-sectional schematic of a device according to the invention.
Figure 2 shows a cross-sectional schematic of a device according to an embodiment of the invention wherein the device is shaped as a cylinder.
Figure 3 shows a three-dimensional cutaway schematic (Figure 3A) of an embodiment of the invention wherein the device is cylindrical, and a cross-section of said device (Figure 3B).
Figure 4 shows a cross-sectional schematic of a device according to an embodiment of the invention wherein the device is shaped as a cylinder, and the exhaust is integral and disposed within the second reactant gas chamber of the device. Figure 4A shows the cross section through the length of the device. Figure 4B shows a cross section through the width of the device.
Figure 5 shows a close-up, cross-sectional schematic of a device according to an embodiment of the invention wherein the device comprises heat transfer structures extending into the reaction chamber of the device from the first wall of said device.
Figure 6 shows a cross sectional schematic of a device according to an embodiment of the invention wherein the device further comprises an insulating chamber disposed between the exhaust and the second reactant gas chamber of the device.
Figure 7 shows a three dimensional cutaway of a device according to embodiments of the invention. Figure 7A shows an embodiment wherein the one or more apertures are disposed as linear apertures down the area of the second wall. Figure 7B shows an embodiment wherein the one or more apertures are disposed as a helical aperture disposed through an area of the second wall. Figure 8 shows a close-up, cross-sectional schematic of a device according to an embodiment of the invention wherein one or more auxiliary apertures are disposed in the second wall between the second reactant gas inlet and the first section.
Figure 9 shows the results of a computational fluid dynamics simulation of a device according to the invention.
Figure 10 shows the results of an alternative computational fluid dynamics simulation of a device according to the invention.
Figure 11 shows the second wall of a device wherein the one or more apertures are evenly spaced.
Figure 12 shows an embodiment of the second wall of the device according to the invention wherein the one or more apertures have differential spacing through the length of the aperture-containing area of the second wall.
Figure 13 shows the temperature profile through time during start up and steadystate operation from four co-ordinates of a device wherein the one or more apertures are evenly spaced.
Figure 14 shows the temperature profile through time during start up and steady state operation from four co-ordinates of an embodiment of the invention wherein the one or more apertures of the device have differential spacing through the length of the aperture-containing area of the second wall.
Figure 15 shows a schematic of a system for generating electricity comprising the device of the first aspect, a gas separator, and a fuel cell.
Detailed description of the invention
W02002/064248A2 relates to an integrated reactor for simultaneous exothermic and endothermic reactions.
US2005/0048333A1 relates, in part, to a system comprising a reaction vessel having multiple staged catalytic combustion chambers which transfer heat to multiple endothermic reaction chambers.
WO1 999/018392 A1 relates to a combustion heater for a reaction process chamber.
US2004/0033455A1 relates to an integrated combustion reactor for simultaneous endothermic and exothermic reactions.
EP1712274A1 relates to a combined reforming reactor and combustion reactor.
US2006/0083675A1 relates to an integrated combustion microreactor.
In a first aspect, the invention provides a device 100 for hydrogen production (an embodiment of which is shown in Figure 1) comprising a reaction chamber 101 containing one or more catalysts disposed therein, a fuel gas inlet 102, and a hydrogen-rich gas outlet 103; a first reactant gas chamber 104 having a first reactant gas inlet 105 for conveying a first reactant gas 106, the first reactant gas chamber 104 being in fluid communication with an exhaust 107; and a second reactant gas chamber 108 having a second reactant gas inlet 109 for conveying a second reactant gas 110; wherein the reaction chamber 101 and the first reactant gas chamber 104 share a first wall 111 therebetween (i.e. have a wall in common, with one face facing the reaction chamber 101 and the opposite face facing the first reactant gas chamber 104), the first wall 111 comprising a thermally conductive substrate and having a reaction chamber face 111a and a first reactant gas chamber face 111 b, wherein the first reactant gas chamber face 111 b of the first wall 111 has a reaction surface 112 which is coated with a reactant gas decomposition catalyst (the reaction surface is an area where oxidation catalyst or reactant gas decomposition catalyst is deposited which at least partially covers the first reactant gas chamber face 111 b of the first wall 111 ); wherein the first reactant gas chamber 104 further comprises a second wall 113 opposite the first wall 111 defining a volume therebetween, the second wall 113 being shared between the first reactant gas chamber 104 and the second reactant gas chamber 108 (i.e. have a wall in common, with one face facing the first reactant gas chamber 104 and the opposite face facing the second reactant gas chamber 108); wherein the second wall 113 comprises a plurality of apertures 114 disposed in an aperture-containing area along a length and width of the second wall 113 such that the second reactant gas chamber 108 and the first reactant gas chamber 104 are in fluid communication with one another, wherein the aperture-containing area is defined as the area of the second wall 113 containing the one or more apertures 114, wherein the aperturecontaining area of the second wall 113 has a first section, a second section, and a third section, the first section being a third of the aperture-containing area distal to the fuel gas inlet 102 and the third section being a third of the aperture-containing area proximal to the fuel gas inlet 102, the second section being a third of the aperture-containing area of the second wall between the first section and the third section, wherein the total cross-sectional area of the one or more apertures disposed in the first section 114a is less than the total cross-sectional area of the one or more apertures disposed in the third section 114c, wherein the total cross-sectional area of the one or more apertures disposed in the second section 114b is greater than the total cross-sectional area of the one or more apertures disposed in the first section 114a and less than the total cross-sectional area of the one or more apertures disposed in the third section 114c; wherein the cross-sectional area of the second reactant gas chamber 108 is greater than the total cross-sectional area of the one or more apertures 114. Each of the one or more of apertures 114 are configured to eject the second combustion gas such that it mixes with the first combustion gas and combusts upon contact with the combustion gas decomposition catalyst.
The reaction chamber can take any shape or size, but generally it will be a sealed chamber except for the fuel gas inlet and the hydrogen-rich gas outlet. The reaction chamber will contain an appropriate catalyst for the production of hydrogen depending on the fuel gas which will be provided in use. For example, where the fuel gas will be ammonia, the reaction chamber could contain ruthenium or platinum, both of which are well known ammonia decomposition catalysts (see Lucentini et al., 2021 ). Where the fuel gas is methanol, ethanol or another hydrocarbon, the reaction chamber could contain nickel-based catalysts, copper-based catalysts, cobalt-based catalysts, platinum-based catalysts, palladium-based catalysts or gold-based catalysts (see Rostami et al., 2023).
The catalyst may be supplied as an internal coating on walls of the reaction chamber, or on any substructures present in the reaction chamber such as fins, meshes, or other surface area increasing substructures. Alternatively or in addition, catalyst may be provided on a substrate disposed within but not integral to the reaction chamber, such as ceramic pellets. In use, the fuel gas flows into the reaction chamber via the fuel gas inlet from a supply, contacts the catalyst therein and reacts to produce a hydrogen-rich gas (i.e. a product gas containing hydrogen and off-gases produced during the reaction), which then flows out of the reaction chamber via the hydrogen-rich gas outlet and onwards to storage or further downstream systems.
The device further comprises a first reactant gas chamber having a first reactant gas inlet for conveying a first reactant gas. The first reactant gas chamber is fluidly connected to a supply for a first reactant gas via the first reactant gas inlet. The first reactant gas chamber is in fluid communication with an exhaust. The device further comprises a second reactant gas chamber having a second reactant gas inlet for conveying a second reactant gas. The second reactant gas chamber is fluidly connected to a supply for the second reactant gas via the second reactant gas inlet.
The reaction chamber is adjacent to and shares a first wall with the first reactant gas chamber. In other words, the first wall is common between the reaction chamber and the first reactant gas chamber. This first wall has a reaction chamber face facing the internal volume of the reaction chamber, and a first reactant gas chamber face facing the internal volume of the first reactant gas chamber. The first reactant gas chamber face has a reaction surface coated with a reactant gas decomposition catalyst (also known as an oxidation catalyst). The reaction surface may cover only part of the first reactant gas chamber face, or the entire face may be covered with the reaction surface. In an embodiment the reaction surface is the first reactant gas chamber face of the first wall said face being coated with said reactant gas decomposition catalyst. The reactant gas decomposition catalyst causes combustion of the first reactant gas and the second reactant gas when mixed. By coating the first wall with said catalyst, the combustion happens on and/or close to the first wall (at the reaction surface) thus maximizing heat generation proximal to the reaction chamber to maximize heat transfer from the first reactant gas chamber to the reaction chamber and thus increase the efficiency of the device. As an example, the reactant gas decomposition catalyst may be platinum. Others will be known to the person skilled in the art. The first reactant gas chamber further comprises a second wall opposite the first wall defining a volume therebetween, the second wall being shared between the first reactant gas chamber and the second reactant gas chamber. In other words, the second wall is common between the first reactant gas chamber and the second reactant gas chamber. The second wall comprises one or more apertures disposed in an aperture-containing area along the length and width of the second wall such that the second reactant gas chamber and the first reactant gas chamber are in fluid communication with one another. Such apertures may be created using known techniques including but not limited to drilling or laser drilling. This arrangement means that, in use, a first reactant gas flows into the first reactant gas chamber and a second reactant gas flows into the second reactant gas chamber, through the one or more aperture(s) of the second wall and into the first reactant gas chamber where the two reactant gases mix. Upon contact with the catalyst coated reaction surface, the mixture of the two gases combusts to produce heat, before the resultant flue gas flows out of the first reactant gas chamber via the exhaust. Gases do not mix and ignite outside of the first reactant gas chamber. In order to achieve this, the pressure drop through the one or more apertures is greater than through the first reactant gas chamber to the exhaust, preventing a backflow into the second reactant gas chamber. A backflow of the first reactant gas into the second reactant gas chamber presents a safety issue as said second reactant gas chamber could reach very high temperatures and suffer structural damage. Additionally, if uncontrolled combustion occurs outside of the first reactant gas chamber, more heat will be lost to the surroundings rather than being directed to heat the endotherm (in the reaction chamber). As such, the one or more apertures are configured such that the second reactant gas is ejected to mix with the first reactant gas and combust upon contact with the reactant gas decomposition catalyst at the reaction surface. In other words, the velocity of the second reactant gas is tuned via configuring the apertures such that the mixing of the first and second reactant gas and the subsequent combustion reaction happens proximal to the first wall to maximize heat transfer from the first reactant gas chamber into the reaction chamber. This tuning of the apertures is achieved by varying the size, shape, and/or number thereof to produce a gas velocity which causes a jet of the second reactant gas to pass through the volume of the first reactant gas chamber largely unmixed before hitting the reaction surface and mixing with the first reactant gas proximal to said surface. For example, the length to diameter ratio of the aperture can alter the jetting profile of the second reactant gas. A greater ratio (length:diameter) will improve the jet as it emerges from the aperture(s). To ensure this effect is achieved, the cross-sectional area of the second reactant gas chamber is greater than the total cross-sectional area of the one or more apertures. The cross-sectional area of the second reactant gas chamber is the internal area of the second reactant gas chamber on a plane which is (optionally substantially) perpendicular to the majority flow of gas through that chamber. For example, in the embodiment shown in Figure 3A and 3B, the cross-sectional area of the second reactant gas chamber is the circular area shown in Figure 3B labelled 308. The flow of gas from the second reactant gas chamber to the first reactant gas chamber via the one or more apertures (not shown) is shown with arrows. As another example, in the embodiment shown in Figure 4A and 4B, the cross-sectional area of the second reactant gas chamber is the annular area labelled 408, exclusive of the area defined by the inner chamber labelled 407. As shown in Figures 1 to 4, this would be the horizontal plane through the device perpendicular (labelled as axis y) to the vertical plane defined from top to bottom (labelled as axis x). As an example, the area is shown in Figure 3B for a cylindrical device, and would be the area defined by the circle whose internal volume is labelled 308. In some embodiments, the cross-sectional area of the second reactant gas chamber is (optionally about) 1.1x, 1.2x, 1.3x 1.4x, 1.5x, 2x, 3x, 4x, 5x, 6x, 7x, 8x, 9x, 10x, 15x, 20x, 25x, 30x, 35x, 40x, 45x, 50x or more of the total cross-sectional area of the one or more apertures (and, optionally, one or more auxiliary apertures). In some embodiments, the cross-sectional area of the second reactant gas chamber is (optionally about) 10x to 50x or more of the total cross-sectional area of the one or more apertures (and, optionally, the one or more auxiliary apertures). This feature is particularly advantageous as it prevents a pressure drop along the length of the second reactant gas chamber and thus ensures that the volumetric flow of the second reactant gas through each aperture is equal. This contributes to the uniform heating effect of the device due to encouraging an appropriate amount of combustion across the reaction surface by preventing a pressure drop along the length of the second reactant gas chamber. Other attributes which can alter the jetting of the second reactant gas through the aperture(s) are the thickness of the second wall (i.e. the length of each aperture in the one or more apertures), the width of the first reactant gas chamber, and the lambda (the mass ratio of air and fuel in the first reactant gas chamber as it relates to the stoichiometric air-fuel ratio).
Having the first and second reactant gas enter the device in this way has several advantages over known devices, as it prevents unintentional combustion (known as ‘flashback’) of the combustible gases prior to entry to the reactant gas chambers or in other locations of the device. A flame front travelling back to the inlet source (flashback) is prevented in the presently described device. In addition, it allows for the fine control of heat production to maximize the transfer to the reaction chamber where the heat is most required. Whilst the flow of fuel gas versus the first and second reactant gases is shown as a counter-flow (in opposing directions) in use, all of the gases may flow in the same direction in use in some embodiments.
The second wall has an aperture-containing area defined as the area containing the one or more apertures. The second wall may contain other portions which do not contain any of the one or more apertures situated at either end of the aperturecontaining area proximal and distal to the second reactant gas inlet. These portions can vary in length. The aperture-containing area of the second wall has three sections, a first section, a second section, and a third section. Each section is one third of the aperture-containing area of the second wall. The first section is the third of the aperture-containing area of the second wall distal (i.e. furthest) to the fuel gas inlet of the reaction chamber. The third section is the third of the aperture-containing area of the second wall proximal (i.e. closest) to the fuel gas inlet of the reaction chamber. The second section is the third of the aperture-containing area in between the first section and the third section. Together, the first section, second section, and third section are the aperture-containing area of the second wall. The one or more apertures are disposed through the aperture-containing area of the second wall. In other words, the one or more apertures are disposed in the first section, second section, and third section of the second wall. The total cross-sectional area of the one or more apertures disposed in the first section is less than the total cross- sectional area of the one or more apertures disposed in the third section. The total cross-sectional area of the one or more apertures disposed in the second section is greater than the total cross-sectional area of the one or more apertures disposed in the first section and less than the total cross-sectional area of the one or more apertures disposed in the third section. In other words, with reference to Figure 1 , the total cross-sectional area of the one or more apertures disposed in the first section of the second wall 114a is lower than the total cross-sectional area of the one or more apertures disposed in the second section of the second wall 114b, which is lower than the total cross-sectional area of the one or more apertures disposed in the third section of the second wall 114c. The effect of this arrangement is that more of the second reactant gas 110 can flow from the second reactant gas chamber 108 into the first reactant gas chamber 104 via the one or more apertures disposed in the third section of the second wall 114c than via the one or more apertures disposed in the second section of the second wall 114b or the one or more apertures disposed in the first section of the second wall 114a.
In an alternative embodiment, the first section is defined as the third of the aperturecontaining area proximal (i.e. closest) to the second reactant gas inlet, the third section is defined as the third of the aperture-containing area distal (i.e. furthest) to the second reactant gas inlet, and the second section is the third of the aperturecontaining area between the first section and the third section. In some embodiments, the first section, second section, and third section are each one third of the length of the aperture-containing area, with the first section being the third of the length of the aperture-containing area proximal (i.e. closest) to the second reactant gas inlet, the third section being the third of the length of the aperturecontaining area distal (i.e. furthest) to the second reactant gas inlet, and the second section being the third of the length of the aperture containing area between the first section and the third section.
These arrangements allow for greater heating of the reaction chamber proximal to the fuel gas inlet, where the fuel gas is at its most concentrated and thus the most heat is required for the endothermic reaction to proceed optimally. The concentration of fuel gas decreases from the fuel gas inlet to the hydrogen-rich gas outlet as the fuel gas decomposes into hydrogen-rich product gas, and so the heating required for optimal reaction conditions reduces. Arranging the apertures fluidly connecting the second reactant gas chamber and the first reactant gas chamber as described above thus ensures even temperatures within the first wall 111 and the reaction chamber 101 . This is advantageous as it prevents the formation of hot or cool spots which could compromise the structure of the device and produce suboptimal conditions for the reaction occurring within the reaction chamber of said device.
The device can take any shape suited to the particular application it is being adapted to. The device may be constructed of any suitable materials which would be apparent to the skilled person. For example, where the device is an ammonia cracker, ammonia-resistant materials are preferred such as Austenitic stainless steels or high nickel chromium content superalloys.
In one particularly advantageous embodiment, the device has the general shape of a cylinder. In such embodiments, the first wall, second wall, and/or third wall may be concentric cylinders. An embodiment of this is shown in Figure 2 as a longitudinal cross section through the center of the device 200. In said embodiment, the outermost wall 221 defines an outer wall of the reaction chamber 201 and is a cylinder, the first wall 211 is a cylinder, with the volume between the outermost wall 221 and the first wall 211 defining the reaction chamber 201 . The second wall 213 is a cylinder, with the volume between the first wall 211 and the second wall 213 defining the first reactant gas chamber 204. When the walls are cylinders or other prism shapes, they may be concentric. The one or more apertures are shown 214. In this embodiment, the width of the second wall is the circumference of the second wall, and the one or more apertures are disposed in the aperture-containing area along the length and circumference of the second wall. In some embodiments, the internal volume defined by the second wall 213 defines the second reactant gas chamber 208. As such, the second reactant gas chamber 208 is disposed within the first reactant gas chamber 204, and the first reactant gas chamber 204 is disposed within the reaction chamber 201 . The chambers are shown herein as concentric cylinders. As before, the first reactant gas chamber 204 is in fluid communication with an exhaust 207. Figure 3A shows a three-dimensional cutaway schematic of the device shown in Figure 2 having a reaction chamber 301 , a first reactant gas chamber 304, and a second reactant gas chamber 308. The one or more apertures 314 creating a fluid connection between the first reactant gas chamber 304 and the second reactant gas chamber 308 are shown. A horizontal cross-section is shown top-down in Figure 3B, showing the reaction chamber 301 , the first reactant gas chamber 304, and the second reactant gas chamber 308 defined by the walls as described above.
In some embodiments, as shown in Figure 4, there is a third wall 415 being a cylinder, with the volume between the second wall 413 and the third wall 415 defining the second reactant gas chamber 408, as shown in Figure 4A. In some embodiments, the third wall defines a cylinder which is the exhaust 407. As such, the exhaust 407 is disposed within the second reactant gas chamber 408, the second reactant gas chamber 408 is disposed within the first reactant gas chamber 404, and the first reactant gas chamber 404 is disposed within the reaction chamber 401 . Figure 4B shows an alternative view from the top down as a horizontal cross-section of the device showing the cylindrical or annular nature of each chamber of this embodiment. The arrows show gas flow from the second reactant gas chamber into the first reactant gas chamber through the one or more apertures (not shown in Figure 4B). Again the device is shown as concentric cylinders disposed within one another, which represents an embodiment of the present invention.
This cylindrical arrangement maximizes the structural integrity of each chamber and provides an ease of manufacture. In addition it is helpful for the uniform heating of the first wall by the combustion of the first and second reactant gases against the reaction surface coated with reactant gas decomposition catalyst. When the chambers are cylindrical, the one or more apertures may be disposed along the length and circumference of the second wall. Therefore, the second reactant gas is ejected or jetted out of the second combustion gas chamber into the first as described above. This contributes to the uniform heating effect described previously. Having the exhaust disposed within the second reaction gas chamber ensures more of the residual combustion heat carried by the flue gas radiates to the chambers of the device instead of to the atmosphere.
It should be understood that whilst a ‘cylinder1 generally refers to a three-dimensional prism having a circular cross-sectional profile which has optimal physical characteristics in this application, the invention is not limited to a circular prism. As such, ‘cylinder’ as used herein can, in some embodiments, refer to any three- dimensional prismatic shapes having the cross-sectional shape of one or more of a triangle, a square, an ellipsoid, a pentagon, a hexagon, an octagon, or any other shape. In addition, ‘cylinder1 may mean an irregular prism wherein the shape can be varied to suit the application and may differ down the length of the device. For example, the ‘cylinder1 could be a conical shape, with the diameter increasing/decreasing down the length of the device or chamber. In such embodiments, two or more or all of the cylinders may be concentric. Alternatively, the device may have a variable prismatic shape. This may be useful in embodiments intended for applications where space is limited, such as incorporation of the device into an engine bay housing other components.
In some embodiments, as shown in Figure 5, the first wall 511 comprises one or more heat transfer structures 516 comprising metal extending into the reaction chamber 501 . These heat transfer structures increase the surface area of the reaction chamber face 511a and may be any suitable shape, for example fins, pins, plates, bumps, bosses, one or more meshes, or any combination thereof. In use, they carry heat from the reaction surface into the reaction chamber to assist with the heating of the catalyst and to optimize conditions for the catalytic reaction in said reaction chamber.
In some embodiments, the first reactant gas comprises hydrogen and the second reactant gas comprises oxygen. In use, this means that a hydrogen containing gas flows into the first reactant gas chamber and an oxygen containing gas flows into the second reactant gas chamber, through the one or more apertures and into the first reaction gas chamber. Each of the first reactant gas and the second reactant gas may have other constituents, but must contain hydrogen or oxygen, respectively. In other embodiments, the first reactant gas comprises oxygen and the second reactant gas comprises hydrogen. In use, this means that an oxygen containing gas flows into the first reactant gas chamber and a hydrogen containing gas flows into the second reactant gas chamber, through the one or more apertures and into the first reaction gas chamber. Each of the first reactant gas and the second reactant gas may have other constituents, but must contain oxygen or hydrogen, respectively. For example, the oxygen containing gas could be air, and the hydrogen containing gas could be impure cracked gas produced from an ammonia decomposition reaction containing nitrogen, ammonia gas, and hydrogen. Alternatively, the oxygen containing gas could be air and the hydrogen containing gas could comprise methane, methanol propane, propanol, or another hydrocarbon gas for which there is a known oxidation catalyst, such as a highly dispersed platinum catalyst. The hydrogen containing gas will also comprise hydrogen. The first reactant gas and the second reactant gas may be referred to as a first combustion gas and a second combustion gas, respectively. This is not to be confused with the products of combustion, which are sometimes called combustion gases in the art. Herein, the term means gases capable of combustion when combined.
In some embodiments, the exhaust is proximal to the second reactant gas chamber. In other words, the exhaust is disposed adjacent to the second reactant gas chamber, meaning that any excess heat from the hot flue gas leaving the device via the exhaust may be transferred into the second reactant gas chamber to heat the second reactant gas. In some embodiments, the exhaust is cylindrical (as described previously) and is disposed within the second reactant gas chamber (as shown, for example, in Figure 4). As previously explained, the exhaust, second reactant gas chamber, and first reactant gas chamber may be formed by cylindrical walls which are concentric. This configuration reduces heat loss via the exhaust by transferring heat from the exhaust gas to the second reactant gas chamber to raise the temperature of the second reactant gas, further boosting the efficiency of the device.
In some embodiments, as shown in Figure 6, the device further comprises an insulating chamber 617 disposed between the exhaust 607 and the second reactant gas chamber 608. In this embodiment, the insulating chamber 617 and the second reactant gas chamber 608 share (i.e. have in common) a first insulating chamber wall 618 therebetween, and the insulating chamber 617 and the exhaust 607 share (i.e. have in common) a second insulating chamber wall 619 therebetween, the second insulating chamber wall 619 disposed opposite to the first insulating chamber wall 618 and defining an insulating volume therebetween.
The volume of the insulating chamber may be filled with air, or with an insulating material which does not transfer heat readily. In some embodiments, the insulating chamber comprises a single aperture 620 (i.e. at least one aperture) such that it is in fluid communication with the first reactant gas chamber 604. In other embodiments, the insulating chamber comprises a single aperture such that it is in fluid communication with the exhaust. This single aperture means that the pressure exerted on the walls of the insulating chamber is kept within acceptable parameters whilst also ensuring a low air flow, meaning that the insulating effect of the air occupying the internal volume of the insulating chamber is maintained.
As outlined previously, the second wall has an aperture-containing area having three sections, and the total cross-sectional area of the one or more apertures disposed therein varies between each section to vary the flow of the second reactant gas from the second reactant gas chamber into the first reactant gas chamber. This variation can be achieved in numerous ways. For example, as shown in Figure 3A, the pitch between rows of apertures could vary down the length of the aperture-containing area of the second wall, such that there are more apertures in the third section than in the second or first section, and more apertures in the second section than the first section.
Alternatively or in addition, the cross-sectional area of each hole in the third section could be greater than the cross-sectional area of each hole in the second section, and the cross sectional area of each hole in the second section could be greater than the cross-sectional area of each hole in the first section.
Alternatively or in addition, the one or more apertures may comprise one or more linear apertures disposed down the length of the aperture-containing area of the second wall as shown in Figure 7A. In this embodiment, each aperture 714a has a first linear portion in the first section, a second linear portion in the second section, and a third linear portion in the third section. The cross-sectional area of the first linear portion is less than the cross-sectional area of the third linear portion, and the cross-sectional area of the second linear portion is greater than the cross-sectional area of the first linear portion and less than the cross-sectional area of the third linear portion. This arrangement allows more of the second reactant gas to flow from the second reactant gas chamber into the first reactant gas chamber in the third linear portion than the second linear portion or first linear portion of each aperture, and allows more gas to flow from the second reactant gas chamber into the first reactant gas chamber through the second linear portion than the first linear portion of each aperture.
Alternatively or in addition, the one or more apertures may, as partially shown in Figure 7B, comprise a helical aperture 714b spiraling down the aperture-containing area of the second wall having a first helical portion disposed in the first section, a second helical portion disposed in the second section, and a third helical portion disposed in the third section of the aperture containing area of the second wall. The distance between each turn of the helical aperture could reduce from the first helical portion to the second helical portion, and from the second helical portion to the third helical portion as shown in order to increase the cross-sectional area of the aperture in the second section compared to the first, and the third section compared to the second. Alternatively or in addition, the width of the helical aperture could increase from the first helical portion to the second helical portion, and from the second helical portion to the third helical portion. This would mean that the cross-sectional area of the aperture would be greater in the third section than the first section, with the cross-sectional area of the aperture in the second section being in between that of the first section and the third section.
In some embodiments, as shown in Figure 8, the second wall 813 comprises one or more auxiliary apertures 815 disposed in the second wall between the second reactant gas inlet and the first section 8141 of the second wall 813, wherein the cross-sectional area of said one or more auxiliary apertures 815 for a given area is greater than the cross-sectional area of the one or more apertures in an equivalent area of the first section 8141 of the second wall 813. The second section 8142 and third section 8143 are shown. The term ‘given area’ means an equivalent area from each section. For example, if the area being compared is 1 m2, the total cross- sectional area of the one or more auxiliary apertures per 1 m2 will be greater than the total cross-sectional area of the one or more apertures in 1 m2 of the first section of the second wall.
As shown in Figure 8, the one or more auxiliary apertures 815 are much closer together than the one or more apertures 814 disposed in the first section 8141 of the second wall 813. This is one way of achieving the greater total cross-sectional area for the one or more auxiliary apertures as described above. Alternatively or in addition, the one or more auxiliary apertures could each have a larger cross- sectional area than the one or more apertures. In some embodiments, the one or more auxiliary apertures comprise a helical auxiliary aperture spiraling down the length of the second wall between the second reactant gas inlet and the first section of the second wall. Alternatively or in addition, the one or more auxiliary apertures comprise one or more auxiliary linear apertures disposed down the length of the second wall between the second reactant gas inlet and the first section of the second wall. Alternatively or in addition, the one or more auxiliary apertures comprise a plurality of auxiliary apertures disposed in the second wall between the second reactant gas inlet and the first section of the second wall. For a given area, the total cross-sectional area of the one or more auxiliary apertures may be 1 .1 x, 1 ,2x, 1 ,3x, 1 ,4x, 1 ,5x, 1 ,6x, 1 ,7x, 1 ,8x, 1 ,9x, 2x, 3x, 4x, 5x, 6x, 7x, 8x, 9x, or 10x the total cross- sectional area of the one or more apertures disposed in an equivalent area of the first section of the aperture-containing area of the second wall.
The effect of the one or more auxiliary apertures having a relatively greater total cross-sectional area than the one or more apertures in an equivalent area of the first section is to increase the temperature of the first reactant gas proximal to the auxiliary apertures in the first reactant gas chamber to ensure that heat does not flow from the reaction chamber to the flue gas. Furthermore, this maintains heat in the portion of the reaction chamber distal to the fuel gas inlet to continue the endothermic reaction therein without overheating it, as there is less endothermic activity in this portion of the reaction chamber. This also prevents localized cold spots from forming in the reaction chamber of the device and is thus optimal for the operation of the device. This arrangement also causes a breakup of the laminar flow of the first reactant gas to make subsequent jets more effective.
In each of Figures 1 , 2, 4, 5, 6, and 8 the grey arrows represent gas flow for each respective chamber. The gas flowing into the reaction chamber is the fuel gas (e.g. ammonia or a hydrocarbon), and the gas flowing out of the reaction chamber is the hydrogen-rich gas (i.e. the product gas). The gas flowing into the first reactant gas chamber is the first reactant gas, and the gas flowing into the second reactant gas chamber is the second reactant gas. The gas flowing out of the first reactant gas chamber and out through the exhaust is the flue gas.
In one example embodiment, the device is an ammonia cracker for the production of hydrogen. This means that the one or more catalysts disposed in the reaction chamber are ammonia decomposition catalysts. Many suitable catalysts are known in the art and may be used in the present invention, for example, supported monometallic catalysts (Fe, Ru, Cu, Ni, Ir, Co, Mo, Pt and Pd) multimetallic catalysts or alloy catalysts (Ni-Pt, Ni-Co, Ir-Ni, Co-Mo, Fe-Co, Fe-Mo, Cu-Zn), nitride and carbide catalysts (Carbides and nitrides of Mo, Fe, Co, Ni, Ti, V, Mn and Cr), and metal amide/imide catalysts (UNH2, NaNH2, KNH2). The product gas may be used as either the first or second reactant gas, as it contains hydrogen.
In another example embodiment, the device is a methanol, ethanol or hydrocarbon reformation device for the production of hydrogen. This means that the one or more catalysts are steam reforming catalysts, partial oxidation catalysts, or autothermal catalysts. Many suitable catalysts are known in the art and may be used in the present invention. For example, nickel oxide catalysts, other base metal catalysts and noble metal catalysts.
In a further aspect, as shown in Figure 15 the invention provides a system for generating electricity comprising the device 15100 of the prior aspect and its embodiments, a gas separator 15200, and a hydrogen fuel cell 15300. This system allows for the generation of electricity from a fuel gas using the device. The device of the first aspect is fluidly connected to a gas separator such as a palladium filter or a pressure-swing adsorption device in order to purify the hydrogen from the product gas for use by the fuel cell. As such the gas separator is fluidly connected to the fuel cell. The outlet from the fuel cell may convey a hydrogen containing gas (leftover from the conversion of hydrogen gas and oxygen into water) as part of the fuel cell reaction. This may be recycled (directly or indirectly) into the first or second reactant gas chamber to fuel the combustion reaction according to the above aspects of the invention. As such, fuel cell may have a gas outlet which is in fluid communication with the first reactant gas inlet or the second reactant gas inlet of the device of the first aspect. Examples
Example 1 : Computational Fluid Dynamics (CFD) showing second rea eta nt gas pathlines in an embodiment of the invention
A device was simulated to show the flow of the second reactant gas from the second reactant gas chamber into the first reactant gas chamber via the one or more apertures. Figure 9 shows the results of a CFD simulation of a 20-degree periodic slice of the device. The composition of the second reactant gas in this example is 75% hydrogen and 25% nitrogen by mole. As shown in Figure 9, the pathlines for the second reactant gas flow up the second reactant gas chamber and jet through the one or more apertures into the first reactant gas chamber, onto the first wall coated in a oxidation catalyst (the reaction surface). The first reactant gas has a mass flow rate eguivalent to a lambda of 1 .05 relative to the total hydrogen flow contained within the second reactant gas. The pathlines of the first reactant gas are not shown in Figure 9 to improve clarity of the figure. The pathlines for the second reactant gas can be seen striking the surface of the first wall.
Figure 10 shows a simulation where the mass flow rate of the second reactant gas is egual to the mass flow rate in the simulation shown in Figure 9. The mass flow rate of the first reactant gas is egual to a lambda of 5 relative to the guantity of hydrogen contained within the second reactant gas stream. The jetting of the second reactant gas from the plurality of apertures is insufficient to reach the oxidation catalyst surface on the first wall. In this condition the first and second reactant gases are unlikely to react, or they will combust further down the first wall which will significantly lower efficiency when compared to the flow conditions shown in Figure 9.
Example 2: Device heating comparison between a device having evenly spaced apertures and a device according to an embodiment of the invention having apertures with varied spacing
An embodiment of the present invention is demonstrated in this example showing a comparison between the start-up and steady state temperature profiles of one embodiment of the device with an even spacing of apertures in the second wall (Figure 11 ), and a device with aperture spacing according to an embodiment of the invention where the one or more apertures have differential spacing through the length (x) of the aperture-containing area of the second wall (e.g. as shown in Figure 8 and Figure 12). In both cases, the second wall also comprises one or more auxiliary apertures as described previously and as shown in the relevant figures. The same reaction chamber is used for both devices, only the distribution of apertures in the second wall is changed as shown in the figures. The results are shown in Figure 13 for the evenly-spaced aperture configuration, and in Figure 14 for the configuration according to the embodiment of the present invention with varied spacing. Hereafter, the end of a feature (e.g. first reactant gas chamber, oxidation catalyst, reaction chamber) closest to the fuel gas inlet (e.g. 802 in Figure 8) is referred to as the ‘top’ of said feature, and the end of the feature furthest from the fuel gas inlet is referred to as the ‘bottom’ of said feature, with the middle of said feature being halfway therebetween along the length of said feature. In both Figures 13 & 14, the top and middle temperatures of the oxidation catalyst (disposed in the first reactant gas chamber) and corresponding reaction chamber temperatures are plotted against time.
Initially, for both devices, the first reactant gas chamber and reaction chamber are heated from ambient temperature using the same reactant gas mass flow rates. For the evenly spaced device, as shown in Figure 13, the top of the first reactant gas chamber (‘T op burner1) is slower to heat than the middle of the first reactant gas chamber (‘Middle Burner’). At the end of the heat-up period, the temperature in the middle of the first reactant gas chamber is 173°C hotter than the temperature at the top of the first reactant gas chamber. For the device shown in Figure 14, the middle and top of the first reactant gas chamber (‘Middle Burner’ and ‘Top Burner’, respectively) heat at a similar rate, and at the end of the heat-up period, the temperature difference between the top and middle of the first reactant gas chamber is 25°C.
The same mass flowrate of fuel gas is then introduced to the reaction chamber for both devices. The temperature difference between a corresponding first reactant gas chamber temperature and reaction chamber temperature is assumed to be representative of the heat transfer into the reaction chamber. For the device shown in Figure 13, the steady state temperature difference between the top of the first reactant gas chamber (i.e. the combustion chamber) and top of the reaction chamber is 52°C. For the device shown in Figure 14, the steady state temperature difference between the top of the first reactant gas chamber and the top of the reaction chamber is 103°C. For the device shown in Figure 13, the steady state temperature difference between the middle and top of the first reactant gas chamber is 134°C. For the device shown in Figure 14, the steady state temperature difference between the middle and top of the first reactant gas chamber is only 76°C.
The results shown in Figure 14 shows a significant improvement for the device according to an embodiment of the present invention (configured as shown in Figure 12) compared to the results shown in Figure 13 for the device having evenly-spaced apertures (configured as shown in Figure 11), with the variable aperture spacing producing a more uniform temperature start-up, as well as transferring more heat to the fuel gas at the inlet end of the reaction chamber.
References
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US2005/0048333A1
WO1 999/018392 A1
US2004/0033455A1 EP1712274A1
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