Catalytic reactions

Abstract

A fixed-bed reactor apparatus for reacting gas-phase reactant with solid-phase catalyst, the reactor comprising at least one inlet for intake of gas-phase reactant, at least one outlet for exhaust of gas-phase product, first and second reactor stages arranged in a series relationship between the at least one inlet and the at least one outlet to thereby define first and second sections of a gas flow path between the at least one inlet and the at least one outlet such that gas-phase reactant may flow along the gas flow path in a direction from the at least one inlet through the first reactor stage and subsequently through the second reactor stage towards the at least one outlet, each of the first and second reactor stages comprising a respective plurality of reaction tubes arranged in a parallel relationship, each of the reaction tubes defining a bore through which the gas-phase reactant may flow, each of the reaction tubes being suitable for containing solid-phase catalyst in the respective bore, wherein a cumulative area of the bores of the plurality of reaction tubes of the first reactor stage is lesser than a cumulative area of the bores of the plurality of reaction tubes of the second reactor stage.

Description

[0001] CATALYTIC REACTIONS

[0002] Field of the Disclosure

[0003] The present disclosure relates to catalytic reactions.

[0004] Background of the Disclosure

[0005] Catalytic reactions may be employed practically to generate substances from feed reactants. For example, methanation is the name given to a catalytic reaction in which methane gas is produced by conversion of carbon oxide to methane. Some catalytic reactions, such as methanation, are highly exothermic, which may present problems such as thermal runaway and / or catalyst damage if the process is not suitably thermally controlled. A challenge for reactor designers is therefore thermal management of the reactor, and in particular avoidance of hot spots in the catalyst bed that may damage the catalyst.

[0006] Highly exothermic catalytic reactions, such as methanation, may conventionally be carried out in a series of adiabatic reactors with interstage cooling. However, in such designs, it can be very difficult to prevent the elevated temperatures that may cause damage to the catalyst. Known fluidized bed designs whilst overcoming certain thermal challenges are faced with other challenges such as catalyst attrition. Other reactor concepts have been considered in the prior art for exothermic catalytic reactions, including micro-structured reactors and slurry reactors. Structured reactors have the advantage of high gas hourly space velocity (GHSV); however a drawback of these reactors is the complex procedure needed to immobilize the catalyst on the structures. Slurry reactors may offer a high efficiency of heat removal due to liquid circulation, but they typically need to be operated at low GHSV due to additional mass transfer resistance and issues related to liquid phase circulation, all of which limit their wider application. Alternatively, known uses of multi -tubular cooled reactors may allow operation at lower temperatures; however, existing cooled reactors may be prone to formation of hot spots and thermal runaway due to restricted heat transfer through the reactor walls and catalyst bed to the cooling medium, which presents challenges under dynamic conditions.

[0007] Summary of the Disclosure

[0008] An object of aspects of the present disclosure is to provide an apparatus and method for carrying out gas-phase catalytic reactions. In particular, aspects of the present disclosure aim to provide an apparatus and method that enables improved thermal control of highly exothermic catalytic reactions, such as methanation of carbon dioxide and hydrogen. A first aspect of the present disclosure provides a fixed-bed reactor apparatus for reacting gasphase reactant with solid-phase catalyst, the reactor comprising: at least one inlet for intake of gas-phase reactant; at least one outlet for exhaust of gas-phase product; and first and second reactor stages arranged in a series relationship between the at least one inlet and the at least one outlet to thereby define first and second sections of a gas flow path between the at least one inlet and the at least one outlet such that gas-phase reactant may flow along the gas flow path in a direction from the at least one inlet through the first reactor stage and subsequently through the second reactor stage towards the at least one outlet, each of the first and second reactor stages comprising a respective plurality of reaction tubes arranged in a parallel relationship, each of the reaction tubes defining a bore through which the gas-phase reactant may flow, each of the reaction tubes being suitable for containing solid-phase catalyst in the respective bore, wherein a cumulative area of the bores of the plurality of reaction tubes of the first reactor stage is lesser than a cumulative area of the bores of the plurality of reaction tubes of the second reactor stage. The reaction tubes are referred to as being in a parallel relationship in the sense that gas flows along the gas flow path through the tubes in parallel, and does not necessarily imply that the reaction tubes are mutually geometrically parallel.

[0009] The reactors splitting of the reaction into two stages may advantageously achieve a good balance of thermal control and conversion efficiency. In the first, upstream, reactor stage, the reactant gas mixture is most concentrated, and so for some reactions, such as methanation, the reaction may be most exothermic. The relatively small open area of the first reactor stage causes relatively high gas velocity therethrough, which desirably elevates effective thermal conductivity within the catalytic bed and heat transfer from the bed to the tube wall. Thus, the reactants may be partial converted in the first reactor stage, albeit at relatively low conversion efficiency due to the relatively small open area, and so relatively low catalyst volume, whilst temperatures in the first reactor stage may be effectively controlled because of the high gas velocity. Whereas the reactant gas mixture may be less concentrated by the second reactor stage, because of the prior conversion, and hence the reaction in the second reactor stage may be relatively less exothermic and so the gas velocity may acceptable be relatively lower. Accordingly, higher conversion efficiency may be practicable achieved in the second reactor stage by the relatively large open area of the second reactor stage, enabling the gas to be exposed to a higher volume of catalyst.

[0010] As a result, the reactor apparatus may desirably enable relatively high conversion efficiency to be achieved, whilst also effectively managing heat generation and thereby preserving the catalyst. The reactor stages could, for example, be provided by separate reactor vessels, or by a unitary reactor vessel having first and second sections.

[0011] In implementations, an average length of the reaction tubes of the first reactor stage is shorter than an average length of the reaction tubes of the second reactor stage. This relatively short length of the reaction tubes of the first reactor stage may desirably counter the increased pressure drop resulting from their relatively small open area, thereby enabling the desired high gas velocity with acceptable pressure drop across the first reactor stage.

[0012] In implementations, the first reactor stage comprises fewer reaction tubes than the second reactor stage. In other words, the relatively small cumulative open area of the reaction tubes of the first reactor stage may be achieved by using relatively few reaction tubes. This may desirably allow for the cumulative open area to be reduced without requiring the use of reaction tubes with individually very small bores, which very small bore tubes may incur disadvantages such as difficult to manufacture and difficult charging the bores with solid-phase catalyst.

[0013] In implementations, an average open area of each reaction tube of the first reactor stage is the same as an average open area of each reaction tube of the second reactor stage. In other words, the reaction tubes of the first and second reactor stage may be formed of substantially the same tube stock, which may simplify manufacture of the tubes.

[0014] In implementations, the reaction tubes of the first reactor stage and / or the second reactor stage have an average inner diameter of between 10 millimetres and 30 millimetres. In other words, the reaction tubes may have a bore diameter of between 10 millimetres and 30 millimetres. The diameter of the reaction tubes defines the ratio of surface area of the inner diameter of the tube to volume of catalyst contained in the tube. The surface area of the inner diameter of the tube influences the heat loss from the tube, and so the thermal control of the reaction, whereas the volume of the catalyst in the tube influences the conversion efficiency. Additionally, it has been found that tube diameters of less than 10 millimetre may be difficult to manufacture and / or charge with solid catalyst. Tube diameters in this range have been found to desirably balance these factors.

[0015] In implementations, an average length of the reaction tubes of the first reactor stage is no greater than half an average length of the reaction tubes of the second reactor stage. This ratio has been found to achieve acceptably low pressure drop in the first reactor stage, and acceptably high conversion efficiency in the second reactor stage.

[0016] In implementations, the first reactor stage comprises no more than a half, or no more than two- fifths, of the number of reaction tubes of the second reactor stage. This ratio has been found to achieve acceptably high gas velocity in the first reactor stage, and acceptably high conversion efficiency in the second reactor stage.

[0017] In implementations, at least some of the reaction tubes of the first reactor stage and / or of the second reactor stage comprise a respective inert rod located in the bore of the tube and extending along the bore at least part of a length of the bore. The rod is inert, in the sense that it does not substantially react with the reactants, and is configured to be resistant to chemical or physical degradation in use. The rod has the function of displacing catalyst from it’s location in the tube. The rod may thereby be placed to exclude catalyst from a region of the tube that may otherwise be susceptible to hotspots that would otherwise risk damaging the catalyst, for example, the rod may be configured to extend approximately centrally along the bore of each tube, for example, approximately along the tube axis of each tube, which central region, being furthest from the tube wall, may otherwise be susceptible to hotspots. The inert rod may thereby avoid hotspots in the catalyst even for relatively large diameter tubes. The inert rod could, for example, have a diameter in the range of one-third to two-thirds the diameter of the bore. These relative dimensions may desirably balance the avoidance of temperature hotspots in the centre of the bore with sufficient volume remaining in the bore to contain an adequate volume of catalyst. The inert rod may extend along the bore substantially the full length of the bore.

[0018] In implementations, the inert rod comprises a thermally-conductive metal to facilitate transfer of thermal energy along the bore of the respective reaction tube. The rod may thereby distribute thermal energy along the catalyst in the bore, to thereby avoid hotspots in the catalyst.

[0019] In implementations, the inert rod is arranged to be in contact with solid-phase catalyst contained in the bore of the respective reaction tube. The rod may thereby distribute thermal energy along the catalyst in the bore, to thereby avoid hotspots in the catalyst.

[0020] In implementations, each of the reaction tubes contains solid-phase catalyst in the respective bore.

[0021] In implementations, the solid-phase catalyst comprises a granular catalyst. In implementations, the solid-phase catalyst is nickel-based.

[0022] In implementations, the apparatus comprises a cooling system for flowing fluid coolant to remove heat from the reaction tubes.

[0023] In implementations, the fluid coolant is silicone-based liquid coolant.

[0024] In implementations, the apparatus comprises a heat recovery system for recovering heat from the fluid coolant.

[0025] In implementations, the apparatus is a fixed-bed methanation reactor for methanation reaction of gas-phase reactant comprising carbon dioxide and hydrogen.

[0026] In implementations, the apparatus comprises at least one source of carbon dioxide and hydrogen fluidly coupled to the inlet.

[0027] In implementations, the apparatus comprises a methane collector for collecting methane gas fluidly coupled to the outlet.

[0028] A second aspect of the present disclosure provides a method of operating a fixed-bed reactor apparatus according to any one of the preceding statements, comprising introducing a flow of gas phase-reactant into the inlet and discharging gas-phase product from the outlet without recirculation of the gas-phase reactant through the gas flow path.

[0029] A third aspect of the present disclosure provides a fixed-bed reactor apparatus for reacting gasphase reactant with solid-phase catalyst, the reactor comprising at least one inlet for intake of gasphase reactant; at least one outlet for exhaust of gas-phase product; a reactor arranged to define at least a section of a gas flow path between the at least one inlet and the at least one outlet such that gas phase reactant may flow from the at least one inlet along the gas flow path through the reactor towards the at least one outlet, the reactor comprising a plurality of reaction tubes arranged in a parallel relationship, each of the reaction tubes defining a bore through which the gas-phase reactant may flow, each of the reaction tubes being suitable for containing solid-phase catalysis in the respective bore, wherein at least some of the reaction tubes of the first reactor stage and / or of the second reactor stage comprise a respective inert rod located in the bore of the tube and extending along the bore at least part of a length of the bore.

[0030] The rod is inert, in the sense that it does not substantially react with the reactants, and is configured to be resistant to chemical or physical degradation in use. The rod has the function of displacing catalyst from its location in the tube. The rod may thereby be placed to exclude catalyst from a region of the tube that may otherwise be susceptible to hotspots that would otherwise risk damaging the catalyst, for example, the rod may be configured to extend approximately centrally along the bore of each tube, for example, approximately along the tube axis of each tube, which central region, being furthest from the tube wall, may otherwise be susceptible to hotspots. The inert rod may thereby avoid hotspots in the catalyst even for relatively large diameter tubes.

[0031] The inert rod could, for example, have a diameter in the range of one-third to two-thirds the diameter of the bore. These relative dimensions may desirably balance the avoidance of temperature hotspots in the centre of the bore with sufficient volume remaining in the bore to contain an adequate volume of catalyst.

[0032] In implementations, each reaction tube of the first reactor stage and / or of the second reactor stage comprises an inert rod extending along the tube axis of the respective tube at least part of a length of the respective tube. The rod may thereby distribute thermal energy along the catalyst in the bore, to thereby avoid hotspots in the catalyst.

[0033] In implementations, the inert rod comprises a thermally-conductive metal to facilitate transfer of thermal energy along the bore of the respective reaction tube. The rod may thereby distribute thermal energy along the catalyst in the bore, to thereby avoid hotspots in the catalyst.

[0034] In implementations, the inert rod is arranged to be in contact with solid-phase catalyst contained in the bore of the respective reaction tube.

[0035] In implementations, the reactor comprises first and second reactor stages arranged in a series relationship between the at least one inlet and the at least one outlet to thereby define first and second sections of the gas flow path such that the gas-phase reactant may flow along the gas flow path in a direction from the at least one inlet through the first reactor stage and subsequently through the second reactor stage towards the at least one outlet, each of the first and second reactor stages comprising a respective sub-plurality of the plurality of reaction tubes arranged in a parallel relationship, wherein a cumulative area of the bores of the sub-plurality of reaction tubes of the first reactor stage is lesser than a cumulative area of the bores of the sub-plurality of reaction tubes of the second reactor stage.

[0036] The reactors splitting of the reaction into two stages may advantageously achieve a good balance of thermal control and conversion efficiency. In the first, upstream, reactor stage, the reactant gas mixture is most concentrated, and so for some reactions, such as methanation, the reaction may be most exothermic. The relatively small open area of the first reactor stage causes relatively high gas velocity therethrough, which desirably elevates effective thermal conductivity within the catalytic bed and heat transfer from the bed to the tube wall. Thus, the reactants may be partial converted in the first reactor stage, albeit at relatively low conversion efficiency due to the relatively small open area, and so relatively low catalyst volume, whilst temperatures in the first reactor stage may be effectively controlled because of the high gas velocity. Whereas the reactant gas mixture may be less concentrated by the second reactor stage, because of the prior conversion, and hence the reaction in the second reactor stage may be relatively less exothermic and so the gas velocity may acceptable be relatively lower. Accordingly, higher conversion efficiency may be practicable achieved in the second reactor stage by the relatively large open area of the second reactor stage, enabling the gas to be exposed to a higher volume of catalyst.

[0037] As a result, the reactor apparatus may desirably enable relatively high conversion efficiency to be achieved, whilst also effectively managing heat generation and thereby preserving the catalyst.

[0038] In implementations, the first reactor stage comprises fewer reaction tubes than the second reactor stage. In other words, the relatively small cumulative open area of the reaction tubes of the first reactor stage may be achieved by using relatively few reaction tubes. This may desirably allow for the cumulative open area to be reduced without requiring the use of reaction tubes with individually very small bores, which very small bore tubes may incur disadvantages such as difficult to manufacture and difficult charging the bores with solid-phase catalyst.

[0039] In implementations, an average open area of each reaction tube of the first reactor stage is the same as an average open area of each reaction tube of the second reactor stage. In other words, the reaction tubes of the first and second reactor stage may be formed of substantially the same tube stock, which may simplify manufacture of the tubes. In implementations, the reaction tubes have an average inner diameter of between 10 millimetres and 30 millimetres. In other words, the reaction tubes may have a bore diameter of between 10 millimetres and 30 millimetres. The diameter of the reaction tubes defines the ratio of surface area of the inner diameter of the tube to volume of catalyst contained in the tube. The surface area of the inner diameter of the tube influences the heat loss from the tube, and so the thermal control of the reaction, whereas the volume of the catalyst in the tube influences the conversion efficiency. Additionally, it has been found that tube diameters of less than 10 millimetre may be difficult to manufacture and / or charge with solid catalyst. Tube diameters in this range have been found to desirably balance these factors.

[0040] In implementations, an average length of the reaction tubes of the first reactor stage is no greater than half an average length of the reaction tubes of the second reactor stage. This ratio has been found to achieve acceptably low pressure drop in the first reactor stage, and acceptably high conversion efficiency in the second reactor stage.

[0041] In implementations, the first reactor stage comprises no more than a half or no more than two- fifths of the number of reaction tubes of the second reactor stage. This ratio has been found to achieve acceptably high gas velocity in the first reactor stage, and acceptably high conversion efficiency in the second reactor stage.

[0042] In implementations, each of the reaction tubes contains solid-phase catalyst in the respective bore.

[0043] In implementations, the solid-phase catalyst comprises a granular catalyst.

[0044] In implementations, the solid-phase catalyst is nickel-based.

[0045] In implementations, the apparatus comprises a cooling system for flowing fluid coolant to remove heat from the reaction tubes.

[0046] In implementations, the fluid coolant comprises silicone-based liquid coolant.

[0047] In implementations, the apparatus comprises a heat recovery system for recovering heat from the fluid coolant. In implementations, the apparatus is a fixed-bed methanation reactor for methanation reaction of gas-phase reactant comprising carbon dioxide and hydrogen.

[0048] In implementations, the apparatus comprises at least one source of carbon dioxide and hydrogen fluidly coupled to the inlet.

[0049] In implementations, the apparatus comprises a methane collector for collecting methane fluidly coupled to the outlet.

[0050] A fourth aspect of the present disclosure provides a method of operating a fixed-bed reactor apparatus according to any one of the preceding statements comprising introducing a flow of gas phase-reactant into the inlet and discharging gas-phase product from the outlet without recirculation of the gas-phase reactant through the gas flow path.

[0051] The present disclosure extends to any combination of the preceding statements.

[0052] These and other aspects of the invention will be apparent from the embodiment(s) described below.

[0053] Brief Description of the Drawings

[0054] In order that the present invention may be more readily understood, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0055] Figure 1 shows schematically an example of fixed bed reactor apparatus embodying an aspect of the present disclosure;

[0056] Figure 2 shows schematically a controller of the fixed bed reactor apparatus;

[0057] Figure 3 shows schematically an example side-sectional view of a first reactor vessel of the fixed bed reactor apparatus;

[0058] Figure 4 shows schematically an example side-sectional view of a second reactor vessel of the fixed bed reactor apparatus; Figure 5 shows schematically an example side-sectional view of a reaction tube of the first and second reactor vessels;

[0059] Figure 6 shows schematically an example end-sectional view of a reaction tube of the first and second reactor vessels along the line A-A in Figure 5; and

[0060] Figure 7 shows schematically operations in a method of controlling the fixed-bed reactor apparatus.

[0061] Detailed Description of the Disclosure

[0062] Example embodiments are described below in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

[0063] Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

[0064] The terminology used herein to describe embodiments is not intended to limit the scope. The articles “a,” “an,” and “the” are singular in that they have a single referent, however the use of the singular form in the present document should not preclude the presence of more than one referent. In other words, elements referred to in the singular can number one or more, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and / or “including,” when used herein, specify the presence of stated features, items, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and / or groups thereof.

[0065] Embodiments of the disclosure are described with reference to accompanying drawings, and it should be understood that the drawings are intended to be merely illustrative of technical features of the embodiment. The drawings are not necessarily drawn to scale, and where the drawings depict a plurality of like features, for simplicity the drawings do not necessarily show all of the plurality of like features.

[0066] Figure 1 depicts a fixed-bed reactor apparatus 101 embodying an aspect ofthe present disclosure. In the example, the fixed-bed reactor apparatus is configured as a methanation reactor, for a methanation reaction of a mixture of carbon dioxide and hydrogen gases with a solid-phase nickel-based catalyst to generate methane gas product.

[0067] The reactor apparatus 101 comprises a source of hydrogen and carbon dioxide gas 102, a source of liquid water 103, inlets indicated generally at 104, a mixer 105, a heater 106, first and second reactor vessels 107, 108 and their respective cooling systems 109, 110, a cooler / condenser 111, an outlet indicated generally at 112, and a methane collector 113. The components 105 to 111 form a gas flow path along which gas may flow between the inlets 104 and the outlet 112.

[0068] The source of hydrogen and carbon dioxide 102 may comprise separate supplies of hydrogen and carbon dioxide, or could instead comprise a single supply of a pre-mixed mixture of hydrogen and carbon dioxide, for example, a tank of hydrogen and carbon-dioxide gas mixture. The source of liquid water 103 may comprise atank of water or another feed of water. The source of hydrogen and carbon dioxide 102 and the source of liquid water 103 are fluidly coupled to the inlets 104. As will be described in further detail herein, the hydrogen and carbon-dioxide gases are chemically reacted in reactor vessels 107, 108 in the presence of a catalyst to form methane gas. The liquid water 103 is utilised for cooling ofthe chemical reaction in the reactor vessels.

[0069] The mixer 105 receives the hydrogen and carbon-dioxide gas mixture and the liquid water from the inlets 104, and mixes the gases and the water to create a mixture.

[0070] The heater 106 receives the gas and water mixture from the mixer, and is controllable to heat the mixture. As will be described in further detail herein, a function of the heater 106 is to heat the gas and water mixture to an optimum temperature for the subsequent chemical reaction of the gases in the reactor vessels 107, 108.

[0071] The first reactor vessel 107 receives the heated gas and water mixture from the heater 106, and is controlled to perform a first stage of the methanation process, to thereby partially convert the reactant gases into methane. The first reactor vessel 17 will be described in further detail with reference to Figure 3. The first cooling system 109 is operable to circulate liquid coolant around a shell of the reactor vessel 107 to absorb heat from the reactor vessel, and the cooling system may further comprise a heat-loss device, such as a coolant-to-air radiator, for dissipating heat from the liquid coolant to thereby cool the coolant.

[0072] The second reactor vessel 108 receives the partially converted gas and water mixture from the first reactor vessel 107, and is controlled to perform a second stage of the methanation process, to thereby complete the conversion of the reactant gases into methane. The second reactor vessel 108 will be described in further detail with reference to Figure 4. Similarly, the second cooling system 110 is operable to circulate liquid coolant around a shell of the reactor vessel 108 to absorb heat from the reactor vessel, and the cooling system may further comprise a heat-loss device, such as a coolant-to-air radiator, for dissipating heat from the liquid coolant to thereby cool the coolant.

[0073] The cooler / condenser 111 is operable to cool the gas-phase product discharged from the second reactor vessel 108 and condense out water from the gas.

[0074] The methane collector 113 is operable to receive the gas-phase methane product from the cooler / condenser 111. For example, the methane collector 113 may comprise a tank for storing the methane gas, and / or could comprise a gas distribution system for piping the methane gas to a remote location.

[0075] The reactor apparatus may further comprise a controller 114 for monitoring and controlling the operation of the mixer 105, heater 106, cooler / condenser 111, and first and second cooling systems 109, 110.

[0076] Referring next to Figure 2, the controller 114 comprises a processor 201, memory 202, graphical display device 203, input / output interface 204, and system bus 206.

[0077] Processor 201 is configured for running control software for controlling the operation of the components of the reactor apparatus. Memory 202 is configured for non-volatile storage of the software, defining machine-readable instructions, for execution by the processor, and for serving as read / write memory for storage of operational data associated with the software executed by the processor. Graphical display device 203 is configured for enabling the user to visualise functionality of the control software via graphical user interfaces. Input / output interface 204 is configured for connection of the controller 114 to the various other components of the reactor apparatus. The components 201 to 204 of the controller 114 are in communication via system bus 206. Referring next to Figures 3 and 4 collectively, Figure 3 depicts the first reactor vessel 107 and Figure 4 depicts the second reactor vessel 108. The reactor vessels 107, 108 are substantially similar, except as will be described herein.

[0078] Each reactor vessel 107, 108 comprises a respective housing 301, having an inlet 302 for receiving gas-phase reactants from the heater 106 and the first reactor vessel 107 respectively, an outlet 303 for discharging partially and completely converted gas-phase reactants respectively, and a plurality of reaction tubes 304 located in the housing in a gas flow path between the respective inlet and the respective outlet. As will be described in further detail with reference to later Figures 5 and 6, the reaction tubes contain a catalyst in their respective bore, such that gas flowing through the reactor vessel between the inlet and the outlet is required to flow through the reaction tubes and thereby contact the catalyst contained therein.

[0079] The housing 301 of each reactor vessel further defines a coolant inlet 305 and a coolant outlet 306 via which the respective cooling system 109, 110 may circulate liquid coolant around the housing 301 to thereby cool the reaction tubes 304 in use. Forthis purpose, the housing 304 includes plural baffles 307 which define a circuitous coolant flow path between the coolant inlet 305 and the coolant outlet 306.

[0080] The first reactor vessel 107 differs from the second reactor vessel 108 principally in the number and length of the reaction tubes 304. The first reactor vessel 107 comprises relatively fewer reaction tubes than the second reactor vessel 107, and the reaction tubes of the first reactor vessel 107 are shorter in length than the reaction tubes of the second reactor vessel 108. For example, the first reactor vessel 107 may comprise less than half of the number of reaction tubes of the second reactor vessel 108. This ratio has been found to achieve acceptably high gas velocity in the first reactor vessel, and acceptably high conversion efficiency in the second reactor vessel. In examples, a length of the reaction tubes of the first reactor vessel 107 is less than half a length of the reaction tubes of the second reactor vessel 108. For example, the reaction tubes of the first reactor vessel 107 may be between 1 metre and 2 metres in length, whereas the reaction tubes of the second reactor vessel 108 may be between 3 metres and 5 metres in length.

[0081] The reaction tubes of the first and second reactor vessels may have the same diameter, and so the same individual open areas. The fewer number of reaction tubes of the first reactor vessel 107 compared to the second reactor vessel 108 means that the cumulative bore area of the reaction tubes of the first reactor vessel 107 is lesser than the cumulative bore area of the reaction tubes of the second reactor vessel 108. Thus, the section of the gas flow path defined by the reaction tubes of the first reactor vessel 107 is more restrictive per unit of length than the section of the gas flow path defined by the reaction tubes of the second reactor vessel 108. The relatively small open area of the first reactor vessel 107 causes relatively higher gas velocity therethrough than in the second reactor vessel 108. This high gas velocity in the first reactor vessel 107 may desirably result in elevated effective thermal conductivity within the catalyst and improved heat transfer from the catalyst to the tube wall, and onward to the cooling system 109. These improved heat transfer characteristics may be particularly desirable in the first reactor vessel 107 because the reactant gas mixture is most concentrated in the first reactor vessel, and the reaction most active, and so for exothermic reactions, such as methanation, thermal control is particularly important in the first reactor vessel 107 to preserve the catalyst and avoid thermal runaway.

[0082] A potential disadvantage however of the small cumulative bore area of the reaction tubes of the first reactor vessel 107 is that the pressure drop for the gas-phase reactants may tend to be relatively high across the first reactor vessel 107. This effect is mitigated however by the reaction tubes of the first reactor vessel 107 being relatively short, thereby minimising pressure drop, albeit at the potential expense of reduced conversion efficiency.

[0083] Accordingly, the first reactor vessel 107 may achieve acceptable conversion of the reactants, thereby weakening the concentration of reactants in the gas flow to the second reactor vessel 108, whilst effectively managing the heat generated by the reaction, with acceptable pressure drop across the first reactor vessel 107.

[0084] The second reactor vessel 108 receives from the first reactor vessel 107 the gas flow having a relatively lower concentration of reactants, and so the resulting reaction may be expected to be less active and so less exothermic. As a result, the second reactor vessel 108 may acceptably prioritise conversion efficiency over thermal management constraints. This is achieved by the larger number of reaction tubes of the second reactor vessel, and the longer length of those reaction tubes, both of which parameters enable a greater volume of catalyst to be located in the gas flow path therethrough.

[0085] The reaction tubes 304 may have an average inner diameter of between 10 millimetres and 30 millimetres, for example, approximately 20 millimetre. The diameter of the reaction tubes defines the ratio of surface area of the inner diameter of the tube to volume of catalyst contained in the tube. The surface area of the inner diameter of the tube influences the heat loss from the tube, and so the thermal control of the reaction, whereas the volume of the catalyst in the tube influences the conversion efficiency. Additionally, it has been found that tube diameters of less than 10 millimetre may be difficult to manufacture and / or charge with solid catalyst. Tube diameters in this range have been found to desirably balance these factors.

[0086] Referring next to Figures 5 and 6 collectively, each of the reaction tubes 304 comprises a cylindrical tube body 501 defining an internal bore extending the length of the tube, perforated end-caps 502, 503, and an inert rod 504. Each reaction tube contains solid-phase catalyst 505 located in the bore. In examples the catalyst comprises a granular nickel-based catalyst.

[0087] The tube body 501 is required to be chemically inert, and chemically and mechanically resistant to degradation and high temperatures in use, and may thus be formed of metal, such as stainless steel. The end-caps 502, 503 may be formed of a same material as the tube body 501.

[0088] Gas flowing through the respective reactor vessel 107, 108 may thus flow pass through the upstream perforated end-cap 502, into and along the bore of the reaction tube, in contact with the catalyst 505, and out through the downstream perforated end-cap 503. As the gas flows through the bores of the reaction tubes it may react with the catalyst located therein, and thereby be converted to methane gas, in a known hydrogenation reaction. Thermal energy generated by the reaction may be absorbed by the tube body 501, for onward dissipation to the coolant of the respective cooling system.

[0089] In the example, each of the reaction tubes of the first and second reactor vessels 107, 108 comprises a respective inert rod 504, located in the bore of the reaction tube to extend along the tube axis in contact with the catalyst 505. The rod is connected at either end to the end-caps 502,

[0090] 503 of each tube. The rod is inert, in the sense that it does not substantially react with the reactants, and is configured to be resistant to chemical or physical degradation in use. For example, the rod

[0091] 504 may be formed from a chemically inert metal.

[0092] The rod has the function of displacing the catalyst from the centreline of the bore, this central region being furthest from the cooled tube wall, and so catalyst located there being most susceptible to thermal damage. The inert rod 504 may thereby avoid hotspots in the catalyst even for relatively large diameter tubes. Advantageously, each of the inert rods 504 is formed of a thermally-conductive metal, to thereby facilitate transfer of thermal energy along the bore of the respective reaction tube. The rod may thereby distribute thermal energy along the catalyst in the bore, to thereby better avoid hotspots in the catalyst. The inert rod could, for example, have a diameter in the range of one-third to two-thirds the internal diameter of the tube body 501. These relative dimensions may desirably balance the avoidance of temperature hotspots in the centre of the bore with sufficient volume remaining in the bore to contain an adequate volume of catalyst.

[0093] Referring finally to Figure 7, in examples, a method for controlling the operation of the reactor apparatus 101 to generate methane in a methanation reaction comprises five operations 701 to 705. Operations 701 to 705 are performed by computer software running on the controller 114.

[0094] At operation 701, the computer software causes the processor 201 of the controller 114 to initiate the methanation reaction procedure. Operation 701 could, for example, be prompted by a user interacting with the controller via input / output interface 204.

[0095] At operation 702, the computer software causes the processor 201 of the controller 114 to control the mixer 105 and the heater 106 to admit hydrogen and carbon dioxide from the source 102, and liquid water from the source 103, and heat the mixture for admittance to the first reactor vessel 107.

[0096] At operation 702, the computer software causes the processor 201 of the controller 114 to control the flow rate and temperature of the gas and liquid mixture into the first reactor vessel 107.

[0097] At stage 703, the computer software causes the processor 201 of the controller 114 to control the cooling systems 109, 110 to control the temperature and flow rate of the circulating coolant, to thereby control the temperature of the first and second reactor vessels 107, 108 and so the temperature of the reactions therein.

[0098] At stage 704, the computer software causes the processor 201 of the controller 114 to control the cooler / condenser 111 to cool the gas mixture discharged by the second reactor vessel 108, and to condense out any residual liquid water from the gas flow.

[0099] At stage 705, the computer software causes the processor 201 of the controller 114 to control the methane collector 113 to collect the methane gas discharged by the cooler / condenser 111. For example, the methane collector 113 may store the methane in a tank under pressure. The system and apparatus described above may use dedicated processor systems, micro controllers, programmable logic devices, microprocessors, or any combination thereof, to perform some or all of the operations described herein. Some of the operations described above may be implemented in software and other operations may be implemented in hardware. Any of the operations, processes, and / or methods described herein may be performed by an apparatus, a device, and / or a system substantially similar to those as described herein and with reference to the illustrated figures. References herein to a device, or similar, do not imply a unitary apparatus, and instead include a system of components, which may or may not be co-located.

[0100] The processor may execute instructions or "code" stored in memory. The memory may store data as well. The processing device may include, but may not be limited to, an analog processor, a digital processor, a microprocessor, a multi-core processor, a processor array, a network processor, or the like. The processing device may be part of an integrated control system or system manager, or may be provided as a portable electronic device configured to interface with a networked system either locally or remotely via wireless transmission.

[0101] The memory may be integrated together with the processing device, for example RAM or FLASH memory disposed within an integrated circuit microprocessor or the like. In other examples, the memory may comprise an independent device, such as an external disk drive, a storage array, a portable FLASH key fob, or the like. The memory and processing device may be operatively coupled together, or in communication with each other, for example by an I / O port, a network connection, or the like, and the processing device may read a file stored on the memory. Associated memory may be "read only" by design (ROM) by virtue of permission settings, or not. Other examples of memory may include, but may not be limited to, WORM, EPROM, EEPROM, FLASH, or the like, which may be implemented in solid state semiconductor devices. Other memories may comprise moving parts, such as a known rotating disk drive. All such memories may be "machine-readable" and may be readable by a processing device.

[0102] Operating instructions or commands may be implemented or embodied in tangible forms of stored computer software (also known as "computer program" or "code"). Programs, or code, may be stored in a digital memory and may be read by the processing device. “Computer-readable storage medium" (or alternatively, "machine-readable storage medium") may include all of the foregoing types of memory, as well as new technologies of the future, as long as the memory may be capable of storing digital information in the nature of a computer program or other data, at least temporarily, and as long at the stored information may be "read" by an appropriate processing device. The term "computer-readable" may not be limited to the historical usage of "computer" to imply a complete mainframe, mini-computer, desktop or even laptop computer. Rather, "computer-readable" may comprise storage medium that may be readable by a processor, a processing device, or any computing system. Such media may be any available media that may be locally and / or remotely accessible by a computer or a processor, and may include volatile and non-volatile media, and removable and non-removable media, or any combination thereof.

[0103] A program stored in a computer-readable storage medium may comprise a computer program product. For example, a storage medium may be used as a convenient means to store or transport a computer program. For the sake of convenience, the operations may be described as various interconnected or coupled functional blocks or diagrams. However, there may be cases where these functional blocks or diagrams may be equivalently aggregated into a single logic device, program or operation with unclear boundaries.

[0104] While the application describes specific examples of carrying out embodiments of the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims. For example, while specific terminology has been employed above to refer to electronic design automation processes, it should be appreciated that various examples of the invention may be implemented using any desired combination of electronic design automation processes.

[0105] One of skill in the art will also recognize that the concepts taught herein can be tailored to a particular application in many other ways. In particular, those skilled in the art will recognize that the illustrated examples are but one of many alternative implementations that will become apparent upon reading this disclosure.

[0106] Although the specification may refer to “an”, “one”, “another”, or “some” example(s) in several locations, this does not necessarily mean that each such reference is to the same example(s), or that the feature only applies to a single example.

Claims

Claims1. A fixed-bed reactor apparatus for reacting gas-phase reactant with solid-phase catalyst, the reactor comprising: at least one inlet for intake of gas-phase reactant; at least one outlet for exhaust of gas-phase product; and first and second reactor stages arranged in a series relationship between the at least one inlet and the at least one outlet to thereby define first and second sections of a gas flow path between the at least one inlet and the at least one outlet such that gas-phase reactant may flow along the gas flow path in a direction from the at least one inlet through the first reactor stage and subsequently through the second reactor stage towards the at least one outlet, each of the first and second reactor stages comprising a respective plurality of reaction tubes arranged in a parallel relationship, each of the reaction tubes defining a bore through which the gas-phase reactant may flow, each of the reaction tubes being suitable for containing solid-phase catalyst in the respective bore, wherein a cumulative area of the bores of the plurality of reaction tubes of the first reactor stage is lesser than a cumulative area of the bores of the plurality of reaction tubes of the second reactor stage.

2. The fixed-bed reactor apparatus of claim 1, wherein an average length of the reaction tubes of the first reactor stage is shorter than an average length of the reaction tubes of the second reactor stage.

3. The fixed-bed reactor apparatus of claim 1, wherein the first reactor stage comprises fewer reaction tubes than the second reactor stage.

4. The fixed-bed reactor apparatus of claim 1, wherein an average open area of each reaction tube of the first reactor stage is the same as an average open area of each reaction tube of the second reactor stage.

5. The fixed-bed reactor apparatus of claim 1, wherein the reaction tubes of the first reactor stage and / or the second reactor stage have an average inner diameter of between 10 millimetres and 30 millimetres.

6. The fixed-bed reactor apparatus of claim 1, where an average length of the reaction tubes of the first reactor stage is no greater than half an average length of the reaction tubes of the second reactor stage.

7. The fixed-bed reactor apparatus of claim 1, wherein the first reactor stage comprises no more than a half, or no more than two-fifths, of the number of reaction tubes of the second reactor stage.

8. The fixed-bed reactor apparatus of claim 1, wherein at least some of the reaction tubes of the first reactor stage and / or of the second reactor stage comprise a respective inert rod located in the bore of the tube and extending along the bore at least part of a length of the bore.

9. The fixed-bed reactor apparatus of claim 8, wherein the inert rod comprises a thermally- conductive metal to facilitate transfer of thermal energy along the bore of the respective reaction tube.

10. The fixed-bed reactor apparatus of claim 1, wherein each of the reaction tubes contains solid-phase catalyst in the respective bore.

11. The fixed-bed reactor apparatus of claim 1 , for methanation reaction of gas-phase reactant comprising carbon dioxide and hydrogen.

12. The fixed-bed reactor apparatus of claim 11 comprising at least one source of carbon dioxide and hydrogen fluidly coupled to the inlet.

13. A fixed-bed reactor apparatus for reacting gas-phase reactant with solid-phase catalyst, the reactor comprising: at least one inlet for intake of gas-phase reactants; at least one outlet for exhaust of gas-phase product; and a reactor arranged to define at least a section of a gas flow path between the at least one inlet and the at least one outlet such that gas phase reactant may flow from the at least one inlet along the gas flow path through the reactor towards the at least one outlet, the reactor comprising a plurality of reaction tubes arranged in a parallel relationship, each of the reaction tubes defining a bore through which the gas-phase reactant may flow, each of the reaction tubes being suitable for containing solid-phase catalyst in the respective bore, whereinat least some of the reaction tubes of the first reactor stage and / or of the second reactor stage comprise a respective inert rod located in the bore of the tube and extending along the bore at least part of a length of the bore.

14. The fixed-bed reactor apparatus of claim 13 , wherein each reaction tube of the first reactor stage and / or of the second reactor stage comprises an inert rod extending along the tube axis of the respective tube at least part of a length of the respective tube.

15. The fixed-bed reactor apparatus of claim 13 , wherein the inert rod comprises a thermally- conductive metal to facilitate transfer of thermal energy along the bore of the respective reaction tube.

16. The fixed bed reactor apparatus of claim 13, wherein the reactor comprises first and second reactor stages arranged in a series relationship between the at least one inlet and the at least one outlet to thereby define first and second sections of the gas flow path such that the gas-phase reactant may flow along the gas flow path in a direction from the at least one inlet through the first reactor stage and subsequently through the second reactor stage towards the at least one outlet, each of the first and second reactor stages comprising a respective sub-plurality of the plurality of reaction tubes arranged in a parallel relationship, wherein a cumulative area of the bores of the sub-plurality of reaction tubes of the first reactor stage is lesser than a cumulative area of the bores of the sub-plurality of reaction tubes of the second reactor stage.

17. The fixed-bed reactor apparatus of claim 16, wherein the first reactor stage comprises fewer reaction tubes than the second reactor stage.

18. The fixed-bed reactor apparatus of claim 16, wherein an average open area of each reaction tube of the first reactor stage is the same as an average open area of each reaction tube of the second reactor stage.

19. The fixed-bed reactor apparatus of claim 13, wherein the reaction tubes have an average inner diameter of between 10 millimetres and 30 millimetres.

20. The fixed-bed reactor apparatus of claim 16. where an average length of the reaction tubes of the first reactor stage is no greater than half an average length of the reaction tubes of the second reactor stage.

21. The fixed-bed reactor apparatus of claim 16. wherein the first reactor stage comprises no more than a half or no more than two-fifths of the number of reaction tubes of the second reactor stage.

22. The fixed-bed reactor apparatus of claim 13, wherein each of the reaction tubes contains solid-phase catalyst in the respective bore.

23. The fixed-bed reactor apparatus of claim 13, for methanation reaction of gas-phase reactant comprising carbon dioxide and hydrogen.

24. The fixed-bed reactor apparatus of claim 13 comprising at least one source of carbon dioxide and hydrogen fluidly coupled to the inlet.

25. A method of operating a fixed-bed reactor apparatus according to any one of the preceding claims, comprising introducing a flow of gas phase-reactant into the inlet and discharging gas-phase product from the outlet without recirculation of the gas-phase reactant through the gas flow path.

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